WO2003078536A2

WO2003078536A2 - Pressure sensitive adhesive for use in vibration/sound-damping

Info

Publication number: WO2003078536A2
Application number: PCT/US2003/006709
Authority: WO
Inventors: Wilson Z. Xia; Deepak Hariharan; David A. Krupa
Original assignee: Adhesives Research, Inc.
Priority date: 2002-03-15
Filing date: 2003-03-17
Publication date: 2003-09-25
Also published as: AU2003216522A1; WO2003078536A3; AU2003216522A8

Abstract

A pressure sensitive adhesive addressing the problem of low volatility and non-corrosivity (i.e. ultra-clean) employed in vibration or sound damping of an article comprises from 0-60 % by weight of (A) a copolymer with a Tg of greater than about -2 degrees C polymerized from (1) an alkyl (meth)acrylate having a Tg of less than 20 degrees C and, optionally, an alkyl (meth)acrylate, N-containing monomer and/or epoxy-containing monomer; and from 40-100 % by weight of (B) a copolymer with a Tg of less than about -20 degrees C polymerized from a C2-C12 alkyl (meth)acrylate, a hydroxy(C1-C5)alkyl (meth)acrylate and, optionally, vinyl acetate or vinyl ether and/or epoxy-containing monomer.

Description

"Pressure Sensitive Adhesive For Use in Nibration/Sound-Damping"

BACKGROUND OF THE PRESENT INVENTION

The present invention is directed to an ultra-clean pressure sensitive

adhesive composition for use in vibration/sound-damping.

A quiet operating environment is often highly desirable in the high

performance computer and PC gaming systems. Computer systems generally

include at least one or more disk drives for storage of information. Such disk

drives are generally in the form of a sealed head-disk assembly chamber which

includes one or more disks stacked on a spindle motor hub. The acoustic noise

of a disk drive arises from the spindle motor and disks ("Idle Acoustics") and

from the moving actuator that supports the read/write heads ("Seek

Acoustics"). On the other hand, during operation of the disk drives, vibration

at various frequencies also occurs as a result of the mechanical resonance of the

various components of the sealed head-disk assembly. It is thus desirable to.

provide means to damp vibration/sound resulting from operation of such

devices.

The problem of vibration/sound-damping is not, however, restricted to

computer systems. Such problems also exist in the automobile industry as

well as conventional appliances, as well as any other application requiring the

use of motors or related vibration or sound-inducing mechanisms.

Many attempts have been made to address this problem. See, for

example, U.S. Patent Nos. 4,942,187 (vibration-damping rubber composition of

hexene-1 type polymer and Si-containing graft copolymer and inorganic reinforcing agent); 5,279,896 (mechanical design for disk drive vibration and

noise damping); 5,464,659 (vibration damping material comprised of acrylic

monomers, silicone adhesive, and optional crosslinker); 5,781,373 (soft metal

substrate for disk drive noise reduction); 5,858,521 (vibration damping material

of a laminate of a viscoelastic layer and a hardenable pressure sensitive

adhesive layer); 5,939,179 (vibration damping material comprised of one

surface of a rigid body and a polymer layer of synthetic rubber); and 6,216,817

(preparation of damping coating by photopolymerization); U.S. published

patent application No. 20010044023 (vibration attenuating article having a

non-tacky film covering substantially all of the article); and EP 390207

(vibration damping material comprised of blend of fluorine-containing polymer

and acrylic polymer). Such attempts have not always been successful. For

example, in the computer industry, any material used in connection with the

computer hardware must be low-volatile and non-corrosive in nature (i.e.,

ultra-clean). Conventional adhesives have not generally satisfied this

requirement. The adhesive material which is employed must also provide

vibration/sound-damping over a wide frequency range, possess both cold flow

and heat resistance, and provide high adhesion and good strippability.

OBJECTS AND SUMMARY OF THE PRESENT INVENTION

It is accordingly an object of the present invention to provide a pressure

sensitive adhesive composition that may be used in vibration/sound damping

applications. It is also an object of the present invention to provide an ultra-clean

composition that exhibits pressure sensitive adhesive properties.

In accordance with the present invention , there is provided a pressure

sensitive adhesive comprised of the following:

(A) a copolymer comprised of the polymerization reaction product of an

alkyl (meth)acrylate monomer having a Tg > 20 °C, optionally a C_1-3o

(meth)acrylate monomer, optionally a nitrogen-containing polar monomer, and

optionally a polymerizable epoxy-containing monomer, said monomers being

present in an amount such that the Tg of said copolymer (A) is greater than

about -2 °C; and

(B) a copolymer comprised of the polymerization reaction product of an

optional vinyl acetate or vinyl ether component, (C_2-12) alkyl (meth)acrylate,

hydroxy(C_1-5)alkyl(meth)acrylate, and optionally a polymerizable epoxy-

containing monomer, said monomers being present in an amount such that the

Tg of said copolymer (B) is less than about -20 °C, and

wherein said copolymers (A) and (B) are present in said composition in

a weight ratio ranging from about 0: 100 to about 40:60.

There is also provided a method of damping vibrations or sound in an

article comprising providing a film or layer of a vibration or sound damping

material to the article such that said film or layer is capable of attenuating said

vibration or sound in at least one vibrational or sound mode, the film or layer

being comprised of the above composition. DETAILED DESCRIPTION OF THE PRESENT INVENTION

The adhesive composition of the present invention is comprised of low

Tg copolymer (B) either alone or together high Tg polymer (A) and which may

be used with particular advantage in vibration/sound-damping.

The composition of the present invention enables a number of benefits

to be achieved. For instance, the composition enables highly desirable

damping and absorption characteristics to be achieved over a wide freguency

range (1Hz to 10 kHz). The tan delta of the composition (measured by

Dynamic Mechanical Analysis) is an indication of energy loss and the

composition of the invention enables values above 0.6 (at 1Hz), 1.2 (at 100

Hz), 2.1 (at 1kHz) and 3.0 (at 10kHz) to be achieved (thus confirming the

ability of the composition to provide vibration/sound-damping).

Dynamic Mechanical Analysis (DMA) provides a useful tool to study

the dynamic properties of a material and is often used to characterize the sound

or vibration damping performance of polymers, particularly viscoelastic

polymers. The tan delta of the material, as defined by the ratio of Loss

Modulus (G) to Storage Modulus (G'), is a valuable indicator of the material's

relative damping ability. Any peak in tan delta (particularly apparent in

temperature profile studies) corresponds to a region where the material

properties are changing rapidly; i.e., the material is undergoing a transition. In

frequency dependent studies, a peak in tan delta indicates that the material

dissipates the incident sound or vibration energy and converts to heat very well at that frequency. High values of tan delta over a wide range of frequency is

generally regarded as the platform for good broadband damping properties.

The composition of the present invention may be used with advantage

in the electronics industry as the composition may be tailored to be ultra-clean

by avoiding the presence of acid or polar components; i.e., the composition will

preferably exhibit a leachable ion concentration below 22 ng/cm² , with

outgassing as measured by Dynamic Headspace Analysis using GC-MS below

910 ng/cm². Such values are within the parameters of the hard disk drive

industry standards.

The demands on the electronics industry to increase memory capacity

are driving the improvements in cleanliness levels. The development of MR

(magnetoresistive) and GMR (giant magnetoresistivity) head technologies, with

recording heads floating over the memory surface on a molecular layer of air,

make trace amounts of VOC's (volatile organic compounds originating from

the adhesive) operate as miniature "speed bumps" when they condense on the

memory surface. This disrupts the reading and writing process, which is the

essence of the electronic data storage and retrieval process.

The composition of the present invention also, due to its crosslinkable

nature, may be crosslinked to exhibit inherent hardness, cold flow resistance,

heat resistance, and broad band vibration attenuation. By way of example, a

typical shear modulus (G') range measured by Dynamic Mechanical Analysis

is 5xl0⁵ dyne/cm² (at 1Hz), 2.1xl0⁶ dyne/cm² (at 100 Hz), 6.2 x 10⁶ dyne/cm²

(at 1 kHz) and 2.6xl0⁷ dyne/cm² (at 10 kHz). The composition of the present invention can be fine tuned to exhibit a

range of adhesion, as desired.

The composition of the present invention may be used to damp

vibrations or sound in an article by providing a film or layer of a vibration or

sound damping material to the article comprised of the composition such that

the film or layer is capable of attenuating vibration or sound in at least one

vibrational or sound mode. For example, the composition may be coated on a

surface of the article which surface is particulary related to the formation of

vibrations or sound.

The high Tg copolymer (A) used in the composition of the present

invention is comprised of the polymerization reaction product of an alkyl

(meth)acrylate monomer having a Tg >20 °C, optionally a C _1-30 (meth)acrylate

monomer, an optional nitrogen-containing polar monomer, and an optional

epoxy-containing monomer, each as defined below. The monomers are

present in an amount such that the Tg of the resulting polymer is greater than -2

°C.

The alkyl (meth)acrylate monomer having a Tg > 20 °C. may be

selected from but not limited to the group consisting of t-butyl (meth)acrylate,

hexadecyl acrylate, isobornyl (meth)acrylate, cyclododecyl acrylate, methyl

methacrylate, secondary butyl methacrylate, ethyl methacrylate, cyclohexyl

methacrylate and mixtures thereof.

The optional C_1-30 (meth)acrylate monomer used in the present invention

may comprise a monomeric (meth)acrylic acid ester of a non-tertiary alcohol wherein the alcohol portion has from 4 to 18 carbon atoms. Exemplary

(meth)acrylate monomers include but are not limited to esters of (meth)acrylic

acid with non-tertiary alcohols such as 1-butanol, 1-pentanol, 2-pentanol, 3-

pentanol, 2-methyl- 1-butanol, 1-methyl-pentanol, 2 -methyl- 1-pentanol, 3-

methyl- 1-pentanol, 2-ethyl-l-butanol, 3,5,5-trimethyl-l-hexanol, 3-heptanol, 2-

octanol, 1-decanol, 1-dodecanol, etc.

Exemplary monomeric (meth)acrylate monomers having a carbon chain

of at least 12 carbon atoms include but are not limited to lauryl acrylate (C₁₂),

tridecylacrylate (C₁₃), myristyl acrylate (C₁₄), palmityl acrylate (C₁₆) and

stearyl acrylate (C₁₈). Such monomers are well-known to those skilled in the

art.

The at least one nitrogen-containing polar monomer may be selected

from a wide range of suitable monomers. Such monomers include, for

example, vinyl monomers having at least one nitrogen atom. Such monomers

include but are not limited to N-mono-substituted acrylamides, such as a

(meth)acrylamide, N-methylacrylamide, N-ethylacrylamide, N-

methylolacrylamide, N-hydroxyethylacrylamide and diacetone acrylamide;

N,N-disubstituted acrylamides such as N,N-dimethylacrylamide, N,N-

diethylacrylamide, N-ethyl-N-aminoethylacrylamide, N-ethyl-N-

hydroethylacrylamide, N,N-dimethylolacrylamide, and N,N-

dihydroxyethylacrylamide, etc.

Exemplary nitrogen-containing monomers may also include but are not

limited to N- vinyl lactam monomers such as N-vinyl-2-pyrrolidone, 5-methyl- N-vinyl-2-pyrrolidone, 5-ethyl-N-vinyl-2-ρyrrolidone, 3 ,3-dimethyl-N-vinyl-2-

pyrrolidone, 3-methyl-N-vinyl-2-pyrrolidone, 3-ethyl-N-vinyl-2-pyrrolidone;

4-methol-N-vinyl-2-pyrrolidone; 4-ethyl-N-vinyl-2-pyrrolidone; N-vinyl-2-

valerolactam; N-vinyl-2-caprolactam; N-vinyl-2-piperidone; and N,N-

dimethylacrylamide and mixtures of any of the foregoing. The corresponding

allyl derivatives thereof are also suitable for use in the present invention. The

noted lactams may also be substituted in the lactam ring by one or more lower

alkyl groups having from 1 to 4 carbon atoms, with methyl; ethyl, or propyl

groups being particularly preferred. The N- vinyl lactam monomer employed

preferably comprises N-vinyl-2-pyrrolidone.

The polymerizable epoxy-containing monomer may be selected from a

variety of vinyl-terminated epoxy-containing monomers. Exemplary

polymerizable monomers include but are not limited to glycidyl esters of an

α,β-ethylenically unsaturated carboxylic acid, such as (meth)acrylic or

crotonoic acid.

Exemplary glycidyl monomers for use in the present invention

accordingly include but are not limited to glycidyl (meth)acrylate, glycidyl

ethacrylate and glycidyl itaconate, acryl glycidyl ether, (meth)allyl glycidyl

ether and 3,4-epoxy-l-vinylcyclohexane.

The alkyl (meth)acrylate monomer is present in the copolymerizable

reactant mixture in an amount ranging from about 20 to 80 percent by weight,

the polymerizable C_1-3o (meth)acrylate monomer is present in the mixture in an

amount ranging from about 0 to 50 percent by weight, the nitrogen-containing polar monomer is present in the mixture in an amount ranging from about 0 to

50 percent by weight, and the polymerizable epoxy-containing monomer is

present in the mixture in an amount ranging from about 0 to 50 percent by

weight. The epoxy-containing monomer is preferably present in an amount

greater than 15 percent by weight.

Other monomers in addition to the above monomers may be optionally

included for reasons such as cost reduction, etc. For example, styrene and

vinyl acetate may be incorporated into the copolymer with advantage. Such

monomers, if present, will be employed in amounts such that the resulting

copolymer will still have a Tg greater than 50 °C.

The alkyl (meth)methacrylate monomer is present together with the

nitrogen-containing monomer in an amount such that the resulting copolymer

exhibits a Tg > 50 °C, and preferably at least 60 °C. Copolymer (A) does not

inherently exhibit pressure sensitive adhesive properties. However, the

polymer finds particular utility when blended with low Tg copolymer (B) to

form a crosslinkable pressure sensitive adhesive composition.

Copolymer (B) a copolymer comprised of the polymerization reaction

product of an optional vinyl acetate or vinyl ether component, C(_2-

₁₂)alkyl(meth)acrylate, hydroxy(C_1-s)alkyl(meth)acrylate, and an optional

polymerizable epoxy-containing monomer (defined in the same manner as

defined in connection with copolymer A). The monomers are present in an

amount such that the Tg of said copolymer (B) is less than about -20 °C. Exemplary hydroxy(C_1-5)alkyl(meth)acrylate monomers include but are

not limited to hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,

hydroxybutyl(meth)acrylate, and corresponding dihydroxy compounds.

While a number of (C_2-12)alkyl(meth)acrylate monomers may be

employed, the preferred monomer is 2-ethylhexylacrylate.

The vinyl acetate or. vinyl ether component is present in copolymer (B)

in an amount ranging from about 0 to about 30 percent by weight, the

(C_2-12)alkyl(meth)acrylate component is present in said copolymer (B) in an

amount ranging from about 70 to about 98 percent by weight, the hydroxy

(C₁.₅)alkyl(meth)acrylate component is present in an amount ranging from

about 2 to about 20 percent by weight, and said polymerizable epoxy-

containing monomer is present in an amount ranging from about 0 to about 5

percent by weight.

It may be particularly desirable to avoid the use of vinyl acetate in a

composition which must meet ultra-clean standards to avoid the potential for

the production of an acid component upon hydrolysis of the vinyl acetate upon

contact with moisture in the ambient atmosphere.

Copolymers (A) and (B) are present in said composition in a weight

ratio ranging from about 0:100 to about 60:40, and preferably in a weight ratio

ranging from about 5:95 to about 40:60. The copolymers (A) and (B) may be

blended together by any suitable means such as mechanical mixing using a

propeller-type mixing blade. Depending on the relative weight percentages of polymers (A) and (B),

and the compatibility of the blend, the final blend may have two separate Tg i values, or a single Tg value.

Copolymers (A) and (B) of the present invention can be prepared by any

suitable reaction technique such as free radical initiation techniques in the

presence of a solvent. Exemplary solvents include but are not limited to ethyl

acetate, cyclohexane, ketones or mixtures thereof. Solids content during

polymerization may typically range from about 40% to 60%. Exemplary free

radical initiators include but are not limited to peresters, acyl peroxides and

those of the azo type, such as 2,2'-azobis(isobutyronitrile)', benzoyl peroxide,

lauroyl peroxide, t-butyiperbenzoate, t-butyl peroxypivalate, dibenzyl

peroxydicarbonate, and diisopropyl peroxydicarbonate. Ultraviolet light and

ionizing radiation may also be employed. The free radical initiator is generally

present in the reaction mixture in an amount ranging from 0.01 to 10 % by wt.

based on the total weight of the monomers in the reaction mixture.

Typical polymerization temperatures range from 20 °C. to 150 °C. for

periods of time of from 2 to 24 hours until the desired degree of conversion

occurs. The resulting polymer will preferably exhibit a molecular weight in the

range of 50,000 to 2,000,000.

Various polymer compositions are known in the art which comprise a

glycidyl monomer and one or more of an acrylate and a nitrogen-containing

monomer. U.S. Patent No. 6,200,639 discloses at column 8, lines 25-36 a

copolymer of glycidyl methacrylate and t-butyl methacrylate, optionally in

association with an aromatic vinyl-functional monomer, one or more hydroxyl-

fϊmctional (meth)acrylic monomers and one or more additional monomers.

U.S. Patent No. 5,723,191 discloses a tackified dual cure pressure

sensitive adhesive comprised of a copolymer having an acrylic backbone, a

glycidyl monomer, an unsaturated carboxylic acid monomer, and a vinyl

lactam monomer, together with a tackifier.

U.S. Patent No. 3,787,380 discloses a copolymer of N- vinyl orN-allyl

heterocyclic monomers, and unsaturated ester monomer and a glycidyl

monomer.

U.S. Patent Nos. 4,812,541 and 5,639,811 disclose a pressure sensitive

adhesive copolymer comprised of a N- vinyl lactam monomer, a glycidyl

monomer and an alkyl (meth) acrylate monomer.

U.S. Patent No. 5,270,416 discloses a thermosetting powder comprised

of a glycidyl monomer, a methyl (meth)acrylate, butyl acrylate and styrene.

U.S. Patent No. 3,857,905 discloses a thermosetting coating

composition comprised of a glycidyl monomer, a lower alkyl acrylate and a

methyl acrylate.

Various polymer compositions are also known in the art which are

comprised of both high and low Tg polymer components. See, for example,

U.S. Patent Nos. 3,846,368; 3,998,768; 4,107,235; 5,098,952; 5,098,956; and

5,827,609. U.S. Patent No. 5,827,609 discloses a multilayer pressure sensitive adhesive construction where each layer exhibits a different glass transition

temperature.

Any conventional solvent/diluent may be admixed with the copolymer

blend to permit coating of the composition comprised of the blend of

copolymers (A) and (B) at a sufficiently low viscosity. Exemplary

solvents/diluents include but are not limited to xylene, toluene, butylacetate,

acetone, methyl ethyl ketone, methyl isobutyl ketone, alcohols such as

methanol, ethanol, propanol, butanol; ethylene glycol monomethyl ether,

ethylene glycol monobutyl ether acetate, ethylene glycol monoethyl ether

acetate, ethylene glycol monomethyl ether, ethylene glycol dibutyl ether;

hexane, mineral spirits, and other aliphatic, cycloaliphatic or aromatic

hydrocarbon solvents and other esters, ethers, ketones and alcohols, or mixtures

thereof.

The resulting blend may be coated onto a backing material by any

conventional manner, such as by roll coating, spray coating, or extrusion

coating, etc. by use of conventional extrusion devices. The blend may be

applied together with a solvent (typically having a solids content of about 30

percent by weight) and the solvent subsequently removed (such as by

evaporation) to leave the tacky adhesive layer on the backing material

(preferably having a solvent content of less than about 1 percent by weight).

Typically, evaporation will occur at a temperature in the range of from about

150 °F to about 250 °F to ensure removal of any solvent as well as to permit

crosslinking of the composition by thermocuring. Desirably, the coated composition will have a thickness within the range of about 0.5 mil to about 50

mils.

Exemplary backing materials include but are not limited to flexible and

inflexible backing materials conventionally employed in connection with

pressure sensitive adhesives. Such materials include creped paper, kraft paper,

fabrics (knits, non-wovens, wovens), foil and synthetic polymer films or sheets

such as polyethylene, polypropylene, peel PMMA, polyvinyl chloride,

polyamide, polyimide, poly(ethylene terephthalate), polycarbonate, and

cellulose acetate, as well as glass, ceramics, metallized polymer films and other

composite sheet materials.

The adhesive may be applied to one or both of the aforementioned

backing materials, or sandwiched in alternating fashion between multiple layers

of the aforementioned backing materials, to yield two sided tapes. Also,

adhesives may be combined in discrete layers with or without benefit of a

backing material.

In another embodiment, the adhesive may be applied between two

release substrates or on a 2 side coated differential release substrate to form a

transfer adhesive.

Various additional components may also be incorporated into the

composition to modify the properties or characteristics thereof. A variety of

fillers may be incorporated into the polymer blend to provide desired physical

characteristics. For example, metallic flake filler such as stainless steel flake

having a particle size of 25-75 microns and aspect ratios of 31-94 may be incorporated into the composition in an amount of up to about 60 percent by

weight to enhance vibration/sound-damping properties. Rigid polymers having

a high Tg such as polymethylmethacrylate may be added to produce a

controlled phase separation within the composition to further enhance

vibration/sound-damping of the composition. A variety of conventional

crosslinking compounds (such as blocked polyamines) may also be

incorporated into the composition to enhance crosslinking of the composition.

The present invention is illustrated by the following Examples which are

intended to be merely illustrative in nature and not limiting in scope.

EXAMPLE 1

A high Tg acrylic polymer (comprised of 40%» by wt. t-butyl

methacrylate, 10%> by wt. butyl acrylate, 20%> by wt. N-vinyl-2-pyrrolidone and

30% by wt. glycidyl methacrylate) was prepared in ethyl acetate solvent using

a free radical initiator l,l-di(t-amylperoxy)cyclohexane to a molecular weight

of approximately 200,000 GPC relative to polystyrene and having a first glass

transition temperature (Tg) of about 60°C (measured by DSC) and a second

glass transition temperature (Tg) of above 90°C.

5.76 parts of a low Tg acrylic polymer synthesized (25% by wt. solids in

ethyl acetate solvent) was mixed with 65.06 parts of a second copolymer

(comprised of about 70%> by wt. 2-ethylhexyl acrylate, about 20% by wt. vinyl

acetate, 10% by wt. hydroxyethylacrylate and 0.2% by wt. glycidyl

methacrylate, about 41% by wt. solids). 0.75 parts of Ancamine 2441 solution

in the mixture of isopropanol and methylethylketone solvents was used in the formulation. The resulting adhesive was coated on polyester film and dried for

3 minutes at 90°C and 3 minutes at 140°C to yield films of various thicknesses.

Such films were colaminated to yield a thickness greater than 0.6 mm for

Dynamic Mechanical Analysis (DMA). The DMA Master Curve for frequency

ranging from 1 Hz to above 10 kHz was generated using a Rheometric

Scientific RAA Dynamic Mechanical Analyzer with a parallel plate fixture.

The Storage Modulus (G'), Loss Modulus (G") and the tan delta at different

frequency are summarized in Table 1 below:

Table 1

Dynamic mechanical analysis results

EXAMPLE 2

An adhesive blend comprised of 55.45 parts of a high Tg acrylic

polymer (synthesized from 40% by wt. t-butyl methacrylate, 10% by wt. butyl

acrylate, 20% by wt. N-vinyl-2-pyrrolidone and 30% by wt. glycidyl

methacrylate) and 137.08 parts of a low Tg acrylic polymer (41% by wt. solids

in ethyl acetate solvent of about 70% by wt. 2-ethylhexyl acrylate, about 20%

by wt. vinyl acetate, 10% by wt. hydroxyethylacrylate and 0.2% by wt.

glycidyl methacrylate) was prepared in the mixed solvent of ethyl acetate and

toluene. A 5-mil pressure sensitive adhesive film was generated by coating the blend on polyester film and subsequently removing the solvent using the

following heating conditions: 5 minutes at 65.5°C, 5 minutes at 90°C and 5

minutes at 140°C. The DMA test results of Storage Modulus (G'), Loss

Modulus (G") and tan delta at 1 Hz, 100 Hz, 1 kHz and 10 kHz are summarized

in Table 2 below:

Table 2 Dynamic mechanical analysis results

The cleanliness of the pressure sensitive film was tested for leachable

ions using the ion chromatography analysis. An adhesive sample of 50 cm

placed on aluminum foil was rinsed with 18 Meg-Ohm water and submerged in

20 mis of 18 Meg-Ohm water for extraction at 85°C for one hour. Following

the extraction, the water was removed, filtered and tested for ionic cleanliness

using a Waters 636 Ion Chromatograph. As shown in Table 3 below, the

leachable ions are within the general acceptance criteria for Hard Disk Drive

industry, indicating the ultra high cleanliness of the adhesive composition. Table 3

Summary of ionic chromatography test results

The same pressure sensitive adhesive sample was tested for outgassing

using Dynamic Headspace GC/MS and the test results are shown in Table 4

below:

Table 4

Summary of Outgassing test results

Example 3

A high Tg acrylic polymer was synthesized in ethyl acetate solvent

based on the monomers of 2-ethyl hexyl acrylate (54% by wt.), hydroxy ethyl

acrylate (10% by wt.) and isobornyl methacrylate (36% by wt.), using free

radical initiators 2,2'-azobis-(2-methylbutyronitrile) (Vazo 67) and l,l'-azobis-

1-cyclohexanecarbonitrile (Vazo 88). 115.8 parts of the synthesized acrylic

polymer (about 53% solids in ethyl acetate) was blended with 223.1 parts of a

second acrylic polymer of low Tg (about 41% by wt. solids in ethyl acetate

solvent of about 70% by wt. 2-ethylhexyl acrylate, about 20% by wt. vinyl

acetate, 10% by. wt. hydroxyethylacrylate and 0.2% by wt. glycidyl

methacrylate). The resulting adhesive was coated on polyester film and dried

for 3 minutes at 90°C and 3 minutes at 140°C to generate films of various

thicknesses. Such films were colaminated to give thickness greater than 0.6

mm for Dynamic Mechanical Analysis (DMA). The DMA Master Curve for

frequency ranging from 1 Hz to above 10 kHz was generated using a

Rheometric Scientific RAA Dynamic Mechanical Analyzer with a parallel

plate fixture. The Storage Modulus (GO, Loss Modulus (G") and tan delta at

different frequency were shown in Table 5 below:

Table 5

Dynamic mechanical analysis results

Claims

WHAT IS CLAIMED IS:

1. A pressure sensitive adhesive comprised of the following

composition:

(A) a copolymer comprised of the polymerization reaction product of:

(1) an alkyl (meth)acrylate monomer having a Tg > 20 °C;

(2) optionally a C_1-30 (meth)acrylate monomer;

(3) optionally a nitrogen-containing polar monomer; and

(4) optionally a polymerizable epoxy-containing monomer,

said monomers being present in an. amount such that the Tg of said

copolymer (A) is greater than about -2 °C; and

(B) a copolymer comprised of the polymerization reaction product of:

(1) optionally vinyl acetate or vinyl ether;

(2) (C_2-12)alkyl(meth)acrylate;

(3) hydroxy(C_1-5)alkyl(meth)acrylate; and

(4) optionally a polymerizable epoxy-containing monomer,

said monomers being present in an amount such that the Tg of said

copolymer (B) is less than about -20 °C, and

wherein said copolymers (A) and (B) are present in said composition in

a weight ratio ranging from about 0:100 to about 60:40, preferably about 5:95

to about 60:40.

2. The composition of claim 1 wherein said nitrogen-containing

monomer comprises an N- vinyl lactam monomers.

3. The composition of claim 2 wherein said an N- vinyl lactam monomer

is selected from the group consisting of N-vinyl-2-pyrrolidone, 5-methyl-N-

vinyl-2-pyrrolidone, 5-ethyl-N-vinyl-2-pyrrolidone, 3,3-dimethyl-N-vinyl-2-

pyrrolidone, 3 -methyl-N-vinyl-2-pyrrolidone, 3 -ethyl-N-vinyl-2-pyrrolidone;

4-methol-N-vinyl-2-pyrrolidone; 4-ethyl-N-vinyl-2-pyrrolidone; N-vinyl-2-

valerolactam; N-vinyl-2-caρrolactam; N-vinyl-2-piperidone; N,N-

dimethylacrylamide and mixtures thereof.

4. The composition of claim 1 wherein said C_1-30 (meth)acrylate

monomer is an ester of (meth)acrylic acid with a non-tertiary alcohol selected

from the group consisting of 1-butanol, 1-pentanol, 2-pentanol, 3 -pentanol, 2-

methyl- 1 -butanol, 1 -methyl-pentanol, 2-methyl- 1 -pentanol, 3 -methyl- 1 -

pentanol, 2-ethyl-l-butanol, 3,5,5-trimethyl-l-hexanol, 3-heptanol, 2-octanol,

1-decanol, 1-dodecanol and octadecanol.

5. The composition of claim 1 wherein said alkyl (meth)acrylate

monomer having a Tg > 20 °C is selected from the group consisting of t-butyl

(meth)acrylate, hexadecyl acrylate, isobornyl (meth)acrylate, cyclododecyl

acrylate, methyl methacrylate, secondary butyl methacrylate, ethyl

methacrylate, cyclohexyl methacrylate and mixtures thereof.

6. The composition of claim 1 wherein said epoxy resin comprises a

glycidyl monomer.

7. The composition of claim 1 wherein the Tg of said copolymer (A) is

at least -2 °C.

8. The composition of claim 1 wherein said alkyl (meth) acrylate is

present in said copolymer (A) in an amount ranging from about 20 to 80 about

percent by weight.

9. The composition of claim 1 wherein said C_1-30 (meth)acrylate

monomer is present in said polymer in an amount ranging from 0 to about 50

percent by weight.

10. The composition of claim 1 wherein said epoxy-containing

monomer is present in said copolymer (A) in an amount ranging from about 0

to about 50 percent by weight, based on the weight of copolymer (B).

11. The composition of claim 1 wherein said epoxy-containing

monomer is present in said copolymer (B) in an amount ranging from about 0

to about 5 percent by weight, based on the weight of copolymer (B).

12. The composition of claim 1 wherein said nitrogen-containing

monomer is present in said copolymer (A) in an amount ranging from about 0

to about 50 percent by weight.

13. The composition of claim 1, wherein said Tg of said copolymer (B)

is below about -20 °C.

14. The composition of claim 1, wherein said vinyl acetate or vinyl ether

is present in said copolymer (B) in an amount ranging from about 0 to about 30

percent by weight.

15. The composition of claim 1, wherein said hydroxy

(C_1-5)alkyl(meth)acrylate is present in said copolymer (B) in an amount

ranging from about 2 to about 20 percent by weight.

16. The composition of claim 1, wherein said (C_2-12)alkyl(meth)acrylate

is present in said copolymer (B) in an amount ranging from about 70 to about

98 percent by weight.

17. The composition of claim 1, together with a backing material.

18. The composition of claim 1, in the form of a film.

19. A method of damping vibrations or sound in an article comprising

providing a film or layer of a vibration or sound damping material to said

article such that said film or layer is capable of attenuating said vibration or sound in at least one vibrational or sound mode, said film or layer being

comprised of a composition comprised of the following:

(A) a copolymer comprised of the polymerization reaction product of:

(1) an alkyl (meth)acrylate monomer having a Tg > 20 °C;

(2) optionally a C_1-30 (meth)acrylate monomer;

(3) optionally a nitrogen-containing polar monomer; and

(4) optionally a polymerizable epoxy-containing monomer,

said monomers being present in an amount such that the Tg of said

copolymer (A) is greater than about -2 °C; and

(B) a copolymer comprised of the polymerization reaction product of:

(1) optionally vinyl acetate or vinyl ether;

(2) (C_2-12)alkyl(meth)acrylate;

(3) hydroxy(C_1-5)alkyl(meth)acrylate; and

(4) optionally a polymerizable epoxy-containing monomer,

said monomers being present in an amount such that the Tg of said

copolymer (B) is less than about -20 °C, and

wherein said copolymers (A) and (B) are present in said composition in

a weight ratio ranging from about 0: 100 to about 60:40, preferably about 5:95

to about 60:40.

20. The method of claim 19, wherein said article comprises a disk drive

in a computer system. .

21. The method of claim 19 wherein said composition is free of any acid or polar monomers.

22. The method of claim 19 wherein said article comprises a part of an

automobile.

23. The method of claim 19 wherein said article comprises a part of a

home appliance.

24. The method of claim 19 wherein said film or layer is crosslinked.