JPS6036215B2 - Rubber composition for tire tread and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for a tire tread that reduces rolling resistance without impairing tire wear resistance and braking performance on wet road surfaces, and a method for producing the same.

In recent years, social demands for resource and energy conservation have become stronger, and efforts are being made to improve the fuel efficiency of automobiles.

The fuel consumption of automobiles is also affected by various characteristics of tires, and among these, it is said to be effective to reduce the rolling resistance of tires. Since the rolling resistance of a tire mainly depends on the energy loss during deformation of the materials that make up the tire, it is best to use rubber that has a small energy loss during deformation in the tread, which has a particularly large volume among the tire constituent parts. Effective. However, these rubbers generally have the disadvantage of reducing the braking performance of tires on wet road surfaces (for example, Automotive Technology No. 32, No. 5, pp. 417-420, 1978), and when deformed Rubber with low energy loss, i.e. natural rubber (
When a rubber composition containing rubber (NR) or polybutadiene rubber (BR) is placed on a tread, tire slip on a wet road surface becomes a problem. On the other hand, tires with treads made of rubber compositions containing styrene-butadiene copolymer rubber (SBR) as the main component have good braking performance on wet roads, but SBR is a rubber that loses a lot of energy when deformed. Therefore, there was a drawback that the rolling resistance of the tire became large. On the other hand, it is known that reducing the size and weight of automobiles is also effective in improving the fuel consumption efficiency of automobiles.

As automobiles become smaller, the interior space of the automobile becomes smaller, so a so-called front-wheel drive system, in which the engine is placed at the front of the automobile, is now used. In this front wheel drive type, the tires mounted on the front wheels wear out particularly quickly, so the rubber composition for tire tread must have excellent wear resistance. As described above, tires, especially treads, are currently required to have three different characteristics: good rolling performance on wet roads, low rolling resistance, and good wear resistance. Therefore, various rubber compositions for tire treads have been proposed, but a rubber composition that completely satisfies the above three properties has not yet been obtained.

In addition, as a rubber material test for these three characteristics, braking performance on a wet road surface was determined by wet skid resistance (Stanley Co., Ltd.,
British Portable Skid Tester, ASTM E303-74, Road surface used: 3M Outdoor Type B Safety Walk, 2500) Transfer resistance is rebound resilience (Lupke rebound test, 50-70℃)
and abrasion resistance are usually evaluated by tests such as pico abrasion loss (Goodrich type pico abrasion test). Attempts have been made to improve the properties of rubber vulcanizates through methods of kneading rubber compositions.

For example, A.K.Sircar
, T.G. Lamond, P.E. Pinter “Rubber Chemistry and Technology”
emistryandTechnology), Vol1
47, pp. 48-56, (1974 and Japanese Unexamined Patent Publication 1974)
The kneading method reported in No. 112445 is a method in which a general-purpose rubber is mixed with the entire amount of carbon black in advance, and then the same type or a different general-purpose rubber is mixed and kneaded with the first-stage kneaded product. Although this method is said to be effective in improving rebound resilience, this drilling method has poor compatibility between the first-stage mixed material and general-purpose rubber, resulting in poorly dispersed lumps. In such a state, there is a drawback that not only the processability is poor but also the abrasion resistance of the rubber composition after vulcanization is reduced. The present invention was made to satisfy these demands, and reduces rolling resistance without deteriorating braking performance and wear resistance on wet road surfaces, and also has good workability when unvulcanized. An object of the present invention is to provide a rubber composition for tire treads and a method for producing the same.

As a result of research in accordance with the above objectives, the present inventors have found that a rubber composition in which a specific amount of carbon black is blended into a raw material rubber made by blending high molecular weight SBR with low molecular weight SBR as a subcomponent satisfies the above objectives. Furthermore, it was discovered that even more preferable physical properties could be obtained by pre-mixing this rubber composition in a specific amount, thereby achieving the present invention.

That is, the rubber composition for tire red of the present invention is a styrene-butadiene copolymer rubber (A) 10 to 10% having a weight average molecular weight of less than 6.5×1 pi and a bound styrene content of 20 to 25% by weight. 4 parts by weight and a weight average molecular weight of 5.
5 x 1" or more and the amount of bound styrene is 20 to 25% by weight
Styrene-butadiene copolymer rubber (B) 90~
It is characterized in that 45 to 6 parts by weight of carbon black is blended with respect to 60 parts by weight of the raw rubber 10. In the present invention, the weight average molecular weight is 5.
5 x 1 perfect and the amount of bound styrene is 20 to 25% by weight
SBR (hereinafter referred to as L-MW-SBR) with a weight average molecular weight of 5.5 x 1 or more and a bound styrene content of 20 to
25% by weight SBR (hereinafter referred to as H-MW-SBR)
The blending ratio with SBR depends on the weight average molecular weight of both SBRs, but generally, the weight percent of L-MW-SBRIO~4, H
-MW-SBR Raw material rubber in the range of 90 to 6% by weight is used.

If L-MW-SBR exceeds 40% by weight, the vulcanized physical properties, such as impact resilience, will deteriorate, which is undesirable, and if it is less than 1% by weight, Mooney viscosity will increase and processability will deteriorate. As mentioned above, the raw rubber component of the present invention contains H-MW-SBR as a main component, but L-MW-SBR
A part of BR or halogenated butyl rubber (ratio 1-11R)
It is also possible to use it in place of Gen-based copolymer rubber such as NR and NR.

In addition, H-MW-SBR and L-MW-SBR are not particularly limited as long as they are polymers synthesized by ordinary emulsion polymerization or solution polymerization. SBR is also preferably used.

In the present invention, the amount of process oil in the oil-extended SBR is not included in the amount of raw rubber. According to the present invention, the weight average molecular weight of L-MW-SBR is preferably less than 5.5 x 1'', particularly within the range of 3.0 x 1 to 5.5 x 1''.

If the weight average molecular weight of L-MW-SBR is less than 3.0 x 1 P, the vulcanized physical properties of the rubber composition after vulcanization will deteriorate, and if it is 5.5 x 1 P or more, the molecular weight of the rubber composition will deteriorate. -The viscosity increases, making it unfavorable for processing. On the other hand, H-MW-S
The weight average molecular weight of BR is 5.5×1 and more than 15.0×1
It is preferable that it is less than or equal to . When the weight average molecular weight of H-MW-SBR is less than 6.0×1, the effect of improving impact resilience, which is the objective of the present invention, is 4. If it exceeds 15.0×1 pi, it has a high Mooney viscosity and is extremely difficult to process.

The amount of bound styrene in L-MW-SBR and H-MW-SBR is preferably in the range of 20 to 25% by weight.
If the amount of bound styrene is less than 2% by weight, the wet skid resistance (British Portable Number according to ASTM E303) of the rubber composition after vulcanization will decrease, and if it exceeds 25% by weight, the impact resilience will decrease. Put it away. The amount of carbon black contained in the rubber composition of the present invention is preferably 45 to 60 parts by weight based on 10 parts by weight of the raw rubber.

If the amount of carbon black is less than 45 parts by weight, the wet skid resistance will decrease, and if it exceeds 6 parts by weight, the impact resilience will decrease, which is not preferable. The weight average molecular weight of H-MW-SBR and L-MW-SBR used in the present invention is determined by dissolving 2 parts of the rubbery polymer as a sample in 10 parts of toluene, and heating it in an oven with a 1.2 part filter. The sample solution was used for gel permeation chromatography (IPermeation Chromatography).
to nail aphy; elution port soot: toluene, flow rate: 1/
min, column: Micro Stylagel).

Further, the amount of bound styrene was determined according to JIS K6383. Further, the manufacturing method of the present invention is as follows.

That is, in the method for producing a rubber composition using H-MW-SBR as a raw material rubber, the ratio of the total amount (x) of L-MW-SBR to carbon black (Q) to the total amount (8) is 1/a in advance. Total amount of bottom cutlet raw rubber (100)
H-
It is characterized by blending and kneading the total amount (y) of MW-SBR and the remaining amount (y) of carbon black, and the formula is as follows.

Three preliminary kneading: 402xZI0 (parts by weight), 1'2≧Q/
8≧x/100 (ratio) Main kneading: 10≧y≧90 (parts by weight) yx+y=10
060≧8=Q+y≧45 The rubber composition of the present invention is further improved in vulcanization properties, especially impact resilience, by the above-described manufacturing method.

In the production method of the present invention, the amount of raw rubber (x ) is required to have a large ratio of carbon black amount (Q) to
If the ratio is smaller than this, the effect of improving the impact resilience of the vulcanizate is small. In addition, the amount of carbon black (
If Q) is blended in an amount exceeding half of the total amount (8), the amount of carbon black (y) used in the main kneading will decrease, resulting in poorly dispersed lumps of H-MW-SBR, which will cause the vulcanizate to deteriorate. Wear resistance decreases. The blending and kneading in the present invention is usually carried out using a mechanical mixer such as an Oyama Bunroll or a Banbury mixer.

In addition to carbon black, the rubber composition of the present invention may optionally contain other commonly used compounding agents, such as fillers,
A softener, anti-aging agent, process oil, vulcanization accelerator, etc. may be mixed as appropriate. The present invention will be specifically described below based on Examples and Comparative Examples.

All compounding figures in the table are parts by weight, and the figures in parentheses indicate the amount of rubber in the oil-extended SBR or carbon black masterbatch. Example 1 and Comparative Example 1~
4 L-MW-SBR and H-MW- according to the formulations shown in Table 1.
A rubber composition was prepared by changing the mixing ratio of SBR and kneading with a B-type Banbury mixer.

In addition, the initial side wall temperature of the rolling process using the Banbury mixer is 5.
The temperature was 0°C and the number of rotations of the rotor was 8 pm, and the raw rubber was introduced. After 1 lapse of sand, carbon black and other compounding agents were added, and the kneading was completed in 3 minutes. This rubber composition was press-vulcanized at 160° C. for 2 minutes to obtain a vulcanized product. Mooney viscosity of this rubber composition (M mountain, 14,100
0C) and vulcanized physical properties were evaluated, and the results are shown in Table 1.
Mooney viscosity is JIS*K6383, vulcanization physical properties are JI
This was done in accordance with SK6301. In addition, the impact resilience was measured by the Lübke impact resilience test (60℃), and the wet skid resistance was measured using a Pritisch portable skid tester (road surface: using a 3M outdoor type B safety walk and moistened with distilled water in an atmosphere of 25 oo). (measured) and pico abrasion loss were conducted using a Goodrich Pico abrasion tester in accordance with ASTM D-2228.
Table 1: Oil-extended SBR containing 2% by weight of aromatic oil based on the base polymer (Mooney viscosity 67, amount of bound styrene 23.5% by weight, weight average molecular weight of base polymer 6.4 x 1% by weight) ), 2: Non-oil extended SBR (Mooney viscosity 5
2. Bound styrene 23.5% by weight, weight average molecular weight 4.
4×1 pi, Nipole 1502, manufactured by Nippon Zeon), 3:
Santoflex 13 (manufactured by Mitsubishi Monsanto Chemical Co., Ltd.), 4
: Seast Kfl (manufactured by Tokai Riki-Bon Co., Ltd.), 5: N-oxyjeterene-2-penzothiazole sulfenamide (Noxera-MSA-F, manufactured by Ouchi Shinko Kagaku) H as a raw material rubber as shown in Table 1 In Comparative Example 1 using only -MW-SBR, the rubber composition had a high Mooney viscosity and was poor in processability when unvulcanized.

In addition to H-MW-SBR, L-MW-S is used as a raw material rubber.
Mooney viscosity decreases when BR is used together,
In formulations with a relatively high proportion of L-MW-SBR as in Comparative Examples 2 and 3, and in formulations containing only L-hada y-SBR as in Comparative Example 4, the vulcanization properties, especially the impact resilience, deteriorated. ,
Pico wear loss also increases. Examples 2 to 6 and Comparative Example 5
~8 Preliminary kneading was carried out based on the results shown in Table 2 using a B-type Banbury mixer to obtain a carbon black masterbatch.

In addition, when mixing rice bran with a Banbury mixer, the initial side wall temperature is 5.
000, rotor rotational speed...8 ratio pm, the raw rubber was introduced, and after 1 minute of rat sand had elapsed, carbon black and other compounding agents were introduced, and the kneading was completed in 2 minutes. The Mooney viscosity of this carbon black masterbatch is also shown in Table 2. Table 2 Using this carbon black masterbatch, a rubber composition was prepared by kneading it in a B-type Banbury mixer according to the formulation shown in Table 2.

When kneading with a Banbury mixer, the initial side wall temperature is 500.
0. After setting the rotor rotation speed to 8pm and adding carbon black masterbatch and raw rubber at the same time,
After seconds had elapsed, carbon black and other compounding agents were added, and the mixed twilling was completed in 2 minutes. Incidentally, the sulfur and the vulcanization accelerator were kneaded for 3 minutes using 8-inch rolls controlled at about 5,000 rolls. This rubber composition was press-vulcanized at 16,000 for 2 minutes to obtain a vulcanizate. The vulcanization properties of this vulcanizate are shown in Table 3. 31 Example 2 is a rubber composition prepared by a normal kneading method in which the entire amount of raw rubber is added and kneaded while carbon black and other compounding agents are simultaneously mixed and kneaded.

On the other hand, in Examples 3 and 4, the carbon black masterbatch was obtained within the blending range of the present invention as a preliminary kneading process, and then the main kneading was performed.
Compared to vulcanized resin, it is possible to improve the rebound resilience without impairing other vulcanized physical properties. Comparative Example 5 is a rubber composition using L-MW-SBR having the same weight average molecular weight as the L-MW-SBR carbon black masterbatch, but the impact resilience is low, the pico abrasion loss is increased, and 300
% tensile stress and tensile strength also show low values.

In Comparative Example 6, on the contrary, H-MW-SB with the same weight average molecular weight was added to the carbon black masterbatch of H-MW-SBR.
Although this is a rubber composition using R, the carbon black masterbatch A used here has a very high Mooney viscosity (129) and is therefore poor in processability. Moreover, Examples 3 to 4
Pico abrasion loss increases and elongation is also poor compared to . Comparative example 7
This method is disclosed in JP-A-50-112445, in which the entire amount of carbon black is blended into the carbon black masterbatch, but although the impact resilience is improved, the pico-abrasion loss is significantly increased, which is not preferable.

Examples 5 and 6 are examples in which the proportion of carbon black masterbatch was increased compared to Example 3, and in both cases, the impact resilience was improved without impairing other vulcanized physical properties.

In Comparative Example 8, the ratio of the carbon black masterbatch was further increased, so the blending amount of L-MW-SBR was increased, and the amount of carbon black in the main cross wire was small, resulting in poor impact resilience. As explained above, the rubber composition according to the present invention has excellent processability during vulcanization and good vulcanization physical properties, so it has low rolling resistance, wear resistance, and braking performance on wet road surfaces. In addition to being used as tire treads that do not damage the tires, they are also used as tire parts such as undertreads, sides, carcass, liners, bead fillers, and rim cushions.

Furthermore, when the rubber composition of the present invention is prepared by a special kneading method using a carbon black masterbatch, the rubber composition can be used as a tire tread with further reduced rolling resistance.

Claims (1)

[Scope of Claims] 1. A styrene-butadiene copolymer rubber (A) having a weight average molecular weight of less than 5.5 x 10^5 and a bound styrene content of 20 to 25% by weight and a weight average of 10 to 40 parts by weight. The molecular weight is 5.5 x 10^5 or more and the amount of bound styrene is 2
A rubber for tire tread, characterized in that 45 to 60 parts by weight of carbon black is blended to 100 parts by weight of raw material rubber consisting of 90 to 60 parts by weight of styrene-butadiene copolymer rubber (B) of 0 to 25% by weight. Composition. 2 10 to 40 parts by weight of styrene-butadiene copolymer rubber (A) having a weight average molecular weight of less than 5.5 x 10^5 and a bound styrene content of 20 to 25 weight % and a weight average molecular weight of 5.5 x 10^5 or more and the amount of bound styrene is 2
A method for producing a rubber composition for tire treads, in which 45 to 60 parts by weight of carbon black is blended to 100 parts by weight of raw material rubber consisting of 90 to 60 parts by weight of styrene-butadiene copolymer rubber (B) of 0 to 25% by weight. In advance, carbon black is added to the total amount of the styrene-butadiene copolymer rubber (A) in an amount not more than 1/2 of the total amount of carbon black, and the total amount of the raw material rubber is equal to or less than the total amount of the styrene-butadiene copolymer rubber (A). The styrene-butadiene rubber (B
) and the remaining amount of carbon black are blended and kneaded.