JP5309730B2 - Rubber composition for undertread - Google Patents

Description

  The present invention relates to a rubber composition for an under tread, and more specifically, a pneumatic composition that achieves a break strength and extrudability at a conventional level or higher while compounding recycled rubber in order to reduce environmental burden. The present invention relates to a rubber composition for a tire undertread.

  From the viewpoint of protecting the global environment, it is required to increase the recycling rate of pneumatic tires, and it is proposed that recycled powder rubber recovered from used tires and tubes be blended into new rubber raw materials (For example, refer to Patent Document 1). However, when such recycled rubber is blended with the rubber composition for an under tread, there are problems that the breaking strength is lowered, the viscosity of the rubber composition is increased, and the extrusion processability at the time of extrusion molding is deteriorated. For this reason, it has been difficult to put into practical use a technique for blending recycled rubber and increasing the recycling rate.

Therefore, it is possible to realize a rubber composition for an under tread that can achieve a break strength and extrudability at or above conventional levels while blending recycled rubber with the rubber composition constituting the under tread and increasing the recycling rate. It is desired.
Japanese Patent Publication No. 11-335488

  An object of the present invention is to provide a rubber composition for an under tread which achieves a break strength and an extrudability at a conventional level or higher while compounding recycled rubber in order to increase a recycling rate and reduce an environmental load. There is to do.

The undertread rubber composition of the present invention that achieves the above object has a nitrogen adsorption specific surface area of 30 to 80 m ² / g with respect to 100 parts by weight of a diene rubber containing 60% by weight or more of natural rubber and / or isoprene rubber. It is a rubber composition containing 20 to 70 parts by weight of a certain carbon black and 1 to 10 parts by weight of recycled rubber. The recycled rubber has a Mooney viscosity of 35 to 65, and the natural rubber content ratio of the rubber component in the recycled rubber is 60. It is characterized by having a weight average molecular weight of 60000 or less by gel permeation chromatography of the sol in the recycled rubber.

  The diene rubber may contain 1 to 40% by weight of at least one rubber selected from butadiene rubber and styrene butadiene rubber.

  This rubber composition for an under tread is suitable for constituting an under tread of a pneumatic tire.

According to the rubber composition for an under tread of the present invention, 20 to 70 parts by weight of carbon black and 1 to 10 parts of recycled rubber with respect to 100 parts by weight of a diene rubber containing 60% by weight or more of natural rubber and / or isoprene rubber. Since it is blended in parts by weight, a decrease in breaking strength can be suppressed while blending recycled rubber. In particular, the nitrogen adsorption specific surface area of carbon black is 30 to 80 m ² / g , the recycled rubber is Mooney viscosity 35 to 65, the natural rubber content ratio of the rubber component in the recycled rubber is 60% by weight or more, and Since the weight average molecular weight of the sol by gel permeation chromatography is 60000 or less, the breaking strength of the rubber composition is ensured and the viscosity increase of the rubber composition is minimized to maintain the extrudability. Therefore, it is possible to achieve the breaking strength and the extrudability that are at or above the level of the conventional rubber composition for an undertread, and to increase the recycling rate.

  In the rubber composition for an under tread of the present invention, the rubber component is a diene rubber, and the diene rubber contains 60% by weight or more of natural rubber and / or isoprene rubber. That is, the diene rubber may contain 60% by weight or more of one of natural rubber or isoprene rubber, or may contain 60% by weight or more of the total of natural rubber and isoprene rubber. The blending amount of natural rubber and / or isoprene rubber in the diene rubber is 60% by weight or more, preferably 60 to 100% by weight, more preferably 60 to 99% by weight, and further preferably 70 to 90% by weight. When the blending amount of the natural rubber and / or isoprene rubber is less than 60% by weight, the breaking strength, extrusion processability, and low heat build-up performance required as a pneumatic tire undertread are lowered.

  The rubber composition for an under tread of the present invention can contain a diene rubber other than natural rubber and isoprene rubber as an optional component. The diene rubber other than natural rubber and isoprene rubber is not particularly limited, and examples thereof include butadiene rubber, styrene butadiene rubber, acrylonitrile-butadiene rubber, and butyl rubber that are usually used in a rubber composition for undertread. Preferred is butadiene rubber or styrene butadiene rubber. These diene rubbers can be used alone or as any blend.

  When the rubber composition for an undertread of the present invention is blended with a diene rubber other than natural rubber or isoprene rubber, particularly butadiene rubber or styrene butadiene rubber, the blending amount thereof is in the diene rubber. The amount is preferably 1 to 40% by weight, more preferably 10 to 30% by weight. When it exceeds 40% by weight, there is a concern that the breaking strength, extrusion processability, and low exothermicity are deteriorated.

  The rubber composition for an under tread of the present invention increases the recycling rate and reduces the environmental load by blending recycled rubber. At the same time, by specifying the properties of the recycled rubber as will be described later, it is possible to suppress a decrease in breaking strength and an increase in the viscosity of the rubber composition, and to maintain the extrusion processability of the rubber composition. The amount of recycled rubber is 1 to 10 parts by weight, preferably 3 to 6 parts by weight, based on 100 parts by weight of the diene rubber. If the amount of recycled rubber is less than 1 part by weight, the recycling rate cannot be increased. Moreover, when the compounding quantity of recycled rubber exceeds 10 weight part, the breaking strength of a rubber composition will 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. Moreover, when Mooney viscosity exceeds 65, the viscosity of a rubber composition will become large and extrusion processability will deteriorate. 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, the Mooney viscosity of the rubber composition increases and the extrudability deteriorates. 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.

  The rubber composition for an under tread of the present invention increases the breaking strength by blending carbon black. The amount of carbon black is 20 to 70 parts by weight, preferably 20 to 59 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 and elastic modulus cannot be sufficiently increased. Moreover, when the compounding quantity of carbon black exceeds 70 weight part, we are anxious about the fall of tire durability and the deterioration of rolling resistance.

The carbon black used in the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 30 to 80 m ² / g. When the nitrogen adsorption specific surface area of carbon black exceeds 80 m ² / g, there is a concern that the tire durability is lowered and the rolling resistance is deteriorated. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black shall be determined according to JIS K6217-2.

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

  In addition, the rubber composition for undertreads can be blended with various additives generally used in rubber compositions such as vulcanizing agents, vulcanization accelerators, anti-aging agents, plasticizers, and oils, Such additives can be kneaded by a general method to form a rubber composition, which can be 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 an under tread can be produced by mixing each of the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for an under tread of the present invention can reduce the breaking strength and the extrudability as much as possible while using a recycled rubber to increase the recycling rate. This rubber composition for an under tread is preferably applied to an under tread portion of a pneumatic tire, and a pneumatic tire having an under tread portion composed of this rubber composition is easy to extrude and has quality stability. And high durability.

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

  Eleven kinds of rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 6) having the compositions shown in Tables 1 and 2 were weighed for the ingredients except for sulfur and vulcanization accelerator, respectively, and 1.7 L Banbury. The mixture was kneaded for 4 minutes with a mixer, and the master batch was discharged at a temperature of 160 ° C. and cooled to 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 an under tread.

  The Mooney viscosity was measured by the method shown below as the extrudability of the 11 types of rubber compositions obtained (Examples 1 to 5, Comparative Examples 1 to 6). Each rubber composition was vulcanized at 150 ° C. for 30 minutes in a mold having a predetermined shape to prepare a test piece, and the breaking strength was measured by the following method.

Breaking strength Based on JIS K6251, it measured on the conditions of No. 3 type | mold dumbbell test piece, 25 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.

Mooney viscosity (extrusion processability)
The Mooney viscosity (ML _{1 + 4} ) of the rubber composition was measured using a Mooney viscometer in accordance with JIS K6300 using an L-shaped rotor, preheating time 1 minute, rotor rotation time 4 minutes, temperature 100 ° C., 2 rpm. Measured under conditions. The obtained results are shown in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. A smaller index means a lower viscosity and better extrudability.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, SIR-20
IR: Isoprene rubber, Nipol IR2200 manufactured by Nippon Zeon
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
SBR: styrene butadiene rubber, Nipol 1502 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 Industrial Co., 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 by applying shear 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 40/60) 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 by shearing for 8 minutes at a volume of 60 cc), (Mooney viscosity (ML _{1 + 4} @ 100 ° C.) = 45, natural rubber ratio in rubber component = 40%, weight average molecular weight of sol = 30000)
Carbon Black 1: Seast F manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area 42 m ² / g)
Carbon black 2: Show black N220 (nitrogen adsorption specific surface area 110 m ² / g) manufactured by Cabot Japan
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Bead oil manufactured by NOF Corporation: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Sulfur: Kristex HS OT 20 manufactured by Akzo Nobel
Vulcanization accelerator: Noxeller NS P manufactured by Ouchi Shinsei Chemical Co., Ltd.

Claims (3)

20 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area of 30 to 80 m ² / g and 1 to 10 of recycled rubber with respect to 100 parts by weight of diene rubber containing 60% by weight or more of natural rubber and / or isoprene rubber A rubber composition containing parts by weight, wherein the recycled rubber has a Mooney viscosity of 35 to 65, the natural rubber content of the rubber component in the recycled rubber is 60% by weight or more, and the gel permeation chromatograph of the sol in the recycled rubber A rubber composition for undertread having a weight average molecular weight of 60000 or less.   The rubber composition for an under tread according to claim 1, wherein the diene rubber contains 1 to 40% by weight of at least one rubber selected from butadiene rubber and styrene butadiene rubber.   The pneumatic tire which comprised the undertread with the rubber composition for undertreads of Claim 1 or 2.