JP2983108B2 - Method of manufacturing magneto-optical disk and magneto-optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk of a magnetic field modulation type and a method of manufacturing the same.

[0002]

2. Description of the Related Art Optical discs have attracted attention as large-capacity information carrying media. Among them, there is a magneto-optical disk of a magnetic field modulation type, and application to a data file or the like is expected. In the magnetic field modulation method, a laser beam is radiated from an optical head to a recording layer of a disc in a DC manner to raise the temperature, and at the same time, a modulated magnetic field is applied from a magnetic head arranged on the opposite side of the optical head. The voltage is applied to the recording layer to perform recording. Therefore, this method allows overwrite recording.

The conventional magneto-optical disk drive mainly employs the CSS system. In the CSS method, a floating magnetic head is used, and the magnetic head contacts the disk surface at the start and end of the disk rotation. For this reason,
A protective coat is provided on the surface of the disk facing the magnetic head to prevent the magnetic head from sticking or crashing.

[0004] For the protective coat of a magneto-optical disk used in the CSS system, for example, a resin composition containing a fluorine-containing polyurethane resin as a main component (JP-A-2-301040)
No. 2-301041) and a resin composition containing a fluorine resin soluble in an organic solvent as a main component (JP-A-3-378).
No. 44) is proposed, and in these, it is also proposed to include a metal element or a sliding material having a higher ionization tendency than the transition metal element constituting the recording film. Further, Japanese Patent Application Laid-Open No. 2-40149 discloses that an ultraviolet curable resin mixed with a lubricant is used.
No. 17844 proposes using a lubricating layer. Japanese Patent Application Laid-Open No. 3-62338 discloses that an overcoat layer formed by coating is coated with a silicone resin or Ni.
It has been proposed to disperse fine particles such as these so as to make unevenness of 0.1 μm or more and 0.5 μm or less exist uniformly on the surface.

[0005]

Recently, a magneto-optical disk capable of recording / reproducing at the same linear velocity as a compact disk (CD) can be shared with a drive device by simply adding or changing an optical system. Attention has been paid. Since the linear velocity of the CD is as low as 1.2 to 1.4 m / s, the magnetic head cannot be floated, and the above-described CSS method cannot be used. Therefore, it is conceivable to use a fixed magnetic head that is kept at a fixed distance from the disk surface.

However, when a fixed magnetic head is used,
The magnetic head may collide with the disk due to the runout of the disk or the vibration of the drive device. Further, in order to make the magnetic head follow the disk runout, it is necessary to provide a servo means, which complicates the configuration of the drive device.

Under such circumstances, the present inventors considered a configuration in which the magnetic head always slides on the disk surface, and conducted research on a magneto-optical disk corresponding to this configuration.

As a result, it has been found that when the magnetic head slides on the disk surface, the various protective coats proposed in the above-mentioned CSS system are insufficiently effective.

That is, since the magnetic head is always slid on the surface of the protective coat, the sustainability of the lubricating effect is insufficient with the protective coat mixed with the lubricant. When a method of dispersing fine particles in a coating film to increase the surface roughness of the protective coat is used, irregularities of 0.1 μm or more and 0.5 μm or less as disclosed in JP-A-3-62338 are formed. Such fine particles have insufficient surface roughness of the protective coating and insufficient friction reduction effect. For these reasons, it is difficult to keep the friction with the magnetic head low at all times. Further, fine particles of metal or ceramics have high hardness, and may damage the magnetic head.

Further, the protective coat disclosed in each of the above publications has a single-layer structure, and the protective coat has defects such as through holes, and thus has a problem in reliability. In particular, in the case of a protective coat in which fine particles are dispersed, cracks may occur in the protective coat in a high-temperature and high-humidity environment, and sufficient reliability cannot be obtained.

The present invention has been made in view of such circumstances, and when producing a magneto-optical disk used in a system in which a magnetic head always slides, the effect of reducing friction between the magnetic head and the magnetic head is great. Good sustainability,
Another object of the present invention is to realize a highly reliable surface coat layer.

[0012]

The above object is achieved by the following constitutions (1) to (8).

(1) A recording layer is provided on a substrate, a lower protective coat made of resin is provided on the recording layer, and an upper protective coat made of resin is provided on the lower protective coat in close contact with the lower protective coat. A method for manufacturing a magneto-optical disk used for magneto-optical recording of a magnetic field modulation system and used so that a magnetic head slides on a surface of the upper protective coat, wherein the lower protective coat is formed by a spin coating method. And forming the upper protective coat by screen printing so that the center line average roughness (Ra) is 0.05 to 1.0 μm.

(2) A recording layer is provided on the substrate, a lower protective coat made of resin is provided on the recording layer, and an upper protective coat made of resin is provided on the lower protective coat in close contact with the lower protective coat. A method for manufacturing a magneto-optical disk used for magneto-optical recording of a magnetic field modulation system and used so that a magnetic head slides on a surface of the upper protective coat, wherein the lower protective coat is formed by a spin coating method. Wherein the upper protective coat is formed by a screen printing method using a screen of 350 mesh or more per inch.

(3) The method of manufacturing a magneto-optical disk according to the above (1) or (2), wherein particles are dispersed in the upper protective coat.

(4) The viscosity of the printing paint used to form the upper protective coat is 100 to 100,000 cp.
s. The method for manufacturing a magneto-optical disk according to any one of (1) to (3) above.

(5) The thickness of the upper protective coat is 5 to 1
The method for manufacturing a magneto-optical disk according to any one of the above (1) to (4), which is 5 μm.

(6) The method of manufacturing a magneto-optical disk according to any one of (1) to (5), wherein a radiation-curable resin is used for the lower protective coat and the upper protective coat.

(7) The method according to any one of (1) to (6), wherein the content of the particles in the upper protective coat is 5 to 50% by weight.

(8) A magneto-optical disk manufactured by the method according to any one of (1) to (7).

[0021]

According to the present invention, a protective layer or a reflective layer made of an inorganic material is formed on a recording layer of a magneto-optical disk, and a lower protective coat is formed thereon by a spin coating method, and further formed by a screen printing method. Form a top protective coat.

In the spin coating method, the lower protective coat can be formed without damaging the uppermost layer of the inorganic material, and the dense upper protective coat formed by the screen printing method can cover the defects of the lower protective coat.

Since the surface roughness of the upper protective coat can be adjusted by changing the mesh density of the screen, the upper protective coat having such a surface roughness that the friction between the upper protective coat and the magnetic head which is in constant contact can be extremely reduced. Is realized.

Further, by dispersing inorganic particles such as carbon particles in the upper protective coat, a more excellent friction reducing effect can be obtained.

Japanese Patent Application Laid-Open No. Hei 1-211257 describes an optical information recording medium having a label print layer on the uppermost part of the medium on a reflective film. In this publication, in the printing step of the label printing layer, a protection film for protecting the reflection film is formed in the first color unit, and label printing is performed in the second color and subsequent units. That is, since the protective film in contact with the reflective film is formed by a printing method, the reflective film may be damaged. In addition, the label printing layer in the same publication is for displaying a character pattern or a graphic pattern, and this causes irregularities on the medium surface of the recording area. Can not. Further, in this publication, an ultraviolet curable ink is used, and the first color contains a pigment by solid printing, but when the pigment is contained, the curability of the resin is reduced. Since the first color is in contact with the metal reflection film, the protection effect of the metal reflection film becomes insufficient, and high reliability cannot be obtained.

Japanese Patent Application Laid-Open No. 1-243251 discloses an optical system in which a pit is formed on one surface of a transparent resin layer, a metal reflective film is provided on the pit, a protective layer, and label printing are sequentially performed. Disc is listed. The protective layer in the publication is made of an ultraviolet-curable acrylic resin containing white titanium, and is formed by spin coating or printing. In this case, as in the case of Japanese Patent Application Laid-Open No. Hei 1-211257, a magnetic head of a constant contact type cannot be used because the uppermost layer of the disk is a label printing layer. Further, the protective layer of this optical disk corresponds to the lower protective coat in the present invention, but when a pigment such as white titanium is added to the protective layer, high reliability cannot be obtained as described above.

Further, JP-A-2-7249 and JP-A-2-7249.
No. 149951 discloses that a protective film made of an ultraviolet curable resin is formed by a screen printing method on a disk substrate provided with a recording film or a reflective film in the same apparatus.
A method of manufacturing an optical disk by forming a printing film made of an ultraviolet curable resin by a screen printing method on a disk substrate provided with the protective film is described. When screen printing is performed directly on the recording film or the reflection film in this manner, the recording film or the reflection film may be damaged. In addition, since the printing film on the protective film is a label printing film, it is not possible to use a constant contact magnetic head as in the above publications.

The above publications do not disclose a preferable medium surface roughness when a constantly sliding magnetic head is used or a preferable mesh density of a printing screen to be used.

[0029]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The magneto-optical disk manufactured according to the present invention has a recording layer on a substrate, has a lower protective coat made of resin on the recording layer, and is in close contact with the lower protective coat on the lower protective coat. And an upper protective coat made of resin. This magneto-optical disk is used for magneto-optical recording of a magnetic field modulation system, and is used so that a magnetic head slides on the surface of the upper protective coat.

FIG. 1 shows a configuration example of a magneto-optical disk manufactured according to the present invention. In FIG. 1, the magneto-optical disk 1 has a protective layer 4, a recording layer 5, a protective layer 6, a reflective layer 7, a lower protective coat 8, and an upper protective coat 9 on the surface of a substrate 2. When the disk is driven, the magnetic head slides on the surface of the upper protective coat 9. The magnetic head is normally supported by a suspension and can follow the runout of the disk, so that it does not separate from the disk surface.

In the present invention, the lower protective coat 8 is formed by a spin coating method, and the upper protective coat 9 is formed by a screen printing method.

In order to keep the friction between the magnetic head and the magnetic head in constant contact with each other, the surface of the upper protective coating should be JIS B 06
The center line average roughness (Ra) specified in 01 is preferably 0.05 to 1.0 μm, particularly 0.1 to 0.5 μm (measuring length 0.5 mm). If Ra is less than the above range, the friction at the time of sliding of the magnetic head becomes too large, and the load on the magnetic head and the driving device becomes a problem. When Ra exceeds the above range, the friction becomes too large. In order to obtain such Ra, various conditions may be appropriately set at the time of screen printing. Among the printing conditions, the most closely related to Ra is the screen mesh density. In the present invention, it is preferable to use a screen of 350 mesh or more per inch, especially 355 to 420 mesh. If the mesh per inch is less than the above range, Ra becomes too small, and the thickness of the upper protective coat becomes too thick. If the mesh per inch exceeds the above range, the printing paint tends to hardly pass through the screen, and printing tends to be difficult.

The Ra of the upper protective coat also relates to the viscosity of the printing paint. The printing paint contains a resin and various pigments and solid lubricants added as needed. When a screen as described above is used, the viscosity of the printing paint is set to 100 to 100,000 cps, particularly to 50,000, because printing becomes easy and an appropriate Ra can be obtained.
It is preferable to set it to 00 to 50,000 cps. When the viscosity is less than the above range, the peeling of the screen becomes worse and printing tends to be difficult, and when the viscosity exceeds the above range, the thickness of the upper protective coat increases, and the disk tends to warp. is there.

It is preferable that particles are dispersed in the upper protective coat 9. As the particles, various kinds of inorganic material particles and organic material particles which themselves exhibit a friction reducing action are preferable. By including particles of an appropriate diameter, the surface Ra
Can be controlled. The shape of the particles is not particularly limited, and may be spherical, flaky, massive, fibrous, or the like, but preferably spherical.

The particles used in the present invention are particularly preferably carbon particles. The carbon particles themselves exhibit a lubricating action, and do not damage the magnetic head because of their low hardness. Note that commercially available carbon particles may be used, or the carbon particles may be produced by firing resin particles or the like. The content of the carbon particles with respect to the entire upper protective coat 9 may be appropriately selected, but is usually 5 to 50% by weight, particularly 10 to 3% by weight.
It is preferably 0% by weight. If the content is less than the above range, the friction reducing effect tends to be insufficient, and if the content is more than the above range, the dispersion state is poor, and the viscosity of the paint is increased so that the coating is performed. It tends to be difficult.

The average diameter of the particles used is not particularly limited, but may be usually selected appropriately from the range of 0.01 to 10 μm.

In the present invention, in addition to carbon particles, fluorine resin particles, alumina particles, titanium oxide particles, and the like may be used, or these particles may be used in combination.

These particles are usually used in the upper protective coat 9
Although it is preferable to uniformly disperse it in the inside, it may be unevenly distributed in the surface layer if necessary.

The resin constituting the upper protective coat 9 is preferably a radiation curable resin. Specifically, it is preferably composed of a radiation-curable compound or a substance obtained by radiation-curing a composition for polymerization thereof. Acrylic acid, methacrylic acid having an unsaturated double bond exhibiting radical polymerizability in response to ionization energy, acrylic double bond such as an ester compound thereof, and diallyl phthalate such as such. Monomers, oligomers, and polymers containing or introducing a group capable of crosslinking or polymerizing by irradiation with radiation, such as an unsaturated double bond such as an allylic double bond, maleic acid, or a maleic acid derivative, into the molecule can be given. These are preferably polyfunctional, especially trifunctional or more, and even when only one
More than one species may be used in combination.

The radiation-curable monomer may have a molecular weight of 2
Compounds having a molecular weight of less than 20
Those having a size of from 00 to 10,000 are suitable. These include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, etc. Examples include pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), acrylic modified urethane elastomer,
Alternatively, those obtained by introducing a functional group such as COOH into these compounds, acrylates (methacrylates) of phenol ethylene oxide adducts, acryl (methacrylic) groups or ε-condensed pentaerythritol condensed rings described in Japanese Patent Application No. 62-072888. Examples include compounds having a caprolactone-acryl group, and acrylic group-containing monomers and / or oligomers such as special acrylates shown in Japanese Patent Application No. 62-072888. In addition,
Examples of the radiation-curable oligomer include an oligoester acrylate or an acrylic modified product of a urethane elastomer, or an oligomer obtained by introducing a functional group such as COOH into these oligomers.

A radiation-curable compound obtained by subjecting a thermoplastic resin to radiation-sensitive modification in addition to or instead of the above compounds may be used. Specific examples of such a radiation-curable resin include acrylic double bonds having an unsaturated double bond exhibiting radical polymerizability, methacrylic acid, or an acrylic double bond such as an ester compound thereof, such as diallyl phthalate. A resin in which a group that crosslinks or polymerizes upon irradiation with radiation, such as an allylic double bond or an unsaturated bond such as maleic acid or a maleic acid derivative, is contained or introduced into a thermoplastic resin molecule. Examples of the thermoplastic resin that can be modified into a radiation-curable resin include a vinyl chloride copolymer, a saturated polyester resin, a polyvinyl alcohol resin, an epoxy resin, a phenoxy resin, and a cellulose derivative. Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (P
(VP olefin copolymer), a polyamide resin, a polyimide resin, a phenol resin, a spiroacetal resin, an acrylic resin containing at least one hydroxyl-containing acrylic ester or methacrylic ester as a polymerization component, and the like are also effective.

Since the coating composition for polymerization is cured by irradiation with radiation, especially ultraviolet irradiation, it is preferable that the polymerization composition contains a photopolymerization initiator or a sensitizer. The photopolymerization initiator or sensitizer used is not particularly limited, and may be appropriately selected from, for example, acetophenone, benzoin, benzophenone, and thioxanthone. In addition, a plurality of compounds may be used in combination as a photopolymerization initiator or a sensitizer. The content of the photopolymerization initiator in the composition for polymerization may be usually about 0.5 to 5% by weight. Such a composition for polymerization may be synthesized according to a conventional method, or may be prepared using a commercially available compound.

As the composition containing the radiation-curable compound for forming the upper protective coat 9, a composition containing an epoxy resin and a cationic photopolymerization catalyst is also preferably used.

As the epoxy resin, an alicyclic epoxy resin is preferable, and particularly, an epoxy resin having two or more epoxy groups in a molecule is preferable. As the alicyclic epoxy resin,
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis- (3,4
-Epoxycyclohexylmethyl) adipate, bis-
(3,4-epoxycyclohexyl) adipate, 2-
(3,4-epoxycyclohexyl-5,5-spiro-
One or more of 3,4-epoxy) cyclohexane-meta-dioxane, bis (2,3-epoxycyclopentyl) ether and vinylcyclohexene dioxide are preferred. There is no particular limitation on the epoxy equivalent of the alicyclic epoxy resin, but from 60 to 3 because good curability is obtained.
00, particularly preferably 100 to 200.

As the cationic photopolymerization catalyst, any known one may be used, and there is no particular limitation. For example, a complex of one or more metal fluoroborates and boron trifluoride,
Bis (perfluoroalkylsulfonyl) methane metal salt, aryldiazonium compound, aromatic onium salt of group 6A element, aromatic onium salt of group 5A element, group 3A ~
Group 5A element dicarbonyl chelate, thiopyrylium salt, MF ₆ anion (where M is P, As or S
Group 6A element having b), triarylsulfonium complex salt, aromatic iodonium complex salt, aromatic sulfonium complex salt and the like can be used. In particular, polyarylsulfonium complex salt, aromatic sulfonium salt or iodonium salt of halogen-containing complex ion, 3A It is preferable to use at least one of aromatic onium salts of Group 5A, Group 5A and Group 6A elements.

Further, a cationic photopolymerization catalyst containing an organometallic compound and an organosilicon compound having photodegradability can also be used. Since such a cationic photopolymerization catalyst is a non-strong acid type, it is possible to avoid adverse effects on a highly corrosive recording layer of a magneto-optical recording disk. As organometallic compounds, Ti, V, Cr, Mn, Fe, Co,
A complex compound in which an alkoxy group, a phenoxy group, a β-diketonato group, or the like is bonded to a metal atom such as Ni, Cu, Zn, Al, or Zr is preferable. Of these, an organoaluminum compound is particularly preferred, and specifically, trismethoxyaluminum, trispropionatoaluminum, tristrifluoroacetylaluminum, and trisethylacetoacetonatoaluminum are preferred.

The organosilicon compound having photodegradability is one that generates silanol upon irradiation with light such as ultraviolet rays.
Silicon compounds having a peroxysilano group, an o-nitrobenzyl group, an α-ketosilyl group and the like are preferred.

The content of the cationic photopolymerization catalyst in the composition is from 0.05 to 0.5% based on 100 parts by weight of the epoxy resin.
It is preferably 7 parts by weight, particularly preferably 0.1 to 0.5 part by weight.

Of these, it is preferable that a radiation-curable compound having an acrylic group is used, and a coating film containing a photopolymerization sensitizer or initiator is cured with radiation, particularly ultraviolet light.

The thickness of the upper protective coat 9 is 5 to 15 μm
And preferably 7 to 12 μm. If the film thickness is too small, it becomes difficult to form a uniform film by the screen printing method, and the durability becomes insufficient. Also,
If the thickness is too large, cracks are generated due to shrinkage during curing, and the disk is likely to be warped.

The upper protective coat 9 is formed, for example, as follows. First, a predetermined amount of particles such as carbon particles are added to the above-described resin, preferably a composition for a radiation-curable resin, if necessary, and a coating film of this is formed on the lower protective coat 8 by a screen printing method. . When a material requiring curing is used for the lower protective coat 8, the lower protective coat 8 is cured before forming the coating film. Since the upper protective coat 9 is formed by a screen printing method,
Unlike spin coating, it can be selectively applied only on the recording area. For this reason, the amount of resin used is small.

Next, the coating film is cured by irradiating ultraviolet rays. In some cases, ultraviolet rays may be irradiated after heating, or an electron beam or the like may be irradiated instead of ultraviolet rays.
The intensity of the ultraviolet light applied to the coating film is usually about 50 mW / cm ² or more, and the amount of irradiation is usually about 500 to 2000 mJ / cm ² . Further, as the ultraviolet ray source, a usual one such as a mercury lamp may be used. The above compounds undergo radical polymerization by irradiation with ultraviolet rays.

The lower protective coat 8 is provided to protect the sputtered laminated film up to the reflective layer 7. The lower protective coat 8 is formed by spin coating. The conditions for spin coating are not particularly limited, and may be appropriately selected from ordinary conditions. The resin used for the lower protective coat 8 is not particularly limited, but preferably uses the above-mentioned radiation curable resin. The thickness of the lower protective coat 8 is 0.1 to 10 μm, particularly 1 to 7 μm.
m is preferable.

The total thickness of the lower protective coat 8 and the upper protective coat 9 is not particularly limited, and may be appropriately determined according to the magnetic field strength required for the recording layer 5, the capability of the magnetic head, the standard of the driving device, and the like. However, it is usually about 8 to 20 μm.

When performing recording and reproduction on the magneto-optical disk of the present invention, the optical head is located on the back side (lower side in the figure) of the substrate 2 and is irradiated with laser light through the substrate. Glass, a transparent resin such as polycarbonate, acrylic resin, amorphous polyolefin, and styrene resin is used. On the surface of the substrate 2 on the recording layer 5 side,
Usually, grooves or pits for tracking, address, etc. are formed.

The protective layer 4 and the protective layer 6 have an effect of improving C / N and preventing corrosion of the recording layer.
It is about 0 nm. It is desirable that at least one, and preferably both, of these protective layers are provided. These protective layers are preferably composed of a dielectric material composed of various oxides, carbides, nitrides, sulfides or mixtures thereof, and are formed by various vapor deposition methods such as sputtering, vapor deposition, and ion plating. It is preferably formed.

In the recording layer 5, information is magnetically recorded by a modulated heat beam or a modulated magnetic field, and the recorded information is reproduced by magneto-optical conversion. The material of the recording layer 5 is not particularly limited as long as it can perform magneto-optical recording. For example, an alloy containing a rare earth metal element, in particular, an alloy of a rare earth metal and a transition metal is formed by sputtering, vapor deposition, ion It is preferably formed as an amorphous film by plating or the like, particularly by sputtering. Specific compositions include TbFeCo, Dy
TbFeCo, NdDyFeCo, NdGdFeCo and the like can be mentioned. The thickness of the recording layer 5 is usually 10 to 100.
It is about 0 nm.

The reflection layer 7 is provided as needed. The material forming the reflective layer 7 is Au, Ag, Pt, Al, T
It may be a metal having a relatively high reflectance such as i, Cr, Ni, Co, or the like, an alloy thereof, or a compound thereof. The reflective layer 7 may be provided in the same manner as the recording layer 5. The thickness of the reflective layer 7 is preferably about 30 to 200 nm.

Incidentally, a transparent hard coat 3 may be formed on the back side of the substrate 2 as shown in the figure. The material and thickness of the hard coat may be the same as those of the lower protective coat 8. The hard coat is preferably imparted with antistatic properties by, for example, adding a surfactant. The hard coat is not limited to the main surface of the disk, but may be provided on the outer peripheral side surface or the inner peripheral side surface of the disk.

[0061]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

The magneto-optical disk samples shown in Table 1 below were prepared.

First, a coating film of a composition for hard coat was formed on one main surface and a peripheral side surface of a polycarbonate resin substrate having an outer diameter of 64 mm, an inner diameter of 11 mm, and a recording portion thickness of 1.2 mm.
This coating film was cured by ultraviolet rays to form a hard coat having a thickness of about 5 μm.

Next, a SiN _x protective layer was formed to a thickness of 80 nm on the main surface opposite to the surface on which the hard coat was formed by high-frequency magnetron sputtering. Next, on this protective layer, Tb
A recording layer having a composition of ₂₃ Fe ₇₂ Co ₅ was formed to a thickness of 20 nm by sputtering. Further, on this recording layer, a 20 nm protective layer having the same composition as the above protective layer was formed by high frequency magnetron sputtering, and an 80 nm A layer was formed on this protective layer.
An alloy reflective layer, a lower protective coat and an upper protective coat were sequentially formed.

The lower protective coating is obtained by forming a coating of the following composition for polymerization by a spin coating method and irradiating the coating with ultraviolet rays to cure the coating. The cured protective coating has an average thickness of about 5 μm. did. The amount of ultraviolet irradiation was 1000 mJ / cm ² .

Polymerization Composition Oligoester Acrylate (Molecular Weight 5,000) 50 parts by weight Trimethylolpropane triacrylate 50 parts by weight 3 parts by weight of acetophenone-based photopolymerization initiator The upper protective coat was formed as follows. Ultraviolet curable resin composition containing carbon particles 粒子 SSD- made by Dainippon Ink
582 (BLACK)｝ or a UV curable resin composition containing no carbon particles (SSD M BASE made by Dainippon Ink) is applied on the cured lower protective coat by screen printing, and the same as the lower protective coat And cured. The average thickness after curing was about 10 μm. Table 1 shows the number of meshes per inch of the screen used for printing.

A comparative sample (sample No. 4) was prepared in the same manner as above except that the upper protective coat was formed by spin coating. Further, a comparative sample (Sample No. 5) without the upper protective coat was also prepared. In this comparative sample, Dainippon Ink SSD-582 (BL
ACK) was applied on the reflective layer by spin coating to form a lower protective coat.

Table 1 shows Ra of the recording layer side surface of each sample. Note that Ra was measured by tally step.

The following evaluation was performed on these samples. Table 1 shows the results. (1) Dynamic friction coefficient Using a 3.5 "magnetic disk drive made by Plus, 1rp
Rotate the disk at m and measure the stress on the head,
From this, the dynamic friction coefficient μ was calculated. The load was 15 g.

(2) Reliability test Using VRF-2000 (manufactured by Nakamichi), the initial byte error rate (BER) and the BER after storage at 80 ° C. and 80% RH for 1000 hours were measured.

[0071]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear.

In the case of sample No. 5, the temperature was 80 ° C./80° C.
After storage at 1000% RH for 1000 hours, cracks had occurred in the lower protective coat. In addition, a sample in which the lower protective coat was formed by a screen printing method was also prepared. However, in this sample, the recording layer was damaged during printing, and VRF-2
000 could not be sampled.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of a magneto-optical disk according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-optical disk 2 Substrate 3 Hard coat 4 Protective layer 5 Recording layer 6 Protective layer 7 Reflective layer 8 Lower protective coat 9 Upper protective coat

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeshi Komaki 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-5-242538 (JP, A) (58) Surveyed field (Int.Cl. ⁶ , DB name) G11B 11/10 541 G11B 11/10 521

Claims (8)

(57) [Claims] 1. A recording medium comprising: a recording layer on a substrate; a lower protective coat made of resin on the recording layer; and an upper protective coat made of resin in close contact with the lower protective coat on the lower protective coat. A method of manufacturing a magneto-optical disk used for magneto-optical recording of a magnetic field modulation system, wherein a magnetic head is slid on the surface of the upper protective coat, wherein the lower protective coat is formed by spin coating. And forming the upper protective coat by screen printing so that the center line average roughness (Ra) becomes 0.05 to 1.0 [mu] m. 2. A recording layer on a substrate, a lower protective coat made of resin on the recording layer, and an upper protective coat made of resin in close contact with the lower protective coat on the lower protective coat. A method of manufacturing a magneto-optical disk used for magneto-optical recording of a magnetic field modulation system, wherein a magnetic head is slid on the surface of the upper protective coat, wherein the lower protective coat is formed by spin coating. And forming the upper protective coat by a screen printing method using a screen of 350 mesh or more per inch. 3. The method according to claim 1, wherein particles are dispersed in the upper protective coat. 4. The method for manufacturing a magneto-optical disk according to claim 1, wherein the viscosity of the printing paint used for forming the upper protective coat is 100 to 100,000 cps. 5. The thickness of the upper protective coat is 5 to 15 μm.
The method for manufacturing a magneto-optical disk according to claim 1, wherein m is m. 6. The method according to claim 1, wherein a radiation curable resin is used for the lower protective coat and the upper protective coat. 7. The method according to claim 1, wherein the content of the particles in the upper protective coat is 5 to 50% by weight. 8. A magneto-optical disk manufactured by the method according to claim 1. Description: