JP7507675B2 - Manufacturing method of spherical silica powder - Google Patents

Description

The present invention relates to a method for producing spherical silica powder. More specifically, it relates to a method for crushing spherical silica particles produced by a wet method, and provides a method for crushing spherical silica particles that have aggregated after a firing process into primary particles, and an evaluation method for quantifying the degree of crushing.

Spherical silica is used as a filler in various resin compositions for electronic materials such as semiconductor encapsulants and liquid crystal sealants, and for film manufacturing.

In semiconductor encapsulation materials, the gap between the element and the substrate is narrowing with the rapid progress of devices becoming smaller, thinner, and more densely packed, and this requires higher thermal conductivity, lower thermal expansion, and better moldability, which requires a higher loading of the spherical silica. At the same time, there is also a demand for low viscosity in resin compositions filled with spherical silica, and there is an increasing demand for pre-surface-treated spherical silica that does not contain coarse particles and has excellent monodispersity.

Conventionally, methods for producing spherical silica particles with high monodispersity (uniform particle size) include wet methods such as the sol-gel method described below and a method for producing colloidal silica using alkali silicate as a starting material. Among the wet methods, the sol-gel method is extremely useful as a method for obtaining spherical silica particles with high purity as well as monodispersity. The method for producing spherical silica particles with high monodispersity using the sol-gel method is a method in which silicon alkoxide such as tetraethoxysilane, which is the raw material, is supplied to a reaction liquid containing a hydrolysis catalyst, water, and an organic solvent, and hydrolyzed and polycondensed. It is known that in this method, the particle size and particle size distribution can be highly controlled by controlling the reaction conditions during the reaction.

Patent Document 1 describes a method for producing highly monodisperse spherical silica particles, which controls particle size and particle size distribution by adjusting the reaction conditions in the sol-gel method, and further suppresses the generation of coarse particles such as adhered particles and agglomerates.

In the silica particle dispersion obtained by the sol-gel method, the silica particles are highly dispersed as primary particles, and substantially no agglomerates are observed. However, when extracting the silica as a dried powder, a process of solid-liquid separation of the silica from the dispersion, a drying process, or a process of firing as necessary is required, and after these processes, agglomerates of the silica particles tightly agglomerated together may be generated. Furthermore, once the silica particles have tightly agglomerated, it is difficult to break them down into primary particles, and as a result, there has been concern that the number of coarse particles will increase.

When coarse particles are present in silica, the resin composition containing this compound will have a lower fluidity as the resin will not flow smoothly when melted due to the presence of coarse particles. As a result, fish eyes and protrusions will occur during the production of molded products such as films. If a resin composition with low fluidity is used as a semiconductor encapsulant or liquid crystal sealant, the molten resin will have a pattern left after flowing, known as "flow marks," and it will not be able to penetrate narrow gaps sufficiently, making it easier for clogging to occur between wiring.

In order to solve the above problem, Patent Document 2 describes how adding a coagulant consisting of a specific compound to a spherical silica particle dispersion obtained by the sol-gel method makes it possible to produce loose aggregates in the post-processing step without producing strong agglomerates, and how these can be easily broken down into primary particles by the shear of a dispersing machine when dispersing in a resin.

In other words, according to this method, if the sol-gel method is carried out in a controlled manner so as to obtain excellent monodispersity of the spherical silica particles, the aggregates formed in the subsequent process can be broken down again into primary particles by a simple crushing process, so that the silica does not substantially contain coarse particles. In other words, it is possible to obtain silica in which coarse particles with a particle size exceeding 5 μm are not detected when measured by a general-purpose particle size distribution measurement method, specifically, the laser diffraction scattering method.

Following this silica manufacturing process that reduces the generation of coarse particles, a surface treatment agent such as a silane coupling agent is added to the silica to treat the particle surface, thereby improving dispersibility in resin, reducing the viscosity of the resin composition, increasing the strength of the resin composition, and imparting various other functions. In general, surface-treated silica is obtained by mixing silica and a surface treatment agent in a mixer with stirring blades, followed by heat treatment.

Patent Document 3 discloses a sol-gel silica powder that has an average particle size of 0.05 μm or more and 2.0 μm or less, a coefficient of variation indicating the spread of the particle size distribution of 40% or less, and when a 5% by mass amount of the powder is dispersed in water by ultrasonication under conditions of an output of 40 W and an irradiation time of 10 minutes, and the amount of the powder remaining on the sieve is 10 ppm or less when the powder is sieved by a wet sieve method using an electroformed sieve with 5 μm openings.

Patent Document 4 also discloses a surface-treated silica in which the surfaces of spherical silica particles are modified with a surface treatment agent, the average particle diameter measured by a laser diffraction scattering method is 0.05 μm or more and 2.0 μm or less, and in a dispersion liquid obtained by ultrasonically dispersing 5% by mass of the silica in ethanol under conditions of an output of 40 W and an irradiation time of 10 minutes, the content of particles having a particle diameter of 5 μm or more is 10 ppm or less on a number basis in the particle size distribution obtained by the Coulter counter method.

The above two patent documents disclose silica powder and surface-treated silica with very few agglomerated particles, but the verification method involves ultrasonically dispersing the silica powder in a solvent and measuring the amount of coarse particles using a specific particle size distribution measurement method. Therefore, it was not possible to determine the extent to which the particles had been crushed together at the powder stage. In particular, when surface-treating silica particles using a dry method, it is extremely important for uniform surface treatment that the particles in the powder before treatment are in a state in which they have been crushed down to primary particles, i.e., in a so-called monodispersed state.

JP 2013-193950 A JP 2012-6823 A WO2018/096876 WO2019/044929

However, silica produced by wet methods such as the sol-gel method often contains organic groups derived from the raw materials, or the solvent used during production remains in the particles. Furthermore, unlike dry method silica, which is produced at high temperatures, it often contains a high density of unreacted silanol groups or a large number of micropores. Therefore, due to these chemical and structural factors, it is usually highly hygroscopic.

Depending on the application of silica, the above characteristics may be welcomed, but when using it as a resin filler, such as a filler for semiconductor encapsulation, a dense material with low moisture absorption is desired.

For this reason, silica produced by the wet method is generally subjected to a firing process at temperatures of around 500°C to 1200°C. However, firing silica produced by the wet method at such high temperatures causes bonds between the particles, resulting in the formation of large amounts of agglomerates, which causes problems with poor dispersibility in resins, etc.

Conventionally, such aggregates have been subjected to various types of disintegration equipment such as jet mills and ball mills. However, even when disintegrated to a level where the presence of coarse particles cannot be detected by measurement using a particle size distribution measuring device, there is a problem in that the above-mentioned flow marks appear when this is used as a resin filler. This means that the conventional disintegration methods are insufficient for applications that have become increasingly demanding in recent years.

In addition, when preparing a resin composition for the above-mentioned applications, it is common to treat the silica surface with various surface treatment agents to modify the surface, but the contact surface of the aggregated particles that have not been separated even after being crushed by a crushing device is difficult to treat with a surface treatment agent. If such aggregated particles remain aggregated even after being kneaded into the resin, problems such as the above-mentioned flow marks will occur, and when they are separated due to high shear during kneading, the separated surface is an untreated surface and may not exhibit sufficient physical properties.

The present invention aims to provide a crushing method that provides a better crushed state for silica produced by a wet method and subjected to a calcination process.

The inventors have conducted extensive research to solve the above problems. As a result, they have discovered that, among the various crushers used to crush pyrolytic silica, by using a swirling jet mill under specific conditions, it is possible to obtain silica in an extremely good crushed state, i.e., highly monodispersed silica, and have completed the present invention.

That is, the present invention is a method for producing spherical silica powder, which includes the steps of forming spherical silica particles by a wet method, calcining the spherical silica particles, and then crushing the calcined product, and is characterized in that a swirling jet mill is used for the crushing, and the pressure difference between the pressure applied when feeding the calcined particles to the jet mill and the swirling pressure inside the jet mill is maintained at 0.2 MPa or less.

The spherical silica powder obtained by the manufacturing method of the present invention is composed of powdered spherical silica particles in which almost all of the particles have been crushed to primary particles. When such silica is dispersed (or kneaded) into a resin or the like, not only can the dispersion (kneading) time be shortened, but contamination during dispersion (kneading) can also be effectively prevented. In addition, when the silica particles are surface-treated, a uniform surface treatment is possible, resulting in surface-treated silica with extremely excellent functionality.

When the silica obtained by the manufacturing method of the present invention and the surface-treated silica obtained by subjecting said silica to surface treatment are blended to form a resin composition, the resulting resin composition has excellent fluidity when melted. This prevents the occurrence of fish eyes and protrusions in the production of molded products such as films. When used to fill resin compositions for electronic materials such as semiconductor encapsulants and liquid crystal sealants, the silica has excellent gap penetration properties and is also highly effective in preventing clogging between wiring that is also becoming narrower. As a result, the productivity and yield of the desired electronic material components are improved, making the product extremely useful.

FIG. 2 is an explanatory diagram of a grinding mechanism of a jet mill. FIG. 2 is an explanatory diagram of the reaction mechanism between silanol groups on the silica surface and HMDS.

1. Formation and Recovery of Silica by a Wet Process In the production method of the present invention, the silica to be calcined (hereinafter, referred to as "raw silica") is produced by a wet process. Here, the wet process refers to a production method in which a reaction for forming a three-dimensionally crosslinked silica skeleton is carried out in a solvent.

Known wet methods include the sol-gel method described below and a method for producing colloidal silica using alkali silicate as the starting material. Among the wet methods, spherical silica synthesized by the sol-gel method is highly pure and is therefore particularly useful for electronic material applications. Spherical silica by the sol-gel method is obtained by synthesizing spherical silica particles by hydrolyzing and polycondensing silicon alkoxide, the raw material, in a reaction medium, and then extracting and drying the resulting solids.

As a method for producing raw silica by the sol-gel method, a known method can be adopted without any particular limitation, and for example, it can be produced by the methods described in the above-mentioned Patent Documents 1 to 4, but briefly described as follows.
(1) A silica alkoxide (or its hydrolyzate) and aqueous ammonia are gradually added to a solvent such as alcohol to produce a silica dispersion in which silica having an average particle size of about 0.05 to 2 μm (measured by a laser diffraction scattering method) is dispersed (sol-gel process);
(2) Solid-liquid separation is performed using a filter or the like to obtain wet silica (solid-liquid separation step), and then
(3) Obtain a dry powder by heat drying, vacuum drying, etc. (drying step);
This is the procedure.

Usually, a coagulant is added prior to the solid-liquid separation to coagulate the silica and facilitate solid-liquid separation. In particular, the effect of the present invention is more easily obtained when a coagulant consisting of at least one compound selected from the group consisting of carbon dioxide, ammonium carbonate, ammonium hydrogen carbonate, and ammonium carbamate is used as the coagulant.

Furthermore, between the sol-gel process and the solid-liquid separation process (before the addition of a coagulant, if performed), the effects of the present invention can be more easily exhibited,
(1b) adding a surface treatment agent to the silica dispersion to treat the silica particle surfaces (silica dispersion surface treatment step);
(1c) A step of subjecting the silica dispersion to wet filtration using a filter medium (filtration step)
It is preferred that the compound contains

The surface treatment agent caps the silanol groups on the surface of the silica particles, preventing condensation of the silanol groups between adjacent particles during drying and the initial stage of firing (until the treatment agent is completely decomposed), thereby reducing the generation of aggregated particles, and thus further reducing the number of coarse particles in the silica powder obtained through the manufacturing process of the present invention. Examples of surface treatment agents that can be used include hexamethyldisilazane, hexamethyldisiloxane, trimethylchlorosilane, and trimethylalkoxysilane.

Wet filtration using a filter medium has the effect of removing coarse particles generated in the previous process. Therefore, it is preferable that the filter medium has a pore size of 5 μm or less. This filtration process is preferably performed after the silica dispersion surface treatment process, since even if coarse particles are generated in that process, the coarse particles can be removed. Naturally, in this filtration process, the target silica particles are contained on the side that has passed through the filter.

Filters can also be used in the solid-liquid separation process to obtain wet silica, but if the coagulant is added, the solids can be recovered without passing through even with a filter diameter of about 5 μm.

Drying can be done at room temperature to about 150°C.

2. Calcination of silica Calcination can be performed using a general-purpose electric furnace or the like. Calcination conditions are not particularly limited, but generally, calcination is performed in an air atmosphere at a temperature of 500°C or higher for 1 hour or more. The calcination temperature and calcination time may be adjusted appropriately depending on the purpose of use of the silica, but if the calcination temperature exceeds 1100°C, sintering (fusion) between silica particles becomes significant, and even if the present invention is applied, the number of coarse particles in the silica powder finally obtained is not sufficiently reduced (it is relatively reduced, but the effect of the invention is not lost). Therefore, it is desirable to set the upper limit temperature to 1100°C. In order to obtain dense silica particles while maintaining the sphericity of spherical silica, the range of 500 to 1100°C, preferably the range of 600 to 1050°C, and more preferably the range of 700 to 1000°C is preferable.

3. Crushing In the manufacturing method of the present invention, the silica obtained by calcination as described above is crushed by a swirling jet mill. The most important feature of the present invention is that the crushing is performed while maintaining the pressure difference between the pushing pressure when the calcined particles are supplied to the jet mill and the swirling pressure in the jet mill at 0.2 MPa or less. If the pressure difference is too large, the silica powder may not be crushed sufficiently. In such silica powder, each particle is not completely broken down, and if this is used as a resin filler, the viscosity increases due to the coarse particles and flow marks occur. Furthermore, even if the silica powder is surface-treated, the resulting silica has a relatively low coverage rate with the surface treatment agent, which is likely to result in insufficient physical properties in various application fields.

Of course, in order to feed raw powder into the jet mill, the pushing pressure (P1) must be equal to or greater than the rotation pressure (P2) (P1 ≥ P2).

Here, a swirling flow jet mill (also called an air flow mill) is a type of equipment that pulverizes objects into powder form. High-pressure air or steam is ejected from a nozzle in an ultra-high-speed jet that collides with particles, pulverizing them into fine particles of a few microns through the impact between the particles. With a swirling flow jet mill, silica particles are not crushed and broken, and energy is used efficiently to break down agglomerated particles.

A typical jet mill is configured with a casing that forms a grinding chamber with a horizontal disk-shaped internal space to form the jet mill body, grinding nozzles that spray multiple high-speed air streams around the circumference of the central part of the side of the casing that forms the grinding chamber, and a raw material supply nozzle that supplies the ground material, and the grinding material supplied from the raw material supply nozzle is entrained in the high-speed jet air stream sprayed from the grinding nozzle, thereby grinding it.

To explain more specifically according to the present invention, the grinding mechanism of a jet mill is generally configured as shown in FIG. 1. Here, 1 is a raw material supply nozzle, and the calcined silica 5, which is the material to be ground, is accompanied by a pushing gas 6 and supplied to the grinding zone 8. The pressure of the pushing gas corresponds to the pushing pressure in the present invention. Also, 2a, 2b, 2c, etc. are called grinding nozzles, and a swirling gas 7 is supplied to the nozzles. The pressure of the swirling gas corresponds to the swirling pressure in the present invention. In addition, there is a feeder (not shown) that supplies raw material powder in front of the raw material supply nozzle, and controls the supply speed of the raw material powder. The material to be ground 5 supplied to the grinding zone is crushed in the grinding zone 8 by being accompanied by the high-speed swirling gas, and is further classified in the classification zone 9, and only the material that has been broken down into primary particles is sequentially taken out of the system from the outlet 10 and collected by a cyclone or the like (not shown).

In the present invention, it is important to perform disintegration while maintaining the pressure difference between the indentation pressure and the swirl pressure at 0.2 MPa or less. In general, processing is performed by increasing the indentation pressure higher than the swirl pressure, but under such general conditions, the degree of monodispersity described below does not increase. Therefore, in the present invention, it is important to perform disintegration while maintaining the pressure difference between the indentation pressure and the swirl pressure at 0.2 MPa or less, preferably 0.15 MPa or less, and more preferably 0.1 MPa or less. In this way, by setting the pressure difference to a constant pressure or less and performing disintegration of silica particles, it is possible to obtain spherical silica with an extremely high degree of disintegration of the silica particles.

The swirl pressure for disintegration in a swirling jet mill can be appropriately selected and set from among general conditions depending on the size of the device, the average particle size of the silica, the processing amount, etc., but is generally 0.4 to 0.8 MPa. The pushing pressure can be determined according to the set swirl pressure.

Both the pushing pressure and the rotation pressure are equipped with a pressure control mechanism in commercially available devices, so they can be controlled according to the method of use of the device.

The exact reason why monodispersity is improved in the manufacturing method of the present invention is unclear, but it is speculated that this is because if the pushing pressure is too high, the residence time of the ground material in the grinding zone becomes shorter, and some of the coarsely ground material is not crushed and is discharged outside the system uncrushed. In other words, it is important to crush the material without disturbing the high-speed jet air stream in the grinding zone by minimizing the pressure difference between the pushing pressure and the swirl pressure.

In the manufacturing method of the present invention, commercially available devices can be used without restrictions as the above-mentioned swirling flow type jet mill. In particular, when considering that the produced silica will be used in applications requiring high purity, such as semiconductor applications, it is desirable that the material of the part of the jet mill that comes into contact with the silica, particularly the material of the area involved in the powder crushing, be made of ceramics. Examples include alumina, zirconia, silicon nitride, silicon carbide, etc. It is also desirable to use ceramic-coated or resin-coated piping, etc.

The fired product (silica) obtained by carrying out the firing may be slightly sintered by the firing, and this tendency is greater the higher the firing temperature. Therefore, in order to perform disintegration in a swirling flow jet mill more efficiently, it is preferable to carry out coarse grinding before the disintegration. If relatively large agglomerates are broken down by coarse grinding, energy is not consumed in disintegrating such large agglomerates in the swirling flow jet mill, and this energy is diverted to disintegrating into primary particles, so that the proportion of silica obtained after disintegration in the jet mill that is disintegrated into primary particles is even higher.

As equipment for the coarse grinding, a grinder, roll crusher, cutter mill, stamp mill, mortar, crusher, stone mill, etc. can be used, with a stone mill being particularly preferred.

4. Silica after crushing The silica powder produced as described above has its primary particles substantially retaining the shape formed during the wet silica particle formation such as the sol-gel process. Generally, silica particles obtained by the sol-gel method are independent spherical particles with a sphericity of 0.9 or more, mostly 0.95 or more. Therefore, in the present invention, the spherical silica particles constituting the silica powder can easily be obtained with a sphericity of 0.90 or more, particularly 0.95 or more.

The sphericity is the arithmetic mean value of the area and perimeter of each silica particle determined by observation under an electron microscope, and the sphericity of each particle calculated according to the formula below for 1,000 or more silica particles.

Sphericity = 4π × (area) / (perimeter) ²

The particle size of the silica particles constituting the silica powder produced in the present invention is not particularly limited as long as it is within a particle size range in which a swirling jet mill can be used, but in consideration of general applications, it is preferable that the average particle size (volume-based cumulative 50% diameter: D50) measured by laser diffraction scattering method is in the range of 0.05 to 2 μm, more preferably in the range of 0.1 to 1.5 μm. In particular, this range is suitable for filling resin compositions for electronic materials in light of the recent progress in miniaturization, thinning, and high-density mounting of semiconductor devices.

In the case of large spherical silica particles with an average particle size exceeding 2 μm, they tend to break down relatively easily into primary particles, and there is little benefit to applying the present invention.

The spherical silica powder produced by the present invention preferably has a coefficient of variation, which is an index showing the spread of the particle size distribution, of 40% or less, more preferably 30% or less, and particularly preferably 25% or less. If the coefficient of variation is larger than the above range, the particle size distribution becomes broad and the number of fine particles increases when compared with powders having the same average particle size. An increase in fine particles may lead to an increase in viscosity when filled into resins, etc. In general, the coefficient of variation of the particle size of spherical silica particles obtained by the sol-gel method is 10% or more. The coefficient of variation can be measured by a laser diffraction scattering method.

To obtain the above average particle size and coefficient of variation, it is sufficient to control the formation of silica particles in a wet process. Since sintering may occur during the firing process, the average particle size and coefficient of variation measured by the laser diffraction scattering method may (apparently) change significantly after only firing, but after crushing with a swirling jet mill, the particle size of the primary silica particles is reduced compared to before firing. Therefore, it is sufficient to anticipate the decrease in particle size due to firing and adjust the conditions so that the average particle size increases accordingly.

The spherical silica powder produced by the present invention has the characteristic that each primary particle is almost completely dissolved at the dry powder stage, and therefore has excellent dispersibility when dispersed in resins, solvents, etc. Furthermore, when surface treatment is performed on the spherical silica powder produced by the present invention, it is possible to perform a very uniform surface treatment over the entire surface of each particle, since each particle is almost completely dissolved at the dry powder stage.

The above state is extremely difficult to distinguish using particle size distribution measurements such as laser diffraction scattering, but it can be understood by determining what proportion of the measurable silanol groups can be converted to trimethylsilyl groups by hexamethyldisilazane.

Hexamethyldisilazane (hereinafter referred to as "HMDS") is highly reactive with silanol groups, and as shown in Figure 2, only one trimethylsilyl group is produced for each silanol group, which allows for more quantitative measurement of the amount reacted than trialkoxysilanes and the like. Furthermore, among compounds with such physical properties, if the physical size is small, i.e., the reaction space is too narrow to react with HMDS, there is almost no problem in assuming that other surface treatment agents cannot react with it either.

On the other hand, the amount of silanol groups on the silica surface can be measured by various methods, one of which is to measure the amount of water generated by heating using coulometric titration with the Karl Fischer method, and then calculate the amount of silanol groups from the amount of water. That is, as shown below, one water molecule is released from two silanol groups to generate a siloxane bond, so it can be seen that for every mole of water generated, two moles of silanol groups are condensed.

≡Si-OH + HO-Si≡ → ≡Si-O-Si≡ + _H2O

Because this is a condensation of silanol groups already present on the silica, the above reaction can also detect silanol groups that cannot be trimethylsilylated with HMDS due to spatial issues. It can be assumed that many of these spaces where HMDS cannot react exist at the bonds between primary particles.

Therefore, the ratio of silanol groups that can react with HMDS to the silanol groups calculated from the amount of water calculated by the Karl Fischer method can be used as an index showing the degree to which primary particles are separated/bonded to each other.

In the present invention, the above ratio is referred to as the "monodispersity" shown in the following formula (1).

Monodispersity=amount of trimethylsilyl groups bonded/amount of silanol groups (1)
(Note that in the above formula (1), the trimethylsilyl group binding amount is the amount (molar basis) of trimethylsilyl groups bound to spherical silica per unit mass after the spherical silica powder is treated with at least twice the saturation amount of HMDS, and the silanol group content is the amount (molar basis) of silanol groups per unit mass possessed by the spherical silica powder before the HMDS treatment.)

The "amount of trimethylsilyl groups bonded" in the above formula (1) refers to the amount of trimethylsilyl groups (molar basis) bonded per unit mass after the spherical silica powder is treated with at least twice the saturation amount of HMDS, and this amount corresponds to the amount of silanol groups that are actually capable of reacting with HMDS among the silanol groups present on the silica. The amount of trimethylsilyl groups can be calculated from the results of analyzing the carbon content of silica after HMDS treatment, as described in the Examples.

In the manufacturing method of the present invention, calcination is performed before crushing, so the carbon content before HMDS treatment is 0.002% by mass or less, and in most cases, as shown in the examples, 0.001% by mass or less (below the measurement limit of a typical device), which is small enough to be ignored when calculating the amount of trimethylsilyl bonds from the amount of carbon. However, in the case of silica in which carbon is present even before HMDS treatment, the amount of trimethylsilyl bonds can be calculated as necessary using the difference in the amount of carbon before and after treatment.

The saturated amount of HMDS here is the amount of HMDS theoretically required to trimethylsilylate all the silanol groups on the silica surface. As shown in Figure 2 above, one molecule of HMDS can trimethylsilylate two silanol groups, and the saturated amount can be easily calculated from this relationship. The silanol groups are measured and calculated using the Karl Fischer method described above, and details will be given later.

In the present invention, in order to ensure a reliable reaction, HMDS is used in an amount at least twice the saturation amount. From the viewpoint of reacting all of the reactive silanol groups, it is sufficient to use at least twice the amount, but considering that some HMDS will not participate in the reaction and will be wasted, and that it is necessary to remove unreacted parts and decomposition products after treatment, the amount used should be no more than five times the amount. In addition, the trimethylsilylation reaction with HMDS proceeds at room temperature, but the reaction is allowed to proceed completely by heating in an enclosed space at 150°C (±10°C), which is above the boiling point of HMDS, for at least one hour and no more than three hours.

Because an amount of HMDS that exceeds the saturation amount (theoretical amount that reacts with silica) is used here, if the excess (or decomposition products) remains on the silica, it will cause an overshoot in the carbon content analysis. Therefore, after HMDS treatment, the material is heated under vacuum at 150°C, which is above the boiling point of HMDS (at normal pressure), for at least one hour to volatilize and remove the above-mentioned components.

The "silanol group content" in the formula (1) refers to the amount of silanol groups (molar basis) per unit mass of the spherical silica powder before the HMDS treatment, and is calculated from the amount of water released by heating as described above. The amount of water can be measured using a commercially available Karl Fischer moisture meter as described in the Examples. In general, a commercially available Karl Fischer moisture meter shows the result as the amount of water (amount of _H2O ) based on the titration amount, so the water content (mass%) of the silica is calculated from the water content, and the silanol group content (mol/g) is calculated based on this water content using the following formula.

Silanol group content=(water content/100)/(18/2)
The denominator 18/2 in the above formula is based on the fact that a water molecule (molecular weight 18) is generated from two silanol groups.

Generally, physically adsorbed water is present on the silica surface, and since this does not introduce trimethylsilyl groups onto the silica surface even when it reacts with HMDS etc., it is removed in advance by drying at 120°C for 12 hours. The dried silica is then immediately heated and the amount of water generated in the range of 130°C to 1000°C is measured using the Karl Fischer method, from which the water content is calculated.

At around 200°C, water begins to be generated by condensation of the two silanol groups mentioned above, but the siloxane bonds generated by condensation near this temperature range are highly reversible and easily return to silanol groups in the presence of water in the environment. This means that, conversely, silanol groups that were not present when the silanol group content was measured using the above method may be generated during storage or various processes prior to surface treatment.

Therefore, when determining the silanol group content in the present invention, the silica is left in an atmosphere of 25°C and 80% relative humidity for 45 days, and all of the highly cleavable siloxane bonds are converted to silanol groups in advance. This operation also causes the adsorption of physically adsorbed water, so after this operation, the amount of silanol groups is measured after drying at 120°C as mentioned above.

The "monodispersity" calculated by the above procedure is often about 0.90 for calcined silica crushed by conventional methods, but if crushed under the above conditions, it can be made 0.95 or more, and even 0.98 or more. Furthermore, silica with such a high monodispersity can suppress the occurrence of flow marks when used as a filler for a resin composition.

Furthermore, the monodispersity shown by the above formula (1) can be used as a method for evaluating the state of disintegration during the process of producing silica powder, which includes a disintegration process.

Measuring this monodispersity makes it possible to evaluate the degree of disintegration of spherical silica particles, which allows precise estimation of particle disintegration conditions, etc., and plays an important role in selecting equipment and establishing manufacturing conditions.

In the manner described above, a powder consisting of spherical silica with a very high degree of crushing down to primary particles can be obtained, which can be used as is for a variety of known applications, but can also be further treated with a surface treatment agent or the like to modify the surface properties.

When the silica powder obtained by the manufacturing method of the present invention is surface-treated, not only is it possible to obtain silica with high monodispersity even after the surface treatment, but the reaction with the surface treatment agent proceeds without fail (there are few surfaces that are difficult to treat), so the resulting surface-treated silica has better storage stability than silica obtained by conventional crushing methods, and when used as an additive to resin, it has excellent dispersibility and compatibility with resin, which can improve the strength of molded products.

Specific embodiments include spherical silica particles whose surfaces are treated with at least one type of surface treatment agent, as well as resin-coated surface-treated spherical silica particles in which at least a portion of the surface of the spherical silica particles is coated with a coating resin, and may also take the form of resin-coated surface-treated spherical silica particles in which the particle surfaces are treated with a surface treatment agent and at least a portion of the particle surfaces are further coated with a coating resin.

Such treatment with a surface treatment agent or coating with a resin can be carried out by appropriately selecting a known method.

The surface treatment agent is not particularly limited as long as it is a known agent used to impart a specific function to the silica surface, but is preferably at least one surface treatment agent selected from silicone oil, silane coupling agents, siloxanes, and silazanes. In particular, it is preferably at least one surface treatment agent selected from the group consisting of silane coupling agents and silazanes. In addition, resins can also be used as a surface treatment agent to coat the silica surface.

It is desirable to select these surface treatment agents having functional groups according to the modification properties to be imparted to the resulting surface-treated silica. For electronic materials such as semiconductor encapsulants and liquid crystal sealants, and for filler applications such as film manufacturing, those having polymerizable groups such as epoxy groups or (meth)acrylic groups are preferred. That is, in these applications, since epoxy resins and (meth)acrylic resins are commonly used as resins to be mixed with surface-treated silica, if the surface-treated silica has a polymerizable group such as epoxy group or (meth)acrylic group corresponding to the polymerizable group of these resins, it can be strongly bonded to the resin when these mixed resins are cured, and can be made high-strength, which is preferable.

When polymerizable groups are introduced onto the silica surface by using such a surface treatment agent, the amount of the groups introduced is preferably 5 to 25 μmol/ ^m2 per specific surface area of the spherical silica particle surface.

Specific examples of the surface treatment agent used in this embodiment include the silicone oil, such as dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, alkyl-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, methacryl-modified silicone oil, polyether-modified silicone oil, and fluorine-modified silicone oil.

Examples of the silane coupling agent include methyltrimethoxysilane, methyltriethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-acryloyloxytrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N,N-dimethyl-3-aminopropyltrimethoxysilane, N,N-diethyl-3-aminopropyltrimethoxysilane, and 4-styryltrimethoxysilane.

Examples of the siloxanes include disiloxane, hexamethyldisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and polysiloxanes such as polydimethylsiloxane.

As the silazanes, any commonly used known compound having a Si-N (silicon-nitrogen) bond can be used without any particular limitation, and may be appropriately selected and used depending on the required performance of the surface-treated silica. Specific examples of the silazane include hexamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, octamethyltrisilazane, hexa(t-butyl)disilazane, hexabutyldisilazane, hexaoctyldisilazane, 1,3-diethyltetramethyldisilazane, 1,3-di-n-octyltetramethyldisilazane, 1,3-diphenyltetramethyldisilazane, 1,3-dimethyltetraphenyldisilazane, 1,3-diethyltetramethyldisilazane, 1,1,3,3-tetraphenyl-1,3-dimethyldisilazane, 1,3-dipropyltetramethyldisilazane, hexamethylcyclotrisilazane, hexaphenyldisilazane, dimethylaminotrimethylsilazane, trisilazane, cyclotrisilazane, and 1,1,3,3,5,5-hexamethylcyclotrisilazane.
Among these, alkyldisilazanes are preferred because of their high reactivity with the silica surface.

(wherein R1 to R3 are each a hydrogen atom, an alkyl group having 10 or less carbon atoms (preferably 1 to 3 carbon atoms) which may have a halogen atom, or an aryl group, at least one of R1 to R3 is an alkyl group having 10 or less carbon atoms which may have a halogen atom, R6 is a hydrogen atom or a methyl group, and R7 to R9 are the same as R1 to R3.) Particularly preferred are tetramethyldisilazane, hexamethyldisilazane, and heptamethyldisilazane.

In addition, in the case where the surface treatment is an embodiment in which the silica surface is coated with a coating resin, the resin for coating (hereinafter also referred to as coating resin) is not particularly limited, and the resin may be directly used to coat the surface of the spherical silica particles. A preferred embodiment is one in which the surface of the spherical silica particles is coated with a polymerizable composition containing a polymerizable monomer, and this is polymerized on the surface of the spherical silica particles. In order to achieve high strength, the resin is preferably a crosslinked polymer. From the viewpoint of stability, the crosslinking of the crosslinked polymer is preferably a covalent bond.

It is desirable to select these coating resins that have functional groups according to the modification properties to be imparted to the resulting surface-treated silica. For the reasons mentioned above, in electronic materials such as semiconductor encapsulants and liquid crystal sealants, and filler applications such as film manufacturing, it is preferable to use resins that have polymerizable groups such as epoxy groups or (meth)acrylic groups.

When a polymer having an epoxy group is used as the coating resin, a polymerizable composition containing a radically polymerizable monomer having an epoxy group (hereinafter also referred to as an "epoxy group-containing radically polymerizable monomer") is polymerized. By using such a monomer, the polymer itself has an epoxy group. As the radically polymerizable group, a (meth)acrylic group, a vinyl group, etc. are preferred.

Because the surface-treated silica can be easily manufactured, it is preferable to use a (meth)acrylic radical polymerizable monomer. Specific examples include glycidyl (meth)acrylate and (meth)acrylic glycidyl ether. These epoxy group-containing radical polymerizable monomers may be used alone or in combination of two or more types depending on the desired coating resin.

The polymerizable composition containing an epoxy group-containing radically polymerizable monomer preferably contains a crosslinking agent to crosslink the polymer. As the crosslinking agent, any compound having two or more radically polymerizable groups in one molecule can be used without any particular limitation. For example, aromatic vinyl monomers such as polyfunctional aromatic vinyl compounds such as divinylbenzene, divinylbiphenyl, trivinylbenzene, and divinylnaphthalene, polyfunctional (meth)acrylic monomers such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, methylene bis(meth)acrylamide, and hexamethylene di(meth)acrylamide, (meth)allyl (meth)acrylate, etc. can be mentioned.

When a polymer having a (meth)acrylic group is used as the coating resin, a polymerizable composition containing a non-radical polymerizable monomer having a (meth)acrylic group is usually polymerized. As such a non-radical polymerizable monomer having a (meth)acrylic group, a polymerizable monomer having a (meth)acrylic group and an epoxy group as a non-radical polymerizable group (hereinafter also referred to as a "(meth)acrylic group- and epoxy group-containing monomer") is preferably used. By using such a monomer, the polymer itself has a (meth)acrylic group. The epoxy group may be polymerized by ring-opening cationic polymerization, or may be polymerized by polyaddition reaction in the presence of an epoxy curing agent.

Specific examples of (meth)acrylic group- and epoxy group-containing monomers include glycidyl acrylate, glycidyl methacrylate, β-methyl glycidyl acrylate, β-methyl glycidyl methacrylate, bisphenol A monoglycidyl ether methacrylate, 4-glycidyloxybutyl methacrylate, 3-(glycidyl-2-oxyethoxy)-2-hydroxypropyl methacrylate, 3-(glycidyloxy-1-isopropyloxy)-2-hydroxypropyl acrylate, and 3-(glycidyloxy-2-hydroxypropyloxy)-2-hydroxypropyl acrylate. Of these, glycidyl (meth)acrylate is preferably used. These (meth)acrylic group- and epoxy group-containing polymerizable monomers may be used alone or in combination of two or more depending on the intended coating resin.

A polymerizable composition containing a non-radically polymerizable monomer having a (meth)acrylic group may contain a crosslinking agent to crosslink the polymer. A compound having two or more epoxy groups in one molecule can be used as the crosslinking agent.

In addition, for the purpose of removing coarse particles generated in the surface treatment process, the calcined silica particles that have been surface-treated after crushing may be dispersed in a solvent to form a dispersion, and the dispersion may be wet-filtered using a filter medium with a pore size of 5 μm or less, after which the calcined silica particles with the surface treatment may be recovered from the filtrate by solid-liquid separation, and then a drying process may be carried out. In addition, when the surface treatment is carried out wet, the dispersion that has been subjected to the surface treatment may be directly filtered.

When the silica or surface-treated silica obtained by the manufacturing method of the present invention described above is used as a filler for electronic materials such as semiconductor encapsulants and liquid crystal sealants, and for various resin compositions for film manufacturing, etc., it can be finely dispersed in the resin without reducing the productivity or yield of the target product.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

1. Measurement and Evaluation Methods of Physical Properties The methods for evaluating the various physical properties used in the examples and comparative examples are as follows.

1-1. Silica properties

(1) Measurement of average particle size, coefficient of variation, and amount of coarse particles of 5 μm or more by laser diffraction scattering method Approximately 0.1 g of silica powder or surface-treated silica powder was weighed out on an electronic balance into a 50 mL glass bottle, and approximately 40 ml of distilled water or ethanol was added. The mixture was dispersed using an ultrasonic homogenizer (Sonifier 250, manufactured by BRANSON) under conditions of 40 W for 10 minutes, and then the volume-based cumulative 50% diameter (D50) and coefficient of variation of the silica powder or surface-treated silica powder were measured using a laser diffraction scattering particle size distribution analyzer (LS-230, manufactured by Beckman Coulter, Inc.).

The measurement also checked for the presence or absence of signals of 5 μm or greater.

(2) Measurement of the amount of coarse particles of 5 μm and 3 μm or more by the Coulter counter method Five 50 mL glass bottles were prepared, and 1 g of silica powder or surface-treated silica powder was weighed out in each bottle using an electronic balance, and 19 g of ethanol was added to each bottle. The bottles were dispersed at 40 W for 10 minutes using an ultrasonic homogenizer (Sonifier 250, manufactured by BRANSON) to obtain measurement samples. The particle size of each of the silica powder or surface-treated silica powder was measured using a Coulter counter (Multisizer 3, manufactured by Beckman Coulter, Inc.) with an aperture diameter of 30 μm. At this time, the number of particles measured per sample was about 50,000, and about 250,000 particles were measured in total for the five samples. Among them, the number of particles with a particle size of 5 μm or more and the number of particles with a particle size of 3 μm or more were calculated, and the amount of coarse particles (ppm) relative to the total number of particles measured was calculated.

(3) Measurement of Sphericity The particle shape of the silica powder was observed with a SEM (JSM-6060, manufactured by JEOL Datum Co., Ltd.) to determine the sphericity. Specifically, 1000 or more silica particles were observed, and the sphericity of each particle was measured using an image processing program (AnalySIS, manufactured by SoftImaging System GmbH), and the average was calculated. The sphericity was calculated according to the following formula.

Sphericity = 4π × (area) / (perimeter) ²

(4) Measurement of α-ray dosage The α-ray dosage (c/( ^cm2 ·h)) of the surface-treated silica powder was measured using a low-level α-ray measuring device (manufactured by Sumika Chemical Analysis Center, LACS-4000M). The measurement was carried out on a sample area of ¹⁰⁰⁰ cm2.

(5) Measurement of the amount of impurities The amount of impurities in the surface-treated silica powder was measured as follows.

U and Th: Surface-treated silica powder was dissolved by heating in hydrofluoric acid/nitric acid (a 5:1 mixture of hydrofluoric acid and nitric acid), and measured by ICP mass spectrometry (Agilent Technologies, Agilent 4500).

Fe, Al, Na, K, Ca, Cr, Ni, Ti: Surface-treated silica powder was heated and dissolved in hydrofluoric and nitric acid, and measured using ICP emission spectrometry (Thermo Scientific, iCAP6500DUO).

Cl ⁻ : The surface-treated silica powder was mixed with ultrapure water and heat-treated at 100° C. under pressure, and the Cl ⁻ concentration (ppm) in the solution after the treatment was measured by ion chromatography (ICS-2100, manufactured by Nippon Dionex).

(6) Measurement of Specific Surface Area The specific surface area (m ² /g) of the calcined spherical silica powder before surface treatment was measured by the BET single point method based on the amount of nitrogen adsorption using a specific surface area measuring device SA-1000 manufactured by Shibata Scientific Instruments Co., Ltd.

(7) Measurement of silanol group content After leaving the silica powder in an atmosphere of 25°C and 80% relative humidity for 45 days, the sample was dried at 120°C for 12 hours (this is referred to as "dried silica powder"). The dried silica powder was heated to 1000°C in a heating furnace, and the amount of moisture generated at 130°C to 1000°C was measured using a Karl Fischer moisture meter MKS-210 manufactured by Kyoto Electronics Manufacturing Co., Ltd. The moisture content was calculated from the amount of dried silica powder used and the obtained moisture amount, assuming that the dried silica powder is 100% by mass. The titration reagent used was "HYDRANAL COMPOSITE 5K" (manufactured by Riedel-de Haen).

From the water content measured by the above method and the specific surface area, the silanol group content per unit mass (mol/g) was calculated according to the following formula.
Silanol group content=(water content/100)/(18/2)
The denominator 18/2 is based on the fact that a water molecule (molecular weight 18) is generated from two silanol groups.

(8) Measurement of Carbon Content The carbon content (mass%) of the silica powder was measured by a combustion oxidation method (EMIA-511, manufactured by Horiba, Ltd.) The sample was dried at 120° C. for 1 hour.

(9) Trimethylsilyl Group Bonding Amount Using the above carbon content, the trimethylsilyl group bonding amount per unit mass (mol/g) was calculated from the following formula.
Amount of trimethylsilyl group bonded=(carbon content/100)/(12×3)
The 12×3 in the denominator is based on having three carbon atoms (atomic weight 12) per trimethylsilyl group.

(10) Monodispersity Degree The monodispersity degree was calculated from the above-mentioned silanol group content and the amount of trimethylsilyl groups bonded according to the following formula.
Monodispersity = trimethylsilyl group binding amount / silanol group content

1-2. Resin composition properties (11) Viscosity and time-dependent change rate measurement 10 g of the surface-treated silica powder was added to 40 g of bisphenol A+F type epoxy resin (ZX-1059, manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.) and mixed by hand. The mixed resin composition was pre-mixed with a planetary centrifugal mixer (THINKY, Awatori Rentaro AR-500) (mixing: 1000 rpm, 8 minutes, degassing: 2000 rpm, 2 minutes). The pre-mixed resin composition was mixed with a three-roll mixer (IMEX, BR-150HCV, roll diameter φ63.5). The mixing conditions were room temperature, 20 μm between the rolls, and 5 times of mixing to obtain a resin composition for viscosity measurement.

The resin composition for viscosity measurement obtained by the above method was measured for initial viscosity (η1) and viscosity after one week (η2) at a measurement temperature of 25° C. and a rotation speed of 2 s ^-1 using a rheometer (ReoStress, manufactured by HAAKE Corporation). The initial viscosity refers to a value measured after storing in a thermostatic water bath at 25° C. for 30 minutes or more after the completion of the fifth kneading. The storage for one week before measurement was performed by placing the resin composition for viscosity measurement in an airtight container and storing it in a thermostatic water bath at 25° C.

Furthermore, the obtained (η1) and (η2) were used to calculate the rate of change in viscosity over time according to the following formula.
Viscosity change rate over time [%] = ((η2/η1) - 1) x 100

(12) Flow Mark Test 25 g of the surface-treated silica powder was added to 25 g of bisphenol A+F type mixed epoxy resin (ZX-1059, manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.) and mixed by hand. The mixed resin composition was pre-mixed with a planetary centrifugal mixer (Thinky, Awatori Rentaro AR-500) (mixing: 1000 rpm, 8 minutes, degassing: 2000 rpm, 2 minutes). The pre-mixed resin composition was mixed with a three-roll mixer (IMEX, BR-150HCV, roll diameter φ63.5). The mixing conditions were room temperature, 20 μm between the rolls, and 5 times of mixing to obtain a resin composition for measuring flow marks.

Two pieces of glass were stacked to leave a gap of 30 μm and heated to 100°C, and a high-temperature penetration test was conducted on the resin composition for measuring flow marks. The resin composition was observed until it penetrated 20 mm or stopped penetrating, and the presence or absence of flow marks was evaluated by visual inspection of the appearance.

2. Method for Producing Raw Silica by Wet Method The calcined silica used for crushing in each of the Examples and Comparative Examples was produced by the following procedure.

2-1. Raw material silica A
(1) Silica dispersion production process A jacketed glass-lined reactor (inner diameter 1200 mm) having an internal volume of 1000 L and equipped with a Max Blend blade (blade diameter 345 mm) was used, and 75 kg of methanol, 30 kg of isopropanol, and 25 kg of aqueous ammonia (25% by mass) were charged as a reaction medium (amount of reaction medium: 150 L). The reaction temperature was set to 40° C., and the mixture was stirred at 52 rpm.

Then, a mixture of 3.0 kg of tetraethoxysilane, 7.0 kg of methanol, and 2.0 kg of isopropanol was added to the reaction medium as raw materials to produce silica seed particles.

Next, 350 kg of tetramethoxysilane and 100 kg of methanol were fed into the reaction medium at a linear discharge velocity of 51 mm/s as the dropping raw materials, and at the same time, 150 kg of ammonia water (25 mass%) was fed at a rate of 0.8 kg/min to grow and synthesize silica particles. The dimensionless mixing time nθm at this time was 78.

(2) Dispersion Silica Particle Surface Treatment Step After the completion of the supply, stirring was continued for 1 hour, and then 4,450 g (200 μmol/g based on the theoretically synthesized silica amount) of HMDS (SZ-31, manufactured by Shin-Etsu Silicone) was added as a surface treatment agent to the silica particle dispersion, and after the completion of the addition, stirring was continued for 2 hours to perform surface treatment.

(3) Surface-treated silica dispersion wet filtration step After 2 hours, the dispersion was passed through a polypropylene filter having an opening of 3 μm to obtain a dispersion from which coarse particles had been removed.

(4) Coagulation step 3 kg of dry ice was added to the dispersion and then left for 20 hours. After 20 hours, the particles had settled, and after solid-liquid separation using quantitative filter paper (retention particle size 5 μm), 190 kg of concentrate (silica concentration 74 mass%) was obtained. The filtrate was transparent, and no leakage of the filtrate was confirmed.

(5) Solid-liquid separation and drying step The obtained silica concentrate was dried under reduced pressure at 100° C. for 15 hours to obtain 132 kg of powder.

(6) Calcination step: The powder obtained in the drying step was calcined in an air atmosphere in a calcination furnace at 800° C. for 10 hours to obtain a calcined silica powder. The silica particles after calcination did not appear to be sintered, and 124 kg of calcined silica powder was obtained.

(7) Coarse grinding process The calcined silica powder obtained through the calcination process was coarsely ground using a mill (Masuko Sangyo Co., Ltd., Serendipiter, MKCA6-3), which is a millstone type grinding machine. The coarse grinding conditions were a grindstone diameter of 120 mm, a grindstone gap of 3 mm, and a grindstone rotation speed of 3000 rpm. A SiC grindstone was used as the grindstone. The powder after coarse grinding was in the form of a powder of about 1 mm.

The silica powder obtained through the above process is called raw silica A.

2-2. Raw material silica B
In the (1) silica dispersion liquid production step in the production of silica A, the amounts of the raw materials added were changed to 90 kg of tetramethoxysilane, 25 kg of methanol, and 40 kg of aqueous ammonia (25% by mass), and the same operation was repeated three times to combine the amounts of the three batches. Thereafter, the same operation was carried out up to the coarse pulverization to obtain a powder of about 1 mm.

The silica powder obtained through the above process is called raw silica B.

2-3. Raw material silica C
In the (1) silica dispersion liquid production step for producing silica A, the reactor was changed to 10,000 L, and the amounts of the raw materials added were changed to 4,200 kg of tetramethoxysilane, 1,200 kg of methanol, and 1,800 kg of aqueous ammonia (25% by mass). The same operations were then carried out up to the coarse pulverization to obtain a powder of about 1 mm.

The silica powder obtained through the above process is called raw silica C.

After completing the silica dispersion manufacturing process, the particle size (D50) of these raw silica particles was 0.77 μm for raw silica A, 0.42 μm for raw silica B, and 1.67 μm for raw silica C.

3. Method for Surface Treatment of Silica Obtained by Crushing The crushed silica obtained in each of the Examples and Comparative Examples was surface-treated in the following manner to obtain surface-treated silica.

As the surface treatment mixer, a rotating shaft was installed on each inner wall surface of the end, and a stainless steel disintegrating blade (200 mm x 20 mm x 2 mm) was attached 2 cm from the wall surface of the shaft, with the shaft passing through the center of gravity of the blade. Into a double-cone type device (Tokuju Manufacturing Co., Ltd., W-150) with an internal volume of 340 L, 80 kg of disintegrated silica powder was charged and the atmosphere was replaced with nitrogen. Next, a specified amount of hexamethyldisilazane (HMDS) was dripped as a surface treatment agent using a peristaltic pump. After dripping the entire amount of surface treatment agent, the rotation speed of the stainless steel disintegrating blade (mass 63 g) was set to 157 rad/s (1500 rpm) (disintegrating energy = 2.6 J), and the mixer was operated at a rotation speed of 0.3 rps, and mixing was performed at room temperature for 3 hours.

The silica powder was then removed from the apparatus, spread on a thin stainless steel tray, and set in the heating apparatus. The temperature inside the system was raised from room temperature to 150°C over one hour under normal pressure and sealed conditions, and then held at 150°C for two hours. The system was then evacuated to a vacuum for one hour while maintaining the internal temperature of the heating apparatus at 150°C, removing any unreacted HMDS or decomposition products. A portion of the sample after vacuum heating was completed (hereinafter referred to as trimethylsilylated silica) was used to measure the carbon content.

Next, a SUS container with a capacity of 40 liters connected to a flow-type ultrasonic dispersion device was prepared, and 15 kg of methanol was added. While stirring with a propeller stirrer at a stirring speed of 100 rpm, 5 kg of the surface-treated silica powder dried by the above method was added, and stirring was continued for 60 minutes to prepare a dispersion with a slurry concentration of 25 mass%. Next, the dispersion was pumped at a speed of 1 L/min with a diaphragm pump, and passed through a polypropylene filter with a mesh size of 3 μm to remove coarse particles. The dispersion after filtration was pressure-filtered with a filter cloth with an air permeability of 0.6 cm ³ /(cm ² ·s), and 6 kg of surface-treated silica was collected as a wet cake.

The recovered cake was then dried under reduced pressure at 120°C for 24 hours to obtain 4.8 kg of dry surface-treated silica powder.

Example 1
The powder of raw material silica A was subjected to a crushing treatment using a swirling jet mill (STJ-200, manufactured by Seishin Enterprise Co., Ltd.). The crushing conditions were a swirling pressure of 0.5 MPa, a swirling air amount of 2.4 ^m3 /min, a pushing pressure of 0.6 MPa, and a supply rate of 10 kg/h. The above crushing process was carried out in a state where the pressure difference between the pushing pressure and the swirling pressure was maintained at 0.1 MPa.

The physical properties of the obtained crushed silica powder were D50 of 0.72 μm, coefficient of variation of 24%, and sphericity of 0.96. No coarse particles of 5 μm or more were detected by the laser diffraction scattering method. The amounts of coarse particles of 5 μm and 3 μm or more by the Coulter Counter method were 5 ppm and 8 ppm. The specific surface area was 3.7 m ² /g, and the silanol group content was 18.1 μmol/g. The carbon content was less than 0.001 wt%. The silanol group density was calculated to be about 3/nm ² from the specific surface area and silanol group content.

The resulting crushed silica powder was surface-treated using the method described above to obtain a dry surface-treated silica powder. The amount of HMDS used in the surface treatment was 258 g. Note that the saturated amount of HMDS calculated from the silanol group content was 117 g, so the amount of HMDS used was approximately 2.2 times the saturated amount.

The physical properties of the trimethylsilylated silica (surface-treated silica) powder obtained in this surface treatment process were measured. As a result, the carbon content was 0.064% by weight. The amount of trimethylsilyl groups bonded calculated from this value was 17.8 μmol/g, and the monodispersity of the crushed silica before surface treatment was calculated to be 0.98.

The D50 and coefficient of variation of the surface-treated silica powder were 0.72 μm and 23%, respectively. No coarse particles of 5 μm or more were detected by the laser diffraction scattering method. The amount of coarse particles of 5 μm and 3 μm or more by the Coulter counter method was less than 4 ppm and 8 ppm, respectively.

A resin composition was made using this surface-treated silica, and various viscosity and flow mark tests were performed. (η1) was 3.2 Pa·s, (η2) was 3.3 Pa·s, and the change in viscosity over time was 3%. No flow marks were observed.

The alpha dose of the surface-treated silica powder was 0.002 c/( ^cm2 ·h), and the amounts of impurities were as follows: U: 0.02 ppb, Th: 0.02 ppb, Fe: 1.5 ppm, Al: 3.0 ppm, Na: 0.2 ppm, K: 0.1 ppm, Ca: 0.1 ppm, Cr: 0.2 ppm, Ni: 0.2 ppm, Ti: 0.0 ppm, and ^Cl- : 0.1 ppm.

Examples 2 and 3 and Comparative Examples 1 and 2
The conditions for disintegration using a jet mill were changed as shown in Table 1 to carry out the disintegration treatment of raw material silica A. The results of evaluation of various physical properties of the obtained disintegrated silica powder are shown in Table 2, and the results of evaluation of various physical properties of the surface-treated silica powder are shown in Table 3.

Example 4
The same procedures as in Example 1 were carried out up to the stage of disintegration, except that raw silica B was used as the silica powder instead of raw silica A, to obtain a disintegrated silica powder. In addition, surface treatment was carried out in the same manner as in Example 1, except that the amount of HMDS used was 450 g. The results of evaluation of the physical properties of the obtained disintegrated silica powder are shown in Table 2, and the results of evaluation of the physical properties of the surface-treated silica powder are shown in Table 3.

The alpha dose of the surface-treated silica powder obtained in Example 4 was 0.002 c/( ^cm2 ·h), and the amounts of impurities were as follows: U: 0.01 ppb, Th: 0.02 ppb, Fe: 0.8 ppm, Al: 2.2 ppm, Na: 0.2 ppm, K: 0.1 ppm, Ca: 0.1 ppm, Cr: 0.2 ppm, Ni: 0.1 ppm, Ti: 0.0 ppm, and ^Cl- : 0.1 ppm.

Example 5
The crushing and surface treatment were carried out under the same conditions as in Example 1, except that raw silica C was used as the silica powder instead of raw silica A (the amount of HMDS used was the same on a mass basis). The results of evaluating the physical properties of the obtained crushed silica powder are shown in Table 2, and the results of evaluating the physical properties of the surface-treated silica powder are shown in Table 3.

The alpha dose of the surface-treated silica powder obtained in Example 5 was 0.002 c/( ^cm2 ·h), and the amounts of impurities were as follows: U: 0.02 ppb, Th: 0.02 ppb, Fe: 1.7 ppm, Al: 6.4 ppm, Na: 0.2 ppm, K: 0.1 ppm, Ca: 0.1 ppm, Cr: 0.4 ppm, Ni: 0.3 ppm, Ti: 0.1 ppm, and ^Cl- : 0.1 ppm.

As can be seen from the above results, crushed spherical silica particles with a monodispersity of 0.95 or more can be obtained by crushing while maintaining the pressure difference between the thrust pressure and the rotational pressure of the jet mill at 0.2 MPa or less. In addition, as shown in the comparative example, it was revealed that when the pressure difference exceeds 0.2 MPa, the monodispersity decreases, and problems such as changes in resin viscosity and the occurrence of flow marks occur due to insufficient crushing of silica.

1 Raw material supply nozzle 2a, 2b, 2c... Crushing nozzle 3 Circumferential wall 4 Concentric vortex flow 5 Crushed material 6 Forced gas (pressure)
7 Swirling gas (pressure)
8 Crushing zone 9 Classification zone 10 Outlet

Claims (6)

A method for producing a spherical silica powder, comprising the steps of forming spherical silica particles by a wet method, calcining the spherical silica particles, and then crushing the calcined product,
A method for producing spherical silica powder, characterized in that a swirling flow type jet mill is used for the crushing, and the crushing is performed while maintaining the pressure difference between the pushing pressure when supplying the fired particles to the swirling flow type jet mill and the swirling pressure inside the jet mill at 0.2 MPa or less. 2. The method for producing spherical silica powder according to claim 1, wherein the spherical silica powder produced has a monodispersity of 0.95 or more, as represented by the following formula (1):
Monodispersity=amount of trimethylsilyl groups bonded/amount of silanol groups (1)
(In the above formula (1),
The amount of trimethylsilyl groups bonded to the spherical silica is the amount of trimethylsilyl groups (molar basis) bonded to the spherical silica per unit mass after the spherical silica powder is treated with hexamethyldisilazane in an amount at least twice the saturation amount.
The silanol group content is the amount of silanol groups (molar basis) per unit mass that the spherical silica powder has before the hexamethyldisilazane treatment. A method for evaluating the state of disintegration in a process for producing silica powder, the process including a disintegration process, the method comprising measuring the degree of monodispersity shown by formula (1) for the silica powder after disintegration. Spherical silica characterized in that the carbon content is 0.002 mass% or less, the sphericity is 0.90 or more, and the monodispersity defined by the formula (1) is 0.95 or more. The spherical silica according to claim 4, wherein the coefficient of variation of the particle size is 40% or less. A method for producing surface-treated spherical silica, comprising surface-treating the spherical silica according to claim 4 or 5.

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