Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-04-19
2001-11-06
Berman, Susan (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550AC, C428S423700, C428S483000, C428S500000, C428S040100, C428S041500, C522S182000, C522S173000, C522S175000, C522S121000, C526S328000, C526S328500, C526S329300
Reexamination Certificate
active
06312799
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a pressure-sensitive acrylic adhesive composition for adhesion of a polyester film and adhesive sheets in the form of sheets, tapes or the like containing the same.
BACKGROUND OF THE INVENTION
In recent years, various plastic materials have been used in, for example, electronic parts.
In these fields with the need for particularly high heat resistant reliability, heat resistant films such as polyimide films and polyether imide films are mainly employed and heat-curing adhesives are employed in adhesion of these films. In the fields where the necessity for high heat resistant reliability is not so strict, there have been employed polyester films and pressure-sensitive adhesives for adhesion of the same.
The pressure-sensitive adhesive provided with a release paper is bonded as such to electronic parts or the like and then subjected to a mounting step such as solder reflow, and after the release paper is peeled, the pressure-sensitive adhesive is adhered to a polyester film. In such a case, it is required that these pressure-sensitive adhesives have a high heat resistance almost comparable to the level of heat-curing adhesives, as well as strong adhesion to a polyester film.
There are various pressure-sensitive adhesives showing tackiness at ordinary temperature. Also, various pressure-sensitive acrylic adhesives are known as being usable in adhesion of electronic parts. Pressure-sensitive acrylic adhesives usually contain, as the main component, a tacky copolymer of a monomer mixture which is composed of an alkyl (meth)acrylate carrying an alkyl group having 2 to 14 carbon atoms on average as the main component together with a monoethylenic unsaturated monomer such as acrylic acid.
Although these pressure-sensitive acrylic adhesives show heat resistance of a certain extent, they are poor in the adhesive strength to polyester films and thus sometimes cause troubles such as peeling. When tackifier resins commonly employed in the art are added thereto to improve the adhesive strength to polyester films, these adhesives are softened and fluidized in the step of solder reflow, which makes them unusable.
SUMMARY OF THE INVENTION
Under these circumstances, the invention aims at providing a highly heat-resistant pressure-sensitive acrylic adhesive composition and adhesive sheets with the use of the same which are excellent in the adhesion to polyester films as adhesive materials having tackiness at ordinary temperature and being usable in adhesion of polyester films in the fields of, for example, electronic parts and have such high heat resistance as withstanding solder reflow during mounting.
In the course of intensive studies to achieve the object as described above, the inventors have found that the use of an alkyl (meth)acrylate carrying an alkyl group having 2 to 14 carbon atoms on average as the main component results in an acrylic copolymer exhibiting poor adhesion to a polyester film, even if it is copolymerized with any monoethylenic unsaturated monomer as a component for improving the cohesive force, and that even if any tackifier resin for improving its adhesion is added, it is hardly possible to prevent the thus obtained acrylic copolymer from softening/fluidization due to the heat in the step of solder reflow.
Based on these findings, the inventors have conducted further studies and, as a result, found that it is possible to obtain a pressure-sensitive acrylic adhesive composition and adhesive sheets thereof, which are excellent in flexibility, softness and cohesiveness and show, as adhesive materials, excellent adhesion to polyester films without undergoing softening or fluidization due to the heat in the step of solder reflow, can be obtained by using as the main component an acrylic monomer with a specific molecular structure, which exhibits as the homopolymer per se a large cohesive force and a high heat resistance and, at the same time, shows excellent adhesion to polyester films, as a substitute for an alkyl (meth)acrylate carrying an alkyl group having 2 to 14 carbon atoms on average, and further copolymerizing the acrylic monomer with appropriate amounts of the alkyl (meth)acrylate as described above for exhibiting adhesion and another monomer component for further improving the heat resistance and adhesion, thereby completing the invention.
Accordingly, the invention relates to a pressure-sensitive acrylic adhesive composition for adhesion of polyester films which comprises a tacky copolymer of a monomer mixture comprising:
a) from 40 to 80% by weight of a (meth)acrylate represented by the following formula (I):
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;
b) from 19 to 40% by weight of an alkyl (meth)acrylate carrying an alkyl group having 2 to 14 carbon atoms on average which is copolymerizable with the monomer component a); and
c) from 1 to 20% by weight of another monoethylenic unsaturated monomer which is copolymerizable with the monomer components a) and b), each based on the monomer mixture.
More particularly, the invention relates to the pressure-sensitive acrylic adhesive composition for adhesion of polyester films of the constitution as described above, wherein the tacky copolymer is one obtained by the irradiation with radiation such as ultraviolet rays. Furthermore, the invention also relates to adhesive sheets for adhesion of polyester films which have at least one layer made of the pressure-sensitive acrylic adhesive composition described above on one or both sides of a base material.
DETAILED DESCRIPTION OF THE INVENTION
The monomer component a) to be used in the invention is a (meth)acrylate represented by formula (I). In formula (I), 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. Since the homopolymer thereof shows a high glass transition temperature (Tg), the component a) contributes to the improvement in the heat resistance of the copolymer and exerts favorable effects on the adhesion thereof to polyester films. More particularly speaking, examples thereof include phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, nonylphenoxyethyl (meth)acrylate and nonylphenoxypropyl (meth)acrylate. It is also preferable to use therefor (meth)acrylates of ethylene oxide adducts or propylene oxide adducts (addition mole number: up to 3) of phenol, cresol or nonylphenol. Either one of these monomers or a mixture of two or more thereof may be used.
The monomer component b) to be used in the invention is an alkyl (meth)acrylate carrying an alkyl group having 2 to 14 carbon atoms on average which is copolymerizable with the monomer component a). This component is employed in order to impart tackiness to the copolymer. Particular examples thereof include ethyl (meth)acrylate, butyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate and dodecyl (meth)acrylate. Either one of these monomers or a mixture of two or more thereof may be used.
The monomer component c) to be used in the invention is a monoethylenic unsaturated monomer which is copolymerizable with the monomer components a) and b). This component is employed in order to further improve the heat resistance or the adhesion of the copolymer by introducing functional groups or polar groups thereinto. Particular examples thereof include (meth)acrylic acid, hydroxyalkyl (meth)acrylates, cyanoalkyl (meth)acrylates, (meth)acrylamide, substituted (meth)acrylamide, N-vinylcaprolactam, (meth)acrylonitrile, 2-methoxyethyl (meth)acrylate, glycidyl (meth)acrylate and vinyl acetate. Either one of these monomers or a mixture of tw
Hosokawa Kazuhito
Ohura Masahiro
Berman Susan
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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