JPH0887779A - Coating method and coating device for optical recording medium - Google Patents

Abstract

PURPOSE: To make it possible to easily decrease the magnitude of the curling of a recording medium while maintaining the surface appearance of a resin by heating a substrate prior to application of an active ray curing resin on this substrate. CONSTITUTION: The optical recording mediums placed on a turn table 8 are coated with the resins to a circular shape on their inner peripheral parts by a dispenser 9 while the media are kept rotated at a low speed of about 60rpm. The recording media are thereafter rotated at a high speed of about 1000 to 6000rpm, by which the resins are applied uniformly to the entire surface of the substrates. The optical recording media placed on a transporting tray pass together with the tray under a UV irradiation device 11 and the active ray curing resins on the media cure. The temp. of the optical recording media is kept by the heat of the transporting tray during this time. The optical recording media are thereafter discharged via another arms, etc., by which the optical recording media are cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method and a coating apparatus for forming a hard coat and / or a protective coat of an optical recording medium for recording, reproducing and / or erasing information by laser light or the like.

[0002]

2. Description of the Related Art In recent years, an optical recording medium for recording, reproducing and / or erasing high density information by using a light beam such as a laser beam has attracted attention. Among optical recording media, magneto-optical disks capable of rewriting information have already been put into practical use and the market is expected to expand. Generally, an optical recording medium is prepared by forming a recording layer on the guide groove of a transparent disc-shaped resin substrate such as polycarbonate, polymethylmethacrylate, or amorphous polyolefin having a guide groove on one side by a sputtering method or the like. At this time, if the surface of the recording layer or the surface of the substrate opposite to the guide groove surface is scratched, it becomes impossible to record and / or reproduce a correct signal. Therefore, the surface of the recording layer or the surface of the substrate may be scratched. A resin film is often provided for the purpose of prevention.

As the resin, an actinic ray curable resin having good workability such as an ultraviolet curable resin is generally used. When an actinic ray curable resin is irradiated with an actinic ray such as an ultraviolet ray or an electron beam to cure the resin, the resin undergoes curing contraction and its volume is reduced. The curing shrinkage depends on the type of resin, but it is about 5% for a small amount and about 15% for a large amount. When an actinic ray curable resin having such a property is applied onto an optical recording medium substrate and cured, a warp having a concave resin coating side occurs due to curing shrinkage of the resin. Since the warp of the optical recording medium substrate causes a recording / reproducing error, it is desired that the warp size be set to a value as small as possible, which is approximately 5 mrad or less.

As a method for reducing the warp of an optical recording medium, Japanese Patent Laid-Open Nos. 1-10445 and 2-1933 are available.
Japanese Patent No. 41 discloses a method of reducing the warpage by reducing the curing shrinkage of the actinic radiation curable resin itself. However, the above-mentioned method has a drawback in that the resin used is limited and other properties required as a coating agent are often sacrificed.

Further, Japanese Patent Laid-Open Nos. 1-269259 and 1-271944 disclose a method of adjusting the warp by using a coating layer having a multi-layer structure and using resins having different characteristics. However, the above-mentioned method has a drawback in that it takes time and effort during coating, which leads to an increase in cost, and that the resin used is limited.

Further, JP-A-3-263625 and JP-A-4-67332 disclose methods for reducing warpage by balancing the stresses of the hard coat and the protective coat. However, in the above method, even if the balance is right after the production and the warpage is small, a large warpage occurs when the balance is lost and one of the stresses becomes large in the long-term, so that the long-term reliability is considered. There was a flaw.

To solve this problem, Japanese Patent Laid-Open No. 4-34
Japanese Patent No. 5936 discloses a method of irradiating ultraviolet rays while making a temperature difference in a thickness direction or a surface inner diameter direction of one surface of a substrate. As a specific method, hot air is blown from the upper portion of an optical recording medium substrate. There is disclosed a method of reducing warpage by irradiating ultraviolet rays while uniformly heating the entire substrate by the method. According to this method
There is no limitation on the ultraviolet curable resin used, and the degree of warpage of the optical recording medium can be easily set to 5 mrad or less. However, in this method, since the substrate is heated by blowing hot air after coating, appearance defects such as wrinkles and streaks occur on the surface, and the ultraviolet curable resin is exposed to a higher temperature than necessary. However, there is a drawback in that the physical properties of are adversely affected.

[0008]

The problem to be solved by the present invention is to solve the above-mentioned drawbacks associated with the heating of the substrate during the irradiation of ultraviolet rays, and to make it easy to light the resin while maintaining the surface appearance of the resin. An object of the present invention is to provide a coating method for an optical recording medium and a coating apparatus capable of reducing the amount of warpage of the recording medium.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and involves heating a substrate before applying an actinic ray-curable resin onto the substrate, and further applying an actinic ray to the substrate. A method for coating an optical recording medium, characterized in that the substrate is continuously or intermittently heated or kept warm from the lower side until the curable resin is applied and the active ray is irradiated, or such coating is performed. To provide a coating device for.

The coating method of the present invention comprises a protective coat for protecting the recording layer formed on the guide groove surface of the substrate of the optical recording medium and / or a hard coat for protecting the substrate surface opposite to the guide groove surface. Applied to the coat. A spin coating method is preferable as a means for performing these coatings.

The actinic ray-curable resin used in the coating of the present invention is a resin which is cured by irradiation with actinic rays such as ultraviolet rays and electron beams, and the cured product thereof is on the surface opposite to the recording layer and the guide groove surface. As long as it has a hardness sufficient to prevent scratches on the substrate surface, it can be used without particular limitation, but one having a low curing shrinkage is preferable, and actinic ray curing used as a hard coat The mold resin is more preferable if the cured product has excellent laser light transmittance.

The cause of the warp of the optical recording medium substrate after curing of the actinic radiation-curable resin is that the curing shrinkage during resin curing acts as a tensile stress on the optical recording medium substrate. When the temperature of the substrate is set higher than the ambient temperature during resin curing, the tensile stress exerted by the cured resin is relaxed due to shrinkage during cooling of the substrate. As a result, the warp of the optical recording medium substrate at room temperature is reduced.

In the present invention, this substrate is heated before the actinic radiation curable resin is applied. As a method for this, there is a method of passing through a heating furnace, blowing hot air, using a turntable for holding the substrate as a hot plate, and so long as the method can heat the substrate to a predetermined temperature, the heating method is Although there is no limitation, a method of blowing hot air is preferable because it can be effectively heated and the apparatus is simple.

Although there is an effect of reducing the warp only by heating before applying the resin, in order to further increase the effect, the substrate is kept until the actinic ray curable resin is applied and the actinic ray is irradiated. It is preferable to continuously or intermittently heat or keep the temperature from the lower side so that the substrate temperature is not lowered until the time of irradiation with actinic rays. At this time, if heated by blowing hot air from above, the applied resin will be exposed to unnecessarily high temperature, and the appearance of abnormalities such as streaks and wrinkles will occur on the applied surface due to the effect of wind. It is preferable to heat.

The method of heating or keeping heat from the lower side is not particularly limited, but for example, a method of heating a turntable on which a substrate is placed like a hot plate is preferable. After heating before applying the resin to the substrate,
Since the temperature of the substrate decreases with the lapse of time and the effect of reducing the warp decreases, it is preferable to continuously perform the heating before applying the resin and the subsequent heating or heat retention from the lower side of the substrate.

Since the optimum value of the substrate heating temperature differs depending on the curing shrinkage ratio, the film thickness, the thickness of the substrate, the material of the substrate, etc. of the actinic ray curable resin used, it is necessary to set it at each time. Polycarbonate, which is generally used as a substrate material for optical recording media, has a thermal expansion coefficient of about 7 × 10 ⁻⁵ , and a length change of about 0.035% can be obtained with a temperature change of 50 ° C. This value is sufficient to relieve the stress between the substrate having a thickness of 1.2 mm and the actinic radiation curable resin layer having a thickness of about 2 to 20 μm on the substrate. Further, the coating apparatus for an optical recording medium of the present invention is preferably a spin coating apparatus, which is an apparatus having a heating device for heating the above-mentioned substrate.

[0017]

The present invention will be described in more detail below with reference to the drawings. FIG. 1 schematically shows an example of the coating apparatus for an optical recording medium of the present invention. This apparatus is a spin coater, and has a substrate heating portion (1), a resin spin coating portion (2), and an ultraviolet ray irradiation portion (3). The substrate heating part (1) is provided with a turntable (5) and a hot air blower (4), and the spin coat part (2) is provided with a turntable (8) and a dispenser () for dropping resin at a predetermined position for a predetermined time. 9) is provided. The ultraviolet irradiation part (3) is provided with an ultraviolet irradiation device (11) and a carrying tray (1) for carrying an optical recording medium thereunder at a predetermined speed.
0) is provided.

The optical recording medium is adsorbed by the substrate adsorbing portion (7) of the conveying arm (6) and conveyed between the respective parts. The optical recording medium is placed on the turntable (5) of the substrate heating portion (1) by the transfer arm (6). The optical recording medium on the turntable is heated by the hot air blown from the hot air blower (4) while rotating. The heated optical recording medium is placed on the turntable (8) at the spin coat site (2) by the transport arm (6). A heating wire, like a hot plate, is embedded in the turntable (8) and can be heated to an arbitrary temperature.

The optical recording medium placed on the turntable (8) is rotated at a low speed of about 60 rpm, and the resin is circularly applied to the inner peripheral portion from the dispenser (9), and thereafter, at a speed of about 1000 to 6000 rpm. By rotating at high speed, the resin is evenly applied to the entire surface of the substrate,
The temperature is maintained by the heat from the turntable (8) heated through this process.

Next, the optical recording medium is transferred to the transfer arm (6).
Then, it is placed on the carrier tray (10) of the ultraviolet irradiation site (3). This transport tray (10) can also be heated to an arbitrary temperature by the same mechanism as the turntable (8). The optical recording medium placed on the transport tray passes under the ultraviolet irradiation device (11) together with the tray, and the actinic ray curable resin film on the medium is cured. During this time, the temperature of the optical recording medium is maintained by the heat of the carrying tray. After that, the optical recording medium is ejected via another arm or the like, and the optical recording medium is cooled.

The above is merely an example of the coating apparatus of the present invention, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. For example, the substrate heating portion (1) can be heated not only by the hot air blower but also by another heating device, or two or more types of heating devices can be used together. Turntable (5) turntable (8)
It is also possible to use a hot plate as in the above. The entire substrate heating part (1) may be provided in a heating furnace to heat the entire part. Even in the spin coat part (2), the heating from the lower side may be performed directly without using a turntable. Further, it is also preferable to provide a nitrogen substitution mechanism on the carrier tray and perform actinic ray irradiation in a nitrogen atmosphere to prevent oxygen from inhibiting the effect. Further, the ultraviolet irradiation device (11) is not limited to ultraviolet rays, and may be another active ray, for example, an electron beam irradiation device.

Next, an example in which an optical recording medium is coated using the coating apparatus of the present invention described above will be described.

(Example) A 3.5-inch polycarbonate optical disk substrate was placed on a turntable (5), and 10
While rotating the disk at 0 rpm, the disk was heated for the time shown in Table 1 by a hot air blower (4) which blows out hot air of about 150 ° C. Next, this substrate was placed on the turntable (8) by the transfer arm (6). The temperature of the turntable (8) at this time is shown in Table 1. While rotating the disc at a low speed of about 60 rpm, the ultraviolet ray curable resin (“Dicure Clear EX-911” manufactured by Dainippon Ink and Chemicals, Inc.) was circled from the dispenser (9) to a disc radial position of 20-25 mm After applying 3g, apply the turntable (8) at 2000rpm for 3
The disk was rotated for 2 seconds to coat the resin on the entire surface of the disk.
The film thickness at this time is about 15 μm.

Next, this substrate was placed on the transfer tray (10) by the transfer arm (6). Carry tray (1
The temperatures of 0) are shown in Table 1. Furthermore, conveyer speed is 10 m / min under the ultraviolet irradiation device (11) (emission length 250 mm, output 3 kw, with cold mirror).
The sample was prepared by passing the resin at a conveying speed of 3 to cure the resin. The maximum tilt angle (TILT) of the prepared sample was measured by a mechanical property evaluation device (manufactured by Shin Denshi Kogyo Co., Ltd.) according to the ISO standard of the optical disc, and the results are shown in Table 1.

All were within 5 mrad, which is the standard of ISO. Although only the heating of the substrate before applying the resin as in Example 3 in Table 1 has a considerable effect of reducing the warp, the subsequent heating further increased the effect as in Examples 1 and 2. Further, when the appearance of the coating surface of the prepared sample was observed, it was found that there was no streak or uneven coating, and there was no discoloration of the resin, and the appearance was very beautiful.

(Comparative Example 1) A sample was prepared in the same manner as in the example, except that the heating before applying the resin was not carried out, and the substrate was heated by blowing hot air of 150 ° C for 10 seconds after the application. The results of the maximum tilt angle of the sample are shown in Table 1 in the same manner as in the example. As shown in Table 1, although the effect of improving the warp is seen, the appearance of the coating surface was examined, and it was observed that streaks were observed, the resin was locally raised, or part of it was extremely thin. The surface of the coating was abnormal due to wind.
Also, the color of the coating surface was considerably yellow due to the high temperature exposure.

(Comparative Example 2) A sample was prepared in the same manner as in Example except that no substrate heating was performed during the coating process. The results of the maximum tilt angle of the sample are shown in Table 1 in the same manner as in the example. As compared with the case where the substrate is heated, a significantly large warp occurs, which exceeds the ISO standard of 5 mrad.

(Comparative Example 3) A sample was prepared in the same manner as in the example except that the heating by the hot air blower before coating the substrate was not performed and only the subsequent heating by the turntable and the transport tray was performed. The results of the maximum tilt angle of the sample are shown in Table 1 in the same manner as in the example. Although a slight reduction in warpage can be seen as compared with Comparative Example 2, the improvement effect is small and it can be seen that heating before coating the substrate is indispensable.

[0029]

[Table 1]

[0030]

As described above, by applying a resin coating to an optical recording medium using the apparatus and method of the present invention, an optical recording medium with less warp and a clean surface appearance can be obtained. Further, since the effect of the present invention does not depend on the type of resin, it is not necessary to sacrifice the characteristics of other coatings for the purpose of reducing the warpage due to the coating, so that it is possible to obtain a coating film with well-balanced characteristics. .

[Brief description of drawings]

FIG. 1 is a schematic view of a coating apparatus of the present invention.

[Explanation of symbols] 1 substrate heating part 2 spin coating part 3 ultraviolet irradiation part 4 hot air blower 5 turntable 6 transfer arm 7 substrate adsorption part 8 turntable 9 dispenser 10 transfer tray 11 ultraviolet irradiation device

Claims (4)

[Claims] 1. A method for coating an optical recording medium, which comprises heating the substrate before applying the actinic radiation curable resin onto the substrate. 2. The optical recording medium according to claim 1, further comprising a step of heating the substrate from the lower side continuously or intermittently after applying the actinic ray curable resin and before irradiating the actinic ray. Coating method 3. A coating device for an optical recording medium having a mechanism for heating a substrate before applying a resin onto the substrate. 4. The optical recording according to claim 3, further comprising a mechanism for coating the substrate with an actinic ray curable resin and heating the substrate continuously or intermittently from the lower side until the actinic ray is irradiated. Media coating equipment