JP4602718B2 - Rubber composition for tire sidewall and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition for a tire sidewall used for a sidewall portion of a pneumatic tire, and a pneumatic tire.

  Conventionally, many tread rubber development studies have been conducted as part of reducing tire hysteresis loss in order to improve tire performance and reduce fuel consumption of automobiles. As a result, tire rolling resistance has been greatly reduced. It is being done. However, in order to further reduce the rolling resistance, when trying to reduce the hysteresis loss only by blending the rubber in the tread portion, other measures such as wear resistance are lowered, so this measure has a limit.

  Therefore, it is desirable to reduce the rolling resistance at a portion other than the tread portion, and such a proposal has been made.

  For example, in Patent Document 1 below, in a rubber composition for a tire sidewall, 5 to 50 parts by weight of carbon black having a specific average particle diameter, a compressed DBP oil absorption amount and a CTAB surface area with respect to 100 parts by weight of a diene rubber. And 10 to 60 parts by weight of precipitated silica having a specific DBP oil absorption amount and BET nitrogen adsorption specific surface area, and a specific amount of a silane coupling agent, the rolling resistance is small, the wear resistance, WET It is described that a tire having excellent performance and low electrical resistance can be obtained.

Patent Document 2 below describes that rolling resistance is reduced by limiting the loss tangent tan δ and the complex elastic modulus E * of each rubber around the bead portion of the tire to a certain range.
JP 10-36559 A JP 2002-178724 A JP-A-3-210345

  The inventor paid attention to a portion other than the tread portion in order to reduce the rolling resistance, and the side wall portion has a lower contribution ratio to the rolling resistance than the tread portion, but the hysteresis of the side wall rubber is other portion. Therefore, it was considered that rolling resistance can be reduced if the hysteresis loss of the sidewall rubber is greatly reduced. As a result of various studies on the rubber composition of the sidewall portion, the fatigue resistance required for the sidewall portion is obtained by combining a specific butadiene rubber synthesized using a neodymium catalyst and a specific carbon black. It has been found that the rolling resistance of tires can be reduced without impairing the properties and cut resistance.

  That is, an object of the present invention is to provide a tire sidewall rubber composition capable of reducing tire rolling resistance and reducing fuel consumption without impairing fatigue resistance and cut resistance, and air using the same. The purpose is to provide tires.

  In Patent Document 3, a rubber composition comprising 30 to 90 parts by weight of a butadiene rubber polymerized using a neodymium catalyst, 5 to 30 parts by weight of a halogenated butyl rubber, and the balance of natural rubber or the like is used for a tire. Is disclosed. However, the rubber composition of Patent Document 3 is used for the tread part, and not only the use site is different from the present invention used for the sidewall part, but also its purpose is to improve the safety of running on snowy and snowy roads. The present invention is intended to enable traveling without trouble on general roads, and is different from the present invention aimed at reducing rolling resistance, and therefore does not suggest the present invention at all.

A rubber composition for a tire sidewall according to the present invention that solves the above problems is a rubber comprising 30 to 60% by weight of a butadiene rubber polymerized using a neodymium catalyst and 70 to 40% by weight of another diene rubber. relative to 100 parts by weight of component a nitrogen adsorption specific surface area of 35~120m ² / g, I der those DBP oil absorption contains 30 to 50 parts by weight of carbon black is 90cm ^3/100 g or more, at 0.99 ° C. The vulcanized product vulcanized for 30 minutes has a hardness measured according to JIS K 6253 type A durometer of 50 to 60, and an initial strain of 15% and dynamic strain using a viscoelastic spectrometer. The tan δ measured under the conditions of ± 2.5%, frequency 10 Hz, temperature 60 ° C. is 0.05 to 0.1.

In the rubber composition for a tire sidewall according to the present invention, it is preferable that the Mooney viscosity (ML1 + 4) at 100 ° C. measured according to JIS K6300 of the butadiene rubber is 44 or more.

  In addition, the pneumatic tire according to the present invention is formed by making a sidewall portion using the rubber composition for a tire sidewall.

  According to the present invention, by using the above-mentioned specific butadiene rubber and specific carbon black in combination, the rolling resistance of the tire is reduced without impairing the fatigue resistance and cut resistance required for the sidewall portion. This can reduce fuel consumption.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

In the rubber composition of the present invention, the butadiene rubber used as the rubber component is polymerized using a neodymium catalyst. By using butadiene rubber synthesized with such a neodymium-based catalyst, tan δ of the vulcanized rubber can be lowered as compared with the case of using butadiene rubber polymerized with other catalysts such as cobalt-based catalysts. Rolling resistance can be reduced. Here, examples of the neodymium-based catalyst include neodymium alone, a compound of neodymium and other metals, and an organic compound, and specific examples thereof include NdCl ₃ , Et-NdCl _{2, and the} like.

  As the butadiene rubber, it is preferable to use a high molecular weight butadiene rubber having a Mooney viscosity of 44 or more in order to enhance the effect of the present invention. More preferably, a butadiene rubber having a Mooney viscosity of 50 or more is used. The upper limit of Mooney viscosity is not particularly limited, but is preferably 70 or less. In the present invention, the Mooney viscosity is a Mooney viscosity (ML1 + 4) at 100 ° C. measured according to JIS K6300.

  A butadiene rubber synthesized with a neodymium catalyst generally has a microstructure with a high cis content and a low vinyl content. In the present invention, the microstructure of the butadiene rubber is not particularly limited. Preferably, the butadiene rubber having a cis-1,4 bond content of 95% or more and a vinyl group content of 1.8% or less is used. That is. The cis-1,4 bond content is more preferably 97% or more, and the vinyl group content is more preferably 1.0% or less. In addition, these cis content and vinyl content are values measured using a nuclear magnetic resonance apparatus (NMR).

  In the rubber composition of the present invention, the rubber component is composed of a blend rubber of 30 to 60% by weight of the butadiene rubber and 70 to 40% by weight of another diene rubber. When the blending ratio of the butadiene rubber is less than 30% by weight, the bending fatigue resistance is poor. On the other hand, when the blending ratio of the butadiene rubber exceeds 60% by weight, the cut resistance is inferior and the rolling resistance reducing effect is also inferior. Examples of other diene rubbers include natural rubber, isoprene rubber, styrene butadiene rubber, butadiene rubber polymerized by other than neodymium catalyst, and these may be used alone or in combination of two or more. . Preferably, natural rubber and / or isoprene rubber is used.

Carbon black used in the rubber composition of the present invention, the nitrogen adsorption specific surface area _(N 2 SA) is 35~120m ² / g, and, DBP (dibutyl phthalate) oil absorption of 90cm ^3/100 g or more Is.

The nitrogen adsorption specific surface area is a value measured according to JIS K6217. When this value is less than 35 m ² / g, the reinforcing property is low and the fatigue resistance and cut resistance required for the sidewall portion are satisfied. I can't. On the other hand, when the nitrogen adsorption specific surface area exceeds 120 m ² / g, the effect of reducing rolling resistance is inferior. As for the more preferable range of a nitrogen adsorption specific surface area, a minimum is 40 m < ² > / g and an upper limit is 100 m < ² > / g.

DBP oil absorption is measured according to JIS K6217, is intended to be a structure of an index of carbon black, when the value is less than 90cm ^3/100 g, fatigue resistance, cut resistance required as the sidewall portion I can not satisfy the sex. The upper limit of the DBP oil absorption amount is not particularly ^limited, is preferably 150 cm 3/100 g or less, and more preferably not more than 130 cm ^3/100 g.

  The compounding amount of the carbon black is 30 to 50 parts by weight with respect to 100 parts by weight of the rubber component. If the amount of carbon black is less than 30 parts by weight, the reinforcing effect will be insufficient and the cut resistance will be reduced. On the other hand, if it exceeds 50 parts by weight, the exothermicity will deteriorate and the effect of reducing rolling resistance will be obtained. Disappear.

  In addition to the above-described components, the rubber composition of the present invention includes tire fillers such as inorganic fillers such as silica, anti-aging agents, zinc white, stearic acid, softeners, vulcanizing agents, vulcanization accelerators, and the like. Various additives generally used in rubber compositions for rubber can be blended.

Tire sidewall rubber composition of the present invention, is 30 minutes vulcanised vulcanized at 0.99 ° C. Ru der those having the following physical properties. In other words, the hardness of the pressurized vulcanizates is Ru 50-60 der. In the present invention, the hardness is a value measured according to JIS K 6253 type A durometer, and if this value is out of the above range, it is difficult to ensure the performance required for the sidewall portion of the tire. .

In addition, the pressurized vulcanizates is, tanδ is Ru der 0.05 to 0.1. In the present invention, tan δ is a loss tangent measured using a viscoelastic spectrometer under conditions of an initial strain of 15%, a dynamic strain of ± 2.5%, a frequency of 10 Hz, and a temperature of 60 ° C., and this value is 0. If the ratio exceeds 1, the rolling resistance improvement effect will be insufficient.

  The rubber composition for a tire sidewall of the present invention comprising the above is used as a rubber composition for a sidewall portion of a pneumatic radial tire, and the sidewall portion is formed by vulcanization molding according to a conventional method. Can do. The rubber composition of the present invention is particularly suitable for sidewalls of heavy-duty tires used in large vehicles such as trucks and buses, but is not limited thereto, and is also applicable to passenger car tires. Can do.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a rubber composition for a sidewall was prepared according to the formulation shown in Table 1 below. The details of each formulation in Table 1 are as follows.

・ NR: Natural rubber (RSS 3)
Co-BR: “BR150B” manufactured by Ube Industries (Butadiene rubber polymerized with a cobalt catalyst, Mooney viscosity (ML1 + 4) = 41, cis-1,4 bond content = 96%, vinyl group content = 2%) .

Nd-BR1: “Buna CB22” manufactured by Bayer (butadiene rubber polymerized with a neodymium catalyst, Mooney viscosity (ML1 + 4) = 63, cis-1,4 bond content = 97%, vinyl group content = 0.2 %).

-Nd-BR2: "Neocis BR60" manufactured by Enichem (butadiene rubber polymerized with a neodymium catalyst, Mooney viscosity (ML1 + 4) = 63, cis-1,4 bond content = 98%, vinyl group content = 0.5 %).

Nd-BR3: “Buna CB25” manufactured by Bayer (butadiene rubber polymerized with a neodymium catalyst, Mooney viscosity (ML1 + 4) = 44, cis-1,4 bond content = 97%, vinyl group content = 0.2 %).

ISAF: “Seast 6” manufactured by Tokai Carbon (nitrogen adsorption specific surface area = 119 m ² / g, DBP oil absorption = 114 ml / 100 g).

HAF: “Seast 3” manufactured by Tokai Carbon (nitrogen adsorption specific surface area = 79 m ² / g, DBP oil absorption = 101 ml / 100 g).

FEF: “Seast SO” manufactured by Tokai Carbon (nitrogen adsorption specific surface area = 42 m ² / g, DBP oil absorption = 115 ml / 100 g).

GPF: “Seast V” manufactured by Tokai Carbon (nitrogen adsorption specific surface area = 27 m ² / g, DBP oil absorption = 87 ml / 100 g).

  In each rubber composition, as a common compound, 2 parts by weight of zinc white (“Zinc Flower 3” manufactured by Mitsui Kinzoku Mining), 2 parts by weight of stearic acid (“Lunac S-20” manufactured by Kao), an anti-aging agent (Sumitomo) 5 parts by weight of “Antigen 6C” manufactured by Chemical Industry, 1 part by weight of wax (“OZOACE-0355” manufactured by Nippon Seiwa), 1 part by weight of vulcanization accelerator (“Soccele CZ” manufactured by Sumitomo Chemical), sulfur (Tsurumi Chemical) 2 parts by weight of industrial “powder sulfur”) was blended.

  About each obtained rubber composition, it vulcanizes at 150 degreeC x 30 minutes, and produces the test piece of a predetermined shape, Hardness, cut resistance, bending fatigue resistance, loss factor using the obtained test piece Tan δ was measured. The measurement method was as described above for hardness and tan δ, cut resistance was measured according to JIS K6252, and flexural fatigue resistance was measured according to JIS K6260. Regarding cut resistance and flex fatigue resistance, Comparative Example 1 was used as a control, and “◯” was evaluated if it was equivalent to this, and “X” was evaluated if it was worse than Comparative Example 1. The results are shown in Table 1.

Further, using each rubber composition as a rubber for a sidewall, a trial tire of 11R22.5 14PR size for truck and bus was prepared, and rolling resistance was evaluated. The rolling resistance was evaluated by measuring the rolling resistance when running on the drum at an internal pressure of 800 kPa, a load of 2900 kg, and a speed of 60 km / h using a uniaxial drum tester, and the tire of Comparative Example 1 was taken as 100. Expressed as an index. The smaller the index, the smaller the rolling resistance and the better the fuel efficiency. The results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 6 according to the present invention, the bending fatigue resistance and cut resistance are impaired as compared with Comparative Example 1 using butadiene rubber polymerized with a cobalt-based catalyst. The rolling resistance has been reduced and fuel consumption has been reduced. In Comparative Example 2, since the blending amount of carbon black is less than the prescribed value, the cut resistance is inferior. In Comparative Example 3, the blending amount of carbon black exceeds the prescribed value, the hardness is high, and tan δ The rolling resistance reduction effect was not recognized. Moreover, in the comparative example 4, since carbon black was not a thing specific to this invention, it was inferior to cut resistance and bending fatigue resistance. Furthermore, in Comparative Example 5, since the blending amount of butadiene rubber was less than the specified value, the bending fatigue resistance was inferior, and the rolling resistance reduction width was small. In Comparative Example 6, since the blending amount of the butadiene rubber exceeded the specified value, the cut resistance was inferior and the reduction width of the rolling resistance was small.

Claims (3)

For 100 parts by weight of a rubber component composed of 30 to 60% by weight of butadiene rubber polymerized using a neodymium catalyst and 70 to 40% by weight of another diene rubber,
A nitrogen adsorption specific surface area of 35~120m ² / g, be those DBP oil absorption contains 30 to 50 parts by weight of carbon black is 90cm ^3/100 g or more,
About the vulcanizate vulcanized at 150 ° C. for 30 minutes, the hardness measured according to JIS K 6253 type A durometer is 50-60, and using a viscoelastic spectrometer, the initial strain is 15%, A rubber composition for a tire sidewall , wherein tan δ measured under conditions of dynamic strain ± 2.5%, frequency 10 Hz, temperature 60 ° C. is 0.05 to 0.1 . The rubber composition for a tire sidewall according to claim 1, wherein the butadiene rubber has a Mooney viscosity (ML1 + 4) at 100 ° C measured in accordance with JIS K6300 of 44 or more. A pneumatic tire obtained by making the side wall portion in the rubber composition according to claim 1 or 2.