JPH08263887A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE: To suppress production of scratches and to stably perform recording and reproducing without changing the surface characteristics of a magneto- optical recording medium even when sliding operation is done by forming a lubricant thin film having a specified compsn. on a protective film comprising an infusible polymer film. CONSTITUTION: This medium has a protective film 5 as the outermost layer on the opposite side of a plastic substrate 1 to the irradiation side of laser light. The protective film 5 consists of an infusible polymer and is formed by crosslinking a reactive resin mixture to make the polymer infusible. Further, a lubricant thin film 6 is formed on the protective film 5. This lubricant consists of a copolymer of polyoxyalkylene (a) and poly-alkylsiloxane or polyarylsiloxane (b) and contains a copolymer having <90mol% component (a) or component (b) by >=80wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to writing and reading of information by a combination of a laser beam emitted from a substrate side and a magnetic field applied from the opposite side of the substrate side with respect to the laser beam emitting side. The present invention relates to a magneto-optical recording medium capable of achieving the above.

[0002]

2. Description of the Related Art Optical recording media have attracted attention as high-density and large-capacity information recording media, and various researches and developments have been carried out. In particular, a magneto-optical recording medium that can erase information and can be repeatedly used has a wide application field, and various magneto-optical recording media have been announced. Then, in this magneto-optical recording medium, a predetermined region of the recording film provided on the substrate is irradiated with laser light from the substrate side to be heated, and at the same time, a magnetic field in a predetermined direction is applied, thereby Is written.

For that purpose, laser light is irradiated from the substrate side, while a predetermined external magnetic field is applied by a magnetic head installed on the side opposite to the laser light irradiation side with the substrate interposed therebetween. Is done.

By the way, in the conventional magneto-optical recording medium, it is difficult to perform direct overwrite. That is, when writing information, it is necessary to first erase the information recorded in the past and then write new information in the next stage. Therefore, there is a problem that it takes a lot of time to process the information. As a means for solving this problem, a magneto-optical recording medium by a magnetic field modulation method has been proposed and has already been put into practical use. In this magnetic field modulation method, the external magnetic field is modulated according to the content of information to be written, so that the erasing of past information and the writing of new information are performed at the same time.

In order to write information on a magneto-optical recording medium by such a magnetic field modulation method, it is necessary to increase the sensitivity of the medium and to bring the magnetic head for applying a magnetic field as close to the medium as possible. Further, even in a magneto-optical recording medium which is not magnetic field modulated, an external magnetic field applying means may be provided close to the medium in order to downsize the recording / reproducing apparatus.

[0006]

The case where the magnetic head and the magneto-optical recording medium are closest to each other means that the magnetic head is in direct contact with the medium surface. The direct contact may be in constant contact with the magnetic head and the magneto-optical recording medium, or may be in contact with the desk-shaped magneto-optical recording medium only at the start and end of rotation. In any case, when the magnetic head comes into contact with the medium, the surface of the medium is eventually rubbed and slid. When the magneto-optical recording medium is deformed by this stress, accurate reading / writing of recording can no longer be performed.

The present invention eliminates such a recording instability factor and suppresses the formation of scratches without changing the surface characteristics of the magneto-optical recording medium even when a sliding operation is performed, thereby writing / writing.
An object of the present invention is to provide a magneto-optical recording medium capable of stable reading.

[0008]

According to the present invention, information is obtained by combining a laser beam applied from the side of a substrate made of a plastic material and a magnetic field applied from the side opposite to the laser beam irradiation side with the substrate interposed therebetween. In a magneto-optical recording medium capable of writing and / or reading, an insoluble polymer film formed by cross-linking and insolubilizing a reactive resin mixture is formed on the outermost layer of the magneto-optical recording medium on the side opposite to the laser light irradiation side. A magneto-optical recording medium comprising a protective film comprising: (a) a polyoxyalkylene having a molecular weight of 200 to 20,000; and (b) a molecular weight of 500 to 20,000.
80% by weight or more of a copolymer with the polyalkyl siloxane or polyaryl siloxane of (1) and the component (a) or the component (b) does not exceed 90 mol% (hereinafter also referred to as "copolymer"). A magneto-optical recording medium characterized in that a thin film of a lubricant contained therein is formed.

The magneto-optical recording medium of the present invention comprises a substrate, a magnetic recording film, and a protective film in this order from the laser light irradiation side, and a thin film of a lubricant is formed on the protective film. In the present invention, as a material constituting the protective film,
An insoluble polymer obtained by insolubilizing a reactive resin mixture by crosslinking is used.

At this time, the protective film is provided for the purpose of preventing deformation caused by friction or sliding of the surface of the magneto-optical recording medium by light, a magnetic head or the like. Therefore, as a material constituting the protective film, It is necessary to have flexibility. Therefore, in the present invention, as the insoluble polymer, a material in which urethane diacrylate is insolubilized by crosslinking as a material having a urethane bond is preferably used. The urethane diacrylate is one or a mixture of two or more selected from the group consisting of tolylene diisocyanate having an isocyanate group, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate and diphenyl ether diisocyanate, and an alcohol group having 2 carbon atoms. Is a urethane diol obtained by reaction with saturated alkylene diglycol of No. 6 to 6 is diacrylated. Specific examples of this saturated alkylenediglycol include 1,2-
Ethylene glycol, 1,3-propylene diol,
Examples include 1,4-butanediol and 1,6-hexanediol.

In this reaction, the stoichiometric ratio (molar ratio) of the isocyanate group and the alcohol group is preferably such that the alcohol group is slightly in excess, and the alcohol group / isocyanate group is 1.05 to 2.0. Particularly preferred.
If the alcohol group is in excess, acrylic acid chloride,
Acrylic acid active ester or the like is used to change the urethane bond into an acrylic acid derivative having a side chain, and to function as a node of the crosslinking reaction. On the other hand, when the isocyanate group is excessive, the isocyanate group which is a reactive functional group remains in the liquid and causes a hydrolysis reaction with moisture in the air, resulting in not forming an elastic film. .

The crosslinking reaction of urethane diacrylate is carried out with trimethylolpropane triacrylate.
The amount of trimethylolpropane triacrylate mixed is
The molar ratio to urethane diacrylate is 0.1 to 0.1.
5.0 is preferable, and 0.5 to 3.0 is particularly preferable. When the molar ratio of the mixing amount of trimethylolpropane triacrylate is less than 0.1, the cross-linking efficiency is poor, so that the film has low hardness, while when it exceeds 5.0, the flexibility is increased due to an extreme increase of the effect point. Is lost and the hardness decreases.

At this time, in order to improve the flexibility of the insoluble polymer, it is preferable to add saturated alkylenediglycol diacrylate having 2 to 6 carbon atoms. Specific examples of the saturated alkylene diglycol diacrylate include ethylene glycol diacrylate, 1,4-butanediol diacrylate, and 1,6-hexanediol diacrylate.

The amount of addition is preferably 10 to 90% by weight, and particularly preferably 20 to 80% by weight, based on the reactive resin mixture. If the amount added is less than 10% by weight, no improvement in flexibility is observed, while if it exceeds 90% by weight, curing becomes unstable and strength is not exhibited. The total amount of urethane diacrylate, saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms and triacrylate derivative of trimethylolpropane is preferably contained in the reactive resin mixture in an amount of 60% by weight or more, particularly 70% by weight or more. . When the total amount is less than 60% by weight,
It is difficult to obtain an elastic protective film.

The reactive resin mixture is crosslinked and insolubilized by an ultraviolet curing reaction, a heat curing reaction, and an electron beam irradiation curing reaction.

The thickness of this protective film is 2 to 100 μm.
m is preferable, and 3 to 15 μm is particularly preferable. Film thickness is 2
When it is less than μm, the function as a protective film is not exerted,
On the other hand, if it exceeds 100 μm, mechanical change as a recording medium may occur.

As described above, a polymer obtained by insolubilizing a reactive resin mixture consisting of urethane diacrylate, saturated alkylenediglycol diacrylate having 2 to 6 carbon atoms and trimethylolpropane triacrylate by crosslinking is used as the protective film. As a result, the flexibility of the protective film is improved and the uniformity of the film is increased.

In the present invention, a thin film of lubricant is formed on the protective film. The lubricant is provided for the purpose of improving the sliding characteristics of the magneto-optical recording medium. Here, it is not always possible for an arbitrary lubricant to be evenly cast on the insoluble polymer film, and in order for the lubricant thin film to be stably formed, the lubricant and the insoluble polymer film must be It is important that they are mutually compatible. For example, when the protective film is made of a polar material such as an insoluble polymer having a urethane bond, if a non-polar lubricant such as polysiloxane is applied as it is, a cissing phenomenon will occur and The agent is exposed and the uniform thin film is not formed.

From this point of view, in the present invention, (a) a polyoxyalkylene having a molecular weight of 200 to 20,000 and (b) a molecular weight of 500 to 20,000 are used as lubricants.
A polymer containing 80% by weight or more of the copolymer of the polyalkylsiloxane or the polyarylsiloxane is used.

Examples of the (a) polyoxyalkylene include polymers such as polymethylene oxide, polyethylene oxide and polypropylene oxide. Usually, these polymers are obtained by ring-opening polymerization of the corresponding cyclic oxides. The molecular weight of (a) polyoxyalkylene is 200 to 20,000, preferably 400 to 16,000. If it is less than 200, the lubricating effect is reduced, while if it exceeds 20,000, solidification occurs and the surface condition becomes unstable, which is not preferable.

Examples of the (b) polyalkyl siloxane or polyaryl siloxane which is one of the copolymer components include polymers such as polydimethyl siloxane, polymethylphenyl siloxane and polydiphenyl siloxane. The molecular weight of the (b) polyalkylsiloxane or polyarylsiloxane is 500 to 2
It is 50,000, preferably 800 to 16,000.
When it is less than 500, there are problems such as volatility and easy flowability, while when it exceeds 20,000, viscosity increases and resistance increases, which is not preferable as a lubricant.

At this time, the molar ratio of the copolymerization of the components (a) and (b) is 10:90 to 90:10, preferably 20:80 to 80:20. When either component (a) or component (b) exceeds 90 mol%,
It is not preferable because the affinity with the protective film is reduced.

It is desirable that these copolymers be in a liquid form or a wax form at room temperature in order to improve sliding characteristics as a lubricant.

The proportion of the copolymer in the lubricant forming the thin film is 80% by weight or more, preferably 90% by weight or more. If it is less than 80% by weight, the affinity with the protective film is lowered, and it is impossible to uniformly coat the protective film.

As a method for forming a thin film using this lubricant, any method may be used as long as the lubricant can be applied uniformly. As the method, for example,
The spin coating method, a bar coater method, a simple dipping method, a liquid draining method, and a natural casting method may be mentioned, but the spin coating method is most preferable from the viewpoint of uniformly forming a thin film. At this time, depending on the viscosity of the lubricant, a method in which a solution previously diluted with ethanol or the like is applied by the above method and then ethanol is evaporated may be used.

The thickness of the lubricant thin film is 0.01 to 1 μm.
m, particularly preferably 0.05 to 0.8 μm.
If the film thickness is less than 0.01 μm, the sliding characteristics cannot be improved as a lubricant, while if it exceeds 1 μm, dusts and the like are likely to adhere, which may cause problems in appearance and function. There is.

As the structure of the magneto-optical recording medium, a protective film made of dielectric film / magneto-optical recording film / dielectric film / light reflecting film / insoluble polymer is provided in this order on the side of the substrate on which magnetism is applied. Is preferred.

As the material of the substrate, not only polycarbonate resin, acrylic resin, epoxy resin, 4-methyl-pentene resin, or their copolymers but also glass can be applied. Among them, polycarbonate resin is preferable from the viewpoint of mechanical strength, weather resistance, heat resistance, and moisture permeability.

Any magnetic recording film can be used as long as it can be written / read by the photothermomagnetic effect. Specifically, it has an easy magnetization direction in the direction perpendicular to the substrate and creates magneto-optical properties by forming an arbitrary inversion domain. A magnetic metal thin film capable of writing / reading information based on the effect can be used. Specifically, TbFe, TbFeCo, GdTbF
e, GdFeCo, NdDyFeCo, NdDyTbF
eCo, NdFe, PrFe, CeFe, TbFeCo
Examples thereof include an amorphous alloy film of a rare earth element such as Cr and a transition metal element, an artificial lattice multilayer film such as Co / Pt, Co / Pd, and the like. Among them, TbFeCoCr is preferable.

In order to maximize the Kerr effect, the light reflecting film is preferably composed of Al, Au, Ti and Ag from the viewpoint of improving the durability of the metal itself without reducing the reflectance as much as possible. . These may be simple substances or alloys, but especially from the viewpoint of C / N, AlAu
Or AgAu alloy, especially AlAuTi alloy or Ag
AuTi alloy is preferred. AlAuTi alloy or Ag
AuTi alloy has a relatively low thermal conductivity, and by using this as a light reflecting film, when the disc rotation speed is high, for example, a double speed of the ISO standard proposal, specifically, 3,600.
Even in the case of rpm, the heat diffusion can be prevented, the overall recording sensitivity becomes high, and the C / N level for reproduction can be sufficiently recorded with the same small recording power of 10 mw or less from the inner peripheral portion to the outer peripheral portion. A medium suitable for transfer is realized. A
In the 1AuTi alloy or the AgAuTi alloy, the addition amount of Au is preferably 0.5 to 20.0 atomic%, 0.5
〜15.0 atom% is more preferable, and 0.5〜10.0
Atomic% is especially preferred. The amount of Ti added is 0.3
˜5.0 at% is preferred. On the other hand, an AlAu alloy or an AgAu alloy is preferable in that it can be used in a magneto-optical recording medium having a simple structure in which the light-reflecting film is provided in contact with the magneto-optical recording film because of its particularly low thermal conductivity. . The thickness of the light reflecting film is preferably 100 to 5,000 Å, more preferably 400 to 2,000 Å.

As described above, the dielectric film can be provided on the substrate side of the magneto-optical recording film or on the light reflecting film side of the magneto-optical recording film. This is to substantially enhance the Kerr rotation by the effect of multiple reflection by providing a dielectric film having an appropriate thickness on the magneto-optical recording film. Therefore, the dielectric film is required to have excellent transparency to the laser light used, and further, in order to exert the effects such as the optical interference effect and the Kerr effect enhancement, a certain high refractive index, that is, a refractive index is required. It is preferably 1.8 or more, particularly preferably 2.0 or more. From such a viewpoint, AlN, MgF ₂ , ZnS, CeF ₃ , AlF ₃ ·.
3NaF, Si ₃ N ₄ , AlSiN, SiO, Si
O ₂ , Zr ₂ O ₃ , In ₂ O ₃ , SnO ₂ , Ta
₂ O ₅ , AlON, SiON, ZrON, InON, S
Examples include nON, TaON, and mixtures thereof. Among them, Al has a refractive index of 2.0 or more.
SiN, ZnS, Zr ₂ O ₃ , Ta ₂ O ₅ , ZrON,
TaON is preferred.

As the method for forming the magneto-optical recording film, the dielectric film, and the light reflecting film on the substrate, various thin film forming methods such as the known vacuum deposition method, PVD method such as sputtering method, or CVD method can be applied. . However, the magneto-optical recording medium is preferably manufactured under the condition that the adhesiveness to the polymer substrate is particularly large in order not to cause peeling which occurs in the high temperature and high humidity environment resistance test. For this purpose, the sputtering method is preferable, and among them, the reactive sputtering method using a mixed gas of argon gas or nitrogen gas is preferable from the viewpoint of safe operation and productivity with less abnormal discharge.

The magneto-optical recording medium obtained by the present invention is
Although it can be used in any magneto-optical recording method, the feature of the magneto-optical recording medium of the present invention is that sliding characteristics are remarkably excellent. Therefore, the magneto-optical recording medium of the present invention is used when it is necessary to bring the magnetic head close to the surface of the medium, such as when a magnetic modulation method is used for writing information or when the apparatus is downsized. To
The effect is most efficiently exhibited.

[0034]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these. Example 1 FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. In the figure, 1 is a plastic substrate having recording pits and guide grooves, 2 is a dielectric film, 3 is a magneto-optical recording film, 4 is a reflective film, 5 is a protective film, and 6 is a lubricant thin film.

First, as a reactive resin mixed solution for forming the protective film 5, 10 parts by weight of urethane diacrylate obtained from tolylene diisocyanate and diethylene glycol, 50 parts by weight of trimethylolpropane triacrylate, and 30 parts of neopentyl diglycol diacrylate. It was prepared by mixing 10 parts by weight of pentaerythritol tetraacrylate with 10 parts by weight of pentaerythritol tetraacrylate. On the other hand, outer diameter 86 mm, inner diameter 15
mm, 1.2 mm thick, on a disk-shaped polycarbonate substrate 1, a dielectric film 2 is formed using silicon nitride,
On this dielectric film 2, a magneto-optical recording film 3 was formed by a sputtering method using an alloy of Tb, Fe, Co and Cr, and a reflective film 4 was formed using an alloy of aluminum and titanium.

Next, the above-mentioned reactive resin mixture liquid was applied onto the reflection film 4 by a spin coating method to a film thickness of 4.5 μm,
The protective film 5 was formed by irradiating light of 75 mW / cm ² or more with a high pressure mercury lamp to perform photo-curing. Also, the molecular weight is about 4
A copolymer of 40 polyethylene glycol and dimethyl siloxane having a molecular weight of 2,000 [polyethylene glycol / dimethyl siloxane (molar ratio) = 1/1] was used as a lubricant, and a 20 wt% ethanol solution of this lubricant was applied on a spin coater. It was applied at 4,500 rpm on the protective film 5 of the disc which was left stationary. After about 1 minute, most of ethanol was evaporated, and it was confirmed from the increase in weight that a thin film of the lubricant made of the copolymer was formed. The estimated film thickness from the residual weight was 0.4 μm.

With respect to the magneto-optical disk thus obtained, the initial value of the signal characteristic and the signal characteristic after the sliding was given by using the simulated head were measured. An optical disk signal characteristic evaluation device (Mopple 90 type) manufactured by Olympus Industry Co., Ltd. was used to measure the signal characteristics. The sliding by the simulated head is performed by mounting the magneto-optical disk of the sample on the rotary plate of the measuring device with the surface having the protective film 5 facing up, and bringing the simulated head with a weight of 10 g into contact with the upper surface of the disk. This was done by spinning the disc for 3 minutes at a spinning speed of 450 rpm. The signal characteristics after sliding did not change at all compared to the initial values.

Example 2 As a reactive resin mixed liquid for forming the protective film 5, 10 parts by weight of urethane diacrylate obtained from isophorone diisocyanate and diethylene glycol, 40 parts by weight of trimethylolpropane triacrylate, and 35 parts of neopentyl diglycol diacrylate. It was prepared using 15 parts by weight of diethylene glycol diacrylate. A magneto-optical disk was prepared in the same manner as in Example 1 except that this reactive resin mixture was used. When the signal characteristics before and after sliding were measured according to Example 1, no change in the signal characteristics was observed.

Example 3 15 parts by weight of urethane diacrylate obtained from diphenylmethane diisocyanate and butanediol, 40 parts by weight of trimethylolpropane triacrylate, neopentyl diglycol diacrylate as a mixture of reactive resins for forming the protective film 5. 35 parts by weight of a mixture of diethylene glycol diacrylate and 1: 2 by weight,
It was prepared using 10 parts by weight of pentaerythritol tetraacrylate. A copolymer of polypropylene glycol having a molecular weight of about 800 and dimethylsiloxane having a molecular weight of 5,000 (molar ratio = 1: 1) was used as a lubricant, and a 10 wt% ethanol solution of this lubricant was allowed to stand on a spin coater. Then, a thin film was applied on the protective film of the disk prepared in the same manner as in Example 1 at 3,000 rpm for about 45 seconds. When the signal characteristics before and after sliding were measured according to Example 1, no change in the signal characteristics was observed.

Comparative Example 1 A magneto-optical disk was prepared in the same manner as in Example 1 except that the lubricant was not applied. When sliding operation was performed according to Example 1, after scratching, large scratches were generated on the surface, and the signal characteristics could not be measured.

Comparative Example 2 A magneto-optical disk was prepared in the same manner as in Example 1 except that the lubricant was applied without providing the protective film of the reactive resin mixture. When sliding operation was carried out according to Example 1, the surface of the magnetic recording layer 3 was peeled off, and evaluation of the recording characteristics was impossible.

Comparative Example 3 A magneto-optical disk was prepared in the same manner as in Example 1 except that polysiloxane having a molecular weight of 20,000 was used as the lubricant. The surface of the magneto-optical disk was uneven when the lubricant was applied. It was confirmed that the recording characteristics deteriorated due to wetting and partial repelling.

Comparative Example 4 As a lubricant, 25% by weight of polydimethylsiloxane having a molecular weight of 30,000, and a copolymer of polyethylene glycol having a molecular weight of about 440 and dimethylsiloxane having a molecular weight of 2,000 [polyethylene glycol / dimethylsiloxane (molar ratio ) = 1/1] A mixture of 75 wt% was used and a magneto-optical disk was prepared in the same manner as in Example 1 except that a 10 wt% ethanol solution of this lubricant was applied. At that time, repelling such as dew was generated, and it was confirmed that the recording characteristics were deteriorated.

[0044]

The magneto-optical recording medium of the present invention eliminates the cause of recording instability and suppresses the formation of scratches without changing the surface characteristics of the magneto-optical recording medium even if the sliding characteristic is performed. Since writing / reading can be performed stably by using the magnetic head, the magnetic head is used close to the surface of the medium, such as when using a magnetic modulation method for writing information or when downsizing the device. can do.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a magneto-optical recording medium of the present invention.

[Explanation of symbols]

 1 substrate 2 dielectric film 3 magneto-optical recording film 4 reflection film 5 protective film 6 thin film of lubricant

Claims (6)

[Claims] 1. Information can be written and / or read by a combination of a laser beam emitted from a substrate side made of a plastic material and a magnetic field applied from a side opposite to the laser beam irradiation side with the substrate interposed therebetween. In a magneto-optical recording medium, a magneto-optical recording medium having a protective film made of an insoluble polymer film formed by cross-linking and insolubilizing a reactive resin mixture is formed on the outermost layer of the magneto-optical recording medium on the side opposite to the laser light irradiation side A recording medium, comprising: (a) polyoxyalkylene having a molecular weight of 200 to 20,000 and (b) on the protective film.
Lubricants containing 80% by weight or more of a copolymer having a molecular weight of 500 to 20,000 and a polyalkyl siloxane or a polyaryl siloxane, and the component (a) or the component (b) does not exceed 90 mol%. 2. A magneto-optical recording medium having a thin film formed thereon. 2. The insoluble polymer film comprises a urethane diacrylate, a saturated alkylenediglycol diacrylate having 2 to 6 carbon atoms, and trimethylolpropane triacrylate in an amount of 60% by weight or more based on the total amount of a reactive resin mixture, which is crosslinked. The magneto-optical recording medium according to claim 1, which is formed by being insolubilized. 3. The urethane diacrylate is at least one isocyanate derivative selected from the group consisting of tolylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate and diphenyl ether diisocyanate, and saturated alkylene diglycol having 2 to 6 carbon atoms. The urethane diol obtained by reacting 1 with the alcohol group of the saturated alkylene diglycol in a stoichiometric excess relative to the isocyanate group of the isocyanate derivative is diacrylated. Magnetic recording medium. 4. The film thickness of the insoluble polymer film is 2 to 100 μm.
3. The magneto-optical recording medium according to claim 1, which is m. 5. The lubricant thin film has a thickness of 0.01 to 1 μm.
The magneto-optical recording medium according to claim 1, wherein m is m. 6. The magneto-optical recording medium according to claim 1, wherein a magnetic field modulation method is used when writing information.