JPS6015844A - Recording medium for high density information signal - Google Patents

Abstract

PURPOSE:To improve reproducibility of a recording medium with substantially no blister on the surface thereof by constituting said medium of a blank material contg. a thermoplastic resin which is suspension-polymerized by using a specific comd. and a conductive material. CONSTITUTION:A titled medium is formed of a blank material contg. a thermoplastic resin which is suspension-polymerized by using sodium polyacrylate as well as a conductive material. The sodium polyacrylate having a degree of polymn. ranging to 5,000-100,000 is suitable. The preferred amt. of use if the sodium polyacrylate having 50,000 polymn. degree is used is 0.005-0.05wt% by the weight of a monomer in the case of a vinyl chloride homopolymer and 0.01- 0.1wt% in the case of a copolymer. the vinyl chloride resin contg. extremely less water soluble high polymer compd. is obtd. by the powerful stabilizing effect for suspension and dispersion of the sodium polyacrylate and the disc produced by using the vinly chloride resin produced in the above-mentioned way decreases generation of a blister on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-density information signal recording medium such as a video disc or a digital audio disc, and in particular, information signals are recorded as changes in the geometrical shape of the surface. In a capacitive recording medium in which information signals are reproduced by changing the capacitance between the electrode of a reproducing needle that scans relative to the electrode according to changes in geometric shape, as the base material of this recording medium. As the thermoplastic resin to be used, for example, a vinyl chloride resin obtained by suspension polymerization using at least a little sodium polyacrylate as a suspension dispersion stabilizer can be used to improve recyclability. The object of the present invention is to provide a density information signal recording medium.

For example, an electrostatic trough type information recording medium uses a stamper with an information signal on its surface to compression-mold a conductive resin composition that has been cross-wire melted into a circle with information signals engraved on both sides. It is a plate-shaped molded body (hereinafter referred to as a disk).

This disk has uneven pits on its surface as signals, or spiral grooves with varying shapes and dimensions on its bottom, but each signal is extremely small and is densely arranged. This signal is traced by a diamond needle with an electrode at the tip and detected as a change in capacitance, and the video and audio are played back. As a system utilizing such a principle, a capacitive video disk system has been put into practical use, but in this system, the quality of the disk, which is an information signal recording medium, is important.

The quality of the disc is determined by the SN, which indicates the level of signal reproduction.
It is required to have high mechanical strength such as ratio, abrasion resistance against repeated playback, impact resistance, and elastic modulus, as well as lateral heat deformability.

As a result of numerous tests conducted in order to manufacture a disk with these properties, the conductive resin composition that makes up the disk consists of vinyl chloride resin, carbon black with a large surface area, and optionally stabilizers, lubricants,
Alternatively, it has been found that it is practically preferable to add a lubricant such as silicone oil.

In addition, the mixing, kneading, and forming of these conductive resin compositions into disks have been investigated in detail, and the equipment and methods for making disks with good performance have been established. Ta.

Although disk manufacturing technology has progressed, the problem of minute bulges occurring on the surface remains.

Signals on the surface of the disk are engraved with extremely high density as minute changes in shape. For example, JP-A-57-16
As described in '9326, the diameter is 26α
With a track pitch of 1.35 μm on both sides of the disk,
Approximately 50 billion signal pits with a depth of 0.3 to 0.4 μIn are carved. In order to accurately read such extremely minute signal pits, the occurrence of bulges that distort the shape of the signal pits and impair the smoothness of the disk surface has become a serious problem.

In other words, minute signals can be read by sliding a diamond needle with an electrode over concentric signal pits while controlled by a tracking signal (a method proposed by Victor Japan Co., Ltd.), or by carving a signal into the bottom. This is done by sliding the guide groove (method proposed by US R (3A company)), but the relative speed between the needle and the disk at this time reaches as much as 10 yn/sec.Therefore, bulges occur on the surface of the disk. And in this part,
The needle 1 jumps up from the surface of the disc, making it impossible to read the signal correctly, resulting in missing parts (hereinafter referred to as "Dronopaui") in the reproduced signal, and the needle jumping up. When it comes into contact with the disk surface again, it scrapes the disk body, erasing the signal in that area, further increasing dropouts, and at the same time generating dust that is undesirable for the disk.

The blisters that cause dropouts are caused by impurities contained in the raw material PVC resin, carbon black, or other additives, or by contamination during mixing or molding of the conductive resin composition. It was discovered that the generation was caused by foreign substances such as heat decomposition products or thermal decomposition products of vinyl chloride resin, and as a result of many studies, we were able to develop methods for producing raw materials with fewer impurities, or to develop highly thermally stable conductive materials. The problem has been solved to a large extent by the development of resin compositions, cross-wire machines, and sealed manufacturing systems, but the situation is still not satisfactory.

As a result of a detailed inspection of the substance that causes this blister using an electron microscope and an X-ray microanalyzer, we found that
The component that causes this swelling is an organic substance, and from its form and behavior, we have previously investigated foreign substances related to the manufacturing process, such as foreign substances from the shredding equipment, air, water, etc., and thermal decomposition of the material itself. It is not a product, and even if a completely different manufacturing method or even a completely different material is used, foreign substances that appear to be organic substances that cause the same swelling occur. We investigated various suspension polymerization dispersants used in the production of vinyl chloride resin, which is the main raw material.

As a result, it was found that the amount of suspension polymerization dispersant used varies depending on the amount of suspension polymerization dispersant used. That is, the type of suspension polymerization dispersant,
Alternatively, we investigated the dropout of vinyl chloride resins suspension-polymerized using different amounts of the suspension polymerization dispersant immediately after molding them into disks and after a period of time, and found that the results showed that the lower the amount of suspension polymerization dispersant used, the better the results. I found out.

The present invention was accomplished based on the above findings by producing and using a vinyl chloride resin suitable as a raw material for disks by a suspension polymerization method. As mentioned above, the vinyl chloride resin used for the disk requires good flowability in order to form fine information signals, so a homopolymer or copolymer with a low degree of polymerization is used.

Vinyl chloride resins with a low degree of polymerization, such as homopolymers with a degree of polymerization of 450, are produced by polymerizing at a polymerization temperature of 81°C, but when polymerized at such a high temperature, they cannot be uniformly mixed with a large amount of carbon black. Quite a lot of suspension dispersion stabilizer is required to make a complete product with a good particle size distribution.

Furthermore, when polymerization is carried out at such high temperatures, the resulting vinyl chloride resin particles become so-called glass beads with low porosity, making it difficult to remove unreacted vinyl chloride monomers. This tendency is more likely to appear in copolymers.

As a suspension dispersion stabilizer used in suspension polymerization of vinyl chloride resin, a water-soluble polymer compound may be used alone or in combination of two or more, or an oil-soluble polymer compound may be used in addition to a water-soluble polymer compound. Molecular compounds and surfactants are used in combination, but the most appropriate one is selected depending on the type of vinyl chloride resin to be manufactured, the degree of polymerization, or the purpose for which the vinyl chloride resin is used. It will be done.

In the suspension polymerization of vinyl chloride resins, depending on the type or combination of suspension polymerization dispersants used, the porosity and microstructure of the resulting particles may change, or the gelatinability, fluorine-yield, and transparency may change. Numerous studies have been conducted on the properties of vinyl chloride resins, such as changing their properties, but in most cases partially saponified polyvinyl acetate (hereinafter referred to as Bock) Compounds such as cellulose derivatives, copolymers of vinyl acetate and maleic anhydride, and polyvinylpyrrolid are used.

The present inventors also carried out studies in order to obtain a vinyl chloride resin suitable as a raw material for disks by suspension polymerization, based on the knowledge described above. In order to manufacture vinyl chloride resin, which is the raw material for discs, we prepare a sufficiently cleaned polymerization vessel, washing dehydration dryer, vinyl chloride monomer filter, ion-exchange water ∆ filter, etc. After conducting a polymerization reaction using various suspension polymerization dispersants, disks were manufactured and dropout was investigated.

As a result, polyacrylic acid l-
The present invention was completed based on the fact that vinyl chloride resin produced using IJum is preferable as a raw material for disks.

IJum (polyacrylic acid) is a highly water-soluble polymer compound that exhibits strong dispersion ability when used as a suspension dispersion stabilizer for vinyl chloride resins, so it can be used in small amounts to achieve fine particle size. A polyvinyl chloride resin with a uniform distribution can be obtained, but when used alone, the porosity of the particles becomes too low, making it difficult to remove unreacted vinyl chloride monomer, making it unsuitable as a raw material for disks. Even if it is suitable, it has the disadvantage of being unsuitable in the production of vinyl chloride resins, so it is preferable to use it in combination with other water-soluble polymer compounds. Water-soluble polymer compounds to be used in combination include poval, which has a strong dispersion power at high temperatures with a degree of saponification of 60 to 8%, and which has a strong effect of increasing porosity, or hydroquinopropyl cellulose, hydroqui-7 Cellulose derivatives such as bilmethylcellulose are preferred.

Polyacrylic acid used) l) Ram has different effects as a suspension dispersion stabilizer depending on its degree of polymerization. For the suspension polymerization of vinyl chloride resin, a polymerization degree in the range of 5,000 to 1.00,000 is suitable.

In the production of vinyl chloride resin, which is the raw material for disks, in order to remove foreign substances, it is necessary to make the suspension dispersion stabilizer into a water solution and then pass it through.
If it is too high above 00, it is 1. The viscosity of the aqueous solution becomes high, which is undesirable because it makes IJ″T filtration difficult, and if the degree of polymerization becomes too small (less than 5,000), emulsifying ability is developed and suspension polymerization is difficult. It becomes unsuitable.

The amount of sodium polyacrylate used varies depending on the type of vinyl chloride resin or the stirring conditions of the polymerization reactor, but for example, if sodium polyacrylate with a degree of polymerization of 50,000 is used, In the case of vinyl chloride homopolymer, 0.005 to 0.0 relative to the monomer
5wt%, 0.01-0.1wt% in case of copolymer
is suitable.

When using storium polyacrylate and other dispersants together, it is preferable that the other dispersants bear about 30 to 70% of the required suspension and dispersion capacity. In this case, the degree of dispersion ability of sodium polyacrylate may be considered to be about 7 to 15 times that of poval type or cellulose derivatives, which have strong dispersion ability.

The effect of using sodium polyacrylate is that, as mentioned above, its strong suspension and dispersion stabilizing effect makes it possible to reduce the amount of water-soluble polymer compounds used.
It is possible to obtain a vinyl chloride resin with a very low content of water-soluble polymer compounds, and discs manufactured using the vinyl chloride resin produced in this way have less blistering on the surface. , and of good quality.

Specific examples of the high-density information signal recording medium according to the present invention will be described below.

-tr, Before explaining the high-density information signal recording medium, the vinyl chloride resin, which is an important point of the present invention, will be explained.

[Production of vinyl chloride resin used in the present invention] Internal volume 60
Polymerization of vinyl chloride was carried out using an autoclave equipped with a 0-ton jacket and a stirrer. The autoclave to be used was filled with methylene chloride with scale attached in advance, and stirred for 1 hour while heating to 40°C. After that, the methylene chloride was extracted, and then, using pressurized water with a pressure of 60 Kg/cry G, the scale remaining in the vessel was completely removed, and then an additional 0.5
The inside of the vessel was washed with ion-exchanged water that had been passed through a μ filter.

The ion-exchanged water used for polymerization was also filtered through a 0.5μ filter. Vinyl chloride monomers and monomers to be copolymerized components were used after being filtered through a 1μ filter.

Sodium polyacrylate used for polymerization is 0.1wt
φ and other suspension dispersion stabilizers were dissolved to 2 wt % using the ion-exchanged water treated with d''j above, and the polymerization initiator was thoroughly filtered through a 1μ filter before use.

Polymerization was carried out according to a conventional method, and when the polymerization reaction rate reached 70%, unreacted vinyl chloride monomer was recovered.

Next, the mixture was extracted through a 42 me' wire mesh into a container equipped with a 1000 t extraction nozzle and a stirrer, which had been previously washed with the filtered ion-exchanged water.

The slurry obtained in this way was made into a cake using a centrifugal dehydrator installed in a pressurized room with clean air passed through a HEPA filter, and then the slurry was made into a cake, taking great care to prevent dust from getting mixed in. The mixture was dehydrated and dried to obtain powdered vinyl chloride resin.

[Manufacture of vinyl chloride resin used in comparative example] In the above [manufacture of vinyl chloride resin used in the present invention], a large amount of poval was used without using sodium polyacrylate,
Powder of vinyl chloride resin was obtained in the same manner.

Details of the vinyl chloride resin obtained as described above are shown in the table.

Table note 2) Poval Co-senol K1-1-17 Nippon Synthetic Chemical Industry ■Example 100 parts by weight of the vinyl chloride resin of experiment number 1 described in the above [Production of vinyl chloride resin used in the present invention],
RE of dibutyltin mercapto stabilizer (trivalent compound synthesis)
, 8=1) 5 parts by weight, fatty acid glycerin ester (RIKEN VITAMIN ■ US-210) 2.0 parts by weight, fatty acid alkyl ester (chemical soap ■ RES-310) 0.5
Part by weight, dimethylpolysiloxane (B of Shin-Etsu Chemical Co., Ltd.)
E S-421) 1.0 part by weight was blended and heated to 110°C using a 20t shell mixer, and then heated to 70°C.
℃, 20 parts by weight of conductive carbon black (08X-15OA manufactured by Cabosoto, USA) was added thereto, the temperature was raised to 110℃ again, stirred at high speed for 15 minutes, and then heated at room temperature 1. Cooling.

Thereafter, the pellets were made into pellets using a kneader PR-46 manufactured by Swissbus, and the metals contained in the pellets were removed through a metal detector and a red sea bream throat, and the pellets were made into pellets using a press machine exclusively for Videotisf. A disk was made.

Comparative Example The vinyl chloride resin j1 of Experiment No. 2 described in the above [Manufacture of vinyl chloride resin used in Comparative Example] was substituted for the vinyl chloride resin in the above Example, and a video was produced in the same manner. A disk was made.

In both the above-mentioned Examples and Comparative Examples, 20 heat discs were pressed using a meta/par disc on which a reference signal for signal measurement was recorded.

Then, the video disc obtained as above,
When the number of dropouts that are unacceptable in terms of playback image quality is measured using a dropout counter, in this example, the average number of dropouts per disc is 075; So, the average number of dropouts per card is 11.9.
Furthermore, as shown by the bar graphs in FIGS. 1 and 2, there are 12 out of 20 discs in which dropout does not occur at all, and even if dropout occurs, the number of dropouts is small. On the other hand, most of the video discs of the comparative example had many dropouts, and the video disc of the present invention is extremely excellent with no playback defects.

In other words, if only Poval is used as a suspending and dispersing agent in the production of the thermoplastic resin that is the base material for video discs, a lot of blistering occurs on the surface of the video disc after molding, which causes many dropouts. However, using sodium polyacrylate to reduce the total amount of suspension dispersant used during suspension polymerization and using a polymerized resin as the base material for video discs, There is almost no blistering on the video disc surface after molding, and therefore fewer dropouts occur.
Playback quality is excellent.

As mentioned above, the high-density information signal recording medium according to the present invention includes:
In a high-density information signal recording medium that records information signals by forming pits, the high-density information signal recording medium is made of a material containing at least a thermoplastic resin suspension polymerized using sodium polyacrylate and a conductive substance. With this structure, almost no blistering occurs on the surface of this high-density information signal recording medium, and the occurrence of dropouts caused by this blistering is extremely reduced, resulting in excellent reproduction.

[Brief explanation of the drawing]

Figures 1 and 2 show the dropout and dropout characteristics of video discs using polymerized resin as a base material, depending on whether or not sulfur/lium polyacrylate was used as a suspending and dispersing agent, respectively.・This is a bar graph showing the relationship with the video disc in which the above occurred. Patent Applicant: Victor Japan Co., Ltd. Tokuyama Sekisui Kogyo Co., Ltd. Agent: Katsumi Utaka Continued from page 1 0 Inventor: Noriki Fujii 3347 Oaza Tomita, Shinnanyo City 0 Applicant: Tokuyama Sekisui Kogyo Co., Ltd. 2 Nishitenma, Kita-ku, Osaka City chome 4-4

Claims (1)

[Claims] In a high-density information signal recording medium that records information signals by forming pits, the high-density information signal recording medium is made of a thermoplastic resin suspension-polymerized using at least sodium polyacrylate and a conductive material. A high-density information signal recording medium characterized by comprising: