JPH05282702A - Substrate of information signal recording medium - Google Patents

Abstract

PURPOSE:To obtain the substrate which prevents the degradation in production efficiency and quality and satisfies both of excellent optical characteristics and transfer characteristics by constituting the substrate of a resin having about 0.1 to 1.0% shrinkage rate at the temp. lower than the glass transition point. CONSTITUTION:A magnetic recording film consisting of Ti/Fe/Co is formed by sputtering on the substrate and further a UV curing film is applied as a protective film thereon and is cured, by which an optical disk is constituted. The optical disk substrate is obtd. in such a case by using, for example, graphite reinforced polyethylene terephthalate as the resin for molding the optical disk substrate and injection molding the resin at 280 deg.C nozzle head temp. and 100 deg.C mold temp. The shrinkage rate of such substrate is 0.04%. The substrate has excellent optical characteristics and enables the exact transfer of pits.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate of an information signal recording medium used in a recording / reproducing system using a laser beam, for example.

[0002]

2. Description of the Related Art In recent years, an optical information recording / reproducing apparatus capable of irradiating a laser beam to record information on a recording medium and reproducing recorded information has been widely used. As a recording medium (optical disk) used in such an apparatus, a compact disk (CD), a video disk (VD), a write-once optical disk (WO), a rewritable magneto-optical disk (MO), etc. are known. As a substrate material for these optical discs, plastic is generally used in terms of productivity and cost, and the substrate is manufactured by injection molding means.

By the way, as a substrate material for optical disks,
BACKGROUND ART Conventionally, polycarbonate resins, acrylic resins and the like have been known, and these resins have a feature of excellent transparency.

[0004]

By the way, as a characteristic required for the plastics substrates used for these optical discs, the surface shape of the stamper arranged in the mold, that is, the information pit row is accurately transferred. Can be mentioned. In addition, it is possible to suppress occurrence of birefringence due to residual strain during injection molding, and high dimensional stability.

However, it cannot be said that the various resins proposed so far can sufficiently satisfy the optical characteristics such as birefringence and the transfer characteristics. For example, when a polycarbonate resin is used as the optical disk substrate material, the resin temperature is raised to solve the above problems, molding is performed under severe conditions, and the cooling time is extended to accurately transfer the information pit row. A means of increasing the cycle time has been considered. As a result, production efficiency decreases,
There is some deterioration in quality.

Incidentally, in Japanese Patent Laid-Open No. 1-264816,
In order to improve transferability, it has been proposed to devise a method of releasing the optical disk substrate at the end of molding, but this has not been fully solved. Therefore, an object of the present invention is to provide a substrate of an information signal recording medium which satisfies both excellent optical characteristics and transfer characteristics.

[0007]

The object of the present invention described above is such that the shrinkage ratio at a temperature lower than the glass transition temperature is about 0.1-1.
This is achieved by the substrate of the information signal recording medium, which is characterized by being made of 0% resin. It is preferable that the resin is made of a resin having a shrinkage ratio of about 0.3 to 0.7% at a temperature lower than the glass transition temperature. Examples of such resin material include polycarbonate, polymethylmethacrylate, epoxy resin, polyolefin resin,
It can be selected from resin materials such as polyesters, polycarbonates or polyester carbonates having a norbornane skeleton or naphthalene or anthracene skeleton in the main chain. Of course, it is not limited to these.

The present invention will be described in detail below. In molding an optical disk substrate, a resin such as polycarbonate that is heated and melted is injected into a mold cavity to which a stamper is attached. The mold has a temperature control mechanism, and the injected resin becomes a target molded product while being cooled. In precision injection molding, it is required to fill the mold cavity with resin at high speed, cool it quickly, and take it out from the mold. However, if it is taken out immediately after being injected into the mold cavity, the volume will decrease due to cooling shrinkage,
Sufficient transfer cannot be obtained. Therefore, in order to improve the transfer characteristics, it is necessary to take time for cooling, and the cycle time of injection molding becomes long. Further, in molding an optical disk substrate, it is required to raise the mold temperature in order to improve the optical characteristics. Therefore, from this aspect as well, the cycle time of injection molding becomes long.

By the way, as a result of research by the present inventors, in order to accurately transfer the surface shape of the stamper arranged in the mold cavity, that is, the pit row, the shrinkage rate in the resin cooling process in the cavity is important. It turns out that they play a different role. Moreover, it has been found that the shrinkage rate in the region of the glass transition temperature (Tg) or lower of the resin used is particularly important. That is, the Tg of the resin used
In the temperature range below, the shrinkage rate becomes slower, and therefore a long cooling time is required to obtain a sufficiently accurate transfer, the cycle time of injection molding becomes longer, and the production efficiency decreases. As I did,
Here, the shrinkage ratio at a temperature lower than the glass transition temperature is about 0.
In the case of 1 to 1.0%, since the shrinkage rate is small, the volume reduction due to cooling shrinkage is much smaller even if the material is taken out of the mold by cooling quickly, and even if the cycle time of injection molding is shortened. A sufficiently accurate transfer was obtained.

The shrinkage ratio described in the present specification means the ratio of the substrate size at the glass transition point to the substrate size taken out from the mold, which means that the above-mentioned precision injection molding process is performed under pressure. Pv using (p), temperature (T), and specific volume (v)
This is explained using the T diagram (FIG. 1). First, injection is started at point A on the pvT diagram, and the pressure in the cavity rises with the injection. Next, at point B, the injection is completed and the pressure is maintained. At this point, cooling starts and the shrinkage progresses to the glass transition temperature at point C. Furthermore, when the point D is reached, the substrate is taken out from the mold. C in FIG.
The specific volume difference between the point and the point D is the contraction, and therefore the contraction rate is the ratio between the substrate size at the glass transition point and the substrate size taken out from the mold.

Hereinafter, the present invention will be described more specifically with reference to Examples.

[0012]

【Example】

Example 1 An optical disk substrate was obtained by injection molding using Panlite AD5503 (polycarbonate manufactured by Teijin Kasei) as a resin for molding an optical disk substrate at a nozzle head temperature of 350 ° C. and a mold temperature of 115 ° C. The shrinkage rate of the obtained substrate was 0.5%.

Then, Tb / Fe / Co is formed on the substrate surface.
A magnetic recording film made of was formed by sputtering, and an ultraviolet curable film was applied and cured thereon as a protective film to form an optical disc. [Example 2] An alicyclic polycarbonate resin having a norbornane skeleton was used as a resin for molding an optical disk substrate,
An optical disk substrate was obtained by injection molding at a nozzle head temperature of 260 ° C and a mold temperature of 110 ° C. The shrinkage rate of the obtained substrate was 0.3%.

Then, Tb / Fe / Co is formed on the substrate surface.
A magnetic recording film made of was formed by sputtering, and an ultraviolet curable film was applied and cured thereon as a protective film to form an optical disc. [Example 3] An alicyclic polyester carbonate resin having an anthracene skeleton was used as a resin for molding an optical disk substrate, a nozzle head temperature was 270 ° C, and a mold temperature was 115 ° C.
An optical disk substrate was obtained by injection molding. The shrinkage rate of the obtained substrate was 0.7%.

Then, Tb / Fe / Co is formed on the substrate surface.
A magnetic recording film made of was formed by sputtering, and an ultraviolet curable film was applied and cured thereon as a protective film to form an optical disc. [Comparative Example 1] Polybutylene terephthalate was used as a resin for molding an optical disk substrate, and the nozzle head temperature was 280.
An optical disc substrate was obtained by injection molding at a mold temperature of 90 ° C. The shrinkage rate of the obtained substrate was 1.8%.

Then, Tb / Fe / Co is formed on the substrate surface.
A magnetic recording film made of was formed by sputtering, and an ultraviolet curable film was applied and cured thereon as a protective film to form an optical disc. Comparative Example 2 An optical disk substrate was obtained by injection molding at a nozzle head temperature of 280 ° C. and a mold temperature of 100 ° C. using graphite reinforced polyethylene terephthalate as a resin for molding an optical disk substrate. The shrinkage rate of the obtained substrate was 0.04%.

Then, Tb / Fe / Co is formed on the substrate surface.
A magnetic recording film made of was formed by sputtering, and an ultraviolet curable film was applied and cured thereon as a protective film to form an optical disc. [Characteristics] The transferability of the pit train on the stamper in the optical discs obtained in each of the above examples was evaluated by measuring the diffraction efficiency with a laser beam of 633 nm. The results are shown in Table 1.

[0018]

[0019]

According to the present invention, a substrate of an information signal recording medium on which optical characteristics and pits are accurately transferred can be obtained.

[Brief description of drawings]

FIG. 1 is a pvT diagram for explaining contraction rate.

Claims (1)

[Claims] 1. A substrate for an information signal recording medium, which is made of a resin having a shrinkage ratio of about 0.1 to 1.0% at a temperature lower than the glass transition temperature.