JP5339627B2 - Nano hollow particles comprising low density silica shell and method for producing the same - Google Patents

Description

  The present invention relates to a nano hollow particle having an outer diameter in the range of 30 nm to 200 nm, and comprising a low density silica shell composed of a low density silica shell (hereinafter referred to as “low density silica nano hollow particle”). And the manufacturing method thereof.

  In recent years, as part of nanotechnology research, applied research on fine particles having a particle size of several hundred nanometers or less has been actively conducted. As an example, there is an invention of highly dispersed silica nano hollow particles described in Patent Document 1 and a method for producing the same. This silica nano hollow particle is a nano hollow particle composed of a dense silica shell, in which pores of 2 nm to 20 nm are not detected in the pore distribution, and the first step of preparing calcium carbonate, which is coated with silica. It is produced by the second step, a third step in which calcium carbonate is dissolved to form silica nano hollow particles.

  The highly dispersed silica nano hollow particles according to Patent Document 1 are hollow and have a thin silica shell, so that they have excellent heat insulating properties and transparency. As shown in Patent Document 2, they are uniform in paints, films, and synthetic fibers. By disperse in the composition, it is possible to obtain a heat insulating paint, heat insulating film, and heat insulating fiber, which can be applied to a wide range of technical fields. In addition, various applications are expected.

  However, since the highly dispersed silica nano hollow particles described in Patent Document 1 are fine particles having an outer diameter of about 30 nm to about 300 nm, they are likely to agglomerate and melt even in a solvent such as water or an organic solvent. Even when mixed in an organic synthetic resin in the state, it immediately aggregates to form huge aggregated particles (secondary particles) with a size of several μm to several tens of μm, and several tens of nm in the paint, film, and synthetic fiber. It is difficult in practice to disperse uniformly as fine-agglomerated particles with a size of up to several hundreds of nanometers. Therefore, the silica nano hollow particles have excellent properties such as heat insulation, transparency, and low dielectric constant. I couldn't let you.

 On the other hand, when the present inventors measured the thermal conductivity of a coating film obtained by applying a paint in which silica nano hollow particles were mixed in an acrylic urethane resin as an organic synthetic resin, the value of extremely low thermal conductivity was found. Obtained. However, when conducting the heat transfer simulation in the film by the finite element method (FEM) and calculating the thermal conductivity as a theoretical value, the theoretical value is about 10 times larger than the measured value. As a result, it has been found that reducing the density of the silica shell of the silica nano hollow particles is effective for obtaining extremely low thermal conductivity. That is, according to the analysis result of the finite element method, it is the density of the silica shell that has the greatest influence on the thermal conductivity of the coating film in which the silica nano hollow particles are mixed, and the smaller the density of the silica shell, It became clear that the thermal conductivity of was also lower.

JP 2005-263550 A JP 2007-070458 A

  However, neither of the above-mentioned Patent Document 1 and Patent Document 2 has any knowledge about such silica nanohollow particles having a low-density silica shell and a method for producing the same, and a method for producing nanohollow particles comprising a low-density silica shell. Was not established.

  Accordingly, the present invention has been made to solve such problems, and is a low-density silica that is effective for obtaining extremely low thermal conductivity by mixing in a material such as a paint. It aims at providing the nano hollow particle which consists of a shell, and its manufacturing method.

The nano hollow particles comprising low density silica shells according to the invention of claim 1 (low density silica nano hollow particles) are nano hollow particles comprising silica shells having an outer diameter in the range of 30 nm to 180 nm as measured by microscopy. there are, the silica shell has a plurality of micropores, the range density of the micropores only silica shell excluding of 0.5g / cm ³ ~1.9g / cm ³ of the silica shell among them, more preferably be within the range of ^{0.5g / cm 3 ~1.4g / cm 3} .

 Here, “microscopy” refers to a method of actually observing particles using a scanning electron microscope (SEM) or transmission electron microscope (TEM) to determine the size of each part of the particles. The “micropore” means a micropore having a pore diameter of 2 nm or less and a size through which nitrogen molecules can pass.

The low-density silica nano hollow particles according to the invention of claim 2 are formed by forming the silica shell of the structure of claim 1 on the surface of the calcium carbonate fine particles by a sol-gel method, and setting the dispersion hydrogen ion concentration index to pH 2 with an acid aqueous solution. In the range of ~ pH 3, the calcium carbonate fine particles inside the silica-coated calcium carbonate fine particles are dissolved, and the nano hollow particles consisting only of the silica shells are in a temperature range of 200 ° C to 500 ° C, more preferably 350 ° C to 400 ° C. It was obtained by heating in the temperature range.

Here, the “sol-gel method” is generally “a method of producing glass by heating after passing through a sol and gel state from a solution. Alkoxides are often used as starting materials. (Saburo Nagakura et al. “Iwanami Rikagaku Dictionary (5th edition)”, page 777, published by Iwanami Shoten Co., Ltd. on February 20, 1998). In the present specification and claims, tetraethoxysilane (TEOS ) And other silicon alkoxides are reacted with water under basic conditions to form a gel-like silica shell in which SiO ₂ molecules are polycondensed. The gel-like silica shell is converted to a glass-like silica shell by heating calcium carbonate in a temperature range of 200 ° C. to 500 ° C.

  The low-density silica nano-hollow particles according to the invention of claim 3 are the structures of claim 1 or claim 2, wherein the thickness of the silica shell measured by microscopy is in the range of 3 nm to 10 nm. Here, “microscopy” refers to a method of actually observing particles using a scanning electron microscope (SEM) or transmission electron microscope (TEM) to determine the size of each part of the particles.

The method for producing low-density silica nanohollow particles according to the invention of claim 4 is a method for producing nanohollow particles comprising silica shells having micropores and having an outer diameter in the range of 30 nm to 180 nm as measured by microscopy. Then, calcium carbonate fine particles as a dry powder having an outer diameter of a predetermined size are dispersed in a solvent, and the calcium carbonate fine particles are blended with silicon alkoxide equal to or less than the same weight and coated by a sol-gel method. A silica coating forming step of forming a silica shell on the surface of the calcium carbonate fine particles, and the calcium carbonate fine particles inside the silica-coated calcium carbonate fine particles by setting the hydrogen ion concentration index of the dispersion system within the range of pH 2 to pH 3 with an acid aqueous solution. And dissolving the calcium carbonate into nano hollow particles made only of the silica shell, Those comprising a heating step of heating the hollow nanoparticles comprising only Rica shells in a temperature range of 200 ° C. to 500 ° C..

Here, as described above, the “sol-gel method” means that silicon alkoxide such as tetraethoxysilane (TEOS) is reacted with water under basic conditions in the present specification and claims. , A method of forming a gel-like silica shell in which SiO ₂ molecules are polycondensed. In addition, this gel-like silica shell becomes a glassy silica shell by being heated in a temperature range of 200 ° C. to 500 ° C. through a calcium carbonate dissolution step.

The method for producing low-density silica nano hollow particles according to the invention of claim 5 is the structure of claim 4, wherein the density of only the silica shell excluding the micropores of the silica shell is 0.5 g / cm ^{3 to} 1.9 g. / in the range of cm ^3, more preferably those in the range of ^{0.5g / cm 3 ~1.4g / cm 3} .

In the method for producing low-density silica nano-hollow particles according to the invention of claim 6, the thickness of the silica shell measured by the microscopic method having the structure of claim 4 or claim 5 is in the range of 3 nm to 10 nm. is there.

The hollow nanoparticle comprising a low-density silica shell according to the invention of claim 1 is a hollow nanoparticle comprising a silica shell having an outer diameter measured by microscopy of 30 nm to 180 nm. since the density of only silica shell excluding is in the range of ^{0.5g / cm 3 ~1.9g / cm 3} , for example, by forming a coating film by applying a coating material mixed in the organic synthetic resin , A coating film having an extremely small thermal conductivity of about 0.027 W / (m · K) can be obtained.

When the density of only the silica shell excluding the micropores is less than 0.5 g / cm ³ , the hollow particles are destroyed when the silica shell strength is too small to be mixed in materials such as paints, Small thermal conductivity cannot be obtained. On the other hand, when the density of the silica shell exceeds 1.9 g / cm ³ , the effect of reducing the thermal conductivity by the low density silica nano hollow particles cannot be obtained. Therefore, the density of only silica shell, excluding the micropores is required to be in the range of ^{0.5g / cm 3 ~1.9g / cm 3} .

Here, the density of only silica shell excluding micropores by in the range of ^{0.5g / cm 3 ~1.4g / cm 3} , can be obtained more reliably extremely low thermal conductivity More preferable. If the density of the silica shell is less than 0.5 g / cm ³ , since the strength of the silica shell is small, the hollow particles may be destroyed when mixed in a material such as a paint, Certainly low thermal conductivity cannot be obtained. On the other hand, when the density of the silica shell exceeds 1.4 g / cm ³ , the effect of reducing the thermal conductivity by the low-density silica nano hollow particles becomes small.

 In this way, by mixing in a material such as a paint, nano hollow particles composed of a low density silica shell that is effective for obtaining extremely low thermal conductivity are obtained.

The low-density silica nano-hollow particles according to the invention of claim 2 are formed by forming a silica shell on the surface of calcium carbonate fine particles by a sol-gel method, and setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 3 with an acid aqueous solution. This is obtained by dissolving the calcium carbonate fine particles inside the coated calcium carbonate fine particles and heating the nano hollow particles composed only of the silica shell in a temperature range of 200 ° C to 500 ° C.

Here, when the hydrogen ion concentration index is lowered to less than pH 2 by the acid aqueous solution , the silica shell is not kept at a low density but becomes high density. On the other hand, in a state where the hydrogen ion concentration index exceeds pH 3, the internal calcium carbonate fine particles cannot be completely dissolved.

At this time, since the solution in which calcium carbonate is dissolved flows out of the silica shell, fine through-holes are formed in the silica shell. The fine through-hole is blocked, and it is composed of a low-density silica shell having a density of 1.9 g / cm ³ or less by heating in a temperature range of 200 ° C. to 500 ° C., more preferably 350 ° C. to 400 ° C. Nano hollow particles. Such low-density silica nano hollow particles are known to exhibit extremely low thermal conductivity when mixed into the material and are effective in forming a low thermal conductor.

Here, when the heating temperature in the heating step is less than 350 ° C., the strength of the silica shell is reduced, and there is a possibility that the hollow particles are destroyed when mixed in a material such as a paint. Moreover, when the heating temperature is less than 200 ° C., the fine pores from which the solution in which calcium carbonate is dissolved cannot be blocked. On the other hand, when the heating temperature in the heating step exceeds 400 ° C., the density of the silica shell tends to increase, and nano hollow particles composed of low-density silica shell with a density of 1.9 g / cm ³ or less may not be obtained. There is sex. Furthermore, when the heating temperature in the heating step exceeds 500 ° C., the density of the silica shell exceeds 1.9 g / cm ³ .

 Therefore, the heating temperature in the heating step needs to be in the range of 200 ° C to 500 ° C, and the heating temperature in the heating step is more preferably in the range of 350 ° C to 400 ° C.

In the low density silica nano hollow particles according to the invention of claim 3, since the thickness of the silica shell measured by microscopy is in the range of 3 nm to 10 nm, in the low density silica nano hollow particles, the thickness of the silica shell In addition to the effect of the invention according to claim 1 or 2, in addition to the effect of the invention according to claim 1 or 2, the density of the silica shell becomes smaller and more surely very small. The effect that heat conductivity can be obtained is obtained. In addition, when the thickness of the silica shell is less than 3 nm, the strength of the silica shell is reduced, and the hollow particles may be destroyed when mixed in a material such as a paint. The thermal conductivity cannot be obtained.

 In the method for producing low-density silica nano hollow particles according to the invention of claim 4, a silica coating that forms a silica shell by a sol-gel method is formed on the surface of the calcium carbonate fine particles as a dry powder in the silica coating forming step. In the calcium dissolution step, the aqueous calcium carbonate fine particles are dissolved by setting the hydrogen ion concentration index of the dispersion system within the range of pH 2 to pH 3 with the acid aqueous solution, and the nano hollow particles consisting only of the silica shell are obtained. Here, when the hydrogen ion concentration index is lowered to less than pH 2, the silica shell is not kept at a low density but becomes high density. On the other hand, when the hydrogen ion concentration index exceeds pH 3, the internal calcium carbonate fine particles cannot be dissolved.

At this time, since the solution in which calcium carbonate is dissolved flows out of the silica shell, fine through-holes are formed in the silica shell. By heating the nano hollow particles made only of the silica shell in the heating step, From the low-density silica shell having a density of 1.9 g / cm ³ or less by heating in the temperature range of 200 ° C. to 500 ° C., more preferably 350 ° C. to 400 ° C. It becomes the nano hollow particle which becomes. Such low-density silica nano hollow particles are known to exhibit extremely low thermal conductivity when mixed into the material and are effective in forming a low thermal conductor.

Here, when the heating temperature in the heating step is less than 350 ° C., the strength of the silica shell is reduced, and there is a possibility that the hollow particles are destroyed when mixed in a material such as a paint. Moreover, when the heating temperature is less than 200 ° C., the fine pores from which the solution in which calcium carbonate is dissolved cannot be blocked. On the other hand, when the heating temperature in the heating step exceeds 400 ° C., the density of the silica shell tends to increase, and nano hollow particles composed of low-density silica shell with a density of 1.9 g / cm ³ or less may not be obtained. There is sex. Furthermore, when the heating temperature in the heating step exceeds 500 ° C., the density of the silica shell exceeds 1.9 g / cm ³ .

 Therefore, the heating temperature in the heating step needs to be in the range of 200 ° C to 500 ° C, and the heating temperature in the heating step is more preferably in the range of 350 ° C to 400 ° C.

  In this way, by mixing into a material such as a paint, a low density silica nano hollow particle production method effective for obtaining extremely low thermal conductivity is obtained.

In the method for producing a low density silica hollow particles according to the invention of claim 5, since the density of only silica shell excluding micropores is in the range of 0.5g / cm ³ ~1.9g / cm ³ Such low density silica nano hollow particles are known to exhibit very low thermal conductivity when incorporated into the material and are effective in forming low thermal conductors, more reliably to extremely low thermal conductivity This is a method for producing low-density silica nano-hollow particles that is effective for obtaining the above.

When the density of only the silica shell excluding the micropores is less than 0.5 g / cm ³ , the hollow particles are destroyed when the silica shell strength is too small to be mixed in materials such as paints, Small thermal conductivity cannot be obtained. On the other hand, when the density of the silica shell exceeds 1.9 g / cm ³ , the effect of reducing the thermal conductivity by the low density silica nano hollow particles cannot be obtained. Therefore, the density of only silica shell, excluding the micropores is required to be in the range of ^{0.5g / cm 3 ~1.9g / cm 3} .

Here, the density of the silica shell by in the range of ^{0.5g / cm 3 ~1.4g / cm 3} , can be obtained more reliably very low thermal conductivity, more preferably. If the density of the silica shell is less than 0.5 g / cm ³ , since the strength of the silica shell is small, the hollow particles may be destroyed when mixed in a material such as a paint, Certainly low thermal conductivity cannot be obtained. On the other hand, when the density of the silica shell exceeds 1.4 g / cm ³ , the effect of reducing the thermal conductivity by the low-density silica nano hollow particles becomes small.

In the method for producing low-density silica nano hollow particles according to the invention of claim 6 , since the thickness of the silica shell measured by microscopy is in the range of 3 nm to 10 nm, the outer diameter in the range of 30 nm to 100 nm is selected. The low-density silica nanohollow particle which has can be obtained more reliably.

FIG. 1 is a flowchart showing a method for producing low-density silica nano hollow particles according to Embodiment 1 of the present invention. FIG. 2 (a) is a schematic view showing a production process of nano hollow particles composed of silica shells used for production of low density silica nano hollow particles according to Embodiment 1 of the present invention, and (b) is a BET method using nitrogen. It is a schematic diagram which shows the mode of adsorption | suction of the nitrogen molecule in the specific surface area measurement by. FIG. 3 is a graph showing the amount of adsorption when the specific surface area is measured by the BET method for solid silica particles having similar particle sizes and the low-density silica nano hollow particles according to Embodiment 1 of the present invention. . FIG. 4 (a) is a schematic diagram for explaining how to obtain the specific surface area of the low-density silica nano hollow particles according to Embodiment 1 of the present invention, and FIG. 4 (b) shows the implementation of the present invention using the value of the specific surface area. 3 is a graph for obtaining the density of silica shells of low-density silica nano hollow particles according to Embodiment 1. FIG. FIG. 5 is a flowchart showing a method for producing low-density silica nano hollow particles according to Embodiment 3 of the present invention. FIG. 6A is an explanatory diagram of a method for calculating the thermal conductivity of a paint mixed with low-density silica nano hollow particles according to Example 1 of Embodiment 3 of the present invention, and FIG. FIG. 5B is an explanatory diagram of a method for calculating the thermal conductivity of a paint mixed with high density silica nano hollow particles, and FIG. 7B is an explanatory diagram of a method of calculating the thermal conductivity of a paint mixed with silica nano hollow particles according to Comparative Example 1.

  In order to carry out the nano hollow particles composed of the low-density silica shell and the production method thereof according to the present invention, it is necessary to produce or obtain calcium carbonate fine particles as a dry powder. In addition, as for the magnitude | size of a calcium carbonate microparticles | fine-particles, it is preferable that the outer diameter measured by the microscope method exists in the range of 8 nm-85 nm. This is because when the outer diameter of the calcium carbonate fine particle dry powder measured by the microscopic method is less than 8 nm or more than 85 nm, low thermal conductivity cannot be obtained when the obtained silica nano hollow particles are mixed in a paint or the like.

  As a method for producing such a calcium carbonate fine particle dry powder, for example, there is a method of growing crystals in an aqueous system. The calcium carbonate crystals produced by this method are calcite and hexagonal, but by controlling the synthesis conditions, they grow into a cubic shape, that is, a “cubic shape”. be able to. Here, the “cubic form” refers to a shape similar to a cube surrounded by a face, not limited to a cube.

 The method of growing crystals in an aqueous system is not particularly limited, and a method of precipitating calcium carbonate by introducing carbon dioxide into a slurry of calcium hydroxide, or a method of carbonation in an aqueous solution of a soluble calcium salt such as calcium chloride. For example, a method in which calcium carbonate is precipitated by adding a soluble carbonate such as sodium is applicable. At this time, in order to obtain calcium carbonate having a target outer diameter in the range of 8 nm to 85 nm, it is desirable to increase the rate of precipitation of calcium carbonate at a relatively low temperature. For example, in the method of introducing carbon dioxide gas into the calcium hydroxide slurry, the liquid temperature when introducing the carbon dioxide gas is 30 ° C. or less, and the rate at which the carbon dioxide gas is introduced is 1.0 L / 100 g of calcium hydroxide. It is preferable to set it to min or more.

  Moreover, as a method for obtaining calcium carbonate fine particles as a dry powder, commercially available calcium carbonate fine particles can be purchased and used. For example, fine particle calcium carbonate of Hayashi Kasei Co., Ltd., synthetic calcium carbonate of Shiroishi Industrial Co., Ltd., etc. can be used.

 Moreover, various silicon alkoxides including tetraethoxysilane (TEOS) can be used as the silicon alkoxide for coating the silica shell by the sol-gel method on the surface of the calcium carbonate fine particles as a dry powder, More specifically, for example, ethyl silicate (product name “high purity ethyl silicate”: tetraethoxysilane (TEOS)) from Tama Chemical Co., Ltd., alkoxysilane (product of functional silane from Shin-Etsu Chemical Co., Ltd.) The name “KBE-04”: tetraethoxysilane (TEOS)), etc. can be used.

  Embodiments of the present invention will be described below with reference to the drawings. In each embodiment, the same symbol and the same reference sign mean the same or corresponding functional part, and the same sign and the same reference sign in the embodiments are the functional parts common to those embodiments. Therefore, the detailed description which overlaps is abbreviate | omitted here.

Embodiment 1
First, the low density silica nano hollow particles according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 4.

 FIG. 1 is a flowchart showing a method for producing low-density silica nano hollow particles according to Embodiment 1 of the present invention. FIG. 2 (a) is a schematic diagram showing a production process of nano hollow particles made of silica shells used for production of low density silica nano hollow particles according to Embodiment 1 of the present invention, and FIG. 2 (b) is a BET using nitrogen ( It is a schematic diagram which shows the mode of adsorption | suction of the nitrogen molecule in the specific surface area measurement by Brunauer-Emmett-Teller) method. Here, the BET (Brunauer-Emmett-Teller) method is a method of adsorbing a molecule whose adsorption occupation area is known on the particle surface at the temperature of liquid nitrogen, and obtaining the specific surface area of the sample from the amount, such as nitrogen This is due to the low temperature physical adsorption of the inert gas.

  FIG. 3 is a graph showing the amount of adsorption when the specific surface area is measured by the BET method for solid silica particles having similar particle sizes and the low-density silica nano hollow particles according to Embodiment 1 of the present invention. . FIG. 4 (a) is a schematic diagram for explaining how to obtain the specific surface area of the low-density silica nano hollow particles according to Embodiment 1 of the present invention, and FIG. 4 (b) shows the implementation of the present invention using the value of the specific surface area. 3 is a graph for obtaining the density of silica shells of low-density silica nano hollow particles according to Embodiment 1. FIG.

 Initially, the outline of the manufacturing method of the nano hollow particle which consists of a silica shell concerning this invention is demonstrated with reference to the flowchart of FIG. 1, and the schematic diagram of Fig.2 (a). As shown in FIG. 1 and FIG. 2 (a), first, calcium carbonate fine particles 2 that become core particles are produced by crystal growth (step S10). The calcium carbonate crystal 2 produced here is calcite and is a hexagonal crystal system. However, by controlling the synthesis conditions, it is grown into a shape as if it is a cubic system, that is, a “cubic shape”. be able to. Here, the “cubic form” refers to a shape similar to a cube surrounded by a face, not limited to a cube.

After growing the crystal so that the outer diameter of the calcium carbonate 2 is 8 nm to 85 nm, it is aged (step S11), dehydrated (step S12), and the calcium carbonate fine particles 2 in the form of a solid fine powder in a dry state are obtained. Thereafter, it is dispersed in ethanol (step S13). Then, by adding silicon alkoxide and ammonia, silica (SiO ₂ ) is coated on the calcium carbonate (CaCO ₃ ) fine particles 2 by a sol-gel method (step S14). Here, the product name “KBE-04” tetraethoxysilane (TEOS) of Shin-Etsu Chemical Co., Ltd. was used as the silicon alkoxide, and 28 wt% ammonia water was used as the ammonia.

 The silica-coated particles 3 thus prepared are washed (step S15), then dispersed in water (step S16), and hydrochloric acid is added to dissolve and discharge the calcium carbonate 2 inside (step S17). ), The nano hollow particles 4 made of a silica shell having a cubic shape having outflow holes are formed. Finally, after drying (step S18), by closing the pores from which calcium carbonate 2 dissolved by heating at 400 ° C. in the heating process flows out (step S19), nano hollow particles (low density) made of low density silica shells Silica nano hollow particles) 1 are produced.

The inner diameter of the hollow portion of the low density silica nano hollow particle 1 is 10 nm to 80 nm, which is the outer diameter of the calcium carbonate fine particle 2 of the core particle, and the thickness of the low density silica shell 1a is 3 nm to 10 nm. The outer diameter of 1 is 30 nm to 100 nm. The density of only the silica shell excluding the micropores of the low-density silica shell 1a is 1.1 g / cm ³ (the density of amorphous silica is 2.2 g / cm ³ ) as will be described later.

 Next, a method for calculating the density of the low density silica shell 1a of the low density silica nano hollow particles 1 according to the first embodiment manufactured as described above will be described with reference to FIGS. . As described above, in the low-density silica nano hollow particles 1 according to the first embodiment, the pores into which the calcium carbonate 2 dissolved by firing at 400 ° C. flows out are blocked, so that the fine particle having a size exceeding 2 nm. There are no pores, but there are micropores having a size of 2 nm or less.

 Here, “micropore” means a micropore having a pore diameter of 2 nm or less and a size through which nitrogen molecules can pass. This fact was confirmed in the measurement of the specific surface area by the BET method for the solid particles of silica and the low density silica nano hollow particles 1 as shown in FIG. 2 (b) and FIG. 3.

 That is, in the measurement of the specific surface area by the BET method using nitrogen molecules, as shown in FIG. 2B, the nitrogen molecules pass through the micropores 1b having a size of 2 nm or less. 1 is adsorbed on both the outer surface and the inner surface of the low-density silica shell 1a, and as a result, more than twice as many nitrogen molecules are adsorbed as compared with solid particles of the same size. become.

 Therefore, as shown in FIG. 3, the amount of nitrogen adsorbed on solid particles of silica is taken on the X axis, the amount of nitrogen adsorbed on low density silica nano hollow particles 1 is taken on the Y axis, and the relative pressure (P / P0) is changed. When plotted, it became a straight line of Y = 2.71X + 3.63, and it was found that 2.71 times as many nitrogen molecules were adsorbed as compared with solid particles. Then, “3.63”, which is the intercept of this straight line with the Y axis, confirms the existence of micropores 1b having a size of 2 nm or less through which nitrogen molecules pass, as shown in FIG. 2 (b). Yes. That is, the amount of adsorption of nitrogen molecules for filling the micropores 1b appears as an intercept with the Y axis.

Therefore, the density ρ of the low-density silica shell 1a is calculated using the phenomenon that the nitrogen molecules are adsorbed on both the outer surface and the inner surface. As shown in FIG. 4A, when the low density silica nano hollow particles 1 having a cubic shape are approximated by a hollow cube having an inner diameter L and a silica shell thickness d, the outer surface area of the cube is 6 × (L + 2d) ^2. Since the inner surface area is 6 × L ² , the total surface area is 6 × {(L + 2d) ² + L ² }.

On the other hand, since the volume of the silica shell 1a is obtained by subtracting the volume of the hollow portion from the volume of the hollow cube, {(L + 2d) ³ −L ³ } is obtained. Therefore, if the density ρ of the silica shell 1a is used, the mass of the low density silica nano hollow particles 1 is ρ × {(L + 2d) ³ −L ³ }. Therefore, the specific surface area is represented by surface area / particle mass = 6 × {(L + 2d) ² + L ² } / ρ {(L + 2d) ³ −L ³ }.

Thus, since the specific surface area is a function of the silica shell thickness d, plotting the calculated values with the density ρ as a parameter, the silica shell thickness d on the horizontal axis, and the specific surface area on the vertical axis. When the density ρ = 2.2 g / cm ³ and ρ = 1.1 g / cm ³ , the inverse proportional curves shown in FIG. 4B are obtained.

When the measured value of the specific surface area by the BET method using nitrogen of the low density silica nano hollow particles 1 having different silica shell thickness d is applied to this graph, as shown in FIG. It has been found that this is not the case for the curve of density ρ = 2.2 g / cm ³ , and is almost true for the curve of ρ = 1.1 g / cm ³ , which is half that density. Moreover, it turned out that the density (rho) shifts to the smaller one as the silica shell thickness d becomes small.

  Thus, in the low density silica nano hollow particle 1 which concerns on this Embodiment 1, it manufactures according to the flowchart shown in FIG. 1, and mixes in materials, such as a coating material, by this. It becomes nano hollow particles having a low density silica shell which is effective for obtaining extremely low thermal conductivity.

Embodiment 2
Next, low density silica nano hollow particles according to Embodiment 2 of the present invention will be described with reference to FIG. The manufacturing method of the low density silica nano hollow particles according to the second embodiment is substantially the same as the low density silica nano hollow particles 1 according to the first embodiment.

The difference is that the heating temperature in the heating step (step S19) of the flowchart shown in FIG. Thus, low density silica nano hollow particles having a density ρ = 0.6 g / cm ³ lower than the density ρ = 1.1 g / cm ³ of the low density silica nano hollow particles 1 according to the first embodiment can be obtained. it can.

Embodiment 3
Next, low density silica nano hollow particles according to Embodiment 3 of the present invention will be described with reference to FIGS.

 FIG. 5 is a flowchart showing a method for producing low-density silica nano hollow particles according to Embodiment 3 of the present invention. FIG. 6A is an explanatory diagram of a method for calculating the thermal conductivity of a paint mixed with low-density silica nano hollow particles according to Example 1 of Embodiment 3 of the present invention, and FIG. FIG. 5B is an explanatory diagram of a method for calculating the thermal conductivity of a paint mixed with high density silica nano hollow particles, and FIG. 7B is an explanatory diagram of a method of calculating the thermal conductivity of a paint mixed with silica nano hollow particles according to Comparative Example 1.

  As shown in FIG. 5, in the third embodiment, first, a dry powder of calcium carbonate (primary particle diameter observed with a scanning electron microscope is 50 nm to 80 nm) 5, tetraethoxysilane (TEOS) 6, Ammonia water 7 is dispersed in an ethanol aqueous solution (step S20). At this time, in order to sufficiently disperse the calcium carbonate dry powder 5, the reaction was performed at 20 ° C. for 100 minutes while applying ultrasonic waves. As a result, silica coated particles 8 in which the silica shell is coated around the calcium carbonate dry powder 5 are generated.

 Here, as dry powder 5 of calcium carbonate, synthetic calcium carbonate from Shiroishi Kogyo Co., Ltd. is used, and as product name “KBE-04” from Shin-Etsu Chemical Co., Ltd. as tetraethoxysilane (TEOS) 6. As the ammonia water 7, an ammonia water reagent having a concentration of 28% by weight was used.

  Since the produced silica coating particles 8 are dispersed in an aqueous ethanol solution, an aqueous hydrochloric acid solution (very thin dilute hydrochloric acid) is added little by little to adjust the hydrogen ion concentration index to pH 3 and stir for 1 hour (step) S21). As a result, while the density of the coated silica shell is kept at a low density, the inner calcium carbonate dry powder 5 is dissolved and allowed to flow out to form nano hollow particles 9 composed of silica shells having outflow holes (pores). Is done. After that, it is dehydrated and dried by centrifugation (3000 rpm) (step S22), and heated and fired at 400 ° C. for 1 hour to block the outflow holes (pores) (step S23), according to the third embodiment. Low-density silica nano hollow particles 10 are obtained.

  Here, in order to examine the influence of the weight ratio of the calcium carbonate dry powder 5 and tetraethoxysilane (TEOS) 6 on the density of only the silica shell excluding the micropores of the low-density silica nano hollow particles 10, carbon dioxide was used as Example 1. Production tests and evaluations were carried out on a blend using almost the same weight of calcium dry powder 5 and tetraethoxysilane 6 and a blend having less tetraethoxysilane 6 than calcium carbonate dry powder 5 as Example 2. For comparison, as Comparative Example 1, a blend containing more tetraethoxysilane 6 than calcium carbonate dry powder 5 was also produced and evaluated. The blending contents of Examples 1 and 2 and Comparative Example 1 are shown in the upper part of Table 1.

  As shown in the upper part of Table 1, Example 1 contains the same parts by weight of calcium carbonate dry powder (26.25 parts by weight) and tetraethoxysilane (26.25 parts by weight). Tetraethoxysilane (21.02 parts by weight) is blended less than calcium carbonate dry powder (26.27 parts by weight). On the other hand, in Comparative Example 1, tetraethoxysilane (31.48 parts by weight) is blended more than calcium carbonate dry powder (26.23 parts by weight). Other compounding components ethanol (262.30 to 262.77 parts by weight), water (52.46 to 52.54 parts by weight), aqueous ammonia (10.49 parts to 10.51 parts by weight) ) In Examples 1 and 2 and Comparative Example 1 are almost the same parts by weight. The ammonia water concentration is 28% by weight.

For each of these formulations, low-density silica nano hollow particles 10 are produced according to the flowchart of FIG. 5, and the density of only the silica shell excluding the micropores is changed to nitrogen molecules as in the first embodiment. The specific surface area measured by the BET method and the thickness of the silica shell were calculated. The density of the silica shell of each formulation is shown in the lower part of Table 1. As shown in the lower part of Table 1, silica nanohollow particles 10 composed of a low-density silica shell were obtained in Example 1 of 1.54 g / cm ³ and in Example 2 of 1.73 g / cm ³ . .

In contrast, Comparative Example 1 is 2.12 g / cm ^3, never change little as 2.2 g / cm ³ of amorphous silica, it was not possible to obtain a silica shell of low density. Thus, in order to reliably produce the low-density silica nano hollow particles 10, it is preferable that tetraethoxysilane (TEOS) 6 is blended with the calcium carbonate dry powder 5 in an amount equal to or less than the same weight. It became clear that it is more preferable to blend each one.

  Furthermore, in order to reconfirm that extremely low thermal conductivity can be obtained by mixing the low-density silica nano hollow particles 10 in a material such as a paint, the silica nano particles according to the formulations of Examples 1 and 2 and Comparative Example 1 are used. The hollow particles were mixed in an acrylic urethane resin paint (Grandex Co., Ltd.) with a solid content of 10% by weight, and the surface of a stainless steel disc (diameter 60 mm) was about 10 μm, about 20 μm, about 30 μm, about 40 μm. The film was applied with the film thickness changed, the total thermal resistance of the sample with the coating film was measured with a laser thermal conductivity measuring machine, and the thermal conductivity was calculated from the correlation with the film thickness of the coating film.

  Silica nano hollow particles according to the formulation of Example 1 were mixed in an acrylic urethane-based resin paint, and the film thickness of a sample with a coating applied by changing the film thickness on the surface of a stainless steel disc, and laser thermal conduction Table 2 shows the relationship with the total thermal resistance of the sample measured by a rate measuring machine. The total thermal resistance was measured twice for each sample.

  As shown in Table 2, the value of the total thermal resistance increases as the thickness of the sample with the coating increases, but in the case of the sample according to the formulation of Example 1, the range of the increase is as follows. Since it is large, it is expected that the thermal resistance of the coating film is large, that is, the thermal conductivity of the coating film is small.

  In addition, the silica nano hollow particles according to the formulation of Example 2 were mixed in an acrylic urethane resin paint, and the film thickness of the sample with the coating film applied by changing the film thickness on the surface of the stainless steel disc was measured, and the laser type Table 3 shows the relationship with the total thermal resistance of the sample measured by a thermal conductivity measuring machine. The total thermal resistance was measured twice for each sample.

  As shown in Table 3, in the case of the sample according to the formulation of Example 2, the value of the total thermal resistance hardly changes even when the thickness of the sample with the coating film is increased. Therefore, the coating film of the sample according to the formulation of Example 2 is expected to have a lower thermal resistance of the coating film than the sample according to the formulation of Example 1, that is, the thermal conductivity of the coating film is large.

  On the other hand, the silica nano hollow particles according to the composition of Comparative Example 1 were mixed in an acrylic urethane resin paint, and the film thickness of the sample with the coating film applied by changing the film thickness on the surface of the stainless steel disc was Table 4 shows the relationship with the total thermal resistance of the sample measured by the laser thermal conductivity measuring machine. The total thermal resistance was measured twice for each sample.

  As shown in Table 4, even in the case of the sample according to the composition of Comparative Example 1, even when the thickness of the sample with the coating film is increased, the value of the total thermal resistance is hardly changed. Therefore, the coating film of the sample according to the formulation of Comparative Example 1 is expected to have a smaller thermal resistance of the coating film than the sample according to the formulation of Example 1, that is, the thermal conductivity of the coating film is large. By plotting the data shown in Tables 2 to 4 in a graph, the value of the thermal conductivity of the coating film according to each formulation can be obtained.

  Specifically, as shown in FIG. 6, the total thermal resistance of a sample with a coating film measured by a laser-type thermal conductivity measuring machine is shown on the horizontal axis, and the film thickness of the coating film is shown on the vertical axis. It plots for every sample, calculates | requires the straight line which fits these plots most by the least square method, and can calculate thermal conductivity from the inclination of the straight line. That is, when the horizontal axis in FIG. 6 is the x-axis and the vertical axis is the y-axis, the coefficient a when the straight line obtained by the least square method is expressed by y = ax + b (a and b are real numbers) is the heat conduction. Become a rate. In addition, the value of the total thermal resistance when the film thickness of the coating film is 0 is obtained by measuring the total thermal resistance of only the stainless steel disc.

  Here, the “least-squares method” generally means “a method for estimating parameters of a theoretical model so as to minimize the sum of square deviations between observed values y1,..., Yn and values derived from the theoretical model. (Saburo Nagakura et al., “Iwanami Rikagaku Dictionary (5th edition)”, page 506, published by Iwanami Shoten Co., Ltd. on February 20, 1998). In this embodiment, the total thermal resistance is x, This is a method of determining the coefficients a and b so that the deviation sum of squares with respect to the straight line y = ax + b, which is a theoretical model of data plotted, is minimized when the film thickness is y.

  As shown in FIG. 6 (a), the thermal conductivity of the coating film obtained by mixing the silica nano hollow particles according to Example 1 of the present Embodiment 3 with the acrylic urethane resin coating is measured by a laser thermal conductivity measuring machine. From the data obtained by plotting the film thickness of the coating film against the total thermal resistance of the measured coating film, it is calculated as about 0.019 W / m · K from the slope a of the straight line obtained by the least square method. Similarly, as shown in FIG. 6B, the thermal conductivity of the coating film obtained by mixing the silica nano hollow particles according to Example 2 of the present Embodiment 3 with the acrylic urethane-based resin paint is about 0.037 W. / M · K.

 Moreover, as shown in FIG.6 (c), the heat conductivity of the coating film which mixed the silica nano hollow particle which concerns on the comparative example 1 with the acrylic urethane type resin coating material is computed with about 0.046 W / m * K. . The above calculation results are summarized in the lower part of Table 1.

 As shown in the lower part of Table 1, it was found that the coating film mixed with the low-density silica nano hollow particles 10 according to Example 1 had an extremely low thermal conductivity of 0.019 W / m · K. Moreover, the coating film in which the low density silica nano hollow particles 10 according to Example 2 were mixed exhibited a low thermal conductivity of 0.037 W / m · K.

 On the other hand, the coating film in which the silica nano hollow particles according to Comparative Example 1 are mixed is 0.046 W / m · K, which is more than the thermal conductivity (0.143 W / m · K) of the acrylic urethane resin coating itself. Although greatly reduced, it has been clarified that the effect of reducing the thermal conductivity is small as compared with Examples 1 and 2.

  Thus, in the low density silica nano hollow particle 10 according to the third embodiment, the low density silica nano hollow particle 10 is manufactured according to the flowchart shown in FIG. It becomes nano hollow particles having a low density silica shell which is effective for obtaining extremely low thermal conductivity.

 In each of the above embodiments, the case where the product name “KBE-04” tetraethoxysilane (TEOS) of Shin-Etsu Chemical Co., Ltd. is used as the silicon alkoxide has been described. Other products such as the product name “high purity ethyl silicate” can also be used. Further, silicon alkoxides such as methyltrimethoxysilane and methyltriethoxysilane other than tetraethoxysilane may be used.

 In practicing the present invention, the low density is also applied to the structure, components, shape, quantity, material, size, production method, etc. of other parts of the nano hollow particles (low density silica nano hollow particles) composed of low density silica shells. The other steps of the method for producing silica nano hollow particles are not limited to the above embodiments.

  The numerical values given in the embodiment of the present invention are not all critical values, and certain numerical values indicate appropriate values suitable for implementation. The implementation is not denied.

1,10 Nano hollow particles made of low-density silica shell 2 Core particles (calcium carbonate)
3 Silica coated particles

Claims (6)

Nano hollow particles composed of silica shells having an outer diameter measured by microscopy of 30 nm to 180 nm ,
The silica shell has a plurality of micropores, a density of only silica shell excluding the micropores of the silica shell is within the range of 0.5g / cm ³ ~1.9g / cm ³ Nano hollow particles comprising a low density silica shell, characterized in that The silica shell is formed on the surface of the calcium carbonate fine particles by a sol-gel method, and the calcium carbonate fine particles inside the silica-coated calcium carbonate fine particles are adjusted with an aqueous acid solution so that the hydrogen ion concentration index of the dispersion system is in the range of pH 2 to pH 3. The nano hollow particle comprising a low-density silica shell according to claim 1, obtained by dissolving and heating the nano hollow particle comprising only the silica shell in a temperature range of 200 ° C to 500 ° C.   The hollow nanoparticle comprising the low-density silica shell according to claim 1 or 2, wherein the thickness of the silica shell measured by microscopy is in the range of 3 nm to 10 nm. A method for producing nano-hollow particles comprising silica shells having micropores and having an outer diameter measured by microscopy of 30 nm to 180 nm,
Calcium carbonate fine particles as a dry powder having an outer diameter of a predetermined size are dispersed in a solvent, silicon alkoxide is blended to the same weight or less with respect to the calcium carbonate fine particles, and coated by a sol-gel method. A silica coating forming step for forming a silica shell on the surface of the calcium fine particles ;
Calcium carbonate dissolution step of dissolving nano-particles made only of silica shells by dissolving the calcium carbonate fine particles inside silica-coated calcium carbonate fine particles with a hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 3 with an acid aqueous solution When,
A method for producing nano-hollow particles comprising low-density silica shells, comprising heating a nano-hollow particle comprising only silica shells in a temperature range of 200 ° C to 500 ° C. Low density silica shell according to claim 4, wherein the density of the silica shell only excluding the micropores of the silica shell is in the range of 0.5g / cm ³ ~1.9g / cm ³ The manufacturing method of the nano hollow particle which consists of. The method for producing nano-hollow particles comprising a low-density silica shell according to claim 4 or 5, wherein the thickness of the silica shell measured by microscopy is in the range of 3 nm to 10 nm.

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