Fumed silica powder with reduced silanol group density

Abstract

Fumed silica powder with reduced silanol group density Silanol density d SiOH is at least 1.2SiOH / nm 2 and the particle size d 90 A process of subjecting surface-untreated fumed silica powder having a particle size of 10 μm or less to a heat treatment at 350° C. to 1,250° C. for 5 minutes to 5 hours. A method for producing a fumed silica powder having a reduced silanol group density, comprising: The temperature and duration of the heat treatment are SiOH However, the d of the untreated silica used SiOH are selected to reduce by 10% to 70%. The heat treatment is carried out while the fumed silica powder is in motion; The method wherein said heat treatment is followed by a surface treatment if necessary. Surface unmodified and modified fumed silica powders obtainable by this method, as well as uses thereof.

Description

[Technical Field]

[0001] This invention relates to fumed silica powder with relatively small particle size and reduced silanol group density, a method for producing the same, and its use. [Background technology]

[0002] Silica powder, particularly fumed silica powder, is a highly useful additive for a wide range of applications. To name just a few, silica can be used as a rheological modifier or anti-settling agent in paints, coatings, silicones, and other liquid systems. Silica powder can also improve powder flowability, optimize the mechanical or optical properties of silicone compositions, and be used as a filler in pharmaceuticals or cosmetics, adhesives or sealants, toners, and other compositions.

[0003] One of the key properties of silica materials that determines their suitability for a particular application is the silanol group density, i.e., the number of free silanol groups (SiOH) relative to the surface area of ​​the silica. ) This is related to the amount of [unspecified element]. Untreated silica is hydrophilic because polar silanol groups are present on its surface. The silanol groups on the silica surface can form hydrogen bonds with each other or with binders containing hydroxyl groups, such as terminal dihydroxypolydimethylsiloxane. As a result of these interactions between fillers and polymers, the viscosity of silica-containing formulations can become unnecessarily high, and the glass transition temperature and crystallization behavior can change.

[0004] On the other hand, fumed silica with a high silanol group density tends to absorb a considerable amount of water, and such silica has an increased water content. However, in some applications, such as additives for lithium-ion battery components (e.g., separators, electrodes, electrolytes), the presence of water is undesirable. For this reason, Korean Patent Application Publication No. 20150099648 discloses a separator film coated with vinyl-modified silica particles that can be used in lithium-ion batteries equipped with gel polymer electrolytes. The water contained in such silica additives will react with some water-sensitive components of lithium-ion batteries, such as LiPF6. LiPF6 is often present in the electrolyte and can cause electrolyte decomposition, releasing reactive substances such as HF, thus contributing to battery deactivation. Therefore, silica with reduced silanol density is necessary or may be useful in applications involving water-sensitive components.

[0005] Explanation of conventional technology Depending on the properties of hydrophilic silica, the density is approximately 2 to 15 SiOH / nm per surface area. 2 The density of silanol groups is observed.

[0006] One typical attempt to reduce the silanol group density of silica is to at least partially cover the free silanol groups with organosilane groups. Thus, European Patent Application Publication No. 1433749 specifies the particle surface nm 2 The preparation of partially hydrophobic silica having a silanol group density of 0.9 to 1.7 SiOH per unit area is described. The preparation of such partially hydrophobic particles is performed with a BET surface area of ​​100 m². 2 This is done by reducing the amount of silica silane by 0.015 to 0.15 millimoles per gram.

[0007] German Patent No. 2123233 specifies the particle surface nm 2 1.18 SiOH / nm 2 This document describes a method for preparing finely powdered silicon dioxide having a silanol group density exceeding [a certain value].

[0008] German Patent No. 1767226 discloses a method for producing pulverized silica by heating pyrolysis silica in a fluidized bed.

[0009] Intentionally reducing the silanol group density of hydrophilic silica is not very common.

[0010] One common method is described in U.S. Patent No. 4,664,679, which discloses the surface treatment of anhydrous silicic acid by reacting silanol groups with various coupling agents.

[0011] U.S. Patent Application Publication No. 2016 / 0355685 describes a method of hydrolyzing tetramethoxysilane, then drying and calcining the resulting product in an electric furnace at 1,050°C for 1 hour, and then producing 2-35 m 2 This paper describes a method for preparing silica by the sol-gel method, which involves preparing silica with a relatively low BET surface area (BET) per g, grinding the resulting coarse particles, and hydrophobizing them with silane.

[0012] U.S. Patent No. 2,866,716 discloses a method for modifying the surface of a colloidal silica substrate having free silanol groups, the method comprising heating the silica substrate at a temperature of 300 to 700°C until the specific surface area is reduced to less than 85% of its initial value, provided that the silanol group density of the heat-treated silica is approximately 2OH / nm 2 That's all.

[0013] European Patent Application Publication No. 1860066 describes a preparation of precipitated silica prepared by spray-drying, then heating in a fluidized bed reactor at 450°C and grinding, with a typical residual moisture content of 3.5% by weight and a silanol group density of approximately 2.7 OH / nm. 2 This document describes the preparation of precipitated silica.

[0014] Since both precipitated silica and colloidal silica are usually prepared in an aqueous medium, they have a relatively high water content and often a high silanol group density. Such types of silica are not as suitable as fumed silica for preparing silica with a low silica group density. Due to the preparation process at high temperature, the silanol group density of fumed silica is usually 2.2 - 3.0 SiOH / nm 2 and is relatively low. Fumed silica is a better precursor for silica with a reduced silanol group density.

[0015] The silanol group density of fumed silica can be reliably measured by methods such as the reaction of silica with lithium aluminum hydride, as described in Journal of Colloid and Interface Science, Volume 125, Issue 1 (1988), pages 61 - 68. Typical hydrophilic silica (Aerosil® OX 50, BET = 50 m 2 / g, Aerosil® 130, BET = 129 m 2 / g, Aerosil® 150, BET = 155 m 2 / g, Aerosil® 200, BET = 196 m 2 / g, Aerosil® 300, BET = 303 m 2 / g, Aerosil® 380, BET = 372 m 2 / g) and surface-treated (hydrophobic) silica (Aerosil® R972, BET = 102 m 2 / g, Aerosil® R812, BET = 245 m 2 / g) were both analyzed using this method, and typical silanol group densities of about 2.0 - 2.5 OH / nm 2 were shown for typical hydrophilic silica and 0.53 - 0.54 OH / nm 2 for hydrophobic silica.

[0016] According to U.S. Patent No. 3,873,337, before hydrophobization with dimethyldichlorosilane, fumed silica is treated in a fluidized bed at 700-1,000°C for 1-60 seconds using a dry inert gas flow to remove physically bound water. Because the drying time is very short, this process can only remove weakly bound water, and the silanol groups of silica are unaffected. In fact, in this method, to achieve large-scale hydrophobization with dimethyldichlorosilane, it is desirable that the silanol group density of the hydrophilic precursor be at its maximum possible value. Therefore, U.S. Patent No. 3,873,337 does not disclose the preparation of hydrophilic silica powder with reduced silanol group density.

[0017] Japanese Patent Publication No. 2014-055072 describes a gas phase method, for example, a pyrolysis method, for 50 to 400 m 2 BET surface area per g and approximately 2.5 OH / nm 2 The preparation of amorphous silica having a silanol group density is described. By mixing such silica powder with a binder and a solvent and heating in an oxygen-containing gas atmosphere at 100-500°C, molded bodies such as granules are formed. The molded bodies thus obtained are calcined at 600-1,200°C for 30 minutes to 24 hours to obtain a silica content of 0.55-2.09 g / cm³. 3 A mechanically stable sintered body in the mm size range having a density in the range is obtained. Japanese Patent Publication No. 2014-055072 does not disclose any preparation of silica powder.

[0018] It is well known from the prior art that sintered molded bodies are obtained by heat-treating compacted silica granules or fragments. Accordingly, International Publication No. 2009 / 007180 discloses a method for preparing silica glass granules, in which fumed silica powder is compressed into small lumps (slag), and then pulverized into fragments with a particle size of 100-800 μm and a tamping density of 300-600 g / L. The latter is heated at 600-1,100°C in an atmosphere suitable for the removal of hydroxyl groups, and then sintered at 1,200-1,400°C. This patent application does not disclose powders with small particle sizes. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] Korean Patent Application Publication No. 20150099648 Specification [Patent Document 2] European Patent Application Publication No. 1433749 [Patent Document 3] German Patent No. 2123233 [Patent Document 4] German Patent No. 1767226 [Patent Document 5] U.S. Patent No. 4,664,679 [Patent Document 6] U.S. Patent Application Publication No. 2016 / 0355685 [Patent Document 7] U.S. Patent No. 2,866,716 [Patent Document 8] European Patent Application Publication No. 1860066 [Patent Document 9] U.S. Patent No. 3,873,337 [Patent Document 10] Japanese Patent Publication No. 2014-055072 Specification [Patent Document 11] International Publication No. 2009 / 007180 Brochure [Non-patent literature]

[0020] [Non-Patent Document 1] Journal of Colloid and Interface Science, Vol. 125, No. 1 (1988), pp. 61-68 [Overview of the project] [Problems that the invention aims to solve]

[0021] Challenges and Solutions The good dispersibility and thixotropic properties of fumed silica fillers in various compositions, such as silicones or deficient compositions, are crucial for many applications. Dispersibility is primarily related to the size of the silica particles and their strong and weak aggregation in the composition. The thixotropic properties of silica depend on the strong and weak aggregation of silica, as well as the density of silanol groups. As is known from prior art, the reduction in silanol group content due to heat treatment is often closely related to a significant decrease in BET surface area and weak aggregation of particles. Therefore, it is difficult to significantly reduce the silanol group density of hydrophilic silica while maintaining a small silica particle size and narrow particle size distribution without changing the BET surface area. Thus, achieving good dispersibility of fumed silica fillers and minimal viscosity increase (thickening effect) in compositions filled with such silica simultaneously is extremely challenging.

[0022] On the other hand, the water content of both hydrophilic silica and surface-treated silica, especially hydrophobic fumed silica, needs to be reduced for applications where water is sensitive, such as lithium-ion batteries.

[0023] Therefore, the technical problem that the present invention aims to solve is to provide a fumed silica powder that has high dispersibility, low viscosity increase in the composition, and low water content, and a method suitable for efficiently producing such silica powder. [Means for solving the problem]

[0024] The present invention BET surface area d measured by reaction with lithium aluminum hydride SiOH The number of silanol groups relative to is at least 1.2SiOH / nm 2 The particle size d was measured by static light scattering (SLS) in a 5 wt% aqueous dispersion of silica after sonication at 25°C for 120 seconds. 95(A) A step in which surface-untreated fumed silica powder, having a particle size of 10 μm or less, is subjected to heat treatment at 350°C to 1,250°C for 5 minutes to 5 hours. A method for producing fumed silica powder containing the following: The temperature and duration of the heat treatment are determined by the silica's d SiOH However, the heat-untreated silica used SiOH In contrast, it is selected to be reduced by 15% to 70%, The heat treatment is performed while the fumed silica powder is moving. This provides...

[0025] Remarkably, the present invention has been found to enable the preparation of fumed silica powder with particularly low water content while maintaining a very small aggregate particle size, that is, while keeping the heat-treated silica particles sufficiently dispersed in various compositions. Furthermore, this method yields heat-treated fumed silica particles with a relatively narrow particle size distribution. The resulting material, like its starting material, is characterized by a low tamping density. This fact makes it possible to use such heat-treated material in any application field where low-tamping-density fumed silica is particularly required, for example, as a filler or flow improver.

[0026] Method for producing silica powder Untreated silica used in step (A) of the method In the context of this specification, the term "powder" means fine particles, i.e., typically with an average particle size of d 50 This includes particles smaller than 50 μm, preferably smaller than 10 μm. In the context of this specification, the term "untreated surface" refers to hydrophilic silica that has not been surface-modified by any surface treatment agent. Such untreated silica typically has a low carbon content of less than 1% by weight, more preferably less than 0.5% by weight, as measured by elemental analysis in accordance with EN ISO 3262-20:2000 (Chapter 8). The sample to be analyzed is weighed into a ceramic crucible, a combustion additive is added, and it is heated in an induction furnace under an oxygen flow. The present carbon is oxidized to CO2. The amount of CO2 gas is quantified by an infrared detector. The stated carbon content refers to all carbon-containing components of silica, excluding non-combustible compounds (e.g., silicon carbide) under the test conditions. The methanol wettability of such untreated fumed silica is typically less than 20% by volume of methanol in a methanol / water mixture, preferably less than 10% by volume, more preferably less than 5% by volume, and more preferably about 0% by volume. The degree of hydrophilicity of silica powder can be measured by its methanol wetting ability, as described in detail, for example, on pages 5-6 of International Publication No. 2011 / 076518. In pure methanol, hydrophilic silica powder completely separates from the methanol without wetting with the solvent. In contrast, in pure water, hydrophilic silica disperses throughout the solvent (complete wetting occurs). During the measurement of the methanol wetting ability of hydrophilic silica powder, the tested silica sample is mixed with various methanol / water mixtures, and the maximum methanol content is measured when the silica is not separated, i.e., when 100% of the silica used remains well dispersed in the test mixture. This methanol content (volume %) in the methanol / water mixture is called methanol wetting ability. The lower the methanol wetting ability, the higher the hydrophilicity of the silica powder being tested.

[0027] The fumed surface untreated silica used in step (A) of the method of the present invention is preferably measured by the reaction with lithium aluminum hydride, and has a BET surface area d SiOH The number of silanol groups relative to is at least 1.3SiOH / nm 2 , more preferably at least 1.4SiOH / nm 2 , more preferably at least 1.5SiOH / nm 2More preferably 1.5 to 3.0 SiOH / nm 2 That is the case.

[0028] Number of silanol groups d relative to the BET surface area SiOH (Also known as silanol group density, nm) 2 The number of OSiOH groups per cubic meter (expressed as the number of OSiOH groups per cubic meter) can be measured by the reaction of silica powder with lithium aluminum hydride, as detailed on page 8, line 17 to page 9, line 12 of European Patent Application Publication No. 0725037. This method is also described in the Journal of Colloid and Interface Science, Vol. 2, No. 1 (1988), pp. 61-68.

[0029] The silanol (SiOH) groups of silica react with lithium aluminum hydride (LiAlH4), and the amount of gaseous hydrogen produced during this reaction, i.e., the amount of silanol groups in the sample, n SiOH The BET surface area (m²) of the tested material is measured (in millimoles of SiOH / g). 2 Using (in units of / g), the silanol group content in millimoles of SiOH / g is expressed as the number of silanol groups relative to the BET surface area d SiOH It can be easily converted to: d SiOH [SiOH / nm2]=(n SiOH [millimoles SiOH / g] × N A ) / (BET[m 2 / g] × 10 21 ) In the formula, N A Avogadro's number (~6.022 * 10) 23 )

[0030] The fumed surface untreated silica used in step (A) of the method of the present invention is 20m 2 More than / g, preferably 20m 2 / g~600m 2 / g, comfortably 30m 2 / g~500m 2 / g, more preferably 40m 2 / g~400m 2It can have a BET surface area of ​​1 / g. Specific surface area, also simply called BET surface area, can be measured by nitrogen adsorption using the Brunauer-Emmett-Teller method in accordance with DIN9277:2014.

[0031] In the context of this specification, the term “silica” refers to individual compounds (silicon dioxide, SiO2), silica-based mixed oxides, silica-based doped oxides, or mixtures thereof. “Silica-based” means that the corresponding silica material contains at least 70% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, more preferably at least 95% by weight, and most preferably at least 98% by weight of silicon dioxide.

[0032] "Fumed" silica, also known as "thermal decomposition" or "thermal decomposition-produced" silica, is prepared by thermal decomposition methods such as flame hydrolysis or flame oxidation. This generally involves the oxidation or hydrolysis of hydrolyzable or oxidizing starting materials in a hydrogen / oxygen flame. Starting materials used in thermal decomposition include organic and inorganic substances. Silicon tetrachloride is particularly suitable. The hydrophilic silica thus obtained is amorphous. Fumed silica is usually in an aggregated form. "Aggregation" means that the so-called primary particles initially formed during production bond tightly to each other in subsequent reactions to form a three-dimensional network. The primary particles are substantially poreless and have free hydroxyl groups on their surface. Such hydrophilic silica can be hydrophobized as needed, for example, by treatment with a reactive silane.

[0033] It is known that pyrolysis mixed oxides can be produced by simultaneously reacting at least two different metal sources, such as volatile metal compounds or chlorides, in an H2 / O2 flame. The components of the mixed oxide thus prepared are generally uniformly distributed throughout the mixed oxide material, in contrast to other types of materials such as mechanical mixtures of several metal oxides or doped metal oxides. In the latter case, for example, a mixture of several metal oxides, there may be separation regions of the corresponding pure oxides, which determine the properties of such a mixture.

[0034] The surface-untreated fumed silica powder used in the method of the present invention has an average primary particle size of 5 nm to 50 nm, preferably 5 nm to 40 nm. 50 It can have the average size d of the primary particles. 50 This can be measured by transmission electron microscopy (TEM) analysis. 50 To calculate a representative average value, it is necessary to analyze at least 100 particles.

[0035] The surface-untreated fumed silica powder used in the method of the present invention is obtained by sonicating a 5% by weight aqueous dispersion of silica at 25°C for 120 seconds, and then measuring the particle size d by static light scattering (SLS) to be 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, more preferably 2 μm or less, and preferably 1 μm or less. 90 It has the following characteristics. The resulting measured particle size distribution is a value that reflects the particle size of 90% of all particles that does not exceed this value. 90 Used to define the above particle size d 90 This refers to the particle size of strongly aggregated and weakly aggregated fumed silica particles.

[0036] The surface-untreated fumed silica powder used in the method of the present invention preferably has a relatively narrow particle size distribution, which is a particle size distribution span (d) of 3.5 or less, preferably 0.7 to 3.5, more preferably 0.8 to 3.5, more preferably 1.0 to 3.2, more preferably 1.1 to 3.1, and more preferably 1.2 to 3.0. 90 ~d 10 ) / d50 It can be characterized by the value of .

[0037] The surface-untreated fumed silica powder used in the method of the present invention preferably has a tamping density of 300 g / L or less, more preferably 250 g / L or less, more preferably 20 g / L to 250 g / L, more preferably 20 g / L to 200 g / L, more preferably 25 g / L to 180 g / L, and more preferably 30 g / L to 150 g / L. The tamping density (also called "tap density") of various powders or coarse-grained granular materials can be measured in accordance with DIN ISO 787-11:1995 "General test methods for pigments and extenders - Part 11: Measurement of tamping volume and apparent density after tamping". This includes measuring the apparent density of the bed after stirring and tamping.

[0038] The untreated fumed silica powder used in the method of the present invention preferably has a water content of 3% by weight or less, more preferably 2% by weight or less, more preferably 1.5% by weight or less, and more preferably 1.2% by weight or less, as measured by Karl Fischer titration. This Karl Fischer titration can be carried out using any suitable Karl Fischer titrator, for example, a Karl Fischer titrator conforming to STN ISO 760.

[0039] heat treatment The heat treatment of the surface-untreated fumed silica powder in the method of the present invention is carried out at a temperature of 350°C to 1,250°C, preferably 400°C to 1,250°C, more preferably 400°C to 1,200°C, more preferably 500°C to 1,200°C, more preferably 700°C to 1,200°C, and more preferably 1,000°C to 1,200°C. The duration of this heat treatment depends on the temperature applied and is generally 5 minutes to 5 hours, preferably 10 minutes to 4 hours, more preferably 20 minutes to 3 hours, and even more preferably 30 minutes to 2 hours.

[0040] It has been observed that the duration of the heat treatment process can significantly affect the properties of the resulting fumed silica powder. Therefore, when the heat treatment process, performed at 350-1250°C, lasts less than 5 minutes, especially when the starting material for the heat treatment is pre-dried before the treatment and is not wet itself (for example, when the water content is 3% by weight or less as measured by Karl Fischer titration), a significant decrease in the water content of the silica is usually not observed. Conversely, when the heat treatment process lasts longer than 5 hours, while the water content of the resulting silica usually does not change significantly further, the particle size of the resulting particles may increase.

[0041] The heat treatment in the method of the present invention clearly reduces the number of free silanol groups by condensation of free silanol groups and formation of O-Si-O bridges.

[0042] The temperature and duration of the heat treatment process are determined by the silica's d SiOH However, the heat-untreated and surface-untreated fumed silica powder used is d SiOH The amount is selected to be reduced by 10% to 70%. Therefore, the fumed silica powder prepared by the method of the present invention is measured by reaction with lithium aluminum hydride to determine the BET surface area d SiOH In contrast, 1.55SiOH / nm 2 Preferably, 0.6SiOH / nm 2 ~1.55SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.5SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.4SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.3SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.2SiOH / nm 2 , more preferably 0.7SiOH / nm 2 ~1.2SiOH / nm 2 , more preferably 0.8SiOH / nm 2 ~1.2SiOH / nm2 More preferably 0.9SiOH / nm 2 ~1.2SiOH / nm 2 It has the number of silanol groups.

[0043] The silica used in step (A) of the method of the present invention SIOH A decrease in silanol density of less than 10% from the original value was found not to be associated with a substantial decrease in silica water content or other beneficial effects. On the other hand, a decrease of more than 70% in silanol group density can only occur if it simultaneously forms larger sintered aggregates, which cannot be easily broken down, for example, by sonication.

[0044] Importantly, in contrast to silanol density, the BET surface area of ​​heat-treated silica typically changes only to a relatively small extent while carrying out step (A) of the method of the present invention. Therefore, during heat treatment, it is preferable that the BET surface area of ​​the fumed silica powder decreases by up to 50%, more preferably up to 45%, more preferably up to 40%, and more preferably up to 35% compared to the BET surface area of ​​the untreated and unsurface-treated silica used in step (A) of the method of the present invention.

[0045] The heat treatment in the method of the present invention may be carried out discontinuously (in batches), semi-continuously, or preferably continuously.

[0046] For discontinuous processes, the "duration of heat treatment" is defined as the total time the untreated fumed silica is heated at the specified temperature. For semi-continuous or continuous processes, the "duration of heat treatment" corresponds to the average residence time of the untreated fumed silica powder at the specified heat treatment temperature.

[0047] The method of the present invention is preferably carried out continuously such that the average residence time of the surface-untreated fumed silica powder in the heat treatment step (A) is 10 minutes to 3 hours.

[0048] In the method of the present invention, the heat treatment is preferably carried out while the fumed silica powder is moving, preferably while it is moving constantly in the method, that is, while the silica is moving during the heat treatment. Such a “dynamic” process is the opposite of a “static” heat treatment process in which the silica particles do not move, for example, the silica particles are present in a layer, for example, in a muffle furnace, during the heat treatment.

[0049] Surprisingly, it was found that by combining such dynamic heat treatment processes with appropriate temperatures and treatment durations, it is possible to produce small particles with a narrow particle size distribution that exhibit particularly good dispersibility in a variety of compositions. In contrast, "static" heat treatment, in which the silica does not move at all, was found to yield sintered aggregates with much larger particle sizes and much worse dispersibility in compositions.

[0050] The method of the present invention can be carried out in any suitable apparatus capable of maintaining the silica powder at the specified temperature for a specified time while moving the silica. Suitable apparatuses include fluidized bed reactors and rotary kilns. A rotary kiln, particularly one with a diameter of 1 cm to 2 m, preferably 5 cm to 1 m, and more preferably 10 cm to 50 cm, is preferred for use in the method of the present invention.

[0051] The silica powder is preferably moved at least temporarily during the heat treatment step (A) at a speed of at least 1 cm / min, more preferably at least 10 cm / min, more preferably at least 25 cm / min, and more preferably at least 50 cm / min. Preferably, the silica is moved continuously at this speed for the entire duration of the heat treatment step. The speed in the rotary kiln corresponds to the peripheral speed of this type of reactor. The speed in the fluidized bed reactor corresponds to the flow rate (fluidity) of the carrier gas.

[0052] Before, during, or after carrying out step (A) of the method of the present invention, it is more preferable not to substantially add water. More preferably, no water is added before, during, or after carrying out step (A) of the method of the present invention. In this way, further evaporation of the absorbed water is avoided, and a heat-treated silica powder with a lower water content can be obtained.

[0053] The heat treatment step (A) can be carried out, for example, under a gas flow such as air or nitrogen, and the gas is preferably essentially free of water or pre-dried.

[0054] "Essentially free of water" means, with respect to the gas, that the humidity of the gas does not exceed the humidity under the use conditions such as temperature and pressure, that is, no vapor or water vapor is added to the gas before use. The water content of the gas used in step (A) of the method of the present invention is preferably less than 5% by volume, more preferably less than 3% by volume, more preferably less than 1% by volume, and more preferably less than 0.5% by volume.

[0055] Surface treatment The method for producing the fumed silica powder of the present invention further comprises Step (B): a step of surface-treating the fumed silica powder obtained in step (A) with a surface treatment agent selected from the group consisting of organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof may be included. Preferred organosilanes are, for example, general formulas (Ia) and (Ib): R’ x (RO) y Si(C n H 2n+1 ) (Ia) R’ x (RO) y Si(C n H 2n-1 ) (Ib) (wherein, R = alkyl, such as methyl-, ethyl-, n-propyl-, i-propyl-, butyl-, etc., R’ = alkyl or cycloalkyl, such as methyl, ethyl, n-propyl, i-propyl, butyl, cyclohexyl, octyl, hexadecyl, etc., n = 1 to 20 x + y = 3 x = 0 to 2, and y = 1 to 3.) It is an alkyl organosilane.

[0056] Among the alkyl organosilanes of formula (Ia) and (Ib), octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, and hexadecyltriethoxysilane are particularly preferred. The organosilane used for surface treatment may contain halogen such as Cl or Br. The following types of halogenated organosilanes are particularly preferred: - General formulas (IIa) and (IIb): X3Si(C n H 2n+1 ) (IIa) X3Si(C n H 2n-1 ) (IIb) (where X = Cl, Br, n = 1 to 20.) of organosilane; - General formulas (IIIa) and (IIIb): X2(R’)Si(C n H 2n+1 ) (IIIa) X2(R’)Si(C n H 2n-1 ) (IIIb) (where X = Cl, Br, R’ = alkyl, such as cycloalkyl like methyl, ethyl, n-propyl, i-propyl, butyl, cyclohexyl, etc., n = 1 to 20.) of organosilane; - General formulas (IVa) and (IVb): X(R’)2Si(C n H 2n+1 ) (IVa) X(R')2Si(C n H 2n-1 ) (IVb) (In the formula, X=Cl, Br, R' = alkyl, for example, methyl, ethyl, n-propyl, i-propyl, butyl, cyclohexyl, and other cycloalkyl groups. n = 1 to 20. Organo Bletilla.

[0057] Among the halogenated organosilanes of formulas (II) to (IV), dimethyldichlorosilane and chlorotrimethylsilane are particularly preferred. The organosilane used may also contain substituents other than alkyl or halogen substituents, such as fluorine substituents or several functional groups. Preferably, the general formula (V): (R' ') x (RO) y Si(CH2) m R' (V) (In the formula, R' ' = alkyl such as methyl, ethyl, or propyl, or halogen such as Cl or Br, R = alkyl such as methyl, ethyl, and propyl. x+y=3, x = 0 to 2, y=1~3, m=1~20, R' = methyl, aryl (e.g., phenyl or substituted phenyl residue), heteroaryl -C4F9, OCF2-CHF-CF3, -C6F 13 , -O-CF2-CHF2, -NH2, -N3, -SCN, -CH=CH2, -NH-CH2-CH2-NH2, -N-(CH2-CH2-NH2)2, -OOC(CH3)C=CH2 , -OCH2-CH(O)CH2, -NH-CO-N-CO-(CH2)5, -NH-COO-CH3, -NH-COO-CH2-CH3, -NH-(CH2)3Si(OR)3, -S x -(CH2)3Si(OR)3, -SH, -NR 1 R 2 R 3 (In the formula, R 1 =alkyl, aryl; R 2=H, alkyl, aryl;R 3 =H, alkyl, aryl, benzyl, C2H4NR 4 R 5 (In the formula, R 4 =H, alkyl and R 5 =H, alkyl. Functionalized organosilanes are used.

[0058] Among the functionalized organosilanes of formula (V), 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, and aminopropyltriethoxysilane are particularly preferred.

[0059] General formula R'R2Si-NH-SiR2R'(VI) (In the formula, R = alkyl such as methyl, ethyl, or propyl; R' = alkyl or vinyl.) Silazanes of formula (VI) are also suitable as surface treatment agents. The most preferred silazane of formula (VI) is hexamethyldisilazane (HMDS).

[0060] Cyclic polysiloxanes such as octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and hexamethylcyclotrisiloxane (D6) are also suitable as surface treatment agents. Among the cyclic polysiloxanes, D4 is the most preferred.

[0061] Another useful type of surface treatment agent is general formula (VII):

[0062] [ka]

[0063] (In the formula, Y=H, CH3, C n H 2n+1 (In the formula, n = 1 to 20.) Si(CH3) a X b(In the equation, a = 2 to 3, b = 0 or 1, and a + b = 3.) X = H, OH, OCH3, C m H 2m+1 (In the formula, m = 1 to 20.) R, R' = C o H 2o+1 (In the formula, o = 1 to 20.) Aryl, heteroaryl, (CH2) residues such as alkyl, phenyl, and substituted phenyl residues. k -NH2 (where k = 1 to 10), H, u = 2 to 1,000, preferably u = 3 to 100. It is a polysiloxane or silicone oil.

[0064] Among the polysiloxanes and silicone oils of formula (VII), polydimethylsiloxane is most preferably used as a surface treatment agent. Such polydimethylsiloxanes typically have a molar mass of 162 g / mol to 7,500 g / mol, a density of 0.76 g / mL to 1.07 g / mL, and a viscosity of 0.6 mPa·s to 1,000,000 mPa·s.

[0065] In step (B) of the method of the present invention, water can be used in addition to the surface treatment agent. The molar ratio of water to the surface treatment agent in step (B) of the method of the present invention is preferably 0.1 to 100, more preferably 0.5 to 50, more preferably 1.0 to 10, more preferably 1.2 to 9, more preferably 1.5 to 8, and more preferably 2 to 7.

[0066] However, when it is necessary to obtain surface-treated silica powder with a low water content, the amount of water used in the process must be minimized, and ideally, no water should be added at all during the process. Therefore, it is preferable that substantially no water is added before, during, or after step (B). In the context of this specification, the term "essentially water-free" refers to an amount of water added to the fumed silica powder used in step (B) that is less than 1%, preferably less than 0.5%, more preferably less than 0.1%, more preferably less than 0.01%, and most preferably no water is added at all.

[0067] The surface treatment agent and, optionally, water, can be used in both vapor and liquid form in the method of the present invention.

[0068] Step (B) of the method of the present invention can be carried out at a temperature of 10°C to 250°C for 1 minute to 24 hours. The time and duration of step (B) can be selected according to specific requirements relating to the process and / or target silica properties. Therefore, the lower the processing temperature, the longer the hydrophobization time is usually required. In one preferred embodiment of the present invention, the hydrophobization of fumed silica powder is carried out at 10°C to 80°C for 3 hours to 24 hours, preferably 5 hours to 24 hours. In another preferred embodiment of the present invention, step (B) of the method is carried out at 90°C to 200°C, preferably 100°C to 180°C, most preferably 120°C to 160°C for 0.5 hours to 10 hours, preferably 1 hour to 8 hours. Step (B) of the method according to the present invention can be carried out under a pressure of 0.1 bar to 10 bar, preferably 0.5 bar to 8 bar, more preferably 1 bar to 7 bar, most preferably 1.1 bar to 5 bar. Most preferably, step (B) is carried out in a closed system under the natural vapor pressure of the surface treatment agent used at the reaction temperature.

[0069] In step B) of the method of the present invention, the fumed silica powder that has been heat-treated in step (A) is preferably sprayed with a liquid surface treatment agent at ambient temperature (about 25°C), and then the mixture is heat-treated at a temperature of 50°C to 400°C for 1 to 6 hours.

[0070] Another method of surface treatment in process (B) is to treat the fumed silica powder, which has been heat-treated in process (A), with a surface treatment agent, which is in vapor form. The mixture is then heat-treated at a temperature of 50°C to 800°C for 0.5 to 6 hours.

[0071] The heat treatment after surface treatment in process (B) can be carried out under a protective gas, such as nitrogen. Surface treatment can be carried out continuously or in batches using a heated mixer and dryer equipped with a spray device. Suitable equipment may be, for example, a plow shear mixer or a plate, cyclone, or fluidized bed dryer.

[0072] The amount of surface treatment agent used varies depending on the type of particles and the type of surface treatment agent applied. However, typically, 1% to 25% by weight, preferably 2% to 20% by weight, and more preferably 5% to 18% by weight of the surface treatment agent is used relative to the amount of fumed silica powder that has been heat-treated in step (A).

[0073] The required amount of surface treatment agent may depend on the BET surface area of ​​the fumed silica powder used. Therefore, the BET specific surface area of ​​the fumed silica powder heat-treated in step (A) is 1 m². 2 It is preferable to use 0.1 μmol to 100 μmol, more preferably 1 μmol to 50 μmol, and more preferably 3.0 μmol to 20 μmol of surface treatment agent per unit.

[0074] In any step C) of the method of the present invention, the fumed silica powder that has been heat-treated in step (A) and / or the fumed silica powder obtained in step (B) of the method is crushed or pulverized to reduce the average particle size of the resulting silica particles.

[0075] The grinding in any step (C) of the method of the present invention can be carried out by any machine suitable for this purpose, such as a suitable mill.

[0076] However, in most cases, any step C) of the method of the present invention is unnecessary and even undesirable. When coarse silica particles are crushed or pulverized, silica particles with a smaller average particle size are usually obtained, but such particles exhibit a relatively wide particle size distribution. Such particles usually contain a relatively large proportion of fine particles, making the handling of these crushed / pulverized particles complicated. Therefore, it is preferable that the method of the present invention does not include any crushing and / or grinding steps.

[0077] Surface-unmodified fumed silica powder The present invention further provides surface-unmodified silica powder obtained by the method of the present invention. The present invention further provides a surface-unmodified silica powder having the following, which can preferably be prepared according to the method of the present invention. (a) Measured by reaction with lithium aluminum hydride, yielding 1.17SiOH / nm 2 Preferably, 0.6SiOH / nm 2 ~1.15SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.14SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.1SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.05SiOH / nm 2 , more preferably 0.6SiOH / nm 2 ~1.05SiOH / nm 2 , more preferably 0.7SiOH / nm 2 ~1.05SiOH / nm 2 , more preferably 0.8SiOH / nm 2 ~1.05SiOH / nm 2 More preferably 0.9SiOH / nm 2 ~1.05SiOH / nm 2 The BET surface area d is SiOH The number of silanol groups relative to the number of groups; (b) Particle size d of a 5 wt% aqueous silica dispersion after sonication at 25°C for 120 seconds, preferably 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, more preferably 2 μm or less, preferably 1 μm or less, measured by static light scattering (SLS). 90 The resulting measured particle size distribution reflects particle sizes that do not exceed 90% of all particles. 90 Used to define values.

[0078] The surface-unmodified silica powder of the present invention, characterized by requirement (a) and requirement (b), can be obtained by the method of the present invention described above. The aforementioned surface-unmodified fumed silica powder is inherently hydrophilic because it is not surface-treated, i.e., not modified by any surface treatment agent. The surface-unmodified fumed silica powder according to the present invention preferably has a carbon content of less than 1.0% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, more preferably less than 0.2% by weight, even more preferably less than 0.1% by weight, and even more preferably less than 0.05% by weight. The carbon content can be measured by elemental analysis in accordance with EN ISO 3262-20:2000 (Chapter 8).

[0079] The surface-unmodified fumed silica powder according to the present invention preferably has a water content of less than 1.0% by weight, more preferably less than 0.7% by weight, more preferably less than 0.5% by weight, more preferably less than 0.4% by weight, more preferably less than 0.3% by weight, and more preferably less than 0.2% by weight. The water content can be measured by Karl Fischer titration.

[0080] The surface-unmodified fumed silica powder of the present invention preferably has a methanol wetting capacity of 15% by volume or less, more preferably 10% by volume or less, more preferably 5% by volume or less, and particularly preferably about 0% by volume of methanol in a methanol / water mixture. The methanol wetting capacity of the surface-unmodified fumed silica powder can be measured, for example, as described in detail on pages 5-6 of International Publication No. 2011 / 076518.

[0081] The surface-unmodified fumed silica powder according to the present invention was subjected to sonication of a 5% by weight aqueous dispersion of silica at 25°C for 120 seconds, and then measured by static light scattering (SLS) with a median particle size d of up to 2 μm, more preferably 0.05 μm to 1.5 μm, more preferably 0.10 μm to 1.2 μm, more preferably 0.15 μm to 1.0 μm, more preferably 0.20 μm to 0.90 μm, and more preferably 0.25 μm to 0.80 μm. 50 It is preferable to have the following. Using the resulting measured particle size distribution, the median d reflects the particle size that does not exceed 50% of all particles. 50 This is defined as the numerical median particle size.

[0082] The surface-unmodified fumed silica powder of the present invention preferably has a relatively narrow particle size distribution, which is a particle size distribution span of less than 7.0, less than 4.0, more preferably 0.8 to 3.5, more preferably 0.9 to 3.2, more preferably 1.0 to 3.1, more preferably 1.0 to 3.0, more preferably 1.0 to 2.5, and more preferably 1.0 to 2.0 (d 90 -d 10 ) / d 50 It can be characterized by the value of . Such hydrophilic silica powder with a narrow particle size distribution is preferred because it has particularly good dispersibility in various compositions.

[0083] The surface-unmodified fumed silica powder of the present invention preferably has a tamping density of 300 g / L or less, more preferably 250 g / L or less, more preferably 20 g / L to 250 g / L, more preferably 20 g / L to 200 g / L, more preferably 25 g / L to 180 g / L, and more preferably 30 g / L to 150 g / L. The tamping density can be measured in accordance with DIN ISO 787-11:1995.

[0084] The surface-unmodified fumed silica powder of the present invention is 20m 2 More than / g, preferably 20m 2 / g~600m 2 / g, comfortably 30m 2 / g~500m 2 / g, more preferably 40m 2 / g~400m 2 / g, comfortable 50m 2 / g~300m 2 It can have a BET surface area of ​​1 / g. Specific surface area, also simply called BET surface area, can be measured by nitrogen adsorption using the Brunauer-Emmett-Teller method in accordance with DIN 9277:2014.

[0085] The surface-unmodified fumed silica powder according to the present invention can be obtained after carrying out step (A) of the method of the present invention, and preferably, the surface-unmodified fumed silica powder according to the present invention is obtained by carrying out step (A) of the method of the present invention.

[0086] Surface-modified fumed silica powder The present invention further provides a surface-modified fumed silica powder obtained by steps (A) and (B) of the method of the present invention, preferably the surface-modified fumed silica powder according to the present invention is obtained by carrying out steps (A) and (B) of the method of the present invention.

[0087] The present invention further provides a surface-modified fumed silica powder having the following: a) Measured by reaction with lithium aluminum hydride, 0.29SiOH / nm2 The following BET surface area d SiOH Silanol group number for a given; b) A 5 wt% methanol dispersion of surface-treated silica was sonicated at 25°C for 120 seconds, and the particle size d of 10 μm or less was measured by static light scattering (SLS). 90 .

[0088] Such surface-modified fumed silica powder according to the present invention, characterized by requirement (a) and requirement (b), can be obtained by the method of the present invention, comprising steps (A) and (B) of the method of the present invention.

[0089] In this invention, the term "surface modified" is used interchangeably with the term "surface treated" and relates to a chemical reaction between untreated hydrophilic silica and a corresponding surface treatment agent that completely or partially modifies the free silanol groups of the silica.

[0090] The surface treatment agent can be selected from the group consisting of organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof. Preferably, organosilanes, silazanes, or mixtures thereof are used in the method. Some particularly useful surface treatment agents are the same as those described above with respect to the surface treatment step (B) of the method of the present invention.

[0091] The surface-modified fumed silica powder of the present invention can preferably be prepared according to the method of the present invention, with a BET surface area d SiOH The number of silanol groups is 0.45SiOH / nm 2 Preferably, 0.43SiOH / nm 2 More preferably, 0.41SiOH / nm 2 More preferably, 0.39SiOH / nm 2 More preferably, 0.37SiOH / nm 2 More preferably, 0.35SiOH / nm 2 More preferably, 0.33SiOH / nm 2 More preferably, 0.31SiOH / nm 2More preferably, 0.29SiOH / nm 2 More preferably, 0.28SiOH / nm 2 More preferably, 0.25SiOH / nm 2 More preferably, 0.20SiOH / nm 2 The following is preferred. Particularly preferred is the surface-modified fumed silica powder of the present invention having a BET surface area d SiOH The number of silanol groups relative to is 0.02SiOH / nm 2 More preferably 0.02SiOH / nm 2 ~0.45SiOH / nm 2 More preferably 0.03SiOH / nm 2 ~0.40SiOH / nm 2 More preferably 0.05SiOH / nm 2 ~0.35SiOH / nm 2 More preferably 0.05SiOH / nm 2 ~0.33SiOH / nm 2 More preferably 0.05SiOH / nm 2 ~0.30SiOH / nm 2 More preferably 0.03SiOH / nm 2 ~0.29SiOH / nm 2 More preferably 0.05SiOH / nm 2 ~0.28SiOH / nm 2 More preferably 0.05SiOH / nm 2 ~0.25SiOH / nm 2 , more preferably 0.07SiOH / ~0.20SiOH / nm 2 More preferably 0.10SiOH / nm 2 ~0.20SiOH / nm 2 That is the case.

[0092] The silanol group density of the surface-modified fumed silica powder of the present invention is unprecedentedly low compared to typical surface-treated fumed silica. This results in unique properties for such silica, such as low water content.

[0093] The surface-modified silica powder of the present invention can be hydrophilic or hydrophobic depending on the chemical structure of the surface treatment agent used. Preferably, a surface treatment agent that imparts hydrophobicity is used to produce a surface-treated silica powder having hydrophobic properties.

[0094] In the context of this specification, the term "hydrophobic" refers to surface-treated silica particles with low affinity for polar media such as water. The degree of hydrophobicity of surface-treated silica powder can be measured by parameters such as methanol wetting, as detailed, for example, on pages 5-6 of International Publication No. 2011 / 076518. In pure water, hydrophobic silica separates completely from the water and floats on its surface without wetting with the solvent. In contrast, in pure methanol, hydrophobic silica is dispersed throughout the solvent, and complete wetting occurs. In measuring methanol wetting, the silica sample to be tested is mixed with various methanol / water mixtures, and the maximum methanol content is measured at a point where wetting of the silica has not yet occurred, i.e., 100% of the silica to be tested is separated from the test mixture. This methanol content (in volume %) in the methanol / water mixture is called methanol wetting. The higher the level of such methanol wetting, the more hydrophobic the silica is.

[0095] The surface-modified fumed silica powder of the present invention has methanol wetting properties when the methanol content in the methanol / water mixture is more than 20% by volume, more preferably 30% to 90% by volume, more preferably 30% to 80% by volume, particularly preferably 35% to 75% by volume, and most preferably 40% to 70% by volume.

[0096] The surface-modified fumed silica powder of the present invention is obtained by sonicating a 5% by weight methanol dispersion of silica at 25°C for 120 seconds, and then measuring the particle size d by static light scattering (SLS) to be 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, more preferably 2 μm or less, and more preferably 1 μm or less. 90 It has the following characteristics. The resulting measured particle size distribution is a value that reflects particle sizes that do not exceed 90% of all particles. 90It is used to define...

[0097] The surface-modified fumed silica powder according to the present invention was subjected to sonication of a 5 wt% methanol dispersion of silica at 25°C for 120 seconds, and then measured by static light scattering (SLS) with a median particle size d of up to 2 μm, more preferably 0.05 μm to 1.5 μm, more preferably 0.10 μm to 1.2 μm, more preferably 0.15 μm to 1.0 μm, more preferably 0.20 μm to 0.90 μm, and more preferably 0.25 μm to 0.80 μm. 50 It is preferable to have this. The resulting measured particle size distribution is the median d, which reflects the particle size that does not exceed 50% of all particles. 50 This is used to define the numerical median particle size. The surface-modified fumed silica powder of the present invention preferably has a relatively narrow particle size distribution, which is the span of the particle size distribution (d 90 -d 10 ) / d 50 The surface-modified fumed silica powder can be characterized by having a particle size distribution of 7.0 or less, more preferably 4.0 or less, more preferably 3.5 or less, preferably 0.7 to 3.5, more preferably 0.8 to 3.5, more preferably 1.0 to 3.2, more preferably 1.1 to 3.1, and more preferably 1.2 to 3.0. Surface-modified fumed silica powder with such a narrow particle size distribution is preferred because it has particularly good dispersibility in various compositions.

[0098] The surface-modified fumed silica powder of the present invention is 15m 2 More than / g, preferably 15m 2 / g~500m 2 / g, comfortably 30m 2 / g~400m 2 / g, more preferably 40m 2 / g~300m 2 / g, comfortable 50m 2 / g~250m 2 It can have a BET surface area of ​​ / g.

[0099] The surface-modified fumed silica powder of the present invention preferably has a tamping density of more than 10 g / L, more preferably 20 g / L to 300 g / L, more preferably 25 g / L to 250 g / L, more preferably 30 g / L to 220 g / L, more preferably 35 g / L to 200 g / L, more preferably 40 g / L to 150 g / L, more preferably 45 g / L to 120 g / L, and more preferably 50 g / L to 100 g / L. The tamping density can be measured in accordance with DIN ISO 787-11:1995.

[0100] The surface-modified fumed silica powder according to the present invention has a carbon content of 0.2% to 10% by weight, preferably 0.3% to 7% by weight, more preferably 0.4% to 5% by weight, more preferably 0.5% to 4% by weight, more preferably 0.5% to 3.5% by weight, more preferably 0.5% to 3.2% by weight, more preferably 0.5% to 3.0% by weight, more preferably 0.5% to 2.5% by weight, more preferably 0.5% to 2.0% by weight, and more preferably 0.5% to 1.5% by weight, as measured by elemental analysis. Elemental analysis can be performed in accordance with EN ISO 3262-20:2000 (Chapter 8). The analytical sample is weighed into a ceramic crucible, a combustion additive is added, and it is heated in an induction furnace under an oxygen flow. The present carbon is oxidized to CO2. The amount of CO2 gas is quantified by an infrared detector.

[0101] Particularly preferred is the surface-modified fumed silica powder according to the present invention, characterized by a very low carbon content, for example, 0.5% to 3.5% by weight, more preferably 0.5% to 3.0% by weight, and even more preferably 0.5% to 2.0% by weight. However, this is sufficient to achieve a wide range of surface treatments; for example, such surface-treated fumed silica in a methanol / water mixture at a concentration of, for example, 30 to 80% by volume, more preferably 35 to 75% by volume, and more preferably 40 to 70% by volume, achieves a high degree of hydrophobicity. In such surface-treated fumed silica powder, a minimum amount of surface treatment agent is used to achieve the maximum degree of surface treatment, for example, the maximum degree of hydrophobicity of the silica powder.

[0102] Furthermore, particularly preferably, the surface-modified fumed silica powder according to the present invention has a low carbon content, such as 0.5% to 3.5% by weight, more preferably 0.5% to 3.0% by weight, and even more preferably 0.5% to 2.0% by weight, and also has a carbon content of, for example, 0.35SiOH / nm 2 More preferably, 0.30SiOH / nm 2 More preferably, 0.25SiOH / nm 2 The BET surface area d is as follows: SiOH The number of silanol groups is low. In this case, the amount of surface treatment agent used can be minimized to minimize the moisture content of the surface-treated fumed silica.

[0103] The loss on drying (LOD) of the surface-modified fumed silica powder of the present invention is preferably less than 5.0% by weight, more preferably less than 3.0% by weight, more preferably less than 2.0% by weight, more preferably less than 1.0% by weight, more preferably less than 0.8% by weight, and more preferably less than 0.5% by weight. The loss on drying can be measured in accordance with ASTM D280-01 (Method A).

[0104] The surface-modified fumed silica powder according to the present invention preferably has a water content of less than 0.8% by weight, more preferably less than 0.6% by weight, more preferably less than 0.4% by weight, more preferably less than 0.3% by weight, more preferably less than 0.2% by weight, and more preferably less than 0.1% by weight. The water content can be measured by Karl Fischer titration.

[0105] Composition containing fumed silica powder Another object of the present invention is a composition comprising the surface-unmodified fumed silica powder and / or the surface-modified fumed silica powder according to the present invention.

[0106] The compositions according to the present invention may contain at least one binder. The binder can bind individual parts of the composition together, and optionally bind one or more fillers and / or other additives, thereby improving the mechanical properties of the composition. Such binders may include organic or inorganic substances. The binder may optionally include reactive organic substances. Organic binders can be selected from the group consisting of, for example, (meth)acrylates, alkyd resins, epoxy resins, gum arabic, casein, vegetable oils, polyurethanes, silicone resins, waxes, cellulose adhesives, and mixtures thereof. Such organic substances may cause curing of the composition used, for example, by evaporation of a solvent, polymerization, crosslinking reactions, or other types of physical or chemical changes. Such curing may occur, for example, thermally or under the action of UV radiation or other radiation. Both single-component (1-C) and multi-component systems, particularly two-component (2-C) systems, can be applied as binders. Particularly preferred for the present invention are (preferably as a two-component system) an aqueous binder or a water-miscible (meth)acrylate binder and an epoxy resin.

[0107] In addition to or as a substitute for organic binders, the compositions of the present invention may contain inorganic hardening substances. Such inorganic binders, also called mineral binders, perform essentially the same role as organic binders in that they bind additives together. Furthermore, inorganic binders are classified into non-hydraulic binders and hydraulic binders. Non-hydraulic binders are water-soluble binders such as calcium lime, dolomite lime, gypsum, and anhydride that harden only in air. Hydraulic binders are binders that harden in air and in the presence of water, and become water-insoluble after hardening. These include hydraulic lime, cement, and stone cement. Mixtures of various inorganic binders can also be used in the compositions of the present invention.

[0108] In addition to, or instead of, a binder, the composition of the present invention may also contain a matrix polymer, such as a polyolefin resin (e.g., polyethylene or polypropylene), a polyester resin (e.g., polyethylene terephthalate), a polyacrylonitrile resin, a cellulose resin, or a mixture thereof. The fumed silica powder of the present invention can be incorporated into such a matrix polymer or form a coating on its surface.

[0109] Apart from the fumed silica powder and binder, the composition according to the present invention may further contain at least one solvent and / or filler and / or other additives.

[0110] The solvent used in the compositions of the present invention can be selected from the group consisting of water, alcohols, aliphatic and aromatic hydrocarbons, ethers, esters, aldehydes, ketones, and mixtures thereof. For example, the solvents used may be water, methanol, ethanol, propanol, butanol, pentane, hexane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, ethyl acetate, and acetone. Particularly preferably, the solvent used in the insulating composition has a boiling point of less than 300°C, and more preferably less than 200°C. Such relatively volatile solvents can be easily evaporated or vaporized during the curing of the compositions according to the present invention.

[0111] The surface-modified fumed silica powder of the present invention is particularly suitable for use in toner compositions.

[0112] Use of fumed silica powder The surface-modified and / or surface-modified silica powder of the present invention can be used as components of paints or coatings, silicones, pharmaceuticals or cosmetics, adhesives or sealants, toner compositions, lithium-ion batteries, particularly separators, electrodes and / or electrolytes, as well as for modifying the rheological properties of liquid systems, as anti-settling agents, for improving powder fluidity, and for improving the mechanical or optical properties of silicone compositions. [Examples]

[0113] Analysis method BET specific surface area [m 2 The value [ / g] was measured by nitrogen adsorption using the Brunauer-Emmett-Teller method, in accordance with DIN 9277:2014. BET surface area d SiOH [SiOH / nm 2 The number of silanol groups for ] was determined by the reaction of a pre-dried silica powder sample with a lithium aluminum hydride solution, as detailed on page 8, line 17 to page 9, line 12 of European Patent Application Publication No. 0725037. This method is also described in the Journal of Colloid and Interface Science, Vol. 125, No. 1 (1988), pp. 61-68. The tamping density [g / L] was measured in accordance with DIN ISO 787-11:1995 "General test methods for pigments and fillers - Part 11: Measurement of tamping volume and apparent density after tamping". Particle size distribution, i.e., d 10 value, d 50 value, d 90 Value and span (d 90 -d 10 ) / d 50 For the [μm] particle size, a 5 wt% methanol dispersion of surface-treated silica (in the case of hydrophobic silica powder) or an aqueous dispersion (in the case of hydrophilic silica powder) was sonicated at 25°C for 120 seconds, and then measured by static light scattering (SLS) using a laser diffraction particle size analyzer (HORIBA LA-950). The methanol wetting properties [volume % of methanol in the methanol / water mixture] were measured according to the method detailed on pages 5-6 of International Publication No. 2011 / 076518. The carbon content [weight %] was measured by elemental analysis in accordance with EN ISO 3262-20:2000 (Chapter 8). The sample to be analyzed was weighed into a ceramic crucible, a combustion additive was added, and it was heated in an induction furnace under an oxygen flow. The present carbon was oxidized to CO2. The amount of CO2 gas was quantified using an infrared detector. The water content [weight %] was measured by Karl Fischer titration using a Karl Fischer titrator.

[0114] Starting material Starting material 1, BET surface area: 46 m² 2 Aerosil® EG50 (manufactured by Evonik Operations GmbH) with a tamping density of 117 g / L was used. Starting material 2 had a BET surface area of ​​282 m². 2 Aerosil® 300 (manufactured by Evonik Operations GmbH) with a tamping density of 43 g / L was used.

[0115] Example 1 Starting material 1 was heat-treated at 400°C in a rotary kiln with a diameter of approximately 160 mm and a length of 2 m. The average residence time of silica in the rotary kiln was 1 hour. With the rotation speed set to 5 rpm, the silica processing rate was approximately 1 kg / hour. Dried and filtered compressed air was then used to process approximately 1 m 3 The heat-treated silica was continuously supplied to the kiln outlet at a flow rate of / hour (in the reverse direction of the flow), and pre-conditioning air was supplied to the convection in the tube. This process was smooth. No clogging of the rotary kiln was observed. The physicochemical properties of the obtained heat-treated silica are shown in Table 1.

[0116] Examples 2-5 and Comparative Example 1 were carried out in the same manner as Example 1, except that a heat treatment temperature of 700-1,300°C was applied. No clogging of the rotary kiln was observed in Examples 2-5, but significant clogging was observed in Comparative Example 1. The physicochemical properties of the obtained heat-treated silica are shown in Table 1.

[0117] Comparative Example 2 was carried out by heat-treating starting material 1 in a chamber kiln (manufacturer: Nabertherm). A layer with a maximum floor height of 1 cm was heat-treated at 1,200°C for 1 hour. The physicochemical properties of the obtained heat-treated silica are shown in Table 1.

[0118] Example 6 Starting material 2 was heat-treated at 400°C in a rotary kiln with a diameter of approximately 160 mm and a length of 2 m. The average residence time of the silica in the rotary kiln was 1 hour. The process was smooth. No clogging of the rotary kiln was observed. The physicochemical properties of the obtained heat-treated silica are shown in Table 2.

[0119] Examples 7-10 and Comparative Example 3 were carried out in the same manner as Example 6, except that the heat treatment temperature was applied between 700 and 1,300°C. No clogging of the rotary kiln was observed in Examples 7-10, but significant clogging was observed in Comparative Example 2. The physicochemical properties of the obtained heat-treated silica are shown in Table 2.

[0120] Comparative Example 4 was performed by heat-treating starting material 2 in a chamber kiln (manufacturer: Nabertherm). A layer with a maximum floor height of 1 cm was heat-treated at 11.00°C for 1 hour. The physicochemical properties of the resulting heat-treated silica are shown in Table 1.

[0121] Example 11 The heat-treated hydrophilic silica (100 g) obtained in Example 10 was surface-treated with hexamethyldisilazane (HMDS). For this purpose, HMDS (8.6 g) was evaporated. The silica powder was heated in a thin layer in a desiccator to 100°C, and then vacuumed. Subsequently, vaporized HMDS was added to the desiccator until the pressure rose to 300 millibars. After purging the sample with air, it was removed from the desiccator. The surface-treated silica thus obtained had a BET surface area of ​​190 m². 2 / g, carbon content 1.13%, silanol density 0.16SiOH / nm 2 The methanol wetting ability in a methanol / water mixture was 45%, and the particle size d was measured by static light scattering (SLS) after sonication of a 5 wt% methanol dispersion of surface-treated silica at 25°C for 120 seconds. 90 The size was less than 10 μm.

[0122] Table 1 shows the physicochemical properties of fumed silica powder obtained by heat treatment of starting material 1 (BET=46m 2 ( / g, tamping density = 117 g / L). The BET surface area, tamping density, and particle size of starting material 1 do not change much in Examples 1-5, where the heat treatment is performed at temperatures up to 1200°C. Conversely, at a high temperature of 1300°C (Comparative Example 1), there is a sharp decrease in BET surface area, and the tamping density and particle size (e.g., d 90 An increase was observed in both the BET surface area and particle size (Table 1). The changes in BET surface area and particle size were even more pronounced in Comparative Example 2, which underwent heat treatment at 1200°C but did not involve silica migration during the heat treatment. Silanol group density of starting material 1 (2.78OH / nm) 2 The silanol group density decreased significantly in Examples 1-5 and Comparative Example 1, with the greatest change occurring in the 400-1000°C range. Interestingly, at higher temperatures of 1300°C (Comparative Example 1), no further reduction in silanol group density was achieved.

[0123] Table 2 summarizes the same results as the tests in Table 1 (Examples 6-10, and Comparative Examples 3 and 4), but the starting material 2 (BET = 282m) 2The tamping density ( / g, tamping density = 43g / L) was used, and the results showed a similar trend to those in Table 1. Therefore, by heat-treating hydrophilic fumed silica powder at a temperature range of 400-1200°C for a certain period of time while moving the fumed silica powder, it was possible to produce silica powder with a relatively small particle size and almost no change in BET surface area and tamping density. Such heat-treated silica powder is particularly characterized by its low water content. By performing this surface treatment of heat-treated silica without adding water, it is possible to produce highly hydrophobic silica powder with particularly low silanol group density and water content (Example 11).

[0124] [Table 1]

[0125] [Table 2]

Claims

1. The surface has not been modified by any surface treatment agent, and the BET surface area d was measured by reaction with lithium aluminum hydride. ＳｉＯＨ The number of silanol groups relative to it is at least 1.2 SiO / nm ２ The particle size d was measured by static light scattering in a 5 wt% aqueous dispersion of silica after ultrasonic treatment at 25°C for 120 seconds. ９０ (A) A step in which surface-untreated fumed silica powder, having a particle size of 10 μm or less, is subjected to heat treatment at 350°C to 1,250°C for 5 minutes to 5 hours. A method for producing fumed silica powder containing the following: The temperature and duration of the heat treatment are determined by the d of the silica. ＳｉＯＨ However, the heat-untreated and surface-untreated fumed silica powder used was d ＳｉＯＨ In contrast, it is selected to reduce by 10% to 70%, A method for producing fumed silica powder, wherein the heat treatment is performed while the fumed silica powder is in motion.

2. The method for producing fumed silica powder according to claim 1, wherein the silica moves at a motion speed of at least 1 cm / min during the heat treatment step (A).

3. A method for producing fumed silica powder according to claim 1, wherein no water is added before, during, or after the above step (A).

4. The method for producing fumed silica powder according to claim 1, wherein the heat treatment is performed in a rotary kiln.

5. A method for producing fumed silica powder according to claim 1, further comprising the step (B) of surface treating the fumed silica powder obtained in step (A) with a surface treatment agent selected from the group consisting of organosilane, silazane, acyclic polysiloxane, cyclic polysiloxane, and mixtures thereof.

6. The method for producing fumed silica powder according to claim 5, wherein water is added in an amount less than 1% by weight of the fumed silica powder used before, during, or after the above step (B).

7. (a) BET surface area d measured by reaction with lithium aluminum hydride ＳｉＯＨ The number of silanol groups relative to this is 1.17 SiO / nm ２ The following: (b) Particle size d measured by static light scattering in a 5 wt% aqueous dispersion of silica after sonication at 25°C for 120 seconds. ９０ Surface-unmodified fumed silica powder with a particle size of 10 μm or less.

8. After subjecting a 5 wt% aqueous dispersion of the silica to ultrasonic treatment at 25°C for 120 seconds, the particle size distribution (d ９０ -d １０ ) / d ５０ is in the range of 0.8 to 3.5, the surface-unmodified fumed silica powder according to claim 7.

9. The surface-unmodified fumed silica powder according to claim 7, wherein the tamping density is 30 g / L to 150 g / L.

10. (a) BET surface area d measured by reaction with lithium aluminum hydride ＳｉＯＨ The number of silanol groups relative to is 0.29 SiO / nm ２ The following: (b) Particle size d in a 5 wt% methanol dispersion of silica after sonication at 25°C for 120 seconds, determined by static light scattering. ９０ It is 10 μm or less. Surface-modified fumed silica powder.

11. The surface-modified fumed silica powder according to claim 10, wherein the carbon content is 0.5% by weight to 3.5% by weight.

12. A composition comprising the surface-unmodified fumed silica powder according to claim 7.

13. Use of surface-unmodified fumed silica powder according to claim 7 for modifying the rheological properties of a liquid system, as an anti-settling agent, as a component of paints or coatings, silicones, pharmaceuticals or cosmetics, adhesives or sealants, toner compositions, and lithium-ion batteries, for improving the flowability of powders, and for improving the mechanical or optical properties of silicone compositions.

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