JP2022187264A - Hydrophobic silica aerogel, and production method of aqueous paste composition - Google Patents

Abstract

To solve the problem in which porous silica added to a cosmetic etc., when having an ionic impurity, may cause such a problem as decrease in an oil absorption amount and so carrying out water washing, etc. is required to reduce an amount of the ionic impurity but a large amount of washing water is required, increasing waste liquid associated therewith.SOLUTION: An acid and a base used in production of porous silica are selected so that a salt to be produced is sodium sulfate. Specifically, sulfuric acid and a sodium-based base such as sodium hydroxide are employed as the acid and the base, respectively, and sodium silicate is used as a silicon source. The sodium sulfate comes to be deposited as decahydrate at a temperature about 32°C as a boundary from which its solubility to water sharply decreases, and thus separation of the deposited sodium sulfate with filtration etc. enables a subsequent step of reducing an ionic impurity to be highly efficient.SELECTED DRAWING: None

Description

The present invention relates to a novel method for producing a hydrophobic silica airgel and a paste-like composition containing hydrophobic silica and water. More specifically, the present invention relates to a manufacturing method capable of reducing the amount of water used for washing to reduce the content of ionic impurities.

Airgel is a material with high porosity and excellent oil absorption. The term "aerogel" as used herein means a solid material having a porous structure and gas as a dispersion medium, particularly a solid material having a porosity of 60% or more. The porosity is a value expressed by volume percentage of the amount of gas contained in the apparent volume. Airgel has excellent oil absorption due to the high porosity.

Silica airgel has various uses, among which it is useful as a cosmetic material. Taking foundation as an example, it is used as an additive to improve the durability of its appearance when applied to the skin. Specifically, since the porous structure of silica airgel absorbs sebum well, it is possible to prevent the skin from getting wet with sebum, thereby increasing the specular reflectance of light and causing shine. Moreover, when the silica airgel is produced by making it hydrophobic, it has a better affinity with the organic components of cosmetic materials such as foundation, and is evenly dispersed.

For example, when used in powder form as a foundation material, silica airgel, which has a high oil absorption capacity, can absorb a large amount of sebum that causes oily shine, so the finished appearance of makeup lasts for a long time. (See Patent Document 3).

In addition, these silica aerogels have a particle size of 1 to several tens of μm in order to obtain a smooth feel when blended in cosmetics, and a spherical shape in order to improve rolling properties on the skin. is desirable.

For example, the following method has been proposed as a method for producing spherical silica airgel having such an appropriate particle size.

Patent Document 1 discloses a process of preparing an aqueous silica sol, a process of dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion, and a process of gelling the silica sol to turn the W/O emulsion into a gel. a step of converting the gel into a dispersion liquid, a step of replacing water in the gel with a solvent having a surface tension of 30 mN/m or less at 20 ° C., and hydrophobizing the gel with a hydrophobizing agent (silylating agent). A method for producing a spherical silica airgel is disclosed which comprises a step of treating (silylation treatment) and a step of removing the substituted solvent in the above order.

Patent Document 2 describes a step of separating the gelled dispersion obtained in the step of converting the W/O emulsion into a gelled dispersion into two layers of an O phase and a W phase. A step of adding a basic substance to the phase to ripen the gelled product dispersed in the W phase, a step of silylating the gelled product dispersed in the W phase, and a step of extracting the gelled product with a hydrophobic organic solvent. , a method for producing a spherical silica aerogel is disclosed, which sequentially comprises steps of recovering a gelled body and obtaining a powder composed of a hydrophobic spherical silica aerogel.

International publication 2012/057086 JP 2018-177620 A JP 2014-88307 A

However, in the methods of Patent Literatures 1 and 2, salts derived from raw materials used in preparation of the aqueous silica sol and hydrophobization tend to remain in the obtained spherical silica airgel powder. If the silica airgel contains a large amount of salts, it will not be able to maintain a high oil absorption and will not be able to absorb a large amount of sebum. After extracting the organic solvent, the organic solvent phase is washed with an aqueous alcohol solution, which is not economical. Furthermore, since the temperature is raised to 45 to 70° C. during washing, there is also the problem that the manufacturing time is lengthened.

In addition, many cosmetics are water-based, but the hydrophobic silica airgel powder obtained as described in the above patent document has a problem that it is difficult to disperse due to its hydrophobicity. In order to solve this problem, the amount of water is prepared as it is from the aqueous dispersion in which the hydrophobized gelled product produced as an intermediate in the production method described in Patent Document 2 is dispersed, and the hydrophobic silica and water are mixed. The present inventors have already proposed to manufacture and use a paste-like composition containing and (Japanese Patent Application No. 2021-014785). That is, the water content in the W phase in which the hydrophobized gel is dispersed can be reduced to such an extent that the gel does not dry out, thereby forming a paste. The pasty composition makes it possible to disperse in water or a medium containing water as a main component, which has been difficult with hydrophobic silica airgel powder.

However, since this production method does not involve the step of extracting the hydrophobized gelled product into a hydrophobic organic solvent to form a dispersion, washing with an aqueous alcohol solution (or water) as described above cannot be carried out. . Therefore, while taking care not to dry the gelled body, salts are removed by performing a washing step different from that in Patent Document 2, in which water is added and removed continuously (or intermittently).

However, in order to sufficiently remove salts, sulfates, etc., there is a problem that a large amount of ion-exchanged water must be used in this washing process. In addition, there is a problem that a large amount of waste liquid is discharged along with this cleaning, which is not economical.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an economically excellent method for producing a hydrophobic spherical silica aerogel having a sufficiently low salt content.

As a result of intensive studies to solve the above problems, the present inventors have found a specific combination of an acid and a basic substance to be used in the production method starting from the preparation of the aqueous silica sol disclosed in these documents. By doing so, the generated salt can be made to have a low solubility, so that the salt can be precipitated and removed, so the amount of water required for washing can be reduced, and it can be produced more economically. and completed the present invention.

That is, the present invention
(1) preparing an aqueous silica sol from sulfuric acid and sodium silicate;
(2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;
(3) a step of gelling the silica sol by heating to convert the W/O emulsion into a dispersion of silica gel;
(4) removing the organic phase after phase separation into an organic phase and an aqueous phase in which the silica gel is dispersed;
(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which silica gel is dispersed to hydrophobize the silica gel;
(6) adding a basic substance containing sodium;
(7) cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate;
(8) removing the precipitated sodium sulfate decahydrate, and
(9) A method for producing a hydrophobic silica airgel powder, comprising a step of collecting and drying the hydrophobized silica gel in the liquid.

Another invention is
(1) preparing an aqueous silica sol from sulfuric acid and sodium silicate;
(2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;
(3) a step of gelling the silica sol by heating to convert the W/O emulsion into a dispersion of silica gel;
(4) removing the organic phase after phase separation into an organic phase and an aqueous phase in which the silica gel is dispersed;
(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which the silica gel is dispersed to hydrophobize the silica gel;
(6) adding a basic substance containing sodium;
(7) cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate;
(8) removing the precipitated sodium sulfate decahydrate, and
(10) A method for producing a paste-like composition containing hydrophobic silica and water, comprising a step of removing part of the water to form a paste.

In the production method of the present invention, sodium sulfate decahydrate with low solubility is generated and a step of removing it is interposed to reduce the amount of water used, resulting in a more economically superior hydrophobic method than conventional methods. It has made it possible to produce a flexible silica airgel. Conversely, if the amount of water used is the same, the content of ionic impurities can be relatively reduced.

The manufacturing method of the hydrophobic silica airgel powder of the present invention includes the following steps. Namely
(1) preparing an aqueous silica sol from sulfuric acid and sodium silicate;
(2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;
(3) a step of gelling the silica sol by heating to convert the W/O emulsion into a dispersion of silica gel;
(4) removing the organic phase after phase separation into an organic phase and an aqueous phase in which the silica gel is dispersed;
(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which silica gel is dispersed to hydrophobize the silica gel;
(6) adding a basic substance containing sodium;
(7) cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate;
(8) removing the precipitated sodium sulfate decahydrate, and
(9) A step of recovering and drying the hydrophobized silica gel in the liquid is carried out in order.

The above manufacturing methods will be described in detail below in order.

(1) Step of preparing an aqueous silica sol from sulfuric acid and sodium silicate

In the production method of the present invention, first, an aqueous silica sol is prepared. The aqueous silica sol can be prepared by using sulfuric acid and sodium silicate as raw materials, and other known methods may be appropriately adopted, but the following method is preferable. The reason why sulfuric acid is used instead of other acids in the preparation of the aqueous silica sol is to limit the salt to be produced to sodium sulfate.

Specifically, sodium silicate is added while stirring sulfuric acid. The amount of sulfuric acid is desirably 1.05 to 1.2 in terms of molar ratio of hydrogen ions to sodium content of sodium silicate. When the amount of sulfuric acid is within this range, the pH of the prepared silica sol is about 1-5. More preferably, the amount of sulfuric acid is adjusted so that the prepared silica sol has a pH of 2.5 to 3.5.

As for the concentration of the silica sol prepared by the above method, the gelation is completed in a relatively short time, and the formation of the skeleton structure of the silica particles is sufficient to suppress shrinkage during drying, and a large pore volume can be obtained. It is preferable that the concentration of silica (concentration in terms of SiO ₂ ) is 50 g/L or more, because it is easy to be eroded. On the other hand, it is preferably 160 g / L or less, and 100 g / L or less, because the density of the silica particles is relatively small, a good pore volume is obtained, and the oil absorption can be easily increased. is more preferable. More preferably 90 to 100 g/L.

Sulfuric acid can be used as an aqueous solution with a concentration of 3 to 12%. Preferably, it is 6-10%. As sodium silicate, an aqueous solution sold as No. 1 to No. 3 sodium silicate can be used. In order to improve the operability, or to adjust the pH and silica concentration after mixing to the desired ranges, the mixture may be diluted with water in advance.

By setting the concentration of the aqueous silica sol to the above lower limit or higher, the finally obtained hydrophobic silica airgel (hereinafter sometimes simply referred to as "aerogel") has a pore volume of 8 mL/g or less by the BJH method. In addition, it becomes easy to make the peak of the pore radius of the airgel by the BJH method 50 nm or less. In addition, by setting the concentration of the aqueous silica gel to the above upper limit or less, it becomes easy to make the pore volume of the airgel by the BJH method 2 mL / g or more, and the pore radius peak of the airgel by the BJH method is 10 nm. It becomes easier to do the above.

(2) a step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;

In the production method of the present invention, the aqueous silica sol obtained by the above method is dispersed in a hydrophobic solvent to form a W/O emulsion. By forming such a W/O emulsion, the silica sol becomes spherical due to surface tension and the like. Therefore, by gelling the spherical silica sol dispersed in a hydrophobic solvent, a spherical gelled product can be obtained. can be obtained. Thus, by passing through the emulsion forming step of forming a W/O emulsion, it is possible to produce an airgel having a high degree of circularity, usually 0.8 or more.

As the hydrophobic solvent, any solvent having a degree of hydrophobicity capable of forming a W/O emulsion with the aqueous silica sol may be used. As such a solvent, for example, organic solvents such as hydrocarbons and halogenated hydrocarbons can be used. More specific examples include hexane, heptane, octane, nonane, decane, dichloromethane, chloroform, carbon tetrachloride, and dichloropropane. Among these, heptane, which has an appropriate viscosity, can be used particularly preferably. In addition, you may mix and use several solvent as needed. A hydrophilic solvent such as a lower alcohol can also be used in combination (used as a mixed solvent) as long as a W/O emulsion can be formed with the aqueous silica sol.

The amount of the hydrophobic solvent to be used is not particularly limited as long as the amount is such that the emulsion becomes a W/O type. However, in general, the amount of the hydrophobic solvent used is about 1 to 10 parts by volume with respect to 1 part by volume of the aqueous silica sol.

A surfactant is preferably added when forming the W/O emulsion. Any of anionic surfactants, cationic surfactants, and nonionic surfactants can be used as surfactants. Among these, nonionic surfactants are preferable because they easily form a W/O emulsion. In the present invention, since the silica sol is aqueous, a surfactant having an HLB value of 3 or more and 6 or less, which is a value indicating the degree of hydrophilicity and hydrophobicity of the surfactant, can be preferably used. In the present invention, "HLB value" means HLB value according to the Griffin method.

As described above, in the present invention, the shape of the airgel particles is substantially determined by the shape of the droplets of the W/O emulsion. The droplet shape depends on the surfactant used. As described above, the shape of the airgel particles is preferably spherical. Specific examples of surfactants that can be preferably used from this point of view include sorbitan monooleate, sorbitan monostearate, sorbitan monosesquiolate, and the like. be done.

The amount of surfactant used is no different from the general amount used to form W/O emulsions. Specifically, the range of 0.05 g or more and 10 g or less per 100 ml of aqueous silica sol can be suitably adopted. When the amount of surfactant used is large, the droplets of the W/O emulsion tend to become finer, and conversely, when the amount of surfactant used is small, the droplets of the W/O emulsion tend to become larger. Therefore, it is possible to adjust the average particle size of the airgel by increasing or decreasing the amount of surfactant used.

As a method for dispersing the aqueous silica sol in the hydrophobic solvent when forming the W/O emulsion, a known W/O emulsion forming method can be employed. From the viewpoint of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specific examples include methods using a mixer, homogenizer, or the like. Preferably, a homogenizer can be used.

Since the average particle size of the silica sol droplets in the W/O emulsion and the average particle size of the airgel generally correspond, the average particle size of the airgel can be controlled by controlling the droplet size here.

By sufficiently reducing the particle size of the silica sol droplets in the emulsion, the shape of the silica sol droplets is less likely to be disturbed, making it easier to obtain a spherical airgel with a higher degree of circularity (however, The average particle size of the airgel is also reduced).

(3) A step of gelling the silica sol by heating to convert the W/O emulsion into a silica gel dispersion.

In the production method of the present invention, the silica sol in the W/O emulsion formed by the method described above is gelled. Silica sol in the acidic region is easily gelled by heating. Therefore, the gelation can be achieved by heating the W/O emulsion.

The gelling temperature is preferably 50°C to 80°C, more preferably 60°C to 70°C. The higher the temperature, the more quickly the gelation proceeds.

Although the gelation time depends on the temperature, it is preferably 30 minutes to 24 hours, more preferably 5 to 12 hours, when the above temperature range is used.

Gelation converts the W/O emulsion into a gel dispersion.

(4) a step of separating the organic phase and the aqueous phase in which the silica gel is dispersed, and then removing the organic phase;

In the production method of the present invention, the dispersion liquid of the gelled body prepared as described above is separated into an O phase and a W phase. After the separation, the gelled body obtained by the above step exists dispersedly on the W phase side.

As the separation method, it is possible to use a method known as a demulsification method of emulsion. Specifically, addition of water-soluble organic solvent, addition of salt, application of centrifugal force, addition of acid, One selected from volume ratio change (addition of water or hydrophobic solvent) or the like, or a combination of a plurality of them, can be implemented. Suitably, a certain amount of water-soluble organic solvent can be added into the emulsion together with water as needed to separate the O and W phases. After the separation process, the upper layer generally becomes the O phase (organic layer) and the lower layer becomes the W phase (aqueous layer). In order to form the W phase in this step, the addition of water is not necessarily essential. A method of discharging may be adopted. Specifically, this method can be carried out by selecting a water-soluble organic solvent having a function of penetrating into the pores of the gelled body and expelling water as the water-soluble organic solvent to be added.

Acetone, methanol, ethanol, isopropyl alcohol, etc. are mentioned as said water-soluble organic solvent. Of these, isopropyl alcohol can be preferably used because it is effective in increasing the efficiency of the treatment even in the hydrophobizing treatment described below.

The amount of the water-soluble organic solvent to be added is preferably adjusted according to the type and amount of the surfactant used during emulsion formation. For example, when sorbitan monooleate is used as a surfactant for a W/O emulsion, a water-soluble organic solvent is added in an amount of about 0.1 to 0.4 times the weight of the O phase, and After stirring, it can be separated into an O phase and a W phase by standing still. However, at this time, it is preferable to add water together with the water-soluble organic solvent in an amount of about 0.6 to 0.9 times the amount of the O phase. Also, the temperature at which the separation operation is carried out is not particularly limited, but it can usually be carried out at about 20 to 70°C.

In carrying out the production method of the present invention, it is preferable to carry out aging subsequently. The aging is carried out by adding a basic substance to the W phase (the gelled body is dispersed) separated from the O phase to adjust the pH of the W phase to weakly acidic or basic.

By adding a basic substance, the pH of the W phase, which is in the acidic range, rises, and becomes weakly acidic or basic. Specifically, the pH of the W phase is from 4.5 to 10 is preferable, 5.5 to 8.5 is more preferable, and 6.0 to 8.0 is particularly preferable.

In the present invention, a basic substance containing sodium is used as the basic substance. As the basic substance, inorganic bases such as sodium hydroxide, sodium hydrogen carbonate and sodium carbonate, sodium salts of organic acids such as sodium acetate, and the like can be used. Therefore, inorganic bases are preferred. Among them, it is preferable to use sodium hydroxide because the pH can be easily adjusted.

Moreover, the aging of the gelled body can be carried out by maintaining the aging temperature at about room temperature to 80.degree. The aging time may be appropriately set depending on the pH of the W phase and the aging temperature, and is about 0.5 to 12 hours.

In the production method of the present invention, the organic phase is then separated from the aqueous phase in which the gelled body is dispersed. This is for the purpose of improving the processing efficiency in the subsequent step of hydrophobizing the gelled body. Although the method of separation is not particularly limited, separation into two phases, the O phase and the W phase, can be easily achieved by removing the O phase by decantation or the like and recovering the W phase.

Here, it is not necessary to completely separate and remove the O phase. The proportion of the phase is preferably as small as possible, preferably 20% by mass or less, more preferably 10% by mass or less, relative to the amount of the W phase (including the mass of the gelled body).

(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which silica gel is dispersed to hydrophobize the silica gel;

In the production method of the present invention, the gelled body obtained as described above is hydrophobized with a hydrophobizing agent. In this hydrophobization, an acid is usually added to increase the efficiency of the reaction to make the liquid strongly acidic again, but in the production method of the present invention, it is essential to use sulfuric acid as the acid. and As in the preparation of the aqueous silica sol, the salts formed by using sulfuric acid can be limited to sodium sulfate.

In other words, except that sulfuric acid is used as an acid, the treatment may be carried out in the same manner as known hydrophobizing methods. More specifically, the process is as follows.

The concentration of sulfuric acid used can be in the range of 5-95%. Preferably, it is 10-80%, more preferably 25-65%. The amount of sulfuric acid to be added (the amount as pure H ₂ SO ₄ ) depends on the type of hydrophobizing agent described later. 300 to 1000 parts by weight per 100 parts by weight of SiO ₂ (calculated from the amount) is suitable. More preferably 350 to 900 parts by mass, still more preferably 400 to 800 parts by mass. When cyclic siloxanes such as octamethylcyclotetrasiloxane are used as hydrophobizing agents, the amount of sulfuric acid added is such that the pH of the W phase is 0.3 to 1.0. This is preferable for improving efficiency.

As the hydrophobizing agent, a compound that reacts with Si—OH to form a Si—O—Si bond may be used. agents can be employed.

More specifically, hydrophobizing agents that can be used in the present invention include silanol groups:
M-OH (2)
[In the formula, M represents a Si atom forming a gelled body. The remaining valences of M are omitted in formula (2). Same for all of the following expressions. ]

and converted to (MO-) _(4-n) SiR _n (3)
[In the formula (3), n is an integer of 1 to 3, R is a hydrocarbon group, and when n is 2 or more, a plurality of R may be the same or different. ] can be mentioned as an example.

By performing hydrophobization treatment using such a hydrophobizing agent, the hydroxy groups on the surface of the airgel powder are end-capped with hydrophobic silyl groups and are inactivated, so dehydration between the surface hydroxy groups Condensation reaction can be suppressed. Therefore, since drying shrinkage can be suppressed even if drying is performed under conditions below the critical point, it is possible to obtain a hydrophobic silica airgel powder having a BJH pore volume of 2 mL/g or more.

A compound represented by the following general formula (4) or (6) is known as the hydrophobizing agent.

RnSiX _{(4-n) (} 4)
[In the formula (4), n represents an integer of 1 to 3; R represents a hydrophobic group such as a hydrocarbon group; represents a group (leaving group) that can be eliminated from When n is 2 or more, multiple R's may be the same or different. Also, when n is 2 or less, a plurality of Xs may be the same or different. ]

[In formula (6), R ⁶ and R ⁷ each independently represent a hydrocarbon group, and m represents an integer of 3 to 6. Plural R ^6s may be the same or different. Moreover, a plurality of R ⁷ may be the same or different. ]
In the formula (4), R is a hydrocarbon group, preferably a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrocarbon group having 1 to 4 carbon atoms, particularly preferably a methyl group. be.

Examples of the leaving group represented by X include alkoxy groups such as a methoxy group and an ethoxy group. A group represented by —O—SiR ₃ (wherein R has the same meaning as R in the above formula (4)) can be exemplified.

Specific examples of the hydrophobizing agent represented by formula (4) include monomethyltrimethoxysilane, monomethyltriethoxysilane, hexamethyldisiloxane, and the like. Hexamethyldisiloxane is particularly preferred because of its good reactivity.

Depending on the number of leaving groups X (4-n), the number of bonding with hydroxy groups on the airgel powder skeleton changes. For example, if n is 2:
(MO-) ₂ SiR ₂ (7)
A connection will occur.

And if n is 3:
MO-SiR ₃ (8)
A connection will occur. By silylating the hydroxy groups in this manner, a hydrophobizing treatment is performed.

In formula (6), R ⁶ and R ⁷ are each independently a hydrocarbon group, and preferred groups include the same groups as R in formula (4). m represents an integer of 3-6. When the gelled body is treated with the compound (cyclic siloxane) represented by this formula (6), on the surface of the airgel powder skeleton in the gelled body,
(MO-) ₂ SiR ⁶ R ⁷ (10)
A connection will occur. Thus, the cyclic siloxanes of the above formula (6) also silylate the hydroxy groups and perform hydrophobic treatment.

Specific examples of the cyclic siloxanes represented by formula (6) include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and the like.

The amount of hydrophobizing agent used in the above hydrophobizing treatment varies depending on the type of treatment agent. SiO ₂ amount) is preferably 10 to 150 parts by mass with respect to 100 parts by mass. More preferably 20 to 130 parts by mass, still more preferably 30 to 120 parts by mass.

The hydrophobizing treatment conditions described above can be carried out by adding sulfuric acid and a hydrophobizing agent to the W phase and allowing them to react for a certain period of time. For example, when hexamethyldisiloxane is used as a hydrophobizing agent and the treatment temperature is 50° C., it can be held for about 6 to 12 hours or more. It can be carried out by holding for about 12 hours or longer. The order of addition of the sulfuric acid and the hydrophobizing agent is not particularly limited, and they may be added at the same time, or one of them may be added first and then the other.

In the hydrophobizing treatment step, it is preferable to add a water-soluble organic solvent for the purpose of increasing the solubility of the hydrophobizing agent in the W phase and enhancing the efficiency of the reaction. Examples of the water-soluble organic solvent include acetone, methanol, ethanol and isopropyl alcohol. Among these, isopropyl alcohol can be preferably used. The amount to be added should be about 15 to 80 wt % in terms of concentration in the W phase containing the gelled body.

(6) adding a basic substance containing sodium;

To produce the hydrophobic silica airgel powder of the present invention, a basic substance containing sodium is added to neutralize the sulfuric acid. This is because drying in a strongly acidic state without neutralization adversely affects the physical properties of the obtained hydrophobic silica airgel powder.

By adding a basic substance to the W phase, the pH of the W phase becomes neutral to weakly acidic. Specifically, the pH of the W phase is 1.0 to 7.5. is preferred, and 1.5 to 7.0 is more preferred.

In the production method of the present invention, a basic substance containing sodium is used as the basic substance. Since sulfuric acid is used as an acid in the production method of the present invention as described above, the acid produced by neutralization is sodium sulfate by using a basic substance containing sodium. As will be described later, this is likely to precipitate as sodium sulfate decahydrate, which has low solubility, so that the amount of ionic substances in the system can be easily reduced by removing the precipitate.

As the basic substance, inorganic bases such as sodium hydroxide, sodium hydrogen carbonate and sodium carbonate, sodium salts of organic acids such as sodium acetate, and the like can be used. Therefore, inorganic bases are preferred. Among them, sodium hydroxide is particularly preferred because it facilitates pH adjustment.

Also, this step can be carried out by holding at about 35.degree. C. to 80.degree. Since an acid-base neutralization reaction, which is an exothermic reaction, occurs in this step, this temperature range can be achieved without particular heating. The time required to add the basic substance may be appropriately set depending on the temperature of the W phase, but it is about 0.5 to 1 hour.

(7) A step of cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate.

Since the above method uses a substance containing sulfuric acid as the acid and sodium as the base, the W phase obtained through the above steps contains sodium sulfate in the form of sulfate ions and sodium ions. ing. Sodium sulfate sharply decreases its solubility in water at the transition temperature of 32.4° C., and precipitates as sodium sulfate decahydrate.

In the production method of the present invention, the low solubility of sodium sulfate decahydrate at low temperatures is utilized to cause precipitation by lowering the liquid temperature. Other sulfates and sodium salts have fairly high solubility even at low temperatures and are difficult to precipitate.

In the production method of the present invention, the temperature of the W phase is set to 30° C. or less in order to precipitate sodium sulfate decahydrate based on the above principle. In the temperature range of 32.4°C or less, as the temperature of the liquid drops, so does the solubility. Cooling is required and the cost tends to increase. Considering these, the temperature of the W phase is more preferably lowered to 25° C. or lower, particularly preferably 23° C. or lower, and the lower limit may be 5° C. or higher, or 10° C. or higher.

The time for which the temperature is maintained at 30° C. or less may be appropriately set depending on the temperature of the W phase, and is about 24 to 48 hours. As long as the temperature is 30° C. or less, it is not necessary to keep the temperature constant all the time. Also, the cooling method does not need to be forced cooling, and natural cooling may be used.

(8) Step of removing precipitated sodium sulfate decahydrate

In the production method of the present invention, the sodium sulfate decahydrate precipitated as described above is then removed.

As a method of removing sodium sulfate decahydrate, for example, it can be carried out by passing through a sieve. The opening of the sieve may be appropriately set to a size that allows the generated gelled product to pass through and removes the precipitated sodium sulfate decahydrate, but is preferably about 0.5 mm to 3 mm.

(9) A step of collecting and drying the hydrophobized silica gel in the liquid

In the W phase from which the sodium sulfate decahydrate precipitated as described above has been removed, the concentration of ionic substances has decreased by the amount removed, so the gelled body is then recovered from the liquid and dried. If a hydrophobic silica airgel powder is obtained, the powder will contain less ionic impurities (all other steps being the same) as compared to not removing the sodium sulfate decahydrate. It is a thing.

The method of recovery and drying may be carried out by appropriately selecting a known method, but the following method is preferable in terms of easily suppressing shrinkage during drying. That is, it is a method in which the hydrophobized gelled product is once extracted with a hydrophobic organic solvent, separated from the used hydrophobic organic solvent by filtration or the like, and then heated to volatilize and remove the remaining organic solvent. This method will be described in more detail below.

First, a hydrophobic organic solvent is added to the W phase from which the precipitated sodium sulfate decahydrate has been removed. Since the gelled body hydrophobized by the hydrophobizing agent has a high affinity for the hydrophobic organic solvent, by adding the hydrophobic organic solvent and stirring, etc., the hydrophobic organic solvent side Moving. Criteria for selecting a hydrophobic organic solvent to be used for extracting the gelated body include low surface tension so as not to cause drying shrinkage during subsequent drying. Specifically, hexane, heptane, nonane, decane, dichloromethane, methyl ethyl ketone, toluene and the like can be used, and hexane, heptane, decane and toluene can be preferably used. The amount of the hydrophobic organic solvent to be used may be appropriately set with a target of 0.5 to 10 times the volume of the W phase.

In the production method of the present invention, the step of removing the precipitated sodium sulfate decahydrate is carried out as described above. However, in order to further reduce the content of ionic impurities, this dispersion is treated with an alcohol aqueous solution or water according to the method described in Patent Document 2. Washing (rinsing with water) may be performed.

By performing the sodium sulfate decahydrate removal step, the amount of ionic impurities can be further reduced if the amount of washing liquid used for washing is the same, or if the amount of ionic impurities is made equal The amount of cleaning liquid (that is, the amount of waste liquid) can be reduced.

As described above, a dispersion is obtained in which the extracted gel is dispersed in a hydrophobic organic solvent. By recovering and drying the gel, a hydrophobized silica airgel powder can be obtained. Recovery may be carried out by appropriately selecting a known method as a so-called solid-liquid separation method. As a simple and low-cost method, a filter having a mesh size (opening diameter) that does not allow the gelled material dispersed in the hydrophobic organic solvent to pass through may be used to separate and collect the gel.

Then, the hydrophobic organic solvent is removed (that is, dried) from the gelled body obtained by filtration. Drying may be carried out by a known method depending on the hydrophobic organic solvent used. For example, the temperature during drying should be above the boiling point of the solvent and below the decomposition temperature of the organic group introduced by the hydrophobizing agent used. It is preferable that the pressure is normal pressure to reduced pressure.

As is clear from the above description, the most important feature of the present invention is that sodium sulfate decahydrate is precipitated and removed. Therefore, sulfuric acid is used as the acid, and a basic substance containing sodium is used as the base. Therefore, it is possible to use other acids and bases in combination as long as the sodium sulfate decahydrate can be precipitated. However, in this case, especially when an acid other than sulfuric acid is used, it should be noted that the acid or acid root may pose a problem as an impurity depending on the application.

A hydrophobic silica airgel powder can be produced by such a production method of the present invention. The obtained hydrophobic silica airgel usually has the following physical properties.

Silica airgel powder means that 50% or more of the powder is composed of silica on a mass basis. It is preferably 60% or more, more preferably 75% or more. Components other than silica include components derived from the hydrophobizing agent.

Silica airgel produced by the production method of the present invention is hydrophobic. Being hydrophobic makes it less likely to adsorb water, which causes deterioration over time, and improves compatibility with hydrophobic resins, making it extremely useful when dispersed in hydrophobic resins. In addition, the fact that the airgel is hydrophobic is also significant from the viewpoint that it can be produced without supercritical drying and solvent replacement. Here, whether or not the silica airgel is hydrophobic can be very easily confirmed by putting the powder together with pure water in a container and stirring the mixture. If it is hydrophobic, the powder will not disperse in water, and if it is allowed to stand still, it will return to a state of being divided into two layers, a lower layer of water and an upper layer of powder.

Hydrophobicity and its degree can also be evaluated by M value. In addition, M value is the value measured according to the measuring method described in the Example.

The M value of the hydrophobic silica airgel powder produced in the present invention is preferably 30-55, more preferably 35-55, and particularly preferably 40-55.

In addition, one of the indexes indicating that the hydrophobic silica airgel powder is hydrophobic is the carbon content. The carbon content in the spherical silica contained in the paste composition is derived from the surface treatment agent, and is generated when oxidation treatment is performed in air or oxygen at a temperature of about 1000 to 1500 ° C. It can be measured by quantifying the amount of carbon dioxide.

The hydrophobic silica airgel powder produced by the production method of the present invention preferably has a carbon content of 5 to 12% by mass, more preferably 6 to 10% by mass. The higher the carbon content, the better, because when the paste composition is used as an additive for foundation, it is possible to prevent the makeup from coming off due to perspiration.

Since the hydrophobic silica airgel powder produced by the production method of the present invention is spherical due to the shape of the droplets when forming the W/O emulsion, it has excellent rolling properties on the skin when used in cosmetics. Considering the application, the average circularity of the silica particles should be 0.8 or more, preferably 0.85 or more.

The above-mentioned "average circularity" is a value C (circularity) defined by the following formula (1) for each particle by image analysis using a scanning electron microscope (SEM) to obtain an observed SEM image. , and this circularity C is obtained as an arithmetic mean value for 2000 or more particles. In this case, a particle group forming one aggregated particle is counted as one particle.

C=4πS/L ² (1)
[In formula (1), S represents the area (projected area) of the particle in the image. L represents the length (perimeter) of the outer periphery of the particle in the image. ]
The closer the average circularity is to 1, the closer the particles are to a true sphere.

The hydrophobic silica airgel powder produced by the production method of the present invention preferably has a volume cumulative 50% diameter (D50) measured by the Coulter counter method in the range of 1 to 30 μm, and the volume cumulative 50% diameter ( D50) is more preferably in the range of 1 to 20 μm, even more preferably in the range of 1 to 10 μm.

Further, the hydrophobic silica airgel powder preferably contains 50% or more, more preferably 60% or more, of particles having a particle diameter of 1 to 30 μm as measured by the same method. Particles with a particle size range of 1 to 30 μm have an appropriate particle size for obtaining a smooth feel when blending the hydrophobic silica airgel powder into cosmetics.

The specific surface area determined by the BET method based on the nitrogen adsorption method is preferably 400 to 1000 m ² /g. The larger the specific surface area of the hydrophobic silica airgel powder, the smaller the particle size of the primary particles that make up the porous structure (network structure) of the independent particles, and the thickening effect increases when used as an additive in cosmetics. . If the thickening effect is high, dripping can be prevented when applied to the skin or hair. Therefore, the specific surface area is preferably 500 m ² /g or more, more preferably 550 m ² /g or more.

On the other hand, if the specific surface area is too large, the pore volume becomes small and the oil absorption becomes small, so the specific surface area is preferably 850 m ² /g or less, more preferably 700 m ² /g or less . Generally, it is difficult to obtain silica with a specific surface area exceeding 1000 m ² /g.

The specific surface area by the BET method is obtained by drying the sample powder to be measured under a vacuum of 1 kPa or less at a temperature of 150 ° C. for 2 hours or more, and then obtaining an adsorption isotherm only on the nitrogen adsorption side at liquid nitrogen temperature. However, the value is obtained by analysis by the BET method, and the range of the partial pressure (P/P ₀ ) at the time of analysis is 0.1 to 0.25.

The pore volume according to the BJH method is usually 2-8 ml/g. The larger the pore volume, the better the oil absorbing performance, which is preferable. The lower limit is more preferably 2.5 ml/g or more, particularly preferably 4 ml/g or more. Further, the upper limit is more preferably 6 ml/g or less. If the pore volume is 2 ml/g or less, excellent oil absorption performance cannot be obtained. Also, it is usually difficult to obtain anything greater than 8 ml/g.

In the present invention, the pore volume of the hydrophobic silica airgel powder by the BJH method is obtained by obtaining an adsorption isotherm in the same manner as in the BET specific surface area measurement, and by the BJH method (Barrett, E.P.; Joyner, L.G.; Halenda, P.P. , J. Am. Chem. Soc. 73, 373 (1951). is a pore with a radius of 1 to 100 nm, and the integrated value of the pore volume in this range is the pore volume in the present invention.

The peak pore radius of the hydrophobic silica airgel powder produced by the production method of the present invention by the BJH method is usually in the range of 10 to 50 nm. The peak of the pore radius was also obtained by obtaining an adsorption isotherm and analyzing it by the BJH method in the same manner as in the measurement of the BET specific surface area. The pore radius peak is the pore radius value at which the cumulative pore volume (volume distribution curve) of the logarithm of the pore radius takes the maximum peak value.

Silica airgel is usually characterized by having a high oil absorption, and the hydrophobic silica airgel powder produced by the production method of the present invention also preferably has an oil absorption of 400 ml/100 g or more, and 550 ml/100 g or more. is more preferable, and 650 ml/100 g or more is particularly preferable. The higher the oil absorption, the better the anti-shiny effect when used in cosmetics, so it is preferable. Although the upper limit of the oil absorption is not particularly limited, it is about 750 mL/100 g at maximum.

The oil absorption shall be measured according to the method described in JIS K6217-4 “Determination of Oil Absorption”.

The content of chloride ions contained in the hydrophobic silica airgel powder can be quantified by ion chromatography. The chloride ion content is preferably 1 ppm or less, more preferably 0.5 ppm or less.

As described above, according to the production method of the present invention having a step of precipitating and removing sodium sulfate decahydrate, it is possible to obtain a hydrophobic silica airgel powder excellent in various physical properties. A paste-like composition containing hydrophobic silica and water can also be produced from the W phase in which the gelled product, which is an intermediate in this production method, is dispersed. That is, the water content in the W phase (aqueous dispersion) in which the hydrophobized gel is dispersed can be reduced to such an extent that the gel does not dry out, thereby forming a paste. By employing the W phase that has undergone the step of precipitating and removing sodium sulfate decahydrate as the W phase, it becomes easy to reduce the ionic impurities contained in the resulting paste-like composition. The method for producing this paste-like composition will be described in detail below.

(10) Step of removing part of the water to form a paste

The W phase that has undergone the above-mentioned (8) step of removing the precipitated sodium sulfate decahydrate is a slurry (with self-fluidity) in which the gelled body is dispersed in water, so it is included in the slurry. By removing part of the water, a paste-like composition (substantially free of self-fluidity) can be obtained.

The method of removing part of the water can be carried out by applying a filter with mesh openings (opening diameter) that does not allow the gelled body to pass through, in the same manner as when the gelled body dispersed in the hydrophobic organic solvent is collected. . The gelled product dispersion (W phase) produced by the above method has poor filterability, and even if it is filtered, the solid-liquid separation will be clean, and the gelled product will not be collected in a wet powder-like state. It is recovered as a sticky paste (gelled product + water) on the filter. Even after it becomes a paste, if it continues to be filtered on the filter, the water content will gradually decrease, so it can be collected when the desired water content is reached, and if the water content is insufficient. can be adjusted by adding fresh water.

As described in the production of the hydrophobic silica airgel powder, in the production method of the present invention, the step of removing sodium sulfate decahydrate is carried out, so that the paste composition also has relatively ionic impurities. Although the content of is small, it is preferable to wash with water at this stage in order to further reduce the content and improve physical properties such as oil absorption.

That is, the W phase passed through the sieve through the step of removing sodium sulfate decahydrate described above usually contains fine crystals and dissolved sodium sulfate decahydrate that could not be completely removed by the sieve. Sodium sulfate (hereinafter referred to as "sodium sulfate" regardless of whether it is crystallized or dissociated into ions) is included.

Therefore, it is preferable to wash with water in order to remove this sodium sulfate. As a method of washing with water, for example, the W phase containing the gelled body is put into a filter and water is allowed to flow therein, that is, washing can be performed by adding and removing water at the same time. At this time, by applying pressure or suction, it is possible to adjust the balance between the water to be introduced and the water to be discharged. In order to increase the cleaning efficiency, it is preferable to use a high temperature within a range not exceeding the boiling point of the water-soluble organic solvent remaining in the gelled body. Usually, it can be carried out in the range of 20 to 60°C. In this cleaning, the reaction residue of the organic solvent and the silylating agent used in each step is also removed. Moreover, addition and removal of water may be performed alternately.

It is preferable to use water having a low content of ionic impurities, such as ion-exchanged water and pure water.

A guideline for completing washing with water can be confirmed by measuring the electric conductivity of the discharged water. The electric conductivity of the discharged water is preferably 100 μS/cm or less, more preferably 70 μS/cm, and even more preferably 40 μS/cm. By setting the electrical conductivity of the discharged water to 100 μS/cm, the finally obtained hydrophobic silica airgel powder has a high oil absorption.

After the electric conductivity of the discharged water falls below a predetermined value, a paste-like composition can be obtained by adjusting the water content as described above.

The operation of reducing ionic impurities by washing with the slurry/paste can also be applied to the above-described method for producing a hydrophobized silica airgel powder (can be performed between steps (8) and (9)). In this case, washing may be performed instead of washing after extracting the gelled product with a hydrophobic organic solvent, or may be used in combination.

The composition ratio in the paste-like composition produced by the above method is not particularly limited, but considering the ease of handling as a paste, water is included in the range of 300 to 1900 parts by weight with respect to 100 parts by weight of hydrophobic silica. It is preferable to be

The paste-like composition produced as described above is composed of hydrophobic silica and water. Silica as used herein means silicon dioxide, and is a general term for substances composed of silicon dioxide, and the chemical composition is represented by SiO ₂ .

The hydrophobic silica is porous due to the manufacturing method, and the temperature is 60 ° C. or more and 150 ° C. or less and the gauge pressure is -100 kPaG or more -20 kPaG until the water content in the residue is 1% by mass or less. If the water is volatilized under the following atmosphere, the pore volume and oil absorption are small, and the physical properties are equivalent to those of the hydrophobic silica airgel powder produced by the above method, except that the peak of the pore radius is small. will have

The pore volume, oil absorption and pore radius peaks are different because in the production of hydrophobic silica airgel powder, the dispersion medium is once replaced with a hydrophobic organic solvent having a low surface tension and then dried. This is because drying shrinkage occurs in the above method because drying is applied directly from water. In other words, in place of the above method, the same physical properties as the hydrophobic silica gel powder can be obtained by replacing with a hydrophobic organic solvent and then drying according to the same procedure as in the method for producing the hydrophobic silica airgel.

(Physical properties and applications)
The hydrophobic silica airgel powder produced in the present invention can be used as an additive for cosmetics, if the production conditions are selected so that it has an appropriate particle size distribution and specific surface area. When used as a material, it has excellent appearance retention and a smooth touch. In addition, as a hydrophobic silica airgel powder, it has a high oil absorption, efficiently absorbs oil on the surface of the skin and scalp, and is hydrophobic and has the effect of repelling sweat. , paste, and cream type make-up/skin care cosmetics, as well as cosmetics such as deodorants and hair styling products.

Moreover, when the paste-like composition produced by the present invention is mixed with water, it easily disperses in water despite the fact that the silica contained therein is hydrophobic. Furthermore, if the production conditions are selected so that the particle size distribution and specific surface area are appropriate for a cosmetic additive, it can be used for the same purpose, specifically as an additive for liquid cosmetics, with excellent appearance retention and smoothness. You can get a nice tactile sensation. In addition, when the hydrophobic silica is porous silica, it has a high oil absorption capacity, efficiently absorbs oil from the surface of the skin and scalp, and is hydrophobic and has the effect of repelling sweat. In addition, it can be suitably used as cosmetics such as paste and cream type make-up/skin care cosmetics, deodorants, and hair styling products.

Of course, since the hydrophobic silica airgel powder and the paste-like composition have the appropriate particle properties, they can be suitably used for various application materials such as heat insulating agents and matting agents.

EXAMPLES Hereinafter, examples will be shown in order to specifically describe the present invention, but the present invention is not limited only to these examples. In addition, the evaluation of Examples and Comparative Examples was carried out by the following methods.

<Evaluation method>
The hydrophobic silica airgel powders and paste compositions produced in Examples 1 and 2 and Comparative Examples 1 to 6 were tested for the following items.

In addition, "hydrophobic silica contained in the paste composition" means that the water content of the paste composition is 150 ° C. under -100 kPaG (gauge pressure) conditions in a vacuum dryer until the water content of the paste composition is 1% by mass or less. It is for the silica remaining after drying for 16 hours and removing the water.

(Electrical conductivity)
Electrical conductivity was measured using COND METER ES-51 manufactured by Horiba, Ltd.

The electrical conductivity of water discharged from washing to remove sodium sulfate was measured directly.

The electrical conductivity of the hydrophobic silica contained in the dried hydrophobic silica airgel powder or paste composition was measured by adding 1 g of the hydrophobic silica airgel powder or the hydrophobic silica contained in the paste composition to a 50 ml screw tube bottle. , 7 g of isopropyl alcohol, and 30 g of ion-exchanged water were added, followed by ultrasonic dispersion for 30 minutes.

(amount of water)
A halogen moisture meter (MB25) manufactured by OHAUS Co., Ltd. was used to measure the moisture content by the following method.

3.0 g of the hydrophobic silica airgel powder or paste composition was put on a dedicated aluminum dish, set in a moisture meter, and analyzed. The measurement conditions were 160° C. and 30 minutes.

(Chloride ion content)
1 g of hydrophobic silica airgel powder or 6.7 g of a paste composition containing hydrophobic silica and 100 ml of ultrapure water are added to a 200 ml beaker and stirred for 15 minutes with a stirrer. After filtering this dispersion with a 0.45 μm syringe filter, the chloride ion content was measured by ion chromatography (ICS-2100) manufactured by Thermo Fisher Scientific. Results are reported as chloride ion content relative to silica mass.

(D50)
The produced hydrophobic silica airgel powder or a paste composition containing hydrophobic silica was added to ethanol and subjected to ultrasonic dispersion for 30 minutes. D50 of the obtained ethanol dispersion was measured using a 100 μm aperture tube with a precision particle size distribution analyzer Multisizer 3 manufactured by Beckman Coulter, Inc.

(Specific surface area, pore volume and oil absorption)
The BET specific surface area and BJH pore volume of the hydrophobic silica contained in the hydrophobic silica airgel powder or paste composition were measured using BELSORP-max manufactured by Microtrack Bell Co., Ltd. according to the above definitions. The oil absorption was measured according to JIS K6217-4 "Determination of oil absorption".

(M value)
Hydrophobic silica powder floats in water, but is completely suspended in methanol. Utilizing this fact, the modified hydrophobicity measured by the following method was used as the M value, which was used as an indicator of the degree of hydrophobization.

0.2 g of the hydrophobic silica airgel powder or the hydrophobic silica contained in the paste composition was added to 50 ml of water in a 200 mL beaker and stirred with a magnetic stirrer. Methanol is added to this using a burette, and the end point is when the entire amount of the hydrophobic silica airgel powder or the hydrophobic silica contained in the paste composition is wetted and suspended in the solvent in the beaker, dropwise. did. At this time, the methanol was led into the solution through a tube so as not to touch the sample directly. The volume % of methanol in the methanol-water mixed solvent at the end point was defined as the hydrophobicity (M value).

M value = Methanol drop amount / (methanol drop amount + 50 ml)

(average circularity)
The hydrophobic silica contained in the hydrophobic silica airgel powder or paste composition was observed using Hitachi High-Technologies SEM (S-5500) at an acceleration voltage of 3.0 kV, secondary electron detection, and magnification of 1000. . By image analysis of the obtained SEM image, the circularity of the hydrophobic silica contained in the hydrophobic silica airgel powder or paste composition was calculated according to the following formula. The average circularity is obtained by calculating the circularity of 2000 or more hydrophobic silica airgel powders or hydrophobic silica contained in the paste-like composition and averaging them.

C=4πS/L ²
[In the above formula, S represents the area (projected area) that the particle occupies in the image. L represents the length (perimeter) of the outer periphery of the particle in the image. ]

(carbon content)
The carbon content of the hydrophobic silica contained in the airgel powder or the paste composition was measured using an elemental analyzer (vario MICRO cube) manufactured by Elementor Japan Co., Ltd.

<Example 1>
While stirring 0.8 kg of 9% sulfuric acid with a stirring blade, 1 kg of sodium silicate was gradually added to prepare an aqueous silica sol. At this time, the pH was 2.9.

To 1.8 kg of the aqueous silica sol prepared above, 1.7 kg of heptane was added, and 0.02 kg of sorbitan monooleate was added. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer to form a W/O emulsion.

The resulting W/O emulsion was gelled at 70° C. for 1 hour while stirring with a stirring blade. Subsequently, 1 kg of isopropyl alcohol and 0.7 kg of ion-exchanged water were added and separated into an upper layer (O phase) and a lower layer (W phase) while stirring with a stirring blade. Subsequently, 0.09 kg of 0.5 mol/L sodium hydroxide aqueous solution was added. At this time, the pH of the W phase was 6.8. The gelled body was aged at 60° C. over 1 hour. The W phase was recovered by removing the O phase by decantation.

Silylation treatment was performed by adding 1.1 kg of 30% sulfuric acid and 0.1 kg of hexamethyldisiloxane to the obtained W phase and keeping the mixture in a water bath at 70° C. for 8 hours while stirring.

After the silylation treatment, 1 kg of a 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade to carry out neutralization treatment. The pH at this time was 2.3.

After the neutralization treatment, it was cooled to 23° C. and allowed to stand for 30 hours.

After standing, the entire liquid was passed through a 1 mm sieve to remove precipitated sodium sulfate decahydrate.

After the liquid was transferred to a pressure filter, ion-exchanged water was flowed, and washing was performed until the electrical conductivity of the liquid that passed through the filter became 100 μS/cm or less. The amount of ion-exchanged water used for washing was 15 kg.

The slurry was transferred to a container, and 1.2 kg of heptane was added to extract the gelled body. After removing the aqueous layer, the gel was collected by filtering with a suction filter. Further, the gelled body was dried by heating at 150° C. for 12 hours or more under vacuum pressure to obtain a hydrophobic silica airgel powder. Table 1 shows each physical property evaluated.

<Comparative Example 1>
After the neutralization treatment, the same operation as in Example 1 was performed except that the step of cooling to precipitate and remove sodium sulfate decahydrate was not performed. 51 kg of ion-exchanged water was used in the washing process. Table 1 shows each physical property evaluated.

<Example 2>
After the solution was transferred to the pressurized filter, the same operation as in Example 1 was performed up to washing with ion-exchanged water. The amount of ion-exchanged water used for washing was 14 kg.

After washing, a part of water was removed by suction with a diaphragm pump to obtain a pasty composition containing hydrophobic silica and water.

The water content in the paste-like composition is 84% by mass, and it is dried in a vacuum dryer at 150° C. under −100 kPaG (gauge pressure) conditions for 16 hours until the water content is 1% by mass or less, and water is removed. Table 2 shows the results of analyzing the silica remaining after removal.

<Comparative Examples 2 to 6>
After the neutralization treatment, the same operation as in Example 2 was performed except that the step of cooling to precipitate and remove sodium sulfate decahydrate was not performed. The electrical conductivity of the washing water was measured at the time points shown in Table 2 for the amount of ion-exchanged water passed through the pressurized filter for washing, and Comparative Examples 2-5 were obtained. In Comparative Example 6, when the electrical conductivity of the washing water became the same as in Example 2, a paste-like composition was obtained and evaluated in the same manner as in Example 2.

Claims (4)

(1) preparing an aqueous silica sol from sulfuric acid and sodium silicate;
(2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;
(3) a step of gelling the silica sol by heating to convert the W/O emulsion into a dispersion of silica gel;
(4) removing the organic phase after phase separation into an organic phase and an aqueous phase in which the silica gel is dispersed;
(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which silica gel is dispersed to hydrophobize the silica gel;
(6) adding a basic substance containing sodium;
(7) cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate;
(8) removing the precipitated sodium sulfate decahydrate, and
(9) A method for producing a hydrophobic silica airgel powder, comprising a step of collecting and drying the hydrophobized silica gel in the liquid. (9) The step of collecting and drying the hydrophobized silica gel in the liquid,
(9a) extracting the hydrophobized silica gel with a hydrophobic organic solvent;
(9b) recovering the hydrophobized silica gel from the hydrophobic organic solvent; and
(9c) drying the recovered hydrophobized silica gel;
The method for producing a hydrophobic silica airgel powder according to claim 1, comprising at least three steps of (1) preparing an aqueous silica sol from sulfuric acid and sodium silicate;
(2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion;
(3) a step of gelling the silica sol by heating to convert the W/O emulsion into a dispersion of silica gel;
(4) removing the organic phase after phase separation into an organic phase and an aqueous phase in which the silica gel is dispersed;
(5) adding a hydrophobizing agent and sulfuric acid to the aqueous phase in which the silica gel is dispersed to hydrophobize the silica gel;
(6) adding a basic substance containing sodium;
(7) cooling the temperature to 30° C. or less to precipitate sodium sulfate decahydrate;
(8) removing the precipitated sodium sulfate decahydrate, and
(10) A method for producing a paste-like composition containing hydrophobic silica and water, which comprises a step of removing part of the water to form a paste. Before or at the same time as performing (10) the step of removing part of the water to form a paste,
(11) The method for producing a paste-like composition containing hydrophobic silica and water according to claim 3, wherein an operation for reducing ionic substances is performed by adding and removing water.