Precipitated Silica

Abstract

A precipitated silica is disclosed. The precipitated silica has a particle size of 165 to 195 m. 2 / g BET specific surface area, 160-180m 2 / g CTAB specific surface area, 14–21% vicinal silanol content, 2–4% geminal silanol content, 2–4 mL / g total intrusion volume, 0.45–0.7 pore volume ratio (V2 / V1), and 52–70 m 2 / g of total pore area.

Description

[Technical Field]

[0001] The present disclosure relates to precipitated silicas that exhibit high dispersibility in elastomeric compositions. [Background technology]

[0002] Silica is well known as a reinforcing filler in vulcanizable rubber mixtures, such as those used in tire formation. Reinforcing fillers used in tire compounds are important for achieving performance requirements, contributing to the strengthening of the rubber network, significantly improving stiffness, tensile strength, and abrasion resistance. This extends tire life and reduces fuel consumption. However, not all types of silica can be used to reinforce elastomers. Silica used in the tire industry is generally precipitated silica, characterized by its particle size, structure, and surface activity.

[0003] It is known that the properties of precipitated silica affect its reinforcing properties, so it is necessary to identify silica properties that suit the requirement profiles of various applications.

[0004] Various grades of precipitated silica are known, depending on their properties. However, there remains a need to develop precipitated silicas that have a desirable combination of properties while exhibiting good dispersibility and reinforcing properties when added to elastomeric compositions. Summary of the Invention

[0005] A precipitated silica is disclosed. The precipitated silica has a viscosity of 165-195 m / s. 2 / g BET specific surface area, 160-180m 2 / g CTAB specific surface area, 14–21% vicinal silanol content, 2–4% geminal silanol content, 2–4 mL / g total intrusion volume, 0.45–0.7 pore volume ratio (V2 / V1), and 52–70 m 2 / g of total pore area. DETAILED DESCRIPTION OF THE INVENTION

[0006] Reference will now be made to embodiments and specific language will be used to illustrate the principles of the present disclosure in order to promote understanding of the principles of the present disclosure, but it will be understood that no limitation of the scope of the disclosure is intended, and that changes and further modifications in the disclosed compositions and methods, and further applications of the principles of the present disclosure, are contemplated as would normally occur to one skilled in the art to which the present disclosure pertains.

[0007] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the present disclosure, but are not restrictive of the disclosure.

[0008] Throughout this specification, reference to "one embodiment," "an embodiment," or similar terminology means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of "in one embodiment," "in an embodiment," and similar phrases throughout this specification do not necessarily all refer to the same embodiment.

[0009] The term "comprise" or variations thereof are intended to cover a non-exclusive inclusion and are not intended to be construed as "consists of only." For example, a process or method including a list of steps does not include only those steps, but may include other steps not expressly listed or inherent to the process or method.

[0010] Similarly, the terms "having" and "including" and grammatical variations thereof are intended to be open-ended, such that the listed items do not exclude other items that may be substituted or added.

[0011] Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated by reference.

[0012] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Those skilled in the art will further understand that the various physicochemical parameters described herein have the same meaning as commonly understood in the art unless otherwise specified.

[0013] "BET surface area" is a term named after Brunauer, Emmett, and Teller and refers to the total surface area of silica as determined by the adsorption of nitrogen onto the silica surface. BET surface area is determined according to ISO 5794-1 / Annex D.

[0014] "CTAB specific surface area" refers to the external surface area of silica as determined by adsorption of cetyltrimethylammonium bromide (CTAB) onto the silica surface. CTAB specific surface area is determined in accordance with ASTM 3765 or NFT 45-007.

[0015] The ratio of these two parameters, BET / CTAB, is an indicator of the porosity.

[0016] "DOA absorption" is a measure of the amount of di-(2-ethylhexyl) adipate (DOA) absorbed by silica. DOA absorption is an indicator of the void volume formed by silica aggregates and agglomerates. DOA absorption is determined according to ASTM D6854.

[0017] The "Sears number" is a measure of the concentration of silanol groups on precipitated silica and is an indicator of the surface activity of the silica. The silanol groups on the surface of precipitated silica serve as potential chemical reaction sites for coupling reagents, allowing the silica to couple to the elastomeric matrix.

[0018] The "Sears number / CTAB specific surface area ratio" indicates the concentration of silanol groups for a given level of CTAB specific surface area.

[0019] The "Sears number / BET specific surface area ratio" indicates the concentration of silanol groups for a given level of BET specific surface area.

[0020] "Vicinal silanol" refers to a hydrogen-bonded silanol group, and "geminal silanol" refers to a silanol with two OH groups attached to the same surface silicon atom to yield a Si(OH)2 moiety. "Siloxane group" refers to a siloxane group connected by oxygen atoms on the silica surface, or ≡Si-O-Si≡. Solid-state Si NMR was used to measure the content of vicinal silanols, geminal silanols, and siloxane groups.

[0021] The "pore volume ratio (V2 / V1)" refers to the ratio of the pore volume V2 calculated from the cumulative pore volume in the pore diameter range of 5.5 to 40 nm to the pore volume V1 calculated from the cumulative pore volume in the pore diameter range of 17.5 to 27.5 nm. The pore volume ratio (V2 / V1) provides the effective pore volume for the filler to reinforce the elastomer / rubber matrix.

[0022] In its broadest scope, the present disclosure relates to precipitated silicas that exhibit high dispersibility in the matrix of an elastomeric composition. In particular, the present disclosure relates to: 165~195m 2 / g BET specific surface area, 160~180m 2 / g CTAB specific surface area, 14-21% vicinal silanol content, 2-4% geminal silanol content, Total infiltration volume: 2-4 mL / g a pore volume ratio (V2 / V1) of 0.45–0.7, and 52~70m 2 / g of total pore area.

[0023] The inventors have found that the above combination of physicochemical parameters leads to an improved dispersion of precipitated silica in an elastomeric matrix, specifically, a precipitated silica that exhibits effective silanization when mixed with an elastomeric composition, resulting in a better silica crosslink density, lower filler-filler interactions, and better macro- and micro-dispersion of the silica in the elastomeric matrix, allowing for better reinforcement when used in the elastomeric composition.

[0024] In one embodiment, the precipitated silica is 170 to 190 m 2 In some embodiments, the precipitated silica has a BET specific surface area in the range of 180 m / g. 2 / g BET specific surface area.

[0025] In one embodiment, the precipitated silica has a pH of 165 to 175 m 2 In some embodiments, the precipitated silica has a CTAB specific surface area in the range of 170 m / g. 2 / g CTAB specific surface area.

[0026] In one embodiment, the BET / CTAB of the precipitated silica is in the range of 1 to 1.15.

[0027] In one embodiment, the precipitated silica has a vicinal silanol content of 14.86 to 20.86%, hi some embodiments, the precipitated silica has a vicinal silanol content of 17.86%.

[0028] In one embodiment, the precipitated silica has a geminal silanol content of 2 to 3.44%. In some embodiments, the precipitated silica has a geminal silanol content of 2.44%.

[0029] In one embodiment, the precipitated silica has a total intrusion volume of 2 to 3.51 mL / g. In some embodiments, the precipitated silica has a total intrusion volume of 2.51 mL / g.

[0030] In one embodiment, the precipitated silica has a pore volume ratio (V2 / V1) of 0.48 to 0.68. In some embodiments, the precipitated silica has a pore volume ratio (V2 / V1) of 0.58.

[0031] In one embodiment, the precipitated silica has a pH of 5. 2 In some embodiments, the precipitated silica has a total pore area in the range of 60 m / g. 2 / g of total pore area.

[0032] In one embodiment, the precipitated silica has a DOA absorption value in the range of 240 to 310 ml / 100 g. In some embodiments, the precipitated silica has a DOA absorption value in the range of 242 to 302 ml / 100 g.

[0033] In one embodiment, the precipitated silica has a siloxane group content of 74-85%. In some embodiments, the precipitated silica has a siloxane group content of 79.69%.

[0034] In one embodiment, the precipitated silica has a total pore volume of 1.50 to 3.6 ml / g. In some embodiments, the precipitated silica has a total pore volume of 2.51 ml / g.

[0035] In one embodiment, the precipitated silica has a particle size distribution D in the range of 14 to 21 μm. 50 In some embodiments, the precipitated silica has a particle size distribution D of 17.9 μm. 50 It has.

[0036] In one embodiment, the precipitated silica has a Sears number (V2) in the range of 19 to 25 ml / (5 g). In some embodiments, the precipitated silica has a Sears number (V2) of 22 ml / (5 g). In one embodiment, the precipitated silica has a silanol density relative to the total surface area of the silica, as measured by the ratio of the Sears number to the BET specific surface area, of 0.11 to 0.13 ml / 5 m. 2 In some embodiments, the ratio of the Sears number to the BET specific surface area is in the range of 0.12 mL / 5 m 2 In one embodiment, the precipitated silica has a silanol density relative to the external surface area of the silica, as measured by the ratio of the Sears number (V2) to the CTAB specific surface area, of 0.11 to 0.15 mL / 5 m 2 In some embodiments, the precipitated silica has a Sears number (V2) to CTAB specific surface area ratio of 0.13 mL / 5 m 2 is.

[0037] In one embodiment, the precipitated silica according to the present disclosure has a ratio of silanol group density to BET specific surface area of 12.24 to 16.24 OH number / nm 2 The range is.

[0038] In one embodiment, the precipitated silica has a particle size distribution D in the range of 14 to 21 μm. 50 In some embodiments, the precipitated silica has a particle size distribution D in the range of 14.9 to 20.9 μm. 50 In some embodiments, the precipitated silica has an average primary particle size of 17.9 μm.

[0039] In one embodiment, the precipitated silica has an average particle aggregate size in the range of 100 to 500 nm, hi some embodiments, the precipitated silica has an average particle aggregate size in the range of 200 to 400 nm.

[0040] In one embodiment, the precipitated silica has a pH value of 6 to 6.5 (5% in water).

[0041] Also described herein is a method for preparing the precipitated silica of the present disclosure, the method comprising: a) reacting an aqueous solution of metal silicate with a mineral acid in the presence of a surfactant solution comprising a C8-C20 sulfosuccinate blend at a reaction temperature in the range of about 75-90°C with stirring to obtain a reaction mixture having a pH of about 8-10; b) feeding an aqueous solution of metal silicate, a mineral acid, and a surfactant solution into the reaction mixture, aging the resulting reaction mixture at a temperature in the range of about 75-90°C for 10-30 minutes, and adjusting the pH of the reaction mixture to about 8-10; c) feeding an aqueous solution of metal silicate, a mineral acid, and a surfactant solution into the reaction mixture, and then aging the mixture at a temperature in the range of about 75-90°C for 5-10 minutes, and adjusting the pH of the reaction mixture to about 3.5-4; d) recovering the precipitated silica from the reaction mixture.

[0042] The inventors have found that the aforementioned surfactants, along with reaction parameters such as reactant concentration, pH, temperature, aging time, and number of reaction phases, act synergistically to control the physicochemical parameters of the precipitated silica of the present disclosure.

[0043] In one embodiment, the surfactant solution is prepared by adding a C8-C20 sulfosuccinate blend to water at ambient temperature. In one embodiment, the surfactant solution comprises the C8-C20 sulfosuccinate blend in an amount of 10-30 g / L. In an exemplary embodiment, a commercially available C8-C20 sulfosuccinate blend, such as Surfactant-OT85AE (manufactured by CYTEC), was used.

[0044] In one embodiment, the metal silicate is selected from the group consisting of alkali metal silicates, alkaline earth metal silicates, and mixtures thereof. In some embodiments, the metal silicate is sodium silicate. In one embodiment, the aqueous solution of the metal silicate is prepared by mixing the alkali metal silicate and / or alkaline earth metal silicate with water with stirring for 1 to 10 hours. In one embodiment, the metal silicate has a pH of 11 to 14. In some embodiments, the metal silicate has a pH of 12.5±0.5.

[0045] In one embodiment, the mineral acid is selected from the group consisting of sulfuric acid, hydrochloric acid, and nitric acid. In one embodiment, the mineral acid has a concentration (in water) of 90-100%.

[0046] In one embodiment, the reaction between the aqueous solution of the metal silicate and the mineral acid is carried out by separately adding the aqueous solution of the metal silicate, the mineral acid, and the surfactant solution to an aqueous medium heated to the reaction temperature. The aqueous solution of the metal silicate, the mineral acid, and the surfactant solution may be simultaneously charged into a reactor containing an aqueous medium and connected to a heater to carry out the reaction. In one embodiment, the aqueous medium consists solely of water.

[0047] In one embodiment, the aqueous solution of metal silicate, mineral acid, and surfactant solution are added in a ratio ranging from 10:1.5:0.5 to 15:2:1.5, hi some embodiments, the aqueous solution of metal silicate, mineral acid, and surfactant solution are added in a ratio of 13:1.7:1.

[0048] In one embodiment, the aqueous solution of metal silicate, mineral acid, and surfactant solution are added continuously, hi another embodiment, the addition may be stopped intermittently to allow for intermittent aging of the reaction mixture.

[0049] In one embodiment, in both steps (b) and (c), the aqueous solution of metal silicate, the mineral acid, and the surfactant solution are added simultaneously to the aqueous medium over a period of 30 minutes to 1 hour. The addition rates of the aqueous metal silicate solution and the mineral acid can be further adjusted to maintain a pH of 8 to 10.

[0050] In one embodiment, in both steps (b) and (c), after the reaction mixture reaches a pH of 8-10, it is aged at a temperature in the range of about 75-90° C. for 5-30 minutes.

[0051] In one embodiment, in step (c), after completion of the reaction, the pH of the reaction mixture is rapidly lowered to about pH 3.5 to 4 by the addition of a mineral acid. The pH of the reaction mixture is adjusted to about pH 3.5 to 4 by the addition of a mineral acid.

[0052] In one embodiment, the reaction mixture is aged for about 5-10 minutes at a pH of about 4. According to a related embodiment, aging is carried out at a temperature in the range of 75-90° C. while continuously stirring the reaction mixture.

[0053] In one embodiment, the precipitated silica obtained upon completion of the reaction is filtered and then washed. The washing is performed to remove by-products, such as sodium sulfate, resulting from the reaction. The precipitated silica thus obtained is then subjected to a drying step. The drying step can be performed by spray drying, spin flash drying, or vacuum tray drying. Alternatively, the wet cake can be dried for a short period of time, followed by the addition of a dispersing agent in a suitable solvent. The dispersion can then be dried to obtain the precipitated silica. In one embodiment, a dispersion of silica is prepared in a suitable solvent selected from the group consisting of butanol, butanone, toluene, and acetone, using a dispersing agent selected from the group consisting of metal salts of saturated and unsaturated fatty esters with long hydrocarbon chains / fatty acids.

[0054] (Example) The following examples are provided to describe and illustrate preferred embodiments of the present disclosure and are not intended to limit the scope of the disclosure as described.

[0055] Example 1: Exemplary Method for Preparing Precipitated Silica For silica synthesis, a sodium silicate solution with a solid content of approximately 30 wt% (NaO / SiO ratio = 1:3.2, silica weight percent = 23%, NaO weight percent = 7.0%) was used, with a pH value of 12.5 ± 0.5.

[0056] Five liters of concentrated sulfuric acid (percentage of sulfuric acid in the solution = 98%, specific gravity of the solution = 1.84) was slowly added to five liters of distilled water to prepare 10 liters of a 50% sulfuric acid solution.

[0057] To prepare the surfactant solution, 17.5 milliliters of C8-C20 sulfosuccinate blend surfactant was added to 600 milliliters of distilled water and stirred.

[0058] To synthesize precipitated silica, 34 liters of distilled water was added to a properly cleaned 70-liter jacketed reactor. The heater was set to 75-90°C, and the reactor agitator was set to a stirring speed of 200 rpm. First, 2 liters of 50% sulfuric acid, 11.7 liters of sodium silicate solution, and 600 milliliters of surfactant solution were placed in three separate beakers. Three metering pumps were calibrated: the first pump for acid, the second pump for sodium silicate, and the third pump for surfactant solution. The pump addition rates were set as follows: pump 1 for sulfuric acid addition: 17 milliliters / min; pump 2 for sodium silicate solution: 130 milliliters / min; and pump 3 for surfactant solution: 10 milliliters / min. Once the reactor temperature reached approximately 75-90°C, the required amount of sodium silicate was added to the reactor, and the pH of the solution in the reaction chamber was confirmed. At this point, the pH of the reaction mixture was confirmed to be between 8 and 10. Furthermore, the reaction was carried out in two stages.

[0059] In the first stage, the metering pumps for sulfuric acid, sodium silicate, and surfactant were operated at addition rates of 17 ml / min, 130 ml / min, and 10 ml / min, respectively. The reaction mixture was stirred at 200 rpm at a temperature of 75-90°C. After 30 minutes, the addition of the surfactant solution was stopped, and the addition of sulfuric acid and sodium silicate was continued for another 15 minutes. Then, while continuing stirring at 200 rpm at a reactor temperature of 75-90°C, the addition of all reactants was stopped. The reaction mixture was then aged for 20 minutes. The pH of the solution in the reaction chamber was checked. At this point, the pH of the reaction mixture was confirmed to be between 8 and 10.

[0060] In the second stage, the addition of sulfuric acid, sodium silicate, and surfactant was initiated at rates of 17 mL / min, 130 mL / min, and 10 mL / min with stirring at 75-90°C for 45 minutes. Thirty minutes after the addition, the addition of the surfactant solution was stopped. The pH of the solution in the reaction chamber was checked. The pH of the reaction mixture was confirmed to be between 8 and 10. After 45 minutes, the addition of sulfuric acid, sodium silicate, and water was stopped. The reaction mixture was aged for an additional 5 minutes with stirring at 75-90°C. After the 5-minute aging period, 50% sulfuric acid was added to the reaction mixture at 100 mL / min. The pH of the reaction mixture was monitored until it reached 3.5-4.0. After adjusting the pH, the addition of sulfuric acid was stopped. The reaction mixture was aged for 5 minutes with continuous stirring at 75-90°C.

[0061] After the reaction was completed, the precipitated slurry was recovered from the reactor. The precipitate was centrifuged, and the cake was thoroughly washed with distilled water to remove sodium sulfate. Washing was continued until the conductivity of the washings was less than 1000 μS / cm. The solids content of the wet cake thus obtained was determined to be 15–20%. The washed silica cake was homogenized to obtain a silica slurry with a total silica content of 10–15%. The pH of the slurry was maintained between 5.5 and 6.5 by adding sulfuric acid or ammonia. The resulting slurry was spray-dried to obtain a powder. The moisture content of the spray-dried silica was 3–6%. After synthesis, detailed characterization of the synthesized precipitated silica was performed.

[0062] After synthesis, the synthesized precipitated silica was subjected to detailed characterization. The properties of the precipitated silica are summarized in Table 1.

[0063] Table 1: Properties of exemplary precipitated silicas JPEG2025526863000001.jpg170170

[0064] Example 2: Comparison of Exemplary Precipitated Silicas with Commercially Available Precipitated Silicas Precipitated silica prepared according to embodiments of the present disclosure was compared with a commercially available precipitated silica, Ultrasil 7000GR (Evonik). Table 2 shows the properties of Ultrasil 7000GR.

[0065] Table 2: Properties of Ultrasil 7000GR JPEG2025526863000002.jpg169170

[0066] Two curable elastomer compositions were prepared: COMP and INV1. COMP consisted of a curable elastomer composition containing Ultrasil 7000GR, while INV1 consisted of a curable elastomer composition containing the precipitated silica prepared in Example 1. Table 3 shows the compositions of the two elastomer compositions.

[0067] Table 3: Composition of INV1 and COMP JPEG2025526863000003.jpg209170*All quantities are in PHR (Parts Per Hundred Rubber).

[0068] The above ingredients were mixed in a 1.6 L mixer (Bainite, Model MB Series 1.6 L IMRES-O-LAB) at a 74% fill rate. Mixing began at a temperature of 50-55°C, and the damping temperature was maintained at 155±2°C with a RAM pressure of 20 kg. For the first 6 minutes, the polymer was mixed at a speed of 40-60 rpm along with silica, coupling agent, carbon black, process oil, stearic acid, and wax. Next, 6PPD, TDQ, and ZnO were added, and the mixture was mixed for another 3-4 minutes to a damping temperature of 155±2°C. The rotation speed was varied between 50-70 rpm during this process to achieve the damping temperature. The mixing procedure is summarized in Table 4 below.

[0069] Table 4: Mixing Procedure for Rubber Compounds JPEG2025526863000004.jpg58170

[0070] Final compacted compound batches were prepared at room temperature on an open two-roll mill, Lab mill (12 x 16"), with a friction ratio of 1:1.25. Accelerator and curative additions were performed while maintaining a nip gap of approximately 1 mm for 4 to 6 minutes. Final sheets were removed from a nip gap of approximately 3.8 mm for all compounds. All compounds were conditioned at room temperature for 24 hours before characterization.

[0071] The properties of the rubber compounds were investigated and are summarized in Table 5 below.

[0072] Table 5: Properties of unvulcanized rubber compounds JPEG2025526863000005.jpg78170 Observations: Improved rubber compound processability (indicated by lower Mooney viscosity) and reduced filler-filler interaction in the rubber matrix (indicated by lower Payne effect) were observed with INV1. INV1 also showed better scorch safety at 160°C and 125°C compared to COMP.

[0073] To test the properties of the vulcanized rubber compounds, rubber slabs and other samples were cured at 160°C according to the cure times shown in Table 6 below.

[0074] Table 6: Curing times for INV1 and COMP JPEG2025526863000006.jpg22170

[0075] All molded samples were found to be free of visible defects. The molded samples were preconditioned at room temperature before being tested for mechanical properties. The test results are summarized in Tables 7, 8, 9, and 10 below.

[0076] Table 7: Elastic modulus at various strains before and after aging (80°C in an air oven for 7 days) JPEG2025526863000007.jpg81170

[0077] Table 8: Tensile strength, elongation, tear strength, and hardness before and after aging (80°C in an air oven for 7 days) JPEG2025526863000008.jpg101170Observation: Cured INV1 showed significantly improved physical properties such as tensile strength and elongation compared to cured COMP both before and after aging.

[0078] Table 9: Abrasion resistance index, crack initiation and crack propagation, specific gravity JPEG2025526863000009.jpg73170 Observation: Hardened INV1 showed significant improvement in crack initiation and crack propagation compared to hardened COMP.

[0079] Table 10: Dynamic mechanical analysis JPEG2025526863000010.jpg39170 Observation: Cured INV1 showed improved wet grip / traction compared to cured COMP. [Industrial Applicability]

[0080] The precipitated silica according to the present disclosure finds use as a reinforcing filler in vulcanizable or vulcanized elastomeric compositions. The vulcanized elastomeric compositions can be used in the manufacture of tires and other rubber products. Any conventional process can be used to form vulcanizable or vulcanized elastomeric compositions using the silica according to the present disclosure as a reinforcing filler.

[0081] The precipitated silicas according to the present disclosure have specific physicochemical properties. When used as fillers in elastomer compositions, the precipitated silicas according to the present disclosure exhibit superior rheological, mechanical, and dynamic properties compared to prior known silica-reinforced elastomer compositions. They also exhibit improved dispersibility in elastomer compositions compared to known precipitated silicas.

[0082] The precipitated silica of the present disclosure can reduce the number of mixing steps required in elastomeric compositions.

Claims

1. 165-195m ２ / g BET specific surface area, 160-180m ２ / g CTAB specific surface area, 14-21% vicinal silanol content, 2-4% geminal silanol content, Total infiltration of 2-4 mL / g; a pore volume ratio (V2 / V1) of 0.45 to 0.7, and 52 to 70 m ２ / g of total pore area.

2. 2. The precipitated silica of claim 1, having a DOA absorption value in the range of 240 to 310 ml / 100 g.

3. 19-25ml (5g) Sears number (V ２ 2. The precipitated silica of claim 1, wherein

4. The ratio of Sears number to BET specific surface area is 0.11 to 0.13 mL / 5 m ２ 2. The precipitated silica of claim 1, wherein

5. The ratio of Sears number to CTAB specific surface area is 0.11 to 0.15 mL / 5 m ２ 2. The precipitated silica of claim 1, wherein

6. The ratio of silanol group density to BET specific surface area is 12.24 to 16.24 OH number / nm ２ 2. The precipitated silica of claim 1, wherein

7. 2. The precipitated silica of claim 1 having a siloxane group content of 74 to 85%.

8. 2. The precipitated silica of claim 1, having a total pore volume of from 1.50 to 3.6 ml / g.

9. Particle size distribution D in the range of 14 to 21 μm ５０ 2. The precipitated silica of claim 1, wherein

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