CA2157891A1 - A method for magnetically and/or electrostatically positioning pressure-sensitive adhesive beads and magnetically positionable pressure-sensitive adhesive beads - Google Patents

Abstract

The present invention provides pressure-sensitive adhesive beads that comprise a tacky pressure-sensitive adhesive core and a non-tacky shell material that surrounds the core wherein the beads are capable of being positioned via magnetic means. The present invention also provides method(s) of preparing adhesive coated substrates using pressure-sensitive adhesive bead(s) that are magnetically responsive, electrostatically responsive or both by using magnetic forces, electrostatic forces or both.

Description

~O 94/20S85 2 ~ ~ 7 ~ 3 ~ PCT/US94/02418 S A METI-IOD C~F MA~NETICALLY AND/OR ELEC~TROSTATIC~LLY
I'OSITIONING PRESSUR~SENSITIVE ADI~ 'E l~l~,AD~
AND MAGNETICALLY I'OSITIONABL~, PRESSUR~SENSI~IVE ADHESl~,r~ I~E~I)S
Field of the Invention The invention relates to a method of positioning pressure-sensitive adhesive bead(s) comprising a pressure-sensitive adhesive core and a non-tacky shell material that surrounds the core wllereill the pressure-sensitive adhesive bead(s) can be positioned via magnctic mealls, electrostatic means, or a combination thereof.
1~ This invention also relates to pressure-sensitive a(lhesive head(s)which comprise a pressure sensitive adhesive core and a non-lacky shell material that surrounds the core wherein the bead(s) are capablc of being positioned on a substrate via magnetic means.

20 Background of the Invention Microencapsulated adhesive beads are generally understood to comprise a shell which surrounds or encapsulates a liquid nr solid adhesive corc. The shell is impervious to the core material and is sufficielltly strong so as to prevent exposure of the core during normal halldlill~ of lh- bcads.

2~ However, upon the application of heat, pressure, mechanical foree, or the like, the shell fractures, ruptures, dissolves, or is absorbed by thc cc)re lllereby exposing the core. Microencapsulation is discussed in Microcapsl-les and Microencapsulation Techniques, by M. H. Gutcllo (published l y Noyes Data Corporation, Park Ridge, New Jersey, 1976) and Microcapsule l'rocessing and ~0 Technology, hy A. Kondo, edited by J.W. Van Valkenburg, pul)lished l~y Marcel Dekker, Inc., New Yor};, New York, 1979. l~escribcd are limited utilities for tlle .shell materials sucll as core retention, dctacl;ific~ltion, or as a portion of thc adhesive system.
'I`wo commonly employed techniqlles lo produc.~
microencapsulated adhesive beads are coacervation and in situ polymerization.
In coacervation, a continuous shell is formed when a watcr solllble polymer is WO 94/20s85 ~ ~ ~; 7 8 ~1 -2- PCT/US94/02418 condenscd from an aqueous solution. The sllcll f~-rnls al~out a nllclells of material which becomes the core. Shells of this type based on gelatin and gum arabic are well known.
For example, U.S. Patent No. 2,907,682 "Adhesive Tape Containing Pressure Rupturable Capsules," issued October 6, 19~9 to H.J. Eichel discloses an adhesive tape comprising a web havin~T ;l c(!ating of two types of pressure-rupturable capsules tllereoll. One type c-t capsule contains a liquid solvent; the other contains a substantially solid adllesive ~hal is soluble in the solvent. When pressure is applied to the tape, the capsules nlpture and the adhesive and solvent become mixed. The capsules include ~ hard shcll formed by coacervation from gelatin and gum arabic. rhese be;lds are coated onto the substrate in dispersion form and dried.
U.S. Patent No. 2,988,460, "Adhesive Tape," i~ssued June 13, 1961 to H.J. Eichel discloses an adhesive tape comprising a wch coated with pressure-fracturable capsules. Each capsule includes a hard shell which surrounds an adhesive core. The capsules are formed by coacervation and are coated in dispersion. Upon the application of pressurc at a teml~cratllre substantially abovc 100F (37.8C), the shells fractllre and thc ;Idhcsive coresbecome tacl~y and flow. U.S. Patent No. 2,988,461, "Adhesivc," issue(l June 13, 1961 to H.J. Eichel is similar to the immediately preccdillg patcnt except that the application of pressure withou~ heat is required ~o activatc theadhesive. In tllis case as well the adllesive is coated in dispersioll form.
Japanese Kokai Patent No. 63-273680, "Capsul- IyF)c Adhesive alld Adtlesioll Mclhod Using Capsulc Type Adllesive," I'ul)lisllc(l Novenll)cr 10, 1988, disclose.s an oil with an adhesive dissolved thereill. lhc oil i~ ~se~icd in a gclatill capsule. Applying pressure to the cap.sulc causes ~he S.llllC lo brcali~hereby releasing the oil/adhesive blend. There is no mentioll of the coating tcchniqllc involved using the capsule adhesive.
Japanese Patent Publication No. 60-124679, "I're.ssllre Sensitive 3() Adhesive Sheet"' published July 3, 1985 discloses sevcral adhcsive microcapsules. For example, Figure 2(d) contained in Japanesc l'atcllt l'ublication No. 60-124679 illustrates a pressure-sensilive adhc.i-c core covered by a fne inorganic powder and then encapsulated by a polymcl rllm which is obtained by coacervation. Pressurc is applied to the microc~lpsllle to expose the adhesive core. The beads are subsequently coalcd using a siml-lc prilner coat with spray coalillg of thc adllesive dispersion or dust coatillg ol ~I drv adllesive material.

~O 94/20585 ~ l ~i 7 ~ ~ ~ PCT/US94/02418 "In Situ" polymerization is a second commonly employed technique for producing microencapsulated adhesive beads. A shell fomled of a gaseous, liquid, water or oil soluble monomer or a low molecular weigllt polymer is polymerized on the surface of a core material to provide a polymer 5 ~llm which covers the entire surface of the core material. Shells based upon urea-formaldehyde are well known. A variety of materials includin~
homopolymers~ copolymers, graft copolymers and block copolymers may be used to form the shell. For example, British Patent Specification No. 989,264, "Microcapsules and Method of Producing Them," published ~pril 14, 1965, 10 discloses microcapsules comprising discrete, distinct and contin~lous aminoplast shell walls upon water-immiscible incrt solid or liqui(l fill par1iclcs. No coating techniques are described. In situ polymerization is also mentionc-~l in JapaneseKokai Patent No. 2-102280, "Microencapsulated Pressure Sensitive ~dhcsive Agent," publishcd April 13, 1990, which discloses a pressure sensitive adhesive 1~ agent in a non-pressure sensitive adhesive shell which surroullds thc agent. A
dust coa~ing techni4ue is employed.
Adhesive beads arc also discussed in olhcr publicatiol1s. i~or example, U.~i. I'atent No. 4,091,162, "Adhcsives," i.s~suc(l May 2:~. 1978 to Henderson et al. discloses a "core-shell" polymer particle comprisil1g a soft, 20 tacky polymeric core surrounded by a hard, non-tacky non-blocl;il1g polymeric~sl1ell. l`he poiymer shells rendcr the adhesive beads nol1-blocl~ing (i.e., non-agglomcrating) in a latex dispersion whicll then may be coatcd from the dispersion, from solution~ or by hot melt. The l)ca(ls ,~rc forn~cll b~
polymerizing the core fo]lowed hy polymerizing the sl1ell ahout the core. A
25 typical "core-shell" polymer particle is illustrated in l~ig. I of ~hc Hendcrson et.al. patent.
Japanese Kokai Patent No. 2-102280 discloses a similar technique for producing a structure which includes an adhesive core and a non-adllesive shcll whicll involvcs polymerizing a core followed by polylllcri7ing ~he shell ~() about the core. l hc above-mentioned Japanese T'atent Pul)licali( n No. (~0-124679 discloses three adhesive microcaps1lle.s o~her thall thc co.lcervate structurc illustratcd in drawing l~igllre 2(d). I~igurc 2(a) ~sllowi .ul adlleslve microcapsule in which a frozen and groulld pressure SCllSitiVC .~dllesive is mixed with a rosin-like or terpene-like resin to form a powdcr that rcl-ortc(lly tlowswell at roolll temperature. The adhesive microcapsule illustralcd in drawing l~iguré 2(b) apr)arel1tly comprises the adl1esive microcapslllc ol I igure 2(a) turthcr coatcd witll an inorganic powder such as silica, bcntonllc, alumina or WO 94/20585 PCT/US94/02418~
~1~7~
talc so as to enhance the flowability of the microcapsules. Thc adllcsive microcapsule of Figure 2(c) comprises an adhesive core coated with an inorganic powder only.
Young et al., U.S. Patent Nos. 4,833,179 and its divisional 4,952,650, "Suspension Polymerization," issued May 23, 198'~ and August 28, 1990, respectively, disclose the production of non-agglomerating pressure sensitive adhesive beads by suspension polymerization. The bcads include an inorganic coating of silica powder which surrounds an adhesive corc.
Application of the beads by hot melt coating is described.
The above-mentioned references that describc an adhcsive core surrounded by a shell fail to disclose a shell which has the abilitY to be used in any way in the positioning of the pressure sensitive adhesive corc.
Japanese Patent Publication No. 62-319-', "Powder ~dhesive for Electrostatic Gravure Printing," published lanuary 2~ 87~ discloscs tlle ability of a shell material to be electrostatically chargcd for thc purpose of gravure coating of powdered hot melt adhesives. Only noll-prcssllrc sensitive adhesives with limited size (5~L to 40~), charge levels, and chat,~illg methods (corona discharge) are disclosed. Tl1ese are claimed lo bc usct~ll for electrostatic gravure printing methods only.
U.S. Patent No. 4,427,481, "Magnetizccl Hot l~lclt ~dhesive And Method of Preparing Same," issued Jan. 24, 19~4 to Mulik et.al. discusses installing a permanently magnetized ferromagnetic substallce hl~O a hot melt adhesive thereby creating a dispersion. It is then fonlled into a stril- material which in turn can be positioned prior to activation of the hot nlc1t ~dhesive.
Upon application of heat the material flows and lhe magnetizcll particles draw ~he adhesive into the joint to be sealed. The patent does not tl~ h a detackified PSA bead containing a magnetically responsive material.
Adhesive beads, in general, have been applied ~ ul-strates by a number of means such as from dispersions, rrom sollltion~s, via hot melt applicatiol1.s and by dusting. Hot melt applications cal1 bc par~icularly disadvantageous in that the application proces~s may rc4llire a higl1 lcmpcrature which can reslllt in thc degrada~ioll ol` the adhcsive. l:urthcrmolc, nlethods of pattern coating such as gravure coating can be inconveniellt dllc to the need tosubstitute a ncw roll for eacll pattern which can be tinle consllllling as wcll as expensive.

~o 94,20585 2 ~ ~ 7 8 ~ ~ PCT/US94tO2418 Summary of the Invention A need exists for an alternative methocl of applying adhesive to a substrate, particularly as a 100% solid system. A need particularly exists for amethod of pattern coating 100% solid adhesives without the inherent 5 disadvantages of hot melt adhesive systems. We have discovered such a method. A need also exists for an adhesive which can easily hc applied to a substrate via a solventless system. We have discovered such ~n acll1esive.
The present invention relates to a method of coating T'SA beads via electrostatic means, magnetic means, or both, pric r to their activatic m The lO pressure-sensitive adhesive bead(s) useful according to the method of the invention comprise a pressure-sensitive adhesive core with a continuous or discontin~lous shell coating on the surface thereof, willl the naturc of the shell being that it has the ability to hold an electrostatic charge and/c r thc nature of the bead being that it is magnetically responsive such that it is llseful in thelS positioning or transport of the PSA bead.
The method of the invention for providing a pressure-sensitive adhesive bead coated substrate comprises the steps of:
(a) providing a substrate and a pres.sure-sensilive adhesive bead(s) wherein each of the bead(s) comprises a press-lre-sensitive adhesive 20 core and a tack-free shell therearound, wherein the pressllre-scnsitive adhesive bead(s) is elcctrostatically chargeable, magnetically re.spollsivc. or l-oth;
(b) positioning thc bead(s) on a subslrale by a m~uls selected from the group consisting of electrostatic force(s), magnelic force(s). bolh electrostatic forces and magnetic forces to form a tac~;-free coating of the 25 bead(s) on the substrate.
The method may further comprise a stcp (c) of aclivating the bead(s) on the substrate to expose the pressure-sensitive adhesivc core and provide a coating of the pressure-sensitive adhesive on the substrate.
The invention also provides an adhesivc bead con-prising a ~0 pressure-sel1sitive adhesive core and a tack free shell thercarolln(l, whercin the bead is capable of being applied to a substratc via magnetic mcans. The adhesive beads of the invention are environmentally acivantageous in that they are produce(i via a solventless process and thlls Cl11it no solvenls upon coating.

35 Brief Description of the Drawings The invention will be more fully understood wi~h reference to the following figures.

WO 94/20585 PCT/US94/02418~
2 ~ 6-~ ig. I illustrates a graph depic~ing the static voltage versus time for the beads of Examples I to 11.
Fig. 2 illustrates the parallel alignment of the magnetically responsive beads of Example 5 on a paper/magnetic lape interlace prepared 5 according to the procedure of Example 13.

Dctailcd Description of the invention The pressure-sensitive adhesive bead useful accordillg to the method of this invention comprises a core comprisillg a pressurc-scllsitive 10 adhesive and a shell disposed about tlle core. This shell Inay bc eilher continuous or discontinuous in nature as long as it dc~ackifics lhc pressure-sensitive adhesive core. The shell is of a nature as lo hc al)le to have imparted an electrost~tic charge to tlle surface and/or tllc .shcll nlay be magnetically responsive and/or the core may be maglletically responsive.
Pressure-Sensitive Adhesive Cores Core will sometimes be referred to hercin as "tllc pressure-sensitive adhesive core", it being understoo(l that lhis mealls that thec ore comprises a pressure-sensitive adhesive material. As used hcrein, 20 "pressure-sensitive adhesive material" means a material which displays pressure-sensitive tack; that is, a material which is tacl;y whcll touched with light pressure. However, as explained below, the shell renders the bea(l nontacky. The PS~s which make up the PSA cores are lyl-ic.llly ol the type which would provide useful PS~ coaled materials sucll as sllee~ matcrials, (e.g., lapcs, labcls, and lhe like) metals, plastics, ccramics, ctc.
The pressure-sensitive adhesive core can comprisc a variety of adhesives. The pressure-sensitive adhesive cores may be dcrive(l from adhesives including but not limited to those selected frolll the grouF) consisting of polyacrylates, conventional mbbers including but not limite~l lo those ~0 sclected frolll lhe group consisting of natural rubbers, styrene-l)uladiene block copolymers, elastomeric rubbers such as bu~yl rubber and pc h,(.llpha-olefins), and bien-ls Ihercol. Plasticizers and/c)r tackifiers are gellcr,~ dcied to produce lhe desired pressure-sensitive adhesive propelties. Slill olhcr suitableadhesive cores include those selected from thc group consislhl~ of vinyl ether olymcrs and silicone pressure-sensilive adhesives, holh of wllich may be ~) 94/20585 ~ i 7 8 ~ :~ PCT/US94/02418 l~lended with acrylic pressure-sensitive adhesives or prepared is acrylic copolymers. For all of these PSA cores the same shell coatin~s may be employed.
The diameter of the PSA core can vary depending upon the S application desired. Typically the ~i~meter of the PSA core ranL~es fron- about 10 microns to about 3200 microns, preferably about 25 to about 500 microns.
Typically, beads having a smaller core diameter will provide a nlor-e continuousPSA coating on a substrate on which they are coated and activated.
Conversely, beads having a greater core diameter will provide ~I more 10 discontinuous coating on a substrate on which thcy are coated alld activated.However, beads llaving a smaller core diameter tend to have ~I highcr shell to core ratio thus resulting in a coating which provides lower adhcsioll values.
The pressure-sensitive adhesive cores may bc plcyared by a number of techniques. For example, the PSA cores nlay be prcpared by 1.~ granulating a bulk pressure sensitive adhesive material at low ~cmpcratures (e.g., about -60C or below). The pressure-sensitive adhesive may be frozen with liqui('i nitrogen so as to detackify the adhesive and then gro1llld to provide granular r,ilatter useful as the adhesive cores. In addilion, the l'SA cores maybe prepared by an aqueous suspension technique, sucl1 as the cores described 20 below.
A polyacrylate pressure sensitive adhesive core m~y be prepared by an aqueous suspension polymerization process similar to th.lt disclosed in U.S. Patcnt No. 4,833,179 and U.S. Patent No. 4,95 ,650. Iil gellcral, the suspension polymerization technique described in the.sc p~tents involves the 25 steps of:
(I) preparing a monomer premix comprisillg:
(a) acrylic acid ester(s) of a noll-terti.1ry alcohol, the alcohol having from 1 to 18 carbon atoms, with the averagc mllllber of carbon atoms being about 4 to about 12;
3() (b) a functiollal mononler col~olymerl~<lblc with the acrylic acid ester;
(c) a free-radical initiator; and (d) a chain transfer agent;
(2) combining the premix with a water phasc containing a 35 diispersion aid and/or a stabilizer to fonn a suspensioll; and WO 94/20585 ~ 1 ~ 7 8 ~ ~ PCT/US94/02418 (3) concurrently agitating the suspension to perlllit the polymerization of the monomer premix until tl-e pressure-sensitive adhesive cores form.
Alkyl acrylate monomers (i.e. acrylic acid ester monolners) 5 useful in preparing the pressure-sensitive adhesive include but are not limited to monofunctional, unsaturated acrylate ester monomers. Included witllin this classof monomers are, for example, isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, n-butyl acrylate, hexylacrylate, and mixtures thereof. The acrylate monomers compri~se at least about 70 parts by weight based on 100 parts by weight total monomcr content, preferably from about 75 parts by weight to about 90 l~arts l-y wcigllt. IJnlessindicated otherwise, all parts are parts by wei~ht.
Alkyl fumarates and alkyl maleates (based, respc-~ively, on fumaric and maleic acid) may also be successfully used. I xamr)les lhereof 1:~ include but are not limited to those selected from the ~roup consistitlg of dihutyl maleate, dioctyl fumarate, dibutyl fumarate, an(l dioc~yl male~te.
The functional monomer copolymcriza~ lc with tllc acl ~lic acid ester, the fulnaric acid ester, or the maleic acid ester is incorporclted into the monomer premix so as to modify a final property (for cxaml-l-. pecl adhesion 20 or shear holding strength) of the resulting adhesive core. The l;mctional monomer may be a polar monomcr. "I'olar monomer~;" illCIUdC I otl~
moderately polar and strongly polar monomers. I'olari~y (i.e., hydrogen-honding ability) is frequently described by tlle use ot` terms sucll as"strongly," "moderately" and "poorly." References dcscril~illg thesc and other 25 solubility tenns include "Solvents," Paint Testing Manual~ 3rd l~,cl., G.G. Seward, ~ditor, ~merican ,Society for Testing and Materials, I'lliladelphia~ Pennsylvania, and "A Three-Dimensional Approaell to .iolut~ility,"
Journal Or ~'ainl 'rechnology, Vol. 38, No. 49~, pp. 2~19-280. ,~;~roll~ly polarmonomers u.seful herein include acrylic acid, metllacrylic acid. it.acollic acid, ~() hydroxyalkyl acrylates, styrene sulfonic acid or tile so(liIllll sal~ ercof, maleic acid, filmaric acid, citraconic acid~ acrylamides, and substilllte(l acrylamides.
Moderately p olar monolllers useful herein includc N-villyl lactallls such as N-vinyl pyrrolidone, N-vinyl caprolactam, acrylonitrile. alld di~ thyl amino-propyl methacrylate.
Otl1er monomeric materials which may he uscd .IS Ihe t;lnCIiO
monomer include macromers of lhe type disclosed in ll.S. I'atcllt No.
~,786,116 such as l-polystyrylethyl methacrylate, vinyl esters sllcll as vinyl ~p 94/2058s 2 ~ ~ 7 8 ~1 PCT/US94/02418 g aeetate and vinyl chloride, dialkyl maleates such as dioetyl maleate and dibutylmaleate, dialkyl fumarates sueh as dioetyl fumarate and dibutyl fumarate, and alkyl methacrylates sueh as methyl methaerylate.
Mixtures of any of the above noted functional monomers may 5 also be employed. For example, a preferred functional monolller comprises a blend of vinyl acetate, methyl methaerylate and methacrylic acid. The funetional monomer may eomprise up to about ~0 parts by weight of the premix based on the total monomer eontent, preferably from about lO to about 25 parts by weight.
Initiators for polymerizing the monomers to provide the adhesive eores of the invention are those which are normally suitahle for free-radieal polymerization of aerylate, fumarate and male<~te monomers and wilich are oil-solut)le and have low solubility in water, which incll~(le but ~re not limited to those selected from the group consisting ot organic peroxides such as 15 benzoyl peroxide, lauryl peroxide and various thermal initiatoIs. An example of a useful thermal initiator is 2,2'-a~obis(isobutyronitrile), conllllercially available from T .l. dul'ont de Nemours & Co. (Wilmingtoll, l)elaware) under the tradename VAZO~64. The initiator is present in an amo~ ranging from about 0.05 to about I part by weight based 011 100 parts by weigllt total 20 monomer content.
In the course of carrying out the SUSpCllSiOIl polymerizatioIl of these adhesive corcs, chain transfer agents, including but not limited to those selected from the group eonsisting of mercaptans, alcohols, an(l carbon tetrabromide, may be useful. Representative examples of usellll ch.lin transfer 25 agents include those selected from the group consisting of isooctyl -thioglycolate, carbon tetrabromide, etc. The chain tr.msfer agellt is present inan amount ranging from about 0.01 to about 0.5 par~ hy weigllt ba.~ed on 100 parts by weight total monomer contenl.
If aqueous suspension polymerization is u~sed to p1-epare these () adhesive cores, conventional dispersion aids, stabilizers an(l, ~pliollally, anionic and nonionic surfactants may be advantageously employed. 'I-llc anlount of surfactant, if included, is preferably from about 2.5 parts per millioll to about 1.0 part by weight based on 10() parts per weight total mononler content.
Representative examples of useful surfactants include those selected frolll the ~5 group consisting of sodium lauryl sulfate, sodiulll dioctyl sulfo.succillate. and mixtures thereof.

21~ 7 ~ PCT/USg4/024l8~

Dispersion aids are those conventionally used in suspension polymerization processes. Typica~ly they are water insoluble or minimally water soluble inorganic powders including but not limited to those selected fromthe group consisting of tribasic calcium phosphate, calcium carbonate, calcium sulfate, barium sulfate, barium phosphate, hydrophilic silicas, ZillC oxide, m~nç,sium carbonate, and mixtures thereof.
Typical stabilizers are water soluble organic compounds, including but not limited to those select~{l from the group consisting of polyvinyl alcohol, poly-N-vinyl-2-pyrrolidone, polyacrylic acid, polyacrylamide, hydroxyalkyl cellulose, and mixtures thereof.
Poly-N-vinyl-2-pyrrolidone and polyvinyl alcohol with a viscosity based molecular weight of about 15,000 to about 630,000 are preferred. The total amount of dispersion aid and stabilizer is present in an amount ranging from about 0.01 part to about 5 parts by weight based on 100 parts per weight total monomer content.
Optionally, photocrosslinking agents may be used in preparing the adhesive cores of the invention. Represent~tive examples of uscful crosslinking agents include copolymerizable aromatic ketone monolllers, such as acryloxybenzophenone. When present, the photocrosslinker generally comprises from about 0.01 part to about 5 parts by weight based Oll 100 parts by weight total monomer content.
Various additives may also be included in the mQIlon~er premix.
Such additives include, for example, bases including but not limited to those selected from the group consisting of ammonia, tertiary amine~s, sodium hydroxide, barium hydroxide, calcium hydroxide, magnesiulll hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof. These additives comprise from about 0.1 part to about 5 parts by weigllt base(l on 100 parts by weight total monomer weight.
According to one method of making the polyacrylate PSA cores the monomers, free-radical initiator, chain transfer agent, and otller additives (if included) are blended in the prescribed ratio to form a monomcr premix. The monomer premix is then combined with an aqueous phase comprisillg water, a dispersion aid, a stabilizer, any optional surfactants (all as discussed more fully herein above) and polymerized, with agitation, for about I to I() hol~rs at a 3~ temperature of about 45C to about 85C to give a suspensiot) wllicll contains the preferred adhesive cores. The cores may be washed and separated from the water by means such as gravity filtration. The filtered product generally ~p 94/20585 2 ~ 5 ~ 8 ~1 PCT/US94/02418 comp~es about 15 to about 30 percent by weight water. The resvltinE
adhesive cores typically have a ~ meter of about 10 microns (~) to about 3200 microns and are usually pearl sh~ped~

5 ~esJ.--e-Sensitive Adhesivç Bead Shells The prcssu,e sensitive adhesive core has a non-tacky shell disposed therearound. As indicated previously, the core may be coated with a shell comprising an electrostatically chargable material and/or the core may be coated with and/or i"~pregl-~t-o4 by a m~Enetically responsive material.
The shell material of the bead may be used to initially position the PSA bçad on the ultimate substrate to be coated or on a first substrate which serves as a transfer mçdium. If desired one may use a series of transfer media This positioning on the ultimate substrate and/or the transfer mçdia may be accomplished by the use of electrostatically chargeable shell materials, 15 such as thosç in the triboelectric series, and/or m~Enetic~lly responsive materials which are embedded andlor dispersed about the PSA core. Normally, the presence of a static charge on an adhesive bead would be considered a hindrance and therefore undesirable, but we have discovered a variety of novel coating techniques which make use of this heretofore undersirable 20 characteristic. We have also discovered novel coating techniques which make use of our novel nl~netically responsive beads.
One form of shell coating is considered to be essenti~lly discontinuous. By "essentially discontinuous" it is meant that the shell coatingcomprises a multiplicity of discrete particles which substantially surround the 2S inherently tacky core such that the core is not substantially exposed. Another form of shell coating is considered to be e~centi~lly continuous. By "essentially continuousn, it is meant that the shell while perhaps cont~ininE fissures or cracks therein does not comprise a multiplicity of discrete particles which subst~nti~lly surround the adhesive core but rather a subst~nti~lly continuous 30 shell.
The particles which surround the core to provide an essentially ~i~ontinuous shell are substantially uniform in size and shape. The particles may be provided in a single layer or more than one layer about the core or may be provided in groups or clusters which cooperate so as to subst~nti~lly 35 surround the core. By "substantially surround" and "not subst~ntially exposed"

SUBSTITUTE SH~ET (RUL~ 26) WO 94/2058~ PCT/US94/02418~ -3 ~ ~ -12-it is recognized that gaps or spaces may exist between individual particles (or clusters thereof) so long as the surface of core is not exposed ~o a degree thatrenders beads not free flowing as explained more fully herein l elow.
The shell materials can be applied in in-sitLI pols~meri7ation, latex or solvent dispersion form, or as a granulated powder. When tlle shell materials are applied as a granulated powder the pressllre-sensitive adhesive cores can be coated by a variety of methods such as by dustin~ the core with or rolling the core in the granulated powder.

~lectrostatically Chargeable Shell Materials Useful electrostatically chargeable shell materiais inclllde a wide variety of non-tacky materials including but not limited to thosc selected from the grollp consisting of non-tacky thermoplastic polylllers; natllral polymers including but not limited to those selected from the group consis~ing of wool, silk, celluloses such as cotton and linen, starch, gelatin, polysaccllarides such as agar and carrageenan, etc.; thermosetting polymers including bll~ not limited tothose selcc~ed from the group consistillg of urea-lorlllaldehydc rcsills, phenol/resorcinol-formaldehyde resins, melamine-forlllaldehydc rcsills; epoxy resins; alkyd resins; organic compounds which can be made in powdered form including b~lt not limited to those selected from the gro~lp consi.s~ing of rosin esters, terpenes; and electrostatically chargable inorg;lllic matel~ ls incl~lding but not limited to tllose selected from the group consisthlg of silica. li~aniunl dixoide, calcuim carbonate, ceramics, talc, kaolin, cl;ly, minctal powders such as quart%, asbestos, galena, gypsum, and the like.
According to one method of providing adhesive cor~.s having an electrostatically chargeable and/or magnetically rcsponsive sllell so as to formadhesive beads according to the invention, a polymeric materi.ll may be combined with the aqueous suspension of formed adhcsivc corcs (if the cores are formcd by an aqueous suspension polymerization). An cxamplc of such a ~0 polymeric material is an organic thennoplastic homopolylller or all organic tllermoplastic copolymer derived from a latex of the homopolynlcr or the copolymcr (collectively referred to hereinat~cr at times as "an organic polymer latex") or derived trom a solvent dispersion of the honlopolymcr or the copolymcr (collectively referred to hereinafter at timc~s as "a solvenl dispersio ~5 of an organic polymer"). Magnetically receptive or magnetizcd particles (magnetically responsive particles) may or may not be added l(l Ille .~olvcnt dispersion of organic polymer latcx and then dricd an(l grollll(l lor Ille pllrpose ~) 94/20585 ~ I ~ 7 8 ~ 1 PCT/US94/02418 of creating seed particles for the formation of the adhesive cores or for improved attraction of the coated particles during post treatment of the adhesive cores. Alternatively, the material from which the shell is formed may be provided as a granulated powder which may optionally encompass magnetically 5 receptive particles.
By "thermoplastic" is meant a material that is capablc of being repeatedly softened by heat and hardened by cooling over a particular temperature range. By "thermosetting" it is meant a material tllat is capable ofbeing rendered hard by the application of heat. "Latex" refers to an aqueous 10 dispersion of the particular material which is typically produced by emulsionpolymerization. By "copolymer" is meant a polymeric material colllprised of two or more monomers.
One type of polymer shell of the invention can colnprise monomers or mixtures thereof which are polymerized by a frec-radical 1~ polymerization process such as emulsion, suspension, or bulk pnlynleriz.l~ion.
When the polymer shell is derived from emulsioll or suspension polymerization processes using redox (redllction-oxidation) or thermally activale(l initiators, it is provided in the form of an organic polymer latex. I'referably, thc polymer additive is provided as a latex having particles with a diameter of 10~ or less.20 If desired, the latex may be dried and ground to provide the polymcr additive in powder or granulated form. This powder may be uscd to dctacl;ify ~he adhesive cores. Alternatively, the powder can thcn 1~ redi~ipcr~i~d in an appropriate organic solwnt so as to provide a solvent disper~ion o f the organicpolymer. Alternatively, the organic polymer latex may be dissolved in an 2.~ approp,iate organic solvent. Suitable organic solvents include low polarity alcohols such as isopropanol and n-butanol, aliphatic hydrocarl)oll solvents such as hexane and heptane, aromatic hydrocarbon solvents such as bcnzene, toluene and xylene, as well as tetrahydrofuran, methyl ethyl ketone, and thc like.
Free-radical bulk or solution polymerization rcquirillg thermal or 3() photochemical initiation using organic peroxides, hydroperoxides. a7(1 or diazo compounds may be employed. Other polymerization processcs such as cationic, anionic and coordination polymerizations can also provide the polynler shell.
References which discuss such processes include F. W. Billmeyer, I extbook of Polymer Science, 3rd Ed., Wiley, Intersciencc 1984, pp. 8~-91. and 3.~ R. Morrison and R. Boyd, Organic Chemistry, ~rd. 1-~., Allyll and Bacon, 1973, pp. 1037- 1039.

WO 94/20585 ~ ~ ~ 7 ~ ~: L PCT/US94/02418 Cationic polymeri_ation is preferably limited to unsaturated hydr~l,on polymer co~tingc such that Lewis acids, protonic acids or carbenium ions are typically used as catalysts along with low reaction le",~cldt,~res (i.e., usually below room temperdture). Anionic polymeri_ation (also known as "living" polyme~i7~qtion) is typically initiated by strong anionsderived from alkyl lithium, sodium in liquid ammonia, and the like at room t~."~dl~lre or below to give essentially monodisperse polymers. Coordination polym~-i7~tion involves Ziegler-Natta cdtalysts usually employed in fluidi~d bed processes to give stereospecific polymers. The polymer produced by any of these methods is usually in bulk or semi-bulk form after removal of the solvent or carrier, if any was used. Granulation of the resulting product provides the polymer additive in microni_ed powder form.
Suitable monomers for the formation of either the thermoplastic homopolymer or copolymer include but are not limited to those selected from the group conci~ting of styrene, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate orbutyl methacrylate and mixtures thereof (i.e., vinyl group and acrylate group containing materials). When the polymer additive is provided as a thermoplastic copolymer, the above monomers may be blended with each other and/or further mixed with a polar comonomer including but not limited to those selected from the group conci~ting of sodium styrene sulfonate, sodium acrylate, sodium methacrylate, acrylic acid, methacrylic acid, maleic acid, fumaric acid, sodium maleate, sodium fumarate, citraconic acid, vinyl betaines, N-vinyl-2-pyrrolidone, 4-vinylpyridine, acrylamides, substituted acryl~mides, and mixtures thereof. Preferred polar comonomers include sodium styrene sulfonate, acrylic acid, sodium acrylate, m~th~crylic acid, sodium meth~rylate~
N-vinyl-2-pyrrolidone and acrylamide. When present, the polar comonomer comprises from about 0.5 part to about 10 parts by weight based on 100 parts by weight total monomer content of the organic copolymer coating.
Both the adhesive cores and the shell coatings may contain one or more adjuvants. Preferred adjuvants include those select~d from the group concicting of tackifiers, plasticizers, pigments, dyes, extenders, fillers, antioxidants, multifunctional cro~slinkPrs, stabilizers, magnetically responsivematerials (di~cusced infra), and mixtures thereof. An especially preferred 3~ additive is bis-vinyl ether which provides high cohesive strength. When present, this additive generally comprises from about 0.5 to about 1 part by weight based on 100 parts by weight total adhesive core monomer content.

S~BST1~ E~ (R~L~ 26) ~ 94120585 21~ 7 8 ~ i PCT/USg4/02418 Preferably, the thermoplastic homopolymer or copolymer has a glass transition temperature (Tg) of at least about 25C, more preferably from about 90 to about 95C, while the adhesive core preferably has a Tg below about 20C. If the Tg of the homopolymer or copolymer of the shcll is less 5 than about 25C, it may be too close to the Tg of thc adhesivc corc material and, as a result, may tend to blend therewith and pos~sibly matcrially adverselyaffect the free-flowing quality of the adhesive beads of the invcntion.
The following are several specific methods of pr(lvidillg the PSA
cores Witll a shell. The shell material whether providcd as an organic polymer 10 latex, a solvent dispersion, or as a powder, may be combined witll the pressure-sensitive adhesive cores by several different techniqucs so as to form adhesive beads according to the invention. In each instance, thc shell material is providccl in an amollnt ranging from about I part to about ~ parts per 100 parts by weight of adhesive cores, preferably from about '' part.s lo abollt 3 1 5 parts.
According to one technique an organic polymer latex derived by cmulsion polymcrization may be coll1bined wilh previously forlllcd alld liltcredadhesive cores and then agitated so as to provide the adhesive cores with an essentially discontinuous organic polymer shell derived from the latex.
20 Alternatively, in situ emulsion polymerization may be employcd to prep.lre a discontinuous coating. According to this approach, the ingredicllts which provide the shell are blended together and emulsion polymcri7~(1 in the presenceof the prcviously formcd adllesivc cores. Accordil1~ lo a tllird Iccllniquc of preparing a discontinuous shell coating, the ingrcdient.s whicll l~r~vide the shell 25 may be addcd lo the adhesive core monomcr premix al`ler the cxolllcrm which occurs during the suspensioll polymerization thereof. The shell matcrials may lhen be cmulsioll polymerized. As a fourlh altemativc of prodllcing a discontinuous shell coating, an organic polymer latex for forming thc shcll may bc combincd wilh the adhesive core monoll1er premix prior to ~he suspellsion ~0 polymerization of the cores. Such an approach may bc regardcd a.s an "in-line"
process.

Magnetically Responsive Materials The beads of the invention can compri.se one or n1orc 3~ magnetically responsive materials to aid in positioning the heads. The term "magnetically responsive materials" as used herein refers to matcrials with sufficient magnetic attraction so as to be usefill in the transporl of the PSA bead WO 94/20585 PCT/US94/02418,~
2~g~ ~ _ of the invention onto a transfer medium and/or substrate. Magnetically responsive materials include but are not limited to ferromagnelic materials, salts of ferromagnetic materials, and alloys of ferromagnetic materials, which may or may not be magnetized. ~or example, a ferromagnetic materi.ll may be 5 petmanently magnetized to form a magnetically responsive ma~crial which is a permanent magnet.
Examples of useful ferromagnetic materials includc but are not limited to those selected from the group consisting of iron, cohalt, nickel, gadolinium, dysprosium, including alloys and salt~s of tllese metals with other 10 elemental materials including but not limited to those selected lrom the group consisting of carbon, silicon, aluminum, copper, chromiulll, mallgallese, magnesium, titanium, barium, strontium, tungsten, vanadiulll, niobillm, platinum, and silver. Nickel is a preferred ferromagnetic matcrial due to its low cost and low reactivity. Iron is less usefill due to its tend~ncy tc oxidize.
It is possible to coat the magne~ically responsivc matcrials with a material to enhance the affinity of the magnetically rc~sponsive material to thePSA core. Such coating is of increased importallce whell a suspellsion polymeri~ation is employed in forming the PSA cores since thc watcr phase can cause the magnetically responsive material to phase scparate. Preferably, the 20 magnetically responsive particle(s) is coated with a thermoplastic material.
Useful themloplastic materials include but are not limited to thnse selcctcd from ~he group consisting of a dispersion of polymcric thermoplastics. su~h as those derived from acrylates, polyolefins, polystyrenes and lhc othcl- ~hcll material discussed infra.
2~ The number and size of the magnctically respollsi~c particles contained within the PSA core or the shell or both can vary. (~ne nlagnetic particle may be sufficient. However, one magnetic particle would nOt bc sufficient to provide the PSA core with a non-tacky shell. Thc rcmaindcr of the non-tacky shell would thus need to be provided by a non-tacky electrostatically ~0 chargeable material (discussed supra) and/or a neutral inert or~al)ic or inorganic non-tacky material which is neither electrostatically chargeablc nor magnetica11y responsive which does not interfere with the r~sA prol.erties ol thc l'~SA core.~xamples of such neutral inorganic materials include l-ut are not limited to those selected from the group consisting of inorganic salls inclll(ling hut not 3~ limited to those selected from the group consisting powdcrs ol` I)~lrilllll sulfate, sodium chloride, calcium sulfate, calcium chloride, ~sodiulll S-ll~l[e~ sodium phosphate, calcium phospllate, mixtures thereof and lhe likc.

~O 94120~85 2 1~ ~ 8 91 PCT/US94/02418 The size and number of the magnetic particles if used without any triboelectric materials must be sufficient to allow for the trat1sfer of theadhesive bead of the invention onto a transfer medium if used, and/or onto the ultimate substrate to be eoated. If a large amount of magnetic material is S employecl it can interfere with the adhesive properties of the ~'SA coating prepared from the beads. If a very large amount of magnetic material i.s included the bead will function more or less as a means for adhering a magnetic material to a substrate rather than as a means for adhcring a PSA to a substrate.
The magnetic particle size ean vary. Typically, each magnetie 10 particle has a smaller diameter than the PSA eores which they sllrround and/or are embedded in. Typieally each magnetic particle(s) has a dialnctcr of about I
to aboul 100 microns.

Methods of Drying Beads Once the basic bead structure comprising the pressure sensitive adhesive core and the non-tacky electrically responsive shell and/or magnetically responsive core and/or magnetically responsive shcll has bcen formed, the beads, if contained in a suspension, may be clried so as to convert the beads to an essentially moisture-free condition. 13y "essentially 20 moisture-free" it is meant that the beads contain no n1ore than al)out 5%
moisture. Any of a variety of conventionally used drying metl1ods such as, for example, free%e drying, heated air flash drying, spray drying, Illlidized bed drying or column drying may be employed. Spray drying is a parlicularly preferred techl1ique. l he beads may be filtered prior to dryim~ USillg, for 25 examplc, a bulk dcwatering process such as a bclt conveycr.

Methods of Coating Beads Pressure-sensitive adhesive beads useful according to the method of the invention are those which are usefill in any application h1 which ~0 pressure-sensitive adhesive would have utility. I'referably, the hcacls are applied to a substrate by coating them as a 100% solids system. Prior to, during, or subsequcnt to the application of t11e adhesivc bcacls ~o tl1c final substrate the beads are activated to expose thc pressure-sensitive adhesive cores.
The beads can be activated by a number of methods inclllcling but not limited to~35 the application of heat, the application of pressure, or both. ~hell the l)eads are in a dry, free-flowing condition the core and the coating m~y be regarded asnon-homogcncolls in the sense that the core an(l the coating arc no~ blen(led with each other at room temperature (about 20-22C). Howe-er, upon the application of heat and/or pressure, the adhesive cores melt or cold flow thus becoming exposed and form a blended adhesive coating. An example of simultaneous heat and pressure activation is tlle passing of a b~acl coate(l 5 substrate between a pair of heated nip rollers or the like.
Conventional pressure sensitive adhesives of 10()~., solids formulations are packaged in drums, pails or cartons. Because of the inllerentlytacky nature of the adhesives, release liners or special unloaders must be employed lo evacuate the adhesive from its pacL;aging. Adhesive hcads useful 10 according to the invention function as a conventional pressure scnsitive adllesive subsequent to activatioll but prior to activation are frce from thesc packaging disabilities due to the free-flowing nature of the beads.
The beads may be coated by any means employin~ elcctrostatic charges (such as triboelectric charges), magnetics, or a combination thereof.
15 Electrostatic charges can be applied to the bead via conduction~ corona treatmellt, photoconduction charging, and the like. Triboelectric charges are defined as cllarges which are impartcd to thc surface of the bcad hy fric~ion.
This may be accomplished by a mechanical process such as tullll)lill~, brushing,air conveyance, or the like. One of the unique features of the electrostatically20 chagerable beads described are their ability to accept cither a positi~e or negative charge. This is accomplished by the metllo(l of char~ing and the electron donatillg or electron withdrawing ability of tlle shell r-c Iymer or copolymer. This capability allows the broadest possible coating melho(is to be employed, independent of the charge required. I lle triboelectr-ic scries can be2~ consulted ~o determine which of lwo substances woul(l becomc ncgatively charged and which would be positively charged when Ihe two ale nlbbed togethcr. The triboelectric properties of certain polylllers in descen(lillg order of electron donorship from positive (donor) to negative (acceplor) are as follows: nylon 6,6 (also wool, silk), cellulose, cellulose acetalc, polymethyl 30 methacrylate, polyacrylonitrile, polyvinyl chlori(lc, polybispllenol carbollate, polychlorocther, polyvinylidene chloride, poly-2,6-dimethyl polypllcllylcne oxide, polystyrene, polyethylene, polypropene, and polytetraflu(-lothylene~ The role played by the tribolelectric series is that, it allows prediction c)~ the polarity and level of charge obtainable.
3~ The beads useful according to the invention may be applied to a substrate via a number of electrostatic processes such as electrostalo~raphic processes (electrographic, electrophotographic, comhinati(lns thcreol, etc.) O 94/20585 ~ 7 8 ~ :L PCT/US94/02418 -i9-An electrostatic charge opposite to that applied to the beads may be applied to the substrate and also to a transfer medium, if uscd, by a number of methods including but not limited to the following: brushine~, conduction, corona treatment, and photoconduction.
A repulsive electrical field may be generated which can aid in positioning the charged beads on the transfer medium~ if used, alld also on the substrate. The repulsive electrical field(s) can be gencrated by a nulllber of methods including but not limited to the following: bmshing, collduction, corona treatment, and photoconduction. The repulsivc field is ot sufficient magnitude and positioned such that a chargcd bead placed therein willbe transported to the transfer medium, if used, and/or dependill~ ul-oll the method of application transported to ~he substra~e.
When the pressure-sensitive adhesive beads are clectrostatically chargeable the pressure-sensitive adhesive bead(s) may be posilione~ on a substrate by attracting and contacting the bead(s) to the substrate by means of an electrostatic force.
The electrostatic force may be applied t)y a wide variety of methods. Included herein are several specific examplc~s, of lhc use of electrostatic forces to apply beads to a substrate. However, this invcntioll is not limited to these specific examples.
As one example, an electrostatic chargc may be ~pplicd on the substrate opposite to an electrostatic cllarge gcnerated on thc pl-essurc-sensitive adhesive beads The charged pressure-sensitive adhesive ~ E;3d j are ~)rought close to the charged substrate so that the beads are attracted to and contact the substrate and form a tack-free coating on the substrate due to tlle elcctrostatic attraction. Alternatively, an electrical field encompassing the .suhstrate may be generated and an electrostatic charge applied to the pressure-scllsitivc adhesive beads. Thc electrical field whicll, in this example, i~s repulsive to the cllarged pressure-sensitive beads is of sumcient strength and is positioncd such tllat it is ~0 capable of positioning the charged beads placcd thercill on the .substrate. The charged pres~sure-sensitive adhesive beads are brought into the ficl(l .co that the prcssure-scnsitivc adhesive beads contact tlle substratc an(l t`c)rlll a t.lcl;-free coating on the substrate. Combinations of two or morc metllo(ls nlay also be employcd.
~5 2~57~3g~ -20-When each of the pressure-sensitive adhesive be~ads is m~netically responsive the beads may be attracted to and contacted witl~ the substrate by means of one or more m~netic forces thereby posi~ioning the pressure-sensitive adhesive beads on the substrate to form a tacl;-frec coating of 5 the pressure-sensitive adhesive beads thereon.
The magnetically responsive beads of tlle invention may bc applied to a substrate via a magnetic process such as a magnetographic process.
A magnetic field may be generated around the transfer mediunl, if used, and/or around the substrate depending on the nature of the bcads and thc naturc of 10 application desired. The magnetic field can be generated, for example, by a pcrmanent nlagnetic and/or by an electrically induced magnetic rleld Included herein are several specific examples of thc use of magnetic forces to apply beads to a substrate. However, the hlvenlion is not limited to these speci~lc example.
As one example, when the magnetically responsivc pressure-sensitive adhesive beads comprise permanent magnetic par~icle(s) the magnetic attraction force can be provided by a magnctically rcsponsive material in the substrate (i.e., the substrate can comprise a magnetically responsive material) or a magnetically responsive material can be positioned on a side of 20 the substrate opposite the pressure-sensitive adhesive beads. l`he pressure-scnsitive adhesive beads are brought close to the subs~ratc Ihereby allowing the magnetic force to position the pressure-se1lsitivc adhesive beads on the substrate to ~orm a tack-free coating thereo11. ~s anothcr cx.~ le, when the magnetically responsive pressure-sensitive adhesive bead~s do not comprise 25 permancnt magnetic particles a magnetic attraction force may bc provided by amagnetic field encompassing the substrate. The pressure-sensitive adhesive beads within the magnetic field are thereby positioned on the slll-strate to form a tack-free coating thereon. Combinations of methods may als~ bc clnployed.
Regardless of the mcthod of apl)licatioll tllc bea(ls can be ~0 activated by a number of methods including bllt not lin1ited to thc a~ lication of heat, prcssure, or both heat and pressure to provide a coating ol` I~ on the substrate.
When a transfer medium is used, tlle adhesive bea(ls nlay be activated prior to transfer to a second substrate, subscquent to tr.msl`er to a 35 second substrate, or simultaneously with transfer to the secoll~ substrate. Thus, in one situation, the pressure-sensitive adhesive beads on the tral)sfcr medium may be activated to provide a coating of pressure-sensitivc adl~csivc on the ~o 94/20585 PCT/US94/02418 -- 21~7891.

transfer medium. The pressure-sensitive adhesive is then transferred to a second substrate to provide a coating of pressure-sensitive adhe.sive on the second substrate. Tn another situation, the pressure-sensitive aclhesive bcads may be transferred to a second substrate by a means selected from ~he group 5 consisting of magnetic means, electrostatic means, and both magtletic means and electrostatic means and simultaneously activated, thus exposing the cores ofthe pressure-sensitive adhesive beads to form a coating of pressure-sensitive adhesive on the second substrate. In still another situation, the pressure-sensitive adhesive beads may be transferred to a second substrate by a l0 means selected from the group con.~istin~ of magnetic means, clectrostatic means, and both magnetic means and electrostatic means, following which the beads are subsequently activated thereby exposing the pressure-lsensitive adhesive beads to form a coating of pressure-sensitive adhesivc on the sccond substrate.
This may be done by a variety of methods. For example. an electrical field repulsive to the beads may be generated such that it encompasses the transfer medium. The electrical field is posilioncct ancl h~ ol su~l~icielltstrength to position ~he charged beads placed in the electrical t-lcld on thc transfer medium. Optionally, a charge opposite to that on tlle bcads can be 20 placed on the transfer medium. Alternatively, the transfer medium can be charged and placed in the above-mentioned electrical tield. Thc beads are then brought close to the transfer medium and/or the optional char~c Otl tlle transfer mediulll and/or within the optional fields encompassing ~hc translcr medium in order to transfer the beads onto the transfer medium lorllling ~ lack-frec coating 25 thereon. The beads can subsequently be activated on the translcl mcdiuln.
As another example, a second substrate, which has been optionally charged with an electrostatic chargc opposi~e to that 011 thc beads, can be brought into contact with unactivated beads on the transfer medillm, and simultaneous activation of the beads can occur (by tllc application ot heat, ~0 pressure, or both heat and pressure, for example) so as to expo~se thc pressure-sensitive adhesive core and form a coating ot a pressurc-sellsitive adhesive on the second substrate.
As another example, a second substrate which has becn optionally charged with an electrostatic charge opposite to that on ~hc bcads can 35 be brought close to the beads on the transfer mediunl. The beads c~n then be allowed or caused to contact the second substrate and form a tack-free coating on the second substrate by various methods depending on the l`orce holding the WO 94120585 ~ ~ ~i 7 8 ~ ~ PCT/US94/0241 beads to the transfer medium. This may involve one or more of the following:
removing the optional charge from the transfer medium; removing the repulsive electrical field keeping the beads in contact with the transfer medium; applyingan el~tric~l force repulsive to the beads on a side of the transfer medium S opposite the beads; providing the second substrate with an electrostatic charge greater than that that has optionally been applied to the transfer medium. The beads can subsequently be activated after transfer to the second substrate so asto expose the pressure-sensitive adhesive core and form a coating of a pressure-sensitive adhesive on the second substrate.
In one situation, when magnetics are involved in holding the beads to the substrate, one can bring a second substrate, which optionally has encomr~in~ therearound a magnetic field, into contact with the beads on the transfer mfflil-m, simultaneously activating the beads so as to expose the pressure-sensitive adhesive core and provide a layer of a pressure-sensitive 15 adhesive on the second substrate.
In another situation when m~netics are involved, one can bring a second substrate, which optionally has encompassing therearound a m~en~tic field of greater m~nitude than that around the transfer medium, close to the beads on the transfer medium, so that the beads contact the second substrate 20 due to the stronger m~gnetic forces. This results in a tack-free coating of the beads on the second substrate. This can be followed by the subsequent step of activating the beads so as to expose the pres~ e-sensitive adhsive core and provide a coating of a prt:s~.lre-sensitive adhesive on the second substrate.
Examples of transfer media for electrostatic processes include but 25 are not limited to those materials that will induce an electrical charge and hold the charge for a working period (insula~ors). Examples thereof include but are not limited to those materials selected from the group consisting of thermoplastics, wood, paper, i",~rt;gnated cloth such as epoxy siliconized cloth, rubberized cloth, etc. Useful transfer media for magnetic processes include but 30 are not limited to those that allow the passage of a nnagnetic field therethrough or those that may be m~gneti7Pd themcPlves. The transfer medium can take the form of a thin mPt~llic film, drum, roll, met~lli7Pd film, cloth, metallized cloth, etc.
Combinations of electrostatics and magnetics can also be 35 employed according to the invention. Included herein are several specific examples. However, the invention is not limited to these specific examples.
Such a method may, for example involve providing a pressure-sensitive SUBSTlTl~ E~ ~ ~R~L~ 26~

~78~1 ~D 94/20585 PCT/US94/02418 adhesive beads, wherein the beads are electrostatically chargeable, magneticallyresponsive, or a combination thereof. An electrostatic charge may optionally be generated on the beads. At least one of the following may be generated: an electrostatic charge on a transfer medium opposite to the charge on the beads;
5 an electrical field, repulsive to the beads, encompassing the transt`er mediumwherein the electrical field is capable of positioning the beads placed within the electrical field on the transfer medium; a magnetic field encompassing the transfer medium. This preceeding step is optional when the beads contain permanent magnetic particles and when the transfer medium is maglletically 10 responsive or when the beads contain permanent magnetic particlcs, the transfer medium is non-magnetically responsive, and a magnetically responsive material is positioned on a side of the non-magnetically respon.sive transfer medium opposite the beads.
The beads are brought close to the transfer medium and/or the 15 optional charge on the transfer medium and/or within the optional field(s) encompassing the transfer medium so that the beads contact the transfer medium and form a tack-free coating on the transfer medium. The beads may he activated so as to expose the pressure-sensitivc adhcsive corc and provide a coating of a pressure-sensitive adhesive on the transfcr medi~ . I he 20 pressure-sensitive adhesive can then be transferred to a second substrate to provide a coating of pressure-sensitive adhesive on the second substrate.
Alternatively, one can bring a second substrate, ~llich has been optionally charged with an electrostatic charge opposite to that 011 the beads and/or which optionally has encompassing therearound a magnclic field into 25 contacl with the beads on the transfer medium, simultaneously activating the beads so as to expose the pressure-sensitive adhesive core and provide a coatingof a pressure-sensitive adhesive on the second substrate.
Alternatively, one can transfer the beads from the transfer medium to a second substrate and then subsequently activate tl~e bcads. One or 30 more of the following transfer methods can be used. One can bring a second substrate whicll has been optionally charged with an electrostatic cllarge opposite to that on the beads, wherein the optional charge on tlle substrate is optionally of greater magnitude than the charge that has been optionally appliedto the transfer medium close to the beads on the transler medi~ . ()ne can 35 bring a second substrate which optionally has encompassing thcrearound a magnetic field of greater magnitude than that around the transfcr medium close to the bead(s) on the transfer medium. The beads are caused or allowed to WO 94/20585 PCT/US94/02418 ~
~1~78~1 _ contact the substrate and form a tack-free coating on the substrate by onc or more of the following: by an optional electrostatic charge on Ihe second substrate; by an optional magnetic field encompassing the second substrate; by removing the optional charge from the transfer medium; by remc)ving the 5 repulsive electrical field holding the beads to the transfer mediulll; by applying an electrical force repulsive to the beads on a side of tlle transfcr mcdium thetransfer medium opposite the beads; by providing the second snbstrate with an electrostatic charge greater than that that has optionally been apl)lie~l to thetransfer medium. Subsequent to transfer to the second substrale the b eads are lO activated to expose the pressure-sensitive adhesive core and provide a coating of a pressure-sensitive adhesive on the substrate.
The PSA formed upon the activation of the beads of invention can be coated on a wide variety of substrates. Examples of suhstrates on which the beads of the invention or the adhesive prepared thcrefrom call bc coated 15 include but are not limited to those selected from the glOIlp consisting of paper, thermoplastic films, metal, cloth, wood, fiberglass, leathcr, glass, porous membranes, circuit boards.
The following is an example of a specirlc transfcr process. A
transfer medium is charged to a negative polarity via corona chargill~. The 20 transfer medium is capable of retaining the charge on its surfacc for a working pcriod. Subsequently, positively charged pressure-scnsitive adhcsivc beads are brushed across the transfer medium surface and are attracted to the negatively charged areas. The greater the amount of negative charge in cach alea of the transfer medium the greater the amount of pressllre-sensitive adlls~sive beads 25 attracte~l thereto. The substrate is brought close ~o the tran.sf ;~r nledillm. A
negative charge greater than that on the transfer mediulll i.s laid dowll on thesurface of the substrate to attract the positive adhesivc beads to the substratefrom the transfer medium. The substrate is then carried to a heated nip roller which contacts the pressure-sensitive adhesive beads and activatcs them on the ~0 substrate surface, thus forming a tacky adhesive surface. Excc~s bcads are vacuumed or blown clear.
The substrate may optionally be coated with a prilller material prior to coating with the unactivated beads of the invention or subsequent to coating with the unactivated beads. The beads can be secured to the substrate simultaneously with positioning on the substrate or suhseq~lent ~o positiolling on the substrate. The beads, which are secured to the substrate, nl?ly then be activated at a later point in time prior to use. Primer materials arc those ~o 94/20585 21~ 7 ~ ~ I PCT/US94102418 defined as having the ability to maintain the PSA beads in position for a sufficient period of time to allow post activation. Examples thereof include butare not limited to those selected from the group consisting of inks, shellacs, varnishes, adhesives, low melt temperature (co)polymers, polyolcfins, and S waxes, such as paraffin and beeswax.
Another method of application of PSA beads to a substrate involves the use of a positioning particle(s). The positioning particle is a particle which is both magnetically responsive and electrostatically chargeable.Preferably, the positioning particle comprises a magnetically responsive particle having an electrostatically chargeable coating. Alternatively, the positioning particle comprises a magnetically responsive material which is also electrostatically chargeable. The positioning particles can be used as a template or positioning aid to position pressure-sensitive adhesive beads on a substrate.The same electrostatically chargeable materials which can form the shell of the PSA beads can also be used to coat magnetically responsive particle.s to form one type of positioning particle. The same magnctically respon.sive matcrials which can be included in the PSA beads can also be used in fonlling the positioning particles. The diameter of the positionillg particle call vary according to use.
The method of application involves providing a tirst substrate and a positioning particle(s). The positioning particles are positioncd on a first substrate by a means selected from the group consisting of electrostatic force(s), magnetic force(s), both electrostatic and magnetic forces to form a coating of the positioning particles on a first substrate. A pressure-sensiti~e a(lhesive bead(s) is provided which is electrostatically chargeable, magnelically responsive, or both. The adhesive beads are then positioned on the positioning particle-coated substrate by attraction and contacting tlle positioning particles and pressure-sensitive adhesive beads by a means selccted from the group consisting of magnetic force(s), electrostatic force(s), both maglltic force(s)and electrostatic force(s) by bringing the bead(s) close to the parlicles on thesubstrate. The beads can be activated on the substrate. Alternatively, the beads can be removed and positioned on a second sul strate by al-propriate magnetic and/or electrostatic forces which do not remove thc positiolling particles themselves.
According to one specific positioning method, the pressure-sensitive adhesive beads need not be magnetically respc)nsive themselves as long as the shell materal is electrostatically cllargeable. The Wo 94/20585 ~CT/US94102418~
2~78~

particles can be positioned on the substrate by means of a ma~netic force(s).
As one example, when the positioning particle comprises a permancnt magnetic particle the magnetic attraction force can be provided by a magnctically responsive material in the substrate or on a side of the substrate opposite the S positioning particles. The positioning particles are brought close to the beads on the substrate thereby allowing the m~gnetic force(s) to position the positioning particles on the substrate to form a tack-free coating thereon. As another example, when the positioning particle does not comprise a permanent magnetic particle a magnetic attraction force may bc providcd l~y a maglletic 10 field encompassing the substrate. The positioning particles witllin the magnetic rleld are thereby positioned on the substrate to form a t~cl;-frce coating tllereon.
Combinations of methods may also be employed. The magllelic force such as a magnetic field may be used to control the coating pattern. The posilioning particles can be placed close to or in the magnetic field encompassillg the 15 substrate, wherein they contact the substrate in the desired pattenl established due to the magnetic field. The electrostatically chargeable shell material on the PSA bead can be identical to an electrostatically chargeable coatillg on the positioning particle. Preferably, the positioning particle has an electron-donating coating and the pressure-sensitive adhesive bca~ has an 20 electron-accepting shell material. Alternatively, the positioning particle preferably has an electron-accepting coating and the pressure-sensitiYe adhesivebead has an electron-donating shell. This can bc accomplishcd 1-~ selecting a different elcctrostatically chargeal)le material t`or the 1~ bea-ls alld ror thepositioning particles. A charge can be generated on the electro~slatically 25 chargeable PSA bead, on the positioning particle~s, or both. Tlle en.slling electrostatically attractive force between the PSA beads and positiolling particles results in the positioning of the pressure-sensitivc adhesivc beads Oll the particle coated substrate.
According to this specific examplc, the electrost,l~ically ~sO chargeable shell material of the pressure-sensitive adhesive bea(l(s) is attracted to and contacts the electrostatically chargeable coating of the positioning particle which is being secured to the substrate by magnetic forccs. The electrostatically chargeable shell material of the adhesive beads tllus contacts the electrostatically chargeable coating of the positioning particles resulling in a35 coating of the adhesive bead(s) on the substrate. The beads c~n thereafter be activated on the substrate to form a coating of PSA on thc sub.strate.
Alternativcly, the bcads can be removed by electrostatic forccs. For example, a 21~78~1 ~O 94/20S85 - PCT/USg4/02418 -27~ - ~
second substrate upon which an electrostatic charge of greater magnitude has been generated which is attractive to the beads but not the positioning particles can be brought close enough to the bead and positioning particle-coated first substrate to attract the PSA beads and remove them via electrostatic forces.
5 The beads can then be subsequently activated on the second substrate.

Test Methods Pourability of Beads - Funnel Discharge Time Test Once dried, the pressure-sensitive adhesive beads accc rding to the invention are non-agglomerating, essentially cluster-free and t`ree-flowing.These terms are used interchangeably and are deflned with refcrence to a modified American Society of Testing and Materials (ASTM) 1)-1895-69 with a funnel discharge time of less than I minute. More particularly, a static free funnel having a volume of about 100 milliliters and a discharge spout diameter of about 12.7 millimeters (mm) is employed. The discharge spout is te~ or;~ily closed by placing a static free object such as a wood tongue deplessor against the distal end thereof and approximately 20 grams (g) of adhesive beads are lightly poured into the funnel so as to avoid any packing thereof. The flat strip of wood is removed and the elapsed time betore the last bead discharges from the funnel is recorded in seconds as the t~ullnei dischargetime.
This test method recognizes that small clusters or clumps of beads are permissible within the scope of the invention so long as thc clusters or clumps do not impede movement of the beads through the fullllel to the extent that the funnel discharge time exceeds I minute. Tlle shcll coating renders the beads non-tacky to the touch and contributes to their free-flowing nature.

Peel Adhesion The pressure-sensitive adhesive beads of Examplcs 2, 3, 5, and I l were each separately tested for adhesion according to the following procedure. Standard, 20 pound (9.1 kg) bond white copier paper was coated with an orange printing ink (Sinclair and Valentine ~f88318, St. Paul, Minnesota) at a weight of 5.37 g/m2 using a 2.5 inch (6.35 cm) rubber roller.
The ink facilitated positioning and visualization of the subsequently applied beads while maintaining the beads on the paper during post treatment. While 2 ~8~ ~ -28-the ink was still slightly wet, it was dusted with the previously dried, free-flowing adhesive beads. Excess adhesive beads were lightly shaken from the paper so as to provide a monolayer coating of beads thereon (appro~im~ely 139 g/m2). The adhesive bead coated paper was air dried and cut into four equally sized sarnples. Ttle adhesive co~tingC were then heat activated with a 4" x 3" (20 cm x 7.6 cm), 2 kilogram heated platé assembly by exposing the coated paper samples to a temperature of 149C under a constant pressure of 25.8 g/cm2 for various times ("Dwell Timen) as indicated in Table 2.
Peel adhesion of the pressure-sensitive adhesive beads to polyester film was determined according to a modified version of American Society of Testing and Materials (ASTM) P3330-78, Method C. More particularly, a strip of double faced adhesive tape (Scotchn' brand No. 410 double coated paper tape commercially available from 3M, St. Paul, Minnesota) was applied to the steel panel of a 90 Degree Peel Jig (Chern~ultants, Mentos, Ohio). The adhesive coated paper samples were applied to the double faced tape with the adhesive bearing surface of the paper substrate facing outwardly.
A 1.25 inch (3.2 cm) by 0.9 mil (0.2 mm) polyester film was applied to the adhesive coated surface of the paper with two passes of a roller. One end of the polyester film was placed in the upper jaw of the adhesion tester and was pulled at a 90 angle relative to the steel plate and at the rate specified in the ASTM test method (30.5 cm/min). The peel adhesion value in grams per centimeter of width (g/cm width) is reported as the average of two samples.

l:)etermination of Charge per Unit Area The following is the test procedure used to determine the charge on the surface of the free flowing pressure-sensitive adhesive beads of the Invention.

Procedure:
1) Prepare a test plate using a 102 x 102 mm by 4.7 mm thick glass plate coated with a thickness of less than 0.005 mm of an acrylate copolymer adhesive as described in U.S. Patent No. Re 24,906, assigned to 3M
Company, St. Paul, Minnesota, incorporated by reference herein (a 95.5:4.5 iso-octyl acrylate:acrylic acid copolymer of 1.5% solids in heptane), the purpose of which is to allow positioning of the adhesive beads to be tested without their activation. The glass plate constructions were tested to determinethe average dielectric constant at 100Hz for use in calculations of charge SU~ U~ ET ~UL~

2~789~
~0 94/20585 PCTIUS94/02418 density. This was accomplished following specifications outlined in ASTM
D-150, titled A-C Loss Characteristics and Permittivity (Dielectric Constant) ofSolid Electrical Insulating Materials, incorporated by reference herein, using - under sized lead foil electrodes with brass dead weighls, with a Hewlett 5 Packard, (San Diego, California) model #4284A, IndLlction, Capacit~nce, Resistance Meter, and measuring the dielectric ccnstant at 10()1-1~, 1 KHz, lOKHz, lOOKHz, and lMHz.
2) Mask off a 2 cm x 2 cm square area in the center of the plate on the adhesive coated side using a TEFLONTM template (avail~ble from 10 E.I. duPont de Nemours & Co.).
3) Grade the beads according to si7e using 4 5 and 500 micrometer opening sieves, and collect the beads retained in the 425 micrometers sieve. This gives a be~d distribution of 425 ~ no ~ or 0.0165 in. ~X~0.0197 in. Charge 2 g of beads by placing the heads in a 15 100 x 15 mm polystyrene petri dish with a non-conductive fibcr board cover and shaking vigorously by hand for 30 seconds.
4) Quickly apply to the pre-masked area of lhc glass plate a monolayer of the charged beads. Apply a TE~LONTM release sllcet (available from E.I. duPont de Nemours & Co.) and roll once using a 6~.~ mm rubber 20 roller to tack the beads to the adhesive surface.
5) Using a Monroe Electronics, Inc., Lyndollvillc, New York. model #244 miniature non-contact elcctro.static vollllleter and a modcl #l()l51~ prol~e, ~)lace the sample on ~he surface of a gro~ -late and adjust lo a l mlll gap between the surface of the beads alld thc pr(-he end.

6) Slowly move the sample un(ler the prol~e ulllil the total surface area has been sampled.

7) Record the voltage every 6 secon(ls.

8) Calculate the mean voltage over the 2 x ' ( nl area.
5~) Record the relative humidity and tempcr.ltllre during ~0 testing.
10) Calculate static charge density and static charge per bead based upon average static volts and average bead diameter IISillg thc formulas below.
Static Charge Density=~ V/47rd Static Charge/Bead=~
Particle Density/Unil Area=11= lcm~/4r?

Wo 94/2058s PCT/US94/02418 ~
~S73~1 ~30-= Dielectric Constant of the Adhesive Coated Glass Plate d = Total Thickness of Plate in cm with Beads Coated Thereon S esV = Recorded Mean Static Volts r = Average Radius of Beads in cm l Static Volt = 300 Volts l Static Coulomb = 3xlO-~ Coulombs Results are reported in Table I wherein the average l'SA bead diameter was 462.5~.

Static Voltage v. Time The following is the test procedure used to determine the static voltage versus time for the free-flowing pressure-sensitive adhesive beads of tlle invention.
(I) Charge 2 g of beads by placing the beads in a 10() x lS
mm polys~yrene pctri dish with a nonconductive fiber board covcr, shal;e vigorously by hand for 30 seconds.
(2) Quickly apply a monolayer of the beads to a standard ASTM 16 gauge stainless steel test plate.
(3) Using a Monroe, Eiectronics Inc., Lyndonville, New York, Model ~244 miniature noncontact electrostatic voltmetcr an-l a Model ~fIOISB probe, place the bead coated test platc on the surface of ~
ground plate and adjust to a I mm gap between the surface of beads and the probe end.
(4) Record the voltage every 15 seconds. Testing was conducted at 23.9C and 20% Relative Humidity.

Examples The invention will be more fully appreciatcd witll reference to the following non-limiting examples. All parts, percentages, ra~ios, etc., in the Examples and the rest of the Specification arc by weight unless indicatc(l otherwise.

~0 94/20585 ~ PCT/US94/02418 The following abbreviations and tradenames are use(l herein.

Abbreviation Material AA Acrylic acid ACM Acrylamide CBr4 Carbon tetrabromide IOA Isooctyl acrylate IOTG Isooctyl thioglycolate IPA Isopropyl alcohol K2S20s Potassium persulfate LiOH Lithium llydroxide MAA Methacrylic acid MMA Methyl metllacrvlate NaHSO3 Sodium bisulfite NaLS Sodium lauryl sultatc NH40H Ammonium hydroxide NVP N-vinyl- -pyrrolidone PMMA l'oly(methyl metllacrylate) PNVP Poly(N-vinyl-2-pyrrolidonc) PS Polystyrene S Styrene SSS Sodium styrene sulfollate THF Tetrahydrofuran VAZorM64* 2,2'-azobis(isoblltyrollitrile 2:~ VOAc Vinyl acetate ZnO Zinc oxide ~ R.H. percent relative humidity Temp. temperature Ex. Example Sec. seconds *Commercially available under this tradename from E.I. duPont de Nemours & Co., Wilmington, Delaware.

Preparation of Pressure-Sensitive Adhesive Cores "A"
The following describes the preparation of pressul-e-sensitive adhesive cores "A" based on acrylic acid esters and usin~ an aqueous suspension polymerization technique. The reaction was carrie-l out in a five WO 94/20585 ~ PCT/US94/02418 liter split flask equipped with a condenser, a motor driven stainless steel stirrer having a speed control, a thermowell, a nitrogen gas inlet, and hea~ing lamps with a temperature control. A dispersion of 7.8 g of ZnO and 1.~6 g of PNVP
in 1~20 g of deionized water was added to the flask, the temperatule ~as 5 maintained at 58C, and the agitator (stirrer) was set at 375 revolutions per minute (rpm). A deg~cced monomer premix comprising :~.2 g of MMA, 260 g of VOAc, 64.5 g of MAA, 1232.4 g of IOA, 0.8324 g of IOTCi, and 7.8 g of VAZO~64 2,2'-azobis(isobutyronitrile) was then added to the tlasl~ followed by 3.9 g of NH40H. An exotherm was observed during which time the 10 temperature was maintained at about 68C with an ice-water l-ath. After 1.5 hours, the temperature was reduced to 65C and the agi~ation increased to 425 rpm. After 5.5 hours the temperature was decreased to 5()"C and ~.12 g of I iOH in 40 milliliters (ml) of deionized water was addcd to the rcaction flaslc.
Agitation at 425 rpm was continued for 0.5 hour. The resulting col~olymer 15 pressure-sensitive adhesive cores were dewatered and isolated at 70% solids by gravity filtration. Upon subsequent drying, the pressure-sensitive adhesive cores were inherently tacky and were not free flowing as defined bY tllc Funnel Discharge Time Test (~STM D-1895-69) descril-~l abovc.

Example I
Example l illustrates tlle formation of adhesive bcads comprising a pressure sensitive adhesive core surrounded by an essentially discontinuous inorganic l-owder coating. More par~icularly, a dispersion coml)rising 450 g of the filtered adhesive cores "A" and 450 g of deionized water ~ s nlixed with 12.6 g of ~EI~OSIL6' R972 hydrophobic fume(l silic~ (commcrciafly available from Degussa Corp., Ridgefield Park, New Jersey) disperscd in 27 g of IPA.
The resulting mixture was heated at 65C Witll agitation for ~() n)inutes. The resulting beads were filtered and dried with constant agitation in a fumc hood under ambient conditions. The resulting beads were free-flowing and had a moisture content of less than 1%. Charge per unit area was calcul.lted and is set fortll in Table 1. Peel adhesion and pourability was calculated and is set forth in Tahle 2. Static voltage vcrsus time lor the head.s is .sl~own in Fig. 1.

Example '' 3;~ Example 2 describcs the formation of adhesive beads comprising pressure-sensitive adhesive cores "A" surrounded by a contimlolls urea formaldellyde shell. More particularlyt a precondensate of thc sllell material ~o 94/20585 2 ~ ~ ~ 8 ~ I I PCT/US94/02418 was prepared by mixing 48 g of urea and 121 g of 37% aqueous formalin and a sufficient amount of a 10% aqueous sodium hydroxide solution to reduce the solution pH to 8Ø The mixture was agitated at 70C for one hour. Upon formation of a linear formalin-urea polymer, 28 g of the precondensate were added to a dispersion comprising 403 g of the filtered pressure-sellsitive adhesive cores "A" and 500 g of deionized water. ~ sufficient amount of 5%
aqueous hydrochloric acid solution was added dropwise until the solution pH
was reduced to 3.5. The resulting solution was agitated at 50C for about five hours. This procedure was repeated until 103 g of thc precondensa~e had been consumed in the formation of the adhesive beads. The coated beads were then filtered and dried under ambient conditions. The resulting beads wcre free-flowing. Charge per unit area was calculated and is set lortll in Table 1.
Peel adhesion and pourability was calculated and is sct fortll in I able 2. Static voltage versus time for the beads is shown in Fig. 1.
Example 3 Example 3 describes a polymeric material, for lorlllillg an essentially discontinuous organic polymer coating which is provi(led as a granulated powder. More particularly, a reaction wa.s carried OUt in a two litersplit flask equipped with a condenser, a motor driven stainless sleel stirrer (agitator) having a speed control, a thermowell, heating lamps witll a temperature control, and a nitrogen gas inlet. An a4uec)us dispcrsion comprising 10.0 g of PNVI', 297.0 g of MMA, and 3.0 g of .~ S in lOt)0 g of deg~seli, deionized water was heated to 55C with agita~ioll .It ~() rpm. The flask was thcll charged with 0.60 g of K2S2O~ and thc reactioll was allowed to proceed for 4 hours at 55C. The reaction mixture was then coole(l to room temperature (about 20-22C) at which time a trace amollnt (abollt 0.01 g) of hydroquinone was added to remove any residual initiator. The rcaction provided an organic polymer latex to produce a polymeric material comprising 99 parts MMA and I part SSS. More specifically, the organic polymcr latex was dried in an oven maintained at 65C for 15 hours and subsequently pulverized so as to form a dry, granular powder having an average particle size of Icss than about l micron in diameter. The polymeric material was subsc(l-lently used to form an essentially discontinuous organic polymer shell ahout ~l~e adhesive cores " A " .

WO 94/20585 ~15 7 8 ~ ~ _34_ PCT/US94/02418 ~

12.6 g of the powder were combined with 450 g of the filtered ssu~-sensitive adhesive cores "A" and 450 g of deionized water in a two liter reaction flask. The mixture was heated to 65C with agitation and maintained at this temperature for approximately 30 minutes. The adhesive beads were filtered and dried with constant agitation under ambient conditions.
The res~-lting beads were free-flowing. The beads had an essentially discontinuous organic polymer coating comprising 99 parts MMA and 1 part SSS. The beads had a moisture content of less than 1%. Static voltage versus time for the beads is shown in Fig. 1.
Example 4 Example 4 describes adhesive beads with a substantially continuous thermoplastic shell coating. More particularly, a reaction was carried out in a two liter split flask equipped with a condenser, a motor drivenst~inless steel stirrer (agitator) having a speed control, a thermowell, heatinglamps with a temperature control, and a helium gas inlet. A suspension was p~e~arcd from 343 g of adhesive cores HA", in 200 ml of deionized water containing 2 drops of AEROSOL~ MA-80 (sodium dihexyl sulfosuccinate surfactant) commercially available from American Cyanamid Co., Wayne, N.J.) and 2 drops of POLYWEI~ Z-1766 (bisulfite termin~t~ sodium salt of polyacrylic acid commercially available from Uniroyal Chemical Co., Middlebury, Connecticut). A redox initiator consisting of 0.1888 g of potassium persulfate and 0.020 g of sodium bisulfite was added to the suspension and the mixture heated to 70C under helium and constant agitation at 350 rpm. MMA monomer was carefully added by syringe pump according to the following schedl-le: 5 g at 5.1 ml/hr; 30 g at 8.4 ml/hr; and a final 10 g at 20 ml/hr by use of a dropping funnel. After 5 hr, the mixture was heated to 80C and another 15 g of MMA monomer was added at 20 ml/hr also by dropping funnel. The adhesive beads were filtered and dried under ambient conditions resulting in a free-flowing bead form with a moisture content of lessthan 1~. Photomicrographs of the beads showed a mainly continuous shell coating which was free of discrete particles. Charge per unit area was calculated and is set forth in Table 1. Peel adhesion and pourability was calculated and is set forth in Table 2. Static voltage versus time for the beadsis shown in Fig. 1.

~BSTITllTE SHEET (RULE 26) ~0 94/20585 2 ~ 5 7 8 91 PCT/US94/02418 Example S
Example 5 describes the preparation of magnetically responsive adhesive beads. The reaction was carried out in a two liter split fiask equippedwith a condenser, a motor driven st~inl~ steel stirrer (agitator) having a speedcontrol, a thermowell, heating lamps with a temperature control, and a nitrogen gas inlet. Prior to the reaction, PMMA homopolymc r was prc duced following the procedure of Example 4 with the exception of 300 g of MMA being used with no SSS. The PMMA emulsion was then dried in a 65.6"C oven and ground by mortar and pestle to produced a powder. The molccular weight as determined by gel permeation chromatogMphy was an average molecular weight of 687,000 and a polydispersity of 3Ø The PMMA holllopc lynler powder was then dispersed in methyl ethyl ketone at 10% by weight dry powder. To 50 g of 10% PMMA homopolymer dispersion was added nickel pow(ler (commercially available from Inco Alloys International, Inc., Hulltitlgton, WV) in the amount of 50 g, with a mean particle size of 50.45 microns (as determined by Leads and Northrup, Microtrac, Full l~ange Analyzer, North Whales, I'emlsylvania). The combined dispersion Or l'MMA an(l nickel was then dried in a 65.6C oven for 2 hours and ground hy mortar and peslle. The powder was sieved to under 53 microns and then used in the following reaction.
A dispersion of 1.5 g of ZnO and 0.30 g of PNVP in 350 g of ieionized water was added to the reactor and the batch temperature was set to 5XC with agitation at 375 rpm. A deg~ced monomer premix consisling of l.0 g of MMA, 50 g of VOAc, 12.3 g of MAA, 237 g of IOA, 0.180'~ g of IOTG and l.S g of VAZO~ 64 2,2'-azobis(isobutyronitrile) was then adde(l. After 1.5 hr.~ the batch temperature was reset to 65C an(l the agitation incrcased to 425 rpm. After 5.5 hr., the batch temperature was reset to 5()C. 6.4 g of coated nickel powder and 6.4 g of micronized polye~hylene wcrc added.
Agitation at 425 rpm was continued for 0.5 hr. The coate~i bca is were then filtered off and dried with constant agitation in a fumc hoocl ull(3er ambient conditions to give free-llowing beads with a moisturc conlellt ol less than 1%.
Charge per unit area was calculated and is set forth in Table l. Stc~tic voltageversus time for the beads is shown in Fig. l.

Example 6 This example describes the preparation of adhesivc beads using a tackified rubber based adhesive system. More particularly, 1''~.9 g of CA-501 rubber based adhesive (available from Century Adhesives Corp., WO 94/20~85 PCT/US94/02418 ~
2~7~

Columbus, Ohio) and 5.16 g of powdered homopolymer PMMA from E~xample 5 were combined and frozen using liquid nitrogem The frozen material was then ground by mortar and pestle to create particles of PMMA coatcd adhesive.
The resulting material was sieved to under 780 microns for further testing.
5 Charge per unit area was calculated and is set forth in Table 1. Static voltage versus time for the beads is shown in Fig. 1.

Determination of Charge per Unit Area Example Ex. I Ex. 2 Ex. 3 Ex. 4 T~x. S Ex. 6 Avg. esV -86.52 81.49 -71.17 -94.13 -46.91 276.33 Static Charge-0.23570.2219 -0.1939 -0.2564 -().1278 0.7527 per Bead (esC/Bead) Static Charge-110.18103.78 -90.6~s -119.87 -59.74 351.90 Density (esC/cm2) Temp. 22.8C 22.8C 22.8C 22.8C 2.8(~ 2.2C
% R.H. 20% 20% 20~ 20% 2()% 20%

Example 7 This example describes the preparation of adhesivc beads according ~o the invention wherein the coating is provid~l by a iatcY di.sperSiOIl of the polymer additive that is added to the adhesive cores sll(-rtly after the observation of the exotherm which occurs during tlle aqucous sllspellsion polymerization of the cores.
More particularly, the reaction was carried out b~ a two liter split flask equipped with a condenser, a motor driven stainless steel stirr~r (agitator) having a speed control, a thermowell, heating lamps with a temT-cralure control,and a nitrogen gas inlet. A dispersion of 1.5 g of ZnO and 0. g of PNVP in 350 g of deioni%ed water was added to the flask and Ihe tempclature was maintained at ~C with agitation at 375 rpm. A dcgassed ml)nolll( r premix for forming the cores comprising 1.0 g of MMA 50 g of VOA~, 1 4 g of MAA, 237 g of IOA~ 0.1606 g of IOTG, and 1.5 g of VAZOrM~-~
2,2'-azobis(isobutyronitrile) was added, followed by ().75 g of NH4OH. After the exotherm was observed (about 1 hour after the start of the rcaction) 53.2 g of the organic polymer latex of Example 3 was add~l. After 1.5 hollrs the 21 ~7~91 ,~0 94/20585 PCT/US94/02418 _37_ ~
te"l~lat.lre was increased to 65C with constant agitation at 375 rpm. After 5.0 hours, the te..,pcldture was decreased to 50C, and 0.16 g of LiOH in 10 ml of deionized water was added to the reaction mixture. Agitation at 375 rpm was continued for 0.5 hour.
The adhesive beads were filtered and dried under constant agitation at ambient conditions to give free-flowing beads with a moisture content of less than 1%. The resulting beads were free-flowing. The beads comprised a pressure sensitive adhesive core surrounded by an essentially discontinuous organic copolymer coating comprising 99 parts MMA and 1 part SSS. Static voltage versus time for the beads is shown in Fig. 1.

FY~mple 8 The procedure of Example 7 was repeated except that the organic polymer latex of Example 3 was combined with the monomer premix for forming the adhesive cores prior to the initiation of the suspension polymerization that formed the cores. The resulting beads comprised a pressure sensitive adhesive core surrounded by an essentially discontinuous organic polymer coating comprising 99 parts MMA and I part SSS. The adhesive beads were filtered and dried under constant agitation at ambient conditions to give free-flowing beads with a moisture content of less than 1%. The resulting beads were free-flowing. This example demonstrates that adhesive beads according to the invention may be formed using an "in-line" process. Static voltage versus time for the beads is shown in Fig. 1.

Example 9 An organic polymer latex was prepared using emulsion polymerization according to Example 3 except that the two liter flask was charged with 333 g of deg~ed and deionized water, 3.33 g of PNVP, and 100 g of MMA. Once the temperature reached 55C, 0.202 g of K2S208 and 0.145 g of NaHSO3 were charged to the reaction flask and the reaction was allowed to proceed for four hours at 55C. Analysis by gel permeation chromatography indicated that the high molecular weight PMMA homopolymer latex formed in this example had a weight average molecular weight of 806,000 and a polydispersity of 3.3.
54.8 g of the high molecular weight PMMA homopolymer latex were added to 450 g of the filtered adhesive cores "A" according to the procedure of Example 3, thereby forming adhesive beads having an e~enti~lly S~T~TU~ aH~T (RU~ 2~) discontinuous orgarlic polymer coating derived from a high molecular weight PMMA homopolymer. The adhesive beads were filtered and dried undcr constant agitation at ambient conditions to give free-flowing beads with a moisture content of less than 1%. The resulting beads were free-flowing.
5 Static voltage versus time for the beads is shown in ~ig. 1.

Example 10 An organic polymer latex was prepared by emulsion polymerization according to Example 3 except that the two litcr flask was charged with 10 g of PNVP, 1000 g of deg~cced and deionized water, 300 g of MMA, and 0.1620 g of CBr4. Once the temperature reached 55C, 0.()0 g of K2S2OX and 0.40 g of NaHSO3 were added to the reaction flasl; alld the reaction was allowed to proceed for four hours at 55C. After four hours at ~5C, 0.05 g of hydroquinone was added to deactivate any excess ini~iator. Analysis l.S by gel permeation chromatography indicated that the low molccular weight PMM~ homopolymer latex formed in this example had a weight average molecular weight of 687,000 and a polydispersity of 3Ø 54.X g of thc low molecular weight PMMA homopolymer latex were added to 4~() g of the filtered adhesive cores of "A" according to the procedure of Example 3 thereby 20 forming adhesive beads having an essentially discontinuous organic polymer coating derived from a low molecular weight PMMA llomopolylller. Peel adhesion and pourability was calculated and is sct forth in Tablc 2. The adhesive beads were filtered and dried under constant agitation at ambiellt conditions to give free-flowing beads with a moi.sture content of less than 1%.
25 The resulting beads were free-flowing. Static voltagc versus tinle t`or the beads is shown in Fig. l.

Example l I
An organic polymer latex was prepare{l by emulsion 30 polymerization according to Example 3 except that the two lit~r flask was charged with 10.0 g of NaLS, 0.132 g of CBr4, 300 g of S, and 1 000 g of degassed and deionized water. Once the temperature reached 55C, 0.(il g of K2S2O8 was added and the reaction was allowed to proceed at this tcmpcrature for 4.5 hours. At this time, the reaction mixturc was allowed to cool to room 35 temperature and 0.01 g of hydroquinone was added to remove any residual ~ ~ ~ ~r' ~5 . ) ~

initiator. Analysis by gel permeation chromatography indicated that the low high molecular weight PS homopolymer latex formed in this example had a weight average molecular weight of 585,000 and a polydispersity of 2.4.
54.8 g of the low molecular weight PS homopolymer latex were 5 added to 450 g of the filtered adhesive cores "A" as described in conjunction - with Example 3, thereby forming adhesive beads which included an esscntially discontinuous organic polymer coating derived from a low molecular w~ight PS
homopolymer. The adhesive beads were filtered and dried under constant agitation at ambient conditions to give free-flowing bcads with a moisture 10 content of less than 1%. The resulting beads were free-flowing. Static voltage versus time for the beads is shown in Fig. 1.

Peel Adhesion (g/cm width`
Dwell Time (Minutes) Ex. 1 Ex. 2 Ex. 4E~;. 10 0.5 1.0 8.4 0.7 83.8 1.0 2.2 1 1.7 0.71 14.6 3.0 4.1 26.8 2.g1~0.8 10.0 35.2 41.~ 4.~2~6.9 I'ourability 4.0 6.0 2.1 5.5 (sec.) Example 12 To demonstrate the use of electrostatics in the coating of the pressure sensitive adhesives beads of the invention an experimcnt was conducted utilizing a Hipotronics Inc., Brewster, N.Y., High Voltage DC
Power Supply, model No. RlOB, and the corona wirc cartridge l'r(llll a 3M
Company, St. Paul, Minnesota, model No. 566A6, copy machine. The surface to be coated was a 15.24 cm wide by I mil thick polyester filnl, masked off by two 5.1 cm strips of ScotchT~ brand No. 81 I removable Magi~ ' tape (commercially available from 3M Company~ St. ~'aul~ Minncsot<l) ICaV;I1g one 5.1 cm strip remaining running down the middle of the polyestcr film. 9000 volts dc were applied to the corona cartridge and the polyester rilm Witll a 15.24 cm wide paper carrier (20 pound, bond by Nekoosa, Ashdown, AR) was pulled through the corona discharge at a rate of approximately 1.8 m per WO 94/20585 PCT/US94/02418 ~
2 1 !~

minute by hand, wherein the film and cartridge were separated by a 0.6~5 cm air gap. A Monroe Electronics, Inc., Lyndonville, New Yorl;~ Model No. 244 miniature non-contact electrostatic voltmeter and a Model No. 1015B probe was used to determine the electrostatic voltage distribution over the film surlace. It was determined to be 2200-2400 electrostatic volts in the non-masked areas and 530-860 electrostatic volts in the masked areas, also determincd lhat a similar distribution of negative polarity was present on the opposite side. Several grams of the beads of each of Examples 1, 2, 4, and 5 were separately charged by placing tlle beads in a 100 x 15 mm polys~yrcne petri dish with a polystyrene cover, and shaking vigorously by hand for 30 seconds. A
monolayer of charged adhesive beads were quickly applied to the film surface.
Beads of Examples 2, 4 and 5 had high bead concentrations in the area that was masked off during corona treatment, whereas the beads of Example 1 were concentrated in the nonmasked area. For the beads of each of Examples 1, 2, 4, and 5 some scattering of beads did occur outside their respcctive areas. The Monroe non-contact voltmeter and a ground plate was used to determine the polarity of the beads. The Monroc non-contact voltmeter and Modcl No.
IOl5B probe was placed on the surface of a ground plate and ad juslcd to a 1 mm gap between the surface of the beads and the probe end. The sanlple was moved slowly under the probe until the total surface area had been sampled. The pressure-sensitive adhesive beads of Examples 4, alld ~ were positive, whereas the pressure-sensitive adhesive bead.s of ~xan1l-le I were negative. Thus, the coating patterns obtained from lhc beads ol Examples 2, 4, and 5 were reversed from that obtained from the beads of Ex~mplc 1.
Example 13 To demonstrate the use of magnetics in the coating of the pressure-sensitive adhesive beads of the invention, an experiment was conducted utilizing the magnetically responsive beads prepared accordillg lo Example 5.
A 21.8 x 21.6 cm piece of standard white medium bond papel was placed on top of the adhesive-free side of 0.152 cm thick, 2.54 cm wide piece of 3MTU
~3rand No. 1317 magnetic tape (available from ~M C~ompany, ~;l. I'aul, Minnesota) which had previously been adhered to a piece of car(lboard. The length of the magnetic tape was such that the edge of tl1e magnetic tape extended beyond tl1e edge of the standard white bond paper. Tlle beads of Example 5 were sprinkled onto the paper and magnetic tapc at tlleir transition point. Excess beads were wiped off to provide a monolayer o f hG'ldS. The ~1O 94/20585 21 ~ 7 8 ~ ~ PCT/US94/02418 ~1_ beads oriented themselves in substantially parallel lines due to the magnetic field created by the underlying magnetic tape. Figure 2 illustrates the parallelalignment of the magnetically responsive beads of the invention at the paper magnetic tape interface the paper constituting the light colored substratc and 5 the magnetic tape constituting the dark colored substrate. The beads retained their pattern even when the composite was moved from a horizontal position to a vertical position and even when the composite was inverted.

Example 14 This example describes the use of non-incorporated magnetically responsive particles having an electrostatically chargeable coating (positioningparticles) for the positioning of electrostatically chargeable pressure-sensitive adhesive beads. Particles of PMMA coated nickel prepared according to the procedure of Example 5 were applied according to the procedure of Example 13 to the standard white bond paper with magnetic tape underlying. Thc PMMA/nickel positioning particles oriented themselves in substalltially parallellines due to the underlying magnetic tape. Low molccular weight polys~yrene coated adhesive beads prepared according to the proccdure of Example 11 were charged to a negative voltage by placing several grams of the beads in a 100 x 15 mm polystyrene petri dish with a non-conductive fiber board cover and shaking vigorously by hand for 30 seconds.
The cllarged beads were then dusted onto the previously positioned PMMA/nickel positioning particles and thc paper sub.itratc. An induced positive charge was developed on the PMMA/nickel pOSitiOllillg particles causing the PSA beads to be aligned between and around tlie PMMA/nickel positioning particles. The resulting eftect was a single stripe-coating of the PSA beads.
This enables the aligned PSA beads to be activated in place to produce a PSA coating over the PMMA/nickel stripes or in turn to be transferred to a second substrate by utilizing a greater static elcctrical charge on a second substrate than that previously induced on the PMMA/nickel positioning particles . The pressure-sensitive adhcsivc beads may then be separated from the positioning particles and transferrcd to the sccolld substrate maintaining the pattern produced by the positioning particles. Tllcse may then be activated (by heat and/or pressure for example) on the second substrate.

wO 94/20585 ' PCT/US94/02418 ~
2157~ ~

Reasonable variations and modifications of the foregoing specification are possible without departing from the scope of the invention which is defined in the accompanying claims.

Claims (25)

What is claimed:

1. An adhesive bead comprising a pressure-sensitive adhesive core and a tack-free shell therearound, wherein the bead is capable of being applied to a substrate via magnetic means<->

2. The adhesive bead of claim 1 wherein the adhesive core comprises a magnetically responsive material, wherein the tack-free shell comprises a magnetically responsive material, or wherein both the adhesive core and the tack-free shell comprise a magnetically responsive material.

3. The adhesive bead of claim 2 wherein the tack-free shell further comprises an electrostatically chargeable material.

4. An adhesive bead comprising a pressure-sensitive adhesive core and a tack-free shell therearound wherein the shell comprises a magnetically responsive material.<->

5. The adhesive bead of claim 1 wherein the shell comprises a discontinuous shell.

6. The adhesive bead of claim 1 wherein the shell comprises a continuous shell.

7. The adhesive bead of claim 1 wherein the bead comprises a pressure-sensitive adhesive core and a tack-free discontinuous shell comprising magnetically responsive material disposed about the core.

8. The adhesive bead of claim 1 wherein the bead comprises a pressure-sensitive adhesive core and a tack-free continuous shell comprising magnetically responsive material disposed about the core.

9. A coated substrate comprising a substrate having a layer of pressure-sensitive adhesive coated thereon, wherein the pressure-sensitive adhesive is formed from the bead(s) of claim 1.

<with the proviso that the pressure-sensitive adhesive has a blocking stroking temperature below 50°C.>

10. A coated substrate comprising a substrate having a layer of the adhesive beads of claim 1 secured thereto.

11. A method for providing a pressure-sensitive adhesive bead coated substrate comprising the steps of:
(a) providing a first substrate and a pressure-sensitive adhesive bead(s) wherein each of the bead(s) comprises a pressure-sensitive adhesive core and a tack-free shell therearound, wherein the pressure-sensitive adhesive bead(s) is electrostatically chargeable, magnetically responsive, or both;
(b) positioning the bead(s) on the first substrate by a means selected from the group consisting of electrostatic force(s), magnetic force(s),both electrostatic force(s) and magnetic forces to form a tack-free coating of the bead(s) on the first substrate.<->

12. The method of claim 11 which further comprises the step (c) of activating the bead(s) on the first substrate to expose the pressure-sensitive adhesive core and provide a coating of the pressure-sensitive adhesive on the first substrate.

13. The pressure-sensitive adhesive coated substrate prepared according to the method of claim 12.

14. The method of claim 12 wherein the pressure-sensitive adhesive coating is selected from the group consisting of discontinuous coatings and continuous coatings.

15. The method of claim 14 wherein the pressure-sensitive adhesive coating is a discontinuous pattern coating.

16. The method of claim 11 which further comprises a step (c) of securing the pressure-sensitive adhesive bead(s) to the first substrate, whereinthe securing step can occur simultaneously with or subsequent to the positioningstep (b).

17. The method of claim 12 which further comprises a step of securing the pressure-sensitive adhesive bead(s) to the first substrate, whereinthe securing step can occur simultaneously with or subsequent to positioning step (b) but must occur prior to activating step (c).

18. The method of claim 11 wherein each of the pressure-sensitive adhesive bead(s) is electrostatically chargeable and wherein each of the bead(s)is attracted to and contacted with the first substrate by means of an electrostatic force(s) thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating of the pressure-sensitive adhesive bead(s)thereon.

19. The method of claim 18 wherein each of the pressure-sensitive adhesive bead(s) is electrostatically chargeable and wherein each of the pressure-sensitive adhesive bead(s) is positioned on the first substrate by attracting and contacting the bead(s) to the first substrate by means of an electrostatic force(s) generated by a method selected from the group consisting of:
(i) generating an electrostatic charge on the first substrate opposite to an electrostatic charge generated on the pressure-sensitive adhesivebead(s) and bringing the charged pressure-sensitive adhesive bead(s) close to the charged first substrate so that the bead(s) contacts the first substrate and forms a tack-free coating on the first substrate;
(ii) generating an electrical field encompassing the first substrate and applying an electrostatic charge to the pressure-sensitive adhesive bead(s) wherein the electrical field is repulsive to the charged pressure-sensitive bead(s) and wherein the electrical field is positioned such that it is capable of positioning the charged bead(s) placed therein on the first substrate and bringing the charged pressure-sensitive adhesive beads into the field so that the pressure-sensitive adhesive bead(s) contacts the first substrate and forms a tack-free coating on the first substrate; and (iii) both (i) and (ii).

20. The method of claim 11 wherein each of the pressure sensitive adhesive bead(s) is magnetically responsive and wherein each of the bead(s) is attracted to and contacted with the first substrate by means of a magnetic force(s) thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating of the pressure-sensitive adhesive bead(s)thereon.

21. The method of claim 20 wherein attracting and contacting the pressure-sensitive e-sensitive adhesive bead(s) to the first substrate occur by means of a magnetic attraction force(s) wherein (i) when the magnetically responsive pressure-sensitive adhesive bead(s) comprises a permanent magnetic particle(s) the magnetic attraction force is provided by a magnetically responsive material in the first substrate or on a side of the first substrate opposite the pressure-sensitive adhesive bead(s);
(ii) when the magnetically responsive pressure-sensitive adhesive bead(s) are free from a permanent magnetic particle(s) the magnetic attraction force is provided by a magnetic field encompassing the first substrate and bringing the pressure-sensitive adhesive beads within the magnetic field thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating thereon, and bringing the pressure-sensitive adhesive beads close to the first substrate thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating thereon; and (iii) both (i) and (ii);
thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating thereon.

22. The method of claim 11 wherein each of the pressure-sensitive adhesive bead(s) is magnetically responsive and electrostatically chargeable andwherein each of the bead(s) is attracted to and contacted with the first substrate both by magnetic force(s) and electrostatic force(s) thereby positioning the pressure-sensitive adhesive bead(s) on the first substrate to form a tack-free coating of the pressure-sensitive adhesive bead(s) thereon.

23. The method of claim 11 which further comprises a step selected from the group consisting of:
(i) activating the pressure-sensitive adhesive bead(s) to provide a coating of pressure-sensitive adhesive on the first substrate and transferring the pressure-sensitive adhesive to a second substrate to provide a coating of pressure-sensitive adhesive on the second substrate;
(ii) transferring the pressure-sensitive adhesive bead(s) to a second substrate by a means selected from the group consisting of magnetic force(s), electrostatic force(s), and both magnetic force(s) and electrostatic force(s) and simultaneously exposing the core of the pressure-sensitive adhesivebead(s) to form a coating of pressure-sensitive adhesive on the second substrate;
and (iii) transferring the pressure-sensitive adhesive bead(s) to a second substrate by a means selected from the group consisting of magnetic force(s), electrostatic force(s), and both magnetic force(s) and electrostatic force(s) and subsequently exposing the core of the pressure-sensitive adhesive bead(s) to form a coating of pressure-sensitive adhesive on the second substrate.

24. The pressure-sensitive adhesive coated substrate prepared according to the method of claim 23.

25. A method for providing a pressure-sensitive adhesive bead coated substrate comprising the steps of:
(a) providing a first substrate and a positioning particles(s) wherein each positioning particle is both electrostatically chargeable and magnetically responsive comprises a magnetically responsive material and an optional electrostatically chargeable tack-free coating thereon;
(b) positioning the positioning particle(s) on a first substrate by a means selected from the group consisting of electrostatic force(s), magnetic force(s), and both electrostatic forces and magnetic forces to form a coating of the positioning particles on the substrate;
(c) providing a pressure-sensitive adhesive bead(s) wherein each of the bead(s) comprises a pressure-sensitive adhesive core and a tack-freeshell therearound, wherein the pressure-sensitive adhesive bead(s) is electrostatically chargeable, magnetically responsive, or both; and (d) positioning the pressure-sensitive adhesive bead on the positioning particle coated substrate by attracting the positioning particle(s) and the pressure-sensitive adhesive bead(s) by a means selected from the group consisting of magnetic force(s), eletrostatic force(s), both magnetic forces andelectrostatic force(s).