JPS636567B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel composition which can be used particularly in a rubber composition for the tread of pneumatic tires and which has good workability and can simultaneously significantly improve wet skid resistance, rolling resistance, fracture resistance, abrasion resistance and uneven wear resistance. styrene-butadiene copolymer rubber. Conventionally, styrene-butadiene copolymer rubber has been widely used for tire treads because it has excellent wet skid resistance on wet road surfaces and good abrasion resistance. However, it is rarely applied to large tires because it causes a large energy loss and tends to generate heat. However, with the spread of expressways, wet skid resistance has become important for large tires.
Furthermore, in relatively small tires in which styrene-butadiene copolymer rubber is already used, it has become important to reduce energy loss, that is, to reduce rolling resistance, from the viewpoint of recent resource and energy conservation. Therefore, it has become important to develop a new rubber that has excellent wet squid resistance and low energy loss and can be used for both large and small tires. For this reason, so-called high vinyl polybutadiene rubber and high vinyl styrene-butadiene copolymer rubber containing 50 to 90% by weight of 1,2 bonds have been proposed, but tires using these rubbers for the tread certainly have poor durability. Although wet threading properties and rolling resistance are improved to some extent, on the other hand, performance such as abrasion resistance and fracture resistance is significantly lower with high vinyl polybutadiene rubber, and even high vinyl styrene-butadiene copolymer rubber is inferior to high vinyl polybutadiene rubber. Although it was not as great, it still deteriorated, and when used under somewhat harsh conditions, rapid wear occurred, which was extremely undesirable for practical use. In order to improve the above-mentioned drawbacks, the present inventors, in Japanese Patent Publication No. 30562/1983, considered the 1.2 bond content to be 25 to 45% by weight and the interaction between each microstructure. In other words, since improving wet skid resistance and decreasing rolling resistance are contradictory, it has been thought that it is relatively difficult to solve this problem. This was difficult because we focused only on the factors that had an influence on each characteristic, and originally
Since many primary properties (e.g. cis-1,4 bond content, bound styrene content, etc.) are involved in these properties, styrene-butadiene is a more comprehensive view of these primary properties. The earlier publication proposed the use of polymer rubber for tire treads. However, although this copolymer was indeed able to satisfy the three properties of wet skid resistance, rolling resistance, and abrasion resistance at the same time, it did not have the same uneven wear resistance that conventional styrene-butadiene copolymers had. It has become clear that the advantage of excellent durability is lost, and that when such tires are run for a long period of time, uneven wear gradually appears. In other words, to date, there has been no pneumatic tire that is extremely useful in practice and has excellent wet skid resistance, rolling resistance, fracture resistance, abrasion resistance, and uneven wear resistance, as well as good workability. This is the actual situation. In view of the above-mentioned current situation, in order to simultaneously improve the wet skid resistance, rolling resistance, fracture resistance, abrasion resistance, and uneven wear resistance of tires using styrene-butadiene copolymer rubber, we have further improved the primary properties mentioned above. As a result of intensive research, it was confirmed that a pneumatic tire that satisfies the above-mentioned conditions can be obtained when the tread is made of a composition containing a new styrene-butadiene copolymer rubber that simultaneously satisfies the specific conditions. We have achieved this goal. That is, the present invention is a copolymer formed by randomly repeating and bonding styrene units and butadiene units, and furthermore, (1) the content of bound styrene is 10 to 30% by weight, and (2) 1.2% of the butadiene moiety. Bond content is 42~
70% by weight, (3) Trans-1,4 bond content in the butadiene moiety is 25% by weight or more, (4) Cis-1,4 bond content in the butadiene moiety based on the trans-1,4 bond content (5) 65≦1.7×Bound styrene content (weight%) +
1.2 Bond content (weight%) ≦100, (6) Weight average molecular weight (w) is 35×10 ⁴ to 65×
10 ⁴ , (7) The ratio (w/n) of the weight average molecular weight (w) to the number average molecular weight (n) is 2.3 or less, (8) The molecular weight distribution curve has two or more peaks, (9) 75≦ Regarding the new styrene-butadiene copolymer rubber that satisfies the condition of w×10 ^-4 +1.3×trans-1.4 bond content (wt%) ≦120, this copolymer rubber may be used alone or in combination with the rubber 30 10 to 120 parts by weight of carbon black and 0.5 to 5 parts by weight of vulcanizing agent per 100 parts by weight of blended rubber of 70 parts by weight or more of other diene rubber.
A pneumatic tire with an improved tread can be obtained by using a rubber composition containing the following parts by weight in the tread. As is clear from the earlier publication, wet skid resistance and rolling resistance are improved at the same time,
In addition, in order to obtain sufficient wear resistance, it is necessary that the ratio (w/n) of the weight average molecular weight (w) to the number average molecular weight (n) regarding the molecular weight distribution is 2.3 or less. The w/n ratio of the styrene-butadiene copolymer rubber used in padded tires must also be 2.3 or less, preferably 2.1 or less. However, when the molecular weight distribution is sharpened in this way, on the other hand, the copolymer rubber tends to suffer uneven wear. Therefore, in order to improve the uneven wear phenomenon described above, it is necessary to increase the 1/2 bond content in the butadiene moiety of the copolymer rubber, and the higher the 1/2 bond content, the better the wet skid resistance. This is in an advantageous direction to satisfy both rolling resistance and rolling resistance. However, as the 1.2 bond content increases, the interaction with carbon black decreases, and the strength at break and abrasion resistance of the copolymer rubber tend to decrease. Therefore, there is an optimum value for the 1/2 bond content, and in the copolymer rubber of the present invention, it should be 42 to 70% by weight, preferably 45 to 60% by weight, in consideration of other primary properties. is necessary. In the copolymer rubber of the present invention, it is necessary to increase the content of 1 and 2 bonds as described above, but for the reasons described later, in order to simultaneously improve wet skid resistance and rolling resistance, it is necessary to increase the content of bound styrene. This means that the amount can be reduced. Here, the bound styrene is closely related to the strength at break of the copolymer rubber, and if the bound styrene content is up to about 35% by weight, the strength at break of the copolymer rubber is if styrene is randomly distributed. increases in proportion to the bound styrene content, but conversely, from the perspective of energy loss, the higher the bound styrene content, the greater the energy loss of the copolymer rubber.From this point of view, the bound styrene content is The lower the content, the better, and the maximum content is up to 30% by weight. However, as will be described later, in consideration of the synergistic effect with the trans-1.4 bond, the bound styrene content must be at least 10% by weight. Therefore, in the copolymer rubber of the present invention, the content of bound styrene is 10 to 30% by weight, preferably 15 to 25% by weight. By the way, random means IM
Kolthoffetal, J. Polymer Sci., 1 , 429 (1946).
This means that the block content in bound styrene is 10% by weight or less when measured by an oxidative decomposition method such as As mentioned above, the copolymer rubber of the present invention has a relatively high 1/2 bond content and contains bonded styrene in order to simultaneously improve wet skid resistance and rolling resistance, and also improve uneven wear resistance. As a result of making the amount relatively small, the strength at break and the wear resistance tend to decrease. Therefore, in order to improve this drawback, it is necessary to increase the weight average molecular weight (w), and in the copolymer rubber of the present invention, w needs to be 35×10 ⁴ or more. However, when w is about 50×10 ⁴ , the workability of kneading etc. deteriorates rapidly, and when it exceeds 65×10 ⁴ , the workability deteriorates to such an extent that it cannot withstand practical use at all. Therefore, in the copolymer rubber of the present invention, w is 35×10 ⁴ to 65×10 ⁴ , preferably 45×10 ⁴ to 55
×10 ⁴ . As mentioned above, the copolymer rubber of the present invention has improved strength at break and abrasion resistance by increasing its molecular weight, so it is undeniable that workability is worse than before, and workability has been improved. This is an absolutely essential condition from the point of view of productivity. Generally, in order to improve workability, it is sufficient to make the molecular weight distribution broader, but this is completely inconsistent with the improvement of wear resistance by sharpening the molecular weight distribution, which was mentioned at the beginning. Put it away. Therefore, in order to improve workability and wear resistance at the same time,
In the copolymer rubber of the present invention, it is necessary that the molecular weight distribution curve has two or more peaks. The method for obtaining such a copolymer rubber is to blend copolymer rubbers that have extremely sharp molecular weight distributions and different w values to obtain a total w/w ratio.
There is a way to make Mn less than 2.3,
In addition, Special Publication No. 42-14172, No. 44-4996
The method described in the above publication is known. Furthermore, the relationship between the bound styrene content and the 1.2 bond content is also a factor that greatly contributes to wet skid resistance and rolling resistance. Among these, the bound styrene content shows a larger contribution, and since the bound styrene content is expressed in weight% of the entire copolymer, it can be considered independently, but if the bound styrene content changes The content of butadiene also varies. Since the 1.2 bond content is expressed in weight percent in the butadiene moiety, it is apparently affected by the bonded styrene content. For this reason, the conditions for satisfying wet skid resistance and rolling resistance are expressed by the bound styrene content and the 1.2 bond content as a function of the bound styrene content. For copolymers in which the content of 1.2 bonds in the butadiene moiety is 25 to 80% by weight, the content of trans-1.4 bonds is 20% by weight or more, and w/n is 2.5 or less, the following formula is used: It turns out that it can be approximated as follows. 65≦1.7×Bound styrene content (weight %) +1.2 bond content (weight %)≦100 That is, within the above range, it is possible to simultaneously satisfy wet skid resistance and rolling resistance. If this value is less than 65, the wet skid resistance decreases, and even if other factors such as the trans-1/4 bond content are changed, the wet skid resistance can no longer be improved, which is undesirable. If it exceeds this, it is not preferable because rolling resistance cannot be improved even if other factors are changed. In addition, the trans-1,4 bonds in the butadiene moiety are a property that greatly contributes to the wear resistance of the copolymer rubber, and the more trans-1,4 bonds, the better the wear resistance. improves. This phenomenon is specific to styrene-butadiene copolymer rubbers that have a relatively large 1/2 bond content and a bound styrene content of 10% by weight or more, and is unique to styrene-butadiene copolymer rubbers with a styrene content of less than 10% by weight In the case of a homopolymer of butadiene that does not contain styrene, the wear resistance decreases as the number of trans 1,4 bonds increases. The copolymer rubber of the present invention must have a trans-1.4 bond content of at least 25% by weight. Furthermore, since the above phenomenon occurs in combination with cis-1.4 bonds, it is not preferable to have too many cis-1.4 bonds in order to fully bring out the wear resistance improving effect of trans-1.4 bonds. Therefore, in the copolymer rubber of the present invention, the value obtained by subtracting the cis-1,4 bond content from the trans-1,4 bond content is 8% by weight or more, preferably 10
It needs to be in weight percent. As mentioned above, the transformer
The 1.4 bonds are highly related, and as this value increases, other primary properties such as the 1.2 bond content are limited, thereby limiting improvements in wet skid resistance and rolling resistance. However, trans-1 and 4 bonds are compatible with the aforementioned w, which is another property related to wear resistance, and even if the trans-1 and 4 bond content is kept low, w can be increased. It was found that it is possible to sufficiently satisfy the wear resistance by doing so. Examining this point in detail, we find that trans-
Comparing 1.4 bond and w, the characteristic that contributes more to the wear resistance is the transformer 1.4 bond, and the conditions for improving wear resistance are w/
In styrene-butadiene copolymers with Mn of 2.5 or less, the trans-1.4 bond content and w
It was found that the relationship between can be approximated by the following equation. 75≦w×10 ⁻⁴ +1.3×trans −1.4 bond content (weight %)≦120 In other words, it is possible to satisfy wear resistance within the above range. If this value is less than 75, the wear resistance will not be sufficient, and if it exceeds 120, workability will deteriorate or the trans-1/4 bond content will be too high, resulting in a decrease in the 1/2 bond content. This is not desirable because it causes The copolymer rubber of the present invention can be used alone as a tread, but if necessary, it can be used with rubber 100%
70 parts by weight or less, preferably 50 parts by weight or less of natural rubber, polybutadiene rubber, synthetic polyisoprene rubber, butadiene-acrylonitrillo copolymer rubber, styrene-butadiene copolymer rubber other than the above copolymer rubbers, etc. It does not matter if a diene rubber is blended. The copolymer rubber of the present invention is produced by copolymerizing styrene and butadiene in the presence of an organolithium initiator in a hydrocarbon solvent to produce a styrene-butadiene copolymer. Various Lewis bases such as compounds, -SO ₃ M group, -OSO ₃ M group or ROM group (M is
One or more anionic surfactants having Na, K, Rb or Cs, R is an alkyl group are present, and after polymerization is carried out under isothermal or elevated temperature conditions, as necessary. Accordingly, a coupling reaction is performed. As a coupling agent, Tokuko No. 44-4996,
The material described in Japanese Patent Publication No. 49-36957 can be used. The copolymer rubber of the present invention is produced, for example, as follows. 25 cyclohexane to 50 reaction vessels
Kg, styrene 1.3Kg, 1,3-butadiene 4.5Kg,
2.54 g of n-butyl lithium, 0.5 g of sodium dedocylbenzenesulfonate and 1.7 g of ethylene glycol dimethyl ether were added, polymerization was carried out in the presence of nitrogen at a polymerization temperature of 52.5°C for 1.3 hours, and then 4 g of stannic chloride was added. After maintaining the temperature at 45°C for 18 hours, adding 100 g of 2,6-di-t-butyl-p-cresol, the solution was removed by steam stripping, and the product was dried with a hot roll at 115°C. It will be done. The content of 1/2 bonds can be determined by changing the polymerization temperature, and the content of other trans-1/4 bonds or cis-1/4 bonds can be determined using sodium dodecylbenzenesulfonate, ethylene glycol dimethyl ether, n-
By changing the addition ratio of butyllithium, each desired ratio can be controlled. Table 1 below lists the manufacturing conditions for copolymer samples No. 1 to 17 used in the present invention.

[Table] Furthermore, in a pneumatic tire using the novel copolymer rubber of the present invention, the rubber composition used for the tread contains 10 to 120 parts by weight of carbon black and 0.5 to 5 parts by weight per 100 parts by weight of rubber. Add vulcanizing agent. If carbon black is less than 10 parts by weight, there will be no reinforcing effect, and if it exceeds 120 parts by weight, workability such as kneading will deteriorate, and if the vulcanizing agent is less than 0.5 parts by weight, sufficient vulcanization effect cannot be expected. This is undesirable because if it exceeds 5 parts by weight, the hardness becomes too high and is not practical for use as a tread.
In addition, in order to make carbon black more suitable for its abrasion resistance and reinforcing properties, it is necessary to increase the iodine adsorption amount (IA).
Carbon black having a dibutyl phthalate oil absorption (DBP) of 60 ml/100 g or more is preferable. Vulcanizing agents include sulfur, p-quinonedioxime, p・p′-dibenzoylquinonedioxime, 4・4′-dithiodimorpholine, poly-p-
One or more of dinitrosobenzene, ammonium benzoate and alkylphenol disulfide are used, and one or more of sulfur, 4,4'-dithiodimorpholine and alkylphenol disulfide are used It is preferable to use two or more types, and it is particularly preferable to use sulfur. In the above pneumatic tire, the above carbon black,
Compounding agents other than the vulcanizing agent include inorganic fillers such as silica, bentonite, clay, titanium oxide, talc, clay, diatomaceous earth, and white clay, N-oxydiethylene-2-benzothiazolesulfenamide, di-2- Benzothiazyl disulfide, N-
Vulcanization accelerators such as cyclohexyl-2-benzothiazolesulfenamide, vulcanization accelerators such as zinc white and stearic acid, softeners such as aroma oil, N-phenyl-N'-isopropyl -p-phenylenediamine, phenyl-β-
Anti-aging agents such as naphthylamine and 2-mercaptobenzimidazole may be blended in amounts within the range commonly used in the rubber industry. The pneumatic tire mentioned above may be reinforced with organic fiber cords such as nylon, vinylon, polyester, or keplar, or inorganic fiber cords such as steel, glass, or carbon, and the carcass may have a radial structure or a bias structure. Although the structure may be any of the above, a radial structure is preferable. The above-mentioned pneumatic tire having the above configuration is
It is a pneumatic tire that is extremely useful in practice because it has excellent wet skid resistance, rolling resistance, fracture resistance, abrasion resistance, and uneven wear resistance, and has good workability. The copolymer rubber of the present invention will be described in more detail below with reference to Examples. Example 1 Thirty-four types of styrene-butadiene copolymer rubbers shown in Table 2 were prepared. Next, to 100 parts by weight of each of these styrene-butadiene copolymer rubbers, 50 parts by weight of ISAF carbon black, 10 parts by weight of aroma oil, 2 parts by weight of stearic acid, and N-phenyl-N'-isopropyl-p-phenylenediamine were added. 1 part by weight, 4.0 parts by weight of zinc white, 0.6 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide, 0.8 parts by weight of di-2-benzothiazyl disulfide, and 1.5 parts by weight of sulfur.
Various rubber compositions were created. These rubber compositions were evaluated for the presence or absence of roll bags during kneading with 10-inch rolls, and further evaluated for strength at break (Tb) in accordance with JISK6301. Tires having a tire size of 165SR13 were then prepared using these rubber compositions, and wet skid resistance, rolling resistance, and abrasion resistance were evaluated. The results are shown in Table 2. The evaluation method and the microstructure of the styrene-butadiene copolymer rubber were conducted as follows. (Wet skid resistance) On a wet concrete road surface with a water depth of 3 mm, 80
Measure the distance from when the wheels lock up to a stop after sudden braking from a speed of Km/hr. A tire using the styrene-butadiene copolymer of Sample No. 34 in Table 2 was used as a control, and the skid resistance of the test tire was evaluated using the following formula. (Stopping distance of control tire) - (Stopping distance of test tire) / (Stopping distance of control tire) x 100 (Rolling resistance) Measured by coasting method. Measurement conditions are tire internal pressure 1.7
Kg/cm ² , JIS 100% load, coasting start speed 120Km/hr.
Similar to the evaluation of wet skid resistance, the rolling resistance of the test tires was evaluated using the following formula. (Rolling resistance of control tire) - (Rolling resistance of test tire) / (Rolling resistance of control tire) x 100 (Wear resistance) After running 10,000 km, measure the remaining tread and find that the tread is 1
Compare the distance traveled required for mm wear.
Displayed as an index with the control tire as 100. The higher the value, the better. (Uneven wear resistance) After running for 20,000 km, the appearance was checked and the presence or absence of uneven wear was observed. (Microstructure) The bound styrene content was measured using a spectrophotometer at 699 cm
Using a calibration curve using the absorbance of ^-1 , the microstructure of the butadiene moiety was determined using the method of D.Morero [Chem.&
Ind., 41 , 758 (1959)]. Further, w/n was determined using a Waters GPC200 using a 0.5 g/100 ml tetrahydrofuran solution.

【table】

[Table] As is clear from Table 2, the pneumatic tires using the novel styrene-butadiene copolymer rubber of the present invention in the tread have excellent wet skid resistance, rolling resistance, fracture resistance, abrasion resistance, and unevenness resistance. It can be seen that the wear resistance is also extremely good. Reference Example A rubber composition having the formulation shown in Table 3 was prepared and examined in the same manner as in Example 1.

[Table] As is clear from Table 3, excellent effects can be obtained if the new copolymer rubber is blended in at least 30 parts by weight in 100 parts by weight of rubber.

Claims (1)

[Scope of Claims] 1 A copolymer formed by repeatedly bonding styrene units and butadiene units, and furthermore, (1) the bound styrene content is 10 to 30% by weight, and (2) 1 in the butadiene moiety.・2 bond content is 42~
70% by weight, (3) Trans-1,4 bond content in the butadiene moiety is 25% by weight or more, (4) Cis-1,4 bond content in the butadiene moiety based on the trans-1,4 bond content (5) 65≦1.7×Bound styrene content (weight%) +
1.2 Bond content (weight%) ≦100, (6) Weight average molecular weight (w) is 35×10 ⁴ to 65×
10 ⁴ , (7) The ratio (w/n) of the weight average molecular weight (w) to the number average molecular weight (n) is 2.3 or less, (8) The molecular weight distribution curve has two or more peaks, (9) 75≦ A new styrene-butadiene copolymer rubber that satisfies the following condition: w×10 ^-4 +1.3×trans-1.4 bond content (weight %)≦120.