JPH0719395B2 - Optical disc - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention comprises a recording metal thin film which is optically writable and readable and which is optically written on an underlayer having a fine structure provided on a transparent plate. The present invention relates to an optical disc having durability and high reproduction ability, which is used as an audio disc, a video disc, and the like.

(Prior Art) An optical disk is constructed as shown in FIG. 1, for example.
This is a transparent substrate made of glass, transparent plastic or the like, on the surface of which a Bi, In, Te, S, etc. is formed on a transparent substrate consisting of a substrate 1'having a fine structure such as grooves and holes for servo tracks.
The metal thin film 2 is usually formed of one or more metals and metal compounds such as e, As, Pb and Sn. This constituent element is usually made up of two processing substrates with an adhesive 4 through a protective film 3 so that the metal thin films 2 face each other and, in some cases, a certain distance via a spacer or the like. It is made by pasting together.

The metal thin film is usually made of a thin film of about 50 to 1000Å, and protecting the metal thin film during handling before and after bonding is a major issue related to the performance of the optical disk.

Generally, the metal thin film of the optical disk is thin and has a fine structure.
Chemical protection required. For this purpose, it is conceivable to form a coating film on the metal thin film for the purpose of protection, but in the process of forming the coating film, deformation or change of the metal thin film having a fine structure should not occur. It is necessary to prevent external force applied to the metal thin film and unnecessary heat from being applied to the substrate.

(Object of the Invention) The present invention has been made in response to such a need, and evaluates the residual stress after curing of a radiation curable coating material used for a protective film of a metal thin film, and shows the residual stress within a certain range. An object of the present invention is to provide an optical disk provided with a protective film having good adhesion to a metal thin film by using a paint.

(Structure of the Invention) The present invention relates to an optical disc in which a cured coating film of a radiation curable coating material is further provided on a metal thin film of an optical disc composed of a metal thin film deposited on a transparent substrate. (A) a polyfunctional vinyl oligomer having a molecular weight of 400 to 4000 and (b) a monofunctional vinyl oligomer [vinyl group concentration (g equivalent / g) of (a) in paint] /
[Concentration (g equivalent / g) of vinyl group (b) in paint] is 2.0
The residual stress of the cured coating film of the radiation-curable paint is calculated by the following formula and measurement method as the shrinkage force P per unit cross-sectional area. Relates to an optical disc with a pressure of 50 kg / cm ² or less.

However, P: shrinkage force per unit cross-sectional area of the coating film h: thickness of the coating film h ₀ : thickness of the aluminum plate E ₀ I ₀ : bending rigidity of the aluminum plate ρ: radius of curvature where H = h ₀ + h Yes, P is a radiation-curable coating applied to an aluminum plate of a specified thickness to a thickness of about 10μ, and is irradiated with a specified amount of radiation to cure it. It is calculated according to the above formula from the change of. The above formula is shown in Industrial Chemistry, Vol. 59, p. 124 (1956).

As a method for forming a coating film for protecting a metal thin film, it is necessary to use a radiation curable paint. Here, the radiation includes ultraviolet rays, visible rays, electron beams, γ rays, etc. By irradiating with these radiations, curing can be achieved without applying unnecessary heat to the coating film. Further, the radiation-curable coating material can generally be solvent-free, in which case it is not necessary to heat the solvent to dry it and the solvent does not affect the metal thin film or the transparent substrate.

The residual stress of the cured coating film calculated by the above of the radiation curable paint applied on the metal thin film is particularly likely to act on the metal thin film, weakening the adhesion between the metal thin film and the transparent substrate, and protecting the metal thin film before protection. It is not preferable because the possibility of damaging it is great. The tendency of the adhesive force between the metal thin film and the transparent substrate to weaken due to this residual stress can be indirectly known by the crocodile tape peeling test, which is generally carried out with paint as a practical test.

For the above-mentioned problems due to residual stress does not occur, the above residual stress when the paint is cured is required to be 50 kg / cm ² or less, preferably 30kg / cm ² or less, 20 kg / cm ²
The following are particularly preferred.

The radiation curable coating material of the present invention has a low viscosity to improve coating workability to reduce residual stress of the cured coating film and damage the metal film during curing (mainly adhesion of the metal thin film and transparent substrate is weakened). ) Containing a monofunctional vinyl monomer. Although a solvent can be used for lowering the viscosity, it is preferable not to use it because the solvent drying step increases and the metal thin film and the transparent substrate may be damaged by the solvent.

If the content of monofunctional vinyl monomer is too low, the above 2
It is not preferable because it does not fulfill one of the two objectives sufficiently, and when the amount is too large, the curing rate decreases. It is necessary to select the monofunctional vinyl monomer content so that the ratio of the vinyl group concentration of the monofunctional vinyl monomer to the vinyl group concentration of the polyfunctional vinyl oligomer in the paint (g equivalent / g ratio) is 2.0 to 7.5. .

The monofunctional vinyl monomer has, for example, the following chemical formula (N is an integer of 0 to 3, R is hydrogen or an alkyl group having 12 or less carbon atoms) _{(III) CH 2 = CHCOOC 2} H 4 OOC-CH 2 CH 2 COOH Some are represented by. A compound having a methacryloyl group instead of the above acryloyl group is also used. These may be added alone or in combination.

As the monofunctional vinyl monomer, (meth) acrylic acid, alkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and hydroxypropyl (meth) acrylate are also used.

In order to obtain a practical curing speed, it is necessary to further include a polyfunctional vinyl oligomer.

Examples of polyfunctional vinyl oligomers are acrylic urethane modified products of both-end hydroxyl group-type polybutadiene (molecular weight 2000) (trade name NISSO-TE2000, manufactured by Nippon Soda Co., Ltd.), polytetraethylene glycol (molecular weight 800-2000) acrylics. Urethane modified product, polypropylene glycol (molecular weight 40
(0-2000) is chain-extended with polyisocyanate, and the terminal double bond is made with hydroxyethyl acrylate. 1,
Examples include those in which 6-hexanediol is chain-extended with polyisocyanate and has a terminal double bond with hydroxyethyl acrylate. For example, trimethylolpropane triacrylate or tetraethylene glycol diacrylate having a relatively low molecular weight is also used.

The radiation curable coating material of the present invention has a compounding ratio of a monofunctional vinyl monomer and a polyfunctional vinyl oligomer, preferably a monofunctional vinyl monomer / polyfunctional vinyl oligomer content of 30 parts by weight or more.
95 parts by weight / 70 parts by weight to 5 parts by weight, more preferably 50 parts by weight to 70 parts by weight / 50 parts by weight to 30 parts by weight, with the total amount being 100 parts by weight.

When curing the radiation-curable paint, a sensitizer is not necessary when the radiation is an electron beam, but it is preferable to include a sensitizer when the radiation is an ultraviolet ray. For example, benzophenone, diethylaminobenzophenone, thioxanthone,
Benzoisopropyl ether or the like is used. You may use these in combination. When a sensitizer is used, it is preferably in the range of 0.5 to 15 parts by weight with respect to 100 parts by weight of the monofunctional vinyl monomer and the polyfunctional vinyl oligomer.

The molecular weight of polyfunctional vinyl oligomer depends on its curability and viscosity.
It is set to 400 to 4000. Further, a thiol may be further added to the coating material, and this addition alleviates the residual stress when it is further cured.

Examples of thiols used include polyfunctional thiols such as 1,4-butanedithiol, 1,10-decanedithiol, trimethylolpropane tris (ω-mercapto-ε-caproate) and the like. Additives such as thermal polymerization inhibitors, dyes and adhesion promoters may be added to the paint.

As a method for applying such a radiation-curable coating material, any method can be used as long as it can be applied to an object to be coated in a preferable state. The method, spray method, depping method, spin method by centrifugal force, etc. can be mentioned.

As a curing method, it is easy to use ultraviolet rays or electron beams as a radiation source, and the irradiation method is not particularly limited.

(Effects of the Invention) The present invention provides an optical disk provided with a protective film having good adhesion to a metal thin film.

(Examples) Examples of the present invention will be described below. In the following, parts are parts by weight.

Example 1 The residual stress after curing of the coating material composed of the above components was measured by the above measuring method. Irradiation is under a high pressure mercury lamp (80 mW / cm ² ) 10
Aluminum piece coated on one side with a film thickness of 10 μm on a conveyor flowing at a distance of cm at 4.7 m / sec (10 mm width × 150 mm length × 0.1 mm thickness)
The aluminum plate had a radius of curvature of 1050 mm and the residual stress calculated from this result was 10 kg / cm ² as a result of the hardening that was carried out by passing the coating surface upward with three passes. However, the bending stiffness E ₀ I ₀ of the aluminum plate was obtained by setting the Young's modulus (E ₀ ) of the aluminum piece to 6.8 × 10 ¹¹ dyne / cm ² and the second moment of area I ₀ to 8.3 × 10 ^-8 (cm ³ ). (same as below).

Next, apply this paint on a polymethylmethacrylate resin plate.
The Bi-coated underlayer with a fine structure
Approximately 10μ applied to the Bi side of
To produce a uniform coating. Then the high pressure mercury lamp (80w / cm)
The coated material on a conveyor flowing at a distance of 10 cm below at 4.7 m / sec.
Was put on and passed 3 times. Cut the finished coating with a cutter
Eye (1mm²), Seromizu of Sekisui Chemical Co., Ltd.
Group (bit eco 24 ) Crimping (5kg / cm²) And quickly
As a result of peeling, no abnormality occurred. In addition, the fine structure
The metal thin film was observed with a microscope of 1200 times, but the curing process
No thermal deformation due to the heat was observed.

Example 2 The same radiation curable coating material as in Example 1 was applied to the lower portion of the transparent plate support, that is, the surface of the polymethylmethacrylate resin.
A coating film was formed by coating and UV curing in the same manner as in. As a result of carrying out a first-eye test on this product in the same manner as in Example 1, no abnormality was found.

Examples 3, 4, 5 and Comparative Examples 1, 2 When the same polyfunctional vinyl oligomer, monofunctional vinyl monomer, and benzophenone as in Example 1 were used in the weight ratios shown in the following table, the same steps as in Example 1 were carried out and cured. The results of the first eye test are shown in Table 1.

The case where peeling occurred between the ultraviolet curable paint and the metal thin film or the metal thin film and the transparent substrate was x, and the case where peeling did not occur was marked with o (same in the following tables).

Examples 6 to 9 Table 2 shows the results of changing the monofunctional vinyl monomer using the same polyfunctional vinyl monomer as in Example 1.

In all cases, the ratio of the vinyl group concentration of the monofunctional vinyl monomer to the vinyl group concentration of the polyfunctional vinyl oligomer (g equivalent / g ratio) in the coating falls between 4 and 6.

Comparative Examples 3 to 8 Table 3 shows the results of changing the polyfunctional vinyl oligomer using the same monofunctional vinyl monomer as in Example 1.

[Brief description of drawings]

 FIG. 1 is a schematic sectional view of an optical disk. DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 1 '... Substrate having fine structure 2 ... Metal thin film, 3 ... Protective film 4 ... Adhesive

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuyuki Hayashi, 4-13-1, Higashimachi, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Ibaraki Research Institute (72) Takashi Yamadera, 4-13, Higashimachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi Chemical Co., Ltd. in Ibaraki Research Laboratory (72) Inventor Hajime Kakumaru 4-13-1, Higashimachi, Hitachi City, Ibaraki Hitachi Chemical Co., Ltd. in Yamazaki Plant (56) Reference Japanese Patent Laid-Open No. 59-171043 (JP, A) JP-A-57-181443 (JP, A) Actually developed S58-58336 (JP, U)

Claims (1)

[Claims] 1. An optical disc comprising a metal thin film of a metal thin film adhered on a transparent substrate and a cured coating film of a radiation curable paint further provided on the metal thin film, wherein the radiation curable paint (a) has a molecular weight of (a). A polyfunctional vinyl oligomer having a viscosity of 400 to 4000 and (b) a monofunctional vinyl monomer [concentration of vinyl group in (a) in coating (g equivalent / g)] /
[Concentration (g equivalent / g) of vinyl group (b) in paint] is 2.0
The residual stress (calculated as the shrinkage force P per unit cross-sectional area by the following formula and measurement method) of the radiation-curable coating cured coating film is 50 kg using An optical disc with / cm ² or less. However, P: Shrinkage force per unit cross-sectional area of the coating film h: Thickness of the coating film h ₀ : Thickness of the aluminum plate E ₀ I ₀ : Bending stiffness of the aluminum plate ρ: Radius of curvature Also, where H = h ₀ + h Yes, P is the degree of curvature of a single-sided aluminum piece in which a radiation-curable coating is applied to an aluminum plate of a predetermined thickness to a thickness of about 10 μm, and a predetermined amount of radiation is applied to cure it, and the application side is curled inward. Is calculated according to the above formula.