JPH02252151A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To obtain the magneto-optical disk which is improved in C/N by forming annular grooves having the depth of the prescribed ratio to the thickness of a plastic disk substrate adhered with a hub to the annular recording regions of the substrate in substantially the same part on both the main surfaces of the substrate. CONSTITUTION:A center hole 2 and a gate 3 having an approximately rectangular cross section are formed on the disk-shaped polycarbonate substrate 1 and the transfer traces of a stamper fixing jig corresponding to the annular grooves having the depth of >=1/5 the substrate thickness are provided in the non-recording region. The annular groove 4 having approximately the rectangular cross section is also formed on the other main plane in substantially the same position. These grooves are also provided at the time of an injection molding. The annular recording film 5 is formed on such substrate 1 and the hub is formed to the center hole 2 by an adhesive agent or by ultrasonic or high-frequency welding. The recording film 5 is formed by disposing the substrate 1 with the guide grooves to a high-frequency magnetron sputtering device and providing a dielectric layer mainly consisting of Si nitride thereon. The residual stresses in the radial direction of the inside of the substrate 1 are decreased and the double refractions thereof are decreased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a rewritable magneto-optical disk, and more particularly to a magneto-optical disk with improved playback performance due to reduced birefringence of a plastic disk substrate. be.

[Prior art and its problems]

Recently, magneto-optical recording using amorphous alloys of rare earth metals and transition metals has been actively researched, and the recording method using this magnetic medium allows not only writing and reading but also rewriting. can.

In magneto-optical disks using this type of recording method, plastic disk substrates are used because of their advantages in terms of mass production and cost.

This plastic board is made of polycarbonate (hereinafter referred to as PC).
PMMA), acrylic (hereinafter abbreviated as PMMA), epoxy, and other resins, and today it is recognized as effective for PC boards in that it has a high heat distortion temperature and a low expansion coefficient due to moisture absorption. .

Incidentally, a magneto-optical disk is rotationally driven by a magnetic clamp method, and for this purpose it is necessary to attach a hub to the center of a plastic substrate.

Proposed methods for attaching the hub include using an adhesive, or melting a portion of the hub and the substrate using ultrasonic waves or high frequency waves to weld the two together.

The former method is not sufficient in terms of cost and workability, and also causes distortion in the joint due to curing and shrinkage of the adhesive, which deteriorates characteristics such as C/N and increases the reproduction error rate. There is a problem.

The latter method is superior in terms of cost and workability, but on the other hand, a part of the substrate melts, and as the melted part cools and solidifies, internal distortion occurs, resulting in C of the inner circumference of the disk.
There was a problem that electrical characteristics such as /N deteriorated.

In view of the above-mentioned problems, the inventors of the present invention conducted extensive research and found that when a hub is bonded to a plastic substrate, residual stress is generated inside the substrate, and this is the cause of increasing birefringence. It has been found that the residual stress can be separated and absorbed by providing grooves in certain areas.

Therefore, the present invention was completed based on the above findings, and its purpose is to reduce the residual stress in the radial direction inside the plastic substrate, reduce its birefringence, and thereby create a magneto-optical disk with an increased C/N. It is about providing.

[Means for solving problems]

The magneto-optical disk of the present invention has a plastic disk substrate on which an annular magneto-optical recording layer is formed and a hub is bonded to the center, and a non-recording area inside the annular recording area has a depth relative to the thickness of the substrate. The present invention is characterized in that annular grooves having a size of one-fifth or more are formed at substantially the same location on both principal surfaces of the substrate.

[For production]

When the above-mentioned annular groove is formed, the residual stress generated when the hub is bonded to the substrate is separated and absorbed, thereby reducing the amount of increase in birefringence in the substrate area corresponding to the annular recording area. Birefringence is significantly reduced in the inner peripheral portion of the substrate region, and as a result, a decrease in C/N due to adhesion of the hub can be prevented.

〔Example〕

The magneto-optical recording layer includes rare earth metal-transition metal amorphous alloys, garnet, PtMnSb alloys, etc., and description will be made by taking an amorphous alloy as an example.

FIG. 1 shows a magneto-optical disk of the present invention, and FIG. 2 shows one shape of an annular groove.

According to FIG. 1, a disk-shaped PC board 1 (outer diameter φ13
0 mm, inner diameter φ15 mm, thickness 1.2 mm) has a center hole 2 and a second gate 3 whose cross section is approximately rectangular (radius r 17.6 to 18.6 mm, depth 0.35 mm).
) is formed, and this second gate 3 corresponds to the annular groove in the present invention, and is usually a transfer trace of the Sukumber fixing jig.

Further, on the other main surface of the substrate, an annular groove 4 (with a depth of 0.3
5 mm and a surface opening width of about 1.0 mm), and this groove 4 is also formed during injection molding.

An annular recording film 5 is formed on such a PC board 1, and a hub 6 (outer diameter 25 mm) is formed in the center hole 2 by adhesive or by welding using ultrasonic waves or high frequency waves. 7 is a clamp that fixes and rotates the substrate 1.

Further, the recording film 5 is formed as follows.

The PC board 1 with guide grooves is placed in a multi-source high-frequency magnetron sputtering device, and a dielectric layer mainly made of silicon nitride, a GdDyFe perpendicular magnetization film, and a titanium oxide layer are sequentially formed. The layer was overcoated to produce eight magneto-optical disks.

A hub was bonded to the thus obtained magneto-optical disk 8 by ultrasonic welding, and the C/N was measured before and after bonding, and the results shown in Table 1 were obtained. Furthermore, this C
/N measurement conditions: r = 30mm, rotation speed 240Or
pm, recording frequency 4.9MJlz, bias magnetic field 30
00e, recording power 6.0mW, reproduction power 1, 5
mW.

The same table also shows, as a comparative example, a magneto-optical disk B which was manufactured in the same manner as the present example without forming the annular a4.

Table 1 As is clear from the results shown in Table 1, magneto-optical disk 8 of the present invention had a small amount of C/N change before and after hub adhesion, and the decrease in C/N due to hub adhesion was significantly reduced. I understand.

The present inventors discovered that, as shown in FIG.
A magneto-optical disk C having a diameter of 5 mm and a surface aperture width of about 1.2 mm was prepared and its C/N was measured, and it was experimentally confirmed that the difference before and after the hub was bonded was as small as 0.6 dB.

In addition, the inventors changed the cross-sectional shape of the annular groove 4 of the magneto-optical disks A and C in many ways and measured the amount of C/N change. It was experimentally confirmed that there was no significant effect.

Therefore, the width of the annular a4 of magneto-optical disks A and C is l m
When the C/N change amount was measured by changing the depth in several ways, it was found that if the depth was less than 0.24 mm, that is, the ratio to the substrate thickness was less than 1/5, the C/N change amount was /N was not observed to increase, and when the depth exceeded 0.6 mm, the strength of the substrate itself decreased and warping occurred after molding. In addition, the inventors have found that the depth is one-fifth or more of the thickness of the substrate.
It has also been experimentally confirmed that it is desirable that it be less than 1/2 and 1/2.

Furthermore, in the above embodiment, the substrate thickness of 1 and 2 mm, which is a standard type according to the ISO standard, was used as an example, but the inventors believe that the same effect can be obtained even if the thickness is varied within the range of ±40χ. think. Moreover, in the above embodiment, the PC
It is thought that the same effect can be obtained even if a PMMA substrate or an epoxy resin substrate is used instead of the substrate, or even if the outer diameter of the substrate is φ86 mm or φ200 mm.

In addition, it goes without saying that the effects of the present invention can be obtained with respect to bonded disks other than those of the above-mentioned embodiments.

〔Effect of the invention〕

As described above, according to the present invention, the residual stress of the plastic disk substrate is separated and absorbed, thereby making it possible to provide a magneto-optical disk with improved C/N.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the magneto-optical disk of the present invention, and FIG. 2 is a sectional view showing the shape of an annular groove.・Polycarbonate substrate ・Annular groove ・Recording film ・Hub Patent applicant (663) Kyocera Corporation Representative Kinju Anjo

Claims (2)

[Claims] (1) A non-recording area inside the annular recording area of a plastic disk substrate on which an annular magneto-optical recording layer is formed and a hub is bonded to the center has a depth of 5% relative to the substrate thickness.
1. A magneto-optical disk characterized in that annular grooves having a diameter of 1/2 or more are formed at substantially the same location on both principal surfaces of a substrate. (2) The magneto-optical disk according to claim (1), wherein the annular groove is formed during injection molding of the plastic disk substrate.