JP7684044B2 - Silica-based hollow particles, method for producing same, and resin composition - Google Patents

Description

The present invention relates to silica-based hollow particles that are useful as a filler for insulating materials in semiconductors, a method for producing the same, and a resin composition.

In recent years, the volume of data communication in information and communications has increased, and there is a demand for high-speed processing in communication devices. Insulating materials in printed wiring boards for semiconductors used in such communication devices are required to have low dielectric constants (low Dk) and low dielectric tangents (low Df) in order to achieve high-speed communication. If the dielectric constant of an insulating material is high, it will lead to dielectric loss, and if the dielectric tangent of an insulating material is high, it will not only lead to dielectric loss, but may also cause problems such as increased heat generation.

In the insulating materials used in printed wiring boards for semiconductors, efforts are being made to develop resin materials that will serve as the main insulating material in order to achieve low dielectric constants and low dielectric loss tangents. Examples of such resin materials that have been proposed include epoxy resins, polyphenylene ether resins, and fluorine resins (see, for example, Patent Documents 1 to 5).

On the other hand, fillers are blended into such resin materials for the sake of durability (rigidity) and heat resistance. Examples of such fillers include silica, boron nitride, talc, kaolin, clay, mica, alumina, zirconia, titania, and other metal oxides (see, for example, Patent Document 3).

WO2009/041137 Special Publication No. 2006-516297 JP 2017-057352 A JP 2001-288227 A JP 2019-172962 A

Among the fillers contained in the insulating materials for semiconductors, silica excels in terms of its low dielectric constant and low dielectric loss tangent. However, in today's world where data communication is rapidly increasing in capacity and processing speed, there is a demand for even lower dielectric constants and dielectric loss tangents. It is also important that the filler in the insulating material for semiconductors does not interfere with the filterability or injectability of the insulating material-forming liquid in the manufacturing process for the insulating material.

The objective of the present invention is to provide silica-based particles that enable the dielectric constant and dielectric tangent of insulating materials to be reduced and that do not impede the filterability and injectability of the insulating material-forming liquid during the manufacturing process, and a method for manufacturing the same.

As data communication is rapidly becoming larger in capacity and faster in processing, the inventors conducted extensive research into silica particles that are useful as fillers for insulating materials in semiconductors. As a result, they discovered that silica-based hollow particles that do not contain coarse particles and meet certain conditions can achieve low dielectric constants and low dielectric tangents in insulating materials, and do not impede the filterability and injectability of the insulating material-forming liquid in the manufacturing process, which led to the completion of the present invention.

That is, the present invention relates to silica-based hollow particles that have cavities inside a non-porous outer shell, have an average particle size (D50) of 0.1 to 10 μm, and are characterized in that, when suspended in water, floating particles a are 0.5 to 7.0 mass%, suspended particles b are 0 to 4.0 mass%, and sinking particles c are 89.0 to 99.5 mass%.

The present invention also relates to a method for producing silica-based hollow particles, which includes a hollow particle preparation step in which an aqueous solution of alkali silicate is spray-dried in a hot air stream to prepare hollow particles, an alkali removal step in which the alkali contained in the prepared hollow particles is neutralized with an acid and removed, and a firing step in which the hollow particles from which the alkali has been removed are fired, and which is characterized in that a classification step is included between the hollow particle preparation step and the firing step in which the hollow particles are classified to remove coarse particles.

The silica-based hollow particles of the present invention can realize a low dielectric constant and low dielectric loss tangent of insulating materials, and can therefore increase the transmission speed of semiconductors and reduce transmission loss. Furthermore, the silica-based hollow particles of the present invention do not impede the filterability and injectability of the insulating material forming liquid in the manufacturing process, and can stably manufacture excellent insulating materials.

[Silica-based hollow particles]
The silica-based hollow particles of the present invention have cavities inside a non-porous outer shell and have an average particle size of 0.1 to 10 μm. When these silica-based hollow particles are suspended in water, the floating particles account for 0.5 to 7.0 mass%, the suspended particles for 0 to 4.0 mass%, and the settling particles for 89.0 to 99.5 mass%.

Here, silica-based means that the main component is silica, and may 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, and even more preferably 95% by mass or more, and it is particularly preferable that the particles consist essentially of silica.

The particles of the present invention are hollow particles having a cavity inside a non-porous outer shell, and contain floating particles (particles with high porosity) with a low specific gravity that float when suspended in water. Therefore, when blended into a resin composition, a low dielectric constant and low dielectric loss tangent are achieved. In addition, since hollow particles with high porosity generally have a large particle diameter, controlling the amount of these floating particles to 0.5 to 7.0 mass% of the total particles controls (reduces) the amount of coarse particles. Therefore, the filterability and injectability of the resin composition forming liquid in the manufacturing process of a resin composition such as an insulating material are improved, and the surface smoothness after molding can be improved. In this case, the content of coarse particles with a particle diameter of more than 8.0 μm is preferably 10 vol% or less, more preferably 5 vol% or less, and even more preferably 1 vol% or less.

Light-weight particles suspended in water tend to have low particle strength because the ratio of shell thickness to particle diameter is small. This can lead to particle cracking during the production of resin compositions such as insulating materials. The occurrence of particle cracking not only prevents the achievement of low dielectric constants and low dielectric tangents, but also deteriorates the fluidity of the resin composition forming liquid, reducing the uniformity of the resin composition (molded product) and causing voids to form inside the resin composition. Particle cracking can be suppressed by controlling the amount of suspended particles.

In the present invention, the amount of suspended particles is particularly controlled, so that the desirable properties of particles with high porosity (particularly low dielectric constant and low dielectric tangent) are secured while the undesirable properties of particles with high porosity (particularly the occurrence of cracks) are suppressed to an acceptable level. Furthermore, even if the suspended particles have a high porosity, there are also small-diameter particles, and such particles are less likely to crack during the manufacturing process than large-diameter particles, so that overall the undesirable properties of particles with high porosity can be suppressed as much as possible.

The content of floating particles is preferably 1.0 to 5.0% by mass, more preferably 1.0 to 4.0% by mass, and even more preferably 2.0 to 4.0% by mass. The content of sinking particles is preferably 91.0 to 99.5% by mass, more preferably 92.0 to 99.0% by mass, and even more preferably 95.0 to 98.0% by mass.

The proportions of floating particles, suspended particles, and sinking particles when suspended in water are calculated by collecting and weighing each type of particle from the suspension. Specific examples will be explained in the Examples.

The average particle size (D50) of the silica-based hollow particles of the present invention is in the range of 0.1 to 10 μm. It is difficult to manufacture particles with an average particle size of less than 0.1 μm using the spray drying method. Silica-based particles with an average particle size of more than 10 μm are not suitable for semiconductor applications. Considering that they are used in semiconductor applications, the average particle size is preferably 0.5 to 10 μm, and more preferably 1.0 to 5.0 μm.

The maximum particle size (D100) is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The maximum particle size (D100) is preferably 10 times or less, and more preferably 8 times or less, the average particle size (D50). It is usually 2 times or more, and may be more than 5 times as long as the requirements of the present invention are met.

The average particle size (D50), maximum particle size (D100) and content of coarse particles are measured by a laser diffraction/scattering method. Specific details are described in the examples.

The porosity of the silica-based hollow particles of the present invention is preferably 5% by volume or more, more preferably 8% by volume or more, and even more preferably 10% by volume or more. The upper limit is preferably 50% by volume or less, more preferably 35% by volume or less, even more preferably 25% by volume or less, and most preferably 20% by volume or less. Such a porosity can reduce the dielectric constant and the dielectric loss tangent, and can effectively suppress particle cracking by maintaining the particle strength at a predetermined level or more. Here, the porosity is calculated from the particle density. Specific examples will be described in the Examples.

The silica-based hollow particles of the present invention are suitable for use as a filler for insulating materials for electronic materials such as semiconductors. Specifically, they can be blended into copper-clad laminates, prepregs, build-up films, etc. for forming printed wiring boards (including rigid and flexible boards). They can also be blended into semiconductor package-related materials such as mold resins, mold underfills, and underfills, and adhesives for flexible boards, etc.

[Resin composition]
The resin composition of the present invention contains the silica-based hollow particles of the present invention. Such a resin composition can be used for applications of the silica-based hollow particles, such as insulating materials for electronic materials such as semiconductors.

As the resin contained in the resin composition (resin composition forming liquid) of the present invention, a curable resin generally used in electronic materials such as semiconductors can be used. A photocurable resin may be used, but a thermosetting resin is 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, and the like. Specific examples of epoxy resins include bisphenol-type epoxy resins, novolac-type epoxy resins, triphenol alkane-type epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, dicyclopentadiene phenol novolac resins, phenol aralkyl-type epoxy resins, glycidyl ester-type epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, halogenated epoxy resins, and the like. These resins may be used alone or in a mixture of two or more.

The content of the silica-based hollow particles in the resin composition (resin composition forming liquid) of the present invention is preferably a mass ratio (A/B) of silica-based hollow particles A to curable resin B of 10/100 to 95/100, more preferably 30/100 to 80/100. Such a mass ratio allows the resin composition forming liquid to fully function as a filler while maintaining its properties such as fluidity.

The resin composition (liquid for forming a resin composition) of the present invention 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 the curing agent 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, and acid anhydrides such as methylhexahydrophthalic acid, methyltetrahydrophthalic acid, and methylnadic anhydride.

Various additives such as colorants, stress relaxation agents, defoamers, leveling agents, coupling agents, flame retardants, and curing accelerators can be added to the resin composition (resin composition forming liquid) as necessary.

The resin composition of the present invention can be obtained by a conventional method. For example, a thermosetting resin, hollow silica particles, a curing agent, additives, etc. are mixed and kneaded with a roll mill or the like to prepare a coating liquid (liquid for forming a resin composition), which is then applied to a substrate and cured by heat, ultraviolet light, etc.

[Method of producing silica-based particles]
The method for producing hollow silica particles of the present invention comprises a hollow particle preparation step of spray-drying an aqueous solution of alkali silicate in a hot air stream to prepare hollow particles, an alkali removal step of neutralizing and removing the alkali contained in the prepared hollow particles with an acid, and a firing step of firing the hollow particles from which the alkali has been removed, and a classification step of classifying the hollow particles to remove coarse particles is provided between the hollow particle preparation step and the firing step. Note that other steps such as a drying step may be provided between each step.

The manufacturing method of the present invention can produce, for example, the silica-based hollow particles of the present invention as described above. That is, the manufacturing method of the present invention can produce silica-based particles that can reduce the dielectric constant and dielectric tangent of insulating materials and do not interfere with the filterability and injectability of the insulating material-forming liquid in the manufacturing process.

In addition, when a classification process is usually performed during the manufacture of sintered particles, it is considered preferable to perform the classification process at the final stage after sintering in order to arrange the final particles, but in the manufacturing method of the present invention, it is performed before the sintering process. If the sintering process is performed without classification, coarse particles with high porosity that should have been removed will remain. These coarse particles with high porosity are prone to cracking, and may crack due to the stress of shrinkage caused by heating. The fragments generated by the cracks have a small particle size and cannot be removed in the subsequent classification process. In addition, since the silica is dense and has no voids, it hinders the reduction of the dielectric constant and dielectric loss tangent. By performing classification before sintering as in the manufacturing method of the present invention, such inconveniences can be avoided, and the manufactured particles can be more reliably reduced in dielectric constant and dielectric loss tangent, resulting in particles that can meet the recent high speed of data communication.

(Hollow particle preparation process)
In the hollow particle preparation step, an aqueous alkali silicate solution is spray-dried in a hot air current to prepare hollow particles.

As the alkali silicate, sodium silicate or potassium silicate, which is soluble in water, is usually used, but sodium silicate is preferred. The SiO ₂ /M ₂ O molar ratio of the alkali silicate (wherein M represents an alkali metal) is preferably 1 to 5, more preferably 2 to 4. If the SiO ₂ /M ₂ O molar ratio of the alkali silicate is less than 1, not only is the amount of alkali too large, making acid washing in the alkali removal step difficult, but the deliquescence of the spray-dried product becomes significant, so that the desired silica-based hollow particles may not be obtained. If the SiO ₂ /M ₂ O molar ratio of the alkali silicate is more than 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 obtained by spray drying.

The _SiO2 concentration of 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 less than 1% by mass, productivity is significantly reduced. If it exceeds 30% by mass, the stability of the alkali silicate aqueous solution is significantly reduced, resulting in high viscosity and making spray drying difficult. Even if spray drying is possible, the particle size distribution, shell thickness, etc. may become extremely non-uniform, and the final use of the particles may be limited.

As a spray drying method, for example, a conventionally known method such as a rotating disk method, a pressure nozzle method, or a two-fluid nozzle method can be used. Here, the two-fluid nozzle method is preferred.

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

(Alkaline removal process)
In the alkali removal step, the alkali contained in the prepared hollow particles is neutralized with an acid and removed.

As the acid, mineral acids such as hydrochloric acid, nitric acid, sulfuric acid, etc., and organic acids such as acetic acid, tartaric acid, malic acid, etc. can be used. Among these, mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid are preferably used, and sulfuric acid is particularly preferred in terms of valence.

The treatment in this step is not particularly limited as long as it is a treatment using an acid, and a treatment in which the prepared hollow particles are immersed in an acid solution is preferred.

When the hollow particles are immersed in an aqueous acid solution, the molar ratio (Ma)/(Msp) of the number of moles of M ₂ O in the hollow particles (Msp) to the number of moles of acid (Ma) is preferably 0.6 to 4.7, more preferably 1 to 4.5. If this molar ratio is less than 0.6, the amount of acid relative to M ₂ O is too small, so that the conversion of silicic acid to a silica skeleton, which is thought to occur with the removal of the alkali, does not proceed, and the hollow particles may partially dissolve or the dissolved alkali silicate may gel. If the molar ratio exceeds 4.7, the conversion to a silica skeleton does not proceed further, and the amount of acid is excessive, which is uneconomical.

The concentration of the hollow particles when immersed in an acid aqueous solution is preferably 1 to 30 mass% as _SiO2 , and more preferably 5 to 25 mass%. If it is less than 1 mass%, there is no problem with alkali removal or cleaning, but the production efficiency decreases. If it exceeds 30 mass%, the concentration is too high and the alkali removal and cleaning efficiency may decrease.

There are no particular limitations on the conditions for the immersion treatment in the acid aqueous solution as long as the desired amount of alkali can be removed. Typically, the treatment temperature is 5 to 100°C, and the treatment time is 0.5 to 24 hours. After the immersion treatment, it is preferable to wash the material by a conventionally known method. For example, filtration and washing with pure water may be performed. The acid treatment and washing may be repeated as necessary.

The amount (mass ratio) of the alkali (M) remaining after completion of the alkali removal process is preferably 300 ppm or less, more preferably 200 ppm or less, even more preferably 100 ppm or less, and particularly preferably 50 ppm or less. By thoroughly removing the alkali in this process, it is possible to prevent the particles from coalescing in the subsequent process and to prevent the generation of sintered particles in the firing process. It is also known that the amount (content) of the alkali remaining affects the dielectric properties. By thoroughly removing the alkali in this process, it is possible to obtain silica-based hollow particles that enable a low dielectric constant and a low dielectric loss tangent, even when an alkali silicate aqueous solution is used as the raw material.

The amount of alkali in the final product (silica-based hollow particles) is preferably within the above range, and the amount of alkali in the final product is usually the same as the amount of alkali after the alkali removal process.

The amount of residual alkali is measured by dissolving particles in acid and measuring Na or K using an atomic absorption spectrophotometer. When sodium silicate is used, Na is measured, and when potassium silicate is used, K is measured. Specific examples will be explained in the Examples.

(Firing process)
The firing step is a step of firing the hollow particles from which the alkali has been removed. The firing temperature is preferably 600 to 1200°C, and more preferably 900 to 1100°C. If the firing temperature is less than 600°C, the amount of remaining SiOH groups is large, the dielectric tangent of the particles is high, and even if the particles are mixed with a resin, it is difficult to obtain a dielectric tangent reduction effect. If the firing temperature exceeds 1200°C, the hollow particles are likely to sinter with each other, becoming particles of irregular shapes or coarse particles, which causes a decrease in the filterability and injectability of the resin composition forming liquid.

(Classification process)
In the classification process, the hollow particles are classified to remove coarse particles. This classification process is carried out between the hollow particle preparation process and the firing process. When the classification process is carried out after the hollow particle preparation, it is necessary to carry out the classification process immediately after granulation in order to prevent the hollow particles from absorbing moisture (deliquescing) and agglomerating or coalescing. Therefore, in actual production, it is preferable to carry out the classification process after the alkali removal process. In addition, when the classification process is carried out after the alkali removal process, the classification process may be carried out consecutively to the alkali removal process, or may be carried out after the drying process after the alkali removal process. In order to enjoy the effects of the present invention more effectively, it is preferable to carry out the classification process after the drying process.

In the classification process, the amount of coarse particles having a particle diameter of more than 8.0 μm is preferably 10 vol. % or less, more preferably 5 vol. % or less, and even more preferably 1 vol. % or less. This classification process makes it possible to control the suspended particle ratio of the silica-based hollow particles of the present invention within a predetermined range.

The classification in the classification step of the present invention refers to particle size classification in which powder is divided according to particle size in order to make the particle size of the powder uniform. An example of this particle size classification operation is fluid classification, which can be divided into dry classification and wet classification. Dry classification is preferred because wet classification requires the classification process to be performed while the particles are suspended in water, which can generate SiOH groups on the particle surface and adversely affect the dielectric properties.

Classifiers used in dry classification can be broadly classified into gravity classifiers, inertial classifiers, and centrifugal classifiers in principle. Any classifier may be used as long as the object of the present invention can be achieved. However, in order to achieve more precise classification, it is preferable to use an inertial classifier that uses the inertial force of particles to classify, or a centrifugal classifier. In particular, since the hollow particles of the present invention are light and centrifugal force is not easily applied to the particles, a classifier that can exhibit its characteristics even with such particles is preferable. Examples of such classifiers include Elbow Jet manufactured by Nittetsu Mining Co., Ltd., SG Separator manufactured by Japan 3M Limited, Aero Fine Classifier manufactured by Nisshin Engineering Inc., and Microspin manufactured by Nippon Pneumatic Industry Co., Ltd. Among these, Elbow Jet manufactured by Nittetsu Mining Co., Ltd. and Aero Fine Classifier manufactured by Nisshin Engineering Inc. are preferable because they can precisely classify light hollow particles.

(drying process)
In the manufacturing method of the present invention, a drying step can be appropriately provided. For example, the drying step can be provided between the alkali removal step and the classification step, between the classification step and the calcination step, or both. The drying step can be provided multiple times as necessary.

The preferred drying method is heat drying. The drying temperature is preferably 50 to 400°C, and more preferably 50 to 200°C. Specifically, examples include a method of drying at a low temperature of about 50 to 200°C over a long period of time, a method of drying by gradually increasing the temperature, and a method of drying by changing the temperature in several stages.

(Sieving process)
It is preferable to provide a sieving step for sieving out particle agglomerates after the drying step and/or the firing step. Note that the particle agglomerates refer to foreign matter having a particle size of, for example, more than 50 μm, and in this step, a sieve with an opening (mesh number) capable of removing such particle agglomerates is appropriately used.

The following is a detailed description of an embodiment of the present invention.

[Example 1]
Using 30,000 g of a water glass aqueous solution ( _SiO2 / _Na2O molar ratio 3.2, _SiO2 concentration 24 mass%), one of the two-fluid nozzles was sprayed with a flow rate of 0.62 kg/hr, and the other nozzle was sprayed with air with a flow rate of 31,800 L/hr (air/liquid volume ratio 63,600) into hot air with an inlet temperature of 400°C to obtain hollow silica particles. At this time, the outlet temperature was 150°C (hollow particle preparation step).

Next, 5000 g of the hollow silica particles were immersed in 32000 g of a 10% by weight aqueous sulfuric acid solution and stirred for 15 hours. At this time, the solid content (SiO ₂ ) concentration was 10.2% by weight, the temperature of the dispersion was 35° C., and the pH was 3.0. The molar ratio (Ma)/(Msp) with respect to the number of moles of acid (Ma) was 1.2. After the immersion treatment, the particles were filtered and washed with pure water (alkali removal process).

Then, the mixture was dried in a dryer at 120°C for 24 hours (drying process). After drying, the mixture was crushed and passed through a sieve with 75 μm openings to remove coarse particles.

Next, dry centrifugal classification was performed using a cyclone manufactured by the company, with the flow rate of the powder transport line set to 5 m/s (classification process). Particles that were not captured by the cyclone and passed through were collected in a bag filter.

Finally, the classified particles were heat-treated at 1000°C for 10 hours to obtain the silica-based hollow particles (A1) of the target embodiment (calcination process). After calcination, particle agglomerates (foreign matter) were removed using a sieve with a mesh size of 150 μm.

The produced silica-based hollow particles (A1) were mixed with the liquid acid anhydride "Rikacid MH700" manufactured by New Japan Chemical Co., Ltd., the imidazole-based epoxy resin curing agent "2PHZ-PW" manufactured by Shikoku Kasei Co., Ltd., and the liquid epoxy resin "ZX-1059" manufactured by Nippon Steel Chemical & Material Co., Ltd., and pre-mixed with a planetary mill, then mixed with a three-roll mill to prepare a resin composition forming liquid. The ratio of "ZX-1059" was 100 parts by mass, "Rikacid MH700" was 86 parts by mass, and "2PHZ-PW" was 1 part by mass. The silica-based hollow particles (A1) were mixed so that their ratio in the resin composition was 35% by volume. The prepared resin composition forming liquid was heated at 170°C for 2 hours to harden, and a plate-shaped resin composition (A1R) of the example of 50 mm x 50 mm x 1 mm was obtained.

[Example 2]
The silica-based hollow particles (A2) and plate-shaped resin composition (A2R) according to the present embodiment were produced in the same manner as in Example 1 except for the classification step. In the classification step, dry inertial classification was performed using an Elbow Jet (EJ-15) manufactured by Nittetsu Mining Co., Ltd. With this device, powder can be classified into three types, F powder (fine powder), M powder (fine powder), and G powder (coarse powder), and among these, the F edge distance was adjusted so that the coarse particles exceeding 8.0 μm contained in the F powder (fine powder) were 5 vol % or less, and the powder was collected by a bag filter and used in the subsequent steps.

[Example 3]
Silica-based hollow particles (A3) and plate-like resin composition (A3R) according to the present invention were produced in the same manner as in Example 2, except that in the classification step, the F edge distance was adjusted so that the amount of coarse particles exceeding 8.0 μm contained in the F powder (fine powder) was 1 vol % or less.

[Example 4]
Silica-based hollow particles (A4) and plate-like resin composition (A4R) according to the present invention were produced in the same manner as in Example 1, except that in the classification step, dry centrifugal (semi-free vortex) classification was performed using an Aero Fine Classifier manufactured by Nisshin Engineering Co., Ltd. The classification was performed by adjusting the blade angle, etc., so that the amount of coarse particles exceeding 8.0 μm contained in the recovered powder was 1 volume % or less.

[Comparative Example 1]
Silica-based hollow particles (B1) and a plate-like resin composition (B1R) according to Comparative Example were produced in the same manner as in Example 1, except that in the alkali removal step, the immersion and stirring time was changed from 15 hours to 1.5 hours and the classification treatment (classification step) was not performed.

[Comparative Example 2]
Silica-based hollow particles (B2) and a plate-like resin composition (B2R) according to comparative examples were produced in the same manner as in Example 1, except that in the hollow particle preparation step, the inlet temperature of the spray dryer was set to 250° C. and the classification step was not performed.

[Comparative Example 3]
Silica-based hollow particles (B3) and a plate-like resin composition (B3R) according to comparative examples were produced in the same manner as in Example 1, except that the classification step was carried out after the baking step (the classification conditions were also the same).

The properties of the silica-based hollow particles and resin compositions produced in the examples and comparative examples were evaluated. Each evaluation was performed as follows.

(1) Average particle size (D50), maximum particle size (D100), and amount of coarse particles of silica-based hollow particles were measured by a laser diffraction/scattering method.
Specifically, the measurement was carried out in a dry state using a Laser Micron Sizer (LMS-3000) manufactured by Seishin Enterprise Co., Ltd.
The amount of coarse particles was calculated as the volume ratio of particles exceeding 8.0 μm.

(2) Residual Na Amount in Silica-Based Hollow Particles The amount was measured by atomic absorption spectrometry.
Specifically, the residual amount of Na was measured by pretreating the silica-based hollow particles with sulfuric acid and hydrofluoric acid, dissolving them in hydrochloric acid, and measuring the amount of Na using an atomic absorption spectrophotometer (Hitachi Z-2310).

(3) Particle Density of Silica-Based Hollow Particles The particle density was measured by a gas pycnometer method.
Specifically, the particle density was measured using an Ultrapyc1200e manufactured by Quantachrome Instruments, Inc. Nitrogen gas was used as the gas.

(4) Porosity of silica-based hollow particles: Calculated from the above particle density.
Specifically, the porosity was calculated using the density of silica = 2.2 g/ ^cm3 and the following formula (1).
Porosity (%)=[2.2-(particle density of silica-based hollow particles)]/2.2×100 Equation (1)

(5) Dielectric constant (Dk) and dielectric loss tangent (Df) of silica-based hollow particles
The measurements were performed using a cavity resonator perturbation method.
Specifically, the dielectric constant (Dk) and dielectric loss tangent (Df) of the silica-based particles were measured using a network analyzer (MS46122B, manufactured by Anritsu Corporation) and a cavity resonator (1 GHz) in accordance with ASTM D2520 (JIS C2565).

(6) Proportions of floating particles a, suspended particles b, and sinking particles c when suspended in water Each particle was recovered from the suspension and weighed, and the proportions were calculated.
Specifically, silica-based hollow particles were mixed with water to a concentration of 0.5% by mass, and ultrasonic treatment was performed for 10 minutes to prepare a dispersion. The dispersion was allowed to stand at 25° C. for 24 hours, and then floating particles a, suspended particles b, and sedimented particles c were collected. Each particle was then dried at 105° C. for 24 hours, after which it was weighed and its proportion was calculated.

(7) Filterability of Resin Composition Forming Liquid Filterability was evaluated using a ROKI TECHNO filter (SHP type: 30 μm) in terms of the amount of liquid passing through per unit area until the filter became clogged.

The evaluation criteria are as follows:
◎: ≧1 g/ ^cm2
◯: 0.5 g/cm2 or ^more and less than 1.0 g/ ^cm2 △: 0.3 g/ ^cm2 or more and less than 0.5 g/ ^cm2 ×: <0.3 g/ ^cm2

(8) Injectability of Resin Composition Forming Liquid Injection was carried out between glass plates having a gap of 20 μm, and the injection property was evaluated based on the time required for filling the resin composition by 25 mm.

The evaluation criteria are as follows:
◎: Within 200 seconds
〇: More than 200 seconds and less than 400 seconds △: More than 400 seconds and less than 600 seconds ×: More than 600 seconds

(9) Dielectric constant (Dk) and dielectric loss tangent (Df) of the resin composition
The dielectric constant (Dk) and dielectric loss tangent (Df) of a 50 mm x 50 mm x 1 mm plate-shaped molded body (resin composition) were measured at 9.4 GHz using a network analyzer (MS46122B, manufactured by Anritsu Corporation) and a coaxial resonator.

The evaluation was carried out in comparison with a resin composition that did not contain silica-based hollow particles (filler). The evaluation criteria were as follows:

Reduction rate (%) of dielectric constant (Dk) = (Dielectric constant without added filler - Dielectric constant with added filler) / Dielectric constant without added filler x 100

○: Reduction rate > 0
△: Reduction rate = 0
×: Reduction rate < 0

Reduction rate (%) of dielectric tangent (Df) = (dielectric tangent without added filler - dielectric tangent with added filler) / dielectric tangent without added filler x 100

◎: 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 of less than 20%

The above results are shown in Table 1.

As shown in Table 1, the silica-based hollow particles according to the examples and the resin composition containing them have a low dielectric constant and a low dielectric loss tangent. In addition, the resin composition forming liquid containing the silica-based hollow particles according to the examples also has excellent filterability and injectability.

INDUSTRIAL APPLICABILITY The silica-based hollow particles of the present invention can be used as a filler for insulating materials for semiconductors, and are therefore industrially useful.

Claims (6)

The silica-based hollow particles have a cavity inside a non-porous outer shell and an average particle diameter (D50) of 0.1 to 10 μm,
When suspended in water, the floating particles are 0.5 to 7.0% by mass, the suspended particles are 0 to 4.0% by mass, and the settling particles are 89.0 to 99.5% by mass;
A silica-based hollow particle, characterized in that the content of coarse particles having a particle diameter exceeding 8.0 μm is 10 volume % or less . A resin composition comprising the silica-based hollow particles according to claim 1 . a hollow particle preparation step of spray-drying an aqueous alkali silicate solution in a hot air stream to prepare hollow particles;
an alkali removing step of neutralizing and removing the alkali contained in the prepared hollow particles with an acid;
a calcination step of calcining the hollow particles from which the alkali has been removed at a temperature of 600 to 1200°C ;
A method for producing silica-based hollow particles comprising the steps of:
A method for producing silica-based hollow particles, comprising the steps of: classifying the hollow particles to reduce the content of coarse particles having a particle diameter exceeding 8.0 μm to 10 volume % or less, between the alkali removal step and the calcination step. 4. The method for producing silica-based hollow particles according to claim 3 , wherein the amount of alkali contained in the hollow particles is reduced to 200 ppm or less in the alkali removal step. 5. The method for producing silica-based hollow particles according to claim 3 , wherein the classification step is carried out after the hollow particles from which the alkali has been removed are dried. The method for producing silica-based hollow particles according to any one of claims 3 to 5 , characterized in that the classification treatment in the classification step is a dry classification treatment.