JPH07307042A - Resin composition for protective coat of magneto-optical recording medium, magneto-optical recording medium with protective coating layer made of same and coating its method - Google Patents

Abstract

PURPOSE:To roughen the surface of a protective film so that the attraction of a levitating magnetic head is prevented by incorporating a compd. which generates bubbles under irradiation into a raditioncuring org. resin compsn. for forming a protective coat. CONSTITUTION:When a magneto-optical recording medium is coated with a protective coating agent and irradiated so as to cure the coating agent, a compd. which discharges gaseous nitrogen, etc., under irradiation in the coating agent as a resin compsn. for a protective coat absorbs radiation and causes a chemical reaction. By this reaction, nitrogen molecules, etc., are released from the compd. and remain as fine bubbles in an uncured protective coat. The bubbles rise by buoyancy until the resin cures well and the viscosity increases. The bubbles gather in the surface of the protective coat and the surface of the protective coat is made finely rugged by continuing irradiation until curing is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording binarized information on a recording film by a laser in the presence of a magnetic field, and more specifically for applying an external magnetic field. A resin composition for forming a protective coat of a magneto-optical disk used in a magnetic field modulation recording method using a floating magnetic head, and a magneto-optical recording medium coated with a cured film of the resin composition, and further using the resin composition The present invention relates to a coating method for forming a protective coat layer.

[0002]

2. Description of the Related Art Magneto-optical recording media include magneto-optical disks,
Although there are types such as cards and tapes, the magneto-optical recording medium described here is usually formed by a combination of an interference film, a recording film, and a reflective film on a substrate having a guide groove, as constituent units. Refers to a magneto-optical disk having a recording layer. Since these recording layers do not have sufficient hardness against dust, contact, etc. in the environment of use, a protective coat layer having sufficient hardness is required to improve scratch resistance.

Both organic and inorganic materials are used for the material of the protective coating layer, and various coating methods such as dipping method, spin coating method, roll coater method and vapor deposition method are used. For production, the spin coating method using a radiation curable resin is preferable because it is a simple and quick method. In the spin coating method, a radiation curable resin is discharged onto a magneto-optical recording medium using a dispenser, and this is rotated at a high speed to spread the resin by centrifugal force to apply the resin.

The applied resin is then cured by irradiation with radiation. The resin used for the protective coat layer preferably has a pencil hardness of F or higher after curing, and more preferably has a hardness of H or higher. The adhesion with the lower layer is measured by a cross-cut cellophane tape peeling test, but is about 20 / 100-
It is practically used in the range of 100/100. Also,
Since the plastic substrate itself has insufficient scratch resistance, a hard coat layer is usually provided on the surface of the substrate opposite to the recording layer using a transparent material having high hardness.

As described above, the protective coat of the magneto-optical disk can be applied by a simple spin coating method, and can be cured by non-heating and is radiation-cured as a solvent-free organic resin coating agent which does not pollute the production environment. Mold resin is widely used. In many cases, the radiation-curable resin protective coating agent is a (meth) acrylate monomer, a di (meth) acrylate monomer, a tri (meth) acrylate monomer, or a higher polyfunctional (meth) acrylate monomer, and a monofunctional or polyfunctional monomer. Compounds having a radiation-curable vinyl group such as epoxy (meth) acrylate monomer, urethane (meth) acrylate monomer, and oligomers thereof are blended, and further a polymerization initiator, a polymerization inhibitor, and various modifiers are added if necessary. And the like are added to the resin composition.

However, when a conventional radiation-curable resin as described above is applied by spin coating and then cured, it is used as a protective coat for a magneto-optical disk,
The surface of the protective coat has no irregularities, and the product is smooth like a mirror surface. When such a product is used in a magnetic field modulation recording type drive device using a floating magnetic head, when the floating magnetic head and the magneto-optical disk surface come into contact with each other, a large contact area is likely to cause vacuum adsorption. When the disk is rotated in the state where such attraction occurs, a force in the rotational direction is applied to the floating magnetic head, and there is a high risk that the arm supporting the head is deformed or destroyed.

As a technique conventionally invented for the purpose of solving such a problem, Japanese Patent Laid-Open No. 02-232836 discloses a technique for protecting a floating magnetic head and a protective coating surface with a minute gap in order to prevent vacuum adsorption. A method of roughening this surface after the coating step of the coat is shown. In Japanese Patent Laid-Open No. 03-2012231, a method of pressing a stamper (mold) to form a concave pattern on the surface after applying a protective coating agent, and a resin composition added with a solvent as described in Japanese Patent Laid-Open No. 04-111243 are applied. A method has been proposed in which it is dried before curing to form a crack on the surface. In addition, JP-A-04-19842 and JP-A-04-19842.
219648 is a means for roughening the surface by mixing non-magnetic powder such as alumina in the resin composition for protective coating,
Further, Japanese Patent Application Laid-Open No. 03-62338 proposes a method in which the powder to be mixed is magnetic powder and is attracted to the surface with a magnet before curing in order to expose the powder to the surface without settling.

[0008]

As described above, in the magnetic field modulation recording method, various methods have been proposed for the purpose of roughening the surface of the magneto-optical disk medium in order to prevent adsorption of the flying magnetic head. However, both methods require new equipment and steps after a normal protective film forming step such as spin coating, which inevitably increases the burden.

The problem to be solved by the present invention relates to the production of a magneto-optical disk used in a magnetic field modulation recording type drive device, and bubbles are generated by irradiation of a radiation-curable organic resin composition provided as a protective coat. By containing the compound, it is possible to achieve the roughening of the surface of the protective film for preventing the adsorption of the flying magnetic head without increasing new steps.

[0010]

In order to solve the above problems, the present invention is an organic resin composition for forming a protective coating layer as the outermost surface layer of a magneto-optical recording medium for recording and reproducing information by applying light and a magnetic field. And a resin composition for protecting a magneto-optical recording medium, comprising a radiation-curable organic resin composition containing a compound having a radiation-curable vinyl group and a compound capable of generating bubbles upon irradiation with radiation. And a resin composition provided on the outermost layer of the magneto-optical recording layer.

As a method of manufacturing a substrate of a magneto-optical disk, a method of forming guide grooves by injection molding using a resin having excellent moldability such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin, or a glass method by a photopolymer method. Alternatively, a method of forming a guide groove on a resin flat plate may be used.

Among the recording layers, the interference film is excellent in transparency,
An inorganic dielectric film having a high refractive index is used. Examples of the material include SiNx, SiOx, AlSiON, AlN,
AlTiN, Ta ₂ O _5, ZnS, and the like. The refractive index of these interference films is preferably in the range of 1.8 to 2.8, and the extinction coefficient is preferably in the range of 0 to 0.1.

As a material for forming the recording film, TbFe is used.
Examples include alloys of transition metals such as Co and NdDyFeCo and rare earth metals.

A metal film or an alloy film having a high reflectance is used for the reflective film. The material is, for example, Al as the metal film,
As an alloy film of Au, Ag, Cu, etc., Al-Ti, Al
-Cr etc. are mentioned. The interference film, the recording film, and the reflective film are formed by physical vapor deposition (PVD) such as sputtering or ion plating, or chemical vapor deposition (CVD) such as plasma CVD.
And the like.

The uppermost layer of the recording layer before applying the protective coat is
Depending on the structure of the magneto-optical disk medium, a recording film, an interference film,
Alternatively, a protective coat layer is provided on each of the reflective films, and a hard coat layer is provided on the surface of the substrate opposite to the magneto-optical recording layer.

A radiation-curable resin is widely used as a solvent-free organic resin coating agent which can be applied to a protective coat of a magneto-optical disk by a simple spin coating method, can be cured by heating and does not pollute the production environment. It is used. Examples of the radiation-curable vinyl group-containing compound used in the present invention include (meth) acrylate monomers, di (meth) acrylate monomers, tri (meth) acrylate monomers, or higher polyfunctional (meth) acrylate monomers. And monofunctional or polyfunctional epoxy (meth) acrylate monomers, urethane (meth) acrylate monomers, and oligomers thereof.

Further, a polymerization initiator, a polymerization inhibitor, various modifiers, etc. may be added to the resin composition for protective coating of the present invention, if necessary.

Examples of the polymerization initiator include acetophenone-based compounds such as 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzoin-based compounds such as benzoin and benzoin methyl ether, benzophenone-based compounds such as benzophenone and benzoylbenzoic acid, thioxanthone, 2 Examples include thioxanthone compounds such as chlorthioxanthone. When a polymerization initiator is used, the mixing ratio is 0.1
The range of 10% by weight is preferable, and the range of 0.5 to 5% by weight is more preferable.

Examples of the polymerization inhibitor include metquinone, hydroquinone, methylethylhydroquinone and t.
-Butyl hydroquinone and the like can be mentioned. When using a polymerization inhibitor, the mixing ratio is preferably in the range of 1 to 5,000 ppm.

Examples of the modifier include organic modified polysiloxane for the purpose of a slip agent, methyl polysiloxane for the purpose of a leveling agent, organic modified silicone for the purpose of a base wetting agent, and an antistatic agent. The use of glycerin monostearate or the like is considered for the purpose.

Specific examples of the radiation curable resin for the protective coat include SD-30 manufactured by Dainippon Ink and Chemicals, Inc.
1. KAYA manufactured by Nippon Kayaku Co., Ltd. containing a polymerization initiator
It is possible to use various commercially available radiation-curable resins for protective coating such as RADNPGDA.

In the present invention, naphthoquinone diazide sulfonic acid ester, diazomeldrum acid, diazodimedone, diazophenylamine, diazodiphenylamine, and derivatives thereof may be used as the diazo compound having the property of generating nitrogen upon irradiation with radiation. I can.

In the present invention, examples of the azide compound having a property of generating nitrogen upon irradiation with radiation include diazidodibenzylidene cyclohexanone, diazidodibenzylidene alkyl, diazidodiphenyl, phenylazide, diazidodiphenyl sulfone, diazidostilbene. , And their derivatives can be used.

The amount of the compound having the property of generating nitrogen upon irradiation with radiation to the protective coating agent is effective as a head adsorption preventing effect in an arbitrary range where it is substantially dissolved, but the surface hardness of the protective coating, Also, considering other characteristics such as peeling resistance, the range of 0.3 to 10.0% by weight is desirable. When the addition amount is less than 0.3% by weight, the head adsorption preventing effect can be seen as compared with the case where the compound is not contained at all, but the effect suitable for practical use cannot be obtained. On the other hand, if the addition amount is more than 10.0% by weight, the surface hardness of the protective coat layer tends to decrease, which is not preferable.

The present invention further relates to a magneto-optical recording medium having a multi-layered protective coat excellent in peeling resistance as well as in the effect of preventing head adsorption. A plurality of protective coats are provided on the recording film, the interference film, or the reflective film of the magneto-optical recording medium, and the content of the compound generating bubbles in the protective coat layer is 0% by weight ≦ It is set so that the lowermost layer of the protective coat <the outermost layer of the protective coat. Further, the content of the compound in the outermost layer is set in the range of 0.3 to 10.0% by weight. The bottom layer may not contain the compound.

Further, the present invention is a method of forming a two-layer protective coat on a magneto-optical recording medium, which is particularly excellent in peeling resistance while sufficiently maintaining the effect of preventing adsorption to the flying magnetic head. And a coating method for obtaining the same. First, a radiation-curable organic resin composition is applied as a protective coat lower layer onto a recording film, an interference film, or a reflective film of a magneto-optical recording medium. Before completely curing this radiation-curable organic resin composition, the content of the compound that generates bubbles upon irradiation with radiation is in the range of 0.3 to 10.0% by weight, and the content thereof is lower than that of the lower layer. A large amount of the radiation curable organic resin composition is applied as an upper layer and then cured. The lower layer may not include a compound that generates bubbles upon irradiation with radiation. Here, “before completely cured” means that the lower layer is not irradiated with radiation.

[0027]

According to the present invention, a protective coating agent is applied to a magneto-optical recording medium, and then radiation is applied to cure the magneto-optical recording medium, so that it is contained in this resin composition for protective coating of the magneto-optical recording medium. A compound that releases nitrogen gas or the like upon irradiation with radiation absorbs the radiation and causes a chemical reaction. As a result of this reaction, nitrogen molecules and the like are desorbed from the compound and remain as fine bubbles in the uncured protective coat. The bubbles continue to rise due to buoyancy while the resin is not sufficiently cured and the viscosity is not so large. That is, they gather on the surface of the protective coat. By irradiating with radiation in this state until the curing is completed, fine irregularities are formed on the surface of the protective coat according to the present invention. When the magneto-optical recording medium having fine irregularities on the surface of the protective coating according to the present invention is used in a drive device of the magnetic field modulation recording system, even if the flying magnetic head contacts the surface, the effective contact area with respect to the entire head is small, Since there are many gaps, they will not stick together. Therefore, an accident such as damage to the floating magnetic head due to vacuum attraction does not occur.

[0028]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[Example 1] SD-301 (radiation-curable resin for protective coating) manufactured by Dainippon Ink and Chemicals, Inc. 9
9.7 wt% and NT-200 manufactured by Toyo Gosei Co., Ltd.
{2,3,4-trihydroxybenzophenone and 1,2
Naphthoquinone- (2) -diazido 5-ester with sulfonic acid chloride} 0.3% by weight was sufficiently mixed to prepare a resin composition. A first dielectric layer made of SiN having a thickness of about 100 nm and a Tb is formed on a polycarbonate substrate for a magneto-optical disk having a diameter of 90 mm formed by an injection molding method.
A recording layer of a magneto-optical recording medium in which a magneto-optical recording layer made of FeCo is formed to have a thickness of about 30 nm, a second dielectric layer made of SiN is made to have a thickness of about 40 nm, and a reflective film layer made of Al is formed to have a thickness of about 80 nm by a sputtering method. 100m of the resin composition on top
It was applied by a spin coating method so as to have a weight of g, and was cured by irradiating with ultraviolet rays for 6 seconds with a light source of a metal halide lamp of 120 W / cm ² in a nitrogen atmosphere.

This magneto-optical disk was attached to a magnetic field modulation type drive device, and after the floating magnetic head was brought into contact with the surface of the protective coat in a stationary state, the head was gently raised to separate the head and the surface of the protective coat layer. The presence or absence of adsorption was examined. When adsorption occurs, deformation of the arm of the head is observed, but when adsorption does not occur, the head can be raised without any resistance. This test of the contact of the head with the surface of the protective coating layer and the subsequent ascent was tested 50
The adsorption was evaluated by the number of times of adsorption, that is, the number of times the deformation of the arm of the head was observed. The results are shown in Table 1. Furthermore, the surface pencil hardness (J
IS K-5400) and a cross-cut cellophane tape peeling test, and the results are shown in Table 1.

[Second Embodiment] In the first embodiment, SD-3 is used.
A resin composition was prepared in the same manner as in Example 1 except that 01 was 99.5% by weight and NT-200 was 0.5% by weight.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Third Embodiment] In the first embodiment, SD-3 is used.
A resin composition was prepared in the same manner as in Example 1 except that 01 was 99.0 wt% and NT-200 was 1.0 wt%.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Fourth Embodiment] In the first embodiment, SD-3 is used.
A resin composition was prepared in the same manner as in Example 1 except that 01 was 96.0% by weight and NT-200 was 4.0% by weight.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Embodiment 5] In Embodiment 1, SD-3
A resin composition was prepared in the same manner as in Example 1 except that 01 was 94.0% by weight and NT-200 was 6.0% by weight.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Sixth Embodiment] In the first embodiment, SD-3 is used.
A resin composition was prepared in the same manner as in Example 1 except that 01 was 92.0 wt% and NT-200 was 8.0 wt%.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Seventh Embodiment] In the first embodiment, SD-3 is used.
01 is 90.0% by weight, NT-200 is 10.0% by weight
A resin composition was prepared in the same manner as in Example 1 except for the above, and the test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Embodiment 8] SD-3 in Embodiment 1
A resin composition was prepared in the same manner as in Example 1 except that 01 was 99.8% by weight and NT-200 was 0.2% by weight.
The test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Embodiment 9] In Embodiment 1, SD-3
01 to 88.0% by weight, NT-200 to 12.0% by weight
A resin composition was prepared in the same manner as in Example 1 except for the above, and the test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Example 10] SD-301 (radiation curable resin for protective coating) manufactured by Dainippon Ink and Chemicals, Inc.
99.5% by weight and 4NT-3 manufactured by Toyo Gosei Co., Ltd.
A resin composition was prepared by thoroughly mixing 50 {2,3,4,4'-trihydroxybenzophenone and 1,2 naphthoquinone- (2) -diazido-5-sulfonic acid chloride} 0.5% by weight. The other conditions were the same as in Example 1 for the test. The results are shown in Table 1.

[Example 11] KAY manufactured by Nippon Kayaku Co., Ltd.
ARAD NPGDA (neopentyl glycol diacrylate) 97.0% by weight was mixed with 3.0% by weight of Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one) manufactured by Merck Ltd. as a polymerization initiator, and radiation for protective coating A curable resin was prepared. To the radiation-curable resin 99.2% by weight, 0.8% by weight of 4NT-350 manufactured by Toyo Gosei Co., Ltd. was mixed to prepare a radiation-curable resin composition for a protective coat, and other conditions were the same as in Example 1. Was tested. The results are shown in Table 1.

[Example 12] KAY manufactured by Nippon Kayaku Co., Ltd.
A radiation-curable resin for protective coating was prepared by mixing 3.0% by weight of ARAD NPGDA with 3.0% by weight of Darocur 1173 manufactured by Merck Ltd. as a polymerization initiator. 98.0% by weight of the radiation-curable resin was added to DAZST (4,4′-diazidostilbene-2,2 ′) manufactured by Toyo Gosei Co., Ltd.
Was added to prepare a radiation-curable resin composition for a protective coat, and the other conditions were the same as in Example 1 and a test was conducted. The results are shown in Table 1.

Example 13 KAY manufactured by Nippon Kayaku Co., Ltd.
ARAD NPGDA 97.0% by weight with 3.0 g of Darocur 1173 manufactured by Ciba Geigy Co., Ltd. as a polymerization initiator.
The mixture was mixed by weight% to prepare a radiation-curable resin for protective coating. The radiation-curable resin composition for protective coat was prepared by mixing 98.0% by weight of the radiation-curable resin with 2.0% by weight of BAC-H {2,6-G (para-azidobenzal) -cyclohexanone} manufactured by Toyo Gosei Co., Ltd. The product was adjusted, and the other conditions were tested in the same manner as in Example 1. The results are shown in Table 1.

[Example 14] SD-301 (radiation curable resin for protective coating) manufactured by Dainippon Ink and Chemicals, Inc.
99.0% by weight and BAC-M manufactured by Toyo Gosei Co., Ltd.
A resin composition was prepared by sufficiently mixing {2,6-sy (para-azidobenzal) -4-methylcyclohexanone} 1.0% by weight. The other conditions were the same as in Example 1 for the test. The results are shown in Table 1.

[Example 15] On a recording layer of a magneto-optical recording medium
50 SD-301 manufactured by Dainippon Ink and Chemicals, Inc.
Spin coat method to achieve a weight of mg, and apply nitrogen.
120 W / cm in atmosphere²Metal halide lamp light source
It was irradiated with ultraviolet rays for 5 seconds to be cured. Further on this
Dainippon Ink and Chemicals, Inc. SD-301, 97.
NT-200 manufactured by Toyo Gosei Co., Ltd. was added to 0% by weight.
The resin composition mixed with 0% by weight becomes 50 mg in weight.
Coating by spin coating as above, and under nitrogen atmosphere 120W
/ Cm ²UV light for 5 seconds with the metal halide light source
Cured. In this way, the magneto-optical system has two layers of protective coating.
The result of the same test as in Example 1 was performed on the recording medium.
It is shown in Table 1.

Example 16 SD-301 manufactured by Dainippon Ink and Chemicals, Inc. was used on the recording layer of a magneto-optical recording medium.
Before coating by spin coating so that the weight becomes mg, and curing, SD-301 manufactured by Dainippon Ink and Chemicals, Inc., NT-200 manufactured by Toyo Gosei Co., Ltd. at 94.0% by weight are applied. The resin composition mixed in an amount of 6.0% by weight was applied by a spin coating method so as to have a weight of 30 mg to give a total application amount of 100 mg. This in a nitrogen atmosphere 1
It was cured by irradiating it with ultraviolet rays for 6 seconds with a metal halide light source of 20 W / cm ² . Table 1 shows the results of the same test as in Example 1 performed on the thus obtained magneto-optical recording medium.

Comparative Example 1 A radiation curable resin SD-301 manufactured by Dainippon Ink and Chemicals, Inc. was applied and cured under the same conditions as in Example 1, and the results of the tests are shown in Table 1.

Comparative Example 2 KAYA manufactured by Nippon Kayaku Co., Ltd.
A radiation-curable resin obtained by mixing 3.0% by weight of Darocur 1173 manufactured by Merck Ltd. as a polymerization initiator in RAD NPGDA was applied and cured under the same conditions as in Example 1, and the results of the tests are shown in Table 1.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

As described above, in the magneto-optical recording medium having the protective coating layer comprising the resin composition for protective coating of the present invention, foaming occurs as the resin composition for protective coating cures, and fine particles are formed on the surface of the protective coating. Unevenness is formed. Therefore, even when it is used for a magnetic field modulation type drive device using a floating magnetic head, vacuum adsorption is extremely unlikely to occur even if the surface of the protective coating and the floating magnetic head come into contact, and the supporting arm of the floating magnetic head is damaged. It is possible to significantly reduce the risk of accidents such as, and to use it with high reliability. Incidentally, in the present invention, the above-mentioned effects can be realized by using the production equipment which has been conventionally used as it is without impairing the productivity. Further, the resin composition for a protective coat of the present invention can obtain the above effect without significantly reducing the pencil hardness of the surface of the protective coat layer. Further, according to the inventions of claims 6 and 7, The above effects can be obtained without significantly lowering the adhesiveness with the lower layer of the protective coat layer.

Claims (7)

[Claims] 1. An organic resin composition for forming a protective coating layer on the outermost surface of a magneto-optical recording medium for recording information by applying light and a magnetic field, the radiation containing a compound having a radiation-curable vinyl group. A curable organic resin composition, wherein the organic resin composition contains a compound capable of generating bubbles upon irradiation with radiation, and a resin composition for protecting a magneto-optical recording medium. 2. The resin composition for a magneto-optical recording medium protective coat according to claim 1, wherein the bubbles generated by irradiation with radiation are nitrogen gas. 3. The resin composition for protecting a magneto-optical recording medium according to claim 2, wherein the compound generating nitrogen gas is a compound selected from the group consisting of diazo compounds and azide compounds. 4. The resin for protecting a magneto-optical recording medium according to claim 1, 2 or 3, wherein the content of the compound that generates bubbles upon irradiation with radiation is in the range of 0.3 to 10% by weight. Composition. 5. A protective coating layer comprising a cured coating of the resin composition for protective coating of a magneto-optical recording medium according to claim 1, 2 or 3 on a recording film, an interference film or a reflective film of a magneto-optical recording medium. A magneto-optical recording medium having: 6. The protective coat layer has at least a two-layer structure, and the content of the compound that generates bubbles upon irradiation with radiation in each layer is 0% by weight ≦ lowermost protective coat layer <lowermost surface layer of protective coat. A magneto-optical recording medium, wherein a protective coating layer comprising a cured film of the resin composition for protective coating of a magneto-optical recording medium according to claim 4 is provided on the outermost layer. 7. A radiation-curable organic resin composition is applied as a first protective coating layer on a recording film, an interference film or a reflective film of a magneto-optical recording medium, and the radiation-curable organic resin composition is completely cured. Before the coating, the radiation-curable resin composition according to claim 4, wherein the content of the compound that generates bubbles by irradiation with radiation is higher than that of the resin composition of the lower layer, on the first protective coat layer, and then cured. A method for coating a protective coat layer of a magneto-optical recording medium, which comprises: