KR20020074281A - Method of preparing ultra-fine silica powder - Google Patents

Abstract

PURPOSE: A method for preparing ultra-fine silica powder with a mean particle size of 0.1 to 2 μm by the reaction of sodium silicate with fluosilicic acid (H2SiF6) is provided. CONSTITUTION: The ultra-fine silica powder is fabricated by slowly dropping 5 to 35 wt.% of sodium silicate to 1 to 25 wt.% of fluosilicic acid (H2SiF6) under agitation at about 70 deg.C until hydrogen-ion concentration comes to pH 4.5 to 10.5 to form precipitate. Further, a surfactant with an HLB value of 3 to 10 is additionally added in an amount of 0.01 to 0.2 wt.% based on the 100 wt.% of sodium silicate. Furthermore, hydrocarbons including benzene and hexane are additionally added.

Description

Method of Preparing Ultra-fine Silica Powder {Method of Preparing Ultra-fine Silica Powder}

The present invention relates to a method for producing ultra-fine silica powder, and more particularly, to a method for producing ultra-fine porous silica powder from the reaction of sodium silicate and silicon silicate fluoride.

Porous silica gel is used in various applications such as petrochemical catalyst carriers, adsorbents, polymer fillers, and the like. Conventional methods for preparing amorphous silica powders include melting and grinding natural raw materials such as silica and quartz at high temperatures (Japanese Patent Application Laid-Open No. 60-21827, Iso 61-63537), and for neutralization of alkali silicates with acids. Method of gelling or granulating the finely prepared fine silica (Japanese Patent Application Laid-Open No. 47-5817, Japanese Patent Application No. 61-48427, Korean Patent Application No. 91-16339), a method using colloidal silica, vapor phase decomposition method of silicon tetrachloride ( A method of granulating silica prepared by CVD (Japanese Patent Laid-Open No. 58-140313, Japanese Patent Application No. 61-186215, Japanese Patent Application No. 62-3011), or a method prepared by the sol-gel method using a metal alkoxide (Japanese Patent Application Laid-Open No. 63). -166777) and a method for producing a silica colloidal solution from which sodium in sodium silicate has been removed through a double spraying process (Korean Patent Application No. 93-17093).

Among them, an acid neutralization method that neutralizes sodium silicate with sulfuric acid is known as a method of producing silica gel or silica powder which is economically most widely used to date. In most cases, however, acid neutralization produces silica precipitates on gels with high moisture content, making it difficult to filter, separate, and wash, making it difficult to remove Na ₂ O contained in sodium silicate. Since a grinding | pulverization process is needed, there exists a problem that it is difficult to obtain a high purity silica powder. In addition, in order to obtain a powdery precipitate, a very low concentration of sodium silicate solution must be used, so that the yield of precipitated SiO ₂ is extremely low. In addition, process control is difficult because of the precise control of concentration, temperature, and pH, while the salt content is high, the density is high, the particle size is large, and the roughness is high, such as an anti-blocking agent. It is difficult to use it as a value-added silica powder material. In particular, the biggest defect is that it is difficult to express transparency that the blocking agent should have.

Therefore, powdered silica sold under the trade name of white carbon and precipitated by the sulfuric acid neutralization method of sodium silicate is used as a low quality silica material.

The method for preparing silica powder from a silica colloidal solution in which sodium is removed from sodium silicate through a double spraying process (Korean Patent Application No. 93-17093) is a colloidal silica through ion exchange resin method developed by Bird in 1941. It can be used as a method of manufacturing high-purity silica powder which is useful as a manufacturing method, but particle nucleation of less than 3㎛ by simple spraying process, grinding of the ball mill, addition of pore former, secondary spray drying, and heat treatment by fluidized bed furnace, etc. Because of adopting the process, it is very difficult to control the physical properties of the product during mass production, and the disadvantage of the process cost is high.

Therefore, the most convenient and economical condition for obtaining fine silica powder is the silica powder, which is easy to filter and has a high porosity and separation by using sodium silicate as a raw material, but by condensation and growing ultrafine silica nuclei to a suitable size. It is to settle at once. In general, when crystals are grown in solution, the entropy of the crystals is lower than the solution due to the high order of the grown crystals, so that impurities are displaced into a relatively chaotic and high entropy solution phase, thereby obtaining high purity crystals. It can be said that how well the solution can be separated from the crystal determines the purity of the crystal. A key problem with existing techniques of neutralizing sodium silicate with acids to produce silica is that solutions containing impurities trapped in the micropores of gels or large particles are obtained because the precipitated silica is obtained as a gel or particles with a size of tens to hundreds of microns. Was difficult to separate from the crystal. Therefore, the method of forming the finely divided fine powdery particles can be said to be a method of rapidly gelling the silica monomer by the catalyst.

An object of the present invention is to provide a method for providing an ultrafine silica powder using a low cost raw material and easily by a simple method in view of the above problems of the prior art.

Another object of the present invention to provide a method for producing a polymer film having excellent transparency and excellent physical properties by applying the ultra-fine silica powder prepared according to the above method.

In order to achieve the above object, in the present invention, ultrafine silica comprising the step of mixing the silicon silicate (H ₂ SiF ₆ ) and sodium silicate so that the pH is in the range of 4.5-10.5 and separating the precipitate obtained It provides a method for producing a powder.

Another object of the present invention described above is achieved by a method of using ultrafine silica powder prepared according to the above-described method as a filler of a polymer film.

The technique to be presented in the present invention is to use the catalytic function of pullulor ions in the gelation reaction by hydrocondensation polymerization of silica. In this case, by using fluorine raw material silicon silicate (H ₂ SiF ₆ ) produced as a by-product from the phosphate fertilizer process, it can be expected to have a triple effect that can serve as a silica raw material as well as a catalyst and a neutralizing agent. Like OH ^- ions, F ^- ions act as a mineralizing agent in the crystallization process by hydrocondensation polymerization of various inorganic cations, and faithfully structure crystals in the synthesis of zeolites or crystalline silicates. It is known to act.

In some cases, it is possible to freely control the pore size and specific surface area of the silica powder by using a micelle formed by the surfactant as a template by adding a surfactant as a pore forming agent. This is previously added with a surfactant to the silicic acid fluoride solution with a surfactant before adding sodium silicate to form a micelle template, and when a precipitant is added, SiO ₂ is precipitated around the micelle template to crystallize.

More preferably, 0.01 to 0.2 parts by weight of a nonionic surfactant having an HLB value of 3 to 10 is added to 100 parts by weight of sodium silicate. More preferably, 0.1 parts by weight is added. In addition, in order to control the pore size, hydrocarbons such as benzene and hexane may be added in an appropriate amount to make microemulsions.

The silica powder precipitated according to the method of the present invention comprises spherical fine particles in which several nanometer-sized silica crystal nuclei are agglomerated to a size of 0.1-5 μm, thereby greatly removing impurities by filtration separation. In addition, the dry powder is well separated in the size of 0.1-3㎛ size is excellent powder properties so that no additional grinding is required. In particular, it has excellent transparency when dispersing glycerin and has suitable physical properties as a filler for polymer films requiring transparency such as PP.

In addition, even if lower sodium silicate is used, SiO ₂ contained in silicon silicate can be used as a raw material for silica, so that the yield can be increased. In this case, silicon silicate is a by-product of the phosphate fertilizer manufacturing process. From this point of view, it can be seen as a very useful method.

The present invention will be described in more detail while maintaining the concentration of the silicon fluoride solution in the range of about 1-25 wt. Sodium silicate solution in the range of 35% by weight is slowly added dropwise to form a precipitate, and immediately or after several hours the precipitate is filtered, separated, washed and dried to obtain a silica powder. At this time, the case where the concentration of the silicic acid is 3% is easily applied, but the concentration of the reagent used is not particularly limited.

At this time, the mixture easily forms a precipitate when the pH of the final composition is adjusted to be in the range of 4.5-10.5. Therefore, the mixing ratio of the two starting materials is preferably adjusted to be in the above pH range.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1

A 3% H ₂ SiF ₆ solution to 4000 ml with stirring and then heated to 70 ℃ No. 3 sodium silicate (Na ₂ O 10 weight%, SiO ₂ 30% by _{weight, SiO 2 / Na 2 O =} 3) 2.00㎏ 1 hour Added over. At this time, the reaction temperature was maintained at 70 ℃ or more. At this time, the pH of the final reaction solution was 6.8. 10 minutes after the end of the addition, the solution containing the precipitate was separated by filtration, washed three more times, and dried to obtain silica powder. Purity, pore distribution, and specific surface area of the prepared silica powder are shown in Table 1 below.

Example 2

3% H ₂ SiF ₆ solution over a 4000 ml with stirring to -5 ℃ No. 3 sodium silicate (Na ₂ O 10 weight%, SiO ₂ 30% by _{weight, SiO 2 / Na 2 O =} 3) 2.00㎏ 1 hour Added. After that, the reaction temperature rose to 70 ° C. or higher to grow silica crystals. At this time, the pH of the final reaction solution was 6.5. The solution containing the precipitate was filtered off, washed three more times, and dried to obtain a silica powder. Purity, pore distribution, and specific surface area of the prepared silica powder are shown in Table 1 below.

Example 3

To 4000 ml of a 3% H ₂ SiF ₆ solution, 400 g of laurylalcohol-15EO, a nonionic surfactant, was added and dissolved completely by heating to 70 ° C. The solution was added over an heated to 70 ℃, with stirring No. 3 sodium silicate (Na ₂ O 10 weight%, SiO ₂ 30% by _{weight, SiO 2 / Na 2 O =} 3) 2.00㎏ 1 hour. At this time, the reaction temperature was maintained at 70 ℃ or more. At this time, the pH of the final reaction solution was 7.4. Ten minutes after the addition was completed, the solution containing the precipitate was filtered off and washed three more times. The wet silica cake thus obtained was dispersed in isopropyl alcohol and heat treated at 1000 ° C. for 10 minutes using a fluid bed calciner to obtain well separated fine silica powder. Purity, pore distribution, and specific surface area of the prepared silica powder are shown in Table 1 below.

Comparative Example 1

3N hydrochloric acid was added over a period of 2 with stirring and then heated to 2500ml to 70 ℃ sodium silicate No. (Na ₂ O 14 weight%, SiO ₂ 34% by _{weight, SiO 2 / Na 2 O =} 2.4) 1.4㎏ 1 hour. At this time, the reaction temperature was maintained at 70 ℃ or more. After the addition was completed, the solution containing the precipitate was reacted with stirring at 90 ° C./3 hours. Filtration separated, washed three more times and dried to obtain a silica powder.

Sample name SiO ₂ (% by weight) Specific surface area (m ² / g) Average particle size (㎛) Pore volume (cc / g) Pore size Example 1 99.93 250 0.5 1.12 90 Example 2 99.92 400 0.2 1.45 60 Example 3 99.9 750 0.8 1.67 30 Comparative Example 1 99.92 230 1.0 1.23 100

As can be seen in Table 1, it can be seen that the silica powder prepared according to the method of the present invention is extremely fine.

Example 4

The silica powder prepared according to Example 1 was applied to a PP film (0.3 wt% of PP) to prepare a film, and the physical properties of the resulting film were evaluated, which is shown in Table 2.

Example 5

The silica powder prepared according to Example 2 was applied to a PP film (0.3 wt% of PP) to prepare a film, and the physical properties of the resulting film were evaluated, which is shown in Table 2.

Comparative Example 2

Japanese-made SL-340 was applied to a PP film (0.3% by weight of PP) to prepare a film, and the physical properties of the resulting film were evaluated, which is shown in Table 2.

Example 4 Example 5 Comparative Example 2 White index (ASTM D2244) 36.51 37.01 39.71 Yellow index (ASTM D2244) 3.72 4.31 3.71 Friction Coefficient (ASTM D1894) 0.78 / 0.45 1.0 / 0.6 0.76 / 0.44 Transparency (Haze, ASTMD1003) 0.82 (30) ^a 0.7 (30) ^a 0.8 (30) ^a Glossiness (Gloss, ASTM D2457) 142 142 142

() ^A: film thickness (㎛)

From the results of Table 2, it can be seen that the film prepared by applying the silica powder prepared according to the method of the present invention exhibits good physical properties without any deterioration compared to the film prepared by applying the conventional silica powder. .

The present invention as described above is a method of precipitating granular silica which is easy to be separated by filtration in a short time under heating and normal pressure conditions by adding sodium silicate solution to a concentration-controlled silicic acid fluoride solution. Not only can the problem of recovery and separation of the gel phase precipitate with high water content be eliminated, but also the SiO ₂ contained in the silicon fluoride acid produced as a by-product of the phosphate fertilizer manufacturing process can be recovered at the same time. .

In addition, the silica precipitated in the present invention is well separated into granules, so that it is easy to remove salts by filtration, and by spray drying, finely divided fine powdered silica having an average particle diameter of 0.1-2 μm can be obtained.

Although the present invention has been described above according to an embodiment of the present invention, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention.

Claims (8)

Mixing silicon silicate (H ₂ SiF ₆ ) and sodium silicate to bring the pH to the range 4.5-10.5; And Method for producing an ultra-fine silica powder comprising the step of separating the precipitate obtained. The method according to claim 1, wherein the surfactant is added in an amount of 0.01 to 0.2 parts by weight based on 100 parts by weight of the sodium silicate. The method according to claim 2, wherein the surfactant is a nonionic surfactant having an HLB value of 3 to 10. The process according to claim 1, further comprising a hydrocarbon comprising benzene and hexane. The method of claim 1, wherein the ultrafine silica powder has a particle size in the range of 0.1 to 5 μm. The method according to claim 1, wherein the silicon silicate (H ₂ SiF ₆ ) is calculated as a byproduct in the phosphoric acid fertilizer process. The method according to claim 1, wherein the sodium silicate is added while the silicon silicate (H ₂ SiF ₆ ) is maintained in a temperature range of -10 to 80 ° C. A method of using the ultrafine silica powder according to claim 1 as a filler of a polymer film.