JPH0452538B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a high-density information signal recording medium such as a video disk or a digital audio disk, and particularly relates to a method for manufacturing a high-density information signal recording medium such as a video disk or a digital audio disk. manufacturing a capacitive information signal recording medium in which information signals are reproduced by changing the capacitance between the electrode and the electrode of a reproducing needle that relatively scans the surface according to changes in geometric shape; It is about the method. [Prior art and problems] Conventionally, pits are formed spirally or concentrically in a plane or groove in accordance with an information signal, and the information signal is recorded as a change in geometrical shape to obtain an information signal recording medium. A reproduction needle made of diamond or the like provided with an electrode is relatively scanned on the recording track of the information signal recording medium, and the electrostatic capacitance formed between the electrode of the reproduction needle and the information signal recording medium is There is a so-called capacitance reproduction method that reproduces recorded information signals by utilizing changes in response to changes in physical shape. A capacitive information signal recording medium used in this type of capacitance reproduction method has, for example, a press-molded recording medium body with a geometric shape change, and static electricity between the surface and the electrode of the reproduction needle. For example, a thin metal film with a thickness of several hundred angstroms is deposited as an electrode to form capacitance, and on top of that, a thin metal film of several hundred angstroms is deposited to protect the metal thin film, prevent short circuits between the electrodes, and increase the dielectric constant between the electrodes. A recording medium with a structure in which a dielectric thin film of 100 Å is attached has been proposed, but recording media with this type of structure require many manufacturing processes, such as press molding of the recording medium body, metal thin film attachment, dielectric thin film attachment, etc. requires,
It has drawbacks such as being complicated and troublesome to manufacture, requiring large-scale manufacturing equipment, and extremely high manufacturing costs. Therefore, vinyl chloride resin, vinyl chloride/vinyl acetate copolymer, vinyl chloride/ethylene copolymer,
Vinyl chloride/propylene copolymer, vinyl chloride/
Acrylic acid alkyl ester copolymer, vinyl chloride/acrylonitrile/styrene copolymer, graft copolymer of ethylene/vinyl acetate copolymer and vinyl chloride, vinyl chloride/α-olefin copolymer, vinyl chloride/styrene copolymer, Thermoplastic resins such as vinyl alcohol copolymers, metal soaps such as calcium stearate, organotin stabilizers, lubricants such as higher alcohols, fatty acids, fatty acid esters, or polysaccharide esters, and even Lubricant such as dimethylpolysiloxane, along with the amount of conductive carbon black required for the capacitance regeneration method,
For example, blend with a high-speed mixer such as a Henschel mixer to sufficiently disperse the carbon black, gel and melt using a highly kneading extruder, etc., and then pelletize, and press the pellets into a press. For example, means for molding video discs have been proposed. In other words, in this way, since capacitance is formed between the recording medium itself and the reproducing needle electrode, there is no need for the process of attaching a metal thin film or the process of attaching a dielectric thin film, which greatly reduces the manufacturing process. Easy and low cost. However, when attempting to reproduce the capacitive information signal recording medium obtained in this manner by installing it in a reproducing apparatus, dropouts often occur. [Disclosure of the Invention] As a result of investigating the cause of this dropout, the inventor found that a protrusion was formed on the surface of the capacitive information signal recording medium, and realized that this was the cause. As a result of further investigation, we found that although there were various types of protrusions (hereinafter referred to as flakes), most of them were decomposition products of the capacitive information signal recording medium composition. I stopped him. In other words, the large amount of conductive carbon black required for the capacitance regeneration method is
DBP oil absorption is very high at around 280ml/100g.
In addition, due to the highly developed structure, the composition itself generates a large amount of heat during the process of gelling, melting, and dispersion using a high-mixing machine, and sometimes decomposition occurs, causing dropouts. This gave rise to Fukurami. Therefore, various stabilizers and plasticizers were added to suppress such decomposition phenomena. but,
Merely increasing the thermal stability of the composition in this way was insufficient at the stage of processing with a high-performance kneader. In other words, a decomposition phenomenon of the composition occurs in localized abnormal heat generation parts or stagnation parts inside the high-kneading machine, and as the dehydrochloric acid reaction progresses from the composition, it is crosslinked while still containing carbon black, and the volume shrinks. It was discovered that hardened particles, which are decomposition products, are dispersed in the composition, and that flaking occurs depending on the size and position of these hardened particles. Therefore, in order to prevent this kind of blistering from occurring, it would be best to prevent the dehydrochloric acid reaction caused by thermal decomposition of the vinyl chloride resin from occurring, but it is extremely difficult to do so. It is only possible to prevent or suppress the chain reaction of thermal decomposition by absorbing and fixing the hydrochloric acid generated in the dehydrochloric acid reaction caused by thermal decomposition of vinyl chloride resin, but this is effective in preventing the occurrence of blisters. It wasn't the point. In the course of research to solve these problems, the present inventor created a conductive resin composition for a capacitive information signal recording medium containing a stabilizer said to have the highest thermal stability effect. From this, we decided to use video discs, and while investigating the occurrence of flakes, we found that the occurrence of flakes was correlated with the apparent density (bulk density, BD) of the thermoplastic resin used in the conductive resin composition, such as vinyl chloride resin. I discovered something. In other words, even when video discs were constructed using vinyl chloride resins with the same composition and the same blending composition, large variations in the occurrence of bulges were observed, and it was found that this variation was caused by the bulk density of the vinyl chloride resins. It is. In other words, when a vinyl chloride resin with a low bulk density was used, there was almost no occurrence of flaking due to hardened particles. Furthermore, as a result of research, it has been found that the bulk density of vinyl chloride resin is determined by the 200 mesh pass rate, and when the 200 mesh pass rate is 15% or more (the bulk density is approximately 0.56 to 0.58 at a 200 mesh pass rate of 15%) The occurrence of flaking due to the hardened grain is small, and preferably the 200 mesh pass rate is 50% or more (bulk density approximately 0.53 to 0.55 at a 200 mesh pass rate of about 50%), and more preferably the 200 mesh pass rate is approximately 80% (200 mesh pass rate is about 80%).
When the mesh pass rate is about 80% and the bulk density is about 0.53 or more), a video disc made of a conductive resin composition using such a vinyl chloride resin can be played without any problem. At this stage, we have not been able to come up with a clear theory as to why the generation of hardened particles can be effectively prevented by using such a finely divided thermoplastic resin, but we believe that it is due to the following reasons. A prima facie inference has been made. In other words, carbon black, which is contained in a large amount as a component of a conductive resin composition that is a constituent material of video disks, has a bulk density of approximately
The bulk density is about 0.14 to 0.20, which is significantly different from vinyl chloride resins, which usually have a bulk density of about 0.6. For this reason, even if a high-mixing mixer or the like is used, local poor dispersion of carbon black is unavoidable, and in particular, the greater the difference in bulk density between the two, the greater the tendency for poor dispersion. In other words, when a vinyl chloride resin with a large particle size and carbon black with a small particle size are mixed, carbon black aggregates tend to enter between the resin particles, and are therefore less likely to receive effective dispersion force. Carbon black remains (for example, with a size of about 500 μm), and such carbon black agglomerates cause abnormally high heat generation during gelation during the extrusion process, which causes blisters on video discs. They reasoned that this would result in the generation of hardened grains. In other words, if a vinyl chloride resin with a small bulk density is used, the gap between the vinyl chloride resin particles will be small, carbon black agglomerates will be less likely to form, and as a result of effective dispersion, the hardened particles will be This is thought to make it less likely to occur. In addition, vinyl chloride resin with fine particle size can be obtained by adjusting the polymerization method, collecting only small particle size after polymerization, or obtaining vinyl chloride resin with large particle size, for example, by mechanical means or other methods. It can be obtained by pulverizing it into a fine powder. The present invention was achieved based on the above knowledge, and uses a vinyl chloride resin with a particle size distribution of 15% or more in 200 mesh passes and a bulk density of 0.14 to 0.20.
The present invention proposes a method for producing a capacitive information signal recording medium, which is characterized by molding a conductive composition comprising conductive carbon black, which is a conductive carbon black, and additives such as a stabilizer and a lubricant. [Vinyl chloride resin] Vinyl chloride was polymerized using an autoclave equipped with a jacket having an internal volume of 600 ml and a stirrer. The autoclave used was filled with methylene chloride with the scale attached in advance, and stirred for 1 hour while heating to 40°C. After this, the methylene chloride is extracted, followed by pressure
After completely removing the scale remaining inside the vessel using pressurized water of 60 kg/cm ² G, the inside of the vessel was further washed with ion-exchanged water passed through a 0.5μ filter. The ion-exchanged water used for polymerization was also passed through a 0.5μ filter before use. Vinyl chloride monomers and monomers to be copolymerized components were filtered through a 1μ filter before use. Sodium polyacrylate used for polymerization is
After dissolving 0.1 wt% of the other suspension dispersion stabilizers and 2 wt% of the other suspension dispersion stabilizers using the above-mentioned filtered ion exchange water, the polymerization initiator was used as it was after being passed through a 1μ filter. Polymerization was carried out according to conventional methods, and the polymerization reaction rate was 70%.
When the temperature reached a certain point, unreacted vinyl chloride monomer was collected. Next, the mixture was extracted through a 42-mesh wire gauze into a container equipped with a 1000 mm extraction nozzle and a stirrer, which had been previously washed with the filtered ion-exchanged water. A portion of the slurry obtained in this way is
After making a cake using a centrifugal dehydrator installed in a pressurized room with clean air passed through a HEPA filter, it is dehydrated and dried while being careful not to mix in dust, and is made into a powder of vinyl chloride resin. Granules were obtained. Details of the vinyl chloride resin produced as described above are shown in Table 1.

[Example 1]

No. 1 vinyl chloride resin 100 in Table 1 above
5 parts by weight of dibutyltin mercapto stabilizer (RES-1 from Sankyoki Gosei Co., Ltd.), 5 parts by weight of fatty acid glycerin ester lubricant (RES from Riken Vitamin Co., Ltd.)
-210) 2 parts by weight, fatty acid alkyl ester lubricant (RES-310 from Kao Soap Co., Ltd.) 0.5 parts by weight, dimethylpolysiloxane (RES- from Shin-Etsu Chemical Co., Ltd.)
421) 1 part by weight was added through a 0.2 μ filter and stirred at high speed with a Henschel mixer to
After raising the temperature to
DBP oil absorption 320ml/100g, _I2 adsorption 1269mg/g)
After sufficiently removing foreign substances contained in the mixture using a foreign substance removing device, 20 parts by weight of the mixture was added, the temperature was raised again to 110 to 120°C, and the mixture was stirred at high speed for 15 minutes, and then cooled to room temperature. Thereafter, this is kneaded into pellets using an extruder manufactured by Swissbus, and after sufficiently removing foreign matter using a foreign matter removal device, it is molded, for example, using a press machine specifically designed for video discs, to produce capacitive video discs. obtain. [Examples 2 to 6] In place of the vinyl chloride resin No. 1 in Table 1 used in Example 1, vinyl chloride resins No. 2 to 6 in Table 1 were used, and the same procedure as in Example 1 was carried out. and get a video disc. [Comparative Example 1] In place of the vinyl chloride resin No. 1 in Table 1 used in Example 1, vinyl chloride resin No. 7 in Table 1 was used, and a video was produced in the same manner as in Example 1. Get the disc. [Performance test] 5,000 to 30,000 video disks obtained in each of the above examples were left at room temperature for 72 hours, and then visually inspected for the presence or absence of flakes. Table 2 shows the defect rate due to the occurrence of blisters, which is considered to be equivalent to the absence of . In addition, it is further attached to a playback device and played back,
Table 2 shows the defect rate due to the occurrence of dropouts of 4 hours or more. When the flaky portion of the defective video disc was analyzed using an X-ray microanalyzer, more than 95% of the flake was found to be caused by hardened grains.

【table】

〔effect〕

For example, thermoplastic resin used as a constituent material for capacitive video disks has a particle size distribution of 200
By setting the mesh pass to 15% or more, it becomes difficult to cause dropouts during playback, and a high-performance recording medium can be easily obtained.

Claims (1)

[Claims] 1. Molding a conductive composition consisting of a vinyl chloride resin with a particle size distribution of 15% or more in 200 mesh passes, conductive carbon black with a bulkiness of 0.14 to 0.20, and additives such as stabilizers and lubricants. A method for manufacturing a capacitive information signal recording medium, characterized in that: