Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-02-20
2002-09-17
Dawson, Robert (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C428S429000, C525S101000
Reexamination Certificate
active
06451156
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sheet- or tape-shaped pressure-sensitive adhesive sheets, which are used to fix a functional film to a display device.
2. Description of the Related Art
Pressure-sensitive adhesive sheets have recently been utilized in various fields because of good bonding operation properties. Among these, pressure-sensitive adhesive sheets comprising, as a base component, a homopolymer or copolymer of a monomer containing, as a base, an acrylic polymer (i.e. an alkyl (meth)acrylate) are superior in durability performances such as weathering resistance, heat resistance, deterioration resistance and the like. Therefore, they are used particularly preferably in the fields where these durability performances are required.
As one of uses of pressure-sensitive adhesive sheets, for example, there has been known a use of bonding/fixing functional films such as conductive film, antiglare film and the like to a display device (glass surface thereof). In view of use such as display device to which severe requirements on the appearance is made, it is required for these pressure-sensitive adhesive sheets to cause neither lifting nor formation of bubbles at the bonding interface when exposed to severe conditions such as high temperature or high temperature and humidity (e.g. inside of automobiles or warehouses in the summer season) for a long time, not to mention at the beginning of standing after bonding/fixing, thus making it possible to maintain good appearance.
To resolve these requirements, it is suggested to use acrylic pressure-sensitive adhesive sheets comprising an acrylic polymer, as a base component, and a silane coupling agent incorporated into the acrylic polymer, thereby to improve the adhesion to the glass surface. Although use of the pressure-sensitive adhesive sheets improves the adhesion to glass to some extent, there still remains such a problem that lifting and formation of bubbles occur at the bonding interface when exposed to severe conditions such as high temperature or high temperature and humidity (e.g. inside of automobiles or warehouses in the summer season) for a long time, thus making it hard to maintain good appearance.
SUMMARY OF THE INVENTION
In light of the circumstances described above, an object of the present invention is to provide pressure-sensitive adhesive sheets for fixing a functional film to a display device, having excellent weathering resistance which cause neither lifting nor formation of bubbles at the bonding interface even when exposed to severe conditions such as high temperature or high temperature and humidity (e.g. inside of automobiles or warehouses in the summer season) for a long time, thus making it possible to maintain good appearance.
As a result of an intensively study about the object described above, the present inventors have found that pressure-sensitive adhesive sheets having excellent weathering resistance, wherein the pressure-sensitive adhesive has a crosslinked structure, are obtained by incorporating a silane coupling agent into an acrylic polymer and crosslinking the acrylic copolymer, and a sol component of the crosslinked pressure-sensitive adhesive having a specific molecular weight distribution with less low-molecular component, and that, when a functional film is bonded/fixed to a display device using the resulting pressure-sensitive adhesive sheets, neither lifting nor formation of bubbles occurs at the bonding interface even during the weathering evaluation test, thus making it possible to maintain good appearance for a long period, whereby the present invention has been completed.
That is, the present invention is directed to a pressure-sensitive adhesive sheet comprising a layer of a crosslinked pressure-sensitive adhesive, which is formed by an acrylic polymermade of a homopolymer or copolymer of a monomer containing a (meth) acrylate as a principal component, a silane coupling agent and a crosslinking agent, wherein a sol component of the crosslinked pressure-sensitive adhesive has a weight-average molecular weight of not less than 300,000 and a proportion of a low-molecular component having a molecular weight of not more than 100,000 in the sol component is not more than 15% by weight in the measurement of the molecular weight by the gel permeation chromatography method. Also the present invention is directed to a method of fixing a functional film, which comprises bonding/fixing the functional film to a display device through the pressure-sensitive adhesive sheets with the constitution described above.
As used herein, the sol component of the layer of the crosslinked pressure-sensitive adhesive refers to a sol component which is a soluble polymer dissolved in ethyl acetate when a predetermined amount Mo (about 0.5 g) of the above layer is covered with a fluororesin film having numerous pores (diameter: 0.2 &mgr;m), followed by dipping in ethyl acetate at 20° C. for 240 hours. The sol fraction thereof is determined by calculating from the formula: (Mt/Mo)×100 (% by weight) where Mt is an amount of the sol component and Mo is an initial weight before dipping.
Using the above soluble polymer (sol component), the weight-average molecular weight of the sol component and the proportion (% by weight) of the low-molecular component having a molecular weight of not more than 100,000 were determined from a molecular weight distribution curve by the gel permeation chromatography method (hereinafter referred to as the GPC method). The measuring conditions of the molecular weight distribution curve by the GPC method are as follows: concentration of sample; 1 mg/ml, amount of sample introduced; 500 mg, column temperature; 40° C., and flow rate; 1.0 ml/minute.
As used herein, the term “pressure-sensitive adhesive sheets” is a general term for pressure-sensitive adhesive tapes and various adhesive products (e.g. pressure-sensitive adhesive labels) having the shape which resembles closely to that of the pressure-sensitive adhesive tapes.
DETAILED DESCRIPTION OF THE INVENTION
The acrylic polymer used as the base polymer in the present invention is a homopolymer or copolymer of a monomer containing an alkyl (meth)acrylate as a principal component, and the other monomer, capable of copolymerizing with the alkyl (meth)acrylate, can be used in combination with the alkyl (meth)acrylate.
The alkyl (meth)acrylate is a monomer represented by the following general formula:
wherein R
1
is a hydrogen atom or a methyl group, and R
2
is an alkyl group having 1 to 18 carbon atoms. Specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate and the like.
The copolymerizable monomer, for example, there can be used any of various monomers, which are known as a monomer for modification of an acrylic pressure-sensitive adhesive, such as vinyl acetate, styrene, (meth)acrylonitrile, (meth)acrylamide, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycidyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate and the like. These copolymerizable monomers are usually used in the proportion of not more than 50% by weight based on the total amount of the alkyl (meth)acrylate and the copolymerizable monomer.
Such an acrylic polymer is preferably a polymer which exhibits a proper molecular weight distribution before crosslinking, particularly the low-molecular component exhibits a molecular weight smaller than as usual, so that the sol component has a weight-average molecular weight of not less than 300,000, preferably not less than 500,000 (usually up to 5,000,000), and the amount of a low-molecular component having a molecular weight of not more than 100,000 is not more than 15% by weight, preferably not more than 10% by weight by weight in the measurement of the molecular weight by the gel permeation chromatography method after forming a crosslinke
Kishioka Hiroaki
Ohura Masahiro
Yoshikawa Takao
Dawson Robert
Keehan Christopher
Nitto Denko Corporation
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