JPS63281238A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obviate the degradation in C/N and recording sensitivity so that long-period reliability is obtd. by specifying the temp. at which the loss on heating of the cured matter of a resin starts at >=150 deg.C. CONSTITUTION:The volatility of a low mol. wt. material from the cured matter of the resin for a 2P method is evaluated by a thermogravimetric analysis (TG) and the resin compsn. is selected with the temp. at which the loss on heating of the cured matter starts as an index. Namely, a substrate is formed by using the cured matter of the resin for the 2P method having >=150 deg.C temp. at which the loss on heating starts and an optical recording medium is produced thereof. A change in the Curie temp. (Tc) of the magnetic recording layer after an environmental durability test is thereby eliminated and the degradation in the C/N and recording sensitivity is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical recording medium that can be read only or recorded, reproduced or recorded, reproduced, and erased using a light beam. More specifically, the present invention relates to a cured resin material used in the production of an optical recording medium using a photopolymerization method having a guide groove made of a cured resin.

[Conventional technology]

Conventionally, glass, acrylic resin, polycarbonate resin, etc. have been used as substrate materials for optical recording media. In order to perform high-density recording on an optical recording medium, it is necessary to form optical guide grooves on the substrate thereof, and two methods are conventionally known for this purpose. One method is to perform injection molding using a mold in which unevenness corresponding to the shape of the guide groove is carved, thereby transferring the guide groove at the same time as molding the substrate.

Another method is to first apply an ultraviolet curable resin or the like on a mold in which unevenness corresponding to the shape of the guide groove has been carved, and then place the substrate on this resin. By irradiating with
This method is called the P method.

The former method is excellent in mass production, but it has the disadvantage of poor transferability of the guide groove shape, and the problem is that only plastics, such as acrylic resin or polycarbonate resin, can be used as the substrate material. There is. That is, in a recording medium using a plastic substrate, since the plastic substrate has air permeability, the recording layer is corroded by moisture, oxygen, etc., and its recording characteristics gradually deteriorate. Therefore, if this method, in which only plastic can be used as the substrate material, is adopted, there is a problem in that it is not possible to manufacture a recording medium that can maintain recording characteristics for a long period of time.

On the other hand, the latter method not only has good transferability of the guide groove shape, but also allows the use of glass instead of plastic as the substrate material. Therefore, by using a glass substrate provided with guide grooves by this method, it is possible to manufacture a recording medium that exhibits high reliability over a long period of time.

However, optical recording media in which a recording layer, a protective layer, etc. are formed on a zP method molded resin layer are subject to environmental durability tests (70°C, 8°C).
After being left at 5% R, H (relative humidity) for 5000 hours, the recording/reproducing characteristics deteriorated, which still posed a practical problem. In particular, when a magnetic recording layer is used as the recording layer, C
There were problems such as a decrease in recording sensitivity, and a sufficient C/N could not be obtained unless the recording laser power was increased compared to the initial level.

[Problem that the invention seeks to solve]

The present invention was made to solve the above problems, and
An object of the present invention is to provide a cured resin material for producing an optical recording medium that exhibits long-term reliability without a decrease in /N or recording sensitivity.

[Means for solving problems]

That is, the present invention is an optical recording medium manufactured by a photopolymerization method having a guide groove made of a curable resin on a substrate, characterized in that a cured product of the resin has a heating loss start temperature of 150°C or higher. It is an optical recording medium.

The present inventors have determined that the C/N of optical recording media after environmental durability tests was
As a result of analyzing and investigating the cause of the decrease in recording sensitivity, we found that it was due to the volatilization and diffusion of low molecular weight substances such as the uncured Kamatsumar 1 photopolymerization initiator and its decomposition products into the recording layer in the cured resin for the 2P method. I found out something. The above resin for the 2P method generally consists of a mixed composition of a prepolymer component (A), a monomer component (B) as a reactive diluent, and a photopolymerization initiator component (C), and the compound (A) 2, (B ) is used (A) 5
-95: (B) 85-5 (weight ratio), (C) is used in a weight ratio of 0.1 to 10% with respect to the composition.

Component (A) includes polyhydric alcohols such as pentaerythritol triacrylate and dipentaerythritol hexaacrylate, or polyether polyols.
Modifications such as acrylates, especially trifunctional or higher polyol polyacrylates, polyacrylates of modified polyols made by modifying polyols with epoxides or lactones, or diacrylates of modified diols made by adding epoxides to polyhydric phenols bisphenol A and bisphenol S. Polyol polyacrylate, or polyester acrylate produced by condensation telomerization of polyhydric alcohol, polybasic alcohol or its anhydride, and acrylic acid, or polyol such as polyether polyol, polyester polyol, polyisocyanate, and acrylate having a hydroxyl group. or epoxy acrylate, which is an oligomer obtained by adding acrylic acid or an acrylate having a terminal carboxyl group to an epoxy compound, or bisphenol A diglycidyl ether type or novolac polyglycidyl ether type resin, Examples include epoxidized fats and oils, epoxidized polybutadiene, and fatty acid-modified epoxy resins.

As component (B), an acrylic ester of a polyhydric alcohol is used, and as a monofunctional acrylic monomer, cyclohexyl acrylate, benzyl acrylate,
Carpitol acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,
Glycidyl acrylate, dicyclopentadiene ethoxy mono(meth)acrylate, inbornyl(meth)acrylate, hydrogenated dicyclopentadiene mono(meth)acrylate
Examples include acrylate. Examples of polyfunctional acrylic monomers include ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate,
Butylene glycol diacrylate, neopentyl glycol diacrylate, 1,4-butanediol diacrylate, 1,4-hexanediol diacrylate,
Examples include diacrylates such as 1.8-hexanediol diacrylate and pentaerythritol diacrylate, and triacrylates such as pentaerythritol triacrylate and trimethylolpropane triacrylate. Examples of the allyl polyfunctional monomer include diallyl phthalate, diallyl isophthalate, diallyl chlorendate, diallyl adipate, diallyl glycolate, triallyl cyanurate, diethylene glycol bisallyl carbonate, and the like.

Component (B) may be one type or a mixture of two or more of these.

Any known photopolymerization initiator can be used as component (C), but those with good storage stability after blending are preferred. For example, benzoin alkyl ethers such as benzoin ethyl ether and benzoin butyl ether,
．． 2-jetoxyacetophenone, 4-phenoxy-2
, 2-dichloroacetophenone and other acetophenones, 2-hydroxy-2-methylpropiophenone, 4
Propiophenones such as °-isopropyl-2-hydroxy-2-methylpropiophenone, benzylmethyl ketal, 1-hydroxycyclohexylphenyl ketone, and anthraquinones such as 2-ethylanthraquinone and 2-chloroanthraquinone , 2,4-dimethylthioxanthone, Michler's ketone, and other thioxanthone types. These may be used alone or in a mixture of two or more in any proportion.

The low molecular weight substances remaining or contained in the cured resin composition for the 2P method include the 7-mer component in the resin composition for the 2P method (
B), a photopolymerization initiator (C), and its decomposition products such as aldehydes such as benzaldehyde and acetaldehyde, ketones such as hexylphenyl ketone and acetone,
Examples include alcohols such as benzyl alcohol and methanol. In particular, as a recording layer, TbCo, GdTbFe,
Using an amorphous magnetic recording layer such as TbFeCo or GdTbFeCo, Y-SiN, SiOx, or Zn as a protective layer.
In the case of a magneto-optical recording medium in which a laminated film of one or a combination of two of S, SiC, etc. is formed on a 2P method resin layer by vacuum evaporation, sputtering, etc., the low-molecular-weight substances volatilize and diffuse into the recording layer. , the Curie temperature (Tc) of the magnetic recording layer increases by 15 to 20°C, which causes C/N,
This results in a decrease in recording sensitivity, and therefore evaporates from the cured resin.
The above problem can be solved by using a cured product in which there are no or few low molecular weight substances that diffuse.

Therefore, the above problem was solved by evaluating the volatility of low molecular weight substances from the cured resin product for the 2P method by thermogravimetric analysis (hereinafter abbreviated as TG) and selecting the resin composition using the temperature at which heating loss of the cured product starts as an index. Settled.

That is, in the TG analysis, if there is volatilization of a lower molecular weight substance than in the cured resin material, it will appear as a weight loss, so the volatility of the lower molecular weight substance from the resin can be evaluated based on the heating weight loss start temperature. It is desirable that this temperature be high, since low molecular weight substances have no or little volatility below the heating loss start temperature.

The present inventors determined the heating loss start temperature and C/N of the cured resin,
As a result of intensive research into the relationship between recording sensitivity, it has been found that the lower limit of the desired heating loss initiation temperature is approximately 150°C. Therefore, 2P whose heating loss start temperature is 150℃ or higher
By creating a substrate using a cured resin and manufacturing an optical recording medium, the T of the magnetic recording layer after an environmental durability test is
The method of the present invention, which can eliminate changes in c and prevent deterioration of C/N and recording sensitivity, is particularly effective in manufacturing magneto-optical recording media.

〔Example〕

(Example 1) As a resin for the 2P method, (A) 360 parts by weight of a resin obtained by esterifying an epoxy acrylate (Ebicor) 112B (manufactured by Shell Petrochemicals) bisphael type epoxy resin with acrylic acid, (B ) A mixture of 37 parts by weight of trimethylolpropane triacrylate CTMPTA (manufactured by Nippon Kaji) and 3 parts by weight of (C) Irgacure 184 (manufactured by Merck ■) was used. The temperature at which heating loss started was 180° C. according to TG analysis of this cured resin. Using the above resin, photopolymerization molding was performed on a donut-shaped blue glass substrate with a diameter of 130 I and a thickness of 11] m. A protective layer of SiO with a thickness of 1200A was formed on this by vacuum evaporation method, and amorphous GdTbFeC layer with a thickness of 1000A was further formed by sputtering method.
Next, a protective layer of SiO with a thickness of 2,000 yen was formed in the same manner as the protective layer described above. Finally, glass substrates similar to those described above were bonded together using an adhesive layer made of a hot-melt adhesive so that each layer faced each other, thereby producing an optical recording medium. The heating loss start temperature of the cured 2F resin was evaluated in accordance with the following method. (
The same applies to the following Examples and Comparative Examples.) Heating loss start temperature: Using a thermal analyzer (TG-DSC) manufactured by Seiko Electronics Co., Ltd., the temperature at which weight loss began was defined as the heating loss start temperature.

[Example 2] (A) Polyester acrylate as resin for 2P method [
obtained by the reaction of hexahydrophthalic anhydride (t mol), trimethylolpropane (2 mol) and acrylic acid] 40 parts by weight, (B) 20 parts by weight triallyl cyanurate, trimethylolpropane triacrylate (TMPTA (Japan) An optical recording medium was prepared in the same manner as in Example 1 except that a mixture of 37 parts by weight of (C) Irgacure and 1843 parts by weight of Irgacure (C) was used.The heating loss start temperature of the cured resin was 160°C. Met.

[Example 3] As a resin for the 2P method, (A) urethane acrylate [Aronixt 1200X (Tsurethane acrylate manufactured by Toagosei Chemical Co., Ltd.)] parts by weight of BO, (B) trimethylolpropane triacrylate (TMPTA (manufactured by Nippon Kagami Co., Ltd.)) )
] Example except that a mixture of 37 parts by weight and (C) Irgacure 1843 parts by weight was used.

An optical recording medium was prepared in the same manner as in Example 1. The heating loss start temperature of the cured resin was 180°C.

[Example 4] (A) Epoxy acrylate (R-
130 (Nippon Kajimi Co., Ltd.)] 770 parts by weight (B) Hydrogenated dicyclopentadiene monoacrylate (FA-513A)
(manufactured by Hitachi Chemical)) 27 parts by weight, (C) Irgacure 1
An optical recording medium was prepared in the same manner as in Example 61 except that 843 parts by weight of the mixture was used. The heating loss start temperature of the cured resin was 200°C.

[Example 5] (A) polyurethane acrylate (N
30 parts by weight of K ester U-108-A (manufactured by Shin Nakamura Chemical Industry ■) difunctional, (B) neopentyl glycol-modified trimethylolpropane diacrylate represented by the following formula (I) [Kayarad R-f104 (manufactured by Nippon Chemical Co., Ltd.)] Made by condiments)〕7
Examples except that a curable resin composition in which 0.5% by weight of (C) photopolymerization initiator [Irgacure 184 (manufactured by Nippon Ciba Geigy ■)] was mixed with 70% by weight of the mixture was used.
An optical recording medium was prepared in the same manner as in Example 1. The heating loss start temperature of the cured resin was 200°C.

(I) [Example 6] As 2P method resin (A) Polyurethane acrylic t, -)
(C-9504 (manufactured by Tomer) bifunctional) 30 parts by weight, [Example 5] (B) neopentyl glycol-modified trimethylolpropane diacrylate represented by formula (I) [Kayarad R-804 (Japan) Made by Kanyakumi)〕440
and dicyclopentanyl acrylate (FA-51
3A (manufactured by Hitachi Chemical)] to a mixture of 30 parts (C
) An optical recording medium was prepared in the same manner as in Example 1 except that a mixture containing 0.5% by weight of a photopolymerization initiator (Irgacure 184 (manufactured by Nippon Ciba Geigy)) was used.

The heating loss start temperature of the cured resin was 180°C.

[Comparative Example, 1] As resin for 2P method (A) PETA (mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (manufactured by Osaka Organic Chemical Industry ■)] 4
5 parts by weight, (B) neopentyl glycol diacrylate) (NPGOA (manufactured by Nippon Kayaku)) 55 parts by weight, (C
) Darocur 1173 (manufactured by Merck ■) An optical recording medium was prepared in the same manner as in Example 1 except that 5 parts by weight of the mixture was used.The heating loss start temperature of the cured resin was 80.
It was ℃.

[Comparative Example, 2] As a resin for 2P method (A) 880 parts by weight of epoxy acrylate [Viscoat #540 (manufactured by Osaka Organic Chemical Industry ■)] (B) 1.8-hexanediol diacrylate C
Example except that a mixture of HDDA (manufactured by Nippon Kayaku ■)] 116 parts by weight (C) and Darocure 11,734 parts by weight was used.
An optical recording medium was prepared in the same manner as in Example 1. The heating loss start temperature of the cured resin was 60°C. Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Environmental durability test (70°C, 85°C) of the optical recording medium prepared according to Comparative Example 2
The results of measurement of C/N and recording sensitivity before and after %R, H, ) are shown in Tables 1 and 2.

Both C/N and recording sensitivity were measured by recording and reproducing a 3 MHz signal using a magneto-optical information recording and reproducing device.

The recording sensitivity was measured by measuring the recording/reproducing laser power to obtain a C/N of 40 dB or more. That is, the decrease in recording sensitivity means that the recording/reproducing laser power to obtain a C/N of 40 dB or more becomes larger than the initial level.

As is clear from Tables 1 and 2, by creating an optical recording medium using a resin for the zP method whose heating loss onset temperature of the cured product is 150°C or higher, after the environmental durability test It is possible to obtain an excellent optical recording medium with little decrease in C/N and no change in recording/reproducing laser power, that is, no decrease in recording sensitivity.

Table-1 Environmental durability test (C/N measurement) Table-2 Environmental durability test (recording sensitivity measurement) [Effects of the invention] According to the present invention, the 2P whose heating loss start temperature of the cured resin by photopolymerization is 150°C or higher By creating a substrate for an optical recording medium using a commercial grade resin, it becomes possible to manufacture an optical recording medium that exhibits long-term reliability.

Claims (1)

[Claims] 1. An optical recording medium manufactured by a photopolymerization method having a guide groove made of a curable resin on a substrate, characterized in that a cured product of the resin has a heating loss initiation temperature of 150°C or higher. recoding media.