Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1998-09-25
2002-08-27
Berman, Susan W. (Department: 1711)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S064700, C156S275500, C156S275700, C522S096000, C522S097000, C522S171000, C522S172000, C522S173000
Reexamination Certificate
active
06440519
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of PCT/NL98/00089, filed Feb. 12, 1998, the entire contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a photocurable resin composition and, in particular, to a photocurable resin composition useful as an adhesive for the manufacture of optical disks.
BACKGROUND OF THE INVENTION
In recent years, development of high-density recording media has been pursued in response to the demand for high capacity recording media, accompanied by advances in the quality of information such as letters, voice, picture images, and the like. An optical disk which is called a digital versatile disk (DVD) is one type of optical disk. A DVD can record a greater amount of information than a CD (compact disk), even though these disks are almost the same in size. At present, DVDs are mainly manufactured by a so called bonding method, which comprises forming recording layers on at least one plastic disk by depositing metal using a sputtering technique. The disks are then laminated together with an adhesive to form a mult-layer DVD.
A hot-melt type or a heat hardening type adhesive have been conventionally used in this method. These adhesives, however, have exhibited problems in the length of time required for manufacturing optical disks. These adhesives not only require a long working time to obtain sufficient adhesion characteristics but also experience decreased adhesion under high temperature-high humidity conditions, because these adhesives are easily softened and melted under such conditions. As a result, DVD disks bonded by conventional adhesives have a tendency to become displaced when the optical disks are preserved under high temperature-high humidity conditions after manufacture, which is unacceptable.
To overcome these problems, ultraviolet radiation (UV) curable type adhesives comprising urethane acrylate as a major component have recently been proposed (for example, Japanese Patent Applications Laid-open No. 142545/1986, No. 89462/1994). However, these recently proposed adhesives much like the other conventional adhesives provide unsatisfactory photo-curability and adhesive properties.
In addition, the use of these UV adhesives have resulted in corrosion of the metal used in the recording layer because of moisture attack.
An object of the present invention is to provide a photocurable resin composition possessing superior curability, producing cured products which exhibit excellent adhesive properties under high temperature-high humidity conditions, and which are free from metal corrosion.
SUMMARY OF THE INVENTION
As a result of extensive studies to solve these problems in the conventional techniques, the present inventors have found that these problems can be solved by a specific photocurable resin composition which comprises:
(A) an oligomer comprising a polymeric backbone, linked via urethane bonds to (meth)acrylate terminal groups (hereinafter referred to as a urethane (meth)acrylate (A)),
(B) a phosphate containing at least one (meth)acryloyl group (hereinafter referred to as (meth)acryloyl phosphate (B)),
(C) a (meth)acrylate compound including multifunctional (meth)acrylate compounds, and optionally,
(D) a photopolymerization initiator, and/or
(E) organosilyl-containing mercapto compound.
It was found that such compositions provide improved adhesion properties especially to gold layers, a substrate either formed of gold or in part having gold covering at least a portion or portions of the surface (e.g., gold sputtered polycarbonate), even after being exposed to a high humidity, high temperature environment. These adhesive compositions are suitable for use in laminating the multi-layers of optical disks because, upon curing, they have excellent optical transparency, low shrinkage, high temperature resistance, high impact resistance, and exhibit good bonding characteristics to a variety of materials.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the present invention exhibits excellent adhesion to transparent resins including, for example, polycarbonates (PC), methyl polymethacrylates (PMMA), and norbornane-type resins; metals including, for example, gold and aluminum; and inorganic materials such as quartz and glass. Therefore, the composition of the present invention is suitable as an adhesive for use in multi-layered or laminated optical disks.
More specifically, the adhesive of the present invention is useful for laminating together two or more disks to form a multi-layered optical disks. Typically, at least one but commonly each of the disks will contain at least one information recording layer, or portion of a layer, composed of a reflective film, semi-transparent film, dielectric film, photo-electromagnetic recording film, or phase alternation film, made from an inorganic material such as a metal, metal oxide, silicon oxide, silicon nitride, or silicon carbide. Other disks that may be useful include those that may or may not be transparent which may further comprise an information recording film of an organic compound such as an organic coloring material or organic photo-chromic compound. For example, the multi-layered optical disk may be formed from a disk with an information recording layer provided on a transparent resin and another transparent disk by adhering the two disks with the information recording layer on the first disk facing inward. A further example may include a multi-layered optical disk comprising an optical disk made from a disk substrate with an information recording layer provided on a transparent resin disk and another disk with a film of an inorganic or organic material having no recording function provided on a transparent resin, wherein the two disks are laminated together with the recording layer of the first disk facing inward.
The photocurable resin composition of the present invention will now be described in more detail.
Urethane (Meth)acrylate (A)
The urethane (meth)acrylate of component (A) comprises a polymeric backbone, urethane bonds and (meth)acrylate terminal groups. This oligomer containing an urethane bond preferably is obtained by condensation of (a) at least one polymeric polyol compound selected from a group consisting of polyester polyols and polycarbonate polyols, (b) a polyisocyanate compound, and (c) a hydroxyl group-containing (meth)acrylate compound. The polyol compound constitutes the backbone, which is connected to the (meth)acrylate terminal groups through the urethane groups that are formed by reaction of the isocyanates with the hydroxyl groups.
The following compounds can be given as examples of the polyester polyols: polyester polyols obtained by the reaction of a polyhydric alcohol, such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane-dimethanol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, or trimethylolpropane, and a dibasic acid, such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, or sebasic acid; and polyester polyols obtained by reaction of &egr;-caprolactone, &bgr;-methyl-&dgr;-valerolactone or the like and the above-mentioned polyhydric alcohol. These polyester polyols may be used either individually or in combinations of two or more.
Given as commercially available products of these polyester polyols are Kurapol A-1010, 1510 and 2010, L-1010, 2010 and 3010, F-1010, 2010 and 3010, PNA-2000 and 2010, P-510, 1010, 1510, 2010, 3010 and 4010, PMIPA-2000, PKA-A, PKA-A2, MPD/IPA, MPD/TPA, CPM-1000 (manufactured by Kuraray Co., Ltd.); Nipporan 4002, 4009, 4010, 4032, 4040, 4042, 4060, 4070, 141, 143, 150, 5018, 5019, 5035 (manufactured by Nippon Polyurethane Industry CO., Ltd.); Adeka New Ace F15-20, F7-37, F18-62, F15-22, F7-68, F7-67, Y4-60, F13-35, F9-30, Y9-10, Y6-22, Y52-13, Y52-51, Y52-21, L4-71, V14-90, YG-108, YG-214, F1212-29, YG-226, Y96-20, YG-240,
Furuta Ryoji
Takahashi Toshihiko
Takase Hideaki
Takehana Yuichi
Ukachi Takashi
Berman Susan W.
DSM N.V.
Pillsbury & Winthrop LLP
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