JP3421875B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording film and a reflection film made of metal formed on a substrate, and made of an ultraviolet-curable resin so as to cover the reflection film. The present invention relates to a magneto-optical recording medium on which a protective film is formed, and more particularly to improvement of a protective film. 2. Description of the Related Art In a magneto-optical recording system, the temperature of a magnetic thin film is partially raised beyond a Curie point or a temperature compensation point, and the coercive force in this portion is eliminated to reduce a recording magnetic field applied from the outside. It is based on the principle of reversing the direction of magnetization in the direction, and is being put to practical use in an optical file system, an external storage device of a computer, or a recording device for audio and video information. The magneto-optical recording method is roughly classified into an optical modulation method and a magnetic field modulation method. Among them, the magnetic field modulation method has attracted attention because overwriting is possible. In the magnetic field modulation system, information is written on a magnetic thin film by reversing an applied magnetic field at a high speed. The application of a magnetic field is usually performed by a magnetic head having a magnetic field generating means. In this case, since the strength of the recording magnetic field is determined by the distance between the magnetic head and the magnetic thin film, the magnetic head must be brought as close as possible to the magnetic thin film. Therefore, in such a magnetic field modulation system, for example, a sliding magnetic head which directly contacts a surface of a magneto-optical disk and performs recording while sliding, or a magneto-optical recording medium. The use of a floating magnetic head that records information while flying and running with a small gap of about 10 μm to a magneto-optical recording medium such as a disk is being studied. If these magnetic heads are employed, a sufficient magnetic force can be applied to the magnetic thin film of the magneto-optical disk. The magneto-optical disk is, for example, a magnetic thin film which has an easy axis of magnetization perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like and has a large magneto-optical effect. In order to form a recording layer by laminating a film (for example, a rare earth-transition metal alloy amorphous thin film) or a dielectric film and further laminating a reflective film, the recording layer is formed to prevent corrosion of the recording magnetic film. Is formed so as to cover a protective film made of an ultraviolet curable resin or the like on a reflective film which is the uppermost layer of the above. When information is recorded on such a magneto-optical disk by the above-mentioned sliding magnetic head, the recording is performed by sliding the magnetic head on the protective film on the recording layer. The same applies to the case where a floating magnetic head is used. Information is recorded by causing the magnetic head to levitate and run with a small gap on a protective film on the recording layer. Then, reproduction light such as laser light is irradiated from the substrate side of the magneto-optical disk to reproduce information recorded on the magneto-optical disk. Therefore, in the above-described magneto-optical disk, in order to prevent the substrate from being damaged, a protective film is also formed on the laser beam irradiation surface opposite to the one main surface on which the recording layer of the substrate is formed. I am trying to do it. Note that the protective film is also formed of an ultraviolet curable resin or the like. [0009] In the above-described magneto-optical disk, if foreign matter such as dust is attracted to the surface of the magneto-optical disk by charging or the like, the following inconvenience occurs. For example, if a foreign substance such as dust is adsorbed on the laser light irradiation surface side of the substrate, the light interferes with reproduction light or reflected light at the time of reproducing information, and causes deterioration in reproduction characteristics. On the other hand, when foreign matter such as dust is attracted to the recording layer side, when a sliding magnetic head is used, the foreign matter such as dust is caught between the magnetic head and the magneto-optical disk. In this case, the recording magnetic film is damaged, the magnetic head is destroyed, and the recording / reproducing characteristics are degraded. Also,
Even when a flying magnetic head is used, the same disadvantage occurs because the flying distance is as small as about 10 μm. Therefore, in the above-described magneto-optical disk, it is required to provide an antistatic function to a protective film formed on the laser beam irradiation surface of the substrate and on the recording layer. In order to provide the protective film with an antistatic function, the surface resistance is reduced and the surface resistance of the glass (10 ¹³ to 1
0 ¹⁴ Ω / cm ² or so) as being that it is preferable to equal. [0012] For example, in the case of a protective film formed on the surface of the substrate irradiated with the laser beam, the protective film is formed of an ultraviolet curable resin containing an antistatic agent, and its surface resistance is 10 ¹⁴ Ω /. It is suppressed to about cm ^2. Similarly, in the protective film formed on one of the reflective films, the surface resistance is suppressed by forming the protective film using an ultraviolet curable resin containing an antistatic agent. However, in the protective film formed on the reflective film, the function of preventing corrosion of the recording magnetic film is also important,
When the above-mentioned UV-curable resin is used, it is very difficult to select the resin and the antistatic agent and to optimize the content thereof, which is not preferable from the viewpoint of productivity. The present invention has been proposed in view of the conventional circumstances, and the surface resistance of the protective film on the side where the magnetic head is disposed is suppressed, so that the protective film has a sufficient antistatic function. It is an object of the present invention to provide a magneto-optical recording medium in which adsorption of foreign matter such as dust is prevented, recording / reproducing characteristics are good, and productivity is good. In order to achieve the above object, the present invention provides a magneto-optical recording medium in which a recording film and a reflective film made of metal are formed on a substrate so as to cover the substrate. A protective film made of an ultraviolet-curable resin is formed on the reflective film on one main surface of the substrate and on the other main surface, and the protective film on the reflective film on the one main surface has a thickness of 5 μm or less. And has a surface resistance of 10 ¹⁴ Ω / cm ² or less. In the above-mentioned magneto-optical recording medium, the protective film is a lower layer and is easily affected by a reflective film made of metal. That is, if the thickness of the protective film is reduced, the protective film is affected by the reflective film having a small surface resistance, and the surface resistance is reduced, so that the above range can be achieved. In the magneto-optical recording medium according to the present invention, a protective film made of an ultraviolet-curable resin is formed on the reflective film on one main surface of the substrate and on the other main surface so as to cover the substrate. Is formed, and the protective film on the reflective film on the one main surface is formed to a thickness of 5 μm or less, and has a surface resistance of 10 ¹⁴ Ω / cm ² or less, so that a sufficient antistatic function is provided. And suppresses adhesion of foreign substances such as dust on the protective film. Preferred embodiments of the present invention will be described below based on experimental results. First, the magneto-optical disk manufactured in this experimental example will be described. In the magneto-optical disk, as shown in FIG. 1, a recording layer 2 and a protective film 3 are sequentially laminated on one main surface 1a of a substrate 1, and also on a main surface 1b opposite to the one main surface 1a. The protective film 4 is formed. The substrate 1 is a transparent substrate having a light-transmitting property and sufficiently transmitting a laser beam as a reproducing light. The material constituting the substrate 1 is usually used for this type of magneto-optical disk. Polycarbonate resin, acrylic resin,
Resin materials such as polyolefin resin and epoxy resin are exemplified. The substrate 1 is formed by molding the resin material into a disk shape by, for example, injection molding. The recording layer 2 comprises a recording magnetic film, a dielectric film, a reflection film, and the like. In this magneto-optical disk, as shown in FIG. 6, the second dielectric film 7 and the reflection film 8 are sequentially laminated. The first dielectric film 5 and the second dielectric film 7
Examples of the material constituting include various oxides or nitrides usually used for this type of magneto-optical disk.
Since oxygen in the oxide may adversely affect the recording magnetic film 6, it is preferable to use a nitride. Since the first dielectric film 5 and the second dielectric film 7 are required to have a property of not allowing oxygen and moisture to pass through and sufficiently transmitting laser light as reproduction light, nitride Among them, silicon nitride and aluminum nitride are preferable. The material constituting the recording magnetic film 6 is an amorphous ferrimagnetic material having an easy axis of magnetization in a direction perpendicular to the film surface, and is of course excellent in magneto-optical characteristics.
A material having a large coercive force at room temperature and having a Curie point around 200 ° C. is desirable. Materials having such properties include, for example, rare earth-transition metal alloys commonly used for this type of magneto-optical disk.
A b-Fe-Co alloy is preferable. In forming the recording magnetic film 6, an element such as Cr may be added to the constituent material in order to improve the corrosion resistance of the recording magnetic film 6. Further, as a material constituting the reflection film 8, it is possible to reflect 70% or more of the laser light which is the reproduction light irradiated from the substrate 1 side at the boundary with the second dielectric band film 7. It is desirable to use a non-magnetic material such as a metal that is a good conductor thermally. Therefore, considering that it is easily available, aluminum or the like, which is usually used for this type of magneto-optical disk, is preferable. The first dielectric film 5 formed on the substrate 1
The recording magnetic film 6, the second dielectric film 7, and the reflection film 8 are formed by vacuum thin film forming means such as evaporation or sputtering. These first dielectric film 5, recording magnetic film 6,
The optical characteristics can be adjusted by appropriately adjusting the thicknesses of the second dielectric film 7 and the reflective film 8. For example, when the thickness of the recording magnetic film 6 is smaller than the wavelength of the laser beam as the reproduction light, the laser beam passes through the recording magnetic film 6 and is reflected multiple times at each layer boundary. The effective optical and optical characteristics of the recording magnetic film 6 are greatly affected by the combination of the thicknesses. The protective film 3 formed on the recording layer 2, that is, on the reflective film 8, protects the recording magnetic film 6 from foreign substances such as external impact and dust, and prevents corrosion of the recording magnetic film 6. This material is provided to prevent such a problem, and examples of the material for the material include an ultraviolet curable resin commonly used for this type of magneto-optical disk. As a method of forming the protective film 3, a method of applying a UV curable resin by a spin coating method or a spray coating method to form a coating film, and then irradiating ultraviolet rays to cure the coating film to form a protective film. No. Further, the protective film 4 formed on the one main surface 1b side of the substrate 1 is provided to prevent foreign substances such as scratches and dust from being attracted to the substrate 1, and as a material constituting the same, Examples include UV-curable resins containing an antistatic agent commonly used for this type of magneto-optical disk. Note that the protective film 4 is formed in the same manner as the protective film 3. First, the relationship between the thickness of the protective film 3 formed on the recording layer 2 and the surface resistance was examined. That is, protective films 3 were formed by changing the film thickness on the recording layer 2 formed on the substrate 1 to manufacture various magneto-optical disks, and the surface resistance of the protective films 3 of these magneto-optical disks was measured. As the substrate 1, a 3.5-inch diameter polycarbonate substrate was used.
Was formed by forming a first dielectric band film 5, a recording magnetic film 6, a second dielectric band film 7, and a reflective film 8 by sputtering. At this time, the reflection film 8 was formed of aluminum. The protective film 3 was formed by applying an acrylic ultraviolet curable resin having a volume resistivity of 10 ¹⁵ Ω · cm by spin coating to form a coating film, and then curing the coating film. Next, the surface resistance of the protective film 3 of each magneto-optical disk was measured at 23.7 ° C. and 47 RH%. FIG. 2 shows the results. From the results of FIG. 2, it was confirmed that the surface resistance of the protective film 3 was dependent on the film thickness.
That is, it was confirmed that the surface resistance could be regulated by controlling the film thickness. From the results shown in FIG. 2, for example, in the case of a magneto-optical disk in which the protective film 3 has a thickness of 5 μm, the surface resistance is 1 × 10 ¹⁴ Ω / cm ² , It was also found that the value was equivalent to that of a protective film made of an ultraviolet curable resin containing an antistatic agent. Further, the volume resistivity is 10 ¹⁵ Ω ·
cm of an acrylic ultraviolet-curing resin was directly applied to the substrate 1 made of polycarbonate to form a protective film, and the surface resistance was measured at 23.7 ° C. and 47 RH% in an environment of 2 × 10 ¹⁶ Ω. / Cm ^2, which is equivalent to that of the substrate 1 made of polycarbonate. That is, it was also confirmed that the surface resistance of the protective film 3 made of an acrylic UV-curable resin was greatly affected by the surface resistance of the underlying film. Next, the relationship between the surface resistance of the protective film 3 of each magneto-optical disk and the amount of foreign matter adsorbed such as dust was examined. As a specific method, the surface of the protective film 3 of each magneto-optical disk is charged by rubbing it 50 times with a polyester cloth, and the magneto-optical disks are placed so that the protective film 3 faces ash of cigarettes. The ash adsorbed on the protective film 3 was taken with an optical microscope photograph, approached with an interval of 5 mm,
The ratio of the area where ash was adsorbed to the total area observed was determined. The results are shown in Table 1 and FIG. In Table 1 and FIG. 3, X represents the ratio of the area where ash is adsorbed to the total observed area, that is, the degree of ash adsorption. [Table 1] From the results shown in Table 1 and FIG. 3, when the thickness of the protective film 3 is 0 μm, that is, when the reflective film 8 of the recording layer 2 is exposed, the surface resistance is close to 0 Ω / cm ² , and the ash is adsorbed. Was found to have hardly happened. From the results shown in Table 1 and FIG. 3, the thickness of the protective film 3 is 5 μm or less, that is, the surface resistance is 1 × 10 ^14.
In the case of Ω / cm ² or less, adsorption of ash due to charging was significantly suppressed, and it was confirmed that a sufficient antistatic function was provided. The surface resistance of the protective film is 10 ¹⁴ Ω / c.
The thickness of the protective film less than m ² depends largely on the specifications of the magneto-optical disk to be manufactured, the characteristics of the lower reflective film, or the characteristics of the ultraviolet curable resin used. for that reason,
If the thickness of the protective film is adjusted in consideration of these conditions so that the surface resistance becomes 10 ¹⁴ Ω / cm ² or less, a sufficient antistatic function can be imparted to the protective film. That is, like the magneto-optical recording medium of the present invention, a recording film and a reflective film made of metal, a protective film covering the reflective film and made of an ultraviolet-curable resin are formed on a substrate. If the surface resistance is set to 10 ¹⁴ Ω / cm ² or less, the protective film has a sufficient antistatic function, foreign matter such as dust hardly adheres to the protective film, and has good recording / reproducing characteristics. Become. Further, like the magneto-optical recording medium of the present invention,
If the surface resistance is regulated by controlling the thickness of the protective film made of the UV-curable resin, it is not necessary to include an antistatic agent or the like in the UV-curable resin. No need to optimize the content,
Productivity is also improved. As is clear from the above description, according to the present invention, a recording film and a reflection film made of metal are formed on a substrate, and the reflection film is covered with an ultraviolet curable resin. In a magneto-optical recording medium on which a protective film is formed, the surface resistance of the protective film is set to 10 ¹⁴ Ω / cm ² or less.
Therefore, the protective film has a sufficient antistatic function, foreign matter such as dust hardly adheres to the protective film, and the recording / reproducing characteristics are good. Further, in the magneto-optical recording medium of the present invention, it is not necessary to include an antistatic agent or the like in the ultraviolet-curable resin forming the protective film, and the selection and content of the resin and the antistatic agent are not required. There is no need to perform optimization, and the productivity is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a structure of a magneto-optical disk. FIG. 2 is a characteristic diagram showing the relationship between the thickness of a protective film and its surface resistance. FIG. 3 is a characteristic diagram showing the relationship between the thickness of a protective film and the degree of ash adsorption. [Description of Signs] 1 Substrate 2 Recording layers 3, 4 Protective film 5 First dielectric band film 6 Recording magnetic film 7 Second dielectric band film 8 Reflective film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 11/105

Claims (1)

(57) [Claim 1] In a magneto-optical recording medium in which a recording film and a reflective film made of metal are formed on a substrate, one of the main surfaces of the substrate is covered so as to cover the substrate. Reflective film
A protective film made of an ultraviolet curable resin is formed on the upper and other main surfaces, and the protective film on the reflective film on the one main surface is formed to a thickness of 5 μm or less and has a surface resistance of 10 ¹⁴ Ω /. cm ² or less.