Silica-based hollow particles and method for producing the same

Abstract

To provide a method for manufacturing silica-based particles that enables lower permittivity and lower dielectric loss tangent of an insulating material.SOLUTION: A method for manufacturing silica-based hollow particles includes: a first step of spray drying an aqueous alkali silicate solution in a hot air stream to prepare hollow particles; a second step of neutralizing alkali contained in the hollow particles in an acid solution and then washing and removing the alkali; and a third step of firing the hollow particles from which the alkali has been removed. In the second step, an acid solution is used where a ratio (MH+ / Msp) of the number of moles of hydrogen ions in the acid (MH+) to the value (Msp) obtained by multiplying the number of moles of alkali metal ions in the hollow particles by the valence exceeds 4.7.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to silica-based hollow particles useful as fillers for semiconductor insulating materials, and to a method for producing the same. [Background technology]

[0002] In recent years, the capacity of data communication in information and communication has been increasing, and high-speed processing of communication equipment is required. Insulating materials used in semiconductor printed circuit boards and other components of such communication equipment require low dielectric constant (low Dk) and low dielectric loss tangent (low Df) to achieve high-speed communication. A high dielectric constant of insulating materials leads to dielectric loss, and a high dielectric loss tangent not only leads to dielectric loss but can also cause problems such as increased heat generation.

[0003] In insulating materials for semiconductor printed circuit boards and the like, development is underway to achieve low dielectric constant and low dielectric loss tangent by developing resin materials that will be the main component of the insulating material. Examples of such resin materials that have been proposed include epoxy resins, polyphenylene ether resins, and fluoropolymer resins.

[0004] On the other hand, fillers are added to such resin materials for reasons such as durability (rigidity) and heat resistance. These fillers include metal oxide particles such as silica (see, for example, Patent Document 1).

[0005] As silica-based particles incorporated as fillers in such resin materials, hollow particles are used, and a method for producing them has been proposed which includes, for example, the steps of (a) preparing silica-based particle precursor particles by spray-drying an alkaline silicate aqueous solution in a hot air stream, (b) immersing the silica-based particle precursor particles in an acidic aqueous solution to remove the alkali, (c) hydrothermal treatment, and (d) drying and heat treatment (see Patent Document 2).

[0006] It has been disclosed that silica-based particles produced by this method have high compressive hardness and excellent moisture resistance. In this method, although the hydrothermal treatment after the dealkalization step can seal the pores present on the surface of the silica-based particle precursor particles, it cannot sufficiently seal the pores present inside the outer shell, and SiOH groups remain in the outer silica layer. Therefore, this method is insufficient for applications requiring low dielectric constant and low dielectric loss tangent.

[0007] Furthermore, as another method for producing silica-based hollow particles, a method for producing silica balloons with controlled pore size has been proposed, in which an aqueous solution of alkali metal silicate is atomized and introduced into an airflow at 100-500°C to form a glass balloon, and then the amount of alkali metal present in the glass balloon is adjusted to control the pore size of the silica balloon (see Patent Document 3). In the example in Patent Document 3, 100 g of glass balloons produced using sodium silicate are neutralized by flowing 200 L or 300 L of 0.01 mol / L hydrochloric acid at a rate of 4 L / min, and then dried at 110°C for 1 hour to obtain silica balloons.

[0008] However, when comparing the cases with hydrochloric acid flow rates of 200L and 300L, it can be confirmed that in the 300L case, the water specific surface area increases, resulting in an increase in pores that allow water molecules to penetrate but not nitrogen molecules. However, the nitrogen specific surface area decreases, and the relationship between alkali metal removal and pore size control is not clear. Furthermore, because rinsing with water is not performed, acid counterions such as chloride ions remain, making it unsuitable for applications requiring low dielectric constant and low dielectric loss tangent.

[0009] On the other hand, solid silica particles are also used as fillers in resin materials. As a method for producing such silica solid particles, for example, raw silica powder is subjected to high-temperature heat treatment or heat treatment in an electric furnace, which is a reducing reaction field, while the powder is flowing under an inert atmosphere. The number of water molecules released at 500°C to 1000°C is 0.01 mmol / g or less, and the specific surface area is 1 to 30 m². 2A method for obtaining spherical silica powder having / g is proposed (see Patent Document 4).

[0010] However, although this spherical silica powder is said to be capable of lowering the dielectric loss tangent of resin materials, solid silica powder generally has a higher dielectric constant than resin materials, so it cannot achieve both low dielectric constant and low dielectric loss tangent, which have been required in recent years.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problem to be Solved by the Invention

[0012] Nowadays, with the rapid progress of large-capacity data communication and high-speed processing, further reduction of dielectric constant and dielectric loss tangent is required for fillers contained in semiconductor insulating materials.

[0013] An object of the present invention is to provide silica-based particles that enable a reduction in dielectric constant and dielectric loss tangent of an insulating material, and a method for producing the same.

Means for Solving the Problem

[0014] The present inventors found that when neutralizing silica-based hollow particles produced using an alkali silicate aqueous solution with an acid, performing neutralization treatment under predetermined conditions allows favorable pore formation in the particles, and can realize a reduction in dielectric constant and dielectric loss tangent of an insulating material, thereby completing the present invention.

[0015] In other words, the present invention is a method for producing silica-based hollow particles, comprising: a first step of preparing hollow particles by spray-drying an aqueous alkali silicate solution in a hot air stream; a second step of neutralizing the alkali contained in the hollow particles in an acid solution and then washing and removing it; and a third step of calcining the hollow particles from which the alkali has been removed, wherein in the second step, the number of moles of hydrogen ions of the acid (M) is given a value (Msp) that is obtained by multiplying the number of moles of alkali metal ions in the hollow particles by their valence. H+ ) ratio (M H+ This concerns a method using an acid solution with a (Msp) value exceeding 4.7.

[0016] Furthermore, the present invention relates to silica-based hollow particles that satisfy the following requirements (i) to (vii). (i) Average particle size (D50) is 0.1 to 20 μm (ii) Porosity of 10-95% (iii) Sears count (ml / SiO2 1.5g) is less than 0.30 (iv) Water vapor / nitrogen specific surface area ratio is less than 0.30 (v) Water vapor adsorption amount is less than 0.20% by mass (vi) 29 In Si-NMR, the peak area consists substantially of a Q3 structure with a chemical shift of -82.0 to -100.0 ppm and a Q4 structure with a chemical shift of -100.0 to -120.0 ppm, with the peak area of ​​the Q4 structure accounting for more than 90% of the total peak area. (vii) Alkali content is 100 ppm or less [Effects of the Invention]

[0017] According to the present invention, silica-based particles that enable the reduction of dielectric constant and dielectric loss tangent in insulating materials can be obtained. [Modes for carrying out the invention]

[0018] [Method for producing silica-based hollow particles] The present invention provides a method for producing silica-based hollow particles, comprising: a first step of preparing hollow particles by spray-drying an alkaline silicate aqueous solution in a hot air stream; a second step of neutralizing the alkali contained in the hollow particles in an acid solution and then washing and removing it; and a third step of calcining the alkali-removed hollow particles, wherein in the second step, the number of moles of hydrogen ions in the acid (M) is compared with the value (Msp) obtained by multiplying the number of moles and valence of alkali metal ions in the hollow particles. H+ ) ratio (M H+ Use an acid solution with a concentration ( / Msp) of 4.7 or higher. Other steps, such as drying and classification steps, may be included before and after each step.

[0019] Here, "silica-based" means that silica is the main component, and it may also contain inorganic oxides such as alumina, zirconia, and titania in addition to silica. The silica content in the particles is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and it is particularly preferable that it consists substantially of only silica.

[0020] According to the manufacturing method of the present invention, by neutralizing (dealkalizing) the silica-based hollow particles produced in the first step with a large amount of acid in the second step, the pores formed within the particles (outer shell) can be made to a size (structure) that is easily closed during the subsequent calcination process. This ultimately leads to obtaining particles with a low SiOH group content, thereby achieving a low dielectric constant and low dielectric loss tangent for the insulating material. Furthermore, such good pore formation suppresses changes in the dielectric loss tangent due to moisture absorption over time, allowing for the maintenance of a low dielectric loss tangent over the long term. In addition, adhesion between particles can be suppressed, improving particle dispersibility. Moreover, since no large pores remain within the pores, particle strength is also improved.

[0021] (first step) In this process, hollow particles are prepared by spray-drying an alkaline silicate aqueous solution in a hot air stream.

[0022] The concentration of SiO2 in the alkali silicate aqueous solution is preferably 1 to 30% by mass, and more preferably 5 to 28% by mass. Although production is possible at concentrations below 1% by mass, productivity is significantly reduced. If the concentration exceeds 30% by mass, the stability of the alkali silicate aqueous solution decreases significantly, resulting in high viscosity, and spray drying may not be possible. Even if spray drying is possible, the particle size distribution, outer shell thickness, etc., become extremely non-uniform, which may limit the applications of the resulting particles. As the alkali silicate, water-soluble sodium silicate and potassium silicate can be used, but sodium silicate is preferred.

[0023] The molar ratio (SiO2 / M2O) of SiO2 to M2O (where M is an alkali metal) in alkali silicate is preferably 1 to 5, and more preferably 2 to 4. If this molar ratio is less than 1, the amount of alkali is too high, making acid washing to remove the alkali difficult, and the deliquescence of the spray-dried product increases, making it difficult to obtain the desired silica-based hollow particles. If this molar ratio exceeds 5, the solubility of the alkali silicate decreases, making it difficult to prepare an aqueous solution, and even if an aqueous solution can be prepared, the desired silica-based hollow particles may not be formed by spray drying.

[0024] Conventional known methods such as the rotating disk method, the pressurized nozzle method, and the two-fluid nozzle method can be used as spray drying methods. In this case, the two-fluid nozzle method is preferred.

[0025] In spray drying, the inlet temperature of the spray dryer is preferably 300 to 600°C, and more preferably 350 to 550°C. The outlet temperature is preferably 120 to 300°C, and more preferably 130 to 250°C. By setting the inlet and outlet temperatures within the above ranges, hollow particles can be obtained stably.

[0026] (Second process) In this step, the alkali contained in the prepared hollow particles is neutralized and removed in an acid solution under predetermined conditions. That is, the hollow particles are immersed in an acid solution to neutralize the alkali contained in the hollow particles. In this process, instead of adding the acid solution to the hollow particles, it is preferable to add the hollow particles to the acid solution. This can prevent a pH condition that causes particle dissolution in the vicinity of the particles, thereby inhibiting particle dissolution. In the column flow method disclosed in Patent Document 3, during the flow of the solution from the upper part to the lower part of the column, the H + concentration of the acid solution decreases (pH increases), and the solution contacts the particles when the pH is not sufficiently low, which may lead to particle dissolution. Therefore, favorable pores as obtained in the present invention are not formed, and the desired effect of the present invention cannot be achieved.

[0027] In this step, the ratio of the number of moles of hydrogen ions of the acid (M H+ ) to the value (Msp) obtained by multiplying the number of moles of alkali metal ions in the hollow particles by their valences (M H+ / Msp) requires the use of an acid solution where this ratio exceeds 4.7. Conventionally, this ratio (M H+ / Msp) has never been used at such a high value. For example, in paragraph

[0032] of Patent Document 2, it is described that "even if this ratio exceeds 4.7, further framework formation does not proceed, and the excess acid makes the process uneconomical". Furthermore, in the examples of Patent Document 3, this ratio is 3.0 (200 L) and 4.4 (300 L). In the present invention, by intentionally performing the neutralization treatment under such conditions, alkali ions can be removed (ion exchange with H + ) while suppressing damage to the silica framework. Large pores are not formed in (the outer shell of) the hollow particles, favorable pores are formed, and the exceptional effect of the present invention can be obtained. This ratio (M H+ / Msp) is preferably 5.0 or more, more preferably 5.2 or more, and still more preferably 5.5 or more. There is no particular limitation on the upper limit, but it is, for example, 7.0 or less.

[0028] In this process, the alkali content in the particle (outer shell) is removed, reducing its mass, while the changes in particle shape and hollow structure (volume) are extremely small. Therefore, when comparing the particles before and after this process, the particle density decreases in proportion to the amount of alkali removed. The particle density can be measured using the gas pycnometer method (JIS Z 8837), with the particles before this process (product after the first process) being measured as is, and the particles after this process being measured using particles that have been dried at 120°C for 24 hours (after washing).

[0029] After alkali removal, pores are formed in the particle (outer shell), so the density value obtained will differ depending on the type of gas used for density measurement. When helium is used, the helium penetrates the pores formed in the outer shell and fills the cavities inside the particle, resulting in a density that is almost equivalent to the theoretical density of silica (approximately 2.2 g / cm³). 3 ) For example, 2.1~2.3 g / cm³. 3 That is the case.

[0030] On the other hand, when nitrogen is used, it does not penetrate the pores in the outer shell, and a density is obtained that reflects the presence of internal cavities. If no pores are formed in the particle (outer shell) through which nitrogen can penetrate, the density of the particle after the second step (theoretical value: ρ 2T ) decreases from the particle density (ρ1) after the first process in proportion to the decrease in the mass of alkali content, and can be calculated using the following formula (X).

[0031] ρ 2T =ρ1×(1-W a )...Equation (X) ρ1: Density after the first step ρ 2T Theoretical value of density after the second process W a : Alkaline content ratio in raw material solids

[0032] After the second step, the more pores that allow nitrogen to enter are formed, the higher the particle density (ρ²) will be compared to the theoretical value (ρ 2T The deviation from ) will increase. The pores formed in this process can be reduced in size by subsequent heat treatment, etc., but if they are too large or too numerous, they cannot be completely blocked and will ultimately remain in the particle (outer shell), causing increased hygroscopicity. Therefore, it is preferable for the pore size to be small and the number of pores to be small, and the particle density (ρ²) measured with nitrogen should be the theoretical value (ρ 2T A smaller deviation from ) is preferable. Specifically, ρ² / ρ 2T However, 1.0 to 1.4 is preferred, 1.0 to 1.3 is more preferred, and 1.0 to 1.2 is even more preferred.

[0033] Furthermore, it is preferable to immerse the hollow particles in an acid solution so that the concentration of SiO2 is 1 to 30% by mass. If the concentration is less than 1% by mass, there are no problems with alkali removal or cleaning performance, but the manufacturing efficiency will decrease. If the concentration exceeds 30% by mass, the concentration may be too high, and alkali removal and cleaning efficiency may decrease. In addition, problems such as particle breakage may occur due to contact and friction between particles. 5 to 25% by mass is even more preferable. The immersion treatment may be carried out in multiple stages.

[0034] The temperature conditions for the immersion treatment are typically 5°C or higher and below the boiling point of the solution. A temperature of 50°C or higher is preferred, and 55°C or higher is more preferred, as this allows for the formation of better pores and more reliably achieves lower dielectric constant and lower dielectric loss tangent of the insulating material. The treatment time is, for example, 0.5 to 24 hours.

[0035] After the immersion treatment, the hollow particles are thoroughly washed using conventionally known methods. For example, they are filtered and washed with pure water.

[0036] The residual amount (mass percentage) of alkali (M) after alkali removal is preferably 100 ppm or less, more preferably 90 ppm or less, and even more preferably 80 ppm or less. By sufficiently removing the alkali in this step, the desired effects of the present invention can be obtained. Furthermore, particle adhesion in subsequent steps can be prevented, and the generation of sintered particles in the firing step can be prevented.

[0037] The amount of residual alkali is determined by dissolving the particles in acid, preparing a sample, and measuring the Na or K content using an atomic absorption spectrophotometer. If sodium silicate is used, Na is measured; if potassium silicate is used, K is measured. Specific details will be explained in the examples.

[0038] Furthermore, the alkali content of the final product (silica-based hollow particles) is preferably within the range described above, and is usually equivalent to the alkali content after the alkali removal process.

[0039] Examples of acids used in this process include mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid, and organic acids such as acetic acid, tartaric acid, and malic acid. Mineral acids are preferably used, and sulfuric acid is particularly preferred in terms of valency. The acid solution is usually an aqueous solution, but it may also be mixed with alcohol or the like.

[0040] (Third step) In this process, the alkali-removed hollow particles are fired. The firing temperature is preferably 900°C or higher, and more preferably 1000°C or higher. There is no particular upper limit, but for example, it is 1200°C. In the second step, neutralization treatment is performed in a solution containing a large amount of acid, and then thorough washing is performed, so that the alkali is sufficiently removed, particle adhesion is prevented, the generation of sintered particles in the firing process is prevented, and high-temperature firing is possible. Therefore, the pores formed by alkali removal can be blocked (the number of SiOH groups is reduced), and particles with low dielectric constant and dielectric loss tangent can be obtained. For example, in Patent Document 2, it is not possible to obtain particles with a dielectric loss tangent of less than 0.0010, but in the present invention, particles with a dielectric loss tangent of less than 0.0010 can be obtained. In addition, particles with high strength can be obtained.

[0041] (Classification process) In the method for producing silica-based hollow particles of the present invention, it is preferable to include a classification step to remove fine particles with a particle diameter of less than 0.1 μm and coarse particles with a particle diameter exceeding 6 times the average particle diameter. This classification step is preferably provided between the first and third steps, and more preferably between the second and third steps.

[0042] When performing classification during the production of calcined particles, it is generally considered preferable to perform the classification after calcination to standardize the final particles. However, it is preferable to perform the classification before the calcination process. If the calcination process is carried out without classification, there will be fine particles that should be removed, which will sinter with the other particles. Even if classification is performed afterward, the sintered particles cannot be removed. In addition, there will be coarse particles with high porosity that should be removed. These coarse particles with high porosity are brittle and may crack due to the stress of shrinkage caused by heating. The fragments generated by cracking have a small particle size and cannot be removed even if classification is performed afterward. Furthermore, since these fragments are dense silica with no voids, they hinder the reduction of dielectric constant and dielectric loss tangent. By performing the classification before calcination, these problems can be avoided, and the reduction of dielectric constant and dielectric loss tangent in the manufactured particles can be more reliably achieved, resulting in particles that can handle high-speed data communication. Note that classification may also be performed after calcination.

[0043] The removal of fine particles and coarse particles may be performed simultaneously or separately. When performed separately, the order of removal of fine particles or coarse particles may be chosen. Furthermore, each of the processes for removing fine particles and coarse particles may be performed in multiple stages.

[0044] In the classification process, it is preferable to reduce the amount of fine particles to 10 volume% or less, more preferably 8 volume% or less, even more preferably 5 volume% or less, particularly preferably 3 volume% or less, and most preferably 1 volume% or less. It is also preferable to reduce the amount of coarse particles to 20 volume% or less, more preferably 15 volume% or less, even more preferably 10 volume% or less, particularly preferably 5 volume% or less, and most preferably 1 volume% or less. Typically, the content of fine and coarse particles in the final product does not change significantly from the content after the classification process.

[0045] In this classification process, classification refers to particle size classification, which separates powders according to their particle size with the aim of standardizing their particle size. One operation of this particle size classification is fluid classification, which can be further classified into dry classification and wet classification.

[0046] Classifiers used in dry classification can be broadly classified into gravity classifiers, inertial classifiers, and centrifugal classifiers. More precise classification is possible by using inertial classifiers, which classify particles using their inertial force, or centrifugal classifiers. Examples of classifiers that exhibit their characteristics even with light particles that are less susceptible to centrifugal force include the Elbow Jet manufactured by Nippon Steel Mining Co., Ltd., the SG Separator manufactured by 3M Japan, the Aerofine Classifier manufactured by Nisshin Engineering Co., Ltd., and the Microspin manufactured by Nippon Pneumatic Mfg. Co., Ltd. Among these, the Elbow Jet and Aerofine Classifier are preferred because they can precisely classify even light, hollow particles.

[0047] Classifiers used in wet classification can be broadly classified into gravity classifiers and centrifugal classifiers in principle. Using a centrifugal classifier allows for more precise classification. Examples of classifiers that perform well even with light particles that are difficult to centrifugal force on include the Hydrocyclone manufactured by Nippon Chemical Machinery Industry Co., Ltd., the Superclon manufactured by Murata Industries Ltd., and the iClassifier manufactured by Satake Multimix Co., Ltd. Among these, the iClassifier, which can precisely classify light, hollow particles, is preferred. When wet classification is performed, coarse particles with a lower specific gravity can be removed along with the fine particles, thereby improving classification efficiency.

[0048] (drying process) The manufacturing method of the present invention may include a drying step. Heat drying is one example of a drying method. The drying temperature is preferably 50 to 400°C, and more preferably 50 to 200°C. Specifically, examples include drying at a low temperature of about 50 to 200°C over a long period of time, drying by gradually increasing the temperature, or drying by changing the temperature in several stages. The drying treatment can be provided between the alkali removal treatment and the classification treatment, between the classification treatment and firing, both, or between the alkali removal treatment and firing. It may be provided multiple times as needed. Alternatively, the drying treatment may be performed before firing, and the classification treatment may be performed between the drying treatment and firing. It is preferable to perform the classification treatment after the drying treatment and then fire.

[0049] (Sieving process) Furthermore, it is preferable to perform a sieving process to remove particle clumps after drying and at least one of the following: after firing. Note that particle clumps refer to foreign matter, such as particles with a diameter exceeding 150 μm. The sieving process is performed using a sieve with an appropriate mesh size (number of sieves) that can remove such particle clumps.

[0050] Next, the silica-based hollow particles of the present invention will be described. The silica-based hollow particles of the present invention can be obtained by the manufacturing method of the present invention described above. The silica-based hollow particles of the present invention are a powder in which the majority are hollow particles, but some solid particles may be included. For example, the amount of hollow particles may be 80% or more of the total, or 90% or more. The proportion of hollow particles can be calculated, for example, by cross-sectional SEM imaging using any 100 particles.

[0051] The silica-based hollow particles of the present invention satisfy the following requirements (i) to (vii). (i) Average particle size (D50) is 0.1 to 20 μm (ii) Porosity of 10-95% (iii) Sears count (ml / SiO2 1.5g) is less than 0.30 (iv) Water vapor / nitrogen specific surface area ratio is less than 0.30 (v) Water vapor adsorption amount is less than 0.20% by mass (vi) In Si-NMR, the structure is substantially composed of a Q3 structure with a chemical shift of -82.0 to -100.0 ppm and a Q4 structure with a chemical shift of -100.0 to -120.0 ppm, with the peak area of ​​the Q4 structure accounting for 90% or more of the total peak area. (vii) Alkali content is 100 ppm or less

[0052] The silica-based hollow particles of the present invention have low dielectric constant and dielectric loss tangent. The dielectric constant is preferably 2.8 or less, and more preferably 2.5 or less. Furthermore, the dielectric loss tangent is preferably less than 0.0010, and more preferably less than 0.0005.

[0053] The requirements are explained below. (i) The average particle size (D50) is between 0.1 and 20 μm. Silica particles with an average particle diameter of less than 0.1 μm contain many fine particles, resulting in a high specific surface area (high SiOH group content) and thus poor dielectric properties. Furthermore, silica particles with an average particle diameter exceeding 20 μm are unsuitable for semiconductor applications. Considering semiconductor applications, an average particle diameter of 0.3 to 10.0 μm is more preferable, and 0.5 to 5.0 μm is even more preferable.

[0054] Furthermore, the maximum particle diameter (D100) is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. The maximum particle diameter (D100) is preferably 10 times or less the average particle diameter (D50), and more preferably 8 times or less. Typically, it is 2 times or more, and may exceed 5 times.

[0055] (ii) The porosity is 10 to 95%. If the porosity is less than 10%, the dielectric constant and dielectric loss tangent will be high, and the desired dielectric constant and dielectric loss tangent cannot be obtained. Also, if the porosity exceeds 95%, the particle strength will be low and the particles will crack. The porosity is preferably 20 to 70%, and more preferably 30 to 50%.

[0056] (iii) The Sears number (ml / SiO2 1.5g) is less than 0.30. The Sears number is an indicator of the amount of OH groups (silanol groups) in silica particles; a higher Sears number indicates a greater amount of OH groups in the particles. For particles with a Sears number of 0.30 or higher, the dielectric constant and dielectric loss tangent become higher, and moisture absorption occurs over time, further increasing the dielectric constant and dielectric loss tangent. Furthermore, adhesion increases, leading to particle aggregation. A Sears number of less than 0.29 is preferable, and less than 0.28 is more preferable.

[0057] The Sears number is measured by titration with sodium hydroxide, in accordance with Sears' description in Analytical Chemistry 28 (1956), 12, 1981-1983. This method measures the amount of OH groups on the particle surface (outside the pores). The Sears number (ml / SiO2 1.5g) indicates the titration volume of 0.1N sodium hydroxide aqueous solution per 1.5g of silica.

[0058] (iv) The water vapor / nitrogen specific surface area ratio is less than 0.30. The water vapor / nitrogen specific surface area ratio indicates the degree of hydrophilicity or hydrophobicity; a higher value indicates greater hydrophilicity. Materials with a water vapor / nitrogen specific surface area ratio of 0.30 or higher are prone to hygroscopicity. A water vapor / nitrogen specific surface area ratio of less than 0.20 is preferable, and less than 0.15 is more preferable.

[0059] (v) The amount of water vapor adsorbed is less than 0.20% by mass. The amount of water vapor adsorbed indicates the stability over time in terms of moisture absorption. Materials with a water vapor adsorption amount of 0.20% by mass or more are prone to moisture absorption and have poor stability over time. A water vapor adsorption amount of less than 0.15% is preferable, and less than 0.10% is more preferable.

[0060] (vi) 29 In Si-NMR, the structure essentially consists of a Q3 structure with a chemical shift of -82.0 to -100.0 ppm and a Q4 structure with a chemical shift of -100.0 to -120.0 ppm, with the peak area of ​​the Q4 structure accounting for 90% or more of the total peak area.

[0061] The silicon atoms in silica particles are 29In Si-NMR analysis, silicon atoms can be classified into five types—Q0, Q1, Q2, Q3, and Q4—based on the number of silicon atoms sharing oxygen with them. Specifically, 29 In Si-NMR analysis, the chemical shifts for the Q0 structure are -73.0 to -73.5 ppm, the Q1 structure is -73.5 to -78.0 ppm, the Q2 structure is -78.0 to -82.0 ppm, the Q3 structure is -82.0 to -100.0 ppm, and the Q4 structure is -100.0 to -120.0 ppm.

[0062] When the abundance (area ratio) of the Q4 structure falls within the above range, there are fewer unstable OH groups and a higher proportion of silicon-to-silicon bonding, resulting in highly stable silica particles. Therefore, when used as a filler material, an insulating material with minimal changes over time can be obtained. If the proportion of Q0-Q3 structures is high, these structures have more OH groups (fewer siloxane bonds) compared to the Q4 structure. Therefore, when used as a filler material, it will absorb moisture over time, leading to an increase in dielectric constant and dielectric loss tangent.

[0063] The peak area of ​​the Q4 structure is more preferably 93% or more of the total peak area (area of ​​Q0 to Q4 structures), and even more preferably 95% or more.

[0064] (vii) The alkali content must be 100 ppm or less. By having an alkali content of 100 ppm or less, it is possible to achieve a low dielectric constant and low dielectric loss tangent. It is also suitable for semiconductor packaging. Furthermore, it prevents particle adhesion in subsequent processes and prevents the generation of sintered particles in the firing process. The alkali content is preferably 90 ppm or less, and more preferably 80 ppm or less.

[0065] Furthermore, in addition to the above requirements (i) to (vii), the silica-based hollow particles preferably have a particle size variation coefficient (CV value) of 60% or less, more preferably 55% or less, and even more preferably 50% or less. Having the particle size variation coefficient within this range allows for more stable achievement of low dielectric constant and low dielectric loss tangent when compounded into a resin. It also improves the surface smoothness of the resin composition.

[0066] [Method for producing resin compositions] The present invention provides a method for producing a resin composition by mixing the above-mentioned silica-based hollow particles with a resin and curing it. Specifically, for example, silica-based hollow particles, a thermosetting resin, etc., are mixed and kneaded in a roll mill or the like to prepare a resin composition forming liquid (coating liquid), which is then applied to a substrate and cured by heat, ultraviolet light, etc.

[0067] The manufactured resin composition can be used as an insulating material for electronic materials such as semiconductors. Specifically, it can be used for copper-clad laminates, prepregs, build-up films, etc., for forming printed circuit boards (including rigid and flexible substrates). It can also be used for semiconductor packaging-related materials such as mold resins, mold underfills, and underfills, as well as adhesives for flexible substrates.

[0068] As the resin to be mixed with silica-based hollow particles, curable resins generally used in electronic materials such as semiconductors can be used. Photocurable resins are also acceptable, but thermosetting resins are preferred. Examples of such curable resins include epoxy resins, polyphenylene ether resins, fluorine resins, polyimide resins, bismaleimide resins, acrylic resins, methacrylic resins, silicone resins, BT resins, cyanate resins, etc. Examples of epoxy resins include bisphenol-type epoxy resins, novolac-type epoxy resins, triphenolalkane-type epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, dicyclopentadienephenol novolac resins, phenol aralkyl-type epoxy resins, glycidyl ester-type epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, halogenated epoxy resins, etc. These resins may be used individually or in mixtures of two or more types.

[0069] The resin composition (resin composition forming liquid) preferably contains silica-based hollow particles A and curable resin B in a mass ratio (A / B) of 10 / 100 to 95 / 100, and more preferably 30 / 100 to 80 / 100. With such a mass ratio, the resin composition forming liquid can fully exhibit its function as a filler while maintaining its properties such as fluidity.

[0070] The resin composition (resin composition forming liquid) preferably contains a curing agent such as a phenol compound, an amine compound, or an acid anhydride. When an epoxy resin is used as the curable resin, examples of curing agents include phenolic resins having two or more phenolic hydroxyl groups in one molecule, such as bisphenol-type resins, novolac resins, triphenolalkane-type resins, resol-type phenolic resins, phenol aralkyl resins, biphenyl-type phenolic resins, naphthalene-type phenolic resins, and cyclopentadiene-type phenolic resins, as well as acid anhydrides such as methylhexahydrophthalic acid, methyltetrahydrophthalic acid, and methylnadic anhydride.

[0071] Various additives such as colorants, stress relievers, defoamers, leveling agents, coupling agents, flame retardants, and curing accelerators may be added to the resin composition (resin composition forming liquid) as needed. [Examples]

[0072] The following describes specific embodiments of the present invention.

[0073] <Manufacturing of silica-based hollow particles> [Example 1] 30,000 g of a water glass aqueous solution (SiO2 / Na2O molar ratio 3.2, SiO2 concentration 24% by mass) was used, and silica hollow particles were obtained by spraying hot air at an inlet temperature of 400°C into one of two fluid nozzles at a flow rate of 0.62 kg / hr and into the other nozzle at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600). At this time, the outlet temperature was 150°C (first step). 5,000 g of silica hollow particles were added to 40,000 g of a 25% by mass sulfuric acid aqueous solution while stirring. The liquid temperature was adjusted to 35°C, and the mixture was stirred for 15 hours and then cooled to room temperature. At this time, the solid content (SiO2) concentration was 8.4% by mass, and the pH of the dispersion after cooling was less than 1.0. Furthermore, the number of moles of hydrogen ions of the acid (M) was compared with the value obtained by multiplying the number of moles and valence of alkali metal ions in the hollow particles (Msp). H+ ) ratio (M H+ The ratio ( / Msp) was 5.2. After separation from sulfuric acid, it was washed with pure water (second step). Then, it was dried in a dryer at 120°C for 24 hours (drying step). After drying, it was crushed and sieved through a 75 μm mesh sieve to remove particulate matter (foreign matter). After that, dry inertial classification was performed using an elbow jet (EJ-15) manufactured by Nippon Steel Mining Co., Ltd. This apparatus can separate the powder into three types: F powder (fine powder), M powder (very fine powder), and G powder (coarse powder). The F edge distance was adjusted so that the amount of particles larger than 24 μm in the F powder (fine powder) was 5% by volume or less, and it was collected using a bag filter and used in subsequent steps (classification step). After that, the powder containing the desired silica-based hollow particles was obtained by heat treatment at 1000°C for 10 hours (third step). After firing, particulate matter (foreign matter) was removed using a sieve with a mesh size of 150 μm (powder A).

[0074] [Example 2] 30,000 g of a water glass aqueous solution (SiO2 / Na2O molar ratio 3.2, SiO2 concentration 24% by mass) was used. Silica hollow particles were obtained by spraying hot air at an inlet temperature of 400°C into one of two fluid nozzles at a flow rate of 0.62 kg / hr and into the other nozzle at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600). At this time, the outlet temperature was 150°C (first step). 5,000 g of silica hollow particles were added to 45,000 g of a 25% by mass sulfuric acid aqueous solution while stirring. The liquid temperature was adjusted to 35°C, and the mixture was stirred for 15 hours and then cooled to room temperature. At this time, the solid content (SiO2) concentration was 7.6% by mass, and the pH of the dispersion after cooling was less than 1.0. Furthermore, the number of moles of hydrogen ions of the acid (M) was compared with the value obtained by multiplying the number of moles and valence of alkali metal ions in the hollow particles (Msp). H+ ) ratio (M H+ The ratio ( / Msp) was 5.8. After separation from sulfuric acid, it was washed with pure water (second step). Then, it was dried in a dryer at 120°C for 24 hours (drying step). After drying, it was crushed and sieved through a 75 μm mesh sieve to remove particulate matter (foreign matter). After that, dry inertial classification was performed using an elbow jet (EJ-15) manufactured by Nippon Steel Mining Co., Ltd. This device can separate the powder into three types: F powder (fine powder), M powder (very fine powder), and G powder (coarse powder). The F edge distance was adjusted so that the amount of particles larger than 24 μm in the F powder (fine powder) was 5% by volume or less, and it was collected using a bag filter and used in subsequent steps (classification step). After that, the powder containing the desired silica-based hollow particles was obtained by heat treatment at 1000°C for 10 hours (third step). After firing, particulate matter (foreign matter) was removed using a sieve with a mesh size of 150 μm (powder B).

[0075] [Example 3] The procedure was the same as in Example 1, except that the liquid temperature was adjusted to 60°C in the second step, to obtain powder C containing silica-based hollow particles.

[0076] [Example 4] 30,000 g of a water glass aqueous solution (SiO2 / Na2O molar ratio 3.2, SiO2 concentration 24% by mass) was used, and silica hollow particles were obtained by spraying hot air at an inlet temperature of 400°C into one of two fluid nozzles at a flow rate of 0.62 kg / hr and into the other nozzle at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600). At this time, the outlet temperature was 150°C (first step). 5,000 g of silica hollow particles were added to 80,000 g of a 10% by mass hydrochloric acid aqueous solution while stirring. The liquid temperature was adjusted to 35°C, and the mixture was stirred for 15 hours and then cooled to room temperature. At this time, the solid content (SiO2) concentration was 4.4% by mass, and the pH of the dispersion after cooling was less than 1.0. Furthermore, the number of moles of hydrogen ions in the acid (M) was compared with the value obtained by multiplying the number of moles and valence of alkali metal ions in the hollow particles (Msp). H+ ) ratio (M H+ The ratio ( / Msp) was 5.6. After separation from hydrochloric acid, it was washed with pure water (second step). Then, it was dried in a dryer at 120°C for 24 hours (drying step). After drying, it was crushed and sieved through a 75 μm mesh sieve to remove particulate matter (foreign matter). After that, dry inertial classification was performed using an elbow jet (EJ-15) manufactured by Nippon Steel Mining Co., Ltd. This apparatus can separate the powder into three types: F powder (fine powder), M powder (very fine powder), and G powder (coarse powder). The F edge distance was adjusted so that the amount of particles larger than 24 μm in the F powder (fine powder) was 5% by volume or less, and it was collected using a bag filter and used in subsequent steps (classification step). After that, the powder containing the desired silica-based hollow particles was obtained by heat treatment at 1000°C for 10 hours (third step). After firing, particulate matter (foreign matter) was removed using a sieve with a mesh size of 150 μm (powder D).

[0077] [Comparative Example 1] 30,000 g of a water glass aqueous solution (SiO2 / Na2O molar ratio 3.2, SiO2 concentration 24% by mass) was used, and silica hollow particles were obtained by spraying hot air at an inlet temperature of 400°C into one of two fluid nozzles at a flow rate of 0.62 kg / hr and into the other nozzle at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600). At this time, the outlet temperature was 150°C (first step). 5,000 g of silica hollow particles were added to 32,000 g of a 25% by mass sulfuric acid aqueous solution while stirring. The liquid temperature was adjusted to 35°C, and the mixture was stirred for 15 hours and then cooled to room temperature. At this time, the solid content (SiO2) concentration was 10.2% by mass, and the pH of the dispersion after cooling was less than 1.0. Furthermore, the number of moles of hydrogen ions of the acid (M) was compared with the value obtained by multiplying the number of moles and valency of alkali metal ions in the hollow particles (Msp). H+ ) ratio (M H+ The ratio ( / Msp) was 4.1. After separation from sulfuric acid, it was washed with pure water (second step). Then, it was dried in a dryer at 120°C for 24 hours (drying step). After drying, it was crushed and sieved through a 75 μm mesh sieve to remove particulate matter (foreign matter). After that, dry inertial classification was performed using an elbow jet (EJ-15) manufactured by Nippon Steel Mining Co., Ltd. This device can separate the powder into three types: F powder (fine powder), M powder (very fine powder), and G powder (coarse powder). The F edge distance was adjusted so that the amount of particles larger than 24 μm in the F powder (fine powder) was 5 volume percent or less, and it was collected using a bag filter and used in subsequent steps (classification step). After that, the powder containing the desired silica-based hollow particles was obtained by heat treatment at 1000°C for 10 hours (third step). After firing, particulate matter (foreign matter) was removed using a sieve with a mesh size of 150 μm (powder E).

[0078] [Comparative Example 2] 30,000 g of aqueous water glass solution (SiO2 / Na2O molar ratio 3.2, SiO2 concentration 24% by mass) was used, and silica hollow particles were obtained by spraying hot air at an inlet temperature of 400°C into one of two-fluid nozzles at a flow rate of 0.62 kg / hr and into the other nozzle at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600). At this time, the outlet temperature was 150°C (first step). 5,000 g of the obtained silica hollow particles were packed into a column, and 80,000 g of aqueous sulfuric acid solution with a concentration of 25% by mass was passed through it. The number of moles of hydrogen ions of the acid (M) was compared with the value obtained by multiplying the number of moles and valency of alkali metal ions in the hollow particles (Msp). H+ ) ratio (M H+ The ratio ( / Msp) was 5.2. After passing sulfuric acid through the material, it was washed with pure water (second step). Then, it was dried in a dryer at 120°C for 24 hours (drying step). After drying, it was crushed and sieved through a 75 μm mesh sieve to remove particulate matter (foreign matter). After that, dry inertial classification was performed using an elbow jet (EJ-15) manufactured by Nippon Steel Mining Co., Ltd. This device can separate the powder into three types: F powder (fine powder), M powder (very fine powder), and G powder (coarse powder). The F edge distance was adjusted so that the amount of particles larger than 24 μm in the F powder (fine powder) was 5% by volume or less, and it was collected using a bag filter and used in subsequent steps (classification step). After that, the powder containing the desired silica-based hollow particles was obtained by heat treatment at 1000°C for 10 hours (third step). After firing, particulate matter (foreign matter) was removed using a sieve with a mesh size of 150 μm (powder F).

[0079] <Manufacturing of resin compositions> The obtained silica-based hollow particles were mixed with liquid acid anhydride "Ricacid MH700" (manufactured by Shin Nippon Rika Co., Ltd.) and imidazole-based epoxy resin curing agent "2PHZ-PW" (manufactured by Shikoku Kasei Co., Ltd.) in liquid epoxy resin "ZX-1059" (manufactured by Nippon Steel Chemical & Material Co., Ltd.). After pre-mixing in a planetary mill, the mixture was kneaded with a three-roll mill to prepare a resin composition forming liquid. In this mixture, "ZX-1059" was added in a ratio of 100 parts by mass, "Ricacid MH700" in a ratio of 86 parts by mass, and "2PHZ-PW" in a ratio of 1 part by mass. The silica-based hollow particles in the resin composition were also added so that they accounted for 35% by volume. The prepared resin composition forming liquid was heated at 170°C for 2 hours to cure, obtaining a plate-shaped resin composition measuring 50 mm × 50 mm × 1 mm. The substrate was then stored for 1000 hours under conditions of 80°C and 80% humidity.

[0080] The physical properties of silica-based hollow particles and resin compositions were measured and evaluated as follows. The results, along with the preparation conditions, are shown in Table 1.

[0081] (1) Average particle size (D50), maximum particle size (D100), amount of coarse particles, and coefficient of particle size variation (CV value) The particle size distribution was measured using a dry method with a particle size analyzer (Seishin Corporation Laser Micron Sizer LMS-3000). From the measurement results, the average particle diameter (D50) and the maximum particle diameter (D100) were obtained. Furthermore, by analyzing this particle size distribution, the amount of coarse particles exceeding six times the average particle diameter was calculated as a volume ratio.

[0082] The coefficient of particle size variation (CV value) was calculated using the following formula. Here, the average particle diameter is the volume-average particle diameter (D 43 The following was used: The particle size of each individual particle was measured using the dry laser diffraction and scattering method.

[0083] CV value (%) = (Standard deviation (τ) / Volume-average particle diameter (D) 43 )) × 100 Standard deviation (τ)=(ΣX i (D i -D 43 )^2 / ΣX i )^(1 / 2) Di: Particle diameter of individual particles

[0084] (2) Discrepancy between theoretical values ​​and actual values ​​of porosity and particle density. Particle density was measured using the gas pycnometer method with an Ultrapyc5000 from Quantachrome Instruments. From this particle density, the following equation [2.2-(particle density)] / 2.2×100 The porosity (%) was calculated using the following formula. In this formula, the density of silica is assumed to be 2.2 g / cm³. 3 That's what I decided.

[0085] Discrepancy between the theoretical value of particle density and actual values. The density of particles dried at 120°C for 24 hours after the second step (ρ²) and the theoretical value of the particle density after the second step (ρ²) 2T ) and the deviation (ρ² / ρ 2T ) was calculated.

[0086] (3) Amount of remaining alkali Silica-based hollow particles were pretreated with sulfuric acid and hydrofluoric acid, then dissolved in hydrochloric acid, and the alkali content was measured by atomic absorption spectrometry using an atomic absorption spectrophotometer (Hitachi Z-2310). In this example, the amount of Na was measured.

[0087] (4) Sears number of silica particles The Sears number was measured by titration using sodium hydroxide, in accordance with Sears' description in Analytical Chemistry 28 (1956), 12, 1981-1983. Specifically, 150 g of silica diluted with pure water to a silica particle concentration of 1% by mass was mixed with 30 g of sodium chloride, the pH was adjusted to 4.0 with hydrochloric acid, and then titrated with a 0.01 N sodium hydroxide solution. The amount required to reach pH 9.0 was divided by 10 and expressed as the amount titrated with a 0.1 N sodium hydroxide solution (i.e., the titration volume of 0.1 N sodium hydroxide solution per 1.5 g of silica). The titration with the 0.01 N sodium hydroxide solution was performed using an automatic titrator at a fixed rate of 0.1 ml / second. (5) Water vapor / nitrogen specific surface area ratio The ratio of the BET specific surface area obtained by the water vapor adsorption method to the BET specific surface area obtained by the nitrogen adsorption method was calculated. A BELSORP-max manufactured by Microtrac-Bel was used for the measurement. (6) Amount of water vapor adsorption Using a BELSORP-max manufactured by Microtrac-Bel, measurements were performed using the water vapor adsorption method to determine the amount of water vapor adsorbed at a partial pressure of 0.9 (p / p0 = 0.9) relative to the powder mass.

[0088] (7) 29 Si-NMR Silica particles 29 Structural analysis using Si-NMR was performed, for example, as follows: After drying the powder sample at 110°C for 1 hour and then conditioned it at 60% relative humidity for 24 hours, the sample was uniformly packed into a 5 mm diameter solid-state NMR sample tube and measured using a 14.1 T NMR spectrometer (Agilent VNMRS-600, 1H resonance frequency 600 MHz) with the single-pulse non-decoupling method. Polydimethylsiloxane (-34.44 ppm) was used as the reference material. Waveform analysis was performed on the obtained spectra, and the area of ​​each peak was calculated. The proportion of each structure was calculated using the ratio of peak areas of each structure (Si / ST) × 100 [%] (where i is a number selected from 0, 1, 2, 3, or 4, and ST is the sum of the peak areas of each structure represented by ST = S0 + S1 + S2 + S3 + S4).

[0089] (8) Dielectric constant (Dk) and dielectric loss tangent (Df) of silica-based hollow particles The dielectric constant (Dk) and dielectric loss tangent (Df) were measured using the cavity resonator perturbation method with a network analyzer (Anritsu MS46122B) and a cavity resonator (1 GHz). The measurements were performed in accordance with ASTMD2520 (JIS C2565).

[0090] (9) Dielectric constant (Dk) and dielectric loss tangent (Df) of the resin composition The dielectric constant (Dk) and dielectric loss tangent (Df) of a 50mm x 50mm x 1mm plate-shaped molded body (resin composition) were measured at 9.4GHz using a network analyzer (Anritsu MS46122B) and a coaxial resonator. The composition was evaluated against a resin composition without silica-based hollow particles (filler) according to the following evaluation criteria.

[0091] Dielectric constant (Dk) reduction rate (%) = (Dielectric constant without filler - Dielectric constant with filler) / Dielectric constant without filler) × 100

[0092] ○: Reduction rate > 0 △: Reduction rate = 0 ×: Reduction rate < 0

[0093] Dielectric loss tangent (Df) reduction rate (%) = (Dielectric loss tangent without filler - Dielectric loss tangent with filler) / Dielectric loss tangent without filler) × 100

[0094] ◎: Reduction rate of 50% or more ○: Reduction rate of 30% or more but less than 50% △: Reduction rate of 20% or more but less than 30% ×: Reduction rate less than 20%

[0095] (10) Change in dielectric constant (Dk) of resin composition due to high temperature and high humidity test The relative ratio of the Dk values ​​before and after = Dk(after) / Dk(before) ◎: 1.0 or less ○: Greater than 1.0 and less than or equal to 1.1 △: Greater than 1.1 and less than or equal to 1.2 ×: Greater than 1.2

[0096] (11) Change in dielectric loss tangent (Df) of resin composition due to high temperature and high humidity test The relative ratio of the Df values ​​before and after = Df(after) / Df(before) ◎: 1.0 or less ○: Greater than 1.0 and less than or equal to 2.0 △: Greater than 2.0 and 3.0 or less ×: Greater than 3.0

[0097] [Table 1] [Industrial applicability]

[0098] The silica-based hollow particles produced by the manufacturing method of the present invention can be used as fillers in insulating materials for electronic materials such as semiconductors, and are industrially useful.

Claims

1. The first step involves preparing hollow particles by spray-drying an alkaline silicate aqueous solution in a hot air stream, A second step involves immersing the hollow particles in an acidic solution at 35°C or higher to neutralize the alkali contained in the hollow particles, and then washing to remove the amount of alkali remaining in the hollow particles to 100 ppm by mass or less. The third step involves firing the hollow particles obtained in the second step at a temperature of 900°C or higher. In the second step, the value obtained by multiplying the number of moles and the valency of alkali metal ions in the hollow particles (M ｓｐ The number of moles of hydrogen ions of the acid (M) Ｈ＋ ) ratio (M Ｈ＋ / M ｓｐ A method for producing silica-based hollow particles, characterized by using an acid solution with a pH of 5.0 or higher.

2. The method for producing silica-based hollow particles according to claim 1, characterized in that the temperature of the acid solution in the second step is 50°C or higher.

3. Furthermore, the method for producing silica-based hollow particles according to claim 1 or 2, characterized by having a classification step.

4. A method for producing a resin composition forming liquid, characterized by mixing silica-based hollow particles produced by the manufacturing method described in Claim 1 with a resin.

5. Silica-based hollow particles characterized by satisfying the following requirements (i) to (vii). (i) Average particle size (D50) of 0.5 to 20 μm (ii) Porosity of 20-70% (iii) Sears number (ml / SiO ２ 1.5g) is less than 0.30 (iv) Water vapor / nitrogen specific surface area ratio is less than 0.30 (v) Water vapor adsorption amount is less than 0.20% by mass (vi) ２９ In Si-NMR, substantially, Q having a chemical shift of -82.0 to -100.0 ppm ３ structure, and Q having a chemical shift of -100.0 to -120.0 ppm ４ consists of structures, wherein the peak area of Q ４ structure accounts for 90% or more of the total peak area (vii) Alkali content is 100 ppm or less

6. The silica-based hollow particle according to claim 5, characterized in that the dielectric constant is 2.8 or less and the dielectric loss tangent is less than 0.0010.

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