Production method of high-purity silica fine particle dispersion liquid and high-purity silica fine particle dispersion liquid

Abstract

To provide a production method of a high-purity silica fine particle dispersion liquid that does not require complicated treatment.SOLUTION: A production method of a high-purity silica fine particle dispersion liquid comprises the following steps 1 to 3: (Step 1) a step of adding a complexing agent and an inorganic acid etc. to a sodium silicate aqueous solution, mixing the same, and further performing cation exchange treatment to obtain an acidic silicic acid solution having a predetermined pH; (Step 2) a step of performing chelate ion exchange treatment on the acidic silicic acid solution obtained in the step 1, followed by cation exchange treatment to obtain a purified acidic silicic acid solution; and (Step 3) a step of adding an alkali hydroxide aqueous solution to a part of the purified acidic silicic acid solution obtained in the step 2, adjusting the pH to a predetermined value, heating at a predetermined temperature, maintaining the predetermined temperature for a predetermined time, and further adding another part of the purified acidic silicic acid solution obtained in the step 2 at a predetermined addition rate while simultaneously adding a pH adjusting agent to obtain a high-purity silica fine particle dispersion liquid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a silica fine particle dispersion (silica sol), particularly a high-purity silica fine particle dispersion (high-purity silica sol).

Background Art

[0002] Conventionally, a silica sol substantially free of metal impurities has been proposed, and such a high-purity silica sol can be preferably used, for example, as an abrasive for electronic materials such as semiconductor silicon wafers. If the silica sol contains metal impurities, the metal impurities diffuse into the wafer during polishing, deteriorating the wafer quality. Then, the performance of semiconductor devices formed using such wafers is significantly reduced. As a method for producing a high-purity silica sol, a production method of synthesizing a silica sol using a purified silicon alkoxide as a raw material is widely known as a means for suppressing impurities as much as possible. However, in the case of this production method, since the raw material silicon alkoxide (alkoxysilane) is expensive, the use of the silica sol obtained by such a production method has been limited to, for example, applications with high added value or special applications (see Patent Document 1). As another method for producing a high-purity silica sol, a method for producing a silica sol including a step of synthesizing silica gel by a wet reaction of an alkali silicate and a mineral acid and further allowing an aqueous solution of tetraammonium hydroxide to act is known. However, in the case of this production method, there are problems in production efficiency and economy, such as precipitating and generating silica gel in an acidic region with an acid concentration of 1 N or more containing a chelating agent and hydrogen peroxide in the step of preparing silica gel, and further requiring separation and washing (see Patent Document 2).

[0003] In the method for producing a high-purity silica sol described in Patent Document 3, in the production process of the silica sol, for the purpose of removing ionic impurities present in the siloxane skeleton constituting silicic acid in the silicic acid solution, the silicic acid solution is acid-treated, specifically including the step of adjusting the pH to 0 to 2.5. For this acid treatment, for example, in Example 1, 500 g of 35% hydrochloric acid is used for a 5% silicic acid solution (presumed to be at least about 4,000 g or more based on the raw material input amount) obtained by cation-exchanging a diluted product of No. 3 sodium silicate solution. When an acidic silicic acid solution containing such a large amount of acid is prepared as a raw material, it impairs the stability of the silica sol and causes gelation and aggregation precipitation. Therefore, usually, a washing treatment or an anion-exchange treatment is required. Also, in the production method described in Patent Document 3, it is disclosed that a treatment such as solvent substitution is performed to remove and purify hydrochloric acid. Thus, the removal treatment of such a large amount of acid is a disadvantageous factor in terms of man-hours, the time required for production, and economy in the production of high-purity silica sol.

[0004] In the method for producing a high-purity large-particle-size silica sol described in Patent Document 4, in the production process of the silica sol, an acid is added to an aqueous colloidal solution of active silicic acid to adjust the pH to 0 to 2.0, followed by aging, cation-exchange, anion-exchange, and cation-exchange to prepare a high-purity active silicic acid solution, and a high-purity large-particle-size silica sol is prepared using this high-purity active silicic acid solution as a raw material. In this production method, for example, in Example 1, 20.2 g of nitric acid (concentration 61.3 mass%) is used for 5,950 g of an aqueous colloidal solution of active silicic acid, and subsequently, it is disclosed that aging, cation-exchange, anion-exchange, and cation-exchange are performed for 48 hours, having the same problems as Patent Document 3. In particular, in the production method described in Patent Document 4, it is necessary to age the active silicic acid solution for 48 hours, resulting in very low production efficiency and problems with economy.

[0005] In the method for producing a high-purity aqueous silica sol described in Patent Document 5, water glass is cation-exchanged to obtain an acidic silicic acid solution, and then a strong acid is added to carry out aging at pH 0 to 2.0, 0 to 100 °C for 0.5 to 120 hours, followed by anion-exchange to obtain a high-purity silica sol. In this method, an aging treatment at 0 to 100 °C for 0.5 to 120 hours is required. Since the aging time is long, the productivity is poor, and practically, improvement has been demanded.

[0006] In the method for producing a high-purity silica sol described in Patent Document 6, a salt of a strong acid is added to water glass for cation-exchange. As the salt of the strong acid, at least one of aminotris(methylenephosphonic acid), 1-hydroxyethane-1,1-diphosphonic acid, or salts thereof is used. Such a silica sol containing an organic acid has problems in that the treatment of wastewater generated during production is troublesome and costly, and the use applications of the silica sol containing an organic acid are limited. In particular, in polishing applications, although it is common to add chemical components to the silica sol to adjust the polishing performance, it has been pointed out that the organic acid may deteriorate the polishing performance.

[0007] In the method for producing a silica sol described in Patent Document 7, a water-soluble alkali metal silicate or an aqueous solution of an alkali metal silicate is mixed with an acidifying agent to produce an acidic aqueous solution of an alkali metal silicate with a pH of less than 2. Subsequently, a predetermined anion-exchange and cation-exchange treatment are carried out to prepare a silicic acid solution, and a stable silica sol is obtained using this silicic acid solution as a raw material. In this method, an acidifying agent is required, and oxidizing agents such as hydrogen peroxide have many explosion incidents, presenting safety problems. Also, there is a problem that the use applications of such a silica sol containing an oxidizing agent are limited due to safety concerns.

[0008] In the method for producing high-purity silica sol described in Patent Document 8, oxalic acid and an inorganic strong acid are added to and mixed with a silicic acid solution, and anion exchange and cation exchange are performed to prepare high-purity silica sol. In this production method, when performing anion exchange treatment after making sodium silicate into a silicic acid solution, there was a problem that the polymerization of silicic acid progressed due to an increase in the pH of the silicic acid solution, and the silicic acid solution became unstable.

[0009] In the method for producing high-purity aqueous silica sol described in Patent Document 9, a strong acid or the like and an alkali metal silicate are dissolved in water under predetermined conditions, cation exchange is performed, followed by anion exchange, and further potassium hydroxide or sodium hydroxide is added to prepare an aqueous silica sol. Further, the aqueous silica sol is cation-exchanged, and ammonia is added to adjust the pH to 8 to 10.5 to obtain a stable and high-purity aqueous silica sol. In Example 1 of the same document, in addition to the above operations, cation exchange is performed again after anion exchange. In this production method, there is a problem that the number of ion exchange treatments is large and the production efficiency is extremely poor. Further, since anion exchange treatment is performed on an acidic silicic acid solution, anions necessary for stabilizing the acidic silicic acid solution are removed, so that the pH of the silicic acid solution increases, and there is also a problem that the stability of the silicic acid solution is significantly reduced and it is likely to gel.

[0010] In the method for producing high-purity large-particle-size silica sol described in Patent Document 4, in addition to the problems found in the production method described in Patent Document 3, as described above, an aging treatment for 48 hours is required, and it can be said that there are further disadvantages in production. The production method described in Patent Document 5 also had the problem of requiring time for aging (holding step).

[0011] In the method for producing high-purity silica sol described in Patent Document 6, wastewater containing an organic acid is generated during production, and there is a problem in that it takes time and cost to treat this wastewater. Further, there was a problem in terms of the influence on polishing performance.

[0012] In the method for producing silica sol described in Patent Document 7, as described above, an acidifying agent is required, and there is a problem in terms of safety. In the method for producing high-purity silica sol described in Patent Document 8, as described above, in addition to the problems associated with the increase in pH during the anion exchange treatment of the silicic acid solution, the silicic acid contained in the raw material sodium silicate aqueous solution polymerizes, and after becoming a silicic acid solution, a series of high-purity treatment is performed. Therefore, there is a limit to the removal of metal impurities.

[0013] In the method for producing high-purity aqueous silica sol described in Patent Document 9, as described above, there are many operations or treatments starting from the ion exchange operation, and improvement has been required in practical use. Since anions are removed from the silicic acid solution, the pH of the acidic silicic acid solution after anion exchange is about 4.0. Such an acidic silicic acid solution has very poor stability and gels extremely quickly. Therefore, the method for producing silica sol that requires such anion exchange has a problem that it is difficult to produce stably.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Summary of the Invention

Problems to be Solved by the Invention

[0015] The present invention aims to provide a method for producing a high-purity silica fine particle dispersion liquid, which eliminates the need for anion exchange treatment for removing acids, aging treatment in which a silicic acid solution in an intermediate stage of the production process is held within a predetermined time range under predetermined conditions (such as pH range or temperature range), and other complicated treatments as seen in the conventional method for producing high-purity silica sol.

Means for Solving the Problems

[0016] According to one aspect of the present invention, there is provided a method for producing a high-purity silica fine particle dispersion liquid, including the following steps 1 to 3. (Step 1) A step of adding and mixing a complexing agent and at least one selected from the group consisting of inorganic acids and inorganic acid salts to an aqueous sodium silicate solution (in the range of 2% by mass or more and 7% by mass or less of SiO2 concentration), and further performing a cation exchange treatment to obtain an acidic silicic acid solution in the range of pH 1.5 or more and 2.5 or less. (Step 2) A step of performing a chelate ion exchange treatment on the acidic silicic acid solution obtained in Step 1, and then performing a cation exchange treatment to obtain a purified acidic silicic acid solution. (Step 3) An aqueous alkali hydroxide solution is added to a part of the purified acidic silicic acid solution obtained in Step 2, adjusted to a pH in the range of 10 or more and 13 or less, then heated at a temperature of 50°C or more and 98°C or less, and the temperature in the range of 50°C or more and 98°C or less is maintained for 20 minutes or more. Further, another part of the purified acidic silicic acid solution obtained in Step 2 is added at an addition rate in the range of 0.001 g / min·g or more and 0.5 g / min·g or less (in terms of silica solid content conversion), and a pH adjuster is added simultaneously to obtain a high-purity silica fine particle dispersion liquid.

[0017] According to one aspect of the present invention, there is provided a high-purity silica fine particle dispersion in which, with respect to the silica solid content, the Al concentration is 5 ppm or more and 30 ppm or less, the Fe concentration is 1 ppm or more and 20 ppm or less, the Ca concentration is 1 ppm or more and 8 ppm or less, the Na concentration is 1 ppm or more and 20 ppm or less, the Mg concentration is 0.2 ppm or more and 4 ppm or less, the Cr concentration is 0.05 ppm or more and 1 ppm or less, the Ni concentration is less than 1 ppm, the Cu concentration is less than 1 ppm, and the Zn concentration is less than 1 ppm (however, the total amount of these metals is limited to 100 ppm or less).

Effects of the Invention

[0018] According to one aspect of the present invention, it is possible to provide a method for producing a high-purity silica fine particle dispersion, which does not require anion exchange treatment for removing an acid, aging treatment in which a silicic acid solution in an intermediate stage of a production process is held under predetermined conditions for a predetermined time range, and other complicated treatments, which are seen in conventional methods for producing high-purity silica sol.

Embodiments for Carrying Out the Invention

[0019] [Method for Producing High-Purity Silica Fine Particle Dispersion] The method for producing a high-purity silica fine particle dispersion according to the present embodiment is a method including the following steps 1 to 3. According to the production method according to the present embodiment, complicated problems as described below can be solved. For example, when the number of ion exchange steps increases, it becomes necessary to provide a tank for receiving or storing the silicic acid solution after ion exchange. Further, there is a problem that the yield decreases because loss of the silica component occurs for each ion exchange process. In addition, maintenance of the tank provided for storing the silicic acid solution, regeneration and washing of the ion exchange resin are also performed, so that the amount of chemicals required for regeneration and the amount of washing water increase, and the process is also loaded with the treatment. Generally, when anion-exchanging a silicic acid solution, the pH of the silicic acid solution rises from weakly acidic to the neutral range, and the silicic acid solution tends to gel. Therefore, the silicic acid solution after anion exchange needs to be used promptly, such as being fed into the next process within an extremely short time, increasing the burden of such process management, time management, and quality control. In addition, when performing an acid treatment with an aging treatment of holding the silicic acid solution for a predetermined time, since it cannot be used unless the silicic acid solution is held for a predetermined time, it is necessary to plan and prepare the silicic acid solution required for preparing silica particles in advance according to the preparation process of the silica particles. Therefore, when continuously performing multiple batches of formulation in the preparation of silica particles, it is necessary to prepare a plurality of tanks for holding the acid treatment in accordance with the holding time and the start time of the silica particle preparation process. In this case, management of a plurality of tanks and the acid-treated silicic acid solution is required, and production becomes extremely complicated. In this specification, the silica fine particle dispersion is also referred to as silica sol.

[0020] [Step 1: Preparation of acidic silicic acid solution] (Aqueous sodium silicate solution) In Step 1, a complexing agent and at least one selected from the group consisting of an inorganic acid and an inorganic acid salt are added to and mixed with the aqueous sodium silicate solution. As the aqueous sodium silicate solution used here, so-called water glass (sodium silicate) or diluted water glass obtained by dissolving sodium silicate in water can be used. The SiO2 concentration contained in the aqueous sodium silicate solution needs to be in the range of 2% by mass or more and 7% by mass or less. The fact that the SiO2 concentration is in the above range is preferable because gelation hardly occurs in the ion exchange resin layer in the ion exchange treatment described later. An aqueous sodium silicate solution in such a concentration range can be obtained, for example, by diluting commercially available water glass with water, ion-exchanged water, pure water, or ultrapure water. Such water glass is represented by, for example, the composition formula of Na2O·nSiO2·mH2O, and examples include those having an SiO2 concentration in the range of 22% by mass or more and 38% by mass or less, a Na2O concentration in the range of 5% by mass or more and 19% by mass or less, an SiO2:Na2O (molar ratio) in the range of 0.5 or more and 4 or less, and a pH of 9 or more.

[0021] (Complexing agent) In this embodiment, when the aqueous sodium silicate solution is subjected to cation exchange to remove cations and becomes a so-called acidic silicic acid solution in which monomers of silicic acid polymerize via siloxane bonds, a complexing agent is added in advance for the purpose of preventing metal ions contained in the aqueous sodium silicate solution from being incorporated into the silicic acid skeleton. The complexing agent in this embodiment is a compound having an acid group and forming a complex ion by binding to a metal ion. When the metal ion becomes a complex ion, cation exchange also becomes easier to remove. Note that the complexing agent is usually a weak acid, and the pH of the acidic silicic acid solution does not become sufficiently low only with the complexing agent, so the effect of "acid leaching" described later is not sufficient. Therefore, an inorganic acid such as sulfuric acid or an inorganic acid salt is added together. Examples of the complexing agent include oxalic acid, metal oxalate salts, carboxylic acids, metal carboxylate salts, aminocarboxylic acids, metal aminocarboxylate salts, phosphonic acids, and metal phosphonate salts. Among these, oxalic acid, sodium oxalate, or calcium oxalate can be preferably used. If the amount of the complexing agent used is in the range of 0.40 parts by mass or more and 7.00 parts by mass or less with respect to 100 parts by mass of the silica content contained in the aqueous sodium silicate solution, the silica fine particle dispersion obtained by the production method according to this embodiment is stable, and the impurity reduction effect is also sufficiently exhibited, which is preferable. When the amount of the complexing agent used is less than 0.40 parts by mass, the impurity reduction effect in the silica fine particle dispersion obtained by the production method according to this embodiment becomes insufficient. When the amount of the complexing agent used exceeds 7.00 parts by mass, when the silica fine particle dispersion obtained by the production method according to this embodiment is applied to polishing applications or the like and then discarded, it is not desirable that the COD (chemical oxygen demand) of the waste liquid is large. The range of the amount of the complexing agent used is more preferably in the range of 0.45 parts by mass or more and 6.50 parts by mass or less.

[0022] (Inorganic acids and inorganic acid salts) The type of the inorganic acid or inorganic acid salt added to the aqueous sodium silicate solution is not particularly limited. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and the like. Examples of the inorganic acid salt include salts of the above inorganic acids. The addition amount of these inorganic acids or inorganic acid salts varies depending on the type of the inorganic acid or inorganic acid salt and the concentration of the aqueous solution of the inorganic acid or inorganic acid salt, but is not particularly limited as long as the pH range of the acidic silicic acid solution after subsequent cation exchange treatment is in the range of pH 1.5 or more and 2.5 or less. In this specification, in some cases, the aqueous sodium silicate solution to which a complexing agent and at least one selected from the group consisting of an inorganic acid and an inorganic acid salt are added in Step 1 may be referred to as "an aqueous sodium silicate solution containing a complexing agent and an inorganic acid or the like". In some cases, the inorganic acid or inorganic acid salt may be referred to as "an inorganic acid or the like". For example, when the complexing agent is oxalic acid and the inorganic acid or the like is sulfuric acid, it may be described as "an aqueous sodium silicate solution containing oxalic acid and sulfuric acid".

[0023] (Regarding the pH of the aqueous sodium silicate solution after acid leaching) Generally, the process of eluting impurities contained in a solid phase with an acid or an alkali is called leaching, which means an operation of dissolving or eluting a specific element from the solid phase into an aqueous solution. For example, the operation of adding an inorganic acid to an acidic silicic acid solution performed in Patent Document 5 is also leaching, and the metal impurities eluted by leaching are removed by ion exchange or the like. Incidentally, leaching with an acid is particularly also referred to as "acid leaching". In Patent Document 5, a strong acid is added to the silicic acid solution to adjust the pH to 0 to 1.54. Also in the acid leaching of water glass (aqueous sodium silicate solution), it is known that the lower the pH of the acidic silicic acid solution after leaching, the more effective it is for eluting a specific element from the solid phase (silica component) in the water glass.

[0024] The impurity ions eluted into the acidic silicic acid solution by leaching are removed by subsequent cation exchange treatment. In the example of Patent Document 5, the cation exchange treatment is carried out after setting the pH of the acidic silicic acid solution to 1.54 or less. However, usually, the cation exchange resin adsorbed with metal impurities is regenerated by the action of strong acids such as hydrochloric acid and sulfuric acid. Therefore, the lower the pH of the acidic silicic acid solution, the more the impurity ions adsorbed on the ion exchange resin elute into the acidic silicic acid solution again, which causes a problem. As a result of actual experimental confirmation by the present inventors, when the pH of the acidic silicic acid solution is less than 1.5, alkali metals such as Na are likely to desorb, and the obtained acidic silicic acid solution contains Na in the range of several tens to one hundred and several tens ppm per 1 g of silica dry.

[0025] As described above, in order to enhance the leaching effect, it is necessary to lower the pH of the acidic silicic acid solution. However, if the pH is too low, there will be a problem that the impurity ions desorb due to the regeneration effect of the ion exchange resin and the impurities cannot be sufficiently removed. Therefore, an optimal pH considering the leaching effect and the resin regeneration effect is required. As a result of the study by the present inventors, the pH of the acidic silicic acid solution obtained by acid leaching and subsequent cation exchange treatment is, as described above, most preferably in the range of 1.5 or more and 2.5 or less. When performing ion exchange on the acidic silicic acid solution, the pH of the acidic silicic acid solution may be adjusted within the range of 1.5 or more and 2.5 or less before ion exchange.

[0026] In addition, as a method of combining ion exchange and leaching, there is a process in which first sodium silicate is cation-exchanged (first ion exchange), an inorganic acid is added to the obtained acidic silicic acid solution to adjust it to a suitable pH, and then ion exchange treatment (second ion exchange) is performed again to remove the eluted impurities. As another method, there is also a process in which an amount of inorganic acid such that the pH of the acidic silicic acid solution after cation exchange is in a suitable range is added to an aqueous sodium silicate solution in advance, the first ion exchange is performed, and the obtained acidic silicic acid solution is subjected to the second ion exchange. In the former process, since leaching does not occur in the first cation exchange, the impurity removal efficiency is inferior. However, in the latter process, leaching occurs from the first ion exchange treatment, so the impurity removal effect is high. Therefore, a method of adding an inorganic acid in an amount such that the pH after ion exchange is within a suitable range to an aqueous sodium silicate solution and then performing ion exchange is desirable. In the latter process, even if an inorganic acid is added in advance to the aqueous sodium silicate solution so that the pH of the acidic silicate solution after cation exchange is 1.5 or more and 2.5 or less, usually the pH of the aqueous sodium silicate solution does not become acidic but is strongly alkaline. Therefore, there is almost no leaching effect at the stage where an inorganic acid is added to the alkali silicate. However, when a cation exchange treatment is performed on the aqueous sodium silicate solution to which an inorganic acid has been added, the alkali is removed from the strongly alkaline aqueous sodium silicate solution in the ion exchange column, and the pH becomes an acidic silicate solution of 1.5 or more and 2.5 or less. Since this acidic silicate solution continues to be ion-exchanged until it reaches the outlet of the ion exchange column, leaching starts inside the ion exchange column, so the impurity removal effect becomes high. Further, in this case, since the pH of the acidic silicate solution is low, the polymerization of the acidic silicate solution hardly proceeds, and impurities such as transition elements are hardly incorporated into the siloxane skeleton of the acidic silicate solution, so the inventors presume that there is also an effect of increasing the impurity removal effect.

[0027] (Mixing by a static mixer) In Step 1, a complexing agent, an inorganic acid, etc. are added to the aqueous sodium silicate solution, and a low-pH acidic silicate solution is generated in the subsequent cation exchange column, and leaching of impurities is performed, and impurities are removed until they flow out from the outlet of the ion exchange column. For this reason, it is very important that the aqueous sodium silicate solution, the complexing agent, the inorganic acid, etc. are uniformly mixed. As described above, since the lower the pH, the higher the leaching effect, when the mixing is non-uniform, there are portions where the pH does not locally decrease, resulting in insufficient leaching and the possibility that impurities cannot be sufficiently reduced. In order to perform the mixing uniformly, it can be made uniform by conducting a long-time stirring operation with a stirrer. However, this is not preferable because the process time becomes too long and the economy deteriorates. Therefore, it is required to perform sufficient uniform mixing in a short time. In order to mix in a short time, a method is known in which, for example, a pipe for an inorganic acid is connected to a pipe through which an aqueous sodium silicate solution flows for mixing. However, in order to sufficiently mix the two liquids, it is necessary to increase the liquid feeding rate to increase the Reynolds number in the pipe. However, with this method, it is difficult to mix uniformly, so it takes time until sufficient mixing is achieved, and there is a possibility of causing leaching failure.

[0028] The inventors of the present invention have found that by using a static mixer, a so-called stationary mixer, within a specific range of the number of its elements and further within a predetermined range of Reynolds numbers, reaching defects can be avoided and mixing can be achieved in a relatively short time. A static mixer is a stationary mixer (line mixer) without a driving part, and its structure has a structure in which a necessary number of elements (a structure like a rectangular plate twisted 180 degrees in the left - right reverse direction) are alternately arranged in a pipe. The required number of elements is set according to the properties of the target fluid and the purpose of the process, respectively. The fluid entering the static mixer is sequentially stirred and mixed by the elements provided in the pipe. There are various types of static mixers. As an example, in an element - type static mixer, right elements and left elements are alternately arranged, and two types of fluids can be uniformly mixed by a method that causes a splitting, conversion, or inversion action. In the present invention, the static mixer is positioned as a mixer for uniformly mixing an aqueous sodium silicate solution, a complexing agent, an inorganic acid, and the like. Here, when the number of elements of the static mixer is n and the Reynolds number is Re, by setting the product B (hereinafter referred to as "mixing factor B") in the range of 1,000 or more and 1,000,000 or less, reaching defects can be prevented, and a uniform mixed solution can be obtained in a short time. The range of this mixing factor B is more preferably in the range of 5,000 or more and 500,000 or less, even more preferably in the range of 8,000 or more and 200,000 or less, and still more preferably in the range of 10,000 or more and 50,000 or less. The number of the above - mentioned elements is arbitrarily set by the manufacturer of the static mixer according to the purpose or application and is commercially available. The number of elements of commercially available static mixers is not particularly limited. For example, those set in the range of 5 or more and 70 or less are known. Note that the mixing factor B is as shown by the following mathematical formula (F1). B = Re×n ···(F1) (B: Mixing factor of the static mixer, n: Number of elements of the static mixer, Re: Reynolds number)

[0029] In Step 1, a cation exchange treatment is performed on an aqueous sodium silicate solution containing a complexing agent obtained by adding a complexing agent for the aqueous sodium silicate solution and at least one selected from the group consisting of inorganic acids and inorganic acid salts, and an inorganic acid or the like to obtain an acidic silicic acid solution having a pH in the range of 1.5 or more and 2.5 or less.

[0030] (Cation exchange resin) The cation exchange resin used for the cation exchange treatment is not particularly limited. For example, it is preferable to use an H-type cation exchange resin. Further, the form of the cation exchange resin may be beads, fibers, or the like. In the present embodiment, a method of filling a column with a cation exchange resin and passing a liquid therethrough is preferable.

[0031] (Cation exchange temperature) Generally, in an ion exchange operation, the ion exchange temperature and the contact time [space velocity (SV)] between the liquid to be ion exchanged and the ion exchange resin are important factors. Here, examples of the ion exchange temperature include the temperature of the solution before passing it through the ion exchange resin, the temperature inside the column filled with the ion exchange resin, the temperature of the solution containing the ion exchange resin, the temperature inside the ion exchange column during ion exchange, and the temperature of the solution flowing out from the column outlet of the ion exchange column. In the present embodiment, as a factor having a great influence on the ion exchange reaction, the ion exchange temperature is the temperature of the solution before passing it through the ion exchange resin. Generally, the higher the temperature of the ion exchange reaction, the higher the ion exchange efficiency, and further, the leaching effect described later also increases. However, in the case of ion exchange of diluted water glass (aqueous sodium silicate solution) or acidic silicic acid solution, when the temperature increases, especially the acidic silicic acid solution tends to polymerize and gel, and the stability of the acidic silicic acid solution decreases. Further, even when gelation does not occur, when particles are prepared using a silicic acid solution in which polymerization has proceeded, self-nucleation by silicic acid may occur, and silica fine particles of a desired size may not be obtained.

[0032] The liquid temperature [T1] of the aqueous sodium silicate solution containing a complexing agent and an inorganic acid, etc., before passing it through a column filled with a cation exchange resin, is preferably in the range of 3°C or more and 18°C or less. When it is within this temperature range, the ion exchange efficiency is excellent and the resulting acidic silicic acid solution is also stable. When the liquid temperature of the aqueous sodium silicate solution is less than 3°C, cation exchange may not proceed efficiently, and even if the temperature is further lowered, the stability of the silicic acid solution does not tend to improve much. When the liquid temperature of the aqueous sodium silicate solution exceeds 18°C, although the adsorption effect of impurities increases, the acidic silicic acid solution tends to polymerize and gel, and the stability of the acidic silicic acid solution tends to decrease easily. Also, when particles are formulated using such an acidic silicic acid solution, self-nucleation by silicic acid may occur, and particles of the desired size may not be obtained. The liquid temperature of the aqueous sodium silicate solution containing a complexing agent and an inorganic acid, etc., before passing it through the column is more preferably in the range of 5°C or more and 15°C or less, even more preferably in the range of 6°C or more and 15°C or less, and most preferably in the range of 7°C or more and 15°C or less. Regarding the temperature of the aqueous sodium silicate solution containing a complexing agent and an inorganic acid, etc., usually, if it is within the above temperature range, it can be passed through as it is. When the liquid temperature exceeds the above temperature range, it is cooled to adjust the temperature. Also, for the cation exchange resin filled in the column, for the purpose of preventing the temperature rise during the liquid passing, it is desirable to adjust the temperature to the range of 3°C or more and 18°C or less in advance using means such as refrigeration. In this specification, in step 1, the liquid temperature before passing the aqueous sodium silicate solution containing a complexing agent and an inorganic acid, etc., through a column filled with a cation exchange resin may be represented as T1.

[0033] (Space velocity) The space velocity [S1] when passing the aqueous sodium silicate solution containing a complexing agent and an inorganic acid, etc., through a column filled with a cation exchange resin is -1 2 h -1 or more and 6 h -1If it is less, although the ion removal effect is enhanced, since ion exchange takes time, productivity is poor and there is a tendency for economic efficiency to be problematic. When the space velocity is 6 h -1 exceeds, the ion exchange time is short and the economic efficiency is good, but the ion removal efficiency decreases, or there is a tendency for uneven flow of the solution to occur in the ion exchange column, and there is a possibility that the solution that is not ion-exchanged flows out, so there is a problem. This space velocity is more preferably in the range of 2.5 h -1 or more and 5.0 h -1 or less. In general, when representing the velocity at which a liquid passes through a filter medium, the space velocity is used. In the case of this specification, when passing a solution through a column filled with an ion exchange resin, the space velocity is the flow velocity per ion exchange resin volume, so the flow velocity (m 3 / h)÷resin volume (m 3 ) = space velocity (h -1 ). In this specification, in step 1, the space velocity when passing a sodium silicate aqueous solution containing a complexing agent and an inorganic acid or the like through a column filled with a cation exchange resin may be represented as S1.

[0034] In step 1, a cation exchange treatment is performed on a sodium silicate aqueous solution containing a complexing agent and an inorganic acid or the like until it becomes an acidic silicic acid solution in the range of pH 1.5 or more and 2.5 or less. When the pH value [P1] of the acidic silicic acid solution is less than 1.5, the amount of acid becomes excessive, and particles tend to aggregate during the steps after step 3, which is not desirable. Also, if we want to maintain the stability of the particles, an anion removal treatment is required, the process becomes longer, and the process load increases. When the pH of the acidic silicic acid solution exceeds 2.5, it is likely that the removal of impurities in the acidic silicic acid solution is insufficient. The pH of the obtained acidic silicic acid solution is preferably in the range of 1.5 or more and 2.4 or less, and more preferably in the range of 1.5 or more and 2.3 or less. In this embodiment, in step 1, it is desirable to perform a cation exchange treatment so as to satisfy the reaction factor A described later. The reaction factor A will be described later. In addition, in this specification, in Step 1, an inorganic acid or the like may be added to and mixed with an aqueous sodium silicate solution, and subsequently, the pH value of the acidic silicic acid solution obtained by cation exchange treatment may be represented as P1.

[0035] [Step 2: Preparation of purified acidic silicic acid solution] In Step 2, a purified acidic silicic acid solution is prepared by performing chelating ion exchange treatment on the acidic silicic acid solution in the range of pH 1.5 or more and 2.5 or less obtained in Step 1, and subsequently performing cation exchange treatment. This chelating ion exchange treatment (which may be referred to as "Treatment 2a") can be performed by passing the acidic silicic acid solution through a column filled with a chelating ion exchange resin. By chelating ion exchange, metal elements other than silicon are removed to achieve further high purity. Chelating ion exchange is particularly efficient in removing polyvalent metal elements.

[0036] As the chelating resin (chelating ion exchange resin) used in this chelating ion exchange treatment, a known chelating ion exchange resin into which a functional group that forms a chelate with a specific metal ion is introduced is used. Examples of the type of functional group include, but are not limited to, iminodiacetic acid group, thiol group, sulfonic acid group, phosphonic acid group, and primary amine group.

[0037] In Step 2, the liquid temperature [T2a] of the acidic silicic acid solution obtained in Step 1 before passing it through a column filled with a chelating ion exchange resin is preferably in the range of 3°C or higher and 18°C or lower. When within this temperature range, the ion exchange efficiency is excellent and the acidic silicic acid solution after passing through the column is also stable. If the liquid temperature of the acidic silicic acid solution before passing it through is less than 3°C, cation exchange may not proceed efficiently. If the liquid temperature of the acidic silicic acid solution before passing it through exceeds 18°C, the acidic silicic acid solution tends to polymerize and gel, and the stability of the acidic silicic acid solution after passing through is likely to decrease. Here, the liquid temperature of the acidic silicic acid solution before passing it through is more preferably in the range of 5°C or higher and 15°C or lower, even more preferably in the range of 6°C or higher and 15°C or lower, and most preferably in the range of 7°C or higher and 15°C or lower. Note that for the temperature of the acidic silicic acid solution before passing it through, usually, if it is within the above temperature range, it can be passed through as it is. If the liquid temperature exceeds the above temperature range, it is cooled to adjust the temperature. Also, for the cation exchange resin filled in the column, for the purpose of preventing the temperature rise during passing through, it is desirable to adjust the temperature to the range of 3°C or higher and 18°C or lower in advance using means such as refrigeration. In this specification, in Step 2, the liquid temperature of the acidic silicic acid solution before passing it through a column filled with a chelating ion exchange resin may be represented as T2a. In this specification, the acidic silicic acid solution after chelating ion exchange in Step 2 is also referred to as "the acidic silicic acid solution after chelating ion exchange" or "the acidic silicic acid solution after chelating ion exchange treatment", etc.

[0038] The longer the contact time between the acidic silicic acid solution obtained in Step 1 and the chelating ion exchange resin, that is, the slower the liquid passing rate through the ion exchange tower filled with the ion exchange resin and the lower the space velocity, the higher the ion exchange efficiency. However, when the space velocity is low, it takes a long time for the operation, so the production efficiency deteriorates. The liquid passing rate [S2a] of the acidic silicic acid solution through the chelating ion exchange resin in Step 2 is not particularly limited, but preferably, it is -1 2 h or more and 6 h -1 or less. More preferably, it is -1 2.5 h or more and 5.0 h -1It is recommended to pass the liquid at a space velocity within the following range. In this specification, in step 2, the space velocity when passing the acidic silicic acid solution obtained in step 1 through a column filled with a chelating ion exchange resin may be denoted as S2a.

[0039] In step 2, the pH of the acidic silicic acid solution before passing it through the chelating ion exchange resin is preferably in the range of 1.5 or more and 2.5 or less. In the production method according to this embodiment, in step 2, the pH of the acidic silicic acid solution before passing it through the chelating ion exchange resin is equal to the pH [P1] of the acidic silicic acid solution obtained in step 1.

[0040] Subsequent to the chelating ion exchange treatment, a cation exchange treatment (which may be referred to as "treatment 2b") is performed. The cation exchange resin used here is as described above.

[0041] The liquid temperature [T2b] of the acidic silicic acid solution after the chelating ion exchange treatment before passing it through a column filled with a cation exchange resin is preferably in the range of 3°C or more and 18°C or less. When it is within this temperature range, the ion exchange efficiency is excellent and the resulting purified acidic silicic acid solution is also stable. When the liquid temperature of the acidic silicic acid solution before passing is less than 3°C, the cation exchange may not proceed efficiently. When the liquid temperature of the acidic silicic acid solution before passing exceeds 18°C, the acidic silicic acid solution tends to polymerize and gel, and the stability of the resulting purified acidic silicic acid solution tends to decrease. The liquid temperature of the acidic silicic acid solution before passing is more preferably in the range of 5°C or more and 15°C or less, even more preferably in the range of 6°C or more and 15°C or less, and most preferably in the range of 7°C or more and 15°C or less. Note that for the temperature of the acidic silicic acid solution before passing, usually, if it is within the above temperature range, it can be passed as it is. When the liquid temperature exceeds the above temperature range, it is cooled to adjust the temperature. Also, for the cation exchange resin filled in the column, for the purpose of preventing the temperature rise during passing, it is desirable to adjust the temperature to the range of 3°C or more and 18°C or less in advance using means such as refrigeration. In this specification, in step 2, the liquid temperature of the acidic silicic acid solution after the chelating ion exchange treatment before passing it through a column filled with a cation exchange resin may be represented as T2b.

[0042] The longer the contact time between the acidic silicic acid solution after the chelating ion exchange treatment and the ion exchange resin, that is, the slower the flow rate through the ion exchange column filled with the ion exchange resin and the lower the space velocity, the higher the ion exchange efficiency. However, when the space velocity is low, the operation takes time and the production efficiency deteriorates. In step 2, chelating ion exchange is performed prior to cation exchange. When ion exchange is performed multiple times in this way, an optimal space velocity may be selected for each ion exchange step. However, if the space velocities vary significantly in each step, the processing times will not match and waiting times will occur in subsequent steps, which is not preferable. Therefore, when performing ion exchange in multiple steps, it is preferable to perform it at approximately the same space velocity. The flow rate [S2b] of the acidic silicic acid solution through the cation exchange resin in step 2 is not particularly limited, but preferably, it is in the range of -1 2 h or more and -1 6 h or less, more preferably, in the range of -1 2.5 h or more and -1 5 h or less. It is recommended to pass the solution at a space velocity within this range. In this specification, in step 2, the space velocity when passing the acidic silicic acid solution after the chelating ion exchange treatment through a column filled with a cation exchange resin may be represented as S2b.

[0043] In step 2, the pH [P2b] of the acidic silicic acid solution before passing it through the cation exchange resin is preferably in the range of 1.5 or more and 2.5 or less. In the production method of the present invention, in step 2, the pH of the acidic silicic acid solution before passing it through the cation exchange resin is approximately equal to the pH of the acidic silicic acid solution before passing it through the chelating ion exchange resin. The pH of the acidic silicic acid solution before passing it through the cation exchange resin is preferably in the range of 1.6 or more and 2.4 or less, more preferably in the range of 1.7 or more and 2.2 or less, and even more preferably in the range of 1.8 or more and 2.0 or less. In this specification, in Step 2, the pH of the acidic silicic acid solution after chelate ion exchange treatment before passing it through a column filled with a cation exchange resin may be represented as P2b.

[0044] In Step 2, the pH value of the purified acidic silicic acid solution after cation exchange preferably ranges from 1.5 to 2.5. Although impurity ions elute from the solid phase to the liquid phase by the leaching treatment, since the eluted impurities are on the ppm order, the pH of the acidic silicic acid solution hardly varies before and after cation exchange. Conversely, if it deviates significantly from this pH range, it is considered that some contamination has occurred during the process. The pH of the purified acidic silicic acid solution is preferably in the range of 1.6 to 2.4, more preferably in the range of 1.7 to 2.2, and even more preferably in the range of 1.8 to 2.0.

[0045] The purified acidic silicic acid solution obtained in Step 2 has an Al concentration of 5 ppm or more and 30 ppm or less, an Fe concentration of 1 ppm or more and 20 ppm or less, a Ca concentration of 1 ppm or more and 8 ppm or less, a Na concentration of 1 ppm or more and 20 ppm or less, a Mg concentration of 0.2 ppm or more and 4 ppm or less, a Cr concentration of 0.05 ppm or more and 1 ppm or less, a Ni concentration of less than 1 ppm, a Cu concentration of less than 1 ppm, and a Zn concentration of less than 1 ppm (however, the total amount of these metals is limited to 100 ppm or less).

[0046] [Step 3: Preparation of Silica Fine Particle Dispersion Liquid] In Step 3, an aqueous alkali hydroxide solution is added to a part of the purified acidic silicic acid solution obtained in Step 2, heated in the temperature range of 50°C or higher and 98°C or lower, the temperature is maintained in the range of 50°C or higher and 98°C or lower for 20 minutes or longer, and further, a part of the purified acidic silicic acid solution obtained in Step 2 is added at an addition rate in the range of 0.001 g / min·g or more and 0.5 g / min·g or less (in terms of silica solid content) while simultaneously adding a pH adjuster to obtain a high-purity silica fine particle dispersion liquid.

[0047] Specifically, a part of the purified acidic silicic acid solution can be used as the seed solution, and another part can be used as the feed solution, and the seed solution can be adjusted to be alkaline. Specifically, it is desirable to add an alkali to the seed solution to adjust the pH of the solution to a range of 10 or more and 13 or less, preferably in a range of 10.5 or more and 12 or less. Next, the temperature of this solution is raised to a range of 50°C or more and 98°C or less, more preferably in a range of 60°C or more and 98°C or less, and even more preferably in a range of 65°C or more and 98°C or less. After the temperature is raised, the temperature is maintained for a predetermined time, and then the feed solution is added to mix the seed solution and the feed solution and grow the particles. Also, the holding temperature at this time is recommended to be in a range of 20 minutes or more, preferably in a range of 25 minutes or more.

[0048] Here, the type of alkali is not particularly limited. For example, potassium hydroxide, sodium hydroxide, and organic alkalis can be used. The amount of alkali used is such that the pH of the seed solution can be adjusted to a range of pH 10 or more and 13 or less. The amount of the feed solution used is such that the feed solution is used in a ratio of 100:100 to 100:10,000 in terms of silica conversion [parts by mass] with respect to the seed solution. The addition rate of the feed solution is preferably added in a range of 0.002 g / min·g or more and 0.3 g / min·g or less, and more preferably in a range of 0.01 g / min·g or more and 0.09 g / min·g or less. Here, the unit of the addition rate, "g / min·g", means the silica dry supply amount per minute of the feed solution added with respect to the silica dry in the seed solution. Here, the unit "g / min·g" can also be expressed as the unit "g / (min·g)".

[0049] Also, by simultaneously adding this feed solution and the pH adjuster, the seed solution and the feed solution can be mixed. Here, the amount of the pH adjuster used is added according to the amount of the inorganic acid contained in the purified silicic acid solution used as the feed liquid. When the inorganic acid is a monovalent inorganic acid, an amount equivalent to that of the inorganic acid is used. When the inorganic acid is a divalent inorganic acid, an amount twice that of the inorganic acid is used. When the inorganic acid is a trivalent inorganic acid, an amount three times that of this inorganic acid is used. Since the addition rate of the pH adjuster varies depending on the concentration of the alkaline aqueous solution, it is not particularly limited. The type of the pH adjuster is not particularly limited, but for example, potassium hydroxide, sodium hydroxide, etc. can be used. The pH adjuster is added for the purpose of dissolving the added purified silicic acid solution and depositing it on the surface of the core particles or silica particles by keeping the pH in the preparation liquid sufficiently alkaline, and is added for the purpose of maintaining the pH of the system composed of the seed liquid, the alkali, and the feed liquid in the range of 10 or more and 13 or less at the time of adding the feed liquid. Here, the liquid temperature of the feed liquid is preferably in the range of 1°C or more and 30°C or less, more preferably in the range of 1°C or more and 20°C or less, and is added to the seed liquid.

[0050] Preferably, when the feed liquid is gradually added to the seed liquid adjusted to the above pH and temperature, silica fine particles grow in the seed liquid, and a silica fine particle dispersion (silica sol) can be obtained. After adding the feed liquid to the seed liquid, if it is held in the range of a temperature of 50°C or more and 98°C or less for about several tens of minutes to several hours, the added purified acidic silicic acid solution is sufficiently deposited on the silica fine particles, and it is preferable because the silica fine particles are likely to grow.

[0051] In step 3, in the first stage, after adding the feed liquid and the pH adjuster, in the second stage, the addition rate of the feed liquid and the pH adjuster may be changed, and the feed liquid may be further added. In the second stage, a feed liquid that is a part of the purified acidic silicic acid solution obtained in step 2 may be added in the range of 1.0 times or more and 10.0 times or less the addition rate of the first stage to obtain a high-purity silica fine particle dispersion.

[0052] In the method for producing a high-purity silica fine particle dispersion according to this embodiment, the following aspect 1 is preferable. [Aspect 1: Reaction Factor A] It is preferable to perform the cation exchange treatment in this embodiment so that the value of the reaction factor (A) represented by the following mathematical formula (F2) satisfies the range of 13 or more and 225 or less. A = p × s × t ···(F2) p: The average value of the pH of the acidic silicic acid solution prepared in Step 1 and the pH of the acidic silicic acid solution before the cation exchange treatment in Step 2, s: The average value of the space velocity (unit: h -1 ) when passing the solution in each ion exchange treatment in Step 1 and Step 2, t: The average value of the temperature (unit: °C) of the solution before passing the solution in each ion exchange treatment in Step 1 and Step 2

[0053] As described above, p in the mathematical formula (F2) is the average value of the pH [P1] of the acidic silicic acid solution prepared in Step 1 and the pH [P2b] of the acidic silicic acid solution before the cation exchange treatment in Step 2. This relationship can be expressed as p = ([P1] + [P2b]) / 2.

[0054] As described above, s in the mathematical formula (F2) represents the average value of the space velocity (unit: h -1 ) when passing the solution in each ion exchange treatment in Step 1 and Step 2. That is, s in the mathematical formula (F2) means the average value of the flow rate [S1] when passing the aqueous sodium silicate solution through the cation exchange resin in Step 1, the flow rate [S2a] when passing the acidic silicic acid solution through the chelating ion exchange resin in Step 2, and the flow rate [S2b] when passing the acidic silicic acid solution through the cation exchange resin in Step 2. This relationship can be expressed as s = ([S1] + [S2a] + [S2b]) / 3.

[0055] As described above, t in the mathematical formula (F2) represents the average value of the liquid temperature before passing the liquid in each ion exchange treatment of the above-described step 1 and step 2. That is, t in the mathematical formula (F2) means the average value of the temperature [T1] before passing the aqueous sodium silicate solution through the cation exchange resin in step 1, the temperature [T2a] before passing the acidic silicic acid solution through the chelating ion exchange resin in step 2, and also the temperature [T2b] before passing the acidic silicic acid solution through the cation exchange resin in step 2. This relationship can be expressed as t = ([T1] + [T2a] + [T2b]) / 3.

[0056] The inventors of the present invention focused on the conditions of cation exchange of raw material water glass and cation exchange of acidic silicic acid solution in an intermediate stage in order to efficiently reduce impurities in the method for producing high-purity silica sol, and completed the present invention. That is, in step 1, an inorganic acid or the like is added to the aqueous sodium silicate solution, and the average value (p) of the pH value [P1] of the acidic silicic acid solution obtained through further cation exchange treatment, the average value (p) of the pH value [P2a] of the purified acidic silicic acid solution after chelating ion exchange treatment in step 2, the space velocity [S1] of the aqueous sodium silicate solution in the cation exchange treatment in step 1, the average value (s) of the space velocity [S2a] in the chelating ion exchange treatment in step 2 and the space velocity [S2b] in the cation exchange treatment in step 2, the liquid temperature [T1] of the aqueous sodium silicate solution before being introduced into the cation exchange treatment in step 1, the liquid temperature [T2a] of the acidic silicic acid solution before being introduced into the chelating ion exchange treatment in step 2, and the average value (t) of the liquid temperature [T2b] of the acidic silicic acid solution before being introduced after the cation exchange treatment in step 2. When the product of p, s and t is A, the inventors have found that if A is in the range of 13 or more and 225 or less, the economy is good, the removal efficiency of metal impurities is also good, and the stability of each acidic silicic acid solution and the purified acidic silicic acid solution during the manufacturing process is maintained. In the present invention, in terms of process setting, the pH value [P1] of the acidic silicic acid solution obtained by adding an inorganic acid to the aqueous sodium silicate solution and further undergoing a cation exchange treatment in step 1 is equal to the pH value of the acidic silicic acid solution before the chelating ion exchange treatment in step 2.

[0057] The value of the reaction factor A is preferably in the range of 60 or more and 173 or less, more preferably in the range of 65 or more and 160 or less, and even more preferably in the range of 70 or more and 144 or less.

[0058] In this embodiment, in the mathematical formula (F2), the value of p is preferably in the range of 1.5 or more and 2.5 or less, more preferably in the range of 1.5 or more and 2.4 or less, and even more preferably in the range of 1.6 or more and 2.4 or less. Also, the value of s is preferably -1 2h or more -1 and 6h or less, preferably 2.5h -1 or more -1 and 5h or less, and even more preferably 3.2h -1 or more -1 and 4.8h or less, particularly preferably 3.2h -1 or more -1 and 4.6h or less. Also, the value of t is preferably in the range of 3°C or more and 18°C or less, even more preferably in the range of 5°C or more and 15°C or less, even more preferably in the range of 6°C or more and 15°C or less, and particularly preferably in the range of 7°C or more and 15°C or less. Note that p represents the average value of the pH of the acidic silicic acid solution prepared in Step 1 and the pH of the acidic silicic acid solution before the cation exchange treatment in Step 2. s represents the average value of the space velocity (unit: h -1 ) when passing the solution in each ion exchange treatment in Step 1 and Step 2. Also, t represents the average value of the temperature (unit: °C) of the solution before passing the solution in each ion exchange treatment in Step 1 and Step 2.

[0059] Also, in this embodiment, the average particle diameter of the silica fine particles in the obtained high-purity silica fine particle dispersion is not particularly limited. For example, a silica fine particle dispersion having an average particle diameter of 3 nm or more and 300 nm or less (dynamic light scattering method) can be obtained.

[0060] [High-purity silica fine particle dispersion] The high-purity silica fine particle dispersion according to this embodiment can be obtained by the method for producing a high-purity silica fine particle dispersion according to the above-described embodiment. The high-purity silica fine particle dispersion liquid according to this embodiment has an Al concentration of 5 ppm or more and 30 ppm or less, an Fe concentration of 1 ppm or more and 20 ppm or less, a Ca concentration of 1 ppm or more and 8 ppm or less, a Na concentration of 1 ppm or more and 20 ppm or less, a Mg concentration of 0.2 ppm or more and 4 ppm or less, a Cr concentration of 0.05 ppm or more and 1 ppm or less, a Ni concentration of less than 1 ppm, a Cu concentration of less than 1 ppm, and a Zn concentration of less than 1 ppm with respect to the silica solid content (however, the total amount of these metals is limited to 100 ppm or less).

Examples

[0061] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way. Also, regarding the measurement methods of various properties of the high-purity silica sol in the examples and comparative examples, unless otherwise specified, the methods described below were used.

[0062] <Measurement of silica sol, purified acidic silicic acid solution, etc.> 1. Purity (1) Metal (Al, Fe, Ca, Mg, Cr, Ni, Cu, Zn, or Na) content 1) Take about 10 g of the sample (silica sol or purified acidic silicic acid solution) into a platinum dish and weigh it to 0.1 mg. 2) Add 5 mL of nitric acid and 20 mL of hydrofluoric acid, heat on a sand bath, and evaporate to dryness. 3) When the liquid volume decreases, add another 20 mL of hydrofluoric acid, heat on a sand bath, and evaporate to dryness. 4) After cooling to room temperature, add 2 mL of nitric acid and about 50 mL of water, and heat to dissolve on a sand bath. 5) After cooling to room temperature, put it into a flask (100 mL) and dilute to 100 mL with water to obtain a sample solution. 6) The content of each metal present in the sample solution was measured using the following measuring device.

[0063] [Contents of Al, Fe, Ca, Mg, Cr, and Zn] Measured by an inductively coupled plasma optical emission spectrometer (manufactured by Seiko Instruments Inc., SPS5520, which introduces a sample solubilized in a high-frequency inductively coupled argon plasma, excites and emits light from each element in the sample, and performs quantitative and qualitative analysis based on the emission spectrum. The measurement wavelength range is 175 - 500 nm). [Contents of Ni and Cu] Measured using an atomic absorption spectrophotometer (manufactured by Agilent Technologies, AA240Z, which atomizes the sample by a flame, irradiates the atomic vapor layer with light of an appropriate wavelength, measures the intensity of the light absorbed by the atoms, and thereby quantifies the element concentration in the sample. A graphite furnace is used. Measurement mode: atomic absorption, and the measurement wavelength range is 190 - 900 nm). [Content of Na] Measured using an atomic absorption spectrophotometer (manufactured by Hitachi, Ltd., Z - 2310, and the measurement wavelength range is 190 - 900 nm).

[0064] (2) SiO2 Concentration The SiO2 concentration in the silica sol or purified acidic silicic acid solution is determined by adding 2 mL of 50% sulfuric acid aqueous solution to 10 g of the sample, evaporating to dryness on a platinum dish, firing the obtained solid at 1000 °C for 1 hour, cooling, and weighing. Next, the weighed solid is dissolved in a small amount of 50% sulfuric acid aqueous solution, 20 mL of hydrofluoric acid is further added, then evaporated to dryness on a platinum dish, fired at 1000 °C for 15 minutes, cooled, and weighed. The silica content is determined from the difference in these weights.

[0065] (3) From the measurement results of (1) - (2) above, the concentration (impurity concentration) of each element (Al, Fe, Ca, Mg, Cr, Ni, Cu, Zn, or Na) with respect to the silica solid content (silica dry) of the silica sol was measured.

[0066] 2. pH Measurement For the pH measurement of the acidic silicic acid solution, the purified acidic silicic acid solution, and the silica sol (silica fine particle dispersion), approximately 50 g of the sample for measurement was collected in a polyethylene sample bottle, immersed in a constant temperature bath at 25°C for 30 minutes or more, and then the glass electrode of the pH meter F22 manufactured by Horiba, Ltd. that had been calibrated with standard solutions of pH 4, 7, and 9 was inserted for the measurement.

[0067] 3. Measurement of average particle diameter For the silica sol (silica fine particle dispersion) obtained in each of the examples and comparative examples, the average particle diameter was measured using nanoSAQLA manufactured by Otsuka Electronics Co., Ltd., which is a particle size measuring device based on the dynamic light scattering method.

[0068] 4. Calculation of Reynolds number In this specification, the Reynolds number (Re) was determined by the following general formula. Reynolds number (Re) = Duρ / μ (D: inner diameter of the pipe [m], u: average flow velocity of the fluid [m / s], ρ: density of the fluid [Kg / m 3 , μ: viscosity of the fluid [m 3 / s])

[0069] [Example 1] (Purification of high-purity purified silicic acid solution) · Step 1 3000.0 g of No. 3 water glass (silica concentration 24.23 mass%) was diluted with pure water to prepare 14,538 g of a diluted sodium silicate aqueous solution (SiO2 concentration 5.0 mass%). Next, 148.3 g of an oxalic acid aqueous solution (oxalic acid concentration 9.8 mass%) and 29.7 g of a sulfuric acid aqueous solution (sulfuric acid concentration 5.0 mass%) were prepared. Using a static mixer (T3-12, number of elements 12, manufactured by Noritake Company Limited), while introducing 14,538 g of the diluted sodium silicate aqueous solution into the static mixer at 300 g / min over 48.1 minutes, simultaneously 148.3 g of the oxalic acid aqueous solution (oxalic acid concentration 9.8 mass%) was introduced into the static mixer at 3.06 g / min and 29.7 g of the sulfuric acid aqueous solution (sulfuric acid concentration 5.0 mass%) was introduced into the static mixer at 0.61 g / min over 48.1 minutes for liquid passing and mixing respectively to obtain a uniform sodium silicate aqueous solution containing oxalic acid and sulfuric acid. Incidentally, the weight ratio of oxalic acid to the aqueous sodium silicate solution before mixing (the ratio of the weight of oxalic acid to the weight of the diluted aqueous sodium silicate solution) was 1,000 ppm, and the Reynolds number during the passage of the solution through the static mixer was 1,264. This sulfuric acid-containing aqueous sodium silicate solution was maintained at 12°C and passed through 6 L of a strongly acidic cation exchange resin (Duolite C255LFH, manufactured by Rohm and Haas) at a space velocity of 4.0 h -1 to obtain an acidic silicic acid solution with a pH of 1.8 and an SiO2 concentration of 4.8 mass%. · Step 2 Next, the acidic silicic acid solution was cooled to 12°C and passed through 6 L of a chelating ion exchange resin (CR-11, manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h -1 After passing through, the SiO2 concentration of the acidic silicic acid solution was 4.6 mass% and the pH was 1.9. Subsequently, the acidic silicic acid solution after chelating ion exchange treatment obtained was cooled to 12°C and passed through 6 L of a strongly acidic cation exchange resin at a space velocity of 4.0 h -1 to obtain a purified acidic silicic acid solution. The pH of the obtained purified acidic silicic acid solution was 1.8 and the SiO2 concentration was 4.4 mass%. (Preparation of silica sol) · Step 3 322.2 g of the purified acidic silicic acid solution was charged into a 10 L separable flask so that the silica dry was 14.7 g. Next, 17.9 g of a 48.7 mass% potassium hydroxide aqueous solution was weighed. Further, 594.8 g of pure water was weighed so that the total of the purified acidic silicic acid solution, potassium hydroxide, and ultrapure water was 945.9 g, and 17.3 g of a 48.7 mass% potassium hydroxide aqueous solution and ultrapure water were stirred until uniform. This diluted potassium hydroxide aqueous solution was charged into a 10 L separable flask and stirred well. The silica concentration of the solution in the 10 L separable flask was 1.55 mass% and the pH was 11.1. Subsequently, while stirring this solution, the temperature was raised to 83°C. After reaching 83°C, the temperature was maintained for 30 minutes. After the holding was completed, 53.1 g of purified acidic silicic acid solution (1207 g of purified acidic silicic acid solution) in terms of silica dry was added at an addition rate of 0.020 g / min·g (in terms of silica solid content) over 3 hours, and at the same time, 86.0 g of a 3.0 mass% potassium hydroxide aqueous solution prepared in advance was added over 3 hours (first-stage addition). Subsequently, 318.8 g of purified acidic silicic acid solution (7244 g of purified acidic silicic acid solution) in terms of silica dry was added at an addition rate of 0.030 g / min·g (in terms of silica solid content) over 12 hours, and at the same time, 516.1 g of a 3.0 mass% potassium hydroxide aqueous solution prepared in advance was added over 12 hours (second-stage addition). After the addition was completed, it was held at 83°C for 1 hour and then cooled to room temperature. The resulting solution was concentrated to 12 mass% using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Chemicals Corporation), and then concentrated to 40 mass% using a rotary evaporator to obtain a high-purity silica sol. When the metal impurity concentrations of the obtained purified acidic silicic acid solution and silica sol were measured, the concentrations of each metal impurity with respect to the silica solid content were as shown in Tables 2 and 3. Also, the manufacturing conditions are shown in Table 1 (the same applies to the following Examples and Comparative Examples). Furthermore, the Reynolds number (Re), mixing factor B, and the calculated values of the p value, t value, s value, and reaction factor A are shown in Table 1 (except when the corresponding values cannot be measured or calculated. The same applies to the following Examples and Comparative Examples). Also, the average particle diameter of the silica fine particles in the obtained silica sol was 38 nm.

[0070] [Examples 2 to 4] Purified acidic silicic acid solution and high-purity silica sol were prepared in the same manner as in Example 1, except that the manufacturing conditions were changed to the conditions shown in Table 1.

[0071] [Comparative Examples 1 and 2] Purified acidic silicic acid solution and silica sol were prepared in the same manner as in Example 1, except that the manufacturing conditions were changed to the conditions shown in Table 1.

[0072] [Comparative Example 3] In Example 1, the treatment is carried out in the order of Step 1, Step 2, and Step 3. In Comparative Example 3, in Step 1, the mixing of the aqueous sodium silicate solution and the aqueous sulfuric acid solution was not performed, and the treatment was carried out in the order of passing the solution through the cation exchange resin in Step 1, Step 2, and Step 3. In each step of Comparative Example 3, except for the conditions described here, the conditions described in Table 1 were implemented. Note that since there is no leaching step in Comparative Example 3, the mixing factor and the reaction factor could not be calculated.

[0073] [Comparative Example 4] In Comparative Example 3, the treatment was carried out in the order of passing the solution through the cation exchange resin in Step 1, Step 2, and Step 3. In Comparative Example 4, in Step 2, the solution was passed through the cation exchange resin without passing through the chelating ion exchange resin. In each step of Comparative Example 4, except for the conditions described here, the conditions described in Table 1 were implemented. Note that since there is no leaching step in Comparative Example 4, the mixing factor and the reaction factor could not be calculated.

[0074]

Table 1

[0075]

Table 2

[0076]

Table 3

Claims

1. A method for producing a highly pure silica fine particle dispersion liquid, comprising the following steps 1 to 3. (Step 1) An aqueous sodium silicate solution (SiO ２ in the range of 2% by mass or more and 7% by mass or less), a complexing agent, and at least one selected from the group consisting of inorganic acids and inorganic acid salts are added and mixed, and further cation exchange treatment is performed to obtain an acidic silicic acid solution in the range of pH 1.5 or more and 2.5 or less. (Step 2) A step of subjecting the acidic silicic acid liquid obtained in the above step 1 to a chelate ion exchange treatment, and then subjecting it to a cation exchange treatment to obtain a purified acidic silicic acid liquid. (Step 3) Add an aqueous alkali hydroxide solution to a part of the purified acidic silicic acid liquid obtained in the above step 2, adjust the pH to a range of 10 or more and 13 or less, then heat at a temperature of 50°C or more and 98°C or less, and maintain the temperature in the range of 50°C or more and 98°C or less for 20 minutes or more. Further, add another part of the purified acidic silicic acid liquid obtained in the above step 2 at an addition rate in the range of 0.001 g / min·g or more and 0.5 g / min·g or less (in terms of silica solid content), and simultaneously add a pH adjuster to obtain a highly pure silica fine particle dispersion liquid.

2. In the above step 1, when adding and mixing the sodium silicate aqueous solution with at least one selected from the group consisting of the complexing agent and the inorganic acid and the inorganic acid salt, a static mixer is used for mixing. At this time, the value of the mixing factor (B) represented by the following mathematical formula (F1) is in the range of 1,000 or more and 1,000,000 or less. The method for producing a highly pure silica fine particle dispersion liquid according to Claim 1. B = Re × n... (F1) (B: Mixing factor of the static mixer, n: Number of elements of the static mixer, Re: Reynolds number)

3. The cation exchange treatment is carried out so that the value of the reaction factor (A) represented by the following mathematical formula (F2) satisfies a range of 13 or more and 225 or less. The method for producing a highly pure silica fine particle dispersion liquid according to Claim 1 or Claim 2. A = p × s × t... (F2) (p: Average value of the pH of the acidic silicic acid liquid prepared in the above step 1 and the pH of the acidic silicic acid liquid before the cation exchange treatment in the above step 2, s: In each ion exchange treatment in the above Step 1 and Step 2, the average value of the space velocity (unit: h －１ ) when passing the liquid t: Average value of the temperature (unit: °C) of the liquid before passing through in each ion exchange treatment in the above step 1 and the above step 2)

4. In the above formula (F2), the value of p is in the range of 1.5 or more and 2.5 or less, and the value of s is 2h －１ or more and 6h －１ or less, and the value of t is in the range of 3°C or more and 18°C or less. The method for producing a highly pure silica fine particle dispersion liquid according to claim 3

5. In the purified acidic silicic acid solution obtained in the step 2, the Al concentration is 5 ppm or more and 30 ppm or less, the Fe concentration is 1 ppm or more and 20 ppm or less, the Ca concentration is 1 ppm or more and 8 ppm or less, the Na concentration is 1 ppm or more and 20 ppm or less, the Mg concentration is 0.2 ppm or more and 4 ppm or less, the Cr concentration is 0.05 ppm or more and 1 ppm or less, the Ni concentration is less than 1 ppm, the Cu concentration is less than 1 ppm, and the Zn concentration is less than 1 ppm (however, the total amount of these metals is limited to 100 ppm or less). The method for producing a high-purity silica fine particle dispersion liquid according to claim 1 or claim 2.

6. A high-purity silica fine particle dispersion liquid, wherein the Al concentration is 5 ppm or more and 30 ppm or less, the Fe concentration is 1 ppm or more and 20 ppm or less, the Ca concentration is 1 ppm or more and 8 ppm or less, the Na concentration is 1 ppm or more and 20 ppm or less, the Mg concentration is 0.2 ppm or more and 4 ppm or less, the Cr concentration is 0.05 ppm or more and 1 ppm or less, the Ni concentration is less than 1 ppm, the Cu concentration is less than 1 ppm, and the Zn concentration is less than 1 ppm (however, the total amount of these metals is limited to 100 ppm or less) with respect to the silica solid content.

Images