JPS62236154A - Grooved master disk - Google Patents

Abstract

PURPOSE:To enormously improve heat resistance, release characteristic and dimensional stability by attracting and fixing a grooves substrate formed by using a poly-4-methyl pentene and molding the same by an injection molding method or injection compression molding method to a metallic plate or glass plate having excellent smoothness by a negative pressure. CONSTITUTION:A nickel master disk formed by subjecting the poly-4-methyl pentene to nickel electroforming or glass master disk formed with grooves by etching is used as the master disk. The grooved substrate obtd. by taking the master disk into a mold for injection molding or injection compression molding is attracted and fixed to the metallic plate or glass plate having the excellent smoothness by the negative pressure. The master disk attracted and fixed with the inexpensively and easily available polymethyl pentene substrate by a vacuum chucking system is used without using the costly metallic or glass master disk and therefore, the heat resistance, release characteristic and dimensional stability which are the characteristics possessed by the poly-4-methyl pentene are effectively utilized.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a grooved master disk for molding a grooved optical disk substrate, and more specifically to a photopolymer method (hereinafter referred to as 2P method) and an integral casting method. Due to the molding method,
This invention relates to a master disk made of poly-4-methylpentene for forming a substrate for a grooved optical disk.

[Prior art]

Optical discs, which are one of the important media, have been rapidly developed and put into practical use in recent years, and their use in computer-related applications is attracting particular attention. With these developments, it has become necessary to economically supply optical discs with high capacity and high quality. When manufacturing a writable and rewritable optical disc, it is necessary to form tracking servo grooves on the optical disc substrate.

In these methods of forming tracking servo grooves, the groove shape is very fine and precision is required, and nickel master disks obtained by nickel electroforming, ion etching, plasma etching, etc. are used. The 2P method uses a glass master disk obtained by directly using an ultraviolet curing resin to form a transfer onto a flat plate such as plastic, glass, or aluminum, or directly uses these master disks as cavities and creates grooves using liquid resin. A method of integrally casting a substrate and a method of molding a grooved substrate by injection molding or the like are known.

Among these methods, the 2P method and the integral molding method have better shapes of transferred grooves than other methods, and are advantageous as methods for obtaining high-quality disk substrates. However, the nickel master discs and glass master discs used in these methods are very expensive, require great care when handling, and there are no perfect methods for cleaning the grooves when dirt or resin adheres to them. Currently, if dust or resin adheres to the disc, it loses its value as a master and must be discarded.In general, grooved optical disc substrates are manufactured in large quantities using the 2P method or the integral cast molding method. The disadvantage was that a large number of master discs were required to perform the process, and a large amount of investment was required to deal with them.

In addition, in the 2P method and the integral casting method, depending on the resin used, there is a problem in releasing the mold from the master disc. Even if a mold release treatment is applied to the mold, the number of man-hours will increase, and there is a risk that new defects or foreign matter will be mixed in due to the treatment.

Therefore, from the viewpoint of inexpensively and easily producing 1 q of master disks, the present inventors investigated a method in which grooves are transferred from a metal or glass standby with plastic, and an optical disk substrate is manufactured using the plastic master disk. With emphasis on productivity, we decided to select a material for the master disc that could be processed by injection molding or injection compression molding. Furthermore, when applying to the monolithic method or photopolymer method, consideration was given to the substrate material or the mold releasability and heat resistance of the photopolymer method.

Materials that can be applied to such conditions include fluororesin,
Poly-4-methylpentene and the like have been mentioned, but fluororesins have poor releasability from metal molds when injection molding is performed, as described in JP-A-60-245515, etc., so they are not suitable for this purpose. Poly 4- as an alternative material
Methylpentene was found to be a suitable material for this purpose because it is easy to injection mold. However, poly-4-methylpentene generally has a large molding shrinkage of 1 to 3%, which causes warping and waviness after molding, so it is impossible to use it as is. As a countermeasure, there is a method of reinforcing the metal plate by lining it with an adhesive, but at present no satisfactory adhesive has been found for poly-4-methylpentene due to its mold releasability.

[Purpose of the invention]

In view of the current situation, the present invention has been made as a result of intensive research into the material and manufacturing method of a master disc for producing grooved optical disc substrates more economically and easily. The purpose of this method is to obtain a grooved master disc with excellent properties and dimensional stability.

[Structure of the invention]

In the present invention, a nickel master disc made of nickel electroformed poly-4-methylpentene or a glass master disc with etched grooves is used as a master master disc, and the master master disc can be molded by incorporating the master master disc into a mold for injection compression molding. The present invention relates to a master disc for the integral casting method and the 2P method, in which a grooved substrate is fixed to a metal plate or glass plate with excellent smoothness by suction under negative pressure, that is, fixed by a vacuum chuck method.

The resin used to form the grooved master must have (1) good heat resistance, (2) good surface precision (good transferability of the grooves from the master master), and (3) good moldability. (4) It has excellent mold release properties from resins that form substrates and grooves, and the surface is not attacked by these resins, and (5) It has excellent moisture resistance. Poly-4-methylpentene is an example of a material that satisfies all of these conditions.

Poly-4-methylpentene is injection molded or injection compression molded to form grooved master discs, and it is desirable that the thickness of these grooved master discs be 5 mm or less so that the grooved surface can be accurately transferred from the master master disc. If the thickness is 58 mm or more, it may be difficult to accurately reproduce the groove portion due to molding distortion, sink marks, etc., and the accuracy of the groove shape may deteriorate.

The injection molding conditions are mainly a molding temperature of 280 to 320°C and a mold temperature of around 130°C. Further, it is preferable that the groove width, groove depth, etc. of the master disc are determined in consideration of the molding shrinkage rate of the poly-4-methylpentene used.

The obtained master disk is suctioned and fixed to a smooth flat plate using a vacuum chuck method to give it smoothness and rigidity. An example of its structure is shown in FIG. The master disc is placed on a smooth flat plate and temporarily held in place with a master disc retainer ring.

In this state, by removing air from 8, the master disk maintains smoothness on the flat plate and is completely adhered to the flat plate. Here, it is preferable that the contact area between the master disc holding ring and the master disc be processed to be extremely smooth in order to maintain tightness, but the gap may be sealed with a sealing material or the like.

A grooved optical disk substrate is manufactured by the integral casting method and the 2P method using the master disc having the above-described configuration.

Next, an example of the manufacturing method will be shown.

]1) One-piece casting method As an example of the structure of a mold used, a cavity as shown in FIG. 3 is assembled, and a thermosetting resin is cast and cured. Here, it is preferable that vacuum adsorption is always performed during curing.

After demolding, a substrate in which the disk substrate and the groove are integrated is obtained.

Thermosetting resin is mainly used as the resin for the integrally molded substrate used in the present invention, and the physical properties of the thermosetting resin as a cured product preferably include a light transmittance of 90% or more, a glass transition point of 120°C or more, There is no particular limitation as long as the birefringence is 10 nm (double pass) or less, but among these, the epoxy resin/curing agent system has well-balanced physical properties and is most suitable as a substrate material.

The combination of epoxy resin/curing agent is not particularly limited as long as it satisfies the above physical properties, and known materials can be used.

2) Photopolymer method FIG. 2 shows the manufacturing process of a grooved substrate by the photopolymer method using a mold according to the present invention. Further, when obtaining a grooved substrate by the 2P method, all known ultraviolet curable resins can be used, and the resin can be selected depending on the purpose.

According to the present invention, an expensive metal or glass master is not used, and a polymethylpentene substrate, which can be easily obtained at low cost, is adsorbed and fixed using a vacuum check method. By taking advantage of its heat resistance, mold releasability, and dimensional stability, and by overcoming its drawback of molding shrinkage, it has sufficient utility as a master disk for producing grooved optical disk substrates, and its industrial significance is great. It can be said.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a master disk in which a grooved substrate of poly-4-methylpentene is closely attached to a smooth metal plate by a vacuum chuck method. FIG. 2 is a process diagram for producing a grooved optical disk substrate by the 2P method using the master disk shown in FIG. 1. FIG. 3 is a diagram showing an example of an integral cast molding method using the master disk shown in FIG. 1. In the figure, 1... Smooth metal plate, 2... Grooved poly-4-methylpentene substrate, 3... Board holding ring, 4...
・・Fixing bolt, 5・Air handling port, 6・・
- Ultraviolet curing resin for 2P, 7... Flat plate carrier for transparent optical disk, 8... Transparent flat plate for pressurization, 9... Light source, 10... Glass template, 11... Resin injection port,
12...Resin fastening part, 13...Resin for two-piece cast molding patent applicant Sumitomo Bakelite Co., Ltd. w & 1 drawing (A-Pa) 1s3 drawing 112 drawing

Claims (1)

[Claims] In a grooved master disk used for manufacturing grooved optical disk substrates for tracking servos, a grooved substrate formed by injection molding or injection compression molding using poly-4-methylpentene is molded into a metal plate or glass plate with excellent smoothness. Grooved master disc for integral casting method and photopolymer method, which is fixed by suction under negative pressure.