CA1193796A - Tacky polymeric microspheres - Google Patents

Abstract

Abstract Or the Disclosure Infusible, solvent-insoluble, solvent-dispersible, inherently tacky, elastomeric polymeric microspheres which are formed from non-ionic monomers and comprise at least one oleophilic water-emulsifiable alkyl acrylate or methacrylate ester, and a suspension polymerization technique for pro-ducing the microspheres.

Description

t` ~13~ 7 3 7 ~ ~

TACKY POLYMERIC MICROSPHERES

This invention relates to inherently tacky, elasto-meric~ solvent-dispersible, solvent-insoluble, polymeric microspheres and a process for preparing same.
In United States Patent 3,691,140 to Silver, there are disclosed inherently tacky acrylate copolymer micro-spheres comprising a major portion of at least one alkyl acrylate est~r and a minor portion of an ionic monomer.
As dlscussed in the Silver patent, the micro-spheres can be unexpectedly prepared by suspension polymer-ization techniques, which historically have been consideredunsuitable for preparation of tacky polymers. In the technique described by Silver, the microspheres are pre-pared utilizing an Pmuls~fier in an amount greater than the critical micelle concentration in the absence of externally added protecti~e colloids or the like. The Silver micro spheres are copolymeric in nature and require an ionic comonomer as an essential component thereof.
It has now been found that inherently tacky micro-spheres having physical properties slmilar to those of the Sllver patent~ i.eO, inherent tack, infusibility9 solvent dispersibility, and solvent insolubility, can be prepared which are not limited to copolymers, but may also be homo-polymers9 and do not contain an ionic comonomer. The micro-spheres are prepared by aqueous suspension polymerization 5 but have as an essential ingredient in their preparation a '~,, ~3~7~

hereinafter defined suspension stabilizer.
In accordance with the invention there are provided inherently tacky, infusible, solvent-insoluble, solvent dispersible, elastomeric polymeric microspheres, having a glass transition temperature below about -20 C, which are formed from non-ionic monomers and are comprised of at least one oleophilic, ~ater-emulsifiable alkyl acrylate or methacrylate ester.
The microspheres of the invention are prepared by an aqueous suspension polymerization techni~ue utilizing emulsifiers in an amount greater than the critical micelle concentration, in combination with an ionic suspension stabilizer.
Accordingly, the invention also provides a suspension polymeriæation process for preparing polymeric microspheres com prising the steps of:
a) charging to a reaction vessel i) at least one alkyl acrylate or methacrylate ester monomer; and ii) at least one emulsifier at a concentration above its critical micelle concentration; and iii) a subs-tantially water-insoluble polymerization initiator; and iv) an ionic suspension stabilizer, having an interfacial tension of at least about 15.0 dynes per ~13 - 2 -~3~

centimeter;
b) agitating the rea~tion vessel charge to create an emulsion;
c) heating said emulsion while maintaining said agitation;
whereby elastomericJ solvent-dispersible polymeric micro-spheres are formed from said emulsion.
Useful alkyl acrylate or methacrylate ester mono-mers are those which are oleophilic, water-emulsifiable, of restricted water-solubility, and which, as homopolymers, generally have glass transition temperatures below about -20C. Exemplary alkyl acrylate and methacylate ester monomers which are suitable for preparation of the micro-spheres of the invention include n-butyl acrylate, sec-butyl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethyl hexyl acrylate, isooctyl acrylate, iso-decyl methacrylate, and the like. Alkyl acrylate and methacrylate ester monomers with glass transition tempera-tures higher than -20C ~i.e., butylmethacrylate, isobornyl acrylate, or the like) may be utilized in conjunction with one of the above-described monomers as long as the glass transition temperature of the resultant polymer is below about -20C.
Additionally, the tacky nature of the microspheres - 2a -7~6 can be varied by incluslon of a minor portion o~ a non-acrylate or methacrylate ester cornonomer which ls non-ionlc and water insolubleg such as divinyl benzene, N-t-octyl-acrylamide, etc.
The microspheres of the invention ~re prepared by an aqueous suspension polymerization technique utllizing at l~ast one emulsifier in a concentration greater than the cr~tlcal micelle concentration. The critical micalle con-centration is that minimum emulslfier concentration necessary for the format~on of mic~lles, and is slightly different for each emulsifier, usable concent~atio~ typically ranging from about 1.0 x 10 4 to about 3.0 moles per liter.
Th~ emulsifiers used for the successful preparation of the inherently tacky microspheres o~ this invention are preferably anionic in nature, typical examples being sodium dodecylben~ene sulfonate 3 sodium salts of alkylaryl ~ther sulfonatesD and the like. Non-ionic emulslfiersy e.g., et,hoxylat~d oleyl alcohol~ can also be utilized alone or in con~unctlon with anionic types. In this latter instance, it is preferrs~ that the anlonic emulsifier predominates.
Catalysts or polymerlzation inltiators for poly-merizing the monomers to provide the microspheres of the lnvention are those which are normally ~uitable for free-radical polymerization of acrylate monomer~ and which are oil-soluble and of very low qolubility in wat~r such as~
for 0xample, benzoyl peroxide. The use of water-~oluble catalyst may cau~e formation of sub~tantial amounts of latex, the extremely small particle size and solvent ~olu-bility of which ar~s undesirable.

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Conc~ntration o~ catalysts may a~ect sphere quality and th~refore, should be on the order of about 0.15 to about o.66 percent by weight of the total monomer~, and more preferably about 0.25 to about 0.45 percenk by weight.
Cataly~t concentrations below about 0.15 p~rcent by weight may t~nd to cause agglomeration of the micro~pheres, whereas concentrations greater than about 0.66 percent may result in low molecular weight polymers which do not exhibit all of the desired properties.
Ionic suspenslon stabilizers that assist in the preparation of the microspheres-can be characterized by an interfacial ten~ion of at least about 15.0 dynes per centi-m~ter. Interfacial tension herein means the value det~r-mined between the monomer phase and a 1.0 percent by weight aqueous solution of the stabilizer. To determlne the inter-facial tenslon~ a ~tandard test, ASTM ~D-1331-56, en~itled l'Standard Methods of Tests for Surface and Intsr~acial Tension of Solutions o~ Sur~ace Active Agents" can be util~
izedO If the interfacial tenslon between the monomer phase and th~ 1,0 p~rc~nt by weight aqueous solution of stabillzer falls below about 15.0 dynes per centimet~r, there iB insuf~i-cient stabillzation of the flnal polymerized droplets and agglomeration may occur.
The approxlmate concentration o~ any singla s~ab-illzer required for succe~sful prepara~ion of ~he ~acky microspheres o~ this inv~ntlon can also be determined by the value o~ the inter~acial tension. Typically~ increasing inter~acial tan~ion values between the monomer pha~e and ~he aqueous stablliz2r phase corre~ponds to a reduction in required concentration of the particular stabilizer for the successrul preparation of the microspheres. Stabilizer concentrations greater than about 10 percent by weight based on the monomer may tend to provide less than optimum properties to the resultant suspension.
Exemplary stabilizers include salts of polyacrylic acld of greater than about 5000 molecular weight ~e.g. 3 the ammonium, sodlum? lithium, and potasslum salts) 9 carboxy modified polyacrylamides (e.~., "Cyanamer A-370" from American Cyanamid), copolymers of acrylic acid and dime~hyl-aminoethylmethacrylate and the llke, quaternary amines (e.g., General Analine and Film~s "Gafquat 7551~, a quaternized polyvinyl-pyrollidone copolymer~ or Union Carbide's liJR-400'1J
a quaternized amine substltuted cellulosic)g and carboxy modified cellulosics (e.g., Hercules' "Natrosol CMC Type 7L", sodium carboxy methylcellulo~e). The following is a table indicating representat~ve s~abilizers, their inter-facial tenslon with the monomer pha~e, and the concentration l~vel found to be requtred for succes~ful micro~pheres prepara~ion.

~37~i Interfaclal Approximate Tension Level ~or Between Succ~ssful Isooctyl- Preparatlon acrylate of Isooctyl-and 1.0% acrylate Solution o~ Homopolymer Stabilizer ~Weight Per~
Stabllizer lnEl20 dynes cent Based 10 Trade Name _ Class ~ L~ @~l_ None 50/50 copolymer of acrylic acid and dimethylamino ethylmethacrylate 21.2 1.0%

Good R~te K714 Polyacrylic acid (neutrali~ed wlth ammonia) 21.0 1.0 GAF aa~quat 20 755 Quaternized poly-vinyl pyrollidone copolymer 18.2 1.0%

Union Carbide JR-400 Quaternlzed cellulosic 18.5 1.0 Cyanamer A 370 Carboxy modified polyacrylamide 21.0 3.0%

Natrosol CMC
30 Type 7L Sodium carboxy-methylcellulose 19.8 5.0%

Gantre~ H~M Copolymer of poly-vinylmethylether and maleic anhy-dride (neutrali~ed with ammonia) 15.4 10.0%

Although ~ome stab~lizers may ~unction at levels gr~ater than 10 percent based on monomer, ~he r~ ultant suspensions may be¢ome und~sirable for several reasons, e.g., they may contain too large an amount o~ undeslrable latex polymer. ~urthermore, control of flnal particle slze can become di~ficult becau~e o~ the high viscosities involved and excess conc~ntration levels may alRo lead ~o 7~

detackificatlon of the resultant polymer spheres~
Followlng polymerizatlon, the aqueous suspension of polymer microspheres is stable to agglomeration or coagulation under room temperature conditions. The polymer suspension may have non-volat~le solids contentæ from about 10 to about 50 percent by weight. Upon prolon~ed standin~
the ~uspension~ may separate into two phases, one phase being aqueous and substantially fre~ of polymer, the other phase being an aqueous suspension of the polymer spheres.
The degree and type of separatlon is dependent on the den-sity of the resultant polymers. Separation of the polymer phase provides a low vi~cosity aqueous suspensisn having a non-volatile solids content on the order of about 75 per-cent which, if shaken with water, will readily redlsperse.
If desired, the aqueous suspension of micro~pheres may be utllized immediately following polymerization to provide inherently tacky coatings or adhesives. The aqueous suspension may also b~ coagulated with methanol 3 satura~ed salt solutions~ or the l~ke9 followed by ~ashing and drying. These dried polymer sphéres, with sufficlent agitation, will readily dispPrse in a wide var~ety of col~on organic solvents~ Once the polymer is drled.
however, lt is not redispersible in water.
The polymer microspheres are typlcally small in size, having diameters in the range of about 1 to about 250 mlcrons, the diameter of the ma~ority of the spheres belng in the range of from about 5 to about 150 microns.
The pheres are normally tacky and elastomeric, are insol-uble in organlc solvents, and ~orm disper~ions in mo~t ~37~

common solvents except such highly polar solvents as water, methanol, and ethanol. Typical useful solvents are ethyl acetate, tetrahydrofuran~ heptane, 2-butanone and other ketones, benzene, cyclohexane, and isopropanol and higher alcohols. When dispersed in such solvents, the microspheres absorb the solvent and swell to about twice their original diameter, or about 8 times their original volume. After dispersion, the microspheres, which contain about 80 percent solvent, remain homogeneously dispersed for extended periods of time. A force applied directly to one of the polymer spheres will deform it; however, the spherical shape is reassumed upon release of the stree. Upon being heated, the spheres typically do not melt or flow, but retain their integrity until their carbonization temperature is reached.
The microspheres can be utilized in aerosol adhesives, they can be applied to substrates as an adhesive, they can be mixed with binder materials, and placed on sub-strates to provide repeatedly reusable adhesive sur~aces, such as disclosed in United States Patent 3,857,731, and they can be comhined with a hot melt adhesive on a substrate to provide a positionable hot melt adhesive system, as is disclosed in our United States Patent No. 4,049,483, issued September 20, 1977.
The invention will now be more specifically described by the following non-limiting examples, wherein all parts are by weight unless otherwise specified.

~ ~379~i g ~xample_l To a 3 liter, 3-nec~ed ~lask equipped with thermometer, reflux condenser~ mechanical stirrer, and vacuum and nitrogen inlet tube, were charged 1407.7 grams of deionized water and 27.0 grams of "Good Rite K714"
(tradename for a 15 percent solids aqueous solution of poly-acrylic acid o~ 200,000 molecular weight~commerclally avail-able from the B~ F. Goodrich Co.). The contents of the fla~k were then agitated until all of the polyacrylic ac~d was dissolved~ and concentrated ammonium hydroxide was added thereto until a pH of 7.0 was obtalned.
To this solution were added 500 grams of isooctyl~
acrylate and 1.75 grams of "Lucidol 70" ttradename for a 70 percent active benzoylperoxide catalyst commercially avallable from Lucidol Division, Pennwalt Corporatlon). A
vacuum was then placed on the contents of the ~lask, the pressure thereln being drawn to 28 inches of mercury and held for one minute to assure removal of dissolvPd air and oxygen. The vacuum was th~n broken with nitrogen. A nltro-gen purge was kept over the batch throughout the reactionperiod. Flve grams Or an emulsifler, "Siponate DS-10"
(tradename for a commercially ava~lable sodium dodecyl benzene sulfonate, commercially available from Alcolac~
Inc.) w~re added to the mixture and the agitation was set at 400 rpm.
Th~ batch was ~hen heated to 60C and maintain~d ~or 16 hours. As the temperature initially approached 60C, a mild exo~herm wa~ noted to approximately 70C, at whlch ~ime cooling was not applled until cessation of the ~3~

exotherm, a~ter which the flask was maintained at 60C.
Afker the 16 hour period9 the suspension was allowed to cool to room temperature, and the resulting suspension polymer was filtered through a 60 mesh screen. The resultant homo-polymer contained 25.14 percent sollds, and upon standing,the polymer spheres creamed to the surface but were easily redispersed. Average particle size of the polymer spheres was from 10 to 20 microns.

These examples were prepared u~illzing the equip-ment, monomer, and general procedure outlined ln Example 1 and illustrate the use of various stabilizers and anionic emulslfiers. The microspheres were ~ound to be inherently tacky 9 infusible, and insoluble but disperYible in organlc solvents.

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Table II

Average Polymer P~rcent Part~cle Size, Ex. Emulsifier Stabil~zer Solids l~r~

2 5g sodium 5g 50-50 molar 24.3 66.1 dodecyl- ratio copolymer benzene of acrylic acld sulfonate and dimethyl-aminoethylmeth-acrylate

3 5g sodium 5g GAF Gafquat 25.8 52 dodecyl- 755 benzene sulfonate

4 5g ~odium 15g Cyanamer 25.2 8.7 dodecyl- A-370 from benzene American sulfonate Cyanamid 5g sodium 5g 50-50 molar 2702 63 salt of ratio copolymer alkyl aryl of acrylic acid polyether and dimethyl-sulfonate aminoethylmeth-acrylate Exam~les_6-9 These examples were prepared utilizlng the equ~p-ment and procedures outllned in Example 13 and lllustrate the preparation of lnherently tacky microspheres from dlfferent monomers9 uslng 5 grams o~ sodium dodecylbenzene-sulfonate as the emulsifier9 and 5 grams of a 50/50 moleratio copolymer of acrylic acid and dimethylaminoethyl-methacryla~e a~ the ~tabilizer.

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Table III
Average Polymer Percent Par~lcle Size, Monomer Solids Microns . . _ , 6 n-butylacrylate 19.2 48.4 7 isodecylmethacrylate 25.4 59.2 8 60/40 weight ratio 25.4 39.7 isooc~ylacrylate n butylacrylate 9 95/5 weight ratio 24.5 45.4 i~ooctylacrylate N-t-octylacrylamide Exam~le 10 This example illustrates the use o~ a non-ionic surfactant and was prepared using the æame equipmen~ and techniques described in Exampl~ 1. The monomer was l~o-octylacrylate (500 grams). The stabilizer was a 50~50 molar ratio copolymer of acrylic acid and dimethylamino-ethylmethacrylate (5 grams)~ and the emulsifier was "Siponic Y-500-70" 9 tradename for an etho~ylated oleyl alcohol from Alcolac, Inc. (5 grams). The aqueou~ suspension of inher-antly taGky microspheres prepared in thi~ ma~mer contained 25.3 percent non-volatlle material and had an average particle size of 37.4 mlcrons.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Infusible, solvent-insoluble, solvent-dispersible, inherently tacky, elastomeric polymeric microspheres having a glass transition temperature below about -20°C, formed from non-ionic monomers and comprising at least one oleophilic, water-emulsifiable alkyl acrylate or methacrylate ester.

2. The microspheres of claim 1 wherein said ester is select-ed from the group consisting of n-butyl acrylate, sec-butyl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethyl hexyl acrylate, isooctyl acrylate, isodecyl methacrylate.

3. The microspheres of claim 1 wherein said microspheres are homopolymers and said ester is isooctyl-acrylate.

4. An article comprising a substrate having disposed on at least one surface thereof infusible, solvent-insoluble, solvent-dispersible, inherently tacky, elastomeric polymeric microspheres having a glass transition temperature below about -20°C, formed from non-ionic monomers and comprising at least one oleophilic, water-emulsifiable alkyl acrylate or methacrylate ester.

5. The article of claim 4 wherein said ester is selected from the group consisting of n-butyl acrylate, sec-butyl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethyl hexyl acrylate, isooctyl acrylate, isodecyl methacrylate.

6. The article of claim 4 wherein said microspheres are homopolymers and said ester is isooctyl acrylate.

7. A suspension polymerization process for preparing the microspheres of claim 1 comprising the steps of:
a) charging to a reaction vessel i) at least one alkyl acrylate or methacrylate ester monomer; and ii) at least one emulsifier at a concentration above its critical micelle concentration; and iii) a substantially water-insoluble polymerization initiator of a concentration of about 0.15 to about 0.66 per cent by weight of the total monomers and iv) an ionic suspension stabilizer, having an inter-facial tension of at least about 15.0 dynes per centimeter;
b) agitating the reaction vessel charge to create an emulsion;
c) heating said emulsion while maintaining said agitation;
whereby elastomeric, solvent-dispersible polymeric microspheres are formed from said emulsion.

8. The process of claim 7 wherein said ester monomer is selected from the group consisting of n-butyl acrylate, sec-butyl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethyl hexyl acrylate, isooctyl acrylate, isodecyl methacrylate.

9. The process of claim 7 wherein said stabilizer is pre-sent at up to about 10 percent of said monomer.

10. An aqueous suspension of inherently tacky microspheres prepared in accordance with the process of claim 7.