JP2709144B2 - Method of manufacturing plastic substrate for optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a plastic substrate for an optical disk.

[Conventional technology]

In recent years, as information recording carriers, compact discs and video discs exclusively used for reproduction, optical discs which can be additionally recorded, and magneto-optical discs which can be recorded / reproduced / erased have been used.

For the substrates of these discs, plastic substrates made by injection molding or injection compression molding are used from the viewpoint of productivity, but in the conventional technology, a flat stamper is mounted on a flat mirror plate, and the side facing the stamper is mounted. A flat mirror substrate is also used to form a flat cavity, and a molten resin is poured into the flat cavity to produce a flat disk substrate.

[Problems to be solved by the invention]

The optical disk substrate molded in this manner has a flat shape immediately after molding as shown in FIG. 4 (1), but as shown in FIG. 4 (2) due to aging and thermal change. Warpage occurs. Further, when a recording film was formed on the substrate, the degree of warpage was further increased as shown in FIG. 4 (3). Such a warp does not cause any particular problem when the disk is used at a low rotation speed such as a compact disk. However, an optical disk which requires high density and high speed as in recent years is not preferable because it causes a malfunction due to vibration or the like.

To solve such a problem, Japanese Patent Laid-Open No. 60-67124,
As disclosed in JP-A-60-131651, JP-A-60-261042, the inner peripheral side of the substrate is thickened to have strength, or by changing the thickness of the substrate from the inner periphery to the outer periphery, rotation is performed. Attempts have been made to reduce vibration, but it is often unacceptable to partially change the thickness of the board due to product design. On the other hand, no significant effect was observed.

[Means for solving the problem]

The present inventors have studied in detail the behavior of the substrate over time and thermal change in order to solve the above problems, and have found that the direction and amount of the deformation fall within a certain range. Then, if heat treatment is performed under certain conditions after molding, the deformation can be caused in a short time, and the change after that is extremely small.

That is, the present invention is a method for manufacturing an optical disk substrate, one surface of which is an information recording surface, wherein the optical disk substrate has an effective inner radius of D ₁ , an effective outer radius of D ₂ , and an effective inner radius of the substrate. When the correction amount indicating the height from the information recording surface to the information recording surface at the effective outer radius is H, 0 <
H / (D ₂ −D ₁ ) ≦ 0.05, wherein the information recording surface has a concave shape, Mirror plate having a convex surface with a radius of curvature R satisfying
A truncated conical mirror plate having an inclined surface having an angle θ satisfying θ = tan ⁻¹ H / (D ₂ −D ₁ ) is incorporated in a mold, and the resin is injected into the mold to form the substrate. The present invention relates to a method of manufacturing a plastic substrate for an optical disk, characterized by including a step of performing the following.

As shown in FIG. 4, the substrate 1 obtained by the conventional method has information or groups 2 formed on the upper surface thereof, and warpage has occurred due to subsequent aging.
For example, effective outer radius (D ₂₎ 60 mm, effective in radius (D ₁₎ 30 m
m, a 1.2 mm thick substrate is almost flat immediately after molding as shown in FIG. 4 (1).
C.) (60-90% RH, 500-1000 hours), the shape changes as shown in FIG. 4 (2). Variation H ₁ at this time was about 50 to 150 [mu] m. Further, when a recording film is formed on the substrate, the recording film is deformed as shown in FIG. 4 (3) by the temperature during the film formation and the stress of the film itself. The change amount H ₂ is about 150
300300 μm. In the present invention, these changes are corrected in advance, and the substrate is formed. As a result, changes over time and changes due to thermal stress, film stress, and the like at the time of film formation on the substrate occur, so that the substrate shape becomes flat. In addition, by forcibly causing a change in the obtained substrate by the heat treatment, a change in shape in the subsequent treatment hardly occurs.

That is, in the present invention, when the correction amount is H as shown in FIG. 1, the above object is achieved by manufacturing a substrate with H / (D ₂ −D ₁ ) in the range of 0 to 0.05.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 A substrate was formed using a mold shown in a schematic sectional view of FIG.

In the drawing, reference numeral 4 denotes a movable mirror plate, 5 denotes a stamper, 6
Denotes a fixed mirror plate, 7 denotes a casting resin, 8 denotes an outer stamper holder, and 9 denotes an inner stamper holder.

Correction amount H = 0.1 m for radius of curvature R of movable mirror plate
m, D ₁ = 30 mm and D ₂ = 60 mm were determined by the following equations.

A mirror plate having a radius of curvature that satisfies the above equation was manufactured and assembled into a mold, and a substrate was formed using a polycarbonate resin as a casting resin.

The obtained substrate is completed at H = 0.08 mm, and this is 90
H is 0 ~ 0.05mm by heat treatment for 3 hours
It became. Thereafter, even when a durability test was performed on this substrate, almost no change in shape occurred.

Example 2 A substrate having a shape as shown in FIG. 3 was produced. In this embodiment, the curved surface was formed into a truncated cone shape, and the angle θ of the mirror plate of the mold used for molding was determined by the following equation.

θ = tan ⁻¹ H / (D ₂ −D ₁ ) The obtained substrate is completed at H = 0.08 mm.
H is 0 ~ 0.03mm by heat treatment for 3 hours
It became. Thereafter, even when a durability test was performed on this substrate, almost no change in shape occurred.

〔The invention's effect〕

As described above, by correcting the amount of change after molding in advance and shaping the substrate, the substrate shape becomes flat due to changes over time and changes due to thermal stress, film stress, etc. when forming a film on the substrate. Become. In addition, by forcibly causing a change in the shape of the obtained substrate by the heat treatment, a change in shape in subsequent processing hardly occurs, and as a result, a substrate with extremely stable mechanical characteristics such as warpage and surface deflection is obtained. It became possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a disk substrate embodying the present invention, and FIG.
FIG. 3 is a schematic sectional view of a mold suitably used for carrying out the present invention, FIG. 3 is a sectional view of another example of a disk substrate embodying the present invention, and FIG. It is a figure showing the deformation behavior of. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Information or groove 3 ... Recording film, 4 ... Mirror plate for movable side 5 ... Stamper, 6 ... Mirror plate for fixed side 7 ... Casting resin, 8 ... Holder for outer periphery stamper 9 ... Holder for inner periphery stamper

Claims (3)

(57) [Claims] 1. A method for manufacturing an optical disk substrate, wherein one surface is an information recording surface, wherein the optical disk substrate has an effective inner radius of D ₁ , an effective outer radius of D ₂ , and When the correction amount indicating the height from the information recording surface to the information recording surface at the effective outer radius is H, 0 <H / (D ₂ −
D ₁ ) satisfying the condition of ≦ 0.05, wherein the information recording surface has a concave shape, A method of manufacturing a plastic substrate for an optical disk, comprising: incorporating a mirror-finished plate having a convex surface having a curvature radius R satisfying the following condition into a mold, and injecting a resin into the mold to mold the substrate. 2. A method for manufacturing an optical disk substrate, wherein one surface is an information recording surface, wherein the optical disk substrate has an effective inner radius of D ₁ , an effective outer radius of D ₂ , and an effective inner radius of the substrate. When the correction amount indicating the height from the information recording surface to the information recording surface at the effective outer radius is H, 0 <H / (D ₂ −
D ₁₎ satisfies the condition ≦ 0.05, cone having said are those information recording surface has a concave ^{shape, θ = tan -1 H / (} D 2 -D 1) the inclined surface of the angle theta which satisfies the A method of manufacturing a plastic substrate for an optical disk, comprising a step of incorporating a trapezoidal mirror plate into a mold and injecting a resin into the mold to mold the substrate. 3. The method for manufacturing a plastic substrate for an optical disk according to claim 1, further comprising a step of heat-treating the substrate manufactured by the method according to claim 1.