JP3263274B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for writing and reading information by combining a laser beam irradiated from the substrate side and a magnetic field applied from the side opposite to the laser beam irradiation side with the substrate interposed therebetween. The present invention relates to a magneto-optical recording medium capable of recording.

[0002]

2. Description of the Related Art Optical recording media have attracted attention as high-density, large-capacity information recording media, and various research and development have been conducted. In particular, magneto-optical recording media capable of erasing information and being repeatedly used have a wide range of application fields, and various magneto-optical recording media have been announced. In this magneto-optical recording medium, a predetermined region of a recording film provided on a substrate is heated by irradiating a laser beam from the substrate side, and at the same time, a magnetic field in a predetermined direction is applied, thereby obtaining information. Is written.

[0003] For this purpose, a laser beam is irradiated from the substrate side, while a predetermined external magnetic field is applied by a magnetic head provided on the side opposite to the laser beam irradiation side with the substrate interposed therebetween. Is done.

Incidentally, it has been difficult to perform direct overwrite (direct overwrite) on a conventional magneto-optical recording medium. In other words, when writing information, it was necessary to take steps of first erasing previously recorded information and then writing new information in the next stage. For this reason, there has been a problem that it takes much time to process information. As a means for solving this problem, a magneto-optical recording medium using a magnetic field modulation method has been proposed, and practical use has already begun. In this magnetic field modulation method, erasing of past information and writing of new information are performed simultaneously by modulating an external magnetic field in accordance with the content of information to be written.

In order to write information on a magneto-optical recording medium using such a magnetic field modulation method, it is necessary to increase the sensitivity of the medium and to place a magnetic head for applying a magnetic field as close to the medium as possible. Further, even in the case of a magneto-optical recording medium that is not a magnetic field modulation, an external magnetic field applying unit may be provided close to the medium in order to reduce the size of the recording and 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 comes into direct contact with the surface of the medium. In this direct contact, the magnetic head and the magneto-optical recording medium are always in contact with each other, or the desk-shaped magneto-optical recording medium is in contact only when the rotation starts and ends. In any case, when the magnetic head comes in contact with the medium, the medium surface is eventually rubbed and slid. When the magneto-optical recording medium is deformed by this stress, it is no longer possible to read / write data accurately.

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

[0008]

According to the present invention, information is obtained by a combination of a laser beam irradiated from a substrate made of a plastic material and a magnetic field applied from a side opposite to the laser beam irradiated side with the substrate interposed therebetween. In a magneto-optical recording medium capable of writing and / or reading data, an insoluble polymer film formed by crosslinking 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 beam irradiation side. A magneto-optical recording medium provided with a protective film comprising: a polyalkylsiloxane or a polyarylsiloxane having a molecular weight of 500 to 20,000 (hereinafter also referred to as “polysiloxane”); Or those in which 0.05 to 20 mol% of aryl groups are modified with carboxyl groups (hereinafter also referred to as “carboxyl group-modified polysiloxane”) ) Is a magneto-optical recording medium, characterized in that the thin film was formed of a lubricant containing 80% by weight or more.

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 side irradiated with the laser beam, 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, since the protective film is provided for the purpose of preventing the surface of the magneto-optical recording medium from being deformed due to friction or sliding caused by light, a magnetic head, or the like, a material constituting the protective film includes: It is necessary to have flexibility. Therefore, in the present invention, as the insoluble polymer, a material having a urethane bond in which urethane diacrylate is insolubilized by crosslinking is preferably used. Urethane diacrylate is a mixture of at least one selected from the group consisting of tolylene diisocyanate having an isocyanate group, isophorone diisocyanate, diphenylmethane dissocyanate, dicyclohexylmethane diisocyanate, and diphenyl ether diisocyanate, and a carbon number having an alcohol group. Urethane diol obtained by reaction with 2 to 6 saturated alkylene diglycols is obtained by diacrylate. Specific examples of the saturated alkylenediglycol include 1,
Examples thereof include 2-ethylene glycol, 1,3-propylene diol, 1,4-butane diol, and 1,6-hexane diol.

In this reaction, the stoichiometric ratio (molar ratio) of the isocyanate group to the alcohol group is preferably a slight excess of the alcohol group, and the ratio of the alcohol group / isocyanate group is preferably 1.05 to 2.0. Particularly preferred.
When the alcohol group is excessive, the excess alcohol group is converted into an acrylic acid derivative having a urethane bond in a side chain by acrylic acid chloride, acrylic acid active ester, or the like, and functions as a node of a crosslinking reaction. Conversely, if the isocyanate group is excessive, the isocyanate group, which is a reactive functional group, remains in the liquid, causing a hydrolysis reaction with moisture in the air and the like, resulting in not forming an elastic film. .

The crosslinking reaction of urethane diacrylate takes place with trimethylolpropane triacrylate.
The mixing amount of trimethylolpropane triacrylate is
The urethane diacrylate is in a molar ratio of 0.1 to
5.0 is preferable, and especially 0.5 to 3.0 is preferable. If the molar ratio of the trimethylolpropane triacrylate is less than 0.1, the crosslinking efficiency is poor, resulting in a protective film having low hardness. If the molar ratio is more than 5.0, the curing point is extremely increased. Flexibility is lost and hardness is reduced.

At this time, in order to improve the flexibility of the insoluble polymer, it is preferable to add a saturated alkylene diglycol 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 addition amount is preferably from 10 to 90% by weight, particularly preferably from 20 to 80% by weight, based on the reactive resin mixture. If the amount is less than 10% by weight, no improvement in flexibility is observed, while if it exceeds 90% by weight, the curing becomes unstable and the strength is not developed. The total amount of the urethane diacrylate, the saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms and the triacrylate derivative of trimethylolpropane is preferably 60% by weight or more, particularly preferably 70% by weight or more in the reactive resin mixture. . When the total amount is less than 60% by weight,
It is difficult to obtain an elastic coating 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 the protective film is 2 to 100 μm.
m is preferable, and particularly preferably 3 to 15 μm. The film thickness is 2
If it is less than μm, the function as a protective film is not exhibited,
On the other hand, if it exceeds 100 μm, there is a possibility that a mechanical change as a recording medium may occur.

As described above, a polymer obtained by insolubilizing a reactive resin mixture comprising urethane diacrylate, a saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms and trimethylolpropane triacrylate by crosslinking is used as the protective film. Thereby, the effect of improving the flexibility of the protective film and increasing the uniformity as a film can be obtained.

In the present invention, a thin film of a 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.

As the lubricant, a molecular weight of 500 to 20,000 is used.
00 polyalkylsiloxane or polyarylsiloxane is used. Here, examples of the polyalkylsiloxane or polyarylsiloxane include polydimethylsiloxane, polymethylphenylsiloxane, and polydiphenylsiloxane. The molecular weight of the polyalkylsiloxane or polyarylsiloxane is from 500 to 20,000, preferably from 800 to 16,
000. If it is less than 500, there are problems such as volatility and easy flow, while if it is more than 20,000, the viscosity increases and the resistance increases, which is not preferable as a lubricant.

However, an arbitrary lubricant cannot always be uniformly cast on the insoluble polymer film. In order to form a stable thin film of the lubricant, the lubricant and the insoluble polymer film are required. It is important that and 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 repelling phenomenon occurs and lubrication occurs. The agent is exposed and a uniform thin film is not formed.

From this viewpoint, the lubricant must be a carboxyl group-modified polysiloxane in which 0.05 to 20 mol% of the alkyl group or the aryl group of the polyalkylsiloxane or polyarylsiloxane is modified with a carboxyl group. When the modification ratio is less than 0.05 mol%, there is almost no difference from the unmodified one, while when it exceeds 20 mol%, the physical properties of the polysiloxane do not appear.

The carboxyl group-modified polysiloxane is contained in the lubricant in an amount of at least 80% by weight, particularly preferably at least 90% by weight. If the content is less than 80% by weight, the affinity with the protective film is reduced, and it is not possible to uniformly coat the protective film.

It is desirable that the lubricant containing carboxyl group-modified polysiloxane or riarylsiloxane as a main component be in a liquid or wax form at room temperature in order to improve the sliding characteristics as a lubricant.

As a method of forming a thin film using this lubricant, any method may be used as long as the lubricant can be applied uniformly. For example, a spin coating method, a method using a bar coater, or a simple method can be used. Immersion,
Draining and natural casting methods are mentioned. From the viewpoint of forming a thin film uniformly, the spin coating method is most preferable. At this time, depending on the viscosity of the lubricant,
A mixed solution diluted with ethanol or the like in advance,
After applying by the above method, a method of evaporating ethanol 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, dust and the like tend to adhere, which may cause problems in appearance and function. There is.

The structure of the magneto-optical recording medium is such that a dielectric film, a magneto-optical recording film, a dielectric film, a light reflecting film, and a protective film made of an insoluble polymer are provided on the magnetic application side of the substrate in this order. It is preferred that

As a material for the substrate, a polycarbonate resin, an acrylic resin, an epoxy resin, a 4-methyl-pentene resin, a copolymer thereof, or glass can be used. Among them, polycarbonate resin is preferable in terms of mechanical strength, weather resistance, heat resistance, and moisture permeability.

The magnetic recording film may be of any type as long as it can be written / read by the photothermal magnetic effect. Specifically, the magnetic recording film has an easy magnetization direction perpendicular to the substrate. A magnetic metal thin film on which information can be written / read based on the effect can be used. Specifically, TbFe, TbFeCo, GdTbF
e, GdFeCo, NdDyFeCo, NdDyTbF
eCo, NdFe, PrFe, CeFe, TbFeCo
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, etc., may be mentioned. Among them, TbFeCoCr is preferable.

The light reflection film is preferably made of Al, Au, Ti or Ag from the viewpoint of improving the durability of the metal itself without reducing the reflectance as much as possible in order to obtain the Kerr effect as much as possible. . These may be a simple substance or an alloy, but in particular, from the viewpoint of C / N, AlAu
Or AgAu alloy, especially AlAuTi alloy or Ag
AuTi alloys are preferred. AlAuTi alloy or Ag
The AuTi alloy has a relatively low thermal conductivity, and is used as a light reflecting film, so that when the disk rotation speed is high, for example, a double speed according to the ISO standard draft, specifically, 3,600
Even in the case of rpm, the diffusion of heat can be prevented, the overall recording sensitivity is increased, and the C / N level for reproduction can be sufficiently recorded from the inner periphery to the outer periphery with the same small recording power of 10 mw or less, and high speed A medium suitable for transfer is realized. A
In the AuTi alloy or the AgAuTi alloy, the addition amount of Au is preferably 0.5 to 20.0 atomic%,
To 15.0 at%, more preferably 0.5 to 10.0 at%.
Atomic% is particularly preferred. The amount of Ti added is 0.3
~ 5.0 at% is preferred. On the other hand, since the thermal conductivity is particularly small, the AlAu alloy or the AgAu alloy is preferable in that it can be used in a magneto-optical recording medium having a simple configuration in which the light reflecting film is provided in contact with the magneto-optical recording film. . The thickness of the light reflecting film is preferably 100 to 5,000, more preferably 400 to 2,000.

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 provide a dielectric film having an appropriate thickness on the magneto-optical recording film to substantially enhance Kerr rotation by the effect of multiple reflection. For this reason, the dielectric film needs to have excellent transparency to the laser light to be used, and furthermore, has a certain high refractive index, that is, a refractive index in order to exhibit effects such as light interference effect and Kerr effect enhancement. It is preferably at least 1.8, particularly preferably at least 2.0. 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
nON, TaON or a mixture thereof, and the like. Above all, 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 a 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 a known PVD method such as a vacuum deposition method and a sputtering method, and a CVD method can be applied. . However, it is preferable that the magneto-optical recording medium is manufactured under the condition that the adhesion to the polymer substrate is particularly large so as not to cause the peeling that occurs in the high-temperature and high-humidity environment resistance test. For this purpose, a sputtering method is preferable, and among them, a reactive sputtering method using a mixed gas of an argon gas and a nitrogen gas is preferable in terms of safe operation and productivity with less abnormal discharge and the like.

The magneto-optical recording medium obtained according to the present invention comprises:
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 the sliding characteristics are extremely 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 medium surface, such as when the magnetic modulation method is used for writing information or when the apparatus is used to reduce the size. To
The effect is exhibited most efficiently.

[0033]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited by these. Embodiment 1 FIG. 1 is a sectional view of a magneto-optical recording medium showing an embodiment 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 thin film of a lubricant.

First, as a reactive resin mixture 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, 30 parts by weight of neopentyl diglycol diacrylate Parts by weight, and 10 parts by weight of pentaerythritol tetraacrylate. On the other hand, the outer diameter is 86 mm and the inner diameter is 15
A dielectric film 2 is formed on a disc-shaped polycarbonate substrate 1 having a thickness of 1.2 mm and a thickness of 1.2 mm using silicon nitride.
A magneto-optical recording film 3 was formed on the dielectric film 2 by sputtering using an alloy of Tb, Fe, Co, and Cr, and a reflection film 4 was formed by using an alloy of aluminum and titanium.

Next, the above-mentioned reactive resin mixture is applied to a thickness of 4.5 μm on the reflective film 4 by spin coating.
Irradiation with light of 75 mW / cm ² or more was performed using a high-pressure mercury lamp to perform photo-curing, thereby forming a protective film 5. From NMR analysis, it was confirmed that 5 mol% of the methyl groups of the dimethylpolysiloxane were modified to carboxymethyl groups. Dimethylpolysiloxane having a molecular weight of 2,000 was used as a lubricant, and 20% by weight of the lubricant was used. % Ethanol solution was applied at 4500 rpm per minute on the protective film 5 of the disk which was left still on a spin coater. After about one minute, most of the ethanol evaporated, and it was confirmed from the increase in weight that a thin film of the lubricant composed of the carboxyl group-modified dimethylpolysiloxane was formed. The estimated film thickness from the remaining weight is
It was 0.4 μm.

With respect to the magneto-optical disk obtained in this manner, the initial value of the signal characteristics and the signal characteristics after the slide was given using the simulation head were measured. For the measurement of the signal characteristics, an optical disk signal characteristic evaluation device (Mopple 90 type) manufactured by Olympus Corporation was used. The sliding by the simulated head is performed by mounting the sample magneto-optical disk on the rotating plate of the measuring apparatus with the surface with the protective film 5 facing upward, and bringing the simulated head with a 10 g weight attached thereto into contact with the upper surface of the disk. This was performed by rotating the disk at 450 rpm for 3 minutes. No change was observed in the signal characteristics after sliding as compared with the initial value.

Example 2 As a reactive resin mixed solution 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, 35 parts of neopentyl diglycol diacrylate 35 And 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 recognized.

Example 3 As a reactive resin mixture for forming the protective film 5, 15 parts by weight of urethane diacrylate obtained from diphenylmethane diisocyanate and butanediol, 40 parts by weight of trimethylolpropane triacrylate, and neopentyl diglycol diacrylate 35 parts by weight of a mixture (1: 2 by weight) of diethylene glycol diacrylate and
It was prepared using 10 parts by weight of pentaerythritol tetraacrylate. From NMR analysis, it was confirmed that 1.5 mol% of the methyl groups of the dimethylpolysiloxane were modified to carboxymethyl groups, and the molecular weight was 1
Using 5,000 dimethylpolysiloxane as a lubricant, a 10% by weight ethanol solution of the lubricant was placed on a spin coater and placed on a protective film of a disk manufactured in the same manner as in Example 1 per minute. The thin film was applied at 3,000 rotations 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 recognized.

Comparative Example 1 A magneto-optical disk was prepared in the same manner as in Example 1, except that no lubricant was applied. When the sliding operation was performed according to Example 1, after the sliding operation, a large scratch was 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 a protective film of the reactive resin mixed solution. When the sliding operation was performed in accordance with Example 1, the surface of the magneto-optical recording film 3 was peeled off, and it was impossible to evaluate the recording characteristics.

Comparative Example 3 A magneto-optical disk was produced in the same manner as in Example 1 except that a polysiloxane having a molecular weight of 20,000, in which a methyl group was not modified with a carboxyl group, was used as a lubricant. When the agent was applied, it was recognized that the surface was unevenly wet, partial repelling occurred, and the recording characteristics deteriorated.

Comparative Example 4 Polysiloxane 2 having a molecular weight of 20,000 was used as a lubricant.
Except that a mixture of 5% by weight and 75% by weight of polydimethylsiloxane having a molecular weight of 2,000 in which 5% by mole of methyl groups were modified to carboxymethyl groups was used, and a 5% by weight ethanol solution of this lubricant was applied. When a magneto-optical disk was prepared in the same manner as in Example 1, it was confirmed that the surface was unevenly wet and the recording characteristics were deteriorated.

[0043]

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 when the sliding characteristics are performed. The magnetic head can be used close to the medium surface, such as when using a magnetic modulation method for writing information or when miniaturizing the device, because writing / reading can be performed stably. can do.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Dielectric film 3 Magneto-optical recording film 4 Reflection film 5 Protective film 6 Lubricant thin film

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-78365 (JP, A) JP-A-7-78368 (JP, A) JP-A-7-78355 (JP, A) JP-A 8-78 263887 (JP, A) JP-A-7-134842 (JP, A) JP-A-7-210906 (JP, A) JP-A-7-282481 (JP, A) JP-A-6-60457 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 11/105

Claims (6)

(57) [Claims] 1. Information writing and / or reading is possible by a combination of a laser beam irradiated from a substrate made of a plastic material and a magnetic field applied from a side opposite to the laser beam irradiated side with a substrate interposed therebetween. 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 on the outermost layer of the magneto-optical recording medium opposite to the side irradiated with the laser beam. A recording medium having a molecular weight of 500
Forming a thin film of a lubricant containing at least 80% by weight of a polyalkylsiloxane or polyarylsiloxane of up to 20,000, wherein 0.05 to 20 mol% of the alkyl or aryl group is modified with a carboxyl group; A magneto-optical recording medium characterized in that: 2. A reactive resin mixture containing urethane diacrylate, saturated alkylene diglycol diacrylate having 2 to 6 carbon atoms and trimethylolpropane triacrylate in an amount of 60% by weight or more based on cross-linking insoluble polymer film. 2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is formed. 3. The urethane diacrylate comprises at least one isocyanate derivative selected from the group consisting of tolylene diisocyanate, isophorone diisocyanate, diphenylmethane dissocyanate, dicyclohexylmethane diisocyanate and diphenyl ether diisocyanate, and a saturated alkylene diglycol having 2 to 6 carbon atoms. 3. The light according to claim 2, wherein urethanediol obtained by reacting a saturated alkylene diglycol 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, wherein m is m. 5. The lubricant thin film has a thickness of 0.01 to 1 μm.
2. 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.