JPH07213989A - Spin coating method for surface of synthetic resin substrate - Google Patents

Abstract

PURPOSE:To prevent a coating agent from overrunning to the back side of a substrate by keeping specified distance between the tip of a coating agent supply nozzle and the surface of a synthetic resin substrate. CONSTITUTION:A synthetic resin substrate, with its coating surface kept horizontally, is rotated at a low speed. The substrate, after being coated with a cure type coating agent, is then rotated at a high speed to get rid of the excessive coating agent, and the coating agent is cured. In this process, the viscosity of the coating agent is 30-200cps, and the distance between the tip of a coating agent supply nozzle and the surface of the synthetic resin substrate is 0.3-2mm. When the viscosity deviates from the range, a coating film with uniform thickness can hardly be obtained. If the distance exceeds 2mm, the coating agent discharged from the nozzle is repelled on the surface to form droplets, causing the undesirable overrunning of the coating agent onto the back of the substrate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for spin coating a surface of a synthetic resin substrate. More specifically, the present invention relates to a spin coating method suitable for forming a coating layer such as a protective layer on the surface of an optical disc having an optical recording layer provided on a transparent synthetic resin substrate.

[0002]

2. Description of the Related Art In recent years, write-once type, rewritable type and other optical recording media have been attracting attention as large capacity memories. An optical recording medium has a recording film on which signals are recorded formed on one surface (hereinafter referred to as the recording film side) of a circular transparent synthetic resin substrate (base material). It is performed by laser beam light from the opposite side (substrate side).
The scratches on the substrate hinder the recording and reproducing of information by laser light.

Therefore, in order to impart scratch resistance to the surface of the substrate, a transparent resin film (hereinafter referred to as a resin film) having a relatively high surface hardness such as an ultraviolet curable resin is formed. A similar resin coating is formed on the recording film side for the purpose of protecting the recording film. The resin film on the substrate side is called a hard coat, and the resin film on the recording film side is called a protective coat. A spin coating method is usually used as a method for forming the ultraviolet curable resin film on the surface of the substrate.

[0004]

In the spin coating method, a phenomenon (return) in which the coating agent goes around on the opposite side of the substrate (disk) may occur depending on the coating conditions. This occurs when the coating agent becomes liquid drops on the disc when the coating agent is supplied onto the substrate.

That is, spin coating is usually
While the substrate to be coated (hereinafter sometimes referred to as "substrate") is rotated at a low speed, the coating agent is supplied from the supply nozzle and the coating agent is placed on the surface of the substrate. Since the affinity is small, the coating agent may be repelled. The coating agent repelled by the surface of the synthetic resin substrate turns into droplets, which can be said to be low speed, but rolls on the surface of the rotating substrate, reaches the end of the substrate, and wraps around to the side edges and the back surface of the substrate. This will contaminate the parts that are not coated.

[0006]

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the problems can be solved by making the spin coating conditions special conditions, and It came to completion. The gist of the present invention is a synthetic resin in which a coating surface of a synthetic resin substrate is made substantially horizontal and is rotated at a low speed, a curable coating agent is applied, then the coating material is rotated at a high speed to shake off the coating agent, and then the coating agent is cured. In the method of spin coating on the surface of a base material, the viscosity of the curable coating agent is 30 to 200.
When the coating agent is applied, the gap between the tip of the coating agent supply nozzle and the surface of the synthetic resin substrate is set to 0.
A method of spin coating on the surface of a synthetic resin substrate is characterized in that it is 3 to 2 mm.

In the present invention, as a base material to be spin-coated, a transparent resin substrate such as a polycarbonate (PC) resin, a polystyrene resin, a polymethylmethacrylate (PMMA) resin, which is typically used as a substrate of an optical disc, is used. Can be mentioned. In the present invention, a curable resin such as an energy ray (for example, ultraviolet ray) curable type or a thermosetting type is used as a coating agent used for spin coating.

As the energy curable resin, a resin composed of a compound having a single or a plurality of acrylate or methacrylate groups, for example, a resin containing epoxy acrylate or urethane acrylate as a main component is preferably used. Further, as the thermosetting resin, silicone type, epoxy type or the like is used. In the present invention, the viscosity of the curable resin when applied is in the range of 30 to 200 cps (centipoise), preferably 50 to 100 cps.

If the viscosity is out of this range, it becomes difficult to obtain a coating having a uniform film thickness. The spin-coating conditions for applying the above-mentioned coating agent include keeping the coating forming surface of the resin substrate substantially horizontal and rotating the disk at 5 to 30 rpm, preferably 10 to 20 rpm, and the tip of the coating agent supply nozzle and the disk. The coating agent is applied from the outer circumference of the disc at a height (spacing) of 0.3 to 2.0 mm, preferably 0.5 to 1.5 mm.

When the height of the tip of the nozzle is larger than the above height, the coating agent discharged from the nozzle is repelled by the surface of the base material to easily form liquid droplets on the surface of the base material. It is not preferable because it causes a return to the surface. Other conditions for the spin coating are not particularly limited, but the inner diameter of the coating agent supply nozzle is generally 0.5 to 2 mm, preferably 0.5 to 1 mm. The number of rotations at the time of applying the coating agent varies depending on the diameter of the substrate, but the above number of rotations is for a substrate having a diameter of 150 mm or less.

The discharge pressure of the coating agent varies depending on the viscosity, nozzle diameter, etc., but is usually 1 to 1.5 kgf / tank pressure.
It is about cm ² . The tank pressure is a pressure applied to the tank containing the coating agent, and a filter or the like may be interposed between the tank and the nozzle, and does not directly represent the pressure at the nozzle. The linear velocity of the coating agent at the time of discharging from the nozzle varies depending on the nozzle diameter, but is usually 0.2
It is about 1 m / sec.

After applying the coating agent on the surface of the substrate, the substrate is rotated at a high speed to shake off the coating agent. In this step, a uniform thickness of the coating agent is obtained. High speed rotation is usually 1000-6000
It is carried out in the range of about rpm, and is selected depending on the viscosity, the film thickness to be obtained, and the like. The coating agent liquid film formed by spin coating may be cured by using a curing method suitable for each coating agent. For example, in the case of energy curing type, that is, ultraviolet curing type, ultraviolet rays are irradiated and electron beam curing type is used. If there is, an electron beam is applied, and if it is a thermosetting type, a method such as heat treatment is applied.

The thickness of the coat film formed after curing is about 0.5 to 100 μm, preferably about 1 to 50 μm in the case of a protective film for an optical disk. Further, it is preferably about 1 to 20 μm, and if it is made thicker than this, the substrate may be deformed due to the contraction stress of the coat film, and if it is too thin, durability such as hardness of the coat film is deteriorated, which is not preferable.

When the method of the present invention is applied to an optical disc or the like, it is applied to the surface of a synthetic resin substrate such as polycarbonate. In the case of an optical disc, there is a surface on which a recording layer such as a metal is provided on the substrate. The surface of this metal or the like may be coated by the method of the present invention. However, since the metal surface has good wettability, there is not much problem even if the distance between the nozzle and the metal surface is increased. Further, even when another resin layer is provided on the surface of the base material, the resin layer can be coated by the method of the present invention.

[0015]

EXAMPLE An example of the present invention will be described below with reference to 5.25 inches (1
An optical disk substrate (base material) having a size of 30 mmφ will be described, but the scope of the present invention is not limited by the following examples unless the gist thereof is exceeded.

Example 1 A rewritable type magneto-optical recording film made of an inorganic material was formed on a polycarbonate substrate having a diameter of 130 mmφ and a thickness of 1.2 mm, and an ultraviolet curable coating agent was formed on the opposite side (substrate side). The nozzle height was changed variously, and other spin coating conditions were fixed under the fixed conditions shown in Table 1 for spin coating. With respect to the prepared disc, the disc surface was observed by visual inspection to confirm whether or not the coating agent was returned to the opposite face of the disc. Table 2 shows the test results.

[0017]

[Table 1]

[0018]

[Table 2]

From the above results, the height between the coating agent supply nozzle and the disk is 2 mm or less, preferably 1.5 m.
By setting the thickness to m or less, the return of the coating agent to the surface opposite to the base material can be reduced.

[0020]

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to prevent the coating agent from returning to the surface opposite to the base material, and it is possible to increase the yield in the surface coating of a plate material such as an optical disk having a synthetic resin as a base material.

Claims (5)

[Claims] 1. A synthetic resin substrate in which a coating surface of a synthetic resin substrate is substantially horizontal and is rotated at a low speed, a curable coating agent is applied, the coating material is rotated at a high speed to shake off the coating agent, and then the coating agent is cured. In the spin coating method on the material surface, the viscosity is 30 to 20 as a curable coating agent.
The spin on the surface of the synthetic resin substrate is characterized in that the space between the tip of the nozzle for supplying the coating agent and the surface of the synthetic resin substrate is 0.3 to 2 mm when applying the coating agent of 0 cps. Coating method. 2. The spin coating method according to claim 1, wherein the curable coating agent is an ultraviolet curable resin. 3. The spin coating method according to claim 1, wherein the substrate has a diameter of 150 mm or less. 4. The spin coating method according to claim 1, wherein the low speed rotation is performed at 5 to 30 rpm. 5. Rotation at high speed is 1000 to 6000 rp
5. The spin coating method according to claim 1, wherein the spin coating method is performed at m.