Method for producing hydrophobic silica powder, and hydrophobizing agent

Abstract

Provided is a method for producing a hydrophobic silica powder using a siloxane-based hydrophobizing agent in a liquid phase, said method having extremely low reactivity compared to hexamethyldisilazane and trimethylchlorosilane and requiring a long time for hydrophobization treatment. The time required for the hydrophobization treatment is made to be short. A method for producing a hydrophobic silica powder, which is characterized by hydrophobizing a silica powder using a liquid mixture comprising concentrated sulfuric acid and a siloxane-based hydrophobizing agent as a hydrophobizing agent.

Description

Technical Field

[0001] This invention relates to a method for manufacturing hydrophobic silica powder, characterized in that a mixture of concentrated sulfuric acid and a siloxane-based hydrophobic agent is used to hydrophobize the silica powder. Background Technology

[0002] Silica powder is used as a thickener, reinforcing filler, and / or colorant for various inorganic and organic powders, such as silicone rubber and / or resins. In these applications, hydrophobic silica powder obtained by surface hydrophobization is sometimes suitable. Additionally, hydrophobization is also performed to reduce particle aggregation caused by surface silanol groups generated during the drying of wet silica obtained by liquid-phase methods, thereby improving water resistance.

[0003] One of the manufacturing processes for silica aerogels, a type of silica, involves hydrophobication. Typically, when drying a moistened gel, drying shrinkage occurs due to capillary tension caused by the surface tension of the solvent and the dehydration condensation of surface silanols, making it difficult to obtain an aerogel. Supercritical drying, where surface tension does not play a role, yields silica aerogels. However, supercritical drying requires high pressure and high temperature, making it less than ideal from an economic standpoint. Hydrophobication of the moistened gel surface is an effective method for obtaining silica aerogel powder without supercritical drying. By replacing the pores with a solvent of low surface tension after hydrophobication, pore shrinkage can be suppressed even during drying below the critical point, thus obtaining silica aerogel powder.

[0004] Patent Document 1 discloses a method for manufacturing spherical silica aerogels, which sequentially comprises the following steps: a step of preparing an aqueous silica sol; a step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion; a step of gelling the silica sol to convert the W / O emulsion into a dispersion of the gel; a step of replacing the water in the gel with a solvent having a surface tension of 30 mN / m or less at 20°C; a step of hydrophobizing the gel with a hydrophobicating agent; and a step of removing the replaced solvent.

[0005] Patent Document 2 discloses a method for manufacturing spherical silica aerogel, which comprises the following steps in sequence: separating the dispersion of the gel obtained by the aforementioned step of converting a W / O type emulsion into a dispersion of gel into two layers, an O phase and a W phase; adding an alkaline substance to the W phase to mature the gel dispersed in the W phase; performing a silylation treatment (hydrophobication treatment) on the gel dispersed in the W phase; extracting the gel using a hydrophobic organic solvent; and recovering the gel to obtain a powder containing hydrophobic spherical silica aerogel.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2012 / 057086

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-177620 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] In the hydrophobication treatment of silica powder, siloxane-based hydrophobic agents such as hexamethyldisiloxane and octamethylcyclotetrasiloxane are widely used. However, when used in the liquid phase, their reactivity is extremely low compared to hexamethyldisilazane and trimethylchlorosilane. Therefore, in the hydrophobication treatment of silica powder using siloxane-based hydrophobic agents, the reactivity is improved by adding catalysts such as acids and bases and by contacting the siloxane-based hydrophobic agents in a mixed solvent of water and hydrophilic organic solvents. However, in Patent Document 2, the hydrophobication treatment time is 12 hours. From the perspective of shortening the manufacturing time, it is desirable to further shorten the hydrophobication treatment time.

[0012] Solution for solving the problem

[0013] In order to solve the above-mentioned problems, the inventors have repeatedly conducted in-depth research and obtained the following insights: In the method for manufacturing hydrophobic silica powder, when silica powder is contacted with a siloxane-based hydrophobic agent in a mixed solvent of water and hydrophilic organic solvent for hydrophobic treatment, the reaction of breaking the siloxane bond of the siloxane-based hydrophobic agent will affect the hydrophobic treatment time.

[0014] Based on the above insights, further repeated studies were conducted, and it was found that: when adding a hydrophobic agent and an acid catalyst to a mixed solvent containing silica and a hydrophilic organic solvent for hydrophobic treatment, the hydrophobic treatment reaction is promoted by pre-mixing the siloxane-based hydrophobic agent with concentrated sulfuric acid to prepare a mixed solution before adding it to the mixed solvent containing silica and a hydrophilic organic solvent. This completed the present invention.

[0015] That is, the present invention is a method for manufacturing hydrophobic silica powder, characterized in that the silica powder is hydrophobized using a mixture of concentrated sulfuric acid and a siloxane-based hydrophobicating agent. The concentrated sulfuric acid is preferably 1.5 to 10 times the mass of the siloxane-based hydrophobicating agent.

[0016] In addition, the second invention is a hydrophobic treatment agent, which is composed of concentrated sulfuric acid and a siloxane-based hydrophobic agent.

[0017] The effects of the invention

[0018] The method for manufacturing hydrophobic silica powder of the present invention accelerates the hydrophobication treatment using siloxane-based hydrophobicating agents. Therefore, the manufacturing time of hydrophobic silica powder can be shortened. Detailed Implementation

[0019] In the method for manufacturing hydrophobic silica powder of the present invention, a mixture of concentrated sulfuric acid and siloxane-based hydrophobic agent is used to hydrophobize the silica powder.

[0020] <Matrix silica powder>

[0021] The silica powder before processing, i.e., the matrix silica powder, can be any silica powder obtained by known methods without particular limitation, with dry silica, wet silica, and sol-gel silica being representative examples. Furthermore, this silica can be partially or completely molten silica powder. Matrix silica powder also includes wet gels obtained in the final stage of the manufacturing process of wet silica and sol-gel silica. Additionally, the matrix silica powder can be in the state of a dispersion.

[0022] The aforementioned dry-process silica is generally obtained by burning silicon compounds such as silicon tetrachloride in an oxyhydrogen flame. It is also commonly referred to as fumed silica. By modifying the manufacturing conditions, dry-process silica can achieve a specific surface area of ​​approximately 50–500 m². 2 The silica ranges from 5 to 200 nm in size. Based on the specific surface area, the primary particle size of silica is approximately 5–200 nm, and it typically exists as aggregates larger than 1 μm.

[0023] In addition, as a wet-process silica, precipitated silica is represented by silica produced by neutralizing sodium silicate with an inorganic acid, causing silica to precipitate from the solution. It is generally also known as white carbon black.

[0024] In addition, gel-process silica produced by neutralizing sodium silicate with acid is also a type of wet-process silica, and the substance obtained by pulverizing it can be used as the matrix silica powder of this invention.

[0025] Various types of silica can be obtained by changing the manufacturing conditions in wet-process silica production, yielding silica with a specific surface area of ​​approximately 50–1000 m². 2 Substances in the range of / g. Wet-process silica, based on its manufacturing method, can be considered as aggregated particles obtained by the aggregation of fine particles with a primary particle size of approximately 3–50 nm during the synthesis process. These wet-process silica particles are typically obtained in powder form after neutralization, filtration, washing, drying, and pulverization as needed. Generally, the average particle size of the obtainable wet-process silica particles ranges from 1 μm to several hundred μm.

[0026] Furthermore, sol-gel silica is produced by hydrolyzing silicon alkoxides such as tetramethoxysilane and tetraethoxysilane in acidic or alkaline aqueous organic solvents. While silicon alkoxides are expensive, the raw materials can be purified to a high degree through distillation, thus enabling the production of silica with extremely high purity. Hydrolysis in concentrated acidic or alkaline solutions yields blocky silica, which, when pulverized, can be broken down into irregularly shaped silica particles ranging from 1 μm to several hundred μm.

[0027] As the aforementioned sol-gel silica, so-called silica-based composite oxides such as silica-titanium dioxide, silica-alumina, and silica-zirconium oxide can also be used as the matrix silica powder of the hydrophobic silica powder of the present invention. These are obtained by co-hydrolyzing silicon alkoxides with metal alkoxides of titanium, aluminum, zirconium, etc. These silica-based composite oxides exhibit useful properties not possessed by ordinary silica due to the chemical and physical properties of the metal oxides other than silicon used. For example, the refractive index of the silica-based composite oxide can be adjusted by changing the content of the metal oxide.

[0028] In this invention, the matrix silica powder is selected from the above types and the appropriate silica and particle size (specific surface area) are used according to the intended application.

[0029]

[0030] In the method for manufacturing hydrophobic silica powder of the present invention, a mixture of concentrated sulfuric acid and siloxane-based hydrophobic agent is used as a hydrophobic treatment agent.

[0031] Concentrated sulfuric acid with a concentration of 90-100% can be used, preferably 95% or higher. When the sulfuric acid concentration is less than 90%, the sulfuric acid and the siloxane-based hydrophobicating agent will not mix, and the cleavage reaction of the siloxane bonds described later will not be promoted, so an increase in the hydrophobication treatment rate cannot be expected.

[0032] As siloxane-based hydrophobic agents, compounds with intramolecular siloxane bonds can be used. Compounds represented by the following general formulas (1) and (2) are known as siloxane-based hydrophobic agents.

[0033]

[0034] [In formula (1), n ​​represents an integer greater than or equal to 0; R represents a hydrophobic group such as a hydrocarbon group; R' represents hydrogen or a hydrocarbon group. Multiple R and R' can be the same or different from each other.]

[0035]

[0036] [In formula (2), m represents an integer from 3 to 10; R represents a hydrophobic group such as a hydrocarbon group; R' represents hydrogen or a hydrocarbon group. Multiple Rs and R's can be chosen to be the same or different from each other.]

[0037] In the aforementioned formula (1), n ​​is preferably an integer from 0 to 8. R and R' are preferably hydrocarbon groups, more preferably hydrocarbon groups with 1 to 10 carbon atoms, even more preferably hydrocarbon groups with 1 to 4 carbon atoms, and particularly preferably methyl groups.

[0038] When treated with the siloxane-based hydrophobic agent shown in formula (1), the number of bonds formed with the hydroxyl groups on the surface of the silica powder varies depending on the number of n in formula (1). For example, if n is 0, the following bonds occur:

[0039] ≡MO-SiRR'2(3)

[0040] [In formula (3), M represents the Si atoms that form silica powder (the same applies to the following formulas).]

[0041] Furthermore, if n is 1 or more, then equation (3) and the following bonding will occur:

[0042] (≡MO-)2SiRR'(4)

[0043] In this way, hydrophobic treatment is achieved by silylating hydroxyl groups.

[0044] If we specifically exemplify the hydrophobic agent shown in formula (1) above, examples include dimethyl polysiloxanes such as hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecylpentasiloxane, and tetradecylhexasiloxane; and methylphenyl silicone oil, etc. From the viewpoint of good reactivity, hexamethyldisiloxane and octamethyltrisiloxane are preferred, and hexamethyldisiloxane is even more preferred.

[0045] In equation (2) above, m is an integer from 3 to 10, and m is preferably an integer from 3 to 5. R and R ’ The preferred group is a hydrocarbon group, and the groups that are the same as R and R' in formula (1) can be listed as preferred groups. When silica powder is treated with the compound shown in formula (2) (hereinafter also referred to as cyclic siloxane), the bonds shown in formula (4) above will be generated on the silica surface in the gel.

[0046] If we specifically exemplify the cyclic siloxanes represented by formula (2) above, examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecylcyclohexasiloxane, tetradecylcycloheptasiloxane, hexadecylcyclooctasiloxane, octadecylcyclononasiloxane, and eicosylcyclodecasiloxane. From the viewpoint of good reactivity, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane are preferred, and octamethylcyclotetrasiloxane is more preferred.

[0047] <Preparation method of a mixture composed of concentrated sulfuric acid and siloxane-based hydrophobic agents>

[0048] The mixture of concentrated sulfuric acid and siloxane-based hydrophobic agent is obtained by mixing concentrated sulfuric acid with the siloxane-based hydrophobic agent.

[0049] It is believed that the siloxane hydrophobic agents listed in formula (1) or (2) are easily mixed with sulfuric acid, and in the mixture, silyl sulfate esters as shown in formula (5) or (6) are generated.

[0050] RR'2Si-OSO3H(5)

[0051] RR'Si-(OSO3H)2(6)

[0052] [In formulas (5) and (6), R represents a hydrophobic group such as a hydrocarbon group; R' represents a hydrogen group or a hydrocarbon group, and multiple R and R' can be chosen to be the same or different.]

[0053] The sulfate groups in formulas (5) and (6) have high desorption capacity and readily mix / react with water to generate silanol groups. It is believed that hydrophobication occurs through the dehydration condensation of these silanol groups with the silanol groups of the matrix silica. However, it is also believed that the generation of silanol groups is promoted by mixing concentrated sulfuric acid with siloxane-based hydrophobic agents, thus accelerating the hydrophobication reaction.

[0054] The amount of siloxane-based hydrophobic agent used depends on the type of siloxane-based hydrophobic agent. For example, when using hexamethyldisiloxane for hydrophobic treatment, a suitable amount is 0.03A to 0.15A parts by mass relative to 100 parts by mass of the matrix silica (where A is the specific surface area (m²) of the matrix silica). 2 / g). More preferably, it is 0.04A to 0.13A parts by mass. When it is desired to adjust the residual silanol groups of the hydrophobic silica, a smaller amount than the above range can be used.

[0055] The amount of concentrated sulfuric acid relative to the amount of the siloxane-based hydrophobicating agent also depends on the type of hydrophobicating agent. However, when using hexamethyldisiloxane or octamethylcyclotetrasiloxane, it is desirable to use concentrated sulfuric acid at 1.5 to 10 times the mass of the siloxane-based hydrophobicating agent to be used. This can be attributed to the fact that when the amount of sulfuric acid used is 1.5 times or more the mass of the hydrophobicating agent, sufficient formation of silyl sulfate esters will occur, and the siloxane-based hydrophobicating agent and concentrated sulfuric acid will form a homogeneous mixture. Therefore, the hydrophobication reaction can be expected to be promoted. Furthermore, if the amount of sulfuric acid is less than 10 times the mass of the hydrophobicating agent, there is no need to worry about the hydrophilic organic solvent reacting with the sulfuric acid (described later). The endpoint of mixing also depends on the hydrophobicating agent and the stirring efficiency, but it is preferable to use the point where the exothermic reaction ceases based on the mixing as the endpoint. For example, when the concentrated sulfuric acid is 46g and the hexamethyldisiloxane or octamethyltetrasiloxane is 8g, the exothermic reaction ceases in about 5 minutes, and the liquid temperature of the mixture no longer rises.

[0056] <Hydrophobic treatment>

[0057] In this invention, the hydrophobic treatment can be performed as follows: a mixture of concentrated sulfuric acid and a siloxane-based hydrophobic agent, adjusted by the above method, is added to a slurry in which silica matrix is ​​dispersed in a solution composed of a hydrophilic organic solvent and water, and the solution is stirred at a specified temperature for a specified time.

[0058] The slurry is prepared by adding a matrix silica to an aqueous solution containing a hydrophilic organic solvent, or vice versa. This can be done using known methods. The silica concentration in the slurry is preferably 2–30% by mass, more preferably 4–20% by mass.

[0059] From the viewpoint of improving the solubility of the hydrophobicating agent in aqueous solution and promoting reactivity, the concentration of the hydrophilic organic solvent in the aqueous solution is preferably set in the range of 15–80 wt%. It should be noted that when the final stage of the manufacturing process of the silica matrix itself is an aqueous solution containing a hydrophilic organic solvent, it can also be considered as a slurry. The type of hydrophilic organic solvent is arbitrary, and low-boiling-point solvents that can be easily distilled off after hydrophobication are suitable. Examples include acetone, methanol, ethanol, and isopropanol. Isopropanol is particularly suitable.

[0060] Furthermore, to improve the efficiency of the hydrophobication reaction and shorten the reaction time, it is preferable to set the pH of the reaction solution to 0–1.0. The pH can be adjusted to this range using the sulfuric acid contained in the aforementioned mixture of concentrated sulfuric acid and a siloxane-based hydrophobicating agent. If this range is not met, an acidic component can be added. The added acidic component is not limited to sulfuric acid; any inorganic or organic acid can be used. These inorganic or organic acids are preferably sulfuric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, thiocyanate, phosphoric acid, formic acid, acetic acid, trifluoroacetic acid, etc., with sulfuric acid and hydrochloric acid being more preferred.

[0061] There are various methods for adding the mixture of concentrated sulfuric acid and siloxane-based hydrophobic agents. For example, it can be added at an appropriate rate to a reaction vessel where the slurry has been stirred using a funnel. When the internal temperature may exceed the temperature range described later due to the exothermic reaction caused by the mixing of concentrated sulfuric acid and the aqueous solution, it is preferable to use a dropping funnel or similar device to adjust the addition rate.

[0062] The preferred temperature for the hydrophobication treatment is 50–70°C, more preferably 60–70°C. If the temperature exceeds this range, although it also depends on the type of hydrophobicating agent and hydrophilic organic solvent, they may be removed by distillation, and the hydrophobication process becomes incomplete. When the treatment is carried out at temperatures exceeding the above range, it is preferable to use a condenser to suppress the distillation removal of the hydrophobicating agent and hydrophilic organic solvent.

[0063] The time required for hydrophobication varies depending on the specific surface area of ​​the silica matrix, the type of siloxane-based hydrophobicating agent, the temperature, and consequently, the hydrophobicity of the target silica powder. Regarding hydrophobicity, the concentration of methanol at which the silica powder becomes suspended is expressed as hydrophobicity (M value), which can also be considered an indicator of the extent of the hydrophobication reaction. For example, relative to a specific surface area of ​​900–1000 m²... 2 Using 100 parts by weight of matrix silica and 73 parts by weight of hexamethyldisiloxane, with the processing temperature set at 60°C, the time required to obtain hydrophobic silica with an M value of approximately 45 Vol% is 1 hour.

[0064] <Treatment after hydrophobication>

[0065] The hydrophobicated slurry contains non-volatile sulfuric acid; therefore, it is preferable to remove the acidic components, which can be achieved using known methods such as neutralization or water washing. Among these methods, adding an alkaline substance for neutralization is suitable. By adding an alkaline substance, the pH of the prepared slurry is made to be neutral to slightly acidic. Specifically, the pH of the slurry is preferably set to 1.0–7.5, and more preferably 1.5–7.0.

[0066] As an alkaline substance, it can be used as long as it is water-soluble. Inorganic bases such as hydroxide salts, carbonates, bicarbonates, and ammonia can be used; organic acid salts such as acetates can also be used.

[0067] Furthermore, this neutralization process can be carried out by maintaining a temperature between 35°C and 80°C. The acid-base neutralization reaction, which is exothermic, occurs in this process; therefore, this temperature range can be maintained even without special heating. The time required to add the alkaline substance can be appropriately set according to the temperature of the slurry, ranging from 0.5 hours to 1 hour.

[0068] After the above neutralization treatment, most of the salts can be removed by removing the water layer generated during the extraction of hydrophobic silica into the hydrophobic organic solvent. The hydrophobic organic solvent used for the extraction of hydrophobic silica is arbitrary, but a low-boiling-point solvent that is easily removed by distillation during drying is suitable. Hexane, heptane, nonane, decane, methyl ethyl ketone, toluene, etc., can be used.

[0069] The hydrophobic silica dispersion obtained through the above operations contains residual salts. Furthermore, when porous silica or silica aerogel is used as a silica matrix, salts also remain within the pores. When further removal of residual salts is required, it is preferable to clean the hydrophobic organic solvent with an aqueous solution of water or alcohol. This cleaning operation can be performed using known methods. To improve cleaning efficiency, it is preferable to use an aqueous solution of isopropanol at several tens of wt%. Additionally, to further improve cleaning efficiency, it is preferable to set the temperature within the range not exceeding the boiling point of the hydrophobic organic solvent. Typically, this can be performed within the range of 45–70°C.

[0070] <Recovery and drying of hydrophobic silica>

[0071] To obtain hydrophobic silica powder, hydrophobic silica is filtered from the hydrophobic silica dispersion after the aforementioned hydrophobication treatment and then dried. The drying temperature is preferably above the boiling point of the solvent and below the decomposition temperature of the surface treatment agent, and preferably carried out under pressure ranging from atmospheric pressure to reduced pressure.

[0072] Example

[0073] The present invention is described below with examples and comparative examples to illustrate the invention in more detail, but the invention is not limited to these examples at all.

[0074] <Evaluation Methods>

[0075] For the hydrophobic silica powders manufactured in Examples 1-4 and Comparative Examples 1-4, tests were conducted on the following items.

[0076] (Carbon content)

[0077] The carbon content and hydrophobicity of silica treated with the same siloxane-based hydrophobicating agent showed a positive correlation. Based on this, the carbon content was determined using an elemental analysis apparatus (varioMICRO cube) manufactured by Elementar Japan, serving as an indicator of the hydrophobic treatment achieved by utilizing hydrophobic groups on the silica surface.

[0078] (M value)

[0079] Hydrophobic silica powder floats on water but is completely suspended in methanol. Using this property, the M value, measured by the following method, is used as an indicator of hydrophobic treatment utilizing the hydrophobic groups on the silica surface. In the following method, silica powder that floats in water even without the addition of methanol is considered hydrophilic silica powder, with an M value of 0. Silica powder with an M value of 1 or higher is considered hydrophobic silica powder, which floats on water without added methanol. The larger the M value, the more methanol is required to suspend the silica powder in water, indicating higher hydrophobicity.

[0080] 0.2 g of hydrophobic silica powder was added to 50 ml of water in a 200 mL beaker and stirred with a magnetic stirrer. Methanol was added dropwise using a burette, and the endpoint was set at the point when all the hydrophobic silica powder was wetted and suspended in the solvent in the beaker. To prevent direct contact between the methanol and the sample, it was introduced into the solution through a tube. The percentage of methanol in the methanol-water mixture at the endpoint was defined as the hydrophobicity (M value).

[0081] M value = methanol addition volume / (methanol addition volume + 50 ml)

[0082] <Example 1>

[0083] While stirring with a stirring blade, 100g of sulfuric acid was slowly added to produce an aqueous silica sol. At this point, the pH was 2.9.

[0084] Add 129g of heptane and 1.5g of sorbitan monooleate to 139g of the aqueous silica sol prepared above. Stir the solution at 4600 rpm for 2.5 minutes using a homogenizer to form a W / O emulsion.

[0085] The resulting W / O emulsion was gelled at 70°C for 60 minutes while being stirred with a stirring blade. Next, 71 g of isopropanol and 58 g of deionized water were added, and the O phase was separated from the W phase while stirring with a stirring blade. Then, 9.63 g of a 0.5 mol / L sodium hydroxide aqueous solution was added to the W phase. At this point, the pH of the W phase was 7.1. The gel was matured at 70°C for 10 minutes. The O phase was removed by decantation, thereby recovering the W phase. The silica concentration of this W phase was 4.2 wt%.

[0086] 7.7 g of hexamethyldisiloxane (HMDSO), used as a siloxane-based hydrophobicating agent, was added to 45.5 g of concentrated sulfuric acid and stirred for 5 minutes to obtain a mixture. This mixture was then added to the W phase described above, and hydrophobication treatment was performed at 60°C for 15 minutes while stirring. The pH of the solution during the hydrophobication treatment was 0.

[0087] After hydrophobication treatment, 130g of a 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade for neutralization. The pH at this point was 2.0.

[0088] Next, 90g of heptane was added to extract the gel, and the W phase was removed by decantation to recover the O phase. The O phase was then washed twice with 129g of 55% isopropanol.

[0089] The washed silica slurry was filtered using a vacuum filter. The gel was dried by heating at -100 kPa and 150°C for more than 16 hours to obtain hydrophobic silica powder. The hydrophobication conditions and the physical properties of the obtained silica powder are shown in Table 1.

[0090] <Comparative Example 1>

[0091] Until the gel is cured, the same procedures as in Example 1 are performed. Regarding the hydrophobication treatment, 45.5 g of concentrated sulfuric acid and 7.7 g of hexamethyldisiloxane are added to the W phase, and the mixture is stirred while being hydrophobized at 60°C for 15 minutes. The pH of the solution during the hydrophobication treatment is 0.

[0092] After hydrophobication treatment, 130g of a 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade for neutralization. The pH at this point was 2.0. Next, 90g of heptane was added in an attempt to extract the gel, but it did not disperse in the heptane. The W phase was transferred to a funnel, the gel was filtered off, and 1500g of pure water was added for salt washing. Then, after adding 300g of isopropanol, the resulting gel was dried by heating at -100kPa and 150℃ for more than 16 hours to obtain hydrophobic silica powder. The hydrophobication conditions and the physical properties of the obtained silica powder are shown in Table 1.

[0093] <Example 2>

[0094] The hydrophobication treatment time was set to 30 minutes, and otherwise the same procedures as in Example 1 were performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0095] <Comparative Example 2>

[0096] In the hydrophobication treatment process, the hydrophobication treatment was carried out at 60°C for 30 minutes. Otherwise, the same operation as in Comparative Example 1 was performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0097] <Example 3>

[0098] The hydrophobication treatment time was set to 60 minutes, and otherwise the same procedures as in Example 1 were performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0099] <Comparative Example 3>

[0100] In the hydrophobication process, the hydrophobication treatment was carried out at 60°C for 60 minutes. Otherwise, the same operation as in Comparative Example 1 was performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0101] <Example 4>

[0102] The hydrophobication treatment time was set to 180 minutes, and otherwise the same procedures as in Example 1 were performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0103] <Example 5>

[0104] While stirring with a stirring blade, 100g of sulfuric acid was slowly added to produce an aqueous silica sol. At this point, the pH was 2.9.

[0105] Add 129g of heptane and 1.5g of sorbitan monooleate to 139g of the aqueous silica sol prepared above. Stir the solution at 4600 rpm for 2.5 minutes using a homogenizer to form a W / O emulsion.

[0106] The resulting W / O emulsion was gelled at 70°C for 60 minutes while being stirred with a stirring blade. Next, 71 g of isopropanol and 58 g of deionized water were added, and the O phase was separated from the W phase while stirring with a stirring blade. Then, 9.63 g of 0.5 mol / L sodium hydroxide aqueous solution was added. At this point, the pH of the W phase was 7.1. The gel was matured at 70°C for 10 minutes. The O phase was removed by decantation, thereby recovering the W phase. 33.9 g of concentrated sulfuric acid was added to this W phase. The silica concentration of the W phase after adding concentrated sulfuric acid was 3.7 wt%.

[0107] 7.7 g of hexamethyldisiloxane (HMDSO), used as a siloxane-based hydrophobicating agent, was added to 11.6 g of concentrated sulfuric acid and stirred for 5 minutes to obtain a mixture. This mixture was then added to the W phase described above, and hydrophobication treatment was carried out at 60°C for 60 minutes while stirring. The pH of the solution during the hydrophobication treatment was 0.

[0108] After hydrophobication treatment, 130g of a 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade for neutralization. The pH at this point was 2.0.

[0109] Next, 90g of heptane was added to extract the gel, and the W phase was removed by decantation to recover the O phase. The O phase was then washed twice with 129g of 55% isopropanol.

[0110] The washed silica slurry was filtered using a vacuum filter. The gel was dried by heating at -100 kPa and 150°C for more than 16 hours to obtain hydrophobic silica powder. The hydrophobication conditions and the physical properties of the obtained silica powder are shown in Table 1.

[0111] <Example 6>

[0112] The hydrophobicating agent was set as 7.7 g of octamethylcyclotetrasiloxane (D4), and the hydrophobication treatment time was set as 30 minutes. Otherwise, the same operation as in Example 1 was performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0113] <Comparative Example 4>

[0114] Until the gel is cured, the same procedures as in Example 6 are performed. Regarding the hydrophobication treatment, 45.5 g of concentrated sulfuric acid and 7.7 g of octamethylcyclotetrasiloxane are added to the W phase, and the mixture is stirred while being hydrophobized at 60°C for 30 minutes. The pH of the solution during the hydrophobication treatment is 0.

[0115] After hydrophobication treatment, 130g of a 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade for neutralization. The pH at this point was 2.0.

[0116] Next, 90g of heptane was added in an attempt to extract the gel, but it did not disperse in the O phase. The W phase was transferred to a funnel, the gel was filtered off, and 1500g of pure water was added to remove salts. Then, 300g of isopropanol was added, and the resulting gel was dried by heating at -100kPa and 150°C for more than 16 hours to obtain silica powder formed from the hydrophobic spherical silica of the present invention. The hydrophobication conditions and the physical properties of the obtained silica powder are shown in Table 1.

[0117] <Example 7>

[0118] The hydrophobication treatment time was set to 60 minutes, and otherwise the same procedures as in Example 6 were performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0119] <Comparative Example 5>

[0120] The hydrophobication treatment time was set to 60 minutes, and otherwise the same procedures as in Comparative Example 4 were performed. Similar to Comparative Example 4, the gelled product after hydrophobication treatment was not dispersed in heptane.

[0121] The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0122] <Example 8>

[0123] The hydrophobication treatment time was set to 120 minutes, and otherwise the same procedures as in Example 6 were performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0124] <Comparative Example 6>

[0125] The hydrophobication treatment time was set to 120 minutes, and otherwise the same procedures as in Comparative Example 4 were performed. Similar to Comparative Example 4, the gel after hydrophobication was not dispersed in heptane. The hydrophobication conditions and the properties of the resulting silica powder are shown in Table 1.

[0126] <Example 9>

[0127] 60 g of hydrophilic silica powder (specific surface area 4.2 m²) prepared by the sol-gel method was used. 2 After adding 188g of pure water and 60g of isopropanol to a slurry with a silica concentration of 17.2wt%, 41.5g of concentrated sulfuric acid was added.

[0128] Add 0.4 g of hexamethyldisiloxane, a siloxane-based hydrophobicating agent, to 4.0 g of concentrated sulfuric acid and stir for 5 minutes to obtain a mixture. Add this mixture to the above slurry and perform hydrophobication treatment at 60°C for 60 minutes while stirring. The pH of the solution during hydrophobication treatment is 0. After hydrophobication treatment, add 130 g of 24% sodium hydroxide aqueous solution while stirring with a stirring blade for neutralization treatment. The pH at this point is 2.0.

[0129] Next, 90 g of heptane was added to extract hydrophobic silica. The W phase was removed by decantation, and the O phase was recovered. Silica was filtered from the O phase and dried by heating at -100 kPa and 150 °C for more than 16 hours to obtain hydrophobic silica powder. The hydrophobication conditions and the physical properties of the obtained silica powder are shown in Table 1.

[0130] <Comparative Example 7>

[0131] Regarding the hydrophobication treatment process, 5g of concentrated sulfuric acid and 0.4g of hexamethyldisiloxane were added to the W phase, and the hydrophobication treatment was carried out at 60°C for 60 minutes while stirring. Except for the hydrophobication treatment process, the same operation as in Example 9 was performed. The hydrophobication conditions and the physical properties of the resulting silica powder are shown in Table 1.

[0132] [Table 1]

[0133] Table 1. Hydrophobication conditions and physical properties of silica powder

[0134]

[0135] *: The amount in parentheses is the amount of concentrated sulfuric acid relative to the hydrophobic agent.

Claims

1. A method for manufacturing hydrophobic silica powder, characterized in that, Silica powder is hydrophobized using a mixture of concentrated sulfuric acid and a siloxane-based hydrophobic agent.

2. The method for manufacturing hydrophobic silica powder according to claim 1, wherein, Concentrated sulfuric acid is 1.5 to 10 times the mass of siloxane-based hydrophobic agents.

3. The method for manufacturing hydrophobic silica powder according to claim 1 or 2, wherein, The siloxane hydrophobic agent is selected from at least one of hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecylpentasiloxane, tetradecylmethylhexasiloxane, methylphenylsiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecylcyclohexasiloxane, tetradecylcycloheptasiloxane, hexamethylcyclooctasiloxane, octadecylcyclononasiloxane, or icosylcyclodecasiloxane.

4. The method for manufacturing hydrophobic silica powder according to claim 3, wherein, The siloxane hydrophobic agent is selected from at least one of hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, or decamethylcyclopentasiloxane.

5. A hydrophobic treatment agent, which is composed of concentrated sulfuric acid and a siloxane-based hydrophobic agent.

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