JPS61258814A - Novel styrene-butadiene copolymer rubber - Google Patents

Abstract

PURPOSE:To provide the titled rubber suitable for pneumatic tire tread, comprising, as a matrix, random copolymer from styrene and 1,3-butadiene with the primary characteristics such as bonded styrene amount and cis-1,4-bond content representing each specific value. CONSTITUTION:The objective rubber can be obtained by incorporating (A) 100pts.wt. of a copolymer prepared by random copolymerization between styrene and 1,3-butadiene with (B) 10-20pts.wt. of carbon black and (C) 0.5-5pts.wt. of curing agent. Said copolymer has the following characteristics: (1) bonded styrene content ... 12-35wt% (2) 1,2-bond content in butadiene section ...30-45wt% (3) cis-1,4-bond content ... <=23wt% (4) trans-1,4-bond content ...>=42wt% (5) difference between trans-1,4-bond and cis-1,4-bond ... >=8wt% (6) 65<=1.7 X bonded styrene (wt%) + 1,2-bond (wt%) <=100 (7) ratio: weight- average molecular weight/number-average molecular weight <=2.3.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a novel styrene-butadiene copolymer rubber, and particularly to a styrene-butadiene copolymer rubber suitable for use in treads for pneumatic tires. . By using a rubber composition containing this novel styrene-butadiene copolymer rubber in a tire tread, wet skid resistance, rolling resistance, fracture resistance and abrasion resistance can be significantly improved at the same time.

[Prior Art] 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.

On the other hand, with the spread of expressways, wet skid resistance has become important for large tires, and relatively small tires that already use styrene-butadiene copolymer rubber have recently been introduced from the viewpoint of resource and energy conservation. Since then, it has become important to reduce energy loss and reduce rolling resistance. Therefore, it has become important to develop a new rubber that has excellent wet skidding resistance and low energy loss and can be used for both large and small tires.

For this reason, so-called high vinyl polybutadiene rubbers and high vinyl styrene-butadiene copolymer combs containing 50 to 90 1.2 bonds by weight have been proposed, but tires using these rubbers for their treads 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, and even with high vinyl styrene-butadiene copolymer rubber, high vinyl Although polybutadiene rubber was not bad, it did have a low strength, and when used under somewhat harsh conditions, it rapidly wore out, making it extremely undesirable for practical use.

[Problems to be Solved by the Invention] To date, no pneumatic tire has been realized that has good wet skid resistance, rolling resistance, fracture resistance, and wear resistance and is extremely useful in practice.

In view of the above-mentioned current situation, the present inventors conducted intensive research on styrene-butadiene copolymer rubber and obtained the following knowledge.

In other words, since conventionally it has been contradictory to improve wet squid resistance and reduce rolling resistance,
Solving this problem was thought to be relatively difficult, but it was difficult because only the factors that had an influence on each characteristic were focused on. Originally, many primary properties (e.g. cis-1,4 bond content, styrene content, molecular weight, degree of branching, etc.) are involved in a single property, so these secondary properties should be considered more comprehensively. From this point of view, it is possible to further improve even the contradictory performance described above.

[Means for solving problems]

Therefore, from the above viewpoint, the present inventors have focused on wet skid resistance and rolling resistance, as well as fracture resistance and abrasion resistance in addition to these, and have arrived at the present invention as a result of various studies. That is, the present invention is obtained by randomly copolymerizing styrene and 1,3-butadiene, and furthermore, 1) the bound styrene content is 12 to 35% by weight, and 2) the 1,2 bond content in the butadiene moiety is 30%. ~45 weight ratio, 3) Cis-1,4 bond content in the butadiene moiety is 23
4) Trans-1,4 bond content in the butadiene moiety is 42% by weight or more; 5) Based on the trans-t44 bond content, is the cis-1,4 bond content in the butadiene moiety? The subtracted value is 8 times It
6) The relationship between the bound styrene content and the 1.2 bond content is 65≦1.7×bonded styrene content (wt%).
) + 1.2 bond content (wt%) ≦ 100. 7) A novel styrene-butadiene copolymer rubber that satisfies the condition that the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) (IIIW/Mn) is 2.3 or less.

In particular, this styrene-butadiene copolymer rubber may be used alone or blended with 100 parts by weight of 30 parts by weight or more of this rubber and 70 parts by weight or less of other diene rubber, and 10 to 120 parts by weight of carmen black and a vulcanizing agent [1L5]. It is advantageous to use a rubber composition containing up to 5 parts by weight in the tread of a pneumatic tire.

In the novel styrene-butadiene copolymer rubber of the present invention, bound styrene is closely related to the strength at break of the copolymer rubber, and the bound styrene content is 35% by weight J1%.
To a certain degree, if styrene is randomly distributed, the strength at break of the copolymer rubber increases in proportion to the bound styrene content, but conversely, from the standpoint of energy loss, the bound styrene content increases. The smaller the amount, the smaller the energy loss of the copolymer rubber. In addition to this,
As will be described later, if the trans-1,4 bond and the synergistic effect are taken into account, the bound styrene content in the present invention is 12 to 12.
55% by weight, preferably 15-28% by weight. What is random?1. M.Kolthoff at al.
J, Folymer8ci,, 1, 429 (1
When measured by an oxidative decomposition method such as 946), it means that the block content in bound styrene is less than 10% by weight.

Regarding the butadiene portion of the copolymer rubber of the present invention, 1
．． 2 bonds have the effect of not increasing energy loss while improving the wet skid resistance of the copolymer, so the higher the 1.2 bond content, the better the wet skid resistance and rolling resistance. This is a favorable direction to satisfy both parties. However, as the 1.2 bond content increases, the interaction with carbon black becomes smaller, resulting in a significant decrease in the strength at break and abrasion resistance of the copolymer rubber. Therefore, in the present invention, the 1.2 bond content must be 30 to 45% by weight, preferably 30 to 40% by weight.

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 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 consider it independently, but when the bound styrene content changes, the butadiene content also changes. 1.2 Since the bond content is expressed in weight% of the butadiene moiety, is the appearance affected by the bonded styrene content? I will receive it. Therefore, the conditions for satisfying wet skid resistance and rolling resistance are expressed by the bonded styrene content and the bond content of 1.2 as a function of the bonded styrene content. The content is 10-35% by weight, 1 in the butadiene part.
,2 bond content 25-80% by weight, trans-1,4
Bond content is 20 wt% or more and Mw/Mn is 2.5
It has been found that for copolymers in the following range, it can be approximated as shown in the following formula.

65≦t7X bonded styrene content (wt%) + 1.2 bond content (wt%)≦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 will deteriorate, and other transformers 1,
4 Even if factors such as bond content are changed, it is no longer possible to improve the wet skid resistance and this is not preferable.
If it exceeds 00, it is not preferable because rolling resistance cannot be improved even if other factors are changed.

The trans-1,4 bonds in the butadiene moiety are greatly involved in the abrasion resistance of the copolymer rubber, and the more trans-1,4 bonds there are, the better the abrasion resistance is. , in the present invention, its content is 42 gw. This phenomenon is specific to styrene-butadiene copolymer rubber when the content of bound styrene is 12% by weight or more, and when the content of bound styrene is less than 12% by weight or butadiene rubber does not contain styrene. In the case of a homopolymer, the wear resistance decreases as the number of trans-1,4 bonds increases. Furthermore, this phenomenon is cis-1,
Since it occurs due to the trade-off with the 4-bond, trans-
The value obtained by subtracting the cis-1,4 bond content from the amount that fully brings out the wear resistance improvement effect of the 1゜4 bond is 8% by weight.
Above, it is necessary that the amount is preferably 10% by weight or more.

The ratio vr/Mn of the number average molecular weight (My) and the number average molecular i (Mn) regarding the molecular weight distribution is trans-1,4
Similar to bonding, it is related to the abrasion resistance of the copolymer rubber, and the smaller Mw/Mn is, the better the abrasion resistance is.
In the present invention, it is necessary that the number of flies is 5 or less, preferably 2.1 or less.

The copolymer rubber of the present invention can be used alone in a tread, but if necessary, natural rubber, polybutadiene or Diene rubbers such as rubber, synthetic polyisoprene rubber, butadiene-acrylonitrile copolymer rubber, and styrene-butadiene copolymer rubber other than the above-mentioned copolymers 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.
Anionic compounds having various Lewis bases such as ether compounds and amine compounds, or 180M groups, -0803M groups, or ROM groups (M, Ma, R'b or Os, R is an alkyl group) in the polymerization system. One or more surfactants are present and the polymerization is carried out under isothermal or elevated temperature conditions.

The copolymer rubber of the present invention is produced, for example, as follows. 25 kg of cyclohexane in a 5Qt reaction vessel, 9.1.3-butadiene a, 5'q, n-butyllithium L6f, sodium dodecylbenzenesulfonate 152 and ethylene glycol dimethyl ether t8? was added and polymerized in the presence of nitrogen at a polymerization temperature of 46°C for t5 hours, and the remaining catalyst ? and drying the product. 1.2 bond content can be determined by changing the polymerization temperature, and other trans-1,4 bond contents and cis-t4 bond contents can be determined using sodium dodecylbenzenesulfonate, ethylene glycol dimethyl ether, n-butyl lithium. By changing the addition ratio of each, each can be controlled to a desired ratio.

Table 1 below lists the manufacturing conditions for copolymer samples 1 to 6 of the present invention.

Table 1 Also, when the copolymer rubber of the present invention is used in the tread of a pneumatic tire, 10 to 120 parts by weight per 100 parts by weight of rubber.
Parts by weight of carbon black and 15 to 5 parts by weight of a vulcanizing agent are blended. If the carbon black is less than 10 parts by weight, there will be no reinforcing effect, and if it exceeds 120 parts by weight, the workability of kneading etc. will deteriorate, and if the vulcanizing agent is less than 5 parts by weight, the vulcanizing effect cannot be expected to be sufficient. Unfavorable, 5 parts by weight? This is because if it exceeds the hardness, the hardness becomes too high and is not suitable for practical use as a tread.

In addition, carbon black must have an iodine adsorption ff1 (IA) of 36q/y or more and a dibutyl phthalate oil absorption (DB
Carbon black having P) of bata/1 aay or more is preferable. Vulcanizing agents include sulfur, p-quinonedioxime, p,p'-dibenzoylquinonedioxime, 4.4'
- One or more of dithiodimol 7-olin, poly-p-dinitrosobenzene, ammonium benzoate and alkylphenol disulfide is used,
It is preferred to use one or more of sulfur, 4,4'-dithiodimorpholine and alkylphenol disulfide, and most preferably sulfur.

In the above-mentioned pneumatic tire, the rubber composition used for the tread further contains inorganic compounds such as silica, bentonite, clay, titanium oxide, talc, white clay, diatomaceous earth, white glaze, etc. as compounding agents other than the above-mentioned carbon black and vulcanizing agent. Fillers, vulcanization accelerators such as N-oxydiethylene-2-benzothiazolesulfenamide, di-2-benzothiazyl disulfide, N-cyclohexyl-2-benzothiazolesulfenamide, etc., vulcanization such as zinc white, stearic acid, etc. Softeners such as sulfur accelerators, aroma oils, etc., anti-aging agents such as M-phenyl-N'-isogloby-p-7 unilene diamine, phenyl-β-naphthylamine, 2-mercaptobenzimidazole, etc. are used in the normal rubber industry. It may be blended in the blending amount within the range.

The pneumatic tires mentioned above are made of organic fiber cords such as nylon, vinylon, polyester, and Kevlar, 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 a pneumatic tire which is extremely useful in practice since it has excellent wet squid resistance, rolling resistance, fracture resistance and abrasion resistance at the same time.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Nineteen types of styrene-butadiene copolymer rubbers shown in Table 1 were prepared. Next, to 100 parts by weight of each of these styrene-butadiene copolymer rubbers, 50 parts by weight of HAIF carbon black, 10 parts by weight of aroma oil, 2 parts by weight of stearic acid, and N-phenyl-N'-isopropyl-p-7 unirange. 1 part by weight of amine, 4.0 parts by weight of zinc white, 6 parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide Q, 6 parts by weight of di-2-benzothiazyl disulfide (8 parts by weight of L and 1.5 parts by weight of sulfur). Nineteen types of rubber compositions were prepared.These rubber compositions were evaluated for strength at break (Tb) according to JIS K 6i1.Next, these rubber compositions were used in the tread of a tire size 165 SR13 to form a tire. were prepared and evaluated for wet skid resistance, rolling resistance and abrasion resistance.The results are shown in Table 1.

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 cm, 801 (m
The vehicle suddenly brakes from a speed of /hr and measures the distance from when the wheels lock until it stops. Using a tire using the styrene-butadiene copolymer of sample NQ20 in Table 1 as a control, the skid resistance of the test tire was evaluated in accordance with the following formula.

(Rolling resistance) Measured by coasting method. Measurement conditions are tire internal pressure 1.7kl/,
2. Load J-work 5100% load, Seeding start speed 1o o
Similar to the evaluation of tan/hr o wet skid resistance, the rolling resistance of the test tire was evaluated using the following formula.

(Wear resistance) After running 10,000 km, the shallow grooves are measured and the distance traveled required for the tread to wear out by 11111 is compared relative to each other. Displayed as an index with the control tire as 100. The value is as good as it gets.

(Microstructure) The bound styrene content was measured using a spectrophotometer at 6996n-1.
absorbance of? The microstructure of the butadiene moiety was determined using the calibration curve used by Morero's method [Ohem.

&Ind. , ill, 758 (1959)
]. Also My/Mnbao, sr/1o
Waters GP020 in o-tetrahydrofuran solution
0'f! : Obtained using.

As is clear from Table 1, the bound styrene content is 12
~35 weight ratio, 1°2 bond content of butadiene moiety is 3
0 to 45 weight ratio, trans=1.4 bond content on 42 weight plate, cis-1,4 bond content below 23 weight plate,
The value obtained by subtracting the cis-1,4 bond content from the trans-1,4 bond content is 8 weight coefficient or more, and 65≦t7X bond styrene content + 1,2 bond content≦100, and Mvr / Pneumatic tires using the novel styrene-butadiene random copolymer rubber of the present invention with an Mn of 2.3 or less for the tread have outstanding wet skid resistance, rolling resistance, fracture resistance, and abrasion resistance at the same time. It can be seen that

Reference Example A rubber composition having the formulation shown in Table 2 was prepared and examined in the same manner as in Example 1.

As is clear from Table 2, it is preferred that the new copolymer rubber be blended in an amount of at least 30 parts by weight in 100 parts by weight of rubber.

Claims (1)

[Scope of Claims] 1. Obtained by randomly copolymerizing styrene and 1,3-butadiene, and 1) having a bound styrene content of 12 to 35% by weight, and 2) containing 1,2 bonds in the butadiene moiety. 3) cis-1,4 bond content in the butadiene moiety is 23% by weight;
4) The content of trans-1,4 bonds in the butadiene moiety is 42% by weight or more, 5) The content of cis-1,4 bonds in the butadiene moiety is subtracted from the trans-1,4 bond content. 6) The relationship between the bound styrene content and the 1,2 bond content is 65≦1.7×bonded styrene content (weight%).
)+1,2 bond content (wt%)≦100, 7) Weight average molecular weight (@M@w) and number average molecular weight (@M
A novel styrene-bucadiene copolymer rubber that satisfies the condition that the ratio of @n) (@M@w/@M@n) is 23 or less.