JPH0319152A - Manufacturing method of plastic substrate for optical disc - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing an optical disc substrate and an optical disc substrate obtained by the manufacturing method.

[Conventional technology]

In recent years, playback-only compact discs and video discs, as well as optical discs that can record additionally, have been used as information recording carriers.
Furthermore, magneto-optical disks that can be recorded, played back, and erased are also used. For the substrates of these disks, 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 A flat mirror plate was used to form a flat cavity, and molten resin was poured into the cavity to produce a flat disk substrate. [Problems to be Solved by the Invention] The optical disc substrate molded in this manner is shown in FIG.
As shown in Figure 4 (2), it has a flat shape immediately after molding, but due to aging and thermal changes, warping occurs as shown in Figure 4 (2). Furthermore, when the recording film was formed on the substrate, the degree of warping was further increased as shown in FIG. 4 (3). Such warping does not pose a particular problem when used at low rotation speeds such as compact discs, but it is not desirable for optical discs that are required to have higher density and higher speed in recent years, as it may lead to malfunctions due to vibrations and the like. In order to solve such problems, Japanese Patent Application Laid-Open No. 1986-671
24, JP-A-60-131651, JP-A-60-26
Attempts have been made to reduce the vibration caused by rotation by thickening the inner periphery of the substrate to give it strength, or by changing the thickness of the substrate from the inner periphery to the outer periphery, as disclosed in No. 1042. In many cases, it is not permissible to partially change the thickness of the substrate in terms of product design, and even if some strength is imparted, it has not been found to have much of an effect on changes over time or heat. [Means for Solving the Problems] In order to solve the above problems, the present inventors investigated in detail the behavior of the substrate over time and thermal changes, and found that the direction and amount of deformation were within a certain range. I found that it fits.
After molding, the deformation can be caused in a short time by heat treatment under certain conditions, and subsequent changes are extremely small. That is, the present invention produces a plastic substrate for an optical disk by correcting in advance changes in the shape of the plastic substrate over time and the amount of change due to thermal stress, film stress, etc. when forming a film on the substrate, and also produces a plastic substrate obtained by the method. The present invention discloses a method for manufacturing an optical disk substrate by heat-treating a substrate obtained by heat treatment, and an optical disk substrate obtained by these methods. As seen in FIG. 4, the substrate l obtained by the conventional method had information or group 2 formed on its upper surface, and warped due to subsequent changes over time. For example, the effective outer radius (D2) is 60 mm, the effective inner radius (D
+) 30mm, plate thickness 1. Immediately after molding, the 2 mm substrate is almost flat as shown in Figure 4 (1), but this substrate was subjected to an endurance test (60 to 90°C, 60 to 90% RH, 5
00 to 1000 hours), the shape changes as shown in FIG. 4 (2). Change at this time IH. was approximately 50 to 150 μm. Further, when a recording film is formed on the substrate, it is deformed as shown in FIG. 4(3) due to the temperature during film formation and the stress of the film itself. The amount of change H2 is about 150~
It was 300μ melon. In the present invention, by correcting these changes in advance and molding the substrate, the shape of the substrate becomes flat due to changes over time and due to thermal stress, film stress, etc. when forming a film on the substrate. Furthermore, by forcibly changing the obtained substrate through heat treatment, the shape hardly changes during subsequent treatments. In other words, in the present invention, as shown in FIG.
In this case, the above objective can be achieved by manufacturing a substrate with H/(D2-D.) in the range of 0 to 0.05. [Example 1] Next, the present invention will be explained by giving examples. A substrate was molded using the mold shown in the schematic cross-sectional view of FIG. In the figure, 4 is a movable side mirror plate, 5 is a stamper, 6 is a fixed side mirror plate, 7 is a casting resin, 8 is an outer stamper holder,
9 is an inner circumference stand bar presser. For the radius of curvature R of the movable mirror plate, the correction amount H = 0.1
It was determined using the following formula, with mm, D+ = 30 mm, and Dz = 60 mm. H= (R"-D+") (R"D2
”) A mirror plate with a radius of curvature that satisfies the above formula was manufactured, incorporated into a mold, and a substrate was molded using polycarbonate resin as the casting resin.The obtained substrate was completed with H = 0.08 mm.
By heat-treating this at 90°C for 3 hours, H is 0 to 0. It became 05mm. Even when this board was subsequently subjected to durability tests, there was almost no change in shape. Example 2 A substrate having a shape as shown in FIG. 3 was produced. In this example, the curved surface shape was a truncated cone shape, and the angle θ of the mirror plate of the mold used for molding was determined by the following formula. θ=tan-' H/ (Dz D+) The obtained substrate has H=0. It is completed with 08mm, and this is 90mm.
By performing heat treatment at ℃ for 3 hours, H becomes 0 to 0.
It became 03mm. Even when this board was subsequently subjected to durability tests, there was almost no change in shape. (Effect of the invention 1 As explained above, by correcting the amount of change after molding in advance and molding the substrate, the substrate The shape becomes flat.Also, by forcibly changing the obtained substrate through heat treatment, the shape hardly changes during subsequent processing, and as a result, mechanical properties such as warping and surface runout are significantly reduced. It became possible to obtain a stable substrate.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a disk substrate embodying the present invention, and FIG.
The figure is a schematic cross-sectional view of a mold preferably used to carry out the present invention, Figure 3 is a cross-sectional view of another example of a disk substrate in which the present invention is implemented, and Figure 4 is a conventional disk substrate after molding. This is a diagram showing the deformation behavior of . 1...Substrate 3...Recording film 5...Stamper 7...Casting resin 9...Inner stamper holder 2...Information or group 4...Movable side mirror plate 6... Fixed side mirror plate 8...outer stamper holder

Claims (1)

[Claims] 1. A plastic substrate for an optical disk is manufactured by correcting in advance changes in the shape of the plastic substrate over time and changes due to thermal stress, film stress, etc. when forming a film on the substrate. A method for manufacturing an optical disc substrate. 2. The manufacturing method according to claim 1, wherein the information recording surface of the obtained optical disc substrate has a concave shape. 3. Manufacturing according to claim 1, characterized in that, where H is the correction amount, D_1 is the effective inner radius of the substrate, and D_2 is the effective outer radius, H/(D_2-D_1) is 0 to 0.05. Method. 4. A method for manufacturing an optical disk substrate, characterized in that the optical disk substrate obtained by the manufacturing method of claim 1 is heat treated. 5. An optical disk substrate manufactured by the method according to any one of claims 1 to 4.