JP4765051B2 - Tin-doped indium oxide powder - Google Patents

Description

  The present invention relates to a transparent conductive powder having high transparency and excellent conductivity, and having high reflectivity for electromagnetic contacts and circuits, and a method for producing the same.

Conventionally, tin-doped indium oxide in which tin dioxide (SnO ₂ ) is added as an impurity to indium trioxide (In ₂ O ₃ ) is known as a transparent conductive material having such high transparency and high conductivity. This tin-doped indium oxide is a semiconductor that is transparent to visible light and exhibits oxygen deficiency-type conductivity, and Sn ⁴⁺ by simultaneously added tin dioxide (SnO ₂ ) is a source of free electrons, ie, a donor. Thus, it is accumulated at the donor level near the lower end of the conduction band and imparts high conductivity.

As a means for obtaining such a tin-doped indium oxide as a film body, a gas phase reaction is carried out using sputtering, vacuum deposition, or a solution of indium trichloride (InCl ₃ ) added with tin tetrachloride (SnCl ₄ ). As a specific means for obtaining a powder, a mixed solution of indium trichloride (InCl ₃ ) and tin tetrachloride (SnCl ₄ ) is dropped into an ammonium carbonate solution. Then, a coprecipitated hydroxide of indium and tin is produced, the coprecipitated hydroxide is washed with water by decantation or centrifugal separation and dried, and further, the dried product is heated and reduced in a hydrogen atmosphere or a vacuum atmosphere. A reduction firing method for pulverization is known.
JP 09-221322 A

However, in the past, those that have been subjected to a low resistance treatment in order to enhance the shielding effect, take measures such as increasing the firing temperature, so that the sintering progresses and the agglomeration is severe and causes poor dispersion. These had problems such as depositing in the paint. Further, there was no blue to green coating film excellent in translucency with good dispersion. As described above, good powders were not obtained in both conductivity and dispersibility.
In view of such conventional problems, an object of the present invention is to provide a transparent conductive powder exhibiting higher conductivity and good dispersibility, and to provide a suitable manufacturing method therefor. .

As a means of obtaining low resistance, the present inventor has conducted diligent research in order to solve such a problem. By using a divalent compound instead of a conventional tetravalent compound of a tin raw material as a doping agent to be added to indium, It has been found that a reducing atmosphere can be easily obtained, O ₂ deficiency increases, and low resistance can be realized.

That is, according to the present invention, first, the Sn content is 0.1 to 30% by weight in terms of SnO ₂ , and the color tone is an x value of 0.280 to 0.370 on the xy chromaticity diagram, and 0.316 to A tin-doped indium oxide powder characterized by a y value of 0.400; second, the zeta potential measured in an aqueous 0.01 mol KCl solution with a Sn content of 0.1-30 wt% in terms of SnO ₂ is +5 mV Tin-doped indium oxide powder characterized by the above; third, a specific surface area of 15 m ² / g or more, a particle size of 10 to 30 nm, and an X-ray diffraction diagram of 2θ = about 30.5 ° Tin dope characterized in that the volume resistivity is 3 × 10 ¹ Ωcm or less in the state of a green compact molded at a pressure of 200 kg / cm ² with a peak half width of 0.2 ° to 0.7 °. Indium oxide powder; Fourth, indium and divalent tin Ammonium carbonate is added to the dissolved acidic solution to form a coprecipitated hydroxide of indium and tin and then dried, and the coprecipitated hydroxide is fired at 500 to 800 ° C. in an inert gas atmosphere containing moisture. A method for producing tin-doped indium oxide powder characterized by the following: Fifth, supply of the inert gas atmosphere containing moisture is 1.0 ml / min · g (amount of supply per minute per 1 g of dry coprecipitated hydroxide) or more The method for producing tin-doped indium oxide powder according to the fourth aspect, characterized in that the flow rate is a flow rate.

  According to the present invention, a transparent conductive powder exhibiting high conductivity and high dispersibility in a high transparent region can be obtained. In addition, the transparent conductive powder can be produced, and does not require a baking treatment in a strong reducing atmosphere, and therefore does not require expensive equipment and high running cost due to the equipment, and is economical and safe. Can be provided.

In the present invention, a soluble indium compound and a divalent soluble tin compound are used as starting materials. For example, InCl ₃ is used as the soluble indium compound. This InCl ₃ can be easily obtained by heating and dissolving indium metal in an acidic hydrochloric acid solution. For example, SnCl ₂ is used as the soluble tin compound. SnCl ₂ is obtained by dissolving tin metal in hydrochloric acid, and when this solution is concentrated, a stable dihydrate is obtained. By using a divalent tin compound (for example, SnCl ₂ ), a sufficient reducing atmosphere can be obtained in the firing step, and sufficient oxygen vacancies can be formed in the crystal lattice of the fired product.

In order to obtain highly conductive powder, the InCl ₃ aqueous solution and the SnCl ₂ aqueous solution are mixed in such a ratio that the Sn content in the tin-doped indium oxide powder after firing is 0.1 to 30% by weight in terms of SnO _2. An ammonium carbonate salt solution, for example, a mixed alkaline solution of ammonium bicarbonate (NH ₄ HCO ₃ ) and aqueous ammonia is added to the mixed solution, and the mixture is stirred and reacted, whereby In (OH) ₃ and Sn (OH) ₂ are reacted. The coprecipitation product is obtained. The reason why the Sn content of the tin-doped indium oxide powder is 0.1 to 30% by weight in terms of SnO ₂ is that, in this range, a high-electron density and a highly conductive powder can be obtained. This is because good conductive powder cannot be obtained if it is detached.
As a means for obtaining high dispersibility, an alkaline solution is added to the mixed aqueous solution of acidic InCl ₃ and SnCl _{2 in} the above reaction step, and the particles are nucleated all at once in the neutral region to achieve uniform particle distribution. At the same time, the generation of coarse particles is suppressed. By doing so, a highly translucent powder can be obtained.

The obtained coprecipitation product is repeatedly washed several times by decantation with warm water, dehydrated, and further dried at 150 ° C. for a long time.
Next, the obtained dried granule is held in an atmosphere furnace, and a baking treatment is performed by holding it at a high temperature of 500 ° C. to 800 ° C. for several hours while passing an inert gas containing moisture. Nitrogen, argon, carbon dioxide, or the like can be used as the inert gas, but nitrogen and argon are preferable from the viewpoint of characteristics and cost, and nitrogen is particularly preferable.
The water content is added to the inert gas so that a good color tone and dispersibility can be obtained. The water content may be, for example, about the saturated water vapor pressure at room temperature.
The firing temperature is preferably in the range of 500 ° C to 800 ° C. When the firing temperature is less than 500 ° C., the firing is insufficient and the resulting powder has high resistance, and when it exceeds 800 ° C., the sintering and aggregation progress, and the dispersibility of the resulting powder becomes poor.

  Further, in the firing step, the atmosphere is made uniform by setting the flow rate of the aeration gas to 1.0 ml / min · g or more (amount supplied per minute per 1 g of dry coprecipitated hydroxide), and partial sintering is performed. Can be suppressed, and a dispersible blue to green powder can be obtained. If the flow rate of the aeration gas is less than 1.0 ml / min · g, the atmosphere varies in the firing furnace, resulting in uneven characteristics, which is not preferable.

The tone of the powder shall indicate an x value of 0.280 to 0.370 and a y value of 0.316 to 0.400 on the xy chromaticity diagram. This color tone is blue to yellowish green, and has almost no light absorption in the vicinity of 500 nm, which is the highest sensitivity of human eyes in visible light, and has good translucency. If one is out of this range, sufficient translucency cannot be obtained.
The zeta potential in water was measured as an index of the dispersibility of the powder, and the stability in a solvent (water) was evaluated. When the zeta potential of the powder shows a positive value, preferably when it is +5 mV or more, more preferably when it is +15 mV or more, the powder in the paint exhibits good dispersibility, and when the zeta potential is 0 or less, sufficient dispersibility Cannot be obtained.

Furthermore, in order to obtain sufficient translucency, the specific surface area is preferably 15 m ² / g or more, more preferably 30 m ² / g or more, and the particle size (primary particle size by TEM photograph) is in the range of 10 to 30 nm. preferable. When the specific surface area is less than 15 m ² / g, atomization is not sufficient, and sufficient translucency cannot be obtained. Further, when the particle size is out of the range of 10 to 30 nm, sufficient light transmission cannot be obtained. In order to obtain even higher conductivity, the crystallinity of the powder is preferably such that the half-value width of the main peak (hereinafter referred to as XRD half-value width) around 2θ = 30.5 ° on the X-ray diffraction diagram is preferably 0. The angle may be within the range of 0.2 ° to 0.7 °, more preferably 0.3 ° to 0.5 °. If the angle is less than 0.2 °, the sintering proceeds and coarsening occurs and the translucency is inhibited. If the angle exceeds 0.7 °, sufficient crystallinity cannot be obtained due to insufficient firing, resulting in poor conductivity.
In order to obtain a high shielding effect, the volume resistivity is preferably 3 × 10 ¹ Ωcm or less, and more preferably 3 × 10 ⁰ Ωcm or less in the state of a green compact molded at a pressure of 200 kg / cm ² .

[Example 1]
Give the InCl ₃ solution indium metal was heated and dissolved with HCl acid solution, to the InCl ₃ solution was added SnCl ₂ solution in a predetermined ratio to make a mixed solution of pH 1-2. To this mixed solution, an ammonium bicarbonate solution was added and stirred to react. The pH at the end of the reaction is 6-7. The obtained coprecipitation product was repeatedly washed by decantation with hot water of 60 ° C. or higher, filtered and dehydrated, and then dried at 150 ° C. for 20 hours.
Further, 400 g of the dried sample was charged into a tubular atmosphere furnace, and calcined at 550 ° C. for 3 hours while aerated with N ₂ gas at a flow rate of 10 ml / min · g (amount supplied per 1 g of dry coprecipitated hydroxide). During the ventilation, the humidity was adjusted to maintain saturated moisture at 30 ° C. The obtained fired product was pulverized by a table mill.

The Sn content was measured by ICP analysis. The primary particle size was measured with a transmission electron microscope (TEM). The specific surface area was measured by the BET single point method. The color tone was measured by a double beam photometry method (color difference meter). X-ray diffraction was performed using a scintillation counter under conditions of CuK-α ₁ and 50 kV. The specific resistivity of the green compact was determined by measuring the resistance of the green compact molded at a pressure of 200 kg / cm ^{2 by} the four-probe method. The zeta potential was measured at an applied voltage of 100 V using a laser rotating prism type zeta potentiometer by dispersing the powder in 0.01 mol of KCl aqueous solution with ultrasonic waves (irradiation for 5 minutes).

The Sn content of the powder obtained by the above method was 5.3% by weight in terms of SnO ₂ , the particle size was 10 nm, and the specific surface area was 56.5 m ² / g.
This tin-doped indium oxide powder had a blue-green color tone, and the x and y values in the xy chromaticity diagram were 0.323 and 0.353, respectively. Further, the XRD half width of the powder was 0.58 °, the volume resistivity of the green compact was 0.1 Ωcm, and the zeta potential was +25 mV.

[Example 2]
The same treatment as in Example 1 was performed except that the firing temperature was changed to 650 ° C. instead of 550 ° C.
Sn content of the obtained tin-doped indium oxide powder was 5.3% by weight in terms of SnO ₂ , the particle size was 15 nm, and the specific surface area was 43.1 m ² / g. The powder had a blue color tone, and the x and y values in the xy chromaticity diagram were 0.301 and 0.317, respectively. Further, the XRD half width of the powder was 0.45 °, the volume resistivity of the green compact was 0.03 Ωcm, and the zeta potential was +23 mV.

[Comparative Example]
Give the InCl ₃ solution indium metal was heated and dissolved with HCl acid solution, to the InCl ₃ solution was added SnCl ₂ solution in a predetermined ratio to make a mixed solution of pH 1-2. The above mixed solution was added to the ammonium bicarbonate solution and stirred to react. The pH at the end of the reaction is 7. The obtained coprecipitation product was washed by repeating decantation 5 times with hot water of 60 ° C. or higher, filtered and dehydrated, and then dried at 150 ° C. for 20 hours.
Further, 400 g of the dried sample was charged into a tubular atmosphere furnace, and calcined at 550 ° C. for 3 hours while aeration of N ₂ gas at a flow rate of 0.5 ml / min · g. No moisture was added to the aeration gas. The obtained fired product was pulverized by a table mill. The Sn content of the obtained powder was 5.3% by weight in terms of SnO ₂ , the particle size was 10 nm, and the specific surface area was 58.0 m ² / g.
This tin-doped indium oxide powder had a yellow-green color tone, and the x value and y value in the xy chromaticity diagram were 0.380 and 0.383, respectively. Further, the XRD half width of the powder was 0.68 °, the volume resistivity of the green compact was 3.0 Ωcm, and the zeta potential was −3.2 mV.

Claims (3)

Sn content is 0.1 to 30 wt% in terms of SnO _2, double beam交照 x value of 0.301 to 0.323 tone was measured on the xy chromaticity diagram by measurement and from 0.317 to 0 a y value of .353, be a zeta potential +. 23 to + 25 mV for using a zeta potential meter was measured at an applied voltage of 100V laser rotating prism schemes dispersed by ultrasonic for 5 minutes irradiation in 0.01molKCl aqueous solution A tin-doped indium oxide powder having a volume resistivity of 0.03 to 0.1 Ωcm measured by a four-probe method in a green compact molded at a pressure of 200 kg / cm ² . The tin-doped indium oxide powder according to claim 1, having a specific surface area of 43.1 to 56.5 m ² / g and a particle size of 10 to 15 nm . The tin-doped indium oxide powder according to claim 1 or 2, wherein a main peak half width in the vicinity of 2θ = 30.5 ° is 0.45 to 0.58 ° on an X-ray diffraction diagram.