Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2002-04-05
2004-03-09
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S221000, C428S041800, C427S384000, C427S385500
Reexamination Certificate
active
06703121
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an adhesive sheet for a precision electronic member. More specifically, the present invention relates to an adhesive sheet for a precision electronic member which generates less amount of gas under high temperature atmosphere and which is suited as a low polluting adhesive sheet for a precision electronic member.
RELATED ART
In recent years, an adhesive sheet is used in a variety of the fields because it has such easiness in use that it does not have to change in a state (for example, from a liquid to a solid) in use as is the case with conventional adhesives and exhibits an adhesive strength which stands practical use immediately after stuck (pressure-sensitive tack) and because it has such non-pollution, safety and good workability that a solvent and heating are not required in use.
Capable of being given as uses of this adhesive sheet are, for example, packaging and binding, business and household, bonding, masking for painting, surface protection, corrosion prevention and water proofing, sealing, electrical insulation, electronic appliances and optical parts, medical and sanitary material, distinguishing and decoration and labeling.
In recent years, particularly in the field of a precision electronic member, a diversification in products and a reduction in lots are advanced, and it has come to be carried out in many cases to stick adhesive labels on which, for example, bar codes are printed onto respective members for production control or to use an adhesive double coated sheet for bonding the members or to use an adhesive sheet for electric insulation. Such adhesive sheet used for a precision electronic member is required not to contaminate the above precision electronic member by gas generated from an adhesive layer. This is because the inside of an electronic appliance equipped with a precision electronic member is exposed to high temperature atmosphere in use in a certain case and gas generated from an adhesive sheet stuck onto the precision electronic member under such high temperature atmosphere causes bringing about such undesirable situation as corrosion and malfunction of the above member.
DISCLOSURE OF THE INVENTION
The present invention has been made under such circumstances, and an object thereof is to provide an adhesive sheet for a precision electronic member which generates less amount of gas under high temperature atmosphere and which is suited as a low polluting adhesive sheet for a precision electronic member.
Intensive researches of a low polluting adhesive sheet repeated by the present inventors have resulted in finding that capable of meeting the object described above is an adhesive sheet in which an adhesive comprising an acrylic copolymer having a specific composition is used for an adhesive layer and in which a gas-generating amount measured on a specific condition is controlled to some value or lower. The present invention has been completed based on such knowledge.
That is, the present invention provides:
(1) an adhesive sheet for a precision electronic member which has an adhesive layer comprising an acrylic copolymer and in which an amount of gas generated in heating at a temperature of 120° C. for 10 minutes is 1.0 &mgr;g/cm
2
or less in terms of a n-decane amount, wherein the acrylic copolymer described above is prepared by copolymerizing a monomer mixture which comprises alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group and vinyl acetate in a proportion of 50:50 to 99.5:0.5 in terms of a weight ratio and in which a total content thereof is 75% by weight or more,
(2) the adhesive sheet for a precision electronic member as described in the above item (1), wherein the acrylic copolymer is prepared by copolymerizing alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group and vinyl acetate with a monomer having a cross-linkable group, and
(3) the adhesive sheet for a precision electronic member as described in the above item (1), wherein the weight average molecular weight of the acrylic copolymer is 150,000 or more.
EMBODIMENT OF THE INVENTION
The adhesive layer in the adhesive sheet of the present invention is constituted from an adhesive comprising an acrylic copolymer, and the above acrylic copolymer comprises alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group and vinyl acetate as essential monomers. In this respect, the alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group includes, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate and t-butyl (meth)acrylate. They may be used alone or in combination of two or more kinds thereof. If the alkyl (meth)acrylate has 5 or more carbon atoms in an alkyl group, a low polluting adhesive sheet in which a gas-generating amount is controlled to a prescribed value or lower is less liable to be obtained.
The function of vinyl acetate copolymerized with these alkyl (meth)acrylates is not necessarily apparent, and it is considered that vinyl acetate has a low polymerization reactivity in itself, so that it has a function to make a polymerization reaction of other monomers to proceed a residual amount of the unreacted other monomers. Even if vinyl acetate having a low polymerization reactivity remains as an unreacted monomer in the adhesive, the above vinyl acetate, which has as low boiling point as 73° C., is volatilized in heating and drying in forming an adhesive layer and therefore does not exert an adverse effect on the gas-generating amount.
In the present invention, the monomer mixture which comprises alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group and vinyl acetate in a proportion of 50:50 to 99.5:0.5 in terms of a weight ratio and in which a total content thereof is 75% by weight or more is polymerized to produce the acrylic copolymer. If a use amount of vinyl acetate is lower than the range described above, the effect of copolymerizing vinyl acetate is not exhibited, and the object of the present invention can not be achieved. On the other hand, if it exceeds the range described above, the performance thereof as an adhesive is unsatisfactory. Because of these reasons, a proportion of the above alkyl (meth)acrylate to vinyl acetate is preferably 70:30 to 99:1, particularly preferably 80:20 to 90:10 in terms of a weight ratio.
Further, if a total content of alkyl (meth)acrylate having 4 or less carbon atoms in an alkyl group and vinyl acetate in the monomer mixture is less than 75% by weight, the performance as an adhesive is unsatisfactory or the gas-generating amount grows larger depending on the kind of the other monomers, and the desired low polluting adhesive sheet is not obtained in a certain case.
In the present invention, other copolymerizable monomers can be used, if necessary, together with the alkyl (meth)acrylate and vinyl acetate each described above as long as the object of the present invention is not damaged. The copolymerizable monomers include, for example, monomers having cross-linking functional groups or olefins such as ethylene, propylene and isobutylene; halogenated olefins such as vinyl chloride and vinylidene chloride; styrene monomers such as styrene and c-methylstyrene; diene monomers such as butadiene, isoprene and chloroprene; nitrile monomers such as acrylonitrile and methacrylonitrile; and N,N-dialkyl-substituted acrylamides such as N,N-dimethylacrylamide and N,N-dimethylmethacrylamide. Among these copolymerizable monomers, monomers having cross-linking functional groups are preferred, and these monomers having cross-linking functional groups include, for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; acrylamides such as acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-methylolacrylamide and N-methylolmethacrylamide; and ethylenically unsaturated carboxylic acids such as acry
Ishiba Kiyoshi
Iwabuchi Hiroaki
Tsukida Tatsuya
Dawson Robert
Keehan Christopher
Lintec Corporation
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