JPH0781316A - Radial tire with porous tread - Google Patents

Abstract

PURPOSE:To improve on-snow traveling performance on a snowy road surface by installing a lot of minute diametral air vent holes continued in the tread of a tire circumference, and setting the rate of an opening total area of these air vent holes to a numerical value in the specified range in relation to the outer diametral area of a tire radial cross section in the tread. CONSTITUTION:A lot of air vent holes extending in the tire circumferential direction are installed in a tread 2, while each form of these air vent holes 21 is a cicle, a polygon and the others optionally, and an average diameter or the diameter of an area equal to a cross section of each of these holes 21 should be set to 2 or 0.5mm. In addition, a rubber material of this tread 2 is set to be more than 70 degrees in JASA (Japanese Industrial Standard-A) hardness after tire forming, and a short fiber 22 is mixed in tread rubber at the rate of less than 0.1 to 0.5 in weight percentage. Likewise, the rate of opening total areas of these air vent holes to the outer diametral area of a tire radial cross section in this tread should be set to 0.1 to 0.7, and each air vent hole to be opened to a tread surface serves as a means of escape for water in consequence, whereby the water being attributable to a slip is removed, so that frictional force is thus securable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a studless tire having improved winter performance, that is, snowy road running performance and freezing road running performance, and to a radial tire having a porous tread made of porous rubber as a tread.

[0002]

2. Description of the Related Art Recently, in order to solve problems such as noise generated during traveling and dust generated by shaving road pavement surfaces with spikes, the use of spiked tires, which have been used in winter, has been prohibited. , Various studless tires that replace spike tires have been researched and developed. In the conventional studless tire, the following means are used individually or in combination. Since the frictional force between the tire tread surface and the road surface is proportional to the actual contact area between the tire tread surface and the road surface, the frictional force on the frozen road surface can be reduced by reducing the proportion of grooves in the tread pattern and increasing the tread width. Improve. When driving on a wet frozen road surface, increase the number of blocks and sipes in the tread pattern to increase the frictional force by breaking the water film that acts as a lubricating film between the tire tread surface and the road surface to increase the frictional force. . To secure the running performance on the snowy road surface, the groove is enlarged to increase the frictional force due to the shearing force of the snow column.

[0003]

However, in the means used in the above-mentioned conventional studless tires, if the proportion of the grooves in the tread pattern is too small, there is no escape of the water film, and the water film acts as a lubricating film. Therefore, the frictional force is rapidly reduced, and if the number of blocks or sipes in the tread pattern is too large,
There is a problem that the rigidity of the block is lowered, the block falls down during traveling, the actual ground contact area is reduced, and the frictional force is reduced. Furthermore, the running performance on snowy roads is inconsistent with the running performance on frozen roads, and if the running performance on snowy roads is emphasized, the frictional force will be reduced, and the running performance on frozen roads may be impaired. was there.

An object of the present invention is to provide a radial tire having a perforated tread capable of ensuring sufficient snow running performance on a snowy road surface and improving ice running performance on a frozen road surface.

[0005]

In order to achieve the above-mentioned object, a radial tire having a porous tread of the present invention is provided with a large number of continuous through holes having an average diameter of 0.2 mm to 5 mm in the tread on the outer circumference of the tire. The ratio of the total area of openings of the above through holes to the outer area of the tire radial cross section is 0.1.
It is set to 0.7. In addition, the through hole provided in the tread on the outer circumference of the tire may be a through hole extending in the tire circumferential direction or the tire axial direction. Further, by further increasing the JIS A hardness of the tread rubber to 70 degrees or more and mixing the short fibers in the tread rubber in a ratio of 0.1 or more and 0.5 or less, further effects can be obtained.

[0006]

The tread has a large number of through holes with an average diameter of 0.2 mm to 5 mm, and the ratio of the total area of the openings of the through holes to the outer area of the tread radial cross section is 0.1 to 0.7. The through holes that open to the surface provide a water escape area, removing water that causes slippage and ensuring frictional force. By providing a large number of through holes, relatively macro unevenness is formed on the tread surface, the edge length that engages with the road surface increases, braking force and driving force are easily generated, and side force during cornering is increased. It is likely to occur and the running performance on a frozen road surface can be remarkably improved, and even when the tire is worn, the next through hole appears to exert the above-mentioned effect. Further, by providing a large number of through holes, the rigidity of the tread is lowered, the flexibility is maintained even at low temperatures, and the frictional force with the road surface is secured. further,
The tread rubber has a JIS A hardness of 70 degrees or more and short fibers are mixed in the tread rubber at a ratio of 0.1 or more and 0.5 or less to compensate for the decrease in rigidity due to the provision of a large number of through holes. To secure the rigidity of.

[0007]

Embodiments of the present invention will be described with reference to the drawings. In FIG. 2, the radial tire 1 includes a tread 2 extending in the circumferential direction on the outer circumference of the tire, a pair of sidewalls 3 extending inward in the tire radial direction from both ends of the tread 2, and a bead formed on the inner end of the sidewall 3. 4, an annular bead wire 5 embedded in the bead 4, a carcass 6 extending through the tread 2 and the sidewall 3,
In the tread portion, there is provided a breaker 7 arranged annularly outside the carcass 6 in the tire radial direction. The tread 2 is formed as a strip separately from the other parts such as the sidewalls 3, and is mounted and joined on the other parts during tire production.

As shown in FIG. 1, the tread 2 is provided with a large number of through holes 21 extending in the tire circumferential direction, and the cross sectional shape of the through holes 21 may be circular, polygonal or any other arbitrary shape.
The average diameter d, which is the diameter of a circle having an area equal to the cross-sectional area of the through hole 21, is 0.2 mm to 5 mm (0.2 mm ≦ d ≦ 5 mm), particularly preferably 0.5 mm to 2 mm (0.5 mm ≦ d ≦ 2 mm). When the average diameter d is smaller than 0.2 mm (d <0.2 mm), the opening area of the through hole 21 is too small, and the possible water flow amount is extremely small, and the water flow passage is crushed when a load is applied. May not be secured, the ability to remove water will be reduced, and the effect of increasing the friction coefficient cannot be sufficiently obtained. On the other hand, the average diameter d is larger than 5 mm (d> 5
mm), the rigidity of the tread 2 decreases, the rigidity of the tread pattern or the block is insufficient, and stress concentration at the time of ground contact causes uneven wear, making it impossible to maintain uniformity. The through holes 21 are not limited to those formed as continuous holes having the same cross section, but elongated beads having a beaded shape or independent holes may be mixed.

The rubber material of the tread 2 has a JISA hardness of 70 degrees or more after tire molding, and the short fibers 22 are mixed in a weight ratio of 0.1 to 0.5 with respect to the tread rubber. By increasing the hardness of the tread rubber, it is possible to suppress an excessive decrease in the rigidity of the tread 2 due to the provision of a large number of through holes 21, and to strengthen the tread rubber by mixing the short fibers. If the weight ratio is less than 0.1, the effect of reinforcing the tread rubber cannot be sufficiently obtained, and if the weight ratio exceeds 0.5, the tread rubber cannot maintain the physical properties as a rubber. The mixing of short fibers is carried out by a conventionally known method as described in, for example, Japanese Patent Laid-Open No. 1-145205.

The tread manufacturing method of the present invention will be described with reference to FIGS. The extrusion nozzle 8 includes an outer frame nozzle 81 having a nozzle opening 80 that forms the outer shape of the tread strip in the longitudinal direction, and an inner mold 82 provided on the rubber inlet side of the outer frame nozzle 81 and separated from the outer frame nozzle 81. It has and. The inner mold 82 is provided with a base frame 83, a plurality of pins 84 of a predetermined length having a predetermined cross-sectional outer shape that are provided upright on the outer frame nozzle 81 side of the base frame 83, and projectingly provided outside the base frame 83. Support member 85
And a fixing means 86 such as a bolt that connects the support member 85 and the outer frame nozzle 81, and secures a sufficient gap for rubber inflow between the base frame 83 and the outer frame nozzle 81. The free end of 84 is located at the rubber inlet 81A of the outer frame nozzle 81, and the ratio of the total cross-sectional area of the pin 84 to the opening area of the rubber outlet 81B of the outer frame nozzle 81 is 0.1 to 0.7. The extrusion nozzle 8
Is attached to the outlet end 91 of the extrusion cylinder 9 of the extruder.

Using the above rubber material, the extrusion conditions are a temperature of 50 ° C. to 90 ° C. (preferably 70 ° C.) and an extrusion pressure of 80.
kg / cm ^{2 to} 170 kg / cm ² (preferably 130 kg / cm ² ),
Extrusion is performed at an extrusion speed of 12 m / min. To 13 m / min. To form a tread strip having a large number of through holes extending in the extrusion direction, that is, the longitudinal direction. If the temperature is less than 50 ° C, the rubber becomes hard and the extrusion pressure is 170 kg / cm ² or less,
Extrusion molding cannot be performed while maintaining an extrusion speed of 12 m / min. Or higher. When the temperature exceeds 90 ° C, the rubber becomes too soft, the extrusion pressure is 80 kg / cm ² or more, and the extrusion speed is 13 m / m.
Extrusion cannot be performed while maintaining the following. In the case of forming a porous tread having an axial through hole, a tread strip having a large number of through holes extending in the longitudinal direction is cut as a tread width in a direction orthogonal to the longitudinal direction, and this cut piece is cut. Are joined together to form a porous tread whose through holes extend in the direction orthogonal to the longitudinal direction, that is, in the axial direction. Further, although the circumferential direction and the axial direction are mentioned as the extending direction of the through hole, the direction may be an angle with respect to the circumferential direction or the axial direction.

The tread strip having a large number of through holes is cut into a predetermined length, that is, both ends of the through holes are open, and the vulcanization conditions are set to a temperature of 130 ° C. to 170 ° C.
(Preferably 150 ℃), pressure 2kg / cm ^{2 to} 6kg / cm
² (preferably 4 kg / cm ² ) and a time of 30 to 60 minutes (preferably 45 minutes) are set to perform semi-vulcanization. If the vulcanization temperature is lower than 130 ° C, the vulcanization time becomes long and the productivity is lowered, and if the vulcanization temperature exceeds 170 ° C, the rubber is burned and the desired physical properties cannot be obtained. Also, if the vulcanization pressure is less than 2 kg / cm ² , the air forming bubbles other than the through holes cannot be expelled from the rubber, and if it exceeds 6 kg / cm ² , the pressure resistance of the vulcanization pipe is significantly increased. It is necessary and expensive. Furthermore, if the vulcanization time is less than 30 minutes, vulcanization cannot be performed,
If it exceeds 60 minutes, the rubber will be burned and the physical properties of the rubber cannot be obtained.

After buffing the surface of the semi-vulcanized tread strip, an adhesive is applied and bonded on a breaker to prepare a raw tire, and then the vulcanization step of the raw tire is performed under normal vulcanization conditions. Done in. The adhesive is obtained by dissolving rubber obtained by removing short fibers from the tread rubber with a solvent such as toluene or naphtha.

Next, the test results of the tire according to the embodiment of the present invention manufactured by the above manufacturing process will be described in comparison with a tire having a conventional structure. Example 1: A porous tread having through holes in the circumferential direction, in which short fibers are mixed. Example 2: A porous tread having through holes in the circumferential direction, in which short fibers are not mixed. Example 3: A porous tread having through holes in the axial direction, in which short fibers are mixed. Example 4: A porous tread having through holes in the axial direction, in which short fibers are not mixed. Comparative Example: A tread having no through holes and no short fibers mixed therein. In the porous tread, the cross-sectional shape of the through hole is circular,
The ratio of the total area of openings of the through holes to the outer area of the tire radial cross section of the tread is 0.2, and the tread pattern is formed by hand engraving. Further, the rubber material has a tread rubber JISA hardness of 72 degrees after tire molding, and the short fiber is mixed in the tread rubber in a ratio of 0.2 to the tread rubber. The tire having the above structure was mounted on a rim 4.5J with a tire size of 165SR13, and a μ (friction coefficient) -S (slip rate) characteristic test was performed. Test method: The μ-S characteristic test is an indoor drum test,
By applying pressure snow to the running surface of the rotating drum, speed 40 km / h,
The test tire was run under the conditions of a tire internal pressure of 1.8 kg / cm ² and a load of 385 kg.

The test results are shown in Table 1 and FIG. [Table 1] Example 1 Example 2 Example 3 Example 4 Comparative example Tread through hole Circumferential direction Circumferential direction Axial direction Axial direction No tread rubber Short fiber Yes Short fiber No Short fiber Yes Short fiber No Short fiber No [Evaluation Results] Maximum on snow-packed road μ 105 105 108 105 100 Snow-packed road lock μ 135 125 140 135 100 The evaluation results are indexed with the maximum μ and lock μ of the comparative example as 100, and the lock μ is the number of rotations of the tire. Is the friction coefficient μ when the slip is zero, that is, when the slip ratio is 100%.

From the above test results, by using a porous tread having through holes, the maximum μ and lock μ on the snow-compacted road can be obtained.
In relation to the slip ratio S, the maximum μ and the lock μ on the snow-covered road become high, and the direction of the through hole is increased either in the tire circumferential direction or in the diamond axis direction, and travels on the snow road surface and the frozen road surface. It has improved performance. Also,
By mixing short fibers in the tread rubber, the maximum μ on the snow-covered road and the lock μ and the slip ratio S obviously increase in the maximum μ on the snow-covered road and the lock μ, and the snow road surface and the frozen road surface Driving performance is improved.

[0017]

Since the present invention is constructed as described above, it has the following effects. Average diameter of 0 in tread.
By providing a large number of 2 mm to 5 mm through holes and setting the ratio of the total area of the openings of the above through holes to the outer area of the tire radial cross section of the tread to be 0.1 to 0.7, the through holes opened on the tread surface are water. It provides an escape area for the water that causes slippage and removes friction. By providing a large number of through holes, relatively macro unevenness is formed on the tread surface and the edge length that engages with the road surface increases,
Braking force and driving force are more likely to be generated and side force is more likely to be generated at the time of cornering, which can significantly improve the running performance on frozen road surfaces. Exert the effect of. Further, by providing a large number of through holes, the rigidity of the tread is lowered, the flexibility is maintained even at low temperatures, and the frictional force with the road surface is secured. In addition, the JIS hardness of the tread rubber
70 degrees or more, and the short fiber is 0.1 with respect to the tread rubber.
By mixing in a ratio of 0.5 or more, the rigidity decrease due to the provision of a large number of through holes is compensated, and especially the rigidity of the block edge is secured.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view of a partly cutaway essential part of an embodiment of the present invention.

FIG. 2 is a sectional view of a tire according to an embodiment of the present invention.

FIG. 3 is a front view of an extrusion nozzle.

FIG. 4 is a plan view of an extrusion nozzle.

FIG. 5 is a perspective view of an extrusion nozzle.

FIG. 6 is a μ-S characteristic diagram of test results.

[Explanation of symbols]

1 radial tire, 2 tread, 21 through holes, 22 short fibers 8 extrusion nozzle, 9 extrusion cylinder

Claims (5)

[Claims] 1. An average diameter of 0.2 in a tread on the outer circumference of a tire.
A radial tire having a porous tread characterized in that a large number of continuous through holes of mm to 5 mm are provided, and the ratio of the total area of openings of the above through holes to the outer area of the tire radial cross section of the tread is 0.1 to 0.7. . 2. A radial tire having a porous tread according to claim 1, wherein the through hole provided in the tread on the outer circumference of the tire is a through hole extending in the tire circumferential direction. 3. The tread rubber has a JISA hardness of 70 degrees or more and a short fiber content of 0.1 to 0.5 with respect to the tread rubber.
The radial tire having the porous tread according to claim 1 or 2, wherein the radial tire is mixed in the following ratio. 4. The radial tire having a porous tread according to claim 1, wherein the through hole provided in the tread on the outer circumference of the tire is a through hole extending in the tire axial direction. 5. The tread rubber has a JISA hardness of 70 degrees or more and a short fiber content of 0.1 to 0.5 with respect to the tread rubber.
The radial tire having the porous tread according to claim 1 or 4, which is mixed in the following ratio.