Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-09-21
2001-07-17
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C522S129000, C522S182000, C525S107000, C525S118000, C525S119000, C428S343000, C428S346000, C428S3550EP, C428S3550EN, C428S3550AC, C427S207100, C427S208000, C427S208200
Reexamination Certificate
active
06261685
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermosetting adhesive which is excellent in heat resistance and withstands the use thereof at a high temperature of 100° C. or more or in a soldering process, and an adhesive sheet shaped in sheet or tape form comprising a base material having provided thereon the adhesive.
BACKGROUND OF THE INVENTION
Recently, various bonding materials have been used for applications such as fixing of electronic parts. The applications of this kind require not only strong adhesion but also high heat resistance such that the bonding material can withstand solder reflow in mounting an electronic part on a substrate. With miniaturization of electronic equipment, the adhering area has a tendency to become minute. In this case, the control of flowability (protrusion of adhesive) becomes significantly important from the problems of appearance and functional reductions of electronic parts. Further, in the applications of this kind, the adhesion treatment is generally carried out by heat pressing for securing the wettability in adhering, and the adhesion has been desired to be conducted under low pressure for a short period of time for improving the productivity and reducing damage of parts in heat adhering.
To such a request, JP-B-3-44592 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-B-7-15090 propose that photopolymerizable compositions prepared by adding epoxy resins and curing agents therefor to photopolymerizable monomers comprising esters of (meth)acrylic acid and alkylene oxide addition products of alcohols or phenols or esters of (meth)acrylic acid and non-tertiary alcohols are irradiated with ultraviolet rays to photopolymerize the above-mentioned photopolymerizable monomers, thereby obtaining thermosetting viscous adhesive compositions.
However, the thermosetting adhesives proposed above are tacky at ordinary temperatures, and bubbles are incorporated therein because of their stickiness in face adhesion by a press. Accordingly, they have the problem that separation and foaming occur at a temperature of 100° C. or more by expansion of the bubbles incorporated. Furthermore, since the adhesives contain imidazole, dicyandiamide or polyamines as the curing agent for the epoxy resin, there is a problem in the storage stability that the curing reaction of the epoxy resin with the curing agent gradually proceeds during storage before or after photo-polymerization to deteriorate the adhesive characteristics.
The curing reaction of the epoxy resin with the curing agent is finally conductedat the time of use for adhesion. Even after this reaction, crosslinkage is not formed between the epoxy resin and the photopolymerized product obtained by photo-polymerization of the photopolymerizable monomers, thereby resulting in insufficient heat resistance. In the thermosetting adhesives proposed above, particularly, the thermosetting adhesive proposed in JP-B-3-44592, the epoxy resin is used in a large amount as the curing component. The unreacted low-molecular weight epoxy resin flows out at the time of heat adhesion by a press to cause adhesive protrusion, which results in disadvantages such as poor appearance.
SUMMARY OF THE INVENTION
Contemplating such a situation, an object of the present invention is to provide a thermosetting adhesive which is not tacky at ordinary temperatures, does not incorporate bubbles in face adhesion to an adherend by a press, can exhibit strong adhesion and high heat resistance by heating under low pressure for a short period of time without the problem of adhesive protrusion, and moreover, is excellent in storage stability.
Another object of the present invention is to provide a sheet-like or tape-like adhesive sheet thereof.
In the course of intensive studies for attaining the above-mentioned objects, the present inventors first studied a photopolymerizable composition obtained by adding a monomer capable of increasing the glass transition temperature of a polymer to be prepared to an alkyl (meth)acrylate containing an alkyl moiety having 2 to 14 carbon atoms on average, which is used generally as the main monomer for an acrylic adhesive sheet, in order to obtain a polymer having reduced tackiness, and further adding an epoxy resin thereto. As a result, an adhesive sheet being not tacky at ordinary temperatures could be prepared, but the adhesion treatment took a very long period of time and the sufficient adhesive characteristics could not be exhibited by heating under low pressure for a short period of time. Then, the present inventors studied a photopolymerizable composition prepared by using an alkyl (meth)acrylate having such an alkyl group that the glass transition temperature of the resulting polymer is −30° C. or more and adding an epoxy resin thereto. The resulting adhesive sheet became very brittle, and those having satisfactory flexibility and softness could not be obtained.
As a result of further studies based on the above-mentioned findings, the present inventors discovered that the use of an acrylic monomer having such a specific structure that the homopolymer has a glass transition temperature of −30° C. or more as the main monomer in place of the above-described alkyl (meth)acrylates, the addition of a monoethylenic unsaturated monomer having functional group(s) for forming crosslinkage with an epoxy resin thereto, the formation of a non-tacky polymer from the resulting monomer mixture by photopolymerization, and the addition of the epoxy resin in a relatively small amount before or after the formation thereof provide a sheet-like product which is excellent in flexibility and softness, which does not incorporate bubbles in face adhesion to an adherend because they does not show the tackiness at ordinary temperatures, which can exhibit strong adhesion and high heat resistance attributable to the curing reaction between the non-tacky polymer and the epoxy resin effected by heating under low pressure for a short period of time without causing adhesive protrusion because of a small amount of the epoxy resin added, and moreover, which has no problem with respect to the storage stability because a usual curing agent such as imidazole, dicyandiamide and polyamines is not incorporated.
That is to say, the present invention provides a thermosetting adhesive comprising (1) a non-tacky polymer of a monomer mixture comprising 70% to 99% by weight of a (meth)acrylic ester represented by the following general formula (I), a homopolymer of which has a glass transition temperature (hereinafter referred to as “Tg”) of −30° C. or more, and 1% to 30% by weight of a monoethylenic unsaturated monomer being copolymerizable therewith and having a functional group capable of reacting with an epoxy resin each based on the monomer mixture and (2) 5 parts to 30 parts by weight of an epoxy resin per 100 parts by weight of the monomer mixture, and not substantially comprising a curing agent for the epoxy resin:
wherein R
1
represents a hydrogen atom or a methyl group; R
2
represents a methylene group, an ethylene group or a propylene group; n is an integer of 1 to 3; and &phgr; represents a phenyl group, a monoalkyl-substituted phenyl group or a dialkyl-substituted phenyl group. When &phgr; is a monoalkyl-substituted phenyl group or a dialkyl-substituted phenyl group, the alkyl group as the substituent for the phenyl group generally has from 1 to 5 carbon atoms. When n is 2 or 3, the plural R
2
may be the same or different.
Further, the present invention provides the above-mentioned thermosetting adhesive in which the ratio of the epoxy resin is 5 parts to 20 parts by weight per 100 parts by weight of the monomer mixture; the above-mentioned thermosetting adhesive in which the monoethylenic unsaturated monomer having the functional group capable of reacting with the epoxy resin is a carboxyl group-containing monomer or a hydroxyl group-containing monomer; the above-mentioned thermosetting adhesive in which the non-tacky polymer is a polymer obtained by irradiation of
Hosokawa Kazuhito
Oura Masahiro
Berman Susan W.
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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