JPS63117072A - Carbon black for capacitance type information recording medium - Google Patents

Abstract

PURPOSE:To provide the title carbon black whose primary particle has a specified particle size and which has a specified ratio of DBP oil absorption to specific surface area and a low alkaline earth metal content and gives a recording medium which has excellent S/N, hardly causes dropout and has a long life. CONSTITUTION:Raw gas obtd. by adding an unsaturated hydrocarbon to one mol of acetylene gas is thermally decomposed by using a gas mixture of 0.5mol of O2 and 0.67mol of steam in a molar ratio of O2 to steam of about 0.75 to give the title carbon black whose primary particle has an average particle size of not larger than 20nm and which has a ratio of DBP oil absorption to specific surface are a not higher than 0.65 and an alkaline earth metal content not higher than 200ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to carbon black used in manufacturing capacitive information recording media.

Capacitive information recording media (hereinafter simply referred to as "recording media") are used as recording media for recording information such as audio and video.
has been developed and put into practical use. This recording medium has a surface of a thermoplastic resin molded product (hereinafter referred to as a "disc") containing carbon black, which is a conductive substance, with a diameter of 0.1 to
A plurality of small holes (pits) of about 1 μm are formed, and information is recorded as geometric changes in the uneven shape, and a playback needle is brought into contact with the recording surface and the space volume due to the uneven shape is statically recorded. This allows the information to be reproduced by reading changes in capacitance.

The following properties are generally required for the conductive material used to make such recording media from the viewpoint of recording and reproducing information.

That is, by press-molding a thermoplastic resin containing a conductive substance using a press mold (hereinafter referred to as the "recording base material"), the required small holes (pits) are transferred and formed on the surface of the disk to record information. In this case, it is important to have a particle size that does not interfere with transfer from the recording base material and does not cause noise during playback, and to improve dispersion performance in the disk to improve conduction efficiency and playback. In order to increase the signal output, the surface area and void ratio of the particles are large.

(Prior art) Conventionally, to reproduce a clear image, the video S/N ratio was 4.
Based on the idea that 2 dB or more is required, it has been proposed (Japanese Unexamined Patent Publication No. 172554/1983) to limit the primary particle diameter of carbon black as the conductive substance to 20 nm or less. However, those with such ultrafine particle diameters were limited to special furnace blacks, so alkaline earth metals such as Mg, Ba, and Ca
Impurities such as compounds are unavoidable, and this may absorb moisture in the recording medium, causing the disk surface to swell and cause dropouts. In order to eliminate this drawback, it is possible to reduce the content of these impurities, but
In the conventional techniques, there is no simple treatment method that can produce sufficient effects, and even if some effects can be achieved, there are problems such as the need to incur significant treatment costs. On the other hand, regarding the dispersibility of bomb black into resin, the DBP oil absorption is 100 to 200 ml/1.
The inventors previously disclosed the usefulness of limiting the amount to 0.00 g in the specification of Japanese Patent Application No. 1982-92182.

(Problems to be Solved by the Invention) The inventors further investigated the problem and found that it is useful for improving the S/N ratio of the recording medium, and also contributes to long-term stability.
Carbon black, which does not damage the recording base material during disk molding, can be easily obtained by thermally decomposing acetylene gas with a base gas of oxygen and water vapor, and is well suited as carbon black for manufacturing information recording media. I found out what to do. After further investigation and research into the factors contributing to its suitability, we found that in addition to the particle size of this carbon black, in particular, the ratio of DBP oil absorption to specific surface area, along with the content of alkaline earth metals, are important for the above performance. Based on the results, the present invention has developed a novel carbon black that can be blended in advance into the thermoplastic resin used for molding the disc to advantageously exhibit the characteristics of the disc. This is what I am trying to propose.

(Means for Solving the Problems) The present invention has properties in which the average particle diameter of primary particles is 20 nm or less, the ratio of DBP oil absorption/specific surface area is 0.65 or less, and alkaline soil The content of similar metals is 200 p.
This carbon black for capacitive information recording media is characterized in that it has a carbon black of pm or less.

In order to refine the particle size of the primary particles, it is achieved by increasing the thermal decomposition temperature, and in that case, the specific surface area by the Cantasorb method increases, while the JIS K62
The DBP oil absorption specified in No. 21 can be increased by increasing the particle impingement speed, which is dependent on the gas injection speed during pyrolysis.

The carbon black of the present invention can be produced using acetylene gas as well as a raw material gas to which unsaturated hydrocarbons are added.
It can also be obtained by thermal decomposition using a mixed gas containing oxygen and water vapor, and in either case, the content of alkaline earth metals is 200pp just by considering the purity of the raw material gas.
m or less.

(Function) In the present invention, the reason why the average particle size of the primary particles of carbon black, the DBP oil absorption amount/specific surface area, and the content of alkaline earth metals as impurities are limited as described above is as follows. .

If the average particle diameter of the primary particles exceeds 200 m, the unevenness of the disk surface will become large and cause noise, making it difficult for video S/S/
The N ratio becomes worse. The preferred average particle size is 14 nm or less,
Smaller is preferable. The average particle size of primary particles is measured using an electron microscope.

The value of DBP oil absorption/specific surface area can be considered to represent the degree of stracture development (the chain ratio of primary particles), and it is considered that the larger this value is, the more developed the stracture structure is.

When carbon black with a DBP oil absorption/specific surface area value of more than 0.65 is blended into a thermoplastic synthetic resin and kneaded, primary particles are added to prevent the behavior of strutural structural units (referred to as secondary particles). Even if the thickness is limited to 20 nm or less, surface irregularities become large and cause noise. The lower limit is not particularly limited, but from the viewpoint of conductivity, it is preferably 0.3 to 0.5.

Next, the amount of alkaline earth metals is preferably as low as 200pp.
m or less, even if the disc absorbs moisture, it is unlikely to cause dropouts. The content of alkaline earth metals can be determined by atomic absorption spectrometry after extraction with hydrochloric acid and evaporation to dryness.

The above average particle diameter of the primary particles and the ratio of DBP oil absorption/specific surface area change the supply amount of oxygen and steam during thermal decomposition, and the alkaline earth metal content changes the purity of the raw material used. It can be adjusted by

The specific surface area of carbon black is desirably 300 m2/g or more by the Cantasorb method in order to obtain the necessary conductive effect with a small amount of use.

The procedure for manufacturing a recording medium using the carbon black of the present invention is the same as the conventional method.

That is, a predetermined amount of thermoplastic resin and various additives as necessary are mixed at room temperature or under heating using a mixer such as a Henschel mixer or a ribbon blender, and further a predetermined amount of carbon black is blended. Mix.

Next, the powder compound is kneaded on rolls heated to about 140 to 190° C. and pulverized into pellets, or a continuous kneader such as a Coney Goo or a twin-screw extruder is used to pelletize the powder compound.

A recording medium is obtained by pressure molding this pellet from a recording base material at a molding temperature.

The thermoplastic resin is not particularly limited, but
Polyvinyl chloride vinyl chloride-vinyl acetate copolymer, vinyl chloride-ethylene copolymer, vinyl chloride-propylene copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylate copolymer, vinyl chloride-vinyl cetyl ether Copolymers, vinyl chloride-ethylene vinyl acetate copolymers, acrylonitrile-styrene copolymers, acrylonitrile-styrene-butadiene copolymers, methyl methacrylate-styrene-butadiene copolymers, and the like are used.

Additives include lubricants such as liquid paraffin and silicone oil, lubricants such as ester wax and stearic acid, stabilizers such as dibutyltin laurate, dibutyltin malate, octyltin malate, and dibutyltin mercapto, and stabilizers such as epoxy chelators. Auxiliary agent, 1.1.3-
) Lis(2-methyl-4-hydroxy-5-t-butylphenyl)butane and other antioxidants.

The blending amounts are: 15 to 40 parts of carbon black according to the present invention, 3 parts or less of lubricant, 3 parts or less of lubricant, 6 parts or less of stabilizer, 5 parts or less of stabilizing aid, and antioxidant, per 100 parts of resin by weight. It is about 2 copies or less.

Carbon black according to the invention can be advantageously produced by the following procedure.

The acetylene gas pyrolysis furnace used was a vertical type with a total length of 2.4 mm.
The inner diameter of the furnace is 0.4 m, the diameter of the outlet is 0.25 m, and the inner wall of the furnace is constructed of refractory bricks.

In order to maintain the pyrolysis furnace temperature at 800°C or higher, 1ONm3/hr of -carbon oxide was supplied into the furnace together with 6ONm'/hr of air, and the temperature was raised to 850°C by combustion.

From the center of the double tube nozzle installed at the center of the top of the pyrolysis furnace,
Oxygen9. QNm'/hr and 4.0 J/am2 of saturated steam (temperature 150°C)12. Mixed gas with ON+n3/hr21. ONm'/hr is supplied, and acetylene gas 18Nm'/hr is supplied from the outer annular part of the double pipe nozzle.
was supplied, acetylene gas, oxygen and water vapor were reacted, and then the acetylene black produced was cooled and collected in accordance with a conventional method.

In this case, the linear velocity of supplying acetylene gas to the pyrolysis furnace is
10 m/sec, and the linear velocity of the mixed gas of oxygen and water vapor is 120 m/sec.

The molar ratio of oxygen and water vapor to acetylene gas is 0.5
．． 0.67, the molar ratio of oxygen to water vapor is 0.75
The primary particles of acetylene black obtained as acetylene black had an average particle diameter of 12 nm, a specific surface area of 350 m2/g, and a DBP oil absorption of 210 m I! /100g.

By changing the oxygen and water vapor molar ratio to 0.85, the average particle size lQ
nm, specific surface area 450m2/DBP oil absorption ff1210m
1/100g was obtained.

(Example) Table 1 shows the relationship between the physical properties and disk performance using carbon blacks having various properties produced in the same pyrolysis furnace as described above.

The physical property measurement method and performance evaluation are as follows.

Average particle size: Measure the average particle size of primary particles using an electron microscope Specific surface area: DBP oil absorption by Cantasorb method (using nitrogen gas) Metal impurity content according to JIS K 6221: Metal impurities are extracted with hydrochloric acid and evaporated The dried material was quantitatively determined by atomic absorption spectrometry (the alkaline earth metal was represented by Ca) Performance evaluation of carbon black: A recording medium was manufactured as follows, and the volume resistivity, melt viscosity, S /N ratio and the life of the recording base material were measured.

Vinyl chloride resin powder (Tose Ace GK manufactured by Tokuyama Zizuku Kogyo 01) 100 parts by weight, 5 parts by weight of dibutyl mercapto stabilizer, 0.5 parts by weight of higher fatty acid lubricant, 0.5 part by weight of higher fatty acid ester lubricant , 1 part by weight of dimethylpolysiloxane lubricant was sufficiently stirred using a super mixer manufactured by Yoda Seisakusho@.
When the temperature inside the mixer reached 120° C., the carbon blacks of Examples and Comparative Examples shown in Table 1 were added and stirred thoroughly again.

Thereafter, the mixer jacket was water-cooled to cool the materials inside the mixer, and when the temperature reached 50°C, the compound content was taken out and sold to Swiss Bus Company.
Pelletization using a 46 type kneading extruder (screw temperature 80℃
, cylinder temperature 110°C, rotation speed 6 Orpm).

The pellets made in this way were preformed using an extruder and then heated and compressed using a heating compression molding machine (hydraulic pressure 140 kg f/cm2).
A press pressure of 1QQton was obtained at
Compression molding was performed at 0 to 190°C and cooling to 20°C to obtain a disc-shaped recording medium (diameter 260 mm, thickness 1.2 mm).

Measured value S/N ratio based on Volume Specific Resistance 2 Japan Rubber Association Standard 2301.
Measured value when measuring the S/N ratio of the luminance signal of 501RE Gray recorded at the position (57 minutes) using a video noise meter (Model 925 manufactured by Shibaku).

Dropout: Count value of the number of dropouts of 0.58 sync or more when playing a VHD type video disc (signal recording for 60 minutes).

Dropout after environmental load test: Counted values obtained by performing the same test as in the previous section after leaving the disc in an environment of 40°C and 90% humidity for 96 hours.

(Effects of the Invention) Using the carbon black of the present invention, a recording medium with a good S/N ratio can be manufactured.

Moreover, as evidenced by environmental stress tests, it has a long life with fewer dropouts.

Claims (1)

[Claims] 1. The average particle size of the primary particles is 20 nm or less, and DBP
Carbon black for capacitive information recording media, characterized in that the ratio of oil absorption/specific surface area is 0.65 or less, and the content of alkaline earth metal is 200 ppm or less.