JP2007204734A - Rubber composition for sidewall - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a sidewall that exhibits an enhanced balance between chipping/cutting resistance and a heat build-up property of the sidewall. <P>SOLUTION: The rubber composition for the sidewall comprises 10-60 wt.% of a butadiene rubber, having dispersed therein a syndiotactic 1,2-polybutadiene having an average primary particle size of at most 100 nm, in the rubber component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a sidewall.

  Among tires, particularly for sidewall rubbers for heavy duty tires such as trucks and buses, rubber compositions mainly composed of natural rubber and butadiene rubber have been used from the viewpoint of flex resistance and strength.

  In addition, since the sidewalls of heavy duty tires tend to generate heat easily (exothermicity tends to decrease), in order to suppress the heat generation, for example, the particle diameter of carbon black is increased, or the carbon black Methods such as reducing the blending amount have been taken. However, in any case, there is a problem that the strength is lowered and resistance due to trauma is reduced.

  Patent Document 1 and Patent Document 2 disclose a rubber composition for a tire containing a butadiene rubber in which syndiotactic-1,2-polybutadiene is dispersed. Syndiotactic-1, Since the average primary particle diameter of 2-polybutadiene was large and not sufficiently dispersed, sufficient performance was not obtained.

JP 2005-75951 A JP 2005-247899 A

  An object of the present invention is to provide a rubber composition for a side wall in which the balance between chip cut resistance and heat generation of the side wall is improved.

  The present invention relates to a rubber composition for a sidewall containing 10 to 60% by weight of a butadiene rubber in which syndiotactic-1,2-polybutadiene having an average primary particle size of 100 nm or less is dispersed in a rubber component.

  According to the present invention, by adding a specific amount of butadiene rubber having syndiotactic-1,2-polybutadiene having a small average primary particle diameter to the rubber composition for the sidewall, chip-cut resistance and heat generation of the sidewall are achieved. The balance can be improved.

  The rubber composition for a sidewall of the present invention contains a rubber component, and the rubber component has a butadiene rubber (SPB-containing BR) in which syndiotactic-1,2-polybutadiene is dispersed.

  In the SPB-containing BR, syndiotactic-1,2-polybutadiene (SPB) is sufficiently finely dispersed in BR serving as a matrix, and the average primary particle diameter of SPB in BR is very small.

  In the SPB-containing BR, the average primary particle diameter of SPB in the BR is 100 nm or less, preferably 80 nm or less, more preferably 50 nm or less. When the average primary particle diameter of SPB exceeds 100 nm, the effect of sufficiently improving the physical properties due to the inclusion of SPB in BR cannot be obtained. In addition, the average primary particle diameter of SPB in BR was measured as an average value of the absolute maximum length by image analysis processing of a transmission electron micrograph.

  The content of SPB in the SPB-containing BR is preferably 7% by weight or more, and more preferably 10% by weight or more. When the content is less than 7% by weight, there is a tendency that sufficient chip cut resistance cannot be obtained. The SPB content in the SPB-containing BR is preferably 20% by weight or less, and more preferably 14% by weight or less. When the content exceeds 20% by weight, rubber kneading becomes difficult and sufficient chip cut resistance tends to be not obtained. In addition, the content rate of SPB in SPB containing BR is shown by the amount of boiling n-hexane insoluble matter.

  The SPB in the SPB-containing BR is preferably a crystal from the viewpoint of providing reinforcement in the tire use temperature range from room temperature.

  Although it does not necessarily limit as a manufacturing method of SPB containing BR which satisfy | fills the said conditions, it can manufacture with the manufacturing method currently disclosed by patent document 2, etc.

  In the rubber composition for a sidewall, the content of SPB-containing BR in the rubber component (including SPB-non-containing BR) is 10% by weight or more, preferably 25% by weight or more. When the content is less than 10% by weight, it is difficult to obtain sufficient bending fatigue resistance. Moreover, the content rate of SPB containing BR in a rubber component is 60 weight% or less, Preferably it is 40 weight% or less. When the content exceeds 60% by weight, sufficient chip cut resistance cannot be obtained.

  The rubber composition for the sidewall is preferably further blended with natural rubber (NR) as a rubber component.

  In the rubber composition for a sidewall, the content of NR in the rubber component is preferably 30% by weight or more, and more preferably 50% by weight or more. When the content is less than 30% by weight, there is a tendency that sufficient chip cut resistance cannot be obtained.

  As the rubber component, in addition to the above-mentioned diene rubber containing syndiotactic-1,2-polybutadiene, NR, as a rubber component, general butadiene rubber not containing syndiotactic-1,2-polybutadiene, styrene You may mix | blend a butadiene rubber etc. together.

  The rubber composition for sidewalls preferably contains carbon black as a reinforcing filler together with the rubber component.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 to 80 m ² / g. When N ₂ SA is less than 40 m ² / g, there is a tendency that sufficient chip cut resistance cannot be obtained. Further, when N ₂ SA exceeds 80 m ² / g, the low heat build-up tends to be impaired.

  By using the rubber composition for sidewalls of the present invention, the hardness can be maintained while reducing the amount of carbon black, and the bending fatigue resistance and low heat generation required for the rubber composition for sidewalls even at a low carbon black content. It becomes possible to maintain or improve the property and breaking strength.

  The content of carbon black may be 20 to 45 parts by weight with respect to 100 parts by weight of the rubber component, and less than the compounding amount in the conventional rubber composition for sidewalls. When the content is less than 20 parts by weight, there is a tendency that sufficient chip cut resistance cannot be obtained. On the other hand, if the content exceeds 45 parts by weight, the low heat build-up tends to be impaired.

  It is preferable to add an adhesive resin to the rubber composition for a sidewall.

The adhesive resin, specifically, aliphatic (C ₅ series) petroleum resin, aromatic (C ₉ series) petroleum resin, alicyclic petroleum resins, terpene resins, and rosin-based resin may be mentioned , in particular, aliphatic (C ₅ series) petroleum resin.

  The softening point of the adhesive resin is preferably 90 to 130 ° C. If the softening point is less than 90 ° C., the low heat buildup tends to be impaired. On the other hand, if the softening point exceeds 130 ° C., the dispersibility during rubber kneading becomes difficult, and the chip cut resistance tends to decrease.

  As for the compounding quantity of adhesive resin, 1-5 weight part is preferable with respect to 100 weight part of rubber components. When the blending amount is less than 1 part by weight, there is a tendency that sufficient tackiness cannot be obtained. On the other hand, if the blending amount exceeds 5 parts by weight, the low heat build-up tends to be impaired.

  In addition to the above, the rubber composition for sidewalls includes reinforcing fillers commonly used in the rubber industry, such as silica, stearic acid, anti-aging agent, wax, zinc oxide, vulcanizing agent, and vulcanization acceleration. An agent or the like can be blended.

  The rubber composition for a sidewall is used for manufacturing a tire by a usual method. That is, an unvulcanized rubber composition obtained by kneading a rubber component, a reinforcing filler and the like is extruded according to the shape of the sidewall, and further bonded to another tire member on a tire molding machine. A tire can be manufactured by forming an unvulcanized tire with vulcanization and further vulcanizing the unvulcanized tire in a vulcanizer.

  Specific examples of the tire include passenger car tires, heavy load tires such as buses and trucks, and the like, and particularly preferably used for heavy load tires.

  The present invention will be described in detail based on examples, but the present invention is not limited to these examples.

The various compounding agents used in the present invention are shown below.
NR: TSR20
BR150B: manufactured by Ube Industries, Ltd. VCR412: manufactured by Ube Industries, Ltd. (BR having dispersed syndiotactic-1,2-polybutadiene crystals, amount of syndiotactic-1,2-polybutadiene: 12% by weight, Shinji (Average primary particle diameter of tactic-1,2-polybutadiene crystal: 250 nm)
VCR prototype: prototype manufactured by Ube Industries, Ltd. (BR with dispersed syndiotactic-1,2-polybutadiene crystals, syndiotactic-1,2-polybutadiene amount: 12% by weight, syndiotactic- (Average primary particle diameter of 1,2-polybutadiene crystal: 43 nm)
CB N330: Carbon black N330 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 80 m ² / g)
Zinc oxide: Toho Zinc Co., Ltd. Stearic acid: Nippon Oil & Fats Co., Ltd. Anti-aging agent: Seiko Chemical Co., Ltd. 6C
Wax: Ozoace wax adhesive resin manufactured by Nippon Seiki Co., Ltd .: Escorrez 1102 manufactured by Exxon Chemical (C5 resin, softening point: 97-103 ° C.)
Powdered sulfur: Accelerator made by Tsurumi Chemical Co., Ltd. NS: TBBS made by Ouchi Shinsei Chemical Co., Ltd.

  In addition, the average primary particle diameter of VCR412 and a VCR prototype was measured as an average value of the absolute maximum length by the image analysis process of a transmission electron micrograph.

  Further, the nitrogen adsorption specific surface area (N2SA) of CB N330 was measured according to the method for determining the specific surface area of the nitrogen adsorption method of JIS K 6217-2.

(Manufacturing method of VCR prototype)
A mixture containing a C4 fraction containing 32% by weight of 1,3-butadiene and cis-2-butene as a main component at a concentration of 68% by weight and dissolving a predetermined amount of water (water content: 2.09 mmol / L) Is supplied to a stainless steel aging tank with a stirrer having a capacity of 2 L and held at 20 ° C. at 12.5 L per hour (containing carbon disulfide 20 mg / L) and diethylaluminum chloride (10 wt% n-hexane solution, 3 .13 mmol / L) and the diethylaluminum chloride / water molar ratio in this reactor solution is adjusted to 1.5. The obtained ripening liquid is supplied to a stainless cis polymerization tank with a stirrer having a capacity of 5 L and maintained at 40 ° C. This cis polymerization tank contains cobalt octoate (cobalt octoate 0.0117 mmol / L, n-hexane solution) and a molecular weight regulator 1,2-butadiene (1,2-butadiene 8.2 mmol / L, 1.535 mol / L). N-hexane solution). The obtained cis polymerization liquid was supplied to a stainless steel 1,2-polybutadiene polymerization tank with a ribbon stirrer having a content of 5 L and continuously polymerized at 35 ° C. for 10 hours. Triethylaluminum (10 wt% n-hexane solution, 4.09 mmol / L) was continuously supplied to the 1,2-polybutadiene polymerization tank. The obtained polymerization solution was supplied to a mixing tank equipped with a stirrer, to which 1 part by weight of 2,6-di-t-butyl-p-cresol was added with respect to 100 parts by weight of rubber, and a small amount of methanol was added. After the polymerization was stopped, unreacted 1,3-butadiene and C4 fraction were removed by evaporation and vacuum dried at room temperature to obtain 8.3 kg of a VCR prototype.

Examples 1-5 and Comparative Examples 1-6
(Test tire manufacturing method)
According to the contents of Table 1, the above ingredients except for sulfur and the vulcanization accelerator were kneaded by a Banbury mixer under conditions of a kneading temperature of up to 150 ° C. and a kneading time of 4 minutes.

  Next, sulfur and a vulcanization accelerator are added, kneaded using an open roll at a kneading temperature of 40 to 60 ° C. and a kneading time of 4 minutes, and an rubber sheet is extruded using an extruder. did.

  The obtained rubber sheet was molded into a sidewall shape and bonded to another tire part, and vulcanized at 150 ° C. for 45 minutes to prepare each test tire (tire size 11R22.5), It used for the following measurement tests.

<Viscoelasticity test>
Using a test piece cut out from a test tire (width 4 mm, thickness 1.8 to 2.2 mm and length 30 mm), a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), temperature 70 ° C., initial strain The loss tangent tan δ of each formulation at a strain of 2% was measured under the conditions of 10% and a frequency of 10 Hz. Then, the loss tangent was displayed as an index according to the following formula to evaluate the heat generation. The higher the index, the better.
(Exothermic index)
= (Tan δ of Comparative Example 1) / (each tan δ) × 100

<Chip cut resistance test>
Each test piece cut out from the test tire was subjected to air heat aging in a gear oven tester at 80 ° C. for 10 days, and then subjected to a tensile test according to JIS K6251 to determine the test specimen's breaking strength (TB) and breaking time. Elongation (EB) was measured. Then, numerical values of the product of the obtained breaking strength and elongation at break (TB × EB) were calculated, and the products were indexed by the following calculation formulas to evaluate chip cut resistance. The higher the index, the better.
(Chip cut resistance index)
= (Each TB × EB) / (TB × EB of Comparative Example 1) × 100

<Hardness (DURO A)>
It was measured at the maximum width position of the tire sidewall in a JIS K6253 durometer test (temperature 23 ° C.). The case where the hardness is 50 ± 2 is good.

<Anti-bending crack growth>
A cut flaw with a width of 5 mm and a depth of 2 mm is placed at the maximum strain position on the sidewall of the test tire, and then the flaw has grown by running a 15,000 km drum at a tire internal pressure of 850 kPa, a load of 37.5 kN, and a speed of 40 km / h. Pass (○).

  The measurement results are shown in Tables 1 and 2.

Claims (2)

A rubber composition for a sidewall, comprising 10 to 60% by weight of a butadiene rubber in which syndiotactic-1,2-polybutadiene having an average primary particle diameter of 100 nm or less is dispersed in a rubber component. A tire having a sidewall made of the rubber composition for a sidewall according to claim 1.