JP2006199832A - Tire tread rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire tread rubber composition which is suitable for a studless tire that is excellent not only in ice performance but also in running performance on the dried or wetted surface of a road in summer. <P>SOLUTION: The rubber composition comprises 100 pts.wt. of a rubber component made of a diene base rubber, 40-60 pts.wt. of carbon black, and 1-30 pts.wt. of a vegetable particle, wherein the carbon black has a nitrogen adsorption specific surface area (N<SB>2</SB>SA) of 80-130 m<SP>2</SP>/g and a dibutylphthalate (DBP) oil absorpton of 110 ml/100 g or more, provided that the nitrogen adsorption specific surface area (N<SB>2</SB>SA) and the dibutylphthalate (DBP) oil absorpton are summed to be 190-250. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a tread rubber composition for studless tires, and in particular, a tread rubber composition having excellent running performance on icy and snowy roads suitable for large-sized studless tires for trucks and buses, as well as low heat generation and fuel efficiency in summer It is about things.

  For large studless tires used for trucks and buses that run on icy and snowy roads, tread rubber compositions that require braking, driving performance, and steering stability on icy and snowy road surfaces are used for the tread rubber.

  Conventionally, as such a tread rubber composition, a plant granule or an inorganic granule is blended and protruded from the tread surface to obtain a scratching effect on an ice / snow road surface (for example, Patent Document 1). Made of foamed rubber to absorb the water film on the ice surface and improve the braking performance on the ice surface (for example, Patent Document 2). Maintaining low rubber hardness at low temperatures by blending a large amount of softener and using a specific polymer. In order to facilitate micro deformation of tread rubber on icy and snowy roads and increase the contact area to improve the cohesive friction force (for example, Patent Document 3), a water repellent such as silicon is added to adhere to the tread surface. Numerous blending techniques are known, such as those that remove water.

In addition, large studless tires are used not only on ice and snow on the snowy road surface in winter, but also on general road surfaces in summer, so they have low heat build-up, wear resistance and low resistance on dry and wet road surfaces. Driving performance such as fuel efficiency is required.
JP-A-10-7841 JP-A 1-1118542 JP 2002-309038 A

  The rubber composition according to the above conventional method can certainly improve the performance on ice and snow roads, but the present situation is that it cannot fully satisfy the recent demand for improvement on ice and performance on snow, especially heavy load. In truck and bus tires that are used under severe conditions such as long-distance running, there is an increasing demand for further improvements.

  The present invention has been made in response to the above requirements, and has a large size excellent in running performance such as braking, driving performance, and driving stability on ice and snow road surfaces, as well as low heat generation and fuel efficiency on dry and wet road surfaces. An object of the present invention is to provide a rubber composition for a tire tread suitable for a studless tire.

  In order to achieve the above object, the present inventors focused on the colloidal characteristics of the carbon black used in the rubber composition and studied the SAF class carbon black that has been generally used for large tires. The use of carbon black, which is a balance between large particle size and high structure, makes it possible to achieve both driving performance on icy and snowy road surfaces and dry and wet road surfaces. As a result, the present invention was completed.

That is, in the present invention, the nitrogen adsorption specific surface area (N ₂ SA) is 80 to 130 m ² / g and the dibutyl phthalate (DBP) oil absorption is 110 ml / 100 g with respect to 100 parts by weight of the rubber component made of diene rubber. 40-60 parts by weight of carbon black having a sum of the nitrogen adsorption specific surface area (N ₂ SA) and dibutyl phthalate (DBP) oil absorption of 190-250, and 1-30 of plant granules A rubber composition for a tire tread characterized by containing a part by weight.

According to the rubber composition for a tire tread of the present invention, carbon black having a colloidal characteristic in which the particle diameter is larger and the structure is developed and the particle diameter and the structure are balanced, that is, N ₂ SA and DBP oil absorption amount. By blending carbon black with a sum of 190 to 250, it has excellent affinity with rubber, increases the modulus at the time of large deformation of the rubber composition, improves viscoelastic properties at low temperature, and storage elasticity at low temperature Suppressing the rate (E ') rise, maintaining rubber elasticity in the low temperature range (around 0 to -10 ° C), and securing the contact area at the time of minute deformation on the icy and snowy road surface, braking and driving performance on the icy and snowy road surface , Improve driving stability (hereinafter referred to as ice performance), increase the particle size of carbon black, improve dispersibility, suppress heat generation, maintain wear resistance and improve summer driving performance It is possible, can be further significantly improved ice performance by scratching effect by the combined use of plant granulate.

  In the present invention, the rubber component is preferably composed of 100 to 50 parts by weight of natural rubber and / or polyisoprene rubber and 0 to 50 parts by weight of butadiene rubber. Further, the butadiene rubber is cis- The 1,4 bond content is more preferably 95% or more, which improves the low-temperature characteristics of the rubber composition. Further, the formation of a high cis reduces heat generation and improves wear resistance.

  The rubber composition for a tire tread of the present invention has a particle size of 30 to 400 μm, preferably 100 to 200 μm, and a particle size of 100 to 400 μm that is surface-treated with a rubber adhesion improver. In addition, it is preferable to include plant granules that are preferably 200 to 300 μm, greatly improving the ice performance due to the scratching effect, and preventing the granules from falling off during running and continuing the effect for a long period of time. it can.

  According to the rubber composition for a tire tread of the present invention, the ice performance of the studless tire and the running in summer can be achieved by using together the carbon black having colloidal characteristics in which the particle size and the structure are balanced and the plant granular material. It is possible to achieve both performance and it can be suitably used as a tread rubber for a large studless tire that is worn and used particularly in summer.

  Hereinafter, embodiments of the present invention will be described in detail.

The rubber composition for a tire tread of the present invention has N ₂ SA and DBP oil absorption in a specific range with respect to 100 parts by weight of a rubber component composed of a diene rubber, and is the sum of N ₂ SA and DBP oil absorption. By adding carbon black with well-balanced colloidal characteristics within the specified range, ice performance and summer driving performance will be improved, and the ice performance will be greatly improved by blending plant granules. .

  As the rubber component used in the present invention, natural rubber and diene synthetic rubber are used, and natural rubber and / or polyisoprene rubber alone or blends of natural rubber and / or polyisoprene rubber with other diene rubbers are used. Can be used. Other rubbers include butadiene rubber (BR) of solution or emulsion polymerization, and various styrene butadiene rubbers (SBR) by solution or emulsion polymerization, and two or more of these may be used as a blend component.

  Among them, the rubber component is preferably composed of 100 to 50 parts by weight of natural rubber and / or polyisoprene rubber and 0 to 50 parts by weight of butadiene rubber, more preferably 90% of natural rubber and / or polyisoprene rubber. -50 parts by weight and butadiene rubber is 10-50 parts by weight.

  The butadiene rubber is preferably a high cis butadiene rubber having a cis-1,4 bond content of 95% or more, which improves the low temperature characteristics of the rubber composition, reduces heat generation, and improves wear resistance. Here, the cis-1,4 bond content is measured by an infrared absorption spectrum method.

The carbon black used in the present invention has N ₂ SA of 80 to 130 m ² / g, DBP oil absorption of 110 ml / 100 g or more, and the sum of N ₂ SA and DBP oil absorption of 190 to 250. And the compounding quantity is 40-60 weight part with respect to 100 weight part of rubber components.

If the N ₂ SA of the carbon black is less than 80 m ² / g, the particle size becomes too large, the modulus and strength decrease, and it becomes difficult to ensure wear resistance, and if it exceeds 130 m ² / g, the dispersion in the rubber The viscoelastic properties are not improved, the viscoelasticity is not improved, the heat generation is increased, and the processability of the compounded rubber is adversely affected. Here, N ₂ SA is measured in accordance with ASTM D3037.

Further, the carbon black having N ₂ SA in the above range and having a DBP oil absorption of 110 ml / 100 g indicating the structure of carbon black is used. This improves the agglomeration form of the carbon black particles, improves the affinity with the rubber molecules, improves the modulus of the rubber composition, and further suppresses the increase in storage elastic modulus (E ′) at low temperatures, thereby improving the rubber elasticity. It is possible to maintain the ground contact area at the time of minute deformation on the icy and snowy road surface. Accordingly, the DBP oil absorption amount is preferably 120 ml / 100 g or more from the viewpoint of improving the modulus at the time of large deformation (300% modulus) and the viscoelastic properties at low temperature, and more preferably 130 ml / 100 g or more.

  When the DBP oil absorption is less than 110 ml / 100 g, the structure development is poor and the carbon particles are bonded together, that is, the particles are connected in a straight chain, and the number of particles linked to each other is small between the particles bonded to rubber molecules. The void volume is insufficient, the affinity with rubber is insufficient, the viscoelastic properties and wear resistance are not sufficiently improved, and the heat generation is also deteriorated. The upper limit of the DBP oil absorption amount is not particularly limited, but if it becomes too high, the structure develops too much and it is easy to form a massive aggregate, the viscosity increases, and the workability and elongation characteristics tend to decrease, The upper limit is about 150 ml / 100 g. The DBP oil absorption is measured according to JIS K6221.

In the present invention, the N ₂ SA and the DBP oil absorption amount are in the above range, and the sum of the N ₂ SA and the DBP oil absorption amount needs to be in the range of 190 to 250. The colloidal properties of the diameter and the structure work in a balanced manner, making it possible to balance various properties such as rubber physical properties, viscoelastic properties, heat generation properties, and wear resistance of the rubber composition. Satisfies driving performance.

If the above sum is less than 190, the effects of both the large particle size and the high structure of carbon black cannot be brought out, and the object of the present invention is not achieved. Is not maintained, that is, if N ₂ SA becomes too large, viscoelastic properties and heat build-up will deteriorate, and if the DBP oil absorption becomes too large, rubber properties will deteriorate and it will be difficult to ensure processability and reinforcement. .

  The adjustment of the colloidal characteristics of these carbon blacks includes, for example, a combustion chamber having an air supply port at the furnace head and a combustion burner mounted in the furnace axial direction, and a raw material oil injection nozzle provided coaxially with the combustion chamber. This is performed by adjusting feedstock introduction conditions, air introduction conditions, fuel oil introduction conditions, and cooling conditions using an oil furnace furnace composed of a multistage small reaction chamber and a large reaction chamber. be able to.

  The compounding amount of the carbon black is 40 to 60 parts by weight with respect to 100 parts by weight of the rubber component, and if it is less than 40 parts by weight, the rubber strength and modulus are lowered, and the wear resistance and fatigue resistance are deteriorated. Exceeding parts by weight increases heat generation.

  Moreover, the rubber composition for tire treads of the present invention contains 1 to 30 parts by weight of plant granules, and in addition to the effect of the specific carbon black, the ice performance of the studless tire due to the scratch effect of the plant granules. Can be remarkably improved.

  The plant granule used in the present invention is granulated by pulverizing the seed shells such as walnuts and persimmons having a Mohs hardness of 2 or more or the cores of fruits such as peaches and plums by a known method. The body is used.

  The rubber composition blended with these granular materials prevents the sliding of the tread rubber by preventing the particles from protruding from the tread surface and being caught in the fine holes of the bubbles formed on the road surface on ice. Is.

  The particle size of the vegetable granule used for the rubber composition of the present invention is 30 to 400 μm, preferably 100 to 200 μm. When the particle diameter is less than 30 μm, the scratching effect is reduced, and when it exceeds 400 μm, the action of destroying the bubbles is reduced because it is larger than the diameter of the bubbles contained in the ice. Cracks are likely to occur due to excessive distortion in the surroundings.

  In addition, since granules with a large particle size are subject to large strains when stress is applied in the rubber matrix, they easily fall off, and those with a particle size larger than 100 μm improve the adhesion to rubber. It is preferable that the surface treatment with an agent is a pneumatic radial tire, and the particle diameter after the surface treatment is 100 to 400 μm, preferably 200 to 300 μm.

  Examples of the rubber adhesion improver include a mixture of a resorcin / formalin resin initial condensate and latex. In addition, known isocyanate compounds, epoxy compounds, and melamine resin initial condensates may be added to a mixture of resorcin / formalin resin initial condensate and latex. The adhesion rate of the above mixture to the plant granules is 1 to 5% by weight, and the plant granules are immersed in the mixture adjusted to a solid content concentration of 5 to 25% by weight or plant. By spraying the mixture onto the granulate and drying, a plant granule that has been subjected to a surface treatment with improved rubber adhesion is obtained. Since the surface-treated plant granules have a large particle size, they are re-ground by a known method, sieved, and adjusted to plant granules having a desired particle size range.

  The blending amount of the vegetable granule is preferably 1 to 30 parts with respect to 100 parts by weight of rubber. When the blending amount is less than 1 part, the ice performance on the road surface on ice is inferior, and when it exceeds 30 parts, the wear resistance is extremely lowered and the durability in the summer driving is remarkably lowered.

  And in this invention, in the range of the compounding quantity of the said vegetable granule, 1-20 parts of the vegetable granule which is 100-400 micrometers in which the particle diameter by which the surface treatment of rubber adhesive improvement was performed, and particle diameter It is preferable to use together 1 to 10 parts of a vegetable granule which is not subjected to a surface treatment for improving rubber adhesion of 30 to 400 μm.

  As a result, plant granules that have not been subjected to a surface treatment with improved rubber adhesion fall off from the tread surface while the tire is running, holes are formed after dropping, and the holes absorb water and form a thin water film on ice. It removes and makes it difficult to slip, and also has the effect of removing water by bringing the tread surface into direct contact with ice, and the ice performance is achieved through a synergistic effect with the hooking effect produced by the plant granule that has been surface-treated to improve rubber adhesion. This can be further improved.

  In the rubber composition of the present invention, in addition to carbon black and plant granules, various compounding agents generally blended in a tread rubber composition can be arbitrarily blended with the rubber component, and the blending amount thereof. Can also be a general amount. Examples of compounding agents to be optionally blended include vulcanizing agents, vulcanization accelerators, carbon blacks other than those described above, silica, softening agents, zinc white, stearic acid, waxes, anti-aging agents, processing aids, etc. It can mix | blend suitably in the range which is not contrary to the objective.

  The rubber composition for a tire tread of the present invention can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader, and can be used as a cap tread for large studless tires such as trucks, buses, and light trucks. A studless tire that is preferably used and is molded and vulcanized according to a conventional method to satisfy ice performance and summer running performance can be obtained.

  Hereinafter, the rubber composition for a tire tread according to the present invention will be described based on examples, but the present invention is not limited to these examples.

  Formulation shown in Table 1 is added to 100 parts by weight of a rubber component obtained by blending 60 parts by weight of natural rubber (RSS3) and 40 parts by weight of butadiene rubber (manufactured by JSR, BR01 (cis-1,4 bond content: 96%)). In the content (parts by weight), the following carbon blacks (CB-A to F) and plant granules (walnuts A and B) are blended with the following various compounding agents (parts by weight) as common blending components. The rubber compositions for tire treads of Examples 1 to 5 and Comparative Examples 1 to 4 were prepared by kneading using a closed Banbury mixer.

[Carbon black (CB-AF)]
CB-A: N ₂ SA = 142 m ² / g, DBP oil absorption = 115 ml / 100 g (Tokai Carbon, Seast 9)
CB-B: N ₂ SA = 119 m ² / g, DBP oil absorption = 114 ml / 100 g (Tokai Carbon, Seast 6)
CB-C: N ₂ SA = 116 m ² / g, DBP oil absorption = 125 ml / 100 g
CB-D: N ₂ SA = 82 m ² / g, DBP oil absorption = 126 ml / 100 g (Tokai Carbon, Seast 3H)
CB-E: N ₂ SA = 84 m ² / g, DBP oil absorption = 133 ml / 100 g
CB-F: N ₂ SA = 79 m ² / g, DBP oil absorption = 101 ml / 100 g (Tokai Carbon, Seast 3)

In addition, the N ₂ SA and DBP oil absorption amounts of CB-C and E are adjusted by adjusting the feedstock introduction conditions, air introduction conditions, fuel oil introduction conditions, and cooling conditions in the production of carbon black using the oil furnace. This was done by adjusting.

[Walnut-A, B]
Walnut-A: ground product of walnut shell with a particle size of 100 to 200 μm, surface untreated product Walnut-B: ground product of walnut shell with a particle size of 200 to 300 μm, surface treated product with rubber adhesion improver (resorcin・ A product obtained by immersing in a mixture of formalin resin initial condensate and latex (solid concentration 15% by weight), surface treatment, drying, pulverizing and sieving)

[Common ingredients and blending amounts]
・ Zinc flower: 3 parts by weight (Mitsui Metal Mining Co., Ltd., Zinc flower No. 1)
・ Stearic acid: 3 parts by weight (manufactured by NOF, flakestearic acid)
Anti-aging agent 6PPD: 1 part by weight (manufactured by Flexis, Santoflex 13)
・ Sulfur: 2 parts by weight (Shikoku Chemicals, powdered oil sulfur)
・ Vulcanization accelerator TBBS: 1 part by weight (manufactured by Sanshin Chemical Industry Co., Ltd., Sunseller NS)

  About each rubber composition, the rubber physical property by a tension test, the viscoelastic property, heat build-up, and the ice performance by an actual vehicle test were evaluated. Each evaluation method is as follows.

[Rubber properties]
Tensile tests were performed in accordance with JIS K6251 (using No. 3 dumbbells), 300% modulus, strength, and elongation at break were measured.

[Viscoelastic properties]
Using a Toyo Seiki spectrometer, the storage elastic modulus (E ′) at −5 ° C. was measured at a frequency of 10 Hz, an initial elongation of 10%, and a strain amplitude of 2%. The comparative example 1 is shown in the table with an index of 100, and the smaller the numerical value, the better.

[Exothermic]
Based on JIS K6265, the exothermic temperature by a flexometer was measured. The comparative example 1 is shown in the table with an index of 100, and the smaller the numerical value, the better.

[Ice performance]
Prototype tires of size 11R22.5 in which each rubber composition was applied to a cap tread were prepared. The same tires were attached to all the wheels of the truck, and after running for 200 km on a dry road, the road surface temperature was -2 ° C. The distance to stop by applying a sudden brake when traveling at a speed of 30 km / h on an ice surface was measured. The reciprocal of the stop distance is set as an ice performance, and the result is shown in the table as an index with Comparative Example 1 being 100. The larger the value, the better.

From Table 1, compared to Comparative Example 1 containing conventional SAF grade carbon black, Comparative Example 2 containing CB-D having a large particle size and a high structure has low heat generation, but has little improvement in ice performance. In Comparative Example 3 in which walnuts A and B are blended, the ice performance is improved, but the exothermic property is deteriorated. In Comparative Example 4 using carbon black having a sum of N ₂ SA and DBP oil absorption of less than 120, there is an effect of improving ice performance by walnuts, but an improvement effect by carbon black is not recognized.

  In contrast to each comparative example, each example according to the present invention clearly shows the combined effect of carbon black having a large particle size and high structure and plant granules (walnuts A and B). While improving the elastic characteristics and heat generation, the ice performance can be remarkably improved by the synergistic effect of carbon black and plant granules, and the winter performance of the studless tire can be satisfied. In each example, although strength and elongation decrease, it is not inferior to Comparative Example 3 in which walnuts A and B are blended, and satisfies the performance as a studless tire.

The rubber composition for a tire tread of the present invention can be used as a tread rubber for various studless tires including large tires such as trucks and buses.

Claims (7)

For 100 parts by weight of the rubber component made of diene rubber,
The nitrogen adsorption specific surface area (N ₂ SA) is 80 to 130 m ² / g, the dibutyl phthalate (DBP) oil absorption is 110 ml / 100 g or more, and the nitrogen adsorption specific surface area (N ₂ SA) and dibutyl phthalate (DBP) ) 40-60 parts by weight of carbon black having a sum of oil absorption of 190-250,
A rubber composition for a tire tread, comprising 1 to 30 parts by weight of a vegetable granule. The rubber composition for a tire tread according to claim 1, wherein the rubber component comprises 100 to 50 parts by weight of natural rubber and / or polyisoprene rubber and 0 to 50 parts by weight of butadiene rubber. The rubber composition for a tire tread according to claim 2, wherein the butadiene rubber has a cis-1,4 bond content of 95% or more. The rubber composition for a tire tread according to any one of claims 1 to 3, wherein a particle diameter of the plant granular material is 30 to 400 µm. The tire tread rubber composition according to claim 4, wherein a particle diameter of the plant granule is 100 to 200 μm. The rubber composition for a tire tread according to any one of claims 1 to 5, comprising a vegetable granule having a particle diameter of 100 to 400 µm that has been surface-treated with a rubber adhesion improver. The rubber composition for a tire tread according to claim 6, wherein a particle size of the plant granule subjected to the surface treatment is 200 to 300 μm.