JPH09110414A - Method for producing anhydrous silica fine powder and water-repellent silica fine powder - Google Patents

Abstract

(57) Abstract: To provide a method for producing anhydrous silica fine powder under relatively mild conditions and at low cost without impairing the surface activity. Furthermore, low cost, simple, and
Provided is a method for producing a water-repellent silica fine powder without performing surface treatment again. SOLUTION: A clay mineral containing silicic acid and / or silicate is acid-treated and then separated to obtain silica hydrogel,
A method for producing anhydrous silica fine powder, which comprises subjecting this to a dispersion treatment in water and / or an organic solvent to obtain a silica dispersion, and then subjecting this to azeotropic dehydration with an organic solvent, followed by drying and / or firing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing anhydrous silica fine powder and water-repellent silica fine powder. More specifically, it relates to a method for inexpensively producing anhydrous silica fine powder and water-repellent silica fine powder from a readily available clay mineral containing silicic acid and / or silicate.

[0002]

2. Description of the Related Art Amorphous synthetic silica is used in various fields such as rubber, resin, adhesives, paints, inks, cosmetics and pharmaceuticals in various fields such as reinforcing agents, thickeners, antisettling agents and dispersants. Is used for. The conventional method for producing anhydrous silica can be roughly classified into a dry method and a wet method. The former includes a method of hydrolyzing silicon halide in an oxyhydrogen flame at high temperature, but the cost is high because the raw material is expensive and it is necessary to perform the treatment at a high temperature of 1000 ° C or higher. There was a problem. Further, it has been confirmed that the anhydrous silica obtained by this method has a structure having no internal surface area, and there is a drawback that its use is limited. On the other hand, the latter wet method is a method of reacting sodium silicate with a mineral acid and salts in an aqueous solution. In this wet method, as a method for producing anhydrous silica fine powder from silica hydrogel, the water content in the silica hydrogel is replaced with an organic solvent, and the organic solvent is vaporized at a critical temperature and a critical pressure in an autoclave. The law is known. In the case of the airgel method, there are problems that an apparatus for forming a critical state is expensive and that treatment at high temperature and high pressure is required, so that the cost is high as in the dry method and there is a problem in safety. Further, the fine particle silica obtained by this method has a drawback that the surface activity is lost due to the severe production conditions as described above. Therefore, it has been desired to develop a method capable of producing anhydrous silica fine particles at a low cost under relatively mild conditions without impairing the surface activity.

Further, the silanol group on the surface of the anhydrous silica is further reacted with a silane compound such as halosilane, alkoxysilane, silazane, and siloxane to hydrophobically modify the surface. The surface-modified water-repellent silica has good affinity with polymer materials and has excellent physical properties such as equilibrium moisture does not rise. Conventional silicone oil, silane coupling agent, titanate / aluminate coupling agent However, since these treating agents are expensive, the problem of the product cost is further increased, and it has been desired to develop a method for easily and inexpensively producing water-repellent silica.

[0004]

Accordingly, the present invention provides
An object of the present invention is to provide a method capable of producing anhydrous silica fine powder under relatively mild conditions and at low cost without impairing the surface activity. A further object of the present invention is to provide a method for producing a water-repellent silica fine powder at low cost, simply and without performing a new surface treatment.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems, and as a result, after directly chemically treating a clay mineral containing silicic acid, a silica hydrogel is formed, and the silica hydrogel is formed in the presence of an organic solvent. It was found that anhydrous silica fine powder and water-repellent silica fine powder can be obtained by azeotropic dehydration, and that the object can be achieved, and the present invention has been completed based on this finding. That is, the present invention comprises (1) acid-treating a clay mineral containing silicic acid and / or a silicate to separate a silicic acid content into silica hydrogel, and the silica hydrogel is subjected to a dispersion treatment to obtain a dispersion liquid. Next, azeotropic dehydration in the coexistence of an organic solvent, followed by drying and / or calcination, a method for producing anhydrous silica fine powder, (2) azeotropic dehydration in the presence of an acid catalyst, followed by calcination (1) The method for producing fine powder of anhydrous silica according to item (1), (3) the silica concentration of the aqueous dispersion of silica hydrogel is 5 to 40% by weight (1) or (2). (4) Dispersing silica hydrogel obtained by acid treatment of clay mineral containing silicic acid and / or silicate in water and / or organic solvent to disperse silica Liquid, then azeotropically in the presence of an acid catalyst A method for producing water-repellent silica fine powder, characterized by azeotropic dehydration with a water-soluble organic solvent, and then drying, and (5) the silica concentration of an aqueous dispersion of silica hydrogel is 5 to 40% by weight. A method for producing the water-repellent silica fine powder according to the item (4) is provided.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, a clay mineral containing silicic acid and / or silicate is used as a raw material. Specifically, those containing silicic acid as the main component include, for example, diatomaceous earth, silica, allophane, Kawara wool clay, silicic acid clay, cristobalite, etc. , Bentonite, talc and other smectite minerals, serpentine and other chrysotile minerals,
Examples thereof include zeolite minerals such as zeolite, kaolin minerals such as halloysite and kaolinite, and natural minerals such as sepiolite minerals such as asbestos and sepiolite. When using clay minerals containing impurities such as talc, kaolinite, bentonite, etc. that are sparingly soluble or insoluble in acids as impurities (components other than silicic acid and / or silicates), chemical treatment, heat treatment, etc. before acid treatment To destroy the crystal structure. These may be used alone or as a mixture of two or more. Smectite minerals, kaolin minerals, sepiolite minerals, serpentine minerals, and zeolites are preferably used.

These clay minerals are treated with acid to separate silicic acid and / or silicates. As the acid used at this time, a mineral acid such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid and an organic acid such as oxalic acid, acetic acid or citric acid can be used, and sulfuric acid, hydrochloric acid, nitric acid or the like can be industrially used. Preferably used. The acid concentration varies depending on the crystal structure, chemical composition, morphology, etc. of the raw material mineral and can be appropriately selected, but is usually 10 to 40% when the acid clay is treated with sulfuric acid. The conditions of the acid treatment also vary depending on the crystal structure of the raw material mineral, etc.
The reaction is carried out at 110 ° C. for 8 hours or more, preferably 10 to 24 hours.

The silica hydrogel is separated from the acid treatment liquid obtained by the treatment in this way. The silica hydrogel can be separated by filtration, centrifugation or the like. The silica hydrogel thus separated from the mother liquor by filtration or the like needs to be sufficiently washed with water by a conventional method.

Next, this silica hydrogel is dispersed in water and / or an organic solvent to obtain a silica dispersion liquid. The dispersion liquid is a sol in which silica is colloidally dispersed or a suspension of silica, and is a silica single dispersion liquid. The organic solvent is preferably the same as that used for azeotropic dehydration. As a method of dispersing, a ball mill, a medium stirring mill, or another method in which silica hydrogel is wet pulverized by an emulsifying disperser or the like to physically change the structure of the gel to disperse, an ion exchange method, addition of a deflocculant, etc. However, wet grinding is preferable. At this time, the silica concentration of the silica dispersion is preferably 5 to 40% by weight, and 10 to 30
It is more preferable to set it as the weight%. If the concentration of the silica dispersion is too high, the viscosity increases as the pulverization of the slurry progresses, and the pulverizing effect decreases, so that it becomes difficult to form a fine powder. On the other hand, if it is too low, the viscosity does not increase, but the pulverization efficiency decreases, and pulverization for a long time is required.

Next, this silica dispersion is azeotropically dehydrated in the presence of an organic solvent. The concentration of silica (silicic acid content) in the dispersion when starting the azeotropic dehydration treatment is preferably 3 to 30.
%, More preferably 5 to 15% by weight. Examples of the organic solvent used include, but are not limited to, acetone, benzene, glycerin, ethyl acetate, ethanol, methanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol and the like. Even when the organic solvent is added in the previous step, the organic solvent can be added if necessary. The amount of water at the time of starting the azeotropic dehydration treatment is preferably 10 to 60% by weight, more preferably 20 to 40% by weight in the dispersion medium, and the organic solvent is preferably 40 to 90% by weight in the dispersion medium. Preferably 50-60
% By weight. By azeotropic dehydration with an organic solvent, the water in the dispersion replaces the organic solvent and the silica is dehydrated,
This is dried and, if necessary, further calcined to obtain anhydrous silica fine powder containing substantially no water. In this azeotropic dehydration, the silanol groups on the silica surface react with an organic solvent to esterify as the silica is dehydrated, and water repellency is exhibited. Therefore, by performing the esterification reaction in the presence of an acid catalyst during the azeotropic dehydration, the silanol groups on the surface of the silica particles are completely replaced, so that water-repellent silica fine particles can be obtained. As the acid at this time, a mineral acid such as sulfuric acid or hydrochloric acid, a fluoroboric acid, aluminum chloride, zinc chloride or the like can be used, and preferably a mineral acid is used. The amount of the acid used is such that the pH of the reaction solution is usually 5 or less, preferably 3 or less. When an acid catalyst is not used, it takes a very long time to complete the esterification reaction, which is not preferable in practice when producing the water-repellent silica fine particles. In order to quickly complete the esterification reaction, it is preferable to replenish the amount of the organic solvent reduced during the azeotropic dehydration as needed to increase the absolute amount of the organic solvent. Water and / or organic solvent evaporated by azeotropic dehydration can be recovered, separated and reused.

After the reaction is completed, the mother liquor is separated by filtration, centrifugation, etc., and if an acid catalyst is used, this is washed,
Dry and / or bake. The drying and firing conditions are selected according to the desired specific surface area and surface properties of the silica fine particles, but usually the drying is 80 to 200 ° C., preferably 1
It is carried out at 00 to 150 ° C. for about 24 hours. After that, 800 ℃
When fired as above, the pores of anhydrous silica fine particles are sealed,
It has a low specific surface area. When it is desired to obtain anhydrous silica fine particles having a high specific surface area, the firing temperature is usually 800 ° C or lower, preferably 300 to 800 ° C. By setting the temperature to 300 ° C or higher, anhydrous silica fine particles in which the alkyl groups on the fine particle surfaces disappear and the silanol groups on the surface are not substituted are obtained. In the case of water-repellent silica fine particles, drying is preferably performed at 300 ° C. or lower, more preferably 150 to 250 ° C. for about 24 hours in order to prevent the alkyl groups on the particle surface from disappearing.

Thus, the anhydrous silica fine particles obtained by the method of the present invention have a composition of SiO ₂ of 99% or more,
After drying or firing, the powder is easily loosened to be submicron powder with a weak force such as shaking in a container.

[0013]

EFFECTS OF THE INVENTION According to the method of the present invention, submicron particles having a high specific surface area are produced by a low-cost process in which a readily available clay mineral is used as a raw material, the surface activity is not easily impaired, and the treatment is relatively mild. It is possible to obtain anhydrous silica in the form of. Further, by simply changing the conditions of azeotropic dehydration, drying, and calcination, the substitution state of silanol groups on the surface of the anhydrous silica fine particles can be changed, and a water-repellent surface can also be obtained. The same surface can be used. Therefore, there is an excellent effect that ultrafine anhydrous silica fine particles having high water repellency can be obtained without performing the surface treatment step again.

[0014]

Next, the present invention will be described in more detail with reference to examples. Example 1 Water was added to 2 kg of acid clay clay ore (produced in Togarita, Karita-gun, Miyagi Prefecture, water content: 16.7% by weight) to obtain a slurry having a concentration of 23.8% and wet-milled, and then a slurry (concentration of 20.4% by weight) separated from the sediment. Concentrated sulfuric acid was added to adjust the sulfuric acid concentration to 35%. This is 70
The mixture was heated to ° C and reacted for 36 hours. During this process, a small amount of sample was taken, washed with water, dried and pulverized to measure X-ray diffraction. The results are shown in FIG. From this result, the peak of smectite almost disappeared after 24 hours and quartz was recognized as an impurity, but the diffraction line was broad due to amorphous silicic acid. Therefore, it can be seen that it was amorphized by the sulfuric acid treatment for 24 hours or more. The specific surface area (BET method) of the sample after amorphization was 465 m ² / g.

After filtering the sample treated with sulfuric acid for 36 hours with a vacuum filter, the silica hydrogel on the filter paper was washed with water, deironed with hydrosulfite, decolorized and purified with a sodium chlorite solution, and 200 ml of water was added, Wet grinding with a ball mill gave a silica dispersion (sol, SiO ₂ concentration 15% by weight). 200 g of this silica dispersion was placed in a three-necked flask having a capacity of 1 liter, 500 ml of 1-butanol was added,
Azeotropic dehydration was performed while heating with a mantle heater and stirring.
Evaporated water and 1-butanol were collected by cooling with a condenser. During the azeotropic dehydration, 1-butanol was additionally added at any time. When the temperature in the flask reaches the boiling point of 1-butanol (117.3 ° C), the heating is stopped, and after cooling,
The mother liquor was separated by filtration. The filter cake was dried in a dryer at 120 ° C. for 24 hours to obtain a dried product of anhydrous silica 1
0.9 g was obtained. Furthermore, 600 parts of the dried product are heated in an electric furnace.
The product was calcined at 3 ° C. for 3 hours to obtain 5.2 g of a calcined product of anhydrous silica. Both the dried and calcined products of this anhydrous silica were bulky, and easily became fine powder with a weak force such as shaking in a container. When the particle size of the fine powder was measured with a centrifugal sedimentation particle size analyzer (manufactured by Shimadzu Corporation, SA-CP3L), both were on average 0.85 μm and were submicron fine powder. The specific surface areas of the fine powder obtained from the dried product and the fine powder obtained from the calcined product were measured by the BET method.
00m ² / g, firing fine紛末was 450m ² / g.
In addition, a transmission electron microscope (JEM-20, manufactured by JEOL Ltd.)
As a result of observation in 10), primary particles of about 10 nm were both confirmed. In addition, dry fine powder and calcined fine powder are respectively FT-IR (manufactured by JASCO Corporation, FT-IR-7300).
A peak of butyl group was found in the dried fine powder. The dried fine powder was suspended in a beaker containing water. The butyl group peak disappeared at the end of the calcined fine powder, and the surface state was the same as that of anhydrous silica obtained by the dry method.

Example 2 A silica dispersion (sol, SiO 2) was prepared in the same manner as in Example 1.
₂ concentration 15% by weight) was obtained, and concentrated sulfuric acid was added to this as an acid catalyst to adjust the pH to 2. This was azeotropically dehydrated with 1-butanol, dried and calcined in the same manner as in Example 1 to obtain a dried product of water-repellent silica and a calcined product of anhydrous silica. Similar to those obtained in Example 1, the dried and fired products were bulky and easily became fine powder with a weak force such as shaking in a container. When the average particle size of the fine powder was measured in the same manner as in Example 1, the dry fine powder was 0.82 μm, and the calcined fine powder was 0.80 μm. When these were measured by FT-IR in the same manner as in Example 1, a butyl group peak was recognized in the dried fine powder. The dried fine powder did not suspend even if dropped into a beaker containing water and stirred, and floated stably for a long time and exhibited strong water repellency. The butyl group peak disappeared at the end of the calcined fine powder, and the surface state was the same as that of anhydrous silica obtained by the dry method.

The results of Examples 1 and 2 are summarized in Table 1. For comparison, the values of the dried and calcined products obtained in the same manner as in Example 1 except that the silica hydrogel was directly azeotropically dehydrated without being dispersed in water are also shown in Table 1. The dried product and the fired product obtained by the method of the present invention were both bulky and easily finely pulverized with a weak force such as shaking in a container. Although it was finely pulverized, the gel lump formed a hard agglomerate as it was, and the lump was not pulverized by putting it in a container and shaking it.

[0018]

[Table 1]

Example 3 Serpentine rock (produced in Hidaka-mura, Takaoka-gun, Kochi) was crushed to a size of 200 mesh (particle size: 74 μm) or less, and 2 kg of wet magnetically selected sample at 20,000 gauss was put in a 10 liter container and 5 M sulfuric acid. 7.5 liters were added, and the mixture was reacted at 100 ° C. for 24 hours while stirring. A small amount of a sample was taken on the way and X-ray diffraction was measured in the same manner as in Example 1. The results are shown in FIG. From these results, it can be seen that the reaction has been made amorphous for 12 hours or more. The sample treated with acid for 24 hours was wet pulverized in the same manner as in Example 1 to obtain a silica dispersion (sol, SiO ₂ concentration: 15% by weight), azeotropically dehydrated with isopropanol, and dried at 120 ° C. for 24 hours to obtain a fine anhydrous silica powder. 29.4 g of powder was obtained.

Example 4 2 kg of asbestos (made in Canada) was pulverized, subjected to magnetic separation and acid treatment in exactly the same manner as in Example 3 and then treated in the same manner as in Example 1 to obtain 10.1 g of anhydrous silica fine powder. It was

Example 5 Example 4 was also applied to 2 kg of zeolite (produced by Kuzu, Tochigi Prefecture).
The same treatment as above was performed to obtain 10.5 g of anhydrous silica fine powder.

Example 6 2 kg of kaolin (produced in China) was purified by a wet method and then 60
Baking was performed at 0 ° C. for 3 hours to obtain amorphized metakaolin. This was treated in the same manner as in Example 3 to obtain 29.2 g of anhydrous silica fine powder.

Example 7 2 kg of sepiolite (produced in Spain) was pulverized and acid-treated to be amorphous in the same manner as in Example 1. After filtering the sample treated with sulfuric acid for 36 hours with a vacuum filter, the silica hydrogel on the filter paper was washed with water, 400 ml of isopropanol was added, and wet pulverized with a ball mill to obtain a silica dispersion (sol, SiO ₂
A concentration of 15% by weight) was obtained. 200 ml of this silica dispersion
Was placed in a three-necked flask having a capacity of 1 liter, and azeotropically dehydrated while heating with a mantle heater and stirring. Evaporated isopropanol was cooled by a condenser and collected. During the azeotropic dehydration, isopropanol was added at any time. The temperature in the flask is the boiling point of isopropanol (8
When the temperature reached 2.4 ° C., heating was stopped, and after cooling, the mother liquor was separated by filtration. Filter cake in a dryer 12
Dry for 24 hours at 0 ° C., dry product of anhydrous silica 10.9 g
I got

[Brief description of the drawings]

FIG. 1 shows that when acid clay is treated with sulfuric acid in Example 1, 0,
It is a measurement result of X-ray diffraction after 1, 3, 6, 9, 13, 24, 28, 32, 36 hours.

FIG. 2 shows 0, 1, when the serpentine is treated with sulfuric acid in Example 3.
It is a measurement result of X-ray diffraction after 2, 12, and 24 hours.

Claims (5)

[Claims] 1. A clay mineral containing silicic acid and / or silicate is treated with an acid and then separated to obtain a silica hydrogel.
A method for producing fine powder of anhydrous silica, which comprises subjecting this to a dispersion treatment in water and / or an organic solvent to obtain a silica dispersion, followed by azeotropic dehydration with an organic solvent, followed by drying and / or calcination. . 2. After azeotropic dehydration in the presence of an acid catalyst,
The method for producing anhydrous silica fine powder according to claim 1, which comprises firing. 3. The method for producing anhydrous silica fine powder according to claim 1, wherein the silica concentration of the silica dispersion is 5 to 40% by weight. 4. A silica hydrogel obtained by subjecting a clay mineral containing silicic acid and / or silicate to an acid treatment with water and / or
Alternatively, it is dispersed in an organic solvent to give a silica dispersion, which is then azeotropically dehydrated with an organic solvent capable of being azeotropically dehydrated in the presence of an acid catalyst, followed by drying. Production method. 5. The method for producing water-repellent silica fine powder according to claim 4, wherein the silica concentration of the silica dispersion is 5 to 40% by weight.