JP2002097308A - Rubber composition and pneumatic tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition capable of giving pneumatic tires improved in on-ice/snow brake performance and wet road surface brake performance, and to provide a pneumatic tire where the composition is used as the tread rubber. SOLUTION: This rubber composition comprises (A) 100 pts.wt. of a rubber component comprising (1) 20-55 wt.% of an emulsion-polymerized styrene- butadiene copolymer rubber, (2) 10-40 wt.% of a solution-polymerized styrene- butadiene copolymer rubber and (3) 25-55 wt.% of natural rubber and/or isoprene synthetic rubber and (B) >=60 pts.wt. of a reinforcing filler comprising silica. The other objective pneumatic tire where the composition is used as the tread rubber is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rubber composition and a pneumatic tire using the same. For more information,
The present invention relates to a rubber composition for providing a pneumatic tire having improved braking performance and handling stability on ice and snow (braking performance on ice and snow) and improved braking performance and handling stability on wet road surfaces (braking performance on wet road surfaces). And a pneumatic tire using the rubber composition as a tread rubber and having improved braking performance on ice and snow and braking performance on wet road surfaces.

[0002]

2. Description of the Related Art In recent years, demand for so-called all-season tires, which can be used in the same manner as in summer without replacing tires in winter, has been increasing. This type of tire has the same dry grip, wet grip, steering stability, durability, and fuel economy in winter as in summer, and has sufficient driving and braking performance on ice and snow. Is required.

[0003] In recent years, as tires with improved performance on ice and snow,
Studless tires are used. For the tread of the studless tire, a polymer having a lower glass transition temperature than a normal tire, particularly a flexible rubber material such as a rubber mainly composed of butadiene rubber is used in order to increase a frictional force with an icy and snowy road surface. Further, in a tire having a tread portion having a cap / tread two-layer structure, the cap rubber on the tread surface portion in contact with the ground is a relatively soft rubber even at a low temperature, for example, a large amount of a softener is compounded or foamed rubber is used. For example, techniques such as the use of However, in these cases, although the braking performance on ice and snow is improved to some extent, there is a problem that the braking performance on wet road surfaces on general roads is inevitably reduced.

On the other hand, as a means for increasing the coefficient of friction on a wet road surface, a rubber composition mainly composed of a styrene-butadiene copolymer having a relatively high glass transition temperature compared with the conventional one is used. Techniques are known for increasing tan δ at 0 ° C. as a measure of hysteresis showing a good correlation with the coefficient of friction. However, in this case, regarding the braking performance on ice and snow, the rubber elasticity in a low-temperature region increases and it is not possible to follow the unevenness of the road surface. As a result, the contribution of energy loss (tan δ) between the rubber and the road surface to braking on ice is reduced.
For this reason, conventionally, it has been difficult to obtain both high braking performance on ice and snow and high braking performance on wet road surfaces.

[0005]

SUMMARY OF THE INVENTION The present invention provides a rubber composition which provides a pneumatic tire having improved braking performance on ice and snow and wet braking performance under such circumstances, and a tread rubber comprising the rubber composition. It is an object of the present invention to provide a pneumatic tire having the above-mentioned performance, which is used as a tire.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that emulsion-polymerized styrene-butadiene copolymer rubber, solution-polymerized styrene-butadiene copolymer rubber, natural rubber, It has been found that a rubber composition in which a reinforcing component mainly containing silica is blended in a proportion of not less than a rubber component containing a predetermined proportion of isoprene synthetic rubber can meet the purpose. The present invention
It has been completed based on such knowledge.

That is, the present invention relates to (A) (a) 20 to 55% by weight of an emulsion-polymerized styrene-butadiene copolymer rubber,
(B) Solution-polymerized styrene-butadiene copolymer rubber
A rubber component comprising 40% by weight and (C) 25 to 55% by weight of natural rubber and / or isoprene synthetic rubber;
It is intended to provide a rubber composition characterized by containing (B) at least 60 parts by weight of a reinforcing filler containing silica per 0 parts by weight. The present invention also provides a pneumatic tire using the rubber composition as a tread rubber.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the rubber composition of the present invention,
As the rubber component (A), a mixture comprising (a) an emulsion-polymerized styrene-butadiene copolymer rubber, (b) a solution-polymerized styrene-butadiene copolymer rubber, and (c) a natural rubber and / or a synthetic isoprene rubber. Is used.

[0009] The emulsion-polymerized styrene-butadiene copolymer rubber of the above-mentioned component (a) is obtained by subjecting 1,3-butadiene and styrene to a known emulsion polymerization method, specifically, an emulsifier and a radical polymerization initiator in an aqueous medium. It is obtained by emulsion polymerization using such as. In the present invention, as the emulsion-polymerized styrene-butadiene copolymer rubber of the component (a), those having an amount of bound styrene of 35% by weight or less are preferably used. When the amount of bound styrene is 3
If it exceeds 5% by weight, the braking performance on ice and snow will decrease. The preferred amount of bound styrene is selected in the range of 20 to 25% by weight.

The solution-polymerized styrene-butadiene copolymer rubber of the component (b) is prepared by subjecting butadiene and styrene to a known solution polymerization method, specifically, in an appropriate organic solvent.
It is preferably obtained by solution polymerization (anion polymerization) using an organic lithium compound as a polymerization initiator. Since one end of the styrene-butadiene copolymer obtained by such a method becomes a polymerization active terminal, it can be easily modified by reacting the polymerization active terminal with various modifiers.

In the present invention, it is preferable to use, as the solution-polymerized styrene-butadiene copolymer rubber (b), at least a terminal-modified solution-polymerized styrene-butadiene copolymer rubber. The terminal-modified solution-polymerized styrene-butadiene copolymer rubber can be produced, for example, by the following method.

First, 1,3-butadiene and styrene are subjected to solution polymerization (anion polymerization) using an organic lithium compound as a polymerization initiator to form a styrene-butadiene copolymer having one terminal being a polymerization active terminal. Hydrocarbyl lithium and lithium amide compounds are preferably used as the organolithium compound of the polymerization initiator.When the former hydrocarbyl lithium is used, one end has a hydrogen atom and the other end is a polymerization active end. A certain styrene butadiene copolymer is obtained. Also,
When the latter lithium amide compound is used, a styrene butadiene copolymer having a nitrogen-containing group at one end and a polymerization active end at the other end is obtained.

As the above-mentioned hydrocarbyl lithium, those having a hydrocarbyl group having 2 to 20 carbon atoms are preferable. For example, ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butyl-phenyllithium, 4-phenyl-butyllithium, cyclohexyllithium, cyclopentyllithium, a reaction product of diisopropenylbenzene with butyllithium, and the like. , Among these,
n-Butyl lithium is preferred.

On the other hand, examples of the lithium amide compound include lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide, lithium heptamethylene imide, lithium dodecamethylene imide, lithium dimethyl amide, lithium diethyl amide, lithium dibutyl amide, and lithium dipropyl. Amide, lithium diheptyl mead, lithium dihexylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide, lithium ethylbutylamide, lithium methylbutylamide, lithium Ethyl benzylamide, lithium methylphenethylamide and the like can be mentioned. Among these, lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide,
Cyclic lithium amides such as lithium heptamethyleneimide and lithium dodecamethyleneimide are preferred, and lithium hexamethyleneimide and lithium pyrrolidide are particularly preferred.

The method for producing a styrene-butadiene copolymer by anionic polymerization using the above-mentioned organolithium compound as a polymerization initiator is not particularly limited, and a conventionally known method can be used. Specifically, styrene and 1,3-butadiene are polymerized with the organic lithium compound in an organic solvent inert to the reaction, for example, an aliphatic, alicyclic, or aromatic hydrocarbon compound. If desired, the desired styrene-butadiene copolymer is obtained by anionic polymerization in the presence of a randomizer used, if desired.

The temperature in this polymerization reaction is usually -80
To 150 ° C, preferably -20 to 100 ° C. The polymerization reaction can be carried out under the pressure generated, but it is usually desirable to operate at a pressure sufficient to keep the monomer in a substantially liquid phase. Higher pressures can be used if desired, and such pressures can be obtained in any suitable manner, such as by pressurizing the reactor with a gas that is inert with respect to the polymerization reaction. The thus obtained styrene-butadiene copolymer having a hydrogen atom or a nitrogen-containing group at one end, and the other end being a polymerization active end,
By reacting various modifiers, a desired terminal-modified solution-polymerized styrene-butadiene copolymer rubber can be obtained.

Examples of the modifying agent include methyltriethoxysilane, tetraethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 1- {3- (triethoxysilyl) propyl ｝ -4,5-dihydroimidazole, N
-(1,3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine, alkoxysilane compounds such as dimethylaminopropyltriethoxysilane, tin tetrachloride, tributyltin, dioctyltin dichloride, dibutyltin dichloride, chloride Tin compounds such as triphenyltin, further, isocyanate compounds such as diisocyanatodiphenylmethane, aminobenzophenone compounds such as 4- (dimethylamino) benzophenone, 4-dimethylaminobenzylideneaniline, dimethylimidazolidinone, N-methylpyrrolidone And other nitrogen-containing compounds.

Further, by copolymerizing using a lithium amide initiator obtained from a secondary amino compound such as diethylamine or an imine compound such as hexamethyleneimine and an organic lithium compound, or
A desired modified polymer can also be obtained by further adding the above modifier to a solution of the copolymer having a lithium active terminal obtained by the copolymerization.

By using the solution-polymerized styrene-butadiene copolymer rubber end-modified in this way, the braking performance on ice and snow and the braking performance on wet roads can be satisfied.
A higher level of low rolling resistance can be obtained.
Such an effect is remarkably exhibited particularly by using a solution-polymerized styrene-butadiene copolymer rubber containing terminal-modified solution-polymerized styrene-butadiene copolymer rubber in a proportion of 60% by weight or more as the component (b). .

In component (A) of the rubber composition of the present invention, natural rubber and / or synthetic isoprene rubber is used as component (c). The synthetic isoprene rubber is obtained by polymerization of isoprene monomer. In particular, the type having a cis 1,4-bond of about 98% has a molecular structure very similar to that of natural rubber, and thus has basic characteristics close to that of natural rubber.

In the rubber composition of the present invention, the content ratio of each rubber component in the component (A) is as follows.
To 55% by weight, the component (b) is 10 to 40% by weight, and the component (C) is 25 to 55% by weight. If the above component (a) is less than 20% by weight, sufficient wet road braking performance will not be exhibited, while if it exceeds 55% by weight, sufficient on-snow braking performance will not be exhibited. On the other hand, if the component (b) is less than 10% by weight, sufficient wet road braking performance will not be exhibited, and sufficient low rolling resistance will not be obtained. On the other hand, if it exceeds 40% by weight, braking performance on ice and snow will be insufficient. . Furthermore, the component (c) is 2
If it is less than 5% by weight, braking performance on ice and snow is insufficient, and abrasion resistance and destruction resistance are reduced. On the other hand, if it exceeds 55% by weight, braking performance on wet road surfaces is significantly reduced. From the viewpoint of balance such as braking performance on ice and snow, wet braking performance on the road, low rolling resistance, abrasion resistance, and destruction resistance, the preferable content ratio of each rubber component is as follows. B)
The component is 15 to 30% by weight and the component (C) is 30 to 55% by weight.

In the rubber composition of the present invention, a reinforcing filler containing silica as the component (B) is used. The silica has a nitrogen adsorption specific surface area of 130 to 280 m.
Those having a range of ² / g are preferred from the viewpoint of workability and wear resistance. The content of the silica in the reinforcing filler is preferably 70% by weight or more. When the content of silica is less than 70% by weight, the braking performance on ice and snow is not sufficiently exhibited. A more preferred content of silica is 80% by weight or more.

The silica is not particularly limited, and may be arbitrarily selected from those conventionally used as reinforcing fillers for rubber. For example, wet silica (hydrous silicic acid), dry silica (silicic anhydride), calcium silicate, aluminum silicate and the like can be mentioned. Among them, wet silica is preferred from the viewpoint of performance. This (B)
The reinforcing filler of the component can include carbon black together with the silica. This carbon black has a nitrogen adsorption specific surface area of 50 in terms of reinforcing property and workability.
Those having a range of 150 m ² / g are preferred. The carbon black is not particularly limited, and any one can be selected from those conventionally used as a reinforcing filler for rubber. Examples of the carbon black include FEF, SRF, HAF, ISA
Among them, HAF, ISAF, and SAF, which are particularly excellent in wear resistance, are preferable.

The content of the carbon black in the reinforcing filler is preferably 30% by weight or less, more preferably 20% by weight or less. In the rubber composition of the present invention, the component (B) is blended in an amount of 60 parts by weight or more based on 100 parts by weight of the rubber component (A). If the amount is less than 60 parts by weight, the wet road surface braking performance cannot be sufficiently exhibited. On the other hand, if the amount is too large, the elastic modulus may increase too much, and the braking performance on ice and snow may decrease. For these reasons, the preferred amount of the component (B) is selected in the range of 70 to 100 parts by weight.

In the rubber composition of the present invention, if necessary, a low-temperature softener can be contained as the component (C). The low-temperature softener preferably has a softening point of 0 ° C. or lower, preferably -10 ° C. or lower. As such a low-temperature softener, those conventionally used as rubber softeners, for example, process oils such as paraffin-based process oils, naphthene-based process oils, aromatic process oils, and polymerized high-boiling strong aromatics Mineral softeners such as oil, liquid paraffin, white oil, etc., and vegetable softeners such as castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, coconut oil, peanut oil, tall oil, etc. Can be used.

These low-temperature softeners are usually added in an amount of 1 to 10 parts by weight based on 100 parts by weight of the rubber component (A). In the rubber composition of the present invention,
70% by weight of silica as a reinforcing filler of the component (B)
Preferably, the reinforcing filler contains a large amount of silica, and when the content of carbon black is small, the silica is poor in conductivity. If the running tire touches a well-conductive material such as a manhole cover, radio noise may be generated, or gasoline may be ignited at a gas station or the like.

In the rubber composition of the present invention, in order to cope with such a problem, an antistatic compound can be contained as a component (D) if necessary. As the antistatic compound, for example, JP-A-10-3305
Examples thereof include polyoxyalkylene glycol compounds as described in JP-A-39, and anionic antistatic agents as described in JP-A-10-273561. Among them, polyethylene glycols are particularly preferable from the viewpoint of performance. These antistatic compounds are preferably used in an amount of 3 to 10 parts by weight, more preferably 4 to 7 parts by weight, based on 100 parts by weight of the rubber component (A).

The rubber composition of the present invention may optionally contain a silane coupling agent. The silane coupling agent is not particularly limited, and may be a known silane coupling agent which is conventionally used in a rubber composition, for example, bis (3-triethoxysilylpropyl) polysulfide,
γ-mercaptopropyltriethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, and the like can be used. .

The compounding amount of the silane coupling agent optionally used is usually selected in the range of 1 to 20% by weight based on the silica in the reinforcing filler of the above-mentioned component (B). If the amount is less than 1% by weight, the effect as a coupling agent is not sufficiently exhibited, and if it exceeds 20% by weight, gelation of a rubber component may be caused. From the point of effect as a coupling agent and prevention of gelation,
The preferred compounding amount of the silane coupling agent is 5 to 1
It is in the range of 5% by weight.

The rubber composition of the present invention may contain various chemicals usually used in the rubber industry, such as a vulcanizing agent, a vulcanization accelerator, an antioxidant, as long as the object of the present invention is not impaired. An anti-scorch agent, zinc white, stearic acid and the like can be contained. The rubber composition of the present invention is obtained by kneading using a kneading machine such as a roll and an internal mixer, and after molding, vulcanization is performed, and the tire tread, undertread, carcass, sidewall, and bead are formed. Starting with tire applications such as parts, anti-vibration rubber,
Although it can be used for belts, hoses and other industrial products, it is particularly suitably used as a rubber for tire treads.

The pneumatic tire of the present invention is manufactured by a usual method using the rubber composition of the present invention. That is, if necessary, the rubber composition of the present invention containing various chemicals as described above is extruded into a member for tread in an unvulcanized stage, and is pasted and molded by a normal method on a tire molding machine. Then, a green tire is formed. The green tire is heated and pressed in a vulcanizer to obtain a tire. The pneumatic tire of the present invention obtained in this way has excellent braking performance and handling stability on ice and snow, and excellent braking performance and handling stability on wet road surfaces.

[0032]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The performance of the test tire was measured according to the following method. (1) Wet road braking performance (wet braking test) A four-wheel test tire was mounted on a domestic FF car at 1800 CC, and the braking distance on a wet road surface was measured at an initial speed of 80 km / h on a test course. The reciprocal of the distance is 1 in Comparative Example 1.
It was expressed as an index value as 00. The larger the value, the better the braking performance.

(2) On-Snow Braking Performance (Snow-Breaking Performance Test) A four-wheel test tire was mounted on a 1800 CC, domestic FF vehicle, and the braking distance on a snow-covered road at an initial speed of 50 km / h on a test course. Measure and calculate the reciprocal of the distance by 1 in Comparative Example 1.
It was expressed as an index value as 00. The larger the value, the better the braking performance.

Synthesis Example 1 (Modified solution polymerized styrene butadiene
Synthesis of copolymer rubber) In a 5-liter autoclave purged with nitrogen,
2000 g of cyclohexane, styrene as monomer
100 g, butadiene 400 g, tet as a polar compound
20 g of lahydrofuran was charged. While stirring the contents
Then, 6 mmol of n-butyllithium was added as a polymerization initiator.
And adiabatic polymerization was performed from 20 ° C. After polymerization,
2 mmol of tin tetrachloride was added as an end modifier and reacted.
Was. 2.5 g of di-t-butyl cresol was added, and a conventional method was used.
Solvent drying was performed. The resulting modified copolymer rubber is separated
As a result, the amount of bound styrene was 20% by weight and the amount of vinyl was 60%.
% By weight, and the glass transition temperature (Tg) was -37 ° C. Synthesis Example 2 (Antistatic compound: polyethylene glycol
Synthesis of polyethylene) in a 500 ml four-necked flask
Recall # 400 (molecular weight 400) with 200 g (0.5
Mol), 173 g (1.2 mol) of caprylic acid and a catalyst
Weigh 0.19 g of dibutyltin oxide as
Stir at 225 ° C for 5 hours while stirring under blowing.
A tellurization reaction was performed. When the hydroxyl value drops to 1.0 or less
After confirming that, to remove excess caprylic acid, at 200 ℃,
Deoxidation was performed under the condition of 0.27 kPa to obtain a sample. this
As a result of analyzing the sample, CH_Three(CH _Two)₆COO (CH_Two
CH_TwoO)₉CO (CH_Two)₆CH_ThreeThat of
It was confirmed.

Examples 1 to 3 and Comparative Examples 1 to 6 Carbon black, silica, aroma oil, spindle oil, polyethylene glycol and a silane coupling agent were added to 100 parts by weight of a rubber component having the composition shown in Table 1, respectively. In addition to the amounts shown in Table 1, 2 parts by weight of stearic acid, 1 part by weight of an antioxidant IPPD (trade name: Nocrack 810NA, manufactured by Ouchi Shinko Chemical Co., Ltd.)
0.2 parts by weight of wax, 2.5 parts by weight of zinc white, 0.7 parts by weight of vulcanization accelerator DM (dibenzothiazyl disulfide), 0.7 parts by weight of vulcanization accelerator DPG (diphenylguanidine) 0.7
Parts by weight, a vulcanization accelerator NS (N-tert-butyl-2-
(Benzothiazylsulfenamide) and 1.5 parts by weight of sulfur and 2 parts by weight of sulfur were blended to prepare a rubber composition.

Using the rubber composition thus prepared as a cap rubber for a tread, a tire having a size of 185 /
A 70R14 radial tire for passenger cars was prototyped by a conventional method. The structure of this prototype tire includes a layer of carcass ply that straddles a pair of bead cores in a toroidal shape, two layers of steel cord belt layers disposed outside the tire in the radial direction, and positions outside the two layers of belt layers. Of nylon cords arranged in parallel at an angle of 0 ° to the circumferential direction
The tread had a cap / base two-layer structure. The braking performance on wet road surface and the braking performance on ice and snow were measured for each tire.
The results are shown in Table 1.

[0037]

[Table 1]

[0038]

[Table 2]

(Note) 1) E-SBR: "17" manufactured by JSR Co., Ltd.
12 ", emulsion-polymerized styrene-butadiene copolymer rubber (oil extended), bound styrene content 23.5% by weight, 37.5% by weight
Oil extension 2) Modified S-SBR: modified solution-polymerized styrene-butadiene copolymer rubber (synthesized according to Synthesis Example 1 above)

3) Carbon black: “Seast 7H” manufactured by Tokai Carbon Co., Ltd. 4) Silica: “Nip Seal A” manufactured by Nippon Silica Industry Co., Ltd.
Q) 5) PEG: polyethylene glycol (synthesized according to Synthesis Example 2 above) 6) Silane coupling agent: bis (3-triethoxysilylpropyl) tetrasulfide As can be seen from Table 1, the rubber composition of the present invention All of the tires of Examples 1 to 3 using the tire as the tread rubber are excellent in both the braking performance on ice and snow and the braking performance on wet road surfaces.

[0041]

By using the rubber composition of the present invention as a tread rubber, braking performance and steering stability on ice and snow (braking performance on ice and snow) and braking performance and steering stability on wet road surfaces (wetness) A pneumatic tire with improved road braking performance can be obtained.

Claims (9)

[Claims] (A) (A) 20 to 55% by weight of an emulsion-polymerized styrene-butadiene copolymer rubber, (B) 10 to 40% by weight of a solution-polymerized styrene-butadiene copolymer rubber, and (C) natural rubber and / or Isoprene synthetic rubber 25-5
A rubber composition comprising 5% by weight of a rubber component and (B) at least 60 parts by weight of a reinforcing filler containing silica per 100 parts by weight of the rubber component. 2. The rubber composition according to claim 1, wherein the amount of bound styrene in the emulsion-polymerized styrene-butadiene copolymer rubber of the component (a) is 35% by weight or less. 3. The rubber composition according to claim 1, wherein the solution-polymerized styrene-butadiene copolymer rubber (A) (b) contains at least a terminal-modified solution-polymerized styrene-butadiene copolymer rubber. 4. The rubber composition according to claim 3, wherein the solution-polymerized styrene-butadiene copolymer rubber (A) (b) contains at least 60% by weight of a terminal-modified solution-polymerized styrene-butadiene copolymer rubber. 5. The rubber composition according to claim 1, wherein (B) the reinforcing filler contains 70% by weight or more of silica. 6. The rubber composition according to claim 1, further comprising (C) 1 to 10 parts by weight of a low-temperature softener per 100 parts by weight of the component (A). 7. The rubber composition according to claim 1, further comprising (D) an antistatic compound. 8. The rubber composition according to claim 7, wherein the antistatic compound as the component (D) is a polyethylene glycol. 9. A pneumatic tire using the rubber composition according to claim 1 as a tread rubber.