JP3391868B2 - Tread rubber composition for lightweight tires - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tread rubber composition for a lightweight tire, and more particularly, it has improved workability, and is particularly suitable for a thinned tread of a radial tire for trucks and buses. The present invention relates to a rubber composition which is used and can exhibit excellent wear resistance, high speed durability and tear resistance.

[0002]

2. Description of the Related Art In recent years, with the progress of motorization, it is a social demand to develop resource-saving and energy-saving technologies for automobiles themselves and to reduce transportation costs based on them, and to reduce the weight of tires as automobile parts. Is regarded as one of the important measures to achieve. When a tire is running, the tread becomes thin and the rolling resistance decreases when the amount of rubber deformation decreases. As can be seen from this, for example, if the tread is positively thinned to make the tire lighter and the rolling resistance is small, it is possible to contribute to the reduction of fuel consumption. Also, in vehicle models with weight restrictions, the lighter the tires, the more the load can be increased, so
The transportation cost can be reduced. Furthermore, there are many merits in reducing the weight of tires, such as being a means for reducing the engine load for exhaust gas regulations.

Thinning the tread is the most effective means for reducing the weight of the tire, but at that time, if the tread rubber composition of the conventional tire is used as it is, the wear life of the tire is shortened. For example, in the tread of truck / bus tires that run on good roads,
Generally, a rubber composition containing 40 to 50 parts by weight of SAF or ISAF carbon black having a relatively small particle size is used per 100 parts by weight of a rubber component composed of natural rubber or a relatively small amount of cis polybutadiene. However, if this type of tire tread is made thinner to make a lightweight tire, the rolling resistance will decrease as the amount of rubber, which is the cause of hysteresis loss, decreases, but the wear life will be shortened and it will be practically used. Absent.

Therefore, as a tread rubber composition for a lightweight tire, a wear-oriented composition is inevitably used. By the way, in the field of tire applications where wear resistance is emphasized, the blending ratio of cispolyptadiene to natural rubber is increased to 25 to 40% by weight, and the compounding amount of SAF or ISAF carbon black is set to 50 parts by weight or more. It is well known that the use of increased amounts of rubber composition significantly improves the wear resistance. However, the rubber composition containing a large amount of cis-polybutadiene and increasing the amount of carbon black as described above is inferior in processability as compared with the above-mentioned formulation for good road use, and generates a large amount of heat due to hysteresis loss, and has a high resistance to heat. It has been pointed out that there is a drawback that the tieredness is greatly deteriorated. Regarding the heat generation property of the drawbacks, it is possible to deal with the weight reduction of the tire by thinning the tread, but it is not possible to solve the problem of poor workability and tear resistance. As described above, a rubber composition having a rubber content of natural rubber or a blend of natural rubber and cis-polybutadiene, having good processability and capable of exhibiting sufficient characteristics as a tread for a lightweight tire has not yet been obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to be inferior to general tires even when the tread thickness is reduced to reduce the weight of the tire. Another object of the present invention is to provide a lightweight tread rubber composition for tires, which has excellent wear resistance, high-speed durability, and tear resistance, and has good processability.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies to achieve the above object, the present inventors have used transpolybutadiene having a specific micro and macro structure as polybutadiene to be blended with isoprene rubber. At the same time, the inventors have found that the desired object can be achieved by combining this with carbon black having a specific range of cetyltrimethylammonium bromide adsorption specific surface area (CTAB) to achieve the intended purpose, thus completing the present invention. Came to. That is, the present invention contains 50 to 85 parts by weight of natural rubber or a blend rubber of natural rubber and synthetic polyisoprene, and 60% or more of trans 1,4 bond, and has a weight average molecular weight (Mw) of 15 × 10 ⁴ to. 35
The molecular weight distribution (Mw / M) represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) in the range of × 10 ^4.
n) is in the range of 1.5 to 3.0, with respect to 100 parts by weight of a rubber component consisting of 15 to 50 parts by weight of trans polybutadiene, a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 135 to 160 m ² / g. The gist is a tread rubber composition for a lightweight tire, which comprises 45 to 65 parts by weight of carbon black in the range.

The trans polybutadiene used in the present invention preferably contains trans bonds in an amount of 60% or more, preferably 65 to 90%. Such trans-polybutadiene has a large temperature dependence of viscosity, and has a characteristic that the viscosity sharply decreases at high temperatures, and the apparent viscosity decreases as the deformation speed increases, so that a relatively large amount of natural rubber is included in natural rubber. Also in the case of blending with, the mixing, extrusion, roll processability, etc. are remarkably better than those with cis-polybutadiene. Further, since this type of trans polybutadiene has elongation crystallinity similar to that of natural rubber, the fracture characteristics are improved and the rib tear resistance and the chipping resistance are improved as compared with the vulcanized rubber containing cis polybutadiene.

When the transformer 1.4 bond is 60% or less, the elongation crystallinity becomes poor and the fracture characteristics deteriorate. M
When w is less than 15 × 10 ⁴ , the fracture resistance such as tensile strength and tear strength deteriorates, and early wear, uneven wear, or rib tears easily occur, and the hysteresis loss increases and the heat generation temperature increases, resulting in high-speed durability. Is reduced. Mw is 3
If it is larger than 5 × 10 ^4, the dispersibility of carbon black or polymer, the cohesion and softness of rubber, the roll winding property, and the workability evaluated by the surface texture and the like deteriorate. Also,
If the molecular weight distribution is less than 1.5, not only cold flow tends to occur, resulting in poor storage stability, but also the processability as described above decreases, and if 3.0 or more, the content in the low molecular weight region increases and hysteresis occurs. It is not preferable because the loss becomes large, the heat generation temperature rises, the fracture resistance deteriorates, and the wear resistance decreases. Therefore, in the present invention,
The trans polybutadiene whose molecular structure of the polymer is shown below is used. Content of trans 1.4 bond> 60% 15 × 10 ⁴ <Mw <35 × 10 ⁴ 1.5 <Mw / Mn <3.0

Natural rubber is usually preferably used as the rubber component to be blended with the trans polybutadiene, but it is also possible to blend a predetermined amount of synthetic polyisoprene with the natural rubber in some cases. A suitable blending ratio of trans polybutadiene is 15 to 50 parts by weight per 85 to 50 parts by weight of the above isoprene-based rubber component. If the blend ratio is less than 15 parts by weight, the effect of improving wear resistance is poor, and if it exceeds 50 parts by weight, the workability becomes poor and the high-speed durability and tear resistance are deteriorated.

In the present invention, carbon black having a smaller particle diameter (larger CTAB) than that of the conventional rubber component is combined with the above-mentioned specific rubber component to improve the wear resistance of the tread for a lightweight tire. And
The colloidal characteristics and the range of the compounding amount are determined for the following reasons. That is, CTAB is 135m
If it is less than ² / g, the effect of improving wear resistance is poor and 155 m
^When it is ² / g or more, the workability deteriorates, the heat generation temperature of the compounded rubber rises, and the tear resistance also decreases, so CTAB is 1
The one in the range of 35 to 155 m ² / g is used. Further, since the CTAB of the carbon black becomes large in the present invention, the DBP associated with dispersibility of carbon black and 110 cm ^3/100 g or more, and mixing, the structure of the destruction in the processing steps of extruding such reduced, In order to maintain high-order structure and improve wear resistance, DB
Ratio of 24M4 DBP to P (24M4 DBP / DBP)
It is preferable to use carbon black having a ratio of 0.85 or more. If the blending amount of carbon black is less than 45 parts by weight, the abrasion resistance effect will be poor, and if it exceeds 65 parts by weight, workability will be deteriorated, and at the same time, heat generation will be high and high-speed durability will be deteriorated, and rib tear and block tear will be reduced. Since it is likely to occur, the compounding amount is in the range of 45 to 65 parts by weight.

In the present invention, in addition to the above-mentioned components, commonly used compounding agents such as vulcanizing agents, vulcanization accelerators, vulcanization accelerating aids, antioxidants, process oils, and other processing aids. It goes without saying that agents and the like are added as appropriate.

[0012]

In the present invention, transpolybutadiene having a specific molecular structure is used in place of the conventionally used cis-polybutadiene in the wear-resistant composition prepared by blending polybutadiene with isoprene-based rubber such as natural rubber. Good roll processability and extrusion processability can be obtained even when blended in a relatively large amount. Further, since such trans polybutadiene has stretch crystallinity similar to natural rubber, the tear resistance of the vulcanized rubber is improved. Further, in the present invention, the above rubber component is combined with carbon black having a smaller particle size than SAF to form a tread rubber composition, so that even if the tread is thinned to reduce the weight of the tire, it is not inferior to a general tire. Wear life is reached.

[0013]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. The polybutadiene used in Table 1 (B
The type of R) and its characteristics are shown.

[Table 1] The cis and trans contents in Table 1 were measured by an infrared spectrophotometer. The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) are values measured by gel permeation chromatography using THF as a developing solvent.

Table 2 shows the types of carbon black used and the colloidal characteristic values.

[Table 2] The cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of carbon black shown in Table 2 is ASTM
D3765, dibutyl phthalate oil absorption (DBP) and iodine adsorption specific surface area (IA) are JIS K6221, compressed dibutyl phthalate oil absorption (24M4 DBP) is ASTM
D3493, nitrogen adsorption specific surface area (N ₂ SA) is ASTM
The values are measured according to D3037.

Table 3 shows the compounding agent composition common to each tread rubber composition.

[Table 3]

The natural rubber / BR shown in Tables 4 and 5 are added to the rubber component and carbon black in the composition table of the compounding agent, respectively.
Apply the blend ratio and each part of carbon black,
Tire size using the obtained rubber composition as a tread rubber
A general or lightweight radial tire of 1000 R 20 14PR was prepared by a conventional method, and the processability of each rubber composition and the performance of the tire were evaluated by the following methods. Workability: Comprehensively evaluated from the collective and softness of discharged rubber when kneading each rubber composition with a Banbury mixer, roll wrapping property and rubber skin, A (very good),
It is displayed in five stages of B (good), C (somewhat inferior), D (bad), and E (extremely bad). Tear resistance: The product of the number of tiers received on the tread surface and the size of each scratch (length x depth) after the vehicle equipped with the above tires was ridden on the curb for testing 10 times and the test was repeated. (Sum of area) was calculated, converted by the following formula, and relative comparison was made. The larger the value, the better. Tier resistance = (A / B) × 100 (where A is the sum of the areas of the tires of Comparative Example 1 and B
Is the sum of the areas of the tested tires. ) Abrasion resistance: After traveling 100,000 km on a highway, the travel distance per wear millimeter of the tread groove of the rear mounted tire was obtained, and the value was expressed as an index with the value of the general tire of Comparative Example 1 as 100, The larger the better. High-speed endurance: After running the drum under the high-speed endurance test conditions (step speed) specified in FMVSS 119, completing the predetermined time and clearing the safety standard conditions, continue running under the same conditions, and the time until failure occurs. The following five ranks are ranked, and the corresponding rank of the general tire of Comparative Example 1 is relatively displayed as a standard level. ◎: 1 rank up, ○: 0.5 rank up, △: Standard level,
×: 0.5 rank down, XX; 1 rank down The results are summarized in Tables 4 and 5. In the table, "actual-" indicates the example, and "ratio-" indicates the comparative example.

[0017]

[Table 4]

[Table 5]

When the tread effective ground contact area of the general tires shown in Comparative Examples 1 and 2 is 100, the weight saving tires described below (including the tires of Examples 1 to 10 and Comparative Examples 3 to 14) are effective. The ground contact area ratio is 95, and
The groove depth of these lightweight tires is set to 12 mm in comparison to the groove depth of 14.5 mm for general tires. As a result, it was possible to reduce the weight by about 6% per 1000 R 20 14PR tire.

As can be seen from Tables 4 and 5, the lightweight tires (Examples 1 to 10) made of the rubber composition satisfying the constitutional requirements of the present invention as described above contain a large amount of trans polybutadiene. Regardless, compared with the case of using cis polybutadiene (Comparative Example 3), the workability and tear resistance are remarkably improved, and the wear resistance is equal to or higher than that of a general tire composed of natural rubber (Comparative Example 1). And high speed durability.

Explaining in more detail, Comparative Example 1 is a conventional general tire in which a natural rubber composition containing SAF carbon black is arranged in a tread, which was used as a control tire for characteristic evaluation. In Comparative Example 2, cis-polybutadiene (BR-J) was blended with the tread rubber of Comparative Example 1, and SAF was added to have a smaller particle size (CTA).
A rubber composition obtained by substituting carbon black (having a large B) and increasing the amount thereof is used. In this case, the wear resistance is improved, but the workability is deteriorated, and the tear resistance and the high speed durability are significantly lowered. Further, when a tire having a thin tread and a lightweight tire is formed by using such a rubber composition, as shown in Comparative Example 3, high-speed durability is 3
Although the rank is improved, poor processability and low tear resistance due to cis-polybutadiene are not improved.

In Comparative Example 4, the tear resistance cannot be improved because the trans content of the BR component is too low. Comparative Example 5 is M
Since w is small, tire performance deteriorates in all of tear resistance, wear resistance, and high-speed durability. Further, when Mw exceeds 35 × 10 ⁴ and becomes large as in Comparative Example 6, the effect of improving workability and tearability is lost. M as in Comparative Example 7
Even when the w / Mn is 1.5 or less and the molecular weight distribution is sharp, the effect of improving the workability and tearing property is not similarly observed.
Comparative Example 8 has an Mw / Mn of more than 3.0 and therefore has good workability, but is inferior in wear resistance to the general tire of Comparative Example 1 and is not preferable. Comparative Example 9 has workability and tear resistance,
There is no problem in high speed durability, but carbon black CTA
Since B is small, carbon black of Comparative Example 1 (SA
Despite the increased use of F), wear resistance is low. On the contrary, in Comparative Example 10, since CTAB is too large,
It is extremely difficult to process, and the tear resistance and high-speed durability deteriorate.

In Comparative Example 11, since the blending ratio of the trans polybutadiene (BR-A) according to the present invention is too high, the processability, the high speed durability and the tear resistance are poor. Further, when the blending ratio of the rubber (BR-A) is low as in Comparative Example 12, the abrasion resistance is reduced, which is not preferable. On the other hand, even when the CTAB of carbon black is within the predetermined range, as in Comparative Example 13, when the blending amount is small, the wear resistance is not improved, and when it is too large, it becomes difficult to process.
The heat generation temperature of the tire rises, high-speed durability deteriorates, and rib tears and block tears easily occur (Comparative Example 1).
4).

As can be seen from the above results, the processability of the tread rubber composition according to the present invention and the colloidal property dependence of tire performance are remarkable for CTAB.
Within the range of the other colloidal properties also shown in Table 2, no significant correlation was observed. Further, the set value of the groove depth in the lightweight tire is a design factor that can be appropriately changed as long as the safety of the tire is guaranteed.

[0024]

As described above, in the present invention, a relatively large amount of trans-polybutadiene having a specific molecular structure is blended with isoprene-based rubber such as natural rubber, and a predetermined amount of carbon black having a small particle size is blended. Since the tread rubber composition was constructed by using the above, it is easier to process than the case of blending cis polybutadiene, and even when the tread thickness is thinned for weight reduction, it has wear resistance comparable to general tires with natural rubber. It is possible to obtain a lightweight tire having high-speed durability and tear resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-242642 (JP, A) JP-A-1-182332 (JP, A) JP-A-3-190944 (JP, A) JP-A-1- 135847 (JP, A) JP 2-24334 (JP, A) JP 2-308834 (JP, A) JP 3-149236 (JP, A) JP 61-16753 (JP, A) JP-A-61-168637 (JP, A) Tokuhyo 5-506870 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 7/00 C08L 9/00 C08K 3/04

Claims (2)

(57) [Claims] 1. A weight average molecular weight (Mw) containing 50 to 85 parts by weight of a natural rubber or a blend rubber of a natural rubber and a synthetic polyisoprene and 60% or more of trans 1,4 bonds.
Is in the range of 15 × 10 ^{4 to} 35 × 10 ⁴ , and the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is 1.5 to 3.0. Cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 135 to 1 with respect to 100 parts by weight of a rubber content of 15 to 50 parts by weight of trans polybutadiene in the range.
45 to 65 carbon black in the range of 60 m ² / g
A tread rubber composition for a lightweight tire, which is characterized by being mixed in parts by weight. Wherein is the dibutyl phthalate absorption of the carbon black (DBP) is 110 cm ^3/100 g or more, and the ratio (24M dibutyl phthalate absorption (DBP) compressed dibutyl phthalate oil absorption for (24M4 DBP)
4. The tread rubber composition for a lightweight tire according to claim 1, having a 4 DBP / DBP) of 0.85 or more.