JPH0432052A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the warpage of a substrate by providing a thin film consisting of the same material as the material of a dielectric layer on the surface of a synthetic resin substrate having a silicon dioxide film over the entire surface on the side opposite from the groove surface thereof. CONSTITUTION:The 1st dielectric layer consisting of an inorg. material, a recording layer, the 2nd dielectric layer consisting of an inorg. material, and a UV curing resin layer are laminated in this order on the groove surface of the synthetic resin substrate and the thin film of the inorg. material of the same material as the material of the 2nd dielectric layer is provided on the other surface. The synthetic resin substrate coated with the silicon dioxide film over the entire surface is used in such a manner and the thin film consisting of the same inorg. material as the material of the dielectric layer is provided on the surface on the opposite side. The generation of the warpage on both surfaces of the substrate is prevented in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium that is prevented from warping and has stable mechanical properties.

[Conventional technology]

Magneto-optical disks are attracting attention as a high-density, large-capacity memory. Magneto-optical recording media such as magneto-optical disks focus laser light onto a rotating disk, and reflect the strength and weakness of the light reflected from the disk. A typical example is a recording layer provided on a transparent synthetic resin substrate such as polycarbonate or polymethyl methacrylate.

By the way, since all the materials used for the recording layer are easily oxidized or hydrolyzed, the recording layer provided on the substrate is generally made of Si mN4, S 1AQN
, S1AJ2ON, etc., is sandwiched between dielectric layers (or protective layers).

However, with such a structure alone, the adhesion between the substrate and the recording layer, dielectric layer, etc. is insufficient, and when an accelerated deterioration test is performed, peeling occurs at the interface, resulting in a lack of long-term reliability. In addition, optical information recording media using synthetic resin substrates may warp due to water absorption and swelling of the substrate, which may cause the recording layer to peel off, make it impossible to read signals, or cause the recording layer to peel due to permeated moisture. There are problems such as deterioration.

These problems can be solved to some extent by using a synthetic resin substrate provided with a silicon dioxide coating.

Furthermore, it has been proposed to provide various synthetic resin layers and transparent dielectric layers as protective layers.
No. 39949 discloses that one or two molecular layers of a coupling agent are provided on the surface of a recording layer provided on one side of a substrate, and a polyvinylidene chloride copolymer-containing layer is formed thereon to improve moisture resistance and corrosion resistance. It is proposed to improve.

However, when only the surface of the recording layer is protected with a polyvinylidene chloride copolymer-containing layer, it is not possible to block moisture permeating from the substrate surface side. On the other hand, if a polyvinylidene chloride copolymer-containing layer is formed on the entire surface, a resin layer with poor scratch resistance will be formed on the surface of the substrate, which serves as a path for light. There is a risk that the basic performance as a recording medium will be significantly impaired. Moreover, even if a polyvinylidene chloride copolymer-containing layer is formed on the entire surface, the moisture resistance is not sufficient and deterioration of the recording layer due to permeated moisture cannot be completely prevented.

In addition, Japanese Patent Application Laid-open No. 1-264647 describes a material for protecting the interface of a magneto-optical recording film in a magneto-optical disk that performs recording, reproduction, and erasing using laser light.
It has been proposed to use a compound consisting of a metal and a chalcogenide. According to this method, a magneto-optical disk is provided which has protection performance against water and oxygen, excellent heat retention performance, and high recording sensitivity.

However, in magneto-optical recording media, the recording layer, dielectric layer, protective layer, etc. are generally formed only on one side (groove surface side) of the substrate. In this case, the hygroscopicity of the substrate becomes uneven on both sides,
As a result, the substrate warps due to aging, which adversely affects recording and reproducing characteristics.

That is, when a magneto-optical recording medium is subjected to an accelerated deterioration test and placed in an environment of, for example, 80°C and 90% RH, there is no damage to the substrate from the groove surface side where the recording layer, dielectric layer, protective layer, etc. are provided. Although the permeation of water vapor is extremely small, the permeation of water vapor from the reading side (the side of the substrate opposite to the recording layer side) is relatively large.As a result, the groove side and reading side of the synthetic resin substrate expand due to moisture absorption. The difference becomes large and the substrate warps.

Furthermore, there is a large difference in thermal expansion between the groove surface side and the reading surface side of the synthetic resin substrate, which, together with the difference in hygroscopic expansion, increases warpage.

However, in conventional single-plate magneto-optical recording media,
No effective means for preventing the occurrence of warpage due to the difference in hygroscopic expansion and thermal expansion on both sides of the substrate has yet been proposed.

[Problems to be Solved by the Invention] The object of the present invention is to have excellent moisture resistance (moisture resistance), corrosion resistance, and scratch resistance, and even when placed in a high temperature and high humidity environment, hygroscopic expansion and The object of the present invention is to provide a magneto-optical recording medium that is prevented from warping due to thermal expansion and has stable mechanical properties.

As a result of intensive research to overcome the problems of the prior art, the present inventors have discovered that on a transparent substrate made of synthetic resin,
In a magneto-optical recording medium having a structure including a recording layer, a dielectric layer, and a protective layer, a synthetic resin substrate whose entire surface is coated with a silicon dioxide film is used, and the surface opposite to the recording layer side (
We have discovered that by providing a thin film made of the same inorganic material as the dielectric layer on the non-grooved surface, it is possible to obtain a magneto-optical recording medium in which warping of the substrate due to hygroscopic expansion and thermal expansion is prevented.

The present invention has been completed based on these findings.

[Means for Solving the Problems 1] Thus, according to the present invention, a first dielectric layer made of an inorganic material, a recording layer, and a second dielectric layer made of an inorganic material are provided on the groove surface of a synthetic resin substrate having a silicon dioxide coating on the entire surface. A magneto-optical device characterized in that a second dielectric layer and an ultraviolet curable resin layer are laminated in this order, and a thin film made of the same inorganic material as the first or second dielectric layer is provided on the other side. A recording medium is provided.

Each component of the present invention will be explained below.

(Synthetic resin substrate) In the present invention, the synthetic resin used as the substrate material includes polycarbonate, polymethyl methacrylate,
Any synthetic resin with excellent transparency that is generally used for magneto-optical recording media, such as polyolefin or epoxy resin, may be used, and there are no particular limitations. Although the film thickness of the substrate can be determined as desired, it is usually 1.2 mm in the case of a magneto-optical recording medium having a single-plate structure.

In the present invention, a silicon dioxide film is formed on the entire surface of the synthetic resin substrate.

By providing a silicon dioxide film, it is possible to impart moisture resistance and improve adhesion to a thin film made of an inorganic material such as a dielectric layer.

In this case, a silicon compound, its hydrolyzate, colloidal silica, etc. is used as a primer layer on the substrate in advance,
When the coating is cured, the adhesion of the silicon dioxide coating to the synthetic resin substrate is improved.

Examples of methods for forming the silicon dioxide film include vacuum evaporation, CVD using silane gas, sputtering using a quartz plate as a target, liquid phase growth, dipping using an organic solvent of an organosilicon compound, or There is a precipitation method in which silicon is immersed in a supersaturated hydrofluorosilicic acid solution to deposit a silicon dioxide film. Among these, the precipitation method is particularly preferred because it is easy to work with and can form a uniform coating.

As for this precipitation method, a known method disclosed in detail in JP-A-61-12734 can be applied. A supersaturated hydrofluorosilicic acid solution of silicon dioxide contains silicon dioxide (silica gel, aerosil, silica glass, and other silicon dioxide-containing substances) in a hydrofluorosilicic acid solution.
After dissolving the silicon dioxide, water or a reagent (boric acid, aluminum chloride, etc.) is added to create a supersaturated state of silicon dioxide. To form a silicon dioxide film, the substrate may be immersed in this treatment liquid or the treatment liquid may be allowed to flow down onto the surface of the substrate, but a dipping method is preferred in order to form a uniform film.

The thickness of the silicon dioxide film is usually 100 to several 100.
The purpose of surface modification can be achieved with 0 people, preferably about 300 to 1000 people.

Examples of the silicon compound used in the brimer include silicon compounds represented by the general formula [I] and hydrolysates thereof.

(R'), Si (R")4-n[I] (wherein, R' is a hydrocarbon group having 1 to 6 carbon atoms, a vinyl group, a meccryloxy group, an epoxy group, an amino group, a mercapto group) , fluorine or chlorine, R
(2 is selected from an alkoxy group, an alkoxyalkoxy group, and a chlorine atom, each of which may be the same or different from each other, and n represents an integer of O to 4). Hydrolysates are silicon compounds in which some or all of the alkoxy groups, alkoxyalkoxy groups, acyloxy groups, and chlorine atoms are substituted with hydroxyl groups, and those in which some of the substituted hydroxyl groups are naturally condensed with each other. Contains. These hydrolysates are obtained, for example, by hydrolysis in a mixed solvent such as water and alcohol in the presence of an acid.

Colloidal silica is a sol obtained by dispersing ultrafine silica particles having a particle size of ~rootLm in water or an alcoholic dispersion medium, or a dry powder obtained by removing the dispersion medium from this sol, and commercially available products can be used.

A known method can be used to form the primer layer. For example, these silicon compounds, their hydrolysates, colloidal silica, etc. are applied as a paint to the substrate surface, and then cured using heat, ultraviolet rays, electron beams, etc. Alternatively, it can be performed using a thin film forming method such as vacuum evaporation, sputtering, plasma polymerization, ion blating, f-ng, etc.

(Dielectric layer, recording layer, and ultraviolet curable resin layer) A first dielectric layer, a recording layer, a second dielectric layer, and an ultraviolet curable resin layer are formed on the groove surface of a synthetic resin substrate on which a silicon dioxide coating is formed on the entire surface. They are stacked in this order.

12ILLI The inorganic material forming the first dielectric layer must have moisture resistance and high light transmittance (preferably 97% or more).
, have a refractive index close to that of the synthetic resin substrate, have good adhesion to the silicon dioxide film, and have low thermal conductivity so that the optimum recording power during recording is as small as possible. Those that satisfy physical properties are desirable, for example, SiN%AβN%Sin, Al2O%AI2*O
,,Ties,SiC,Sis N4.5iAI2O
Examples include N.

The thickness of the first dielectric layer is usually 0.01 to 0.2 μm.

L Indigo 1 As the recording layer, for example, TbFeCo, GdDyFe
%TbDyFeCo, DyFe, NdDyFeCo, T
bFe, GdFeB1. Any conventionally known recording film made of an amorphous magnetic alloy such as GdTbFe, or a film made of a phase change recording material or a dye-based recording material can be used. A single layer or a composite layer of one or a combination thereof is preferable.

The thickness of the recording layer is usually preferably 0.01 to 0.1 μm.

H1 difference 1 The same type of inorganic material as that forming the first dielectric layer can be used, but among them, those with high hardness and good scratch resistance are preferred.

The thickness of the second dielectric layer is usually 0.01 to 0.2 μm.

As a method for creating the first dielectric layer, the recording layer, and the second dielectric layer, for example, vacuum film forming methods such as vacuum evaporation, sputtering, and ion blasting are used to form a hard inorganic material into a uniform thickness. It is preferable because it can be formed into a film.

The ultraviolet curable resin layer may be formed by any method,
For example, it is formed by applying ultraviolet curing resin such as acrylic or epoxy resin on the second dielectric layer by a spin cord method, and then irradiating it with ultraviolet rays. The thickness of the ultraviolet curable resin layer is usually preferably 10 to 30 μm.

By forming the ultraviolet curable resin layer, durability, chemical resistance, mechanical strength, etc. can be improved, and the second dielectric strength layer can be protected.

(Thin Film Made of Inorganic Material) A thin film made of the same inorganic material as the first or second dielectric layer is provided on the side of the substrate opposite to the recording layer side (reading surface side).

As the film forming method, the same method as in the formation of the dielectric layer described above can be adopted. Also, the thickness of this layer is usually
The thickness is approximately 0.1 to 0.3 μm, but if the thickness is approximately the same as the total thickness of the first dielectric layer and the second dielectric layer, the internal stress of the synthetic resin substrate can be offset and warpage can be more effectively prevented. This is preferable because it can prevent the occurrence.

Since the magneto-optical recording medium of the present invention is provided with a thin film made of the above-mentioned inorganic material on the reading surface side of the substrate, it can exhibit the following effects.

(2) Even when placed in a high temperature and high humidity environment such as 80° C. and 90% RH, it is possible to prevent warping due to the difference in thermal expansion between the groove surface side and the reading surface side.

(2) By laminating a moisture-proof silicon dioxide coating and a thin film made of inorganic material on the reading surface side of the substrate, it is possible to suppress moisture absorption and expansion of the synthetic resin substrate and prevent the occurrence of warping.

■ By providing inorganic thin films of the same material and preferably the same (total) film thickness on the groove surface and the reading surface, the internal stress of the synthetic resin substrate can be offset and warping can be prevented. can.

■ Scratch resistance can be further improved by providing a thin film made of inorganic material on the reading surface side.

(Margins below) [Examples] The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited only to these Examples. In addition, parts and % in these examples
are based on weight unless otherwise specified.

Further, the method of accelerated deterioration test in Examples and Comparative Examples is as follows.

Accelerated deterioration test> After holding the magneto-optical recording medium (magneto-optical disk) for 100 hours in a constant temperature machine at 80°C and 90% RH,
Appearance and warpage were evaluated.

(2) = The magneto-optical disk after the accelerated deterioration test was visually observed to evaluate the presence or absence of peeling at the interface between the substrate and each layer.

A: The radial tilt of the magneto-optical disk after the accelerated deterioration test was measured. The measurement position was 45 mm in the radial direction from the center of the disk. The initial value was set to O, and the warp in the direction in which the recording layer side became concave was set to +.

[Example 1] Each layer was formed on a magneto-optical disk substrate (diameter 130 mm, thickness 1.2 mm) made of polycarbonate (PC) by the following operations.

(1) Formation of Brimer Layer First, γ-Glydoxypropyltrimethoxysilane 35
0 parts, 14 parts of water-dispersed colloidal silica, 9 parts of distilled water, and 3 parts of a 1.2N hydrochloric acid aqueous solution were mixed, and after refluxing at 80°C for 4 hours, 57 parts of the solvent was distilled off at 80 to 90°C. γ-Glydoxypropyltrimethoxysilane hydrolyzate solution 66 containing colloidal silica thus obtained
100 parts of ethyl cellosolve, a curing catalyst, and a small amount of a flow control agent were added to prepare a paint.

This paint was applied to the substrate by dipping, and then treated in a hot air drying oven at 120° C. for 30 minutes.

(2) Formation of silicon dioxide coating The entire surface of the substrate on which the brimer layer has been provided in this way is coated with silicon dioxide using a silicon dioxide coating production apparatus similar to that shown in JP-A No. 61-12734. A film was deposited.

That is, the silicon dioxide coating manufacturing apparatus has a dipping tank consisting of an outer tank and an inner tank, and the space between the inner tank and the outer tank is filled with water. This water is heated with a heater to a temperature of 35° C., and is stirred with a stirrer to make the temperature distribution uniform. The inner tank consists of a front part, a middle part, and a rear part, and each part is filled with an aqueous solution of hydrofluorosilicic acid at a concentration of 2.0 mol/I2 in which silicon dioxide is dissolved and saturated using industrial silica gel powder as a source of silicon dioxide. It is filled with a 3°C reaction solution diluted to 20% using . At this point, the circulation pump was activated to discharge a certain amount of the reaction liquid from the rear of the inner tank, filter it with a filter, and start circulating the treated liquid back to the front of the inner tank. Then 0
．． A 5 mol/ρ boric acid aqueous solution was continuously poured into the rear part of the inner tank and maintained for 10 hours. In this state, the reaction solution became a treatment solution having an appropriate degree of silicon dioxide supersaturation. Here, the absolute removal rate of the filter is set to 1.5 μm, and the processing liquid circulation amount is set to 2.
The circulation rate was adjusted to 40 mρ/min (since the total amount of treatment liquid was about 312, the circulation rate was 8%/min).

Then, the optical disk substrate subjected to the above-mentioned brimer treatment was immersed vertically into the center of the inner tank, and the condition (0.5 mol/I
Add the boric acid aqueous solution from step 2 at 0.2 mβ/min, circulate at 8%/min, and filter with a 1.5 μm filter)
It was held for 6 hours.

As a result, a substrate was obtained whose entire surface was coated with a silicon dioxide film having a thickness of approximately 500 nm.

(3) Formation of dielectric layer, recording layer, and ultraviolet curing resin layer The polycarbonate substrate having the silicon dioxide coating on the entire surface was introduced into the vacuum chamber of the Kubata device, and the IX10-
'After exhausting to Torr, argon gas 1 x 1
0-” Torr is introduced, and S is applied as the first dielectric layer on one side.
1000 people formed iN films. Then, increase the argon gas pressure to 5. TbF of the recording layer as Qx l O-”Torr
500 people formed a film of eCo, and 1000 people formed a film of SiN thereon as a second dielectric layer.

On the second dielectric layer, an ultraviolet curable resin (manufactured by Dainippon Ink Co., Ltd., ultraviolet curable resin 5D-301; viscosity 400 c
P) was applied by a spin code method and then irradiated with ultraviolet rays to form an ultraviolet curable resin layer with a thickness of 15 μm.

(4) Formation of an inorganic material thin film A thin film of SiN is deposited on the silicon dioxide coating on the reading surface side of the polycarbonate substrate by sputtering.
It was formed with a film thickness of 0.00 people.

The results of the accelerated deterioration test of the magneto-optical disk obtained are as follows:
Shown in the table.

Comparative Example 1 A magneto-optical disk was produced in the same manner as in Example 1, except that a polycarbonate substrate without a silicon dioxide coating was used.

[Comparative Example 2] The same procedure as in Example 1 was carried out except that in Example 1, a polycarbonate substrate without a silicon dioxide coating was used and a thin film made of an inorganic material was not formed on the reading surface side of the substrate. Created a magneto-optical disk.

The results are summarized in Table 1.

Table 1 Table 1 shows that by using a synthetic resin substrate with a silicon dioxide film formed on the entire surface and providing a thin film made of an inorganic material of the same material as the dielectric layer on the reading surface side, it is possible to withstand high temperatures. Regardless, it can be seen that a magneto-optical recording medium with little change in substrate warpage and with good appearance can be obtained.

〔Effect of the invention〕

According to the present invention, it has excellent moisture resistance, corrosion resistance, and scratch resistance, and even when placed in a high temperature and high humidity environment, warping is prevented and stable mechanical properties are achieved. A magneto-optical recording medium is provided.

Claims (1)

[Claims] (1) A first dielectric layer made of an inorganic material, a recording layer, a second dielectric layer made of an inorganic material, and an ultraviolet curable resin layer are laminated in this order on the groove surface of a synthetic resin substrate having a silicon dioxide coating on the entire surface. . A magneto-optical recording medium, characterized in that the other surface is provided with a thin film made of the same inorganic material as the first or second dielectric layer.