JPS63129544A - Method for protecting magneto-optical information recording medium - Google Patents

Abstract

PURPOSE:To suppress generation of pinholes and to improve long-period reliability by roll-coating a hot-melt on a recording film surface of magneto-optical recording medium to form a protective film thereon, then subjecting the film to a post treatment at the same temp. as the roll temp. at the time of the coating. CONSTITUTION:The protective film 4 is subjected to the post treatment at the same temp. as the temp. at the time of the coating in a method for forming the recording film 3 of the magneto-optical recording medium having substrates 1, 1' and the recording film 3 (2, 2' are antireflective and moistureproof layers), then coating the protective film 4 of hot-melt synthetic resin therein. For example, another sheet of the substrate 1' is adhered by a hot-melt adhesive agent 5 thereto over the entire surface to form magneto-optical disk. The magneto-optical recording medium disposes with the protective film 4, for example, the magneto-optical disk, is subjected to the post treatment at the same temp. as the roll temp. at the time of the coating of the protective film 4 in the above-mentioned manner, by which the moisture absorption to the recording layer 3 is suppressed and the generation of the pinholes is hardly admitted; in addition, the increase rate of pit errors during long-period preservation is decreased. the long- period reliability of the magneto-optical disk, etc., is thereby enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for protecting a magneto-optical recording medium. More specifically, the present invention relates to a method for protecting a magneto-optical recording medium, such as a magneto-optical disk recording film, in which a protective film is coated with a hot-melt synthetic resin by a roll coater coating method and then post-treated.

(Prior art) - Conventionally, magneto-optical disks have been used in erasable and rewritable high-density memories, and are recorded by heating with light irradiation, and can be read using magneto-optical effects such as magnetic force and Faraday effects. be.

Amorphous thin films made of GdTbFeCo are particularly excellent as recording films for magneto-optical disks, and have excellent film formability when producing large-area thin films at temperatures near room temperature, and write efficiency for writing signals and using small photothermal energy. , and read efficiency for accurately reading the S/N ratio of the written signal.

Since it has a Curie point of around 150'C, it is most suitable as a magneto-optical recording medium.

However, magneto-optical recording films such as GdTbFeCo generally have a drawback of poor corrosion resistance. That is, when it comes into contact with the atmosphere or water vapor, it is oxidized and its magnetic properties deteriorate, and eventually it becomes completely oxidized and becomes transparent.

Sin, 5i02°8i to prevent oxidation of the recording film
The recording film is covered with an inorganic protective film such as 3Na or Al2O3, or it is coated with a moisture-proof halogenated organic resin, ultraviolet curing acrylic resin, thermosetting epoxy resin, hot melt synthetic resin, etc. A method has been proposed.

(Problems to be Solved by the Invention) However, the protective layer of inorganic materials such as Sin and 5i02 must be formed using vacuum equipment such as evaporation and sputtering, and it takes time to form the film, which requires investment in equipment. This also resulted in enormous personnel costs, causing an increase in the cost of recording media.

In addition, halogenated organic resins, ultraviolet curing acrylic resins,
In the case of a protective film made of organic resin such as thermosetting epoxy resin, it can be applied uniformly onto the recording layer etc. using coating methods such as spray, coater, printing, spinner, and dipping, and can be coated uniformly on the recording layer, etc. by solvent evaporation, heating, and two-component coating. Since it can be cured by heating, ultraviolet irradiation, etc., a protective film is formed in a short time, equipment costs are low, and it is superior in terms of workability and can be manufactured at low cost, which is superior to inorganic protective layers.

However, the magneto-optical recording film provided on the resin substrate has some air permeability, and the adhesion between the recording film and the substrate is not strong. The solvents and monomers that are absorbed permeate the recording film, causing spots, spots, pinholes, etc. on the recording film. When such a disc is irradiated with a laser beam to record or reproduce data, bit errors appear. Also, when cured by heating, ultraviolet rays, etc., the substrate may warp (curve) due to curing shrinkage.
, the head that irradiates the laser beam during recording and playback cannot follow the laser beam, resulting in focus errors and tracking errors.
In extreme cases, recording and playback may not be possible at all. Normally, two identical disks with a protective film provided to correct warping of the disks are glued together with the recording film on the inside. In this way, the warpage is corrected, but at the time when the warp (curvature) occurs due to curing shrinkage, stress strain is generated between the substrate, recording film, and protective film, and at this time, there are already many A pinhole has occurred. This pinhole is thought to be caused by part of the recording film peeling off from the substrate due to stress fracture. It is also believed that pinholes appear as a result of mechanical scratching, pulling, pressing, centrifugal force, and other forces that occur when coating with various methods. Therefore, no matter which coating method is used, it is still not possible to prevent the increase in pinholes.
The pinholes that occur here are not only caused by the recording film becoming transparent due to oxidation.

On the other hand, the pinholes that increase in the accelerated durability test under conditions such as 60°C and 290% relative humidity are due to a part of the recording film being completely oxidized and becoming transparent, and the number of pinholes is still increasing. The reality is that there is no easy way to completely prevent this.

(Means for Solving the Problem) The method for protecting a magneto-optical disk recording film of the present invention is a roll coater coating method in which the recording film of a magneto-optical recording medium consisting of a substrate and a recording film is coated with a hot melt synthetic resin as a protective film. A method for protecting a magneto-optical recording medium is characterized in that the magneto-optical recording medium provided with the protective film is post-treated at the same temperature as the temperature of the roll when coating the protective film.

The method for protecting a magneto-optical disk recording film of the present invention uses glass or polymethyl methacrylate (
Plastic molded products such as PMMA) and polycarbonate (PC) are used. Plastic substrates are less likely to break than glass substrates, and can be easily mass-produced using an injection molding machine, resulting in low cost.

However, plastic substrates have water absorption properties and are also permeable to oxygen, and when a thin film of inorganic, metal, organic, etc. is layered on one side of the substrate, temperature increases.

Changes in environmental conditions such as humidity cause the disk substrate to warp (curve), further oxidize the recording film and deteriorate magnetic properties.

In order to overcome this drawback, Japanese Patent Application Laid-Open No. 61-68750 proposed a method in which two disks were bonded together using an epoxy resin adhesive, using an ultraviolet curing resin as a protective film for the recording film, and a method in which EVA was used as a protective film for the recording film. A method has been proposed in which two disks are overcoated with a rubber-based hot-melt adhesive and then bonded together using a rubber-based hot-melt adhesive. These methods are very good, and were able to hold for 1000 hours in an endurance test at 45°C2 and 95% relative humidity, but the coercive force was only 10%.
However, when considering the practical level guaranteed for 10 years, it cannot be said that the level of technology is sufficient.

The present inventors have focused on the fact that hot melt protective films and hot melt bonding methods using a roll coater require less equipment investment, have good workability, and can be manufactured at low cost, and have conducted various studies. As a result, in the roll coater coating method in which the recording film of a magneto-optical recording medium consisting of a substrate and a recording film is coated with a protective film using hot melt synthetic resin, the magneto-optical recording medium provided with the protective film is The present invention was completed based on the discovery that the durability of magneto-optical disks can be significantly improved by post-processing the disks at the same temperature as the roll temperature during coating with the protective film.

Although the reason for this is not clear, observation and measurement of the following phenomena suggests that it is because the shape of the protective film is different before and after heat treatment. That is, the hot melt protective film applied with a roll coater is opaque, and the film thickness A measured by a digital micrometer and the film thickness B calculated by the gravimetric method always have a relationship of A/B = 10/7, and The hot-melt protective film heat-treated at the same temperature as the roll becomes transparent, and A changes so that A and B are equal.

This suggests that the hot melt protective film before heat treatment has voids. Therefore, since the hot melt protective film before heat treatment has voids, the recording film layer absorbs moisture and is oxidized through the voids, and a portion thereof becomes transparent, resulting in an increase in pinholes. It is thought that this can be observed.

On the other hand, a hot melt protective film made transparent by heat treatment,
Since there are no voids, moisture absorption into the recording film is significantly reduced.
Almost no increase in pinholes is observed.

(Effects of the Invention) Compared to conventional methods, the magneto-optical recording medium protection method of the present invention has been shown to reduce pinholes due to oxidation of the recording film in accelerated durability tests under conditions of 60% and 90% relative humidity. Not only the occurrence of bit errors is significantly reduced, but also the increase rate of bit errors during long-term storage can be significantly reduced, which greatly contributes to improving the long-term reliability of magneto-optical disk products.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Example 1 and FIG.

Example 1 A donut-shaped tracking grooved substrate 1 made of polycarbonate resin with a diameter of 130 mm and a thickness of 1.2 mm was coated with an anti-reflection and moisture-proof layer 2 having a thickness of 50 mm.
After magnetron sputtering the OA alkali-free glass layer, a GdTbFeCo film with a thickness of 700 mm was used as the recording film 3.
was laminated on the antireflection and moistureproof layer 2 by the same sputtering method, and then again the antireflection and moistureproof layer 2, such as a 500A thick alkali-free glass layer, was laminated on the recording film according to the present invention. This was used as a sample for coating a protective layer.

Then, using a roll coater, apply EVA hot melt protective coating agent 4 (9550B, manufactured by Sekisui Chemical Co., Ltd.) to a thickness of 10 pm at a hot melt resin temperature of 120°C.
It was applied so that The protective film 4 at this time was opaque, and the thickness measured by a digital micrometer was 10 pm, and the thickness calculated from the gravimetric method was 7 pm.

Next, this sample carrier substrate was placed in a hot air dryer at 120°C for 5 minutes for thermal post-treatment, and the protective film 4 became transparent, and the film thickness measured with a digital micrometer was 7 pm, the same as the gravimetric method. Ta.

This disk carrier substrate was bonded to another substrate having no recording film using a rubber-based hot melt adhesive layer 5 (9145L, Tsukisui Kagaku) with the recording film facing inside. The thickness of the adhesive layer 5 at this time was 30 pm.

This fully laminated magneto-optical disk is heated at 60°C290%.
An accelerated durability test was conducted by leaving it for 1000 hours under conditions of relative humidity. The evaluation method was to visually count the number of pinholes produced when the recording film was oxidized and became transparent. When the size of the pinhole was later examined using a microscope, it was found to be 20 pm to 0.5 mmφ by visual observation.

The number of pinholes before the durability test was 60, but after the durability test there were 75 pinholes, an increase of only 15.

Comparative Example 1 The carrier substrate coated with the protective layer 4 was treated in the same manner as in Example 1, except that the heat post-treatment of placing the carrier substrate coated with the protective layer 4 in a 120°C2 hot air dryer for 5 minutes was not performed.

The number of pinholes before the durability test was 60, but after the durability test there were countless pinholes, a number that was difficult to count.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of a magneto-optical single-sided laminated disk of the present invention. (Explanation of symbols) 1.1'... Polycarbonate resin substrate 2.2
'... Anti-reflection, moisture-proof layer 3... Recording film 4... Protective film

Claims (1)

[Claims] In a roll coater coating method in which the recording film of a magneto-optical recording medium consisting of a substrate and a recording film is coated with a protective film using hot-melt synthetic resin, the magneto-optical recording medium provided with the protective film is coated with the roll temperature at the time of coating the protective film. A method for protecting a magneto-optical recording medium, the method comprising post-processing at the same temperature as that of the magneto-optical recording medium.