JP2018188601A - Rubber composition for studless tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a studless tire rubber composition having improved performance on ice and snow, fracture characteristics (durability) and wear resistance in a well-balanced manner, and a studless tire using the same. SOLUTION: The rubber component, silica having a nitrogen adsorption ratio surface area of 120 m2 / g or more and less than 200 m2 / g, and carbon black are contained, and the content of unmodified natural rubber is 10% by mass or more in 100% by mass of the rubber component. High-purity natural rubber with a phosphorus content of 500 ppm or less is 10% by mass or more, synthetic polyisoprene rubber is 20% by mass or less, and cis polybutadiene rubber with a cis content of 95% by mass or more is 25% by mass. % Or more, and the content of the silica is 10 to 50 parts by mass and the content of the carbon black is 30 parts by mass or more with respect to 100 parts by mass of the rubber component. [Selection diagram] None

Description

The present invention relates to a rubber composition for studless tires, and a studless tire using the rubber composition.

Studless tires for passenger cars and trucks and buses use a rubber compounded with natural rubber and butadiene rubber, which has excellent low-temperature properties, and a carbon black or silica reinforcing agent added to ensure the friction on ice. Techniques for foaming tread rubber or mixing various foreign substances (eg eggshell powder, threshing powder, walnut shell powder, micro glass balloon, nylon powder, etc.) have been applied (see Patent Document 1).

However, increasing the foaming rate and the amount of foreign matters to give better low-temperature performance increases the frictional force on ice, but the durability of the tread rubber when running on a road without snow is significantly reduced. Running increases the risk of early tread rubber wear and chunking where a portion of the tread is missing on a truck bus. A method of improving the performance on ice by increasing the polybutadiene ratio is also conceivable, but since the strength characteristics are significantly lower than that of natural rubber, there are also problems such as chunking.

As a method to solve these problems, a technology has been proposed that increases the compounding ratio of silica, which makes rubber harder at low temperatures than carbon black, improves the flexibility of rubber at low temperatures, and improves performance on ice. ing. However, from spring to summer when the temperature exceeds 20 ° C, sufficient durability cannot be ensured, and in particular for truck bus tires, there is a problem that deterioration of wear performance due to the increase in silica ratio is inevitable due to the large contact pressure. is there.

JP 2010-168427 A

An object of the present invention is to solve the above-mentioned problems and to provide a studless tire rubber composition in which performance on ice and snow, fracture characteristics (durability), and wear resistance are improved in a well-balanced manner, and a studless tire using the same.

The present invention includes a rubber component, a silica having a nitrogen adsorption specific surface area of 120 m ² / g or more and less than 200 m ² / g, and carbon black, and the content of unmodified natural rubber is 10% by mass in 100% by mass of the rubber component. As described above, the content of high-purity polybutadiene rubber having a phosphorus content of 500 ppm or less, a high-purity natural rubber content of 10% by mass or more, a synthetic polyisoprene rubber content of 20% by mass or less, and a cis content of 95% by mass or more. It is 25 mass% or more, It is related with the rubber composition for studless tires whose content of the said silica is 10-50 mass parts and whose content of the said carbon black is 30 mass parts or more with respect to 100 mass parts of said rubber components.

The rubber composition has a complex elastic modulus E * (temperature 0 ° C., frequency 10 Hz, initial elongation strain 5%, dynamic elongation strain 2%) of 15 MPa or less, breaking strength TB (temperature 23 ° C.) of 15 MPa or more, breaking elongation. EB (temperature 23 ° C.) is preferably 420% or more.

The highly purified natural rubber has a nitrogen content of 0.30% by mass or less, the carbon black has a nitrogen adsorption specific surface area of 120 m ² / g or more, and the non-modified rubber component in 100% by mass of the rubber component. The total content of the natural rubber, the highly purified natural rubber and the synthetic polyisoprene rubber is preferably 50% by mass or more.

It is preferable that a terpene resin having a softening point of 120 ° C. or lower is included with respect to 100 parts by mass of the rubber component.
The present invention also relates to a studless tire having a tread produced using the rubber composition.

According to the present invention, a rubber component including non-modified natural rubber, predetermined high-purity natural rubber, synthetic polyisoprene rubber and high-cis polybutadiene rubber, silica having a predetermined nitrogen adsorption specific surface area, and carbon black are specified. Since the rubber composition for studless tires contained in is, the performance on ice and snow, fracture characteristics (durability), and wear resistance are improved in a well-balanced manner.

The rubber composition for studless tires of the present invention comprises a rubber component, a silica having a nitrogen adsorption specific surface area of 120 m ² / g or more and less than 200 m ² / g, and carbon black. A high-purity natural rubber content of 10 mass% or more, a phosphorus content of 500 ppm or less, a high content of 10 mass% or more, a synthetic polyisoprene rubber content of 20 mass% or less, and a cis content of 95 mass% or more. The content of cis-polybutadiene rubber is 25% by mass or more, the content of silica is 10 to 50 parts by mass, and the content of carbon black is 30 parts by mass or more with respect to 100 parts by mass of the rubber component.

In the present invention, in order to solve the above-mentioned problems, a predetermined amount of high-cis polybutadiene rubber, high specific surface area silica, carbon black is used in the blend of a studless tire including isoprene-based rubber, butadiene rubber, silica, and carbon black, and particularly rubber. By using unmodified natural rubber (ordinary natural rubber) and high-purity natural rubber in combination in specified amounts, the fracture characteristics (durability), wear resistance, and performance on ice and snow are improved in a well-balanced manner. The inventors have found knowledge and have completed the present invention.

For high-purity natural rubber, by reducing the amount of proteins and phospholipids contained as impurities in natural rubber, the proportion of natural rubber polyisoprene component that can be in direct contact with carbon black increases, and carbon black dispersibility is promoted. By exhibiting the effect of improving the reinforcing force by increasing the contact area, low exothermic properties and high reinforcing properties can be obtained. Furthermore, the improvement in the dispersibility of carbon black lowers the elastic modulus in the micro-deformation region and improves the flexibility of the tread rubber at low temperatures.

On the other hand, as for the application of silica to highly purified natural rubber, silica has a highly polar functional group on the surface, so that it is difficult to disperse silica in highly purified natural rubber compared to natural rubber. Tend.

Based on such characteristics, the present invention is capable of maximizing the reinforcing effect of carbon black and silica by blending a predetermined amount of natural rubber and highly purified natural rubber while using high specific surface area silica, and is excellent. It improves the performance on ice while imparting wear resistance and durability (destructive properties). Therefore, in the present invention, the performance balance of performance on ice and snow, fracture characteristics (durability), and wear resistance can be remarkably and specifically improved.

The rubber composition contains 10% by mass or more of non-modified natural rubber in 100% by mass of the rubber component. By setting it to the lower limit or more, good silica dispersion is obtained in the highly purified natural rubber, and excellent fracture characteristics tend to be obtained. Preferably it is 13 mass% or more, More preferably, it is 15 mass% or more. Although an upper limit is not specifically limited, 70 mass% or less is preferable and 55 mass% or less is more preferable.

Unmodified natural rubber is normal natural rubber (NR) that has not been modified or modified. As the NR, for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20 and the like can be used.

The rubber composition contains 10% by mass or more of highly purified natural rubber having a phosphorus content of 500 ppm or less in 100% by mass of the rubber component. When the content is 10% by mass or more, a good filler dispersibility promoting effect and reinforcement enhancing effect can be obtained, and excellent fracture characteristics tend to be obtained. Preferably it is 13 mass% or more, More preferably, it is 15 mass% or more. Although an upper limit is not specifically limited, 70 mass% or less is preferable and 55 mass% or less is more preferable.

The phosphorus content in the highly purified natural rubber is preferably 400 ppm or less, more preferably 300 ppm or less, and even more preferably 200 ppm or less. The phosphorus content can be measured by a conventional method such as ICP emission analysis.

The highly purified natural rubber preferably has a nitrogen content of 0.50% by mass or less, more preferably 0.30% by mass or less, after being immersed in acetone at room temperature (25 ° C.) for 48 hours. More preferably, it is 0.15 mass% or less, Most preferably, it is 0.10 mass% or less. The nitrogen content is a measured value after removing an artificial anti-aging agent in rubber by extraction with acetone. The nitrogen content can be measured by a conventional method such as Kjeldahl method or trace nitrogen meter. Nitrogen is derived from proteins and amino acids.

As said highly purified natural rubber, what was highly purified and pH was adjusted to 2-7 can be used conveniently, for example. The highly purified natural rubber can be prepared by a production method disclosed in International Publication No. WO2014 / 125700.

The highly purified natural rubber preferably has a pH of 2 to 7, more preferably 3 to 6, still more preferably 4 to 6. The pH of the highly purified natural rubber is cut to a size of 2 mm square on each side, immersed in distilled water, extracted at 90 ° C. for 15 minutes while irradiating with microwaves, and the immersion water is measured with a pH meter. It is the value measured using, and specifically, it measures by the method as described in the below-mentioned Example.

The highly purified natural rubber includes, for example, a step 1-1 for saponifying natural rubber latex, a step 1-2 for washing the saponified natural rubber latex, and a step 1-3 for treating with an acidic compound. It can be prepared by a production method or the like.

[Production method 1]
(Step 1-1)
In step 1-1, natural rubber latex is saponified. The saponification treatment can be performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain period of time. Stirring may be performed as necessary.

(Step 1-2)
In step 1-2, the saponified natural rubber latex obtained in step 1-1 is washed.
Step 1-2 includes, for example, aggregating (coagulating) the saponified natural rubber latex obtained in Step 1-1 to produce an agglomerated rubber (coagulated rubber), and then converting the obtained agglomerated rubber with a basic compound. It can be carried out by processing and further washing. Specifically, after the agglomerated rubber is produced, the non-rubber component can be removed by diluting with water and transferring the water-soluble component to the aqueous layer and removing the water, and further by treating with a basic compound after agglomeration. Non-rubber components confined in the rubber during agglomeration can be redissolved. Thereby, non-rubber components such as proteins and fatty acids strongly adhered to the agglomerated rubber can be removed.

Examples of the aggregation method (coagulation method) include a method of adjusting pH by adding an acid such as formic acid or sulfuric acid, and further adding a polymer flocculant as necessary. Thereby, not a large aggregate but a granular rubber having a diameter of about 20 mm is formed from a diameter of several mm to 1 mm or less, and proteins and the like are sufficiently removed by the basic compound treatment. The pH is preferably adjusted in the range of 3.0 to 5.0, more preferably 3.5 to 4.5.

Next, the obtained agglomerated rubber (coagulated rubber) is treated with a basic compound. Here, although it does not specifically limit as a basic compound, A basic inorganic compound is suitable from the point of removal performance, such as protein and a fatty acid.

Examples of basic inorganic compounds include metal hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides; metal carbonates such as alkali metal carbonates and alkaline earth metal carbonates; alkali metal hydrogen carbonates and the like Metal phosphates such as alkali metal phosphates; metal acetates such as alkali metal acetates; metal hydrides such as alkali metal hydrides; ammonia and the like. Of these, metal hydroxides, metal carbonates, metal hydrogen carbonates, metal phosphates, and ammonia are preferable, and sodium carbonate and sodium hydrogen carbonate are more preferable.

The method for treating the agglomerated rubber with the basic compound is not particularly limited as long as the agglomerated rubber is brought into contact with the basic compound. For example, the method of immersing the agglomerated rubber in an aqueous solution of the basic compound, And a method of spraying an aqueous solution of the active compound. An aqueous solution of a basic compound can be prepared by diluting and dissolving each basic compound with water.

As pH of the aqueous solution of the said basic compound, 9-13 are preferable and 10-12 are more preferable from the point of processing efficiency. The treatment temperature is preferably 10 to 50 ° C., and the treatment time is usually 1 minute to 48 hours.

After the basic compound treatment, a washing treatment is performed. The washing treatment sufficiently removes non-rubber components such as proteins and fatty acids trapped in the rubber during aggregation, and at the same time sufficiently removes not only the surface of the aggregated rubber but also basic compounds existing inside. It becomes possible. In particular, by removing the basic compound remaining in the entire rubber in the washing step, it becomes possible to sufficiently treat the entire rubber with an acidic compound described later, and not only the surface of the rubber but also the internal pH is 2 Can be adjusted to ~ 7.

As a washing method, means capable of sufficiently removing non-rubber components, basic compounds, etc. contained in the whole rubber can be suitably used. For example, a method of diluting a rubber component with water and washing and then centrifuging. There is a method in which the rubber is floated by standing, and the rubber component is taken out by discharging only the aqueous phase. The number of washings can be any number of times that can reduce non-rubber components such as proteins and fatty acids and basic compounds to a desired amount, but dehydrated after adding 1000 mL of water to 300 g of dry rubber and stirring. 3 times (3 cycles) or more is preferable, 5 times (5 cycles) or more is more preferable, and 7 times (7 cycles) or more is more preferable.

The washing treatment is preferably carried out until the phosphorus content in the rubber is 500 ppm or less and / or the nitrogen content is 0.50 mass% or less.

(Step 1-3)
In Step 1-3, the washed rubber obtained in Step 1-2 is treated with an acidic compound. As described above, by performing the treatment, the pH of the entire rubber is adjusted to 2 to 7, and a highly purified natural rubber excellent in various performances can be provided.

The acidic compound is not particularly limited, and inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, polyphosphoric acid, metaphosphoric acid, boric acid, boronic acid, sulfanilic acid, sulfamic acid; formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, Examples thereof include organic acids such as malonic acid, succinic acid, adipic acid, maleic acid and malic acid. Of these, acetic acid, formic acid and the like are preferable.

The method of treating the agglomerated rubber with an acid is not particularly limited as long as the agglomerated rubber is brought into contact with the acidic compound. For example, a method of immersing the agglomerated rubber in an aqueous solution of the acidic compound, an aqueous solution of the acidic compound in the agglomerated rubber The method of spraying etc. are mentioned. The treatment temperature is preferably 10 to 50 ° C., and the treatment time is usually 3 seconds to 24 hours.

In the treatment such as immersion of the acidic compound in an aqueous solution, the pH is preferably adjusted to 6 or less. The upper limit of the pH is more preferably 5 or less, still more preferably 4.5 or less. The lower limit is not particularly limited, and although it depends on the immersion time, it is preferably 1 or more, more preferably 2 or more, because if the acid is too strong, the rubber deteriorates or the wastewater treatment becomes troublesome. The immersion treatment can be performed by leaving the agglomerated rubber in an acidic compound aqueous solution.

After the treatment, the compound used for the treatment of the acidic compound may be removed, and then the agglomerated rubber after the treatment may be appropriately washed. Examples of the washing treatment include the same methods as described above. For example, the washing may be repeated to further reduce non-rubber components and the like and adjust the content to a desired content. Further, the agglomerated rubber after the treatment with the acidic compound may be squeezed with a roll type squeezer or the like to form a sheet. By adding a step of squeezing the agglomerated rubber, the pH of the agglomerated rubber surface and inside can be made uniform, and a rubber having a desired performance can be obtained. If necessary, after carrying out a washing or squeezing step, the highly purified natural rubber is obtained by cutting through a creper and drying. In addition, drying can be implemented using a normal dryer.

In the rubber composition, the content of the synthetic polyisoprene rubber (IR) in 100% by mass of the rubber component is 20% by mass or less. Synthetic polyisoprene rubber itself has lower fracture characteristics than natural rubber, and therefore, good fracture characteristics tend to be obtained by adjusting to 20% by mass or less. Preferably it is 15 mass% or less, More preferably, it is 10 mass% or less.

In the rubber composition, the total content of the unmodified natural rubber, the highly purified natural rubber and the synthetic polyisoprene rubber in 100% by mass of the rubber component is 50% by mass or more. By setting it to the lower limit or more, good dispersibility of the filler can be obtained, and excellent fracture characteristics tend to be obtained. Preferably it is 55 mass% or more, More preferably, it is 60 mass% or more. Although an upper limit is not specifically limited, 75 mass% or less is preferable and 70 mass% or less is more preferable.

The rubber composition contains 25% by mass or more of high-cis polybutadiene rubber having a cis content of 95% by mass or more in 100% by mass of the rubber component. By setting the lower limit or more, E * at a low temperature is suppressed from increasing, and sufficient performance on ice tends to be obtained. Preferably it is 28 mass% or more, More preferably, it is 30 mass% or more. Although an upper limit is not specifically limited, 60 mass% or less is preferable and 45 mass% or less is more preferable.

The cis content of the high cis polybutadiene rubber is preferably 97% by mass or more.
In the present specification, the cis content is a value calculated by infrared absorption spectrum analysis.

The high cis polybutadiene rubber is not particularly limited as long as it is a butadiene rubber having a cis content of 95% by mass or more. Examples thereof include BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B and BR150B manufactured by Ube Industries, Ltd., and tire industry. Common ones can be used.

As the rubber component, other rubber components may be blended in addition to the above. 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 butyl rubber. . In addition, other isoprene-based rubbers such as deproteinized natural rubber (DPNR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber are also included.

The rubber composition contains silica having a nitrogen adsorption specific surface area of 120 m ² / g or more and less than 200 m ² / g (high specific surface area silica). Examples of the silica include dry method silica (anhydrous silica), wet method silica (hydrous silica), and the like. Of these, wet-process silica is preferred because it has many silanol groups.

Content of a high specific surface area silica is 10-50 mass parts with respect to 100 mass parts of rubber components. By setting the lower limit or more, there is a tendency that flexibility (E *) at a sufficiently low temperature can be secured. By setting it to the upper limit or less, good silica dispersibility can be obtained, and flexibility at low temperatures (E *) tends to be ensured. The lower limit is preferably 12 parts by mass or more. The upper limit is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less.

The nitrogen adsorption specific surface area (N ₂ SA) of the high specific surface area silica is preferably 150 m ² / g or more, more preferably 165 m ² / g or more from the viewpoint of obtaining sufficient fracture characteristics. The N ₂ SA is preferably 195 m ² / g or less, more preferably 185 m ² / g or less, from the viewpoint of ensuring silica dispersibility and low temperature flexibility (E *).
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The rubber composition preferably contains a silane coupling agent together with high specific surface area silica. The content of the silane coupling agent is preferably 1 to 15 parts by mass, more preferably 3 to 10 parts by mass with respect to 100 parts by mass of the high specific surface area silica.

As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry, and examples thereof include sulfide systems such as bis (3-triethoxysilylpropyl) disulfide, 3- Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltrimethoxy Examples thereof include nitro compounds such as silane and chloro compounds such as 3-chloropropyltrimethoxysilane. Of these, sulfide systems are preferred.

The rubber composition includes carbon black.
The content of carbon black is 30 parts by mass or more with respect to 100 parts by mass of the rubber component. Preferably it is 33 mass parts or more, More preferably, it is 35 mass parts or more. By setting the lower limit or more, good fracture characteristics and durability tend to be obtained. Moreover, although an upper limit is not specifically limited, Preferably it is 80 mass parts or less, More preferably, it is 60 mass parts or less. By making it below the upper limit, good dispersion of carbon black tends to be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 120 m ² / g or more, and more preferably 130 m ² / g or more. By setting the lower limit or more, good fracture characteristics, durability, and wear resistance tend to be obtained. Further, the _N 2 SA is preferably 200 meters ² / g or less, more preferably 170m ² / g, more preferably not more than 155m ² / g. By making it below the upper limit, good dispersion of carbon black tends to be obtained.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by JISK6217-2: 2001.

Examples of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, and the like. These may be used alone or in combination of two or more.

Examples of carbon black include products such as Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Shin-Nikka Carbon Co., Ltd., Columbia Carbon Co., etc. Can be used.

The rubber composition preferably contains a terpene resin from the viewpoint of performance on ice and snow.
The content of the terpene resin is preferably 12 parts by mass or less, more preferably 1 to 10 parts by mass, and further preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component.

The softening point of the terpene-based resin is preferably 120 ° C. or less, more preferably 100 to 120 ° C., and still more preferably 105 to 120 ° C. from the viewpoints of performance on ice and snow, wear resistance, elongation at break, and the like.
The softening point of the terpene resin is a temperature at which the sphere descends when the softening point specified in JIS K 6220-1: 2001 is measured with a ring and ball softening point measuring device.

The hydroxyl value (mgKOH / g-gel) of the terpene resin is preferably 10 or less, more preferably 5 or less, still more preferably 1 or less, particularly preferably from the viewpoints of performance on ice and snow, wear resistance, elongation at break, and the like. Is 0.
The hydroxyl value of the terpene resin is the amount of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl group when 1 g of the terpene resin is acetylated. The potentiometric titration method is used. It is a value measured according to (JIS K0070: 1992). Therefore, in the case of a terpene resin that does not contain a phenol compound, the hydroxyl value is usually 0.

The SP value of the terpene resin is preferably 8.60 or less, more preferably 8.40 or less. On the other hand, a preferable lower limit is 8.10 or more.
The SP value means a solubility parameter calculated by the Hoy method based on the structure of the compound. The Hoy method is, for example, K.K. L. Hoy "Table of Solubility Parameters", Solvent and Coatings Materials Research and Development Department, Union Carbites Corp. (1985).

As the terpene resin, a polyterpene resin obtained by polymerizing a terpene compound, an aromatic modified terpene resin obtained by polymerizing a terpene compound and an aromatic compound, or the like can be used. These hydrogenated products can also be used.

The polyterpene resin is a resin obtained by polymerizing a terpene compound. The terpene compound is a hydrocarbon represented by a composition of (C ₅ H ₈ ) _n and an oxygen-containing derivative thereof. Monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂₎ ), Etc., which are classified into terpenes, for example, α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-ferrandrene, α-terpinene, γ-terpinene, terpinolene. 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, γ-terpineol and the like.

Examples of the polyterpene resin include a pinene resin, a limonene resin, a dipentene resin, and a pinene / limonene resin made from the above-mentioned terpene compound. Of these, pinene resin is preferred. The pinene resin usually contains both α-pinene and β-pinene having an isomer relationship, but due to the difference in the components contained, β-pinene resin containing β-pinene as a main component and α-pinene It is classified into α-pinene resin mainly composed of pinene. In the present invention, β-pinene resin can be preferably used.

Examples of the aromatic modified terpene resin include a terpene phenol resin using the terpene compound and the phenolic compound as raw materials, and a terpene styrene resin using the terpene compound and the styrene compound as raw materials. Moreover, the terpene phenol styrene resin which uses the said terpene compound, a phenol type compound, and a styrene type compound as a raw material can also be used. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol. Examples of the styrene compound include styrene and α-methylstyrene.

As the terpene-based resin, a polyterpene resin is preferable and a β-pinene resin is more preferable because the effects of the present invention can be obtained well.

The rubber composition preferably contains oil.
The content of oil is preferably 1 to 10 parts by mass, more preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component, from the viewpoint that the effect of the present invention can be satisfactorily obtained.

Examples of the oil include process oil, vegetable oil and fat, or a mixture thereof. Examples of the process oil include paraffinic process oil, aroma based process oil, and naphthenic process oil. As vegetable oils and fats, castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut hot water, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples are olive oil, sunflower oil, palm kernel oil, cocoon oil, jojoba oil, macadamia nut oil, tung oil and the like. Of these, process oil is preferred.

Examples of the oil include Idemitsu Kosan Co., Ltd., Sankyo Oil Chemical Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H & R Co., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu Co., Ltd., Fuji Kosan Co., Ltd. , Etc. products can be used.

The rubber composition preferably contains eggshell powder from the viewpoint of performance on ice and snow.
The content of the eggshell powder is preferably 1 part by mass or more, more preferably 5 parts by mass or more, from the viewpoint that good performance on ice and snow can be obtained with respect to 100 parts by mass of the rubber component. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, from the viewpoint that good wear resistance, fracture characteristics and the like can be obtained.

The average particle diameter of the eggshell powder is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint that good performance on ice and snow can be obtained. The average particle size is preferably 50 μm or less, more preferably 30 μm or less, from the viewpoint that good wear resistance, fracture characteristics, and the like are obtained.
In addition, the average particle diameter of eggshell powder is measured using a particle size distribution measuring device.

The rubber composition preferably contains sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur that are generally used in the rubber industry. Examples of commercially available products include products such as Tsurumi Chemical Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexis Co., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Co., Ltd.

The sulfur content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 3 parts by mass or less. Within the above numerical range, the effects of the present invention tend to be obtained satisfactorily.

The rubber composition preferably contains a vulcanization accelerator.
Examples of the vulcanization accelerator include thiazole vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, N-cyclohexyl-2-benzothiazylsulfenamide; tetramethylthiuram disulfide (TMTD ), Tetrabenzylthiuram disulfide (TBzTD), tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N) and other thiuram vulcanization accelerators; N-cyclohexyl-2-benzothiazolesulfenamide, Nt-butyl- 2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N, N′-diisopropyl-2-benzothiazolesulfenamide, etc. The sulfenami And guanidine vulcanization accelerators such as diphenyl guanidine, diortolyl guanidine, and orthotolyl biguanidine. Of these, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred because the effects of the present invention can be obtained more suitably.

The content of the vulcanization accelerator is preferably 0.3 parts by mass or more, and more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less. Within the above numerical range, the effects of the present invention tend to be obtained satisfactorily.

The rubber composition includes a resin other than the terpene resin (coumarone indene resin, α-methylstyrene resin, pt-butylphenol acetylene resin, acrylic resin, etc.), wax, anti-aging agent, stearic acid, Inorganic fillers and organic fillers other than zinc oxide, silica, and carbon black, softeners other than oil, vulcanizing agents other than sulfur (such as organic crosslinking agents), and the like may be blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

As kneading conditions, when kneading additives other than the vulcanizing agent and the vulcanization accelerator (base kneading), the kneading temperature is usually 50 to 200 ° C. (preferably 80 to 190 ° C.), and the kneading time is usually 30 seconds to 30 minutes (preferably 1 to 30 minutes). During kneading of the vulcanizing agent and vulcanization accelerator (finish kneading), the kneading temperature is usually 100 ° C. or lower (preferably room temperature to 80 ° C.). The obtained kneaded product (unvulcanized rubber composition) is usually subjected to vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200 ° C (preferably 140 to 180 ° C).

The rubber composition (rubber composition after vulcanization) has a complex elastic modulus E * of 15 MPa or less under conditions of a temperature of 0 ° C., a frequency of 10 Hz, an initial elongation strain of 5%, and a dynamic elongation strain of 2%. preferable. When E * is 15 Mpa or less, sufficient performance on ice and snow tends to be obtained. E * is more preferably 14 MPa or less. Although the minimum of this E * is not specifically limited, 5 MPa or more is preferable and 8 MPa or more is more preferable.

The rubber composition (rubber composition after vulcanization) preferably has a breaking strength TB at a temperature of 23 ° C. of 15 Mpa or more, and more preferably 16 MPa or more. By being 15 Mpa or more, in particular, tread chunking during use of truck bus tires during summer tends to be suppressed. The upper limit of TB is not particularly limited, but is preferably 50 MPa or less, and more preferably 40 MPa or less.

The rubber composition (rubber composition after vulcanization) preferably has a breaking elongation EB at a temperature of 23 ° C. of 420% or more, and more preferably 440% or more. By being 420% or more, in particular, tread chunking during use of truck bus tires during summer tends to be suppressed. Although the upper limit of EB is not specifically limited, 900% or less is preferable and 800% or less is more preferable.

The complex elastic modulus E *, the breaking strength TB, and the breaking elongation EB are measured by the methods described in Examples below.

The rubber composition is used for a tread (cap tread) of a studless tire.

A studless tire is manufactured by a normal method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a vulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

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

Below, the various chemical | medical agents used by preparation of an anti-aging agent dispersion and manufacture of highly purified natural rubber are demonstrated.
Field Latex: Field Latex Emar E-27C (surfactant) obtained from Muhiba Latex Co., Ltd .: Emar E-27C (Polyoxyethylene lauryl ether sodium sulfate, 27% by mass of active ingredient) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Wingstay L (anti-aging agent): WINGSTAY L (compound obtained by butylating the condensate of ρ-cresol and dicyclopentadiene) manufactured by ELIOKEM
Emulvin W (surfactant): Emalvin W (aromatic polyglycol ether) manufactured by LANXESS
Tamol NN9104 (surfactant): Tamol NN9104 manufactured by BASF (Naphthalenesulfonic acid / formaldehyde sodium salt)
Van gel B (surfactant): Van gel B (magnesium aluminum silicate hydrate) manufactured by Vanderbilt

(Preparation of anti-aging agent dispersion)
462.5 g of water was mixed with 12.5 g of Emulvin W, 12.5 g of Tamol NN9104, 12.5 g of Van gel B, and 500 g of Wingstay L (total of 1000 g) for 16 hours by a ball mill to prepare an antioxidant dispersion.

(Manufacture of highly purified natural rubber)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex. Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Next, formic acid was added with slow stirring to adjust the pH to 4.0, and then a cationic polymer flocculant was added and stirred for 2 minutes for aggregation. The diameter of the aggregate (aggregated rubber) thus obtained was about 0.5 to 5 mm. The obtained agglomerates were taken out and immersed in 1000 ml of a 2% by weight aqueous sodium carbonate solution at room temperature for 4 hours, and then the rubber was taken out. To this, 2000 ml of water was added and stirred for 2 minutes to remove water as much as possible 7 times. Thereafter, 500 ml of water was added, 2% by mass formic acid was added until pH 4 was reached, and the mixture was allowed to stand for 15 minutes. Further, after removing the water as much as possible, repeating the operation of adding water again and stirring for 2 minutes three times, squeezing the water with a water squeezing roll to form a sheet, and then drying at 90 ° C. for 4 hours to obtain a solid rubber Obtained.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
High-purity natural rubber: Solid rubber manufactured as described above IR: IR2200 manufactured by JSR Corporation
High cis BR: BR150B manufactured by Ube Industries, Ltd. (cis content 97% by mass)
Silica A: ZEOSIL115GR (N ₂ SA110m ² / g) manufactured by Rhodia Japan
Silica B: ULTRASIL VN3 (N ₂ SA175m ² / g) manufactured by Evonik
Silica C: Nipsil AQ (N ₂ SA ²⁰⁰ m ² / g) manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Evonik Degussa
Carbon Black N134: Show Black N134 (N ₂ SA148m ² / g) manufactured by Cabot Japan
Anti-aging agent 6PPD: Nocrack 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Oil: X140 (Aroma Oil) manufactured by Japan Energy Co., Ltd.
Eggshell powder: Egg calcium (calhope) manufactured by Kewpie Co., Ltd. (average particle size: 15 μm)
Terpene resin: YS resin PX1150 manufactured by Yashara Chemical Co., Ltd. (softening point: 115 ° C., Tg: 62 ° C., hydroxyl value: 0, SP value: 8.26, β-pinene resin)
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Tsubaki stearic acid bead manufactured by NOF Co., Ltd .: Powdered sulfur vulcanization accelerator TBBS manufactured by Tsurumi Chemical Industry Co., Ltd. Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Chemical Industry Co., Ltd.

[Examples and Comparative Examples]
The materials described in the item of the base kneading step in Table 2 were kneaded using a 270 L Banbury mixer (base kneading: rotation speed 45 rpm, discharge temperature 150 ° C., re-kneading: rotation speed 45 rpm, discharge temperature 140 ° C.).
Using an open roll, the kneaded material obtained in the base kneading step and the materials described in the items of the finishing kneading step in Table 2 are kneaded (rotation speed: 30 rpm) and discharged when the rubber temperature reaches 105 ° C. did.
The kneaded product (unvulcanized rubber composition) obtained in the finishing kneading process is extruded into a tread shape, bonded together with other tire members on a tire molding machine, and vulcanized at 150 ° C. for 44 minutes. A test studless tire (tire size 275 / 80R22.5) was prepared.

The obtained solid rubber (high purity natural rubber), NR (TSR20), and test studless tire were evaluated as follows, and the results are shown in Tables 1-2.

<Measurement of pH>
Cut 5 g of solid rubber into a total of 5 mm or less (about 1-2 × about 1-2 × about 1-2 (mm)), put it in a 100 ml beaker, add 50 ml of room temperature distilled water in 2 minutes. The temperature was raised to 90 ° C., and then microwave (300 W) was applied for 13 minutes (15 minutes in total) while adjusting the temperature so as to maintain 90 ° C. Next, the immersion water was cooled with an ice bath to 25 ° C., and then the pH of the immersion water was measured using a pH meter.

<Measurement of nitrogen content>
(Acetone extraction (test piece preparation))
About 0.5 g of a sample obtained by chopping solid rubber or NR into 1 mm square was prepared. The sample was immersed in 50 g of acetone, and after 48 hours at room temperature (25 ° C.), the rubber was taken out and dried to obtain each test piece (extracted with anti-aging agent).
(Measurement)
The nitrogen content of the obtained test piece was measured by the following method.
The nitrogen content was determined by decomposing and gasifying each of the acetone-extracted test pieces obtained above using a trace nitrogen carbon measuring device “SUMIGRAPH NC95A (manufactured by Sumika Chemical Analysis Center)”. The nitrogen content was quantified by analyzing with a gas chromatograph “GC-8A (manufactured by Shimadzu Corporation)”.

<Measurement of phosphorus content>
About solid rubber or NR, phosphorus content was calculated | required using the ICP emission spectrometer (P-4010, Hitachi Ltd. make).

(Viscoelasticity test)
After cutting and removing 1 mm of the tread surface of the test studless tire, a test piece having a width of 4 mm, a length of 2 mm, and a thickness of 2 mm was produced (collected). Using a viscoelasticity testing machine manufactured by Iwamoto Seisakusho, the complex elastic modulus (E *) of each test piece was measured under the conditions of 0 ° C., frequency 10 Hz, initial elongation strain 5%, and dynamic elongation strain 1%.

(Tensile test)
After removing 1 mm of the surface of the shoulder rib portion of the tread of the test studless tire, a rubber sheet having a thickness of 2 mm was produced (collected) to obtain a dumbbell No. 7 type test piece. A tensile test was carried out under the conditions of a test temperature of 23 ° C. and a tensile test speed of 200 mm / min using an A & D Corporation tensile tester (RTG-1210). It shows that it is excellent in a fracture | rupture characteristic (durability) and abrasion resistance, so that breaking strength TB and breaking elongation EB are large.
TB: represents the strength TB (Mpa) at break per cross-sectional area of the finest detail (dumbbell constricted part located in the center) of the test piece.
EB: A test piece was set in a testing machine with a distance between chucks of 20 mm, and a tensile test was performed. The distance between chucks at the time of fracture was measured, and the value calculated from the following formula determined the elongation at break EB (%).
Distance between chucks at break (mm) / Distance between initial chucks (20mm) x 100

(Performance on ice and snow)
At the Nayoro Snow Test Center of Sumitomo Rubber Industries, Ltd., 4-D4 (two front wheels, four rear wheels) 16 ton trucks were used, and four test studless tires were mounted on the rear wheels. Under the conditions of on-ice temperature of −1 ° C. to + 3 ° C., the start was started from the stop, and the time (seconds) required to reach 10 km / h was indexed. Based on Comparative Example 1, it was displayed as an index. The larger the index, the better the grip performance on ice.

From Tables 1 and 2, the rubber compositions of the examples containing NR, highly purified natural rubber, IR, high cis polybutadiene rubber, high nitrogen adsorption specific surface area silica, and carbon black in a predetermined composition had excellent performance on ice and snow. . Moreover, TB and EB were large, and the fracture characteristics, wear resistance, and durability were excellent.

Claims (5)

A rubber component, a nitrogen adsorption specific surface area of 120 m ² / g or more and less than 200 m ² / g of silica, and carbon black,
In 100% by mass of the rubber component, the content of unmodified natural rubber is 10% by mass or more, the content of highly purified natural rubber having a phosphorus content of 500ppm or less is 10% by mass or more, and the content of synthetic polyisoprene rubber is The content of the high cis polybutadiene rubber having a cis content of 95% by mass or more is 25% by mass or less,
A rubber composition for a studless tire, wherein the silica content is 10 to 50 parts by mass and the carbon black content is 30 parts by mass or more with respect to 100 parts by mass of the rubber component. Complex elastic modulus E * (temperature 0 ° C., frequency 10 Hz, initial elongation strain 5%, dynamic elongation strain 2%) is 15 MPa or less, breaking strength TB (temperature 23 ° C.) is 15 MPa or more, breaking elongation EB (temperature 23 ° C.) The rubber composition for studless tires according to claim 1, wherein is 420% or more. The highly purified natural rubber has a nitrogen content of 0.30% by mass or less,
The carbon black has a nitrogen adsorption specific surface area of 120 m ² / g or more,
The rubber composition for a studless tire according to claim 1 or 2, wherein a total content of the non-modified natural rubber, the highly purified natural rubber and the synthetic polyisoprene rubber in 100% by mass of the rubber component is 50% by mass or more. object. The rubber composition for studless tires according to any one of claims 1 to 3, comprising a terpene resin having a softening point of 120 ° C or lower with respect to 100 parts by mass of the rubber component. The studless tire which has a tread produced using the rubber composition in any one of Claims 1-4.