JP2009051935A - Rubber composition for tire and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tires, which has improved processability due to excellent silica dispersibility, has excellent low temperature characteristics without deteriorating characteristics such as abrasion resistance, rolling resistance characteristics and the like, and has excellent ice performance especially suitable for studless tires. <P>SOLUTION: This rubber composition for the tires is characterized by comprising 100 pts.wt. of a dienic rubber, 20 to 120 pts.wt. of silica, a silane coupling agent in an amount of 2 to 20 wt.% based on the amount of the silica, 1 to 20 pts.wt. of plant-based granules such as crushed walnut crest, and an organic silane compound represented by general formula (1): SiR<SB>1n</SB>(OR<SB>2</SB>)<SB>4-n</SB>[wherein, R<SB>1</SB>is a 5 to 20C alkyl group, an alkenyl group, a cycloalkenyl group or an aromatic hydrocarbon; R<SB>2</SB>is a 1 to 3C alkyl; (n) is an integer of 0 to 3] in an amount of 20 to 50 wt.% based on the amount of the silane coupling agent instead of the silane coupling agent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for tires, and more specifically, a rubber composition for tires with improved low-temperature characteristics and improved ice performance while improving the processability of silica, and a pneumatic tire using the same for treads About.

  Conventionally, rubber compositions used in treads for pneumatic tires have been strongly demanded to reduce rolling resistance due to market needs for low fuel consumption, and also have improved braking performance and handling stability on wet roads in terms of safety. Improvement is demanded, and further, wear resistance excellent in terms of durability and economy is demanded.

  In winter tires such as studless tires, in addition to the above requirements, braking performance (ice performance) on icy and snowy road surfaces and frozen road surfaces is important, and various tread rubber compositions that improve ice performance, such as tread pattern improvements, are available. For example, maintenance of low-temperature hardness with a polymer with low glass transition temperature and excellent low-temperature characteristics, use of foamed rubber to provide fine unevenness on the grounding part to obtain water removal effect and scratch effect, organic and inorganic granules Have been proposed to improve the low-temperature properties of the rubber composition by using silica instead of the conventional carbon black as a reinforcing filler and improve the adhesion friction (Patent Document 1). ~ 3).

  In particular, in recent years, silica compounding that can improve the low temperature characteristics of rubber compositions has attracted attention, but silica has hydrophilicity and has a strong self-aggregation property because the surface is covered with silanol groups, When mixing into rubber, it is not easy to disperse in rubber, so the rubber kneading time is lengthened and temperature control is required, and the workability in the subsequent process due to poor dispersion and the resulting deterioration in rubber properties. There is a drawback.

Therefore, a silane coupling agent that binds to the silanol group and prevents the silica from aggregating is used, increasing the affinity between silica and rubber, improving the dispersibility of the silica, maintaining the workability, and binding the two It has been attempted to increase the force to develop the inherent rubber characteristics of silica (for example, Patent Document 4).
JP-A-11-21381 JP 2000-158907 A JP-A-10-7841 JP-A-10-1565

  However, although the effects of the above technical improvements are recognized, there is still room for improvement in improving the dispersibility of silica. To achieve these objectives, the silica and polymer are chemically mixed during processing and processing via a silane coupling agent. Must be combined.

  However, if the functional group part in the silane coupling agent partially reacts with the rubber due to the temperature during processing such as kneading, it gels and causes a scorch phenomenon, and if kneaded at a low temperature that does not cause scorch, silica There is a contradiction that the reaction between the silane coupling agent and the silane coupling agent becomes insufficient, and there is a need for further improvements in terms of workability and scorch problems, compatibility between rolling resistance characteristics and wet performance, or improvement in low temperature characteristics required for studless tires. Has been.

  The present invention has been made in view of the above points, and has improved dispersibility of silica, improved processability, and excellent low temperature characteristics without impairing rubber characteristics such as wear resistance and rolling resistance characteristics. Another object of the present invention is to provide a rubber composition for tires excellent in ice performance, particularly suitable for a tread of a studless tire.

  As a result of earnest studies to solve the above problems, the present inventor improved the dispersibility of silica by using a specific organosilane compound that can promote the reaction between silica and a silane coupling agent, and The inventors have found that the low temperature characteristics of the rubber composition can be improved with the improvement effect, and have reached the present invention.

That is, the tire rubber composition according to the present invention is composed of 20 to 120 parts by weight of silica and 2 to 20% by weight of silane coupling agent based on the silica amount, based on 100 parts by weight of diene rubber. 1 to 20 parts by weight of a plant granule such as a pulverized shell and an organic silane compound represented by the following general formula (1) to 20 to 50% by weight of the silane coupling agent: It is characterized by including in substitution.
SiR _1n (OR ₂ ) _4-n (1)
(In the formula (1), R ₁ is any of an alkyl group having 5 to 20 carbon atoms, an alkenyl group, a cycloalkenyl group, and an aromatic hydrocarbon, R ₂ is an alkyl group having 1 to 3 carbon atoms, and n is It is an integer from 0 to 3.)

  The pneumatic tire according to the present invention is obtained by applying the tire rubber composition to a tread.

  According to the rubber composition for tires of the present invention, the alkoxyl part of the organosilane compound acts on the silanol group of silica to weaken the hydrophilicity of the silica surface, and has a long chain structure with high affinity and steric effect with the polymer. By having it, the movement of the polymer is ensured, and it becomes difficult to form an agglomerate of silica, and the dispersibility to the polymer is improved. As a result, the hardness of the rubber composition can be kept low to ensure a low temperature elastic modulus, and the ice performance can be remarkably improved by a synergistic effect with the scratching effect of the plant granules.

  This significantly improves silica dispersibility during rubber kneading, improves workability during rubber processing, and maintains the balance of rolling resistance and wet performance by taking advantage of the characteristics of silica without compromising wear resistance. Thus, it is possible to provide a rubber composition for tires excellent in fuel economy, safety and economy and a pneumatic tire to which the rubber composition is applied.

  Embodiments of the present invention will be described below.

  In the tire rubber composition of the present invention, a diene rubber is used as a rubber component. Examples of the diene rubber include natural rubber (NR) and various diene synthetic rubbers.

  Examples of the diene synthetic rubber used in the present invention include styrene butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber ( NBR) and the like, and these diene rubbers may be contained singly or in combination of two or more.

  The molecular weight and microstructure of the diene-based synthetic rubber are not particularly limited. The polymerization method, microstructure such as styrene content and vinyl content, molecular weight, molecular weight distribution, or terminal modification with a functional group such as a hydroxyl group or an amino group. However, when used in tire treads, especially treads of studless tires, the glass transition temperature is low and the low-temperature characteristics are excellent. The 1,4-cis content is 95% or higher. It is preferable to use a blend of BR or high cis type BR and other diene rubber.

  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 is preferable because it has both an improvement effect and a low rolling resistance characteristic and wet performance, and is also excellent in terms of 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, commercial products such as Nipsil AQ and VN3 manufactured by Tosoh Silica Co., Ltd., Toxeal UR, U-13, USG-SL manufactured by Tokuyama Co., Ltd., and Ultrazil VN3 manufactured by Degussa are used. it can. The BET of silica 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 surface-treated with amines or organic polymers to improve the affinity with the polymer may 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 amount of silica is less than 20 parts by weight, the effects of the present invention such as reinforcement and low heat build-up due to the silica will not be achieved, and the object of the present invention will not be achieved. If the amount exceeds 120 parts by weight, the dispersibility of silica will be improved by the present invention. Even so, the Mooney viscosity and hardness of the rubber are increased, making it difficult to maintain the workability, and the wear resistance is also lowered, which is not preferable.

  In the present invention, 2 to 20% by weight of a silane coupling agent is used with respect to the amount of silica. More preferably, it is used in the range of 5 to 15% by weight. The silane coupling agent is not particularly limited as long as it is a silane coupling agent for rubber.

Examples of the silane coupling agent include a silane coupling agent having a sulfide bond represented by the following formula (2).
(C _a H _{2a + 1} O) ₃ —Si— (CH ₂ ) _b —S _c — (CH ₂ ) _b —Si— (OC _a H _{2a + 1} ) ₃ (2)
In formula (2), a is an integer of 1 to 3, and b is an integer of 1 to 4. c represents the number of sulfur in the sulfide part, and the average value is 2-4.

  Examples of the silane coupling agent represented by the formula (2) include bis (3-triethoxysilylpropyl) polysulfide, bis (2-triethoxysilylethyl) polysulfide, and bis (4-triethoxysilylbutyl). ) Polysulfide, bis (3-trimethoxysilylpropyl) polysulfide, bis (2-trimethoxysilylethyl) polysulfide and the like. Among them, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferable, and commercially available products such as “Si-69” and “Si-75” manufactured by Degussa are used. can do.

Moreover, the silane coupling agent represented by following formula (3) can also be used.
_{(C x H 2x + 1 O} ) 3 Si- (CH 2) y -S-CO-C z H 2z + 1 ...... (3)
In formula (3), x is an integer of 1 to 3, y is an integer of 1 to 5, and z is an integer of 5 to 9.

  The silane coupling agent represented by the above formula (3) is a protected mercaptosilane. In the formula (3), x = 2, y = 3, and z = 7, “NXT” of GE Silicones Co., Ltd. Listed as a commercial product.

  When the amount of the silane coupling agent is less than 2% by weight, the coupling effect of the silane coupling agent itself is not sufficient, and the interaction with the organic silane compound becomes insufficient. As a result, the rubber composition itself is softened, which may reduce wet performance, reinforcement, and wear resistance.

  In the tire rubber composition of the present invention, a specific organic silane compound represented by the following general formula (1) replaces 20 to 50% by weight of the amount of the silane coupling agent with the silane coupling agent. Included and used.

SiR _1n (OR ₂ ) _4-n (1)
(In the formula (1), R ₁ is any of an alkyl group having 5 to 20 carbon atoms, an alkenyl group, a cycloalkenyl group, and an aromatic hydrocarbon, R ₂ is an alkyl group having 1 to 3 carbon atoms, and n is It is an integer from 0 to 3.)

Examples of the alkyl group having 5 to 20 carbon atoms in R ₁ include pentyl, isopentyl, secondary pentyl, neopentyl, tertiary pentyl, hexyl, secondary hexyl, heptyl, secondary heptyl, octyl, 2-ethylhexyl and secondary octyl. , Nonyl, secondary nonyl, decyl, secondary decyl, undecyl, secondary undecyl, dodecyl, secondary dodecyl, tridecyl, isotridecyl, secondary tridecyl, tetradecyl, secondary tetradecyl, pentadecyl, hexadecyl, secondary hexadecyl, heptadecyl, octadecyl , Nonadecyl, eicosyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldecyl, 2 -Octyldodecyl, 2-decyltetradecyl, 2-dodecylhexadecyl, 2-hexadecyloctadecyl, 2-tetradecyloctadecyl group and the like.

Among these alkyl groups, those having a straight chain structure having 6 or more carbon atoms, preferably 8 or more carbon atoms are preferable because they form a long-chain alkyl group. R ₁ may contain two or more of the above-described alkyl groups.

When the number of carbon atoms is less than 5, the reactivity between R ₁ and the polymer is insufficient, the combined use effect with the silane coupling agent is not exhibited, and the dispersibility of silica is not improved. On the other hand, when the number of carbon atoms exceeds 20, there is a tendency for the rubber physical properties, particularly the rubber hardness, to decrease.

Examples of the alkenyl group for R ₁ include vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl, oleyl and the like.

  Examples of the cycloalkenyl group include cyclopentenyl, cyclohexenyl, cycloheptenyl and the like.

  Aromatic hydrocarbons include benzene, toluene, xylene, styrene, ethylbenzene and the like.

R ₂ in the general formula (1) is an alkyl group having 1 to 3 carbon atoms, that is, a methyl, ethyl, or propyl group. This R ₂ is bonded to an oxygen atom in the formula to form an alkoxyl group, that is, R ₂ O is any one of methoxy, ethoxy and propoxy groups.

  In the above organosilane compound, the alkoxysilane portion interacts with the silica surface, and when it exists on the silica surface, it reacts with silanol groups to make it difficult to form agglomerates of silica, thereby improving the dispersibility of silica. In this way, silica aggregation can be suppressed, the movement of the polymer can be secured, the hardness increase of the rubber composition at a low temperature can be suppressed, and the low temperature elastic modulus can be kept low.

  The compounding amount of the organic silane compound is used by replacing 20 to 50% by weight of the silane coupling agent with the silane coupling agent. If the blending amount is less than 20% by weight of the amount of the silane coupling agent, the interaction with the silane coupling agent is insufficient and the effect of improving the low temperature elastic modulus cannot be sufficiently obtained. As a result, the rubber composition itself is softened, and other properties such as wet performance, reinforcement, and abrasion resistance are deteriorated.

  In the tire rubber composition of the present invention, 1 to 20 parts by weight of a plant granular material such as a pulverized walnut shell is blended with 100 parts by weight of the rubber component. By using vegetable granules together, the above-mentioned low-temperature elastic modulus and the effect of scratching can be combined to further improve ice performance, and the plant granules are made of natural materials and are environmentally safe. .

  When the blending amount of the plant granules is less than 1 part by weight, the scratching effect on the frozen road surface is small and the slip resistance is not exhibited, and when it exceeds 20 parts by weight, the wear resistance tends to decrease.

  As the above-mentioned plant granules, the seed husks such as walnuts and persimmons that are harder than ice, that is, Mohs hardness of 2 or more, or the cores of fruits such as peaches and plums are pulverized by a known method. What was made is mentioned as a preferable example.

  Moreover, in order to ensure adhesiveness with rubber | gum, the granular material in which the surface treatment for rubber adhesiveness improvement was given may be sufficient. As a surface treatment agent for improving rubber adhesion, for example, a mixture (RFL treatment liquid) of resorcin / formalin resin initial condensate and natural rubber latex or diene synthetic rubber latex can be used.

  The particle size of the plant granular material is preferably 50 to 600 μm. If the particle size is less than 50 μm, the amount of protrusion from the rubber surface is small and the catching effect is insufficient, and if it exceeds 600 μm, bubbles contained in ice are included. Therefore, the effect of destroying the bubbles is reduced, and the distortion of the matrix rubber around the granular body is excessively increased, so that cracks are easily generated and easily fall off from the tread.

  The tire rubber composition of the present invention includes the rubber component, silica, a silane coupling agent, an organic silane compound, a vegetable granule, a vulcanizing agent such as sulfur usually used in the tire industry, and vulcanization. Various compounding agents such as accelerators, process oils, anti-aging agents, zinc white, stearic acid, and vulcanization aids can be appropriately blended and used as necessary within the range not impairing the effects of the present invention.

  The rubber composition for tires of the present invention can be produced according to a conventional method using various kneaders such as a Banbury mixer, a roll, and a kneader by blending various compounding agents with the raw rubber and the above components. Suitable for treads, especially treads for studless tires.

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

[Preparation of Tire Rubber Composition]
A rubber composition for tires was prepared according to the formulation (parts by weight) shown in Table 1 below using a closed banbury mixer with a capacity of 20 liters. Each component and common compounding component described in Table 1 are as follows.

[component]
・ Natural rubber: RSS # 3 (made in Malaysia)
-Butadiene rubber: Ube Industries, Ltd. “BR150B” (high cis type: 1,4-cis content = 97 wt%, glass transition temperature = −104 ° C.)
・ Silica: Tokuyama Co., Ltd. “Toc Seal USG-SL”
・ Process oil: Japan Energy “JOMO Process NC140”
Silane coupling agent: “Si75” manufactured by Degussa
・ Organic Silane Compound (1): Shin-Etsu Chemical Co., Ltd. “KBM3103C”
・ Organic Silane Compound (2): Shin-Etsu Chemical Co., Ltd. “KBM3063”
・ Plant granules (walnut shell powder): Nippon Walnut Co., Ltd. “Soft Grip # 46”

  In each rubber composition, as a common compounding agent, 2 parts by weight of stearic acid (“Lunac S-20” manufactured by Kao), zinc white (“Zinc Flower Type 1” manufactured by Mitsui Mining & Mining Co., Ltd.) with respect to 100 parts by weight of the rubber component ) 3 parts by weight, anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical) 2 parts by weight, 2 parts by weight of wax (“Sannok N” manufactured by Ouchi Shinsei Chemical Industry), vulcanization accelerator (“Sokucinol CZ” manufactured by Sumitomo Chemical) ) 1.5 parts by weight, 2.1 parts by weight of sulfur (“powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.) was blended.

  About each obtained rubber composition, Mooney viscosity was used as an index of workability, and elongation at break and tensile strength, low-temperature elastic modulus, and ice performance were evaluated as indexes of mechanical properties by the following methods. The results are shown in Table 1.

[Mooney viscosity]
The Mooney viscosity (ML _{1 + 4} ) at 100 ° C. was measured according to ASTM D1646.

[Elongation at break, tensile strength]
In accordance with JIS K6251, a tensile test was performed using an automatic tensile tester manufactured by Ueshima Seisakusho Co., Ltd. (using dumbbell No. 3).

[Low temperature modulus]
Using a spectrometer manufactured by Toyo Seiki Co., Ltd., the storage elastic modulus (E ′) at −5 ° C. was measured under the conditions of a frequency of 10 Hz, an initial elongation of 10%, and a strain amplitude of 2%. The comparative example 2 is indicated by an index of 100. The larger the value, the better.

[Ice performance]
Each tire rubber composition was applied to a cap tread to produce a 185 / 65R14 studless tire according to a conventional method. Four tires were assembled using a standard rim and with an air pressure of 200 kPa, mounted on a 2000ccFF domestic car, and braked by running an ABS from 40km / h on an icy road (road surface temperature -5 ± 3 ° C). The distance was measured. The average value of the number of measurements was 10 and the index was shown as an index with Comparative Example 2 taken as 100. The larger the index, the shorter the braking distance and the better the ice performance.

  The rubber composition for tires of the present invention has good processability, excellent low-temperature characteristics, and can improve ice performance, and various pneumatic tires ranging from passenger car tires to large tires for trucks and buses, particularly studless It can be suitably used for tire treads.

Claims (2)

20 to 120 parts by weight of silica, 100 to 20 parts by weight of diene rubber, 2 to 20% by weight of silane coupling agent based on the amount of silica, and 1 to 1 of plant granules such as pulverized walnut shells 20 parts by weight and an organic silane compound represented by the following general formula (1) containing 20 to 50% by weight of the silane coupling agent in place of the silane coupling agent. Composition.
SiR _1n (OR ₂ ) _4-n (1)
(In the formula (1), R ₁ is any of an alkyl group having 5 to 20 carbon atoms, an alkenyl group, a cycloalkenyl group, and an aromatic hydrocarbon, R ₂ is an alkyl group having 1 to 3 carbon atoms, and n is It is an integer from 0 to 3.) A pneumatic tire comprising the tire rubber composition according to claim 1 applied to a tread.