JPH09190647A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence of warpage of a plastic substrate panying change in temp. and humidity environment by providing one side of this plastic substrate with a layer which does not hygroscopically expand, forming this surface as an adhesive surface and affixing the surface to the recording surface side of an optical recording medium. SOLUTION: The surface of an optical transparent substrate 1 is provided with a first inorg. dielectric layer 2 on which a recording layer 3 is formed. Furthermore, on the recording layer 3, a second inorg. dielectric layer 4 and a reflection layer 5 are provided. These films are continuously formed. On the other hand, on the one side of a plastic film to be pasted, a layer 8 which itself does not hygroscopically expand, is previously formed. The plastic film 9 having such layer 8 is pasted onto the org. protective layer 6 in such a manner that the surface of the layer 8 exists on the recording layer 3 side. The layer 8 is preferably a metallic film or inorg. dielectric film.

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 and a magneto-optical disc having a single plate structure.

[0002]

2. Description of the Related Art In recent years, as a recording medium having characteristics such as rewritability, high density, large storage capacity, and non-contact with a recording / reproducing head, magnetization reversal of a magnetic film has been performed by using thermal energy such as semiconductor laser light. A magneto-optical disk that records information by using it and reads it out by utilizing a magneto-optical effect and a phase change disk that utilizes phase change from crystalline to amorphous have been developed and put to practical use.

In the above optical recording medium, the laser light is tracked along a group provided on the substrate and the recording film is focused (focusing).
By doing so, recording, erasing and reproducing are performed. Depending on the medium, there are overwritable magneto-optical recording media and phase change disks.

Therefore, the medium is required to have accurate dimensions and so-called mechanical characteristics. Among these mechanical characteristics, the warp has a great influence on tracking and focusing. Therefore, it is desirable that the medium has no warp or is as small as possible. In particular, a magneto-optical recording medium used in a 3.5-inch single-plate state requires a low error rate, which is an important problem.

Further, in order to further increase the capacity in the future, shortening of the wavelength of laser light, miniaturization of recording marks, and narrowing of tracks are being studied. In this case, crosstalk from adjacent tracks becomes a problem. Since this crosstalk is affected by the warp, it is required that the warp of the medium is smaller.

By the way, a single-plate optical recording medium is generally prepared by providing a recording film, a dielectric film, a metal reflection film, an organic protective film, etc. on a plastic substrate. However, the optical recording medium having such a structure has a difference in moisture permeability between the laser light incident surface side, that is, the substrate side and the film surface side, and the moisture absorption amount in the substrate is constant in the thickness direction as the plastic substrate absorbs moisture or dries. Until the equilibrium is reached, an imbalance of hygroscopic swelling occurs in the substrate, the substrate warps, and an error occurs during signal reproduction.

Therefore, as a method for solving this problem, Japanese Patent Laid-Open No. 59-79445 discloses that a transparent dielectric film for preventing moisture absorption and drying of the substrate is provided on the surface of the substrate opposite to the recording film surface. . However, although this method is effective, it has a drawback that the cost is increased because an extra film forming step of forming a transparent dielectric film on the surface of the substrate opposite to the recording film forming surface is required.

A recording medium is also proposed in which a plastic film having a thickness of 0.1 to 0.2 mm, which causes a warp in the opposite direction to the warp of the substrate, is attached on the organic protective film to cancel the warp of the substrate. (Japanese Patent Laid-Open No. 3-160637).

However, even if an optical recording medium having such a countermeasure is prepared and studied, the laser beam is 680 nm.
With a wavelength shorter than the conventional 780 nm, the track is 1.6 μm.
In the magneto-optical recording medium narrowed from m to 1.1 μm,
When a warp occurs due to the expansion of the plastic substrate due to moisture absorption, there is a problem that the influence of tilt on the crosstalk becomes large and a reproduction error occurs.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an inexpensive optical recording medium having a single plate structure in which warpage is improved even in an environment where a plastic substrate absorbs moisture. is there.

[0011]

In order to achieve the above object, according to the present invention, in an optical recording medium having at least a recording layer and an organic protective layer provided on a plastic substrate, the optical recording medium is provided outside the organic protective layer. A single-plate type optical recording medium is obtained by adhering a plastic film, which is a plastic film having a layer that does not expand due to hygroscopic expansion on one side, so that the layer of material that does not expand due to hygroscopic expansion is on the organic protective layer side. Will be achieved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the optical recording medium of the present invention,
Since a structural symmetry is taken on both sides of the organic protective layer or the adhesive layer as a center, the warpage of the plastic substrate is canceled. Specifically, the plastic substrate corresponds to the plastic film, and the layers made of the inorganic material such as the first and second inorganic dielectric layers, the recording layer, and the reflective layer correspond to the layers that do not swell due to moisture absorption.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view showing an example of the structure of the optical recording medium of the present invention. In the figure, 1 indicates an optically transparent substrate made of plastic. A first inorganic dielectric layer 2 made of an inorganic dielectric material such as SiN _x is provided on the substrate 1 to obtain an interference effect and a corrosion prevention effect. Further, an amorphous magnetic layer which is the recording layer 3 is formed thereon. Furthermore, a second inorganic dielectric layer 4 and the reflective layer 5 of metal is an inorganic dielectric layer such as SiN _X is provided to produce an interference effect and to prevent corrosion of the magnetic layer. These films are continuously formed without breaking the vacuum. afterwards,
An organic protective layer 6 such as an ultraviolet curable resin is formed. On the other hand, the plastic film to be pasted has a layer 8 which is not swelling due to its own hygroscopic expansion on one side. The layer 8 that does not expand due to moisture absorption is made of a metal film or an inorganic dielectric film. This is convenient for implementing the present invention. The plastic film 9 on which the layer 8 that does not absorb and swell due to moisture is formed on the organic protective layer 6 with the surface of the layer 8 facing the recording layer 3 via the adhesive layer 7 such as a hot melt adhesive. .

As the material of the plastic substrate 1, polycarbonate, PMMA or the like known in this field can be used. The thickness of the substrate is preferably about 1.2 mm in consideration of compatibility with a popular CD-ROM and compatibility with a 3.5-inch magneto-optical disk which is becoming popular. When the substrate thickness is thin, the influence of tilt on crosstalk is small, but it is not possible to make it too thin because there is a concern that molding will be difficult and mechanical characteristics such as surface wobbling will deteriorate and tracking will affect servos. The optimum substrate thickness may be selected according to the usage conditions.

The first and second inorganic dielectric layers are provided for the purpose of improving corrosion resistance and optical characteristics by multiple reflection. The material is SiN, SiO, S
iC, SiAlON, ZnS.SiO ₂ or the like is used.

As the recording layer 3, a rare earth-transition metal amorphous magnetic layer or a phase change material typified by a chalcogen compound is used. As a magnetic material for the rare earth-transition metal amorphous magnetic layer, an alloy of a rare earth element such as Gd, Tb, Dy, and Nd and an iron group transition metal such as Fe and Co is used. For example, Tb-Fe, Tb-Fe-Co, D
They are yFeCo and TbDyFeCo. Alternatively, a laminated film of these materials may be used. The present invention can be carried out with or without those magnetic layers being exchange-coupled with each other. Further, elements such as Cr, Ti and Ta may be added to improve the corrosion resistance. As a material for the chalcogen compound, a chalcogenide compound made of an alloy such as Te, Se, Ge, Sb is used. For example, SbTe, Ge
SbTe and SbSe. Pd, Nb, and Pt may be added so that they can be repeatedly rewritten many times.

Further, the reflection layer 5 is provided to adjust the Kerr effect increase, the phase difference, the light absorptance difference, etc. by reflecting the laser light transmitted through the recording layer and each dielectric layer. For this reason, metals such as Al, Cu, Ag and alloys to which additional elements are added are usually used.

A metal film or an inorganic dielectric film is particularly preferably used in the present invention as a material of the layer 8 which does not expand due to moisture absorption. Particularly, the metal film is preferable because it does not swell because it does not absorb moisture. Materials used for the metal film include Al, Cr, T
Metals having corrosion resistance, such as i, Ni, and Ta, are preferable. Other elements may be added to these as an alloy. As a forming method, a means such as sputtering or vapor deposition is used. The film thickness to be formed is preferably substantially equal to the total film thickness of the first and second inorganic dielectric layers, the recording layer and the reflective layer, but the amount of warpage caused by the plastic substrate 1 is substantially adjusted. It can be appropriately decided depending on how much the cancellation is made.
The material of the inorganic dielectric film used here is Si
Materials such as N, SiO, SiO ₂ and Ta ₂ O _{5 which} are stable against moisture are used. The forming method is sputtering or vapor deposition. The film thickness has already been described for the metal film. The layer that does not expand due to moisture absorption is not limited to a single layer film of an inorganic dielectric film or a metal film, and may be a laminated film of these.

Polycarbonate, polymethylmethacrylate, epoxy resin, amorphous polyolefin, polyethylene and the like are used as the material of the plastic film. A material having low moisture permeability is preferable.

As the material for the adhesive layer 7, various adhesives can be used, but a hot melt type adhesive is preferably used.

Details will be described below with reference to examples.

[0023]

【Example】

Example 1 On a polycarbonate substrate with a pre-group of φ86 mm having a thickness of 1.2 mm, a magnetron sputtering device was used to record SiN of 100 nm as a first inorganic dielectric layer in order to obtain an antioxidant effect and an interference effect. T as a layer
28 nm of amorphous magnetic layer made of bFeCo, then 30 nm of SiN as the second inorganic dielectric layer and 50 nm of AlCr film as the reflection layer in order to enhance oxidation prevention and interference effect, successively without breaking vacuum, After that, 10 μm of UV curable resin is formed on the film surface as the organic protective layer 6.
m coated. Then, a 0.2 mm thick polycarbonate film having an AlCr film of 200 nm formed on one side as a layer 8 which does not expand due to moisture absorption is formed by a hot-melt type adhesive.
The optical recording medium of the present invention was obtained by bonding the 1Cr film side to the magneto-optical disk as an adhesive surface.

When the magneto-optical disk thus obtained was put into an environment of normal temperature and normal humidity of 30 ° C. and 90% RH, the maximum amount of warpage was 1.5 mrad.

Comparative Example 1 As shown in FIG. 2, a magneto-optical disk similar to that of Example 1 was prepared except that the plastic film was not provided with a layer that did not expand due to moisture absorption. This recording medium was placed in the same environment as in Example 1. The maximum amount of warp at this time is 2.5 mrad
Met.

Comparative Example 2 A magneto-optical disk similar to that of Example 1 was prepared except that a plastic film was not attached as shown in FIG. This recording medium was placed in the same environment as in Example 1. The maximum amount of warp at this time was 4 mrad.

Example 2 A magneto-optical disk similar to that of Example 1 was prepared except that a Cr layer having a thickness of 100 nm was formed in place of the AlCr layer, which was a layer which did not expand due to moisture absorption of the plastic film of Example 1.

When the magneto-optical disk thus obtained was put into an environment of normal temperature and normal humidity of 30 ° C. and 90% RH, the maximum amount of warpage was 1.7 mrad.

Example 3 SiO was used as a non-hygroscopic layer of a plastic film.
A magneto-optical disk similar to that in Example 1 was prepared except that the layers were formed to 100 nm as in Example 1.

When the magneto-optical disk thus obtained was put into an environment of normal temperature and normal humidity from 30 ° C. and 90% RH, the maximum amount of warpage was 1.8 mrad.

Example 4 A first inorganic dielectric layer 2 was formed as a first inorganic dielectric layer 2 on a polycarbonate substrate having a pre-group of φ86 mm having a thickness of 1.2 mm by using an RF magnetron sputtering device in order to obtain oxidation prevention and interference effect. 170n ZnS / SiO ₂
m, a chalcogen recording layer made of PdGeSbTe as the recording layer 25 nm, then ZnS.SiO ₂ as the second inorganic dielectric layer 4 25 nm, and an AlCr film 5 130 nm as the reflective layer 5 in order to enhance the oxidation prevention and interference effect. The film was continuously formed without breaking the vacuum, and then the film surface was coated with an ultraviolet curable resin as an organic protective layer 10 to a thickness of 10 μm. Then, a 0.2 mm thick polycarbonate film having an AlCr film of 200 nm formed as a layer 8 which does not absorb and expand on one side is bonded to the magneto-optical disk by using a hot-melt type adhesive with the AlCr film side as an adhesive surface. An optical recording medium was obtained.

The maximum value of the amount of warp when the magneto-optical disk thus obtained was put in an environment of normal temperature and normal humidity from 30 ° C. and 90% RH was 1.5 mrad.

[0033]

As described in detail above, according to the present invention, a layer which does not swell due to hygroscopicity is provided on one side of a plastic film, for example, and this surface is used as an adhesive surface to adhere to the recording surface side of an optical recording medium. It was possible to reduce the occurrence of warpage due to changes in the temperature and humidity environment of the plastic substrate.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an optical recording medium of the present invention.

FIG. 2 is a schematic diagram showing an example of a conventional optical recording medium.

FIG. 3 is a schematic diagram showing an example of another conventional optical recording medium.

[Explanation of symbols]

 1 Plastic Substrate 2 First Inorganic Dielectric Layer 3 Recording Layer 4 Second Inorganic Dielectric Layer 5 Reflective Layer 6 Organic Protective Layer 7 Adhesive Layer 8 Non-Hygroscopic Expansion Layer 9 Plastic Film

Claims (3)

[Claims] 1. An optical recording medium comprising a plastic substrate and at least a recording layer and an organic protective layer provided on the outer side of the organic protective layer. A single-plate type optical recording medium, characterized in that the above plastic film is adhered so that the layer of the material that does not expand due to moisture absorption is on the organic protective layer side. 2. The layer formed of a material that does not expand due to moisture absorption is a metal film or an inorganic dielectric film.
An optical recording medium according to claim 1. 3. The plastic film is made of polycarbonate, and the layer made of a material that does not swell due to moisture absorption is AlC.
The optical recording medium according to claim 1, which is made of any one of r, Cr, and SiO.