JP2011042522A - Colloidal silica and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a colloidal silica useful for ink absorbing fillers for printing paper, spreading improvers for coatings, hydrophilic coating material for various types of material surfaces, high-strength binders, high-purity silica gels, raw material for high-purity ceramics, binders for catalysts, abrasives for electronic materials, and the like. <P>SOLUTION: The colloidal silica comprises a group of nonspherical deformed silica particles inside which urea is immobilized, or a group of nonspherical deformed silica particles in which urea is immobilized by disposing a coating containing silica containing urea as a main component, on the surface of the particles. The colloidal silica can be manufacture by bringing a silicic acid alkali aqueous solution into contact with a cation exchange resin to prepare an active silicic acid aqueous solution, thereafter adding urea and an alkali agent to the active silicic acid aqueous solution to make the solution alkali, thereafter heating the solution to form silica particles, and then growing silica particles by build-up means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink-absorbing filler for printing paper, a spreadability improving agent for paints, a hydrophilic coating material for various material surfaces, a high-strength binder, a high-purity silica gel, a raw material for high-purity ceramics, a binder for catalysts, and an electronic material. The present invention relates to a colloidal silica useful for abrasives for manufacturing and a method for producing the same.

Many methods for reducing the content of alkali metal have been proposed for colloidal silica produced using alkali metal silicate (mainly sodium silicate) as a raw material. For example, Patent Document 1 describes that colloidal silica with less sodium can be obtained by using an active silicic acid aqueous solution of a water glass method and tetraalkylammonium hydroxide.
Even if sodium is removed by cation exchange from ordinary colloidal silica produced using water-silica active silicic acid aqueous solution and sodium hydroxide, the sodium present in the silica particles is gradually eluted into the liquid phase. It is well known. Therefore, in Patent Document 2, after sodium is removed from colloidal silica by cation exchange, ammonia is added to make it alkaline, and it is treated in an autoclave at 98 to 150 ° C. to forcibly dispose sodium present in the silica particles. It describes a method of elution in the liquid phase and removal by cation exchange.

  Many colloidal silicas composed of non-spherical silica particles have also been proposed. In Patent Document 3, elongated amorphous colloidal silica particles having a uniform thickness within a range of 5 to 40 millimicrons as observed by an electron microscope and extending only in one plane are dispersed in a liquid medium. A stable silica sol is described. Patent Document 4 describes a silica sol composed of elongated silica particles obtained by a production method in which a metal compound such as an aluminum salt is added before, during or after the addition of a silicic acid solution. Patent Document 5 describes colloidal silica composed of bowl-shaped silica particles having a major axis / minor axis ratio of 1.4 to 2.2 obtained by hydrolysis of alkoxysilane. Patent Document 6 describes a colloidal containing non-spherical silica particles using a hydrolyzed solution of alkoxysilane instead of an active silicic acid aqueous solution of the water glass method, and using tetraalkylammonium hydroxide as an alkali. It is described that silica is obtained.

JP 2003-89786 A JP 2004-189534 A (Claims) JP-A-1-317115 (Claims) Japanese Patent Laid-Open No. 4-187512 Japanese Patent Laid-Open No. 11-60232 (Claims) JP 2001-48520 A (Claims and Examples)

The colloidal silica described in Patent Document 1 is preferable in terms of a small amount of sodium, but the shape of the particles has not been studied at all. The method for producing colloidal silica described in Patent Document 2 contains ammonia as an essential component, so that ammonia is contained inside the particles, and the use is limited. In addition, the production process is not long and the use of energy is excessive, which is disadvantageous. There is one side.
Since colloidal silica described in Patent Document 3 includes a step of adding a water-soluble calcium salt, magnesium salt or a mixture thereof in the production process, they remain as impurities in the product. Since the colloidal silica described in Patent Document 4 includes a step of adding a water-soluble aluminum salt in the production process, they remain in the product as impurities.
Since the colloidal silica described in Patent Document 5 and Patent Document 6 uses alkoxysilane as a silica source, the product has high purity, but a process for recovering a large amount of by-product alcohol having a mole number four times that of silica is required. In addition, there is a problem that the price of alkoxysilane itself is high.

  Accordingly, an object of the present invention is to produce a colloidal silica containing a non-spherical deformed silica particle group without using a polyvalent metal compound other than silicon such as calcium salt, magnesium salt, aluminum salt, and the production method thereof. It is providing the colloidal silica obtained by this.

As a result of intensive studies, the present inventors have been able to obtain a novel colloidal silica and have also solved the above problems.
That is, the first invention is colloidal silica containing a group of non-spherical irregularly shaped silica particles in which urea is immobilized inside the particles.
Moreover, 2nd invention is colloidal silica containing the non-spherical irregular-shaped silica particle group by which urea was fix | immobilized by arrange | positioning the film which has a silica containing urea as a main component on the surface.

The scope of the present invention includes those in which urea is immobilized both on the inside of the particles and on the surface coating. In the following, non-spherical irregular-shaped silica particles in which urea is immobilized inside the particles, non-spherical irregular-shaped silica particles in which urea is immobilized by disposing a coating mainly containing silica containing urea on the surface The non-spherical irregular-shaped silica particle group in which urea is immobilized on both the inner surface and the coating on the surface of the group may be collectively referred to as “non-spherical irregular-shaped silica particle group in which urea is immobilized”.
The colloidal silica in the first and second inventions preferably has a silica / urea molar ratio of 20 to 300.
The colloidal silica in the first and second inventions contains urea in the liquid phase, and the major axis / minor axis ratio of the non-spherical irregularly shaped silica particles observed by a transmission electron microscope is in the range of 1.2 to 15. The average value of the major axis / minor axis ratio is preferably 1.3-10. The colloidal silica in the first and second inventions preferably has an average minor axis of silica particles of 5 to 30 nm and a silica concentration of 10 to 50% by weight as observed with a transmission electron microscope.
In the colloidal silica in the first and second inventions, the alkali metal content is preferably 50 ppm or less per silica.

The method for producing colloidal silica in the first and second inventions includes the following steps: (a) a step of preparing an aqueous active silicic acid solution by contacting an aqueous alkali silicate solution with a cation exchange resin;
(B) a step of adding urea and an alkali agent to the activated silicic acid aqueous solution to make it alkaline, and then heating to form colloidal particles; and (c) subsequently, while maintaining the alkalinity while heating, There is a step of growing silica particles by adding an aqueous silicic acid solution and urea and an alkali agent, or by adding an aqueous active silicic acid solution and an alkali agent.
Moreover, it is preferable that this manufacturing method of colloidal silica further has the process of concentrating a silica after (c) process.
The formation of silica particles and the growth of silica particles may be collectively referred to as “particle growth” or “growth” below.

  The manufacturing method of the said colloidal silica is substantially the same as the manufacturing method which used the alkali metal hydroxide and alkali silicate which are the usual methods for the alkali agent. That is, in the above-mentioned colloidal silica production method, the process of producing an active silicic acid aqueous solution from sodium silicate is the same as that in a conventional method, except that urea and an alkaline agent are used in the silica particle formation process. In the process of growing silica particles, urea may or may not be added. The step of concentrating the obtained colloidal silica is the same as the conventional method. The alkali agent may be an alkali metal hydroxide used in a conventional manner or an organic alkali.

  According to the present invention, an ink-absorbing filler for printing paper, a spreadability improving agent for paints, a hydrophilic coating material for various material surfaces, a high-strength binder, a high-purity silica gel, a raw material for high-purity ceramics, and a catalyst Colloidal silica useful for binders, abrasives for electronic materials and the like can be provided at low cost.

2 is a TEM photograph of colloidal silica that has undergone the silica particle growth step of Example 1; 2 is a TEM photograph of colloidal silica obtained in Example 1. FIG. 3 is a TEM photograph of colloidal silica obtained in Example 2. FIG. 4 is a TEM photograph of colloidal silica obtained in Example 3. 4 is a TEM photograph of colloidal silica that has undergone the silica particle growth step of Example 4. FIG. 4 is a TEM photograph of colloidal silica obtained in Example 4.

The present invention will be further described below.
The colloidal silica of the present invention is obtained using an active silicic acid aqueous solution as a raw material in the presence of urea. Therefore, in the colloidal silica of the present invention, urea is (1) a form in which the urea is fixed to the inside of the particle and / or a coating on the particle surface in the course of particle growth, and (2) a form in which the urea is attached to the particle surface after the particle growth. , (3) may exist in three forms: dissolved in the liquid phase. The coating mainly composed of silica containing urea in the present invention is defined as a silica portion grown when particle growth is performed in the presence of urea, and the thickness thereof is not particularly limited. Usually, it is 3 nm to 20 nm.
The colloidal silica of the present invention preferably has a major axis / minor axis ratio in the range of 1.2 to 15 by observation with a transmission electron microscope of the non-spherical irregularly shaped silica particle group and an average value of the major axis / minor axis ratio. Is 1.3-10. The major axis / minor axis ratio in the present invention is determined by assigning a scale to the obtained transmission electron micrograph of colloidal silica and, for 100 randomly selected silica particles, the longest side a and the shortest side b of the silica particles. , And using this value (a1, a2,..., A100 and b1, b2,..., B100), the major axis / minor axis ratio (a1 / b1, a2 / b2,... A100 / b100) is calculated, and the arithmetic average value of the five values on the minimum value side is set as the upper limit, and the arithmetic average value of the five values on the maximum value side is set as the lower limit. The average value of the major axis / minor axis ratio in the present invention refers to the longest side a of the silica particles of 100 randomly selected silica particles by assigning a scale to the obtained transmission electron micrograph of colloidal silica. And the shortest side b, and using this value (a1, a2,..., A100 and b1, b2,..., B100), the major axis / minor axis ratio (a1 / b1, a2 / b2,..., a100 / b100), and is an arithmetic average value of 90 values excluding 5 values on the maximum value side and the minimum value side.

  The colloidal silica of the present invention contains urea, and the preferred molar ratio of silica / urea is 20-300. It is preferable to contain urea used in the process of grain growth. A 1% aqueous solution of urea has a pH of about 6 to 7 and is not alkaline, so it does not contribute to particle growth. However, it affects the shape of the silica particles during particle growth. Urea appears to bind or adsorb to the growing silica particle surface to inhibit particle growth at the binding site and prevent spherical growth. When the silica / urea molar ratio is smaller than 20 during particle growth, particle growth cannot be performed at all, and silica gel may be generated. If the molar ratio of silica / urea is larger than 300 during particle growth, the shape of the silica particles becomes nearly spherical. However, this silica / urea molar ratio is a value determined from the amount of urea present in the final product that has undergone the manufacturing process. Urea dissolved in the liquid phase is decomposed into ammonia and carbonic acid by heating in the presence of alkali components in the silica particle formation process and silica particle growth process, and further decreases with water in the concentration process by ultrafiltration. . Therefore, the amount of urea used in the manufacturing process is more than twice the amount of urea present in the final product.

  However, the presence of organic matter may cause secondary problems in wastewater treatment. Considering such a case, a product from which urea is removed is also required. A method for reducing urea as much as possible by effectively utilizing ultrafiltration is also included in the category as one of the production methods of the present invention.

  The colloidal silica containing the non-spherical irregular-shaped silica particle group in the present invention is a colloidal shape having a cocoon-like shape or a bent rod-like shape such as a worm, and containing silica particles having different shapes. Silica. Specifically, it is colloidal silica containing silica particles having a shape as shown in FIGS. The major axis / minor axis ratio of the non-spherical irregularly shaped silica particles is preferably in the range of 1.2 to 15. Non-spherical particles occupy the majority, and some particles are nearly spherical. The silica particles shown in FIGS. 1 to 6 are merely examples, and the shapes thereof vary depending on the production conditions. However, in the colloidal silica of the present invention, most of the silica particles are not spherical.

  The silica particles contained in the colloidal silica of the present invention have a shape very similar to that of fumed silica. The silica particles of fumed silica are generally a group of elongated and irregularly shaped silica particles having a major axis / minor axis ratio of 5 to 15. The primary particle diameter of fumed silica (sometimes simply referred to as the particle diameter) is the short diameter (thickness) of the primary particles and is usually 7 to 40 nm. Further, the primary particles aggregate to form secondary particles, and the appearance of the slurry is white. For this reason, there are defects such as a problem that the particles settle when the slurry is left for a long time and a transparent film or coating film is not formed.

  However, the silica particles contained in the colloidal silica of the present invention do not form secondary particles due to aggregation as seen in fumed silica, and the appearance of the slurry is transparent or translucent. There is no problem that the particles settle, and a transparent film or coating film can be obtained.

  The method for producing colloidal silica of the present invention is characterized in that an active silicic acid aqueous solution of a water glass method is used as a silica source, and urea and an alkaline agent are used in the particle forming step. In the particle formation process, the presence of urea is essential. On the other hand, in the particle growth step, since the urea added in the previous step remains in the liquid phase, the silica particles may be grown by adding only the active silicic acid aqueous solution and the alkali agent, but the active silicic acid aqueous solution, urea and Silica particles may be grown by adding an alkali agent.

  As the alkali agent, an alkali metal hydroxide such as sodium hydroxide is the most suitable material. When alkali metals are not preferred, nitrogen-containing organic alkali compounds such as amines and quaternary ammonium hydroxide can be used. As amines, tertiary amines with low volatility such as triethanolamine, secondary amines such as piperazine, and aliphatic amines such as ethylenediamine can be used. As quaternary ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethyl-2-hydroxyethylammonium hydroxide (also known as choline hydroxide) can be used.

  By using the nitrogen-containing organic alkali compound, the alkali metal content per silica can be 50 ppm or less. In applications such as ceramics, catalyst binders, and abrasives for electronic materials, it is necessary to set the alkali metal content to this level. More preferably, it is 30 ppm or less.

  As the alkali silicate aqueous solution used as a raw material, a sodium silicate aqueous solution generally called water glass (water glass No. 1 to No. 4 etc.) is preferably used. This is relatively inexpensive and can be easily obtained. Moreover, in the semiconductor use which dislikes Na ion, it is preferable to use a potassium silicate aqueous solution as a raw material instead of a sodium silicate aqueous solution. There is also a method of preparing an alkali silicate aqueous solution by dissolving solid alkali metal silicate in water. Alkali metasilicates are produced through a crystallization process, and therefore some of them have few impurities. The aqueous alkali silicate solution is diluted with water as necessary.

  The cation exchange resin used in the present invention can be appropriately selected from known ones and is not particularly limited. The contact step between the aqueous alkali silicate solution and the cation exchange resin is, for example, diluted with an aqueous alkali silicate aqueous solution to a silica concentration of 3 to 10% by weight, then contacted with an H-type strongly acidic cation exchange resin for dealkalization, and if necessary It can carry out by making it contact with OH type strong basic anion exchange resin, and carrying out a deanion. By this step, an active silicic acid aqueous solution is prepared. There have been various proposals for details of the contact conditions, and any known conditions can be adopted in the present invention.

  Next, silica particles are formed. In this particle formation step, the usual operation is performed except that urea is added to the active silicic acid aqueous solution. For example, silica particles (seed particles) can be formed by adding urea and an alkaline agent to the active silicic acid aqueous solution so that the pH is 8 or more and heating to 60 to 240 ° C. Either the urea or alkaline agent may be added first. Urea may be added as a solid, but it is preferably added in the form of an aqueous solution preliminarily dissolved in water.

  Next, particle growth is performed using a build-up method using the silica particles formed above as a seed sol. In this particle growth step, a seed sol having a pH of 8 or more is heated to 60 to 240 ° C., and while maintaining the pH at 8 to 10, an active silicic acid aqueous solution, urea and an alkaline agent are added, or an active silicic acid aqueous solution. And an alkali agent are added to grow silica particles. In this way, the average minor axis of the silica particles by observation with a transmission electron microscope is preferably 5 to 30 nm.

  The colloidal silica obtained through the particle formation step and the particle growth step may be concentrated as necessary. The silica may be concentrated by evaporating water, but in terms of energy, ultrafiltration is more advantageous.

  The ultrafiltration membrane used when concentrating silica by ultrafiltration will be described. Separation to which the ultrafiltration membrane is applied targets particles of 1 nm to several microns, but also targets dissolved polymer substances, and therefore, filtration accuracy is expressed by a molecular weight cut off in the nanometer range. In the present invention, an ultrafiltration membrane having a fractional molecular weight of 15,000 or less can be preferably used. When a film in this range is used, particles of 1 nm or more can be separated. More preferably, an ultrafiltration membrane having a fractional molecular weight of 3,000 to 15,000 is used. If the membrane is less than 3,000, the filtration resistance is too large and the treatment time becomes long and uneconomical. If it exceeds 15,000, the degree of purification is low. The material of the membrane includes polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon, etc., any of which can be used. Polysulfone membranes are easy to use in terms of heat resistance and filtration speed. The shape of the membrane includes a spiral type, a tubular type, and a hollow fiber type, and any of them can be used. Hollow fiber membrane is compact and easy to use. In addition, if the ultrafiltration process also serves to wash out and remove excess urea, if necessary, it is further washed out and removed by adding pure water after reaching the target silica concentration to remove urea. You can also work to increase the rate. In this step, it is preferable to concentrate so that the silica concentration is 10 to 50% by weight.

  As described above, colloidal silica containing non-spherical irregular-shaped silica particles to which urea is immobilized can be obtained by producing colloidal silica using an active silicic acid aqueous solution as a raw material in the presence of urea. The colloidal silica thus obtained contains no polyvalent metal compounds other than silicon such as calcium salt, magnesium salt, aluminum salt, etc., so that the ink absorbent filler for printing paper, the paint spreadability improving agent, It is useful for hydrophilic coating materials on the surfaces of various materials, high-strength binders, high-purity silica gel, raw materials for high-purity ceramics, binders for catalysts, abrasives for electronic materials, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples. The following apparatus was used for the measurement in the examples.
(1) TEM observation: Hitachi, Ltd., transmission electron microscope H-7500 type was used.
(2) BET specific surface area: Shimadzu Corporation, Flowsorb 2300 type was used.
(3) Total urea analysis: Shimadzu Corporation, total organic carbon meter TOC-5000A, SSM-5000A were used. The amount of carbon was converted to urea. Specifically, after measuring the total carbon content (TC) and the inorganic carbon content (IC), the total organic carbon content (TOC) was determined by TOC = TC-IC. It is presumed that the IC component is mainly carbonic acid dissolved in sodium silicate. A glucose aqueous solution having a carbon content of 1% by weight was used as a standard for TC measurement, and sodium carbonate having a carbon content of 1% by weight was used as a standard for IC measurement. A calibration curve was prepared using ultrapure water as a standard with 0% by weight of carbon, using the above-mentioned standards, TC of 150 μl and 300 μl, and IC of 250 μl. In the TC measurement of the sample, about 100 mg of the sample was collected and burned in a 900 ° C. combustion furnace. In IC measurement, about 20 mg of a sample was collected, about 10 ml of (1 + 1) phosphoric acid was added, and the reaction was promoted in a 200 ° C. combustion furnace.
Moreover, in the sample containing tetramethylammonium hydroxide, tetramethylammonium was quantified by the following method (7), subtracted from TC, and converted into the amount of urea.
(4) Liquid phase urea analysis: The liquid phase was taken out from the sample by ultrafiltration and measured by the same method as in (3) above.
(5) Calculation of immobilized urea: The amount of urea immobilized was calculated by subtracting the amount of liquid phase urea from the total amount of urea.
(6) Metal element analysis: HORIBA, Ltd., ICP emission analyzer, ULTIMA2 was used.
(7) Ion chromatographic analysis of tetramethylammonium (TMA): Dionex Corporation, ion chromatography ICS-1500 was used. Specifically, the liquid phase TMA was measured by diluting a sample with pure water from 1,000 times to 5,000 times. For the measurement of total TMA, 3 g of 20 wt% NaOH and pure water was added to 5 g of sample as a pretreatment, and heated at 80 ° C. to completely dissolve silica. This solution was diluted with pure water from 1,000 times to 5,000 times and measured to obtain the amount of TMA.

[Example 1]
(A) Preparation of active silicic acid aqueous solution 28 kg of deionized water and 5.2 kg of JIS No. 3 sodium silicate (SiO ₂ : 28.8 wt%, Na ₂ O: 9.7 wt%, H ₂ O: 61.5 wt%) Was added and mixed uniformly to prepare diluted sodium silicate having a silica concentration of 4.5% by weight. This diluted sodium silicate was passed through a 20 liter column of H-type strongly acidic cation exchange resin (Amberlite (registered trademark) IR120B manufactured by Organo Corp.) regenerated with hydrochloric acid in advance, and the silica concentration was 3.7% by weight. 40 kg of an active silicic acid aqueous solution having a pH of 2.9 was obtained.

(B) Formation of silica particles Next, an alkaline agent was added to the obtained active silicic acid aqueous solution to make it alkaline, and then a 10 wt% aqueous urea solution (prepared by adding urea (reagent) to pure water) was added. Heated to form silica particles. That is, to 500 g of a part of the obtained active silicic acid aqueous solution, a 5 wt% sodium hydroxide aqueous solution was added with stirring to a pH of 8.5, 12 g of 10 wt% aqueous urea solution was added, Keep time and let cool.

The obtained colloidal silica was 460 g by evaporation of water, and the silica concentration was 4.0% by weight. Further, this colloidal silica has a pH of 10.0 at 25 ° C., and has a minor axis of about 5 nm and a major axis / minor axis ratio in the range of 1.2 to 3 when observed with a transmission electron microscope (TEM). And it consisted of the non-spherical irregular-shaped silica particle group whose average value of major axis / minor axis ratio is 1.5.
This colloidal silica was calculated to have a silica / urea molar ratio of 21 based on the amount of active silicic acid aqueous solution used and the analytical value of urea. Since the total urea concentration of colloidal silica was 0.196 wt% and the liquid phase urea concentration was 0.166 wt%, the immobilized urea was calculated to be 0.037 wt%. It was confirmed that urea was fixed to silica.

(C) Growth of Silica Particles Subsequently, the obtained colloidal silica was heated again to 100 ° C., and a build-up method was taken. 1,000 g of active silicic acid aqueous solution and 12 g of 10 wt% urea aqueous solution were taken for 2 hours. Added. During the addition of the active silicic acid aqueous solution and the urea aqueous solution, a 5 wt% sodium hydroxide aqueous solution was simultaneously added so that the pH was in the range of 9 to 10 while maintaining 100 ° C. After cooling by evaporation of water during addition, 1,360 g of colloidal silica was obtained. The silica concentration was 4.1% by weight. This colloidal silica has a pH of 9.4 at 25 ° C., has a minor axis of about 10 nm as observed with a transmission electron microscope (TEM), and has a major axis / minor axis ratio of 1.2 to 4 and a major axis. / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 2. A TEM photograph is shown in FIG. The particle diameter in terms of specific surface area by BET method was 9.7 nm.
The colloidal silica was calculated to have a silica / urea molar ratio of 42 based on the amount of active silicic acid aqueous solution used and the analytical value of urea. Since the total urea concentration of colloidal silica was 0.097 wt% and the liquid phase urea concentration was 0.077 wt%, the immobilized urea was calculated to be 0.023 wt%. It was confirmed that urea was fixed to silica.

Further, the obtained colloidal silica was heated again to 100 ° C., and 1,000 g of an active silicic acid aqueous solution and 12 g of a 10 wt% urea aqueous solution were added over 2 hours. During the addition of the active silicic acid aqueous solution and the urea aqueous solution, a 5 wt% sodium hydroxide aqueous solution was simultaneously added so that the pH was in the range of 9 to 10 while maintaining 100 ° C. After cooling by evaporation of water during addition, 1,700 g of colloidal silica was obtained. The silica concentration was 5.4% by weight. This colloidal silica has a pH of 9.4 at 25 ° C., has a minor axis of about 12 nm, and has a major axis / minor axis ratio in the range of 1.2 to 4 and a major axis in transmission electron microscope (TEM) observation. / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 1.5. A TEM photograph is shown in FIG.
This colloidal silica was calculated to have a silica / urea molar ratio of 102 based on the amount of active silicic acid aqueous solution used and the analytical value of urea. Since the total urea concentration of colloidal silica was 0.0588% by weight and the liquid phase urea concentration was 0.0535% by weight, the immobilized urea was calculated to be 0.0082% by weight. It was confirmed that urea was fixed to silica.

(D) Concentration of colloidal silica Finally, by pump circulation using a hollow fiber type ultrafiltration membrane having a molecular weight cut off of 6,000 (Microsa (registered trademark) UF module SIP-1013 manufactured by Asahi Kasei Co., Ltd.) Pressure filtration was performed to concentrate the colloidal silica to a silica concentration of 17.7% by weight, and about 520 g of colloidal silica was recovered. This colloidal silica has a pH of 9.0 at 25 ° C., has a minor axis of about 12 nm as observed with a transmission electron microscope (TEM), and has a major axis / minor axis ratio of 1.2 to 4 and a major axis. / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 1.5. Moreover, the particle diameter in terms of specific surface area by BET method was 12.1 nm.
The total urea concentration of the colloidal silica was 0.0610% by weight and the silica / urea molar ratio was 290. Since the liquid phase urea concentration was 0.0535% by weight, the immobilized urea was calculated to be 0.0171% by weight. It was confirmed that urea was fixed to silica. The sodium content per silica was 16,900 ppm.

[Example 2]
To 500 g of the same active silicic acid aqueous solution as used in Example 1, a 5 wt% aqueous sodium hydroxide solution was added with stirring to adjust the pH to 8.3, and 20 g of 10 wt% aqueous urea solution was added. It was kept for 1 hour and allowed to cool.
The obtained colloidal silica has a pH of 9.7 at 25 ° C., a short diameter of about 6 nm, a long diameter / short diameter ratio in the range of 2 to 10 and a long diameter as observed with a transmission electron microscope (TEM). / It consisted of a group of non-spherical irregularly shaped silica particles having an average value of the minor axis ratio of 5.
Subsequently, the obtained colloidal silica was heated again to 100 ° C., and 1,500 g of an active silicic acid aqueous solution was added over 5 hours. During the addition of the active silicic acid aqueous solution, a 5% by weight sodium hydroxide aqueous solution was simultaneously added so that the pH was in the range of 9 to 10 while maintaining 100 ° C. After cooling by evaporation of water during addition, 1,617 g of colloidal silica was obtained. The silica concentration was 4.6% by weight. This colloidal silica has a pH of 9.2 at 25 ° C., a transmission electron microscope (TEM) observation has a minor axis of about 12 nm, a major axis / minor axis ratio of 1.5 to 5 and a major axis. / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 2. A TEM photograph is shown in FIG.
Finally, pressure filtration by pump circulation is performed using a hollow fiber type ultrafiltration membrane with a molecular weight cut off of 6,000 (Microsa (registered trademark) UF module SIP-1013 manufactured by Asahi Kasei Co., Ltd.), and silica The colloidal silica was concentrated to a concentration of 15.0% by weight, and about 493 g of colloidal silica was recovered. This colloidal silica has a pH of 9.0 at 25 ° C., has a minor axis of about 13 nm, and has a major axis / minor axis ratio in the range of 1.5 to 5 and a major axis in transmission electron microscope (TEM) observation. / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 2. The particle diameter in terms of specific surface area by BET method was 12.6 nm.
The total urea concentration of the colloidal silica was 0.0635% by weight, and the silica / urea molar ratio was 236. Since the liquid phase urea concentration was 0.0610% by weight, the immobilized urea was calculated to be 0.0116% by weight. It was confirmed that urea was fixed to silica. Further, the sodium content per silica was 19,300 ppm.

Example 3
About 526 g of colloidal silica was recovered in the same manner as in Example 2 except that the amount of 10 wt% urea aqueous solution added was 28 g. The silica concentration was 14.1% by weight. This colloidal silica has a pH of 9.0 at 25 ° C., a short diameter of about 11 nm as observed by a transmission electron microscope (TEM), a long diameter / short diameter ratio in the range of 1.5 to 6 and a long diameter. / It consisted of a group of non-spherical irregularly shaped silica particles having an average value of the minor axis ratio of 3. A TEM photograph is shown in FIG.
The total urea concentration of the colloidal silica was 0.0889% by weight and the silica / urea molar ratio was 159. Since the liquid phase urea concentration was 0.0898% by weight, the immobilized urea was calculated to be 0.0118% by weight. It was confirmed that urea was fixed to silica. The sodium content per silica was 21,300 ppm.

Example 4
To 500 g of the same active silicic acid aqueous solution used in Example 1, 16 g of 25 wt% tetramethylammonium hydroxide aqueous solution was added with stirring to pH 8.3, and 12 g of 10 wt% urea aqueous solution was added. It was kept at 100 ° C for 1 hour and allowed to cool.
The obtained colloidal silica was 460 g by evaporation of water, and the silica concentration was 4.0% by weight. Further, this colloidal silica has a pH of 9.7 at 25 ° C., a short diameter of about 6 nm, a long diameter / short diameter ratio in the range of 4 to 12 and a long diameter as observed with a transmission electron microscope (TEM). / It consisted of a group of non-spherical deformed silica particles having an average value of the minor axis ratio of 8. A TEM photograph is shown in FIG. The particle diameter in terms of specific surface area by BET method was 5.9 nm.
This colloidal silica was calculated to have a silica / urea molar ratio of 21 based on the amount of active silicic acid aqueous solution used and the analytical value of urea. Since the total urea concentration of colloidal silica was 0.196 wt% and the liquid phase urea was 0.166 wt%, the immobilized urea was calculated to be 0.037 wt%. It was confirmed that urea was fixed to silica. The sodium content per silica was 27 ppm.

Subsequently, the obtained colloidal silica was heated again to 100 ° C., and 1,000 g of an active silicic acid aqueous solution was added over 2 hours. During the addition of the active silicic acid aqueous solution, a 25 wt% tetramethylammonium hydroxide aqueous solution was simultaneously added so that the pH was in the range of 9 to 10 while maintaining 100 ° C. After cooling by evaporation of water during addition, 1,360 g of colloidal silica was obtained. The silica concentration was 4.1% by weight. The colloidal silica has a pH of 9.1 at 25 ° C., a transmission electron microscope (TEM) observation has a minor axis of about 10 nm, a major axis / minor axis ratio in the range of 2 to 7, and a major axis / short axis. It consisted of non-spherical irregular-shaped silica particles having an average diameter ratio of 4. A TEM photograph is shown in FIG. The particle diameter in terms of specific surface area by the BET method was 10.1 nm.
The colloidal silica was calculated to have a silica / urea molar ratio of 69 based on the amount of active silicic acid aqueous solution used and the analytical value of urea. Since the total urea concentration of colloidal silica was 0.059 wt% and the liquid phase urea was 0.050 wt%, the immobilized urea was calculated to be 0.011 wt%. It was confirmed that urea was fixed to silica. The sodium content per silica was 19 ppm.

Claims (8)

  A colloidal silica comprising a group of non-spherical irregularly shaped silica particles in which urea is fixed inside the particles.   Colloidal silica comprising a group of non-spherical irregularly shaped silica particles in which urea is immobilized by disposing a coating mainly composed of silica containing urea on the surface.   3. The colloidal silica according to claim 1, wherein the silica / urea molar ratio is 20 to 300.   The liquid phase contains urea, and the non-spherical irregularly shaped silica particles have a major axis / minor axis ratio in the range of 1.2 to 15 by observation with a transmission electron microscope, and an average value of the major axis / minor axis ratio is 1.3 to The colloidal silica according to claim 1, wherein the colloidal silica is 10.   The colloidal silica according to claim 1 or 2, wherein the average minor axis of the silica particles by observation with a transmission electron microscope is 5 to 30 nm, and the concentration of silica is 10 to 50% by weight.   The colloidal silica according to claim 1 or 2, wherein the alkali metal content per silica is 50 ppm or less. The following steps: (a) A step of bringing an alkali silicate aqueous solution into contact with a cation exchange resin to prepare an active silicate aqueous solution;
(B) a step of adding urea and an alkali agent to the activated silicic acid aqueous solution to make it alkaline, and then heating to form silica particles, and (c) subsequently, while maintaining the alkalinity under heating, 3. The method of adding colloidal silica according to claim 1 or 2, further comprising a step of growing silica particles by adding an aqueous silicic acid solution, urea and an alkali agent, or adding an active silicic acid aqueous solution and an alkali agent. Production method.   The method for producing colloidal silica according to claim 7, further comprising (d) a step of concentrating silica after the step (c).

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