Hollow particle, resin composition, and circuit board

Abstract

Provided is a hollow particle having higher shock resistance. A hollow particle according to an embodiment of the present invention contains silica and includes an inner portion formed from a hollow shell. The hollow particle has a number distribution-based median diameter (D50) of 0.5-5.0 μm as measured by a dry laser diffraction-type particle size distribution measurement device. The value obtained by dividing the compression displacement of the hollow particle by the thickness of the shell is 0.0030 or higher.

Description

Hollow particles, resin composition, and circuit board

[0001] The present invention relates to hollow particles constituted by a hollow shell inside, a resin composition, and a circuit board.

[0002] In recent years, in the field of information and communication equipment, in order to adapt to communication in high frequency bands, further requirements have been placed on lowering the dielectric constant and dielectric loss tangent of electronic materials (typically resin materials). To achieve this, for example, it has been proposed to use hollow particles that allow air, which has a low relative dielectric constant, to be contained in the material (see, for example, Patent Document 1). In addition, in order to effectively prevent hollow particles from breaking when producing a resin composition, hollow particles having a predetermined breaking strength are also known (see, for example, Patent Document 2).

[0003] Japanese Patent Application Laid-Open No. 2007-56158 Japanese Patent Application Laid-Open No. 2022-172938

[0004] By the way, due to the expansion of the usage environment of information and communication equipment, electronic members containing hollow particles may be subjected to impact, and it is considered that hollow particles with higher impact resistance are required.

[0005] The present invention has been made to solve the above problems, and one of its objects is to provide hollow particles with higher impact resistance.

[0006] (1) The hollow particle of the present disclosure contains silica and is constituted by a hollow shell inside. When measured by a dry laser diffraction particle size distribution analyzer, the median diameter (D50) of the number distribution of the hollow particles is 0.5 µm or more and 5 µm or less. In the hollow particles, a value obtained by dividing the compressive displacement by the thickness of the shell is 0.0030 or more.

[0007] (2) The hollow particle of the present disclosure is the hollow particle according to (1) above, wherein the strain rate immediately before fracture is 0.11 or more.

[0008] (3) The hollow particle of the present disclosure is the hollow particle according to (1) or (2) above, wherein the dielectric constant at 10 GHz is 1.7 or less.

[0009] (4) The hollow particle of the present disclosure is the hollow particle according to any one of (1) to (3) above, wherein the shell contains Fe. The Fe content in the shell is 10 ppm or more and 50 ppm or less.

[0010] (5) The hollow particle of the present disclosure is the hollow particle according to any one of (1) to (4) above, and has a density of 0.1 g / ml to 2.2 g / ml.

[0011] (6) The hollow particle of the present disclosure is the hollow particle according to any one of (1) to (5) above, and has a fracture strength of 5 MPa to 100 MPa.

[0012] (7) The hollow particle of the present disclosure is the hollow particle according to any one of (1) to (6) above, and the thickness of the shell is 25 nm or more and 500 nm or less.

[0013] (8) The hollow particle of the present disclosure is the hollow particle according to any one of (1) to (7) above, wherein the silica is amorphous silica.

[0014] (9) The resin composition of the present disclosure comprises the hollow particle according to any one of (1) to (8) above and a resin.

[0015] (10) The high-frequency circuit board of the present disclosure comprises the hollow particle according to any one of (1) to (8) above, and a material selected from glass epoxy resin, polyimide resin, liquid crystal polymer, aromatic hydrocarbon resin, modified polyphenylene ether resin, fluororesin, and ceramics.

[0016] According to an embodiment of the present invention, hollow particles with higher impact resistance can be provided.

[0017] It is a cross-sectional view schematically showing hollow particles in one embodiment of the present invention. It is an SEM observation photograph of the hollow silica particles of Example 1. It is a TEM observation photograph of the hollow silica particles of Example 1. It is an SEM observation photograph of core particles of Example 6 observed at a magnification of 10,000 times. It is an SEM observation photograph of core particles of Example 6 observed at a magnification of 20,000 times. It is a graph showing the particle size distribution of core particles of Example 6.

[0018] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0019] A. Hollow Particle Figure 1 is a schematic cross-sectional view showing a hollow particle in one embodiment of the present invention. This hollow particle 2 is composed of a hollow shell 4. In the hollow particle 2, a hollow portion 6 is formed inside, surrounded by the shell 4. Note that in Figure 1, hatching has been omitted from the cross-section of the hollow particle for clarity.

[0020] The above shell contains silica. The silica contained in the shell is typically amorphous silica. The silica content of the shell may be, for example, 95% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more.

[0021] The particle diameter of the hollow particles may be, for example, 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. On the other hand, the particle diameter of the hollow particles may be, for example, 100 μm or less, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. Here, the particle diameter of the hollow particles is the median diameter (D50) of the number distribution determined by measurement using a dry laser diffraction particle size distribution analyzer. Preferably, the hollow particles according to the embodiment of the present invention have a median diameter (D50) of the number distribution of 0.5 μm or more and 5 μm or less when measured using a dry laser diffraction particle size distribution analyzer.

[0022] Hollow particles can have any suitable shape. Examples of hollow particle shapes include spherical, elliptical, aggregated, flaky, plate-like, film-like, cylindrical, prismatic, flattened, disc-like, and grain-like shapes.

[0023] In one embodiment, the hollow particles are spherical. When the hollow particles are spherical, stress is dispersed, and impact resistance can be achieved. The aspect ratio of the hollow particles may be, for example, 1.00 or more. On the other hand, the aspect ratio of the hollow particles may be, for example, 3.0 or less, preferably 2.0 or less, and more preferably 1.50 or less. When the aspect ratio of the hollow particles is 1.0 or more and 1.5 or less, the shape of the hollow particles can be made closer to a perfect sphere, so that stress is stably dispersed and impact resistance can be achieved. The aspect ratio of the hollow particles is the ratio of the average major axis to the average minor axis of the hollow particles. In this specification, "average minor axis" means the average value of the minor axes of 100 randomly selected particles when the particles are observed by a scanning electron microscope (SEM), and "average major axis" means the average value of the major axes of 100 randomly selected particles when the particles are observed by a scanning electron microscope (SEM). Furthermore, the "standard deviation" of the mean short axis refers to the square root of the mean square of the deviations of each short axis measurement value from the mean short axis, measured for 100 randomly selected particles observed using a scanning electron microscope (SEM). Similarly, the "standard deviation" of the mean major axis refers to the square root of the mean square of the deviations of each major axis measurement value from the mean major axis, measured for 100 randomly selected particles observed using a scanning electron microscope (SEM). In other words, it is the square root of the variance. Moreover, "deviation" refers to the value obtained by subtracting the mean value of the short axis from the measured value of each short axis of 100 randomly selected particles, or the value obtained by subtracting the mean value of the major axis from the measured value of each major axis of 100 randomly selected particles.

[0024] The standard deviation of the major axis of the hollow particles may be, for example, 1.90 μm or less, and preferably 1.50 μm or less. On the other hand, the lower limit of the standard deviation of the major axis of the hollow particles is typically 0 μm. The standard deviation of the minor axis of the hollow particles may be, for example, 1.30 μm or less, and preferably 1.00 μm or less. On the other hand, the lower limit of the standard deviation of the minor axis of the hollow particles is typically 0 μm.

[0025] The shell thickness of the hollow particle is preferably 25 nm or more, more preferably 50 nm or more, and may be 75 nm or more. Having such a shell thickness of hollow particle can result in excellent fracture strength. For example, fracture of hollow particles can be effectively prevented when manufacturing resin compositions, etc. On the other hand, the shell thickness of the hollow particle may be, for example, 500 nm or less, 350 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less. With such a thickness, a good space can be formed in the hollow particle, which can greatly contribute to improved dielectric properties and weight reduction. The shell thickness can be measured by TEM observation. For example, it can be determined by measuring the shell thickness of randomly selected hollow particles and calculating the average value of the measured shell thicknesses.

[0026] The density of the hollow particles may be, for example, 2.2 g / ml or less, preferably 1.0 g / ml or less, and more preferably 0.7 g / ml or less. Hollow particles satisfying such densities may have excellent shell flexibility and excellent fracture strength. Furthermore, for example, the thickness of the shell can be reduced. In addition, hollow particles of such density may contain air within the shell and may have extremely excellent dielectric properties. On the other hand, the density of the hollow particles may be, for example, 0.1 g / ml or more, may be 0.3 g / ml or more, or may be 0.4 g / ml or more.

[0027] The BET specific surface area of ​​the hollow particles is preferably 30 m². ２ It is less than or equal to / g, and more preferably 20m ２ / g or less, 10m ２ It may be less than / g. On the other hand, the BET specific surface area of ​​a hollow particle is, for example, 0.5 m². ２ It can be more than / g, and 1m ２ It may be more than / g.

[0028] The dielectric constant of the hollow particle at 10 GHz may be, for example, 2.0 or less, preferably 1.9 or less, more preferably 1.7 or less, and even more preferably 1.65 or less. On the other hand, the dielectric constant of the hollow particle at 10 GHz may be, for example, 1.0 or more, may be 1.1 or more, and may be 1.3 or more. The dielectric loss tangent of the hollow particle at 25°C and 10 GHz is preferably 0.0025 or less, more preferably 0.0015 or less. On the other hand, the dielectric loss tangent of the hollow particle at 25°C and 10 GHz may be, for example, 0.0001 or more.

[0029] The compressive displacement of the hollow particles may be, for example, 0.20 μm or more, preferably 0.25 μm or more, and may also be 0.30 μm or more, or 0.35 μm or more. On the other hand, the compressive displacement of the hollow particles may be, for example, 0.50 μm or less.

[0030] The value obtained by dividing the compressive displacement of a hollow particle (in μm) by the thickness of the hollow particle's shell (in nm) can be, for example, 0.001 to 0.1, and preferably 0.0030 or higher. This value represents the amount of deformation per unit thickness of the shell and can serve as an indicator of the flexibility of the shell itself. Specifically, the larger the value obtained by dividing the compressive displacement of a hollow particle by the thickness of its shell, the softer the shell is and the better its impact resistance. In other words, by having a predetermined value obtained by dividing the compressive displacement by the thickness of the shell, a hollow particle can enhance its impact resistance, unlike mere fracture strength.

[0031] Soft-shelled hollow particles, for example, can impart flexibility and improve impact resistance when mixed with resin. Furthermore, substrates for automobiles and smartphones equipped with high-speed, high-capacity communication functions are constantly subjected to impact; however, even in such applications, substrates containing soft-shelled hollow particles can prevent damage.

[0032] The strain rate of the hollow particle immediately before fracture may be, for example, 0.01 or higher, preferably 0.05 or higher, more preferably 0.10 or higher, and even more preferably 0.11 or higher. On the other hand, the strain rate of the hollow particle immediately before fracture may be, for example, less than 1, may be 0.5 or lower, or 0.3 or lower.

[0033] The fracture strength of the hollow particles may be, for example, 5 MPa or more, preferably 10 MPa or more, but may also be 12 MPa or more, 14 MPa or more, 16 MPa or more, 18 MPa or more, 20 MPa or more, 25 MPa or more, or 30 MPa or more. With such a fracture strength, for example, when manufacturing a resin composition, the fracture of the hollow particles can be effectively prevented. As a result, the hollow state of the particles is maintained, which can greatly contribute to improving the dielectric properties of the resulting component. On the other hand, the fracture strength of the hollow particles may also be, for example, 100 MPa or less.

[0034] The hollow particles according to the embodiments of the present invention can contain extremely few impurities in their shells. Specifically, the low-density, highly flexible shells allow for good removal of impurities during the manufacturing process. Hollow particles with suppressed impurity content can have extremely excellent dielectric properties. Furthermore, shells with suppressed impurity content can be even more flexible.

[0035] Examples of impurities contained in hollow particles include S, Al, Na, K, Mg, Cl, Ca, and Fe. Hollow particles may contain one or more types of impurities. In hollow particles containing two or more types of impurities, these impurities may form chemical bonds.

[0036] The sulfur contained in hollow particles as an impurity is sulfate ions (SO4). ４ ２－may be formed. For example, the content of sulfate ions in the shell may be, for example, 5000 ppm or less, preferably 3000 ppm or less, more preferably 2000 ppm or less, still more preferably 1000 ppm or less. On the other hand, the content of sulfate ions in the shell may be, for example, 0 ppm or more, and may be, for example, 100 ppm or more. The content of sulfate ions in the shell can be determined, for example, by compositional analysis using high frequency inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0037] When the content of sulfate ions in the shell falls within this range, the breaking strength of the hollow particles can be stably improved. In particular, when the content of sulfate ions in the shell is not more than the above upper limit, Na ２ SO ４ can be sufficiently reduced in the shell of the hollow particles. Na ２ SO ４ reacts with SiO ２ during firing to form a low-melting-point Na silicate liquid phase, which may remain as a grain boundary glass layer. This grain boundary glass layer (alkali glass) loosens the -Si-O-Si- network, accelerates diffusion, and may strongly promote the nucleation and growth of crystalline silica (cristobalite). When crystalline silica is present in the shell of hollow particles, stress concentrates on the crystalline silica, which may adversely affect the breaking strength of the hollow particles.

[0038] Further, for example, the Al content in the shell may be, for example, 10000 ppm or less, preferably 5000 ppm or less, more preferably 5500 ppm or less, still more preferably 4000 ppm or less, particularly preferably 3000 ppm or less. On the other hand, the Al content in the shell may be, for example, 500 ppm or more, preferably 1000 ppm or more, more preferably 2000 ppm or more. The Al content in the shell can be determined, for example, by compositional analysis using high frequency inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0039] When the Al content of the shell is within this range, the fracture strength of the hollow particles can be more stably improved, and the influence of Na on the dielectric properties can be reduced. In particular, when the Al content of the shell is above this lower limit, some of the Si can be stably substituted with Al in the -Si-O-Si- network, and an aluminosilicate can be formed in the shell of the hollow particle. In other words, when Al enters the -Si-O-Si- network, AlO ４－ This can take the form of AlO, which can increase the viscosity of silica. Therefore, it can improve the fracture strength of hollow particles while suppressing crystallization. Furthermore, the shell containing aluminosilicate is AlO ４－ Due to its presence, it locally acquires a negative charge. Therefore, even if the shell contains Na as an impurity, Na tends to remain near Al. Generally, Na ＋ When an AC voltage is applied while Na is present in a dielectric (insulator), ＋ Electrical signals are lost when ions move. However, Na tends to stay near Al, and Al "binds" Na, that is, Na ＋ By restricting ion movement, the free mobility of Na can be reduced, which may in some cases reduce the loss of electrical signals and minimize the deterioration of dielectric properties due to Na.

[0040] For example, the Na content of the shell may be, for example, 5000 ppm or less, preferably 3000 ppm or less, more preferably 2000 ppm or less, even more preferably 1500 ppm or less, particularly preferably 1000 ppm or less, and especially preferably 600 ppm or less. On the other hand, the Na content of the shell may be, for example, 10 ppm or more, preferably 50 ppm or more, and more preferably 100 ppm or more. The Na content can be determined, for example, by compositional analysis using atomic absorption spectrometry (AAS).

[0041] When the Na content of the shell is within this range, the fracture strength of the hollow particles can be improved more stably. In particular, when the Na content of the shell is below this upper limit, Na ２ O can be sufficiently reduced in the shell of the hollow particle. ２O may break the -Si-O-Si- network and form non-crosslinked oxygen. This can reduce the viscosity of the glass phase of the hollow particles, potentially negatively affecting their fracture strength. Furthermore, if the Na content in the shell is below this upper limit, the formation of crystalline silica (cristobalite) in the hollow particle shell can be suppressed, and the hydrolysis of the -Si-O-Si- network can also be suppressed. If the Na content in the hollow particle shell exceeds the above range, crystalline silica is more likely to form in the hollow particle shell. The formation of crystalline silica in the hollow particle shell can cause a rapid volume change due to firing, potentially inducing cracking during cooling, and stress concentration in the crystalline silica can negatively affect the fracture strength of the hollow particles. In addition, because Na has a relatively high affinity for water, if the Na content in the hollow particle shell exceeds the above range, it can cause hydrolysis of the -Si-O-Si- network, potentially negatively affecting the fracture strength of the hollow particles.

[0042] In one embodiment, the shell impurities may include at least one selected from K, Mg, Cl, Ca, and Fe. For example, the Fe content of the shell is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less. Shells satisfying such Fe content may have excellent flexibility. On the other hand, the Fe content of the shell may be, for example, 10 ppm or more. The Fe content of the shell can be determined, for example, by compositional analysis using inductively coupled plasma emission spectrometry (ICP-AES).

[0043] In one embodiment, it is preferable that the hollow particles are surface-treated with any suitable surface treatment agent. As the surface treatment agent, at least one selected from the group consisting of higher fatty acids, anionic surfactants, cationic surfactants, nonionic surfactants, phosphate esters, coupling agents, esters of polyhydric alcohols and fatty acids, acrylic polymers, and silicone treatment agents may be used.

[0044] Any suitable method can be used as the method for producing the hollow particles described above. A method for producing hollow particles according to one embodiment of the present invention includes coating core particles with a shell-forming material to obtain core-shell particles, and removing core particles from the core-shell particles.

[0045] The particle diameter of the core particles may be, for example, 0.01 μm or more, preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. On the other hand, the particle diameter of the core particles may be, for example, 100 μm or less, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. Here, the particle diameter of the core particles is the median diameter (D50) of the number distribution determined by measurement using a laser diffraction particle size distribution analyzer. Preferably, the core particles have a median diameter (D50) of the number distribution of 0.5 μm or more and 5 μm or less when measured using a laser diffraction particle size distribution analyzer.

[0046] The core particles can have any suitable shape. Examples of core particle shapes include spherical, elliptical, aggregated, flaky, plate-like, film-like, cylindrical, prismatic, flattened, disc-like, and grain-like shapes.

[0047] In one embodiment, the core particle is spherical. When the core particle is spherical, the aspect ratio of the hollow particle produced can be stably adjusted to the above range. The aspect ratio of the core particle may be, for example, 1.0 or more. On the other hand, the aspect ratio of the core particle may be, for example, 3.0 or less, preferably 2.0 or less, and more preferably 1.5 or less. When the aspect ratio of the core particle is 1.0 or more and 1.5 or less, the shape of the hollow particle produced can be stably brought close to a perfect sphere. The aspect ratio of the core particle is the ratio of the average major axis to the average minor axis in the core particle.

[0048] The standard deviation of the major axis of the core particles may be, for example, 1.00 μm or less, and preferably 0.80 μm or less. On the other hand, the lower limit of the standard deviation of the major axis of the core particles is typically 0. The standard deviation of the minor axis of the core particles may be, for example, 1.00 μm or less, and preferably 0.80 μm or less. On the other hand, the lower limit of the standard deviation of the minor axis of the core particles is typically 0.

[0049] Any suitable material can be used as the core particle formation material. In one embodiment, the core particles are preferably composed of an alunite-type compound represented by the following general formula (I). ａ [Al １－ｘ M' ｘ ] ３ (SO ４ ２－ ) ｙ (OH) ｚ ・mH ２ O...(I) In equation (I), M is Na ＋ _K ＋ NH ４ ＋ and H ３ O ＋ It is at least one cation selected from the group consisting of the following. In formula (I), M' is Cu ２＋ , Zn ２＋ Ni ２＋ Sn ４＋ , Zr ４＋ and Ti ４＋ It is at least one cation selected from the group consisting of the following. In equation (I), a satisfies 0.8 ≤ a ≤ 1.35. In equation (I), m satisfies 0 ≤ m ≤ 5. In equation (I), x satisfies 0 ≤ x ≤ 0.4. In equation (I), y satisfies 1.7 ≤ y ≤ 2.5. In equation (I), z satisfies 4 ≤ z ≤ 7.

[0050] To produce such core particles, first, an aqueous solution of raw materials containing an aluminum salt and a sulfate is prepared. In the following, this aqueous solution of raw materials may be referred to as the raw material.

[0051] Aluminum salts contain at least Al ３＋It is an inorganic salt containing aluminum. Examples of aluminum salts include aluminum sulfate, aluminum chloride, aluminum fluoride, aluminum bromide, aluminum iodide, aluminum perchlorate, aluminum dihydrogen phosphate, potassium aluminum sulfate, ammonium aluminum sulfate, aluminum nitrate, aluminum nitrite, aluminum phosphate, aluminum hydroxide, aluminum oxyhydroxide, polyaluminum chloride, potassium hexafluoroaluminate, aluminum acetate, aluminum lactate, aluminum citrate, aluminum oxalate, aluminum stearate, aluminum palmitate, aluminum oleate, and combinations thereof. Among the aluminum salts, aluminum sulfate is preferred. The final concentration of the aluminum salt in the aqueous solution of the raw material is, for example, 0.01 mol / L to 1.00 mol / L, preferably 0.05 mol / L to 0.75 mol / L, more preferably 0.10 mol / L to 0.50 mol / L, and even more preferably 0.20 mol / L to 0.30 mol / L.

[0052] Examples of sulfates include sodium sulfate, potassium sulfate, ammonium sulfate, and combinations thereof. Among sulfates, sodium sulfate is preferred. The ratio of sulfate added is, for example, 0.1 mol to 2.0 mol, preferably 0.5 mol to 1.5 mol, and more preferably 0.9 mol to 1.1 mol per mol of aluminum salt.

[0053] Other metal salts besides aluminum salts may be added to the raw material aqueous solution. Examples of metal salts other than aluminum salts include Cu ２＋ Copper salts containing Zn ２＋ Zinc salts containing Ni ２＋ Nickel salts containing Sn ４＋ Tin salts containing Zr ４＋ Zirconium salts containing Ti ４＋ Examples include titanium salts containing [the specified compound], and combinations thereof.

[0054] Furthermore, by adding an organic acid to the raw material aqueous solution, the shape of the resulting core particles can be controlled, and as a result, hollow particles with a desired shape can be produced. If citric acid is selected as the organic acid added to the raw material aqueous solution, the core particles can be controlled to a spherical shape, and spherical hollow particles can be stably produced.

[0055] The proportion of organic acid added is, for example, 0.001 mol to 3 mol per mol of aluminum salt, preferably 0.005 mol to 2 mol, and more preferably 0.01 mol to 1 mol.

[0056] Next, a hydroxide is added to the aqueous raw material solution. Examples of hydroxides include sodium hydroxide, potassium hydroxide, ammonium hydroxide, and combinations thereof. Among the hydroxides, sodium hydroxide is preferred. The addition ratio of the hydroxide is, for example, 0.1 mol to 100 mol per mol of aluminum salt, preferably 1 mol to 10 mol, and more preferably 3.0 mol to 5.0 mol.

[0057] Subsequently, the aqueous raw material solution to which hydroxide has been added is typically adjusted to a predetermined temperature and stirred for a predetermined time. Such temperature adjustment is carried out, for example, by autoclave. The adjustment temperature is, for example, 40°C to 200°C, preferably 90°C to 190°C, and more preferably 100°C to 180°C. When the adjustment temperature is within this range, the core particles can be stably adjusted to the desired shape. In particular, by adjusting the temperature of the aqueous raw material solution containing citric acid and hydroxide in this way, the core particles can be stably brought close to a perfect sphere.

[0058] This yields a slurry containing core particles. The core particles are then separated from the slurry by any suitable means and dried as necessary. Thus, core particles are produced.

[0059] Examples of the shell-forming materials mentioned above include alkoxysilanes and sodium silicate (Na ２ O・nSiO ２) is used. In one embodiment, an alkoxysilane is preferably used as the shell-forming material. Among alkoxysilanes, tetraethoxysilane (Si(OCH)) is preferred. ２ CH ３ ) ４ TEOS is preferably used. In this case, for example, core-shell particles can be obtained by hydrolyzing the alkoxysilane in the presence of core particles to precipitate silica on the surface of the core particles. The pH during the hydrolysis of the alkoxysilane is preferably 10 or higher. By hydrolyzing the alkoxysilane, hollow particles satisfying the above characteristics can be obtained well, and the coating process with the shell-forming material can be simplified.

[0060] When coating core particles with a shell-forming material, it is preferable that the core particles are dispersed in a dispersion medium such as ethanol or water. The conditions for hydrolysis of the alkoxysilane can be set, for example, from the viewpoint of obtaining a low-density, highly flexible shell. The temperature during hydrolysis of the alkoxysilane is preferably 10°C to 60°C. The time for hydrolysis of the alkoxysilane is preferably 10 minutes to 24 hours.

[0061] The amount of shell-forming material covering the core particles can be adjusted, for example, by controlling the concentration and blending amount of the shell-forming material during the coating process. When the core particles are coated with a shell-forming material containing alkoxysilane, the concentration of alkoxysilane in the shell-forming material can be, for example, 0.1 M to 12 M.

[0062] The removal of the core particles is typically carried out by dissolving them in an acidic solution. Examples of acidic solutions include hydrochloric acid, sulfuric acid, and nitric acid. The dissolution temperature can be, for example, 30°C to 95°C, and preferably 50°C to 90°C. At such temperatures, the core particles can be efficiently dissolved while suppressing problems such as the shell becoming easily broken. In one embodiment, for example, sulfuric acid is used as the acidic solution from the viewpoint of reusing the substance obtained by reacting with the core particles. Examples of substances obtained by reacting with the core particles include salts. The concentration of sulfuric acid can be, for example, 0.1 M to 3.5 M, and preferably 0.5 M or higher.

[0063] The above method for producing hollow particles may include calcining the core-shell particles before removing the core particles. If the core particles contain the alunite-type compound, it is preferable to perform calcination before removing the core particles. Calcination is preferably performed, for example, under an atmospheric environment. Since the alunite-type compound may have acid resistance, the alunite-type compound may change upon calcination, and the core particles after calcination may become easily soluble in acidic solutions. Specifically, core particles containing the alunite-type compound tend to dissolve easily in acidic solutions in portions with low aggregation density, but are less soluble in acidic solutions in portions with high aggregation density, and the amount dissolved in acidic solutions may be limited to, for example, about 30% by weight. Upon calcination, the alunite-type compound is converted into aluminum oxide (Al), which is easily soluble in acidic solutions. ２ O ３ This can generate a compound that improves the solubility of the core particles in acidic solutions.

[0064] The firing temperature for the core-shell particles can be, for example, 300°C to 900°C, preferably 300°C to 650°C. Such firing temperatures can suppress the crystallization of the shell and generate the aluminum oxide mentioned above. The firing time can be, for example, 0.5 hours to 20 hours. The firing may be carried out continuously or in multiple stages at different temperatures. In the case of multi-stage firing, the above firing time is the sum of the firing times for each stage.

[0065] For example, the shell obtained by removing the core particles may be coated again with a shell-forming material. However, when the core particles are coated with a shell-forming material containing alkoxysilane, hollow particles satisfying the above characteristics can be obtained well even without coating the shell with the shell-forming material.

[0066] The above method for producing hollow particles preferably includes firing the shells obtained by removing the core particles. By firing the shells, the silanol groups that may be contained in the shells can be changed to siloxanes, making the shells hydrophobic and improving their dielectric properties. The firing temperature of the shells may be, for example, 300°C or higher, preferably 700°C or higher, more preferably 900°C or higher, and even more preferably 1000°C or higher. With such firing temperatures, the above hydrophobicity can be well achieved. On the other hand, the firing temperature of the shells may be, for example, 1300°C or lower, preferably 1200°C or lower. With such firing temperatures, shells with low density and excellent flexibility can be well obtained. The firing time of the shells may be, for example, 0.1 hours to 10 hours. From the viewpoint of obtaining shells with low density and excellent flexibility, the firing time is preferably 3 hours or less. The firing may be carried out continuously or in multiple stages. When firing is carried out in multiple stages, the above firing time is the sum of the firing times of each stage.

[0067] In one embodiment, the shell is fired in multiple stages. More specifically, the shell is fired at a relatively low primary firing temperature, and then fired at a relatively high secondary firing temperature. With this method, when the shell is first fired at the primary firing temperature, H is produced by the dehydration condensation of silanol groups present on the inside of the shell. ２O can be smoothly discharged to the outside of the shell through holes formed in the shell. This can improve the dielectric properties of the hollow particles produced. The holes formed in the shell may occur, for example, when the core particles are melted. Subsequently, the holes formed in the shell can be sealed by firing the shell at a secondary firing temperature. As a result, the impact resistance of the hollow particles can be improved. The primary firing temperature may be, for example, 300°C or higher, preferably 700°C or higher. On the other hand, the primary firing temperature may be, for example, 1000°C or lower, preferably 900°C or lower, and more preferably 850°C or lower. The secondary firing temperature may be, for example, 900°C or higher, preferably 1000°C or higher, and more preferably 1050°C or higher. On the other hand, the secondary firing temperature may be, for example, 1300°C or lower, preferably 1200°C or lower.

[0068] The above method for producing hollow particles may include subjecting the core-shell particles and the shells to washing treatments, which are substantially dehydration, washing, and drying treatments, respectively. Typically, ethanol, water, etc., can be used for washing. Washing of shells, which may be of low density, can be carried out simply. For example, the number of washing steps can be reduced. The conditions for the above drying treatment can be set, for example, from the viewpoint of obtaining shells that are of low density and have excellent flexibility. The drying temperature may be, for example, 50°C to 120°C, and preferably 90°C or higher. The drying time is preferably 3 hours to 48 hours. Drying may be carried out continuously or in multiple stages. When drying is carried out in multiple stages, the above drying time is the sum of the drying times for each stage.

[0069] In one embodiment of the present invention, the hollow particles are used as a functional agent for a resin material. A resin composition containing the hollow particles will be described below.

[0070] B. Resin Composition The resin composition in one embodiment of the present invention comprises the hollow particles and the resin. In the resin composition, the hollow state of the hollow particles can be well maintained. Furthermore, in a resin molded article that can be molded using the resin composition, the hollow state of the hollow particles can be well maintained.

[0071] The above-mentioned resin can be any suitable resin selected depending on the intended use of the resulting resin composition. For example, the resin may be a thermoplastic resin or a thermosetting resin. Specific examples of resins include epoxy resins, polyimide resins, polyamide resins, polyamide-imide resins, polyetheretherketone resins, polyester resins, polyhydroxypolyether resins, polyolefin resins, fluororesins, liquid crystal polymers, and modified polyimides. These can be used individually or in combination of two or more.

[0072] The content of the hollow particles in the above resin composition is preferably 0.1% by volume or more, and more preferably 0.5% by volume or more. On the other hand, the content is preferably 90% by volume or less, and more preferably 85% by volume or less.

[0073] In the resin composition, it is preferable to contain 0.5 parts by volume or more of hollow particles per 100 parts by volume of resin, and more preferably 1 part by volume or more. On the other hand, it is preferable to contain 300 parts by volume or less of hollow particles per 100 parts by volume of resin, and more preferably 200 parts by volume or less.

[0074] The above resin composition may contain optional components. Examples of optional components include curing agents, stress-reducing agents, colorants, adhesion enhancers, release agents, flow regulators, defoaming agents, solvents, and fillers. These may be used individually or in combination of two or more. In one embodiment, the resin composition contains a curing agent. The content of the curing agent may be, for example, 1 to 150 parts by weight per 100 parts by weight of resin.

[0075] Any suitable method can be used to produce the above-mentioned resin composition. Specifically, the resin composition can be obtained by dispersing the above-mentioned hollow particles in the resin using any suitable dispersion method. Examples of dispersion methods include dispersion using various stirrers such as homomixers, dispersers, and ball mills; dispersion using a rotary-orbit mixer; dispersion using shear force with a three-roll system; and dispersion using ultrasonic treatment.

[0076] The above resin composition can typically be a resin molded article formed into a desired shape. For example, it can be a resin molded article formed into a desired shape using a mold. During the molding of the resin article, the resin composition can be subjected to any appropriate treatment. For example, the resin composition can be subjected to a curing treatment.

[0077] C. High-Frequency Circuit Board A high-frequency circuit board in one embodiment of the present invention includes the above-mentioned hollow particles. According to the embodiment of the present invention, the high-frequency circuit board can be used, for example, in equipment with an operating frequency of 300 MHz or higher. For example, the high-frequency circuit board may be formed from the above-mentioned resin composition. Alternatively, for example, the high-frequency circuit board may include the above-mentioned hollow particles and a material selected from glass epoxy resin, polyimide resin, liquid crystal polymer, aromatic hydrocarbon resin, modified polyphenylene ether resin, fluororesin, and ceramics.

[0078] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" and "ppm" are based on weight.

[0079] [Example 1] (Preparation of core particles) Raw material A was prepared by adding deionized water to 125 ml of 1 M aluminum sulfate aqueous solution and 18.47 g of sodium sulfate powder to make up to 500 ml. Raw material A was stirred while being kept at 40°C, and 117 ml of 3.7 N sodium hydroxide aqueous solution was added to it. Then, the mixture of raw material A and sodium hydroxide aqueous solution was stirred under pressure at 170°C in an autoclave for 2 hours. The slurry thus obtained was filtered using a Nutsche filter to obtain an alunite cake. After washing the obtained cake, the cake was collected and dried at 105°C for 12 hours or more. Then, the dried material was sieved to obtain alunite powder. The median diameter (D50) of the obtained alunite powder was measured in accordance with JIS R 1629 using a particle size distribution analyzer (Microtrac-Bell Co., Ltd., "MT3000II") and was found to be 1.9 μm.

[0080] (Preparation of Hollow Silica Particles) TEOS was diluted with ethanol to prepare 125 ml of a 4 M TEOS solution. Additionally, 0.5 g of a high-molecular-weight polycarboxylic acid compound (NOF Co., Ltd., "Marialim SC-1015F") was added as a dispersant, along with 67 ml of 14.8 M aqueous ammonia, 250 ml of ethanol, and 8 ml of deionized water. These were mixed in a stirrer to obtain a mixture, to which 100 g of the obtained Alnite powder was added to obtain an Alnite dispersion. While stirring the Alnite dispersion, the entire amount of the prepared TEOS solution was added. Next, while stirring the Alnite dispersion with the added TEOS solution, 25 ml of deionized water was added to obtain a reaction slurry. The pH of the reaction slurry was confirmed to be above 10.5. After filtering the obtained reaction slurry, the resulting cake was washed, collected, and dried at 60°C for 4 hours to obtain core-shell powder.

[0081] Next, the obtained core shell powder was calcined at 500°C for 4 hours. It is believed that the alunite in the core changed as follows during calcination, resulting in a core shell weight loss of approximately 18%. NaAl ３ (SO ４ ) ２ (OH) ６ →NaAl(SO ４ ) ２ +Al ２ O ３ +3H ２ O

[0082] Next, deionized water was added to the calcined core shell powder, stirred to resuspend it, and sulfuric acid was added to this to a final concentration of 1 M. The mixture was heated to 90°C to dissolve the core and obtain a hollow silica precursor slurry. The obtained hollow silica precursor slurry was filtered using a Nutsche filter to obtain a hollow silica precursor cake. After washing the obtained cake, the cake was collected and dried at 105°C for 24 hours to obtain hollow silica precursor powder.

[0083] Next, the obtained hollow silica precursor powder was calcined at 800°C for 1 hour in an air atmosphere, and then calcined at 1100°C for 1 hour. The calcined material was then pulverized to obtain hollow silica particles.

[0084] [Example 2] Hollow silica particles were obtained in the same manner as in Example 1, except that the amount of 4M TEOS solution added was 160 ml.

[0085] [Example 3] Hollow silica particles were obtained in the same manner as in Example 1, except that the amount of 4M TEOS solution added was 210 ml.

[0086] [Example 4] 100 g of Alnite particles were suspended in 675 ml of deionized water to obtain a slurry of Alnite particles.

[0087] Next, the obtained arunite particle slurry is heated to 90°C while being stirred, and then 0.5 M No. 3 water glass (Na) is added to it. ２ O・3.14SiO ２ 73.12 ml of (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The slurry thus obtained was aged for 1 hour, then dehydrated and washed with water to obtain a cake of core-shell particle precursor 1.

[0088] Next, the obtained core-shell particle precursor 1 cake was suspended in 675 ml of deionized water and heated to 90°C while stirring. 73.12 ml of 0.5 M No. 3 water glass was added to this. The resulting slurry was aged for 1 hour, then left for 15 hours while stirring, after which it was dehydrated and washed with water to obtain the core-shell particle precursor 2 cake. The obtained core-shell particle precursor 2 cake was suspended in 675 ml of deionized water and heated to 90°C while stirring. 73.12 ml of 0.5 M No. 3 water glass was added to this. The resulting slurry was aged for 1 hour, then dehydrated and washed with water, and then dried at 105°C for 1 day to obtain core-shell particle powder.

[0089] Next, the obtained core-shell particle powder was calcined at 500°C for 3 hours, and then at 550°C for 1 hour. It is believed that the alunite particles underwent the following changes during calcination: NaAl ３ (SO ４ ) ２ (OH) ６ →NaAl(SO ４ ) ２ +Al ２ O ３+3H ２ O

[0090] Next, 101.4 g of calcined core-shell particles were added to 1000 ml of deionized water and resuspended under stirring at room temperature. 866 ml of 1.1 N sulfuric acid was then added, and the mixture was heated to 90°C and reacted for 5 hours to dissolve the core particles, obtaining a slurry of hollow silica precursor 1. The obtained slurry of hollow silica precursor 1 was dehydrated and washed with water to obtain a cake of hollow silica precursor 1.

[0091] Next, the resulting hollow silica precursor 1 cake was suspended in 1000 ml of deionized water and heated to 90°C while stirring. 5.49 ml of 0.5 M No. 3 water glass was added, followed by 27.43 ml of 0.5 M No. 3 water glass and 42.99 ml of 0.5 N sulfuric acid. The resulting slurry was aged for 30 minutes, then dehydrated and washed with water to obtain the hollow silica precursor cake. This same procedure was repeated two more times to obtain the hollow silica precursor 2 cake.

[0092] Next, 675 ml of deionized water and 46 ml of 2N sulfuric acid were added to the resulting hollow silica precursor 2 cake and left at 90°C for 1.5 hours to obtain a slurry of hollow silica precursor 3. After that, the cake was dehydrated and washed with water, and dried at 105°C for 1 day to obtain a powder of hollow silica precursor 3.

[0093] Next, the obtained hollow silica precursor 3 powder was calcined at 900°C for 2 hours in an air atmosphere to obtain hollow silica particles.

[0094] [Example 5] Hollow silica particles were obtained in the same manner as in Example 4, except that the total amount of 0.5 M No. 3 water glass added to hollow silica precursor 1 was 60.16 ml.

[0095] [Comparative Example 1] Hollow silica particles were obtained in the same manner as in Example 4, except that the total amount of 0.5 M No. 3 water glass added to the hollow silica precursor 1 was 144.54 ml, and the number of times the 0.5 M No. 3 water glass was added to the hollow silica precursor 1, i.e., the number of repetitions described above, was a total of 2 times.

[0096] [Example 6] (Preparation of core particles) Raw material A was prepared by adding deionized water to 158 ml of 1 M aluminum sulfate aqueous solution, 22.48 g of sodium sulfate powder, and 3.80 g of citric acid to make up to 514 ml. Raw material A was stirred while being kept at 40°C, and 186 ml of 3.4 N sodium hydroxide aqueous solution was added to it. Then, the mixture of raw material A and sodium hydroxide aqueous solution was stirred under pressure at 130°C for 2 hours using an autoclave. The slurry thus obtained was filtered using a Nutsche filter to obtain an alunite cake. After washing the obtained cake, the cake was collected and dried at 105°C for 12 hours or more. Then, the dried material was sieved to obtain alunite powder. Furthermore, the obtained arunite powder was measured using a particle size distribution analyzer (Microtrac-Bell Co., Ltd., "MT3000EXII") in accordance with JIS R 1629, and the volume-based median diameter (D50) was found to be 0.8 μm.

[0097] (Preparation of Hollow Silica Particles) TEOS was diluted with ethanol to prepare 125 ml of a 4 M TEOS solution. Additionally, 0.5 g of a high-molecular-weight polycarboxylic acid compound (NOF Co., Ltd., "Marialim SC-1015F") was added as a dispersant, along with 67 ml of 14.8 M aqueous ammonia, 250 ml of ethanol, and 8 ml of deionized water. These were mixed in a stirrer to obtain a mixture, to which 100 g of the obtained Alnite powder was added to obtain an Alnite dispersion. While stirring the Alnite dispersion, the entire amount of the prepared TEOS solution was added. Next, while stirring the Alnite dispersion with the added TEOS solution, 25 ml of deionized water was added to obtain a reaction slurry. The pH of the reaction slurry was confirmed to be above 10.5. After filtering the obtained reaction slurry, the resulting cake was washed, collected, and dried at 60°C for 4 hours to obtain core-shell powder.

[0098] Next, the obtained core shell powder was calcined at 500°C for 4 hours. Ion-exchanged water was added to the calcined core shell powder, stirred and resuspended, and sulfuric acid was added to this to a final concentration of 1 M. The mixture was heated to 90°C to dissolve the core and obtain a hollow silica precursor slurry. The obtained hollow silica precursor slurry was filtered using a Nutsche filter to obtain a hollow silica precursor cake. After washing the obtained cake, the cake was collected and dried at 105°C for 24 hours to obtain hollow silica precursor powder.

[0099] Next, the obtained hollow silica precursor powder was calcined at 800°C for 1 hour in an air atmosphere, then at 900°C for 1 hour, and the calcined material was pulverized to obtain hollow silica particles.

[0100] [Example 7] Hollow silica particles were obtained in the same manner as in Example 6, except that the hollow silica precursor powder was calcined at 800°C for 1 hour, and then calcined at 1100°C for 1 hour.

[0101] <XRD Measurement> The hollow silica particles in each example and comparative example were analyzed by X-ray diffraction (using "EMPYRIAN" manufactured by PANallytical), and were found to be amorphous silica.

[0102] <FE-SEM Observation> Hollow silica particles in each example and comparative example were observed at a magnification of 5000x using a scanning electron microscope (JEOL Ltd.'s "JSM-7600F"). As a representative example, the observation results for the hollow silica particles of Example 1 are shown in Figure 2.

[0103] Furthermore, the aspect ratio of the hollow silica particles was calculated from the observation results of the hollow silica particles in Example 6. More specifically, 100 hollow silica particles were randomly selected from scanning electron microscope (SEM) images, and the average minor diameter, standard deviation of the minor diameter, average major diameter, and standard deviation of the major diameter of these hollow silica particles were calculated. For the hollow silica particles, the average minor diameter was 0.89 μm, the standard deviation of the minor diameter was 0.061 μm, the average major diameter was 0.98 μm, and the standard deviation of the major diameter was 0.090 μm. Subsequently, the average value of the average major diameter of the hollow silica particles relative to the average minor diameter of the hollow silica particles was calculated as the aspect ratio. The aspect ratio (average major diameter / average minor diameter) of the hollow silica particles in Example 6 was 1.11.

[0104] Furthermore, the core particles (alunite) prepared in Example 6 were observed at magnifications of 10,000x and 20,000x using a scanning electron microscope (JEOL Ltd.'s "JSM-7600F"). Figure 4 shows the observation results of the core particles of Example 6 at a magnification of 10,000x, and Figure 5 shows the observation results of the core particles of Example 6 at a magnification of 20,000x. Subsequently, the particle size of the core particles was measured using a laser diffraction particle size distribution analyzer (Microtrac-Bell, "MT-3300EX-II"). Specifically, the median diameter (D50) of the number distribution was measured by wet dispersion and used as the particle size. The obtained number distribution is shown in Figure 6.

[0105] <TEM Observation> Hollow silica particles from each example and comparative example were observed at a magnification of 10,000x using a transmission electron microscope (JEM-2100PLUS manufactured by JEOL Ltd.). In all cases, it was confirmed that the particles were hollow particles that maintained the shape of the core particles. As a representative example, the observation results of the hollow silica particles from Example 1 are shown in Figure 3.

[0106] The hollow silica particles in each example and comparative example were also evaluated as follows. The evaluation results are summarized in Table 1. 1. Particle size The particle size was measured using a dry laser diffraction particle size distribution analyzer (Seishin Corporation, "LMS-3000"). Specifically, the median diameter (D50) of the number distribution was measured by dry dispersion and defined as the particle size. 2. Shell thickness of hollow particles The shell thickness of the particles was calculated by TEM observation. Specifically, the shell thickness of 20 primary particles randomly selected from the TEM images of the particles was measured, and the arithmetic mean (average thickness) of the obtained measurements was calculated. The magnification of the TEM observation was 20,000x. 3. BET specific surface area The specific surface area was measured using Microtrac-Bell Co., Ltd.'s "BELsorb-mini". Specifically, it was measured using a constant-volume gas adsorption method with nitrogen gas, and the specific surface area was determined by analysis using the BET multipoint method. 4. 1. Density The density was measured using the nitrogen gas displacement method with the "BELPYCNO MICROTRAC MRB" density measuring device from Microtrac-Bell Co., Ltd. 5. Dielectric Constant The dielectric constant was measured using the cavity resonance method with a dielectric constant measuring device for powders. The measurement was performed at a temperature of 25°C, a humidity of 44% RH, and a frequency of 10 GHz. The density required for calculating the dielectric properties was the density value obtained by the nitrogen gas displacement method described above. 6. Compression Displacement The compression displacement was measured using a micro-compression tester ("MCT-510" manufactured by Shimadzu Corporation) under the following conditions: ・Test type: Compression test ・Surface detection mode: Soft surface detection mode ・Test force: 0.20 mN ・Loading speed: 0.0089 mN / sec ・Target particle size: 2 μm ・Upper pressure indenter: Flat Φ20 μm ・Number of tests: 10 7. Average particle diameter of compressed displacement measured particles The average particle diameter of the 10 particles on which the compressed displacement was measured was calculated. 8. Strain rate immediately before fracture This was calculated by dividing the compressed displacement by the average particle diameter of the compressed displacement measured particles. 9. Fracture strength The fracture strength was measured using a micro-compression tester ("MCT-510" manufactured by Shimadzu Corporation) with a length measuring kit and a side observation kit. Specifically, a minute amount of the sample was scattered on the lower pressure plate, and fracture tests were performed on each particle under the following conditions.- Test force: 0.980 mN - Loading speed: 0.0223 mN / sec - Upper pressure indenter: flat φ20 μm Measurements were taken for 10 particles, and the fracture strength Cs (MPa) was calculated from the particle diameter d (mm) and the test force P (N) at the fracture point of the measured particles, and the average value was calculated. The fracture strength Cs was calculated from the following formula in JIS R 1639-5 "Method for measuring the properties of fine ceramic granules - Part 5: Single granule crushing strength": Cs = 2.48P / πd. ２10. Al Content The Al content was determined by preparing an Al content sample from hollow silica particles through pretreatment and analyzing it using inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. The hollow silica particles were then mixed with ultrapure water, and 3 ml of nitric acid and 5 ml of hydrofluoric acid were added and heated to dissolve them. After concentrating to 5 ml, a 1% boric acid aqueous solution was added to mask the remaining hydrofluoric acid and inactivate the solution to avoid damaging the analytical instrument, and then heated for 10 minutes. After cooling, the solution was diluted to 50 ml with ultrapure water to prepare an Al content sample, which was then subjected to analysis. The Al content percentage was calculated from the obtained results. 11. Na Content The Na content was determined by preparing a Na content sample from hollow silica particles through pretreatment and analyzing it using atomic absorption spectrometry (AAS). Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. The hollow silica particles were then mixed with ultrapure water, followed by the addition of 3 ml of nitric acid and 5 ml of hydrofluoric acid. The mixture was heated and dissolved, then concentrated to 5 ml. A 1% boric acid aqueous solution was added to mask the remaining hydrofluoric acid, inactivating the solution to avoid damaging the analytical instrument, and the mixture was heated for 10 minutes. After cooling, the solution was diluted to 50 ml with ultrapure water to prepare a sample for Na content measurement, which was then subjected to analysis. The Na content percentage was calculated from the obtained results. 12. Sulfate Ion Content The sulfate ion content was measured by preparing a sulfate ion content sample from the hollow silica particles using the pretreatment method, and then analyzing it by inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. Subsequently, the hollow silica particles were soaked in ultrapure water, then 3 ml of nitric acid and 5 ml of hydrofluoric acid were added and heated to dissolve them. After concentrating to 5 ml, a 1% boric acid aqueous solution was added to mask the remaining hydrofluoric acid and inactivate the solution to avoid damaging the analytical instrument, and then heated for 10 minutes. After cooling, the solution was diluted to 50 ml with ultrapure water to prepare a sample for sulfate ion content measurement, which was then subjected to analysis. The sulfate ion content was calculated from the obtained results. In the hollow silica particles of Example 7, the sulfate ion content was below the detection limit (less than 10 ppm, making measurement impossible).13. Fe Content The Fe content was determined by preparing a sample for Fe content measurement from hollow silica particles through pretreatment and analyzing it using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Specifically, 250 mg of hollow silica particles were weighed into a PMP resin beaker. The hollow silica particles were then mixed with ultrapure water, and 3 ml of nitric acid and 5 ml of hydrofluoric acid were added and heated to dissolve them. After concentrating to 5 ml, a 1% boric acid aqueous solution was added to mask the remaining hydrofluoric acid and inactivate it to avoid damaging the analytical instrument, and then heated for 10 minutes. After cooling, the sample for Fe content measurement was prepared by diluting it with ultrapure water to 50 ml and subjected to analysis. From the obtained results, the percentage of Fe content was calculated.

[0107]

[0108] If the value obtained by dividing the compressive displacement by the shell thickness is 0.0030 or higher, it was found to be a hollow particle with excellent impact resistance.

[0109] The hollow silica particles according to embodiments of the present invention can typically be suitably used in electronic materials. They can also be used, for example, as thermal insulation materials, soundproofing materials, shock-absorbing materials, stress-absorbing materials, lightweight materials, optical materials such as low-refractive-index films, and cosmetic materials.

[0110] 2. Hollow particle 4. Shell 6. Space (hollow part)

Claims

1. Hollow particles containing silica and composed of a hollow shell, wherein, as measured by a dry laser diffraction particle size distribution analyzer, the median diameter (D50) of the number distribution is 0.5 μm or more and 5 μm or less, and the value obtained by dividing the compressive displacement by the thickness of the shell is 0.0030 or more.

2. The hollow particle according to claim 1, wherein the strain rate immediately before fracture is 0.11 or greater.

3. The hollow particle according to claim 1, wherein the dielectric constant at 10 GHz is 1.7 or less.

4. The hollow particle according to claim 1, wherein the shell contains Fe, and the Fe content of the shell is 10 ppm or more and 50 ppm or less.

5. The hollow particle according to claim 1, wherein the density is 0.1 g / ml to 2.2 g / ml.

6. The hollow particle according to claim 1, wherein the fracture strength is 5 MPa to 100 MPa.

7. The hollow particle according to claim 1, wherein the thickness of the shell is 25 nm or more and 500 nm or less.

8. The hollow particle according to claim 1, wherein the silica is amorphous silica.

9. A resin composition comprising hollow particles according to any one of claims 1 to 8 and a resin.

10. A high-frequency circuit board comprising hollow particles according to any one of claims 1 to 8, and a material selected from glass epoxy resin, polyimide resin, liquid crystal polymer, aromatic hydrocarbon resin, modified polyphenylene ether resin, fluororesin, and ceramics.

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