EP2462594A1

EP2462594A1 - Conductive powder

Info

Publication number: EP2462594A1
Application number: EP10740515A
Authority: EP
Inventors: Tetsuji Honjo; Satoru Kobayashi; Atsuko Iwabuchi
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2009-08-03
Filing date: 2010-07-08
Publication date: 2012-06-13
Also published as: JP2013501320A; WO2011015268A1

Abstract

The present invention relates to electrically conductive particles which gives conductivity especially to polymer matrixes in the various applications of resin compositions. It has now been found that inorganic base materials, in particular TiO₂ particles, coated with tungsten and phosphorus doped tin oxide (TPTO), have conductivities which are sufficiently high for all uses, especially for the conductive primer of electrostatic coating on automotive plastic parts.

Description

Conductive powder

The present invention relates to electrically conductive particles which give conductivity especially to polymer matrixes in the various applications of resin compositions. The conductive powder is suitable for blending into polymer matrixes in the application of resin compositions, paints and primers to give them electrical conductivity.

Electrically conductive particles are used in various fields of applications, for example, antistatic treatment of plastic materials (coating films, films, sheets, molded pieces, etc.), or conductive lacquers for the electrostatic coating of plastic materials.

As a coating method of plastic materials, a electrostatic spray coating with little discharge of the lacquer to environment has come to be widely adopted. In the case of electrostatic coating the electric resistance value of a plastic base material is high, the higher conductivity is given by coating the conductive layer (primer) on the surface of plastic base material and the electrostatic spray coating can be performed for the colored painting.

Especially, in order to create white and light color on black plastic base material, it is necessary to develop a conductive powder with whitish hiding power.

Apart from conductivity and low costs, carbon black has the disadvantage that only black or gray shades can be achieved and thus it cannot be used in transparent and light colored coatings.

From the viewpoint of the color, antimony doped tin oxide (ATO) is currently used in various applications of antistatic coatings. However, the toxicity of antimony contained in ATO has been recently concerned, and an electrically conductive powder without antimony is needed.

There is therefore a need for stable electrically conductive pigments, which are antimony free and which can be used in transparent and light colored coatings. Antimony free conductive materials are known from WO 95/1 1512 which is directed to tungsten and/or phosphorus doped tin oxide. On the other hand, tungsten doped tin oxide (TTO) and phosphorus doped tin oxide (PTO) coated on inorganic particles have been reported. JP 2002-179948 A and DE 10148055 describe TTO coated on inorganic particles. However, the conductivity of TTO coated inorganic particles is insufficient for various antistatic coatings applications. One of the reasons is that the tungsten doping content is limited to less than 3 atomic % to tin element which means the carrier density to create the conductivity is lower compared to ATO and PTO.

JP 3357107, JP 1995-250997 and JP 2004-349167 describe PTO coated on inorganic particles. However, PTO coated inorganic particles cause the problem that the conductivity of powder decreases with the passage of time when kept in air. Thus, the conductivity of PTO is easily affected by oxygen and humidity.

Tungsten and phosphorus doped tin oxide (TPTO) coated on platelet shaped aluminum oxide is reported in WO 2009/018984. However, the purpose of this invention is to provide an electrically conductive powder which has enough transparency.

There is therefore a need for stable electrically conductive particles which show a white and light color on black base materials and which apart from conductivity impart a whitish hiding power. These features are key issues of the conductive primer for electrostatic coating on the black base materials.

The purpose of the present invention is to provide electrically conductive particles which have enough hiding power and show superior long term stability.

It has surprisingly now been found that the coating of inorganic substrates on the surface with a conductive layer, the conductive layer being a tungsten and phosphorus doped tin oxide (hereafter, referred as TPTO) layer leads to conductive powders having none of the above mentioned disadvantages. TPTO coated on inorganic substrates show high conductivity and superior long term stability for all uses, especially for the conductive primer of electrostatic coating on automotive plastic parts, which show the requested white and light color and have an excellent whitish hiding power.

Further, the purpose of the present invention is to provide a process for manufacturing the electrically conductive particles bearing the above- mentioned properties. According to the present invention, there are provided electrically conductive particles, which particularly have superior dispersibility into solvents or polymer matrixes and which at the same time even have enough

conductivity. Therefore, in particular, the electrically conductive particles can be advantageously used in plastic materials like coating films, plastic sheets, molded pieces or conductive lacquers, especially for the

electrostatic coating of plastic materials.

Base substrates for the conductive particles according to the present invention which can be employed as inorganic materials can be selected from TiO₂, ZnO, BaSO₄, AI₂O₃, SiO₂, ZrO₂, glass, alkali titanate, natural or synthetic mica, phyllosilicates, such as talc, kaolin, wollastonite or sericite, and mixtures thereof. A preferred substrate is TiO₂ in view of the whitish hiding power due to high refractive index. The crystal system of TiO₂ can be selected from rutile, anatase, brookite or can be amorphous. Especially, the preferred crystal system is rutile which is the same crystal system as the tin oxide, since use of rutile TiO₂ makes it easy to achieve conductivity.

The shape of base substrates can be selected from grains, spheres, plates, needles, fibers, columns, rods, and these mixtures. Especially, the grain or sphere-shaped substrates are preferable to get good smooth surface of plastic films.

In terms of the size of the base substrates, the mean diameter is in the range of 0.01 to 100 μm, in particular 0.01 - 10 μm, especially preferred 10 - 500 nm. - A -

The grain or sphere-shaped substrates have preferably a mean radius of 0.01 - 10 μm, in particular 0.01 - 1 μm, especially preferred 10 - 500 nm. These mean diameters of substrates are desirable at the half of wavelength of visible light, since the whitish hiding power can be obtained on black base materials.

In the case of plate, needle, fiber, column, rod-shaped substrates, the ratio of its long axis and short axis (i.e., long axis/short axis) ranges from 2 to 200, preferably 10 to 50. In the case of spheres (including oval spheres), the ratio of its long axis and short axis (i.e.; long axis/short axis) ranges from 1 to 10, preferably 1 to 5.

Preferred spherical base substrate is selected from TiO₂, ZnO₁ BaSO₄, glass, alkali titanate, AI₂O₃, SiO₂, ZrO₂ Or mixtures thereof. Especially preferred base substrates are TiO₂, alkali titanate and ZnO which have a whitish hiding power due to high refractive index.

Preferred plate, needle, fiber, column and rod-shaped base substrate is selected from natural or synthetic mica, talc, kaolin, sericite, glass, TiO₂, ZnO, BaSO₄, AI₂O₃, SiO₂, ZrO₂, alkali titanate, wollastonite or mixtures thereof. Especially preferred base substrates are TiO₂, alkali titanate and ZnO which have a whitish hiding power due to high refractive index.

The base substrates to be coated with an electrically conductive layer can also consist of a mixture of different substrates. The base substrates can be mixed in all proportions. Preferred mixtures contain not more than two different substrates. In this case, the preferred mixture ratio is from 1 : 1 to 10 : 1. Preferred mixtures of base (carrier) substrates are grain or spherical shaped TiO₂ and platelet-shaped substrates which are selected from natural or synthetic mica, talc, kaolin, sericite, glass, alkali titanate, ZnO, BaSO₄, AI₂O₃, SiO₂ and mixtures from these. Especially preferred platelet shaped substrates are TiO₂, alkali titanate and ZnO which have a whitish hiding power due to high refractive index. Preferred substrate mixtures contain

- spherical TiO₂ and one or more platelet-shaped substrates selected from TiO₂, alkali titanate or ZnO particles;

- platelet-shaped TiO₂ and one or more spherical substrates selected from alkali titanate and ZnO particles.

The amount of TPTO on the substrates is in the range of 20 - 80 wt.%, in particular 30 - 60 wt.%, and most preferably in the range of 35 - 50 wt.%, based on the weight of final particles. The layer thickness of TPTO layer on the substrates is in the range of 10 - 200 nm, preferably 30 - 100 nm.

Larger amounts of TPTO on the base substrates, although possible per se, do not provide any further increase in conductivity, and the particles become increasingly darker. On the other hand, smaller TPTO amounts have the disadvantage that the high conductivity of the particles cannot be achieved.

In the conductive layer, the atomic ratio of tungsten and phosphorus in the tin oxide layer is 0.01 - 30 atomic% (at.%), preferably 0.1 - 20 at.%, in particular 3 - 10 at.%. If the doping content of tungsten and phosphorus is less than 0.01 at.% or more than 30 at.%, the high conductivity cannot be achieved.

The ratio of tungsten and phosphorus in the tin oxide layer is preferably 0.1 : 3 to 5 : 20, especially preferred 0.5 : 15 to 3 : 10.

The ratio of tin and tungsten and phosphorus used in the TPTO coating layer is the range from 98.9 : 0.1 : 1 to 70 : 10 : 20 in terms of atomic ratio. Preferably, it is from 96 :1 : 3 to 85 : 5 : 10. Especially preferred are TiO₂ particles (spherical, grain-shaped) having a mean radius of 150 - 500 nm which are coated with 30 - 50 wt.% of TPTO based on the weight of the final particles. In this case the layer thickness of the TPTO layer is preferably in the range of 30 - 100 nm. The invention also provides a process for preparing the novel conductive particles which is characterized in that the inorganic base substrates are suspended into water, preferably at elevated temperature, for example 40- 90 ⁰C. The tin salt and tungsten salt and the phosphate are added to the suspension at a suitable pH, the pH of the substrate suspension being maintained, by simultaneous addition of a base or of an acid, within the range which brings about the hydrolysis of the tin, phosphorus and tungsten salt, and the substrate coated in this way by TPTO, is separated off, washed, dried, preferably at temperatures at 100 - 150 ⁰C for 1 - 12 h and calcined at temperatures of 600 - 1000 ⁰C, preferably at 700 - 900 ⁰C, in an oxygen / nitrogen atmosphere or inert gas atmosphere, preferably N₂ atmosphere.

Use can be made judiciously of the bases which are readily obtainable industrially, such as NaOH, KOH or ammonia, for example, and of the acids of dilute mineral acids, for example HCI. Since the bases and acids serve only to change the pH, their nature is not critical, so that other acids and bases can also be employed.

The desired homogeneous distribution of tungsten and phosphorus in the tin oxide layer is preferably readily achieved by metering the tin compounds and tungsten salt and phosphorus compound in water, either together in one solution or in two or three separate solutions, continuously and in the predetermined mixing ratio, in the substrate suspension at a suitable pH of from 1 to 5 and at a suitable temperature of from about 50 to 90 ⁰C, in such a way that hydrolysis and deposition on the substrate takes place

immediately in each case.

Suitable water-soluble tin salts are preferably sulfates, nitrates, halides, chlorides, stannate salts including sodium stannate, potassium stannate, lithium stannate. Especially preferred are the chlorides.

Suitable tin salts are preferably the 2- and 4-valent halides, sulfates or nitrates, preferably the halides, and especially the chlorides, thereof.

Particular preference is given to a tin salt solution consisting of SnCI₄. The tin salts can also be added in solid form to the aqueous substrate suspension. As the tungsten compounds used for tungsten compound solution, ammonium tungstate, potassium tungstate, sodium tungstate, ammonium meta tungstate, potassium meta tungstate, sodium meta tungstate, ammonium para tungstate, potassium para tungstate, sodium para tungstate, tungsten oxychloride and the like are exemplified.

As the phosphorus compounds used for the phosphorus compound solution, orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, phosphorous acid, hypophosphorous acid and the like are exemplified.

The metal salts can be precipitated using any acid or base. The optimum concentrations and pH values can be determined by means of routine experiments. Normally, once established for the precipitation, the pH is maintained throughout the precipitation in order to obtain uniform particles.

At the end of the coating process, the particles are separated off the suspension, washed, dried and calcined at high temperatures, preferably at 600 - 1000 ⁰C, in an oxygen and nitrogen containing atmosphere, preferably in the absence of oxygen, for 5 min. to 60 min., for example.

Depending on the choice of the starting material and the layer thickness of the doped tin oxide layer, the particles according to the present invention are cream-colored, yellowish, whitish and light gray.

The tungsten and phosphorous doped tin oxide layer gives the novel particles a stable and high conductivity and the powder volume resistivity (Rv) is in general less than 100 Ω• cm, even if the powder is kept in humidity atmosphere.

In a typical embodiment of the composition of the present invention comprising the conductive powder component in a resin matrix, the surface resistivity (Rs) is not higher than 100 MΩ/sq., preferably not higher than 1 MΩ/aq., in the coating film (10 - 15 μm in thickness) formed by using a lacquer containing the powder of 50 wt.% as a p_owder weight concentration (hereafter, referred to as PWC) based on the weight of coating film. In addition to the high electrical conductivity, the novel particles are characterized by the whitish hiding power compared to the conductive particles known from the prior art. The whitish hiding power is measured by a lightness (L^* value) in the L*a^*b^* color system as defined in JIS Z 8729. The electrically conductive powder of the present invention can form a coating layer with high whiteness, i.e., a lightness (L* value) of 80 or more in the coating film (10 - 15 μm in thickness) formed by using a lacquer containing the powder of 50 wt.% as a PWC. Therefore, the resultant conductive powder can form the whitish plastic films on black base materials.

Depending on their specific embodiment, the particles according to the present invention can be used for a whole range of different applications, such as for conductive lacquers for the electrostatic coating of plastic materials, antistatic coatings, for antistatic plastics, floor coverings, etc. In addition they are useful in paints, varnishes, printing inks and plastics.

The invention therefore likewise provides formulations which comprise the TPTO coated particles according to the present invention.

Further, application examples using the electrically conductive particles of the present invention is explained hereafter. The electrically conductive particles of the present invention can be used in comprehensive field of applications. Examples of applications include resin compositions, primers, concoctions (preparation mixture), paints, lacquer, printing inks, plastics, and films; more specifically, antistatic treatment for plastic materials (coating films, films, sheets, molded products, etc.) or electrically conductive primers in use for electrostatic coating. These applications are explained in more details below. As an example for using in resin compositions, when the electrically conductive particles of the present invention is incorporated into resin, the powder may be directly mixed with the resin, or forming pellets beforehand and then mixing with the resin to give various molded products by extrusion molding, calendaring, blow molding and so on. Resin components used include any thermoplastic resins such as polyolefin-based resins and any thermosetting resins such as epoxy-based resins, polyester-based resins and polyamide (nylon)-based resins.

Further, the electrically conductive particles of the present invention can be used for especially manufacturing electrically conductive films and plastics, for example, the electrically conductive films and sheets, plastic containers and molded products for any applications needing electrical conductivity which a person skilled in the art knows (for example, including antistatic applications). The plastics suitable for the integration of the electrically conductive particles of the present invention include any commonly used plastic, for example, thermosetting materials and thermoplastic materials.

When the electrically conductive particles of the present invention is used for paints for antistatic coating, organic solvent-based paints, NAD-based, water-based paints, emulsion paints, colloidal paints and powder paints may be exemplified. These paints may be used for coating of lumbers, plastics, metal steel sheets, glass, ceramics, papers, films, sheets, the translucent membranes for reflector of LC display and the like. As the applications of paints, use for automobiles, for constructions, for ships, for electronics, for cans, for industrial equipments, for road marking, for plastics and for household use and the like may be exemplified. Method for coating includes, but not limited to, spray coating, electrostatic coating, electro- deposition coating and the like. Regarding the structures of painted film, examples include, but not limited to, a structure having the order of a foundation layer, an intermediate coat layer, a layer containing the electrically conductive powder of the present invention and a clear layer, or a structure having the order of a foundation layer, an intermediate coat layer containing the electrically conductive particles of the present invention and a clear layer. Furthermore, for the paints of the present invention, the below listed pigments may be used in combination with the electrically conductive particles of the present invention. As the examples of using the primers, a resin mixed with at least one of modified resin selected from the group consisting of polyolefin resin, acrylic resin, polyester resin and polyurethane resin, and a water-based paint or organic solvent-based paint containing a cross-linker may be utilized.

Water-based primers typically contain binder components. The binder components are not restricted as long as they have enough hydrophilic groups for solubility or dispersion in water. In addition, the primers may contain other additives including antifoaming agent, thickener, surfactant, etc.. Articles to be coated with the above-mentioned primers are not limited, and for example, interior and exterior automotive trims, outer panel parts of interior and exterior housing trims and home electric appliances and so on are exemplified. Further, the substrates of the above-mentioned coated products are not specifically restricted, and include metal boards, resin boards, glass boards, ceramic board and the like, and specific example of resin boards include those from polyolefin resin, polycarbonate resin, ABS resin, urethane resin, nylon, polyphenylene oxide resin and the like. If needed, the above-mentioned substrate may be treated with degreasing, water washing.

As application use for ink, plastic, rubber and other prepared mixtures, the electrically conductive particles of the present invention are particularly suitable for prepared mixtures intending electrical conductivity, and may be combined with any types of generally-used materials and auxiliaries.

Specifically, they may be used for printing inks (printing ink for gravure, offset, screen and flexographic printing), toner for copy machines, laser marking, cosmetic preparations and so on.

The examples for the pigments that may be used in combination with the electrically conductive particles of the present invention in the above- mentioned resin compositions, paints, lacquer, primers and prepared mixtures are exemplified below. The examples include titanium dioxide, calcium carbonate, clay, talc, barium sulfate, white carbon, chromium oxide, zinc oxide, zinc sulfide, zinc powder, metal powder pigment, iron black, yellow iron oxide, colcothar, chrome yellow, carbon black, molybdate orange, iron blue, ultramarine blue, cadmium-based pigment, fluorescent pigment, soluble azo pigment, insoluble azo pigment, condensation-type azo pigment, phthalocyanine pigment, condensation polycyclic pigment, composited oxide pigment, graphite, mica (for example, muscovite, brown mica, synthetic mica, fluorine four silicon mica and so on), metal oxide coating mica (for example, titanium oxide coating mica, titanium dioxide coating mica, (hydration) iron oxide coating mica, iron oxide and titanium oxide coating mica, lower-oxidation number titanium oxide coating mica and so on), metal oxide coating graphite (for example, titanium dioxide coating graphite and so on), platelet-like alumina, metal oxide coating alumina (for example, titanium dioxide coating alumina, iron oxide coating platelet-like alumina, ferric trioxide platelet-like alumina, triiron tetroxide platelet-like alumina, interference color metal oxide coating platelet-like alumina and so on), MIO, metal oxide coating MIO, metal oxide coating silica flake, and metal oxide coating glass flake.

These pigment mixtures are also part of the present invention.

Furthermore, the electrically conductive particles of the present invention may be used as an electrically conductive material for displays replacing ITO, for solar cells, for printing electronic components, for antistatic and for anticounterfeit.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder or the disclosure in any way whatsoever.

In the following and in the following examples, all temperatures are set forth uncorrected in degrees Celsius and unless other indicated, all parts and percentages are by weight.

Examples The examples of the present invention will be explained below to illustrate the present invention without limiting it. Throughout the entire description and in these examples

- "TTO" denotes the layer of tungsten-doped tin oxide,

- "PTO" denotes the layer of phosphorus-doped tin oxide, and

- "TPTO" denotes the layer of tungsten- and phosphorus-doped tin oxide.

Example 1 : TPTO coated on TiO₂ powder

15O g of spherical TiO₂ particles (KR-310 from Titan Kogyo, Ltd., TiO₂ particles having a mean radius of 0.3 - 0.5 μm) are dispersed in 2 I of deionized water. The suspension is heated at 75 ⁰C under stirring and the pH is adjusted by diluted HCI. In the next step, a 21 wt.% of SnCI₄ solution (722 ml) added 7 g of 85 wt.% of H₃PO₄ and a 1 wt.% Na₂WO₄ solution (242 ml) are simultaneously dropped to the suspension while maintaining the pH 1 - 3 constant by addition of 32 wt.% of NaOH solution. After the complete dropping of the two raw solutions, the TPTO coated spherical TiO₂ particles are filtered, washed with deionized water and dried at 105 ⁰C for 12 h. The dried powder is calcined at 900 ⁰C for 10 min. in an N₂ atmosphere

(containing 1.2 % of O₂).

Comparative Example 1 : TTO coated on TiO₂ particles

150 g of spherical TiO₂ particles (KR-310 from Titan Kogyo, Ltd., TiO₂ particles having a mean radius of 0.3 - 0.5 μm) are dispersed in 2 I of deionized water. The suspension is heated at 75 ⁰C under stirring and the pH is adjusted by diluted HCI. In the next step, a 21 wt.% of SnCI₄ solution (766 ml) and a 3 wt.% Na₂WO₄ solution (255 ml) are simultaneously dropped to the suspension while maintaining the pH 1 - 3 constant by addition of 32 wt.% of NaOH solution. After the complete dropping of the two raw solutions, the TTO coated spherical TiO₂ particles are filtered, washed with deionized water and dried at 105 ⁰C for 12 h. The dried powder is calcined at 900 ⁰C for 10 min. in an N₂ atmosphere (containing 1.2 % of O₂). Comparative Example 2: PTO coated on TiO₂ particles

150 g of spherical TiO₂ particles (KR-310 from Titan Kogyo, Ltd., TiO₂ particles having a mean radius of 0.3 - 0.5 μm) are dispersed in 2 I of deionized water. The suspension is heated at 75 ⁰C under stirring and the pH is adjusted by diluted HCI. In the next step, a 21 wt.% of SnCI₄ solution (730 ml) added 7 g of 85 wt.% of H₃PO₄ is simultaneously dropped to the suspension while maintaining the pH 1 - 3 constant by addition of 32 wt.% of NaOH solution. After the complete dropping of the raw solution, the PTO coated spherical TiO₂ particles are filtered, washed with deionized water and dried at 105 ⁰C for 12 h. The dried powder is calcined at 900 °C for 10 min. in an N₂ atmosphere (containing 1.2 % of O₂).

Comparative Example 3: TPTO coated on platelet-shaped AI₂O₃ and grain- shaped SiO₂ particles

90 g of platelet-shaped AI₂O₃ prepared by WO 2009/018984 (average particle diameter: 10 - 20 μm, average thickness: 100 - 300 nm, aspect ratio: 50 - 200) and 60 g of grain-shaped SiO₂ particles (FS-3DC from Denki Kagaku Kogyo Co. Ltd., SiO₂ particles having a mean radius of 2.2 - 3.8 μm) are dispersed in 2 I of deionized water. The suspension is heated at 75 °C under stirring and the pH is adjusted by diluted HCI. In the next step, a 21 wt.% of SnCI₄ solution (722 ml) added 7 g of 85 wt.% of H₃PO₄ and a 1 wt.% Na₂WO₄ solution (242 ml) are simultaneously dropped to the

suspension while maintaining the pH 1 - 3 constant by addition of 32 wt.% of NaOH solution. After the complete dropping of the two raw solutions, the TPTO coated platelet-shaped AI₂O₃ and grain-shaped SiO₂ particles are filtered, washed with deionized water and dried at 105 ⁰C for 12 h. The dried powder is calcined at 900 ⁰C for 10 min. in an N₂ atmosphere (containing 1.2 % of O₂). Method for measuring "powder volume resistivity: Rv (Ω• cm)":

In this patent application and in the given examples "electrically conductive powder" is defined as follows:

The electrically conductive powder is characterized by its powder volume resistivity (Rv). In this patent application, the electrically conductive powders have Rv of less than 300 Ω• cm, preferably less than 100 Ω^• cm. These requirements arise from the applications of the conductive powders in conductive, antistatic or static dissipative coatings, such as, floorings. For instance, the surface resistivity (Rs) permitted for conductive primer of electrostatic coating is preferably less than 10⁶ Ω/sq. In order to achieve these limits in a formulation containing one or more binders and conductive powders, the Rv of applied conductive particles must be at least four orders of ten below the required surface resistivity value of the formulation.

The Rv (Ω• cm) can be calculated from the measurement of the resistance (Ω), the area (cm²) and height of the pressed powder by a load of 5kN (cm). The Rv is measured by DC 4-probe method in the resistivity measurement system (MCP-PD51 from Dia Instruments Co., Ltd.).

In addition, the stability of conductivity for air and humidity was evaluated by the Rv of powder which was kept at 40 ⁰C and 90 % humidity for 10 days (Humidity test).

Table 1 shows the Rv values of TPTO, TTO and PTO coated TiO₂ particles.

Table 1

These results demonstrate that the conductivity of TPTO coated spherical TiO₂ particle according to Example 1 is better compared to that of TTO and PTO coated spherical TiO₂ particle.

When the powders of Example 1 , Comparative Example 1 and Comparative Example 2 are left at 40 ⁰C and 90 % humidity for 10 days, the conductivity of the TPTO coated spherical TiO₂ particle according to Example 1 is more stable compared to TTO and PTO coated on spherical TiO₂ particle.

Method for measuring "Surface resistivity of coating films: Rs (Ω/sq.)":

The electrically conductive powder of the present invention can form a coating layer with high conductivity, i.e., a surface resistivity (Rs) of 10⁶ Ω/sq. or less in the Rs measurement method as defined in JIS K 7194. The Rs can be measured as follows. The powders are blended with a lacquer (Seikaprene 100 from Dainichiseika Color & Chemicals Mfg. Co., Ltd.) as the concentration of PWC = 50 wt.%, and then are coated on a hiding power test chart by using a bar-coater (#20) and are dried at 105 ⁰C for 5min.. The dried thickness of coated films is 10 - 15 μm. The Rs of coated films is measured by using a resistivity meter (MCP-T610 from Dia Instruments Co., Ltd.). In addition, the stability of conductivity for air and humidity was evaluated by the Rs of coating film blended with powder which was kept at 40 ⁰C and 90 % humidity for 10 days (Humidity test).

Table 2 shows the Rs values of coating films blended with TPTO and PTO coated Tiθ₂ particles.

Table 2

These results demonstrate that the conductivity of coating film blended with TPTO coated spherical Tiθ₂ particle according to Example 1 is more stable compared to that of PTO coated spherical TiO₂ particles.

Method for measuring "Whitish hiding power of powder":

The electrically conductive powder of the present invention can form a coating layer with high whiteness, i.e., a lightness (L^* value) of 80 or more in the L^*a^*b^* color system as defined in JIS Z 8729.

The lightness can be measured as follows. The powders are blended with a lacquer (Seikaprene 100 from Dainichiseika Color & Chemicals Mfg. Co., Ltd.) as the concentration of PWC = 50 wt.%, and then are coated on a hiding power test sheet by using a bar-coater (#20) and are dried at 105 ⁰C for 5min. The dried thickness of coated films is 10— 15 μm. The L^* value of coated sheets is measured by using CHROMA meter (CR-400 from Minorta Co., Ltd.). Table 3 shows the L* values of TPTO coated TiO₂ particles and TPTO coated platelet-shaped AI₂O₃ and grain-shaped SiO₂ particles. Table 3

These results demonstrate that the whitish hiding power of TPTO coated spherical TiO₂ particles according to Example 1 is better compared to that of TPTO coated platelet-shaped AI₂O₃ and grain-shaped SiO₂ particles.

Claims

1. Electrically conductive particles based on inorganic substrates

characterized in that the substrates are coated on the surface with a tungsten and phosphorus doped tin oxide (hereafter, referred as

TPTO) layer.

2. Electrically conductive particles according to Claim 1 , characterized in that the substrate is selected from TiO₂, alkali titanate, ZnO, BaSO₄, AI₂O₃, SiO₂, ZrO₂, glass, natural mica, synthetic mica, talc, kaolin, sericite or mixtures thereof.

3. Electrically conductive particles according to Claim 1 , characterized in that the substrate is TiO₂.

4. Electrically conductive particles according to one or more of Claims 1 to 3, characterized in that the substrates have a mean particle size of 0.01 - 10 μm.

5. Electrically conductive particles according to one or more of Claims 1 to 4, characterized in that a TiO₂ particle is coated with a layer of tungsten-and phosphorus-doped tin oxide.

6. Electrically conductive particles according to one or more of Claims 1 to 5, characterized in that the amount of the TPTO layer is 20 - 60 wt. % based on the weight of the final particle.

7. A process for manufacturing of electrically conductive particles

according to one or more of Claims 1 to 6, characterized in that the inorganic base substrates are suspended into water, the aqueous tin salt solution, the aqueous tungsten salt solution and the phosphorus compound are added simultaneously to the suspension at a suitable pH, the pH of the substrate suspension being maintained by simultaneous addition of a base or of an acid, within the range which brings about the hydrolysis of the tin, phosphorus and tungsten salt, and the substrate coated in this way by TPTO, is separated off, washed, dried and calcined in an oxygen / nitrogen atmosphere or inert gas atmosphere.

8. A paint, ink, plastic, printing ink, rubber, varnish, lacquer, resin

composition, electrically conductive primer containing the electrically conductive particles according to one or more of Claims 1 to 6.

9. A coated film formed by applying a paint containing the electrically conductive particles according to one or more of Claims 1 to 6.

10. A particle mixture of two or more particles characterized in that one particle is the conductive particle according to one or more of Claims 1 to 6.