JPH09204701A - Magneto-optical disk and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magneto-optical disk having excellent performance by applying a resin by spin coating to form a protective layer while maintaining the viscosity and surface tension of the resin to specified cps or smaller and to specified dyn/cm or smaller, respectively, and controlling the difference in film thickness between the inner and the outer circumferences in a data area of the protective layer to specified % or smaller of the average film thickness of the protective film. SOLUTION: A UV-curing resin 1 to form a protective layer is charged in a resin storage tank 2 of a coating device. The resin 1 is supplied to a dispenser through a resin feeding pipe 3 by pressurizing the inside of the tank 2, and then applied on a substrate 6 through a resin coating nozzle 5. The device is equipped with a heating device 11 to maintain the UV-curing resin in the resin storage tank 2 at a specified temp. and an insulating equipment 10 to insulate the resin storage tank 2. For example, the resin is applied by spin coating method to form a protective layer while the viscosity and surface tension of the resin are maintained at <=30cps and <=30dyn/cm, respectively. Thus, the difference in the film thickness between the inner and outer circumferences of the protective layer can be controlled <=25% of the average film thickness of the protective layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk and a method for manufacturing the same, and more particularly, a magneto-optical disk having a protective film having excellent film thickness uniformity and few defects due to bubbles and a method for manufacturing the same. Regarding

[0002]

2. Description of the Related Art Generally, the reading surface of a magneto-optical disk using a substrate made of an organic polymer such as polycarbonate is
A protective layer called a so-called hard coat is often formed in order to prevent scratches on the disc surface during handling. In the present invention, the reading surface of the disc is the surface on the side irradiated with laser light for reproducing the recorded information, and refers to the substrate surface on the side opposite to the surface on which the recording layer and the like are formed. I shall. An ultraviolet curable resin is generally used as a resin for forming the protective layer of such a magneto-optical disk, and a spin coating method is generally used as a method for forming the protective layer.

The formation of the protective layer by applying the above-mentioned ultraviolet curable resin onto the substrate by spin coating and curing it is generally carried out by the following procedure. First, while rotating the substrate at a low speed, a predetermined amount of resin is ejected from the nozzle onto the substrate. Next, the substrate is stopped or the substrate is rotated at a low speed to spread the discharged resin on the substrate. After the resin has spread to some extent on the substrate, the substrate is rotated at a high speed to shake off excess resin. After that, the protective layer is formed by irradiating with ultraviolet rays to cure.

However, in the protective layer formed by this method, the film thickness locally becomes extremely thick at the outer peripheral edge of the substrate due to the liquid pool generated at the outer peripheral edge of the substrate due to the surface tension and viscosity of the resin. (Hereinafter, this portion is referred to as "protrusion of the protective layer") will occur. If the film thickness of the protective layer on the reading surface of the disc changes abruptly, the reflectance of the laser beam for recording / reproducing information changes, which increases the error rate and hinders the recording / reproducing of information. Like

On the other hand, in order to satisfy the demand for increasing the storage capacity of the disk, in addition to narrowing the track pitch,
It has been proposed to further increase the outermost radius of the data area to the outer peripheral side. In these high density magneto-optical disks, the influence of the swelling of the protective layer at the outer peripheral edge of the substrate on the recording / reproducing characteristics is a problem. It was.

The size of the swelling of the protective layer on the outer peripheral edge of the substrate is determined by performing high-speed rotation of the substrate for a long time to shake off excess resin when the resin is applied to the substrate by spin coating. Although it can be reduced, there is a problem that the time required for forming the protective layer is increased and the number of disks produced per unit time is reduced.

Further, in a protective layer formed by a spin coat method using a conventional protective film forming apparatus, air bubbles contained in a resin may cause defects such as dents in the formed protective layer. It was Since such a dent affects the reflectance of the laser beam, normal recording / reproduction cannot be performed in that portion, which is one of the causes of a decrease in the yield rate. In order to prevent such an adverse effect of bubbles, for example, in Japanese Patent Laid-Open No. 5-50009, a resin containing bubbles is not supplied onto a substrate by a differential refractive index detector provided in a piping system for supplying the resin to a discharge nozzle. A method of doing so is disclosed. However, this method has a problem that the bubbles themselves in the resin cannot be reduced and the resin containing the bubbles must be discarded.

[0008]

SUMMARY OF THE INVENTION The present invention enables the data area to be expanded to the outer circumference by reducing the rise of the protective layer at the outer peripheral edge of the above-mentioned disk, and also the depression of the protective layer due to air bubbles. It is an object of the present invention to provide a high-density magneto-optical disk and a manufacturing method thereof, in which the occurrence of defects is reduced and the yield rate is improved.

[0009]

Means for Solving the Problems The inventors of the present invention apply a UV curable resin by a spin coating method to form a protective layer and have a viscosity of the resin of 30 cps or less and a surface tension of 30 dyn / cm or less. By this, it is possible to reduce the swelling of the protective layer at the outer peripheral edge of the disc,
As a result, the inventors have found that the film thickness distribution of the protective layer in the data area of the high-density magneto-optical disk is reduced, and a magneto-optical disk in which the electric signal on the outer periphery is not reduced can be obtained, and the present invention has been completed.

That is, the magneto-optical disk of the present invention is a magneto-optical disk having a protective layer on the information reading surface side of the disk substrate, and the film thickness difference between the inner and outer peripheries of the data area is the protective layer. It is characterized by being 25% or less of the average film thickness. The inner and outer radii of the data area of the 3.5-inch high-density magneto-optical disk are 21.6 mm and 41.3 mm, respectively. The method of manufacturing a magneto-optical disk according to the present invention is a method of manufacturing a magneto-optical disk, which comprises a step of applying a resin to the information reading surface side of the disk substrate by a spin coating method to form a protective layer. When discharging, the viscosity of the resin is 30 cps or less and the surface tension is 30 dyn.
/ Cm or less, the difference in film thickness between the inner and outer circumferences of the data area of the formed protective layer is 25% or less of the average film thickness of the protective layer. is there. The viscosity of the resin when ejected onto the disk substrate is 3
In order to adjust the surface tension to 0 cps or less and the surface tension to 30 dyn / cm or less, the viscosity of the resin at room temperature is 30 cps or less and the surface tension is 30 dyn / cm or less by adjusting the monomer composition of the resin and adding a surfactant. Alternatively, it can be achieved by providing a mechanism for heating the tank for storing the resin to a predetermined temperature. In addition, in order to prevent the resin temperature from being lowered during the transportation of the resin from the storage tank to the nozzle, it is more preferable to provide a function of keeping heat or warming the resin transportation piping system from the tank to the nozzle.

By reducing the viscosity and surface tension of the resin forming the protective layer, it becomes difficult for the excess resin to remain on the edge (outermost periphery) of the substrate during the step of shaking off the excess resin during spin coating, and the viscosity is 30 cps. A more uniform film thickness can be obtained than when a resin having a surface tension of more than 30 d or a resin having a surface tension of more than 30 dyn / cm is used. Further, since the viscosity and surface tension of the resin are lowered, the bubbles contained in the resin are easily removed, so that the occurrence of defects such as dents in the coating film due to the bubbles is reduced.

Examples of the resin used in the present invention include ultraviolet curable resins such as acrylic and / or methacrylic acid esters, and more specifically, monofunctional, difunctional and trifunctional or higher functional acrylic and / or methacrylic acid. It is an ester.

Examples of the monofunctional acrylic acid ester or methacrylic acid ester that can be used in the present invention include tetrahydrofurfuryl acrylate and isobornyl acrylate.

The amount of monofunctional acrylic acid ester or methacrylic acid ester used is preferably 0% by weight or more and 50% by weight or less, and more preferably 5% by weight or more and 45% by weight or less. When it is used in an amount of more than 50% by weight, the three-dimensional crosslinked structure of the cured film may be difficult to be formed.

Polyethylene glycol (PEG) # 400 is a typical example of the bifunctional acrylic acid ester or methacrylic acid ester that can be used in the present invention.
Diacrylate, polyethylene glycol (PEG) #
600 diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate,
Examples thereof include ethylene oxide-modified bisphenol A diacrylate and hydrogenated dicyclopentadienyl diacrylate.

The amount of the bifunctional acrylic acid ester or methacrylic acid ester used is preferably 10% by weight or more and 60% by weight or less. If the concentration is lower than 10% by weight, the adhesion to the polycarbonate substrate may not be exhibited,
When it is used in an amount exceeding the weight percentage, the protective ability of the membrane may be reduced.

Typical examples of trifunctional or higher functional acrylic acid ester or methacrylic acid ester that can be used in the present invention include trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate and the like. Can be illustrated.

The amount of trifunctional or higher functional acrylic and / or methacrylic acid ester used is preferably 5% by weight or more and 50% by weight or less, more preferably 20% by weight or more and 40% by weight.
The range is as follows. If it is less than 5% by weight, the hardness and scratch resistance required for protection may be reduced, and if it exceeds 50% by weight, the viscosity of the resin may increase or the curing shrinkage during curing of the resin may increase. There is.

Two or more kinds of acrylic acid ester or methacrylic acid ester used in the present invention may be used in combination.

Examples of the photoinitiator in the present invention include acetophenone-based, benzophenone-based, benzoin ether-based, thioxanthone-based and benzophenone-based photoinitiators. Moreover, you may add a hydrogen donor as needed.

The photoinitiator which can be used in the present invention is
For example, diethoxyacetophenone, 2-hydroxy-
2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-2
-Morpholino (4-thiomethylphenyl) propane 1-
On, 2-benzyl-2-dimethylamino-1- (4-
Morpholinophenyl) -butanone, benzoin methyl ether, benzoyl isopropyl ether, 3,3 ',
4,4'-tetra (t-butylperoxycarbonyl)
Examples thereof include benzophenone and 2-isopropylthioxanthone.

The addition amount of the photoinitiator in the present invention is preferably 1% by weight or more and 10% by weight or less, more preferably 2% by weight or more and 8% by weight or less in the composition. 10% by weight
When added in excess, the unreacted photoinitiator during curing may reduce the stability of the film over time. Further, if the addition amount is less than 1% by weight, the curability is remarkably deteriorated, which is not practical.

Further, one or more kinds of leveling agents can be added for the purpose of imparting a uniform coating property, suppressing the occurrence of orange peel and craters, and lowering the surface tension. Silicone-based surfactants and fluorine-based surfactants are generally known as leveling agents.
These can be used within a range that does not impair the performance of the intended protective film.

Further, if necessary, generally used additives may be added to the composition of the present invention.

When the viscosity of the resin at room temperature is 30 cps or less and the surface tension thereof is 30 dyn / cm or less, in the step of shaking off the excess resin on the substrate during spin coating, a short shaking time of 10 seconds or less, The film thickness difference between the inner and outer protective layers of the data area can be 25% or less of the average film thickness of the protective layer. Also, the viscosity of the resin at room temperature exceeds 30 cps, or the surface tension is 30 d.
If it exceeds yn / cm, the resin viscosity is 30 cps
By heating so as to have a surface tension of 30 dyn / cm or less, the film thickness difference between the inner and outer protective layers of the data area is the average film of the protective layer in a short shaking time of 10 seconds or less. It can be 25% or less of the thickness.

The present invention has a mechanism for heating the resin in the resin storage tank to a predetermined constant temperature, and in order to keep the resin temperature during transportation at the predetermined constant temperature, the resin transportation pipe from the tank to the nozzle. It can be carried out by a coating device having a mechanism for keeping the system warm.

[0027]

INDUSTRIAL APPLICABILITY According to the present invention, by spin coating while maintaining the viscosity of the resin at 30 cps or less and the surface tension at 30 dyn / cm or less, data can be obtained with a short takt time even in the production of a high recording density magneto-optical disk. It is possible to form a small film thickness difference of the protective layer in the area, and as a result, Icross /
It is possible to manufacture a magneto-optical disk without a decrease in Iol signal.

[0028]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

FIG. 1 shows an example of the structure of a protective layer coating apparatus for carrying out the present invention. In this coating apparatus, an ultraviolet curable resin (protective coating agent) 1 for forming a protective layer is put into a resin storage tank 2 and the inside of the resin storage tank 2 is pressurized to transport the ultraviolet curable resin 1 to a resin. It is supplied to the dispenser 4 through the pipe 3, and is supplied as the resin 7 from the resin coating nozzle 5 onto the substrate 6. The substrate 6 is fixed to the spinner head 8 by a vacuum chuck method, and when the resin is being applied, the entanglement prevention air 9 is provided to prevent the resin from wrapping around the back surface of the substrate.
Is being washed away. A heating device 11 for keeping the ultraviolet curable resin 1 in the resin storage tank 2 at a predetermined constant temperature and a warming facility 10 for keeping the resin storage tank 2 warm are installed, and the resin is transported from the resin storage tank 2. A heat insulation facility is also installed in the resin transport pipe 3 to be used.

In the examples and the comparative examples, the viscosity and surface tension of the resin were measured by E type viscometer VISCONIC ED type manufactured by Toki Sangyo Co., Ltd. and Dunois surface tension meter B type manufactured by Yamato Scientific Co., Ltd., respectively. Was performed using. The film thickness of the formed protective layer was measured using an electron microscope after preparing a fracture surface of the protective layer. FIG. 2 shows the shape of a cross section of the magneto-optical disk taken along a plane perpendicular to the disk surface (the film thickness of the protective layer and the like are exaggerated in the drawing). 3.5 inch 650M
For the B disc, d1 = 21.6 mm, d2 = 4
The thickness of the protective layer was measured at 6 points including 1.3 mm and d3 = 43.5 mm and including the inner circumference (film thickness h1) and the outer circumference (film thickness h2) of the data area.

The following method was used to measure the time taken for the bubbles contained in the resin to escape. Put 40cc of resin in a 50ml sample bottle and shake for 10 minutes on a shaker.
Force the resin to contain air bubbles. Then, the time from when the shaking of the sample bottle is stopped to when the bubbles are removed is measured.

Example 1 The resin used in this example was 350 g of pentaerythritol triacrylate and 4 g of polyethylene glycol (PEG) # 400 diacrylate.
00g, 1,6 hexanediol diacrylate 150
g, Darocur 1173 (manufactured by Ciba Geigy) as a photoinitiator, a silicone-based coating additive as a leveling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KP-305")
It consists of 10 g. The viscosity of this resin is 55 at 25 ° C.
The cps and the surface tension were 28 dyn / cm. FIG. 3 shows the temperature dependence of the time taken for the bubbles to escape from the resin measured by the above method. As can be seen from this figure, when the viscosity is 30 cps or less, the time for bubbles to escape is less than half that at room temperature. Since the viscosity of this resin is 28 cps at a temperature of 40 ° C., the resin was put into the resin storage tank of the coating apparatus shown in FIG. 1 and left at 40 ° C. for a certain period of time to reach a resin temperature of 40 ° C. After confirming, the coating was performed on the substrate. The amount of resin discharged onto the substrate is 2.
The rotation speed of the spin table when the resin was shaken off was 3800 rpm for 5 seconds. Then, light was irradiated using a high pressure mercury lamp to form a protective layer. The result of measuring the film thickness of the protective layer thus formed with an electron microscope is shown in FIG.
Are indicated by ●. The swelling of the film thickness was small at 41.3 mm which is the outermost periphery of the data area of the 3.5 inch 650 MB disc. At this time, the film thickness difference between the inner circumference and the outer circumference of the data area was 1.0 μm, and the average film thickness of the protective layer at this time was 4.8 μm. The film thickness difference between the inner and outer circumferences of the data area is 20.8% of the average film thickness.
No decrease in Icross / Iol in mm was observed. As a result of forming a protective layer on 100 substrates under the same conditions, no defects due to bubbles were observed.

(Example 2) The resin used in this example was 300 g of dipentaerythritol hexaacrylate, 450 g of polyethylene glycol (PEG) # 200 diacrylate, and 1,6 hexanediol diacrylate 1
25 g, tetrahydrofurfuryl acrylate 125
g, methylphenylglyoxylate 5 as a photoinitiator
0 g, 10 g of a silicone-based paint additive as a leveling agent (Shin-Etsu Chemical Co., Ltd., trade name "KP-306")
Consists of The viscosity of this resin is 27 cp at 25 ° C.
s, surface tension was 29 dyn / cm. FIG. 4 shows the temperature dependence of the time taken for the bubbles to escape from the resin measured by the above method. From this figure, it can be seen that air bubbles easily escape from this resin even at room temperature. This resin is
Using the above apparatus, the substrate was spin-coated at room temperature without heating the resin. The amount of resin discharged onto the substrate is 1.8g
Therefore, the rotation speed of the spin table when the resin is shaken off is 35
It was carried out at 00 rpm for 5 seconds. Then, light was irradiated using a high pressure mercury lamp to form a protective layer. The result of measuring the thickness of the protective layer thus formed with an electron microscope is shown in FIG.
Shown by a mark. The swelling of the film thickness was small at 41.3 mm which is the outermost periphery of the data area of the 3.5 inch 650 MB disc. At this time, the film thickness difference between the inner circumference and the outer circumference of the data area was 0.9 μm, and the average film thickness of the protective layer at this time was 4.75 μm. The film thickness difference between the inner and outer circumferences of the data area is 18.9% of the average film thickness, which is 41.3 m.
No decrease in Icross / Iol was observed in m. As a result of forming a protective layer on 100 substrates under the same conditions, no defects due to bubbles were observed.

Comparative Example 1 The resin used in Example 1 was spin-coated on the substrate at room temperature using the apparatus shown in FIG. 1 without heating the resin. The amount of resin discharged onto the substrate is 2.0
g, and the resin is shaken off at 4500 rpm.
Seconds. The thickness of the protective layer obtained in the same manner as in Example 1 was measured by an electron microscope, and the result is shown by ⋄ in FIG.
The difference in film thickness between the inner circumference and the outer circumference of the data area of the 3.5-inch 650 MB disc was 2.7 μm, and the average film thickness of the protective layer at this time was 4.5 μm. The film thickness difference between the inner and outer circumferences of the data area is 60.0% of the average film thickness.
A reduction in Icross / Iol in mm was confirmed. As a result of forming a protective layer on 100 substrates under the same conditions, defects due to bubbles were observed on 5 substrates.

Comparative Example 2 The resin used in this comparative example was 400 g of pentaerythritol triacrylate and 4 g of polyethylene glycol (PEG) # 600 diacrylate.
00g, 1,6 hexanediol diacrylate 100
g, 100 g of tetrahydrofurfuryl acrylate, and 50 g of methylphenylglyoxylate as a photoinitiator. The viscosity of this resin is 87 cps at 25 ° C,
The surface tension was 45 dyn / cm. FIG. 5 shows the temperature dependence of the time taken for the bubbles to escape from the resin measured by the above method. Using the apparatus of FIG. 1, the substrate was spin-coated at room temperature without heating the resin. The amount of resin discharged onto the substrate was 2.2 g, and the rotation speed of the spin table when the resin was shaken off was 4500 rpm for 8 seconds. Then, light was irradiated using a high pressure mercury lamp to form a protective layer. The result of measuring the film thickness of the protective layer thus formed by an electron microscope is shown by □ in FIG. The difference in film thickness between the inner circumference and the outer circumference of the data area was 2.0 μm, and the average film thickness of the protective layer at this time was 4.5 μm. The film thickness difference between the inner circumference and the outer circumference of the data area is 44.4% of the average film thickness.
A decrease in Icross / Iol was confirmed at 3 mm. As a result of forming a protective layer on 100 substrates under the same conditions, defects due to bubbles were observed on 7 substrates.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a coating device for a resin for forming a protective layer of a magneto-optical disk for carrying out the present invention.

FIG. 2 is a diagram showing a cross-sectional shape of a magneto-optical disk.

FIG. 3 is a diagram showing the relationship between the time taken for the bubbles contained in the resin to escape, the viscosity, and the resin temperature for the resins used in Example 1 and Comparative Example 1.

FIG. 4 is a graph showing the relationship between the time taken for the bubbles contained in the resin used in Example 2 to escape, the viscosity, and the resin temperature.

FIG. 5 is a diagram showing the relationship between the time taken for the bubbles contained in the resin used in Comparative Example 2 to escape, the viscosity, and the resin temperature.

FIG. 4 is a diagram showing a film thickness of a protective film in Examples and Comparative Examples.

[Explanation of symbols]

 1 Resin 2 Resin Storage Tank 3 Resin Transport Piping 4 Dispenser 5 Nozzle 6 Substrate 7 Resin 8 Spinner Head 9 Backing Prevention Air 10 Heat Insulation Equipment 11 Heating Device 12 Temperature Sensor

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[Procedure amendment]

[Submission date] May 10, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a coating device for a resin for forming a protective layer of a magneto-optical disk for carrying out the present invention.

FIG. 2 is a diagram showing a cross-sectional shape of a magneto-optical disk.

FIG. 3 is a diagram showing the relationship between the time taken for the bubbles contained in the resin to escape, the viscosity, and the resin temperature for the resins used in Example 1 and Comparative Example 1.

FIG. 4 is a graph showing the relationship between the time taken for the bubbles contained in the resin used in Example 2 to escape, the viscosity, and the resin temperature.

FIG. 5 is a diagram showing the relationship between the time taken for the bubbles contained in the resin used in Comparative Example 2 to escape, the viscosity, and the resin temperature.

FIG. 6 is a diagram showing a film thickness of a protective film in Examples and Comparative Examples.

[Explanation of reference symbols] 1 resin 2 resin storage tank 3 resin transport piping 4 dispenser 5 nozzle 6 substrate 7 resin 8 spinner head 9 back prevention air 10 heat insulation equipment 11 heating device 12 temperature sensor

Claims (5)

[Claims] 1. In a magneto-optical disk having a protective layer on the information reading surface side of a disk substrate, the film thickness difference between the inner and outer periphery of the data area is 25% or less of the average film thickness of the protective layer. A magneto-optical disk characterized by being present. 2. The magneto-optical disk according to claim 1, wherein the inner and outer radii of the data area are 21.6 mm and 41.3 mm, respectively. 3. A method of manufacturing a magneto-optical disk, which comprises a step of applying a resin on the information reading surface side of the disk substrate by a spin coating method to form a protective layer, and the viscosity of the resin when ejected onto the disk substrate. Is maintained at 30 cps or less and the surface tension thereof is kept at 30 dyn / cm or less, so that the film thickness difference between the inner and outer circumferences of the formed protection layer data area is 25% or less of the average film thickness of the protection layer. A method for manufacturing a magneto-optical disk, comprising: 4. The method for manufacturing a magneto-optical disk according to claim 3, wherein a resin having a viscosity at room temperature of 30 cps or less and a surface tension of 30 dyn / cm or less is used. 5. By heating the resin to a predetermined temperature,
The viscosity of the resin when ejected onto the disc substrate is 30 cp
4. The method for manufacturing a magneto-optical disk according to claim 3, wherein the surface tension is kept at s or less and the surface tension is kept at 30 dyn / cm or less.