JPS61267950A - Optical disk - Google Patents

Abstract

PURPOSE:To obtain the titled one-face recording optical disk without generating waviness in the lapse of time by using 1,2-polybutadiene which hardly absorbs moisture as a protective film. CONSTITUTION:Many pits 3 are cut on a part of a discoid substrate and an A reflective film 4 is formed thereon by sputtering. A protective film 5 consisting of 1,2-polybutadiene is further formed on the reflective film 4. Since polycarbonate used as the material of the substrate on the surface has a low coefficient of moisture absorption, 1,2-polybutadiene which hardly absorbs moisture is used as the protective film to prevent the ageing waviness of the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protective film used for an optical disc on which information signals such as video or audio are recorded at high density.

[Technical background of the invention and its problems]

Generally, optical discs such as video discs or digital audio discs have optical information engraved on their surfaces as many minute bits. The compact disc, which is one of these optical discs, has a metal reflective film deposited on the recording area recorded by minute pits on the disc. In order to prevent the reflective film from being damaged during subsequent handling, it is usually overcoated with a protective film made of photocurable or hot-melt material, and a label is printed on the snow by screen printing as a single-sided disc. Manufactured. In this case, the disc base material should be one that has good transparency when read by the pickup laser beam during playback, one that has excellent heat resistance from the viewpoint of the durability of the disc, and one that has moisture, which is considered to be the cause of warping and twisting of the disc. Polycarbonate (PC)
.

Polymethyl methacrylate (PMMA), poly-
4-) f-rupentene-1, styrene-acrylonitrile (As), polyamide (FA), polymethylpentene, polystyrene (ps), polypropylene (
pp), polyvinyl chloride (PVC), polyvinyl chloride acetate (PVCA), saturated polyester, epoxy (BP), etc., but polycarbonate is generally used particularly from the viewpoint of transparency and low hygroscopicity. The reflective film has a reflectance of 70 to 9
0%, and usually an At vapor-deposited film or an At sputtering film, which is inexpensive to manufacture, is used.

However, since these reflective films are extremely soft, they are susceptible to damage during handling, and all this damage causes dropouts. Therefore, the synthetic resin is preserved on the surface of the reflective film! ig
It is put into practical use by overcoating it to prevent damage, then irradiating it with laser light from the back side, and detecting a signal based on the change in the amount of reflected light.

The protective film is usually provided by spray coating with solvent-based acrylic paint, spin cording or roll coating of photocurable acrylic liquid resin, epoxy liquid resin, or the like. However, polycarbonate, which is the base material on the front surface, has a low moisture absorption rate of 0.3% or less, whereas acrylic or epoxy resin, which is the protective film material on the back side, has a high moisture absorption rate.
Due to this imbalance, there is a problem in that the disk becomes undulating over time even if it is initially flat. Discs with large undulations have a negative effect on tracking performance during playback.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a single-sided recording optical disc that does not cause waviness over time.

[Summary of the invention]

The present inventors have completed the present invention as a result of extensive research in order to prevent the above-mentioned drawbacks in single-sided recording type optical discs. In other words, the present invention replaces the conventional protective film material that causes disk waviness with a material that is almost non-hygroscopic.
．． This method is characterized by using 2-polybutadiene. Preservation sg of 1,2 polybutadiene used in the present invention
The thickness of t and te is preferably between 0.1 and 0.3 cm,
If the thickness is less than 0.1, there is a possibility of damage due to strength issues. Moreover, if the thickness is 0.3 or more, there is a risk that the weight balance will be impaired. The method of providing the protective film is not particularly limited, and may be applied using a spinner, hot melt, or the like.

[Embodiments of the invention]

Embodiment 1 FIG. 1 is a sectional view of a compact disc (1) of the present invention, in which a large number of pits (3
), and a K At reflective film (4) is formed thereon by sputtering. Further, on this reflective film (4), as a retention film (5), 20 parts by weight of 1.2 polybutadiene (trade name, JSR, 805, manufactured by Japan Synthetic Rubber Co., Ltd.) and 100 parts by weight of n-hexane were mixed and heated at 50°C. It is made by stirring and dissolving it while heating, and then applying it with a spinner. The number (6) is 7/Tahor.

Example 2. ~5゜Constructed in the same manner as in Example 1, and using JSR as above with the protective film (5)
RB810. J8RRB820. J8R 几 f3sao,
, 20 parts by weight each of r8RRB840, and 100 parts of normal hexane! Amounts of each were mixed, heated and melted at 50°C, and applied.

Next, the compact disc (1) formed above was subjected to an accelerated deterioration test, and the results are shown in Table 1. The condition is 65
℃ in 95% BH for 7 days, and the deformation and measurement of waviness was carried out at a distance 55 degrees from the center of the base of the disk shown in Figure 1.
The unevenness of the disk surface in the center direction at the 5■ position was investigated and the maximum value of the value between the peaks (Peak to Peak) was recorded.

[Comparative Example 1] Table IK shows the results of an accelerated deterioration test performed on a protective film made of a conventionally used photocurable acrylic resin as described above.

[Example 6.7] Polycarbonate disk base, protective film K.

J8RR, 20 parts by weight of Ba2O (1,2 polybutadiene), photo-Ning agent, 1. Hydroxycyclohexylphenyl ketone (trade name: Irugakiea, 184) & benzyl dimethyl ketal (trade name: Irugakiea.

651) was added to 100 parts by weight of n-hexane while heating at 50° C. with stirring to dissolve the coating, and then applied using a spinner, the solvent was evaporated, and then UV rays were irradiated to complete curing. The reflective film is At. Table 1 shows the results of an accelerated deterioration test conducted in the same manner as described above.

[Example 8. 〕 Polycarbonate disc base, J8 几几B protective film
830 (1,2 polyptadiene/) 20 parts by weight.

0.5 parts by weight of benzoyl peroxide and 10 parts by weight of nortulhexane
After stirring and heating at 50° C. to dissolve 0 parts by weight, the solution was coated with a spinner. After air drying, it was further heated and cured (crosslinked) at 110°C for 2 hours.

The reflective film is At.

As shown in Table 1, the waviness of compact discs using 1.2 polybutadiene as a protective film is improved by about 60 to 70% when compared with conventional discs that do not use 1.2 polybutadiene. The effects of this technology used in the protective film are clearly visible.

Furthermore, as a result of listening to the compact discs that had undergone the accelerated deterioration test using a playback device, it was found that the compact discs using 1.2 polybutadiene as a protective film did not cause skipping and were able to obtain clear reproduced sound.

Table 1 Compact disc waviness (μr
n) Unit [Effect of the Invention] As explained above, it can be seen that the optical disc using the 1.2 polybutadiene of the present invention as a protective film is excellent in that it has small waviness.

Furthermore, it is applicable not only to compact discs but also to DBAW discs and fiasable discs.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the optical disc of the present invention. 1...Compact disc 5...Protective film Agent: Patent Attorney Noriyuki Chika (1 other person) and others Figure 1

Claims (2)

[Claims] (1) An optical disc characterized by using 1.2 polybutadiene as a protective film. (2) The optical disc according to claim 1, wherein the protective film is made of 1.2 polybutadiene added with a photocuring agent and cured by irradiating it with ultraviolet rays.