JPH06150372A - Substrate for optical recording medium and optical recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] Used for an optical recording medium in which a substrate material is made of plastic, and a recording layer is provided on one side of the substrate, and a hard coat layer is provided on a side of the substrate opposite to the recording layer. In this case, to obtain an optical recording medium substrate capable of reducing the warp of the medium, and to obtain an optical recording medium with a small warp. As a disc-shaped substrate for an optical recording medium used for an optical recording medium, the substrate surface on the side where the recording layer is provided has a concave shape that is substantially rotatable with the center of the substrate as the bottom, and a concave surface in the radial direction of the substrate. The value of the slope of is constantly positive and further increases from the inner circumference to the outer circumference of the substrate. As the optical recording medium, when a recording layer is provided on the concave surface side of the substrate of the present invention and a hard coat layer is provided on the substrate surface side opposite to the recording layer, a photocurable or thermosetting organic polymer is used. Consisting of and cured JI
A hard coat material having an S pencil hardness of HB or higher is used.

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 for recording, reproducing and erasing information by light such as laser light.
Among them, the recording layer is a magneto-optical recording layer formed of a metal thin film having an easy axis of magnetization in a direction perpendicular to the film surface, the recording layer recording information by the photothermomagnetic effect and reproducing the information by the magnetooptical effect. It is particularly preferably applicable to the magneto-optical recording medium. In particular, it is suitable for a 3.5 inch diameter magneto-optical recording medium used in a single plate state.

[0002]

2. Description of the Related Art An optical recording medium has characteristics such as high density, large capacity, and non-contact with a recording / reproducing head. Compact discs and video discs for reproduction only, recordable optical discs, and recording / reproducing, Erasable magneto-optical recording disks have been developed and put to practical use.

In the above optical recording medium, recording, erasing and reproduction are performed by causing the laser beam to follow (track) along the groove provided on the substrate and to focus on the recording film (focusing). Therefore, accurate size and shape of the medium, so-called mechanical characteristics are required. Among these mechanical characteristics, especially warpage is tracking,
It is preferable that the medium is not warped as much as possible because it greatly affects focusing. In particular, 3.5-inch magneto-optical recording media are important because they are used in a single plate state and require a low error rate.

However, since the medium is manufactured by providing a recording film, a dielectric film, a metal reflection film, a protective film and the like on the substrate, the warp of the medium is determined as a result of the combined action of the stress of each layer. Therefore, in order to reduce the final warp of the medium, a method of adjusting the warp of the substrate to be used is proposed in JP-A-2-89241 and JP-A-2-232835.

This Japanese Unexamined Patent Publication (Kokai) No. 2-89241 describes a method of forming a surface of a substrate on which a recording film is provided with a concave shape in order to prevent deformation of a film formed by sputtering, particularly a dielectric film, due to compressive stress. Has been done. On the other hand, Japanese Patent Laid-Open No. 2-2328
JP-A-35-35 describes a method in which the surface of the substrate on which the recording film is formed has a convex shape in order to prevent the deformation of the protective layer formed on the sputtering film due to the contracting force.

[0006]

Under these circumstances, a so-called hard coat layer is provided on the surface of the substrate on which the recording film is not formed to harden the surface of the substrate in order to prevent scratches and the like from being formed. It has come to be requested. However, it has become clear that when the hard coat layer is provided, the above-mentioned method cannot sufficiently reduce the warp of the medium.

The present invention solves the above problems and provides an optical recording medium substrate capable of reducing the warp of the medium when used in an optical recording medium having a hard coat layer on the side of the substrate opposite to the recording layer. The purpose is to obtain an optical recording medium with a small warp.

[0008]

In a substrate for an optical recording medium according to the present invention, the substrate material is made of plastic, a recording layer is provided on one side of the substrate, and a hard coat layer is provided on the side of the substrate opposite to the recording layer. In the disk-shaped optical recording medium substrate used for the optical recording medium provided, the substrate surface on the side where the recording layer is provided is a concave shape that is substantially symmetrical with the substrate center as the bottom,
Further, the inclination of the concave surface in the radial direction of the substrate is always a positive value, and the inclination is further increased from the inner circumference to the outer circumference of the substrate. At this time, it is more preferable that the maximum value of the inclination of the concave surface in the radial direction of the substrate is 4 to 10 mrad.

The optical recording medium according to the present invention uses the substrate for optical recording medium according to the present invention, provides a recording layer on the concave surface side of the substrate, and has a hard coat layer on the substrate surface side opposite to the recording layer. In the optical recording medium provided with, the hard coat layer is made of a photocurable or thermosetting organic polymer, and the JIS pencil hardness of the hard coat layer after curing is H.
It is characterized by being B or more.

The characteristics of the present invention have been obtained as a result of the inventors' earnest studies to investigate the cause of the warpage.

That is, it has been found that there are the following two major difficulties in providing the hard coat layer.
(1) Not only the shrinkage rate of the hard coat layer is overwhelmingly larger than the stress of the sputtering film (recording film, dielectric film, metal reflection film) and protective film, which have been conventionally discussed, but (2) the hard coat layer Usually formed by spin coating,
According to this method, a film thickness distribution in the radial direction occurs in which the film thickness increases toward the outer circumference, and the stress also changes accordingly.

There are several types of optical recording media, such as a phase change type, a shape change type such as concavo-convex, and a magneto-optical recording type, depending on the recording method. For this purpose, a groove is provided or a partial unevenness (in the case of the sample servo system) is formed.

Since the hard coat layer having a large shrinkage force at the time of film formation is provided on the surface opposite to the recording surface forming side, in order to reduce the warp of the optical recording medium, the hard coating layer on the side where the recording layer is provided is formed. The substrate surface is a concave shape with the center of the substrate as the bottom and is almost symmetrical to rotate, and the inclination of the concave surface in the radial direction of the substrate is constantly positive, and the inclination increases from the inner circumference to the outer circumference of the substrate. Need to be.

Here, the positive value of the inclination in the radial direction of the substrate as referred to in the present invention means that the substrate surface on the side where the recording layer is provided warps in a concave direction, while conversely. The negative value means that the substrate surface on the side where the recording layer is provided is warped in the convex direction.

When the substrate surface is formed in a concave shape, the inclination of the substrate surface in the radial direction of the substrate is shown in FIG. 3 with the radial measurement position (mm) as the horizontal axis and the substrate inclination (mrad) as the vertical axis. As described above, when the inclination of the substrate continues to increase monotonically (distribution state A), the inclination increases overall but the increase of the inclination is partially leveled (distribution state B), or There is a case where the slope is increased overall but the slope is partially reduced (distribution state C).
In the present invention, the inclination of the concave surface in the radial direction of the substrate increases from the inner circumference to the outer circumference of the substrate when the inclination continues to increase monotonically or when the inclination increases partially. Even if it is crawling, the slope is increasing as a whole, which is also the case (distribution state A and distribution state B in FIG. 3).

Further, it is more preferable that the maximum value of the inclination of the concave surface in the radial direction of the substrate is 4 to 10 mrad. If it is smaller than this, it becomes difficult to reduce the warp of the medium. Conversely, if it is too large, not only the surface wobbling tends to increase during molding of the substrate and the yield decreases, but also the warp of the substrate remains even when it becomes a medium. It is easy to end up.

Further, it is more preferable that the distribution of the substrate inclination in the circumferential direction of the substrate has no variation, that is, the surface deviation of the substrate is as small as possible.

Here, as the plastic used as the material of the substrate for the optical recording medium in the present invention, polycarbonate resin, acrylic resin, epoxy resin, 4-methylpentene resin and their copolymers, amorphous polyolefin resin and the like are used. Among them, polycarbonate resin is preferable in terms of mechanical strength, weather resistance, heat resistance, and moisture permeability.

For molding this substrate, methods such as injection molding, injection compression molding, and extrusion molding can be used, but injection compression molding is preferable in terms of stability of substrate quality and ease of molding. Used.

As the recording layer used in the optical recording medium of the present invention, various recording layers are selected depending on the recording system. For example, a physically uneven medium, Se, Te-based alloy, and in the case of a magneto-optical recording layer, TbFeCo, NdDyFe-based alloy, etc. are used. Further, in order to improve reflectance, durability, light interference characteristics, etc., a metal reflection film, a dielectric film, etc. may be appropriately provided.

On the other hand, the film used for the hard coat layer is required to have a high surface hardness in order to cover the softness of the plastic substrate surface and prevent scratches, and for that purpose, it is required to have JIS pencil hardness HB or more. preferable. Generally, when the cross-linking density of the polymer is increased, the surface hardness increases, but conversely, the shrinkage rate of the film increases and the deformation of the medium also increases. That is, when using a hard coat layer having a high surface hardness, it is necessary to use the substrate of the present invention.

As the hard coat material, a photocurable or thermosetting organic polymer is used. These resins can be selected by adding materials, starting materials, curing conditions, etc.
Any resin may be used as long as the hardness of the finally obtained film is HB or more in JIS pencil hardness, but acrylate, methacrylate, epoxy compound and isocyanate compound are preferably used. Among these, polyfunctional acrylates and methacrylates are particularly preferable. Among these, sulfonate to reduce surface resistance in addition to surface hardness,
You may add amine, surfactant, etc. Further, a crosslinkable oligomer, an allyl resin, a vinyl resin or the like may be added in order to adjust the surface hardness, the viscosity before curing and the like.

The hard coat layer can be formed by a known coating method. Among them, the spin coating method using a spinner is most preferable in practice because the film thickness can be easily controlled.

The film thickness is such that the surface JIS pencil hardness is HB.
The above is selected. If it is too thin, the surface hardness will not be sufficient, and if it is too thick, not only will productivity be poor,
Adhesion with the substrate is adversely affected due to film stress or the like. The optimum film thickness depends on the material, but is generally 0.5 to 50
μm, more preferably 1 to 20 μm.

The present invention will be described below with reference to an embodiment of a magneto-optical disk. The present invention can take many modes and is not limited to the following examples.

[0026]

Examples and Comparative Examples A polycarbonate disc-shaped substrate having a diameter of 90 mm and a thickness of 1.2 mm was molded by injection compression molding. At that time, by changing the mold temperature, the injection speed, and the timing of compression, Examples 1 to 1 shown in FIG.
Substrates having a total of 7 types of inclination distributions in the radial direction of the substrate 4 and Comparative Examples 1 to 3 were obtained.

In other words, in Examples 1 to 3, the value of the inclination of the concave surface in the radial direction of the substrate is always a positive value, and the inclination increases from the inner circumference to the outer circumference of the substrate. A substrate having a maximum inclination value within the range of 4 to 10 mrad was obtained. Further, in Example 4, the value of the inclination of the concave surface in the radial direction of the substrate is always a positive value, and the inclination increases from the inner circumference to the outer circumference of the substrate, but the maximum value of the inclination is Substrates not within the range of 4-10 mrad were obtained.

As Comparative Example 1, a substrate was obtained in which the value of the inclination of the concave surface in the radial direction of the substrate was constantly a negative value, and the inclination decreased further from the inner circumference of the substrate to the outer circumference. . In Comparative Example 2, the value of the inclination of the concave surface in the radial direction of the substrate is constantly positive and the maximum value is 4 to 4.
A substrate was obtained which was within the range of 10 mrad, but whose inclination decreased from the inner circumference to the outer circumference of the substrate. Further, in Comparative Example 3, the value of the inclination of the concave surface in the radial direction of the substrate is always a positive value, and the maximum value thereof is within the range of 4 to 10 mrad, but the inclination goes from the inner circumference to the outer circumference of the substrate. A substrate having an increasing portion and a decreasing portion was obtained.

Here, the horizontal axis of FIG. 1 represents the substrate radial direction measurement position (mm), and the vertical axis represents the substrate radial direction inclination (mrad) at the measurement location. Further, the radial inclination distribution of each substrate was measured at a measurement position selected at a pitch of 5 degrees in the circumferential direction on a circle having a radius of 25 to 40 mm and a pitch of 5 mm. 1 and Table 1 show the maximum value on the same circumference as the inclination of the substrate at each measurement position in the radial direction. For the measurement, an ODA-2A mechanical property measuring device manufactured by Shin Denshi Kogyo Co., Ltd., which can measure mechanical properties such as the inclination of the substrate, was used.

On this substrate, a first dielectric layer made of AlSiN having a thickness of 120 nm, an amorphous alloy film of TbFeCo having a thickness of 20 nm, and a thickness of 35 nm were formed by using a magnetron sputtering method.
A second dielectric layer made of AlSiN and a reflective film layer made of Al having a thickness of 65 nm were formed in this order to form a magneto-optical recording film.

Subsequently, a hard coat layer was applied on the surface of the substrate opposite to the side on which the recording layer was provided by a spin coater and then irradiated with a 3 kW high pressure mercury lamp for 10 seconds to cure the hard coat layer. At this time, the coating liquid for the hard coat layer was 8 wt% 1,6-hexanediol diacrylate, 7 wt% pentaerythritol triacrylate, 10 wt% pentaerythritol tetraacrylate, 42 wt% dipentaerythritol hexaacrylate, A polypentaerythritol polyacrylate of 30 wt% and hydroxycyclohexyl phenyl ketone of 3 wt% was used.

Further, an organic protective layer was formed on the Al film in the same manner as the hard coat layer. However, the irradiation time at this time is
It took 15 seconds. At this time, as the coating liquid for the organic protective layer, urethane diacrylate consisting of polytetramethylene glycol and tolylene diisocyanate is 20 wt%, tetramethylene glycol diacrylate is 20 wt%, hexanediol diacrylate is 25 wt%, and hexylene glycol is used. Diacrylate 25 wt%, trimethylolpropane triacrylate 7 wt% and hydroxycyclohexyl phenyl ketone 3 wt% were used.

The obtained 90 mm magneto-optical medium was placed in a clean oven, heat-treated at 80 ° C. for 8 hours, and then the inclination in the radial direction of the substrate was measured in the same manner as in the case of the above-mentioned measurement of the substrate alone. The measurement results are shown in FIG. 2 and Table 1.

As shown in FIG. 2 and Table 1, Examples 1-3 are shown.
In the case of, the value of the inclination in the radial direction was relatively small, and the amount of change was small and stable, and a medium having excellent mechanical properties was obtained. Further, in Example 4, although not as great as in Examples 1 to 3, the value of the inclination in the radial direction was relatively small and the amount of change thereof was small and stable, and a medium having excellent mechanical properties was obtained.

On the other hand, in Comparative Example 1, the medium was inferior in mechanical properties, that is, the inclination in the radial direction was very large and the amount of change was large. In Comparative Example 2, the gradient in the radial direction was relatively small, but the amount of change was large and the medium had poor mechanical properties. Further, in Comparative Example 3, the medium was inferior in mechanical properties, in which the amount of change increased and decreased although the radial inclination was relatively small.

[0036]

[Table 1]

[0037]

As described above, when the optical recording medium substrate and the optical recording medium of the present invention are used, the optical recording medium is provided with a hard coat layer on the side of the substrate opposite to the recording layer. It has become possible to obtain a substrate for an optical recording medium that can reduce the warp of the medium and an optical recording medium with a small warp.

[Brief description of drawings]

[Figure 1] Substrate tilt distribution

[Fig. 2] Inclination distribution of medium

[Fig. 3] Example of substrate tilt distribution

Claims (3)

[Claims] 1. A disc-shaped light used for an optical recording medium, wherein the substrate material is plastic, and a recording layer is provided on one side of the substrate, and a hard coat layer is provided on the side of the substrate opposite to the recording layer. In the substrate for recording medium, the substrate surface on the side on which the recording layer is provided has a concave shape that is substantially symmetric with the substrate center as the bottom, and the value of the inclination of the concave surface in the radial direction of the substrate is constantly a positive value. A substrate for an optical recording medium, wherein the inclination thereof increases from the inner circumference to the outer circumference of the substrate. 2. The maximum value of the inclination of the concave surface in the radial direction of the substrate is 4 to
The optical recording medium substrate according to claim 1, wherein the substrate has a length of 10 mrad. 3. An optical recording medium substrate according to claim 1, wherein a recording layer is provided on the concave surface side of the substrate, and a hard coat layer is provided on the substrate surface side opposite to the recording layer. In the provided optical recording medium, the hard coat layer is made of a photocurable or thermosetting organic polymer, and the cured hard coat layer has a JIS pencil hardness of HB or more. .