JP2001011240A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire excellent in braking properties on ice and rolling resistance without detriment to running performances on an oven road (dry road and wet road) from a tread rubber composition with improved workability in kneading and extrusion processes in a factory. SOLUTION: This pneumatic tire has a tread part comprising a multi-layered structure, at least one layer of which is composed of a rubber composition comprising 100 pts.wt. of a rubber component, containing at least 10 wt.% of a conjugated diene-based polymer bearing in the molecule a functional group derived from an alkoxysilane, having incorporated therewith at least 10 pts.wt. of silica and short fibers having an average length of not more than 10 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire, which is excellent in braking performance on ice and rolling resistance without impairing running performance on a general road (dry road, wet road), and is refined. The present invention relates to a pneumatic tire having improved factory workability of a tread rubber composition during extrusion.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made for tires having improved performance on ice, for example, by adding a large amount of a softening agent or a plasticizer to a tread in contact with the ground to reduce the hardness at low temperatures. Lower (Japanese Patent Laid-Open No. 55-135149)
JP-A-8-15080) or using foamed rubber.
No. 7, JP-A-9-216970), or a method of improving the performance on ice by using rubber mixed with short fibers (JP-A-9-216970). However, in these conventional tires, although the performance on ice is improved,
There is a problem that wear resistance on a general road (dry road, wet road) and particularly wet performance (wet road braking performance) are deteriorated. On the other hand, it is known that silica is blended as a filler in order to improve wet performance (Japanese Patent Application Laid-Open No.
No. 149950). However, the affinity between silica and the diene-based polymer is low, and it is difficult to obtain a uniform rubber composition by kneading. To compensate for this, a large amount of an expensive silane coupling agent is used in many cases. And since this silane coupling agent is easily hydrolyzed in the atmosphere,
Care must be taken in handling, and in particular, during the rubber scouring and extrusion steps, there has been a problem that rubber gelation or blister (porous) occurs, resulting in a significant decrease in workability.

[0003]

SUMMARY OF THE INVENTION The present invention provides a tread rubber composition having excellent braking performance on ice and rolling resistance without impairing the running performance on general roads (dry roads and wet roads). An object of the present invention is to provide a pneumatic tire with improved workability of a product, that is, workability in a factory.

[0004]

Means for Solving the Problems The present inventors have found that in a rubber composition for a tread of a pneumatic tire, gelation of a silica-containing rubber composition during rubber scouring and generation of a porous body at the time of extrusion are carried out by a silane coupling agent. And the reaction with silica, and furthermore, by using a specific modified diene rubber and blending short fibers, it is possible to solve the above-mentioned problems and exhibit excellent tire performance. I found it.

That is, the present invention relates to a pneumatic tire having a tread portion having a multilayer structure, wherein a rubber composition forming at least one layer of the multilayer structure has a functional group derived from alkoxysilane in a molecule. A pneumatic tire comprising 100 parts by weight of a rubber component containing 10% by weight or more of a conjugated diene-based polymer, 10 parts by weight or more of silica, and short fibers having an average length of 10 mm or less. Is provided.

Here, the conjugated diene polymer is at least one selected from a homopolymer of a conjugated diene compound, a copolymer of a conjugated diene compound, and a copolymer of a conjugated diene compound and an aromatic vinyl compound. It is preferable that the following general formula (I)

[0007]

Embedded image

[Wherein P represents a polymer chain, and R ¹ and R
² represents a group independently selected from aliphatic, alicyclic and aromatic hydrocarbon groups having 1 to 20 carbon atoms, and when there are a plurality of groups, they may be the same or different. n
Is an integer of 1 to 3, m is an integer of 1 to 3, and n + m
Represents an integer of 2 to 4. ] Are preferable. The rubber component preferably contains a styrene-butadiene copolymer in an amount of 20% by weight or more. Further, it is preferable to add a silane coupling agent in an amount of 0 to 15% by weight based on the amount of silica. The short fibers preferably have an average diameter of 0.01 to 0.1 mm, and the type thereof is preferably polyethylene, polypropylene or polyester, or a water-soluble fiber. When the short fibers are water-soluble fibers, the water-soluble temperature is preferably from 0 ° C. to 20 ° C., and the type thereof is preferably polyvinyl alcohol. Further, the blending amount of the short fibers is preferably 1 to 20 parts by weight based on 100 parts by weight of the rubber component.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A specific conjugated diene polymer used as an essential rubber component of the rubber composition forming at least one layer of the tread portion of the pneumatic tire of the present invention is derived from alkoxysilane in its molecule. It is preferably a compound having a functional group represented by the above general formula (I). Where R ¹ and R
² is, for example, an aliphatic hydrocarbon group having 1 to 20 carbon atoms (specifically, a methyl group, an ethyl group, a propyl group, a butyl group,
An alkyl group such as an amyl group), an alicyclic hydrocarbon group having 3 to 20 carbon atoms (specifically, a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group), and an aromatic hydrocarbon group having 6 to 20 carbon atoms (specifically, Phenyl, tolyl, xylyl, etc.).

The conjugated diene polymer used in the present invention has the following general formula (II):

[0011]

Embedded image

[Wherein P represents a polymer chain;¹And R
^TwoIs the same as described above, and R^ThreeAnd R ^FourAlso these R¹Passing
And R^TwoIs the same as Also, R^ThreeAnd R^FourAre connected to each other
May form a cyclic structure containing a nitrogen atom.
In addition, this ring structure may further include another hetero atom (an oxygen atom or
Is a nitrogen atom) as a ring member
Is also good. a, b and c each represent an integer of 1 to 3
And a + b + c represents an integer of 2 to 4. ]
At least one end of the chain contains nitrogen.
May be provided at the same time, and the rolling resistance
Has the advantage of being reduced. Thus, the nitrogen atom
At least one conjugated diene polymer powder containing a functional group
By having it at the edge, it is possible to improve low heat generation
it can.

As the polymer chain of the conjugated diene polymer used in the present invention, a polymer chain of a conjugated diene such as 1,3-butadiene or isoprene can be mentioned.
Butadiene polymer chains are preferred. When the polymer chain is a conjugated diene / vinyl aromatic hydrocarbon copolymer comprising a copolymer of the conjugated diene compound and an aromatic vinyl compound (vinyl aromatic hydrocarbon), the vinyl aromatic hydrocarbon is Styrene, vinyltoluene, p-methylstyrene, α-methylstyrene and the like, and styrene is preferred. In this case, the content of the vinyl aromatic hydrocarbon in the copolymer is preferably from 5 to 50% by weight. When the polymer chain is a copolymer, it can have a random structure, a block structure, or a structure having short intermediate blocks. The microstructure of the conjugated diene portion of the polymer chain can be appropriately adjusted by changing the polymerization conditions. For example, the vinyl structure is obtained by adding an ether such as tetrahydrofuran or a tertiary amine such as triethylamine to the polymerization system. The amount of binding can be changed. Further, when there are a plurality of polymer chains, they may be made of different polymers.

The conjugated diene polymer used in the present invention can be obtained by a conventional method. For example, the polymerization of a conjugated diene or a monomer of a conjugated diene monomer and an aromatic vinyl hydrocarbon is initiated using a lithium polymerization initiator. It is produced by adding an alkoxysilane compound to a polymer solution having a lithium active terminal.

As the polymerization initiator used for producing the above-mentioned conjugated diene-based polymer, a lithium compound may be mentioned (hereinafter sometimes referred to as lithium-based polymerization initiator). Here, as the lithium compound, n-butyllithium, sec-butyllithium, ethyllithium, propyllithium, t-butyllithium, alkyllithium such as hexyllithium, alkylenedilithium such as 1,4-dilithiobutane, phenyllithium, Organolithium compounds such as stilbene dilithium, a reaction product of butyllithium and divinylbenzene; organometallic lithium compounds such as tributyltin lithium; lithium hexamethyleneimide, lithium diethylamide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, Examples thereof include lithium amides such as lithium dodecamethylene imide. Among them, butyl lithiums are preferred as the organic lithium compound, and lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide, lithium piperidide, and lithium amide are considered as the lithium amide in view of the interaction effect on carbon black and the polymerization initiating ability. Cyclic lithium amides such as heptamethylene imide and lithium dodecamethylene imide are preferable, and among them, lithium hexamethylene imide and lithium pyrrolidide, which are particularly effective, are most preferable. These lithium-based polymerization initiators may be used alone or in combination of two or more. When using lithium amide as the polymerization initiator, the polymerization initiator may be adjusted in advance before polymerization,
Alternatively, the lithium compound and the amine may be separately charged into the polymerization system, and the initiator may be adjusted in the polymerization system.

Further, as a polymerization initiator, an organic alkali metal other than a lithium compound and an organic alkaline earth metal are also effective. For example, as the organic alkali metal, n-butyl sodium is used, and as the organic alkaline earth metal, Is n-butylmagnesium, n-hexylmagnesium, ethoxycalcium, calcium stearate, t-butoxystrontium, ethoxybarium,
Isopropoxy barium, t-butoxy barium, phenoxy barium, ethyl mercapto barium, diethyl amino barium, barium stearate, ketyl barium, 3,7-dimethyl-3-octoxy barium and the like, and these may be used alone. And two or more kinds may be used in combination. Further, an organic alkali metal polymerization initiator and an organic alkaline earth metal polymerization initiator other than the lithium compound can be used in combination with the above-mentioned lithium-based polymerization initiator. The amount of the polymerization initiator used is usually 10
It is preferable to use in the range of 0.2 to 20 mmol per 0 g.

The rubber composition used in the present invention contains, as a filler, 10 parts by weight or more of silica per 100 parts by weight of the rubber component. The silica used here may be either wet silica (hydrous silicic acid) or dry silica (silicic anhydride). If the amount of silica is less than 10 parts by weight, it is difficult to obtain sufficient wet road braking performance. The preferred amount is 30 to
100 parts by weight. Further, the nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably from 130 to 280 m ² / g from the viewpoint of ensuring workability and abrasion resistance.

In the present invention, a silane coupling agent may be used in combination. The amount of the silane coupling agent is preferably from 0% by weight to 15% by weight with respect to the silica blending amount. However, since the rubber component containing the conjugated diene polymer is used, the silane coupling agent is used. It is not necessary or only a small amount is required. More preferably, it is 5 to 12% by weight. By reducing the amount of the silane coupling agent, in the refining and extrusion steps, gelation of rubber and generation of porous material are suppressed, and the workability in the factory is remarkably improved.

In the present invention, carbon black can be further blended as a filler. By blending carbon black, the effect of improving various physical properties of the rubber composition is increased. Carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 5 for reinforcement and workability.
0~150m is preferably ² / g.

In the present invention, it is essential that the rubber component contains at least 10% by weight of the conjugated diene-based polymer, and the balance is composed of other rubber components. Here, the other rubber component is not particularly limited, but is preferably a diene rubber, and specifically, natural rubber (NR), styrene-
Butadiene rubber (SBR), butadiene rubber (BR),
Examples include isoprene rubber (IR), butyl rubber (IIR), and ethylene-propylene rubber (EPDM), and these can be used alone or as a mixture of two or more. Further, it is preferable that the total rubber component contains styrene-butadiene copolymer rubber in an amount of 20% by weight or more,
In particular, the content is preferably 20 to 90% by weight.

Next, the short fibers used in the present invention have an average length of 10 mm or less. If it exceeds 10 mm, the workability at the time of compounding the rubber will deteriorate. The blending amount of the short fiber is 1-2 for 100 parts by weight of the rubber component.
It is preferably 0 parts by weight.

The type of the short fibers is not particularly limited, and may include known fibers such as polyvinyl alcohol (PVA), polyester, polystyrene, nylon, aramid, and polyethylene. Or PVA
And the like. When using a water-soluble fiber, especially in order to express a high friction coefficient in all road surface conditions, the water-soluble temperature has high water solubility even at a relatively low temperature of 0 ° C to 20 ° C, and when kneading rubber. For example, polyvinyl alcohol (PVA) fibers having the required mechanical properties and having a low degree of saponification are preferred. Here, the aqueous solution temperature refers to the temperature of the water at the time when a fiber with a load of 2 mg / denier suspended in water, heated from about 0 ° C. at a rate of 2 ° C. per minute, and dissolved.

The diameter or the maximum diameter of the short fibers is not particularly limited. However, when the same amount is blended, the smaller the fibers, the greater the number of grooves on the tire surface and the better the groove dispersibility. It is preferable from the viewpoint of performance improvement. However, if the fiber is too thin in the production of fibers, thread breakage frequently occurs and the rubber scouring workability also deteriorates. As a fiber diameter at the time of compounding, 0.01 to 0.1 m
m is preferable. Here, the diameter or the maximum diameter of the fiber is a value determined as an average value obtained by randomly selecting 20 places of the fiber and measuring the diameter with an optical microscope.

The rubber composition constituting the tread portion of the pneumatic tire of the present invention is not particularly limited in the components other than those described above, and includes process oils commonly used in the rubber industry.
Zinc oxide, stearic acid, a vulcanizing agent, a vulcanization accelerator, an antioxidant, an ozone deterioration inhibitor and the like can be appropriately compounded. When the tread has a cap / base structure in the pneumatic tire of the present invention, the tread may be used as a rubber composition for the cap or the base rubber, or both.

[0025]

EXAMPLES The present invention will be described below in more detail with reference to examples and comparative examples, but the present invention is not limited by these examples. [Various Measurement Methods] Various measurements on the test tire and its tread rubber composition were performed according to the following methods. (1) Wet road braking performance A test tire was mounted on a test course, a four-wheel test tire was mounted on a passenger car, and the braking distance on a wet road was measured at an initial speed of 70 km. As 100
Expressed as an index. The larger the numerical value, the better the braking performance. (2) Road braking performance on ice The test tire is mounted on a passenger car, and a four-wheel test tire is mounted on the passenger car on a test course. The braking distance on the ice road is measured at an initial speed of 20 km, and the reciprocal of the distance Comparative Example 1
Was set to 100 and expressed by an index. The larger the numerical value, the better the braking performance. (3) Factory workability In the process of extruding the tread in the factory, the extrusion speed was measured, and the value of each example was divided by the value in Comparative Example 1 to obtain an index. The larger the index is, the better the factory workability is. (4) Rolling resistance Coasting when rotating at a speed of 0 to 180 km / h using a rotating drum having a steel smooth surface and an outer diameter of 1707.6 mm and a width of 350 mm under a load of 300 kg. The measurement was carried out by a method, and the result was represented by an index with Comparative Example 1 being 100. The larger the index, the better the rolling resistance.

(Preparation of PVA fiber) As a spinning dope,
An average polymerization degree of 75% of polyvinyl alcohol unit and 25 mol% of vinyl acetate unit, and a saponification degree of 7
5% polymer 45% by weight dimethyl sulfoxide (D
(MSO) solution. This spinning stock solution is passed through a nozzle at 2 ° C.
Extruded into an acetone / DMSO mixed solution (weight ratio 85/15), passed through a spinning roll, stretched 4 to 5 times in an acetone / DMSO mixed solution (weight ratio 95/5), and further removed DMSO in acetone. And drying was carried out. The fiber diameter was adjusted by controlling the nozzle diameter and the spinning stock solution extrusion speed. The obtained fibers were bundled thick and then cut with a guillotine cutter to a desired length.

(Preparation of Conjugated Diene-Based Polymer) (1) Modified conjugated diene-based polymer of the general formula (I) 300 g of cyclohexane and 1,3-butadiene monohydrate were placed in an 800 ml pressure-resistant glass container dried and purged with nitrogen. Monomer, 32.5 g, styrene monomer 17.5 g, potassium-
0.025 mmol of t-amylate and 1 mmol of tetrahydrofuran (THF) were injected, and 0.45 mmol of n-butyllithium (BuLi) was added thereto.
Polymerization was performed at 0 ° C. for 2 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%. 0.25 mmol of methyltriethoxysilane is further added as a modifier to this polymerization system.
, And denatured at 60 ° C. for 30 minutes. Then, 0.5 ml of a 5% solution of 2,6-ditert-butylparacresol (BHT) in isopropanol was added to stop the reaction, and the solid was dried according to a conventional method. As a result, a modified conjugated diene polymer (conjugated diene polymer 1) was obtained.

(2) Modified conjugated diene-based polymer of the general formula (II):
315 g of cyclohexane, 36 g of 1,3-butadiene monomer, 24 g of styrene monomer, 0.025 mmol of potassium-t-amylate and 0.5 mmol of di-n-hexylamine were injected, and 0.5 mmol of n-butyllithium was added thereto. The polymerization was carried out at 50 ° C. for 2 hours. To the obtained polymerization solution, 0.25 mmol of methyltriethoxysilane was added as alkoxysilane,
After denaturing at 30 ° C. for 30 minutes, isopropyl alcohol was added and the solid was dried to obtain a modified conjugated diene polymer (conjugated diene polymer 2).

Examples 1 to 9 and Comparative Examples 1 to 3 The conjugated diene-based polymer 1 or 2 thus obtained
, A tread rubber composition having the composition shown in Table 1 was prepared, and a radial tire for a passenger car having a tire size of 205 / 60R15 was trial-produced by an ordinary method, and the braking performance on a wet road and the braking performance on ice were measured. went. In addition, the above-mentioned factory workability was evaluated as workability during tire production. The results are shown in Table 1.

[0030]

[Table 1]

[Note] Conjugated diene-based polymer 1: polymer equivalent to general formula (I) Conjugated diene-based polymer 2: polymer equivalent to general formula (II) 1) Trade mark: # 1712 manufactured by JSR Corporation (37.5 parts by weight oil per 100 parts by weight of rubber) 2) Trade mark: BR01 manufactured by JSR Co., Ltd. 3) Trade name: Seast 7H manufactured by Tokai Carbon Co., Ltd. 4) Trade mark: Nip Seal manufactured by Nippon Silica Industry Co., Ltd. AQ 5) Bis (3-triethoxysilylpropyl) tetrasulfide 6) N-tert-butyl-2-benzothiazyl-sulfenamide

As can be seen from the above table, the pneumatic tires of Examples 1 to 9 according to the present invention have significantly improved braking performance on icy roads, improved rolling resistance, without significantly deteriorating wet braking performance. It can be seen that the properties have been greatly improved. On the other hand, in Comparative Example 2, although the same modified conjugated diene-based polymer as in Example 1 was used,
Rolling resistance and factory workability are improved because the system does not contain short fibers.
It can be seen that the braking performance on ice has not been improved at all. Also,
In Comparative Example 3, although short fibers were blended, the conjugated diene-based copolymer used in the present invention was not blended, so that the braking performance on ice was improved, but the braking performance on wet roads and rolling were improved. It can be seen that resistance and factory workability have not been improved at all.

[0033]

According to the present invention, by using a specific modified conjugated diene-based polymer and silica together, a silane coupling agent can be used without using a small amount or with a small amount.
As in the case of using the conventional amount of the silane coupling agent, excellent improvement on wet road performance is observed and rolling resistance is reduced. At the same time, a pneumatic tire having excellent performance on ice and significantly improved factory workability of the tread rubber composition at the time of scouring and extrusion can be obtained in combination with the effect of using short fibers.

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Claims (11)

[Claims] 1. A pneumatic tire in which a tread portion has a multilayer structure, wherein a rubber composition constituting at least one layer of the multilayer structure is a conjugated diene-based compound having a functional group derived from alkoxysilane in a molecule. A pneumatic tire comprising 100 parts by weight of a rubber component containing 10% by weight or more of a polymer, 10 parts by weight or more of silica, and short fibers having an average length of 10 mm or less. 2. The conjugated diene-based polymer is at least one selected from a homopolymer of a conjugated diene compound, a copolymer of a conjugated diene compound, and a copolymer of a conjugated diene compound and an aromatic vinyl compound. The pneumatic tire according to claim 1. 3. The conjugated diene polymer having a functional group derived from the alkoxysilane is represented by the following general formula (I): [Wherein, P represents a polymer chain, R ¹ and R ² each independently represent a group selected from aliphatic, alicyclic, and aromatic hydrocarbon groups having 1 to 20 carbon atoms; When there are individual pieces, they may be the same or different. n is 1 to 3
M is an integer of 1 to 3, and n + m is 2 to 4
Represents an integer. 3. The pneumatic tire according to claim 1, further comprising a polymer represented by the following formula: 4. The pneumatic tire according to claim 1, wherein the rubber component contains at least 20% by weight of a styrene-butadiene copolymer. 5. The pneumatic tire according to claim 1, further comprising a silane coupling agent in an amount of 0 to 15% by weight based on the amount of silica. 6. The pneumatic tire according to claim 1, wherein the short fibers have an average diameter of 0.01 to 0.1 mm. 7. The pneumatic tire according to claim 1, wherein the short fibers are polyethylene, polypropylene or polyester. 8. The pneumatic tire according to claim 1, wherein the short fibers are water-soluble fibers. 9. The pneumatic tire according to claim 8, wherein the water-soluble fiber has a water-soluble temperature of 0 ° C. to 20 ° C. 10. The pneumatic tire according to claim 8, wherein the short fibers are polyvinyl alcohol. 11. The pneumatic tire according to claim 1, wherein the short fibers are blended in an amount of 1 to 20 parts by weight based on 100 parts by weight of a rubber component.