JPS6412018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-density information recording carrier (hereinafter simply referred to as a disk) such as a video disk. More specifically, the present invention relates to a disk manufactured by injection molding using a new plastic material as a disk base material.

As is well known, such a disk records a video signal together with an audio signal as uneven information bits on a disc-shaped recording medium, that is, a disk, and to reproduce the signal, an optical method using a laser beam or the like is used. Alternatively, there is a method such as a capacitance method that uses a change in capacitance.

In the manufacture of such disks, many methods are used to mold plastic, but this involves machining embossments corresponding to the information to be recorded on the plastic sheet using a stamper, which is a compound body of signals. Alternatively, there is a method of incorporating a stamper into a mold and molding the disk by injection molding. Of these two methods, the latter injection molding method has the advantage of requiring fewer manufacturing processes and requiring less heat energy during processing, resulting in lower manufacturing costs.

However, there are some difficulties in molding such a disk by injection molding. In particular, since this disk is a disk with a diameter of 300 mm and a wall thickness of approximately 1.2 mm, the plastic material must have extremely good fluidity to be able to obtain such a molded product. First of all, the unique flow characteristics of the material must be excellent, in other words, the molding conditions during injection molding, especially the distance that the material flows within the mold at the specified injection pressure and injection speed, that is, the flow length must be large. It is. Next, the material must have the ability to accurately transfer a large number of uneven shapes. Furthermore, in the case of a detection method using a laser beam, that is, a so-called optical reproduction method, the material itself must have a high light transmittance (preferably 88% or more). However, no plastic material having such excellent fluidity was known.

The present inventors have conducted extensive research on plastic materials that can be used for such purposes, particularly regarding their ability to accurately transfer unevenness.
It was discovered that the methyl methacrylate copolymer containing the above is significantly superior to polymethyl methacrylate in such performance, and the present invention was completed.

That is, the present invention provides a high-density information recording carrier for optically reading information, in which a disk base material is made of methacrylate consisting of 97 to 20% by weight of methyl methacrylate and 3 to 80% by weight of a vinyl monomer copolymerizable with methyl methacrylate. The present invention relates to a high-density information recording carrier characterized by using an acid methyl copolymer.

Vinyl monomers copolymerizable with methyl methacrylate that can be used in the present invention include aromatic vinyl monomers such as styrene, α-methylstyrene, m
- Methylstyrene, p-methylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,5-dichlorostyrene, m-bromstyrene, p-bromstyrene; unsaturated nitrile monomer, For example, acrylonitrile, methacrylonitrile; methacrylic acid alkyl esters, such as ethyl methacrylate, propyl methacrylate, butyl methacrylate, stearyl methacrylate, octyl methacrylate; acrylic acid alkyl esters, such as methyl acrylate, ethyl acrylate, propyl acrylate , butyl acrylate, octyl acrylate, stearyl acrylate; etc., and each can be used alone or in a mixture thereof.

Among the above, methyl methacrylate-styrene copolymer is particularly preferred.

The reason why methyl methacrylate copolymers such as methyl methacrylate-styrene copolymers have good transferability of uneven shapes is not yet clear, but it is thought to be as follows. In other words, the molten plastic injected into the mold cavity from the nozzle of the injection molding machine does not sequentially transfer the fine shape of the mold from the gate side to form the molded product, but is first injected into the mold cavity. It is thought that the filled high-temperature molten plastic is filled all at once, and by holding the injection pressure for a predetermined period of time, it is pressed into the fine shape of the mold, transferred, and then solidified. From this point of view, by copolymerizing with methyl methacrylate a certain amount or more of a monomer that can be copolymerized with methyl methacrylate, such as styrene,
It is presumed that the fluidity increases under high shear stress, making it easier to adhere to the mold surface having such fine irregularities, and as a result, the irregularities can be accurately transferred.

The disk of the present invention has information pits carved on one side, the surface is coated with metal, and the disk is suitable for use in an optical system that uses a laser beam to read information by irradiating a laser beam from the back side. preferable.

Such optical high-density information recording carriers are used to make products called optical disks, and optical disks are divided into playback-only disks such as video disks and CDs, and optical recording disks. The latter are classified into write-once optical disks, which are permanent records once recorded, and rewritable optical disks, which can be erased and written. Rewritable optical disks are currently in the development stage by applying phenomena such as optomagnetic or phase change. The disc base material of the present invention is extremely useful for manufacturing these optical discs.

The typical manufacturing process for these optical discs is as follows: First, a master disc is created from a resist master in which a resist is applied onto polished glass using a short wavelength Ar ⁺ or He-Cd gas laser of approximately 450 nm. A stamper, which is a resin molding mold, is made via a nickel master, which is a press mold, and this stamper is assembled into the mold to make a disk plate by resin injection molding. After this, a recording film and a reflective film are formed by vapor deposition, etc., and the upper part is covered with a transparent protective layer.
Optical video discs, CDs, optical recording discs, etc. are completed.

In carrying out the present invention, the surface of the disk plate can also be subjected to antistatic treatment.

Next, examples of the present invention will be shown.

Example 1 Methyl methacrylate/styrene = 60/40 (weight ratio), weight average molecular weight 130000, number average molecular weight by injection molding using a mold equipped with a stamper.
35,000 copolymers were molded. When the disk obtained by vapor-depositing aluminum on the signal surface of the molded product was used to reproduce images using a Phillips-type player, images were reproduced with extremely little jitter or signal dropout.

Example 2 In Example 1, methyl methacrylate/styrene = 85/15 (weight ratio), weight average molecular weight 117000,
A disk was obtained in the same manner except that a copolymer having a number average molecular weight of 65,000 was used. This disk showed good performance similar to that of Example 1.

Example 3 In Example 1, methyl methacrylate/acrylic acid = 95/5 (weight ratio), weight average molecular weight
A disk was obtained in the same manner except that a copolymer having a number average molecular weight of 124,000 and a number average molecular weight of 65,000 was used. This disk showed good performance similar to that of Example 1.

Example 4 Methyl methacrylate/ethyl acrylate = 90/10 (weight ratio), weight average molecular weight 91000, number average molecular weight 52000 by injection molding using a grooved stamper
A copolymer was molded. The grooves were sufficiently transferred onto the molded product. Next, a magnetic film of cobalt and gadolinium was sputtered onto the molded product to obtain a disk. Information recorded on the disc was reproduced with almost no noise.

Claims (1)

[Claims] 1. In a high-density information recording carrier that reads information optically, the disk base material is a methyl methacrylate system consisting of 97 to 20% by weight of methyl methacrylate and 3 to 80% by weight of a vinyl monomer copolymerizable with methyl methacrylate. A high-density information recording carrier characterized by using a copolymer.