JPH11315170A - Rubber composition and pneumatic tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire retaining steering stability on both dry and wet road surfaces in the initial stage of its use and capable of improving steering stability on wet road surface after worn, in particular after exposure of base rubber. SOLUTION: This pneumatic tire is such one as to use a rubber composition for its base tread comprising 100 pts.wt. of a rubber component containing >=20 pts.wt. of a styrene-butadiene rubber, 30-120 pts.wt. of carbon black and short fibers <=10 mm in length and 0.01-0.1 mm in diameter, and has such a structure that the outer circumference of the crown portion of the carcass ply astride toroidally between a pair of bead cores is successively disposed with a belt ply and thread rubber, wherein the tread rubber consists of two-ply tread composed of base rubber with the height from the groove bottom to its upper end accounting for >=20% of the groove depth and cap rubber, and the base tread consists of the above rubber composition.

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 steering stability on dry and wet road surfaces (hereinafter abbreviated as "DRY steering stability" and "WET steering stability", respectively) at the beginning of tire use, and tires. The present invention relates to a pneumatic tire having improved WET steering stability during wear and braking performance on wet road surfaces (hereinafter abbreviated as WET braking performance).

[0002]

2. Description of the Related Art In order to improve steering stability, a conventional two-layer tread uses a relatively soft rubber having a high coefficient of friction as a cap tread rubber and a block tread rubber as a base tread rubber to increase block rigidity. A relatively hard rubber is used.

[0003]

In a tire having a tread as described above, when the tire is worn due to friction with a road surface and base tread rubber (hereinafter abbreviated as base rubber) appears on the tire surface, Due to the rubber properties, there is a problem that the wet handling stability and the wet braking ability are rapidly reduced. Therefore, an object of the present invention is not to impair the DRY steering stability and the WET steering stability in the initial stage of using the tire, and to reduce the wear after the abrasion, especially after the exposure of the base rubber.
An object of the present invention is to provide a pneumatic tire with improved ET steering stability and wet braking performance.

[0004]

That is, the first aspect of the present invention is as follows.
Is a rubber component containing 20 parts by weight or more of styrene-butadiene rubber, 100 parts by weight of a reinforcing filler, 30 KARA to 120 parts by weight, a length of 10 mm or less, and a diameter of 0.01 And a short fiber having a diameter of 0.1 mm to 0.1 mm. The reinforcing filler is made of carbon black, and has a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 1
It is 50 m ² / g, also the reinforcing filler consists of carbon black and silica, the silica N ₂
SA is from 130 to 280 m ² / g, and the ratio of silica to the total amount of the reinforcing filler is 95% by weight or less;
And the silane coupling agent is used in an amount of 5 to 20 of the silica compounding amount.
%. Further, the compounding amount of the short fiber is 1 to 25 parts by weight based on 100 parts by weight of the rubber component, and the short fiber is a water-soluble fiber;
It is preferable that the water-soluble temperature of the short fibers is 20 ° C. or less, and the short fibers are polyvinyl alcohol short fibers.

[0005] Next, a second embodiment of the present invention relates to a pair of beads.
A pneumatic tire in which a belt layer and a tread rubber are sequentially arranged on the outer periphery of a crown portion of a carcass layer straddling in a toroidal shape between cores, and the tread rubber has a height from a groove bottom to an upper end of a base tread. A two-layer tread composed of a base tread and a cap tread having a groove depth of 20% or more, and a base tread having a length of 10 mm or less,
It is a pneumatic tire containing short fibers having a diameter of 0.01 to 1 mm, and it is preferable to use a rubber composition having any of the above characteristics for the rubber composition of the base tread.

[0006] The rubber component used in the rubber composition for a base tread of the present invention is a styrene-butadiene rubber (SBR) due to the high market demand for WET performance of summer tires.
At least 20% by weight. The rubber component used in combination with the SBR is not particularly limited, and is usually used.
Natural rubber (NR), butadiene rubber (BR), isoprene rubber (IR) and the like can be used as appropriate. In order to maintain the wet performance, it is preferable that the butadiene rubber is less than 20 parts by weight.

In the present invention, in a tire having a so-called cap / base structure, short fibers are blended with a rubber composition of a base tread. The material of the short fiber is not particularly limited, and polyvinyl alcohol (PVA), cellulose
Fiber, polyalginate fiber, water-soluble fiber such as polyalkylene fiber, polyester, nylon, aramid,
Known materials, such as water-insoluble fibers such as carbon, glass, polyethylene, and polypropylene, can be mentioned. Incorporation of water-soluble fibers, particularly during use of the tire,
On wet road surfaces such as in rainy weather, the micro-grooves can improve the drainage of the rubber surface, and can also soften only the rubber surface efficiently, so that the coefficient of friction (μ) of the rubber composition on the wet road surface can be effectively used. In particular, the rubber composition has good shape retention during rubber production, has a large degree of improvement in the physical properties of the rubber composition, and has a high molecular modulus while maintaining a high modulus of elasticity of the fiber affecting block rigidity. Polyvinyl alcohol which can increase the low-temperature water solubility by adjusting the value of is preferred.

[0008] The short fiber preferably has a water-soluble temperature of 20 ° C or lower, more preferably 10 ° C or lower. By using the short fiber having a low water-soluble temperature, the effect of blending the water-soluble fiber can be efficiently obtained even under the condition where the surface temperature of the road is low.

The blending amount of the short fibers is not particularly limited. However, if the amount is too small, the effect of improving the performance becomes small. If the amount is too large, the extruding workability and the performance decrease due to a remarkable increase in the modulus of elasticity cause the performance of the base rubber to decrease. It is preferably from 1 to parts by weight, more preferably from 2 to parts by weight, per 100 parts by weight of the rubber component.

[0010] The length of the short fibers must be less than 10 mm. When the length of the short fibers exceeds 10 mm, there is a concern that remarkable deterioration in workability and deterioration in wear resistance will occur.

The diameter of the short fibers must be 0.01 to 1 mm, based on the size of the long voids after melting. If the diameter of the short fibers is less than 0.01 mm, thread breakage occurs frequently in the fiber manufacturing process, resulting in reduced fiber productivity, and even if manufactured, rubber scouring workability deteriorates. Furthermore, when it is blended into the tread of a tire, the depth of the generated groove is too small, and the groove is crushed by a load. On the other hand, when the diameter of the short fibers exceeds 0.1 mm, the compounding amount of the short fibers must be increased in order to secure a certain number of grooves on the tread surface of the tire, and the kneading workability of the rubber composition is increased. Decrease.

The short fibers preferably have a melting point of 120 ° C. or higher. If the melting point is less than 120 ° C., the short fibers may be melted in the kneading step or the extrusion step, and the fiber shape may not be maintained. In the vulcanization step, when it is preferable to fuse the rubber with the rubber, the melting point of the short fiber is preferably 200 ° C. or less.

The interface between the short fibers and the matrix rubber is preferably joined to some extent. The joining method is not particularly limited. For example, a method of vulcanizing and fusing at a temperature equal to or higher than the melting point of the short fiber is effective. When the short fiber is polyvinyl alcohol, a method of blending a silane coupling agent, a method of introducing a thioalcohol unit or the like into a molecule, and modifying the resin of the short fiber itself are also effective. The joining rate is preferably 80% or more, and more preferably 90% or more.

In the present invention, as a reinforcing filler,
Preferably, carbon black is used, and further, silica can be used in combination. The compounding amount of the reinforcing filler is 30 to 120 parts by weight, preferably 50 to 120 parts by weight, based on 100 parts by weight of the rubber component for reasons such as workability. Whether carbon black is used alone or in combination with silica, the total amount must be 30 to 120 parts by weight based on 100 parts by weight of the rubber component.

When silica is used in combination, it is preferable that the ratio of silica to the total amount of silica and carbon black is 95% by weight or less, and that the silane coupling agent contains 5 to 20% by weight of the silica compounding amount. When the amount of silica exceeds 95% by weight, the reinforcing property (abrasion resistance), particularly the abrasion resistance at high stiffness, is significantly reduced.

The carbon black used in the present invention is:
Nitrogen adsorption specific surface area (N ₂ S
A) is preferably from 50 to 150 m ² / g,
The silica preferably has an N ₂ SA of 130 to 280 m ² / g from the viewpoint of ensuring workability and abrasion resistance.

In the pneumatic tire of the present invention, the tread is a two-layer tread comprising a base rubber and a cap rubber whose height from the groove bottom to the upper end of the base rubber is 20% or more of the depth of the groove. And the base tread is length 10
mm or less short fibers. If the height from the groove bottom to the upper end of the base rubber is less than 20% of the groove depth, the influence of the physical properties of the top tread rubber becomes dominant, and sufficient block rigidity is obtained even if the base rubber rigidity is increased. Not possible, early DR
Y steering stability and WET steering stability decrease.

[0018]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to the embodiment as long as it does not exceed the gist of the present invention.

Short fiber, rubber composition, physical properties of tire,
The performance was measured according to the following measurement method.

(I) Physical Properties of Short Fibers (i) Diameter and length In the fiber after cutting, 20 places were randomly selected, and the diameter, the diameter and the length were measured with an optical microscope. The average value was the diameter or length of the short fiber, respectively. (Rotation) Aqueous Solution 1 g of a water-soluble resin was placed in 200 cc of water, and the temperature was raised at 2 ° C./min while stirring with a stirrer (about 0 ° C.). Start from ℃
G). The temperature of the water when it becomes transparent by visual observation is defined as the dissolution temperature. (H) Melting point Using a differential thermal analyzer DSC200 manufactured by Seiko Denshi Co., Ltd., the temperature was raised at a rate of 10 ° C./min from 30 ° C. to 250 ° C., and the melting point temperature was determined from the obtained endothermic peak. It was measured.

(II) Physical Properties of Rubber Composition (i) Dynamic Storage Modulus (E ') Using a spectrometer manufactured by Toyo Seiki Co., Ltd., a test piece having a width of 5 mm, a thickness of 2 mm and a length of 20 mm was subjected to an initial load of 150 g, The dynamic storage modulus at 30 ° C. was measured at a frequency of 50 Hz and a dynamic strain of 1%. The value was taken as an index, taking Comparative Example 1 as a control as 100. The larger the value, the higher the block rigidity and the greater the initial DRY and WET steering stability. However, if the value is too high, the filling may deteriorate. (R) Bonding rate at interface between short fiber and matrix rubber A vulcanized rubber in which short fibers are oriented in one direction was cut out at a thickness of about 1 mm perpendicular to the longitudinal direction of the short fibers to obtain a sample. Next, the rubber sample was fixed with a jig in a state where a strain of 100% was applied in the cutting direction, and the cut surface was observed with a scanning microscope. Measure the part where the fiber and rubber are bonded and the part where the interface between the fiber and rubber is dissociated and a void is formed, and express the percentage of the bonded part in% as short fiber and matrix. The bonding rate at the interface with rubber was used.

(III) Tire Performance (i) Initial Driving Stability On a dry road surface and a wet road surface of a test course, two test drivers drive an actual vehicle, and drive, braking, steering wheel responsiveness, and control during driving are performed. The stability was comprehensively evaluated and the steering stability was evaluated. The result is 10 in Comparative Example 1.
It is indicated by an index when it is set to 0, and the larger the numerical value, the better. (R) WET steering stability after running The test tire was mounted on a passenger car, and the vehicle was run for 30,000 km to expose the base rubber. After that, on the test course, four test tires were mounted on the passenger car and two test drivers performed actual driving on wet road surface, driving performance,
The braking performance, steering wheel responsiveness, and controllability at the time of steering were comprehensively evaluated, and the WET steering stability after traveling was evaluated. The results are shown by an index when Comparative Example 1 is set to 100, and the larger the value, the better. (A) WET braking performance after running The test tire was mounted on a passenger car and run for 30,000 km to expose the base rubber. Thereafter, on a test course, four test tires were mounted on a passenger car, and the braking distance on a wet road surface was measured at an initial speed of 60 km. The reciprocal of the distance was expressed as an index, with Comparative Example 1 being 100. The larger the numerical value, the better the braking performance. (2) Wear Resistance After traveling 50,000 km on a general road with an actual vehicle, the traveling distance per 1 mm of wear was calculated from the remaining groove in the tread portion, and the value of the tire of Comparative Example 1 was set to 100 and indicated as an index. The larger the index, the better the wear resistance.

Preparation of Water-Soluble PVA Fiber <Samble A> 45% by weight DMS of a polymer having an average polymerization degree of 75 mol% of polyvinyl alcohol unit and 25 mol% of vinyl acetate unit and a saponification degree of 75%
The O solution was used as a spinning solution, extruded from a nozzle into a 2 ° C acetone / DMSO mixed solution (weight ratio 85/15), passed through a spinning roll, and then mixed with an acetone / DMSO mixed solution (weight ratio 9/9).
The film was stretched 4 to 5 times in 5/5), and the DMSO in acetone was further removed, followed by drying to obtain a water-soluble polyvinyl alcohol fiber A. Aqueous solution temperature is 2 ℃, melting point is 169 ℃
Met.

<Samble B> 45 of a polymer having an average degree of polymerization of 750 and a saponification degree of 80%, comprising 81 mol% of a polyvinyl alcohol unit and 19 mol% of a vinyl acetate unit.
Using a weight% DMSO solution as a spinning solution, the mixture was extruded from a nozzle into an acetone / DMSO mixed solution (weight ratio 85/15) at 2 ° C., passed through a spinning roll, and then mixed with an acetone / DMSO mixed solution (weight ratio 95/5). The film was stretched 4 to 5 times, and the DMSO in acetone was further removed, followed by drying to obtain a water-soluble polyvinyl alcohol fiber B. The aqueous solution temperature was 3 ° C and the melting point was 191 ° C.

<Samble C> 45 of a polymer having an average degree of polymerization of 700 and a saponification degree of 88%, comprising 88 mol% of a polyvinyl alcohol unit and 12 mol% of a vinyl acetate unit.
Using a weight% DMSO solution as a spinning solution, the mixture was extruded from a nozzle into an acetone / DMSO mixed solution (weight ratio 85/15) at 2 ° C., passed through a spinning roll, and then mixed with an acetone / DMSO mixed solution (weight ratio 95/5). The film was stretched 4 to 5 times, and the DMSO in acetone was further removed, followed by drying to obtain a water-soluble polyvinyl alcohol fiber C. The aqueous solution temperature was 8 ° C and the melting point was 196 ° C.

<Samble D> A 45% by weight DMSO solution of a polymer having an average degree of polymerization of 700 and a saponification degree of 92%, comprising 91 mol% of a polyvinyl alcohol unit and 9 mol% of a vinyl acetate unit, was used as a stock solution for spinning.
Extruded into acetone / DMSO mixed solution (weight ratio 85/15), passed through spinning roll, and stretched 4-5 times in acetone / DMSO mixed solution (weight ratio 95/5). After removing DMSO, water-soluble polyvinyl alcohol fiber D was obtained. The aqueous solution temperature was 14 ° C and the melting point was 211 ° C.

<Samble E> A 45% by weight DMSO solution of a polymer having an average degree of polymerization of 800 and a degree of saponification of 96%, comprising 95 mol% of polyvinyl alcohol units and 5 mol% of vinyl acetate units, was used as a stock solution for spinning.
Extruded into acetone / DMSO mixed solution (weight ratio 85/15), passed through spinning roll, and stretched 4-5 times in acetone / DMSO mixed solution (weight ratio 95/5). After removing DMSO, water-soluble polyvinyl alcohol fiber E was obtained. The aqueous solution temperature was 29 ° C and the melting point was 214 ° C. The fiber diameter was adjusted by adjusting 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.

Sample rubber compositions were prepared according to the formulations shown in Table 1, and the dynamic storage modulus was measured. Table 2 shows the results.
In addition, the composition 1 is a control in which no short fiber is blended, and the compositions 4, 5, and 6 have the length of the short fiber or the diameter of the fiber, and the composition 12 has the amount of the SBR within the range of the present invention. Off. Further, Formulations 13 to 16 are examples in which materials having different aqueous temperatures and melting points are mixed as short fibers.

[0029]

[Table 1] 1) Trademark, emulsion polymerization SBR, trade mark #, manufactured by JSR Corporation
1500 2) Tokai Carbon Co., Ltd., Trademark: Seat 7H (N
₂ SA 126 m ² / g) 3) Tokai Carbon Co., Ltd., trademark: Seat 9 (N
₂ SA 143 m ² / g) 4) Nip Seal AQ (N
₂ SA 200 m ² / g) 5) Degussa AG Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) 6) diphenylguanidine 7) dibenzothiazyl disulfide 8) Nt-butyl-2-benzothiazyl sulf Phenamide 9) Preparation

[0030]

[Table 2]

Using the sample rubber composition for the base tread, test tires having a size of 205 / 60R16 were manufactured by a conventional method, and the tire performance was measured. Table 2 shows the measurement results of the height of the base tread in the block and the tire performance of each test tire. In addition, when the tires after traveling 30,000 km were observed, in Comparative Example 12 in which the base groove height was out of the range of the present invention, the base tread was not sufficiently exposed, so that the wet braking test after traveling was canceled.

Comparative Example 1 is a control tire using a rubber composition containing no fibers as a base rubber. Even if the length and diameter of the fibers are changed, the wear resistance is not impaired as long as it is within the range of the present invention. WET steering stability and WE after running
T braking performance is improved. From Comparative Example 1 and Examples 1 and 2, the tire performance is improved by blending the fiber, but if the blending amount is too large, the wear resistance tends to decrease, so the blending amount is 1 to 25 parts by weight. It can be seen that it is preferable to perform Further, even if the rubber component and the reinforcing filler are changed, the effect can be obtained as long as it is within the range of the present invention. However, in Comparative Example 5 containing no SBR, the abrasion resistance, the WET steering stability after running, and the after running It can be seen that all of the wet braking performance of the present invention has been reduced. Further, from Comparative Example 6 and Examples 4 and 8, if the height of the base rubber in the groove is less than 20%, the effect of improving the base rubber is small, and the effect of improving the DRY steering stability at the beginning of running is small. It turns out that it cannot obtain enough. Furthermore, although the effects of the present invention can be obtained even if the physical properties of the short fibers are changed as compared with Examples 9 to 12, it can be seen that an increase in the aqueous solution temperature affects the wet handling stability after running. Further, in Example 12 using Formulation 16 in which Resin E having a high aqueous solution temperature was blended, it was observed that short fibers remained on the worn surface.

[0033]

According to the present invention, the rubber is hardened by blending the short fibers with the base tread, and the steering stability at the initial stage of tire use is improved. At the time of base exposure, short fibers are detached from the tire surface, especially in the case of water-soluble fibers, which are dissolved by water on the road surface and the like, and long voids are formed on the surface, so that drainage of the surface is enhanced, and Only the softening occurs and the surface distortion is applied to the block surface, so that the coefficient of friction on the wet road surface is improved.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 5/54 C08K 5/54 L 7/02 7/02 C08L 9/06 C08L 9/06 29/04 29/04 C

Claims (11)

[Claims] 1. 30 to 12 parts by weight per 100 parts by weight of a rubber component containing at least 20 parts by weight of a styrene-butadiene rubber.
A rubber composition comprising 0 parts by weight of a reinforcing filler and short fibers having a length of 10 mm or less and a diameter of 0.01 to 0.1 mm. 2. The rubber composition according to claim 1, wherein the reinforcing filler comprises carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 150 m ² / g. 3. The rubber composition according to claim 2, wherein the reinforcing filler comprises carbon black and silica. 4. The rubber composition according to claim 1, wherein the ratio of silica to the total amount of the reinforcing filler is 95% by weight or less, and the rubber composition contains 5 to 20% by weight of the silica in the silane coupling agent. The rubber composition according to claim 3. 5. The silica has an N ₂ SA of 130 to 280 m.
The rubber composition according to claim 3 or 4, wherein the rubber composition is ² / g. 6. The rubber composition according to claim 1, wherein the amount of the short fiber is 1 to 25 parts by weight based on 100 parts by weight of the rubber component. Stuff. 7. The rubber composition according to claim 1, wherein the short fibers are water-soluble short fibers. 8. The rubber composition according to claim 7, wherein the short fiber has an aqueous solution temperature of 20 ° C. or less. 9. The rubber composition according to claim 1, wherein the short fibers are polyvinyl alcohol short fibers. 10. A pneumatic tire in which a belt layer and a tread are sequentially arranged on the outer periphery of a crown portion of a carcass layer straddling in a toroidal manner between a pair of bead cores. 100% by weight of a rubber component containing a styrene-butadiene rubber with a base tread having a height to the upper end of the base tread of 20% or more of the groove depth and a cap tread and a base tread having a weight of at least 20 parts by weight. A pneumatic tire comprising 30 to 120 parts by weight of carbon black per part and short fibers having a length of 10 mm or less and a diameter of 0.01 to 0.1 mm. 11. A pneumatic tire according to claim 10, wherein the rubber composition according to any one of claims 1 to 7 is used as a rubber composition for a base tread. .