JP2021059462A - Hydrous silicic acid slurry and its production method - Google Patents

Abstract

To provide a hydrous silicic acid slurry having a form in which nano-sized primary particles are agglomerated and which does not settle easily, despite having a BET specific surface area of 35 m2/g or less.SOLUTION: A hydrous silicic acid slurry comprises a hydrous silicic acid having a BET specific surface area of 10 to 35 m2/g, a volume average particle size (D50) of 0.4 to 0.9 μm as measured by laser diffraction, and a particle size (D90) of 1.0 to 5.0 μm at 90% of volume integrated cumulative values from the bottom in particle size distribution as measured by laser diffraction. A method for producing the hydrous silicic acid slurry comprises the steps of mixing a hydrous silicic acid having a BET specific surface area of 10 to 35 m2/g and a volume average particle size (D50) of 1.0 μm or more as measured by laser diffraction with a dispersing medium to make a slurry, and wet-milling the resulting slurry until having a volume average particle size (D50) of 0.4 to 0.9 μm as measured by laser diffraction and a particle size (D90) of 1.0 to 5.0 μm at 90% of volume integrated cumulative values from the bottom in particle size distribution as measured by laser diffraction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hydrous silicic acid slurry and a method for producing the same.

There are a wide variety of silica slurries in which silica is dispersed in an aqueous dispersion medium. In addition to colloidal-type and sol-type silica-containing slurries that are synthesized in advance in a slurry state, slurries in which dry silica supplied as powder is dispersed in a solvent are also widely used. These are silica slurries in which nano-sized silica primary particles have a monodisperse or a cohesive structure close to monodisperse.

On the other hand, the hydrous silicic acid slurry, which has a structure in which primary particles of about 10 to 30 nm are strongly aggregated to a size of about 50 to 500 nm and the hydrous silicic acid supplied as a powder is dispersed in an aqueous dispersion medium, contains hydrous silicic acid. By having an agglomerated structure, it has properties different from colloidal silica and dry silica, and therefore various types are being studied.

As a method for producing a hydrous silicic acid slurry, a method of dispersing hydrous silicic acid in powder in an aqueous dispersion medium such as water and adjusting the particle size using a wet pulverizer such as a bead mill or a high-pressure homogenizer is disclosed. .. (Patent Documents 1 to 3)

Further, since the hydrous silicic acid in the hydrous silicic acid slurry has an aggregated structure, there is a drawback that aggregation and precipitation are likely to occur. As a countermeasure, a method of adding a cationic resin or the like is disclosed. (Patent Documents 1 and 3)

Hydrous silicic acid slurry is used for inkjet glossy paper (Patent Document 1), abrasives (Patent Documents 2 and 4), film and resin coating additives (Patent Document 3), paints, and ink matting agents. and so on. In the field of coating additives for inkjet glossy paper and film resins, which require transparency, hydrous silicic acid having a high BET specific surface area and a large pore capacity (or oil absorption) is preferred.

Japanese Unexamined Patent Publication No. 10-181190 Japanese Unexamined Patent Publication No. 2003-146645 Japanese Unexamined Patent Publication No. 2006-69870 Japanese Unexamined Patent Publication No. 2016-1000034

In recent years, a non-spherical submicron size having a small BET specific surface area (for example, BET specific surface area of 35 m ² / g or less), a large primary particle diameter (for example, 60 nm or more in diameter), and an aggregated morphology, which has never been seen before. There is an increasing need for a slurry of hydrous silicic acid. Hereinafter, in the present specification, the submicron size refers to a size of 0.1 to 1.0 micron, if not numerically limited.

When such a slurry is used as an abrasive, for example, the smoothness of the polished surface is inferior to that of other types of hydrous silicic acid slurries such as colloidal silica, but an improvement in polishing speed can be expected. In addition, when used as a film or resin coating additive, although the transparency is inferior, the adhesive strength is improved due to the improved adhesion to the coating material, the blocking performance of the coated surface is improved, and the surface is rubbed against something. It can be expected to improve the scratch resistance at the time.

Hereinafter, in the present specification, unless otherwise specified, the hydrous silicic acid refers to a hydrous silicic acid in a powder state, and the slurry refers to a hydrous silicic acid slurry.

Silicic acid is synthesized by growing primary particles precipitated by the neutralization reaction of sodium silicate and mineral acid. Therefore, even hydrous silicic acid having a BET specific surface area of 35 m ² / g or less can be prepared. However, in this method, the deposited small primary particles usually grow while maintaining the agglomerated state. Therefore, when the hydrous silicic acid is grown to a BET specific surface area of 35 m ² / g or less, it is hard and large agglomerates. It becomes a particle.

According to the experiments of the present inventors, when ^{a hydrous silicic acid having a BET specific surface area of 35 m 2} / g or less is prepared by a conventional method, it becomes a hard amorphous silicic acid having an aggregated particle size of several tens of μm in size, and then becomes a hard amorphous silicic acid. It was difficult to grind, and it was practically impossible to grind to a submicron size of less than 1 μm.

Further, as a problem peculiar to hydrous silicic acid, there is a problem of sedimentation of hydrous silicic acid in the slurry. This was particularly noticeable with hydrous silicic acid with a BET specific surface area of 35 m ^{2 / g or less.} As described in Patent Documents 1 to 3, a method of adding a cationic resin or the like has been proposed as a method for preventing sedimentation of hydrous silicic acid, but this addition effect is low for hydrous silicic acid ^{having a BET specific surface area of 35 m 2 / g or less.} It was. Further, when a cationic resin or the like is added to the slurry, for example, in a coating additive application, there is a problem that gelation occurs at a later pH adjustment, and in a polishing application, the polishing speed decreases due to a decrease in frictional resistance due to the cationic resin component. There was a problem such as doing. As described above, depending on the application, these sedimentation prevention methods may not be preferable.

Therefore, in order to solve these problems, the present inventors have a slurry in which nano-sized primary particles are aggregated and hard to settle even though ^{the BET specific surface area is 35 m 2 / g or less.} Was examined in various ways.

As described above, the hydrous silicic acid having a BET specific surface area of 35 m ² / g or less prepared by the conventional method has a strong cohesive force and cannot be pulverized to a submicron region of less than 1 μm. Therefore, we investigated a new method for synthesizing hydrous silicic acid that can be pulverized to a submicron region of less than 1 μm by wet pulverization while having a BET specific surface area of 35 m ^{2 / g or less.}

As a result, although it is a method using a neutralization reaction of sodium silicate and mineral acid as in the conventional method as described later, the BET ratio is obtained by using a mineral acid having a low concentration and allowing the particles to grow more slowly than before. We have succeeded in synthesizing hydrous silicic acid, which has a surface area of 35 m ² / g or less, has an aggregated form of nano-sized primary particles, and can be pulverized to a submicron region of less than 1 μm.

Furthermore, the hydrous silicic acid with a BET specific surface area of 35 m ² / g or less synthesized by this method is wet-pulverized to a submicron region of less than 1 μm, and has a form in which nano-sized primary particles are aggregated and is difficult to settle. Succeeded in preparing a silicic acid slurry, and completed the present invention.

In addition, it was also found that by adding a specific inorganic salt to the prepared hydrous silicic acid slurry, the precipitation of the hydrous silicic acid is suppressed and the dispersed state can be maintained.

The present invention is as follows.
[1]
The BET specific surface area is 10 to 35 m ² / g, the volume average particle size (D50) measured by the laser diffraction method is 0.4 to 0.9 μm, and the cumulative volume from the bottom in the particle size distribution measured by the laser diffraction method is cumulative. A hydrous silicic acid slurry comprising a hydrous silicic acid having a particle size (D90) of 90% of the value of 1.0 to 5.0 μm.
[2]
The hydrous silicic acid slurry according to [1], wherein the hydrous silicic acid concentration is 20 to 45% by weight.
[3]
The hydrous silicic acid slurry according to [1], which further contains an inorganic salt excluding a weak acid and a strong base.
[Four]
The hydrous silicic acid slurry according to [3], which contains the inorganic salt in a proportion of 2.0 to 5.0 parts by weight with respect to 100 parts by weight of the slurry.
[Five]
The hydrous silicic acid slurry according to [1], wherein the dispersion medium of the slurry is water or a water-containing solution.
[6]
The hydrous silicic acid slurry of [1], the slurry having a pH of 3.0 to 8.0 and an electrical conductivity (EC) of 15 to 100 mS / cm (millisiemens).
[7]
A step of mixing a hydrous silicic acid having a BET specific surface area of 10 to 35 m ² / g and a volume average particle diameter (D50) of 1.0 μm or more measured by a laser diffraction method with a dispersion medium to form a slurry, and obtaining a slurry. The volume average particle diameter (D50) of the obtained slurry measured by the laser diffraction method is 0.4 to 0.9 μm, and the particle diameter (D50) is 90% of the volume integrated cumulative value from the lower part in the particle size distribution measured by the laser diffraction method. A process of wet pulverization until D90) reaches 1.0 to 5.0 μm,
The method for producing a hydrous silicic acid slurry according to [1].
[8]
The production method according to [7], wherein the hydrous silicic acid and the dispersion medium are mixed so as to obtain a slurry having a concentration of 20 to 45% by weight.
[9]
The production method according to any one of [7] to [8], wherein the dispersion medium of the slurry is water or a water-containing solution.
[Ten]
The water-containing silicic acid slurry containing the inorganic salt is obtained by adding an inorganic salt other than a weak acid and a strong base to the slurry obtained after the wet pulverization step, according to any one of [7] to [9]. Production method.
[11]
The production method according to [10], wherein the inorganic salt is added at a ratio of 2.0 to 5.0 parts by weight with respect to 100 parts by weight of the slurry.

According to the present invention, the BET specific surface area is 10 to 35 m ² / g, the volume average particle size (D50) is 0.4 to 0.9 μm, and the volume integrated cumulative value 90% (D90) is 1.0 to 5.0 μm. It is possible to provide a hydrous silicate slurry having a form in which nano-sized primary particles are aggregated and which is difficult to settle.

Further, the hydrous silicic acid slurry of the present invention can increase the hydrous silicic acid concentration to a high concentration of 20 to 45% by weight.

In addition, according to the present invention, it is possible to provide a hydrous silicic acid slurry having more excellent sedimentation stability by adding an inorganic salt excluding a weak acid and a strong base to the slurry.

A primary particle growth model of hydrous silicic acid with a BET specific surface area of 35 m ^{2 / g or less is shown.} Production flow of hydrous silicic acid slurry of Examples and Comparative Examples Laser diffraction volume particle size distribution before and after wet grinding in Example 3 Laser diffraction volume particle size distribution before and after wet pulverization of Comparative Example 1

In the present invention, the BET specific surface area is 10 to 35 m ² / g, the volume average particle diameter (D50) measured by the laser diffraction method is 0.4 to 0.9 μm, and the particle size distribution measured by the laser diffraction method is from the bottom. Containing a hydrous silicic acid having a cumulative cumulative value of 90% (D90) of 1.0 to 5.0 μm.

The BET specific surface area of the hydrous silicic acid contained in the hydrous silicic acid slurry of the present invention is in the range of 10 to ^{35 m 2 / g.} A hydrous silicic acid slurry having a BET specific surface area ^{of more than 35 m 2} / g has an insufficient polishing rate, for example, in the polishing field, and has insufficient adhesive strength and scratch resistance in coating applications. On the other hand, when the BET specific surface area is ^{less than 10 m 2} / g, it is difficult to produce hydrous silicic acid itself. BET specific surface area of hydrous silicic acid contained in the hydrated silica slurry is preferably in the range of 15 to 30 m ² / g, more preferably 15~25 m ² / g. The smaller the BET specific surface area, the higher the concentration of the slurry. Further, in polishing applications and the like, further improvement in polishing speed and further improvement in adhesion to the coating agent can be expected.

The volume average particle size (D50) of the hydrous silicic acid contained in the hydrous silicic acid slurry of the present invention is in the range of 0.4 to 0.9 μm, and the volume integrated cumulative value 90% particle size (D90) is in the range of 1.0 to 5.0 μm. is there. The measurement of the particle size of the hydrous silicic acid of the present invention indicates the value of the volume distribution reference measured by the laser diffraction method for the size of the non-spherical aggregated particles of the hydrous silicic acid, and the D50 value is the cumulative volume integration in the particle size distribution. The value is 50% (Median diameter), and D90 is the value of the cumulative volume integration value in the particle size distribution of 90% (or the top 10%) from the bottom. These can be measured with commercially available laser diffraction particle size distribution meters such as the Microtrac series (MicrotracBEL), Mastersizer series (Malvern), and LS series (BECKMAN COULTER).

D50 indicates the median diameter of hydrous silicic acid particles having a non-spherical structure in which several to several hundred primary particles of about 100 to 200 nm are aggregated. When D50 is less than 0.4 μm, it means that the primary particles are not sufficiently aggregated, which deviates from the object of the present invention to provide a slurry of non-spherical submicron-sized hydrous silicic acid having an aggregated morphology. When D50 exceeds 0.9 μm, it means that a large number of micron-sized particles are present because the aggregated particles have a particle size distribution, which is not preferable. D50 is preferably in the range of 0.5 to 0.8 μm.

D90 is 1.0 μm or more. Since D50 is in the range of 0.4 to 0.9 μm, it is practically difficult to prepare a slurry of hydrous silicic acid with D90 of less than 1.0 μm. The value of D90 and the maximum particle size should be as small as possible, and the closer to the value of D50, ideally, but at least 5.0 μm or less. If D90 exceeds 5.0 μm, it causes scratches in polishing applications, and causes so-called bumps in coating applications. D90 is preferably in the range of 1.0 to 3.0 μm, more preferably in the range of 1.0 to 2.0 μm.

The hydrous silicic acid slurry of the present invention preferably has a hydrous silicic acid concentration of 20 to 45% by weight. The hydrous silicic acid concentration of the hydrous silicic acid slurry is preferably high in consideration of economic aspects such as transportation cost, and is preferably 20% by weight or more. However, it is not intended to exclude slurries less than 20% by weight. The slurry can be diluted with water or the like to adjust the concentration of hydrated silicic acid, and a high concentration is practically preferable. However, when the concentration exceeds 45% by weight, the viscosity sharply increases. It becomes difficult to maintain the slurry form. The rapid increase in viscosity is due to the pore structure of hydrous silicic acid having an aggregated form. Considering the viscosity of the slurry, the hydrous silicic acid concentration is preferably in the range of 20 to 45%. Further, considering the long-term stability and viscosity of the slurry, the hydrous silicic acid concentration is preferably in the range of 20 to 40% by weight, more preferably in the range of 25 to 35% by weight.

Generally, it is preferable that the slurry viscosity is low, and the viscosity of the industrially used slurry is 500 mPa · s or less, more preferably 200 mPa · s or less. When the concentration of the slurry of the present invention is 45% by weight or less, the viscosity of the slurry is generally within the range of the viscosity of the slurry used industrially.

In the hydrous silicic acid slurry of the present invention, the hydrous silicic acid precipitates over time, but does not form hard cakes, and the soft cakes and soft gels formed by the sedimentation over time can be easily stirred or shaken. Liquidity can be easily regained by various operations. The change with time within the range where such redispersion is possible is a practically acceptable level. Since the hydrous silicic acid slurry of the present invention has such redispersibility, it can be used as an abrasive, as a film or resin coating additive, as an ink matting agent or the like, even after being manufactured and stored for a long period of time. It can be usefully used in the above applications. However, a hydrous silicic acid slurry that does not settle over time is more preferable.

The hydrous silicic acid slurry of the present invention preferably further contains an inorganic salt excluding a weak acid and a strong base. By containing the inorganic salts, it is possible to suppress or prevent the water-containing silicic acid from settling over time in the slurry. The salt contained in the slurry of the present invention may be an inorganic salt other than a weak acid and a strong base salt. Specific examples of the inorganic salt include sodium sulfate, potassium sulfate, sodium chloride, potassium nitrate and the like as examples of strong acid strong bases, and ammonium chloride, ammonium nitrate and the like as examples of strong acid weak bases. The principle of preventing sedimentation due to the addition of inorganic salts has not been clarified in detail, and there is no intention to stick to the theory, but it is thought that it is due to some interaction between the surface charge of hydrous silicic acid and the ionic charge in the aqueous dispersion medium. Be done. In the case of a weak acid strong base salt, which will be described later in the description of pH, it is not suitable for the present invention because the pH of the slurry becomes alkaline, silica dissolves, and the properties of the slurry change.

The concentration of the inorganic salt (excluding the weak acid and the strong base) depends on the type of the inorganic salt, but is appropriately in the range of, for example, 2.0 to 5.0 parts by weight with respect to 100 parts by weight of the slurry. When the concentration of the inorganic salt is 2.0 parts by weight or more, a sufficient effect of preventing precipitation can be seen, and hard cake formation due to precipitation of particles can be avoided. Further, if the content of the inorganic salt is 5.0 parts by weight or less, the viscosity does not increase. In addition, it is preferable to suppress the content of inorganic salts, which are impurities for hydrous silicic acid in the first place. From this point of view, the content of the inorganic salt is preferably in the range of 2.0 to 4.0 parts by weight, more preferably 2.0 to 3.0 parts by weight with respect to 100 parts by weight of the slurry.

The addition of a salt having an organic functional group represented by a quaternary alkylammonium salt, an alkylcarboxylic acid salt, or the like to the hydrous silicic acid slurry of the present invention is preferable from the viewpoint of the object of the present invention and the long-term stability of the slurry. Absent. In particular, the quaternary alkylammonium salt causes thickening of the slurry and often contains a surfactant component, so that, for example, it causes a decrease in frictional resistance in polishing applications and a decrease in coating film strength in matting applications. It is not easy and unfavorable, and alkylcarboxylic acid salts and the like cause problems such as decomposition over time and discoloration.

It is appropriate that the dispersion medium of the hydrous silicic acid slurry of the present invention is water or a water-containing solution. The water-containing solution can be a solution containing, for example, a water-soluble organic solvent such as alcohol or ethylene glycol in addition to water. However, the single use of water is most preferable. If a water-containing solution containing a water-soluble organic solvent such as alcohol or ethylene glycol is used as the dispersion medium, heat may be generated due to the crushing energy during wet crushing in the manufacturing process. Most preferably used alone.

The hydrous silicic acid slurry of the present invention preferably has a pH in the range of 3.0 to 8.0. The pH of the slurry is the pH of the slurry itself, and specifically means a value measured by inserting a pH electrode into the slurry. If the pH is 3.0 or higher, it will not become too strong acid and there is no concern that its intended use will be limited. If the pH is 8.0 or less, there is no concern that the hydrous silicic acid will dissolve over time and the slurry performance will change. The pH is preferably in the range of 3.0 to 7.5, more preferably 4.0 to 7.0.

The hydrous silicic acid slurry of the present invention preferably has an electrical conductivity (E.C.) in the range of 15 to 100 mS / cm (millisiemens). The electrical conductivity of the slurry is the electrical conductivity of the slurry itself, and specifically means a value measured by inserting an electrode for measuring electrical conductivity into the slurry. When the slurry does not contain an inorganic salt, the electrical conductivity of the slurry depends on the degree of cleaning, but is generally 1 mS / cm or less, and is therefore an index indicating the salt concentration in the slurry. When the hydrous silicic acid slurry of the present invention contains an inorganic salt, if the electrical conductivity is 15 mS / cm or more, the decrease in stability over time caused by the low concentration of the inorganic salt can be suppressed, and it should be 100 mS / cm or less. For example, it is preferable that there is not too much inorganic salt. The electrical conductivity is preferably in the range of 15-80 mS / cm, more preferably 15-60 mS / cm.

<Manufacturing method of hydrous silicic acid slurry>
The hydrous silicic acid slurry of the present invention
(1) Disperse hydrous silicic acid (hereinafter referred to as raw material hydrous silicic acid) having a BET specific surface area of 10 to 35 m ² / g and a volume average particle diameter (D50) of 1.0 μm or more measured by laser diffraction method. The process of mixing with a medium to form a slurry, and
(2) The volume average particle size (D50) of the obtained slurry measured by the laser diffraction method is 0.4 to 0.9 μm, and the cumulative volume value from the lower part in the particle size distribution measured by the laser diffraction method is up to 90%. Wet pulverization until the particle size (D90) of
It can be manufactured by a method including.

Process (1)
Prepare a raw material hydrous silicic acid having a BET specific surface area of 10 to 35 m ² / g and a volume average particle size (D50) of 1.0 μm or more measured by a laser diffraction method. Generally, low BET hydrous silicic acid having a BET specific surface area of 35 m ² / g or less is produced by adding an additive during the reaction of a mineral acid with an aqueous alkali silicate solution to promote particle aggregation. On the other hand, in the present invention, the raw material hydrous silicic acid uses a mineral acid such as sulfuric acid having a low concentration and slowly grows the hydrous silicic acid particles, so that the primary particles are large and low without adding additives. Synthesize BET hydrous silicic acid. Low BET hydrous silicic acid due to aggregation generally strengthens the particle skeleton and makes it difficult to pulverize. On the other hand, in the present invention, the hydrous silicic acid uses an aqueous alkali silicate solution and a low-concentration mineral acid in the neutralization reaction to slowly grow particles over a long period of time, so that the hydrous silicic acid has a low BET but is grindable. A good raw material hydrous silicic acid can be obtained.

Specifically, the concentration of mineral acid (for example, sulfuric acid) is in the range of 5 to 20%, and the time for particle growth is, for example, in the range of 500 to 700 minutes, depending on the scale of the reaction. It is preferable to take 3 times or more time as compared with the conventional method. Further, when a circulation pump, a line mixer, or the like is used in combination during the neutralization reaction, a raw material hydrous silicic acid having a low BET but good grindability can be prepared more effectively.

After the neutralization reaction, the volume average particle size (volume average particle size) measured by laser diffraction method after filtering, washing, drying, dry pulverization, dry classification, etc. of the hydrous silicic acid by the same method as the general method for producing hydrous silicic acid. Obtain a micron-sized hydrous silicic acid having a D50) of 1.0 μm or more. The method of filtration and washing with water is not limited, but a general filter type filtration can be used. After the filtration, washing with water is performed to remove the salt generated by the neutralization reaction and remaining in the hydrous silicic acid. For drying, general static drying, fluid drying, spray drying and the like can be used. A commercially available pin mill, jet mill, or the like can be used for the dry pulverization, and if necessary, classification is performed using a wind power classifier or the like to remove coarse particles.

However, it is difficult to pulverize the raw material hydrous silicic acid synthesized above to a submicron size only by using the dry crusher and the dry classifier illustrated above. Therefore, in the dry crushing / classification stage, it is desirable to limit the atomization to the extent possible. As a result, although it takes longer to neutralize and synthesize than the conventional method, hydrous silicic acid (powder to be the raw powder) having good wet grindability in the subsequent step can be obtained.

Although the raw material hydrous silicic acid obtained by the above-exemplified production method has a low BET specific surface area, unlike conventional hydrous silicic acid, aggregation between primary particles is not strong, so that it is pulverized to a size of submicron in a subsequent step. It is thought that it can be done. For easy understanding, FIG. 1 shows a primary particle growth model of hydrous silicic acid having a BET specific surface area of 35 m ^{2 / g or less.} Hydrous silicic acid synthesized by the conventional method grows with the primary particles agglomerated at the initial stage, so when the BET specific surface area grows to 35 m ² / g or less, the bonds between the primary particles become stronger and become hard agglomerated particles. On the other hand, the hydrous silicic acid of the present invention grows primary particles slowly at a low concentration over time as described above, so that there are few bonds between the primary particles and the aggregate structure is not strong. Therefore, pulverization is relatively easy, and it is considered that pulverization can be performed to a submicron size in a later process.

The slurry of the present invention can be produced by using the raw material hydrous silicic acid produced above, but if necessary, the slurry is heat-treated with respect to the hydrous silicic acid in a powder state and controlled to the extent that it is not sintered. (Baking) may be added. Specifically, hydrous silicic acid is heat-treated at 600 ° C to 1,000 ° C for 1 hour or more using equipment such as a roller herskilln or rotary kiln to harden the agglomerates and adjust the strength of the cohesive force. can do.

The raw material hydrous silicic acid is mixed with a dispersion medium to form a slurry. The dispersion medium is water or a water-containing solution. The dispersion medium, which is water or a water-containing solution, has the same meaning as described above. The dispersion medium is most preferably water alone.

The slurry concentration of the hydrous silicic acid slurry (final product) of the present invention is preferably in the range of 20 to 45% by weight. However, the slurry concentration of the raw material hydrous silicic acid prepared in the step (1) shall be in the range having a viscosity within the range in which the wet pulverization is possible in the step (2). Considering the types of the raw material hydrous silicic acid and the dispersion medium, the range may be, for example, 1 to 25% by weight. It is preferably in the range of 10 to 20% by weight. However, it is not intended to be limited to this range.

Process (2)
The volume average particle size (D50) of the slurry obtained in step (1) measured by the laser diffraction method is 0.4 to 0.9 μm, and the particle size (D50) is 90% of the cumulative volume-accumulated value from the lower part of the particle size distribution. Wet grinding is performed until D90) reaches 1.0 to 5.0 μm. Since the raw material hydrous silicic acid has a D50 of 1.0 μm or more, it is wet-pulverized until it reaches 0.4 to 0.9 μm.

Since the hydrous silicic acid of the present invention has a pore structure, the viscosity also increases as the concentration increases, so that it is difficult to increase the concentration. Therefore, first prepare a low-concentration slurry using a commercially available stirrer or disperser, and then repeat wet pulverization, and when the viscosity becomes low, add hydrous silicic acid to increase the concentration and submicron at the same time. It is good to let it. For wet pulverization, for example, a commercially available high-performance wet pulverizer such as a wet jet mill, a bead mill, or a high-pressure homogenizer can be used, and adjustment is performed by repeating circulation pulverization until a desired particle size distribution is obtained. In this method, the slurry concentration can be increased to, for example, in the range of 20 to 45% by weight to obtain the hydrous silicic acid slurry of the present invention. However, the slurry concentration is not intended to be limited to this range.

Process (3)
Inorganic salts other than weak acids and strong bases can be added to the hydrous silicic acid slurry obtained in step (2). To 100 parts by weight of the slurry obtained in step (2), for example, an inorganic salt excluding a weak acid strong base is added so as to be 2.0 to 5.0 parts by weight, and the mixture is stirred and mixed to remove the weak acid strong base. A hydrous silicic acid slurry containing the above can be prepared.

The hydrous silicic acid slurry of the present invention can be expected to be used as a water-based slurry useful for, for example, abrasives, coating additives such as films and resins, and ink matting agents.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are examples of the present invention, and the present invention is not intended to be limited to the examples.

[Evaluation method]
Various physical property measurements and tests in Examples and Comparative Examples were carried out by the following methods.

1) BET specific surface area Hydrous silicic acid was measured by a one-point method using a fully automatic specific surface area measuring device (model: Macsorb (R) HM model-1200, manufactured by Mountech).

2) Average particle size (D50) and 90% particle size (D90)
Measure the particle size distribution using a laser diffraction type particle size distribution measuring device (model: Microtrack MT-3000, manufactured by Microtrac Bell), and the value (D50 value) of 50% of the cumulative volume integration value in the particle size distribution and the lower The value (D90 value) of 90% of the cumulative volume-accumulated value was obtained from.

3) Measurement of pH The pH of the slurry (as is) was measured using a commercially available glass electrode pH meter (model: F-53, manufactured by HORIBA, Ltd.).

4) Electric conductivity The electric conductivity of the slurry (as is) was measured using a commercially available electric conductivity meter (model CM-30R, manufactured by DKK-TOA CORPORATION) (measurement temperature 25 ° C).

5) Viscosity measurement
Put 200 ml of slurry (as is) in a 200 ml tall beaker, and immediately after that, use a commercially available B-type viscometer (model: TVB-10M, manufactured by Toki Sangyo Co., Ltd.), No. 20 rotor, 60 rpm x 1 minute later. The viscosity of was measured.

6) Hydrous silicic acid concentration The hydrous silicic acid concentration in the slurry was calculated from the amount of hydrous silicic acid added to water during production. In addition, using a commercially available infrared moisture meter (model: K-600, manufactured by Kett Science Institute Headquarters), the moisture content was measured under the conditions of 150 ° C x 60 minutes, and the value of the solid content concentration excluding the moisture was also used. confirmed.

7) Amount of inorganic salt Calculated from the amount added to the slurry. In addition, the solid content of hydrous silicic acid excluding water was subjected to elemental qualitative analysis using a scanning fluorescent X-ray analyzer (model: ZSX PrimusII, manufactured by Rigaku) to confirm the amount of inorganic salts. ..

8) Evaluation of sedimentation state of slurry 10 g of slurry was placed in a container with a 20 ml lid and allowed to stand for 1 week. Then, it was shaken for 5 minutes with a shaker (model: V-SX, manufactured by Iwaki Co., Ltd.) to prepare an observation sample in a sedimented state. The settling state was confirmed by the ratio of hard cake remaining on the bottom of the container when the container was inverted so that the lid was on the bottom. The sedimentation state was evaluated in the following three stages A to C, and evaluation A was passed (see also the state of the sedimentation test [with photo]).

A: After shaking and reversing, there is almost no hard cake on the bottom of the container, and sedimentation of hydrous silicic acid cannot be confirmed.
B: After shaking and reversing, a slight sedimentation of hydrous silicic acid can be confirmed (difficult to sediment) on the bottom of the container.
C: Even after shaking and reversing, a hard cake is formed on the bottom of the container, and the sedimentation of hydrous silicic acid can be clearly confirmed.

[Production example of hydrous silicic acid a to f]
(Hydrophilic silicic acid a)
Hydrous silicic acid was produced through the following steps (i) to (v). The following steps (i) to (ii) were carried out in a steam-heated stainless steel container having a capacity of 240 L equipped with a stirrer while constantly stirring while keeping the temperature at 90 ° C. In addition, the sodium silicate aqueous solution described uses _{No. 3 silica with a SiO 2} concentration of 12.8 wt%, Na ₂ O concentration of 4.0 wt%, and a SiO ₂ / Na ₂ O molar ratio of 3.2, and sulfuric acid uses 9.0 wt% dilute sulfuric acid. did.

(i) An aqueous solution of sodium silicate was added to 36.8 kg of warm water until the pH reached 10.5.
Next, 87.27 kg of an aqueous solution of sodium silicate and sulfuric acid were added dropwise simultaneously over 660 minutes so that the pH was maintained at 10.0 to 11.0, and a neutralization reaction was carried out.
(ii) Stop dropping the aqueous solution of sodium silicate, drop only sulfuric acid, and stop dropping sulfuric acid when the pH reaches 3.0 to completely complete the neutralization reaction, and the hydrous silicate a A slurry was obtained.
(iii) The obtained hydrous silicic acid slurry was filtered with a filter press and thoroughly washed with water to obtain a hydrous silicic acid cake.
(iv) The water-containing silicic acid cake was dried using a spray dryer (model: AN-40R type manufactured by Ashizawa Niro Atomizer Co., Ltd.) so that the water content was less than 6%.
(v) Dry hydrous silicic acid is crushed by a jet mill (model: PJM-100NP manufactured by Nippon Pneumatic Co., Ltd.) and dried using a classifier (model: Classy N-01 manufactured by Seishin Enterprise Co., Ltd.). The agglomerated coarse particles were removed to obtain hydrous silicic acid a as a raw powder.
The BET specific surface area of hydrous silicic acid a was 20 m ² / g.

(Hydrophilic silicic acid b)
After adding the same amount of warm water and sodium silicate aqueous solution as in step (i) of hydrous silicic acid a, add the same amount of sodium silicate aqueous solution and dilute sulfuric acid as in step (i) for 585 minutes while maintaining pH 10.0 to 11.0. A hydrous silicic acid b having ^{a BET specific surface area of 25 m 2} / g was obtained by the same method as the hydrous silicic acid a, except that the aqueous solution was added dropwise at the same time while adjusting the flow rate so as to carry out the neutralization reaction in (time reduction).

(Hydrophilic silicic acid c)
After adding the same amount of warm water and sodium silicate aqueous solution as in step (i) of hydrous silicic acid a, add the same amount of sodium silicate aqueous solution and dilute sulfuric acid as in step (i) for 540 minutes while maintaining pH 10.0 to 11.0. A hydrous silicic acid c having ^{a BET specific surface area of 30 m 2} / g was obtained by the same method as the hydrous silicic acid a except that the aqueous solution was added dropwise at the same time while adjusting the flow rate so as to carry out the neutralization reaction in (time reduction).

(Hydrophilic silicic acid d)
Hydrous silicic acid was produced according to a conventional method for producing low BET hydrous silicic acid.
That is, although the same container as hydrous silicic acid a, the same aqueous solution of sodium silicate, the same temperature, and the same stirring conditions are used, 95 wt% concentrated sulfuric acid is used as sulfuric acid, and the neutralization reaction is completed in a short time.
In step (i) of hydrous silicic acid a, a sodium silicate aqueous solution was charged to 56.6 kg of a 0.20 mol / L sodium sulfate aqueous solution so that the pH became 10.5, and then 116.17 kg of the sodium silicate aqueous solution and concentrated sulfuric acid were added to the pH. The neutralization reaction was carried out while simultaneously dropping over 120 minutes so that the pH was maintained at 10.0 to 11.0.
^{After that, the hydrous silicic acid d having a BET specific surface area of 30 m 2} / g was obtained through the same steps as the steps (ii) to (v) of the hydrous silicic acid a.

(Hydrophilic silicic acid e)
Hydrous silicic acid was produced according to a conventional method for producing low BET hydrous silicic acid.
The neutralization reaction takes place in the same container as hydrous silicic acid a, the same sodium silicate aqueous solution, and the same stirring conditions, except that the temperature of the container is 86 ° C and the sulfuric acid is 95 wt% concentrated sulfuric acid, which is the same as the hydrous silicic acid d. In order to complete the process in a short time, the step (i) of hydrous silicic acid a is carried out by adding a sodium silicate aqueous solution to 102.1 kg of a 0.05 mol / L sodium sulfate aqueous solution so that the pH becomes 10.5, and then the sodium silicate aqueous solution. A neutralization reaction was carried out by simultaneously dropping 55.17 kg of an aqueous solution and concentrated sulfuric acid over 200 minutes so as to maintain a pH of 10.0 to 11.0, and thereafter, the same steps as steps (ii) to (v) of hydrous silicic acid a were performed. As a result, hydrous silicic acid e having a BET specific surface area of 50 m ^{2 / g was obtained.}

(Hydrophilic silicic acid f)
Hydrous silicic acid a was heat-treated at 950 ° C. for 2 hours using a muffle furnace (model: S100G manufactured by Yamato Scientific Co., Ltd.) to prepare the BET specific surface area and the hardness of the hydrous silicic acid aggregate.
The BET specific surface area of hydrous silicic acid f was 13 m ² / g.

[Examples 1 to 10, Comparative Examples 1 to 2]
Figure 2 shows the production flow of the hydrous silicic acid slurry produced in Examples and Comparative Examples. However, the method for producing a hydrous silicic acid slurry of the present invention is not limited to this method.
Table 1 shows the physical characteristics of the hydrous silicic acid and the slurry obtained in Examples and Comparative Examples.
Figures 3 and 4 show the volumetric particle size distributions of Example 3 and Comparative Example 1 by laser diffraction before and after wet pulverization.
State of sedimentation test Table 2 (with photo) shows.

Example 1
700 g of pure water was placed in a 2 L plastic container, and 175 g of hydrous silicic acid a was added while stirring with a commercially available stirrer (model: ZZ-1200, manufactured by Tokyo Rika Kikai Co., Ltd.) to prepare a 20 wt% slurry first. Next, this slurry was subjected to wet pulverization by oblique collision at an injection pressure of 200 to 240 MPa using a wet jet mill (model: Starburst HJP-25005, manufactured by Sugino Machine Limited). After 0.5-pass crushing (here, crushing 1,000 g of slurry was defined as 1-pass), 75 g of hydrous silicic acid a was additionally added in order to increase the concentration of the slurry, and the mixture was pulverized again after stirring. After pulverizing for 0.5 pass, after confirming that the viscosity had decreased, 50 g of hydrous silicic acid a was further added, and after stirring, a 30 wt% slurry was prepared. This slurry was further pulverized for 10 passes to obtain a high-concentration slurry of 1,000 g.

Example 2
To 100 g of the high-concentration slurry obtained in Example 1, 1 g of sodium sulfate was added and mixed well with a commercially available stirrer to obtain the desired hydrous silicic acid slurry.

Example 3
A hydrous silicic acid slurry was produced in the same manner as in Example 2 except that the amount of sodium sulfate added was changed to 2 g with respect to 100 g of the high-concentration slurry.

Example 4
A hydrous silicic acid slurry was produced in the same manner as in Example 2 except that the amount of sodium sulfate added was changed to 4 g with respect to 100 g of the high-concentration slurry.

Example 5
After the slurry concentration was set to 20 wt%, wet pulverization was performed in the same manner as in Example 1 except that no additional hydrous silicic acid a was added and the final concentration was set to 20 wt%, and 875 g of 20 wt was performed. % Slurry was obtained.
To 100 g of the obtained 20 wt% slurry, 2 g of sodium sulfate was added and mixed well with a commercially available stirrer to obtain a hydrous silicic acid slurry.

Example 6
To the 30 wt% slurry of Example 1, 167 g of hydrous silicic acid a was further added in 4 portions to increase the concentration to 40 wt%, and then pulverization was performed for 10 passes in the same manner as in Example 1. A 40 wt% high concentration slurry of 1,167 g was obtained.
To 100 g of the obtained 40 wt% high-concentration slurry, 2 g of sodium sulfate was added and mixed well with a commercially available stirrer to obtain a hydrous silicic acid slurry.

Example 7
A hydrous silicic acid slurry was produced by the same method as in Example 3 except that the hydrous silicic acid was changed to hydrous silicic acid b.

Example 8
A hydrous silicic acid slurry was produced by the same method as in Example 3 except that the hydrous silicic acid was changed to hydrous silicic acid c.

Example 9
A hydrous silicic acid slurry was produced by the same method as in Example 3 except that the hydrous silicic acid was changed to hydrous silicic acid f.

Example 10
A hydrous silicic acid slurry was produced by the same method as in Example 3 except that sodium sulfate was changed to 2 g of ammonium chloride with respect to 100 g of the obtained high-concentration slurry.

Comparative example 1
A 20 wt% hydrous silicic acid slurry was obtained in the same manner as in Example 5 except that the hydrous silicic acid was changed to hydrous silicic acid d.

Comparative example 2
A 20 wt% hydrous silicic acid slurry was obtained in the same manner as in Example 5 except that the hydrous silicic acid was changed to hydrous silicic acid e.

[Explanation of Examples and Comparative Examples]
As shown in Examples, Comparative Examples and Table 1, in the present invention, by producing hydrous silicic acid by a method different from the conventional method, the volume measured by the laser diffraction method even if the ^{BET specific surface area is 10 to 35 m 2 / g.} It is possible to provide a hydrous silicic acid slurry having an average particle size (D50) of 0.4 to 0.9 μm and a cumulative volume of 90% (D90) of 1.0 to 5.0 μm. In particular, in Examples, the BET specific surface area is lower than that of Comparative Examples 1 and 2 (hydrous silicic acid produced by the conventional method), but the particles can be further pulverized.

Further, in the slurry of the example, even if the hydrous silicic acid concentration is 20 to 40% by weight, 1.0 to 5.0 parts by weight of an inorganic salt excluding a weak acid strong base is added to the slurry with respect to 100 parts by weight of the hydrous silicic acid. Therefore, even if the BET specific surface area was 35 m ² / g or less, unlike Comparative Examples 1 and 2, the hydrous silicic acid slurry did not settle or did not easily settle.

[Particle size distribution (laser diffraction method volume distribution)]
[Explanation of particle size distribution map]
In the hydrous silicic acid (d of Comparative Example 1) produced according to the conventional method for producing hydrous silicic acid having a low BET specific surface area, the particle size was hardly reduced even after wet pulverization [Fig. 4] However, with the hydrous silicic acid produced by a method different from the conventional method as in Example (hydrous silicic acid a in Example 1), even hydrous silicic acid having a low BET specific surface area could be pulverized into small pieces [Fig. 3].
[State of sedimentation test]

[Explanation of sedimentation test state; Comparison of salt addition amount and sedimentation state]
Since the hydrous silicic acid slurry of Example 1 was produced by the method of Example, _{it hardly settled even though Na 2} SO ₄ (salt) was not added. The hydrous silicic acid slurry of Examples 3 and 6 uses the hydrous silicic acid produced by the method of Example, _{and 2 parts by weight of Na 2} SO ₄ is further added, so that the hydrous silicic acid concentration is 30 to 40 wt%. It does not settle at all even if it is aged at a high concentration of. The hydrous silicic acid slurry of Comparative Example 1 used hydrous silicic acid d produced by a conventional method, _{and although 2 parts by weight of Na 2} SO ₄ was added, it settled over time.

The present invention is useful in fields related to hydrous silicic acid slurries.

Claims (11)

The BET specific surface area is 10 to 35 m ² / g, the volume average particle size (D50) measured by the laser diffraction method is 0.4 to 0.9 μm, and the cumulative volume from the bottom in the particle size distribution measured by the laser diffraction method is cumulative. A hydrous silicic acid slurry comprising a hydrous silicic acid having a particle size (D90) of 90% of the value of 1.0 to 5.0 μm. The hydrous silicic acid slurry according to claim 1, wherein the hydrous silicic acid concentration is 20 to 45% by weight. The hydrous silicic acid slurry according to claim 1, further containing an inorganic salt excluding a weak acid and a strong base. The hydrous silicic acid slurry according to claim 3, wherein the inorganic salt is contained in a ratio of 2.0 to 5.0 parts by weight with respect to 100 parts by weight of the slurry. The hydrous silicic acid slurry according to claim 1, wherein the dispersion medium of the slurry is water or a water-containing solution. The hydrous silicic acid slurry of claim 1, wherein the slurry has a pH of 3.0 to 8.0 and an electrical conductivity (E.C.) of 15 to 100 mS / cm (millisiemens). A step of mixing a hydrous silicic acid having a BET specific surface area of 10 to 35 m ² / g and a volume average particle diameter (D50) of 1.0 μm or more measured by a laser diffraction method with a dispersion medium to form a slurry, and obtaining a slurry. The volume average particle diameter (D50) of the obtained slurry measured by the laser diffraction method is 0.4 to 0.9 μm, and the particle diameter (D50) is 90% of the volume integrated cumulative value from the lower part in the particle size distribution measured by the laser diffraction method. A process of wet pulverization until D90) reaches 1.0 to 5.0 μm,
The method for producing a hydrous silicic acid slurry according to claim 1. The production method according to claim 7, wherein the hydrous silicic acid and the dispersion medium are mixed so as to obtain a slurry having a concentration of 20 to 45% by weight. The production method according to any one of claims 7 to 8, wherein the dispersion medium of the slurry is water or a water-containing solution. The production method according to any one of claims 7 to 9, wherein an inorganic salt other than a weak acid and a strong base is added to the slurry obtained after the wet pulverization step to obtain a hydrous silicic acid slurry containing the inorganic salt. .. The production method according to claim 10, wherein the inorganic salt is added at a ratio of 2.0 to 5.0 parts by weight with respect to 100 parts by weight of the slurry.

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