JPH03215311A - Electrically conductive silicic anhydride fine powder and its production - Google Patents

Abstract

PURPOSE:To improve electrical conductivity of fine powder of silicic anhydride by simultaneously adding a solution of SnCl4 and SbCl3 in hydrochloric acid and an alkali to heated suspension of silicic anhydride so as to maintain the suspension at a specific pH and coating silicic anhydride with SnO2 and Sb2O3. CONSTITUTION:A suspension of silicic anhydride having >= about 15nm average particle diameter is heated to about 50-100 deg.C, a solution of SnCl4 and SbCl3 in hydrochloric acid and an alkali such as ammonia water are simultaneously added to the suspension while maintaining the suspension at pH 3-9. 50-300wt.% based on silicic anhydride of a coating layer comprising 1-20wt.% Sb2O3 and the rest of SnO2 is formed, dried and then at about 500-700 deg.C to give electrically conductive fine powder of silicic anhydride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transparent and electrically conductive fine powder in which the surface of silicic anhydride is uniformly coated with antimony solid solution tin oxide.

The conductive fine powder of the present invention is of course useful for imparting good conductivity to transparent synthetic resin films or coatings without impairing their transparency, and is also useful in electrophotographic developers. It can also be used as a conductive agent.

11 To Shito Transparent conductive powders coated with conductive materials have been proposed.

In recent years, transparent conductive films and transparent conductive paints have been widely used in the production of display electrodes, protective films, antistatic films, transparent heating elements, etc.

Metal powder, carbon powder, or white conductive powder is widely used as an agent for imparting conductivity to films, paints, etc., but these powders themselves are gray or black, or have strong pay-hiding properties. Therefore, the transparency of the film or coating cannot be maintained. On the other hand, known transparent conductive powders include powders in which antimony is dissolved in tin oxide, and those obtained by coating the surface of a flat material such as mica or kaolinite with a conductive substance. However, conductive powder made by dissolving antimony in tin oxide has a fine average particle size of 0.1μ or less, so it is necessary to disperse it for a long time to uniformly disperse it in the resin.
Since tin oxide has a much higher refractive index than the refractive index of resin, it has drawbacks such as loss of transparency when the resin film becomes thicker.

In addition, conductive powder, which is obtained by coating the surface of a tabular material with a conductive material, has good transparency because it uses a material with a low refractive index as a base material, but has a large particle size of 1 to 100 μm.
Due to its openness, it is difficult to obtain a coating film with good surface smoothness when used in paints, and if dispersion is strengthened to obtain a smoother coating film, particle fragmentation occurs and conductivity deteriorates. There are drawbacks to this. As mentioned above, there is no conductive powder to date that satisfies both transparency and conductivity, and improvements are desired. As is well known, silicic anhydride has a refractive index of about 1.45, which is close to that of resin, and has a low specific gravity and high bulk density.

For this reason, it becomes almost transparent when dispersed in a vehicle,
In addition, the present inventors have discovered the characteristics of silicic anhydride, which is used in large quantities as a reinforcing agent for rubber, a filler for paints, and synthetic resins because it is effective in thickening and reinforcing vehicles with a small amount of filling. We focused on the idea of using silicic anhydride as a base material and coating the surface with a conductive material.

As a result, we used silicic anhydride with an average primary particle diameter of 15 nm or more as a base material, and suspended a dilute hydrochloric acid solution in which tin oxide and antimony chloride were dissolved in a heated suspension of silicic anhydride and an alkali. If they are added simultaneously while controlling the pH of the solution, the hydration reaction product of antimony and tin will be deposited uniformly on the surface of silicic anhydride, and when this product is washed with water, dried, and calcined, it retains the characteristics of silicic anhydride. It has been found that it has good dispersibility, good transparency in situ when dispersed in a resin, and good conductivity can be obtained with a smaller amount of filling compared to other cases based on spherical particles.

The present invention was developed based on the above findings, and
A solution of tin chloride and antimony chloride dissolved in a dilute hydrochloric acid solution sufficient to prevent hydrolysis and an alkali are heated at a temperature of 50 to
In a silicic anhydride suspension adjusted to 100°C, the suspension's p
By simultaneously adding H while maintaining it between 3 and 9,
A transparent conductive fine powder comprising a coating layer containing 1 to 20% by weight of antimony and the remainder consisting of tin oxide, which is treated with silicic anhydride at 50 to 300°C, and then subjected to heat treatment after filtration and water washing. and its manufacturing method.

The anhydrous silicic acid that can be used in the present invention is preferably one produced by a dry method in which silicon tetrachloride is reacted with hydrogen and oxygen or in air at around 1000°C, but hydrated silicic acid obtained by a wet method is preferable. An acid calcined at a temperature of 600 to 1000°C can also be used. The particle diameter of the silicic anhydride is suitably one in which the average primary particle diameter is 15 r++s or more; if it is less than 15 ns+, dispersion becomes difficult and conductivity and transparency are undesirably reduced. Further, although it is desirable that the purity is as high as possible, it can be used even if it contains a small amount of impurities.

In the present invention, in order to impart good electrical conductivity to silicic anhydride, it is necessary to form a uniform coating layer.

For this purpose, it is desirable to maintain the temperature of the aqueous suspension at 50 to 100°C, and the pH during treatment is preferably 3 to 9, preferably 6.
．． It is desirable to maintain the ratio between 5 and 8.5 and add them simultaneously.

As the alkali added to adjust the pH, aqueous ammonia, ammonia gas, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. can be used.

Regarding the antimony content of the coating layer, if it is less than 1%, good conductivity cannot be obtained, whereas if it is more than 20%, both transparency and conductivity become poor, which is not preferable.

Substantially, the remaining portion of the coating layer may be tin oxide, and may contain a small amount of impurities as long as the object of the present invention can be achieved.

The processing amount of the coating layer is 50~
300% by weight, preferably 150-250% by weight.

If the coating amount is less than the above range, good conductivity cannot be ensured, and if it is greater than the above range, a corresponding improvement in conductivity cannot be expected, and furthermore, transparency deteriorates, which is not preferable.

The anhydrous silicic acid coated with tin oxide and antimony oxide is then adjusted to a pH of 6 to 8 as necessary, filtered and washed to remove soluble salts, dried and then calcined at a temperature of 500 to 700°C. Conductive anhydrous silicon by pulverization! i Make it into a fine powder. If the firing temperature is less than 500°C, good conductivity cannot be obtained, and if it is more than 700°C, the conductivity deteriorates and sintering occurs, resulting in poor transparency, which is not preferable. The conductive silicic anhydride fine powder obtained by the present invention exhibits good conductivity with a powder resistance value of several ohms to several hundred ohms, and when added to resins or paints, it can be applied to the surface without impairing transparency. Resistance value 1
It is useful as a conductivity-imparting agent for transparent conductive films and transparent conductive paints because it can impart good conductivity of 0.05 to 10 Ω/Sq. Furthermore, since the conductive silicic anhydride fine powder is characterized by its fine particle size and high bulk density, it is also useful as a conductive agent used in electrophotographic developers.

The present invention will be explained in more detail with reference to Examples below, but the present invention is of course not limited to these.

K1 salmon example 1. A slurry in which silicic anhydride SO, having a specific surface area of 2/g and a primary particle diameter of 40 ns was dispersed in 1.5 L of water, was heated to 70°C. In this, tin chloride (Sn(1..5)
H20) 232.8f! and chloride 7 + mo'l (
S ba! 3)15. 0fI in 2N hydrochloric acid 35ml
and 25% ammonia water to bring the pH of the system to 7~7.
9 for 90 minutes to form a coating layer consisting of tin oxide and antimony oxide on the surface of the silicic anhydride particles. After filtering, washing and drying the product, 650℃
The coated powder according to the present invention was produced by calcination for 15 minutes. The resulting powder had a specific resistance of 27Ω·c1l.

Example 2. Tin chloride 232.8g, antimony chloride 56.81F,
Example 1 except that the 2N salt was changed to 1 to 70 all.
It was processed and manufactured in the same manner. The resulting powder had a specific resistance of 60Ω·c11.

Example 3. Tin chloride 232.81F, antimony chloride 56.8,
Add 75 wl of 2N hydrochloric acid and 7.5N of 25% ammonia water.
The treatment and production were carried out in the same manner as in Example 1, except that the sodium hydroxide solution was used. The resulting powder had a specific resistance of 210Ω·ell.

Example 4. A slurry prepared by dispersing 50 g of anhydrous silicon having a specific surface area of 130 m2/g and a primary particle size of 16 nm in 4 L of water was
It was heated to ℃. In this, 291 g of tin chloride and 18.8 g of antimony chloride were dissolved in 2N salt @90 ml, and 2
5% ammonia water was added over 120 minutes while maintaining the pH of the system at 7 to 9 to form a coating layer consisting of tin oxide and antimony oxide on the surface of the anhydrous silicon particles. The product is similar to Example 1. 6 at 650°C.
Baked for 0 minutes. As a result, the obtained powder has a specific resistance of 95
It had Ω・CI1. Comparative example 1. Methanol: 300ee and Snα. : 86.4, and sbα, : 10.4, and a 5N ammonia aqueous solution (alkaline aqueous solution): 300
cc and water heated and maintained at a temperature of 90℃・3000e
e was slowly injected over 2 hours with vigorous stirring to precipitate sb-containing Sn02 powder (during this reaction, the pH and concentration of the reaction solution were maintained at 8 to 9 by the ammonia aqueous solution). >>Subsequently, the resulting sb-containing S n O 2 fine powder was separated, washed, and then heated in air at a temperature of 500°C for 2 hours in order to improve the crystal grain size. An sb-containing SnO2 fine powder was produced by applying the following steps.The obtained powder had a specific resistance of 1.8 Ω·cm.

Comparative example 2. Specific surface area 50M2/I? , titanium dioxide 100. with a primary particle size of 30 ns. 7 liters of slurry dispersed in 2 liters of water.
Heated to 0°C. A solution prepared by dissolving 232.8 g of tin chloride and 56.89 of antimony chloride in 35 ml of 2N hydrochloric acid and 25% ammonia water were added to this solution over a period of 90 minutes while maintaining the pH of the system at 7 to 9. A coating layer consisting of tin oxide and antimony was formed on the particle surface. After filtering, washing and drying the product, it was heated at 550°C for 15 minutes.
A coated powder was produced by firing for a minute. The obtained powder had a specific resistance of 18 Ω·cm.

Comparative example 3. Tin chloride 88.1 for 100 g of aluminum oxide with specific surface Wl7lI2/g, primary particle size 200 nm
1? , Example 1 except that a solution prepared by dissolving 7.83 of antimony chloride in 50 d of 2N hydrochloric acid was added. Process in the same way as 5
It was baked at 50°C for 15 minutes. The obtained powder has a specific resistance of 12
It had Ω·ci+.

The conductive fine powders of the Examples and Comparative Examples were tested for their performance, and the results shown in Table 1 were obtained. Note that the evaluation in Table 1 was performed as follows.

(1) Powder Resistance The resistance of the powder was measured using an LCR meter manufactured by Yokogawa-Hewlett-Packard Co., Ltd. under a pressure of 200 kg and 7 cm 2 .

(2) After mixing the surface resistance powder with vinyl chloride vinyl acetate copolymer resin and making it into a paint,
It was applied to a polyester film using a 2 mil doctor blade, and after air drying, the surface resistance of the coating film was measured using an LCR meter.

(3) The total light transmittance (%) and haze (%) of the coating film applied to the transparent polyester film were measured using a direct reading haze computer manufactured by Suga Test Instruments Co., Ltd.

As is clear from Table 1, the conductive silicic anhydride according to the present invention had low powder resistance, and when mixed in a resin medium, the silica had good transparency and conductivity.

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Claims (1)

[Claims] 1. 1 to 2 antimony oxides are added to the surface of the silicic anhydride particles.
1. A conductive fine powder of silicic anhydride, characterized in that the coating layer contains 50 to 300% by weight of silicic anhydride, with the remainder substantially consisting of tin oxide. 2. The particle size of silicic anhydride is 15 nm as the average diameter of primary particles.
The conductive silicic anhydride fine powder according to claim 1, which is as follows. 3. Antimony oxide is produced by simultaneously adding a hydrochloric acid solution in which tin chloride and antimony chloride are dissolved and an alkali to a heated aqueous solution in which silicic anhydride is dispersed so as to maintain the pH of the suspension between 3 and 9. 1. A method for producing conductive silicic acid anhydride fine powder, characterized in that the conductive silicic acid anhydride fine powder contains 1 to 20% by weight of the anhydrous silicic acid, and has a coating layer substantially consisting of tin oxide in an amount of 50 to 300% by weight based on the silicic anhydride.