JPH09161330A - Production of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve mechanical characteristics by applying a protective coating material by a spraying method on a optical disk surface and flattening the coating surface by ultrasonic vibration, then curing the same. SOLUTION: An acrylic UV curing resin is used as the coating material and a substrate is spray coated with this resin to 7μm thickness by an air atomizing method. The coating is then subjected to the ultrasonic vibration and is cured by irradiation with UV rays, by which a hard coating layer is formed on the incident surface of the substrate. An overcoating layer is formed on the surface of the metallic film formed on the substrate. In some cases, the coating material is diluted with a solvent to prepare a soln. of a solid content of 70wt.%. In other case, the coating material is formed of a silicon thermosetting resin and is diluted with the solvent to prepare the soln. of the solid content of 70wt.% and this soln. is cured by thermosetting of 100 deg.C×10min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc manufacturing method, and more particularly to an optical disc overcoating process and a hardcoating process.

[0002]

2. Description of the Related Art An optical disk comprises an optically transparent plastic substrate and a metal film formed on the plastic substrate. Ultraviolet rays are applied to the optical film for the purpose of protecting the metal film from oxidation and mechanical protection. A so-called overcoat treatment is performed in which protective coating is performed with a cured resin or the like. Further, the plastic substrate has a low surface hardness and is easily scratched, and is more likely to be charged with static electricity, so dust is likely to be generated, but these scratches and dust hinder the progress of laser light, which causes a data error. Therefore, a so-called hard coat, which is a protective coat, is also performed on the incident light side surface of the plastic substrate with an ultraviolet curable resin having an antistatic function. Generally, as a method for coating a substrate with a liquid material, spin coating, roll choro, spray coating, dip coating, etc. can be mentioned. Conventionally, the spin coating method has been used for overcoating and hard coating of optical disks.

[0003]

In the spin coating method, after the liquid coating material is dropped on the disk coating surface, the coating material is evenly spread over the entire surface to give a predetermined coating film thickness on the disk surface. Performs high-speed rotation and material shunting at several hundred to several thousand revolutions per minute with a vertical axis passing through the center of the disc as the axis of rotation. Therefore, as the protective coat processing time for the disk, the material dropping time and the high-speed rotation / material shaking-off time are required. Reducing the protective coat processing time per disc, that is, reducing the tact time directly contributes to the productivity of the optical disc.
However, in order to shorten the time using this spin coating method, there is a limit in obtaining a good protective coat with a predetermined film thickness, although there are differences due to properties such as viscosity of the coating material.

Further, since spin coating is basically performed for each sheet, there is a problem in productivity. In spin coating, most of the dropped coating material is thrown away in the high-speed rotation / shaking process. Although it is conceivable to recover and reuse the coating material discarded in this high-speed rotation / shake-off process, there is a problem that the cost of the device increases due to the inclusion of impurities and the installation of recovery equipment. As a spin coater, a high-speed and stable rotation mechanism is required, and at present, there are problems of complicated mechanism and high cost for the processing capacity of the apparatus. The problems of the productivity of the protective coat, the use efficiency of the coat material, and the initial cost of the apparatus as described above cause the price increase of the optical disc itself, which is disadvantageous to both the producer and the consumer.

The present inventors have confirmed that the above problems can be solved by applying the spray coating method to the protective coating forming method for an optical disk in Japanese Patent Laid-Open No. 7-201092. Furthermore, in order to form a protective coat using the above-mentioned spray coating method, optimum conditions must be set, and the range has been found (Japanese Patent Application No. 6-169112).
This made it possible to flatten the coat surface. However, due to the range of optimum conditions, the conventional spray coating method reduces the degree of freedom in the process and places a large limitation on the protective coating material. If the optimum condition range is not met, the flatness of the coat surface will be lost. A disk having a hard coat surface with poor flatness causes a signal error due to refraction and scattering of laser light. Further, in the case of a disc having a poor flatness of the overcoat surface, the coating film thickness has a distribution, which adversely affects the mechanical properties such as the warp of the disc and is ugly in appearance.

[0006]

In view of the above problems, the inventors of the present invention have conducted extensive studies, and as a result, focused on the fact that the coating surface of the protective coating material is flattened by ultrasonic vibration, Completed That is, the present invention is characterized in that a protective coating material is applied on the surface of an optical disc by a spray method, and then the coated surface is flattened by ultrasonic vibration, and then cured to form a protective coating layer on the surface of the optical disc. The gist is a method of manufacturing an optical disc. This will be described in more detail below.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The frequency of ultrasonic vibration used in the present invention is preferably 10 kHz or more and 1 MHz or less. If the frequency is less than 10 kHz, the energy density transmitted to the coating film is not sufficient, and it becomes difficult to flatten the coating surface. If the frequency exceeds 1 MHz, the displacement amplitude due to ultrasonic waves becomes too small to flatten the coating surface. It becomes difficult to contribute. The time for applying ultrasonic vibration to the coating film is preferably 0.1 seconds or more and 10 seconds or less. If the time is shorter than 0.1 seconds, the flattening of the coat surface does not proceed sufficiently, and if the time exceeds 10 seconds, the fine pattern such as pits and grooves formed by injection molding on the surface of the plastic substrate is likely to be deformed. . The ultrasonic energy applied to the coating film is 0.1 W / cm ² or more, 3
It is preferably W / cm ² or less. 0.1 W / cm
^When the energy is less than ² , flattening of the coat surface does not proceed sufficiently, and when the energy exceeds 3 W / cm ² , fine patterns such as pits and grooves formed by injection molding on the surface of the plastic substrate are likely to be deformed.

Ultrasonic vibrations on the coating film are transmitted from the plastic substrate through the diaphragm. At this time, the plastic substrate needs to be kept horizontal, but the plastic substrate may be rotated at the same time. Rotation speed is 10
-100 rpm, preferably 30-100 rpm.

The protective coating material may be of a known ultraviolet-curing type or thermosetting type, and generally, liquid acrylic resin, silicone resin and the like are exemplified. Also,
It may be of a solvent type in which a solvent is added if necessary. UV curing or heat curing of the coating material may be performed under known curing conditions. The viscosity of the coating material used in the present invention is preferably 2 cP to 100 cP at room temperature, and when a coating material having a viscosity of more than 100 cP is used, the coating surface leaves a particle state of spray as it is,
It becomes rough and it becomes difficult to flatten with ultrasonic waves,
If it is less than 2 cP, it becomes difficult to mount the resin amount required for a predetermined film thickness on the substrate. The thickness of the protective coating layer is preferably 1 μm to 15 μm, and if it is less than 1 μm, the scratch resistance is not sufficient, and if it exceeds 15 μm, there is a problem of warpage of the disk due to curing shrinkage.

The atomizing method in the spray coating method according to the present invention may be a known method such as an air atomizing method or an airless atomizing method.

[0011]

EXAMPLES Next, examples of the present invention and comparative examples will be described. Examples 1 to 6 A silicon nitride film 1100Å and a TbFeCo alloy amorphous film 2 were formed on a 3.5 inch diameter MO polycarbonate substrate by a sputtering method.
A 50 Å film, a 300 Å silicon nitride film, and a 500 Å aluminum reflective film were sequentially formed to form a metal film. Then, under the conditions shown in Table 1, a protective coat was formed on this substrate as follows. Acrylic UV curable resin was used as the coating material, and was spray-coated to a thickness of 7 μm by the air atomization method, and then Table 1
Ultrasonic vibration is applied under the conditions of, and further cured by ultraviolet irradiation to hard coat layer on the light incident surface of the substrate (H.
C.) and an overcoat layer (abbreviated as OC in Table 1) on the metal film surface of the substrate. In addition, in Example 4, the coating material was diluted with a solvent to prepare a solution having a solid content of 70% by weight. Further, in Example 5, the coating material was a silicone-based thermosetting resin, which was diluted with a solvent to obtain a solid content of 70.
The solution was made into a weight% solution and cured by heat curing at 100 ° C. for 20 minutes.

As the flatness of the substrate after forming the protective coat,
Ra (center line surface roughness) and Wa (center line surface waviness) were measured for each of 10 substrates. Note that Ra and Wa
Each of the measurement methods was performed by a stylus type surface roughness meter. Table 1 also shows the measurement results. Furthermore, information is recorded / reproduced for 10 optical disks consisting of this protective coat forming substrate, and the byte error rate (BER)
Was measured. The results are also shown in Table 1.

[0013]

[Table 1]

Comparative Example 1 An optical disc was prepared under the same conditions as in Example 1 except that the ultrasonic vibration treatment was not applied to the coated surface. The results of measuring the flatness are also shown in Table 1. In addition, tracking error occurred due to laser scattering due to coating roughness, and BER could not be measured.

[0015]

According to the present invention, it becomes possible to form a protective film having an appropriate film thickness and a good flatness on the coat surface by a spray method, which is inexpensive and has good information recording / reproducing characteristics. An optical disc can be provided.

Claims (1)

[Claims] 1. A protective coating material is applied to the surface of an optical disc by a spray method, and then the coated surface is flattened by ultrasonic vibration and then cured to form a protective coating layer on the surface of the optical disc. Optical disk manufacturing method.