Coating processes – Coating remains adhesive or is intended to be made adhesive – Pressure sensitive adhesive
Reexamination Certificate
1999-12-07
2001-05-01
Pianalto, Bernard (Department: 1762)
Coating processes
Coating remains adhesive or is intended to be made adhesive
Pressure sensitive adhesive
C427S244000, C427S420000, C427S434200
Reexamination Certificate
active
06224938
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a foamed pressure-sensitive adhesive tape or sheet having a foamed pressure-sensitive adhesive layer containing fine foams and an apparatus for producing the same.
BACKGROUND OF THE INVENTION
It has been conducted that by making a pressure-sensitive adhesive layer of pressure-sensitive adhesive tapes or sheets be a fine foamed structure, an apparent modulus of elasticity is decreased to improve properties such as an initial pressure-sensitive adhesive property, adhesive property to a rough surface or repulsion resistance, and the amount of a pressure-sensitive adhesive used is decreased to reduce a material cost.
Conventional methods for producing the above-described foamed pressure-sensitive adhesive tape or sheet include a method of incorporating a thermal decomposition type chemical foaming agent into a pressure-sensitive adhesive layer followed by heating as disclosed in, for example, JP-A-62-263278) (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), and a method of intermixing fine hollow particles such as microcapsules in a pressure-sensitive adhesive layer as disclosed in, for example, JP-A-2-240182. However, those methods have involved various problems such that the foaming agent or fine hollow particles are difficult to uniformly disperse, fine cells are difficult to obtain, it is difficult to control the foamed cell structure, and a cost increases.
JP-A-8-199125 discloses a method foaming the pressure-sensitive adhesive layer by placing an existing pressure-sensitive adhesive sheet under a high pressure gas atmosphere to dissolve the atmospheric gas therein and then releasing the pressure. However, this method can form a fine cell structure, but the conventional production steps of a pressure-sensitive adhesive sheet, such as coating and drying the pressure-sensitive adhesive, remain unchanged, and in addition to this, a foaming step is necessary. As a result, the steps become complicated, and the cost is unavoidably increased as compared with the production cost of the conventional pressure-sensitive adhesive sheet. Also, since the foaming step is mainly carried out in a high-pressure room of a batch system, this method is very disadvantageous from the standpoint of a continuous productivity.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a method for producing a foamed pressure-sensitive adhesive tape or sheet having a fine cell structure with a good production efficiency without through complicated steps.
Another object of the present invention is to provide an apparatus for producing the foamed pressure-sensitive tape or sheet.
As a result of various investigations to attain the above-described objects, it has been found that if monomers of a polymer constituting a pressure-sensitive adhesive layer are polymerized under specific conditions and a layer of the resulting polymer is applied on a substrate under specific conditions, not only the problems in the conventional method using a chemical foaming agent, etc., can be overcome but also a foamed pressure-sensitive adhesive tape or sheet is obtained with a good productivity by simple steps as compared with the method of using a high pressure gas described in the above-described patent publication. 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 pressure-sensitive adhesive tape or sheet having a foamed pressure-sensitive adhesive layer, which comprises polymerizing a mixture containing monomers of a polymer constituting the foamed pressure-sensitive adhesive layer under pressure in an inert fluid of a supercritical state or a liquid state, and then ejecting the polymerized composition obtained on a substrate under a pressure lower than the above-described pressure to form a foamed pressure-sensitive adhesive layer applied on the substrate.
According to another embodiment of the present invention, there is provided an apparatus for producing a foamed pressure-sensitive adhesive tape or sheet, which comprises a pressure vessel for polymerizing monomers of a polymer constituting a foamed pressure-sensitive adhesive layer under pressure, an inert fluid supplying means for supplying an inert fluid in a supercritical state or a liquid state to the pressure vessel, and an ejection means for ejecting the polymerized composition obtained by polymerizing the monomers.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
According to the method of the present invention, a mixture of the monomers of the polymer constituting the foamed pressure-sensitive adhesive layer is polymerized under pressure in an inert fluid in a supercritical state or a liquid state.
The polymer used is not particularly limited so long as it can be used as a pressure-sensitive adhesive. Examples of the polymer include acrylic polymers and rubber-based polymers. Of those, acrylic polymers such as acrylic acid ester copolymers are preferable, and examples thereof include a copolymer of at least two kinds of acrylic acid ester monomers and a copolymer comprising at least an acrylic acid ester monomer and a function group-containing unsaturated monomer as the monomer components.
Examples of the acrylic acid ester monomer include acrylic acid C
1-10
alkyl esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate or isononyl acrylate. However, the acrylic acid ester monomers used in the present invention are not limited to those monomers.
Examples of the functional group-containing unsaturated monomer include carboxyl-containing monomers such as acrylic acid, methacrylic acid or itaconic acid, acid anhydride-containing monomers such as maleic anhydride, monomers having a nitrogen-containing group (an amide group, a cyano group, an amino group, etc.), such as acrylamide, acrylonitrile or dimethylaminoethyl methacrylate, hydroxyl-containing monomers such as hydroxyethyl acrylate or hydroxyethyl methacrylate, and epoxy group-containing monomers such as glycidyl acrylate. However, the monomers are not limited to those.
The acrylic acid copolymer may further contain vinyl esters such as vinyl acetate, aromatic vinyl compounds such as styrene or vinyltoluene, methacrylic acid esters such as methyl methacrylate or ethyl methacrylate, as other monomer component other than the above-described monomers.
The mixture containing the above monomers may contain additives usually added to pressure-sensitive adhesives, such as a tackifier resin, a softening agent, an antioxidant or a filler.
The polymerization method is not particularly limited so long as the polymerization can be carried out in an inert fluid. Example of the polymerization method includes a free radical polymerization method using the conventional radical initiator, for example, an azo-based radical initiator such as 2,2′-azobisisobutyronitrile, or a peroxide-based radical initiator such as benzoyl peroxide.
The inert fluid that can be used in the present invention can be any substances that are gas at ordinary temperature and atmospheric pressure, and also are inert under the polymerization conditions. Examples of the inert fluid include rare gases such as helium or argon, and inorganic gases such as nitrogen or carbon dioxide. Of those, carbon dioxide can most suitably be used in that carbon dioxide has a relatively high affinity for high molecular weight materials in a supercritical state or a liquid state, does not almost adversely affect the environment, and is advantageous in cost.
The pressure in polymerization is under pressure (particularly, under high pressure) and can appropriately be selected from the range of, for example, from about 1 MPa to 40 MPa according to the kind of the inert fluid used. For example, where carbon dioxide is used as the inert fluid, the pressure is preferably in the range of from about 5
Bamba Tomohide
Kanada Mitsuhiro
Minamizaki Yoshihiro
Taruno Tomohiro
Yamamoto Takayuki
Nitto Denko Corporation
Pianalto Bernard
Sughrue Mion Zinn Macpeak & Seas, PLLC
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