WO2001044400A1

WO2001044400A1 - Low outgassing pressure sensitive adhesives and method of use

Info

Publication number: WO2001044400A1
Application number: PCT/US2000/027260
Authority: WO
Inventors: Huimin Yang
Original assignee: Brady Worldwide, Inc.
Priority date: 1999-12-14
Filing date: 2000-10-04
Publication date: 2001-06-21

Abstract

An improved pressure sensitive adhesive (PSA), comprising at least one polymer selected from natural rubber, styrenic-elastomer copolymers, acrylate copolymers, polyurethanes or combinations thereof; and at least one tackifying resin, was disclosed which uses a scavenger to capture impurities inherent in the polymer and/or the tackifying resin. Additionally, a method for making improved, cleaner computer devices by using the improved PSA on computer device components that contain a PSA. The component thus produced was ideally suited to be used in disk drives. Also disclosed were computer devices, preferably computer data storage devices, made by the method disclosed.

Description

LOW OUTGASSING PRESSURE SENSJTINE ADHESIVES AND METHOD OF USE

This invention relates to pressure sensitive adhesives (PSA). More particularly,

this invention relates to PSA's for use with computer devices, and to methods for

preparing cleaner computer devices, such as cleaner data storage devices.

Computer disk drives were complex assemblages of surface treated alloys,

plastics, elastomeric, and ceramic parts containing various lubricants and a variety of

adhesives. Pressure sensitive adhesives were used for various applications such as seals,

labels, damping, etc. in today's computer data storage devices. The use of PSA's has been

an effective means of lowering unit cost for storage devices. A typical drive may include

at least one component which bears a PSA, e.g., a tape, which was used to hold the

housing of the disk drive together.

Demand for increased storage capacity of disk drives has produced product

designs requiring a higher level of concern for adhesive contamination. New disk drive

technology, such as decreasing flying heights, use of magneto-resistive head technology,

and pseudo-contact recording, have improved the performance and capacity of disk drive

components. Use of this new technology has also left the disk drive more susceptible to

damage from environmental factors. Building drives with contaminated or outgas-prone

parts can result in stiction/wear and functional problems, including electrical error issues

from thermal asperities.

The cleanliness of PSA materials has been a concern for disk drive engineers.

Physical contamination such as dust particles, skin flake, and moisture, along with

possible chemical contamination by the materials used in the PSA, can affect the drive life or reliability of the device. Adhesive materials can deposit contaminants on disk and

reading heads and cause reading problems or disk crashes.

Specific ions and organic tins were particularly harmful to heads and disks. Small

levels of chlorine containing materials have been identified to be responsible for disk

corrosion. Organic materials capable of undergoing polymerization were unacceptable at

very low levels. Organic or inorganic acids or bases can corrode the sensitive layers of

the storage disk. Typical types of microcontamination commonly found in the disk drive

industry include organic contamination that can cause stiction; corrosion from residual

anions (particularly, chloride and sulfate ions); outgassing, which can result in stiction;

and airborne particulates.

Polyacrylate-based PSA's have been used extensively in the components for disk

drives. A select few were considered useable; none were totally satisfactory. The chemical byproducts from the initiators used in the initial polymerization of acrylates can

be unacceptable even at relatively low levels in disk drives. The solvents and their

impurities used to dissolve and coat polyacrylate PSA's can be a problem if not

thoroughly dried from the finished adhesive coating. Most polyacrylate pressure sensitive

adhesives must be chemically cross-linked to provide the necessary performance

characteristics. The chemicals used for, or byproducts produced from, the cross-linking

can be unacceptable or at unacceptable levels. The levels of unreactive monomers and

their impurities in polyacrylate PSA's have been known to cause drive failures.

The disk drive industry was resorting to two strategies in order to minimize the

presence of microcontaminants in the environment of the disk drive. The first strategy

was to use one of a variety of cleaning methods in order to remove the microcontaminants

from the finished disk drive parts. Typically, such cleaning methods were either aqueous cleaning, solvent cleaning, or carbon dioxide cleaning. All of these cleaning methods

have their advantages and difficulties. However, no cleaning method can remove all

contaminants. Cleaning was a percentage removal process, and it targets specific

contaminants. The higher the initial level of contaminants, the higher the final level of

contaminants in the finished product.

The second strategy used by the disk drive industry was to use parts and processes

that contain or produce fewer contaminants. These more stringent specification

requirements were a challenge to the suppliers of components for the disk drive industry.

Specific requirements include low outgassing and low ionic contamination. For example,

a typical limit for outgassed materials may be as low as 2500 nanograms per square

centimeter (ng/cm²); the limit for anions may be a maximum of 800 ng/cm².

Further disclosure on microcontaminants in the disk drive industry can be found in

Peter Mee et al, Management of Disk Drive Component Microcontamination. IDEMA® Insite, Vol. IX, No. 2 (March/April 1997).

It has been a difficult challenge for the adhesive industry to meet the requirements

of the disk drive engineers with polyacrylate adhesives. This invention relates to a

method for preparing a computer device in a manner that a lower level of

microcontaminants was present around the disk drive.

In one embodiment, the invention comprises an improved PSA comprising:

A. at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof;

B. at least one tackifying resin; and

C. at least one scavenger. In another embodiment, the invention comprises an improved method for preparing a computer device which includes at least one component bearing a PSA, the

method comprising the steps of:

A. forming a solution by dissolving in a solvent

(1) at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof,

(2) at least one tackifying resin, and

(3) at least one scavenger, wherein at least one of the polymer or the tackifying

resin includes at least one impurity, the impurity comprising a compound

with at least one polar reactive moiety;

B. contacting the scavenger with the impurity to form a reaction product;

C. applying the filtered solution to a substrate;

D. drying the solution on the substrate; and

E. applying the substrate to a computer device.

In yet another embodiment, the invention comprises a computer device comprising

at least one component containing a PSA, wherein the PSA comprises:

A. at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof;

B. at least one tackifying resin; and

C. at least one scavenger. As used herein, the tern "styrenic" refers to mono-alkenyl arenes. Thus, a

styrenic polymer or copolymer was formed by the polymerization of at least one mono-

alkenyl arene.

A "block copolymer" was a polymer containing long stretches of two or more

monomeric units linked together by chemical valences in one single chain, such that the

long monomeric stretches alternate with each other in which a block(s) of one type of

polymer structure was attached to a block(s) of another type of polymer structure. A

"diblock copolymer" was a block copolymer that has the general structure A-B, where A

was a long stretch of one homopolymer structure and B was a long stretch of a second

homopolymer structure. A "triblock copolymer" was a block copolymer that has the

general structure A-B-A, where A was a long stretch of one homopolymer structure and B

was a long stretch of a second homopolymer structure.

A "tackifying resin" was a resin that, when added to a rubber or an elastomer, the

resulting composition has the properties of a pressure sensitive adhesive. "Pressure sensitive adhesives" were permanently and aggressively tacky (sticky) solids which form

immediate bonds when two parts were brought together under pressure. For pressure

sensitive adhesives, "tack" can be described as the property whereby the adhesive will

adhere tenaciously to any surface with which it comes into contact under light pressure.

The strength of the bond will be greater under increasing pressure, hence the term

pressure sensitive. Tack can be quantified as the force required to separate an adherend

and an adhesive at the interface shortly after they have been brought rapidly into contact

under a light load of short duration. Tack can be measured by using the ASTM D-2979

procedure. A "scavenger" was a substance added to a system or mixture to consume or

inactivate traces of impurities.

A "hydrocarbon resin" was a resin in the number molecular weight range of a few

hundred up to about 8,000, which was obtained or synthesized from rather basic

hydrocarbonaceous materials such as petroleum, coal, tar, and turpentine.

An improved computer device was prepared by preparing at least one adhesive as

described below and affixing the adhesive to at least one component of the computer

device. Preferably, the component was a film, tape or label which was used to seal or

identify one or more components of the computer device. The computer device was

preferably a disk drive or other data storage device.

The Pressure Sensitive Adhesive

The adhesive used in this invention comprises (i) at least 10, preferably at least 40,

and not in excess of 90, preferably not in excess of 75, weight percent of a polymer, (ii) at

least abut 10, preferably at least 25, and not in excess of 90, preferably not in excess of

60, weight percent of a tackifying resin, and, (iii) at least 0.1 , preferably at least 2, more

preferably at least 3, and not in excess of 8, preferably not in excess of 6, more preferably

not in excess of 4 weight percent of a scavenger, all percentages based on the total weight

of the adhesive.

Polymers

The PSA of this invention comprises polymers typically known in the art of

making PSAs. In general, such polymers impart an elastic or viscoelastic property to the

PSA. Polymers that were useful for the PSAs of this invention include rubbers, such as

natural rubber, and elastomers, such as styrenic-elastomer copolymers, acrylate

copolymers, polyurethanes and combinations thereof. Certain block copolymers have been found useful for making PSAs and, preferably, the polymer of this invention was at

least one hydrogenated block copolymer.

Block copolymers were well-known in the field of PSAs. Any one of these well-

known block copolymers can be included within the composition of this invention,

including those described in some detail within U.S. P. 3,239,478 and 3,917,607. These

particular block copolymers typically take on the general configuration A-B-A or A-B-A-

B, wherein each "A" block, which was generally characterized as an end block, was a

thermoplastic polymer block prepared by a polymerization of a styrenic monomer such as

styrene, a-methyl-styrene, tert-butyl-styrene, and vinyl-toluene.

The elastomer "B" blocks, which were characteristically identified as "mid

blocks," were prepared by the propagation of a polymer chain of a conjugated diene such

as butadiene or isoprene from the end of the end block already synthesized. Then either

using sequential monomer addition or a coupling agent, the desired block copolymers, A-

B-A or A-B-A-B, were generated. If the block copolymers, A-B-A or A-B-A-B were

hydrogenated, a saturated mid block would be obtained. Such block copolymers, which

were prepared by known procedures, include styrene-butadiene-styrene block copolymer

(SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene butyl ene-styrene

block copolymer (SEBS), styrene-ethylene propylene-styrene (SEPS), anda-

methylstyrene-ethylene propylene-a-methylstyrene. A typical molecular weight for such

block copolymers was between 10,000 and 500,000, expressed as number average

molecular weight.

Preferably, the block copolymer of this invention was a hydrogenated block

copolymer. Hydrogenation minimizes the presence of double bonds in potentially

outgassed materials that could result in those outgassed materials polymerizing on the computer device components. Such polymerization can interfere with the recording,

storage or reading of data in a computer data storage device.

The hydrogenated block copolymer was preferably a block copolymer of

polystyrene and a polydiene, the polydiene typically selected from the group consisting of

polybutadiene and polyisoprene, wherein the unsaturated mid block of either

polybutadiene or polyisoprene was hydrogenated to yield a saturated mid block. The

saturated mid block of the hydrogenated block copolymer has the structure of

poly(ethylene-propylene), poly(ethylene-butylene), or both.

More preferably, the block copolymers of this invention comprise styrene end

blocks and hydrogenated polybutadiene and/or hydrogenated polyisoprene mid blocks.

Such block copolymers were also disclosed in U.S.P. 4, 136,699; 4,361.672; 4,460,364;

4,714,749; and 5,459,193, and in KRATON® Thermoplastic Rubbers published by Shell

Chemical Company.

Most preferably, the block copolymer has end blocks of styrene whose number

average molecular weight was in the range of 10,000 to 30,000, and the mid block was a

block of hydrogenated polyisoprene having a number average molecular weight of

125,000. Such hydrogenated block copolymers were known as styrene-ethylene-

propylene-styrene (SEPS) copolymers. Such block copolymers were commercially

available from the Shell Chemical Company under the trademark KRATON® G.

The KRATON® G hydrogenated block copolymers have a number average

molecular weight (M_n) of 25,000 to 300,000, as measured by gel permeation

chromatography (GPC). Among the KRATON® G polymers, the most preferred were

KRATON® G1650, KRATON® G1652, KRATON® G1654, KRATON® G1657, and KRATON® G1730, or a comb nation thereof. More information on KRATON® G polymers was disclosed in KRATON® Polymers for Adhesives and Sealants, available

from Shell Chemical Company.

In one preferred embodiment of the invention, the block copolymer, in combination with the tackifying resin(s), outgasses less than 1500 ng/cm² as measured by

Modified IDEMA Ml 1-98 (described later). Optionally, the outgassing content of the

polymer can be reduced by applying removal means to the polymer prior to the

scavenging reaction. Such removal means can comprise extreme high temperature drying,

spray drying, aqueous cleaning, solvent cleaning, or CO, cleaning.

A further embodiment of this invention comprises using a polyurethane as the

polymer. Polyurethanes were thermoplastic polymers produced by the condensation

reaction of a polyisocyanate and a hydroxyl-containing material, e.g., a linear polyester or

polyesters containing hydroxyl groups. The basic polymer unit was formed as shown in

Formula I:

OCNR,NCO + HOR₂OH -> -[-CONHR,NHCOOR₂O-]_n- (I)

where R, and R₂ were hydrocarbon radicals or substituted hydrocarbon radicals. Such

polymers were discussed in U.S. P. 4,661,542. An example of such a polyurethane was

ESTANE® 5703 which was commercially available from BF Goodrich.

Natural rubber was a well-known material. Natural rubber was a polyisoprene

derived from latex obtained from Hevea trees, coagulated with acetic or formic acid.

Natural rubber can also be made synthetically. Acrylate copolymers were known in the art. Such acrylic adhesives were discussed in U.S.P. 5,981,666.

Tackifying Resins

Tackifying resins of this invention were resins that associate predominantly with

the elastomeric block or mid block and were substantially incompatible with

nonelastomeric or end blocks. These mid block associating resins were compatible with

the mid block in that between 100 and 200 or more parts by weight of the mid block

associating resin show a clear film when the particular mid block associating resin was

combined with 100 parts of the mid block of the block copolymer and cast from solution in toluene.

In one embodiment of this invention, the tackifying resins usable in this invention,

in combination with the block copolymer(s), outgasses less than 1500 ng/cm² as measured

by Modified IDEMA Ml 1-98 (described later). Optionally, the outgassing content of the

tackifying resins can be reduced by applying removal means to the tackifying resins prior

to the scavenging reaction. Such removal means can comprise extreme high temperature

drying, spray drying, aqueous cleaning, solvent cleaning, or CO, cleaning.

Examples of tackifying resins that may be useful in this invention include

polyhydric esters of rosin or hydrogenated rosin esters, such as glycerol and

pentaerythritol esters of hydrogenated rosins and of highly stabilized rosins, esters of

polyhydric alcohol, synthetic polyterpenes, terpene-olefin copolymers, terpene-phenols,

tall oil rosin, synthetic saturated hydrocarbon resins, such as saturated alicyclic

hydrocarbons, olefinic resins, aromatic containing resins, phenol-aldehyde resins, a-

pinene resins, a-pinene resins, terpene-phenolic resins, and copolymers such as of 1 ,3-

pentadiene and 2-methyl-2-butene, or mixtures thereof. Other examples of tackifying resins were disclosed in U.S.P. 4,361 ,663 and 4,399,249, and in U.S.P. 4,136,699; 4,361 ,672; 4,714,749; and 5,459,193.

The preferred tackifying resin of this invention was of the type known as

"hydrocarbon resins". A good description of hydrocarbon resins can be found in Kirk-

Othmer, Encyclopedia of Chemical Technology, Second Edition, Vol. 1 1, Interscience,

New York, 1966, pg. 242. Many of the so-called hydrocarbon resins commercially

available today were teφene resins, i.e., polymers with (repeating) isoprene (C₅H₈) or

C_]0H|₆ units. These polymers can be natural or synthetic and can be copolymers

(including terpolymers, etc.), since isoprene was an olefin which can be copolymerized

with other olefins. Teφene-phenols were also produced.

Aromatic monomers useful in forming the aromatic containing resin compositions

of this invention can be prepared from any monomer containing substantial aromatic

qualities and a polymerizable unsaturated group. Typical examples of such aromatic

monomers include: styrenic monomers, e.g., styrene, a-methylstyrene, vinyl toluene,

methoxy styrene, tertiary butyl styrene, chlorostyrene, etc.; indene monomers including

indene, methyl indene and others. Aliphatic monomers were typically natural and

synthetic teφenes which contain C₆ and C₅ cyclohexyl or cyclopentyl saturated groups

that can additionally contain a variety of substantial aromatic ring substituents.

Aliphatic tackifying resins can be made by polymerizing a feed stream containing

sufficient aliphatic monomers such that the resulting resin exhibits aliphatic

characteristics. Such feed streams can contain other aliphatic unsaturated monomers such

as 1 ,3-butadiene, cis-l ,3-pentadiene, trans- 1,3-pentadiene, 2 -methyl- 1 ,3-butadiene, 2-

methyl-2-butene, cyclopentadiene, dicyclopentadiene, teφene monomer, teφene phenolic

resins and others. Mixed aliphatic aromatic resins contain sufficient aromatic monomers and sufficient aliphatic monomers to produce a resin having both aliphatic and aromatic

character. The article by Davis, "The Chemistry of Resins," discusses synthetic C₅

resin technology. The preferred tackifying agents were hydrogenated to C,₂ resins,

preferably a C₉ resin.

Representative examples of useful aliphatic resins include hydrogenated synthetic

C₉ resins, synthetic branched and unbranched C₅ resins and mixtures thereof.

Representative examples of aromatic tackifying resins include styrenated teφene resins,

styrenated C₅ resins or mixtures thereof.

Preferably, the tackifying resin was derived by the polymerization and

hydrogenation of pure monomer hydrocarbon feed stocks (wherein the hydrocarbon

monomer has 5 or 9 carbon atoms). Such hydrocarbon resins were highly stable, light

colored, low molecular weight, non-polar resins and were suggested for use in plastics,

adhesives, coatings, sealants and caulks. Hydrogenation minimizes the presence of

double or triple bonds in potentially outgassed materials that could result in those

outgassed materials polymerizing on the computer device components. Such

polymerization can interfere with the recording, storage or reading of data in a computer

data storage device.

More preferably, the tackifying resin of this invention was low molecular weight

nonpolar hydrocarbon resin commercially available under the trademark REGALREZ®

from Hercules Incoφorated. Most preferably, the tackifying resin was at least one of

REGALREZ® 1018, REGALREZ® 1085, REGALREZ® 1094 and REGALREZ® 1 126. Scavengers

In an electronic assembly, pure hydrocarbons may be tolerated to a relatively higher level than that of the chemicals containing reactive moieties, such as acid, alcohol

or amine, which were undesirable, if not outright unacceptable, even at relatively low

levels. Some of these chemicals containing reactive moieties can be substantially

removed from film-type polymers or formulated adhesives by appropriate drying

conditions. However, chemicals containing reactive moieties may not be fully removed

during drying, especially as the thickness of the adhesive was increased. These chemicals

may then slowly escape from the adhesive to become microcontaminants in a computer

device.

This invention reduces the level of these chemicals that was outgassed, from a

polymer or an adhesive composition, through an "anchoring reaction". The anchoring

reaction was a reaction between reactive groups on the scavengers and reactive moieties

on the outgassing chemicals. The products of these anchoring reactions were either less

susceptible to outgassing, or were less reactive if they do outgas, or both. In this

invention, the anchoring reaction was typically conducted in a solution prepared by

dissolving or suspending the PSA components in a suitable liquid, such as, e.g., toluene.

While the anchoring reaction was normally substantially completed in the solution phase,

it was also possible for trace levels of scavengers to continue reacting at the elevated

temperatures that occur during drying.

The scavengers of this invention react with impurities, such as acids, amines

and/or alcohol, at moderate temperatures, preferably room temperature, and for short time

periods. The products resulting from this achoring reaction must be non- volatile even at elevated temperatures such as 85 °C. The scavengers must be compatible with the PSA system.

Typical scavengers of this invention were low molecular weight compounds and

oligomers that contain groups that react with the reactive moieties of the impurities or

have the ability to absorb chemical impurities. The scavengers used in this invention

were typically chosen based on the impurities present in the adhesive composition or

constituents of the adhesive. Mixtures of scavengers can provide for the capture of

multiple impurities.

Preferably, the scavengers of this invention have moieties that react with the polar

reactive moieties (such as acid, alcohol, amine, etc.) present in typical outgassed materials

found in PSAs. Examples of scavengers usable in this invention include polyisocyanates,

aziridines, aluminum oxide (Al₂O₃), metallic hydrides, monohydrogen suicides, and

mixtures thereof. Preferred scavengers were polyisocyanates and aluminum oxide.

Suitable polyisocyanates include the DESMONDUR™ series polymers

commercially available from Mobay Coφoration, preferably, DESMONDUR™ 3300 and

DESMONDUR™ 3390. DESMONDUR™ 3300 and DESMONDUR™ 3390 have the

preferred characterisitics of relatively high isocyanate content and low free monomers

content.

The PSA of this invention was conveniently prepared by adding at least 0.1 ,

preferably at least 2, more preferably at least 3, up to 8, preferably not to exceed 6, more

preferably not to exceed 4 weight percent, based on the weight of the total PSA, of the

scavenger(s) to an adhesive system, stirring for a period of time, filtering or decanting the

adhesive when necessary, coating the PSA solution onto a substrate, then drying properly.

Typically, a filtering or decanting step was only needed to remove the anchoring reaction

products formed when aluminum oxide or similar absorbent was used as a scavenger. Optional Components

The PSA's of this invention can optionally include other components known in the

art. These components can include plasticizing oils, resin modifiers, and antioxidants.

A "plasticizing oil", also known as an extending oil, was an organic compound

added to a high polymer both to facilitate processing and to increase the flexibility and

toughness of the final product by internal modification (solvation) of the polymer

molecule. The latter was held together by secondary valence bonds; the plasticizing oil

replaces some of these with plasticizing oil-to-polymer bonds, thus aiding movement of

the polymer chain segments. Among the more important plasticizing oils were

nonvolatile organic liquids and low-melting solids, e.g., phthalate, adipate, and sebacate

esters, polyols, such as ethylene glycol and its derivatives, tricresyl phosphate, castor oil,

etc.

These optional components tend to be "dirty" in that they contain undesirable ions

and/or contribute to outgassing from the PSA. Antioxidants in particular can be harmful

if outgassed into a disk drive system. Therefore, the current preferred embodiments of the

invention do not include these optional components. However, the invention

contemplates use of these ingredients at levels wherein the PSA containing these

ingredients outgasses less than 1500 ng/cm² as measured by Modified IDEMA Ml 1-98

(described later).

Method of Forming the PSA

The PSA compositions of hydrogenated block copolymers and tackifying resins

can be formed by technologies well known in the art, such as the technologies disclosed

in U.S.P. 4,361,672. Examples of suitable methods for forming PSA's include, inter alia:

(i) compounding on a hot two-roll mill; (ii) melting the block copolymer and the

tackifying resin and mixing the melted components until homogeneous; (iii) other

methods employed in the plastic and elastomer industries, such as high shear intensive

mixing, twin screw extrusion or tandem extrusion techniques; and (iv) dissolving the

mixtures in suitable organic solvents such as toluene and heptane, taking care to form

homogeneous solutions that were then coated on a substrate (e.g., on a film backing)

before the solvent was evaporated.

Hot-melt compounding (any of methods i-iii, above) was not a favored

embodiment of this invention. The heat from these methods can degrade the components

of the PSA, thereby creating more material that can potentially outgas from the PSA.

However, the invention contemplates use of these methods provided that the resulting

PSA outgasses less than 1500 ng/cm² as measured by Modified IDEMA M l 1 -98.

Preferably, the PSA of this invention was formed by dissolving the mixtures in

suitable organic solvents taking care to form homogeneous solutions that were then

coated on the component for the computer device before the solvent was evaporated.

Preferably, these solutions contain at least 10, more preferably at least 20, most preferably

at least 30, up to preferably 80, more preferably not in excess of 60, most preferably not in

excess of 50, weight percent solids based on the total weight of the solution.

Suitable organic solvents must be inert to the block copolymer and the tackifying

resin. Additionally, the organic solvent must be selected such that substantially all of the solvent can be evaporated from the PSA. "Substantially all of the solvent" refers to removal of the solvent such that the residual levels of solvent were less than 5 percent,

preferably less than 2 percent of the total outgassed materials per Modified IDEMA Ml 1-

98. Preferred organic solvents include toluene, cyclohexane and heptane, more preferably

toluene.

Optionally, the solution can be filtered or decanted after the scavenging reaction

has been accomplished. This option was preferred when aluminum oxide or similar

absorbent was used as a scavenger.

The solvent can be evaporated from the PSA by any technique known in the art,

such as vacuum drying or, preferably, exposure to hot air in a drying oven. The

temperature of the hot air must be maintained below the autoignition point of the solvent.

The appropriate drying conditions were dependent on the substrate to which the PSA was

applied and the process time available for drying. For example, when using a substrate

comprising a Type S polyester film (available from Du Pont), the preferred hot air

temperature for evaporating toluene from the PSA of this invention was 250 °F to 350 °F

for a drying time of 2 to 3 minutes. The practical upper limit on drying time was

deteπnined from the available equipment and the desired production rate.

In one preferred embodiment the PSA was formed by:

A. forming a solution by dissolving in a solvent

(1) at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof, preferably the polymer was at least one of a

hydrogenated styrene-elastomer-styrene block copolymer or a

hydrogenated styrene-elastomer-styrene-elastomer block copolymer, (2) at least one tackifying resin, and

(3) at least one scavenger, wherein at least one of the polymer or the tackifying resin includes at least one impurity, the impurity comprising a compound

with at least one reactive moiety;

B. contacting the scavenger with the impurity to form a reaction product;

C. removing the reaction product from the solution, when necessary;

D. applying the solution to a substrate;

E. drying the solution on the substrate; and

F. applying the substrate to a computer device.

In another preferred embodiment, the substrate of the steps D and E, above, was a

component of a computer device, more preferably, a component of a computer data

storage device.

A hallmark of the PSA of this invention was that the PSA with a scavenger has

lower outgassing, especially of chemicals harmful to a disk drive, than the same adhesive

without a scavenger produced under the same drying temperature and time.

The following specific examples will more precisely describe the invention and

teach the procedures presently preferred in practicing the same, as well as the

improvements and advantages realized thereby. These examples were provided for

illustration puφoses only and shall not be construed to limit the scope of the subject

matter of the invention.

EXAMPLES

Example 1 - Measurement of Outgassed Materials Outgassed materials were measured using the IDEMA Ml 1-98 Dynamic

Headspace Outgas Procedure with the following method details or exceptions (Modified

IDEMA Ml 1-98).

The permanent and expendable equipment (Section 2) consists of a: (a) Type 303

stainless steel cylindrical chamber with approximate internal dimensions: 1.25 inches

deep by 2.25 inches in diameter; (b) Supelco' stainless steel thermal desoφtion tubes

packed with the following sorbent: bed A= 100 milligrams Tenax TA, bed B= 250

milligrams Carbotrap B; (c) Hewlett-Packard² 6890 Gas Chromatograph/ 5973 Mass

Spectrometer; (d) Perkin Elmer³ ATD-400 Automated Thermal Desoφtion Unit; (e)

Reztek⁴ XTf -5 gas chromatograph column, Reztek pn# 12223; and, n-hexadecane

(Fisher Scientific⁵ pn# 03035) in dichloromethane employed as external standard for

semi-quantitation.

The sample collection and analysis (Section 3) was conducted as follows. The

thermal desoφtion tubes were conditioned at 320 °C for 8 minutes. Desoφtion tubes were installed and the samples were placed in the sample outgassing chambers. The

sample chamber flow rate was set at approximately 50 milliliters per minute (ml/min.)

using 99.99 percent nitrogen gas. The outgassing chamber was continuously heated at 85

°C. The desorber was programmed to desorb at 320 °C for 8 minutes at 50 ml/min. The

cold trap was set at -30 °C and desorbed at 350 °C, with a hold time of 8 minutes, and

valve and line temperatures set at 200°C. The outlet split was set at 54 ml/min. The

sample split ratio was approximately 49: 1. The gas chromatograph flow rate was

approximately 1 ml/min.

Semi-quantitation was accomplished by injecting 5 microliters of a 200 nanogram

per microliter dichloromethane solution of n-hexadecane into a heated sample chamber via an in-line injection port and outgassing onto reconditioned thermal desoφtion tubes for 185 minutes at 85 °C. The response factor was calculated by averaging the peak area

of the total ion chromatogram for at least 6 replicates.

The amount of target compound or compounds was calculated (Section 4) by

dividing the total ion count for the peak of the target compound or compounds by the

external standard response factor and multiplying by 1 ,000 nanograms. The total

outgassing for the sample was determined by integrating the top 20 ± 2 peaks. The final

result was expressed as nanograms per square centimeter where the sample area was

determined by summing the area of both sides of a film sample.

Notes

( 1 ) Supelco, Supelco Park, Bellefonte, PA 16823-0048 USA.

(2) Hewlett-Packard Company, Chemical Analysis Group, 2850 Centerville Road, Wilmington, DE 19808-1610 USA.

(3) The Perkin-Elmer Coφoration, 761 Main Avenue, Norwalk, CT 06859- 0010 USA.

(4) Reztek Coφoration, 1 10 Benner Circle, Bellfonte, PA 16823 USA.

(5) Fisher Scientific, 71 1 Forbes Avenue, Pittsburgh, PA 15219-4785 USA

Example 2 - Block Copolymer PSA Examples

A Comparative Sample (A) and three examples of the PSA of the invention (B, C,

D) were prepared by dissolving the components in toluene to form a 35.5 percent solids

solution. The formulas for each of these examples were shown in TABLE 1. None of the

adhesive solutions of B, C or D were filtered or decanted.

TABLE 1 - Block Copolymer PSA Formulas

* SEBS - polystyrene-(polyethylene-butylene)-polystyrene

** SEPSEP - polystyrene-(polyethylene-propylene)-polystyrene-(polyethylene-propylene)

3 weight percent based on total composition weight

4 weight percent based on total composition weight

MORESTER 49007 is a registered trademark owned by Morton international which was added as a modifier but has no eftect on the final properties of the adhesive

Each adhesive solution was coated onto a separate polyester film and dπed at 300

°F for 3 minutes The dπed adhesive films were 1 mil thick Then the coated polyester

film was die-cut into the same size specimens and their outgassing was tested using a gas

chromatograph-mass spectrometer according to Modified IDEMA Ml 1-98. The results

of the outgassing measurements were shown in TABLE 2 These results demonstrate that

the use of a scavenger substantially decreases, by at least 16 percent, the amount of

outgassed mateπal in a PSA compπsing hydrogenated block copolymers TABLE 2 - Outgassing Results for Block Copolymer PSAs

Example 3 - Polyurethane PSA Examples

This example demonstrates the reduction of outgassed material in a polyurethane

which can then be used to prepare a PSA. A high level of butylated hydroxytoluene

(BHT) was measurable in ESTANE® 5703 (a polyurethane available from BF Goodrich)

as shown in TABLE 3. A comparative example (E) was prepared by dissolving

ESTANE® 5703 in dioxolane to form a 10 percent solution. An example of the invention

(F) was prepared by making a solution containing 10 percent ESTANE® 5703, 0.5

percent of Al₂O₃ and 89.5 percent of dioxolane, all percentages were by weight based on

the total weight of the solution. Both Comparative Example E and Example F were

stirred for 24 hours at room temperature. The Al,O₃ and the product of the scavenging

reactions formed a precipitate from which the polymer solution was decanted. These

solutions were carefully coated onto separate pieces of TESLIN™ paper (a porous

polyproplene film available from DuPont). Preferably, the solution was uniformly

absorbed into the paper. The coated paper samples were then dried at room temperature

until no weight change was detected after 1 hour. The outgassing was measured

according to Modified IDEMA Ml 1-98 and the results were shown in TABLE 3. These results demonstrate that the use of a scavenger of this invention also decreases outgassing

in polyurethanes by at least 30 percent.

TABLE 3 - Outgassing Results for Polyurethane

ESTANE® is a trademark of BF Goodrich.

Claims

WHAT IS CLAIMED IS:

1. An improved pressure sensitive adhesive (PSA) comprising:

A. at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof;

B. at least one tackifying resin; and

C. at least one scavenger.

2. The PSA of Claim 1 wherein the polymer comprises at least one of a hydrogenated

styrene-elastomer-styrene block copolymer or a hydrogenated styrene-elastomer-

styrene-elastomer block copolymer.

3. The PSA of Claim 1 wherein the scavenger was selected from the group

consisting of polyisocyanates, aziridines, aluminum oxide, metallic hydrides,

monohydrogen suicides, and mixtures thereof.

4. The PSA of Claim 1 in which the PSA outgasses less than 1500 ng/cm² as

measured by Modified IDEMA M 1 1 -98.

5. The PSA of Claim 1 in which the PSA outgasses less than 500 ng/cm² as

measured by Modified IDEMA Ml 1 -98.

6. The PSA of Claim 1 in which the PSA outgasses at least 16 percent less material,

as measured by Modified IDEMA Ml 1 -98, than a similar PSA, without a

scavenger.

7. The PSA of Claim 2 in which the PSA outgasses at least 16 percent less material,

as measured by Modified IDEMA Ml 1-98, than a similar PSA, without a

scavenger.

8. The PSA of Claim 2 in which the elastomer component of the hydrogenated

styrene-elastomer-styrene block copolymer or the hydrogenated styrene-elastomer- styrene-elastomer block copolymer was composed of poly(ethylene-propylene) or

poly(ethylene-butene) or both.

9. The PSA of Claim 2 in which the elastomer component of the hydrogenated

styrene-elastomer-styrene block copolymer or the hydrogenated styrene-elastomer- styrene-elastomer block copolymer was made by the polymerization of one or

more of (i) isoprene, or (ii) 1,3-butadiene.

10. The PSA of Claim 2 in which the PSA comprises between 10 to 90 weight percent

of the block copolymer, between 10 to 90 weight percent of the tackifying resin,

and between 0.1 to 10 weight percent of the scavenger, based on the weight of the

PSA.

1 1. The PSA of Claim 1 in which the tackifying resin was a hydrocarbon resin.

12. The PSA of Claim 1 1 in which the tackifying resin was hydrogenated.

13. An improved method for preparing a computer device which includes at least one

component bearing a PSA, the method comprising the steps of:

A. forming a solution by dissolving in a solvent

(1) at least one polymer selected from the group consisting of natural

rubber, styrenic-elastomer copolymers, acrylate copolymers,

polyurethanes and combinations thereof,

(2) at least one tackifying resin, and

(3) at least one scavenger, wherein at least one of the polymer or the

tackifying resin includes at least one impurity, the impurity

comprising a compound with at least one reactive moiety; B. contacting the scavenger with the impurity to form a reaction product;

C. applying the solution to a substrate;

D. drying the solution on the substrate; and

F. applying the substrate to a computer device.

14. The method of Claim 13 wherein the polymer was a hydrogenated styrene-

elastomer-styrene block copolymer or a hydrogenated styrene-elastomer-styrene-

elastomer block copolymer.

15. The PSA of Claim 13 wherein the scavenger was selected from the group

consisting of polyisocyanates, aziridines, aluminum oxide, metallic hydrides,

monohydrogen silicides, and mixtures thereof.

16. The method of Claim 13 further comprising the step of separating the reaction

product from the solution prior to applying the solution to the substrate.

17. The method of Claim 13 in which the computer device was a data storage device.

18. The method of Claim 13 wherein the PSA outgasses less than 1500 ng/cm² as

measured by Modified IDEMA M 1 1 -98.

19. The method of Claim 13 in which the PSA outgasses at least 16 percent less

material, as measured by Modified IDEMA 1 1 -98, than a second PSA of the

same composition except that the second PSA does not comprise a scavenger.

20. A computer device comprising at least one component containing a PSA, wherein

the PSA comprises:

A. at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof; B. at least one tackifying resin; and

C. at least one scavenger.

21. The computer device of Claim 20 wherein the polymer comprises at least one of a

hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated

styrene-elastomer-styrene-elastomer block copolymer.

22. The computer device of Claim 20 in which the computer device was a computer

data storage device.

23. The computer device of Claim 20 wherein the scavenger was selected from the

group consisting of polyisocyanates, aziridines, aluminum oxide (Al₂O₃), metallic

hydrides, monohydrogen suicides, and mixtures thereof.

24. The computer device of Claim 20 wherein the PSA outgasses less than 1500

ng/cm² as measured by Modified IDEMA Ml 1-98.

25. The computer device of Claim 20 in which the PSA outgasses at least 16 percent

less material, as measured by Modified IDEMA M l 1-98, than a second PSA of

the same composition except that the second PSA does not comprise a scavenger.

26. The computer device of Claim 21 in which the PSA outgasses at least 16 percent

less material, as measured by Modified IDEMA Ml 1 -98, than a second PSA of

the same composition except that the second PSA does not comprise a scavenger.

27. An improved PSA consisting essentially of:

A. at least one polymer selected from the group consisting of natural rubber,

styrenic-elastomer copolymers, acrylate copolymers, polyurethanes and

combinations thereof;

B. at least one tackifying resin; and

C. at least one scavenger.

8. The PSA of Claim 27 wherein the polymer comprises at least one of a hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated

styrene-elastomer-styrene-elastomer block copolymer.