JPH0778913B2 - Magneto-optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-density information recording carrier for recording / reproducing a recording layer by using a laser beam, and particularly to an optical disc using a plastic substrate, particularly an optical disc. It relates to a magnetic disk.

(Prior Art) In an optical disc, the most technically important point at present is how to improve durability, that is, reliability when a plastic substrate is used. That is, the recording layer formed on the plastic substrate, which has various advantages as compared with the glass substrate, is deteriorated or deteriorated by the moisture and the monomer remaining in the plastic substrate or the moisture penetrating through the plastic substrate. There was a drawback.

The inventors of the present invention disclosed in Japanese Patent Application No. 59-32230, entitled "Optical Information Recording Carrier", filed on February 22, 1984, as a method for solving the above-mentioned drawbacks. It was proposed to provide a thin film of alkali glass. Although this method extends the durability of the optical disk astonishingly and is completely satisfactory, the present inventors conducted an experiment to further develop the above invention and further improve the durability, and maintained the durability. The present invention has been completed by finding a method for increasing the film formation rate.

(Object of the Invention) An object of the present invention is to solve the above-mentioned conventional problems.
The plastic substrate is made of glass and improved in smoothness, hardness, moisture absorption deformation and moisture resistance to prevent deterioration of the functional film based on the substrate, and at the same time, a long-term stable optical information recording carrier with improved film formation speed is provided. To provide.

Another object of the present invention is to provide an optical information recording carrier which has a greatly improved magneto-optical characteristic in a magneto-optical recording carrier using a rare earth-transition metal amorphous alloy as the functional film.

(Structure of the Invention) The present invention provides a high-density information recording carrier in which a high-density information recording layer is formed on a transparent plastic substrate via an inorganic glass thin film, wherein the inorganic glass thin film is equivalent to an alkaline earth metal oxide. A high-density information recording carrier, characterized in that it is composed of an inorganic glass contained in a range of 20% by weight to 35% by weight.

The above alkaline earth metal oxides are BaO, CaO, MgO, SrO, Be.
It is at least one compound selected from the group consisting of O, in particular, CaO and BaO are preferable as main components, and BaO is particularly preferable.

The other component constituting the above-mentioned inorganic glass may be a material which becomes a glass when used together with the above-mentioned alkaline earth metal, but is usually silicon, aluminum, boron, an oxide of lead, SiO ₂ , Al ₂ O. ₃ , B ₂ O ₃ , PbO and the like.

If the amount of the alkaline earth metal oxide is less than 20% by weight, the melting temperature becomes high, it is difficult to vitrify, and the sputtering rate also decreases. On the other hand, if this amount exceeds 35% by weight, the water resistance and the oxidation resistance decrease.

As a result, the moisture resistance of the inorganic glass thin film produced from this is lowered, and the characteristics as a disk are lowered. That is,
According to the present invention, by setting the amount of alkaline earth metal within the above range, the durability of the disk can be improved and at the same time the film forming rate can be increased. Although the reason why the durability is improved by setting the amount of the alkaline earth metal in the above range is unknown, it is considered that there is some relation to the formation of the inorganic glass layer because the sputtering rate is improved.

Another feature of the present invention is that the above-mentioned inorganic glass further contains an alkali metal in an amount of 1% by weight or less, preferably 0.8% by weight or less in terms of alkali metal oxide. That is, the durability and moisture resistance of the disk can be improved by setting the amount of the alkaline earth metal in the above range, but in order to further improve these characteristics, the alkali metal content in the inorganic glass is further increased. The amount is preferably 1% by weight or less, more preferably 0.8% by weight or less in terms of alkali metal oxide.

The amount of alkali metal is 1% by weight in terms of alkali metal oxide.
When it exceeds, the recording layer is cracked and the recording is destroyed.
Although the reason for this is not clear, it is considered that the alkali metal may deteriorate the recording layer by reacting with moisture or monomers coming through the plastic substrate or moisture in the outside air. The amount of this alkali metal is more preferably 0.8% by weight or less in terms of alkali metal oxide, and is preferably as small as possible unless the properties of the glass are impaired. However, it is industrially difficult to reduce the alkali metal to zero, and if it is 1% by weight or less, there is no practical problem.

The alkali-free glass of the present invention does not include so-called silicate glass consisting of SiO ₂ . That is, it is well known that SiO ² is vapor-deposited alone as a moisture-resistant protective layer, but this silicate glass thin film has almost no moisture resistance.

The thickness of the alkali-free glass thin film of the present invention is preferably 100 to 2,000 Å, and if it is less than 100 Å, the role of protection is insufficient and 2,000 Å
If it exceeds, problems such as laser absorption will occur, and it is not economical.

The present invention is particularly preferably applied to a high-density information recording layer, for example, an optical disk using a magneto-optical recording material made of a rare earth-transition metal amorphous alloy such as TbFeCo. It is obviously applicable to all other high-density record carriers using a recording material that is deteriorated by external moisture and the like.

Of course, the protective layer of the alkali-free glass thin film of the present invention can be formed outside the recording layer, that is, on the side opposite to the substrate to shield the recording layer from the outside air.

The alkali-free glass thin film of the present invention can be easily formed by any physical vapor deposition method such as sputtering, vapor deposition, or ion plating. Theoretically, any method in which the amount of alkaline earth metal and / or alkali metal falls within the above definition, for example forming an inorganic glass.
The above-mentioned inorganic glass layer may be formed on a plastic substrate by simultaneously vapor-depositing each component from the above vapor deposition sources, but industrially, a vapor-deposition source of alkali-free glass having the above-mentioned composition is prepared, and it is subjected to physical vapor deposition. You can do it.

Hereinafter, the present invention will be described using examples.

(Example) As a plastic substrate, a 1.2 mm thick acrylic substrate (P
An MMA) and a polycarbonate substrate (PC) were prepared. On each of these substrates, an inorganic glass of each composition shown in Table 1 was formed into a thin film with a film thickness of 500Å by using a sputtering device (RF magnetron sputtering device manufactured by Nippon Vacuum Conventional Technology Co., Ltd.), and then formed on the substrate. Gd0.12, Tb0.1
2. A recording layer of Fe0.76 was formed into a thin film 1000 Å by using the above-mentioned sputtering device, and the same inorganic glass was sputtered thereon to form a thin film layer with a film thickness of 1,000 Å.

The evaluation of the obtained magneto-optical disc was performed at 45 ° C and 90 ° C for each disc.
C / N change rate after maintaining at RH% for 30 days, BER (initial value is 1
And the sputtering rate as the film formation rate, and the results are shown in Table 1.

As can be seen from Table 1, when the alkali-free glass according to the present invention in which the composition ratio of the alkaline earth metal and / or the alkali metal is limited, an optical disk excellent in durability and productivity can be obtained.

Claims (3)

[Claims] 1. A magneto-optical disk comprising a transparent plastic substrate and a magneto-optical information recording layer formed on the transparent plastic substrate via an inorganic glass thin film layer, wherein the inorganic glass thin film layer is BaO or 20-calculated as CaO
A magneto-optical disk characterized by being composed of an inorganic glass containing in the range of 35% by weight. 2. The magneto-optical disk according to claim 1, wherein the inorganic glass contains an alkali metal in an amount of 1% by weight or less in terms of alkali metal oxide. 3. The magneto-optical disk according to claim 1, wherein the magneto-optical recording layer is a rare earth-transition metal amorphous film.