JP3207885B2 - Rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a base portion of a steel belt radial tire for a passenger car having a tread portion having a two-layer structure of a cap portion and a base portion, and more particularly to such a rubber for the base portion. The purpose of the present invention is to reduce the rolling resistance of tires by improving the composition, and to contribute to reducing fuel consumption of automobiles in order to meet resource and energy savings demanded by society today.

[0002]

2. Description of the Related Art It is known that the rolling loss of a tire can be reduced by reducing the energy loss of a compounded rubber. It is also known that the tread portion of the tire has a two-layer structure, and the cap portion in direct contact with the ground is improved to improve steering stability, while the base portion is improved to reduce energy loss.

Conventionally, in order to reduce the energy loss of the base rubber, techniques such as increasing the particle size of the carbon black to be used and decreasing the amount of the carbon black have been adopted.

[0004]

However, there has been a problem that the strength of the rubber is reduced according to the method conventionally employed to reduce the energy loss. Tires in which rubber having reduced strength as a result of reduced energy loss is used for the base portion of the tread portion have a problem that chunking occurs in the shoulder portion in a turning test on a passenger car. In order to prevent this, it is said that the tensile product at a high temperature of about 100 ° C. needs to be 3 × 10 ⁴ % kg / cm ² or more (JP-A-56-128204). Here, the tensile product is used to evaluate the breaking properties of rubber, JIS K630
According to the tensile test specified in 1, tensile strength (kg
/ Cm ² ) and elongation (%) are measured and the product is obtained.

In the prior art, it is difficult to reduce the rolling resistance and to achieve low fuel consumption because the strength of the rubber is reduced in order to reduce the energy loss. There is a strong need for a solution to the problem.

Accordingly, an object of the present invention is to provide a technique for reducing the energy loss and the rolling resistance of a rubber composition for a base portion of a tire tread portion while maintaining rubber strength. is there.

[0007]

Means for Solving the Problems In order to solve the above problems, the present inventors have found that the loss tangent tan δ is smaller than that of a conventional tire from the viewpoint of rubber properties, and the tensile product does not cause a problem. As a result of intensive studies to develop a rubber composition having a lower limit (3.5 × 10 ⁴ % · kg / cm ² ) or more, the nitrogen adsorption conventionally used for carbon black grading was obtained in order to obtain such a rubber composition. It was found that not only the specific surface area (N ₂ SA) but also the contribution of dibutyl phthalate oil absorption (DBP) was extremely large.

That is, with respect to N ₂ SA, which is one of the colloidal properties of carbon black, it is difficult to reduce the energy loss in a region exceeding 120 m ² / g, and the particle diameter of carbon black becomes small. The dispersibility in rubber is inferior, and it tends to be heterogeneous especially when the amount of carbon black is small.On the other hand, as for DBP, the larger the value, the more the compounding amount can increase the tensile product, and at 130 ml / 100 g or more, We have found that this tendency is significant.

In order to achieve the above object, a rubber composition of the present invention for a base portion of a steel belt radial tire for a passenger car having a tread portion having a two-layer structure of a cap portion and a base portion comprises a diene rubber 100 relative to the weight parts, N ₂ SA is 40~120m ² / g (but, 120 m ² / g excluding.) a and DBP is carbon black having the above characteristics 140 ml / 100 g 3 to 35 parts by weight (however 30 Excluding 35 parts by weight), the loss tangent tan δ at a temperature of 60 ° C is 0.08 or less, and the tensile product at 100 ° C is 3.5 × 10 ⁴ % kg / c
m ² or more.

In the rubber composition for a base portion of the present invention, if the rubber component is a diene rubber, natural rubber may be used.
(NR), styrene butadiene rubber (SBR), butadiene rubber
Various rubbers such as (BR) alone or blends can be used.

The carbon black used in the present invention uses a raw material having a high aromatic component, uses a reaction furnace according to a usual oil furnace method, produces a reaction temperature, a reaction time, a flow rate of a combustion gas, a raw material in a chalk portion. It can be manufactured by controlling the oil concentration and the like.

The rubber composition of the present invention may contain, if necessary, a compounding agent usually used in the rubber industry, such as a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerator, an antioxidant and a softening agent. Needless to say, they can be appropriately blended.

[0013]

As a means for improving rolling resistance while maintaining rubber strength in order to prevent tire chunking, the inventors of the present invention used a highly reinforcing carbon black having specific colloidal characteristics with a rubber component of 100%. 3 to parts by weight
It has been found that it is better to use in the range of 35 parts by weight (excluding 30 to 35 parts by weight). If the N ₂ SA of such carbon black is less than 40 m ² / g, sufficient strength cannot be secured, while if it is 120 m ² / g or more, the rolling resistance cannot be sufficiently reduced. Furthermore, DBP is for difficult aim to achieve both reduction of securing the rolling resistance of the rubber strength be less than 140 ml / 100 g, with N ₂ SA is 40~120m ² / g (excluding 120m ² / g.) And DBP is 140ml / 100g or more, preferably N ₂ SA
In the present invention, carbon black having a size of 50 to 100 m ² / g and a DBP of 150 ml / 100 g or more is selected.

On the other hand, if the amount of the carbon black is less than 3 parts by weight per 100 parts by weight of the rubber component, a sufficient reinforcing effect cannot be obtained, while if it is more than 30 parts by weight, the effect of reducing rolling resistance cannot be obtained. For this reason, in the present invention, 3 to 30 parts by weight, preferably 5 to 30 parts by weight is blended.

Further, in the present invention, in order to ensure practically sufficient rubber strength and further reduce rolling resistance as compared with conventional fuel-efficient tires, the loss tangent tan δ at 60 ° C.
Must be 0.08 or less, preferably 0.05 or less. If this value exceeds 0.08, the effect of reducing the rolling resistance cannot be expected as compared with the conventional base portion rubber.
In the present invention, the most advantageous compounding system for achieving both the optimum loss tangent tan δ value and high-temperature strength at the same time is described in Example 9 below.
The polymer is natural rubber and carbon black is DB
This is a system in which a compound with a high P is blended around 15 parts by weight with respect to 100 parts by weight of the rubber component.

The above-described rubber composition for a base portion of the present invention can sufficiently exhibit its effects by being combined with a rubber composition for a cap portion capable of ensuring steering stability.

[0017]

Next, the present invention will be described in detail with reference to examples. In this example, various carbon blacks shown in Table 1 below were used. The N ₂ SA in the table is ASTM D 3037
And DBP sought in accordance with ASTM D 2414.

[0018]

Using the above various carbon blacks, various rubber compositions were prepared in accordance with the formulation (parts by weight) shown in Table 2 below. The results of various measurement tests in the table were obtained as follows.

The loss tangent tan δ was measured using a spectrometer manufactured by Iwamoto Seisakusho under the conditions of an initial strain of 10%, a frequency of 60 Hz, a dynamic strain of 1% and a temperature of 60 ° C.

Tensile product (% kg / cm ² ) The tensile strength (kg / cm ² ) and elongation (%) of the test rubber were measured at 100 ° C. by a tensile test specified in JIS K 6301. The product was defined as the tensile product.

Rolling Resistance Index Based on the current commercially available tires (size PSR 185/70 R13 cap / base structure), various types of tires were manufactured in which only the base rubber was changed. Incidentally, the cap tread rubber was common to all, and the tan δ at 60 ° C. was 0.28, and the volume of the base rubber relative to the entire tread was 15%. The rolling resistance of the prototype tire as described above was measured at a speed of 60 km / hr on a steel drum having a diameter of 1707 mm, and an index was obtained by the following equation based on a conventional control tire (Comparative Example 5). displayed. The smaller the value, the better the result.

Turning durability The durability was evaluated in a severe turning test (lateral acceleration 0.8 ± 0.1 G). The number of turns until a part of the steel belt inside one of the left and right wheels of the test tire mounted on the front wheel of a vehicle turning with a diameter of 15 m was measured, and the control tire (Comparative Example 5) was used as a reference. An exponent was given by the following equation. The higher the value, the better the result.

[0024] In turning tests fracture morphology above, to observe whether there is breakage in the base rubber inside the periphery of the belt exposed portion, when the rubber fracture is present, and the fracture morphology is inferior. The obtained results are also shown in Table 2.

[0025]

[Table 2]

From the measurement results shown in Table 2, the following was confirmed. When the rolling resistance was reduced by reducing the amount of carbon black as in the conventionally employed method, the turning durability as compared with Comparative Example 5 was significantly reduced as in Comparative Example 4.

[0027] Also, carbon black is a low grade
Although the rolling resistance was low even when it was changed to (N ₂ SA is small), the durability was reduced as in Comparative Example 8 with this.
In addition, high-grade grade with high reinforcement (large N ₂ SA)
It was thought that if the amount of use was reduced instead of the above, it was possible to achieve both low rolling resistance and high durability, but it was impossible to achieve both as in Comparative Examples 1 and 2.

Furthermore, if the amount of the carbon black having colloidal properties is too small, the reinforcing effect is not obtained as in Comparative Examples 9 and 12, and even if the amount is too large, Comparative Examples 10, 11 and 11 cannot be obtained.
As shown in Fig. 13, low rolling resistance was not obtained. Incidentally, among these, those having no numerical value in the tire evaluation were evaluations of only rubber quality, and were not tested.

On the other hand, in Examples 1 to 10, both reduction of rolling resistance and improvement of durability became possible.

[0030]

As described above, in the composition for the base portion of the present invention, N ₂ SA and DBP are added in an amount of 3 to 35 parts by weight (30 to 30 parts by weight) of carbon black having specific characteristics within a predetermined range. (Excluding 35 parts by weight) and by maintaining the tan δ value at a temperature of 60 ° C of 0.08 or less to maintain rubber strength, that is, to ensure both durability and reduced rolling resistance. be able to.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 9/00 B60C 1/00 B60C 11/00 C08K 3/04

Claims (2)

(57) [Claims] 1. A rubber composition for a base portion of a steel belt radial tire for a passenger car having a tread portion having a two-layer structure of a cap portion and a base portion, wherein a nitrogen adsorption specific surface area is based on 100 parts by weight of a diene rubber. 40
3 to 35 parts by weight (excluding 30 to 35 parts by weight) of carbon black having a characteristic of not more than 120 m ² / g (excluding 120 m ² / g) and having a dibutyl phthalate oil absorption of 140 ml / 100 g or more.
) The compound has a loss tangent tan δ value of 0.08 or less at a temperature of 60 ° C and a tensile product at 100 ° C of 3.5 x 10 ⁴ % kg / c.
m ² or more. 2. A carbon black having a nitrogen adsorption specific surface area of 50 to 100 m ² / g and a dibutyl phthalate oil absorption of 150 ml / 100 g or more per 100 parts by weight of a diene rubber.
The rubber composition according to claim 1, wherein the rubber composition is blended in parts by weight (excluding 30 parts by weight) .