Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-12-22
2002-10-15
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S025000, C522S066000, C522S100000, C522S110000, C522S111000, C522S113000, C522S120000, C522S121000, C522S122000, C522S150000, C522S153000, C522S154000, C522S170000, C522S181000, C522S182000
Reexamination Certificate
active
06465537
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photocurable composition, a photocurable pressure-sensitive adhesive utilizing the photocurable composition, and methods for producing the photocurable composition and photocurable pressure-sensitive adhesive. More particularly, the present invention relates to a photocurable composition which can be converted to a tackifying polymer via radical polymerization and finally caused to cure via cationic polymerization, a photocurable pressure-sensitive adhesive and methods for production thereof.
BACKGROUND ART
So-called pressure-sensitive adhesives have been proposed which facilitate bonding operations, eliminate safety concerns by excluding volatiles, and provide adhesive strength and film strength comparable in levels to general adhesives.
For example, Japanese Patent Laying-Open No. Hei 2-272076 discloses a pressure-sensitive adhesive tape using a pressure-sensitive thermally-curable adhesive prepared from a photopolymerizable composition containing an acrylate monomer and an epoxy resin. In the preparation of pressure-sensitive adhesive tape, only the acrylate monomer in the photopolymerizable composition is caused to polymerize. The pressure-sensitive tape such prepared is interposed between the adherends to combine them and then exposed to heat so that the epoxy resin is caused to cure to build sufficient adhesive strength.
However, the method disclosed in Japanese Patent Laying-Open No. Hei 2-272076 relies upon thermal cure of the epoxy resin to build the adhesive strength. This prevents application of the disclosed tape to adherends made from materials insufficient in heat-resistance, such as plastics, thereby limiting the type of the adherend to be bonded.
In Japanese Patent Kohyo No. 5-506465, a pressure-sensitive adhesive is disclosed containing a free-radically photopolymerizable component such as an acrylate monomer, a cationic photopolymerizable component such as an epoxy compound, and an organometallic complex salt initiator. This pressure-sensitive adhesive is proposed as providing enhanced tackiness. In the production of such a pressure-sensitive adhesive, the adhesive composition is irradiated so that its free-radically photopolymerizable component and cationic photopolymerizable component are both caused to undergo polymerization. That is, the concurrent initiation of free-radical polymerization and cationic polymerization results in constitution of the pressure-sensitive adhesive.
Accordingly, such polymerization reactions complete before the pressure-sensitive adhesive is formed, for example, into a sheet. The adhesive sheet is thus designed to show satisfactory strength when formed. While the resulting adhesive sheet exhibits sufficient tackiness to combine adherends, further enhancement in adhesive strength thereof is hardly expected even if an external stimulus, such as heat or radiation, is applied thereto.
Epoxy adhesives have been widely used to join various types of members for their capabilities to exhibit excellent creep resistance, light stability, water resistance, heat resistance, chemical resistance and the like after they have been cured, and to bond a wide variety of materials, such as metals, plastics and glasses (“Newly-revised Epoxy Resin”, Hiroshi Kakiuchi, Shoko-do, published in 1985).
However, epoxy resin adhesives are generally used in a liquid form. The liquid form increases a tendency of the epoxy resin adhesives to be applied unevenly. The epoxy resin adhesive, when applied excessively, sometimes bleed out from joint surfaces to provide a poor appearance. Because of its liquid form, the epoxy resin adhesives can not be reapplied onto a surface once coated therewith. Also, the epoxy resin adhesives are generally supplied in two parts. This limits a mixing ratio of a curing agent to a base resin, and accordingly increases a tendency to produce adhesive defects as a result of incorrect mixing.
As a solution to the aforementioned problems, sheet- or film-form epoxy resin adhesives have been proposed (Japanese Patent Laying-Open No. Sho 60-173076). Such sheet-form epoxy resin adhesives however lack provisional holding properties because of their inherent high elastic modulus and low initial adhesive strength in an ordinary state. This has led to a problem of insufficient workability during a joint operation. Also, the sheet-form epoxy resin adhesives exhibit insufficient adhesion to adherends. In order to firmly join those adherends, they must be placed under severe curing conditions, such as hot pressing or pressing at elevated pressures. This prevents its application to adherends which can not endure such severe curing conditions.
The inventors of the present application have previously proposed a photopolymerizable composition which can be polymerized by two different modes (Japanese Patent Laying-Open No. Hei 9-279013). This composition contains a free-radically polymerizable monomer such as an acrylic monomer, a free-radical polymerization catalyst, an epoxy-containing compound, and a cationic polymerization catalyst capable of initiating cure of the epoxy-containing compound. Here, the photopolymerizable composition is pre-irradiated to activate the free-radical polymerization catalyst which initiates polymerization of the free-radically polymerizable monomer. After production of a tackifying polymer, the composition is formed into a sheet. When in use, this sheet is irradiated so that the cationic polymerization catalyst is activated to initiate curing of the epoxy resin, thereby obtaining satisfactory adhesive strength.
However, there remains a problem that the sheet must be left to react for a long period of time after it has been irradiated in order to perfect the cure of the epoxy resin.
Also, the inventors of the present application have previously proposed a curable pressure-sensitive adhesive which can achieve joining of adherends under the curing conditions that impose little restriction on the types of the adherends used (Japanese Patent Laying-Open No. Hei 10-120988). The reference discloses a curable pressure-sensitive adhesive sheet which contains an acrylic polymer, an epoxy resin and a cationic photopolymerization initiator. When this curable pressure-sensitive adhesive sheet is irradiated, the cationic photopolymerization initiator is activated to initiate curing of the epoxy resin. Therefore, the mere irradiation of curable pressure-sensitive adhesive sheet, either before or after it is applied to an adherend, results in providing firm adhesion between the adherends.
The heat-resistance of adherends can be left out of consideration.
However, the above-described curing reaction is caused to proceed as soon as the curable pressure-sensitive adhesive sheet is irradiated. Within a short period of time, the curable pressure-sensitive adhesive sheet shows a marked increase in elastic modulus. If this results, the curable pressure-sensitive adhesive sheet loses a sufficient tackiness to adhere to adherends. That is, there remains a problem that a period of time the adhesive sheet remains uncured after it has been irradiated, i.e., an open time, is short.
The inventors of the present application have found that the addition of. vinyl ether compounds successfully extends the open time of the aforementioned curable pressure-sensitive adhesive sheet (EPO 819746 A2). However, the increase in adhesion strength of the adhesive sheet when cured was in some cases insufficient.
In Japanese Patent Laying-Open No. Sho 63-248825, a slow-curing type UV-curable epoxy resin composition is disclosed which incorporates a fixing agent containing a poly(alkylene oxide) residue portion. Here, the fixing agent containing a poly(alkylene oxide) residue portion is added to reduce the occurrence of a so-called skinning phenomenon whereby photocurable epoxy resin compositions lose their surface wettability or tackiness soon after they are exposed to an ultraviolet light.
However, the addition of fixing agent containing a poly(alkylene oxide) residue portion is directed:to develop an adhesive proper
McClendon Sanza L.
Seidleck James J.
Sekisui Chemical Co. Ltd.
Townsend & Banta
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