JP3367149B2 - Method for producing conductive oxide powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is typified by tin-doped indium oxide (ITO) and antimony-doped tin oxide (ATO). The present invention relates to a method for producing oxide powder (n-type oxide semiconductor powder).

More specifically, the present invention has a primary particle size of 0.
2 μm or less, preferably 0.1 μm or less, and compact
The present invention relates to a method capable of producing a conductive oxide powder having a volume resistivity of (50 kgf / cm ² ) of 10 Ω · cm or less, which is excellent in transparency and conductivity, by a method excellent in mass productivity. In particular, when the method of the present invention is applied to the production of ITO powder, it is possible to mass-produce a low resistance ultrafine conductive oxide powder having a primary particle diameter of 0.05 μm or less and a volume resistivity of 0.1 Ω · cm or less. it can.

[0003]

2. Description of the Related Art As a general method for producing an electrically conductive type conductive oxide powder, an aqueous solution containing two or more kinds of raw material transition metal ions (eg, in the case of ITO powder, Sn and In are chlorides). (Or an aqueous solution dissolved as a nitrate) is reacted with an alkaline aqueous solution to coprecipitate a hydroxide of the raw material metal, and the coprecipitated hydroxide is used as a starting material to be heat-treated in the atmosphere to be converted into an oxide. There is a way. This method
It is known that not only the ITO powder but also the ATO powder and other electron-conducting conductive oxide powders can produce stable, low-resistance submicron fine powders.

The field of application of the conductive oxide powder produced by such a method is, for example, an average primary particle size of 0.1
There is a conductive coating material (film forming material) which is made into a paint by dispersing a fine powdery conductive oxide powder controlled to be not more than μm in a solution consisting of a solvent and a binder resin. The transparent conductive film can be formed on the base material by applying this coating material to a base material such as glass or plastic by means such as dipping, coating, printing, spin coating or spraying, and drying.

This transparent conductive film is effective for preventing static electricity such as glass and plastics and for preventing dust from adhering, and is used, for example, for preventing electrostatic charge and preventing dust from adhering to window glass of TV Braun tubes and measuring instruments.

In recent years, fine powders of conductive oxides such as ITO powders have been used in IC package circuit formation, clean room interior materials, various glass and films to prevent static electricity and dust from adhering, coating type transparent electrodes or It is being used or studied for applications such as surface heating elements, and future demand growth is expected.

With the expansion of such use, the required performance of the conductive oxide powder is also increasing, and especially I
In applications where TO powder is applied by a coating means such as coating or printing to form a transparent conductive film, higher transparency and conductivity are required. For this reason, while the dispersion technique for making a coating material is being investigated, a means for further atomizing and reducing the resistance of the conductive oxide powder itself is also being sought.

The conductive mechanism of the conductive oxide powder (n-type oxide semiconductor) due to electronic conductivity is, for example, in the case of ITO, in which the trivalent In site of the In ₂ O ₃ crystal is replaced with tetravalent Sn. It is known that, in addition to the action of the n-type donor due to the arrangement (generation of carrier electrons), the carrier electron density in the bulk is increased by the donor effect of oxygen vacancies due to lattice defects. There is. In the production of ITO, the Sn content of the dope is adjusted within the range of 1 to 15 mol% to further enhance the conductivity due to oxygen defects,
It is known to reduce the resistance by controlling the oxygen partial pressure in the firing atmosphere or by firing with a reducing air flow.

However, in such a method, there is a difference in the susceptibility to oxygen defects between the upper part (surface part) and the lower part of the raw material charged in the firing furnace, and the conductivity becomes nonuniform.
Therefore, in order to satisfy the requirements of ultrafine particles and low resistance at the same time, it is necessary to spread the charging raw material as thin as possible and fire at a low temperature. However, firing under such a condition causes variations in characteristics and There is also a problem in mass productivity. For this reason, it has been difficult to industrially mass-produce ITO, which is a low resistance ultrafine powder having a primary particle diameter of 0.05 μm or less and a volume resistivity of 0.1 Ω · cm or less, which has been particularly demanded recently.

[0010]

The object of the present invention is to have a primary particle diameter of 0.2 μm or less, preferably 0.1 μm or less, and a powder compact (50 kgf / cm ² ) having a volume resistivity of 10 Ω · cm or less. An object of the present invention is to provide a manufacturing method capable of mass-producing a conductive oxide powder having excellent transparency and conductivity.

Another object of the present invention is to have a primary particle size of 0.05 μm.
Hereinafter, it is an object of the present invention to provide a method for producing a conductive oxide powder, which enables mass production of low-resistance ultrafine powder ITO powder having a volume resistivity of 0.1 Ω · cm or less.

[0012]

Means for Solving the Problems The inventors of the present invention have used a raw material for a conductive oxide powder (a mixed hydroxide and / or oxide of two or more transition metals) under an inert gas sealed and pressurized condition. The present invention has been completed by finding that the above object can be achieved by heat-treating.

In the present invention, a starting material composed of a mixed hydroxide and / or oxide of two or more transition metals is heated at a pressure of 2 kgf / cm ² or more in a closed pressurized inert gas atmosphere. The gist is a method for producing a conductive oxide powder, which is characterized by performing heat treatment at 350 to 1000 ° C.

As the starting material, (1) a hydrous mixed hydroxide obtained by coprecipitation by the reaction of an aqueous solution containing two or more transition metal ions and an alkaline aqueous solution, (2) heating of this hydrous mixed hydroxide Dehydrated and dried mixed hydroxide and / or heat dehydrated mixed oxide, (3) conductive oxide powder obtained by a known method, or (4) hydrous hydroxide of two or more transition metals,
Mixed powders of hydroxides and / or oxides can be used.

The present invention provides an ITO powder in which the transition metal is a combination of Sn and In, an ATO powder in which the transition metal is a combination of Sb and Sn,
Furthermore, Al, Sn, In, Fe, Ga, Co, Si, Ge, Sb or Pb
It can be applied to the production and treatment of zinc oxide-based conductive oxide powder, which is a combination of Zn and Zn.

[Starting Raw Material] The starting raw material in the method for producing a conductive oxide powder of the present invention comprises a mixed hydroxide and / or oxide of two or more transition metals. As the starting material, (1) a hydrous mixed hydroxide obtained by coprecipitation by the reaction of an aqueous solution containing two or more kinds of transition metal ions and an alkaline aqueous solution, or (2) heating and drying of this hydrous mixed hydroxide Alternatively, it is preferable to use a mixed hydroxide and / or oxide obtained by heat dehydration, since the effect of ultrafine graining and low resistance is high.

However, (3) conductive oxide powder obtained by a known method, or (4) hydrous hydroxide of two or more transition metals,
It is also possible to use mixed powders of hydroxides and / or oxides.

To obtain the hydrous hydroxide of the above (1), a water-soluble salt of two or more different transition metals is dissolved in water,
An aqueous solution containing these transition metal ions is prepared.
The type of water-soluble salt is not limited, but examples thereof include inorganic acid salts such as hydrochlorides, nitrates and sulfates, and organic acid salts such as acetates. Mixtures of two or more salts may be used. On the other hand, as an alkaline aqueous solution,
Aqueous solutions of (eg, sodium or potassium) or ammonium hydroxides, carbonates, bicarbonates can be used. The concentrations of the transition metal salt aqueous solution and the alkaline aqueous solution are not particularly limited, but usually will be in the range of 200 to 400 g / l.

The two types of aqueous solutions are mixed with stirring to carry out the reaction. By this reaction, each transition metal salt is hydrolyzed and two or more kinds of transition metal hydroxides are coprecipitated. In order to obtain a fine precipitate, it is preferable to drop one aqueous solution into the other aqueous solution with stirring and gradually mix them. The reaction temperature may be appropriately determined by experiments because the ease of hydrolysis varies depending on the type, concentration, dope amount, etc. of the transition metal, but it may normally be in the range of room temperature to 100 ° C. The amount of the alkaline aqueous solution used in the reaction varies depending on the type of the conductive powder, but it is preferable that the mixed solution has a pH of 4 to 9. If desired, stirring may be continued after mixing.

When the precipitate is collected by a suitable means such as sedimentation or filtration, a mixed hydrous hydroxide of two or more transition metals can be obtained. If necessary, the precipitate may be washed with water before or after collection. The hydrous hydroxide obtained by this coprecipitation can be directly used as a starting material (1) for the method of the present invention without being dried.

When the water-containing mixed hydroxide of two or more transition metals is dried by heating, it becomes a mixed hydroxide, and if it is further heated and dehydrated, it becomes a mixed oxide. Depending on the heating conditions, a mixture of hydroxide and oxide can be obtained. The mixed hydroxide and / or oxide thus obtained can be used as the starting material (2) in the present invention. These mixed hydroxides and / or oxides have a primary particle size of 0.1
It is preferably μm or less.

If the heating temperature is limited to drying, 200 ° C. or lower, preferably 150 ° C. or lower is generally sufficient. In the case of dehydration and conversion into an oxide, the heating temperature can be up to 900 ° C, but it is preferably kept at 500 ° C or lower. If the heating temperature at this time is too high, grain growth occurs during heating and the finally obtained conductive oxide powder tends to become coarse. The heating may be performed in the air, but the atmosphere is not particularly limited. The heating time is preferably as short as possible so long as the desired drying or dehydration is achieved. In particular, when dehydrating oxides, it is desirable to set heating conditions so as to prevent grain growth as much as possible.

When the starting material is a mixed oxide, it is preferable that the mixed oxide is obtained by heating and dehydrating the hydrous mixed hydroxide obtained by the coprecipitation as described above. As described above, the conductive oxide powder itself obtained by calcining the hydroxide and / or the oxide by a known method can also be used as the starting material. For example, a conductive oxide powder obtained by firing the starting material (1) or (2) in a reducing atmosphere according to a known method can be used as the starting material for the method of the present invention. In this case, the volume resistivity of the powder can be further reduced by applying the method of the present invention to this conductive oxide powder.

Even when the conductive oxide powder obtained by the known method is used as a starting material, if the average primary particle diameter of the oxide powder is 0.1 μm or less, it is effective for ultrafine graining and low resistance. Is preferable because it is high. Particle size is 0.1-0.2 μm
To a certain extent, even if heat treatment is performed under pressure in an inert atmosphere according to the method of the present invention, it is non-uniform and is not very effective in reducing resistance. Further, if the particle size exceeds 0.2 μm, it is difficult to exhibit excellent transparency in the dispersion system.

Further, although not so preferable, as the starting material (4), 2 obtained by individual precipitation instead of coprecipitation
It is also possible to use mixed powders of hydrous hydroxides, hydroxides and / or oxides of one or more transition metals. Also in this case, the average primary particle diameter is preferably 0.1 μm or less, as in the above.

As the combination of transition metals in the conductive oxide powder, a combination of groups different from each other in the periodic table is selected. That is, a combination of a transition metal element of the oxide serving as a base and an element that can serve as a donor (a transition metal element on the right side of the periodic table with respect to the base element) is selected, and a conductor having electronic conductivity is selected.
(n-type semiconductor) is generally formed. The transition metal element serving as the donor is used as a dopant in a small amount relative to the base material transition metal element.

As an example of the conductive oxide powder to which the method of the present invention can be preferably applied, Sn is added to In ₂ O ₃ Sn / (Sn + In) molar ratio =
ITO powder SnO ₂ doped to 0.01 to 0.15
ATO powder doped with Sb so that Sn / (Sb + Sn) molar ratio = 0.01 to 0.15, and Al in ZnO with Al / (Al + Zn) molar ratio =
A typical example is AZO powder (aluminum-doped zinc oxide) that is doped to have a concentration of 0.01 to 0.15. The dopant is not limited to this, and any dopant may be used as long as it enhances conductivity (donor), and two or more transition metal elements can be doped. For example, ZnO can be doped with one or more of Sn, In, Fe, Ga, Co, Si, Ti, Ge, Sb and Pb in addition to Al. Further, the base oxide may be a composite oxide composed of two or more kinds of metal elements, and for example, a conductive oxide caused by a difference in stoichiometric composition between Zn and Sn in ZnSnO ₃ (zinc stannate). Powder, and Al, In, Fe, Ga, Co, S
A doping agent such as i, Ti, Ge, Sb or Pb may be added.

[Pressure Heat Treatment Method with Inert Gas] The above starting materials are heat-treated at a temperature of 350 to 1000 ° C. in a closed pressurized inert gas atmosphere having a pressure of 2 kgf / cm ² or more. As the inert gas, a rare gas such as argon or helium,
Nitrogen or a mixed gas of these can be used. Here, the pressure means the pressure (total pressure) at room temperature of the pressurized atmosphere.

In the heat treatment, for example, a starting material is charged in a closed container (eg, a closed tube), and air in the container is replaced with an inert gas used as an atmosphere in order to purge oxygen in the container. Alternatively, after degassing in vacuum, pressurize the container with inert gas to a pressure of 2 kgf / cm ² or more and seal it.
It can be carried out by raising the temperature to a predetermined temperature within the range of 1000 ° C. and maintaining this temperature.

The inert gas atmosphere may contain a small amount of other gas in addition to the inert gas. However, if the oxygen partial pressure in the atmosphere exceeds 0.2 kgf / cm ² (150 Torr), not only the resistance will not be lowered, but also grain growth will be remarkable, so mixing oxygen is more than the oxygen partial pressure of 0.2 kgf / cm ² . Suppress it to be low. The oxygen partial pressure is preferably 0.02 kgf / cm ² (15 Torr) or less in order to enhance the effects of low resistance and atomization.

The pressurizing condition of the heat treatment is that the atmospheric pressure is 2
It should be at least kgf / cm ² . It is known that firing in an inert atmosphere accelerates grain growth of the powder as compared with firing in an atmosphere (oxygen-containing atmosphere), but according to the present invention, the atmosphere pressure is set to 2 kgf / cm 2. It was found that when the pressure atmosphere was ² or more, the grain growth during the heat treatment was suppressed even in the inert gas atmosphere. Moreover, the pressurized atmosphere makes the atmosphere in the system uniform, and the resistance can be relatively uniformly lowered from the upper portion (surface portion) of the starting material charged in the firing furnace to the lower portion. . Therefore, unlike the conventional case, it is not necessary to spread the starting material thinly and fire it, and a large amount of starting material can be processed.

When the pressure is 2 kgf / cm ² or less, atomization is difficult, and the upper and lower parts of the raw material have non-uniform characteristics, and there is almost no effect of lowering the resistance. It is preferable that the pressure of the atmosphere is in the range of 5 to 60 kgf / cm ² because the above effect is further enhanced. When the pressure exceeds 60 kgf / cm ² , the improvement of the effect is hardly recognized, and the cost required for pressurization increases, so it is useless to add more pressure in practice.

The temperature of the heat treatment may be in the range of 350 to 1000 ° C, but is preferably in the range of 400 to 800 ° C. If the treatment temperature is lower than 350 ° C, even if atomization is achieved, the resistance cannot be lowered. On the other hand, the processing temperature is 10
If it exceeds 00 ° C., grains grow to 0.1 μm or more during the heat treatment, which makes it difficult to obtain low resistance and atomization.
The heat treatment time depends on the relationship between the charged and charged amount of the raw material and the temperature, but it is sufficient if the uniform heat treatment of the raw material is achieved, and it is generally within the range of 1 to 4 hours. There is no particular limitation on the temperature raising and lowering times.

[0034]

EXAMPLES Next, the present invention will be described based on examples, but the present invention is not limited to the examples.

[Preparation of Starting Material] Starting materials are as follows.
The water-containing mixed hydroxides prepared by the coprecipitation method according to the methods described in (A) to (C) are either undried as shown in Table 1 or dried or dehydrated by heat treatment.

(A) A raw material of ITO powder (hydrous hydroxide) InC1 ₃ aqueous solution (containing 600 g of In metal) 1.8 L and a mixed aqueous solution of 0.2 L of SnC1 ₄ aqueous solution (containing 30 g of Sn metal) were mixed with NH ₄ HCO
During ₃ 3000 g / 12 L solution of it was added dropwise with stirring under heating at 70 ° C., in the final pH8 to precipitate In-Sn coprecipitated hydroxide. Next, after allowing the precipitate to settle by allowing it to stand still, the supernatant liquid is removed, and ion-exchanged water is added to perform the operations of standing and settling and the removal of the supernatant liquid 6 times (the amount of water added is 10 L each time). By repeating the above procedure, the precipitate was sufficiently washed with water, and then the precipitate was filtered by suction filtration to obtain a precipitate of hydrous hydroxide.

(B) ATO powder raw material (hydrous hydroxide) SnC1 ₄ aqueous solution (containing 600 g of Sn metal) 1.8 L and a mixed aqueous solution of 0.2 L of SbC1 ₃ aqueous solution (containing 80 g of Sb metal) were mixed with NaOH 90
In a 0 g / 12 L aqueous solution, the mixture was added dropwise with stirring under heating at 90 ° C. to a final pH of 7 to precipitate Sn—Sb coprecipitated hydroxide. Then, the precipitate was washed and filtered in the same manner as in the above (A) to obtain a precipitate of hydrous hydroxide.

[0038] (C) AZO powder material (the aqueous hydroxide) ZnC1 ₂ 1360g (Zn metal 652.3g containing) and AlC1 ₃ · 6H ₂ O 1
10 L of 35 ° C aqueous solution in which 25 g (containing 14 g of Al metal) was dissolved
An aqueous solution of Na ₂ CO ₃ 1250 g / 10 L was added dropwise with stirring to the final pH of 7 to precipitate an Al—Zn coprecipitated hydroxide. Then, the precipitate was washed and filtered in the same manner as in the above (A) to obtain a precipitate of hydrous hydroxide.

[0039]

[Table 1]

[Pressure heat treatment] The pressure heat treatment has an inner diameter of 70 m.
In a closed pressure tube furnace using Incoloy 800 tube of m, 700 mm in length, 250 g of raw material was placed in a 250 mm long half-quartz quartz boat and charged with the inert gas used. After purging with oxygen, pressurize to the specified pressure, then 8 ℃ / mi
It was performed by raising the temperature to a predetermined temperature with n and maintaining the temperature for 3 hours. Table 2 shows the processing conditions (atmosphere, pressure, temperature).

The average primary particle diameter of the conductive oxide powder obtained by the heat treatment was calculated as a (μ) from the measured value of the specific surface area (BET).
m) = 6 / (ρ × B) [a: average particle size, ρ: true specific gravity,
B: specific surface area (m ² / g)] Thus, the particle size obtained from the specific surface area is almost the same as the particle size directly observed by the transmission electron microscope. The specific surface area by the BET method was measured using a Betasorb automatic surface area meter Model 4200 manufactured by Microtrac.

The volume resistivity of the conductive oxide powder (50
(kgf / cm ² green compact) was determined using a Loresta AP powder resistance system manufactured by Mitsubishi Yuka. Measurement of volume resistivity is performed separately for samples taken from the top and bottom of the boat,
The average value is displayed. The results of these tests are also shown in Table 2.

[0043]

[Table 2]

[0044]

As can be seen from the results shown in Table 2, all of Examples 1 to 8 of the present invention, which are Examples, formed conductive oxide powder having extremely fine and low resistance. Further, the volume resistivity was uniform in the upper part and the lower part. On the other hand, in Comparative Examples 1 to 3 which are heat-treated under an inert atmosphere at normal pressure, the volume resistivity differs between the upper portion and the lower portion by 1 to 2 digits, and the volume resistivity is not uniform, and the volume resistivity itself is also the It was higher than the result in the example. Further, the average particle size was also larger than that of the examples of the present invention.

According to the method of the present invention, the average primary particle size is 0.
When the particle size is 1 μm or less, it is possible to manufacture a fine-particle / low-resistance conductive oxide powder having a very low volume resistivity, uniform characteristics and little variation with good mass productivity. In particular, when the ITO powder is produced by the method of the present invention, as can be seen from the results in Table 2, low resistance ultrafine powder having an average primary particle diameter of 0.05 μm or less and a volume resistivity of 0.1 Ω · cm or less is used. Therefore, it becomes possible to mass-produce it. As a result, the use of ITO powder for transparent electrodes, surface heating elements, etc. can be expanded, including the prevention of electrification of glass and films and the prevention of dust adhesion by applying a dispersion ink using this powder to a substrate. Therefore, the present invention contributes to expanding the use of various conductive oxide powders such as ITO powder.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-46925 (JP, A) JP-A 61-86421 (JP, A) JP-A 1-100023 (JP, A) JP-A 2- 120374 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01B 13/00 503 C01G 19/02 H01B 5/00

Claims (2)

(57) [Claims] 1. A hydrous mixed hydroxide obtained by coprecipitation by the reaction of an aqueous solution containing two or more transition metal ions and an alkaline aqueous solution, and (2) a mixture obtained by heating and drying the hydrous mixed hydroxide. Hydroxide and / or heat-dehydrated mixed oxide,
(3) selected from the group consisting of conductive oxide powder obtained by a known method, and (4) hydrous hydroxide of two or more transition metals, mixed powder of hydroxide and / or oxide, Starting materials composed of mixed hydroxides and / or oxides of two or more transition metals (provided that the starting materials for oxides have an average primary particle size of
A powder having a particle diameter of 0.1 μm or less) is heat-treated at a temperature of 350 to 1000 ° C. in a closed pressurized inert gas atmosphere having a pressure of 2 kgf / cm ² or more. 2. The transition metal is Sn and In, Sb and Sn, or Al, Sn, In, Fe, Ga, Co, Si, Ge, Sb or Pb.
The method for producing a conductive powder according to claim 1, which is a combination with Zn.