JPH0455967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing conductive hydrated silicic acid, and particularly provides a method for easily producing white conductive hydrated silicic acid that does not discolor at high temperatures. Hydrous silicic acid has traditionally been used as a filler for natural rubber and synthetic rubber, as an opaque and anti-blocking agent for various synthetic resins, as a filler for paper, as a binder compound, as a pesticide adsorption carrier,
It is used in a wide range of fields, including as a viscosity modifier. In recent years, there has been a demand for hydrated silicic acid having electrical conductivity, particularly in order to impart electrical conductivity to rubber, synthetic resins, paints, paper, etc. as mentioned above. However, hydrated silicic acid is generally an electrical insulator and does not have electrical conductivity. For this reason, for example, Japanese Patent Application Laid-Open No. 1986-
Nos. 114215 to 114218 propose a white conductive composite powder obtained by coating a white metal oxide powder such as titanium oxide with tin oxide or ammothymony and a tin compound, and a method for producing the same. That is, these manufacturing methods involve adding tin chloride or an alcoholic solution of antimony chloride and tin chloride to a suspension of white metal oxide powder. On the other hand, in order to obtain hydrated silicic acid having good and stable conductivity, the present inventors added a tin compound or a tin compound to the reaction system when producing hydrated silicic acid by neutralizing alkali silicate with acid. A method was proposed in which a compound and an antimony compound were made to exist. (Japanese Patent Application No. 58-63756) As a result of further intensive research into the production method of silicic acid having electrical conductivity, the present inventors have found that by reacting an alkali silicate with a tin compound and a water-soluble fluorine compound, an extremely The present inventors have discovered that a white hydrated silicic acid having good conductivity and not discolored at high temperatures can be obtained, leading to the provision of the present invention.That is, the present invention provides a silicic acid containing an alkali silicate, a tin compound, and a water-soluble fluorine compound. This is a method for producing hydrated silicic acid having conductivity, which is characterized by reacting a solution.According to the present invention, since an alkali silicate is reacted with a tin compound and a water-soluble fluorine compound, the silicic acid is simultaneously produced with hydrated silicic acid. Fluorine-doped tin oxide is uniformly contained and precipitated. Therefore, the hydrated silicic acid obtained by the present invention contains fluorine-doped tin oxide strongly on the surface and inside of the hydrated silicic acid, so it cannot be heated at high temperatures. It is presumed that it is possible to stably exhibit the desired conductivity without causing any build-up.In the present invention, the method of reacting an alkali silicate with a tin compound and a water-soluble fluorine compound can be used without any particular restrictions.Generally, After raising the temperature of an aqueous alkali silicate solution and adjusting the pH by adding an aqueous solution containing a water-soluble tin compound and a water-soluble fluorine compound to the aqueous solution, the alkali silicate particles are completely precipitated.
The recommended method is to filter, wash with water, dry, grind if necessary, and then sinter the pulverized product at a temperature of 500 to 900°C. Examples of the alkali silicate of the present invention include sodium silicate, potassium silicate, lithium silicate, and ammonium silicate, which are generally used as an aqueous solution, and in particular, an aqueous solution of sodium silicate (soda) is used industrially. Molar ratio of SiO ₂ and Na ₂ O in sodium silicate (Na ₂ O・SiO ₂ ) (SiO ₂ /
Na ₂ O) is preferably 1.5 to 2.5; if the molar ratio is less than 1.5, the amount of alkali increases, making it uneconomical; if the molar ratio is more than 2.5, the amount of tin compound supported on the silica decreases. Therefore, silica with good conductivity cannot be obtained. In order to impart desired conductivity to the hydrated silicic acid of the present invention, it is preferable to add alcohol to the aqueous alkali silicate solution. The amount of alcohol added is preferably 10% or less by volume in the aqueous alkali silicate solution; if it exceeds 10%, esterification of the alkali silicate and alcohol will occur, resulting in a gelled product, making stirring difficult. . As alcohol, methyl alcohol,
Ethyl alcohol, isopropyl alcohol, etc. are preferably used. In the present invention, the tin compound and the water-soluble fluorine compound are generally preferably used after being dissolved in a solvent such as water or alcohol in order to stably and uniformly impart the desired conductivity to the resulting hydrated silicic acid. Therefore, the tin compound and the water-soluble fluorine compound need only be soluble in the solvent. For example, tin chloride is generally used as the tin compound, and sulfates, oxides, etc. may also be used as appropriate. Moreover, ammonium fluoride is preferably used as the water-soluble fluorine compound. Further, in order to impart desired conductivity to the hydrated silicic acid of the present invention, it is preferable that the tin compound is present in an alkaline silicate solution in a weight ratio of 1.6 to 2.2 relative to the tin compound Na ₂ O. In other words, if the amount of the tin compound is less than 1.6 above, the precipitation of tin oxide is insufficient and the desired conductivity cannot be imparted to the hydrated silicic acid, and even if the amount is more than 2.2, the desired conductivity cannot be imparted to the hydrated silicic acid. No further improvement is permitted. On the other hand, the water-soluble fluorine compound is 3-8% of the tin compound (weight).
(by weight)%.
That is, the water-soluble fluorine compound is 3% (by weight) above.
If the amount is less than 8% (by weight), the desired conductivity cannot be imparted to the obtained hydrated silicic acid because the amount of fluorine doped in the tin oxide is small. No further improvement was observed. The reaction of adding a tin compound and a water-soluble fluorine compound to the above-mentioned alkali silicate to produce a silicate sol is as follows:
Concentration of alkali silicate charged, temperature, and at the end of the reaction
It is greatly influenced by pH, stirring, etc. In other words, if the concentration of the alkali silicate charged is high, it will gel,
Since stirring becomes difficult, SiO ₂ is generally
It is preferable to set it as 10g/100ml. The above SiO ₂
Less than 2g/100ml is not only uneconomical;
It becomes difficult to generate silicate kelp. Temperature is generally 40~
The temperature is preferably 100°C, and if the temperature is lower than 40°C, the viscosity of the reaction liquid increases, which affects the specific surface area of the obtained hydrous silicic acid, so it may be adjusted as appropriate. After the reaction
PH affects conductivity, and when PH becomes 7 or less, conductivity decreases. It is desirable that the stirring be sufficiently effective so that the reaction does not occur locally. After completion of the reaction, the silicic acid slurry is filtered and washed with water in a conventional manner to remove by-product salts, and then dried, pulverized, and classified. Furthermore, if necessary, this hydrated silicic acid is heated in an electric furnace.
By firing at a temperature of 500 to 700°C for 1 to 2 hours, hydrated silicic acid having desired conductivity can be obtained. As the firing method, any known method may be used without particular limitation, but an electric furnace or a method of instantaneous contact with flame is preferably used. In the method for producing hydrated silicic acid described above, the present invention makes it possible to obtain fine hydrated silicic acid having good conductivity by reacting an alkali silicate with a tin compound and a water-soluble fluorine compound. The conductive hydrated silicic acid of the present invention thus obtained is extremely useful as a filler for, for example, electrically conductive thermal paper, electrostatic recording paper, electrostatic paint, antistatic plastic, rubber material, and the like. Examples are given below, but the present invention is not limited thereto. Note that the measurement methods in Examples and Comparative Examples are shown below. (1) Specific resistance (Ω・cm) Measured with a Britsch circuit (manufactured by Yokogawa Electric) (2) Whiteness Kett photoelectric whiteness meter (manufactured by Kett Scientific Research) Example 1 SiO concentration 44.41% and Na ₂ O concentration 21.65% Sodium silicate solution 540ml, water 2220ml, ethanol 240ml
was charged into an internally heated reactor with a volume of 5 liters, and the liquid temperature was set at 60 degrees. Next, a mixture of 210 g of tin chloride SnCl ₄ and 12.6 g of ammonium fluoride dissolved in 600 ml of water was added to the reaction tank over 90 minutes, and after the addition was completed, the reaction temperature was raised to 90°C and aged in this state for 20 minutes. The pH of the solution was set to 9.10.
The obtained slurry solution was filtered and washed with water, and the obtained cake was dried at 110°C to obtain hydrous silicic acid. Then,
Grind, classify, and bake in electricity at 650℃ for 60 minutes.
It was used for measuring specific resistance and whiteness. Table 1 shows the measured values for the hydrated silicic acid. Example 2 In Example 1, 270 ml of acid Zoda solution, water
2484 ml, ethanol 246 ml, tin chloride 117 g, and ammonium fluoride 7.0 g, but were produced in the same manner.
The results are shown in Table 1. Example 3 In Example 1, SiO ₂ concentration 44.63% and Na ₂ O
53ml of sodium silicate solution with a concentration of 22.24%, 2216ml of water,
It was produced in the same manner except that 246 ml of ethanol, 240 g of tin chloride, and 14.4 g of ammonium fluoride were used. The results are shown in Table 1. Example 4 In Example 1, ethanol was not used and water was used.
It was manufactured in the same manner except that the volume was changed to 2460 ml. The results are shown in Table 1. Comparative Example 1 1034 ml of a sodium silicate solution with a SiO concentration of 27.09% and a Na ₂ O concentration of 9.24% and 1767 ml of water were charged into a 5 liter internally heated reactor, and the liquid temperature was set at 60°C. Next, 196 g of tin chloride (SnCl ₄ ) was dissolved in 700 ml of water, and this was added to the reaction tank over 90 minutes.
The pH of the solution was adjusted to 7.38. The cake obtained by filtering and washing the slurry solution with water is
It was dried at 110°C to obtain hydrous silicic acid. Next, crush and
It was classified and fired for 60 minutes in an electric furnace at 650°C, and then used for measurement of specific resistance and whiteness. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. A method for producing hydrated silicic acid having electrical conductivity, which comprises reacting an alkali silicate with a solution containing a tin compound and a water-soluble fluorine compound. 2. The manufacturing method according to claim 1, wherein the alkali silicate is sodium silicate. 3. The manufacturing method according to claim 2, wherein the sodium silicate has a molar ratio of SiO ₂ to Na ₂ O (SiO ₂ /Na ₂ O) of 1.5 to 2.5. 4. The manufacturing method according to claim 1, which is an aqueous alkali silicate solution containing alcohol. 5. The manufacturing method according to claim 4, wherein the volume ratio of alcohol in the aqueous alkali silicate solution is 10% or less. 6. The manufacturing method according to claim 1, wherein a mixed solution containing a water-soluble fluorine compound and a water-soluble tin compound is added to the alkaline silicate solution. 7 Claim 1 in which the tin compound is tin chloride
Manufacturing method described in section. 8. The manufacturing method according to claim 1, wherein the tin compound is added at a weight ratio of 1.6 to 2.0 to the alkali silicate. 9. The manufacturing method according to claim 1, wherein the water-soluble fluorine compound is ammonium fluoride. 10 Water-soluble fluorine compound to tin compound
The manufacturing method according to claim 1, wherein 8% by weight is added. 11. The manufacturing method according to claim 1, wherein the reaction product is calcined at 500 to 900°C.