WO2001018138A2

WO2001018138A2 - Pressure sensitive adhesives for use with data storage devices

Info

Publication number: WO2001018138A2
Application number: PCT/US2000/017782
Authority: WO
Inventors: Huimin Yang; Gerald T. Downing
Original assignee: Brady Worldwide, Inc.
Priority date: 1999-09-10
Filing date: 2000-06-28
Publication date: 2001-03-15
Also published as: KR20020035869A; WO2001018138A3; JP2003519428A; CN1538999A

Abstract

A method is disclosed for making improved, cleaner computer devices by using a cleaner pressure sensitive adhesive (PSA) on the computer device components that contain a PSA. The cleaner PSA comprises at least one hydrogenated styrene-elastomer-styrene block copolymer or the hydrogenated styrene-elastomer-styrene-elastomer block copolymer, and at least one tackifying resin. Hydrogenated styrene-ethylene butylene-styrene or styrene-ethylene propylene-styrene block polymers in combination with certain 'clean' tackifying resins are formulated into a liquid coating, coated and properly dried on an acceptable substrate. The component thus produced is ideally suited to be used in disk drives. The component produced in the manner described, has a much lower total aggregate concentration of materials considered harmful by the industry, compared to most polyacrylate adhesive components of the same design. Also disclosed are computer devices, preferably computer data storage devices, made by the method disclosed.

Description

PRESSURE SENSITIVE ADHESIVES FOR USE WITH DATA STORAGE DEVICES

This invention relates to computer devices. More particularly, this invention

relates to pressure sensitive adhesives (PSA) for use with computer devices, and to

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

Computer disk drives are complex assemblages of surface treated alloys, plastics,

elastomeric, and ceramic parts containing various lubricants and a variety of adhesives.

Pressure sensitive adhesives are 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 is 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, using 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 are 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 are 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 parti culates.

Polyacrylate-based PSA's have been used extensively in the components for disk drives. A select few are considered useable; none are 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 is resorting to two strategies in order to minimize the

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

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 are 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 is 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 is to use parts and processes that contain or produce fewer contaminants. These more stringent specification

requirements are 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 is present around the disk drive. Hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated

styrene-elastomer-styrene-elastomer block polymer in combination with certain "clean" or

"cleanable" tackifying resins are formulated into a liquid coating, coated and properly

dried on an acceptable substrate. The component, e.g., a tape, label, seal. etc.. thus produced is ideally suited for use in disk drives. The component produced in this manner, has a much lower total aggregate concentration of materials considered harmful by the

industry, compared to most polyacrylate adhesive components of the same design.

In one embodiment, the invention comprises an improved method for preparing a

computer device which includes at least one component bearing a PSA, the method

comprising applying an improved PSA to the PSA bearing component, wherein the

improved PSA comprises:

A. at least one of a hydrogenated styrene-elastomer-styrene block copolymer

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

B. at least one tackifying resin.

In another embodiment, the invention comprises a computer device comprising at least one component containing a PSA comprising:

A. at least one of a hydrogenated styrene-elastomer-styrene block copolymer

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

B. at least one tackifying resin.

A "block copolymer" is 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. A "diblock copolymer" is a block

copolymer that has the general structure A-B, where A is a long stretch of one copolymer

and B is a long stretch of a second copolymer. A "triblock copolymer" is a block copolymer that has the general structure A-B- A, where A is a long stretch of one copolymer and B is a long stretch of a second copolymer.

A "tackifying resin" is 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" are permanently and aggressively tacky (sticky) solids which form immediate bonds when two parts are 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 "hydrocarbon resin" is a resin in the number molecular weight range of a few

hundred up to about 6,000 or 8,000, which is obtained or synthesized from rather basic hydrocarbonaceous materials such as petroleum, coal, tar, turpentine, and the like.

An improved computer device is 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 is a film, tape or label which is used to seal or identify

one or more components of the computer device. The computer device is preferably a

disk drive or other data storage device. The Adhesive

The adhesive used in this invention comprises at least about 10, preferably at least

about 40, up to about 90, preferably up to about 75, weight percent of a block copolymer

and at least about 10, preferably at least about 25, up to about 90, preferably up to about

60, weight percent of a tackifying resin, all percentages based on the total weight of the

adhesive.

Block Copolymers

Any one of the variety of 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, both of which are incorporated herein by reference. These particular block copolymers typically take on the general configuration A-B-A or A-B-A-

B, wherein each "A" block, which is generally characterized as an end block, is a thermoplastic polymer block prepared by a polymerization of a mono-alkenyl-arene such as styrene, -methyl-styrene, tert-butyl-styrene, and vinyl-toluene.

The elastomer "B" blocks, which are characteristically identified as "mid blocks," are 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, are generated. If the block copolymers, A-B-A or A-B-A-B are

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

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

(SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene butylene-styrene

block copolymer (SEBS), styrene-ethylene propylene-styrene (SEPS), and a- methylstyrene-ethylene propylene-a-methylstyrene. A typical molecular weight for such block copolymers is between about 10,000 and about 500,000, expressed as number

average molecular weight.

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

copolymer. 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.

The hydrogenated block copolymer is 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 is 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 are also disclosed in U.S.P. 4,136,699; 4,361,672; 4,460,364;

4,714,749; and 5,459,193, all incorporated herein by reference, and in KRATQN®

Thermoplastic Rubbers published by Shell Chemical Company.

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

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

of hydrogenated polyisoprene having a number average molecular weight of about

125,000. Such hydrogenated block copolymers are known as styrene-ethylene-propylene- styrene (SEPS) copolymers. Such block copolymers are 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 about 25,000 to about 300,000, as measured by gel permeation

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

KRATON® G1650, KRATON® G1652, KRATON® G1654, KRATON® G1657, and

KRATON® G1730, or a combination thereof. More information on KRATON® G

polymers is disclosed in KRATON® Polymers for Adhesives and Sealants, available from Shell Chemical Company. In one embodiment of the invention, the block copolymer is a "clean block

copolymer". A clean block copolymer contains no more than about 200, preferably less than about 100, more preferably less than about 50, ng/cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate anions combined, and less than about 200,

preferably less than about 100, more preferably less than about 50, ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1 (described later).

Additionally, a clean 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).

In another embodiment of the invention, the block copolymer is a "cleanable

block copolymer." A cleanable block copolymer contains more outgassable contaminants and anions than does a clean block copolymer, but the outgassable contaminants and

anions can be substantially removed, through removal means, such that the levels of the

remaining outgassable contaminants and anions are no greater than for a clean block copolymer. Such removal means can comprise extreme high temperature drying, spray drying, aqueous cleaning, solvent cleaning, or CO₂ cleaning. For practical reasons,

aqueous cleaning is the preferred means for ion removal.

Tackifying Resins Tackifying resins of this invention are resins that associate predominantly with the

elastomeric block or mid block and are substantially incompatible with nonelastomeric or end blocks. These mid block associating resins are compatible with the mid block in that

between about 100 and about 200 or more parts by weight of the mid block associating

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

must be "clean". A "clean tackifying resin" contains no more than about 200, preferably less than about 100, more preferably less than about 50, ng cm² of bromide, chloride,

fluoride, nitrate, nitrite, phosphate and sulfate anions combined, and less than about 200, preferably less than about 100, more preferably less than about 50, ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1 (described later). Additionally,

a clean tackifying resin, in combination with the block copolymer(s), outgasses less than 1500 ng cm² as measured by Modified IDEMA Ml 1-98 (described later).

In another embodiment of the invention, the tackifying resin is a "cleanable

tackifying resin." A cleanable tackifying resin contains more outgassable contaminants

and anions than does a clean tackifying resin, but the contaminants can be substantially

removed, through removal means, such that the levels of remaining contaminants are no

greater than for a clean tackifying resin. Such removal means can comprise extreme high temperature drying, spray drying, aqueous cleaning, solvent cleaning, or CO₂ cleaning. For practical reasons, aqueous cleaning is the preferred means for ion removal.

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, α-pinene

resins, β-pinene resins, teφene-phenolic resins, and copolymers such as of 1,3-pentadiene and 2-methyl-2-butene, or mixtures thereof. Other examples of tackifying resins are

disclosed in U.S.P. 4,361,663 and 4,399,249, both incoφorated herein by reference, 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 is 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. 11, Interscience,

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

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

C₁₀H₁₆ units. These polymers can be natural or synthetic and can be copolymers (including teφolymers, etc.), since isoprene is an olefin which can be copolymerized with

other olefins. Teφene-phenols are 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, c -methylstyrene, vinyl toluene, methoxy styrene, tertiary butyl styrene, chlorostyrene, etc.; indene monomers including

indene, methyl indene and others. Aliphatic monomers are 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- 1,3-pentadiene, trans- 1,3-pentadiene, 2-methy 1-1, 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 C₅ Resins," discusses synthetic C₅ resin technology. The preferred tackifying agents are hydrogenated C₅ to C₁₂ 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 is derived by the polymerization and

hydrogenation of pure monomer hydrocarbon feed stocks (wherein the hydrocarbon

monomer has about 5 or about 9 carbon atoms). Such hydrocarbon resins are highly

stable, light colored, low molecular weight, non-polar resins and are 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 is low molecular weight

nonpolar hydrocarbon resin commercially available under the trademark REGALREZ® from Hercules Incoφorated. Most preferably, the tackifying resin is at least one of

REGALREZ® 1018, REGALREZ® 1085, REGALREZ® 1094 and REGALREZ®

1126.

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, is 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 is 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 are 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 contains no more than about 200, preferably less than about 100, more

preferably less than about 50, ng/cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate anions combined, and less than about 200, preferably less than

about 100, more preferably less than about 50, ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1 (described later). Additionally, such a PSA 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 are then coated on a substrate (e.g., on a film backing) before

the solvent is evaporated.

Hot-melt compounding (any of methods i-iii, above) is 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 Ml 1-98 (described later). Preferably, the PSA of this invention is formed by dissolving the mixtures in

suitable organic solvents taking care to form homogeneous solutions that are then coated on the component for the computer device before the solvent is evaporated. Preferably, these solutions contain at least about 10, more preferably at least about 20, most

preferably at least about 30, up to preferably about 80, more preferably up to about 60, most preferably up to about 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 are less than about 5% of the total outgassed materials per Modified IDEMA Ml 1-98 (described later). Preferred

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

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 are dependent on the substrate to which the PSA is

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 is about 250 °F to about 350 °F for a drying time of 2 to 3 minutes, more preferably about 325 °F to about 350 °F for a drying time of 3 minutes. The practical upper limit on drying time is determined from the available equipment and the desired production rate.

A hallmark of the PSA of this invention is that the PSA outgasses less than 1500,

preferably less than 700, more preferably less than 50, ng/cm² as measured by Modified

IDEMA Ml 1-98 (described later).

Another hallmark of the PSA of this invention is that the PSA contains less than about 200 ng/cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate

anions combined, and less than about 200 ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1 (described later).

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 are 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 are measured using the IDEMA Ml 1-98 Dynamic

(5/28/99DRAFT) Headspace Outgas Procedure (incoφorated by reference) 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) Supelco¹ 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 Scientific⁶ pn# 03035) in dichloromethane employed as external standard for semi-

quantitation.

The sample collection and analysis (Section 3) is conducted as follows. The thermal desoφtion tubes are conditioned at 320 °C for 8 minutes. Desoφtion tubes are installed and the samples are placed in the sample outgassing chambers. The sample chamber flow rate is set at approximately 50 milliliters per minute (ml/min.) using

99.99% nitrogen gas. The outgassing chamber is continuously heated at 85 °C. The desorber is programmed to desorb at 320 °C for 8 minutes at 50 ml/min. The cold trap is 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 is set at 54 ml/min. The sample split ratio is approximately 49:1. The gas chromatograph flow rate is approximately 1 ml/min.

Semi-quantitation is 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 is calculated by averaging the peak area of

the total ion chromatogram for at least 6 replicates.

The amount of target compound or compounds is 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 is determined by integrating the top 20 ± 2 peaks. The final result is expressed as nanograms per square centimeter where the sample area is 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, 110 Benner Circle, Bellfonte, PA 16823 USA.

(5) XTI is a registered trademark of Reztek Coφoration.

(6) Fisher Scientific, 711 Forbes Avenue, Pittsburgh, PA 15219-4785 USA

Example 2 - Measurement of Ions

Ion analysis is performed on an extracted sample by ion chromatography following EPA Method 300.0 revision 2.1 (August 1993)(incoφorated by reference) as modified in Table 1 (Modified EPA method 300.0 revision 2.1). In this method, a small volume (typically 2 to 3 ml) of a sample is introduced into an ion chromatograph. The ions of interest are separated and measured, using a system comprised of a guard column, analytical column, suppressor device, and conductivity detector. The specific details of the method are as follows. The ion chromatagraph system consists of a Dionex DX500 Ion Chromatograph equipped with ED40 electrochemical detector, GP40 gradient pump, and AS40 auto sampler, all equipment available from Dionex Coφoration. The sample extraction is prepared by cutting 100 cm² surface area

of the sample (one side) by using a 4.4 cm x 22.6 cm template. The liner is removed from

the sample and positioned in a clean 200 ml pyrex beaker with the adhesive side inward so no part of the strip has the adhesive face to face. 100 ml of 18.3 MΩ-cm deionized water is added to the beaker which is then covered with 80 x 40 (No. 3140) pyrex top. The beaker is placed in a water bath and heated to 80 °C ± 5 °C. The temperature of the sample is held at 80 °C for one hour. After one hour, the beaker is removed from the water bath and allowed to cool to room temperature. The water with extracted ions is now ready for analysis.

TABLE 1

Modifications to EPA Method 300.0 Revision 2.1

Example 3 -Formulations

Below are examples of tape components which comprise the PSAs of this invention. Examples A - D are prepared with hydrogenated triblock S-EB-S copolymers, hydrogenated S-EP-S-EP block copolymers, hydrocarbon resins and an optional resin modifier for adhesion. The formulas of Examples A - D are shown in Table 2.

TABLE 2 Example PSA Formulas

KRATON® is a trademark of Shell Chemical Company for block copolymers: G-l 650 is a S-EB- S containing 30% styrene and 0% Diblock; G-1657 is a S-EB-S containing 13% styrene and 29% Diblock; G-l 730 is a S-EP-S-EP containing 22% styrene and 0% Diblock. REGALREZ® is a trademark of Hercules Incoφorated for hydrocarbon resins. MOR-ESTER® is a trademark of Morton International Inc. for a semi-rigid, tacky polyester resin designed as an adhesive resin.

Adhesive solutions of samples A - D are prepared by dissolving the components in toluene to achieve a concentration of about 40% solids. A reverse roll coating device is used to coat the solution to a thickness of 0.0025" on each side of 0.0005" thick Type S

polyester film available from DuPont. Each coated side of the film is dried by passing through a 12-ft, two-zone drying oven at 4 ft/min. The resulting dried adhesive layers are 0.001" in thickness. The air temperature in Zone 1 of the oven is 325°F, and the air temperature in Zone 2 of the oven is 350°F for the second coated side.

A Hewlett-Packard 6890 Gas Chromatograph/ 5973 Mass Spectrometer, used according to Modified IDEMA Ml 1-98, is used to measure outgassing of Examples A - D. The results of the outgassing measurements are shown in Table 3 along with typical ion levels for the formulas A - D. The total ion results shown in Table 3 are averages of several measurements and are reported as precisely as the accuracy and precision of the

test method permits.

(A Dionex DX500 ion chromatograph equipped with an ED40 electrochemical detector, used according to EPA Method 300.0 Revision 2.1 , is used to measure total ions for adhesive formulations.)

TABLE 3

Outgassing and Ion Data

Example Outgassing (ng/cm²) Total Ions (ng/cm²) A 30 <100

B 16 <100

C 28 <100

D 21 <100

The results shown in Table 3 demonstrate that the PSA components of this invention (Examples A - D) outgas quantities of material well below a typical industry limit of 1500 ng/cm², and, in fact, can be made to outgas less than 50 ng/cm². PSA's

made according to this invention also outgas substantially less material than does a comparative current polyacrylate PSA made under similar conditions. The total ion contents reported in Table 3 demonstrate that the PSA's of this invention easily meet or exceed the industry standards of 800 ng/cm², and in fact, can be produced with total ion contents below about 100 ng/cm².

Claims

WHAT IS CLAIMED IS:

1. An improved method for preparing a computer device which includes at least one component bearing a PSA, the method comprising applying an improved PSA to the PSA bearing component, wherein the improved PSA comprises: A. at least one of a hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated styrene-elastomer-styrene-elastomer block copolymer, and B. at least one tackifying resin.

2. The method of Claim 1 in which the PSA outgasses less than about 1500 ng/cm² as measured by Modified IDEMA Ml 1-98.

3. The method of Claim 1 in which the PSA outgasses less than about 700 ng cm² as measured by Modified IDEMA Ml 1-98.

4. The method of Claim 1 in which the PSA outgasses less than about 50 ng/cm² as measured by Modified IDEMA Ml 1-98.

5. The method of Claim 2 in which the PSA contains less than about 200 ng/cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate anions combined and less than about 200 ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1.

6. The method of Claim 1 in which the PSA contains less than about 100 ng cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate anions combined and less than about 100 ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1.

7. The method of Claim 1 in which the PSA contains less than about 50 ng/cm² of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate anions combined and less than about 50 ng/cm² of ammonium, as measured by Modified EPA Method 300.0 Revision 2.1.

8. The method of Claim 1 in which the elastomer component of the hydrogenated styrene-elastomer-styrene block copolymer or the hydrogenated styrene- elastomer-styrene-elastomer block copolymer has the structure of at least one of poly(ethylene-propylene) and poly(ethylene-butylene).

9. The method of Claim 1 in which the elastomer component of the hydrogenated styrene-elastomer-styrene block copolymer or the hydrogenated styrene- elastomer-styrene-elastomer block copolymer is made by the polymerization of (i) isoprene, or (ii) 1,3-butadiene.

10. The method of Claim 1 in which the PSA comprises between about 5 to about 95 weight percent of the block copolymer and between about 5 and about 95 weight percent of the tackifying resin, both based on the weight of the PSA.

11. The method of Claim 1 in which the tackifying resin is a hydrocarbon resin.

12. The method of Claim 11 in which the tackifying resin is hydrogenated.

13. The method of Claim 1 in which the computer device is a data storage device.

14. A computer device comprising at least one component containing a PSA comprising:

A. at least one of a hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated styrene-elastomer-styrene-elastomer block copolymer,

and B. at least one tackifying resin.

15. A computer data storage device comprising at least one component containing a PSA comprising:

A. at least one of a hydrogenated styrene-elastomer-styrene block copolymer or a hydrogenated styrene-elastomer-styrene-elastomer block copolymer, and

B. at least one tackifying resin.