Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-02-29
2001-12-04
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...
C522S012000, C522S026000, C522S028000, C522S039000, C522S042000, C522S044000, C522S050000, C522S096000, C522S090000, C522S182000, C522S135000, C522S137000, C522S142000, C526S301000
Reexamination Certificate
active
06326414
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ultraviolet (UV)-curable adhesive for bonding optical disks, and more particularly to an ultraviolet-curable adhesive for bonding optical disks, which exhibits a sufficient curability of the surface (light irradiation side) and the inner portion (portion in the vicinity of the interface with an optical disk located on the opposite side to the light irradiation side) even by a slight amount of UV rays, the adhesive layer formed from which shows a uniform cured state and does not exert a bad influence upon a recording film even under high temperature and high humidity conditions, and which does not cause deposition of components even if stored for a long term.
As an ultraviolet-curable adhesive for bonding optical disks are popular those wherein a polymerization initiator is incorporated in a radical-polymerizable vinyl compound. These adhesives are required to be curable in a short period of time by irradiation of light that has passed through a disk having an information recording film and accordingly is low in energy.
As a technique satisfying such a requirement, WO 97/40115 discloses an adhesive that uses an &agr;-hydroxyalkylphenone compound and an acylphosphine oxide compound as a photopolymerization initiator. Optical disks having a low light transmittance can be easily bonded in a short time by this adhesive without impairing the appearance of the disks. However, the adhesive has the problems that deposition is easy to occur since the melting point of the photopolymerization initiator is high, phosphate ion is generated at the time of reaction and remarkably corrodes the recording film, and the stability under fluorescent lamp is poor and the viscosity is easy to increase. Thus, the proposed adhesive is not suitable for use in bonding optical disks.
Japanese Patent Publication Kokai No. 9-169957 discloses an adhesive that uses an acylphosphine oxide compound and/or an &agr;-aminoacetophenone compound as a photopolymerization initiator. However, use of the acylphosphine oxide compound causes the same problems as above. When the &agr;-aminoacetophenone compound is used alone without using the acylphosphine oxide compound, balance in curability between the surface and the depths and the stability under fluorescent lamp are inferior and, since the adhesive is easy to cause yellowing, the appearance of disks is easy to be impaired.
It is an object of the present invention to solve the above-mentioned problems and to provide an ultraviolet-curable adhesive for bonding optical disks which can prepare optical disk products which are small in warping of disks, retain sufficient performances even under high temperature and high humidity and have a good appearance.
In accordance with the present invention, there is provided an ultraviolet-curable adhesive for bonding optical disks, which comprises, as essential components,
(A) a radical-polymerizable vinyl compound,
(B) an &agr;-hydroxyalkylphenone compound, as a photopolymerization initiator, represented by the formula (1):
wherein R
1
is a hydrogen atom or an aliphatic group having 1 to 10 carbon atoms, R
2
and R
3
are the same or different and each is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R
2
and R
3
may be joined to form a single ring having 4 to 8 carbon atoms, and
(C) 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one.
Preferably, the total amount of the components (B) and (C) is from 0.1 to 10 parts by weight per 100 parts by weight of the component (A).
It is preferable that the component (A) contains a urethane (meth)acrylate oligomer and a difunctional component. An oligomer derived from a caprolactone-based polyol, an alicyclic diisocyanate and (meth)acrylic acid is preferred as the urethane (meth)acrylate oligomer, and a bisphenol type di(meth)acrylate and/or tetraethylene glycol diacrylate are preferred as the difunctional component.
DETAILED DESCRIPTION
The ultraviolet-curable adhesive for bonding optical disks according to the present invention contains, as essential components, (A) a radical-polymerizable vinyl compound, (B) a photopolymerization initiator which is an &agr;-hydroxyalkylphenone compound (hereinafter also referred to as “initiator (B)”), and (C) 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one (hereinafter also referred to as “initiator (C)”). By the combination use of the initiator (B) and the initiator (C), there can be obtained optical disks which are excellent in balance between curability of the surface and inner portions, uniformity in cured state of an adhesive layer, moisture resistance and heat resistance under high humidity and high temperature conditions, storage stability for a long term and appearance.
As the radical-polymerizable vinyl compound (A), compounds having at least one radical-polymerizable double bond in the molecule can be used alone or in combination of two or more (compound having one radical-polymerizable double bond in the molecule, compound having two radical-polymerizable double bonds in the molecule, compound having three radical-polymerizable double bonds in the molecule, and compound having at least two radical-polymerizable double bonds in the molecule being hereinafter also referred to as “monofunctional component”, “difunctional component”, “trifunctional component” and “polyfunctional component”).
It is preferable that the component (A) contains a urethane (meth)acrylate oligomer from the viewpoint of imparting a softness to an adhesive layer, and contains a polyfunctional component from the viewpoint of imparting excellent moisture and heat resistances thereto. As the polyfunctional component are more preferred difunctional components, since components having tri or higher functionality tend to render the adhesive layer hard and fragile to lower the strength of disks.
The molecular weight of the urethane (meth)acrylate oligomer is preferably from 700 to 5,500, more preferably from 1,000 to 5,000, from the viewpoints of mechanical properties, polymerizability, viscosity and the like. If the molecular weight is too small, the moisture resistance of the adhesive tends to lower or the mechanical properties of the adhesive layer tend to lower. If the molecular weight is too large, there is a tendency that the viscosity of the adhesive raises, crystallization occurs or the polymerizability lowers.
From the viewpoint of being excellent in moisture resistance, weatherability and heat resistance, it is preferable that the urethane (meth)acrylate oligomer is those derived from a caprolactone-based polyol, an alicyclic diisocyanate and (meth)acrylic acid.
As the caprolactone-based polyol are preferred those having a molecular weight of 74 to 4,000 and a functionality of 1 to 4. Examples of such a caprolactone-based polyol are, for instance, reaction products of a caprolactone with an alcohol having an aliphatic, aromatic or heterocyclic group such as butanol, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane, diethylene glycol, 1,4-dimethylolcyclohexane, bisphenol A polyethoxydiol having a molecular weight of 300 to 1,500 or polytetramethylene glycol having a molecular weight of 500 to 1,500. These may be used alone or in admixture thereof. Of these, caprolactone-based diols or triols having a molecular weight of 250 to 3,000 are preferred from the viewpoints of good balance of moisture resistance, heat resistance and softness and easiness in synthesis. Examples of the caprolactone-based diols are, for instance, caprolactone-based diols of the formula (2):
wherein p and q are independently from 1 to 5, and R
4
is a bivalent group that hydroxyl groups are removed from dihydric alcohols among the above-mentioned alcohols. Examples of the caprolactone-based triol are, for instance, caprolactone-based triols of the formula (3):
wherein x, y and z are independently from 1 to 5, and R
5
is a trivalent group that hydroxyl groups are removed from trihydric alcohols among the above-mentioned alcohols. A
Armstrong, Westerman, Hattori, McLeland, LLP
McClendon Sanza L.
Nagase Chemtex Corporation
Seidleck James J.
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