JPS6381640A - Optical recording medium - Google Patents

Abstract

PURPOSE:To exhibit excellent weatherability and to improve recording sensitivity by providing inorg. protective layers having specified heat conductivity in mutual contact with a recording layer. CONSTITUTION:This optical recording medium is constituted by forming an under coating layer 2 on a writing side substrate 1a, providing the protective layer 3, the recording layer 4, the protective layer 5, a spacer layer 6 and a reflection layer 7 successively thereon and sticking a substrate 1b for protection via an adhesive layer 8 thereto. The protective layers 3, 5 are formed to about 300Angstrom thickness by sputtering and the substrate temp. at the time of film formation at a low temp. below a room temp. in such a manner that said film attain <=1W/m.K heat conductivity. As a result, the excellent weatherability against the atm. and steam is exhibited and the satisfactory temp. rise is permitted. The recording sensitivity which is heretofore sacrificed for the purpose of improving the weatherability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which recording and reproduction can be performed using a light beam. In particular, the present invention relates to an optical recording medium in which a protective layer is provided on the recording layer for storage stability of the recording layer.

(Prior art) Conventionally, optical memory materials used in optical disks include rare earth-transition metal alloy films, thin films of reducing oxides such as chalcogen compounds that utilize phase transition from amorphous to crystalline, and heat-reducing materials. Mode recording media, thermoplastic recording media, etc. are known.For example, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film, MnB1
．． Mn (: polycrystalline thin film such as uBi, GdCo, GdF
e, TbFe, DyFe, GdTbFe.

Amorphous thin films such as TbDyFe and single crystal thin films such as TbFeO3 are known.

Among these thin films, there are various issues such as film formability when manufacturing large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, and readout of written signals with a good S/N ratio. Considering read efficiency,
Recently, the amorphous thin film is considered to be excellent as a magneto-optical recording medium. In particular, GdTbFe, which has a Curie point of about 150 to 200° C., and GdTbFe (:o (JP-A-196639-1983), which has a large Kerr rotation angle and excellent reproduction performance) are most suitable as magneto-optical recording media.

However, amorphous magnetic materials generally used in magnetic recording media such as magneto-optical recording media such as GdTbFe have a drawback of poor corrosion resistance. That is, when it comes into contact with air or water vapor, its magnetic properties deteriorate, and eventually it becomes completely oxidized and becomes transparent.

In order to eliminate such drawbacks, conventionally, a material such as a 5-layer film, which almost transmits the recording light and the reproducing light, has been used on both sides of the optical memory material layer.
i02. SiO, Si3N4, AIN (7) A disk-shaped recording medium provided with a protective layer has been proposed. In order to further enhance the protective effect, various materials for the protective layer are being studied.

[Problem that the invention seeks to solve]

However, as a protective film, Si3N4, AIN, S
When a material with good thermal conductivity such as iG is used and its film thickness is increased to increase the protective effect, the thermal energy generated when the recording light is converted in the optical memory material is conducted to the protective film and is lost. As the ratio increases, there is a problem in that the temperature of the recording layer due to the light beam is not sufficiently increased, resulting in a decrease in recording sensitivity. Until now, no material has been found that has low thermal conductivity and has a sufficient protective effect, and the reality is that recording sensitivity has been sacrificed to some extent in order to improve durability.

The present invention has been made in view of this problem, and provides a magnetic recording medium that has excellent corrosion resistance against moisture and oxygen and excellent durability without impairing the magnetic properties of the magnetic recording layer. The purpose is to improve the

[Means for solving problems]

The above purpose is to have a thermal conductivity of I 17m adjacent to the recording layer,
This is achieved by providing an inorganic protective layer as follows.

The optical recording medium of the present invention can have either a laminated structure or an air sandwich structure.

An example of an embodiment of the optical recording medium of the present invention having a laminated structure is shown in FIG.

In the optical recording medium shown in FIG. 1, a subbing layer 2 is formed on a writing side substrate Ia, and a protective layer 3, a recording layer 4, a protective layer 5 are sequentially formed.
, a spacer layer 6 and a reflective layer 7 are provided, and further bonded to the protective substrate 1b via an adhesive layer 8.

〔Example〕

EXAMPLES Below, the present invention will be described in more detail by way of examples in which the present invention is applied to a magneto-optical recording medium.

Example 1 A magneto-optical recording medium having the structure shown in FIG. 1 was manufactured as follows.

On a plastic substrate 1a made of polycarbonate resin,
About 900 people used a SiO film as the undercoat layer 2, about 300 people used a ZnS film as the protective layer 3, and used GdTbFeC as the recording layer 4.
About 150 layers of O film and about 3 layers of ZnS film as protective layer 5.
000 people, and furthermore a SiO film as a spacer layer 6 of about 1000 people.
Finally, about 700 people deposited an Al film as the reflective layer 7, and each layer was successively deposited by high-frequency sputtering without breaking the vacuum. This was bonded to a protective plastic substrate 1b via an adhesive layer 8 made of hot melt adhesive to obtain a magneto-optical recording medium.

Here, the thermal conductivity of the protective layer 3 and the protective layer 5 is I 17
The substrate temperature during the film formation of the two shingle layers was maintained at a low temperature below room temperature so that the temperature was as follows. As a result, a film with the desired thermal conductivity was obtained.

A solid line 1 in FIG. 2 shows the relationship between the linear velocity of the magneto-optical disk of this embodiment and the recording power on the disk surface.

For comparison, a magneto-optical film with the same layer structure was prepared in exactly the same manner as above, except that the protective layers 3 and 5 were formed from SiN films with a conventional thermal conductivity of about 20 W/m. A disk was produced and the same measurements as above were performed. The measurement results of this comparative sample are shown by broken line 3 in FIG.

Furthermore, in order to examine the durability of the obtained recording medium,
A humidity test was conducted for 200 hours in a constant temperature and humidity chamber at ℃ and relative humidity of 95%, and the rotation angle θk and coercive force H were determined after the humidity test.
The rate of deterioration of a from the initial value was measured. The results are shown in Table 1.

As seen in FIG. 2, the optical recording medium of the present invention is different from conventional recording media by providing an inorganic protective layer adjacent to the recording layer with a thermal conductivity of I17m or less. Recording sensitivity has improved in comparison.

Further, as shown in Table 1, the recording medium of the present invention is similar to conventional recording media in terms of durability, and no particular deterioration of magnetic properties is observed.

Example 2 As the material of the protective layer 3 and the protective layer 5, Si3N is used.

A magneto-optical recording film having the same film structure as in Example 1 was obtained, except that a protective film with a thermal conductivity of f W/m or less was formed by high-frequency sputtering in an Ar sputtering gas atmosphere of about 100 mTorr. Created media.

Solid line 2 in FIG. 2 shows the relationship between the linear velocity of the magneto-optical disk of this embodiment and the recording power on the disk surface.

Furthermore, the same moisture resistance test as in Example 1 was conducted.

The results are shown in Table 1.

As seen in FIG. 2, the recording sensitivity of the magneto-optical recording medium of this example also showed almost the same value as that of Example 1, and the recording sensitivity was improved compared to the conventional recording medium. Furthermore, as shown in Table 1, the durability was the same as that of conventional recording media, and no particular deterioration of magnetic properties was observed.

Table 1 (Effects of the Invention) The optical recording medium of the present invention is provided with an inorganic protective layer adjacent to the recording layer and having a thermal conductivity of I W/m or less:
It not only showed excellent durability and reliability, but also improved recording sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic side sectional view showing the structure of an optical recording medium that is one of the embodiments of the present invention, and FIG. 2 is a diagram showing the linear velocity and disk surface of the optical recording medium disk of the present invention and a comparative example. 1 is a graph showing the relationship between the recording powers of 1 and 2, and the numbers in FIG. 1 represent the following parts, respectively. ]a...Writing side substrate 2...Undercoat layer 3.5...Protective layer 4...
Recording layer 6...Spacer layer 7...Reflection layer
8... Adhesive layer 1h... Protective substrate

Claims (1)

[Claims] In an optical recording medium in which information is recorded by heating a recording layer by irradiating it with a light beam, a layer adjacent to the recording layer has a thermal conductivity of 1 W/m. An optical recording medium characterized in that it is provided with an inorganic protective layer having a molecular weight of k or less.