Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-09-13
2003-11-04
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550RA, C428S3550EP, C522S134000, C522S141000, C522S142000, C522S143000, C522S146000, C522S168000, C522S170000, C522S179000
Reexamination Certificate
active
06641912
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photocurable pressure-sensitive adhesive composition which has pressure-sensitive adhesive properties in its ordinary state and can be cured by irradiation, and also to a sheet utilizing the same.
BACKGROUND ART
Generally, adhesives are provided in a liquid form, applied to adherends which are subsequently joined together, and allowed to solidify via vaporization of a solvent or via a reaction toward higher molecular weights so that the adherends are adhered firmly to each other. Such adhesives provide high bond strength. However, restrictions exist in handling them; an operation of applying them to adherends is troublesome, the vaporization of a solvent or the reaction is relatively time-consuming, and adherends must be somehow held in position until the adhesives solidify.
On the other hand, pressure-sensitive adhesives are basically semi-solid viscoelastic substances which appear adsorptive due to the so-called “tack” and often provided in the form of being applied on a filmed base material. Pressure-sensitive adhesives are easy to handle for their ability to be adhered to adherends by application of a light pressure. However, pressure-sensitive adhesives provide lower bond strength than adhesives.
As a so-called curable pressure-sensitive adhesive which shows both features of a pressure-sensitive adhesive and an adhesive, can be handled like a pressure-sensitive adhesive when adherends are combined, and initiates curing upon application of heat or radiation to develop high bond strength, Japanese Patent Kohyo No. Hei 10-508636 proposes a photocurable pressure-sensitive adhesive composition which comprises a combination of a free-radically polymerizable polymer, a cationically photopolymerizable compound and a cationic photoinitiator.
However, when an acrylic resin, representative of free-radically polymerizable polymers, is used, the resulting composition when cured shows insufficient bond strength to adherends composed of polyethylene terephthalate (PET), polyvinyl chloride (PVC), a metal or the like. This lowers reliability of such a composition when used to combine these adherends.
A polyester resin may be considered to be an effective alternative to improve adhesion to PTE, PVC, a metal or the like. However, there is a possibility that polyester resins when placed under high temperature and high moisture conditions may reduce bond strength via hydrolysis of esters. This provides concerns about adhesive reliability.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a photocurable pressure-sensitive adhesive composition which shows pressure-sensitive adhesive properties in its ordinary state, initiates curing upon exposure to an active energy radiation, shows good adhesion to high-polarity adherends such as PET, PVC and metals, and exhibits superior heat-resisting and moisture-resisting bond strength, and also to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet both derived from the composition.
In accordance with a broad aspect of a first invention of this application, a photocurable pressure-sensitive adhesive composition is provided which contains a polyester resin having a glass transition temperature of 25° C. or above, a cationically photopolymerizable compound and a cationic photoinitiator.
In a particular aspect of the first invention, a polyester resin having a glass transition temperature of below 25° C. is further contained. In a more limited aspect, the polyester resin having a glass transition temperature of 25° C. or above accounts for 50 or higher % of the total weight of the polyester resin.
In another particular aspect of the first invention, the cationically photopolymerizable compound is incorporated in the amount of 10-100 parts by weight, based on 100 parts by weight of the polyester resin.
According to a broad aspect of a second invention, a photocurable pressure-sensitive adhesive composition is provided which contains a polyester resin having a glass transition temperature of 25° C. or above, a cationically photopolymerizable compound, a cationic photoinitiator and a rosin comprised chiefly of abietic acid.
In a particular aspect of the second invention, the rosin is either hydrogenated or disproportionated.
In a more limited aspect of the second invention, the rosin is incorporated in the form of a rosin ester obtained by reacting carboxyl groups present in the rosin with an epoxy-containing compound.
In accordance with a broad aspect of a third invention, a photocurable pressure-sensitive adhesive composition is provided which contains a polyester resin, a cationically photopolymerizable compound and a cationic photoinitiator, with a polycarboxylic acid constituting the polyester resin being an aromatic ring-containing polycarboxylic acid.
According to a broad aspect of a fourth invention, a photocurable pressure-sensitive adhesive composition is provided which contains a polyester resin, a cationically photopolymerizable compound and a cationic photoinitiator as essential components, with the polyester resin being a resin containing an ether bond in a molecule.
In a particular aspect of the fourth invention, the ether bond is an ether bond derived from polytetramethylene ether glycol.
In accordance with a fifth invention, a photocurable pressure-sensitive adhesive sheet is provided comprising any of the pressure-sensitive adhesive compositions according to the first through third inventions.
The present invention is below described in detail.
The photocurable pressure-sensitive adhesive composition in accordance with the first invention contains a polyester resin with a glass transition temperature of 25° C. or above, a cationically photopolymerizable compound and a cationic photoinitiator as essential components. The photocurable pressure-sensitive adhesive composition of the first invention permits easy application since it contains a polyester resin, a cationically photopolymerizable compound and a cationic photoinitiator as essential components and shows pressure-sensitive properties at ordinary temperature. Also, when irradiated, the cationically photopolymerizable compound initiates curing so that a crosslinked structure is formed. The incorporation of molecular chains of the polyester resin in the structure is effective to develop high bond strength.
Also, the photocurable pressure-sensitive adhesive composition of the first invention, because of incorporation of the polyester resin, shows good adhesion to substrates such as PET, PVC and metals and, because of improved hydrolysis resistance due to its high glass transition temperature, shows superior moist heat-resisting adhesive properties.
Further, since the cure reaction occurs in the form of cationic photopolymerization initiated by irradiation, it is allowed to proceed even after the irradiation is stopped and thus provides a firm adhesion between the adherends.
The polyester resin with a glass transition temperature of 25° C. or above is not particularly specified. Examples of such polyester resins include those available in the trade under the designations VYLON 103, 200, 240, 280, 290, 296 and 600 (manufactured by Toyobo Co., Ltd.) and ELEETHER UE-3200, 3201, 3203, 3210, 3215, 3216, 3240, 3250, 3500, 3600, 3620, 3660 and 3690 (manufactured by Unitika Ltd.). The glass transition temperature of the polyester resin needs to be 25° C. or above. If below 25° C., there is an increasing tendency that hydrolysis is caused to go proceed under high temperature and high moisture conditions. If the glass transition temperature is too high, the adhesive composition when formed into a sheet or tape may show the increased hardness to result in the reduced bond strength. The preferred glass transition temperature is 30-100° C. The above-listed polyester resins may be used alone or in any combination thereof.
Preferably, a polyester resin having a glass transition temperature of below 25° C. is further incorporated in the polyester resin in the first invention to modify or adjust propert
Hatai Munehiro
Ishizawa Hideaki
Nakata Masakazu
Yagi Motohiro
Berman Susan W.
Sekisui Chemical Co. Ltd.
Townsend & Banta
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