JPH024063B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing conductive disk-type recording media such as capacitive video disks, and in particular, by using conductive carbon black that has been purified by removing impurities, disks with excellent reliability and manufacturing yield can be manufactured. The aim is to provide a type recording medium. Conventionally, in the field of the record industry, disc records have been manufactured by compression molding a copolymer of vinyl chloride and vinyl acetate, using a stamper with information signals on its surface, for example. . On the other hand, conductive disk-type recording media such as capacitive video disks are also manufactured using substantially the same manufacturing method to obtain disks having the shape shown in the figure. In FIG. 1, 1 is a disk-shaped disk body;
2 is a hole provided in the center. FIG. 2 is a partially enlarged view showing the state of the pits provided on the surface, and 3 indicates the pits. Further, FIG. 3 shows a cross section of the disk. In the case of conductive disk-type recording media, unlike conventional records, a considerable amount of conductive carbon black particles are mixed into the resin material to provide sufficient conductivity to enable capacitive signal reading. Therefore, various problems arise in the manufacturing method or physical properties of the disk. For example, an increase in the proportion of carbon black leads to an increase in foreign substances such as ash contained therein, which causes major problems such as defects on the disk surface and damage to the stamper. The present invention was developed after intensive studies on the treatment of highly conductive carbon black, which is classified as conductive furnace black, and found that a large portion of the ash contained in these carbon blacks is soluble in hydrochloric acid and sulfuric acid, and that it is inorganic. This is based on the knowledge that acid-soluble ash causes the defects on the media as described above, and that the properties of carbon black change as a result of treatment to remove ash. This provides an effective method to solve the above problems. The origin of the ash contained in carbon black is
There are various factors such as raw materials, reactors, additives, cooling water, granulating agents, etc., but the highest proportion is due to the components dissolved in the cooling water. Some ash components are soluble in water, but inorganic acids, especially
Because it dissolves very well in acids heated to 70°C or higher, more than 95% of the ash content of some types of conductive carbon black can be removed. On the other hand, when observing the surface of a disk obtained by molding a mixture of conductive carbon black and thermoplastic resin, the presence of minute protrusions is often observed, which has a considerable negative effect on the reproduced image of the disk. It is. When such a defect is observed from a cross-section, a foreign object is found under the protrusion, which indicates that local strain remains near the foreign object during disk molding, and this strain is resolved over time. It is thought that as time progresses, protrusions are formed. When such foreign substances are analyzed with an X-ray microanalyzer, not only water-soluble salts of alkali metals and alkaline earth metals, but also acid-soluble oxides such as iron oxide are confirmed. In addition, the conductive black contains a large amount of ash,
Moreover, if the ash contains a large amount of water-soluble components, problems will arise in terms of moisture resistance. In other words, if a disk is left in a high humidity environment for a long time, water-soluble ash aggregates near the disk surface absorb moisture and expand, resulting in the generation of new protrusions on the disk surface. It is necessary to remove The washed black then needs to be dried, and it has been observed that the PH value of the black decreases when it is dried in air at a temperature of about 120°C for a long time. This is particularly noticeable in the case of black, which has an extremely large surface area and high surface activity. PH
Black values that are extremely small indicate that when vinyl chloride is used as a thermoplastic resin, the decomposition of vinyl chloride is accelerated during processes such as heating, kneading, and molding, which not only causes deterioration of the resin itself, but also hydrogen chloride gas. This can cause problems such as corrosion of the kneading equipment, stun bar, etc. The reason why the PH value decreases when the cleaned black is dried in the air is that the inorganic acid used may remain, but it is also possible that oxygen binds to the surface of the black, and in order to prevent this, teeth,
It is preferable to heat in an inert gas such as N ₂ or under reduced pressure. In addition, after cleaning,
If it is impregnated with a dilute aqueous solution of sodium or potassium salts, hydroxides, or ammonia, which become basic when dissolved in water, it is possible to reduce changes in PH value by drying in air. Next, examples of thermoplastic resins that can be used in the present invention include vinyl chloride, vinyl chloride/vinyl acetate copolymer, vinyl chloride/ethylene copolymer, vinyl chloride/propylene copolymer, vinyl chloride/(meth)
Examples include acrylic acid alkyl ester copolymers, acrylonitrile/styrene copolymers, acrylonitrile/styrene/butadiene copolymers, acrylonitrile/styrene/ethylene copolymers, methyl methacrylate, and methyl methacrylate/butadiene copolymers. In addition to these thermoplastic resins, heat stabilizers, plasticizers,
Needless to say, use a lubricant. Regarding the addition rate of carbon black to the resin used in the present invention, it must be added in an amount that imparts sufficient conductivity to enable capacitance reading from the disk, and the aim is to The volume resistivity of is 1000Ω·cm or less, preferably 100Ω·cm or less. The amount of carbon black as conductive fine particles suitable for satisfying these conditions is 10 to 40 parts by weight, preferably 15 to 35 parts by weight, per 100 parts by weight of the disk-constituting resin. If the amount of carbon black added is less than 15 parts by weight, especially less than 10 parts by weight, the conductivity of the disk cannot be sufficiently increased. On the other hand, if the amount added is 35 parts by weight or more, especially 40 parts by weight or more, the processability of the kneaded product will decrease and the brittleness of the finished disc will increase, making it unsuitable for practical use. An embodiment of the present invention will be explained in detail below.
This invention is not meant to be limited to these. [Example] Particle size 30 mμ (electron microscopy), surface area (nitrogen adsorption method) 950 m ² /g, oil absorption (DBP) 350 ml/100
200 g of conductive carbon black particles (manufactured by Nippon EC Co., Ltd.) with a pH of 9.0 and an ash content of 0.50% were dispersed in 0.6 N hydrochloric acid 2.5, stirred at room temperature for 1 hour, filtered by suction, and diluted with pure water 5. Washed. Then add this to 28
After washing with 1.5% pure water containing 2g of aqueous ammonia, it was further washed with 3% pure water. When this was dried in air at 120℃ for 15 hours, the ash content was
It decreased to 0.12%. Of the ash contents, those with particularly large reduction rates were Na, K, Ca, V, Al, Fe, and Ni. The pH of the black after washing and drying was 6.5. Next, wash the above and dry black... (20
parts), vinyl chloride/lauryl acrylate copolymer, (composition ratio 95:5, degree of polymerization 430)... (100 parts),
Stabilizer (manufactured by Sankyoki Co., Ltd., Stan JF-20u)...
(3 parts), lubricant (manufactured by Henkel Japan, LoxiolGE-
2)...(2 parts) was sufficiently mixed using a high-speed stirrer, melt-kneaded using hot rolls, and then compressed to produce a disk. [Example 2] In Example 1, the conductive carbon black was
The dispersion in 0.2N hydrochloric acid heated above 0.degree. C. was stirred for 1 hour, and then washed and dried in the same manner.
At this time, the ash content in the black decreased to 0.04%. Also, the pH became 6.4. Using this washed and dried black, a disk was produced in the same manner as in Example 1. [Comparative Example 1] A disk was produced in the same manner as in Example 1 using black that was not washed or dried. Next, we took five disks each prototyped by the methods of Examples 1 and 2 and Comparative Example 1, observed their surfaces, and measured the number of defects with a diameter of 50 μm or more, and the results shown in Table 1 were obtained. .

[Example 3]

Particle size 20mμ (electron microscopy), surface area (nitrogen adsorption method) 1350m ² /g, oil absorption (DBP) 320ml/100
When a conductive carbon black (manufactured by Cabot) with a pH of 8.0 and an ash content of 1.52% was washed and dried in the same manner as in Example 2, the ash content was reduced to 0.09%. Among the ash contents, the decrease rate was particularly large for Na, K, Ca, Mg, Sr, Ni, Fe, Si, etc. After washing and drying, the pH of the black was 2.9. Next, a disk was produced in the same manner as in Example 1. When the stamper was observed after the disk was manufactured, evidence of corrosion by hydrochloric acid, which was thought to be due to decomposition of vinyl chloride, was observed. [Example 4] In Example 3, when drying after washing was performed in a nitrogen gas atmosphere, the PH value was 5.5, and the degree of decrease in the PH value was smaller than when drying in air. A disk was produced using this black in the same manner as in Example 1, but no stamper corrosion was observed. [Example 5] In Example 3, when drying after washing was performed in a vacuum dryer, a black with a pH value of 5.8 was obtained. [Example 6] In Example 3, the concentration of the black after washing was
After dispersing in 0.1% ammonia water, it is filtered by suction.
When dried in air at 120°C for 15 hours, a black with a pH value of 6.4 was obtained. No increase in ash content was observed due to the use of ammonia water. [Example 7] In Example 6, instead of ammonia water, the concentration
PH7.1 using 0.05% sodium carbonate aqueous solution
Black was obtained. The ash content of this black was 0.15%, and the increased ash content due to the use of soda carbonate was 0.06%. [Example 8] 0.05% instead of ammonia water in Example 6
When using an aqueous solution of sodium hydroxide, the PH value was
A black of 7.2 was obtained. The ash content of this black was 0.18%, and the increased ash content due to the use of sodium hydroxide was 0.08%. Disks were produced using the blacks of Examples 5 to 8 in the same manner as in Example 1, but no corrosion of the stamper was observed in any of them. [Comparative Example 2] In Example 3, a disk was produced in the same manner as in Example 1 using black that was not washed or dried. Next, we took five disks each prototyped by the methods of Examples 3 to 8 and Comparative Example 2, observed the surfaces, and measured the number of defects with a diameter of 50 μm or more.
The results shown in the table were obtained.

【table】

[Table] As is clear from the results in Tables 1 and 2, it was confirmed that the method of the present invention significantly reduced defects on the disk surface, and as a result, the reproduced screen also had fewer defects such as dropouts. It can be seen from the results in Tables 1 and 2 that the number and condition of defects are not necessarily in a comparative relationship with the ash content, but are also closely related to the properties of the ash content. As described above, as a result of the method of the present invention, the ash content is significantly reduced, the manufactured disks are of high quality with fewer defects, and the manufacturing yield can also be significantly improved.

[Brief explanation of drawings]

1 to 3 show a disk-type recording medium according to the present invention, in which FIG. 1 is a top view, FIG. 2 is a partially enlarged view, and FIG. 3 is a sectional view. 1...Disc body, 2...Center hole, 3...Bit corresponding to the information signal.

Claims (1)

[Claims] 1. By molding a conductive material made of thermoplastic resin and conductive carbon black particles, bits corresponding to information signals are formed on a flat surface in a spiral or concentric manner at predetermined intervals. 1. A method for manufacturing a disk-type recording medium in which the conductive carbon black particles are washed with an inorganic acid and then with water. 2. The method for manufacturing a disk-type recording medium according to claim 1, wherein the thermoplastic resin is a resin whose main component is vinyl chloride. 3 Add 10 to 40 parts by weight of conductive carbon black to the resin.
10. The method for manufacturing a disk-type recording medium according to claim 1, wherein the content is 100 parts by weight. 4. The method for manufacturing a disk-type recording medium according to claim 1, wherein the temperature of the inorganic acid is 70° C. or higher. 5. The method for producing a disk-type recording medium according to claim 1, characterized in that the washed carbon black is heated and dried in an inert gas or reduced pressure. 6. The method for manufacturing a disk-type recording medium according to claim 1, wherein the inorganic acid contains at least one of hydrochloric acid and sulfuric acid. 7. The disk type according to claim 1, characterized in that the washed carbon black is impregnated with a dilute aqueous solution of an alkali metal hydroxide or salt or ammonia, the aqueous solution of which is basic, and then dried. A method for manufacturing a recording medium.