JP2013133250A - Nano hollow particle made of silica shell, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve low agglomeration to secondary particles, high dispersibility, a low cost, and environmental protection.SOLUTION: Nano hollow particles 1 made of silica shells is manufactured by dispersing hydroxyapatite particles 2 which are calcium phosphate particles in a dry powdery state having a predetermined size and shape in ethanol as an organic solvent, and mixing therewith tetraethoxysilane as a silicon alkoxide and ammonia water as a basic catalyst to form silica-coating particles 3 having the silica shells 1a formed on the surface of the hydroxyapatite particles 2, and then setting the hydrogen ion concentration exponent in a range of pH 2-4 with an aqueous solution of dilute hydrochloric acid as an aqueous acid solution to dissolve the hydroxyapatite 2 inside the silica-coating particles 3 therein.

Description

  The present invention relates to a nano hollow particle composed of a nano-sized silica shell (hereinafter also simply referred to as “silica nano hollow particle”) and a method for producing the same, and in particular, silica nano particles that are less agglomerated into secondary particles and highly dispersible. The present invention relates to hollow particles and a method for producing the same.

In recent years, hollow bodies called microcapsules have attracted attention.
For example, in the field of medicine and cosmetics, in addition to sustained-release medicines and sustained-release cosmetics encapsulating active ingredients inside hollow bodies, protection of substances that degrade or deteriorate due to contact with the external environment, drug delivery systems Research has been actively conducted to utilize a hollow body (microcapsule) as a carrier for the purpose.
In the papermaking field, hollow bodies (microcapsules) containing dyes are used for pressure-sensitive paper.
In addition to this, the hollow body is expected to be applied in many fields, such as its use as a lightweight filler, and various studies have been made on its production.
In recent years, as part of nanotechnology research, application research on particles with particle sizes of several hundred nanometers or less has been actively conducted. In order to respond to the flow of technology, nano-sized ones are desired.

Here, as a technique related to hollow particles, particularly siliceous hollow particles, for example, in Patent Document 1, hollow silica powder is obtained by hydrolyzing after mixing and spraying an organosilicon compound such as methoxysilicate and ethoxysilicate and a foaming agent. Is obtained.
In Patent Document 2, alcohol, water, and an acid catalyst are added to tetraethyl orthosilicate to cause partial hydrolysis, and then dibutyl phthalate is added, and this solution is added to an aqueous ammonia solution containing a surfactant. Has been proposed to produce spherical and hollow porous silica particles by mixing and stirring, emulsifying and polycondensation reaction.

Furthermore, in Patent Document 3, micron-sized spherical silica synthesized by hydrolysis and polycondensation reaction caused by tetraalkoxysilane and water, and the shell constituting the silica particles is denser on the outer side and closer to the inner side. Micron-sized hollow spherical silica particles having a coarse concentration gradient structure have been proposed.
Moreover, in Patent Document 4, hollow silica particles composed of a dense silica shell are obtained by precipitating active silica on a support other than silica from an alkali metal silicate under specific conditions, and then removing the support. A manufacturing method has also been proposed.

Among these, the techniques described in Patent Documents 1 to 3 utilize a so-called interfacial reaction in which silica is precipitated at the gas-liquid or liquid-liquid (water phase-oil phase) interface. The resulting hollow silica particles have a spherical particle shape and a particle size of micron order or larger, and it is not possible to obtain nano-order hollow particles from submicrons.
Moreover, although it is described in Patent Document 4 that hollow silica particles of 20 nm or more can be produced, according to the experiments of the present inventors, the aggregation becomes intense when it becomes nano order, and as a result, it becomes micron order. It has been confirmed that it becomes aggregated particles. Further, in Patent Document 4, the silica shell constituting the hollow particle is formed by agglomeration of silica fine particles, and as a result, the silica shell is fine but has fine pores. They have confirmed.

  In view of such a situation, in developing nano-sized hollow particles, the present inventors wanted to have a controlled dispersion and good dispersibility in order to more effectively express the nano-sized features. As a result of diligent research focusing on the necessity of technology for controlling the properties of the shells constituting the hollow particles, in particular, pores at the molecular size, as described in Patent Document 5, highly dispersed silica nano hollow Succeeded in developing particles and has obtained a patent for this invention.

The highly dispersed silica nano hollow particles described in Patent Document 5 are nano hollow particles composed of a dense silica shell, and the primary particle diameter by transmission electron microscopy is 30 to 300 nm, and the particle diameter by dynamic light scattering is 30 to 30. In the pore distribution measured by 800 nm, mercury intrusion method or gas adsorption method, 2-20 nm pores are not detected.
And the silica nano hollow particle concerning invention of this patent document 5 prepares calcium carbonate in a water-containing cake state, uses this as a core, disperses this calcium carbonate core in a water-containing cake state in alcohol, and silicon alkoxide or the like It is manufactured by adding silica and then dissolving and removing calcium carbonate as a core by acid treatment.

JP-A-6-91194 Japanese Patent No. 2590428 Japanese Patent Laid-Open No. 11-29318 Japanese Patent No. 3419787 Japanese Patent No. 4654428

However, in the invention of Patent Document 5, calcium carbonate is used as a core, and in order to completely dissolve calcium carbonate inside after silica coating, a strongly acidic aqueous solution having a pH of less than 2 must be used. It is necessary to subject the reaction vessel to a corrosion resistance treatment or to use a material having corrosion resistance, which causes a problem of an increase in cost and a load on the surrounding environment.
Further, when silica coating particles are dispersed in a strongly acidic aqueous solution for the purpose of removing calcium carbonate as a core, unreacted silicon alkoxide or hydrolyzed silicic acid is present on the silica coating particle surface. The reaction silicon alkoxide and hydrolyzed silicic acid start a new condensation reaction with the acidic catalytic function of the strong acid aqueous solution, and form a covalent bond on the surface of the silica particle and the hollow particle in which the core inside the silica particle is dissolved As a result, there is a problem that aggregation between particles is caused.

  In addition, according to the experimental study by the present inventors, from the viewpoint of cost reduction and environmental conservation, the calcium carbonate as the core is recovered and recovered, and then the calcium carbonate is re-synthesized. It has been confirmed that the re-synthesized calcium carbonate can be reused as a core. However, reuse by resynthesis of calcium carbonate requires recovery of carbon dioxide gas generated when calcium carbonate dissolves, and a large-scale device is required to recover it, leading to increased costs. There was a problem.

Therefore, the present invention has been made to solve such problems, and from a silica shell that is less agglomerated into secondary particles, has high dispersibility, and can achieve cost reduction and environmental conservation. It is an object of the present invention to provide nano hollow particles and a method for producing the same.

  The nano-hollow particles comprising the silica shell of the invention of claim 1 are obtained by dispersing calcium phosphate particles in a dry powder state having a predetermined size and shape in an organic solvent, and mixing silicon alkoxide and a base catalyst to thereby surface the calcium phosphate particles. Then, silica shells are formed to form silica-coated particles, and then the calcium phosphate inside the silica-coated particles is dissolved by setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4 with an acid aqueous solution.

  Here, the “calcium phosphate” may be a salt composed of calcium ion and phosphate ion or diphosphate ion. For example, hydroxyapatite, oxyapatite, α-tricalcium phosphate, β-phosphate triphosphate. Examples include calcium and γ-tricalcium phosphate. Among them, since it is relatively easy to produce and obtain particles having various outer shapes, and further, the silica shell is easily coated, and the reaction efficiency can be increased to increase the generation efficiency of silica nano hollow particles. It is preferable to use it.

  The “organic solvent” is not particularly limited as long as it is soluble in silicon alkoxide and water, and further can promote the hydrolysis reaction of silicon alkoxide. For example, alcohols such as methanol, ethanol, propanol, etc. And simple solvents such as glycols, glycol esters, ketones such as acetone, aliphatic hydrocarbons such as n-hexane, aromatic hydrocarbons such as xylene, or a mixed solvent of two or more of these. In particular, it is desirable to use alcohols because the interaction between the calcium phosphate particles and the silicon alkoxide can be improved to increase the reaction efficiency and the production efficiency of the silica nano hollow particles.

Furthermore, as the “silicon alkoxide”, any substance that can generate silica by hydrolysis / condensation polymerization thereof may be used. For example, tetraethoxysilane, trimethoxysilane, tetramethoxysilane, triethoxysilane, tripropoxysilane. Tetrapropoxysilane, tributoxysilane, tributoxysilane, and the like can be used.
Examples of the “base catalyst” include ammonia and amines.

  The “acid aqueous solution” has a hydrogen ion concentration index of the dispersion system of pH 4 or less at which calcium phosphate dissolves, and it is not necessary to subject the reaction vessel to a corrosion resistance treatment or to use a material having corrosion resistance. Any aqueous solution having a pH of 2 or more may be used, and examples thereof include dilute aqueous solutions such as hydrochloric acid, oxalic acid, nitric acid, and acetic acid. In particular, when the hydrogen ion concentration index is within the range of pH 2 to pH 4, when the hydrogen ion concentration index of the dispersion exceeds pH 4, the calcium phosphate inside the silica-coated particles cannot be completely dissolved and unreacted. Calcium phosphate particles may remain. Further, when the pH is less than 2, if unreacted silicon alkoxide or hydrolyzed silicic acid remains on the surface of the core shell, it may cause a condensation reaction by an acid catalyst during the acid treatment and cause aggregation of particles. Furthermore, a reaction vessel that has been subjected to acid resistance treatment is required. That is, when the pH is less than 2, it is necessary to subject the reaction vessel to a corrosion resistance treatment or to use a material having corrosion resistance. Accordingly, the hydrogen ion concentration index of the dispersion system is set within the range of pH 2 to pH 4.

  In addition, “particles” are generally “fine particles composing a substance” (from Shinmura, edited by “Kojien (4th edition)”, page 2693, published by Iwanami Shoten Co., Ltd. on November 15, 1991) In the present specification and claims, regardless of whether the substance constitutes or exists alone, the term “hollow particle” means a particle having a space inside. Say.

  The hollow nanoparticle composed of the silica shell of the invention of claim 2 has a shape of any one of a spherical shape, a spheroid shape and a cubic shape.

Here, the “spherical form” is not limited to a true sphere, but refers to a shape similar to a sphere.
The "spheroid shape" refers to a three-dimensional shape surrounded by an ellipsoid and having a difference in length depending on the direction, and a spheroid obtained by rotating an ellipse around its major axis or minor axis as a rotation axis. The shape is also included.
Furthermore, the “cubic shape” refers to a shape similar to a cube surrounded by a surface, not limited to an accurate cube.
The hollow particles made of silica shells having such a spherical form, spheroid form, or cubic form are, for example, calcium phosphate having a spherical form, spheroid form, or cubic form in a dry powder state. It is obtained by coating the silica shell on the particles as a template.

The thickness of the silica shell of the nano-hollow particle comprising the silica shell of the invention of claim 3 is in the range of 2 nm to 25 nm, more preferably in the range of 3 nm to 20 nm.
By the way, the thickness of the silica shell is measured by a microscope, and the term “microscope” as used herein refers to the actual measurement of particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). This is a method of observing and obtaining the size of each part of the particle.

  The nano hollow particles comprising the silica shell of the invention of claim 4 have different silica shell thicknesses depending on the part, and the silica shell thickness is non-uniform.

The particle volume space ratio of the nano hollow particles comprising the silica shell of the invention of claim 5 is in the range of 25 vol% to 90 vol%, more preferably in the range of 30 vol% to 85 vol%.
Here, the “particle inclusion volume ratio” indicates the ratio of the volume of the internal space of the silica nano hollow particles to the total volume including the internal space of the silica nano hollow particles.

The hollow nanoparticle comprising the silica shell of the invention of claim 6 is such that the calcium phosphate is hydroxyapatite {Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ }.

  The hollow nanoparticle comprising the silica shell of the invention of claim 7 is such that the organic solvent is an alcohol, more preferably ethanol.

  The method for producing nano-hollow particles comprising silica shells of the invention of claim 8 includes a dispersion step of dispersing calcium phosphate particles in a dry powder state having a predetermined size and shape in an organic solvent, and an organic solvent in which the calcium phosphate particles are dispersed. In addition, a silica coating forming step in which a silica shell is formed on the surface of the calcium phosphate particles by mixing silicon alkoxide and a base catalyst to form silica coating particles, and a hydrogen ion concentration index of the dispersion system in the range of pH 2 to pH 3 with an acid aqueous solution. And a calcium phosphate dissolution step of dissolving the calcium phosphate inside the silica coating particles.

  The method for producing nano hollow particles comprising a silica shell according to the invention of claim 9 is such that the nano hollow particles comprising the silica shell have a spherical shape, a spheroid shape or a cubic shape. It is.

  In the method for producing nano-hollow particles comprising silica shells according to claim 10, the thickness of the silica shell of the nano-hollow particles comprising silica shells is in the range of 2 nm to 25 nm, more preferably in the range of 3 nm to 20 nm. It is what is.

  In the method for producing nano-hollow particles comprising silica shells according to the invention of claim 11, the silica shells of the nano-hollow particles comprising silica shells have different thicknesses depending on the site and are non-uniform in thickness.

  The method for producing nano-hollow particles comprising silica shells according to the invention of claim 12, wherein the volume ratio of hollow particles comprising silica shells is in the range of 25 vol% to 90 vol%, more preferably 30 vol% to 85 vol. %.

  The method for producing nano-hollow particles comprising the silica shell according to the invention of claim 13 is such that the calcium phosphate is hydroxyapatite.

  In the method for producing nano-hollow particles comprising the silica shell according to the invention of claim 14, the organic solvent is an alcohol, more preferably ethanol.

  The hollow nanoparticle comprising a silica shell according to the invention of claim 1 is obtained by dispersing calcium phosphate particles in a dry powder state having a predetermined size and shape in an organic solvent, and mixing silicon alkoxide and a base catalyst to thereby form the calcium phosphate particles. Silica shells are formed on the surface to form silica-coated particles, and then the calcium phosphate inside the silica-coated particles is dissolved by setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4 with an acid aqueous solution.

As described above, in the nano-hollow particles composed of the silica shell according to the present invention, the calcium phosphate particles are used as the core particles. Therefore, in the step of dissolving the calcium phosphate particles inside the silica coating particles, the dispersion system is formed with an acid aqueous solution. By setting the hydrogen ion concentration index within the range of pH 2 to pH 4, the calcium phosphate particles can be completely dissolved, and the condensation reaction of unreacted silicon alkoxide and hydrolyzed silicic acid present on the silica coating particle surface is promoted. Thus, it is not necessary to use a strongly acidic aqueous solution that causes aggregation of silica-coated particles or hollow particles in which calcium phosphate therein is dissolved. That is, in the step of dissolving the calcium phosphate particles inside the silica coating particles, even if there is unreacted silicon alkoxide or hydrolyzed silicic acid on the surface of the silica coating particles, such unreacted silicon alkoxide or hydrolyzed The condensation reaction of silicic acid by an acid catalyst is prevented, and aggregation of silica coated particles and hollow particles is prevented.
For this reason, calcium phosphate particles are used as core particles, and the calcium phosphate particles are dispersed in an organic solvent, and a silicon alkoxide and a base catalyst are added thereto to form a silica shell on the surface of the calcium phosphate particles. Nano hollow particles composed of silica shells obtained by dissolving and removing calcium phosphate particles with an aqueous acid solution so that the hydrogen ion concentration index of the dispersion is in the range of pH 2 to pH 4 is low in aggregation to secondary particles and highly dispersible. It becomes.

  Furthermore, by using the calcium phosphate particles as the core particles in this way, as described above, in the step of dissolving the calcium phosphate particles inside the silica coating particles, the hydrogen ion concentration index of the dispersion is adjusted to within the range of pH 2 to pH 4 by the acidic aqueous solution. In this case, the calcium phosphate particles, which are the core particles, are completely dissolved, and it is not necessary to use a strongly acidic aqueous solution. Therefore, it is not necessary to use a corrosion-resistant material or a corrosion-resistant treatment for the reaction vessel in the production process. Therefore, the load on the surrounding environment can be reduced and the cost can be reduced.

  In addition, by using calcium phosphate particles as core particles, when calcium phosphate particles inside silica coating particles are dissolved by acidic aqueous solution, calcium hydroxide, calcium chloride, phosphoric acid aqueous solution, etc. are discharged as waste acid aqueous solution, and these aqueous solutions The calcium phosphate particles can be re-synthesized simply by recovering the particles, and can be reused as core particles. And at this time, there is no generation of gas or the like at the time of dissolution like the calcium carbonate of the conventional core particles, and there is no need for a large apparatus for gas recovery. Will not take. Therefore, contribution to environmental conservation and cost reduction can be achieved.

  In this way, nano hollow particles composed of silica shells that are less agglomerated into secondary particles, have high dispersibility, and can achieve cost reduction and environmental conservation.

  According to the nano-hollow particle comprising the silica shell according to the invention of claim 2, since it has any one of the spherical form, the spheroid form, and the cubic form, it is mixed into the object such as a resin or paint. In this case, the filling rate (packing density) can be increased. Therefore, in addition to the effect of claim 1, in the object to be mixed, the silica nano hollow particles can sufficiently exhibit the optical properties such as transparency and translucency, heat insulation, light weight, etc. it can. In particular, nano hollow particles made of silica shells having a cubic shape are difficult to cause refraction of incident light and have extremely high light transmittance. In addition, in nano hollow particles composed of silica shells having a spheroid shape, the length varies depending on the direction, so that anisotropy of optical properties such as transparency and translucency and physical properties such as heat insulation Is granted.

  According to the nano-hollow particle comprising the silica shell according to the invention of claim 3, since the thickness of the silica shell is in the range of 2 nm to 20 nm, in addition to the effect of claim 1 or claim 2, Visible light has high transparency and transparency, and does not hinder the visibility of the target object even when mixed into the target object (material) such as resin or paint.

  According to the nano-hollow particle comprising the silica shell according to the invention of claim 4, the thickness of the silica shell varies depending on the site and is non-uniform, so that the effect according to any one of claims 1 to 3 is achieved. In addition, anisotropy of physical properties is imparted compared to the case where the thickness of the silica shell is uniform, and in the target object such as a resin or paint to be mixed, the physical properties are improved, in particular, the optical properties are improved. Can be planned. In addition, since the silica shell becomes a low-density particle compared with a uniform thickness of the silica shell, it is difficult to cause coagulation sedimentation when mixed in a target material such as a resin or paint, It is possible to prevent deterioration of physical properties.

  According to the nano-hollow particle comprising the silica shell according to the invention of claim 5, the particle inclusion space volume ratio is 25 vol% to 90 vol%, and the effect according to any one of claims 1 to 4 In addition, high heat insulating properties (low thermal conductivity) can be secured.

  According to the nano-hollow particle comprising the silica shell according to the invention of claim 6, the calcium phosphate is hydroxyapatite, and hydroxyapatite is relatively easy to produce and obtain particles having various outer shapes. In addition to the effect described in any one of claims 1 to 5, hollow particles having various outer shapes can be manufactured at low cost. Further, since hydroxyapatite is easily coated with a silica shell, the reaction efficiency can be increased and the production efficiency can be improved.

  According to the nano hollow particle composed of the silica shell according to the invention of claim 7, since the organic solvent is an alcohol, the interaction between the calcium phosphate particle and the silicon alkoxide can be improved and the reaction efficiency can be increased. Therefore, in addition to the effect of any one of claims 1 to 6, production efficiency can be increased.

  According to the method for producing nano-hollow particles comprising silica shells according to the invention of claim 8, in the dispersing step, the calcium phosphate particles in a dry powder state having a predetermined size and shape are dispersed in an organic solvent, followed by silica coating formation. In the step, a silicon alkoxide and a base catalyst are mixed in an organic solvent in which the calcium phosphate particles are dispersed to form silica shells on the surface of the calcium phosphate particles to form silica coating particles. Further, in the calcium phosphate dissolution step, an acid aqueous solution is used. By setting the hydrogen ion concentration index of the dispersion system within the range of pH 2 to pH 3, the calcium phosphate inside the silica coating particles is dissolved to form nano hollow particles made of silica shells.

Thus, in the manufacturing method of the nano hollow particle which consists of a silica shell concerning this invention, since the calcium phosphate particle is used as a core particle, in the process of dissolving the calcium phosphate particle inside a silica coating particle, by acid aqueous solution By setting the hydrogen ion concentration index of the dispersion within the range of pH 2 to pH 4, calcium phosphate particles can be completely dissolved, and condensation reaction of unreacted silicon alkoxide and hydrolyzed silicic acid present on the surface of silica coating particles It is not necessary to use a strongly acidic aqueous solution that promotes the agglomeration of the silica-coated particles and the hollow particles in which the calcium phosphate therein is dissolved. That is, in the step of dissolving the calcium phosphate particles inside the silica coating particles, even if there is unreacted silicon alkoxide or hydrolyzed silicic acid on the surface of the silica coating particles, such unreacted silicon alkoxide or hydrolyzed The condensation reaction of silicic acid by an acid catalyst is prevented, and aggregation of silica coated particles and hollow particles is prevented.
For this reason, calcium phosphate particles are used as core particles, and the calcium phosphate particles are dispersed in an organic solvent, and a silicon alkoxide and a base catalyst are added thereto to form a silica shell on the surface of the calcium phosphate particles. Nano hollow particles composed of silica shells obtained by dissolving and removing calcium phosphate particles with an aqueous acid solution so that the hydrogen ion concentration index of the dispersion is in the range of pH 2 to pH 4 is low in aggregation to secondary particles and highly dispersible. It becomes.

  Furthermore, by using the calcium phosphate particles as the core particles in this way, as described above, in the step of dissolving the calcium phosphate particles inside the silica coating particles, the hydrogen ion concentration index of the dispersion is adjusted to within the range of pH 2 to pH 4 by the acidic aqueous solution. In this case, the calcium phosphate particles, which are the core particles, are completely dissolved, and it is not necessary to use a strongly acidic aqueous solution. Therefore, it is not necessary to use a corrosion-resistant material or a corrosion-resistant treatment for the reaction vessel in the production process. Therefore, the load on the surrounding environment can be reduced and the cost can be reduced.

  In addition, by using calcium phosphate particles as core particles, when calcium phosphate particles inside silica coating particles are dissolved by acidic aqueous solution, calcium hydroxide, calcium chloride, phosphoric acid aqueous solution, etc. are discharged as waste acid aqueous solution, and these aqueous solutions The calcium phosphate particles can be re-synthesized simply by recovering the particles, and can be reused as core particles. And at this time, there is no generation of gas or the like at the time of dissolution like the calcium carbonate of the conventional core particles, and there is no need for a large apparatus for gas recovery. Will not take. Therefore, contribution to environmental conservation and cost reduction can be achieved.

  In this way, a method for producing nano-hollow particles composed of a silica shell that is less agglomerated into secondary particles, has high dispersibility, and can achieve cost reduction and environmental conservation.

  In the method for producing nano hollow particles comprising silica shells according to the invention of claim 9, the obtained nano hollow particles comprising silica shells have a spherical form, a spheroid form or a cubic form. It is possible to increase the filling rate (packing density) when it is mixed into the object such as resin or paint. Therefore, in addition to the effect of claim 8, the obtained hollow nanoparticle composed of silica shell is an object to be mixed, and the optical properties such as transparency and translucency of silica nanohollow particle, heat insulation, light weight Effects such as sex can be sufficiently exhibited. In particular, when the obtained nano hollow particles made of silica shells have a cubic shape, refraction of incident light hardly occurs and the light transmittance is extremely high. In addition, in the obtained nano hollow particles composed of silica shells having a spheroid shape, there are differences in length depending on the direction, so that optical properties such as transparency and translucency and physical properties such as heat insulation Anisotropy of is imparted.

  In the method for producing nano-hollow particles comprising silica shells according to the invention of claim 10, the thickness of the silica shells of the resulting nano-hollow particles comprising silica shells is in the range of 2 nm to 20 nm. Alternatively, in addition to the effect of claim 9, the obtained nano hollow particles composed of silica shells have high visible light transparency and transparency, and are also mixed into a target object (material) such as a resin or paint. The visibility of the target object is not hindered.

  In the method for producing nano-hollow particles comprising silica shells according to the invention of claim 11, the thickness of the silica shells of the nano-hollow particles comprising silica shells obtained varies depending on the site and is non-uniform. In addition to the effect described in any one of Items 10, in the hollow nanoparticle composed of the silica shell to be obtained, anisotropy of physical properties is imparted and mixed as compared with the case where the silica shell has a uniform thickness. In a target object such as a resin or a paint, the physical properties can be improved, in particular, the optical characteristics can be improved. In addition, since the silica shell becomes a low-density particle compared with a uniform thickness of the silica shell, it is difficult to cause coagulation sedimentation when mixed in a target material such as a resin or paint, It is possible to prevent deterioration of physical properties.

  In the method for producing nano-hollow particles made of silica shells according to the invention of claim 12, the volume ratio of the particles enclosing the hollow nano-particles made of silica shells is 25 vol% to 90 vol%. In addition to the effect described in any one of claims 11 to 11, high heat insulation (low thermal conductivity) can be secured in the nano hollow particles made of the silica shell to be obtained.

  In the method for producing nano hollow particles comprising silica shells according to the invention of claim 13, the calcium phosphate is hydroxyapatite, and hydroxyapatite is relatively easy to produce and obtain particles having various outer shapes. From the above, in addition to the effects described in any one of claims 8 to 12, hollow particles having various outer shapes can be produced at low cost. Further, since hydroxyapatite is easily coated with a silica shell, the reaction efficiency can be increased and the production efficiency can be improved.

  According to the method for producing nano-hollow particles composed of the silica shell according to the invention of claim 14, since the organic solvent is an alcohol, the interaction between the calcium phosphate particles and the silicon alkoxide can be improved to increase the reaction efficiency. it can. Therefore, in addition to the effect described in any one of claims 8 to 13, production efficiency can be increased.

FIG. 1 is a flowchart showing a method for producing silica nano hollow particles according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a process for producing silica nano hollow particles according to an embodiment of the present invention, wherein (a) is a schematic diagram showing the production of cubic silica nano hollow particles, and (b) is a spherical silica nano particle. Schematic diagram showing the production of hollow particles, (c) is a schematic diagram showing the production of silica nano hollow particles having a spheroid shape. FIG. 3 is a transmission electron microscope (TEM) photograph of silica nano hollow particles according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, the same symbols and the same reference numerals mean the same or corresponding functional parts, and therefore, detailed description thereof is omitted here.

The nano hollow particles composed of silica shells according to the embodiment of the present invention and the manufacturing method thereof will be described with reference to FIGS.
First, in order to carry out the production of nano hollow particles 1 made of silica shells, in this embodiment, hydroxyapatite particles (HAp) 2 were synthesized by a wet method as calcium phosphate particles serving as core particles (core particles). .
Specifically, in a closed container at room temperature, calcium hydroxide [Ca (OH) ₂ ] is dissolved in ion-exchanged water from which carbon dioxide (CO ₂ ) has been removed by stirring, and phosphoric acid is further added to this solution. The suspension (so-called slurry) formed by adding the (H ₃ PO ₄ ) aqueous solution (buffer solution) was stirred at a temperature of about room temperature to 85 ° C. Thereafter, the precipitate obtained by filtering the suspension is thoroughly washed with distilled water and finally dried to obtain hydroxyapatite particles 2 in a dry powder state (solid fine powder in a dry state). It was. The hydroxyapatite particles 2 obtained by this synthesis method were extremely high purity.

Here, the hydroxyapatite particles 2 generated in this way can be formed into a predetermined dimensional shape of a spherical shape, a spheroid shape, or a cubic shape by controlling the synthesis conditions.
Incidentally, the “spherical form” here is not limited to a true sphere, but a shape similar to a sphere. The “spheroid shape” refers to a three-dimensional shape surrounded by an ellipsoid and having a difference in length depending on the direction, and a rotation ellipse obtained by rotating the ellipse around its major axis or minor axis as a rotation axis. Various substantially spheroid shapes are included, such as a body shape, a rice grain shape, and an elongated shape (approximate to a rod shape). Furthermore, the “cubic shape” refers to a shape similar to a cube surrounded by a surface, not limited to an accurate cube.

In the production of the nano hollow particles 1 composed of the silica shells of the present embodiment, the hydroxyapatite particles 2 in a dry powder state can be obtained by microscopy [transmission electron microscope (TEM: JEOL JEM 2000 FX / JEOL Ltd.)]. ], The outer diameter of the cubic form is 250 nm or less, the diameter of the spherical form is 250 nm or less, and the maximum diameter (major axis) of the spheroid form is 250 nm or less. By using these particles, the outer diameter, diameter, and maximum diameter (major axis) measured by the microscopic method in the finally obtained silica nano hollow particles 1 can be made nano-sized.
Moreover, when implementing this invention, the means to obtain the hydroxyapatite particle | grains 2 of a dry powder state is not limited to the above-mentioned manufacturing method, It is also possible to manufacture by other well-known methods, and is commercially available. It is also possible to purchase and use hydroxyapatite particles.

In the present embodiment, the hydroxyapatite particles 2 in the dry powder state thus obtained are used as core particles. As shown in FIG. 1, first, the hydroxyapatite particles 2 in the dry powder state are prepared. It was dispersed in ethanol as an organic solvent (Step S1). This step corresponds to the “dispersing step” in the present invention for producing the nano hollow particles 1 made of silica shells.
In the present embodiment, the hydroxyapatite particles 2 are set to a concentration of 1 w / v% in the dispersion.

  Here, the type of the disperser (stirrer) used in the step of dispersing the hydroxyapatite particles 2 in a dry powder state in ethanol (step S1) is not particularly limited, and examples thereof include a homomixer, a homogenizer, and an ultrasonic wave. A disperser or the like can be used. Examples of the commercially available disperser (stirrer) include Disper (manufactured by PRIMIX), Clearmix (manufactured by M-Technique), Cavitron (manufactured by Taiheiyo Kiko), and the like.

Subsequently, the ethanol dispersion in which the hydroxyapatite particles 2 are dispersed is mixed with tetraethoxysilane (TEOS) as a silicon alkoxide, an aqueous ammonia (NH ₄ OH) solution as a base catalyst, and distilled water. Distributed processing was performed.
Here, in the above-described dispersion step (step S1), by dispersing the hydroxyapatite particles 2 in ethanol as an organic solvent, the surface of the hydroxyapatite particles 2 interacts with the ethanol, and the surface of the hydroxyapatite particles 2 is dispersed. Where ethanol is coated, tetraethoxysilane as silicon alkoxide and ammonia water as a base catalyst are mixed, so that ethanol and tetraethoxysilane interact with the surface of the hydroxyapatite particles 2, Hydroxyapatite-ethanol and ethanol-tetraethoxysilane complexes are formed. Then, tetrahydroxysilane (Si (OH) ₄ ) generated by the hydrolysis of tetraethoxysilane is dehydrated and polycondensed to precipitate silica (SiO ₂ ), and the silica shell 1 a is deposited on the entire surface of the hydroxyapatite particles 2. Formation is promoted.
As a result, as shown in FIG. 2, the silica coating particle 3 is obtained in which the entire surface of the hydroxyapatite particle 2 is coated with the silica shell 1 a. That is, silica (SiO ₂ ) 1a is coated on the entire surface of the hydroxyapatite particles 2 by a sol-gel reaction (sol-gel method) of tetraethoxysilane to form silica-coated particles 3 (step S2). This step corresponds to the “silica coating forming step” in the present invention.

Incidentally, the above-mentioned “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., Edited by “Iwanami Rikagaku Dictionary (5th edition)”, page 777, published by Iwanami Shoten Co., Ltd. on February 20, 1998), where tetraethoxysilane is treated under basic conditions with aqueous ammonia. It refers to a method of reacting with water to form a gel-like silica shell 1a in which SiO ₂ molecules are polycondensed. The gel-like silica shell 1a is converted into a glassy silica shell 1a by dissolving hydroxyapatite in a calcium phosphate dissolving step (step S3) described later and then drying.

Here, in the present embodiment, as tetraethoxysilane (tetraethyl silicate) for coating the silica shell 1a on the surface of the hydroxyapatite particles 2 by a sol-gel method, specifically, for example, Tama Chemical Industry Ethyl silicate Co., Ltd. (Product name “High purity ethyl silicate”: Tetraethoxysilane (TEOS)), Alkoxy silane (Product name “KBE-04”: Tetraethoxysilane) among functional silanes of Shin-Etsu Chemical Co., Ltd. (TEOS)) or the like can be used.
However, when carrying out the present invention, the silicon alkoxide is not limited to tetraethoxysilane, and other compounds such as tetramethoxysilane, trimethoxysilane, triethoxysilane, tetrapropoxysilane, tetrabutoxysilane, etc. Any silicon alkoxide such as a so-called silane coupling agent can be used.

In this embodiment, ammonia water is used as the base catalyst. However, when the present invention is carried out, other examples of the base catalyst include amines, amides, sodium hydroxide (NaOH), hydroxides. It is also possible to use potassium (KOH), calcium hydroxide [Ca (OH) ₂ ] or the like. However, considering the good reaction efficiency, price, availability, ease of handling, etc., ammonia is the most suitable base catalyst. By using ammonia as the base catalyst, it is ensured and efficient. Silicon alkoxide such as ethoxysilane and water are reacted to precipitate silica in which SiO ₂ molecules are polycondensed to form silica shell 1 a on the entire surface of calcium phosphate particles such as hydroxyapatite particles 2.

Furthermore, in the present embodiment, the reaction is performed while applying ultrasonic waves (frequency: 20 KHz to 40 KHz) in order to form the silica shell 1a by the sol-gel method while sufficiently dispersing the hydroxyapatite particles 2. As an apparatus used for ultrasonic irradiation, an ultrasonic horn is directly put into a solution (UH-600S frequency 20 KHz / SMT, Inc., SONFIER 4020-800 frequency 40 KHz / BRANSON), or a solution circulation type (UH-600SR frequency 20 KHz / SMT Co., Ltd.) or a bath type (ultrasonic cleaner type) that indirectly irradiates a container containing a solution from the outside can be used.
In addition, in the process of forming the silica coating particles 3 in this way, by performing ultrasonic treatment, the hydroxyapatite particles 2 that are calcium phosphate particles are easily dispersed, and aggregation of the particles is prevented, and further, the particles are dispersed. Since the silica shell 1a is formed in a state where the particles are in the same state, the silica coating particles 3 are also prevented from aggregating with each other. For this reason, in this Embodiment, the nano hollow particle 1 which consists of a silica shell with less aggregation to a secondary particle than the case where an ultrasonic treatment is not performed is obtained. Furthermore, since the silica shell 1a is easily adsorbed to the surface of the hydroxyapatite particles 2 by ultrasonic waves, the production efficiency can be improved in the present embodiment.

  Next, after the silica coating particles 3 thus formed are dispersed in distilled water, a diluted hydrochloric acid aqueous solution is added thereto, and the hydrogen ion concentration index of the dispersion system falls within the range of pH 2 to pH 4. Thus, the hydroxyapatite 2 inside the silica coating particle 3 was dissolved to allow the hydroxyapatite 2 to flow out while opening fine through holes in the silica shell 1a (step S3). This step corresponds to the “calcium phosphate dissolving step” in the present invention.

Here, in the state where the hydrogen ion concentration index of the dispersion exceeds pH 4, the calcium phosphate inside the silica coating particles cannot be completely dissolved, and there is a possibility that unreacted hydroxyapatite (HAp) particles 2 remain. . Furthermore, when the pH is less than 2, if unreacted tetraethoxysilane (TEOS) or hydrolyzed silicic acid remains on the surface of the core shell, it may cause a condensation reaction by an acid catalyst during the acid treatment and cause aggregation of particles. Furthermore, a reaction vessel that has been subjected to acid resistance treatment is required. That is, when the pH is less than 2, it is necessary to subject the reaction vessel to a corrosion resistance treatment or to use a material having corrosion resistance. For these reasons, the hydrogen ion concentration index of the dispersion system is set within the range of pH 2 to pH 4. In the present embodiment, an aqueous solution of dilute hydrochloric acid 10 ⁻⁴ M is added so that the hydrogen ion concentration index of the dispersion becomes pH 3.5 to pH ⁴ . Of course, when carrying out the present invention, dilute acid aqueous solutions such as carboxylic acids such as sulfuric acid, nitric acid, acetic acid / benzoic acid, citric acid, and butyric acid may be used.

Then, after the hydroxyapatite 2 in the silica coating particles 3 was dissolved and flowed out, it was washed with distilled water (step S3a) and further dried under reduced pressure (step S3b).
Thereby, the nano hollow particle 1 which consists of a silica shell is manufactured.

  Thus, the nano hollow particle 1 made of the silica shell according to the present embodiment is obtained by dispersing hydroxyapatite particles 2 as calcium phosphate particles in a dry powder state having a predetermined size and shape in ethanol as an organic solvent, By mixing tetraethoxysilane as silicon alkoxide and aqueous ammonia as a base catalyst, silica shell 1a is formed on the surface of hydroxyapatite particles 2 to form silica-coated particles 3, and then dispersed with dilute hydrochloric acid aqueous solution as acid aqueous solution. The hydroxyapatite 2 in the silica coating particle 3 is dissolved in such a manner that the hydrogen ion concentration index is within the range of pH 2 to pH 4.

  Moreover, the manufacturing method of the nano hollow particle 1 which consists of a silica shell which concerns on this Embodiment is a dispersion | distribution process which disperse | distributes the hydroxyapatite particle | grains 2 as the calcium phosphate particle of the dry powder state which has a predetermined dimension shape to ethanol as an organic solvent. (Step S1) and ethanol as an organic solvent in which hydroxyapatite particles 2 are dispersed are mixed with tetraethoxysilane as a silicon alkoxide and ammonia water as a base catalyst to mix silica shell 1a on the surface of hydroxyapatite particles 2. A silica coating forming step (step S2) to form silica coating particle 3 and a hydroxyapatite inside silica coating particle 3 with a hydrogen ion concentration index of the dispersion within a range of pH 2 to pH 4 by dilute hydrochloric acid aqueous solution as acid aqueous solution Those comprising calcium phosphate dissolution step of dissolving the door particles 2 and the (step S3).

Here, when the hydroxyapatite particle 2 as the core particle has a cubic shape, the silica-coated particle 3 in which the surface of the hydroxyapatite particle 2 having the cubic shape is coated with silica by a hydrolysis reaction of tetraethoxysilane is a hydroxyapatite. The cubic form of the particles 2 is transferred to form a cubic form, and the nano hollow particles 1 made of a silica shell obtained by dissolving the hydroxyapatite 2 inside the silica-coated particles 3 having the cubic form are also in the cubic form. Become.
That is, after the surface of the core particle is coated with silica in this way, the nano hollow particle 1 made of a silica shell manufactured by the template method, which is a method for removing the core particle, has a shape reflecting the shape of the core particle. Become.
For this reason, when the hydroxyapatite particle 2 that is the core particle has a spherical shape, the resulting nano hollow particle 1 made of the silica shell has a spherical shape, and the hydroxyapatite particle 2 that is the core particle has a spheroid shape The resulting hollow nanoparticle 1 made of silica shell is in the form of a spheroid.

  The hollow nanoparticle 1 made of the silica shell having a cubic shape thus obtained has a nano hollow made of a silica shell having an outer diameter in the range of 30 nm to 300 nm as measured by microscopy. Particle 1 has a diameter in the range of 30 nm to 300 nm, similarly measured by microscopy, and nano hollow particle 1 made of a silica shell having a spheroid shape is also measured by microscopy. The maximum diameter (major axis) was in the range of 30 nm to 300 nm. In addition, the measurement by the microscope method here is the size (primary particle diameter) of the primary particle observed by the transmission electron microscope (TEM: JEOL JEM 2000 FX / JEOL Ltd.), and the transmission electron microscope. The primary particle size by means the single particle size of each individual particle. On the other hand, the particle diameter by the static light scattering method described later refers to the dispersed particle diameter when dispersed in the liquid phase.

  Furthermore, the nano hollow particle 1 made of silica shell thus obtained has a particle diameter of 30 nm to 800 nm by a static light scattering method (measured by ZETASIZER 3000HSA / Malvern Instrument Ltd), and a mercury intrusion method (mercury porosimeter: 2-20 nm pores are not detected in the pore distribution (Autosorb-1 / Quantachrome Corp) measured by PASCAL140, PASCAL240 (FISONS Instruments)) or gas adsorption method (here, nitrogen gas) In addition, there was little aggregation to the secondary particles and the dispersibility was high.

One reason for this is that in the present embodiment, hydroxyapatite particles 2 that are calcium phosphate particles are used as the core particles, and the surface of the hydroxyapatite particles 2 is coated with silica shell 1a to form silica-coated particles 3. In the step of dissolving the hydroxyapatite 2 inside the silica coating particle 3, it is mentioned that aggregation between particles due to the acid catalyst of the acidic aqueous solution is prevented.
That is, conventionally, as described above, calcium carbonate is used as the core particle, and since a strongly acidic aqueous solution is required to dissolve this calcium carbonate, in the step of dissolving the core, silica is used. When unreacted silicon alkoxide such as tetraethoxysilane and hydrolyzed silicic acid are present on the surface of the coating particle, the condensation reaction of this unreacted silicon alkoxide and hydrolyzed silicic acid is caused by the acidic catalytic function of the strongly acidic aqueous solution. Is promoted to form a covalent bond on the surface of the hollow particle in which the silica coating particle and the core inside the silica coating particle are dissolved, causing aggregation of the particles. In contrast, in the present embodiment, the hydroxyapatite particles 2 which are calcium phosphate particles are used as the core particles, and a dilute acidic solution such as hydrochloric acid is not required without dissolving a strongly acidic aqueous solution for dissolving the hydroxyapatite particles 2. Since the hydroxyapatite particles 2 can be completely dissolved by setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4 with an aqueous solution, unreacted tetraethoxy in the step of dissolving the core inside the silica coating particles 3. Even if silane (silicon alkoxide) or hydrolyzed silicic acid is present, the promotion of the condensation reaction by the acid catalyst of such unreacted tetraethoxysilane or hydrolyzed silicic acid is prevented, and aggregation of particles is prevented. Is prevented.

In addition, since calcium carbonate, which is a conventional core particle, contains water in a water-containing cake state, calcium carbonate tends to agglomerate over time, whereas hydroxyapatite particles 2 are stable even in a dry powder state. In the process until the silica shell 1a is formed, aggregation of the particles due to the hydroxyapatite particles 2 absorbing moisture is prevented.
For this reason, the nano hollow particle 1 made of the silica shell according to the present embodiment has a high degree of dispersibility with little aggregation to the secondary particles.

Moreover, the nano hollow particle 1 which consists of the silica shell manufactured in this way is the thickness of the silica shell 1a in the range of 2 nm-25 nm regardless of the shape, and also the thickness of the silica shell 1a is There were many things that differed and differed from site to site. In addition, the nano hollow particle 1 made of this silica shell had a particle inclusion space volume ratio in the range of 25 vol% to 90 vol%.
The “particle inclusion space volume ratio” indicates the ratio of the volume of the internal space of the hollow particles to the total volume including the internal space of the hollow particles, and was calculated by the following formula here. Is.
[When the nano hollow particles are in a cubic form]
{R- (2 · t _R )} ³ / R ³ · 100
R: outer diameter of nano hollow particle t _R : thickness of silica shell [when nano hollow particle is in spherical form]
{4/3 · π · (rt)} ³ / {4/3 · π · r ³ } · 100
π: Circumference r: Radius of nano hollow particle t: Thickness of silica shell [when nano hollow particle is in spheroid form]
{4/3 · π · (a−t _a ) · (b−t _b ) · (c−t _b )} / {4/3 · π · a · b · c} · 100
π: Circularity ratio a: Radius in the x-axis direction of the nano hollow particle b: Radius in the y-axis direction of the nano hollow particle c: Radius in the z-axis direction of the nano hollow particle t _a : Thickness of the silica shell in the x-axis direction t _b : thickness of silica shell in the y-axis direction t _c : thickness of silica shell in the z-axis direction

Here, by changing the synthesis conditions, specifically, the weight ratio of the hydroxyapatite (HAp) particles 2 in a dry powder state to tetraethoxysilane (TEOS) as silicon alkoxide is variously changed. As Comparative Examples 1 to 3, Tables 1 to 3 show the results of manufacturing tests performed in accordance with the flowchart of FIG.
In Examples 1 to 3 and Comparative Example 1, cubic hydroxyapatite particles 2 as core particles were used. The mixing ratio of hydroxyapatite (HAp) particles and tetraethoxysilane (TEOS) at this time is shown in the upper part of Table 1. In Examples 4 to 6 and Comparative Example 2, spherical hydroxyapatite particles 2 as core particles were used. The upper part of Table 2 shows the mixing ratio of the hydroxyapatite (HAp) particles 2 and tetraethoxysilane (TEOS) at this time. Furthermore, in Examples 7 to 9 and Comparative Example 3, spheroid-shaped particles were used as the hydroxyapatite particles 2 as the core particles. The mixing ratio of hydroxyapatite (HAp) particles 2 and tetraethoxysilane (TEOS) at this time is shown in the upper part of Table 3.

As shown in Tables 1 to 3, when the weight ratio between the hydroxyapatite (HAp) particles 2 and tetraethoxysilane (TEOS) changes, the thickness of the silica shell 1a of the hollow particles to be generated and the volume ratio of the particle inclusion space It was confirmed that it changed.
Therefore, in the present embodiment, the thickness of the silica shell 1a and the volume ratio of the particle inclusion space can be controlled by adjusting the blending amount of the hydroxyapatite particles 2 and tetraethoxysilane. The outer diameter of the particle 1 can be controlled.
In particular, by controlling the thickness of the silica shell 1a, when a substance such as an active ingredient is encapsulated in the nano hollow particles 1 made of silica shell, it becomes possible to impart sustained release performance of the encapsulated substance. . Further, by controlling the particle inclusion space volume ratio, substances of various sizes can be included.

From the comparison of Examples 1 to 3 and Comparative Example 1 shown in Table 1, when hydroxyapatite particles 2 having a cubic shape are used as the core particles, tetraethoxysilane (TEOS) / hydroxyapatite (HAp) is used. If the blending ratio of the particles 2 is 0.15 or less, nano hollow particles composed of cubic silica shells may not be obtained. By the way, according to the experimental study by the present inventors, when the amount of ammonia water as a base catalyst is not sufficient with respect to the amount of tetraethoxysilane (TEOS), the nano hollow particles composed of cubic-shaped silica shells It has been confirmed that it cannot be obtained. Further, according to experimental studies by the present inventors, when the mixing ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 exceeds 2.00, unreacted tetraethoxysilane (TEOS) increases and is recovered. It has been confirmed that the production efficiency is lowered due to considerable labor.
For this reason, in order to reliably and efficiently produce the cubic nano silica particles 1, the mixing ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 is 0.18 to 2.00. Is preferably in the range of 0.20 to 1.80.

Further, from comparison between Examples 4 to 6 and Comparative Example 2 shown in Table 2, when spherical hydroxyapatite particles 2 are used as core particles, tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles When the mixing ratio of 2 is 0.03 or less, nano hollow particles composed of a spherical silica shell may not be obtained depending on the amount of a base catalyst such as aqueous ammonia. As a result of experiments conducted by the present inventors, when the ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 exceeds 1.00, unreacted tetraethoxysilane (TEOS) increases and is recovered. It has been confirmed that the production efficiency is lowered due to considerable labor.
Therefore, in order to reliably and efficiently produce the spherical silica nano hollow particles 1, the mixing ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 is 0.04 to 1.00. It is preferable to be within the range, and more preferably within the range of 0.05 to 0.90.

Furthermore, from the comparison between Example 7 to Example 9 and Comparative Example 3 shown in Table 3, when hydroxyapatite particles 2 having a spheroidal shape were used as core particles, tetraethoxysilane (TEOS) / hydroxyapatite ( When the blending ratio of the HAp) particles 2 is 1.80 or less, depending on the amount of a base catalyst such as aqueous ammonia, nano hollow particles composed of a spheroidal silica shell may not be obtained. Further, according to experimental studies by the present inventors, when the ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 exceeds 20.00, unreacted tetraethoxysilane (TEOS) increases and is recovered. It has been confirmed that the production efficiency is lowered due to considerable labor.
For this reason, in order to reliably and efficiently produce the silica nano-hollow particles 1 having a spheroid shape, the mixing ratio of tetraethoxysilane (TEOS) / hydroxyapatite (HAp) particles 2 is set to 3.00-20. It is preferable to be within the range of 0.00, and more preferably within the range of 4.00 to 19.00.

  For reference, among the obtained hollow particles 1 made of silica shell, a TEM photograph of the hollow particles according to Example 7 actually observed using a transmission electron microscope (TEM) is shown in FIG. . From the TEM image of FIG. 3, the obtained hollow particles 1 made of the silica shell according to Example 7 have a spheroid shape including an ellipsoid shape, and the thickness of the silica shell 1 a is not uniform. It can be seen that there are many that are.

  Incidentally, according to an experimental study by the present inventors, it is clear that the thickness of the silica shell 1a is increased by increasing the amount of ammonia water as a base catalyst. That is, in addition to the blending amount of the hydroxyapatite particles 2 and tetraethoxysilane, the thickness of the silica shell 1a and the volume ratio of the particle inclusion space can also be controlled by adjusting the blending amount of aqueous ammonia as a base catalyst. As a result, the outer diameter of the silica nano hollow particle 1 can be controlled. In the present embodiment, it is possible to control the outer diameter of the silica nano hollow particle 1 by adjusting the particle diameter of the hydroxyapatite particle 2 serving as the core particle.

Moreover, the nano hollow particle 1 which consists of the silica shell which concerns on this Embodiment by the present inventors is excellent in an optical characteristic, heat insulation, and lightness, if the upper limit of the thickness of the silica shell 1a is in the range of 25 nm. It was confirmed to be a thing. And the nano hollow particle 1 which consists of a silica shell which concerns on this Embodiment in this way is thin in the range whose thickness of the silica shell 1a is 2 nm-25 nm, and the particle inclusion space volume ratio is also the range of 25 vol%-90 vol%. It has been confirmed to have a high space ratio and has excellent optical characteristics such as transparency and translucency, heat insulation (low thermal conductivity), and light weight. In addition, because of its high dispersibility, excellent optical properties such as transparency and translucency and excellent properties such as heat insulation (low thermal conductivity) can be obtained when it is mixed into a target object (material) such as resin or paint. Can be demonstrated.
When the thickness of the silica shell 1a is in the range of 2 nm to 25 nm, the visible light has high transparency and transparency, and obstructs the visibility of the target object even when mixed into the target object such as resin or paint. There is no. Further, since the thickness of the silica shell 1a is 2 nm or more, the necessary strength can be ensured and the silica shell 1a is not easily destroyed by an external environment such as when mixed in a material such as a paint. Therefore, it can respond also to the use for which the high strength and high transparency of the silica shell 1a are required. From the viewpoint of strength and optical characteristics, it is more preferable that the thickness of the silica shell 1a is in the range of 3 nm to 20 nm.
Moreover, although it has what has high heat insulation (low thermal conductivity) because particle | grain inclusion space volume ratio is in the range of 25 vol%-90 vol%, from a viewpoint of intensity | strength, heat insulation, etc., More preferably, The particle inclusion space volume ratio is in the range of 30 vol% to 85 vol%.

  Furthermore, according to the nano hollow particles 1 made of a silica shell having a cubic shape, a spherical shape, or a spheroid shape, the filling rate is higher than that of an indefinite shape when mixed into a target object such as a resin or paint. The (filling density) can be increased, and the target object can sufficiently exhibit the optical properties such as transparency and translucency, heat insulating properties, light weight and the like of the silica nano hollow particles 1. Among them, in the nano hollow particles 1 made of silica shells having a cubic shape, refraction of incident light hardly occurs (low refractive index) and the light transmittance is extremely high, and furthermore, a high antireflection / antiglare effect is achieved. can get. Moreover, in the nano hollow particle 1 which consists of a silica shell which has a spheroidal form, the anisotropy of optical properties, such as transparency and translucency which the silica nano hollow particle 1 has, and physical properties, such as heat insulation, are provided. .

In addition, the hollow nanoparticle 1 composed of the silica shell obtained as described above often has a silica shell 1a having a non-uniform thickness because the thickness of the silica shell 1a varies depending on the part. According to the nano hollow particle 1 made of a shell, since the silica shell 1a has anisotropy of physical properties as compared with a uniform thickness of the silica shell 1a, Improvement, in particular, improvement of optical characteristics can be achieved.
Specifically, when silica nano hollow particles 1 having a non-uniform thickness of silica shell 1a are mixed into a target object such as a resin or a paint, the light transmittance of the visible light is high in a portion where silica shell 1a is thin. In addition, at a portion where the thickness of the silica shell 1a is large, visible light can be refracted and scattered to achieve high light diffusion. That is, it is possible to efficiently diffuse and reflect visible light at a portion where the silica shell 1a is thick while effectively capturing visible light at a portion where the silica shell 1a is thin. For this reason, by using this light transmittance and light diffusibility, for example, in use for a lighting fixture such as an LED light, the luminous efficiency can be increased, and high-brightness wide-area diffused light can be obtained. Can be reduced. In addition, when used for cosmetics (for example, lipsticks and foundations), it is possible to expect the effect of making wrinkles less noticeable or producing an optical lift-up effect by changing the texture of the skin.

  Furthermore, according to the nano hollow particles 1 made of silica shells with non-uniform thickness of the silica shell 1a, the particles become lower density than those with uniform thickness of the silica shell 1a. It is difficult for coagulation and sedimentation to occur when it is mixed in a target product such as the above, and it is possible to prevent a decrease in physical properties of the target product due to coagulation sedimentation.

  Here, in the present invention, the hydroxyapatite particles 2 that are calcium phosphate are used as the core particles as described above, and hydrochloric acid is not required to dissolve the hydroxyapatite particles 2 without using a strongly acidic aqueous solution. Since the hydroxyapatite particles 2 as the core particles are completely dissolved by setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4 with a dilute acidic aqueous solution such as There is no need to use materials or handle corrosion resistance. Therefore, the load on the surrounding environment can be reduced and the cost can be reduced.

  In addition, calcium carbonate as a conventional core particle is in a water-containing cake state, and the core particle grows and agglomerates over time and easily changes in quality. On the other hand, in the present invention, since the hydroxyapatite particles 2 in a dry powder state are used as the core particles, the raw material hardly changes in quality, and the quality control of the raw material does not cost. Further, since the raw material hardly changes, it is possible to improve production efficiency and mass productivity.

  Furthermore, in the present invention, when the hydroxyapatite particles 2 that are calcium phosphate particles are dissolved by a dilute acidic aqueous solution such as hydrochloric acid, calcium hydroxide, calcium chloride, a phosphoric acid aqueous solution, etc. are discharged as a waste acid aqueous solution. By collecting these aqueous solutions, the hydroxyapatite particles 2 can be re-synthesized, and can be reused as core particles. At this time, unlike calcium carbonate which is a conventional core particle, no gas or the like is generated at the time of dissolution, and a large apparatus for gas recovery is not necessary. There is no cost. Therefore, contribution to environmental conservation and cost reduction can be achieved.

In this way, the agglomeration into the secondary particles is small and the dispersibility is high, and the cost can be reduced and the environment can be reduced by simplifying the quality control of the reaction vessel and the raw material and reusing the core particles. It becomes the nano hollow particle 1 which consists of a silica shell, and its manufacturing method.
This makes it suitable for mass production (scale-up) for mass-producing nano hollow particles 1 made of silica shells in the industrial field.
Furthermore, the nano hollow particle 1 composed of the silica shell thus produced uses various materials such as paints, films, and synthetic fibers by utilizing its heat insulating property, transparency, translucency, light weight and the like. It can be mixed and dispersed uniformly and applied to a wide range of technical fields such as thermal insulation paints, thermal insulation films, and thermal insulation fibers. Further, it can be used as a sustained-release pharmaceutical product / sustained-release cosmetic product, a delivery system, a catalyst carrier, etc. containing a substance such as an active ingredient or a catalyst by utilizing a hollow structure. In addition, the calcium phosphate particles dissolved in the step of dissolving and removing the calcium phosphate particles such as the hydroxyapatite particles 2 as the core particles by firing the nano hollow particles 1 made of the silica shells by the inventors' experimental research, It has been confirmed that the fine through-holes generated in the silica shell 1a are closed by flowing out of the particles 3 to become hollow particles having high strength and are not destroyed even when pressure is applied.

  In the above embodiment, the hydroxyapatite particles 2 are used as the calcium phosphate that is the core particle. However, the calcium phosphate is not limited to this, and in addition, oxyapatite, α-tricalcium phosphate, β -It is also possible to use tricalcium phosphate, γ-tricalcium phosphate or the like. However, since hydroxyapatite is relatively easy to produce and obtain particles having various outer shapes, hollow particles having various outer shapes can be produced at low cost. Furthermore, since the silica shell 1a is easily coated, the production efficiency of the silica nano hollow particles 1 can be increased. For this reason, hydroxyapatite is suitable as the calcium phosphate.

  In the above embodiment, ethanol is used as the organic solvent. However, when the present invention is carried out, the organic solvent is soluble in silicon alkoxide and water, and further, hydrolysis of silicon alkoxide is performed. In addition, alcohols such as methanol and propanol, glycols, glycol esters, ketones such as acetone, aliphatic hydrocarbons such as n-hexane, and aromatics such as xylene Hydrocarbons and the like can also be used. However, by using alcohols such as ethanol, the interaction between calcium phosphate particles such as hydroxyapatite particles 2 and silicon alkoxides such as tetraethoxysilane can be improved, and the production efficiency of silica nano hollow particles 1 can be improved. As the organic solvent, alcohols such as ethanol are preferable.

  In addition, since the numerical value quoted in the embodiment of the present invention does not indicate a critical value but indicates a preferable value suitable for implementation, even if the numerical value is slightly changed, the implementation is denied. is not.

1 Nano hollow particles made of silica shell 2 Hydroxyapatite particles (calcium phosphate particles)
3 Silica coated particles

Claims (14)

  The calcium phosphate particles in a dry powder state having a predetermined size and shape are dispersed in an organic solvent, and silicon alkoxide and a base catalyst are mixed to form silica-coated particles in which a silica shell is formed on the surface of the calcium phosphate particles. A nano hollow particle comprising a silica shell, wherein the calcium phosphate inside the silica coating particle is dissolved with an aqueous solution having a hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4.   2. The nano hollow particle comprising a silica shell according to claim 1, wherein the nano hollow particle comprising the silica shell has any one of a spherical form, a spheroid form, and a cubic form.   The nano hollow particle comprising a silica shell according to claim 1 or 2, wherein the thickness of the silica shell of the nano hollow particle comprising the silica shell is in the range of 2 nm to 25 nm.   The nano hollow particle made of silica shell according to any one of claims 1 to 3, wherein the thickness of the silica shell of the nano hollow particle made of silica shell varies depending on the site and is non-uniform.   The particle hollow space volume fraction of the nano hollow particles made of the silica shell is in the range of 25 vol% to 90 vol%, and consists of the silica shell according to any one of claims 1 to 4. Nano hollow particles.   6. The nano hollow particle comprising a silica shell according to any one of claims 1 to 5, wherein the calcium phosphate particles are hydroxyapatite particles.   The nano hollow particle comprising a silica shell according to any one of claims 1 to 6, wherein the organic solvent is an alcohol. A dispersion step of dispersing calcium phosphate particles in a dry powder state having a predetermined size and shape in an organic solvent;
A silica coating forming step of forming silica shells on the surface of the calcium phosphate particles by mixing silicon alkoxide and a base catalyst in the organic solvent in which the calcium phosphate particles are dispersed; and
And a calcium phosphate dissolution step of dissolving the calcium phosphate inside the silica coating particle by setting the hydrogen ion concentration index of the dispersion in the range of pH 2 to pH 4 with an acid aqueous solution. Production method.   The nano hollow particle made of silica shell according to claim 8, wherein the shape of the nano hollow particle made of silica shell is any one of a spherical shape, a spheroid shape and a cubic shape. Method.   The method for producing nano-hollow particles comprising silica shells according to claim 8 or 9, wherein the thickness of the silica shell of the nano-hollow particles comprising silica shells is in the range of 2 nm to 25 nm.   The thickness of the silica hollow of the nano hollow particle made of the silica shell varies depending on the site and is non-uniform, The nano hollow particle made of the silica shell according to any one of claims 8 to 10, Production method.   The nanoparticle made of silica shell according to any one of claims 8 to 11, wherein the volume ratio of the particle-containing space of the hollow particle made of silica shell is in the range of 25 vol% to 90 vol%. A method for producing hollow particles.   The method for producing nano hollow particles comprising silica shells according to any one of claims 8 to 12, wherein the calcium phosphate particles are hydroxyapatite particles.   The method for producing nano-hollow particles comprising silica shells according to any one of claims 8 to 13, wherein the organic solvent is an alcohol.