Pneumatic tire

Abstract

The purpose of the present invention is to provide a pneumatic tire with which wet grip performance, low fuel consumption and wear resistance are all attained to a high degree, and which has excellent discoloration resistance, without a deterioration in cut resistance. To this end, a pneumatic tire (1) includes a tread rubber layer (8) and a carcass ply (9) located inside the tread rubber layer (8) in the tire radial direction and obtained by coating PET fiber cords with a coating rubber. The tread rubber layer (8) comprises a rubber component, a filler, and a silane coupling agent, wherein the rubber component comprises a styrene / butadiene rubber (A) having a glass transition temperature of -50°C or lower and modified using a modifier including atoms of at least one kind selected from among nitrogen, silicon, and tin and an unmodified styrene / butadiene rubber (B) having a glass transition temperature higher by at least 30°C than that of the styrene / butadiene rubber (A). The carcass ply (9) satisfies relationship (1): (A / B) / (total cord fineness)≥0.3.

Description

pneumatic tires

[0001] The present invention relates to a pneumatic tire.

[0002] Conventionally, from the viewpoint of improving vehicle safety, various studies have been conducted to improve braking performance on wet road surfaces (hereinafter referred to as "wet grip performance"). For example, Patent Document 1 below discloses that applying a rubber composition containing a rubber component containing 70% by mass or more of natural rubber, a thermoplastic resin, and a filler containing silica to the tire tread rubber improves the braking performance of the tire on both dry and wet road surfaces. Meanwhile, in connection with the recent global movement toward carbon dioxide emission regulations due to growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. To meet such demands, improved fuel efficiency (reduced rolling resistance) is also required in tire performance, but it has been found that the technology described in Patent Document 1 leaves room for improvement in fuel efficiency and wear resistance.

[0003] Therefore, Patent Document 2 discloses a rubber composition containing an emulsion-polymerized styrene-butadiene rubber and a solution-polymerized styrene-butadiene rubber, both of which have a glass transition temperature Tg of −25° C. or higher, a polymer with a low Tg, and further containing a filler and a specific hydrocarbyloxysilane compound, with the aim of achieving both wet grip performance and rolling resistance of a tire.

[0004] International Publication No. WO 2015 / 079703 International Publication No. WO 2017 / 188139

[0005] However, the inventors of the present invention have found that while the technology described in Patent Document 1 can improve the wet grip performance of tires, the addition of a resin, which is a softening component, reduces the rigidity of the rubber, which in turn reduces the plunger level of the tire and can result in insufficient cut resistance. Furthermore, when an attempt is made to improve the cut resistance of a tire, the amount of resin, which is a softening component, that can be added is limited, which can result in insufficient wet grip performance.

[0006] Furthermore, while the technology described in Patent Document 2 makes it possible to achieve both wet grip performance and rolling resistance of a tire to some extent, there is a problem in that rubber compositions containing a hydrocarbyloxysilane compound having a thiol group or the like, which can be used in the tread rubber layer of a pneumatic tire, tend to undergo changes in appearance, such as the development of a black luster, over time.

[0007] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a pneumatic tire that has excellent discoloration resistance and that achieves a high level of wet grip performance, fuel efficiency, and wear resistance without deteriorating cut resistance.

[0008] The gist of the pneumatic tire of the present invention that solves the above problems is as follows.

[0009] [1] A pneumatic tire comprising a tread rubber layer located on the outermost surface of a tread portion, and a carcass ply located radially inward of the tread rubber layer and formed by covering PET fiber cords with coating rubber, wherein the tread rubber layer contains a rubber component, a filler, and a silane coupling agent, the rubber component contains styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or less, and unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or higher than that of the styrene-butadiene rubber (A), the filler contains at least silica, the silane coupling agent contains at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, the total content of the silane coupling agent (A) and the silane coupling agent (B) is 1 to 15 parts by mass relative to 100 parts by mass of the silica, the total gauge of the carcass ply is 1.2 mm or less, and the carcass ply satisfies the following formula (1): (A / B) / total cord fineness≧0.3 (1) (A: cord strength (N)×fiber occupancy rate, fiber occupancy rate: cross-sectional area of ​​PET fiber cord (mm２ ) / (total gauge of carcass ply (mm) × (diameter of PET fiber cord (mm) + distance between PET fiber cords (mm))) B: tan δ of coating rubber × rubber occupancy rate Rubber occupancy rate: 1 - fiber occupancy rate Total cord fineness: total value (dtex) of the fineness of the PET fibers constituting the cord.

[0010] [2] The pneumatic tire according to [1], wherein the styrene-butadiene rubber (A) is modified with a modifier having a nitrogen atom and a silicon atom.

[0011] [3] The pneumatic tire according to [2], wherein the styrene-butadiene rubber (A) is modified with a modifier having a functional group containing a nitrogen atom and an alkoxy group.

[0012] [4] The pneumatic tire according to any one of [1] to [3], characterized in that the mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is 0.3 or more and less than 3.

[0013] [5] The pneumatic tire according to any one of [1] to [4], characterized in that the filler further contains carbon black, and the content ratio of the silica in the total amount of the silica and the carbon black is 80 mass % or more and less than 100 mass %.

[0014] [6] The pneumatic tire according to any one of [1] to [5], wherein the content of the silica is 20 parts by mass or more and less than 100 parts by mass per 100 parts by mass of the rubber component.

[0015] [7] The pneumatic tire according to any one of [1] to [6], wherein the silane coupling agent (A) has a carbon number of 20 to 75.

[0016] [8] The pneumatic tire according to any one of [1] to [7], wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (A).

[0017] [9] The pneumatic tire according to any one of [1] to [8], wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (B).

[0018]

[10] The pneumatic tire according to any one of [1] to [9], wherein the tread rubber layer further contains 1 to 50 parts by mass of a resin per 100 parts by mass of the rubber component.

[0019]

[11] The pneumatic tire according to

[10] , wherein the resin is a hydrogenated resin.

[0020]

[12] The pneumatic tire according to any one of [1] to

[11] , wherein the PET fiber cord has a cord strength of 160 N or more.

[0021]

[13] The pneumatic tire according to any one of [1] to

[12] , wherein the tensile strength of the carcass ply is greater than 23,000 N / dm.

[0022]

[14] The pneumatic tire according to any one of [1] to

[13] , wherein the PET fiber cord has a fineness of 1100 / 2 to 2000 / 2 dtex.

[0023]

[15] The pneumatic tire according to any one of [1] to

[14] , wherein the carcass ply satisfies the following formula (1)': (A / B) / total cord fineness≧0.45 (1)'.

[0024] According to the present invention, it is possible to provide a pneumatic tire that has excellent discoloration resistance and that achieves a high level of wet grip performance, fuel efficiency, and wear resistance without deteriorating cut resistance.

[0025] 1 is a cross-sectional view of an embodiment of a pneumatic tire according to the present invention; FIG. 2 is a diagram schematically illustrating a cross section of a carcass ply coated with a PET fiber cord according to an embodiment of the present invention;

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The pneumatic tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0027] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0028] In this specification, the glass transition temperature of styrene-butadiene rubber is determined in accordance with ISO 22768:2006 by recording a DSC curve while raising the temperature within a predetermined temperature range, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

[0029] In this specification, the "molecular weight" of the rubber component is a standard polystyrene-equivalent molecular weight obtained by GPC (gel permeation chromatography).

[0030] In this specification, the softening point of the resin component is measured in accordance with JIS-K2207-1996 (ring and ball method).

[0031] In this specification, the weight average molecular weight of the resin component is measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

[0032] In this specification, the tan δ of the coating rubber is a value measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under the conditions of a temperature of 24° C., a strain of 1%, and a frequency of 52 Hz.

[0033] <Pneumatic tire> Fig. 1 is a cross-sectional view of one embodiment of a pneumatic tire of the present invention. The pneumatic tire 1 shown in Fig. 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 continuous with both sidewall portions 3. The pneumatic tire 1 also includes a carcass 5 extending toroidally between the pair of bead portions 2 to reinforce these portions 2, 3, and 4, and a belt 6 disposed radially outward of a crown portion of the carcass 5. Fig. 2 is a schematic diagram showing a cross-section of a carcass ply formed by coating PET fiber cords according to one embodiment of the present invention. The carcass ply 9 shown in Fig. 2 is formed by coating PET fiber cords 10 with coating rubber 20.

[0034] The carcass 5 of the pneumatic tire shown in Figure 1 is composed of one carcass ply 9 formed by covering a plurality of parallel-arranged cords with a coating rubber. The carcass 5 also includes a main body portion extending toroidally between the bead cores 7 embedded in the bead portions 2, and turn-up portions wound radially outward from the tire widthwise interior toward the exterior around each bead core 7. However, the number and structure of the ply of the carcass 5 in the pneumatic tire of the present invention are not limited to these. The belt 6 of the pneumatic tire shown in Figure 1 is composed of two belt layers 6A, 6B. However, the number of belt layers constituting the belt 6 in the pneumatic tire of the present invention is not limited to this, and the number of belt layers may be three or more. Here, the belt layer is typically composed of a rubberized layer of metal cords (preferably steel cords) extending at an angle relative to the tire equatorial plane. The two belt layers are stacked so that the metal cords constituting the belt layers cross each other across the tire equatorial plane.

[0035] The pneumatic tire 1 of this embodiment includes a tread rubber layer 8 located on the outermost surface of a tread portion 4, and a carcass ply 9 located radially inward of the tread rubber layer 8 and formed by covering PET fiber cords with a coating rubber, wherein the tread rubber layer includes a rubber component, a filler, and a silane coupling agent, wherein the rubber component includes styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or less, and unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or higher than that of the styrene-butadiene rubber (A), wherein the filler includes at least silica, and the silane coupling agent includes at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and wherein the content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 100 parts by mass of the silica, the total content of the silane coupling agent (A) and the silane coupling agent (B) is 1 to 15 parts by mass relative to 100 parts by mass of the silica, the total gauge of the carcass ply is 1.2 mm or less, and the carcass ply satisfies the following formula (1): (A / B) / total cord fineness≧0.3 (1) (A: cord strength (N)×fiber occupancy rate, fiber occupancy rate: cross-sectional area of ​​PET fiber cord (mm ２ ) / (total gauge of carcass ply (mm) × (diameter of PET fiber cord (mm) + distance between PET fiber cords (mm))) B: tan δ of coating rubber × rubber occupancy rate Rubber occupancy rate: 1 - fiber occupancy rate Total cord fineness: total value (dtex) of the fineness of the PET fibers constituting the cord. The pneumatic tire described above achieves a high level of compatibility between wet grip performance, fuel economy, and abrasion resistance without deteriorating cut resistance, and also has excellent discoloration resistance.

[0036] The pneumatic tire 1 of the present invention may be modified in various ways as long as it includes the tread rubber layer 8 located on the outermost surface of the tread portion 4 and the carcass ply 9 formed by covering PET fiber cords with coating rubber and located on the inner side in the tire radial direction of the tread rubber layer 8. For example, the tread rubber layer 8 of the pneumatic tire 1 shown in Fig. 1 can be divided into a cap rubber located on the outermost surface side and a base rubber located on the inner side in the tire radial direction.

[0037] In the pneumatic tire 1 of the present embodiment, the tread rubber layer includes a rubber component, a filler, and a silane coupling agent, wherein the rubber component includes styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or less, and unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or higher than that of the styrene-butadiene rubber (A), the filler includes at least silica, the silane coupling agent includes at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, When the total content of the silane coupling agent (A) and the silane coupling agent (B) is 1 to 15 parts by mass per 100 parts by mass of the silica, wet grip performance, fuel economy and abrasion resistance are highly compatible, and excellent discoloration resistance is achieved.

[0038] In the pneumatic tire 1 of the present embodiment, the total gauge is 1.2 mm or less, and the following formula (1) is satisfied: (A / B) / total cord fineness≧0.3 (1) (A: cord strength (N)×fiber occupancy rate, fiber occupancy rate: cross-sectional area of ​​the PET fiber cord (mm ２) / (total gauge of carcass ply (mm) × (diameter of PET fiber cord (mm) + distance between PET fiber cords (mm)) B: tan δ of coating rubber × rubber occupancy rate Rubber occupancy rate: 1 - fiber occupancy rate Total cord fineness: total value (dtex) of the fineness of the PET fibers constituting the cord) By using, as the carcass 5, the carcass ply 9 formed by coating PET fiber cords 10 with coating rubber 20, the strength of the carcass 5 is improved, the plunger level is improved, and the cut resistance of the pneumatic tire 1 is supplemented. Therefore, the tire 1 of this embodiment achieves a high level of wet grip performance, fuel economy, and wear resistance without deteriorating cut resistance, and also achieves excellent discoloration resistance.

[0039] <<Tread Rubber Layer>> In the pneumatic tire of the present embodiment, the tread rubber layer contains a rubber component, a filler, and a silane coupling agent. The tread rubber layer can be made from, for example, a rubber composition containing the rubber component, the filler, and the silane coupling agent.

[0040] (Rubber Component) The rubber component contains a styrene-butadiene rubber (A) modified with a modifier containing at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or lower, and an unmodified styrene-butadiene rubber (B) having a glass transition temperature at least 30° C. higher than that of the styrene-butadiene rubber (A). Other rubber components may also be contained.

[0041] By including the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) in the rubber component, the wet grip performance of the pneumatic tire can be improved. In addition, in the present invention, by using the styrene-butadiene rubber (A) modified with a modifier containing at least one atom of nitrogen, silicon, and tin as the rubber component, the dispersibility of fillers such as silica in the rubber composition can be improved. As a result, the pneumatic tire of the present invention has significantly improved low heat buildup properties and improved filler dispersibility, which can also improve reinforcement and physical properties such as the fuel efficiency and wear resistance of the pneumatic tire.

[0042] As described above, the styrene-butadiene rubber (A) is a styrene-butadiene rubber modified with a modifier having at least one atom of nitrogen, silicon, and tin, and having a glass transition temperature of −50° C. or lower.

[0043] The styrene-butadiene rubber (A) has a glass transition temperature of −50° C. or lower, preferably −55° C. or lower, and preferably higher than −90° C. When the styrene-butadiene rubber (A) has a glass transition temperature of −50° C. or lower, the fuel economy and wear resistance of the pneumatic tire can be sufficiently improved. In addition, styrene-butadiene rubber having a glass transition temperature higher than −90° C. is easy to synthesize.

[0044] The glass transition temperatures of the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) described later can be measured, for example, as follows: Using each styrene-butadiene rubber as a sample, a DSC curve is recorded using a DSC250 manufactured by TA Instruments, while increasing the temperature from −100° C. at a rate of 20° C. / min under a helium flow of 50 mL / min, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

[0045] The content ratio of the styrene-butadiene rubber (A) in the rubber component is preferably 15% by mass or more and less than 85% by mass, more preferably 20% by mass or more and less than 85% by mass, more preferably 30% by mass or more and 80% by mass or less, and even more preferably 40% by mass or more and 80% by mass or less. When the content ratio of the styrene-butadiene rubber (A) in the rubber component is 15% by mass or more and less than 85% by mass, the fuel economy performance and wet grip performance of the pneumatic tire can be further improved.

[0046] Furthermore, the styrene-butadiene rubber (A) preferably has a bound styrene content of less than 15% by mass. The bound styrene content of the styrene-butadiene rubber (A) refers to the proportion of styrene units contained in the styrene-butadiene rubber. When the bound styrene content is less than 15% by mass, the glass transition temperature tends to be low. From the same viewpoint, the bound styrene content is more preferably 14% by mass or less, more preferably 13% by mass or less, and even more preferably 12% by mass or less. From the viewpoint of the wear resistance of the pneumatic tire of the present invention, the bound styrene content is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the styrene-butadiene rubber (A) can be adjusted by the amount of monomers used in the polymerization of the styrene-butadiene rubber, the degree of polymerization, etc. The amount of bound styrene in the styrene-butadiene rubber (A) can be measured as the amount of bound styrene (mass%) relative to 100 mass% of the sample using a spectrophotometer "UV-2450" manufactured by Shimadzu Corporation, based on the amount of absorption of ultraviolet light at a wavelength (near 254 nm) by the phenyl group of styrene.

[0047] As described above, the styrene-butadiene rubber (A) is modified with a modifier having at least one atom of nitrogen, silicon, and tin, but from the viewpoint of achieving a higher level of fuel economy, wear resistance, and wet grip performance in a pneumatic tire, the styrene-butadiene rubber (A) is preferably modified with a modifier having a nitrogen atom and a silicon atom, and more preferably modified with a modifier having a nitrogen-containing functional group and an alkoxy group. When the styrene-butadiene rubber (A) is modified with such a modifier, the pneumatic tire of this embodiment achieves a higher level of wet grip performance, fuel economy, and wear resistance.

[0048] Here, the "modifier having a nitrogen atom-containing functional group and an alkoxy group" is a general term for modifiers having at least one nitrogen atom-containing functional group and at least one alkoxy group. The nitrogen atom-containing functional group is preferably selected from the following: The monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a linear, branched, alicyclic, or aromatic ring, has a functional group selected from the group consisting of a primary amino group, a primary amino group protected with a hydrolyzable protecting group, an onium salt residue of a primary amine, an isocyanate group, a thioisocyanate group, an imine group, an imine residue, an amide group, a secondary amino group protected with a hydrolyzable protecting group, a cyclic secondary amino group, an onium salt residue of a cyclic secondary amine, an acyclic secondary amino group, an onium salt residue of an acyclic secondary amine, an isocyanuric acid triester residue, a cyclic tertiary amino group, an acyclic tertiary amino group, a nitrile group, a pyridine residue, an onium salt residue of a cyclic tertiary amine, and an onium salt residue of an acyclic tertiary amine, or a monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a linear, branched, alicyclic, or aromatic ring, which may contain at least one heteroatom selected from an oxygen atom, a sulfur atom, and a phosphorus atom.

[0049] Furthermore, the styrene-butadiene rubber (A) is preferably modified with an aminoalkoxysilane compound, and from the viewpoint of having a high affinity for fillers such as silica, it is more preferable that the terminals are modified with an aminoalkoxysilane compound. When the terminals of the styrene-butadiene rubber are modified with an aminoalkoxysilane compound, the interaction between the styrene-butadiene rubber (A) and the filler (particularly silica) becomes particularly strong.

[0050] The modified site of the styrene-butadiene rubber (A) may be the molecular terminal as described above, or may be the main chain. The styrene-butadiene rubber (A) having a modified molecular terminal can be produced, for example, by reacting various modifiers with the terminal of a styrene-butadiene copolymer having an active terminal, according to the methods described in WO 2003 / 046020 and JP 2007-217562 A. In one preferred embodiment, the styrene-butadiene rubber (A) having a modified molecular terminal can be produced, according to the methods described in WO 2003 / 046020 and JP 2007-217562 A, by reacting an aminoalkoxysilane compound with the terminal of a styrene-butadiene copolymer having an active terminal with a cis-1,4 bond content of 75% or more, and then reacting the resulting mixture with a carboxylic acid partial ester of a polyhydric alcohol for stabilization.

[0051] The carboxylic acid partial ester of a polyhydric alcohol refers to an ester of a polyhydric alcohol and a carboxylic acid, which has one or more hydroxyl groups. Specifically, esters of fatty acids with sugars or modified sugars having 4 or more carbon atoms are preferably used. More preferred examples of this ester include (1) fatty acid partial esters of polyhydric alcohols, particularly partial esters (monoesters, diesters, or triesters) of saturated or unsaturated higher fatty acids having 10 to 20 carbon atoms with polyhydric alcohols, and (2) ester compounds in which 1 to 3 partial esters of polycarboxylic acids and higher alcohols are bonded to a polyhydric alcohol. Polyhydric alcohols used as raw materials for the partial esters are preferably sugars (whether hydrogenated or unhydrogenated) having 5 or 6 carbon atoms and at least three hydroxyl groups, glycols, polyhydroxy compounds, and the like. Furthermore, the raw fatty acids are preferably saturated or unsaturated fatty acids having 10 to 20 carbon atoms, such as stearic acid, lauric acid, and palmitic acid. Among the fatty acid partial esters of polyhydric alcohols, sorbitan fatty acid esters are preferred, and specific examples include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.

[0052] The aminoalkoxysilane compound is not particularly limited, but is preferably an aminoalkoxysilane compound represented by the following general formula (i): １１ ａ -Si-(OR １２ ) ４－ａ ... (i)

[0053] In general formula (i), R １１ and R １２ each independently represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R １１ and R １２ At least one of the groups is substituted with an amino group, a is an integer of 0 to 2, and OR １２If there are multiple, each OR １２ may be the same or different, and the molecule does not contain any active protons.

[0054] The aminoalkoxysilane compound is also preferably an aminoalkoxysilane compound represented by the following general formula (ii).

[0055] In the general formula (ii), n1+n2+n3+n4=4 (wherein n2 is an integer of 1 to 4, and n1, n3, and n4 are integers of 0 to 3). １ is at least one functional group selected from a saturated cyclic tertiary amine compound residue, an unsaturated cyclic tertiary amine compound residue, a ketimine residue, a nitrile group, a (thio)isocyanate group, an isocyanuric acid trihydrocarbyl ester group, a nitrile group, a pyridine group, a (thio)ketone group, an amide group, and a primary or secondary amino group having a hydrolyzable group. １ may be the same or different, and A １ may be a divalent group that bonds with Si to form a cyclic structure. ２１ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when n1 is 2 or more, they may be the same or different. ２２ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, both of which may contain a nitrogen atom and / or a silicon atom. ２２ may be the same or different, or may be joined together to form a ring. ２３ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom, and when n3 is 2 or greater, may be the same or different. ２４represents a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and may be the same or different when n4 is 2 or greater. As the hydrolyzable group in the primary or secondary amino group having a hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0056] The aminoalkoxysilane compound represented by the above general formula (ii) is preferably an aminoalkoxysilane compound represented by the following general formula (iii).

[0057] In the general formula (iii), p1+p2+p3=2 (wherein p2 is an integer of 1 to 2, and p1 and p3 are integers of 0 to 1). ２ is NRa (Ra is a monovalent hydrocarbon group, a hydrolyzable group, or a nitrogen-containing organic group). ２５ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ２６ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a nitrogen-containing organic group, any of which may contain a nitrogen atom and / or a silicon atom. ２６ may be the same or different, or may be joined together to form a ring. ２７ R is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom. ２８ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. As the hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0058] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (iv) or (v).

[0059] In the general formula (iv), q1+q2=3 (wherein q1 is an integer of 0 to 2, and q2 is an integer of 1 to 3). ３１ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３２ and R ３３ are each independently a hydrolyzable group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３４ are monovalent aliphatic or alicyclic hydrocarbon groups having 1 to 20 carbon atoms or monovalent aromatic hydrocarbon groups having 6 to 18 carbon atoms, and when q1 is 2, they may be the same or different. ３５ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when q2 is 2 or more, may be the same or different.

[0060]

[0061] In the general formula (v), r1+r2=3 (where r1 is an integer of 1 to 3, and r2 is an integer of 0 to 2). ３６ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３７ represents a dimethylaminomethyl group, a dimethylaminoethyl group, a diethylaminomethyl group, a diethylaminoethyl group, a methylsilyl(methyl)aminomethyl group, a methylsilyl(methyl)aminoethyl group, a methylsilyl(ethyl)aminomethyl group, a methylsilyl(ethyl)aminoethyl group, a dimethylsilylaminomethyl group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when r1 is 2 or more, they may be the same or different. R ３８represents a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and may be the same or different when r2 is 2. A specific example of the aminoalkoxysilane compound represented by general formula (v) is N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propanamine.

[0062] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (vi) or (vii):

[0063] In general formula (vi), R ４０ is a trimethylsilyl group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４１ R is a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４２ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, where TMS represents a trimethylsilyl group (the same applies hereinafter).

[0064]

[0065] In general formula (vii), R ４３ and R ４４ are each independently a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４５ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and each R ４５ may be the same or different.

[0066] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (viii) or the following general formula (ix).

[0067] In general formula (viii), s1+s2 is 3 (wherein s1 is an integer of 0 to 2, and s2 is an integer of 1 to 3). ４６ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ and R ４８ are each independently a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ or R ４８ may be the same or different.

[0068]

[0069] In general formula (ix), X is a halogen atom. ４９ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ are each independently a hydrolyzable group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or R ５０ and R ５１ are bonded to form a divalent organic group. ５２ and R ５３ are each independently a halogen atom, a hydrocarbyloxy group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ As the hydrolyzable group, a hydrolyzable group is preferred, and as the hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0070] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (x), the following general formula (xi), the following general formula (xii), or the following general formula (xiii).

[0071] In the general formulas (x) to (xiii), the symbols U and V are each an integer of 0 to 2 and satisfy U+V=2. ５４ ~ ９２ may be the same or different and are monovalent or divalent aliphatic or alicyclic hydrocarbon groups having 1 to 20 carbon atoms, or monovalent or divalent aromatic hydrocarbon groups having 6 to 18 carbon atoms. α and β in general formula (xiii) are integers of 0 to 5.

[0072] Among the compounds satisfying general formula (x), general formula (xi), or general formula (xii), N1,N1,N7,N7-tetramethyl-4-((trimethoxysilyl)methyl)heptane-1,7-diamine, 2-((hexyl-dimethoxysilyl)methyl)-N1,N1,N3,N3-2-pentamethylpropane-1,3-diamine, N1-(3-(dimethylamino)propyl)-N3,N3-dimethyl-N1-(3-(trimethoxysilyl)propyl)propane-1,3-diamine, and 4-(3-(dimethylamino)propyl)-N1,N1,N7,N7-tetramethyl-4-((trimethoxysilyl)methyl)heptane-1,7-diamine are particularly preferred. Among the compounds satisfying general formula (xiii), N,N-dimethyl-2-(3-(dimethoxymethylsilyl)propoxy)ethanamine, N,N-bis(trimethylsilyl)-2-(3-(trimethoxysilyl)propoxy)ethanamine, N,N-dimethyl-2-(3-(trimethoxysilyl)propoxy)ethanamine, and N,N-dimethyl-3-(3-(trimethoxysilyl)propoxy)propan-1-amine are particularly preferred.

[0073] The present invention also provides a method for producing the styrene-butadiene rubber (A) using a modifier containing an aminoalkoxysilane compound represented by the general formula (i). The method for producing the styrene-butadiene rubber (A) specifically includes the steps of: 1) polymerizing styrene-butadiene rubber in a hydrocarbon solvent in the presence of an organic alkali metal compound to produce an activated polymer having an alkali metal bonded to at least one end; and 2) reacting the activated polymer with a modifier containing the aminoalkoxysilane compound represented by the general formula (i).

[0074] Step 1) is a step for preparing an activated polymer having an alkali metal bonded to at least one end thereof, and can be carried out by polymerizing a styrene-based monomer and a butadiene-based monomer in a hydrocarbon solvent in the presence of an organic alkali metal compound.

[0075] The hydrocarbon solvent is not particularly limited, but may be, for example, one or more selected from the group consisting of n-pentane, n-hexane, n-heptane, isooctane, cyclohexane, toluene, benzene, and xylene.

[0076] The organic alkali metal compound can be used in an amount of 0.1 to 1.0 mmol based on 100 g of the total monomers. The organic alkali metal compound is not particularly limited, and examples thereof include at least one selected from the group consisting of methyl lithium, ethyl lithium, propyl lithium, n-butyl lithium, s-butyl lithium, t-butyl lithium, hexyl lithium, n-decyl lithium, t-octyl lithium, phenyl lithium, 1-naphthyl lithium, n-eicosyl lithium, 4-butylphenyl lithium, 4-tolyl lithium, cyclohexyl lithium, 3,5-di-n-heptylcyclohexyl lithium, 4-cyclopentyl lithium, naphthyl sodium, naphthyl potassium, lithium alkoxide, sodium alkoxide, potassium alkoxide, lithium sulfonate, sodium sulfonate, potassium sulfonate, lithium amide, sodium amide, potassium amide, and lithium isopropyl amide.

[0077] The polymerization in step 1 may be optionally carried out by further adding a polar additive. The polar additive may be added in an amount of 0.001 to 1.0 part by weight based on 100 parts by weight of the total monomers. Specifically, the polar additive may be added in an amount of 0.005 to 0.5 parts by weight, more specifically, 0.01 to 0.3 parts by weight based on 100 parts by weight of the total monomers. Examples of the polar additive include at least one selected from the group consisting of tetrahydrofuran, ditetrahydrofurylpropane, diethyl ether, cycloamethyl ether, dipropyl ether, ethylene dimethyl ether, ethylene dimethyl ether, diethyl glycol, dimethyl ether, tert-butoxyethoxyethane, bis(3-dimethylaminoethyl)ether, (dimethylaminoethyl)ethyl ether, trimethylamine, triethylamine, tripropylamine, and tetramethylethylenediamine.

[0078] In the above-mentioned production method, when a conjugated diene monomer and an aromatic vinyl monomer are copolymerized by using the polar additive, the difference in reaction rate between them can be compensated for, thereby guiding the formation of a random copolymer.

[0079] The polymerization in step 1) can be carried out via adiabatic polymerization or isothermal polymerization. Here, the adiabatic polymerization refers to a polymerization method that involves polymerizing the organic alkali metal compound by heat of self-reaction without adding any heat after adding the organic alkali metal compound, while the isothermal polymerization refers to a polymerization method that maintains a constant temperature of the polymer by adding or removing heat after adding the organic alkali metal compound.

[0080] Furthermore, the polymerization may be carried out in a temperature range of 20°C to 200°C, specifically in a temperature range of 0°C to 150°C, more specifically in a temperature range of 10°C to 120°C.

[0081] The step 2) is a modification reaction step in which the activated polymer is reacted with a modifier containing an aminoalkoxysilane compound represented by the general formula (i) to produce styrene-butadiene rubber (A).

[0082] The aminoalkoxysilane compound represented by the general formula (i) can be used in a ratio of 0.1 to 2.0 moles per mole of the organic alkali metal compound. Furthermore, the reaction in step 2) is a modification reaction for introducing functional groups into the polymer, and each reaction can be carried out at a temperature ranging from 0°C to 90°C for 1 minute to 5 hours.

[0083]

[0033] The above-described preparation method may further include, after step 2), one or more steps of recovering the solvent and unreacted monomer and drying, if necessary.

[0084] Furthermore, the content ratio of the styrene-butadiene rubber (A) modified with a modifier containing the aminoalkoxysilane compound represented by the general formula (i) in the rubber component is not particularly limited, but is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 60% by mass or less, and more preferably 50% by mass or less. When the content ratio of the styrene-butadiene rubber (A) in the rubber component is 15% by mass or more, the fuel economy performance and wear resistance of the pneumatic tire can be further improved. On the other hand, when the content ratio of the styrene-butadiene rubber (A) in the rubber component is 60% by mass or less, the styrene-butadiene rubber (B) described below can be sufficiently contained, and the wet grip performance of the pneumatic tire can be maintained at a good level.

[0085] In addition to the styrene-butadiene rubber (A), the rubber component further contains an unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or more higher than that of the styrene-butadiene rubber (A). By including the styrene-butadiene rubber (B) having a high glass transition temperature as the rubber component, the wet grip performance of the pneumatic tire can be improved.

[0086] The styrene-butadiene rubber (B) must have a glass transition temperature higher than the glass transition temperature of the styrene-butadiene rubber (A) by at least 30° C., and preferably by at least 35° C. When the rubber component in the tread rubber layer contains such a styrene-butadiene rubber (B), the flexibility of the rubber can be increased, and the fuel economy and wear resistance of the pneumatic tire can be sufficiently improved.

[0087] Furthermore, the content ratio of the styrene-butadiene rubber (B) in the rubber component is not particularly limited, but is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably less than 85% by mass, and more preferably 80% by mass or less. When the content ratio of the styrene-butadiene rubber (B) in the rubber component is 15% by mass or more, the wet grip performance of the pneumatic tire can be further improved. On the other hand, when the content ratio of the styrene-butadiene rubber (B) in the rubber component is less than 85% by mass, the fuel economy and wear resistance of the pneumatic tire can be maintained well. In one embodiment, the rubber component preferably contains 15% by mass or more and less than 80% by mass of the styrene-butadiene rubber (B). In this case, the pneumatic tire achieves wet grip performance, fuel economy, and wear resistance at a higher level.

[0088] Furthermore, from the viewpoint of achieving a higher level of wet grip performance, fuel economy, and wear resistance of a pneumatic tire, it is preferable that the content ratio of the styrene-butadiene rubber (B) is larger than the content ratio of the styrene-butadiene rubber (A) (i.e., content ratio of styrene-butadiene rubber (B) / content ratio of styrene-butadiene rubber (A)>1).

[0089] The rubber component may contain rubbers (other rubbers) different from the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) as a rubber component, for the purpose of improving the fuel economy and wear resistance of the pneumatic tire. The other rubbers may be appropriately selected depending on the required performance, and may be, for example, one or more of diene rubbers such as natural rubber (NR), polybutadiene (BR), polyisoprene (IR), ethylene-propylene copolymer rubber, etc., or non-diene rubbers such as butyl rubber.

[0090] However, from the viewpoint of achieving a higher level of wet grip performance, fuel economy, and wear resistance of the pneumatic tire of the present invention, it is preferable that the rubber component consists of only the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B).

[0091]

[0023] (Filler) The tread rubber layer of the pneumatic tire of the present invention contains, in addition to the rubber component described above, a filler containing at least silica. By using the filler together with the rubber component containing the styrene-butadiene rubber (A), the dispersibility of the filler is improved, and the fuel economy and wear resistance of the pneumatic tire can be improved.

[0092] Here, the content of the filler is not particularly limited, but is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 120 parts by mass or less. This is because optimizing the amount of filler makes it possible to achieve a higher level of wet grip performance, fuel economy, and wear resistance of a pneumatic tire. When the content of the filler is 20 parts by mass or more per 100 parts by mass of the rubber component, sufficient wet grip performance, fuel economy, and wear resistance are obtained, and when the content of the filler is 160 parts by mass or less per 100 parts by mass of the rubber component, deterioration of low heat buildup and processability can be suppressed.

[0093] The silica contained in the filler is not particularly limited and can be appropriately selected depending on the required performance. For example, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. can be used as the silica, and among these, wet silica is preferred. These silicas may be used alone or in combination of two or more. Precipitated silica can also be used as the wet silica. Precipitated silica is silica obtained by reacting a reaction solution at a relatively high temperature in a neutral to alkaline pH range in the early stages of production to grow primary silica particles, and then adjusting the pH to the acidic side to cause the primary particles to aggregate.

[0094] From the viewpoint of reducing environmental impact, silica derived from siliceous plants is also preferred as the silica. Examples of siliceous plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo, and sugarcane, with rice being preferred. Rice is widely cultivated for food and therefore can be procured locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient supply. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs involved in transportation and storage, which is environmentally preferable from various viewpoints. The rice husk silica may be a powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet process using an alkali silicate aqueous solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be pulverized using a known pulverizer (e.g., a ball mill), and then sorted and classified into a predetermined particle size range to obtain rice husk charcoal powder. The rice husk-derived precipitated silica can be produced by the method described in JP 2019-38728 A, for example.

[0095] The silica preferably has a CTAB (cetyltrimethylammonium bromide) specific surface area of ​​50 m ２ / g~350m ２ / g. The CTAB specific surface area of ​​silica is 50 m ２ / g or more, the wear resistance of the pneumatic tire is further improved, and the CTAB specific surface area of ​​the silica is 350 m ２ / g or less, the rolling resistance of the pneumatic tire is reduced.

[0096] Furthermore, the silica has a nitrogen adsorption specific surface area (BET method) of 80 m２ / g or more 330m ２ The nitrogen adsorption specific surface area (BET method) of silica is preferably less than 80 m ２ / g or more, the pneumatic tire can be sufficiently reinforced, and the fuel efficiency of the tire can be further improved. ２ When the silica has a nitrogen adsorption specific surface area (BET method) of 130 m / g or less, the elastic modulus of the rubber composition that can be used in the tread rubber layer does not become too high, and the wet grip performance of the pneumatic tire is further improved. ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ From the viewpoint of further improving the wet grip performance of the tire, the nitrogen adsorption specific surface area (BET method) of the silica is more preferably 300 m ２ / g or less, and ２ / g or less is more preferable, and 270m ２ It is more preferable that the tensile strength is 1 / g or less.

[0097] Furthermore, the content of the silica is preferably 20 parts by mass or more but less than 100 parts by mass per 100 parts by mass of the rubber component. By optimizing the amount of silica, wet grip performance, fuel economy, and abrasion resistance can be achieved at a higher level. When the silica content is 20 parts by mass or more, sufficient wet grip performance, fuel economy, and abrasion resistance can be obtained, while when the silica content is less than 100 parts by mass, deterioration of low heat buildup and processability can be suppressed. From the same viewpoint, the content of the silica is more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 62 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 68 parts by mass or more per 100 parts by mass of the rubber component. In addition, the content of the silica is more preferably 90 parts by mass or less, even more preferably 85 parts by mass or less, and particularly preferably 82 parts by mass or less per 100 parts by mass of the rubber component.

[0098] Preferably, the filler further contains carbon black in addition to the silica. The carbon black can improve the wear resistance of pneumatic tires. The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more. The carbon black may also be recycled carbon black.

[0099] In this specification, "recycled carbon black" refers to carbon black recovered from raw materials that are waste materials that have been recycled. Examples of the waste materials that have been recycled include rubber products (particularly vulcanized rubber products) containing carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" differs from carbon black that is produced directly from hydrocarbons such as petroleum and natural gas, i.e., non-recycled carbon black. Note that "used" here refers not only to carbon black that has been discarded after actual use, but also to carbon black that has been produced but discarded without actually being used.

[0100] In the filler, the content of silica in the total amount of the silica and the carbon black is preferably 80% by mass or more but less than 100% by mass, more preferably 85% by mass or more but less than 100% by mass, and even more preferably 90% by mass or more but less than 100% by mass. This is because, when the content of silica in the total amount of the silica and the carbon black is 80% by mass or more, a decrease in fuel efficiency due to an increase in carbon black can be suppressed, and when the content is less than 100% by mass, the reinforcing effect of carbon black can be reliably secured.

[0101] In addition to silica and carbon black, other inorganic compounds represented by the following formula (I) can also be used as the filler: nM.xSiO ｙ ・zH ２ O ... (I) (In the formula, M is at least one selected from the group consisting of a metal selected from the group consisting of Al, Mg, Ti, Ca and Zr, an oxide or hydroxide of these metals, a hydrate thereof, and a carbonate of these metals; and n, x, y and z are integers of 1 to 5, an integer of 0 to 10, an integer of 2 to 5, and an integer of 0 to 10, respectively.) When the filler contains other inorganic compounds, the content thereof is preferably about 5 to 30 parts by mass per 100 parts by mass of the rubber component.

[0102] The inorganic compound of the above formula (I) includes alumina (Al) such as γ-alumina and α-alumina. ２ O３ alumina monohydrate (Al) such as boehmite and diaspore; ２ O ３ ・H ２ O); aluminum hydroxides such as gibbsite and bayerite [Al(OH) ３ ]; aluminum carbonate [Al ２ (CO ３ ) ３ ], magnesium hydroxide [Mg(OH) ２ ], magnesium oxide (MgO), magnesium carbonate (MgCO3), talc (3MgO.4SiO ２ ・H ２ O), attapulgite (5MgO.8SiO ２ ・9H ２ O), titanium white (TiO ２ ), titanium black (TiO ２ｎ－１ ), calcium oxide (CaO), calcium hydroxide [Ca(OH) ２ ], magnesium aluminum oxide (MgO.Al ２ O ３ ), clay (Al ２ O ３ 2SiO ２ ), kaolin (Al ２ O ３ 2SiO ２ ・2H ２ O), pyrophyllite (Al ２ O ３ 4SiO ２ ・H ２ O), bentonite (Al ２ O ３ 4SiO ２ ・2H ２ O), aluminum silicate (Al ２ SiO ５ , Al ４ 3SiO ４ ・5H ２ O, etc.), magnesium silicate (Mg ２ SiO ４ , MgSiO ３ etc.), calcium silicate (Ca ２ SiO ４ etc.), calcium aluminum silicate (Al ２ O ３CaO 2SiO ２ etc.), magnesium calcium silicate (CaMgSiO ４ ), calcium carbonate (CaCO ３ ), zirconium oxide (ZrO ２ ), zirconium hydroxide [ZrO(OH) ２ ・nH ２ O], zirconium carbonate [Zr(CO ３ ) ２ ], crystalline aluminosilicates containing hydrogen, alkali metals or alkaline earth metals to compensate for the charge, such as various zeolites, and the like.

[0103] (Silane Coupling Agent) The tread rubber layer in the pneumatic tire of the present invention further contains a silane coupling agent in addition to the rubber component and the filler. The inclusion of the silane coupling agent in the tread rubber layer improves the dispersibility of the silica contained as a filler, contributing to achieving both wet grip performance and fuel economy and wear resistance.

[0104] In the present invention, the silane coupling agent contains at least the silane coupling agent (A) having a thiol group and the silane coupling agent (B) having a sulfide bond.Although the silane coupling agent (A) having a thiol group has a high effect of enhancing the dispersibility of silica as described above, if the content is too high, it may cause discoloration such as blackening of the tire over time.Therefore, by further containing the silane coupling agent (B) having a sulfide bond as the silane coupling agent and adjusting the content of these silane coupling agents, it is possible to achieve wet grip performance, low fuel consumption performance and wear resistance, while suppressing discoloration such as blackening (excellent discoloration resistance).

[0105] Here, the total content of the silane coupling agent (A) and the silane coupling agent (B) is preferably 1 to 15 parts by mass per 100 parts by mass of the silica. When the total content of the silane coupling agents is 1 part by mass or more per 100 parts by mass of the silica, wet grip performance, fuel economy performance, and abrasion resistance can be sufficiently achieved, and when the total content of the silane coupling agents is 15 parts by mass or less per 100 parts by mass of the silica, discoloration resistance can be sufficiently ensured. From the same viewpoint, the total content of the silane coupling agents (A) and the silane coupling agents (B) is preferably 2 to 14 parts by mass per 100 parts by mass of the silica, more preferably 3 to 13 parts by mass, and even more preferably 5 to 12 parts by mass.

[0106] Further, the content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 100 parts by mass of the silica. When the content of the silane coupling agent (A) is 1 part by mass or more relative to 100 parts by mass of the silica, wet grip performance, fuel economy performance, and abrasion resistance can be sufficiently achieved, and when the content of the silane coupling agent (A) is 10 parts by mass or less relative to 100 parts by mass of the silica, discoloration resistance can be sufficiently ensured. From the same viewpoint, the content of the silane coupling agent (A) is preferably 2 to 9.5 parts by mass, more preferably 3 to 9 parts by mass, relative to 100 parts by mass of the silica.

[0107] Furthermore, from the viewpoint of achieving both wet grip performance and fuel economy and abrasion resistance, as well as a balanced effect of discoloration resistance, the mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is preferably 0.3 or more and less than 3.0. When the content mass ratio (B / A) of the silane coupling agents (A) and (B) is 0.3 or more, the effect of discoloration resistance is more reliably obtained, and when the content mass ratio (B / A) of the silane coupling agents (A) and (B) is less than 3.0, the wet grip performance, fuel economy and abrasion resistance are more reliably achieved. From the same viewpoint, the content mass ratio (B / A) of the silane coupling agents (A) and (B) is preferably 0.31 or more and 3.0 or less, more preferably 0.32 or more and 2.9 or less.

[0108] The silane coupling agent (A) is not particularly limited as long as it has a thiol group. Examples thereof include 3-(trimethoxysilyl)-1-propanethiol, 3-(triethoxysilyl)-1-propanethiol, 3-(methyldimethoxysilyl)-1-propanethiol, 2-(trimethoxysilyl)-1-ethanethiol, 2-(triethoxysilyl)-1-ethanethiol, 2-(methyldimethoxysilyl)-1-ethanethiol, (trimethoxysilyl)methanethiol, (triethoxysilyl)methanethiol, (methyldimethoxysilyl)methanethiol, 3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propanethiol {manufactured by Evonik Degussa, trade name "Si363" and [C １３ H ２７ O (CH ２ CH ２ O) ５ ] ２ (CH ３ CH ２ O)Si(CH ２ ) ３ SH} and the like.

[0109] Furthermore, among the above-mentioned silane coupling agents, the silane coupling agent (A) preferably has a carbon number of 20 to 75. This is because such a silane coupling agent (A) more reliably achieves both wet grip performance, fuel economy, and wear resistance of a pneumatic tire, and has better discoloration resistance.

[0110] The silane coupling agent (B) is not particularly limited as long as it has a sulfide bond. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, and the like.

[0111] Bioethanol can also be used as a raw material for silane coupling agents. Bioethanol is produced primarily using sugars and / or cellulose as biological resources, and does not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0112] (Resin) The tread rubber layer in the pneumatic tire of the present invention preferably further contains a resin. When the tread rubber layer further contains a resin, processability can be improved and the wet grip performance of the pneumatic tire can be further improved.

[0113] The type of the resin is not particularly limited. ５ based resin, C ５ -C ９ based resin, C ９ These resins may be used alone or in combination of two or more.

[0114] Said C ５ As a resin based on C, there is C obtained by thermal decomposition of naphtha in the petrochemical industry. ５ and aliphatic petroleum resins obtained by (co)polymerizing the distillate. ５The fraction usually contains olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene. ５ Commercially available resins can be used.

[0115] Said C ５ -C ９ The C-based resin is ５ -C ９ It refers to synthetic petroleum resin, ５ -C ９ Examples of the resin include petroleum-derived C ５ -C １１ The fraction was treated with AlCl ３ , B.F. ３ More specifically, copolymers containing styrene, vinyltoluene, α-methylstyrene, indene, etc. as the main component may be mentioned. ５ -C ９ As the resin, ９ Resins containing less of the above components are preferred from the viewpoint of compatibility with the rubber component. ９ "Low amount of the above components" means that the C ９ This means that the above components are contained in an amount of less than 50% by mass, preferably 40% by mass or less. ５ -C ９ Commercially available resins can be used.

[0116] Said C ９ The C-based resin is ９ This refers to synthetic petroleum resins, such as AlCl ３ or BF ３ Using a Friedel-Crafts type catalyst such as C ９ It refers to a solid polymer obtained by polymerizing the fraction. ９ Examples of the resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0117] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously when rosin is extracted from pine trees, or a polymerization component separated from the blend, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Furthermore, a representative example of a terpene-aromatic compound resin is terpene-phenol resin. This terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene with formalin. There are no particular limitations on the terpenes used as raw materials; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred. Styrene or the like may also be included in the skeleton.

[0118] The dicyclopentadiene resin is, for example, AlCl ３ or BF ３ This refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as

[0119] Furthermore, the resin is preferably at least partially hydrogenated (hydrogenated resin). By at least partially hydrogenating the resin, the hysteresis loss (tan δ) in the low temperature range can be improved, thereby improving the wet grip performance of the pneumatic tire. Note that the at least partially hydrogenated resin refers to a resin obtained by reducing and hydrogenating a resin.

[0120] The resin that is the raw material for the hydrogenated resin is, for example, C ５ A resin (C) copolymerized with the fraction and dicyclopentadiene (DCPD) ５ -DCPD-based resin). When the dicyclopentadiene-derived component is 50% by mass or more in the total amount of the resin, C ５ -DCPD-based resins are included in dicyclopentadiene-based resins. When the dicyclopentadiene-derived component is less than 50% by mass in the total amount of resin, C ５ -DCPD resin is C ５The same applies to cases where a small amount of a third component is contained.

[0121] The resin preferably has a softening point higher than 110°C and a polystyrene-equivalent weight average molecular weight of 200 to 1600 g / mol. In this case, the tread rubber layer is sufficiently reinforced, and abrasion resistance can be further improved. From the viewpoint of abrasion resistance of the tire, the softening point of the resin is more preferably 116°C or higher, more preferably 120°C or higher, more preferably 123°C or higher, and even more preferably 127°C or higher. Furthermore, from the viewpoint of processability, the softening point of the resin is preferably 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, more preferably 141°C or lower, and even more preferably 136°C or lower. The polystyrene-equivalent weight average molecular weight of the resin can be calculated, for example, by measuring the average molecular weight by gel permeation chromatography (GPC) under the following conditions. Column temperature: 40°C Injection volume: 50 μL Carrier and flow rate: tetrahydrofuran 0.6 mL / min Sample preparation: About 2.5 mg of resin component was dissolved in 10 mL of tetrahydrofuran. The softening point of the resin component can be measured, for example, in accordance with JIS-K2207-1996 (ring and ball method).

[0122] When the polystyrene-equivalent weight-average molecular weight of the resin is 200 g / mol or more, the resin is less likely to precipitate from the tire and the effects of the resin can be fully exhibited, and when it is 1600 g / mol or less, the resin is more likely to be compatible with the rubber component. From the viewpoint of suppressing the resin's precipitation from the tire and suppressing deterioration in tire appearance, the polystyrene-equivalent weight-average molecular weight of the resin is preferably 500 g / mol or more, more preferably 550 g / mol or more, even more preferably 600 g / mol or more, even more preferably 650 g / mol or more, and still more preferably 700 g / mol or more. Furthermore, from the viewpoint of increasing the compatibility of the resin with the rubber component and further enhancing the effects of the resin, the polystyrene-equivalent weight average molecular weight of the resin is preferably 1350 g / mol or less, more preferably 1330 g / mol or less, more preferably 1300 g / mol or less, more preferably 1200 g / mol or less, more preferably 1100 g / mol or less, more preferably 1000 g / mol or less, and even more preferably 950 g / mol or less.

[0123] The weight average molecular weight (Mw ＨＲ ) (unit: g / mol) to the softening point (Ts ＨＲ ) (unit: °C) ratio (Ts ＨＲ / Mw ＨＲ ) is preferably 0.07 or more, more preferably 0.083 or more, more preferably 0.095 or more, more preferably 0.104 or more, more preferably 0.125 or more, more preferably 0.135 or more, more preferably 0.14 or more, and even more preferably 0.141 or more. ＨＲ / Mw ＨＲ ) is preferably 0.25 or less, more preferably 0.24 or less, more preferably 0.23 or less, more preferably 0.19 or less, more preferably 0.18 or less, and even more preferably 0.17 or less.

[0124] The content of the resin is preferably 1 to 50 parts by mass per 100 parts by mass of the rubber component. When the content of the resin in the tread rubber layer is 1 part by mass or more per 100 parts by mass of the rubber component, the effect of the resin is fully exhibited and wet grip performance is improved. When the content of the resin in the tread rubber layer is 50 parts by mass or less, the resin is less likely to precipitate from the tire and the effect of the resin can be fully exhibited. On the other hand, when the content of the resin exceeds 50 parts by mass per 100 parts by mass of the rubber component, the fuel economy and wear resistance of the pneumatic tire deteriorate. From the viewpoint of further enhancing the effect of the resin, the content of the resin in the rubber composition is preferably 5 parts by mass or more per 100 parts by mass of the rubber component, more preferably 7 parts by mass or more, and even more preferably 9 parts by mass or more. From the viewpoint of suppressing resin precipitation from the tire and suppressing deterioration of the tire appearance, the content of the resin in the rubber composition is preferably 45 parts by mass or less per 100 parts by mass of the rubber component, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

[0125] (Other Components) In addition to the rubber component, filler, silane coupling agent, and resin component described above, the tread rubber layer in the pneumatic tire of the present invention may contain, as necessary, various components commonly used in the rubber industry, such as antioxidants, waxes, softeners, processing aids, stearic acid, zinc oxide (zinc white), vulcanization accelerators, vulcanizing agents, etc., appropriately selected within ranges that do not impair the object of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0126] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), etc. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0127] Examples of the wax include paraffin wax, microcrystalline wax, etc. The content of the wax is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0128] The content of the zinc oxide (zinc white) is not particularly limited, but is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably less than 4 parts by mass, per 100 parts by mass of the rubber component. If the content of the zinc white is too high (more than 8 parts by mass), non-dispersion may occur, resulting in a decrease in fracture properties.

[0129] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0130] The vulcanizing agent may be sulfur, etc. The content of the vulcanizing agent is preferably in the range of 0.1 to 10 parts by mass, more preferably 1 to 4 parts by mass, in terms of sulfur content, per 100 parts by mass of the rubber component.

[0131] (Method for manufacturing tread rubber layer) The method for manufacturing the tread rubber layer is not particularly limited. For example, a rubber composition for the tread rubber layer can be manufactured by blending various components appropriately selected as necessary with the above-mentioned rubber component, filler, silane coupling agent, and resin component, and kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to form a vulcanized rubber.

[0132] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0133] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0134] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0135] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of vulcanization apparatus include a molding vulcanizer using a mold used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0136] <<Carcass Ply>> In the pneumatic tire of this embodiment, the carcass ply 9 is formed by covering a PET fiber cord 10 with a coating rubber 20, as shown in FIG.

[0137] The carcass ply 9 of the pneumatic tire of this embodiment has a total gauge of 1.2 mm or less, and satisfies the following formula (1): (A / B) / total cord fineness≧0.3 (1) (A: cord strength (N)×fiber occupancy rate, fiber occupancy rate: cross-sectional area of ​​the PET fiber cord (mm ２) / (total gauge of carcass ply (mm) × (diameter of PET fiber cord (mm) + distance between PET fiber cords (mm))) B: tan δ of coating rubber × rubber occupancy rate Rubber occupancy rate: 1 - fiber occupancy rate Total cord fineness: total value of fineness of PET fibers constituting the cord (dtex)) Here, A in the above formula (1) represents "cord strength (N) × fiber occupancy rate". By increasing the value of A, the strength of the carcass ply can be increased. Also, the fiber occupancy rate in A is determined by the ratio of "cross-sectional area of ​​PET fiber cord (mm ２ ) / (total gauge of carcass ply (mm) × (diameter of PET fiber cord (mm) + distance between PET fiber cords (mm)))) and increasing this value allows for a thinner coating rubber 20, which contributes to reducing rolling resistance. In addition, B in the above formula (1) is "tan δ of coating rubber × rubber occupation rate." Reducing this value reduces the volume of rubber in the carcass ply, which contributes to weight reduction and reduced rolling resistance. Furthermore, the total cord fineness in the above formula (1) is the sum of the finenesses of the PET fibers 11. The larger this value, the thicker the PET fiber cord 10 is, and the higher the strength but the greater the mass. In the present invention, by setting the ratio of "A / B" to the above-mentioned "total cord fineness" to be 0.3 or more, it is possible to increase the strength of the carcass ply even when using cords with low fineness (when the mass of the PET fiber cords is small).

[0138] From the same viewpoint, it is preferable that the carcass ply 9 of the pneumatic tire of the present embodiment satisfies the following formula (1)': (A / B) / total cord fineness≧0.45 (1)'.

[0139] The PET fiber cords and coating rubber that constitute the carcass ply of the pneumatic tire of this embodiment will be described below.

[0140] (PET fiber cord) The PET fiber cord is a cord made of polyethylene terephthalate fibers, and has an excellent balance of properties such as strength, modulus, dimensional stability, and manufacturing cost. The PET fiber cord may be a single-twisted cord or a multi-twisted cord using two or more original yarns. The type can be appropriately selected depending on the performance required of the PET fiber cord.

[0141] The raw material of the PET fiber cord is not particularly limited, and may be, for example, derived from a synthetic product, or derived from a biological resource such as a plant resource, an animal resource, or a microbial resource, or may be derived from a mechanical recycling method in which a resin product is crushed, melted, and respun, or may be derived from a chemical recycling method in which a resin product is depolymerized and repolymerized.

[0142] Examples of the polyethylene terephthalate fibers include polyethylene terephthalate obtained by mechanically or chemically recycling PET products, clothing, and the like.

[0143] The cord strength of the PET fiber cord is preferably 160 N or more, and more preferably 165 N or more. This allows the strength of the carcass ply to be further increased, effectively achieving both cut resistance and fuel economy. The cord strength of the PET fiber cord can be appropriately controlled by, for example, adjusting the total cord fineness, the number of twists, the raw yarn strength, etc.

[0144] Furthermore, the raw yarn strength of the PET fibers constituting the PET fiber cord is preferably 7.8 cN / dtex or more, and more preferably 8.0 cN / dtex or more. As a result of being able to increase the strength of the PET fiber cord, the strength of the carcass ply can be further increased. The raw yarn strength of the PET fiber can be increased by adjusting the molecular weight, crystallinity, degree of crystal orientation, etc. of the PET resin.

[0145] The total fineness of the PET fiber cord is preferably 1000 to 4800 dtex, and more preferably 2000 to 4000 dtex. When the total fineness of the PET fiber cord is 1000 dtex or more, the strength of the carcass ply can be further increased. On the other hand, when the total fineness of the PET fiber cord is 4800 dtex or less, deterioration of rolling resistance when applied to a tire as a carcass ply can be more reliably suppressed. Here, the total fineness of the PET fiber cord is the sum of the finenesses of the PET fibers constituting the cord, and the total fineness can be controlled by adjusting the fineness of the PET fibers, the number of twists, etc.

[0146] Furthermore, the fineness of the PET fiber is preferably 550 to 2200 dtex, and more preferably 1100 to 1670 dtex. When the fineness of the PET fiber is 550 dtex or more, the strength of the carcass ply can be further increased. On the other hand, when the fineness of the PET fiber is 2200 dtex or less, deterioration of rolling resistance can be more reliably suppressed when the PET fiber is used as a carcass ply in a tire. The fineness of the PET fiber can be controlled by adjusting the type of fiber, manufacturing conditions, etc.

[0147] The PET fiber cord preferably has a fineness of 1100 / 2 to 2000 / 2 dtex. This means the fineness when two fibers are twisted together. When the PET fiber cord has a fineness in the above range, it is possible to effectively achieve both cut resistance and fuel economy in a pneumatic tire.

[0148] The diameter of the PET fiber cord is preferably 0.45 mm or more, more preferably 0.50 mm or more, from the viewpoint of maintaining plunger energy, and is preferably 0.80 mm or less, more preferably 0.70 mm or less, from the viewpoint of reducing rolling resistance.

[0149] The placement density of the PET fiber cords is preferably 120 cords / 10 cm or more, and more preferably 140 cords / 10 cm or more, because this can further increase the strength of the carcass ply. The placement density of the PET fiber cords is the number of PET fiber cords per 10 cm in the direction in which the cords are arranged side by side in the carcass ply (the horizontal direction in Figure 1).

[0150] Furthermore, the fiber occupancy rate in the carcass ply is not particularly limited as long as it satisfies the above formula (1), but from the viewpoint of achieving both strength and low rolling resistance when applied to a tire at a higher level, it is preferably 30% or more and 40% or less, and more preferably 35% or more and 40% or less. Note that, as described above, the fiber occupancy rate is determined based on the cross-sectional area (mm ２ ) / (total gauge of carcass ply (mm)×(diameter of PET fiber cord (mm)+distance between PET fiber cords (mm))).

[0151] Here, the diameter of the PET fiber cord is the diameter b in the cross section of the PET fiber cord 10 constituting the carcass ply 9, as shown in Fig. 2. In addition, the cross-sectional area of ​​the PET fiber cord is the area S in the cross section of the PET fiber cord 10 constituting the carcass ply 9, as shown in Fig. 2. Furthermore, the inter-cord distance of the PET fiber cord is the shortest distance a between each cord 10 and the adjacent cord 10 in the cross section of the PET fiber cord 10 constituting the carcass ply 9, as shown in Fig. 2.

[0152] (Adhesive Composition) The PET fiber cord is preferably treated with an adhesive composition.

[0153] Examples of the adhesive composition include an adhesive composition containing a thermoplastic polymer (A) having at least one crosslinkable functional group as a pendant group and substantially no addition-reactive carbon-carbon double bonds in its main chain structure, a heat-reactive aqueous urethane resin (B), and an epoxy compound (C), and optionally further containing a rubber latex (D). Treating a PET fiber cord with such an adhesive composition can improve the adhesion between the PET fiber cord and an elastomer (coating rubber) at high temperatures.

[0154] Conventionally, adhesive treatment of PET fiber cords has been performed using a so-called two-bath process, in which epoxy or isocyanate is applied to the cord surface, followed by treatment with a resin (hereinafter referred to as RFL resin) made by mixing resorcinol, formaldehyde, and latex. However, with this method, the resin used in the first bath becomes very hard, which can increase strain input to the PET fiber cord and reduce cord fatigue resistance. Furthermore, while such RFL resins can exhibit sufficient cord-elastomer adhesive strength at room temperature, adhesive strength can be significantly reduced at temperatures above 130°C. In contrast, by using a one-bath mixed liquid (adhesive composition) containing a thermoplastic polymer (A) having at least one crosslinkable functional group as a pendant group and substantially not containing addition-reactive carbon-carbon double bonds in its main chain structure, a thermally reactive aqueous urethane resin (B), and an epoxy compound (C), it is possible to ensure sufficient adhesion to the elastomer (coating rubber) even at high temperatures of 180°C or higher without curing the PET fiber cord.

[0155] The main chain of the thermoplastic polymer (A) mainly has a linear structure, and the main chain is preferably, for example, an ethylenic addition polymer such as an acrylic polymer, a vinyl acetate polymer, or a vinyl acetate-ethylene polymer; a urethane high molecular weight polymer, etc. However, the thermoplastic polymer (A) is not limited to the above-mentioned ethylenic addition polymer and urethane high molecular weight polymer as long as it has the function of suppressing resin fluidity at high temperatures and ensuring the breaking strength of the resin by crosslinking the functional groups of the pendant groups.

[0156] The functional group of the pendant group of the thermoplastic polymer (A) is preferably an oxazolidine group, a bismaleimide group, a (blocked) isocyanate group, an aziridine group, a carbodiimide group, a hydrazino group, an epoxy group, an epithio group, or the like.

[0157] In addition, with respect to the above-mentioned thermoplastic polymer (A), heat-reactive aqueous urethane resin (B), epoxy compound (C), and rubber latex (D), those described in Japanese Patent Application No. 2023-040157 and those described in Japanese Patent Application No. 2023-030762 can be used.

[0158] In the adhesive treatment of the PET fiber cord, it is preferable to use a three-type mixed liquid (adhesive composition) of the thermoplastic polymer (A), the heat-reactive aqueous urethane resin (B), and the epoxy compound (C) as a one-bath treatment liquid, and to use a normal RFL resin liquid as a two-bath treatment liquid. In addition, in the adhesive treatment, it is also possible to treat with only one bath using a mixed liquid (adhesive composition) of the thermoplastic polymer (A), the heat-reactive aqueous urethane resin (B), the epoxy compound (C), and the rubber latex (D).

[0159] In the adhesive composition, the proportion (dry mass ratio) of the thermoplastic polymer (A) is preferably 2 to 75%, the proportion (dry mass ratio) of the heat-reactive aqueous urethane resin (B) is preferably 15 to 87%, the proportion (dry mass ratio) of the epoxy compound (C) is preferably 11 to 70%, and the proportion (dry mass ratio) of the rubber latex (D) is preferably 20% or less.

[0160] On the other hand, from the viewpoint of environmental protection, it is preferable to use a dip treatment liquid that does not contain resorcinol or formalin as an adhesive composition for PET fiber cords. Examples of such dip treatment liquids include a composition containing (a) a rubber latex having an unsaturated diene and (b) one or more compounds selected from a compound having a polyether skeleton structure and an amine functional group, a compound having an acrylamide structure, a polypeptide, a polylysine, and a carbodiimide. Examples of such dip treatment liquids include a composition containing, in addition to the rubber latex having an unsaturated diene (a) and the compound (b), one or more compounds selected from (c) an aqueous compound having a (thermally dissociable blocked) isocyanate group, a polyphenol (d), and a polyvalent metal salt (e).

[0161] Other examples of the dipping treatment liquid that does not contain resorcinol or formalin include a composition containing polyphenols (I) and aldehydes (II). Such a composition may further contain at least one of an isocyanate compound (III) and a rubber latex (IV) in addition to the polyphenols (I) and aldehydes (II).

[0162] The adhesive composition for treating (coating) the PET fiber cord with an adhesive contains polyphenols (I) and aldehydes (II), so that good adhesive properties can be exhibited even when resorcinol is not used in consideration of the environmental load.

[0163] [Polyphenols (I)] The adhesive composition contains polyphenols (I) as a resin component, thereby improving adhesion to PET fiber cords. The polyphenols (I) are typically water-soluble polyphenols, and are not particularly limited as long as they are polyphenols other than resorcinol (resorcinol). The number of aromatic rings or hydroxyl groups in the polyphenols (I) can be appropriately selected.

[0164] From the viewpoint of realizing better adhesive properties, the polyphenols (I) preferably have two or more hydroxyl groups, and more preferably three or more hydroxyl groups. When the polyphenols have three or more hydroxyl groups, the polyphenol or polyphenol condensate is soluble in the adhesive composition (dip treatment liquid) containing water. This allows the polyphenols to be uniformly distributed in the adhesive composition, thereby realizing better adhesive properties. Furthermore, when the polyphenols (I) are polyphenols containing multiple (two or more) aromatic rings, each of the aromatic rings has two or three hydroxyl groups at the ortho, meta, or para positions.

[0165] As the polyphenols (I), for example, those described as polyphenol compounds in WO 2022 / 130879 can be used. These polyphenols (I) may be used alone or in combination of two or more.

[0166] [Aldehydes (II)] When the adhesive composition contains aldehydes (II) as a resin component in addition to the polyphenols (I), high adhesiveness can be achieved together with the polyphenols (I). Here, the aldehydes (II) are not particularly limited and can be appropriately selected depending on the required performance. In this specification, the aldehydes (II) also include derivatives of aldehydes that are generated from aldehydes.

[0167] Examples of the aldehydes (II) include monoaldehydes such as formaldehyde, acetaldehyde, butylaldehyde, acrolein, propionaldehyde, chloral, butylaldehyde, caproaldehyde, and allylaldehyde, and aliphatic dialdehydes such as glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, and adipaldehyde, aldehydes having an aromatic ring, and dialdehyde starch. These aldehydes (II) may be used singly or in combination of two or more.

[0168] The aldehydes (II) are preferably aldehydes having an aromatic ring or contain aldehydes having an aromatic ring, because this allows for better adhesiveness to be obtained. Furthermore, the aldehydes (II) preferably do not contain formaldehyde. Here, "does not contain formaldehyde" means, for example, that the formaldehyde content of the total mass of the aldehydes is less than 0.5 mass%.

[0169] In the adhesive composition, polyphenols (I) and aldehydes (II) are in a condensed state, and the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) is preferably 0.1 or more and 3 or less. In this case, the hardness and adhesive properties of the resin, which is the product of the condensation reaction between the polyphenols and the aldehydes having an aromatic ring, are more suitable. From the same viewpoint, the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) in the adhesive composition is more preferably 0.25 or more and more preferably 2.5 or less. Note that the above mass ratio is the mass of the dry product (solid content ratio).

[0170] The total content of polyphenols (I) and aldehydes (II) in the adhesive composition is preferably 3 to 30% by mass. This is because better adhesion can be ensured without deteriorating workability, etc. From the same viewpoint, the total content of polyphenols (I) and aldehydes (II) in the adhesive composition is more preferably 5% by mass or more, and more preferably 25% by mass or less. The above total content is the mass of the dry product (solid content ratio).

[0171] [Isocyanate Compound (III)] The adhesive composition preferably further contains an isocyanate compound (III) in addition to the polyphenols (I) and aldehydes (II) described above. In this case, the adhesive composition can further enhance the adhesiveness due to a synergistic effect with the polyphenols (I) and the aldehydes (II).

[0172] Here, the isocyanate compound (III) is a compound that has the effect of promoting adhesion of the adhesive composition to a resin material (e.g., a phenol / aldehyde resin obtained by condensing polyphenols (I) and aldehydes (II)) that is the adherend, and is a compound that has an isocyanate group as a polar functional group. These isocyanate compounds (III) may be used alone or in combination of two or more.

[0173]

[0033] The isocyanate compound (III) is not particularly limited, but from the viewpoint of further improving adhesion, it preferably contains a (blocked) isocyanate group-containing aromatic compound. When the adhesive composition contains a (blocked) isocyanate group-containing aromatic compound, the (blocked) isocyanate group-containing aromatic compound is distributed in a position near the interface between the PET fiber cord and the adhesive composition, resulting in a further adhesion-promoting effect. This effect can further enhance the adhesion of the adhesive composition to the PET fiber cord.

[0174] As the (blocked) isocyanate group-containing aromatic compound, those described in Japanese Patent Application No. 2023-040157 and Japanese Patent Application No. 2023-030762 can be used.

[0175] The content of the isocyanate compound (III) in the adhesive composition is not particularly limited, but from the viewpoint of more reliably ensuring excellent adhesion, it is preferably 5 to 65% by mass. From the same viewpoint, the content of the isocyanate compound (III) in the adhesive composition is more preferably 10% by mass or more, and more preferably 45% by mass or less. The above content is the mass of the dry product (solid content ratio).

[0176] [Rubber Latex (IV)] The adhesive composition may further contain substantially rubber latex (IV) in addition to the polyphenols (I), aldehydes (II), and isocyanate compound (III) described above, which can further enhance the adhesiveness of the adhesive composition to rubber members.

[0177] Here, the rubber latex (IV) is not particularly limited, and examples thereof include natural rubber (NR), as well as synthetic rubbers such as polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and vinylpyridine-styrene-butadiene copolymer rubber (Vp). These rubber latexes (IV) may be used alone or in combination of two or more.

[0178] When preparing the adhesive composition containing the rubber latex (IV), it is preferable to mix the rubber latex (IV) with the phenol (I) and the aldehyde (II) before compounding the isocyanate compound (III).

[0179] The content of the rubber latex (IV) in the adhesive composition is preferably 20% by mass or more, more preferably 25% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less.

[0180] The method for producing the adhesive composition is not particularly limited, and examples thereof include a method of mixing raw materials such as polyphenols (I), aldehydes (II), and rubber latex (IV) and aging the mixture, or a method of mixing polyphenols (I) and aldehydes (II) and aging the mixture, and then adding rubber latex (IV) and aging the mixture. When an isocyanate compound (III) is contained in the raw materials, the method for producing the adhesive composition may also be a method of adding rubber latex (IV), aging the mixture, and then adding the isocyanate compound (III).

[0181] (Coating Rubber) The coating rubber is rubber that coats the PET fiber cords. The carcass ply of the pneumatic tire of this embodiment is not particularly limited except that the rubber occupation rate of the coating rubber is specified so as to satisfy the above formula (1), and the composition and physical properties of the coating rubber can be appropriately selected depending on the required performance.

[0182] For example, from the viewpoint of further improving low rolling resistance when applied to a tire as a carcass ply, the coating rubber may comprise a rubber component containing 60 mass % or more of natural rubber and 40 mass % or less of non-oil-extended styrene-butadiene rubber, and 30 to 60 mass parts of a rubber component having a nitrogen adsorption specific surface area (N ２ SA) is 60m ２ / g or less of carbon black. A coating rubber having such a composition is excellent in low heat buildup, and can further reduce rolling resistance when applied to a tire.

[0183] The rubber component of the coating rubber is not particularly limited, but as described above, it preferably contains 60% by mass or more of natural rubber and 40% by mass or less of non-oil-extended styrene-butadiene rubber. By containing 60% by mass or more of natural rubber and 40% by mass or less of non-oil-extended styrene-butadiene rubber in the rubber component of the coating rubber, it can contribute to low rolling resistance when the carcass ply (PET fiber-rubber composite) is applied to a tire. The rubber component may also contain rubbers other than the natural rubber and non-oil-extended SBR described above, such as diene rubbers such as polyisoprene rubber (IR), polybutadiene rubber (BR), acrylonitrile-butadiene copolymer rubber (NBR), isoprene-isobutylene copolymer rubber (IIR), ethylene-propylene-diene copolymer rubber (EPDM), halogenated butyl rubber (HR), and chloroprene rubber (CR), as well as non-diene rubbers.

[0184] The coating rubber has a nitrogen adsorption specific surface area (N ２ SA) is 60m ２It is preferable that the coating rubber contains carbon black of not more than 1 / g. ２ SA is 60m ２ / g or less, the strength of the carcass ply can be maintained high, while suppressing deterioration of rolling resistance when applied to a tire. ２ SA is 45m ２ / g or less is more preferable. By setting the content of the carbon black in the coating rubber to 30 parts by mass or more per 100 parts by mass of the rubber component, the strength of the carcass ply (PET fiber-rubber composite) can be increased, and by setting the content of the carbon black to 60 parts by mass or less per 100 parts by mass of the rubber component, deterioration of rolling resistance when applied to a tire as a carcass ply can be suppressed. From the same viewpoint, the content of the carbon black is more preferably 35 to 45 parts by mass per 100 parts by mass of the rubber component. The carbon black may be recycled carbon black.

[0185] In addition to the rubber component and carbon black described above, the coating rubber may contain additives commonly used in the rubber industry, such as fillers such as silica, vulcanizing agents, vulcanization accelerators, bismaleimide compounds, softeners, stearic acid, zinc oxide, resins, waxes, and oils, as appropriate, provided that the effects of the present invention are not impaired.

[0186] (Physical Properties of Carcass Ply, etc.) The carcass ply 9 of the pneumatic tire of this embodiment is not particularly limited as long as it has a total gauge of 1.2 mm or less and satisfies the above formula (1), but from the viewpoint of obtaining superior strength, it is preferable that its tensile strength (ply strength) exceeds 23,000 N / dm. The tensile strength (N / dm) of the carcass ply is calculated by multiplying the tensile strength of one cord measured according to ASTM D885 by the number of cords per 10 cm width. When the tensile strength of the carcass ply exceeds 23,000 N / dm, the cut resistance and fuel economy of the pneumatic tire are effectively compatible.

[0187] The distance between the PET fiber cords in the carcass ply is preferably 0.15 mm or more, more preferably 0.17 mm or more, from the viewpoint of tire high-speed running durability, and is preferably 0.45 mm or less, more preferably 0.40 mm or less, from the viewpoint of maintaining plunger energy.

[0188] The total gauge of the carcass ply is 1.2 mm or less, and particularly preferably 1.0 mm or less. A total gauge of 1.2 mm or less of the carcass ply contributes to weight reduction of the carcass ply, and can more reliably suppress deterioration of rolling resistance when applied to a tire. The total gauge of the carcass ply refers to the thickness T of the carcass ply when cut at a plane perpendicular to the direction in which the cords extend in the carcass ply, as shown in FIG. 2 .

[0189] As described above, the carcass ply of the pneumatic tire of this embodiment must satisfy the above formula (1), and preferably satisfies the above formula (1)'. In formula (1), the larger A (cord strength × fiber occupancy) indicates a higher carcass ply strength, and the smaller B (tan δ of coating rubber × rubber occupancy) indicates a higher degree of reduction in rolling resistance. As described above, by setting (A / B) / total cord fineness to 0.3 or more (satisfying formula (1)), it is possible to reduce the number of cords and achieve high strength while reducing rolling resistance.

[0190] Furthermore, the tan δ of the coating rubber of the carcass ply measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under conditions of a temperature of 24°C, a strain of 1%, and a frequency of 52 Hz is preferably 1.5 or less, and more preferably 1.0 or less, from the viewpoint of reducing rolling resistance.

[0191] (Method for Manufacturing Carcass Ply) The method for manufacturing the carcass ply of the pneumatic tire of this embodiment is not particularly limited, and the carcass ply can be manufactured by a known method. Note that the method for covering the PET fiber cords with the coating rubber can be, for example, the following method. This method involves forming a predetermined number of PET fiber cords into a blind shape, sandwiching the PET fiber cords from above and below between unvulcanized rubber sheets of any thickness made of the coating rubber (rubber composition), and then vulcanizing the PET fiber cords at a temperature of about 160°C for about 20 minutes, for example, to obtain a carcass ply.

[0192] <Method for manufacturing pneumatic tire> Depending on the type of tire to be applied, the pneumatic tire of this embodiment may be obtained by molding an unvulcanized rubber composition or an unvulcanized treat (a cord-rubber composite in which cords are coated with rubber), etc., followed by vulcanization. Alternatively, the pneumatic tire of this embodiment may be obtained by molding a semi-vulcanized rubber that has undergone a pre-vulcanization process or the like, instead of the unvulcanized rubber composition, followed by full vulcanization. The components of the pneumatic tire of this embodiment other than the tread rubber layer and carcass ply are not particularly limited, and known components can be used. Furthermore, the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0193] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0194] <Preparation and Evaluation of Carcass Ply> Carcass plies were prepared by coating PET fiber cords with coating rubber under the conditions shown in Table 1. Table 1 shows the specifications of the PET fiber cords, the main composition of the coating rubber, and the conditions and evaluation of the prepared carcass plies. (1) Ply Strength The ply strength was calculated using the strength per PET fiber cord measured in accordance with ASTM D885 and the end count per unit of the PET fiber cord using the following formula. The larger the value, the higher the ply strength. Formula: Ply strength (N / dm) = strength per PET fiber cord (N) × end count per unit of the PET fiber cord (cords / 10 cm) The evaluation results were expressed as an index, with the ply strength of carcass ply 1 set to 100. The higher the index value, the higher the ply strength. (2) Tan δ of Coating Rubber Tan δ of coating rubber was measured by using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under the conditions of a temperature of 24° C., a strain of 1%, and a frequency of 52 Hz, as the loss tangent of the coating rubber.

[0195]

[0196] *1 SBR1: Solution-polymerized SBR, non-oil extended *2 SBR2: Emulsion-polymerized SBR, 27.3% oil extended *3 CB1: GPF-grade carbon black, N ２ SA 28m ２ / g, DBP 89 ml / 100 g *4 CB2: HAF grade carbon black, N ２ SA 71m ２ / g, DBP 103ml / 100g

[0197] <Analysis Method of Rubber Component> The glass transition temperature (Tg) and bound styrene content of styrene-butadiene rubber were measured by the following methods.

[0198] (1) Glass Transition Temperature (Tg) Using the synthesized styrene-butadiene rubber as a sample, a DSC curve was recorded using a DSC250 manufactured by TA Instruments, while increasing the temperature from −100° C. at a rate of 20° C. / min under a helium flow of 50 mL / min, and the peak top (inflection point) of the DSC differential curve was determined as the glass transition temperature.

[0199] (2) Bound Styrene Amount The synthesized styrene-butadiene rubber was used as a sample, and 100 mg of the sample was diluted with chloroform to 100 mL and dissolved to prepare a measurement sample. The amount of bound styrene (mass%) relative to 100 mass% of the sample was measured based on the amount of absorption at the ultraviolet absorption wavelength (near 254 nm) by the phenyl group of styrene. A spectrophotometer "UV-2450" manufactured by Shimadzu Corporation was used as the measurement device.

[0200] <Preparation of Rubber Compositions> Rubber compositions of Examples and Comparative Examples were prepared by blending and kneading each component according to the formulations shown in Tables 2 and 3. The blending amounts of the rubber components shown in Tables 2 and 3 are shown as values ​​including the amount of oil extender. The blending amount of each component is shown as the amount (parts by mass) per 100 parts by mass of the rubber component. The obtained rubber compositions of Examples and Comparative Examples were vulcanized to obtain vulcanized rubber test pieces.

[0201] The "low Tg modified SBR" in Tables 2 and 3 was prepared under the following conditions. (Synthesis of low Tg modified SBR (*5)) A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to a dried, nitrogen-purged 800 mL pressure-resistant glass vessel so that the total amount of 1,3-butadiene and styrene became 67.5 g, respectively. 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium were then added, and polymerization was carried out at 50°C for 1.5 hours. The polymerization reaction system reached a polymerization conversion rate of nearly 100%, and 0.72 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine was added as a modifying agent, and the modification reaction was carried out at 50°C for 30 minutes. Thereafter, 2 mL of a 5% by mass solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol was added to terminate the reaction, and the mixture was dried in a conventional manner to obtain a modified SBR. Measurement of the microstructure of the obtained modified SBR revealed that the bound styrene content was 10% by mass, and the glass transition temperature (Tg) was −65° C.

[0202] <Evaluation of Rubber Composition> The test specimens were evaluated for wet blip performance, fuel economy, abrasion resistance, discoloration of appearance, and modulus of elasticity by the following methods. The results are shown in Tables 2 and 3.

[0203] (1) Wet Grip Performance The loss tangent (tan δ) of the test specimen was measured using a viscoelasticity measuring device (manufactured by GABO) under conditions of a temperature of -5°C, a strain of 1%, and a frequency of 15 Hz. The evaluation results are shown in Tables 2 and 3 as an index, with the tan δ of Comparative Example 1 set to 100. The larger the index value, the larger the tan δ and the better the wet grip performance.

[0204] (2) Fuel Economy Performance The loss tangent (tan δ) of the test specimen was measured using a viscoelasticity measuring device (manufactured by GABO) under conditions of a temperature of 50°C, a strain of 1%, and a frequency of 15 Hz, and the reciprocal of the measured value was calculated. The evaluation results are shown in Tables 2 and 3 as index values, with the reciprocal of tan δ of Comparative Example 1 set to 100. A larger index value indicates a smaller tan δ and better fuel economy.

[0205] (3) Abrasion Resistance Performance For the test specimens, sandpaper was attached to the grinding wheel using a Lambourn abrasion tester manufactured by Ueshima Seisakusho in accordance with JIS K 6264-2:2005, and the abrasion volume was measured at room temperature at slip ratios of 5%, 7%, 10%, 12%, and 15%. The reciprocal of the abrasion volume in Comparative Example 1 was set to 100, and the abrasion volume was calculated as an index using the following formula. The larger the index value, the smaller the abrasion volume and the better the abrasion resistance performance. The abrasion volume was calculated by multiplying it by a coefficient for the expected occurrence frequency for each slip ratio, and further correcting the value so that the contact area was constant, taking into account the elastic modulus of the rubber. Abrasion Resistance Index = {(Abrasion volume of the test specimen in Comparative Example 1) / (Abrasion volume of each test specimen)} x 100

[0206] (4) Discoloration of appearance After storing the test piece for 7 days under the conditions of 40°C and 50 pphm ozone atmosphere, the presence or absence of discoloration on the surface was confirmed by visual inspection. The evaluation was performed according to the following criteria, and the evaluation results are shown in Tables 2 and 3. Good: No black luster occurred. Poor: Black luster occurred.

[0207] (5) Elastic Modulus The storage elastic modulus (E') of the test specimen was measured using a viscoelasticity measuring device (manufactured by Rheometrics) under conditions of a temperature of 25°C, a strain of 1%, and a frequency of 52 Hz. The elastic modulus (E') of Comparative Example 1 was set to 100, and the results were expressed as an index. A larger index value indicates a larger elastic modulus (E'). The results are shown in Tables 2 and 3.

[0208]

[0209]

[0210] * 5 Low Tg modified SBR: Modified SBR obtained by synthesizing the above low Tg modified SBR, equivalent to styrene butadiene rubber (A) * 6 Medium Tg modified SBR: SBR obtained using butyl lithium as an initiator, having a Tg of -38 ° C., and modified at the end with N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propaneamine, styrene-butadiene rubber * 7 High Tg unmodified SBR: ENEOS Material Corporation, trade name "HP755B", glass transition temperature -19 ° C., blending amount contains 37.5 parts by mass of oil added to 100 parts by mass of SBR, equivalent to styrene butadiene rubber (B) * 8 Silica: Tosoh Silica Corporation, trade name "Nipsil AQ" * 9 Carbon black (CB): Asahi Carbon Co., Ltd., trade name "# 80" * 10 Inorganic filler: Showa Denko K.K., "Hijilite (registered trademark)" * 11 Silane coupling agent (A): Mercapto-based silane coupling agent, manufactured by EVONIK, trade name "Si 363" * 12 Silane coupling agent (B): Sulfide-based silane coupling agent, manufactured by EVONIK, trade name "S 2.5" * 13 Oil: Manufactured by Idemitsu Kosan Co., Ltd., trade name "Diana Process NH-70S" * 14 Hydrogenated C ５ Resin: Eastman Co., trade name "Impera E1780", softening point = 130°C, weight average molecular weight (Mw) = 909 g / mol *15 Other components: total amount of stearic acid, wax, antioxidant, zinc oxide, vulcanization accelerator, sulfur, retarder and workability improver

[0211] Tables 2 and 3 show that Examples 1 to 8 have a high level of wet grip performance, fuel economy, and abrasion resistance, and are also excellent in discoloration resistance, compared to the Comparative Examples. In addition, even if the tread modulus is lower than that of the Comparative Examples, it is expected that the carcass ply strength is high and cut resistance can be maintained. ​

[0212] According to the present invention, it is possible to provide a pneumatic tire that has excellent discoloration resistance and that achieves a high level of wet grip performance, fuel efficiency, and wear resistance without deteriorating cut resistance.

[0213] 1: Pneumatic tire, 2: Bead portion, 3: Sidewall portion, 4: Tread portion, 5: Carcass, 6: Belt, 6A, 6B: Belt layer, 7: Bead core, 8: Tread rubber layer, 9: Carcass ply, 10: PET fiber cord, 11: PET fiber, 20: Coating rubber

Claims

1. A pneumatic tire comprising a tread rubber layer located on the outermost surface of a tread portion, and a carcass ply located radially inward of the tread rubber layer and formed by covering PET fiber cords with a coating rubber, wherein the tread rubber layer contains a rubber component, a filler, and a silane coupling agent, the rubber component contains a styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of -50°C or lower, and an unmodified styrene-butadiene rubber (B) having a glass transition temperature 30°C or higher than that of the styrene-butadiene rubber (A), the filler contains at least silica, the silane coupling agent contains at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, a total content of the silane coupling agent (A) and the silane coupling agent (B) is 1 to 15 parts by mass relative to 100 parts by mass of the silica, a total gauge of the carcass ply is 1.2 mm or less, and the carcass ply satisfies the following formula (1): (A / B) / total cord fineness≧0.3 (1) (A: cord strength (N)×fiber occupancy rate, fiber occupancy rate: cross-sectional area (mm ２ ) / (total gauge of carcass ply (mm)×(diameter of PET fiber cord (mm)+distance between PET fiber cords (mm))) B: tan δ of coating rubber × rubber occupancy rate Rubber occupancy rate: 1-fiber occupancy rate Total cord fineness: total value (dtex) of the fineness of the PET fibers constituting the cord.

2. The pneumatic tire according to claim 1, wherein the styrene-butadiene rubber (A) is modified with a modifier having nitrogen atoms and silicon atoms.

3. The pneumatic tire according to claim 2, wherein the styrene-butadiene rubber (A) is modified with a modifying agent having a functional group containing a nitrogen atom and an alkoxy group.

4. The pneumatic tire according to claim 1, wherein the mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is 0.3 or more and less than 3.

5. The pneumatic tire according to claim 1, characterized in that the filler further contains carbon black, and the content of the silica in the total amount of the silica and the carbon black is 80 mass % or more and less than 100 mass %.

6. The pneumatic tire according to claim 1, wherein the content of the silica is equal to or greater than 20 parts by mass and less than 100 parts by mass per 100 parts by mass of the rubber component.

7. The pneumatic tire according to claim 1, wherein the silane coupling agent (A) has a carbon number of 20 to 75.

8. The pneumatic tire according to claim 1, characterized in that the rubber component contains 15 mass % or more and less than 85 mass % of the styrene-butadiene rubber (A).

9. The pneumatic tire according to claim 1, characterized in that the rubber component contains 15 mass % or more and less than 85 mass % of the styrene-butadiene rubber (B).

10. The pneumatic tire according to claim 1, wherein the tread rubber layer further contains 1 to 50 parts by mass of a resin per 100 parts by mass of the rubber component.

11. The pneumatic tire according to claim 10, wherein the resin is a hydrogenated resin.

12. The pneumatic tire according to claim 1, wherein the PET fiber cord has a cord strength of 160 N or more.

13. The pneumatic tire according to claim 1, wherein the carcass ply has a tensile strength of more than 23,000 N / dm.

14. The pneumatic tire according to claim 1, wherein the PET fiber cord has a fineness of 1100 / 2 to 2000 / 2 dtex.

15. The pneumatic tire according to claim 1, wherein the carcass ply satisfies the following formula (1)': (A / B) / total cord fineness ≧0.45 ... (1)'.