JPH02236836A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To allow the use of the recording medium in the form of a veneer even under the conditions of a high temp. and high humidity by forming a protective layer on a recording film or reflecting layer of a 3-layered structure consisting of an over coating layer, adhesive layer and hard coating layer consisting of UV curing resins which are respectively different in properties. CONSTITUTION:The protective layer consisting of the 3-layered structure consisting of the over coating layer 4, adhesive layer 5 and hard coating layer 6 consisting of the UV curing resins is formed on the magneto-optical recording layer 2 or the reflecting layer 3. The resins which are respectively different in properties are used for the respective layers. The layer 4 is formed by spin coating of the UV curing resin of a urethane system having excellent environmental resistance and the layer 5 by spin coating of the UV adhesive agent of an epoxy acrylate system and curing the same to improve the adhesive property of the layer 6. The layer 6 is formed by spin coating of a UV hard coating layer of a multifunctional acrylate system to have the good adhesive property without repelling. The use of the recording medium in the form of the veneer even under the conditions of the high temp. and high humidity is possible in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording medium on which recording, reproduction and erasing can be performed using a light beam. More specifically, the present invention relates to a protective film for a magneto-optical recording medium.

(Prior art) Conventionally, there is a magneto-optical recording medium used in erasable and rewritable high-density memory, which is recorded by heating with light irradiation and can be read using magnetic effects such as the magnetic Kerr effect and Faraday effect. .

The recording film of the magneto-optical recording medium contains Gd, Tb,
Amorphous thin films made of Fe and Co are excellent in film formability when producing large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small energy, and high efficiency in writing written signals. It is ideal as a magneto-optical recording medium because it has a high readout efficiency with a good S/N ratio, a large Kerr rotation angle, and a Curie point of around 1506C.

However, generally Gd, Tb, Fe,
A magneto-optical recording layer made of Go or the like has a drawback of poor corrosion resistance. That is, when it comes into contact with air or water vapor, it is oxidized and its magnetic properties deteriorate, eventually becoming completely oxidized and becoming transparent. This phenomenon is further accelerated under high temperature and high humidity environmental conditions.

Conventionally, in order to prevent oxidation of the recording film, SiO 2 , Si0
2, Si3N4, AI203, and other inorganic protective Jtt' recording films have been proposed and implemented, but sufficient antioxidation effects have not been obtained, and furthermore, C
A method of sealing with a double anti-oxidation film has been proposed, such as coating a protective film in a vacuum system with a metal such as r, Ti, Au, Hf, or AI by vapor deposition or sputtering. However, since sufficient antioxidant effects cannot be obtained, there is a method of further protecting the recording layer with moisture-proofing halogenated organic resins, ultraviolet-curable acrylate resins, thermosetting Evoki resins, and hot-melt resins. Unexamined Japanese Patent Publication 1986-68
750. 61-139961. 62-
167635.

(Problem to be Solved by the Invention) However, in a magneto-optical recording medium in which a protective layer made of an ultraviolet curable resin is provided on a magneto-optical recording layer, high temperature and high humidity (85°C, 85% relative humidity) Under harsh environmental conditions, an ultraviolet curable resin is required that does not cause cracks or holes in the recording layer, natural peeling of the protective layer, or deformation of the substrate. For example, a viscosity of 300 to 700 cps/
The present inventors previously proposed that urethane acrylate at 25°C is optimal for the protective layer (overcoat layer) (Japanese Patent Application No. 63-230882).

This overcoat layer has poor surface hardness and is easily scratched when rubbed with steel wool, so it could not be used as a single plate as it is, and a dummy plate was attached to it via an adhesive layer.

An object of the present invention is to provide a magneto-optical recording medium that does not lose its reliability even under high temperature and high humidity conditions and can be used as a single plate.

(Means for Solving the Problems) The magneto-optical recording medium of the present invention is a magneto-optical recording medium having a recording layer on one side, and a protective layer of an ultraviolet curing resin is provided on the recording film or reflective film. It consists of a three-layer structure of ultraviolet curing resins with different properties, and is characterized in that an overcoat layer, an adhesive layer, and a hard coat layer are sequentially laminated on a recording film or a reflective film.

(Operations and Examples) Examples of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view of a magneto-optical recording medium in which a single-sided dummy plate is bonded together according to the prior art.
FIG. 2 is a schematic cross-sectional view of the magneto-optical recording medium of the present invention which can be used as a single-sided single plate.

When the magneto-optical recording medium is a magneto-optical disk, the substrate 1 is made of glass or plastic such as polymethyl methacrylate, polycarbonate, polyolefin, etc., and has, for example, a guide groove (with an outer diameter of 130 m/mΦ and a thickness of 1.20 m/m).
The recording layer 2 is formed by magnetron sputtering on the surface of the substrate group.
800 N4 layers, 1000 Gd, Tb, Fe, Co magnetic recording layers, and 800 Si3N4 layers are laminated in this order. This disk substrate was used as a sample for the protective coat of the present invention.

The protective coat of the present invention has a three-layer structure including a protective layer made of ultraviolet curable resins having different properties on the magneto-optical recording layer 2 or the reflective layer 3, including an overcoat layer 4, an adhesive layer 5
, a hard coat layer 6. In other words, the overcoat layer 4 protects the magneto-optical disk from high temperatures and high humidity (
(85°C, 85% relative humidity) for extended periods of time (10
00 hours) A protective layer that does not generate cracks or holes in the recording layer and does not cause deformation such as warping or surface wobbling on the substrate even if left as it is, and has a viscosity of, for example, 300 to 700 cps.
/ It is preferable to use a urethane acrylate-based ultraviolet curable resin that does not contain a solvent at 25°C. If the hard coat layer 6 is directly provided without providing the overcoat layer 4, high temperature
If left for a long time under high-temperature environmental conditions, cracks and holes may occur in the recording film, and the hard coat film 6 may naturally peel off from the recording layer 2, which is undesirable.

In many cases, when the hard coat film 6 is coated on the recording film 2, the hard coat agent cannot be applied by repelling. Even when the UV hard coating agent is spin-coated directly onto the UV (ultraviolet) overcoat layer 4, it cannot be applied by repelling. Moreover, even if it can be applied, the adhesion is poor and the hard coat film 6 may spontaneously peel off under high temperature and high humidity environmental conditions. UV
Epoxy acrylate U on overcoat layer 4
By spin-coating the V-adhesive to form the adhesive layer 5, irradiating it with UV light, and curing the adhesive layer 5, spin-coating a polyfunctional acrylate-based UV hard coat agent will result in a UV hard coat with good adhesion and no repelling. Layer 6 is obtained. The thickness of each layer is preferably 410-2011 for the overcoat layer, 520-40l1 for the adhesive layer, and 65-10μ for the hard coat layer.

(Effect of the invention) A UV overcoat layer on the magneto-optical recording film or the reflective film,
The magneto-optical recording medium of the present invention, which is formed by sequentially applying a UV adhesive layer and a UV hard coat layer, does not cause any damage to the recording layer side even if it is used as a single plate, and can withstand high temperatures and high humidity (85°C, Even when left for a long time (1000 hours) under environmental conditions (85% relative humidity), the plastic substrate does not deform, and the recording layer does not develop cracks or pinholes. Furthermore, since no dummy plates are pasted together, manufacturing costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a conventional single-sided dummy plate bonded type magneto-optical recording medium. FIG. 2 is a schematic cross-sectional view of a single-sided (single-plate) type magneto-optical recording medium of the present invention. (Explanation of symbols) 1. ...... Substrate 2. ...... Magneto-optical recording layer 3.・・・・・・
... Reflective layer 4.・・・・・・・・・ Over coat｝Protective layer 5.
・・・・・・Adhesive layer 6.・・・・・・・・・ Hard coat (surface hardening)
Layer 7.・・・・・・・・・ Dummy board

Claims (2)

[Claims] (1) In a magneto-optical recording medium that has a recording layer on one side and has a protective layer of UV-curable resin on the recording film or reflective film, the protective layer must have a three-layer structure of UV-curable resins with different properties. A magneto-optical recording medium characterized by: (2) The three-layer structure of the ultraviolet curable resin of the protective layer is formed by sequentially laminating an overcoat layer, an adhesive layer, and a hard coat layer on a recording film or a reflective film. The magneto-optical recording medium described in .