JP5224160B2 - White conductive powder and production method and use thereof - Google Patents

Description

  The present invention relates to a white powder having excellent conductivity without containing harmful components such as antimony. More specifically, the present invention relates to a white conductive powder that uses white fibrous inorganic powder as a base material, has excellent conductivity without containing harmful components such as antimony, and does not cause environmental pollution.

  Conductive powders are currently widely used in applications such as antistatic, charge control, antistatic, and dustproof. Conventionally, conductive powder doped with antimony or the like has been used in order to increase conductivity, but antimony is a toxic substance, and antimony-free conductive materials have recently been demanded from the viewpoint of preventing environmental pollution. Yes. Furthermore, conventional conductive powders are difficult to disperse in water and are used dispersed in organic solvents. However, in order to reduce environmental impact, conductive powders that can be dispersed in water and have good adhesion to plastics. Is required.

  Specifically, conventionally, as the white conductive powder, for example, white conductive powder in which a tin oxide film doped with antimony oxide is formed on the surface of zinc oxide doped with aluminum oxide, titanium dioxide powder or the like (patent) Literature 1, Patent Literature 2, Patent Literature 3). Moreover, the white conductive fiber which formed the conductive film which consists of tin oxide containing an antimony component in the potassium titanate fiber is known (patent documents 4 and patent documents 5). Furthermore, white conductive titanium dioxide powder in which a conductive layer containing tin oxide and phosphorus is formed on the surface of titanium dioxide particles is known (Patent Document 6). Further, a surface-modified transparent conductive tin oxide powder that does not contain these dope components is known (Patent Document 7).

  However, although the white conductive powder having a tin oxide film doped with antimony oxide is stable in conductivity, antimony-free conductive powder is required because antimony is a toxic component. On the other hand, titanium oxide having a tin oxide film doped with phosphorus has unstable conductivity and has a problem of uneven distribution of phosphorus. In addition, transparent conductive tin oxide powder made of surface-modified non-doped tin oxide has problems such as carbon residue, and is not a white powder, so it is suitable for applications that require a white environment in terms of appearance and functionality. There is also the problem of not. Furthermore, those using granular powder as a support for tin oxide have problems such as requiring a relatively large amount of addition to the resin in order to ensure contact between the particles.

In addition, a method for forming a fluorine-containing tin oxide film having a low resistance by forming a fluorine-containing tin oxide film on the substrate surface by a gas phase reaction and heat-treating the film in an inert gas with oxygen introduced is known. However, Patent Document 8 is not suitable as a method for treating a powder raw material, because a coating of a powder raw material is not sufficiently formed on the powder surface.
JP 59-145262 A JP 58-209002 A Japanese Patent Laid-Open No. 62-180903 JP-A 61-136532 Japanese Patent Application Laid-Open No. 07-053217 International Publication WO2005 / 012449 JP 2006-59806 A JP 2003-81633 A

  The present invention solves the above-mentioned problems in the conventional white conductive powder, is based on white fibrous inorganic powder, has excellent conductivity without containing harmful components such as antimony, environmental pollution, etc. The present invention provides a white conductive powder that can obtain good conductivity with a small amount of addition, can be dispersed in water, and has a low environmental burden.

This invention provides the white electrically conductive powder which solved the said subject with the following structures.
[1] Disperse the white fibrous inorganic powder of the base material in water, add a tin source to this, hydrolyze it at pH 4 or lower to precipitate a tin compound on the surface of the powder, wash, dry with adding a fluorine source after the presence of an inert gas atmosphere and water vapor, a white conductive powder having an oxygen fluorine-containing tin oxide layer formed by heat treatment at below to 800 ° C. 400 ° C. or higher to eliminate, oxide tin layer 0.1 to 0.5% by mass of fluorine, and 30 to 60% by mass of the tin oxide layer in the powder has a powder volume resistance of 10 kΩ · cm or less, L = 77 to 80 in the Lab color system, a White conductive powder containing no antimony, phosphorus and indium, wherein == 2.5 to -1.2 and b = -3.0 to -2.0.

The present invention further provides the following production methods and uses.
[2] Disperse the white fibrous inorganic powder of the base material in water, add a tin source to this, hydrolyze it at a pH of 4 or less to precipitate a tin compound on the powder surface, wash it, add a fluorine source and dry it Then, a fluorine-containing tin oxide layer is formed on the powder surface by excluding oxygen in the presence of an inert gas atmosphere and water vapor, and heat treatment at 400 ° C. to 800 ° C., and 0% in the tin oxide layer. 0.1 to 0.5% by mass of fluorine, 30 to 60% by mass of the tin oxide layer in the powder has a powder volume resistance of 10 kΩ · cm or less, Lab color system L = 77 to 80, a = − A method for producing a white conductive powder not containing antimony, phosphorus and indium, in which 2.5 to -1.2 and b = -3.0 to -2.0.
[3] A dispersion obtained by dispersing the white conductive powder described in [1] above in water.
[4] A paint containing the white conductive powder according to [1].
[5] A conductive coating film formed from a paint containing the white conductive powder described in [1] above.

  The conductive powder of the present invention is a white fibrous conductive powder having white conductive inorganic powder as a base material and high conductivity. Therefore, it is suitable as a conductive material in applications requiring a white environment in terms of appearance and function, for example, interior materials or carpets for semiconductor manufacturing clean rooms, computer rooms, hospitals, and the like.

  Moreover, since the white conductive powder of the present invention does not contain any of antimony, phosphorus, and indium in the tin oxide layer, there is no concern of causing environmental pollution. Further, since it does not contain antimony, phosphorus, and indium, it is low cost. In the present invention, “antimony, phosphorus, and indium are not included” means that no source of antimony, phosphorus, and indium is used in the raw materials and processes, and therefore these elements are detected by a standard measuring device having a detection limit of 500 ppm. It is said that it is not detected.

White conductive powder of the present invention has a high conductivity without containing dope components such as the antimony has a stable and high conductivity because fluorine is contained in the tin oxide layer, a secure conductive As a material, it can be widely used for various devices. Specifically, for example, as conductive materials in electrostatic coating primers, resins and tiles having antistatic effects, conductive paints, electrostatic recording materials, copier-related charging rollers, photosensitive drums, toners, electrostatic brushes, etc. Is preferred.

  Since the white conductive powder of the present invention can be dispersed in water, it can be used as a conductive material such as an aqueous paint.

Hereinafter, the present invention will be specifically described based on embodiments. Unless otherwise indicated, “%” means “% by mass” unless otherwise specified.
[White conductive powder]
Conductive powder according to the present invention, the white fibrous inorganic powder of the base material is dispersed in water, to which tin source was added, to precipitate a tin compound in powder surface was hydrolyzed under pH4 or less, after washing, fluorine A white conductive powder having a fluorine-containing tin oxide layer formed by drying after adding a source and excluding oxygen in the presence of an inert gas atmosphere and water vapor and heat-treating at 400 ° C. to 800 ° C., The tin oxide layer contains 0.1 to 0.5% by mass of fluorine, and 30 to 60% by mass of the tin oxide layer in the powder has a powder volume resistance of 10 kΩ · cm or less, and the Lab color system L = 77 to 80, a = −2.5 to −1.2, b = −3.0 to −2.0, white conductive powder containing no antimony, phosphorus and indium.

  In the white conductive powder of the present invention, potassium titanate fibers can be used as the white fibrous inorganic powder of the base material. The potassium titanate fiber preferably has a fiber diameter of 0.1 μm to 1.0 μm and a fiber length of 5 μm to 25 μm.

  The tin oxide layer formed on the substrate surface does not contain antimony, phosphorus, and indium. The conventional conductive powder has improved conductivity by doping with antimony, phosphorus, etc., but the white conductive powder of the present invention forms a tin compound by wet treatment on the surface of the white fibrous inorganic powder substrate. Since the high conductivity is achieved by forming a tin oxide layer by heat treatment in an inert gas atmosphere in which the atmosphere is adjusted, it is not necessary to contain each of the above elements.

Moreover, in the white conductive powder having a fluorine-containing tin oxide layer of the present invention, a tin compound is formed on the surface of the white fibrous inorganic powder by wet treatment, and fluorine is introduced into this, so that this tin oxide layer has conductivity. High and stable.

In the white conductive powder of the present invention, the proportion of the fluorine-containing tin oxide layer in the powder is suitably 30 to 60%. If this amount is less than 30%, it is difficult to obtain the desired conductivity. If it exceeds 60%, the resistance becomes low, but the problem of aggregation occurs, which is not preferable.

  In the tin oxide layer containing fluorine, the amount of fluorine in the tin oxide layer is preferably 0.1 to 5.0%. When the fluorine content is less than 0.1%, the powder volume resistance does not decrease. Even if the fluorine content is more than 5.0%, the powder volume resistance is not much different from the case of 5.0%, and the ratio of decreasing the resistance value is small.

The conductivity of the white conductive powder of the present invention is such that when the amount of the tin oxide layer in the powder is 30 to 60% and the tin oxide layer contains fluorine, the powder volume resistance is 10 kΩ · cm or less, preferably 5 kΩ · cm. It can have the following conductivity. If the powder volume resistance is greater than 100 kΩ · cm, the surface resistance when this powder is mixed into the resin is approximately 10 ¹⁰ Ω / □ or more, so that the antistatic effect is insufficient at a powder content of 60%. The conductivity of the white conductive powder of the present invention does not have such a problem because the powder volume resistance is small.

The white conductive powder of the present invention has L = 77 to 80, a = −2.5 to −1.2, and b = −3.0 to −2.0 in the Lab color system. If the value of Lab is out of the above range, the chromaticity related to whiteness is impaired in the items of brightness, green to red, and blue to yellow. The white conductive powder of the present invention has each value of Lab within the above range, and has a good white color without turbidity.

〔Production method〕
About white conductive powder of the present invention, a tin compound formed by a wet treatment on the surface of the white fibrous inorganic powder, under an inert gas atmosphere with atmospheric adjustment, to form the tin oxide layer by heat treatment.

Specifically, the white fibrous inorganic powder of the base material is dispersed in water, a tin source is added to this, and the tin compound is precipitated on the surface of the base powder by hydrolysis at a low pH, for example, pH 4 or less, and then dried. Thereafter, oxygen is removed in the presence of an inert gas atmosphere and water vapor, and heat treatment is performed to form a conductive tin oxide layer on the surface of the substrate.

In order to contain fluorine in the tin oxide layer, a tin compound is deposited on the surface of the white fibrous inorganic powder by wet treatment, fluorine is introduced into this, and heat treatment is performed in an inert gas atmosphere in which the atmosphere is adjusted to contain fluorine. A tin oxide layer can be formed.

  Preferably, the white fibrous inorganic powder of the base material is dispersed in water, a tin source is added thereto, and the tin compound is precipitated on the surface of the base powder by hydrolysis at a low pH, for example, pH 4 or less. Or, after that, fluorine is introduced to form a fluorine-containing tin compound on the powder surface, and after drying, oxygen is removed in the presence of an inert gas atmosphere and water vapor, and heat treatment is performed to form a fluorine-containing tin oxide layer on the substrate surface. Form.

  As the white fibrous inorganic powder of the base material, for example, fibrous potassium titanate is used. The fibrous potassium titanate preferably has a fiber diameter of 0.1 μm to 1.0 μm and a fiber length of 5 μm to 25 μm. The base powder is dispersed in water and heated to 40 to 100 ° C., a tin source is added thereto, and this is hydrolyzed to precipitate a tin compound on the surface of the base powder. As the tin source, tin chloride, tin nitrate, tin acetate, and other soluble tin salts can be used.

  After depositing a tin compound on the surface of the substrate powder, the residual salt is removed by decantation and dried. When tin chloride is used as the tin source, an aqueous hydrochloric acid solution is added to precipitate a tin compound at a pH of 4 or lower, and the subsequent washing should be stopped to the extent that hydrochloric acid remains slightly.

  To introduce fluorine, a fluorine source, for example stannous fluoride, is added after decantation. At this time, the hydroxyl group and fluorine are substituted and fluorine is taken in. By containing fluorine, the powder is slightly yellowish. Almost all of this fluorine is taken into the tin compound, so there is no free fluorine and the furnace is less likely to be damaged during heat treatment.

  Conventionally, it is known that a fluorine-doped tin oxide film is formed on the surface of a silica substrate by a gas phase reaction such as a CVD method (Patent Document 8). However, when a powder raw material is used, the gas phase treatment is sufficient for the entire powder. A tin oxide layer cannot be formed.

The white conductive powder of the present invention is dried after the wet treatment and heat-treated to form a fluorine- containing tin oxide layer. The heat treatment temperature is preferably 400 ° C. or higher and 800 ° C. or lower. When the heat treatment temperature is lower than 400 ° C., sufficient conductivity cannot be obtained, and when it is higher than 800 ° C., powder sintering starts, and aggregates may be present when a coating film is formed.

  This heat treatment is preferably performed in an inert gas atmosphere whose atmosphere is adjusted. Specifically, it is preferably performed in the presence of an inert gas atmosphere such as nitrogen gas or argon gas and water vapor, excluding oxygen. The water vapor may be alcohol vapor. The method for introducing water vapor or alcohol vapor is not limited. Water vapor or alcohol vapor may be introduced into the inert gas atmosphere of the heat treatment furnace, the raw material powder after the wet treatment may be appropriately dried to be moistened, or the raw material powder may be sprayed with water or alcohol. good. Alternatively, an inert gas may be bubbled through water or alcohol and introduced into the heat treatment furnace.

  The vapor pressure of water or alcohol is preferably 30% or higher. In order to perform the heat treatment while maintaining the vapor pressure, it is preferable to use a closed heat treatment furnace. In addition, since a water | moisture content lose | disappears at the time of the heating of a tin compound, you may make it acquire the same effect using this water | moisture content.

  Also, heating is performed by removing oxygen from the atmosphere. Conventionally, a method of performing a heat treatment under an inert gas containing oxygen is known (Patent Document 8). However, if oxygen is contained, a low-resistance powder cannot be produced stably and becomes non-uniform.

A low-resistance white conductive powder can be obtained by heat-treating the wet-processed raw material powder in an inert gas atmosphere containing water vapor or alcohol vapor while eliminating oxidation. Incidentally, those having a fluorine-containing tin oxide layer is relatively low powder even resistance When the inert gas does not contain water vapor or alcohol vapor is obtained, to form a fluorine-containing tin oxide layer, water vapor or alcohol vapor The resistance of the powder can be further reduced by heat treatment in the presence.

Examples of the present invention are shown below together with comparative examples. In Examples and Comparative Examples, the powder volume resistance was measured with a digital multimeter (Yokogawa Electric product: Model 7561-02) after putting the sample powder into a pressure vessel and compressing the powder at 100 kgf / cm ² . The L value, a value, and b value of the powder were measured using an apparatus (SM-7-IS-2B) manufactured by Suga Test Instruments. The surface resistance of the coating film was measured using a surface resistance meter (Hiresta: Mitsubishi Yuka product: model HT-210, supply voltage 100 V) for a thin film having a thickness of about 100 μm containing white conductive powder. In addition, the properties of the coating film (presence or absence of irregularities due to aggregates) were confirmed visually, and the hiding power of the coating film was observed according to the standard (JIS K5600).

[ Reference Example 1]
50 g of potassium titanate fiber (fiber diameter 0.3 to 0.6 μm, length 10 to 20 μm) was dispersed in 300 cc of water and heated to 90 ° C. A predetermined amount of tin chloride was added to this dispersion so that the tin oxide content in the powder would be the value shown in Table 1, and an aqueous hydrochloric acid solution was added over 20 to 30 minutes to adjust the pH to 3 to 4. The wet-processed powder was taken out, washed and dried. The entire amount of tin chloride added by the wet treatment was hydrolyzed, and a tin compound (tin hydroxide showing SnO2 pattern in X-ray diffraction) was precipitated on the powder surface. 20 g of this dry powder was put into a quartz tube furnace, and nitrogen gas saturated with water vapor through water was passed through the furnace at a rate of 0.3 L / min for 30 minutes to exclude oxygen and heat treatment was performed at the temperature shown in Table 1. . The treated powder was taken out and pressed at 100 kgf / cm @ 2 to measure the powder volume resistance. Moreover, the value of the Lab color system of the powder was measured. The results are shown in Table 1. Furthermore, it was confirmed by X-ray diffraction of this powder that a tin oxide layer was formed on the powder surface. Also, none of antimony, phosphorus, or indium was detected.

[Comparative Example 1]
A white conductive powder was produced in the same manner as in Example 1 except that the tin oxide content, the heat treatment temperature, and the heating atmosphere were changed to the conditions shown in Table 2. The powder volume resistance and Lab color system values of this powder were measured. The results are shown in Table 1.

[ Reference Example 2 / Comparative Example 2]
4.2 g of the white conductive fine powder produced in Reference Example 1 and Comparative Example 1 was added to 100 g of a commercially available acrylic paint (resin content: 10%) and stirred for 30 minutes with a paint shaker containing beads. This paint was applied to a PET film with an applicator to a film thickness of about 100 μm, and the surface resistance after drying was measured with a surface resistance meter. Moreover, the property and hiding power of the coating film were confirmed visually. The results are shown in Table 1.

  As shown in Table 1, all of the samples A1 to A3 have a high volume conductivity with a powder volume resistance of 100 kΩ · cm or less. On the other hand, all of the samples B1, B2, B3, and B5 have high powder volume resistance at each stage and low conductivity. Sample B4 has an aggregate in the coating film. Moreover, all the coating films of Samples B1 to B5 have poor hiding power.

[ Example 1 ]
50 g of potassium titanate fiber was dispersed in 300 cc of water and heated to 90 ° C. A predetermined amount of tin chloride was added to this dispersion so that the tin oxide content in the powder would be the value shown in Table 2, and an aqueous hydrochloric acid solution was added over 20 to 30 minutes to adjust to pH 3 to 4. The wet-processed powder was taken out and washed. The entire amount of tin chloride added by the wet treatment was hydrolyzed, and a tin compound (tin hydroxide showing SnO ₂ pattern in X-ray diffraction) was precipitated on the powder surface. A predetermined amount of stannous fluoride was added to the fluorine content shown in Table 2, and the mixture was stirred and dried. 20 g of this dry powder was placed in a quartz tube furnace, and nitrogen gas saturated with water vapor through water was passed through the furnace at a rate of 0.3 L / min for 30 minutes to exclude oxygen and heat treatment was performed at the temperature shown in Table 2. The treated powder was taken out and pressed at 100 kgf / cm ² to measure the powder volume resistance. Moreover, the value of the Lab color system of the powder was measured. The results are shown in Table 2. Furthermore, it was confirmed by X-ray diffraction of this powder that a tin oxide layer was formed on the powder surface. Also, none of antimony, phosphorus, or indium was detected.

[Comparative Example 3]
A white conductive powder was produced in the same manner as in Example 3 except that the tin oxide content, the fluorine content in tin oxide, the heat treatment temperature, and the heating atmosphere were changed to the conditions shown in Table 2. The powder volume resistance and Lab color system values of this powder were measured. The results are shown in Table 2.

[ Example 2 and Comparative Example 4]
4.2 g of the white conductive fine powder produced in Example 1 and Comparative Example 3 was added to 100 g of a commercially available acrylic paint (resin content: 10%), and stirred for 30 minutes with a paint shaker containing beads. This paint was applied to a PET film with an applicator to a film thickness of about 100 μm, and the surface resistance after drying was measured with a surface resistance meter. Moreover, the property and hiding power of the coating film were confirmed visually. The results are shown in Table 2.

  As shown in Table 2, all of Samples C1 to C5 have a powder volume resistance of 10 kΩ · cm or less and high conductivity. On the other hand, samples D1 to D3 and D5 are powders having high powder volume resistance at each stage and low conductivity. Moreover, an aggregate exists in the sample D5 coating film. Furthermore, all of the coating films of Samples D3 to D5 have poor hiding power.

Claims (5)

After dispersing the white fibrous inorganic powder of the base material in water, adding a tin source to this, hydrolyzing at pH 4 or lower to precipitate a tin compound on the powder surface, washing, adding a fluorine source and drying, A white conductive powder having a fluorine-containing tin oxide layer formed by heat treatment at 400 ° C. or higher and 800 ° C. or lower with oxygen excluded in the presence of an inert gas atmosphere and water vapor; 1 to 0.5% by mass of fluorine, 30 to 60% by mass of the tin oxide layer in the powder has a powder volume resistance of 10 kΩ · cm or less, Lab color system L = 77 to 80, a = −2 White conductive powder containing no antimony, phosphorus, and indium, characterized in that 0.5 to -1.2 and b = -3.0 to -2.0. After dispersing the white fibrous inorganic powder of the base material in water, adding a tin source to this, hydrolyzing at pH 4 or lower to precipitate a tin compound on the powder surface, washing, adding a fluorine source and drying, A fluorine-containing tin oxide layer is formed on the powder surface by excluding oxygen in the presence of an inert gas atmosphere and water vapor and heat treatment at 400 to 800 ° C., and 0.1 to 0.1 in the tin oxide layer. 0.5% by mass of fluorine, 30 to 60% by mass of the tin oxide layer in the powder has a powder volume resistance of 10 kΩ · cm or less, Lab color system L = 77 to 80, a = −2.5 A method for producing a white conductive powder not containing antimony, phosphorus, and indium, which is ˜−1.2 and b = −3.0 to −2.0. A dispersion obtained by dispersing the white conductive powder according to claim 1 in water. A paint containing the white conductive powder according to claim 1. The electroconductive coating film formed with the coating material containing the white electrically conductive powder of Claim 1.