GB2138992A - High density information record made of a resin composition comprising specifically treated carbon black - Google Patents

Abstract

A high density information record of the electrostatic capacitance type which comprises a record substrate on which signal information is recorded as geometric variations is described. The substrate is made of a conductive resin composition comprising a thermoplastic resin, and a predetermined amount of deashed carbon black particles. The particles are surface-treated with a fatty acid having from 12 to 24 carbon atoms. Specific resins and fatty acids are disclosed, as are concentrations and preparation.

Description

SPECIFICATION High density information record made of a resin composition comprising specifically treated carbon black This invention relates to playback systems of a variable electrostatic capacitance form and more particularly to, high density information records, such as video disc or digital audio discs, on which signal information is recorded as geometrical variations.

In certain information playback systems, signal information is encoded as geometric variations or pits in a spiral plane or groove or in concentric planes or grooves on an information recording medium. The medium on which the signal information has been recorded is reproduced as follows.

When a pickup stylus such as of diamond having an electrode is scanned relative to a recorded track of the medium, capative variations are established between the pickup stylus and the medium due to the geometric variations in the plane or groove.

Several types of information records have been proposed for use in the above-described type of electrostatic capacitance playback system. In one such record, an electrode is provided on the surface of a record substrate on which geometric variations are press molded according to signal information.

This permits formation of an electrostatic capacitance to be established between the record electrode and the stylus electrode. For instance, the record substrate is covered with a thin metallic film of several hundreds angstrom in thickness and a several hundred angstrom thick dielectric layer overlying the metallic film. The dielectric layer serves to prevent short circuiting of the electrodes and increase the dielectric constant between the electrodes. The record of the above-described type needs a number of fabricating steps including a press molding of the recording medium substrate, steps of depositing the thin metallic film and the dielectric layer and the like. Thus, the fabrication is complicate and troublesome with the need of a relatively large-scale manufacturing apparatus.

Thus, production cost becomes very high.

Another type of known information record of the elecrostatic capacitance form is one which is obtained by press molding a conductive plastic composition comprising a resin such as polyvinyl chloride in admixture with a conductive material such as carbon black so that signal information is recorded as geometric variations. This type of record is fabricated without needing the step of depositing a thin metallic film because the record itself is conductive and an electrostatic capacitance is formed between the electrode of a pickup stylus and the record. Moreover, fine carbon black powder is substantially covered with the resin, so that any dielectric layer is not necessary. In view of the above, this type of record is very simple in manufcture and can be manufactured at low cost.

However, especially when carbon black is used as the conductive material, the following problem arises. In view of the manufacturing process of ordinary carbon black, it is inevitable that relatively large amounts of impurities or ash components are contained in carbon black. These impurities tend to appear or precipitate on the surface of record articles during or after molding, so that irregularities are formed on the record or tracking surfaces. These irregularities give an adverse influence on playback characteristics.

Another problem is that when the record made of a conductive resin composition comprising carbon black is mounted in a playback system and reproduced over a long term, its surface as well as the pickup stylus itself is worn by means of the pickup stylus contacting therewith. This results in deformation of the geometric variations or pits formed on the record, causing capative variations to change. Thus, reliable playback is not possible. Especially, when a video disc is subjected to still reproduction or freeze frame, a given portion of the disc is repeatedly contacted with a pickup stylus at a pressure of 400 to 500 Kg/cm2 at a rate of 15 times/second or about 10 m/second, causing the disc surfaces as well as the pickup stylus to be considerably worn.The wear of such disc may be overcome to some extent by addition of a suitable type of lubricant. on the other hand, the wear of the pickup stylus was found to have a close relation with surface characteristics of carbon black. Generally, carbon black used for these purposes are contained in several tens wt% of resin.

Even though lubricants are contained in conductive resin compositions, all particles of carbon black cannot always be covered or applied with such lubricants. Presence of carbon black particles having little lubricants absorbed or adsorbed thereon is a main reason why the life of the pickup stylus becomes short.

It is accordingly an object of the present invention to provide high density information records which can solve the problems discussed above.

It is another object of the invention to provide high density information records which can effectively prevent wear of a pickup stylus and record surfaces contacting therewith with prolonged lives of the stylus and the record.

it is a further object of the invention to provide high density information records which ensure reliable information playback operations over a long term.

It is a still further object of the invention to provide high density information records made of conductive resin compositions whereby record articles are manufactured simply without need of any complicate procedures.

The present invention is characterized by use of deashed carbon black combined by ester bonds with fatty acids serving as a lubricant. More particularly, the invention provides a high density information record of the electrostatic capacitance type which comprises a record substrate on which signal information is recorded as geometric variations, the substrate being made of a conductive resin composition comprising a thermoplastic resin, and deashed carbon black particles which are surface-treated with a fatty acid having from 12 to 24 carbon atoms, the deashed carbon black being used in an amount of from 5 to 30 wt% based on the thermoplastic resin.

Preferably, the fatty acid is applied to the carbon black particles in an amount of from 1 to 10 wt% of the carbon black particles.

A sole figure is a graph showing the relation between diagonal length of a contact face of a pickup stylus and reproduction time for different types of records.

High density information records of the present invention are, as described above, made of a conductive resin composition which comprises a thermoplastic resin and specifically treated carbon black particles.

The thermoplastic resins useful in the practice of the invention include, for example, vinyl chloride resin, vinyl-chloride acetate copolymers, vinyl chloride-ethylene copolymers, vinyl chloride-propylene copolymers, vinyl chloride-alkyl acrylates, acrylonitrile-styrene-vinyl chloride copolymers, ethylenevinyl acetate copolymers grafted with vinyl chloride, and the like.

Deashed, surface-treated carbon black used in the present invention is prepared as follows. Commercially sold carbon black particles usually contain ashes of about 1% with metal components of Ca, Na, K, Fe, Ni, Al, Cu, Zn, Mg, V and the like as will be particularly described in examples appearing hereinafter. Such carbon black particles are placed in an aqueous acid solution and agitated sufficiently, followed by removing the solution such as, for example, by decantation to collect the particles. The thus collected particles are washed sufficiently with pure water. Subsequently, the washed particles are neutralized with an alkaline solution such as an ammoniacal solution, followed by washing with water twice or more. By the above procedure, deashing treatment is complete.It will be noted that the deashed carbon black particles should preferaly be controlled to have a pH ranging from 5 to 10. The deashed carbon black particles are so activated that its pH tends to lower. Too low a pH value will adversely affect thermoplastic resins and particularly vinyl chloride resin especially when such a resin composition is heated for shaping or molding.

The acids used for the above procedure may be any mineral acids such as hydrochloride acid, nitric acid and the like.

Next, the deashed carbon black particles are mixed with a fatty acid having from 12 to 24 carbon atom in an amount ranging from 1 to 10 wt% based on the carbon black particles and are agitated for sufficient time. The mixture is then dried under a pressure of 14 to 45 Torr., at a temperature of from 100 to 200 C, preferably 110 to 1 40 C. Thereafter, it is further heated in an atmosphere of an inert gas such as nitrogen at a temperature of from 250 to 600 C for 1 to 10 hours. By the heating, the fatty acid is combined with carbon black by ester bonds, Thus, the carbon black is chemically modified.

Specific examples of the fatty acids include satu rated acids such as tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, stearic acid, nonadecan acid, arachic acid, behenic acid lignoceric acid and the likem and unsaturated acids such as oleic acid. Of these, stearic acid is preferable because of its availability and inexpensiveness.

By the treatment, the carbon black is much more compatible with thermoplastic resins and is thus more uniformly dispersed in the resin. This will reduce the opportunity of the direct contact of the carbon black particles with a pickup stylus. Even though the direct contact takes place, the stylus is less worn with the carbon black because of the surface lubrication imparted to the carbon black.

In the practice of the invention, starting carbon black particles are preferred to have such a surface area and porosity as defined by a DBP absorption of from 250 to 450 and an 12 absorption of from 800 to 1400.

For fabrication of record articles such as video or audio discs, the deashed, modified carbon black particles are mixed with thermoplastic resins in an amount of from 5 to 30 wt% of the thermoplastic resin in order to ensure good conductivity of the resulting composition. As a matter of course, additives ordinarily used for these purposes may be also added to the composition in amounts not impeding the effects of the composition. Examples of such additives include heat stabilizers, plasticizers, lubricants and the like.

The conductive resin composition is usually pelletized by a suitable means. The pellets are used to press mold a video or audio disc as usual. These mixing, pelletizing and press-molding techniques are well known in the art and are not further described herein.

The present invention is more particularly described by way of examples and comparative examples.

Example 1 One hundred grams of conductive carbon black particles having a bulk density of 0.17g/cc, a weight loss by heating of 1.46%, a pH of 9.6, a DBP oil absorption of 320 ml/1 00g, and an 12 absorption of 1269 mg/g (available from Cabot Co., Ltd., U.S.A.) was placed in a 5 liters flask containing 2 liters of a 5% hydrochloric acid solution therein and sufficiently mixed under agitation. The solution was removed by decantation, followed by adding about 2 liters of pure water and agitated. Thereafter, the water was removed by decantation. Washing with pure water was repeated at least three more times, followed by neutralization with an ammoniacal solution and washing with pure water at least two times. By the above procedure, the carbon black was deashed.

The deashed carbon black had an ash content of of 0.04 to 0.05%, a pH of 6.7 to 7.0 and a thermal stability of 10.5 minutes with metal components of 46 ppm of Ca, 8 to 28 ppm of Na, below 5 ppm of K, 16 ppm of Fe, below 5 ppm of No, 114to 121 ppm of Al, below 5 ppm of Cu, below 5 ppm of Zn, below 2 ppm of Mg, and below 20 ppm of V. The thermal stability was determined by a method using Plastograph Plasti-Corder made by Brabender Co., Ltd., West Germany in which a time before a Congo Red test paper was turned blue was measured.

One hundred grams of the deashed carbon black particles was mixed with 5 g of stearic acid powder, followed by sufficiently mixing and agitating. Thereafter, the mixture was dried in a rotary evaporator under a pressure of 14 to 45 Torr., at a temperature of 110 C and then heated in an electric furnace of 400 C for 4 hours in an atmosphere of an inert gs. By the heating, the carbon black particles were reacted with the stearic acid through ester bonds.

Next, 100 parts by weight of ethylene-vinyi chloride copolymer having a degree of polymerization of 430 and an ethylene content of 1.5% (VE-N, made by Tokuyama Sekisui Ind. Co., Ltd.), 5 parts by weight of chlorinated polyethylene (Elaslen 301A, made by Showa Denko Co., Ltd.), 5 parts by weight of a dibutyl tin mercapto ester stabilizer (STAN N JF9595, made by Sankyo Organic Chemicals Co., Ltd.),1.5 parts by weight of a high molecular weight ester (Loxiol G-70, made by Bippon Henkel Co., Ltd.), 0.5 part by weight of an aliphatic alcohol and dibasic acid ester (Loxiol G-60, made by Nippon Henkel Co., Ltd.) and 1.0 part by weight of dimethylpolysiloxane having a viscosity of 20 cps at 25 C were blended in a 20 liters Henschel mixer at a highopeed until the temperature reached 110 C. The mixture was subsequently cooled down to 700C by rotating the mixer at a low speed. Thereafter, 20 parts by weight of the surface-treated conductive carbon black was added to the mixture and blended at 110 C for 1 minutes, and the mixer was rotated at a low speed so that the temperature decreased to 50 C. The mixture was pelletized by a kneader, PR-46, of Buss Co., Ltd., Switzerland. Metals contained in the resulting pellets were removed by a metal separator machine. Thereafter, the pellets were placed in a video disc press to obtain video discs.

Comparative Example 1 The general procedure of Example 1 was repeated using non-treated carbon black particles instead of the surface-treated carbon black, thereby obtaining video discs.

The carbon black particles used in this comparative example had an ash content of 0.94%, a pH of 9.6 and a thermal stability of 7 minutes, and contained 1120 ppm of Ca, 32 ppm of Na, below 5 ppm of K, 55 ppm of Fe, 6 ppm of Ni, 265 ppm of Al, below 5 ppm of Cu, 7 ppm of Zn, 9 ppm of Mg, and below 20 ppm of V.

Comparative Example 2 The general procedure of Example 1 was repeated except that the deashed carbon black was not surface treated with stearic acid. More particularly, the deashed carbon black was dried in an rotary evaporator under a pressure of 15 to 45 Torr., at a temperature of 1 10"C and further heated in an electric furnace of 400 C for 4 hours in an atmosphere of an inert gas. Thereafter, the procedure of Example 1 was repeated, thereby obtaining video discs.

The deashed carbon black obtained in this comparative example had an ash content of from 0.01 to 0.03, a pH of from 6.8 to 7.2 and a thermal stability of 9 minutes, and contained 50 ppm of Ca, 7 to 8 ppm of Na, below 5 ppm of K, 5 ppm of Fe, below 5 ppm of Ni, to 49 ppm of Al, below 5 ppm of Cu, below 5 ppm of Zn, below 2 ppm of Mg and below 20 ppm of V.

The video discs obtained in the above example and comparative examples were each set in a reproducing apparatus and continuous reproduction was repeated to measure a diagonal length of a sliding contact surface of a pickup stylus. Form this, a degree of wear of the stylus was determined. It will be noted that the degree of wear is higher at a longer diagonal length. The results are shown in the sole figure in which the solid line is for the video disc obtained in Example 1,the dash-and-dot line is for the video disc obtained in Comparative Example 1, and the two dots-and-dash line is for the video disc of Comparative Example 2.

The results of the figure reveal that the video disc of the present invention ensures a very long life of the pickup stylus. However, with the video disc of Comparative Example 1, the life is shorter. In the case of the video disco Comparative Example 2, the life is much shorter. Moreover, the video disc of Comparative Example 1 which made use of the non-deashed carbon black deteriorated in the quality of reproduced image such as by drop-out. On the contrary, the video discs of Example 1 and Comparative Example 2 involved no such deterioration.

In short, use of non-deashed carbon black leads to a relatively long life of the pickup stylus but results in a lowering of the reproduced image quality. When carbon black which is merely deashed without further surface treatment with fatty acids is used, the life of the pickup stylus is considered to be shortened though little lowering of the image quality takes place. In contrast, the use of deashed, surfacetreated carbon black can remarkably prolong the stylus life without a lowering of the pickup stylus.

Example 2 The general procedure of Example 1 was repeated using tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, nonadecn acid, arachic acid, behenic acid, lignoceric acid and oleic acid, instead of stearic acid, thereby obtaining video discs. These discs were each tested in the same manner as described above. Similar results as in the case of stearic acid were obtained.

Claims (6)

1. A high density information record of the electrostatic capacitance type which comprises a record substrate on which signal information is recorded as geometric variations, the substrate being made of a conductive resin composition comprising a thermoplastic resin, and deashed carbon black particles which are surface-treated with a fatty acid having from 12 to 24 carbon atoms, the deashed, surface-treated carbon black being used in an amount of 5 to 30 wt% based on the thermoplastic resin.

2. The high density information record according to Claim 1, wherein the deashed, surface-treated carbon black particles have the fatty acid chemically combined through ester bonds.

3. The high density information record according to Claim 1, wherein the fatty acid is stearic acid.

4. The high density information record according to Claim 1, wherein the carbon black particles after deashing has a pH of from 5 to 10.

5. The high density information record according to Claim 1, wherein said fatty acid is used in an amount of from 1 to 10wt% of the carbon black particles.

6. The high density information record according to Claim 1, wherein said carbon black particles have a DBP absorption of from 250 to 450 and an 12 absorption of from 800 to 1400.