Powder, production method therefor, and resin composition production method

Abstract

The present invention relates to a powder including hollow particles, each having a cavity inside a non-porous outer shell. The powder has an average particle size (D50) of 2.0-10.0 μm, and contains microparticles of a particle size under 2.0 μm in the amount of 20 vol% or less. When the powder is suspended in water, the proportions of floating particles, suspended particles, and settled particles are 7.0-25.0 mass%, 0-4.0 mass%, and 71.0-93.0 mass%, respectively.

Description

Powder and method for producing the same, and method for producing resin composition

[0001] The present invention relates to a powder suitable for use as a filler in insulating materials for semiconductors, and more particularly to a powder containing hollow particles having cavities inside a non-porous outer shell.

[0002] In recent years, information and communications have become faster and larger in capacity. Therefore, materials used in communications equipment are required to have a low dielectric constant (low Dk) and a low dielectric loss tangent (low Df). For example, printed wiring boards on which semiconductor elements are mounted require insulating materials with low dielectric constants and low dielectric loss tangents. A high dielectric constant of an insulating material can result in dielectric loss, and a high dielectric loss tangent of an insulating material can increase not only dielectric loss but also heat generation.

[0003] In order to realize low dielectric constants and low dielectric loss tangents for insulating materials, development of resin materials, which are the main insulating materials, has been underway. As such resin materials, epoxy resins, polyphenylene ether resins, fluorine resins, etc. have been proposed (see, for example, Patent Documents 1 to 5).

[0004] Fillers are blended into such resin materials in terms of durability (rigidity), heat resistance, etc. Known fillers include silica, boron nitride, talc, kaolin, clay, mica, alumina, zirconia, titania, and other metal oxides (see, for example, Patent Document 3).

[0005] WO2009 / 041137 Patent Publication No. 2006-516297 Patent Publication No. 2017-057352 Patent Publication No. 2001-288227 Patent Publication No. 2019-172962

[0006] Among materials used as fillers, silica is excellent in terms of low dielectric constant and low dielectric loss tangent. However, due to the rapid progress in data communication capacity and high-speed processing, there is a demand for even lower dielectric constant and dielectric loss tangent.

[0007] The present inventors have found that hollow particles that do not contain fine particles and that satisfy certain conditions can achieve a low dielectric constant and a low dielectric loss tangent for an insulating material.

[0008] That is, the powder according to the present invention contains hollow particles having a cavity inside a non-porous outer shell, has an average particle size (D50) of 2.0 to 10.0 μm, and contains 20% by volume or less of fine particles with a particle size of less than 2.0 μm. When this powder is suspended in water, the floating particles account for 7.0 to 25.0% by mass, the suspended particles for 0 to 4.0% by mass, and the settling particles for 71.0 to 93.0% by mass.

[0009] The method for producing powder according to the present invention comprises a first step of preparing particles by spray-drying an aqueous alkali silicate solution in a hot air stream, a second step of removing the alkali contained in the particles, and a third step of firing the particles from which the alkali has been removed, with a classification step being provided between the first and third steps to remove fine particles of less than 2.0 μm.

[0010] The powder of the present invention enables the dielectric constant and dielectric loss tangent of insulating materials to be reduced, which in turn enables the transmission speed of semiconductors to be increased and the transmission loss to be reduced.

[0011] The powder of the present invention contains hollow particles having cavities inside a non-porous outer shell and has an average particle size of 2.0 to 10.0 μm. Furthermore, the content of fine particles with a particle size of less than 2.0 μm is 20% by volume or less. When this powder is suspended in water, the floating particles are 7.0 to 25.0% by mass, the suspended particles are 0 to 4.0% by mass, and the settling particles are 71.0 to 93.0% by mass. The powder of the present invention may contain a small amount of solid particles in addition to hollow particles. This is because solid particles may be unintentionally produced during the production of hollow particles. Solid particles without internal cavities have a high specific gravity and are therefore considered to be essentially hidden among the settling particles. It is preferable that 90% by mass or more of the particles contained in the powder are hollow particles.

[0012] Here, particles that disperse in water when suspended in water are defined as suspended particles, and particles with a low specific gravity that float in the upper layer (near the water surface) are defined as floating particles. Such suspended particles typically have a high porosity. Therefore, the more suspended particles incorporated into a resin material, the lower the dielectric constant and dielectric loss tangent of the resin product. Generally, particles with a higher porosity have a larger particle diameter (smaller particle diameters have a lower porosity). Therefore, controlling the amount of suspended particles to 7.0 to 25.0 mass% of the total particles results in controlling (reducing) the amount of coarse particles. Because there are no large amounts of coarse particles, resin compositions for molding resin products (e.g., insulating materials) have good filterability and injectability. This improves the surface smoothness of the molded resin product. Because fine particles have a low porosity, reducing the content of particles with a particle diameter of less than 2.0 μm (fine particles) can reduce the dielectric constant without increasing the amount of large particles with a high porosity. Furthermore, a smaller amount of fine particles reduces the total surface area of ​​all particles. As a result, the amount of SiOH groups is reduced, and the dielectric constant and the dielectric loss tangent can be reduced.

[0013] In this way, by using the powder of the present invention as a filler, the filterability and injectability of the resin composition for molding can be improved, and a resin product with excellent surface smoothness can be obtained. In addition, powders with a small number of fine particles have low adhesion and improved fluidity. Therefore, handling and dispersibility are also improved.

[0014] The content of the fine particles is preferably 15% by volume or less, more preferably 10% by volume or less, even more preferably 5% by volume or less, and most preferably 3% by volume or less.

[0015] Suspended particles tend to have low particle strength due to the small ratio (t / d) of particle diameter (d) to shell thickness (t). Therefore, there is a risk of particles cracking between the process of mixing the resin material and particles and molding the resin product (i.e., during the manufacturing process). Broken particles not only hinder the achievement of low dielectric constant and low dielectric loss tangent, but also impair the fluidity of the resin composition, reducing the uniformity of the resin product (molded product) and causing voids within the resin product. However, particle cracking can be suppressed by controlling the amount of suspended particles.

[0016] Furthermore, by controlling the amount of suspended particles, it is possible to ensure the desirable properties of high-porosity particles (e.g., low dielectric constant and low dielectric loss tangent) while suppressing the undesirable properties of high-porosity particles (e.g., cracking) to an acceptable level. Suspended particles include particles with high porosity even though they are small in diameter, and such particles are less likely to crack during the manufacturing process than large-diameter particles. As a result, the undesirable properties of high-porosity particles can be minimized overall.

[0017] The content of floating particles is preferably 8.0 to 24.0% by mass, more preferably 8.0 to 23.0% by mass, even more preferably 8.0 to 22.0% by mass, and most preferably 8.0 to 15.0% by mass. The content of sinking particles is preferably 72.0 to 92.0% by mass, more preferably 73.0 to 92.0% by mass, even more preferably 74.0 to 92.0% by mass, and most preferably 81.0 to 92.0% by mass.

[0018] The powder has an average particle size (D50) in the range of 2.0 to 10.0 μm. If the average particle size is less than 2.0 μm, the powder contains many fine particles, resulting in a high specific surface area (high SiOH group content), making it difficult to obtain excellent dielectric properties. Powders with an average particle size exceeding 10 μm are unsuitable for semiconductor applications. For semiconductor applications, the average particle size is preferably 2.5 to 10.0 μm, and more preferably 3.0 to 10.0 μm.

[0019] 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, more preferably 8 times or less, of 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.

[0020] The porosity of the powder is preferably 20% by volume or more, more preferably 30% by volume or more, and even more preferably 40% by volume or more. It is also preferably 70% by volume or less, more preferably 65% ​​by volume or less, even more preferably 60% by volume or less, and most preferably 55% by volume or less. Such a porosity can reduce the dielectric constant and dielectric loss tangent, and can maintain particle strength at a predetermined level to effectively prevent particle cracking.

[0021] Here, the particles constituting the powder are suitably silica-based particles containing silica as the main component. Therefore, the hollow particles (shells) contained in the powder may contain inorganic oxides such as alumina, zirconia, titania, etc. 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 preferred that the particles consist essentially of silica only.

[0022] [Resin Composition] A resin composition is prepared by blending the above-mentioned powder with a resin material. Such a resin composition can be used as an insulating material for electronic materials such as semiconductors, specifically, copper-clad laminates, prepregs, build-up films, etc. for forming printed wiring boards (including rigid and flexible boards). It can also be used as a semiconductor package-related material such as a mold resin, mold underfill, underfill, etc., or an adhesive for flexible boards.

[0023] The resin can be a curable resin commonly used in electronic materials such as semiconductors. Photocurable resins are also acceptable, but thermosetting resins are preferred. Examples of curable resins include epoxy resins, polyphenylene ether resins, fluorine-based resins, polyimide resins, bismaleimide resins, acrylic resins, methacrylic resins, silicone resins, BT resins, and cyanate resins. 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, and halogenated epoxy resins. These resins may be used alone or in combination.

[0024] The resin composition preferably contains powder A and curable resin B in a mass ratio (A / B) of 10 / 100 to 95 / 100. This allows the resin composition to fully function as a filler while maintaining its properties such as fluidity. The mass ratio (A / B) is more preferably 30 / 100 to 80 / 100.

[0025] Furthermore, the resin composition preferably contains a curing agent such as a phenolic compound, an amine compound, or an acid anhydride. When an epoxy resin is used as the curable resin, examples of the curing agent include resins having two or more phenolic hydroxyl groups per molecule (phenolic resins such as bisphenol resins, novolac resins, triphenolalkane resins, resol phenolic resins, phenol aralkyl resins, biphenyl phenolic resins, naphthalene phenolic resins, and cyclopentadiene phenolic resins), and acid anhydrides such as methylhexahydrophthalic acid, methyltetrahydrophthalic acid, and methylnadic anhydride. Various additives (colorants, stress relaxation agents, antifoaming agents, leveling agents, coupling agents, flame retardants, curing accelerators, etc.) may be added to the resin composition as needed.

[0026] The resin composition can be produced by a conventional method. For example, a curable resin, powder, curing agent, additives, etc. are mixed and kneaded using a roll mill, etc. The resulting resin composition is applied to a substrate and cured by heat, ultraviolet light, etc.

[0027] [Method for producing powder] The method for producing powder of the present invention comprises a first step of spray-drying an alkali silicate aqueous solution in a hot air stream to prepare particles, a second step of removing the alkali contained in the prepared particles, and a third step of firing the particles from which the alkali has been removed, and between the first and third steps, a step of classifying the particles to remove fine particles of less than 2.0 μm (classification step) is provided. Note that other steps such as a drying step may be provided between each step. The above-mentioned powder can be obtained by these steps.

[0028] Generally, when producing particles by firing, it is considered preferable to perform classification after firing to regulate the particle diameter. However, here, classification is performed before firing. If the firing process is performed without classification, the fine particles that should be removed will remain present during firing, and the fine particles will sinter with other particles. Therefore, even if classification is performed later, the fine particles cannot be removed. If classification is performed before firing, the fine particles can be reliably reduced. This more reliably achieves a low dielectric constant and low dielectric loss tangent of the particles, resulting in particles that are compatible with faster data communication speeds. Note that classification may be performed again after firing. Each process will be described in detail below.

[0029] (First Step) In this step, an aqueous solution of alkali silicate is spray-dried in a hot air stream to granulate silica-based particles. This step is carried out to obtain hollow particles, but it is difficult to make all particles hollow, and the granulated silica-based particles may contain solid particles as a result. In this case, the powder obtained through the steps described below also contains solid particles. However, as long as the powder has the above-mentioned properties, the expected effect can be obtained even if solid particles are contained.

[0030] Alkali silicate SiO ２ and M ２ O (M is an alkali metal) molar ratio (SiO２ / M ２ O) is preferably 1 to 5, more preferably 2 to 4. If this molar ratio is less than 1, the amount of alkali is too large, making it difficult to sufficiently remove it even by acid washing in the alkali removal step. Furthermore, the deliquescence of the spray-dried product increases, making it difficult to obtain the desired hollow particles. If this molar ratio exceeds 5, the solubility of the alkali silicate decreases, making it difficult to prepare an aqueous solution. Even if an aqueous solution can be prepared, it may not be possible to form hollow particles by spray drying.

[0031] SiO of alkaline silicate solution ２ The concentration of the alkali silicate is preferably 1 to 30% by mass, more preferably 5 to 28% by mass. Although production is possible at a concentration of less than 1% by mass, productivity is significantly reduced. If the concentration exceeds 30% by mass, the stability of the alkali silicate aqueous solution is significantly reduced, resulting in high viscosity and in some cases making spray drying impossible. Even if spray drying is possible, the particle size distribution, shell thickness, etc. may become extremely non-uniform, which may limit the uses of the obtained particles. As the alkali silicate, sodium silicate or potassium silicate, which is soluble in water, can be used. Sodium silicate is preferred.

[0032] As the spray drying method, a conventionally known method such as a rotating disk method, a pressure nozzle method, a two-fluid nozzle method, etc. can be used. Here, the two-fluid nozzle method is preferred.

[0033] 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 setting the temperatures in this manner, hollow particles can be stably obtained.

[0034] (Second step) Next, the alkali contained in the particles granulated in the first step is removed. A suitable method is to remove the alkali by adding an acid to neutralize it. A treatment in which the particles are immersed in an acid solution is preferred. At this time, the M in the particles is removed. ２ The molar ratio (Ma / Msp) of the number of moles of O (Msp) to the number of moles of acid (Ma) is preferably 0.6 to 4.7, more preferably 1 to 4.5. When this molar ratio is less than 0.6, M ２The amount of acid relative to O is too small. As a result, the formation of a silica skeleton from silicic acid, which is thought to occur with the removal of alkali, does not proceed, and the particles may partially dissolve or the dissolved alkali silicate may gel. Even if the molar ratio exceeds 4.7, the formation of a silica skeleton does not proceed further, and the acid is excessive, which is uneconomical.

[0035] In addition, the particle concentration is SiO ２ It is preferable to immerse the substrate in an acid aqueous solution so that the concentration is 1 to 30% by mass. If the concentration is less than 1% by mass, there will be no problem with alkali removal or cleaning, but production efficiency will decrease. If the concentration exceeds 30% by mass, the concentration will be too high and alkali removal and cleaning efficiency may decrease. A concentration of 5 to 25% by mass is even more preferable.

[0036] The conditions for immersion in the acid aqueous solution are not particularly limited 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 this, it is preferable to wash the substrate by a conventionally known method. For example, the substrate is filtered and washed with pure water. The acid treatment and washing may be repeated as necessary.

[0037] The amount (mass proportion) of the alkali (M) remaining after alkali removal is preferably 300 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. By thoroughly removing the alkali in this step, particle coalescence in subsequent steps can be prevented, and the generation of sintered particles in the firing step can be prevented. Furthermore, the amount (content) of the alkali remaining is known to affect dielectric properties. By thoroughly removing the alkali in this step, particles that enable a low dielectric constant and a low dielectric loss tangent can be obtained, even when an alkali silicate aqueous solution is used as the raw material.

[0038] The amount of alkali in the final product (particles constituting the powder) is also preferably in the above-mentioned range, and is usually the same as the amount of alkali after the alkali removal step.

[0039] The amount of residual alkali can be measured using an atomic absorption spectrophotometer with a powder dissolved in acid as a sample. When sodium silicate is used, Na is measured, and when potassium silicate is used, K is measured. Specific examples will be described later.

[0040] The acid used in this step may be a mineral acid (hydrochloric acid, nitric acid, sulfuric acid, etc.) or an organic acid (acetic acid, tartaric acid, malic acid, etc.). Mineral acids are preferably used, and sulfuric acid, which has a large valence, is particularly preferred.

[0041] (Third Step) Next, the particles after alkali removal treatment are fired. The firing temperature is preferably 600 to 1200°C, more preferably 900 to 1100°C. If the firing temperature is less than 600°C, the amount of remaining SiOH groups is large, and the dielectric loss tangent of the particles becomes high. Therefore, even if the particles are blended into a resin, it is difficult to obtain the effect of reducing the dielectric loss tangent. If the firing temperature exceeds 1200°C, the particles tend to sinter together, and irregularly shaped particles or coarse particles are likely to be generated. This causes a decrease in the filterability and injectability of the resin composition-forming liquid.

[0042] (Classification step) By performing classification between the first and third steps, fine particles of less than 2.0 μm are removed. When the classification step is performed before alkali removal, it is necessary to perform the classification step immediately after granulation to prevent the hollow particles from absorbing moisture (deliquescing) and agglomerating or coalescing. When the classification step is performed before firing, the classification step may be performed immediately after the alkali removal step.

[0043] The classification process reduces the amount of fine particles with a particle diameter of less than 2.0 μm to 20% by volume or less. This is preferably 15% by volume or less, more preferably 10% by volume or less, even more preferably 5% by volume or less, and most preferably 3% by volume or less. This classification process allows the proportion of suspended particles in the powder to be controlled within a predetermined range. Note that the content of fine particles and coarse particles in the final product usually does not change significantly from the content after the classification process.

[0044] The classification process in this classification step refers to particle size classification, which separates powders according to particle size in order to make the particle size of the powder uniform. Fluid classification can be categorized into dry classification and wet classification. In wet classification, particles are classified while suspended in water. This can result in the formation of SiOH groups on the particle surface, which can adversely affect the dielectric properties. Therefore, dry classification is preferred.

[0045] In principle, classifiers used in dry classification can be broadly divided into gravity classifiers, inertial classifiers, and centrifugal classifiers. Using an inertial classifier or centrifugal classifier enables more precise classification. Examples of classifiers capable of precisely classifying even light particles, such as those used in the present invention, include the Elbow Jet manufactured by Nittetsu Mining Co., Ltd., the SG Separator manufactured by Japan 3M Limited, the Aerofine Classifier manufactured by Nisshin Engineering Inc., and the Microspin manufactured by Nippon Pneumatic Mfg. Co., Ltd. Among these, the Elbow Jet and the Aerofine Classifier are preferred.

[0046] Furthermore, a drying treatment step may be appropriately performed during the manufacturing process. The drying treatment may be performed between the alkali removal treatment and the classification treatment, between the classification treatment and the calcination, or both, or between the alkali removal treatment and the calcination. It may be performed multiple times as necessary. Alternatively, the drying treatment may be performed before the calcination, and the classification treatment may be performed between the drying treatment and the calcination. To obtain the effects of the present invention more effectively, it is preferable to perform the classification treatment after the drying treatment and then calcination. Heat drying is suitable as the drying treatment. The drying temperature is preferably 50 to 400°C, and more preferably 50 to 200°C. Specific 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.

[0047] Furthermore, it is preferable to carry out a sieving process to remove particle agglomerates at least either after drying or after firing. Note that particle agglomerates refer to particle agglomerates having a particle size of, for example, more than 50 μm, and a sieve with an opening size (mesh number) that can remove such particle agglomerates is appropriately used.

[0048] Examples of the present invention will be specifically described below.

[0049] [Example 1] Aqueous solution of water glass (SiO ２ / Na ２ O molar ratio 3.2, SiO ２Using 30,000 g of cellulose acetate (24% by mass), hollow particles were granulated by spraying hot air at an inlet temperature of 400°C into one of the two-fluid nozzles at a flow rate of 0.62 kg / hr and air at a flow rate of 31,800 L / hr (air / liquid volume ratio 63,600) into the other nozzle. The outlet temperature was 150°C (first step). In the first step, a small amount of solid particles may also be granulated, but it is not necessary to remove the solid particles before proceeding to the next step.

[0050] Next, 5000 g of the hollow particles (i.e., the particles granulated in the first step) were immersed in 32000 g of a 10% by mass aqueous sulfuric acid solution and stirred for 15 hours. ２ The concentration of sulfuric acid is 10.2% by mass. Since sulfuric acid is a divalent acid, the moles of acid (Ma) and alkali (Na ２ The ratio (Ma / Msp) of the number of moles (Msp) of hydroxybenzoates (H2O) to the number of moles (Msp) of hydroxybenzoates (H2O) was 3.3. The temperature of the dispersion was 35°C and the pH was 3.0. After this immersion treatment, the dispersion was filtered and washed with pure water (second step).

[0051] The mixture was then dried in a dryer at 120° C. for 24 hours. After drying, the mixture was crushed and passed through a sieve with 75 μm openings to remove particle agglomerates.

[0052] 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. The particles captured in the cyclone were recovered.

[0053] The collected particles were heat-treated at 1000°C for 10 hours to obtain a powder containing hollow particles (third step). After firing, particle agglomerates (foreign matter) were removed using a sieve with 150 µm openings.

[0054] The resulting powder was blended with a liquid epoxy resin (ZX-1059, manufactured by Nippon Steel Chemical & Material Co., Ltd.) along with a liquid acid anhydride (Rikacid MH700, manufactured by New Japan Chemical Co., Ltd.) and an imidazole-based epoxy resin curing agent (2PHZ-PW, manufactured by Shikoku Chemicals Co., Ltd.). The blending ratios were 100 parts by weight of ZX-1059, 86 parts by weight of Rikacid MH700, and 1 part by weight of 2PHZ-PW, resulting in a powder content of 35% by volume in the blend (paste). This blend was pre-mixed using a planetary mill and then kneaded using a three-roll mill to obtain a paste (resin composition). This paste was then heated at 170°C for 2 hours to harden, yielding a 50 mm x 50 mm x 1 mm plate-shaped resin molded product (resin product).

[0055] The physical properties of the powder and resin moldings obtained as described above were measured and evaluated as follows. The results, along with the preparation conditions, are shown in Table 1. The same procedures were carried out for the other Examples and Comparative Examples.

[0056] (1) Average particle size (D50), maximum particle size (D100), and amount of fine particles The particle size distribution of the powder was measured in a dry state using a particle size analyzer (Laser Micronsizer LMS-3000, manufactured by Seishin Enterprise Co., Ltd.). From the measurement results, the average particle size (D50) and maximum particle size (D100) were obtained. Furthermore, this particle size distribution was analyzed, and the volume ratio of particles less than 2.0 μm was calculated, which was used as the amount of fine particles.

[0057] (2) Residual Amount of Alkali After pre-treating the powder with sulfuric acid and hydrofluoric acid, it was dissolved in hydrochloric acid and the amount of Na was measured by atomic absorption spectrometry using an atomic absorption spectrophotometer (Hitachi Z-2310).

[0058] (3) Particle Density, Porosity Using an Ultrapyc 1200e manufactured by Quantachrome Instruments, the average density of particles contained in the powder (particle density) was measured by the gas pycnometer method. Nitrogen gas was used. From this particle density, the porosity (%) was calculated using the formula "[2.2 - (particle density)] / 2.2 x 100". Assuming that the powder is composed of silica particles, this formula uses the density of silica, 2.2 g / cm. ３ was used.

[0059] (4) Dielectric Constant (Dk) and Dielectric Loss Tangent (Df) of Powder The dielectric constant (Dk) and dielectric loss tangent (Df) of the powder were measured by a cavity resonator perturbation method using a network analyzer (MS46122B, manufactured by Anritsu Corporation) and a cavity resonator (1 GHz) in accordance with ASTM D2520 (JIS C2565).

[0060] (5) Proportions of Floating Particles, Suspended Particles, and Settled Particles When Suspended in Water First, powder and water were mixed to a concentration of 5% by mass, and ultrasonic treatment was performed for 10 minutes. The resulting dispersion was allowed to stand at 25°C for 24 hours, and then the floating particles, suspended particles, and settled particles were collected. Next, each particle was dried at 105°C for 24 hours, weighed, and their proportions were calculated.

[0061] (6) Dielectric constant (Dk) and dielectric loss tangent (Df) of resin moldings The dielectric constant (Dk) and dielectric loss tangent (Df) of a 50 mm x 50 mm x 1 mm plate-shaped molding (resin molding) were measured at 9.4 GHz using a network analyzer (MS46122B, manufactured by Anritsu Corporation) and a coaxial resonator. The results were compared with those of a resin molding containing no powder (filler) using the following formula and evaluated according to the following criteria.

[0062] Reduction rate (%) of dielectric constant (Dk)=(dielectric constant without powder blending−dielectric constant with powder blending) / dielectric constant without powder blending×100

[0063] ◯: Reduction rate > 0 △: Reduction rate = 0 ×: Reduction rate < 0

[0064] Reduction rate (%) of dielectric loss tangent (Df) = (dielectric loss tangent without powder blending - dielectric loss tangent with powder blending) / dielectric loss tangent without powder blending x 100

[0065] ◎: Reduction rate of 50% or more 〇: 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%

[0066] [Example 2] In the classification process, dry inertial classification was performed using an Elbow Jet (EJ-15) manufactured by Nittetsu Mining Co., Ltd. This device can classify powder into three types: F powder (fine powder), M powder (fine powder), and G powder (coarse powder). At this time, the F edge distance was adjusted so that the M powder (fine powder) contained 2% or less by volume of microparticles less than 2.0 μm. The M powder was recovered, and the subsequent steps were carried out. Except for this, the powder and resin molded product were prepared in the same manner as in Example 1.

[0067] [Example 3] In the classification step, dry centrifugal (semi-free vortex) classification was performed using an Aero Fine Classifier manufactured by Nisshin Engineering Co., Ltd. The blade angle and other factors were adjusted to classify the recovered powder so that the content of fine particles less than 2.0 μm was 20% by volume or less. Except for this, the powder and resin molding were prepared in the same manner as in Example 1.

[0068] [Example 4] Powder and resin moldings were prepared in the same manner as in Example 3, except that the angle of the blades and other factors were adjusted so that the collected particles contained 10% by volume or less of fine particles having a size of less than 2.0 μm.

[0069] Comparative Example 1 A powder and a resin molding were prepared in the same manner as in Example 1, except that the classification treatment (classification step) was not carried out.

[0070] Comparative Example 2: In the first step, the inlet temperature of the spray dryer was changed to 250°C, and in the second step, the immersion stirring time was changed to 1.5 hours. Furthermore, the classification step was not performed. Other than this, a powder and a resin molded product were prepared in the same manner as in Example 1.

[0071] Comparative Example 3 In the first step, the inlet temperature of the spray dryer was changed to 420° C., and no classification treatment (classification step) was performed. Except for this, a powder and a resin molded body were prepared in the same manner as in Example 1.

[0072] Comparative Example 4 A powder and a resin molding were prepared in the same manner as in Example 1, except that the classification treatment (classification step) was carried out after firing.

[0073]

[0074] As shown in Table 1, the powder according to the example and the resin molding containing this powder have low dielectric constants and dielectric loss tangents.

Claims

1. A powder comprising hollow particles having a cavity inside a non-porous outer shell, The powder has an average particle size (D50) of 2.0 to 10.0 μm, and the content of microparticles having a particle size of less than 2.0 μm is 20 vol % or less; The powder is characterized in that, when the powder is suspended in water, the floating particles are 7.0 to 25.0 mass%, the suspended particles are 0 to 4.0 mass%, and the settling particles are 71.0 to 93.0 mass%.

2. A method for producing a resin composition, comprising blending the powder according to claim 1 with a resin material.