JP5514435B2 - Method for producing white conductive powder - Google Patents

Description

  The present invention relates to a white conductive inorganic powder having excellent conductivity and causing no environmental pollution, and a method for producing the same. More specifically, the present invention is a white conductive inorganic powder having a conductive tin oxide layer on the surface of a carrier such as titanium oxide, has no risk of causing environmental pollution, has excellent conductivity, and is manufactured. The present invention relates to an easily white conductive inorganic powder and a method for producing the same.

  White conductive powder is currently widely used for antistatic, charge control, antistatic control, dustproof and other applications. Conventionally, conductive powder doped with antimony or the like has been used in order to enhance conductivity, but recently, an antimony-free conductive material is required from the viewpoint of preventing environmental pollution.

  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). Moreover, the white conductive fiber which formed the conductive film which consists of a tin oxide containing an antimony component in the potassium titanate fiber is known (patent documents 3 and patent documents 4).

Furthermore, a white conductive titanium dioxide powder is known in which a conductive layer containing tin oxide and phosphorus is formed on the surface of titanium dioxide particles (Patent Document 5). However, these powders do not have transparency. As the transparent conductive powder, antimony-doped tin oxide is known (Patent Document 6). However, although the conductive powder doped with antimony oxide has stable conductivity, an antimony-free conductive powder is required from the viewpoint of preventing environmental pollution. As the antimony-free conductive powder, one doped with phosphorus is known, but this has unstable conductivity and has a problem of uneven distribution of phosphorus. Moreover, although the powder which reduced hydrogenation of stannic oxide is also known (patent document 7), in hydrogen reduction, it reduces to metal tin and control of reaction is difficult. There are transparent conductive tin oxide powders made of surface-modified non-doped tin oxide, but there are problems such as carbon remaining. Moreover, since it is not a white powder, there also exists a problem that it is not suitable for the use for which a white environment is requested | required from the point of an external appearance or functionality.
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 2005-108733-5 A

The present invention is a solution of the above-mentioned problems in conventional conductive powder, and is a white conductive inorganic powder having a conductive tin oxide layer on the surface of a carrier such as titanium oxide, and there is no risk of causing environmental pollution or the like. It has excellent conductivity, provides antimony easy manufacturing, phosphorus, and a method for manufacturing a white conductive inorganic powder that does not contain indium.

The present invention relates to a method for producing a white conductive inorganic powder that solves the above-described problems with the following configuration.
[1] A white inorganic powder having a surface layer of stannic oxide and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a solid state stannic oxide layer containing divalent ions. Contact with stannous ions, heat drying, reducing the above-mentioned stannic oxide with stannous ions to form a conductive tin oxide layer, white conductivity free from antimony, phosphorus and indium Manufacturing method of inorganic powder.
[2] A white inorganic powder having a surface layer of stannic oxide and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a solid state stannic oxide layer containing divalent ions. The method for producing a white conductive inorganic powder according to the above [1], wherein the tin oxide is brought into contact and heated in a non-oxidizing stannous ion-soluble solvent atmosphere to reduce the stannic oxide .
[3] A stannous ion solution (excluding a stannous fluoride solution) is added to a white inorganic powder having a surface layer of stannic oxide to obtain a paste , which is heat-dried. The method for producing a white conductive inorganic powder according to the above [1], wherein the conductive tin oxide layer is formed by reduction with ions .
[4] A white inorganic powder having a surface layer of stannic oxide and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a slurry, and the slurry or the slurry dried The method for producing a white conductive inorganic powder according to the above [1], wherein the conductive tin oxide layer is formed by reducing the stannic oxide by heating in an oxidizing stannous ion-soluble solvent atmosphere.

  The white conductive inorganic powder of the present invention has excellent conductivity, there is no risk of causing environmental pollution, and the burden on the environment is small. Moreover, since the white electroconductive inorganic powder of this invention does not dope special elements, such as antimony, manufacture is easy and can be manufactured cheaply. In addition, since the conductivity can be controlled by changing the ratio of stannous ions to stannic oxide, a powder having the desired conductivity can be easily produced.

  Hereinafter, the present invention will be specifically described based on embodiments. Unless otherwise indicated, “%” means “% by mass” unless otherwise specified.

[Conductive inorganic powder]
The white conductive inorganic powder of the present invention is a white conductive inorganic powder characterized by having a conductive tin oxide layer on the surface of the white inorganic powder and having a powder volume resistance of 10 ⁴ Ω · cm or less.

  The white conductive inorganic powder of the present invention preferably uses a white inorganic powder having a stannic oxide layer on the powder surface, and the conductive tin oxide layer is reduced by reducing the stannic oxide layer with stannous ions. Is a white conductive inorganic powder. As the white inorganic powder supporting the conductive tin oxide layer, for example, powders such as titanium oxide, potassium titanate, and white mica can be used.

In order for stannic oxide to have conductivity, oxygen defects must be present, and the white conductive inorganic powder of the present invention preferably has a stannic oxide layer (SnO ₂ ) on the surface of the powder as the first. By reducing with tin ions (Sn ²⁺ ), oxygen defects are caused to develop conductivity.

  Conventionally, a method for producing a tin oxide powder having conductivity by reducing stannic with hydrogen or the like is known. On the other hand, the white conductive inorganic powder of the present invention reduces the stannic oxide by allowing divalent stannous ions to act on the solid stannic oxide layer that is not ionized, thereby conducting conductive oxidation. A tin layer is formed. Such a method of directly reducing the solid state tin oxide layer with stannous ions is a completely new and innovative method.

Specifically, for example, the following method can be used to form the conductive tin oxide layer.
[A] A method of forming oxygen defects by reducing stannic oxide by adding a stannous ion-containing solution to a white inorganic powder having a stannic oxide surface layer to form a paste.
[B] A white inorganic powder having a stannic oxide surface layer and a stannous ion solution are made into a slurry, and the slurry or the dried slurry is heated in a non-oxidizing stannous ion soluble solvent atmosphere. A method of reducing stannic oxide to form oxygen defects.

The reduction reaction with stannous ions is possible even when stannous ions are not present as a starting material. As shown in the following reaction formula, for example, if hydrochloric acid is present even in a trace amount, it reacts with stannic oxide to produce stannous ions, and thereby the reduction reaction proceeds. The production reaction of the present invention includes such a reaction.
SnO ₂ + 4HCl → SnCl ₂ + 2H ₂ O + Cl ₂

Examples of stannous salts that supply stannous ions include stannous chloride, stannous sulfate, stannous oxide, stannous nitrate, tin pyrophosphate, tin sulfamate, and stannate. Inorganic soluble salts can be used, and organic soluble salts such as stannous alkanol sulfonate, stannous sulfosuccinate, stannous aliphatic carboxylate, and the like can be used.

The white conductive inorganic powder of the present invention has a powder volume resistance of 500 Ω · cm or less. If the powder volume resistance is greater than 10 ⁴ Ω · cm, the amount necessary to obtain a surface resistance of 10 ⁹ Ω / □ that exhibits an antistatic effect increases (the amount mixed into the resin), which degrades the physical properties of the resin. End up. Since the white conductive inorganic tin powder of the present invention has low powder volume resistance and high conductivity, there is no such problem.

The amount (upper limit) of the stannous compound used for the reduction is suitably 10 mol% or less, preferably 5 mol% or less of stannous with respect to stannic oxide, and the lower limit is 0.1 mol% or more of stannous. Is appropriate. Even if the amount of stannous is more than 10 mol%, there is no great difference in conductivity, but rather the burden of cleaning treatment after the reduction reaction is increased. On the other hand, if the amount of stannous is less than 0.1 mol%, the powder volume resistance tends to be greater than 10 ⁴ Ω · cm and the conductivity tends to be low.

  In the white conductive inorganic powder of the present invention, the color tone of the powder has an L value of 70 or more in the Lab color system, specifically, as shown in Examples 1 to 4, an L value of 70 or more, A white powder having an L value of 80 or more is preferable. Note that the more oxygen defects in the tin oxide layer, the higher the conductivity and the lower the L value. An L value lower than 70 is not preferable because the color becomes dark and cannot be used in a white environment.

  Since the white conductive inorganic powder of the present invention does not contain antimony, phosphorus, or indium, 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.

  Since the white conductive inorganic powder of the present invention has high conductivity without containing a doping component such as antimony, it is used in applications where a white environment is required in terms of appearance and function, for example, interiors of semiconductor clean rooms, computer rooms, hospitals, etc. It is suitable as a conductive material for materials or carpets.

  Since the white conductive inorganic powder of the present invention can be dispersed in water, it can be used as a conductive material such as a dispersion or water-based paint, and a conductive film composition can be formed with this paint.

〔Production method〕
The white conductive inorganic powder of the present invention can be produced by bringing stannous ions into contact with the surface layer of stannous oxide in a soluble solvent of stannous ions or in a soluble solvent atmosphere and reducing it.

  The soluble solvent for stannous ions is water, alcohol, ethyl acetate, glacial acetic acid, etc., but water or alcohol is preferable because it is easy to handle and low in cost. In order to generate stannous ions in the soluble solvent of stannous ions, the stannous salt may be dissolved in the soluble solvent, or the stannous salt may be dissolved in the soluble solvent to which an acid or an alkali is added. .

  In the reduction reaction, a white inorganic powder having a stannic oxide surface layer is dispersed in a soluble solvent, and a stannous ion salt or a stannous ion solution is added thereto, or stannic oxide is added to the stannous ion solution. You may disperse | distribute the inorganic powder which has a surface layer. The reduction reaction proceeds even with a small amount of stannous ions, and the reduction reaction proceeds even at room temperature. Heating may be performed to promote the reduction reaction.

  The reaction under a soluble solvent atmosphere is performed by excluding oxygen in the presence of an inert gas atmosphere and a soluble solvent vapor of stannous ions, heat treatment, and reacting the stannous oxide surface layer with stannous oxide ions. Just do it. In addition, an inorganic powder having a stannic oxide surface layer and a stannous ion solution may be slurried and used in a slurry state, or a dried product thereof may be used.

  The heat treatment should be performed in an inert gas atmosphere with an adjusted atmosphere. Specifically, oxygen is removed in the presence of an inert gas atmosphere such as nitrogen gas or argon gas and a soluble solvent vapor of stannous ions. Preferably.

  The method for introducing the soluble solvent vapor of stannous ions is not limited. Soluble solvent vapor may be introduced into the inert gas atmosphere of the heat treatment furnace, or the slurry may be left in a slurry state or may be moistened with moderate drying. Alternatively, an inert gas may be bubbled through the soluble solvent.

  The vapor pressure of the soluble solvent is preferably a saturated vapor pressure of 30% or more. In order to perform the heat treatment while maintaining the vapor pressure, it is preferable to use a closed heat treatment furnace. Also, heating is performed by removing oxygen from the atmosphere. Conventionally, a heat treatment method using an inert gas containing oxygen is known. However, when oxygen is contained, a low-resistance powder cannot be stably obtained, and the reaction is non-uniform. By these treatments, the conductive tin oxide layer can be formed by reducing the stannous oxide layer on the surface of the white inorganic powder with stannous ions, and a low resistance white conductive inorganic powder can be obtained. it can.

  Cleaning after the reaction is not particularly required. However, when the impurity element remains problematic, cleaning may be performed to remove the impurity element.

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 (manufactured by Yokogawa Electric Corporation: Model 7561-02) after putting the sample powder in a pressure vessel and compressing it at 100 kgf / cm ² . The L value was measured with a device manufactured by Suga Test Instruments Co., Ltd. (SM-7-IS-2B).

[Example 1]
150 g of titanium oxide powder (rutile type) was dispersed in 1 L of water and heated to 90 ° C. 100 g (0.19 mol) of 50% stannic chloride solution and 1N sodium hydroxide solution were added dropwise over 30 minutes while maintaining pH 3-4 while stirring. This was collected by filtration, dried and then heat treated at 600 ° C. in the air for 1 hour to obtain a titanium oxide powder having a stannic oxide layer on the powder surface.
This was added to a stannous ion solution in which 4.3 g (0.019 mol% = 10 mol%) of stannous chloride dihydrate was dissolved in 200 ml of ion-exchanged water and kneaded in a mortar to form a paste. This was dried at 90 ° C. to obtain a conductive inorganic powder. A paste was prepared in the same manner as above except that stannous chloride was changed to 2.1 g (5 mol%) and 1.1 g (2.5 mol%), and dried to obtain a conductive inorganic powder. These powder volume resistances were measured. The L value of the powder was measured. The results are shown in Table 1.

[Example 2]
150 g of titanium oxide powder (rutile type) was dispersed in 1 L of water and heated to 90 ° C. 100 g (0.19 mol) of 50% stannic chloride solution and 1N sodium hydroxide solution were added dropwise over 30 minutes while maintaining pH 3-4 with stirring. This was collected by filtration, dried and then heat treated at 600 ° C. in the air for 1 hour to obtain a titanium oxide powder having a stannic oxide layer on the powder surface.
This was added to a stannous ion solution in which 4.1 g (0.019 mol% = 10 mol%) of stannous sulfate was dissolved in 200 ml of ion-exchanged water and kneaded in a mortar to form a paste. This was dried at 90 ° C. to obtain a conductive inorganic powder. A paste was prepared in the same manner as above except that stannous sulfate was changed to 2.0 g (5 mol%) and 1.0 g (2.5 mol%), respectively, and dried to obtain a conductive inorganic powder. These powder volume resistances were measured. The L value of the powder was measured. The results are shown in Table 2.

Claims (4)

A white inorganic powder having a stannic oxide surface layer and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a divalent stannous ion in a solid stannic oxide layer. A white conductive inorganic powder containing no antimony, phosphorus, and indium, wherein the conductive tin oxide layer is formed by reducing the stannic oxide with stannous ions . Production method. A white inorganic powder having a stannic oxide surface layer and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a divalent stannous ion in a solid stannic oxide layer. The method for producing a white conductive inorganic powder according to claim 1, wherein the stannic oxide is reduced by heating in a non-oxidizing stannous ion-soluble solvent atmosphere . Add stannous ion solution (excluding stannous fluoride solution) to white inorganic powder with stannic oxide surface layer, paste to heat and dry, reduce the above stannic oxide with stannous ions The method for producing a white conductive inorganic powder according to claim 1, wherein a conductive tin oxide layer is formed . A white inorganic powder having a surface layer of stannic oxide and a stannous ion solution (excluding a stannous fluoride solution) are mixed to form a slurry, and the slurry or the dried slurry is made non-oxidizing. The method for producing a white conductive inorganic powder according to claim 1, wherein the conductive tin oxide layer is formed by heating in a stannous ion-soluble solvent atmosphere to reduce the stannic oxide.