JPH05325285A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To improve friction characteristic and to enhance durability by incorporating fine particles having secondary agglomeration structure in a resin layer to form a protective layer having a prescribed roughness formed by a small amount of the fine particles. CONSTITUTION:The magneto-optical disk 1 is formed by successively laminating on the surface of a substrate 2 a protective layer 4, an interlayer 5, a recording layer 6, a protective layer 7, a reflective layer 8, and the protective coat 9 made of the resin containing the fine particles having secondary agglomeration structure, thus permitting the protective coat to have a prescribed roughness formed on the surface by a small amount of the fine particles.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Optical discs have attracted attention as large-capacity information carrying media. Among these, there is a magnetic field modulation type magneto-optical disk that can be overwritten, and its application to data files and the like is expected. In this magnetic field modulation method, a magnetic layer of a magneto-optical disk is irradiated with DC light from an optical pickup to raise its temperature, and at the same time, a magnetic head arranged on the side opposite to the optical pickup is used. A recording magnetic field is applied to the magnetic layer to perform overwrite recording.

In this case, the CSS system in which the magnetic head and the disk rotate from the contact state and returns to the contact state after the stop is mainly adopted.

Therefore, in the magneto-optical disk, the surface protective film provided on the magnetic head side is required to have an anti-adsorption measure and durability against a head crash.

For these reasons, various proposals have been made for the above protective film. For example, Japanese Patent Laid-Open No.
No. -301040 and No. 2-301041 use a resin composition containing a fluorine-containing polyurethane resin as a main component, and in JP-A-3-37844, a fluorine resin soluble in an organic solvent is a main component. It has been proposed to use the resin compositions described below. Also in these,
It has also been proposed to include a metal element or a lubricant having a higher ionization tendency than the transition metal element forming the recording film.

Further, Japanese Patent Application Laid-Open No. 2-40149 discloses that a stearic acid ester is added as a lubricant to a liquid ultraviolet curable resin and stirred, and this is cured by irradiation with ultraviolet rays after coating. .. In addition, Japanese Patent Laid-Open No. 3-
No. 17844 discloses that a lubricating layer is used,
It is described that this lubricating layer is formed by coating, vapor deposition, sputtering or the like using a carbon compound.

However, none of these is sufficient. For example, a smooth surface made only of resin does not have sufficient lubricity, and if a hard material is used for a material mixed with a metal or a lubricant, the head may be damaged. Also,
Sufficient lubricity cannot be obtained even if only a lubricant is added.

Further, JP-A-3-62338 proposes that unevenness of 0.1 μm or more and 0.5 μm or less is uniformly present on the surface of the overcoat layer.

In this method, in order to form the unevenness, a method of dispersing silicone resin fine particles or a method of dispersing ferromagnetic fine particles such as Ni and then attracting the fine particles with a magnet is used.

However, using the silicone resin fine particles,
It is necessary to contain a relatively large amount of particles in order to form predetermined irregularities and obtain predetermined characteristics, which is disadvantageous in terms of cost and the like.

Further, when the ferromagnetic fine particles are used, the operation is complicated because it is necessary to use a magnet.

Therefore, improvement of this point is desired.

By the way, recently, attention has been paid to a magneto-optical disk which can be used as a compact disk (CD) and a drive unit by simply adding or changing an optical system. In such a magneto-optical disk, a method in which a magnetic head is constantly in contact with the disk surface is adopted.

In the magneto-optical disk used in the constant contact system, it is desired to further improve the friction characteristics and durability of the protective coat, as compared with the CSS system.

[0015]

DISCLOSURE OF THE INVENTION The object of the present invention is to form a predetermined unevenness with a small content of fine particles, which is advantageous in terms of cost, has good friction characteristics, and is excellent in magnetic field modulation. The purpose is to provide a magneto-optical disc of the type.

[0016]

The above objects are achieved by the present invention described in (1) to (11) below. (1) In a magnetic field modulation type magneto-optical disk having a recording layer on a substrate and a protective coat on the recording layer, the protective coat is a resin layer containing fine particles having a secondary aggregate structure. A magneto-optical disk characterized by the above.

(2) The above-mentioned (1), wherein the average particle size of the entire particle group constituting the secondary aggregate structure is 0.5 to 10 μm.
The magneto-optical disk described in.

(3) The number (1) of the primary particles constituting the secondary aggregate structure is 100 to 10,000.
Alternatively, the magneto-optical disk according to (2).

(4) The magneto-optical disk as described in any of (1) to (3) above, wherein the average particle diameter of the primary particles constituting the secondary aggregate structure is 0.05 to 0.5 μm.

(5) The magneto-optical disk as described in any of (1) to (4) above, wherein the content of the fine particles in the protective coat is 3 to 20 wt%.

(6) The magneto-optical disk according to any one of (1) to (5) above, wherein the resin containing the fine particles is a radiation curable resin.

(7) The surface roughness of the protective coat is JIS
The magneto-optical disk as described in any one of (1) to (6) above, which has a center line average roughness (Ra) according to the definition of B0601 of 0.1 to 0.5 μm.

(8) The surface roughness of the protective coat is JIS
The ten-point average roughness (Rz) according to the definition of B0601 is 0.
The magneto-optical disk as described in any one of (1) to (7) above, which has a thickness of 5 to 2.5 μm.

(9) The protective coat further has a melting point of 6
The magneto-optical disk according to any one of (1) to (8) above, which contains a lubricant at 0 ° C. or lower.

(10) The magneto-optical disk according to the above (9), wherein the content of the lubricant in the protective coat is 2 to 20 wt%.

(11) The thickness of the protective coat is 1 to 30.
The magneto-optical disk as described in any one of (1) to (10) above, which has a size of μm.

[0027]

[Specific Structure] The specific structure of the present invention will be described in detail below.

The magneto-optical disk of the present invention has, for example, the structure shown in FIG.

The magneto-optical disk shown in FIG. 1 will be described as an example. The magneto-optical disk 1 shown in FIG.
On the surface, protective layer 4, intermediate layer 5, recording layer 6, protective layer 7,
The reflective layer 8 and the protective coat 9 are sequentially provided. At this time, the hard coat 3 may be provided on the front surface of the disk, that is, on the back surface side of the substrate 2.

In the present invention, the protective coat 9
Is a resin layer containing fine particles having a secondary aggregate structure.

By containing such fine particles, it becomes possible to form predetermined irregularities on the surface of the protective coat even if the content of the fine particles is reduced, which is advantageous in terms of cost and has the effect of the present invention.

For example, when compared with the fine particles made of a silicone resin disclosed in JP-A-3-62338, the use amount thereof can be remarkably reduced in the present invention.

The average diameter of the entire particle group constituting the secondary aggregate structure is 0.5 to 10 μm, preferably 1 to 5 μm.

By using such an average diameter, the effect of the present invention is improved. If the average diameter is too small, the effect of forming the secondary aggregate structure cannot be obtained. On the other hand, when the average diameter is too large, the surface roughness becomes too large.

The presence of the secondary aggregate structure is confirmed by observing the surface of the protective coat 9 with an optical microscope, and further observing the surface of the protective coat 9 or the inside of the film with a scanning electron microscope (SEM). can do. Further, the average diameter of the entire particle population forming the secondary aggregate structure can be determined by the same optical microscope and SEM observation as above. The average diameter at this time is a value obtained by converting the projected area into a circle when the particle group forming the secondary aggregate structure is not spherical.

The number of primary particles constituting the secondary aggregate structure is 100 to 10,000, preferably 1,
It is preferable that the number is 000 to 10,000.

By using such a number, the effect of the present invention is improved. If this number is too small, the effect of forming the secondary aggregate structure cannot be obtained. On the other hand, if the number is too large, the average diameter becomes too large and the surface roughness becomes large.

This number can be determined by observing the inside of the film of the protective coat 9 by SEM.

The secondary aggregate structure in the present invention is SEM.
From observations and the like, it is confirmed that it has a considerably large void structure.

It is considered that having such a void structure is also preferable for improving the effect of the present invention.

In the present invention, the average particle size of the primary particles constituting the secondary aggregate structure is 0.05 to 0.5 μm, preferably 0.1 to 0.3 μm.

The effect of the present invention is improved by setting the average particle diameter of the primary particles within the above range. If the average particle size is too small, it becomes difficult for the secondary aggregate to have a void structure. On the other hand, if the average particle size becomes too large, it becomes difficult to form secondary aggregates.

The average particle size of the primary particles can be determined by SEM observation. When the primary particles are not spherical, it is a value obtained by converting the projected area into a circle.

In the present invention, organic fine particles composed of a thermosetting resin obtained by subjecting urea and formaldehyde to condensation and cross-linking reaction are preferably used as a constituent of the secondary aggregate structure.

This is a fluid white fine powder, which is commercially available under the trade name of "organic filler" (manufactured by Nippon Kasei Co., Ltd.), and a commercially available product can be used as it is. Also,
It has a true specific gravity of about 1.51 and a bulk density of about 0.1 to 0.2 g / ml, and is excellent in dispersibility in water and general organic solvents.

In addition, examples of the secondary agglomerate structure include inorganic fine particles such as carbon black and γ-alumina having an average particle size of 100 nm or less. Of organic fine particles are preferred.

The content of the fine particles having such a secondary aggregate structure in the protective coat 9 may be 3 to 20 wt%, preferably 3 to 10 wt%.

With such a content, the effects of the present invention are improved. If the content is too low, the effect of the present invention cannot be obtained, and if the content is too high, the dispersibility deteriorates, not only the coating liquid has a high viscosity, but also wasteful use and cost reduction. Will be at a disadvantage.

In the present invention, the fine particles having the secondary aggregate structure are preferably uniformly dispersed in the protective coat 9. Then, in this case, it is preferable that the secondary aggregates are also uniformly distributed correspondingly.

Further, the fine particles may be unevenly distributed on the surface layer of the protective coat 9 by multi-layer coating or the like, and in this case, it is preferable that the secondary agglomerates are uniformly distributed on the surface layer. ..

In the present invention, the secondary agglomerates may have a part of the aggregated tertiary agglomerates.

The surface roughness of the protective coat layer, which is the resin layer formed as described above, is 0.1 to 0.5 μm (measurement length 0.5 mm) in terms of center line average roughness (Ra) according to the definition of JISB0601. ). The ten-point average roughness (Rz) is 0.5 to 2.5 μm (reference length 0.5 mm).

By setting the surface roughness within the above range,
It has good friction characteristics and excellent durability.

The coefficient of dynamic friction in this case is 0.18 to
It becomes about 0.25, and the change is small even after repeated use.

In the present invention, the protective coat 9 preferably contains a lubricant having a melting point of 60 ° C. or lower. Furthermore, it is preferable to use a lubricant that is liquid at room temperature and has a melting point of room temperature or lower.

By incorporating such a lubricant, the friction characteristics and durability are further improved. That is, the dynamic friction coefficient is about 0.13 to 0.20.

Further, in the present invention, since the lubricant is absorbed by the void structure existing in the secondary aggregate structure, the lubricant is not attached to the head.

On the other hand, the above-mentioned Japanese Unexamined Patent Publication No. 3-62338.
Since the silicone resin fine particles as disclosed in JP-A No. 2004-114242 do not have a secondary aggregate structure, when a lubricant is added in the same manner, the lubricant adheres to the head.

Specific examples of the lubricant used in the present invention include fatty acid esters such as oleic acid ester and stearic acid ester, organic alcohols and their derivatives, and silicone oil.

The content of the lubricant in the protective coat 9 is 2 to 20% by weight, preferably 3 to 15% by weight.

With such a content, the effect of improving the friction characteristics and durability can be seen. If the content is low, such an effect of improvement cannot be obtained, and if the content is too high, the bleed out of the lubricant is too high.

The resin containing the fine particles in the protective coat 9 is preferably a radiation curable resin. Specifically, it is preferable that the radiation-curable compound and the composition for polymerization thereof are radiation-cured. Examples thereof include acrylic acid having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, methacrylic acid, an acrylic double bond such as an ester compound thereof, or a diallyl phthalate. Examples thereof include monomers, oligomers and polymers having or introduced in the molecule a group capable of being crosslinked or polymerized by radiation such as an allyl double bond, an unsaturated double bond such as maleic acid and a maleic acid derivative. These are preferably polyfunctional, particularly trifunctional or more, and may be used alone or in combination of two or more.

The radiation curable monomer has a molecular weight of 2
A compound of less than 000 has a molecular weight of 20 as an oligomer.
Those of 00 to 10,000 are preferable. 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., but particularly preferred ones As, pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), acrylic modified urethane elastomer,
Alternatively, those into which a functional group such as COOH is introduced, acrylate (methacrylate) of a phenol ethylene oxide adduct, an acrylic group (methacrylic group) or ε-in the pentaerythritol condensed ring shown in Japanese Patent Application No. 62-072888. Examples thereof include caprolactone-acryl group-containing compounds, and acrylic group-containing monomers and / or oligomers such as special acrylates disclosed in Japanese Patent Application No. 62-072888. Besides this,
Examples of radiation-curable oligomers include oligoester acrylates, acrylic modified urethane elastomers, and those into which a functional group such as COOH is introduced.

In addition to the above compounds, or in place of this, a radiation curable compound obtained by radiation-sensitively modifying a thermoplastic resin may be used. Specific examples of such a radiation curable resin include acrylic double bonds having an unsaturated double bond exhibiting radical polymerizability, acrylic double bonds such as methacrylic acid, or ester compounds thereof, and diallyl phthalate. It is a resin that contains or introduces into the molecule of a thermoplastic resin a group capable of being crosslinked or polymerized by irradiation with radiation, such as an allyl double bond, an unsaturated bond such as maleic acid or a maleic acid derivative. Examples of thermoplastic resins that can be modified into radiation curable resins include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, and fibrin derivatives. Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (P
VP olefin copolymer), polyamide resin, polyimide resin, phenol resin, spiro acetal resin, acrylic resin containing at least one hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component are also effective.

Since the coating composition for polymerization is cured by irradiation of radiation, especially irradiation of ultraviolet rays, it is preferable that the composition for polymerization contains a photopolymerization initiator or a sensitizer. The photopolymerization initiator or sensitizer used is not particularly limited, and may be appropriately selected from ordinary ones such as acetophenone-based, benzoin-based, benzophenone-based, and thioxanthone-based. A plurality of compounds may be used in combination as the photopolymerization initiator or the 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 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 one having two or more epoxy groups in the molecule is particularly preferable.

Examples of the alicyclic epoxy resin include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis- (3,4-epoxycyclohexylmethyl) adipate and bis- (3,4-
Epoxy cyclohexyl) adipate, 2- (3,4-
One or more of epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (2,3-epoxycyclopentyl) ether, vinylcyclohexene dioxide and the like are preferable. The epoxy equivalent of the alicyclic epoxy resin is not particularly limited,
From the viewpoint of obtaining good curability, it is preferably from 60 to 300, particularly preferably from 100 to 200.

The photocationic polymerization catalyst may be any known one and is not particularly limited. For example, a complex of one or more metal fluoroborate and boron trifluoride,
Bis (perfluoroalkylsulfonyl) methane metal salt, aryldiazonium compound, aromatic onium salt of 6A group element, aromatic onium salt of 5A group element, 3A group ~
Dicarbonyl chelate of Group 5A element, thiopyrylium salt, MF ₆ anion (where M is P, As or S
Group 6A elements having b), triarylsulfonium complex salts, aromatic iodonium complex salts, aromatic sulfonium complex salts and the like can be used, and in particular, polyarylsulfonium complex salts, aromatic sulfonium salts or iodonium salts of halogen-containing complex ions, 3A It is preferable to use one or more aromatic onium salts of Group 5A, Group 5A and Group 6A elements.

A photocationic polymerization catalyst containing an organometallic compound and a photodegradable organosilicon compound can also be used. Since such a cationic photopolymerization catalyst is a non-strong acid type, it is possible to avoid adverse effects on the highly corrosive recording layer of the magneto-optical recording disk. As the organometallic compound, 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. Among these, organoaluminum compounds are particularly preferable, and specifically, trismethoxyaluminum, trispropionatoaluminum, tristrifluoroacetylaluminum, and trisethylacetoacetonatoaluminum are preferable.

The photodegradable organic silicon compound produces silanol upon irradiation with light such as ultraviolet rays,
A silicon compound having a peroxysilano group, an o-nitrobenzyl group, an α-ketosilyl group or the like is preferable.

The content of the photocationic polymerization catalyst in the composition is 0.05 to 0.
It is preferably 7 parts by weight, particularly 0.1 to 0.5 parts by weight.

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

The protective coat 9 is formed, for example, as follows. First, a predetermined amount of the fine particles and preferably a lubricant are added to the above resin, preferably a composition for a radiation curable resin, and the mixture is mixed by, for example, ball mill dispersion, and a coating film of this is formed on the reflective layer 8. Form. In addition,
In the present invention, it is preferable to add a lubricant as described above from the viewpoint of durability and the like, but in some cases, after forming the protective coat 9, a liquid lubricant is applied to the inside of the protective coat. Can also be contained in.

The method for forming the coating film is not particularly limited, and is usually
It may be formed by combining various known methods such as spin coating, screen printing, gravure coating, spray coating, and dipping. The coating conditions at this time may be appropriately determined in consideration of the viscosity of the composition for polymerization, the target coating film thickness, and the like.

Then, ultraviolet rays are irradiated to cure the coating film. 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 ultraviolet rays applied to the coating film is usually 50.
mW / cm ² or more, irradiation dose is usually 500 to 2000 mJ
It should be about / cm ² . Further, as the ultraviolet ray source, a normal one such as a mercury lamp may be used. The above compounds undergo radical polymerization upon irradiation with ultraviolet rays.

The protective coat 9 thus obtained has a thickness of 1 to 30 μm, preferably 2 to 20 μm.

With such a film thickness, the effects of the present invention are improved. If the film thickness is too thin, it becomes difficult to form a uniform film and the durability becomes insufficient. On the other hand, if it is too thick, cracks are likely to occur due to shrinkage during curing, and the disc is likely to be warped.

The material of the substrate 2 in the present invention is not particularly limited as long as it is transparent, and glass and various transparent resins are used. Examples of the transparent resin include polycarbonate resin, acrylic resin, amorphous polyolefin resin, styrene resin and the like.

Further, as shown in FIG. 1, a transparent hard coat 3 is formed on the back surface side of the substrate 2. The hard coat 3 may be made of the same radiation curable resin material as the preferable resin forming the protective coat 9.

The thickness of this hard coat 3 is 1 to 30 μm.
It is preferably m, particularly 3 to 10 μm.

The transmittance of the substrate 2 coated with such a hard coat 3 for recording light and reproducing light is preferably 80% or more, and more preferably 85% or more. Further, the hard coat may be formed not only on the main surface of the disk but also on the outer peripheral side surface and the inner peripheral side surface.

A groove for tracking may be formed on the surface of the substrate 2 on which the recording layer 6 is formed.

In the magneto-optical recording disk shown in FIG. 1, a protective layer 4 as an underlayer and an intermediate layer 5 are provided on a substrate 2.
The recording layer 6 is formed via. The intermediate layer 5 is C /
It is provided to improve the N ratio, and is preferably formed of various dielectric materials, and its layer thickness is 30 to 150 nm.
It is preferably about the same.

Further, the protective layer 7 may be provided on the recording layer 6 together with the protective layer 4. When used in combination, the compositions of the protective layer 4 and the protective layer 7 may be the same or different. Protective layer 4 and protective layer 7 provided as necessary
Is provided to improve the corrosion resistance of the recording layer 6, and it is preferable that at least one of these is provided, and preferably both are provided. These protective layers are preferably composed of an inorganic thin film made of various oxides, carbides, nitrides, sulfides or mixtures thereof. Further, the protective layers 4 and 7 may be formed of the above intermediate layer material. The thickness of the protective layer is preferably about 30 to 300 nm from the viewpoint of improving corrosion resistance. Such protective layers 4 and 7 and the intermediate layer 5
Is preferably formed by various vapor phase film forming methods such as sputtering, vapor deposition and ion plating, and particularly by sputtering.

Information is magnetically recorded on the recording layer 6 by a modulated heat beam or a modulated magnetic field, and the recorded information is magnetic-optically converted and reproduced. The material of the recording layer 6 is not particularly limited as long as it can perform magneto-optical recording, but an alloy containing a rare earth metal element, particularly an alloy of a rare earth metal and a transition metal is sputtered, vapor deposited, or ion plated. It is particularly preferable that the amorphous film is formed by sputtering. Rare earth metals include Tb, Dy, Nd, Gd, S
It is preferable to use at least one of m and Ce. Fe and Co are preferable as the transition metal. In this case, the total content of Fe and Co is preferably 65 to 85 at%. And the balance is substantially a rare earth metal.

The composition of the recording layer preferably used is as follows.
TbFeCo, DyTbFeCo, NdDyFeCo,
There are NdGdFeCo and the like. In the recording layer, 10
Cr, Al, Ti, Pt, Si, M in the range of at% or less
O, Mn, V, Ni, Cu, Zn, Ge, Au, etc. may be contained. In the range of 10 at% or less, Sc,
Y, La, Ce, Pr, Pm, Sm, Eu, Ho, E
Other rare earth metal elements such as r, Tm, Yb and Lu may be contained. The layer thickness of the recording layer 6 is usually 10 to 10.
It is about 1000 nm. Then, a metallic reflective layer 8 is provided on the protective layer 7.

The material forming the reflective layer 8 is Au, Ag,
It may be a metal such as Pt, Al, Ti, Cr, Ni or Co, an alloy thereof, or a compound thereof. The reflective layer 8 may be provided in the same manner as the recording layer 6. The thickness of the reflective layer 8 is about 30 to 200 nm.

Although the above description has been made according to the configuration of FIG. 1, the magneto-optical disk of the present invention is not limited to this configuration.

For example, in FIG. 1, only one layer of the protective coat 9 containing the fine particles is provided, but two layers of the protective coat may be provided.

The structure in which the protective coat has two layers is particularly effective in the magneto-optical disk used in the constant contact system.

In this case, the fine particles may be contained only in the uppermost protective coat which contacts the head, and the fine particles below may not be contained in the protective coat located therebelow.

In the case of such a two-layered protective coat, the film thickness of the uppermost layer is 1 to 20 μm, preferably 2 to 10 μm, and the film thickness of the layer below is 1 to 20 μm.
The thickness is preferably 2 to 10 μm.

Although the intermediate layer 5 is provided in FIG. 1, it is not always necessary.

[0096]

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

Example 1 A coating film of the composition for a hard coat layer was formed on the back surface and the peripheral surface of the recording layer forming side 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. The coating film was UV-cured to form a hard coat. The hard coat was obtained by applying the following composition (A) for polymerization by spin coating and irradiating it with ultraviolet rays to cure it, and the average thickness after curing was 5 μm.

Polymerization composition (A) oligoester acrylate (molecular weight 5,000) 50 parts by weight trimethylolpropane triacrylate 50 parts by weight acetophenone photopolymerization initiator 3 parts by weight

Then, a protective layer made of glass was formed in a layer thickness of 40 nm on the other surface of the substrate on which the hard coat was formed as described above by high frequency magnetron sputtering. An SiN _x intermediate layer was formed on the protective layer by high frequency magnetron sputtering to have a layer thickness of 80 nm. Next, a recording layer having a composition of Tb ₂₃ Fe ₇₂ Co ₅ was formed on the intermediate layer by sputtering so as to have a layer thickness of 20 nm.

Further, a 20 nm protective layer having the same composition as that of the protective layer was formed on the recording layer by high frequency magnetron sputtering, and an 80 nm Al alloy reflection layer was further formed on the protective layer, and a protective coating was formed thereon. Was set up.

The protective coat is obtained by mixing the following composition (1) for polymerization in a ball mill, a coating film of this product is formed by spin coating, and the coating film is cured by irradiation with ultraviolet rays. The average thickness after curing was 5 μm. Ultraviolet irradiation was performed under the condition of an irradiation amount of 1000 mJ / cm ² .

Composition for Polymerization (1) 50 parts by weight of oligoester acrylate (molecular weight 5,000) 50 parts by weight of trimethylolpropane triacrylate 3 parts by weight of acetophenone-based photopolymerization initiator Formaldehyde-urea resin fine particles [trade name "organic filler "Nippon Kasei Co., Ltd .: true specific gravity of about 1.51: bulk density of about 0.1 to 0.2 g / ml] 6 parts by weight

This is designated as Sample No. 1.

The SEM observation of the protective coat film confirmed that the fine particles had a secondary aggregate structure. The average diameter of the entire secondary aggregate structure was about 3 μm, and the average particle diameter of the primary particles constituting this structure was about 0.2 μm. Further, the number of primary particles constituting the secondary aggregate structure was about 1000 to 5000. The average diameter and the average particle diameter are values obtained by converting the projected area into a circle when it is not spherical. In addition, some tertiary aggregates were also found.

In the protective coat of sample No. 1, silicone resin fine particles (Toshiba Silicone Tospearl 1 were used instead of the above fine particles according to JP-A-3-62338.
Sample No. 2 was obtained in the same manner except that 6 parts by weight of 20: average particle size 2 μm) was used.

According to the result of SEM observation, the silicone resin fine particles did not have a secondary aggregate structure.

Sample No. 3 was obtained in the same manner except that the protective coat of Sample No. 2 contained 45 parts by weight of silicone resin fine particles. According to the result of SEM observation, even this product did not have a secondary aggregate structure.

In the protective coat of Sample No. 1, fine particles were changed to α-alumina having an average particle size of 0.3 μm, and 45 parts by weight of this was used in the same manner as in Sample No. 1.
I got No. 4.

As a result of SEM observation, this product also did not have a secondary aggregate structure.

Regarding the above sample Nos. 1 to 4, J
Ra according to the definition of IS B0601 (measurement length 0.5 mm)
And Rz (reference length 0.5 mm) were measured.

Further, the following evaluation was performed using a (Mn-Zn ferrite) composite head.

(1) Dynamic Friction Coefficient μ ₁ Plus 3.5 "magnetic disk drive, 1rp
Rotate the disk at m and measure the stress on the head,
From this, μ ₁ was calculated. The load was 15 g.

(2) Contact durability test Using a 3.5 "magnetic disk drive manufactured by PLUS, the head was contacted and rotated at 1.4 m / s, and μ ₁ after 200,000 passes was obtained to determine the friction durability. Examined.

The results are shown in Table 1. Table 1 also shows the content of the fine particles in the protective coat and the like.

[0115]

[Table 1]

As is clear from Table 1, in Sample No. 1 of the present invention, it is possible to obtain a predetermined effect by reducing the content of fine particles. On the other hand, comparative sample No. 3
Then, when compared with Sample No. 2 using the same fine particles, it can be said that an effect equivalent to that of Sample No. 1 of the present invention is exhibited by increasing the content of fine particles, but it is disadvantageous in cost.

Example 2 In the protective coat of Sample Nos. 1 to 4 of Example 1,
Samples were obtained in the same manner except that 8 parts by weight of a lubricant was added to each of the composition (1) for polymerization.
These samples are referred to as sample Nos. 21 to 24 corresponding to those of the first embodiment.

The lubricant is oleyl oleate (melting point-
10 ° C.) was used.

The same measurements and evaluations as in Example 1 were carried out on the above samples No. 21 to No. 24. The secondary aggregate structure and the like in Samples No. 21 to No. 24 were almost the same as those in Samples No. 1 to No. 4.

The results are shown in Table 2.

[0121]

[Table 2]

As is clear from the results of Table 2, in the sample No. 21 of the present invention, the sample No. 21 of Example 1 was used.
Compared with No. 1, the frictional properties were improved, and no deposits were found on the head after the contact durability test.

On the other hand, in Comparative Sample No. 23, although the friction characteristics at the initial stage and after the test were improved,
After the contact durability test, deposits on the head were found.

In addition, comparative sample Nos. 22 and No.
Even in No. 24, although the frictional properties at the initial stage and after the test are improved, they are not at a sufficient level.

[0125]

EFFECTS OF THE INVENTION According to the present invention, it is possible to form a predetermined unevenness by reducing the content of fine particles, and it is excellent in friction characteristics and durability. It is also advantageous in terms of cost.

[Brief description of drawings]

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

[Explanation of symbols]

 1 magneto-optical disk 2 substrate 3 hard coat 4 protective layer 5 intermediate layer 6 recording layer 7 protective layer 8 reflective layer 9 protective coat

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Endo Inventor Hiroyuki Endo 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation

Claims (11)

[Claims] 1. A magnetic field modulation type magneto-optical disk having a recording layer on a substrate and a protective coat on the recording layer, wherein the protective coat is a resin layer containing fine particles having a secondary aggregate structure. A magneto-optical disk characterized in that. 2. The magneto-optical disk according to claim 1, wherein the average particle diameter of the entire particle group constituting the secondary aggregate structure is 0.5 to 10 μm. 3. The magneto-optical disk according to claim 1, wherein the number of primary particles forming the secondary aggregate structure is 100 to 10,000. 4. The magneto-optical disk according to claim 1, wherein the average particle size of the primary particles constituting the secondary aggregate structure is 0.05 to 0.5 μm. 5. The magneto-optical disk according to claim 1, wherein the content of the fine particles in the protective coat is 3 to 20 wt%. 6. The magneto-optical disk according to claim 1, wherein the resin containing the fine particles is a radiation curable resin. 7. The surface roughness of the protective coat is JIS B
Centerline average roughness (Ra) according to the definition of 0601 is 0.1
7. The magneto-optical disk according to claim 1, wherein the magneto-optical disk has a thickness of 0.5 μm. 8. The surface roughness of the protective coat is JIS B
The ten-point average roughness (Rz) according to the definition of 0601 is 0.5 to
The magneto-optical disk according to claim 1, which has a size of 2.5 μm. 9. The protective coat further has a melting point of 60 ° C.
The magneto-optical disk according to claim 1, further comprising the following lubricant. 10. The magneto-optical disk according to claim 9, wherein the content of the lubricant in the protective coat is 2 to 20 wt%. 11. The protective coat has a thickness of 1 to 30 μm.
The magneto-optical disk according to any one of claims 1 to 10.