JP2020176037A - Hollow nano-silica particle, core-shell particle, and method for producing them - Google Patents

Abstract

To provide: hollow nano-silica particles in which association particles are prevented from being produced and in which light is prevented from scattering; core-shell particles capable of producing the hollow nano-silica particles; and methods for producing them.SOLUTION: This invention relates to hollow nano-silica particles, wherein: (1) an average particle diameter thereof is 50-150 nm; (2) average thickness in a shell thereof is 5-25 nm; (3) a ratio (IQ2/IQ4), measured through solid NMR(29Si/MAS), of integrated intensity (IQ2) in a peak (Q2) attributed to Si having a cross-linked oxygen number of 2 to integrated intensity (IQ4) in a peak (Q4) attributed to Si having the cross-linked oxygen number of 4 is 0.20 or less; and (4) in a particle size distribution in a range of a particle diameter of 50-500 nm, measured by using a disk centrifugal-type particle size distribution-measuring apparatus, a ratio Psa/Psm of peak intensity Psa in association particles to peak intensity Psm in main particles, non-associated hollow nano-silica particles, is 0.4 or less.SELECTED DRAWING: None

Description

The present invention relates to hollow nanosilica particles, core-shell particles, and a method for producing them.

In recent years, research on inorganic oxide fine particles has been conducted. When an inorganic oxide becomes nano-sized, the properties of the substance change, and the properties such as electrical, optical, and thermal properties also change significantly. Therefore, it may be applied as a new highly functional material.

The structure of the inorganic oxide fine particles includes a dense type, a porous type, and a hollow type. Among them, hollow type hollow particles are attracting attention as a new highly functional material because they have features such as low density and large specific surface area. For example, hollow nanosilica with a particle size of 100 nm or less is used for an antireflection film.

As a method for producing hollow inorganic oxide fine particles, a method for producing hollow silica particles using polystyrene particles as a core and hollow polystyrene particles produced by the production method have been proposed (see, for example, Non-Patent Document 1). ..

When hollow nanosilica is used for an antireflection film, there is a problem that if a large amount of associated particles is present, light is scattered and the antireflection function is deteriorated. Therefore, hollow nanosilica with a small amount of associated particles is preferably used for products that require an antireflection function such as an antireflection film. However, the dispersibility of the hollow silica particles described in Non-Patent Document 1 has not been sufficiently investigated.

Therefore, the development of hollow nanosilica particles in which the formation of associated particles is suppressed and the scattering of light is suppressed is required, and the core-shell particles capable of producing the hollow nanosilica particles and the method for producing these are required. Development is required.

Bull.Korean Chem.Soc.2011, Vol.32, No5 Fabrication of Uniform Hollow Silica Nanospheres using a Cationic Polystyrene Core

The present invention has been made in view of the above, and hollow nanosilica particles in which the formation of associated particles is suppressed and light scattering is suppressed, core-shell particles capable of producing the hollow nanosilica particles, and these. It is an object of the present invention to provide the manufacturing method of.

As a result of diligent research to achieve the above object, the present inventor has a peak attributed to Si having two crosslinked oxygen numbers in the average particle size, the average shell thickness, and the solid NMR ( ²⁹ Si / MAS) measurement. (Q2) integrated intensity _{(I Q2)} and the ratio of the integrated intensity _{(I Q4)} of the peak (Q4) of crosslinked number of oxygen are attributed to Si is a four _(I Q2 _/ I _Q4), and, associated We have found that the above object can be achieved by using hollow nanosilica particles in which the ratio Psa / Psm of the peak intensity Psm of the main particles, which are not hollow nanosilica particles, to the peak intensity Psa of the associated particles is in a specific range. Has been completed.

That is, the present invention relates to the following hollow nanosilica particles, core-shell particles, and a method for producing them.
1. 1. Hollow nanosilica particles
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) In the solid-state NMR ( ²⁹ Si / MAS) measurement, the integrated intensity (I _Q2 ) of the peak (Q2) attributed to Si having two crosslinked oxygen numbers and Si having four crosslinked oxygen numbers. the ratio of the integrated intensity of the assigned the peaks _{(Q4) (I Q4) (} I Q2 / I Q4) is, is 0.20 or less,
(4) The peak intensity Psa of the associated particles and the peak of the main particles which are hollow nanosilica particles that are not associated in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Psa / Psm to the strength Psm is 0.4 or less.
Hollow nanosilica particles characterized by that.
2. The half-value width of the distribution curve of the main particles, which are non-associative hollow nanosilica particles, in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device is 15 nm or less. The hollow nanosilica particles according to 1.
3. 3. Core-shell particles having organic polymer particles as a core and silica as a shell for coating the organic polymer particles.
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) Peak intensity Pca of associated particles and peak intensity of main particles which are not associated core-shell particles in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Pca / Pcm to Pcm is 0.5 or less.
The core shell particles are characterized by that.
4. The half-value width of the distribution curve of the main particles, which are non-associative hollow nanosilica particles, in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device is 20 nm or less. 3. The core-shell particles according to 3.
5. Item 3. The core-shell particles according to Item 3 or 4, wherein the organic polymer particles are polystyrene particles.
6. A method for producing hollow nanosilica particles.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) A solution is prepared by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring them. In the solution, the step 2 of forming the core-shell particles having the organic polymer particles as the core and having a shell covering the organic polymer particles, and
(3) A step 3 of removing the organic polymer particles which are the cores of the core-shell particles by thermally decomposing the core-shell particles in the presence of an organic acid is included.
A method for producing hollow nanosilica particles.
7. Item 6. The method for producing hollow nanosilica particles according to Item 6, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone, hydroxypropyl cellulose, and polyvinyl alcohol.
8. Item 6. The method for producing core-shell particles according to Item 6 or 7, wherein in the step 2, the alkoxysilane contains tetraalkoxysilane, and the concentration of the alkoxysilane in the solution is 3 to 7% by mass.
9. Item 8. The method for producing hollow nanosilica particles according to any one of Items 6 to 8, wherein the organic acid is citric acid.
10. Item 2. The method for producing hollow nanosilica particles according to any one of Items 6 to 9, further comprising a step 4 of coating a shell on the surface of the hollow nanosilica particles after the step 3.
11. A method for producing core-shell particles.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) A solution is prepared by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring the mixture. 2. The step 2 of forming core-shell particles having the organic polymer particles as a core and having a shell covering the organic polymer particles in the solution.
A manufacturing method characterized by that.
12. Item 2. The method for producing core-shell particles according to Item 11, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone, hydroxypropyl cellulose, and polyvinyl alcohol.

Since the hollow nanosilica particles of the present invention suppress the formation of associated particles and suppress the reflection of light, they can be suitably used for various articles that require antireflection characteristics of light. Further, since the core-shell particles of the present invention also suppress the formation of associated particles, the hollow nanosilica particles of the present invention can be easily produced. Further, in the method for producing hollow nanosilica particles of the present invention, the formation of associated particles is suppressed, and hollow nanosilica particles in which light reflection is suppressed can be easily produced. Further, in the method for producing core-shell particles of the present invention, association of the produced core-shell particles is suppressed, and core-shell particles that can be suitably used for producing the hollow nanosilica particles of the present invention can be easily produced. it can.

It is a figure which shows the particle size distribution of the hollow nanosilica particle of Example 5 measured by using the disk centrifugal type particle size distribution measuring apparatus. It is a figure which shows the particle size distribution of the core-shell particle of Example 1 measured by using the disk centrifugal type particle size distribution measuring apparatus. It is a figure which shows the SEM image of the core-shell particle of Comparative Example 3 with a magnification of 100,000 times. It is a figure which shows the SEM image of the core-shell particle of Comparative Example 4 with a magnification of 100,000 times.

Hereinafter, a method for producing hollow nanosilica particles, core-shell particles, hollow nanosilica particles, and a method for producing core-shell particles of the present invention will be described in detail.

The hollow nanosilica particles of the present invention
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) In the solid-state NMR ( ²⁹ Si / MAS) measurement, the integrated intensity (I _Q2 ) of the peak (Q2) assigned to Si having two crosslinked oxygen numbers and Si having four crosslinked oxygen numbers the ratio of the integrated intensity of the assigned the peaks _{(Q4) (I Q4) (} I Q2 / I Q4) is, is 0.20 or less,
(4) Peak intensity Psa of associated particles and peak of main particles which are hollow nanosilica particles that are not associated in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Psa / Psm with the strength Psm is 0.4 or less. The hollow nanosilica particles of the present invention meet the requirements (1), (2) and (4) above, and are not associated with the average particle size, the average thickness of the shell, and the peak intensity Psa of the associated particles. Since the ratio Psa / Psm of the main particles, which are hollow nanosilica particles, to the peak intensity Psm is in a specific range, the aggregation of the hollow nanosilica particles is suppressed, the formation of associated particles is suppressed, and the scattering of light is suppressed. Will be done. Further, since the above requirement (3) is satisfied, the shell structure is dense and the refractive index is low. That is, by satisfying the above requirements (1) to (4), the hollow nanosilica particles of the present invention can suppress light scattering due to these requirements, and are required to have light antireflection characteristics. It can be suitably used for various articles.

Further, the core-shell particles of the present invention are
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) Peak intensity Pca of associated particles and peak intensity of main particles which are not associated core-shell particles in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. Since the ratio Pca / Pcm to Pcm is 0.5 or less, aggregation of core-shell particles is suppressed and formation of associated particles is suppressed. By using the core-shell particles of the present invention, the above-mentioned present invention Hollow nanosilica particles can be easily produced.

Further, according to the method for producing core-shell particles of the present invention, by preparing organic polymer particles using a specific mixed solvent and dispersant in step 1, aggregation of core-shell particles formed in step 2 is suppressed. The formation of associated particles is suppressed. Therefore, aggregation of the obtained hollow nanosilica particles is suppressed by the method for producing hollow nanosilica particles of the present invention, which comprises the step 3 of thermally decomposing and removing the organic polymer particles which are the cores of the core-shell particles in the presence of an organic acid. Since the formation of associated particles is suppressed, the produced hollow nanosilica particles can suppress light scattering and can be suitably used for various articles that require light antireflection characteristics. Nanosilica particles can be easily produced.

1. 1. Hollow nanosilica particles The hollow nanosilica particles of the present invention have (1) an average particle diameter of 50 to 150 nm, (2) an average shell thickness of 5 to 25 nm, and (3) solid-state NMR ( ²⁹ Si / MAS) measurement. In, the integrated intensity (I _Q2 ) of the peak (Q2) attributed to Si having two cross-linked oxygen numbers and the integrated intensity (I) of the peak (Q4) attributed to Si having four cross-linked oxygen numbers. _Q4) and the ratio of _(I Q2 _{/ I Q4)} is, is 0.20 or less, in the particle size distribution in the range of particle diameter 50~500nm measured using the (4) disk centrifugal type particle size distribution measuring apparatus, The ratio Psa / Psm of the peak intensity Psa of the associated particles to the peak intensity Psm of the main particles which are not associated hollow nanosilica particles is 0.4 or less.

The silica-based compound that forms the hollow nanosilica particles is not particularly limited as long as it contains silica, and may be formed only of silica.

When the silica-based compound contains a compound other than silica, the hollow nanosilica particles preferably contain silica and a metal oxide. Examples of the metal oxide include oxides of metals capable of forming metal alkoxides, and specific examples thereof include oxides of aluminum, titanium, zirconium and the like. The oxide of aluminum can be used to adjust the surface charge (zeta potential, etc.) of the shell. Further, the refractive index of the shell can be adjusted by using oxides of titanium and zirconium.

The average particle size of the hollow nanosilica particles of the present invention is 50 to 150 nm. If the average particle size of the hollow nanosilica particles is larger than the above range, the optical characteristics may deteriorate. If it is smaller than the above range, the formation of associated particles may not be suppressed. The average particle size of the hollow nanosilica particles is preferably 50 to 120 nm, more preferably 50 to 110 nm, and even more preferably 50 to 100 nm.

In the present specification, the average particle size of the hollow nanosilica particles is arbitrarily determined by taking a photograph of the particles using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) under the condition of an acceleration voltage of 200 kV. It is a value obtained by measuring the minor axis of 100 selected particles and calculating an average value.

The average thickness of the shell (film) forming the hollow nanosilica particles is 5 to 25 nm. If the average thickness of the shell is larger than the above range, the formation of associated particles may not be suppressed. If the average thickness of the shell is smaller than the above range, the shell may be damaged. The average thickness of the shell is preferably 6 to 22 nm, more preferably 7 to 18 nm.

In the present specification, the thickness of the shell is a shell of 100 particles arbitrarily selected by taking a photograph of particles under the condition of 200 kV by TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.). It is an average value obtained by measuring the thickness.

It is preferable that the hollow nanosilica particles of the present invention are not substantially associated. When the hollow nanosilica particles are not associated, the reflection of light is further suppressed, and it can be more preferably used for various articles that require antireflection characteristics of light. In the present specification, the state in which the silica-based hollow particles are associated indicates a state in which the hollow portions of the plurality of hollow nanosilica particles are joined to form one hollow portion. The fact that the nanosilica particles are not substantially associated means a state in which the hollow portions of the hollow nanosilica particles are not bonded. Further, the fact that the hollow nanosilica particles of the present invention are not associated can be confirmed by observing a photograph of the hollow nanosilica particles taken by using the above TEM.

In the solid-state NMR ( ²⁹ Si / MAS) measurement, the hollow nanosilica particles of the present invention have an integral intensity (I _Q2 ) of a peak (Q2) attributed to Si having two cross-linked oxygen numbers and a cross-linked oxygen number of 4. The ratio (I _Q2 / I _Q4 ) of the peak (Q4) attributed to the Si to the integrated intensity (I _Q4 ) is 0.20 or less. The hollow nanosilica particles of the present invention have a dense shell structure in which the silanol groups are condensed and _IQ4 is increased when the core is removed by firing. If _IQ2 / _IQ4 exceeds the above range, the refractive index will not be low and the shell will be easily damaged. _IQ2 / _IQ4 is preferably 0.18 or less, more preferably 0.16 or less.

In this specification, _I Q2 _{/ I Q4} hollow nanosilica particles is a value calculated from the ²⁹ Si- solid state NMR spectrum is measured by the following measuring methods.

( ²⁹ Si-Solid State NMR Spectrum Measurement)
^{The 29} Si-solid-state NMR spectrum is measured by using JNM-ECA400 (manufactured by JEOL Ltd.) for a hollow nanosilica powder vacuum-dried at room temperature under the following conditions.
-Resonance frequency: 78.65 Hz
・ Measurement mode: CP / MAS method ・ Measurement nucleus: 29Si
-Sample rotation speed: 6 kHz
・ Measurement temperature: Room temperature ・ Number of integrations: 16384 times

(I _Q2 / I _Q4 ) is calculated from the spectrum measured by the above measurement method. In the ²⁹ Si-solid-state NMR spectrum obtained by solid-state NMR ( ²⁹ Si / MAS) measurement, the peak (Q2) exists between -90 and -93 ppm, and the peak (Q4) is between 110-112 ppm. Exists in.

The true density of the hollow nanosilica particles of the present invention measured by the immersion method using isooctane as a solvent is preferably 0.8 to 1.5 g / ml, more preferably 0.9 to 1.4 g / ml. 0 to 1.3 g / ml is more preferable. When the upper limit of the true density is in the above range, the reflectance when used for the antireflection film is further increased. When the lower limit of the true density is in the above range, damage to the shell is further suppressed.

In the present specification, the true density measured by the immersion method using the above isooctane as a solvent is measured by the following measuring method.

(True density by immersion method)
Inject isooctane into a 5 mL specific gravity bottle and let stand in a constant temperature water bath at about 25 ° C. for 30 minutes. After standing, the temperature inside the specific gravity bottle is measured, and the isooctane density is calculated based on the following formula.
(Isooctane density) = [-0.0011 x (measurement temperature (° C))] +0.7142

Then, the specific gravity bottle is taken out from the constant temperature water tank, the droplets are wiped off, and the isooctane-filled specific gravity bottle is precisely weighed. The volume of the specific gravity bottle is calculated based on the following formula.
(Volume of specific gravity bottle (ml)) = [(Weight of specific gravity bottle filled with isooctane (g))-(Weight of specific gravity bottle (g))] ÷ (Isooctane density (g / ml))

Next, 10 g of the hollow nanosilica particle dispersion is weighed with a petri dish and dried on a hot plate at a temperature of 140 ° C. to obtain a hollow nanosilica powder. The obtained powder is dried under reduced pressure at a temperature of 120 ° C. for 2 hours. Add dry powder to a 5 mL specific gravity bottle and inject isooctane. Let stand at room temperature for 30 minutes, and after leaving, degas for 1 hour using a vacuum pump. The degassed surface-treated hollow nanosilica particle-filled specific gravity bottle is allowed to stand in a constant temperature water tank at about 25 ° C. for 30 minutes. After standing, the temperature inside the specific gravity bottle is measured, and the isooctane density is calculated based on the following formula.
(Isooctane specific gravity) = [-0.0011 x (measurement temperature (° C))] +0.7142

Next, the specific gravity bottle is taken out from the constant temperature water tank, the droplets are wiped off, and the surface-treated hollow nanosilica-filled specific gravity bottle is precisely weighed. Using the specific gravity bottle volume, the true density of hollow nanosilica by the immersion method is calculated based on the following formula.
(True density (g / ml)) = (Dry powder weight (g)) ÷ {(Specific gravity bottle volume (ml))-[(Isooctane weight (g)) ÷ (Isooctane density (g / ml))]}

The true density of the hollow nanosilica particles of the present invention measured using a gas pycnometer is preferably 1.9 to 2.2 g / ml, more preferably 1.92 to 2.18 g / ml, and 1.95 to 2. .15 g / ml is more preferred. When the true density is in the above range, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

In the present specification, the true density measured by the immersion method using the above isooctane as a solvent is measured by the following measuring method.

(True density by gas pycnometer)
10 g of the hollow nanosilica particle dispersion is weighed with a petri dish and dried on a hot plate at a temperature of 140 ° C. to obtain a surface-treated hollow nanosilica powder. The obtained powder is dried under reduced pressure at a temperature of 120 ° C. for 1 hour. The true density of the dried hollow nanosilica particle powder is measured using a helium gas pycnometer (Micro-ULTRAPYC1200e manufactured by Kantachrome Instruments Japan GK).

The hollow nanosilica particles of the present invention are hollow nanosilica particles that are not associated with the peak intensity Psa of the associated particles in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Psa / Psm of a certain main particle to the peak intensity Psm is 0.4 or less. If Psa / Psm exceeds 0.4, light scattering is not suppressed. Psa / Psm is preferably 0.35 or less, more preferably 0.3 or less, further preferably 0.25 or less, and particularly preferably 0.2 or less. Further, the lower limit of Psa / Psm may be 0, 0.01, or 0.02.

In the present specification, the Psa / Psm is measured by the following measuring method.

(Psa / Psm)
(I) The hollow nanosilica particles obtained in step 5 and the organic solvent are mixed at a ratio of 0.2% by mass of the hollow nanosilica particles to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm is measured.
(Iii) The peak intensity Psm of the main particles, which are hollow nanosilica particles that are not associated, and the peak intensity Psa of the associated particles, which are the hollow nanosilica particles that are associated, are measured, and the peak intensity Psm of the main particles and the associated particles The ratio Psa / Psm with the peak intensity Psa is calculated.

In the above method for measuring Psa / Psm, in (i), the hollow nanosilica particles may be a dispersion liquid dispersed in water or other solvent, and the hollow nanosilica is prepared by mixing with an organic solvent in the measurement sample. The content of the particles may be 0.2% by mass. Further, the particles are not associated with the main particles, and have the largest particle size among the particle size distributions in the particle size of 50 to 500 nm measured by the above-mentioned disk centrifugal type particle size distribution measuring device (manufactured by DC24000UHR CPS). The small peak is the peak of the main particle. Further, among the particle size distributions having a particle diameter of 50 to 500 nm, peaks other than the peaks of the main particles are peaks of associated particles.

FIG. 1 shows the particle size distribution of the hollow nanosilica particles of Example 6 measured using a disk centrifugal particle size distribution measuring device. In FIG. 1, a peak having a particle diameter in the range of 90 to 100 nm is a peak of a main particle, and a peak having a particle diameter in a range of more than 100 nm is a peak of an associated particle.

Half of the distribution curve of the main particles, which are non-associative hollow nanosilica particles, in the particle size distribution of the hollow nanosilica particles of the present invention in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The price range is preferably 15 nm or less, more preferably 13 nm or less, and even more preferably 12 nm or less. When the upper limit of the half width of the distribution curve of the main particles is within the above range, the particle size distribution is further narrowed and the sphericality is further increased. Further, the lower limit of the half width of the distribution curve of the main particles is not particularly limited, and is about 3 nm.

In the present specification, the half width of the distribution curve of the main particles of the hollow nanosilica particles is measured by the following measuring method.

(Measurement method of half width of distribution curve of main particles of hollow nanosilica particles)
(I) The hollow nanosilica particles obtained in step 5 and the organic solvent are mixed at a ratio of 0.2% by mass of the hollow nanosilica particles to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm is measured.
(Iii) The full width at half maximum is calculated from the interval between two points of 1/2 intensity of the peak of the main particle which is a hollow nanosilica particle which is not associated.

In the hollow nanosilica particles of the present invention, the hollow nanosilica particles having an aspect ratio of 1.5 or less are preferably 95% or more, more preferably 97% or more, still more preferably 99% or more, assuming that the total number of hollow nanosilica particles is 100%. .. When the proportion of particles having an aspect ratio of 1.5 or less is in the above range, aggregation of hollow nanosilica particles is further suppressed.

In the present specification, the ratio of the hollow nanosilica particles having an aspect ratio of 1.5 or less to the total particles, and the ratio of the core-shell particles to be described later to the total particles having an aspect ratio of 1.5 or less. Is measured by the following method. That is, using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.), photographs of particles were taken under the conditions of a magnification of 200,000 times and an acceleration voltage of 200 kV, and each of the 100 arbitrarily selected particles was taken. The particle major axis and the particle minor axis of the particles are measured, and the aspect ratio of each particle is obtained based on the following formula. Next, the number of particles having an aspect ratio of 1.5 or less out of 100 particles is counted, and the number is defined as the ratio (%) of the particles having an aspect ratio of 1.5 or less to the total number of particles.
(Aspect ratio) = (Particle major axis) ÷ (Particle minor axis)

The hollow nanosilica particles of the present invention preferably have a coefficient of variation of average particle size of 5 to 20%, more preferably 5 to 18%, and even more preferably 5 to 15%. When the coefficient of variation of the average particle size of the hollow nanosilica particles is within the above range, the aggregation of the hollow nanosilica particles can be further suppressed, and when the hollow nanosilica particles are packed in various articles, they are easily filled uniformly.

In the present specification, the coefficient of variation of the hollow nanosilica particles and the core-shell particles described later is measured by using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) under the condition of an acceleration voltage of 200 kV. It is a value calculated based on the following formula after taking a picture and measuring the minor axis of 100 arbitrarily selected particles to obtain an average value.
(Coefficient of variation) = [(standard deviation of particle minor axis) ÷ (mean value of particle minor axis)] × 100

Since the hollow nanosilica particles of the present invention have the above-mentioned constitution, the formation of associated particles is suppressed and the reflection of light is suppressed, so that they are suitable for various articles that require antireflection characteristics of light. Can be used for. Therefore, it is suitable as a high-performance material, and in particular, it can be suitably used as an antireflection film material, an insulating film material, or a heat insulating material.

2. Core-shell particles The core-shell particles of the present invention are core-shell particles having an organic polymer particle as a core and silica as a shell for coating the organic polymer particles, and (1) have an average particle diameter of 50 to 150 nm, and (2). The average thickness of the shell is 5 to 25 nm, and (3) the peak intensity Pca of the associated particles in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device is associated with. The ratio Pca / Pcm to the peak intensity Pcm of the main particles, which are not core-shell particles, is 0.5 or less. Since aggregation of the core-shell particles is suppressed and formation of associated particles is suppressed, the hollow nanosilica particles of the present invention can be easily produced by thermally decomposing the organic polymer particles.

The average particle size of the core-shell particles of the present invention is 50 to 150 nm. If the average particle size of the core-shell particles is larger than the above range, the optical characteristics may deteriorate. If it is smaller than the above range, the formation of associated particles may not be suppressed. The average particle size of the core-shell particles is preferably 50 to 120 nm, more preferably 50 to 110 nm, and even more preferably 50 to 100 nm.

In the present specification, the average particle size of the core-shell particles is arbitrarily selected by taking a photograph of the particles using a TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) under the condition of an acceleration voltage of 200 kV. It is a value obtained by measuring the minor axis of only 100 particles and calculating the average value.

The organic polymer particles are not particularly limited, and organic polymer particles that are easily burnt down by thermal decomposition after forming a shell are preferable. Examples of such organic polymer particles include polystyrene particles and PMMA particles. Among these, polystyrene particles are preferable in that the formation of associated particles can be further suppressed by applying a positive zeta potential.

The silica-based compound that forms the shell that coats the organic polymer particles is the same as the silica-based compound that forms the hollow nanosilica particles described above. Further, the thickness of the shell is the same as the film thickness of the shell (film) forming the above-mentioned hollow nanosilica particles.

The core-shell particles of the present invention associate with the peak intensity Pcm of the main particles, which are non-associative core-shell particles, in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Pca / Pcm of the particles to the peak intensity Pca is 0.5 or less. When Pca / Pcm exceeds 0.5, light scattering of hollow nanosilica particles produced by using the core-shell particles of the present invention is not suppressed. The Pca / Pcm is preferably 0.45 or less, more preferably 0.4 or less, further preferably 0.35 or less, and particularly preferably 0.3 or less. Further, the lower limit of Pca / Pcm may be 0, 0.01, or 0.02.

In the present specification, the Pca / Pcm is measured by the following measuring method.

(Pca / Pcm)
(I) The core-shell particle dispersion obtained in step 2 and the organic solvent are mixed at a ratio of the core-shell particle content of 0.02% by mass to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm is measured.
(Iii) The peak intensity Pcm of the main particles which are not associated core-shell particles and the peak intensity Pca of the associated particles which are the associated core-shell particles are measured, and the peak intensity Pcm of the main particles and the peak intensity of the associated particles are measured. Calculate the ratio Pca / Pcm with Pca.

In the above Pca / Pcm measuring method, in (i), the core-shell particle dispersion obtained in step 2 of the manufacturing method described later and water are mixed with the core-shell particle dispersion: water = 1: 100 (mass ratio). A sample for measurement may be prepared by mixing at the ratio of. Further, in (i), the core-shell particles may be a dispersion liquid dispersed in water or other solvent, and the content of the core-shell particles is 0.2% by mass in the measurement sample prepared by mixing with an organic solvent. It should be. Further, the particles are not associated with the main particles, and the smallest peak in the particle size distribution at a particle size of 50 to 500 nm measured by the above-mentioned disk centrifugal type particle size distribution measuring device (manufactured by DC24000UHR CPS) is This is the peak of the main particle. Further, among the particle size distributions having a particle diameter of 50 to 500 nm, peaks other than the peaks of the main particles are peaks of associated particles.

FIG. 2 shows the particle size distribution of the core-shell particles of Example 1 measured using a disk centrifugal particle size distribution measuring device. In FIG. 2, the peak having a particle size in the range of 90 to 100 nm is the peak of the main particle, and the peak having the particle size in the range of more than 100 nm is the peak of the associated particle.

The half-value width of the distribution curve of the main particles, which are non-associative core-shell particles, in the particle size distribution of the core-shell particles of the present invention in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. , 20 nm or less is preferable, 18 nm or less is more preferable, and 15 nm or less is further preferable. When the upper limit of the half width of the distribution curve of the main particles is within the above range, the particle size distribution is further narrowed and the sphericality is further increased. Further, the lower limit of the half width of the distribution curve of the main particles is not particularly limited, and is about 3 nm.

In the present specification, the half width of the distribution curve of the main particles of the core-shell particles is measured by the following measuring method.

(Measurement method of half width of distribution curve of main particles of core shell particles)
(I) The core-shell particle dispersion obtained in step 2 and the organic solvent are mixed at a ratio of the core-shell particle content of 0.02% by mass to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm is measured.
(Iii) The full width at half maximum is calculated from the interval between two points of 1/2 intensity of the peak of the main particle which is a hollow core shell particle which is not associated.

In the core-shell particles of the present invention, the proportion of core-shell particles having an aspect ratio of 1.5 or less and the coefficient of variation of the core-shell particles when the total number of core-shell particles is 100% are the same as those of the above-mentioned hollow nanosilica particles. ..

The organic polymer particles preferably contain a dispersant. When the organic polymer particles contain the dispersant, the dispersant is present on the surface of the organic polymer particles, and the aggregation of the organic polymer particles can be further suppressed. The dispersant is not particularly limited as long as it can produce organic polymer particles, and a known dispersant can be used. Examples of the dispersant include polyvinylpyrrolidone, hydroxypropyl cellulose, polyvinyl alcohol (PVA), polyethylene oxide, polypropylene oxide, collagen, polysaccharide (Arabic gum) and the like, and among them, suppress the aggregation of organic polymer particles. Therefore, polyvinylpyrrolidone and hydroxypropyl cellulose are preferable because they can suppress the aggregation of core-shell particles. The above-mentioned dispersant can be used alone or in combination of two or more.

The content of the dispersant in the organic polymer particles is not particularly limited, but is preferably 0.01 to 100% by mass, more preferably 0.05 to 100% by mass, based on 100% by mass of the organic polymer particles. When the content of the dispersant is in the above range, the aggregation of the organic polymer particles can be further suppressed.

Among the organic polymer particles forming the core-shell particles of the present invention, the average particle size of the organic polymer particles, the proportion of the organic polymer particles having an aspect ratio of 1.5 or less when the total number of the organic polymer particles is 100%, and The variation coefficient of the organic polymer particles is the same as that of the core-shell particles described above.

The core-shell particles of the present invention are preferably not substantially associated. When the core-shell particles are not associated, the hollow nanosilica particles obtained by thermally decomposing the organic polymer particles which are the cores of the core-shell particles are easily obtained in a state where they are not substantially associated, and light is reflected. Can be more preferably used for various articles that are further suppressed and require light antireflection characteristics. In the present specification, the state in which the core-shell particles are associated means a state in which the organic polymer particles that are the cores of the plurality of core-shell particles are joined to form one secondary particle. The fact that the core-shell particles are not substantially associated means that the organic polymer particles that are the cores of the core-shell particles are not bonded. Further, the fact that the core-shell particles of the present invention are not associated can be confirmed by observing a photograph of the core-shell particles taken by using the above TEM.

In the core-shell particles of the present invention, the proportion of core-shell particles having an aspect ratio of 1.5 or less and the coefficient of variation of the core-shell particles when the total number of core-shell particles is 100% are the same as those of the above-mentioned hollow nanosilica particles. ..

3. 3. Method for producing hollow nanosilica particles The method for producing hollow nanosilica particles of the present invention is as follows.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) A solution is prepared by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring the mixture. In the solution, the step 2 of forming the core-shell particles having the organic polymer particles as the core and having a shell covering the organic polymer particles, and
(3) The step 3 of removing the organic polymer particles which are the cores of the core-shell particles by thermally decomposing the core-shell particles in the presence of an organic acid is included.

<Step 1>
Step 1 is a step of preparing organic polymer particles by polymerizing the organic monomer in a solution containing (1) an organic monomer, a dispersant, and a mixed solvent. The mixed solvent is water. 45 in a mixing ratio of the mass ratio of methanol: 55-80: a 20, Z-average molecular weight of the dispersant is a step is 180 × 10 ⁴ or more.

(Organic monomer)
The organic monomer is not particularly limited as long as it can produce organic polymer particles, but an organic monomer capable of forming organic polymer particles that are easily burnt down by thermal decomposition after forming a shell is preferable. Examples of such an organic monomer include polystyrene, PMMA and the like. Among these, polystyrene is preferable in that the formation of associated particles can be further suppressed by imparting a positive zeta potential to the organic monomer particles.

The polystyrene is not particularly limited, but one containing a structural unit derived from a hydrophobic monomer such as alkyl (meth) acrylate and other copolymerizable monomer structural units is preferable. Preferable examples thereof include alkyl (meth) acrylate styrene having an alkyl group having 3 to 22 carbon atoms, 2-methyl styrene and the like.

The concentration of the organic monomer used in step 1 in the solution is not particularly limited, but is preferably 0.1 to 20% by mass, preferably 0.2 to 10% by mass, based on 100% by mass of the above solution. More preferred. By setting the above concentration, it becomes easier to control the average particle size of the obtained organic polymer particles and the average particle size of the hollow nanosilica particles which are the final products by about 50 to 150 nm.

(Dispersant)
The dispersant is not particularly limited as long as it can produce organic polymer particles, and a known dispersant can be used. Examples of the dispersant include polyvinylpyrrolidone, hydroxypropyl cellulose, polyvinyl alcohol (PVA), polyethylene oxide, polypropylene oxide and the like. Among them, the core shell formed in step 2 described later by suppressing the aggregation of polystyrene particles. Polyvinylpyrrolidone and hydroxypropyl cellulose are preferable because they can suppress the aggregation of particles. The above-mentioned dispersant can be used alone or in combination of two or more.

Z average molecular weight of the dispersant is 180 × 10 ⁴ or more. When the Z average molecular weight of the dispersant is in the above range, the association of core-shell particles can be suppressed. Z average molecular weight of the dispersant is preferably 185 × 10 ⁴ or more, more preferably 190 × 10 ⁴ or more. Moreover, Z-average molecular weight of the dispersant is preferably 250 × 10 ⁴ or less, more preferably 240 × 10 ⁴ or less. When the upper limit of the Z average molecular weight of the dispersant is within the above range, the association of core-shell particles can be further suppressed.

The concentration of the dispersant used in step 1 in the solution is not particularly limited, but is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, based on 100% by mass of the solution. By setting the above concentration, the aggregation of the organic polymer particles can be further suppressed, and the aggregation of the core-shell particles formed in step 2 described later can be further suppressed.

(Mixed solvent)
The mixed solvent used in step 1 is a mixed solvent of water and methanol. By using such a mixed solvent, the agglomeration of the organic polymer particles can be suppressed, and the agglomeration of the core-shell particles formed in step 2 described later can be suppressed.

The mass ratio of water to methanol in the mixed solvent is 45: 55-80: 20. By setting the mass ratio of water to methanol in the above range, the aggregation of organic polymer particles can be suppressed, and the aggregation of core-shell particles formed in step 2 described later can be suppressed. The mass ratio of water to methanol is preferably 48:52 to 75:25, more preferably 50:50 to 70:30.

(Cationic polymerization initiator)
In step 1, the solution preferably contains a cationic polymerization initiator. The cationic polymerization initiator is not particularly limited as long as organic polymer particles can be obtained, and known inorganic peroxides, organic initiators, redox agents and the like can be used. Above all, it is more preferable to use a radical polymerization initiator such as an organic oxide or an azo compound. Organic oxides are represented by the general formula RO-OR, and azo compounds are represented by the general formula A-CN = CN-A. Specifically, benzoyl peroxide, 2,2'-azobis (isobutylamidin) dihydrochloride (AIBA), 4,4'-azobis-4-cyanovaleric acid, azobisisobutyronitonicyl (AIBN), 2 , 2'-azobis (2-methylpropioamide) dihydrochloride (AAPH), preferably 2,2'-azobis (isobutylamidin) dihydrochloride (AIBA), 2,2'-azobis (2-methylpro). Pioamide) dihydrochloride (AAPH). Of these, 2,2'-azobis (isobutylamidine) dihydrochloride (AIBA) and 4,4'-azobis-4-cyanovaleric acid are more preferable, and 2,2'-azobis (isobutylamidine) dihydrochloride (AIBA). Is more preferable.

The concentration of the cationic polymerization initiator used in the above step 1 in the solution is not particularly limited, but is preferably 0.01 to 1% by mass with the solution as 100% by mass. By setting the above concentration, it becomes easier to control the average particle size of the obtained organic polymer particles and the average particle size of the hollow nanosilica particles which are the final products by about 50 to 150 nm.

(Polymerization reaction)
In step 1, the polymerization reaction of the organic monomer is carried out in a solution containing the organic monomer, the dispersant, and the mixed solvent. The polymerization reaction can be carried out by mixing and stirring the above solutions.

The temperature during the polymerization reaction of the solution in step 1 is not particularly limited, but is preferably 40 ° C. or higher and lower than the boiling point of the solvent, and more preferably 50 to 90 ° C. If the reaction temperature is too low, the reaction rate may slow down, and if it is too high, the solvent may evaporate and the polymerization reaction may not be able to continue.

The reaction time of the above-mentioned polymerization reaction is not particularly limited, but is preferably 1 to 720 minutes, and more preferably 10 to 600 minutes. If the reaction time is too short, the reaction may be insufficient.

Organic polymer particles are prepared by the above polymerization reaction. The average particle size of the organic polymer particles is preferably 50 to 150 nm, more preferably 25 to 120 nm, still more preferably 25 to 100 nm. By setting the average particle size of the organic polymer particles in the above range, the average particle size of the core-shell particles formed in step 2 and the average particle size of the silica-based hollow particles produced in step 3 are set in an appropriate range. Can be done.

The organic polymer particles are prepared by the step 1 described above.

<Process 2>
In step 2, (i) the organic polymer particles, (ii) alkoxysilane, or alkoxysilane and metal alkoxide, and (iii) basic catalyst are added to and stirred in a solvent to prepare a solution. This is a step of forming core-shell particles having the organic polymer particles as a core and a shell for coating the organic polymer particles in the solution.

(solvent)
Water is preferably used as the solvent used in step 2. By using water, core-shell particles can be formed inexpensively and safely.

As the solvent, a hydrophilic solvent can also be used. Examples of the hydrophilic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol and 1,4-butandiol, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate. be able to. Among these, alcohols are preferably used, and methanol, ethanol, and isopropanol are more preferable. As the solvent, it is more preferable to use an alcohol of the same type as the alcohol produced by hydrolysis of the silicon compound. By using an alcohol of the same type as the alcohol produced by hydrolysis of the silicon compound, the solvent can be easily recovered and reused.

One of the above solvents may be used alone, or two or more kinds of solvents may be mixed and used.

As the solvent, water and a hydrophilic solvent may be mixed and used. The mass ratio of hydrophilic solvent: water is not limited, but 90:10 to 10:90 is preferable, and 50:50 to 10:90 is more preferable. By setting the mass ratio in the above range, the average particle size of the obtained hollow nanosilica particles can be easily controlled to about 50 to 150 nm.

As the solvent, a hydrophobic solvent can also be used. Examples of the hydrophobic solvent include organic hydrocarbon solvents having a water solubility of less than about 1 g per 100 g at 100 ° C. As such a hydrophobic solvent, a linear or branched or cyclic alkane having 6 to 10 carbon atoms, for example, hexane, cyclohexane, heptane, octane, or isooctane can be used. Among them, octane is more preferable.

(Organic polymer particles)
As the organic polymer particles used in the step 2, the organic polymer particles prepared in the above step 1 may be used.

The concentration of the organic polymer particles in the solution is preferably 0.01 to 50% by mass, more preferably 0.01 to 20% by mass.

(Alkoxysilane)
The alkoxysilane used in step 2 is not particularly limited, and for example, the general formula (1)
Si (OR ¹ ) ₄ (1)
Examples thereof include tetraalkoxysilanes and derivatives thereof. In the above general formula (1), R ¹ is the same or different and is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, and more preferably a lower alkyl group having 1 to 4 carbon atoms. More preferably, it is a lower alkyl group having 1 to 3 carbon atoms. Specifically, methyl group, ethyl group, propyl group, isobutyl group, butyl group, pentyl group, hexyl group and the like can be exemplified, and tetramethoxysilane in which R ¹ is a methyl group can be obtained, and a dense shell can be obtained. (TMOS), tetraethoxysilane (TEOS) in which R ² is an ethyl group is more preferable, and TMOS is further preferable. Further, if the carbon number is too large, silica may be difficult to be produced. The dense shell is a shell in which siloxane bonds are more completely formed and there are few remaining silanol groups.

As the alkoxysilane used in step 2, the general formula (2) is also used.
Si (OR ¹ ) ₃ R ² (2)
Examples thereof include trialkoxysilanes represented by and derivatives thereof. In the general formula (2), R ¹ is the same as R ^{1 in the} general formula (1), and R ² is hydrogen or the same alkyl group as the alkyl group described as R ¹ .

Examples of the derivative of the alkoxysilane include a low condensate obtained by partially hydrolyzing the alkoxysilane.

The above-mentioned alkoxysilane may be used alone or in combination of two or more. Above all, it is preferable to contain trialkoxysilane and tetraalkoxysilane in that aggregation can be prevented at the stage of core-shell particles and surface modification with a silane coupling agent or the like is facilitated.

The concentration of alkoxysilane in the above solution is preferably 0.01 to 50% by mass, more preferably 0.01 to 20% by mass, further preferably 1 to 10% by mass, and 3 It is particularly preferably ~ 7% by mass.

(Metal alkoxide)
In step 2, arcosisisilane and the metal alkoxide may be mixed and used. The metal alkoxide is not particularly limited, and known metal alkoxides can be used. Examples of such metal alkoxides include aluminum alkoxides, titanium alkoxides, zirconium alkoxides and the like. Aluminum alkoxide can be used to adjust the surface charge (zeta potential, etc.) of the shell. Further, when titanium alkoxide or zirconium alkoxide is used, the refractive index of the shell can be adjusted.

The concentration of the metal alkoxide in the solution is preferably 0.01 to 50% by mass, more preferably 0.01 to 20% by mass.

In step 2, the alkoxysilane and the metal alkoxide may be added separately to prepare a solution, or the alkoxysilane and the metal alkoxide may be mixed and hydrolyzed before being added to the solution. By mixing alkoxysilane and metal alkoxide, hydrolyzing them, and then adding them to the solution, the following formula (1)
Si-OM (1)
It is possible to form a shell having a bond represented by the above and uniformly containing the metal represented by M in the formula (1).

In the above formula (1), M represents a metal, preferably aluminum, titanium, or zirconium.

Examples of the method of mixing the above-mentioned alkoxysilane and the metal alkoxide, hydrolyzing the mixture, and then adding the metal alkoxide to the solution include the methods described in JP-A-2005-41722.

(Basic catalyst)
The basic catalyst used in step 2 is not particularly limited, and a known basic catalyst can be used, but in particular, an organic base catalyst containing no metal component and a metal in terms of avoiding mixing of metal impurities. Inorganic catalysts containing no components are suitable. Examples of the organic base catalyst include nitrogen-containing organic base catalysts such as ethylenediamine, diethylenetriamine, triethylenetetraamine, urea, ethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, and basic amino acids. .. Moreover, the ammonia water is mentioned as the said inorganic base catalyst. An organic base catalyst having low volatility is preferable because it does not volatilize in the temperature range when the step 2 is performed. In the case of volatilizing base, it may be added continuously to maintain the pH of the solution. In addition, ammonia water is preferable because it is inexpensive and economically superior.

The basic catalyst may be used alone or in combination of two or more.

The concentration of the basic catalyst in the above solution is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass.

In step 2, a solution is prepared by adding (i) polystyrene particles, (ii) alkoxysilane, or alkoxysilane and metal alkoxide, and (iii) basic catalyst to the above solvent and stirring to prepare a solution. Among them, a core-shell particle having an organic polymer particle as a core and a shell covering the organic polymer particle can be formed.

The temperature of the solution in the above step 2 is not particularly limited, but is preferably 5 to 200 ° C, more preferably 5 to 150 ° C. If the temperature is too low, the reaction rate may slow down, and if it is too high, the solvent may evaporate.

The stirring time in the above step 2 is not particularly limited, but is preferably 1 to 1200 minutes, and more preferably 1 to 600 minutes. If the stirring time is too short, the reaction may be insufficient.

By the step 2 described above, it is possible to form core-shell particles having the polystyrene particles as the core and having a silica-based shell covering the polystyrene particles.

<Step 3>
Step 3 is a step of removing the organic polymer particles which are the cores of the core-shell particles by thermally decomposing the core-shell particles in the presence of an organic acid. Since the inside of the core-shell particles is filled with organic polymer particles as a core, the inside of the shell is made hollow by removing the organic polymer particles in the presence of an organic acid, and hollow nanosilica that can be used as a highly functional material. Particles can be produced.

In step 3, the organic polymer particles are removed by thermal decomposition in the presence of an organic acid. The thermal decomposition is not particularly limited, and examples thereof include firing. In the case of firing, if the firing temperature is too low, organic polymer particles and other organic components may remain in the hollow nanosilica particles, and if the firing temperature is too high, the shell may be destroyed. Therefore, as a method for removing organic polymer particles by firing, for example, an organic acid is added to the solution prepared in step 2 and sprayed into an electric furnace using an ultrasonic atomizer, a two-fluid nozzle, or the like. Examples thereof include a method of firing in a high temperature region of preferably 350 to 1500 ° C., more preferably 400 to 1200 ° C., and further preferably 600 to 1000 ° C. in an electric furnace. By firing for a sufficient period of time to remove the organic polymer particles by this method, the organic polymer particles can be removed from the core-shell particles with almost no destruction of the shell. Hollow nanosilica powder obtained by removing organic polymer particles from the organic core-shell particles is referred to as single-layer coated hollow nanoparticles. The obtained one-layer coated hollow nanosilica powder can be dispersed in a solvent by a disperser, and can be subjected to a two-layer coating or a hydrophobizing treatment. Examples of the disperser include an ultrasonic homogenizer and a bead mill.

When organic polymer particles are removed by adding an organic acid to the solution prepared in step 2 and spraying it into an electric furnace and firing it, the temperature is 150 to 250 ° C. before the high temperature region of the electric furnace. It is preferable to provide a low temperature region in a temperature range of about 2 so that the sprayed solution passes through the low temperature region and then is sprayed into the high temperature region. As the sprayed solution passes through the low temperature region, the solvent in the solution gradually evaporates, which promotes the formation of hollow nanosilica particles in the droplets of the spray solution. If the low temperature region is not provided, the formation of the hollow nanosilica particles is insufficient, and the shape of the hollow nanosilica particles may be distorted.

The average particle size of the hollow nanosilica particles obtained through the above steps is preferably 50 to 150 nm, more preferably 35 to 120 nm, and even more preferably 35 to 100 nm. When the average particle size of the obtained hollow nanosilica particles is in the above range, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

In the hollow nanosilica particles obtained through the above steps, particles having an aspect ratio of 1.5 or less preferably occupy 95% of the total particles, more preferably 97% or more, still more preferably 99%. When the proportion of the obtained hollow nanosilica particles having an aspect ratio of 1.5 or less is 1.5 or less, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

The aspect ratio of the hollow nanosilica particles obtained through the above steps is preferably 1.0 to 1.6, more preferably 1.0 to 1.4, and even more preferably 1.0 to 1.2. When the aspect ratio of the obtained hollow nanosilica particles is in the above range, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

The coefficient of variation of the particle size of the hollow nanosilica particles obtained through the above steps is preferably 5 to 20%, more preferably 5 to 18%, still more preferably 5 to 15%. preferable. When the coefficient of variation of the particle size of the obtained hollow nanosilica particles is within the above range, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

The step 3 is a step of thermally decomposing the core-shell particles in the presence of an organic acid. When thermal decomposition is not performed in the presence of an organic acid, the formation of associated particles is not suppressed and the scattering of light cannot be suppressed.

The organic acid is not particularly limited, and examples thereof include citric acid and malic acid. Among these, citric acid is preferable in that the formation of associated particles is further suppressed and the reflection of light is further suppressed.

The content of the organic acid in the solution in step 3 is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, with the silica shell contained in the solution as 100% by mass. When the content of the organic acid is in the above range, the formation of associated particles is further suppressed, and the reflection of light is further suppressed.

By the step 3 described above, the organic polymer particles, which are the cores of the core-shell particles, are thermally decomposed in the presence of an organic acid, and the organic polymer particles can be removed.

<Step 4>
The method for producing hollow nanosilica particles of the present invention may further include a step 4 of coating the surface of the hollow nanosilica particles with a shell after the step 3. By having step 4, the average thickness of the shell can be adjusted.

The method of coating the surface of the hollow nanosilica particles with the shell is not particularly limited. For example, the organic polymer particles in step 2 are changed to the hollow nanosilica particles obtained in step 3 by the same method as in step 2. The surface of the hollow nanosilica particles may be further coated with a shell.

<Step 5>
The method for producing hollow nanosilica particles of the present invention may include a step 5 of subjecting the hollow nanosilica particles to a water-sulfurizing treatment after the step 3 or the step 4. By having the step 5, it is possible to impart water resistance to the surface of the hollow nanosilica particles.

The method of the hydroponic treatment is not particularly limited, and examples thereof include a method of adding trialkoxysilane and organosilazane to the hollow nanosilica particles obtained in step 3 or step 4 and heating the particles.

The trialkoxysilane is not particularly limited, and for example, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl). ) Ethyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, trifluoropropyltrimethoxysilane, and more preferably 3-methacryloxypropyltrimethoxysilane. , N-Phenyl-3-aminopropyltrimethoxysilane, trifluoropropyltrimethoxysilane and the like.

The above trialkoxysilane may be used alone or in combination of two or more.

The concentration of trialkoxysilane in the liquid prepared in step 5 is preferably 0.01 to 30% by mass, more preferably 0.05 to 25% by mass.

The hydrophobizing treatment with trialkoxysilane is heated at 30 ° C. or higher. If the heating temperature is less than 30 ° C., the reaction between the silica particles and the trialkoxysilane is insufficient, and the particles aggregate in the dispersion medium. The preferred lower limit of the heating temperature is 35 ° C, and the more preferable lower limit is 40 ° C. The upper limit of the heating temperature is 90 ° C, and a more preferable upper limit is 80 ° C.

The heating time of the hydrophobizing treatment with trialkoxysilane is not particularly limited, and is preferably 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, further preferably 1 hour to 20 hours, and 1.5 hours to 18 hours. Especially preferable.

The organosilazane is not particularly limited, and known organosilazanes can be used. Specific examples thereof include tetramethyldisilazane, hexamethyldisilazane, and pentamethyldisilazane.

The above-mentioned organosilazane may be used alone or in combination of two or more.

The hydrophobizing treatment with organosilazane is heated at 30 ° C. or higher. If the heating temperature is less than 30 ° C., the reaction between the silica particles and organosilazane becomes insufficient, so that the silica particles aggregate in the dispersion medium. The preferred lower limit of the heating temperature is 35 ° C, and the more preferable lower limit is 40 ° C. Further, the upper limit of the heating temperature is 90 ° C., and a more preferable upper limit is 80 ° C.

The heating time of the hydrophobizing treatment is not particularly limited, and is preferably 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, further preferably 1 hour to 20 hours, and particularly preferably 1.5 hours to 18 hours.

Trialkoxysilane and organosilazane may be used in combination.

The solution containing the hydrophobized hollow nanosilica can replace the solvent with another solvent.

Further, the solution containing the hydrophobized hollow nanosilica can be removed by filtration or drying, and the solution powder containing the hydrophobized hollow nanosilica can be taken out.

5. Method for producing core-shell particles The method for producing core-shell particles of the present invention is as follows.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) To prepare a solution by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring. 2. The step 2 of forming core-shell particles having the organic polymer particles as a core and having a shell covering the organic polymer particles in the solution is included.

The steps 1 and 2 are the same as the steps 1 and 2 described in the method for producing hollow nanosilica particles. The core-shell particles produced by the method for producing core-shell particles of the present invention can be removed by thermally decomposing the organic polymer particles that are the core of the core-shell particles. Therefore, step 3 of the method for producing hollow nanosilica particles described above. It is suitable as a core-shell particle used in.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples.

Example 1
Polystyrene particles and core-shell particles were prepared according to the formulation and production conditions shown in Tables 1 to 4, and hollow nanosilica particles were produced. Specifically, it is as follows.

(Step 1: Production of polystyrene particles)
Polystyrene particles were produced under the formulations and conditions shown in Table 1. Styrene monomer (manufactured by Aldrich), mixed solvent of ultrapure water and acetone, 2,2'-azobis (isobutylamidine) dihydrochloride (AIBA) (manufactured by Sigma-Aldrich) as a cationic polymerization initiator, dispersant It was synthesized by a batch type reaction system using PVP (polyvinylpyrrolidone) as a solvent.

Specifically, first, 4500 g of ultrapure water, 4500 g of methanol, and PVP (K90 molecular weight 640,000 manufactured by Ashland) as a dispersant are injected into a four-necked flask, and the stirring conditions are 250 rpm in a nitrogen atmosphere. The mixture was refluxed with stirring and heated for 60 minutes until the temperature did not change. The temperature at this time was 75 ° C. Then, the styrene monomer was added and heated for 5 minutes until the temperature did not change to uniformly disperse the styrene monomer to prepare a solution. The temperature of the solution was 75 ° C. A 5 wt% AIBA aqueous solution previously dissolved in ultrapure water was added to the solution as a polymerization initiator to initiate the polymerization reaction. After a polymerization reaction was carried out at 75 ° C. for 6 hours in a nitrogen atmosphere, the mixture was cooled to room temperature to prepare a polystyrene particle reaction solution, and polystyrene particles, which are organic polymer particles, were prepared in the solution.

<Yield of polystyrene particles>
2 g of the polystyrene particle reaction solution was weighed with a petri dish and dried on a hot plate at a temperature of 120 ° C. for 1 hour, and the yield of polystyrene particles was calculated by the following formula.

(Yield of polystyrene particles (%))
= {[(Sample weight (g) after drying)-(Weight of PVP charged in sample before drying (g))]
÷ [Styrene charge weight (g) in sample before drying]} × 100

Next, 1800 g of a polystyrene particle reaction solution was injected into a four-necked flask, the same weight of polystyrene particle reaction solution was added dropwise, and the mixture was concentrated twice by heated atmospheric distillation while maintaining the same volume or more to prepare a concentrated solution. Then, pure water was added dropwise, and methanol in the concentrated solution was replaced with water by heated atmospheric distillation while maintaining the same volume or more to prepare a water-replaced solution. The temperature of the water replacement solution was 90 ° C. Cool to room temperature and use a flat membrane concentrator (Model UHP-150K, manufactured by Advantech, fractional molecular weight 20,000) to make the polystyrene particle water-substituted solution so that the polystyrene concentration is 4.3 wt% or more. Was concentrated to obtain a polystyrene particle dispersion.

<Polystyrene concentration>
Weigh 1 g of polystyrene particle dispersion with a petri dish and dry it on a hot plate at a temperature of 120 ° C. for 1 hour. Using the yield of the polystyrene particles, polystyrene in the polystyrene particle dispersion is based on the following formula. The concentration was calculated.

(Polystyrene concentration (%))
= {[(Sample weight after drying (g) ÷ Sample weight before drying (g)) × 100] × (Yield of polystyrene particles)} ÷ {Yield of polystyrene particles (%) + PVP addition amount to polystyrene (%) ) (30%)}

(Step 2: Manufacture of core-shell particles)
Core-shell particles were produced according to the formulations and conditions shown in Table 2. Specifically, first, a reactor equipped with a four-necked flask, a stirring blade, and a water bath was prepared. Solution A was prepared by mixing 46.1 g of TMOS and 103.4 g of methanol. Further, 182.6 g of the polystyrene particle dispersion (polystyrene concentration 4.3 wt%) produced in the above step 1 was placed in the flask, 374.0 g of methanol was added as a solvent, and 43.9 g of a 25% aqueous ammonia solution was added. B solution was prepared. While keeping the solution B at 30 ° C., the mixture was stirred at 250 rpm, and the solution A was added over 3 hours and 20 minutes. A core-shell particle dispersion was prepared by using polystyrene particles as a core in a solution and forming core-shell particles having a silica-based shell covering the polystyrene particles.

(Step 3: Production of single-layer coated hollow nanosilica particles)
6.1 g of citric acid (citric acid (anhydrous) manufactured by Fuso Chemical Industry Co., Ltd.) was added to the core-shell particle dispersion obtained in step 2. The core-shell particle powder was then obtained by drying on a hot plate at a temperature of 130 ° C. The obtained core-shell particle powder was heat-treated at a temperature of 700 ° C. for 1 hour to remove polystyrene particles to produce a single-layer coated hollow nanosilica powder. Pure water was added to the obtained hollow nanosilica powder (silica concentration 20 wt%), and dispersion treatment was performed for 3 hours using an ultrasonic homogenizer (UP-400S, manufactured by Heelsher Co., Ltd.). The obtained dispersion is centrifuged once at a rotation speed of 5,500 rpm for 15 minutes using a micro high-speed centrifuge (himac CF-15RN, manufactured by Hitachi Koki Co., Ltd.) to recover the supernatant. Filtration was performed using a 0.0 μm syringe filter to obtain a single-layer coated hollow nanosilica dispersion (silica concentration 15 wt%). The silica concentration was calculated from the remaining amount of the one-layer coated hollow nanosilica particle dispersion liquid after drying and heating at 800 ° C.

(Step 4: Production of two-layer coated hollow nanosilica particles)
Solution C was prepared by mixing 3.2 g of TMOS and 21.2 g of methanol. Further, 82.8 g of the single-layer coated hollow nanosilica dispersion prepared in the above step 3 was placed in the flask, 270.6 g of methanol was added as a solvent, and 27.6 g of a 25% aqueous ammonia solution was added to prepare the D solution. did. While keeping the solution D at 30 ° C., the mixture was stirred at 250 rpm, and the solution C was added over 20 minutes. Two-layer coated hollow nanosilica particles were prepared in solution.

(Step 5: Production of surface-treated hollow nanosilica particles)
First, a reactor equipped with a four-necked flask, a stirring blade, and a water bath was prepared. 132.5 g of the two-layer coated hollow nanosilica dispersion obtained in step 4 was injected into the flask, 265.0 g of the two-layer coated hollow nanosilica dispersion was added dropwise, and the mixture was distilled under heating at atmospheric pressure while maintaining the same volume or more. It was concentrated 3 times (silica concentration 10%). Then, methanol was added dropwise, and water and ammonia in the concentrate were replaced with methanol by hot atmospheric distillation while maintaining the same volume or more to prepare a methanol sol. The temperature of the methanol sol was 67 ° C. After replacement with methanol, the mixture was cooled to room temperature, 1.4 g of 3-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the mixture was refluxed for 8 hours while stirring under stirring conditions of 250 rpm. .. The reflux temperature was 67 ° C. After refluxing, the mixture was cooled to room temperature, twice the weight of methyl isobutyl ketone was added dropwise to the methanol sol, and while maintaining the same volume or more, methanol in the sol was replaced with methyl isobutyl ketone by hot vacuum distillation to obtain methyl. Isobutyl ketone sol was prepared. The obtained methyl isobutyl ketone sol was centrifuged 20 times at a rotation speed of 5,500 rpm for 15 minutes using a micro high-speed centrifuge (himac CF-15RN, manufactured by Hitachi Koki Co., Ltd.) to recover the supernatant. , A dispersion of surface-treated hollow nanosilica particles was prepared by filtering using a 0.45 μm syringe filter (silica concentration 10 wt%).

Examples 2-6, Comparative Examples 1-13
Polystyrene particles, core-shell particles, and hollow nanosilica particles were produced in the same manner as in Example 1 except that the formulations and production conditions in Tables 1 to 4 were changed.

The characteristics of the polystyrene particles, core-shell particles and hollow nanosilica particles obtained in Examples and Comparative Examples were measured by the following methods.

(Average particle size)
Using hollow nanosilica particles and core-shell particle TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.), photographs of the particles were taken under the condition of an acceleration voltage of 200 kV, and 100 particle minor diameters arbitrarily selected were selected. The length was measured and the average value was calculated, which was used as the average particle size.
Take a picture of the particles using a polystyrene particle SEM (scanning electron microscope: JSM-6700F, manufactured by JEOL Ltd.) under the condition of an acceleration voltage of 5 kV, and measure the minor axis of 100 arbitrarily selected particles. The average value was calculated and used as the average particle size.

(Thickness of shell)
A TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.) was used to photograph the particles under the condition of 200 kV, and the average value obtained by measuring the shell thickness of 100 arbitrarily selected particles was calculated. The thickness of the shell was used. The core-shell particles were fired to remove the core particles, and then the thickness of the shell was measured.

(Coefficient of variation of particle size)
Using hollow nanosilica particles and core-shell particle TEM (transmission electron microscope: JEM-2010, manufactured by JEOL Ltd.), photographs of the particles were taken under the condition of an acceleration voltage of 200 kV, and 100 particle minor diameters arbitrarily selected were selected. The length was measured to obtain the average value, which was calculated based on the following formula.
(Coefficient of variation) = [(standard deviation of particle minor axis) ÷ (mean value of particle minor axis)] × 100
Using a polystyrene particle SEM (scanning electron microscope: JSM-6700F, manufactured by JEOL Ltd.), a photograph of the particles was taken under the condition of an acceleration voltage of 5 kV, and the minor axis of 100 arbitrarily selected particles was measured. The average value was calculated and calculated based on the following formula.
(Coefficient of variation) = [(standard deviation of particle minor axis) ÷ (mean value of particle minor axis)] × 100

(Ratio of particles with an aspect ratio of 1.5 or less to the total particles)
Using hollow nanosilica particles and core-shell particle TEM (transmission electron microscope: JEM-2010, manufactured by Nippon Denshi Co., Ltd.), photographs of the particles were taken under the conditions of a magnification of 200,000 times and an acceleration voltage of 200 kV, and 100 arbitrarily selected. The particle major axis and the particle minor axis of each of the individual particles were measured, and the aspect ratio of each particle was determined based on the following formula. Next, the number of particles having an aspect ratio of 1.5 or less out of 100 particles was counted, and the number was taken as the ratio of the particles having an aspect ratio of 1.5 or less to the total number of particles.
(Aspect ratio) = (Particle major axis) ÷ (Particle minor axis)
Using a polystyrene particle SEM (scanning electron microscope: JSM-6700F, manufactured by JEOL Ltd.), photographs of the particles were taken under the conditions of a magnification of 100,000 times and an acceleration voltage of 5 kV, and each of the 100 arbitrarily selected particles was taken. The particle major axis and the particle minor axis of the particles are measured, and the aspect ratio of each particle is obtained based on the following formula. Next, the number of particles having an aspect ratio of 1.5 or less out of 100 particles is counted, and the number is defined as the ratio of the particles having an aspect ratio of 1.5 or less to the total number of particles.
(Aspect ratio) = (Particle major axis) ÷ (Particle minor axis)

(Psa / Psm)
(I) Hollow nanosilica particles and an organic solvent were mixed at a ratio of the content of the hollow nanosilica particles to 0.2% by mass to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm was measured.
(Iii) The peak intensity Psm of the main particles, which are hollow nanosilica particles that are not associated, and the peak intensity Psa of the associated particles, which are the hollow nanosilica particles that are associated, are measured, and the peak intensity Psm of the main particles and the associated particles The ratio Psa / Psm with the peak intensity Psa was calculated.

(Pca / Pcm)
(I) The core-shell particle dispersion obtained in step 2 and water were mixed at a ratio of core-shell particle dispersion: water = 1: 100 (mass ratio) to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm was measured.
(Iii) The peak intensity Pcm of the main particles which are not associated core-shell particles and the peak intensity Pca of the associated particles which are the associated core-shell particles are measured, and the peak intensity Pcm of the main particles and the peak intensity of the associated particles are measured. The ratio Pca / Pcm to Pca was calculated.

(Half width of distribution curve of main particles)
Hollow nanosilica particles (i) The hollow nanosilica particles obtained in step 5 and an organic solvent were mixed at a ratio of 0.2% by mass of the hollow nanosilica particles to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm was measured.
(Iii) The full width at half maximum was calculated from the interval between two points of 1/2 intensity of the peak of the main particle which is a hollow nanosilica particle which is not associated.
Core-shell particles (i) The core-shell particle dispersion obtained in step 2 and an organic solvent are mixed at a ratio of which the content of core-shell particles is 0.02% by mass to prepare a sample for measurement.
(Ii) Using a disk centrifugal particle size distribution measuring device (manufactured by DC24000UHR CPS), the particle size distribution of the measurement sample at a particle size of 50 to 500 nm is measured.
(Iii) The full width at half maximum was calculated from the interval between two points of 1/2 intensity of the peak of the main particle which is the core-shell particle which is not associated.

(Reflectance)
A resin mixture was prepared by mixing 1.0 g of pentaerythritol triacrylate (manufactured by Aldrich), 0.05 g of Irgacure 184 (manufactured by BASF Japan Ltd.), and 8.95 g of methyl isobutyl ketone. 1.0 g of the above resin mixture, 1.2 g of the surface-treated hollow nanosilica particle dispersion obtained in step 5, and 3.4 g of methyl isobutyl ketone were mixed to obtain a silica particle-containing composition. The obtained silica particle-containing composition was coated on a TAC film (TAC-100μ, manufactured by IPI) with a film thickness of 100 μm using a bar coater to form a surface-treated hollow nanosilica particle-containing layer, and laminated. The body was made. Surface treatment The film surface on the side where the hollow nanosilica particle-containing layer is not formed is coated with black magic, then a black tape is attached to prepare a measurement sample, and the side to which the silica particle-containing composition is applied is the light source side. , The reflectance was measured using an ultraviolet visible spectrophotometer (UV-2600, manufactured by Shimadzu Corporation).

(SCE)
A measurement sample was prepared in the same manner as in the above-mentioned reflectance measurement. The SCE of the Y value on the side coated with the silica particle-containing composition of the measurement sample was measured using a spectrocolorimeter (CM-600d, manufactured by Konica Minolta Co., Ltd.).

(True density by immersion method)
Isooctane was injected into a 5 mL specific gravity bottle and allowed to stand in a constant temperature water bath at about 25 ° C. for 30 minutes. After standing, the temperature inside the specific gravity bottle was measured, and the specific gravity of isooctane was calculated based on the following formula.
(Isooctane specific gravity) = [-0.0011 x (measurement temperature (° C))] +0.7142

Then, the specific gravity bottle was taken out from the constant temperature water tank, the droplets were wiped off, and the isooctane-filled specific gravity bottle was precisely weighed. The volume of the specific gravity bottle was calculated based on the following formula.
(Volume of specific gravity bottle (ml)) = [(Weight of specific gravity bottle filled with isooctane (g))-(Weight of specific gravity bottle (g))] ÷ (Isooctane specific gravity)

Next, 10 g of the surface-treated hollow nanosilica particle dispersion obtained in step 5 was weighed with a petri dish and dried on a hot plate at a temperature of 140 ° C. to obtain a surface-treated hollow nanosilica powder. The obtained powder was dried under reduced pressure at a temperature of 120 ° C. for 2 hours. Dry powder was added to a 5 mL specific gravity bottle and isooctane was injected. It was allowed to stand at room temperature for 30 minutes, and after standing, it was degassed for 1 hour using a vacuum pump. The degassed surface-treated hollow nanosilica particle-filled specific gravity bottle was allowed to stand in a constant temperature water tank at about 25 ° C. for 30 minutes. After standing, the temperature inside the specific gravity bottle was measured, and the specific gravity of isooctane was calculated based on the following formula.
(Isooctane specific gravity) = [-0.0011 x (measurement temperature (° C))] +0.7142

Next, the specific gravity bottle was taken out from the constant temperature water tank, the droplets were wiped off, and the surface-treated hollow nanosilica-filled specific gravity bottle was precisely weighed. Using the above specific gravity bottle volume, the true density of the surface-treated hollow nanosilica by the immersion method was calculated based on the following formula.
(True density (g / ml)) = (Dry powder weight (g)) ÷ {(Specific gravity bottle volume (ml))-[(Isooctane weight) ÷ (Isooctane specific gravity)]}

(True density by gas pycnometer)
10 g of the surface-treated hollow nanosilica dispersion obtained in step 5 was weighed with a petri dish and dried on a hot plate at a temperature of 140 ° C. to obtain a surface-treated hollow nanosilica powder. The obtained powder was dried under reduced pressure at a temperature of 120 ° C. for 1 hour. The true density of the dried surface-treated hollow nanosilica powder was measured using a helium gas pycnometer (Micro-ULTRAPYC1200e manufactured by Kantachrome Instruments Japan GK).

(I _Q2 / I _Q4 )
_IQ2 / _IQ4 was calculated from the ²⁹ Si-solid-state NMR spectrum measured by the following measurement method.

²⁹ Si-Solid State NMR Spectrum Measurement
^{The 29} Si-solid-state NMR spectrum is measured by using JNM-ECA400 (manufactured by JEOL Ltd.) for a hollow nanosilica powder vacuum-dried at room temperature under the following conditions.
-Resonance frequency: 78.65 Hz
・ Measurement mode: CP / MAS method ・ Measurement nucleus: 29Si
-Sample rotation speed: 6 kHz
・ Measurement temperature: Room temperature ・ Number of integrations: 16384 times

(I _Q2 / I _Q4 ) was calculated from the spectrum measured by the above measurement method. In the ²⁹ Si-solid-state NMR spectrum obtained by solid-state NMR ( ²⁹ Si / MAS) measurement, the peak (Q2) exists between -90 and -93 ppm, and the peak (Q4) is between 110-112 ppm. Exists in.

The results are shown in the table below.

In Comparative Examples 3 and 4, since the number of particles whose shape can be clearly determined in the TEM photograph is small, the coefficient of variation of the particle size, the proportion of particles having an aspect ratio of 1.5 or less, and the average particle size could not be measured.

In Table 3, in Comparative Example 3, a large number of fine particles were generated as shown in FIG. 3, and in Comparative Example 4, a large number of agglomerates of particles were generated as shown in FIG. 4, so that some characteristics of the core-shell particles could be measured. There wasn't. Further, in Comparative Examples 5 and 6, the particle size distribution was wide and Pca / Pcm could not be measured.

In Table 4, in Comparative Example 9, a large number of fine particles were generated, the true density (isooctane) was high, and the structure was not hollow. Further, in Comparative Example 10, hollow nanosilica particles were not present in the filtered solution. Further, in Comparative Examples 11 and 12, the particle size distribution was wide and Psa / Psm could not be measured. Moreover, since the peak of the main particle could not be discriminated, the half width could not be measured. Further, in Comparative Example 13, since the thermal decomposition of the core-shell particles was not performed in the presence of the organic acid in the step 3, the formation of the associated particles was not suppressed and the light scattering of the hollow nanosilica particles was not suppressed.

(result)
Since the hollow nanosilica particles of Examples 4 to 6 had few associations of the core-shell particles formed in step 2, the number of associated particles when dispersed in the organic solvent was small. Therefore, the reflectance and SCE became low.

Claims (12)

Hollow nanosilica particles
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) In the solid-state NMR ( ²⁹ Si / MAS) measurement, the integrated intensity (I _Q2 ) of the peak (Q2) assigned to Si having two crosslinked oxygen numbers and Si having four crosslinked oxygen numbers the ratio of the integrated intensity of the assigned the peaks _{(Q4) (I Q4) (} I Q2 / I Q4) is, is 0.20 or less,
(4) Peak intensity Psa of associated particles and peak of main particles which are hollow nanosilica particles that are not associated in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Psa / Psm to the strength Psm is 0.4 or less.
Hollow nanosilica particles characterized by that. Claimed that the half-value width of the distribution curve of the main particles, which are non-associative hollow nanosilica particles, in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device is 15 nm or less. Item 2. The hollow nanosilica particles according to Item 1. Core-shell particles having organic polymer particles as a core and silica as a shell for coating the organic polymer particles.
(1) The average particle size is 50 to 150 nm.
(2) The average thickness of the shell is 5 to 25 nm.
(3) Peak intensity Pca of associated particles and peak intensity of main particles which are not associated core-shell particles in a particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device. The ratio Pca / Pcm to Pcm is 0.5 or less.
The core shell particles are characterized by that. Claim that the half-value width of the distribution curve of the main particles, which are unassociated core-shell particles, in the particle size distribution in the particle size range of 50 to 500 nm measured using a disk centrifugal particle size distribution measuring device is 20 nm or less. 3. The core-shell particles according to 3. The core-shell particles according to claim 3 or 4, wherein the organic polymer particles are polystyrene particles. A method for producing hollow nanosilica particles.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) A solution is prepared by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring the mixture. In the solution, the step 2 of forming the core-shell particles having the organic polymer particles as the core and having a shell covering the organic polymer particles, and
(3) A step 3 of removing the organic polymer particles which are the cores of the core-shell particles by thermally decomposing the core-shell particles in the presence of an organic acid is included.
A method for producing hollow nanosilica particles. The method for producing hollow nanosilica particles according to claim 6, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone, hydroxypropyl cellulose, and polyvinyl alcohol. The method for producing core-shell particles according to claim 6 or 7, wherein in the step 2, the alkoxysilane contains tetraalkoxysilane, and the concentration of the alkoxysilane in the solution is 3 to 7% by mass. The method for producing hollow nanosilica particles according to any one of claims 6 to 8, wherein the organic acid is citric acid. The method for producing hollow nanosilica particles according to any one of claims 6 to 9, further comprising a step 4 of coating a shell on the surface of the hollow nanosilica particles after the step 3. A method for producing core-shell particles.
(1) A step of preparing organic polymer particles by carrying out a polymerization reaction of the organic monomer in a solution containing an organic monomer, a dispersant, and a mixed solvent, wherein the mixed solvent is water and methanol. mixing ratio in weight ratio 45: 55 to 80: a 20, step 1 Z-average molecular weight of the dispersant is 180 × 10 ⁴ or more and,
(2) To prepare a solution by adding (i) the organic polymer particles, (ii) alcoholicsilane, or alkoxysilane and metal alkoxide, and (iii) a basic catalyst to a solvent and stirring. 2. The step 2 of forming core-shell particles having the organic polymer particles as a core and having a shell covering the organic polymer particles in the solution.
A manufacturing method characterized by that. The method for producing core-shell particles according to claim 11, wherein the dispersant is at least one selected from the group consisting of polyvinylpyrrolidone, hydroxypropyl cellulose, and polyvinyl alcohol.