JP2014218601A - Rubber composition for tread of high load tire and high load tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tread of a high load tire excellent in abrasion resistance, fracture characteristics and workability in a good balance, and a high load tire having a tread using the rubber composition.SOLUTION: There is provided a rubber composition for a tread of a high load tire containing a rubber component containing an isoprene rubber of 50 to 100 mass% and a butadiene rubber of 0 to 50 mass%, the isoprene rubber having the magnesium content of 20 ppm or less and containing low gelation natural rubber having the gel percentage content measured as a toluene insoluble part of 10 mass% or less, and there is also provided a high load tire having a tread consisting of the rubber composition.

Description

  The present invention relates to a rubber composition for a tread of a high-load tire and a high-load tire having a tread using the rubber composition.

  High-load tires mounted on trucks and buses are used under severe conditions, and therefore require high wear resistance and high fracture characteristics to prevent tread chipping. Therefore, it is common to use natural rubber and butadiene rubber as the rubber component of the rubber composition for treads of high-load tires.

  In recent years, butadiene rubber has been improved for the purpose of further improving the wear resistance performance of high-load tires. Improvements in butadiene rubber include high cis, high molecular weight, carbon black modification and the like. Natural rubber, on the other hand, is also a natural product, and no development has been made to improve the tread characteristics of high-load tires such as butadiene rubber. The main purpose is to improve processability. .

  Natural rubber is mainly composed of cis polyisoprene, but unlike synthetic polyisoprene rubber, it contains many gel components in addition to cis polyisoprene. This gel component is a non-rubber component in the raw rubber and means a component that is hardly soluble in a solvent, and is considered to be caused by impurities such as proteins and lipids contained in natural rubber. Natural rubber containing this gel content has a high apparent molecular weight, and in the production of rubber compositions, it must be kneaded with a kneading roll machine or a closed mixer, and the processability will be poor unless the molecular weight is lowered. Can not do it. However, such mastication often randomly cuts the molecular main chain of cis polyisoprene, which is the main component, rather than cutting the branched portion that causes the gel content.

  The protein in natural rubber can be cited as a cause of the gel content. This protein is contained in an amount of about 3 to 5% by mass based on the solid content of fresh natural rubber latex, and is known to induce immediate allergy when contacted with a rubber product. Patent Document 1 describes a method for producing a deproteinized natural rubber that prevents allergies, has a large green strength, and is excellent in processability. However, it reduces gel content and improves tread characteristics of high-load tires. This is not taken into consideration.

  Patent Document 2 describes that the gel content can be reduced by removing magnesium phosphate generated by treating natural rubber latex with a phosphate to reduce the magnesium content, and solidifying. Has been. Furthermore, it is described that the gel content can be further reduced by using a deproteinization treatment in combination. However, no consideration is given to improving the tread characteristics of high-load tires.

Japanese Patent Application Laid-Open No. 06-056903 Japanese Patent No. 4563651

  An object of the present invention is to provide a rubber composition for a tread of a high-load tire excellent in a balance between wear resistance, fracture characteristics, and workability, and a high-load tire having a tread using the rubber composition.

  The present invention contains a rubber component containing 50 to 100% by mass of isoprene-based rubber and 0 to 50% by mass of butadiene rubber. The isoprene-based rubber has a magnesium content of 20 ppm or less and is measured as a toluene insoluble matter. The present invention relates to a rubber composition for a tread of a high load tire containing a low gelled natural rubber having a gel content of 10% by mass or less.

  It is preferable that the rubber component is not produced by the kneading step of the rubber component without containing the peptizer and the kneading step of the natural rubber.

  The magnesium content of the low gelled natural rubber is preferably 8 ppm or less, and the gel content measured as a toluene insoluble content is preferably 5 mass% or less.

  The nitrogen content of the low gelled natural rubber is preferably 0.10% by mass or less.

  It is preferable to contain 20 to 80 parts by mass of carbon black and 0 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component.

  Moreover, this invention relates to the high load tire which has a tread which consists of a rubber composition for treads of the said high load tire.

  According to the present invention, a rubber composition for a tread for a high-load tire containing a low gelled natural rubber having a magnesium content of 20 ppm or less and a gel content measured as a toluene insoluble content of 10% by mass or less; By doing so, it is possible to provide a rubber composition for a tread of a high-load tire excellent in balance in wear resistance, fracture characteristics and workability, and a high-load tire having a tread using this rubber composition.

  The rubber composition for a tread of a high-load tire of the present invention is characterized by containing a predetermined amount of isoprene-based rubber and butadiene rubber, and the isoprene-based rubber contains a predetermined low gelled natural rubber.

  Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), and epoxidized natural rubber (ENR). These rubber components can be used alone or in combination of two or more.

  The rubber composition for a tread of a high-load tire of the present invention is characterized by containing a predetermined low gelled natural rubber (low gelled NR), and improves the balance of wear resistance, fracture characteristics, and processability. In view of this, it is preferable to contain only low gelling NR as isoprene-based rubber. Here, the low gelled NR in the present specification refers to a natural rubber in which the magnesium content and the gel content are reduced from those of ordinary natural rubber.

  The magnesium content of the low gelled NR is 20 ppm or less, preferably 10 ppm or less, and more preferably 8 ppm or less. When the magnesium content exceeds 20 ppm, the gel content tends to be high and processability tends to deteriorate. The magnesium content of natural rubber can be measured by ICP (inductively coupled plasma) emission spectroscopy.

The gel content of the low gelation NR is 10% by mass or less, preferably 8% by mass or less, and more preferably 5% by mass or less. When the gel content exceeds 10% by mass, processability tends to deteriorate. In addition, the gel content rate in this specification is a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and is called a gel content rate or a gel content in this specification. The gel content of natural rubber is measured by the following measurement method. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

  As a method for preparing the low gelation NR (magnesium content reduction method), a method described in Japanese Patent No. 4563651 can be used. For example, there is a method for preparing natural rubber in which a natural rubber latex is treated with a phosphate and the magnesium phosphate produced is removed to reduce the magnesium content, and then solidified to reduce the gel content. Can be mentioned. According to this preparation method, the magnesium content and gel content of the resulting low gelled natural rubber can be adjusted by adjusting the time (number of days) from collection of natural rubber latex to solidification. In other words, by setting the number of days until solidification within 10 days, natural rubber having a gel content of 10% by mass or less can be prepared, and by further speeding up the process, the natural content of the gel is further reduced. A rubber can be prepared.

  Furthermore, the low gelation NR is preferably a low gelation deproteinization NR that has been subjected to a deproteinization treatment from the viewpoint of further improving wear resistance, fracture characteristics, and processability. As a method for deproteinizing natural rubber, conventionally known methods described in Japanese Patent Application Laid-Open Nos. 06-056903 and 2000-198881 can be employed for low gelling NR.

  The nitrogen content of the low gelled deproteinized NR is preferably 0.10% by mass or less, and more preferably 0.08% by mass or less. When the nitrogen content exceeds 0.10% by mass, the effect of deproteinization tends to be insufficient. Further, the lower limit of the nitrogen content is preferably lower, and it is desirable not to contain nitrogen if possible. However, the lower limit is usually 0.03% by mass due to limitations such as the production method. The nitrogen content of natural rubber is measured by the Kjeldahl test method.

  The content of the isoprene-based rubber in the rubber component is 50% by mass or more, and preferably 70% by mass or more. When the content of the isoprene-based rubber is less than 50% by mass, the fracture characteristics and processability tend to deteriorate. Further, the content of the isoprene-based rubber is 100% by mass or less, preferably 90% by mass or less, and more preferably 80% by mass or less. The content of isoprene-based rubber is preferably 100% by mass from the viewpoint of excellent fracture characteristics and workability, and is preferably 90% by mass or less from the viewpoint of excellent wear resistance.

  Further, the content of the low gelling NR in the rubber component is preferably 20% by mass or more, and more preferably 40% by mass or more. When the content of the low gelling NR is less than 20% by mass, the effect of containing the low gelling NR tends to be insufficient.

  When producing a rubber composition containing natural rubber that has not been gelled, it is necessary to add a kneading accelerator to the natural rubber before the kneading step, and knead with a kneading roll machine or a closed mixer. is there. However, when the rubber composition of the present invention, particularly when it contains only low gelling NR as an isoprene-based rubber, or when it contains only isoprene-based rubber that does not require mastication such as low gelling NR and IR, In spite of containing (low gelling NR), the kneading step of the rubber component can be carried out without containing the kneading accelerator and without carrying out the NR kneading step.

  Examples of the butadiene rubber (BR) include high-cis 1,4-polybutadiene rubber (high-cis BR), butadiene rubber containing 1,2-syndiotactic polybutadiene crystals (SPB-containing BR), and modified butadiene rubber (modified BR). It is done.

  The high cis BR is a butadiene rubber having a cis 1,4 bond content of 90% by mass or more. Examples of such high-sis BR include BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., and BR150B.

  The SPB-containing BR is not a dispersion in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in BR but may be dispersed after chemically bonding with BR. Examples of such SPB-containing BR include VCR-303, VCR-412 and VCR-617 manufactured by Ube Industries.

  The modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further the terminal of the modified BR molecule is bonded with a tin-carbon bond. Is mentioned. Examples of such modified BR include BR1250H (tin modified) manufactured by Nippon Zeon Co., Ltd., and S modified polymer (silane modified) manufactured by Sumitomo Chemical Co., Ltd.

  Among these various BRs, it is preferable to use a high cis BR such as BR130B and BR150B from the viewpoint of excellent workability, wear resistance and fracture characteristics.

  The content of BR in the rubber component is 0% by mass or more, and preferably 10% by mass or more. The content of BR is preferably 0% by mass from the viewpoint of excellent fracture characteristics and workability, but is preferably 10% by mass or more from the viewpoint of excellent wear resistance. The BR content is 50% by mass or less, preferably 40% by mass or less, and more preferably 20% by mass or less. When the content of BR exceeds 50% by mass, the fracture characteristics and wear performance tend to be significantly deteriorated.

  The rubber component used in the present invention may contain other rubber components other than isoprene-based rubber and butadiene rubber. Examples of other rubber components include styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and the like.

  When the other rubber component is contained, the content in the rubber component is preferably 10% by mass or more, and more preferably 20% by mass or more. When the content of the other rubber component is less than 10% by mass, the effect of containing the other rubber component tends not to be obtained. Moreover, 70 mass% or less is preferable and, as for content of another rubber component, 60 mass% or less is more preferable. When the content of other rubber components exceeds 70% by mass, the fracture characteristics and wear resistance performance tend to deteriorate.

  The rubber composition for a tread of the high-load tire of the present invention is a compounding agent usually used in the rubber industry, for example, a reinforcing filler such as carbon black and silica, sulfur, silane coupling with the rubber component. Agents, various oils, softeners, waxes, various anti-aging agents, zinc oxide, stearic acid, various vulcanization accelerators and the like can be suitably contained.

  It is preferable to contain carbon black from the viewpoint of improving the reinforcing property, ultraviolet deterioration resistance and crack resistance of the rubber composition. Examples of carbon black include SAF, ISAF, HAF, FF, FEF, GPF and the like that are generally used in tire production. These carbon blacks can be used alone or in combination of two or more. .

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 35 m ² / g or more, and further preferably 70 m ² / g or more. When N ₂ SA is less than 20 m ² / g, there is a possibility that sufficient reinforcing properties cannot be obtained. Also, N ₂ SA of carbon black is preferably not more than 200 meters ² / g, more preferably at most 150m ² / g. When it exceeds 200 m < ² > / g, there exists a tendency for it to become difficult to disperse | distribute favorably and there exists a tendency for workability to deteriorate. Incidentally, N ₂ SA of the carbon black is a value measured by the A method of JIS K6217-2.

  In the case of containing carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 40 parts by mass or more. If the carbon black content is less than 20 parts by mass, sufficient reinforcing properties may not be obtained. Moreover, 80 mass parts or less are preferable, as for content of carbon black, 70 mass parts or less are more preferable, and 60 mass parts or less are more preferable. When the content of carbon black exceeds 80 parts by mass, it tends to be difficult to disperse well and processability tends to deteriorate.

  It is preferable to contain silica from the viewpoint of improving the wet braking performance and low heat build-up of the tire. Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrous silica), and wet process silica is preferred because it has many silanol groups.

Nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably not less than 50 m ² / g, more preferably at least ^{80m 2 / g, 100m 2 /} g or more is more preferable. When N ₂ SA is less than 50 m ² / g, there is a possibility that sufficient reinforcement cannot be obtained. The N ₂ SA of the silica is preferably not more than 500 meters ² / g, more preferably at most 300m ² / g. When it exceeds 500 m < ² > / g, workability may be significantly deteriorated. The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

  The content with respect to 100 parts by mass of the rubber component when silica is contained is preferably 0 part by mass or more, more preferably 5 parts by mass or more, and further preferably 8 parts by mass or more. By containing 5 parts by mass or more of silica, fracture characteristics can be improved. Moreover, 150 mass parts or less are preferable, as for content of a silica, 100 mass parts or less are more preferable, and 80 mass parts or less are more preferable. If the silica content exceeds 150 parts by mass, the processability may be deteriorated.

  When silica is contained, it is preferable to use a silane coupling agent in combination. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, Si75, Si266 (bis (3-triethoxysilyl) manufactured by EVONIK-DEGUSSA Propyl) disulfide), sulfides such as Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by the same company, 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, NXT manufactured by Momentive, etc. Mercapto type (silane coupling agent having a mercapto group), vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitro B pills trimethoxysilane nitro-based, such as, 3-like chloropropyl chloro system such as trimethoxysilane. These may be used alone or in combination of two or more. Of these, sulfide type and mercapto type are preferable from the viewpoints of strong bonding strength with silica and excellent low heat build-up. In addition, the use of a mercapto system is more preferable from the viewpoint that rolling resistance characteristics and durability can be suitably improved.

  In the case of containing a silane coupling agent, the content with respect to 100 parts by mass of silica is preferably 2 parts by mass or more, and more preferably 3 parts by mass or more. When the content of the silane coupling agent is less than 2 parts by mass, the silica dispersibility improving effect tends not to be sufficiently obtained. Further, the content of the silane coupling agent is preferably 25 parts by mass or less, and more preferably 20 parts by mass or less. When the content of the silane coupling agent exceeds 25 parts by mass, a sufficient coupling effect and silica dispersion effect cannot be obtained, and the reinforcing property tends to decrease and the cost tends to deteriorate.

  It does not specifically limit as a manufacturing method of the rubber composition for treads of the high load tire of this invention, A well-known method can be used. For example, each of the above components can be produced by a method of kneading using a rubber kneading apparatus such as an open roll, a Banbury mixer, a close-kneading kneader, and then vulcanizing.

  The rubber composition of the present invention can be applied to each member of a tire, and among them, it is preferably applied to a tread of a high-load tire because it is excellent in wear resistance, fracture characteristics and workability. Moreover, when the tread is a tread having a multilayer structure having a cap tread and a base tread, it is preferably applied to the cap tread.

  The high load tire of the present invention can be produced by a usual method using the rubber composition for a tread of the high load tire of the present invention. That is, a rubber composition for a tread of a high-load tire according to the present invention in which the above-described compounding agent is blended as necessary with respect to a rubber component is extruded into a tread shape at an unvulcanized stage, and a tire is molded. The unvulcanized tire is formed by bonding together with other tire members on the machine and molded by a normal method, and the unvulcanized tire is heated and pressurized in the vulcanizer to improve the performance of the present invention. A load tire can be manufactured.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber: TSR20 (used in preparation of natural rubber sample E)
Kneading accelerator: Nouchitizer SD manufactured by Ouchi Shinsei Chemical Co., Ltd.
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd. (High cis BR, cis-1,4 bond content: 96%)
Carbon Black: Show Black N220 (N220, N ₂ SA: 114 m ² / g) manufactured by Cabot Japan
Silica: ULTRASIL VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by EVONIK-DEGUSSA
Anti-aging agent: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Zinc stearate made by Nippon Oil & Fats Co., Ltd .: Zinc Hua No. 1 made by Mitsui Kinzoku Mining Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator made by Tsurumi Chemical Co., Ltd. Noxeller NS (N-tert-butyl-2-benzothiazylsulfenamide)

Preparation of natural rubber sample Natural rubber A
To the collected natural rubber latex (solid content 30%), ammonium phosphate was added so that the total mass would be 0.1% and allowed to stand overnight, then the supernatant was recovered and the precipitated magnesium phosphate was removed. did. Next, the rubber latex recovered as a supernatant was solidified according to a method for preparing a smoked sheet (RSS) to obtain a raw rubber (natural rubber A). That is, dilute rubber latex with ion exchange water to a solid content concentration of about 15% by mass, add 2-20% by mass formic acid to coagulate the rubber component, and squeeze the serum while passing the coagulated rubber through a roll. It was made into a sheet. This was dried in an oven at 45 ° C. to prepare solid natural rubber A. The collection from natural rubber latex to solidification was performed in 10 days.

Natural rubber B
Raw rubber (natural rubber B) was prepared in the same manner as the natural rubber A production method, except that each step was speeded up and natural rubber latex was collected and solidified in 7 days.

Natural rubber C
To the collected natural rubber latex (solid content 30%), ammonium phosphate was added so that the total mass would be 0.1% and allowed to stand overnight, then the supernatant was recovered and the precipitated magnesium phosphate was removed. did.
And the rubber latex collect | recovered as a supernatant was deproteinized according to the method as described in Unexamined-Japanese-Patent No. 2000-198881 after progress for 2 days. That is, 0.067 parts by mass of protease (proteolytic enzyme), 1.5 parts by mass of 10% sodium polyoxyethylene lauryl ether sulfate (surfactant) with respect to about 167 parts by mass of latex (100 parts by mass of rubber solid content) Agent, KP4401 manufactured by Kao Corporation) was added and diluted with water to prepare a natural rubber latex having a rubber solid content of 30% by mass. Next, the latex was aged with stirring at room temperature for 16 hours to decompose the protein, and about 333 parts by mass of the latex after treatment (100 parts by mass of rubber solids) was diluted with water to obtain a total amount of 1000 parts by mass ( After adjusting to a rubber solid content of about 10% by mass, centrifugation was performed at 10,000 rpm (gravity acceleration of about 9000 G) for 30 minutes. After the centrifugal separation treatment, the creamy rubber component separated into the upper layer was taken out and further diluted with water to adjust the rubber solid content to 60% by mass to obtain a deproteinized natural rubber latex. The resulting deproteinized natural rubber latex was diluted with ion exchange water to a solid content concentration of about 15% by mass, and 2 to 20% by mass of formic acid was added thereto to coagulate the rubber. The serum was squeezed into a sheet by passing the solidified rubber through a roll. This was dried in an oven at 45 ° C. to prepare solid raw rubber (natural rubber C). The collection from natural rubber latex to solidification was performed in 10 days.

Natural rubber D
A natural rubber D was prepared in the same manner as the natural rubber C except that the step of adding ammonium phosphate and removing magnesium phosphate was omitted.

Natural rubber E
A natural rubber E was prepared by adding 0.4 parts by mass of a peptizer to 100 parts by mass of TSR20 and performing mastication using 1.7 L Banbury.

  The following measurements were performed on the prepared natural rubbers A to D and TSR20. The measurement results are shown in Table 1.

<Measurement of gel content>
Each natural rubber sample was cut into 1 mm × 1 mm, 70.00 mg was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Next, the mixture was centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to precipitate a gel content insoluble in toluene, and the soluble content of the supernatant was removed. Only the gel content was solidified with methanol, and then dried to obtain a mass. Was measured. The gel content (mass%) was determined by the following formula.
Gel content (mass%) = [mass after drying / initial sample mass] × 100

<Measurement of magnesium (Mg) content>
The magnesium content in each natural rubber sample was measured using an ICP emission spectroscopic analyzer (ICPS-8100 manufactured by Shimadzu Corporation).

<Measurement of nitrogen content>
The nitrogen content in each natural rubber sample was measured by the Kjeldahl test method.

Examples 1-9 and Comparative Examples 1-6
According to the formulation shown in Table 2, using a 1.7 L closed Banbury mixer, chemicals other than sulfur and vulcanization accelerator were kneaded for 3 to 5 minutes until reaching 150 ° C. to obtain a kneaded product. . Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 2 minutes at 70 ° C. to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition was press vulcanized for 15 minutes at 170 ° C. to obtain a vulcanized rubber composition.

  The obtained unvulcanized rubber composition and vulcanized rubber composition were used for evaluation by the following methods. The evaluation results are shown in Table 2.

<Processability>
In accordance with JIS K6300, the Mooney viscosity of the unvulcanized rubber composition at 130 ° C. was measured. The results are shown as an index with Comparative Example 3 as 100. The larger the index, the lower the viscosity and the better the workability.

<Abrasion resistance>
Each vulcanized rubber composition was tested under the conditions of a surface rotation speed of 50 m / min, a load load of 3.0 kg, a falling sand amount of 15 g / min, and a slip rate of 20% using a Lambourne abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. The amount of lamborn wear was measured. The results are shown as an index with Comparative Example 3 as 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

<Destructive properties>
Using a No. 3 dumbbell-shaped test piece made of a vulcanized rubber composition, a tensile test was conducted at room temperature in accordance with JIS K 6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The elongation EB (%) was measured. The results are shown as an index with Comparative Example 1 as 100. The larger the index, the stronger the rubber strength, the better the chip cutting resistance, and the better the fracture characteristics.

  From the results shown in Table 2, the rubber composition containing low-gelling natural rubber having a magnesium content of 20 ppm or less and a gel content measured as toluene insoluble content of 10% by mass or less is resistant to abrasion and fracture. It can be seen that the properties and workability are well balanced.

Claims (6)

A rubber component containing 50 to 100% by mass of isoprene-based rubber and 0 to 50% by mass of butadiene rubber;
A rubber composition for a tread for a high-load tire, wherein the isoprene-based rubber contains a low gelled natural rubber having a magnesium content of 20 ppm or less and a gel content measured as a toluene insoluble content of 10% by mass or less. The rubber composition for a tread of a high-load tire according to claim 1, wherein the rubber composition is produced by performing a kneading step of a rubber component without containing a kneading accelerator and without performing a kneading step of natural rubber. The rubber composition for a tread of a high-load tire according to claim 1 or 2, wherein the low gelled natural rubber has a magnesium content of 8 ppm or less and a gel content measured as a toluene insoluble content is 5 mass% or less. The rubber composition for a tread of a high-load tire according to any one of claims 1 to 3, wherein the low gelled natural rubber has a nitrogen content of 0.10% by mass or less. The rubber composition for a tread of a high-load tire according to any one of claims 1 to 4, comprising 20 to 80 parts by mass of carbon black and 0 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component. The high load tire which has a tread which consists of a rubber composition of any one of Claims 1-5.