JP2006282946A - Rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition which improves a low rolling resistance and a wet performance in a well-balanced relationship without decreasing wear resistance.
SOLUTION: 100 parts by weight of a rubber component includes 40 parts by weight or more of styrene butadiene rubber (SBR-A), and at least one diene rubber other than the SBR-A is used as a rubber component, and includes silica. It is a rubber composition, Comprising: The value of the styrene amount Z calculated | required from the bound rubber of the said rubber composition exists in the range shown by following (1) Formula.
((A * A + b * B) / 100) * (0.9-2.9 / A) <Z <((a * A + b * B) / 100) * (0.92 + 8.3 / A) ... ( 1)
(In the formula, A is the amount of SBR-A blended (parts by weight), a is the amount of styrene in SBR-A (%), B is the amount of rubber other than SBR-A (parts by weight), and b is SBR-A. (The amount of styrene in rubber other than (%))
[Selection figure] None

Description

  The present invention relates to a rubber composition. More specifically, the present invention relates to a rubber composition capable of achieving both a low rolling resistance and a braking performance on a wet road surface in a well-balanced manner without reducing wear resistance, and a tread of the rubber composition. It relates to a pneumatic tire applied to.

  Rubber compositions used in tire treads are strongly demanded to reduce rolling resistance due to market needs for low fuel consumption, and also have braking performance and handling stability (hereinafter referred to as wet performance) on wet roads in terms of safety. Improvements are required, and excellent wear resistance is required in terms of durability and economy, and these low rolling resistance and wet performance, which exhibit a contradiction tendency as rubber properties, are required to be improved in a balanced manner at a high level. It has been.

  In response to these requirements, instead of carbon black, which has been conventionally used as a reinforcing filler for rubber, a rubber composition containing silica, in which a balance between the low rolling resistance and the wet performance is easily obtained, is a tire. Used for tread.

  However, silica has hydrophilicity and has a strong self-aggregation property because the surface is covered with silanol groups, and it is excellent in rubber when compounded into rubber using a rubber kneading device such as a Banbury mixer. Is difficult to disperse, requires a long rubber kneading time, tends to cause poor dispersion, and blend rubber tends to be unevenly distributed in a rubber phase having a high affinity with silica. It has the disadvantage of being difficult to obtain.

Conventionally, there have been many disclosures of improving the affinity between silica and rubber by using a silane coupling agent in combination, and improving the rubber properties of silica blending by enhancing the binding force between the two (for example, patent documents) 1) In addition, a proposal of surface-treated silica that improves properties such as kneading work and rolling resistance (for example, Patent Document 2), and further uses a thiuram compound specific to silica formulation as a vulcanization accelerator ( Many studies have been made to improve the above-mentioned drawbacks of silica blending, such as Patent Document 3), and although an effect is recognized by the technical improvement, there is a social demand for satisfying higher requirements.
JP-A-11-269305 Japanese Patent Laid-Open No. 11-124474 JP 2001-172432 A

  In tread rubber for tires that generally use blended rubber, silica is compounded to improve the temperature dependence of tan δ of the rubber composition, improve low rolling resistance and wet performance, and suppress wear reduction by reducing the reinforcement. It has been made to maintain sex. However, in order to maximize the features of this silica formulation, it is important to distribute the silica uniformly in each rubber phase of the blend rubber. As described above, the silanol groups on the silica surface are bonded together to form agglomerates. In fact, the dispersibility in rubber tends to be low, and the rubber phase tends to be biased to one of the high affinity rubbers.

  In conventional rubber compounding, many improvements have been made to the polymer, blending, silica surface, additives, etc., but the investigation from the silica distribution in the blended rubber has not been sufficient, The optimal distribution of silica in blended rubber, which can achieve a high degree of compatibility between the rubber properties that are a trade-off between low rolling resistance and wet performance, has not been grasped.

  The present invention has been made in view of the above points, and in a rubber composition in which silica is blended with a blend system using styrene butadiene rubber, the distribution state of silica in the blend rubber is quantitatively controlled. An object of the present invention is to provide a rubber composition suitable for a tire tread that can improve a low rolling resistance and wet performance in a well-balanced manner without reducing wear resistance, and a pneumatic tire to which the rubber composition is applied. Is.

  Based on the conventional knowledge that silica is likely to be unevenly distributed in a high affinity rubber phase, the present inventors have studied the relationship between silica dispersion, uneven distribution state and rubber properties by blend rubber combination and mixing method. As a result, it was found that it is important not only to combine those having a close affinity with silica among the blend rubbers but also to disperse the silica uniformly in both phases of the blend rubber. That is, when the affinity between rubber and silica was verified from the microstructure of the bound rubber of the rubber composition, it was found that the one having a microstructure in the middle of the blended rubber blend solves the above problem.

That is, the present invention includes 40 parts by weight or more of styrene butadiene rubber (SBR-A) in 100 parts by weight of a rubber component, at least one diene rubber other than the SBR-A as a rubber component, and contains silica. The rubber composition is characterized in that the value of the styrene amount Z obtained from the bound rubber of the rubber composition is in the range represented by the following formula (1).
((A * A + b * B) / 100) * (0.9-2.9 / A) <Z <((a * A + b * B) / 100) * (0.92 + 8.3 / A) ... ( 1)
(In the formula, A is the amount of SBR-A blended (parts by weight), a is the amount of styrene in SBR-A (%), B is the amount of rubber other than SBR-A (parts by weight), and b is SBR-A. (The amount of styrene in rubber other than (%))

In the rubber composition of the present invention, the silica is contained in an amount of 20 to 120 parts by weight with respect to 100 parts by weight of the rubber component, the nitrogen adsorption specific surface area (BET) of the silica is 100 to 300 m ² / g, and the DBP oil absorption is 150. It is preferable that it is -300ml / 100g.

  According to the rubber composition of the present invention, the value of the styrene amount Z obtained from the bound rubber of the rubber composition is in the range represented by the formula (1), so that the silica is biased to one rubber phase of the blend rubber. Therefore, the blend rubber is uniformly dispersed according to the blending ratio in both phases of the blend rubber, and the characteristics of blending silica into each blend rubber can be maximized.

  According to the pneumatic tire of the present invention, by applying the rubber composition to a tread, low rolling resistance and wet performance can be balanced and improved without reducing wear resistance.

  Since the rubber composition for tires of the present invention can disperse silica uniformly in both phases of the blended rubber and can highly balance the rubber properties utilizing the characteristics of silica compounding, a pneumatic tire using this for a tread Can provide a pneumatic tire that satisfies both the low rolling resistance and wet performance without lowering the wear resistance, and meets the social needs of low fuel consumption and safety.

  The rubber composition of the present invention contains 40 parts by weight or more of styrene butadiene rubber (referred to as SBR-A) in 100 parts by weight of a rubber component, and at least one diene rubber other than the SBR-A as a rubber component. Blend formulation.

  The SBR-A is not limited by the polymerization method, microstructure such as the amount of styrene, vinyl content, molecular weight, or presence or absence of terminal modification with a functional group such as a hydroxyl group or amino group, but the strength and low heat generation. Selected from SBR obtained by solution polymerization or emulsion polymerization conventionally used for tire treads, etc., which has excellent properties, wear resistance, workability, etc., and 40 parts by weight as the main rubber component of the blend rubber The content is preferably 50 parts by weight or more.

  The SBR-A is preferably 15 to 45% by weight of styrene, more preferably 20 to 40% by weight, and SBR having a vinyl content of about 30 to 60% by weight is used for tire treads. It is preferable because of its excellent properties. If the amount of styrene exceeds 45% by weight, the glass transition temperature (Tg) increases and the wet performance is maintained, but the rolling resistance increases and the wear resistance tends to decrease. By setting the range, the TBR of SBR can be set to an appropriate range.

  The rubber component other than SBR-A is not particularly limited as long as it is a diene rubber other than SBR-A. Examples of these diene rubbers include natural rubber (NR), SBR other than SBR-A, butadiene rubber (BR), isoprene rubber (IR), nitrile rubber (NBR), and the like. A blend is selected from two or more.

  In the rubber composition of this invention, SBR-A which comprises a main component in the said rubber component is 40 weight part or more, Preferably it contains 50 weight part or more. When this SBR-A is less than 40 parts by weight, it becomes difficult to obtain the basic performance as a tread rubber such as the above-mentioned strength, low heat build-up, wear resistance, and workability, that is, the silica dispersibility of the blend rubber is improved. Even if it does, the reinforcement property and abrasion resistance of a rubber composition will fall, and coexistence with low rolling resistance and wet performance will not fully be show | played. On the contrary, when the blending ratio of SBR-A is increased, it is difficult to draw out the advantages of the other blend rubber components. Therefore, the ratio of SBR-A as the main rubber component is 95 parts by weight, preferably about 90 parts by weight. To do.

  Examples of the silica used in the tire rubber composition of the present invention include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. Wet silica having the best improvement effect as well as the effect of achieving both low rolling resistance and wet performance is preferred, and is also preferred from the viewpoint of excellent silica productivity.

The silica preferably has a nitrogen adsorption specific surface area (BET) of 100 to 300 m ² / g and a DBP oil absorption of 150 to 300 ml / 100 g. When the BET is less than 100 m ² / g, a silica reinforcing effect is obtained. When it exceeds 300 m ² / g, the dispersibility of silica is remarkably lowered, and the processability (mixing and extrudability) tends to deteriorate. Moreover, a dispersibility can be favorably maintained by making DBP oil absorption amount 150-300 ml / 100g. As such silica, commercially available products such as Nipsil AQ and VN3 manufactured by Nippon Silica Kogyo Co., Ltd., Toxeal UR and U-13 manufactured by Tokuyama Co., Ltd., and Ultrazil VN3 manufactured by Degussa Corporation can be used. The silica BET is measured according to the BET method described in ISO 5794, and the DBP oil absorption is measured according to the method described in JIS K6221.

  Furthermore, as the silica, surface-treated silica that has been treated with amines or organic polymers to improve the affinity with rubber can be used.

  The amount of the silica is 20 to 120 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount of silica is less than 20 parts by weight, effects such as reinforcement and low heat build-up due to the blending of silica cannot be obtained. If it exceeds 120 parts by weight, the Mooney viscosity of the rubber will increase even if the dispersibility of silica is improved. The wear resistance also decreases.

  In the rubber composition of the present invention, any silane coupling agent that has been conventionally used in combination with silica is preferably blended. Examples of the silane coupling agent include sulfide systems such as bis- (3- (triethoxysilyl) propyl) tetrasulfide, mercapto systems such as 3-mercaptopropyltrimethoxysilane, amino systems such as 3-aminopropyltrimethoxysilane, Examples of the commonly used silane coupling agent such as vinyl type such as vinyltriethoxysilane may be used alone or in combination of two or more.

  The compounding amount of this silane coupling agent is 1 to 20% by weight of the silica compounding amount. If the silane coupling agent is less than 1% by weight, the coupling effect is not sufficiently obtained, and the advantages of silica compounding are not exhibited, If it exceeds 20% by weight, no further coupling effect can be obtained for the cost increase, and conversely, the reinforcement and wear resistance tend to be lowered and the workability tends to be deteriorated.

The rubber composition of the present invention is characterized in that the value of the styrene amount Z obtained from the bound rubber of the rubber composition is in the range represented by the following formula (1).
((A * A + b * B) / 100) * (0.9-2.9 / A) <Z <((a * A + b * B) / 100) * (0.92 + 8.3 / A) ... ( 1)
(In the formula, A is the amount of SBR-A blended (parts by weight), a is the amount of styrene in SBR-A (%), B is the amount of rubber other than SBR-A (parts by weight), and b is SBR-A. (The amount of styrene in rubber other than (%))

  In the present invention, “bound rubber” refers to a rubber component that remains unextracted while being bonded to a filler such as silica or carbon black when unvulcanized rubber mixed with a filler is extracted with a solvent.

  The above formula (1) indicates that the styrene amount Z of the bound rubber is within a certain range with respect to the average styrene amount in the blend rubber, that is, the styrene amount Z bonded to the silica is the formula (1). If it is within the range, it means that the silica dispersed in the blend rubber is dispersed on average in each rubber phase.

  More specifically, if the amount of styrene in the bound rubber of SBR-A which is the main rubber component represented by A in the formula (1) is an average position, the silica present in the SBR-A The amount is also an average abundance in the blend rubber, and silica is also present on average in the other rubber phases. Accordingly, when the styrene amount Z is less than the value on the left side of the formula (1), the silica is unevenly distributed in a rubber phase other than SBR-A, and when it exceeds the value on the right side of the formula (1), the silica is the main rubber. The SBR-A phase, which is a component, is unevenly distributed, and the features of both rubber components are not expressed in a well-balanced manner, and the respective features may be offset, making it impossible to achieve the object of the present invention.

  When the third rubber component C is included in the blend component, ((a × A + b × B) / 100) in the formula (1) is ((a × A + b × B + c × C) / 100) (C is The blending amount (parts by weight) of the three rubber components and c may be replaced with the styrene amount (%) of the third rubber component.

  The amount of styrene Z in the bound rubber is chopped from unvulcanized rubber and placed in a cage made of 325 mesh wire netting. The toluene insoluble matter (bound rubber) after being immersed in toluene for 24 hours is air-dried. Thereafter, styrene is determined by pyrolysis gas chromatography. Furthermore, the rubber component of the blend rubber can be specified using a calibration curve prepared in advance by measuring the microstructure of the thermal decomposition product of the bound rubber by the infrared absorption spectrum method.

  In the rubber composition of the present invention, silica is blended with SBR-A which is the main rubber component of the blend rubber and other rubber components, and the styrene amount Z of the bound rubber is adjusted within the range of the above formula (1). If so, the blending order of the blended rubber and the adjusting method thereof are not particularly limited, and the silica distribution in each rubber phase of the blended rubber is in a uniform state according to the blending ratio. The characteristics of each rubber component will be highly balanced and will be demonstrated without regret.

  As the adjustment method, for example, the difference in the microstructure, Tg, aggregation state, etc. of the polymer between the rubber components is combined using the characteristics of silica, surface treatment, etc., and blending conditions are added to the blend rubber. It can be carried out as appropriate depending on the combination of the blending method, the mixing method, the type of the mixer, and the like.

  For example, a method of adjusting the mixing conditions such as mixing temperature and time, Banbury mixer rotor rotational torque, a method of combining silica master batches, and the like by simultaneously blending the rubber component and the total amount of silica can be used.

  In the rubber composition of the present invention, carbon black may be used in combination with the silica as a reinforcing filler. By blending carbon black, reinforcement and wear resistance can be improved, and problems of heat generation (burning) and deterioration of workability when mixed with silica can be improved. For tire treads, HAF, ISAF SAF grade carbon black is suitable for practical use, and two or more of these may be used in combination.

  In addition to the rubber component and silica, the rubber composition for tire tread of the present invention includes carbon black, a vulcanizing agent such as sulfur usually used in the rubber industry, a vulcanization accelerator, a process oil, an anti-aging agent, Various compounding agents such as zinc white, stearic acid, and vulcanization aid can be appropriately blended and used as necessary within the range not impairing the effects of the present invention.

  In the present invention, various compounding agents can be blended with raw rubber and silica, or a silica masterbatch, and can be produced according to a conventional method using various kneaders such as a Banbury mixer, roll, kneader, etc. It can be used for tire parts such as sidewalls and bead parts, but it is particularly suitable as a rubber for tire tread that achieves both low rolling resistance and wet performance by making the distribution of silica uniform in each rubber phase Used for.

  The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

  The following three types of SBR-1 to 3 and butadiene rubber (BR) were used as rubber components, and SBR-1 was used as the main rubber component to prepare a rubber composition containing silica in the blend ratios shown in Table 1.

  For each rubber composition, a silica masterbatch having the following silica content adjusted was prepared, and the following common compounding ingredients were blended into the masterbatch and kneaded with a 20 liter Banbury mixer. In addition, the rubber composition of Comparative Example 1 is obtained by mixing the blend rubber component and the entire amount of silica into a mixer at the same time and kneading them.

[SBR-1 to 3, BR, silica, silane coupling agent]
SBR-1: Styrene content 35.5% by weight (Asahi Kasei Corporation, TUFDENE 3335)
-SBR-2: Styrene content 18.0% by weight (Asahi Kasei Kogyo Co., Ltd., TUFDENE 1530)
SBR-3: Styrene content 20.0% by weight (Nippon Zeon Corporation, NIPOL NS 116)
BR: Styrene content 0% by weight (JSR Corporation, BR01)
Silica: Nippon Silica Kogyo Co., Ltd., Nip Seal AQ (BET: 210 m ² / g)

[Common ingredients]
Aroma oil: 30 parts by weight (Japan Energy Co., Ltd., Process X-140)
・ Zinc flower: 3 parts by weight (Mitsui Metal Mining Co., Ltd., Zinc flower No. 1)
・ Wax: 1 part by weight (Ouchi Shinsei Chemical Co., Ltd., Sunnock)
Anti-aging agent 6C: 2 parts by weight (Ouchi Shinsei Chemical Co., Ltd., NOCRACK 6C)
Silane coupling agent: Si69 manufactured by Degussa
・ Sulfur: 1.8 parts by weight (Hosoi Chemical Co., Ltd., powdered sulfur for rubber 150 mesh)
・ Vulcanization accelerator CZ: 1 part by weight (Ouchi Shinsei Chemical Co., Ltd., Noxeller CZ)

  About each obtained rubber composition, the amount Z of styrene (St) from bound rubber is a pyrolysis gas chromatography apparatus (Nippon Analytical Industrial Co., Ltd., JHP-22 type), and an infrared absorption spectrum apparatus (made by Perkin Elmer, Quantitative determination using Paragon type is shown in Table 1.

  Next, a radial tire of size 205 / 60R14 in which each rubber composition was applied to the tread portion was manufactured, and the rolling resistance, wet performance, and wear resistance of each tire were evaluated according to the following methods. The tires are shown in Table 1 with an index of 100.

Test method [Rolling resistance]
Using a uniaxial drum tester, the rolling resistance when running on the drum at an internal pressure of 200 kPa, a load load of 400 kg, and a speed of 80 km / h was measured, and the rolling resistance index of each test tire was calculated by the following formula. The smaller the value, the better the fuel efficiency and the better. Rolling resistance (index) = (rolling resistance of each test tire) × 100 / (rolling resistance of the tire of Comparative Example 1)

[Wet performance]
The distance from applying a sudden brake while stopping on an asphalt road surface submerged to a depth of 2 to 3 mm at a speed of 60 Km / h until stopping after the same type of test tire is adjusted to 200 kPa on a domestic passenger car with a displacement of 2000 cc. Was measured, the wet braking index of each test tire was calculated by the following formula, and the wettability was evaluated. The larger the value, the better and better the braking performance. Wetness (index) = (stop distance of test tire of Comparative Example 1) × 100 / (stop distance of each test tire)

[Abrasion resistance]
Two types of test tires are installed on a domestic passenger car with a displacement of 2000 cc, and the internal pressure is adjusted to 200 kPa and attached to the front and rear wheels, respectively. After running 20,000 km on a general road while rotating every 5,000 km, The residual groove depth of the tread was measured to determine the amount of wear, and the wear resistance index of each test tire was calculated by the following formula to evaluate the wear resistance. The higher the value, the better the wear resistance. Abrasion resistance (index) = (Abrasion amount of test tire of Comparative Example 1) × 100 / (Abrasion amount of each test tire)

  As shown in Table 1, in the tire in which the rubber composition of each example in which the amount of styrene of the bound rubber is within the range of the formula (1) is applied to the tread, the silica distribution in each rubber phase of the blend rubber is made uniform. It was possible to maintain wear resistance and achieve both low rolling resistance and wet performance. In particular, it can be seen from the results of Examples 4 and 5 that the blending effect due to the uniform dispersion of silica is expressed by changing the blend rubber component.

  On the other hand, in the comparative example 1 by the conventional kneading method in which the silica is unevenly distributed in the SBR-1 phase, the comparative example 2 in which the silica is unevenly distributed in the SBR-2 phase, and the comparative example 4 in which the silica is unevenly distributed in the BR phase are balanced tire performance. In Comparative Example 3 in which the amount of SBR-1 as the main rubber component is small, even if the styrene amount Z is within a predetermined range and the silica distribution is uniform in both phases, the tire basic characteristics by SBR-1 Can not be pulled out.

The rubber composition of the present invention effectively exhibits each feature of the blended rubber component by blending silica, and improves the low rolling resistance, wet performance and wear resistance in a balanced manner, resulting in low fuel consumption and safety. It can be used for a tread rubber of a pneumatic tire excellent in performance and durability, and is particularly suitable for a tire for a passenger car.

Claims (4)

A rubber composition comprising 40 parts by weight or more of styrene butadiene rubber (SBR-A) in 100 parts by weight of a rubber component and at least one diene rubber other than the SBR-A as a rubber component, and containing silica. There,
The rubber composition, wherein the value of the styrene amount Z obtained from the bound rubber of the rubber composition is in the range represented by the following formula (1).
((A * A + b * B) / 100) * (0.9-2.9 / A) <Z <((a * A + b * B) / 100) * (0.92 + 8.3 / A) ... ( 1)
(In the formula, A is the amount of SBR-A blended (parts by weight), a is the amount of styrene in SBR-A (%), B is the amount of rubber other than SBR-A (parts by weight), and b is SBR-A. (The amount of styrene in rubber other than (%)) The rubber composition according to claim 1, wherein the silica is contained in an amount of 20 to 120 parts by weight with respect to 100 parts by weight of the rubber component. 3. The rubber composition according to claim 1, wherein the silica has a nitrogen adsorption specific surface area (BET) of 100 to 300 m ² / g and a DBP oil absorption of 150 to 300 ml / 100 g. A pneumatic tire, wherein the rubber composition according to any one of claims 1 to 3 is applied to a tread.