JP2000191831A - Rubber composition, vulcanized rubber and tire using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition and vulcanized rubber that can be suitably used for a pneumatic tire excellent in braking properties on ice and on a rainy road by compounding a matrix rubber comprising a rubber component selected from natural rubbers and diene-based synthetic rubbers, a water-soluble resin having a specific melting point and a blowing agent. SOLUTION: There are compounded 100 pts.wt. of a matrix rubber comprising a rubber component comprising at least one selected from natural rubbers and diene-based synthetic rubbers, 2-15 pts.wt. of a water-soluble resin having a melting point of 120-200 deg.C and 1-30 pts.wt. of a blowing agent to give a rubber composition. Preferably, the blowing agent is incorporated into the water-soluble resin before it is admixed with the rubber component and the water-soluble resin has a shape of a short fiber 10-100 μm in diameter and 1-10 mm in length. A vulcanized rubber obtained by vulcanizing this rubber composition preferably has an expansion ratio of 10-40% and contains oblong bubbles oriented toward a certain direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition, a vulcanized rubber and a pneumatic tire using the same, and more particularly, to a pneumatic tire having excellent braking performance on ice and on rainy roads, and the tire. The present invention relates to a vulcanized rubber and a rubber composition thereof which can be suitably used for a tread or the like of the present invention.

[0002]

2. Description of the Related Art Since spiked tires have been regulated for social reasons, much research has been conducted on treads of tires in particular in order to improve the braking / driving performance (on-ice performance) of tires on icy and snowy road surfaces. Is coming. BACKGROUND ART Conventionally, it is known that a water film is easily generated on a snowy and snowy road surface due to frictional heat with a tire or the like, and this water film causes a reduction in a coefficient of friction between the tire and the backside of the snow and ice. For this reason, the performance of the tire on ice largely depends on the ability of the tread to remove the water film and the edge effect. Therefore, in order to improve the on-ice performance of the tire, it is necessary to improve the water film removing ability and the edge effect of the tread.

Therefore, it is necessary to provide a large number of micro drain grooves (both in depth and width of about 100 μm) on the surface of the tire to eliminate a water film by the micro drain grooves and to increase the friction coefficient of the tire on ice and snow road surfaces. Proposed. However, in this case, although the on-ice performance in the early stage of use of the tire can be improved, there is a problem that the on-ice performance gradually decreases with the wear of the tire. Further, it has been proposed to use foamed rubber for the tread in order to prevent the performance on ice from deteriorating even when the tire is worn. However, the bubbles in a mere foamed rubber are spherical and do not have anisotropy and cannot function as the micro drains, so that the performance on ice cannot be improved to the extent that the market demand level is satisfied. There is.

On the other hand, JP-A-4-38207 discloses that
A method of forming a micro drainage groove on the surface of the tread by using a short fiber-containing foamed rubber for the tread is described. However, in this case, even if the tread is worn by running, the short fibers that are not substantially parallel to the friction surface do not easily separate from the tread, and a micro-drainage groove as originally aimed cannot be effectively formed, The coefficient of friction is not sufficiently improved on ice and snow. Further, since the detachment of the short fibers is greatly affected by running conditions and the like, there is a problem that the performance on ice cannot be reliably improved. Further, Japanese Patent Application Laid-Open
JP-A-216970 proposes a method in which a water-soluble polyvinyl alcohol fiber having excellent low-temperature water-solubility is used as a short fiber in a foamed rubber in order to improve the poor detachability of the short fiber. However, in this case, although the coefficient of friction on ice is improved due to the improved detachability as compared with conventional short fibers, the volume of short fibers is not sufficient compared to the amount of spherical bubbles in foamed rubber. In other words, the amount of anisotropic micro drains on the surface of the tread rubber is insufficient, and it cannot be said that the performance on ice has been enhanced to the level required by the market. On the other hand, when the amount of short fibers is too large, there arises a problem that the performance on ice is reduced due to the effect of rubber physical properties, and the workability of rubber kneading is deteriorated.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems under such circumstances, and provides a pneumatic tire having a performance satisfying a high level of braking performance on ice and rainy roads required by the market. It is intended to provide.

[0006]

Means for Solving the Problems In the present invention, as a result of diligent studies on the above-mentioned problems, excellent performance on ice can be obtained by using a rubber composition containing a specific water-soluble resin and a foaming agent as a tire tread. Thus, the present inventors have found that a tire having performance on a rainy road surface can be obtained, and have completed the present invention. That is, means for solving the above problems are as follows. (1) a rubber matrix containing at least one rubber component selected from natural rubber and diene-based synthetic rubber, a water-soluble resin having a melting point of 120 ° C to 200 ° C,
A rubber composition comprising 1 to 30 parts by weight of a foaming agent with respect to 100 parts by weight of the rubber component. (2) a matrix rubber containing at least one rubber component selected from natural rubber and diene-based synthetic rubber, and 1 to 30 parts by weight based on 100 parts by weight of the rubber component.
And a water-soluble resin containing parts by weight of a foaming agent. Here, the melting point of the water-soluble resin is 120C to 20C.
Preferably it is 0 ° C. It is preferable that the foaming agent is previously contained in the water-soluble resin, but a part of the foaming agent may be added alone as a rubber compounding agent. In the rubber compositions of the above (1) and (2), the water-soluble resin is preferably polyvinyl alcohol. The water-soluble resin is preferably a short fiber. The water-soluble resin may contain an insoluble component, but may be any resin that is water-soluble as a whole. (3) The present invention further includes a matrix rubber and a water-soluble resin layer containing air bubbles, and has a foaming rate of 10%.
It provides a vulcanized rubber that is greater than 40%. Here, the vulcanized rubber is obtained by vulcanizing the rubber composition of the above (1) or (2). The bubbles in the vulcanized rubber are preferably long. (4) The present invention also relates to a tire having a pair of beat portions, a carcass connected to the beat portions in a toroidal shape, a belt portion for tightening a crown portion of the carcass, and a tread portion. The present invention also provides a pneumatic tire in which the vulcanized rubber of the above (3) is disposed at least in the ground contact portion. Here, it is preferable that the bubbles in the tread rubber exist in a long shape and are oriented in the tire circumferential direction.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber composition of the present invention contains a specific water-soluble resin and a specific amount of a foaming agent, and the vulcanized rubber contains a matrix rubber and a water-soluble resin, particularly long bubbles. Contains water-soluble resin. That is, the vulcanized rubber is a water-soluble resin, particularly a water-soluble resin having a melting point of 120 ° C. to 200 ° C., and 1 to 30 parts by weight of a rubber component.
It is obtained by vulcanizing a rubber composition containing parts by weight of a foaming agent. In this case, it is preferable to mix a water-soluble resin containing a foaming agent in advance. The melting point of the water-soluble resin is measured as a melting peak temperature by, for example, a DSC measurement device.

[0008] In the pneumatic tire of the present invention to which the above rubber composition or vulcanized rubber is applied, the foaming ratio of the tread rubber is more than 10% and not more than 40%, especially 15 to 35%. preferable. The foaming rate referred to here includes all cells such as long closed cells and spherical closed cells mixed in the vulcanized rubber, and the foaming rate Vs is
Vs = (ρ ₀ / ρ ₁ -1) × 100 (%)
₁ is the density of the foamed rubber (g / cm ³ ), and ρ ₀ is the density of the solid phase portion of the foamed rubber (g / cm ³ ). If the foaming rate is 10% or less, sufficient water is not removed from the generated water film due to the lack of absolute concave volume, and the performance on ice is not so significant. If the foaming ratio exceeds 40%, the performance on ice is sufficient, but the voids inside the rubber are too large, and the breaking limit of the compound is greatly reduced, which is not preferable in terms of durability. Also, on a rainy road surface, the tread block rigidity may be too low, rather causing a reduction in braking performance.

By the way, the amount of short fibers used in tread rubber to improve the ice and snow performance in the prior art depends on the kneading of unvulcanized rubber, the workability of extrusion, the performance of tires, the cost and the like. It is limited in tire manufacturing. However, in the present invention, by setting the melting point of the water-soluble resin within the above range, the foaming gas generated from the foaming agent during vulcanization stays in the resin, and the resin portion actually mixed is A bubble-containing resin layer having a larger volume than the volume can be easily formed. And
When the water-soluble resin is in the form of short fibers, particularly long bubbles are formed. Therefore, when the water-soluble resin or the water-soluble short fiber is blended into the tire tread rubber, the same amount of the conventional normal short fiber is blended on the tire surface by dissolving or releasing the resin due to rubber wear. Since the number of micro drains is increased as compared with the case, better performance on ice is exhibited. The melting point of the water-soluble resin used in the present invention is preferably 120 ° C. or more in the unvulcanized rubber, particularly in order to maintain a fibrous form.
If the melting point is lower than 120 ° C., the rubber is melted during the kneading and extrusion steps of general rubber, so that the fiber shape cannot be maintained, and it is difficult to form a drainage channel on the tread surface. At the time of rubber compounding, it is not particularly limited at which stage of the rubber kneading the short fibers are mixed, but it is desirable to avoid mixing at the stage where the short fibers are melted, that is, at the initial mastication stage. It is.

On the other hand, the reason why the melting point of the water-soluble resin is set to 200 ° C. or lower is that the resin is melted during vulcanization, and the water-soluble resin containing a bubble portion is formed during vulcanization by combination with a foaming agent. That's why. That is, when the water-soluble resin does not melt during vulcanization, the gas generated from the foaming gas does not migrate into the resin. Also, in that case, even if the foaming agent is contained in the water-soluble resin, the foaming gas generated from the foaming agent in the resin flows out into the matrix rubber outside the resin due to the vulcanization pressure, and is elongated. It is difficult to form bubble-like bubbles. However, if the temperature is 200 ° C. or less, not all are good, and it is necessary to adjust the vulcanization conditions (temperature, pressure, time, etc.) of a product such as a tire to be actually used so that the resin is melted. The viscosity of a water-soluble resin generally used as a fiber before melting is much higher than the cross-linking end viscosity (maximum viscosity value) of the matrix rubber, but once the resin is melted, the viscosity is greatly reduced, The foaming gas can be left in the molten resin. As a result, after vulcanization, long bubbles covered with the solidified resin layer are formed again. Here, the long bubbles may have a plurality of closed cells dispersed in a long form in the fibrous resin, or may be present in the resin in a state where the bubbles are connected. Good.
Even if the melting point of the water-soluble resin is higher than the vulcanization temperature, some predetermined bubbles can be obtained even when the melting point peak is broad and the melting point start temperature is equal to or lower than the vulcanization temperature. Is preferably equal to or lower than the vulcanization temperature of rubber.

When the vulcanized rubber having long bubbles in the rubber is applied to the tread in this manner, the water-soluble resin exposed on the tire surface undergoes a dissolution reaction due to water on an icy or rainy road surface. By forming a micro drain groove corresponding to the sum of the volume of the resin portion and the volume of the bubble portion, it is possible to increase the tread surface void volume. At the same time, the resin is not restrained by the aqueous solution, so that the rubber surface is softened. Therefore, the ability to follow an icy road or a rainy road surface is improved and the coefficient of friction with the road surface is increased, which is effective. Although the vulcanized rubber in the present invention contains a water-soluble resin layer containing air bubbles, spherical air bubbles similar to those in ordinary foamed rubber may coexist in the rubber. When blended in short fibers containing part or all of the foaming agent, the braking performance on ice and on rainy roads can be further improved. In particular,
By blending the short fibers containing all of the foaming agent in advance, it becomes possible to make all the closed cells in the vulcanized rubber elongated, and the above-mentioned braking performance is remarkably improved. That is, as the foamed state in the vulcanized rubber, the ratio of the spherical closed cell and the cylindrical (including fibrous) volume to the entire cylindrical (including fibrous) volume measured by the method described later is preferably as large as possible, Specifically, it is 60% or more, especially 8
It is preferably 0% or more. When the water-soluble resin contains a foaming agent, the ratio of the resin component to the foaming agent may be 150 parts by weight or less, preferably 30 to 120 parts by weight, based on 100 parts by weight of the resin. preferable. If the amount is more than 150 parts by weight, yarn breakage frequently occurs particularly during the fiber production process, and fiber production becomes difficult.

The blowing agent which can be used in the present invention is not particularly limited, but includes dinitrosopentamethylenetetraamine (DPT), azodicarbonamide (ADCA),
There are dinitrosopentastyrenetetramine, benzenesulfonylhydrazide derivative, oxybisbenzenesulfonylhydrazide (OBSH) and the like, and among them, azodicarbonamide (ADCA) is preferable in consideration of production processability. In particular, when a foaming agent is contained in the water-soluble fiber, it is preferable to reduce the particle diameter as much as possible from the viewpoint of operability in fiber production. Further, the total amount of the foaming agent used in the rubber composition of the present invention is preferably 1 to 30 parts by weight, particularly preferably 2 to 20 parts by weight based on 100 parts by weight of the rubber component. Further, the method for producing the water-soluble resin containing a blowing agent is not particularly limited, for example, in the production of water-soluble fibers, mixed with the raw material resin,
Fiber formation at a temperature that hardly causes a foaming reaction,
It is preferable to perform hot stretching. The foaming reaction temperature varies depending on the type of the foaming agent and the foaming aid, but the fiber contains a foaming agent having a relatively high foaming temperature, and the foaming aid is not contained in the fiber but is contained in the matrix rubber. By blending in the fiber, the foaming reaction of the blowing agent in the fiber by vulcanization can be easily caused selectively in the fiber.

That is, when it is necessary to add a foaming aid to accelerate the foaming reaction during vulcanization, it is preferable to directly blend a predetermined amount of the foaming aid into the rubber composition. However, as long as the foaming reaction does not occur during the fiber manufacturing process,
A foaming aid may be contained in the fiber. As the foaming auxiliary, an auxiliary usually used in the production of foamed products, such as urea, zinc stearate, zinc benzenesulfinate and zinc white, is preferably used, but other than the above may be used.

Next, although the components of the water-soluble resin are not particularly limited, they have high water-solubility even at a low temperature close to 0 ° C. in order to exhibit a high coefficient of friction on all road conditions. Further, for example, a polyvinyl alcohol (PVA) fiber having a low saponification degree and having mechanical properties necessary for rubber kneading is preferable. The water-soluble resin or the fiber preferably has a water dissolving temperature of 10 ° C. or lower, particularly preferably 5 ° C. or lower. In the present invention, the water-soluble resin is preferably used as short fibers. In this case, the diameter and length of the short fibers are not particularly limited, but the fiber diameter is smaller in view of improving tire braking performance. However, when the same amount is blended, the number of grooves on the tire surface is increased, and the groove dispersibility is improved, which is preferable. However, in the production of fibers, if the fiber is too thin, thread breakage occurs frequently and the rubber refining workability deteriorates, so that the fiber cannot be made extremely thin. Therefore, the fiber diameter at the time of compounding is 10 to 100 μm, particularly 15 to 50 μm.
μm is preferred. In general, the fiber length is preferably longer from the viewpoint of improving the tire braking performance, but in fact, indentation by the pattern in the tire vulcanizing pot is more likely to occur as the fiber length increases, and the rubber refining workability also deteriorates. It cannot be extremely long. Therefore, the water-soluble short fiber has a fiber length of 1 to 1
0 mm, particularly preferably 2 to 5 mm.

When the amount of the water-soluble resin used in the present invention is less than 1 part by weight per 100 parts by weight of the rubber component, the effect of improving the performance on ice is small. 2 to 15 parts by weight is preferable, and 3 to 5 parts by weight is preferable, since such problems as poor operation, poor workability at the time of extruding rubber (rough skin), and cracks in the tire tread occur.
-10 parts by weight is preferred. Further, the rubber composition containing the water-soluble resin, by orienting the fibers in one direction in the rubber extrusion process, it is possible to control the direction of the long bubbles, when used as a tire product, It is preferable to orient the water-soluble fibers particularly in the tire circumferential direction, because the water rejection on the rear side in the tire rotation direction on the ground contact surface is improved, and the braking force on ice and the braking force on rainy road surface can be greatly improved.

The rubber component used in the rubber composition of the present invention is at least one rubber selected from the group consisting of natural rubber and diene-based synthetic rubber. -Butadiene copolymer rubber, cis-1,4-polyisoprene, cis-
Various polybutadiene rubbers including 1,4-polybutadiene are included. Among them, especially the glass transfer temperature is low,
In view of the great effect of the performance on ice, cis-1,4-polybutadiene is suitably used, and in particular, polybutadiene having a cis content of 90% is preferable. In addition to the above components, the rubber composition of the present invention contains carbon black, silica, process oil, vulcanizing agent, vulcanization accelerator, antioxidant, zinc oxide, stearic acid, silane coupling agent, antiozonant For example, additives commonly used in the rubber industry can be blended.

[0017]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited by these examples. <Various Measurement Methods> Various measurements and evaluation methods for water-soluble fibers, rubber compositions and tires were performed according to the following methods. (1) Measurement of water dissolution temperature of water-soluble fiber Put a fiber with a load of 2 mg / denier suspended in water,
The temperature was raised from around 0 ° C. at a rate of 1 ° C. to 2 ° C. per minute, and the water temperature at the time of dissolution was taken as the water dissolution temperature. (2) Measurement of Water-Soluble Fiber Diameter Twenty locations of the fiber were randomly selected, the diameter was measured with an optical microscope, and the average value was taken as the fiber diameter. (3) Evaluation of Fiber Dispersibility The scouring workability of the unvulcanized tread rubber at the time of tire production was evaluated based on the following three criteria of ○, Δ, and ×. ：: no problem level 〇: partially poor fiber dispersion (lumps with a diameter of less than 5 mm) Δ: poor fiber dispersion at many locations (lumps with a diameter of 5 mm or more)

(4) Observation of foaming state A center block piece was cut off from the tire tread,
Further, the surface is cut with a sharp razor perpendicular to the tire circumferential direction and perpendicular to the tread surface to obtain an observation surface.
The observation surface is photographed with a normal scanning microscope (SEM) at a magnification of 100 times. Next, the spherical closed cell portion and the long closed cell portion provided with the resin outer layer portion in this photograph were separated, and their respective areas were measured, and the spherical closed cell and the long closed cell within a certain area were measured. Is calculated. The above measurement was performed 10 times, and the average of the area ratio was obtained. This was defined as the volume ratio between the spherical closed cells and the elongated closed cells. In addition, also about what was the same fibrous as the time of compounding after vulcanization, the area of the short fiber part was measured and the volume ratio was calculated. (5) Test method of braking performance on ice The tire was mounted on a 1600 cc passenger car in Japan and was driven on a flat road on ice. At a speed of 20 km / hr, the brake was depressed to lock the tire, and the distance until the tire stopped was measured. . As a result, the reciprocal of the distance was set to 1 for the tire of Comparative Example 1.
The index was indicated as 00. The larger the value, the better the braking performance on a rainy road surface. (6) Test method of braking performance on rainy road surface Tires were mounted on a domestically produced 1600 cc passenger car, and the vehicle was run on a dry road surface for 100 km and on a wet road for 10 km. At a speed of 60 km / hr / h, the brake was depressed to lock the tire, and the distance to the stop was measured. The result was expressed as an index with the reciprocal of the distance taken as 100 for the tire of Comparative Example 1. The larger the value, the better the braking performance on a rainy road surface.

<Production Example of PVA Fiber Prototype> Next, a method for producing the foaming agent-containing PVA fiber used in Examples and Comparative Examples will be described. (1) Sample A: 70 mol% of vinyl alcohol units and 30% of vinyl acetate units, a polymerization degree of 600 and a saponification degree of 70
Mol% of PVA and dimethylsulfoxide (DMSO) were mixed and dissolved under stirring at 90 ° C. for 12 hours under a reduced pressure nitrogen atmosphere of 100 Torr or less, so that PVA was 40%
A DMSO solution was prepared. Further, a foaming agent A is added to the solution.
A predetermined amount of DCA particles was charged, and stirring was continued for 4 hours to obtain a mixed solution in which the foaming agent was uniformly dispersed. This mixture was extruded from an extruder set at 90 ° C. through a nozzle having a diameter of 0.2 mm, and acetone / DMS kept at 2 ° C.
The mixture was wet-spun in a mixed solution bath having an O weight ratio of 85/15 and fixed. Further, the spun fibers were mixed with acetone / DMSO at a weight ratio of 98 /
Stretching was performed in the mixed solution of No. 2 and then DMSO was extracted and removed in heated acetone and dried with a hot air drier at 80 ° C. to obtain a foaming agent-containing fiber. The obtained fiber had a saponification degree of 71% and a melting point of 173 ° C. Further, the water solubility was 2 ° C., and the water solubility at low temperature was excellent. The obtained fiber was cut into a length of 2 mm with a guillotine cutter. (2) Sample B In the production of the sample A, the procedure was the same as that of the sample A, except that the blowing agent ADCA particles were not added at all. (3) Sample C PVA and DMSO having a vinyl alcohol unit of 92 mol% and a vinyl acetate unit of 8%, a degree of polymerization of 600 and a saponification degree of 92 mol% were mixed in the same manner as in Example 1. Short-fibers containing a foaming agent were prepared in the same manner as in Example 1 except that methanol was used instead of acetone in this mixed solution. The obtained fiber has a saponification degree of 91% and a melting point of 210 ° C.
The solubility in water was worse than that of Example 1 and was dissolved in water at about 10 ° C. The obtained fiber was cut into a length of 2 mm with a guillotine cutter.

(4) Sample D: 83 mol% of vinyl alcohol units and 17% of vinyl acetate units, and a degree of polymerization of 83 with a degree of polymerization of 700
Mol% of PVA and DMSO were mixed in the same manner as in Example 1. From this mixed solution, a water-soluble short fiber containing a foaming agent was prepared in the same manner as in Example 1. The saponification degree of the obtained fiber was 81%, the melting point was 190 ° C, and the water dissolution temperature was 5 ° C. The obtained fiber was cut into a length of 2 mm with a guillotine cutter. (5) Sample E: 76 mol% of vinyl alcohol unit, 17% of maleic acid unit, 7% of vinyl acetate unit,
Maleic acid-modified PVA having a degree of polymerization of 500 and DMSO were mixed in the same manner as in Example 1. From this mixed solution, a water-soluble short fiber containing a foaming agent was prepared in the same manner as in Example 1.
The obtained fiber had a melting point of 160 ° C. and a water dissolution temperature of 2 ° C. or less. The obtained fiber is guillotine cutter 2
It was cut into mm length.

<Manufacture of Test Tire> A radial tire for a passenger car having a tire size of 185 / 70R13 was produced by a conventional method using a rubber composition having the composition described in Table 1 as a tread rubber. The maximum temperature during vulcanization of the tire was 180 ° C., and the temperature during vulcanization of the tread portion was measured with a thermocouple. As a result, the maximum temperature of the tread portion was also 180 ° C.

Comparative Example 1 and Example 1 In Comparative Example 1, water-soluble short fibers having a melting point higher than the range of the present invention were blended with foamed rubber. In Example 1, the melting point of the water-soluble short fiber blended in the foamed rubber was 173 ° C., which was within the range of the present invention. Since the rubber melted during vulcanization of the tire, the gas generated from the foaming agent reduced the viscosity during vulcanization. After the vulcanization, the bubbles migrated into the fibers and formed long bubbles. Since the long bubbles effectively increase the volume of the anisotropic void component functioning as a drainage channel on the tread surface, both the performance on ice and the braking performance on a rainy road surface are significantly improved. In addition, when the surface of the test tire was observed, the water-soluble short fiber was dissolved by the water on the test road surface in both Comparative Example 1 and Example 1. The results are shown in Table 1. Examples 2 to 4 In Examples 2 to 4, water-soluble short fibers containing a foaming agent in the ratio shown in Table 1 were blended. In this case, the experiment was carried out under substantially the same conditions as in Example 1 except that the foaming rate and the amount of the resin component in the water-soluble fiber were substantially combined. It can be seen that the ratio of the air bubbles increases, and as a result, the braking performance on ice and on a rainy road surface is significantly improved. The results are shown in Table 1.

[0023]

[Table 1]

Examples 5 to 7 Examples 5 and 6 are examples in which the same amount of the short fiber containing a blowing agent as in Example 4 was added to increase the foaming rate. In Example 5, although the braking performance on ice and on rainy road surfaces was improved, poor dispersion during scouring workability was observed. In Example 6, the rubber scouring workability was further deteriorated, and fibrous lumps were slightly more observed in the unvulcanized rubber. Also, on ice compared to Example 5,
The braking performance on rainy roads has also been reduced. Example 7 is an example in which the compounding amount of the foaming agent-containing short fiber was reduced to reduce the rubber foaming rate in Example 4, but the ratio of long bubbles was extremely high. Irrespective of the low foaming ratio, it shows higher braking performance on ice and rainy road surface than Comparative Example 1.
The results are shown in Table 2. Examples 8 and 9 Examples 8 and 9 were performed in the same manner as in Example 2 except that only the melting point of the water-soluble short fiber was changed. The braking performance and the braking performance on a rainy road surface are shown. The results are shown in Table 2.

[0025]

[Table 2]

Note) * Blowing agent content: Resin part 1 in blowing agent-containing PVA fiber
1 part by weight of blowing agent with respect to 00 parts by weight 1) BR01 manufactured by JSR Corporation 2) Carbon N220 manufactured by Asahi Carbon Co., Ltd. 3) Dibenzothiazyl sulfide 4) N-cyclohexyl-2-benzothiazyl sulfenamide 5) Zinc benzenesulfinate manufactured by Otsuka Chemical Co., Ltd. 6) Urea / zinc stearate manufactured by Otsuka Chemical Co., Ltd. (8
5/15) Blend

[0027]

According to the present invention, a rubber in which a specific water-soluble resin containing a foaming agent is blended in a rubber composition is used as a tread rubber, whereby an anisotropic micro drain groove on the tread surface can be effectively formed. Since the pneumatic tire can be formed, when the foaming rate of the tread rubber is set to be more than 10% and not more than 40% at the same time, a pneumatic tire having excellent braking performance on ice and on the upper surface of a rainy road can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 5/16 C08K 5/16 C08L 9/00 C08L 9/00 29/04 29/04 B

Claims (10)

[Claims] 1. A matrix rubber containing at least one rubber component selected from natural rubber and a diene-based synthetic rubber, a water-soluble resin having a melting point of 120 ° C. to 200 ° C., and 100 parts by weight of the rubber component A rubber composition comprising 1 to 30 parts by weight of a foaming agent. 2. A matrix rubber containing at least one rubber component selected from a natural rubber and a diene-based synthetic rubber, and 1 to 3 parts by weight based on 100 parts by weight of the rubber component.
A water-soluble resin containing 0 parts by weight of a foaming agent. 3. A matrix rubber containing at least one rubber component selected from natural rubber and a diene-based synthetic rubber, and 1 to 3 parts by weight based on 100 parts by weight of the rubber component.
The resin contains 0 parts by weight of a blowing agent and has a melting point of 12 parts.
A water-soluble resin having a temperature of 0 ° C to 200 ° C. 4. The rubber composition according to claim 1, wherein the water-soluble resin is polyvinyl alcohol. 5. The rubber composition according to claim 1, wherein the water-soluble resin is a short fiber. 6. A vulcanized rubber comprising a matrix rubber and a water-soluble resin layer containing air bubbles, and having a foaming ratio of from more than 10% to 40% or less. 7. A rubber composition obtained by vulcanizing the rubber composition according to any one of claims 1 to 5.
The vulcanized rubber according to the above. 8. The vulcanized rubber according to claim 7, wherein the bubbles are elongated. 9. A tire having a pair of beat portions, a carcass connected to the beat portions in a toroidal shape, a belt portion for tightening a crown portion of the carcass, and a tread portion, wherein at least the tread portion is grounded. A pneumatic tire using the vulcanized rubber according to any one of claims 6 to 8 for a part. 10. The pneumatic tire according to claim 9, wherein the bubbles in the tread are present in a long shape and are oriented in the tire circumferential direction.