tire

Abstract

A tire having a tread is provided, wherein the tread includes at least a first layer constituting a tread surface, a second layer adjacent to the inner side of the first layer in the radial direction, and a third layer existing on the inner side of the second layer in the radial direction; the first layer, the second layer, and the third layer are each composed of a rubber composition containing a rubber component, the rubber composition constituting the first layer and the second layer containing silica and a mercapto-based silane coupling agent; the silica content is greater than the carbon black content based on 100 parts by mass of the rubber component; the tread has a land portion separated by a plurality of circumferential grooves; the deepest portion of the groove bottom of each of the circumferential grooves is formed closer to the inner side in the radial direction of the tire than the outer surface of the second layer; and when the distance between an extension line of each of the land portions and an extension line of the deepest portion of the groove bottom of each of the circumferential grooves is defined as H1 and the distance between an extension line of the outer surface of the second layer and an extension line of the deepest portion of the groove bottom of each of the circumferential grooves is defined as H2, H2 / H1 is at least 0.20.

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] The important properties required for tires include wet grip performance and wear resistance. In addition, in recent years, from the perspective of saving resources, it is necessary to improve tire rolling resistance and thus improve fuel efficiency. The improvement of fuel efficiency requires low hysteresis loss, while the improvement of wet grip performance requires high wet sliding resistance. However, low hysteresis loss and high wet sliding resistance are contradictory, and it is difficult to improve fuel efficiency and wet grip performance in a well-balanced manner. Although reducing the weight of fillers (such as silica, carbon black, etc.) leads to a reduction in rolling resistance, strengthening properties, wear resistance and wet grip performance tend to decrease.

[0003] Patent Document 1 discloses a rubber composition for tires in which the fuel efficiency, wet grip performance, and wear resistance of the rubber composition are improved by compounding a specific liquid resin and silica.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: JP 2013-053296 A Summary of the Invention

[0007] Problems to be solved by the present invention

[0008] To improve the balance between fuel efficiency, wet grip performance, and wear resistance, a tire has been proposed that features a tread rubber layer composed of three layers: a surface layer, an intermediate layer, and a base layer. The tread rubber layer also includes circumferential grooves that are deeper than the outer surface of the intermediate layer. However, with this type of tire, when the surface and intermediate layers are composed of different rubber layers, strain concentrates around the interface, which tends to reduce adhesion at that interface. Furthermore, if the groove depth in the intermediate layer increases by more than a predetermined ratio relative to the depth of the circumferential grooves, durability can be synergistically reduced.

[0009] An object of the present invention is to provide a tire having overall improved performance in fuel efficiency, wet grip performance, wear resistance, and durability.

[0010] Means of solving the problem

[0011] As a result of intensive research, the inventors have found that the aforementioned problems can be solved by providing a tread portion having three or more predetermined rubber layers, manufacturing the rubber layers in a specific mixing ratio, and setting the groove depth in the intermediate layer to the depth of the circumferential groove to a predetermined ratio, and completed the present invention.

[0012] In other words, the present invention relates to:

[0013] [1] A tire having a tread, wherein the tread includes at least a first layer constituting a tread surface, a second layer arranged radially adjacent to the inner side of the first layer, and a third layer present radially on the inner side of the second layer, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component; wherein the rubber composition constituting the first layer and the second layer contains silica and a mercapto-based silane coupling agent; wherein the silica content of each of the rubber compositions constituting the first layer and the second layer is greater than the carbon black content of each based on 100 parts by mass of the rubber component; wherein the tread has a land portion separated by a plurality of circumferential grooves, wherein the deepest portion of the groove bottom of the circumferential groove is formed to be located on the inner side of the outer surface of the second layer in the radial direction of the tire; and wherein, when the distance between an extension line of the land portion and an extension line of the deepest portion of the groove bottom of the circumferential groove is defined as H1, and the distance between an extension line of the outer surface of the second layer and an extension line of the deepest portion of the groove bottom of the circumferential groove is defined as H2, H2 / H1 is 0.20 or more.

[0014] [2] The tire according to [1] above, wherein the difference between the softener content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the softener content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 50 parts by mass or less.

[0015] [3] The tire according to [1] or [2] above, wherein the difference between the sulfur content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the sulfur content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 1.0 part by mass or less.

[0016] [4] The tire according to any one of [1] to [3] above, wherein the difference between the vulcanization accelerator content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the vulcanization accelerator content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 3.5 parts by mass or less.

[0017] [5] The tire according to any one of [1] to [4] above, wherein H2 / H1 is 0.30 or greater.

[0018] [6] The tire according to any one of [1] to [5] above, wherein at least one of the rubber compositions constituting the first layer and the second layer contains 100 parts by mass or more of silica based on 100 parts by mass of the rubber component.

[0019] [7] The tire according to any one of [1] to [6] above, wherein the rubber compositions constituting the first layer and the second layer each contain 50 to 130 parts by mass of silica based on 100 parts by mass of the rubber component, and the proportion of silica relative to the total content of silica and carbon black is 60% by mass or more.

[0020] [8] The tire according to any one of [1] to [7] above, wherein the rubber compositions constituting the first layer and the second layer each contain 10 parts by mass or more of a softener based on 100 parts by mass of the rubber component.

[0021] [9] The tire according to any one of [1] to [8] above, wherein the rubber components constituting the first layer and the second layer each contain 40% by mass or more of styrene-butadiene rubber based on 100 parts by mass of the rubber component.

[0022]

[10] The tire according to any one of [1] to [9] above, wherein the content of the diene rubber modified with a functional group having affinity for silica in 100% by mass of the rubber components constituting the first layer and the second layer is 40% by mass or more.

[0023]

[11] The tire according to any one of [1] to

[10] above, wherein the rubber composition constituting the first layer contains 1.0 part by mass or more of aluminum hydroxide based on 100 parts by mass of the rubber component.

[0024]

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

[11] above, wherein the thickness of each of the first layer, the second layer, and the third layer is 1.0 mm or greater.

[0025]

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

[12] above, wherein a ratio (t2 / t1) of a thickness t2 of the second layer to a thickness t1 of the first layer is 0.4 to 5.0.

[0026]

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

[13] above, wherein a ratio (t3 / t2) of a thickness t3 of the third layer to a thickness t2 of the second layer is 0.2 to 3.0.

[0027]

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

[14] above, wherein the tire inner cavity is provided with at least one selected from the group consisting of a sealant, a noise damping body, and an electronic component for tire monitoring.

[0028]

[16] The tire according to any one of [1] to

[15] above, wherein the tire is a tire for a passenger vehicle.

[0029] Effects of the Invention

[0030] According to the present invention, a tread portion is provided with three or more predetermined rubber layers, the rubber layers are made in a specific compounding ratio, and the groove depth at the intermediate layer relative to the depth of the circumferential groove is set to a predetermined ratio, thereby allowing a tire with overall improved performance in fuel efficiency, wet grip performance, wear resistance, and durability to be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is an enlarged cross-sectional view showing a portion of a tread of a tire according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] A tire according to one embodiment of the present disclosure is a tire having a tread, wherein the tread includes at least a first layer constituting a tread surface, a second layer arranged adjacent to the inner side of the first layer in the radial direction, and a third layer present on the inner side of the second layer in the radial direction, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component; wherein the rubber composition constituting the first layer and the second layer contains silica and a mercapto-based silane coupling agent; wherein based on 100 parts by mass of the rubber component, the rubber composition constituting the first layer and the second layer has a relative humidity of 1%. The silicon oxide content is respectively greater than the carbon black content; wherein the tread has a ground portion separated by a plurality of circumferential grooves; wherein the deepest part of the groove bottom of the circumferential groove is formed to be located on the inner side of the outer surface of the second layer in the radial direction of the tire; and wherein, when the distance between the extension line of the ground portion and the extension line of the deepest part of the groove bottom of the circumferential groove is defined as H1, and the distance between the extension line of the outer surface of the second layer and the extension line of the deepest part of the groove bottom of the circumferential groove is defined as H2, H2 / H1 is greater than 0.20 (preferably greater than 0.30).

[0033] While not intending to be bound by theory, the present disclosure proposes that the mechanism for improving tire durability may be as follows. Specifically, a highly active coupling agent, such as a mercapto-based silane coupling agent, may be added to more firmly connect the polymer in the first layer and the silica in the second layer, or vice versa, thereby enhancing adhesion at the interface between the rubber layers. This is believed to improve durability even when the ratio of the groove depth in the second layer relative to the depth of the circumferential grooves is increased.

[0034] The difference between the softener content of the rubber composition constituting the first layer and the softener content of the rubber composition constituting the second layer, based on 100 parts by mass of the rubber component, is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, further preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less. Setting the softener content difference between the first and second layers within the aforementioned range can suppress a decrease in durability due to strain concentration around the interface caused by an increase in the hardness difference between the first and second layers. Furthermore, while the softener content of the first layer can be greater or less than that of the second layer, as long as the difference is within the aforementioned range, the softener content of the first layer is preferably greater than that of the second layer to suppress a decrease in wet grip performance after abrasion of the first layer.

[0035] The difference between the sulfur content of the rubber composition constituting the first layer and the sulfur content of the rubber composition constituting the second layer, based on 100 parts by mass of the rubber component, is preferably 1.0 part by mass or less, more preferably 0.8 part by mass or less, further preferably 0.6 part by mass or less, even more preferably 0.4 part by mass or less, and particularly preferably 0.3 part by mass or less. Setting the sulfur content difference between the first and second layers within the aforementioned range can suppress a decrease in durability caused by a decrease in strength around the interface due to sulfur transfer from the rubber layer with more sulfur to the rubber layer with less sulfur during vulcanization. Furthermore, while the sulfur content of the first layer may be greater or less than that of the second layer, as long as the difference is within the aforementioned range, the sulfur content of the first layer is preferably less than that of the second layer from the perspective of fuel efficiency.

[0036] The difference between the vulcanization accelerator content of the rubber composition constituting the first layer and the vulcanization accelerator content of the rubber composition constituting the second layer, based on 100 parts by mass of the rubber component, is preferably 3.5 parts by mass or less, more preferably 3.0 parts by mass or less, further preferably 2.5 parts by mass or less, and particularly preferably 2.0 parts by mass or less. Setting the difference in vulcanization accelerator content between the first and second layers within the aforementioned range can suppress a decrease in durability caused by a decrease in strength around the interface due to transfer of the vulcanization accelerator from the rubber layer with more sulfur to the rubber layer with less sulfur during vulcanization. Furthermore, while the vulcanization accelerator content of the first layer can be greater or less than that of the second layer, as long as the difference is within the aforementioned range, the vulcanization accelerator content of the first layer is preferably greater than that of the second layer. As described above, when the softener content of the first layer is greater than that of the second layer, the vulcanization rate of the rubber composition constituting the first layer tends to be slow. Furthermore, when the silica content of the rubber composition constituting the first layer is increased to improve wet grip performance, the vulcanization rate of the rubber composition constituting the first layer tends to be slow. For these reasons, it is preferable to make the vulcanization accelerator content of the first layer greater than that of the second layer in order to ensure the vulcanization rate of the rubber composition constituting the first layer.

[0037] At least one of the rubber compositions constituting the first layer and the second layer preferably contains 100 parts by mass or more of silica based on 100 parts by mass of the rubber component.

[0038] Preferably, the rubber compositions constituting the first and second layers each contain 50 to 130 parts by mass of silica based on 100 parts by mass of the rubber component, and the proportion of silica relative to the total content of silica and carbon black is 60% by mass or more.

[0039] The rubber compositions constituting the first layer and the second layer each preferably contain 10 parts by mass or more of a softener based on 100 parts by mass of the rubber component.

[0040] The rubber components constituting the first layer and the second layer each contain 40% by mass or more of styrene-butadiene rubber.

[0041] The rubber composition constituting the first and second layers preferably contains, as the rubber component, a diene rubber modified with a functional group having an affinity for silica. The content of this rubber component is preferably 40% by mass or greater, more preferably 50% by mass or greater, further preferably 60% by mass or greater, and particularly preferably 70% by mass or greater.

[0042] The rubber composition constituting the first layer preferably contains aluminum hydroxide in an amount of preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, based on 100 parts by mass of the rubber component.

[0043] The thickness of each of the first layer, the second layer, and the third layer is preferably 1.0 mm or more.

[0044] The ratio of the thickness t2 of the second layer to the thickness t1 of the first layer (t2 / t1) is preferably 0.4 to 5.0.

[0045] The ratio of the thickness t3 of the third layer to the thickness t2 of the second layer (t3 / t2) is preferably 0.2 to 3.0.

[0046] For the tire of the present disclosure, the tire inner cavity is preferably provided with at least one selected from the group consisting of a sealant, a noise dampening body, and an electronic component for tire monitoring.

[0047] The tire of the present disclosure is suitably used as a tire for passenger vehicles.

[0048] The following describes in detail the process of manufacturing a tire as one embodiment of the present disclosure. Note that the following description is intended to illustrate the present invention and is not intended to limit the technical scope of the present invention to that described. Furthermore, in this specification, numerical ranges indicated using the expression "to" include the numerical values at both ends.

[0049] Figure 1 is an enlarged cross-sectional view showing a portion of the tread of a tire according to the present disclosure. Figure 1 , the up-down direction is the tire radial direction, the left-right direction is the tire axial direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0050] As shown, the tread portion of the tire of the present disclosure includes a first layer 6, a second layer 7, and a third layer 8. The outer surface of the first layer 6 constitutes the tread surface 3, the second layer 7 is arranged adjacent to the inner side of the first layer 6 in the radial direction, and the third layer 8 is present on the inner side of the second layer 7 in the radial direction. The third layer 8 is preferably arranged adjacent to the inner side of the second layer 7 in the radial direction. In addition, as long as the purpose of the present invention is achieved, one or more rubber layers may be provided between the second layer 7 and the third layer 8 and / or between the third layer 8 and the belt layer.

[0051] exist Figure 1 In FIG, the double-headed arrow t1 is the thickness of the first layer 6, the double-headed arrow t2 is the thickness of the second layer 7, and the double-headed arrow t3 is the thickness of the third layer 8. Figure 1In FIG, an arbitrary point on the tread surface (at which no groove is formed) is shown as a symbol P. A straight line shown as a symbol N is a straight line (normal line) passing through the point P and perpendicular to the contact plane of the point P. In this specification, Figure 1 In the cross section of , thicknesses t1 , t2 , and t3 are measured along a normal line N drawn from a point P on the tread surface where no groove exists.

[0052] Although the thickness t1 of the first layer 6 is not particularly limited in the present disclosure, from the perspective of wet grip performance, it is preferably 1.0 mm or greater, more preferably 1.5 mm or greater, and further preferably 2.0 mm or greater. On the other hand, from the perspective of heat generation, the thickness t1 of the first layer 6 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0053] Although the thickness t2 of the second layer 7 is not particularly limited in the present disclosure, it is preferably 1.5 mm or more, more preferably 2.0 mm or more, and further preferably 2.5 mm or more. In addition, the thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0054] Although the thickness t3 of the third layer 8 is not particularly limited in the present disclosure, it is preferably 1.0 mm or more, more preferably 1.5 mm or more. In addition, the thickness t3 of the third layer 8 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and more preferably 8.0 mm or less.

[0055] From the perspective of fuel efficiency, the ratio of the thickness t2 of the second layer 7 to the thickness t1 of the first layer 6 (t2 / t1) is preferably 0.4 or greater, more preferably 0.5 or greater, further preferably 0.7 or greater, and particularly preferably 0.9 or greater. On the other hand, from the perspective of wet grip performance, it is preferably 5.0 or less, more preferably 4.5 or less, further preferably 4.0 or less, and particularly preferably 3.5 or less.

[0056] From the perspective of better exhibiting the effects of the present disclosure, the ratio of the thickness t3 of the third layer 8 to the thickness t2 of the second layer 7 (t3 / t2) is preferably 0.2 or greater, more preferably 0.3 or greater, and even more preferably 0.4 or greater. On the other hand, from the perspective of better exhibiting the effects of the present disclosure, the ratio of the thickness t3 of the third layer 8 to the thickness t2 of the second layer 7 (t3 / t2) is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 0.9 or less.

[0057] The thickness t2 of the second layer 7 is preferably 20% to 90% of the thickness of the entire tread portion, more preferably 25% to 80%, and more preferably 30% to 75%. In addition, the thickness of the entire tread portion in the present disclosure refers to the total thickness of the rubber layers constituting the tread portion and is determined by the shortest distance from the tread surface 3 to the belt layer.

[0058] The tread of the present disclosure has a plurality of circumferential grooves 1 that extend continuously in the tire circumferential direction. The circumferential grooves 1 may extend linearly in the circumferential direction or may extend in a zigzag manner in the circumferential direction.

[0059] The tread of the present disclosure has land portions 2 partitioned by circumferential grooves 1 in the tire width direction.

[0060] The groove depth H1 of the circumferential groove 1 is determined by the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1. In addition, in the case where there are multiple circumferential grooves 1, for example, the groove depth H1 can be set to be the distance between the extension line 4 of the land portion 2 and the circumferential groove 1 having the largest groove depth among the multiple circumferential grooves 1 ( Figure 1 The distance between the extension line 5 of the deepest part of the groove bottom of the left circumferential groove 1).

[0061] The tire of the present disclosure is formed so that the deepest portion of the groove bottom of the circumferential groove 1 is located on the inner side of the outer surface of the second layer 7 in the tire radial direction. When the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 is defined as H1, and the distance between the extension line 9 of the outer surface of the second layer 7 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 is defined as H2, H2 / H1 is 0.20 or greater, preferably 0.25 or greater, more preferably 0.30 or greater, further preferably 0.35 or greater, and particularly preferably 0.40 or greater. Setting H2 / H1 within the aforementioned range enables well-balanced improvements in fuel efficiency and wet grip performance. Furthermore, the deepest portion of the groove bottom and the outer surface of the second layer 7 are separated, ensuring the durability of the groove bottom.

[0062] For the tire of the present disclosure, the tire cavity may be provided with sealants, noise dampeners, electronic components for tire monitoring, and the like.

[0063] Suitable sealants include those commonly used on the inner circumferential surface of tires in the tread portion to prevent puncture. Specific examples of such sealant layers include those disclosed in JP 2020-023152 A. Typically, the sealant thickness is preferably 1 mm to 10 mm. Typically, the sealant width is preferably 85% to 115%, and more preferably 95% to 105%, of the maximum belt width.

[0064] Any noise damping body can be appropriately used as long as it can exhibit a noise damping effect in the inner cavity of the tire. For example, specific examples of noise damping bodies include those disclosed in JP 2019-142503 A. For example, the noise damping body is composed of a porous sponge material. The sponge material is a porous structure with multiple chambers, and in addition to the so-called sponge itself having interconnected chambers in which, for example, rubber or synthetic resin is foamed, it also includes a mesh body, which is an animal fiber, plant fiber or synthetic fiber, etc. that is entangled or integrally coupled with each other. In addition, the "porous structure" includes a body that has not only interconnected chambers but also closed chambers. Examples of noise damping bodies include sponge materials having interconnected chambers made of polyurethane. As sponge materials, for example, synthetic resin sponges such as ether polyurethane sponge, ester polyurethane sponge, polyethylene sponge; and rubber sponges such as chloroprene rubber sponge (CR sponge), ethylene-propylene rubber sponge (EDPM sponge), nitrile rubber sponge (NBR sponge), etc. can be appropriately used. In particular, from the perspective of noise damping properties, lightweight properties, controllability of foaming, durability, etc., polyurethane sponges including ether polyurethane sponge or polyethylene sponge are preferred.

[0065] The noise damping body has an elongated belt-like shape, having a bottom surface fixed to the inner cavity surface of the tread portion and extending in the tire circumferential direction. Here, its outer ends in the circumferential direction may be made to contact each other to form a substantially annular shape, or its outer ends may be spaced apart in the circumferential direction.

[0066] In this disclosure, unless otherwise specified, the dimensions and angles of each component of the tire are measured with the tire incorporated into a normal rim and filled with air to achieve a normal internal pressure. No load is applied to the tire during measurement. Furthermore, in this specification, a "normal rim" is a rim defined for each tire by a standard within a standard system that includes the standard on which the tire is based, and includes, for example, JATMA's standard rim, TRA's "design rim," and ETRTO's "measurement rim." In this specification, "normal internal pressure" is the air pressure defined for each tire by a standard, and includes JATMA's maximum air pressure, the maximum value specified in TRA's table "Tire Load Limits at Various Cold Inflation Pressures," and ETRTO's "Inflation Pressure."

[0067] [Rubber composition for tread]

[0068] As described above, the rubber composition constituting each rubber layer of the tread (the rubber composition for the tread) includes a rubber component and a plasticizer.

[0069] <Rubber Component>

[0070] The rubber composition (tread rubber composition) constituting each rubber layer of the tread according to the present disclosure preferably includes at least one selected from the group consisting of isoprene-based rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR) as a rubber component. The rubber component constituting the first layer 6 and the second layer 7 preferably includes SBR, more preferably includes SBR and BR, or may be a rubber component consisting solely of SBR and BR. The rubber component constituting the third layer 8 preferably includes isoprene-based rubber, more preferably includes isoprene-based rubber and BR, or may be a rubber component consisting solely of isoprene-based rubber and BR.

[0071] (Isoprene rubber)

[0072] As the isoprene-based rubber, those commonly used in the tire industry, such as isoprene rubber (IR) and natural rubber, can be used. Natural rubber includes, in addition to unmodified natural rubber (NR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deprotected natural rubber (DPNR), ultrapure natural rubber, and modified natural rubber including grafted natural rubber. These isoprene-based rubbers can be used alone or in combination of two or more.

[0073] The NR is not particularly limited, and those generally used in the tire industry, such as SIR20, RSS#3, TSR20, etc., can be used.

[0074] When the rubber composition constituting the first layer 6 and the second layer 7 includes isoprene-based rubber, from the perspective of wet grip performance, the content of isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)) in 100% by mass of the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less. Furthermore, while the lower limit of the content of isoprene-based rubber when the rubber composition includes isoprene-based rubber is not particularly limited, it may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more. For example, when the rubber composition constituting the third layer 8 includes isoprene-based rubber, the content of isoprene-based rubber in 100% by mass of the rubber component is not particularly limited and may be 10% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more.

[0075] (SBR)

[0076] SBR is not particularly limited, and its example includes solution polymerization SBR (S-SBR), emulsion polymerization SBR (E-SBR), their modified SBR (modified S-SBR, modified E-SBR) etc. The example of modified SBR includes SBR at its end and / or main chain modification, with tin, silicon compound etc. coupled modified SBR (condensate or modified SBR with branched structure etc.), etc. Wherein, S-SBR and modified SBR are preferred. In addition, the hydrogenated additive (hydrogenated SBR) etc. of these SBRs can also be used. These SBRs can be used alone, or two or more thereof can be used in combination.

[0077] As SBR, oil-extended SBR or non-oil-extended SBR may be used. When oil-extended SBR is used, the oil-extending amount of SBR, i.e. the amount of oil-extended SBR contained in SBR, is preferably 10 to 50 parts by mass based on 100 parts by mass of the rubber solid content of SBR.

[0078] S-SBR that can be used in the present disclosure include those commercially available from JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomer Corporation, and the like.

[0079] From the viewpoint of wet grip performance and abrasion resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and more preferably 20% by mass or more. In addition, from the viewpoint of temperature dependence of grip performance and blow-off resistance, it is preferably 60% by mass or less, more preferably 55% by mass or less, and more preferably 50% by mass or less. In addition, in this specification, the styrene content of SBR is expressed by 1 Calculations based on H-NMR measurements.

[0080] From the perspective of ensuring reactivity with silica, wet grip performance, rubber strength and wear resistance, the vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and more preferably 20 mol% or more. In addition, from the perspective of preventing an increase in temperature dependence, elongation at break and wear resistance, the vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and more preferably 60 mol% or less. In addition, in this specification, the vinyl content (1,2-bonded butadiene unit amount) of SBR is measured by infrared absorption spectroscopy.

[0081] From the perspective of wet grip performance, the weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 250,000 or more, and further preferably 300,000 or more. Furthermore, from the perspective of crosslinking uniformity, the weight average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight average molecular weight of SBR can be determined based on a measured value obtained by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation) according to standard polystyrene.

[0082] When the rubber composition constituting the first layer 6 and the second layer 7 includes SBR, from the perspective of wet grip performance, the content of SBR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, and particularly preferably 70% by mass or more. In addition, the upper limit of the content of SBR in the rubber component is not particularly limited and can be 100% by mass. In addition, when the rubber composition constituting the third layer 8 includes SBR, the content of SBR in 100% by mass of the rubber component is not particularly limited.

[0083] (BR)

[0084] BR is not particularly limited, and those commonly used in the tire industry can be used, for example, BR having a cis content of less than 50% by mass (low-cis BR), BR having a cis content of 90% or more (high-cis BR), rare earth butadiene rubber synthesized using a rare earth element catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis-modified BR, low-cis-modified BR), etc. Examples of modified BR include BR modified with functional groups similar to those described above for SBR. These BRs can be used alone, or two or more of them can be used in combination.

[0085] High-cis BR commercially available from companies such as Zeon, Ube Industries, Ltd., and JSR Corporation can be used. The inclusion of high-cis BR improves low-temperature properties and wear resistance. The cis content is preferably 95% by mass or greater, more preferably 96% by mass or greater, further preferably 97% by mass or greater, and particularly preferably 98% by mass or greater. In this specification, the cis content (cis-1,4-butadiene unit content) is a value calculated by infrared absorption spectroscopy.

[0086] Rare earth BRs can be synthesized using rare earth element catalysts and have a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less, and a cis content of preferably 95% by mass or more, more preferably 96% by mass or more, further preferably 97% by mass or more, and particularly preferably 98% by mass or more. Rare earth BRs commercially available from LANXESS and the like can be used, for example.

[0087] Examples of SPS-containing BR include those in which 1,2-syndiotactic polybutadiene crystals are chemically bonded to and dispersed in BR, but not those in which crystals are simply dispersed in BR. Thus, those commercially available from Ube Industries, Ltd. can be used.

[0088] As the modified BR, a modified butadiene rubber (modified BR) modified at its terminal and / or main chain with a functional group including at least one element selected from the group consisting of silicon, nitrogen, and oxygen is suitably used.

[0089] Examples of other modified BR include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, wherein the modified BR molecules are bonded at their terminals by tin-carbon bonds (tin-modified BR). In addition, the modified BR may or may not be hydrogenated.

[0090] The previously listed BRs may be used alone, or two or more thereof may be used in combination.

[0091] From the viewpoint of wear resistance, the weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and more preferably 400,000 or more. In addition, from the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, more preferably 1,000,000 or less. In addition, the weight average molecular weight of BR can be determined based on the measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMTOREHZ-M, manufactured by Tosoh Corporation) according to standard polystyrene.

[0092] From the perspective of wet grip performance, when the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 includes BR, the BR content in 100% by mass of the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less. Furthermore, while the lower limit of the BR content when the rubber composition includes BR is not particularly limited, it may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0093] As the rubber component according to the present disclosure, diene rubber modified with a functional group having an affinity for silica is suitably used. Specifically, examples thereof include diene rubber modified with a functional group having an affinity for silica at its terminal and / or main chain. When such diene rubbers are mixed, the interaction between polymer and silica increases and the reinforcing performance is improved, resulting in improved wear resistance. In addition, the interaction with silica makes it difficult for silica and polymer to move and reduces internal friction, thereby improving fuel efficiency. In particular, when the terminal has a functional group having an affinity for silica, the movement of the terminal, which is prone to internal friction, is regulated, thereby allowing the internal friction between the polymers to be more effectively reduced.

[0094] Examples of functional groups having affinity for silica include epoxy, silyl, amino, hydroxyl, carboxyl, amide, mercapto, and the like, but are not limited thereto. Examples of silyl groups include, for example, alkoxysilyl groups such as trimethoxysilyl, triethoxysilyl, triisopropoxysilyl, dimethoxymethylsilyl, diethoxymethylsilyl, dimethylmethoxysilyl, dimethylethoxysilyl, and the like; acetoxysilyl groups such as triacetoxysilyl, diacetoxymethylsilyl, acetoxydimethylsilyl, and the like; chlorosilyl groups such as chlorodimethylsilyl, dichloromethylsilyl, trichlorosilyl, and the like; and the like.

[0095] Specific examples of the diene rubber modified with a functional group having affinity for silica include SBR or BR modified with an alkoxysilyl group, and SBR modified with an alkoxysilyl group is preferred.

[0096] When the rubber component contains a diene rubber modified with a functional group having an affinity for silica, the content thereof is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, and particularly preferably 70% by mass or more. Furthermore, the upper limit of the content of the diene rubber in the rubber component is not particularly limited and may be 100% by mass.

[0097] (Other rubber components)

[0098] As the rubber component according to the present disclosure, the rubber component other than the above-mentioned isoprene rubber, SBR and BR can be included. As other rubber components, the crosslinkable rubber component commonly used in the tire industry can be used, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyvinyl chloride rubber, fluororubber (FKM), acrylic rubber (ACM), epichlorohydrin rubber etc. These other rubber components can be used alone, or two or more thereof can be used in combination.

[0099] <Packing>

[0100] In the rubber composition for the tread, according to the present disclosure, fillers containing carbon black and / or silica are suitably used. The rubber composition constituting the first layer 6 and the second layer 7 includes silica, more preferably carbon black and silica, as fillers. The rubber composition constituting the third layer 8 includes carbon black as a filler.

[0101] (Carbon Black)

[0102] As carbon black, those commonly used in the tire industry can be appropriately used. For example, examples thereof include GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks can be used alone or in combination of two or more thereof.

[0103] From the perspective of enhancing properties, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 10 m 2 / g or more, more preferably 20m 2 / g or more. In addition, from the viewpoint of fuel efficiency and workability, it is preferably 200m 2 / g or less, more preferably 150m 2 / g or less, more preferably 100m 2 / g or less, more preferably 80m 2 / g or less, and particularly preferably 50m 2 The N2SA of carbon black is a value measured in accordance with Japanese Industrial Standard JIS K6217-2 "Carbon black for rubber - Basic properties - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[0104] When the rubber composition contains carbon black, from the perspective of abrasion resistance and wet grip performance, the amount thereof is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the perspective of fuel efficiency, the amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, further preferably 20 parts by mass or less, further preferably 10 parts by mass or less, and particularly preferably 8 parts by mass or less.

[0105] (Silicon dioxide)

[0106] Silica is not particularly limited, and those commonly used in the tire industry, such as silica produced by a dry process (anhydrous silica), silica produced by a wet process (hydrous silica), etc., can be used. Among them, hydrous silica produced by a wet process is preferred because it has many silanol groups. These silicas can be used alone or in combination of two or more.

[0107] From the perspective of fuel efficiency and wear resistance, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 140 m 2 / g or more, more preferably 170m 2 / g or more, and more preferably 200m 2 / g or more. In addition, from the perspective of fuel efficiency and processability, 350m 2 / g or less, more preferably 300m 2 / g or less, and more preferably 250m 2 In addition, the N2SA of silica in this specification is a value measured by the BET method according to ASTM D3037-93.

[0108] From the perspective of wet grip performance, when the rubber composition contains silica, the silica content in the rubber composition is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, further preferably 70 parts by mass or more, further preferably 80 parts by mass or more, further preferably 90 parts by mass or more, and particularly preferably 100 parts by mass or more, based on 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance, the silica content is preferably 140 parts by mass or less, more preferably 130 parts by mass or less, further preferably 120 parts by mass or less, and particularly preferably 110 parts by mass or less.

[0109] At least one of the rubber compositions constituting the first layer 6 and the second layer 7 includes preferably 70 parts by mass or more, more preferably 80 parts by mass or more, further preferably 90 parts by mass or more, and particularly preferably 100 parts by mass or more of silica, based on 100 parts by mass of the rubber component.

[0110] From the perspective of wear resistance, the total content of silica and carbon black per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 60 parts by mass or more. Furthermore, from the perspective of fuel efficiency and elongation at break, it is preferably 160 parts by mass or less, more preferably 140 parts by mass or less, and further preferably 120 parts by mass or less.

[0111] From the perspective of balancing fuel efficiency, wet grip performance, and abrasion resistance, the rubber composition comprising the first and second layers 6 and 7 preferably contains more silica than carbon black, per 100 parts by mass of the rubber component. In the first and second layers 6 and 7, the proportion of silica relative to the total content of silica and carbon black is preferably 60% by mass or greater, more preferably 70% by mass or greater, even more preferably 80% by mass or greater, even more preferably 85% by mass or greater, and particularly preferably 90% by mass or greater. Furthermore, the percentages of silica and carbon black in the third layer 8 are not particularly limited, but the proportion of carbon black relative to the total content of silica and carbon black can be, for example, 50% by mass or greater, 70% by mass or greater, 90% by mass or greater, or 100% by mass or greater.

[0112] (Silane coupling agent)

[0113] Silica is preferably used in combination with a silane coupling agent. The rubber composition constituting the first layer 6 and the second layer 7 contains a mercapto-based silane coupling agent as a silane coupling agent, and other silane coupling agents may be used in combination with the silane coupling agent. Compounding with a mercapto-based silane coupling agent further enhances the reactivity of silica and the polymer.

[0114] The mercapto-based silane coupling agent is preferably a compound represented by the following formula (1) and / or a compound comprising a bonding unit A represented by the following formula (2) and a bonding unit B represented by the following formula (3):

[0115] [Chemical Formula 1]

[0116]

[0117] (Among them, R 101 、R 102 and R 103 Each independently represents C 1-12 Alkyl, C 1-12 Alkoxy or -O-(R 111 -O) z -R 112 The group represented by (z R 111 Each independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 Indicates C 1-30 Alkyl, C 2-30Alkenyl, C 6-30 Aryl or C 7-30 aralkyl; z represents an integer from 1 to 30); and R 104 Indicates C 1-6 Alkylene.)

[0118] [Chemical Formula 2]

[0119]

[0120] [Chemical Formula 3]

[0121]

[0122] (wherein x represents an integer greater than 0; y represents an integer greater than 1; R 201 Represents a hydrogen atom or C 1-30 Alkyl, C 2-30 Alkenyl or C 2-30 Alkynyl, which may be substituted by a halogen atom, a hydroxyl group or a carboxyl group; R 202 Indicates C 1-30 Alkylene, C 2-30 Alkenylene or C 2-30 Alkynylidene; wherein R 201 and R 202 Can form a ring structure.)

[0123] Examples of the compound represented by formula (1) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and a compound represented by formula (4) below (Si363 manufactured by Evonik Degussa), and compounds represented by formula (4) below can be appropriately used. They can be used alone, or two or more thereof can be used in combination.

[0124] [Chemical Formula 4]

[0125]

[0126] Examples of the compound including the bonding unit A represented by formula (2) and the bonding unit B represented by formula (3) include, for example, those manufactured by Momentive Performance Materials, Inc., etc. They may be used alone, or two or more thereof may be used in combination.

[0127] From the perspective of enhancing the dispersibility of silica, the content of the mercapto-based silane coupling agent is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.5 parts by mass or more, based on 100 parts by mass of silica. Furthermore, from the perspective of cost and workability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further preferably 10 parts by mass or less.

[0128] In addition to the mercapto-based silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used, and examples thereof include, for example, sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide, etc.; vinyl-based silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, etc.; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3- Aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, etc.; glycidoxy-based silane coupling agents, such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc.; nitro-based silane coupling agents, such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, etc.; chlorine-based silane coupling agents, such as 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, etc.; etc. Among them, sulfide-based silane coupling agents are preferred. These silane coupling agents can be used alone or in combination of two or more.

[0129] From the perspective of improving the dispersibility of silica, the content of the silane coupling agent (when using multiple silane coupling agents, the total content of all silane coupling agents) is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, based on 100 parts by mass of silica. Furthermore, from the perspective of cost and workability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further preferably 10 parts by mass or less.

[0130] As fillers, in addition to carbon black and silica, other fillers may also be used. While such fillers are not particularly limited, any commonly used fillers in the art may be used, such as aluminum hydroxide, aluminum oxide (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, and the like. Among these, aluminum hydroxide is preferably used because it exhibits excellent wear resistance, durability, wet grip performance, and fuel efficiency. These other fillers may be used alone or in combination of two or more.

[0131] From the perspective of wet grip performance, the nitrogen adsorption specific surface area (N2SA) of aluminum hydroxide is preferably 5m 2 / g or more, more preferably 10m 2 / g or more. In addition, from the perspective of dispersibility of aluminum hydroxide, prevention of reaggregation and wear resistance, it is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, and more preferably 30m 2 In addition, the BET specific surface area of aluminum hydroxide herein is a value measured by the BET method according to ASTM D3037-81.

[0132] From the perspective of dispersibility, prevention of reaggregation, and wear resistance of aluminum hydroxide, the average particle size (D50) of aluminum hydroxide is preferably 0.1 μm or more, more preferably 0.2 μm or more, and further preferably 0.3 μm or more. In addition, from the perspective of wear resistance, it is preferably 3.0 μm or less, more preferably 2.0 μm or less. In addition, the average particle size (D50) in this specification is the particle size at 50% of the cumulative mass value on the particle size distribution curve determined by a particle size distribution measuring device.

[0133] When the rubber composition contains aluminum hydroxide, the amount of aluminum hydroxide is preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, based on 100% by mass of the rubber component. Furthermore, from the perspective of wear resistance, the amount of aluminum hydroxide is 50 parts by mass or less, 40 parts by mass or less, or 30 parts by mass or less.

[0134] <Softener>

[0135] According to the present invention, the rubber composition for a tread preferably contains a softener. Examples of the softener include resin components, oils, liquid rubbers, ester plasticizers, and the like.

[0136] The resin component is not particularly limited, and examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, etc., which are generally used in the tire industry. These resin components may be used alone, or two or more thereof may be used in combination.

[0137] In this specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions corresponding to 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0138] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of C9 fractions include, for example, petroleum fractions equivalent to 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. As specific examples of aromatic petroleum resins, for example, coumarin indene resins, coumarone resins, indene resins, and aromatic vinyl resins are suitably used. As aromatic vinyl resins, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred because it is economical, easy to process, and good in terms of heat generation. As aromatic vinyl-based resins, for example, those commercially available from Kraton Corporation, Eastman Chemical Corporation, etc. can be used.

[0139] In this specification, "C5-C9 type petroleum resin" refers to a resin obtained by copolymerizing a C5 fraction and a C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fractions. As C5-C9 type petroleum resin, for example, those commercially available from Tosoh Corporation and Zibo Luhua Hongjin New Materials Group Co., Ltd. (LUHUA) can be used.

[0140] Examples of terpene resins include: polyterpene resins composed of at least one selected from terpene compounds (e.g., α-pinene, β-pinene, limonene, dipentene, etc.); aromatic modified terpene resins made from terpene compounds and aromatic compounds; terpene phenol resins made from terpene compounds and phenol-based compounds; and those obtainable by hydrogenating these terpene resins (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include, for example, styrene, α-methylstyrene, vinyltoluene, divinyltoluene, etc. Examples of phenol-based compounds used as raw materials for terpene phenol resins include, for example, phenol, bisphenol A, cresol, xylenol, etc.

[0141] The rosin-based resin is not particularly limited, and examples thereof include, for example, natural resin rosin and rosin-modified resins which are natural resin rosin modified by hydrogenation, disproportionation, dimerization, or esterification.

[0142] The phenol-based resin is not particularly limited, and examples thereof include phenol resins, alkylphenol formaldehyde resins, alkylphenol acetylene resins, oil-modified phenol resins, and the like.

[0143] From the perspective of wet grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher. Furthermore, from the perspective of processability and improved dispersibility of the rubber component and filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. Furthermore, in this specification, the softening point can be defined as the temperature at which a ball drops when measuring the softening point specified in Japanese Industrial Standard JIS K 6220-1:2001 using a ring-and-ball softening point measuring device.

[0144] When the rubber composition contains a resin component, from the perspective of wet grip performance, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, from the perspective of suppressing heat generation, its content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0145] Examples of oils include, for example, process oils, vegetable oils, animal fats, and the like. Examples of process oils include paraffinic process oils, naphthenic process oils, aromatic process oils, and the like. In addition, as an environmental measure, process oils with low polycyclic aromatic compounds (PCA) content may also be used. Examples of process oils with low PCA content include mild extraction solvates (MES), treated distillate aromatic extracts (TDAE), heavy naphthenic oils, and the like.

[0146] When the rubber composition contains oil, from the perspective of workability, the amount thereof is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further preferably 15 parts by mass or more, based on 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance, the amount thereof is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and further preferably 90 parts by mass or less. In this specification, the oil content also includes the amount of oil contained in the oil-extended rubber.

[0147] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25° C.), and examples of the liquid rubber include, for example, liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene polymer (liquid SIR), liquid farnesene rubber, etc. These may be used alone, or two or more thereof may be used in combination.

[0148] When the rubber composition contains liquid rubber, its content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more, based on 100 parts by mass of the rubber component. Furthermore, the liquid rubber content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and further preferably 20 parts by mass or less.

[0149] Examples of ester-based plasticizers include, for example, dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di(2-ethylhexyl) azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), tricresyl phosphate (TXP), etc. These ester-based plasticizers may be used alone or in combination of two or more thereof.

[0150] From the perspective of wet grip performance, the amount of the softener (when multiple softeners are used, the total amount of all softeners) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the perspective of workability, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, further preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0151] <Other compounding agents>

[0152] In addition to the aforementioned components, the rubber composition according to the present disclosure may also appropriately contain compounding agents commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, vulcanization accelerators, and the like.

[0153] When the rubber composition contains wax, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component, from the perspective of weather resistance of the rubber. Furthermore, from the perspective of preventing tire whitening due to blooming, its content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0154] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, and the like. These processing aids may be used alone or in combination of two or more. As processing aids, those commercially available from, for example, Schill & Seilacher, Performance Additives, and the like may be used.

[0155] When the rubber composition contains a processing aid, from the perspective of exhibiting an effect of improving processability, the amount thereof is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, based on 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance and breaking strength, the amount thereof is preferably 10 parts by mass or less, more preferably 8 parts by mass or less.

[0156] The antioxidant is not particularly limited, and examples thereof include, for example, amine compounds, quinoline compounds, quinone compounds, phenolic compounds, and imidazole compounds, as well as antioxidants such as carbamate metal salts, preferably phenylenediamine antioxidants such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,4-trimethyl-1,2-dihydroquinoline, etc. These antioxidants may be used alone, or two or more thereof may be used in combination.

[0157] When the rubber composition contains an antioxidant, from the perspective of ozone crack resistance, its content is preferably 0.5 parts by mass, more preferably 1 part by mass or more, based on 100 parts by mass of the rubber component. Furthermore, from the perspective of abrasion resistance and wet grip performance, its content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0158] When the rubber composition contains stearic acid, from the viewpoint of processability, the content thereof is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, based on 100 parts by mass of the rubber component. In addition, from the viewpoint of vulcanization rate, the content thereof is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0159] When the rubber composition contains zinc oxide, from the viewpoint of workability, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component. In addition, from the viewpoint of wear resistance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0160] Sulfur is preferably used as a vulcanizing agent. Examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0161] When the rubber composition contains sulfur as a vulcanizing agent, the sulfur content is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component from the perspective of ensuring a sufficient vulcanization reaction. Furthermore, from the perspective of preventing degradation, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. Furthermore, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent should be the total content of the pure sulfur contained in the oil-containing sulfur.

[0162] Examples of the vulcanizing agent other than sulfur include, for example, alkylphenol-sulfur chloride condensate, 1,6-hexamethylene-sodium dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. As these vulcanizing agents other than sulfur, those commercially available from Taoka Chemical Co., Ltd., LANXESS, Flexsys, etc. can be used.

[0163] Examples of vulcanization accelerators include, for example, sulfenamides, thiazoles, thiurams, thioureas, guanidines, dithiocarbamates, aldehyde-amines or aldehyde-ammonias, imidazolines, and xanthate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from sulfenamides, guanidines, and thiazoles are preferred, and a combination of sulfenamides and guanidines is more preferred.

[0164] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among them, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0165] Examples of guanidine vulcanization accelerators include, for example, 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of biscatechol borate, 1,3-di-o-cumylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumyl-2-propylguanidine, etc. Among them, 1,3-diphenylguanidine (DPG) is preferred.

[0166] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazole disulfide, etc. Among them, 2-mercaptobenzothiazole is preferred.

[0167] When the rubber composition contains a vulcanization accelerator, its content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, based on 100 parts by mass of the rubber component. In addition, the content of the vulcanization accelerator is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and further preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. When the content of the vulcanization accelerator is within the above range, there is a tendency to ensure breaking strength and elongation.

[0168] The rubber composition according to the present disclosure can be produced by a known method and can be produced by kneading the aforementioned components using a rubber kneading device such as an open roll or a closed mixer (Banbury mixer, mixer, etc.).

[0169] The kneading step includes, for example, a basic kneading step of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) step of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the basic kneading step and kneading the mixture. In addition, the basic kneading step may be divided into a plurality of steps if necessary.

[0170] The kneading conditions are not particularly limited, and examples include kneading at a discharge temperature of 150° C. to 170° C. for 3 to 10 minutes in the basic kneading step and kneading at 70° C. to 110° C. for 1 to 5 minutes in the final kneading step. The vulcanization conditions are not particularly limited, and for example, a method of vulcanizing at 150° C. to 200° C. for 10 to 30 minutes is exemplified.

[0171] [tire]

[0172] The tire according to the present disclosure includes a tread comprising a first layer 6, a second layer 7, and a third layer 8, and can be either a pneumatic tire or a non-pneumatic tire. Examples of pneumatic tires include tires for passenger cars, tires for trucks and buses, tires for motorcycles, and high-performance tires, with pneumatic tires being particularly suitable for use as passenger car tires. The term "high-performance tire" in this specification refers to a tire having particularly good grip performance, and is a concept that even includes racing tires used for racing cars.

[0173] A tire including a tread comprising the first layer 6, the second layer 7, and the third layer 8 can be manufactured by a conventional method using the aforementioned rubber composition. In other words, the tire can be manufactured by extruding an unvulcanized rubber composition, compounded as needed with each of the above-mentioned components based on the rubber component, into the shapes of the first layer 6, the second layer 7, and the third layer 8 using an extruder having a base having a predetermined shape, connecting them together with other tire components on a tire molding machine, molding them into an unvulcanized tire by a conventional method, and then heating and pressurizing the unvulcanized tire in a vulcanizer.

[0174] Example

[0175] Although the present disclosure will be described based on embodiments, the present disclosure is not limited to these embodiments.

[0176] Various chemicals used in Examples and Comparative Examples are shown below:

[0177] NR:TSR20

[0178] SBR: Modified solution-polymerized SBR prepared in Preparation Example 1 below (styrene content: 30% by mass, vinyl content: 52 mol%, Mw: 250,000, non-oil-extended product)

[0179] BR: UBEPOI BR (registered trademark) 150B (vinyl content: 1.5 mol%, cis content: 97%, Mw: 440,000), manufactured by Ube Industries, Ltd.

[0180] Carbon black: Diablack N220 (N2SA: 115m 2 / g), manufactured by Mitsubishi Chemical Co.

[0181] Silica: ULTRASIL (registered trademark) 9100GR (N2SA: 230m 2 / g, average primary particle size: 15 nm), manufactured by Evonik Degussa.

[0182] Aluminum hydroxide: APYRAL 120E (average particle size: 0.9 μm, N2SA: 11 μm 2 / g), manufactured by Nabaltec AG.

[0183] Silane coupling agent 1: NXT-Z45 (mercapto-based silane coupling agent), manufactured by Momentive Performance Materials.

[0184] Silane coupling agent 2: Si266 (bis(3-triethoxysilylpropyl)disulfide)), manufactured by Evonik Degussa.

[0185] Oil: Processing oil X-140, manufactured by JXTG Energy Corporation.

[0186] Resin component: SYLVARES SA85 (copolymer of α-methylstyrene and styrene, softening point: 85°C), manufactured by Kraton Corporation.

[0187] Liquid rubber: Ricon 100 (liquid SBR), manufactured by Clay Valley Company.

[0188] Wax: Sunnock N, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0189] Antioxidant 1: NOCRAC 6C (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0190] Antioxidant 2: NOCRAC 224 (2,4-trimethyl-1,2-dihydroquinoline polymer), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0191] Stearic acid: Bead stearic acid "Tsubaki", manufactured by NOF Corporation.

[0192] Zinc oxide: Zinc oxide No. 2, manufactured by Mitsui Mining and Smelting Co., Ltd.

[0193] Sulfur: Powdered sulfur (powdered sulfur containing 5% oil) manufactured by Tsurumi Chemical Co., Ltd.

[0194] Vulcanization accelerator 1: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0195] Vulcanization accelerator 2: Soxinol DG (N,N'-diphenylguanidine), manufactured by Sumitomo Chemical Co., Ltd.

[0196] Preparation Example 1: Synthesis of SBR1

[0197] Cyclohexane, tetrahydrofuran, styrene and 1,3-butadiene are added to a nitrogen-substituted autoclave reactor. The temperature of the reactor contents is adjusted to 20°C, and n-butyl lithium is added to initiate polymerization. The polymerization is carried out under adiabatic conditions, and the temperature reaches a maximum temperature of 85°C. When the polymerization conversion reaches 99%, 1,3-butadiene is added, and after further polymerization for 5 minutes, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane is added as a denaturant to react. After the polymerization reaction is completed, 2,6-di-tert-butyl-p-cresol is added. Next, the solvent is removed by steam stripping and dried by a heated roller with the temperature adjusted to 110°C to obtain SBR 1.

[0198] (Examples and Comparative Examples)

[0199] According to the compounding formula shown in Table 1, all chemicals except sulfur and the vulcanization accelerator were kneaded for 1 to 10 minutes using a 1.7L closed Banbury mixer until the discharge temperature reached 150°C to 160°C to obtain a kneaded product. Next, sulfur and the vulcanization accelerator were added to the obtained kneaded product using a twin-screw open roll, and the mixture was kneaded for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was extruded into the shape of the first, second, and third layers of the tread and connected together with other tire components to produce an unvulcanized tire. It was then vulcanized at 150°C for 30 minutes to obtain each test tire shown in Table 2 (size: 205 / 55R15, rim: 15x6.0J, internal pressure: 230kPa).

[0200] <Fuel Efficiency>

[0201] Rolling resistance was measured using a rolling resistance tester, with each test tire operating under conditions of a 15×6JJ rim, 230 kPa internal pressure, 3.43 kN load, and 80 km / h speed. The rolling resistance was expressed as an index value using the following calculation equation, with the rolling resistance of the test tire in Comparative Example 8 set at 100. A larger value indicates better fuel efficiency.

[0202] (Fuel efficiency index)=(rolling resistance of the tire in Comparative Example 8) / (rolling resistance of each test tire)×100

[0203] <Wet grip performance>

[0204] Each test tire was mounted on all wheels of a 2000cc Japanese-made FF vehicle, and the braking distance was measured from the moment the brakes were applied while traveling at 100 km / h on a wet asphalt road surface. The following calculation equation was used to express wet grip performance as an index value, with the braking distance of the test tire in Comparative Example 8 set at 100. This indicates that larger values indicate better wet grip performance.

[0205] (Wet grip performance index) = (braking distance of the tire of Comparative Example 8) / (braking distance of each test tire) x 100

[0206] <Abrasion resistance>

[0207] Each test tire was mounted on all wheels of a 2000cc Japanese FF vehicle and driven, and the change in pattern groove depth after 50,000 km of driving was measured. The reciprocal value of the change was expressed as an index value, with Comparative Example 8 set to 100. The larger the value, the better the wear resistance.

[0208] Durability

[0209] Each test tire was mounted on all wheels of a 2000cc Japanese FF vehicle. The vehicle was driven during the test, and the presence of cracks around the interface between the first and second tread layers was determined during zigzag driving with critical grip. The following calculation equation was used to determine the durability index. A larger value indicates better durability.

[0210] (Durability index) = (number of cracks in the tire of Comparative Example 8) - (number of cracks in each test tire) + 100

[0211] For the overall performance of fuel efficiency, wet grip performance, wear resistance and durability (the sum of the fuel efficiency index, wet grip performance index, wear resistance index and durability index), more than 400 is set as the target performance value.

[0212]

[0213]

[0214] Based on the results of Tables 1 and 2, it is apparent that, for the tire of the present disclosure, in which the tread portion is provided with three or more predetermined rubber layers, the rubber layers are made in a specific compounding ratio, and the groove depth in the second layer relative to the depth of the circumferential groove is set to a predetermined ratio, there is an improvement in the overall performance of fuel efficiency, wet grip performance, wear resistance, and durability.

[0215] Reference numerals

[0216] 1 Circumferential groove

[0217] 2 Landing area

[0218] 3 Tread surface

[0219] 4 Extension line of the landing part

[0220] 5 Extension line of the deepest part of the groove bottom of the circumferential groove

[0221] 6 First Floor

[0222] 7 Second Floor

[0223] 8 Third Floor

[0224] 9 Extension line of the outer surface of the second layer

Claims

1. A tire having a tread, wherein the tread includes at least a first layer constituting a tread surface, a second layer arranged adjacent to an inner side of the first layer in a radial direction, and a third layer existing on an inner side of the second layer in a radial direction, wherein the first layer, the second layer and the third layer are composed of a rubber composition comprising a rubber component, wherein the rubber composition constituting the first layer and the second layer comprises silica and a mercapto-based silane coupling agent, wherein the rubber compositions constituting the first layer and the second layer each have a silica content greater than their carbon black content based on 100 parts by mass of the rubber component, wherein the rubber composition constituting the third layer contains carbon black as a filler, in, the softener content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component is greater than the softener content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component, wherein the tread has a land portion separated by a plurality of circumferential grooves, wherein the deepest portion of the groove bottom of the circumferential groove is formed on the inner side of the outer surface of the second layer in the tire radial direction, and In which, when the distance between the extension line of the landing portion and the extension line of the deepest part of the groove bottom of the circumferential groove is defined as H1, and the distance between the extension line of the outer surface of the second layer and the extension line of the deepest part of the groove bottom of the circumferential groove is defined as H2, H2 / H1 is greater than 0.

20.

2. The tire according to claim 1, wherein The difference between the softener content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the softener content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 50 parts by mass or less.

3. The tire according to claim 1 or 2, wherein: The difference between the sulfur content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the sulfur content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 1.0 part by mass or less.

4. The tire according to claim 1 or 2, wherein: The difference between the vulcanization accelerator content of the rubber composition constituting the first layer based on 100 parts by mass of the rubber component and the vulcanization accelerator content of the rubber composition constituting the second layer based on 100 parts by mass of the rubber component is 3.5 parts by mass or less.

5. The tire according to claim 1 or 2, wherein: H2 / H1 is 0.30 or more. 6 . The tire according to claim 1 , wherein at least one of the rubber compositions constituting the first layer and the second layer contains 100 parts by mass or more of silica based on 100 parts by mass of the rubber component.

7. The tire according to claim 1 or 2, wherein: The rubber compositions constituting the first and second layers each contain 50 to 130 parts by mass of silica based on 100 parts by mass of the rubber component, and the proportion of silica relative to the total content of silica and carbon black is 60% by mass or more.

8. The tire according to claim 1 or 2, wherein: The rubber compositions constituting the first layer and the second layer each contain 10 parts by mass or more of a softener based on 100 parts by mass of the rubber component.

9. The tire according to claim 1 or 2, wherein: The rubber components constituting the first layer and the second layer each contain 40% by mass or more of styrene-butadiene rubber based on 100 parts by mass of the rubber component.

10. The tire according to claim 1 or 2, wherein: The content of the diene-based rubber modified with a functional group having affinity for silica in 100% by mass of the rubber component constituting the first layer and the second layer is 40% by mass or more.

11. The tire according to claim 1 or 2, wherein: The rubber composition constituting the first layer includes 1.0 part by mass or more of aluminum hydroxide based on 100 parts by mass of the rubber component.

12. The tire according to claim 1 or 2, wherein: The thickness of each of the first layer, the second layer, and the third layer is 1.0 mm or greater.

13. The tire according to claim 1 or 2, wherein: A ratio (t2 / t1) of a thickness t2 of the second layer to a thickness t1 of the first layer is 0.4 to 5.

0.

14. The tire according to claim 1 or 2, wherein: A ratio (t3 / t2) of a thickness t3 of the third layer to a thickness t2 of the second layer is 0.2 to 3.

0.

15. The tire according to claim 1 or 2, wherein: The tire inner cavity is provided with at least one selected from the group consisting of a sealant, a noise damping body, and an electronic component for tire monitoring.

16. The tire according to claim 1 or 2, wherein: The tire is a tire for a passenger car.

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