JP6595898B2 - Hollow particles and method for producing the same - Google Patents

Description

  The present invention relates to hollow particles and a method for producing the same.

  A metal oxide particle having a small particle diameter and a hollow shape has a smaller apparent specific gravity than a non-hollow particle, and has a low dielectric constant effect due to the form of the hollow particle. It is expected to be used in fields where there is a need for a low dielectric constant, such as substrates, wire coating materials, and semiconductor encapsulants. Also, since it can contain air and various compounds and materials inside, it can be used as a volatilization control base material, and for various applications such as the use of various materials such as fillers for antireflection films and light diffusion films. Has been studied or realized.

  As known hollow particles of a metal oxide, for example, a hollow sphere having a spherical shell composed of primary particles having a particle size of 100 μm or less and fine secondary particles to which the particles are bonded, and having a diameter of 1000 μm or less. The hollow particle which consists of is mentioned (refer patent document 1). The hollow particles are produced by introducing primary particles into a spherical oil droplet dispersed phase in a liquid, adhering the primary particles to the surface of the oil droplets, and then adding a component that generates secondary particles in the liquid. It is manufactured by a method in which particles are deposited as a binder in a gap between primary particles attached to the oil droplets, and then an oil phase is extracted to obtain a hollow body having a shell in which primary particles and secondary particles are combined.

  In Patent Document 2, a mixed liquid containing organic polymer particles dispersible in an aqueous medium, metal oxide nanoparticles, and an aqueous medium is prepared, and the resulting mixed liquid is dried to obtain an organic-inorganic composite. A method of obtaining a metal oxide porous body by removing organic polymer particles from the organic-inorganic composite has been proposed.

  Patent Document 3 describes silica-based fine particles having cavities inside the outer shell layer. The silica-based fine particles are produced by a so-called sol-gel method. In Patent Document 4, a core-shell particle having a polystyrene particle as a core and silica coated with the polystyrene particle as a shell is formed, and then the polystyrene particle, which is the core of the core-shell particle, is thermally decomposed to remove the polystyrene particle. Thus, a method for producing hollow silica particles is described.

JP-A-5-154374 JP2012-224509A JP2013-121911A JP 2014-94867 A

  However, when the porosity of the hollow particles is increased for the purpose of reducing the specific gravity or increasing the amount of the encapsulating agent, the outer shell becomes thinner accordingly, resulting in the strength of the outer shell. It tends to decrease, and the structure of the hollow particles tends to collapse.

  Accordingly, an object of the present invention is to improve the hollow particles, and more specifically, to provide hollow particles having a high strength of the outer shell, and the structure of the hollow particles does not easily collapse even when the outer shell is thinned.

The present invention has an outer shell portion that is an aggregate of metal oxide nanoparticles, and a hollow portion that is defined inside the outer shell portion by the outer shell portion, and has an average particle diameter of 0.1 μm or more It is 10 μm or less, the porosity is 2% by volume or more and 70% by volume or less, the peak of the pore diameter measured by the nitrogen adsorption method is 20 nm or less, and the total pore volume measured by the nitrogen adsorption method is 0 The present invention provides hollow particles having a density of ¹ cm ³ / g or more and 1.0 cm ³ / g or less.

Further, the present invention has an outer shell portion that is an aggregate of metal oxide nanoparticles, and a hollow portion that is defined inside the outer shell portion by the outer shell portion, and has an average particle diameter of 0.1 μm. Hollow particles having a size of 10 μm or less,
The metal oxide nanoparticles include two types of small particle size particles and large particle size particles having different particle sizes,
The present invention provides hollow particles in which the particle size of the small particle size is from 1 nm to 50 nm and the particle size of the large particle size is from 20 nm to 300 nm.

  Furthermore, the present invention electrostatically sprays a raw material liquid containing metal oxide nanoparticles having at least two different particle sizes, a solvent, and a polymer component within a range of 1 nm to 300 nm. The present invention provides a method for producing hollow particles, which has an electrostatic spraying step of drying generated droplets in a gas phase.

  According to the present invention, there is provided a hollow particle in which the strength of the outer shell is high and the structure of the hollow particle does not easily collapse even when the outer shell is thinned in a predetermined range of particle diameters.

FIG. 1 is a schematic cross-sectional view showing an example of the hollow particles of the present invention. 2 (a) to 2 (d) are diagrams showing changes from charged droplets to hollow particles in the electrostatic spraying step, and FIG. 2 (e) is a diagram showing a state when the particles are not hollow particles. is there. FIG. 3 is a diagram showing a schematic configuration of an apparatus suitably used for producing the hollow particles of the present invention. 4 is a cross-sectional view showing the main part of the liquid spraying part of the apparatus shown in FIG. FIG. 5 is a front view of the liquid spraying unit when the liquid spraying unit of the apparatus shown in FIG. 3 is viewed from the lower side in FIG. 1. FIG. 6 is a perspective view showing the main part of the liquid spraying part of the apparatus shown in FIG.

Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. FIG. 1 schematically shows a cross-sectional structure of an embodiment of the hollow particles of the present invention. The hollow particle 3 has an outer shell portion 33 and a hollow portion 32 defined inside the outer shell portion 33 by the outer shell portion 33. That is, the hollow particle 3 has a hollow portion 32 and an outer shell portion 33 surrounding the hollow portion 32. The outer shell portion 33 has a spherical shell shape. The outer shell portion 33 is composed of an aggregate of a plurality of metal oxide nanoparticles. The outer shell portion 33 preferably has a porous structure. The hollow particles 3 are substantially spherical. The substantially spherical shape means that when the projected image of the hollow particles 3 is observed, the roundness of the projected image is 0.8 or more. The roundness is an arithmetic average value of values calculated from the following equation by observing 100 projected images of the hollow particles 3.
Roundness = 4π (area of projected image) / (perimeter of projected image) ²

  The hollow particles 3 preferably have an average particle diameter of 0.01 μm or more and 10 μm or less. The average particle diameter can be appropriately adjusted in consideration of the application and the like, more preferably 0.1 μm or more and 5 μm or less, and further preferably 0.3 μm or more and 3 μm or less. The method for measuring the average particle diameter will be described in detail in Examples described later.

  The hollow particles 3 preferably have a porosity of 2% by volume or more and 70% by volume or less. When the porosity is 2% by volume or more, various advantageous effects due to being hollow can be obtained. On the other hand, when the porosity is 70% by volume or less, hollow particles having strength that can withstand various uses are obtained. The porosity of the hollow particles 3 is more preferably 4% by volume or more and 50% by volume or less, and further preferably 5% by volume or more and 40% by volume or less. The method for measuring the porosity will be described in detail in Examples described later.

  The outer shell portion 33 in the hollow particle 3 is preferably composed of metal oxide nanoparticles having at least two different particle diameters within a range of 1 nm to 300 nm. Specifically, as shown in FIG. 1, the metal oxide nanoparticles constituting the outer shell portion 33 preferably include two types of small particle size particles 35A and large particle size particles 35B having different particle sizes. The particle diameter of the small particle diameter particle 35A and the particle diameter of the large particle diameter particle 35B are both preferably in the range of 1 nm to 300 nm. By using at least two types of metal oxide nanoparticles having different particle diameters as described above, the small particle diameter particles 35A fill the voids formed between the large particle diameter particles 35B. The density of the outer shell 33 is thereby improved.

When the small particle size particle 35A and the large particle size particle 35B are used as the metal oxide nanoparticles, the small particle size particle 35A preferably has a particle diameter D1 of ₁ nm or more, more preferably 5 nm or more, More preferably, it is 30 nm or more. It is preferable that the small particles 35A is a particle diameter _{D 1} is 50nm or less, and more preferably 45nm or less. Particle diameter _{D 1} of the small particles 35A is preferably 1nm or more 50nm or less, still more preferably 5nm or more 45nm or less, and still more preferably 30nm or more 45nm or less. The particle diameter D ₁ of the small particles 35A By setting in this manner, the gap formed between the and if large particles 35B, small particles 35A is successfully filled.

On the other hand, with regard to large particles 35B, the particle diameter _{D 2,} subject to be larger than the particle diameter of the small particles 35A, preferably at 20nm or more, further preferably 30nm or more, More preferably, it is 80 nm or more. It is preferable that large particles 35B is the particle diameter _{D 2} is 300nm or less, and more preferably, further preferably 200nm or less, 130nm or less. Particle diameter _{D 2} of the large particles 35B is preferably 20nm or more 300nm or less, further preferably 30nm or more 200nm or less, and more preferably 80nm or more 130nm or less. By the particle diameter D ₂ of the large particles 35B thus set, the small particles 35A, it is possible to successfully fill the gap formed between and do large particles 35B.

A gap formed between and do large particles 35B, small particles 35A from the viewpoint of filling more successfully, the particle diameter D ₁ of the small particles 35A, large particles 35B of the particle diameter D particle diameter ratio _D 1 / _{D 2} and ₂ is more preferably preferably 0.1 or more, 0.2 or more. Further, the particle diameter ratio D ₁ / D ₂ is preferably 0.6 or less, more preferably 0.5 or less, and further preferably 0.4 or less. The particle diameter ratio _D 1 / _{D 2} is preferably 0.1 to 0.6, more preferably 0.1 to 0.5, 0.2 to 0.4 Is more preferable.

  From the viewpoint of further successfully filling the gap formed between the large particle size particles 35B with the small particle size particles 35A, the small particle size particles occupy the total of the small particle size particles 35A and the large particle size particles 35B. The mass fraction of 35A is preferably 0.35 or more, and more preferably 0.6 or more. Further, the mass fraction is preferably 0.95 or less, and more preferably 0.9 or less. The mass fraction is preferably from 0.35 to 0.95, and more preferably from 0.6 to 0.9.

The mass fraction is measured by the following method. The surface or cross section of the hollow particle 3 is imaged with a transmission electron microscope (TEM) or a scanning electron microscope (SEM), 100 arbitrary metal oxide nanoparticles are selected from the photographed image, and the maximum transverse length is selected. taking measurement. The maximum transverse length is regarded as the particle diameter of the metal oxide nanoparticles, the particle diameter is taken on the horizontal axis, and the volume ratio in terms of sphere is taken on the vertical axis to obtain the volume-based particle size distribution. When the particle diameter of the horizontal axis was observed two peaks in 300nm following range of 1 nm, the particle diameter at the peak of the smaller particle size and D _1, also in the larger peak of the particle size the particle size and _{D 2.} Further, the volume fraction of each peak was towards the small particles and X _1, towards the large particles and X _2, the mass ratio of the small particles and large particles constituting the hollow particles 3 Are M ₁ and M ₂ , respectively, M ₁ and M ₂ are determined by the following equations.
Mass ratio M ₁ of small particle diameter particles of the hollow particle 3
= (Density of the metal ^{_{oxide) × πD 1 3/6 ×}} X 1/100
Mass ratio M ₂ of the large particle diameter of the hollow particles 3
= (Density of the metal ^{_{oxide) × πD 2 3/6 ×}} X 2/100
And the mass fraction of a small particle size particle | grain can be calculated | required by substituting the mass ratio of the small particle size particle | grains obtained above and the large particle size particle | grain into the following formula | equation.
Mass fraction (%) = M ₁ / (M ₁ + M ₂ )
In addition, as another method, the mass fraction of the small particle size particles determined from the blending ratio of the metal oxide nanoparticles in the raw material liquid, which will be described later, is almost the same as the mass fraction of the small particle size particles of the hollow particles 3. If the mass of the small particle size compounded in the raw material liquid is M ₁ ′ and the mass of the large particle size is M ₂ ′, the mass fraction of the small particle size can be obtained by the following equation.
Mass fraction (%) = M ₁ ′ / (M ₁ ′ + M ₂ ′)

Particle diameter _{D 2} of a particle diameter _{D 1} and large particles 35B of the small particles 35A is measured by the following method. An electron microscope image of the hollow particle 3 is photographed, 100 arbitrary metal oxide nanoparticles are selected from the photographed electron microscope image, and the maximum transverse length is measured. The maximum transverse length is regarded as the particle diameter of the metal oxide nanoparticles, the particle diameter is taken on the horizontal axis, and the volume ratio in terms of sphere is taken on the vertical axis to obtain the volume-based particle size distribution. Then, the particle diameter of the horizontal axis when the two peaks in the range of 1nm or 300nm or less was observed, defines the particle diameter at the peak of the smaller particle size and particle size D ₁ of the small particles 35A. Also, define the particle size of the larger peak of the particle size and particle size D ₂ of the large particles 35B.

Further, when three or more peaks are observed in the range of 1 nm or more and 300 nm or less, and peaks are also observed at 50 nm or more, and when two or more peaks appear between 1 nm and less than 50 nm, mass calculated from the particle size distribution defines the largest particle size particle as the particle diameter D ₁ of the small particles 35A in the middle. Note the two or more mass of the particle is the same, and if the mass is greatest, define what a large particle diameter and particle diameter D ₁ of the small particles 35A. Also, if appearing peaks more than one between 50nm or 300nm or less, to define particles of the largest particle size mass calculated from the particle size distribution in which the particle diameter D ₂ of the large particles 35B. Note the two or more mass of the particle is the same, and if the mass is greatest, define what a large particle diameter and the particle diameter D ₂ of the large particles 35B.

  On the other hand, when three or more peaks are observed in the range of 1 nm or more and 300 nm or less, and no peak is observed in the range of 50 nm or more, the particle having the largest mass calculated from the particle size distribution is the second largest. A particle having a large particle size is selected, and a particle having a small particle size is defined as the particle size D1 of the small particle size particle 35A. A particle having a large particle size is defined as a particle size D2 of the large particle size particle 35B. In addition, when mass is the same rate, a thing with a large particle diameter is selected.

The mass calculated from the particle size distribution can be obtained from the particle diameter and frequency at the peak and the true density by the following formula.
Mass calculated from the particle size distribution = [pi (particle diameter) ^3/6 × (frequency) × (true density)
For example, in the case of silicon oxide, a true density of 2.2 (g / cm ³ ) can be used.

  As described above, the hollow particle 3 has the small particle size particle 35A and the large particle size particle 35B, which are two kinds of metal oxide nanoparticles having different particle diameters in the range of 1 nm or more and 300 nm or less, in the outer shell portion 33. It is preferable to include. In this case, in the range of 1 nm or more and 300 nm or less, one or more kinds of metal oxide nanoparticles having a particle diameter smaller than that of the small particle diameter particle 35 </ b> A may be further included. Moreover, in the range of 1 nm or more and 300 nm or less, one or more kinds of metal oxide nanoparticles having a particle diameter larger than that of the large particle diameter particle 35 </ b> B may be further included. Furthermore, in the range of 1 nm or more and 300 nm or less, one or more metal oxide nanoparticles having a particle diameter larger than that of the small particle diameter particle 35A and smaller than that of the large particle diameter particle 35B may be further included. Furthermore, in the range not impairing the effects of the present invention, one or more metal oxide nanoparticles having a particle diameter of less than 1 nm may be contained, or one metal oxide nanoparticle having a particle diameter of more than 300 nm. The above may be included. However, from the viewpoint of making the effects of the present invention more remarkable, it is preferable that the metal oxide nanoparticles constituting the outer shell portion 33 all have a particle diameter of 1 nm to 300 nm in accordance with the above definition. .

  As described above, the outer shell portion 33 in the hollow particle 3 of the present invention includes a plurality of types of metal oxide nanoparticles having different particle diameters, and each metal oxide nanoparticle may be of the same material, Alternatively, it may be of a different material.

The hollow particle 3 having the outer shell portion 33 having the above-described structure has a microscopic porous structure due to the structure of the outer shell portion 33. It is different from hollow particles having an outer shell portion composed of nanoparticles. Specifically, the outer shell portion 33 of the hollow particle 3 preferably has a total pore volume of 0.1 cm ³ / g or more and 1.0 cm ³ / g or less. When the total pore volume is 0.1 cm ³ / g or more, the substance permeability inside and outside the outer shell portion 33 is increased, and therefore, the volatilization control substrate is excellent in volatility. Further, when the total pore volume is 1.0 cm ³ / g or less, the outer shell portion 33 does not become excessively low in density, so that the particle strength is excellent. From the viewpoint of making these advantages more remarkable, the total pore volume of the hollow particles 3 is more preferably 0.1 cm ³ / g or more and 0.5 cm ³ / g or less. The method for measuring the total pore volume will be described in detail in Examples described later.

  The hollow particles 3 preferably have a mesopore pore diameter peak of the outer shell portion 33 of 20 nm or less. When the peak of the mesopore diameter is 20 nm or less, the outer shell portion 33 has a high density, and the hollow particles 3 have excellent strength. From this viewpoint, the peak of the mesopore pore diameter is more preferably 20 nm or less. On the other hand, the lower limit of the peak of the mesopore diameter is preferably 1 nm or more, and more preferably 5 nm or more. By setting the lower limit in this way, the hollow particles 3 have excellent permeability to the inside of the various components, sustained release of the components infiltrated inside, and disintegration due to physical impact. Become. A method for measuring the peak of the pore diameter of the mesopores will be described in detail in Examples described later.

  Examples of the metal oxide in the metal oxide nanoparticles constituting the outer shell portion 33 of the hollow particle 3 include silicon oxide, titanium oxide, alumina, iron oxide, zinc oxide, zirconia, magnesium oxide, tin oxide, indium oxide, and oxidation. Examples thereof include composite oxides such as yttrium, cerium oxide, copper oxide, manganese oxide, cobalt oxide, calcium oxide, and indium tin oxide. These may be used alone or in combination of two or more. From the viewpoint of availability and control of the hollow structure, it is preferable to use silicon oxide or titanium oxide.

  The hollow particles 3 may include a polymer component in the outer shell portion 33. As the polymer component, those functioning as a binder for binding the metal oxide nanoparticles constituting the outer shell portion 33 are preferably used. Details of the polymer component will be described later. The higher the proportion of the polymer component in the outer shell portion 33, the higher the strength of the outer shell portion 33. From this point of view, it is preferable that the proportion of the polymer component is high. On the other hand, if the proportion of the polymer component is excessively high, the properties of the porous structure of the outer shell portion 33 tend to be reduced. From this viewpoint, when the outer shell portion 33 includes a polymer component, the ratio of the polymer component to the metal oxide nanoparticles is preferably 0.01% by mass or more, and preferably 1% by mass or more. Is more preferable. Moreover, it is preferable that it is 5 mass% or less, and it is still more preferable that it is 4 mass% or less. The ratio of the polymer component to the metal oxide nanoparticles is preferably 0.01% by mass to 5% by mass, and more preferably 1% by mass to 4% by mass.

The proportion of the polymer component in the outer shell portion 33 is measured by the following method.
Using a thermogravimetric apparatus (for example, EXSTAR6000, TG / DTA6300 manufactured by Seiko Instruments Inc.), the mass A (mg) of the hollow particles 3 is heated from 30 ° C. to 1000 ° C. in an oxidizing atmosphere at a rate of temperature increase of 5 ° C. / Heat in minutes. When the mass decrease at the thermal decomposition temperature of the polymer component is B (mg), the content of the polymer component in the outer shell portion 33 of the hollow particle 3 can be calculated by the following equation.
Polymer component content (% by mass) of outer shell portion 33 = (B / A) × 100
In addition, the solid content ratio (mass ratio) of the metal oxide nanoparticle and the polymer component contained in the raw material liquid used in the method for manufacturing the hollow particle 3 described later is the metal of the outer shell portion 33 of the hollow particle 3 as it is. When it becomes mass ratio of an oxide nanoparticle and a high molecular component, it can also be set as the content rate of the high molecular component of the outer shell part 33 of the hollow particle 3 from the solid content ratio or compounding ratio in a raw material liquid. In addition, the polymer component is extracted from the hollow particles 3 with a solvent in which the polymer component can be dissolved, and the extracted liquid is subjected to heat such as high performance liquid chromatography, gas chromatography, mass spectrometry, differential scanning calorimetry, thermogravimetry, etc. The content of the polymer component in the outer shell portion 33 can also be measured by instrumental analysis such as analysis or a combination thereof.

  In addition to being able to enclose various components in the hollow portion 32, the hollow particles 3 having the outer shell portion 33 having the above-described structure have a sustained release property or a disintegration property due to physical impact, It has one or two or more advantageous properties such as having properties, and can be used for various applications by utilizing one or more of these properties. For example, it can be used as a sustained release agent for pharmaceuticals, perfume ingredients and functional ingredients. Further, when the outer shell portion 33 includes a polymer component, the hollow particles 3 have one or more advantageous properties such as flexibility due to the polymer component and disintegration due to the solvent or heat of the outer shell portion. One or more of them can be utilized for various purposes. For example, it can be used as a drug delivery substrate in which various functional components are encapsulated in the hollow portion 32 and the functional components are gradually released according to the external environment. Moreover, it can mix | blend with a resin film or a composition for coating materials, and can be used as the filler etc. which provide the air phase filled in the hollow part to those membrane materials, and various functional components.

  Next, the suitable manufacturing method of the hollow particle 3 demonstrated so far is demonstrated. In this production method, within a range of 1 nm or more and 300 nm or less, a raw material liquid containing at least two kinds of metal oxide nanoparticles having different particle diameters, a solvent, and a polymer component is electrostatically sprayed, thereby An electrostatic spraying step of drying the generated droplets in the gas phase; As the raw material liquid, a solution in which metal oxide nanoparticles are dispersed in a solution in which a polymer component is dissolved or dispersed in a solvent is preferably used. Further, within the range of types and amounts that can solve the problems of the present invention, known fillers, colorants such as pigments, surfactants, silane coupling agents, inorganic particles, resin particles, crosslinking agents, electrolytes, acids and bases Perfumes, oily ingredients, waxes, heat storage materials, pharmaceutical ingredients, and the like can be blended.

  As the metal oxide nanoparticles contained in the raw material liquid, each metal oxide nanoparticle has a particle size distribution that shows peaks at different particle diameter positions when the particle size distribution is measured by the dynamic light scattering method. It is preferable. In this case, the position of each peak is preferably in the range of 1 nm to 300 nm. By using such two or more kinds of metal oxide nanoparticles having different particle diameters, the hollow particles 3 having the outer shell portion 33 having the structure shown in FIG. 1 can be successfully obtained.

  In particular, when the particle size distribution is measured for each metal oxide nanoparticle, it is preferable that the respective peaks do not overlap with each other, and the variation coefficient of each particle diameter, that is, the CV value is 20% or less. The coefficient of variation CV is defined by σ / r. In the formula, r is a volume-based arithmetic mean diameter when the particle size distribution of each metal oxide nanoparticle is measured with a dynamic light scattering particle size distribution measuring apparatus. σ is the standard deviation of the volume-based arithmetic mean diameter when the particle size distribution of each metal oxide nanoparticle is measured with a dynamic light scattering particle size distribution measuring device. Note that “the peaks do not overlap” includes not only the case where the adjacent peaks do not overlap at all, but also the case where the tails of the adjacent peaks partially overlap. The case where the skirts of adjacent peaks partially overlap means that the particle size distribution obtained when the particle size distribution of the small particle size particle and the large particle size particle are overlapped remains without disappearing the two peaks. . That is, the case where the particle size distribution peak obtained by superimposing both particle size distributions is not included.

The raw material liquid preferably contains two kinds of small particle diameter particles 35a and large particle diameter particles 35b having different particle diameters as metal oxide nanoparticles. The small particle size particle 35 a is a source of the small particle size particle 35 A included in the outer shell portion 33. The large particle size particle 35 b is a source of the large particle particle 35 B included in the outer shell portion 33. The small particle size particles 35a preferably have a particle size d1 of ₁ nm or more, more preferably 5 nm or more, and even more preferably 30 nm or more. It is preferable that the small particles 35a is the particle diameter _{d 1} is 50nm or less, and more preferably 45nm or less. Particle size _{d 1} of the small particles 35a is preferably 1nm or more 50nm or less, still more preferably 5nm or more 45nm or less, and still more preferably 30nm or more 45nm or less. On the other hand, with regard to large particles 35b, the particle diameter _{d 2,} subject to be larger than the particle diameter of the small particles 35a, preferably at 20nm or more, further preferably 30nm or more, More preferably, it is 80 nm or more. It is preferable that large particles 35b is the particle diameter _{d 2} is 300nm or less, and more preferably, further preferably 200nm or less, 130nm or less. Particle size _{d 2} of the large particles 35b is preferably 20nm or more 300nm or less, further preferably 30nm or more 200nm or less, and more preferably 80nm or more 130nm or less. By doing so, the hollow particles 3 having the outer shell portion 33 having the structure shown in FIG. 1 can be successfully obtained.

Particle size d ₂ of the particle diameter d ₁ and the large particles 35b of the small particles 35a is the arithmetic mean diameter on a volume basis when each measured by a dynamic light scattering particle size distribution analyzer. The particle diameters d ₁ and d ₂ of the small particle diameter particles 35 a and the large particle diameter particles 35 b contained in the raw material liquid are the small particle diameter particles 35 A and the large particle diameters 35 A included in the outer shell portion 33 constituting the hollow particles 3, respectively. The particle diameter substantially coincides with the particle diameters D ₁ and D ₂ of the particle 35B.

Metal oxide nanoparticles contained in the raw material solution is, if it contains small particles 35a and large particles 35b, and the particle size d ₁ of the small particles 35a which are individually measured, large particles The particle diameter ratio d ₁ / d _{2 to} the particle diameter d _{2 of} 35b is preferably 0.1 or more, and more preferably 0.2 or more. The particle diameter ratio d ₁ / d ₂ is preferably 0.6 or less, more preferably 0.5 or less, and even more preferably 0.4 or less. The particle diameter ratio d ₁ / d ₂ is preferably 0.1 or more and 0.6 or less, more preferably 0.1 or more and 0.5 or less, and 0.2 or more and 0.4 or less. Is more preferable. By doing so, the hollow particles 3 having the outer shell portion 33 having the structure shown in FIG. 1 can be successfully obtained.

  When the metal oxide nanoparticles contained in the raw material liquid include the small particle size particle 35a and the large particle size particle 35b, the small particle size particle 35a occupies the total of the small particle size particle 35a and the large particle size particle 35b. The mass fraction of is preferably 0.35 or more, and more preferably 0.6 or more. Further, the mass fraction is preferably 0.95 or less, and more preferably 0.9 or less. The mass fraction is preferably from 0.35 to 0.95, and more preferably from 0.6 to 0.9. By doing so, the hollow particles 3 having the outer shell portion 33 having the structure shown in FIG. 1 can be successfully obtained.

  In the electrostatic spraying process, as shown in FIG. 2A, the charged droplets 31 sprayed by electrostatic spraying are subjected to Rayleigh splitting along with the evaporation of the solvent 36, and as shown in FIG. Thus, the small-diameter droplet 31A is generated, and the solvent is evaporated from the surface of the droplet 31A, so that the concentrations of the metal oxide nanoparticles 35a and 35b and the polymer component 34 in the vicinity of the surface are increased. As the drying proceeds further, as shown in FIG. 2C, particles 37 having a coating 33A made of metal oxide nanoparticles 35a and 35b and a polymer component 34 are generated in the vicinity of the surface. As shown in FIG. 2D, the solvent inside the particle 37 on which the coating 33A is formed has a hollow portion 32 and an outer shell portion 33, and the outer shell portion 33 has a polymer component. 3 A of hollow particles 3A containing 34 are obtained.

  In order to obtain the minute hollow particles 3A having the hollow portion 32, the timing at which the coating 33A is formed is important. For example, when a film is formed on a droplet immediately after spraying by electrostatic spraying, subsequent splitting is inhibited, and it becomes difficult to obtain fine hollow particles having an average particle diameter of 10 μm or less. On the other hand, even if the droplets sprayed by electrostatic spraying are repeatedly formed into particles by repeating Rayleigh splitting, if a coating is not formed, the average particle diameter becomes fine particles of 10 μm or less, but as shown in FIG. The solid particles 38 having no hollow portion are likely to be obtained.

  In the present invention, as described above, the metal oxide nanoparticles included in the raw material liquid are in the range of 1 nm or more and 300 nm or less as described above from the viewpoint of efficiently generating the minute hollow particles 3A with an appropriate timing for forming the coating. The metal oxide nanoparticles 35a and 35b having at least two kinds of different particle diameters are used. When the particle diameters of the metal oxide nanoparticles 35a and 35b are less than 1 nm, the metal oxide nano particles 35a and 35b have a speed equal to or greater than the rate of decrease in the radius of the droplet accompanying the evaporation of the solvent from the surface of the droplet 31A. Since the particles 35a and 35b are easily diffused toward the center of the droplet 31A, the concentration of the metal oxide nanoparticles 35a and 35b in the vicinity of the surface of the droplet 31A is not easily increased. As a result, the outer shell portion 33 is obtained. The coating 33A is difficult to be formed. On the other hand, when the particle diameter of the metal oxide nanoparticles 35a and 35b is 1 nm or more, particularly 10 nm or more, the metal oxide nanoparticle 35a and 35b has a metal oxide nanoparticle with respect to the decreasing speed of the droplet radius accompanying the evaporation of the solvent from the surface of the droplet 31A. The diffusion rate of the particles 35 toward the center of the droplet 31 </ b> A tends to be slow, and the coating 33 </ b> A that becomes the outer shell portion 33 is easily formed.

  On the other hand, when the particle diameter of the metal oxide nanoparticles 35a and 35b is more than 300 nm, a film is easily formed at an early stage after electrostatic spraying, and Rayleigh splitting and evaporation from the surface are suppressed, and the average particle diameter is reduced. However, it is difficult to obtain fine hollow particles having a particle size of 10 μm or less. Thus, when the timing at which the coating 33A is formed after spraying is too early, hollow particles are easily formed, but it is difficult to obtain minute hollow particles. In addition, the distance between the metal oxide nanoparticles increases, and the density of the outer shell portion 33 tends to decrease. Therefore, in order to obtain fine hollow particles, (a) a film is formed at an appropriate timing after spraying until reaching the collection surface, and (b) metal oxide nano It is advantageous to use a small particle size particle 35a and a large particle particle size 35b as the particles to increase the density of the outer shell portion 33.

  Factors affecting the timing of film formation include, in addition to the particle diameters of the metal oxide nanoparticles 35a and 35b described above, viscosity of the raw material liquid, environmental conditions for spraying the raw material liquid, easiness of volatilization of the solvent, etc. Is mentioned. These factors are adjusted as appropriate so that a film is formed when the electrostatically sprayed droplets are appropriately finely divided by Rayleigh splitting.

  The polymer component contained in the raw material liquid is an organic polymer, which may be a water-soluble polymer or a water-insoluble polymer. Natural polymers or synthetic polymers may be used. Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyacrylic acid, sodium polyacrylate, polymethacrylic acid, polysodium methacrylate, polyvinylpyrrolidone, chitosan, pullulan, hyaluronic acid, chondroitin sulfate, poly -Γ-glutamic acid, modified corn starch, β-glucan, gluco-oligosaccharide, heparin, mucopolysaccharide such as keratosulfate, cellulose, pectin, xylan, lignin, glucomannan, galacturonic acid, psyllium seed gum, tamarind seed gum, gum arabic, tragacanth gum , Soybean water-soluble polysaccharides, alginic acid, carrageenan, laminaran, agar (agarose), gelatin, fucoidan, methylcellulose, hydroxypropylcellulose, hydro Examples thereof include xylethylcellulose, hydroxypropylmethylcellulose, partially saponified polyvinyl alcohol, low saponified polyvinyl alcohol, and carboxymethylcellulose. Examples of the water-insoluble polymer include polypropylene, polyethylene, polystyrene, polybutyl alcohol, polyurethane, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, poly-m-phenylene terephthalate, poly-p-phenylene isophthalate, and polyfluoride. Vinylidene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polyvinylidene chloride-acrylate copolymer, polyacrylonitrile, polyacrylonitrile-methacrylate copolymer, polycarbonate, polyarylate, polyester carbonate, nylon, aramid, poly Examples include caprolactone, polylactic acid, polyglycolic acid, collagen, polyhydroxybutyric acid, polyvinyl acetate, and polypeptide Kill. The polymer component to be used is not limited to one type, and any plurality of types can be used in combination from the exemplified polymer components.

  When a solution in which a polymer component is dissolved or dispersed in a solvent is used as the raw material liquid, the solvent includes water, methanol, ethanol, 1-propanol, 2-propanol, hexafluoroisopropanol, tetraethylene glycol, triethylene glycol, Dibenzyl alcohol, 1,3-dioxolane, 1,4-dioxane, methyl ethyl ketone, methyl isobutyl ketone, methyl-n-hexyl ketone, methyl-n-propyl ketone, diisopropyl ketone, diisobutyl ketone, acetone, hexafluoroacetone, phenol, Formic acid, methyl formate, ethyl formate, propyl formate, methyl benzoate, ethyl benzoate, propyl benzoate, methyl acetate, ethyl acetate, propyl acetate, dimethyl phthalate, diethyl phthalate, dipropyl phthalate, salt Methyl, ethyl chloride, methylene chloride, chloroform, o-chlorotoluene, p-chlorotoluene, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, trichloroethane, dichloropropane, dibromoethane, dibromopropane, methyl bromide , Ethyl bromide, propyl bromide, acetic acid, benzene, toluene, hexane, cyclohexane, cyclohexanone, cyclopentane, o-xylene, p-xylene, m-xylene, acetonitrile, tetrahydrofuran, N, N-dimethylformamide, pyridine, etc. It can be illustrated. The solvent to be used is not limited to one type, and a plurality of arbitrary types may be selected from the exemplified solvents and mixed.

  In particular, when water or water containing more than 50% by mass is used as the solvent, it is preferable to use water-soluble polymers such as the various water-soluble polymers described above. A water-soluble polymer can be used individually by 1 type or in combination of 2 or more types. Among water-soluble polymers, water-soluble polysaccharides or water-soluble polysaccharide derivatives are suitable. As the water-soluble polysaccharide derivative, alkyl cellulose or hydroxyalkyl cellulose such as methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose is particularly suitable. Examples of the solvent containing 50% by mass of water include a mixture of water and alcohols (methanol, ethanol, etc.). The content (mass%) of the polymer component in the raw material liquid is preferably 0.01% or more, more preferably 1% or more, preferably 5% or less, more preferably 4% or less. Preferably they are 0.01% or more and 5% or less, More preferably, they are 1% or more and 4% or less.

  From the viewpoint of obtaining minute hollow particles 3A having an average particle diameter of 10 μm or less, the droplets 31 are dried so that the coating 33A is formed at an appropriate timing after spraying until reaching the collection surface. The dew point temperature of the gas phase is preferably −50 ° C. or higher, more preferably −30 ° C. or higher, still more preferably −20 ° C. or higher, and preferably 20 ° C. or lower, more preferably 10 ° C. or lower, still more preferably 0. It is preferably -50 ° C or higher and 20 ° C or lower, more preferably -30 ° C or higher and 10 ° C or lower, and further preferably -20 ° C or higher and 0 ° C or lower.

  FIG. 3 shows a schematic configuration of an example of a hollow particle production apparatus preferably used in the electrostatic spraying process. The hollow particle manufacturing apparatus 1 shown in the figure includes a liquid spray unit 2 that sprays a liquid 30 that is a raw material liquid, and a raw material liquid supply unit that supplies the liquid 30 that is a raw material liquid to the liquid spray unit 2 (see FIG. (Not shown), compressed air supply means (not shown) for supplying compressed air 4 to the liquid spraying section 2, high voltage generating means 5, and the liquid discharge port 23 formed in the liquid spraying section 2 The counter electrode 6 is provided.

  The liquid spray unit 2 includes a liquid discharge nozzle 22 including a conductive metal thin tube 21 through which a liquid 30 as a raw material liquid passes, a liquid discharge port 23 formed at one end of the liquid discharge nozzle 22, a liquid discharge A first injection port 24 for discharging compressed air from the periphery of the outlet 23 and a second injection port 25 for injecting compressed air are provided. The second injection port 25 may be provided with a corona discharge needle electrode 26 to generate an ion transport flow including air ions generated by the corona discharge. The high voltage generating means 5 can apply a high voltage to the conductive metal thin tube 21 and can also apply a high voltage to the corona discharge needle electrode 26 to generate a corona discharge. A potential difference may be generated between the metal thin tube and the needle electrode and the counter electrode. The counter electrode 6 is grounded or a voltage having a polarity opposite to that of the charged particles sprayed from the liquid discharge port 23 is applied.

  The manufacturing apparatus 1 will be further described. The liquid discharge nozzle 22 is composed of a conductive metal thin tube 21 itself. The metal thin tube 21 is a straight straight tube, and the liquid 30 which is a raw material liquid can circulate inside. The inner diameter of the metal thin tube 21 is, for example, not less than 0.1 mm and not more than 1.0 mm, preferably not less than 0.3 mm and not more than 0.5 mm. The outer diameter of the metal thin tube 21 is, for example, 0.2 mm or more and 2.0 mm or less, preferably 0.3 mm or more and 1.5 mm or less. By setting the inner diameter and the outer diameter of the metal thin tube 21 within this range, the liquid 30 as the raw material liquid can be easily and quantitatively fed, and the electric field is concentrated in a narrow region around the nozzle, The liquid can be charged efficiently.

  The metal thin tube 21 and the liquid discharge nozzle 22 are supported by the case body 20 of the liquid spray unit 2 such that a common central axis extends in one direction X, and an opening opening at one end of the liquid discharge nozzle 22 However, the liquid discharge port 23 is formed. When the liquid spray unit 2 is viewed from the front, the liquid discharge port 23 has a circular shape, and a compressed air first injection port 24 that ejects compressed air is formed around the liquid discharge port 23. As shown in FIG. 5, the first injection ports 24 are preferably formed in an annular shape surrounding the liquid discharge ports 23, but a plurality of, preferably 3 to 20, are formed around the liquid discharge ports 23. The first injection port 24 may be arranged in an annular shape so as to surround the liquid discharge port 23. The front view of the liquid spray unit 2 refers to a state in which the liquid discharge port 23 of the liquid discharge nozzle 22 is viewed from the front. In the apparatus 1 of the present embodiment, the liquid spray unit 2 is viewed from the lower side in FIG. It is in a state of viewing.

  The first injection port 24 is formed at one end of the first flow path 24A communicating with the internal space 42 to which compressed air is supplied by the compressed air supply means, and the compressed air 4 is introduced into the internal space 42 by the compressed air supply means. Is supplied, the compressed air that has passed through the first flow path 24 </ b> A is ejected from the first injection port 24 as the atomized compressed air 41. Further, the raw material liquid supply means can quantitatively supply the liquid 30 which is a fine particle raw material liquid to the liquid discharge nozzle 22. The liquid discharge nozzle 22 and the first injection port 24 function as a two-fluid nozzle by supplying the liquid 30 as the raw material liquid to the liquid discharge nozzle 22 while ejecting the atomized compressed air from the first injection port 24. Then, the liquid 30 as the raw material liquid is atomized and sprayed from the liquid discharge port 23.

  FIG. 4 shows an example in which the extending direction X of the central axis of the liquid discharge nozzle 22 coincides with the vertical direction, and the first flow path 24A extends along the central axis of the liquid discharge nozzle 22. In the present invention, the direction in which the compressed air 4 or the atomized liquid 3 is ejected is not particularly limited, and may be a horizontal direction, an obliquely upward direction, an obliquely downward direction, or the like instead of the downward direction in the vertical direction. The first flow path 24A may be parallel to the central axis of the liquid discharge nozzle 22 or may be non-parallel.

  Further, the counter electrode 6 disposed opposite to the liquid discharge port 23 is provided at a position separated from the liquid discharge port 23 of the liquid discharge nozzle 22. Specifically, the counter electrode 6 is disposed facing the opening of the liquid discharge port 23 at a position in front of the opening of the liquid discharge port 23 of the liquid discharge nozzle 22. The counter electrode 6 is made of metal or the like and has conductivity. The distance (shortest distance) between the tip of the liquid discharge nozzle 22 and the counter electrode 6 is preferably 200 mm or more and 1500 mm or less, and more preferably 300 mm or more and 1000 mm or less.

  As shown in FIG. 3, the high voltage generating means 5 is configured to be able to apply a high voltage between the conductive metal thin tube 21 of the liquid discharge nozzle 22 and the counter electrode 6. In the example shown in FIG. 3, a negative voltage is applied to the metal thin tube 21 of the liquid discharge nozzle 22, the metal thin tube 21 is negative, the counter electrode 6 is grounded, and the metal thin tube 21 and the counter electrode 6 are interposed between them. Produces an electric field. In order to generate an electric field between the metal thin tube 21 and the counter electrode 6, a positive voltage is applied to the metal thin tube 21 of the liquid discharge nozzle 22 instead of applying the voltage shown in FIG. The counter electrode 6 may be grounded. Further, the counter electrode 6 is not necessarily grounded, and a voltage having a polarity opposite to that of the metal thin tube 21 may be applied. The voltage generated by the high voltage generating means 5 is preferably a DC voltage.

  For the high voltage generating means 5, a known device such as a high voltage power supply device can be used. The potential difference applied between the metal thin tube 21 and the counter electrode 6 is 1 kV or more, particularly 5 kV or more. This sufficiently charges the liquid droplets of the raw material liquid sprayed from the liquid discharge port 23 and causes Rayleigh splitting of the liquid droplets. It is preferable from the point of promoting. The potential difference applied between the metal thin tube 21 and the counter electrode 6 is preferably 1 kV to 60 kV, more preferably 5 kV to 50 kV.

  The liquid spray unit 2 in the manufacturing apparatus 1 illustrated in FIG. 3 includes a second injection port 25 that injects compressed air. As shown in FIG. 5, the second ejection port 25 in the manufacturing apparatus 1 is farther from the center of the liquid ejection port 23 than the first ejection port 24, and the first ejection port 24 to the second ejection port. The distance L3 to 25 is longer than the distance L1 from the center of the liquid discharge port 23 to the first ejection port 24. As shown in FIG. 5, it is preferable that a pair of the second ejection ports 25 is formed at least on both sides of the liquid ejection port 23. Further, as shown in FIG. 6, the second ejection port 25 is formed on an inclined surface 27 that is formed around the liquid ejection port 23 with a space between the second ejection port 23 and the liquid ejection port 23. The inclined surface 27 has an inclined lower end on the side close to the liquid discharge port 23 and an inclined upper end on the side far from the liquid discharge port 23. The inclined surface 27 is preferably planar, but may be convex or concave. Instead of providing a pair of the second ejection ports 25 so as to sandwich the liquid ejection port 23, three or more second ejection ports 25 can be equally provided around the liquid ejection port 23.

  As shown in FIGS. 3 and 4, the second injection port 25 is connected to the above-described internal space 42 via the inclined channel 25 </ b> B having an angle with respect to the central axis of the distal channel 25 </ b> A and the liquid discharge nozzle 22. Communicate. When the compressed air 4 is supplied to the internal space 42 by the compressed air supply means, a part of the compressed air 4 is ejected from the first injection port 24 as the atomized compressed air 41 through the first flow path 24A as described above. On the other hand, the other part is injected from the second injection port 25 through the distal flow path 25A and the inclined flow path 25B. The first flow path 24A, the distal flow path 25A, and the inclined flow path 25B each preferably have a cylindrical inner surface. The distal flow path 25A and the inclined flow path 25B communicate with each other to form a continuous flow path for supplying air to the second injection port 25. The distal flow path 25A is compared to the inclined flow path 25B. And far from the second injection port 25. The distal flow path 25A shown in FIG. 4 is formed in parallel with the central axis of the liquid discharge nozzle 22, but may be non-parallel, and the distal flow having an angle with respect to the inclined flow path 25B. The path 25A itself may not exist.

  Further, the second injection port 25 may be provided with a needle electrode 26 for generating corona discharge. The high voltage generating means 5 of the present embodiment is configured to be able to apply a high voltage for causing corona discharge to the needle electrode 26 as well. As shown in FIG. 3, in the present embodiment, a voltage having the same polarity is applied to the metal thin tube 21 and the needle electrode 26 of the liquid discharge nozzle 22 via the branched metal conductor 51. Yes.

  The needle electrode 26 is preferably arranged so that the tip of the needle electrode 26 protrudes from the second injection port 25. The needle electrode 26 may be fixed to the inner surface of the distal channel 25A or the inclined channel 25B, and is supported so as not to contact either the inner surface of the distal channel 25A or the inner surface of the inclined channel 25B. May be. As the needle electrode 26, a discharge metal wire or the like can be preferably used. As the material for the discharge metal wire used as the needle electrode, a material that is difficult to corrode with a conductive metal material such as tungsten, brass, copper, or molybdenum is preferable. In addition, the needle electrode 26 is preferably strong enough to withstand the injection of compressed air and has an appropriate thickness that does not hinder the injection. For example, the diameter of the needle electrode 26 is 60% or less of the diameter of the second injection port. Is more preferable, and more preferably 40% or less. For example, when the diameter of the second injection port is 0.5 mm, 0.2 to 0.3 mm is preferable. The needle electrode 26 is used with its tip sharpened like a needle to facilitate discharge. When using a discharge metal wire or the like having a sharp tip as the needle electrode 26, the diameter of the needle electrode 26 is the diameter at the maximum diameter portion. Further, the needle electrode 26 may be a rod-shaped body with a sharp tip.

  In addition, the protrusion length L5 (see FIG. 4) of the needle electrode 26 from the second injection port 25 is preferably 0.5 mm or more, more preferably 1 mm or more, from the viewpoint of easy occurrence of corona discharge. From the viewpoint of reducing the degree of obstructing the air flow and preventing the adhesion of the liquid, it is preferably 3 mm or less, more preferably 2 mm or less. In addition, when the member in which the distal flow path 25A and the inclined flow path 25B are formed is a conductor, the needle electrode 26 is fused to the member, and the metal lead 51 from the high voltage generating means 5 and the like are attached to the member. May be connected.

  The example shown in FIG. 3 is a case where the same negative voltage as the metal thin tube 21 of the liquid discharge nozzle 22 is applied to the needle electrode 26, but instead of the method of applying the voltage shown in FIG. A positive voltage may be applied to the metal thin tube 21 of the discharge nozzle 22 and the counter electrode 6 may be grounded. The voltage generated by the high voltage generating means 5 is preferably a DC voltage.

  The potential difference applied between the needle electrode 26 and the counter electrode 6 is preferably 15 kV or more, particularly 20 kV or more from the viewpoint of generating a large amount of air ions by corona discharge. On the other hand, it is preferable that this potential difference is 60 kV or less, particularly 50 kV or less because it is not necessary to make the insulation of the device excessive. The potential difference applied between the needle electrode 26 and the counter electrode 6 is preferably 15 kV to 60 kV, more preferably 20 kV to 50 kV. The high voltage generating means 5 may have a device for applying a voltage to the needle electrode 26 in addition to a device for applying a voltage to the metal thin tube of the liquid discharge nozzle 22, and has a function of generating different voltages. Different voltages may be applied independently to the thin metal tube of the liquid discharge nozzle 22 and the needle electrode 26 using the power supply device provided.

  The manufacturing apparatus 1 of the present embodiment includes a particulate collection unit 7 on the surface of the counter electrode 6. The fine particle collection unit 7 may be the surface of the counter electrode 6 made of a conductive material, but the surface of the counter electrode 6 may be covered with a thin film or the like and used as the collection unit 7.

  In order to perform the electrostatic spraying process using the manufacturing apparatus 1 described above, the compressed air is supplied to the liquid spray unit 2 of the manufacturing apparatus 1 by the compressed air supply means, and a known raw material liquid such as a metering pump is used. The liquid 30 which is a raw material liquid is supplied to the liquid spray part 2 by a supply means (not shown). By supplying the compressed air, the atomized compressed air 41 is ejected from the first ejection port 24 located around the liquid discharge port 23 opened to one end of the metal thin tube 21, and the compressed air is ejected from the second ejection port 25. Be injected.

  In this state, when the high voltage generating means 5 is operated and a negative DC high voltage is applied to the conductive metal thin tube 21 and the needle electrode 26 through which the liquid as the raw material liquid for fine particles passes, The flowing liquid 30 is negatively charged, and the charged liquid 30 is atomized and sprayed from the liquid discharge port 23 by the atomized compressed air 41 ejected from the periphery of the liquid discharge port 23. The liquid 30 is formed into droplets by spraying and charged charged droplets 31. The charged droplets 31 generated by the spray ride on the airflow generated by the injection of the compressed air from the first injection port 24 and flow toward the counter electrode 6 along the electric field generated in the metal thin tube 21 and the counter electrode 6. .

In addition, air ions are generated by corona discharge from the needle electrode 26 due to the application of a negative high voltage to the needle electrode 26, and air currents including air ions are generated by the injection of compressed air from the second injection port 25. An ion carrier stream 45 is generated. Air ions contained in the ion transport flow 45 are negatively charged with the same polarity as the charged droplets 31. Further, the second ejection port 25 is formed on an inclined surface 27 having an inclined lower end on the side close to the liquid discharge port 23, and the ion transport flow 45 containing air ions is the above-described charged liquid as shown in FIG. The droplet stream F is sprayed at an angle. As air ions (negative ions) generated by corona discharge, for example, O ₂ ⁻ (H ₂ O) _n , O ₃ ⁻ (H ₂ O) _n , NO ₂ ⁻ (H ₂ O) _n , NO ₃ ⁻ ( H ₂ O) _n , CO ₃ ⁻ (H ₂ O) _n , NO ₃ ⁻ , NO ₃ ⁻ (HNO ₃ ) _n , NO ₃ ⁻ NO _{3 and the} like.

  By blowing the ion transport flow 45 containing air ions charged to the same polarity as the charged droplet 31 to the flow F of charged droplets generated by spraying, the charge amount of the charged droplet 31 in the flow F increases. The reason why the amount of charge increases is that charged droplets and air ions are usually of the same polarity, and if they are parallel flows, they will not repel and coalesce. Since air ions are collided, the air ions are taken into the charged droplets, and as a result, the charge amount is considered to increase.

  As shown in FIGS. 2 (a) to 2 (d), the charged droplet 31 sprayed by electrostatic spraying causes Rayleigh splitting along with the evaporation of the solvent 36, thereby generating a small-sized droplet 31A. The solvent is also evaporated from the surface of the droplet 31A, the concentration of the metal oxide nanoparticles 35a and 35b and the polymer component 34 in the vicinity of the surface is increased, and further drying proceeds, whereby the hollow particle 3A is obtained. Then, the hollow particles 3 </ b> A are collected in the collection unit 7. Collection is performed when the counter electrode 6 is grounded, or when the counter electrode has a polarity opposite to that of the fine particles, that is, a positive voltage when the fine particles are negatively charged, and a negative voltage when the fine particles are positively charged. You may carry out in the state which applied. Further, it is possible to inject compressed air from the second injection port 25 without installing the needle electrode 26. At that time, since the jetted airflow does not contain air ions, the charge amount of the charged droplets 31 does not increase.

  From the viewpoint of more effectively increasing the amount of charge due to the blowing of the ion carrier flow 45, the central axis 25c of the second jet port 25, which is a jet port for jetting compressed air for generating the ion carrier flow, and liquid It is preferable that the central axis 23c of the discharge port 23 intersects at an intersecting angle θ (see FIG. 4) of 40 degrees or more and 80 degrees or less in a range where the distance L from the liquid discharge port 23 is 2 mm or more and 6 mm or less. By setting the distance L within the range of 2 mm or more and 6 mm or less, the ion transport flow 45 can be sprayed on the charged droplet flow F in a state where the charged droplets do not diffuse so much and the concentration of air ions is high. By increasing the charging efficiency and setting the crossing angle θ within the range of 40 degrees or more and 80 degrees or less, the ion transport flow 45 can be strongly collided with the flow F of the charged droplets, and the charging efficiency is increased. It is also possible to prevent the droplets from being scattered widely because the angle is too large.

  Note that the intersection of the central axis 25c of the second ejection port 25 and the central axis 23c of the liquid discharge port 23 may intersect at the point P even if the central axes are in a twisted position. The central axis 25c of the second injection port 25 preferably passes through a spherical shell with a radius of 0.5 mm centered on the point P on the central axis 23c of the liquid discharge port 23, and the spherical shell with a radius of 0.35 mm More preferably, the central axis 25c of the second injection port 25 passes through the inside. If the central axis 25c of the second ejection port 25 passes through the inside of the spherical shell having the radius centered on the point P on the central axis 23c of the liquid discharge port 23, it is assumed that the point P intersects. .

  From the same point of view, the central axis 25c of the second ejection port 25 and the central axis 23c of the liquid discharge port 23 intersect at an angle θ of 45 to 60 degrees within a range of a distance L from the liquid discharge port 23 of 3 to 5 mm. It is more preferable to cross at The central axis 23c of the liquid discharge port 23 is the central axis of the flow path of the liquid 30 adjacent to the liquid discharge port 23, and protrudes from the liquid discharge port 23 in addition to the portion located in the flow path of the liquid 30. An extension in the axial direction is also included. In the present embodiment, the central axis 23c of the liquid discharge port 23 coincides with the central axis of the liquid discharge nozzle 22 and an extension portion thereof in the axial length direction. The central axis 25c of the second injection port 25 is a flow channel adjacent to the second injection port 25, that is, the central axis of the inclined flow channel 25B described above. In addition to the portion located in the flow channel 25B, the second injection port An extension in the axial length direction protruding from the mouth 25 is also included.

  In the electrostatic spraying process of the present invention, an electrospray method that does not use compressed air can be used. However, from the viewpoint of improving the production efficiency of hollow particles by increasing the spray amount, it is performed by a method using a two-fluid nozzle. It is preferable. The two-fluid nozzle atomizes a liquid by using a flow of a high-speed gas such as compressed air, and atomizes and sprays a large amount of liquid as compared to the conventional electrospray method that generates a Taylor cone. Can do.

  In the manufacturing apparatus 1 described above, the liquid discharge nozzle 22 and the first injection port 24 function as a two-fluid nozzle, and the liquid 30 that is a raw material liquid is atomized and sprayed from the liquid discharge port 23. In an aspect in which the raw material liquid is electrostatically sprayed by a method using a two-fluid nozzle, in addition to the liquid discharge nozzle 22 and the first injection port 24, the second injection port 25 is used as in the manufacturing apparatus shown in FIG. In addition, a mode in which compressed air is jetted, a mode in which compressed air is jetted only from the first jet port 24 without providing the second jet port 25, and the like are also included.

  By performing electrostatic spraying of the liquid 30, which is a raw material liquid, using a two-fluid nozzle, the spray amount can be made relatively large. The spray amount of the raw material liquid is preferably 0.1 mL / min to 100 mL / min, and more preferably 0.2 mL / min to 50 mL / min. The spray amount here is the same as the amount of the raw material liquid supplied to the liquid discharge nozzle or the like for spraying. For example, in the manufacturing apparatus 1, the liquid 30 that is a raw material liquid is fed to the liquid discharge nozzle 22 and discharged from the liquid discharge nozzle 22, but the liquid that is the raw material liquid for the liquid discharge nozzle 22. The supply amount of 30 is the spray amount of the raw material liquid.

  When the hollow particles 3A are thus obtained, a thermal decomposition step of removing the polymer component by heating at a temperature equal to or higher than the thermal decomposition temperature of the polymer component contained in the outer shell portion 33A may be performed. For the heating, any heating device capable of heating the hollow particles 3A obtained in the electrostatic spraying process can be used. For example, an electric furnace or the like that can arbitrarily set the temperature inside the furnace can be used.

  The “thermal decomposition temperature of the polymer component” is the thermal decomposition temperature of the polymer component 34 contained in the outer shell portion 33 and is measured, for example, as follows, that is, a thermogravimetric measurement device ( For example, the polymer component 34 is heated from 30 ° C. to 1000 ° C. in an oxidizing atmosphere at a heating rate of 5 ° C./min using an Seiko Instruments Inc. product, EXSTAR6000, TG / DTA6300, etc. taking measurement. The temperature at which the mass reduction rate is 90% or more is defined as the thermal decomposition temperature.

  The thermal decomposition temperature of the polymer component varies depending on the type of polymer component, etc., but is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, and preferably 600 ° C. or lower, more preferably 500 ° C. or lower. And preferably 200 ° C. or more and 600 ° C. or less, more preferably 300 ° C. or more and 500 ° C. or less. The treatment time at the thermal decomposition temperature or higher of the polymer component is preferably 10 minutes or more, more preferably 60 minutes or more, preferably 2880 minutes or less, more preferably 1440 minutes or less, and preferably 10 minutes. It is not less than 2880 minutes, more preferably not less than 60 minutes and not more than 1440 minutes.

  After the hollow particles 3 are obtained in this way, the metal oxide nanoparticles contained in the outer shell portion 33 of the hollow particles 3 are sintered as needed at a temperature below the melting point of the metal oxide nanoparticles. A ligation step may be performed. In the sintering step, after performing the above-described polymer decomposition step, the heating temperature may be subsequently increased to perform the sintering step, or the hollow particle 3 obtained after the polymer decomposition step is performed. May be once cooled to room temperature by storage or the like, and then heated again to perform the sintering step. Further, the hollow particles 3A obtained by the electrostatic spraying process are heated at a time to the temperature at which the metal oxide nanoparticles 35 contained in the outer shell portion 33 are sintered. Oxide nanoparticles may be sintered. For the heating, any heating device capable of heating the particles can be used. For example, an electric furnace capable of arbitrarily setting the temperature inside the furnace can be used.

  The preferred temperature for sintering the metal oxide nanoparticles varies depending on the type and particle size of the metal oxide nanoparticles, the amount of impurities, etc., but in the step of sintering the metal oxide nanoparticles. The heating temperature is preferably 600 ° C. or higher, more preferably 800 ° C. or higher, more preferably 850 ° C. or higher, more preferably 900 ° C. or higher, and preferably 1500 ° C. or lower, more preferably 1300 ° C. or lower, Preferably it is 1200 degrees C or less. The heating temperature is preferably 600 ° C to 1500 ° C, more preferably 800 ° C to 1500 ° C, more preferably 850 ° C to 1300 ° C, and still more preferably 900 ° C to 1300 ° C. However, the upper limit of the heating temperature in the step of sintering the metal oxide nanoparticles is the melting point of the metal oxide nanoparticles determined for each type of metal oxide nanoparticles. When performing separately the sintering process performed after a polymer decomposition process, the heating time in a sintering process is 10 minutes or more and 2880 minutes or less, for example, More preferably, they are 60 minutes or more and 1440 minutes or less. In the sintering step performed continuously or simultaneously with the polymer decomposition step, the heating time after the temperature reaches the sintering temperature is, for example, 10 minutes to 2880 minutes, more preferably 60 minutes to 1440 minutes.

Since the hollow particles obtained by such a sintering process have a reduced porous state in the outer shell compared to the hollow particles 3 having the outer shell 33 having a porous structure shown in FIG. The molten resin does not permeate or hardly permeate inside the shell, and has high airtightness. Further, the outer shell portion has high strength and heat resistance. Furthermore, the BET specific surface area of the hollow particles is lower than before sintering. Specifically, the sintered hollow particles preferably have a BET specific surface area of 10 m ² / g or less, more preferably 1.0 m ² / g or less, and 0.6 m ² / g or less. It is more preferable that The lower limit value of the BET specific surface area is preferably 0.01 m ² / g or more, and more preferably 0.1 m ² / g or more.

  The sintered hollow particles can be used for various applications by taking advantage of one or more advantageous properties described above. For example, it can be used as a filler for a resin and can impart properties such as low dielectric constant, low specific gravity, light diffusibility, or antireflection to the molded product. A resin sheet in which the sintered hollow particles are blended is preferably used as an interlayer insulating film used for a package substrate such as a CPU.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to embodiment mentioned above, It can change suitably.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
A raw material liquid having a formulation shown in Table 1 was prepared, and the raw material liquid was electrostatically sprayed using a hollow particle manufacturing apparatus shown in FIG. 3 to obtain fine particles. However, the needle electrode 26 was removed, and compressed air containing no air ions was injected from the second injection port.
As metal oxide nanoparticles, as shown in Table 1, silica having particle diameters of 40 nm and 125 nm, respectively, was used. The particle diameter is a volume-based arithmetic average diameter measured with a dynamic light scattering particle size distribution measuring device (nanoparticle analysis device nano Partica SZ-100 / Horiba, Ltd.). The setting conditions were nano-analysis mode, volume reference, monodispersion, narrow, and detection angle: 173 °. “HPC” and “MC” in Table 1 are hydroxypropylcellulose (Wako Pure Chemical Industries, 6.0-10.0 mPa · s) and methylcellulose (Shin-Etsu Chemical Co., Ltd., Metrolose 60SH-15). (Registered trademark)). The raw material liquid contained methyl cellulose and hydroxypropyl cellulose in a mass ratio of 3: 1. The total content of the polymer components in Table 1 shows the total amount.

The spray amount of the raw material liquid was 1 mL / min.
Other conditions were as follows.
Spraying air pressure: 0.4 MPa
Gas phase dew point: 13 ° C
Applied voltage to capillary: +20 kV
Distance from spray port to counter electrode (collecting part): 850 mm

  With respect to the hollow particles thus obtained, the average particle diameter, porosity, peak of pore diameter, total pore volume, BET specific surface area, and content of polymer component in the outer shell are shown below. It was measured by. Furthermore, about the obtained hollow particle, the particle defect rate and particle shape were measured and evaluated by the following methods. The results are shown in Table 1.

[Measurement method of average particle diameter]
Using a scanning electron microscope (JEOL Ltd., JSM-6510), the particles were observed at an acceleration voltage of 20 kV and a magnification of 5000 times. The particle size of 100-300 particles is individually measured manually with image analysis software (A Image-kun / Asahi Kasei Engineering Co., Ltd.). The number average particle diameter was calculated.

[Measurement method of porosity]
The density of the particles was measured using a dry automatic densimeter (Shimadzu Corporation, AccuPyc II 1340-10CC). In the measurement, about 1 g of particles was put in a sample cell, and the density was measured under a nitrogen gas atmosphere. From the measured density value, the porosity of the particles was calculated from the following formula.
Porosity (%) = 100 × (true density of metal oxide−measured density) / true density of metal oxide When the metal oxide is silicon oxide, the true density is 2.2 g / cm ³ . did.

[Measurement method of pore diameter peak, total pore volume, BET specific surface area]
When measuring the peak of the pore diameter and the total pore volume, a pyrolysis step was performed, and the hollow particles were heated at 500 ° C. for 2 hours to remove the polymer component. When measuring the BET specific surface area, a pyrolysis step and a sintering step were performed, and the hollow particles were heated at 1000 ° C. for 10 hours to seal pores on the particle surface.
Using a specific surface area / pore distribution measuring device (Nippon Bell Co., Ltd., trade name: BELSORP mini II), the BET specific surface area of the particles is measured by a multipoint method using liquid nitrogen, and the adsorption parameter C is positive. Values were derived within a range. The BJH method was adopted for deriving the BET specific surface area, and the peak top in the pore distribution of 100 nm or less was defined as the peak of mesopore pore diameter, and the cumulative total volume was defined as the total pore volume. The measurement sample was pretreated by heating at 110 ° C. for 1 hour.

[Method for measuring content of polymer component in outer shell]
Using a thermogravimetric measuring apparatus (for example, EXSTAR6000, TG / DTA6300, etc., manufactured by Seiko Instruments Inc.), a heating rate of 5 ° C./min. Heat with. When the mass decrease at the thermal decomposition temperature of the polymer component (measurement method described above) is B (mg), the content of the polymer component in the outer shell of the hollow particle can be calculated by the following equation. .
Content of polymer component in outer shell (%) = (B / A) × 100

[Particle defect rate]
After performing the pyrolysis step, the hollow particles before the firing step are targeted and imaged with an electron microscope with a 5000 × field of view (manufactured by SEM / JEOL), and the number of holes on the surface of the hollow particles is measured to determine the particle defect rate. Calculated. The particle defect rate is defined by the ratio of the number of particles having a roundness of 0.8 or less or the number of particles having through holes to 50 or more particles in a 5000 × field of view. The particle defect rate is a measure of the strength of the hollow particles, and the lower the particle defect rate, the higher the strength of the hollow particles.

(Particle shape)
Based on the particle defect rate measured by the above method, the particle shape was evaluated according to the following criteria.
A: Less than 20% (very few defects)
○: Less than 40% (few defects)
Δ: 40% or more and less than 60% (partially defective)
X: 60% or more (there are many defects)

[Examples 2 to 4]
Hollow particles were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were employed. About the obtained hollow particle, the same measurement and evaluation as Example 1 were performed. The results are shown in Table 1 below.

[Comparative Example 1]
This comparative example is an example in which the particle size of the small particle size particles contained in the raw material liquid is made larger than each example. Other conditions were as shown in Table 1 below. Otherwise, hollow particles were obtained in the same manner as in Example 1. About the obtained hollow particle, the same measurement and evaluation as Example 1 were performed. The results are shown in Table 1 below.

[Comparative Example 2]
This comparative example is an example in which the particle size of the small particle size particles contained in the raw material liquid is made smaller than each example. Other conditions were as shown in Table 1 below. Otherwise, hollow particles were obtained in the same manner as in Example 1. About the obtained hollow particle, the same measurement and evaluation as Example 1 were performed. The results are shown in Table 1 below.

[Comparative Examples 3 and 4]
In this comparative example, the mass fraction of small particle size particles contained in the raw material liquid is an example smaller than each example. Other conditions were as shown in Table 1 below. Otherwise, hollow particles were obtained in the same manner as in Example 1. About the obtained hollow particle, the same measurement and evaluation as Example 1 were performed. The results are shown in Table 1 below.

  As is clear from the results shown in Table 1, it can be seen that the hollow particles obtained in each example have a particle defect rate lower than that of the hollow particles obtained in the comparative example and become particles having a shape close to a sphere.

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus of hollow particle 2 Liquid spray part 21 Conductive metal thin tube 22 Liquid discharge nozzle 23 Liquid discharge port 24 1st injection port 24A Vertical flow path 25 2nd injection port 25c Center axis of 2nd injection port 26 Needle electrode 27 Inclined surface 3 Hollow particles 30 Liquid as raw material liquid 31 Charged droplet 33 Outer shell 34 Polymer component 35A Small particle size 35B Large particle size 4 Compressed air 41 Atomized compressed air 45 Ion carrier flow 5 High voltage generation Means 6 Counter electrode 7 Collection part

Claims (16)

It has an outer shell portion that is an aggregate of metal oxide nanoparticles, and a hollow portion defined inside the outer shell portion by the outer shell portion, and an average particle diameter is 0.1 μm or more and 10 μm or less. The porosity is 2% by volume or more and 70% by volume or less, the peak of the pore diameter measured by the nitrogen adsorption method is 20 nm or less, and the total pore volume measured by the nitrogen adsorption method is 0.1 cm ³ / Hollow particles having a particle size of g to 1.0 cm ³ / g.   The hollow particle according to claim 1, wherein the outer shell part is constituted by the metal oxide nanoparticles having at least two kinds of different particle diameters within a range of 1 nm to 300 nm. The metal oxide nanoparticles include two types of small particle size particles and large particle size particles having different particle sizes,
The particle diameter ratio D ₁ / D ₂ is 0.1 or more and 0.6 or less, where D ₁ is the particle diameter of the small particle and D ₂ is the particle diameter of the large particle. Hollow particles according to 2. Small particle diameter _{D 1} of the size particles is at 1nm or 50nm or less, the hollow particles according to any one of claims 1 to 3 particle size _{D 2} of the large particles is 20nm or more 300nm or less. It has an outer shell portion that is an aggregate of metal oxide nanoparticles, and a hollow portion defined inside the outer shell portion by the outer shell portion, and an average particle diameter is 0.1 μm or more and 10 μm or less. Hollow particles,
The metal oxide nanoparticles include two types of small particle size particles and large particle size particles having different particle sizes,
Hollow particles in which the particle size of the small particle size is from 1 nm to 50 nm and the particle size of the large particle size is from 20 nm to 300 nm.   The hollow particles according to claim 5, wherein the porosity is 2 vol% or more and 70 vol% or less, and the pore diameter peak measured by a nitrogen adsorption method is 20 nm or less.   The hollow particles according to any one of claims 3 to 6, wherein the mass fraction of the small particle diameter particles occupies 0.35 or more and 0.95 or less in the total of the small particle diameter particles and the large particle diameter particles.   The hollow particles according to any one of claims 1 to 7, wherein the metal oxide nanoparticles are silica. The outer shell includes a polymer component;
The hollow particles according to any one of claims 1 to 8, wherein a ratio of the polymer component to the metal oxide nanoparticles is 0.01% by mass or more and 5% by mass or less. In the range of 1 nm to 300 nm, at least two kinds of metal oxide nanoparticles having different particle diameters, a solvent, and a raw material liquid containing a polymer component are electrostatically sprayed, and droplets generated thereby A method for producing hollow particles having an electrostatic spraying step for drying in a gas phase ,
The solvent is water or contains more than 50% by weight of water,
A method for producing hollow particles, wherein the polymer component is a water-soluble polysaccharide or a water-soluble polysaccharide derivative . The metal oxide nanoparticles contained in the raw material liquid show peaks at positions of different particle diameters when the particle size distribution of each metal oxide nanoparticle is measured by a dynamic light scattering method,
The method for producing hollow particles according to claim 10, wherein the peaks do not overlap and the coefficient of variation of the particle diameter is 20% or less. The metal oxide nanoparticles include two types of small particle size particles and large particle size particles having different particle sizes,
The particle diameter ratio d ₁ / d ₂ is 0.1 or more and 0.6 or less, where d ₁ is the particle diameter of the small particle and d ₂ is the particle diameter of the large particle. Of manufacturing hollow particles. Small particles have a particle diameter _{d 1} is 1nm or more 50nm following method for producing hollow particles according to claim 12 particle size _{d 2} of the large particles is 20nm or more 300nm or less.   The method for producing hollow particles according to claim 12 or 13, wherein the mass fraction of the small particle diameter particles occupies 0.35 or more and 0.95 or less in the total of the small particle diameter particles and the large particle diameter particles.   The hollow particle production according to any one of claims 10 to 14, further comprising a thermal decomposition step of removing the polymer component by heating at a temperature equal to or higher than a thermal decomposition temperature of the polymer component after the electrostatic spraying step. Method. A hollow having a BET specific surface area of 10 m ² / g or less measured by a nitrogen adsorption method, comprising a step of sintering the hollow particles according to claim 1 at 600 ° C. or more and 1500 ° C. or less. Particle production method .

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