JPH06223410A - Optical disk and its production - Google Patents

Abstract

PURPOSE:To make it possible to prevent hindrance of curing by oxygen, to improve the hardness and scratching resistance of protective layers to provide the protective layers resistant to flawing and to lessen the deformation of the disk at the time of curing an active energy ray curing resin. CONSTITUTION:The protective layer resin of the optical disk which has the protective layers consisting of the radical polymerizable active energy ray curing resin on one or both surfaces of a substrate and with which one or more of reading out, recording and erasing can be executed is cured by irradiating the resin with the active energy rays under reduced pressure conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk which can be read, recorded and erased by light, particularly laser light.

[0002]

2. Description of the Related Art Optical discs have become popular rapidly in recent years due to the development of semiconductor laser technology, medium technology and the like. Play-only discs, recordable discs, and recordable / erasable discs are used for various purposes. The above-mentioned optical disc usually has a thin film such as a recording layer and a reflective layer on a glass or a resin substrate such as an acrylic resin or a polycarbonate resin, and a protective layer is provided to protect these thin films.
In addition, a protective layer may be provided in order to prevent scratches on the light incident surface of the substrate and to prevent charging. A radical polymerization type active energy ray curable resin is used for these protective layers from the viewpoint of workability. Then, conventionally, a resin having a high cross-linking density has been used because of problems in hardness and scratch resistance.

However, the use of a resin having a high cross-linking density is not preferable because the curing shrinkage is large, the deformation of the disk is large, and the residual stress is large, and in particular, in the case of a single plate type medium, the deformation is reduced. It sacrificed productivity and yield. Also, when recording or reproducing at a low speed like a compact disc, there was no problem even if the deformation was a little large, but when recording, erasing or reproducing at a high speed, the servo could not follow the deformation and correct recording and reproducing should be performed. Was difficult.

When a resin having a low crosslink density is used, the deformation of the medium can be suppressed to a small level. However, when an active energy ray-curable resin having a low crosslink density is cured in air, the inventors of the present invention have found that the resulting protective layer is The hardness and scratch resistance were poor, and it did not have a sufficient protective function. The reason is that the active energy ray-curable resin is susceptible to curing inhibition by oxygen during curing, and the resin surface in contact with air is impeded by curing due to oxygen, and the crosslink density decreases. A method of curing in an atmosphere of an inert gas such as nitrogen has been proposed as a method of preventing the curing inhibition by oxygen, but it has not been put into practical use because of problems in terms of economy and safety.

[0005]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above-mentioned problems of the protective layer of the optical disc, the present inventors have found that the curing inhibition of oxygen by the curing of the active energy ray-curable resin is prevented. In order to prevent this, they have found that it can be performed under reduced pressure conditions. On the other hand, on the other hand, as the pressure is reduced, the problem of foaming of the resin due to the degassing of the dissolved gas in the resin occurs, but it is found that the depressurizing condition of not foaming depends on the resin viscosity, and the protective layer resin does not foam during curing, Further, the inventors have found the conditions in which the hardness and scratch resistance of the protective film are excellent, and arrived at the present invention.

[0006]

That is, the present invention provides an optical disc having a protective layer made of a radical polymerization type active energy ray curable resin on both sides or one side of a substrate and capable of performing one or more of reading, recording and erasing. There is an optical disc characterized in that the protective layer is cured by active energy rays under a reduced pressure condition, and a method for producing the same. More preferably, when the protective layer resin is cured, immediately before irradiation with active energy rays. When the viscosity of the protective layer resin is η (centipoise) and the degree of vacuum of the irradiation atmosphere is P (mmHg), the protective layer resin is activated by the active energy ray under the condition of P ≦ 120 and η ^1/2 × P ≧ 120. use but is intended cured, it is intended protective layer resin is cured by active energy ray by P ≦ 80, and η ^1/2 × P ≧ 180 becomes conditions and the protective layer The viscosity of the active energy ray curable resin η for is not lower than 50 centipoises.

The present invention will be described in detail below. In the optical disc of the present invention, one or more thin films such as a recording layer and a reflective layer are provided on the substrate, and a protective layer is provided to protect these thin films, or a recording layer and a reflective layer are provided. A protective layer is provided on the opposite surface (light incident surface) to protect the surface of the substrate.

As the material of the substrate, any material can be used as long as it is a material that substantially transmits the light of the semiconductor laser and is used for a general optical recording medium. For example, resins such as glass, polycarbonate resin, acrylic resin, polystyrene resin, vinyl chloride resin, epoxy resin, polyester resin and amorphous polyolefin can be used. The substrate may have pits or grooves in advance.

In the present invention, thin films such as a recording layer and a reflective layer are formed on the substrate, but the materials used for these recording layer and reflective layer are not particularly limited. The recording layer is a layer that absorbs light for recording, and examples of materials used for the recording layer include alloys containing a metal such as Te used in write-once discs, cyanine dyes, phthalocyanine dyes, and naphthalocyanine dyes. Examples thereof include organic dyes such as naphthoquinone dyes, TbFeCo alloys used for magneto-optical discs, alloys containing metals such as Sn, Sb and Se used for phase change discs. Further, it may be a disc having no recording layer as in the case of a read-only disc.

As the reflective layer, aluminum, gold, copper,
Typical examples are metals such as platinum, silver, tin, alloys containing these metals, and dielectric multilayer films. Of course, a disc having no reflective layer may be used. Further, in addition to the recording layer and the reflection layer, a dielectric layer, a heat insulation layer, a heat diffusion layer, an antireflection layer, etc. may be provided. Further, the light incident surface may have a conductor layer for preventing charging. These layers may be a single layer or multiple layers, and the order in which they are provided is not particularly limited.

In the disc of the present invention, a protective layer is provided on these recording layer and reflective layer in order to protect these layers. Further, a scratch on the surface (light incident surface) opposite to the surface on which the recording layer or the reflective layer is provided also affects recording and reading, so that a protective layer may be provided on this surface as well.

At this time, various substances can be used for the protective layer, but in the present invention, a radical polymerization type active energy ray curable resin is preferable from the viewpoint of productivity, workability and the like. Specific examples of the radical polymerization type active energy ray curable resin include a resin having a (meth) acryloyl group and a polyene-thiol resin. These resins usually increase the hardness of the cured resin when the number of reactive double bonds such as acryloyl groups in one molecule increases, but
Hardening shrinkage increases. In addition, the viscosity of the resin increases as the average molecular weight of the resin increases. Further, a thermoplastic resin, an antistatic agent, a leveling agent, a slick agent, a defoaming agent, a coupling agent, an inorganic or organic filler, etc. may be added to these resins.

In the present invention, the active energy ray-curable resin is applied to the surface on which the recording layer, the reflective layer and the like are provided and / or the light incident surface of the substrate. The coating method is not particularly limited, and examples thereof include spin coating, screen printing, and dipping. The spin coating method is preferable from the viewpoints of ease of forming the protective layer and uniformity of the film. At this time, when the viscosity of the resin is high, it may be diluted with a solvent before use. When a solvent is used, it is preferable to dry it and remove the solvent before curing. Further, it is preferable that the protective layer is formed beyond the recording layer and the reflective layer.

Next, the resin is cured by irradiation with active energy rays. Examples of the active energy rays in the present invention include ultraviolet rays and electron beams. When irradiating with this active energy ray, the irradiation atmosphere must be under reduced pressure. The degree of vacuum when the pressure is reduced is preferably as low as possible from the viewpoint of curability. However, if the pressure is reduced too much, the resin foams, which is not preferable. The problem of foaming of this resin depends on the viscosity of the resin immediately before irradiating the active energy ray, and the degree of vacuum of the irradiation atmosphere is P (mmHg), and the viscosity of the resin immediately before irradiating the active energy ray is η (centipoise). Then, it was found that the condition of η ^1/2 × P ≧ 120 is preferable, and the condition of η ^1/2 × P ≧ 180 is more preferable. Further, P is preferably 120 or less, and more preferably 80 or less from the viewpoint of deterioration of hardness, scratch resistance and the like of the protective film due to curing inhibition of the protective layer resin by oxygen. From the viewpoint of medium deformation due to curing shrinkage, the viscosity of the resin immediately before irradiation with active energy rays is preferably 50 centipoise or more. The reason is not only that the degree of vacuum can be increased, but as described above,
This is because the higher the viscosity of the resin is, the smaller the curing shrinkage is. In addition, the viscosity of the resin immediately before irradiation with the active energy ray means that foaming due to degassing of the resin occurs during depressurization. On the other hand, as described above, when the resin is applied, if the viscosity of the resin is too high, the resin may be diluted with a solvent before use. When a solvent is used, it is preferable to remove the solvent before irradiating with active energy rays, and the viscosity of the resin at this time means the viscosity after removing the solvent. In the present invention, the protective layer resin may be heated when it is cured with an active energy ray, or may be heated after being cured. Furthermore, you may print on a protective layer.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the embodiment of the present invention is not limited to this.

Example 1 A spiral groove having a thickness of 1.2 mm and a diameter of 120 mm (depth 120 nm, width 0.5 μm, pitch 1.6 μ)
m) on an injection molded polycarbonate resin substrate having
A 3 wt% n-octane solution of a Pd-tetra- (1,2-dimethylpropoxy) -phthalocyanine brominated (average of 3.8 / molecule) n-octane solution was added dropwise, and the resin substrate was applied at a speed of 1100 rpm for 20 minutes. It spun for a second. The recording layer was formed.

A thickness of 120 is formed as a reflective layer on the recording layer.
After forming a thin film having a thickness of nm by sputtering, a 120-cmpoise radical polymerization type ultraviolet curable resin was formed as a protective layer by spin coating (4500 rpm). Then 3
The resin was cured by irradiating ultraviolet rays under a vacuum of 0 mmHg (η ^1/2 × P = 329).

No bubbling was observed in the protective layer of the optical disc manufactured in this manner, and deformation such as warp, tilt and surface wobbling of the disc was small. The hardness of the protective layer is 4H in pencil hardness, the diameter is 4.5 mm, and the protective layer is 20 mm / s while applying a weight of 100 g to a sharp diamond needle.
The scratch resistance test was carried out at the speed of No. 1, but the protective layer was slightly scratched, but there was no problem in recording and reproducing.

Comparative Example 1 In Example 1, ultraviolet rays were irradiated at a vacuum degree of 10 mmHg (η
^1/2 × P = 110), the entire surface of the protective layer foamed. Further, when irradiated with a vacuum degree of 130 mmHg, the pencil hardness of the protective layer was lowered to F, and a scratch resistance test was conducted in the same manner as in Example 1, but deep scratches were formed, making recording / reproduction impossible. It was

Example 2 A spiral groove having a thickness of 1.2 mm and a diameter of 90 mm (depth: 120 nm, width: 0.5 μm, pitch: 1.6 μ)
m) on an injection molded polycarbonate resin substrate having
After stacking SiN film, TbFeCo film, SiN, and Al film, 150 centipoise radical polymerization type UV curable resin is applied by spin coating method (6000 rpm), and is cured by irradiating UV ray under vacuum of 20 mmHg (η ^{1 / 2} x P = 245) A protective layer was formed. The hardness of the protective layer was 3H and the deformation of the disc was small. A scratch resistance test was carried out in the same manner as in Example 1, and there were slight scratches, but there was no problem in recording / reproduction.

Example 3, Comparative Example 2 In order to form an antistatic hard coat layer on the light incident surface of the optical disk of Example 2, an ultraviolet curable resin (viscosity 70 centipoise) was applied by spin coating (4000 rpm). , 70mmH
It was cured at a vacuum degree of g (η ^1/2 × P = 586), and an antistatic protective layer was formed on the light incident surface. The pencil hardness of the protective layer was 3H, and the disc was hardly deformed. A scratch resistance test was conducted in the same manner as in Example 1. The protective layer was slightly scratched, but there was no problem in recording and reproducing.

On the other hand, when the degree of vacuum is hardened at 14 mmHg (η
^1/2 × P = 117), and foaming occurred on the entire surface of the protective layer. Also 1
When cured at 30 mmHg, the pencil hardness decreased to F, and a scratch test was conducted in the same manner as in Example 1, but deep scratches were made and recording / reproduction was impossible.

[0023]

INDUSTRIAL APPLICABILITY In a readable optical disk having a protective layer made of a radical polymerization type active energy ray curable resin on one side or both sides of the substrate of the present invention, when the resin is cured, the viscosity of the resin is η ( Centipoise), and P (mmHg) as the degree of vacuum in the curing atmosphere, P ≦ 120, P × η ^1/2 ≧ 1
By irradiating and curing with active energy rays under the condition of 20, there is no defect due to foaming, the hardness of the protective layer is high, and it is possible to make the scratch resistant and to reduce the deformation of the disk.

Claims (8)

[Claims] 1. An optical disc having a protective layer made of a radical polymerization type active energy ray-curable resin on both sides or one side of a substrate and capable of performing one or more of reading, recording and erasing, wherein the protective layer is under a reduced pressure condition. An optical disk characterized by being hardened by active energy rays in. 2. When curing the protective layer resin, when the viscosity of the protective layer resin immediately before irradiation with active energy rays is η (centipoise) and the degree of vacuum of the irradiation atmosphere is P (mmHg), P ≦ 120, The optical disc according to claim 1, wherein the protective layer resin is cured by an active energy ray under the condition of η ^1/2 × P ≧ 120. 3. The optical disc according to claim 2, wherein the protective layer resin is cured by active energy rays under the condition of P ≦ 80 and η ^1/2 × P ≧ 180. 4. The optical disk according to claim 2, wherein the active energy ray-curable resin used for the protective layer has a viscosity η of 50 centipoise or more. 5. A method for producing an optical disc, comprising a protective layer made of a radical polymerization type active energy ray-curable resin on both sides or one side of a substrate and capable of performing one or more of reading, recording and erasing. A method for manufacturing an optical disk, which comprises curing with active energy rays under a reduced pressure condition. 6. When curing the protective layer resin, when the viscosity of the protective layer resin immediately before irradiation with active energy rays is η (centipoise) and the degree of vacuum of the irradiation atmosphere is P (mmHg), P ≦ 120, The method for producing an optical disk according to claim 5, wherein the protective layer resin is cured with an active energy ray under the condition of η ^1/2 × P ≧ 120. 7. The method of manufacturing an optical disk according to claim 6, wherein the protective layer resin is cured by active energy rays under the condition of P ≦ 80 and η ^1/2 × P ≧ 180. 8. The method for producing an optical disc according to claim 6, wherein the active energy ray-curable resin used for the protective layer has a viscosity η of 50 centipoise or more.