AU643017B2

AU643017B2 - Electrically conductive barium sulfate and process of producing it

Info

Publication number: AU643017B2
Application number: AU77269/91A
Authority: AU
Inventors: Clemens Aderhold; Wolf-Dieter Griebler; Takao Hayashi; Jorg Hocken; Manabu Hosoi; Nobuyoshi Kasahara; Uwe Rosin; Gunther Rudolph; Norihiro Sato
Original assignee: Metallgesellschaft AG; Mitsui Mining and Smelting Co Ltd
Current assignee: GEA Group AG; Mitsui Kinzoku Co Ltd
Priority date: 1990-05-26
Filing date: 1991-05-22
Publication date: 1993-11-04
Anticipated expiration: 2011-05-22
Also published as: JPH0688785B2; KR950009165B1; EP0459552B1; CA2043171A1; KR910019908A; JPH1171110A; AU7726991A; DE4017044A1; DE4017044C2; JP3167119B2; JPH0640719A; EP0459552A1; DE59107373D1

Description

643017

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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00 0 Name and Address of Applicant: Actual Inventor(s): Mitsui Mining Smelting Co., Ltd.

1-1, Nihonbashi Muromachi 2-chome Chuo-ku Tokyo

JAPAN

Metallgesellschaft Aktiengesellschaft Reuterweg 14 D-6000 Frankfurt am Main 1 FEDERAL REPUBLIC OF GERMANY Takao Hayashi, Norihiro Sato, Manabu Hosoi, Nobuyoshi Kasahara, Clemens Aderhold, Wolf-Dieter Griebler, Jorg Hocken, Uwe Rosin and Gunther Rudolph Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Electrically Conductive Barium Sulfate and Process of Producing It Address for Service: Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845 4 Electrically Conductive Barium Sulfate and Process of Producing It This invention relates to electrically conductive barium sulfate, to the use of the electrically conductive barium sulfate, and to a process of producing it.

In some applications of plastics, their electrically insulating properties give rise to technical problems. The electrically insulating properties of plastics will be particularly undesirable, for instance, when electronic components must be shielded from relatively large electromagnetic fields, such as is the case with computer housings, or when electric charges are to be discharged from 6 e components. The electrically insulating properties of plastics give also rise to difficulties when high explosives go• or IC components are to be kept in storage, and in the manufacture of medical rubber articles or carpeting provided with and antistatic finish or in the production of electrically conductive adhesives for metal. It is known that S. S polymers can be rendered electrically conductive by addition of conductive particles. Such conductive particles may consist of metal or carbon black particles as well as of SS Se particles consisting of semiconducting oxides, such as zinc oxide, or iodides, such as copper iodide. A disadvantage involved in the use of metal or carbon black particles resides in that the polymers containing the additives have a black color, which is not desired in numerous cases. The use of particles of zinc oxide will result in undesired -2temperature-dependent fluctuations of the electrical conductivity. Because polymers which contain copper iodide have only a low chemical stability, they can be used only for a limited number of applications.

JP-56-157438-A describes a process of producing a powder mixture which can be added to plastics in order to render them electrically conductive. In that process a solution which contains SnCl1 and SbCl 3 is added to an aqueous dispersion of barium sulfate which has been heated. A precipitation is effected in an acid medium and results in mixed powders consisting of SnO2 powder and BaSO 4 powder.

But the plastics to which said mixed powders have been added ~have an electrical conductivity which is thermally unstable.

e• Besides, the mixed powders have a relatively poor :dispersibility in plastics so that problems arise in the production of a homogeneous mixture consisting of the mixed powders and plastics.

For this reason it is an object of the invention to 0 provide an electrically conductive barium sulfate which has a thermally stable electrical conductivity and a high dispersibility in plastics. An object of the invention resides also in the provision of a process by which the electrically conductive barium sulfate can be produced with Se s S* the aid of simple technical means and at a high reaction rate.

The object of the invention is accomplished in that the electrically conductive barium sulfate consists of particles of BaSO4 which are covered by a coating of SnO 2 that is doped with Sb 2 03 The content of Sb 2 03 in the coating of Sn02 -3amounts to from 1 to 15% by weight. The coating has a thickness from 2 to 80nm. The particle of BaSO4 have in an uncoated state a specific surface from 0.1 to 150m 2 The electrical conductivity of the substance provided by the invention amounts to from 1.2x 10-' to 7x 10-' (ohm x cm)-' It has surprisingly been found that the electrically conductive barium sulfate in accordance with the invention has a high dispersibility in plastics, particularly in resins.

The plastics to which the electrically conductive barium sulfate in accordance with the invention has added also distinguish by having a constant electrical conductivity even i at fluctuating temperatures so that the plastics to which the *0 electrically conductive barium sulfate in accordance with the

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.0 invention has been added can be used for a large variety of purposes.

In accordance with a preferred feature of the invention, the content of Sb20a in the coating amounts to from 6 to 12% by weight. In that case the electrically conductive barium sulfate will have a relatively high electrical conductivity so Sthat the content of the coating in the electrically conductive barium sulfate may be relatively low on weight basis and, as a result, the cost of the electrically conductive barium sulfate will be relatively low too.

*e In accordance with a further preferred feature of the invention the coating has a thickness from 10 to 30nm. In that case the strength of the bond between the coating consisting of SnO2 doped with Sb 2 0 and the particles of BaSO4 will be relatively high. A coating having a thickness from -4to 30nm will ensure that the coating will not become detached from the particles of BaSO 4 during the incorporation of the electrically conductive barium sulfate in a matrix.

In accordance with a further feature of the invention the particles of BaS04 have a specific surface from 0.1 to 3 or from 12 to 150m2/g. In that case the electrically conductive barium sulfate will be transparent so tnat it can desirably be processed together with paints, which will then be electrically conductive whereas the covering power of additional pigments will not adversely be effected.

The object of the invention is also accomplished by the provision of a process which serves to produce an electrically ee conductive barium sulfate and wherein a first acid solution S" which contains SnC14 is added to an aqueous dispersion of 0 BaS04 to provide a mixture and a second acid solution which lo contains SbCls is added to said mixture and which process is characterized in that the aqueous dispersion contains BaSO4 in a concentration from 50 to 800g/l, the first acid solution contains SnCl 4 in a concentration from 1 to 95% by weight, the second acid solution contains SbCI 3 in a concentration from eS to 60% by weight, a basic solution is added and at the same time or subsequently the first acid solution is add to the dispersion of BaSO 4 to adjust its pH value to a value from 9 to 14, the pH value of the mixture is decreased to a value between 4 and 1 by an addition of acid thereafter a basic solution is added together with the second acid solution, and the resulting electrically conductive barium sulfate is separated, dried and calcined at a temperature of 300 to 800°C.

Aqueous solutions of NaOH or KOH may be used, as the basic solution. That process will afford the advantage that the particles of BaSO are entirely covered by a coating of SnO 2 which is doped with Sb 2 03 The process can easily be carried out within a short time and the electrically conductive barium sulfate which has been produced by the process has a high dispersibility in plastics.

In accordance with a further feature of the invention a third acid solution which has a pH value from 0 to 3 and contains SnCl 4 in a concentration from 1 to 95% by weight is added to the dispersion of BaSO 4 and the resulting starting 06 mixture is stirred for 10 to 200 minutes before the basic solution and the first acid solution is added. This will afford the advantage that the surface of the particles of BaSO 4 S **oo is etched by the SnCl, which is contained in the third acid solution before the first acid solution is added so that a S stronger bond will be formed between the coating of SnO 2 which is doped with Sb 2 Os and particles of BaSO In accordance with a further preferred feature of the invention the mixture is stirred for 10 to 200 minutes after the first acid solution and the basic solution have been added and the pH value of the mixture is subsequently decreased to a value from 4 to 1 by an addition of acid before the basic solution and the second acid solution is added.

This will afford the advantage that the particles of BaSO 4 will be entirely covered by a coating of SnO 2 before the SnO 2 is doped with Sb 20 3. As a result, the Sb203 will be -6homogeneously distributed in the coating of SnO 2 In accordance with a further preferred feature of the invention the electrically conductive barium sulfate is separated, dried and ignited when 1 to 30 hours have passed after the addition of the second acid solution has been completed. This will result in an electrically conductive barium sulfate having a relatively high chemical stability.

In accordance with a further preferred feature of the invention the electrically conductive barium sulfate is used in the production of electrically conductive adhesives, electrically conductive paints, electrically conductive plastics, electrically conductive laminated papers or 0* electrically conductive synthetic fibers. The quality of said products can thus be improved.

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The subject matter of the invention will be explained a 0o0 more in detail with reference to the following Examples.

Example 1 100g BaSO 4 having an average particle diameter of 10 u m and a specific surface of 0.1m2/g are dispersed in 400ml water at a temperature of 70 "C The pH value is subsequently adjusted to 2 by an addition of 1ml concentrated hydrochloric acid. Thereafter, 500ml water at a temperature of 70°C and a third acid solution consisting of 1ml SnCl 4 and Iml concentrated hydrochloric acid are added to the acid dispersion of BaS04. The resulting starting mixture is stirred for 60 minutes so that it assumes a pH value of Thereafter, 800ml of a 10% solution of NaOH and a first acid solution consisting of 31ml SnC14 dissolved in 100ml 2-molar -7hydrocloric acid are added. The mixture is stirred for minutes while its temperature is kept at 70° During the next 90 minutes the pH value is decreased to 2.5 by an addition of 110ml 2-molar hydrochloric acid. Thereafter a second solution consisting of 100ml 5.3g SbCl 3 in 100ml 2molar hydrochloric acid and 170ml of 10% solution of NaOH are added in drops at the same time. After further 20 hours the electrically conductive barium sulfate is separated and dried. When the electrically conductive barium sulfate has been calcined at 600°C for two hours, it has an electrical conductivity of 1.ix 10-' (ohm x Example 2 100g BaSO 4 having an average particle diameter of 100 A m and a specific surface of 30m 2 /g are dispersed in 900ml 8 distilled water. A third acid solution consisting of 1ml SnC1 and 1ml concentrated hydrochloric acid is added to the resulting suspension to adjust its pH value to 1.5. The S resulting starting mixture is stirred for 1 hour.

Thereafter, 800ml of a 10% solution of NaOH and a first acid solution containing 31ml SnCl4 dissolved in 100ml 2-molar e e hydrochloric acid are added at the same time. The mixture is then stirred for further 30 minutes while its temperature is kept at 70C During the next 90 minutes the pH value is decreased to 2.5 by an addition of 110ml 2-molar hydrochloric acid. Thereafter a second solution consisting of 100ml 5.3g SbCl 3 in 100ml 2-molar hydrochloric acid and 170ml of solution of NaOH are added in drops at the same time. After further 20 hours, the electrically conductive barium sulfate -8is separated and dried. It has conductivity of 2.3x< 10 (ohm x after having been calcined at 400"C for two hours and of 1.7X 10 2 (ohm x cm) after having been calcined at 600°C for two hours.

Example 3 100g BaSO4 having an average particle diameter of 100 i m and a specific surface of 30m2/g are dispersed in 900ml distilled water. 1ml concentrated hydrochloric acid are added to adjust the pH value to 2. A third acid solution consisting of 1ml SnCl 4 and 1ml concentrated hydrochloric acid is then added to provide a starting mixture, which is 0* 000 stirred for 60 minutes to adjust its pH value to Thereafter a first acid solution containing 72ml SnCl4 S" dissolved in 150ml 2-molar hydrochloric acid and 1 liter of a 0. 10% solution of NaOH are added at the same time. The mixture is subsequently stirred for 30 minutes while it is kept at a temperature of 70C In the next 90 minutes the pH value is S decreased to 2.5 by an addition of 110ml hydrochloric acid. A second solution consisting of 8g SbCl 3 in 150ml 2-molar hydrochloric acid and 150ml of 10% solution of NaOH are

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subsequently added in drops at the same time. After further hours the electrically conductive barium sulfate is separated and dried. When it has calcined at 600'C for two hours it has a conductivity of 1.9x 10" 2 (ohm x cm) Example 4 200g BaSO 4 having an average particle diameter of m and a specific surface of 4m /g are dispersed in 800ml water. By an addition of 1ml concentrated hydrochloric acid -9the pH value is adjusted to 2. A third acid solution consisting of an acid solution of SnCl 4 in a concentration of is then added and the resulting slurry is stirred for 1 hour to assume a pH value of 1.5. Thereafter, 1000ml of a solution of NaOH are added to the starting mixture to initially adjust its pH value to 14. Subsequently a first acid solution consisting of 62ml SnCl 4 in 138ml 2-molar hydrochloric acid is added whereby the pH value is decreased to 11.5. The mixture is subsequently stirred for 30 minutes while it is kept at temperature of 70 "C By an addition of 470ml 2-molar hydrochloric acid during the next 90 minutes the pH value is decreased to 2.5. Thereafter a second acid

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solution consisting of 10.6g SbCl 3 in 200ml 2-molar hydrochloric acid is added. For an adjustment to a pH value of 2.5, a total of 200ml of a 10% solution of NaOH must be added. After further 20 hours the electrically conductive barium sulfate is separated and dried. When it has been S calcined at 600°C for two hours it has a conductivity of x 10 3 (ohm x cm)'.

f-.-Hampl CcymPflrc-r\J&e Gfag'is. This Example differs from the preceding Examples 1 to 4 in that the BaSO4 is coated in an acid medium and an increase of the pH value to a value from 9 to 14 by a simultaneous addition of a basic solution together with a SnCl -containing first acid solution is intentionally omitted.

200g BaSO 4 having an average particle diameter of m and a specific surface of 4m 2 /g are dispersed in 800ml water. 1ml concentrated hydrochloric acid is added to the 1 0dispersion to adjust its pH value to 2.2ml SnCl4 are subsequently added and the resulting slurry is stirred for 1 hour to adjust its pH value to 1.5. The starting mixture is then heated to 70"C and its pH value is increased only to by means of a 10% solution of NaOH. 62ml SnCl 4 dissolved in 2-molar hydrochloric acid and 10.6g SbCl 3 dissolved in 2-molar hydrochloric acid together with 1100ml of a 10% solution of NaOH are added at the same time within 90 minutes. After further 20 hours the BaSO4 is separated and dried and after having been calcined for two hours at 600'C it has a conductivity of 2x 10 (ohm x That relatively low conductivity and the results of investigations with a transmission electron microscope prove that BaSO 4 cannot be coated in an acid medium but mixed powders consisting of particles of SnO2 doped with Sb 20 3 and of particles of BaSO 4

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will be obtained in that case.

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Claims

1. Electrically conductive barium sulfate powder, characterised in that it consists of particles of BaSO 4 which are coated with SnO 2 doped with Sb 2 0 3 the coating containing from 1 to 15% by weight Sb 2 0 3 and having a thickness of from 2 to 80nm, and the particles of BaSO 4 having in an uncoated state a surface of from 0.1 to 150m2/g.

2. Barium sulfate according to claim 1, characterised in that the coating contains from 6 to 12% by weight Sb 2 0 3

3. Barium sulfate according to claim 1 or claim 2, characterised in that the coating has a thickness of from 10 to

4. Barium sulfate according to any one of claims 1 to 3, characterised in that the particles of BaSO 4 have in an uncoated state a specific surface of from 0.1 to 3m2/g or from 12 to 150m2/g.

A process of producing an electrically conductive barium sulfate powder, wherein a first acid solution which contains SnC14 is added to an aqueous dispersion of BaSO 4 to provide a mixture and a second acid solution which contains SbC13 is added to said mixture, characterised in that the aqueous dispersion contains 50 to 800g/L of BaSO 4 the first acid solution contains 1 to 95% by weight of SnC1 4 20 the second acid solution contains 0.5 to 60% by weight of SbC1 3 a first basic solution is added with or subsequently to the first acid S" solution to adjust its pH to from 9 to 14, the pH of the mixture is decreased to between 4 and 1 by an addition of acid, thereafter a second basic solution is added together with the second acid solution, and the resulting electrically conductive barium sulfate is separated, dried and calcined at a temperature of 300 to 800 0 C.

6. A process according to claim 5, characterised in that a third acid solution which has a pH of from 0 to 3 and which contains 1 to by weight of SnC14 is added to the dispersion of BaSO 4 before the 30 first acid solution is added and the resulting mixture is stirred for to 200 minutes before the first acid solution is added.

A process according to claim 5 or 6, characterised in that the mixture is stirred for 10 to 200 minutes after the first solution and the first basic solution have been added and the pH of the mixture is subsequently decreased to from 4 to 1 by the addition of acid before the second solution is added.

8. A process according to any one of claims 5 to 7, characterised in that the electrically conductive barium sulfate is separated, dried c and calcined after 1 to 30 hours have passed after the addition of the 81 a ii *fwUR'/ 12 second acid solution has been completed.

9. A process of producing an electrically conductive barium sulfate powder substantially as hereinbefore described with reference to any one of Examples 1 to 4.

10. The product of the process of any one of claims 5 to 9.

11. Electrically conductive barium sulfate powder substantially as hereinbefore described with reference to any one of Examples 1 to 4.

12. A process of producing an electrically conductive adhesive, an electrically conductive paint, an electrically conductive plastic, an electrically conductive laminated paper or an electrically conductive synthetic fiber by incorporating therein an electrically conductive barium sulfate powder according to any one of claims 1 to 4, 10 or 11. DATED this SIXTEENTH day of AUGUST 1993 Mitsui Mining Smelting Co., Ltd. Metallgesellschaft Aktiengesellschaft Patent Attorneys for the Applicants t SPRUSON FERGUSON 0. 0* 0 0 o *06 7' BNO 1781a/ii ABSTRACT An electrically conductive barium sulfate is described which consists of particles of BaSO 4 which are covered by a coating of Sn02 that is doped with Sb 2 03 A process of producing the electrically conductive barium sulfate is also described. The electrically conductive barium sulfate distinguishes by having a thermally stable electrical conductivity and a particularly high dispersibility in plastics. 6 6O S g o*