JPH01194152A - Protective coating method for magneto-optical disk - Google Patents

Abstract

PURPOSE:To suppress formation of pinholes by coating a magnetic recording layer with a hot-melt resin layer then a UV curing resin layer. CONSTITUTION:An alkali-free glass layer 2 is laminated on the doughnut-shaped substrate 1 with concentrical grooves consisting of, for example, a polycarbonate resin and a ZnS layer 3 is laminated thereon; further, GdTbFeCo is laminated as the magnetic recording layer 4 and the alkali-free glass layer 2 are respectively laminated thereon. A hot melt resin 5 is coated as a protective layer by a roll coater on the recording layer 4 of the magneto-optical disk and further, a UV curing resin 6 is spin-coated thereon and is cured by UV rays, by which two-layered coatings are formed. The generation of the pinholes by the coating is thereby prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a protective coating method for protecting a recording layer of a magneto-optical disk using a resin substrate.

(Prior Art) Conventionally, there is a magneto-optical disk which is used for 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.

The recording film of the magneto-optical disk contains Gd, Tb,
Fe.

The amorphous thin film made of Co has excellent film-forming properties when producing a large-area thin film at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, and S/ Readout efficiency for good readout of N ratio,
Large car rotation angle.

Since it has a Curie point of around 150°C, it is optimal as a magneto-optical recording medium.

However, generally Gd, Tb, Fe,
A magneto-optical recording layer made of Go or the like has a drawback of poor corrosion 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.

Furthermore, the disk substrate is made of polycarbonate (compared to glass).
In the case of resin substrates such as PC, inorganic thin films or alloy thin films deposited by vacuum evaporation or sputtering do not have sufficient adhesion to the PC substrate, so Magnetic recording film (Gd, Tb,
(Fe, Co) may not adhere properly or may peel off due to insufficient adhesion.

This phenomenon is observed as a pinhole and can be easily identified by placing a fluorescent light under the magneto-optical disk substrate and viewing it through a magnifying glass from above, and the size of the pinhole is often 20 to 80 pm. .

In addition to what is already observed as pinholes, there are parts of the recording layer with weak adhesion on the substrate surface. (
(Hereafter, these are referred to as pinhole reserves) Pinholes are generated by being oxidized and made transparent by contact with the atmosphere or water vapor, and by peeling off the recording film in areas with weak adhesion from the substrate, which are called pinhole reserves. It can be roughly divided into two types.

The occurrence of pinholes is undesirable because it not only deteriorates the appearance of the product, but also appears as a decrease in the bit error rate when recording and reproducing by irradiating laser light.

Conventionally, SiO was used to prevent oxidation of the recording film.

The recording film is sandwiched between a protective layer of an inorganic material such as 5i02, Si3N4, or Al2O3, or a halogenated organic resin with moisture resistance, an ultraviolet curable acrylic resin, a thermosetting epoxy resin, or a hot melt resin is used. A method of protecting a recording film, or Cr, Ti.

A method of coating a protective film in a vacuum system by vapor deposition or sputtering of Au, Hf, etc. has been proposed.

(Problem to be solved by the invention) However, SiO, 5i02, Si3N4,
Protective layer of inorganic material such as Al2O3, Cr, Ti, A
A protective layer of a metal thin film such as U or Hf must be formed using vacuum equipment such as evaporation or sputtering, and it also takes time to form a film, resulting in enormous equipment investment and personnel costs. , which caused an increase in the cost of recording media.

Also, Japanese Patent Application Publication No. 61-68750, Japanese Patent Application No. 61-260
219, in the case of a protective layer made of an organic resin such as a halogenated organic resin, an ultraviolet curable acrylic resin, a thermosetting epoxy resin, or a hot melt resin, recording may be performed using a coating method such as spray, coater, or spinner dipping method. It can be applied uniformly over the layer and cured by solvent volatilization, heating, heating of two liquids, ultraviolet irradiation, etc., so a protective layer is formed in a short time, equipment costs are low, and it has excellent workability and low cost. It is superior to protective layers made of inorganic materials, metal thin films, etc. 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 solvents and monomers contained permeate, causing spots, spots, pinholes, etc. on the recording film layer.

This phenomenon can also occur due to other causes. For example, when spraying, the recording layer in areas with weak adhesion (preliminary pinholes) is peeled off due to force and becomes pinholes, and when coating with a roll coater, the pressing pressure of the roll and the passage of the substrate Due to slight discrepancies in speed, potential pinholes appear as pinholes. The same goes for printing, where potential pinholes adhere to the screen side, causing pinholes to occur on the substrate. In a spinner, potential pinholes appear as pinholes due to the centrifugal force caused by high-speed rotation.

Furthermore, the rate of curing and shrinkage of the resin due to heating, cooling, ultraviolet curing, etc. is different from the rate of expansion and contraction of the recording layer and substrate, which causes stress distortion in the recording layer, and in this case too, potential pinholes become pinholes. appears.

Furthermore, the water absorption rates of the protective layer, the recording layer, and the resin substrate are also different, and the difference in water absorption and expansion coefficients also causes stress distortion in the recording film, causing potential pinholes to turn into pinholes.

(Means for Solving the Problems) The protective coating method for a magneto-optical disk of the present invention has at least a resin substrate, a magnetic recording layer for recording information is provided on the substrate, and the magnetic recording layer A magneto-optical disk capable of recording, reproducing, and erasing information by irradiating light onto the disk, wherein the magnetic recording layer is coated with a hot melt resin layer, and then an ultraviolet curing resin layer on the hot melt resin N. This is a characteristic feature.

(Preferred mode for carrying out the invention) In the protective coating method for a magneto-optical disk of the present invention, the substrate is made of transparent plastic such as polymethyl methacrylate (PMMA) or polycarbonate (PC), and the guide groove side surface of the substrate is A non-alkali glass layer, a ZnS layer, Gd, and Tb were then formed by magnetron sputtering.

A magnetic recording layer was provided by laminating Fe, Co layers, and alkali-free glass layers in this order. This magneto-optical disk was used as a sample for the protective coat of the present invention.

The protective coating method of the present invention is to apply a hot melt resin onto the magnetic recording layer using a roll coater, then apply an ultraviolet curable resin on top of that using a spinner, and irradiate it with ultraviolet rays to form a protective coating layer. be.

The hot melt resin used in the present invention has a softening point of 90
Any material can be used as long as it has a small solidification shrinkage at temperatures above .degree. C., but ethylene-vinyl acetate-wax-based hot melt resins are particularly preferred.

When applying hot melt resin onto the magnetic recording layer using a roll coater, special care must be taken to prevent potential pinholes scattered on the surface of the magnetic recording layer from turning into pinholes. The method is to ensure that the magnetic recording layer never touches the upper (metal) roll when the magneto-optical disk is passed between the upper and lower rolls. To do this, the clearance between the upper and lower rolls must be set accurately on the order of microns to match the thickness of the substrate + the thickness of the hot melt layer. That is, the pressure applied to the magnetic recording layer is completely reduced to zero.

Furthermore, another factor that causes potential pinholes to become pinholes is that the hot melt molten resin is caused by a slight discrepancy between the passing speed of the substrate and the peripheral speed of the upper metal roll to which the molten hot melt resin is attached. Pinholes are generated by the action of peeling off potential pinholes.

To deal with this, it is important to reduce the substrate speed as much as possible to reduce deviation from the roll circumferential speed, and to also ensure that the hot melt resin adheres to the magnetic recording layer and becomes a solidified film at the same time. Therefore, it is preferable that the substrate passing speed is 1 m/min and the temperature of the hot melt resin attached to the roll is as low as possible as close to the softening point as possible, that is, around 100°C.

The thickness of the hot melt protective layer is preferably 10 to 10011p, preferably 30 to 60p. If it is thinner than that, pinholes are likely to occur in the recording layer, and if it is too thick, the recording layer will be damaged.

Cracks occur in the hot melt layer.

Next, a UV-curable acrylate protective coat layer is applied onto the hot melt protective coat layer using a spinner. Although any ultraviolet (UV)-curable acrylate resin can be used, urethane acrylate resins have a coating hardness that is between that of hard coat agents and adhesives, and have a low curing shrinkage rate (5% or less). UV of
Protective coating agents are preferred. The thickness of the UV protective coating layer is 5
The film thickness is in the range of 50 p to 50 p, and a film thickness of 10 to 30 p is particularly preferable. If the film thickness is less than 5p, pinholes will occur if left for a long time at 60°C and 290% relative humidity.
A film thickness of 5011 mm or more not only takes time for UV curing, but also tends to cause deformation of the PC board due to "degree warpage".

Note that when only a hot melt resin is used as the protective layer applied on the magnetic recording layer and no UV curing protective coating layer is provided thereon, almost no pinholes occur initially. However, when left for 100 hours under conditions of 60'C and 90% relative humidity, more than 300 pinholes were generated.

Furthermore, if a UV protective coating is applied directly onto the magnetic recording layer (without a hot-melt protective coating), about 20 pinholes will occur initially due to the centrifugal force of the spin coater and curing shrinkage due to UV irradiation. 60°C290
When placed under conditions of % relative humidity for 24 hours, the number of pinholes increases by about 20, and when left in that environment for 1,000 hours, there are 50 to 100 pinholes in total.

Therefore, the pinhole prevention effect of the present invention can be obtained by applying a hot melt protective layer on the magnetic recording layer using a roll coater.
This can only be achieved by applying an ultraviolet (UV) cured resin protective layer on top of the coating using a spinner and UV curing to form a two-layer protective coating.

Since the magneto-optical disk of the present invention has excellent durability, it can be used as a single disk as it is, or it can be used by bonding two disks together with an adhesive with the recording layer inside.

(Effects of the Invention) The hot melt resin of the present invention is applied as a protective layer on the magneto-optical disk recording layer using a resin substrate using a roll coater, and then an ultraviolet curable resin is further applied using a spinner.
The protective coating method of the present invention, which is UV-cured to form a two-layer coating, eliminates the occurrence of pinholes due to coating, and
Even if left for a long time under 90% relative humidity conditions, there are very few pinholes, so it has good commercial value in terms of appearance, and it is durable because there is little bit error rate drop during recording and playback after durability tests. , a magneto-optical disk with excellent reliability can be obtained.

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

Example 1 A non-alkali glass layer 2 having anti-reflection and moisture-proofing effects was applied to a donut-shaped substrate 1 with concentric grooves made of a polycarbonate (PC) resin by magnetron sputtering at 500 Å.
On top of that, a Zn8 layer 3 was layered to a thickness of 850 mm as an enhancement layer by the same sputtering method, and then a GdTbFeCo layer 4 with a thickness of 100A was layered on top of it by a sputtering method. Alkali glass layer 2 at 50O
Each of A was laminated to form a sample for the protective coat of the present invention.

(PC board diameter 130 mm, thickness 1.2 mm) Next, hot melt resin (ethylene-vinyl acetate-wax system, manufactured by Sekisui Co., Ltd., 955) was placed in the upper hopper of the roll coater.
0) and melted at 120°C.

Both the upper metal roll and lower rubber roll have a diameter of 50m.
m, and the clearance between the rolls is 1.2 mm + 50
It was set accurately so that p. The metal roll to which the upper hot melt resin is welded was set to 100°C, the circumferential speed of the upper and lower rolls and the belt conveyor speed were adjusted to 1 m/min, and the substrate was placed between the upper and lower rolls with the magneto-optical recording layer facing upward. I let it pass. Hot melt overcoat layer 5 at this time
The film thickness was 60p.

Subsequently, an ultraviolet curing protective coating agent (Daicure Clear, EX-301, manufactured by Dainippon Ink Co., Ltd.) was dripped onto the hot melt overcoat layer 5 using a spinner.
Rotate at 500 rpm for 5 seconds and then at 200 rpm for 10 seconds to overcoat, and UV curing with high pressure mercury lamp 1.
The test was carried out twice in air at 60 watt/cm2, irradiation distance 15 cm, and irradiation time 10 seconds. The thickness of the UV overcoat layer (protective coat layer) 6 was 2,011 mm. This sample was heated to 100% at 60°C and 290% relative humidity.
It was left for 0 hours. Table 1 shows the occurrence of pinholes and the reduction in bit error rate.

Comparative Example 1 Same as Example 1 except that no ultraviolet curing protective coating agent was applied. Only (hot melt protective coat layer 5) was applied. The results are shown in Table 1.

Comparative Example 2 Same as Example 1 except that hot melt protective coat layer 5 was not used. Only (ultraviolet curing protective coat layer 6) was applied. 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. (Explanation of symbols) 1: Polycarbonate substrate 2: Alkali-free glass layer 3: Enhance layer (ZnS) 4: Recording layer (GdTbFeCo) 5: Hot melt resin protective layer 6: UV cured resin protective layer

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. The magnetic recording layer is a hot melt resin layer,
A protective coating method for a magneto-optical disk, characterized in that the hot melt resin layer is then coated with an ultraviolet curing resin layer.