Hollow silica particles and method for producing the same

Abstract

The present invention provides hollow silica particles which have low dielectric loss, while exhibiting good dispersibility in a resin. Each one of the hollow silica particles according to the present invention is provided with a shell layer that contains silica, while having an empty space inside the shell layer. With respect to the hollow silica particles, the intensity of a peak associated with SiOH around the wavenumber of 3,746 cm-1 as determined by infrared spectroscopy is 0.60 or less; the relative dielectric constant at 1 GHz is from 1.3 to 5.0; and the dielectric loss tangent at 1 GHz is from 0.0001 to 0.05.

Description

Technical Field

[0001] The present invention relates to hollow silica particles and a method for producing the same.

Background Art

[0002] In recent years, miniaturization of electronic devices, high-speed signals, and high-density wiring have been demanded. In order to meet this requirement, it is required to reduce the relative dielectric constant, dielectric loss tangent, and thermal expansion of insulating resin sheets such as adhesive films and prepregs, and resin compositions used for insulating layers formed on printed wiring boards.

[0003] In order to meet these requirements, studies have been conducted using hollow particles as fillers, and various proposals have been made. For example, Patent Document 1 describes a resin composition containing (A) an epoxy resin, (B) a curing agent, (C) hollow silica, and (D) fused silica. Further, Patent Document 2 describes a low dielectric resin composition containing hollow particles and a thermosetting resin, wherein the hollow particles are formed of silica in an amount of 98% by mass or more of the entire shell, the average porosity is 30 to 80% by volume, and the average particle diameter is 0.1 to 20 μm.

[0004] Also, various proposals have been made for hollow silica materials used as low relative dielectric constant materials. For example, Patent Document 3 proposes a hollow silica material having a closed cavity structure with a shell having pores, a cavity volume ratio of 0 to 86%, a relative dielectric constant of 1.5 to 3.3, a relative dielectric constant for flow in the 20 to 43.5 GHz frequency band of 1.5 to 3.3, and a dielectric loss tangent of 0.0005 to 0.004.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, when conventional hollow silica particles are added to a solvent, the solvent may penetrate into the particles, making it impossible to achieve the intended use. For example, when hollow silica particles are added to methyl ethyl ketone, the inside of the particles is impregnated with methyl ethyl ketone, increasing the viscosity of the composition, preventing the addition amount of the hollow silica particles from being increased, and making it impossible to achieve sufficient reduction in the relative dielectric constant.

[0007] In addition, in the hollow silica material described in Patent Document 3, in its examples, silica is coated on an inorganic compound of a template, and after removing the template, a silica sol is added and aged to obtain hollow silica particles. However, in this method, the inorganic compound of the template is likely to aggregate, and there are problems such as aggregation between primary particles and inability to control the aggregation diameter.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide new hollow silica particles having sufficiently small relative dielectric constant and dielectric loss tangent and excellent dispersibility. Means for Solving the Problems

[0009] The present invention relates to the following (1) to (13). (1) Hollow silica particles having a shell layer containing silica and having a space portion inside the shell layer, wherein the peak intensity derived from SiOH in the vicinity of a wave number of 3746 cm -1 by infrared spectroscopy is 0.60 or less, the relative dielectric constant at 1 GHz is 1.3 to 5.0, and the dielectric loss tangent at 1 GHz is 0.0001 to 0.05. (2) The density of the particles determined by density measurement using a dry pycnometer with helium gas is 2.00 to 2.30 g / cm 3The hollow silica particles according to (1) above. (3) The density of the particles determined by density measurement using a dry pycnometer with argon gas is 0.35 to 2.00 g / cm 3 The hollow silica particles according to (1) or (2) above. (4) The hollow silica particles according to any one of (1) to (3) above, wherein the average primary particle diameter is 50 nm to 10 μm. (5) The BET specific surface area is 1 to 300 m 2 / g. The hollow silica particles according to any one of (1) to (4) above. (6) The hollow silica particles according to any one of (1) to (5) above, wherein the sphericity is 0.75 to 1.0. (7) The hollow silica particles according to any one of (1) to (6) above, wherein the oil absorption amount is 15 to 1300 mL / 100 g. (8) The hollow silica particles according to any one of (1) to (7) above, wherein the median diameter of the secondary particles is 0.20 to 60 μm. (9) The hollow silica particles according to any one of (1) to (8) above, wherein the coarse particle diameter (D90) of the secondary particles is 1 to 100 μm. (10) The pore volume is 0.2 cm 3 / g or less. The hollow silica particles according to any one of (1) to (9) above. (11) The hollow silica particles according to any one of (1) to (10) above, wherein the surface of the hollow silica particles is surface-treated with a silane coupling agent. (12) The hollow silica particles according to any one of (1) to (11) above, wherein the hollow silica particles contain one or more metals M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba, and the concentration of the metal M contained in the hollow silica particles is 50 ppm by mass or more and 5% by mass or less. (13) A method for producing hollow silica particles, comprising forming a shell layer containing silica on the outer periphery of a core to obtain a hollow silica precursor, removing the core from the hollow silica precursor, performing heat treatment at 800 °C or higher, and surface-treating the particles after heat treatment with a silane coupling agent.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide hollow silica particles having a dense shell layer and having both a relative permittivity and a dielectric loss tangent that are sufficiently small. Since the solvent such as methyl ethyl ketone or N-methylpyrrolidone hardly penetrates into the hollow silica particles of the present invention, excellent low relative permittivity and low dielectric loss tangent can be exhibited even in a resin composition. Further, it has an appropriate aggregation diameter and is excellent in dispersibility in a resin.

Brief Description of Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described, but the present invention is not limited by the examples in the following description.

[0013] (Hollow Silica Particles) The hollow silica particles of the present invention include a shell layer containing silica and have a space portion inside the shell layer. The fact that the hollow silica particles have a space portion inside the shell layer can be confirmed by transmission electron microscope (TEM) observation or scanning electron microscope (SEM) observation. In the case of SEM observation, it can be confirmed that the particles are hollow by observing damaged particles with a part of them opened. Spherical particles having a space portion inside, which can be confirmed by TEM observation or SEM observation, are defined as "primary particles". In addition, since the primary particles are partially bonded to each other by a firing or drying process, the hollow silica particles obtained in the production are often an aggregate of secondary particles in which the primary particles are aggregated.

[0014] In this specification, the shell layer being "containing silica" means that silica (SiO 2) means containing 50 mass% or more. The composition of the shell layer can be measured by ICP emission spectrometry, flame atomic absorption spectrometry, etc. The silica contained in the shell layer is preferably 80 mass% or more, more preferably 95 mass% or more. The upper limit is theoretically 100 mass%. The silica contained in the shell layer is preferably less than 100 mass%, more preferably 99.99 mass% or less. Examples of the residue include alkali metal oxides and silicates, alkaline earth metal oxides and silicates, carbon, etc. In addition, "having a space part inside the shell layer" means a hollow state in which when observing the cross section of one primary particle, the shell layer surrounds the periphery of one space part. That is, one hollow particle has one large space part and a shell layer surrounding it.

[0015] The hollow silica particles of the present invention have a peak intensity derived from SiOH (silanol group) in the vicinity of a wave number of 3746 cm -1 by infrared spectroscopy of 0.60 or less, a relative permittivity at 1 GHz of 1.3 to 5.0, and a dielectric loss tangent at 1 GHz of 0.0001 to 0.05. By the peak intensity derived from SiOH in the vicinity of a wave number of 3746 cm -1 by infrared spectroscopy, the relative permittivity, and the dielectric loss tangent satisfying the above relationships, a substrate having low dielectric loss and sufficient to cope with high-frequency circuits can be provided.

[0016] The peak intensity derived from SiOH in the vicinity of a wave number of 3746 cm -1 by infrared spectroscopy is 0.60 or less. When the peak intensity derived from the SiOH is greater than 0.60, a component of the dielectric loss tangent derived from SiOH is likely to appear, and the dielectric loss tangent tends to deteriorate. The peak intensity derived from SiOH in the vicinity of the wave number of 3746 cm -1 is preferably 0.40 or less, more preferably 0.30 or less, still more preferably 0.20 or less, and particularly preferably 0.10 or less. The lower the peak intensity derived from SiOH in the vicinity of a wave number of 3746 cm -1 the lower the dielectric loss tangent can be reduced, so the lower the lower limit is, the better, and the lower limit is not particularly limited.

[0017] Here, "in the vicinity" means that in the case of the vicinity of a wavenumber of 3746 cm -1 the wavenumber at the peak center is 3746 cm -1 and the width before and after that is 14 cm -1 which refers to the range from a wavenumber of 3732 cm -1 to a wavenumber of 3760 cm -1 . The same applies to other wavenumbers.

[0018] The peak intensity derived from SiOH in the vicinity of a wavenumber of 3746 cm by infrared spectroscopy can be obtained by normalizing the absorption intensity of SiOH (in the vicinity of a wavenumber of 3746 cm) in the FT-IR spectrum by the peak intensity derived from various SiOHs in the vicinity of a wavenumber of 1060 cm -1 to 1. -1 -1

[0019] The hollow silica particles of the present invention have a relative permittivity of 1.3 to 5.0 at 1 GHz. In particular, in the measurement of the permittivity of powders, since the sample space becomes small and the measurement accuracy deteriorates at 10 GHz or higher, the present invention employs the measured value at 1 GHz. When the relative permittivity at 1 GHz is within the above range, the low relative permittivity required for electronic devices can be achieved. It is substantially difficult to synthesize hollow silica particles having a relative permittivity at 1 GHz of less than 1.3. The relative permittivity at 1 GHz preferably has a lower limit of 1.4 or more, more preferably 1.5 or more. The upper limit is preferably 4.5 or less, more preferably 4.0 or less, still more preferably 3.5 or less, particularly preferably 3.0 or less, and most preferably 2.5 or less.

[0020] In addition, the hollow silica particles of the present invention have a dielectric loss tangent of 0.0001 to 0.05 at 1 GHz. When the dielectric loss tangent at 1 GHz is 0.05 or less, the low relative permittivity required for electronic devices can be achieved. Also, it is substantially difficult to synthesize hollow silica particles having a dielectric loss tangent at 1 GHz of less than 0.0001. ​​The dielectric tangent at 1 GHz preferably has a lower limit of 0.0005 or more, more preferably 0.0006 or more. The upper limit is preferably 0.04 or less, more preferably 0.03 or less, still more preferably 0.02 or less, even more preferably 0.01 or less, particularly preferably 0.005 or less, and most preferably 0.003 or less.

[0021] The relative permittivity and the dielectric tangent can be measured by the perturbation method resonator method using a dedicated device (for example, "Vector Network Analyzer E5063A" manufactured by Keycom Co., Ltd.).

[0022] The density of the hollow silica particles of the present invention obtained by density measurement using a dry pycnometer using helium gas (hereinafter, also referred to as the helium pycnometer method) is 2.00 to 2.30 g / cm 3 It is preferably. From the density obtained by the helium pycnometer method, it can be determined whether or not the shell layer of the hollow silica particles has pores. When the density of the hollow silica particles obtained by the helium pycnometer method is 2.00 g / cm 3 or more, it can be seen that helium gas has penetrated into the particles and remains in the internal space, so it can be seen that the shell layer has pores.

[0023] When the density of the hollow silica particles obtained by the helium pycnometer method is 2.00 g / cm 3 or more, the shell layer becomes a dense silica layer, and the hollow silica particles are less likely to be damaged. When it is 2.30 g / cm 3 or less, it becomes amorphous silica with low crystallinity, and the relative permittivity can be suppressed low. The density of the hollow silica particles obtained by the helium pycnometer method preferably has a lower limit of 2.05 g / cm 3 or more, more preferably 2.07 g / cm 3 or more, still more preferably 2.09 g / cm 3 or more, particularly preferably 2.10 g / cm 3 or more, most preferably, and the upper limit is preferably 2.25 g / cm 3 or less.

[0024] And, the density of the hollow silica particles of the present invention, as determined by density measurement using a dry pycnometer with argon gas (hereinafter also referred to as the argon pycnometer method), is 0.35 to 2.00 g / cm 3 It is preferably that. Whether the hollow silica particles are hollow or not can be determined by the density determined by the argon pycnometer method. Since argon gas has a larger molecular size than helium gas, if the shell layer is dense, it cannot pass through the shell layer, and the apparent density of the particles is measured.

[0025] When the density of the hollow silica particles determined by the argon pycnometer method is 2.00 g / cm 3 or less, since the apparent density is smaller than the true density of silica (about 2.20 g / cm 3 ), it can be determined that there is a space inside the particles. Also, when the density is 0.35 g / cm 3 or more, the shell strength of the hollow silica particles can be maintained. Further, since the density determined by the argon pycnometer method is lower than the density determined by the helium pycnometer method, minute gas molecules can move in and out inside the hollow silica particles, so that the inside of the particles becomes normal pressure. In the case of particles having a very dense shell (hull) like a glass balloon, since there is a pressure difference between the inside of the particles and the atmosphere, when forming a resin composition, it is likely to be crushed when performing operations such as stirring and kneading. However, since the hollow silica particles of the present invention have a small pressure difference between the inside of the particles and the atmosphere, they are not easily crushed by the above operations.

[0026] From the viewpoint of the strength of the shell of the particles, the density of the hollow silica particles determined by the argon pycnometer method preferably has a lower limit of 0.40 g / cm 3 or more, more preferably 0.50 g / cm 3 or more, and most preferably 0.50 g / cm 3 or more. Also, from the viewpoint of maintaining the air content and suppressing the increase in the relative dielectric constant, the upper limit is more preferably 1.70 g / cm 3 or less, further preferably 1.60 g / cm3 The following is particularly preferred: 1.40 g / cm 3 The following is most preferred.

[0027] The apparent density of the hollow silica particles can also be measured using a pycnometer. Put the sample (hollow silica particles) and an organic solvent into the pycnometer, and measure after standing at 25°C for 48 hours. Depending on the density of the shell of the hollow silica particles, it may take time for the organic solvent to penetrate, so it is preferable to let it stand for the above-mentioned time. The result measured by this method corresponds to the result of density measurement using a dry pycnometer with argon gas.

[0028] The apparent density of the hollow silica particles of the present invention can be adjusted by adjusting the primary particle diameter and the shell thickness. By changing the density of the particles, it is possible to adjust whether they sink, continue to disperse, or float in the solvent. When it is desired to disperse in the solvent, it is desirable that the density of the solvent and the apparent density of the particles are close. For example, when it is desired to disperse in water with a density of 1.0 g / cm 3 it is preferable to adjust the apparent density of the particles to 0.8 g / cm 3 or more and 1.2 g / cm 3 or less.

[0029] In the sample of hollow silica particles, the ratio of complete hollow particles in which the shell layer is not damaged and there is a space inside is called the hollow particle ratio. Since the shell layer of the hollow silica particles of the present invention is dense, various solvents, argon gas, and gases with a dynamic molecular diameter larger than that of argon molecules are difficult to penetrate, but if there are particles with a damaged shell layer (damaged particles), they will penetrate inside. Therefore, the apparent density changes with the hollow particle ratio. The higher the hollow particle ratio, the lower the apparent density of the hollow silica sample, and the lower the hollow particle ratio, the higher the apparent density of the hollow silica sample. Utilizing this, when assuming a yield of 100%, the hollow particle ratio can be obtained from the theoretical density obtained from the charged amount of the raw material and the apparent density measured by a dry pycnometer. In addition, when manufacturing hollow silica particles, the hollow particle ratio can also be determined from the weight change during heat treatment using the cake after filtration before removing the oil core. When the cake after filtration is loosened and dried overnight, the oil component in the damaged particles volatilizes, while the oil component in the complete hollow particles is retained. Since the weight change amounts during heat treatment when all the charged oil components have volatilized (hollow particle ratio 0%) and when all are retained (hollow particle ratio 100%) can be calculated from the amount of raw material charged, the hollow particle ratio can be determined from the weight change when the sample dried overnight after filtration is heat-treated up to 800 °C.

[0030] The size of the primary particles of the hollow silica particles is determined by directly observing the particle diameter (diameter) through SEM observation. Specifically, the sizes of the primary particles of 100 particles are measured from the SEM image, and the distribution of the sizes of the primary particles obtained by aggregating them is estimated as the distribution of the sizes of the overall primary particles. The primary particle diameter of particles that are difficult to deflocculate can be directly measured by SEM observation. Since the size of this primary particle is reflected in the particle surface state of the aggregated particles, it is a parameter that determines the specific surface area and oil absorption amount.

[0031] The average value of the size of the primary particles (average primary particle diameter) is preferably in the range of 50 nm to 10 μm. When the average primary particle diameter is less than 50 nm, the specific surface area, oil absorption amount, and pore volume increase, the amount of SiOH and adsorbed water on the particle surface increase, and the dielectric loss tangent tends to increase. Also, when the average primary particle diameter is 10 μm or less, it is easy to handle as a filler. From the perspective of manufacturing reproducibility, the lower limit of the average primary particle diameter is more preferably 70 nm or more, most preferably 100 nm or more, and the upper limit is more preferably 5 μm or less, particularly preferably 3 μm or less.

[0032] The hollow silica particles preferably have a BET specific surface area of 1 to 300 m 2 / g. When the BET specific surface area is 1 m 2 / g or more, adhesion to the resin can be ensured when made into a resin composition, and 300 m 2When it is below / g, the oil absorption amount can be suppressed and the adsorbed water can be reduced. Since the BET specific surface area becomes smaller as the denser shell is formed, the BET specific surface area is preferably 200 m 2 / g or less, more preferably 100 m 2 / g or less, even more preferably 50 m 2 / g or less, particularly preferably 30 m 2 / g or less, most preferably. Also, the BET specific surface area is more preferably 2 m 2 / g or more, most preferably 3 m 2 / g or more.

[0033] The value of the specific surface area is proportional to the primary particle diameter of the hollow silica and the thickness of the shell. When the radius of the primary particle is r and the thickness of the shell is d, the value of the BET specific surface area is 3r 2 / (r 3 -(r - d) 3 ) × 2.2 or more is preferable.

[0034] Here, the measurement of the BET specific surface area can be carried out by using a specific surface area measuring device (for example, "TriStar II 3020" manufactured by Shimadzu Corporation). After drying the hollow silica particles at 230 °C until it reaches 50 mTorr as a pretreatment, it can be measured by the multipoint method using liquid nitrogen.

[0035] The sphericity of the hollow silica particles is preferably 0.75 to 1.0. When the sphericity is low, the hollow silica particles are likely to be damaged, the density by the argon pycnometer method decreases, the specific surface area increases, and the dielectric tangent may increase. The sphericity can be represented by the average value calculated by measuring the maximum diameter (DL) and the minor axis (DS) orthogonal to it for any 100 particles in the photographic projection diagram obtained by photographing with a scanning electron microscope (SEM). From the viewpoints of light scattering property, touch feeling, etc., the sphericity is more preferably 0.80 or more, further preferably 0.82 or more, still further preferably 0.83 or more, particularly preferably 0.85 or more, especially preferably 0.87 or more, and most preferably 0.90 or more.

[0036] The shell thickness of the hollow silica particles is preferably 0.01 to 0.3 with respect to the diameter 1 of the primary particles. If the shell thickness is less than 0.01 with respect to the diameter 1 of the primary particles, the strength of the hollow silica particles may decrease. If this ratio is greater than 0.3, the internal space part becomes small, and the characteristics due to the hollow shape will not appear. The shell thickness is more preferably 0.02 or more with respect to the diameter 1 of the primary particles, further preferably 0.03 or more, and more preferably 0.2 or less, further preferably 0.1 or less.

[0037] Here, the shell thickness is determined by measuring the shell thickness of individual particles with a transmission electron microscope (TEM).

[0038] Since the hollow silica particles have a space part inside, substances can be encapsulated inside the particles. Although the shell layer of the hollow silica particles of the present invention is dense and various solvents hardly penetrate, if there are damaged particles, the solvent will penetrate into the inside. Therefore, the oil absorption amount changes depending on the ratio of damaged particles.

[0039] The oil absorption amount of the hollow silica particles is preferably 15 to 1300 mL / 100 g. When the oil absorption amount is 15 mL / 100 g or more, the adhesion to the resin can be ensured when used in the resin composition. When it is 1300 mL / 100 g or less, the strength of the resin can be guaranteed when used in the resin composition, and the viscosity of the composition can be reduced. Since the viscosity increases when the oil absorption amount is large, the oil absorption amount of the hollow silica particles is more preferably 1000 mL / 100 g or less, even more preferably 700 mL / 100 g or less, particularly preferably 500 mL / 100 g or less, and most preferably 200 mL / 100 g or less. Further, since the adhesion between the powder and the resin may deteriorate when the oil absorption amount is too low, it is more preferably 20 mL / 100 g or more.

[0040] In addition, from the relationship between the ratio of damaged particles and the oil absorption amount as described above, the oil absorption amount can be adjusted by adjusting the ratio of damaged particles. Further, since the space between primary particles is also a space that can hold oil, it is considered that the oil absorption amount increases when the median diameter of secondary particles in which primary particles are aggregated is large, and the oil absorption amount decreases when the median diameter of secondary particles is small.

[0041] The median diameter of the secondary particles of the hollow silica particles is preferably 0.20 to 60 μm. If the median diameter is too small, the viscosity may increase or the dispersibility may deteriorate when forming a resin composition. Therefore, it is preferably 0.20 μm or more, more preferably 0.25 μm or more, and even more preferably 0.30 μm or more. Further, if the median diameter is too large, it may cause graininess when the resin composition is formed into a film. Therefore, it is preferably 60 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, particularly preferably 20 μm or less, and most preferably 10 μm or less.

[0042] The particle size of the secondary particles (the aggregation diameter at the time of aggregation of primary particles) is preferably measured by laser scattering. This is because when measuring the aggregation diameter by SEM, the boundary between particles is unclear and it does not reflect the dispersion in a wet state. Also, in the measurement by a Coulter counter, the electric field change between hollow particles and solid particles is different, and it is difficult to obtain a numerical value corresponding to solid particles.

[0043] The coarse particle size (D90) of the secondary particles of the hollow silica particles is preferably 1 to 100 μm. When producing particles with a small coarse particle size, it is necessary to lower the concentration of the silica source in the reaction solution, which deteriorates productivity. Therefore, from the perspective of production efficiency, the coarse particle size is preferably 1 μm or more. Also, if the coarse particle size is too large, it will cause graininess when the resin composition is formed into a film, so it is preferably 100 μm or less. The lower limit of the coarse particle size is more preferably 3 μm or more, most preferably 5 μm or more, and the upper limit is more preferably 70 μm or less, even more preferably 60 μm or less, particularly preferably 50 μm or less, and most preferably 30 μm or less.

[0044] Note that, as described above, the coarse particle size is determined by measuring the particle size of the secondary particles by laser scattering.

[0045] The pore volume of the hollow silica particles is preferably 0.2 cm 3 / g or less. If the pore volume is larger than 0.2 cm 3 / g, it becomes easier to adsorb moisture, and the dielectric loss of the resin composition may deteriorate. The pore volume is more preferably 0.15 cm 3 / g or less, even more preferably 0.1 cm 3 / g or less, particularly preferably 0.05 cm 3 / g or less.

[0046] The surface of the hollow silica particles is preferably treated with a silane coupling agent. When the surface of the hollow silica particles is treated with a silane coupling agent, the remaining amount of surface silanol groups decreases, the surface is hydrophobized, moisture adsorption is suppressed, and the dielectric loss can be improved. At the same time, when making a resin composition, the affinity with the resin is improved, and the dispersibility and the strength after resin film formation are improved.

[0047] Examples of the silane coupling agent include aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, organosilazane compounds, etc. The silane coupling agent may be used alone or in combination of two or more kinds.

[0048] The adhesion amount of the silane coupling agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, still more preferably 2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, still more preferably 5 parts by mass or less with respect to 100 parts by mass of the particles of the hollow silica particles.

[0049] Whether the surface of the hollow silica particles is treated with the silane coupling agent can be confirmed by detecting the peak due to the substituent of the silane coupling agent by IR. Further, the adhesion amount of the silane coupling agent can be measured by measuring the carbon amount or thermogravimetric measurement (TG).

[0050] The hollow silica particles preferably contain at least one metal M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba. When the metal M is contained in the hollow silica particles, it acts as a flux during firing, and the specific surface area can be reduced to lower the dielectric tangent. The metal M is contained during the reaction step to the washing step in the production of the hollow silica particles. For example, in the reaction step, the metal salt of the metal M is added to the reaction solution when forming the shell of silica, or the hollow silica precursor is washed with a solution containing the metal ions of the metal M before sintering, whereby the hollow silica particles can contain the metal M.

[0051] The concentration of metal M contained in the hollow silica particles is preferably 50 mass ppm or more and 5 mass% or less. When the concentration of metal M is 50 mass ppm or more, the condensation of the bonded silanol groups is promoted by the flux effect during firing, and the remaining silanol groups can be reduced, so the dielectric loss tangent can be decreased. If the concentration of metal M is too high, the amount of components that react with silica to form silicate increases, and the hygroscopicity of the hollow silica particles may deteriorate. Therefore, it is preferably contained at 5 mass% or less. The concentration of metal M is more preferably 100 mass ppm or more, still more preferably 150 ppm or more, and preferably 1 mass% or less, preferably 5000 mass ppm or less, and most preferably 1000 mass ppm or less.

[0052] The measurement method of metal M can be carried out by adding perchloric acid and hydrofluoric acid to the hollow silica particles, heating strongly to remove the main component silicon, and then measuring by ICP emission spectrometry. In addition, when an alkali metal silicate is used as the silica raw material, the carbon (C) component derived from the raw material in the shell layer of the obtained hollow silica particles is less than when a silicon alkoxide is used as the silica raw material.

[0053] (Method for producing hollow silica particles) As a method for producing the hollow silica particles of the present invention, for example, there is a method in which an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is used, a hollow silica precursor is obtained in the emulsion, and hollow silica particles are obtained from this precursor. This oil-in-water emulsion is an emulsion in which the oil phase is dispersed in water. When a silica raw material is added to this emulsion, the silica raw material adheres to the oil droplets, and oil core-silica shell particles can be formed.

[0054] The method for producing hollow silica particles of the present invention includes forming a shell layer containing silica on the outer periphery of a core to obtain a hollow silica precursor, removing the core from the hollow silica precursor, performing heat treatment at 800 °C or higher, and subjecting the particles after heat treatment to surface treatment with a silane coupling agent. When obtaining the hollow silica precursor, it is preferable to add a first silica raw material to a water-in-oil emulsion containing an aqueous phase, an oil phase, and a surfactant to form a first-stage shell, and then add a second silica raw material to the emulsion in which the first-stage shell has been formed to form a second-stage shell, thereby obtaining a hollow silica precursor. Hereinafter, the water-in-oil emulsion may also be simply referred to as an emulsion. Also, a dispersion in which oil-core silica shell particles generated by adding the first silica raw material and before adding the second silica raw material are dispersed, and a dispersion in which oil-core silica shell particles after adding the second silica raw material are dispersed may also be referred to as an emulsion. The latter dispersion in which oil-core silica shell particles after adding the second silica raw material are dispersed may be equivalent to the hollow silica precursor dispersion.

[0055] <Formation of the first-stage shell> First, a first silica raw material is added to a water-in-oil emulsion containing an aqueous phase, an oil phase, and a surfactant to form a first-stage shell.

[0056] The aqueous phase of the emulsion mainly contains water as a solvent. Additives such as water-soluble organic liquids and water-soluble resins may be further added to the aqueous phase. The proportion of water in the aqueous phase is preferably 50 to 100% by mass, more preferably 90 to 100% by mass.

[0057] The oil phase of the emulsion preferably contains a water-insoluble organic liquid that is immiscible with the aqueous phase components. This organic liquid forms droplets in the emulsion and forms the oil-core portion of the hollow silica precursor.

[0058] Examples of the organic liquid include aliphatic hydrocarbons such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, n-nonane, isononane, n-pentane, isopentane, n-decane, isodecane, n-dodecane, isododecane, pentadecane, or paraffinic base oils which are mixtures thereof; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclohexene, or naphthenic base oils which are mixtures thereof; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, mesitylene, tetralin, styrene; ethers such as propyl ether, isopropyl ether; esters such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, butyl lactate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate; vegetable oils such as palm oil, soybean oil, rapeseed oil; fluorinated solvents such as hydrofluorocarbon, perfluorocarbon, perfluoropolyether, etc. Further, polyoxyalkylene glycol which becomes a hydrophobic liquid at the shell-forming reaction temperature can also be used. For example, polypropylene glycol (molecular weight 1000 or more), polyoxyethylene-polyoxypropylene block copolymers in which the proportion of oxyethylene units is less than 20% by mass and the cloud point (1% by mass aqueous solution) is 40°C or lower, preferably 20°C or lower, etc. can be mentioned. Among them, polyoxypropylene-polyoxyethylene-polyoxypropylene type block copolymers are preferably used. These may be used alone or in combination of two or more within the range of forming an oil phase in a single phase.

[0059] As the organic liquid, hydrocarbons having 8 to 16 carbon atoms, particularly 9 to 12 carbon atoms, are preferred. The organic liquid is selected by comprehensively considering operability, safety with respect to fire, separability between the hollow silica precursor and the organic liquid, shape characteristics of the hollow silica particles, solubility of the organic liquid in water, and the like. The hydrocarbon having 8 to 16 carbon atoms may be a linear, branched or cyclic hydrocarbon as long as its chemical stability is good, and hydrocarbons having different carbon numbers may be mixed and used. As the hydrocarbon, a saturated hydrocarbon is preferred, and a linear saturated hydrocarbon is more preferred.

[0060] As the flash point of the organic liquid, those of 20°C or higher are preferred, and those of 40°C or higher are more preferred. When using an organic liquid having a flash point of less than 20°C, since the flash point is too low, measures for fire prevention and working environment are required.

[0061] The emulsion contains a surfactant in order to enhance the emulsion stability. The surfactant is preferably water-soluble or water-dispersible, and is preferably added to the aqueous phase for use. Preferably, it is a nonionic surfactant. Examples of the nonionic surfactant include the following surfactants. Polyoxyethylene-polyoxypropylene copolymer type surfactant, Polyoxyethylene sorbitan fatty acid ester type surfactants: polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, Polyoxyethylene higher alcohol ether type surfactants: polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, Polyoxyethylene aliphatic ester type surfactants: polyoxyethylene glycol monolaurate, polyoxyethylene glycol monostearate, polyoxyethylene glycol monooleate, Glycerin fatty acid ester surfactants: monoglyceride stearate, monoglyceride oleate. Furthermore, polyoxyethylene sorbitol fatty acid ester surfactants, sucrose fatty acid ester surfactants, polyglycerin fatty acid ester surfactants, polyoxyethylene hydrogenated castor oil surfactants, etc. may also be used. These may be used alone or in combination of two or more.

[0062] Among the above nonionic surfactants, polyoxyethylene-polyoxypropylene copolymer surfactants can be preferably used. The polyoxyethylene-polyoxypropylene copolymer is a block copolymer in which a polyoxyethylene block (EO) and a polyoxypropylene block (PO) are bonded. Examples of the block copolymer include EO-PO-EO block copolymers and EO-PO block copolymers, and preferably EO-PO-EO block copolymers. The proportion of oxyethylene units in the EO-PO-EO block copolymer is preferably 20% by mass or more, and more preferably 30% by mass or more. The weight average molecular weight of the polyoxyethylene-polyoxypropylene copolymer is preferably 3,000 to 27,000, and more preferably 6,000 to 19,000. With respect to the entire polyoxyethylene-polyoxypropylene copolymer, the total amount of the polyoxyethylene block is preferably 40 to 90% by mass, and the total amount of the polyoxypropylene block is preferably 10 to 60% by mass.

[0063] The amount of surfactant used varies depending on conditions such as the type of surfactant, the HLB (Hydrophile - lipophile balance), which is an index representing 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, and more preferably 1,000 to 10,000 ppm by mass. At 500 ppm by mass or more, the emulsion can be more stabilized. Also, at 20,000 ppm by mass or less, the amount of surfactant remaining in the hollow silica particles can be reduced.

[0064] The aqueous phase and the oil phase may be blended in a mass ratio of 200:1 to 5:1, preferably 100:1 to 9:1.

[0065] The method for preparing the oil - in - water emulsion is not limited to the following. The aqueous phase and the oil phase can be prepared in advance, and the oil phase is added to the aqueous phase and sufficiently mixed or stirred to prepare it. Furthermore, methods such as ultrasonic emulsification, stirring - type emulsification, and high - pressure emulsification, which apply a physically strong shear force, can be applied. Also, there are methods such as membrane emulsification in which the oil phase made fine through a membrane with fine pores is dispersed in the aqueous phase, phase - inversion emulsification in which the surfactant is dissolved in the oil phase and then the aqueous phase is added for emulsification, and phase - inversion temperature emulsification that utilizes the change of the surfactant from water - soluble to oil - soluble at a temperature near the cloud point. These emulsification methods can be appropriately selected according to the specification of the target particle size, particle size distribution, etc. In order to reduce the particle size of the obtained hollow silica particles and narrow the particle size distribution, it is preferable that the oil phase is sufficiently dispersed and emulsified in the aqueous phase. 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.

[0066] In the step of forming the first - stage shell, a first silica raw material is added to the oil - in - water emulsion. As the first silica raw material, for example, an aqueous solution in which water-soluble silica is dissolved, an aqueous dispersion in which solid silica is dispersed, a mixture thereof, and one or more selected from the group consisting of alkali metal silicates, active silica, and silicon alkoxides, or an aqueous solution or aqueous dispersion thereof can be mentioned. Among these, one or more selected from the group consisting of alkali metal silicates, active silica, and silicon alkoxides, or an aqueous solution or aqueous dispersion thereof are preferable in terms of high availability.

[0067] Examples of the solid silica include silica sol obtained by hydrolyzing an organosilicon compound and commercially available silica sol. Examples of the alkali metal of the alkali metal silicate include lithium, sodium, potassium, rubidium, etc. Among them, sodium is preferable due to easy availability and economic reasons. That is, sodium silicate is preferable as the alkali metal silicate. Sodium silicate has a composition represented by Na 2 O·nSiO 2 ·mH 2 O. The ratio of sodium to silicic acid is preferably 1.0 to 4.0 in terms of the molar ratio n of Na 2 O / SiO 2 , and more preferably 2.0 to 3.5.

[0068] Active silica is obtained by substituting the alkali metal with hydrogen by cation exchange treatment of the alkali metal silicate, and the aqueous solution of this active silica shows weak acidity. For cation exchange, a hydrogen-type cation exchange resin can be used. It is preferable to dissolve or disperse the alkali metal silicate and active silica in water and then add them to the emulsion. The concentration of the alkali metal silicate and active silica aqueous solution is preferably 3 to 30% by mass in terms of SiO 2 concentration, and more preferably 5 to 25% by mass.

[0069] As the silicon alkoxide, for example, tetraalkylsilanes such as tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane can be preferably used. In addition, composite particles can also be obtained by mixing other metal oxides or the like together with the silica raw material. Examples of other metal oxides include titanium dioxide, zinc oxide, cerium oxide, copper oxide, iron oxide, tin oxide, and the like.

[0070] As the first silica raw material, the above-mentioned silica raw materials can be used alone or in combination of two or more. Among them, it is preferable to use an aqueous solution of alkali metal silicate, particularly an aqueous solution of sodium silicate, as the first silica raw material.

[0071] The addition of the first silica raw material to the water-in-oil emulsion is preferably carried out under acidic conditions. By adding the silica raw material in an acidic environment, silica fine particles are generated to form a network, thereby forming the first coating film. The reaction temperature is preferably 80°C or lower, more preferably 70°C or lower, still more preferably 60°C or lower, particularly preferably 50°C or lower, and most preferably 40°C or lower in order to maintain the stability of the emulsion. Also, from the viewpoint of controlling the network formation rate of silica fine particles to make the thickness of the coating film uniform, it is preferably 4°C or higher, more preferably 10°C or higher, still more preferably 15°C or higher, particularly preferably 20°C or higher, and most preferably 25°C or higher.

[0072] The pH of the water-in-oil emulsion is more preferably less than 3, still more preferably 2.4 or less, and also more preferably 1 or more, from the viewpoint of making the thickness of the coating film more uniform and making the silica shell layer of the obtained hollow silica denser.

[0073] To make the pH of the water-in-oil emulsion acidic, adding an acid can be mentioned. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, acetic acid, perchloric acid, hydrobromic acid, trichloroacetic acid, dichloroacetic acid, methanesulfonic acid, benzenesulfonic acid, and the like.

[0074] In the addition of the first silica raw material, the addition amount of the first silica raw material is SiO in the first silica raw material with respect to 100 parts by mass of the oil phase contained in the emulsion.2 It is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass.

[0075] In the addition of the first silica raw material, after adding the first silica raw material, it is preferable to hold for 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more while maintaining the pH of the emulsion acidic.

[0076] Next, it is preferable to maintain the pH of the emulsion to which the first silica raw material has been added at 3 or more and 7 or less (weakly acidic to neutral). Thereby, the first silica raw material can be immobilized on the surface of the oil droplets. For example, there is a method of making the pH of the emulsion 3 or more by adding a base to the emulsion to which the first silica raw material has been added.

[0077] Examples of the base include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, ammonia, amines, and the like. Alternatively, a method of exchanging anions such as halogen ions with hydroxide ions by anion exchange treatment may be used.

[0078] When adding the base, it is preferable to gradually add the base while stirring the emulsion to which the first silica raw material has been added, and gradually increase the pH of the emulsion. If the stirring is weak or a large amount of base is added at once, the pH of the emulsion may become non-uniform, and the thickness of the first layer of the film may become non-uniform.

[0079] The emulsion is preferably held while stirring. This holding time may be 10 minutes or more, preferably 1 hour or more, and may be 4 hours or more. This holding temperature is preferably 100°C or lower to maintain the stability of the emulsion, more preferably 95°C or lower, even more preferably 90°C or lower, and particularly preferably 85°C or lower. Also, in order to promote aging, the holding temperature is preferably 35°C or higher, more preferably 40°C or higher, and particularly preferably 45°C or higher.

[0080] <Formation of the second shell> Next, in the presence of alkali metal ions, a second silica raw material is added to the emulsion. Thereby, a hollow silica precursor dispersion is obtained. Here, the hollow silica precursor is in the form of oil core-silica shell particles.

[0081] The addition of the second silica raw material to the emulsion is preferably carried out under alkaline conditions. In the addition of the first silica raw material, in order to make the adhesion of the first silica raw material to the oil droplets more uniform, a method is used in which the emulsion is once made acidic and then the pH is adjusted to 3 or more and 7 or less (from weakly acidic to neutral). The first silica layer obtained by this method is porous and has insufficient density, so its strength is low. 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 first silica layer obtained previously.

[0082] When adding the second silica raw material, the pH of the emulsion is preferably 8 or more, more preferably 8.5 or more, still more preferably 8.7 or more, particularly preferably 8.9 or more, and most preferably 9 or more in order to suppress the generation of new fine particles. Also, if the pH is too high, the solubility of silica increases, so it is preferably 13 or less, more preferably 12.5 or less, still more preferably 12 or less, particularly preferably 11.5 or less, and most preferably 11 or less.

[0083] To make the pH of the water-in-oil emulsion alkaline, adding a base can be mentioned. As the base, the same compounds as those described above are used.

[0084] As the second silica raw material, the same ones as the above-mentioned first silica raw material can be used alone or in combination of two or more. Among them, in the addition of the second silica raw material, at least one of an aqueous sodium silicate solution and an aqueous active silica solution can be preferably used. When adding a second silica raw material to the emulsion under alkaline conditions, a method of adding an alkali metal hydroxide simultaneously with the second silica raw material may be used. Also, a method using sodium silicate as an alkali metal silicate for the second silica raw material may be used. In this case, since the sodium silicate component, which is an alkaline component, is added to the weakly acidic emulsion with a pH of 5 or more after the addition of the first silica raw material, the pH of the emulsion can be maintained alkaline while adding the second silica raw material. Also, alkali metal ions will come to exist in the emulsion.

[0085] In addition, when using an aqueous sodium silicate solution for the second silica raw material and the pH rises too much, an acid may be added to adjust the pH. As the acid used here, the same acid as when adding the first silica raw material may be used.

[0086] The addition of the second silica raw material is preferably carried out in the presence of alkali metal ions. These alkali metal ions may be derived from the first silica raw material, the second silica raw material, or the base added for pH adjustment, and can also be incorporated by adding additives to the emulsion or the like. For example, this is the case when using an alkali metal silicate for at least one of the first silica raw material and the second silica raw material. Also, this is the case when using a halide, sulfate, nitrate, fatty acid salt, etc. of an alkali metal for the additive of the emulsion.

[0087] The addition of the second silica raw material may, for example, be adding one of an aqueous sodium silicate solution and an aqueous solution of active silica to the emulsion after the addition of the first silica raw material, or both may be added. When adding both, the aqueous sodium silicate solution and the aqueous solution of active silica may be added together or added in sequence.

[0088] For example, the addition of the second silica raw material can be carried out by adding an aqueous sodium silicate solution and adding an aqueous solution of active silica, while adjusting the pH, in order to promote the adhesion of the silica raw material onto the first layer of silica, either once or repeated two or more times.

[0089] The second silica raw material is preferably added to the heated emulsion in order to promote the adhesion of the silica raw material onto the first silica layer. The heating temperature is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, particularly preferably 45°C or higher, and most preferably 50°C or higher in order to suppress the generation of new fine particles. Since the solubility of silica increases as the temperature increases, it is preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower, particularly preferably 85°C or lower, and most preferably 80°C or lower. When using the heated emulsion, after adding the second silica raw material, it is preferable to gradually cool the resulting emulsion to room temperature (about 23°C).

[0090] In the addition of the second silica raw material, the addition amount of the second silica raw material is preferably adjusted so that the SiO 2 in the second silica raw material is 20 to 500 parts by mass with respect to 100 parts by mass of the oil phase, and more preferably adjusted so that it is 40 to 300 parts by mass. In the addition of the second silica raw material, after adding the second silica raw material, it is preferable to hold the emulsion at a pH maintained alkaline for 10 minutes or more.

[0091] Throughout the addition of the first silica raw material and the addition of the second silica raw material, the total amount of the addition amounts of the first silica raw material and the second silica raw material is such that the total of the SiO 2 in the first silica raw material and the SiO 2 in the second silica raw material is preferably adjusted to be 30 to 500 parts by mass with respect to 100 parts by mass of the oil phase, and more preferably adjusted to be 50 to 300 parts by mass.

[0092] The silica shell layer of the present invention is mainly composed of silica, but may contain other metal components such as Ti and Zr as necessary, such as for refractive index adjustment. The method of containing other metal components is not particularly limited, but for example, methods such as simultaneously adding a metal sol solution or an aqueous metal salt solution in the step of adding the silica raw material are used.

[0093] The hollow silica precursor dispersion is obtained as described above.

[0094] As a method for obtaining a hollow silica precursor from the hollow silica precursor dispersion, for example, there are a method of filtering the dispersion, a method of heating to remove the aqueous phase, a method of separating the precursor by sedimentation or centrifugation, and the like. As an example, there is a method of filtering the dispersion using a filter of about 0.1 μm to 5 μm and drying the filtered hollow silica precursor.

[0095] Also, if necessary, the obtained hollow silica precursor may be washed with water, an acid, an alkali, an organic solvent, or the like.

[0096] <Heat treatment of hollow silica precursor> Then, the oil core is removed from the hollow silica precursor and heat-treated. As a method for removing the oil core, for example, there are a method of firing the hollow silica precursor to pyrolyze the oil, a method of volatilizing the oil by drying, a method of adding an appropriate additive to decompose the oil, a method of extracting the oil using an organic solvent, and the like. Among them, a method of heat-treating a hollow silica precursor with less oil residue is preferable.

[0097] In the method of removing the oil core by firing the hollow silica precursor, it is preferable to perform heat treatment at at least two different temperatures. The firing temperature in the second stage is preferably higher than the heat treatment temperature in the first stage. Also, after the first firing, the hollow silica precursor may be returned to room temperature before the second heat treatment, or the temperature may be raised from the first firing temperature to the second heat treatment temperature while maintaining the first firing temperature.

[0098] In the first-stage heat treatment, the organic components of the oil core and the surfactant are removed. Since it is necessary to thermally decompose the oil inside the hollow particles, a temperature of 100°C or higher is preferable, 200°C or higher is more preferable, and 300°C or higher is most preferable. If the first-stage heat treatment is too high in temperature, the densification of the silica shell progresses and it becomes difficult to remove the internal organic components. Therefore, a temperature below 800°C is preferable, 550°C or lower is preferable, 530°C or lower is more preferable, 520°C or lower is further preferable, 510°C or lower is particularly preferable, and 500°C or lower is most preferable.

[0099] Then, in the second-stage heat treatment, the hollow silica particles are calcined to densify the shell, reduce the surface silanol groups, and lower the dielectric tangent. Since it is preferably carried out at a temperature higher than that of the first-stage heat treatment, 800°C or higher is preferable, 900°C or higher is more preferable, and 1000°C or higher is most preferable. Also, as the temperature increases, crystallization of amorphous silica occurs and the relative dielectric constant increases. Therefore, 1200°C or lower is preferable, 1150°C or lower is more preferable, and 1100°C or lower is most preferable. Note that the temperature of the second-stage heat treatment is preferably 200°C or higher higher than that of the first-stage heat treatment, more preferably 200 - 800°C higher, and even more preferably 400 - 700°C higher.

[0100] <Surface treatment of hollow silica calcined particles> Thereafter, the hollow silica calcined particles obtained in the above step are surface-treated with a silane coupling agent. By this step, the silanol groups present on the surface of the hollow silica calcined particles react with the silane coupling agent, reducing the surface silanol groups and enabling a reduction in the dielectric tangent. Also, the surface becomes hydrophobic, improving the affinity for the resin, and thus the dispersibility in the resin is enhanced.

[0101] There are no particular restrictions on the conditions for the surface treatment, and general surface treatment conditions may be used. The wet treatment method or the dry treatment method is employed. From the viewpoint of performing a uniform treatment, the wet treatment method is preferable.

[0102] Examples of the silane coupling agent used for the surface treatment include an amino-silane coupling agent, an epoxy-silane coupling agent, a mercapto-silane coupling agent, a silane coupling agent, an organosilazane compound, etc. These may be used alone or in combination of two or more kinds.

[0103] Specifically, examples of the surface treatment agent include amino-silane coupling agents such as aminopropylmethoxysilane, aminopropyltriethoxysilane, ureidopropyltriethoxysilane, N-phenylaminopropyltrimethoxysilane, N-2(aminoethyl)aminopropyltrimethoxysilane; epoxy-silane coupling agents such as glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, glycidoxypropylmethyldiethoxysilane, glycidylbutyltrimethoxysilane, (3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercapto-silane coupling agents such as mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane; silane coupling agents such as methyltrimethoxysilane, vinyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, methacryloxypropyltrimethoxysilane, imidazolesilane, triazinesilane; CF 3 (CF 2 ) 7 CH 2 CH 2 Si(OCH 3 ) 3 、CF 3 (CF 2 ) 7 CH 2 CH 2 SiCl 3 、CF 3 (CF 2 ) 7 CH 2 CH 2 Si(CH 3 )(OCH 3 ) 2 、CF 3 (CF 2 ) 7 CH 2 CH 2 Si(CH3 )C1 2 、CF 3 (CF 2 ) 5 CH 2 CH 2 SiCl 3 、CF 3 (CF 2 ) 5 CH 2 CH 2 Si(OCH 3 ) 3 、CF 3 CH 2 CH 2 SiCl 3 、CF 3 CH 2 CH 2 Si(OCH 3 ) 3 、C 8 F 17 SO 2 N(C 3 H 7 )CH 2 CH 2 CH 2 Si(OCH 3 ) 3 、C 7 F 15 CONHCH 2 CH 2 CH 2 Si(OCH 3 ) 3 、C 8 F 17 CO 2 CH 2 CH 2 CH 2 Si(OCH 3 ) 3 、C 8 F 17 -O-CF(CF 3 )CF 2 -O-C 3 H 6 SiCl 3 、C 3 F 7 -O-(CF(CF 3 )CF 2 -O) 2 -CF(CF 3 )CONH-(CH 2 )3 Si(OCH 3 ) 3 and other fluorine-containing silane coupling agents; organosilazane compounds such as hexamethyldisilazane, hexaphenyldisilazane, trisilazane, cyclotrisilazane, 1,1,3,3,5,5-hexamethylcyclotrisilazane, etc.

[0104] The treatment amount of the silane coupling agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less with respect to 100 parts by mass of the particles of the hollow silica particles.

[0105] Examples of the method of treating with the silane coupling agent include a dry method of spraying the silane coupling agent onto the fired hollow silica particles, and a wet method of dispersing the fired hollow silica particles in a solvent and then adding the silane coupling agent to react.

[0106] The hollow silica particles obtained by the above process may be aggregated by a drying or firing process, and thus may be crushed to have an easily handleable aggregation diameter. Examples of the crushing method include a method using a mortar, a method using a dry or wet ball mill, a method using a vibrating sieve, and a method using a crusher such as a pin mill, a cutter mill, a hammer mill, a knife mill, a roller mill, a jet mill, etc. The preferred aggregation diameter of the secondary particles (specifically, the median diameter and the coarse particle diameter) is as described above.

[0107] Since the hollow silica particles of the present invention have a densified shell layer, the permeability of various solvents is low when added to an organic solvent such as methyl ethyl ketone or N-methylpyrrolidone. Therefore, the dispersibility in various solvents is good, and the properties peculiar to the hollow particles in the solvent can be maintained.

[0108] The hollow silica particles of the present invention can be used as various fillers, and are particularly suitable as fillers for resin compositions used in the production of electronic substrates used in electronic devices such as personal computers, notebook computers, digital cameras, etc., and communication devices such as smartphones and game machines.

Examples

[0109] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. In the following description, the same components are used. Also, unless otherwise specified, “%” and “parts” represent “mass %” and “parts by mass”, respectively. Also, Examples 1 to 23 are examples, and Example 24 is a comparative example.

[0110] <Test Example 1> (Example 1) "Preparation of Emulsion" 7 g of an EO-PO-EO block copolymer (Pluronic F68 manufactured by ADEKA) was added to 1250 g of pure water and stirred until dissolved. 42 g of n-dodecane was added to this aqueous solution, and the mixture was stirred using a homogenizer manufactured by IKA until the whole liquid became uniform to prepare a crude emulsion. This crude emulsion was emulsified 3 times at a pressure of 400 bar using a high-pressure emulsifier (LAB2000 manufactured by SMT) to prepare a fine emulsion with an emulsion diameter of 0.3 μm.

[0111] "First-stage Shell Formation" To 1300 g of the obtained fine emulsion, 41 g of a diluted sodium silicate aqueous solution (SiO 2 concentration 10.4 mass%, Na 2 O concentration 3.6 mass%) and 2M hydrochloric acid were added, and the mixture was stirred well while maintaining at 30 °C (the conditions described in (ii) of Table 1). While stirring this liquid well, a 1M aqueous sodium hydroxide solution was slowly dropped until the pH reached 6 (the conditions described in (iii) of Table 1) to obtain an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was held and aged.

[0112] "Second-stage shell formation" The total amount of the oil core-silica shell particle dispersion obtained in the first-stage shell formation was heated to 70 °C, and 1 M NaOH was slowly added while stirring to adjust the pH to 9. Next, 460 g of a diluted aqueous sodium silicate solution (SiO 2 concentration 10.4% by mass, Na 2 O concentration 3.6% by mass) was gradually added together with 0.5 M hydrochloric acid so that the pH became 9. After maintaining this suspension at 70 °C for 2 days, it was slowly cooled to room temperature to obtain a hollow silica precursor dispersion.

[0113] "Filtration, washing, drying, firing" The total amount of the hollow silica precursor dispersion was filtered by pressure filtration (pressure 0.28 MPa) using a 0.45-μm hydrophilic PTFE (polytetrafluoroethylene) membrane filter. Then, 350 ml of distilled water at 40 °C was added and pressure filtration was performed again to wash the hollow silica cake. The cake after filtration was dried in a nitrogen atmosphere at 60 °C for 1 hour and then at 400 °C for 4 hours (heating rate 5 °C / min) to remove organic components and obtain a hollow silica precursor. The obtained precursor was fired at 1000 °C for 4 hours (heating rate 5 °C / min) to densify the shell and obtain hollow silica fired particles.

[0114] "Surface treatment" 10 g of the above-mentioned hollow silica fired particles, 120 ml of methyl ethyl ketone, and 0.8 g of hexamethyldisilazane were added to a 200-ml glass beaker and stirred at room temperature for 3 hours. Then, vacuum filtration was performed using a hydrophobic PTFE membrane filter, washed with 20 ml of methyl ethyl ketone, and vacuum dried in a vacuum dryer adjusted to 150 °C for 2 hours. The obtained solid was ground in an agate mortar to obtain surface-treated hollow silica particles.

[0115] "Evaluation" 1. Measurement of infrared absorption spectrum The infrared absorption spectrum was measured by the diffuse reflection method using IR Prestige-21 (manufactured by Shimadzu Corporation), after dispersing it in diamond powder. The measurement range was 400 to 4000 cm -1 , the resolution was 4 cm -1 , and the number of integrations was 128 times. Dilution with diamond powder was defined as [mass dilution ratio] = ([sample mass]) / ([diamond mass] + [sample mass]), and [mass dilution ratio] = 85 - 2.5 × [BET specific surface area]. In addition, the hollow silica particles used were those vacuum-dried at 180 °C for 1 hour. Among the obtained IR spectra, the peak intensities derived from various SiOH near 1060 cm -1 were normalized with 1 as the peak intensity of various SiOH near 1060 cm, and the peak intensity near the wave number 3746 cm -1 was obtained. The results are shown in Table 2.

[0116] 2. Density measurement using a dry pycnometer The density was measured using a dry pycnometer (AccuPycII 1340 manufactured by Micromeritics). The measurement conditions are as follows. The results are shown in Table 2. · Sample cell: 10 cm 3 cell · Sample weight: 1.0 g · Measurement gas: helium or argon · Number of purge times: 10 times · Purge treatment filling pressure: 135 kPag · Number of cycles: 10 times · Cycle filling pressure: 135 kPag · Rate of ending pressure equilibrium: 0.05 kPag / min

[0117] 3. Sphericity and average primary particle diameter The hollow silica particles obtained in Example 1 were photographed with a scanning electron microscope. The scanning electron microscope image (SEM image) is shown in Fig. 1. For any 100 particles from Fig. 1, the maximum diameter (DL) and the minor axis diameter (DS) perpendicular to it were measured for each particle, and the sphericity was determined from the average value calculated for the ratio (DS / DL) of the minor axis diameter (DS) to the maximum diameter (DL). Similarly, the average value of the distribution obtained by aggregating the primary particle sizes of any 100 particles was taken as the average primary particle diameter. The results are shown in Table 2.

[0118] 4. Median Diameter The obtained hollow silica particles were measured using a diffraction scattering type particle size distribution measuring device (MT3300) manufactured by Microtrac Bell Co., Ltd., and the median value of the particle size distribution (diameter) was measured twice and the average value was obtained. As a result, the median diameter was 2 μm.

[0119] 5. Specific Surface Area, Pore Volume The hollow silica particles were dried under reduced pressure at 230 °C to completely remove moisture and used as a sample. For this sample, the multi-point BET method specific surface area and pore volume were measured using argon gas with an automatic specific surface area and pore distribution measuring device "TriStar II" manufactured by Micromeritics. The results are shown in Table 2.

[0120] 6. Oil Absorption The oil absorption was measured in accordance with JIS K 5101-13-1. The results are shown in Table 2.

[0121] 7. Concentration of Metal M (M = Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba) Perchloric acid and hydrofluoric acid were added to the spherical hollow silica particles and heated strongly. After removing the main component silicon, measurement was carried out by ICP-AES (high frequency inductively coupled plasma optical emission spectrometry) using ICPE-9000 (manufactured by Shimadzu Corporation). By the above measurement, Na, K, Mg, and Ca were detected as metal M. The total amount of metal M is shown in Table 2.

[0122] 8. Relative Permittivity, Dielectric Loss Tangent The relative permittivity and dielectric loss tangent were measured using a dedicated device (Vector Network Analyzer E5063A, manufactured by Keycom Co., Ltd.) by the perturbation method resonator method at a test frequency of 1 GHz, a test temperature of about 24 °C, a humidity of about 45%, and 3 measurement times. Specifically, after vacuum drying the hollow silica particles at 150 °C, the powder was filled into a PTFE cylinder while tapping the powder sufficiently, and the relative permittivity of the whole container was measured. Then, the relative permittivity and dielectric tangent of the powder were converted using the logarithmic mixing rule. The results are shown in Table 2.

[0123] (Examples 2 - 4) As shown in Table 1, the experiments were carried out under the same conditions as in Example 1, except that the firing temperature was changed.

[0124] (Examples 5 - 8, 18 - 21) As shown in Table 1, the experiments were carried out under the same conditions as in Example 1, except that the amount of aqueous sodium silicate solution in the second - stage shell formation was changed and the washing conditions of the hollow silica cake were changed.

[0125] (Examples 9 - 10) An emulsion was prepared using only the homogenizer manufactured by IKA, and the experiments were carried out under the same conditions as in Example 1, except that an emulsion with the particle size shown in Table 1 was obtained.

[0126] (Example 11) In the emulsion preparation process, the amount of EO - PO - EO block copolymer (Pluronic F68 manufactured by ADEKA) was changed to 70 g, n - dodecane was changed to olive oil, and high - pressure emulsification was carried out 5 times at a pressure of 400 bar to obtain an emulsion with the particle size shown in Table 1. Also, the experiments were carried out under the same conditions as in Example 1, except that the firing temperature was changed to 800 °C.

[0127] (Examples 12 - 15) As shown in Table 1, the experiments were carried out under the same conditions as in Example 1, except that the conditions for the first - stage shell preparation were changed.

[0128] (Example 16) In the emulsion preparation process, the amount of EO - PO - EO block copolymer (Pluronic F68 manufactured by ADEKA) was changed to 20 g, n - dodecane was changed to n - hexadecane, and high - pressure emulsification was carried out 3 times at a pressure of 400 bar to obtain an emulsion with the particle size shown in Table 1. Also, the experiments were carried out under the same conditions as in Example 1, except that the conditions for the first - stage shell formation were changed as shown in Table 1.

[0129] (Example 17) It was carried out under the same conditions as in Example 1 except that the surface treatment step was not performed.

[0130] (Examples 22, 23) In the emulsion preparation step, n-dodecane was changed to decane, and high-pressure emulsification was performed 3 times at a pressure of 400 bar. Example 22 was left standing at room temperature for 48 hours, and Example 23 was left standing at room temperature for 96 hours to obtain a fine emulsion with the particle size shown in Table 1. It was carried out under the same conditions as in Example 1.

[0131] (Example 24) As shown in Table 1, it was carried out under the same conditions as in Example 1 except that the firing temperature was changed.

[0132] The above results are summarized and shown in Table 2. For Example 1, the SEM image of the hollow silica particles is shown in FIG. 1.

[0133]

Table 1

[0134]

Table 2

[0135] As shown in Table 2, in the density measurement using a dry pycnometer, when helium was used as the measurement gas, a value equivalent to the true density of silica, 2.20 g / cm 3 was obtained, indicating that helium gas passed through the shell and penetrated into the inner cavity of the hollow silica. On the other hand, when argon gas was used, in any example, a value smaller than that obtained by the helium pycnometer method was obtained. Since the rate at which argon gas passes through the shell is slow, it is considered that the particle density not including the inner cavity of the hollow silica was obtained.

[0136] In addition, in Examples 1 to 23, the relative permittivity and dielectric loss tangent at 1 GHz were small, whereas in Example 24, both the relative permittivity and dielectric loss tangent at 1 GHz were large, and the desired effects of the present invention could not be obtained. In particular, as can be seen from the comparison between Examples 1 to 4 and Example 24, as a result of changing the peak intensity near the wave number 3746 cm -1 in the infrared spectroscopy, when the peak intensity exceeded 0.60, neither the relative permittivity nor the dielectric loss tangent resulted in satisfactory values. This is presumably because the firing temperature was insufficient, the remaining amount of surface silanol groups was large, and the sintering of silica was insufficient, so that the shell did not become dense. Also, it was found that when the firing temperature exceeded 1200 °C, the relative permittivity tended to increase. This is presumably because the crystallization of amorphous silica progressed. Further, the firing temperature corresponded to the density measured by a helium pycnometer, and it was found that the density measured by the helium pycnometer increased up to 1000 °C and saturated at 1000 °C. This is presumably because the silanol groups contained in silica dehydrated and approached the theoretical density of silica.

[0137] <Test Example 2> In order to examine the resin dispersibility of the hollow silica particles, the following test was conducted. As the hollow silica particles, Examples 1, 14 to 16 prepared in Test Example 1 were used. 100 parts of a toluene solution of a styrene-modified polyphenylene ether resin (「OPE-2St (number average molecular weight 1200)」 manufactured by Mitsubishi Gas Chemical Company, Inc., non-volatile content 64.4 wt%) and 100 parts of the hollow silica particles were mixed in 15 parts of methyl ethyl ketone (MEK), and kneaded at 2000 rpm for 5 minutes using a rotation / revolution mixer 「Avatori Rentaro」 (trade name, model: ARE-250, manufactured by Shinchi Co., Ltd.) to prepare a resin varnish.

[0138] The obtained resin varnish was measured according to the particle gauge method described in JIS K5400 to obtain the median diameter particle gauge. For the median diameter of the secondary particles of the hollow silica particles and the coarse particle diameter (D90) of the secondary particles, they were measured using a diffraction scattering type particle size distribution measuring device (MT3300) manufactured by Microtrac Bell Co., Ltd. The average value of the median value of the particle size distribution (diameter) measured twice was taken as the median diameter of the secondary particles, and the average value of the particle diameter at which the cumulative particle size distribution (diameter) reached 90% was taken as the coarse particle diameter (D90) of the secondary particles. The results are shown in Table 3.

[0139]

Table 3

[0140] From the results in Table 3, it was found that in Example 16 where the median diameter of the secondary particles was 0.22 μm, there was a tendency for secondary aggregation to occur and the value of the particle gauge became large. Also, in Example 15 where the median diameter of the secondary particles was 60 μm, the proportion of large particles was high, and similarly, the value of the particle gauge tended to become large. Moreover, it was found that as the coarse particle diameter (D90) of the secondary particles increased, the proportion of large particles increased and the value of the particle gauge tended to become large.

[0141] <Test Example 3> In order to confirm the density of the shell of the hollow silica particles, the following test was carried out. As the hollow silica particles, Examples 1, 12, and 13 prepared in Test Example 1 were used. Using a 10 mL Gay-Lussac type specific gravity bottle, the density in methyl ethyl ketone (MEK) was measured. 0.20 g of hollow silica particles was added to the specific gravity bottle, the specific gravity bottle was filled with MEK, and the density after standing at 25 °C for 48 hours was measured. The results are shown in Table 4.

[0142]

Table 4

[0143] From Table 4, it was confirmed that the density in MEK decreased corresponding to the decrease in density by the argon pycnometer method. From this, it was found that the hollow silica particles obtained in this example have a dense shell and can maintain the hollow structure even in an organic solvent.

[0144] <Test Example 4> In order to measure the hygroscopicity of the obtained hollow silica particles, the following test was conducted. As the hollow silica particles, Examples 1, 3, 17, and 24 prepared in Test Example 1 were used. After drying the hollow silica particles at 200 °C, the ones left in an environment of 40 °C and RH 90% for 24 hours were measured by the Karl Fischer method (coulometric titration method). The results are shown in Table 5. [Conditions of the Karl Fischer method (coulometric titration method)] Trace moisture measuring device (CA-200 type, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) Moisture vaporization device (VA-200, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) Anolyte (Hydranal Coulomat AG-OVEN, manufactured by Rinsho Yakuhin Co., Ltd.) Catholyte (Hydranal Coulomat CG, manufactured by Rinsho Yakuhin Co., Ltd.) Heating temperature: 200 °C Nitrogen flow rate: approximately 250 ml / min

[0145]

Table 5

[0146] From Table 5, it was found that as the firing temperature increased, the hydrophilicity on the surface of the hollow silica particles decreased, so the moisture adsorption amount decreased. Also, it was found that when the silane treatment was carried out, the hydrophilicity on the surface decreased, so the moisture adsorption amount decreased. It was found that the smaller the moisture adsorption amount, the smaller the moisture absorption amount when the hollow silica particles were made into a resin composition, and the dielectric loss of the resin composition could be suppressed.

[0147] Although the present invention has been described in detail with reference to specific embodiments, 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 present invention. This application is based on Japanese Patent Application No. 2020-032046 filed on February 27, 2020, Japanese Patent Application No. 2020-161378 filed on September 25, 2020, and Japanese Patent Application No. 2020-161379 filed on September 25, 2020, the contents of which are incorporated herein by reference.

Claims

1. Hollow silica particles having a shell layer containing silica and having a space portion inside the shell layer, The peak intensity derived from SiOH near a wave number of 3746 cm by infrared spectroscopy is 0.60 or less, the relative permittivity at 1 GHz is 1.3 to 5.0, and the dielectric tangent at 1 GHz is 0.0001 to 0.

05. －１ The peak intensity derived from SiOH near a wave number of 3746 cm by infrared spectroscopy is 0.60 or less, the relative permittivity at 1 GHz is 1.3 to 5.0, and the dielectric tangent at 1 GHz is 0.0001 to 0.

05. The hollow silica particles having a pore volume of 0.2 cm3 / g or less.

2. The density of the particles determined by density measurement using a dry pycnometer with helium gas is 2.00 to 2.30 g / cm ３ The hollow silica particles according to claim 1, wherein the density is as described above.

3. The density of the particles determined by density measurement using a dry pycnometer with argon gas is 0.35 to 2.00 g / cm ３ The hollow silica particles according to claim 1 or 2, wherein the density is as defined above.

4. The hollow silica particles according to any one of Claims 1 to 3, having an average primary particle diameter of 50 nm to 10 μm.

5. The BET specific surface area is 1 to 300 m ２ / g, and the hollow silica particles according to any one of claims 1 to 4.

6. The hollow silica particles according to any one of Claims 1 to 5, having a sphericity of 0.75 to 1.

0.

7. The hollow silica particles according to any one of Claims 1 to 6, having an oil absorption of 15 to 1300 mL / 100 g.

8. The hollow silica particles according to any one of Claims 1 to 7, having a median diameter of secondary particles of 0.20 to 60 μm.

9. The hollow silica particles according to any one of Claims 1 to 8, having a coarse particle diameter (D90) of secondary particles of 1 to 100 μm.

10. The hollow silica particles according to any one of Claims 1 to 9, wherein the surface of the hollow silica particles is surface-treated with a silane coupling agent.

11. The hollow silica particles according to any one of Claims 1 to 10, containing at least one metal M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba, and having a concentration of the metal M contained in the hollow silica particles of 50 ppm by mass or more and 5% by mass or less.

12. Forming a shell layer containing silica on the outer periphery of the core to obtain a hollow silica precursor, removing the core from the hollow silica precursor, heat-treating at 800 °C or higher, and surface-treating the particles after the heat treatment with a silane coupling agent, A method for producing hollow silica particles having a pore volume of 0.2 cm3 / g or less.

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