JPH02199646A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain high corrosion resistance and high repetitive characteristics by providing a polyurethane resin layer contg. a plasticizer via an intermediate layer made of a polyurethane resin consisting of polytetramethylene ether glycol and polyisocyanate on a recording layer. CONSTITUTION:The polyurethane resin layer contg. the plasticizer is provided via the intermediate layer consisting of the polyurethane resin made of the polytetramethylene ether glycol and polyisocyanate on the recording layer. Since the intermediate layer which does not contain the plasticizer is interposed, the possibility of the direct contact of the plasticizer-contg. polyurethane resin of an adhesive layer or org. protective layer with a substrate to cause reaction is eliminated. The magneto-optical recording medium having the excellent corrosion resistance and repetitive recording characteristics is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magneto-optical recording medium, and particularly to a magneto-optical recording medium used for optical recording.

[Prior Art] Among optical memory devices, magneto-optical recording is at the closest stage to practical use for erasable memory, which allows additional recording and erasing. At present, rare earth/transition metal thin films are often used as the recording layer of magneto-optical recording media in view of their overall characteristics.

Since such recording layers are generally very susceptible to oxidation,
A protective layer made of metal oxide, metal nitride, etc. is provided on the recording layer. Furthermore, it is common to apply a resin coating as a protective layer in the case of a single-panel specification, and as an adhesive layer that also serves as a protective layer in the case of a double-sided lamination specification. The resin used for the organic protective layer and adhesive layer made of this resin coat must have low moisture permeability and low stress.

Polyurethane resin containing a plasticizer is an excellent resin that satisfies the characteristics of low moisture permeability and low stress.
The 100% tensile stress specified in 301 is 3 K g f
/ cm', and the moisture permeability at 25°C specified by JIS ZO208 was 5 g/m'' in 24 hours for a 200 μm thick film. Medium: 80°C, 85%
A 2000 hour accelerated test of RH showed almost no increase in error rate.

[Problems to be Solved by the Invention] However, the above-mentioned polyurethane resin containing a plasticizer has a drawback that it has a slight reactivity with the resin of the substrate when it is in contact with a resin substrate at high temperature.

In order to repeatedly erase and record, which is a feature of magneto-optical recording, the recording layer is repeatedly heated to a temperature close to the Curie point, that is, several hundred degrees Celsius, and then cooled. Therefore, even if the reactivity is slight, if the resin that is in direct contact with the substrate through the pinhole in the recording layer has reactivity toward the substrate, this resin will react with the substrate, causing the substrate to physically cause a chemical or chemical change, resulting in
A reduction in reflectance occurs over a wide area.

This phenomenon occurs when recording and erasing are performed on the same track.
Although this phenomenon only occurs after 105 repetitions, it becomes a big problem in terms of high reliability of the medium.

The detailed process of the reaction that causes this phenomenon has not been clarified, but since this phenomenon does not occur if no plasticizer is added to the resin, it is likely that the plasticizer is involved in some way. it is conceivable that. However, polyurethane resins to which no plasticizer is added have a high viscosity and are difficult to handle in the coating and laminating steps, so it is not practical to exclude the plasticizer.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide a magneto-optical recording medium that prevents reaction between a polyurethane resin layer containing a plasticizer and a substrate when the resin layer is provided.

[Means for Solving the Problems] The magneto-optical recording medium of the present invention includes a magneto-optical recording layer provided on a resin substrate, and an intermediate layer of polyurethane resin made of polytetramethylene ether glycol and polyisocyanate on the recording layer. A polyurethane resin layer containing a plasticizer is provided through the polyurethane resin layer.

That is, as a result of intensive studies aimed at providing a magneto-optical recording medium that overcomes the above-mentioned drawbacks, the present inventors have created an intermediate layer of polyurethane resin consisting of polytetramethylene ether glycol and polyisocyanate between the medium and the polyurethane resin layer. The present inventors have discovered that a magneto-optical recording medium having both high corrosion resistance and high repeatability can be obtained by providing the above, and have completed the present invention.

The present invention will be explained in detail below.

Note that in this specification, when the surface of a single plate of a recording medium having a recording layer is coated with polyurethane containing a plasticizer,
The polyurethane layer is called an organic protective layer, and when two recording media are placed facing each other and bonded together with a polyurethane layer, the polyurethane layer is called an adhesive layer.

First, examples of the substrate used in the present invention include resin substrates such as polycarbonate resin, acrylic resin, and polyolefin resin. The thickness of this board is 1-2mm
The degree is common.

Examples of the magneto-optical recording layer formed on such a resin substrate include TbFe and TbFeCo.

Amorphous magnetic alloys of rare earth elements and transition metals such as TbCo and DyFeCo, MnB1. A polycrystalline perpendicular magnetization film such as MnCuB1 is used. A single layer may be used as the magneto-optical recording layer, or a GdTbFe/TbFe layer may be used.
Two or more recording layers may be stacked and used as shown in FIG.

An interference layer can also be provided between the substrate and the magneto-optical recording layer. This layer reduces noise by lowering the reflectance due to the light interference effect of a transparent film with a high refractive index.
This is to improve the /N ratio. The interference layer may be a single layer film or a multilayer film. Metal oxides and metal nitrides are used as materials for forming the interference layer.

The metal oxides are AA20S and Ta205.

Examples include metal oxides such as SiO2, Sin, and TiO2 alone or mixtures thereof, and composite oxides such as AfL-Ta-0. Furthermore, these oxides contain other elements such as Ti, Zr, W, and Mo.

The interference layer made of these metal oxides is dense and prevents moisture and oxygen from entering from the outside. It can prevent intrusion, has high corrosion resistance, has low reactivity with the reflective layer described below, and has excellent adhesion to the resin constituting the substrate.

Examples of metal nitrides include silicon nitride and aluminum nitride. Among these metal nitrides, it is preferable to use silicon nitride because it is particularly dense and has an excellent effect of preventing moisture and oxygen from entering from the outside.

The optimal thickness of the interference layer made of such a metal oxide or metal nitride varies depending on its refractive index, but it is usually 4.
It is appropriate to set it to about 00 to 1500A, especially about 500 to 100OA.

It is desirable to provide a protective layer made of a telephone body made of the same material as the interference layer on the side of the recording layer opposite to the interference layer.The thickness of this protective layer is usually about 500 to 1500A. .

In addition, in the case of a medium having a structure in which a reflective layer is provided, a layer of a highly reflective metal (for example, AJ2.Cu, etc.) or an alloy thereof is placed in contact with the recording layer or through several hundred dielectric layers. It is also possible to further provide a dielectric layer on the 0-reflection layer provided as a 0-reflection layer.

In the present invention, an intermediate layer of polyurethane resin made of polytetramethylene ether glycol and polyisocyanate is provided on the above-mentioned recording layer, or further on top of the protective layer, reflective layer, or dielectric layer when the protective layer, reflective layer, or dielectric layer is provided. Furthermore, an adhesive layer or an organic protective layer consisting of a polyurethane layer containing a plasticizer is provided.

The polytetramethylene ether glycol that forms the polyurethane resin consisting of polytetramethylene ether glycol and polyisocyanate in the intermediate layer is as follows:
A linear polyether glycol having primary hydroxyl groups represented by the formula at both ends is used.

HO−+−CH2CH2CH2CH20←−H in the formula, n
indicates the degree of polymerization, and the average degree of polymerization is usually 5 to 40,
The average molecular weight is preferably in the range of 5 to 20, and the average molecular weight is preferably in the range of 500 to 3,000, preferably 500 to 1,500. Examples of polyisocyanates include tetramethylene diisocyanate, hexamethylene diisocyanate, ethylene diisocyanate, phenylene diisocyanate, tolylene diisocyanate, diphenylene diisocyanate, 1,5-naphthalene diisocyanate, dicyclohexylmethane diisocyanate)-, 1,4-isopropylbenzene. Examples include diisocyanate and 1,3,6-hexane triisocyanate, and these compounds may be used singly or in combination.
More than one species is used as a mixture.

The polyurethane resin used for the intermediate layer is a blend of the polytetramethylene ether glycol and polyisocyanate such that N COlo H = 0.8 to 1.3, preferably NC010 H = 0.9 to 1.1. Preferably, the polymerization reaction method is one in which the components are mixed at the same ratio and then cured by polymerization reaction. Either a one-shot method or a prepolymer method can be adopted as the polymerization reaction method. In particular, considering workability and safety, it is preferable to use the above polyisocyanate compound in the form of a prepolymer which has been reacted with a part of polytetramethylene ether glycol in advance. The hardness and elasticity after curing can also be adjusted by using them together.

The polyurethane resin used for the intermediate layer has an appropriate viscosity when both of the above components are mixed, and can be easily coated onto the recording layer of the resin substrate by a normal coating method such as a spin code method. It can be membraned. Even if the polyurethane resin comes into direct contact with the substrate through a pinhole in the recording layer, since no plasticizer is added to the polyurethane resin, there is no risk of reaction with the substrate and deterioration of the magneto-optical recording medium.

The thickness of this intermediate layer is preferably about 1 to 20 μm, more preferably about 3 to 10 μm. If the intermediate layer is too thick, stress may be applied to the medium and cranking may occur; if it is too thin, the effectiveness of blocking the polyurethane resin of the adhesive layer or organic protective layer from the substrate is reduced.

The polyurethane resin used as the adhesive layer or the organic protective layer contains a hydrocarbon polyol as the main component and an isocyanate compound as N COlo H = 0.8 to 1.3.
, preferably mixed at a distribution ratio of NC010H-0.9 to 1.1, and then cured.

The hydrocarbon polyol used here can be prepared by a known method.
For example, it is easily produced by a method such as hydrogenating a butadiene polymer described in JP-A-50-90894. Moreover, polyurethane using this can be easily produced by a known method, for example, the method described in JP-A-50-142895, in which the above-mentioned polyol is reacted with a polyisocyanate.

The adhesive layer or organic protective layer has a 100% tensile stress of 50 K g f /
cm' or less and the moisture permeability specified by JIS ZO208 is 20 g/m'' or less in 24 hours, preferably 100% tensile stress of 30 K g f / c as specified above.
rn' or less and the moisture permeability specified above is 10 in 24 hours.
Although an organic content of less than g/m'' gives good results, the above-mentioned polyurethane resin satisfies this tensile stress and moisture permeability.

A plasticizer is added to the adhesive or the polyurethane resin of the organic protective layer in order to improve handling properties in the coating process and the like. Examples of the plasticizer include paraffinic process oil, diundecyl phthalate, alkylbenzene, etc., and these plasticizers are usually used in an amount of about 10 to 70% by weight relative to the polyurethane resin.

The thickness of the adhesive layer or organic protective layer made of such a polyurethane resin containing a plasticizer is preferably about 14 m to 200 m, more preferably about 3 m to 100 m.

In the present invention, methods for forming each layer such as the interference layer, recording layer, reflective layer, and protective layer on the substrate include physical vapor deposition (PvD) such as sputtering, and chemical vapor deposition (CvD) such as plasma CVD. ) etc. are commonly used. Furthermore, a method using ion blating is also considered.

To form interference layers, magneto-optical recording layers, reflective layers, protective layers, etc. using the PVD method, each layer is deposited on a substrate by electron beam evaporation or sputtering using a target with a predetermined composition. is the usual method.

If the film deposition rate is too fast, it will increase the film stress, and if it is too slow, the productivity will decrease, so it is usually set at 0. 1~100A
/sec.

The intermediate layer of polyurethane resin and the adhesive layer (or organic protective layer) made of polyurethane resin containing a plasticizer can be easily formed by a spin-coating method or other conventional coating methods.

[Function] When the intermediate layer according to the present invention is not provided, the polyurethane resin (plasticizer in the resin) constituting the adhesive layer or organic protective layer may come into direct contact with the substrate through the pinhole in the recording layer and cause a reaction. However, by interposing the intermediate layer, there is no possibility that the polyurethane resin containing a plasticizer in the adhesive layer or the organic protective layer will come into direct contact with the substrate.

However, since the polyurethane resin composed of polytetramethylene ether glycol and polyisocyanate that constitutes the intermediate layer has a moderate viscosity, it can be easily formed into a film by a normal method without using a plasticizer. Since it does not contain , it does not react with the substrate and deteriorate the magneto-optical recording medium even if it is directly bonded to the substrate through the holes in the recording layer.

[Examples] The present invention will be explained below in more detail by giving production examples, working examples, and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. .

First, a method for producing the polyurethane resin for forming the intermediate layer and the polyurethane resin for forming the adhesive layer used in the Examples is shown in Production Example 1 and Production Example 2 below.

Production Example 1 Production of polyurethane resin for forming intermediate layer - A two-component mixed polyurethane resin obtained from components A and B was produced according to the following procedures.

■ Manufacture of liquid A “Polytetramethylene ether glycol” (manufactured by Mitsubishi Kasei Corporation. Average molecular weight: 650, hydroxyl equivalent:: 2.9)
7 meq/g) and 68 g of 2.4-)-lylene diisocyanate were mixed and reacted at 80° C. for 5 hours to obtain Solution A.

The viscosity of liquid A was 12000 cp/25°C.

■ Production of liquid B 91 g of polytetramethylene ether glycol and 9 g of “Abcafuodrol” (trade name) (manufactured by Asahi Denka ■. Tetrafunctional polyol: hydroxyl group equivalent: 13.5 meq/g)
were mixed uniformly at 50°C to obtain Solution B. The viscosity of liquid B was 400 cp/25°C.

■ The weight ratio of liquid A and liquid B prepared in ■ and ■ above is 2.
: Mixed at 1.

Production Example 2 Production of polyurethane resin for adhesive layer formation: A two-component hot-melt type polyurethane resin obtained from components C and D was produced according to the following procedures.

■ Production of liquid C "Polytail HA" (trade name) (manufactured by Mitsubishi Kasei ■) Number average molecular weight: approximately 2000, hydroxyl equivalent: 0.907me
q/g of polyolefin polyol) 100 g and "Abcafuodrol" (trade name) (manufactured by Asahi Denka ■. Tetrafunctional polyol: hydroxyl group equivalent; 13.7 meq/g) 1
9.8g, 1 tag of “paraffinic process oil” (plasticizer) (manufactured by Kyodo Oil Co., Ltd. P-200), and “
"Tin-based urethanization catalyst" (manufactured by MD Kasei Co., Ltd. UL-2
2) and 138 mg were uniformly mixed at 50°C to obtain liquid C. The viscosity of liquid C was 1800 cps at 25°C.

■ Production of Liquid D 100 g of "Polytail HA" and 116 g of 'paraffinic process oil P-200' (plasticizer) were mixed uniformly at room temperature in a separable flask.
．． Add 14.2 g of 4-tolylene diisocyanate,
The reaction was carried out at 80° C. for 6 hours to obtain Solution D. The viscosity of liquid D is 25
The temperature was 3800 cps.

■ The weight ratio of liquid C and liquid D prepared in the above ■ and ■ is 1.
: Mixed at 5.

Example 1 A polycarbonate substrate with a diameter of 130 mm was introduced into a sputtering apparatus, and the temperature was first evacuated to below 8xlO''''torr. Ar was introduced for 20 sec, O2 was introduced for 5 sec, and the pressure was adjusted to 0.8 Pa. 500 in this condition
A tantalum oxide interference layer having a thickness of 80 OA was formed at a rate of 4 A/sec by direct current sputtering using a 4-inch diameter Ta target with a power of W. Then, Tb target and F
Simultaneous sputtering of e9°CO+o is performed, and Tb2s (Feeoc O+o
) 77 recording layers were formed to a thickness of 30 OA. Furthermore,
Sputtering was performed in Ar gas using an AJ2 target equipped with Ta chips to form a 300 mm thick reflective layer made of an alloy of A It 97T a 3 on the recording layer. On this reflective layer, a protective layer of tantalum oxide was further formed to a thickness of 30 OA using the same method as for the interference layer.

Thereafter, the substrate was taken out from the sputtering apparatus, and a polyurethane resin made of polytetramethylene ether glycol and polyisocyanate obtained in Production Example 1 was applied by a spin cord method to form an intermediate layer. That is, the A liquid and the B liquid of Production Example 1 were mixed at a weight ratio of 2:1, vacuum defoamed, and then heated at 500 rpm using a spin coater.
After coating at m/2 seconds, sputtering at 5000 rpm/60 seconds to coat, and curing at 80° C. for 60 minutes to form an intermediate layer.

Similarly, another medium was produced in which an interference layer, a recording layer, a reaction layer, a protective layer, and an intermediate layer were sequentially formed on a substrate.

Next, using the polyurethane resin obtained in Production Example 2 as an adhesive layer, the two produced media were bonded together facing each other.

That is, liquid C and liquid D of Production Example 2 were mixed at a weight ratio of 1:5,
After vacuum defoaming, it was applied to one of the media, the two media were bonded facing each other, and the mixture was cured at 80° C. for 60 minutes to form an adhesive layer.

When the thus obtained magneto-optical recording medium was repeatedly written and erased 108 times with a power of 8 mW, no change in reflectance was observed. There was no change at all in the area where the pinhole existed in the recording layer.

This disc was heated for 1000 cycles at 80℃ and 85%RH.
When an accelerated time test was performed, almost no deterioration was observed.

Comparative Example 1 A magneto-optical recording medium was produced in the same manner as in Example 1 except that no intermediate layer was formed. When the obtained magneto-optical recording medium was repeatedly written and erased 106 times at 8 mW,
The reflectance of the area where the pinhole exists in the recording layer decreases,
The area where the reflectance had decreased gradually expanded,
After 106 times, the reflectance decreased over a large area.

As a result of analyzing this abnormal area, there was no abnormality in the membrane, but
A recess was formed on the board.

[Effects of the Invention] As detailed above, the magneto-optical recording medium of the present invention has no possibility of direct contact and reaction between the organic image layer II or adhesive layer made of polyurethane resin containing a plasticizer and the resin substrate. ,
It is a magneto-optical recording medium in which the substrate is well protected without deteriorating over a long period of time, and has excellent corrosion resistance and repeated recording characteristics.

Agent: Patent attorney Tsuyoshi Shigeno

Claims (1)

[Claims] (1) A magneto-optical recording layer is provided on a resin substrate, and an intermediate layer of polyurethane resin made of polytetramethylene ether glycol and polyisocyanate is interposed on the recording layer.
A magneto-optical recording medium characterized by being provided with a polyurethane resin layer containing a plasticizer.