Hollow silica particles, inorganic filler containing hollow silica particles, slurry, resin composition, and method for producing hollow silica particle material

Abstract

Provided are hollow silica particles that have a dense silica shell and in which relative permittivity and the dielectric loss tangent are reduced by reducing silanol groups on the inner surface and the outer surface of the shell. The hollow silica particles have therein one or more voids isolated from the exterior by a shell layer containing silica as a main component. When a first amount of desorbed water desorbed from the hollow silica particles when the hollow silica particles are heated from 200°C to 550°C is denoted by A (ppm) and a second amount of desorbed water desorbed from the hollow silica particles when the hollow silica particles are heated from 550°C to 900°C is denoted by B (ppm), the expression 0.5 < (A / B) < 2.2 is satisfied between the first amount of desorbed water and the second amount of desorbed water.

Description

Hollow silica particles, inorganic fillers, slurries, resin compositions containing hollow silica particles, and methods for producing hollow silica particle materials.

[0001] The present invention relates to hollow silica particles with a low surface moisture content, inorganic fillers, slurries, and resin compositions containing the hollow silica particles, and a method for producing the hollow silica particle material.

[0002] As signal transmission in information devices becomes faster and higher capacity, signal delay and loss become more pronounced. The degree of delay is related to the relative permittivity of the resin composition used in the electronic material, and the loss is related to the dielectric loss tangent. Resin compositions with low relative permittivity, low dielectric loss tangent, and low thermal expansion coefficient are required. Furthermore, in order to minimize signal reflection and loss and to transmit signals smoothly, it is necessary to match the characteristic impedance. When dealing with high-speed signals, mismatch in characteristic impedance is likely to cause data transfer errors and performance degradation.

[0003] With the recent miniaturization and increased density of electronic devices, there is a demand to reduce the width and spacing of copper wiring on circuit boards. This width and spacing are factors that affect characteristic impedance. Another characteristic that affects characteristic impedance is relative permittivity, and for example, when trying to reduce the width and spacing of copper wiring while keeping the characteristic impedance fixed in printed circuit board design, the relative permittivity needs to be reduced. For this reason, resins that exhibit lower relative permittivity and dielectric loss tangent have been developed in recent years.

[0004] However, in order to reduce the coefficient of thermal expansion, silica must be mixed in as a filler. Ordinary silica has poor dielectric properties compared to modern high-performance resins, and thus degrades the dielectric properties of the resin composition.

[0005] Therefore, hollow silica is being considered as a candidate material that satisfies all of the above characteristics. Air generally exhibits the lowest dielectric constant among all substances except vacuum, and the addition of hollow silica, which is a composite of silica and air, is being investigated to achieve a reduction in the thermal expansion coefficient and dielectric constant of resin compositions.

[0006] International Publication WO2023 / 175994

[0007] The Journal of Physical Chemistry A 2011, 115, 11221-11228Colloids and Surfaces, A: Physicochemical and Engineering Aspects 173, (2000), 1-38

[0008] One factor that degrades the dielectric properties of silica is the presence of silanols on the particle surface. This is due to the high polarization of silanols. As a method of improvement, chemical modification of surface silanols by reacting them with organic silane compounds is frequently used. This method greatly improves the dielectric properties of solid silica. However, unlike solid silica, hollow silica shows little improvement through chemical modification. Hollow silica has an outer surface and an inner surface, and silanols are present on both surfaces. Although the silanols on the outer surface are eliminated by chemical modification, the silanols on the inner surface are isolated from the outside environment by the silica shell after the hollow silica synthesis is complete, and cannot be chemically modified, thus not contributing to the improvement of dielectric properties.

[0009] Methods for manufacturing hollow silica particles often involve a firing process at temperatures above 800°C to densify the silica layer. Therefore, even if chemical modifiers are impregnated into the silica during the hollow silica synthesis process to chemically modify the inner surface silanols, the introduced organic functional groups are thermally decomposed and removed during the firing process, ultimately restoring the inner surface silanols. Thus, modifying the inner surface silanols is difficult, and to suppress the deterioration of dielectric properties due to the presence of inner surface silanols, it is necessary to synthesize hollow silica with a low amount of surface silanols to begin with.

[0010] Hollow silica particles are often manufactured by first obtaining core-shell particles as precursors, which are formed by accumulating a substance that transforms into silica upon firing, on a core material that serves as a template in an aqueous reaction solution. Then, the core material is removed and the silica is densified. Methods for generating the substance that transforms into silica include so-called wet silica and wet silica particle synthesis methods. Specifically, there are two methods: one in which silica is directly generated by polymerizing silicic acid in water, and another in which organosilicon polymer compounds that transform into silica upon firing are generated.

[0011] In the former, many methods have been reported that involve deionizing silicates such as water glass and hydrolyzing orthosilicate esters such as tetraethoxysilane (TEOS) / tetramethoxysilane (TMOS) in situ. In the latter, the general chemical formula (RSio) is used as a precursor. １．５ ) ｎ Polysilsesquioxane represented by the general chemical formula (R ２ SiO) ｎ A known method involves using polysiloxanes, etc., represented by [formula].

[0012] Among these, it was found that using a shell layer mainly composed of polysilsesquioxane as a precursor resulted in fewer surface silanols compared to the case where the shell layer was formed by hydrolysis of orthosilicate ester. In particular, it was discovered that the amount of two silanols located on adjacent silicon atoms separated by one oxygen atom (vicinal silanols) and two silanols with close silanol distances that are capable of hydrogen bonding (interacting silanols) was reduced, leading to the completion of the present invention.

[0013] The hollow silica particles of the present invention have a dense silica shell, and because the amount of silanol on the inner and outer surfaces of the shell is low, both the dielectric constant and dielectric loss tangent are sufficiently low. Furthermore, because the hollow silica particles of the present invention are not easily penetrated by resins or solvents, they can exhibit excellent low dielectric constant and low dielectric loss tangent even in resin compositions. In addition, because the amount of silanol on the outer surface of the hollow silica particles of the present invention is low, they have excellent dispersibility in resins.

[0014] This is a scanning electron microscope image of the hollow silica particles prepared in Example 1. This is a scanning electron microscope image of the hollow silica particles prepared in Comparative Example 2.

[0015] (Hollow Silica Particles) The hollow silica particles of this embodiment have a shell layer (solid film) containing silica and have a space inside the shell layer. The presence of a space inside the shell layer of hollow silica particles can be confirmed by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and scanning electron microscopy (SEM) observations. In the case of SEM observation, in addition to observing the cross-section of the resin-embedded particles, the hollow nature can be confirmed by observing the internal structure of the particles by increasing the acceleration voltage of the electron beam, and by observing broken particles with a partial opening. In this embodiment, spherical particles with an internal space confirmed by TEM and SEM observations are defined as "primary particles." Note that, since the primary particles of hollow silica particles partially bond together during the firing and drying processes, the hollow silica particles obtained in the manufacturing process are often aggregates of secondary particles formed by the aggregation of primary particles.

[0016] The void ratio is the ratio of the volume of voids contained within a hollow silica particle, relative to its volume. The calculation method will be described later. A higher void ratio results in hollow silica with lower relative permittivity and dielectric loss tangent. However, if the void ratio becomes extremely high, the thickness of the shell layer decreases, and the mechanical strength decreases. Therefore, a void ratio is selected that is above the lower limit of the void ratio specified by the required dielectric properties and has sufficient mechanical strength for practical purposes.

[0017] The relative permittivity required for hollow silica particles must be 2.8 or less, and is more preferably 2.3 or less, in the applications where the embodiment is applied as a product. The relative permittivity of silica constituting the shell layer is 3.6 to 4.2. Combined with the relative permittivity of vacuum which is 1.0, the relative permittivity of hollow silica is calculated using the Maxwell-Garnett formula used for measuring the permittivity of composite materials. As a result, the larger the hollow ratio, the smaller the permittivity, and the hollow ratios that achieve a relative permittivity of 2.8 and further 2.3 are approximately 35% and 53%, respectively. Considering that the permittivity of hollow silica increases due to the influence of surface silanols, the lower limit of the hollow ratio is at least 40%, preferably 50%, more preferably 55%.

[0018] The hollow ratio of hollow silica is defined as the density measured for a hollow silica powder sample using a helium gas pycnometer being ρ Ｈｅ , and the density measured using a nitrogen gas pycnometer being ρ Ｎ２ , a method (1) calculates it as {1−(ρ Ｎ２ / ρ Ｈｅ )}×100 (%), and when the particle diameter (D) of hollow silica particles and the thickness (t) of the shell layer of hollow silica particles are obtained from a TEM image or SEM image, a method (2) calculates it as {1−(2t / D)} ３ ×100 (%).

[0019] It is preferable that the shell layer does not have pores (mesopores and macropores) that allow molecules such as solvents and resins to pass through. If such pores are present, the dielectric properties of the particles are highly likely to be equivalent to those of solid silica when the resin composition is formed. So-called micropores, which are sufficiently small for molecules such as solvents and resins, may be present.

[0020] Helium gas can pass through micropores, while nitrogen gas cannot pass through micropores. Therefore, in the hollow ratio calculation method (1), it is possible to obtain the volume of the region inside the particle that is isolated from the outside of the particle by the shell layer having no macropores. However, when macropores are present, ρ Ｎ２ =ρ Ｈｅand the powder sample is a mixture of particles with and without macropores, so ρ Ｎ２ the value of increases as the number of particles having macropores increases.

[0021] (Dielectric properties of hollow silica) The relative dielectric constant is as described above. In consideration of the application of the hollow silica material, the dielectric loss tangent must also be sufficiently low. The dielectric loss tangent of the hollow silica material as a single substance is desirably 0.005 or less, preferably 0.003 or less, more preferably 0.002 or less, and still more preferably 0.001 or less.

[0022] (Surface silanol) It is known that silanol undergoes dehydration condensation and weight loss upon heating. It is known in the art that silica obtained by reducing silanol through heat treatment has superior dielectric properties compared to untreated silica. Therefore, the smaller the amount of dehydratable silanol by heating, that is, the smaller the amount of moisture desorbed by heating, the more suitable it is as a filler for electronic materials. Silanols on the silica surface are classified into the following four types according to the positional relationship between adjacent silanols and the presence or absence of interaction (the aforementioned Non-Patent Document 1). Since these have different desorption energies, they undergo dehydration condensation in different temperature ranges (the aforementioned Non-Patent Document 2).

[0023] (1) Vicinal Vicinal is a silanol structure where two silicon atoms are adjacent to each other with one oxygen atom in between, and they are within a distance where hydrogen bonding is possible. Vicinal is relatively easy to dehydrate and dehydrates at a low temperature of about 400°C. (2) Interacting Interacting is structurally distant, but sterically close, and within a distance where hydrogen bonding is possible. Interacting is also easy to dehydrate like Vicinal and dehydrates at about 400°C. (3) Geminal Geminal is a structure where two silanols are located on a single silicon atom. Although spatially close, they are in a position unfavorable for hydrogen bonding. For this reason, Geminal is dehydrated at a higher temperature (600 to 900°C) than silanols in the Vicinal and Interacting positions. (4) Isolated Isolated silica is a silanol located on two silicon atoms with multiple atoms in between, and the silanol distance is sufficiently large to be outside the range where hydrogen bonding is possible. Dehydration requires a significant change in the silica structure and is carried out at an even higher temperature (above 1000°C) than for Geminal silica.

[0024] The amount of silanols in structures with a relative positional relationship of "vicinal," "interacting," and "geminal" can be quantified by the temperature range at which desorption occurs. For simpler analysis, a method of heating the sample at three points: 200°C, 550°C, and 900°C is employed. Specifically, the moisture measured when the sample is heated to about 200°C is mainly water physically adsorbed on the silica surface, the moisture measured when heated to 550°C (moisture desorbed between 200°C and 550°C) is derived from "vicinal" or "interacting" silanols, and the moisture measured when heated to 900°C (moisture desorbed between 550°C and 900°C) is derived from "geminal" silanols.

[0025] By comparing the absolute amount of detachable moisture (or the moisture content per surface area), the quality of properties of silica (e.g., dielectric properties) can be determined. Furthermore, it has been found that the ratio of the moisture content derived from "Vicinal" or "Interacting" silanols to the moisture content derived from "Geminal" silanols allows sensitive and easy determination of the quality of silica properties, and the smaller the ratio, the better the dielectric properties. The absolute amount of detachable moisture is convenient for comparing the quality of materials and / or production methods, that is, comparing the absolute amount of surface silanols capable of dehydration condensation in silica synthesized by the materials and / or production methods. When similar materials and / or production methods are used, the ratio of the moisture content derived from "Vicinal" or "Interacting" silanols to the moisture content derived from "Geminal" silanols can be used as an indicator for selecting materials and / or production methods that can further reduce residual silanols. In addition, this ratio can serve as a hint for estimating the bonding state and structure of silica.

[0026] When the moisture content desorbed from 200°C to 550°C is defined as A [ppm] and the moisture content desorbed from 550°C to 900°C is defined as B [ppm], A / B < 2.2 is preferred, and A / B < 2.0 is more preferred. If this ratio is too small, the effect of improving affinity with contacting materials achieved by the surface treatment of hollow silica described later will be reduced, so the lower limit is preferably 0.5 < A / B.

[0027] Moisture desorbed from 200°C to 550°C, derived from "Vicinal" or "Interacting" silanols, has a content of 30 µg / m per surface area ２ or less is preferred, and 28 µg / m ２ or less is more preferred, and 25 µg / m ２ or less is even more preferred. If the desorbed moisture content per surface area is too low, the effect of improving affinity with contacting materials achieved by the surface treatment of hollow silica described later will be reduced, so the lower limit is 5 µg / m ２ or more is preferred. Moisture desorbed from 550°C to 900°C, derived from "Geminal" silanols, has a content of 20 µg / m per surface area ２ or less is preferred, and 18 µg / m ２ or less is more preferred. The lower limit is 5 µg / m２ The above is preferable.

[0028] (Surface treatment of hollow silica) Surface treatment is expected to improve dielectric properties and affinity with other materials. The primary purpose of surface treatment is to remove silanol groups remaining on the surface of hollow silica particle material by so-called capping. For example, compounds having trimethylsilyl groups, more specifically methoxytrimethylsilane and hexamethyldisilazane (HMDS), can be used as surface treatment agents.

[0029] A second objective of surface treatment is the use of surface treatment agents to improve the affinity with the material that will ultimately come into contact with the surface. For example, silane compounds are used as surface treatment agents. Examples of silane compounds include compounds having alkyl groups, vinyl groups, phenyl groups, methacrylic groups, epoxy groups, and alkyl groups having these groups as side chains as functional groups. More specifically, and not limited by the examples, examples include methyltrialkoxysilane, dimethyldialkoxysilane, phenyltrialkoxysilane, dialkoxydiphenylsilane, n-propyltrialkoxysilane, hexyltrialkoxysilane, octyltrialkoxysilane, decyltrialkoxysilane, 3,3,3-trifluoropropyltrialkoxysilane, vinyltrialkoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrialkoxysilane, 3-glycidoxypropylmethyldialkoxysilane, 3-glycidoxypropyltrialkoxysilane, p-styryltrialkoxysilane, 3-methacryloxypropylmethyldialkoxysilane, 3-methacryloxypropyl Examples include 3-trialkoxysilane, 3-acryloxypropyltrialkoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldialkoxysilane, N-2-(aminoethyl)-3-aminopropyltrialkoxysilane, 3-aminopropyltrialkoxysilane, N-phenyl-3-aminopropyltrialkoxysilane, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldialkoxysilane, 3-mercaptopropyltrialkoxysilane, 3-isocyanatetopropyltrialkoxysilane, and 3-trialkoxysilylpropylsuccinic anhydride (where alkoxy is a functional group derived from alcohols such as methoxy, ethoxy, and isopropoxy).

[0030] (Method for producing hollow silica particle material) The method for producing hollow silica particles (hollow silica particle material) in the embodiment is a method that can suitably produce the hollow silica particles of the embodiment described above. Core-shell particles, in which a core material is the core and silica is the shell, serve as a precursor, and hollow silica particles are produced by removing the core from the precursor and extracting the shell. The method for producing hollow silica particles in the embodiment includes a core material dispersion preparation step, a core-shell composite formation step, a calcination step, and other necessary steps.

[0031] <Core Material Dispersion Preparation Process> The core material dispersion preparation process is a process of preparing a core material dispersion by dispersing the core material in a dispersion medium. A catalyst that promotes silica polymerization (typically an acid or alkali, but not limited to these) is added to the dispersion medium as needed. The core material may be dispersed before or after the addition of other components to the dispersion medium, or the other components and the core material may be dispersed simultaneously. If a catalyst that promotes silica polymerization is added, it may be added when preparing the core material dispersion, after preparing the core material dispersion, simultaneously with the addition of the hydrolyzable silane compound, or after the addition of the hydrolyzable silane compound has been completed.

[0032] The dispersion medium may be water or an aqueous solvent mainly composed of water as described below. The aqueous solvent is a solvent that is miscible with water and is selected from monoalcohols having 1 to 3 carbon atoms (methanol, ethanol, 1-propanol, 2-propanol), dialcohols (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol), or trialcohols (glycerol), and may also be a mixture of two or more of these.

[0033] - Core Material: By selecting the core material, it is possible to synthesize hollow silica of various sizes. Voids are formed with sizes and shapes that correlate with the size and shape of the selected core material. As the core material, a particulate material dispersed in water or dispersible in water is preferred.

[0034] The core material is preferably composed of an easily removable organic material, and is particularly preferably formed from a resin material. It is preferable to construct the core material from a resin material and remove the resin core material by firing. For example, a resin dispersed in water, such as a resin emulsion, is suitable for the core material. It may be synthesized by known methods, or commercially available products can be used. The type and method of obtaining the resin are not limited here.

[0035] Generally, silica nuclei are weakly negatively charged. Therefore, if a material other than particles that are strongly negatively charged under the reaction conditions for generating silica nuclei is used as the core material, the repulsion between the surrounding core material and the generated silica nuclei decreases, and a silica shell layer is formed around the core material in a suitable form. From various experiments, it has been found that the surface potential in liquid of the resin that is preferably used as the core material is -3 mV or higher, and more preferably 3 mV or higher.

[0036] The core material should preferably have high sphericity and a small specific surface area. The sphericity of the core material greatly affects the shape of the hollow silica after firing. If the sphericity of the core material is low, the sphericity of the core-shell composite will also be low, and the sphericity of the hollow silica after firing will also be low. This can lead to an increased specific surface area and increased brittleness, which can result in deterioration of the dielectric constant, dielectric loss tangent, and viscosity during resin mixing.

[0037] The core material should preferably be free of fine particles and have a narrow particle size distribution. If there are many fine particles, a large amount of fine particles will form in the core-shell composite and the hollow silica after firing, increasing the specific surface area. This leads to a deterioration of the dielectric loss tangent and viscosity during resin mixing. Furthermore, a large amount of fine particles promotes fusion during firing. Fusion leads to cracking, which worsens the dielectric constant, dielectric loss tangent, and viscosity during resin mixing.

[0038] The core material is preferably removed by thermal decomposition at a temperature between 200°C and 400°C. If resin particles or resin emulsions that do not meet this condition are used as the core material, they can be used after converting their surface potential to positive by a known method.

[0039] <Core-shell composite formation process> The core-shell composite formation process involves mixing and stirring a hydrolyzable silane hydrolysate into a core material dispersion, thereby forming an adsorption composite on the surface of the core material where the hydrolyzable silane is adsorbed. The hydrolyzable silane hydrolysate to be mixed is added as hydrolyzable silane when added, and can be converted into a hydrolyzable silane by allowing hydrolysis and polymerization to proceed in the core material dispersion.

[0040] • Hydrolyzable silanes are those represented by the following chemical formula 1, where n is an integer from 0 to 3. １ The main skeleton is an alkane or alkene having 1 or more carbon atoms, and may have substituents containing heteroatoms, and when n is 2 or 3, R １ They may be identical or have different structures. Also, R ２ The main skeleton is an alkane with 1 to 4 carbon atoms, and may have a hydroxyl group in the side chain. Chemical formula 1: R １ ｎ Si ( OR ２ ) ４－ｎ

[0041] Although hollow silica can be synthesized using only orthosilicate esters (n=0), such as TEOS (tetraethyl silicate), the dielectric properties after calcination were not easily improved. On the other hand, when precursors were prepared using monoalkyltrialkoxysilane (n=1) and dialkyldialkoxysilane (n=2), and these precursors were calcined, they exhibited lower dielectric properties than those prepared from orthosilicate esters alone. Starting with orthosilicate esters alone, amorphous silica is directly formed from orthosilicic acid in the precursor's shell layer. However, microscopically, the four bonds of orthosilicic acid form a three-dimensional four-coordinate structure, i.e., a three-dimensionally continuous cage-like structure, resulting in a rigid structure that hinders dehydration between free silanols present at grain boundaries during calcination. On the other hand, starting with monoalkyltrialkoxysilane and dialkyldialkoxysilane, polysilsesquioxane and polysiloxane are formed in the precursor's shell layer, respectively. Because these molecules have two-dimensional and one-dimensional molecular structures, respectively, it is thought that the intermolecular positions can be easily altered during firing, and as a result, dehydration due to the resulting silanol content is more likely to occur.

[0042] Specific examples of monoalkyltrialkoxysilanes are not limited by the examples provided, but include methyltrialkoxysilane, phenyltrialkoxysilane, n-propyltrialkoxysilane, hexyltrialkoxysilane, octyltrialkoxysilane, decyltrialkoxysilane, vinyltrialkoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrialkoxysilane, 3-glycidoxypropyltrialkoxysilane, p-styryltrialkoxysilane, 3-methacryloxypropyltrialkoxysilane, 3-acryloxypropyltrialkoxysilane, N-2-(aminoethyl)-3-aminopropyltrialkoxysilane, 3-aminopropyltrialkoxysilane, N-phenyl-3-aminopropyltrialkoxysilane, 3-ureidopropyltrialkoxysilane, 3-mercaptopropyltrialkoxysilane, 3-isocyanatetopropyltrialkoxysilane, 3-trialkoxysilylpropylsuccinic anhydride, etc. (where alkoxy is a functional group derived from alcohols such as methoxy, ethoxy, and isopropoxy).

[0043] Specific examples of dialkyldialkoxysilanes are not limited by the examples provided, and include dimethyldialkoxysilane, dialkoxydiphenylsilane, 3-glycidoxypropylmethyldialkoxysilane, 3-methacryloxypropylmethyldialkoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldialkoxysilane, 3-mercaptopropylmethyldialkoxysilane, etc. (in each case, the alkoxy is a functional group derived from alcohols such as methoxy, ethoxy, and isopropoxy). These are sold by various companies.

[0044] Monoalkyltrialkoxysilanes and dialkyldialkoxysilanes may be used individually or mixed in any proportion. They may also be mixed with orthosilicate esters, trialkylmonalkoxysilanes, etc., in any proportion to adjust the rigidity of the shell layers.

[0045] Specific examples of orthosilicate esters are not limited by the examples provided, but include tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetrapropoxysilane, etc. Similarly, specific examples of trialkylmonalkoxysilanes are not limited by the examples provided, and in addition to trimethylmethoxysilane, triethylmethoxysilane, etc., silazanes whose hydrolysates have a similar structure, such as hexamethyldisilazane, can also be used.

[0046] Orthosilicate esters, monoalkyltrialkoxysilanes, dialkyldialkoxysilanes, and trialkylmonalkoxysilanes are almost always oil-soluble compounds. To adjust their water solubility, these compounds may be converted to compounds in which a hydroxyl group is introduced to the side chain of the alkoxy group by transesterification in the presence of a polyhydric alcohol and an acid. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerol.

[0047] <Casturing Process> The calcination process involves calcining the core-shell composite to decompose and remove the core material, and further decompose and remove the organic components of the shell layer, thereby converting it into silica. Simultaneously, the shell layer is densified. All processes may be carried out in a single heating process, or a separate process may be added before densifying the shell layer, which involves heating at a lower temperature of around 500°C for the purpose of decomposing and removing the core material and organic components, i.e., a "degreasing process". The process is not particularly limited as long as the core material is decomposed and removed and the shell layer formed on the surface of the core material is not destroyed, and heating under an oxidizing atmosphere is an example. For example, calcination is carried out in air at a temperature and time at which the core material is decomposed and removed. Examples of calcination temperatures include 700°C or higher, 800°C or higher, 900°C or higher, 1000°C or higher, 1100°C or higher, etc. Higher calcination temperatures are preferable, but they should be below the temperature at which the hollow silica aggregates or melts. Even if agglutination occurs, it is acceptable to allow it to occur if it can be separated into primary particles by a crushing operation. Since the core-shell composite is manufactured while immersed in the mother liquor, a process of separating it from the mother liquor may be included before the calcination process. For example, processes such as filtration, centrifugation, and drying may be employed. Furthermore, a crushing operation to break down agglutination may be incorporated between each individual operation as appropriate. The heating rate during calcination is preferably 5°C / min or less, more preferably 1°C / min or less, and particularly preferably 0.5°C / min or less.

[0048] <Control of shell thickness and hollow silica particle size> To summarize the manufacturing method of hollow silica particles (hollow silica particle material) in the embodiment, in order to increase the shell thickness, methods such as increasing the ratio between the amount of hydrolyzable silane and the amount of core material, or using a core material with a high surface potential are employed. Control of the hollow silica size is achieved by controlling the size of the core material, controlling the shell thickness, or a combination of these.

[0049] (Slurry Composition) The slurry composition of the embodiment is a composition in which the hollow silica of the embodiment described above is dispersed in a dispersion medium. The slurry composition of the embodiment is used for electronic materials such as semiconductor substrate materials, and is particularly preferably used for high-frequency substrate materials. The dispersion medium is substantially free of water, and is particularly preferably 1000 ppm or less in water content, and more preferably 500 ppm or less.

[0050] The mixing ratio of hollow silica to dispersion medium in the slurry composition is not particularly limited, but it is preferable to have as much hollow silica as possible. Since viscosity tends to increase with increasing hollow silica content, the hollow silica particles (hollow silica particle material) are mixed until the viscosity is as high as possible while considering handling. For example, the ratio of (hollow silica particles):(dispersion medium) can be mixed in a mass ratio of approximately 20:80 to 80:20.

[0051] The dispersion medium is not particularly limited and includes silicone oil, methyl ethyl ketone, alcohol, organic solvents such as hexane, epoxy resin precursors, polyester precursors, and silicone resin precursors.

[0052] It is preferable that the hollow silica particles are surface-treated. In the surface treatment, it is preferable to introduce functional groups that can improve the affinity between the dispersion medium used and the mating material that the hollow silica will ultimately come into contact with when used.

[0053] (Resin Composition) The resin composition of this embodiment is a cured product comprising the aforementioned hollow silica particles (hollow silica particle material) and a resin material that disperses the hollow silica particles. The resin material preferably has a water content of 1000 ppm or less, and more preferably 500 ppm or less.

[0054] The resin composition is preferably used in electronic materials, and such electronic materials are preferably applied to high-frequency applications such as high-frequency substrates. Because the hollow silica particles of the embodiment have a low Df value (dielectric loss tangent), losses are reduced even when used in applications where high frequencies are transmitted.

[0055] The mixing ratio of hollow silica particles to resin material in the resin composition is not particularly limited, but it is preferable to have as much hollow silica particle content as possible. For example, (hollow silica particles):(resin material) is mixed in a mass ratio of about 10:90 to 90:10.

[0056] The resin material is not particularly limited and can be any common resin material such as thermosetting resins (either pre-cured or post-cured state when mixed), thermoplastic resins, etc. Examples include epoxy resins, melamine resins, acrylic resins, polycarbonate resins, polyesters, silicone resins, liquid crystal polymers (LCPs), polyimides, cyclic olefin polymers (COPs), and polyphenylene oxides (PPOs). The resin material can be used alone or by mixing (alloying, etc.) multiple types of resin materials. The moisture content of the resin material is preferably 1000 ppm or less, and more preferably 500 ppm or less. The hollow silica particles are preferably surface-treated. In the surface treatment, it is preferable to introduce functional groups that can improve the affinity with the resin material used.

[0057] (Analysis Methods) Unless otherwise explicitly limited in this specification, each analysis shall be performed by the following methods.

[0058] (1) Particle Size Distribution Optical particle size distribution measurement is the simplest method for analyzing the aggregation state of primary particles. On the other hand, since the refractive index of hollow silica particles (hollow silica particle material) is different from that of the inorganic materials that constitute it, the average particle size obtained will deviate from the true average particle size. Therefore, optical particle size distribution measurement is performed to analyze the aggregation state of the particles, and the average particle size is determined by image analysis.

[0059] (1a) Analysis of aggregation state The particle size distribution was measured using a laser diffraction particle size distribution analyzer (SALD-7500nano, manufactured by Shimadzu Corporation) under the following conditions: • Dispersion medium: Isopropyl alcohol • Refractive index: 1.45 • Calculation mode: Volume

[0060] (1b) A slurry of average particle size hollow silica particles was dropped onto a silicon wafer and dried. The particles were allowed to adhere in a single layer. The particles were then observed using a scanning electron microscope (SEM). The SEM images were observed at a magnification that allowed approximately 100 to 1000 particles to be observed in one field of view, and the size of approximately 1000 particles obtained from 1 to 10 fields of view was measured. Based on the measurement results, the volume particle size distribution was determined, and the particle size at which the cumulative frequency of the volume particle size distribution reached 50% was defined as the average particle size. For image analysis, the image analysis software "A-zo-kun" (registered trademark) (manufactured by Asahi Kasei Engineering Corporation) was applied.

[0061] (2) When measuring the void ratio, if it was possible to independently measure hollow silica particles weighing 1 g or more, (2a) a gas hydrometer was used. When the particles were filled into a resin composition, or when there was less than 1 g of sample, or when (2a) a gas hydrometer could not be used for other reasons, (2b) SEM image analysis was used.

[0062] (2a) Gas hydrometer The density was measured using a gas hydrometer (AccuPyc II 1340, manufactured by Micrometrics) under the following measurement conditions: Sample cell: 10 cm ３ Cell / sample weight: 1 to 3 g; Measurement gas: Helium and nitrogen; Purge: 10 times, 135 kPa (G); Measurement: 10 times, 135 kPa (G)

[0063] The same sample was measured using both helium and nitrogen. Because helium can reach the inner lumens of hollow silica particles through micropores, the density (ρ) when helium is used as the measurement gas is different. Ｈｅ ) represents the density of the shell layer. On the other hand, the density when nitrogen is used (ρ Ｎ２ ) represents the density of hollow silica. Therefore, the hollowness ratio is {1 - (ρ Ｎ２ / ρ Ｈｅ The calculation was performed using )} × 100 (%).

[0064] (2b) Image Analysis: For each hollow silica particle, the particle size (D) was determined using the same method as described in the explanation of average particle size, from TEM (including STEM) or SEM images that emphasized the shell layer portion of the hollow silica particles. At the same time, the shell layer thickness (t) was recorded. For individual particles, the value calculated using the following formula was used, or, when examining the properties of the powder as a whole, the average value of the calculated values ​​for 1000 or more particles was used. {1 - (2t / D)} ３ ×100 (%)

[0065] TEM (including STEM) images are ideal for this analysis. However, for a simpler approach, a scanning electron microscope (SU8000, Hitachi High-Technologies Corporation) can be used to record SEM images with enhanced shell layers under the following conditions: • Acceleration voltage: 10 kV • Probe distance: 15 mm • Detector: Lower detector and SE detector

[0066] (3) Hollow silica particles of the specific surface area embodiment were dried under reduced pressure at 200°C to obtain a sample. The specific surface area and pore volume of this sample were measured using an automated specific surface area / pore distribution analyzer (Trister II, manufactured by Micrometrics) by multipoint BET method with nitrogen gas, or by single-point BET specific surface area measurement.

[0067] (4) Dielectric Properties The dielectric properties of the powder were measured by filling a PTFE tube measuring 8 mmφ (diameter) x 30 mm (tube length) with hollow silica particles and using an empty tube as a control sample. Each sample was placed in a cavity resonator connected to a network analyzer, and the resonant frequency and Q value in the 1 GHz band were determined. From these values, the complex dielectric constant was calculated using the "Perturbation Method Dielectric Constant Calculation Application" (manufactured by Keycom Co., Ltd.). In the case of resin compositions, a rectangular prism of approximately 4 mm x 7 mm x 30 mm was cut from the resin composition and used as a measurement sample, and the complex dielectric constant was calculated using the sample without being placed in a cavity resonator as a control.

[0068] (5) Coefficient of thermal expansion A rectangular parallelepiped with sides of approximately 4 mm was cut from the resin composition to be used as a sample for measurement. This was heated from -50°C to 250°C at a heating rate of 5°C / min using a thermomechanical analyzer (TA Instruments, TMA Q400), and the linear expansion was recorded. From the plot, the average rate of change from 0 to 50°C and from 180 to 220°C were defined as CTE1 and CTE2, respectively.

[0069] (6) Hydrophobic treatment (capping of silanol groups) A mixture of silica particle powder and 500% by mass of hexamethyldisilazane relative to the powder was heated at 120°C for 3 hours to dry out and remove unreacted hexamethyldisilazane.

[0070] (7) Determination of silanol content 5 g of silica powder was added to 35 g of methyl ethyl ketone and shaken for 10 minutes using a shaker. The precipitate was collected by centrifugation (14000 G x 30 minutes). This operation was repeated twice to remove the methyl ethyl ketone soluble component, and then dried to obtain a sample for carbon content measurement. The carbon content of this sample was measured using a LECO CS-444LS carbon / sulfur simultaneous analyzer. JSS061-8 was used as the carbon standard sample. From the change in carbon content before and after hydrophobic treatment, the amount of trimethylsilyl groups that reacted with the silanol groups on the surface was calculated and defined as the amount of silanol groups. Further standardization by specific surface area was used to obtain the surface silanol density.

[0071] (8) Moisture content The moisture content was measured by the Karl Fischer method. By gradually raising the temperature from room temperature (25°C) to 200°C, 550°C, and 900°C, it is possible to measure the amount of moisture generated between room temperature and 200°C (physically adsorbed on the silica surface), the amount of moisture generated between 200°C and 500°C (generated by dehydration condensation of vicinal or interacting silanols on the silica surface), and the amount of moisture generated between 550°C and 900°C (generated by dehydration condensation of geometric silanols on the silica surface).

[0072] (Example 1) <Synthesis of core-shell particles> 1000 g of acrylic resin emulsion (average particle size 300 nm, surface potential +52 mV, solid content concentration 40 wt%) was mixed with 8600 g of water. Subsequently, 500 g of methyltrimethoxysilane was added and the mixture was stirred for 3 hours while maintaining the temperature at 40°C. Then, 40 g of tetraethylammonium hydroxide aqueous solution (35 wt%) was added and the mixture was stirred for 2 hours. This aqueous solution was allowed to cool to room temperature. The resulting solid was filtered under reduced pressure using filter paper (JIS P 3801 (1995) standard, No. 5A) and the precipitate was recovered.

[0073] <Degreasing by calcination> The recovered precipitate was heated to 1000°C at a heating rate of 1°C / min and held at 1000°C for 6 hours. The resulting silica was aggregated, so it was crushed to obtain the hollow silica material that served as the example test sample.

[0074] (Example 2) The "methyltrimethoxysilane: 500 g" in Example 1 was replaced with "a mixture of methyltrimethoxysilane: 250 g and TEOS: 382 g". Otherwise, the preparation was carried out in the same manner as in Example 1.

[0075] (Comparative Example 1) Silica (180 nm) manufactured by Admatex Co., Ltd. using the VMC method (Vaporized Metal Combustion Method) was used. The VMC method is a type of dry synthesis method that directly oxidizes metallic silicon to obtain silica (see, for example, Japanese Patent No. 3229353).

[0076] (Comparative Example 2) The "methyltrimethoxysilane: 500g" in Example 1 was changed to "TEOS: 765g". Otherwise, it was prepared in the same manner as in Example 1.

[0077] (Evaluation) The appearance of the hollow silica particles obtained in Example 1 and Comparative Example 2 is shown in the photographs in Figures 1 and 2 (both at a magnification of 100,000). The surface of the particles obtained in Example 1 was smooth. In contrast, the particles obtained in Comparative Example 2 had an uneven surface. When the specific surface area and true specific gravity (density) were measured, the specific surface area of ​​Example 1 was 53 m² in both cases. ２ / g, 1.0g / cm ３ Comparative Example 2 is 63m２ / g, 1.0g / cm ３ (See Table 1). In Comparative Example 2, the specific surface area was higher despite having the same density as Example 1. This is thought to be due to the unevenness of the particle surface.

[0078] The characteristics of each sample are summarized in Table 1. Examples 1, 2, and Comparative Example 2, all of which are hollow silica, have similar particle sizes and hollowness ratios. Although the particle size of the solid silica in Comparative Example 1 is slightly larger than that of the other hollow silica samples, the silanol density has been standardized to a per-surface area ratio, making comparison possible. The moisture content at 200–550°C and 550–900°C has also been standardized to a per-surface area ratio.

[0079] Regarding the silanol density, Comparative Example 2 using TEOS had a density of 3.9 μmol / m³. ２ The value was almost the same as that of VMC-processed silica. Comparative Example 2, although having a hollow structure, was suggested to have a surface condition equivalent to that of general solid silica. Example 1 was 1.2 μmol / m ２ And, Comparative Example 2: 3.9 μmol / m ２ It was found to be a significantly smaller value than that. Furthermore, in Example 2, where methyltrimethoxysilane and TEOS were mixed in a 1:1 silica equivalent ratio, the value was 2.5 μmol / m³, which is an intermediate value between Example 1 and Comparative Example 2. ２ This was shown.

[0080] We analyzed the specific differences in the amount of silanol present in this difference. In Comparative Example 2, the water content per surface area was 80 μg / m² between 200°C and 550°C. ２ Between 550°C and 900°C, the concentration is 31 μg / m³. ２ The silanol density was comparable to that of silica produced by the VMC method. This suggests that the proportion of each silanol type, such as Geminal and Vicinal, present on the particle surface is also comparable to that of typical solid silica.

[0081] In Example 1, the concentration was 10 μg / m² between 200°C and 550°C. ２ Between 550°C and 900°C, the concentration is 12 μg / m³. ２The values ​​were smaller than those of Comparative Examples 1 and 2. In particular, the amount of water released between 200°C and 550°C by the dehydration of vicinal and interacting silanols showed a significant difference compared to Comparative Examples 1 and 2. Focusing on the amount of water between 200°C and 550°C relative to the amount of water between 550°C and 900°C, the value in Comparative Example 2 was 2.6, while in Example 1 it was a significantly smaller value of 0.8. Example 2 showed 1.9. From these results, it was found that silica containing siliceous material derived from methyltrimethoxysilane contains less vicinal and interacting silanols compared to geometric silanols. Furthermore, this ratio and the small amount of geometric silanol per unit surface area, i.e., the amount of water released between 550°C and 900°C per unit surface area, suggest that the overall amount of silanols is reduced.

[0082]

[0083] Next, we consider the dielectric properties (relative permittivity and dielectric loss tangent) when the silanol on the outer surface is removed (Table 2). 1,1,1,3,3,3-Hexamethyldisilazane was mixed at 600% by mass relative to the mass of the hollow silica obtained in Examples 1 and 2 and Comparative Examples 1 and 2. The excess 1,1,1,3,3,3-Hexamethyldisilazane was then removed by drying at 120°C for 3 hours. Analysis of the dielectric properties of these treated powders revealed that in all samples, the relative permittivity and dielectric loss tangent were smaller than those before treatment with 1,1,1,3,3,3-Hexamethyldisilazane. This suggests that the excess 1,1,1,3,3,3-Hexamethyldisilazane acted to eliminate the silanol on the outer surface of the particles by trimethylsilylation. For the evaluation of dielectric properties, materials with a dielectric loss tangent equivalent to or smaller than that of Comparative Example 1 (solid silica with approximately the same particle size as Examples 1, 2, and Comparative Example 2) after the surface silanol was removed were rated as "good," and those with a dielectric loss tangent larger were rated as "poor."

[0084] This surface treatment is thought to have caused all silanols present on the outer surface of the particles to react, and the difference in dielectric loss tangent is thought to be due to the contribution of silanols inside and on the inner surface of the shell. Examples 1 and 2, which have silica in their shells produced by calcining a precursor containing polysilsesquioxane, showed dielectric loss tangents equivalent to or better than Comparative Example 1, despite the presence of residual silanols on the inner surface of the hollow silica. That is, in the situations in which these particles are used, it is thought that they can be used as a substitute for solid silica without worsening the dielectric loss tangent. On the other hand, the dielectric loss tangent worsened in Comparative Example 2. Since the dielectric loss tangent worsens when solid silica is replaced with these particles, substitution is not possible.

[0085]

[0086] The hollow silica obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was reacted with 2.5% by mass of vinyltrimethoxysilane to prepare epoxy resin compositions with a filler volume fraction of 2.8% by volume (27% by mass of hollow silica and 42% by mass of solid silica). The dielectric properties and thermal expansion coefficients of resin pieces of these resin compositions were determined (Table 3). In Table 3, "vinyl" refers to vinyltrimethoxysilane.

[0087] The coefficient of thermal expansion (CTE) was found to be nearly identical for both CTE1 (0-50°C) and CTE2 (180-220°C). That is, hollow silica can impart thermomechanical properties equivalent to those of solid silica of the same volume to the resin composition. On the other hand, differences were observed in dielectric properties. When hollow silica was used as a filler in Examples 1 and 2 and Comparative Example 2, the relative permittivity was lower than that of solid silica in all cases. However, regarding the dielectric loss tangent, similar to the dielectric loss tangent when trimethylsilylated, the dielectric constant of the resin composition deteriorated in Comparative Example 2.

[0088] Therefore, the hollow silica particles in this embodiment are suitable for applications that improve the dielectric constant while maintaining thermomechanical properties. Furthermore, the deterioration of the dielectric loss tangent, which was a problem with conventional hollow silica, is suppressed, and a dielectric loss tangent equivalent to that of solid silica can be maintained.

[0089] Furthermore, the silanol density of Example 2 was 2.5 μmol / m³. ２ Therefore, we concluded that hollow silica with a modifiable surface silanol density below this value can be simply substituted for VMC-processed silica. Focusing on the positional relationship of the silanols at this time, it became clear that good dielectric properties are observed when there are few vicinal or interacting silanols, that is, when the amount of moisture between 200°C and 550°C is less than 2.2 relative to the amount of moisture between 550°C and 900°C.

[0090]

[0091] The hollow silica particle material of this embodiment is suitable for use as a filler added to semiconductor materials in terms of purity and dielectric properties. Furthermore, it is expected to improve the performance of slurries or resin compositions containing the hollow silica particle material or inorganic filler.

Claims

1. Hollow silica particles having one or more voids inside the particle that are isolated from the outside by a shell layer mainly composed of silica, wherein when the hollow silica particles are heated from 200°C to 550°C, the amount of first desorbed moisture that is desorbed from the hollow silica particles is A [ppm], and when the hollow silica particles are heated from 550°C to 900°C, the amount of second desorbed moisture that is desorbed from the hollow silica particles is B [ppm], and the relationship between the first desorbed moisture amount and the second desorbed moisture amount satisfies 0.5 < (A / B) < 2.

2.

2. The specific surface area of ​​hollow silica particles is C[m²] ２ When [ / g] is set, between the first amount of desorbed water and the specific surface area, 5 ≤ (A / C) ≤ 30 μg / m ２ The hollow silica particles according to claim 1.

3. Between the second amount of desorbed water and the specific surface area, 5 ≤ (B / C) ≤ 20 μg / m² ２ The hollow silica particles according to claim 2.

4. The hollow silica particles according to claim 1, wherein the average particle size of the hollow silica particles is 0.05 μm or more and 1.5 μm or less.

5. The density of hollow silica particles measured using nitrogen gas was 0.7 g / cm³. ３ Above, 1.4g / cm ３ The hollow silica particles according to claim 1, which are as follows:

6. The hollow silica particle according to claim 1, wherein the relative permittivity of the hollow silica particle measured at 1 GHz is 2.5 or less, and the dielectric loss tangent of the hollow silica particle measured at 1 GHz is 0.01 or less.

7. In the following general formulas (1) and (2), R １ represents an alkyl group, a phenyl group, an alkyl group having a substituent or a phenyl group having a substituent, R ２ represents an alkyl group having 1 to 5 carbon atoms, or a group in which a part of the alkyl group is substituted with a heteroatom. General formula (1): R １ nSi(OR ２ ) （４－ｎ） alkoxysilane having the structure of, and General formula (2): (R １ ３ Si) ２ The hollow silica particles according to claim 1, which have been surface-treated with at least one surface treatment agent selected from the group consisting of silazanes having the structure of NH.

8. An inorganic filler characterized by comprising the hollow silica particle material described in claim 1 and another inorganic particle material mixed in a ratio of 50% or more and 800% or less based on the mass of the hollow silica particle material.

9. A slurry characterized in that the hollow silica particles described in claim 1, or the inorganic filler described in claim 8, are dispersed in a dispersion medium in a mass ratio of 40% by mass or more and 700% by mass or less.

10. A resin composition characterized in that hollow silica particles according to claim 1, or an inorganic filler according to claim 8, are dispersed in a resin material in a mass ratio of 40% by mass or more and 500% by mass or less.

11. A method for producing a hollow silica particle material according to claim 1, comprising: a core material dispersion preparation step of preparing a core material dispersion in which a core material is dispersed in water; a core-shell composite formation step of mixing a hydrolyzable silane hydrolysate with the core material dispersion and stirring, and carrying out a polymerization reaction of the hydrolysate on the surface of the core material to obtain a core-shell composite; and a calcination step of calcining the core-shell composite to remove the core material.

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