JPS618752A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a photomagnetic recording medium which is easily formed and is superior in corrosion resistance and recording stability and has high repeatability in writing and erasing, by providing a protective film consisting of a polymer layer on a recording layer on a substrate. CONSTITUTION:A recording layer 2 is provided on a substrate 1, and the protective layer consisting of a polymer layer 3 of PMMA, polystyrene, or the like is formed on the layer 2. Since the protective layer 3 consists of the polymer layer, the photomagnetic recording medium is easy to form and the corrosion resistance is improved, and as the result, the stability is improved, and the repeatability in writing and erasing is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to optical recording media, particularly magneto-optical recording media.

(Prior Art) In the field of information processing technology, with the rapid increase and diversification of information, demands for further increases in magnetic memory recording capacity, number of writes, etc. have been increasing in recent years. There is. Therefore, as an alternative to the conventional recording method, an optical recording method using an optical recording medium is proposed, for example, for magazines (e.g.
November issue (1883) Seibundo Shinkosha, p. 63-74)
has been disclosed.

The conventional example disclosed herein will be explained.

First, there are those using metal thin films or metal-containing polymer materials. In this method, the recorded portion of the recording medium is melted and evaporated using a laser beam, and a hole is punched for writing, making it impossible to rewrite.

On the other hand, an example of a rewritable optical recording medium is one that utilizes the photodarkening phenomenon of amorphous chalcogenide, but such amorphous chalcogenide materials generally have low recording sensitivity and have a light absorption edge with a short wavelength. Furthermore, since absorption is small at wavelengths near the absorption edge, recording sensitivity for long wavelength light is extremely low. Incidentally, since laser light generally has good directivity and can be focused to an extremely small spot, it is suitable for use as a light source for optical recording media. Furthermore, since semiconductor lasers can be made extremely compact, they are attracting particular attention as light sources. However, at present, the oscillation wavelength range of semiconductor lasers is 750 to 800 nm or more, and it will probably be a relatively long wavelength of about -700 nm in the future. In addition, He-
Even a He laser has a wavelength range of 832.8 nm, and Ar, Kr, etc. lasers have short wavelengths, but they are slightly more unstable and the equipment itself is large. Therefore, when a semiconductor laser or a He-Ne laser is used as a light source, the amorphous chalcogenide described above
The recording sensitivity becomes low, and on the other hand, if a laser such as Ar or Kr is used, the memory device becomes significantly large.

Another optical recording medium is a medium that combines a thermoplastic and a photoconductor, and this recording medium has the advantage that the wavelength range used can be changed by freely selecting the photoconductor.

The number of times that it can be rewritten is at most 100 times,
In addition, there is a drawback that individual recorded bits cannot be selectively erased, and the entire area within a certain area is erased, and processing corresponding to the recent increase in the amount and diversity of information cannot be performed satisfactorily.

By the way, there is another recording medium using a magneto-optical recording material. This type of recording medium has no restrictions on the light source used, and is viewed as promising because it can be rewritten many times. Among these, alloys of rare earth elements such as cd, 'rb, and Dy and iron elements such as Fe and Go are particularly promising as materials for magneto-optical recording. however,
These materials for magneto-optical recording are divided into Go-based and Fe-based materials. The system has the important practical disadvantage of being very susceptible to oxidation.

Therefore, the literature (Journal of Applied Magnetics Society, Utsu, [2] (1984
), p. 93), a recording layer is formed on a substrate using such a magneto-optical recording material, and a protective film such as an oxide film such as 5i02 or an AQN film is formed on this recording layer. Providing such a nitride film is practiced.

(Problems to be Solved by the Invention) However, forming such an oxide film and nitride film on the recording layer is time-consuming and costly, and furthermore, it requires a complicated process to apply these protective films. The disadvantage is that it requires equipment. Furthermore, the reality is that many of the conventional optical recording media described above do not necessarily have satisfactory rewritability and performance characteristics during rewriting as described above.

Therefore, an object of the present invention is to be able to form a protective film without requiring much effort, cost, or complicated equipment, and which has excellent corrosion resistance, good recording stability, and easy writing. The object of the present invention is to provide a magneto-optical recording medium in which the repeatability of erasing is significantly increased.

Another object of the present invention is to provide a magneto-optical recording medium that can be used for high-density recording and has good recording sensitivity.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, a magneto-optical recording medium is provided which includes a recording layer of a magneto-optical recording material provided on a substrate. , the protective film is formed of a polymer layer.

(Function) By forming the protective film with a polymer layer in this way,
It does not take much time to form, it does not cost much, it does not require a device with a complicated structure, and it also has improved corrosion resistance.This improved corrosion resistance also increases the stability of recording. The repeatability will also increase significantly.

Further, due to the properties of the magneto-optical recording material itself used for the recording layer, the magneto-optical recording medium of the present invention is suitable for high-density recording and has high recording sensitivity.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the magneto-optical recording medium of the present invention to the extent that its structure can be understood. In the figure, reference numeral 1 denotes a substrate, and a sufficiently smooth and transparent glass substrate or resin substrate is used as the substrate 1. 2 is a recording layer provided on the upper side of this substrate l. The recording layer 2 is formed as an alloy layer using a photo-optical recording material, and in this embodiment, it is, for example, a Tb3(+Fed0 alloy film).

In this invention, a polymer layer 3 is deposited on this recording layer 2. The polymer layer 3 can be formed directly on the recording layer 2 or indirectly through a dielectric layer, but in this example, three types of polymers, for example, PMMA, polystyrene, and polyester, are A test was conducted by directly forming the film on the recording layer 2. The thickness of the polymer layer is preferably about 1 to 2p, rs, but is not limited thereto.

For the magneto-optical recording medium thus formed, 10
Record writing is performed using a He-Me laser beam of less than mw in a writing time of about 1 gs to obtain a minute record with a diameter of about l#LI11 or less, and it can withstand repeated erasing and rewriting more than 1000 times. It was confirmed.

Further, when a comparative test of corrosion resistance was conducted on a medium coated with the polymer layer 3 and a medium not coated with the polymer layer 3 (referred to as a non-coated medium), it was confirmed that the magneto-optical recording medium of the present invention has extremely excellent corrosion resistance.

This corrosion resistance will be described below. Figure 2 shows a PMM using PMMA (thickness 1 gm) as the polymer layer 3.
A: 120°C for coated media and non-coated media
The relationship between the retention time in the dryer (plotted on the horizontal axis) and the Kerr rotation angle ratio θ/θ〆ρ (plotted on the vertical axis) is shown. This is the value measured from the polymer side at the Kerr rotation angle θ, and the initial value θ is the Kerr rotation angle before putting it into the dryer. As can be understood from this figure, in the case of non-coated media,
It can be seen that the Kerr rotation angle ratio decreases significantly as the holding time increases. It is presumed that this decrease is due to oxidation of the surface of the recording layer 2. Compared to this,
It can be seen that the decrease in the Kerr rotation angle ratio of the PMMA coated medium is small, indicating that it has excellent corrosion resistance.

Figure 3 shows the results of PMMA: Ipm media, polystyrene coated (Igm) fi media, and non-coated media held in an atmosphere at a temperature of 85°C and relative humidity (RH) of 85% for 368 minutes (horizontal axis Changes in the Kerr rotation angle ratio of each magneto-optical recording medium (plotted on the vertical axis)
shows. As can be understood from this figure, the PMMA-coated medium and the polystyrene-coated medium have almost no decrease in the Kerr rotation angle ratio compared to the conventional non-coated medium, and therefore it can be seen that they have excellent corrosion resistance.

Furthermore, magneto-optical recording materials tend to suffer from pitting corrosion in high humidity atmospheres, and this pitting corrosion penetrates through thin films. Therefore, as the amount of pitting corrosion increases, the transmittance increases. Therefore, corrosion resistance can be evaluated based on the transmittance.

Table 1 shows temperature 8 for uncoated media and polymer coated media of PMMA, polystyrene, and polyester.
The experimental results of the change in transmittance ratio (T/To) after being kept in an atmosphere of 5° C. and 85% relative humidity for 368 minutes are shown. Here, the initial value To is the transmittance before entering this atmosphere. The results show that the polymer-coated media according to the present invention have significantly better corrosion resistance than the non-coated media.

Table 1 Table 2 also shows the experimental results of the change in transmittance ratio of the same sample as in Table 1 after immersion in lN NaCl aqueous solution for 2 minutes. This result also shows that the polymer coated medium according to the present invention has high corrosion resistance.

Table 2 Note that the fact that the polymer layer 3 was deposited on the recording layer 2 itself caused no decrease in the absolute value of the Kerr rotation angle θ;
Moreover, almost no decrease in reflectance was observed.

In this way, the magneto-optical recording medium coated with the polymer layer according to the present invention has no deterioration in its magneto-optical properties.
It was confirmed that corrosion resistance was significantly improved.

In addition, since this polymer is used, unlike conventional oxide films or nitride films, it does not take much time or cost to form on the recording layer or dielectric layer. The equipment used for forming the film is simpler than that for forming oxide films or nitride films.

In addition to the polymers described in the examples above, for example,
A variety of polymeric materials can be used, such as polyurethane, epoxy, polyimide, fluorocarbon, polyxylene, polyvinyl, polyamide, polycarbonate, polysulfide, and the like.

Further, the substrate used in the magneto-optical recording medium of the present invention is not limited to the above-mentioned transparent glass, but may be in any desired shape, whether transparent or opaque, plate-like, sheet-like, tape-like or other. A substrate made of any material may be used.

In addition, in the above embodiment, Tb3o is used as the magneto-optical material.
Although Fe7θ alloy is used, the present invention is not limited to this, and various rare earth-iron alloys or higher binary alloys can be used.

Furthermore, the medium structure is not limited to the structure shown in FIG. 1, and may include a dielectric layer between the substrate and the recording layer and between the recording layer and the polymer layer, or both. Alternatively, the recording layer may be separated into a writing layer and a reading layer.

(Effects of the Invention) As is clear from the above, since the magneto-optical recording medium according to the present invention uses a polymer layer as a protective layer, it is easier to form the protective layer than in the case of conventional recording media of this type. This method has the advantage that it does not require much time and effort, does not require any cost, and requires only a simple device for forming the protective layer.

Furthermore, this polymer layer improves the corrosion resistance of the magneto-optical recording medium, and this improvement in corrosion resistance has the advantage of significantly improving recording stability.

Further, since the protective layer is a polymer layer, there is an advantage that the repeatability of writing and erasing is significantly increased.

Furthermore, since the recording layer of the recording medium of the present invention is formed of a magneto-optical recording material, it has the advantage of enabling high-density recording and having good recording sensitivity.

Further, the magneto-optical recording medium of the present invention can be written and erased using a laser beam, and has the advantage that various conventional restrictions regarding the light source used are significantly alleviated.

The magneto-optical recording medium of this invention is suitable as a recording medium.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of the magneto-optical recording medium of the present invention, and FIGS. 2 and 3 show the experimental results of the Kerr rotation angle ratio, which are used to explain the characteristics of the magneto-optical recording medium of the present invention. FIG. 1...Substrate, 2...Recording layer 3...
Protective layer (polymer layer). Patent applicant Oki Electric Industry Co., Ltd. Procedural amendment September 5, 1985

Claims (1)

[Claims] 1. A magneto-optical recording medium comprising a protective film on a recording layer of a magneto-optical recording material provided on a substrate, wherein the protective film is formed of a polymer layer.