JP2613043B2 - Rubber composition for tread - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tire tread which generates less heat during running, has excellent fuel efficiency, and has abrasion resistance, braking performance on wet road surfaces, and snow and ice surfaces. The present invention relates to a rubber composition for a tread, which has significantly improved braking performance at the same time, and particularly has excellent rolling resistance performance.

(Prior art)

2. Description of the Related Art In recent years, under the social demands for resource saving and energy saving, demands for low fuel consumption of automobiles have been extremely increased. For this reason, not only the development of automobile bodies, such as the development of engines that consume less gasoline, but also the study of fuel-efficient tires with less energy loss has been rapidly conducted.

Conventionally, rubber materials with low hysteresis loss have been required as rubbers for tire materials of fuel-efficient tires. Among them, natural rubber with low hysteresis loss as a rubber component is used in the tread portion, which is said to account for 50% or more of the tire hysteresis loss. , Polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber having a low glass transition point (Tg), and blends thereof have been used. Further, as the rubber composition, a rubber composition in which carbon black having a relatively large particle diameter is blended in a relatively small blending amount and a blending amount of a softening agent such as an aromatic oil is used as small as possible has been used. It has been.

By the way, recently, more functions are required for tires at a higher level. For example,
In the fuel-efficient tires developed as described above, the fuel-efficient performance is not reduced, and the wear performance is further improved in terms of economy. There is a strong demand for high braking performance that can cope with various road surfaces such as road surfaces.

However, as described above, natural rubber with low hysteresis loss, polyisoprene rubber, polybutadiene rubber, Tg
When a styrene-butadiene copolymer rubber having a low viscosity is used for the tread portion, there is a disadvantage that braking performance (wet skid resistance) particularly on wet road surfaces is inferior, and running stability is extremely reduced. . In addition, when carbon black having a large particle diameter is used, although the fuel economy performance is excellent, deterioration of characteristics such as braking performance and abrasion resistance on a wet road surface is inevitable. In addition, the tread rubber of conventional fuel-efficient tires tends to become harder at low temperatures due to a reduced amount of softening agent, and as a result, braking performance on snowy and icy roads (ice-skid resistance)
Had not yet reached a satisfactory level.

On the other hand, recently, as a material that satisfies both characteristics of fuel efficiency and wet skid resistance of a tire, a so-called high vinyl polybutadiene rubber or a high vinyl styrene-butadiene copolymer rubber containing 50% or more of 1,2-vinyl bonds has been recently developed. Has been proposed. However, these rubbers all have a high glass transition point (Tg), so they are inferior in abrasion resistance, are easily hardened at low temperatures, and are extremely inferior in braking performance on snow-covered or icy road surfaces. Again, it is not enough to satisfy all properties.

As described above, at present, no tire has been proposed that satisfies all the characteristics such as low fuel consumption performance, high braking performance on wet road surfaces, and high braking performance on snow-covered or icy road surfaces. In the past, in the winter, when the road surface becomes slippery due to snow and ice, the braking performance on ordinary roads including fuel-efficient tires was extremely small, and the use of snow tires had to be used. . However, the time and labor required for the user to change tires is considerable, and the emergence of all-season tires that satisfy the above three characteristics in general summer tires is highly desired.

[Object of the invention]

The present invention has been made to meet such a demand, and generates less heat in a tire tread portion during running, has excellent fuel efficiency, and has abrasion resistance, braking performance on a wet road surface and snow and snow. It is an object of the present invention to provide a rubber composition for a tread which has significantly improved braking performance on an icy road surface, and particularly has excellent rolling resistance performance. The composition is useful as a tread for a so-called all-season pneumatic tire that can be used throughout the year regardless of summer and winter.

[Configuration of the invention]

For this reason, the present invention relates to a natural rubber and / or polyisoprene rubber of 20 to 80 parts by weight, a bound styrene amount of 10 to 30% by weight, and a 1,2-vinyl bond amount of a butadiene portion of 10 to 80 parts by weight.
% Of a styrene-butadiene copolymer rubber in an amount of 80 to 20 parts by weight, and a total of 100 parts by weight of rubber, wherein the styrene-butadiene copolymer rubber has the following formula at the molecular chain terminal or in the molecular chain. , Has been introduced, and as a reinforcing agent, IA
_{= 60~70, N 2 SA / IA} = 1.22~1.40, ΔD 50 (Dst) = 70~1
The gist of the present invention is a rubber composition for a tread, which contains 30 to 80 parts by weight of carbon black having a particle diameter of 30 μm based on 100 parts by weight of a raw rubber.

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

(1) The tread rubber composition of the present invention comprises 20 to 80 parts by weight of natural rubber (NR) and / or polyisoprene rubber (IR) and 80 to 20 parts of a specific styrene-butadiene copolymer rubber.
It is contained by weight (100 parts by weight of rubber). If the compounding ratio is out of this range, one of the characteristics of fuel economy, braking on a wet road surface, and braking on a snow-covered or icy road surface is deteriorated, which is not preferable. However, other diene rubbers, for example, polybutadiene rubber, acrylonitrile-butadiene copolymer rubber, unmodified styrene-butadiene copolymer rubber, etc., may be contained in an amount of 30 parts by weight or less.

In the styrene-butadiene copolymer rubber used here, an atomic group represented by the following formula is introduced at the molecular chain terminal or in the molecular chain.

The introduction of the atomic group represented by the above formula (I) is achieved by the bonding of the following formula (Wherein M represents an O atom or an S atom) (hereinafter, referred to as compound A) is reacted with a styrene-butadiene copolymer.

Compound A includes N, N-dimethylformamide, N, N
-Diethylformamide; N, N-diethylacetamide;
Aminoacetamide, N, N-dimethyl-N ', N'-dimethylaminoacetamide, N-phenyldiacetamide; N, N-dimethylacrylamide, N, N-dimethylmethacrylamide; propionamide, N, N-dimethylpropionamide ; 4-pyridylamide, N, N-dimethyl-
4-pyridylamide; N, N-dimethylbenzamide, p-
Aminobenzamide, N ', N'-(p-dimethylamino) benzamide, N, N-dimethyl-N '-(p-ethylamino) benzamide, N-acetyl-N-2-naphthylbenzamide; nicotinamide, N, N-diethylnicotinamide; succinamide, maleic amide, N,
N, N ', N'-tetramethylmaleamide; succinimide, maleimide, N-methylmaleimide, N-methylphthalimide, 1,2-cyclohexanedicarboximide, N-methyl-1,2-cyclohexanedicarboximide; Oxamide, 2-furamide, N, N, N ', N'-tetramethyloxamide, N, N-dimethyl-2-furamide; N, N
-Dimethyl-8-quinolinecarboxamide; N, N-dimethyl-p-amino-benzalacetamide, N, N-dimethyl-N ', N'-(p'-dimethylamino) cinnamylideneacetamide; N, N -Dimethyl-N ', N'-(2-dimethylamino) vinylamide; N '-(2-methylamino) vinylamide; urea, N, N'-dimethylurea, N, N,
N ', N'-tetramethylurea; methyl carbamate, N, N
-Methyl diethylcarbamate; ε-caprolactam,
N-methyl-ε-caprolactam, N-acetyl-ε-
Caprolactam, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, 2-piperidone, N-methyl-2-piperidone, 2-quinolone, N
-Methyl-2-quinolone, 2-indolinone, N-methyl-2-indolinone; isocyanuric acid, N, N ', N "-
Examples include trimethyl isocyanuric acid and the corresponding sulfur-containing compounds. Particularly preferred compounds are compounds in which an alkyl group is bonded to nitrogen.

The method for producing the styrene-butadiene copolymer rubber into which the atomic group represented by the formula (I) has been introduced includes, for example, (a) using an alkali metal base catalyst and / or an alkaline earth metal base catalyst. A method in which styrene and butadiene are polymerized, and compound A is added to a solution in which the polymerization reaction is completed. (B) In a solution in which a styrene-butadiene copolymer is dissolved in an appropriate solvent, an alkali is added to the copolymer. For example, a method in which a metal and / or an alkaline earth metal is added, followed by adding compound A to cause a reaction and the like can be exemplified.

In this case, the alkali metal-based catalyst used in the polymerization reaction and the addition reaction is a metal itself such as lithium, rubidium, and cesium, or a complex thereof with a hydrocarbon compound or a polar compound (for example, n-butyllithium, -Naphthyllithium, potassium-tetrahydrofuran complex, potassium-diethoxyethane complex, etc.). Further, alkaline earth metal based catalysts are disclosed in JP-A-51-11.
Examples of such catalyst systems include compounds such as barium, strontium, and calcium described in JP-A-5590, JP-A-52-9909, and JP-A-57-100146. Any metal-based catalyst may be used as a catalyst for ordinary solution polymerization, and is not particularly limited.

After the completion of the reaction, the unsaturated rubbery polymer into which the compound A has been introduced is recovered from the reaction solution by using a usual separation method such as addition of a coagulant such as methanol and stripping with steam. In the resulting unsaturated rubbery polymer, at the molecular chain terminal or in the molecular chain, Compound A is introduced as an atomic group.

The site into which compound A is introduced may be at the end of the molecular chain or at any other site, but is preferably at the end of the molecular chain. This is because the use of the polymer obtained by the reaction between the copolymer having a dienyl structure at the terminal of the molecular chain and the compound A further improves the fuel efficiency.

It is an essential component of the present invention that the styrene-butadiene copolymer rubber has the atomic group represented by the above formula (I) at the terminal or in the molecular chain. The rubber composition containing the styrene-butadiene copolymer rubber is remarkably improved as compared with a rubber composition comprising a normal styrene-butadiene copolymer rubber having no atomic group represented by the above formula (I). Exhibit rebound resilience. Therefore, a pneumatic tire using this rubber composition for a tread can significantly improve fuel economy while maintaining other characteristics at a high level.

The styrene-butadiene copolymer rubber used in the present invention has a bound styrene content of 10 to 30% by weight,
The 1,2-vinyl bond content of the butadiene portion is 10 to 80%.

If the amount of bound styrene is less than 10% by weight, the wet skid resistance of the rubber composition is reduced, and the braking performance of the tire on a wet road surface is undesirably deteriorated. On the other hand, when the content exceeds 30% by weight, the braking performance on wet road surfaces increases, but the braking performance and wear resistance on snow-covered or icy road surfaces deteriorate.

If the amount of 1,2-vinyl bond is less than 10%, the effect of improving the braking performance on wet road surfaces is small, while if it exceeds 80%, the heat generation increases and the braking performance and wear resistance on icy road surfaces are significantly increased. It is not preferable because it decreases.

In addition, the styrene-butadiene copolymer rubber used in the present invention may contain a branched polymer bonded by a tin-butadienyl bond in order to obtain good processability during tire production.

(2) The rubber composition for a tread of the present invention contains 30 to 80 parts by weight of carbon black as a reinforcing agent based on 100 parts by weight of the raw rubber.

If the compounding amount of carbon black is less than 30 parts by weight, sufficient braking performance and abrasion resistance on a wet road surface cannot be obtained as a tire. On the other hand, if it exceeds 80 parts by weight, the fuel economy of the tire is deteriorated, and in addition, the hardness of the tread portion is increased at low temperatures, so that the tire becomes slippery on an iced road surface, which is not preferable.

The characteristics of the carbon black used here are: iodine adsorption amount (IA) = 60 to 70, ratio of nitrogen specific surface area (N ₂ SA) to iodine adsorption amount (IA) (N ₂ SA / IA) = 1.22 to 1.40. , ΔD ₅₀
It is necessary that (Dst) = 70 to 130 mμ.

If the IA is less than 60, the abrasion resistance will be significantly reduced, while if it is more than 70, the fuel economy will deteriorate, which is not preferable.

The N ₂ SA / IA ratio is considered to be a measure of the surface activity of carbon black, and the higher the value, the higher the activity. N ₂ SA / IA is 1.2
If it is less than 2, sufficient abrasion resistance and low fuel consumption cannot be obtained, and if it exceeds 1.40, granulation becomes difficult during production of carbon black, and the kneading property of rubber is unpreferably deteriorated.

Δ ₅₀ (Dst) is the half width of the particle size distribution of the carbon black particles and is a measure of the distribution. When ΔD ₅₀ (Dst) is less than 70 μm, the fuel economy deteriorates, while when it exceeds 130 μm, the abrasion resistance decreases.

In the present invention, by using carbon black having the above characteristics, the rebound resilience of the rubber composition is increased, thereby reducing the rolling resistance of the tire (low fuel consumption) and enhancing the reinforcing property against rubber. It improves abrasion.
In other words, the surface irregularities are large (the N ₂ SA / IA ratio is large (N ₂ SA /
IA = 1.22~1.40)), of the particle size distribution greater (Δ ₅₀ (Ds
t) = 70-130mμ) By blending carbon black, the interaction between carbon black and rubber is increased (reducing energy loss due to rubbing between carbon particles) and rubber is prevented by rubbing between carbons. The heat generation is reduced to reduce the rolling resistance, and the reinforcement is enhanced to improve the wear resistance.

The rubber composition of the present invention may contain vulcanizing agents, vulcanization accelerators, vulcanization aids, antioxidants, softeners, and the like, which are compounding agents used in the general rubber industry. Further, the rubber composition of the present invention can be applied to all tires such as tires for passenger cars, trucks, and buses, and is not particularly limited to the types of tires.

 Examples and comparative examples are shown below.

Examples and Comparative Examples The styrene-butadiene copolymer rubber used here (SB
The properties of R) are shown in Table 1, and the properties of carbon black (CB) are shown in Table 2. Further, Table 3 shows Examples and Comparative Examples (compounding parts by weight).

As for the mixing method, the ingredients shown in Table 3 were mixed for 4 minutes using a Banbury mixer of 1.7, and sulfur and a vulcanization accelerator were added by a roll. Vulcanization was performed at 160 ° C. for 15 minutes, and the 300% tensile stress, Lupke rebound resilience, wet skid resistance and pico abrasion were measured. For the Rupke rebound resilience, the lower the index value at both 0 ° C and 60 ° C, the lower the value of Lupke elasticity, the lower the value at 0 ° C, the better the wet performance, and the higher the value at 60 ° C, the lower the rolling resistance. Is shown. Pico abrasion is represented by the amount of abrasion, and a smaller value indicates better abrasion resistance.

Note) * 1 Measured by the method of JIS K6221.

* 2 Measured by JIS K6221.

* 3 ΔD ₅₀ (Dst) is measured by the following method using a disc centrifuge (manufactured by Joyce Loebl, UK). That is, a carbon black is precisely weighed, a 20-volume aqueous ethanol solution and a surfactant are added, and the mixture is ultrasonically dispersed so that the carbon black concentration becomes 5 mg / 100 cc to prepare a sample solution. Next, at a rotation speed of the disk centrifuge of 8000 rpm, 0.5 mm of the sample solution was injected into 10 ml of a spinning solution composed of distilled water, and centrifugal sedimentation was started all at once. , The half-width ΔD ₅₀ (Ds
t).

Table 3 shows that the carbon blacks of the present invention (CB-3, CB-
It can be seen that the use of 4) improves the rebound resilience without lowering the wet skid resistance and wear resistance.

Next, rolling resistance was tested on 145SR12 size tires using the rubber compositions of Comparative Example 2 and Example 3 as tread rubbers, respectively. The results are shown in Table 4 below as indices. In this case, the rolling resistance test was performed with a tire pressure of 1.7 kg /
It was measured at a speed of 60 km / h on a steel dorm with a diameter of 1707 mm in cm ² .

Table 4 shows that the rubber composition of the present invention (Example 3) has low rolling resistance.

As described above, by combining the above-mentioned specific carbon black with the modified SBR / NR blend system, the tread compound with particularly improved rolling resistance performance while maintaining wet performance, low temperature performance and abrasion resistance at a high level Can be obtained.

〔The invention's effect〕

As described above, according to the present invention, by using SBR having a high interaction with carbon black as a polymer and using a combination of highly active carbon black, excellent fuel economy and wear resistance Thus, a rubber composition suitable for treads of pneumatic tires for all seasons, which simultaneously satisfies braking performance on wet road surfaces and snow / ice road surfaces, can be obtained.

Claims (1)

(57) [Claims] (1) 20 to 80 parts by weight of natural rubber and / or polyisoprene rubber, and the amount of bound styrene is 10 to 30% by weight.
Wherein the butadiene moiety has a 1,2-vinyl bond content of 10 to 80%
Containing 80 to 20 parts by weight of a styrene-butadiene copolymer rubber, and a total of 100 parts by weight of the rubber component, and the styrene-butadiene copolymer rubber has the following formula in a molecular chain terminal or in a molecular chain: (2) As reinforcing agents, IA = 60 to 70, N ₂ SA / IA = 1.22 to
1. A rubber composition for a tread, comprising 30 to 80 parts by weight of carbon black having a ΔD ₅₀ (Dst) of 70 to 130 mμ per 100 parts by weight of a raw rubber.