Rubber composition for stud tires and stud tires

Abstract

To solve a problem wherein in a racing tire on ice and snow, a reduction in lap time is competed by using a tire with stud pins, in order for a tire to follow on icy and snowy surfaces, a tread rubber must have a certain degree of softness, on the other hand, if the tread rubber is soft, the blocks formed on the tread will twist in a high speed and high load area and the stud pins will pull out during continuous driving.SOLUTION: There is provided a sulfur-vulcanized rubber composition for a stud tire which is obtained by blending 50 pts.mass or more of carbon black based on 100 pts.mass of a diene-based rubber and has 8 to 18 mass% of a monosulfide bond, wherein the volume fraction of the carbon black is 22 to 25%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rubber composition for stud tires and stud tires, and more particularly to a rubber composition for stud tires that can highly balance the followability on icy and snowy road surfaces, the block rigidity in the high-speed and high-load regions, and the holding ability of stud pins, and a tire using the same.

Background Art

[0002] In tires for ice and snow competitions, tires with stud pins are used to compete for shorter lap times. In order to make the tire follow on the ice and snow road surface, it is necessary to make the tread rubber have a certain degree of softness. On the other hand, when the tread rubber is soft, the blocks formed on the tread in the high-speed and high-load regions will twist, and there is also a drawback that the stud pins will come out during continuous driving. Therefore, in order to shorten the lap time, it is required to highly balance the followability on icy and snowy road surfaces, the block rigidity in the high-speed and high-load regions, and the holding ability of stud pins.

[0003] As a stud tire with high holding ability of stud pins and improved ice and snow performance and wet performance, for example, there is a disclosure in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a rubber composition for stud tires that can highly balance the followability on icy and snowy road surfaces, the block rigidity in the high-speed and high-load regions, and the holding ability of stud pins, and a tire using the same.

Means for Solving the Problems

[0006] As a result of diligent research, the inventors discovered that the above problems can be solved by blending carbon black in a specific amount or more with diene rubber, and by appropriately determining the amount of monosulfide bonds after sulfur vulcanization and the volume fraction of carbon black, thus completing the present invention.

[0007] In other words, the present invention provides a sulfur-vulcanized rubber composition for stud tires, comprising 100 parts by mass of diene rubber and 50 parts by mass or more of carbon black, characterized in that it has 8 to 18% by mass of monosulfide bonds and the volume fraction of carbon black is 22 to 25%. The present invention also provides a stud tire using the aforementioned rubber composition for stud tires in the cap tread. [Effects of the Invention]

[0008] The rubber composition for stud tires of the present invention is a sulfur-vulcanized rubber composition for stud tires comprising 100 parts by mass of diene rubber and 50 parts by mass or more of carbon black, characterized in having 8 to 18% by mass of monosulfide bonds and a volume fraction of 22 to 25% of carbon black, thereby enabling a high-level balance of road-following ability on icy and snowy surfaces, block rigidity in high-speed and high-load regions, and stud pin retention ability.

[0009] According to the present invention, the volume fraction of carbon black in the composition is made relatively large as described above, imparting appropriate hardness to the rubber composition after sulfur vulcanization and increasing block rigidity in the high-speed, high-load region. On the other hand, increasing the hardness of the rubber composition after sulfur vulcanization generally reduces the ability to follow the road surface on ice and snow and the ability to hold stud pins. However, in the present invention, since the volume fraction of carbon black is limited to the range of 22-25%, it is possible to increase the hardness of the rubber composition after sulfur vulcanization while minimizing the adverse effects on the ability to follow the road surface on ice and snow and the ability to hold stud pins. Furthermore, since the rubber composition for stud tires of the present invention has a monosulfide bond content of 8-18% by mass, the temperature dependence of hardness is suppressed and the ability to follow the road surface on ice and snow can be improved. Therefore, according to the present invention, it is possible to provide a rubber composition for stud tires and a tire using the same that can achieve a high-order balance of ability to follow the road surface on ice and snow, block rigidity in the high-speed, high-load region and the ability to hold stud pins. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a front view of a stud tire after stud pins have been driven in, according to an embodiment of the stud tire of the present invention. [Figure 2] Figure 2 is a side view showing an example of a stud pin that constitutes the stud tire of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing an example of stud holes formed in the tread of a stud tire. [Figure 4] Figure 4 is a cross-sectional view illustrating the state in which the stud pins shown in Figure 2 are embedded in the planting holes shown in Figure 3. [Modes for carrying out the invention]

[0011] The present invention will be described in more detail below.

[0012] (Diene-based rubber) The diene rubber used in the present invention is not particularly limited, but from the viewpoint of improving the effects of the present invention, a preferred form is one in which natural rubber (NR) and / or synthetic isoprene rubber (IR) and butadiene rubber (BR) are essential components, and when the total diene rubber is 100 parts by mass, it is preferable that the NR and / or IR accounts for 50 to 80 parts by mass and the BR accounts for 50 to 20 parts by mass. Furthermore, styrene-butadiene copolymer rubber (SBR) can also be blended, and in this form, when the total diene rubber is 100 parts by mass, it is preferable that the NR and / or IR accounts for 40 to 60 parts by mass, the BR accounts for 10 to 40 parts by mass and the SBR accounts for 5 to 10 parts by mass. The molecular weight and microstructure of the diene rubber are not particularly limited, and it may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or it may be epoxidized.

[0013] (Carbon Black) The carbon black used in this invention has a nitrogen adsorption specific surface area (N2SA) of 40 to 320 m², from the viewpoint of improving the effectiveness of this invention. 2 It is preferably 50-220 m / g 2 It is even more preferable that it be / g. The specific surface area for nitrogen adsorption (N2SA) can be determined in accordance with JIS K6217-2.

[0014] (Ratio of rubber composition for stud tires) The rubber composition for stud tires of the present invention is characterized by comprising 100 parts by mass of the diene-based rubber and 50 parts by mass or more of carbon black. If the amount of carbon black added is less than 50 parts by mass per 100 parts by mass of the diene-based rubber, the cornering performance in high-speed and high-load ranges will decrease. The amount of carbon black added is preferably 50 to 90 parts by mass, and more preferably 60 to 80 parts by mass, per 100 parts by mass of the diene rubber.

[0015] (Other ingredients) In addition to the above-described components, the rubber composition of the present invention can be blended with various additives generally blended in rubber compositions, such as vulcanizing or crosslinking agents; vulcanization or crosslinking accelerators; fillers; antioxidants; plasticizers; resins; curing agents, etc. Such additives can be kneaded by a general method to form a composition and can be used for vulcanization or crosslinking. The blending amounts of these additives can also be set to conventional general blending amounts as long as they do not conflict with the object of the present invention.

[0016] In addition, the blending amount of sulfur as a vulcanizing agent is preferably 0.5 to 2.0 parts by mass, more preferably 1.0 to 1.8 parts by mass, based on 100 parts by mass of the diene rubber.

[0017] Further, from the viewpoint of preventing stud pin removal during running and maintaining stud pin retention, the rubber composition for stud tires of the present invention preferably has a 300% modulus of not less than 14.5 MPa, more preferably 14.5 to 17.5 MPa. The 300% modulus shall be measured in accordance with JIS K6251 using a JIS No. 3 dumbbell-shaped test piece (thickness: 2 mm) under the conditions of temperature of 23°C and tensile speed of 500 mm / min in accordance with JIS K6251.

[0018] The rubber composition for stud tires of the present invention has a monosulfide bond of 8 to 18% by mass after vulcanization and a volume fraction of the carbon black of 22 to 25%. By setting the monosulfide bond to 8% by mass or more, the temperature dependence of the hardness can be suppressed and the followability on an ice / snow road surface can be improved. Also, by setting the monosulfide bond to 18% by mass or less, the followability on an ice / snow road surface can be improved. Further, by setting the volume fraction of the carbon black to 22 to 25%, while increasing the hardness of the rubber composition after sulfur vulcanization, it is possible to suppress the adverse effects on the followability on an ice / snow road surface and the retention ability of the stud pins to the maximum extent. The monosulfide bond is more preferably 8 to 14% by mass. The monosulfide bond can be controlled, for example, by adjusting the amount of vulcanization accelerator or by adjusting the vulcanization temperature to a lower temperature. Specifically, it is preferable to set the ratio of vulcanization accelerator to sulfur (vulcanization accelerator / sulfur) within the range of 0.4 to 2.0 and adjust the vulcanization temperature within the range of 135°C to 160°C. The volume fraction of carbon black can be controlled by adjusting the amount of carbon black added.

[0019] The amount of monosulfide bond is measured by the toluene swelling method. The toluene swelling method involves treating a vulcanized rubber composition (test piece: 7 mm × 7 mm × 1 mm) with a reagent that selectively cleaves sulfide bonds (see Table 1 below), and then determining the polysulfide network chain density by applying the Flory-Rehner formula to the degree of toluene swelling of the untreated sample and each treated sample. In this invention, this method is carried out in accordance with the method described on pages 407-409 of "Rubber Testing Methods" (edited by the Japan Rubber Association, Maruzen Co., Ltd., published January 30, 2006). In Table 1 below, "THF / toluene (1:1)" refers to a mixture of 90 mL of tetrahydrofuran (THF) and 90 mL of toluene; "THF / toluene (1:1) + 2-propanethol + piperidine" refers to a mixture of 90 mL of THF, 90 mL of toluene, 3.31 mL (0.4 mol) of 2-propanethol, and 3.35 mL (0.4 mol) of piperidine; and "THF / toluene (1:1) + lithium aluminum hydride" refers to a mixed solution of 200 mL of THF, 200 mL of toluene, and 10 g of lithium aluminum hydride. Furthermore, each reagent treatment is performed by immersing the test specimen and stirring it at room temperature for 8 hours. Afterward, the sample is immersed in toluene for 16 hours to determine the degree of swelling with toluene.

[0020] [Table 1]

[0021] νt: Total network chain density (100%) νm / νt × 100: Monosulfide network chain density νd(=(νm+d)-νm) / νt×100: Disulfide network chain density νp(=νt-(νm+d)) / νt×100: Polysulfide network chain density

[0022] Furthermore, the volume fraction of carbon black can be determined as the ratio of volume A to volume B (A / B), where volume A is obtained by dividing the blending weight of carbon black in the composition by the specific gravity of each raw material, and volume B is obtained by dividing the total weight of the composition by the specific gravity of the composition.

[0023] Furthermore, the rubber composition for stud tires of the present invention can be used to manufacture stud tires according to conventional tire manufacturing methods. The rubber composition for stud tires of the present invention can achieve a high-level balance of road-following ability on icy and snowy surfaces, block rigidity in high-speed and high-load regions, and stud pin retention ability, making it suitable for use in the tread of stud tires, especially in cap treads. Furthermore, the tire of the present invention is preferably a pneumatic tire, and can be filled with air, an inert gas such as nitrogen, and other gases.

[0024] Figure 1 is a front view of a stud tire after stud pins have been driven in, according to an embodiment of the stud tire of the present invention.

[0025] As shown in Figure 1, the tread portion 1 has multiple longitudinal grooves 2 formed in the circumferential direction of the tire and multiple transverse grooves 3 extending in the width direction of the tire, and these longitudinal grooves 2 and transverse grooves 3 divide the area into multiple blocks 4.

[0026] Block 4 has multiple stud pins 20 embedded in it. Figure 2 is a side view illustrating a stud pin 20, Figure 3 is a cross-sectional view illustrating a stud hole 10 formed in the tread, and Figure 4 is a cross-sectional view showing the stud pin from Figure 2 embedded in the stud hole from Figure 3. Although these illustrated examples describe a double-flange type stud pin, the stud tire of the present invention can also use a single-flange type stud pin.

[0027] As shown in Figure 2, the stud pin 20 is composed of a cylindrical body portion 21, a tread-side flange portion 22, a bottom-side flange portion 23, and a tip portion 24. The tread-side flange portion 22 is formed on the tread side (outer side in the tire radial direction) of the body portion 21 so that its diameter is larger than that of the body portion 21. The tip portion 24 is made of a harder material than the other components so that it protrudes from the tread-side flange portion 22 in the direction of the pin axis. The bottom-side flange portion 23 is formed on the bottom side (inner side in the tire radial direction) of the body portion 21 so that its diameter is larger than that of the body portion 21.

[0028] On the other hand, as shown in Figure 3, the planting hole 10 comprises an upper cylindrical portion 11 positioned to correspond to the tread-side flange portion 22 of the stud pin 20, a lower cylindrical portion 12 positioned to correspond to the body portion 21 of the stud pin 20, and a bottom portion 13 adjacent to the lower cylindrical portion 12. Here, the inner diameters of the upper cylindrical portion 11 and the bottom portion 13 are larger than the inner diameter of the lower cylindrical portion 12.

[0029] In the case of a single-flange type stud pin, the diameter of the tread-side flange portion 22 can be made the same as the diameter of the cylindrical body portion 21. Furthermore, for the mounting hole corresponding to the single-flange type, the inner diameter of the upper cylindrical portion 11 can be made the same as the inner diameter of the lower cylindrical portion 12.

[0030] In both the double-flange and single-flange stud pins, the diameter of the bottom flange portion 23 is larger than the diameter of the cylindrical body portion 21. Also, the inner diameter of the lower cylindrical portion 12 is smaller than the inner diameter of the bottom portion 13 of the planting hole.

[0031] As shown in Figure 4, when a stud pin 20 is planted in a stud hole 10 provided in the tread, the constricted lower cylindrical portion 12 of the stud hole 10 tightens the stud pin 20, making it difficult for the stud pin 20 to come out. Furthermore, since the diameter of the bottom flange portion 23 of the stud pin 20 is made larger than the inner diameter of the lower cylindrical portion 12, the stud pin 20 becomes even more difficult to remove.

[0032] The ratio (D / d) between the diameter D of the bottom flange portion 23 of the stud pin 20 and the inner diameter d of the lower cylindrical portion 12 of the planting hole 10 is not particularly limited, but is preferably 2.5 to 5.5, more preferably 3.0 to 4.0. By setting the ratio (D / d) within this range, it is possible to suppress the stud pin from falling out. [Examples]

[0033] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0034] Standard example, Examples 1-4, and Comparative Examples 1-7 Sample preparation In the formulations (parts by mass) shown in Table 2, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. Subsequently, the composition was put back into the Banbury mixer, the vulcanization system was added and kneaded to obtain a rubber composition. Next, the obtained rubber composition was press-vulcanized in a predetermined mold at 150°C for 30 minutes to prepare vulcanized rubber test pieces. The physical properties of the obtained rubber composition were measured using the test methods described below. The carbon black volume fraction (CB volume fraction), the amount of monosulfide bonds, and the 300% modulus (300% Mod) were measured using the methods described above.

[0035] Ice Driving Stability: The vulcanized rubber composition obtained above was used for the tread portion, and a pneumatic tire with a tire size of 225 / 40R18 was manufactured. The pneumatic tire had the shape of the tread portion 1 as shown in Figure 1, and a total of 100 stud pins 20 were driven into the block 4. The resulting pneumatic tire was mounted on a wheel with a rim size of 17×8J and fitted to a domestic 2-liter class test vehicle. Actual vehicle driving was conducted on a 1.2km test course consisting of ice surface under the condition of an air pressure of 240kPa, and the lap time was measured. The results are shown as an index with the lap time of the standard example set to 100. A larger index indicates a shorter lap time and superior ice driving stability. High-Load Driving Stability: Lap times were measured for the high-speed corner section of the test course described above. The results are shown as an index with the standard example lap time set to 100. A higher index indicates a shorter lap time in the high-speed corner section and superior high-load driving stability. Pin Retention: The test vehicle equipped with the pneumatic tire obtained above was driven 10,000 km on the dry surface of the test course described above. Afterwards, the number of stud pins remaining in block 4 was counted. The results are shown as an index, with the number of remaining stud pins in the standard example set to 100. A higher index indicates a larger number of remaining stud pins and superior pin retention.

[0036] The results are shown in Table 2. Volumes A and B are also shown in Table 2. Volume A is the volume obtained by dividing the weight of carbon black in the composition by the specific gravity of each raw material, while Volume B is the volume of the composition obtained by dividing the total weight of the composition by the specific gravity of the composition. The volume fraction of carbon black is determined by the ratio of Volume A to Volume B (A / B).

[0037] [Table 2] *1: NR (RSS#3) *2: SBR (Nipol 1502, manufactured by Nippon Zeon Co., Ltd.) *3: BR (Nipol BR1220, manufactured by Nippon Zeon Co., Ltd.) *4: Carbon Black 1 (Tokai Carbon Co., Ltd. product name Seest 9, nitrogen adsorption specific surface area (N2SA) = 139m²) 2 / g) *5: Carbon Black 2 (DIABLACK GT2 manufactured by Mitsubishi Chemical Corporation, Nitrogen adsorption specific surface area (N2SA) = 320m²) 2 / g) *6: Oil (Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd.) *7: Anti-aging agent (PILFLEX 13 manufactured by NOCIL LIMITED) *8: Zinc oxide (3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd.) *9: Stearic acid (YR bead stearic acid manufactured by NOF Corporation) *10: Vulcanization accelerator (product name: Noxellar CZ-G, manufactured by Ouchi Shinko Chemical Co., Ltd.) *11: Sulfur (Mucron OT-20 manufactured by Shikoku Chemicals, Inc.)

[0038] From the results in Table 2, it can be seen that the rubber composition of each example is formulated by blending 50 parts by mass or more of carbon black with 100 parts by mass of diene rubber, and the monosulfide bond content after sulfur vulcanization is 8 to 18% by mass, and the volume fraction of carbon black is 22 to 25%, so that it is possible to achieve a higher-order balance of followability on icy and snowy road surfaces (stability on ice as described above), block rigidity in the high-speed and high-load range (stability on high loads as described above), and stud pin holding ability (pin holding ability as described above) compared to the standard rubber composition.

[0039] On the other hand, in Comparative Examples 1, 2, and 4, the volume fraction of carbon black exceeds the upper limit defined in the present invention, and the monosulfide bond is below the lower limit defined in the present invention. Therefore, it is not possible to achieve a high-level balance of followability on icy and snowy road surfaces (stability on ice), block rigidity in high-speed and high-load regions (stability under high load), and stud pin retention ability (pin retention). In Comparative Example 3, the volume fraction of carbon black exceeded the upper limit specified in the present invention, resulting in reduced road-following ability on icy and snowy surfaces (the above-mentioned ice driving stability). In Comparative Example 5, the volume fraction of carbon black and the number of monosulfide bonds were below the lower limits specified in the present invention, resulting in reduced followability on icy and snowy road surfaces (ice driving stability) and reduced block rigidity in high-speed, high-load regions (high-load driving stability). In Comparative Example 6, the monosulfide bond exceeded the upper limit defined in the present invention, resulting in reduced road-following ability on icy and snowy surfaces (the above-mentioned ice driving stability). In Comparative Example 7, the volume fraction of carbon black exceeded the upper limit specified in the present invention, resulting in reduced followability on icy and snowy road surfaces (the above-mentioned ice driving stability).

[0040] The present invention encompasses the following embodiments. Embodiment 1: A sulfur-vulcanized rubber composition for stud tires, comprising 100 parts by mass of diene rubber and 50 parts by mass or more of carbon black, It has 8 to 18% by mass of monosulfide bonds, and The volume fraction of the carbon black is 22-25%. A rubber composition for stud tires characterized by the following features. Embodiment 2: The rubber composition for stud tires according to Embodiment 1, characterized in that the diene rubber comprises natural rubber and / or synthetic isoprene rubber and butadiene rubber as essential components, and when the total diene rubber is 100 parts by mass, the natural rubber and / or synthetic isoprene rubber accounts for 50 to 80 parts by mass and the butadiene rubber accounts for 50 to 20 parts by mass. Embodiment 3: The rubber composition for stud tires according to Embodiment 1 or 2, characterized in that the 300% modulus of the rubber composition for stud tires is 14.5 MPa or higher. Embodiment 4: A stud tire using the rubber composition for stud tires described in any of Embodiments 1 to 3 as the cap tread. [Explanation of Symbols]

[0041] 1. Tread section 2. Longitudinal grooves 3 Yokomizo 4 blocks 10 planting holes 11 Upper cylindrical section 12 Lower cylindrical section 13 Bottom 20 stud pins 21 Torso 22 Tread-side flange portion 23 Bottom flange section 24 Chip section

Claims

1. A sulfurized vulcanized rubber composition for stud tires, comprising 100 parts by mass of diene rubber and 50 parts by mass or more of carbon black, The aforementioned diene-based rubber does not contain any rubber components other than natural rubber or synthetic isoprene rubber, butadiene rubber, and styrene-butadiene copolymer rubber. It has 8 to 18% by mass of monosulfide bonds, The volume fraction of the carbon black is 22-25%, A rubber composition for stud tires, characterized in that the 300% modulus of the rubber composition for stud tires is 14.5 MPa or higher.

2. The rubber composition for stud tires according to claim 1, characterized in that the diene rubber comprises natural rubber and / or synthetic isoprene rubber and butadiene rubber as essential components, and when the total diene rubber is 100 parts by mass, the natural rubber and / or synthetic isoprene rubber accounts for 50 to 80 parts by mass and the butadiene rubber accounts for 50 to 20 parts by mass.

3. A stud tire using the rubber composition for stud tires described in claim 1 as the cap tread.

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