JPS6241171B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing conductive zinc oxide. Conductive zinc oxide is used in the production of various types of recording paper for the information industry such as electrostatic recording paper, current-carrying thermal recording paper, and discharge destruction recording paper, as well as as an antistatic agent for plastics, etc., and is also used in the paint industry, It is also used in the resin industry, etc., and since it is originally white, it is useful because it can be colored with other colorants, and so on. It is known that adding aluminum oxide to non-conductive zinc oxide increases its conductivity. However, simply mixing zinc oxide and aluminum oxide and subjecting the mixture to heat treatment does not allow aluminum oxide to penetrate into the lattice of zinc oxide, and therefore, it is not possible to increase the electrical conductivity of zinc oxide. Furthermore, when used in paints, etc., only those with inferior pigment properties can be obtained. On the other hand, as mentioned above, when using conductive zinc oxide for recording paper for the information industry such as facsimiles,
It is necessary to apply conductive zinc oxide in the form of paint, and the properties of the paint surface are also required. Therefore, in order to make conductive zinc oxide into fine particles, when it is made into fine particles using a pulverizer such as a ball mill or sand mill, it must be easily dispersed in a dispersion medium, and no mechanochemical changes occur at that time, and the conductivity associated with this must be Zinc oxide itself is required to have little change in color, not to settle during the process from forming the paint to the coating process, and to be able to be easily redispersed even when settling occurs. As conductive zinc oxide, HC-238 is commercially available from New Jersey Zinc Co., Ltd. in the United States, and it has an average particle size of 1.1μ, a pale yellow color, and a volume resistivity of about 300Ω・cm, and it still needs improvement. desired. In the production of electrostatic recording paper, sedimentation of HC-238 is observed after the paint is prepared and before the coating process, and the pigment is deposited at the bottom of the paint layer, and a powerful dispersion process is required to redisperse it. It has the disadvantage of requiring In consideration of the various properties required of conductive zinc oxide as described above, we completed the present invention described below as a result of intensive research to obtain even more excellent conductive zinc oxide. That is, the present invention contains 100 parts by weight of zinc oxide, and
5 to 100 parts by weight of an oxide of at least one metal selected from the group consisting of aluminum, titanium, and tin or a salt that decomposes at high temperature to form an oxide (hereinafter referred to as an activator); in an aqueous system in the presence of one or more compounds selected from the group consisting of ammonium carbonate, ammonium bicarbonate, ammonium nitrate, ammonium sulfate and urea, followed by dehydration and the resulting product in a reducing atmosphere. An object of the present invention is to provide a method for producing conductive zinc oxide, which comprises firing. As the raw material zinc oxide used in the present invention, zinc oxide powder produced by the so-called French method or American method can be used. In addition to aluminum oxide, titanium oxide, and tin oxide, salts that can be decomposed at high temperatures to form oxides of these can also be used as activators that can be used in the present invention. Such salts include aluminum formate;
Aluminum acetate, aluminum chloride, aluminum sulfate, aluminum nitrate, stannous chloride, tin chloride, stannous nitrate, tin nitrate, metastannic acid, stannous sulfate, tin sulfate, metatitanic acid, sulfuric acid There are titanyl and titanium chloride. These activators are used in an amount of 0.5 to 20 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of zinc oxide. If it is less than 0.5 parts by weight, zinc oxide that is sufficiently conductive cannot be produced, and if it is used more than 20 parts by weight, it will hardly contribute to improving conductivity and may increase coloration in some cases. This is not preferable because it may cause problems and may have an adverse effect on pigment properties. It is believed that ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium nitrate, ammonium sulfate and urea used in the present invention act as corrosive agents for zinc oxide crystals, as described below. These corrosive agents are preferably used in an amount of 5 to 100 parts by weight, preferably 20 to 60 parts by weight, per 100 parts by weight of zinc oxide. If it is less than 5 parts by weight, it is insufficient as a corrosive agent for zinc oxide crystals as described below, and furthermore, it is insufficient for the activator to penetrate into the zinc oxide crystals and achieve uniform distribution. Moreover, even if more than 100 parts by weight is used, no further effect will be obtained and it will only be wasted. The above-mentioned ammonium carbonate can also be formed in situ by reacting ammonia and carbon dioxide gas in water when carrying out the method of the present invention. In carrying out the method of the present invention, there are no strict restrictions on the order of addition of zinc oxide, the activator, and the corrosive agent. However, in general, an aqueous dispersion or solution of the above corrosive agent is prepared, non-conductive zinc oxide powder is added thereto and thoroughly dispersed, and then an activator is added and thoroughly stirred. Alternatively, the corrosive agent is dispersed or dissolved in an aqueous solution of the activator, and finally the non-conductive zinc oxide powder is added. Treatment with the aqueous dispersion prepared as described above can generally be carried out at room temperature to 100°C;
°C is preferred. However, if urea is used, the temperature will be 80℃.
is preferred. Generally, a treatment time of 30 to 90 minutes is sufficient, but as described later, the needle-like or plate-like crystals (hexagonal crystals) of non-conductive zinc oxide become amorphous crystals, and the activator is sufficiently oxidized. It is sufficient if it is distributed in the lattice of the zinc crystal. As mentioned above, after the aqueous treatment, the resulting product is dehydrated, dried or precalcined if necessary, and then calcined in a reducing atmosphere. A hydrogen atmosphere can be used as the reducing atmosphere. This〓〓〓〓
Since this is well known to those skilled in the art, we do not think it is necessary to explain it in detail. Further, firing is usually carried out at a temperature of 600 to 1000°C for 15 minutes to 1 hour. We believe that this firing is also fully obvious to those skilled in the art. Although the mechanism by which highly conductive zinc oxide is obtained by the method of the present invention is not clear, it is thought to be as follows. The mechanism by which oxides of aluminum, tin, and titanium as activators impart conductivity to nonconductive zinc oxide is a well-known fact and does not require any particular explanation. The key to obtaining conductive zinc oxide is how to easily and sufficiently distribute the above-mentioned activator in the non-conductive zinc oxide crystal lattice. Non-conductive zinc oxide produced by French or American methods is usually 0.2-0.7μ needle-shaped or plate-shaped crystals.
X-ray diffraction gives a hexagonal diffraction pattern. However, when the corrosive agent and non-conductive zinc oxide used in the present invention are treated in the absence of an activator, the resulting zinc oxide does not exhibit a hexagonal system according to X-ray diffraction and becomes amorphous. Therefore, it is thought that this zinc oxide becomes a porous and very fine powder and has a high surface activity. When an activator is mixed here, these permeate into the zinc oxide and form a conductive zinc oxide precursor. If this precursor dispersion is excessively dehydrated, then dried or pre-calcined if necessary, and then calcined according to the present invention, the desired electrically conductive zinc oxide powder can be obtained. According to X-ray diffraction, the electrically conductive zinc oxide powder obtained in this way has an original size of 0.1 to 0.8μ.
It is a hexagonal zinc oxide, and it can be seen that the activator penetrates evenly into the zinc oxide crystal. This material is resistant to mechanochemical changes,
It is white and has excellent pigment properties. The present invention will be explained below with reference to Examples. The volume resistivity value of the conductive zinc oxide in the example was measured by placing 10 g of the sample in a Teflon-treated cylinder with an inner diameter of 25 mm, applying a pressure of 100 Kg/cm ² , and using a tester 3223 manufactured by Yokogawa Electric Corporation (Ω cm ). The average particle diameter was measured using the specific surface area measuring device SS manufactured by Shimadzu Corporation.
-Measured using 100 type (air permeation type) (μ). Conductive zinc oxide 20 as one of the measurements of paint properties
g was placed in 300 c.c. of water and dispersed using a homogenizer. The resulting dispersion was placed in a sedimentation tube, and the degree of sedimentation after 24 hours was determined from the volume of the clear liquid at the top (cm ³ ). Example 1 Reagent 30 g of primary ammonium carbonate (Wako Pure Chemical Industries, Ltd.) was dissolved in 500 c.c. of water, and separately, 5 g of aluminum sulfate [Al ₂ (SO ₄ ) _{3.18H 2} O] was dissolved in 50 cc. of water. The solution was poured into the above ammonium carbonate solution. Separately, this solution was placed in a dispersion prepared by dispersing 100 g of French zinc white in 200 c.c. of water, heated to 60°C,
After stirring and washing with water for 1 hour, the cake was dried and then baked at 800° C. for 60 minutes in a hydrogen atmosphere. In this way, highly conductive zinc oxide was obtained. The obtained powder was white in color, and its average particle size, volume resistivity, and dispersibility data are shown in Table 1. Example 2 Industrial ammonium bicarbonate (manufactured by Nissan Chemical) 70g
was dispersed in 500 c.c. of water, and separately, a solution of 7 g of stannous chloride (SnCl ₂ .2H ₂ O) dissolved in 50 c.c. of water was added to the above dispersion of ammonium bicarbonate. This liquid was added to a dispersion prepared by dispersing 100 g of American zinc white in 300 c.c. of water, heated and stirred at 40°C for 1 hour,
After washing with water, dry, crush and 900 min in hydrogen atmosphere.
Baked at ℃ for 60 minutes. In this way, highly conductive zinc oxide was obtained. Table 1 shows the average particle diameter, volume resistivity, and dispersibility data of the conductive zinc oxide obtained. Example 3 100g of French method zinc oxide was dispersed in 200c.c. of water,
Separately, a solution was prepared by dissolving 100 g of urea in 500 c.c. of water, and the two were mixed and then heated to 80°C. A solution of 4 g of aluminum chloride (AlCl ₃ .6H ₂ O) dissolved in 100 cc of water was added to this, and a reaction was carried out at 80° C. for 1 hour. After washing with water, it was dried and fired at 850°C in a hydrogen atmosphere. In this way, zinc oxide with excellent conductivity was obtained. The obtained powder was white, and its average particle size, volume resistivity, and dispersibility data are shown in Table 1. Example 4 100 g of French method zinc oxide was dispersed in 300 c.c. of water, and a solution of 100 g of ammonium carbonate dispersed in 500 c.c. of water was added thereto, heated to 60°C, and aluminum formate was added to the reaction solution. 150g of the solution (approximately 20%) was added, and the reaction was carried out at 60°C for 1 hour. After the reaction solution was excessively dehydrated, it was calcined at 800°C in a hydrogen stream. The obtained powder is white in color, and its average particle size and size are
Data on product resistance and dispersibility are shown in Table 1. Example 5 100 g of French zinc white was dispersed in 500 c.c. of 2% ammonia aqueous solution, and 5 g of aluminum sulfate was added to this.
A solution prepared by dissolving 50 cc of water was added thereto, and then CO ₂ gas was blown in at a rate of 0.2/min for 1 hour to carry out a reaction. The reaction solution was filtered, dried at 110°C, and calcined at 800°C for 60 minutes in a hydrogen atmosphere. The obtained powder was white, and its average particle size, volume resistivity, and dispersibility data are shown in Table 1. Example 6 100 g of zinc oxide and 100 g of ammonium nitrate were dispersed in 50 c.c. of water, and 5 g of aluminum nitrate was dispersed.
It was mixed with a solution of 30 c.c. in water, heated to 80°C, and reacted for 3 hours. After the reaction solution was filtered, it was calcined at 500°C. The obtained fired product was heated at 800℃ in a hydrogen atmosphere.
was fired. The obtained powder was white, and its average particle size, volume resistivity, and dispersibility data are shown in Table 1. Example 7 100 g of French method zinc oxide was dispersed in 300 c.c. of water. Separately, a solution prepared by dispersing 80 g of ammonium carbonate in 500 c.c. of water was added thereto, and the mixed solution was heated to 60°C. 30 g of titanium trichloride solution (20% by weight) was added to this reaction solution, and the reaction was carried out at 60° C. for 1 hour. After excessive dehydration of the reaction solution, it was heated at 850℃ in a hydrogen stream.
Bake for 50 minutes. The obtained powder was white, and its average particle size, volume resistivity, and dispersibility data are shown in Table 1.

[Table] 〓〓〓〓

Claims (1)

[Claims] 1. 100 parts by weight of zinc oxide and 0.5 to 20 parts by weight of an oxide of at least one metal selected from the group consisting of aluminum, titanium and tin, or decomposed at high temperature to form an oxide. The salt is treated in an aqueous system in the presence of 5 to 100 parts by weight of one or more compounds selected from the group consisting of ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium nitrate, ammonium sulfate and urea, and then dehydrated to obtain a A method for producing conductive zinc oxide, which comprises firing the resulting product in a reducing atmosphere. 2. Ammonium carbonate is formed in situ by reacting ammonia and carbon dioxide gas in water,
The method according to claim 1, wherein the method is present in an aqueous system. 3. The method according to claim 1 or 2, wherein the aqueous treatment is carried out at room temperature to 100°C. 4. The method according to claim 1 or 3, wherein the product is pulverized after the pre-calcination. 5. The method according to claim 1, wherein the firing is carried out at a temperature of 600 to 1000°C. 6 Salts that decompose at high temperatures to form oxides include aluminum formate, aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum sulfate, aluminum nitrate, stannous chloride, tin chloride, stannous nitrate, and di nitrate. 2. The method according to claim 1, wherein the material is tin, metastannic acid, stannous sulfate, stannic sulfate, metatitanic acid, titanyl sulfate or titanium chloride. 7. The method according to claim 1 or 6, wherein the reducing atmosphere is a hydrogen-containing atmosphere.