JP2006063285A - Rubber composition for tire side wall and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire side wall capable of lowering fuel cost by reducing rolling resistance of a tire without impairing fatigue resistance, cutting resistance and processability. <P>SOLUTION: The rubber composition for a tire side wall comprises 100 pts. wt. rubber component composed of 30-60 wt.% butadiene rubber containing (A) a polybutadiene polymerized by using a neodymium-based catalyst and (B) a terminal-modified polybutadiene having 5-50% cis-1,4 bond content in 1-2 weight ratio (A/B) of the polybutadiene (A) to the polybutadiene (B) and 70-40 wt.% other diene-based rubber and 30-50 pts. wt. carbon black having 35-120 m<SP>2</SP>/g nitrogen adsorption specific surface area and ≥90 cm<SP>3</SP>/100g DBP oil absorption. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.
Japanese Patent Laid-Open No. 10-36559. 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 significantly reduced. As a result of various studies on the rubber composition of the sidewall portion, a blend of polybutadiene synthesized using a neodymium catalyst and a specific low cis polybutadiene was used as a rubber component, and this was used as a specific carbon black. It has been found that the rolling resistance of the tire can be reduced without impairing the fatigue resistance and cut resistance required for the sidewall portion and further without damaging the workability.

  That is, an object of the present invention is to provide a tire sidewall rubber composition that can reduce tire rolling resistance and reduce fuel consumption without impairing fatigue resistance, cut resistance, and workability, and It is to provide a used pneumatic tire.

  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 make it possible to travel without hindrance even 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.

The rubber composition for a tire sidewall according to the present invention that solves the above-described problems includes a polybutadiene (A) polymerized using a neodymium catalyst and a terminal modification having a cis-1,4 bond content of 5 to 50%. The nitrogen adsorption specific surface area is 35 to 120 m ² / g with respect to 100 parts by weight of a rubber component composed of 30 to 60% by weight of butadiene rubber composed of the polybutadiene (B) and 70 to 40% by weight of another diene rubber. in, in which a DBP oil absorption contains 30 to 50 parts by weight of carbon black is 90cm ^3/100 g or more.

  In the tire sidewall rubber composition of the present invention, it is preferable that the weight ratio A / B of the polybutadiene (A) to the polybutadiene (B) is 1 to 2. The Mooney viscosity of the polybutadiene (A) and the Mooney viscosity of the polybutadiene (B) are both preferably 44 or more. Further, the rubber composition preferably has a vulcanizate having a hardness of 50 to 60 and a tan δ of 0.05 to 0.1.

  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, a butadiene rubber composed of a polybutadiene (A) polymerized with a neodymium-based catalyst and a specific low cis polybutadiene (B) and a specific carbon black are used in combination, whereby the resistance required as a sidewall portion is increased. The tire rolling resistance can be reduced while maintaining the workability without impairing the fatigue and cut resistance, and fuel consumption can be reduced.

  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 polybutadiene (A) polymerized using a neodymium-based catalyst, and terminal modification having a cis-1,4 bond content of 5 to 50%. Polybutadiene (B). Thus, by using polybutadiene (A) synthesized with a neodymium catalyst as the butadiene rubber, tan δ of the vulcanized rubber is lowered as compared with the case of using polybutadiene polymerized with another catalyst such as a cobalt catalyst. The rolling resistance of the tire can be reduced. On the other hand, when the polybutadiene (A) synthesized with such a neodymium catalyst is used alone as the butadiene rubber, there is a problem that the workability is impaired as shown in Examples below. Therefore, in this invention, the low cis polybutadiene (B) is used together with the said polybutadiene (A), and, thereby, the fall of workability is prevented.

In the polybutadiene (A), examples of the neodymium 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. Polybutadiene synthesized with such a neodymium-based catalyst generally has a microstructure with a high cis content and a low vinyl content. In the present invention, the microstructure of the polybutadiene (A) is not particularly limited. Preferably, the polybutadiene (A) has a cis-1,4 bond content of 95% or more and a vinyl group content of 1.8% or less. Is to use. 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 addition, as the polybutadiene (A), it is preferable to use a high molecular weight polybutadiene having a Mooney viscosity of 44 or more from the viewpoint of enhancing the effect of the present invention, and more preferably, the Mooney viscosity is 50 or more. The upper limit of Mooney viscosity is not particularly limited, but is preferably 70 or less. In the present invention, the Mooney viscosity is the Mooney viscosity (ML1 + 4) at 100 ° C. measured according to JIS K6300.

  The polybutadiene (B) is composed of a low cis polybutadiene having a cis-1,4 bond content of 5 to 50%, and the polymerization catalyst for the low cis polybutadiene is not particularly limited. For example, an organic Li catalyst is used. It can be prepared by the solution polymerization used. The cis-1,4 bond content is more preferably 30 to 40%.

  In the polybutadiene (B), the low cis polybutadiene needs to be terminal-modified. This is because if low cis polybutadiene that is not terminally modified is blended, the effect of reducing rolling resistance by blending the polybutadiene (A) is impaired. The reason why such a defect is eliminated by using a terminal-modified product is not necessarily clear, but by terminal modification, the interaction between the polymer and carbon black is enhanced, and the polymer terminal that causes hysteresis loss is also eliminated. This is thought to be due to restrained movement.

  As a terminal modification method in the polybutadiene (B), a method of modifying the active terminal of the low cis polybutadiene using a modifier can be used. The modifier is not particularly limited, and examples thereof include ketones such as acetone, benzophenone, aminobenzophenone, and acetylacetone, esters such as ethyl acetate, ethyl adipate, and methyl methacrylate, aldehydes such as benzaldehyde and pyridine aldehyde, and ethylene. Epoxys such as oxide, propylene oxide, 1,2-epoxybutane, 3,4-epoxy-1-butene, glycidyl methyl ether, glycidyl phenyl ether, N, N-dimethylaminopropyl acrylamide, N, N-dimethylaminopropyl N, N-disubstituted aminoalkyl (meth) acrylamide compounds such as methacrylamide, N, N-disubstituted amino such as N, N-dimethylaminoethylstyrene, N, N-diethylaminoethylstyrene N-substituted lactams such as aromatic vinyl compounds, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, N-methyl-ε-caprolactam and the corresponding N-substituted thiolactams , N-substituted ethyleneureas such as 1,3-dimethylethyleneurea, 1,3-diphenylethyleneurea and the corresponding N-substituted thioethyleneureas, 4,4′-bis (dimethylamino) benzophenone, 4,4 ′ N-substituted aminoketones such as bis (diethylamino) benzophenone and corresponding N-substituted aminothioketones, N-substituted aminoaldehydes such as 4-dimethylaminobenzaldehyde, 4-diphenylaminobenzaldehyde and the corresponding N-substituted amino Thioaldehydes, tin tetrachloride, tin tetrabromide, etc. Tin halide, silicon tetrachloride, silicon compounds such as chlorotriethylsilane, and isocyanate compounds such as phenyl isocyanate. As a specific example of such a terminal-modified low cis polybutadiene, polybutadiene “BR1250H” manufactured by Nippon Zeon Co., Ltd. is commercially available as having a terminal group having an active hydrogen-containing group such as a hydroxyl group or an amino group as a modifying group (functional group). And its use is recommended.

  Moreover, as said polybutadiene (B), it is preferable to use the high molecular weight polybutadiene whose Mooney viscosity (ML1 + 4) in 100 degreeC is 44 or more, More preferably, Mooney viscosity is 50 or more. The upper limit of Mooney viscosity is not particularly limited, but is preferably 70 or less.

In the butadiene rubber, the blending ratio of the polybutadiene (A) and the polybutadiene (B) preferably satisfies the following formula in terms of weight ratio.
1 ≤ A / B ≤ 2
If A / B is less than 1, that is, polybutadiene (B) is more, it becomes difficult to ensure cut resistance, and the effect of reducing rolling resistance is inferior. On the other hand, when A / B exceeds 2, the effect of improving workability is reduced.

  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 poor. Examples of other diene rubbers include natural rubber, isoprene rubber, styrene butadiene rubber, and the like. 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. A more preferable range of the nitrogen adsorption specific surface area is a lower limit of 40 m ² / g and an upper limit of 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, it 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.

  The rubber composition for a tire sidewall of the present invention preferably has a vulcanized product having the following physical properties. That is, the hardness of the vulcanizate is preferably 50-60. 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. .

  The vulcanizate preferably has a tan δ of 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 tire sidewall rubber composition of the present invention comprising the above is used as a rubber composition for a sidewall portion of a pneumatic radial tire, and 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)
BR1: “Buna CB22” manufactured by Bayer (polybutadiene polymerized by a neodymium catalyst, Mooney viscosity (ML1 + 4) = 63, cis-1,4 bond content = 97%, vinyl group content = 0.2%).

BR2: “Neocis BR60” manufactured by Enychem (polybutadiene polymerized by a neodymium catalyst, Mooney viscosity (ML1 + 4) = 63, cis-1,4 bond content = 98%, vinyl group content = 0.5%).

BR3: “BR1250H” manufactured by Zeon Corporation (cis-1,4 bond content = 35% low cis polybutadiene, Mooney viscosity (ML1 + 4) = 50, end-modified product).

BR4: “BR150B” manufactured by Ube Industries (polybutadiene polymerized by a cobalt catalyst, Mooney viscosity (ML1 + 4) = 41, cis-1,4 bond content = 96%, vinyl group content = 2%).

BR5: “D.NF35” manufactured by Asahi Kasei (cis-1,4 bond content = 33% low cis polybutadiene, Mooney viscosity (ML1 + 4) = 31, no terminal modification).

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, while evaluating workability, it vulcanizes at 150 ° C x 30 minutes, produces a test piece of a predetermined shape, and using the obtained test piece, hardness, cut resistance, Bending fatigue resistance and loss factor tan δ were 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. Regarding the workability, a case where the roll workability was equal to or higher than that of Comparative Example 1 was evaluated as “◯”, and a case where the roll workability was inferior was evaluated as “X”. 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 trucks and buses was produced, 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, when Examples 1 to 4 according to the present invention are used, Comparative Examples 1 and 7 using polybutadiene polymerized by a cobalt catalyst impair bending fatigue resistance and cut resistance. Without rolling, the rolling resistance has been reduced, and a reduction in fuel consumption has been realized. Further, in Comparative Example 2, by using polybutadiene (BR1) polymerized with a neodymium-based catalyst, the rolling resistance was reduced without impairing the bending fatigue resistance and the cut resistance as in the Examples. Sex was getting worse. On the other hand, when it was Examples 1-4, the reduction effect of rolling resistance, etc. were acquired, without impairing workability.

  In Comparative Example 3, the amount of low cis polybutadiene (BR2) was larger than that of polybutadiene (BR1) polymerized with a neodymium catalyst, and therefore the cut resistance was poor. 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 an unmodified terminal product was used as the low cis polybutadiene, the effect of reducing rolling resistance was inferior. Moreover, in the comparative example 6, since the compounding quantity of butadiene rubber exceeded a regulation value, it was inferior to cut resistance.

Claims (5)

Butadiene rubber 30-60% by weight comprising polybutadiene (A) polymerized using a neodymium-based catalyst and terminal-modified polybutadiene (B) having a cis-1,4 bond content of 5-50%; For 100 parts by weight of a rubber component consisting of 70 to 40% by weight of another diene rubber,
Nitrogen adsorption specific surface area of at 35~120m ² / g, DBP oil absorption amount 90cm ^3/100 g and is a carbon black or tire sidewall rubber composition characterized in that it contains 30 to 50 parts by weight.   The rubber composition for a tire sidewall according to claim 1, wherein a weight ratio A / B of the polybutadiene (A) to the polybutadiene (B) is 1 to 2.   The rubber composition for a tire sidewall according to claim 1 or 2, wherein the Mooney viscosity of the polybutadiene (A) and the Mooney viscosity of the polybutadiene (B) are both 44 or more.   The rubber composition for a tire sidewall according to any one of claims 1 to 3, wherein the vulcanizate has a hardness of 50 to 60 and a tan δ of 0.05 to 0.1.   A pneumatic tire comprising a sidewall portion made of the rubber composition according to claim 1.