JPS63257939A - Protective coating agent for magneto-optical disk - Google Patents

Abstract

PURPOSE:To eliminate warpage and to decrease the pinholes to be generated in a recording layer by forming an org. synthetic resin coating layer of a mixture composed of a UV curing type resin contg. a photosensitizing agent and an epoxy resin without contg. a hardener. CONSTITUTION:This coating agent consists of the mixture composed of the UV curing type resin contg. the photosensitizing agent and the epoxy resin without contg. the hardener. The photosensitizing agent to be used may be exemplified by a benzophenone system, acetophenone system, anthraquinone system, oxime ester system, etc. The UV curing type resin may be any of an acrylic multifunctional compd., urethane modified multifunctional acryl system, epoxy modified multifunctional acryl system, polyester modified multifunctional acryl system, etc. The agent contains preferably no solvent and monomers and has the viscosity ranging 500-1,000cps/25 deg.C. Generation of the warpage is thereby obviated and the pinholes are less generated in the recording layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coating for protecting the recording layer of a magneto-optical disk. More specifically, the present invention relates to a protective coating for a magneto-optical disk using a resin substrate, which is made of a mixture of an ultraviolet curable resin containing a photosensitizer and an epoxy resin.

(Prior Art) Conventionally, there is a magneto-optical disk which is used in erasable and rewritable high-density memory and is recorded by heating by light irradiation and can be read using magneto-optical effects such as the magnetic Kerr effect and the Faraday effect.

Amorphous thin films made of GdTbFeCo are particularly excellent as recording films for magneto-optical disks, and have excellent film formability when producing large-area thin films at temperatures near room temperature, and write efficiency for writing signals and using small photothermal energy. It is ideal as a magneto-optical recording medium because it has a readout efficiency for reading written signals with a good S/N ratio, a large Kerr rotation angle, and a single Curie point around 150°C.

However, in general, magneto-optical recording layers made of GdTbFeCo or the like have a drawback of poor resistance. That is, when it comes into contact with air or water vapor, it is oxidized and its magnetic properties deteriorate, and eventually it becomes completely oxidized and becomes transparent.

Sin, 5i02°Si to prevent oxidation of the recording film
3N4. Sandwich the recording film with an inorganic protective layer of Al2O3 or! Alternatively, a method has been proposed in which the recording film is coated with a moisture-proof halogenated organic resin, an ultraviolet curable acrylic resin, or a thermosetting epoxy resin.

(Problems to be solved by the invention) However, the protective layer of an inorganic material such as Sin or 5i02 must be formed using a vacuum device such as evaporation or sputtering, and it also takes time to form the film. The equipment investment and personnel costs were enormous, causing an increase in the cost of recording media.

In the case of protective layers made of organic resins such as halogenated organic resins, ultraviolet curable acrylic resins, EVA hot melt resins, and thermosetting epoxy resins, coating methods such as spraying, coater, printing, spinner, and dipping methods may be used. It can be coated uniformly on the recording layer and cured by solvent volatilization, heating, heating of two liquids, UV irradiation, etc., so a protective layer is formed in a short time, equipment costs are low, and it is excellent in terms of workability. It is superior to inorganic protective layers in that it can be manufactured at low cost.

However, the magneto-optical recording layer provided on the resin substrate has some air permeability, and the adhesion between the recording film and the substrate is not strong. The solvent and salt contained therein permeate and cause spots, spots, pinholes, etc. on the recording film layer. When such a disc is irradiated with a laser beam to record or reproduce data, bit errors appear. Also, when cured by heating, ultraviolet irradiation, etc., the board may warp due to curing shrinkage (Bay 1111
), the head that irradiates the laser beam during recording and playback cannot follow the laser beam, resulting in focus errors and tracking errors.
In extreme cases, recording and playback may not be possible at all.

2. A protective layer is provided to correct the warping of a normal disc.
Two identical discs are glued together with the recording film on the inside. In this way, the warpage is corrected, but at the time when the warp (curvature) occurs due to curing shrinkage, stress strain is generated between the substrate, recording film, and protective film, and at this time, there are already many A pinhole has occurred.

Therefore, even if the warpage is corrected by pasting the two sheets together, the bit error due to the increase in pinholes cannot be resolved. Therefore, the present inventors filed a patent application No. 61+244780 for a protective coating material as a protective layer that does not generate pinholes in the magnetic recording layer.
is proposed. This coating material is an ultraviolet curable resin, and is made of a mixture of a resin having a curing shrinkage of 5% or less and a resin having a curing shrinkage of more than 5%.

However, although the protective layer made of this coating material can reduce the number of pinholes that occur in the recording layer,
In an accelerated durability test under conditions of 60'C and 90% relative humidity, the protective layer cracked at approximately 1000 hours.

This crack will disappear if you take it indoors and leave it for a few days, and there is no problem with the appearance, but such a rack is not desirable because it causes a worsening of the noise level.

(Means for Solving the Problems) The protective coating for the magneto-optical disk of the present invention comprises at least one
A magneto-optical disk has two resin substrates, a magnetic recording layer for recording information is provided on the substrate, and information can be recorded, reproduced, and erased by irradiating the magnetic recording layer with light. In the magneto-optical disk in which the magnetic recording layer is covered with an organic synthetic resin and is closed off from an external space, the organic synthetic resin coating is made of an ultraviolet curable resin containing a photosensitizer and an epoxy resin that does not contain a curing agent. It is characterized by consisting of a mixture with resin.

(Preferred embodiment for carrying out the invention) The protective coating for the magneto-optical disk using the resin substrate of the present invention is made of a mixture of an ultraviolet curable resin containing a photosensitizer and an epoxy resin containing no curing agent. .

Examples of the curing agent include amine-based, polyamide-based, maleic anhydride-based, and the like. The coating can be applied uniformly onto the magneto-optical recording layer provided on the resin substrate by a coating method such as a spray applicator, wire bar roll coater, flow coater, screen printing, spin coater, or dipping method.

Examples of the photosensitizer used in the present invention include benzophenone type, acetophenone type, anthraquinone type, oxime ester type and the like. The ultraviolet curable resin may be any of acrylic polyfunctional compounds, urethane-modified polyfunctional acrylics, epoxy-modified polyfunctional acrylics, polyester-modified polyfunctional acrylics, and the like. Preferably a solvent,
Contains no monomer and has a viscosity of 500 to 1000 cps/
A range of 25°C is preferred. In addition, the curing shrinkage rate is 5%
Preferably before and after. As the ultraviolet curable resin having a curing shrinkage rate of 5% or less, most commercially available ultraviolet curable resins can be used. Although some UV-curable surface hardening (hard coat) agents have cure shrinkage rates of 5% or less, most surface hardeners contain solvents and acrylic monomers, which is undesirable. Most commercially available UV-curable protective coating agents can be used as UV-curable resins having a UV-curing ratio of more than 5%.

On the other hand, the epoxy resin may be any one of glycidyl ether type, phenol novolac type, cresol novolac type, alicyclic type, glycidyl ester type, linear aliphatic type, halogenated type, etc. Preferably does not contain solvent or monomer and has a viscosity of 500 to 1000 cps/25
A range of °C is preferred. Further, it is preferable that it is compatible with the ultraviolet curable resin used in the present invention, and that the applied protective film is colorless and transparent.

Next, the mixing ratio of both ultraviolet curable resin and epoxy resin should be 60° if the amount of epoxy resin mixed is too small.
C2 Cracks occur in the protective layer during a durability test under conditions of 90% relative humidity. Furthermore, if the amount of epoxy resin mixed is too large, not only the protective layer becomes soft, but also pinholes are likely to occur in the recording layer, which is undesirable. The mixing ratio ranges from 90% by weight of ultraviolet curable resin and 10% by weight of epoxy resin to 60% by weight of ultraviolet curable resin and 40% by weight of epoxy resin, preferably 80% by weight of ultraviolet curable resin. , 20% by weight of epoxy resin.

The thickness of the protective layer is usually 0.5 to 1100 pm, preferably 20 to 50 pm. If the thickness is too small, the recording film may be destroyed by scratches, and if it is too thick, proper curing will not occur.

Since the disk of the present invention does not have warp (curvature), it can be used as a single disk, or it can be used by bonding two disks together with an adhesive with the recording layer inside.

(Effect of the invention) A coating material made of a mixture of an ultraviolet curable resin containing the photosensitizer of the present invention and an epoxy resin containing no curing agent is applied as a protective layer on the magneto-optical disk recording layer using a resin substrate. Even if the coated magneto-optical disk is used as a single plate, it will not warp (curve a), so it will not cause focus errors or tracking errors, and the stress strain between the substrate, recording layer, and protective layer is small, so the recording layer There are fewer occurrences of pin-related errors, so bit errors can be reduced.

Furthermore, the low stress strain means that the shape of the substrate, recording film, and protective film does not change much during long-term storage, and no cracks occur even in an accelerated durability test under conditions of 60'C and 90% relative humidity.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples, with FIG. 1 also attached.

Example 1 A non-alkali glass layer 2 having an anti-reflection and moisture-proofing effect was laminated to a thickness of 50 OA by the mag-tron sputtering method on a donut-shaped substrate 1 with concentric grooves made of polycarbonate resin, and recording layers 3 and 1 were laminated to a thickness of 50 OA. ．． Gd thickness of 700 people
A non-alkali glass layer 4 of 50 OA was laminated on TbFeCo by sputtering, and then a protective layer 5 of 80% by weight of an acrylic ultraviolet curable resin (INC-117, Nippon Kakuwa Co., Ltd.) and an epoxy resin ( ecobond 4
5. The protective coating of the present invention containing 20% by weight of Emerson & Cumming Co.
pm thickness on the alkali-free glass layer 4, irradiated for 10 seconds using a high-pressure mercury lamp at 160 W/cm and an irradiation distance of 15 cm, cooled in air for 1 minute, and then irradiated for another 10 seconds to harden the protective coating and form the protective layer. I gave it a 5.

This magneto-optical disk had almost no warpage (curvature) and almost no increase in pinholes. Further, even when this disk was left at 60° C. and 290% relative humidity for 1000 hours, the warpage and pinholes remained almost the same as before the durability test, and no cracks occurred in either the recording layer or the protective layer. The results are shown in Table 1.

Example 2 Acrylic ultraviolet curable resin (IN
40% by weight of C-117, I (Ippon Kayaku Co., Ltd.), 40% by weight of an acrylic UV-curable protective film coating agent (EX-1, Dainippon Ink Co., Ltd.), and 40% by weight of epoxy resin (Ecobond 45).
．． A magneto-optical disk was prepared in the same manner as in Example 1, except that t-20ffl (Emerson & Cumming Company) was mixed and applied as the protective layer 5 by the spin code method. Even when this disk was left at 60° C. and 290% relative humidity for 1000 hours, the warpage and pinholes were almost unchanged from the values before the durability test, and no cracks occurred in the recording layer or the protective layer. The results are shown in Table 1.

Example 3 80% by weight of an acrylic ultraviolet curing protective coating agent (EX-1, Dainippon Ink Co., Ltd.) was used as a protective coating agent.

Mix 20% by weight of epoxy resin (Ecobond 45. Emerson & Cumming Company) and
Example 1 except that the coating was performed by the spin code method as No. 5.
A magneto-optical disk was created in the same manner. Even when this disk was left at 60° C. and 290% relative humidity for 1,000 hours, the warpage and pinholes remained almost unchanged from the values before the durability test, and neither the recording layer nor the protective layer exhibited cracks or light emission. The results are shown in Table 1.

Comparative Example 1 Acrylic ultraviolet curing resin (IN
A magneto-optical disk was prepared in the same manner as in Example 1, except that only C-117, Nippon Kaya Kuwa Co., Ltd.) was applied as the protective layer 5 by the spin code method. This disc is 60°C99
When left for 1000 hours under conditions of 0% relative humidity, the substrate warped (curved) inward (with the recording film outward) and cracks appeared in both the recording film and the protective film. The results are shown in Table 1.

Comparative Example 2 Acrylic ultraviolet curable resin (IN
C-117, Nippon Kaya Kuwa Co., Ltd.) 50 weight and acrylic ultraviolet curing protective coating agent (EX-1, Dainippon Ink Co., Ltd.) 5
A magneto-optical disk was prepared in the same manner as in Example 1, except that 0% by weight was mixed and applied as the protective layer 5 by the spin code method. This disc is compatible with 60°C990%.
When left for 1000 hours under conditions of +-1 degrees, the substrate did not warp, but both the recording film and the protective film had cracks. The results are shown in Table 1.

SI □S -I+1 State * * Comparative Example 3 Example 1 except that an acrylic ultraviolet curing protective coating agent (EX-1, Dainippon Ink Co., Ltd.) was applied as the protective layer 5 by the spin code method as a protective coating agent. A magneto-optical disk was created in the same manner. This disc is 60°C99
If left for 1,000 hours under conditions of 0% relative humidity, the recording film would warp (curve) inward (with the substrate outward), the number of pinholes in the recording layer would increase, and cracks would occur in both the recording film and the protective film. Ta. The results are shown in Table 1.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a magneto-optical disk of the present invention. (Brief explanation of symbols) 1: Resin substrate 2: 1 Anti-reflection 11-cum-moisture-proof layer 3: Recording layer 4: Anti-reflection/moisture-proof layer 5: Protective layer Laser light

Claims (1)

[Claims] A magneto-optical disk having at least one resin substrate, provided with a magnetic recording layer for recording information on the substrate, and capable of recording, reproducing, and erasing information by irradiating the magnetic recording layer with light. In the magneto-optical disk in which the magnetic recording layer is covered with an organic synthetic resin and is closed from an external space, the organic synthetic resin coating layer contains an ultraviolet curable resin containing a photosensitizer and a curing agent. A protective coating for a magneto-optical disk, characterized in that it is made of a mixture with an epoxy resin.