JPH0318258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording medium, and particularly to constructing an optical information recording medium from a specific thermoplastic synthetic resin.

2. Description of the Related Art Optical information recording media provide information through reflected or transmitted light when exposed to light. This has already been used as a video disk, audio disk, information file disk, etc.

An optical information recording medium is based on a transparent plate with little deviation, and information is recorded by grooves or irregularities provided on the substrate. In practice, in order to record a large amount of information on one substrate, the grooves or irregularities have a small width of several microns or less, and are placed closely together. Since light is shined on the closely spaced small-width grooves or irregularities and the reflected or transmitted light is used as information, the base must be transparent and have extremely few irregularities. . That is, the substrate is required to have excellent shape stability, and in particular, it is required to have high heat resistance and low moisture absorption. Additionally, the base must be easy to form into a board.

Because of this need, the base of optical information recording bodies has been made of synthetic resin. The synthetic resins that have been used so far are mainly polymethyl methacrylate (hereinafter referred to as PMMA) and polycarbonate (hereinafter referred to as PC). All of these have excellent transparency and shape stability. However, upon careful consideration,
PMMA is highly hygroscopic and therefore has the disadvantage that the base will warp and deform if it is placed in a humid place. In addition, although PC does not easily deform due to moisture absorption, its surface hardness is low and it is easily scratched, and it is difficult to mold, and when molded, the orientation at the time of molding remains in the base, resulting in birefringence. Therefore, there was a drawback that reflected or transmitted light was disturbed. Therefore, none of the synthetic resins used so far have been satisfactory.

Therefore, the inventor set out to find a synthetic resin suitable for forming the base of an optical information recording medium. To this end, the inventor created various transparent hard synthetic resins and examined their properties. Among these, the inventor noticed that acetalized polyvinyl alcohol is hard and transparent, and that increasing the degree of acetalization reduces hygroscopicity and therefore improves shape stability. However, I have found that polyvinyl acetal generally has a drawback of having a low softening point and poor heat resistance. Therefore, it was found that it was necessary to further improve heat resistance. It has been found that it is effective to bring polyvinyl acetal into contact with fluorine gas to partially fluorinate the hydrogen in the polyvinyl acetal molecules in order to improve its heat resistance. This invention was completed based on such knowledge.

This invention provides an information recording medium based on a transparent synthetic resin plate, in which the synthetic resin is fluorinated polyvinyl acetal which is made by contacting polyvinyl acetal powder with fluorine gas to fluorinate it to increase the weight by 1% or more. The present invention relates to an optical information recording medium characterized by comprising:

The synthetic resin used in this invention is fluorinated polyvinyl acetal obtained by fluorinating polyvinyl acetal. First, polyvinyl acetal will be explained. Polyvinyl acetal is obtained by acetalizing polyvinyl alcohol with aldehydes or ketones. As polyvinyl alcohol, one having a saponification degree of 95% or more is suitable, and one having a polymerization degree of 100 to 2000 is suitable. Examples of aldehydes include aliphatic aldehydes such as formaldehyde, acetaldehyde, propylaldehyde, n-butyraldehyde, and isobutyraldehyde, aromatic aldehydes such as benzaldehyde, and alicyclic aldehydes such as cyclohexanecarbaldehyde. The ketones include polyvinyl acetal using aromatic ketones such as cyclohexanone. The degree of acetalization is preferably 65 mol% or more.

For fluorination, polyvinyl acetal is first ground into fine particles with a particle size of 0.5 to 50 microns. For example, a crusher is used for the crushing. The powder thus obtained is packed or arranged thinly so that as much gas as possible can pass therethrough, and fluorine gas is passed through the powder to bring it into contact with the powder. At this time, in order to prevent explosive fluorination, the fluorine gas is diluted with an inert gas, such as nitrogen, and brought into contact with the powder. The degree of dilution is, for example, 20% fluorine and 80% nitrogen by volume. Further, in order to accelerate the reaction, it is desirable to slightly warm the reaction system.

When polyvinyl acetal is brought into contact with fluorine gas as described above, the hydrogen atoms in the acetal are replaced by fluorine atoms, producing a fluorinated polyvinyl acetal. The fluorinated product produced is a mixture of compounds in which some hydrogen atoms in the polyvinyl acetal molecule are replaced with fluorine atoms. The weight of the produced fluoride gradually increases as fluorination progresses. Therefore, the degree of fluorination can be estimated by measuring the weight of the fluorinated product produced.

In this invention, the weight of the produced fluoride is 1%
It is assumed that the target fluorinated polyvinyl acetal has been produced when the amount has increased by the above amount. The reason is that according to experiments, when the weight increases by 1%, fluorination has already progressed to a considerable extent, and compared to the original polyvinyl acetal, the heat resistance has improved. This is because it is recognized that hygroscopicity has decreased.

The fluorinated polyvinyl acetal thus produced is then washed with water and dried to obtain a resin. This resin is a transparent hard thermoplastic resin, and compared to the original polyvinyl acetal,
It has excellent heat resistance and low moisture absorption. Even if it has excellent heat resistance, it becomes fluid when heated. Therefore, shape stability is good,
Easy to mold. The fluorinated polyvinyl acetal can also be mixed with the original non-fluorinated polyvinyl acetal and used as a resin.

Therefore, a small amount of a stabilizer, an antioxidant, a lubricant, etc. may be added to this resin and mixed, and this mixture may be formed into a plate shape to form an optical information recording medium. Conveniently, the molding is by an injection molding method. In the injection molding method, a resin mixture is heated and melted, and the molten resin is poured into a cooled mold for molding, so it is extremely efficient in molding. Therefore, the quality of moldability is determined primarily by the difficulty of injection molding, and therefore the quality of information recording bodies is also determined based on the board obtained by the injection molding method.

The optical information recording medium according to the present invention is made of a resin containing fluorinated polyvinyl acetal whose weight is increased by 1% or more by fluorinating polyvinyl acetal powder by contacting it with fluorine gas. As mentioned above, fluorinated polyvinyl acetal has excellent heat resistance and low hygroscopicity, so this information recording medium does not suffer from distortion during storage. In addition, fluorinated polyvinyl acetal has high fluidity when melted, so it is easy to mold, and it hardly leaves any distortion or orientation during molding, so it does not produce birefringence. Therefore, the use of this recording medium has the advantage that high-quality disks with large capacity can be easily created.

The advantages of the information recording medium according to the present invention will be explained below with reference to Examples and Comparative Examples, and the properties of the plates obtained therein were measured by the method described below.

(1) Measurement of heat resistance Measure the viscoelasticity using an ordinary viscoelastic spectrometer, calculate the storage modulus E' from this, and calculate the temperature dependence of the storage modulus E' as d(log10E')/dT= The temperature at 1/20°C was defined as the softening temperature Ts. Ts is a value approximately 5° C. lower than the usual glass transition point Tg.

(2) Measurement of moisture resistance A rectangular resin plate with a thickness of 0.5 mm, a width of 2 cm, and a length of 10 cm was left in a vacuum at 60°C for 24 hours to dry. The thus dried resin plate was immediately placed in a desiccator at 20°C, left to cool, and then its length was measured. Thereafter, it was immersed in pure water at 20°C for 72 hours, the length was measured again, and the water absorption elongation rate β was determined.

(3) Measurement of total light transmittance Measured according to ASTM D1003.

(4) Measurement of haze value Measured according to ASTM D1003.

Example 1 As polyvinyl acetal, polyvinyl alcohol having a degree of polymerization of 1700 was acetalized to 76.2 mol % with isobutyraldehyde.
This polyvinyl acetal is crushed in a grinder,
Particles with a particle size of 5 to 200 microns were obtained.

Spread this polyvinyl acetal on a plate to a thickness of about 2
The plate was spread to a size of 1.5 mm, placed in a reactor, and fluorine gas was introduced onto the plate to carry out a fluorination reaction. Fluorine gas is diluted with nitrogen gas to make the volume ratio of fluorine to nitrogen 20:80.
This mixed gas was fed at a rate of approximately 200 ml/min. The temperature inside the reaction vessel was set at about 50°C, and the fluorination reaction was carried out for 3 hours while stirring the inside of the reaction vessel with a fan under a pressure of 1 atmosphere. In this way, a fluorinated polyvinyl acetal was obtained. The weight increase of this product was 24%.

The fluorinated polyvinyl acetal thus obtained was pressed to form plates of 0.5 mm and 1 mm in thickness, and their properties were measured using the method described above. As a result, the heat resistance Ts is 80℃, and the humidity resistance β is
The total light transmittance was 93.3%, and the haze value was 1.5%.

Comparative Example 1 The polyvinyl acetal used in Example 1 (polyvinyl alcohol with a degree of polymerization of 1700 was acetalized to 76.2 mol% with isobutyraldehyde) was pressed to form a plate in exactly the same manner as in Example 1, and its properties were determined. It was measured. As a result, the heat resistance Ts was 77°C, the humidity resistance β was 0.2%, the total light transmittance was 93.9%, and the haze value was 0.9%.

Comparing this result with Example 1, it becomes clear that the plate of the present invention is superior.

Example 2 In this example, polyvinyl alcohol with a degree of polymerization of 1700 was acetalized to 72 mol % with benzaldehyde as the polyvinyl acetal. Polyvinyl acetal was obtained. The weight increase at this time was 11%.

A plate was made from the fluorinated polyvinyl acetal thus obtained in exactly the same manner as in Example 1, and its properties were measured. As a result, the heat resistance Ts is 110℃, and the humidity resistance β
was 0.55%, total light transmittance was 88.2%, and haze value was 0.2%.

Comparative Example 2 For comparison, the polyvinyl acetal used in the example (polyvinyl alcohol with a degree of polymerization of 1700 was acetalized to 72 mol % with benzaldehyde) was pressed to form a plate in exactly the same manner as in Example 2, and the following results were obtained. The properties were measured. As a result, the heat resistance Ts was 110°C, the humidity resistance β was 0.95%, the total light transmittance was 87.0%, and the haze value was 1.4%.

Comparing this result with Example 2, it becomes clear that the plate of the present invention is superior.

Claims (1)

[Claims] 1. An information recording medium based on a transparent synthetic resin plate, wherein the synthetic resin contains fluorinated polyvinyl acetal which is obtained by contacting polyvinyl acetal powder with fluorine gas to fluorinate it and increasing the weight by 1% or more. An optical information recording medium characterized by: