JPH07109657B2 - Light disk - Google Patents

Description

The present invention relates to an optical disc capable of reproducing an information signal by irradiating a light beam, and more particularly to a protective film for a substrate.

[Conventional technology]

Generally, PC (polycarbonate resin) and PMMA are used as the substrate material for optical discs from the viewpoint of productivity and cost.
A thermoplastic resin such as (polymethylmethacrylate resin) or a thermosetting resin such as an epoxy resin is used.
A substrate made of such a plastic material, that is,
On one surface of the plastic substrate, a track composed of a pit row representing an information signal is formed, and by irradiating a light beam from the other surface to scan the track, the information signal can be reproduced.

In such an optical disc, in order to reproduce the information signal satisfactorily, it is necessary that the surface of the plastic substrate on which the light beam is irradiated, that is, the light beam irradiation surface is uniformly flat and dust and the like are not attached. .

However, in the prior art, the light beam irradiation surface is exposed, which often causes scratches, dust, and the like. Further, the surface of the substrate may be erroneously contaminated by a solvent or the like. When the light beam irradiation surface is scratched, the light beam irradiated there is diffusely reflected, and the level of the reproduced information signal fluctuates. Also, if dust or solvent adheres, the amount of light beam transmission changes and reproduction is performed. Level fluctuations occur in the information signal. In particular, when a solvent or the like is attached, the plastic substrate is dissolved by this, and the light beam irradiation surface is damaged. If dust or solvent adheres to them, they can be wiped off.However, since the plastic substrate is relatively soft, the light beam irradiation surface is easily scratched, and the light beam irradiation surface is charged and dust is more likely to adhere to it. It will be easier.

On the other hand, it is known to provide a protective film on the light beam irradiation surface side of the plastic substrate. As an example, Shokai 54
Japanese Patent Publication No. 179104 discloses an optical disk in which a mixture of a silicon compound and a vinyl compound is used as a protective film, and an antifogging property and an abrasion resistance of a light beam irradiation surface are improved.

[Problems to be solved by the invention]

However, such a mixture is a thermosetting resin, and in order to form a protective film by this, it is necessary to apply heat to the plastic substrate and then to cure it. It takes time and there is a problem in the productivity of the optical disk. Moreover, since the heating temperature for curing is relatively high, the plastic substrate is thermally deformed.

In addition, since the silicone resin is easily immersed in a strong alkaline solvent, its hardness is too high, and its coefficient of thermal expansion is different from that of the plastic material, so if the plastic substrate expands or contracts due to temperature changes, it will be protected. There are problems that the film is cracked and the protective film is peeled off.

An object of the present invention is to solve the above problems, and to provide an optical disk having excellent scratch resistance on the light beam irradiation surface side and improved performance and productivity.

[Means for solving problems]

To achieve the above object, the present invention provides a protective film made of a solvent-type ultraviolet curable resin on the light beam irradiation surface side.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of an optical disk according to the present invention, in which 1 is a plastic substrate, 1a is a recording surface, 1b is a light beam irradiation surface, 2 is a recording film, and 3 is a protective film.

In the figure, the plastic substrate 1 is, for example, a PC or PMM.
The recording surface is made of a thermoplastic resin such as A or a thermosetting resin such as an epoxy resin, and one surface 1a thereof is a recording surface on which a screw-shaped or concentric track made of a pit row is formed. A recording layer 2 is provided on the recording surface 1a.

The other surface 1b of the plastic substrate 1 is a surface irradiated with a light beam, and the light beam irradiation surface 1b is provided with a protective film 3. The protective film 3 is made of a solvent type ultraviolet curable resin, has a high hardness, and has an excellent antistatic effect as compared with the plastic substrate 1. As a result, scratch resistance on the light beam irradiation surface 1b side is improved, adhesion of dust and the like due to charging can be prevented, and corrosion by a solvent is prevented.

The solvent-type ultraviolet curable resin is excellent in mechanical strength as described above, but when it is used as the protective film 3,
The shrinkage rate upon curing by ultraviolet irradiation must be small (about 15% or less), the adhesion of the formed film to the plastic substrate 1 is good, and the refractive index and the thermal expansion coefficient are the same as those of the plastic substrate 1. It should be comparable and not corrosive to solvents. As a solvent-type UV-hardening resin that satisfies these conditions, the protective film material is dissolved in any one solvent such as toluene, acetone, methyl ethyl ketone, methyl alcohol, ethyl alcohol, propyl alcohol, or a mixed solvent of two or more kinds. However, it depends on the material of the plastic substrate 1,
The solvent must be selected and used. Here, as one specific example, when the plastic substrate 1 is made of PC, UVX-HM.185-2 manufactured by ThreeBond Co., Ltd. is a solvent-type ultraviolet curable resin that satisfies the above conditions as the protective film 3. is there.

Next, the method and performance of forming a protective film for an optical disc using the solvent-type ultraviolet curable resin as the protective film 3 will be described.

First, regarding the protective film forming method, the light beam irradiation surface of the plastic substrate made of PC is spin-coated,
Solvent type UV curable resin (previous UVX-HM / 185-2) 3-5
150mW / cm ² after coating with a thickness of μm and predrying for 1 minute in an atmosphere of 80 ° C (thus removing the solvent)
The ultraviolet ray of 10 is irradiated for 10 seconds to cure the solvent type ultraviolet curable resin. Thereby, a protective film is obtained.

When various tests were performed on the protective film formed in this manner as follows, extremely good results were obtained.

A cross-hatch test (100/100) was carried out in which the protective film was cut into 100 sections, and these were peeled off with cellophane tape, but no peeling part was found. in this way,
The adhesion to the PC board was extremely good. Also, if the temperature is
1000 hours or more in an atmosphere of 60 ° C and 90% humidity, with a temperature of 0
No change in adhesion was observed even in an environmental test in which the sample was left in an atmosphere of 0 ° C and a humidity of 0% for 500 hours or more.

A steel wool (# 0000) test was conducted in which the surface of the protective film was rubbed 5000 times under a load of 200 g, but no scratch was found on the surface. This shows that the protective film has sufficiently high scratch resistance.

We measured the retardation change (birefringence) associated with contraction, but there was no problem because the retardation increased by a few nm. The light transmittance (transparency) of the protective film is
It was about the same as the PC board.

A thermal cycle test was conducted in which the temperature was changed from -40 ° C to + 90 ° C in a 2-hour cycle, and this was repeated 250 times, but there was no change in adhesion or retardation, and there was no crack on the protective film. It never happened. Further, a solvent resistance test was conducted, but the protective film was not corroded by all the solvents used.

As described above, as the protective film on the light beam irradiation surface side of the plastic substrate made of PC, the above solvent-type ultraviolet curable resin (UVX-HM • 185-2) is suitable. When this solvent-type UV curable resin was applied to a PC substrate, the solvent dissolved the surface of the PC substrate, causing a so-called anchor effect in which the UV curable resin penetrates into the PC substrate, thereby forming the PC substrate. It has good adhesion to the protective film. In addition, this solvent-based ultraviolet curable resin has a hydrophilic functional group, and its water permeability is reasonably larger than that of the PC substrate. As a result, water does not stay at the interface with the PC board and peel off from the PC board.This also improves the adhesion to the PC board, and compared to PC boards. As a result, an antistatic effect can be obtained.

[Effects of the Invention] As described above, according to the present invention, the scratch resistance on the light beam irradiation surface side of the plastic substrate is, of course, significantly improved, and the adhesion of the protective film to the plastic substrate, It also has excellent scratch resistance, shrinkage and transparency.
The protective film itself is also excellent in solvent resistance, and since the protective film can be formed in an extremely short time, it is possible to obtain an effect that the productivity of the optical disk capable of maintaining excellent performance is significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an optical disc according to the present invention. 1 ... Plastic substrate, 1a ... recording surface, 1b ... light beam irradiation surface, 2 ... recording film, 3 ... protective film.

Claims (1)

[Claims] 1. A protective film made of a solvent-type ultraviolet curable resin having a light beam irradiation surface dissolved by a solvent is provided on the light beam irradiation surface of the transparent plastic substrate opposite to the recording surface. Light disk to do.