JP7211024B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire excellent in crack resistance and low rolling resistance.

Heavy-duty tires used as truck and bus tires are required to have excellent crack resistance and high tire durability. On the other hand, in recent years, regulations on rolling resistance have become stricter, and demand for improved low rolling resistance is increasing. Adding silica or large-diameter carbon black to pneumatic tires, or reducing the amount of carbon black, has been considered in order to provide low rolling resistance, but crack resistance is reduced. There is a problem.

For this reason, Patent Document 1 discloses a tire member composed of a tire rubber composition that satisfies a specific relationship between a dynamic elastic modulus E* and a loss tangent tan δ, and a breaking strength TB and an elongation at break EB that satisfy a specific relationship. Discloses that a tire provided with has good steering stability, tire durability and low fuel consumption performance. However, although the tire described in Patent Document 1 has good performance required for passenger car tires, it does not have sufficient crack resistance required for heavy-duty pneumatic tires used for trucks and buses.

JP 2017-141325 A

An object of the present invention is to provide a pneumatic tire with improved crack resistance and low rolling resistance over conventional levels.

In the pneumatic tire of the present invention that achieves the above object, the swelling degree A and tan δ at 60° C. of the side rubber constituting the sidewall portion satisfy the following formula (1), and the side rubber is composed of 30 to 80 masses of natural rubber. 35 to 47 parts by mass of carbon black having a nitrogen adsorption specific surface area of 20 to 130 m ² /g to 100 parts by mass of diene rubber composed of 20 to 70% by mass of butadiene rubber, and a sulfenamide vulcanization accelerator. 0.5 to 1.0 parts by mass and 1.2 to 1.8 parts by mass of sulfur are blended, and the blending amount (Va) of the sulfenamide vulcanization accelerator and the blending amount (S) of sulfur It is characterized by being made of a rubber composition having a ratio (Va/S) of 0.47 to 0.59 .
0.0006A-0.083≤tan δ≤0.0006A-0.038 (1)
(In the formula, tan δ is tan δ at 60° C., A is the degree of swelling (%) when immersed in toluene at room temperature for 3 days, and 220≦A≦340.)

In the pneumatic tire of the present invention, the degree of swelling A and tan δ at 60° C. of the side rubber constituting the sidewall portion satisfy the above formula (1). can be improved to

The free sulfur content B and tan δ at 60° C. of the side rubber should preferably satisfy the following formula (2), and the crack resistance and low rolling resistance can be further improved.
−0.3B+0.09≦tan δ≦−0.3B+0.14 (2)
(In the formula, tan δ is tan δ at 60° C., and B is the amount of free sulfur (%) measured based on JIS K6234, and 0≦B≦0.2.)

The tan δ at 60° C. is preferably 0.07 or more and 0.14 or less, which can reduce heat generation and further improve low rolling resistance.

Heavy-duty tires having the above-described side rubber are excellent in crack resistance and can reduce rolling resistance to a conventional level or higher, and are suitable as tires for trucks and buses.

FIG. 1 is a cross-sectional view along the meridian line showing an example of an embodiment of the heavy duty pneumatic tire of the present invention.

When the pneumatic tire of the present invention is applied to a heavy-duty tire, its characteristics can be further utilized. Heavy-duty tires refer to large pneumatic tires mounted on trucks, buses, and construction vehicles. As illustrated in FIG. 1, the heavy duty pneumatic tire has a tread portion 1, sidewall portions 2, and bead portions 3. A carcass layer 4 is mounted between the left and right bead portions 3, 3, and both ends of the carcass layer 4 are mounted. The portion is folded back around the bead core 5 from the inside of the tire to the outside. A three-layer belt layer 6 is arranged outside the carcass layer 4 in the tread portion 1 in the tire radial direction, and a tread rubber 9 is arranged outside the outermost belt layer 6 . An inner liner 7 is arranged on the innermost side of the tire. Also, the sidewall portion 2 is formed of a side rubber 8 .

As described above, the sidewall portion 2 forming the pneumatic tire is composed of the side rubber 8, and the degree of swelling A and tan δ at 60° C. of the side rubber 8 satisfy the following formula (1).
0.0006A-0.083≤tan δ≤0.0006A-0.038 (1)
(In the formula, tan δ is tan δ at 60° C., A is the degree of swelling (%) when immersed in toluene at room temperature for 3 days, and 220≦A≦340.)

When the degree of swelling A and tan δ at 60° C. satisfy the above formula (1), the crack resistance and low rolling resistance can be improved beyond conventional levels. If the value of tan δ at 60°C is smaller than the value of (0.0006A-0.083), the strength of the side rubber will decrease. Also, if the tan δ value at 60° C. is larger than the value (0.0006A−0.038), the heat generation of the side rubbers increases and the rolling resistance deteriorates.

The degree of swelling A is 220% or more and 340% or less, preferably 240% or more and 310% or less, more preferably 240% or more and 280% or less. If the degree of swelling A is less than 220%, crack resistance cannot be improved. Further, when the degree of swelling A exceeds 340%, the rolling resistance increases.

Tan δ at 60 ° C. is not particularly limited as long as it satisfies the above formula (1), but is preferably 0.07 or more and 0.14 or less, more preferably 0.07 or more and 0.12 or less, still more preferably 0 0.07 or more and 0.10 or less. If the tan δ at 60°C is less than 0.07, the strength of the side rubber is lowered. On the other hand, if tan δ at 60°C exceeds 0.14, the heat buildup of the side rubber will increase and the rolling resistance will deteriorate.

In the present specification, tan δ at 60°C is loss tangent tan δ measured using a viscoelastic spectrometer at a strain rate of 10 ± 2%, a frequency of 20 Hz and a temperature of 60°C. The degree of swelling A is the mass change (%) when immersed in toluene at room temperature for 3 days, measured according to JIS K6258.

The side rubber that satisfies the above formula (1) can be produced by adjusting the compounding and vulcanization conditions of the rubber composition that constitutes the side rubber. Specifically, the content of the rubber composition, especially the content of the sulfenamide-based vulcanization accelerator (Va), the content of sulfur (S), and these It is preferable to adjust the ratio (Va/S) of the blending amount and increase or decrease the vulcanization temperature and vulcanization time.

The free sulfur content B and tan δ at 60° C. of the side rubber preferably satisfy the following formula (2), so that crack resistance and low rolling resistance can be improved.
−0.3B+0.09≦tan δ≦−0.3B+0.14 (2)
(In the formula, tan δ is tan δ at 60° C., and B is the amount of free sulfur (%) measured based on JIS K6234, and 0≦B≦0.2.)

When the free sulfur content B and tan δ at 60° C. satisfy the above formula (2), crack resistance and low rolling resistance can be further improved. If the value of tan δ at 60° C. is smaller than the value of (−0.3B+0.09), the strength of the side rubber will decrease. Also, if the tan δ value at 60° C. is greater than the value of (−0.3B+0.14), the heat buildup of the side rubber will increase and the rolling resistance will deteriorate.

The free sulfur content B is 0% or more and 0.2% or less, preferably more than 0% and 0.15% or less, more preferably 0.05% or more and 0.15% or less. If the amount of free sulfur B exceeds 0.2%, the properties of vulcanized rubber cannot be obtained. Moreover, by making the amount of free sulfur B larger than 0%, heat buildup can be reduced, which is preferable.

In this specification, the free sulfur content B is the content (%) of sulfur not participating in vulcanization in the side rubber measured by the sodium sulfite method according to JIS K6234.

The rubber composition constituting the side rubber that satisfies the above formula (1) and preferably satisfies the above formula (2) is preferably 30 to 80% by mass of natural rubber and 20 to 70% by mass of butadiene rubber, and 100 mass of diene rubber. 35 to 50 parts by mass of carbon black having a nitrogen adsorption specific surface area of 20 to 130 m ² /g, 0.5 to 1.0 parts by mass of a sulfenamide vulcanization accelerator, and 1.0 to 1.0 parts by mass of sulfur. 2.0 parts by mass is blended, and the ratio (Va/S) of the blending amount (Va) of the sulfenamide-based vulcanization accelerator and the blending amount (S) of sulfur is preferably 0.3 to 0.7. .

As the natural rubber, those commonly used in rubber compositions for tires can be used, and modified natural rubbers may also be used. The content of natural rubber is preferably 30 to 80% by mass, more preferably 35 to 70% by mass, and still more preferably 40 to 65% by mass based on 100% by mass of diene rubber. If the content of natural rubber is less than 30% by mass, cut resistance deteriorates. On the other hand, if the content of natural rubber exceeds 80% by mass, the crack resistance is lowered.

The content of the butadiene rubber is preferably 20 to 70% by mass, more preferably 30 to 65% by mass, and still more preferably 35 to 60% by mass based on 100% by mass of the diene rubber. By containing butadiene rubber, crack resistance can be improved. If the content of butadiene rubber is less than 20% by mass, the crack resistance is lowered. On the other hand, when the content of butadiene rubber exceeds 70% by mass, the tensile strength at break of the rubber composition is lowered, and the cut resistance is deteriorated when used as a heavy-duty tire.

In the rubber composition constituting the side rubber, preferably 35 to 50 parts by mass, more preferably 37 to 47 parts by mass of carbon black are blended with 100 parts by mass of the above diene rubber. By blending 35 parts by mass or more of carbon black, the strength of the side rubber can be ensured. By blending 50 parts by mass or less of carbon black, heat build-up can be reduced. Carbon black can be blended singly or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20-130 m ² /g, more preferably 40-100 m ² /g. If the N ₂ SA of the carbon black is less than 20 m ² /g, the crack resistance may deteriorate. On the other hand, when the N ₂ SA of carbon black exceeds 130 m ² /g, there is a possibility that the heat build-up of the side rubber may deteriorate. In this specification, the N ₂ SA of carbon black shall be measured according to JIS K6217-2.

In the present invention, inorganic fillers other than carbon black can be blended. Other inorganic fillers include silica, clay, talc, mica, calcium carbonate, and the like. By blending other inorganic fillers, the rubber composition becomes inexpensive.

The rubber composition constituting the side rubber is preferably 0.5 to 1.0 parts by mass, more preferably 0.6 to 0.9 parts by mass of a sulfenamide vulcanization accelerator to 100 parts by mass of the diene rubber described above. It is preferable to mix parts by mass. Addition of 0.5 parts by mass or more of the sulfenamide-based vulcanization accelerator improves the heat build-up of the side rubber. Moreover, by blending 1.0 parts by mass or less of the sulfenamide-based vulcanization accelerator, the crack resistance is improved.

For the rubber composition constituting the side rubber, preferably 1.0 to 2.0 parts by mass, more preferably 1.2 to 1.8 parts by mass of sulfur are blended with 100 parts by mass of the diene rubber described above. Addition of 1.0 parts by mass or more of sulfur improves the heat build-up of the side rubber. Moreover, by blending 2.0 parts by mass or less of sulfur, the crack resistance is improved.

The ratio (Va/S) of the blending amount (Va) of the sulfenamide-based vulcanization accelerator to the blending amount (S) of sulfur is preferably 0.3 to 0.7, more preferably 0.4 to 0.4. 6 is preferable. When performing vulcanization suitable for other tire members such as the tread portion and the bead portion by setting the ratio (Va/S) of the amount of the sulfenamide-based vulcanization accelerator to sulfur to be 0.3 or more, It becomes easier to adjust the vulcanization conditions so that the amount of free sulfur becomes a predetermined amount. Also, by setting the ratio (Va/S) of the amount of the sulfenamide-based vulcanization accelerator to the amount of sulfur to be 0.7 or less, the crack resistance is improved.

Various additives commonly used in rubber compositions for tires, such as vulcanization retarders, antioxidants, peptizers, various oils, and plasticizers, are added to the rubber composition constituting the side rubber of the present invention. These additives can be kneaded by a common method to prepare a rubber composition and used for vulcanization or crosslinking.

The vulcanization conditions for producing the side rubber are such that the amount of free sulfur in the vulcanized side rubber is preferably 0 to 0.2%, more preferably more than 0% to 0.15%, still more preferably 0.05 to 0. The vulcanization temperature and vulcanization time should be adjusted with reference to the formulation of the rubber composition constituting the side rubber so as to achieve 15%. The vulcanization temperature for producing the side rubber is preferably 120 to 170°C, more preferably 130 to 160°C. Further, the vulcanization time is preferably 5 to 160 minutes, more preferably 20 to 60 minutes.

The pneumatic tire of the present invention has improved crack resistance and low rolling resistance over conventional levels, and is particularly suitable as a heavy-duty pneumatic tire for use in large vehicles such as trucks and buses.

EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

Twelve kinds of rubber compositions (Examples 1 to 6 and Comparative Examples 1 to 6) having a common formulation of the compounding agents shown in Table 2 and having the compounding shown in Table 1 were vulcanized using sulfur and a vulcanization accelerator. After kneading the ingredients except the sulfur-based compounding agent for 5 minutes in a 1.7 L internal Banbury mixer, the mixture was discharged from the mixer and cooled to room temperature. A rubber composition for a tire was prepared by putting this into a 1.7 L internal Banbury mixer, adding sulfur and a vulcanization accelerator, and mixing. The compounding amounts of the compounding agents shown in Table 2 are shown in parts by mass with respect to 100 parts by mass of the diene rubber shown in Table 1.

Using a mold of a predetermined shape, the obtained rubber composition was vulcanized and molded based on the vulcanization temperature and vulcanization time shown in Table 1 to prepare a test sample, which was then cured to 60°C by the method shown below. tan δ, swelling degree A and free sulfur content B were measured.

tan δ (60°C)
The dynamic viscoelasticity of the obtained test sample was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz, and tan δ at a temperature of 60 ° C. was obtained. . The results obtained are shown in Table 1 in the column "tan δ at 60°C".

Swelling degree A
The swelling degree A of the test sample was immersed in toluene at room temperature for 3 days according to JIS K6258, and the mass change (%) was measured. Assuming that the mass of the test sample before immersion is M0 and the mass of the test sample after immersion is M1, the degree of swelling A is obtained by the following formula.
A (%) = M1/M0 x 100 (%)
The obtained results are shown in the column of "swelling degree A" in Table 1. Also, the values (0.0006A-0.083) and (0.0006A-0.038) of formula (1) calculated from the degree of swelling A were determined and shown in Table 1.

Free sulfur content B
The free sulfur content B of the test sample was measured by the sodium sulfite method according to JIS K6234. The obtained results are shown in the column of "Amount of free sulfur B" in Table 1. Also, the values (-0.3B+0.09) and (-0.3B+0.14) of formula (2) calculated from the amount of free sulfur B were determined and shown in Table 1.

Twelve types of heavy-duty pneumatic tires (tire size 11R22.5, truck bus tires) using the rubber composition obtained above as the side rubber were vulcanized and molded, and the rolling resistance and crack resistance were measured by the following test methods. was measured.

Rolling resistance The heavy-duty pneumatic tire obtained above was mounted on a standard rim, filled with air pressure of 1000 kPa, and subjected to an indoor drum tester conforming to JIS D4230 with a drum diameter of 1707 mm, a test load of 4.82 kN, and a speed of 80 km/h. The resistance was measured and used as the rolling resistance. The obtained results are shown in the "rolling resistance" column of Table 1 as an index with the value of Comparative Example 1 set to 100. The smaller the index, the lower the rolling resistance. If the index is 105 or less, it is considered that the rolling resistance is below the conventional level.

Crack resistance After the heavy-duty pneumatic tire obtained above was run on a public road for 100,000 km, the number of cracks generated in the side rubber per tire was taken as an index of crack resistance, and the number of cracks in Comparative Example 1. was set to 100. The obtained results are shown in the "crack resistance" column of Table 1 as an index with the value of Comparative Example 1 set to 100. The larger the index, the better the crack resistance. If the index is 105 or more, the crack resistance is considered to be superior to the conventional level.

The types of raw materials used in Table 1 are shown below.
・NR: natural rubber, TSR20
・ BR: NIPOL BR1220 (unmodified BR, manufactured by Nippon Zeon Co., Ltd.), the content of cis 1,4 bonds is 96%
CB: HAF grade carbon black, Showa Cabot Show Black N330, nitrogen adsorption specific surface area: 75 m ² /g
・Vulcanization accelerator: sulfenamide-based vulcanization accelerator, Noccellar NS-P manufactured by Ouchi Shinko Kagaku Co., Ltd.
・ Sulfur: Sulfax 5 manufactured by Tsurumi Chemical Industry Co., Ltd.

The types of raw materials used in Table 2 are shown below.
・Oil: VIVATEC500 manufactured by H&R Chemicals
· Anti-aging agent 1: Nocrack 6C manufactured by Ouchi Shinko Chemical Co., Ltd.
・ Anti-aging agent 2: Nonflex RD manufactured by Seiko Chemical Co., Ltd.
・Wax: Sannok, manufactured by Ouchi Shinko Kagaku Co., Ltd. ・Stearic acid: Bead stearic acid, manufactured by NOF Corporation ・Zinc oxide: 3 types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.

As is clear from Table 1, the pneumatic tires of Examples 1 to 6 are excellent in low rolling resistance and crack resistance.

The pneumatic tires of Comparative Examples 2 and 3 are outside the range of formula (1), and as is clear from the fact that the amount of free sulfur B is excessive, the side rubber is close to an unvulcanized state, and the rolling resistance deteriorates. However, the crack resistance was lowered, and the characteristics as a pneumatic tire could not be obtained.
The pneumatic tire of Comparative Example 4 was outside the range of formula (1), had low strength of the side rubber, and had low crack resistance.
The pneumatic tire of Comparative Example 5 was out of the range of formula (1), had a high degree of swelling of the side rubber, and had low crack resistance.
The pneumatic tire of Comparative Example 6 was outside the range of formula (1), and had poor heat build-up and poor rolling resistance.

1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 belt layer 7 inner liner 8 side rubber 9 tread rubber

Claims (4)

The swelling degree A and tan δ at 60° C. of the side rubber constituting the sidewall portion satisfy the following formula (1), and the side rubber is a diene system consisting of 30 to 80% by mass of natural rubber and 20 to 70% by mass of butadiene rubber. 100 parts by mass of rubber, 35 to 47 parts by mass of carbon black having a nitrogen adsorption specific surface area of 20 to 130 m ² /g, 0.5 to 1.0 parts by mass of a sulfenamide vulcanization accelerator, and 1 part of sulfur .2 to 1.8 parts by mass, and the ratio (Va/S) of the amount (Va) of the sulfenamide vulcanization accelerator to the amount (S) of sulfur is 0.47 to 0.47. 59. A pneumatic tire characterized by comprising a rubber composition of No. 59 .
0.0006A-0.083≤tan δ≤0.0006A-0.038 (1)
(In the formula, tan δ is tan δ at 60° C., A is the degree of swelling (%) when immersed in toluene at room temperature for 3 days, and 220≦A≦340.) The pneumatic tire according to claim 1, wherein the free sulfur content B of the side rubber and tan δ at 60°C satisfy the following formula (2).
−0.3B+0.09≦tan δ≦−0.3B+0.14 (2)
(In the formula, tan δ is tan δ at 60° C., and B is the amount of free sulfur (%) measured based on JIS K6234, and 0≦B≦0.2.) The pneumatic tire according to claim 1 or 2, wherein the tan δ at 60°C is 0.07 or more and 0.14 or less. The pneumatic tire according to any one of claims 1 to 3 , which is a tire for heavy loads.

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