JP7278110B2 - Method for producing spherical silica airgel powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing silica airgel powder, and more particularly to a method for producing powder made of spherical silica airgel having excellent strength.

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. Due to the high porosity, airgel has excellent oil absorption, and several methods for producing the same have been proposed (see, for example, Patent Documents 1 to 4).

Such silica airgel has various uses, among which it is useful as a cosmetic material. That is, taking the foundation as an example, the silica airgel is used as an additive for improving the durability of the appearance when applied to the skin. More specifically, the porous structure of silica airgel absorbs sebum well, so it is possible to prevent the skin from getting wet with sebum, increasing the specular reflectance of light, and causing shine. In addition, when the silica airgel is manufactured by being hydrophobized, it has a good affinity with the organic component of cosmetic materials such as foundation and is uniformly dispersed, so that the effect of maintaining the appearance of preventing shine is further enhanced. .

In addition, these silica aerogels should 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. As a method for producing such spherical silica airgel having an appropriate particle size, for example, the following method has been proposed (Patent Document 5). That is, after dispersing a W phase composed of an aqueous silica sol in an organic solvent phase to form a W/O emulsion, the spherical W phase is gelled and then demulsified to separate the W phase and the O phase. After extracting the gelled product, it is hydrophobized and recovered. Here, the gelation of the W phase is performed in a state adjusted to be weakly acidic or basic, and the demulsification operation for separating the W phase and O phase includes addition of salt, application of centrifugal force, addition of acid, and filtration. , change the volume ratio, etc.

Further, in a similar method for producing spherical silica airgel, the demulsification operation is carried out by adding water and a water-soluble organic solvent to the emulsion, and the separated W phase is heated to ripen the gelled body. A method is also known (Patent Document 6). In this case, the gelation of the W phase before the demulsification operation is carried out by adding a base to adjust the pH in all the examples.

Furthermore, in a similar method for producing spherical silica airgel, a method of separating the O phase and the W phase after the demulsification operation, adding a basic substance to the W phase, and aging the gelled body dispersed in the W phase. known (Patent Document 7).

U.S. Pat. No. 4,402,927 JP-A-10-236817 JP-A-06-040714 JP-A-07-257918 Japanese Patent No. 4960534 JP 2014-210671 A JP 2018-177620 A

However, although the spherical silica airgel obtained by the above method is extremely useful for cosmetic applications due to its highly porous structure, there is still room for improvement due to the low compressive strength of the particles. That is, when spherical silica airgel is used for cosmetics, if it enters into the recessed parts of the skin such as skin pores and wrinkles and partially remains on the skin surface when the cosmetics are removed, On the contrary, there is a problem that the roughness of the skin is conspicuous. However, if the spherical silica airgel has the appropriate size, the penetration into the recessed portions of the skin does not occur so remarkably.

However, the spherical silica airgel obtained by the above-mentioned conventional method is brittle and easily broken because the compressive strength of the particles is not sufficient, and some of the particles are broken during the manufacturing process and application of cosmetics, and the broken pieces are on the skin. It gets into the recessed portions and remains even when the makeup is ruined, causing a problem that the roughness of the skin is conspicuous. In addition, when the particles are broken in such a way that the cosmetics contain a large amount of broken pieces, the rolling property on the skin is lowered and the smoothness of the touch is greatly impaired.

In addition to cosmetic applications, attempts have been made to impart various functionalities to silica airgel.

The present inventors have made intensive studies to solve the above problems, and as a result, in a method for producing a spherical silica airgel including a step of gelling an aqueous silica sol, a gel in which nanofibers are dispersed in the aqueous silica sol The inventors have found that when the particles are combined, the obtained spherical silica airgel is composited with the nanofibers, and thus various physical properties derived from the nanofibers can be expressed, leading to the completion of the present invention. .

That is, the present invention
(1) Step of preparing an aqueous silica sol in which nanofibers are dispersed (2) Step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion (3) Gelating the silica sol by heating A spherical silica airgel powder characterized by comprising a step of converting the W/O type emulsion into a dispersion liquid of a gelled body by allowing the W/O emulsion to separate and recover the gelled body in the above order. is a manufacturing method.

The silica airgel produced by the production method of the present invention has spherical independent particles as a main component and exhibits various physical properties due to the composite nanofibers. For example, by combining with organic nanofibers, it is possible to obtain a spherical silica airgel powder in which each particle has a high compressive strength. Since such particles can maintain their shape even when a load is applied, they are less likely to contain fragments of broken particles or pieces that fall off due to chipping of a part of the particle surface. For this reason, it has excellent filling properties and dispersibility, and when used in cosmetics, it can maintain its shape even when a load is applied. In addition, since it has a high porosity and excellent oil absorption, it is excellent in preventing shine.

Such a property of high compressive strength can be used not only as an additive for cosmetic materials, but also for other uses, because the silica of the present invention can maintain its shape even under load during processing. Airgel powder can also be usefully used as various application materials such as a heat insulating agent and a matting agent.

Further, for example, by combining conductive nanofibers, it is possible to obtain a spherical silica airgel powder exhibiting conductivity.

The method for producing spherical silica airgel powder of the present invention includes the following steps. Namely
(1) Step of preparing an aqueous silica sol in which nanofibers are dispersed (2) Step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion (3) Gelating the silica sol by heating and (4) a step of converting the W/O emulsion into a dispersion liquid of the gelled body and a step of separating and recovering the gelled body.

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

In the production method of the present invention, first, an aqueous silica sol in which nanofibers are dispersed is prepared. In this step, the aqueous silica sol may be prepared and the nanofibers dispersed therein, or the preparation of the aqueous silica sol and the dispersion of the nanofibers may be performed at the same time, and the procedure is not particularly limited. , the former is preferred.

The ratio of the aqueous silica sol and the nanofibers is appropriately set according to the spherical silica aerogel to be produced, assuming that the silica content (in terms of SiO ₂ ) and the nanofibers in the aqueous silica sol are all constituent components of the spherical silica aerogel. Generally, the total amount of silica content and nanofibers is 100% by mass, and the nanofiber component is preferably 0.05 to 30% by mass, more preferably 0.1 to 20% by mass. preferable. If the silica content is too low, it becomes difficult to develop physical properties as silica airgel.

The nanofibers may be organic nanofibers or inorganic nanofibers, and known nanofibers may be appropriately selected and used according to the purpose. The nanofiber generally corresponds to a fiber having a fiber diameter of about 1 to 100 nm and an aspect ratio of 10 or more, preferably 100 or more. Specific examples of organic nanofibers include natural organic nanofibers such as cellulose nanofibers, chitin nanofibers, and chitosan nanofibers, and synthetic resin-based nanofibers such as aramid nanofibers, polyester nanofibers, and polyurethane nanofibers. Organic nanofibers include, but are not limited to. Examples of inorganic nanofibers include, but are not limited to, alumina nanofibers, glass nanofibers, silica nanofibers, and carbon nanofibers.

The nanofibers to be used should be able to be dispersed in the aqueous silica sol and should be hydrophilic to the extent that they are not distributed to the W phase (oil phase) side when the W/O emulsion is formed in the process described later. . In this case, if necessary, surface treatment may be performed to make it hydrophilic.

As a method for preparing the aqueous silica sol, a known method may be appropriately adopted, and as an example, a method using an alkali metal silicate is as follows.

When an alkali metal silicate is used, it is preferable to prepare a silica sol by neutralizing with a mineral acid such as hydrochloric acid or sulfuric acid. Examples include a method of adding an aqueous solution of an alkali metal silicate, and a method of impinging and mixing an aqueous acid solution and an aqueous solution of an alkali metal silicate in a pipe (see, for example, Japanese Patent Publication No. 4-54619). More specifically, the amount of acid used in preparing the aqueous silica sol is desirably 1.05 to 1.2 in terms of the molar ratio of hydrogen ions to the alkali metal content of the alkali metal silicate. When the amount of acid is within this range, the pH of the prepared silica sol is about 1-5. More preferably, the amount of 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.

By setting the concentration of the aqueous silica sol to the above lower limit or more, it becomes easy to make the pore volume of the obtained airgel by the BJH method 8 mL / g or less, and the pore radius peak of the airgel by the BJH method is 50 nm. It becomes easier to: 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.

In order to produce the spherical airgel powder of the present invention, nanofibers as described above are dispersed in the aqueous silica sol obtained by the above method. That is, an aqueous silica sol is mixed as a dispersion medium, and nanofibers are mixed as a dispersoid. As a method for dispersing the nanofibers in the aqueous silica sol, mechanical dispersion is preferable, and specific examples thereof include a method using a mixer, a homogenizer, or the like. Preferably, a homogenizer can be used. Whether the nanofibers are uniformly dispersed in the aqueous silica sol can be visually confirmed. If the dispersion is insufficient, it can be confirmed that the nanofibers are aggregated and suspended or sedimented in the aqueous silica sol.

As the nanofibers, it is also preferable to employ those that have been dispersed in an aqueous medium in advance, and to mix the dispersion with the aqueous silica sol, since good dispersibility can be obtained. Such nanofiber dispersions are commercially available and can be used. When such a nanofiber dispersion is used, after mixing with the aqueous silica sol, it is preferable to adjust the concentration of silica (in terms of SiO ₂ ) in the mixture so that it falls within the above range.

To produce the spherical airgel powder of the present invention, the nanofiber-dispersed aqueous silica sol prepared as described above 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 becomes possible to produce an airgel having a high degree of circularity of 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. Specific examples of surfactants that can be preferably used include sorbitan monooleate, sorbitan monostearate, sorbitan monosesquiolate, and the like.

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. The average particle size of the silica sol droplets in the W/O emulsion and the average particle size of the airgel generally correspond to each other. At the same time, 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 spherical airgel with a higher degree of circularity. .

To produce the spherical airgel powder of the present invention, the silica sol in such W/O emulsion 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. If the gelation temperature is higher than the above range, the specific surface area will be low, and if it is lower, the gelation will not proceed sufficiently.

The gelling time is preferably 30 minutes to 24 hours, more preferably 5 to 12 hours.

Gelation converts the W/O emulsion into a gel dispersion. Since the organic nanofibers are dispersed in the silica sol, they are incorporated (dispersed) into the formed silica during the gelation.

In order to produce the spherical airgel powder of the present invention, the gelled body thus obtained is separated and recovered. As the recovery method, a known method may be appropriately adopted, but it is preferable to carry out the following method, that is, the following steps (5) to (7).

(5) A step of separating into an O phase and a W phase containing a gelled body.
(6) A step of hydrophobizing the gelled body dispersed in the W phase.
(7) A step of recovering the hydrophobized gelled body.

In the above method, the operation of first separating the O phase and W phase is generally called demulsification. After demulsification, the gelled body obtained by the above step exists dispersedly on the W phase side.

As the demulsification method, a known method can be adopted. Specifically, addition of a water-soluble organic solvent, addition of salt, application of centrifugal force, addition of acid, filtration, volume ratio One selected from 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 demulsification process, the upper layer generally becomes the O phase (organic layer) and the lower layer becomes the W phase (aqueous layer).

Acetone, methanol, ethanol, isopropyl alcohol, etc. are mentioned as said water-soluble organic solvent. Among these, isopropyl alcohol can be preferably used because it is effective in increasing the efficiency of the silylation treatment, which will be described later.

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 the surfactant for the W/O type emulsion, a water-soluble organic solvent is added in an amount of about 0.1 to 0.4 times the amount of the O phase by mass. Depending on the conditions, the O phase and the W phase can be preferably separated by allowing the mixture to stand after stirring. In addition to the water-soluble organic solvent, it is preferable to add water 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 the production method of the present invention, it is preferred that the gelled body is aged after obtaining the gelled body dispersed in the W phase as described above. The aging is carried out by adding a basic substance to the W phase separated from the O phase (the gelled body is dispersed) to adjust the pH of the W phase to weakly acidic or basic, and aging the gel. .

By adding a basic substance to the W phase, the pH of the W phase, which is below the acidic range, rises and becomes weakly acidic or basic. Specifically, the pH of the W phase is It is preferably 4.5 to 10, more preferably 4.5 to 8.0, and particularly preferably 4.5 to 5.5. Ammonia, caustic soda, alkali metal silicate and the like can be used as the basic substance. Among them, it is preferable to use caustic soda because the pH can be easily adjusted.

Also, the aging of the gel can be carried out by maintaining the aging temperature at about room temperature to 80°C. 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.

As described above, a liquid in which the hydrophilic gel (porous silica) is dispersed in the W phase can be obtained, and the gel is simply collected by filtration or the like and dried. Otherwise, the pores will collapse due to shrinkage, and an airgel cannot be obtained. As a method for suppressing the shrinkage, supercritical drying and a method of hydrophobizing a gelled body as described below and then drying are known.

When silylating the gelled product, it is desirable to separate the W phase from the O phase in order to improve the efficiency of the treatment. The separation method is not particularly limited, but the O phase and W phase, which are separated into two phases, can be removed by, for example, decantation or the like, and the W phase can be recovered. This separation may be performed before the aging.

Here, it is not necessary to completely separate and remove the O phase. The smaller the better, and it is preferably 20 wt % or less, more preferably 10 wt % or less, relative to the amount of W phase.

Hydrophobization of the gelled product can be achieved by subjecting the gelled product to silylation treatment using a silylating agent. Spherical silica airgel obtained by silylation treatment becomes hydrophobic, shrinkage is suppressed when the gelled body is dried, and it is possible to obtain a powder that retains the porous structure of an airgel. Let

Silanol groups as silylating agents that can be used in the present invention:
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). In the following formulas, all the same. ]
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 silylation treatment using such a silylating 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, drying shrinkage can be suppressed even if drying is performed under conditions below the critical point, so it is possible to obtain a metal oxide powder having a BJH pore volume of 2 mL/g or more.

Compounds represented by the following general formulas (4) to (6) are known as the silylating 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 (5), R ¹ represents an alkylene group; R ² and R ³ each independently represent a hydrocarbon group; R ⁴ and R ⁵ each independently represent a hydrogen atom or a hydrocarbon group. ]

[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 above 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 leaving groups represented by X include halogen atoms such as chlorine and bromine; alkoxy groups such as methoxy and _ethoxy groups; are synonymous), etc. can be exemplified.

Specific examples of the silylating agent represented by formula (4) include chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, monomethyltrimethoxysilane, monomethyltriethoxysilane, hexamethyldisilazane, and the like. Chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, octamethylcyclotetrasiloxane and/or hexamethyldisilazane and hexamethyldisiloxane are particularly preferred in terms of 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. The silylation treatment is performed by silylating the hydroxy groups in this way.

In the above formula (5), R ¹ is an alkylene group, preferably an alkylene group having 2 to 8 carbon atoms, particularly preferably an alkylene group having 2 to 3 carbon atoms.

In the above formula (5), R ² and R ³ are each independently a hydrocarbon group, and preferred groups include the same groups as R in formula (4). R ⁴ represents a hydrogen atom or a hydrocarbon group, and when it is a hydrocarbon group, preferred groups include the same groups as R in formula (4). When the gelled body is treated with the compound (cyclic silazane) represented by this formula (5), the Si—N bond is cleaved by the reaction with the hydroxyl group, so that the surface of the airgel powder skeleton in the gelled body (MO-) ₂ SiR ² R ³ (9)
A connection will occur. In this way, the cyclic silazanes of the above formula (5) also silylate the hydroxy group and carry out the silylation treatment.

Specific examples of the cyclic silazanes represented by formula (5) include hexamethylcyclotrisilazane and octamethylcyclotetrasilazane.

In the above 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 the silylation treatment.

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

The amount of silylating agent used in the above silylation treatment varies depending on the type of the treating 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 conditions for the above silylation treatment can be carried out by adding a silylating agent to the W phase and allowing it to react for a certain period of time. For example, when hexamethyldisiloxane is used as the silylating 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.

Further, when cyclic siloxanes such as octamethylcyclotetrasiloxane are used as the silylating agent, adding hydrochloric acid to adjust the pH of the solution to 0.3 to 1.0 enhances the efficiency of the reaction. preferred above.

In the silylation treatment step, it is preferable to add a water-soluble organic solvent for the purpose of enhancing the solubility of the silylating 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 above water-soluble organic solvent is preferably added so that the concentration in the W phase containing the gelled product is about 20 to 80 wt %.

From the point of view of easily suppressing shrinkage during drying, it is preferable to once extract the gelled body into a hydrophobic organic solvent after the hydrophobizing treatment. That is, since the hydrophobized gel has a high affinity for the hydrophobic organic solvent, it moves to the side of the hydrophobic organic solvent when the hydrophobic organic solvent is added and stirred. Criteria for selecting the hydrophobic organic solvent used for extracting the gelled product include low surface tension so as not to cause drying shrinkage in the subsequent drying step. 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.

After the above extraction into the hydrophobic organic solvent, the organic solvent is washed with water or an alcohol aqueous solution in order to remove salts contained in the gelled body and sulfates contained in the hydrophobic organic solvent. Washing is preferred. This washing operation can be performed by a known method, and a method known as a so-called liquid/liquid extraction operation can be employed. In order to increase the cleaning efficiency, it is preferable to use an aqueous solution of isopropyl alcohol of about several tens of wt %. 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 hydrophobic organic solvent. Usually, it can be carried out in the range of 45 to 70°C.

The gelled body from which impurities such as salts have been removed as described above is recovered from the liquid. For recovery, the gelled product dispersed in the hydrophobic organic solvent may be separated by filtration. Then, the hydrophobic organic solvent is removed (that is, dried) from the gelled product obtained by filtration. The drying temperature is preferably higher than the boiling point of the solvent and lower than the decomposition temperature of the surface treatment agent such as the silylating agent and the organic nanofibers, and the pressure is preferably normal pressure or reduced pressure.

In this way, a spherical silica airgel in which nanofibers are dispersed (complexed) in silica can be produced.

The powder produced as described above is composed of spherical silica aerogel. The term "silica" as used herein means silicon dioxide, and is a general term for substances composed of silicon dioxide, and is expressed as SiO ₂ . 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 a component that constitutes the nanofiber used, and a component derived from a hydrophobizing treatment agent when hydrophobization is performed.

Further, according to the above production method, the silica airgel particles are generally spherical with an average circularity of 0.8 or more. The average circularity is 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.

[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.

Moreover, the spherical silica airgel powder produced by the production method of the present invention described above usually has the following properties.

Regarding the particle size, the volume cumulative 50% diameter (D50) measured by the Coulter counter method is usually in the range of 1 to 30 μm, and can be in the range of 1 to 20 μm, further in the range of 1 to 10 μm. is. The particle size depends on the particle size when forming the W/O emulsion.

The specific surface area determined by the BET method based on the nitrogen adsorption method is usually 400 to 1000 m ² /g. The larger the specific surface area of the spherical silica airgel powder, the smaller the particle size of the primary particles that make up the porous structure (network structure) of the independent particles, which enhances the thickening effect 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 of the spherical silica airgel powder becomes too ^large , the pore volume becomes small and the oil absorption becomes small. more preferred. Generally, it is difficult to obtain an airgel powder with a specific surface area greater than 1000 m ² /g.

In the present invention, the specific surface area by the BET method is obtained by drying the sample to be measured under a vacuum of 1 kPa or less at a temperature of 150 ° C. for 2 hours or more, and then only on the nitrogen adsorption side at liquid nitrogen temperature. It is a value obtained _by obtaining an adsorption isotherm and analyzing it by the BET method.

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 spherical 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., 73, 373 (1951) (hereinafter sometimes referred to as "BJH pore volume"). , are pores with a radius of 1 to 100 nm, and the cumulative value of the volume of pores in this range is the pore volume in the present invention.

The peak pore radius of the spherical silica airgel powder 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 powder is usually characterized by having a high oil absorption, and the spherical silica airgel powder of the present invention also generally has an oil absorption of 400 mL/100 g or more, and is 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 700 mL/100 g at maximum.

In the present invention, the oil absorption is measured according to the method described in JIS K6217-4 "Determination of Oil Absorption".

The spherical silica airgel powder produced by the present invention is usually hydrophobic when subjected to hydrophobization as described above. Moreover, since it is hydrophobic, it absorbs less water, which causes deterioration over time, and improves compatibility with hydrophobic resins, so it is 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. Hydrophobization of the spherical silica airgel can be achieved, specifically, by treating the spherical silica airgel with a silylating agent to introduce organic silyl groups onto the surface thereof.

Here, whether or not the silica airgel powder 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 powder composed of the spherical silica airgel of the present invention preferably has an M value of 30 to 55 vol%, more preferably 35 to 55 vol%, and particularly preferably 40 to 55 vol%.

In addition, carbon content can be cited as one of the indexes indicating that the spherical silica airgel powder is hydrophobic. The carbon content contained in the powder made of hydrophobic spherical silica airgel is derived from organic nanofibers and surface treatment agents, and is oxidized in air or oxygen at a temperature of about 1000 to 1500 ° C. It can be measured by quantifying the amount of carbon dioxide generated during treatment.

The spherical 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 more preferable it is because when the powder made of spherical silica airgel is used as an additive for foundation, it is possible to prevent the makeup from falling off due to sweat, but the powder made of hydrophobic spherical silica airgel is preferable. , it is difficult to obtain a large amount exceeding 12% by mass by general hydrophobizing treatment.

The following physical properties can also be expressed due to the nanofibers used. That is, when 0.2 to 2% by mass of organic nanofibers, particularly cellulose nanofibers are used to form a composite, the compressive strength can be increased.

That is, conventional spherical silica airgel has a compressive strength of less than 35 MPa at the highest, but it is possible to obtain a compressive strength of 35 MPa or more, particularly 40 MPa or more by combining with organic nanofibers.

The compressive strength is the arithmetic mean value of the compressive strength of particles with a particle diameter within the range of D50±20% as determined by microscopic observation when the particles are deformed by 10%.

(Application)
The spherical silica airgel powder produced by the production method of the present invention can be used for various purposes. For example, those compounded with organic nanofibers have high compressive strength and are used as additives for cosmetics, specifically foundations. When used as an agent, it has excellent appearance retention and provides a smooth touch. In addition, as a silica airgel, 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. It can be suitably used as cosmetics such as make-up/skin care cosmetics, deodorants, and hair styling products.

EXAMPLES Examples are given below to specifically describe the present invention. However, 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 powder composed of hydrophobic spherical silica airgel produced in Examples 1 to 5 and Comparative Examples 1 and 2 was tested for the following items.

(D50)
Silica airgel powder was added to ethanol and ultrasonically dispersed for 30 minutes. The volume cumulative 50% diameter (D50) of the resulting ethanol dispersion was measured using a precision particle size distribution analyzer Multisizer 3 manufactured by Beckman Coulter, Inc. using a 50 μm aperture tube.

(compressive strength)
A microcompression tester (MZCT-W510-J) manufactured by Shimadzu Corporation was used. Using the "specimen size measurement function (microscope)" attached to the tester, randomly select 10 particles with a particle size of D50 (μm) ± 20%, load rate 4.5 mN / sec, load maintenance The compressive strength at 10% deformation was measured for each particle under the measurement conditions of 5 seconds, and the arithmetic mean was obtained.

(Specific surface area, pore volume and oil absorption)
BET specific surface area and BJH pore volume 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 airgel floats in water, but is completely suspended in methanol. Utilizing this fact, the modified hydrophobicity measured by the following method was defined as the M value and used as an indicator of the hydrophobization treatment by the silica airgel surface hydrophobic group.

0.2 g of silica airgel was added to 50 ml of water in a 200 mL beaker and stirred with a magnetic stirrer. Methanol was added to this using a burette, and added dropwise at the end point when the entire amount of the silica airgel was wetted and suspended in the solvent in the beaker. 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 silica airgel powder was observed using a Hitachi High-Technologies SEM (S-5500) at an acceleration voltage of 3.0 kV, secondary electron detection, and a magnification of 1000 times. By image analysis of the obtained SEM image, the circularity of the silica airgel particles was calculated according to the following formula. The average circularity is obtained by calculating the circularity of 2000 or more silica airgel particles 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 was measured using an elemental analyzer (vario MICRO cube) manufactured by Elementor Japan Co., Ltd.

<Example 1>
While stirring 100 g of sulfuric acid with a stirring blade, 100 g of sodium silicate was gradually added to prepare an aqueous silica sol. At this time, the pH was 3.0.

Cellulose nanofibers (product name: Rheocrysta I-2SX, solid content 2.1%, Daiichi Kogyo Seiyaku Co., Ltd.) are added to 200 g of the aqueous silica sol prepared by the above method, and the amount of nanofibers is 0 with respect to the silica content in the aqueous silica sol. .2 wt % was added and dispersed by stirring for 1 minute at 8400 rpm using a homogenizer (manufactured by IKA, T25BS1).

108 g of the prepared nanofiber-dispersed aqueous silica sol was taken, 160 g of heptane was added, and 1.6 g of sorbitan monooleate was added. This solution was stirred for 2.5 minutes at 9000 rpm using a homogenizer to form a W/O emulsion.

The resulting W/O emulsion was gelled at 70° C. for 6 hours while stirring with a stirring blade. Subsequently, 40 g of isopropyl alcohol and 60 g of ion-exchanged water were added, and the O phase and W phase were separated while stirring with a stirring blade. Subsequently, 1.60 g of 0.5 mol/L sodium hydroxide aqueous solution was added. At this time, the pH of the W phase was 5.0. The gelled body was aged at 70° C. over 3 hours. The W phase was recovered by removing the O phase by decantation.

Silylation treatment was performed by adding 10 g of 35% hydrochloric acid and 12 g of hexamethyldisiloxane to the obtained W phase and keeping the mixture in a water bath at 70° C. for 12 hours while stirring.

After the silylation treatment, 7.14 g of a 48% sodium hydroxide aqueous solution was added while stirring with a stirring blade to carry out neutralization treatment. Subsequently, 100 g of heptane was added to extract the gelled product, which was washed twice with 100 g of deionized water.

The obtained gelled product after silylation was filtered with a suction filter. The gelled body was dried and heated at 100° C. for 16 hours or more under vacuum pressure to obtain a powder composed of hydrophobic spherical silica aerogel. Table 1 shows the evaluation results of physical properties.

<Example 2>
The same operation as in Example 1 was performed, except that the amount of cellulose nanofiber was added so as to be 2 wt % with respect to the silica content in the aqueous silica sol. Table 1 shows the evaluation results of physical properties.

<Example 3>
The same operation as in Example 1 was performed, except that the amount of cellulose nanofiber was added so as to be 10 wt % with respect to the silica content in the aqueous silica sol. Table 1 shows the evaluation results of physical properties.

<Example 4>
A nanofiber-dispersed aqueous silica sol was prepared in the same manner as in Example 1, except that the amount of cellulose nanofibers added was 2 wt % relative to the silica content in the aqueous silica sol. Subsequently, 108 g of the prepared nanofiber-dispersed aqueous silica sol was taken, 160 g of heptane was added, and 1.6 g of sorbitan monooleate was added. This solution was stirred for 3 minutes at 5000 rpm using a homogenizer to form a W/O emulsion. After that, the same operations as in Example 1 were performed. Table 1 shows the evaluation results of physical properties.

<Example 5>
A nanofiber-dispersed aqueous silica sol was prepared in the same manner as in Example 1, except that the amount of cellulose nanofibers added was 2 wt % relative to the silica content in the aqueous silica sol. Subsequently, 108 g of the prepared nanofiber-dispersed aqueous silica sol was taken, 160 g of heptane was added, and 1.6 g of sorbitan monooleate was added. This solution was stirred for 3 minutes at 11000 rpm using a homogenizer to form a W/O emulsion. After that, the same operations as in Example 1 were performed. Table 1 shows the evaluation results of physical properties.

<Comparative Example 1>
In Example 1, a spherical silica airgel was produced without the step of dispersing cellulose nanofibers. Table 1 shows the evaluation results of physical properties.

<Comparative Example 2>
In Example 4, a spherical silica airgel was produced without the step of dispersing cellulose nanofibers. Table 1 shows the evaluation results of physical properties.

Claims (3)

(1) Step of preparing an aqueous silica sol in which nanofibers are dispersed (2) Step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W/O emulsion (3) Gelating the silica sol by heating A spherical silica airgel powder characterized by comprising a step of converting the W/O type emulsion into a dispersion liquid of a gelled body by allowing the W/O emulsion to separate and recover the gelled body in the above order. manufacturing method. 2. The method for producing spherical silica airgel powder according to claim 1, further comprising a step of hydrophobizing the gelled body before separating and recovering the gelled body. 3. The method for producing spherical silica airgel powder according to claim 1, wherein the nanofibers are organic nanofibers.