Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-09-21
2001-04-03
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S046000, C522S129000, C522S170000, C522S182000, C528S220000, C528S405000, C528S408000, C528S421000
Reexamination Certificate
active
06211261
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thermosetting pressure-sensitive adhesive excellent in heat resistance which 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
For simplifying work and improving safety and sanitation, a process which comprises using a previously prepared adhesive sheet to effect adhesion treatment has been widely used instead of the conventional process which comprises applying and drying a liquid adhesive. As the adhesive sheet, a thermosetting adhesive sheet to be cured by heat treatment has been proposed in use for adhering electronic parts.
The conventional thermosetting adhesive sheet is excellent in adhesive strength and heat resistance, but poor in tackiness at room temperatures, resulting in the difficulty of positioning and temporarily adhering the sheet. Therefore, complicated treatments have been carried out, that is, the adhesive sheet is heated or swelled with a solvent to give tackiness thereto, followed by positioning and temporary adhesion. Furthermore, a low molecular weight ingredient not crosslinked is contained in a large amount before curing and this causes the problem of paste protrusion. Further, the conventional thermosetting adhesive sheets have disadvantages in that those excellent in storage stability take a lot of time for curing, and in that those curable for a short period of time is poor in storage stability.
On the other hand, a pressure-sensitive adhesive sheet has a tackiness at ordinary temperatures, can be adhered to an object without any previous operation, and can immediately exhibit the adhesive strength. However, the pressure-sensitive adhesive sheet has the disadvantage that it is generally poor in adhesive strength and heat resistance, compared with the adhesive. In JP-A-5-117593 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), strong adhesion and high heat resistance are realized by the use of a photopolymerizable composition containing an alkyl acrylate as the main ingredient. However, it does not exceed the level of the conventional pressure-sensitive adhesive sheet. That is, it has been desired to provide an adhesive sheet which can exhibit adhesion as the pressure-sensitive adhesive sheet at the beginning of adhesion to an adherend and can exhibit a high adhesion and a high heat resistance comparable to those of the adhesive after adhesion.
As a sheet which can meet this requirement, a so-called viscous adhesive, i.e., an adhesive having both characteristics of a pressure-sensitive adhesive and an adhesive has been proposed. For example, JP-A-2-272076 discloses a thermosetting pressure-sensitive adhesive in which a photopolymerizable composition obtained by adding an epoxy resin to an acrylic ester monomer is used as a raw material. Further, JP-A-7-2978 discloses a thermosetting pressure-sensitive adhesive in which a photopolymerizable composition obtained by adding an ester of an epoxy group-containing alcohol and (meth)acrylic acid and an epoxy resin to an alkyl (meth)acrylate is used as a raw material.
In the adhesives according to these proposals, the photopolymerizable compositions are photopolymerized by irradiation of ultraviolet rays to form the thermosetting adhesives having both characteristics of pressure-sensitive adhesives and adhesives. These compositions contain a curing agent such as imidazole, dicyandiamide, polyamines and phenol resin, and the curing reaction thereof with an epoxy group is conducted.
In this case, the curing reaction gradually proceeds in storage before or after photopolymerization to thereby deteriorate the adhesive characteristics, which raises a problem with regard to the storage stability. In particular, the adhesive disclosed in JP-A-2-272076 also has the problem that the acrylic polymer formed by photopolymerization is not crosslinked with the epoxy resin even after the curing reaction, resulting in insufficient heat resistance.
Further, when the photopolymerizable compositions of this kind each is provided on a base material and photopolymerized by irradiation of ultraviolet rays to prepare an adhesive sheet, even if the layer thickness of the photopolymerizable composition is increased for securing good adhesive strength, the rate of polymerization is not increased. As a result, unreacted monomers remain to cause inhospitable odors or the occurrence of foaming due to vaporization of the unreacted monomers. Further, in applications such as electronic parts, there is a possibility of bringing about corrosion of the electronic parts by vaporization of the residual monomers. Furthermore, when the amount of photopolymerization initiator is increased for increasing the rate of polymerization, the amount of unreacted monomers is decreased, but the resulting polymer has a reduced molecular weight to thereby cause a deteriorated heat resistance.
SUMMARY OF THE INVENTION
Contemplating such a situation, an object of the present invention is to provide a thermosetting pressure-sensitive adhesive which can exhibit a high rate of polymerization without a decrease in the molecular weight on photopolymerization, thereby can show the tackiness at ordinary temperatures to permit easy temporary adhesion to an adherend, can be cured by heating after that for a short period of time to exhibit strong adhesive strength and high heat resistance, and is scarcely cured during storage before heating, thus being excellent in storage stability.
Another object of the present invention is to provide a sheet-like or tape-like adhesive sheet thereof.
As a result of intensive studies for attaining the above-mentioned objects, the present inventors have discovered that the rate of polymerization can be increased without a decrease in the molecular weight by photopolymerizing an acrylic monomer with a specific photopolymerization initiator. Even when the layer thickness of a photopolymerizable composition is increased, the various disadvantages caused by unreacted monomers and the problem of deteriorated heat resistance due to a reduction in the molecular weight can be avoided, and when a specific monomer containing a carboxyl group in the molecule is added to this photopolymerization system and allowed to react with an epoxy resin after photopolymerization, the acrylic polymer after photopolymerization is crosslinked with the epoxy resin to exhibit strong adhesive strength and high heat resistance, and the adhesive before the above-mentioned reaction and after photopolymerization shows the tackiness at ordinary temperatures to permit temporary adhesion to an adherend, and can be cured by the above-mentioned reaction for a short period of time, and the adhesive is excellent in storage stability before the above-mentioned reaction, because a conventional curing agent such as imidazole, dicyandiamide, polyamine and a phenol resin is not incorporated.
That is to say, the present invention provides:
a thermosetting pressure-sensitive adhesive comprising a photopolymerized product of a composition comprising the following ingredients (a) to (c) and not substantially containing any curing agent for an epoxy resin as ingredient (c):
a) 100 parts by weight of a monomer mixture comprising 70% to 99% by weight of an alkyl (meth) acrylate whose alkyl group has 2 to 14 carbon atoms on average, and 1% to 30% by weight of a monoethylenic unsaturated acid copolymerizable therewith based on the monomer mixture;
b) 0.01 part to 20 parts by weight of a cleavage type photopolymerization initiator having 3 or more peroxide groups in its one molecule; and
c) 5 parts to 30 parts by weight of an epoxy resin;
a sheet-like or tape-like adhesive sheet comprising a base material having provided on one side or both sides thereof the above-mentioned thermosetting pressure-sensitive adhesive layer or layers; and
the above-mentioned adhesive sheet wherein the above-mentioned thermo
Hosokawa Kazuhito
Oura Masahiro
Berman Susan W.
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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