JPH0778368A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To reduce surface scratchability and to suppress warp in a magneto- optical recording, medium performing writing and/or reading of information by combining a laser light radiated from the plastic substrate side with a magnetic field applied from the other side. CONSTITUTION:This magneto-optical recording medium has a crosslinked thin polymer film formed from a mixture contg. >=60wt.%, in total, of a multifunctional deriv. obtd. by modifying three or more hydroxyl groups in a dehydration condensation product of a mono-to hexamer of pentaerythritol with an acrylate and hydrogenated dicyclopentadienyl diacrylate on the surface of the plastic substrate on the laser light radiated side and a crosslinked thin polymer film formed from a mixture contg. >=260wt.%, in total, of urethane acrylate, 2-6C satd. alkylene diglycol diacrylate and a triacrylate deriv. of on the outermost layer on the magnetic field applied side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a combination of 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 side irradiated with the laser beam with the substrate sandwiched therebetween. A magneto-optical recording medium for writing and / or reading.

[0002]

2. Description of the Related Art In a recording / reproducing system of information only by magnetism, which has shown remarkable progress in recent years, the storage amount of information has become insufficient for the recent advanced information society.

On the other hand, in the method using laser light as a means for writing and / or reading, it is theoretically possible to read the light up to the wavelength limit. For this reason, optical recording or magneto-optical recording has begun to be performed as a recording method with a larger capacity and a higher density. Optical discs, video discs, large-capacity computer storage discs, and the like are generally called optical discs using these methods.

In particular, magneto-optical recording capable of repeatedly writing information has a wide application field, and various magneto-optical recording media are under development. In many of such magneto-optical recording media, information is written and / or read by a combination of a laser beam emitted from the substrate side and a magnetic field applied from the side opposite to the laser beam irradiation side with the substrate interposed therebetween. I do.

At this time, as the substrate for the magneto-optical recording medium, glass, polycarbonate, polymethylmethacrylate, or a plastic represented by amorphous polyolefin is used as a substrate which is transparent to the irradiation laser beam. it can.

Here, glass has an advantage that it is generally hard and hardly scratched. However, there is also a drawback that it makes it difficult to form the guide groove required for the servo mechanism for reading the recorded location. Therefore, there is an attempt to compensate for this point by etching or separately forming a polymer thin film, but this lacks mass productivity. Further, in terms of impact resistance and the like, handling in use is often limited, which is not preferable as a substrate material.

On the other hand, plastic is preferable as a substrate material because there is a merit that if a stamper is formed in advance by mastering, mass production can be performed by injection molding from this stamper.

However, the plastic used for the substrate material is
Since it has a certain degree of softness and flexibility, surface scratches are likely to occur. For this reason, in a structure in which the substrate surface directly touches the outside as it is, the writing / reading characteristics of information are deteriorated, which is often not preferable as a magneto-optical recording medium.

The magneto-optical recording medium has a dielectric film, a magneto-optical recording film, a dielectric film, and a light reflecting film in this order on the above-mentioned plastic material substrate as a main component. That is, the outermost layer side is a light-reflecting film, which is a very thin film because of its structure. Therefore, it is often difficult to maintain a stable reflective state when used as it is.

In order to supplement these points, a protective film having a relatively high hardness obtained by separately carrying out a cross-linking polymerization reaction may be formed, or a thin organic film may be laminated to serve as a protective film. Be seen. However, the former method is preferably used from the viewpoint of productivity.

[0011]

However, in general, when a polymer is formed by a cross-linking reaction, it often shrinks as compared with the initial state in which a monomer is present. Then, when such a protective film is formed on the magneto-optical recording medium, the medium is deformed by this contraction stress, and the shape becomes a "bow". For this reason, the optical axis of the irradiated laser light and the surface of the magneto-optical medium are no longer at right angles, and the reflected light does not return to the objective lens. And when such deformation in the plane axis direction occurs,
The servomechanism for reading the recorded location is unable to adequately follow, resulting in the inability to write / read information.

The present invention solves the above problems and suppresses the scratches on the surface of the substrate and the magneto-optical recording medium, reduces the warpage state, and excels in information writing / reading characteristics. The purpose is to obtain the medium.

[0013]

One feature of the magneto-optical recording medium according to the present invention is that the laser light irradiated from the side of a substrate made of a plastic material is opposite to the laser light irradiated side with the substrate interposed therebetween. In a magneto-optical recording medium in which information is written and / or read by a combination with a magnetic field applied from the side, 1 to 1 of pentaerythritol is formed on the surface of the plastic substrate on the side to which the laser light is irradiated.
A hexameric dehydration condensate, a polyfunctional derivative in which three or more of the hydroxy groups are modified with acrylate,
A cross-linked polymer thin film formed from a mixture containing 60% by weight or more of two kinds of hydrogenated dicyclopentadienyl diacrylate.

Here, the plastic substrate has a wavelength of 450 to
In the region of 900 nm, it is a kind selected from polycarbonate, polymethylmethacrylate, and amorphous polyolefin which have excellent transparency. Such materials are still widely used as optical recording material substrates and are industrial materials that are easily available. Usually, this substrate is used after being molded to a thickness of about several mm.

In order to stably form a crosslinked polymer thin film on such a substrate, it is necessary to have excellent polymerization reactivity. From this viewpoint, an acrylic acid derivative is required as a reactive group. In addition, from the viewpoint of increasing the number of cross-linking points, it is necessary to have a low molecular weight and three or more reaction sites in one molecule like pentaerythritol.

However, under these conditions alone, the compatibility with other reactive molecules may be reduced. Further, since it is a low molecular weight compound, it has volatility, which may reduce workability.
Therefore, from the viewpoint of the reaction of molecules, it is a dehydration condensate of pentaerythritol 1-hexamer for the purpose of improving the reaction site density per molecule, and its hydroxy group 3
In the present invention, it is necessary to use a polyfunctional derivative, one or more of which is modified with acrylate, as a main component.

Further, in order to reduce the warp angle, it is desirable that the change in the morphology of the polymer is small before and after the crosslinking reaction. However, with ordinary vinyl materials, with the progress of the polymerization reaction,
The π-electron conjugated sp2 type hybrid orbital causes a large morphological change from the sp3 type hybrid orbital. This often causes shrinkage and expansion of the formed polymer.
Therefore, like the above-mentioned derivative of pentaerythritol,
Only the one having a flexible basic skeleton causes a large change, resulting in a large warp angle.

Therefore, coexistence of hydrogenated dicyclopentadienyl monoacrylate is required in the present invention. The dicyclopentadienyl skeleton is typical of a bridged cyclic hydrocarbon, and even if the peripheral polymerization reaction group changes, this structure has a small strain as a structure and little basic change.

In order to efficiently exhibit such effects, it is necessary that the mixture for forming the crosslinked polymer thin film on the substrate contains 60% by weight or more of these two kinds of materials. Further, each of these two types of materials is more preferably contained in the mixture in an amount of at least 12% by weight or more.

At this time, other components may be added for the purpose of stabilizing the crosslinked polymer or improving the affinity with the substrate. As such components,
For example, a petroleum resin containing a fraction having 9 carbon atoms as a main component, a polyalkylene glycol diacrylate having 2 to 6 carbon atoms and a polymerization degree of 1 to 20 can be used.

Another feature of the present invention is that the outermost layer of the magneto-optical recording medium on the side to which a magnetic field is applied has urethane acrylate, saturated alkylenediglycol diacrylate having 2 to 6 carbon atoms, and trimethylol. A crosslinked polymer thin film formed from a mixture containing 60% by weight or more of three types of propane triacrylate derivatives, wherein urethane acrylate is tolylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, Alternatively, a urethane diol obtained by reacting a single or a mixture of isocyanate derivatives selected from diphenyl ether diisocyanate with a stoichiometric excess of saturated alkylene diglycol having 2 to 6 carbon atoms is used as a diacrylate. It is that one in which turned into.

As a result, there is an effect that the flexibility of the protective film formed on the inorganic layer called the reflective film is improved and the uniformity of the film is increased. The crosslinking reaction itself
Although it is carried out with a triacrylate derivative of trimethylolpropane, it has 2 to 2 carbon atoms in order to further impart flexibility.
It is necessary to allow the saturated alkylenediglycol diacrylate of 6 to coexist.

In order to efficiently bring out such effects, 60% by weight of these three kinds of materials are contained in the mixture for forming the crosslinked polymer thin film on the outermost layer of the magneto-optical recording medium on the side to which the magnetic field is applied. % Or more must be contained.
Furthermore, each of these three types of materials is more preferably contained in the mixture in an amount of at least 12% by weight or more. Further, in order to improve physical conditions such as crosslink density and sliding properties, an acrylic acid derivative, a nonionic surfactant, polysiloxane or the like may be added depending on the purpose.

Thus, by forming a cross-linked polymer thin film on the surface of the plastic substrate on the side to which the laser beam is applied and on the outermost layer of the magneto-optical recording medium on the side to which the magnetic field is applied, respectively, the mutual cross-linking polymer thin film is formed. The difference in the warp direction and the introduction of the urethane bond having high elasticity to improve the flexibility make it possible to obtain a magneto-optical recording medium having a small warp angle.

When forming such a crosslinked polymer film,
It is preferable to use a coating film forming method by spin coating in order to uniformly form a thin film. Alternatively, a method using a bar coater, or a method such as simple dipping, draining, or natural casting can be used as long as it can be applied uniformly.

The thickness of such a crosslinked polymer thin film is 3
It is preferably ˜100 μm. When the film thickness is thinner than this, it is not preferable because the recording medium layer may be physically destroyed due to the situation of the crosslink density, while a too thick film reduces the production efficiency and causes the substrate to contract due to the shrinkage effect. It may warp in a bowl shape, and in that case, it is difficult to follow the recording, which is not preferable. And even more preferably, the film thickness is set to 3 to 50 μm.

[0027]

Example 1 As a resin liquid 1, 40% by weight of dipentaerythritol hexaacrylate, 20% by weight of hydrogenated dicyclopentadienyl diacrylate, 13% by weight of pentaerythritol diacrylate, and acrylic acid ester of tetrapentaerythritol. 13% by weight, degree of polymerization is 4
A uniform solution was prepared by mixing 14% by weight of a diacrylate of a mixture of polyethylene glycol of 10 to 10.

As the resin liquid 2, a mixed liquid of 15% by weight of urethane acrylate obtained from tolylene diisocyanate and diethylene glycol, 50% by weight of trimethylolpropane triacrylate and 35% by weight of neopentyl glycol diacrylate was prepared.

A plastic substrate made of polycarbonate (outer diameter 86 mm, inner diameter 15 mm, thickness 1.2 m)
The resin liquid 1 is applied onto one surface of m) by a spin coating method, and then is irradiated with ultraviolet rays to be photo-cured to give a film thickness
A 0 μm tack-free crosslinked polymer thin film was formed.

This was sufficiently dried and deaerated to form a dielectric film / magneto-optical recording film / dielectric film / reflection film in this order on the surface of the substrate not coated with the resin liquid. At that time, silicon nitride was formed as the dielectric film, terbium, iron, cobalt, and chromium alloy were sputtered as the magneto-optical recording film, and aluminum-titanium alloy was formed as the reflecting film.

Further, the resin liquid 2 was applied on the reflection film by a spin coating method, and thereafter, ultraviolet irradiation was performed to photo-cure the resin liquid 2 to form a transparent crosslinked polymer film having a thickness of 8 μm.

The warp angle of the sample of the magneto-optical recording medium thus obtained was measured. At that time, the warp angle was measured by an optical disk mechanical characteristic device ODA-2 type manufactured by Shin Denshi Kogyo Co., Ltd. However, the warp angle here is defined as one of the common basic characteristics of the optical recording information medium in accordance with the international standard ISO standard. There are two types of sled components when it comes to the "bow" type. That is, the radial warp (Tr) and the circumferential warp (T)
θ). The warpage angle of the substrate is determined by the maximum warpage (Tmax) obtained by the square root of the sum of the squares of both. Since this value differs depending on the measurement location, statistical processing is performed, and the maximum warp angle at any recording location is successively verified to determine the physical properties of the substrate.

As a result, the warp angle was -0.5 mrad, and this disk was 2 at 80 ° C. and a humidity of 85%.
A durability test was carried out by holding for 000 hours, and the value was -1.0 mrad, which showed almost no change. The recording / reproducing signal characteristics were not changed before and after the durability test.

[0034]

Example 2 As resin liquid 1, 40% by weight of dipentaerythritol hexaacrylate, 20% by weight of hydrogenated dicyclopentadienyl diacrylate, 10% by weight of hydrogenated dicyclopentadienyl monoacrylate, tetrapenta A 15% by weight acrylic acid ester of erythritol and 15% by weight of a diacrylate of a mixture of polyethylene glycol having a degree of polymerization of 4 to 10 were mixed to prepare a uniform solution.

As the resin liquid 2, a mixture of 12% by weight of urethane acrylate obtained from isophorone diisocyanate and diethylene glycol, 50% by weight of trimethylolpropane triacrylate, 20% by weight of neopentyl glycol diacrylate and a polyethylene glycol having a degree of polymerization of 4 to 10 is used. A mixed solution of 18% by weight of diacrylate was prepared.

First, a plastic substrate made of polycarbonate (outer diameter 86 mm, inner diameter 15 mm, thickness 1.2 m)
A dielectric film / magneto-optical recording film / dielectric film / reflection film was formed in this order on one surface of m). At that time, silicon nitride was formed as the dielectric film, terbium, iron, cobalt, and chromium alloy were sputtered as the magneto-optical recording film, and aluminum-titanium alloy was formed as the reflecting film.

After that, the resin liquid 2 is applied on the reflection film of the magneto-optical recording medium thus obtained by a spin coating method, and then the resin liquid 2 is irradiated with ultraviolet rays to be photo-cured to have a film thickness of 8 μm.
m transparent cross-linked polymer film was formed.

Then, the resin liquid 1 was applied onto the other surface of the substrate by a spin coating method, followed by UV irradiation and photocuring to form a transparent crosslinked polymer film with a thickness of 9 μm.

The warp angle of the thus obtained sample was evaluated in the same manner as in Example 1. As a result, the warp angle was 1.2 mrad, which was a warp angle at which the signal characteristics could be sufficiently evaluated.

[0040]

Example 3 The resin liquid 1 used in Example 2 was used, and the resin liquid 2 used in Example 1 was used. Then, a sample of the magneto-optical recording medium was prepared in the same manner as in Example 1. However, the film thickness of the crosslinked polymer film on the surface of the substrate and on the reflective film was 10 μm.

For the sample thus obtained, Example 1
The warp angle was evaluated in the same manner as in. As a result, it was observed that the warp angle was -1.2 mrad. Further, when the same durability test as in Example 1 was conducted, it was found that the warp angle was -0.5 mrad, and no change in the signal read / write characteristics was observed.

[0042]

Comparative Example 1 In Example 1, a sample was prepared such that the film thickness of the crosslinked polymer film on the substrate surface and the reflective film was 2 μm by increasing the rotation speed of the spin coater. Was not constant, and the substrate or the reflective film was partially exposed, and it was easily damaged.

[0043]

INDUSTRIAL APPLICABILITY As described above in detail, the present invention suppresses the scratching of the surface of the plastic substrate on the side to which the laser beam is irradiated and the outermost layer of the magneto-optical recording medium on the side to which the magnetic field is applied, and causes the warp. It is possible to obtain a magneto-optical recording disk having excellent signal writing / reading characteristics by reducing the above condition. At that time, the total warp angle is 5m in absolute value.
It is possible to obtain a magneto-optical recording disk of rad or less.

Claims (2)

[Claims] 1. Writing and / or reading of information is performed 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 the magneto-optical recording medium to be performed, a dehydration condensation product of a pentamer of pentaerythritol is formed on the surface of the plastic substrate on the side irradiated with laser light, and three or more of the hydroxy groups are modified with acrylate. 2 kinds of polyfunctional derivative and hydrogenated dicyclopentadienyl diacrylate
The outermost layer of the magneto-optical recording medium, which comprises a cross-linked polymer thin film formed from a mixture containing 0 wt% or more, has a urethane acrylate and a saturated alkylenediglycol diacrylate having 2 to 6 carbon atoms. A cross-linked polymer thin film formed from a mixture containing 60% by weight or more of three kinds of acrylate and a triacrylate derivative of trimethylolpropane, wherein urethane acrylate is tolylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate. Urethane obtained by reacting a single or mixture of isocyanate derivatives selected from dicyclohexylmethane diisocyanate and diphenyl ether diisocyanate with a stoichiometric excess of saturated alkylene diglycol having 2 to 6 carbon atoms. Magneto-optical recording medium, characterized in that all the is obtained by diacrylated. 2. The crosslinked polymer thin film has a thickness of 3 to 50 μm.
The magneto-optical recording medium according to claim 1, wherein