JP2000230079A - Tread rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition which can give a tire tread having excellent steering performance on ice or snow as well as good abrasion resis tance and wet grip performance by compounding a diene rubber component based on a natural rubber and a butadiene rubber with two types of carbon black having different nitrogen adsorption specific surface areas, silica, and sulfur in a specified ratio. SOLUTION: One of the two types of carbon black has a nitrogen adsorption specific surface area (N2 SA) x of below 120, and the other has a nitrogen adsorption specific surface area y of at least 120. The rubber composition is produced by compounding 100 pts.wt. rubber component with at least 0.8 pt.wt. sulfur, two types of carbon black, and silica in amounts satisfying the relationships: 20<(A+B)<=40; B>A;C>=10;50<=(A+B+C)<=60; and (Ax+By)/(A+ B)<120 wherein A is the amount (pts.wt.) of the carbon black having an N2 SA x of below 120; B is the amount of the carbon black having an N2SA y of 120 or above; and C is the amount of the silica.

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 tire mainly used for a tire tread, having excellent ice and snow steering performance while maintaining good wear resistance.

[0002]

2. Description of the Related Art Conventionally, a rubber composition used for a tread portion of a studless tire has been used to maintain good handling performance on ice and snow (ice and snow performance, the same applies hereinafter), abrasion resistance and wet performance. Various improvements have been made. Specifically, there may be mentioned, for example, a method of blending silica to improve ice and snow performance, and a method of blending a softener to reduce rubber hardness. Combinations of various compounds,
Although the amount is adjusted, it is hard to say that the improvement of the wet performance still lowers the ice and snow performance and the like, and that the wear resistance and the wet performance are not compatible.

In general, a large amount of a softening agent is mixed in a rubber composition used for a tread portion of a studless tire in order to ensure flexibility and abrasion resistance of the tread portion on ice and snow road surfaces. And has the disadvantage of moving into the atmosphere. Therefore, it is difficult to maintain flexibility over a long period of time, and it is difficult to say that such a problem has been sufficiently improved. In order to solve the above-mentioned problem, JP-A-8-73657 and the like have attempted to mix silica and a predetermined carbon black in a predetermined amount in a rubber component (conventional example). As a result, a pneumatic tire suitable for a road surface on ice has been successfully produced.

[0004]

In order to obtain the rubber composition in the above-mentioned conventional example, a predetermined amount of carbon black is used. It is important that the particle size of the carbon black is small. This is because when carbon black with a small particle size is used, the interaction with the polymer is strong, so that the abrasion resistance is good, but the hardness becomes high, and the suppleness to the ice and snow road surface is lost. is there. However, since carbon black having a small particle diameter has a strong interaction with the polymer at the same time, even when blended for the purpose of flexibility, the hardness of the rubber composition may be increased. Here, when carbon black having a large particle diameter is used instead, the interaction with the polymer is weakened, and as a result, the hardness is reduced and the flexibility can be obtained. Lower, the same applies hereinafter).

The present invention has been made to solve such a problem, and an object of the present invention is to provide excellent ice and snow performance while maintaining good abrasion resistance and wet performance. It is an object of the present invention to effectively obtain a rubber composition particularly suitable for a studless tire traveling on an icy and snowy road surface, by maintaining a good balance between the performance of the rubber composition, particularly the flexibility and the wear resistance.

[0006]

Means for Solving the Problems In order to achieve the above object, the following technical means have been taken in the present invention. That is, the tread rubber composition of the present invention is obtained by blending sulfur, carbon black and silica in a diene rubber component mainly composed of natural rubber and butadiene rubber, and the carbon black has a nitrogen adsorption specific surface area (N ₂ SA). ) Is a mixture of two different carbon blacks, wherein the value x of the N ₂ SA of one of the _two carbon blacks is less than 120 and the value of the N ₂ SA of the other carbon black is less than 120. The value y is 120 or more, and the sulfur content is 0.8% with respect to 100 parts by weight of the rubber component.
The above two types of carbon black and the silica are blended so as to satisfy the following formulas (1) to (5). Formula 1: 20 <(A + B) ≦ 40 Formula 2: B> A Formula 3: C ≧ 10 Formula 4: 50 ≦ (A + B + C) ≦ 60 Formula 5: (Ax + By) / (A + B) <120 (where A is The compounding amount of the carbon black having the value x of the N ₂ SA less than 120, and B represents the value y of the N ₂ SA of 120
The above-mentioned compounding amount of carbon black, C represents the compounding amount of the silica, and the unit is all parts by weight. If the above-mentioned means are taken, a predetermined amount of carbon black having a difference in particle diameter is mixed, whereby the particle diameter is reduced. The trade-off property of small carbon black, specifically, the property of imparting abrasion resistance to the rubber composition and at the same time curing the rubber composition, can be reduced. Further, even if such an effect is obtained, physical properties such as wear resistance and running properties do not decrease. As a result, the above-mentioned problem when using carbon black having a small particle diameter can be effectively improved, which is preferable.

[0007] In general the N ₂ SA value (N ₂ SA value,
Hereinafter the same) of 120 m ² / g or more of carbon black, it indicates the nature of the small particles the particle size, N ₂ SA
Since carbon black having a value of less than 120 m ² / g exhibits properties as particles having a large particle diameter, the numerical value is adopted as a criterion for judging the size of the particle diameter. Further, the SHORE-A hardness of the tread rubber composition is 4
It is preferable that it is 7 ° or less. This is because it is possible to provide suitable flexibility on an ice and snow road surface. Further, it is preferable that the two carbon blacks each have an oil absorption of 24M4DBP of 95 ml / 100 g or more. By taking this measure, the wear resistance can be effectively improved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber component used in the present invention is a diene rubber containing natural rubber (NR, the same applies hereinafter) and butadiene rubber (BR, the same applies hereinafter) as main components. NR and BR
Is not particularly limited. Also, N
R and BR may be used in combination with another diene rubber. In this case, it is preferable that 70 parts by weight or more of NR and BR are combined in 100 parts by weight of the rubber component. Carbon black, silica and sulfur are mixed with 100 parts by weight of the diene rubber component. The carbon black is a mixture of two kinds of carbon blacks having different N ₂ SA values. One of these two types of carbon black is a carbon black having an N ₂ SA value x of less than 120, and the other is a carbon black having an N ₂ SA value y of 1
The carbon black is 20 or more.

The reason why the N ₂ SA value 120 is used as a reference is that, as described above, there is a difference in properties depending on the size of the particle diameter at the value. When the N ₂ SA value is less than 120, the particles generally exhibit properties of a large particle diameter (large particle diameter, the same applies hereinafter), and conversely, when the N ₂ SA value is 12
If it is 0 or more, it generally exhibits the property of a small particle diameter (small particle diameter, the same applies hereinafter). For convenience, the following describes carbon black having a large particle diameter as carbon I (N ₂ S
Carbon black having an A value of less than 120) and a small particle diameter is referred to as carbon II (N ₂ SA value is 120 or more).

The two types of carbon black and silica are blended so as to satisfy the following formulas 1 to 5 when the blending amount of carbon I is A, the blending amount of carbon II is B, and the blending amount of silica is C. I do. A, B, and C are compounding amounts with respect to 100 parts by weight of the diene rubber component, and the unit is parts by weight (hereinafter, phr). Formula 1: 20 <(A + B) ≦ 40 Formula 2: B> A Formula 3: C ≧ 10 Formula 4: 50 ≦ (A + B + C) ≦ 60 Formula 5: (Ax + By) / (A + B) <120 where x is carbon I The N ₂ SA value, y represents the N ₂ SA value of carbon II.

Formula 1 shows that the total amount of the two types of carbon black must be more than 20 phr and 40 phr or less. If the total is less than 20 phr, the abrasion resistance decreases, and if it exceeds 40 phr, the hardness of the rubber increases, which causes a problem that ice and snow performance deteriorates. Equation 2 shows that it is necessary to increase the amount of carbon II to be greater than the amount of carbon I. N ₂ S
When the A value is 120 m ² / g or more, sufficient abrasion resistance can be provided, but the decrease in flexibility caused by the blending of carbon black II is caused by the N ₂ SA value of less than 120 m ² / g. This can be prevented by blending carbon black I.

Conversely, if the compounding amount B of carbon II is smaller than the compounding amount A of carbon I (A> B), the carbon II
Is not preferable because it is difficult to compensate for the decrease in wear resistance caused by the low blending amount of carbon I. Formula 3 shows that the compounding amount of silica is 10 ph
r is required. The amount of silica is 10p
If it is less than hr, the ice and snow performance will be insufficient. Equation 4 shows that the total amount of the two types of carbon black and silica to be blended must be 50 phr or more and 60 phr or less. If the total amount is less than 50 phr, the abrasion resistance decreases, and if it exceeds 60 phr, the hardness of the rubber increases and the ice and snow performance deteriorates.

Equation 5 shows that when two types of carbon blacks are used, the weighted average of their N ₂ SA values is 12
It indicates that it is necessary to mix to less than 0 m ² / g. When the weighted average N ₂ SA value is 120 m ² / g or more, the rubber becomes hard and the ice and snow function deteriorates. The type and properties of the silica used are not particularly limited. Further, in addition to the above-mentioned components, 0.8 phr or more of sulfur is blended as a vulcanizing agent. If the amount of sulfur is less than 0.8 phr, the wear resistance deteriorates, which is not preferable. It should be noted that a substance other than sulfur can be further used as a part of the vulcanizing agent.

In addition, additives such as a silane coupling agent, a vulcanization accelerator, an antioxidant, and an oxidizing agent can be appropriately mixed as needed. A predetermined amount of all the components and additives described above is mixed and vulcanized to obtain a tread rubber composition. Its SHORE-A hardness is 47 ° at 0 ° C.
The following is preferred. If the angle exceeds 47 °, the ice and snow performance becomes insufficient. The 24M4DBP oil absorption of the two carbons I and II used was 95% for both.
It is preferably at least ml / 100 g. This is because the DBP oil absorption of 95 ml / 100 g or more greatly contributes to the improvement of wear resistance.

Actually, the above-mentioned rubber component, carbon black, silica and sulfur were mixed in the above-mentioned prescribed amounts and vulcanized to obtain four types of tread rubber compositions (Example 1). 4). At the same time, a tread rubber composition in which the amount of the composition component was out of the predetermined range was also prepared (Comparative Example 1).
To 11). The specific components and additives actually used are as follows. These Examples 1-4,
In Comparative Examples 1 to 11, the above-mentioned additives are also appropriately mixed. (1) Rubber component: NR and BR were used. (2) Silica: Ultrasil VN3 (trade name, D
egussa). (3) Carbon I: N ₂ SA value is 112 m ² / g, 24
M4DBP oil having an oil absorption of 99 ml / 100 g was used. (4) Carbon II: N ₂ SA value is 125 m ² / g, 2
4M4DBP oil having an oil absorption of 100 ml / 100 g was used. (5) Additive: Aromatic oil, and although not shown in Tables 1 and 2, an antioxidant, zinc oxide, stearic acid, a silane coupling agent and the like were appropriately blended.

The above-mentioned composition components are specific examples, and are not limited thereto. As the additives, those other than those described in the above (5) can be appropriately mixed as needed. Comparative Examples 1 to 5
11, SHORE-A hardness, abrasion resistance, and ice and snow performance were measured for Examples 1 to 4, respectively. Table 1 shows Comparative Examples 1 to 11, and Table 2 also shows Examples 1 to 4.

[0017]

[Table 1]

[0018]

[Table 2]

The methods for evaluating SHORE-A hardness, wear resistance and ice and snow performance are as follows. (1) SHORE-A hardness: according to JIS K6253
The SHORE-A hardness at 0 ° C. was measured. (2) Abrasion resistance: Evaluated by a pico abrasion test. Comparative Example 1
Is represented as an index with 100 as the index. The larger the value, the better. (3) Ice and snow performance: tire size TL195 / 65R15
The vehicle was run on an icy and snowy road surface, and the steering performance was evaluated by an index (the evaluation of Comparative Example 1 was set to 100). The higher the value, the better.

In Comparative Example 1, silica was used as the rubber component and N_TwoS
A value is 120m^Two/ G or less particle size
A mixture of racks. With carbon black
Conventional compounding example of rubber composition prepared by mixing silica
However, the wear resistance and ice and snow performance of this rubber composition are standard.
(Index 100), evaluation of other rubber compositions of comparative examples
Was done. From these evaluations, the carbon black II
Only, that is, N_TwoSA value is 120m ^Two/ G or more particle size
Hardness when only a certain amount of carbon black is blended
And the ice and snow performance deteriorates (Comparative Example 2). Also,
N of two kinds of carbon black_TwoWeighted average of SA values,
Hard even when (Ax + By) / (A + B) is 120 or more
The degree of ice and snow performance deteriorates (Comparative Example 3).

When the compounding amount A of the carbon black I is larger than the compounding amount B of the carbon black II, the abrasion resistance is inferior to that of the comparative example 1 (comparative example 4). When the compounding amount of silica is less than 10 phr, the ice and snow performance becomes insufficient (Comparative Example 5). Further, even when silica is blended in an amount of 10 phr or more, if the (A + B) value exceeds 40, the hardness becomes high and the ice and snow performance deteriorates (Comparative Example 6). Furthermore, (A
When the (+ B + C) value exceeds 60, the amount of the aromatic oil is increased to decrease the hardness, or the amount of the sulfur is decreased to lower the abrasion resistance (Comparative Example 7). Even if the value of (A + B + C) is 60 or less, (A + B + C)
B) If the value is 20 or less, the wear resistance is reduced (Comparative Example 8).

When the amount of sulfur is less than 0.8 phr, the abrasion resistance decreases (Comparative Example 9), and when the amount of silica is zero, no improvement in ice and snow performance is observed (Comparative Example 1).
0). On the other hand, the rubber compositions of Examples 1 to 4 all obtained good evaluation results. It can be seen that the rubber hardness is suitable, and the ice and snow performance is improved as well as the wear resistance (Experiment 1). By the way, even when a rubber component other than NR and BR was used as a main component, it was examined whether or not a high-performance rubber composition could be obtained by mixing silica as in the example of Experiment 1 described above. . Therefore, apart from the production and evaluation of the rubber composition described above, a plurality of new compounding examples were produced, and an experiment 2 for examining the physical properties of each rubber composition was performed.

Specifically, what kind of running performance of a rubber composition obtained by mixing SBR (styrene-butadiene rubber, hereinafter the same) as a main component and carbon black and silica on a dry road surface and a wet road surface? Find out. In order to be able to say that the running performance is good, it is required that the abrasion resistance is improved without lowering the grip force, and that the occurrence of so-called heat sag (deterioration in tire performance due to running) can be suppressed. In general, when the grip performance of a tire is improved, problems such as a decrease in wear resistance and generation of heat sagging occur. As a result of repeated experiments to avoid such a problem, the main component of the rubber component was S to improve the grip performance without causing the above-mentioned problems.
Even in the case of the rubber composition which is BR, it became clear that BR was used as a part of the rubber component and silica was suitable as in the result of Experiment 1.

More specifically, it can be said that grip performance can be obtained by using SBR having a high styrene and vinyl content, and the grip performance can be improved by blending carbon black and silica. Particularly, silica contributes to improving wet grip performance. The content of the rubber composition will be described below. The amount of each component is based on 100 parts by weight of the rubber component.
The unit is parts by weight (hereinafter represented by phr). SBR and BR are used as the rubber component. SBR has a property of improving grip performance due to its high glass transition point Tg, and BR has a property of suppressing a decrease in wear resistance and heat sagging which are likely to occur due to improvement in grip force. . The blending amount is 80 to 90 phr for SBR and B for
R is preferably 20 to 10 phr (in 100 parts by weight of the rubber component).

When the BR exceeds 20 phr, the grip performance is deteriorated, which is not preferable. On the other hand, if it is less than 10 phr, it is not preferable because the prevention of heat sag is insufficient and the abrasion resistance is lowered. For SBR, the styrene and vinyl content in the total weight of SBR are both 3%.
It is preferably at least 0% by weight. If the styrene content and the vinyl content are each 30% by weight or more, the glass transition point (Tg, the same applies hereinafter) increases, and the grip performance is improved. Conversely, if the content is less than 30% by weight, the improvement in grip performance is insufficient, which is not preferable.

Further, two or more kinds of SBR may be used as a mixture. The content of styrene and vinyl at that time,
It is 30% by weight or more based on the total weight of SBR after mixing. As for the blending amount, the blending amount of the whole SBR after mixing is 80 to 90 phr. Carbon black and silica are blended with the above rubber component as described above. 70-90 carbon black
phr is preferred. If it is less than 70 phr, the abrasion resistance is reduced, and if it is more than 90 phr, the heat sag preventing performance is undesirably reduced. Furthermore,
The carbon black used has an I ₂ SA value of 130 mg / g
It is preferable that it is above. The I ₂ SA value is 130 mg /
g or more of carbon black tends to have a small particle size,
This is because such carbon black greatly contributes to the improvement of grip power.

The DBP oil absorption is 100 ml / 100
g or more. DBP oil absorption is 100m
This is because 1/100 g or more of carbon black tends to have a large structure, and if the structure is large, abrasion resistance can be improved. The amount of silica is preferably 20 to 40 phr. 20
If it is less than phr, the effects of preventing heat sagging and improving the wet grip performance are insufficient, and if it is more than 40 phr, problems such as reduced wear resistance and high cost are undesirable.

Further, the total amount of carbon black and silica is preferably at least 100 phr. 10
If it is less than 0 phr, grip performance and abrasion resistance decrease. An appropriate amount of a vulcanizing agent, a vulcanization accelerator, an antioxidant, an oxidizing agent and the like (additives, the same applies hereinafter) may be mixed as necessary in addition to the above-mentioned components. A rubber composition was actually produced using the above composition components and additives. In preparation, a rubber composition that does not satisfy the above compounding conditions (Formulation Example 1)
6) and a rubber composition to be filled (formulation examples 7 to 9). The content and evaluation of these components will be described in detail below. (1) Rubber component: BR, three types of SBR (A),
(B) and (C) were used. Table 4 shows the styrene and vinyl contents of each of the three types of SBR. (2) Carbon black: Carbon black III (I
₂ SA value 134mg / g, DBP oil absorption 107ml / 1
00g), carbon black IV (I ₂ SA value: 119 m)
g / g, DBP oil absorption 115 ml / 100 g). (3) Silica: Ultrasil VN3 (trade name, D
egussa). (4) Silane coupling agent: Si69 (trade name) was used.

The above-mentioned composition components and additives were mixed in the contents shown in Table 3 and vulcanized to obtain Formulation Examples 1 to 9. In addition,
Specific examples of the components described above are merely examples, and the present invention is not limited to these. The additives are compounded in addition to those described above, as described above. The evaluation was performed from the viewpoint of whether or not the rubber composition was suitable for a high-performance tire. Specifically, the steering stability (dry road surface and wet road surface), heat sag, and abrasion resistance were measured as follows. The tire used for the measurement has a size of TL225 / 50R16. (1) Steering stability: A tire was prepared from the rubber composition obtained as a formulation example, and was mounted on a car and evaluated by running on dry and wet road surfaces. (2) Heat sagging: After running on a circuit on a dry road surface for 30 minutes, deterioration in performance due to running was evaluated. (3) Abrasion resistance: Lambourn abrasion test (slip ratio = 3
0%).

Table 3 shows the contents and evaluations of the above-mentioned components. Table 4 shows the SBR and carbon black used.

[0031]

[Table 3]

[0032]

[Table 4]

The evaluation of each of the formulation examples was carried out by an index evaluation using formulation example 1 in which BR was not used at all as a standard. The evaluation index of Formulation Example 1, which is a standard example, is 5, and an index from 1 to 10 is used. The larger the numerical value, the better. When the content of styrene and vinyl in the SBR is out of the predetermined range, the steering stability on dry and wet road surfaces is not improved, and the heat dripping prevention performance and the wear resistance are not improved (formulation example 2). ). Further, even if the styrene content in the BR and SBR is out of the predetermined range, no improvement in steering stability can be expected (Compounding Example 3).

When the amount of BR is out of the predetermined range,
No improvement in heat dripping prevention performance and abrasion resistance is observed (Formulation Example 4). If the compounding amount of carbon black is out of the predetermined range, the abrasion resistance is not improved, and the steering stability on a dry road surface is lower than the standard value (Compounding Example 5). Further, the compounding amount of carbon black and silica is 1
When the amount is less than 00 parts by weight, there is a problem that the steering stability on a dry road surface is remarkably reduced, which causes only a decrease in the steering stability and abrasion resistance on a wet road surface (composition example 6). As described above, a rubber composition whose content does not satisfy the predetermined conditions causes a problem in any of the evaluation results. vice versa,
Formulation Examples 7 to 9 are rubber compositions satisfying the predetermined conditions, and show that the grip performance is improved and the abrasion resistance and the heat sagging prevention performance are well maintained. Therefore,
The rubber compositions of Formulation Examples 7 to 9 can be said to be rubber compositions suitable for high-performance tires.

From the above experimental results, it is found that the grip power can be increased by using SBR having a high content of styrene and vinyl and increasing the blending amount of carbon black and silica. It can be seen that the deterioration of abrasion resistance and heat sag that occur can be suppressed by using BR and silica. In other words, without compromising grip performance on dry and wet road surfaces,
This makes it possible to obtain a rubber composition suitable for high-performance tires that does not generate heat sag and has good abrasion resistance.

As described above, even when a rubber component other than NR and BR is used as a main component (SBR in Experiment 2), it is suitable for a high-performance tire if certain conditions are applied to the amounts of carbon black and silica. A rubber composition can be obtained.

[0037]

According to the tread rubber composition of the present invention,
A tread rubber composition having excellent ice and snow performance while maintaining good abrasion resistance and wet performance can be obtained. In particular, by maintaining the performance of both flexibility and abrasion resistance in a well-balanced manner, it is possible to obtain a rubber composition particularly suitable for a studless tire traveling on an icy and snowy road surface.

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Claims (3)

[Claims] 1. Mainly composed of natural rubber and butadiene rubber
Sulfur, carbon black and silica in diene rubber component
The rubber composition containing
The rack has a nitrogen adsorption specific surface area (N_TwoSA) are different from each other
A mixture of two types of carbon black,
One of the two carbon blacks
N_TwoThe SA value x is less than 120 and the other carbon black
Ku N _TwoThe SA value y is 120 or more,
0.8 parts by weight or more of the sulfur is blended with respect to 100 parts by weight
And the two carbon blacks and the silica are
It is noted that they are blended so as to satisfy the following formulas 1 to 5.
Tread rubber composition. Formula 1: 20 <(A + B) ≦ 40 Formula 2: B> A Formula 3: C ≧ 10 Formula 4: 50 ≦ (A + B + C) ≦ 60 Formula 5: (Ax + By) / (A + B) <120 (where A is The N_TwoCarbohydrate with SA value x less than 120
B is the amount of N_TwoSA value y is 120
The above-mentioned amount of carbon black, C is the distribution of the silica.
Total weight, all units are parts by weight) 2. The tread rubber composition according to claim 1, wherein the SHORE-A hardness at 0 ° C. is 47 ° or less. 3. The two carbon blacks of 24M4
The tread rubber composition according to claim 1 or 2, wherein the DBP oil absorption is 95 ml / 100 g or more.