阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 大下雅树 松井僚儿 滨田敏彰 于 2020-05-07 设计创作，主要内容包括：提供了耐磨性优异、在极冷道路上的操纵稳定性优异同时重量降低的充气轮胎。本发明涉及充气轮胎,其具有：胎面,所述胎面在-20℃下的硬度为90以下、在30℃下的硬度为60以上,且最大厚度为8.5mm以下；以及胎体,所述胎体具有一层胎体帘布层。(Provided is a pneumatic tire having excellent wear resistance, excellent steering stability on extremely cold roads, and reduced weight. The present invention relates to a pneumatic tire, comprising: a tread having a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less; and a carcass having one carcass ply.)

1. A pneumatic tire, comprising:

a tread having a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less; and

a carcass having a carcass ply.

2. The pneumatic tire as set forth in claim 1,

wherein the tread is formed from a tread rubber composition comprising at least one rubber component including a styrene-butadiene rubber and at least one filler.

Technical Field

The present invention relates to a pneumatic tire.

Background

In recent years, environmental performance has become increasingly important, and the demand for lighter tires has increased. A possible technique to reduce the weight of the tire is to reduce the number of carcass plies in the carcass. However, this technique generally has a problem of lowering physical properties (such as durability and abrasion resistance) of the tire.

In addition, there is an increasing demand for all season tires that can be used in any season or at any atmospheric temperature. For example, it is desirable to provide good tire physical properties while ensuring steering stability on extremely cold roads.

Patent document 1 proposes a tire having a specific bead to achieve good durability and good wear resistance while reducing an increase in mass. However, other techniques and further improvements are needed.

Reference list

Patent document

Patent document 1: JP 2018-supplement 83475A

Disclosure of Invention

Technical problem

The present invention aims to solve the above problems and provide a pneumatic tire excellent in wear resistance, excellent in steering stability on an extremely cold road, and reduced in weight.

Means for solving the problems

The present invention relates to a pneumatic tire, comprising: a tread having a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less; and a carcass having one carcass ply.

Preferably, the tread is formed from a tread rubber composition comprising at least one rubber component including styrene-butadiene rubber and at least one filler.

The invention has the advantages of

The present invention provides a pneumatic tire, comprising: a tread having a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less; and a carcass having a carcass ply; the pneumatic tire has excellent wear resistance, excellent steering stability on an extremely cold road, and reduced weight.

Drawings

Fig. 1 is a cross-sectional view showing a portion of a pneumatic tire.

Fig. 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 of the tire 2 in fig. 1.

Detailed Description

The pneumatic tire of the present invention includes: a tread having a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less; and a carcass, the carcass being one carcass ply. Such a pneumatic tire has excellent wear resistance, excellent steering stability on an extremely cold road, while reducing weight.

The reason for the above-described advantageous effect is not clear, but is considered as follows.

If the tread becomes stiff when in contact with extremely cold roads, the steering force will increase. Further, if the tire has a structure including one carcass (shell) and a thin tread and thus has low overall rigidity, steering stability may be lowered. According to the present invention, the tread has a relatively soft hardness of 90 or less at low temperatures (-20 ℃), and therefore steering stability in extremely cold regions can be ensured. Further, the tread has a relatively hard hardness of 60 or more at 30 ℃, and therefore even a thin tire having a maximum tread thickness of 8.5mm can secure durability (e.g., wear resistance), thereby maintaining the tire life. Therefore, it is considered that the tire has excellent wear resistance and excellent steering stability on an extremely cold road while reducing the weight.

Therefore, the tire solves the following technical problems (objects) by its structure comprising a tread having a hardness of 90 or less at-20 ℃, a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less, and a carcass having one carcass ply: provides excellent wear resistance and excellent steering stability on extremely cold roads while reducing weight. In other words, the technical problem (object) is not defined by the structure including a tread having a hardness of 90 or less at-20 ℃, a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less, and a carcass having one carcass ply; the technical problem here is: provides excellent wear resistance and excellent steering stability on extremely cold roads while reducing weight. To solve this technical problem, a structure satisfying these parameters is designed.

Examples of techniques for satisfying a hardness of 90 or less at-20 ℃ and a hardness of 60 or more at 30 ℃ (i.e., techniques for making a difference between a hardness at an extremely low temperature (-20 ℃) and a hardness at normal temperature (30 ℃) relatively small) include: (a) a method using a styrene-butadiene rubber having a broad molecular weight distribution; (b) a method of reducing oil content; (c) a method for controlling the polybutadiene rubber content; (d) a method of controlling a mixing ratio of styrene-butadiene rubber and polybutadiene rubber; (e) a method using a liquid resin; and other methods, which may be used alone or in appropriate combination.

Further, examples of the technique of reducing the hardness at-20 ℃ include: a method of using an oil-extended styrene-butadiene copolymer as a styrene-butadiene rubber; a process using a styrene-butadiene rubber with a lower Mw; a process using a styrene-butadiene rubber having a broader Mw/Mn ratio; a method of using a styrene-butadiene rubber having a lower styrene content; a method of using a styrene-butadiene rubber having a lower vinyl content; a method for reducing the content of styrene-butadiene rubber; a method for increasing the polybutadiene rubber content; a method of reducing the filler content; using N₂A lower SA silica process; and a method of increasing the liquid resin content.

Examples of techniques for increasing hardness at 30 ℃ include: a method of using an oil-extended styrene-butadiene copolymer as a styrene-butadiene rubber; a process using a styrene-butadiene rubber with a higher Mw; a method of increasing the filler content; using N₂Higher SA silica; and a method for reducing the liquid resin content.

The invention is described in detail below on the basis of an exemplary preferred embodiment and with reference where appropriate to the accompanying drawings.

Fig. 1 shows a pneumatic tire 2. In fig. 1, the vertical direction corresponds to the radial direction of the tire 2, the horizontal direction corresponds to the axial direction of the tire 2, and the direction perpendicular to the paper corresponds to the circumferential direction of the tire 2. In fig. 1, a chain line CL indicates an equatorial plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equatorial plane, except for the tread pattern.

The tire 2 has: a tread 4, a pair of sidewalls (sidewalls) 6, a pair of wings (wing)8, a pair of clinchs (clinch)10, a pair of beads 12, a carcass 14, a belt (belt)16, a liner (band)18, an inner liner (inliner) 20, and a pair of chafers (chafer) 22. The tyre 2 is a tubeless tyre. The tire 2 may be mounted on a passenger vehicle.

The tread 4 has a radially outwardly convex shape. The tread 4 forms a tread surface 24 (which will contact the road). Grooves 26 are engraved in the tread 4. The grooves 26 define a tread pattern. The tread 4 includes a base layer 28 and a cap layer 30. The running surface layer 30 is located radially outwardly of the base layer 28. The running surface layer 30 overlies the base layer 28. The base layer 28 is formed of a crosslinked rubber excellent in adhesion. The base rubber of the base layer 28 is typically natural rubber. The running surface layer 30 is formed of a crosslinked rubber excellent in properties such as abrasion resistance and steering stability on a cold road.

From the viewpoint of steering stability on an extremely cold road, the hardness (Hs) of the (crosslinked) running surface layer 30 at-20 ℃ is 90 or less, preferably 83 or less, more preferably 81 or less, and still more preferably 78 or less. The lower limit is not limited, but from the viewpoint of ensuring driving stability on a cold road, it is preferably 70 or more, more preferably 72 or more, and still more preferably 74 or more.

From the viewpoint of steering stability on an extremely cold road, the hardness (Hs) of the (crosslinked) running surface layer 30 at 30 ℃ is 60 or more, preferably 62 or more, more preferably 64 or more, and still more preferably 65 or more. The upper limit is not limited, and it is preferably 75 or less, more preferably 73 or less, further preferably 71 or less, from the viewpoint of dry grip performance and wet grip performance.

In the example shown in fig. 1, the tread 4 has a two-layer structure (including a cap layer 30 and a base layer 28). In the case where the tread 4 has a single-layer structure, the single-layer tread 4 satisfies the above-described hardness. In the case where the tread 4 has a three-or-more-layer structure, the cap layer 30 (outermost surface layer) satisfies the above hardness.

In principle, samples for analysis of physical properties are cut from the tire 2. If a sample cannot be cut out from the tire 2, a sheet that reproduces the conditions of the tire component in the tire 2 is prepared, from which the sample is cut out and used. Hardness can be measured according to JIS K6253-3(2012) "vulcanized or thermoplastic rubber-determination of hardness-part 3: durometer method "measurements were performed using a type a durometer.

For example, the cap layer 30 (a single-layer tread for the tread 4 having a single-layer structure, or a cap layer (outermost surface layer) for the tread 4 having a three-or more-layer structure) may be composed of a tread rubber composition (cap layer rubber composition) containing one or more rubber components (including styrene-butadiene rubber) and one or more fillers.

Any SBR may be used for the cap ply 30. Examples include SBR commonly used in the tire industry, such as emulsion SBR (E-SBR) and solution SBR (S-SBR). They may be used alone or in combination of two or more.

The amount of SBR is preferably 30% by mass or more, more preferably 40% by mass or more, further more preferably 50% by mass or more, and particularly preferably 60% by mass or more, based on 100% by mass of the rubber component in the tread rubber composition (cap rubber composition). The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less, and particularly preferably 70% by mass or less. When the amount of SBR is within the above range, excellent wear resistance and excellent steering stability on an extremely cold road tend to be provided while reducing the weight.

The weight average molecular weight (Mw) of SBR is preferably 300,000 or more, more preferably 600,000 or more, further preferably 800,000 or more, particularly preferably 850,000 or more, and most preferably 900,000 or more, but is preferably 1,500,000 or less, more preferably 1,300,000 or less, further more preferably 1,100,000 or less, and particularly preferably 950,000 or less. When Mw is within the above range, it tends to provide excellent wear resistance and excellent steering stability on an extremely cold road while reducing weight.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the SBR is preferably 1.5 or more, more preferably 2.0 or more, further more preferably 2.2 or more, particularly preferably 2.6 or more, preferably 6.0 or less, more preferably 4.0 or less, further preferably 3.0 or less. When the Mw/Mn ratio of SBR is within the above range, it tends to provide excellent abrasion resistance and excellent steering stability on an extremely cold road while reducing the weight.

The styrene content of SBR is preferably 25% by mass or more, more preferably 28% by mass or more, further more preferably 30% by mass or more, and particularly preferably 33% by mass or more, but is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, and particularly preferably 35% by mass or less. When the styrene content of SBR is within the above range, it tends to provide excellent abrasion resistance and excellent steering stability on an extremely cold road while reducing weight.

The vinyl group content of SBR is preferably 20 mass% or more, more preferably 25 mass% or more, further preferably 30 mass% or more, particularly preferably 34 mass% or more, and preferably 60 mass% or less, more preferably 50 mass% or less, further preferably 45 mass% or less, particularly preferably 42 mass% or less. When the vinyl content of SBR is within the above range, it tends to provide excellent abrasion resistance and excellent handling stability on an extremely cold road while reducing weight.

Herein, the weight average molecular weight (Mw) and the number average molecular weight (Mn) can be determined by Gel Permeation Chromatography (GPC) (GPC series GPC-8000 available from Tosoh corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M available from Tosoh corporation) calibrated with polystyrene standards. The cis content (cis 1, 4-butadiene unit content) and the vinyl content (1, 2-butadiene unit content) can be determined by infrared absorption spectroscopy. The styrene content can be determined by¹H-NMR analysis.

The SBR may suitably be an oil-extended styrene-butadiene copolymer. The oil-extended styrene-butadiene copolymer is prepared by oil-extending a styrene-butadiene copolymer with an extender oil. Therefore, by including the oil-extended styrene-butadiene copolymer (oil-extended with the extender oil in advance), the dispersibility of the extender oil and the filler in the rubber component can be enhanced as compared with a rubber composition prepared by kneading the oil during compounding.

The oil-extended styrene-butadiene copolymer is preferably a copolymer into which a branched structure is introduced. Examples of the styrene-butadiene copolymer into which the branched structure is introduced include: polymers whose chain ends are modified with at least one polyfunctional coupling agent selected from the group consisting of epoxy compounds, halogen-containing silicon compounds and alkoxysilane compounds, and polymers polymerized in the presence of a small amount of at least one branching agent. Among these, polymers whose chain ends are modified with at least one polyfunctional coupling agent are preferred.

For example, a styrene-butadiene copolymer can be prepared by copolymerizing styrene and butadiene using a polymerization initiator. The polymerization initiator is preferably a lithium-based initiator. The lithium initiator is preferably an organolithium compound. Examples of the organolithium compound include: alkyl lithium such as n-butyl lithium, sec-butyl lithium, tert-butyl lithium; lithium alkylenes, such as 1, 4-dilithiobutane; lithium arenes such as phenyl lithium, stilbenium, lithium diisopropenylbenzene, and the reaction products of alkyl lithium (e.g., butyl lithium) with divinyl benzene and the like; polynuclear hydrocarbon lithium such as naphthalene lithium; lithium amide; and tributyltin lithium.

The polymerization may be optionally carried out using an ether compound, an amine, or the like as a styrene randomizer for copolymerization or as a vinyl bond content regulator. Examples of the ether compound, the amine, and the like include: dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, triethylamine, pyridine, N-methylmorpholine, N, N, N ', N' -tetramethylethylenediamine and dipiperidinoethane. In addition, activators (e.g., potassium dodecylbenzenesulfonate, potassium linolenate, potassium benzoate, potassium phthalate, potassium tetradecylbenzenesulfonate) may also be used for the same purpose.

The polymerization solvent used may be n-hexane, cyclohexane, heptane, benzene, etc. The polymerization may be carried out in a batch or continuous mode, but it is preferable to employ a continuous mode in order to suitably obtain a styrene-butadiene copolymer having the above properties. The polymerization conditions were as follows: the polymerization temperature is usually from 0 to 130 ℃, preferably from 10 to 100 ℃; the polymerization time is usually 5 minutes to 24 hours, preferably 10 minutes to 10 hours. The monomer concentration in the polymerization solvent (total monomer/(total monomer + polymerization solvent)) is usually 5 to 50 mass%, preferably 10 to 35 mass%.

Generally, when a lithium-based initiator is used, the polymerization rate of styrene is different from that of butadiene. In addition, the rate of polymerization of these monomers can be affected by the polymerization temperature and monomer concentration. Therefore, in the latter half of the simple reaction where the polymerization temperature is elevated, many styrene molecules may react due to the polymerization temperature and the high styrene monomer concentration, forming many long styrene chains, resulting in an increase in the proportion of long styrene chains. Therefore, the ratio of the styrene single chains and the ratio of the styrene long chains can be adjusted to appropriate values, for example, by controlling the polymerization temperature so that styrene and butadiene react at the same rate; alternatively, the reaction is started by adding a reduced amount of butadiene before the reaction to increase the uptake of styrene at the initial stage of the polymerization, and then a reduced portion of butadiene is continuously introduced.

Specific examples of the method of introducing a branched structure into the styrene-butadiene copolymer include: reacting a living polymer having active lithium terminals, produced by batch or continuous polymerization, with at least one polyfunctional coupling agent selected from: halogen-containing silicon compounds (e.g., silicon tetrachloride), alkoxysilane compounds, alkoxysilane sulfides, (poly) epoxy compounds, urea compounds, amide compounds, imide compounds, thiocarbonyl compounds, lactam compounds, ester compounds, ketone compounds; among these, halogen-containing silicon compounds (e.g., silicon tetrachloride), alkoxysilane compounds, alkoxysilane sulfides, and (poly) epoxy compounds are preferable, and halogen-containing silicon compounds, alkoxysilane compounds, and (poly) epoxy compounds are more preferable. Alternatively, in the case of polymerization in the presence of a small amount of a branching agent, examples of the branching agent include divinylbenzene. The incorporation amount is preferably 10% by mass or less based on 100% by mass of the styrene-butadiene copolymer.

Examples of extender oils for oil-extending styrene-butadiene copolymers include: naphthenic extender oil, paraffinic extender oil, and aromatic extender oil. Among these, aromatic extender oils are preferred. Further, a naphthenic or paraffinic rubber extender oil may be used in combination. For example, oil extension may be performed as follows: after completion of the polymerization, extender oil is added, and then the solvent is removed by a conventional method and dried.

The amount of the extender oil is preferably 5 to 50 parts by mass, more preferably 10 to 50 parts by mass, and further more preferably 30 to 50 parts by mass, relative to 100 parts by mass of the styrene-butadiene copolymer.

The SBR may be an unmodified SBR or a modified SBR.

Any modified SBR having functional groups that interact with fillers (e.g., silica) may be used. Examples include: chain end-modified SBR (chain end-modified SBR terminated with a functional group) obtained by modifying at least one chain end of SBR with a compound having a functional group (modifier); a main chain-modified SBR having a functional group in the main chain; a main chain and chain end-modified SBR in which both the main chain and the chain end have a functional group (for example, a main chain and chain end-modified SBR in which the main chain has a functional group and at least one chain end is modified with a modifier); and chain end-modified SBR in which a hydroxyl group or an epoxy group is introduced by modification (coupling) with a polyfunctional compound (having two or more epoxy groups in the molecule). They may be used alone or in combination of two or more.

Examples of functional groups include: amino, amide, silyl, alkoxysilyl, isocyanate, imino, imidazolyl, ureido, ether, carbonyl, oxycarbonyl, mercapto, thioether, disulfide, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazono, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxyl, oxy, and epoxy groups. These functional groups may have a substituent. Of these, preferred are amino groups (preferably amino groups in which a hydrogen atom is substituted with a C1-C6 alkyl group), alkoxy groups (preferably C1-C6 alkoxy groups), alkoxysilyl groups (preferably C1-C6 alkoxysilyl groups), and amide groups.

SBR products manufactured or sold by Sumitomo chemical Co., Ltd., JSR company, Asahi Kasei corporation, Riwen Co., Ltd., and the like can be used.

Examples of the rubber component other than SBR that can be used for the tread rubber composition (cap layer rubber composition) include diene rubbers such as isoprene-based rubber, polybutadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), Chloroprene Rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). Examples of the isoprene-based rubber include: natural Rubber (NR), polyisoprene rubber (IR), purified NR, modified NR and modified IR. Among these, BR is preferable from the viewpoint of properties (e.g., abrasion resistance). The rubber component (e.g., SBR) may be used alone or in combination of two or more.

The amount of BR is preferably 10% by mass or more, more preferably 20% by mass or more, further more preferably 25% by mass or more, and particularly preferably 30% by mass or more, based on 100% by mass of the rubber component in the tread rubber composition (cap layer rubber composition). When the amount is not less than the lower limit, good properties (e.g., abrasion resistance) tend to be obtained. The upper limit is preferably 70% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less, and particularly preferably 40% by mass or less. When the amount is not higher than the upper limit, the SBR content tends to be secured, so that good performance (e.g., steering stability on an extremely cold road) can be obtained.

Any BR can be used, examples include high cis BR and syndiotactic BR containing polybutadiene crystals. The BR can be unmodified BR or modified BR. Examples of the modified BR include BR into which the above-mentioned functional group is introduced. They may be used alone or in combination of two or more. In particular, BR having a cis content of 90 mass% or more, preferably 95 mass% or more is suitable for enhancing abrasion resistance. Cis content can be measured by infrared absorption spectroscopy.

BR can be purchased from Utsuki Kagaku K.K., JSR Kabushiki Kaisha, Asahi Kabushiki Kaisha, Rui Weng K.K.

Examples of fillers include those known in the rubber art, such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, alumina, and mica. Among these, silica or carbon black is preferable.

Examples of the silica usable for the tread rubber composition (cap rubber composition) include: dry silica (anhydrous silica) and wet silica (hydrous silica). Of these, wet silica is preferable because it has a large amount of silanol groups.

The amount of silica is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, further more preferably 70 parts by mass or more, particularly preferably 80 parts by mass or more, and most preferably 100 parts by mass or more, relative to 100 parts by mass of the rubber component in the tread rubber composition (cap layer rubber composition). When the amount is not less than the lower limit, good properties (e.g., abrasion resistance) tend to be obtained. The upper limit is preferably 170 parts by mass or less, more preferably 150 parts by mass or less, further preferably 140 parts by mass or less, and particularly preferably 135 parts by mass or less. When the amount does not exceed the upper limit, good dispersibility tends to be obtained.

Nitrogen adsorption specific surface area (N) of silica₂SA) is preferably 50m²A value of 80m or more, more preferably 80m²(ii) at least g, and more preferably 90m²A total of 115m or more, particularly preferably 115m²More than g. When N is present₂When SA is not less than the lower limit or more, good properties (e.g., abrasion resistance) tend to be obtained. N of silicon dioxide₂SA is preferably 200m²A ratio of not more than 150 m/g, more preferably²A value of 130m or less, more preferably 130m or less²The ratio of the carbon atoms to the carbon atoms is less than g. When N is present₂When SA does not exceed the upper limit, good dispersibility tends to be obtained.

Measurement of N of silica by BET method according to ASTM D3037-93₂SA。

Silica is available from degussa, luodia, donghao silica co, solvyo japan, german corporation, and the like.

The rubber composition preferably comprises one or more silane coupling agents and silica.

Any silane coupling agent may be used, examples including: sulfide-based silane coupling agents such as bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide and bis (3-trimethoxysilylpropyl) tetrasulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and NXT-Z (both available from Meiji Seen); vinyl silane coupling agents such as vinyltriethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane; a glycidoxy-based silane coupling agent such as gamma-glycidoxypropyltriethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane; chlorine-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based silane coupling agents or mercapto-based silane coupling agents are preferable.

The silane coupling agent is commercially available from Degussa, Myograph, Xinyue silicone, Tokyo chemical industries, AZmax Co., Ltd., Dow Corning Tokyo Li Ltd. The amount of the silane coupling agent is preferably about 3 to 25 parts by mass with respect to 100 parts by mass of silica.

Any carbon black may be used in the tread rubber composition (cap rubber composition), including GPF, FEF, HAF, ISAF, and SAF. Commercially available products from Asahi carbon Co., Ltd, Kabet Japan K.K., Toshiba carbon Co., Ltd, Mitsubishi chemical Co., Ltd, Shiwang carbon Co., Ltd, and Columbia carbon Co., Ltd can be used. The addition of carbon black provides reinforcement and thus can significantly improve properties (e.g., abrasion resistance).

The amount of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further more preferably 5 parts by mass or more, relative to 100 parts by mass of the rubber component in the tread rubber composition (cap layer rubber composition). When the amount is not less than the lower limit, the effect of adding carbon black tends to be obtained. The amount of carbon black is also preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. When the amount does not exceed the upper limit, good dispersibility tends to be obtained.

Nitrogen adsorption specific surface area (N) of carbon black in tread rubber composition (cap rubber composition)₂SA) is preferably 50m²A value of at least one of,/g, more preferably 70m²A total of 85m or more, preferably 85m²A total of 96m or more, particularly 96m²More than g. When N is present₂When SA is not less than the lower limit, a good reinforcing effect tends to be obtained. N of carbon black₂The upper limit of SA is not limited, but is preferably 150m²A ratio of 120m or less per gram²A total of 110m or less, more preferably²The ratio of the carbon atoms to the carbon atoms is less than g.

The nitrogen adsorption specific surface area of carbon black was measured according to method A defined in JIS K6217.

The tread rubber composition (cap rubber composition) preferably contains one or more resins. Examples of usable resins include liquid resins (resins that are liquid at room temperature (25 ℃) and solid resins (resins that are solid at room temperature (25 ℃).

The amount of the resin is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, further more preferably 5 parts by mass or more, and particularly preferably 10 parts by mass or more, relative to 100 parts by mass of the rubber component in the tread rubber composition (cap layer rubber composition). When the amount is not lower than the lower limit, good performance (e.g., steering stability on an extremely cold road) tends to be obtained. The upper limit of the amount of the resin is not limited, but is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and further preferably 15 parts by mass or less, from the viewpoint of abrasion resistance. The amount of the liquid resin is also suitably within the above range.

From the viewpoint of performance (e.g., steering stability on an extremely cold road), it may be preferable to use a liquid resin as the resin in the tread rubber composition (cap layer rubber composition). The liquid resin refers to a thermoplastic resin as follows: the weight average molecular weight is usually several hundred to several thousand, and a rubber component (e.g., natural rubber or synthetic rubber) may be incorporated to impart tackiness. Examples of the liquid resin include liquid petroleum or coal resins such as coumarone-indene resin, α -methylstyrene resin, vinyltoluene resin and polyisoprene resin. Other examples of liquid resins include: liquid natural resins such as coumarone resins, cycloalkane resins, phenol resins, terpene-phenol resins, rosin esters, hydrogenated rosin resin derivatives, and hydrogenated terpene resins; and liquid synthetic resins such as alkyl phenol resins, C5 petroleum resins, C9 petroleum resins, aliphatic petroleum resins, xylene formaldehyde resins, phenol-modified C9 petroleum resins, carboxylic acid-modified C9 petroleum resins, and dicyclopentadiene-modified C9 petroleum resins. Among these liquid resins, at least one selected from the group consisting of a liquid coumarone-indene resin, a liquid indene resin and a liquid α -methylstyrene resin is preferred, and a liquid coumarone-indene resin is more preferred.

The coumarone-indene resin refers to a resin containing coumarone and indene as monomer components constituting the main chain (skeleton) of the resin. Examples of the monomer component that may be contained in the main chain in addition to coumarone and indene include: styrene, alpha-methylstyrene, methylindene and vinyltoluene. The indene resin and the α -methylstyrene resin refer to resins containing indene and α -methylstyrene, respectively, as monomer components mainly constituting the main chain (main chain) of the resin.

The softening point of the liquid resin in the tread rubber composition (cap rubber composition) is preferably-30 ℃ or higher, more preferably-25 ℃ or higher, and still more preferably-20 ℃ or higher. When the softening point is not lower than the lower limit, good kneadability with the rubber component tends to be obtained. The softening point of the liquid resin is preferably 15 ℃ or lower, more preferably 5 ℃ or lower, and still more preferably-10 ℃ or lower.

Herein, the softening point is measured with a ring and ball softening point measuring device according to JIS K6220, and is defined as the temperature at which the ball falls.

The tread rubber composition (cap rubber composition) may contain one or more oils. From the viewpoint of abrasion resistance, the amount of the oil is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and further more preferably 27 parts by mass or less, relative to 100 parts by mass of the rubber component. The lower limit is not limited, but is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 18 parts by mass or more, and particularly preferably 22 parts by mass or more.

The amount of oil, if used, includes the amount of oil contained in the rubber (oil-extended rubber).

Examples of oils include process oils and vegetable oils and mixtures thereof. Examples of the process oil include: paraffinic process oils, aromatic process oils and naphthenic process oils. Examples of vegetable oils include: castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. They may be used alone or in combination of two or more. Of these, naphthenic process oils are preferred to better achieve the beneficial effects of the present invention.

The oil can be purchased from Shifting company, Sanko oil chemical industries, Japan energy Co., Ltd, Oliisoy, H & R, Fengkou oil Co., Ltd, Showa Shell oil Co., Ltd, Fuji oil Co., Ltd, etc.

The tread rubber composition (cap rubber composition) preferably contains sulfur. The amount of sulfur is preferably 0.5 to 5.0 parts by mass, more preferably 0.7 to 3.0 parts by mass, relative to 100 parts by mass of the rubber component.

Examples of sulfur include those commonly used in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Commercially available products from Hello chemical industries, Sulfur, Quita chemical industries, Flexsys, Nippon Tokukaki, Mitsui chemical industries, and the like can be used.

The tread rubber composition (cap rubber composition) preferably contains one or more vulcanization accelerators. The amount of the vulcanization accelerator is preferably 1.0 to 5.0 parts by mass, more preferably 1.5 to 4.5 parts by mass, relative to 100 parts by mass of the rubber component.

Examples of the vulcanization accelerator include: thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazole disulfide and N-cyclohexyl-2-benzothiazolesulfenamide; thiuram based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, N-t-butyl-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N' -diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine and orthotolylbiguanide. They may be used alone or in combination of two or more. Among these, sulfenamide-based vulcanization accelerators or guanidine-based vulcanization accelerators are preferable.

The tread rubber composition (cap rubber composition) may contain one or more of wax, antioxidant, stearic acid, zinc oxide, or organic crosslinking agent.

In the tire 2 shown in fig. 1, the maximum thickness of the tread 4 is 8.5mm or less.

Fig. 2 is an enlarged cross-sectional view of the tire 2 of fig. 1 near the tread 4. In fig. 2, the vertical direction corresponds to the radial direction of the tire 2, the horizontal direction corresponds to the axial direction of the tire 2, and the direction perpendicular to the paper corresponds to the circumferential direction of the tire 2.

In fig. 2, symbol P denotes a point on the tread surface 24. Point P is located outside of groove 26 (axially innermost). The double-headed arrow T indicates the thickness of the tread 4 measured at the point P. The thickness T is the sum of the thicknesses of the running surface layer 30 and the base layer 28 measured at point P. The thickness T is measured along a normal to the tread surface 24 at point P. Fig. 1 and 2 show an example of a two-layer tread 4 (with a cap layer 30 and a base layer 28); however, in the case of a single-layer tread 4, the thickness T of the tread is the thickness of the single-layer tread measured at point P; in the case of a three or more layer tread, the thickness T of the tread is the sum of the thicknesses of the three or more layers measured at point P, where the thickness T at point P is also measured along the normal to the tread surface 24 at point P.

In fig. 1, the maximum thickness of the tread 4 refers to the maximum thickness (the sum of the thicknesses of the cap layer 30 and the base layer 28 in fig. 1) among the thicknesses of the tread measured at the respective points on the tread surface 24, and is 8.5mm or less. Such a maximum thickness enables weight reduction. In addition, good tire physical properties, such as abrasion resistance and steering stability on extremely cold roads, can be provided despite the reduced weight. The maximum thickness of the tread 4 is preferably 8.0mm or less, more preferably 7.5mm or less, still more preferably 7.0mm or less, and particularly preferably 6.5mm or less. The lower limit is preferably 5.5mm or more, more preferably 6.0mm or more, from the viewpoint of the physical properties of the tire.

In the tire 2 shown in fig. 1, each sidewall 6 extends substantially radially inward from an end of the tread 4. The radially outer portion of the sidewall 6 is bonded to the tread 4. The radially inner portion of the sidewall 6 is joined to the clinch 10. The sidewall 6 is formed of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewalls 6 prevent damage to the carcass 14.

Each of the beads 8 is located between the tread 4 and the sidewall 6. The wings 8 join the tread 4 and sidewalls 6. The bead 8 is formed of a crosslinked rubber excellent in adhesion.

Each bridge 10 is located substantially radially inside the sidewall 6. The clinch 10 is located axially outward of the bead 12 and carcass 14. The lap portion 10 is formed of a crosslinked rubber excellent in wear resistance.

Each bead 12 is located axially inside the clinch 10. The bead 12 includes a core 32 and an apex 34 extending radially outward from the core 32. The core 32 has an annular shape and contains a wound non-stretchable wire. The material of the wire is typically steel. Apex 34 tapers radially outward. The apex 34 is formed of a cross-linked rubber of high hardness.

The carcass 14 includes a carcass ply 36. In the tire 2, the carcass 14 is composed of one carcass ply 36, which enables weight reduction.

In the tire 2, the carcass ply 36 extends along the tread 4 and sidewalls 6 between the beads 12 on opposite sides. The carcass ply 36 is folded axially from the inside outwards around each core 32. The thus-folded carcass ply 36 is provided with a main portion 36a and a pair of folded portions 36 b. That is, the carcass ply 36 includes a main portion 36a and a pair of folded portions 36 b.

Although not shown, the carcass ply 36 is formed from a plurality of parallel cords (cord) and a topping rubber (topping rubber). The absolute value of the angle of each cord with respect to the equatorial plane is suitably 75 ° to 90 °. In other words, the carcass 14 preferably has a radial structure. The cord is formed of an organic fiber. Preferred examples of the organic fiber include: polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and polyaramide fibers.

The belt 16 is located radially inward of the tread 4. The belt 16 is superposed on the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 is composed of an inner layer 38 and an outer layer 40. As best seen in FIG. 1, inner layer 38 is slightly wider in the axial direction than outer layer 40. In the tire 2, the axial width of the belt 16 is preferably at least 0.6 times, but preferably not more than 0.9 times the cross-sectional width of the tire 2 (see JATMA).

Although not shown, both inner layer 38 and outer layer 40 are formed from a plurality of parallel cords and a topcoat. In other words, the belt 16 contains a large number of parallel cords. Each cord is inclined with respect to the equatorial plane. The absolute value of the tilt angle is generally at least 10 ° but not more than 35 °. The cords in the inner layer 38 are inclined in a direction opposite to the equatorial plane as the cords in the outer layer 40. The material of the cords is preferably steel. The cord may comprise organic fibers. In this case, examples of the organic fiber include: polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and polyaramide fibers.

The cushion 18 is located radially outward of the belt 16. The width of the cushion 18 is equal to the width of the belt 16 in the axial direction. The width of the cushion 18 may be greater than the width of the belt 16.

Although not shown, the liner 18 is formed of cord and apex. The cords are helically wound. The gasket 18 has a so-called seamless structure. The cords extend substantially in the circumferential direction. The angle of the cords with respect to the circumferential direction is 5 ° or less, even 2 ° or less. The cords restrain the belt 16, thereby reducing the lifting of the belt 16. The cord is formed of an organic fiber. Preferred examples of the organic fiber include nylon fiber, polyester fiber, rayon fiber, polyethylene naphthalate fiber, and aramid fiber.

The belt 16 and the liner 18 form a reinforcing layer. The reinforcing layer may be formed only by the belt 16.

An inner liner 20 is positioned inside the carcass 14. An inner liner 20 is bonded to the inner surface of the carcass 14. The inner liner 20 is formed of a cross-linked rubber having excellent air-shielding properties. The base rubber of the inner liner 20 is typically butyl rubber or halogenated butyl rubber. The inner liner 20 maintains the internal pressure of the tire 2.

Each chafer 22 is located adjacent to a bead 12. In this embodiment, the chafer 22 is formed of a cloth and rubber impregnated in the cloth. The chafer 22 may be integrally molded with the bridge 10, in which case the material of the chafer 22 is the same as the material of the bridge 10.

In the tire 2, the grooves 26 in the tread 4 include main grooves 42. As shown in fig. 1, a plurality of (specifically, three) main grooves 42 are engraved on the tread 4. The main grooves 42 are axially spaced apart. Four ribs (rib)44 extending in the circumferential direction are defined by three main grooves 42 engraved on the tread 4. In other words, each primary groove 42 is located between one rib 44 and the other rib 44.

The main groove 42 extends in the circumferential direction. The main groove 42 is continuous without interruption in the circumferential direction. For example, the main groove 42 may accelerate the discharge of water existing between the road surface and the tire 2 in a rainy day. Therefore, the tire 2 can sufficiently contact the road surface even in a wet condition. The main grooves 42 contribute to the wet grip of the tire 2.

In the process of manufacturing the tire 2, a plurality of rubber members are assembled into a green tire (raw cover) (unvulcanized tire 2). The green tyre is introduced into a mould. The outer surface of the green tire abuts against the cavity surface of the mold. The inner surface of the green tire abuts the bladder or core. The green tire is pressurized and heated in a mold. The pressurization and heating causes the rubber composition in the green tire to flow. Heating causes a rubber crosslinking reaction to obtain the tire 2. A mold having a cavity surface with a relief pattern may be used to form the relief pattern on the tire 2.

For example, the pneumatic tire of the present invention may be used as a tire for passenger cars, large SUVs, heavy vehicles (such as trucks and buses), light trucks, motorcycles, or as a racing tire (high performance tire). Further, for example, the pneumatic tire may be used as an all season tire, a summer tire, or a studless winter tire (winter tire). Among these, the pneumatic tire is suitable for use as an all season tire.

Examples

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

The chemicals used in the examples and comparative examples are listed below.

SBR No. 1: tufdene 3830 (solution polymerization SBR, styrene content: 33 mass%, vinyl content: 34 mass%, Mw: 950,000, Mn: 370,000, Mw/Mn: 2.6, oil content: 37.5 parts by mass per 100 parts by mass of rubber solids) available from Asahi Kasei corporation;

SBR 2: SL563 (styrene content: 20% by mass, vinyl content: 55.5% by mass) was purchased from JSR corporation;

SBR No. 3: tufdene 4850 (solution polymerized SBR, styrene content: 40 mass%, vinyl content: 45 mass%, Mw: 900,000, Mn: 300,000, Mw/Mn: 3.0, oil content: 50 parts by mass per 100 parts by mass of rubber solids) available from Asahi Kasei corporation;

SBR 4: production example 1 below;

BR: BR150B (cis content: 98 mass%) obtained from Kyoho, Utsu;

carbon black: DiabalackN 339 (N)₂SA：96m²(g), purchased from Mitsubishi chemical corporation;

silicon dioxide: zeosil 115GR (N2 SA: 115 m)²Per g), from solvay japan;

silane coupling agent: si69 (bis (3-triethoxysilylpropyl) tetrasulfide), purchased from tomayurvedic;

liquid resin: nitto resin coumarone L-20 (a (liquid) copolymer of coumarone, indene and styrene, softening point: -20 to-10 ℃ C., viscosity: 20 Pa.s) available from Nissan chemical Co., Ltd;

solid resin: SYLVARES SA85 (copolymer of alpha-methylstyrene and styrene, Tg: 43 ℃, softening point: 85 ℃, Mw: 1,000) from Arizona chemical;

antioxidant: antigene 3C (N-phenyl-N' -isopropyl-p-phenylenediamine), available from Sumitomo chemical;

stearic acid: tsubakki, available from japan oil co;

zinc oxide: zinc oxide #1, available from mitsui metal mining, inc;

wax: sunnoc N, available from Innovative chemical industries, Inc.;

processing aid: WB16 (mixture of fatty acid metal salts (fatty acid calcium salts, fatty acid components: C14-C20 saturated fatty acids) and fatty acid amides), available from Struktol;

sulfur: powdered sulfur from crane, chemical industries co;

vulcanization accelerator 1: NOCCELER CZ (N-cyclohexyl-2-benzothiazolesulfenamide), available from New chemical industries, Inc., in Dai;

vulcanization accelerator 2: NOCCELER D (1, 3-diphenylguanidine), available from Innovation chemical industries, Inc.

Production example 1

To an autoclave reactor (equipped with a stirrer and a jacket and having an internal volume of 20L) sufficiently purged with nitrogen were continuously charged styrene (10.5g/min), 1, 3-butadiene containing 100ppm of 1, 2-butadiene (19.5g/min), cyclohexane (150g/min), tetrahydrofuran (1.5g/min) and n-butyllithium (0.117mmol/min), while controlling the temperature at 70 ℃. Silicon tetrachloride was continuously added from the top outlet of the first reactor at 0.04mmol/min, and the mixture was introduced into the second reactor connected to the first reactor to conduct the modification reaction. After the completion of the modification reaction, 2, 6-di-t-butyl-p-cresol was added to the resulting polymer solution. Next, 37.5phr (37.5 parts by mass, relative to 100 parts of the rubber component) "VIVATEC 500" (trade name, H & R) was added for oil extension, and then the solvent was removed by stripping, followed by drying on a hot roll adjusted to 110 ℃ to obtain an oil-extended styrene-butadiene copolymer (SBR 4). SBR No. 4 had a styrene content of 35 mass%, a vinyl content of 42 mass%, an Mw of 850,000, an Mw/Mn ratio of 2.2 and an oil content of 37.5 parts by mass per 100 parts by mass of rubber solids.

(examples and comparative examples)

According to each formulation shown in Table 1, chemicals other than sulfur and a vulcanization accelerator were kneaded at 150 ℃ for 5 minutes using a 1.7L Banbury mixer (Kobe Steel Co.) to obtain a kneaded mixture. Next, sulfur and a vulcanization accelerator were added to the kneaded mixture, and kneaded at 80 ℃ for 5 minutes using an open roll mill to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is formed into a shape of a tread surface and assembled with other tire components to obtain an unvulcanized tire. The unvulcanized tire was press-vulcanized at 170 ℃ for 10 minutes to obtain a test all season tire (size: 235/60R18) shown in FIG. 1 or FIG. 2.

The test all season tires prepared as above were evaluated as follows. The results are shown in Table 1.

< hardness (Hs) of Tread rubber >

Samples were collected from the running surface of each test all season tire. "vulcanized rubber or thermoplastic rubber-determination of hardness-according to JIS K6253-3(2012) -part 3: durometer method ", the hardness of A sample (JIS-A hardness) is measured using A type A durometer. The measurements were carried out at 30 ℃ and-20 ℃.

< maximum thickness of tread >

The maximum thickness of the tread (maximum sum of cap layer thickness and base layer thickness) was measured for each tested all-season tire.

< extreme Cold handling stability index >

The test all season tires were mounted on a 2,000cc displacement front engine, rear wheel drive automobile manufactured in japan. Handling properties were (subjectively) evaluated under conditions including an atmospheric temperature on ice of-22 to-18 ℃ and a road surface temperature of-25 to-20 ℃. Specifically, the test taker subjectively evaluates the starting, acceleration, and stopping of the vehicle. The subjective evaluation results are given relative to comparative example 1 (set to 100) with the following scores: 110, the judgment performance of the driver is obviously improved; 120, performance is higher than ever; 90, on the contrary, the performance is significantly reduced.

< tire Life index >

The test all season tires were mounted on four wheels of a 2,000cc displacement front engine, rear wheel drive automobile manufactured in japan. After running 8000 km, the depth of the tread groove of the tire was measured. The estimated lifetime is calculated from the measurement results and expressed as an index using the following equation. A higher index indicates better wear resistance. Tires with indices above 95 are practically acceptable.

(tire life index) × 100 (estimated life of each example or comparative example)/(estimated life of comparative example 1) × 100

[ Table 1]

Table 1 shows that the tires of the examples (including a tread having a hardness of 90 or less at-20 ℃, a hardness of 60 or more at 30 ℃ and a maximum thickness of 8.5mm or less, and a carcass having one carcass ply) have excellent wear resistance and excellent steering stability on an extremely cold road while reducing weight. Although the treads of examples 18 and 19 were thin (maximum thicknesses of 6.5mm and 6.0mm, respectively), they still exhibited practically acceptable wear resistance.

List of reference numerals

2 pneumatic tire

4 Tread

6 side wall

8 tyre wing

10 lap joint part

12 tyre bead

14 tyre body

16 belts

18 liner

20 inner liner layer

22 chafer

24 tread surface

26 groove

28 base layer

30 running surface layer

32 core

34 triangular glue

36 carcass ply

36a main part

36b folded part

38 inner layer

40 outer layer

42 main groove

44 rib

Equatorial plane of CL tire 2

P points on the tread surface 24

Thickness of the T-tread 4