JPH07282481A - Magneto-optical disk and magneto-optical recording method using the same - Google Patents

Abstract

PURPOSE:To obtain sufficient durability and good lubricity by forming the sliding protective film of a magnetic disk which executes recording while sliding a magnetic head to pencil lead hardness of gHB to <=2H and specifying the contact angle with water to 85 deg.. CONSTITUTION:This magneto-optical disk has a magneto-optical recording layer on a substrate and has the sliding protective film consisting of a curing resin directly thereon or via another layer and executes recording while sliding the magnetic head. The surface hardness of the sliding protective film is >=H to <=2H in pencil hardness and the contact angle thereof with the water is specified to >=85 deg.. The magnetic head is slid on the sliding protective layer by using such magneto-optical disk and the disk is irradiated with recording light or reproducing light from the substrate side while modulating magnetic fields are applied thereon. In such a case, the damage and wear by the sliding magnetic head are prevented and the generation of servo errors is suppressed.

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 and a magneto-optical recording method using the same, which is used in a magneto-optical recording system for recording while sliding a magnetic head on the magneto-optical disk. Regarding the disc.

[0002]

2. Description of the Related Art As a conventional magneto-optical disk, there is a magneto-optical disk formed of a protective film made of resin on a magneto-optical recording layer made of TbFeCo or the like provided on a substrate directly or through another layer. In recent magneto-optical recording, a magnetic field modulation method capable of overwriting information, that is, laser light is continuously or intermittently irradiated on the magneto-optical recording layer, and at least a portion irradiated with laser light is A method of recording by modulating the direction of the magnetic field by an external magnetic field applying means has attracted attention.

The magnetic field is usually applied by a magnetic field head having a magnetic field generating means. At present, a magnetic head applying such a high-speed reversal magnetic field can generate only a weak magnetic field. Therefore, it is necessary to bring the magnetic head as close to the recording magnetic layer as possible. From such a demand, a so-called sliding type magnetic head has been proposed which is used while sliding on a magneto-optical disk during recording.

This sliding type magnetic head is used for a music recording magneto-optical disk having a diameter of 64 mm and a diameter of 120 mm. However, when recording is performed with this sliding type magnetic head, the rotating magneto-optical disk and the magnetic head come into contact with each other, so that the recording magnetic layer is damaged by the magnetic head and the recorded information is destroyed. There's a problem.

Therefore, a protective film is provided for the purpose of protecting the recording magnetic layer. An ultraviolet curable resin is generally used as the protective film. However, the conventional ultraviolet curable resin has some problems as a protective film for a magneto-optical disk using a sliding type magnetic head. First, there is a problem that the hardness is not sufficient. If the hardness of the protective film is insufficient, the magnetic head may damage the protective film and further damage the recording magnetic layer.

The lubricity of the protective film is also a serious problem. Since the conventional protective film is inferior in lubricity, the absolute value of the frictional force applied to the disc increases and the fluctuation of the frictional force also increases. Then, the rotation of the disc becomes unstable, which may cause a recording error or a tracking error.

Furthermore, the surface hardness of the protective film is required to be higher, and if the hardness is insufficient, it will be worn or damaged. In addition, the lubricity of the protective film must be good under a wide range of environmental conditions, but even a protective film that exhibits good lubricity under low humidity conditions usually has a high friction coefficient in a high humidity environment. It will increase.

[0008]

SUMMARY OF THE INVENTION The present invention was devised in view of the above problems and provides sufficient durability and good lubricity at high humidity even when the magnetic head is slid. It is an object of the present invention to provide a magneto-optical disk that can be secured even under the environment.

[0009]

According to the present invention, a magneto-optical recording layer is provided on a substrate, and a sliding protective film made of a curable resin is provided on the substrate directly or through another layer. A magneto-optical disk for recording while sliding the
The magneto-optical disk is characterized in that the sliding protection film has a pencil hardness of HB or more and 2H or less and a contact angle with water of 85 degrees or more.

Further, according to the present invention, by using the above-mentioned magneto-optical disk, recording light or reproducing light is emitted from the substrate side while a magnetic head is slid on the sliding protection layer to apply a modulation magnetic field. This is a magnetic recording method. Needless to say, the performance required of the sliding protection film is appropriate hardness and surface lubricity because the magnetic head slides on the protection film.

When the characteristic evaluation criteria and the characteristic evaluation method of the sliding protective film are compared with the experimental results when the magnetic head is actually continuously run, it is found that the sliding protective film must have the following or are preferable. all right. (1) The sliding protective film is obtained by curing a resin composed of a mixture of an ultraviolet curable resin and a lubricity imparting agent. (2) The hardness of the sliding protection film is HB to 2H in pencil hardness.
And the contact angle with water is 85 degrees or more. (3) According to the abrasion test method (JIS K7204) of the plastic for the sliding protection film by a wear wheel, CS-10 was used as a wear wheel, a load of 500 gf was applied, and 100 cycles of wear were performed before and after the wear. The difference in haze value (delta haze) is preferably 7% or less.

Here, the hardness evaluation of the sliding protection film is performed by the following two methods (a) and (b). The protective film for hardness evaluation is a transparent polycarbonate substrate (thickness 1.2 mm)
It is formed by the same method as that on the magneto-optical disk. (A) Pencil hardness according to JIS K5400 (b) Abrasion test method for plastics with an abrasion wheel (JI
According to SK7204), CS-10 is used as a wear wheel, a load of 500 gf is applied, and wear is performed for 100 rotations. Before and after this abrasion test, the haze value of the polycarbonate substrate was measured by the method defined in (JIS K7105),
The difference in haze value before and after the abrasion test is obtained and evaluated. The smaller the haze value, the less wear the wear test has. That is, it is considered to be a hard sliding protection film.

The haze value before the abrasion test is 0%. After the abrasion test, the haze value usually deteriorates by about 3%. Hereinafter, the present invention will be described in detail. In the present invention, the substrate is not particularly limited, and a resin substrate such as a polycarbonate resin, an acrylic resin, or a polyolefin resin, a glass substrate or the like can be usually used.

The thickness of the substrate is generally 0.5 to 1.5 mm. A magnetic thin film having perpendicular magnetic anisotropy is used as the magneto-optical recording layer. For example, DyFeCo, Tb
Rare earth-transition metal alloy amorphous thin films such as FeCo, GdFeCo, NdFeCo, and noble metal / transition metal artificial laminated films such as Pt / Co are preferably used.

The thickness of the magneto-optical recording layer is preferably about 5 to 50 nm. Usually, S is formed above and below the magneto-optical recording layer.
_{iO 2, Al 2 O 3,} Ta 2 O 3, Si 3 N oxide such _4, nitrides, and mixtures thereof, that provide a dielectric layer made of a composite compound such as Al-Ta-O preferred . The dielectric layer is intended for a moisture permeation preventing effect, an optical interference effect, a heat insulating effect and the like.

Furthermore, it is preferable to provide a reflective layer on the dielectric layer for sensitivity adjustment and signal level adjustment. A for the reflective layer
1 alloy or the like is preferable. Each of these layers is formed by a sputtering method, a vapor deposition method, or the like. In the magneto-optical disk of the present invention, since recording is performed while sliding the magnetic head against the disk surface, a sliding protection film is provided directly on the magneto-optical recording layer or through the dielectric layer and the reflective layer. It ensures durability and lubricity.

It has been found that this sliding protection film is preferably obtained by curing a mixture of a resin and a lubricity-imparting agent. Among them, it is costly to use an ultraviolet curable resin as the resin. From the viewpoint of productivity, etc., it is preferable as compared with other resins such as thermosetting resins. The sliding protection film is preferably obtained by applying a resin, which is a mixture of an ultraviolet curable resin and a lubricity imparting agent, onto a magneto-optical disk by a spin coating method or the like, and then irradiating it with ultraviolet rays to cure it.

The thickness of the sliding protection film is preferably in the range of 1 to 50 μm. If the film thickness is less than 1 μm, the durability becomes insufficient. When it exceeds 50 μm, cracks are likely to occur in the recording magnetic layer or the dielectric layer and warp of the disk tends to be large due to shrinkage during curing of the resin. UV curable resin is 25
A mixture of a 1 to 2 functional (meth) acrylate having a viscosity at 100 ° C. or lower, a bifunctional or higher (meth) acrylate having a viscosity under the same condition of 100 cps and a photopolymerization initiator is preferably used.

Further, an antistatic agent, a leveling agent, a silane coupling agent or the like can be added as an optional component. Specific examples of the 1 to 2 functional (meth) acrylate having a viscosity of 100 cps or less include tetrahydrofurfuryl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate. An acrylate etc. can be mentioned.

Examples of the bifunctional or higher (meth) acrylate having a viscosity of 100 cps or more include polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate and the like. As the photopolymerization initiator, any known one may be used, but one having good storage stability after blending is preferable.

Examples of such compounds include benzophenone, 1-hydroxycyclohexyl phenyl ketone,
Benzoin isopropyl ether and the like can be mentioned. When selecting the structure and amount of the lubricity-imparting agent, it is necessary to consider the effectiveness of the final sliding protection film.
It is necessary to select it in consideration of the contact angle with water described later.

Examples of such lubricity imparting agents include silicon compounds and fluorine-based compounds. Preferred specific examples include polydimethylsiloxane, for example, polydimethylsiloxane (L-45 (trade name) manufactured by Nippon Unicar Co., Ltd.), polydimethylsiloxane / polyether block copolymer (PS072 (trade name) manufactured by Chisso Co., Ltd.). , L-7001 (trade name) manufactured by Nippon Unicar Co., Ltd., polysiloxanes such as alkyl group-modified polydimethylsiloxane (KF412 (trade name) manufactured by Shin-Etsu Chemical Co., Ltd.), and fluorinated compounds (Sumitomo 3M Co., Ltd.) Fururad FC-430 (trade name)) and the like can be mentioned.

The amount of the lubricity-imparting agent added to the resin varies depending on the structure of the lubricity-imparting agent and cannot be generally stated, but it is usually 0.1 to 20 parts by weight per 100 parts by weight of the resin. Preferred is 1 to 15 parts by weight, and particularly preferred. If it is 0.1 parts by weight or less, sufficient lubricity cannot be imparted, and if it is 20 parts by weight or more, the hardness of the protective film after curing decreases, so that the protective film tends to be broken during sliding of the magnetic head. Therefore, neither is preferable.

The sliding protection film has a pencil hardness of HB or more 2
Use of H or less and delta haze value of 7% or less, preferably 5% or less (usually 3% or more and 7% or less) The reason for this is not fully clarified, but it is considered as follows. It is considered that the hardness of the sliding protection film is closely related to the fact that the resin after the curing reaction has a crosslinked structure.

It is considered that the denser the crosslinked structure is, the harder the protective film can be obtained. On the other hand, it is considered necessary for the lubricity imparting agent to be present on the surface of the protective film in order to exert good lubricating properties. Here, making the crosslinked structure of the resin dense so that the protective film becomes hard and making a large amount of the lubricity-imparting agent on the surface of the protective film are contradictory requirements.

That is, if the resin cross-linking structure is dense, the amount of the lubricity-imparting agent that can be present on the surface decreases,
Lubricity decreases. On the contrary, if a large amount of the lubricity imparting agent is made to exist on the surface, the hardness of the protective film will be reduced, and eventually the sliding characteristics will be reduced. Like this,
It is considered that there are upper and lower limits for the preferable value of hardness achieved by controlling the resin crosslink density.

The lower limit value is the pencil hardness HB and the upper limit value is 2H. The delta haze value after the abrasion test is 3% ~
It is preferably 7%. Further, the contact angle of the sliding protection film with water is 85 degrees or more. Again, the reason is not clear, but it can be thought as follows. The good lubricity required for the sliding protection film is that the magnetic head is not easily attracted to the protection film.

By the way, the contact angle with a liquid is generally known as an index for estimating the free energy of the surface of a solid and determining whether or not it is easily bonded. Since water is often used as the liquid for reasons such as ease of measurement, the contact angle with water is often used as the index.
In other words, Young-Dupr, which is well known for contact angles
The work of adhesion can be known by the equation (1) of e.

[0029]

[Equation 1] W = γ (1 + cos θ) (1) W: Adhesion work γ: Liquid surface tension in adsorption equilibrium with liquid vapor θ: Contact angle Here, the adhesion work is the work by which the liquid wets the solid surface. However, since it is the work of separating the two phases of solid and liquid to form the surface of each layer, it is considered that the smaller the adhesion work, the weaker the adhesion and adsorption of the two phases.

In the formula (1), when only water is used as the liquid, γ is constant. Therefore, the smaller cos θ, that is, the larger θ, the smaller the bonding work W, that is, the two-phase bonding. Is considered weak. It is considered that the lubricity suitable as a sliding protection film is expressed by using a contact angle with water, which is an index of whether or not adhesion is easy.

By the way, the protective film made of the ultraviolet curable resin alone has poor slipperiness, but its contact angle with water is usually about 60 to 75 degrees. Therefore, it is possible to reduce the surface free energy of the sliding protective film and improve the lubricity by adding a lubricity-imparting agent to the resin and allowing it to exist also on the surface of the protective film. The contact angle is required to be 85 degrees or more, in particular, in order to obtain good characteristics even under high humidity environment conditions.

Incidentally, these protective films not only have a sliding resistance property, but also play a role of preventing corrosion of the magneto-optical recording layer.

[0033]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 80 nm of silicon nitride, 26 nm of Tb ₂₂ Fe ₇₀ Co ₈ (numerical values are component ratios, atomic%) and 20 n of silicon nitride were formed on a polycarbonate resin substrate by a sputtering method.
m, an Al alloy film having a thickness of 80 nm in this order, a curable resin containing a lubricity imparting agent having the following composition 1 was applied thereon by a spin coating method, and cured by ultraviolet irradiation to form a slide protective film. did.

The thickness of the sliding protection film was 7 μm, the pencil hardness was H, and the contact angle was 91 degrees. The abrasion test (JIS K7204) was carried out in exactly the same manner as the test object in which the sliding protective film was formed only on the polycarbonate substrate.
In conformity with the above, using CS-10 as a wear wheel, load 50
The difference between the haze values before and after the abrasion test (delta haze) was 4.6% when 0 gf was applied and abrasion was performed for 100 rotations.

As an endurance test, a magnetic head RF320-74G manufactured by Sony Corporation was loaded with a load of 2 gf on a disk under an environmental condition of a temperature of 23 ± 2 ° C. and a relative humidity of 50 ± 5% (hereinafter referred to as environmental condition 1). The disk surface was observed after continuous running for 60 hours at a disk rotation speed of 600 rpm. As a result, no scratch was found.

In addition, the coefficient of friction during the test was 0.3 or less, showing good slipperiness. Next, temperature 70 ± 2
An endurance test was conducted under the same conditions as above under an environment of 90 ° C. and a relative humidity of 90 ± 5% (hereinafter referred to as environmental condition 2). As a result, even when the magnetic head was continuously run for 60 hours, no scratch was generated on the surface.

[0037]

Table 1 Composition 1 <Resin> 1-2 functional (meth) acrylate having a viscosity of 100 cps or less at 25 ° C. Tetrahydrofurfuryl acrylate: 12 parts by weight · Bifunctional or higher (meth) acrylate having a viscosity of 100 cps or more at 25 ° C. Pentaerythritol triacrylate: 30 parts by weight Pentaerythritol tetraacrylate: 30 parts by weight Dipentaerythritol hexaacrylate: 14 parts by weight Photopolymerization initiator 1-hydroxycyclohexyl phenyl ketone: 6 parts by weight <Lubricity imparting agent> Amino group-modified poly Dimethylsiloxane (KF-861 (trade name) manufactured by Shin-Etsu Silicone Co., Ltd.): 8 parts by weight

Example 2 A magneto-optical disk produced in the same manner as in Example 1 was coated with a curable resin containing a lubricity imparting agent having the following composition 2 by the spin coating method as in Example 1, and then ultraviolet rays were applied. Was irradiated to cure. The thickness of the sliding protection film was 6 μm. This sliding protection film has a pencil hardness of 2H and a contact angle of 90.
It was degree. The delta haze value of the sliding protective film measured in the same manner as in Example 1 was 3.4%. Under the same conditions as in Example 1, a durability test was conducted under environmental conditions 1 and 2. As a result, the magnetic head is set to 6 under both environmental conditions 1 and 2.
The disc was not scratched even after running continuously for 0 hours.

[0039]

[Table 2] Composition 2 <Resin> 1 to 2 functional (meth) acrylate having a viscosity of 100 cps or less at 25 ° C 2-hydroxypropyl acrylate: 7 parts by weight 1,6-hexanediol diacrylate: 10 parts by weight 25 ° C (Meth) acrylate having a viscosity of 100 cps or more Trimethylolpropane triacrylate: 17 parts by weight Pentaerythritol triacrylate: 17 parts by weight Dipentaerythritol hexaacrylate: 27 parts by weight Urethane acrylate (Toagosei M-1210)
(Brand name): 8 parts by weight Photoinitiator benzoin isopropyl ether: 6 parts by weight <Lubricity imparting agent> Epoxy-modified polydimethylsiloxane (KF-101 (Brand name) manufactured by Shin-Etsu Silicone Co., Ltd.): 8 parts by weight Department

Comparative Example 1 On the magneto-optical disk produced in the same manner as in Example 1, a protective coating agent having the following composition 3 was applied by a spin coating method and further cured by ultraviolet rays to form a sliding protective film.
The thickness of the sliding protection film was 7 μm, the pencil hardness was 2H, and the contact angle was 76 degrees. The delta haze value of the sliding protective film measured in the same manner as in Example 1 was 3.2%.

A durability test was conducted under the same conditions as in Example 1 under the environmental condition 1, and no scratches were found on the disk surface even after continuous running for 60 hours. On the other hand, environmental condition 2
The endurance test was carried out in 1 hour, and the friction coefficient was 0.5 immediately after the start of the test, but after 10 minutes, the friction coefficient increased to 0.9, and the endurance test was stopped in 1 hour to observe the disk surface. There were some scratches.

[0042]

Table 3 Composition 3 <Resin> 1-2 functional (meth) acrylate having a viscosity at 25 ° C. of 100 cps or less Tetrahydrofurfuryl acrylate: 15 parts by weight · Bifunctional or higher (meth) acrylate having a viscosity at 25 ° C. of 100 cps or more Trimethylolpropane triacrylate: 11 parts by weight Pentaerythritol triacrylate: 18 parts by weight Pentaerythritol tetraacrylate: 30 parts by weight Dipentaerythritol hexaacrylate: 16 parts by weight Photoinitiator 1-hydroxycyclohexyl phenyl ketone: 6 parts by weight <Lubricant> Polydimethylsiloxane / ethylene oxide propylene oxide block copolymer (PS manufactured by Chisso Corporation)
072 (trade name): 4 parts by weight

Comparative Example 2 A magneto-optical disk manufactured in the same manner as in Example 1 was loaded with a resin containing a lubricity imparting agent described in the following composition 4 in Example 1.
After applying by the spin coating method in the same manner as described in (1) above, it was irradiated with ultraviolet rays and cured to form a sliding protective film. The thickness of the sliding protection film was 7 μm, the contact angle was 95 degrees, and the pencil hardness was F. The delta haze value of the sliding protective film measured in the same manner as in Example 1 was 8.5%. When a durability test was performed under the same conditions as in Example 1 under the environmental condition 1, the friction coefficient gradually increased from the start of the test.
It was stopped in a minute, and when the disk surface was observed, it was scratched.

[0044]

[Table 4] Composition 4 <Resin> 1-2 functional (meth) acrylate having a viscosity at 25 ° C of 100 cps or less Tetrahydrofurfuryl acrylate: 13 parts by weight · Bifunctional or higher (meth) acrylate having a viscosity at 25 ° C of 100 cps or more Pentaerythritol triacrylate: 18 parts by weight Pentaerythritol tetraacrylate: 25 parts by weight Dipentaerythritol hexaacrylate: 13 parts by weight Photopolymerization initiator 1-hydroxycyclohexyl phenyl ketone: 6 parts by weight <Lubricity imparting agent> Amino group-modified poly Dimethyl siloxane (KF-861 (trade name) manufactured by Shin-Etsu Silicone Co., Ltd.): 25 parts by weight

[0045]

The magneto-optical disk according to the present invention is provided with a slide protection film exhibiting an appropriate surface hardness and a good lubricity under a wide range of environmental conditions, and therefore has a sliding resistance property against a sliding magnetic head. Significantly improved. Therefore, damage and wear due to the magnetic head are prevented, and since the magnetic head runs stably, occurrence of servo error due to disturbance of disk rotation is suppressed, so that a highly reliable magneto-optical disk can be provided.

Claims (4)

[Claims] 1. A magneto-optical recording layer is provided on a substrate, and a slide protection film made of a curable resin is provided on the substrate directly or through another layer, and recording is performed while sliding a magnetic head. A magneto-optical disk for use in the method, wherein the surface hardness of the sliding protection film is HB or more and 2H or less in pencil hardness, and the contact angle with water is 85 degrees or more. 2. A magneto-optical recording layer is provided on a substrate, and a sliding protective film made of a curable resin is provided on the substrate directly or through another layer, and recording is performed while sliding a magnetic head. And a sliding protection film according to JIS K
7204 Wear test (wear wheel CS-10, weight 50)
The magneto-optical disk according to claim 1, wherein the change in the haze value due to 0 gf) is 7% or less before the abrasion test and after 100 rotation abrasion. 3. A magneto-optical recording layer is provided on a substrate, and a sliding protection film made of a curable resin is provided on the substrate directly or through another layer to perform recording while sliding a magnetic head. The magneto-optical disk according to claim 1 or 2, wherein the cured product of the ultraviolet curable resin contains a lubricity imparting agent. 4. The recording / reproducing light is applied from the substrate side while using the magneto-optical disk according to claim 1 and applying a modulation magnetic field by sliding a magnetic head on the slide protection layer. A magneto-optical recording method characterized by irradiation.