JPH05128590A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent adherence of dusts by imparting low surface energy and charge preventive characteristics to a protective layer to be formed on the side to be avoided from dusts of an optical recording medium such as an optical disk or an optomagnetic disk. CONSTITUTION:An optical recording medium having an optically transparent board 1 has a protective layer 4 provided at least on one of an optical pickup surface and a recording layer surface and having H or more of pencil lead hardness, a low energy surface of 80 degrees or more of a contact angle to water and less than 1X10<4>OMEGA/square of surface resistance value. Thus, the medium having excellent dust adherence prevention mainly even in a high humidity environment can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium such as an optical disc.

[0002]

2. Description of the Related Art An optical disc will be described as an example of an optical recording medium. As shown in FIG. 1, the structure of an optical disc is such that a recording layer 2 is provided on one surface of a substrate 1 made of optically transparent glass or plastic, and a resin material is provided outside the recording layer 2 to protect the recording layer 2. Made of overcoat 3
Has been given. A hard coat (protective layer) 4 made of a resin material is applied to the other surface (optical pickup surface) of the substrate 1 to protect the substrate. It is most effective to apply the present invention to the protective layer 4 which should avoid the attachment of dust as much as possible, but it may be applied to the overcoat 3. The case where the present invention is applied to the protective layer 4 will be described below.

When such an optical disk is installed in a drive and operated for a long period of time, dust in the air adheres to the surface of the optical disk and the light transmittance is reduced, so that the protective layer is provided with measures against dust. Is considered. Specifically, there is a technique of lowering the surface resistance value in order to avoid dust collection due to charging (see, for example, JP-A-2-304773). Although it is a method of adding an activator type antistatic agent or a conductive filler, considering the required properties such as transparency of the protective layer, scratch resistance and coating property, the method of adding a surfactant type antistatic agent is preferable.

By the way, the surfactant-type antistatic agent is one which adsorbs water molecules to the polar groups in the antistatic agent to form a conductive layer of water, thereby exhibiting conductivity.
Its conductivity has the disadvantage that it is greatly affected by the external environment, especially temperature and humidity. In addition, the introduction of polar groups suppresses dust adhesion due to charging,
Since the surface energy becomes high, there is a disadvantage that it is difficult to remove dust once attached to the surface.

Further, in a high-humidity environment, water molecules are excessively adsorbed on the surface, and the water molecules increase the concentration of dust, so that there is also a disadvantage that the adsorption power of dust becomes extremely large. Here, the relationship between the surface energy and the number of dust deposits on the disk will be described with reference to FIG. The horizontal axis indicates the surface energy, and the contact angle to water (24 ℃, 80
% RH), and the vertical axis shows the number of dust particles (particle size 10 μm) attached in a certain area during the dirt chamber test. The hard coat used in the experiment was destaticized by corona discharge.

According to this, it can be seen that the dust adhering property drastically changes in the contact angle range of 50 to 60 degrees. When a polar group is introduced, the treated surface has a contact angle of less than 60 degrees, which shows that dust adhesion increases, but when using an optical disk in a normal office, Is relatively calm and stable, so no major problems are expected.

[0007]

[Problems to be Solved by the Invention] However, in the future,
Assuming that optical discs are used in general and used in various environments, especially in high-humidity environments, the current countermeasures against dust (antistatic treatment) are not sufficient, and simply reduce the surface energy. It seems that it is not possible to avoid troubles caused by garbage by taking measures.

It is an object of the present invention to provide an optical recording medium such as an optical disk which is provided with a protective layer having a small surface energy and an antistatic property and which has an excellent dust adhesion preventing property even in a high humidity environment. To do. Further, in a magnetic field modulation type overwritable magneto-optical disk, if dust adheres to the recording layer side, it causes a head crash, and the protective layer targeted by the present invention includes such a protective layer on the recording layer side. Including.

[0009]

In order to achieve the above object, in the present invention, an optical recording medium having an optically transparent substrate has a pencil hardness on at least one of an optical pickup surface and a recording layer surface. The protective layer is H or more, a low energy surface having a contact angle with water of 80 degrees or more, and a surface resistance value of less than 1 × 10 ¹⁴ Ω / □.

The base material of the protective layer is an acrylic or methacrylic radiation-curable resin, and the polysiloxane compound has a surface resistance of less than 1 × 10 ¹⁴ Ω / □ to reduce the surface energy. Therefore, it is preferable to contain a reactive antistatic agent. Further, the polysiloxane compound is preferably a compound represented by the following general formula.

[0011]

[Chemical 3]

(Where R is₁Is an alkyl group, an acrylic group,
Methacrylic group, epoxy group, R ₂Is H, CH₃so
Yes, 1 ≦ s ≦ 40 and 10 ≦ p + q + r ≦ 500. )
In addition, the reactive antistatic agent is represented by the following general formula:
It is preferably a compound.

[0013]

[Chemical 4]

(Wherein A ⁻ is an anion and R ₃ is C
_n H _{2n + 1} and _n is ₁ to 16. Here, in consideration of productivity, the film forming method of the protective layer is preferably an ultraviolet curable type or an electron beam curable type, and the base material is a (meth) acrylic ultraviolet curable resin or an electron beam curable type. Resin is preferred. In addition, in order to improve scratch resistance, which is an important characteristic of the protective layer, it is desirable to include a component effective in surface protection, and specific examples thereof will be shown below.

That is, polyfunctional (meth) acrylates such as trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta. One or more (meth) acrylates having three or more reactive groups such as (meth) acrylate and dipentaerythritol hexa (meth) acrylate are included, and in addition, in consideration of adhesion to a substrate and coating property. , Diethylene glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate,
2 reactive groups such as hexanediol diacrylate
(Meth) acrylate having one or two (meth) acrylates having one reactive group such as 2-hydroxyethyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are used to design the base material. Good.

In order to reduce the surface energy, it is possible to add a silicon-based material or a fluorine-based material. In consideration of the compatibility with the above-mentioned base material,
Alkyl- and polyoxyalkylene-modified polysiloxane compounds are desirable, for example, the compounds represented by the general formula of Chemical formula 3 above are preferable, and in this case, more desirably p
+ Q + r = 50 to 100, (q + r) /p≧0.2 in consideration of compatibility with the base material, and s is preferably 4 or more in consideration of antistatic property. Considering compatibility, 15
It is below.

Further, in order to develop the antistatic property,
Considering the hardness, transparency and coating of the protective layer,
A method of mixing a surfactant is desirable, and can be arbitrarily selected from any of the known surfactants.
Considering that the characteristics do not deteriorate even after long-term use, solvent wiping, etc., those that can be fixed by copolymerization with the base material are preferable, such as (meth) acrylic group in the molecule,
A reactive surfactant having an acrylamide group or the like is preferable.

Specific examples include the compounds represented by the general formulas of Chemical Formula 5, Chemical Formula 6, and Chemical Formula 7. The acrylamide-type quaternary ammonium salt of Chemical Formula 7 is a hydrolytically stable reactive group. It is the most excellent and desirable.

[0019]

[Chemical 5]

[0020]

[Chemical 6]

[0021]

[Chemical 7]

(Wherein A ⁻ is an anion, R ₄ , R ₅ and R
₆ , R ₇ are H and CH ₃ . The surface resistance is more preferably 1 × 10 ¹³ Ω / □ or less.

[0023]

【Example】

Example 1 5 parts by weight of N, N-dimethylaminopropyl acrylamide (manufactured by Kojin Co., Ltd.) was completely dissolved in 70 parts by weight of 2-hydroxyethyl acrylate, and further pentaerythritol triacrylate (PET manufactured by Nippon Kayaku Co., Ltd. was used. −
30) Dissolve completely in 100 parts by weight.

Then, polyether modified silicone XF
-42-812 (manufactured by Toshiba Silicone Co., Ltd.) 3 parts by weight,
5 parts by weight of a photoinitiator Irg.500 (manufactured by Ciba-Geigy Co., Ltd.) was added, and the mixture was heated to about 40 ° C. and completely dissolved to obtain a resin for a protective layer. Next, this resin is applied to a polycarbonate substrate by spin coating to a thickness of about 5 μm (cured film thickness),
It was irradiated with 1600 mJ / cm ² of ultraviolet rays (H lamp manufactured by Fusion) and cured to form a protective layer. Example 2 5 parts by weight of N, N-dimethylaminopropyl acrylamide (manufactured by Kojin Co., Ltd.) was completely dissolved in 70 parts by weight of 2-hydroxyethyl acrylate, and further pentaerythritol triacrylate (PET manufactured by Nippon Kayaku Co., Ltd. was used. −
30) Dissolve completely in 100 parts by weight.

Then, polyether modified silicone XF
5 parts by weight of -42-812 (manufactured by Toshiba Silicone Co., Ltd.),
5 parts by weight of a photoinitiator Irg.500 (manufactured by Ciba-Geigy Co., Ltd.) was added, and the mixture was heated to about 40 ° C. and completely dissolved to obtain a resin for a protective layer. Next, this resin is applied to a polycarbonate substrate by spin coating to a thickness of about 5 μm (cured film thickness),
It was irradiated with 1600 mJ / cm ² of ultraviolet rays (H lamp manufactured by Fusion) and cured to form a protective layer. Comparative Example 1 5 parts by weight of N, N-dimethylaminopropyl acrylamide (manufactured by Kojin Co., Ltd.) was completely dissolved in 70 parts by weight of 2-hydroxyethyl acrylate, and further pentaerythritol triacrylate (PET manufactured by Nippon Kayaku Co., Ltd. was used. −
30) Dissolve completely in 100 parts by weight.

Then, 5 parts by weight of a photoinitiator Irg.500 (manufactured by Ciba-Geigy Co., Ltd.) was added and heated to about 40 ° C. to completely dissolve it to obtain a resin for a protective layer. Next, this resin is applied to a polycarbonate substrate by spin coating to a thickness of approximately 5 μm.
(Cured film thickness) Apply and UV rays (H lamp made by Fusion)
Was irradiated with 1600 mJ / cm ² for curing to form a protective layer. Comparative Example 2 70 parts by weight of 2-hydroxyethyl acrylate was mixed with pentaerythritol triacrylate (P manufactured by Nippon Kayaku Co., Ltd.).
ET-30) Dissolve completely in 100 parts by weight.

Then, polyether modified silicone XF
-42-812 (manufactured by Toshiba Silicone Co., Ltd.) 3 parts by weight,
5 parts by weight of a photoinitiator Irg.500 (manufactured by Ciba-Geigy Co., Ltd.) was added, and the mixture was heated to about 40 ° C. and completely dissolved to obtain a resin for a protective layer. Next, this resin is applied to a polycarbonate substrate by spin coating to a thickness of about 5 μm (cured film thickness),
It was irradiated with 1600 mJ / cm ² of ultraviolet rays (H lamp manufactured by Fusion) and cured to form a protective layer.

The following table shows the evaluation results of each of the above protective layers (Examples 1 and 2 and Comparative Examples 1 and 2).

[0029]

[Table 1]

The hardness is evaluated on a polycarbonate substrate. Also, the surface resistance value is 23 ℃, 70% RH.
And the measurement method complies with JIS k-6911. The applied voltage was 500 V and the measurement was performed 90 seconds after the application. Also,
The rubbing test was conducted at 23 ° C and 70% RH with BEMCOTM-3 (manufactured by Asahi Kasei Co., Ltd.) 10 times to rub the surface of the protective layer strongly, and dust (10 μm toner) was applied by the dirt chamber (ASTM D2741-68) method.
Was evaluated as A, when no dust adhesion was observed, B when a slight dust adhesion was observed, and C when a dust adhesion was observed on the entire surface.

The contact angle is a value for water. In the high humidity test, the sample was completely discharged by corona discharge, and the evaluation was performed under the same method and conditions as the friction test. The physical properties shown in the above table did not change after the surface was wiped with ethanol-soaked BEMCOT M-3 for about 100 times and after the durability test at 80 ° C, 85% RH, and 1000 hours. ..

[0032]

As described above, according to the present invention,
Of optical recording media such as optical disks or magneto-optical disks,
The protective layer formed on the side where dust should be avoided has a low surface energy and has the property of exhibiting antistatic properties,
It is possible to embody an optical recording medium which is excellent in dust adhesion prevention property even in a high humidity environment.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing the structure of an optical disc.

FIG. 2 is a diagram showing the relationship between the contact angle and the number of dust deposits on a conventional protective layer on a disc.

[Explanation of symbols]

 1 substrate 4 protective layer

Claims (4)

[Claims] 1. An optical recording medium having an optically transparent substrate, at least one of an optical pickup surface and a recording layer surface, having a pencil hardness of H or more and a low energy of 80 ° or more in contact angle with water. An optical recording medium comprising a protective layer which is a surface and has a surface resistance value of less than 1 × 10 ¹⁴ Ω / □. 2. The base material of the protective layer is an acrylic or methacrylic radiation-curable resin, and a polysiloxane compound is used to reduce the surface energy, and the surface resistance value is set to less than 1 × 10 ¹⁴ Ω / □. The optical recording medium according to claim 1, further comprising a reactive antistatic agent. 3. The polysiloxane compound according to claim 2,
An optical recording medium represented by the following general formula. [Chemical 1](In the formula, R₁Is an alkyl group, acrylic group, methacrylic group
Group, an epoxy group, R ₂Is H, CH₃And 1 ≦
s ≦ 40 and 10 ≦ p + q + r ≦ 500. ) 4. An optical recording medium, wherein the reactive antistatic agent according to claim 2 is represented by the following general formula. [Chemical 2] (In the formula, A ⁻ is an anion, R ₃ is C _n H _{2n + 1} and _{n is}
Is 1 to 16. )