阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 前川哲哉 田中健宏 于 2019-04-17 设计创作，主要内容包括：本发明的课题在于提供高温抓地性能和耐磨性优异的充气轮胎。本发明是一种充气轮胎,其特征在于,具备由橡胶组合物构成的胎面,所述橡胶组合物包含：含有异戊二烯系橡胶的二烯系橡胶、炭黑、二氧化硅、含有规定的结合单元I和结合单元II的化合物以及规定的化学式所示的化合物。(The invention provides a pneumatic tire with excellent high-temperature gripping performance and wear resistance. The present invention is a pneumatic tire provided with a tread made of a rubber composition, the rubber composition comprising: a diene rubber containing an isoprene rubber, carbon black, silica, a compound containing a predetermined bonding unit I and a predetermined bonding unit II, and a compound represented by a predetermined chemical formula.)

1. A pneumatic tire provided with a tread composed of a rubber composition, the rubber composition comprising: a diene rubber containing an isoprene rubber, carbon black, silica, a compound containing a bonding unit I represented by the formula (1) and a bonding unit II represented by the formula (2), and a compound represented by the formula (3),

Wherein R ¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or a group in which hydrogen at the terminal of the above alkyl group is substituted with a hydroxyl group or a carboxyl group, R ² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms, R ¹ and R ² may form a ring structure,

Wherein R ³ to R ⁶ each independently represents a straight-chain or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms.

2. The pneumatic tire according to claim 1, wherein the average particle diameter of the carbon black is 31nm or less.

3. The pneumatic tire according to claim 1 or 2, wherein the silica has an average particle diameter of 31nm or less.

4. The pneumatic tire according to any one of claims 1 to 3, wherein the diene rubber contains 10 to 80 mass% of a natural rubber, and the nitrogen content of the natural rubber is 0.40 mass% or less.

5. The pneumatic tire according to claim 1, wherein the content of the isoprene-based rubber in the rubber component is 10 to 80 mass%.

6. The pneumatic tire according to claim 4 or 5, wherein the diene rubber further contains 15 to 45 mass% of a styrene butadiene rubber.

7. The pneumatic tire according to claim 4 or 5, wherein the diene rubber further contains 5 to 45 mass% of a butadiene rubber.

8. The pneumatic tire according to any one of claims 1 to 7,

The rubber composition contains 100 parts by mass of a diene rubber component, 20 to 100 parts by mass of carbon black, 10 to 60 parts by mass of silica,

The content of the compound containing the binding unit I and the binding unit II is 3 to 15 parts by mass relative to 100 parts by mass of silica,

The content of the compound represented by the formula (3) is 10 to 200 parts by mass per 100 parts by mass of the compound containing the binding unit I and the binding unit II.

9. The pneumatic tire according to any one of claims 1 to 8, wherein the rubber composition further contains 0.5 to 3.0 parts by mass of a compound represented by formula (4),

R⁷-S-S-Y-S-S-R⁸ (4)

Wherein Y represents an alkylene group having 2 to 10 carbon atoms, and R ⁷ and R ⁸ are the same or different and each represents a 1-valent organic group containing a nitrogen atom.

10. The pneumatic tire according to any one of claims 1 to 9, wherein a mixing ratio of carbon black to silica is 1.0 to 3.0.

11. The pneumatic tire according to claim 9 or 10, wherein the ratio of the content of the isoprene-based rubber in parts by mass to the total content of the compound containing the bonding unit I represented by formula (1) and the bonding unit II represented by formula (2) and the compound represented by formula (4) in parts by mass is 1 to 40.

Technical Field

The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire having a tread made of a predetermined rubber composition.

Background

Tires require grip performance on various road surfaces. In summer, in which the temperature is high, the road surface temperature increases, and the temperature of the tread during running also increases, and therefore, it is expected to improve the grip performance on a high-temperature road surface. However, as a general characteristic of the rubber composition, as the temperature increases, the hysteresis loss (tan δ) which greatly contributes to grip performance tends to decrease, and therefore, there is a problem that grip performance decreases.

Heretofore, for the purpose of improving the grip performance on a high-temperature road surface, in a rubber composition for a tread, in order to increase the hysteresis loss, a method of changing a softening agent from oil to a liquid polymer, a method of increasing the amount of a resin, a method of adding a resin having a high softening point, or the like has been employed. In particular, a method of adding a large amount of a resin having a high softening point is effective for improving the grip performance on a high-temperature road surface, and is widely used.

Patent document 1 gives such a scheme: a method of blending fine particles of carbon black or the like into the modified natural rubber in order to improve wet grip performance, abrasion resistance, and the like, but no mention is made of grip performance on high-temperature road surfaces (high-temperature grip performance).

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a pneumatic tire having excellent high-temperature grip performance and wear resistance, said pneumatic tire having a tire tread composed of a predetermined rubber composition.

Means for solving the problems

The inventors intensively studied and found that: the above problems can be solved by mixing a predetermined silane coupling agent and a predetermined crosslinking assistant in predetermined amounts into a rubber composition containing a diene rubber component containing an isoprene rubber, carbon black and silica, and further, the present invention has been completed by further studies.

Namely, the present invention relates to the following aspects.

[1] A pneumatic tire provided with a tread composed of a rubber composition, the rubber composition comprising: a diene rubber containing an isoprene rubber, carbon black, silica, a compound containing a bonding unit I represented by the formula (1) and a bonding unit II represented by the formula (2), and a compound represented by the formula (3).

(wherein R ¹ represents hydrogen, halogen, branched or unbranched alkyl having 1 to 30 carbon atoms, branched or unbranched alkenyl having 2 to 30 carbon atoms, branched or unbranched alkynyl having 2 to 30 carbon atoms, or a group in which hydrogen at the terminal of the above alkyl group is substituted with a hydroxyl group or a carboxyl group; R ² represents branched or unbranched alkylene having 1 to 30 carbon atoms, branched or unbranched alkenylene having 2 to 30 carbon atoms, or branched or unbranched alkynylene having 2 to 30 carbon atoms; R ¹ and R ² may form a ring structure.)

(wherein R ³ to R ⁶ each independently represents a straight-chain or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms.)

[2] The pneumatic tire according to the above [1], wherein the carbon black has an average particle diameter of 31nm or less, preferably 17 to 29nm, more preferably 19 to 27 nm.

[3] The pneumatic tire according to the above [1] or [2], wherein the silica has an average particle diameter of 31nm or less, preferably 11 to 30nm, more preferably 13 to 29nm, and further preferably 15 to 28 nm.

[4] The pneumatic tire according to any one of the above [1] to [3], wherein the diene rubber contains 10 to 80 mass%, preferably 15 to 75 mass%, and more preferably 20 to 70 mass% of a natural rubber, and the nitrogen content of the natural rubber is 0.40 mass% or less, preferably 0.30 mass% or less, more preferably 0.20 mass% or less, and more preferably 0.10 mass% or less.

[5] The pneumatic tire according to the above [4], wherein the diene rubber contains 15 to 45 mass%, preferably 16 to 44 mass%, more preferably 18 to 42 mass%, and still more preferably 20 to 40 mass% of styrene butadiene rubber.

[6] The pneumatic tire according to the above [4] or [5], wherein the diene rubber further contains 5 to 45 mass%, preferably 6 to 44 mass%, more preferably 8 to 42 mass%, and still more preferably 10 to 40 mass% of a butadiene rubber.

[7] The pneumatic tire according to any one of the above [1] to [6], wherein the content of the diene rubber component in the rubber composition is 100 parts by mass; the content of the carbon black is 20 to 100 parts by mass, preferably 25 to 90 parts by mass, more preferably 30 to 80 parts by mass, and further preferably 35 to 70 parts by mass; the content of the silica is 10 to 60 parts by mass, preferably 15 to 55 parts by mass, more preferably 18 to 50 parts by mass, and further preferably 20 to 40 parts by mass; the content of the compound containing the binding unit I and the binding unit II is 3 to 15 parts by mass, preferably 4 to 12 parts by mass, and more preferably 5 to 10 parts by mass, based on 100 parts by mass of silica; the content of the compound represented by the formula (3) is 10 to 200 parts by mass, preferably 15 to 180 parts by mass, more preferably 20 to 150 parts by mass, and still more preferably 30 to 150 parts by mass, based on 100 parts by mass of the compound containing the binding unit I and the binding unit II.

[8] The pneumatic tire according to any one of the above [1] to [7], wherein the rubber composition further contains 0.5 to 3.0 parts by mass, more preferably 0.7 to 2.5 parts by mass, still more preferably 1.0 to 2.0 parts by mass of a compound represented by the formula (4),

R⁷-S-S-Y-S-S-R⁸ (4)

(wherein Y represents an alkylene group having 2 to 10 carbon atoms; and R ⁷ and R ⁸ may be the same or different and each represents a nitrogen atom-containing 1-valent organic group.)

[9] The pneumatic tire according to any one of the above [1] to [8], wherein a mixing ratio of the carbon black to the silica is 1.0 to 3.0, preferably 1.5 to 2.5.

[10] The pneumatic tire according to the above [8] or [9], wherein the ratio of the content (parts by mass) of the isoprene-based rubber to the total content (parts by mass) of the compound containing the binding unit I represented by the formula (1) and the binding unit II represented by the formula (2) and the compound represented by the formula (4) is 1 to 40, preferably 5 to 39, more preferably 8 to 38, further preferably 10 to 37, further preferably 10 to 36, further preferably 10 to 35.

Effects of the invention

According to the present invention, a pneumatic tire excellent in high-temperature grip performance and wear resistance can be provided. Further, the pneumatic tire of the present invention is excellent in steering stability and can be improved in cut chipping resistance.

Although not wishing to be bound by theory, in the present invention, the bonding force between silica and polymer can be strengthened by using a compound containing a bonding unit I represented by formula (1) and a bonding unit II represented by formula (2) as a silane coupling agent. This silane coupling agent is considered to have an oligomer-type molecular structure, so that the bonding surface with silica is wide, and a part of the bonding points with the polymer side is a highly reactive "thiol group (mercapto group)", and this factor contributes to strengthening the bonding force with the polymer. On the other hand, strengthening the bonding force with the polymer causes a decrease in tan δ on the high temperature side, and a decrease in grip performance. However, it is believed that: the silane coupling agent has a "thioester group" in addition to a "thiol group" at a bonding point with a polymer, and thus can achieve an improvement in abrasion resistance and can suppress a decrease in tan δ on the high-temperature side. In the present invention, the compound represented by the formula (3) is further used as a crosslinking assistant, so that the "thiol group" in the silane coupling agent can be blocked during kneading. Consider that: this suppresses excessive gel formation (bonding to the polymer), thereby further increasing the high-temperature tan δ (i.e., exerting a synergistic effect).

Detailed Description

A pneumatic tire according to an embodiment is characterized by having a tread formed of a rubber composition containing: a diene rubber containing an isoprene rubber, carbon black, silica, a compound containing a bonding unit I represented by the formula (1) and a bonding unit II represented by the formula (2), and a compound represented by the formula (3).

< rubber component >

The rubber component is a diene rubber containing an isoprene rubber. Here, examples of the isoprene-based rubber include Natural Rubber (NR), Isoprene Rubber (IR), and the like. As the isoprene-based rubber, NR is preferably used from the viewpoint of grip performance and abrasion resistance. The isoprene-based rubber may be used alone or in combination of 2 or more.

Examples of the diene rubber other than the isoprene rubber include Butadiene Rubber (BR), Styrene Butadiene Rubber (SBR), Styrene Isoprene Rubber (SIR), Styrene Isoprene Butadiene Rubber (SIBR), Chloroprene Rubber (CR), and acrylonitrile butadiene rubber (NBR). As the diene rubber other than the isoprene rubber, SBR is preferably used in combination, and BR is preferably further used in combination from the viewpoint of grip performance and abrasion resistance. The diene rubber other than the isoprene rubber may be used alone or 2 or more kinds may be used in combination.

(NR)

As the NR, natural rubber used in the general rubber industry, Epoxidized Natural Rubber (ENR), Hydrogenated Natural Rubber (HNR), modified natural rubber (modified NR), and the like can be suitably used. These may be formulated by conventional methods. Among them, modified natural rubber is preferable.

For example, the modified natural rubber is a natural rubber in which components (mainly proteins) other than the natural polyisoprenoid component contained in the natural rubber latex are reduced and removed (preferably, a natural rubber in which impurities such as phospholipids and gel fractions are also removed). The natural rubber particles contained in the natural rubber latex have a structure in which the isoprenoid component is covered with the impurity component. Presume that: by removing impurities on the surface of the natural rubber particles, the structure of the isoprenoid component is changed, and the interaction with the compounding agent is also changed, so that the effects of reducing energy loss and improving durability are obtained. Further, by removing impurities from the natural rubber latex, odor peculiar to natural rubber can be reduced.

As the modification treatment, any known method such as saponification treatment, enzyme treatment, mechanical treatment such as ultrasonic treatment or centrifugal separation can be used without limitation, and among them, saponification treatment is preferable from the viewpoint of production efficiency, cost, and dispersibility of the white filler.

Examples of the natural rubber latex include raw latex (field latex) collected by tapping hevea trees, concentrated latex (purified latex, high ammonia latex to which ammonia is added according to a conventional method, LATZ latex stabilized by zinc white, TMTD (tetramethylthiuram disulfide), and ammonia) obtained by concentrating raw latex by a centrifugal separation method or a creaming method, and the like. Among them, the field latex is preferably used because high purity is easily achieved by pH control.

The rubber component (solid rubber portion) in the natural rubber latex is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, from the viewpoint of stirring efficiency and the like.

Examples of the method of the saponification treatment include the methods described in, for example, Japanese patent laid-open Nos. 2010-138359 and 2010-174169. Specifically, the process may be carried out by adding the basic compound and the surfactant as needed to the natural rubber latex and allowing the natural rubber latex to stand at a predetermined temperature for a predetermined time, or by stirring as needed.

The basic compound is not particularly limited, but a basic inorganic compound is preferable in view of the removal performance of proteins and the like. Examples of the basic inorganic compound 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; metal hydrogen carbonates such as alkali metal hydrogen carbonates; 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.

Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkaline earth metal hydroxide include magnesium hydroxide, calcium hydroxide, and barium hydroxide. Examples of the alkali metal carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the alkaline earth metal carbonate include magnesium carbonate, calcium carbonate, and barium carbonate. Examples of the alkali metal bicarbonate include lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, and the like. Examples of the alkali metal phosphate include sodium phosphate and sodium hydrogen phosphate. Examples of the alkali metal acetate include sodium acetate and potassium acetate. Examples of the alkali metal hydride include sodium hydride and potassium hydride. Among them, from the viewpoint of saponification efficiency and ease of handling, metal hydroxides, metal carbonates, metal bicarbonates, metal phosphates, and ammonia are preferable, and sodium hydroxide and potassium hydroxide, which are alkali metal hydroxides, are more preferable. These basic compounds may be used alone, or 2 or more of them may be used in combination.

The surfactant is not particularly limited, and known anionic surfactants such as polyoxyethylene alkyl ether sulfate, nonionic surfactants, amphoteric surfactants, and the like can be mentioned, but from the viewpoint of being able to saponify a rubber well without coagulating the rubber, known anionic surfactants such as polyoxyethylene alkyl ether sulfate are suitable. In the saponification treatment, the amounts of the alkali compound and the surfactant to be added, and the temperature and time of the saponification treatment may be appropriately set.

The coagulation drying step is a step of coagulating the modified product obtained in the modification step and then drying the coagulated product to obtain a modified natural rubber. Consider that: the natural rubber obtained in the coagulation drying step has impurities on the surface of the natural rubber particles removed in the previous modification step, and therefore the rubber composition containing the natural rubber has excellent rubber properties.

The coagulation method is not particularly limited, and examples thereof include a method in which an acid such as formic acid, acetic acid, or sulfuric acid is added to adjust the pH to 4 to 7, and if necessary, a polymeric flocculant is further added thereto and stirred. The rubber portion of the modified product can be coagulated by coagulation to obtain a coagulated rubber.

The drying method is not particularly limited, and may be carried out using a general dryer such as a contact dryer, a vacuum dryer, or a drum dryer, which is used in the drying step of a general natural rubber production method such as TSR.

It is preferable to dry the coagulated rubber obtained after washing. The washing method is not particularly limited as long as impurities contained in the entire rubber can be sufficiently removed, and examples thereof include a method in which a rubber portion is diluted with water, washed, and then centrifuged; and a method of allowing the mixture to stand to float the rubber, discharging only the aqueous phase, and taking out the rubber portion. Further, when the obtained coagulated rubber is treated with an alkaline compound and then washed, impurities enclosed in the rubber may be redissolved at the time of coagulation and then washed, and impurities strongly adhering to the coagulated rubber may be removed.

the modified natural rubber has a nitrogen content of 0.40 mass% or less. By setting the range as described above, the effect of the present invention can be exhibited. The nitrogen content is preferably 0.30% by mass or less, more preferably 0.20% by mass or less, and still more preferably 0.10% by mass or less. The nitrogen content can be measured by a conventional method such as Kjeldahl method. The nitrogen is derived from a protein. The lower limit of the nitrogen content is preferably small. It is considered that the value is sufficiently low when the content is, for example, 0.06% by mass or 0.01% by mass.

The phosphorus content of the modified natural rubber is preferably 200ppm or less. By setting the range as above, the rubber physical properties such as low fuel consumption tend to be improved. The phosphorus content is more preferably 150ppm or less, and still more preferably 100ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. The phosphorus is derived from phospholipids (phosphorus compounds).

⁵The gel content in the modified natural rubber is preferably 20 mass% or less, and by setting the gel content to such a range, the rubber physical properties such as low fuel consumption tend to be improved, the gel content is more preferably 10 mass% or less, and further preferably 7 mass% or less, the gel content is a value measured as an insoluble fraction with respect to toluene as a nonpolar solvent, and may be hereinafter simply referred to as "gel content" or "gel content" as a short term.

(content of isoprene rubber)

The content of the isoprene-based rubber in the rubber component is 10 to 80 mass%. When the content of the isoprene-based rubber is within this range, the effects of the present invention tend to be sufficiently exhibited. The content of the isoprene-based rubber is preferably 15% by mass or more, and more preferably 20% by mass or more. On the other hand, the content of the isoprene-based rubber is preferably 75% by mass or less, and more preferably 70% by mass or less.

In addition, the content of the isoprene-based rubber in the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and further preferably 60% by mass or more, from the viewpoint of cut resistance and chipping resistance. The content in this case is preferably 80 mass%, for example.

(SBR)

The SBR is not particularly limited, and examples thereof include unmodified emulsion-polymerized styrene butadiene rubber (E-SBR), solution-polymerized styrene butadiene rubber (S-SBR), modified emulsion-polymerized styrene butadiene rubber (modified E-SBR) obtained by modifying these rubbers, and modified SBR such as modified solution-polymerized styrene butadiene rubber (modified S-SBR). Further, as the SBR, there are oil-extended rubber in which flexibility is adjusted by adding an extended oil and non-oil-extended rubber in which an extended oil is not added, and these rubbers can be used.

Among these, modified SBR is preferably used. The modified SBR is not particularly limited as long as it is a styrene butadiene rubber having a styrene content of 15 to 50 mass%, a weight average molecular weight (Mw) of 20 ten thousand or more, and a terminal modification ratio of 30 to 100%, and any of solution polymerization SBR (S-SBR) and emulsion polymerization SBR (E-SBR) may be used, and SBR having not only a terminal modified but also a main chain modified, SBR coupled with a tin compound, a silicon compound, or the like (a condensate, SBR having a branched structure, or the like) may be used. The terminal modifying group is not particularly limited as long as it is a group having affinity for silica, and examples of the introduced group include metal atoms such as alkoxysilyl group, amino group, hydroxyl group, glycidyl group, amide group, carboxyl group, ether group, thiol group, cyano group, hydrocarbon group, isocyanate group, imino group (imino group), imidazole group, urea group, carbonyl group, oxycarbonyl group, thio group (sulfide group), disulfide group (disulfide group), sulfonyl group, sulfinyl group, thiocarbonyl group, ammonium group, imide group, hydrazono group, azo group, diazo group, cyano group (nitrile group), pyridyl group, alkoxy group, oxy group, epoxy group, tin, and titanium. Further, these functional groups may have (with or without) a substituent. Among them, preferred are a primary amino group, a secondary amino group, a tertiary amino group (particularly, a glycidylamino group), an epoxy group, a hydroxyl group, an alkoxy group (preferably, an alkoxy group having 1 to 6 carbon atoms), an alkoxysilyl group (preferably, an alkoxysilyl group having 1 to 6 carbon atoms), and a hydrocarbon group. The modified SBR can be produced, for example, by the method described in Japanese patent laid-open No. 2014-19841.

The styrene content of SBR is preferably 5.0 mass% or more, more preferably 10.0 mass% or more for the reason of obtaining sufficient grip performance and rubber strength, and is preferably 60.0 mass% or less, more preferably 50.0 mass% or less from the viewpoint of low fuel consumption, and the styrene content of SBR in the present specification is a value calculated by ¹ H-NMR measurement.

The vinyl group content (1, 2-bonded butadiene unit content) of the SBR is preferably 10.0% or more, more preferably 15.0% or more, for the reason that sufficient grip performance and rubber strength are obtained. Further, the vinyl content of SBR is preferably 65.0% or less, more preferably 60.0% or less, from the viewpoint of low fuel consumption. In addition, the vinyl content of SBR in the present specification can be determined by infrared absorption spectrometry.

The content of SBR in the rubber component is preferably 15 to 45 mass%. When the content of SBR is within this range, the effects of the present invention tend to be sufficiently exhibited. The content of SBR is preferably 16% by mass or more, more preferably 18% by mass or more, and still more preferably 20% by mass or more. On the other hand, the content of SBR is preferably 44 mass% or less, more preferably 42 mass% or less, and further preferably 40 mass% or less. When oil-extended SBR is used as SBR, the content of SBR itself, which is a solid content contained in the oil-extended SBR, is defined as a content in the rubber component.

the SBR may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

(BR)

the BR is not particularly limited, and various kinds of BR such as high cis-1, 4-polybutadiene rubber (high cis BR), butadiene rubber containing 1, 2-syndiotactic polybutadiene crystals (SPB-containing BR), modified butadiene rubber (modified BR) and the like can be used.

The high cis-BR is a butadiene rubber having a cis-1, 4-linkage content (cis content) of 90% or more. Examples of such high-cis BR include BR1220 manufactured by japan ruiweng corporation, BR130B manufactured by yuken corporation, BR150B, and the like. By containing high cis BR, low temperature characteristics and abrasion resistance can be improved. The cis content is preferably 95% or more, more preferably 96% or more, and still more preferably 97% or more. Further, the cis content of the butadiene rubber is a value determined by infrared absorption spectrometry.

The BR containing SPB includes a product in which 1, 2-syndiotactic polybutadiene crystals are dispersed not simply by dispersing the 1, 2-syndiotactic polybutadiene crystals in BR but by chemically bonding the 1, 2-syndiotactic polybutadiene crystals to BR. Examples of such SPB-containing BRs include VCR303, VCR412, VCR617, and the like, manufactured by yokokken co.

Examples of the modified BR include the following BR: the modified BR is obtained by polymerizing 1, 3-butadiene with a lithium initiator and then adding a tin compound, and the terminal of the modified BR molecule is further bonded with a tin-carbon bond. Examples of such modified BR include BR1250H (tin-modified) manufactured by japan ruing corporation, and S-modified polymer (silica-modified) manufactured by sumitomo chemical corporation.

Among these various BR, high cis BR is preferably used from the viewpoint of excellent abrasion resistance.

The content of BR in the rubber component when BR is contained is preferably 5 to 45 mass%, preferably 6 mass% or more, more preferably 8 mass% or more, and further preferably 10 mass% or more, from the viewpoint of abrasion resistance. The content of BR in the rubber component is preferably 44 mass% or less, more preferably 42 mass% or less, and still more preferably 40 mass% or less.

The BR may be used in 1 kind or in combination of 2 or more kinds.

< other rubber Components >

The rubber component may contain other rubber components other than the diene rubber, and examples of such rubber components include ethylene propylene diene rubber (EPDM), Chloroprene Rubber (CR), and the like. Other rubber components may be used in 1 or 2 or more.

< Filler >

carbon black and silica are used as fillers, but other fillers may also be used. Examples of such fillers include any fillers generally used in the art, such as calcium carbonate and clay.

(carbon Black)

The carbon black is not particularly limited, and a material generally used in the rubber industry, such as SAF, ISAF, HAF, FF, and GPE, can be used.

The average particle diameter of the carbon black is preferably 31nm or less, more preferably 29nm or less, and still more preferably 27nm or less from the viewpoints of good fracture strength and sufficient abrasion resistance. From the viewpoint of good processability, the average particle diameter of the carbon black is preferably 15nm or more, more preferably 17nm or more, and still more preferably 19nm or more. The average particle diameter of the carbon black is a number average particle diameter, and can be measured as an average value for any 100 particles by a transmission electron microscope.

The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is preferably 80m ²/g or more, more preferably 90m ²/g or more from the viewpoints of breaking strength, abrasion resistance and the like, on the other hand, the N ₂ SA of the carbon black is preferably 200m ²/g or less, more preferably 150m ²/g or less from the viewpoint of processability, and further, the N ₂ SA of the carbon black is obtained according to method A of JIS K6217.

The dibutyl phthalate (DBP) oil absorption of the carbon black is preferably 100mL/100g or more, more preferably 105mL/100g or more, and still more preferably 110mL/100g or more, from the viewpoints of reinforcing properties, abrasion resistance, and the like. On the other hand, the DBP oil absorption of carbon black is preferably 160mL/100g or less, more preferably 150mL/100g or less, from the viewpoint of enabling the production without difficulty. Further, the DBP oil absorption of the carbon black was measured according to the method of JIS K6217-4.

The content of carbon black is preferably 20 to 100 parts by mass per 100 parts by mass of the rubber component. It is preferably 20 parts by mass or more from the viewpoint of reinforcement, abrasion resistance and the like, and preferably 100 parts by mass or less from the viewpoint of low fuel consumption. The content of carbon black is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 35 parts by mass or more. On the other hand, the content of carbon black is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 70 parts by mass or less.

The carbon black may be used in 1 kind or in combination of 2 or more kinds.

(silica)

When silica is mixed, the silica is not particularly limited, and examples thereof include dry silica (silicic anhydride) and wet silica (hydrated silicic acid), but wet silica is preferable because of the large silanol group.

From the viewpoint of reinforcing properties for rubber, the average particle diameter of silica is preferably 31nm or less, more preferably 30nm or less, still more preferably 29nm or less, and still more preferably 28nm or less. From the viewpoint of good processability, the average particle diameter of the silica is preferably 11nm or more, more preferably 13nm or more, and further preferably 15nm or more. The average particle diameter of silica is a number average particle diameter, and can be measured as an average value for any 100 particles by a transmission electron microscope.

From the viewpoint of reinforcing effect and dispersibility, the nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 100m ²/g or more, more preferably 130m ²/g or more, still more preferably 150m ²/g or more, still more preferably 180m ²/g or more, and further preferably 300m ²/g or less, still more preferably 280m ²/g or less, and still more preferably 260m ²/g or less.

The content of silica is preferably 10 to 60 parts by weight with respect to 100 parts by weight of the rubber component. It is preferably 10 parts by mass or more from the viewpoint of heat generation, and 60 parts by mass or less from the viewpoint of workability. The content of silica is more preferably 15 parts by mass or more, still more preferably 18 parts by mass or more, and still more preferably 20 parts by mass or more. On the other hand, the content of silica is more preferably 55 parts by mass or less, further preferably 50 parts by mass or less, further preferably 40 parts by mass or less, further preferably 30 parts by mass or less.

The silica may be used in 1 kind or in combination of 2 or more kinds.

(content of Filler)

The content of the total filler containing silica is preferably 30 to 160 parts by mass with respect to 100 parts by mass of the rubber component. When the content is within the above range, the effects of the present invention tend to be sufficiently exhibited. The content of the filler is preferably 35 parts by mass or more, more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 60 parts by mass or more. On the other hand, the content of the filler is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and further preferably 90 parts by mass or less. The mixing ratio of carbon black (part by mass) to silica (part by mass) is preferably 1.0 to 3.0, and more preferably 1.5 to 2.5, from the viewpoint of the effect of the present invention.

< silane coupling agent >

The silane coupling agent includes a compound containing a binding unit I represented by formula (1) and a binding unit II represented by formula (2). By mixing the silane coupling agent containing the binding unit I and the binding unit II, it is possible to ensure good processability while improving low fuel consumption properties and wear resistance.

(wherein R ¹ represents hydrogen, halogen, branched or unbranched alkyl having 1 to 30 carbon atoms, branched or unbranched alkenyl having 2 to 30 carbon atoms, branched or unbranched alkynyl having 2 to 30 carbon atoms, or a group in which hydrogen at the terminal of the alkyl group is substituted with a hydroxyl group or a carboxyl group; R ² represents branched or unbranched alkylene having 1 to 30 carbon atoms, branched or unbranched alkenylene having 2 to 30 carbon atoms, or branched or unbranched alkynylene having 2 to 30 carbon atoms; R ¹ and R ² may form a ring structure.)

A compound comprising a binding unit I represented by the formula (1) and a binding unit II represented by the formula (2) is inhibited from increasing in viscosity during processing as compared with a polysulfide silane such as bis- (3-triethoxysilylpropyl) tetrasulfide. This is considered to be because the thioether moiety of the bonding unit I is a C-S-C bond, and therefore is more thermally stable than tetrasulfide or disulfide, and therefore the Mooney viscosity is less increased.

The reason is considered to be that, although the bonding unit II has a mercaptosilane structure, the-C ₇ H ₁₅ moiety of the bonding unit I covers the-SH group of the bonding unit II, and therefore, the bonding unit II is hard to react with the polymer and is hard to cause scorching (rubber scorching).

In the silane coupling agent having the above structure, the content of the binding unit I is preferably 30 mol% or more, more preferably 50 mol% or more, and further preferably 99 mol% or less, more preferably 90 mol% or less, from the viewpoint of obtaining the effects of the present invention well. The content of the binding unit II is preferably 1 mol% or more, more preferably 5 mol% or more, further preferably 10 mol% or more, and further preferably 70 mol% or less, more preferably 65 mol% or less, further preferably 55 mol% or less. The total content of the bonding unit I and the bonding unit II is preferably 95 mol% or more, more preferably 98 mol% or more, and still more preferably 100 mol%. Further, the content of the binding unit I, II is an amount included in the case where the binding unit I, II is located at the terminal of the silane coupling agent. The form of the case where the binding unit I, II is located at the end of the silane coupling agent is not particularly limited as long as a unit corresponding to formulae (1) and (2) representing the binding unit I, II is formed.

Examples of the halogen of R ¹ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms as R ¹ include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl and the like, and the alkyl group preferably has 1 to 12 carbon atoms.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms as R ¹ include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 1-hexenyl group, a 2-hexenyl group, a 1-octenyl group and the like, and the number of carbon atoms of the alkenyl group is preferably 2 to 12.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms as R ¹ include an ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, nonynyl group, decynyl group, undecylynyl group, dodecylynyl group and the like, and the number of carbon atoms of the alkynyl group is preferably 2 to 12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms as R ² include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, and an octadecylene group, and the number of carbon atoms of the alkylene group is preferably 1 to 12.

Examples of the branched or unbranched alkenylene group having 2 to 30 carbon atoms represented by R ² include vinylene, 1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, 2-pentenylene, 1-hexenylene, 2-hexenylene, 1-octenylene and the like, and the number of carbon atoms of the alkenylene group is preferably 2 to 12.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms in R ² include ethynylene, propynylene, butynylene, pentynylene, hexynylene, heptynylene, octynylene, nonynylene, decynylene, undecylynylene, and dodecylynylene groups, and the carbon number of the alkynylene group is preferably 2 to 12.

In the silane coupling agent having the above structure, the total number of repetition (x + y) of the number of repetition (x) of the binding unit I and the number of repetition (y) of the binding unit II is preferably in the range of 3 to 300, and in this range, the mercapto silane of the binding unit II is covered with-C ₇ H ₁₅ of the binding unit I, so that the scorch time can be suppressed from being shortened, and good reactivity with silica and a rubber component can be secured.

Examples of the silane coupling agent having the above structure include NXT-Z30, NXT-Z45, NXT-Z60 manufactured by Meiji corporation. These may be used alone, or 2 or more kinds may be used in combination.

The content of the silane coupling agent having the above structure is preferably 3 to 15 parts by mass with respect to 100 parts by mass of silica. From the viewpoint of rubber strength and abrasion resistance, it is preferably 3 parts by mass or more. From the viewpoint of the effect matching the cost, it is preferably 15 parts by mass or less. The content is preferably 4 parts by mass or more, and more preferably 5 parts by mass or more. On the other hand, the content is preferably 12 parts by mass or less, more preferably 10 parts by mass or less.

The silane coupling agent may be used in 1 kind or 2 or more kinds in combination.

< vulcanization aid >

The vulcanization aid is a compound represented by the formula (3).

(wherein R ³ to R ⁶ each independently represents a C1-18 straight-chain or branched-chain alkyl group, or a C5-12 cycloalkyl group.)

R ³ to R ⁶ in the formula (3) each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms, examples of the linear or branched alkyl group represented by R ³ to R ⁶ include methyl, ethyl, n-propyl, isopropyl, n-butyl, 4-methylpentyl, 2-ethylhexyl, octyl, octadecyl and the like, and examples of the cycloalkyl group include cyclopentyl, cyclohexyl, cyclooctyl and the like, among which R ³ to R ⁶ are preferably linear or branched alkyl groups having 2 to 8 carbon atoms, and more preferably n-butyl, n-propyl, isopropyl, n-octyl from the viewpoints of easy dispersion in the rubber component and easy production.

As the compound represented by the formula (3), for example, TP-50, ZBOP-50, which are manufactured by Rhine chemical Co., Ltd., compounds similar to these compounds (for example, compounds wherein R ³ to R ⁶ are n-propyl, isopropyl, or n-octyl), and the like can be used.

The content of the compound represented by formula (3) (content of the active ingredient) is preferably 10 to 200 parts by mass per 100 parts by mass of the compound including the binding unit I and the binding unit II. In such a range, the effects of the present disclosure tend to be exhibited. The content is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more. On the other hand, the content is preferably 200 parts by mass or less, more preferably 180 parts by mass or less, and further preferably 150 parts by mass or less.

The vulcanization accelerator represented by the formula (3) may be used in 1 kind or in combination of 2 or more kinds.

As the vulcanization aid, a compound represented by the formula (3) can be used, and a conventionally used vulcanization aid can be used.

< vulcanizing agent >

As the vulcanizing agent, a usual vulcanizing agent such as sulfur may be used, but it is preferable to use a compound represented by the formula (4). By using this vulcanizing agent, the rubber composition can retain CC bonding having high bonding energy and high thermal stability. Thereby, the wear resistance and mechanical strength can be improved while maintaining good low fuel consumption.

R⁷-S-S-Y-S-S-R⁸(4)

(wherein Y represents an alkylene group having 2 to 10 carbon atoms; and R ⁷ and R ⁸ may be the same or different and each represents a nitrogen atom-containing 1-valent organic group.)

The alkylene group (having 2 to 10 carbon atoms) of Y is not particularly limited, and examples thereof include linear, branched, and cyclic alkylene groups, and among them, a linear alkylene group is preferable. The number of carbon atoms is more preferably 4 to 8. When the number of carbon atoms of the alkylene group is 1, thermal stability is poor and the effect of having the alkylene group tends not to be obtained; when the number of carbon atoms of the alkylene group is 11 or more, it tends to be difficult to form a crosslinked chain represented by-S-Y-S-.

Examples of the alkylene group satisfying the above conditions include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, and a decylene group. Among them, hexamethylene is preferable because the crosslink and thermal properties represented by-S-Y-S-are formed smoothly between the polymers.

R ⁷ and R ⁸ are not particularly limited as long as they are 1-valent organic groups containing a nitrogen atom, but groups containing at least 1 aromatic ring are preferred, and groups containing a bonding group represented by N — C (═ S) -in which a carbon atom is bonded to a dithio group are more preferred.

R ⁷ and R ⁸ may be the same or different from each other, but are preferably the same for reasons of ease of production and the like.

Examples of the compound satisfying the above conditions include 1, 2-bis (N, N '-dibenzylthiocarbamoyldithio) ethane, 1, 3-bis (N, N' -dibenzylthiocarbamoyldithio) propane, 1, 4-bis (N, N '-dibenzylthiocarbamoyldithio) butane, 1, 5-bis (N, N' -dibenzylthiocarbamoyldithio) pentane, 1, 6-bis (N, N '-dibenzylthiocarbamoyldithio) hexane, 1, 7-bis (N, N' -dibenzylthiocarbamoyldithio) heptane, 1, 8-bis (N, N '-dibenzylthiocarbamoyldithio) octane, 1, 9-bis (N, N' -dibenzylthiocarbamoyldithio) nonane, and mixtures thereof, 1, 10-bis (N, N' -dibenzylthiocarbamoyldithio) decane, and the like. Among them, 1, 6-bis (N, N' -dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

The content of the compound represented by formula (4) is preferably 0.5 to 3.0 parts by mass per 100 parts by mass of the rubber component. In such a range, the effects of the present disclosure tend to be exhibited. The content of the compound represented by formula (4) is preferably 0.7 parts by mass or more, and more preferably 1.0 parts by mass or more. On the other hand, the content of the compound represented by formula (4) is preferably 2.5 parts by mass or less, and more preferably 2.0 parts by mass or less.

When sulfur is further added as a vulcanizing agent in addition to the compound represented by formula (4), the content thereof is more than 0 part by mass and not more than 2 parts by mass per 100 parts by mass of the rubber component. The sulfur content is limited so as not to impair the effect obtained by the compound represented by the mixed formula (4). The content of sulfur is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, further preferably 0.3 part by mass or more, and further preferably 0.4 part by mass or more. On the other hand, the content of sulfur is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less.

The compound represented by the formula (4) may be used in 1 or 2 or more.

< other Mixed Components >

The rubber composition may contain, in addition to the above components, compounding agents conventionally used in the rubber industry, such as plasticizers, oils, antioxidants, vulcanization accelerators, and the like.

Examples of the vulcanization accelerator include guanidine-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, sulfenamide-based, thiourea-based, thiuram-based, dithiocarbamate-based, and xanthate-based compounds. These vulcanization accelerators may be used alone, or 2 or more kinds may be used in combination. When the vulcanization accelerator is contained, the content of the vulcanization accelerator is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. The content of the vulcanization accelerator is preferably 2.0 parts by mass or less, and more preferably 1.5 parts by mass or less. When the content of the vulcanization accelerator is within the above range, there is a tendency that a suitable crosslinking density is obtained.

When the plasticizer is contained, the content of the plasticizer is 1 part by mass or more, preferably 3 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of processability. Further, the content of the plasticizer is 40 parts by mass or less, preferably 20 parts by mass or less from the viewpoint of abrasion resistance and handling stability. The content of the plasticizer in the present specification also includes oil components contained in the oil-extended rubber and the insoluble sulfur.

Examples of the oil include process oil, vegetable oil and fat, and animal oil and fat. When the oil is contained, the content of the oil is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of processability. In addition, the content of the oil is preferably 40 parts by mass or less from the viewpoint of the load on the process.

< others >

The ratio of the content (parts by mass) of the isoprene-based rubber to the total content (parts by mass) of the compound containing the binding unit I represented by the formula (1) and the binding unit II represented by the formula (2) and the compound represented by the formula (4) is preferably 1 to 40. When the ratio is within such a range, the effects of the present invention tend to be sufficiently exhibited. The ratio is more preferably 2 or more, further preferably 5 or more, further preferably 8 or more, further preferably 10 or more, and on the other hand, the ratio is more preferably 39 or less, more preferably 38 or less, further preferably 37 or less, further preferably 36 or less, further preferably 35 or less.

< production of rubber composition >

the rubber composition can be produced by a known method, for example, by the following method: among the above components, a method of kneading the components other than sulfur and the vulcanization accelerator with a banbury mixer, a kneader, an open mill, or the like, adding sulfur and the vulcanization accelerator to the resulting kneaded mixture, kneading the mixture, and then vulcanizing the mixture can be used.

< production of tire >

A predetermined tire according to one embodiment can be produced by a usual method using the rubber composition. Namely, the production can be carried out by the following method: the rubber composition is extruded and processed into a tread shape at an unvulcanized stage, and the tread shape is laminated with other tire members on a tire molding machine, and molded by a usual method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizing machine.

The tire obtained in this way can be used as a pneumatic tire for any vehicle by being inflated, and is excellent in high-temperature grip performance and wear resistance, and therefore is particularly suitable for a high-performance tire used as a racing tire for racing, such as racing, and particularly a high-performance dry tire used on a dry road surface.