Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-12-07
2002-10-08
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S041500, C428S317300, C428S317500, C428S317700, C428S3550RA, C427S208400, C427S244000
Reexamination Certificate
active
06461725
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a finely foamed pressure-sensitive adhesive tape or sheet having a pressure-sensitive adhesive layer having fine foams or cells formed therein.
BACKGROUND OF THE INVENTION
It has been attempted to improve an adhesive force, a tearing force and a shearing force and impart a shape follow-up property and a cushion property by forming gas bubbles or fine pores in a pressure-sensitive adhesive layer of a pressure-sensitive adhesive tape or sheet, and to reduce a material cost by lowering the density of the pressure-sensitive adhesive layer.
Conventional method of forming gas bubbles in the pressure-sensitive adhesive layer includes a method of coating or adding a chemical foaming agent or a physical foaming agent (organic solvent, water, etc.) on or to a backing or a pressure-sensitive adhesive layer and decomposing or evaporating the foaming agent by heating and a method of mechanically intermixing foams in a pressure-sensitive adhesive layer. For example, JP-A-10-140107 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a method of coating a volatile substance on a backing, coating a pressure-sensitive adhesive thereon, and gasifying the volatile substance by heating to form many closed cells in the pressure-sensitive adhesive layer. JP-A-9-221614 discloses a method of intermixing hollow fillers into a pressure-sensitive adhesive layer. Further, JP-A-8-67861 discloses a method of adding a thermal decomposition-type foaming agent into a hot-melt pressure-sensitive adhesive and foaming it by heating.
However, in those methods, contamination of impurities such as decomposition residues of chemical foaming agent, water, etc., into the pressure-sensitive adhesive layer is unavoidable, and such impurities are undesirable in using as the pressure-sensitive adhesive. Further, it is difficult to control the size and the content of foams and it is also difficult to obtain a uniform cell size. Furthermore, in those methods, it is very difficult to form foams having a foam size of 100 &mgr;m or smaller.
As a method of forming finer foams, JP-A-8-199125 discloses a method of placing a pressure-sensitive adhesive sheet in a high-pressure gas atmosphere to dissolve the atmospheric gas in the pressure-sensitive adhesive layer, and then releasing the pressure. However, since in this method, the atmospheric gas is introduced into the pressure-sensitive adhesive layer in a gaseous state, the amount of the gas impregnated is insufficient and it is therefore difficult to obtain a foamed pressure-sensitive adhesive layer having a cell structure having a fine cell size and a fine cell wall thickness. As a result, a foamed pressure-sensitive adhesive tape having an excellent resistance to repulsion is not obtained.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a finely formed pressure-sensitive adhesive tape or sheet provided with a pressure-sensitive adhesive layer having a cell structure with a fine cell size and a fine cell wall thickness, which have not yet been realized by the conventional chemical foaming agents or physical foaming agents, and a method for producing the same.
Another object of the present invention is to provide a finely foamed pressure-sensitive adhesive tape or sheet having a high pressure-sensitive adhesive property and an excellent resistance to repulsion, and a method for producing the same.
Still another object of the present invention is to provide a finely foamed pressure-sensitive adhesive tape or sheet that a pressure-sensitive adhesive constituting a pressure-sensitive adhesive layer is not contaminated and the material cost can be reduced, and a method for producing the same.
As a result of various investigations to attain the above-described objects, it has been found that if a pressure-sensitive adhesive layer is foamed with carbon dioxide in a liquid state or a supercritical state, a fine cell structure constituted of fine cell size and fine cell wall thickness can be formed. The present invention has been completed based on this finding,
According to one embodiment of the present invention, there is provided a method for producing a finely foamed pressure-sensitive adhesive tape or sheet, which comprises impregnating a pressure-sensitive adhesive tape or sheet provided with a pressure-sensitive adhesive layer with carbon dioxide in a liquid state or a supercritical state, and foaming the pressure-sensitive adhesive layer by reducing a pressure. The main constituent of the pressure-sensitive adhesive layer is, for example, an acrylic resin or a rubber-based resin.
According to another embodiment of the present invention, there is provided a finely foamed pressure-sensitive adhesive tape or sheet provided with a pressure-sensitive adhesive layer having a fine cell structure having an average cell sized of from 0.01 to 1,000 &mgr;m, an average cell wall thickness t of from 0.01 to 2,000 &mgr;m, and a ratio t/d of the average cell wall thickness t to the average cell size d in the range of from 0.5 to 3.5.
According to still another embodiment of the present invention, there is provided a finely foamed pressure-sensitive adhesive tape or sheet provided with a pressure-sensitive adhesive layer having a fine cell structure having an average cell size d of from 0.01 to 15 &mgr;m and an average cell wall thickness t of from 0.01 to 30 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
In the present invention, carbon dioxide in a liquid state or a supercritical state is used as the means of foaming the pressure-sensitive adhesive layer. Of inert gases, carbon dioxide can be converted into a liquid state and a supercritical state at comparatively low temperature and low pressure, and also gives small influence to pressure-sensitive adhesives, such that it does not modify or decompose the pressure-sensitive adhesives. For this reason, its production equipment is not so complicated and the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is not contaminated. Further, since carbon dioxide is inexpensive, the production cost can be reduced. The critical temperature T
c
of carbon dioxide is 31° C. and the critical pressure p
c
thereof is 75.3 kgf/cm
2
(7.38 MPa).
Rubber-based pressure-sensitive adhesives and acrylic resin-based pressure-sensitive adhesives are suitably used as the pressure-sensitive adhesive in the present invention.
The rubber-based pressure-sensitive adhesives are obtained by using an elastomer as the main component and adding thereto a tackifier resin, a softening agent, an antioxidant, a filler, etc. The elastomer is a polymer having a low glass transition point and having a wide rubbery flat region up to high temperature, and examples thereof include natural rubbers (NR); synthetic rubbers such as an isoprene rubber (IR), a styrene•butadiene rubber (SBR), a styrene•butadiene block copolymer (SBS), a styrene•isoprene block copolymer (SIS), a butyl rubber, polyisobutylene, polyvinyl isobutyl ether, a chloroprene rubber, a nitrile rubber or a graft rubber, and a thermoplastic elastomer. However, the elastomer used in the present invention is not limited to those.
Th tackifier resin, softening agent, antioxidant and filler are not particularly limited, and conventional materials can be used. For example, examples of the tackifier resin include a rosin-based resin, a terpene-based resin, a petroleum resin (e.g., an aliphatic petroleum resin, an aromatic petroleum resin or a hydrogenize petroleum resin), a coumarone•indene resin and a styrene-based resin. A particularly preferred rubber-based pressure-sensitive adhesive includes a pressure-sensitive adhesive comprising a styrene•isoprene block copolymer or a natural rubber-based elastomer as the main component.
The acrylic pressure-sensitive adhesive is a copolymer comprising an acrylic acid ester as the main monomer component and more specifically is a copolyme
Bamba Tomohide
Kanada Mitsuhiro
Minamizaki Yoshihiro
Taruno Tomohiro
Yamamoto Takayuki
Nitto Denko Corporation
Zirker Daniel
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