JP2005126556A - Rubber composition and tire obtained by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition having excellent processability and reduced rolling resistance characteristics, and a tire using the same for a tread. <P>SOLUTION: The rubber composition comprises a rubber component which comprises at least 50 wt% of a solution polymerization styrene-butadiene rubber having its molecular weight increased by coupling, at most 40 wt% of a natural rubber and at most 40 wt% of a butadiene rubber and contains 1-12 wt% of a low-molecular weight butadiene rubber having a weight-average molecular weight of at most 10,000 and being terminally modified with a functional group selected from the group consisting of a carboxy group, a vinyl group and a hydroxy group. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rubber composition and a tire using the rubber composition, and more particularly to a rubber composition excellent in processability and rolling resistance reduction effect, and a tire using the rubber composition in a tread.

  Conventionally, in order to reduce the rolling resistance of tires, solution-polymerized styrene butadiene rubber (S-SBR) is used as a rubber component, the molecular weight of S-SBR is set high, and the molecular weight distribution has been sharpened. It was. Further, by adding silica as a reinforcing agent, further reduction in fuel consumption has been achieved. However, when silica is blended, it is possible to achieve both reduction in rolling resistance and improvement in wet grip performance, but it is easy to form a gel by combining with a polymer during rubber kneading. When the gel is formed, the dispersibility of the silica is lowered, so that the process problem that the extruded rubber fabric is deteriorated frequently occurs, and the productivity is greatly lowered.

  In order to solve this problem, it is known that the rubber fabric can be improved by using a large amount of low molecular weight polymer or oil. However, if a large amount of oil is used, it will become hard at the end of the run due to the loss of oil. There were various problems such as deterioration of the early wear state.

  In addition, a method of kneading a low molecular weight polymer, for example, a method of adding liquid styrene-butadiene rubber (SBR) after kneading at the time of kneading has been studied, but low molecular weight SBR is a viscous liquid. Therefore, there is a problem that the rolling resistance increases due to deterioration of workability and mixing.

  It is also known to improve the properties of rubber compositions by using terminally modified or coupled rubber components and fillers (see Patent Documents 1 to 4). However, according to these techniques, the workability and the effect of reducing rolling resistance are not sufficient.

Japanese Patent Laid-Open No. 10-87887 JP 2000-273245 A JP 2000-344944 A JP 2002-322319 A

  An object of the present invention is to provide a rubber composition having excellent processability and rolling resistance reduction effect, and a tire using the rubber composition.

The present invention relates to a low molecular weight butadiene rubber having a weight average molecular weight of 10,000 or less, comprising 50% by weight or more of solution-polymerized styrene-butadiene rubber polymerized by coupling, 40% by weight or less of natural rubber and 40% by weight or less of butadiene rubber. A rubber component containing 1 to 12% by weight, silica having a nitrogen adsorption specific surface area of 100 m ² / g or more and less than 200 m ² / g, and a nitrogen adsorption specific surface area of 145 m ² / g or more, and cetyltrimethylammonium It consists of carbon black whose bromide adsorption specific surface area (m ² / g) is 1.2 times or more of iodine adsorption amount (mg / g), and 60% by weight of silica with respect to the total content of silica and carbon black The present invention relates to a rubber composition containing 40% by weight or less of carbon black.

The low-molecular-weight butadiene rubber is terminal-modified with a functional group selected from the group consisting of a carboxyl group, a vinyl group, and a hydroxyl group. The present invention also relates to a tire having a tread composed of the rubber composition.

  According to the present invention, by mixing ultra-low molecular weight (10,000 or less) BR, the rubber fabric at the time of mixing and extrusion can be improved. Furthermore, terminal modification of the ultra-low molecular weight BR can increase the reactivity with silica, improve the deterioration of workability during kneading, and suppress the increase in rolling resistance when used in a tire.

  The rubber composition of the present invention comprises a rubber component and a reinforcing agent.

  In the present invention, solution-polymerized styrene-butadiene rubber (S-SBR) is used as the rubber component. The amount of styrene units in S-SBR is preferably 5 to 45% by weight, and the amount of vinyl units is preferably 20 to 65% by weight. When the styrene unit amount is less than 5% by weight and the vinyl unit amount exceeds 65% by weight, the vulcanization speed becomes slow, the productivity at the time of tire production is inferior, and the tire performance also causes wear resistance due to chipping. Tend to be inferior. On the other hand, when the styrene unit amount exceeds 45% by weight and the vinyl unit amount is less than 20% by weight, the heat generated by the rubber tends to increase, and the rolling resistance tends not to be reduced.

  As the S-SBR used in the present invention, one having a high molecular weight coupled with Sn or Si is used. Rolling resistance as a polymer can be reduced by increasing the molecular weight of S-SBR and further modifying the terminal so that it can react with silica.

  The coupling method of S-SBR is performed by, for example, reacting an alkali metal (such as Li) or alkaline earth metal (such as Mg) at the molecular chain end of S-SBR with, for example, tin halide or silicon halide. Can be obtained.

  The S-SBR content in the rubber component is 50% by weight or more, preferably 60 to 90% by weight, more preferably 60 to 80% by weight. If the S-SBR content is less than 50% by weight, there is a tendency that the balance between the grip performance of the tire, particularly the grip performance on the wet road surface and the rolling resistance reducing effect, is poor, and if the content exceeds 90% by weight, the grip performance on the wet road surface tends to be poor. However, there is no problem in summer, but it tends to be inferior on ice and snow in winter.

  In the present invention, natural rubber (NR) is further used as the rubber component. The content of NR is 40% by weight or less, preferably 20% by weight or less in the rubber component. When the NR content exceeds 40% by weight, rolling resistance is reduced, but wet grip performance is inferior.

  In the present invention, butadiene rubber (BR) is further used as the rubber component. The content of BR is 40% by weight or less, preferably 20% by weight or less in the rubber component. When the NR content exceeds 40% by weight, there is no problem with wet grip performance at low temperatures, particularly around 0 ° C., but dry grip performance and wet grip performance at room temperature or higher are inferior.

  In the present invention, all or part of the BR is a low molecular weight BR having a weight average molecular weight of 10,000 or less. Since the extruded dough deteriorates due to the blending of the S-SBR, the properties of the dough are improved by mixing low molecular weight BR.

  The low molecular weight BR has a weight average molecular weight of 10,000 or less, preferably 1000 to 10,000, more preferably 1000 to 4000, and further preferably 1500 to 3500. When the weight average molecular weight of BR exceeds 10,000, BR becomes too viscous, polymerization is difficult, and productivity of low-molecular BR is inferior. Moreover, if it is less than 1000, there exists a tendency for the rolling resistance of a tire not to be reduced.

  Furthermore, in order to suppress the increase in rolling resistance as much as possible, the BR is preferably terminal-modified to improve the reactivity with silica. As a functional group introduced into the molecular chain terminal of BR in order to improve the reactivity with silica, a vinyl group, an amino group, a carboxyl group, or the like is used because it easily reacts with silica. These functional groups are preferably introduced at both ends of the molecular chain of BR.

  The content of the low molecular weight BR is 1 to 12% by weight, preferably 3 to 10% by weight, more preferably 5 to 8% by weight in the rubber component. If the BR content is less than 1% by weight, the fabric is not sufficiently improved, and if it exceeds 12% by weight, the rolling resistance of the tire is not reduced.

  Next, in the present invention, silica is used as a reinforcing agent. Using a large amount of silica as a reinforcing agent for the rubber component is more effective than using silica in a conventional polymer for blending carbon black. Compared to carbon black, silica has a better balance between wet grip performance and rolling resistance reduction effect, and is more likely to have effects due to modification of polymer molecular chain ends and the like. Therefore, the ratio of silica to carbon black needs to be increased.

Silica used in the present invention, nitrogen adsorption specific surface area (N ₂ SA) is preferably 100 to 200 m ² / g, in particular a 110~180m ² / g. If N ₂ SA is less than 100 m ² / g, the reinforcing property tends to be inferior, and if it exceeds less than 200 m ² / g, the viscosity tends to be high when rubber is kneaded in the factory, and a large amount of coupling agent is required, which tends to be costly. is there.

  Furthermore, in the present invention, carbon black is used as a reinforcing agent. Conventionally, when carbon black is used in combination with silica, carbon black having a large surface area (small particle diameter) is often used in consideration of the large electric resistance of silica. In this case, since there is a concern about an increase in rolling resistance, the surface activity of carbon black is increased in order to increase the reactivity with the molecular chain end (the ratio of cetyltrimethylammonium bromide adsorption specific surface area / iodine adsorption amount is increased). Therefore, it is necessary to reduce the rolling resistance value.

Nitrogen adsorption specific surface area of carbon black used in the present invention (N ₂ SA) is, 145m ² / g or more, preferably 160~220m ² / g, more preferably 170~190m ² / g. If N ₂ SA is less than 145 m ² / g, the electrical conductivity when the ratio of carbon black is lowered is inferior and the dry grip performance is greatly deteriorated. If it exceeds 220 m ² / g, rolling resistance is not reduced, or kneaded rubber There is a tendency for the viscosity of to increase too much.

The carbon black preferably has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of 140 to ²⁰⁰ m ² / g. When the CTAB adsorption specific surface area is less than 140 m ² / g, the electrical conductivity when the ratio of carbon black is lowered is inferior and the dry grip performance is greatly deteriorated. When the CTAB adsorption specific surface area exceeds 200 m ² / g, the rolling resistance is not reduced. Or the viscosity of kneaded rubber tends to increase too much.

  The iodine adsorption amount (IA) of the carbon black is preferably 140 to 200 mg / g. If the IA is less than 140 mg / g, the electrical conductivity when the ratio of carbon black is lowered is inferior and the dry grip performance is greatly reduced. If the ratio exceeds 200 mg / g, the rolling resistance is not reduced, or the viscosity of the kneaded rubber Tend to rise too much.

The ratio of CTAB (m ² / g) to IA (mg / g) (CTAB / IA ratio) is 1.1 or more, preferably 1.15 to 1.29, more preferably 1.18 to 1. 25. If the CTAB / IA ratio is less than 1.1, the balance between the rolling resistance reduction effect and the dry grip performance is poor, and the productivity of carbon black tends to be greatly inferior.

  The content of the silica is 60% by weight or more, preferably 60 to 80% by weight with respect to the total content of silica and carbon black. The carbon black content is 40% by weight or less, preferably 20 to 35% by weight, based on the total content of silica and carbon black. If the content of silica is less than 60% by weight and the content of carbon black exceeds 40% by weight, the rolling resistance is not reduced.

  When kneading the rubber component and the reinforcing agent, it is preferable to set a high reaction temperature in a kneading machine (Banbury mixer or the like) in order to efficiently react the rubber component and silica. Specifically, it is preferably set to 160 ° C. or higher, particularly 160 to 180 ° C. If the reaction temperature is less than 160 ° C, the reaction between the silica and the coupling agent tends to be difficult to complete, and if it exceeds 180 ° C, the viscosity of the kneaded rubber tends to increase too much.

  In this case, the coupling agent for silica is changed from conventional Si69 (four sulfur atoms in one molecule) to Si266 (two sulfur atoms in one molecule, high purity), etc. to improve heat resistance. It is desirable to knead after mixing. Moreover, it is preferable to use 2-12 weight% of silane coupling agents with respect to a silica. If the silane coupling agent is less than 2% by weight, the performance of the silica is not sufficiently brought out and the wet grip performance and wear resistance tend to be inferior. If the silane coupling agent exceeds 12% by weight, the coupling agent is excessive and the cost is increased. Wear tends to be inferior.

  The rubber composition of the present invention thus obtained preferably has a toluene swelling degree of 180 to 320%, particularly 220 to 310%. If the toluene swelling degree is less than 180%, the durability of the rubber tends to be inferior and the wear resistance tends to deteriorate, and if it exceeds 320%, the dry grip performance and the rolling resistance reduction effect tend to be inferior. Here, the degree of toluene swelling is determined by immersing a rubber cube whose side is adjusted to about 5 mm in toluene for 24 hours, and then measuring the weight ratio after immersion and before immersion.

  Since the rolling resistance is reduced, the rubber composition of the present invention is suitably used for tire treads.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

The materials used in the examples and comparative examples will be described together below.
NR: RSS # 3
Polymer A: SBR E15 manufactured by Asahi Kasei Corporation (S-SBR coupled with an epoxy group, styrene unit amount: 23% by weight, vinyl unit amount: 64% by weight, end group: none)
Polymer B: Hiker CTB manufactured by Ube Industries, Ltd. (molecular weight: 4800, end group: carboxyl group)
Polymer C: Sertomer Company Inc. Ricon 100 (liquid SBR)
Polymer D: Liquid BR, POLYOIL130 manufactured by Nippon Zeon Co., Ltd.
Silica: 115GR manufactured by Rhodia (N ₂ SA: 115 m ² / g)
Carbon black N134: SAF manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 145 m ² / g, CTAB adsorption specific surface area: 136 m ² / g, IA: 142 mg / g)
Aroma oil: AH40 made by Idemitsu Kosan Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator made by Tsurumi Chemical Co., Ltd. CBS: Noxeller CZ-G made by Tsurumi Chemical Co., Ltd.
Vulcanization accelerator DPG: Soxoseal D manufactured by Sumitomo Chemical Co., Ltd.

Examples 1-2 and Comparative Examples 1-3
In accordance with the formulation shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded at 160 ° C. for 1 minute using a Banbury mixer (270F, Kobe Steel). Furthermore, sulfur and a vulcanization accelerator were added and kneaded at 120 ° C. for 1.5 minutes. Next, the obtained rubber composition was vulcanized under the conditions of 250 kPa and 180 ° C. The following tests were performed on the obtained vulcanized rubber. The test results are shown in Table 1.

(Rubber hardness)
The hardness (Hs) of the prepared rubber composition was measured with a JIS-A hardness meter at 25 ° C.

(Loss tangent)
Using a VES-F-3 manufactured by Iwamoto Seisakusho, loss tangent (tan δ) at 60 ° C. was measured at a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%. The smaller the tan δ value, the less heat is generated.

(Kneaded dough)
Extrusion was performed at 120 ° C., a tread was prepared, and the state of the kneaded dough was evaluated in three stages by visual judgment.
○: Smooth fabric △: Shark-like fabric ×: Fabric with many bumps

Claims (3)

Solution polymerized styrene-butadiene rubber polymerized by coupling 50% by weight or more, natural rubber 40% by weight or less, and butadiene rubber 40% by weight or less, low molecular weight butadiene rubber having a weight average molecular weight of 10,000 or less 1 to 12 weights %, A silica having a nitrogen adsorption specific surface area of 100 m ² / g or more and less than 200 m ² / g, and a nitrogen adsorption specific surface area of 145 m ² / g or more, and a cetyltrimethylammonium bromide adsorption specific surface area (M ² / g) is composed of carbon black that is 1.2 times or more with respect to the iodine adsorption amount (mg / g), and 60% by weight or more of silica with respect to the total content of the silica and the carbon black; A rubber composition containing 40% by weight or less of carbon black. 2. The rubber composition according to claim 1, wherein the low molecular weight butadiene rubber is terminal-modified with a functional group selected from the group consisting of a carboxyl group, a vinyl group and a hydroxyl group. A tire having a tread comprising the rubber composition according to claim 1.