JP2583536B2 - Method for producing conductive zinc oxide fine powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention not only acts as a conductivity-imparting component, but also has an average particle diameter of 0.10 μm or less, can impart transparency to a dried film, and can be dispersed. The present invention relates to a method for producing a conductive zinc oxide fine powder having excellent properties.

[Conventional technology] Conductive zinc oxide is used in various information industry recording papers such as electrostatic recording papers, current-sensitive recording papers, discharge breakdown recording papers, electrophotographic papers, paints, adhesives, inks, and various resins. It has a wide range of uses as conductive pigments and antistatic components, and further as a developer for electrophotography, and especially has the characteristic that this powder is white and can be easily colored by other colorants. It is widely used industrially.

By the way, conductive zinc oxide is obtained by activating non-conductive zinc oxide with aluminum oxide or the like, but a good conductive material can be obtained simply by mixing non-conductive zinc oxide and aluminum oxide and heating. The conductivity is not always limited, and the conductivity varies considerably depending on the processing conditions. Therefore, various proposals have been made for the purpose of improving the conductivity. For example, Japanese Patent Publication Nos. 55-19896 and 55-19897 disclose a method of heat-treating a non-conductive zinc oxide and an aluminum compound in the presence of fixed carbon. Discloses a method in which zinc oxide is wet-processed together with an organoaluminum compound or the like, dried, pulverized, and finally fired in a non-oxidizing atmosphere.
Any of these methods is evaluated as an excellent method from the original purpose of imparting conductivity, but is not suitable as a material for forming a transparent conductive film due to a large particle diameter. JP-A-56-69266 discloses a water-soluble zinc salt and A
How l ₂ O ₃ or coprecipitated with the alkali carbonate from water-soluble metal salt serving as a generation source of SnO ₂ or the like, and then to produce a fine powder of electrically conductive zinc oxide by firing in a non-oxidizing atmosphere Is disclosed. However, this method not only requires complicated and time-consuming removal of C1 ions and the like when using a salt such as ZnCl ₂ , but also has a particle size of at most about 1 to 1.3 μm, which is a characteristic required for a transparent conductive film. It cannot be said to be satisfied.

Under such circumstances, the present applicant has been conducting research for the purpose of establishing a method for producing a conductive zinc oxide fine powder having a particle size composition that satisfies characteristics for a transparent conductive film. The method described in JP-A-58-161923 was previously developed. In this method, zinc oxide is treated with an aqueous dispersion in the presence of an aluminum salt that acts as an activator and ammonium carbonate that acts as an erosion agent (disintegrant), dehydrated, dried, and then calcined at 600 to 1000 ° C. According to this method, the zinc oxide is made porous and fine by the action of the zinc oxide disintegrant, and the mixing with the activator is performed densely and uniformly. In comparison, it is possible to obtain particles having a considerably small particle size. However, even with this method, the particle size of the conductive zinc oxide obtained is limited to about 0.15 μm in specific surface area diameter required by the BET method, and cannot be said to completely satisfy the properties for a transparent conductive film. .

That is, as means for obtaining transparency in a pigment-filled system, it is necessary to make the particle size of the pigment smaller than visible light, or to minimize the difference in the refractive index from the resin that is the vehicle component in paints and the like. The purpose of imparting transparency is achieved by setting the particle diameter of the pigment itself to 0.10 μm or less in terms of the specific surface area (hereinafter, a value determined by the BET method unless otherwise specified) as a characteristic of the pigment itself. But,
At present, conductive zinc oxide having such a fine particle size composition has not been obtained.

From such a place, as the conductive powder to be transparency requirements, it generally used SnO ₂ Keishirubeden powder or In ₂ O ₃ Keishirubeden powder which can be obtained as a fine powder of the following specific surface area diameter 0.10μm However, both are very expensive and have problems in economy and versatility.Moreover, the former is not only bluish, but also becomes more colored by the action of ultraviolet rays when mixed in the coating film. There is a problem that it is easy.

[Problems to be Solved by the Invention] The present invention has been made in view of such circumstances, and its object is to use a zinc oxide that can be obtained industrially at a low cost as a main raw material to obtain a fine and stable material. An object of the present invention is to provide a method for producing a conductive zinc oxide fine powder which is excellent in conductivity and dispersibility and can impart transparency to a coating film.

[Means for Solving the Problems] The structure of the production method according to the present invention which can achieve the above object is as follows: [I] non-conductive zinc oxide: 100 parts by weight, [II] water solubility or water dispersion Aluminum compound: 0.1 to 10 parts by weight in terms of aluminum oxide, [III] one or more compounds selected from the group consisting of ammonium carbonate, ammonium bicarbonate, nitric acid, ammonium and urea: 5 to 100 parts by weight Is stirred in an aqueous dispersion in the presence of an oxide fine powder and / or a silicate fine powder having a specific surface area of 0.10 μm or less, and after dehydration, heat-treated at a temperature of 600 ° C. or less in a non-oxidizing atmosphere. It has a gist where it does.

[Action] As disclosed in the above-mentioned JP-A-58-161923, [I] zinc oxide produced by the French method or the American method is converted into [II] water-soluble or water-soluble Coexistence of one or more of a dispersible (hereinafter sometimes simply referred to as water-soluble) aluminum compound and [III] an erosion agent (disintegrant) selected from the group consisting of ammonium carbonate, ammonium bicarbonate, ammonium nitrate and urea The method is based on a method in which a stirring treatment is carried out in an aqueous dispersion system, and a heat treatment is carried out after dehydration. This method will be described in more detail as follows.

That is, the particle size composition of the non-conductive zinc oxide [I] obtained by the French method or the like is generally about 0.2 to 0.8 μm.
According to X-ray diffraction, a hexagonal diffraction pattern is shown. This non-conductive zinc oxide [I] is converted to a disintegrant [II] such as ammonium carbonate.
When treated with an aqueous dispersion together with [I], the hexagonal crystal structure is broken and fine particles having a specific surface area of about 0.01 μm or less are obtained. The particulate zinc oxide no longer exhibits a hexagonal diameter diffraction characteristic and becomes amorphous. This is very fine and has a high surface activity. If an aluminum compound [II] is coexistent as a conductive activator in this existing system, these adhere to the particle surface, and in the subsequent drying or firing step, It is considered that part of the aluminum is taken into the crystal lattice of zinc oxide, and as a whole becomes conductive.

Examples of the disintegrant [III] used for the above purpose include ammonium salts selected from ammonium carbonate, ammonium bicarbonate, and ammonium nitrate, and urea that generates ammonia when heated. Since it is removed in the drying or heat treatment process, it hardly affects the conductivity and the like of the final product.
The addition amount of the disintegrant [III] for effectively achieving the above-mentioned addition purpose is 5 to 100 parts by weight, more preferably 10 to 50 parts by weight, and preferably less than 5 parts by weight based on 100 parts by weight of zinc oxide. In this case, the crystal disintegration is insufficient and the purpose of miniaturization is not achieved,
Further, since their crystal disintegration effect is saturated at 100 parts by weight, further addition is useless.

Incidentally, among the above disintegrants, ammonium carbonate and ammonium bicarbonate can also be generated in situ by blowing ammonia and carbon dioxide gas into the aqueous dispersion.

The water-soluble aluminum compound [II] used as the conductive activator is for imparting conductivity to the zinc oxide as described above, and can be uniformly distributed in fine zinc oxide in an aqueous system. For example, water-soluble or water-dispersible ones such as formate, acetate, halide, hydroxide, sulfate and nitrate are selectively used. And among these water-soluble aluminum compounds, except for the hydroxide,
Neutralized by a part of the ammonium carbonate or the like added into the treatment system, generates hydroxide and is uniformly mixed into the zinc oxide slurry, and when hydroxide is used, itself is fine. It is uniformly distributed as particulate matter in the aqueous system, becomes aluminum oxide in the subsequent drying and firing steps, and is evenly distributed in the zinc oxide fine powder to give conductivity. In order to impart satisfactory conductivity to the final product, the aluminum compound must be converted to aluminum oxide based on 100 parts by weight of zinc oxide.
0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight must be added.
On the other hand, even if it exceeds 10 parts by weight, the conductivity is not further improved,
In some cases, the final calcined powder may be colored or adversely affect its properties as a pigment.

By the way, in the method disclosed in the above-mentioned publication, three of the above [I] non-conductive zinc oxide, [II] a water-dispersible aluminum compound (activator) and [III] aluminum carbonate are mixed with water. Normal temperature to about 100 ° C in the dispersion system (However, when urea is used as a disintegrant, it is 80 to 100 ° C to promote decomposition.
The mixture is heated for about 30 minutes to 90 minutes, dehydrated, dried, and calcined at about 600 to 1000 ° C. in a non-oxidizing atmosphere to obtain conductive zinc oxide fine powder. As a result of the effective addition effect, a finer powder can be obtained as compared with the conventional conductive zinc oxide powder.

However, after further research, the zinc oxide refined by the disintegrant was reagglomerated or sintered in the final drying or firing step, and the particle size of the fired material was used as the raw material after all. It returned to the vicinity of the particle size (0.2 to 0.8 μm) of the non-conductive zinc oxide powder, and it was not possible to obtain a particle having a particle size composition capable of exhibiting transparency.

That is, since the particle size of the powder that can ensure transparency is about 0.10 μm or less, which is smaller than the wavelength of visible light, as described above, in order to satisfy such requirements, aggregation or sintering during drying and firing is prevented. There is a need to.

Therefore, as a result of further research from the above viewpoint,
When the three components of [I] non-conductive zinc oxide, [II] activator (water-soluble aluminum compound) and [III] disintegrant are stirred in an aqueous dispersion, the specific surface area of the aqueous dispersion is 0.10. μ
m or less, and the heat treatment temperature after dehydration is kept at 600 ° C. or less, agglomeration of conductive zinc oxide fine particles during dehydration / drying or heat treatment. Was prevented, and it became clear that the particles were very fine having a size of 0.10 μm or less.

The reason why the aggregation of zinc oxide particles is prevented by the coexistence of the oxide fine powder and / or the silicate fine powder has not been completely elucidated, but the oxide fine powder and / or the silicate fine powder cannot be oxidized. It is presumed that the intercalation between the zinc particles suppresses the cohesion and adhesion between the zinc oxide particles, and that the grain growth is suppressed in combination with the effect of suppressing the heat treatment temperature to 600 ° C. or lower. Specific examples of the oxide fine powder and / or silicate fine powder exhibiting such an aggregation preventing effect include oxide fine powders of silica, alumina, titania and the like, and various silicate fine powders, such as colloidal silica and alumina sol. The smaller the particle size is, the more excellent the aggregation inhibiting effect is. The volume resistivity of the inorganic fine powder itself is 10 ¹⁰ Ωcm or more, which does not seem to have a good effect on conductivity, and at a temperature of 600 ° C or less, it reacts with zinc oxide to increase conductivity. They do not have the effect of increasing the concentration, and they exclusively function as anti-agglomeration agents. The effect of the addition of the oxide fine powder and / or the silicate fine powder is extremely small if the particle size is very small like colloidal silica, so that a clear lower limit cannot be determined. However, based on commercially available colloidal silica, the purpose can be achieved by adding at least 0.05 part by weight, more preferably at least 0.1 part by weight, based on 100 parts by weight of zinc oxide. On the other hand, if the added amount of the oxide fine powder and / or the silicate fine powder is too large, the conductivity is adversely affected. Therefore, the added amount is not more than 10 parts by weight, more preferably not more than 5 parts by weight, per 100 parts by weight of zinc oxide. It should be kept below parts by weight.

Even if an appropriate amount of oxide fine powder and / or silicate fine powder is added, the heat treatment temperature is 600 ° C.
If the temperature exceeds 600 ° C., secondary agglomeration occurs due to the fusion of the zinc oxide fine particles and the particles become coarse.
It must be done below. Although the lower limit of the heat treatment temperature is not particularly defined, it is more than 200 ° C. in order to achieve the original purpose of complete drying or baking, and it is more certain that the temperature is more than 300 ° C.
° C or higher.

Another important role of the heat treatment is to exhibit conductivity by the addition of an activator. For this purpose, the heat treatment is performed in a non-oxidizing atmosphere (specifically, hydrogen, nitrogen, ammonia, etc.). Gas atmosphere)
Since the heat treatment was performed in an oxidizing atmosphere, even if an appropriate amount of an activator was added, conductivity could not be given.

Moreover, zinc oxide originally has an absorption band for light around 350 to 400 nm, which is an ultraviolet region, but the conductive zinc oxide of the present invention is not exceptional and has an absorption band in the ultraviolet region, It also has a function as an ultraviolet shielding material.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples.

[Example] A predetermined amount of a disintegrant was dissolved in 500 cc of water according to the raw material mixing amount shown in Table 1 below, and a solution obtained by dissolving an activator in 50 cc of water was added to the above aqueous solution containing a disintegrant and mixed I do. This mixture is poured into a 200 cc water dispersion of 100 g of separately prepared French method zinc flower (average specific surface area diameter: 0.3 μm), and the temperature is 60 to 90 ° C.
Then, a predetermined amount of oxide fine powder and / or silicate fine powder is added, and the mixture is stirred at the same temperature for 1 hour. After completion of the stirring, the mixture was filtered, washed with water, dried, and then heat-treated in a hydrogen, nitrogen or ammonia gas atmosphere at 200 to 900 ° C. for 30 minutes to 2 hours to obtain a conductive zinc oxide fine powder.

Table 1 shows the treatment conditions and the like, and Table 2 shows the specific surface area and the like of the obtained zinc oxide fine powder.

The details of each compounding raw material shown in Table 1 and the methods for measuring the specific surface area and the like shown in Table 2 are as follows.

(Disintegrant) Ammonium bicarbonate: manufactured by Nissan Chemical Industries, industrial Ammonium carbonate: manufactured by Wako Pure Chemical Industries, reagent grade 1 Urea: manufactured by Yoneyama Pharmaceutical Co., Ltd., reagent grade 1 Ammonium nitrate: manufactured by Yoneyama Pharmaceutical Co., reagent grade 1 (activator ) aluminum sulfate: Yoneyama Yakuhin _{Ltd., Al 2 (SO 4) 3} · 18H 2 O aluminum chloride: Yoneyama Yakuhin Ltd., AlCl ₃ · 6H ₂ O Ammonium nitrate: Kishida chemical Co., _{Ltd., Al (NO 3) 3 ·} 9H 2 O (Inorganic fine powder) Aerosil 200: manufactured by Nippon Aerosil Co., Ltd., SiO ₂ specific surface area 200 m ² / g Specific surface area diameter 0.03 μm Aerosil P25: manufactured by Nippon Aerosil Co., Ltd., TiO ₂ specific surface area 50 m ² / g Specific surface area diameter 0.03 μm Aerosil C : Nippon Aerosil Co., Ltd., Al ₂ O ₃ specific surface area 100 m ² / g Specific surface area diameter 0.02 μm Nip seal VN-3: Nippon Silica Co., Ltd., SiO ₂ specific surface area 200 m ² / g Specific surface area diameter 0.015 μm Alumina sol-200: Nissan Chemical 10% average particle size 10mμ as Al ₂ O ₃ Snowtex-O: manufactured by Nissan Chemical Co., Ltd., 20% as SiO ₂ Particle size: 10-20 μm Raponide RD: manufactured by Nippon Silica Co., Ltd., synthetic sodium / magnesium / lithium silicate (SiO ₂ : 59.5%, MgO: 27.3%, Li ₂ O: 0.8%, Na ₂ O: 3.8%, structured water: 8.1%), specific surface area 270m ² / g specific surface area diameter about 0.01μm (volume resistivity) 10g of each sample powder after heat treatment, Teflon on the inner surface It was charged into a processed inner cylinder having an inner diameter of 25 mm, pressurized to 100 kg / cm ² (filling rate: 20%), and volume resistivity (Ωcm) was measured with a 3223 type tester manufactured by Yokogawa Electric Corporation.

(Specific surface area diameter) The specific surface area (Sg: m ² / g) of each test powder was measured using a quick area measuring device SA-1000 manufactured by Shibata Chemical Machinery Co., Ltd., and the measured value and the true specific gravity of the test powder were measured. (5.6 for σ: ZnO), the specific surface area diameter (d: μm) was determined by the following equation.

(Dispersibility) 20 g of the test powder was poured into 300 cc of water, uniformly dispersed by a homogenizer, placed in a 300 cc sedimentation tube, and allowed to stand. After 24 hours, the volume (cm ² ) of the upper clarified portion was measured. Then, the dispersibility when blended in a paint or the like was evaluated.

As is clear from Tables 1 and 2, the specific surface area diameters of the conductive zinc oxide powders obtained in Examples (Nos. 1 to 5, 8 to 20) satisfying the requirements of the present invention were all 0.10 μm. The following are very fine and the dispersibility is good.

In contrast, Experiments Nos. 6 and 7 were comparative examples in which the amount of the disintegrant or inorganic fine powder was appropriate, but the heat treatment conditions exceeded 600 ° C. Fusion occurs and the grains are coarsened. In addition, the tendency that coarsening progresses remarkably as the heat treatment temperature becomes higher clearly appears.

Experiment Nos. 21 and 22 are comparative examples in which the addition of the inorganic fine powder for preventing aggregation was omitted. In each case, the specific surface area diameter of the conductive zinc oxide fine powder exceeded the target value of 0.10 μm.

Reference Example The conductive zinc oxide fine powder (specific surface area diameter: 0.024 μm) obtained in the above Experiment No. 3 and a commercially available conductive zinc oxide powder (specific surface area diameter: 0.3 μm) were each combined with an acrylic resin film forming composition. (Mitsubishi Rayon product name: LR-472) in solid content conversion
40% by weight, mixed well with a homogenizer, and coated on a polyester film (film thickness: about
10 μm). When the surface resistance and the transparency of the coating after drying were compared, no difference was observed in the surface resistance at 10 ⁸ Ωcm, but the transparency was white and opaque when the commercial product was used. The sample using the conductive zinc oxide fine powder of Experiment No. 3 was transparent.

[Effects of the Invention] The present invention is constituted as described above, and is made fine by the action of a zinc oxide crystal disintegrant and coagulation prevention by specifying the heat treatment temperature in combination with the use of oxide fine powder and / or silicate fine powder. By the additive or synergistic effect of the effect, the specific surface area diameter can be very fine as 0.10 μm or less, which can provide transparency to the coating film, and can provide a conductive zinc oxide powder excellent in dispersibility at low cost. is what happened.

Therefore, this conductive zinc oxide fine powder can be used for clean rooms, windows of automobiles and vehicles, antistatic films such as cathode ray tubes, various electronic devices including computers, and CRTs.
It can be used as a conductivity-imparting component for the antistatic film formed on the surface of various touch panels such as displays, EL panels, and liquid crystal cells, as well as various information industry recording papers such as transparent electrostatic recording paper and magnetic tape. In addition, it can be used as a conductivity imparting material, an electrophotographic developing material, an antistatic material, and a component for imparting conductivity or antistatic property to paints, plastics, adhesives, inks, fibers, etc. By utilizing the effect, it can be mixed as a UV cut material in glass and transparent plastic materials for show windows, etc., or used as a surface coating agent for various resin molded products to suppress deterioration of the resin itself. .

Claims (7)

(57) [Claims] 1. [I] non-conductive zinc oxide: 100 parts by weight, [II] water-soluble or water-dispersible aluminum compound: 0.1 to 10 parts by weight in terms of aluminum oxide, [III] ammonium carbonate, ammonium bicarbonate, One or more compounds selected from the group consisting of ammonium nitrate and urea: 5 to 100 parts by weight of the three components having a specific surface area of 0.10 as measured by the BET method.
a conductive material characterized by being subjected to a stirring treatment with a water-acid system in the presence of an oxide fine powder and / or a silicate fine powder having a particle size of not more than μm, followed by heat treatment at a temperature of 600 ° C. or less in a non-oxidizing atmosphere after dehydration Method for producing fine zinc oxide powder. 2. The method according to claim 1, wherein the ammonium carbonate and / or ammonium bicarbonate is produced by blowing carbon dioxide gas into an aqueous dispersion containing ammonia. 3. The method according to claim 1, wherein the diffusion treatment in the aqueous dispersion system is performed at a temperature from room temperature to 100 ° C. 4. The method according to claim 1, wherein the aluminum compound is formate, acetate,
The method according to any one of claims 1 to 3, wherein the method is at least one selected from the group consisting of halides, hydroxides, sulfates, and nitrates. 5. The method according to claim 1, wherein said oxide fine powder and / or silicate fine powder is at least one fine powder selected from silica, alumina, titania and silicates. The production method according to any one of the above. 6. The method according to claim 1, wherein the oxide fine powder and / or the silicate fine powder is present in an amount of 0.05 to 10 parts by weight based on 100 parts by weight of zinc oxide. . 7. The production method according to claim 1, wherein the heat treatment is performed in an atmosphere of nitrogen, ammonia or hydrogen.