Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-05-15
2001-03-27
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C525S218000, C428S344000, C427S208400
Reexamination Certificate
active
06207272
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a peelable heat-conductive and pressure-sensitive adhesive and an adhesive sheet thereof in a tape, sheet, or another form which both are used, for example, for fixing electronic parts to radiating members or for the purpose of member fixing in various fields including building materials, vehicles, aircraft, and ships.
BACKGROUND OF THE INVENTION
Electronic parts such as hybrid packages, multimodules, and integrated circuits sealed with a plastic or metal have come to generate a larger amount of heat as a result of the progress in the degree of integration in IC's, etc. Due to the enhanced increase in temperature, there is a fear that such electronic parts may have a functional fault. A generally employed technique for avoiding this trouble is to attach a radiating member, e.g., a heat sink, to an electronic part by means of an appropriate adhesive material.
Many adhesive materials for use in the above application are known. Examples thereof include an adhesive comprising an acrylic monomer, aluminum particles, and a polymerization initiator (see U.S. Pat. No. 4,722,960), an electroconductive adhesive tape in which the adhesive layer contains silver particles having a diameter larger than the thickness of the adhesive layer (see U.S. Pat. No. 4,606,962), and a heat-conductive, electrical insulating, pressure-sensitive adhesive comprising an acrylic polymer having polar groups and a heat-conductive filler randomly dispersed in the polymer (see JP-A-6-88061 which corresponds to EP 566093 A1). The term “JP-A” as used herein means an “unexamined published Japanese patent application”.
Recently, radiating members, e.g., heat sinks, which have been bonded with an adhesive to electronic parts are frequently detached therefrom for reuse when the electronic parts are discarded or subjected to module exchange. In this case, the adhesive material is required not only to have tight adhesion during use to satisfactorily perform its fixing function, but to have easy peeling which enables the radiating members to be easily detached when the electronic parts are discarded or subjected to module exchange. However, none of the known adhesive materials described above can meet these requirements.
Known design ideas which have been employed for controlling adhesive properties are to reduce adhesive strength by increasing crosslinking density and to improve wetting ability by softening. However, the former technique, based on increasing crosslinking density, reduces wetting ability to impair adhesion to adherends, while the latter technique, based on softening, causes an increase in adhesive strength. Consequently, it is exceedingly difficult to use the design ideas described above for obtaining tight adhesion during use and obtaining easy peeling at the time of discarding or module exchange as described above, i.e., for obtaining both of the two properties.
Under these circumstances, a curable pressure-sensitive adhesive has been proposed in JP-A-56-61468, JP-B-1-53989, JP-B-2-42393, etc. The term “JP-B” as used herein means an “examined Japanese patent publication”. This curable adhesive has been designed to be in a soft state for attaining high adhesive strength in the initial stage and to be capable of being reduced in adhesive strength at the time of detachment by increasing the crosslinking density of the adhesive through curing treatment with light or heat or by foaming the adhesive. However, such pressure-sensitive adhesives have drawbacks, for example, that they necessitate the step of treatment with light or heat to complicate the process, equipment, etc., and that the applications thereof are limited because of limited allowable conditions therefor.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a peelable heat-conductive and pressure-sensitive adhesive which is a noncuring adhesive material unlike the proposed pressure-sensitive adhesive described above, and is capable of achieving both high adhesion during use and easy peeling after use. Another object of the present invention is to provide an adhesive sheet containing the adhesive.
The present inventors made intensive studies in order to accomplish the above objects. As a result, they have found that a noncuring adhesive material obtained by incorporating a large amount of a specific plasticizer into an acrylic polymer as the base polymer and further adding a heat-conductive filler thereto is excellent in heat conductivity and wetting ability, has tight adhesion to adherends even when applied at a low pressure, and has excellent peeling after use because the adhesive strength thereof is moderately low. Namely, they have found that the above noncuring adhesive material, when used for bonding electronic parts to radiating members, shows excellent radiating properties and can be easily peeled off at the time of discarding or module exchange. The present invention has been completed based on this finding.
The present invention provides a peelable heat-conductive and pressure-sensitive adhesive comprising: (a) 100 parts by weight of a polymer produced from a monomer mixture comprising from 70 to 100% by weight of an alkyl (meth)acrylate having 2 to 14, on average, carbon atoms in the alkyl group and from 0 to 30% by weight of a monoethylenic monomer copolymerizable therewith, each based on the total amount of the monomer mixture; (b) from 20 to 400 parts by weight of a plasticizer having a boiling point of 150° C. or higher; and (c) from 10 to 1,000 parts by weight of a heat-conductive filler. The present invention further provides an adhesive sheet comprising a substrate and, formed on one or each side thereof, a layer of the peelable heat-conductive and pressure-sensitive adhesive having the constitution described above.
DETAILED DESCRIPTION OF THE INVENTION
The polymer used as ingredient (a) in the present invention basically governs adhesive properties such as wetting ability and flexibility. This polymer is an acrylic polymer produced by polymerizing one or more monomers comprising from 70 to 100% by weight, preferably from 75 to 100% by weight, more preferably from 85 to 95% by weight of one or more alkyl (meth)acrylates in which the alkyl groups on the average have 2 to 14 carbon atoms and from 30 to 0% by weight, preferably from 25 to 0% by weight, more preferably from 15 to 5% by weight of one or more monoethylenic monomers copolymerizable therewith.
Among the above monomers, the alkyl (meth)acrylates having 2 to 14, on average, carbon atoms in the alkyl group are preferably the esters of acrylic or methacrylic acid with nontertiary alkyl alcohols. Examples of the alkyl group include methyl, ethyl, propyl, butyl, isobutyl, pentyl, isopentyl, hexyl, heptyl, octyl, isooctyl, nonyl, isononyl, decanyl, and isodecanyl. A mixture of (meth)acrylates in which the alkyl groups on the average have 2 to 14 carbon atoms may also be used.
The monoethylenic monomers copolymerizable with the alkyl (meth)acrylates are used for improving adhesive properties by incorporating functional groups or polar groups, for improving cohesive force or heat resistance by controlling the glass transition temperature of the polymer, or for other purposes. Examples thereof include carboxyl- or hydroxyl-containing monomers such as acrylic acid, methacrylic acid, maleic acid, caprolactone-modified acrylates, 2-acryloyloxyethylsuccinic acid, 2-acryloyloxyethylphthalic acid, caprolactone-modified hydroxyethyl (meth)acrylates, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyhexyl acrylate and nitrogen-containing monomers such as acrylamide, N-vinylpyrrolidone, and acryloylmorpholine. One or more of such monoethylenic monomers can be used, if desired.
The polymer of ingredient (a) can be obtained by polymerizing the monomers described above according to the solution, emulsion, bulk, or suspension polymerization method or another method. In bulk polymerization, it is possible to conduct the polymerization by irradiation with a radiation such as ultravio
Kitakura Kazuyuki
Muta Shigeki
Oura Masahiro
Takahira Hitoshi
Yoshikawa Takao
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Zirker Daniel
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