JP2007277023A - High-concentration silica slurry and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-concentration silica slurry which has a solid concentration of 20 wt.% or more and is stable for a long time with a positive charge. <P>SOLUTION: There is used a high-concentration silica slurry having a silica concentration of 20-50%, a pH of 1.5-5.5, a conductivity of 300-1,500 μS/cm, and a zeta potential of silica particles in the high-concentration silica slurry of +10 to +80 mV. Such a high-concentration silica slurry is produced by grinding and dispersing a silica gel in water to obtain a negatively charged slurry, mixing the obtained slurry with a cationic polymer having a molecular weight of 2,000-100,000, washing the obtained water-containing silica with water to remove a salt, and then re-dispersing the resulting gel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-concentration silica slurry and a method for producing the same. The high-concentration silica slurry produced by the method of the present invention is useful for various applications such as recording paper, abrasives and cosmetics.

The silica slurry referred to in the present invention is a silica colloid in which silica represented by SiO ₂ is stably dispersed in a solvent without being precipitated.

  A common silica colloid is silica sol. Silica sol is industrially produced by a method such as an ion exchange resin method. For example, there are Ludox manufactured by Du Pont, Snotex manufactured by Nissan Chemical Co., Ltd., Cataloid manufactured by Catalytic Chemical Industry Co., Ltd., and the like.

The particle size of silica sol is about 0.007 to 0.04 μm, the specific surface area measured by BET method is about 70 to 400 m ² / g, and silica sol has silica fine particles of about 0.007 to 0.04 μm in the solvent. And dispersed without agglomeration. As a high-purity silica colloid, a silica colloid synthesized by a sol-gel method using alkoxysilane as a raw material is known. For example, there is a quatron made by Fuso Chemical Industry Co., Ltd. The particle diameter of the silica colloid synthesized by the sol-gel method is 0.3 to 25 μm, the specific surface area is about 0.3 to 12 m ² / g, and the silica fine particles of about 0.3 to 25 μm are not aggregated in the solvent. It is distributed.

  These silica colloids are stably dispersed by the electrostatic repulsion due to the zeta potential of negative charges due to the dissociation of silanol groups on the surface of the silica particles.

  For example, if a silica colloid having a negative charge is used in a coating liquid for inkjet paper that has been widely applied in recent years, the ink component often has a negative charge, which tends to cause problems with fixability and water resistance. An alumina hydrate colloid having a positive charge may be used for a paper coating solution. However, the alumina hydrate colloid tends to cause a problem in ink absorbability, and a stable silica slurry having a positive charge with a silica colloid excellent in ink absorbability is desired.

  Further, the negatively charged silica sol tends to be unstable when used in the acidic region. For example, a silica colloid having a positive charge is desired for a coating liquid for ink jet paper used in the weakly acidic region.

  In recent years, as a positively charged sol, for example, a silica-alumina composite sol is a colloidal solution in which agglomerated particles containing silica and alumina are dispersed in an aqueous solvent, and the silica has a spherical primary particle and an average particle diameter of 2 to 30 nm, Silica-alumina composite sol (for example, Patent Document 1) in which the average particle diameter of the aggregated particles is 100 to 1000 nm, the zeta potential of the aggregated particles is +10 mV or more, and the pH of the solution is 3 to 9, inorganic fine particle dispersion in which inorganic fine particles are dispersed Liquid containing inorganic fine particles (for example, vapor phase method silica) and a water-soluble polyvalent metal compound (for example, basic polyaluminum hydroxide), and having a zeta potential of +60 mV or more (for example, patent literature) 2) is disclosed.

  On the other hand, a method of mixing silica and a cationic resin has been proposed.

For example, a mixed liquid obtained by mixing silica fine particles having an average particle diameter of less than 200 nm and a cationic resin in a polar solvent is allowed to collide at a treatment pressure of 300 kgf / cm ² or more, or the inlet side and the outlet side of the orifice It has been reported that the dispersion liquid is re-dispersed to the original dispersion state by passing through the orifice under the condition that the pressure difference on the side is 300 kgf / cm ² or more. (For example, patent document 3) Moreover, it is the dispersion liquid which disperse | distributed wet silica and cationic resin in the polar solvent, Comprising: The silica density | concentration in this dispersion liquid is over 22 weight%, and in this dispersion liquid There is disclosed a cationic resin-modified silica dispersion in which the silica particles have an average particle diameter of less than 0.5 μm and the cationic resin is a cyclic ammonium salt type cationic resin having an average molecular weight of 10,000 or less. (For example, Patent Document 4)
Generally, when negatively charged silica particles and a cationic polymer are mixed, the viscosity increases, and further gelation and aggregation occur. In Patent Document 3 and Patent Document 4, a silica dispersion having a positive charge is obtained by redispersing an unstable mixture of silica particles and a cationic resin.

  However, in Patent Document 3 and Patent Document 4, a mixed solution obtained by mixing silica particles and a cationic polymer is mechanically dispersed, and an ammonium salt type cationic polymer or sulfuric acid is contained in the dispersion. Therefore, the stability of the high concentration silica slurry has not been sufficient yet.

  In addition, a method for storing a mixed solution of silica and a cationic resin has been proposed. For example, using a dry silica as the silica, the dry silica is dispersed in a polar solvent together with a cationic resin, and then a cationic resin-modified silica dispersion (for example, aging at a temperature in the range of 5 to 45 ° C. for 10 days or more) Patent Document 5) and a cationic resin-modified silica dispersion in which a cationic resin-modified silica dispersion in which silica and a cationic resin are dispersed in a polar solvent is stored in a temperature range of 5 ° C. to 30 ° C. (for example, Patent Document 6) is disclosed.

  However, the cationic resin-modified silica dispersions of Patent Document 5 and Patent Document 6 are not washed after being aged for a long time in Patent Document 5, but at a temperature of 30 ° C. or less in Patent Document 6. Although it has been stored and transported, it was not washed, and the stability was not sufficient.

JP-A-2001-180926 (Claim 4) JP-A-2004-285308 (column 0010) JP 2000-239536 (column 0009) JP-A-2005-762 (Claim 1) JP-A-2001-207078 (Claim 2) JP 2003-129395 A (Claim 1)

  In the present invention, the silica concentration having high stability is 20 to 50%, the pH is 1.5 to 5.5, the conductivity is 300 to 1500 μS / cm, and the zeta potential of the silica particles in the high concentration silica slurry is +10. The present invention provides a high concentration silica slurry of ˜ + 80 mV and a production method thereof.

  As a result of intensive studies focusing on the stability mechanism of colloidal particles in the method for producing the high-concentration fine silica slurry of the present invention industrially easily and at low cost, the inventor has found that the silica concentration is 20 to 50%. In a high concentration silica slurry in which the pH is 1.5 to 5.5, the conductivity is 300 to 1500 μS / cm, and the zeta potential of the silica particles in the high concentration silica slurry is +10 to +80 mV, It is stable without sedimentation, and such high-concentration silica slurry is pulverized and dispersed by a media mill using silica gel with a high purity silica ball of 0.5 to 5 mm and a purity of 99.95% or more as a medium. After obtaining a negative charge high-concentration slurry, the silica hydrogel obtained by mixing a cationic polymer having a molecular weight of 2,000 to 100,000 is washed with water to remove salts. The present invention has been completed by finding out that it can be obtained by redispersion.

  The present invention focuses on the stability mechanism of colloidal particles, particularly the influence of electrolyte concentration on the stability of colloidal particles, and is particularly characterized in the conductivity of high-concentration silica slurry. And a cationic polymer, and the resulting cationic polymer-containing silica-containing silica gel containing an electrolyte such as a cationic polymer or an acid is washed with water to remove salts.

  Hereinafter, the present invention will be described in detail.

  The silica concentration of the high concentration silica slurry of the present invention is 20 to 50%, preferably more than 25% and 45% or less. When the silica concentration is less than 20%, the industrial utility value is low. On the other hand, when the silica concentration exceeds 50%, it is difficult to obtain the viscosity within the range of the present invention.

  The silica concentration in the present invention refers to the weight percent calculated from the remaining solid content obtained by evaporating the solvent in the high concentration silica slurry.

  The pH of the high concentration silica slurry of the present invention is particularly preferably 1.5 to 5.5. When the pH exceeds 5.5, it is difficult to obtain a particle state in the range of the present invention, and there is a problem in stability. On the other hand, when the pH is less than 1.5, a problem with stability is likely to occur.

  The high-concentration silica slurry of the present invention needs to have a conductivity of 300 to 1500 μS / cm. Such conductivity is achieved by a low electrolyte concentration.

  If the conductivity exceeds 1500 μS / cm, there is a problem in stability, while a slurry of less than 300 μS / cm becomes very difficult to purify and is difficult to manufacture industrially.

  The high concentration silica slurry obtained by the present invention has a high surface charge and excellent stability, and in particular, the zeta potential is +10 to +80 mV. If the zeta potential is less than +10, problems with stability are likely to occur. On the other hand, the upper limit is not particularly limited, but it is difficult to produce a product exceeding +80 mV.

  The zeta potential is not particularly limited, and can be measured by electrophoresis, ultrasonic method, ESA (Electrokinetic Sonic Amplitude) method or the like.

  In the high-concentration silica slurry of the present invention, the cationic polymer is adsorbed on the surface of the negatively charged silica particles to generate a positive charge, while promoting the aggregation of the silica particles.

The silica particles in the high concentration silica slurry of the present invention preferably have an average particle size of 0.01 to 0.5 μm and a specific surface area of 150 to 700 m ² / g.

In general, it is known that the smaller the particle and the higher the concentration, the more unstable the silica colloid becomes and it becomes difficult to obtain a stable silica colloid. The high concentration slurry of the present invention is fine particles of 0.004 to 0.02 μm (equivalent diameter calculated from specific surface area value, equivalent diameter D2 (μm) = (2720 / As) / 1000, As is specific surface area (m ² / G)) is preferably a high-concentration slurry in which agglomerated particles having a size of 0.01 to 0.5 μm are stably dispersed in a solvent. Is different.

  In the present invention, silica particles having an average particle size of 0.01 μm or more and less than 0.1 μm are particularly preferable in that the particles do not settle for a long time, and those having an average particle size of 0.1 μm or more and 0.5 μm or less It is particularly preferred in that it is difficult to gel and is easy to handle.

  If the average particle diameter exceeds 0.5 μm, particles will settle and it will be difficult to obtain a stable slurry. On the other hand, it is industrially difficult to produce particles having an average particle size of less than 0.01 μm.

  In addition, although the measuring method of the average particle diameter of this invention is not specifically limited, For example, it can measure easily by a laser diffraction scattering method or the centrifugal sedimentation method.

The specific surface area of the silica particles in the high-concentration silica slurry of the present invention is preferably 150 to 700 m ² / g. The specific surface area as used herein refers to a value obtained by measuring the silica gel obtained by evaporating and drying the solvent in the silica slurry by the BET method.

When the specific surface area is less than 150 m ² / g, the viscosity exceeds the range of the present invention. On the other hand, it is difficult to industrially produce ultrafine silica particles exceeding 700 m ² / g.

Furthermore, the high concentration silica slurry of the present invention has an average particle diameter of 0.01 to 0.5 μm (D1), a specific surface area of 150 to 700 m ² / g (equivalent diameter D2 = 0.004 to 0.02 μm), and a degree of aggregation. D1 / D2 = high concentration silica slurry containing aggregated silica particles of 3 or more (here, equivalent diameter D2 (μm) = (2720 / As) / 1000, As is specific surface area (m ² / g)) Particularly preferred.

In the conventional silica sol, a BET specific surface area of 70 to 400 m ² / g (BET equivalent diameter D2 = 0.007 to 0.04 μm) or a particle diameter (D1) of 0.007 to 0.04 μm is satisfied alone. There were some, but none at the same time. Particularly, silica fine particles having a D1 / D2 ratio of less than 3 were only dispersed in a solvent without agglomeration.

  On the other hand, in the high-concentration silica slurry of the present invention, fine particles (D2) of about 0.004 to 0.02 μm aggregate to 0.01 to 0.5 μm (D1), D1 / D2 becomes 3 or more, and D1 / It differs from the conventional silica sol in the D2 ratio, that is, the degree of aggregation.

For example, the specific surface area, the silica colloid by a conventional sol-gel method, specific surface area of about 0.3~12m ² / g, different from the 150~700m ² / g of specific surface area of the high concentration silica slurry of the present invention .

  The viscosity of the high concentration silica slurry of the present invention is preferably 5 to 300 mPa · s. When it exceeds 300 mPa · s, a problem occurs in handling. On the other hand, the lower limit is not particularly limited, but it is difficult to produce a slurry of less than 5 mPa · s. In addition, although the measuring method in particular of a viscosity is not restrict | limited, For example, a B-type viscosity meter etc. can be illustrated as a general method.

  Since the high concentration silica slurry of the present invention has a positive charge, it is stable over a long period of time. In the high-concentration silica slurry of the present invention, the rate of change in viscosity after standing at room temperature for 1 month is preferably ± 50% or less with respect to the initial viscosity. When the rate of change of viscosity exceeds ± 50%, a problem occurs in handling. On the other hand, the lower limit is not particularly limited, and a change rate of 0% is preferable.

  Next, the manufacturing method of the high concentration silica slurry of this invention is demonstrated.

  The high-concentration silica slurry of the present invention is a silica gel, particularly preferably a silica having a high specific surface area obtained from silicate soda, and a high-purity silica ball having a purity of 0.5 to 5 mm of 99.95% or more is used as a medium. To obtain a negatively charged silica slurry by mixing and dispersing the obtained negatively charged silica slurry and a cationic polymer having a molecular weight of 2,000 to 100,000. It can be produced by re-dispersing after washing with water and removing the salt.

  The high-concentration silica slurry of the present invention uses a cationic polymer having a relatively large molecular weight that is strongly adsorbed and hardly desorbed. Excess salt and unadsorbed polymer are removed from silica particles adsorbed by the cationic polymer. There is a special feature.

  The cationic polymer is not particularly limited as long as it shows cationicity when dissolved in water, but primary to tertiary amine groups (alkylamine salts, dialkylamine salts, etc.), quaternary ammonium groups ( Tetraalkylammonium salt, benzalkonium salt, alkylpyridium salt, imidazolinium salt, etc.), polyethyleneimine, polyvinylimidazoline, aminoalkyl (meth) acrylate acrylamide copolymer, polyacrylamide Mannich modified product, chitosan Etc. can be used.

  The molecular weight of the cationic polymer is 2000-100000. If the molecular weight is less than 2000, problems with stability are likely to occur. On the other hand, when the molecular weight exceeds 100,000, handling tends to be difficult. This cationic polymer is preferably contained in an amount of 0.5 to 10% by weight based on silica.

  The production of the high-concentration silica slurry having a positive charge according to the present invention includes a slurrying step of pulverizing and dispersing the raw silica gel with a media mill using a high-purity silica ball as a medium to obtain a negatively-charged silica slurry, and the obtained negative charge. It comprises a cationic polymer adsorption step in which a cationic polymer is mixed with a silica slurry to form a gel, a washing step in which the obtained gel is washed with water, and a dispersion step in which the washed gel is redispersed.

  As the raw material silica gel in the present invention, it is preferable to use a silica gel produced from silicate soda. There are other raw materials, for example, sol-gel silica using dry process silica using silicon tetrachloride as a raw material, but it is difficult to obtain a high specific surface area, and sol-gel silica gel using alkoxysilane as a raw material is expensive. It is difficult to mass-produce industrially.

Although the specific surface area in the silica gel raw material stage used for the high concentration silica slurry of the present invention is not particularly limited, it is preferably 150 to 800 m ² / g. 150m less than ² / g, if it exceeds 800 m ² / g, a high concentration silica slurry of the present invention - it is difficult to obtain a.

  The negative charge high concentration silica slurry of the present invention can be obtained by pulverizing and dispersing silica gel by a media mill using a high purity silica ball having an average diameter of 0.5 to 5 mm and a purity of 99.95% or more as a medium. preferable. In the present invention, it is preferable to preliminarily pulverize a slurry prepared by adding silica gel to pure water and adding alkali before pulverizing and dispersing by a media mill using a resin ball.

  The average diameter of the high purity silica balls used as the grinding media in the present invention is preferably 0.5 to 5 mm. If it is less than 0.5 mm, it is difficult to separate the ball from the high concentration silica slurry. On the other hand, when it exceeds 5 mm, it is difficult to obtain 0.1 to 0.5 μm fine silica particles of the present invention.

  The purity of the high purity silica ball used as the grinding media in the present invention is 99.95% or more. The purity mentioned here means Al, Ba, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, Sn, Sr, Ti, Zn, contained in the silica ball. It is obtained by converting the amounts of Zr, U and Th as impurities.

  When the purity of the high-purity silica ball is less than 99.95%, for example, when used as a medium for pulverization and dispersion, metal impurities are likely to be mixed. The upper limit of the purity of 99.95% or more is not particularly limited, and can be used up to 100% according to the application.

  In the present invention, a high-purity silica ball is used as a pulverization medium for pulverization and dispersion. However, the media mill used for pulverization is not particularly limited, and can be appropriately selected if the silica ball of the present invention is used. For example, a ball mill, a sand mill, a bead mill and an attritor can be used.

  In a slurry that is pulverized and dispersed using a high-purity silica ball as a pulverizing medium, the colloidal particles can be stably dispersed in order to obtain a slurry in which silica fine particles are stably dispersed at a high concentration. It must be in a surface potential state.

  There is no particular limitation as long as the present invention is satisfied, but the silica concentration is 20 to 50%, the conductivity is 10 to 1500 μS / cm, and the zeta potential of the silica particles in the high concentration silica slurry is − 30 mV or more is preferable.

The silica particles in the high-concentration silica slurry are not particularly limited as long as they satisfy the present invention, but the average particle diameter is 0.01 to 0.5 μm (D1) and the specific surface area is 150 to 700 m. ² / g (equivalent diameter D2 = 0.004 to 0.02 μm) and aggregation degree D1 / D2 = 3 or more are preferable.

  As slurrying conditions, it is preferable to add water to silica gel and adjust the pH to 4 to 9.5 by adding an alkaline aqueous solution or the like. The alkaline aqueous solution is not particularly limited, and ammonia water, sodium hydroxide aqueous solution, amine solution, cationic surfactant, anionic surfactant, nonionic surfactant and the like can be used.

From the method described so far, first, the silica concentration is 20 to 50%, the conductivity is 10 to 1500 μS / cm, the zeta potential of the silica particles in the high concentration silica slurry is −30 mV or more, and the average particle size is 0.01 to 0.00. A negatively charged silica slurry having 5 μm (D1), a specific surface area of 150 to 700 m ² / g (equivalent diameter D2 = 0.004 to 0.02 μm), and a degree of aggregation D1 / D2 = 3 or more is obtained.

  In the present invention, the negatively charged silica slurry obtained by the above method and the cationic polymer are then mixed to obtain a mixed solution.

  The mixing method is not particularly limited, but mixing in the acidic region of pH 1 to 4 is preferable. When the pH exceeds 4, the particles tend to aggregate, while when the pH is less than 1, handling is difficult.

  The obtained mixed solution has a conductivity of 2000 μS / cm or more, and gels upon standing for several hours to several days at room temperature. The state of gelation is not particularly limited, but it is preferably left in a closed container that prevents evaporation of moisture for several hours to several tens of hours at a temperature of 30 ° C to 80 ° C. In addition, the gelation said here is a state which has the intensity | strength which can be crushed.

  Next, the obtained water-containing silica gel containing the cationic polymer is washed with water to remove the salt.

  The washing method is not particularly limited. For example, in order to perform washing uniformly and efficiently, the water-containing silica gel containing a cationic polymer is crushed into a size of several millimeters to several centimeters and then washed with pure water. Is preferred.

  As the washing method, filtration washing in which pure water is passed through the gel, decantation washing in which pure water is added to the gel and the supernatant is removed are preferable. The amount of water washing is not particularly limited as long as the conditions of the present invention are satisfied, but it is preferable to wash with pure water until the conductivity of the washing water becomes 100 to 700 μS / cm. When the conductivity of the cleaning water exceeds 700 μS / cm, it is difficult to satisfy the conductivity of the high-concentration silica slurry of the present invention finally obtained, and the conductivity of the cleaning water is less than 100 μS / cm. Difficult.

  The high-concentration silica slurry having a stable positive charge that satisfies the conditions of the present invention can be obtained by re-dispersing the water-containing silica gel containing the cationic polymer obtained by the above method in water.

  The redispersion method is not particularly limited as long as the conditions of the present invention are satisfied. For example, stirring dispersion using a stirring blade or ultrasonic dispersion, use of a media mill using a high-purity silica ball as a medium, etc. Can be easily redispersed.

  By the above method, the silica concentration having high stability is 20 to 50%, the pH is 1.5 to 5.5, the conductivity is 300 to 1500 μS / cm, and the zeta potential of the silica particles in the high concentration silica slurry is high. A high concentration silica slurry of +10 to +80 mV is obtained.

  The high concentration silica slurry of the present invention is a high concentration silica slurry having a high silica concentration of 20 to 50% and a stable viscosity for a long period of time. Furthermore, since the manufacturing process is simple and inexpensive silicate soda can be used as a raw material, the cost is low.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

  In the following description, the average particle diameter, specific surface area, viscosity, silica concentration and purity (impurity analysis) are measured by the following method.

  The average particle diameter is a volume average particle diameter measured by MICROTRC (UPA150 particle size analyzer manufactured by Nikkiso Co., Ltd.). The specific surface area is a value measured by BET method using MONOSORB (manufactured by QUANTA CHROME) at a pretreatment temperature of 200 ° C. after drying silica slurry or silica gel at 110 ° C.

  Viscosity was measured according to rotor No. according to TOKIMEC VISCOMETER (TOKYO KEIKI B8L). It is a value measured at 2, 30 RPM.

  The conductivity is a value measured using CONDUCTIVITY METER DS-14 (Horiba Seisakusho).

  Silica concentration is weight percent calculated from the weight of silica slurry evaporated to dryness at 110 ° C.

  The purity is obtained by adding sulfuric acid and hydrofluoric acid to silica, heating and evaporating to dryness, then dissolving the impurity components in nitric acid and water, and quantifying with IMPA · S, Al, Ba, Ca, Cr, It is a calculated value by weight% converted from Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, Sn, Sr, Ti, Zn, Zr, U, and Th as impurities.

  The zeta potential was measured using an ES 9.800 Zeta Potential Analyzer manufactured by Matec Applied Science, and the zeta potential of the slurry itself and a data potential in the range of pH 2.5 to 9.5 were adjusted with aqueous nitric acid and water. The measurement was performed by the potentiometric titration method using an aqueous potassium oxide solution.

Example 1
In a 1 L polyethylene container, pure water is added to 700 g of high-purity silica balls having an average diameter of 1.5 mm (0.5 to 3 mm) and a purity of 99.98%, and 90 g of nip seal LP (manufactured by Tosoh Silica Co., Ltd.) which is a commercially available silica gel. 185 g was added to make a slurry, and pulverized with a ball mill for 80 hours to obtain a silica slurry (A) having a slurry concentration of 30%.

Next, hydrochloric acid was added to the obtained silica slurry to adjust the pH to 2.0 to obtain an acidic silica slurry. Acidic silica slurry and PD-30 (manufactured by Yokkaichi Gosei Co., Ltd.), which is a commercially available cationic polymer, are mixed so that the cationic polymer / SiO ₂ = 4% (% by weight) is obtained, and at 60 ° C. Gelation was performed in a sealed container for 15 hours to obtain a hydrogel (C).

  The obtained hydrogel (C) was pulverized to a size of about 1 mm to 2 cm square, pure water was added and left for 1 hour, and then the supernatant was removed. This operation was repeated until the supernatant had a conductivity of 300 μS / cm.

The washed hydrogel was put in a plastic container and dispersed for 1 hour with an ultrasonic disperser to obtain a high-concentration silica slurry. The resulting slurry had a slurry concentration of 28%, an average particle size of 0.045 μm (D1), a specific surface area of 221 m ² / g (D2 = 0.014 μm), D1 / D2 = 3.2, pH 3.12, conductivity. It was a high concentration silica slurry (B) having a viscosity of 686 μS / cm, a viscosity of 35 mPa · s, and a zeta potential of +37 mV.

  Next, the data potential in the range of pH 2.5 to 9.5 was measured by the potentiometric titration method using an aqueous nitric acid solution and an aqueous potassium hydroxide solution. FIG. 1 shows the relationship between the pH and zeta potential of the silica slurry (A) shown above and the high concentration slurry (B) of the present invention.

  The viscosity of the high-concentration silica slurry (B) of the present invention after standing at room temperature for 1 month was 35 mPa · s and was stable with no increase in viscosity for a long period of time.

Example 2
The hydrogel (C) obtained under the same conditions as in Example 1 was crushed to about 1 mm to 2 cm square, pure water was added and allowed to stand for 1 hour, and then the supernatant was removed. This operation was repeated until the supernatant had a conductivity of 200 μS / cm.

The washed hydrogel was put in a plastic container and dispersed for 1 hour with an ultrasonic disperser to obtain a high-concentration silica slurry. The high concentration silica slurry has a slurry concentration of 28%, an average particle size of 0.045 μm (D1), a specific surface area of 221 m ² / g (D2 = 0.014 μm), D1 / D2 = 3.2, pH 5.1, conductivity. It was a high concentration silica slurry having 350 μS / cm, a viscosity of 210 mPa · s, and a zeta potential of +48 mV.

Example 3
Hydrochloric acid was added to the silica slurry (A) obtained under the same conditions as in Example 1 to adjust the pH to 1.8 to obtain a silica slurry.

Polyethyleneimine (reagent) having a molecular weight of 70000 is mixed with the silica slurry and the cationic polymer so as to be a cationic polymer / SiO ₂ = 4% (weight%), and gelled in a sealed container at 60 ° C. for 15 hours. To obtain a hydrous gel.

  The obtained hydrogel was crushed to about 1 to 2 cm square, pure water was added, and the mixture was allowed to stand for 1 hour, and then the supernatant was removed. This operation was repeated until the supernatant had a conductivity of 500 μS / cm.

The washed hydrogel was put in a plastic container and dispersed for 1 hour with an ultrasonic disperser to obtain a high concentration silica slurry of the present invention. The resulting high-concentration silica slurry has a slurry concentration of 25%, an average particle size of 0.08 μm, a specific surface area of 210 m ² / g, a pH of 2.20, a conductivity of 1300 μS / cm, a viscosity of 55 mPa · s, and a high concentration of zeta potential +24 mV. This was a silica slurry, and its viscosity after standing at room temperature for 1 month was 30 mPa · s.

Example 4
SiO ₂ concentration of 25 wt%, Na ₂ O concentration of 8% by weight of silica source - mixed with da solution and mixing nozzle 40 weight percent aqueous sulfuric acid solution, SiO ₂ concentration of 17% by weight, pH is 0. 8 silica sols were produced. The silica sol gelled after about 5 minutes. The obtained gel was crushed and washed with pure water at 70 ° C., sieved with 1 mm sieve, and dried at 110 ° C. for 15 hours to obtain silica gel. The specific surface area of the obtained silica gel was 760 m ² / g.

  A slurry was prepared by adding 3.70 g of pure water to 180 g of the silica gel and adjusting the pH to 9.2 with aqueous ammonia (Slurry-C). A 2 L polyethylene container was charged with 2 kg of slurry C and a 15 mmφ cored resin ball, and pulverized with a ball mill for 15 hours to obtain slurry D having an average particle diameter of 15 μm.

  Next, 700 g of 99.9.8% silica ball having an average diameter of 0.5 mm (0.3 to 3 mm) and 400 ml of the above slurry D are put into a 1 L polyethylene container and pulverized with a ball mill for 24 hours. A silica slurry having a slurry concentration of 31% was obtained, and hydrochloric acid was added to the silica slurry to adjust the pH to 2.0 to obtain an acidic silica slurry.

Acidic silica slurry and PD-30 (manufactured by Yokkaichi Gosei Co., Ltd.), which is a commercially available cationic polymer, are mixed so that the cationic polymer / SiO ₂ = 4% (% by weight) is obtained, and at 60 ° C. Gelation was performed in a sealed container for 15 hours to obtain a hydrous gel.

  The obtained hydrogel was crushed to about 1 to 2 cm square, pure water was added, and the mixture was allowed to stand for 1 hour, and then the supernatant was removed. This operation was repeated until the supernatant had a conductivity of 300 μS / cm.

The washed hydrogel was put in a plastic container and dispersed for 1 hour with an ultrasonic disperser to obtain a high-concentration silica slurry. The resulting high-concentration silica slurry has a slurry concentration of 31%, an average particle size of 0.25 μm (D1), a specific surface area of 380 m ² / g, a pH of 4.50, an electrical conductivity of 880 μS / cm, a viscosity of 25 mPa · s, and a zeta potential of +30 mV. The viscosity after standing at room temperature for 1 month was 45 mPa · s.

Comparative Example 1
Hydrochloric acid was added to the silica slurry (A) obtained under the same conditions as in Example 1 to adjust the pH to 2.0 to obtain an acidic silica slurry.

Acidic silica slurry and PD-30 (manufactured by Yokkaichi Gosei Co., Ltd.), which is a commercially available cationic polymer, are mixed so as to be cationic polymer / SiO ₂ = 4% (% by weight), without washing. The mixed solution was used as it was. The conductivity of the obtained mixed solution was 11000 μS / cm, which did not satisfy the conditions of the present invention.

  The viscosity of the resulting mixed solution was unstable and gelled after 4 hours at room temperature.

Comparative Example 2
Hydrochloric acid was added to the silica slurry (A) obtained under the same conditions as in Example 1 to adjust the pH to 2.0 to obtain an acidic silica slurry.

  The obtained acidic silica slurry had an electrical conductivity of 7000 μS / cm, and the zeta potential of the silica particles in the slurry was −2 mV, which did not satisfy the conditions of the present invention.

  The resulting acidic high concentration silica slurry was unstable and gelled after 5 days at room temperature.

Comparative Example 3
This was carried out in the same manner as in Example 1 except that the conductivity of the washing supernatant of the hydrous gel obtained by mixing the cationic polymer was 900 μS / cm. Hydrochloric acid was added to the silica slurry (A) obtained under the same conditions as in Example 1 to adjust the pH to 2.0 to obtain an acidic silica slurry.

The acidic silica slurry and a commercially available cationic polymer, PD-30 having a molecular weight of 7900 (manufactured by Yokkaichi Gosei Co., Ltd.), are mixed so as to be a cationic polymer / SiO ₂ = 4% (wt%), and 60 ° C. And gelled in a sealed container for 15 hours to obtain a water-containing gel (C) similar to Example 1. The obtained hydrogel (C) was crushed to about 1 to 2 cm square, added with pure water, allowed to stand for 1 hour, and then the supernatant was removed to obtain a hydrogel. The obtained hydrogel was placed in a plastic container and dispersed with an ultrasonic disperser for 1 hour to obtain a high-concentration silica slurry having a concentration of 30%.

  The conductivity of the obtained mixed solution is 2100 μS / cm, which does not satisfy the conditions of the present invention, the viscosity is unstable, the viscosity is increased from about 5 hours, and gelled after 15 hours. .

Comparative Example 4
It implemented on the following conditions similarly to Example 2 except the molecular weight of cationic polymer being 1800.

Polyethyleneimine (reagent) having a molecular weight of 1800 is mixed with the acidic silica slurry and the cationic polymer so as to be a cationic polymer / SiO ₂ = 4% (weight%), and gelled in a sealed container at 60 ° C. for 15 hours. To obtain a hydrous gel.

  The obtained hydrogel was crushed to about 1 to 2 cm square, pure water was added and the mixture was allowed to stand for 1 hour, and then the supernatant was removed. This operation was repeated until the supernatant had a conductivity of 300 μS / cm. The washed hydrogel was put in a plastic container and dispersed with an ultrasonic disperser for 1 hour to obtain a high concentration silica slurry having a concentration of 30%.

  The obtained slurry was a negative charge having a zeta potential of −8 mV, and a high-concentration silica slurry satisfying the present invention was not obtained.

It is a figure which shows the change of the zeta potential by pH of the high concentration silica slurry obtained in Example 1. (A) Polymer addition / washing re-dispersion not performed (B) High concentration silica slurry of the present invention

Claims (10)

The silica concentration is 20 to 50%, the pH is 1.5 to 5.5, the conductivity is 300 to 1500 μS / cm, and the zeta potential of the silica particles in the high concentration silica slurry is +10 to +80 mV. Concentration silica slurry. 2. The high-concentration silica slurry according to claim 1, wherein the silica particles contained in the high-concentration silica slurry have an average particle diameter of 0.01 to 0.5 μm and a specific surface area of 150 to 700 m ² / g. The high-concentration silica slurry according to claim 2, wherein the aggregation degree D1 / D2 of the silica particles is 3 or more (where D1 (μm) = average particle diameter, D2 (μm) = (2720 / As) / 1000, As Is the specific surface area (m ² / g). The high-concentration silica slurry according to claim 1, wherein a cationic polymer having a molecular weight of 2,000 to 100,000 is adsorbed on the surface of silica particles. The high-concentration silica slurry according to claim 4, wherein the cationic polymer is contained in an amount of 0.5 to 10% by weight based on the silica particles. The high-concentration slurry according to claim 1, which has a viscosity of 5 to 300 mPa · s. The high-concentration silica slurry according to claim 1, wherein the rate of change in viscosity after standing at room temperature for 1 month is ± 50% or less with respect to the initial viscosity. After the silica gel and water were pulverized and dispersed by a media mill using a high purity silica ball having an average diameter of 0.5 to 5 mm and a purity of 99.95% or more as a medium, a negative charge high concentration slurry was obtained. The high-concentration silica slurry according to any one of claims 1 to 7, wherein the high-concentration silica slurry according to claim 1 is mixed with 2000 to 100,000 cationic polymer, washed with water to remove the salt, and then redispersed. Manufacturing method. 9. The high-concentration silica slurry according to claim 8, wherein the silica gel is added to pure water, added with alkali to form a slurry, and pulverized with a resin ball before being pulverized and dispersed by a media mill. Production method. 10. The method for producing a high-concentration silica slurry according to claim 8, wherein the silica gel is silica gel made from silicate soda.

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