JPS61293212A - Styrene/butadiene copolymer rubber - Google Patents

Abstract

PURPOSE:The title rubber which can give a pneumatic tire excellent in wet-skid resistance, rolling resistance, breaking resistance, (partial) abrasion resistance and workability, obtained by random-copolymerizing styrene with 1,3-butadiene so that the obtained copolymer may satisfy specified requirements. CONSTITUTION:Styrene and 1,3-butadiene are dissolved in an organic solvent such as cyclohexane and random-copolymerized in the presence of N2 or the like at a polymerization temperature with amounts of addition of sodium dodecylbenzenesulfonate, ethylene glycol dimethyl ether, n-butyllithium, etc., that the obtained copolymer may satisfy the desired requirements, to obtain the title rubber having a combined styrene content of 10-30wt%, a 1,2-bond content in the butadiene portion of 42-70wt%, a trans-1,4-bond content in that portion >=25wt% and a difference between the trans 1,4-bond content and the cis-1,4-bond content >=8wt%, satisfying the relationships I and II and having a weight-average MW of 35X10<4>-65X10<4>, a weight-average MW/number- average MW ratio <=2.3 and a peak of a MW distribution curve >=2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is particularly applicable to rubber compositions for treads of pneumatic tires, which have good workability, wet skidding resistance, rolling resistance, fracture resistance, abrasion resistance and uneven wear resistance. The present invention relates to a new styrene-butadiene copolymer rubber that can simultaneously significantly improve the properties of the 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, and recent resource and energy conservation improvements have become important for relatively small tires that already use styrene-butadiene copolymer rubber. From this point of view, it has become important to reduce energy loss, that is, reduce rolling resistance. Therefore, it has become important to develop a new rubber that has excellent wet skid 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 stereo/-butadiene copolymer rubber containing 50 to 90% by weight of 1,2 bonds have been proposed, but tires using these rubbers for the tread have not been produced. Although wet skid resistance 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. Polybutadiene rubber was not as bad, but it still deteriorated, and when used under somewhat harsh conditions, it rapidly wore out, making it extremely undesirable for practical use.

In order to improve the above-mentioned drawbacks, the present inventors proposed in Japanese Patent Publication No. 60-50562 that the amount of 1.2 bonded metal is 25 to 45% by weight and the interaction between each microstructure is considered. did. In other words, since improving wet skid resistance and lowering rolling resistance are contradictory, it has been thought that it is relatively difficult to solve this problem. This was difficult because the focus was only on factors that had an influence on each characteristic, and originally there were many primary characteristics (for example, cis-
1,4 bound metal content, bound styrene content, etc.), therefore, the use of styrene-butadiene copolymer compositions in tire treads was investigated from a more comprehensive perspective. This was proposed in the earlier publication.

However, while this copolymer is indeed able to satisfy the three properties of wet skid resistance, rolling resistance, and abrasion resistance at the same time, it does not have the same resistance as conventional styrene dipoles/copolymers. It has become clear that the advantage of excellent uneven wear resistance is lost, and uneven wear gradually appears when such tires are run for a long period of time.

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 developed the primary properties mentioned above. As a result of further intensive research, it was confirmed that when the tread is made of a composition containing a new styrene-butadiene copolymer rubber that simultaneously satisfies specific conditions, a pneumatic tire that satisfies the above conditions can be obtained. The present invention has been achieved.

That is, the present invention is obtained by randomly copolymerizing styrene-1,5-butadiene, and furthermore, (1) the content of bound styrene is 10-50% by weight, and (2) the content of 1,2-bonded gold in the butadiene moiety is (3) The amount of trans-1,4 bound gold in the butadiene moiety is 25% by weight or more; (4) The amount of trans-1,4 bound gold in the butadiene moiety is determined from the amount of trans-1,4 bound gold in the butadiene moiety. , 4 The value after deducting the amount of bound metal is 8% by weight or more, (5) 65≦167×Bound styrene content (weight%) +
1.2 Binding gold content (weight 96)≦100° (6) Weight average molecular weight (Mw) is 35×10′ to 65×104
, (7) the weight average molecular weight (Mw), number average molecular weight (Mn) and fD ratio (Mw/Mn) is less than or equal to 2.5, (8) the molecular weight distribution curve has two or more peaks, (9) 7
5≦MWX 1 G-'+1.5X) U/suit. 4
Regarding the new spray/-Putage/copolymer rubber that satisfies the condition of binder content (wt%)≦120, this copolymer rubber may be used alone or in combination with the rubber 5.
10 to 100 parts by weight of blended rubber containing 0 parts by weight or more and 70 parts by weight or less of other diene rubber, 10 to 10 parts by weight of carbon black.
A pneumatic tire with an improved tread can be obtained by using a rubber composition containing 120 parts by weight of the rubber composition and 5 to 5 parts by weight of the vulcanizing agent CL in the tread.

As is clear from the above-mentioned earlier publication, in order to simultaneously improve wet skidding resistance and rolling resistance and obtain sufficient wear resistance, the weight average molecular weight (Mw) and number average molecular weight (Mn) regarding the molecular weight distribution must be adjusted. ratio (Mw/Mn
) is required to be 2.5 or less, and also in the stainless-butadiene copolymer rubber used in the pneumatic tire of the present invention, My/Mn must be 2.5 or less, preferably 2.1 or less. Must be. However, when the molecular weight distribution is sharpened in this manner, on the other hand, the copolymer rubber tends to suffer uneven wear.

Therefore, in order to improve the above-mentioned uneven wear phenomenon, it is necessary to increase the content of 1,2-bond gold in the Butashev portion of the copolymer rubber. This is advantageous for satisfying both wet skid resistance and rolling resistance. However, as the amount of 1,2-bond metal increases, the interaction with carbon black becomes smaller, and the strength at break and abrasion resistance of the copolymer rubber tend to decrease. Therefore, there is an optimum value for the amount of 1,2-bond metal, and in the copolymer rubber of the present invention, it is 42 to 70% by weight, preferably 45 to 60% by weight, in consideration of other primary properties. It is necessary.

In the copolymer rubber of the present invention, it is necessary to increase the amount of 1.2 bond metal as described above, but this is necessary to simultaneously improve wet kidding resistance and rolling resistance for the reason described later. This means that the bound styrene content may 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 around 35% by weight, the strength at break of the copolymer rubber is if the 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 Less is preferred, and at most 50% by weight.

However, as will be described later, in consideration of the synergistic effect with the trans-1,4 bond, the bound stereo content should be at least 10% by weight. Therefore, in the copolymer rubber of the present invention, the bound styrene content is from 10 to 50% by weight, preferably from 15 to 25% by weight. Furthermore, what does random mean?
M, Kolth Offetal, J, Polymer
8ci, 1, 429 (1946), the block content in bound styrene is less than 10% by weight.

In the copolymer rubber of the present invention, in order to simultaneously improve wet skid resistance and rolling resistance as described above, and also improve uneven wear resistance, the copolymer rubber has a relatively large amount of 1.2 bond and binds styrene. As a result of keeping the content relatively low, strength at break and wear resistance tend to decrease. Therefore, in order to improve this drawback, it is necessary to increase the weight average molecular weight (MY), and in the copolymer rubber of the present invention, M
It is necessary that y is 35×104 or more. However, when My is about 50 x 10', the workability of kneading etc. deteriorates rapidly, and when it exceeds 65 x 104, the workability deteriorates to such an extent that it can no longer withstand practical use. Therefore, in the copolymer rubber of the present invention, My is 35
104-65 X 104, preferably 45 X 1
04-35X104.

Since the copolymer rubber of the present invention has improved strength at break and abrasion resistance by increasing its molecular weight as described above, it is undeniable that workability is worse than conventional ones, and it is necessary to improve workability. 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 completely contradicts the improvement in abrasion resistance by sharpening the molecular weight distribution mentioned above. Therefore, in order to simultaneously improve workability and abrasion resistance, it is necessary for the copolymer rubber of the present invention to have two or more peaks in the molecular weight distribution curve. One way to obtain such a copolymer rubber is to blend copolymer rubbers with extremely sharp molecular weight distributions and different MY so that the overall My/Mn is 2.5 or less. However, there are also other publications such as Japanese Patent Publication No. 42-14172,
The method described in JP-A-4996 and the like is known.

Furthermore, the relationship between the content of bound styrene and the amount of 1,2 alloy is also a factor that greatly contributes to wet skid resistance and rolling resistance.

Among them, the bound styrene content shows a larger contribution, and the bound styrene content is the weight% of the entire copolymer.
Since it is expressed as , it is possible to think about it independently, but
As the bound styrene content changes, the butadiene content also changes.

1.2 Since the amount of bound gold is expressed in weight percent in the butadiene moiety, the appearance is affected by the content of bound styrene. Therefore, the conditions for satisfying wet skid resistance and rolling resistance are expressed by the amount of 1,2-bond metal as a function of the bound styrene content and the bound styrene content. is 10 to 35% by weight, the 1゜2 bond gold content in the butadiene moiety is 25 to 80% by weight, the trans-1,4 bond gold content is 20% by weight or more, and My/Mn is 2.5 or less. It was found that for the copolymer of , it can be approximated as follows.

65≦1.7×Bound styrene content (wt%) +1.2
If the amount of alloy (weight qb)≦100 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 amount of trans-1,4 alloy are changed, the wet skid resistance cannot be improved anymore, which is not preferable. On the other hand, if it exceeds this value, rolling resistance cannot be improved even if other factors are changed, which is undesirable.

In addition, the trans-1,4 bonds in the butadiene moiety are characteristics that greatly contribute to the abrasion resistance of the copolymer rubber, and the more trans-1,4 bonds, the better the abrasion resistance. will improve. This phenomenon is specific to styrene-Ptadier/copolymer rubbers that have a relatively large amount of 1,2-bond metal and a bound styrene content of 10% by weight or more. However, in the case of a butadiene homopolymer that does not contain styrene, the wear resistance decreases as the number of trans 1,4 bonds increases. In the copolymer rubber of the present invention, trans-1,
It is necessary that the amount of 4-bond metal is 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 dis-1,4-bond gold content from the trans-1,4-bond gold content must be 8% by weight or more, preferably 10% by weight. .

As mentioned above, the transformer-1,4 bond has a great deal to do with wear resistance, and when this value increases, other primary properties such as the 1,2 bond content are limited, and as a result, the wear resistance decreases. Improvements in wet skidding properties and rolling resistance are limited. However, the trans-1,4 bond is compatible with the aforementioned My, which is another property related to wear resistance, and even if the trans-1,4 bond gold content is kept low, the MW can be reduced. It has been found that by increasing the size, it is possible to sufficiently satisfy the wear resistance. Examining this point in detail, if we compare the trans-1,4 bond and My, the property that contributes more to the wear resistance is the trans-1,4 bond. For the stereo/-butadiene copolymer with My/Mn of 2.5 or less, the conditions are the trans-1,4 bond gold content and M
It was found that the relationship with y can be approximated by the following equation.

75≦MWX10”4-)-1,5×Trans-1,4
If the content of the alloy is within the above range (weight qb)≦120, it is possible to satisfy the wear resistance. If this value is less than 75, the wear resistance is insufficient, and if it exceeds 120, workability deteriorates or the amount of trans-1,4 alloy is too large, resulting in 1,
This is not preferable because the amount of 2-bond gold decreases.

The copolymer rubber of the present invention can be used alone in the tread, but if necessary, 70 parts by weight of the copolymer rubber in 100 parts by weight of rubber may be used.
Less than 50 parts by weight, preferably 50 parts by weight or less, of natural rubber, polybutadiene rubber, synthetic polyisoprene rubber, butadiene-acrylonitrile copolymer rubber, styrene-butadiene copolymer rubber other than the above-mentioned copolymer rubbers, etc. ″
/fF rubber may be blended.

The copolymer rubber of the present invention is produced by copolymerizing styrene and butadiene in a hydrocarbon solvent in the presence of an organolithium initiator to produce a styrene-butadiene copolymer.
In the polymerization system, various Lewis bases such as ether compounds and amine compounds, or -803M group, -0808M group, or ROM group (M is Na, K, Rb t or C8, R
One or more anionic surfactants having an alkyl group) are present, and after polymerization is carried out under isothermal or elevated temperature conditions, a coupling reaction is carried out, if necessary.

As the coupling agent, those described in Japanese Patent Publication No. 44-4996 and Japanese Patent Publication No. 56957-56957 can be used.

The copolymer rubber of the present invention is produced, for example, as follows. In a 501 reaction vessel, add 25 yu of cyclohexa, 1.5 yu of styrene, and 1. S-butadiene/45 to 9, n-butyllithium 2.54? , sodium dodecylbenzenesulfonate 0.5? and 1.7 f of ethylene glycol dimethyl ether were added, and the polymerization temperature was 52.5 in the presence of nitrogen.
Polymerization was carried out for 1.5 hours at ℃, then stannic chloride was
The 2,6-di-t
After adding 100 t of -butyl-p-cresol, the solution is removed by steam dripping, and the product is dried with a hot roll at 115°C. 1.2 The amount of bound gold can be determined by changing the polymerization temperature, and the amount of other trans-1゜4 bound gold and cis-1,4 bound gold can be determined using sodium dodecylbenzenesulfonate, ethylene glycol dimethyl ether, etc. , n-7'chilllithium can be added to a desired ratio by changing the ratio of addition.

Table 1 below lists the manufacturing conditions for copolymer samples 1 to 17 used in the present invention.

Furthermore, in a pneumatic tire using the novel copolymer rubber of the present invention, rubber 1 is added to the rubber composition used for the tread.
00 parts by weight, 10 to 120 parts by weight of carbon black and 15 to 5 parts by weight of a vulcanizing agent are blended. This is because if carbon black is less than 10 parts by weight, there is no reinforcing effect, and if it exceeds 120 parts by weight, workability such as wire crosstalk will deteriorate.
If the vulcanizing agent is less than LL5 parts by weight, a sufficient vulcanizing effect cannot be expected, which is undesirable, and if it exceeds 5 parts by weight, the hardness is too high and is not practically preferred as a tread. In addition, in order to make carbon black more suitable for wear resistance and reinforcing properties, the amount of iodine adsorption (A) must be 56 m
y/ or more and dibutyl phthalate oil absorption (DBP
) is preferably 60d/1001F or more. Vulcanizing agents include sulfur, p-quinonedioxime, I
), P'-dibenzoylquinone dioxime, 4.4'-
One or more of dithiodimorpholine, poly-p-dinitrosobenzea, ammonium fluoroate, and alkylphenol disulfide are used, and sulfur, 4,4'-dithiodimorpholine and It is preferable to use one or more types of alkylphenol disulfides, and it is particularly preferable to use sulfur.

In the above-mentioned pneumatic tire, the rubber composition used for the tread further contains inorganic fillers such as silica, bentonite, clay, titanium oxide, Merck, white clay, diatomaceous earth, white glaze, etc. as compounding agents other than the above-mentioned carbon black and vulcanizing agent. agent, N-Oyashidietele/-2-benzothiazole sulfenamide, di-2-benzothiazyl disulfide, N-cyclohexyl-2-bea'/fazole 7
Vulcanization accelerators such as enamide, vulcanization accelerators such as zinc white and stearic acid, softeners such as aroma oil, N-phenyl-ke-isopropyl-p-phenylenediamine, phenyl-naphtheramine, 2-
Anti-aging agents such as mercaptobenzimidazole may be incorporated in amounts within the range used in the ordinary rubber industry.

The pneumatic tires mentioned above are made of organic fiber cords such as nylon, vinylon, polyester, and Kepler, steel,
The carcass may be reinforced with inorganic fiber cords such as glass or carbon, and the carcass may have either a radial structure or a bias structure, but the radial structure is preferable.

The above-mentioned pneumatic tire having the above-mentioned structure is extremely useful in practical use because it has excellent wet skid resistance, rolling resistance, fracture resistance, abrasion resistance, and uneven wear resistance, as well as good workability. It is a pneumatic tire.

The copolymer rubber of the present invention will be described in more detail below with reference to Examples.

Example 1 Four types of styrene-butadiene copolymer rubber shown in Table 2 were prepared. Next, ISA? 50 parts by weight of carbon black, 10 parts by weight of aroma oil, 2 parts by weight of stearic acid, 1 part by weight of N-phenyl-N'-isopropyl-p-phenyl diamine, zinc ia.

11i, 16 parts by weight of N-oxydiethylene-2-penzthiazolesulfenamide, 18 parts by weight of di-2-benzothiazyl disulfide, and 1.5 parts by weight of sulfur were blended into 34 types of rubber compositions. These rubber compositions were evaluated for the presence or absence of roll bags when kneaded using 10-inch rolls, and further evaluated for strength at break (TI) according to J.E. Elf 6501. Next, tires were prepared using these rubber compositions in treads with a tire size of 1658R15, 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 are as follows.

(Wet skid resistance) On a wet concrete road surface with a water depth of 311 Il, a
The vehicle suddenly brakes from a speed of 0 km/hr and measures the distance from when the wheels lock until it stops. Sample S in Table 2
A tire using a styrene-butadiene copolymer of Sa was used as a control, and the skid resistance of the test tire was evaluated using the following formula.

(Stopping distance of control tire) (Rolling resistance) Measured by coasting method. Measurement conditions are tire internal pressure 1.7 Akebono/c
m”, JI day 100% load, coasting start speed 120 k
Similarly to the m/hro wet skid resistance evaluation, the rolling resistance of the test tire was evaluated using the following formula.

(Wear Resistance) After running 1 [1, OOO km, residual damage is measured and the distance traveled required for the tread to wear out by 1111 km is compared relative to each other.

Displayed as an index with the control tire as 100. The value is as good as it gets.

(Uneven wear resistance) After running OOOkm in 2Q, the appearance was checked and the presence or absence of uneven wear was observed.

(Microstructure) The bound styrene content was measured using a spectrophotometer using a calibration curve using the absorbance of 699x-1, and the microstructure of the butadiene portion was determined by Morsro's method (Oham.

& Ind., al., 758 (1959)). Moreover, My/Mn was determined using a Waters GP0200 with a Q, 5f, /, 100-tetrahydrofuran solution.

As is clear from Table 2, the pneumatic tires using the novel styrene-butadiene copolymer rubber of the present invention in their treads have excellent wet skidding resistance, rolling resistance, fracture resistance,
It can be seen that the wear resistance and uneven wear resistance are both extremely excellent.

Reference Example A rubber composition having the formulation shown in Table 5 was prepared and examined in the same manner as in Example 1.

As is clear from Table 3, excellent effects can be obtained if the new copolymer rubber is blended in at least 50 parts by weight in 100 parts by weight of rubber.

Claims (1)

[Claims] 1. Obtained by randomly copolymerizing styrene and 1,5-butadiene, and (1) having a bound styrene content of 10 to 50% by weight; (2)
1,2 bond gold content in the butadiene moiety is 42 to 70% by weight, (3) trans-1,4 bond gold content in the butadiene moiety is 25% by weight or more, (4) the trans-1,4 bond The value obtained by subtracting the amount of cis-1,4 bound gold in the butadiene moiety from the amount of gold is 8% by weight or more, (5) 65≦1.7×Bound styrene content (% by weight) +
1,2 bond content (wt%)≦100, (6) weight average molecular weight (@M@w) is 35×10^4 to 65×10^4
, (7) the ratio of the weight average molecular weight (@M@w) to the number average molecular weight (@M@n) (@M@w/@M@n) is 2.3 or less, (8) a molecular weight distribution curve. 2 or more peaks, (9)
75≦＠M＠w×10＾-＾4+1.5×Trans-1
A novel styrene-butadiene copolymer rubber that satisfies the following condition: , 4-bond metal content (weight %)≦120.