JP2002109785A - Optical disk and ultraviolet-setting composition used for the optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet-setting type composition that can satisfy both durability and a high transmission rate of its hardened film at a wavelength of about 400 nm, which are suitable for the light-transmitting film of an optical disk, to which recording or reproducing is made with a blue laser, and the optical disk in which the composition is used. SOLUTION: The hardened film of the ultraviolet-setting type composition containing a (meth) acrylic compound and a photoradical polymerization initiator, whose laser beam-transmission rate is 75% or more, is used as a light- transmitting layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light-transmitting layer formed of an ultraviolet-curable composition on an upper layer of a substrate having an information recording layer.
The present invention relates to an optical disc on which recording or reproduction is performed by a semiconductor laser having an oscillation wavelength within the range described above (hereinafter referred to as a blue laser), and an ultraviolet-curable composition used for producing the optical disc.

[0002]

2. Description of the Related Art In recent years, the development of information technology has made it possible to transmit large-capacity information records. Accordingly, a high-density, large-capacity optical disk capable of recording and reproducing large-capacity video, music, computer data, and the like has been demanded.

[0003] D which is growing as a high-density recording medium
The VD (Digital Versatile Disc) has a structure in which two substrates having a thickness of 0.6 mm are bonded with an adhesive.
In order to achieve high-density recording in DVD, CD (Comp
The optical system uses a 650 nm laser with a shorter wavelength than that of act discs, and the optical system has a higher numerical aperture.

However, HDTV (High Definition Tele)
vision) In order to record or reproduce an image of image quality, further densification is required. Further high-density recording methods and optical disks for the next generation of DVD are being studied, and high-density recording using a new disk structure using a blue laser with a shorter wavelength and an optical system with a higher numerical aperture than DVD is being studied. A scheme has been proposed. These new disk structures are described in, for example, Nikkei Electronics (199).
No. 9.8.9, pp. 47-53).

[0005] Regarding the discs of any structures, since the blue laser passes through the light transmitting layer, the wavelength of the laser light is 4.
High transmittance near 00 nm is required.

As an optical disk corresponding to an optical system of a blue laser, an optical disk in which an information recording layer and a light reflecting film are formed on a circular substrate, and a photo-curable resin is applied and cured, and a light-transmitting layer is laminated, It is proposed in Japanese Patent Application Laid-Open No. H11-191240, in which a cation-polymerizable ultraviolet-curable resin is used as a light transmitting layer forming material. However, the photopolymerization initiator used in the cationically polymerizable UV-curable resin generates a Lewis acid having a property of easily corroding a light reflection film or a recording film by irradiation with ultraviolet light, so that long-term storage stability is obtained. There are drawbacks that are hard to find. As a countermeasure, a first layer of a radical polymerizable UV-curable composition having a thickness of about 10 μm is usually provided to prevent corrosion of the light reflecting film and the recording film, and a cationic polymerizable UV-curable resin is formed thereon. It is common to form a light transmitting layer made of In that case, there was a problem that the manufacturing process became complicated and the production efficiency was poor.

On the other hand, a conventional protective coating agent for an optical disk or an adhesive for a DVD made of an ultraviolet-curable composition containing a (meth) acrylate compound and a photoradical polymerization initiator as main components is used to increase productivity. It is designed to have sufficient sensitivity to light sources such as high pressure mercury lamps and metal halide lamps. In addition, the adhesive for DVD has a thickness of 400 nm so that it can be cured even with ultraviolet light attenuated through a plastic substrate such as polycarbonate.
It is designed to increase sensitivity in the vicinity. for that reason,
There is a problem that the transmittance of the cured coating film near the wavelength of 400 nm is reduced.

In a high-density optical disk on which recording or reproduction is performed by using a blue laser, it is necessary to minimize the warpage of the disk in order to accurately read and write information. Required. 10% of existing optical disk protective coating agent
1.2mm thick CD with above cure shrinkage
Even if the substrate is coated with a thin film of about 10 μm, warpage occurs, and thus there is a problem that it is not suitable for a high-density optical disk which performs recording or reproduction by a blue laser requiring low warpage.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is suitable as a light transmitting film of an optical disc on which recording or reproduction is performed by using a blue laser.
It is an object of the present invention to provide an ultraviolet-curable composition capable of satisfying both durability and high transmittance of a cured film near a wavelength of 400 nm, and an optical disc using the same.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result of exploring the practical critical condition of the transmittance of the light transmitting layer with respect to blue laser light, as a result, The layer is formed of a UV-curable composition containing a (meth) acrylate compound and a photoradical polymerization initiator as main components, and good characteristics are realized by designing the transmittance at a laser wavelength within a specific range. This led to the completion of the present invention.

That is, the present invention provides the following. (1) In an optical disc which performs recording or reproduction with a semiconductor laser having an oscillation wavelength in the range of 370 to 430 nm through a light transmitting layer, the light transmitting layer contains a (meth) acrylate compound and a photo radical polymerization initiator as main components. An optical disc, comprising a cured film of an ultraviolet-curable composition contained therein, wherein the transmittance of the laser beam is 75% or more.

(2) An ultraviolet-curable composition used for forming the light-transmitting layer according to (1), wherein the curing shrinkage is 10% or less.

(3) The ultraviolet-curable composition according to (2), wherein the average molecular weight between crosslinking points is 170 or more.

In the optical disk of the present invention, since the light transmitting layer is composed of a cured film of an ultraviolet curable composition containing a (meth) acrylate compound and a radical photopolymerization initiator as main components, no corrosive acid is generated. Thus, an optical disk for blue laser having excellent durability can be obtained. Further, the ultraviolet-curable composition of the present invention has a small curing shrinkage and can realize a high-precision optical disk.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In preparing the ultraviolet-curable composition of the present invention, an ultraviolet-curable compound and a photo-radical polymerization initiator are used as essential components. As the ultraviolet curable compound, a monofunctional (meth) acrylate or a polyfunctional (meth) acrylate can be used as a polymerizable monomer component. These can be used alone or in combination of two or more. Here, in the present invention,
Acrylate and methacrylate are collectively referred to as (meth) acrylate.

As the photo-radical polymerization initiator used in the present invention, any known and commonly used one capable of curing an ultraviolet-curable compound represented by a polymerizable oligomer and / or a polymerizable monomer can be used. As the photo-radical polymerization initiator, a molecular cleavage type or a hydrogen abstraction type is suitable for the present invention.

In the present invention, when recording or reproducing recorded information with a blue laser, it has been found that there is a performance branch point in the vicinity of 75% of the transmittance of the light transmitting layer with respect to the laser light, and this is determined by the lower limit in the structure. Value. The reason that such a critical condition exists is explained as follows. That is, when the number of the light transmitting layers is one, the laser light once transmitted through the light transmitting layer is reflected by the reflecting film and transmitted through the light transmitting layer again. Therefore, when the transmittance of the light transmitting layer is, for example, 70% or less, the intensity of the reflected light is attenuated to 49% or less with respect to the input laser light. The study of high power and long life of blue laser is being actively conducted.
Since the output is unstable compared to the laser beam used in DVD and the laser beam reflectance of the first layer is required to be 45% or more in the case of DVD, the transmittance of the light transmitting layer is low. It is considered that it can be used stably at 75% or more.

To make the transmittance 75% or more, for example,
It is effective to select a photo-radical polymerization initiator having as small an absorbance as possible at the wavelength of the blue laser, or to design the light-transmitting layer as thin as practically acceptable for an optical disc.

Suitable photoradical polymerization initiators for use in the present invention include, for example, 1-hydroxycyclohexyl phenyl ketone, benzoin ethyl ether, benzoin isobutyl ether, 2-hydroxy-2-methyl-1
-Phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropane-
Examples include a molecular cleavage type photopolymerization initiator such as 1-one and 2-methyl-1- (4-methylthiophenyl) -2-morpholinopropan-1-one. Examples of the molecular cleavage type which can be used in combination with these photopolymerization initiators include, for example, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, benzyl, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-benzyl-2 -Dimethylamino-1- (4-morpholinophenyl) -butan-1-one, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, benzyldimethyl ketal and the like. Since the absorbance at the wavelength of the blue laser is relatively large, it is preferable that the amount of use is minimized even if used. Further, benzophenone, 4-phenylbenzophenone, isophthalphenone, 4-benzoyl-4′-methyl-diphenyl sulfide, which is a hydrogen abstraction type photopolymerization initiator, can also be used in combination.

As far as the effects of the present invention are not impaired, sensitizers such as trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, and p-dimethylaminobenzoate may be used as long as the effects of the present invention are not impaired. Amines which do not cause an addition reaction with the above-mentioned polymerizable components, such as ethyl acid, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine and 4,4′-bis (diethylamino) benzophenone, can also be used in combination. .

Next, it has been found that it is necessary for the ultraviolet curable composition of the present invention to have a curing shrinkage of 10% or less for the accuracy of the optical disk. For this purpose, the average molecular weight between crosslinking points is desirably 170 or more.

The average molecular weight between crosslinking points in the present invention is calculated as follows. Among the (meth) acrylate compounds in the composition, in the case of bifunctional, the molecular weight of (meth) acrylate is unchanged, and in the case of trifunctional or higher, the molecular weight of (meth) acrylate divided by the functional number is represented by each (meth) acrylate compound. the inter-crosslinking molecular weight M _i. The sum of the contents (parts by mass) of each (meth) acrylate compound is defined as A (= ΔC _i : where C _i = content of the i component). The content (parts by mass) of each (meth) acrylate compound C _i分子 the molecular weight M _i between cross-links is defined as the total number B of cross-links. (B = Σ (C _i / M _i )) The average molecular weight between crosslinking points = A 架橋 B.

By setting the content of the polyfunctional monomer component in the ultraviolet-curable composition within a specific range so that the average molecular weight between cross-linking points obtained by the above calculation becomes 170 or more, the curing shrinkage is 10%. % Or less, and a composition suitable for a high-density optical disc which performs recording or reproduction with a blue laser requiring low warpage can be obtained.

Examples of the polymerizable monomer that can be used in the present invention include the following. Examples of the monofunctional (meth) acrylate include, as a substituent, methyl, ethyl, propyl, butyl, amyl, 2-ethylhexyl,
Octyl, nonyl, dodecyl, hexadecyl, octadecyl, cyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, tetrahydrofurfuryl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-chloro-
Having a group such as 2-hydroxypropyl, dimethylaminoethyl, diethylaminoethyl, nonylphenoxyethyltetrahydrofurfuryl, caprolactone-modified tetrahydrofurfuryl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, etc. A) acrylate and the like.

Examples of the polyfunctional (meth) acrylate include 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, and 3-methyl-methacrylate.
1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, tricyclodecanedimethanol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol ,
Di (meth) acrylates such as tripropylene glycol and polypropylene glycol, di (meth) acrylates of tris (2-hydroxyethyl) isocyanurate,
Di (meth) acrylate of diol obtained by adding 4 moles or more of ethylene oxide or propylene oxide to 1 mole of neopentyl glycol, and di (meth) acrylate of diol obtained by adding 2 moles of ethylene oxide or propylene oxide to 1 mole of bisphenol A 4 moles or more of ethylene oxide or propylene oxide are added to 1 mole of (meth) acrylate or triol obtained by adding 3 moles or more of ethylene oxide or propylene oxide to 1 mole of trimethylolpropane. Di (meth) acrylate of diol obtained by addition, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, poly (meth) acrylate of dipentaerythritol ) Acrylate, ethylene oxide-modified phosphoric acid (meth) acrylate, ethylene oxide-modified alkylated phosphoric acid (meth) acrylate.

Among these polymerizable monomers, it is preferable that the composition contains a monofunctional monomer in that the cure shrinkage of the composition is reduced. Further, among the monofunctional monomers, a monomer having an alicyclic structure is more preferable, and for example, a (meth) group having a group such as cyclohexyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, etc. Acrylate and the like

Further, those which can be used together with the polymerizable monomer include polyester (meth) acrylate, polyether (meth) acrylate, epoxy (meth) acrylate, urethane (meth) acrylate and the like as polymerizable oligomers.

The UV-curable composition may be used at room temperature to 40
It is preferable to use one that is liquid at a temperature of ° C. It is preferable not to use a solvent, and even if it is used, it is better to keep it as small as possible. When the composition is applied by a spin coater, the viscosity is 20 to 1000 mPa · s.
It is preferable to adjust the thickness to be 100 to 1000 mPa · s when a relatively thick film is to be formed.

The composition of the present invention may further contain, if necessary, other additives, such as a thermal polymerization inhibitor, an antioxidant represented by a hindered phenol, a hindered amine, and a phosphite, a plasticizer, and an epoxy resin. A silane coupling agent typified by silane, mercaptosilane, (meth) acryl silane, or the like can be blended for the purpose of improving various characteristics. These are selected from those having excellent solubility in ultraviolet curable compounds and those that do not inhibit ultraviolet transmittance.

Next, a method for manufacturing an optical disk according to the present invention will be described. Pits, an information recording layer such as a phase change film or a magneto-optical recording film, aluminum, on a circular resin substrate on which a light reflection film such as gold or silver is formed, after applying the composition of the present invention by spin coating or the like, Cured by UV irradiation,
An optical disk having a light transmitting layer can be obtained.

Further, a resin substrate on which an information recording layer and a translucent film are formed, and a resin substrate on which an information recording layer and a light reflection film are formed are prepared. The composition of the present invention is dropped on one substrate in a ring shape, the other substrate is overlaid, the composition is spread by a spin coating method or the like, and then cured by irradiation with ultraviolet light to form a bonded disc. You can also get. In this case, the adhesive layer becomes a light transmitting layer.

In the optical disk of the present invention, the thickness of the light transmitting layer is usually set to about 3 to 200 μm. However, since the thickness directly affects the light transmittance, sufficient management is required.

As a method of ultraviolet irradiation, a flash irradiation method may be used in addition to general continuous light irradiation. As the lamp, a metal halide lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a xenon lamp, or the like can be used. The irradiation amount of the ultraviolet rays is preferably in the range of 0.05 to ² J / cm ² .

[0034]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Hereinafter, “parts” in the examples means “parts by mass”.

Example 1 Unidick V-5500 (manufactured by Dainippon Ink and Chemicals, Inc.) 9 as a bisphenol A type epoxy acrylate
Part, an aliphatic urethane acrylate, 1 mol of polytetramethylene glycol (molecular weight: 1000) was reacted with 2 mol of isophorone diisocyanate, and then 22 mol of urethane acrylate obtained by reacting 2 mol of hydroxyethyl acrylate, tricyclodecane dimethanol dimer 37 parts of acrylate, 24-ethoxyethoxyethyl acrylate 24
Parts, ethylene oxide-modified phosphate methacrylate 0.
2 parts, Irgacure 184 as a radical photopolymerization initiator
(Ciba Specialty Chemicals Co., Ltd.) (5 parts) was added and mixed and dissolved for 1 hour, and the viscosity was 230 mPa · s (25
° C).

Comparative Example 1 In the composition of Example 1, only the radical photopolymerization initiator was used, from 5 parts of Irgacure 184 (manufactured by Ciba Specialty Chemicals) to 4 parts of Irgacure 184 (manufactured by Ciba Specialty Chemicals). And a 2,4,6-trimethylbenzoyldiphenylphosphine oxide combination was changed to a composition having a viscosity of 250 mPa · s (25 ° C.).

Comparative Example 2 Unidick V-5500 (manufactured by Dainippon Ink and Chemicals, Inc.) 9 as a bisphenol A type epoxy acrylate
Parts, trimethylolpropane triacrylate 46 parts,
30 parts of neopentyl glycol diacrylate, 5 parts of tetrahydrofurfuryl acrylate, 0.2 parts of ethylene oxide-modified phosphoric acid methacrylate, 7 parts of benzophenone as a photoradical polymerization initiator, and 3 parts of p-dimethylaminoacetophenone are added and mixed and dissolved for one hour. And viscosity 3
A composition of 0 mPa · s (25 ° C.) was prepared.

Test Method 1 (Permeability of Cured Film) The above composition was sandwiched between glass plates so that the thickness of the obtained coating film was 100 μm, and the irradiation amount was 1 J / cm 2 using a metal halide lamp 120 W / cm with a cold mirror.
cm ² (Light meter UVPF-3 manufactured by Eye Graphics Co., Ltd.)
The ultraviolet ray of 6) was irradiated. The cured film was peeled from the glass plate, and the transmittance of each cured film at a wavelength of 400 nm was measured with a spectrophotometer UV-3100 (manufactured by Shimadzu Corporation).

Test Method 2 (Curing Shrinkage Ratio) After leaving the above composition in a constant temperature water bath at 25 ° C., the liquid specific gravity D1 was measured using a float scale. Next, the above composition is sandwiched between glass plates so that the thickness of the obtained coating film becomes 100 μm, and about 1 J / cm ^{2 by} a metal halide lamp.
Irradiated. The specific gravity D2 of this coating film was determined according to JIS-Z8807-1976, and the curing shrinkage was determined by the following formula. Curing shrinkage (%) = (D2−D1) / D2 × 100

[0040]

[Table 1]

As is clear from Table 1, the composition of Example 1 using only the photoradical polymerization initiator having a large light transmittance near 400 nm has a high transmittance at a wavelength of 400 nm and a small curing shrinkage. It can be seen that it is suitable for an optical system of a blue laser. On the other hand, the compositions of Comparative Examples 1 and 2 using the ordinary photoradical polymerization initiator alone or in combination have a low transmittance at a wavelength of 400 nm and are not practical. Further, the composition of Comparative Example 2 having a small average molecular weight between crosslinking points has a curing shrinkage rate of more than 10%, which is also unfavorable in this respect.

[0042]

According to the present invention, 370 to 430 nm is passed through the light transmitting layer.
In an optical disc on which recording or reproduction is performed by a laser beam having an oscillation wavelength within the range described above, by adopting a specific light-transmitting film, the transparency of the laser beam and an excellent light-transmitting film having excellent durability An optical disc with high performance can be obtained.

Continued on front page F-term (reference) 4J100 AL03P AL04P AL05P AL08P AL09P AL10P AL62Q AL63Q AL66Q AL67Q BA03P BA03Q BA04P BA05P BA07Q BB01P BC03P BC04P BC27P BC37P BC43P BC43Q BC53P BC74Q CA23 JA36 5D0329 LC

Claims (3)

[Claims] 1. An optical disc which performs recording or reproduction with a laser beam having an oscillation wavelength in the range of 370 to 430 nm through a light transmitting layer, wherein the light transmitting layer is formed of (meta)
An optical disc comprising a cured film of an ultraviolet curable composition containing an acrylate compound and a photoradical polymerization initiator as main components, and having a transmittance of the laser light of 75% or more. 2. An ultraviolet-curable composition used for forming the light-transmitting layer according to claim 1, wherein the ultraviolet-curable composition has a curing shrinkage of 10% or less. 3. The ultraviolet-curable composition according to claim 2, wherein the average molecular weight between crosslinking points is 170 or more.