JP2000109608A - Rubber composition and pneumatic tire using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber compsn. with an enhanced high hysteresis loss property without lowering fracture characteristics, and a pneumatic tire excellent in gripping properties. SOLUTION: This rubber compsn. contains 10-200 pts.wt. of a styrene- isobutylene random copolymer (b) having a polystyrene-converted wt. average mol.wt. of 2,000-50,000 with the content of bonded styrene [St(b) (wt.%)] of 20-70 wt.%, based on 100 pts.wt. of a rubber component comprising a styrene- butadiene copolymer (a) with the content of bonded styrene [St(a) (wt.%)] of 10-50 wt.% and with the content of vinyl bond of the polybutadiene part of 10-70%. In the rubber compsn. the styrene content St(a) in the copolymer (a) has a relationship represented by the formula: St(b)>St(a)+10, with the styrene content St(b) in the copolymer (b). This rubber compsn. is for use in a tread for a pneumatic tire.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition, and more particularly to a rubber composition having improved hysteresis loss without deteriorating fracture characteristics, and a grip using the rubber composition. The present invention relates to a pneumatic tire having excellent properties.

[0002]

2. Description of the Related Art Conventionally, in order to enhance the grip properties of rubber compositions, aromatic softeners have been favorably blended.

[0003] However, in order to obtain grip properties, a large amount of a softening agent must be incorporated, and when an aromatic softening agent is used, there is a problem in that the breaking characteristics are reduced.

In order to improve this point, the use of a butyl-based softening agent has been studied, but the butyl-based softening agent is compatible with a diene-based rubber which is suitably used as a rubber component of a matrix. However, when the molded product is combined with other members to form a final product, there is a problem that the adhesion between the members is reduced.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rubber composition which is difficult to achieve by such a known method, and which can simultaneously provide a high level of fracture characteristics and high hysteresis loss, and a dry composition. Another object of the present invention is to provide a tire that exhibits high grip performance on both wet and wet road surfaces.

[0006]

Means for Solving the Problems As a result of intensive studies on a rubber composition containing various softening agents, the present inventors have found that a copolymer of isobutylene and styrene obtained by cationic polymerization is compounded in the rubber composition. The inventors have found that a tire exhibiting high grip characteristics on both dry and wet road surfaces can be obtained by using this rubber composition for a tread, and have completed the present invention.

That is, the present invention has the following configuration. (1) The bound styrene content (St _(a) (% by weight)) is 10
100% by weight of a rubber component containing a styrene-butadiene copolymer rubber (a) having a vinyl bond content of a polybutadiene portion of 10% to 70% by weight, and a weight average molecular weight in terms of polystyrene of 2,000 to 5%.
0000, 10 to 200 parts by weight of a styrene-isobutylene random copolymer (b) having a bound styrene content (St _(b ) (% by weight)) of 20 to 70% by weight. The bound styrene content (St _(a) ) of the copolymer _(a ) and the bound styrene content (S
t _(b) ) satisfying the following formula (1): St _(b) > St _(a) +10 (1) (2) The above-mentioned copolymer (b) is added at least 20 parts by weight to 100 parts by weight of the above-mentioned copolymer (a) in advance. The rubber composition according to (1). (3) A pneumatic tire using the rubber composition according to (1) or (2) for a tread. (4) A competition tire using the rubber composition according to (1) or (2) for a tread.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The copolymer rubber (a) used in the present invention is obtained by copolymerizing styrene and butadiene, and has a bound styrene content of 10%.
From 50% by weight to 10% by weight
To 70%. When the bound styrene content is 10% by weight or less, sufficient breaking strength of the rubber composition cannot be obtained, and when it is more than 50% by weight, the elasticity of the rubber composition becomes high, so that the gripping property decreases, which is not preferable. As used herein, the bound styrene content refers to the content of styrene units present in the main chain of the polymer, and the vinyl bond content refers to the content of 1 in a portion derived from polymerization of butadiene in the main chain of the polymer. , 2-bonds.

[0009] The copolymer rubber (a) contains
Preferably, the content is at least 10% by weight. If the amount is less than 10% by weight, the effect of the present invention cannot be sufficiently obtained.

In the present invention, the rubber component used in combination with the copolymer (a) is not particularly limited, but a diene rubber component is preferable, and a homopolymer of a diene monomer and a diene monomer are particularly preferable. It is a copolymer of one another or a copolymer of a diene monomer and a vinyl aromatic monomer. Specifically, natural rubber (NR), synthetic polyisoprene rubber (IR), polybutadiene (BR), styrene-butadiene copolymer (SBR), butyl rubber (IIR), ethylene-propylene-diene copolymer (EPDM) Examples thereof include acrylonitrile-butadiene copolymer (NBR), and particularly preferred are BR and SBR. These rubber components may be used alone or as a mixture of two or more.

The copolymer (b) of the present invention is a styrene-isobutylene random copolymer obtained by cationic polymerization in a hydrocarbon solvent using a Lewis acid catalyst as an initiator. It can be obtained by cationic polymerization using a method as described on page 201 of Experimental Method for Molecular Synthesis (Kagaku Dojinsha), and a method described in Polymer Chemistry, Vol. 18, pages 389 to 395.

As the polymerization solvent, a solvent generally used for cationic polymerization can be appropriately used, and for example, a hydrocarbon solvent such as an aliphatic hydrocarbon, an aromatic hydrocarbon, and a halogenated hydrocarbon is used. Of these, aromatic hydrocarbons are preferred, and toluene is more preferred. Specific examples of such aliphatic hydrocarbons include pentane and hexane, and aromatic hydrocarbons include benzene, toluene, and xylene. Specific examples of halogenated hydrocarbons include chloromethane, chloroethane, and methylene chloride. , 1,1-dichloroethane, chloroform, 1,2-dichloroethane and the like. These are used alone or as a mixture of two or more. Furthermore, these solvents may be used in combination with a smaller amount of another solvent, for example, an acetate compound such as ethyl acetate or an organic compound having a nitro group such as nitroethane.

As the Lewis acid catalyst, those represented by MX'p (M is a metal atom, X 'is a halogen atom, p is an integer of 2 or more), for example, boron trichloride (BCl ₃ ), aluminum chloride (Al) Cl ₃ ), tin tetrachloride (Sn Cl ₄ ), titanium tetrachloride (Ti Cl ₄ ), vanadium pentachloride (VCl ₅ ),
Ferric chloride (Fe Cl _5), boron fluoride (BF ₃₎ or the like and chloro diethylaluminum (Et ₂ Al Cl), and organic aluminum compounds such as dichloroethyl aluminum (Et Al Cl ₂₎ are mentioned, these It is not limited. Of these Lewis acids, titanium tetrachloride (TiCl ₄ ) is particularly preferred.

The polymerization temperature is specifically from -100 ° C to -3 ° C.
0 ° C. is mentioned as a preferable range. If the temperature is lower than -100 ° C, the polymerization activity tends to decrease. If the temperature exceeds -30 ° C, the chain transfer reaction is intense, and the molecular weight tends to decrease significantly. Further, the polymerization reaction of the copolymer of the present invention can be carried out under generated pressure, but it is usually desirable to operate at a pressure sufficient to keep the monomer substantially in a liquid phase. That is, the pressure depends on the individual substances to be polymerized,
Depending on the diluent used and the polymerization temperature, higher pressures can be used if desired, and such pressures can be obtained by any suitable method, such as by pressurizing the reactor with a gas inert with respect to the polymerization reaction.

In general, it is preferred to remove water, oxygen, carbon dioxide and other catalyst poisons from all materials involved in the polymerization process, such as initiator components, solvents, monomers, and the like.

In the present invention, the copolymer (b) having a molecular weight of 2,000 to 50,000 is used. Molecular weight 20
If it is less than 00, the breaking strength of the rubber composition decreases, and
If it exceeds 0, the hysteresis loss of the rubber composition will not be sufficiently large, and the compatibility with the diene rubber will further decrease.

The combined styrene content of the copolymer (b) used in the present invention must be from 20% by weight to 70% by weight, preferably from 30% by weight to 70% by weight, more preferably from 40% by weight. % To 70% by weight. If the bound styrene content is less than 20% by weight, the copolymer tends to bleed because the compatibility with the rubber component is reduced, and if it is more than 70% by weight, the elasticity of the rubber composition is increased, so that the tire grip property is increased. Decrease.

It is necessary that the bound styrene content of the copolymer (b) is larger than the bound styrene content of the copolymer rubber (a) by 10% by weight or more from the viewpoint of compatibility.

In the present invention, the copolymer (b) must be contained in an amount of 10 to 200 parts by weight based on 100 parts by weight of the rubber component. If the amount is less than 10 parts by weight, the hysteresis loss of the rubber composition cannot be sufficiently increased, and if the amount exceeds 200 parts by weight, the breaking strength of the rubber composition decreases.

Further, in the rubber composition of the present invention,
Preliminarily mixing at least a part of the copolymer rubber (a) and at least a part of the copolymer (b) for the purpose of improving the dispersion of the filler and securing high breaking characteristics and wear characteristics. Can be. In this case, the mixing amount of the copolymer (b) is preferably 20 parts by weight or more with respect to 100 parts by weight of the copolymer rubber (a), because the effect is higher and more preferable.

In the present invention, a commonly used aromatic softener can be used in combination, but also in this case, it is preferable that the total amount of the softener does not exceed 200 parts by weight. In order to sufficiently obtain the effects of the present invention, it is preferable to use the copolymer of the present invention in an amount of 15% by weight or more based on the total amount of the softener.

The rubber composition of the present invention may be appropriately compounded with other fillers, vulcanizing agents, vulcanization accelerators, antioxidants and other chemicals usually used in the rubber industry according to the purpose.

[0023]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention.

In the examples, parts and% mean parts by weight and% by weight, respectively, unless otherwise specified. Various measurements were made according to the following methods.

(1) Physical Properties of Polymer The weight average molecular weight (Mw) of the polymer was measured by gel permeation chromatography [GPC;
8020, column: Tosoh GMH-XL (two in series)], using a differential refractive index (RI) in terms of polystyrene using monodisperse polystyrene as a standard. The bound styrene content and vinyl bond content in the polymer were calculated from the integral ratio of the ¹ H-NMR spectrum. The compatibility was evaluated by separately adding only a polymer to the rubber component of the rubber composition of each example, and observing the state of the surface by an electron microscope after 24 hours. The better the compatibility, the higher the bleed resistance. The evaluation was ◎, ○, Δ, ×.

(2) Physical Properties of Rubber Composition The loss characteristics of the rubber composition were measured using a mechanical spectrometer manufactured by Rheometrics Inc. at a shear shear of 5%, at a temperature of 60 ° C., at a frequency of 15 Hz, and tan δ. The exponent was expressed. The larger the index, the greater the hysteresis loss and the better the high loss property. The breaking characteristics were measured by measuring the breaking strength in accordance with JIS K6301-1995, and expressed as an index with the control as 100. The larger the index, the better the fracture characteristics.

(3) Tire Performance Four test tires were mounted on a 3000CC passenger car, and the grip performance was evaluated based on the best lap time when the test course completed 10 laps. In each composition, the difference (best time: T ₁ ) between the best lap time of the control tire and the best lap when the aroma oil of the composition was increased by 10 parts by weight (shortening time: T ₁ ) was 100, and the control in the test tire of each composition was taken. The difference between the best lap and the tire (shortening time: T ₂ ) was measured three times, and the average value was represented by an index (T ₂ / T ₁ ). The larger the index, the better the grip.

Regarding the physical properties of the rubber composition and the performance of the tire, Comparative Example 1 was used as a control for Examples 1 to 13, Comparative Example 2 was used for Example 14, and Comparative Example 3 was used for Examples 15 and 16, respectively. .

(Production of Polymer) An experiment was carried out using raw materials which were dried and purified, unless otherwise specified.

A 200 ml toluene, 12.0 g isobutylene monomer and 15.4 g styrene monomer were charged into a 300 ml eggplant-shaped flask which had been dried and purged with nitrogen, and titanium tetrachloride (TiCl ₄ ) was used as an initiator. 0.75
After adding mmol, polymerization was carried out at −78 ° C. for 2.5 hours. The polymerization system was uniform and transparent without any precipitation from the start to the end of the polymerization. The polymerization conversion was almost 100%. Add methyl alcohol to the polymerization solution and dry,
A rubbery copolymer A was obtained. The amount of bound styrene and the weight average molecular weight of this copolymer were measured. Table 1 shows the results.

[0031]

[Table 1]

E was obtained from polymer B by substituting the amount of this initiator TiCl _{4 and} the amounts of isobutylene and styrene added as monomers. For these copolymers, the amount of bound styrene and the weight average molecular weight were measured.
Table 1 shows the results.

Each of the rubber components in Tables 3-1 to 3-4 was polymerized by a solution polymerization method of a lithium initiator,
Obtained by coupling with silicon tetrachloride. * 1 indicates that the bound styrene content is 25% by weight and the vinyl bound content is 35%.
%, A styrene-butadiene copolymer rubber having a weight average molecular weight of 1.3 million (rubber component 1), * 3 indicates a bound styrene content of 5% by weight, a vinyl bond content of 30%, and a weight average molecular weight of 1
300,000 styrene-butadiene copolymer rubber (rubber component 3) * 4: vinyl bond content 15%, weight average molecular weight 1
200,000 butadiene rubber (rubber component 4).

Comparative Examples 1 and 2 and Examples 1 to 12 Using the copolymers A to E described above, a rubber composition was prepared according to the formulations shown in Tables 3-1 and 3-2, using the basic formulations shown in Table 2. Then, the loss characteristics and the breaking characteristics were evaluated. further,
Each rubber composition is used for a tread contact part, and the size is 255.
A / 40R17 tire was prepared and the grip performance of the tire was evaluated. The results are shown in Tables 3-1 and 3-2.

[0035]

[Table 2] * 1: N234 (manufacturer: Tokai Carbon Co., Ltd., trade name: SEIST 7HM) * 2: N-phenyl-N'-isopropyl-p-phenylenediamine * 3: 2,2'-dithiobisbenzothiazole * 4: 1 , 3-diphenylguanidine

[0036]

[Table 3-1]

[0037]

[Table 3-2] * 2: In Example 7, a styrene-butadiene copolymer rubber (rubber component 2) having a bound styrene content of 35% by weight, a vinyl bond content of 40%, and a weight average molecular weight of 1.4 million was used as the copolymer (a). ing.

In Comparative Examples 1 and 2 and Examples 1 to 7, 100% of the copolymer (a) was used as a rubber component. From Comparative Examples 1 and 2, and Examples 1 to 7, the type of copolymer (b)
It can be seen that changing the amount and the type of the copolymer rubber (a) is also effective. Further, from Examples 8 to 12, it can be seen that the effect of the present invention can be obtained even if a part of the rubber is replaced by another rubber.

Comparative Examples 3 and 4 and Examples 13 to 15 Similar tests were conducted by changing the amount and method of the softener. Comparative Example 3 and Example 13 are examples in which the blending amount is small, and Comparative Example 4 and Examples 14 and 15 are examples in which a softening agent is oil-extended to a polymer in advance. The polymer (b) is oil-extended on the copolymer rubber (a). Table 4 shows the results.

[0040]

[Table 4]

Comparative Examples 3 and 4, and Examples 13 to 15
Thus, it can be seen that the effects of the present invention can be obtained even if the amount of the softener and the method of blending are changed.

[0042]

According to the present invention, it is possible to provide a rubber composition having excellent hysteresis loss while maintaining the breaking characteristics. Further, by using the rubber composition for a tread, it is possible to provide a tire grip. Since the performance can be greatly improved, it is particularly effective for so-called high performance passenger car tires and competition tires that require a high level of steering stability.

Claims (4)

[Claims] 1. A styrene-butadiene copolymer rubber (a) having _a bound styrene content (St _(a) (% by weight)) of 10% to 50% by weight and a polybutadiene portion having a vinyl bond content of 10% to 70%. ) Containing rubber component 100
The weight average molecular weight in terms of polystyrene is 20 relative to parts by weight.
Styrene having a bound styrene content (St _(b) (% by weight)) of from 20 to 70% by weight.
Isobutylene random copolymer (b) from 10 parts by weight to 2
And the bound styrene content (St _(a) ) of the copolymer _(a ) and the bound styrene content (St _(b) ) of the copolymer _(b ) are represented by the following formula (1): A rubber composition having a relationship satisfying the following. St _(b) > St _(a) +10 (1) 2. The rubber according to claim 1, wherein the copolymer (b) is added in advance in an amount of at least 20 parts by weight based on 100 parts by weight of the copolymer (a). Composition. 3. A pneumatic tire using the rubber composition according to claim 1 for a tread. 4. A competition tire using the rubber composition according to claim 1 for a tread.