JPH0472297B2 - - Google Patents

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, and the surface is Added to the resin base of the recording medium in capacitive recording media in which information signals are reproduced by changing the capacitance between the electrode and the electrode of the reproducing needle that scans according to the change in geometric shape. The particle size of the conductive carbon black (in the following explanation, the particle size is defined as the size of the particles as an aggregate of granulated carbon black) is mainly about 20 μm or less. The object of the present invention is to provide a capacitive high-density information signal recording medium that almost eliminates drop-out and needle skipping phenomena when reproducing data by scanning electrodes, and therefore has extremely excellent reproduced image quality. do.

Conventionally, pits are formed in a plane or groove according to an information signal, the information signal is recorded as a change in geometrical shape to obtain an information signal recording medium, and electrodes are placed on the recording track of this information signal recording medium. Recorded information is recorded by scanning the provided reproducing needle relatively and utilizing the fact that the capacitance formed between the electrode of the reproducing needle and the information signal recording medium changes in accordance with the change in the geometrical shape. There is a so-called capacitive regeneration method for regenerating signals.

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 metal thin film of several hundred Å is deposited as an electrode to form a capacitance, and on top of that a metal thin film of several hundred Å 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 is attached has been proposed, but a recording medium with this structure requires many manufacturing processes, such as a press molding process for the recording medium body, a process for attaching a metal thin film, and a process for attaching a dielectric thin film. However, manufacturing is complicated and troublesome, large-scale manufacturing equipment is required, and manufacturing costs are extremely high.

Therefore, a conductive plastic made by mixing several tens of parts by weight of a conductive material such as carbon black with a resin such as vinyl chloride-vinyl acetate copolymer is press-molded as a raw material, and the information signal is shaped into a geometric shape. A capacitance-type information signal recording medium has been proposed as a change in the recording medium, and since a capacitance is formed between the recording medium itself and the playback needle electrode, the metal thin film deposition process is required. Moreover, since the carbon black fine powder particles themselves are coated with resin, there is no need for a dielectric thin film attachment process, making manufacturing extremely simple and low-cost. There is.

However, recording media made by forming predetermined pits with resin containing carbon black as described above often suffer from dropouts and needle skipping phenomena when played back by scanning the playback needle. The reproduced image has screen defects and is not good.

As a result of studying why fatal defects such as reproduction screen defects occur, the inventors of the present invention discovered that, for example, powder additives added to vinyl chloride resins, such as carbon black and vanadium contained in carbon black. , found that the particle size of impurities such as nickel, iron, silica, copper, aluminum, magnesium, calcium, sodium, chromium or graphitized carbon is the main factor causing dropout and needle skipping phenomena,
It has been discovered that by considering the size of these powder additives, it is possible to significantly eliminate dropout and needle skipping phenomena, resulting in a good reproduced screen. Furthermore, they have found that the quality of the reproduced screen deteriorates depending on the hardness and high reactivity of impurities contained in conductive carbon such as carbon black.

Therefore, the inventor of the present invention has developed a method in which conductive carbon black as a conductive substance mixed into a base material such as vinyl chloride resin is mixed into an aqueous solution or an organic solvent to have a viscosity of about 10,000 cP or less, preferably about 3,000 cP or less. This slurry is filtered using a suitable filtration material with an opening of, for example, 20 μm or less, preferably about 10 μm or less, particularly preferably about 5 μm or less, and the conductive material is The conductive carbon black has a particle size of, for example, about 20 μm or less, preferably about 10 μm or less, particularly preferably about 5 μm or less, and then a liquid containing only small particle sizes of the conductive carbon black is dried. By using this, factors that cause screen defects were removed. That is, by keeping the particle size of the conductive carbon black added to the resin base of the recording medium small, it is possible to prevent large particles from being present in the layer near the surface of the resin base of the recording medium. By keeping
This prevents shrinkage strain from occurring on the surface of the base material after pressing the recording medium, prevents swelling of the recording medium surface caused by shrinkage strain, and prevents drop-outs and needle-flying phenomena from occurring.

Hereinafter, specific embodiments in which the capacitive high-density information signal recording medium according to the present invention is applied to a video disc will be described.

First, the base materials for video discs, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-cetyl vinyl ether copolymer, vinyl chloride-vinyl ether copolymer, and
Ketchen black, which is carbon black, is used as a conductive substance added to vinyl chloride resin such as ethylene copolymer to impart conductivity.
As a pretreatment for EC (manufactured by Lion Akzo), add KETSUTIEN BLACK EC to water or an organic solution such as benzene or toluene in the presence of a suitable surfactant, for example, at a concentration of about 1000 cP or less, preferably about 3000 cP.
This slurry is then subjected to pressure filtration treatment using a filtration material with an opening of approximately 10 μm. This filtration treatment removes the highly hard or highly reactive substances such as vanadium, nickel, iron, silica, copper, aluminum, magnesium, calcium, sodium, chromium, and graphitized carbon contained in Ketschen Black EC. Most of the impurities are removed and the filtrate contains approximately
Particles with a particle size of 10 μm or more are removed and the particle size is approx.
Only those with a size of 10 μm or less are accepted. and,
This filtrate containing only particles with a particle size of about 10 μm or less is dried and made into a powder.

In addition, other powder additives added to the base such as vinyl chloride resin are also sieved with a mesh size of about 10 μm, and only those with a particle size of about 10 μm or less are selected.

After the above pretreatment, about 100 parts by weight of a resin base for video discs, about 3 parts by weight of dibutyltin laurate, and about 3 parts by weight of epoxidized soybean oil were added.
0.5 parts by weight and about 0.7 parts by weight of dimethylpolykiloxane are placed in a Henschel type high speed mixer and thoroughly stirred, then carbon black is added and thoroughly stirred. After kneading these mixed powders for about 10 minutes using, for example, twin 8-inch open rolls, they are cut into sheets, made into pellets, passed through an extruder, preformed, and the preformed material is molded into a mold. A capacitive video disc is made by pressing with a compression molding machine equipped with a video disc stamper. In other words, the particle size of the powder additive added to the base of the video disc is mainly approximately
Using only materials with a diameter of 10 μm or less, video discs were made using conventional methods.

Further, as a comparative example, a capacitive video disk was prepared in the same manner using conductive carbon black having a particle size of about 40 .mu.m.

When the capacitive video disc of the present invention produced as described above and the capacitive video disc of the comparative example are installed in a predetermined playback device and playback is attempted, the capacitive video disc of the present invention becomes the capacitive video disc of the present invention. In the case of video discs, the number of dropouts is approximately 5 per hour, whereas in the case of the capacitive video disc of the comparative example, there are approximately 100 to 200 dropouts per hour. There is almost no needle skipping phenomenon, whereas it occurs frequently in the comparative example.In other words, the reproduced image of the capacitive video disc of the present invention is good, whereas the capacitive video disc of the comparative example In this case, the quality was poor, with screen defects occurring. That is, Figures 1 and 2
As shown in the electron micrograph in the figure, if the conductive carbon black particles added to the base of the video disc have a diameter of about 40 μm, the area near the part where the particles of about 40 μm are located during molding of the video disc. There is a difference in the shrinkage rate of the base between the base and other parts, and this causes swelling on the video disc surface near particles of about 40 μm, which causes dropouts and needle skipping during playback, causing the video disc to become damaged. In contrast, in the case of the present invention, the surface of the video disk does not swell when the video disk is molded, and therefore no defects occur in the playback screen.

In addition, since most of the highly hard or highly reactive impurities such as chromium and sodium contained in Ketsuen Black EC have been removed, the quality of the reproduced image due to these highly hard or highly reactive impurities is reduced. I was able to get rid of things that happened.

As described above, the capacitive high-density information signal recording medium according to the present invention is a high-density information signal recording medium in which information signals are recorded by forming pits. Since conductive carbon black particles with a diameter of approximately 20 μm or less are used, drop-out and needle skipping phenomena during playback are significantly reduced compared to conventional ones, and therefore, for example, playback screen defects are eliminated and playback image quality is improved. Since the conductive carbon black particles only need to have a particle size of about 20 μm or less, they can be easily carried out by, for example, a filtration treatment method, and can be carried out at extremely low cost. It has characteristics.

[Brief explanation of the drawing]

Figure 1 is an electron micrograph for explaining the particle structure of a cross-sectional perspective part of a video disk containing particles of conductive carbon black with a size of approximately 10 μm, and Figure 2 is a conductive carbon black with a size of approximately 40 μm. This is an electron micrograph for explaining the grain structure of a cross-sectional oblique section of a video disc containing black particles.

Claims (1)

[Claims] 1. In a high-density information signal recording medium in which information signals are recorded by forming pits, conductive carbon black added to the base material of this high-density information signal recording medium mainly has a particle size of about 20 μm or less. A capacitive high-density information signal recording medium characterized by: