JPH0440645A - optical disk - Google Patents

Abstract

PURPOSE:To suppress a change in the warpage of a plastic substrate having hygroscopicity by a low hygroscopic film and a high hygroscopic film to a lower level by providing both hygroscopic films on an information recording layer side provided on the substrate. CONSTITUTION:An interference film 2 consisting of SiOy, SiNy, etc., a magneto- optical recording film 3 consisting of TbFeCo, and an inorg. protective film 4 consisting of SiOy are successively formed by a sputtering method on one surface of the polycarbonate substrate 1 formed with spiral grooves. The low hygroscopic film 5 and the high hygroscopic film 6 are respectively formed to prescribed film thicknesses on the inorg. protective film 4 by applying a UV curing type resin by a spin coating method. The substrate warps if the humidity environment varies on both surfaces of the plastic substrate of the optical disk. The warpage changes if the environment changes. Proper moisture is supplied to one surface of the substrate through the information recording layer by the hygroscopic films provided on the information recording layer in such a manner, by which the humidity environments on both surfaces of the substrate are controlled and the change in the warpage of the substrate is suppressed to the lower level.

Description

[Detailed description of the invention] Ru.

FIG. 1 is a sectional view showing one embodiment of the present invention. As shown in Figure 1, a spiral groove with a diameter of 130 mm with a groove width of 0.6 μm, a groove depth of 700 mm, and a groove pitch of 1.6 μm is formed.
mm, thickness 1.2 mm polycarbonate (hereinafter referred to as PC)
) on one side of the substrate 1.

0.07 μm thick interference film (inorganic protective film) made of SiN, etc. 2, 0.08 μm thick made of TbFeCo
An inorganic protective film 4 consisting of a magneto-optical recording film 3 and 5 iOy of 1 t rn is sequentially formed by sputtering, and the inorganic protective film 4 is
A single-sided optical disk was prepared by forming a low hygroscopic film 5 and a highly hygroscopic film 6 on the disc to a predetermined thickness using ultraviolet curable resin using a spin cord method.

The material for forming the above-mentioned low hygroscopic film 5 is selected from materials whose water absorption rate is less than 0.4%, but both inorganic and organic materials can be used as long as the water absorption rate is satisfied.

In this example, an ultraviolet curing resin was used. The water absorption rate here is based on JIS K 7209, and is the mass of the test object before water absorption and the mass increase after the object is immersed in water at 23 ± 2 ° C for 24 ± 1 hour and absorbed. It is a percentage of the ratio of minutes to minutes.

In addition, the material with a water absorption rate of less than 0.4% was used for the low hygroscopic film 5 because PC, which is preferably used as a substrate material, was used for the low hygroscopic film 5.
, PMMA, epoxy and other resins (0, 1 in order)
5%, 0.30%, and 0.15%) are all less than 0.4%, and if the water absorption rates are close to these, the humidity environments on both sides of the substrate can be controlled to approximately the same degree.

Further, as the material for forming the highly hygroscopic film 6, a material with a water absorption rate of 0.4% or more is selected, but both inorganic and organic materials can be used as long as the water absorption rate condition is satisfied. In this example, the same type of ultraviolet curable resin as the low hygroscopic film 5 was used.

The reason why the highly hygroscopic film 6 is provided on the low hygroscopic film 5 is that most of the moisture around the optical disk is absorbed by the highly hygroscopic film 6, and only a part of the external moisture is absorbed by the highly hygroscopic film 6. This is for the purpose of infiltrating the low hygroscopic film 5 through the film 6 and maintaining the humidity environment on the substrate surface at a predetermined level by the low hygroscopic film 4.

The thickness of each of the low hygroscopic film 5 and the highly hygroscopic film 6 can be arbitrarily set by controlling the amount of resin applied, the number of rotations of the spin code, the spin code time, and the like.

Water absorption rate (%) of the low hygroscopic membrane 6 in this example! 3 and film thickness (μff1) are shown in Table 1.

Table 1 The water absorption rates in Table 1 were determined in accordance with JIS K 7209 by immersing the resin in water at 24° C. for 24 hours and calculating the ratio between the original mass of the ultraviolet curable resin and the mass increase before and after water absorption.

The layer thickness is the result of measuring the difference in thickness before and after applying the ultraviolet curable resin using a microgauge.

One of the two single-sided optical discs produced in this way was used as an example, and the other one from which the highly hygroscopic film 6 was removed was used as a comparative example, and a temperature-humidity jump test was conducted on each of them.

This temperature/humidity jump test first tested an optical disc at 35°C and 8°C.
It was left in a 0% RH atmosphere for 50 hours, and then heated at 50°C.
This is to measure the change over time in the tilt angle [mrad] when transferred to a 50% RH atmosphere. Measurement of tilt angle is ISO
The evaluation was carried out using an evaluation device conforming to the standard DP-10089.

The measurement results are shown in Figure 2.

From Figure 2, in the comparative example, the amount of change from the initial tilt angle of 1.8 mrad is very large, approximately 5.0 mrad, due to changes in the environment, while in the example, the initial tilt angle is 2.6 mrad.
It can be clearly seen that the change in the tilt angle from ad is as small as about 1.5 mrad.

In the comparative example, the disk reversibly thickens (changes) due to stress due to moisture absorption and dehumidification on the surface of the PC board opposite to the magneto-optical recording film, but in the example, the humidity environment changes on both sides of the PC board. This is probably because the balance is maintained.

In the above embodiment, polycarbonate (PC) was used as the plastic substrate, but transparent resins such as polymethyl methacrylate (PMMAI, epoxy, etc.) are also suitable as substrate materials, and even when these resins are used, these By providing a hygroscopic film on a magneto-optical recording film (information recording layer) on a substrate made of resin, an optical disc that can withstand environmental changes can be obtained.

Furthermore, even in a double-sided disc manufactured by bonding two single-sided optical disc substrates provided with the low hygroscopic film 5 and high hygroscopic film 6 described above, the hygroscopic film maintains a well-balanced humidity environment around the substrates. As a result, the substrate is not warped or deformed, and the recording film is less likely to peel off or crack, resulting in high durability and reliability.

[Effect of the Invention 1 As explained above, according to the present invention, since a low hygroscopic film and a highly hygroscopic film are provided on the information recording layer side provided on a hygroscopic plastic substrate, both hygroscopic films As a result, changes in the amount of warpage of the substrate can be minimized, and an optical disk with long life and high reliability can be provided.

3... magneto-optical recording film, 4...Inorganic protective film, 5...Low hygroscopic membrane, 6... Highly hygroscopic membrane.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing an embodiment of the present invention, and Fig. 2 shows a change over time in the tilt angle [mrad] when a temperature/humidity jump test was conducted on an embodiment of the present invention. It is a graph. 1...Plastic substrate, 2...Interference film,

Claims (1)

[Claims] 1) In an optical disc having an information recording layer formed on one surface of a plastic substrate, a low hygroscopic film is formed on the information recording layer, and a highly hygroscopic film is further formed on the low hygroscopic film. An optical disc characterized in that: 2) The optical disk according to claim 1, wherein the water absorption rate of the low hygroscopic film is close to the water absorption rate of the plastic substrate. 3) The optical disc according to claim 1, wherein the water absorption rate of the low hygroscopic film is less than 0.4%, and the water absorption rate of the highly hygroscopic film is 0.4% or more.