JP7234758B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire having a tread portion made of a rubber composition in which silica and/or carbon black are blended with diene rubber.

In recent years, as the performance of vehicles has improved and the required performance has become more sophisticated, there has been a demand for a rubber composition that constitutes the tread portion of a pneumatic tire to achieve both a reduction in rolling resistance and an increase in hardness. Various countermeasures have been taken for this purpose (see, for example, Patent Document 1), but in a tire that achieves both a reduction in rolling resistance and an increase in hardness, the crosslink density of the rubber composition generally increases. Tend. When the crosslink density increases in this way, the elongation at break of the rubber composition may decrease and the chipping resistance may deteriorate. There is a demand for measures to maintain good properties.

JP 2016-104840 A

An object of the present invention is to provide a pneumatic tire having a tread portion composed of a rubber composition in which silica and/or carbon black are blended with a diene rubber, the pneumatic tire having excellent chipping resistance. to provide.

The pneumatic tire of the present invention for achieving the above object comprises a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a tire of these sidewall portions. A pneumatic tire comprising a pair of bead portions arranged radially inward, wherein the tread portion is a cured rubber composition in which silica and/or carbon black are blended with diene rubber. The tensile product TB × EB calculated as the product of the strength at break TB [MPa] and the elongation at break EB [%] of the cured product, and the secant elastic modulus MA [MPa] of the cured product ] and the difference ΔHs between the initial hardness of the cured product and the hardness after aging treatment under the conditions of 60 ° C. × 336 hours, Log (TB × EB) > 3.85, MA < 5.3 MPa, It is characterized by satisfying the relationships of ΔHs<5.0 and ΔHs<9.0×Log(TB×EB)−31.

As a result of intensive research on the physical properties of the cured rubber composition constituting the tread portion of a pneumatic tire, the inventor of the present invention found that the tensile product TB, which is calculated as the product of the tensile strength TB and the breaking elongation EB, If the EB, the secant modulus MA, and the difference ΔHs between the initial hardness and the hardness after aging treatment under the conditions of 60° C. for 336 hours satisfy the above-mentioned relationship, the pneumatic tire can be obtained. It was found that excellent chipping resistance can be exhibited when used in the tread portion of. Therefore, in the pneumatic tire of the present invention, the cured product of the rubber composition forming the tread portion has the above-described composition and physical properties, so that chipping resistance can be improved.

Regarding the tensile product of the rubber composition, the strength at break TB and the elongation at break EB of the rubber composition were obtained by punching out a JIS No. 3 dumbbell-shaped test piece (thickness: 2 mm) in accordance with JIS K6251 and measuring the temperature at 20°C. , stress at break (strength at break, unit: MPa) and elongation at break (elongation at break, unit: %) measured under the condition of a tensile speed of 500 mm/min. Also, the logarithm Log(TB×EB) of the tensile product TB×EB is the common logarithm. The secant elastic modulus MA of the rubber composition is an elastic modulus (unit: MPa) obtained by connecting the origin of the stress-strain curve and the point giving the maximum deflection in the measurement range in accordance with JIS K6254. The hardness of the rubber composition shall be measured at a temperature of 20° C. under each condition with a durometer type A according to JIS K6253.

In the present invention, the rubber composition preferably contains silica, and the amount of silica compounded is 30 parts by mass to 200 parts by mass with respect to 100 parts by mass of the diene rubber. As a result, the physical properties of the cured product of the rubber composition forming the tread portion are further improved, which is advantageous for improving the chipping resistance.

1 is a meridional cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention; FIG.

The pneumatic tire of the present invention comprises a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portion 2. It has Although FIG. 1 is a meridional sectional view and is not depicted, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction and form an annular shape. A toroidal basic structure is constructed. All of the other tire constituent members depicted in the meridional cross-sectional view also extend in the tire circumferential direction and form an annular shape unless otherwise specified.

A carcass layer 4 is mounted between the pair of left and right bead portions 3 . The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the vehicle inner side to the outer side around bead cores 5 arranged in the respective bead portions 3 . A bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4. - 特許庁On the other hand, a plurality of belt layers 7 (two layers in FIG. 1) are embedded in the outer peripheral side of the carcass layer 4 in the tread portion 1 . Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, a belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7 . The belt reinforcing layer 8 contains organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the organic fiber cords with respect to the tire circumferential direction is set to 0° to 5°, for example.

A tread rubber layer 11 is arranged on the outer peripheral side of the carcass layer 4 in the tread portion 1, a side rubber layer 12 is arranged on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a side rubber layer 12 is arranged on the bead portion 3. A rim cushion rubber layer 13 is arranged on the outer peripheral side (the outer side in the tire width direction) of the carcass layer 4 . The tread rubber layer 11 may have a structure in which two types of rubber layers (a cap tread rubber layer and an undertread rubber layer) having different physical properties are laminated in the tire radial direction.

The pneumatic tire of the present invention includes a tire rubber composition (hereinafter referred to as "the tire rubber composition of the present invention") constituting the tread rubber layer 11 of these rubber layers, and a cured product thereof (hereinafter referred to as "the present rubber composition"). The physical properties of the cured product of the invention) are not limited to those described above.

In the rubber composition for tires of the present invention, the rubber component is a diene rubber, such as natural rubber, butadiene rubber, isoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. rubbers commonly used for These diene rubbers may be end-modified rubbers. These diene rubbers can be used alone or as any blend.

The rubber composition for tires of the present invention always contains silica and/or carbon black as a filler. By blending these fillers, the rubber strength and rubber hardness of the rubber composition can be improved. Both silica and carbon black that are commonly used in rubber compositions for tires can be used. That is, as silica, for example, wet-process silica, dry-process silica, and surface-treated silica can be used. As the carbon black, for example, those classified according to ASTM 1765 of SAF grade, ISAF grade, HAF grade, GPF grade, and FEF grade can be used.

When silica is used as a filler, the amount of silica compounded is preferably 30 to 200 parts by mass, more preferably 50 to 150 parts by mass, per 100 parts by mass of the diene rubber. When the silica content is less than 30 parts by mass, the secant elastic modulus and breaking strength are lowered. If the amount of silica added exceeds 200 parts by mass, the breaking strength decreases.

When carbon black is used as a filler, the amount of carbon black compounded is preferably 5 parts by mass to 100 parts by mass, more preferably 15 parts by mass to 80 parts by mass, with respect to 100 parts by mass of the diene rubber. . If the amount of carbon black is less than 5 parts by mass, the secant elastic modulus is excessively lowered. If the amount of carbon black to be blended exceeds 100 parts by mass, there is a risk that the breaking strength and breaking elongation will decrease due to an excessive increase in the secant modulus of elasticity.

In the present invention, fillers other than silica and carbon black can be blended. Examples of other fillers include clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, titanium oxide and the like. By blending other fillers, the mechanical properties of the rubber composition can be further improved. These other fillers can be used alone or in any blend.

When silica is used as a filler, a silane coupling agent can be used together in order to improve the dispersibility of silica. When a silane coupling agent is used, its content is preferably 3% to 20% by weight, more preferably 4% to 15% by weight, based on the weight of silica. If the amount of the silane coupling agent is less than 3% by weight, the dispersibility of silica cannot be sufficiently improved. If the amount of the silane coupling agent is more than 15% by weight, the rubber composition tends to undergo premature vulcanization, possibly deteriorating moldability.

The silane coupling agent is not particularly limited as long as it can be used in rubber compositions for tires. -triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthio-1-propyltriethoxysilane (NXT), and the like. These silane coupling agents may be blended singly or in combination.

Furthermore, compounding agents other than those described above can be added to the rubber composition for tires of the present invention. Examples of other compounding agents include various compounding agents commonly used in rubber compositions for tires, such as vulcanizing agents or cross-linking agents, vulcanization accelerators, anti-aging agents, plasticizers, and processing aids. can be done. The blending amount of these compounding agents can be a conventional general blending amount as long as it does not contradict the object of the present invention. Such a rubber composition for tires can be produced by mixing each of the above components using a common rubber kneading machine such as a Banbury mixer, a kneader, and a roll.

The tread portion 1 (tread rubber layer 11) of the pneumatic tire of the present invention is composed of a cured product of the various tire rubber compositions described above, and the cured product (cured product of the present invention) has a strength at break. Tensile product TB×EB calculated as the product of TB and elongation at break EB, secant elastic modulus MA, and initial hardness and hardness after thermal aging treatment at a temperature of 60° C. for 336 hours. The difference ΔHs (hereinafter referred to as “hardness change amount ΔHs”) satisfies a specific relationship described later. That is, as long as the physical properties of the cured product satisfy the relationships described later, the specific compounding of the rubber composition for tires of the present invention is not particularly limited. Therefore, the composition of the rubber composition of the present invention can be arbitrarily set according to the tire performance to be emphasized other than the improvement of the chipping resistance which is the main purpose of the present invention.

The tensile product TB×EB of the cured product of the present invention satisfies the relationship of Log(TB×EB)>3.85, preferably 3.90≦Log(TB×EB)≦4.50. The secant modulus MA of the cured product of the present invention satisfies the range of MA<5.3 MPa, preferably 2.00 MPa≦MA≦7.00 MPa. Furthermore, the amount of change in hardness ΔHs of the cured product of the present invention satisfies the range of ΔHs<5.0, preferably 0≦ΔHs≦4.0. Furthermore, the aforementioned tensile product TB×EB and hardness change amount ΔHs satisfy the relationship ΔHs<9.0×Log(TB×EB)−31. According to the knowledge obtained by the inventors of the present invention through intensive research on the physical properties of the cured rubber composition that constitutes the tread portion of the pneumatic tire, the cured product satisfies the above-described physical properties, thereby improving chipping resistance. can be effectively enhanced. Therefore, the pneumatic tire using the cured tire rubber composition satisfying the above physical properties for the tread rubber layer 11 can exhibit excellent chipping resistance.

If the tensile product TB×EB of the cured product of the present invention satisfies the relationship of Log(TB×EB)≦3.85, chipping resistance deteriorates. If the secant modulus MA of the cured product of the present invention satisfies the relationship of MA≧5.3 MPa, the tensile product is lowered, and as a result, the chipping resistance is deteriorated. When the amount of change in hardness ΔHs of the cured product of the present invention satisfies ΔHs≧5.0, the tensile product is lowered, and as a result, the chipping resistance is deteriorated. If the aforementioned tensile product TB×EB and hardness change amount ΔHs have a relationship of ΔHs≧9.0×Log(TB×EB)−31, chipping resistance deteriorates.

The strength at break TB and the elongation at break EB of the cured product of the present invention are not particularly limited as long as the tensile product TB×EB satisfies the above range. The elongation EB is preferably in the range of 350% or more, for example.

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.

Nine types of rubber compositions for tires (standard example 1, comparative examples 1-2, examples 1-6) having the formulations shown in Table 1 were weighed for each compounding component except the vulcanization accelerator and sulfur. After kneading for 5 minutes in an 8 L internal Banbury mixer, the masterbatch was discharged at a temperature of 150° C. and cooled to room temperature. Thereafter, this masterbatch was supplied to a 1.8 L internal Banbury mixer, a vulcanization accelerator and sulfur were added, and mixed for 2 minutes to prepare a rubber composition for tires.

In addition, "Log (TB × EB)" and "9.0 × Log (TB × EB) -31" in Table 1 are based on JIS K6251 for each rubber composition, JIS No. 3 dumbbell-shaped test piece ( 2 mm thick) is punched out, and the strength at break TB (stress at break, unit: MPa) and elongation at break EB (elongation at break, unit: %) are measured under the conditions of a temperature of 20 ° C and a tensile speed of 500 mm / min. were measured and calculated based on these measurements. "Secant elastic modulus MA" in Table 1 is the elastic modulus (unit: MPa) obtained by connecting the origin of the stress/strain curve and the point giving the maximum deflection in the measurement range (at 300% elongation) in accordance with JIS K6254. ). "Hardness change ΔH" in Table 1 is the initial hardness at a temperature of 20°C with a durometer type A according to JIS K6253, and the aging after performing heat deterioration treatment at 60°C for 336 hours. After the hardness was measured, the difference between them was calculated.

A pneumatic tire (tire size: 205/55R16) having the basic structure shown in FIG. 1 was manufactured using the obtained tire rubber composition for a tread rubber layer, and the presence or absence of chipping was evaluated by the method shown below. did

Presence or absence of chipping Each pneumatic tire was assembled to a wheel with a rim size of 16 inches, mounted on a test vehicle, and the air pressure was set to 230 kPa. It was determined visually. As for the evaluation results, "yes" indicates that chipping occurred, and "no" indicates that no chipping occurred.

The types of raw materials used in Table 1 are shown below.
・SBR1: Solution-polymerized styrene-butadiene rubber, E581 manufactured by Asahi Kasei Corporation
・SBR2: Styrene-butadiene rubber synthesized by the following method ・BR: Butadiene rubber, Nipol 1220 manufactured by Nippon Zeon Co., Ltd.
・NR: natural rubber, RSS#1
・ IR: Isoprene rubber, IR2200 manufactured by Nippon Zeon Co., Ltd.
・ Silica 1: Zeosil 1165MP manufactured by Rhodia
・Silica 2: Dry silica, Tokuyama's Rheoloseal QS300
・ CB: Carbon black, show black N339 manufactured by Cabot Japan Co., Ltd.
- Silane coupling agent 1: bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT), Si69 manufactured by Evonik
- Silane coupling agent 2: VP Si363 manufactured by Evonik
Silane coupling agent 3: (CH ₃ CH ₂ O) ₃ Si(CH ₂ ) ₃ S—CO—(CH ₂ ) ₆ CH ₃ , NXT manufactured by Momentive Performance Materials
・Stearic acid: YR stearate manufactured by NOF
・Zinc oxide: 3 types of zinc oxide manufactured by Seido Chemical Co., Ltd. ・Process oil: Extract No. 4 manufactured by Showa Shell Co., Ltd. ・DEG: Diethylene glycol, manufactured by Nippon Shokubai Co., Ltd. ・Sulfur: Oil treatment sulfur manufactured by Karuizawa Refining Co., Ltd. ・Vulcanization accelerator 1 : NOXCELLER CZ-G manufactured by Ouchi Shinko Kagaku Co., Ltd.
- Vulcanization accelerator 2: PERKACIT DPG manufactured by FLEXSYS

Synthesis method of SBR2 n-BuLi (manufactured by Kanto Chemical Co., Ltd.: 1.60 mol / L (hexane solution), 18 mL, 28.8 mmol), barium bis (2-ethylhexoxide) (Ba (OCH ₂ CH (C ₂ H ₅ ) CH ₂ CH ₂ CH ₂ CH ₃ ) ₂ ) (manufactured by Strem Chemicals: 1 M (toluene/hexane solution) 7.5 mL), trioctyl aluminum (manufactured by Aldrich: 25 wt % (hexane solution), 45 mL) and Of the initiator solution (equivalent to the specific initiator described above) prepared using cyclohexane (manufactured by Kanto Chemical Co., Ltd.: 10 mL), 60 mL was added to 1,3-butadiene (708 g, 13098 mmol) and styrene (manufactured by Kanto Chemical Co., Ltd. : 300 g, 2883 mmol) and 4-tert-butylpyrocatechol (4.79 g, 28.8 mmol) in cyclohexane (4.24 kg) and stirred at 60°C for 14 hours. After cooling to room temperature, methanol (manufactured by Kanto Kagaku Co., Ltd.: 3.44 g) was added to terminate the polymerization. The styrene-butadiene copolymer (Mn=390,000, Mw=550,000) obtained by the above method was used as SBR2.

As is clear from Table 1, the tire rubber compositions of Examples 1 to 6 effectively prevented chipping. On the other hand, in Comparative Example 1, Log (TB×EB) was small and the amount of change in hardness ΔH was large, so the effect of preventing chipping was not obtained. In Comparative Example 2, since the amount of change in hardness ΔH was large, the effect of preventing chipping was not obtained.

1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 11 tread rubber layer 12 side rubber layer 13 rim cushion rubber layer CL tire equator

Claims (2)

A tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inside the tire outer diameter direction of the sidewall portions. A pneumatic tire comprising
The tread portion is composed of a cured product of a rubber composition in which silica and/or carbon black are blended with diene rubber,
Tensile product TB×EB calculated as the product of the strength at break TB [MPa] of the cured product and the elongation at break EB [%], the secant elastic modulus MA [MPa] of the cured product, and the cured product The difference ΔHs between the initial hardness and the hardness after aging treatment under the conditions of 60 ° C. × 336 hours is Log (TB × EB) > 3.85, MA < 5.3 MPa, ΔHs < 5.0, A pneumatic tire characterized by satisfying the relationship ΔHs<9.0×Log(TB×EB)−31. 2. The pneumatic tire according to claim 1, wherein the rubber composition contains silica, and the amount of silica compounded is 30 parts by mass to 200 parts by mass with respect to 100 parts by mass of the diene rubber.

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