JPH11236208A - Hydrous silica for rubber reinforcement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain wet process hydrous silica capable of improving the breaking strength and wear resistance of rubber and not deteriorating the processability of rubber when added to the rubber. SOLUTION: The hydrous silica has 250-400 m<2> /g N2 method specific surface area (A), 200-300 m<2> /g Hg method specific surface area (B) and 1.7-2.5 ml/g N2 method pore volume (C), satisfies the relation of A×C/B>=2.3 and preferably has <=2.5 ml/g Hg method pare volume. The ratio of the N2 method specific surface area of the silica to the CTAB method specific surface area is preferably >=1.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel wet hydrated silicic acid. More specifically, the present invention relates to a wet-process hydrous silicate which is useful as a rubber reinforcing filler having improved rubber breaking characteristics and abrasion resistance. The hydrous silicic acid of the present invention is useful for reinforcing all rubber industrial products such as automobile tires, footwear and belts.

[0002]

2. Description of the Related Art Conventionally, carbon black has been frequently used as a filler for reinforcing rubber, particularly for tires. In addition, hydrated silicic acid is widely used as a rubber reinforcing filler along with carbon black. Furthermore, in recent years, development for further improving the performance of tires has been promoted worldwide, and the characteristics of hydrated silica have been reviewed accordingly, and the use amount has been increased due to its advantages, and further improvements have been made. Attempted. However, satisfactory properties have not yet been obtained.

[0003]

In the rubber field, particularly in the field of automobile tires, tires having higher performance are being developed. For example, by increasing the performance of tires, improving steering stability, etc., and reducing the rolling resistance, energy saving has been attempted, and products with such functions have actually been marketed. It is getting. These high performance tires are required to have higher breaking strength and wear resistance than conventional products. As a result, hydrated silica, which is a reinforcing filler for tires, is required to have unprecedented and higher performance, that is, performance capable of improving the breaking strength and abrasion resistance of rubber. It has become so.

It is well known that the rubber reinforcing function is affected by the specific surface area and the pore volume of hydrated silica as a filler. Usually, the larger the specific surface area and the pore volume, the better the reinforcing property. What is generally known as rubber reinforcing silica has an N2 specific surface area of 140 to
In the range of 220 m ² / g, but is also known for the 220 m ² / g or more precipitated silica from the viewpoint of obtaining a higher reinforcing properties. However, the N2 specific surface area is 2
When it is 20 m ² / g or more, the cohesive force of the hydrated silicic acid is too strong, causing poor dispersion, resulting in reduced workability and, on the contrary, reduced reinforcement. It has also been proposed to compensate for the reduction in workability due to poor dispersion with a chemical such as a silane coupling agent. However, there is a limit to improvement in physical properties by a silane coupling agent or the like.

Accordingly, an object of the present invention is to provide wet-process hydrous silicic acid which can improve the breaking strength and abrasion resistance of rubber and does not reduce the processability when compounding the rubber. is there.

[0006]

According to the present invention, the specific surface area (A) of the N2 method is in the range of 250 to 400 m ² / g, and Hg
The method specific surface area (B) is in the range of 200 to 300 m ² / g, the N2 method pore volume (C) is in the range of 1.7 to 2.5 ml / g, and A × C / B is 2. The present invention relates to wet hydrated silicic acid having 3 or more.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in more detail. Numerous studies have been made on the rubber reinforcing mechanism of hydrous silicate. Among them, the present inventors have repeated various studies paying attention to the correlation between the primary particle diameter (surface area) of hydrated silicic acid which seems to be particularly involved in rubber reinforcement and its pore volume.

In general, the reinforcing property of rubber is usually related to the specific surface area by the N2 method, and the reinforcing performance tends to increase as the surface area increases. However, hydrous silicic acid has a silanol group (Si-OH) on the surface, and if the surface area is too large, cohesive strength is increased, poor dispersion tends to occur, and reinforcing properties tend to be reduced. Regarding the pore volume, the larger the pore size, the richer the structure and the reinforcing effect, but on the other hand, the viscosity of the rubber increases and the processability deteriorates. is there.

As described above, control of the surface area and pore volume of hydrated silicic acid as a filler is important and is a factor having a great effect on rubber reinforcement. That is, it can be imagined that the rubber reinforcement performance can be largely influenced by controlling the balance between the two. However, it has not been known how these factors can be changed to improve the breaking strength and abrasion resistance of rubber without lowering the workability when compounding the rubber. . Thus, the present inventors have conducted various studies, and as a result,
Hydrous silicic acid whose physical properties are in the range specified above,
It has been found that an excellent reinforcing effect can be exhibited, and the present invention has been completed.

The wet hydrated silicic acid of the present invention has an N2 specific surface area (A) in the range of 250 to 400 m ² / g.
g method specific surface area (B) is in the range of 200 to 300 m ² / g, and N2 method pore volume (C) is 1.7 to 2.5 ml / g.
And A × C / B is 2.3 or more.

Conventionally, hydrous silicic acid used as a filler for reinforcing rubber has a specific surface area of 220 m ² / g or less according to N2 method and a low pore volume of 1.7 ml / g or less according to N2 method. It is a target. It is presumed that this area came from the fact that the main purpose was to make dispersion easier.

On the other hand, the hydrated silicic acid of the present invention contains N
2 method specific surface area (hereinafter abbreviated as N2SA) is 250 to
400 m ² / g, and the N2 method pore volume (hereinafter, referred to as
(Abbreviated as N2Po) is in the range of 1.7 to 2.5 ml / g, which is higher than that of the conventional product.
Having. The hydrated silicic acid of the present invention having such physical properties exhibits excellent reinforcing properties when blended with rubber.

When N2SA is less than 250 m ² / g, the reinforcing property is low, and when it exceeds 400 m ² / g, the cohesive force of hydrated silica is too strong. It is not preferable because the viscosity decreases and the viscosity of the rubber compound becomes too high to deteriorate the processability. Preferably it is in the range of 250 to 370 m ² / g. N2Po ranges from 1.7 to 2.5 ml / g. N2Po is an index of structural properties with a micropore volume of 3000 mm or less in diameter. If N2Po is less than 1.7 ml / g, the reinforcing property is reduced. The higher N2Po is, the stronger the reinforcement is,
The upper limit is about 2.5 ml / g from the viewpoint that production is possible by the precipitation method.

Further, the hydrous silicic acid of the present invention has a relatively low Hg method pore volume (hereinafter abbreviated as HgPo).
Hg method specific surface area (hereinafter abbreviated as HgSA) is N2S
Compared with A, it is not so high as 200 to 300 m ² / g.
In addition, the calculation method of HgSA is as follows, assuming that the pores are cylindrical.
Calculate at 2V / r. (However, A = surface area (m ² / g), V
= Total pore volume (ml / g), r = average pore radius (μm)) That is, it can be said that the feature is that there are few mesopores and there are many micropores. HgSA is preferably 200 to 270 m ² /
g. HgSA is N2SA (A) × described below.
It is important in adjusting N2Po (C) / HgSA (B).

Usually, as described above, those having high N2SA tend to cause poor dispersion and hardly increase the reinforcing performance, but in the present invention, this was solved by adjusting the balance with other physical properties. . That is, in the present invention, N2
N2SA (A) × N2Po despite high SA
By adjusting (C) / HgSA (B), it was possible to prevent dispersion failure and improve reinforcement performance. That is, in the hydrous silicic acid of the present invention, A × C / B is 2.3 or more, which is higher than that of the conventional product, thereby improving the reinforcing performance (fracture characteristics and abrasion resistance) without causing poor dispersion. I was able to. Although there is no upper limit for the value of A × C / B in relation to the object of the present invention, the upper limit may be about 3.3 in production technology. The hydrated silicic acid of the present invention is preferably in the range of 2.3 to 3.3. Aqueous silicic acid having an A × C / B of less than 2.3 is inferior in reinforcement, and if it is 2.3 or more,
Good compatibility with rubber and good dispersion.

In the present invention, the surface area is increased (the primary particle diameter is small), the fine pores (micropores) are increased, and H
It is presumed that reinforcement performance was improved by reducing gPo (mesopore) and controlling the balance between particle size and voids. By increasing N2SA, the number of contact points with rubber is increased to increase the reinforcing effect, N2Po is increased to enhance the structural properties, the entanglement with rubber molecules is strengthened, the reinforcing effect is achieved, and HgSA is adjusted to an appropriate value. Balance
It is considered that high dispersion was achieved and reinforcement was improved.

Further, the hydrous silicic acid of the present invention preferably has an Hg method pore volume (HgPo) of not more than 2.5 ml / g. The Hg method pore volume is more preferably 2.
It is in the range of 0-2.5 ml / g. As described above, the hydrated silicic acid of the present invention has a high N2SA and N2Po, and if the HgPo, which is an indicator of mesopores, is too high, the viscosity of the rubber compound becomes too high and the processability deteriorates. Or the rubber agent is adsorbed and the reinforcing effect is reduced. Furthermore, when HgPo is too low, poor dispersion is likely to occur. Therefore, it is preferable to set the above range.

Further, the hydrous silicic acid of the present invention preferably has an N2 specific surface area / CTAB specific surface area of 1.2 or more. More preferably, the N2 specific surface area / CTAB specific surface area is in the range of 1.2 to 1.6. The CTAB method specific surface area is frequently used as one of the measuring methods for expressing the external surface area of hydrous silicic acid. In the hydrous silicic acid of the present invention having many micropores, the value is not so high, and the value of N2 method specific surface area / CTAB method specific surface area value is larger than that of general hydrous silicic acid. If the specific surface area of the CTAB method is as large as the specific surface area of the N2 method, the viscosity of the rubber compound becomes too high, thereby deteriorating the processability and causing poor dispersion. The specific surface area is preferably 1.2 or more.

The method for producing hydrous silicic acid of the present invention will be described below. The hydrated silicic acid of the present invention requires adjustment of the reaction conditions, but can be produced basically by the same method as the method for producing hydrated silicic acid by a conventional wet method. That is, this is a method of obtaining hydrous silicic acid as a precipitate by the reaction of an aqueous solution of an alkali metal silicate with a mineral acid. More specifically, a one-sided dropping method in which a mineral acid is added to an aqueous solution of an alkali metal silicate and an alkali metal There are two simultaneous dropping methods in which a silicate aqueous solution and a mineral acid are simultaneously added to a reaction vessel. However, the hydrated silicic acid of the present invention can be prepared by the simultaneous dropping method, as described below, by continuing the reaction in a high alkali region to keep N2SA high and to obtain a value of A × C / B. To 1.2
It is appropriate from the viewpoint of adjusting as described above.

The N2SA of the present invention is 250 to 400 m ² /
g, HgSA is in the range of 200 to 300 m ² / g, N2Po is in the range of 1.7 to 2.5 ml / g, and A × C / B is 2.3 or more. In order to produce an acid, it is necessary to set a reaction condition that has not existed before, and this will be described below. In the method for producing hydrous silicic acid by a wet method, the reaction conditions that can be varied are mainly SiO ₂ concentration in the reaction solution, reaction temperature, pH of the reaction solution, and reaction time, and these factors are appropriately varied. .

First, a characteristic of the present invention is the pH of the reaction solution. In the conventional method, the pH of the reaction solution
Is in the range of 7.5 to 10.5, more typically 8
-9. In contrast, in the present invention, N2
From the viewpoint of making SA and HgSA higher values,
The pH of the reaction solution is in the range of 10.5-11.5. The reaction temperature is set in the range of 70 to 85 ° C. from the viewpoint of increasing N2SA and HgSA to higher values. The specific surface area tends to decrease as the reaction temperature increases, and the reaction temperature in the conventional production of hydrated silicic acid with N2SA of 150 to 200 m ² / g is 85 to 95 ° C.

[0022] In a SiO ₂ concentration of the reaction solution, SiO ₂ concentration during simultaneous completion of the dropwise addition, the range of 40 and 80 g / l. Preferably it is in the range of 50 to 70 g / l. In this case, it is appropriate that the SiO ₂ concentration of the reaction solution at the start of simultaneous dropping is 12 g / l or more, preferably 13 to 25 g / l. If the SiO ₂ concentration at the end of simultaneous dropping is too low, N2SA will increase and HgS will increase.
A is also undesirably high. Conversely, if the SiO ₂ concentration is too high, N2SA will be low, which is not preferable.
Further, at the start of simultaneous dropping, it is necessary to adjust the SiO ₂ concentration at the beginning of the reaction. That is, by setting the SiO ₂ concentration at the beginning of the reaction high, the N2SA and N2Po are increased, and the HgS
A can be adjusted relatively low. However, it is not preferable that the height is too high because N2SA becomes too high.

By appropriately setting a reaction time and a reaction temperature, which will be described later, and selecting these conditions, N2SA
, The value of A × C / B can be increased to 1.2 or more. In the conventional method, the initial SiO
₂ concentration is generally in the range of 10 g / l or less, and N2SA of hydrated silicate obtained under these conditions is also related to the reaction time and the reaction temperature.
² / g or less, and the ratio to the CTAB specific surface area is close to 1.

The reaction time ranges from 60 to 120 minutes, preferably from 60 to 110 minutes. If the reaction time is too short, N2SA increases, but N2Po does not increase so much. If the reaction time is too long, N2S
A becomes smaller. The reaction temperature is 85 ° C. or lower, more preferably in the range of 70 to 85 ° C. When the reaction temperature is too high, N2SA decreases, and at the same time, N2Po decreases. When the reaction temperature is too low, N2SA becomes too high. The reaction temperature in the conventional method is generally in the range of 85 to 95 ° C., and N2SA of hydrated silicate obtained under these conditions is generally 220 m ² / g or less, although it is related to the reaction time.

[0025]

The present invention will be described below in detail with reference to examples and comparative examples. However, the present invention is not limited to these examples. The measurement of each device and each physical property value used in the present invention was performed by the following methods. (1) N2 method specific surface area (BET method) Measured by a one-point method using Cantasorb (manufactured by Quantachrome Co., USA). (2) Hg method specific surface area and pore volume Mercury porosimeter 2000 type (manufactured by Ino Carlo Erba)
Measured at (3) Barre using N2 method pore volume ASAP2400 (manufactured by Shimadzu Corporation)
Measured by t-Joyner-Halenda method. (4) CTAB method specific surface area ASTM D3765 (CARBON BLACK-CTAB SURFACE ARE
Measured according to A). However, to calculate the adsorption cross sectional area of the CTAB molecule as 35 Å ^2. (5) Mooney viscosity Measured with an L-type rotor at 125 ° C. using a Mooney viscometer SMV-200 (manufactured by Shimadzu Corporation). (6) Curast time T90 The optimum vulcanization time (T90) was measured by a JSR type curast meter IIF.

(7) Properties of vulcanizates-General vulcanizates properties Measured according to the test method of JIS K6301.・ Abrasion test is measured by Akron type abrasion tester. Tilt: 15 °, Load: 6 pounds Number of tests: Wear reduction at 2000 rpm was measured, and Comparative Example 1 was indicated as an index with 100 as 100. (8) The higher the numerical value, the better the abrasion resistance. (8) Formulation of formulation A : JSR using a 1.7 liter Banbury mixer.
After 110 parts of 1712 and 20 parts of BR01 were masticated for 30 seconds, 2 parts of stearic acid, 1 part of paraffin wax, 20 parts of aroma oil, 80 parts of hydrous silicic acid and 7.1 to 13 of silane Si69. Charge in the range of 6 parts and take out after 5 minutes of total kneading time. The compound temperature at the time of removal is adjusted to 140 to 150 ° C. by the ram pressure and the number of rotations. After cooling the compound at room temperature, 1 part of old protection 810NA,
4 parts of zinc white, 1.5 parts of vulcanization accelerator D, and 1 part of CZ
5 parts and 1.75 parts of S were added and kneaded for about 1 minute (the temperature at the time of removal was set to 110 ° C. or less), followed by sheeting with an 8-inch roll to determine the properties of the unvulcanized product and the vulcanized product. It was measured. The results are shown in Table 1. Formulation B was prepared in the same manner as Formulation A, but the rubber, formulation and results are shown in Table 2.

Example 1 In a 240-liter jacketed stainless steel container equipped with a stirrer, 125 liters of water and 13.9 liters of an aqueous sodium silicate solution (S
iO ₂ 150 g / l, SiO ₂ / Na ₂ O weight ratio 3.3)
And heated to a temperature of 82 ° C. At this time, the pH was 10.9, and the SiO ₂ concentration was 15 g / l. To this aqueous solution, an aqueous solution of sodium silicate and sulfuric acid (1
8.4 mol / l) was added evenly so that the SiO2 concentration became 60 g / l in 100 minutes while maintaining pH 10.9 ± 0.2 and temperature 82 ± 1 ° C., and sodium silicate was added in 100 minutes. Only the aqueous solution was stopped. Subsequently, the same sulfuric acid was added until pH 3 was obtained to obtain a precipitate. Thereafter, the obtained reaction product was filtered, washed with water, and dried to obtain hydrous silicic acid by a wet precipitation method.

(Example 2) Using the same container and the same raw materials as in Example 1, 120 liters of water and an aqueous solution of sodium silicate were charged and heated to a temperature of 80 ° C. At this time, the pH was 11.1 and the SiO ₂ concentration was 18 g / l. Thereafter, simultaneous addition was performed while maintaining the pH at 11.1 ± 0.2 and the temperature at 80 ± 1 ° C., and hydrous silicic acid was obtained in the same manner as in Example 1.

(Example 3) Using the same container and the same raw materials as in Example 1, 115 liters of water and an aqueous solution of sodium silicate were charged, and heated to a temperature of 80 ° C. At that time, the pH was 11.3 and the SiO ₂ concentration was 20 g / l. Thereafter, hydrous silicic acid was obtained in the same manner as in Example 1. (Example 4) The same container and raw materials as in Example 1 were used,
15 liters and an aqueous solution of sodium silicate were charged, and heated to a temperature of 78 ° C. The pH at that time was 11.3, S
The iO ₂ concentration was 21 g / l. Thereafter, hydrous silicic acid was obtained in the same manner as in Example 1. (Example 5) Hydrous silicic acid was obtained in the same manner as in Example 4 except that the temperature was changed to 75 ° C.

(Comparative Example 1) Nipsil AQ (Nippon Silica Industry Co., Ltd.) (Comparative Example 2) Nipsil NS-KR (Nippon Silica Industry Co., Ltd.) (Comparative Example 3) Nipsil HD-R (Nippon Silica Industry Co., Ltd.) Comparative Example 4) Ultrasil VN3 (manufactured by Degussa, Germany)

[0031]

[Table 1]

[0032]

[Table 2]

In the table, TB is tensile strength, M300 is 300
% Tensile stress, Eb indicates elongation, and Hs indicates hardness.
Regarding the variation of the silane Si69, the surface area of the hydrous silicic acid and the vulcanization rate have a large correlation, and the vulcanization deficiency occurs as the surface area increases, so that a preferable vulcanization rate is obtained. Was blended.

[0034]

According to the hydrated silicic acid of the present invention, the conventional hydrated silicic acid is free from the problem of processability such as poor dispersion when producing a rubber compound, which is a disadvantage of silica. The tensile strength and wear resistance can be greatly improved.

Claims (4)

[Claims] 1. The specific surface area (A) of the N2 method is from 250 to 400.
m ² / g, and the Hg method specific surface area (B) is 200
３００300 m ² / g, and the N2 method pore volume (C)
Is in the range of 1.7 to 2.5 ml / g, and A × C /
A wet hydrated silicic acid wherein B is 2.3 or more. 2. The hydrous silicic acid according to claim 1, wherein A × C / B is 2.3 to 3.3. 3. The hydrous silicic acid according to claim 1, wherein the Hg method pore volume is in a range of 2.5 ml / g or less, and the N2 method specific surface area / CTAB method specific surface area is 1.2 or more. 4. The pore volume of the Hg method is 2.0 to 2.5 ml /
The hydrous silicic acid according to claim 3, wherein the ratio is in the range of 1.2 to 1.6 and the ratio of the N2 method specific surface area / CTAB method specific surface area is 1.2 to 1.6.