JPH07121904A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain a very excellent antistatic effect keeping sufficient resistance to scratching in a laser light incident surface. CONSTITUTION:In an optical disk having a recording layer 4 on a resin transparent substrate 2, a ground layer 8 with a surface resistance below 1X10<10>OMEGA/squ. in the environment of 25 deg.C and RH of 50% is provided on the surface of a substrate on the incoming side of a laser light of the optical disk. Moreover, at least an area 7 into which a laser light is incident of the ground layer 8 is covered with a hard coated layer 6 comprising a hardened film of an active light beam hardening type resin while the whole or a part of the area into which no laser light is incident of the ground layer 8 is exposed to a hard coat layer 6 not being covered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc for recording, reproducing and / or erasing information with a light beam such as a laser beam.

[0002]

2. Description of the Related Art In recent years, an optical disk for recording, reproducing and / or erasing high density information by using a light beam such as a laser beam has attracted attention.

Optical discs are classified into ROM discs, write-once discs, phase-change discs, discs having an organic photochromic material as a recording layer, magneto-optical discs utilizing the magneto-optical effect, etc., depending on the recording system and recording layer. You can Among them, the magneto-optical disk is said to be the disk that can rewrite information freely, has a wide range of applications, and is closest to practical use, and has attracted particular attention among optical disks. Some have already been put to practical use.

A general 3.5-inch magneto-optical disk will be described as an example. As shown in FIG. 1, a groove called a groove is formed in a region having a radius of 23 mm to 41 mm from the center. 21mm radius from the center to cover
A recording layer is formed in an area of about 42 mm. The recording layer is usually an alloy of a transition metal and a rare earth metal, and is composed of an amorphous magnetic alloy film having an easy axis of magnetization in the direction perpendicular to the film surface, a dielectric film, a reflective film, and the like. Since the recording layer is easily corroded by oxygen and moisture in the air, the recording layer is covered with a resin film called a protective coat.

Further, since the disk-shaped transparent substrate generally used for the magneto-optical disk is made of a resin which is easily scratched such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin, in order to prevent scratches on the substrate surface,
A hard coat is formed on the substrate surface opposite to the surface on which the protective coat is formed. Although the above-mentioned configuration takes a general 3.5-inch magneto-optical disc as an example, other types of optical discs usually have the same configuration as the above.

In an optical disc, information is recorded, reproduced and / or erased by irradiating a light beam such as a laser beam from a hard-coated surface. For this reason, the hard coat is required to be smooth and transparent, and scratch resistance and dust are required to prevent scratches and foreign matter such as dust in the air from adhering to the path of the light beam. Anti-adhesion property is required. Therefore, the hard coat of the optical disk needs to satisfy these required characteristics in a well-balanced manner.

Among these characteristics, the adhesion of dust to the hard coat surface often occurs when the hard coat surface is electrified and the dust in the air is electrostatically adsorbed. In order to prevent such an inconvenience that dust is attracted due to electrification of the hard coat surface, it has been proposed to impart an antistatic effect to the hard coat.

As means for imparting an antistatic effect to the hard coat, for example, as disclosed in JP-A-61-222042, an inorganic material such as ITO formed by a method such as a sputtering method or a vapor deposition method is used. A method in which a transparent conductive film is used as a hard coat, or JP-A-1-1993
As disclosed in Japanese Patent Laid-Open No. 4 (1994), there is known a method in which a substrate surface is coated with a cured film of a resin which is cured by an actinic ray such as an ultraviolet ray or an electron beam, and an inorganic transparent conductive film is formed on the cured film. There is. However, the inorganic transparent conductive film of this method, due to its manufacturing method, can only obtain a very thin film,
Moreover, the obtained film is hard and brittle, and is easily broken, so that the scratch resistance required as a hard coat is inferior.

Further, for example, as disclosed in JP-A-2-123534, there is a method of coating the substrate surface with an actinic ray curable resin containing fine particles of a metal oxide such as In, Sn and Zn. Are known. In this method, the hard coat layer can be formed by a simple method such as a spin coat method which is excellent in mass productivity, but in order to impart a sufficient antistatic effect, it is necessary to increase the content ratio of oxide fine particles. However, in this case, it becomes extremely difficult to maintain the smoothness of the surface of the hard coat layer or the optical uniformity of the hard coat layer, and there is a drawback that the recording / reproducing characteristics of the optical disc deteriorate.

On the other hand, as a method of imparting antistatic property to the hard coat, a method of using an actinic ray curable resin containing an organic antistatic agent such as a surfactant as the hard coat is also known. In this case, the spin coating method, which is excellent in mass productivity, can be applied, and since the coating agent is basically a homogeneous system, the smoothness of the hard coat surface and the optical uniformity of the hard coat layer are not impaired. There are advantages. However, this method has a drawback in that the antistatic effect is highly dependent on humidity because the antistatic effect is exhibited by the adsorption of water to the polar groups of the antistatic agent component on the hard coat surface. It is necessary to use a large amount of antistatic agent components in order to develop a sufficient antistatic effect in winter with low humidity.In this case, in summer with high humidity, a large amount of water is adsorbed on the surface of the hard coat surface. It has a drawback that it becomes sticky and, on the contrary, it becomes easier to adsorb dust. Further, when the proportion of the antistatic agent component increases, the scratch resistance of the hard coat may be impaired.

As described above, in the hard coat of an optical disk, it is actually very difficult to achieve both antistatic property and scratch resistance and smoothness.

Therefore, the surfaces of the above various antistatic layers are
There has been proposed a method of coating with a cured film of a resin that is curable by an actinic ray such as ultraviolet rays and has excellent scratch resistance. For example, in Japanese Patent Laid-Open No. 4-64932,
First, an optical disk is disclosed in which an inorganic transparent conductive film such as ITO is formed on a substrate surface by a vacuum film forming method such as sputtering, and the film is covered with a cured film of an actinic ray curable resin.

[0013]

However, in a hard coat in which the surface of the antistatic layer is coated with a cured film of an actinic ray curable resin, an electric current flows through the underlying antistatic layer at the time of measuring the surface resistance, and therefore, it is apparent. Although the surface resistance value of is low, the outermost layer is still a cured coating of actinic ray curable resin with high insulation properties.For example, if the surface is rubbed or corona discharge is applied, high voltage can be easily generated. It has the drawback that it is charged up to the maximum and that the potential does not decay easily. Therefore, it cannot be said that the true antistatic property can be achieved even if the apparent surface resistance value is low.

The problem to be solved by the present invention is to provide an optical disk having a hard coat layer which is excellent in antistatic property in the true sense, exhibits sufficient dust adsorption preventing performance, and has sufficient scratch resistance. To provide.

[0015]

In order to solve the above-mentioned problems, the present invention is an optical disc having a recording layer on a resin transparent substrate, wherein the substrate surface on the laser light incident side is 25
Surface resistance of 1 × 10 ¹⁰ Ω in the environment of ℃ and 50% RH
/ □ or less is provided, and further, at least the region of the underlayer on which the laser light is incident is covered with a hard coat layer made of a cured film of an actinic radiation curable resin, and the laser light of the underlayer is There is provided an optical disc in which the whole or a part of the non-incident region is exposed without being covered with the hard coat layer.

The present invention will be described in detail below with reference to the drawings.
It The configuration of the optical disk of the present invention is a 3.5-inch magneto-optical
A disk is shown as an example in FIG. Optical disc of the present invention
Is the laser light incident surface, that is, the surface on which the recording layer is formed.
Is the reverse surface of the substrate in the environment of 25 ℃, 50% RH
Sheet resistance is 1 × 10 ^TenΩ / □ or less underlayer provided
Has been. This underlayer, on the laser light incident surface,
It is also formed in areas other than the area where the laser light is incident.
It Here, the region where the laser light enters is the light of the present invention.
Recording, reproduction, and
Laser light for erasing may be incident
It means the entire area and is usually opposite to the laser light incident surface.
The region where the groove is formed on the opposite surface corresponds to this.

Further, on the surface of this underlayer, at least the region where the laser light is incident is covered with a hard coat layer made of a cured film of an actinic radiation curable resin, and the entire region where the laser light is not incident or The base layer is partially exposed.

In the present invention, the region where the underlayer is exposed is usually a concentric band-shaped region inside the laser light incident region, as shown in FIG. In this case, the width of the strip-shaped region in the radial direction is preferably 3 mm or more, more preferably 5 mm or more. If the width is less than the above range, the static electricity leakage property is deteriorated, which is not preferable. The shape of the exposed region of the underlayer is not limited to the shape illustrated in FIG. 2 and may be any shape as long as sufficient static electricity leakage is exhibited.

The underlayer having a surface resistance value of 1 × 10 ¹⁰ Ω / □ or less in an environment of 25 ° C. and 50% RH should have high transparency to laser light to such an extent that recording / reproduction is not hindered. Good. Examples of such an underlayer include (1)
Inorganic transparent conductive film made of metal oxide, (2) transparent conductive cured film of actinic ray curable resin containing fine particles of metal oxide, (3) organic compound layer containing organic antistatic agent And (4) a film comprising a layer containing a silicon-based antistatic agent.

As the inorganic transparent conductive film made of a metal oxide, for example, an inorganic conductive film made of a metal oxide containing at least one of In, Sn and Zn is preferable because of its high transparency. Among them, a film made of an oxide of In and Sn (ITO) is particularly preferable because it has high transparency and a film having a low electric resistance value can be obtained. These inorganic transparent conductive films can be formed by a vacuum vapor deposition method or a sputtering method. This inorganic transparent conductive film is 85% at the wavelength of laser light used for recording and reproduction.
It is preferable to have the above transmittance. In order to achieve the above transmittance, the thickness of the inorganic transparent conductive film is usually 100 to 4
000 Angstrom range.

Examples of the metal oxide fine particles using the actinic radiation curable resin containing the metal oxide fine particles as the underlayer include, for example, a metal containing at least one of In, Sn, Zn and Sb. The oxide fine particles may be mentioned. Among these, tin oxide and indium oxide are preferably used from the viewpoint of transparency and electric resistance value. You may dope these oxides with a phosphorus atom etc. A cured film of an actinic ray curable resin in which fine particles of metal oxide are uniformly dispersed is applied on a substrate by a method such as a spin coat method, and is cured by irradiating with actinic rays such as ultraviolet rays. Can be formed by. The average particle size of the fine particles is preferably in the range of 0.01 to 1 μm, and the film thickness of the cured film is preferably in the range of 0.5 to 5 μm. In addition,
In the present invention, the laser light incident surface of the underlayer made of a cured coating of an actinic ray curable resin containing metal oxide fine particles is covered with a hard coat layer made of another actinic ray curable resin. The formation is not required to have scratch resistance. Therefore, it is possible to make the underlayer extremely thin, and transparency is not impaired even if the content of the metal oxide fine particles in the resin is made higher than usual to lower the electric resistance value. Further, even if the transparency of the surface of the underlayer is reduced due to the irregular reflection due to the protrusion of fine particles, the irregular reflection is suppressed and the transparency is restored by hard coating on the surface. Therefore, the present invention solves the drawbacks in the case where the hardened coating of the actinic radiation curable resin containing the metal oxide fine particles is solely used as the hard coat as in JP-A-2-123534.

When an organic compound layer containing an organic antistatic agent is used as an underlayer, these are (1) an organic antistatic agent dissolved in a volatile solvent, which is then applied to the substrate surface by a method such as spin coating. And then dried, or (2) an actinic ray curable resin containing an organic antistatic agent is applied to the surface of the substrate by a method such as a spin coating method and is cured by irradiation with an actinic ray. be able to. Since the method (1) takes time to dry and is inferior in productivity, the method (2) is preferable.

In the present invention, the organic antistatic agent means
It is a compound having both a hydrophilic portion and a hydrophobic portion mainly composed of an organic compound in its molecule, and can be used regardless of whether the hydrophilic portion is cationic, anionic or nonionic. The hydrophilic portion of the cationic antistatic agent includes primary amine, secondary amine, and tertiary amine.
Examples thereof include secondary amines, pyridine derivatives and salts thereof, and quaternary ammonium salts. Examples of the hydrophilic portion of the anionic antistatic agent include sulfonic acid, carboxylic acid, phosphoric acid, and metal salts thereof. And the like, and examples of the hydrophilic portion of the nonionic antistatic agent include alcohols, amides, esters, and ethylene oxide adducts or propylene oxide adducts thereof. Further, an antistatic agent usually called an amphoteric surfactant can also be used.

The hydrophobic portion of these organic antistatic agents is not particularly limited, but is irradiated with an actinic ray such as an ultraviolet ray in the presence of a suitable photopolymerization initiator such as an acryloyl group and / or a methacryloyl group. Accordingly, an antistatic agent having a curable functional group is preferable, because a coating film can be easily formed by irradiation with an actinic ray and the antistatic effect is excellent in sustainability.

In the present invention, as the silicon-based antistatic agent, those having a siloxane bond such as polysiloxane are preferably used. These silicon-based antistatic agents are usually provided in a form diluted with a solvent, but after being uniformly applied on a substrate by a method such as a spin coating method, a film is formed by a method such as heating or leaving at room temperature. It can be the underlayer of the present invention.

In the present invention, the hard coat layer shown in FIG. 2 may be a cured coating of an acrylic actinic ray curable resin or the like which is generally used as a hard coat agent for optical disks. Examples of such actinic ray curable resins include actinic ray curable oligomers such as urethane acrylate, epoxy acrylate and polyester acrylate; propylene glycol di (meth).
Acrylate, polypropylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, tetramethylene glycol di (meth) acrylate, hexamethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, tri Actinic radiation curable polyfunctional monomers such as poly (meth) acrylates such as methylolpropane tri (meth) acrylate, glycerin and pentaerythritol;
Ethyl (meth) acrylate, hydroxyethyl (meth) acrylate, n-butyl (meth) acrylate,
Actinic ray curable monofunctional monomers such as hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, phenyl (meth) acrylate and isobornyl (meth) acrylate; and a photopolymerization initiator, if necessary,
A composition is used in which a polymerization inhibitor, a leveling agent, a resin additive such as a lubricant, and the like are appropriately mixed.

It is also possible to add an antistatic component such as a surfactant and / or conductive inorganic fine particles to the composition for hard coating within the range where the scratch resistance is not impaired. By slightly reducing the electric resistance in the film thickness direction of the coat layer, the effect of the present invention is remarkably improved. The surface resistance of the hard coat containing the antistatic component is preferably 1 at 25 ° C. and 50% RH.
It is sufficient if it is 0 ¹⁵ Ω / □ or less, more preferably 10 ¹⁴ Ω / □ or less. Usually, when a hard coating agent having such a surface resistance is used alone, the antistatic effect is insufficient, but according to the method of the present invention, a remarkably good antistatic effect is obtained due to the synergistic effect with the underlayer. Express. The hard coat layer shown in FIG. 2 can be formed by applying the above resin composition to the surface of the underlayer by a spin coating method and irradiating it with an actinic ray. The thickness of the hard coat layer at this time is preferably in the range of 1 to 10 μm. When the film thickness is less than 1 μm, the scratch resistance as a hard coat is poor, and when the film thickness is more than 10 μm, the antistatic effect on the hard coat surface tends to be poor, which is not preferable. In addition, the cured film of the actinic ray curable resin that constitutes the hard coat layer has a pencil hardness of 2H from the viewpoint of scratch resistance.
The above is preferable.

An optical disk usually has a recording layer formed by a combination of an interference film, a recording film and a reflective film as a constituent unit on a substrate having a guide groove.

As the substrate having the guide groove, for example, a mold having a guide groove formed at a position corresponding to the substrate surface is injection-molded by using a resin having excellent moldability such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin. Or a guide groove formed on a resin flat plate by a photopolymer method.

An inorganic dielectric film having a high transparency and a high refractive index is used for the interference film. As the material, for example, SiN _x ,
SiO _x , AlSiON, AlSiN, AlN, AlT
iN, Ta ₂ O _5, ZnS, and the like. The refractive index of these interference films is preferably in the range of 1.8 to 2.8, and the absorption coefficient is preferably in the range of 0 to 0.1.

The material for the recording film is, for example,
In a write-once optical disc, a chalcogenite alloy such as Te or SnSe, or an organic dye such as cyanine, in a magneto-optical disc, an alloy of a transition metal and a rare earth metal such as TbFeCo or NdDyFeCo, in a phase-change optical disc, T
Examples include chalcogenite alloys such as eO _x , InSe, and SnSb.

A metal film or an alloy film having a high reflectance is used for the reflection film. The material is, for example, A as a metal film.
l, Au, Ag, Cu, etc., Al-Ti as an alloy film,
Al-Cr etc. are mentioned.

The interference film, the metal-based recording film, and the reflective film are formed by physical vapor deposition (PV, such as sputtering or ion plating).
D), a chemical vapor deposition method (CVD) such as plasma CVD, or the like, and the organic dye-based recording film is formed by applying a solution by a spin coating method, a roll coating method, or the like, and then removing the solvent.

Further, a protective coat layer may be provided on the reflective film.

Both organic and inorganic materials are used for the material of the protective coat layer. When forming an organic protective coat layer, methods such as a dipping method, a spin coat method, a roll coater method, and a vapor deposition method are used. on the other hand,
When forming the inorganic protective coat layer, a method such as a sputtering method, a vapor deposition method, an impregnation method or the like is used.

Among the methods for forming these protective coat layers,
The spin coating method using an ultraviolet curable resin is preferable because it is a simple and quick method. In this method, an ultraviolet curable resin is discharged onto a substrate using a dispenser, the magneto-optical recording medium is rotated at a high speed, and the resin is spread by centrifugal force for application. The applied resin is then cured by UV irradiation. The spin coating method can also be suitably used for resins other than the ultraviolet curable resin. In any case, the resin used for the protective coat layer preferably has a pencil hardness of H or higher after curing.

[0037]

In general, if the surface resistance of the outermost layer is 10 ¹⁰ Ω / □ or less, static electricity easily leaks into the air and is not charged, but in the present invention, it is 10 ¹⁰ Ω / □ or less. Since the underlayer having a low surface resistance is partially exposed, the static electricity charged in the hard coat layer made of the actinic radiation-curable resin film once moves to the underlayer and then leaks quickly from the exposed part. be able to. Therefore, the optical disk of the present invention has excellent static electricity leakage. In addition, this effect is to contain a small amount of antistatic component in the hard coat layer,
It is further improved by slightly lowering the electric resistance of the hard coat layer in the vertical direction.

Further, since the actinic ray curable resin film having excellent scratch resistance is formed on the outermost layer in the region where the laser light is incident and scratch resistance is required, the optical disk of the present invention is a laser. Excellent scratch resistance in the light incident area.

[0039]

EXAMPLES The present invention will be described in more detail below with reference to examples. In the examples, "part" means "part by weight". Surface resistance value is Hiresta I manufactured by Mitsubishi Petrochemical Co., Ltd.
It was measured using P. In addition, the attenuation of the charged voltage was measured by a static Honest meter manufactured by Shishido Electrostatic Co., Ltd. The scratch resistance was evaluated by the wear haze value which is the difference between the haze values before and after the Taber wear test (wear wheel CS-10F, load 250 g, rotation number 100 times, rotation speed 70 rpm) defined in JIS-K5400. The wear haze value was measured before the recording layer was formed.

Example 1 A metal oxide film was formed on a laser light incident surface of a polycarbonate substrate having a diameter of 86 mm by a sputtering method. That is, the substrate was set in a vacuum chamber and evacuated to 3 × 10 ⁻⁷ Torr, and then a mixed gas of argon and oxygen (flow ratio = 37: 3) was introduced to 5 × 10 ⁻³ Torr, and In ₂ O ₃ · SnO
An ITO film of about 500 angstrom was formed on the region of the substrate at a radial position of 15 to 41 mm by magnetron sputtering using a ₂ (SnO ₂ : 5%) target.

Next, a hard coat layer made of a cured film of an actinic ray curable resin was formed on the surface of the metal oxide film outside the position of a radius of 23 mm from the center of the substrate by spin coating. . That is, an acrylic UV curable resin (“DICURE CLEAR EX-704” manufactured by Dainippon Ink and Chemicals, Inc.) was applied by a spin coater to a film thickness of about 3 μm, and was irradiated with UV rays to be cured.
This resin has a pencil hardness of 5H on the glass plate.
The resin was excellent in scratch resistance.

Further, on the surface of the substrate opposite to the hard coat layer, a dielectric layer made of SiN and having a film thickness of 100 nm, Tb.
A recording film layer made of FeCo and having a thickness of 25 nm and a reflective film layer made of AlTi and having a thickness of 150 nm were sequentially formed by sputtering.

Furthermore, the reflective coating layer was placed on a spin coater, and the disc was rotated at a speed of 60 rpm while a protective coating agent "Dicure Clear EX-911" manufactured by Dainippon Ink and Chemicals, Inc. was used. 20 from the center of the disc
It was applied concentrically at the position of mm. This disk is 2,0
The protective coating agent was spread over the entire surface of the substrate by rotating it at a rotation speed of 00 rpm for 3 seconds, and the peripheral portion of the substrate was irradiated with ultraviolet rays to cure the protective coating agent to form a protective coating layer.

25 of the hard coat surface of this optical disk
Surface resistance value in the environment of ℃, 50% RH is 8 × 10 ^10.
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage of the hard coat surface was 0.5 kV, and this charge leaked quickly. Further, in this example, the abrasion haze value was measured at a stage before forming the recording layer, and it was 4.0, showing sufficient scratch resistance on the laser light incident surface.

(Comparative Example 1) In Example 1, an ITO film was formed at a position having a radius of 24 to 40 mm from the center of the substrate,
An optical disk was obtained in the same manner as in Example 1 except that the ITO film was completely covered with the hard coat layer.

25 of the hard coat surface of this optical disk
Surface resistance is 3 × 10 ¹¹ in the environment of ℃ and 50% RH.
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage of the hard coat surface is 1.5 kV, and after the corona discharge is completed, 1
The voltage after 50 seconds was 1.2 kV, and the charge was hardly attenuated. Thus, if the undercoat layer is completely covered with the hard coat layer, the apparent surface resistance is lowered, but the charge leakage property is poor.

Comparative Example 2 An optical disk was obtained in the same manner as in Example 1 except that the hard coat layer was not formed after the ITO film was formed.

25 of the hard coat surface of this optical disk
Surface resistance is 3 × 10 ⁵ in the environment of ℃ and 50% RH.
It was Ω / □. In addition, the static Honest meter is used to perform corona discharge of 10 kV on the surface of the ITO layer,
The surface charge was measured. The saturation voltage on the surface was 0.1 kV or less, and the surface was not charged at all. However, the abrasion haze value before forming the recording layer was 40, which was equivalent to that of the polycarbonate of the substrate and did not have a scratch resistance function.

Example 2 A resin composition A was prepared by adding 1% by weight of an antistatic agent Nopcostat 092 (manufactured by San Nopco Ltd.) to "Dicure Clear EX-704" in Example 1. This resin was a resin having a pencil hardness of 4H on the glass plate and excellent scratch resistance.

In the first embodiment, "Dicure clear E
An optical disc was obtained in the same manner as in Example 1 except that this resin composition A was used instead of "X-704".

25 of the hard coat surface of this optical disk
Surface resistance value in environment of ℃, 50% RH is 8 × 10 ⁸
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage on the surface of the hard coat was 0.1 kV or less, it was not charged at all, and showed a very good antistatic effect. Further, the abrasion haze value was measured in the stage before forming the recording layer in this example, and it was 4.4, showing sufficient scratch resistance on the laser light incident surface.

(Comparative Example 3) In Example 2, except that a hard coat made of the resin composition A was directly provided on the surface of the substrate opposite to the surface having the recording film layer without providing an underlayer.
An optical disc was produced in the same manner as in Example 2.

25 of the hard coat surface of this optical disk
Surface resistance value in the environment of ℃, 50% RH is 9 × 10 ¹³
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage of the hard coat surface is 2.5 kV, and after the completion of corona discharge, 1
The voltage after 50 seconds was 2.1 kV. That is, the resin composition A alone had no antistatic effect.

Example 3 A cured coating of an actinic ray curable resin containing fine particles of a metal oxide was formed on the laser light incident surface of a polycarbonate substrate having a diameter of 86 mm by spin coating. That is, an ultraviolet curable resin containing a metal oxide (“Shintron C-4456” manufactured by Shinto Chemitron Co., Ltd.) was used to form a 0.5 μm film in a region outside a radius of 20 mm from the center of the substrate. It was applied and cured so as to be thick.

Next, a hard coat layer having a layer thickness of 5 μm and formed of the cured coating of the resin composition A of Example 2 was formed on the portion outside the radial position of 23 mm of the cured layer by spin coating.

Further, on the surface opposite to the hard coat layer of this substrate, in the same manner as in Example 1, a dielectric layer, a recording film layer,
A reflective film layer was sequentially formed by a sputtering method, and a protective coat was further applied to obtain an optical disk of the present invention.

25 of the hard coat surface of this optical disk
Surface resistance is 1 × 10 ¹⁰ in the environment of ℃ and 50% RH.
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage of the hard coat surface was 0.2 kV, and the surface was hardly charged. In addition, the haze value of the disc itself was 3.0 before the recording layer was formed, and the transparency of the disc was not a problem. The wear haze value was the same as in Example 2.

(Comparative Example 4) In Example 3, the metal oxide-containing actinic radiation curable resin layer was provided with a radius of 24 to 40 from the substrate.
An optical disk was obtained in the same manner as in Example 3 except that the resin layer was formed at the position of mm and the resin layer was completely covered with the hard coat layer.

25 of the hard coat surface of this optical disk
Surface resistance is 3 × 10 ¹⁰ in the environment of ℃ and 50% RH.
It was Ω / □. Further, a corona discharge of 10 kV was performed on the hard coat surface with a static Honest meter to measure the charge on the hard coat surface. The saturation voltage on the surface of the hard coat was 1.6 kV, and the voltage after 150 seconds was 1.3 kV, which was hardly attenuated. That is, even in the combination of the resin composition A and the underlayer having a low resistance value, the charge leakage was inferior unless the underlayer was exposed.

Comparative Example 5 An optical disk was obtained in the same manner as in Example 3, except that the hard coat layer was not formed after the resin layer containing the metal oxide was formed.

The surface of the underlayer of this optical disk is at 25 ° C., 5
The surface resistance value in the environment of 0% RH is 1 × 10 ⁸ Ω / □
The resistance was low. A corona discharge of 10 kV was performed on the surface of the hard coat with a static Honest meter to measure the decay of the charge on the surface, but it was hardly charged. However, the haze value of the disc itself before the formation of the recording layer was 22.2, and the transparency as the underlayer was remarkably inferior. The wear haze value is also 3
There was no scratch resistance function in No. 3.

Example 4 In Example 3, the organic antistatic agent “SAT-5” (Nippon Pure Chemical Co., Ltd.) was used in place of the underlayer made of the ultraviolet curable resin containing the metal oxide fine particles. An optical disc was prepared and evaluated in the same manner as in Example 3 except that the dry coating of (1) was used.

The surface resistance of "SAT-5" itself is 2 × 10.
^{It was 9} Ω / □ and 1 × 10 ¹¹ Ω / □ after hard coating. The saturated electrification voltage measured by the static Honest meter was 0.3 kV, and there was almost no charging.

(Example 5) In Example 3, the silicon-based antistatic agent "Si Coat T" was used in place of the underlayer made of the ultraviolet curable resin containing the metal oxide fine particles.
2 "(manufactured by Daihachi Chemical Industry Co., Ltd.)
An optical disc was prepared and evaluated in the same manner as in Example 3.

The surface resistance of "Si coat T2" itself is 1 ×.
It was 10 ⁹ Ω / □ and 3 × 10 ¹¹ Ω / □ after hard coating. The saturated electrification voltage measured by the static Honest meter was 0.2 kV, and there was almost no charging.

[0066]

As described above, the optical disk of the present invention has a two-layer structure of an underlayer having a low electric resistance and a hard coat having an excellent scratch resistance, and has an electric resistance at a portion where the scratch resistance is not required. Since the underlayer having a low heat resistance is exposed, a very excellent antistatic effect is exhibited, and excellent abrasion resistance is exhibited at the site where the laser light is incident. Therefore, the optical disk of the present invention is excellent in reliability, in which a recording / reproducing error due to scratches on the laser light incident surface or adhesion of dust hardly occurs.

Further, in the optical disk of the present invention, the electric resistance of the hard coat layer is slightly lowered, and the antistatic effect is remarkably improved by the synergistic effect with the underlayer.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a general configuration of a conventional optical disc.

FIG. 2 is a schematic cross-sectional view showing the configuration of the optical disc of the present invention.

[Explanation of symbols]

 1 disk center line 2 disk-shaped transparent substrate 3 groove 4 recording layer 5 protective coat 6 hard coat 7 laser light incident area 8 base layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoaki Hara 1-28-A-208 Rokuzakidai, Sakura City, Chiba Prefecture

Claims (6)

[Claims] 1. An optical disc having a recording layer on a transparent resin substrate, wherein the substrate surface on the laser light incident side of the optical disc has a surface resistance of 1 × 10 ¹⁰ Ω / 25 ° C. and 50% RH. □ The following underlayer is provided, and at least the region of the underlayer on which the laser light is incident is covered with a hard coat layer made of a cured coating of actinic radiation curable resin, and the laser light of the underlayer is incident. An optical disc, wherein the whole or a part of the area not exposed is exposed without being covered with the hard coat layer. 2. The optical disc according to claim 1, wherein the underlayer is an inorganic transparent conductive film made of a metal oxide. 3. The optical disk according to claim 1, wherein the underlayer is a transparent conductive cured film made of an actinic ray curable resin containing fine particles of metal oxide. 4. The optical disk according to claim 1, wherein the underlayer is an organic compound layer containing an organic antistatic agent. 5. The optical disc according to claim 1, wherein the underlayer is a layer containing a silicon-based antistatic agent. 6. The optical disc according to claim 1, wherein the actinic radiation curable resin constituting the hard coat layer in claim 1 contains an antistatic component.