JPH02185747A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve oxidation resistance, corrosion resistance and adhesion strength to an adjacent inorg. matter or UV curing resin by completely covering a recording layer with a copolymer film of tetrafluoroethylene and ethylene. CONSTITUTION:An inorg. dielectric film 2 is coated with an org. protective film 4 consisting of a copolymer of tetrafluoroethylene and ethylene (tetrafluoroethylene copolymer). As the tetrafluoroethylene copolymer has polymerization chains in which hydrogen atoms are surrounded by fluorine atoms, the copolymer has equivalent properties such as chemical resistance, weather resistance and water repellent property to those of 'Teflon(R)', and moreover, the copolymer has lower gas transmittance for O2 and N2 by one figure than 'Teflon(R)'. The copolymer shows good adhesion to other material as it contains CH bonds in its polymerization chains.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk on which information is recorded, reproduced and erased by irradiation with a light beam such as a laser beam.

[Conventional technology]

Magneto-optical disks using rare earth-transition metal amorphous alloy films as recording layers are about to be put into practical use, but films containing such rare earth elements are generally very easily oxidized, so they are usually made of St, N4゜5IAtN, At
The recording film is covered with an inorganic dielectric film such as N or ZnS,
The structure is such that the recording layer does not come into contact with oxygen gas or moisture.

For example, JP-A-60-63747. %Opened in 1986-801
44.

JP-A-60-145525. % Kaisho 62-40651.
This is disclosed in Japanese Patent Laid-Open No. 62-197939.

However, since the surface of such an inorganic dielectric film is generally hydrophilic, it easily adsorbs moisture in the air, and therefore, if there are minute pinholes in the dielectric film, moisture will be removed from there. enters, causing pitting corrosion in the recording layer and reducing the durability of the magneto-optical disk. In order to improve this, we developed (1) Teflon, which is easy to fill pinholes on the inorganic protective film and has excellent environmental resistance.

A method of coating with epoxy resin or polyimide (Japanese Unexamined Patent Publication No. 62-293536); (2) coating the area of the magneto-optical recording medium that comes into contact with the outside with water-repellent resin Teflon (tetrafluoroethylene) or low moisture permeable resin polyimide; Method of coating with matrix xylylene and modified urethane resin (Japanese Patent Application Laid-Open No. 63-2074
5) etc. have been reported.

[Problem that the invention seeks to solve]

Among such organic resins, Teflon (tetrafluoroethylene) has the best heat resistance, chemical resistance, weather resistance, and water repellency, and is therefore considered to have the most effective anticorrosion effect.

However, there are some problems even when such a Teflon membrane is used. First, although Teflon resin has a large waterproofing effect, it has relatively high gas permeability to oxygen 02 and nitrogen N2, and is also permeable to water vapor. Not necessarily helpful. That is, in Teflon, the gas permeability is 02
1050. 390cc-ml/for N2
The problem of selective oxidation of the rare earth elements in the recording layer by the oxidizing gas cannot be avoided, which is as large as l OOin .multidot.24 hr-atm.

The second problem is adhesion. Magneto-optical disks have an inorganic electrically shielding film (SIO□, 810.Si, N4.AtN, Zn
However, since such an inorganic film is hard and brittle, cracks may occur due to slight deformation (shrinkage, expansion) of the substrate or stress during handling.

Therefore, in order to suppress this, it is generally done to form an organic protective layer with a thickness of 10 to 40 μm by spin-coding and curing an ultraviolet curable resin on the outermost surface of a medium (for example, JP-A-57 -27451 Publication)
.

Therefore, instead of this ultraviolet curing resin, it would be effective to apply a thick coating of the Teflon film mentioned above, but the spin code method cannot be used because Teflon is not chemically soluble in solvents. . Therefore, it is necessary to form a film by a dry process such as evaporation, ion blasting, or suffix, but in this case, it is difficult to increase the film thickness.

Therefore, even if the inorganic electrically shielding film is coated with a Teflon film by the sputtering method as in JP-A-62-293536, due to handling problems, it is necessary to further coat the outermost surface of the medium with an ultraviolet curing resin using the spin cord method. . However, since Teflon consists of C-F bonds, its polarizability is low, it is electrically neutral, and its surface is inert, so it has poor adhesion and wettability with other substances, and is difficult to protect UV-curable resins. There is a problem that the film cannot be applied uniformly.

This problem applies not only to magneto-optical recording media but also to phase-change optical disk bodies. In order to avoid this, a method has been reported in which a thin film made of an inorganic material is formed on a fluororesin film such as Teflon, and then an ultraviolet curable resin layer is formed on it (I! #Kaisho 63-26848 ). However, in this method, SiO2,513N4. Go
, st, *z, sb, etc., must be formed by layering or vapor deposition, which increases the number of steps for manufacturing the optical disk, making it impractical from the viewpoint of manufacturing costs.

[Problem to be solved by the invention]

The present invention addresses the problems of the Teflon (tetrafluoroethylene) film, which is the most excellent organic adhesive, and which is further coated on top of the inorganic electric film to improve the durability of magneto-optical disks, namely its gas permeability. And, the task is to solve the problem of adhesion.

[Means to solve the problem]

In order to solve the above problems, the present invention uses a [j combination (tetrafluoroethylene copolymer) of tetrafluoroethylene and ethylene] having the following structure instead of a Teflon (tetrafluoroethylene) membrane. For example, there is something like this. A substituent such as CH3 may be substituted for H or F. The material with the above structure has a melting point of 265-270°C and a melt viscosity of 104-270°C.
Since the temperature is 105 poise (300 to 320°C), the film can be formed not only by sputtering but also by vacuum evaporation. On the other hand, in the case of simple tetrafluoroethylene resin, the melt viscosity is 10 to 10 poise (340 to 38
It is difficult to form a film by vapor deposition because the temperature is as high as 0°C).

Next, regarding the chemical properties, the above-mentioned tetrafluoroethylene copolymer has polymer chains formed by fluorine atoms sandwiching hydrogen atoms, so it has properties equivalent to Teflon in terms of chemical resistance, weather resistance, and water repellency. while maintaining the gas permeability coefficient of 148° for 02 and 45cc-mit for N2.
/100 ln and 24 hra itm, both of which are one order of magnitude smaller than Teflon.

Furthermore, since it contains a CH bond, its adhesion to other substances is improved.

As mentioned above, in the present invention, in order to improve the durability of the magneto-optical disk, a film of a copolymer of tetrafluoroethylene and ethylene (tetrafluoroethylene copolymer) is formed on an inorganic dielectric film to improve oxidation resistance. , corrosion resistance and adhesion to adjacent inorganic substances or UV-curable resins were improved.

〔Example〕

Embodiments of the magneto-optical recording medium of the present invention will be described below with reference to the drawings.

(Example 1) FIG. 1 schematically shows a cross section of a magneto-optical recording medium of the present invention. 1 is polycargonate (PC) substrate (
1301111φ, with 1.6μm pitch group),
2 are Si 3N4 dielectric films each having a thickness of 80 nm.

This film was formed by sputtering using St and N4 as targets using a high frequency sputtering method at an argon gas pressure of 5 tlTorr and an input power of 1 kW for about 15 minutes. 3 is a TbFICo magneto-optical recording film with a thickness of 11
It is 00n. This film was made using a DC sputtering method using an alloy target of Tb25F/70CO5 at an argon gas pressure of 5 m.
Torr.

It was formed by sputtering for about 5 minutes at an input power of 0.7 kW. 4 is a copolymer film of tetrafluoroethylene and ethylene with a thickness of 200 n1ll.

This film was produced using a high-frequency sputtering method using a target of Asahi Glass Co., Ltd.'s tetra7fluoroethylene copolymer (trade name: Niacron cop) under argon gas of 5 mTorr and input power of 0.3 kW.
It was formed by sputtering for about 15 minutes.

The thus obtained magneto-optical disk was heated at 80°C and 85°C.
%RH, and conducted an accelerated deterioration test for 2000 hours to determine the C/N and defect error rate (
The results of measuring DIR) are shown in Table 1.

Here, the C/N ratio is determined by rotating the disk at 180 rpm and recording on the 40th radius of the disk using a semiconductor laser with a wavelength of 830 t+m at an output of 5 mW, a dat of 750%, and a recording frequency of I MHz. is reproduced using a semiconductor laser with a reproduction output of 1 mW,
The signal was measured using an overlapping tram analyzer with a bandwidth of 30 kHz.

In addition, the DER for the unrecorded portion was determined using a semiconductor laser/power supply power of 1 mW, rotation speed of 4 m/S, and γ = 45 m.
, measurement track fi4000) rack, the threshold level was set to +25% of the amount of reflected light, and the number of defects was counted.

Next, a magneto-optical recording medium on a 5x5cm test polycargenate substrate prepared at the same time was immersed in a 1N NaC2 aqueous solution for 5 hours, and the presence or absence of pitting corrosion was observed using a transmission optical microscope.
The result (photograph) of observation with 00 times magnification is shown in FIG. As shown in FIG. 6, it can be seen that no pinholes were generated in the entire field of view of the test piece.

(Comparative Example 1) Optical magnetism was carried out in the same manner as in Example 1, except that tetrafluoroethylene resin (trade name: Teflon 820-J) manufactured by Mitsui-DuPont Fluorochemical Co., Ltd. was used instead of Afro 70020 in Example 1. A disk and its test piece were produced.

This sample was subjected to the same accelerated deterioration test as in Example 1, and the C/N and DIR were measured. Table 1 shows the results.

As a result, although there was little change in C/N, DI
R is reduced by one order of magnitude or more compared to Example 1.

Moreover, FIG. 7 shows a transmission micrograph (100x magnification) after immersion in a 1N NaCl aqueous solution for 5 hours.

As shown in FIG. 7, it can be seen that pinholes with a diameter of 10 to 100 μm are partially formed, and pitting corrosion occurs and grows.

(Comparative Example 2) A magneto-optical disk and its test piece were produced in the same manner as in Example 1, except that the film of tetrafluoroethylene copolymer was not deposited in Example 1. These samples were subjected to the same accelerated deterioration test as in Example 1. The results are shown in Table 1 for C/N and DIR, and in FIG. 8 for a micrograph (100x magnification). The DIR decreased by about two orders of magnitude, and pitting corrosion occurred significantly in the NaC2 aqueous solution immersion test.

(Example 2) After applying approximately 30 μm of ultraviolet curable resin (5D-301 manufactured by Dainippon Ink) to the outermost surface of the recording medium using a spin code method in a magneto-optical disk produced in the same manner as in Example 1. The material was cured by irradiation with ultraviolet rays to produce a magneto-optical disk. Its structure is shown in Figure 2. This sample was subjected to the same accelerated deterioration test as in Example 1, and the results are shown in Table 1.
It was shown to.

From this, similar to Example 1, almost no deterioration was observed in both C/N and DER.

(Comparative Example 3) A magneto-optical disk/s/pull was produced in the same manner as in Example 2 except that the film of tetrafluoroethylene copolymer was not deposited. Its structure is shown in Figure 3. When this sample was subjected to the same accelerated deterioration test as in Example 1, as shown in Table 1, although there was almost no decrease in C/N, some deterioration in DIR was observed.

(Example 3) In Example 1, polycar? In advance, apply a heptano-ethylene copolymer film at approximately 1000X on the base substrate of Neato.
A magneto-optical disk sample was prepared thereon in the same manner as in Example 1. A schematic diagram of its structure is shown in FIG. When this sample was subjected to the same accelerated deterioration test as in Example 1, no deterioration was observed in both C/N and DER.0 (Example 4) In Example 1, the side opposite to the recording layer side of the polycarbonate substrate was fluorinated. A magneto-optical disk was prepared in the same manner as in Example 1 except that an ethylene copolymer film was applied (Fig. 5).The obtained sample was subjected to an accelerated deterioration test in the same manner as in Example 1. Stability similar to that of 1 was obtained.

/ 60,000' / Tables 1 to 8 are microscopic photographs showing the presence or absence of pitting corrosion.

DESCRIPTION OF SYMBOLS 1... Substrate, 2... Inorganic dielectric film, 3... Magneto-optical recording layer, 4... Fluorinated ethylene copolymer retention layer, s
...UV curable resin layer.

〔Effect of the invention〕

As described above, according to the present invention, in a magneto-optical recording medium in which a magneto-optical recording layer on a transparent substrate is irradiated with light to perform recording, reproduction and erasing, the outside world and/or the area that contacts the substrate is By coating K with a film of tetrafluoroethylene copolymer, storage stability is improved and it becomes possible to provide a highly reliable magneto-optical recording medium.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. A magneto-optical recording medium comprising a recording layer formed on an optically transparent substrate, characterized in that the recording layer is completely covered with a film of a copolymer of tetrafluoroethylene and ethylene.