JP5503395B2 - Heavy duty vehicle tread rubber composition and heavy duty vehicle tire - Google Patents

Description

The present invention relates to a rubber composition for a tread of a heavy-duty vehicle and a heavy-duty vehicle tire using the same.

Tires used in heavy-duty vehicles such as trucks and buses are required to have excellent heat resistance and low heat generation to improve fuel efficiency. In particular, in a dump truck tire mainly used for traveling on rough roads, damage to the tread rubber, such as chip cut, occurs. Therefore, it is necessary to ensure durability (chip resistance) against the chip cut. Therefore, the tread rubber of the tire for a dump truck is composed of a natural rubber that can obtain high rubber strength and low heat buildup, in whole or in large part.

On the other hand, wear resistance is also required as the durability performance of tires, and all-season tires and the like mainly used for driving on good roads are formulated with butadiene rubber to improve wear resistance. However, when butadiene rubber is blended in a dump truck tire, although there is a tendency to improve the wear resistance, the chip-cut performance deteriorates, and it is difficult to achieve both of these performances.

In addition, natural rubber has a higher Mooney viscosity than synthetic rubber, so the processability is poor, and it is usually used after mastication with a masticant added to lower the Mooney viscosity. It is inferior to. Further, there is a problem that the molecular chain of natural rubber is cut by mastication and the characteristics of the high molecular weight polymer inherent to natural rubber are lost. As described above, it is difficult to provide a tread rubber that is excellent in both wear resistance and chipping resistance, and has low heat buildup and good workability in heavy-duty vehicle tires, particularly dump truck tires. .

For example, Patent Document 1 discloses a rubber composition for steel cords that uses deproteinized natural rubber having a total nitrogen content equal to or less than a predetermined value, reduces unvulcanized viscosity, and has good processability. However, there is still room for improvement in terms of achieving both wear resistance and chipping resistance, as well as excellent exotherm and workability.

JP 2009-24073 A

The present invention provides a rubber composition for a heavy-duty vehicle tread and a tire for a heavy-duty vehicle that can solve the above-mentioned problems and can achieve both wear resistance and chipping-resistance performance, and at the same time improve low heat buildup and workability. For the purpose.

The present invention relates to a rubber composition for a tread of a heavy-duty vehicle including a modified natural rubber having a phosphorus content of 200 ppm or less.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 10% by mass or more.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 50% by mass or more.

The modified natural rubber preferably has a gel content measured as a toluene insoluble content of 20% by mass or less and a nitrogen content of 0.3% by mass or less.

The modified natural rubber is preferably obtained by saponifying natural rubber latex.

The rubber composition for a tread of the present invention preferably further contains natural rubber.

The present invention also relates to a heavy duty vehicle tire having a tread produced using the rubber composition.

The heavy-duty vehicle tire is preferably used for a dump truck.

According to the present invention, since a specific modified natural rubber is used, a rubber composition for a tread of a heavy-duty vehicle that can achieve both wear resistance and chipping resistance, and is excellent in low heat generation and workability. Can provide.

The rubber composition for a tread of a heavy-duty vehicle according to the present invention includes a modified natural rubber having a phosphorus content of 200 ppm or less. By using modified natural rubber (HPNR), which reduces and removes phospholipids contained in natural rubber (NR), wear resistance can be improved without using BR and chip resistance can be improved. Can be improved at the same time. In addition, low heat build-up and processability can be improved. Furthermore, by reducing not only phospholipids but also proteins and gels, these performances can be further improved.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. By making it 200 ppm or less, chipping resistance and wear resistance can be improved at the same time, and low heat build-up and workability can also be improved. The phosphorus content is preferably 150 ppm or less, and more preferably 100 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the processability tends to decrease, for example, the Mooney viscosity increases. Moreover, there is a tendency that sufficient chipping resistance, wear resistance, and low heat generation cannot be obtained. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. 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.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity tends to increase during storage. Moreover, there is a tendency that sufficient chipping resistance, wear resistance, and low heat generation cannot be obtained. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

Examples of the method for producing the modified natural rubber include a method of producing natural rubber latex by saponification with alkali, washing the saponified and agglomerated rubber, and then drying. The saponification treatment is performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a predetermined time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed. In the present invention, alkali can be added to natural rubber latex for saponification, but by adding it to natural rubber latex, there is an effect that saponification can be efficiently performed.

Natural rubber latex is collected as sap of heavy trees and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is thought to be based on the complex presence of various impurities. . In the present invention, raw latex produced by tapping a heavy tree or purified latex concentrated by centrifugation can be used. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used in order to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex.

Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and an amine compound. From the viewpoint of the effect of the saponification treatment and the influence on the stability of the natural rubber latex, it is particularly hydroxylated. Sodium or potassium hydroxide is preferably used.

The amount of alkali added is not particularly limited, but the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is 12 parts by mass or less with respect to 100 parts by mass of the solid content of natural rubber latex. Is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount of alkali added is less than 0.1 parts by mass, saponification may take time. Conversely, if the amount of alkali added exceeds 12 parts by mass, the natural rubber latex may be destabilized.

As the surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants. Examples of nonionic surfactants include nonionic surfactants such as polyoxyalkylene ethers, polyoxyalkylene esters, polyhydric alcohol fatty acid esters, sugar fatty acid esters, and alkyl polyglycosides. Examples of the amphoteric surfactant include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Among these, an anionic surfactant is preferable, and a sulfonic acid anionic surfactant is more preferable.

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1.1 parts by mass or more with respect to 100 parts by mass of the solid content of the natural rubber latex. The upper limit is preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, and further preferably 3.5 parts by mass or less. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6.0 parts by mass, the natural rubber latex may be overstabilized and coagulation may be difficult. Moreover, when it is 1.1 mass parts or more, the phosphorus content, the nitrogen content, and the gel content in the natural rubber can be further reduced.

The temperature of the saponification treatment can be appropriately set within a range where the saponification reaction with alkali can proceed at a sufficient reaction rate and within a range where the natural rubber latex does not undergo alteration such as coagulation, but is usually 20 to 70 ° C. Preferably, 30-70 degreeC is more preferable. Further, the treatment time is 3 to 48 hours in consideration of both sufficient treatment and productivity improvement, depending on the treatment temperature when the treatment is performed with natural rubber latex standing. Is preferable, and 3 to 24 hours is more preferable.

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the aggregation method include a method of adjusting pH by adding an acid such as formic acid. Examples of the washing treatment include a method of diluting the rubber with water and washing it, and then performing a centrifugal separation treatment to take out the rubber. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. After completion of the washing treatment, a saponified natural rubber latex is obtained. The modified natural rubber according to the present invention is obtained by drying the saponified natural rubber latex.

In the above production method, the saponification, washing and drying steps are preferably completed within 15 days after collecting the natural rubber latex. More preferably, it is within 10 days, and more preferably within 5 days. This is because the gel content increases if the sample is left for more than 15 days without solidification after collection.

In the rubber composition for a tread of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 50% by mass or more, and further preferably 70% by mass or more. It is. If it is less than 10% by mass, the effects of the present invention may not be sufficiently obtained. The upper limit of the content of the modified natural rubber is not particularly limited, but is preferably 95% by mass or less, and more preferably 85% by mass or less. If it exceeds 95% by mass, the wear resistance may be reduced.

Examples of the rubber component used in the present invention include diene rubbers generally used in tire rubber compositions in addition to the modified natural rubber. Specific examples of the diene rubber include natural rubber (NR) other than the modified natural rubber (saponified natural rubber), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), ethylene propylene. Examples include, but are not limited to, diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), styrene isoprene butadiene rubber (SIBR), and epoxidized natural rubber. . These may be used alone or in combination of two or more. Among these, it is preferable to use NR from the viewpoint of ensuring sufficient tire strength and exhibiting excellent wear resistance.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

In the rubber composition for a tread of the present invention, when NR is used, the content of NR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 15% by mass or more. If it is less than 5% by mass, the crack growth resistance may be deteriorated. The NR content is preferably 90% by mass or less, more preferably 50% by mass or less, and still more preferably 30% by mass or less. If it exceeds 90% by mass, the blended amount of the modified natural rubber decreases, and the effects of the present invention may not be obtained.

In the rubber composition for a tread of the present invention, when NR is used, the total content of the modified natural rubber and NR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more. More preferably, it is 90 mass% or more, Most preferably, it is 100 mass%. Thereby, the effect of this invention can be acquired favorably.

The rubber composition for a tread of the present invention preferably contains carbon black. By using carbon black together with HPNR, excellent reinforcement is exhibited, so that wear resistance can be improved without using BR, and chipping resistance can also be improved.

When carbon black is used in the rubber composition for a tread of the present invention, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 90 m ² / g or more, more preferably 100 m ² / g or more, and 105 m ² / g. Is more preferable. If it is less than 90 m < ² > / g, there exists a possibility that sufficient reinforcement may not be obtained. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 200 meters ² / g or less, more preferably 150 meters ² / g, more preferably at most 120 m ² / g. When it exceeds 200 m ² / g, there is a tendency that low heat build-up and processability are lowered.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

Carbon black has a dibutyl phthalate (DBP) oil absorption of preferably 90 ml / 100 g or more, more preferably 100 ml / 100 g or more, and even more preferably 110 ml / 100 g or more. The DBP oil absorption of carbon black is preferably 200 ml / 100 g or less, more preferably 160 ml / 100 g or less, and still more preferably 120 ml / 100 g or less. When it exceeds 200 ml / 100 g, there is a tendency that low heat build-up and processability are lowered.
In addition, the DBP oil absorption amount of carbon black is calculated | required by the measuring method of JISK6217-4.

When the rubber composition for a tread of the present invention contains carbon black, the content of carbon black is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 100 parts by mass of the rubber component. It is 40 parts by mass or more. If it is less than 10 mass parts, there exists a possibility that reinforcing property cannot fully be improved. The carbon black content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less. When it exceeds 70 mass parts, there exists a tendency for low exothermic property to fall.

In addition to the above components, the tread rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, oils such as aroma oils, waxes, etc. Further, a vulcanizing agent, a vulcanization accelerator and the like can be appropriately blended.

In the present invention, sulfur can be suitably used as a vulcanizing agent. By vulcanizing HPNR with sulfur, it is possible to obtain a vulcanized rubber composition having excellent wear resistance and chipping resistance and good low heat buildup. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

The sulfur content is preferably 0.5 parts by mass or more, and more preferably 0.7 parts by mass or more with respect to 100 parts by mass of the rubber component. The sulfur content is preferably 1.5 parts by mass or less, more preferably 1 part by mass or less, and still more preferably 0.9 parts by mass or less. If it is out of the above range, the wear resistance and chipping resistance tend to decrease.

The rubber composition for a tread of the present invention preferably contains a predetermined amount of stearic acid. By blending and vulcanizing a predetermined amount of stearic acid, a vulcanized rubber composition having excellent performance can be prepared.

When the rubber composition for treads of the present invention contains stearic acid, the content of stearic acid is preferably 2.5 parts by mass or more, more preferably 3.5 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. Moreover, this content becomes like this. Preferably it is 7 mass parts or less, More preferably, it is 5 mass parts or less. By adjusting within the above range, a vulcanized rubber composition having excellent performance can be prepared.

The rubber composition for a tread of the present invention preferably contains an antiaging agent. As the anti-aging agent, amine-based, phenol-based, and imidazole-based compounds, carbamic acid metal salts, waxes, and the like can be appropriately selected and used. Of these, amines are preferable because of their excellent ozone resistance and heat resistance, and N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine is more preferable.

When the rubber composition for a tread of the present invention contains an anti-aging agent, the content of the anti-aging agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, with respect to 100 parts by mass of the rubber component. It is. If it is less than 1 part by mass, the durability may be reduced. Further, the content is preferably 4 parts by mass or less, more preferably 2.5 parts by mass or less. If it exceeds 4 parts by mass, the anti-aging agent may be deposited on the tire surface and discolored.

The rubber composition for a tread of the present invention preferably contains a vulcanization accelerator. Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). These vulcanization accelerators may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators such as TBBS and CBS are superior because they have excellent vulcanization characteristics, excellent physical properties of rubber after vulcanization, excellent low heat build-up, and great effects of improving mechanical hardness. TBBS is preferable.

When the vulcanization accelerator is blended in the tread rubber composition, the blending amount is preferably 1 part by mass or more, and more preferably 1.3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the rubber composition may not be sufficiently vulcanized and the required rubber properties may not be obtained. The blending amount is preferably 2 parts by mass or less, more preferably 1.7 parts by mass or less. If it exceeds 2 parts by mass, there is a risk of rubber burning.

In the rubber composition for a tread of the present invention, the oil content is preferably 5 parts by mass or less, more preferably 1 part by mass or less, and particularly preferably no oil, with respect to 100 parts by mass of the rubber component. . Excellent chipping resistance and wear resistance can be obtained by reducing the amount of oil. Further, since the Mooney viscosity can be reduced by using HPNR as compared with the use of NR, good workability can be maintained even if the amount of oil is reduced.

The rubber composition for a tread of the present invention is produced by a general method. That is, it can be produced by a method of kneading each component with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition for a tread of the present invention is used for a tread (cap tread) of a heavy-duty vehicle tire (for trucks and buses). Especially, it is preferable to use for the tread (cap tread) of the tire for dump trucks.

The tire for heavy-duty vehicles of the present invention is manufactured by a usual method using the rubber composition for tread. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of the tread of the tire at an unvulcanized stage, molded by a normal method on a tire molding machine, etc. The tire members are bonded together to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E (Polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
NR: RSS # 3
HPNR-A: Production Example 1 below
HPNR-B: Production Example 2 below
Untreated natural rubber: Production Example 3 below
Carbon N220: Cabot Japan made of (stock) Show black ^{_{N220 (N 2 SA: 111m 2}} / g, DBP oil ^absorption: 115cm 3 / 100g)
Wax: Sunnock wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. (6C): Nocrack 6C (N- (1,3-dimethylbutyl) -N′-phenyl manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) -P-phenylenediamine)
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc Hua 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS (N-tert-butyl manufactured by Ouchi Shinsei Chemical Co., Ltd.) -2-Benzothiazolylsulfenamide)

(Production of saponified natural rubber with alkali)
Production Example 1
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (HPNR-A).
Production Example 2
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 15 g of NaOH, followed by a saponification reaction at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (HPNR-B).
Production Example 3
After adjusting the solid content concentration (DRC) of the natural rubber latex to 30% (w / v), the formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 and agglomerate. The agglomerated rubber was pulverized and dried at 110 ° C. for 2 hours to obtain a solid rubber (untreated natural rubber).

Nitrogen content, phosphorus content, and gel content were measured by the method shown below about solid rubber and RSS # 3 obtained by Production Examples 1-3. The results are shown in Table 1.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Industries). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of natural rubber obtained in each production example was weighed, and an average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 1, HPNR-A and HPNR-B had reduced nitrogen content, phosphorus content, and gel content as compared to untreated natural rubber and RSS # 3.
Further, HPNR-A, in ³¹ P NMR measurement of the extract extracted from HPNR-B, did not detect the peak due to phospholipids -3Ppm～1ppm.

(Production of rubber test pieces and tires)
In accordance with the formulation shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer manufactured by Kobe Steel. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. In Comparative Example 1 using RSS # 3, 0.4 parts by mass of a peptizer was added to 100 parts by mass of the rubber component of RSS # 3, and kneaded in advance using a 1.7 L Banbury mixer. Went. On the other hand, in Examples 1 to 3 and Comparative Example 2, natural rubber was not masticated.

Next, the obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition (vulcanized rubber sheet).
Further, the obtained unvulcanized rubber composition was molded into a tread shape on a tire molding machine, bonded to another tire member, and vulcanized at 150 ° C. for 30 minutes to test tires (tire size: 11R22. 5) was produced.

The obtained unvulcanized rubber composition, vulcanized rubber composition and test tire were evaluated as follows. The results are shown in Table 2.

(Processability)
In accordance with JIS K6300-1, “Unvulcanized rubber—Physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”, 130 heated with a Mooney viscosity tester by preheating for 1 minute. Under the temperature condition of ° C., the small rotor was rotated, and the Mooney viscosity (ML _{1 +} 4/130 ° C.) of the unvulcanized rubber composition after 4 minutes was measured. And the Mooney viscosity of the comparative example 1 was set to 100, and it represented by the index | exponent by the following formula. It shows that Mooney viscosity is so low that a numerical value is large, and it is excellent in workability.
(Mooney viscosity index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Rubber strength)
A rubber test piece collected from the tread of the test tire was subjected to a tensile test according to JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tensile Properties”, and the elongation at break EB (%) was measured. . Then, assuming that the elongation at break of Comparative Example 1 was 100, the EB of each formulation was displayed as an index according to the following formula. The larger the value, the higher the rubber strength and the better the chip cut resistance.
(Rubber Strength Index) = (EB of each formulation) / (EB of Comparative Example 1) × 100

(Rolling resistance)
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd., the loss tangent (tan δ) of the vulcanized rubber sheet was measured and compared under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The loss tangent (tan δ) of Example 1 was set to 100, and the rolling resistance characteristics of each formulation were indicated by an index according to the following formula. It shows that it is excellent in rolling resistance characteristics, so that an index | exponent is large.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Abrasion test)
Using a Lambone abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd., Lambbone abrasion of the above vulcanized rubber composition under conditions of a surface rotation speed of 50 m / min, a load load of 3.0 kg, a sandfall amount of 15 g / min, and a slip rate of 20%. The amount was measured. Then, the volume loss amount was calculated from the measured lamborn wear amount, and the volume loss amount of Comparative Example 1 was set as 100, and the volume loss amount of each formulation was indicated by an index according to the following calculation formula. It shows that it is excellent in abrasion resistance, so that a numerical value is large.
(Abrasion resistance index) = (volume loss amount of Comparative Example 1) / (volume loss amount of each formulation) × 100

From Table 2, compared with the comparative example which does not mix | blend HPNR, in the Example which mix | blends HPNR, both performance of abrasion resistance and chip-cut performance could be improved simultaneously, without mix | blending BR. In addition to these performances, it was possible to improve the performance of low heat generation and workability.

Claims (7)

Heavy rubber containing a modified natural rubber having a phosphorus content of 200 ppm or less is obtained by saponifying natural rubber latex with alkali, repeatedly washing the saponified and agglomerated rubber, and washing away the phosphorus compound separated by saponification. Rubber composition for treads of load vehicles. The rubber composition for a tread of a heavy-duty vehicle according to claim 1, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 10% by mass or more. The rubber composition for a tread of a heavy duty vehicle according to claim 1 or 2, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 50% by mass or more. The tread of a heavy-duty vehicle according to any one of claims 1 to 3, wherein the modified natural rubber has a gel content of 20% by mass or less and a nitrogen content of 0.3% by mass or less, measured as toluene insoluble matter. Rubber composition. The rubber composition for a tread of a heavy-duty vehicle according to any one of claims 1 to 4 , further comprising natural rubber. A heavy-duty vehicle tire having a tread produced using the rubber composition according to any one of claims 1 to 5 . The heavy-duty vehicle tire according to claim 6 used in a dump truck.