pneumatic tires

Abstract

This suppresses the deterioration of handling stability and wet grip performance that occurs over time due to changes in the tread. [Solution] A pneumatic tire in which the tread portion has an intermediate rubber layer 2C between a cap rubber layer 2A and a base rubber layer 2B, and the cap rubber layer is formed to have a thickness of 40-95%, the intermediate rubber layer 5-30%, and the base rubber layer 1-50%, wherein the rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of filler per 100 parts by mass of rubber component, the acetone extract amount is 15% by mass or more, the toluene swelling rate is 250% or less, the hardness of the cap rubber layer and the base rubber layer is less than the hardness of the intermediate rubber layer, and the acetone extract amount AEc (mass%) of the cap rubber layer, the acetone extract amount AEb (mass%) of the base rubber layer, and the acetone extract amount AEm (mass%) of the intermediate rubber layer satisfy (Equation 1) and (Equation 2). AEb / AEc<0.9 (Formula 1) 1.0

Description

[Technical Field]

[0001] This invention relates to a pneumatic tire. [Background technology]

[0002] The hardening phenomenon in the tread of pneumatic tires (hereinafter also simply referred to as "tires") due to changes over time is a factor that leads to a deterioration in the performance of various tires, and various methods have been proposed to suppress the changes in the tread over time (for example, Patent Documents 1 and 2), but these methods are still not sufficient in terms of suppressing the deterioration of handling stability and wet grip performance. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-185520 [Patent Document 2] Patent No. 4357227 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention aims to suppress the deterioration of handling stability and wet grip performance that occurs over time due to changes in the tread portion of a pneumatic tire. [Means for solving the problem]

[0005] The present invention A pneumatic tire having a tread portion comprising a cap rubber layer constituting the tread surface and a base rubber layer disposed radially inward of the cap rubber layer, and a breaker layer disposed radially inward adjacent to the tread portion, The tread portion has an intermediate rubber layer between the cap rubber layer and the base rubber layer, and the thickness of the cap rubber layer is 40 to 95%, the thickness of the intermediate rubber layer is 5 to 30%, and the base rubber layer is 1 to 50% with respect to the total thickness of the tread portion. The rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of a filler with respect to 100 parts by mass of the rubber component, and the acetone extraction amount (mass%) determined in accordance with JIS K6229:2015 "Rubber - Method for Determination of Solvent Extracts (Quantitative)" is 15 mass% or more. The toluene swelling ratio (%) in the intermediate rubber layer is 250% or less. In the type A durometer hardness determined in accordance with JIS K 6253-3:2012 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determination of Hardness - Part 3: Durometer Hardness" of the cap rubber layer, the base rubber layer, and the intermediate rubber layer, both the type A durometer hardness of the cap rubber layer and the base rubber layer are smaller than the type A durometer hardness of the intermediate rubber layer. When the acetone extraction amount of the cap rubber layer determined in accordance with JIS K6229:2015 is AEc (mass%), the acetone extraction amount of the base rubber layer is AEb (mass%), and the acetone extraction amount of the intermediate rubber layer is AEm (mass%), it is a pneumatic tire characterized by satisfying the following (Equation 1) and (Equation 2). AEb / AEc < 0.9 (Equation 1) 1.0 < AEm / AEc < 1.4 (Equation 2)

Effect of the Invention

[0006] According to the present invention, it is possible to suppress a decrease in handling stability and wet grip performance accompanying the change over time of the tread portion of a pneumatic tire.

Brief Description of the Drawings

[0007] [Figure 1] It is a schematic cross-sectional view of a pneumatic tire according to an embodiment of the present invention. [Figure 2]It is an enlarged schematic cross-sectional view of a tread portion of a pneumatic tire according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0008] [1] Features of the Tire According to the Present Invention First, the features of the tire according to the present invention will be described.

[0009] 1. Overview The tire according to the present invention includes a tread portion having a cap rubber layer constituting a tread surface and a base rubber layer disposed radially inward of the cap rubber layer in the tire radius direction, and a breaker layer disposed radially inward of the tire in the tire radial direction adjacent to the tread portion. The tread portion has an intermediate rubber layer between the cap rubber layer and the base rubber layer. With respect to the total thickness of the tread portion, the thickness of the cap rubber layer is 40 to 95%, the thickness of the intermediate rubber layer is 5 to 30%, and the base rubber layer is 1 to 50%.

[0010] And the rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of a filler with respect to 100 parts by mass of the rubber component, and the acetone extraction amount (mass%) determined in accordance with JIS K6229:2015 "Rubber - Method for Determining Solvent Extracts (Quantitative)" is 15 mass% or more, and the toluene swelling rate (%) in the intermediate rubber layer is 250% or less.

[0011] Also, in the type A durometer hardness determined in accordance with JIS K 6253-3:2012 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Hardness - Part 3: Durometer Hardness" of the cap rubber layer, the base rubber layer, and the intermediate rubber layer, the type A durometer hardness of both the cap rubber layer and the base rubber layer is smaller than the type A durometer hardness of the intermediate rubber layer.

[0012] Furthermore, when the acetone extraction amount of the cap rubber layer is AEc (mass%), the acetone extraction amount of the base rubber layer is AEb (mass%), and the acetone extraction amount of the intermediate rubber layer is AEm (mass%), the following (Formula 1) and (Formula 2) are satisfied. AEb / AEc < 0.9 (Equation 1) 1.0 < AEm / AEc < 1.4 (Equation 2)

[0013] By having these characteristics, as described later, it is considered that it is possible to suppress the deterioration of handling stability and wet grip performance associated with the change over time of the tread portion of the tire.

[0014] 2. Mechanism of Effect Expression in the Tire According to the Present Invention Regarding the mechanism of the above-described effect expression in the tire according to the present invention, it is considered as follows.

[0015] In the present invention, as described above, an intermediate rubber layer is provided between the cap rubber layer and the base rubber layer that constitute the tread portion. By configuring it in this way, organic low-molecular compounds such as softeners present in the tread portion (especially the cap rubber layer) are suppressed from migrating to the breaker layer via the base rubber layer, and the time-dependent hardening phenomenon of the tread portion associated with the migration of these organic low-molecular compounds can be suppressed. Therefore, it is considered that it is possible to suppress the deterioration of handling stability and wet grip performance associated with the change over time of the tread portion.

[0016] And in the present invention, the suppression of the migration of organic low-molecular compounds in such a tread portion is manifested because each rubber layer constituting the tread portion has a specific ratio of thickness. Specifically, with respect to the total thickness of the tread portion, the cap rubber layer is formed to be 40 to 95%, the intermediate rubber layer is 5 to 30%, and the base rubber layer is 1 to 50%. At the same time, the intermediate rubber layer contains a filler of 80 parts by mass or more with respect to 100 parts by mass of the rubber component, and is formed using a rubber composition having an acetone extraction amount (mass%) of 15 mass% or more determined in accordance with JIS K6229:2015 "Rubber - Method for Determination of Solvent Extracts (Quantitative)". Furthermore, the toluene swelling rate (%) in the intermediate rubber layer is controlled to be 250% or less and is disposed between the cap rubber layer and the base rubber layer.

[0017] As one of the factors causing the tread portion of a tire to change over time, organic low-molecular compounds such as softeners inside the tread portion migrate from the surface side of the tread portion with a high concentration to the inner side in the tire radial direction with a low concentration due to their concentration gradient, and the content of softeners etc. in the cap rubber layer decreases. The content of such organic low-molecular compounds can be grasped by the acetone extraction amount (AE amount: Acetone Extract) (mass %) determined in accordance with JIS K6229:2015 "Methods for Determination of Rubber - Solvent Extracts (Quantitative)".

[0018] In the present invention, regarding this acetone extraction amount, when the acetone extraction amount of the cap rubber layer is AEc (mass %), the acetone extraction amount of the base rubber layer is AEb (mass %), and the acetone extraction amount of the intermediate rubber layer is AEm (mass %), it is controlled such that (AEb / AEc) is less than 0.9 (AEb / AEc < 0.9) and (AEm / AEc) is more than 1.0 and less than 1.4 (1.0 < AEm / AEc < 1.4).

[0019] Thereby, the diffusion of softeners etc. from the cap rubber layer to the base rubber layer is appropriately controlled, and the change over time of the tread portion is appropriately controlled. Therefore, it is considered that the deterioration of handling stability and wet grip performance accompanying the change over time can be suppressed. In the present invention, the specific acetone extraction amount of the intermediate rubber layer is 15 mass % or more.

[0020] And in the present invention, the toluene swelling ratio (%) in the intermediate rubber layer is controlled to be 250% or less. This toluene swelling ratio can also be considered as an index indicating the degree of vulcanization of the rubber. By immersing the cut test piece in toluene at room temperature for a certain period of time to swell it and obtaining the change rate of the mass of the test piece before and after swelling [(rubber mass after swelling / rubber mass before swelling) × 100], and appropriately controlling it to be 250% or less, it is considered that the deterioration of wet grip performance accompanying the change over time can be suppressed under a sufficient vulcanized state.

[0021] Furthermore, in the present invention, the Type A durometer hardness of the cap rubber layer, base rubber layer, and intermediate rubber layer, as determined in accordance with JIS K 6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness", is set so that the Type A durometer hardness of both the cap rubber layer and the base rubber layer is lower than the Type A durometer hardness of the intermediate rubber layer. This is thought to reduce the impact on the surface of the tread (cap rubber layer) during driving in the intermediate rubber layer, thereby suppressing the decrease in handling stability due to changes over time.

[0022] In addition, the aforementioned JIS K6229:2015 "Method for determining (quantification) of rubber-solvent extracts" specifies two methods, Method A and Method B. However, in this invention, it refers to the mass % obtained by adopting Method A.

[0023] Furthermore, the organic low-molecular-weight compounds that are acetone extract components include, in addition to softeners, antioxidants, vulcanizing agents, vulcanization accelerators, foaming agents, coupling agents, stabilizers, emulsifiers, and activators, as well as rubber monomers and oligomers. Among these, softeners are considered to have a particularly important influence on the hardening phenomenon of the tread.

[0024] [2] Embodiment The present invention will be described in detail below based on embodiments.

[0025] 1. Pneumatic tires Figure 1 is a schematic cross-sectional view of a tire according to this embodiment. In Figure 1, 1 is the tire, 2 is the tread portion, 3 is the sidewall portion, 4 is the bead portion, 6 is the carcass, and 7 is the breaker layer. The tread portion 2 is constructed by laminating a cap rubber layer 2A, an intermediate rubber layer 2C, and a base rubber layer 2B in order from the outer radial side of the tire. The bead portion 4 includes a bead core 5 and a bead apex 8.

[0026] As shown in Fig. 1, the tire 1 according to this embodiment has a tread portion 2, a sidewall portion 3, and a bead portion 4. A bead core 5 is embedded in the bead portion 4. And extending from one bead portion 4 to the other bead portion (not shown), there is a carcass 6 that folds back and locks both ends with respect to the bead core 5, and a breaker layer 7 composed of two plies is disposed outside the crown portion of the carcass 6. Further, in the region surrounded by the carcass 6 and its folded-back portion, a bead apex 8 that extends in the sidewall direction from the upper end of the bead core 5 is disposed.

[0027] Fig. 2 is an enlarged schematic cross-sectional view of the tread portion 2 of the tire shown in Fig. 1. As shown in Fig. 2, the tread portion 2 (total thickness 10) includes a cap rubber layer 2A (thickness 11) on the ground contact side and a base rubber layer 2B (thickness 12) on the side adjacent to the breaker layer 7 on the carcass 6, and has an intermediate rubber layer 2C (thickness 13) between the cap rubber layer 2A and the base rubber layer 2B.

[0028] (1) Structure of the tread portion As described above, the tread portion 2 includes a cap rubber layer 2A and a base rubber layer 2B, and has an intermediate rubber layer 2C between the cap rubber layer 2A and the base rubber layer 2B.

[0029] Since the cap rubber layer 2A forms the ground contact surface, it is desirable that it has excellent abrasion resistance and grip force. On the other hand, the base rubber layer 2B has a function of reducing heat generation and energy loss caused by repeated bending distortion that occurs with the rotation of the tire.

[0030] And as described above, the intermediate rubber layer 2C contains a filler amount of a certain amount or more and an acetone extraction amount of a certain amount or more, and the acetone extraction amount is controlled to be (1.0 < AEm / AEc), and has organic low-molecular compounds at a higher concentration than the cap rubber layer 2A. Therefore, due to the action of this concentration gradient, it is considered that the transfer of organic low-molecular compounds from the cap rubber layer 2A to the base rubber layer can be suppressed, and the curing phenomenon of the tread portion over time can be suppressed.

[0031] (2) Thickness of the tread As shown in Figure 2, the tread portion, avoiding the area where the tire grooves are provided, has a total thickness of 10, which includes the thickness of the cap rubber layer 11, the thickness of the intermediate rubber layer 13, and the thickness of the base rubber layer 12, based on the thickness of the tread portion at the center of the tire.

[0032] As described above, the thickness of each of these layers is such that the cap rubber layer 11 accounts for 40-95% of the total tread thickness 10, the intermediate rubber layer 13 accounts for 5-30%, and the base rubber layer 12 accounts for 1-50%.

[0033] If the thickness 11 of the cap rubber layer is less than 40% of the total thickness 10 of the tread section, the cap rubber layer itself will disappear prematurely due to wear from driving, which may shorten the period during which tire performance such as grip can be maintained. On the other hand, if the thickness 11 of the cap rubber layer is more than 80% of the total thickness 10 of the tread section, the thickness of the intermediate rubber layer will become relatively too thin, which may prevent the intermediate rubber layer from adequately suppressing the migration of low-molecular-weight organic compounds.

[0034] Furthermore, if the thickness 13 of the intermediate rubber layer is less than 5% of the total thickness 10 of the tread section, there is a risk that the migration of organic low-molecular-weight compounds will not be sufficiently suppressed. On the other hand, if the thickness 13 of the intermediate rubber layer is more than 30% of the total thickness 10 of the tread section, there is a risk that it will adversely affect the handling stability of the tire, and the migration of organic low-molecular-weight compounds to the base rubber layer will increase, and the amount of organic low-molecular-weight compounds that migrate from the base rubber layer to internal tire materials such as the breaker layer will increase, which may reduce the durability of the tire.

[0035] Also, when the thickness 12 of the base rubber layer is less than 1% of the total thickness 10 of the tread portion, the migration of the organic low-molecular compound into the base rubber layer cannot be suppressed, and the durability of the tire may decrease. On the other hand, when the thickness 12 of the base rubber layer exceeds 50% of the total thickness 10 of the tread portion, the thickness of the cap rubber layer becomes relatively too thin, and thus the tire performance such as grip force may not be maintained.

[0036] In addition, the thickness of the cap rubber layer is more preferably 45 to 90% of the total thickness of the tread portion, and further preferably 50 to 85%. And the thickness of the intermediate rubber layer is more preferably 10 to 25% of the total thickness of the tread portion, and further preferably 15 to 20%. Also, the thickness of the base rubber layer is more preferably 10 to 40% of the total thickness of the tread portion, and further preferably 20 to 30%.

[0037] (3) Acetone extraction amount As described above, since the content of the organic low-molecular compound can be grasped by the acetone extraction amount, it can be considered that the higher the acetone extraction amount, the higher the concentration of the organic low-molecular compound contained in each layer. This acetone extraction amount can be considered to be not only a mere index of the organic low-molecular compound concentration, but also an optimal index as a concentration gradient that rules whether the organic low-molecular compound migrates between layers. That is, in these organic low-molecular compounds, it is considered that there is some correlation between the extraction property by acetone in the rubber composition and whether or not it migrates between layers.

[0038] In the present invention, as described above, when the acetone extraction amount of the cap rubber layer is AEc (mass%), the acetone extraction amount of the base rubber layer is AEb (mass%), and the acetone extraction amount of the intermediate rubber layer is AEm (mass%), it is controlled so that (AEb / AEc) is less than 0.9 (AEb / AEc < 0.9) and (AEm / AEc) is more than 1.0 and less than 1.4 (1.0 < AEm / AEc < 1.4).

[0039] If the (AEb / AEc) ratio is 0.9 or higher, it means that the cap rubber layer does not contain enough oil, which may reduce wet grip. In addition, because the base rubber layer contains more oil, the amount of organic low-molecular-weight compounds that migrate from the base rubber layer to internal tire materials such as the breaker layer increases, which may reduce the durability of the tire in terms of its shape.

[0040] Furthermore, (AEb / AEc) is more preferably less than 0.8, and even more preferably less than 0.7. On the other hand, the lower limit is preferably greater than 0.45, and more preferably greater than 0.55.

[0041] Furthermore, if (AEm / AEc) is 1.4 or higher, it means that the cap rubber layer does not contain enough oil, which may reduce wet grip. Also, because the intermediate rubber layer contains more oil, the amount of organic low-molecular-weight compounds migrated from the base rubber layer to the internal tire materials such as the breaker layer increases, which may reduce the tire's durability in terms of shape. On the other hand, if it is 1.0 or lower, the amount of oil contained in the cap rubber layer is insufficient, which may increase the amount of organic low-molecular-weight compounds migrated from the cap rubber layer to the base rubber layer, which may reduce the tire's durability in terms of shape.

[0042] (AEm / AEc) is more preferably less than 1.35, and even more preferably less than 1.30. On the other hand, the lower limit is preferably greater than 1.10, and more preferably greater than 1.15.

[0043] Furthermore, in this invention, the amount of acetone extracted from the intermediate rubber layer is 15% by mass or more, as described above. If the amount of acetone extracted is less than 15% by mass, it may lead to a decrease in the tire's handling stability and wet grip performance.

[0044] The amount of acetone extracted from the intermediate rubber layer is more preferably 17% by mass or more, and even more preferably 19% by mass or more. On the other hand, the upper limit is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0045] In the present invention, the amount of acetone extracted from the cap rubber layer is preferably 10 to 20% by mass, and the amount of acetone extracted from the base rubber layer is preferably 10 to 30% by mass.

[0046] By appropriately controlling (AEb / AEc) and (AEm / AEc) under the acetone extraction amounts in each rubber layer as described above, it is possible to suppress the hardening phenomenon of the tread over time, and thereby suppress the deterioration of handling stability and wet grip performance associated with changes in the tread over time.

[0047] (4) Filler content of the intermediate rubber layer In the present invention, the rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of filler per 100 parts by mass of rubber component, as described above. If it is less than 80 parts by mass, it may lead to a decrease in wet grip performance. It is more preferable to have 90 parts by mass or more, and even more preferable to have 100 parts by mass or more. On the other hand, as an upper limit, for example, it is preferable to have 120 parts by mass or less, more preferably 115 parts by mass or less, and even more preferable to have 110 parts by mass or less.

[0048] (5) Toluene swelling rate of the intermediate rubber layer In the present invention, as described above, the toluene swelling rate (%) of the intermediate rubber layer is controlled to 250% or less, more preferably 245% or less, and even more preferably 240% or less.

[0049] (6) Filler content of the intermediate rubber layer / Thickness of the breaker layer In the present invention, the ratio of the filler content (parts by mass) per 100 parts by mass of rubber component in the intermediate rubber layer to the thickness (mm) of the breaker layer (filler content in the intermediate rubber layer / thickness of the breaker layer) is preferably 40 or more. More preferably 45 or more, and even more preferably 50 or more. On the other hand, the upper limit is preferably 60 or less, and more preferably 55 or less. If the ratio (filler content in the intermediate rubber layer / thickness of the breaker layer) is less than 40, the amount of organic low molecular weight compounds migrated through the intermediate rubber layer and the base rubber layer increases, which may reduce the durability of the tire in terms of shape.

[0050] (7) Organic low molecular compounds In the present invention, the following are examples of the aforementioned organic low molecular weight compounds.

[0051] (i) Softener Examples of softening agents include petroleum-based softening agents such as process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, and petrolatum; fatty oil-based softening agents such as castor oil, linseed oil, rapeseed oil, and coconut oil; tall oil; subsulfate; waxes such as beeswax, carnauba wax, and lanolin; and linoleic acid, palmitic acid, stearic acid, and lauric acid.

[0052] Specific product names include Trilene CP40 (Type B viscosity (100℃) 4600cP), Trilene CP80 (Type B viscosity (100℃) 59000cP), Trilene 66 (Type B viscosity (100℃) 110000cP), and Trilene 67 (Type B viscosity (100℃) 94000cP) from Shiraishi Calcium Co., Ltd., as well as Samper 2280 (Paraffin oil: Type B viscosity (100℃) 28cP) from Nippon Sun Oil Co., Ltd., and Lucant HC3000X (Ethylene-α-olefin oil: Type B viscosity (100℃) 2900cP) from Mitsui Petrochemical Co., Ltd.

[0053] (b) Anti-aging agents Examples of anti-aging agents (degradation inhibitors) include amines, phenols, imidazoles, metal carbamates, and waxes.

[0054] (h) vulcanizing agent Examples of vulcanizing agents include organic peroxides or sulfur-based vulcanizing agents, such as benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexine-3 or 1,3-bis(t-butylperoxypropyl)benzene, di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylsiloxane, n-butyl-4,4-di-t-butylperoxyvalerate, and morpholine disulfide.

[0055] (ii) vulcanization accelerator Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators.

[0056] Examples of sulfenamide compounds include CBS (N-cyclohexyl-2-benzothiadylsulfenamide), TBBS (N-tert-butyl-2-benzothiadylsulfenamide), N,N-dicyclohexyl-2-benzothiadylsulfenamide, N-oxydiethylene-2-benzothiadylsulfenamide, and N,N-diisopropyl-2-benzothiazolesulfenamide.

[0057] Examples of thiazole derivatives include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiadyl disulfide), sodium salt, zinc salt, copper salt, cyclohexylamine salt of 2-mercaptobenzothiazole, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole.

[0058] Examples of thiuram-based compounds include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram hexasulfide, tetrabutylthiuram disulfide, and pentamethylenethiuram tetrasulfide.

[0059] Examples of thiourea compounds include thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, and diortotolylthiourea. Examples of guanidine compounds include diphenylguanidine, diortotolylguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate.

[0060] Examples of dithiocarbamate derivatives include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate, complex salts of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl)isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, and cadmium diamyldithiocarbamate.

[0061] Examples of aldehyde-amine or aldehyde-ammonia systems include acetaldehyde-aniline reaction products, butyraldehyde-aniline condensates, hexamethylenetetramine, and acetaldehyde-ammonia reaction products.

[0062] Examples of imidazoline derivatives include 2-mercaptoimidazoline. Examples of xanthate derivatives include zinc dibutylxanthonate.

[0063] (e) Foaming agent Examples of foaming agents include azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, hydrazodicarbonamide, and p-toluenesulfonylacetone hydrazone.

[0064] (H) Coupling agent Examples of coupling agents include aluminate-based coupling agents, silane-based coupling agents, and titanium-based coupling agents.

[0065] Examples of aluminate coupling agents include acetalkoxyaluminum diisopropylate. Examples of silane coupling agents include vinyltrichlorosilane, vinyltris(2-methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

[0066] Examples of titanium-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctys(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl) phosphite titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylate isostearoyl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, and isopropyl tri(N-aminoethyl-aminoethyl) titanate.

[0067] (t) Activating agent Examples of activators include diethylene glycol and polyethylene glycol.

[0068] (8) Hardness of each rubber layer In the present invention, as described above, the hardness (Type A durometer hardness) of the cap rubber layer and the base rubber layer is made lower than the hardness of the intermediate rubber layer, thereby achieving improved handling stability and, furthermore, improved ride comfort.

[0069] The specific hardness of the intermediate rubber layer is preferably 45 to 80 degrees on the Type A durometer hardness scale. A hardness of less than 45 degrees may impair handling stability, while a hardness of more than 80 degrees may lead to a decrease in ride comfort. A hardness of 55 to 70 degrees is more preferable, and 60 to 65 degrees is even preferable.

[0070] Furthermore, the specific hardness of the cap rubber layer is preferably 55 to 65 degrees on the Type A durometer hardness scale. A hardness below 55 degrees may lead to a decrease in durability. On the other hand, a hardness above 65 degrees may lead to a decrease in ride comfort performance.

[0071] Furthermore, the specific hardness of the base rubber layer is preferably 60 to 70 degrees on the Type A durometer hardness scale. A hardness below 60 degrees may lead to a decrease in durability. On the other hand, a hardness above 70 degrees may lead to a decrease in ride comfort performance.

[0072] 2. Rubber composition constituting each rubber layer In the present invention, the rubber compositions constituting each rubber layer can be manufactured by kneading conventionally known materials in a formulation according to the properties required for each rubber layer. For example, the cap rubber layer, being a rubber layer constituting the contact surface, is a rubber composition with excellent abrasion resistance and grip. The base rubber layer is a rubber composition that can reduce heat generation and energy loss resulting from repeated bending strain associated with tire rotation. The intermediate rubber layer is a rubber composition that can prevent the migration of low-molecular-weight organic compounds and suppress the hardening phenomenon of the tread over time.

[0073] Examples of conventionally known materials include rubber components, carbon black, white fillers, vulcanization aids, plasticizers, scorch inhibitors, as well as the aforementioned softeners, antioxidants, vulcanizing agents, vulcanization accelerators, foaming agents, coupling agents, stabilizers, emulsifiers, and activators.

[0074] Regarding compounding agents such as softeners, while organic low-molecular-weight compounds were given as examples above, the compounding agents used in the rubber composition forming each rubber layer are not limited to such organic low-molecular-weight compounds. For example, inorganic compounds such as sulfur used as a vulcanizing agent, as well as organic polymer compounds, may also be included.

[0075] (i) Rubber components Examples of rubber components include natural rubber (NR), styrene-butadiene rubber (SBR), solution-polymerized SBR, emulsion-polymerized SBR, polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), styrene-isoprene rubber, butadiene-isoprene rubber, solution-polymerized styrene-butadiene-isoprene rubber, emulsion-polymerized styrene-acrylonitrile-butadiene rubber, etc. These can be used individually or in combination of two or more. In particular, rubber components commonly used for tire treads, such as natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene rubber, or solution-polymerized SBR, can be suitably used.

[0076] (b) Fillers Examples of fillers include carbon black and white fillers.

[0077] Examples of carbon black include various grades such as FEF, HAF, ISAF, and SAF, which can be used individually or in combination of two or more types.

[0078] Examples of white fillers include silica, clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, and titanium dioxide, which can be used individually or in combination of two or more.

[0079] (h) vulcanization aid Examples of vulcanization aids include stearic acid and zinc oxide. Such vulcanization aids can be added in an amount of 1 to 10 parts by mass per 100 parts by mass of the rubber component.

[0080] (ii) Plasticizers Examples of plasticizers include DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (diisodecyl phthalate), BBP (butyl benzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), anhydrous hydrophthalates, TCP (tricresyl phosphate), TEP (triethyl phosphate), TBP (tributyl phosphate), TOP (trioctyl phosphate), TCEP (tri(chloroethyl) phosphate), TDCPP (trisdichloropropyl phosphate), and TBXP (tributoxyethyl phosphate). Examples include TCPP (tris(β-chloropropyl) phosphate), TPP (triphenyl phosphate), octyldiphenyl phosphate, phosphoric acid (trisisopropylphenyl), DOA (dioctyl adipate), DINA (diisononyl adipate), DIDA (diisodecyl adipate), D610A (dialkyl 610 adipate), BXA (dibutyl diglycol adipate), DOZ (di-2-ethylhexyl azelaate), DBS (dibutyl sebacate), DOS (dioctyl sebacate), acetyltriethyl citrate, acetyltributyl citrate, DBM (dibutyl maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate), etc.

[0081] (Ho) Scorch prevention agent Scorch inhibitors, also known as anti-scorch agents, are chemicals that prevent or delay scorching. Examples include organic acids such as phthalic anhydride, salicylic acid, and benzoic acid, nitroso compounds such as N-nitrosodiphenylamine, and N-cyclohexylthiophthalimide.

[0082] (h) Use of sustainable materials In light of the strong demand for environmental protection in recent years, it is preferable to replace each material with sustainable materials such as those shown below when manufacturing each rubber composition.

[0083] (i) Rubber materials For example, the raw materials (monomers) for synthetic rubbers such as SBR and BR can be recycled from rubber products such as tires or non-rubber products such as polystyrene, instead of being derived from petroleum.

[0084] The monomers obtained by recycling (recycled monomers) are not particularly limited, but include recycled butadiene and recycled aromatic vinyl. Examples of butadiene include 1,2-butadiene and 1,3-butadiene, and examples of aromatic vinyl include styrene, although these are not particularly limited. In particular, it is preferable to use recycled butadiene and / or recycled styrene as raw materials.

[0085] The method for producing recycled monomer is not particularly limited, and for example, it can be synthesized from recycled naphtha obtained by decomposing rubber products such as tires. Furthermore, the method for producing recycled naphtha is not particularly limited, and for example, rubber products such as tires may be decomposed under high temperature and pressure, decomposed by microwaves, or extracted after mechanical grinding.

[0086] Furthermore, the raw materials (monomers) for synthetic rubbers such as SBR and BR may be derived from biomass. Biomass-derived monomers (biomass monomers) are not particularly limited and include biomass-derived butadiene and biomass-derived aromatic vinyls. Examples of butadiene include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyls are not particularly limited but include styrene. In addition, the method for producing biomass monomers is not particularly limited and includes, for example, biological and / or chemical and / or physical conversion of plants and animals. Typical biological conversions include fermentation by microorganisms, while chemical and / or physical conversions include those by catalysts, high heat, high pressure, electromagnetic waves, critical liquids, and combinations thereof. Examples of biomass sources for these monomers include sugars, wood, plant residues after obtaining useful components, plant-derived ethanol, and biomass naphtha.

[0087] The polymer synthesized from biomass monomer components (biomass polymer) is not particularly limited, and examples include polybutadiene rubber synthesized from biomass-derived butadiene, and aromatic vinyl / butadiene copolymers synthesized from biomass-derived butadiene and / or biomass-derived aromatic vinyl. Examples of the aromatic vinyl / butadiene copolymer include styrene-butadiene rubber synthesized from biomass-derived butadiene and / or biomass-derived styrene.

[0088] Furthermore, whether or not the polymer raw materials are biomass-derived can be determined by measuring pMC (percent Modern Carbon) in accordance with ASTMD6866-10.

[0089] pMC stands for Modern Standard Reference Carbon. 14 Sample relative to C concentration 14 This is the ratio of C concentrations, and this value is used as an indicator of the biomass ratio of the compound (rubber). The significance of this value is described below.

[0090] One mole (6.02×10 23 atoms) of carbon atoms contains approximately 6.02×10 11 atoms of 14 C, which is about one trillionth of ordinary carbon atoms. 14 C is called a radioactive isotope, and its half-life is 5730 years, decreasing regularly. It takes 226,000 years for all of them to decay. Therefore, after carbon dioxide in the atmosphere is taken up and fixed by plants, etc., in fossil fuels such as coal, oil, and natural gas, where it is considered that more than 226,000 years have passed, all of the 14 C element has decayed. Thus, in the 21st century, at present, fossil fuels such as coal, oil, and natural gas do not contain 14 any 14 C element. Therefore, chemical substances produced from these fossil fuels also do not contain

[0091] On the other hand, 14 C is constantly generated by nuclear reactions of cosmic rays in the atmosphere, and the decrease due to radioactive decay is balanced. In the earth's atmospheric environment, 14 the amount of 14 C is constant. Therefore, the -12 C concentration of substances derived from biomass resources that are circulating in the current environment is about 1×10

[0092] This 14 C is generally measured as follows. Using accelerator mass spectrometry based on a tandem accelerator, 13 the 13 C concentration ( 12 C / 14 the 14 C concentration ( 12 C / 14As a modern standard reference for the concentration of C, the amount of cyclic carbon in nature as of 1950 14 The C concentration will be used. The specific standard material will be the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific radioactivity of carbon in this oxalic acid (per gram of carbon) will be used. 14 The radioactivity intensity of C is separated by carbon isotope, 13 The standard value is obtained by correcting C to a constant value and applying decay correction from 1950 AD to the measurement date. 14 This value is used as the C concentration value (100%). The ratio of this value to the value of the sample actually measured is the pMC value.

[0093] Therefore, if rubber is made from 100% biomass (natural) materials, it will have a value of approximately 110 pMC, although there are regional differences (currently, under normal conditions, it is often not 100). On the other hand, regarding chemical substances derived from fossil fuels such as petroleum, 14 When the C concentration is measured, it will show approximately 0 pMC (for example, 0.3 pMC). This value corresponds to a biomass ratio of 0% as mentioned above.

[0094] Based on the above, using materials such as rubber with a high pMC value, that is, materials such as rubber with a high biomass ratio, in rubber compositions is preferable from an environmental protection standpoint.

[0095] (ii) Silica The silica can be derived from biological sources such as rice husks (for example, silica made from biomass materials such as rice husks), or it can be recycled silica from products containing silica.

[0096] Silica derived from biomass materials can be obtained, for example, by extracting silicates from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then using these silicates to react with sulfuric acid in the same way as conventional wet silica, the precipitate of silicon dioxide is filtered, washed with water, dried, and pulverized.

[0097] The silica recycled from silica-containing products can be, for example, silica recovered from products containing silica such as semiconductors and other electronic components, tires, desiccants, and diatomaceous earth and other filter materials. The recovery method is not particularly limited and can include thermal decomposition and decomposition by electromagnetic waves. Among these, silica recovered from semiconductors and other electronic components or tires is preferred.

[0098] When silica crystallizes, it becomes insoluble in water, and its component, silicic acid, cannot be utilized. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash can be suppressed (see Japanese Patent Publication No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol.6, pp.216-222, etc.).

[0099] Amorphous silica extracted from rice husks can be commercially available from companies such as Wilmar.

[0100] These silicas may be used individually or in combination of two or more types. Using sustainable silica such as biomass silica or recycled silica is preferable from an environmental protection standpoint.

[0101] (iii) Carbon Black The raw materials for carbon black may be biomass materials such as lignin and vegetable oil, or pyrolysis oil obtained by thermally decomposing rubber products containing carbon black, such as waste tires (recycled carbon black). Using these sustainable carbon blacks is preferable from an environmental protection standpoint.

[0102] (iv) Moisturizer The softener may be derived from biomass, or from naphtha recycled from rubber or non-rubber products. Alternatively, low molecular weight hydrocarbon components obtained by thermal decomposition and extraction of used tires or products containing various components may be used as a softener. Among these, softeners derived from biomass or recycled materials are preferred as sustainable softeners.

[0103] In addition, in the rubber composition, among the materials described above, the various materials containing carbon atoms (for example, rubber, oil, resin, vulcanization accelerator, antioxidant, surfactant, etc.) may be derived from carbon dioxide in the atmosphere. As a method for obtaining the compound of the present invention from carbon dioxide, carbon dioxide may be converted directly, or methane obtained through a methanation process in which methane is synthesized from carbon dioxide may be converted.

[0104] 3. Tire manufacturing The tire according to this embodiment can be manufactured by conventional methods using the above-mentioned materials.

[0105] (1) Preparation of rubber composition Each rubber composition is produced by a general method, for example, a manufacturing method that includes a base mixing step of mixing a rubber component and a filler, and a finish mixing step of mixing the mixture obtained in the base mixing step with a crosslinking agent.

[0106] Mixing can be carried out using known (closed) mixers such as Banbury mixers, kneaders, and open roll mixers.

[0107] The mixing temperature in the base mixing process is, for example, more than 50°C and less than 200°C, and the mixing time is, for example, more than 30 seconds and less than 30 minutes. In the base mixing process, in addition to the above components, compounding agents conventionally used in the rubber industry, such as softeners such as oils, zinc oxide, antioxidants, waxes, and vulcanization accelerators, may be added and mixed as needed.

[0108] In the final mixing step, the mixture obtained in the base mixing step and the crosslinking agent are mixed together. The mixing temperature in the final mixing step is, for example, above room temperature but below 80°C, and the mixing time is, for example, more than 1 minute but less than 15 minutes. In the final mixing step, in addition to the above components, vulcanization accelerators, zinc oxide, etc., may be added and mixed as needed.

[0109] The rubber compositions obtained in the final mixing process are extruded into predetermined shapes and laminated to form the tread section.

[0110] (2) Tire manufacturing Next, an inner liner portion, which is a component to ensure the airtightness of the tire, a carcass portion, which is a component to withstand the load, impact, and air pressure of the tire, and a belt portion, which is a component to tighten the carcass portion and increase the rigidity of the tread are wound onto the molding drum. The ends of the carcass ply are fixed to both sides of the edge, and a bead portion, which is a component to fix the tire to the rim, is placed thereto. After forming it into a toroid shape, the tread portion is attached to the center of the outer circumference, and the sidewall is attached to the radially outer side to form the side portion, thereby creating an unvulcanized tire.

[0111] Subsequently, the unvulcanized tire produced as described above is heated and pressurized in a vulcanizing machine to obtain a tire. The vulcanization process can be carried out by applying known vulcanization methods. The vulcanization temperature is, for example, greater than 120°C and less than 200°C, and the vulcanization time is, for example, greater than 5 minutes and less than 15 minutes.

[0112] As mentioned earlier, the resulting tire can suppress the hardening phenomenon of the tread over time, thereby suppressing the deterioration of handling stability and wet grip performance that occurs due to changes in the tread over time. [Examples]

[0113] The following are examples (examples) that are considered preferable for implementation, but the scope of the present invention is not limited to these examples.

[0114] We examined tires made from treads molded from the various compound materials listed below, as well as other rubber components, and the results calculated based on the evaluation methods described later regarding handling stability and wet grip performance are shown in Table 2.

[0115] 1. Manufacturing of rubber compositions First, the rubber compositions for each rubber layer that makes up the tread are manufactured.

[0116] (1) Compounding materials (a) Rubber component (i) NR (Natural Rubber): RSS#3 (b) BR (Butadiene rubber): Nipol BR1220 manufactured by Nippon Zeon Co., Ltd. (h) SBR (Styrene-Butadiene Rubber): SBR1502 manufactured by ENEOS Material

[0117] (b) Compounding materials other than rubber components (i) Carbon Black: Dia Black N220 manufactured by Mitsubishi Chemical Corporation (b) Silica: UltraSil VN3 manufactured by Evonik Industries (h) Coupling agent: Si69 manufactured by Evonik Industries (ii) Softener: PS-32 manufactured by Idemitsu Kosan Co., Ltd. (H) Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (h) Anti-aging agent: Nocrack 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (T) Stearic acid: NOF Corporation's bead stearic acid "Tsubaki" (C) Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. (R) Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. (Nu) Vulcanization accelerator 1: Noxellar CZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (L) Vulcanization accelerator 2: Noxellar D manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0118] 2. Tire molding According to the formulations for the intermediate rubber layer, cap rubber layer, and base rubber layer shown in Table 1, the materials other than sulfur and vulcanization accelerator were kneaded in a Banbury mixer at 150°C for 5 minutes to obtain the kneaded mixture. The amounts of each ingredient are in parts by mass.

[0119] Next, sulfur and a vulcanization accelerator are added to the mixture, and it is kneaded using an open roll at 80°C for 5 minutes to obtain each rubber composition.

[0120] [Table 1]

[0121] Next, each tread section is manufactured by extruding and laminating each rubber composition so that the rubber layers of each compound shown in Table 2 have the thickness ratios shown in Table 2.

[0122] Subsequently, the tire components are bonded together to form an unvulcanized tire, which is then press-vulcanized for 10 minutes under conditions of 170°C to produce the test tires for Examples 1-5 and Comparative Examples 1-4 shown in Table 2 (tire size: 195 / 65R15, total tread thickness: 10 mm, breaker layer thickness: 2 mm).

[0123] 3. Measurement of acetone extraction amount for each rubber layer Next, for each test tire, the amount of acetone extracted from each rubber layer (mass%) is measured in accordance with JIS K6229:2015 "Method for determining solvent extracts of rubber (quantitative)".

[0124] Specifically, test pieces cut from each rubber layer of each test tire are immersed in acetone for 24 hours, and then the mass of each test piece (before and after the initial immersion) is measured and calculated using the following formula. Acetone extraction amount (mass%) ={(Mass before extraction - Mass after extraction) / (Mass before extraction)}×100

[0125] 4. Calculation of parameters Next, for each test tire, we calculate (filler content in the intermediate rubber layer / thickness of the breaker layer), (AEb / AEc), and (AEm / AEc).

[0126] 5. Performance evaluation test Next, the following evaluation tests will be performed on each of the test tires.

[0127] (1) Evaluation of changes in tread surface hardness over time First, the Type A durometer hardness (H0) of the surface of each test tire after manufacturing (new) is determined as the hardness of the tread surface before deterioration, in accordance with JIS K 6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness".

[0128] Next, each new test tire was left to stand in an 80°C oven for two weeks, after which the cap rubber layer was shaved off by 2 mm to create a degraded test tire. Then, the Type A durometer hardness (H1) of the tread surface was determined in the same manner as the hardness of the degraded tread surface.

[0129] Next, the change in tread surface hardness before and after deterioration is determined based on the formula (H1 / H0) × 100.

[0130] Next, using the hardness change in Comparative Example 1 as the "evaluation standard," the hardness change of each test tire is indexed based on the following formula to evaluate the change in hardness over time. A larger numerical value indicates a smaller change in hardness over time, and that the tire's performance is maintained at a high level. Evaluation of changes in hardness over time =[(Hardness change of Comparative Example 1) / (Hardness change of the test tire)]×100

[0131] (2) Evaluation of handling stability Each degraded test tire was mounted on a domestically produced FR car with a displacement of 2000cc, and the car was driven at speeds of 60-120 km / h. The driver then subjectively evaluated the handling stability. The evaluation was expressed as an index, with the handling stability of the pneumatic tire in Comparative Example 1 being rated at 10, and a higher index indicating superior handling stability.

[0132] (3) Evaluation of the maintenance of wet grip performance Each new test tire, as well as each deteriorated test tire, will be mounted on a 2000cc domestic FR vehicle. The brakes will be applied at a maximum speed of 100 km / h on a wet asphalt road surface with a 1 mm water film, and the braking distance from that point (wet braking distance) will be measured.

[0133] Next, the percentage change in braking distance before and after deterioration of each test tire is calculated based on the following formula, and this is used as the wet grip performance maintenance index. A higher value indicates that the wet grip performance is maintained. (Wet grip performance maintenance index) =[(Braking distance of new tires) / (Braking distance of deteriorated tires)]×100

[0134] [Table 2]

[0135] Although the present invention has been described above based on embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equivalent scope as the present invention.

[0136] The present invention (1) is, A pneumatic tire having a tread portion comprising a cap rubber layer constituting the tread surface and a base rubber layer disposed radially inward of the cap rubber layer, and a breaker layer disposed radially inward adjacent to the tread portion, The tread portion has an intermediate rubber layer between the cap rubber layer and the base rubber layer, and the thickness of the cap rubber layer is 40 to 95%, the thickness of the intermediate rubber layer is 5 to 30%, and the base rubber layer is 1 to 50% with respect to the total thickness of the tread portion. The rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of a filler with respect to 100 parts by mass of the rubber component, and the acetone extraction amount (mass%) determined in accordance with JIS K6229:2015 "Rubber - Method for determining solvent extract (quantitative)" is 15 mass% or more. The toluene swelling ratio (%) in the intermediate rubber layer is 250% or less. In the type A durometer hardness determined in accordance with JIS K 6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness" for the cap rubber layer, the base rubber layer, and the intermediate rubber layer, the type A durometer hardness of both the cap rubber layer and the base rubber layer is smaller than the type A durometer hardness of the intermediate rubber layer. When the acetone extraction amount of the cap rubber layer determined in accordance with JIS K6229:2015 is AEc (mass%), the acetone extraction amount of the base rubber layer is AEb (mass%), and the acetone extraction amount of the intermediate rubber layer is AEm (mass%), an air-filled tire is characterized by satisfying the following (Formula 1) and (Formula 2). AEb / AEc < 0.9 (Formula 1) 1.0 < AEm / AEc < 1.4 (Formula 2)

[0137] The present invention (2) In the tread portion, the thickness of the cap rubber layer is 45 to 90% with respect to the total thickness of the tread portion, and it is the air-filled tire according to the present invention (1).

[0138] The present invention (3) In the tread portion, the thickness of the intermediate rubber layer is 10 to 25% with respect to the total thickness of the tread portion, and it is the air-filled tire according to the present invention (1) or (2).

[0139] The present invention (4) is, The tread portion is characterized in that the thickness of the base rubber layer is 10 to 40% of the total thickness of the tread portion, and is a pneumatic tire in any combination with any of the present invention (1) to (3).

[0140] The present invention (5) is, The above (AEb / AEc) is characterized in that it is less than 0.8, and is a pneumatic tire in any combination with any of the present invention (1) to (4).

[0141] The present invention (6) is, The above (AEm / AEc) is characterized in that it is less than 1.35, and is a pneumatic tire in any combination with any of the present invention (1) to (5).

[0142] The present invention (7) is, The present invention provides a pneumatic tire characterized in that the amount of acetone extracted from the intermediate rubber layer is 17% by mass or more, and is in any combination with any of the present invention (1) to (6).

[0143] The present invention (8) is, The present invention provides a pneumatic tire characterized by having an acetone extraction amount of 10 to 20% by mass in the cap rubber layer, and is available in any combination with any of the present invention (1) to (7).

[0144] The present invention (9) is, The pneumatic tire is characterized in that the amount of acetone extracted from the base rubber layer is 10 to 30% by mass, and is any combination of any of the present invention (1) to (8).

[0145] The present invention (10) is, The present invention provides a pneumatic tire characterized in that the toluene swelling rate of the intermediate rubber layer is 245% or less, and is in any combination with any of the present invention (1) to (9).

[0146] The present invention (11) is, A breaker layer is provided beneath the base rubber layer. The present invention provides a pneumatic tire characterized in that the ratio of the filler content (parts by mass) per 100 parts by mass of rubber component in the intermediate rubber layer to the thickness (mm) of the breaker layer (filler content of the intermediate rubber layer / thickness of the breaker layer) is 40 or more, and is any combination of any of the present invention (1) to (10).

[0147] The present invention (12) is, The intermediate rubber layer is characterized by having a Type A durometer hardness of 45 to 80 degrees, and is a pneumatic tire in any combination with any of the present invention (1) to (11).

[0148] The present invention (13) is, The intermediate rubber layer is characterized by having a Type A durometer hardness of 55 to 70 degrees, and is a pneumatic tire according to the present invention (12).

[0149] The present invention (14) is, The aforementioned cap rubber layer has a Type A durometer hardness of 55 to 65 degrees, The base rubber layer is characterized by having a Type A durometer hardness of 60 to 70 degrees, and is a pneumatic tire in any combination with any of the present invention (1) to (11). [Explanation of Symbols]

[0150] 1. Pneumatic tire 2 Tread section 2A Cap rubber layer 2B Base rubber layer 2C Intermediate rubber layer 3. Sidewall section 4. Bead section 5 Bead core 6 Carcass 7. Breaker layer 8 Bead Apex 10 Total thickness of the tread section 11. Thickness of the cap rubber layer 12. Thickness of the base rubber layer 13. Thickness of the intermediate rubber layer

Claims

1. A pneumatic tire having a tread portion comprising a cap rubber layer constituting the tread surface and a base rubber layer disposed radially inward of the cap rubber layer, and a breaker layer disposed radially inward adjacent to the tread portion, The tread portion has an intermediate rubber layer between the cap rubber layer and the base rubber layer, and is formed such that the thickness of the cap rubber layer is 40-95% of the total thickness of the tread portion, the thickness of the intermediate rubber layer is 5-30%, and the thickness of the base rubber layer is 1-50%. The rubber composition constituting the intermediate rubber layer contains 80 parts by mass or more of filler per 100 parts by mass of rubber component, and the amount of acetone extracted (mass%) determined in accordance with JIS K6229:2015 "Method for determining solvent extracts of rubber (quantitative)" is 15% by mass or more. The toluene swelling rate (%) in the aforementioned intermediate rubber layer is 250% or less. In the Type A durometer hardness of the cap rubber layer, the base rubber layer, and the intermediate rubber layer, as determined in accordance with JIS K 6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness", the Type A durometer hardness of both the cap rubber layer and the base rubber layer is smaller than the Type A durometer hardness of the intermediate rubber layer. A pneumatic tire characterized in that, when the amount of acetone extracted from the cap rubber layer, the amount of acetone extracted from the base rubber layer, and the amount of acetone extracted from the intermediate rubber layer, as determined in accordance with JIS K6229:2015, is AEc (mass%), the amount of acetone extracted from the base rubber layer is AEb (mass%), and the amount of acetone extracted from the intermediate rubber layer is AEm (mass%), the following equations (Equation 1) and (Equation 2) are satisfied. AEb / AEc<0.9 (Formula 1) 1.0<AEm / AEc<1.4 (Formula 2)

2. The pneumatic tire according to claim 1, characterized in that the thickness of the cap rubber layer in the tread portion is 45 to 90% of the total thickness of the tread portion.

3. The pneumatic tire according to claim 1, characterized in that the thickness of the intermediate rubber layer in the tread portion is 10 to 25% of the total thickness of the tread portion.

4. The pneumatic tire according to claim 1, characterized in that the thickness of the base rubber layer in the tread portion is 10 to 40% of the total thickness of the tread portion.

5. The pneumatic tire according to claim 1, characterized in that the (AEb / AEc) ratio is less than 0.

8.

6. The pneumatic tire according to claim 1, characterized in that the (AEm / AEc) ratio is less than 1.

35.

7. The pneumatic tire according to claim 1, characterized in that the amount of acetone extracted from the intermediate rubber layer is 17% by mass or more.

8. The pneumatic tire according to claim 1, characterized in that the amount of acetone extracted from the cap rubber layer is 10 to 20% by mass.

9. The pneumatic tire according to claim 1, characterized in that the amount of acetone extracted from the base rubber layer is 10 to 30% by mass.

10. The pneumatic tire according to claim 1, characterized in that the toluene swelling rate of the intermediate rubber layer is 245% or less.

11. A breaker layer is provided beneath the base rubber layer. The pneumatic tire according to claim 1, characterized in that the ratio of the filler content (parts by mass) of the intermediate rubber layer to the thickness (mm) of the breaker layer (filler content of the intermediate rubber layer / thickness of the breaker layer) is 40 or more.

12. The pneumatic tire according to claim 1, characterized in that the intermediate rubber layer has a Type A durometer hardness of 45 to 80 degrees.

13. The pneumatic tire according to claim 12, characterized in that the intermediate rubber layer has a Type A durometer hardness of 55 to 70 degrees.

14. The aforementioned cap rubber layer has a Type A durometer hardness of 55 to 65 degrees, The pneumatic tire according to claim 11, characterized in that the base rubber layer has a Type A durometer hardness of 60 to 70 degrees.

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