JP2000302912A - Hydrous silicic acid for rubber reinforcement filling and rubber composition using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrated silica capable of improving the tensile strength and abrasion resistance of rubber, a rubber composition having improved tensile strength and abrasion resistance, and a tensile strength and abrasion resistance. To provide a pneumatic tire using a rubber composition having improved properties. SOLUTION: It is a silicic acid having a BET specific surface area (m ² / g) in a range of 120 to 220, and a Sears titration V (NaOH titration ml /
g) and the BET specific surface area BET (m ² / g): V = (1.5 / 10
0) The C value in × BET + C is in the range of 4.0 to 5.5, and
A hydrous silicic acid for rubber reinforcing filling, wherein the ratio A / B between the peak value A (angstrom) of the pore diameter measured by the N ₂ method and the peak value B (angstrom) of the pore diameter measured by the mercury method is 1.4 or more. A rubber composition comprising 5 to 100 parts by weight of the above hydrated silicic acid with respect to 100 parts by weight of natural rubber and / or diene synthetic rubber. A pneumatic tire using this rubber composition for tread rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to silicic acid for filling rubber reinforcement. In particular, the present invention relates to hydrated silicic acid for rubber reinforcing filling capable of improving the tensile strength and wear resistance of vulcanized rubber, a rubber composition using the hydrated silicic acid, and a pneumatic tire using the rubber composition.

[0002]

2. Description of the Related Art Conventionally, carbon black has been frequently used as a filler for reinforcing rubber in tires. However, with the improvement of rubber technology, hydrated silica, which is a white filler among inorganic fillers, has been reviewed because it can be freely colored, and has been used in elastic rubber mixtures for tires. Hydrous silicic acid is excellent in heat aging resistance, tear resistance, flex crack resistance, adhesiveness, etc. of the vulcanized rubber. On the other hand, at the time of high filling compounding, the viscosity of the compound is high and processability is inferior, and among general rubber properties, tensile strength and abrasion resistance are inferior to carbon black. In order to solve these disadvantages, a combination use of a silane coupling agent and other organic compounds has been performed. However, hydrous silicic acid which can provide satisfactory rubber properties has not yet been obtained, and further improvement of hydrous silicic acid is strongly desired along with research on rubber compounding formulations.

[0003]

In recent years, rubber has been diversified in the field of rubber, and environmental pollution has been taken up as a global problem. Particularly in the automobile tire sector, the necessity of energy saving by reducing rolling resistance has been advocated, and accordingly, improvement in tire performance has been strongly demanded. In recent trends, it has been reconsidered that hydrated silica is advantageous as a reinforcing filler in tire formulations pursuing energy saving, and research in that direction is being actively pursued.
However, in these propulsion, improvement of tensile strength and abrasion resistance, which are the drawbacks of the above-mentioned hydrated silica, is a major problem. Then, an object of the present invention is to provide hydrated silica capable of improving the tensile strength and abrasion resistance of rubber. It is a further object of the present invention to provide a rubber composition having improved tensile strength and abrasion resistance and a pneumatic tire using the rubber composition having improved tensile strength and abrasion resistance. .

[0004]

SUMMARY OF THE INVENTION The present invention relates to a silicic acid having a BET specific surface area (m ² / g) in the range of 120 to 220, comprising a Sears titration V (NaOH titration ml / g) and a BET Normal specific surface area BET (m ² / g)
And the C value at V = (1.5 / 100) × BET + C is 4.
In the range of 0 to 5.5, and the peak value A (angstrom) of pore diameter measured by N ₂ method and the peak value of pore diameter measured by mercury method B (Å) ratio A / B of 1.4 or more Hydrated silica for rubber reinforcement filling. Furthermore, the present invention relates to a rubber composition obtained by blending 5 to 100 parts by weight of the hydrous silicate of the present invention with 100 parts by weight of natural rubber and / or a diene-based synthetic rubber. In addition, the present invention relates to a pneumatic tire using the rubber composition of the present invention for a tread rubber.

[0005] The mechanism of rubber reinforcement is considered to be the dispersion function and structure of hydrated silica as a filler. The dispersing function depends on the specific surface area of the filler, the bonding strength between particles, or the so-called structural properties such as the number of surface silanol groups, pore volume, particle diameter, and three-dimensional structure called structure. In general, carbon black has a well-developed structure, has various types of functional groups on the particle surface, has a strong bond with polymer molecules, and has been widely used as a rubber reinforcing agent to date.

On the other hand, hydrous silicic acid has a surface silanol group (Si
—OH) presents a reinforcing effect, but has the disadvantage of inhibiting dispersion and reducing the effect of the drug. As described above, the hydrous silicic acid has only siloxane groups and silanol groups on the particle surface and does not have the same functional group as carbon black, so that the reactivity with the polymer is weak and the rubber reinforcing performance is relatively low. . On the other hand, the use of a silane coupling agent or the like has been used to enhance the reinforcing effect, but this alone is insufficient as silica for tires.

Therefore, the physical properties of hydrated silica are improved by changing the primary particle diameter (2700 / BET = primary particle diameter nm) calculated from the BET surface area, the density of surface silanol groups, the particle cohesion and the structure of the particles. It is possible. In particular, the structure of the hydrous silicic acid is important for improving the wear resistance, and the strong entanglement between the hydrous silicic acid and the polymer is important together with the chemical bonding with the polymer molecules. In order for the hydrated silica and the polymer to be strongly entangled with each other, the hydrated silica must have a primary particle size and a particle structure that easily enters the rubber,
It is considered that the reinforcing effect can be enhanced by compensating for the bond between the hydrated silica and the rubber molecules. From such a viewpoint, the present inventor has conducted intensive studies, and as a result, has demonstrated that an excellent reinforcing effect is obtained in the above-mentioned hydrous silicate in the specified range, thereby improving the tensile strength and wear resistance of rubber. The present invention has been completed.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in more detail. The hydrous silicic acid of the present invention is a silicic acid having a BET specific surface area (m ² / g) in the range of 120 to 220. BET specific surface area is 120m ² /
If it is less than g, the rubber reinforcing effect is inferior, and the abrasion resistance and tensile strength decrease. On the other hand, when it exceeds 220 m ² / g, the vulcanization delay phenomenon is liable to occur, the cohesive force of the hydrous silicic acid is too strong, causing poor dispersion, poor workability and poor wear resistance in some cases. In particular, the BET specific surface area is preferably in the range of 140 to 180 m ² / g from the viewpoint that the effect of improving wear resistance is excellent. Furthermore, as a result of various investigations on the particle structure such as surface silanol group density and pore distribution, hydrated silica having a Sears titer V and a ratio A / B in the following ranges is particularly improved in tensile strength and wear resistance. It has been found.

The hydrated silica of the present invention has a Sears titration V (Na
OH titer ml / g) and relationship between the BET specific surface area ^{BET (m 2 / g) V} =
The C value at (1.5 / 100) × BET + C is in the range of 4.0 to 5.5. When the BET specific surface area is in the above range, no improvement in abrasion resistance or the like is observed even when the V value as the Sears titer is too small or too large, and when the C value is in the range of 4.0 to 5.5. Only the effect of improving excellent wear resistance can be obtained. When the C value is less than 4.0, the number of surface silanol groups becomes too small, so that the rubber reinforcing effect is reduced, and the abrasion resistance tends to be reduced. On the other hand, when the C value exceeds 5.5, the surface silanol groups become too large, and self-aggregation of silica tends to occur, which tends to inhibit dispersion and reduce the effect of a drug (such as a vulcanization accelerator), which is not preferable. For example, an existing commercially available nip seal E-200A (Comparative Example 3 described later)
C and the nip seal NS-T (Comparative Example 2 described later) have a small C value of 2.5 to 2.7, and have insufficient wear resistance. The C value is preferably in the range of 4.4 to 5.0.

The hydrated silica of the present invention further comprises N_TwoMethod
Peak diameter A (angstrom) and the mercury method
Measured pore diameter peak value B (angstrom)
The ratio A / B is 1.4 or more. By the ratio A / B being 1.4 or more,
The tensile strength and wear resistance are particularly improved. The ratio A / B is
Preferably it is 2.5 or less. Generally, pores of hydrous silica
The arc position is compared with the value measured by the mercury intrusion method, _Two
The value measured by the adsorption method tends to be larger.
You. In the mercury intrusion method, this is
Crushing of the hydrated silicate particles, leaving micropores
This causes a difference in apparent pore peak position. Reverse
On the other hand, those which are susceptible to crushing are the structural strength of hydrated silicate particles.
It is expected to disperse well in rubber with a low degree. However
And a hydrated silica having a BET specific surface area larger than the above range.
This tendency is also observed for acids. However, BET ratio table
If the area is too high, the cohesiveness of the particles becomes strong, and the particles are dispersed.
It is not preferable because it causes defects and the like. From this point of view,
The ratio A / B of light hydrated silica is 1.4 or more. A / B ratio
If it is less than 1.4, the particle structure of the hydrated silica becomes too strong,
During the mercury injection by the silver method, the destruction of secondary particles
Less, difficult to disperse even in rubber, rubber reinforcing effect
Fruits also decrease.

It is known that the wet process for producing hydrous silicic acid is generally carried out by reacting an aqueous solution of an alkali metal silicate with a mineral acid. The method for producing hydrous silicic acid of the present invention is also basically based on this method. The hydrous silicic acid of the present invention is, for example, a method in which an alkali metal silicate and a mineral acid are added to a reaction vessel in parallel, and the temperature of the reaction solution is adjusted to 90.
C. or more, preferably 96 ° C. or more, and adjusting the addition amount of the alkali silicate and the mineral acid so that the alkali concentration of the reaction solution becomes excessive in the range of 0.01 to 0.03 mol / L, It can be produced by a method in which the reaction is carried out until the solid concentration in the reaction solution is in the range of 40 to 65 g / liter.

In the above reaction, the alkali metal silicate is not particularly limited. For example, an aqueous solution of sodium silicate can be used. The mineral acid is not particularly limited, but sulfuric acid is preferred. The reaction temperature has a correlation with the BET specific surface area of the obtained hydrous silicate, and the higher the reaction temperature, the faster the primary particles grow and the lower the BET specific surface area. When the reaction temperature is lower than 90 ° C., the growth of the sol is slow, and it is difficult to obtain a hydrous silicic acid having good dispersibility in the rubber, which is the object of the present invention. Thus, hydrous silicic acid having good dispersibility can be obtained.

The excess concentration of the alkali is 0.01 mol.
If the amount is less than 1 / liter, it is difficult to maintain the entire reaction solution in an alkaline region, the reaction solution is likely to be partially in an acidic region, and it is difficult to obtain hydrous silicic acid having stable physical properties. When the excess concentration of the alkali is 0.03
If it exceeds mol / liter, the specific surface area of the BET method becomes too high, and the C value in the relational expression between the Sears titer and the BET exceeds 5.5. It is difficult to obtain silicic acid. In addition, in the above reaction, if the solid concentration in the reaction solution is less than 40 g / liter at the end of the dropwise addition of the alkali silicate and the mineral acid,
In some cases, the obtained hydrous silicic acid has a BET specific surface area exceeding 220 m ² / g. Furthermore, the obtained hydrous silicate is
The cohesive force is strong, and poor dispersion is likely to occur. If the solid concentration at the end of the reaction exceeds 65 g / l, the resulting hydrous silicic acid tends to have a BET specific surface area of less than 120 m ² / g, and at the same time the reinforcing effect of rubber is reduced. Absent.

In the above reaction, for example, a predetermined amount of water and a Na ₂ O concentration of 0.01 to 0.03 are added to a reaction vessel equipped with a stirring blade.
The reaction can be carried out by filling an aqueous solution of an alkali metal silicate so as to have a mol / liter, and simultaneously dropping the aqueous solution of an alkali metal silicate and a mineral acid while maintaining a predetermined reaction solution temperature with stirring. During the course of the reaction, a gelation phenomenon occurs in which the reaction solution becomes cloudy and the viscosity sharply increases. When the solid concentration of the reaction solution reaches a predetermined value, p
The reaction is stopped by adding a mineral acid so that H is 5 or less. The precipitated silicic acid of the present invention can be obtained by filtering, washing, drying and, if necessary, pulverizing or granulating the obtained precipitate. Specifically, the obtained precipitate is filtered with a filter press or the like, and washed with water until the pH becomes 5.5 to 7.5 and the electric conductivity becomes 200 μs / cm or less, to obtain a hydrated silica cake. After drying the obtained wet cake, if necessary, pulverization classification or granulation can be performed to obtain the hydrous silicic acid of the present invention.

In the rubber composition of the present invention, natural rubber (NR) or diene-based synthetic rubber can be used alone or as a blend of these rubbers. Examples of the synthetic rubber include synthetic polyisoprene rubber (IR),
Polybutadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NB
R), butyl rubber (IIR) and the like. The hydrous silicic acid of the present invention can be blended in an amount of 5 to 100 parts by weight with respect to 100 parts by weight of natural rubber and / or a diene-based synthetic rubber. If the amount of the hydrous silicic acid is less than 5 parts by weight, the reinforcing property and wear resistance become insufficient. In addition, the dispersion of hydrated silicic acid containing more than 100 parts by weight of hydrated silicic acid tends to be inferior, and the reinforcing property and abrasion resistance deteriorate. The compounding amount of the hydrous silicic acid of the present invention is preferably in the range of 10 to 90 parts by weight based on 100 parts by weight of natural rubber and / or diene-based synthetic rubber.

The silane coupling agent used in the present invention is
At least one of the following formulas (I) to (III) is exemplified.

## STR1 ## _{(C n H 2n + 1 O} ) m X 3-m Si- (CH 2) p -S q - (CH 2) p -Si (C n H 2n + 1 O) m X 3-m ... (I) (wherein, X is an alkyl group having 1 to 3 carbon atoms or a chlorine atom,
n is an integer of 1 to 3, m is an integer of 1 to 3, p is an integer of 1 to 9, and q is an integer of 1 or more and may have a distribution.)

_{Embedded image} (C _n H _{2n + 1} O) _m X _3-m Si— (CH ₂ ) _p —Y (II) (wherein X is an alkyl group having 1 to 3 carbon atoms or a chlorine atom;
Y is a mercapto group, vinyl group, amino group, imide group, glycidoxy group, methacryloxy group or epoxy group, n
Represents an integer of 1 to 3, m represents an integer of 1 to 3, and p represents an integer of 1 to 9. )

## STR3 ## _{(C n H 2n + 1 O} ) m X 3-m Si- (CH 2) p -S q -Z ... (III) ( wherein, X is 1 to 3 carbon atoms alkyl group or a chlorine atom,
Z is a benzothiazolyl group, N, N-dimethylthiocarbamoyl group or methacrylate group, n is an integer of 1 to 3,
m represents an integer of 1 to 3, p represents an integer of 1 to 9, and q may be an integer of 1 or more and has a distribution. )

Specifically, bis (3-triethoxysilylpropyl) polysulfide, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-aminopropyltrimethoxysilane,
γ-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, 3-trimethoxysilylpropyl-N, N- Examples include dimethylcarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazolyltetrasulfide, and 3-trimethoxysilylpropyl methacrylate monosulfide.
The compounding amount of the silane coupling agent is 1 to 20% by weight, preferably 2 to 15% by weight, based on the weight of the hydrous silicic acid. If the amount of the silane coupling agent is less than 1% by weight, the coupling effect is small.
Both the reinforcing property and the abrasion resistance are deteriorated, which is not preferable.

In the present invention, in addition to the rubber, hydrous silicic acid, and silane coupling agent, carbon black, a softener (wax, oil), if necessary,
Compounding agents usually used in the rubber industry, such as an antioxidant, a vulcanizing agent, a vulcanization accelerator, and a vulcanization accelerator, can be appropriately compounded. The rubber composition of the present invention can be prepared by kneading the rubber component, hydrated silicic acid, a silane coupling agent, the above-described carbon black, a rubber compounding agent, and the like, as necessary, with a kneader such as a Banbury mixer.

The rubber composition of the present invention can be suitably applied to rubber products such as tires, conveyor belts and hoses, and the resulting rubber products such as tires, conveyor belts and hoses have reinforcing properties and high durability. It is excellent in abrasion property and the like. In addition, since the pneumatic tire of the present invention uses the rubber composition for a tire tread portion, a pneumatic tire having excellent tire tread portion reinforcement and high abrasion resistance can be obtained. .

[0020]

According to the present invention, a water-containing rubber for filling rubber reinforcement has improved dispersibility in rubber, excellent workability and reinforcement, and excellent properties of vulcanized rubber in tensile strength and abrasion resistance. Silicic acid can be provided. Further, according to the present invention, it is possible to provide a rubber composition and a tire excellent in tensile strength and wear resistance.

[0021]

EXAMPLES Hereinafter, the hydrous silicic acid of the present invention and the method for producing the same will be described more specifically with reference to examples and comparative examples. The method for measuring the physical properties of hydrous silicic acid and the method for testing the physical properties of rubber are shown below. Measurement of BET specific surface area The BET specific surface area conforms to JIS Z-8830 (a method for measuring the specific surface area of powder by gas adsorption), and a fully automatic powder specific surface area measuring device AMS-8000 (manufactured by Okura Riken Co., Ltd.) Was measured by a one-point method. The sample is approximately 0.
05 g was pretreated at 200 ° C. for 30 minutes and measured.
Unit = m ² / g Sears titration (NaOH titration; ml / g) According to the W Sears method. (ANALYICAL CH
EMISTRY VOLUME28, No12, DEC
EMBER, The method according page 1956,1981～83) with N ₂ method peak pore diameter ASAP2400 [manufactured by Shimadzu Corporation], the amorphous silica 200 ° C., under the following conditions 100 millitorr, was degassed for 2 hours, The adsorption and desorption isotherms of nitrogen were measured, and the results were measured using the Barrett-Joyner-Halenda method, J. Am. Chem. Soc., 73, 37.
3 (1951), the peak pore diameter was determined. Mercury Pore Volume Using a mercury porosimeter 2000 (manufactured by Carlo Erba, Italy), the pore volume was measured by a mercury intrusion method. Pressure 1
~ Up to 2000 bar, pore diameter 15μm ~
The mercury intrusion at 74 ° was measured, and the peak position of the pore diameter was determined. Mooney Viscosity Using a Mooney Viscometer SMV-200 (manufactured by Shimadzu Corporation), the value was read at 125 ° C. for 5 minutes using an L-type rotor. Others are based on the Mooney viscosity test method of JIS K6300. Curast time T90 The optimal vulcanization time (T90) was measured by a JSR type curast meter IIF [manufactured by Nichigo Corporation]. T9
In the case of 0, the vulcanization curve obtained at the measurement temperature of 150 ° C. was divided into 10 equal parts, and 90% thereof was shown as a numerical value. Vulcanizate properties General vulcanizate properties Measured according to the rubber physical properties test method of the former JIS K6301. Abrasion test was measured with an Akron abrasion tester. Tilt: 15 °, Load: 6 pounds, Test frequency: 2000r
The loss in abrasion in pm was measured, and the result was indicated by an index with Comparative Example 1 being 100. (The higher the numerical value, the better the abrasion resistance.) Mixing and Preparation Method 11 with Banbury mixer (1.7 liter capacity)
After kneading 0 parts of JSR1712 and 20 parts of BR01 for 30 seconds, 2 parts of stearic acid and 1 part of paraffin wax are mixed.
Parts, 20 parts of aroma oil, 80 parts of precipitated silicic acid of Example or Comparative Example, and 8 parts of silane Si69 at a ratio of 5 minutes. The compound temperature at the time of removal is adjusted by the ram pressure and the number of revolutions so as to be 140 to 150 ° C. After cooling the compound at room temperature, 1 part of anti-aging agent 810NA, 4 parts of zinc white, vulcanization accelerator D
1.5 parts of Noxeller DP (diphenylguanidine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. Amide) and 1.75 parts of sulfur as a vulcanizing agent were added and kneaded for about 1 minute (the temperature at the time of removal was set to 110 ° C. or less). The sulphate and vulcanizate properties were measured and the results are shown in Table 1.

[0022] (Example 1) In a stainless steel 200 liters reaction vessel equipped with a stirrer, water 85 liters and an aqueous solution of sodium silicate (SiO ₂ 160 g / l, SiO ₂ /
Na ₂ O weight ratio 3.3) 2.3 liters, 96 ° C
Heated. At this time, the solution pH was 10.4, the Na ₂ O concentration was 0.02 mol / L, and the silica concentration was 5.5 g.
/ Liter. While maintaining the temperature of the aqueous solution at 96 ° C, the sodium silicate aqueous solution (above concentration) flow rate 70
0 ml / min and a flow rate of sulfuric acid (18 mol / l) of 25 ml / min were simultaneously started, and the flow rates were adjusted so that the Na ₂ O concentration in the reaction solution was maintained at 0.015 to 0.025 mol / l. Perform the reaction. During the course of the reaction, the reaction solution became cloudy and the viscosity increased at 35 minutes to become a gel-like solution. The addition was continued and the reaction was stopped in 60 minutes. At this time, the silica concentration in the solution was 54 g / liter. Subsequently, the same sulfuric acid as above was added, and the acidification was completed at a solution pH of 3 to obtain a silicic acid slurry. The obtained silicic acid slurry was filtered with a filter press and washed with water to obtain a wet cake. Next, the wet cake was formed into a slurry using an emulsifying apparatus and dried with a spray drier to obtain wet-process hydrous silicic acid.

Example 2 Using the same apparatus and raw materials as in Example 1, 85 liters of water and 2.3 liters of an aqueous solution of sodium silicate were added and heated to 98 ° C. while maintaining the temperature of the aqueous solution. An aqueous solution flow rate of 700 ml / min and a sulfuric acid flow rate of 25 ml / min were simultaneously added, and the Na ₂ O concentration in the reaction solution was adjusted to 0.015 to 0.05.
The reaction is performed while adjusting the flow rate so as to maintain 25 mol / liter. During the course of the reaction, the reaction solution became cloudy and the viscosity increased at 33 minutes to become a gel-like solution. The addition was continued and the reaction was stopped for 60 minutes. At this time, the silica concentration in the solution was 52 g / liter. Subsequently, the same sulfuric acid as above was added, and the acidification was completed at a solution pH of 3 to obtain a silicic acid slurry. Thereafter, wet hydrated silica was obtained in the same manner as in Example 1.

Example 3 Using the same apparatus and raw materials as in Example 1, 105 liters of water and 1.4 liters of an aqueous solution of sodium silicate were charged, and heated to 98 ° C. At this time, the solution pH was 9.8, the Na ₂ O concentration was 0.01 mol / L, and the silica concentration was 2.0 g / L. While maintaining the temperature of the aqueous solution at 98 ° C., the addition of a sodium silicate aqueous solution at a flow rate of 148 ml / min and a sulfuric acid flow rate of 59.5 ml / min was simultaneously started, and Na in the reaction solution was started.
Simultaneous dropping reaction was performed while maintaining the ₂ O concentration at 0.01 to 0.015 mol / L. The reaction solution became cloudy from the middle of the reaction, and the solution viscosity increased at 22 minutes to become a gel-like solution. The addition was continued, and the reaction was stopped in 50 minutes. At this time, the silica concentration in the solution was 58 g / liter. Subsequently, sulfuric acid was added to terminate the acidification at a solution pH of 3 to obtain a silicic acid slurry. Thereafter, wet method hydrous silicic acid was obtained in the same manner as in Example 1.

(Comparative Example 1) Nipsil AQ (Nippon Silica Industry Co., Ltd.) (Comparative Example 2) Nipsil NST (Nippon Silica Industry Co., Ltd.) (Comparative Example 3) Nipsil E-200A (Nippon Silica Industry Co., Ltd.) (Comparative Example) 4) Nipsil HD-R (manufactured by Nippon Silica Industry Co., Ltd.) (Comparative Example 5) Ultrasil VN3 (manufactured by Degussa, Germany)

[0026]

[Table 1]

Claims (7)

[Claims] 1. A BET specific surface area (m ² / g) is a silicate in the range of 120 to 220, Sears titration V (NaOH titer ml /
g) and the BET specific surface area BET (m ² / g): V = (1.5 / 10
0) The C value in × BET + C is in the range of 4.0 to 5.5, and
A hydrous silicic acid for rubber reinforcing filling, wherein the ratio A / B between the peak value A (angstrom) of the pore diameter measured by the N ₂ method and the peak value B (angstrom) of the pore diameter measured by the mercury method is 1.4 or more. 2. The hydrous silicic acid according to claim 1, wherein the BET specific surface area (m ² / g) is in the range of 140 to 180. 3. The hydrous silicic acid according to claim 1, wherein the C value is in the range of 4.4 to 5.0. 4. The hydrous silicic acid according to claim 1, wherein the ratio A / B is 2.5 or less. 5. Natural rubber and / or diene synthetic rubber 1
A rubber composition comprising 5 to 100 parts by weight of the hydrous silicic acid according to any one of claims 1 to 4 based on 00 parts by weight. 6. A silane coupling agent comprising a hydrated silicic acid
The rubber composition according to claim 5, which is blended at a ratio of 1 to 20% by weight based on 100 parts by weight. 7. A pneumatic tire using the rubber composition according to claim 5 for a tread rubber.