JPH0467332A - Optical disk and its manufacture - Google Patents

Abstract

PURPOSE:To prevent the warp of an optical disk by making stress of the film of synthetic resin for substrate protection smaller than that of the film of synthetic resin for protecting an optical recording medium film and cancelling the stress of the optical recording medium film by means of the difference of the stress of two films. CONSTITUTION:The protection films 6 and 8 composed of ultraviolet ray hardening resins are provided on the surface and back of the substrate 2 composed of the transparent synthetic resin. The protection film 6 is for protecting the optical recording medium film and the protection film 8 is for protecting the back of the substrate 2. They are manufacture by a spin coat and the like and a pull stress is given by using contraction at the time of hardening. The pull stress is made large in the protection film 6 and small in the protection film 8. The stress of the optical recording medium film 4 is cancelled by the difference of stress in the protection films 6 and 8. Thus, the warp of the optical disk can be prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to the prevention of warping of optical discs, and in particular, to applying stress to synthetic resin films such as ultraviolet curing resin provided on both sides of a substrate to prevent warping. Regarding things.

[Prior Art] Optical disks in which a film of an optical recording medium is provided on a substrate are attracting attention as high-capacity next-generation recording elements.

Optical recording media include those that use materials such as GdDyFe, write by applying a magnetic field under local heating with laser light, and read out using the Kerr effect, and those that utilize phase transition due to local heating with laser light. Yes.

Since glass substrates pose problems in mass production and cost, transparent synthetic resin substrates such as polycarbonate and acrylic are generally used as substrates for optical discs. However, with synthetic resin substrates, warping occurs due to stress in the optical recording medium film. This warping makes tracking and focusing of the optical disc difficult.

In order to eliminate the warpage of the substrate, the following methods have been proposed.

(1) To offset the warpage caused by the optical recording medium film,
Manufacturing a pre-warped substrate.

(2) Select film forming conditions for the optical recording medium film to prevent warping.

(3) A film of the same type as the optical recording medium film is formed on the back surface of the substrate to offset stress (Japanese Patent Application Laid-open No. 57-441-1983).

The first method is difficult to manufacture and is impractical. Second
This method has limitations because the stress of the optical recording medium film is closely related to its characteristics. The third method is also not preferable because it requires a complicated vacuum process to form the film in order to eliminate warpage.

(Problem of the Invention) An object of the present invention is to provide a new method for preventing warpage of an optical disc, and to prevent warpage by utilizing the stress of a synthetic resin film formed on both the front and back surfaces of a substrate. .

[Structure and operation of the invention] The optical disc of the present invention includes an optical recording medium film and a synthetic resin film for protecting the film on one side of a transparent synthetic resin substrate, and a synthetic resin film for protecting the substrate on the back side of the substrate. In an optical disk provided with a resin film, the stress of the synthetic resin film for protecting the substrate is made smaller than the stress of the synthetic resin film for protecting the optical recording medium film, and the stress difference between the two films is used to reduce the stress of the optical recording medium film. It is characterized by canceling out the stress of

To manufacture such optical discs, for example, synthetic resin films on both the front and back sides are formed by spin coating with ultraviolet curable resin, and the curing shrinkage rate of the ultraviolet curable resin on the optical recording medium film side is adjusted by the curing shrinkage of the ultraviolet curable resin on the opposite side. It is sufficient if it is larger than the shrinkage rate.

The optical recording medium film provided on the synthetic resin substrate has compressive stress. As a result, the substrate tends to warp with the optical recording medium film side as a convex surface, as shown in FIG. In the figure, 2 is a transparent synthetic resin substrate, and 4 is an optical recording medium film. Here board 2
Protective films 6 and 8 made of ultraviolet curing resin or the like are provided on the front and back sides of the substrate.

The protective film 6 is for protecting the optical recording medium film 4, and the protective film 8 is for protecting the substrate 2.
It is for protection of the back side of. The protective film 6.8 is manufactured by spin coating or the like, and is given tensile stress by utilizing shrinkage during curing. The tensile stress is large in the protective film 6 and small in the protective film 8, and the stress in the optical recording medium film 4 is offset by the difference in stress between the protective films 6.8. In order to provide the protective films 6.8 with a difference in stress, for example, the curing shrinkage rate of the resin used for the protective film 6 may be increased, and the curing shrinkage rate of the resin used for the protective film 8 may be decreased.

[Example] FIG. 1 shows the basic concept of the example. In the figure, 2
is a transparent substrate made of synthetic resin such as polycarbonate resin, and may also be made of epoxy resin, polyester resin, acrylic resin, or the like. Reference numeral 4 denotes an optical recording medium film, which is made by sandwiching a magneto-optical recording medium film such as GdDyFe between two dielectric films and laminating a metal reflective film on top thereof. Reference numeral 6 denotes a protective film made of ultraviolet curing resin, which is used to protect the optical recording medium film 4 .

8 is a protective film made of ultraviolet curing resin for protecting the back surface of the substrate 2.

The optical recording medium film 4 has a compressive stress in the direction of the black arrow in the figure, which tends to warp the substrate 2 as shown in the figure. The reason for the presence of compressive stress is that (1) compressive stress is generated during film formation of the optical recording medium film 4, and (2) the characteristics of the optical recording medium film 4 are related to the compressive stress. This is because recording characteristics deteriorate.

The compressive stress of the optical recording medium film 4 is offset by the difference in stress between the protective films 6 and 8. That is, by utilizing the shrinkage of the protective film during curing, stress is generated in the protective films 6 and 8 in the direction of the white arrow in the figure. Here, the curing shrinkage rate of the protective film 6 is increased to increase the stress. - Reduce the curing shrinkage rate of the blade protective film 8 and reduce the stress.

The difference between the two stresses cancels out the stress in the optical recording medium film 4 and prevents the substrate from warping. The stress of the protective film 6.8 is affected by the film thickness in addition to the curing shrinkage rate, and the stress is proportional to the film thickness. Therefore, the difference in stress can be controlled by adjusting the thickness of the protective films 6 and 8.

hot shade A polycarbonate resin substrate 2 with a diameter of 130 mm.

Using this method, an optical disc shown in FIG. 2 was manufactured. The optical recording medium film 4 was formed using a four-chamber magnetron sputtering device. First, amorphous yttrium sialon film 1
0 was formed to a thickness of 920A, and then a GdDyFe-based magneto-optical recording film 12 was formed to a thickness of 200A. Further, a yttrium sialon film 14 was provided to a thickness of 300 Å, and a metal A1 reflective film 16 was laminated to a thickness of 80 Å. Yztrium Sialon is Sing, Si○, Ce0z, ZrO2, T
iO2, Bi2O2, ZnS, Sb2S3, 513N4
GdDyFe can be changed to other materials such as GdD
yFeCo.

GdTbFe, TbFeCo, DyFeCo, GdTb
DyFe.

GdTbFeCo, TbDyFeCo, NdGdDyF
e.

Materials such as NdDyFeCo and NdGdDyFeCo can be used. For the metal reflective layer 16, T1, Cr, etc. may be used instead of AI.

A protective film 6°8 was provided on both the front and back surfaces of the substrate 2 by spin coating. The protective films 6 and 8 are made of ultraviolet curing resin,
The protective film 6 is made of a resin with a curing shrinkage rate of 11.4% (Koshi A,
An acrylic acid ester polymer-based product (trade name: 5DI7"5D17 manufactured by Dainippon Ink and Chemicals) was used. Protective film 8
A resin with a curing shrinkage rate of 7.6% (Katsuo B, a copolymer of urethane acrylate and acrylic ester polymer, "5D301" 5D301 manufactured by Dainippon Ink and Chemicals) was used.
(trade name) was used. In addition to these materials, the protective film 6.8 may be made of ultraviolet curing resins such as epoxy, polyester, and acrylic resins. In addition, resin B with a small curing shrinkage rate may include, for example, acrylic ester polymer "5DI" manufactured by Dainippon Ink and Chemicals.
There are "OI" (SDIOI is a trade name) and "EX-3" (EX-3 is a trade name) which is also an acrylic acid ester polymer.

Table 1 shows the types and warp angles of the optical discs obtained.

Table l Heat! Protective film 6 Protective film 8 Warp angle (mRad)
l AX9μm Bx5μm 2.52
AX5μm Bx5μm 3.23
BX5μm Bx5μm 4.84 BX
5μm AX5μm 7-55...0
μm...0μm 4.5* A is contraction rate 11
．． 4 (%cm/c+i) of resin.

B indicates a resin with a shrinkage rate of 7.6 (%am/Cm).

As is clear from Table 1, the shrinkage rate of the protective film 6 is increased.
By reducing the shrinkage rate of the protective film 8, the warpage of the optical disc can be reduced. This is because the compressive stress of the optical recording medium film 4 is offset by the stress difference between the protective films 6 and 8. In sample 1 in which the protective film 6 was thicker and the tensile stress was increased, the warp angle was particularly small. Next, in sample 3 in which the protective film 6.8 had the same shrinkage rate, the warp angle was almost the same as in sample 4 in which the protective film 6.8 was not provided. In addition, in sample 3 in which the shrinkage rate relationship was reversed, the warp angle increased.

Two optical disks shown in FIG. 2 were bonded together by roll coating with hot melt adhesive 18 so that the optical recording medium films 4 faced each other to obtain the optical disk shown in FIG. 3. In the case of this optical disk, although the initial value of the curvature angle of the hot melt adhesive 18 is small, the curvature returns when exposed to a harsh environment. Table 2 shows that 100
The results of a 0-hour durability test are shown.

Table 2 1 1.5 2.0 Not occurred 2
1.3 2.1 Not occurred3 1.4
4.0 Two occur on the outer periphery 4 1.5
6.2 8 occurred on the outer periphery This sample number is the same as the sample number in Table 1.

In the sample shown in FIG. 3, the initial value of the warp angle is small because of the hot melt adhesive 18. However, when a durability test is carried out, the warpage angle returns to its original tendency, and large warpage occurs in sample 3.4 in which the stress of the optical recording medium film 4 is not offset by the stress difference of the protective film 6°8. In the case of these samples, the occurrence of warpage also affects the durability of the optical recording medium film 4, and corrosion occurred in samples 3 and 4 during the durability test.

Although a specific embodiment has been described here, the present invention is not limited to this, and for example, a phase change type may also be used for the optical recording medium film 4. Further, fine conductive ceramic particles or the like may be mixed in the protective films 6 and 8 to prevent dust and the like from adhering to the protective films 6 and 8.

[Effects of the Invention] In this invention, warping of an optical disk is prevented by the difference in stress between the protective films provided on both sides of the substrate. In the case of a laminated optical disc, it prevents warping and corrosion of the optical recording medium film, increasing the durability of the optical disc.

FIG. 1 is a sectional view of an optical disk according to an embodiment, FIG. 2 is an enlarged sectional view of a main part thereof, and FIG. 3 is a sectional view of a modified example.

In the figure, 2 substrate, 4 optical recording medium film 6, ultraviolet curable resin protective film for optical recording medium film 8, ultraviolet ray effect resin protective film for protecting the back surface of the substrate.

Claims (2)

[Claims] (1) In an optical disc in which an optical recording medium film and a synthetic resin film for protecting this film are provided on one side of a transparent synthetic resin substrate, and a synthetic resin film for protecting the substrate is provided on the back side of the substrate, the substrate is protected. The stress of the synthetic resin film for protection of the optical recording medium film is made smaller than the stress of the synthetic resin film for protecting the optical recording medium film, and the stress of the optical recording medium film is offset by the difference in stress between the two films. ,optical disk. (2) In an optical disc manufacturing method in which an optical recording medium film is provided on one side of a transparent synthetic resin substrate and an ultraviolet curable resin film is spin-coated on both the front and back surfaces of the substrate, curing shrinkage of the ultraviolet curable resin on the optical recording medium film side. A method for manufacturing an optical disc, characterized in that the curing shrinkage rate of the ultraviolet curable resin on the opposite side is made larger than the curing shrinkage rate of the ultraviolet curing resin on the opposite side.