JP6966247B2 - Spherical silica airgel, its manufacturing method, and its use - Google Patents

Description

The present invention relates to a spherical silica airgel, specifically a spherical silica airgel having a particle D50 diameter of more than 20 μm and 200 μm or less, and a method for producing the same.

In recent years, due to the importance of preventing and controlling global warming, which is a global environmental problem, energy saving has been desired, and heat is efficiently used in equipment for cooling and heat insulation of living environments, and for cooling and heating. Insulation materials have been developed for use. In addition, the development of super-insulated wall materials is also active in order to reduce energy consumption by heating and cooling houses and buildings.

General heat insulating materials include inorganic fibers such as glass wool and rock wool, inorganic foams, and resin foams such as urethane foam. However, for energy saving, higher performance heat insulating materials are strongly required. Has been done.

Silica airgel is a material having a high porosity and has excellent heat insulating properties. The silica airgel referred to here means a solid material having a porous structure and accompanied by a gas as a dispersion medium, and particularly means a solid material having a porosity of 60% or more. The porosity is a value obtained by expressing the amount of gas contained in the apparent volume as a volume percentage.

Solid conduction (propagation of thermal vibration), convection, and radiation each contribute to heat conduction inside an object, and convection generally contributes the most to materials with a large porosity. On the other hand, in silica airgel, since the pore diameter is as small as about 10 to 100 nm, the movement of gas in the voids is greatly restricted, and heat conduction due to convection is significantly hindered. Therefore, silica airgel has excellent heat insulating properties.

For example, as a method for producing silica airgel, a method is known in which an alkoxysilane is used as a raw material and a gel-like compound obtained by polycondensing the hydrolysis product of the alkoxysilane is dried under supercritical conditions of a dispersion medium. (Patent Document 1). Alternatively, a sol is prepared by using an alkali metal silicate as a raw material and contacting the alkali metal silicate with a cation exchange resin or adding a mineral acid to the alkali metal silicate. There is also known a method of gelling the gel and then drying the gel under supercritical conditions of a dispersion medium (Patent Documents 2 and 3).

Since the silica airgel produced by such a method has a fine silica skeleton, it exhibits excellent mechanical strength in spite of having a high porosity.

In the above-mentioned known production method, by drying and removing the dispersion medium in the gel under supercritical conditions, the dispersion medium can be replaced with a gas while suppressing drying shrinkage, and a silica airgel having a high porosity can be produced. I have to. However, since the cost of silica airgel dried under the above supercritical conditions is high to realize the supercritical conditions, the actual use is limited to special ones commensurate with such high cost. Therefore, an atmospheric drying method has been proposed for the purpose of cost reduction (Patent Document 4).

Applications of silica airgel as a heat insulating agent include applications of using it as an additive for heat insulating paint, use of it as a core material of a vacuum heat insulating material, and use of it as a heat insulating sheet in combination with a non-woven fabric. In such applications, the characteristics of silica airgel that contributes to heat insulation performance include a large pore capacity, a small bulk density, and a large porosity, and silica airgel is considered to be an effective heat insulating material.

When filling a base material such as resin as an additive for heat insulating paint, the heat insulating performance depends on the amount of addition, but in silica airgel, the increase in viscosity at the time of addition is remarkably difficult to increase the amount of addition.

In order to suppress the increase in the viscosity of the base material, it is considered effective to reduce the surface area of the filler with respect to the base material. For example, there are methods such as making the shape of the filler spherical instead of amorphous, increasing the particle size of the filler, and making the particle size distribution broad.

In producing the spherical silica airgel, as described in the applicant's prior application patent (Patent Document 5), the silica sol aqueous solution is emulsified using a homogenizer to obtain a W / O type emulsion, and then the silica sol is gelled. A method has been proposed to make it. Since the homogenizer is excellent in refining dispersed particles in an emulsion, a more stable emulsion can be obtained, but it is difficult to obtain dispersed particles having a large particle size, and a spherical silica airgel having a D50 diameter of more than 20 μm has actually been obtained. No.

Further, a method for producing a spherical airgel in which silica sol is discharged from a tube to form droplets has also been proposed (Patent Documents 6 and 7). However, in this method, the D50 diameter of the resulting airgel is as large as several hundred μm to several mm, and it is difficult to obtain a spherical silica airgel having a diameter of 200 μm or less.

U.S. Pat. No. 4,402,927 Japanese Unexamined Patent Publication No. 10-236817 Japanese Unexamined Patent Publication No. 06-040714 Japanese Unexamined Patent Publication No. 07-257918 Japanese Patent No. 4960534 Special Table 2002-500557 Gazette Japanese Unexamined Patent Publication No. 2002-509069 Japanese Unexamined Patent Publication No. 2014-083007

Since the spherical silica airgel obtained by the above-mentioned prior art has a spherical shape as described above, it can be blended into a base material such as a resin with considerably good filling property. However, in order to sufficiently exert the effect of the compounding purpose in each application such as exerting the heat insulating effect more effectively, it is desired to further improve the filling property. However, the spherical airgels obtained by the conventional manufacturing method have a D50 diameter in the range of 1 to 20 μm and a range of several hundred μm to several mm, and there are spherical silica airgels in the range of more than 20 μm and 200 μm or less. I wasn't. Therefore, from the viewpoint of dense filling by adding aerogels having different particle sizes in combination, it is necessary to develop a spherical silica airgel having a D50 diameter of more than 20 μm and 200 μm or less.

Therefore, an object of the present invention is to obtain a silica airgel having a good spherical property in the above D50 diameter range.

As a result of diligent studies to solve the above problems, the present inventors have made it possible to disperse the aqueous silica sol at the time of forming an emulsion in the method for producing spherical silica airgel by using a mixer having rotary blades. A novel spherical silica airgel having a diameter of D50 was obtained, and it was found that the above-mentioned problems could be solved, and the present invention was completed.

That is, in the present invention, the specific surface area by the BET method is 300 to 1000 m ² / g.
The peaks of the pore volume and the pore radius by the BJH method are 3 to 8 ml / g and 10 to 50 nm, respectively.
In the particle size distribution measured by the laser diffraction / scattering method, the volume-based cumulative 50% diameter (D50) value is more than 20 μm and 200 μm or less.
The average circularity obtained by the image analysis method Ri der 0.8 or higher,
Volume-based ratio of cumulative 10% diameter and (D10) and volume-reduced cumulative 90% diameter (D90) (D10 / D90) is spherical silica airgel, characterized in 0.1-0.5 der Rukoto.

Since the spherical silica airgel of the present invention has an appropriate particle size, the filling rate of the airgel particles is high when mixed with the airgel particles obtained by the production methods of Patent Documents 5, 6 and 7 and mixed with the binder. , A heat insulating material with high heat insulating performance can be obtained.

For example, when it is added to a base material as a heat insulating filler, it exerts a heat insulating effect more effectively. Further, examples of other uses include general methods of using silica airgel, such as cosmetics and pharmaceutical carriers.

The flowchart which shows the preferable manufacturing method of the airgel of this invention. The schematic diagram explaining the mixer which has a rotary vane. SEM image of the spherical airgel of the present invention produced in Example 2.

The forms shown below are examples of the present invention, and the present invention is not limited to these forms. Unless otherwise specified, the notation "A to B" in the numerical range means "A or more and B or less". When a unit is attached only to the numerical value B in such a notation, the unit shall be applied to the numerical value A as well.

Generally, silica airgel is a porous silica in which a solvent contained in wet silica gel is dried while maintaining a solid network structure and replaced with air, and has a porosity of 80% or more. The spherical silica airgel in the present specification is not limited to those obtained by supercritical drying, but also includes those obtained by atmospheric drying.

Further, the shape of the silica airgel of the present invention is spherical, and due to this, the filling property is superior to that of the crushed type.

The individual independent particles (secondary particles) constituting the spherical silica airgel of the present invention have an average circularity of 0.8 or more. It is preferably 0.85 or more. The "average circularity" is defined as SEM images observed with secondary electron detection, low acceleration voltage (1 kV to 3 kV), and magnification of 100 times using a scanning electron microscope (SEM). The value C (circularity) defined by the equation (1) is obtained (image analysis), and this circularity C is obtained as an additive average value for 2000 or more particles (image analysis method). At this time, the particle group forming one aggregated particle is counted as one particle.

[In the formula (1), S represents the area (projected area) that the particles occupy in the image. L represents the length (peripheral length) of the outer peripheral portion of the particle in the image. ]
As the average circularity becomes larger than 0.8 and approaches 1, the individual particles constituting the spherical silica airgel have a shape close to a true sphere, and the number of agglomerated particles decreases.

Spherical silica airgel of the present invention, the ratio by BET method surface area (BET specific surface area) is 300~1000m ² / g, preferably, 400~900m ² / g, more preferably, is 500~800m ² / g .. The larger the specific surface area, the smaller the particle size of the primary particles constituting the porous structure (mesh structure) of the independent particles (secondary particles) of the spherical silica airgel, and the more complicated the network structure, the higher the particle strength. , Which is preferable in preventing pore destruction when added or dispersed in the substrate. However, if it becomes larger than the above range, it becomes difficult to form the pore structure of the spherical silica airgel, and as a result, the pores are crushed.

For the specific surface area by the BET method, the sample to be measured is dried at a temperature of 200 ° C. for 3 hours or more under a vacuum of 1 kPa or less, and then an adsorption isotherm of only the adsorption side of nitrogen at the liquid nitrogen temperature is drawn. It is a value obtained and analyzed by the BET method.

The spherical silica airgel of the present invention has a pore volume of 3 to 8 mL / g according to the BJH method, preferably 3 to 7 mL / g, and more preferably 3.5 to 6 mL / g. If the pore volume is smaller than the above range, the heat insulating effect per weight becomes small, which is not preferable.

Further, it is difficult to obtain a spherical silica airgel having a pore volume larger than the above, and even if it is obtained, the skeletal strength for forming the pore structure is reduced, so that a load when adding or dispersing the airgel to the substrate, etc. May cause the pores to collapse.

In the present invention, the pore volume of the spherical silica airgel by the BJH method obtains an adsorption isotherm in the same manner as in the above-mentioned BET specific surface area measurement, and the BJH method (Barrett, EP; Joyner, LG; Halenda, PP, J) It was obtained by analysis according to Am. Chem. Soc. 73, 373 (1951). (Hereinafter, it may be referred to as "BJH pore volume".) The pores measured by this method are The pores have a radius of 1 to 100 nm, and the integrated value of the volume of the pores in this range is the pore volume in the present invention.

In the spherical silica airgel of the present invention, when the specific surface area and the pore volume are within the above-mentioned suitable ranges, the peak of the pore radius by the BJH method is usually in the range of 10 to 50 nm, preferably 10. It is in the range of ~ 40 nm, more preferably 10-30 nm. If the pore radius peak is larger than the above range, the heat insulating effect is reduced due to the convection heat transfer of the gas, which is not preferable. Further, when the pore radius peak is smaller than the above range, it is difficult to obtain a spherical silica airgel. The peak of the pore radius by the BJH method is obtained by analyzing the adsorption side of the adsorption isotherm by the BJH method in the same manner as the pore volume described above, and the cumulative pores based on the logarithmic pore radius. The pore radius (volume distribution curve) plotted with the volume differentiation on the vertical axis and the pore radius on the horizontal axis is the pore radius that takes the maximum peak.

In the spherical silica airgel of the present invention, the volume-based cumulative 50% diameter (D50), that is, the so-called median diameter in the particle size distribution measured by the laser diffraction / scattering method is more than 20 μm and 200 μm or less, preferably more than 50 and 150 μm or less. It is more preferably 60 to 150 μm.

Specifically, the median diameter is such that a container containing 0.3 g of a sample added to 40 mL of ethanol (99.5 vol%) is placed in an ultrasonic cleaner and dispersed at 90 W for 5 minutes as a sample solution. , A cumulative 50% diameter based on the volume obtained by measuring by a laser diffraction / scattering method. Similarly, the volume-based cumulative 10% diameter is represented by D10, and the volume-based cumulative 90% diameter is represented by D90.

In spherical silica airgel of the present invention, D10 / D90 is Ri 0.1-0.5 der, good Mashiku to be 0.15 to 0.45, still to be 0.15 to 0.25 preferable. Within the above range, the filling property when filling the base material is excellent. In general, the larger the value of D10 / D90, the sharper the particle size distribution, and the smaller the value of D10 / D90, the broader the particle size distribution. That is, the smaller D10 / D90 is, the better the filling property is, but it is difficult to obtain a spherical silica airgel in which D10 / D90 exceeds the above lower limit range and is small. Even if it is obtained, the average circularity of the spherical silica airgel decreases and does not fall within the above range, or the crushed silica airgel is mixed in the spherical silica airgel and the yield of the spherical silica airgel decreases. It is normal.

The spherical silica airgel of the present invention is usually hydrophobic. Generally, when the silica airgel is hydrophobized, it is extremely useful because it adsorbs less water, which causes deterioration over time. Further, it is preferable that it is hydrophobized from the viewpoint that it can be produced without using a supercritical drying process.

As a specific example of the embodiment in which the spherical silica airgel of the present invention is hydrophobized, there is an embodiment in which a methylsilyl group is introduced on the surface by treating with a silylating agent or the like.

Whether or not the spherical silica airgel of the present invention is hydrophobic can be confirmed extremely easily by putting the powder together with pure water in a container and stirring or the like. If it is hydrophobized, the powder does not disperse in water, and if it is allowed to stand, it regains a state of being divided into two layers, one with water as the lower layer and the other with powder as the upper layer.

Further, as one of the indexes indicating that the spherical silica airgel of the present invention is hydrophobic, it can be determined whether or not it is hydrophobic by measuring the M value by the method described later.

To measure the M value, first, 0.2 g of the spherical silica airgel sample of the present invention is added to a beaker having a capacity of 250 mL containing 50 mL of water, and the mixture is stirred with a magnetic stirrer. To this, methanol is added using a burette using a tube so as not to come into direct contact with the sample, and titration is performed starting from the point where the entire amount of the sample is dispersed and suspended in the solution. The volume percentage (vol%) of methanol in the methanol-water mixed solvent at the end point is defined as the M value.

When the spherical silica airgel is hydrophobized, the M value is 20 to 70 vol%, preferably 30 to 60 vol%, and more preferably 40 to 60 vol%.

In addition, carbon content can be mentioned as one of the indicators indicating that the spherical silica airgel of the present invention is hydrophobized. The carbon content contained in the spherical silica airgel can be measured by quantifying the amount of carbon dioxide generated during the oxidation treatment in air or oxygen at a temperature of about 1000 to 1500 ° C.

When the spherical silica airgel of the present invention is hydrophobized, the carbon content contained therein is 3 to 12% by mass, preferably 4 to 11% by mass, and more preferably 5 to 10% by mass. .. It is difficult to obtain a large spherical silica airgel exceeding 12% by mass while maintaining the above physical characteristics by a general hydrophobizing treatment.

It is also possible to remove the hydrophobizing agent by performing an oxidation treatment in air or oxygen as described above to obtain a hydrophilic spherical silica airgel. The oxidation treatment can be carried out in a commonly used electric furnace, and can be carried out by holding at a temperature of 400 to 700 ° C., preferably 500 to 600 ° C. for 3 hours or more.

In the spherical silica airgel of the present invention, the surfactant used in the production may remain. The upper limit of the residual amount of the surfactant is preferably 1% or less, preferably 8000 ppm or less, and more preferably 6000 ppm or less. The lower limit of the residual amount of the surfactant is 100 ppm or more, preferably 1000 ppm or more.

When the residual amount of the surfactant is too large, for example, in an application in which spherical silica airgel is dispersed in an aqueous emulsion in which a resin is dispersed to be an additive for a heat insulating paint, the resin easily infiltrates into the pores. Insulation performance may not be fully exhibited.
Further, when the residual amount of the surfactant is less than the above range, the dispersibility of the spherical silica airgel tends to decrease, and for example, in the application as an additive for heat insulating paint, it can be sufficiently dispersed in the system. However, thermal cross-linking may occur and the heat insulating property may decrease.

The amount of surfactant remaining in the spherical silica airgel can be measured by pyrolysis gas chromatography. The principle is that the surfactant is thermally decomposed by a pyrolyzer which is a thermal decomposition apparatus, and the decomposition product is quantified by gas chromatography.

The method for producing the spherical silica airgel of the present invention is not particularly limited, but according to the study by the present inventors, as shown in FIG. 1, it can be suitably produced by the same flow as in Patent Document 8. In particular, in the emulsion forming step S2 of the above flow, it is important to select a mixer having rotary blades as a method for dispersing the aqueous silica sol in the hydrophobic organic solvent. In particular,
(1) Step of preparing aqueous silica sol (aqueous silica sol adjusting step S1);
(2) A step of forming a W / O type emulsion using the aqueous silica sol as the W phase (emulsion forming step S2);
(3) A step of gelling the silica sol by heating to use the W / O type emulsion as a dispersion liquid of a gelled product (gelling step S3).
(4) A step of separating into two layers, an O phase and a W phase (W phase separation step S4);
(5) A step of recovering the W phase to obtain a dispersion liquid in which the gelled product is dispersed in the W phase (W phase recovery step S5);
(6) A step of adding a silylating agent to the dispersion (silylation treatment step S6);
(7) A step of extracting the gelled product with a hydrophobic organic solvent (gelled product extraction step S7);
(8) Step of recovering gelled product (gelled product recovery step S8);
Is a method for producing a spherical silica airgel, which comprises the above-mentioned items in the above order.

The greatest feature of the present invention is that in the above-mentioned "(2) Emulsion forming step S2", a mixer having rotary blades is used as a method for dispersing the aqueous silica sol in a hydrophobic organic solvent. That is, by using a specific mixer, it has become possible to obtain an airgel having a particle size range of the present invention. Hereinafter, they will be described in order.

(Aqueous silica sol adjusting step S1)
The aqueous silica sol adjusting step S1 (hereinafter, may be abbreviated as “S1”) may be carried out by appropriately selecting a known adjusting method for the aqueous silica sol. Typical methods for preparing an aqueous silica sol include a method using an alkali metal silicate or the like as a raw material and a method for hydrolyzing alkoxysilane.

Specific examples of alkoxysilanes that can be preferably used in the present invention include tetramethoxysilane and tetraethoxysilane.

Examples of the alkali metal silicate include potassium silicate and sodium silicate, and the composition formula is represented by the following formula (3).
m (M2O) ・ n (SiO2) (3)
[In equation (3), m and n each independently represent a positive integer, and M represents an alkali metal atom. ]
Among the above-mentioned raw materials for producing a silica sol, an alkali metal silicate can be preferably used because of its low cost, and sodium silicate, which is easily available, is preferable. Hereinafter, a form in which sodium silicate is used as a raw material for producing a silica sol and silica is produced as a spherical silica airgel will be described as a typical example, but even when other raw materials are used, an aqueous silica sol is produced and gelled by a known method. The spherical silica airgel of the present invention can be obtained in the same manner.

When an alkali metal silicate such as sodium silicate is used, it can be neutralized with a mineral acid such as hydrochloric acid or sulfuric acid, or ^{a cation exchange resin whose counter ion is hydrogen ion (H +} ) (hereinafter referred to as cation exchange resin). , "Acid-type cation exchange resin"), the silica sol can be prepared by substituting the alkali metal atom in the alkali metal silicate with a hydrogen atom.

As a method for preparing a silica sol by neutralizing with the above acid, a method of adding an aqueous solution of an alkali metal silicate to an aqueous solution of an acid while stirring the aqueous solution, or an aqueous solution of an acid and an alkali silicate. Examples thereof include a method of colliding and mixing an aqueous solution of a metal salt in a pipe (see, for example, Japanese Patent Publication No. 4-54419).

In the present invention, it is preferable that the pH of the adjusted silica sol is in the acidic range. Specifically, the amount of acid used when preparing the aqueous silica sol is preferably 1.05 to 1.2 as the molar ratio of hydrogen ions to the alkali metal content of the alkali metal silicate. When the amount of acid is in this range, the pH of the prepared silica sol is about 1 to 5. It is preferably 2.5 to 3.5.

The method for preparing a silica sol using the acid type cation exchange resin described above can be carried out by a known method. For example, a method of passing an aqueous solution of an alkali metal silicate having an appropriate concentration through a packed bed filled with an acid cation exchange resin, or adding an acid cation exchange resin to an aqueous solution of an alkali metal silicate and adding an acid cation exchange resin. Examples thereof include a method of separating the acid type cation exchange resin by mixing, chemically adsorbing the alkali metal ion on the cation exchange resin, removing it from the solution, and then filtering it. At that time, the amount of the acid-type cation exchange resin used needs to be equal to or larger than the amount at which the alkali metal contained in the solution can be exchanged.

As the acid type cation exchange resin, known ones can be used without particular limitation. For example, a styrene-based, acrylic-based, methacryl-based, or other ion-exchange resin having a sulphonic acid group or a carboxyl group as an ion-exchange group can be used. Of these, a so-called strong acid type cation exchange resin having a sulfonic acid group can be preferably used.

The acid type cation exchange resin can be regenerated by contacting it with a known method, for example, sulfuric acid or hydrochloric acid, after using it for exchanging an alkali metal. The amount of acid used for regeneration is usually 2 to 10 times the exchange capacity of the ion exchange resin.

As for the concentration of the silica sol prepared by the above method, gelation is completed in a relatively short time, shrinkage during drying can be suppressed by sufficiently forming the skeleton structure of the silica particles, and a large pore capacity is obtained. The concentration of silica (SiO2 equivalent) is preferably 20 g / L or more, more preferably 40 g / L or more, and particularly preferably 50 g / L or more. On the other hand, good heat insulation performance can be easily obtained by relatively reducing the density of silica particles, obtaining a good pore volume, and reducing heat conduction (solid conduction) by the silica skeleton itself. Therefore, it is preferably 160 g / L or less, more preferably 120 g / L or less, and particularly preferably 100 g / L or less.

(Emulsion forming step S2)
The emulsion forming step S2 (hereinafter, may be simply referred to as “S2”) is a step of dispersing the aqueous silica sol obtained in S1 in a hydrophobic organic solvent to form a W / O emulsion. That is, an emulsion is formed using the aqueous silica sol as a dispersoid and a hydrophobic organic solvent as a dispersion medium. By forming such a W / O emulsion, the dispersoid silica sol becomes spherical due to surface tension or the like. Therefore, by gelling the silica sol which has a spherical shape and is dispersed in a hydrophobic solvent, it becomes spherical. Gelled product can be obtained. Further, by going through the emulsion forming step S2 for forming the W / O emulsion in this way, it becomes possible to produce an airgel having a high circularity of 0.8 or more.

In particular, in the present invention, in the S2, a W / O emulsion is formed so that the D50 diameter of the droplet is roughly the D50 diameter of the target spherical silica airgel in the particle size distribution of the dispersoid (W phase) droplet. It is important to. This is because there is a general correspondence between the average particle size of the silica sol droplets in the W / O emulsion and the average particle size of the target spherical silica airgel.

As a method of forming a W / O emulsion, that is, dispersing an aqueous silica sol in a hydrophobic organic solvent, means such as membrane emulsification and mechanical emulsification can be mentioned. Mechanical emulsification using a stirring and mixing device is preferable because it is likely to occur and it is difficult to control the particle size. Examples of the stirring / mixing device include a mixer, a homogenizer, and a static mixer. Generally, the smaller the particle size of the dispersed particles, the better the stability of the emulsion. Therefore, conventionally, a homogenizer has been preferably used.

The homogenizer is a mechanical device that generally applies a vigorous mechanical action to a two-phase flow of solid and liquid, liquid and liquid, etc. to produce a uniform and stable emulsion or suspension, and is a strong stirring of a high-speed rotary blade. There are methods that utilize the action, methods that utilize the strong shearing action that is received when a high-pressure fluid flows through a narrow flow path, methods that use ultrasonic waves, etc., and methods that utilize the strong stirring action of the rotary blade are generally used. The rotation speed is 1000 rpm or more. Specific examples include a milder manufactured by Matsubo, an ultra-talax homogenizer manufactured by IKA, and a laboratory solution manufactured by Primix.

The above-mentioned static mixer is a static mixer without a drive unit. Specifically, a static mixer manufactured by Noritake Co., Ltd. and SS. M, OHR mixer manufactured by OHR Fluid Engineering Laboratory Co., Ltd. and the like can be mentioned.

The mixer is generally a device for stirring and mixing by applying power to a uniform layer, and is generally used at a rotation speed of less than 1000 rpm. Specific examples thereof include a mixer having a rotary blade, a mixer that jets and agitates a fluid, and the like.

In order to obtain the spherical silica airgel of the present invention, it is necessary to use a mixer having a rotary blade among the above-mentioned stirring and mixing devices.

By the way, in the case of forming a W / O type emulsion to produce a spherical silica airgel as in the present invention, it takes a gelation time after the emulsion is formed until the silica sol gels in the gelation step S3 described later. Therefore, it is necessary to keep the dispersed state of the emulsion stable until the gelation is completed.

Here, when a mixer is selected as the stirring and mixing device for mechanical emulsification, the stability of the obtained emulsion is low because the particle size is larger than that when the homogenizer is selected. However, in the gelation step described later, even if stirring is continued using a mixer having rotary blades, the circularity is not significantly impaired. Therefore, after forming the emulsion, stirring can be continued under the same conditions using a mixer having rotary blades even in the gelation step. That is, even if the stability of the emulsion is low, it is possible to maintain the dispersed state of the aqueous silica sol in the emulsion by continuing stirring under the same conditions.

On the other hand, when a homogenizer is used, if the homogenizer is similarly stirred in the gelling step, it becomes difficult to maintain the circularity due to the rotation speed and the shearing action due to the principle. That is, when a homogenizer is used, a highly stable emulsion that can maintain the dispersed state of the emulsion after the emulsion is formed until the gelation is completed is required.

In the present invention, the "mixer having rotary blades" is a container in which a predetermined amount of an aqueous silica sol and a hydrophobic solvent can be charged, and is provided with rotary blades capable of adjusting the rotation speed from the upper part of the container. ..

Examples of the shape of the rotary blade include a paddle blade, an inclined paddle blade, a swept wing, an anchor blade, and the like, and the number of blades is generally 2 to 6. Among these, a four-inclined paddle blade and a three-sheet swept wing are preferably used in that an appropriate shearing force can be adjusted while performing uniform stirring.

In order to obtain the spherical silica airgel having the particle size range of the present invention, the mixer having the above-mentioned rotary blade is used, and further, the peripheral speed of the rotary blade is 30 m / s to 400 m / s as the stirring condition. It is preferably 50 to 350 m / s. Although it depends on the shape of the rotor blade and the like, when the same rotor blade is used, the smaller the peripheral speed, the larger the particle size of the W-phase droplet and the larger the particle size distribution. Therefore, the peripheral speed of the rotary blade may be adjusted within the above range according to the particle size of the target spherical silica airgel. Further, the larger the peripheral speed, the easier it is to make the inside of the container uniform, so that the particle size distribution tends to be narrowed.

The rotational speed of the rotary blade at the time of obtaining the peripheral speed depends on the size of the rotary blade used and the like, and therefore cannot be unconditionally stated, but is 20 to 1000 rpm, preferably 40 to 800 rpm. That is, the longer the length from the center of the rotor, the lower the rotation speed can be. In general, when the peripheral speed is the same, the longer the rotor blade is, the lower the speed at the center of the rotor blade is, so that the particle size distribution of the obtained spherical silica airgel tends to be wider.

In the present invention, the shape, length, peripheral speed, etc. of the rotor blade may be selected at any time so that a spherical silica airgel having a desired particle size and particle size distribution can be obtained.

The capacity of the mixer is not particularly limited, but usually, it may be determined in consideration of the size and capacity of the selected rotor blade, the processing amount, and the like. Specifically, it is 0.5 L to 20 m ³ , preferably 0.5 to 15 m ³ , and more preferably 1 to 10 m ³ .

Further, when the aqueous silica sol forming the W layer gels, the W / O emulsion changes to W / O suspension (suspension) to fix the particle shape, and after that point, the spherical shape is maintained. Since it cannot be refined as it is, the stirring time is limited to the time from the start of stirring until the aqueous silica sol gels.

On the other hand, since the stirring speed is low, the minimum time is required to uniformly mix the whole, so the time required for stirring is 5 to 180 minutes, more preferably 15 to 120 minutes. Minutes, more preferably 30-60 minutes.

In the stirring container, the presence / absence of accessories other than the rotor blades, for example, the presence / absence of a baffle plate and the shape thereof are not particularly limited, but accessories that assist liquid mixing of the baffle plate and the like for uniform mixing in low-speed stirring. Is preferably installed.

The liquid temperature of the hydrophobic organic solvent and the aqueous silica sol affects the gelation time of the aqueous silica sol, but the time to adjust the D50 diameter of the W / O emulsion by the rotation of the rotary blade is such that the aqueous silica sol does not gel. It is preferable that the liquid temperature of the hydrophobic organic solvent and the aqueous silica sol is maintained at 5 to 20 ° C. in order to suppress gelation.

Examples of the above-mentioned hydrophobic organic solvent include aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, and dodecane, dichloromethane, chloroform, carbon tetrachloride, dichloropropane, and kinematic viscosity of 0.65 to 10 cS. Dichloromethane oil and the like can be preferably used. Among these, heptane having an appropriate viscosity can be particularly preferably used. If necessary, a plurality of solvents may be mixed and used.

The amount of the hydrophobic organic solvent used is not particularly limited as long as the amount of the emulsion becomes W / O type. However, the amount of the hydrophobic organic solvent is preferably about 1 to 10 parts by volume with respect to 1 part by volume of the aqueous silica sol, and further, 1 to 5 parts by volume, particularly preferably 1 to 2 parts by volume.

In the present invention, it is preferable to add a surfactant when forming the above W / O emulsion. As the surfactant to be used, any of an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. Among these, nonionic surfactants are preferable because they can easily form W / O emulsions. In the present invention, since the silica sol is aqueous, a surfactant having an HLB value of 3 or more and 5 or less, which is a value indicating the degree of hydrophilicity and hydrophobicity of the surfactant, can be preferably used. In the present invention, the "HLB value" means the HLB value by the Griffin method. Specific examples of the surfactant that can be preferably used include sorbitan monooleate, sorbitan monostearate, sorbitan monosesquiolate and the like.

The amount of the surfactant used varies depending on the type and amount of the hydrophobic organic solvent used, but when heptane is used as the hydrophobic organic solvent and the amount is 2 parts by volume with respect to 1 part by volume of the silica sol, the silica sol It is preferably 0.4 to 1.2 g with respect to 100 ml. If the amount of the surfactant used exceeds this range, the separability in the gelled product extraction step S7 tends to deteriorate, and separation becomes difficult. On the other hand, if the amount exceeds this range, the stability of the emulsion deteriorates, and the circularity of the finally obtained spherical silica airgel tends to decrease.
(Gelification step S3)
The gelation step S3 (hereinafter, may be abbreviated as “S3”) is carried out in a state where droplets of the aqueous silica sol are dispersed in the hydrophobic organic solvent following the formation of the W / O emulsion in S2. This is a step of gelling an aqueous silica sol. In this step, it is preferable that the dispersed state of the emulsion formed in S2 is maintained until the gelation is completed. Specifically, the rotor blades are formed in the same manner as in the case of forming the emulsion in the S2 step. It is preferable to gel the mixture while continuing stirring using a mixer having the mixture. This makes it easy to maintain the dispersed state of the emulsion until the gelation is completed.

From the viewpoint of maintaining the dispersed state of the emulsion, it is preferable that the stirring conditions and the like are the same as those in the S2 step.

In the droplets of the aqueous silica sol, primary particles of silica are dispersed as dispersoids, and the primary particles form a three-dimensional network structure by gelation in the step to form secondary particles.

Usually, as a means for gelling the silica sol, a method of heating to a high temperature or a method of adjusting the pH of the silica sol to weakly acidic or basic is used, but in the gelling step of the present invention, the pH is maintained in an acidic range. It is preferable to carry out gelation by heating while maintaining the gel.

The pH is preferably in the range of 2 to 5, more preferably in the range of 2.5 to 3.5, and more preferably 2.5 to 3. It is particularly preferable to keep it within the range of 0.

The upper limit of the gelation temperature depends on the hydrophobic organic solvent used, and is preferably equal to or lower than the temperature at which the hydrophobic organic solvent boils. Further, in order to shorten the time required for gelation, a high temperature is preferable, and when heptane is used as the hydrophobic organic solvent, the temperature is 50 to 70 ° C, preferably 60 to 70 ° C. preferable.

The gelling time (the time from the start of gelation to the end of gelation) depends on the pH and temperature of the sol and the concentration of silica in the silica sol, so it cannot be said unconditionally. When the concentration of the silica content in the silica sol (SiO2 conversion) is 80 g / L at 70 ° C., it is preferably 30 minutes to 24 hours, more preferably 5 to 12 hours. The lower the pH, temperature and silica concentration of the sol, the longer the gelation time.

(W phase separation step S4)
In the W phase separation step S4 (hereinafter, may be abbreviated as "S4"), the dispersion solvent is separated into an O phase and a W phase, which is also generally called weaning. Is. The gelled product obtained from the above step is present on the W phase side obtained by separation.

As the W phase separation method, a known method can be adopted. Specifically, the addition of a water-soluble organic solvent, the addition of a salt, the addition of centrifugal force, the addition of an acid, the filtration, and the volume ratio It can be carried out by one or a combination of two or more selected from the changes (addition of water or hydrophobic organic solvent) and the like. Preferably, a certain amount of a water-soluble organic solvent can be added to the emulsion to separate it into an O phase and a W phase. After this step, the upper layer generally becomes the O phase and the lower layer becomes the W phase.

Examples of the above-mentioned water-soluble organic solvent include acetone, methanol, ethanol, isopropyl alcohol and the like. Of these, isopropyl alcohol can be preferably used because it is effective in increasing the efficiency of the treatment even in the silylation treatment described later.

The amount of the above-mentioned water-soluble organic solvent added is preferably adjusted according to the type and amount of the surfactant used at the time of forming the emulsion. For example, when sorbitan monooleate is used as the surfactant of the W / O type emulsion, it is necessary to add a water-soluble organic solvent having a mass of about 0.1 to 0.4 times the amount of the O phase. It can be preferably separated into an O phase and a W phase by allowing it to stand after stirring according to the above. Further, it is preferable to add water together with the water-soluble organic solvent in an amount of about 0.6 to 0.9 times by mass with respect to the amount of the O phase.

The temperature at which the S4 step is performed is not particularly limited, but it can usually be performed at about 20 to 70 ° C.

(Gelified body aging step S4')
After the above S4 step, a gelled body aging step S4'(hereinafter, may be abbreviated as "S4'") is carried out to gel by the above-mentioned operation, and then the gel is aged. preferable.

From the viewpoint of improving the compressive strength of the particles constituting the spherical silica airgel of the present invention, the gelation reaction (dehydration condensation reaction) can be further promoted by aging for about 0.5 to 12 hours after gelation. preferable. The aging can be carried out by keeping the temperature at room temperature to about 80 ° C. It is preferably held at 50 to 70 ° C, more preferably 60 to 70 ° C.

Further, in the aging step, in order to promote the gelation reaction (dehydration condensation reaction), the pH of the W phase may be adjusted by adding an alkaline agent. The alkaline agent is not particularly limited, but NaOH, KOH, ammonia and the like are generally used. The adjusted pH of the W layer is 3 to 10, preferably 5 to 8.

In this S4'step, it is preferable to leave the separated O phase as it is in the system. By leaving the O phase, the surfactant adsorbed on the gelled product can be extracted into the O phase, so that the amount of the surfactant contained in the finally obtained spherical silica airgel is adjusted. It becomes possible.

(W phase recovery step S5)
In the W phase recovery step S5 (hereinafter, may be abbreviated as “S5”), the W phase is recovered. In order to improve the treatment efficiency of the subsequent silylation treatment of the gelled product, the O phase is removed from the O phase and W phase separation solvent obtained in S4 above by, for example, decantation, and the W phase is recovered. be able to.

Here, it is not necessary to completely remove the O phase, but in the step of silylating the gelled product contained in the W phase, the O contained in the W phase can be efficiently silylated. The ratio of the phases should be as small as possible, and the amount contained in the W phase is preferably 20 wt% or less, more preferably 10 wt% or less.

(Cyrilization treatment step S6)
In the silylation treatment step S6 (silylation treatment step S6; hereinafter, it may be simply abbreviated as “S6”), the gelled product is silylated using a silylating agent after the W phase recovery step S5. .. The spherical silica airgel obtained in the silylation treatment becomes hydrophobic, and in the gelled body recovery step S7, which is performed later, shrinkage is suppressed when the gelled body is dried, and the airgel becomes porous. It makes it possible to obtain a powder that retains a high quality structure.

As a silylating agent that can be used in the present invention, a hydroxy group existing on the surface of a metal oxide (here, silica):
M-OH (4)
[In equation (4), M represents a metal atom. In formula (4), the remaining valences of M are omitted. ]
Reacts with (MO-) (4-n) SiRn (5)
[In the formula (5), n is an integer of 1 to 3, R is a hydrocarbon group, and when n is 2 or more, a plurality of Rs may be the same or different from each other. ] Can be mentioned as an example of a silylating agent capable of converting to.

By performing the silylation treatment using such a silylating agent, the hydroxy groups on the surface of the silica airgel are endcapped with hydrophobic silyl groups and inactivated, so that dehydration condensation between the surface hydroxy groups is carried out. The reaction can be suppressed. Therefore, since drying shrinkage can be suppressed even if drying is performed under conditions below the critical point, it becomes possible to obtain a hydrophobic silica airgel having a BJH pore volume of 3 mL / g or more.

As the above silylating agent, compounds represented by the following general formulas (6) to (7) are known.
RnSiX (4-n) (6)
[In formula (6), n represents an integer of 1 to 3; R represents a hydrophobic group such as a hydrocarbon group; X represents a molecule in which the bond with a Si atom is cleaved in a reaction with a compound having a hydroxy group. Represents a group that can be eliminated from (leaving group). When n is 2 or more, a plurality of Rs may be the same or different. Further, when n is 2 or less, a plurality of Xs may be the same or different. ]

[In formula (7), R1 represents an alkylene group; R2 and R3 each independently represent a hydrocarbon group; R4 and R5 each independently represent a hydrogen atom or a hydrocarbon group. ]

[In formula (8), R6 and R7 each independently represent a hydrocarbon group, and m represents an integer of 3 to 6. The plurality of R6s may be the same or different. Further, the plurality of R7s may be the same or different. ]
In the above formula (6), 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, and particularly preferably a methyl group. be.

The leaving group represented by X is a halogen atom such as chlorine or bromine; an alkoxy group such as a methoxy group or an ethoxy group; a group represented by −NH-SiR3 (in the formula, R is synonymous with R in the formula (6)). ) Etc. can be exemplified.

Specific examples of the silylating agent represented by the above formula (6) include chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, monomethyltrimethoxysilane, monomethyltriethoxysilane, and hexamethyldisilazane. 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 bonds with hydroxy groups on the silica airgel skeleton varies. For example, if n is 2, for example:
(MO-) 2SiR2 (9)
Will occur. If n is 3, then:
MO-SiR3 (10)
Will occur. By silylating the hydroxy group in this way, the silylation treatment is performed.

In the above formula (7), R1 is an alkylene group, preferably an alkylene group having 2 to 8 carbon atoms, and particularly preferably an alkylene group having 2 to 3 carbon atoms.

In the above formula (7), R2 and R3 are each independently a hydrocarbon group, and preferred groups include groups similar to R in the formula (6). R4 represents a hydrogen atom or a hydrocarbon group, and when it is a hydrocarbon group, a preferable group may be a group similar to R in the formula (6). When the gelled product is treated with the compound represented by this formula (7) (cyclic silazane), the Si—N bond is cleaved by the reaction with the hydroxy group, so that the silica airgel skeleton surface in the gelled product is cleaved. Is (MO-) 2SiR2R3 (11)
Will occur. As described above, the hydroxy group is also silylated by the cyclic silazanes of the above formula (7), and the silylation treatment is performed.

Specific examples of the cyclic silazanes represented by the above formula (7) include hexamethylcyclotrisilazane and octamethylcyclotetrasilazane.

In the above formula (8), R6 and R7 are each independently a hydrocarbon group, and preferred groups include groups similar to R in the formula (6). m represents an integer of 3 to 6. When the gelled product is treated with the compound (cyclic siloxane) represented by this formula (8), the silica airgel skeleton surface in the gelled product is exposed to
(MO-) 2SiR6R7 (12)
Will occur. As described above, the hydroxy group is also silylated by the cyclic siloxanes of the above formula (8), and the silylation treatment is performed.

Specific examples of the cyclic siloxanes represented by the above formula (8) include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.

The amount of the treatment agent used in the above silylation treatment depends on the type of treatment agent, but when hexamethyldisiloxane is used as the treatment agent, the weight is 10 to 150 parts by weight based on 100 parts by weight of silica. The part is suitable. It is more preferably 20 to 130 parts by weight, and even more preferably 30 to 120 parts by weight.

The above conditions for the silylation treatment can be carried out by adding a silylation treatment agent to the W phase separated in the S5 step and reacting the W phase for a certain period of time. For example, when dimethyldichlorosilane is used as the silylation treatment agent and the treatment temperature is 50 ° C., it can be carried out by holding for about 4 to 12 hours or more, and octamethylcyclotetrasiloxane is used and the treatment temperature is 70 ° C. In the case of, it can be carried out by holding for about 6 to 12 hours or more.

When cyclic siloxanes such as octamethylsiloctetrasiloxane are used as the silylation treatment agent, the pH of the solution is adjusted to 0.3 to 1.0 by adding hydrochloric acid to improve the reaction efficiency. Preferred above.

In the silylation treatment step, it is preferable to add a water-soluble organic solvent for the purpose of increasing the solubility of the treatment agent in the W phase and increasing the efficiency of the reaction. Examples of this water-soluble organic solvent include acetone, methanol, ethanol, isopropyl alcohol and the like. Of these, isopropyl alcohol can be preferably used.

The water-soluble organic solvent is preferably added so that the concentration in the W phase is about 20 to 80 wt%. When a water-soluble organic solvent is added when separating the W phase in the S4 step, it can be used as it is in the present S6 step.

(Gelified body extraction step S7)
In the gelled product extraction step S7 (hereinafter, may be abbreviated as “S7”), the gelled product is extracted into a hydrophobic organic solvent after the silylation treatment in S7. As a criterion for selecting the hydrophobic organic solvent used for the gelled product extraction, it is mentioned that the surface tension is small so that the drying shrinkage does not occur in the subsequent drying step. Specifically, hexane, heptane, dichloromethane, methyl ethyl ketone, toluene and the like can be used, and hexane, heptane and toluene can be preferably used.

After the above extraction to the hydrophobic organic solvent, in order to remove the salt contained in the gelled product, the sulfate contained in the hydrophobic organic solvent, etc., the organic solvent is mixed with water or an aqueous solution of alcohol. It is preferable to perform cleaning. This cleaning operation can be performed by a known method. In order to improve the cleaning efficiency, it is preferable to use an aqueous solution of isopropyl alcohol of about several tens of wt%. Further, it is preferable to raise the temperature within a range not exceeding the boiling point of the hydrophobic organic solvent in order to improve the cleaning efficiency. Usually, it can be carried out in the range of 45 to 70 ° C.

(Gelized body recovery step S8)
In the gelled product recovery step S8 (hereinafter, may be abbreviated as “S8”), the gel dispersed in the hydrophobic organic solvent obtained in the gelled product extraction step in S8 is filtered off. Remove (ie dry) the hydrophobic organic solvent. The temperature at the time of drying is preferably higher than the boiling point of the solvent and lower than the decomposition temperature of the surface treatment agent, and the pressure is preferably normal pressure or reduced pressure.

In the production method, the spherical silica airgel of the present invention can be obtained by passing through S1 to S8.

In the above description of the present invention, a method for producing a spherical silica airgel has been mainly exemplified, but the present invention is not limited to this form.

(Physical characteristics and uses)
Since the hydrophobic silica airgel of the present invention has an appropriate particle size distribution, when mixed with the particles of Patent Documents 4, 5 and 6 in a binder, the filling rate of the airgel particles is high and the heat insulating performance is high. Insulation is obtained. Therefore, it can be suitably used for a wide range of applications, but in particular, as described in detail below, it is suitable as a heat insulating paint, a heat insulating agent such as a heat insulating sheet, and an additive for cosmetics.

(Use as a heat insulating agent)
When the spherical silica airgel of the present invention is used by filling a resin or paint as a heat insulating agent, it is preferable that the base material does not bury or destroy the pore structure of the silica airgel.

For example, when used as a heat insulating paint, the base material is preferably an aqueous emulsion resin or a water-soluble resin, and the water content is preferably less than 90 vol%.

Examples of these substrates include vinyl acetate homopolymer dispersion, vinyl acetate copolymer dispersion, ethylene-vinyl acetate dispersion, styrene-acrylate copolymer dispersion, styrene-butadiene copolymer dispersion, and the like. There are acrylate dispersion liquid, water glass (sodium silicate), polyvinyl alcohol aqueous solution and the like.

Further, when the spherical silica airgel of the present invention is added to the base material as a heat insulating agent, if bubbles are generated, the bubbles can be defoamed by a known method. For example, it may be in a reduced pressure environment, or it may be centrifugally defoamed.

(For cosmetics)
The spherical silica airgel of the present invention can be suitably used as an additive for cosmetics. For example, when used as an additive for foundations, it has an appropriate particle size and specific surface area, so that it has excellent appearance retention and a smooth feel. In addition, silica airgel has a high oil absorption as a general property and efficiently absorbs oils on the surface of the skin and scalp, so that it has excellent anti-shininess. In addition, since it is hydrophobic and has the effect of repelling sweat, it can be suitably used as a paste, cream-type make-up / skin care cosmetic, and further as a cosmetic such as a deodorant product and a hair styling product. ..

(Use as a heat insulating agent)
When the spherical silica airgel of the present invention is used by filling a resin or paint as a heat insulating agent, it is preferable that the base material does not bury or destroy the pore structure of the silica airgel.

For example, when used as a heat insulating paint, the base material is preferably an aqueous emulsion resin or a water-soluble resin, and the water content is preferably less than 90 VOL%.

Examples of these substrates include vinyl acetate homopolymer dispersion, vinyl acetate copolymer dispersion, ethylene-vinyl acetate dispersion, styrene-acrylate copolymer dispersion, styrene-butadiene copolymer dispersion, and the like. There are acrylate dispersion liquid, water glass (sodium silicate), polyvinyl alcohol aqueous solution and the like.

Further, when the spherical silica airgel of the present invention is added to the base material as a heat insulating agent, if bubbles are generated, the bubbles can be defoamed by a known method. For example, it may be in a reduced pressure environment, or it may be centrifugally defoamed.

(For cosmetics)
The spherical silica airgel of the present invention can be suitably used as an additive for cosmetics. For example, when used as an additive for foundations, it has an appropriate particle size distribution and specific surface area, so that it has excellent appearance retention and a smooth feel. In addition, silica airgel has a high oil absorption as a general property and efficiently absorbs oils on the surface of the skin and scalp, so that it has excellent anti-shininess. In addition, since it is hydrophobic and has the effect of repelling sweat, it can be suitably used as a paste, cream-type make-up / skin care cosmetic, and further as a cosmetic such as a deodorant product and a hair styling product. ..

(Matte use)
When the spherical silica airgel of the present invention is used as a matting agent, D10 / D90 is small, that is, it has a broad particle size distribution, so that the filling rate in the coating film is high, and therefore good matting property is obtained. Obtainable.
When used as a matting agent, the spherical silica airgel of the present invention is usually dispersed in an organic resin.

In the matte coating material containing the matting agent and the organic resin in the present invention, any organic resin can be used. For example, depending on the type of resin, conventional paints such as oil-based paints, nitrocellulose paints, alkyd resin paints, amino alkyd paints, vinyl resin paints, acrylic resin paints, epoxy resin paints, polyester resin paints, and rubber chloride paints themselves. In addition to known paints, rosin, ester gum, pentaresin, kumaron inden resin, phenol-based resin, modified phenol-based resin, malein-based resin, alkyd-based resin, amino-based resin, vinyl-based resin, petroleum resin, epoxy-based resin. , Polyester resin, styrene resin, acrylic resin, silicone resin, rubber base resin, chlorinated resin, urethane resin, polyamide resin, polyimide resin, fluorine resin, natural or synthetic lacquer, etc. Examples thereof include paints containing one type or two or more types. Further, the paint to be used may be any of a solvent type paint, an ultraviolet curable paint, a powder paint and the like, depending on how it is used.

Examples of the organic solvent of this solvent-type coating material include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as n-heptane, n-hexane and isoper; and alicyclic hydrocarbon solvents such as cyclohexane. Ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohol solvents such as ethanol, propanol, butanol and diacetone alcohol; ether solvents such as tetrahydrofuran and dioxane; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; One or two or more kinds of ester solvents such as ethyl acetate and butyl acetate; aprotonic polar solvents such as dimethylformamide, dimethylacetamide and dimethylsulfoxide can be used.
As the ultraviolet (UV) curable paint, high solid resin, for example, UV curable acrylic resin, epoxy resin, vinyl urethane resin, acrylic urethane resin, polyester resin and the like are used alone or in combination of two or more.
Examples of the powder coating include thermoplastic resins such as polyamide, polyester, acrylic resin, olefin resin, cellulose derivative, polyether, vinyl chloride resin, epoxy resin, epoxy / novolak resin, isocyanate or epoxy curable polyester resin. Be done.

The amount of the matting agent added to the resin in the present invention can be added at an arbitrary ratio, but 1 to 90 parts by mass, preferably 3 to 80 parts by mass is appropriate with respect to 100 parts by mass of the organic resin. As a result, a high degree of matting effect can be imparted to the surface of the coating film with a small amount of compounding. At the same time, it is presumed that the scratch resistance of the coating film surface is also improved.

(Use for drug carriers)
The spherical silica airgel of the present invention can be suitably used as a drug carrier. Specifically, by including the drug in the spherical silica airgel, the drug can be gradually released in the living body continuously for a longer period of time. Therefore, the duration of drug effect can be maintained for a long time.

Hereinafter, examples will be shown in order to specifically explain the present invention. However, the present invention is not limited to these examples. The evaluation of Examples and Comparative Examples was carried out by the following method.

<Evaluation method>
The following items were tested on the spherical silica airgel produced in Examples 1 to 5.

(Measurement of average circularity and median diameter by image analysis)
Image analysis of SEM images observed at 100x magnification using SEM (S-5500 manufactured by Hitachi High-Technologies Corporation, acceleration voltage 3.0 kV, secondary electron detection) for 2000 or more spherical silica airgels was performed, and averaged according to the above definition. The circularity was calculated.
(Measurement of particle size distribution and median diameter by laser diffraction / scattering method)
The particle size distribution and median diameter were measured with LA-950V2 manufactured by HORIBA, Ltd. according to the above definitions.
(Specific surface area, pore volume and oil absorption)
The BET specific surface area and the BJH pore volume were measured by BELSORP-mini manufactured by Nippon Bell Co., Ltd. according to the above definitions.
(Measurement of other physical property values)
The thermal conductivity was measured with a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Denshi Kogyo Co., Ltd.

The carbon content (“C value” in Table 1) is measured by participating in the treatment using an oxide vario MICRO cube at a temperature of 1150 ° C. while flowing oxygen and helium, and quantifying the amount of carbon dioxide generated. It was calculated by mass% with the total amount of metal oxide powder as a reference (100 mass%).

<Example 1>
(S1: Aqueous silica sol adjusting step)
While stirring 100 g of sulfuric acid (concentration 9.2 g / 100 mL) with a stirring blade, sodium silicate (concentration SiO ₂ 19.1 g / 100 mL, Na ₂ O 6.2 g / 100 mL, SiO ₂ mol / Na ₂ O mol = 3. 2) 100 g was gradually added to prepare an aqueous silica sol. At this time, the pH was 3.0.

(S2: Emulsion forming step)
108 g of the aqueous silica sol prepared in S1 was dispensed, 160 g of heptane was added, and 0.8 g of sorbitan monooleate was added to the apparatus in which the rotary blade of a 0.5 L 4-sloping paddle blade was installed. This solution was cooled to 20 ° C. and stirred at a peripheral speed of 57 m / s for 15 minutes to form a W / O emulsion.

(S3: Gelation step)
The obtained emulsion was gelled at 70 ° C. for 1 hour while stirring with a stirring blade.

(S4: W phase separation step)
40 g of isopropyl alcohol and 60 g of ion-exchanged water were added, and the O phase and the W phase were separated while stirring with a stirring blade. Subsequently, 2 g of a 0.5 mol / L sodium hydroxide aqueous solution was added. At this time, the pH of the W phase was 5.0.

(S4': Gelled body aging process)
The gelled product was aged at 70 ° C. for 2.5 hours.

(S5: W phase recovery step)
The W phase was recovered by removing the O phase by decantation.

(S6: Cyrilization treatment step)
The silylation treatment was carried out by adding 17 g of 35% hydrochloric acid and 12 g of hexamethyldisiloxane to the obtained W phase and holding the mixture at 70 ° C. for 12 hours with stirring.

(S7: Gelled product extraction step)
After the silylation treatment, 12.6 g of a 48% sodium hydroxide aqueous solution was added while stirring with a stirring blade to perform a neutralization treatment. Subsequently, 100 g of heptane was added, the gelled product was extracted, and the mixture was washed twice with 100 g of ion-exchanged water.

(S8: Gelled product recovery step)
The obtained gelled product after silylation was filtered off by a suction filter. The spherical silica airgel of the present invention was obtained by heating the gelled product at 150 ° C. for 16 hours or more under vacuum pressure.
Table 1 shows the stirring conditions at the time of emulsion formation and the results of physical property evaluation of the obtained spherical silica airgel.

<Example 2>
In S2, the same operation as in Example 1 was carried out except that the stirring time for forming the W / O emulsion was set to 60 minutes. Table 1 shows the stirring conditions at the time of emulsion formation and the results of physical property evaluation of the obtained spherical silica airgel.

<Example 3>
In S2, the same operation as in Example 1 was performed except that the stirring speed when forming the W / O emulsion was set to a peripheral speed of 94 m / s and the stirring time was set to 60 minutes. Table 1 shows the stirring conditions at the time of emulsion formation and the results of physical property evaluation of the obtained spherical silica airgel.

<Example 4>
In S2, the same operation as in Example 1 was carried out except that the stirring speed at the time of forming the W / O emulsion was 170 m / s and the stirring time was 60 minutes. Table 1 shows the stirring conditions at the time of emulsion formation and the results of physical property evaluation of the obtained spherical silica airgel.

<Example 5>
(S1: Aqueous silica sol adjusting step)
While stirring 200 kg of sulfuric acid (concentration 9.2 g / 100 mL) with a stirring blade, sodium silicate (concentration SiO ₂ 19.1 g / 100 mL, Na ₂ O 6.2 g / 100 mL, SiO ₂ mol / Na ₂ O mol = 3. 2) 200 kg was gradually added to prepare an aqueous silica sol. At this time, the pH was 3.0.

(S2: Emulsion forming step)
324 kg of the aqueous silica sol prepared in S1 was dispensed, 480 kg of heptane was added, and 2.4 kg of sorbitan monooleate was added to the device in which the rotor blades of three swept wings of 1.5 m ^{3 were installed.} This solution was cooled to 20 ° C. and stirred at a peripheral speed of 109 m / s for 60 minutes to form a W / O emulsion.

(S3: Gelation step)
268.8 g of the W / O emulsion formed in S2 was taken, and the subsequent operations were the same as in Example 1. Table 1 shows the stirring conditions at the time of emulsion formation and the results of physical property evaluation of the obtained spherical silica airgel.

Claims (4)

The specific surface area by the BET method is 300 to 1000 m ² / g.
The peaks of the pore volume and the pore radius by the BJH method are 3 to 8 ml / g and 10 to 50 nm, respectively.
In the particle size distribution measured by the laser diffraction / scattering method, the volume-based cumulative 50% diameter (D50) value is more than 20 μm and 200 μm or less.
The average circularity obtained by the image analysis method Ri der 0.8 or higher,
The ratio of the volume-reduced cumulative 10% diameter and (D10) and volume-reduced cumulative 90% diameter (D90) (D10 / D90) is spherical silica airgel, characterized in 0.1-0.5 der Rukoto. The heat insulating agent comprising the spherical silica airgel according to claim 1. The cosmetic additive comprising the spherical silica airgel according to claim 1. The drug carrier comprising the spherical silica airgel according to claim 1.

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