JPH04172636A - Optical disc - Google Patents

Abstract

PURPOSE:To suppress double refraction which takes place in a substrate by subjecting a plastic disc substrate having center hole adhered with a hub to heat treatment. CONSTITUTION:A center hole 2 is made through a polycarbonate disc board(PC board) 1 while an annular recording film 3 is formed on the PC board 1. The PC boards 1 formed with the recording film 3 are then superposed through an adhesive layer 4 with the recording films 3 opposing each other thus encapsulating the recording film 3 in the disc. A hub 5 is fixed to the periphery of the center hole 2 and bonded through ultrasonic welding of the PC board 1 or through various adhesives followed by heat treatment. According to the constitution, distortion of the substrate 1 due to adhesion of the hub 5 can be eliminated resulting in suppression of double refraction.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to optical discs, and more particularly to improvements in substrates for optical discs.

<Prior Art> As optical disks, recordable optical disks such as magneto-optical recording disks and read-only optical disks such as compact disks are known.

In these optical discs, recording and reproduction of recorded information is performed by irradiating the recording surface with laser light and detecting the reflected light or transmitted light, so that the light passes through the disc substrate. For this reason, the optical disk substrate is required to be transparent to reproduction light.

Furthermore, since extremely high-density recording is performed on optical discs, errors may occur in recorded signals due to deformation or dimensional changes in the substrate. For this reason, optical disk substrates are required to have high durability and low water absorption.

Polycarbonate resin has attracted attention because it satisfies these conditions, has excellent mass productivity, and is low cost, and has been put to practical use in compact discs, magneto-optical recording discs, and the like.

However, polycarbonate resin substrates have thick birefringence (due to internal residual stress) and poor optical uniformity.In optical discs, playback light passes through the substrate, so if the substrate has large birefringence, recording An error occurs when playing the signal.

In particular, magneto-optical recording disks perform reproduction by detecting minute rotations of reproduction light due to the Kerr effect, and are therefore susceptible to the effects of birefringence occurring in the substrate.

Incidentally, a magneto-optical disk is rotationally driven by a magnetic clamp method or the like, and for this purpose it is necessary to attach a hub to a center hole of a plastic substrate. Proposed methods for attaching it include melting parts of the hub and board using ultrasonic waves or high frequency waves and welding them together, or bonding the hub and board using an adhesive that hardens with ultraviolet light, etc. has been done.

Among these, methods of welding using ultrasonic waves and high frequencies are particularly
Although it is superior in terms of cost and workability, when a part of the substrate melts and the melted part cools and solidifies, internal distortion occurs, which increases the birefringence of the substrate and causes errors during playback. There was a problem that this occurred. Furthermore, even in methods using adhesives, since heat is applied to the substrate during curing, internal distortion tends to occur during cooling.

<Problems to be Solved by the Invention> The present invention has been made in view of the above-mentioned drawbacks of the conventional technology, and its purpose is to eliminate distortion of the substrate due to hub adhesion and provide an optical disk with low birefringence. It's about doing.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (4).

(1) An optical disk characterized in that a plastic disk substrate with a hub bonded to a center hole is heat-treated.

(2) The optical disc according to (1) above, wherein the hub is bonded by ultrasonic welding.

(3) The substrate is made of polycarbonate (1).
) or the optical disc according to (2).

(4) The optical disc according to any one of (1) to 3) above, wherein the substrate is heat-treated at about 60 to 120''C.

<Embodiment> FIG. 1 shows an embodiment of a magneto-optical disk according to the present invention.

As shown in FIG. 1, a center hole 2 is bored in a disc-shaped polycarbonate substrate (hereinafter referred to as "PC board") 1, and an annular recording film 3 is formed on the PC board 1. is formed. The PC board 1 on which the recording film 3 is formed is stacked with the recording film 3 facing each other via the adhesive layer 4, and the recording film 3 is enclosed within the disk.

Further, a hub 5 is bonded and fixed to the peripheral edge of the center hole 2.

Although the hub 5 is made of polycarbonate and metal in this embodiment, it may also be made of other metals.

The hub 5 is bonded to the PCC board by ultrasonic welding.

Other methods of adhering the hub 5 include using various adhesives.

As described above, the PC base 1 to which the hub 5 is attached is heat-treated under, for example, the following conditions.

■Heat treatment details (1) Heating method Heat evenly throughout the oven.

The heating means is not limited to an oven, but is preferably one that can uniformly heat the entire substrate.

iii) The heating temperature is preferably about 60 to 120°C, preferably about 70 to 100°C.

(iii) Heating time (number of times) It is usually 2 to 20 hours, about 10 to 20 hours at a heating temperature of about 60 to 80°C, and about 2 to 10 hours at a heating temperature of about 80 to 120°C.

Alternatively, these steps may be repeated multiple times or in combination.

Heat treatment is performed by combining each of the above elements, and such heat treatment is effective when the hub is bonded by ultrasonic welding, where the strain caused by bonding becomes particularly large.

Specific examples will be given below.

■　Example (i) PC board outer diameter 130mm Center hole diameter 1.5mm Thickness 121 (11) Hub　Outer diameter 25mm Inner diameter 4mm Thickness 2+am Material polycarbonate, steel composite (iii) The hub was attached using sonic welding.

(iv) Heat treatment contents Sample A: Heated at 80℃ for 18 hours Sample B: Heated at 80℃ for 2 hours Sample C: 2 hours Heated at 80℃ for 2 hours 1
Sample D heated at 00°C: Sample E heated at 100°C for 2 hours Sample F heated at 100°C for 18 hours Sample G heated at 60°C: Standing ■ Method for measuring birefringence Each substrate subjected to the above heat treatment Measure the birefringence of
The average value was calculated.

Birefringence was measured using a straight beam with a wavelength of 633 nm at a position with a radius of 29 mm in reflection mode.

(2) Results The average value of birefringence of each sample before attaching the hub was about -20 nm, and the average value of birefringence after attaching the hub and before heat treatment was about -60 nm.

Average value of birefringence [Unit: nml] As can be seen from the above results, there was a significant decrease in birefringence for the substrates that were heat-treated under the predetermined conditions after the hub was bonded, compared to the substrates that were not heat-treated. It was done.

In addition, in the examples described above, the samples were those with hubs bonded by ultrasonic welding, but similar effects were obtained with other substrates with hubs bonded by bonding with adhesives or high-frequency welding. .

In addition, the material of the plastic disk substrate may be acrylic resin, epoxy resin, styrene resin, etc. in addition to the polycarbonate mentioned above (similar results have been obtained, but especially when polycarbonate is used, the above effects are is remarkable.

Furthermore, although the above embodiments have been described with respect to magneto-optical disks, the present invention is also applicable to various other types of removable and write-once optical recording disks, as well as read-only optical disks, as long as they are of the type provided with a hub. You can.

<Effects of the Invention> According to the optical disc of the present invention as explained above, the birefringence of the substrate is reduced, and troubles such as errors are less likely to occur (
There are advantages such as:

[Brief explanation of drawings]

FIG. 1 is a front partial sectional view of an optical disc. Explanation of symbols 1... Board 2...Center hall 3...Recording film 4...adhesive layer 5...Hub

Claims (4)

[Claims] (1) An optical disk characterized in that a plastic disk substrate with a hub bonded to a center hole is heat-treated. (2) The optical disc according to claim 1, wherein the hub is bonded by ultrasonic welding. (3) Claim 1, wherein the substrate is made of polycarbonate.
or the optical disc described in 2. (4) The optical disc according to any one of claims 1 to 3, wherein the substrate is heat-treated at about 60 to 120°C.