JPH0636373A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium excellent in weather resistance by forming a UV-curing acrylate resin layer as a protective layer with UV-curing acrylate resin having a specified photopolymerizable oligomer content. CONSTITUTION:When a magneto-optical recording layer is formed on a resin substrate and a protective layer is formed on the recording layer optionally with other layer in-between to obtain a magneto-optical recording medium, the protective layer is formed by applying and curing UV-curing acrylate resin contg. a photopolymerizable oligomer, a photopolymerizable monomer and a photopolymn. initiator. The amt. of the photopolymerizable oligomer is 30-80wt.% of the total amt. of the three components. The objective magneto- optical recording medium excellent in weather resistance and usable at both high temp. and low temp. is obtd.

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,
In particular, the present invention relates to a magneto-optical recording medium excellent in weather resistance in which a protective layer is formed in a magneto-optical recording medium using a resin substrate.

[0002]

2. Description of the Related Art Among optical memory devices, an erasable memory capable of write-once recording and erasing is at a stage where a magneto-optical recording medium is the most practical. A magneto-optical recording medium is a recording medium which is recorded by heating a recording layer formed on a transparent substrate by heating with light irradiation and is read out by utilizing a magneto-optical effect such as a force-effect or a Faraday effect. As the recording layer, TbFe, TbFeCo, DyFeCo,
Rare earth / transition metal thin films such as GdFeCo and GdTbFeCo are often used.

These recording layers generally have a drawback that they are easily oxidized and have poor corrosion resistance. Therefore, a protective layer made of a metal oxide, a metal nitride or the like is provided on the recording layer. However, even when a protective layer made of a metal oxide, a metal nitride, etc. is formed, fine film defects (hereinafter referred to as "pinholes") are formed in this protective layer.
Say. ), Or because sufficient adhesion is not obtained, layer peeling occurs, and further, cracks occur due to large internal stress in the layer, so a sufficient protective effect cannot be obtained. was there.

Therefore, in order to solve such a drawback, an organic protective film may be further formed on the protective layer of metal oxide, metal nitride or the like. As a material for forming an organic protective film, generally, an ultraviolet-curable acrylic coating agent and a thermosetting hard coating agent such as a silicone-based or titanium-based agent are often used. Not only on the surface of the protective layer such as metal oxide or metal nitride, but also on the transparent substrate surface or the recording layer surface in order to protect the transparent substrate surface or the recording layer surface from scratches or dust adhesion. is there.

[0005]

However, when the magneto-optical recording medium having such a structure is used under the environment of high temperature and high humidity, the recording film is gradually deteriorated and the error rate is increased. It has been found that the reliability of the magnetic recording medium is significantly reduced. That is, when the magneto-optical recording medium is used in a special environment such as high temperature and low temperature, the problem of weather resistance becomes very important.

[0006]

In view of the above-mentioned problems, the inventors of the present invention have made earnest studies to provide a magneto-optical recording medium having high weather resistance, and as a result, the content of the photopolymerizable oligomer as a protective layer was determined. By forming an ultraviolet-curable acrylate resin layer using a thing of a specific amount range, a magneto-optical recording medium having remarkably excellent weather resistance can be obtained, and it was found that the above object can be achieved and the present invention is completed. I arrived.

That is, the gist of the present invention is a magneto-optical recording medium comprising a magneto-optical recording layer on a resin substrate and a protective layer provided directly on the recording layer or via another layer, wherein the protective layer is UV curing, which comprises 3 components of a photopolymerizable oligomer, a photopolymerizable monomer, and a photopolymerization initiator, and the photopolymerizable oligomer is 30 to 80% by weight based on the total amount of the 3 components. The present invention relates to a magneto-optical recording medium, characterized in that it is formed by applying a UV-curable acrylate resin and then curing the UV-curable acrylate resin.

The present invention will be described in detail below. Examples of the substrate used in the present invention include resin substrates such as polycarbonate resin, acrylic resin, and polyolefin resin. The thickness of this substrate is generally about 1 to 2 mm. The layer structure of the magneto-optical recording layer formed on such a resin substrate is not particularly limited, and a known layer structure of the magneto-optical recording layer can be adopted. For example, TbFe, T
Amorphous magnetic alloy of rare earth and transition metal such as bFeCo, TbCo, DyTbFeCo, MnBi, MnCuBi
A polycrystalline perpendicular magnetization film or the like is used. A single layer may be used as the magneto-optical recording layer, or GdTbFe / Tb
Two or more recording layers such as Fe may be stacked and used.

An interference layer may be provided between the substrate and the magneto-optical recording layer. This layer is for reducing the noise by improving the C / N ratio by lowering the reflectance due to the light interference effect of the transparent film having a high refractive index. The interference layer may be a single layer film or a multilayer film. A metal oxide or a metal nitride is used as a constituent material of the interference layer. As the metal oxide, Al ₂ O ₃ , Ta ₂ O ₅ , SiO ₂ , Si
Metal oxides such as O and TiO ₂ or a mixture thereof,
Alternatively, an Al-Ta-O composite oxide or the like can be given. In addition to these oxides, other elements such as Ti, Z
r, W, Mo, Yb, etc. are in the form of oxides alone or A
It may be one that forms an oxide in combination with l and Ta. The interference layer made of these metal oxides is dense and can prevent invasion of moisture and oxygen from the outside, has high corrosion resistance, and has low reactivity with the reflective layer described later. Furthermore, when a resin substrate is used as the substrate, it has excellent adhesion to the resin that constitutes the substrate.

Examples of metal nitrides include silicon nitride and aluminum nitride. Among these metal nitrides, silicon nitride is preferably used because it is particularly dense and has an excellent effect of preventing intrusion of moisture or oxygen from the outside. The optimum thickness of the interference layer made of such metal oxide or metal nitride varies depending on its refractive index, but it is usually about 400 to 1500 Å, preferably about 500 to 1000 Å.

On the surface of the magneto-optical recording layer opposite to the interference layer, a layer made of a dielectric material having the same material as that of the interference layer, that is, a dielectric layer is preferably provided for protection. The thickness of this dielectric layer is usually about 500 to 1500Å.
In a medium having a structure in which a reflective layer is provided, a metal having a high reflectance (for example, A
1, Cu, etc.) or its alloy layer is provided as a reflection layer. It is also possible to further provide a dielectric layer on the reflective layer.

In the present invention, the interference layer on the substrate,
As a method for forming each layer such as a recording layer, a dielectric layer, a reflective layer, and a dielectric layer, a physical vapor deposition method such as sputtering (PV
D), a chemical vapor deposition method (CVD) such as plasma CVD, or the like is applied. Alternatively, a method using ion plating may be used. In order to form an interference layer, a magneto-optical recording layer, a dielectric layer, a reflection layer, a dielectric layer, etc. by PVD, a target having a predetermined composition is used to form a film on the substrate by electron beam evaporation or sputtering. It is common practice to deposit each layer. If the deposition rate of the film is too fast, the film stress will increase, and if it is too slow, the productivity will decrease.
It is appropriately determined within the range of about 100 Å / sec.

Hereinafter, the interference layer, the magneto-optical recording layer, the dielectric layer and the reflective layer, and if desired, the dielectric layer are collectively referred to as a "recording layer". The magneto-optical recording medium of the present invention cures an ultraviolet-curable acrylate resin in which the content of the photopolymerizable oligomer is within a specific range on the recording layer of the substrate on which the recording layer is formed, directly or through another layer. It is characterized in that a protective layer thus formed is provided.

The UV-curable acrylate resin is mainly composed of three components consisting of a photopolymerizable oligomer, a photopolymerizable monomer and a photopolymerization initiator, and other additives such as, for example,
It may contain a leveling agent, a thermal polymerization inhibitor and the like.
As the photopolymerizable oligomer, an oligomer containing a double bond of acrylic acid ester or methacrylic acid ester, an acryloyl group or a methacryloyl group is used, and the main chain structure of the base oligomer is a polyester type, an epoxy type or a urethane type. , Polyether type, acrylic type,
Examples thereof include polythiol type and polyimide type. Specifically, polymerizable oligomers such as polyester acrylate, epoxy acrylate, urethane acrylate, polyether acrylate, and polyacrylate are preferably used.

Further, as the photopolymerizable monomer, a monofunctional monomer or a polyfunctional monomer is used. Monofunctional monomers include N-vinylpyrrolidone phenoxyethyl acrylate, isodecyl acrylate, n-hexyl acrylate, stearyl acrylate, lauryl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate. , 2-hydroxyethyl acrylate, 2-methoxyethoxyethyl acrylate, benzyl acrylate,
Examples thereof include cyclohexyl acrylate, tetrahydrofurfuryl acrylate, dicyclopentadienyl acrylate, and the like. Further, as the polyfunctional monomer, 1,4-butanediol diacrylate, 1,6-hexanediol acrylate, polyethylene glycol diacrylate, diethylene glycol diacrylate,
Neopentyl glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane diacrylate, bis (acryloxyethoxy) bisphenol A, 3-methylpentanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, tris (2- Hydroxyethyl) isocyanate, dipentaerythritol hexaacrylate and the like can be mentioned. Further, as the photopolymerization initiator, acetophenone, benzophenone and their derivatives, benzoyl ethers such as benzoyl ethyl ether, 1-hydroxycyclohexyl phenyl ketone, benzoyl peroxide, di-tert-butyl peroxide, methyl benzoyl formate, methyl phenyl. Glyoxylate, 2-methyl-1- [4-
(Methylthio) phenyl] -2-morpholinopropane-
1 etc. are mentioned.

In the present invention, the coating agent (coating agent) of the UV-curable acrylate resin composition containing the above-mentioned three components of the photopolymerizable oligomer, the photopolymerizable monomer and the photopolymerization initiator as the main components is used as the recording layer of the substrate. After coating directly on or through another layer, ultraviolet rays are irradiated to cause a polymerization reaction to form a protective layer made of a cured resin layer. In the present invention, the content of the photopolymerizable oligomer contained in the coating agent is 30 to 80% by weight, preferably 30 to 80% by weight based on the total amount of the three components consisting of the photopolymerizable oligomer, the photopolymerizable monomer and the photopolymerization initiator. The adjustment is performed in the range of 40 to 70% by weight. Since the photopolymerization initiator is usually used in an amount of 0.3 to 10% by weight, the content of the photopolymerizable monomer is 69.7 to the total amount of the above three components.
It becomes 10% by weight.

If the content of the photopolymerizable oligomer is less than the lower limit (30 wt%), the weather resistance is insufficient, and
The warpage of the surface of the protective layer becomes large, and the upper limit (80 wt.
%), The viscosity becomes high and it becomes difficult to form a coating film, or sufficient hardness is not obtained and scratches easily occur, which is not preferable. The above coating agent (UV curable resin)
The coating can be carried out by a known method such as spin coating, dipping, spray coating or gravure coating directly on the recording layer of the substrate or through another layer. The coating conditions for the coating film may be appropriately determined in consideration of the viscosity of the coating composition mixture, the state of the recording layer surface of the substrate, the coating film thickness, and the like.

It is desirable that the protective layer formed of the ultraviolet curable resin covers not only the upper surface of the recording layer but also the side surface thereof. Therefore, for example, when the recording layer is provided on the substrate, the peripheral portion of the central hole of the substrate and the substrate are provided. The outer edge of the substrate is covered so that the recording layer is not formed on this portion, and the protective layer is in direct contact with the substrate at the periphery of the central hole of the substrate and the outer edge so as to protect the recording layer. Is good.

In order to cure such a coating film to form a protective layer for the cured film, the coating film is irradiated with ultraviolet rays and a photopolymerizable oligomer and a monomer are polymerized by the photopolymerization initiator to produce a cured resin. Allow the layers to form. The thickness of the protective layer (after curing) is usually 4 to 20 μm, preferably 5 to 20.
It is in the range of μm. When the thickness of the protective layer is less than 4 μm, the weather resistance of the cured film is insufficient, and when it is more than 20 μm, the cured film is insufficiently cured, and the surface thereof becomes sticky (poor), which is not desirable.

Further, the total amount of residual monomers in the cured resin is usually preferably 10% by weight or less, and if it is more than 10% by weight, unreacted acrylate monomer is easily decomposed into acrylic acid under high temperature and high humidity. May corrode the membrane. The amount of the photopolymerization initiator used is at least 0.3% by weight, preferably 1 to 10% by weight, and more preferably 3 to 100 parts by weight of the ultraviolet curable resin composition.
Used within the range of 10% by weight.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist. The following devices were used for measuring physical properties and the like in the present specification and examples.

(1) Film thickness measurement Product name: Alpha-Step 200 (alpha-S
company name: Tencor Instruments (TENCOR)
INSTRUMENTS) Method: A glass plate is spin-coated with a coating agent, irradiated with ultraviolet rays, and then the film thickness of the inner circumference of 25 mm to 40 mm is measured using the above-mentioned apparatus.

(2) Measurement of residual monomer amount Product name: GC: Shimadzu GC-14A Column: GL Science NB-1 Company name: Shimadzu Corporation Method: Spin coating a coating agent on a glass plate, irradiate with ultraviolet rays and then cure The coated agent was extracted with a chloroform solution containing an internal standard solution and measured by gas chromatography using the above equipment.

(3) BER The obtained magneto-optical disk was subjected to an acceleration test under conditions of 80 ° C. and 90% RH for 1000 hours, and the elalate before and after the acceleration test was measured using a commercially available magneto-optical disk drive. Then, the increase rate of the error rate was obtained.

(4) Tilt angle (Tilt) An acceleration test similar to the BER of (3) above was performed, and the amount of Tilt change before and after the acceleration test was measured by the following method. Product name: LM-100 (LM-100) Company name: Ono Sokki Method: When measuring the vertical displacement of a disc at a fixed pitch, the vertical direction of a point several mm outside the vertical displacement of a certain point Displacement, and the inclination between two points is measured (unit: mrad (milliradian)

Example 1 A transparent substrate having a diameter of 15 mm at the center and a diameter of 8
Magneto-optical recording is performed by using a polycarbonate injection molded substrate on a circular flat plate with a guide groove having a thickness of 6 mm and a thickness of 1.2 mm, and forming a recording film having the following layer structure (the parentheses indicate the film thickness) on the continuous sputtering device. A disc was manufactured.

TaO _x (900Å) / TbFeCo (2
50Å) / SiN _x (300Å) / AlTa (800
Å) Epoxy acrylate (Osaka Organic Co., Ltd., trade name: biscoat 540) as an oligomer component, N-vinylpyrrolidone (Toagosei Co., Ltd., trade name: Aronix M-150) as a monofunctional monomer, and polyfunctional monomer (A) 1,4-Butanediol diacrylate (Osaka Organic Co., Ltd., trade name: Viscoat 195), Neopentyl glycol diacrylate as polyfunctional monomer (B) (Osaka Organic Co., Ltd., trade name: Biscoat 215), as a polymerization initiator An ultraviolet curable resin using 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba-Geigy (Germany), trade name: Irgacure 184) was prepared with the composition ratio (% by weight) shown in Table 1.

Example-2 Example-2 was carried out in the same manner as in Example-1 except that an ultraviolet curable resin having a composition shown in Table-I (oligomer ratio: 54%) was used. As a result, the amount of residual monomers in the protective layer after curing was 2.9%. The rate of increase in BER and the amount of change in Tilt after 1000 hours in an atmosphere of a temperature of 80 ° C. and a humidity of 90% RH were measured to be 0.94 times and 1.7 (mr), respectively.
Ad) and good results were obtained. The appearance after coating was also very good.

Example-3 Example 3 was carried out in the same manner as in Example-1 except that the ultraviolet curable resin having the composition (oligomer ratio: 72%) shown in Table-I was used. As a result, the residual monomer amount in the protective layer after curing was 3.1%. The rate of increase in BER and the amount of change in Tilt after 1000 hours in an atmosphere of a temperature of 80 ° C. and a humidity of 90% RH were measured to be 0.97 times and 2.1 (mr), respectively.
Ad) and good results were obtained. The appearance after coating was also very good.

Example 4 By using an ultraviolet curable resin having a composition (oligomer ratio: 54%) shown in Table I and changing the coating amount, the thickness of the protective layer after ultraviolet curing (film thickness: 8 to 12 μm) was changed, and the same procedure as in Example-1 was performed. as a result,
The amount of residual monomers in the protective layer after curing was 4.4%. When the rate of increase in BER and the amount of change in Tilt after 1000 hours in an atmosphere of temperature 80 ° C. and humidity 90% RH were measured, good results were obtained with 1.01 times and 2.3 (mrad), respectively. The appearance after coating was also very good.

Example-5 By using an ultraviolet curable resin having a composition (oligomer ratio: 54%) shown in Table-I and further changing the coating amount, the thickness of the protective layer after ultraviolet curing (film thickness: 15 to 15: 18 μm) was changed, and the same procedure as in Example-1 was performed. As a result, the amount of residual monomers in the protective layer after curing was 8.7%. 100 in an atmosphere of temperature 80 ° C and humidity 90% RH
When the rate of increase in BER and the amount of change in Tilt after 0 hour were measured, they were 1.15 times and 3.5 (mrad), respectively, and good results were obtained. The appearance after coating was also very good.

Comparative Example-1 The procedure of Example-1 was repeated except that an ultraviolet curable resin having the composition shown in Table-I (oligomer ratio: 18%) was used. As a result, the residual monomer in the protective layer after curing was 2.8%. The rate of increase in BER and the amount of change in Tilt after 1000 hours in an atmosphere of a temperature of 80 ° C. and a humidity of 90% RH were measured to be 2.33 times and 4.2 (mr), respectively.
ad). It is considered that this is because the rate of increase in BER was large because the oligomer ratio was as small as 18%. It cannot be put to practical use. The appearance after coating was good.

Comparative Example-2 By using an ultraviolet curable resin having a composition (oligomer ratio: 54%) shown in Table-I, and further changing the coating amount, the film thickness (21 μm to 24 μm) of the protective layer after ultraviolet curing was obtained. The same procedure as in Example 1 was carried out except that it was changed. As a result, the residual monomer in the protective layer after curing was 13.0 (%).
showed that. In an atmosphere of temperature 80 ° C and humidity 90% RH 10
When the rate of increase in BER and the amount of change in Tilt after 00 hours were measured, they were 3.57 times and 5.3 (mrad), respectively. It is considered that this is because the protective layer was too thick and the amount of residual monomer increased.

Comparative Example-3 By using an ultraviolet curable resin having a composition (oligomer ratio: 18%) shown in Table-I, and further changing the coating amount, the film thickness (2 to 3 μm) of the protective layer after ultraviolet curing was obtained. The procedure was the same except that it was changed. As a result, the residual monomer content was 2.0%. When the rate of increase in BER and the amount of change in Tilt after 1000 hours in an atmosphere of temperature 80 ° C. and humidity 90% RH were measured, they were 3.05 times and 1.2 (mr, respectively).
ad). It is considered that this is because the oligomer ratio was 18% and the film thickness was as thin as 2 to 3 μm, so that the rate of increase in BER was large.

Comparative Example-4 The procedure of Example 1 was repeated, but the coating amount was changed to obtain a cured film thickness of 2 to 3 .mu.m. As a result, the residual monomer is 1.8%
showed that. In an atmosphere of temperature 80 ° C and humidity 90% RH 10
The rate of increase in BER and the amount of change in Tilt after measuring 00 hours were measured to be 2.81 times and 2.7 (mrad), respectively.
showed that. It is considered that this is because the film thickness was too thin.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

Since the optical disk of the present invention has excellent weather resistance, it is suitable as an optical disk for use under severe conditions and for long-term storage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Wakabayashi 3-10 Shiodori Kurashiki City Okayama Prefecture Mitsubishi Kasei Co., Ltd. Mizushima Plant

Claims (3)

[Claims] 1. A magneto-optical recording medium having a magneto-optical recording layer on a resin substrate and a protective layer provided directly or via another layer on the recording layer, wherein the protective layer is photopolymerizable. An ultraviolet-curable acrylate resin containing three components of an oligomer, a photopolymerizable monomer and a photopolymerization initiator, and the photopolymerizable oligomer being 30 to 80% by weight relative to the total amount of the above three components. A magneto-optical recording medium, which is formed by applying the ultraviolet-curable acrylate resin and then curing it. 2. The magneto-optical recording medium according to claim 1, wherein the protective layer has a thickness of 4 μm or more and 20 μm or less. 3. The magneto-optical recording medium according to claim 1, wherein the residual monomer amount in the protective layer is 10% or less.