JPS59223962A - Highly dense information signal recording medium - Google Patents

Abstract

PURPOSE:To obtain a highly dense information signal recording medium having an excellent reproducing characteristic to be used for video disk, digital audio disk, etc., at a high yield and low cost, by making the recording medium of a base material containing a conductive material and a cleaned thermoplastic resin. CONSTITUTION:Stamper contamination is minimized by reducing the quantity of suspension dispersant adhering to a polyvinyl chloride resin. Cleaning of a polymerized slurry is performed by using cleaned water, from which fine foreign matters are removed. It is most desirable to use ion-exchanged water. Practically, however, the cleaning of the polymerized slurry is performed by repeating procedures of making cake from the slurry by using a dehydrator and making the slurry again from the cake by adding water to the cake. Cleaning frequency or the quantity of water to be used depend upon the kind and quantity of the used suspending polymerization dispersant or cleaning method, but, when the dehydrator is used, water is used more than twice as much as the polyvinyl chloride resin at one time cleaning. It is not necessary to specify the temperature for making this cleaning, but it is recommendable to set the temperature to 10- 50 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-density information signal recording medium such as a video disk or a digital audio disk, and in particular, information signals are recorded as changes in the geometrical shape of the surface. An essential component of a capacitive recording medium in which information signals are reproduced by changing the capacitance between the electrode and the reproducing needle that scans the reproducing needle in accordance with changes in geometric shape. As a thermoplastic resin used as a component, for example, a vinyl chloride resin obtained by suspension polymerization using a suspension dispersant mainly composed of a water-soluble polymer compound is substantially purified by washing and purifying means such as washing with water. By removing the suspending dispersant and using purified vinyl chloride resin obtained by drying, high-density information signal recording media with good playback characteristics can be obtained at a high yield and at a low cost. The object of the present invention is to provide a density information signal recording medium.

For example, a capacitance type information signal recording medium is made by compression molding a conductive resin composition that has been cross-wire-melted using a stamper with information signals on its surface, and is shaped like a disk with information signals engraved on both sides. This is a molded body (hereinafter referred to as a disk). This disk has concentric circles or helical grooves with concave and convex pits or changes in bottom geometry carved into the surface as signals. Each signal is extremely small and densely arranged, and this signal is detected as a change in capacitance while being traced by a diamond needle with an electrode at the tip, and is amplified and reproduced. A capacitive video disc system has been put into practical use as a system that utilizes this principle, but the quality of the disc, which is the information signal recording medium, is extremely important in this system3. There are items necessary to maintain the performance of a disc for a long period of time, such as SN ratio indicating the level of signal reproduction, durability against repeated reproduction, mechanical strength, heat resistance, and humidity resistance, and it is necessary to ensure these performances. In order to achieve this goal, numerous studies were conducted on conductive resin compositions and molding techniques for making the disks.

As a result, the conductive resin composition used to make the disk is made of vinyl chloride resin, carbon black with a large surface area, and, if necessary, a stabilizer, lubricant, or lubricant such as silicone oil. It turned out to be the most suitable.

Mixing or kneading these conductive resin compositions,
Also, with regard to molding into discs, detailed machining tests have been carried out, and equipment and methods for producing discs with good performance have been established.

The signals on the surface of the disk are minutely shaped changes that are carved at a very high density and are precisely sized. For example, JP-A-57-16
As described in Publication No. 9326, 1.35 μm
With a track pitch of , there are approximately 50 billion signal pits with a depth of 0.3 to 0.4 μm.

This signal pit has a diameter of 9 cnL at the innermost point and a diameter of 25 cHL at the outermost point on the surface of the disk with a diameter of 26 cn'L.
In between, the pits are arranged in concentric circles with a pitch of 1.35 μm, but in the innermost part, the pit-to-pit distance is approximately Q, 67 tm, and at the outermost part, it is extremely fine, approximately 1.7 μm1. . Furthermore, the tracking stop signal has a width of 06 to
A pit of 0.7 μm and a depth of 0.05 μm is cut to an appropriate size.

In order to read such minute signals, a diamond needle with electrodes can be controlled by a tracking signal and be slid over concentric signal pits (a method proposed by Victor Japan Co., Ltd.), or a signal can be carved into the bottom of the diamond needle. This is done as a change in capacitance by sliding the guide groove (a method proposed by ROA in the United States).
It is played back as video and audio, but in this case it is important that the signal is shaped accurately. In other words, if signal shaping is inaccurate, high-quality video and audio cannot be obtained, and the quality of the product deteriorates. In addition, if the signal formation is very poor, the S/N may decrease, signals from adjacent signal pits may leak into each other, or if the signal formation is extremely poor, the tracking signal may become unclear, or the shape of the guide groove may deteriorate. It may even become distorted, making it impossible to track correctly.

There are many reasons why such signal shaping cannot be performed accurately, and many studies have been conducted to solve them.

In other words, the type of raw material vinyl chloride resin, selection of stabilizers, lubricants, etc., crosstalk conditions, press molding conditions, etc. affect the formation of minute signals. Using the molding equipment proposed in 2013, it has become possible to manufacture satisfactory discs using selected raw materials and optimal conditions.

However, in carrying out full-scale production, a problem arose in that the stamper was contaminated and the signal was poorly formed. In particular, as the number of sheets pressed increased, dirt accumulated on the stamper, resulting in a deterioration in S/N and crosstalk.

To manufacture a disk, a lump of molten conductive resin composition is compression-molded in a mold equipped with a stamper having minute convex projections corresponding to signals on the surface, and then cooled.
Alternatively, the molten material is injected between the molds equipped with stun nozzles, cooled, and shaped. In either case, after the molten material flows from the center of the disk toward the periphery, It is cooled and becomes a thin plate.

The stamper is made from a mother plate by nickel electroforming, and the process is well controlled to ensure that minute protrusions corresponding to signals are formed accurately, so while the stamper is new, it can be molded under good conditions. The disc has an accurate signal formed. However, as disks were manufactured using the same stamper, the S/N of the disks began to decline. The decrease in S/N starts from the center of the disc and spreads toward the outer periphery, but in such a state, the quality is significantly degraded and the disc cannot be used as a commercial product. Although it was found that this problem could be solved by replacing the stamper with a new one, this greatly hindered commercialization from the standpoint of manufacturing costs of the disk. In other words, not only is the expensive stamper worn out, but also the time lost in replacing it.
After replacing the molding machine, high costs arise due to the loss of raw materials needed to optimize the molding conditions of the molding machine.

Therefore, we decided to find another way to solve this problem.

First of all, when we closely observed the formation of signal pits on a disk with a reduced S/N using a scanning electron microscope, we found that
It was found that even though the signal pits were formed accurately on the center side of the disk, they were inaccurate on the outer circumferential side of the disk. When the outer peripheral side of the signal was observed in more detail, it was found that the conductive resin composition was insufficient in this area.

Next, when we observed the surface condition of the stamper that had been used until the S/N decreased using a scanning electron microscope, we found that the shape of the protrusions in the areas corresponding to the areas where the signal formation on the disk was inaccurate was uneven. It was observed that it was deformed.

In order to understand why this deformation occurred, we used a scanning electron microscope to observe video discs and stampers whose S/N ratio had deteriorated in the order of the number of sheets pressed, and found that it was not due to deformation of the stamper itself, but that some kind of material had formed during the molding of the disc. It was assumed that this was precipitated. Therefore, an attempt was made to analyze this precipitate, but it was not possible to obtain clear results because the amount was extremely small.

From the above results, the problem of S/N decreasing as disk manufacturing continues is due to the stamper surface,
In particular, it has become clear that constituent components of the conductive resin composition, which is the molding material for the disk, are deposited on the outer periphery of the projections corresponding to the signals (hereinafter referred to as stamper stain).

The phenomenon of stamper stains is known to occur during the molding of conventional audio records, so when molding video discs, this point must be taken into consideration when determining the composition and molding conditions. However, there are major differences in the composition, such as the inclusion of a large amount of carbon black and incompatible substances such as silicone oil.Also, in the molding, the dimensions of the irregularities corresponding to the signal are extremely small, and the audio In this case, the fact that deposition on the stamper was allowed up to about 10 μm was of little help.

For this reason, even in the production of video discs, it has become necessary to solve the problem of stamper stains.

First, since it was not possible to identify the substance that caused stamper stains, we investigated components other than carbon black and vinyl chloride resin, and selected stabilizers, lubricants, and lubricants that caused less precipitation. As compounding agents with less precipitation, preferred results were obtained using a liquid organic tin-based stabilizer and a liquid ester-based lubricant. It was also found that silicone oil as a lubricant had almost no effect. The compounding agent selected in this way has a relatively low molecular weight that has good compatibility with vinyl chloride resin, as has been known for a long time, and since it is a liquid, it must be filtered before use. This was advantageous in the manufacture of disks, as it also made it possible to remove foreign substances.

Next, we investigated vinyl chloride resins by keeping the types of compounding agents constant. As the vinyl chloride resin, vinyl chloride homopolymer with a degree of polymerization of 450, vinyl chloride-ethylene copolymer containing 2% ethylene, or ethylene-vinyl acetate containing 5% ethylene and vinyl acetate copolymer.
We selected three types of vinyl chloride graft copolymers and made them into pellets of conductive compositions with the same composition to manufacture disks, and investigated the occurrence of stamper stains.As a result, we found that vinyl chloride homopolymer However, compared to the other two types of copolymers, it was found that there was less stamper staining.

Therefore, we further investigated the cause of this difference and found that stamper stains were not caused by the type of vinyl chloride resin, but rather by the amount of suspension polymerization dispersant used in the process of manufacturing vinyl chloride resin. It is presumed that this is due to the fact that the vinyl homopolymer has a low
I found a way to solve this problem.

The vinyl chloride resin that is the raw material for capacitive video discs is preferably manufactured by suspension polymerization, which has an appropriate particle size distribution, is easy to handle, contains few impurities, and has good thermal stability. has been done. However, as mentioned above, it was completely unexpected that the amount of suspension polymerization dispersant used in the polymerization reaction would affect stamper staining.

When producing a vinyl chloride resin by suspension polymerization, a water-soluble polymer compound is used as a suspension polymerization dispersion stabilizer in order to obtain a polymer with an appropriate particle size distribution. A large number of water-soluble polymer compounds are used singly or in combination, but generally, partially saponified polyvinyl acetate (hereinafter referred to as poval), cellulose derivatives, and vinyl acetate (11) are used. Copolymers of maleic anhydride and polyvinylpyrrolidone are used. There are many types of cellulose derivatives depending on the molecular weight, degree of saponification, or combination with a third component, etc., and the type and amount of substituents, but in any case, the target vinyl chloride resin selected according to its characteristics.

Vinyl chloride resin, which is the raw material for video discs, has a low polymerization degree of 350 to 500, so it polymerizes at a relatively high temperature of 60°C to 80°C, so the porosity of the resulting vinyl chloride resin particles is tends to become smaller, resulting in poor gelling properties and difficulty in removing unreacted J-enriched vinyl monomers. Poval, which has a small molecular weight and a saponification degree of 60 to 80, and cellulose derivatives such as hydroxypropyl cellulose and Nekkel 4114
Hydroxypropyl methyl cellulose which is heated to 70° C. or higher is suitable.

After obtaining this knowledge, we made polymerizations of the three types of vinyl resins mentioned above (12) using the same type of dispersant and polymerizations with different amounts, and from this polymerization slurry, we made a single polymerization slurry. The part is that'-jf. After dehydration and drying, some parts were repeatedly dehydrated and washed with three times the amount of water as the vinyl chloride resin to remove the water-soluble polymer compound used as a dispersant, and then dried to produce the product.

After binding a conductive resin composition of the same composition into pellets using the vinyl chloride resin produced in this way, the disks were continuously pressed and the S/N of the molded disks was measured. The degree of stamper staining was then examined.

As a result, it became clear that, as previously estimated, stamper stains are greatly affected by the amount of the water-soluble polymer compound used during polymerization remaining attached to the vinyl chloride resin, and it was possible to complete the present invention. done.

In other words, even for ethylene-vinyl acetate-vinyl chloride copolymers that require a large amount of dispersant, if the polymerization slurry is sufficiently washed to remove water-soluble polymer compounds, stamper stains will be greatly reduced, making cleaning easier. It was found that the vinyl chloride homopolymerates obtained were almost the same.

Furthermore, even with vinyl chloride homopolymer, when the polymerization slurry was not washed, the degree of stamper staining was higher than when it was washed, and a clear effect of washing the slurry was recognized.

Furthermore, if we talk about the types of water-soluble polymer compounds,
Poval-based and cellulose-based showed similar effects.

The present invention has been accomplished as described above.

The present invention aims to reduce stamper stains by reducing the suspension dispersant attached to the vinyl chloride resin, but in order to remove the suspension dispersant, the already dried vinyl chloride If the PVC-based resin is washed, it is difficult to wet the particle surface of the dried vinyl chloride-based resin, making it difficult to obtain a sufficient cleaning effect.Additionally, the number of steps increases, the contamination of foreign matter increases, and the energy cost of drying is reduced. ]・There is also a drawback that . is high, so it is most preferable to wash the slurry after the polymerization reaction is completed.

The polymerization slurry is washed using clean water from which fine foreign substances have been removed, preferably clean ion-exchanged water. Specifically, the polymerization slurry is turned into a cake using a dehydrator.
After repeatedly adding water to this cake to make a slurry again, or leaving the slurry in a tank to settle the vinyl chloride resin, and removing the supernatant,
Adding water to form a slurry can be repeated.

The number of times of washing or the amount of water used is determined by the type of suspension polymerization dispersant, the amount used, or the washing method, but in the case of using the above-mentioned dehydrator, the number of times of washing or the amount of water used is determined by the type of suspension polymerization dispersant, the amount used, or the washing method. On the other hand, if you use more than twice as much water, you can expect a significant effect.

In addition, the temperature for cleaning is not particularly limited, but is 10~
50°C is suitable.

In addition, this method does not use only a water-soluble polymer compound as a suspension polymerization dispersant, but also uses a water-insoluble polymer such as ethyl cellulose (however, it dissolves in vinyl chloride), or polyethylene ( 15) It is also effective when used in combination with a low molecular weight surfactant such as a recall type surfactant.

Next, before explaining the present invention by giving examples, 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 sealed after removing previously attached scale using a souffle bar, filled with methylene chloride, and stirred for 1 hour while heating to 40°C. After this, methylene chloride is extracted, followed by pressure 6
After the scale remaining inside the vessel was completely removed using pressurized water of 0 kg/crj G, the inside of the vessel was further washed with ion-exchanged water filtered through a 0.5μ filter.

The ion-exchanged water used in the polymerization was also filtered through a 05μ filter. Vinyl chloride monomers and monomers to be copolymerized components were used after being filtered through a 1μ filter. Suspension (16) used in polymerization The dispersion stabilizer was made into a 2 weight aqueous solution using the above-mentioned ion-exchanged water, and the polymerization initiator was filtered with a 1μ filter for use.

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

Nitrogen gas was introduced from the bottom of the autoclave while being filtered through a 0.5μ filter to completely remove the vinyl chloride monomer, and then the internal pressure was increased to IKg/ff1G using nitrogen pressure.

Next, the mixture was extracted by nitrogen pressure from an autoclave through a 42-mesh wire mesh into a container equipped with a 100 t extraction nozzle and a stirrer, which had been previously washed with the filtered ion-exchanged water.

A part of the slurry obtained in this way is made into a cake using a centrifugal dehydrator installed in a pressurized room with clean air filtered with a HEPA filter, and then the slurry is made into a cake, which is 3 times the amount of vinyl chloride resin. An amount of the above-mentioned clean ion-exchanged water was added to form a slurry.

After stirring the slurry for 1 hour, repeating the same operation as above twice, and then dehydrating and drying the dehydrated cake for the fourth time using a conical dryer, being careful not to introduce dust. A powdered material of vinyl chloride resin was obtained.

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

(Note 1) Polymerization initiator Kayaester 0, Kayaku Nu 1-■ (Note 2) Poval Gosenol K1-
1-17, Nippon Gosei Kagaku Kogyo ■ (19) [Manufacture of vinyl chloride resin used as a comparative example] Regarding experiment numbers 1 and 3, a part of the slurry extracted from the polymerization vessel was sifted and subjected to the dehydration process described above. Powder and granules of vinyl chloride resin were obtained without passing through a water washing process using a machine and a dryer.

Examples 1 to 3 Purified vinyl chloride resin obtained in the above experiment numbers 1 to 3 (vinyl chloride resin from which the suspension dispersant used in suspension polymerization was substantially removed by washing with water after polymerization) 100 Parts by weight, dibutyltin mercap I/system stabilizer (three-group organic synthesis ■) ES
-1) 5 parts by weight, fatty acid glycerin ester (RIKEN VITAMIN ■R, ES-210) 2.0 parts by weight, fatty acid alkyl ester (chemical soap ■) RES-310) 0.5 parts by weight, dimethylpolysiloxane (Shin-Etsu Chemical industry ■R,
ES-421) was blended and heated to 110°C using a 20t Henschel mixer, cooled at low speed in a 70°C shaker, and then mixed with conductive carbon black (08X-15OA from Cabot, USA). ) was added thereto, the temperature was again raised to 110°C, the mixture was stirred at high speed for 15 minutes, and then cooled at room temperature (20).

Thereafter, the pellets were pelleted using Nigu PR, -46 manufactured by Swissbus, metals contained in the pellets were removed using a metal detector, and video discs were produced using a press machine exclusively for video discs.

Comparative Examples 1 and 3 Instead of the purified vinyl chloride resin used in Example 1, the unpurified vinyl chloride resin of Experiment No. 1.3 (after polymerization, for example, without washing with water, but dehydrated and dried) was used. A video disc was produced in the same manner as in Example 1.

In addition, in both the above examples and comparative examples, the video disc was pressed using a stamper on which a reference signal for signal measurement was recorded.
Approximately 300 sheets were continuously pressed using the .

Regarding the video disc obtained as described above, the degree of degradation of Y-8/N of the recording signal of the video disc was measured, and the results were as shown in the graph.

According to this, as in the present invention, a video disc in which the vinyl chloride resin substantially contains the suspending and dispersing agent used in polymerization has no signal defects and has good playback characteristics. If the suspending dispersant is not substantially removed as in the comparative example, stamper stains will occur as pressing continues, and if pressing is performed with such stamper stains, the signal will be This results in a defective video disc with poor playback characteristics. In other words, video discs made using vinyl chloride resin from which suspending and dispersing agents have been substantially removed, as in the present invention, require very few stamper replacements, which improves production efficiency and yields. It can be obtained easily and at low cost.

Similarly, when the stamper in the above example was examined using a scanning electron microscope after 300 presses, almost no foreign matter was observed on the stamper surface.

As mentioned above, the high-density information signal recording medium according to the present invention includes:
In a high-density information signal recording medium in which information signals are recorded by forming pits, this high-density information signal recording medium is made of a material containing a conductive substance and a washed thermoplastic resin. It has the advantage of being able to manufacture products with good /N with high efficiency and at low cost.

[Brief explanation of the drawing]

Figures 1 and 2 show N (N
is a natural number) is a graph showing Y-8/N of the videotiff obtained by the press. Patent applicant: Victor Japan Co., Ltd. Tokuyama Sekisui Kogyo Co., Ltd. Agent: Katsumi Utaka (23) Continued from page 1 ■Applicant: Tokuyama Sekisui Kogyo Co., Ltd. 2-4-4 Nishitenma, Kita-ku, Osaka 338-

Claims (1)

[Claims] A high-density information signal recording medium that records information signals by forming pits is characterized in that the high-density information signal recording medium is made of a material containing a conductive substance and a washed thermoplastic resin. Density information signal recording medium.