Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-01-19
2001-10-09
Ogden, Necholus (Department: 1751)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S411100, C522S104000, C522S106000, C526S082000, C524S833000
Reexamination Certificate
active
06299975
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sheet-form or tape-form pressure-sensitive adhesive sheet having a layer of a photopolymerized acrylic pressure-sensitive adhesive and to a production method thereof.
BACKGROUND OF THE INVENTION
Acrylic pressure-sensitive adhesive tapes are excellent in the adhesive force, the cohesive force, etc., and are used as fixing tapes, masking tapes, etc., for electronic parts. The pressure-sensitive adhesive tapes of this kind are usually produced by a method of solution-polymerizing a (meth)acrylic acid alkyl ester and, if necessary, other monomer such as acrylic acid in an organic solvent, compounding the polymer obtained with a tackifier resin and a crosslinking agent and the like, to prepare a pressure-sensitive adhesive, and after coating the pressure-sensitive adhesive on a base material or a releasing liner, removing the organic solvent by heating.
The acrylic pressure-sensitive adhesive sheets produced as described above are liable to cause discoloring such as yellowing under a high-temperature atmosphere or an exposure in the open air by, perhaps, the influence of the compounded component such as a crosslinking agent or in the pressure-sensitive adhesive sheets. Furthermore, there is a possibility that an organic solvent remained in the layer of the pressure-sensitive adhesive causes the occurrence of bubbles at the adhered interface. Furthermore, when the pressure-sensitive adhesive sheets are applied to electronic instruments such as a display, there is a possibility that the remained solvent causes the corrosion of electronic parts.
On the other hand, recently, a method of obtaining acrylic pressure-sensitive adhesive sheets by a photopolymerization has been investigated. In the method, after coating a composition composed of a (meth)acrylic acid alkyl ester as the main constituent added with a photopolymerization initiator on a base material or a releasing liner, by photopolymerizing the coated layer by the irradiation of a ultraviolet ray, etc., a layer of a pressure-sensitive adhesive is formed without using an organic solvent. The pressure-sensitive adhesive sheets produced by the method do not substantially cause problems of the occurrences of bubbles and corrosions caused by the remaining organic solvent and thus, have been expected as preferred pressure-sensitive adhesive sheets from the points of safety and an environmental hygiene.
However, in the photopolymerization type pressure-sensitive adhesive sheets, there are problems that the pressure-sensitive adhesive sheets are inferior in the adhesion to an adherend having a low polarity, such as a polycarbonate plate which is used as a protective plate for a display, etc., and bubbles generate at the adhered interface by the influence of moisture generated from the adherend, etc., to lower the appearance and the visuality. Also, when a large amount of a photopolymerization initiator is used for increasing the polymerization ratio, the initiator remains in the photopolymerization product to cause discoloring under a high-temperature atmosphere, while when the amount of the initiator is less, many unreacted monomers remain in the photopolymerization product, which cause bubbling at the adhered interface and gives a possibility of causing corrosions of electronic parts. Furthermore, depending on the surface state of a base material or a releasing liner on which the layer of the pressure-sensitive adhesive composed of the photopolymerized product is formed, the transparency is sometimes greatly reduced.
SUMMARY OF THE INVENTION
The present invention has been made under such circumstances and an object of the present invention is to provide a pressure-sensitive adhesive sheet, which is excellent in the foaming resistance and the low out-gas property, namely, being hard to cause a foaming phenomenon lowering the appearance and the visuality at the adhered interface and giving less volatile components such as unreacted monomers causing the corrosion of electronic parts, is hard to cause discoloring such as yellowing under a high-temperature atmosphere or the exposure in the open air, is excellent in the discoloring resistance (heat resistance and weather resistance), and further is excellent in the transparency, as a photopolymerization type pressure-sensitive adhesive sheet suitably used for sticking a plastic protective plate and a glass plate of a display.
As the result of various investigations for attaining the above-described object, the present inventors have discovered that in the composition containing an acrylic monomer and a photopolymerization initiator, the amount of the photopolymerization initiator is restrained to a small amount but not hindering the photopolymerization, specific amounts of a radical chain inhibitor, a crosslinking agent, and a silane coupling agent are added to the composition and the composition is coated on releasing-treated film having a good surface smoothness as a releasing liner followed by carrying out the photopolymerization, a layer of a pressure-sensitive adhesive excellent in the foaming resistance, the low gas-out property, the discoloring resistance (heat resistance and weather resistance), and the transparency can be formed.
That is, the first aspect of the present invention is a pressure-sensitive adhesive sheet of a sheet form, a tape form, etc., having the layer of a pressure-sensitive adhesive comprising the photopolymerized product of a composition containing the following five components a) to e);
a) 100 parts by weight of monomers composed of from 70 to 100% by weight of a (meth)acrylic acid alkyl ester having on an average from 2 to 14 carbon atoms of the alkyl group, and from 0 to 30% by weight of a monoethylenically unsaturated monomer copolymerizable therewith, each based on the total amount of the monomers,
b) from 0.1 to 5 parts by weight of a radical chain inhibitor,
c) from 0.02 to 5 parts by weight of a polyfunctional (meth)acrylate as a crosslinking agent,
d) from 0.005 to 2 part by weight of a photopolymerization initiator, and
e) from 0.01 to 10 parts by weight of a silane coupling agent,
wherein the pressure-sensitive adhesive layer has a haze value of not higher than 1% and a total light transmission of at least 90%.
The second aspect of the present invention is a production method of the pressure-sensitive adhesive sheet having the above-described construction, which comprises coating a composition containing the above-described five components (a) to (e) on a film which has been subjected to release treatment and has a good surface smoothness (hereinafter referred to as “releasing-treated film having a good surface smoothness”) and photopolymerizing the coated layer to form a pressure-sensitive adhesive layer having a haze value of not higher than 1% and a total light transmission of at least 90%.
Particularly, the third aspect of the present invention is the production method of a pressure-sensitive adhesive sheet of the above-described second aspect wherein in the above-described releasing-treated film having the good surface smoothness, the center-line mean roughness (Ra) is 0.2 &mgr;m or lower and the maximum height (Rmax) is 0.6 &mgr;m or shorter.
As described above, in the present invention, by restraining the amount of a photopolymerization initiator to a small amount and incorporating a radical chain inhibitor, an improved discoloring resistance (heat resistance and weather resistance), which is hard to cause discoloring such as yellowing even when the pressure-sensitive adhesive sheet is exposed under a high-temperature atmosphere and in the open air after photopolymerization, is obtained. Also, even though the amount of the photopolymerization initiator is small, the amount is not too small to give an hindrance to the photopolymerization, and also a crosslinking agent is contained, whereby a photopolymerized product containing less volatile components such as unreacted monomers and satisfying a cohesive force and an adhesive force can be formed, furthermore, by incorporating a silane c
Kishioka Hiroaki
Oura Masahiro
Takahira Hitoshi
Yoshikawa Takao
Nitto Denko Corporation
Ogden Necholus
Sughrue Mion Zinn Macpeak & Seas, PLLC
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