Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Polymerizing – cross-linking – or curing
Reexamination Certificate
2000-03-09
2001-09-04
Berman, Susan W. (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Polymerizing, cross-linking, or curing
C522S039000, C522S042000, C522S053000, C522S018000, C522S064000, C522S096000, C522S103000, C522S182000, C428S064200, C428S065200, C430S270110, C430S278100
Reexamination Certificate
active
06284185
ABSTRACT:
TECHNICAL FIELD
This invention relates to an ultraviolet-curable adhesive, more particularly to an adhesive capable of bonding substrates which show transmittances of 0.01 to 20% to all of energy beams having wavelengths of not less than 280 nm but not more than 380 nm, to one another.
BACKGROUND ART
When opaque substrates are bonded to one another, it is difficult to use usual photocuring adhesives because the substrates do not sufficiently transmit lights. In this case, therefore, heat-bonding is generally adopted. In the heat-bonding, a resin of epoxy type, melamine type, alkyd type, urethane type or acrylate type and a heat-curing agent are used in many cases and the use of a hot-melt type resin or the like is also known.
However, in the heat-bonding, there have been such problems that the substrates are warped or distorted owing to heat, and hence, the kind of substrate to which the heat-bonding can be applied has been limited. Moreover, the hot-melt type resin is inferior in thermal stability and weather resistance, and has been difficult to use under high temperature circumstances. In addition, the heat-bonding has required a curing time of several tens of minutes and hence has had a problem that it is inferior in productivity.
Therefore, there has been desired a development of an adhesive and a bonding method which are free from such problems as warpage and distortion of substrate, productivity and the like. In particular, in order to bond optical discs which will be required to have a higher recording density in future, there must be used an adhesive which causes neither warpage nor distortion of disc and is endowed with excellent characteristics.
DISCLOSURE OF THE INVENTION
The present inventors have made extensive research for solving the above problems; have consequently found that contrary to the prior common knowledge that opaque substrates cannot be bonded with a photocurable resin, opaque substrates which even slightly transmit light can be bonded with a photocurable resin; and have made this invention.
This invention is an ultraviolet-curable adhesive composition comprising at least one photopolymerization initiator whose molar absorption coefficient at a wavelength of 360 nm or more, particularly 360-400 nm is at least 200 and an ultraviolet-curable compound.
This invention is also an ultraviolet-curable adhesive composition consisting of at least one photopolymerization initiator whose molar absorption coefficient at a wavelength of 360-450 nm is at least 400 and an ultraviolet-curable compound.
This invention is further a method for bonding substrates which comprises coating the above-mentioned ultraviolet-curable adhesive composition on a substrate which shows transmittances of 0.01 to 20% to all of energy beams having wavelengths of 280-380 nm, thereafter firmly contacting the coating surface of this substrate with another substrate and then irradiating them with ultraviolet rays.
BEST MODE FOR CARRYING OUT THE INVENTION
The ultraviolet-curable adhesive composition of this invention comprises at least one photopolymerization initiator whose molar absorption coefficient at a wave-length of 360 nm or more, particularly 360-400 nm, is at least 200.
In another aspect, the ultraviolet-curable adhesive composition of this invention comprises at least one photopolymerization initiator whose molar absorption coefficient at a wavelength of 360-450 nm is at least 400.
Here, that the molar absorption coefficient in a range of the above-mentioned absorption wavelengths is at least 200 or at least 400 means that in this wavelength region, there is at least a wavelength portion at which molar absorption coefficient is at least 200 or at least 400, respectively, and it is not necessary that the molar absorption coefficient is at least 200 or at least 400 over the whole wavelength range. The content of the above photopolymerization initiator in this invention is usually 0.01-20% by weight, preferably 0.1-20% by weight, more preferably 0.5-20% by weight, and further preferably 0.5-10% by weight, approximately, in the ultravioletcurable adhesive composition. Theses photopolymerization initiators may be used alone or in admixture of two or more in any proportion. As far as the above-mentioned conditions are satisfied, other polymerization initiators may be co-used.
As the photopolymerization initiator whose molar absorption coefficient at a wavelength of 360 nm or more is at least 200, there can be mentioned, for example, camphorquinone, 2-methyl-1-(4-methylthiophenyl)-2-(4-morphonyl)-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, (1-6-&eegr;-cumene)(&eegr;-cyclopentadienyl)iron (1+) hexafluorophosphate (1-) and the like.
In particular, as the photopolymerization initiator whose molar absorption coefficient at a wavelength of 360-400 nm is at least 200, there can be mentioned, for example, 2-methyl-1-(4-methylthiophenyl)-2-(4-morphonyl)-1-propanone, 2-benzyl-2-dimethylarnino-1-(4i-morpholinophenyl)butanone-1, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, (1-6-&eegr;-cumene)(&eegr;-cyclopentadienyl)iron (1+) hexafluorophosphate (1−) and the like.
The photopolymerization initiator used in this invention may be one of those whose molar absorption coefficient at a wavelength of 360-450 nm is at least 400. Among them, preferable initiators are compounds whose molar absorption coefficient at a wavelength of 360-450 nm is at least 500, for example, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. More preferable initiators are compounds whose molar absorption coefficient at a wavelength of 360-450 nm is at least 1,000, for example, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1, 2-chlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, isopropylthioxanthone and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.
In this invention, such photopolymerization initiating assistants as amines and the like can be co-used. Such photopolymerization initiating assistants as amines and the like include, for example, 2-dimethylaminoethylbenzoate, dimethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate and the like. The amount of the photopolymerization initiating assistant used is usually preferably 0-15% by weight, more preferably 0-10% by weight, approximately, in the composition.
The ultraviolet-curable adhesive composition of this invention comprises, in addition to the above-mentioned photopolymerization initiator, an ultraviolet-curable compound. The ultraviolet-curable compound includes, for example, monomers having one or more (meth)acryloyl groups in the molecule. When a higher bonding strength and higher durability (deterioration resistance) is required, an oligomer can be co-used.
The monomers having one or more (meth)acryloyl groups in the molecule include monofunctional acrylic monomers having one (meth)acryloyl group in the molecule and polyfunctional acrylic monomers having two or more (meth)acryloyl groups in the molecule.
The monofunctional acrylic monomer includes, for example, acrylic monomers having a ring structure such as aliphatic ring, aromatic ring, heterocyclic ring or the like, aliphatic acrylates having a hydroxyl group and the like.
The acrylic monomer having a ring structure such as aliphatic ring, aromatic ring, heterocyclic ring or the like includes, for example, tricyclodecane (meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl (meth)acrylate, adamant
Ishii Kazuhiko
Tokuda Kiyohisa
Berman Susan W.
Nields & Lemack
Nippon Kayaku Kabushiki Kaisha
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