JP5181322B2 - Method for producing conductive tin oxide powder - Google Patents

Description

The present invention relates to a method for producing a tin oxide powder excellent in electrical conductivity, and more specifically, has an electrical conductivity equivalent to that of ATO powder without containing antimony, has a low environmental burden, and has a high transparency. The present invention relates to a method for producing conductive tin oxide powder.

  Conventionally, as the conductive tin oxide powder, antimony-doped tin oxide (ATO), phosphorus-doped tin oxide (PTO), niobium-doped tin oxide (NbTO), tantalum-doped tin oxide (TaTO), and fluorine-doped tin oxide (FTO) are known. ing. As other conductive metal oxide powders, tin-doped indium oxide (ITO) and aluminum-doped zinc oxide (AZO) are known. As a method for introducing a dope component, a metal oxide precursor and a dopant are mixed in an aqueous solution adjusted in pH, and the generated precipitate is recovered and heated to introduce the dope component into the metal oxide. A method, a method of introducing a dope component by kneading two or more different metal oxides containing a dope component, and heating the same are known.

  In recent years, conductive powders such as ATO, ITO, and AZO have been used for electrodes, transparent conductive films, touch panels, and the like of flat panel displays such as liquid crystal displays and plasma displays. However, with the growing interest in environmental development and the development of the electronics field, there is a need for new materials with a high added value and low environmental impact. In addition, in terms of the environment, there is a concern that antimony of ATO and indium of ITO may affect the environment and the human body, and a safe material that does not contain these harmful components is required. Furthermore, ATO has a property of absorbing light because antimony absorbs light, while ITO is poor in transparency at the time of film formation, while ITO is concerned about an extreme increase in price of indium as a main raw material and exhaustion of the raw material.

Moreover, about the said tin oxide type powder, it replaced with antimony etc. and the tin oxide (FTO) which doped the fluorine is also known. Although conductivity is improved by doping fluorine in tin oxide, there are problems such as complicated processes and difficulty in obtaining stable conductivity. Furthermore, conductive zinc oxide powders such as AZO are known instead of tin oxide-based powders, but AZO and the like have a problem with the conductive stability (Patent Documents 1 to 6).
Japanese Patent No. 2605855 Japanese Patent No. 2724248 JP 2004-359521 A Japanese Patent No. 2992572 JP 2003-081633 A Japanese Patent Publication No. 07-105166

The present invention solves the above-mentioned conventional problems with respect to conductive tin oxide powder, has the same conductivity as ATO powder without containing antimony, has a low environmental burden, and is highly transparent. A method for producing conductive tin oxide powder is provided.

This invention relates to the manufacturing method of the electroconductive tin oxide powder which solved the said problem by having the following structures.
[1] A tin source powder comprising a tin dioxide powder, a second tin hydroxide powder or a mixture thereof is dispersed in water, a fluorine source is added to the aqueous dispersion, and the tin source powder and the fluorine source are dispersed in the aqueous solution. A conductive tin oxide powder containing fluorine and nitrogen is produced by mixing and contacting to uniformly deposit fluorine on the surface of the tin source powder, followed by dehydration and heat treatment in a nitrogen atmosphere. A method for producing conductive tin oxide powder.
[2] Powder volume under 100 kgf / cm ² pressure, containing 0.01 to 0.2 moles of fluorine and 0.001 to 0.01 moles of nitrogen with respect to 1 mole of tin without containing antimony The method for producing a conductive tin oxide powder as described in [1] above, wherein a conductive tin oxide powder having a resistivity of 10 Ω · cm or less is produced.
[3] The conductive tin oxide powder according to [1] or [2] above, wherein a conductive tin oxide powder having a 90% particle diameter (D90) of 5 μm or less and a crystal lattice diameter of 5 to 20 nm is produced. Manufacturing method.

The conductive tin oxide powder produced by the method of the present invention (hereinafter referred to as the conductive tin oxide powder of the present invention) contains a predetermined amount of fluorine and nitrogen. Preferably, fluorine is introduced by a wet process, Since is introduced by heat treatment in a nitrogen atmosphere, fluorine and nitrogen are uniformly contained, and have high conductivity without containing antimony. Specifically, the conductive tin oxide powder of the present invention is, for example, a low resistance powder having a powder volume resistivity of 10 Ω · cm or less. Therefore, by using the conductive tin oxide powder of the present invention, in a thin film having a tin oxide content of 20% or more and a film thickness of 1 μm or more, a film composition having a surface resistance of 1 × 10 ¹⁰ Ω / □ or less is obtained. Can be obtained. The conductivity of this film composition is stable. For example, the ratio of the surface resistance when held at 40 ° C. under normal pressure for 500 hours is less than 2.

  Furthermore, the conductive tin oxide powder of the present invention preferably has a crystal lattice diameter of 5 to 20 nm and is much smaller than the visible light wavelength, and has a 90% particle diameter (D90) of 5 μm or less. It is a powder with a high rate and excellent transparency. Specifically, for example, in a thin film having a tin oxide content of 20% or more and a film thickness of 1 μm or more, the visible light transmittance is 87% or more, and a similar thin film containing conventional fluorine-containing tin oxide powder (FTO) is used. With a visible light transmittance of 83 to 86%, a highly transparent conductive film can be formed.

  In the production method of the present invention, since the tin source and the fluorine source are mixed in the aqueous solution, a predetermined amount of fluorine can be uniformly introduced. Nitrogen can be introduced uniformly. In addition, these dope amounts can be controlled by adjusting the amount of fluorine source added, heating temperature, heating time, etc., so that high-quality conductive tin oxide whose powder resistivity is controlled within a desired range A powder can be produced.

Hereinafter, the present invention will be specifically described based on examples.
[Conductive tin oxide powder]
The conductive tin oxide powder of the present invention is a tin oxide powder obtained by bringing tin dioxide or stannic hydroxide into contact with a fluorine source in water and heat-treating in a nitrogen atmosphere, and does not contain antimony, tin It is a conductive tin oxide powder characterized by containing 0.01 to 0.2 mol of fluorine and 0.001 to 0.01 mol of nitrogen with respect to 1 mol.
“No antimony” means that no antimony source is used in the raw material and process, and therefore no antimony is detected by a standard measuring device having a detection limit of 500 ppm.

  The conductive tin oxide powder of the present invention contains 0.01 to 0.2 mol of fluorine and 0.001 to 0.01 mol of nitrogen with respect to 1 mol of tin. By containing the predetermined amount of fluorine and nitrogen, the powder resistance is lowered. This is considered to be due to the action of fluorine and nitrogen involved in oxygen defects of tin oxide.

  If the amount of fluorine is less than 0.01 mol, the effect of reducing powder resistance is insufficient, and good conductivity cannot be obtained. Further, when a fluorine source having an amount of fluorine exceeding 0.2 mol is added to the raw material, a free fluorine source that is not doped with tin oxide remains, which hinders a current-carrying path, so that conductivity is lowered.

If the amount of nitrogen is less than 0.001 mol , the effect of reducing powder resistance is insufficient, and good conductivity cannot be obtained. On the other hand, if the nitrogen content exceeds 0.01 mol, doping of fluorine with tin oxide is hindered, and good conductivity cannot be obtained.

The conductive tin oxide powder of the present invention can have conductivity with a powder volume resistivity of 10 Ω · cm or less. The powder volume resistivity is the volume resistivity of powder compressed at a pressure of 100 kgf / cm ² . On the other hand, the dust volume resistivity of the conventional fluorine-containing tin oxide powder is approximately 100 Ω · cm or more, and the dust volume resistivity of the conductive tin oxide powder of the present invention is 1/10 or less of the conventional.

The conductive tin oxide powder of the present invention can be used in the form of a dispersion (liquid) dispersed in a solvent such as water, and can be mixed with a resin component to form a conductive thin film. By using the conductive tin oxide powder of the present invention, a conductive thin film having a surface resistance of 1 × 10 ¹⁰ Ω / □ or less is formed in a thin film having a tin oxide content of 20% or more and a film thickness of 1 μm or more. be able to.

  The film composition using the conductive tin oxide powder of the present invention is stable in electrical conductivity, for example, the surface resistivity Rs when held at 40 ° C. and normal pressure for 500 hours, and the surface resistivity Ro before the test. The ratio (Rs / Ro) is less than 2.

〔Production method〕
The conductive tin oxide powder of the present invention can be produced by bringing tin dioxide or stannic hydroxide into contact with fluorine or a fluorine compound in water, followed by heat treatment in a nitrogen atmosphere after dehydration.

  As the fluorine source, ammonium fluoride, ammonium silicofluoride, ammonium hydrofluoride, tin fluoride, fluorostannic acid, hydrogen fluoride, hydrofluoric acid, boron fluoride, bromine fluoride, or the like can be used.

Specifically, for example, a tin source powder consisting of the second tin oxide powder or the second tin hydroxide powder or a mixture thereof is dispersed in water, was added to the fluorine source to the dispersion solution, the tin source powder and a fluorine source Are mixed in an aqueous solution and brought into contact with each other to allow fluorine to uniformly adhere to the surface of the tin source powder.

  This powder is recovered, dried, and heat-treated in a nitrogen atmosphere. By performing the heat treatment in a nitrogen atmosphere, a minute amount of nitrogen can be introduced uniformly. Since these dope amounts can be controlled by adjusting the amount of fluorine source added, the heating temperature and the heating time, etc., producing a conductive tin oxide powder with reduced powder volume resistivity within a desired range Can do.

  In the heat treatment, the heating temperature is preferably 400 ° C to 700 ° C. When the heating temperature is lower than this, the doping effect of fluorine and nitrogen becomes insufficient, and it becomes difficult to obtain conductivity. Also, if the heating temperature is higher than this, since many oxygen defects of tin oxide occur, the black color of the resulting powder becomes strong, and the powder sinters into coarse particles, so a thin film is formed. Sometimes transparency is greatly reduced.

  Furthermore, the heat treatment of the powder is preferably performed while eliminating oxygen in the nitrogen atmosphere as much as possible. Conventionally, in a method of forming a fluorine-containing tin oxide film on a substrate surface, a heat treatment method is known in a nitrogen atmosphere into which a constant concentration of oxygen is introduced. When oxygen is present, a good low-resistance powder is obtained. It is difficult.

  According to the above production method, containing 0.01 to 0.2 mol of fluorine and 0.001 to 0.01 mol of nitrogen with respect to 1 mol of tin without containing antimony, and the powder volume resistivity is 10 Ω · cm. The following conductive tin oxide powder can be obtained.

  Moreover, according to the said manufacturing method, the electroconductive tin oxide powder whose 90% particle diameter (D90) is 5 micrometers or less and whose crystal lattice diameter is 5-20 nm can be obtained. Since the crystal lattice diameter of this powder is much smaller than the visible light wavelength and the 90% particle diameter (D90) is also small, the powder has high visible light transmittance and excellent transparency.

  Therefore, by using the conductive tin oxide powder of the present invention, for example, a highly transparent conductive film having a visible light transmittance of 87% or more is formed in a thin film having a tin oxide content of 20% or more and a film thickness of 1 μm or more. can do.

[Use]
The conductive tin oxide powder of the present invention is a safe powder that does not contain antimony and indium, which may have an impact on the environment, and is manufactured using simple processes and inexpensive raw materials. It is an excellent powder with low environmental impact. Therefore, it can be used in a wide range of fields. Specifically, for example, (a) the field of food packaging materials and packaging materials where toxicity is regarded as a problem, (b) the field of flat panel displays such as liquid crystal displays and plasma displays, and (c) charge control characteristics are required. Field of touch panel, (d) Field of magnetic recording medium such as optical disk, (e) Field of thin film paint, (f) Field of internal electrode and electrode modifier of solar cell and various devices, (g) Electrostatic recording material Printers that require charge control, photocopier-related charging rollers, photosensitive drums, toners, electrostatic brushes, and other fields, (h) fields such as sintered powder for gas sensors, and (i) dust prevention Required fields such as FPD, CRT, CRT,
In addition, the conductive tin oxide powder of the present invention can be easily dispersed and kneaded in paints, inks, emulsions, fibers and other polymers when used, and when added to the paint and coated as a thin film. It is possible to obtain a dispersion and a film composition of conductive powder which is highly transparent and excellent in conductivity.

Examples of the present invention are shown below together with comparative examples. Table 1 shows the production conditions, fluorine and nitrogen doping amounts, powder particle diameter, volume resistivity, and thin film surface resistance. The measurement method is as follows.
[Fluorine content / nitrogen content] The fluorine and nitrogen contents were measured by composition analysis of an ICP emission spectrometer.
[Pressure Volume Resistivity] The powder volume resistivity is measured with a digital multimeter (Yokogawa Electric product: Model 7561-02) after putting the sample powder in a pressure vessel and compressing it at 100 kgf / cm ^2. did.
[Particle size] D90 was measured by dispersing a sample powder in water and using a laser diffraction particle size distribution measuring apparatus (Shimadzu Corporation product: model SALD-1100).
[Formation of thin film] The thin film containing the sample powder is formed by adding the sample powder to a mixed solution of xylene / toluene together with a commercially available acrylic resin (product name: Acrydic A-168, resin content: 50%), and using a paint shaker A dispersion having a sample powder content of 20% was prepared. The dispersion was applied to a PET film and air-dried for 1 hour to form a thin film having a thickness of 1 μm. The surface resistance value of the thin film was measured.
[Surface Resistance] The surface resistance was measured on a thin film having a thickness of 2 μm containing a sample powder using a surface resistance meter (HIRESTA: Mitsubishi Yuka product: Model HT-210, supply voltage 100 V).

[Example 1]
Stannous dioxide and ammonium fluoride are added to water so that the F / Sn molar ratio is 10, and after stirring so that they are in uniform contact, they are recovered, dehydrated and dehydrated in a nitrogen atmosphere at 550 ° C. for 2 hours. After heating and cooling, a grayish brown powder was obtained. The volume resistivity of the powder was 2.4 Ω · cm. Moreover, the fluorine amount with respect to 1 mol of tin was 0.03 mol, and the nitrogen amount was 0.008 mol. The 90% particle size (D90) was 4.7 μm. Furthermore, when a thin film containing this powder was formed and the surface resistance value was measured, it was 6.6 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

[Example 2]
A powder was produced in the same manner as in Example 1 except that tin dioxide and ammonium fluoride were added to water so that the F / Sn molar ratio of the powder became the value shown in Example 2 of Table 1 . The powder had a volume resistivity of 0.8 Ω · cm, a fluorine content of 0.05 mol, a nitrogen content of 0.005 mol, and a D90 of 4.8 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 2.5 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Example 3
A powder was produced in the same manner as in Example 1 except that tin dioxide and tin fluoride were added to water so that the F / Sn molar ratio was 50. The powder had a volume resistivity of 0.8 Ω · cm, a fluorine content of 0.12 mol, a nitrogen content of 0.003 mol and a D90 of 4.5 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 2.0 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Example 4
A powder compact of this powder was obtained in the same manner as in Example 1 except that stannous hydroxide and ammonium fluoride were added to water so that the F / Sn molar ratio was 20, and the heating temperature was 650 ° C. The volume resistivity was 0.4 Ω · cm, the fluorine content relative to 1 mol of Sn was 0.06 mol, the nitrogen content was 0.005 mol, and D90 was 4.7 μm. The surface resistance of the thin film containing this powder was 1.3 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Example 5
A powder was produced in the same manner as in Example 1 except that second tin hydroxide and tin fluoride were added to water so that the F / Sn molar ratio was 20, and the heating temperature was changed to 450 ° C. This powder had a powder volume resistivity of 8.9 Ω · cm, a fluorine content of 0.01 mol, a nitrogen content of 0.006 mol, and a D90 of 4.5 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 7.1 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Example 6
A powder was produced in the same manner as in Example 1 except that the heating time was 5 hours. The powder had a volume resistivity of 0.7 Ω · cm, a fluorine content of 0.16 mol, a nitrogen content of 0.009 mol, and a D90 of 4.8 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 3.1 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Example 7
A powder was produced in the same manner as in Example 1 except that tin dioxide and ammonium fluoride were added to water so that the F / Sn molar ratio was 150. This powder had a powder volume resistivity of 0.3 Ω · cm, a fluorine content of 0.20 mol, a nitrogen content of 0.001 mol, and a D90 of 4.5 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 1.7 × 10 ⁸ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

[Comparative Example 1]
A powder was produced in the same manner as in Example 1 except that the fluorine source was not added. The powder had a volume resistivity of 1.2 × 10 Ω · cm, a fluorine content of 0 mol, a nitrogen content of 0.11 mol, and a D90 of 4.8 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 5.9 × 10 ¹² Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

[Comparative Example 2]
A powder was produced in the same manner as in Example 1 except that heating was performed in an air atmosphere. This powder had a compact volume resistivity of 6.3 × 10 ⁵ Ω · cm, a fluorine content of 0.002 mol, a nitrogen content of 0.01 mol, and a D90 of 5.1 μm with respect to 1 mol of Sn. The surface resistance of the thin film containing this powder was 4.4 × 10 ¹³ Ω / □. Moreover, the surface resistance value when it hold | maintains under 40 degreeC normal pressure for 500 hours was measured, and ratio with the previous surface resistance value was calculated | required. This ratio is shown in Table 1.

Claims (3)

A tin source powder consisting of tin dioxide powder, tin hydroxide powder or a mixture thereof is dispersed in water, a fluorine source is added to this dispersed aqueous solution, and the above tin source powder and fluorine source are mixed and contacted in the aqueous solution. Then, after the fluorine is uniformly deposited on the surface of the tin source powder, the conductive tin oxide powder containing fluorine and nitrogen is produced by dehydration and heat treatment in a nitrogen atmosphere. For producing porous tin oxide powder. Contains no antimony and contains 0.01 to 0.2 moles of fluorine and 0.001 to 0.01 moles of nitrogen with respect to 1 mole of tin, and has a powder volume resistivity under a pressure of 100 kgf / cm ^2. The manufacturing method of the electroconductive tin oxide powder of Claim 1 which manufactures the electroconductive tin oxide powder which is 10 ohm * cm or less. The manufacturing method of the electroconductive tin oxide powder of Claim 1 or Claim 2 which manufactures electroconductive tin oxide powder whose 90% particle diameter (D90) is 5 micrometers or less and whose crystal lattice diameter is 5-20 nm.