JPH09204697A - Method and apparatus for forming a protective film for optical disc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent swelling of resin at the side surface of a substrate by setting a surface tension of the external circumference surface of an optical disc substrate to the particular value or less, and thereafter coating the surface with a protection film-forming resin by the spin coating method. SOLUTION: In this optical disc protection film-forming method, a surface tension of the side surface of substrate is set smaller than the surface tension of the resin coated in order to prevent drooping of resin to the side surface of substrate and creeping of resin to the opposite side of the coating surface at the time of forming a protection film on the substrate by the spin coating method. Thereby, resin coated to form a protection film is never repelled at the edge portion and drooped on the side surface of the substrate. Moreover, since the resin is dropped to the side surface of substrate, two kinds of resin are never overlapped at the side surface of substrate at the time of forming a protection film on the surface in the opposite side and generation of swelling of resin at the side surface of substrate can be prevented. In this case, the surface tension at the side surface of substrate is preferably set to 20 dyne/cm or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a protective film on an optical disk substrate and an improvement in an apparatus therefor.

[0002]

2. Description of the Related Art Generally, a protective film is formed on the surface of an optical disc such as a magneto-optical disc using a substrate made of an organic polymer such as polycarbonate to prevent the disc surface from being scratched during handling. . Various resins have been conventionally proposed as a resin for forming a protective film of such an optical disk, particularly a magneto-optical disk, but an ultraviolet curable resin is generally widely used as a hard coating agent or the like. A spin coating method is generally used as a method for forming this protective film.

The formation of the protective film by coating the above ultraviolet curable resin on the substrate by the spin coating method 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 film is formed by irradiating ultraviolet rays to cure the coating film.

However, in this method, the resin sometimes hangs down on the end surface of the substrate, and in severe cases, the resin wraps around on the surface opposite to the surface coated with the resin (coated surface) as shown in FIG. , This could lead to product defects.

Further, in a method of forming a resin-made protective film in the manufacture of an optical disc, a substrate is injection-molded, a protective film on the reading surface side is formed, then a recording film and the like are formed, and then the recording surface side is formed. There is a method of forming a protective film, and a method of forming a recording film and the like on an injection-molded substrate and then forming a protective film in the order of the recording surface side and the reading surface side. And the two kinds of protective films on the read surface side may overlap on the outer peripheral side surface of the substrate, and depending on the conditions, the protective film formed later may form a bulge on the side surface of the substrate, as shown in FIG. . When the resin bulge on the side surface of the substrate is severe, d1 of FIG. 6 is 130.
Can reach micron.

On the other hand, in the hub attaching step, which is a step after the formation of the protective film, the center of the substrate is generally searched by chucking several places on the side face of the substrate, so that the resin swelling on the side face of the substrate as described above occurs. If this is the case, the center search of the substrate is not normally performed, which is a factor of lowering the yield.

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to the production of an optical disk such as a magneto-optical disk, when a resin protective film is formed on a substrate by a spin coating method, when the resin drips onto the side surface of the substrate. A method of forming a protective film capable of preventing two kinds of resins from overlapping on the side surface of the substrate by preventing the resin from wrapping around to the opposite side of the coated surface and preventing the resin from rising on the side surface of the substrate. And an apparatus therefor.

[0008]

Means for Solving the Problems The present inventors have made it possible, when forming a protective film on a substrate by a spin coating method, to make the surface tension of the side surface of the substrate smaller than the surface tension of a resin to be coated. It is possible to prevent resin dripping onto the side surface of the substrate and resin from wrapping around to the opposite side of the coating surface. Furthermore, by preventing liquid dripping onto the side surface of the substrate, it is possible to prevent two types of resin from overlapping on the side surface of the substrate. As a result, they have found that it is possible to prevent the resin from rising on the side surface of the substrate, thus completing the present invention.

That is, according to the method of forming a protective film for an optical disk of the present invention, the surface tension of the outer peripheral side surface of the optical disk substrate is set to 2 mm.
The protective film is formed on the substrate by applying a resin for forming a protective film using a spin coating method after setting the protective film to 0 dyn / cm or less. To reduce the surface tension of
Before the resin for forming the protective film is applied by the spin coating method, a surfactant is applied to the outer peripheral side surface of the optical disc substrate.

Furthermore, the protective film forming apparatus for an optical disk of the present invention is a protective film forming apparatus for forming a protective film on an optical disk substrate by a spin coating method, before the resin for forming the protective film is spin coated. It is characterized in that a surfactant is applied to the outer peripheral side surface of the. Further, the application of the surfactant to the outer peripheral side surface of the substrate is performed to remove foreign matters on the substrate before spin-coating the resin for forming the protective film in order to shorten the time required to form the protective film. While performing the electrostatic blow, it is preferable to perform it at the same time.

Hereinafter, the present invention will be described in more detail.

The surface tension of a polycarbonate substrate used for an optical disk such as a magneto-optical disk is 46.6 at 20 ° C.
dyn / cm. On the other hand, the surface tension of the ultraviolet curable resin such as an acrylic polymer used for forming the protective film is generally about 35 to 40 dyn / cm, but the protective film on the reading surface side has been changed as the recording density of the optical disc increases. In order to form a more uniform film thickness, a surface active agent tends to be reduced to 22 to 30 dyn / cm by adding a surfactant or the like. Since it is not necessary to make the film thickness of the protective film on the recording surface side uniform even when the recording density is increased, the surface tension of the recent resin is 35 to 40 dyn / cm as before.

As described above, since the surface tension of the substrate is larger than the surface tension of the resin such as acrylic polymer used for forming the protective film at present, the substrate is rotated at a high speed after the application of the resin in order to shake off the excess resin. Even if it is done, the resin may drip on the side surface of the substrate, and depending on the situation, the resin may wrap around to the side opposite to the coated surface.

When two kinds of protective films on the recording surface side and the reading surface side overlap on the outer peripheral side surface of the substrate, the surface tension of the protective film 2 to be formed later is formed first, as shown in FIG. When the surface tension of the protective film 1 is smaller than the above, there is no problem because the resin does not rise due to the overlap of the two kinds of resin on the side surface of the substrate. However, as shown in FIG. 6, when the surface tension of the protective film 4 formed later is larger than that of the protective film 3 formed earlier, the protective film 4 formed later is repelled on the side surface of the substrate. As a result, the resin rises on the side surface of the substrate.

Therefore, in the above situation, when the protective film on the recording surface side is formed after the protective film on the reading surface side is formed, the surface tension of the protective film on the recording surface side causes the read surface to be formed first. Since the surface tension of the protective film on the side is higher than that on the side of the substrate, the resin on the side of the recording surface repels the resin on the side of the reading surface dripping on the side surface of the substrate, and thus the resin rises on the side surface of the substrate.

In the present invention, when the protective film is formed on the substrate by the spin coating method, in order to prevent the resin from dripping onto the side surface of the substrate and the wraparound of the resin to the side opposite to the coated surface, The surface tension is made smaller than the surface tension of the applied resin. By doing so, the applied resin for forming the protective film is repelled at the outermost peripheral edge portion of the substrate and does not drip onto the side surface of the substrate. Further, since the resin does not drip onto the side surface of the substrate, the two types of resin do not overlap on the side surface of the substrate even when the protective layer on the opposite surface is formed thereafter, and therefore the resin on the side surface of the substrate does not overlap. Occurrence of swell can be prevented. As described above, the surface tension of the protective layer forming resin on the reading surface side is 22 to 30.
Since it is about dyn / cm, the surface tension on the side surface of the substrate is 22d.
Preferably less than yn / cm, 20 dyn / c
More preferably, it is m or less.

As a method for reducing the surface tension on the side surface of the substrate, for example, a material having a low surface tension such as a surfactant is applied. As the surfactant to be used, those having a surface tension smaller than the surface tension of the protective film-forming resin to be applied may be used, and examples thereof include silicone-based surfactants and fluorine-based surfactants. Is a product of Shin-Etsu Chemical Co., Ltd. under the trade name of "KP-301", "KP-302", "KP-"
Examples thereof include silicone-based surfactants such as "305" and "KP-306". Also, since the surface tension of Teflon, which is a compound having —CF ₂ , is 19 dyn / cm, and the surface tension of a polymer in which CF ₃ is densely packed is 6 dyn / cm, a fluorine-based surfactant should also be used. You can

The optical disk protective film forming apparatus of the present invention comprises:
Before spin-coating the resin for forming the protective film, a surfactant is applied to the outer peripheral side surface of the substrate in order to reduce the surface tension on the outer peripheral side surface of the substrate. Increasing the number of manufacturing processes such as installation and lengthening the manufacturing time are problems in terms of productivity. Conventional spin coating equipment is generally equipped with electrostatic blow equipment that sprays clean air ions (ionized clean air) onto the substrate surface, before applying the resin for forming the protective film. The electrostatic blow is used to remove foreign matter on the substrate surface. Therefore, the protective film forming apparatus for an optical disc of the present invention is
As the manufacturing time is the same as before, the above-mentioned surfactant is applied.Therefore, in the electrostatic blowing process before coating the resin for forming the protective film on the substrate, electrostatic blowing is performed and at the same time, the surface activation is performed on the outer peripheral surface of the substrate. The agent can be applied.

[0019]

According to the present invention, the surface tension of the outer peripheral side surface of the substrate is reduced to 20 dyn / cm or less before the resin for forming the protective film is applied onto the substrate by the spin coating method, and then the protective film is formed. By forming the resin, it is possible to prevent the resin from dripping onto the side surface of the substrate and the wraparound of the resin to unnecessary areas, and as a result, it is possible to prevent the resin from rising on the outer peripheral side surface of the substrate. The yield in the manufacture of optical disks can be improved.

[0020]

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 is a plan view of an example of a protective film forming apparatus for an optical disc according to the present invention, which is seen from above.
Shows an elevation view from the side. Substrates are conveyed one by one from the disc supply cassette 1 of FIGS. 1 and 2 to the disc position for electrostatic blowing by the disc supply arm 2. FIG. 3 shows a schematic view of the electrostatic blow section of this apparatus. The substrate moves to the disk position 4 for electrostatic blowing shown in FIG. 3 and then rotates at 100 rpm or less, and the electrostatic blow nozzle 6 moves from the nozzle position A to the nozzle position B while spraying clean air ions on both sides of the substrate. To do. The exhaust air at this time is exhausted from the electrostatic blow exhaust duct 7. The surfactant coating device 8 includes a tank for storing the surfactant and a sponge-like nozzle 17 into which the surfactant is constantly penetrating. When the substrate moves to the disk position 4, the tip of the sponge-like nozzle 17 provided in the surfactant coating device 8 and the outer peripheral side surface 18 of the substrate come into contact with each other, and clean air ions are sprayed onto the substrate surface, and at the same time, the substrate is removed. Since the rotation starts, the surfactant stored in the tank of the surfactant applying device 8 can be applied to the side surface 18 of the substrate. In this example, as the surfactant applied to the side surface 18 of the substrate, a silicone-based surfactant manufactured by Shin-Etsu Chemical Co., Ltd. under the trade name "KP-306" was used.
After the electrostatic blow, the substrate is conveyed to the coater house 9 by the disc conveying arm 5, the resin is ejected onto the substrate from the resin ejection nozzle 10, and the excess resin is shaken off by the high speed rotation of the substrate to make the resin uniform on the substrate. It will be applied. The substrate coated with the resin is the ultraviolet transfer arm 11
Thus, the resin passes under the ultraviolet lamp, is irradiated with ultraviolet rays in the ultraviolet lamp house 12, and the resin is cured. The substrate on which the protective film has been formed in this manner is conveyed again to the electrostatic blow section 14 by the disc discharge arm 13 and electrostatically blown, and then conveyed to the disc discharge cassette 15. In this way, a commercially available resin for forming a protective film (made by Mitsubishi Rayon, trade name “UR” on 100 polycarbonate substrates (surface tension 46.6 dyn / cm (20 ° C.))
−4501 ”: surface tension 24.5 dyn / cm (20
)), The amount of resin discharged onto the substrate: 1.5 g, the rotation speed of excess resin for turning off: 3500 rpm, the time for turning off: 7
As a result of applying under the condition of seconds to form a protective film having a film thickness of 5 μm, no phenomenon of the resin wrapping around to the opposite side of the coated surface was observed. Further, with respect to the substrate manufactured in this manner, other commercially available protection is performed in the same manner as above except that the surface of the substrate on the opposite side is not coated with the surfactant on the outer peripheral side surface 18 of the substrate. Resin for film formation (Dainippon Ink,
Product name "SD-301": Surface tension 40 dyn / cm
(20 ° C.)) was applied under the conditions that the amount of resin discharged onto the substrate was 2.5 g, the rotation speed of excess resin was 2000 rpm, and the shake-off time was 7 seconds to obtain a protective film having a film thickness of 15 μm. The results of observing the cross section of the substrate thus produced are shown in FIG. 7. No resin swelling due to resin overlap on the outer peripheral side surface of the substrate was observed, and d2 was 12 microns.

[Brief description of drawings]

FIG. 1 is a plan view showing an outline of an example of a protective film forming apparatus for an optical disc of the present invention.

FIG. 2 is an elevational view schematically showing an example of a protective film forming apparatus for an optical disc according to the present invention.

FIG. 3 is a diagram schematically showing an example of an electrostatic blow unit of the optical disk protective film forming apparatus of the present invention.

FIG. 4 is a view showing a cross section of a conventional optical disc having a protective film formed on one surface.

FIG. 5 is a diagram showing a cross section of an optical disc in which a protective film having a small surface tension is formed after forming a protective film having a large surface tension.

FIG. 6 is a diagram showing a cross section of an optical disc in which a protective film having a large surface tension is formed after forming a protective film having a small surface tension.

FIG. 7 is a view showing a cross section of an optical disc having protective films formed on both sides according to the present invention.

[Explanation of symbols]

 1 Disc Supply Cassette 2 Disc Supply Arm 3 Electrostatic Blow 4 Disc Position 5 Disc Conveying Arm 6 Electrostatic Blow Nozzle 7 Electrostatic Blow Exhaust Duct 8 Surfactant Treatment Device 9 Coater House 10 Resin Discharge Nozzle 11 UV Conveying Arm 12 UV Lamp house 13 Disc ejection arm 14 Electrostatic blow 15 Disc ejection cassette 16 Operation panel 17 Nozzle 18 Side of substrate

Claims (3)

[Claims] 1. A protective film is formed on the substrate by setting the surface tension of the outer peripheral side surface of the optical disk substrate to 20 dyn / cm or less and then applying a resin for forming a protective film by spin coating. A method for forming a protective film for an optical disc, comprising: 2. The protective film is formed on the substrate by applying a surfactant to the outer peripheral side surface of the optical disk substrate and then applying a resin for forming the protective film by spin coating. And a method for forming a protective film on an optical disc. 3. A protective film forming apparatus for forming a protective film on an optical disk substrate by a spin coating method, wherein electrostatic blow is performed to remove foreign matter on the substrate before spin coating a resin for forming the protective film. A protective film forming apparatus for an optical disk, wherein a surfactant is applied to the outer peripheral side surface of the substrate while performing the above step.