JP5223446B2 - Rubber composition for side reinforcing liner - Google Patents

Description

  The present invention relates to a rubber composition for a side reinforcing liner, and more specifically, while incorporating a recycled rubber in order to reduce an environmental load, the extrusion processability, breaking strength and low heat build-up are at a conventional performance level or higher. The present invention relates to a rubber composition for a side reinforcing liner of a run flat tire that is maintained.

  There are two types of run-flat tires that can safely travel a certain distance during tire punctures: a tread support core is inserted inside the tire and a side reinforcement method that reinforces the side of the tire itself. . The latter side reinforcement system generally has a side wall portion in which a thick side reinforcement liner having a crescent cross section having a high modulus is inserted. The side reinforcing liner is required to use a rubber composition having a high elastic modulus to support the vehicle weight and a low heat generation property in order to ensure durability during run-flat running. In addition, the rubber composition of the side reinforcing liner is characterized by blending a large amount of butadiene rubber in order to ensure the elastic modulus and low heat-generating properties. However, when a large amount of butadiene rubber is blended, there is a problem that it is easy to shrink during extrusion molding, and insertion into the side portion becomes difficult.

  As a countermeasure against shrinkage, Patent Document 1 discloses that extrusion processability is improved by blending a rubber composition for a side reinforcing liner of a run flat tire with a butadiene rubber containing syndiotactic-1,2-polybutadiene. Has proposed.

  On the other hand, from the viewpoint of protecting the global environment, it has become necessary to increase the recycling rate of pneumatic tires, and recycled powder rubber recovered from used tires and tubes must be blended into new rubber raw materials. Has been proposed (see, for example, Patent Document 2). However, when such recycled rubber is blended with the rubber composition for the side reinforcing liner, the extrusion processability is lowered, tan δ is increased, and the heat generation is deteriorated. Moreover, since the breaking strength of the rubber composition is lowered, there is a problem that durability during run flat running is lowered along with deterioration of heat generation.

Therefore, extrudability, breaking strength and low heat build-up can be maintained at or above conventional performance levels while increasing the recycling rate by blending recycled rubber with the rubber composition that constitutes the side reinforcement liner of run-flat tires. Realization of a rubber composition for a side reinforcing liner is desired.
JP 2006-199864 A Japanese Patent Publication No. 11-335488

  It is an object of the present invention to provide a rubber composition for a side reinforcing liner which maintains extrusion processability, breaking strength and low heat build-up at a conventional performance level or higher while compounding recycled rubber.

The rubber composition for a side reinforcing liner of the present invention that achieves the above object is a diene system comprising 10 to 30% by weight of butadiene rubber containing syndiotactic-1,2-polybutadiene and 10 to 30% by weight of natural rubber. 20 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface area of 100 m ² / g or less, 3 to 8 parts by weight of sulfur, and 2 to 20 parts by weight of recycled rubber are added to 100 parts by weight of rubber. The rubber has a Mooney viscosity of 35 to 65, the natural rubber content ratio of the rubber component in the recycled rubber is 60% by weight or more, and the weight average molecular weight by gel permeation chromatography of the sol in the recycled rubber is 60000 or less. And

  This rubber composition for a side reinforcing liner is suitable for constituting a side reinforcing liner of a run flat tire.

According to the rubber composition for a side reinforcing liner of the present invention, 100% by weight of a diene rubber containing 10-30% by weight of butadiene rubber containing syndiotactic-1,2-polybutadiene and 10-30% by weight of natural rubber. 20 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface area of 100 m ² / g or less, 3 to 8 parts by weight of sulfur, and 2 to 20 parts by weight of recycled rubber, While increasing the recycle rate, the extrudability, breaking strength and low heat build-up can be brought to conventional performance levels or higher. In particular, the properties of the recycled rubber are such that the Mooney viscosity is 35 to 65, the natural rubber content of the rubber component in the recycled rubber is 60% by weight or more, and the weight average molecular weight by gel permeation chromatography of the sol in the recycled rubber. Therefore, the low exothermic property can be maintained without decreasing the extrudability and breaking strength associated with the blending of the recycled rubber and without increasing the tan δ.

  FIG. 1 is a half cross-sectional view in the tire meridian direction illustrating a pneumatic run-flat tire having a side reinforcing liner made of the rubber composition of the present invention.

  In FIG. 1, the pneumatic run-flat tire has a tread portion 1, a sidewall portion 2 and a bead portion 3, and a two-ply carcass 5 is mounted between a pair of left and right bead cores 4 on the inner side of the tread portion 1. A belt layer 6 composed of a plurality of plies (2 plies in the figure) is disposed over the circumference of the tire on the outer peripheral side of the carcass 5, and a belt cover layer 7 is disposed outside the belt layer 6. An inner liner layer 8 is disposed as an air permeation preventive layer on the innermost side of the tire, and a rubber reinforcing liner 9 having a crescent cross section is inserted inside the carcass 5 in each of the left and right sidewall portions 2. The position where the rubber reinforcing liner 9 having a crescent-shaped cross section is inserted is not limited to the illustrated example, and may be inserted between the two carcass 5.

  The rubber composition for a side reinforcing liner of the present invention is used as a rubber reinforcing liner having a crescent cross section as described above. The rubber component of this rubber composition is a diene rubber, and the diene rubber contains 10 to 30% by weight of butadiene rubber containing syndiotactic-1,2-polybutadiene and 10 to 30% by weight of natural rubber. Like that. The natural rubber in the diene rubber is 10 to 30% by weight, preferably 15 to 25% by weight. When the blending amount of natural rubber is less than 10% by weight, the breaking strength decreases. On the other hand, when the blending amount of the natural rubber exceeds 30% by weight, tan δ increases and the exothermic property deteriorates. Recycled rubber is excluded from 10 to 30% by weight of natural rubber in the rubber component of the matrix.

  The butadiene rubber containing syndiotactic-1,2-polybutadiene is 10 to 30% by weight, preferably 15 to 25% by weight in the diene rubber. If the butadiene rubber containing syndiotactic-1,2-polybutadiene is less than 10% by weight, the breaking strength and extrudability cannot be increased to the conventional performance level or higher. If the butadiene rubber containing syndiotactic-1,2-polybutadiene exceeds 30% by weight, the exothermic property of the rubber composition for a side reinforcing liner deteriorates.

  Syndiotactic-1,2-polybutadiene is a resin having high crystallinity and is finely dispersed in butadiene rubber. The content of syndiotactic-1,2-polybutadiene in the butadiene rubber is preferably 1 to 20% by weight, more preferably 3 to 15% by weight. If the amount is less than 1% by weight, the effect of improving the breaking strength and the extrusion processability cannot be obtained. If the amount exceeds 20% by weight, the exothermic property of the rubber composition is deteriorated. As the butadiene rubber containing the above-mentioned syndiotactic-1,2-polybutadiene, commercially available rubber can be used, and examples thereof include UBEPOL-VCR412, VCR617, VCR450, VCR800 and the like manufactured by Ube Industries, Ltd. .

  The diene rubber other than butadiene rubber including natural rubber and syndiotactic-1,2-polybutadiene is not particularly limited, and isoprene rubber and styrene-butadiene rubber which are usually used in rubber compositions for side reinforcing liners. Butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber and the like. Preferred are butadiene rubber, isoprene rubber, and styrene-butadiene rubber. These diene rubbers can be used alone or as any blend.

  The rubber composition for the side reinforcing liner is preferably 40 to 80% by weight, more preferably 50 to 70% by weight of diene rubber other than butadiene rubber including natural rubber and syndiotactic-1,2-polybutadiene. Good. For example, when butadiene rubber is blended, if the butadiene rubber is less than 40% by weight in the diene rubber, tan δ is increased and heat generation is deteriorated. On the other hand, if the butadiene rubber exceeds 80% by weight, shrinkage increases during extrusion molding and the sheet surface becomes rough, and the extrusion processability deteriorates. In addition, the breaking strength decreases.

  Of the mixture blended with the rubber component, the amount of recycled rubber is 2 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of the diene rubber. If the amount of recycled rubber is less than 2 parts by weight, the recycling rate cannot be increased. On the other hand, when the amount of recycled rubber exceeds 20 parts by weight, tan δ increases and heat generation increases, and the breaking strength and extrudability deteriorate.

  The recycled rubber used in the present invention is a recycled rubber of automobile tires, tubes and other rubber products defined in JIS K6313, and has the same properties. The type of recycled rubber may be any one selected from tube recycled rubber, tire recycled rubber, and other recycled rubbers, and a plurality of types may be combined. Of these, tire recycled rubber is preferable. In the present invention, the recycled rubber is a recycled rubber that has been subjected to desulfurization treatment other than so-called powder rubber in accordance with the provisions of JIS K6313.

The recycled rubber has a Mooney viscosity (ML _{1 + 4} ) of 35 to 65, preferably 40 to 60. If the Mooney viscosity is less than 35, the dispersibility during mixing deteriorates. On the other hand, when the Mooney viscosity exceeds 65, the extrusion processability deteriorates. Here, Mooney viscosity (ML _{1 + 4} ) refers to a value measured at 100 ° C. in accordance with JIS K6300.

  The rubber component in the recycled rubber has a natural rubber content of 60% by weight or more, preferably 60 to 85% by weight. When the content ratio of the natural rubber is less than 60% by weight, the breaking strength and the extrudability are deteriorated. In addition, the natural rubber content ratio in recycled rubber means the value calculated | required by the measurement of pyrolysis gas chromatography (PyGC).

  The recycled rubber used in the present invention has a sol molecular weight of 60,000 or less, preferably 30,000 to 60,000, as a weight average molecular weight determined by gel permeation chromatography. When the weight molecular weight of the sol exceeds 60000, tan δ increases and heat generation increases. Here, the sol in the recycled rubber is a component that dissolves in toluene at room temperature. The molecular weight of the sol is obtained by cutting a regenerated rubber film into small pieces, dipping in about 200 times the amount of toluene, and allowing to stand for 24 hours. Next, the toluene solution in which the regenerated rubber was immersed in a 200-mesh wire mesh was filtered, and the molecular weight of the sol contained in the filtrate was measured by gel permeation chromatography (GPC) in terms of weight average molecular weight (polystyrene conversion). Say things.

  Of the mixture blended with the rubber component, the amount of carbon black is 20 to 60 parts by weight, preferably 25 to 55 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than 20 parts by weight, the breaking strength cannot be increased. On the other hand, if the blending amount of carbon black exceeds 60 parts by weight, the exothermic property deteriorates.

Carbon black used in the present invention, the nitrogen adsorption specific surface area _(N 2 SA) of 100 m ² / g or less, preferably used ones 20~95m ² / g. When the nitrogen adsorption specific surface area of carbon black exceeds 100 m ² / g, the exothermic property deteriorates. Nitrogen adsorption specific surface area _(N 2 SA) of carbon black shall be determined in accordance with JIS K6217-2.

  You may mix | blend inorganic fillers other than carbon black with the rubber composition for side reinforcement liners of this invention. Examples of the inorganic filler include silica, clay, calcium carbonate, aluminum hydroxide, mica, talc and the like. Of these, silica and clay are preferable.

  In the rubber composition for a side reinforcing liner of the present invention, the amount of sulfur is 3 to 8 parts by weight, preferably 4 to 8 parts by weight, based on 100 parts by weight of the diene rubber. When the amount of sulfur is less than 3 parts by weight, the breaking strength decreases and heat generation increases. On the other hand, if the amount of sulfur exceeds 8 parts by weight, low exothermic properties can be obtained, but the breaking strength decreases.

  The rubber composition for side reinforcing liners can be blended with various additives generally used in rubber compositions such as vulcanization accelerators, anti-aging agents, and plasticizers. The rubber composition can be kneaded by a conventional method and used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used.

  The rubber composition for a side reinforcing liner can be produced by mixing the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a side reinforcing liner of the present invention uses recycled rubber to increase the recycle rate, while improving the extrudability and maintaining the breaking strength at a conventional performance level or higher. Can be made small and low heat generation can be achieved. The rubber composition for a side reinforcing liner is preferably applied to a side reinforcing liner portion of a run flat tire, and a pneumatic run flat tire having a side reinforcing liner portion made of this rubber composition is used during run flat running. Excellent durability.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  16 kinds of rubber compositions (Examples 1 to 4 and Comparative Examples 1 to 12) having the composition shown in Table 1 were weighed with the composition ingredients except sulfur and a vulcanization accelerator, respectively, and a 1.7 L Banbury mixer. The mixture was kneaded for 4 minutes, and the master batch was discharged at a temperature of 160 ° C. and cooled at room temperature. This master batch was subjected to a 1.7 L Banbury mixer, and sulfur and a vulcanization accelerator were added and mixed to prepare a rubber composition for a side reinforcing liner.

  The obtained 16 types of rubber compositions (Examples 1 to 4 and Comparative Examples 1 to 12) were each vulcanized at 150 ° C. for 30 minutes in molds having predetermined shapes to prepare test pieces, and the breaking strength was obtained. The exothermic property (tan δ) was measured by the following method. Moreover, the extrusion processability of these rubber compositions was measured by the method shown below.

Breaking strength Based on JIS K6251, it measured on the conditions of No. 3 type | mold dumbbell test piece, 20 degreeC, and the tension speed of 500 mm / min. The obtained results are shown in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. A larger index means a higher breaking strength.

Exothermic (tan δ)
Using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, tan δ at a temperature of 60 ° C. was measured under the conditions of static strain 10%, dynamic strain ± 2%, and frequency 20 Hz. The obtained results are shown in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. It means that the smaller the index of tan δ, the smaller the hysteresis loss and the better the low heat buildup.

Extrudability Using a single screw extruder (Plastacoder manufactured by Brabender, screw rotation speed 40 rpm, cylinder temperature 100 ° C.), each rubber composition is transferred for 20 seconds from a die having a crescent-shaped die shape. Five panelists evaluated the degree of shrinkage and the skin condition of the surface of the extruded product when extruded, the average value was obtained, and the obtained results are shown in Tables 1 and 2. The larger the score, the better the extrudability, and a score of 3 is set as a standard (a level that causes no practical problem).

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, STR-20
VCR: butadiene rubber containing syndiotactic-1,2-polybutadiene, UBEPOL VCR412 manufactured by Ube Industries, Ltd. (the content of syndiotactic-1,2-polybutadiene is 12% by weight)
BR: butadiene rubber, Nipol BR-1220 manufactured by Nippon Zeon
Recycled rubber 1: GR555 manufactured by Gujarat, (Mooney viscosity (ML _{1 + 4} @ 100 ° C.) = 45, natural rubber ratio in rubber component = 80%, weight average molecular weight of sol = 30000)
Recycled rubber 2: TBR 100% tire Riku, manufactured by Muraoka Rubber Industries, Ltd. (Mooney viscosity (ML _{1 + 4} @ 100 ° C.) = 60, natural rubber ratio in rubber component = 80%, weight average molecular weight of sol = 60,000)
Recycled rubber 3: Laboplast mill (at a weight ratio of NR / BR of 80/20) vulcanized rubber with an acetone extraction amount of 4.5% by weight and a chloroform extraction amount of 2.2% by weight adjusted to 180 ° C. Desulfurized and produced by shearing for 4 minutes at a volume of 60 cc) (Mooney viscosity (ML _{1 + 4} @ 100 ° C.) = 70, natural rubber ratio in rubber component = 80%, weight average molecular weight of sol = 100000)
Recycled rubber 4: Laboplast mill (at a weight ratio of NR / BR of 20/80) vulcanized rubber having an acetone extraction amount of 4.5% by weight and a chloroform extraction amount of 2.2% by weight adjusted to 180 ° C. Desulfurized by shearing for 8 minutes at a volume of 60 cc) (Mooney viscosity (ML _{1 + 4} @ 100 ° C.) = 40, natural rubber ratio in rubber component = 20%, weight average molecular weight of sol = 30000)
Carbon black 1: Seest FM manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area 42 m ² / g)
Carbon black 2: Seast 7HM manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area 126 m ² / g)
Zinc Hana: Zinc Oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearate: Beads manufactured by Nippon Oil & Fats Co., Ltd .: Stearate Oil: Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.
Sulfur: Kristex HS OT 20 manufactured by Akzo Nobel
Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

1 is a half cross-sectional view in the tire meridian direction showing an example of a run-flat tire using a rubber composition for a side reinforcing liner of the present invention.

Explanation of symbols

1 Tread part 2 Side wall part 3 Bead part 9 Side reinforcement liner

Claims (2)

The nitrogen adsorption specific surface area is 100 m ² / g or less with respect to 100 parts by weight of diene rubber containing 10 to 30% by weight of butadiene rubber containing syndiotactic-1,2-polybutadiene and 10 to 30% by weight of natural rubber. 20 to 60 parts by weight of carbon black, 3 to 8 parts by weight of sulfur, and 2 to 20 parts by weight of reclaimed rubber, the reclaimed rubber has a Mooney viscosity of 35 to 65, and the natural rubber component in the reclaimed rubber A rubber composition for a side reinforcing liner having a rubber content ratio of 60% by weight or more and a weight average molecular weight by gel permeation chromatography of a sol in the recycled rubber of 60000 or less.   A run flat tire having a side reinforcing liner constituted by the rubber composition for a side reinforcing liner according to claim 1.