Hollow silica particles and method for producing hollow silica particles

Abstract

The present invention provides novel hollow silica particles with a densified shell and a method for producing the hollow silica particles. The hollow silica particles of the present invention have a shell layer containing silica, have a space portion inside the shell layer, and have a particle density of 2.00 g / cm 3 or less, as determined by density measurement based on a dry pycnometer using helium gas. 3 or less, as determined by density measurement based on a dry pycnometer using oxygen gas.

Description

[0001] This application is a divisional application of the application filed on February 22, 2021, with application number 202180017150.1 and invention title "Hollow Silica Particles and Method for Manufacturing Hollow Silica Particles". Technical Field

[0002] This invention relates to hollow silica particles and a method for manufacturing hollow silica particles. Background Technology

[0003] Hollow particles possess various properties such as low density, low refractive index, and the ability to encapsulate substances. These properties are utilized in a wide range of fields, including lightweight materials, thermal insulation materials, and coloring materials.

[0004] Hollow particles include hollow resin particles and hollow inorganic particles, but due to increasing concerns about marine pollution caused by microplastics, activities to replace hollow resin particles with hollow inorganic particles have been underway in recent years.

[0005] A representative example of hollow inorganic particles is hollow silica particles, which are particles with a hollow space inside a shell formed of silica. Due to their diverse particle size, fine porous structure of the shell, and surface properties, hollow silica particles are widely used in catalysts, catalyst supports, cosmetic pigments, resin fillers, adsorbents, desiccants, thermal insulation materials, coatings, drug delivery systems, and filters. Furthermore, due to their low refractive index based on their hollow shape, they are also useful as anti-reflective coating materials.

[0006] Various proposals have been put forward for such hollow silica particles. For example, Patent Document 1 describes a method for synthesizing micron-sized spherical silica particles by forming a water-in-oil emulsion, using soluble water encapsulated in the water-in-oil emulsion as the reaction site, and synthesizing them through a hydrolysis and condensation reaction caused by tetraalkoxysilane and water.

[0007] Furthermore, as nano-sized hollow silica particles, for example, Patent Document 2 describes a method for manufacturing hollow silica microparticles. In this method, an organosol containing the hollow silica microparticles is prepared, and a silane compound and an alkaline catalyst are added to the organosol at a temperature range of 30°C to 300°C. The silane compound and the hollow silica microparticles are then reacted under conditions where the water content relative to the silica content is 0.1% to 50% by weight. Furthermore, a hollow silica microparticle is described, which, as determined by dynamic light scattering, has an average particle size of 5 to 300 nm and a specific surface area of ​​50 to 1500 m². 2 / g, with cavities formed inside the shell, and by thermogravimetric analysis (TG), it shows a weight loss of more than 1.0% by weight in the temperature range of 200℃ to 500℃.

[0008] Furthermore, Patent Document 3 describes a method for manufacturing silica-based hollow particles, which includes: using polystyrene particles as a core, covering the polystyrene particles with alkoxysilanes or the like, and thermally decomposing the polystyrene particles. Moreover, it describes silica-based hollow particles with an aspect ratio of 1.5 or less comprising more than 95% of the total particle size, a particle size variation coefficient of 20-60%, and an average particle size of 30-150 nm.

[0009] Furthermore, Patent Document 4 discloses a method for manufacturing amorphous spherical hollow silica powder, which includes feeding silica raw material powder into a high-temperature flame and spherizing / hollowing it. It also describes an amorphous spherical hollow silica powder with an average particle size of 0.5–8 μm, an average sphericity of 0.85 or higher, a 50% breaking pressure of 10 MPa or higher, an average hollowness of 20–70% by volume calculated from the density measured using a hydrometer bottle method, and a maximum particle size of no more than 5 times the average particle size.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 11-029318

[0013] Patent Document 2: Japanese Patent Application Publication No. 2013-014506

[0014] Patent Document 3: Japanese Patent Application Publication No. 2017-226567

[0015] Patent Document 4: Japanese Patent No. 4244323 Summary of the Invention

[0016] The problem the invention aims to solve

[0017] In the conventional hollow silica particles described in Patent Documents 1-4, when added to solvents such as water, the solvent sometimes penetrates into the interior of the particles, preventing them from being utilized. For example, if water enters the interior of the particles when they are added to water, the hollow silica particles may become translucent and lose their light scattering properties, or they may settle and lose their dispersibility.

[0018] Furthermore, the conventional hollow silica particles produced in a high-temperature flame as described in Patent Document 4 have thin shells and negative pressure inside, making them prone to cracking. For example, if hollow silica particles are added to resin or the like and mixed, the hollow silica particles may sometimes crack, thereby losing the internal space of the particles and failing to obtain the required properties of hollow silica particles.

[0019] The present invention was made in view of the above-mentioned problems. The problem is to provide a novel hollow silica particle that has a dense silica shell, which makes it difficult for solvents such as water to penetrate into the particle, and allows gases such as helium to pass through the shell, thereby maintaining the interior at normal pressure and reducing cracking during mixing.

[0020] Solution for solving the problem

[0021] This invention relates to the following (1) to (9).

[0022] (1) A hollow silica particle comprising a shell containing silica, having a space inside the shell, wherein the density of the hollow silica particle, determined by density measurement using a dry specific gravity bottle using helium, is 2.00 g / cm³. 3 The density of the particles, as determined by density measurement using a dry density bottle with oxygen, is less than 2.00 g / cm³. 3 .

[0023] (2) The hollow silica particles described in (1) above, wherein the density of the particles, determined by density measurement using a dry specific gravity bottle with helium, is 2.00–2.40 g / cm³. 3 .

[0024] (3) The hollow silica particles according to (1) or (2) above, wherein the density of the particles, determined by density measurement based on a dry specific gravity bottle using oxygen, is 0.40 to 1.90 g / cm³. 3 .

[0025] (4) The hollow silica particles according to any one of (1) to (3) above have an average primary particle size of 10 nm to 10 μm.

[0026] (5) The hollow silica particles according to any one of (1) to (4) above have a BET specific surface area of ​​5 to 2600 m². 2 / g.

[0027] (6) The hollow silica particles according to any one of (1) to (5) above have a sphericity of 0.8 to 1.0.

[0028] (7) The hollow silica particles according to any one of (1) to (6) above have an oil absorption capacity of 30 to 1000 mL / 100 g.

[0029] (8) Hollow silica particles according to any one of (1) to (7) above, wherein the aggregate size (D50) of the secondary particles is 0.1 to 50 μm.

[0030] (9) A method for manufacturing hollow silica particles, wherein a shell containing silica is formed on the periphery of the core to obtain a hollow silica precursor, the core is removed from the hollow silica precursor, and heat treatment is performed at 700°C or above.

[0031] The effects of the invention

[0032] According to the present invention, hollow silica particles with a dense shell can be provided. The hollow silica particles of the present invention are not easily permeated by solvents such as water and oil, and therefore exhibit excellent light scattering properties even in solvents with similar refractive indices. Furthermore, they also exhibit excellent dispersibility in solvents. Attached Figure Description

[0033] Figure 1 The image shown is a scanning electron microscope (SEM) image of the hollow silica particles obtained in Example 6.

[0034] Figure 2 The spectroscopic spectrum of the hollow silica particles obtained in Example 6 is shown.

[0035] Figure 3 The Raman spectra of the hollow silica particles obtained in Examples 1 and 6 are shown.

[0036] Figure 4 The solid hollow silica particles obtained in Examples 1 and 6 are shown. 29 Si-NMR spectroscopy.

[0037] Figure 5 The total transmittance of the films obtained in Examples 30 and 31 before and after accelerated weathering tests is shown.

[0038] Figure 6 The parallel light transmittance of the films obtained in Examples 30 and 31 before and after accelerated weathering tests is shown.

[0039] Figure 7 The sum of total transmittance and parallel light transmittance of the films obtained in Examples 30 and 31 before and after accelerated weathering tests is shown.

[0040] Figure 8 A scanning electron microscope (SEM) image of the hollow silica particles obtained in Example 32 is shown.

[0041] Figure 9 A scanning electron microscope (SEM) image of the hollow silica particles obtained in Example 8 is shown. Detailed Implementation

[0042] The present invention will now be described, but the present invention is not limited to the examples illustrated in the following description.

[0043] It should be noted that in this instruction manual, "mass" and "weight" have the same meaning.

[0044] (Hollow silica particles)

[0045] The hollow silica particles of this invention have a shell containing silica, and a space within the shell. The presence of this space within the shell can be confirmed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM). In SEM observation, the hollow nature of the particles can be confirmed by observing partially open, broken particles. In this specification, spherical particles with internal spaces that can be confirmed by TEM or SEM observation are defined as "primary particles." It should be noted that, for hollow silica particles, the primary particles are partially bonded together through a firing and drying process; therefore, the hollow silica particles obtained during manufacturing are mostly aggregates of secondary particles formed by the aggregation of primary particles.

[0046] In this specification, "containing silicon dioxide" in the shell means containing 50% by mass or more silicon dioxide (SiO2). The composition of the shell can be determined by ICP emission spectroscopy, flame atomic absorption spectrometry, etc. Preferably, the shell contains 80% by mass or more, more preferably 95% by mass or more of silicon dioxide. Theoretically, the upper limit is 100% by mass. Preferably, the shell contains less than 100% by mass, more preferably 99.99% by mass or less of silicon dioxide. Examples of the remaining components include alkali metal oxides, carbon, etc.

[0047] Furthermore, "having a space inside the shell" refers to the hollow state in which the shell surrounds a space when a cross-section of a primary particle is observed. That is, a hollow particle has a large space and a shell surrounding it.

[0048] The hollow silica particles of this invention have a density of 2.00 g / cm³, determined by density measurement using a dry hydrometer bottle with helium (hereinafter also referred to as the helium hydrometer method). 3 The density of the particles, as determined above and by density measurement using a dry hydrometer flask (also known as the oxygen hydrometer flask method), is less than 2.00 g / cm³. 3 It can be seen that by simultaneously satisfying the relationship between the two, the particle is a hollow shape formed by a shell with fine pores, and the shell is densified so that the solvent cannot easily penetrate it.

[0049] Whether hollow silica particles have fine pores in their shells can be determined by density measurement using a dry density bottle filled with helium. The true density of silica is approximately 2.2 g / cm³. 3Hollow silica particles have internal spaces, so their actual particle density is lower than the true density of silica. However, by introducing helium gas into the particles, the density can be made closer to the true density of silica. The density of hollow silica particles determined by the helium flask method is 2.00 g / cm³. 3 The above describes the state where helium gas has penetrated into the interior of the particle and remained within the internal space, indicating that the shell has fine pores. Because of these pores, gases with small molecular sizes, such as helium, can pass through the shell. Therefore, the interior of the hollow silica particle maintains normal pressure, thereby reducing breakage during mixing.

[0050] The density of the hollow silica particles, determined by the helium specific gravity bottle method, is preferably 2.00–2.40 g / cm³. 3 Specifically, the lower limit is more preferably 2.05 g / cm³. 3 The above, further optimized, is 2.07 g / cm³. 3 Above, especially preferred 2.09g / cm 3 The above, the optimal value is 2.10 g / cm³. 3 The above, and preferably an upper limit of 2.40 g / cm³. 3 Below, more preferably 2.30 g / cm 3 the following.

[0051] Furthermore, by measuring the density using a dry density bottle with oxygen, it can be determined whether the hollow silica particles are hollow. Since oxygen molecules are larger than helium molecules, when the shell is dense, the particles cannot pass through, allowing for the determination of the actual particle density. The density of the hollow silica particles determined using the oxygen density bottle method is less than 2.00 g / cm³. 3 When the particle density is less than the true density of silicon dioxide, it can be determined that there is a space inside the particle.

[0052] The density of silica particles determined by the oxygen specific gravity bottle method is preferably 0.40–1.90 g / cm³. 3 Specifically, the upper limit is preferably 1.90 g / cm³. 3 Below, more preferably 1.80 g / cm 3 The following is a further preferred value of 1.60 g / cm³. 3 The following is a preferred value: 1.50 g / cm³ 3 The optimal value is 1.40 g / cm³. 3 Furthermore, from the viewpoint of the strength of the hollow particle shell, a lower limit of 0.40 g / cm³ is preferred. 3 Above, more preferably 0.50 g / cm 3 The above, further optimized, is 0.60 g / cm³. 3 Above, with a preferred concentration of 0.70 g / cm³ 3The above, the optimal value is 0.80 g / cm³. 3 above.

[0053] When the particle density of hollow silica is greater than that of water, a specific gravity bottle and water can also be used to determine the density. The sample (hollow silica particles) and water are placed in a specific gravity bottle, and the bottle itself is then placed in a sealed PTFE (polytetrafluoroethylene) container. The mixture is left to stand in a constant temperature bath at 110°C for 16 hours before measurement. Due to the density of the hollow silica shell, water penetration may sometimes take time; therefore, the above pretreatment is preferred. The density measured after pretreatment is considered to be 2.00 g / cm³. 3 At this point, water has undergone osmosis, and its density is less than 2.00 g / cm³. 3 At this time, water does not permeate, maintaining the hollow part. The results measured by this method correspond to the density measurements based on dry density bottles using oxygen.

[0054] By adjusting the ratio of the shell (shell layer) thickness to the particle size of the hollow silica primary particles of the present invention, the particle density of the hollow silica primary particles can be adjusted. When the hollow silica primary particles are perfectly spherical, the following formula holds true.

[0055] Primary particle volume: 4πr 3 / 3

[0056] Volume of the spatial part: 4π(rd) 3 / 3

[0057] Single particle weight: 4π(r) 3 -(rd) 3 )ρ / 3

[0058] Primary particle density: (r 3 -(rd) 3 )ρ / r 3

[0059] Here, r is the radius of a single particle, d is the thickness of the shell, and ρ is the true density of silica.

[0060] In a sample of hollow silica particles, the proportion of intact hollow particles with unbroken shells and internal spaces is called the hollow particle ratio. The hollow silica particles of this invention have dense shells, making them difficult for various solvents and gases with dynamic molecular diameters larger than argon and oxygen molecules to penetrate. However, if particles with broken shells (broken particles) are present, they can penetrate into the interior. Therefore, the particle density of the secondary particles varies depending on the hollow particle ratio. A higher hollow particle ratio results in a lower particle density of the secondary hollow silica particles, and vice versa. Using this principle, assuming a 100% yield, the hollow particle ratio is calculated based on the theoretical density derived from the amount of raw material input and the density obtained using the oxygen specific gravity bottle method.

[0061] Furthermore, based on SEM and TEM images, the primary particle size and shell thickness of particles with intact shells can be determined, thereby estimating the particle density. The hollow particle ratio is then calculated based on the particle density obtained from the image information and the density obtained using the oxygen specific gravity bottle method.

[0062] The density determined by the oxygen specific gravity bottle method or by using a specific gravity bottle is equivalent to the average particle density of secondary particles.

[0063] Furthermore, using the filter cake from the manufacturing process of hollow silica particles, before removing the oil cores, the hollow particle ratio was determined based on the weight change before and after heat treatment. When the filtered filter cake was loosened and dried overnight, the oil components within the broken particles evaporated, while the oil components within the intact hollow particles were retained. The weight change during heat treatment when all the added oil components evaporated (0% hollow particle ratio) and when all were retained (100% hollow particle ratio) can be calculated based on the amount of raw material input. Therefore, the hollow particle ratio can be determined based on the weight change when the sample dried overnight after filtration is heat-treated to 800°C.

[0064] By changing the primary and / or secondary particle density, the settling, continued dispersion, or floating of hollow silica particles in a solvent can be adjusted. Ideally, the solvent density should be close to the particle density for dispersing hollow silica particles in a solvent. For example, to disperse hollow silica particles in a solvent with a density of 1.0 g / cm³... 3 In the case of water, ideally the particle density should be adjusted to 0.8 g / cm³. 3 Up to 1.2 g / cm 3 the following.

[0065] The size of the primary particles of hollow silica particles is determined by directly observing their particle size (diameter) using SEM. Specifically, the size of the primary particles of 100 particles is measured using SEM images, and the distribution of the primary particle sizes obtained by statistically analyzing these measurements is used to estimate the size distribution of all primary particles.

[0066] The average size of the primary particles (average primary particle size) is preferably in the range of 10 nm to 10 μm. From the viewpoint of manufacturing reproducibility, the lower limit is more preferably 20 nm or more, further preferably 50 nm or more, particularly preferably 70 nm or more, and most preferably 100 nm or more. In addition, from the viewpoint of processability as a filler, the upper limit is more preferably 7 μm or less, further preferably 5 μm or less, particularly preferably 3 μm or less, and most preferably 1 μm or less.

[0067] The size of the secondary particles (aggregate size (D50)) of the hollow silica particles is preferably 0.1 to 50 μm.

[0068] From a processability perspective, the aggregate particle size (D50) of the secondary particles is more preferably 0.2 μm or more, further preferably 0.3 μm or more, particularly preferably 0.4 μm or more, and most preferably 0.5 μm or more. Furthermore, from the viewpoint of dispersibility when mixed with water, oil, fluororesin, etc., the aggregate particle size (D50) of the secondary particles is more preferably 35 μm or less, further preferably 30 μm or less, further more preferably 25 μm or less, especially more preferably 15 μm or less, particularly preferably 10 μm or less, and most preferably 6 μm or less.

[0069] Here, as a method for determining the aggregate size (D50) of secondary particles, for example, a method can be given by measuring the central value of the particle distribution (diameter) measured by a diffraction scattering particle distribution measuring device twice and calculating the average value.

[0070] The preferred BET specific surface area of ​​hollow silica particles is 5–2600 m². 2 / g.

[0071] From the perspective that a denser shell has a smaller specific surface area, a specific surface area of ​​2000m² is preferred for BET. 2 / g or less, further preferred 1000m 2 / g or less, especially preferred 500m 2 / g or less, optimal choice 300m 2 / g or less. Furthermore, a BET specific surface area of ​​8m² is preferred. 2 / g or more, further preferred 10m 2 / g or more.

[0072] The specific surface area depends on the primary particle size and shell (shell layer) thickness of the hollow silica. When the primary particle size of the hollow silica is perfectly spherical and the surface is smooth, the following formula holds true when the radius of the primary particle is r, the shell thickness is d, and the true density of silica is ρ.

[0073] Single particle weight: 4π(r)3 -(rd) 3 )ρ / 3

[0074] Primary particle surface area: 4πr 2

[0075] Specific surface area: 3r 2 / (r 3 -(rd) 3 )ρ

[0076] The shell preferably contains no pores through which oxygen can pass, therefore the specific surface area is preferably close to the theoretical value mentioned above. The BET specific surface area is preferably 5 times or less than the theoretical value, more preferably 4 times or less, further preferably 3 times or less, and most preferably 2 times or less.

[0077] Here, the BET surface area can be determined using a surface area measuring device (e.g., "Macsorb" manufactured by MOUNTECH Co., Ltd.) and by a single-point method using a mixed gas (30% nitrogen as the adsorbent gas and 70% helium as the carrier gas).

[0078] The sphericity of the hollow silica particles is preferably 0.8 to 1.0. For sphericity, the diameters of the circumscribed circle (DL) and the inscribed circle (DS) of any 100 particles in a photographic projection obtained by scanning electron microscopy (SEM) are measured, and the average value is expressed as the ratio of the inscribed circle diameter (DS) to the circumscribed circle diameter (DL) (DS / DL). From the viewpoints of light scattering and tactile properties, a sphericity of 0.83 or higher is more preferred, 0.85 or higher is even more preferred, 0.87 or higher is particularly preferred, and 0.9 or higher is most preferred.

[0079] The shell thickness of the hollow silica particles is preferably 0.01 to 0.3 times the diameter of the primary particles. When the shell thickness is less than 0.01 times the diameter of the primary particles, the strength of the hollow silica particles may decrease. When the ratio is greater than 0.3, the hollow portion inside the particles becomes smaller, and the characteristics resulting from the hollow shape are not exhibited.

[0080] The shell thickness is more preferably 0.02 or more, more preferably 0.03 or more, and even more preferably 0.2 or less, and more preferably 0.1 or less, relative to the diameter of the primary particle.

[0081] Here, the shell thickness is determined by measuring the shell thickness of each particle using a transmission electron microscope (TEM).

[0082] Hollow silica particles have a hollow interior, allowing them to encapsulate substances within the particles. The shell of the hollow silica particles of this invention is dense, making it difficult for various solvents to penetrate. However, if broken particles are present, solvents can seep into the particles. Therefore, the oil absorption rate varies depending on the proportion of broken particles.

[0083] The preferred oil absorption capacity of hollow silica particles is 30–1000 mL / 100 g.

[0084] If the oil absorption is too high, the viscosity will increase. Therefore, the oil absorption is more preferably 900 mL / 100g or less, further preferably 850 mL / 100g or less, particularly preferably 830 mL / 100g or less, and most preferably 800 mL / 100g or less. Furthermore, low oil absorption means that the powder is not easily wetted by oil. Therefore, the oil absorption is more preferably 35 mL / 100g or more, further preferably 40 mL / 100g or more, particularly preferably 45 mL / 100g or more, and most preferably 50 mL / 100g or more.

[0085] It should be noted that, based on the relationship between the proportion of broken particles and oil absorption as described above, the oil absorption can be adjusted by changing the proportion of broken particles. Furthermore, the space between primary particles is also a space that can hold oil; therefore, it is believed that when the aggregate size of secondary particles is large, the oil absorption is greater, and when the aggregate size of secondary particles is small, the oil absorption is less.

[0086] Oil absorption can be measured according to JIS K 5101-13-1 (established in 2004).

[0087] The hollow silica particles of this invention, which possess a dense shell, can also be confirmed through a water dispersion test. Specifically, 1% by mass of hollow silica particles are added to 5 mL of pure water, and the particles are dispersed by ultrasonic irradiation for 30 seconds. The state after standing for one week is then confirmed. When the sample that has been dispersed after one week is compared with the sample that was just dispersed and observed visually, if it remains white, it can be considered that water has not penetrated into the interior of the particles. If water has penetrated into the interior of the hollow silica particles, they become translucent to transparent.

[0088] Furthermore, the hollow silica particles of this invention, which possess a dense shell, can also be confirmed through a redispersion test. Specifically, 1% by mass of hollow silica particles are added to 5 mL of pure water, and the particles are dispersed by ultrasonic irradiation for 30 seconds. The redispersion is then confirmed after standing for one week. The sample vial containing the dispersion is then tightly capped and slowly inverted twice. If no filter cake remains at the bottom, it can be assessed that water has not penetrated. If water penetrates into the interior of the hollow silica particles, the apparent density will increase, and a hard filter cake will form during particle settling, making redispersion more difficult.

[0089] Furthermore, the hollow silica particles of the present invention, which are particles with a dense shell, can also be confirmed by studying the peaks of the fine pore size measured using the nitrogen adsorption method. For example, measurements were performed using a fine pore distribution measuring device manufactured by Micromeritics, thereby studying the fine pore size. If there are fine pores in the shell that allow nitrogen to pass through, a peak of the fine pore size can be observed in the range of 2 to 15 nm. If the fine pore size is so small that nitrogen cannot pass through, no peak of the fine pore size can be observed. Therefore, it can be confirmed that the particles are hollow silica particles with a dense shell.

[0090] In this invention, it is preferable that the shell of the hollow silica particles contains an alkali metal component. If the alkali metal component is insufficient, the shell becomes porous, making it difficult to obtain a dense and strong shell. When using silicides as the silica raw material, this alkali metal component is practically undetectable.

[0091] For example, when using an aqueous sodium silicate solution as the silica raw material, the mass concentration of Na in the shell of the obtained hollow silica particles is preferably 200 ppm or more, more preferably 300 ppm or more, further preferably 500 ppm or more, particularly preferably 800 ppm or more, and most preferably 1000 ppm or more. On the other hand, the mass concentration of Na in the shell of conventional hollow silica particles made using tetraethyl orthosilicate as the silica raw material is 100 ppm or less.

[0092] The Ca content is preferably 10 ppm by mass or more, more preferably 30 ppm by mass or more, and even more preferably 50 ppm by mass or more. The Mg content is preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, and even more preferably 50 ppm by mass or more. However, if a large amount of alkali metals or alkaline earth metals are present, when hollow silica is dispersed in water or the like, it may dissolve and cause the dispersion to become alkaline, hindering the function of the surfactant. From the viewpoint of the stability of the compound, it is preferable to include a certain amount or less. In addition, it is believed that if a component containing hollow silica containing a large amount of alkali metals or alkaline earth metals is used for electronic applications, it will cause ion migration. Therefore, the Na content is preferably 1500 ppm by mass or less. The Ca content is preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, and even more preferably 500 ppm by mass or less. The Mg content is preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less, and even more preferably 100 ppm by mass or less.

[0093] The method for determining the alkali metal content and alkaline earth metal content involves adding perchloric acid and hydrofluoric acid to the obtained hollow silica, applying strong heat to remove the silicon component, and then performing the determination by ICP emission spectroscopy.

[0094] In addition, when alkali metal silicates are used as silica raw materials, the resulting hollow silica particles have less carbon content derived from the raw materials in their shells compared to when silanols are used as silica raw materials.

[0095] Assuming the hollow silica particles are used in a state of dispersion in resin, solvent, water, etc., it is preferable to maintain the dispersion without sedimentation. Dispersion stability can be evaluated using the following method: An aqueous dispersion of hollow silica particles with a concentration of 250 ppm by mass is prepared, dispersed by ultrasonic irradiation for 30 seconds, and the absorbance at a wavelength of 310 nm is observed and evaluated over time using a spectrophotometer (Shimadzu Corporation, UV-1280). The time immediately after preparing the aqueous dispersion is set as 0 hours, and the absorbance at 0 hours is set as 1. The absorbance ratio after 1 hour, 2 hours, and 15 hours at 25°C is used to evaluate dispersion stability. After the specified time, water permeates into the interior of the open particles or hollow silica particles with water-permeable shells. Due to water permeation, the absorbance decreases accordingly as the amount of sediment, which is close to the true density of silica with an apparent specific gravity close to that of the particles. After 1 hour, the absorbance ratio is preferably 0.2 or higher, more preferably 0.5 or higher, even more preferably 0.6 or higher, particularly preferably 0.8 or higher, and most preferably 0.9 or higher. It is assumed that when the dispersion stability is ideal, the absorbance is constant; therefore, the maximum value of the absorbance ratio is 1.0 or lower. After 2 hours, the hollow silica particles slowly settle or float according to their apparent specific gravity, thereby reducing the absorbance. After 15 hours, the absorbance ratio is preferably 0.2 or higher, more preferably 0.3 or higher, even more preferably 0.6 or higher, particularly preferably 0.7 or higher, and most preferably 0.8 or higher.

[0096] Titanium oxide and zinc oxide, inorganic materials used as white pigments, exhibit a bluish-white appearance due to their reflection peaks near 400 nm. Whiteness can be evaluated based on reflectance and spectrophotometry using an optical layer formed by mixing inorganic particles with a fluororesin coating agent and coating it onto a glass plate. In particular, reflectance can be measured using a spectrophotometer.

[0097] The reflectance ratio of the hollow silica particles of the present invention at a wavelength of 400 nm to that at a wavelength of 800 nm is preferably 2.00 or less, more preferably 1.50 or less, further preferably 1.35 or less, particularly preferably 1.20 or less, and most preferably 1.10 or less. If the reflectance ratio at a wavelength of 400 nm to that at a wavelength of 800 nm is too small, a reddish tint can be observed. Therefore, the aforementioned reflectance ratio is preferably 0.5 or more, more preferably 0.8 or more, and further preferably 0.9 or more.

[0098] L represents brightness * Values ​​and b representing chromaticity *The value can be measured using a spectrophotometer. The L value of the hollow silica particles of this invention... * The value is preferably 30.0 or higher, more preferably 40.0 or higher, further preferably 45.0 or higher, and particularly preferably 50.0 or higher. Ideally, L represents perfect diffuse reflection. * =100, therefore L * The value is below 100. (b) of hollow silica particles. * The preferred value is -5.0 or higher, more preferably -4.5 or higher, further preferably -4.0 or higher, especially preferably -3.5 or higher, and most preferably -3 or higher. * The preferred values ​​are +5.0 or less, more preferably +4.5 or less, further preferably +4.0 or less, especially preferably +3.5 or less, and most preferably +3 or less.

[0099] Hollow silica particles are sealed in a sealed bag and then subjected to static pressure at a specified pressure. The strength of the hollow silica particles can be evaluated based on the proportion of broken particles. The higher the pressure required for a certain amount of breakage of the hollow silica particles, the greater the pressure they can withstand. The pressure required for 10% breakage during static pressure treatment is preferably 1 MPa or higher, more preferably 5 MPa or higher, further preferably 10 MPa or higher, particularly preferably 20 MPa or higher, and most preferably 30 MPa or higher. There is no particular upper limit to this pressure, but it is preferably below 1 GPa.

[0100] The amount of silanol (Si-OH) on the surface of hollow silica particles was determined by IR measurement. Specifically, using an 800 cm⁻¹... -1 The IR spectrum was normalized at 3800 cm⁻¹. -1 After matching with the baseline, the Si-OH / Si-O-Si peak intensity ratio is determined, which allows for evaluation. If there is a high content of surface silanols, the dielectric loss will increase when the component obtained by mixing with the resin is used for electronic applications. The Si-OH / Si-O-Si peak intensity ratio is preferably 0.50 or less, more preferably 0.30 or less, further preferably 0.20 or less, particularly preferably 0.15 or less, and most preferably 0.10 or less. Amorphous silica typically contains a large amount of silanols. It is considered that if the amount of silanols is too low, it will approach crystalline silica; therefore, the Si-OH / Si-O-Si peak intensity ratio is preferably 0.01 or more.

[0101] The water vapor adsorption capacity of hollow silica particles is determined using water vapor as the gas and a device capable of observing gas adsorption. A high water vapor adsorption capacity means a large number of adsorption sites, which is not preferable for electronic component applications. The maximum water vapor adsorption capacity is preferably 5.0 (cm³). 3 / gSTP) / (m 2 / g) or less, more preferably 4.0 (cm)3 / gSTP) / (m 2 / g) or less, further preferably 3.0 (cm) 3 / gSTP) / (m 2 / g) or less, especially preferred 2.0 (cm) 3 / gSTP) / (m 2 / g) or less, with the optimal value being 1.0 (cm) 3 / gSTP) / (m 2 / g) or less. Silanols can be cited as a component capable of adsorbing water vapor. It is considered that if this water vapor adsorption capacity is too small, it will approximate crystalline silica; therefore, the maximum water vapor adsorption capacity is preferably 0.1 (cm³). 3 / gSTP) / (m 2 / g) or above.

[0102] Hollow silica particles can scatter light of a wide range of wavelengths, from ultraviolet to near-infrared, in all directions without absorbing it, depending on their concentration. Furthermore, hollow silica particles do not exhibit the photocatalytic properties found in white pigments such as titanium oxide, and can be used as a safe white pigment formed from amorphous silica.

[0103] By mixing hollow silica particles into a fluoropolymer resin with high UV resistance and UV transmittance, a highly weather-resistant white film can be obtained. Such a white film is suitable for membrane structures where plants requiring UV light can be cultivated (natural grass sports fields, farmhouses). Furthermore, this white film can prevent direct sunlight while allowing UV light to pass through moderately as scattered light, thus providing a bactericidal effect within the membrane structure. Additionally, this white film reflects or transmits most of the sunlight, does not absorb energy, and its temperature does not easily rise.

[0104] The weather resistance of fluoropolymer films containing hollow silica particles can be evaluated using an accelerated weathering tester by observing changes in haze, total transmittance, and parallel light transmittance at regular intervals. Less haze indicates better weather resistance; therefore, relative to the initial haze, the haze after 10-16 hours of weathering testing is preferably 1.50 or less, more preferably 1.20 or less, further preferably 1.10 or less, and particularly preferably 1.05 or less. If the fluoropolymer containing hollow silica deteriorates, the haze will increase; therefore, the lower limit of this haze value is 1.00 or more.

[0105] The hollow silica particles of the present invention have a dense shell, so even when mixed with resin, the resin will not penetrate into the interior of the hollow silica particles, thus maintaining a void layer. Furthermore, since the hollow silica particles of the present invention form secondary particles, voids also exist between the primary particles. Air is a substance with low thermal conductivity; therefore, it is believed that the addition of the hollow silica particles of the present invention to form an air layer reduces the thermal conductivity of the resin and improves its thermal insulation performance. For example, lightweight resin films and resin sheets with excellent thermal insulation properties can be produced. Additionally, by mixing with coatings, it can also be used as a thermal insulation coating that can be applied to houses and windows.

[0106] When 20 vol% of hollow silica particles are added to an unporous, blocky resin, the thermal conductivity is preferably 5% or more lower, more preferably 10% or more lower, and most preferably 15% or more lower than that of the resin monomer. Furthermore, while the addition of hollow silica particles increases thermal conductivity, it also means that the insulation performance deteriorates; therefore, the rate of change in the direction of increased thermal conductivity is preferably 1% or less.

[0107] (Manufacturing method of hollow silica particles)

[0108] The method for manufacturing hollow silica particles according to the present invention includes the following operations: forming a shell containing silica around the core to obtain a hollow silica precursor, removing the core from the hollow silica precursor, and performing heat treatment at 700°C or above.

[0109] Specifically, as a method for manufacturing hollow silica particles according to the present invention, the following method can be cited: using an oil-in-water emulsion comprising an aqueous phase, an oil phase, and a surfactant, a hollow silica precursor with a silica-containing shell formed on the periphery of the core is obtained in the emulsion; the core is removed from the precursor, and heat treatment is performed to obtain hollow silica particles. This oil-in-water emulsion is an emulsion in which an oil phase is dispersed in water. If a silica raw material is added to this emulsion, the silica raw material adheres to the oil droplets, forming oil core-silica shell particles.

[0110] The above-mentioned method for manufacturing hollow silica particles includes: a step of adding a first silica raw material to an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant to form a first shell; a step of adding a second silica raw material to an emulsion having the first shell to form a second shell, thereby obtaining a hollow silica precursor; and a step of obtaining hollow silica particles from the hollow silica precursor.

[0111] Hereinafter, oil-in-water emulsions will also be abbreviated as emulsions. Additionally, dispersions containing oil core-silica shell particles generated by adding a first silica raw material and before adding a second silica raw material, as well as dispersions containing oil core-silica shell particles after adding a second silica raw material, are sometimes also referred to as emulsions. The latter dispersion containing oil core-silica shell particles after adding a second silica raw material can be considered equivalent to a hollow silica precursor dispersion.

[0112] <The formation process of the first shell>

[0113] First, a first silica raw material is added to an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant to form the first shell.

[0114] The aqueous phase of the emulsion mainly contains water as a solvent. Water-soluble organic liquids, water-soluble resins, and other additives may also be added to the aqueous phase. The water content in the aqueous phase is preferably 50–100% by mass, more preferably 90–100% by mass.

[0115] The oil phase of the emulsion preferably comprises a non-water-soluble organic liquid that is incompatible with the aqueous phase components. This organic liquid forms droplets in the emulsion, creating the oil-core portion of the hollow silica precursor.

[0116] Examples of organic liquids include, for example, aliphatic hydrocarbons such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, n-nonane, isononane, n-pentane, isopentane, n-decane, isodecane, n-dodecane, isodecane, pentadecane, etc., or paraffinic base oils as mixtures thereof; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclohexene, etc., or cycloalkane base oils as mixtures thereof; benzene, toluene, xylene, ethylbenzene, propylbenzene, isobenzene, etc. Aromatic hydrocarbons such as propylbenzene, mesitylene, tetrahydronaphthalene, and styrene; ethers such as propyl ether and isopropyl ether; esters such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, butyl lactate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, and butyl butyrate; vegetable oils such as palm oil, soybean oil, and rapeseed oil; fluorinated solvents such as hydrofluorocarbons, perfluorocarbons, and perfluoropolyethers. Alternatively, polyoxyalkylene glycols that are hydrophobic liquids at the shell-forming reaction temperature can also be used. Examples include polypropylene glycol (molecular weight 1000 or higher), polyoxyethylene-polyoxypropylene block copolymers with a ethylene oxide unit ratio of less than 20% by mass and a cloud point (1% by mass aqueous solution) of 40°C or lower, preferably 20°C or lower. Among these, polyoxypropylene-polyoxyethylene-polyoxypropylene type block copolymers are preferred.

[0117] These can be used individually, or in combination of two or more within the range where the oil phase is formed by a single phase.

[0118] As an organic liquid, hydrocarbons with 8 to 16 carbon atoms, especially 9 to 12 carbon atoms, are preferred. The organic liquid is selected by comprehensively considering factors such as operability, fire safety, separability of the hollow silica precursor from the organic liquid, the shape characteristics of the hollow silica particles, and the solubility of the organic liquid in water. Hydrocarbons with 8 to 16 carbon atoms can be straight-chain, branched, or cyclic, provided they have good chemical stability; a mixture of hydrocarbons with different carbon atoms can also be used. Saturated hydrocarbons are preferred, and straight-chain saturated hydrocarbons are more preferred.

[0119] The flash point of an organic liquid is preferably 20–90°C, more preferably 30–80°C. When using organic liquids with a flash point below 20°C, countermeasures regarding fire prevention and the operating environment are required due to the excessively low flash point.

[0120] To improve emulsion stability, the emulsion contains a surfactant. The surfactant is preferably water-soluble or water-dispersible, and is preferably added to the aqueous phase for use. Nonionic surfactants are preferred.

[0121] Examples of nonionic surfactants include the following surfactants.

[0122] Polyoxyethylene-polyoxypropylene copolymer surfactants,

[0123] Polyoxyethylene sorbitan fatty acid ester surfactants: polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate; Polyoxyethylene higher alcohol ether surfactants: polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oil ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether.

[0124] Polyoxyethylene aliphatic ester surfactants: Polyoxyethylene glycol monolaurate, Polyoxyethylene glycol monostearate, Polyoxyethylene glycol monooleate,

[0125] Glyceryl fatty acid ester surfactants: glyceryl stearate and glyceryl oleate.

[0126] Alternatively, surfactants such as polyoxyethylene sorbitol fatty acid esters, sucrose fatty acid esters, polyglycerol fatty acid esters, and polyoxyethylene hydrogenated castor oil can also be used.

[0127] These can be used individually or in combination of two or more.

[0128] Among the aforementioned nonionic surfactants, polyoxyethylene-polyoxypropylene copolymer surfactants are preferred. Polyoxyethylene-polyoxypropylene copolymers are block copolymers formed by the bonding of polyoxyethylene blocks (EO) and polyoxypropylene blocks (PO). Examples of block copolymers include EO-PO-EO block copolymers and EO-PO block copolymers, with EO-PO-EO block copolymers being preferred. The proportion of ethylene oxide units in the EO-PO-EO block copolymer is preferably 20% by mass or more, more preferably 30% by mass or more.

[0129] The weight-average molecular weight of the polyoxyethylene-polyoxypropylene copolymer is preferably 3,000 to 27,000, more preferably 6,000 to 19,000.

[0130] The total amount of polyoxyethylene blocks is preferably 40-90% by mass and the total amount of polyoxypropylene blocks is preferably 10-60% by mass, relative to the total amount of the polyoxyethylene-polyoxypropylene copolymer.

[0131] The amount of surfactant used varies depending on the type of surfactant, the HLB (Hydrophile-lipophile balance) index indicating the degree of hydrophilicity or hydrophobicity of the surfactant, and the particle size of the target silica particles. However, the content in the aqueous phase is preferably 500 to 20,000 ppm by mass, more preferably 1,000 to 10,000 ppm by mass. A content of 500 ppm by mass or higher can further stabilize the emulsion. Conversely, a content of 20,000 ppm by mass or lower can reduce the amount of residual surfactant in the hollow silica particles used as the product.

[0132] The aqueous phase and oil phase can be mixed in a mass ratio of 200:1 to 5:1, preferably 100:1 to 9:1.

[0133] The methods for preparing oil-in-water emulsions are not limited to the following. An aqueous phase and an oil phase can be prepared separately beforehand, and the oil phase can be added to the aqueous phase, allowing for thorough mixing and / or stirring. Furthermore, methods such as ultrasonic emulsification, stirred emulsification, and high-pressure emulsification, which physically apply strong shear forces, can be applied. Other methods include: membrane emulsification, where an oil phase, refined by passing through a membrane with micropores, is dispersed in an aqueous phase; phase-inversion emulsification, where a surfactant is dissolved in the oil phase, and then an aqueous phase is added and emulsified; and phase-inversion temperature emulsification, where the surfactant changes from water-soluble to oil-soluble at a temperature near its cloud point. These emulsification methods can be appropriately selected based on the characteristics of the target particle size, particle size distribution, etc.

[0134] To achieve a smaller particle size and narrower particle size distribution in the obtained hollow silica particles, it is preferable that the oil phase is sufficiently dispersed in the aqueous phase and emulsified. For example, the mixture can be emulsified using a high-pressure homogenizer at a pressure of 100 bar or more, preferably 400 bar or more.

[0135] In the first shell formation process, a first silica raw material is added to the oil-in-water emulsion.

[0136] Examples of first silica raw materials include, for example, aqueous solutions containing dissolved water-soluble silica, aqueous dispersions containing dispersed solid silica, mixtures thereof, and aqueous solutions or dispersions of one or more selected from the group consisting of alkali metal silicates, active silicic acid, and silanolates. Among these, aqueous solutions or dispersions of one or more selected from the group consisting of alkali metal silicates, active silicic acid, and silanolates are preferred for ease of acquisition.

[0137] Examples of solid silica include, for example, silica sol obtained by hydrolyzing organosilicon compounds and commercially available silica sol.

[0138] Examples of alkali metal silicates include lithium, sodium, potassium, and rubidium, among which sodium is preferred due to its ease of acquisition and economic considerations. Specifically, sodium silicate is preferred as an alkali metal silicate. Sodium silicate has a composition expressed as Na₂O·nSiO₂·mH₂O. The ratio of sodium to silicic acid, expressed as the molar ratio n of SiO₂ / Na₂O, is preferably 1.0 to 4.0, and more preferably 2.0 to 3.5.

[0139] Activated silicic acid is obtained by replacing the alkali metal in alkali metal silicates with hydrogen through cation exchange treatment. The aqueous solution of this activated silicic acid is weakly acidic. Hydrogen-form cation exchange resins can be used in the cation exchange process.

[0140] Alkali metal silicates and active silicic acid are preferably dissolved and / or dispersed in water before being added to the emulsion. The concentration of the aqueous solution of alkali metal silicates and active silicic acid, based on the SiO2 concentration, is preferably 3-30% by mass, more preferably 5-25% by mass.

[0141] As a silanol salt, tetraalkylsilanes such as tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane are preferred.

[0142] Alternatively, composite particles can be obtained by mixing other metal oxides with silica raw materials. Examples of other metal oxides include titanium dioxide, zinc oxide, cerium oxide, copper oxide, iron oxide, and tin oxide.

[0143] The aforementioned silica raw materials can be used alone or in combination with two or more. Among them, aqueous solutions of alkali metal silicates, particularly sodium silicate, are preferred as the first silica raw material.

[0144] The addition of the first silica raw material to the oil-in-water emulsion is preferably carried out under acidic conditions. By adding the silica raw material in an acidic environment, silica particles are generated and form a network, thereby forming the first coating.

[0145] To maintain the stability of the emulsion, a reaction temperature of 80°C or below is preferred, more preferably 70°C or below, even more preferably 60°C or below, particularly preferably 50°C or below, and most preferably 40°C or below. Furthermore, from the viewpoint of controlling the network formation rate of silica particles to ensure uniform film thickness, a temperature of 4°C or above is preferred, more preferably 10°C or above, even more preferably 15°C or above, particularly preferably 20°C or above, and most preferably 25°C or above.

[0146] From the viewpoint of making the coating thickness more uniform and the resulting hollow silica shell more dense, the pH of the water-in-oil emulsion during the reaction is more preferably set to 3.0 or less, further preferably 2.4 or less, and even more preferably 1.0 or more.

[0147] To make the pH of an oil-in-water emulsion acidic, the following steps can be taken: adding acid.

[0148] Examples of acids include hydrochloric acid, nitric acid, sulfuric acid, acetic acid, perchloric acid, hydrobromic acid, trichloroacetic acid, dichloroacetic acid, methanesulfonic acid, and benzenesulfonic acid.

[0149] Regarding the addition of the first silica raw material, the amount of the first silica raw material added is preferably 1 to 50 parts by mass of SiO2 in the first silica raw material, more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the oil phase contained in the emulsion.

[0150] In the addition of the first silica raw material, it is preferable to maintain the pH of the emulsion at an acidic state for more than 1 minute, more preferably more than 5 minutes, and even more preferably more than 10 minutes after adding the first silica raw material.

[0151] Next, it is preferable to maintain the pH of the emulsion containing the first silica material at a level of 5 or higher and 7 or lower. This allows the first silica material to be immobilized on the surface of the oil droplets.

[0152] For example, there is a method to make the pH of an emulsion above 5 by adding an alkali to an emulsion in which a first silica raw material has been added.

[0153] Examples of bases include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, ammonia, and amines.

[0154] Alternatively, a method can be used to exchange anions such as halide ions for hydroxide ions through anion exchange treatment.

[0155] When adding alkali, it is preferable to add it slowly while stirring the emulsion containing the first silica raw material, so that the pH of the emulsion rises slowly. If the stirring is weak or a large amount of alkali is added at once, the pH of the emulsion may become uneven, and the thickness of the first coating layer may become uneven.

[0156] The emulsion is preferably held while being stirred. This holding time can be 10 minutes or more, preferably 1 hour or more, or even 4 hours or more. To maintain the stability of the emulsion, the holding temperature is preferably below 100°C, more preferably below 95°C, further preferably below 90°C, and particularly preferably below 85°C. Furthermore, to promote maturation, the holding temperature is preferably above 35°C, more preferably above 40°C, and particularly preferably above 45°C.

[0157] <The Formation Process of the Second Shell>

[0158] Next, a second silica raw material is added to the emulsion in the presence of alkali metal ions. This yields a hollow silica precursor dispersion. Here, the hollow silica precursor consists of oil-core silica-shell particles.

[0159] The addition of the second silica raw material to the emulsion is preferably carried out under alkaline conditions.

[0160] In the addition of the first silica raw material, a method is used to temporarily acidify the emulsion to a pH of 5 or higher in order to achieve more uniform adhesion of the first silica raw material to the oil droplets. The first silica layer obtained by this method is porous and not sufficiently dense, thus resulting in lower strength. In the addition of the second silica raw material, by making the emulsion alkaline, a high-density second silica layer can be formed on the previously obtained first silica layer.

[0161] To suppress the formation of new particles, the pH of the emulsion when the second silica raw material is added is preferably 8 or higher, more preferably 8.5 or higher, further preferably 8.7 or higher, particularly preferably 8.9 or higher, and most preferably 9 or higher. Furthermore, if the pH is too high, the solubility of silica increases; therefore, a pH of 13 or lower is preferred, more preferably 12.5 or lower, further preferably 12 or lower, particularly preferably 11.5 or lower, and most preferably 11 or lower.

[0162] To make the pH of an oil-in-water emulsion alkaline, an example of adding a base can be given. The base used is the same compound as described above.

[0163] As the second silica raw material, the same silica raw material as the first silica raw material can be used alone, or two or more can be used in combination. Among them, at least one of sodium silicate aqueous solution and active silicic acid aqueous solution is preferred in the addition of the second silica raw material.

[0164] When adding the second silica raw material to the emulsion under alkaline conditions, a method can be used to simultaneously add the alkali metal hydroxide and the second silica raw material. Alternatively, sodium silicate can be used as the alkali metal silicate in the second silica raw material. In this case, since the sodium silicate component, acting as an alkaline component, is added to the weakly acidic emulsion with a pH of 5 or higher after the addition of the first silica raw material, the pH of the emulsion can be maintained at alkalinity while the second silica raw material is added. Furthermore, this ensures that alkali metal ions are present in the emulsion.

[0165] It should be noted that, in cases where sodium silicate aqueous solution is used in the second silica raw material, and the pH rises excessively, acid may be added to adjust the pH. The acid used here can be the same acid used when adding the first silica raw material.

[0166] The addition of the second silica raw material is preferably carried out in the presence of alkali metal ions. These alkali metal ions can originate from the first silica raw material, the second silica raw material, or from an alkali added to adjust the pH, or can be added as additives to the emulsion. For example, an alkali metal silicate may be used in at least one of the first and second silica raw materials. Additionally, alkali metal halides, sulfates, nitrates, fatty acid salts, etc., may be used as additives in the emulsion.

[0167] Regarding the addition of the second silica raw material, for example, one of a sodium silicate aqueous solution and an active silicic acid aqueous solution can be added to the emulsion after the addition of the first silica raw material, or both can be added. When adding both, the sodium silicate aqueous solution and the active silicic acid aqueous solution can be added simultaneously or sequentially.

[0168] For example, regarding the addition of the second silica raw material, in order to adjust the pH and promote the adhesion of the silica raw material to the first silica layer, the steps of adding sodium silicate aqueous solution and adding active silicic acid aqueous solution can be repeated more than twice.

[0169] To promote the adhesion of the silica raw material to the first silica layer, the second silica raw material is preferably added to the heated emulsion. To suppress the formation of new particles, the heating temperature is preferably 30°C or higher, more preferably 35°C or higher, further preferably 40°C or higher, particularly preferably 45°C or higher, and most preferably 50°C or higher. If the temperature increases, the solubility of silica increases; therefore, the temperature is preferably below 100°C, more preferably below 95°C, further preferably below 90°C, particularly preferably below 85°C, and most preferably below 80°C. When using a heated emulsion, it is preferable to slowly cool the resulting emulsion to room temperature (23°C) after the addition of the second silica raw material.

[0170] In the addition of the second silica raw material, the amount of the second silica raw material is preferably adjusted such that, relative to 100 parts by mass of the oil phase, the SiO2 in the second silica raw material is 20 to 500 parts by mass, and more preferably adjusted such that it is 40 to 300 parts by mass.

[0171] In the addition of the second silica raw material, it is preferable to maintain the pH of the emulsion at an alkaline state for more than 10 minutes after adding the second silica raw material.

[0172] Preferably, by adding the first silica raw material and the second silica raw material, the total amount of the first silica raw material and the second silica raw material is adjusted to 100 parts by mass relative to the oil phase, and the total amount of SiO2 in the first silica raw material and the second silica raw material is 30 to 500 parts by mass, more preferably adjusted to 50 to 300 parts by mass.

[0173] The silica shell of this invention is mainly composed of silica, but it may also contain other metal components such as Ti and Zr, depending on the need for refractive index adjustment. There are no particular limitations on the method of adding other metal components; for example, methods such as simultaneously adding a metal sol or a metal salt aqueous solution during the process of adding silica raw materials can be used.

[0174] Hollow silica precursor dispersion was obtained as described above.

[0175] Methods for obtaining hollow silica precursors from hollow silica precursor dispersions include, for example, filtering the dispersion, removing the aqueous phase by heating, and separating the precursor by sedimentation or centrifugation.

[0176] As an example, there is a method of filtering the dispersion using a filter of about 0.1μm to 5μm and then drying the filtered hollow silica precursor.

[0177] Alternatively, hollow silica precursors can be obtained by cleaning with water, acid, alkali, organic solvents, etc., as needed.

[0178] <Process for obtaining hollow silica particles from hollow silica precursor>

[0179] Then, the oil core is removed from the hollow silica precursor (first stage treatment), followed by heat treatment at above 700°C (second stage treatment) to obtain hollow silica particles. The first stage treatment removes the oil core and organic components such as surfactants, while the second stage treatment sintersects the hollow silica particles to densify the shell.

[0180] Methods for removing oil cores include: calcining a hollow silica precursor to burn off the oil, drying to evaporate the oil, adding appropriate additives to decompose the oil, and extracting the oil using organic solvents. Among these, from the viewpoint of reducing oil residue and improving operational efficiency during heat treatment at 700°C or higher, the method of calcining a hollow silica precursor to burn off the oil cores and then heat-treating at 700°C or higher is preferred.

[0181] The following explanation will focus on the method of removing oil cores by sintering a hollow silica precursor.

[0182] In the first stage of processing, the oil inside the hollow particles needs to be thermally decomposed. Therefore, the firing temperature is preferably above 30°C, more preferably above 100°C, further preferably above 200°C, particularly preferably above 250°C, and most preferably above 300°C. Furthermore, if the firing temperature is too high, it will promote the densification of the silica shell, making it difficult to remove the organic components inside the particles. Therefore, the firing temperature is preferably at least 100°C lower than the second stage heat treatment temperature, more preferably at least 300°C lower, and further preferably at least 400°C lower.

[0183] In order to fully remove oil cores and organic components, the firing time of the first stage treatment is preferably 5 minutes or more, more preferably 1 hour or more, and even more preferably 3 hours or more. In addition, from the point of view of operational efficiency, it is preferably 12 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less.

[0184] In the first stage of processing, the process can be carried out at a constant firing temperature for a specified time, or it can be carried out gradually at multiple temperatures. It should be noted that, from the point of view of operational efficiency, it is preferable to carry out the process within the firing time mentioned above when processing is carried out at multiple temperatures.

[0185] Next, in the second stage of processing, heat treatment is carried out at a temperature above 700°C. It should be noted that the hollow silica precursor can be allowed to return to room temperature after the first stage of processing and before the second stage of processing, or the temperature can be increased from the firing temperature of the first stage of processing to the heat treatment temperature of the second stage of processing.

[0186] The heat treatment temperature is more preferably 750°C or higher, and even more preferably 800°C or higher. In addition, if the temperature is too high, it will cause crystallization of amorphous silica. Therefore, the heat treatment temperature is preferably 1200°C or lower, more preferably 1150°C or lower, even more preferably 1000°C or lower, particularly preferably 950°C or lower, and most preferably 900°C or lower.

[0187] In order to improve the densification of the shell, the heat treatment time of the second stage is preferably more than 1 hour, more preferably more than 3 hours, and from the point of view of operational efficiency, it is preferably less than 12 hours, more preferably less than 8 hours, and even more preferably less than 6 hours.

[0188] The hollow silica particles obtained through the above processes may sometimes aggregate due to the drying and sintering processes. Therefore, they can be crushed to achieve an easily manageable aggregate particle size. Crushing methods include, for example, using a mortar and pestle, using a dry or wet ball mill, using a vibrating screen, or using a pin mill, cutting mill, hammer mill, knife mill, roller mill, or other crushers. It should be noted that the preferred aggregate particle size for the secondary particles is as described above.

[0189] The hollow silica particles of this invention have a dense shell, resulting in low permeability to various solvents such as water and oil when added. Therefore, they exhibit good dispersibility in various solvents such as water, oil, and fluoropolymers, and sedimentation can be suppressed by making the specific gravity of the hollow silica particles close to that of the solvent. Furthermore, the unique properties of the hollow particles in the solvent can be maintained.

[0190] Therefore, the hollow silica particles of the present invention have the following characteristics. Compared with non-hollow silica particles, they are superior in terms of the ability to adjust the specific gravity to control non-settling properties, high scattering in the ultraviolet and visible regions, and high concealment. Furthermore, compared with titanium oxide particles, they are less toxic, have no photocatalytic activity, and their specific gravity can be adjusted to control non-settling properties. Additionally, compared with resin hollow particles, they are superior in terms of low environmental pollution, heat resistance, and safety. They can be used as additives with characteristics of low environmental impact, gentleness on skin, easy particle dispersion, and ease of use.

[0191] Therefore, the hollow silica particles of the present invention can be applied to various fields, such as cosmetic pigments, low refractive index materials, insulating fillers, heat-insulating fillers, low dielectric constant fillers, white pigments, drug carriers, fragrance carriers, pesticide carriers, ultraviolet scattering agents, etc.

[0192] Example

[0193] The present invention will now be described in more detail by way of examples, but the invention is not limited thereto. In the following description, the common components refer to the same substances. Furthermore, unless otherwise specified, "%" means "mass %". Examples 1-3, 32, and 33 are comparative examples, and Examples 4-31, 34, and 35 are exemplary examples.

[0194] <Experimental Example 1>

[0195] (Examples 1 to 6)

[0196] "The making of lotion"

[0197] Add 7g of EO-PO-EO block copolymer (Pluronic F68 manufactured by ADEKA) to 1250g of pure water and stir until dissolved. Add 42g of n-dodecane to the aqueous solution and stir using an IKA homogenizer until the liquid becomes homogeneous to prepare a crude emulsion.

[0198] The crude emulsion was emulsified three times at a pressure of 400 bar using a high-pressure emulsifier (LAB2000 manufactured by SMT Co., Ltd.) to produce a fine emulsion.

[0199] "First shell formation"

[0200] The first and second shell formations were carried out using a 2L glass reaction vessel. The resulting microemulsion was then allowed to stand at room temperature (25°C) for 15 hours before use.

[0201] 41 g of diluted sodium silicate aqueous solution (SiO2 concentration 10.4 wt%, Na2O concentration 3.6 wt%) and 2M hydrochloric acid were added to 1300 g of microemulsion at pH 2 (condition (i)) and stirred thoroughly while maintaining at 25 °C (condition (iii)).

[0202] While thoroughly stirring the liquid, slowly add 1M sodium hydroxide aqueous solution to bring the pH to 5 (condition (ii)) to obtain an oil core-silica shell particle dispersion. Keep the obtained oil core-silica shell particle dispersion and allow it to mature.

[0203] "Second shell formation"

[0204] The entire oil core-silica shell particle dispersion obtained in the first stage of shell formation was heated to 70°C, and 1M NaOH was slowly added while stirring, and the pH was set to 9.

[0205] Next, 460g of diluted sodium silicate aqueous solution (SiO2 concentration 10.4% by mass, Na2O concentration 3.6% by mass) was slowly added together with 0.5M hydrochloric acid to bring the pH to 9.

[0206] The suspension was kept at 70°C for 2 days and then slowly cooled to room temperature to obtain a hollow silica precursor dispersion.

[0207] "Filtering, drying, firing"

[0208] The entire hollow silica precursor dispersion was filtered using a 0.45 μm hydrophilic PTFE membrane filter via pressure filtration (0.28 MPa).

[0209] The filtered cake was dried at 60°C for 1 hour under a nitrogen atmosphere, followed by drying at 400°C for 4 hours (heating time 5°C / minute) to remove organic components, thereby obtaining the hollow silica precursor.

[0210] The obtained precursor was divided into 6 parts and fired at the firing temperature recorded in Table 1 for 4 hours (heating time 5℃ / min) to sinter the shell and obtain hollow silica particles.

[0211] "evaluate"

[0212] The following tests were conducted on the hollow silica particles of Examples 1 to 6.

[0213] 1. Scanning electron microscope image

[0214] Scanning electron microscope (SEM) images of the hollow silica particles obtained in Example 6 are shown below. Figure 1 SEM images were observed using an S4800 from Hitachi High-Tech Corporation at an accelerating voltage of 3kV. Figure 1 As shown, the open particles contained within indicate that the structure is hollow.

[0215] right Figure 1 The diameters of the circumcircle (DL) and incircle (DS) of any 100 particles were measured. The sphericity was calculated by taking the average of the ratio of the incircle diameter (DS) to the circumcircle diameter (DL) (DS / DL), and the result was 0.91. Furthermore, since particles ranging in size from approximately 100 nm to 1 μm were present, a distribution was observed. The primary diameter of any 100 particles was measured, and the average value was calculated based on the statistical distribution obtained from these measurements. The result was an average primary diameter of 370 nm.

[0216] 2. Aggregate size

[0217] The hollow silica particles obtained in Example 6 were measured using a diffraction scattering particle distribution measuring device (MT3300) manufactured by Microtrac BEL Corp. The average value of the central value of the particle distribution (diameter) was calculated, and the aggregated particle size (D50) was found to be 12 μm.

[0218] 3. Specific surface area

[0219] Table 1 shows the BET specific surface area of ​​the hollow silica particles obtained in Examples 1 to 6 based on the nitrogen adsorption method. The BET specific surface area was measured using a fully automated specific surface area measuring device "Macsorb" manufactured by MOUNTECH Co., Ltd., and by a single-point method using a mixed gas (30% nitrogen as the adsorbent gas and 70% helium as the carrier gas). The higher the firing temperature, the smaller the BET specific surface area, therefore it is considered that the shell has been densified.

[0220] 4. Confirmation of the fine pore diameter peak

[0221] Table 1 shows the presence or absence of fine pore size peaks in the hollow silica particles obtained in Examples 1-6, as determined by nitrogen adsorption. The fine pore size peaks were measured using a Micromeritics "3Flex" fine pore distribution measuring device. The position of the peak was recorded where its presence could be confirmed; otherwise, it was recorded as "absent." Higher firing temperatures resulted in less observable fine pore size peaks by nitrogen adsorption, indicating that the shell had been densified.

[0222] 5. Density determination using a specific gravity bottle

[0223] The density in water was determined using a 10 mL Gay-Lussac specific gravity bottle. As a pretreatment, the sample and water were placed in the specific gravity bottle, and the bottle was placed together in a sealed PTFE container and left to stand in a constant temperature bath at 110°C for 16 hours. After being removed from the constant temperature bath and cooled to room temperature, the density was measured, and the results are shown in Table 1.

[0224] It is believed that Examples 1-3 are close to the true density of silicon dioxide (approximately 2.2 g / cm³). 3 Therefore, water seeps in, as seen in Examples 4-6 where the density is less than 2.00 g / cm³. 3 Therefore, water did not penetrate, maintaining the hollow part.

[0225] 6. Density determination using a dry specific gravity bottle

[0226] The density was determined using a dry specific gravity bottle (Micromeritics AccuPycII 1340). The determination conditions are as follows.

[0227] • Sample cell: 10cm 3 Pond

[0228] • Sample weight: 1.5g

[0229] • Gas to be measured: Helium or oxygen

[0230] Number of purging cycles: 30

[0231] • Purging filling pressure: 135 kPag

[0232] • Number of cycles: 10

[0233] • Circulating filling pressure: 135 kPag

[0234] • Rate of pressure equilibrium termination: 0.05 kPag / minute

[0235] The results are shown in Table 1. When helium was used for gas determination, the sample concentration was approximately 2.2 g / cm³. 3 The result showed a true density equivalent to that of silica, indicating that helium gas passed through the shell and penetrated into the interior of the hollow silica. On the other hand, when oxygen was used, approximately 1.1 g / cm³ was obtained in Examples 4-6. 3 The value is assumed to be the particle density excluding the interior of the hollow silica, because oxygen passes through the shell slowly. In Examples 1 to 3, oxygen passes through the shell. In addition, due to accumulation or adsorption in some pores, a value higher than the true density is obtained, or the pressure does not reach equilibrium within the specified time, resulting in an error of "cannot be measured".

[0236] Based on these results, it is believed that the pore size of the shell decreases with increasing firing temperature, as shown in Examples 4 to 6, where the pore size is equivalent to or less than the diameter of an oxygen molecule.

[0237] [Table 1]

[0238] Table 1

[0239]

[0240] <Experimental Example 2>

[0241] (Examples 7~14)

[0242] The conditions for the first shell-forming reaction were changed to those described in Table 2. Hollow silica particles were then produced using the same method as in Example 6.

[0243] i) pH after adding sodium silicate aqueous solution

[0244] ii) pH after adding 1M NaOH

[0245] iii) Reaction temperature during the formation of the first shell

[0246] [Table 2]

[0247] Table 2

[0248]

[0249] (Examples 15~17)

[0250] Hydrochloric acid was replaced with sulfuric acid. Example 15 used a glass reaction vessel with a capacity of 2L, Example 16 used a glass reaction vessel with a capacity of 5L, and Example 17 used a glass reaction vessel with a capacity of 10L. Otherwise, hollow silica particles were produced by the same method as in Example 14.

[0251] (Examples 18~21)

[0252] Hollow silica particles were prepared by changing the amount of silica added relative to the oil used in the core, except that the method was the same as in Example 14. Specifically, the silica-to-oil ratio was 1.2 in Example 14, 1.6 in Example 18, 1.8 in Example 19, 2.2 in Example 20, and 0.8 in Example 21.

[0253] (Examples 22~24)

[0254] The process was changed to rapidly adding 1M NaOH to bring the pH to 9 during the formation of the second shell. Otherwise, hollow silica particles were produced using the same method as in Example 8. Specifically, NaOH was added for 1 minute in Example 22, for 5 minutes in Example 23, and for 10 minutes in Example 24.

[0255] (Examples 25~29)

[0256] The standing time and temperature after the microemulsion were changed, but hollow silica particles were prepared using the same method as in Example 14. Specifically, Example 25 was left to stand at 25°C for 12 hours, Example 26 for 24 hours, Example 27 for 192 hours, Example 28 for 112 hours, and Example 29 for 15 hours at 70°C.

[0257] "evaluate"

[0258] The following tests were conducted on the hollow silica particles of Examples 7 to 29.

[0259] 1. Sphericity and average primary particle size

[0260] Sphericity and average primary particle size were determined using scanning electron microscopy images in the same manner as in Example 6. The results are shown in Table 3.

[0261] 2. Aggregate size of secondary particles

[0262] The aggregate size (D50) of the secondary particles was determined using the same method as in Example 6. The results are shown in Table 3.

[0263] 3. Specific surface area

[0264] The specific surface area was determined using the same method as in Examples 1 through 6. The results are shown in Table 3.

[0265] 4. Density determination using a dry specific gravity bottle

[0266] Density was determined using the same method as in Examples 1 to 6, employing a dry specific gravity bottle. The results are shown in Table 3.

[0267] 5. Hollow particle ratio

[0268] When the filter cake, after filtration and before oil core removal, is loosened and air-dried overnight, the oil components in the open particles evaporate, while the oil components in the completely covered hollow particles are retained. Based on the amount of raw material input, the weight change during heat treatment was calculated when all the input oil components evaporated (0% hollow particle ratio) and when all were retained (100% hollow particle ratio). The hollow particle ratio was then estimated based on the weight change when the filter cake was air-dried overnight and heat-treated to 800°C. The results are shown in Table 3.

[0269] 6. Oil absorption capacity

[0270] The oil absorption rate was calculated according to JIS K 5101-13-1 (established in 2004). The results are shown in Table 3. It is assumed that the higher the hollow particle ratio, the lower the oil absorption rate; therefore, the internal space of the open particles contributes to the oil absorption rate.

[0271] 7. Shell thickness

[0272] The shell thickness was determined by measuring the shell thickness of each particle using transmission electron microscopy (TEM). For TEM images, hollow silica particles were dispersed on a hydrophilically treated polyvinyl alcohol formal film and observed using a HITACHI HT7700 with an accelerating voltage of 100 kV. The average shell thickness of any 50 particles was taken as the shell thickness.

[0273] [Table 3]

[0274] Table 3

[0275]

[0276] According to the results in Table 3, the higher the hollow particle ratio, the less oil is absorbed. Therefore, it is believed that the internal space of some open, broken particles contributes to the oil absorption capacity. Thus, the oil absorption capacity can be adjusted by the proportion of broken particles, i.e., the hollow particle ratio.

[0277] <Experimental Example 3>

[0278] The particle size distribution of hollow silica particles prepared in Examples 7-14 and 22-24 in Experiment 2 was determined.

[0279] Particle size distribution was determined using a laser diffraction particle size distribution measuring device (Microtrac BEL Corp. MT3300). Within the device, the particles were dispersed by ultrasonic waves irradiating the device three times over 60 seconds before measurement. Measurements were performed twice over 120 seconds each, and the average values ​​are shown in Table 4.

[0280] The particle size distribution observed here is not the particle size distribution of a single hollow silica particle, but rather the particle size distribution of aggregates formed by two aggregations. According to Table 4, the size of the aggregates formed by the two aggregations is distributed in the range of several hundred nm to tens of μm.

[0281] [Table 4]

[0282] Table 4

[0283] D10(μm) D50(μm) D90(μm) Example 7 1.2 3.1 6.1 Example 8 4.8 29.3 51.8 Example 9 0.2 0.3 15.7 Example 10 23.5 37.7 58.1 Example 11 10.0 30.9 56.5 Example 12 9.9 32.3 59.6 Example 13 7.5 30.9 53.5 Example 14 0.4 4.4 22.1 Example 21 0.5 2.2 4.1 Example 22 0.4 5.5 19.7 Example 23 5.4 14.1 27.1

[0284] <Experimental Example 4>

[0285] The impurity concentration was determined for the hollow silica particles prepared in Examples 14-17 of Experiment 2.

[0286] For the determination, perchloric acid and hydrofluoric acid were added to hollow silica particles, and strong heating was applied to remove the silicon of the main component. The amount of alkali metals and alkaline earth metals was quantified by high-frequency inductively coupled plasma atomic emission spectrometry using an ICPE-9000 manufactured by Shimadzu Corporation.

[0287] The hollow silica particles from Examples 14-17 were prepared into an aqueous dispersion with a concentration of 14% and allowed to stand in a constant temperature bath at 110°C for 17 hours. This was to accelerate the penetration of water through the shell and into the interior of the hollow silica particles. The aqueous dispersion was then diluted to 0.008%, and UV scattering properties were evaluated using a spectrophotometer (Shimadzu UV-1280, Ltd.). The absorbance at a wavelength of 310 nm was measured, and the water permeability was compared. The results are shown in Table 5.

[0288] It is known that when there are abundant alkali metals such as Na and alkaline earth metals such as Ca, the absorbance at a wavelength of 310 nm is high, forming a shell that is difficult for water to penetrate. It is known that alkali metals and alkaline earth metals affect the dissolution / re-precipitation of silica, and it is believed that their presence will promote the densification of the shell during heat treatment.

[0289] [Table 5]

[0290] Table 5

[0291]

[0292] <Experimental Example 5>

[0293] The absorbance ratio of hollow silica particles prepared in Examples 1 to 6 of Experiment 1 was measured.

[0294] Using the hollow silica particles from Examples 1-6, an aqueous dispersion of 250 ppm by mass was prepared and dispersed by ultrasonic irradiation for 30 seconds. Absorbance was measured using a quartz cuvette (AS ONE Corporation Azlab quartz cuvette (two transparent sides) Q-102, depth 4.5 mm × width 12.5 mm × height 45 mm, optical path length 2 mm × optical path width 10 mm). A spectrophotometer (Shimadzu Corporation UV-1280) was used, and absorbance was measured at a wavelength of 310 nm to also evaluate UV scattering. The cuvette was set with the center of the light beam 15 mm from the bottom. The time immediately following the preparation of the aqueous dispersion was set to 0 hours, and the absorbance at 0 hours was set to 1. The dispersion stability was evaluated by comparing the absorbance after standing at room temperature for 1 hour, 2 hours, and 15 hours. The results are shown in Table 6.

[0295] Regarding the absorbance ratio after 1 hour, it is believed that water permeates into the interior of open particles or hollow silica particles with a water-permeable shell, causing the specific gravity to approach the true density of silica and resulting in sedimentation, thus reducing absorbance accordingly. It is also believed that after 2 hours, the hollow silica particles gradually settle or float according to their specific gravity, thus reducing absorbance.

[0296] [Table 6]

[0297] Table 6

[0298]

[0299] <Experimental Example 6>

[0300] Spectroscopic spectra were obtained for the hollow silica particles of Examples 1 to 6 prepared in Experiment 1.

[0301] 0.1 g of hollow silica particles from Examples 1-6 were placed in a powder sample holder (manufactured by Shimadzu Corporation) attached to an integrating sphere apparatus. The diffuse reflectance in the wavelength range of 300 nm to 800 nm was measured using a spectrophotometer (Shimadzu Corporation, UV-3100PC and MPC-3100) to obtain the spectroscopic spectrum. It should be noted that the incident angle of the measured light was set to 0 degrees. The spectroscopic spectrum of Example 6 at this time is shown below. Figure 2 .

[0302] according to Figure 2 No peaks were observed at any specific wavelength, indicating no wavelength dependence. The hollow silica particles of Examples 1 to 5 also showed the same spectroscopic spectra as those of Example 6.

[0303] <Experimental Example 7>

[0304] The reflectivity, L* value, and b* value of the optical layer were measured using the hollow silica particles prepared in Examples 8 to 14 of Experiment 2.

[0305] Add 18.2 g of fluoropolymer coating agent (AGC COAT-TECH Co., Ltd. product Obbligato), 1.8 g of hollow silica particles from Examples 8-14, and 0.5 g of defoamer (Teikoku Printing Inks Mfg. Co., Ltd. product SM-257). Stir at 200 rpm for 1 minute using a mixer (THINKY Corporation product AWATORIRENTARO). Then, add 6 g of curing agent (Asahi Kasei Corporation product TPA-B80E), and stir at 200 rpm for 1 minute to obtain the coating liquid.

[0306] Using a screen printing machine (MTVC-320 manufactured by Micro-tec Co., Ltd.), the obtained coating liquid was applied to one side of a sodium-calcium silicate glass plate (AGC KFL, 150mm x 75mm, average thickness: 3.2mm) serving as the substrate layer, with a thickness of approximately 30μm. Subsequently, it was cured by heating and drying in a constant temperature bath at 130°C for 30 minutes, resulting in an optical layer comprising a glass plate as the substrate layer and a coating layer disposed on the substrate layer.

[0307] The reflectance of the optical layer was measured using a spectrophotometer (V-670, manufactured by Nippon Spectrophotometer Co., Ltd.) in the wavelength range of 200–1500 nm, at 5 nm intervals, and at a scan rate of 1000 nm / min. The ratio of reflectance at wavelength 400 nm to reflectance at wavelength 800 nm is shown in Table 7.

[0308] It can be seen that the higher the reflectivity ratio, the greater the reflection at a wavelength of 400nm, and the more blue it appears. However, the optical layer of the hollow silica particles used in Examples 8 to 14 is all below 1.4, so no blue tint is observed.

[0309] The L* and b* values ​​of the optical layer were measured using a spectrophotometer (SD6000, manufactured by Nippon Denshoku Kogyo Co., Ltd.). During measurement, a black plate was placed against the sample background, and water was placed between the black plate and the sample. Measurement light was incident from the glass substrate side. The results are shown in Table 7.

[0310] It was confirmed that the higher the hollow silica particle ratio, the higher the L* value and brightness of the optical layer. It is believed that the more particles maintaining the hollow structure in the mixed resin, the greater the light scattering and the higher the brightness. Regarding the b* value, all samples were above -5, indicating a non-bluish white color.

[0311] [Table 7]

[0312] Table 7

[0313]

[0314] <Experimental Example 8>

[0315] The strength of the hollow silica particles prepared in Example 2 (Examples 14, 18-20) was determined.

[0316] Two g of hollow silica particles from Examples 14, 18-20 were measured and added to a sealed bag (ASAHIKASEI PAXCORPORATION commercial POLYFLEX bag). The bag was sealed using a cavity vacuum sealer (FUJI IMPULSE CO., LTD. FCB-2000). After sealing, a CIP apparatus (NPa SYSTEM CO., LTD. CPA-50) was used to apply static pressure at a specified pressure for one minute. The density of the samples before and after static pressure treatment was determined using the oxygen specific gravity bottle method to obtain the proportion of particles broken by static pressure treatment. The pressure at which 10% of the particles were broken by static pressure treatment is shown in Table 8.

[0317] It is known that the more silica is added, the greater the pressure required to break 10% of the particles, and therefore the stronger the particles become.

[0318] [Table 8]

[0319] Table 8

[0320]

[0321] <Experimental Example 9>

[0322] The surface silanol group content of hollow silica particles prepared in Examples 1 to 6 of Experiment 1 was determined.

[0323] Hollow silica particles from Examples 1 to 6 were applied to a diamond plate, and IR measurements were performed using a Nic-plan / Nicolet 6700 instrument manufactured by Thermo Fisher Scientific. The Si-O-Si peak was observed at 800 cm⁻¹. -1 Standardization was performed, with the peak rising to 3800 cm⁻¹ in Si-OH. -1By matching with the baseline, the intensity ratio of the Si-OH / Si-O-Si peaks was determined to evaluate the amount of silanol on the particle surface. The results are shown in Table 9.

[0324] According to the results in Table 9, the higher the firing temperature, the smaller the intensity ratio of the Si-OH / Si-O-Si peaks, and the less surface silanol is present.

[0325] [Table 9]

[0326] Table 9

[0327]

[0328] <Experimental Example 10>

[0329] Raman spectra and solid-state spectra of the hollow silica particles prepared in Examples 1 and 6 in Experiment 1 were obtained. 29 Si-NMR spectroscopy.

[0330] Raman spectra were obtained using a LabRAM HR Evolution instrument manufactured by Horiba, Ltd. The excitation wavelength was 532 nm, the power was 15 mW per sample, the objective lens was ×100, NA (Numerical Aperture) = 0.8, the confocal aperture was a 200 μm aperture, the grating was 600, and the center wavelength was 950 cm⁻¹. -1 The exposure time was 10 seconds, and the number of cumulative measurements was 20. The results of Examples 1 and 6 are shown below. Figure 3 .

[0331] Example 1, with its lower sintering temperature, exhibits a higher intensity of the Si-OH peak and a higher intensity of the D2 peak (605 cm⁻¹). -1 The high strength of the structure suggests the presence of a large amount of Si-OH, low crosslinking degree, and many unstable planar three-membered ring structures.

[0332] Additionally, using AVANCE-III-HD400 manufactured by Bruker Biospin, a solid was obtained. 29 Si-NMR spectroscopy. A 7mm CP / MAS probe was used, and measurements were performed at D1 = 300 seconds, NS = 700, and NS = 500. Samples from Examples 1 and 6 were loaded into... The ZrO2 sample tubes were used to measure the results. Figure 4 .

[0333] In Example 1, which had a low firing temperature, the Q3 peak detected on the shoulder of the Q4 peak in the low magnetic field side was slightly stronger, indicating the presence of a large amount of Si-OH.

[0334] <Experimental Example 11>

[0335] The water vapor adsorption capacity of hollow silica particles prepared in Examples 1 to 6 of Experiment 1 was determined.

[0336] Using water vapor as a gas, the water vapor adsorption capacity of hollow silica particles in Examples 1 to 6 was studied using a Micromeritics 3Flex. The maximum adsorption capacity of each sample is shown in Table 10.

[0337] According to the results in Table 10, since the maximum adsorption of water vapor is less when the firing temperature is higher, it can be seen that there are fewer adsorption sites (parts that can adsorb water vapor).

[0338] [Table 10]

[0339] Table 10

[0340]

[0341] <Experimental Example 12>

[0342] (Example 30)

[0343] 31 g of hollow silica particles obtained in Example 14 of Experiment 2 and 1.3 g of phenylmethyl organosilicon (PMS) were dispersed in 200 g of toluene. Then, the toluene was evaporated at 140 °C to remove it, resulting in 32.3 g of hollow particles that had been surface-treated with phenylmethyl organosilicon.

[0344] 1500g of ETFE (manufactured by AGC Corporation, Fluon ETFE88AXB) and 32.3g of surface-treated hollow granules were dry-blended and then melt-blended and extruded at 300°C using a twin-screw extruder to obtain granules. The extrusion pressure during granule forming was 12MPa. The granules were then extruded and formed at 300°C using a single-screw extruder with a T-die connected to the outlet to obtain a film with a thickness of 102μm.

[0345] (Example 31)

[0346] The granules prepared in Example 30 were further dry-mixed with 19 times the amount of ETFE and then extruded using a single-screw extruder at 300°C to obtain a film with a thickness of 251 μm.

[0347] "evaluate"

[0348] The optical properties of the thin films in Examples 30 and 31 were measured.

[0349] The thickness of the thin film is measured using a micrometer.

[0350] The haze of the film was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., device name: NDH-5000).

[0351] The total transmittance and parallel light transmittance of the film were measured using a UV-VIS-NIR spectrophotometer (manufactured by Shimadzu Corporation, device name: UV-3600) according to JIS R 3106:1998.

[0352] Weathering resistance testing was conducted using an accelerated weathering tester (manufactured by Suga Test Instruments Co., Ltd., device name: EYE Super UV Tester). The weathering test employed a 1600W / m² system, which involved condensation at 63°C for 2 hours, followed by 10 hours of further weathering. 2 The cycle of ultraviolet radiation.

[0353] The initial and post-accelerated weathering test optical properties are shown in Table 11, and... Figure 5 , 6 7. The figures represent total transmittance, parallel ray transmittance, and the sum of total transmittance and parallel ray transmittance, respectively.

[0354] For the films in Examples 30 and 31, it is evident that they remain stable in performance, unaffected by ultraviolet radiation and humidity during accelerated weathering tests, and do not absorb energy across a wide wavelength range, instead dispersing light to both the transmission and reflection sides. Furthermore, no degradation of the resin (high haze) caused by the photocatalyst was observed.

[0355] [Table 11]

[0356] Table 11

[0357]

[0358] <Experimental Example 13>

[0359] (Example 32)

[0360] The pH during the formation of the second shell was set to 7, and otherwise, hollow silica particles were prepared using the same method as in Example 8. The density of the hollow silica particles in Example 32, based on the oxygen specific gravity bottle method, was 2.77 g / cm³. 3 .

[0361] SEM images were taken of the hollow silica particles in Examples 32 and 8.

[0362] For SEM images, an S4800 from Hitachi High-Tech Corporation was used for observation at an accelerating voltage of 3kV. The SEM images of Examples 32 and 8 are shown below. Figure 8 , 9 .

[0363] The outer shell of the hollow silica particles in Example 32 shows an aggregated state of particles tens of nm in size, with a highly uneven surface. The outer shell of the hollow silica particles in Example 8 shows a smoother, less uneven surface.

[0364] Furthermore, when observing the inner side of the shell from the open particles, it can be seen that both Examples 32 and 8 show a smooth surface with few bumps. This is believed to be because the process of adding silica raw materials in the manufacturing of hollow silica particles of the present invention is divided into two or more steps. The first silica raw material is added to an emulsion containing a surfactant under acidic conditions, thereby forming a first silica coating, which is the characteristic observed.

[0365] <Experimental Example 14>

[0366] (Example 33)

[0367] The fluoropolymer coating agent (AGC COAT-TECH Co., Ltd. product Obbligato) (27.29 g) and the defoamer (Teikoku Printing Inks Mfg. Co., Ltd. product SM-257) (0.78 g) were mixed and stirred at 200 rpm for 1 minute using a mixer (THINKY Corporation product AWATORIRENTARO). Then, the curing agent (Asahi Kasei Corporation product TPA-B80E) (9.09 g) was added, and the mixture was stirred at 200 rpm for 1 minute to obtain the final mixture.

[0368] The resulting mixture was placed into a plastic ointment bottle (made of high-density polyethylene with a large inner diameter). The film is dried at room temperature for 3 days to cure it. The cured film is then recovered to obtain a resin sheet.

[0369] (Example 34)

[0370] 2.91 g of hollow silica particles prepared in Example 14 in Test Example 2 (10 wt% and 21 vol% after curing and drying) were added to prepare a mixture. Otherwise, resin sheets were prepared by the same method as in Example 33.

[0371] (Example 35)

[0372] 2.91 g of hollow silica particles (10 wt% and 25 vol% after curing and drying) prepared in Example 29 were further added to prepare a mixture. Otherwise, resin sheets were prepared by the same method as in Example 33.

[0373] "evaluate"

[0374] The following tests were conducted on the resin sheets of Examples 33-35.

[0375] 1. Thermal conductivity measurement

[0376] The thermal conductivity at ambient pressure and 25°C was measured using a thermal conductivity measuring device (FOX50 manufactured by Eiko Seiki Co., Ltd.). The results are shown in Table 12.

[0377] 2. Determination of density

[0378] The diameter of the resin sheet was measured using a ruler. Additionally, the thickness of the resin sheet was also measured while clamping it with a thermal conductivity measuring device. Therefore, the volume of the resin sheet was calculated based on the diameter and thickness values. The density was then calculated by weighing the resin sheet. The results are shown in Table 12.

[0379] According to Table 12, it can be confirmed that, compared with Example 33 which only contains fluororesin, Examples 34 and 35, which contain 10% hollow silica particles, have lower densities and can thus introduce an air layer, resulting in a reduction of thermal conductivity of approximately 20%. Based on this result, it can be seen that by adding the hollow silica particles of the present invention to the resin sheet or coating liquid, the thermal insulation performance can be improved.

[0380] [Table 12]

[0381] Table 12

[0382] Sample diameter × thickness Weight (g) <![CDATA[Density (g / cm 3 )]]> Thermal conductivity (W / mK) Example 33 φ50mm×55mm 17.2 0.40 0.124 Example 34 φ50mm×69mm 16.6 0.31 0.102 Example 35 φ50mm×70mm 18.7 0.34 0.104

[0383] The present invention has been described in detail with reference to specific embodiments; however, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese patent applications filed on February 27, 2020 (Japanese Patent Application No. 2020-032046) and September 25, 2020 (Japanese Patent Application Nos. 2020-161378 and 2020-161379), the contents of which are incorporated herein by reference.

Claims

1. A hollow silica particle comprising a shell containing silica, having a space on the inner side of the shell, the shell having pores of a size that allows helium molecules to pass through but prevents oxygen molecules from passing through. The density of the hollow silica particles, determined by density measurement using a dry density bottle filled with helium, is 2.00 g / cm³. 3 The density of the particles, as determined by density measurement using a dry density bottle with oxygen, is less than 2.00 g / cm³. 3 .

2. The hollow silica particles according to claim 1, wherein, The density of the particles, determined by density measurement using a dry density bottle filled with helium, is 2.00~2.40 g / cm³. 3 .

3. The hollow silica particles according to claim 1 or 2, wherein, The density of the particles, determined by density measurement using a dry density bottle with oxygen, is 0.40~1.90 g / cm³. 3 .

4. The hollow silica particles according to claim 1 or 2 have an average primary particle size of 10 nm to 10 μm.

5. The hollow silica particles according to claim 1 or 2, having a BET specific surface area of ​​5~2600 m². 2 / g.

6. The hollow silica particles according to claim 1 or 2 have a sphericity of 0.8 to 1.

0.

7. The hollow silica particles according to claim 1 or 2 have an oil absorption capacity of 30~1000mL / 100g.

8. The hollow silica particles according to claim 1 or 2, wherein, The aggregate size (D50) of the secondary particles is 0.1~50μm.

9. A method for manufacturing hollow silica particles according to any one of claims 1 to 8, wherein, A hollow silica precursor is obtained by forming a shell containing silica around the core, removing the core from the hollow silica precursor, and then heat-treating it at a temperature above 700°C.

Images