Tire for heavy load, green tire for tire for heavy load, and method for manufacturing tire for heavy load

Abstract

In this tire for a heavy load 1: tread rubber 7 includes a cap layer 7c and a base layer 7b that is disposed on the tire inner circumferential side relative to the cap layer 7c; the cap layer 7c includes a cap surface layer 7c1 and a cap intermediate layer 7c2 that is disposed on the tire inner circumferential side relative to the cap surface layer 7c1 and is formed from a type of rubber different from the rubber that forms the cap surface layer 7c1; and in at least one tire half Q relative to the tire equatorial plane CL, the thickness of the cap intermediate layer 7c2 between a prescribed tire width direction position X that is a prescribed distance from the tire equatorial plane CL and a tire width direction position D at a contact patch edge TE is thinner than the thickness of the cap intermediate layer 7c2 inward in the tire width direction relative to the prescribed tire width direction position X.

Description

Heavy-duty reuse tire, green tire for heavy-duty reuse tire, and method for manufacturing heavy-duty reuse tire

[0001] This application claims priority based on Japanese Patent Application No. 2024-224395 filed in Japan on December 19, 2024, the entire content of which is incorporated herein by reference. The present invention relates to a heavy-duty reuse tire, a green tire for a heavy-duty reuse tire, and a method for manufacturing a heavy-duty reuse tire.

[0002] Conventionally, in the manufacture of heavy-duty reuse tires, before vulcanization molding, there are cases where the tread rubber portion in a region substantially corresponding to the region where the lug grooves are to be formed in the tread rubber of the green tire is removed by grooving (for example, Patent Document 1).

[0003] WO2024 / 024255A1

[0004] Since heavy-duty reuse tires are large-sized, the amount of the tread rubber portion removed by grooving (also referred to as "removed rubber" in this specification) also increases. Therefore, it is considered preferable from the viewpoint of reducing waste of resources and the like to recover the removed rubber and reuse it when manufacturing another tire. However, when the tread rubber has three layers of a cap surface layer, a cap intermediate layer, and a base layer, there is a high possibility that the removed rubber will contain not only the rubber constituting the cap surface layer (cap surface layer rubber) but also rubber of a different type from the cap surface layer rubber (particularly, the rubber constituting the cap intermediate layer (cap intermediate layer rubber)). If the mixing rate of the different-type rubber in the removed rubber is high, for example, when the removed rubber is reused for the cap surface layer of another heavy-duty reuse tire, there is a possibility that the physical properties of the cap surface layer in the other heavy-duty reuse tire will be significantly different from the expected ones.

[0005] An object of the present invention is to provide a heavy-duty reuse tire, a green tire for a heavy-duty reuse tire, and a method for manufacturing a heavy-duty reuse tire, which are capable of reducing the mixing rate of different-type rubber in the tread rubber portion (removed rubber) removed by grooving.

[0006] The above object is solved by the following means.

[0007] [1] A heavy-duty tire having a tread rubber comprising a cap layer and a base layer disposed on the inner circumference side of the tire from the cap layer, wherein the cap layer comprises a cap surface layer and a cap intermediate layer disposed on the inner circumference side of the tire from the cap surface layer and made of a different type of rubber than the rubber constituting the cap surface layer, wherein in at least one half of the tire with respect to the tire equator, the thickness of the cap intermediate layer between a predetermined tire width direction position at a predetermined distance from the tire equator and a tire width direction position at the contact end is thinner than the thickness of the cap intermediate layer in the tire width direction inward from the predetermined tire width direction position.

[0008] [9] A green tire for heavy loads, wherein the tread rubber comprises a cap layer and a base layer disposed on the inner circumference side of the tire from the cap layer, the cap layer comprises a cap surface layer and a cap intermediate layer disposed on the inner circumference side of the tire from the cap surface layer and made of a different type of rubber than the rubber constituting the cap surface layer, and in at least one half of the tire with respect to the tire equator, the thickness of the cap intermediate layer between a predetermined tire width direction position at a predetermined distance from the tire equator and a tire width direction position at the contact end is thinner than the thickness of the cap intermediate layer inside the tire width direction position from the predetermined tire width direction position.

[0009]

[10] A method for manufacturing a heavy-duty tire, comprising: a pre-grooving green tire manufacturing step of manufacturing a pre-grooving green tire; a grooving step of grooving the pre-grooving green tire to obtain a grooved green tire; and a vulcanization molding step of vulcanizing the grooved green tire using a vulcanization molding die to obtain a vulcanized heavy-duty tire, wherein the pre-grooving green tire has a tread rubber comprising: a cap layer; a base layer disposed on the inner circumference side of the tire from the cap layer; and the cap layer comprising: a cap surface layer; and a cap intermediate layer disposed on the inner circumference side of the tire from the cap surface layer and made of a different type of rubber from the rubber constituting the cap surface layer. A method for manufacturing heavy-duty tires, wherein in the raw tire before grooving, the thickness of the cap intermediate layer between a predetermined tire widthwise position at a predetermined distance from the tire equator and a tire widthwise position at the contact end is thinner than the thickness of the cap intermediate layer inward in the tire widthwise direction from the predetermined tire widthwise position, and in the grooving step, the portion of the tread rubber of the raw tire before grooving that is in a region substantially corresponding to the region where lug grooves will be formed in the vulcanization molding step is removed by grooving.

[0010] According to the present invention, it is possible to provide a heavy-duty tire, a green tire for heavy-duty tires, and a method for manufacturing heavy-duty tires that can reduce the mixing rate of different types of rubber in the tread rubber portion (removed rubber) that is removed by grooving.

[0011] This is a schematic cross-sectional view in the tire width direction showing a raw tire and a heavy-duty tire for heavy-duty use according to one embodiment of the present invention, which may have the tread rubber configuration of any embodiment of the present invention. This is a schematic cross-sectional view in the tire width direction showing the tread rubber in a raw tire and a heavy-duty tire for heavy-duty use according to the first embodiment of the present invention. This is a schematic cross-sectional view in the tire width direction showing the tread rubber in a raw tire and a heavy-duty tire for heavy-duty use according to the second embodiment of the present invention. This is a schematic cross-sectional view in the tire width direction showing the tread rubber in a raw tire and a heavy-duty tire for heavy-duty use according to the third embodiment of the present invention. This is a schematic diagram for explaining the grooving step in a heavy-duty tire manufacturing method according to one embodiment of the present invention. This is a schematic view of one of the plurality of removed rubbers removed by grooving in the grooving step illustrated in Figure 5, as seen in the direction of the arrow S in Figure 5.

[0012] The heavy-duty tire, the green tire for heavy-duty tires, and the method for manufacturing heavy-duty tires according to the present invention can be suitably used for any type of heavy-duty tire, and are particularly suitable for tires for construction and mining vehicles (off-the-road tires).

[0013] Hereinafter, embodiments of the heavy-duty tire, the green tire for heavy-duty tires, and the method for manufacturing heavy-duty tires according to the present invention will be illustrated with reference to the drawings. In each figure, common members and parts are denoted by the same reference numerals. In this specification, for convenience, the heavy-duty tire is also simply referred to as "tire," and the green tire for heavy-duty tires is also simply referred to as "green tire." In this specification, a tire is a pneumatic tire. Furthermore, in this specification, unless otherwise specified, "heavy-duty tire" or "tire" refers to a tire that has been vulcanized and molded, and is distinguished from a "green tire" that is in the state before vulcanization and molding.

[0014] In this specification, for the sake of convenience, the configurations of the green tires R1B, R1A and tire 1 according to various embodiments of the present invention will be described in parallel. Strictly speaking, the green tires R1B and R1A before vulcanization molding and the tire 1 after vulcanization molding may differ in various configurations such as shape, but for the sake of convenience, Figures 1 to 4 show the configurations of the green tires R1B, R1A and tire 1 according to various embodiments of the present invention in a very schematic manner using common drawings. As will be explained in detail later, Figure 1 shows the green tire R1B before grooving, and Figures 2 to 4 show the green tire R1B before grooving and the green tire R1A after grooving.

[0015] Figure 1 is a schematic cross-sectional view in the width direction of a tire, showing a raw tire R1B and a heavy-duty tire 1 for heavy loads according to one embodiment of the present invention, which may have the configuration of the tread rubber 7 in any embodiment of the present invention described herein. The raw tire R1B and tire 1 in the embodiment of Figure 1 are configured as a raw tire and tire for construction and mining vehicles (off-the-road use), respectively. However, the raw tires R1B, R1A and tire 1 in each embodiment of the present invention described herein may be configured as any type of raw tire and tire for heavy loads.

[0016] Unless otherwise specified, the positional relationships and dimensions of each element shall be measured under standard conditions, with the green tire R1B, R1A, or tire 1 mounted on the applicable rim, filled to the specified internal pressure, and unloaded. Furthermore, with the green tire R1B, R1A, or tire 1 mounted on the applicable rim, filled to the specified internal pressure, and under maximum load, the width of the contact surface in the tire width direction that contacts the road surface shall be called the "contact width TW," and the end of the contact surface in the tire width direction shall be called the "contact end TE."

[0017] In this specification, "Applicable Rim" refers to the standard rim for the applicable size (Measuring Rim in ETRTO's STANDARDS MANUAL, Design in TRA's YEAR BOOK) which is an industrial standard valid in the region where the pneumatic tire is produced and used, and which is described or will be described in the future in publications such as the JATMA YEAR BOOK of JATMA (Japan Automobile Tire Association) in Japan, the STANDARDS MANUAL of ETRTO (The European Tyre and Rim Technical Organization) in Europe, and the YEAR BOOK of TRA (The Tire and Rim Association, Inc.) in the United States. This refers to the rim, but in the case of sizes not listed in these industry standards, it refers to a rim with a width corresponding to the bead width of the pneumatic tire 1. "Applicable rims" include current sizes as well as sizes that will be listed in the aforementioned industry standards in the future. An example of "sizes that will be listed in the future" is the size listed as "FUTURE DEVELOPMENTS" in the ETRTO 2013 edition.

[0018] In this specification, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size and ply rating as described in the aforementioned industrial standards such as the JATMA YEAR BOOK. For sizes not listed in the aforementioned industrial standards, it refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted. Furthermore, in this specification, "maximum load" refers to the load corresponding to the maximum load capacity of a tire of the applicable size as described in the aforementioned industrial standards, or, for sizes not listed in the aforementioned industrial standards, the load corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted.

[0019] In this specification, "tire circumferential direction" refers to the direction in which the tire R1B, R1A, or tire 1 rotates around the central axis (tire rotation axis O) of the tire R1B, R1A, or tire 1; "tire radial direction" refers to the direction perpendicular to the tire rotation axis O; and "tire width direction" refers to the direction parallel to the tire rotation axis O. In some drawings, the tire circumferential direction is indicated by the symbol "CD", the tire radial direction by the symbol "RD", and the tire width direction by the symbol "WD". Furthermore, in this specification, the side of the tire radial direction closer to the tire rotation axis O is referred to as the "inner side of the tire radial direction (RDI)", and the side of the tire radial direction further from the tire rotation axis O is referred to as the "outer side of the tire radial direction (RDO)". In addition, in this specification, the side of the tire width direction closer to the tire equatorial plane CL is referred to as the "inner side of the tire width direction", and the side of the tire width direction further from the tire equatorial plane CL is referred to as the "outer side of the tire width direction".

[0020] First, the overall structure of the green tires R1B, R1A, and tire 1 will be described. In Figure 1, the green tire shown is the pre-grooving green tire R1B, which will be described later, and the grooved green tire R1A, which will be described later, is not shown. However, the grooved green tire R1A has the same configuration as the pre-grooving green tire R1B, except that it has the grooved recess k (Figures 2 to 4) described later. As shown in Figure 1, the green tires R1B, R1A, and tire 1 each include a tread portion 1a, a pair of sidewall portions 1b extending inward in the tire radial direction from both ends of the tread portion 1a in the tire width direction, and a pair of bead portions 1c provided at the inner ends of each sidewall portion 1b in the tire radial direction. The bead portions 1c are configured to contact the rim on the inner side in the tire radial direction and the outer side in the tire width direction when the green tire R1B, R1A, or tire 1 is mounted on the rim. Furthermore, the green tires R1B, R1A, and tire 1 each include a pair of bead cores 4a, a pair of bead fillers 4b, a carcass 5, a belt 6, a tread rubber 7, a side rubber 8, and an inner liner 9.

[0021] Each bead core 4a is embedded in the corresponding bead portion 1c. The bead core 4a comprises a plurality of bead wires, each covered with rubber. The bead wires are preferably made of metal (e.g., steel). The bead wires can be, for example, monofilaments or stranded wires.

[0022] Each bead filler 4b is located radially outward relative to the corresponding bead core 4a. The bead fillers 4b taper outward in the radial direction of the tire. The bead fillers 4b are made of rubber. Generally, bead fillers 4b are sometimes called "stiffeners".

[0023] The carcass 5 spans between a pair of bead cores 4a and extends in a toroidal manner. The carcass 5 is composed of one or more (one in the example in Figure 1) carcass plies 5a. Each carcass ply 5a includes one or more carcass cords and a covering rubber covering the carcass cords. The carcass cords can be formed from monofilaments or stranded wires. The carcass 5 is preferably radial in structure, but may also be biased.

[0024] The belt 6 is positioned radially outward relative to the crown portion of the carcass 5. The belt 6 comprises one or more belt layers 6a (six layers in the example shown in Figure 1). Each belt layer 6a includes one or more belt cords and a covering rubber covering the belt cords. The belt cords can be made of monofilament or stranded wire. The belt cords are preferably made of metal (e.g., steel), but may also be made of organic fibers such as polyester, nylon, rayon, or aramid.

[0025] The tread rubber 7 is located on the outer side of the belt 6 in the tire radial direction in the tread portion 1a. The tread rubber 7 constitutes the tread tread surface 2, which is the outer surface of the tread portion 1a in the tire radial direction. A tread pattern is formed on the tread tread surface 2 of the tire 1 by grooves and / or sipes. The tread pattern is formed by vulcanization molding of the green tire R1A. Therefore, the green tires R1B and R1A do not have a tread pattern (and consequently, grooves and / or sipes on the tread tread surface 2). For example, in the example in Figure 1, a plurality of lug grooves h are formed on the tread tread surface 2 of the tire 1 in the tire half Q on at least one side (both sides in the example in Figure 1) with respect to the tire equatorial plane CL. Each lug groove h opens at the contact end TE, extends inward in the tire width direction from the contact end TE, and terminates just before reaching the tire equatorial plane CL. In at least one side (both sides in the example in Figure 1), a plurality of lug grooves h are arranged at intervals from each other along the circumferential direction of the tire in the tire half Q. Note that the position and shape of the lug grooves h illustrated in Figure 1 are merely examples, and the position and shape of the lug grooves h formed in tire 1 may differ from those in Figure 1. In Figure 1, grooves and / or sipes that may be provided on the tread surface 2 other than the lug grooves h are not shown. In green tires R1B and R1A, the tread rubber 7 is made of raw rubber (unvulcanized rubber). The tread rubber 7 in green tires R1B and R1A can be molded, for example, by extrusion molding. In tire 1, the tread rubber 7 is made of vulcanized rubber. Further details of the tread rubber 7 will be described later.

[0026] The side rubber 8 is located on the sidewall portion 1b. The side rubber 8 constitutes the outer surface of the sidewall portion 1b on the outside in the tire width direction. The side rubber 8 is located further outward in the tire width direction than the carcass 5. The side rubber 8 is located further outward in the tire width direction than the bead filler 4b. The side rubber 8 is formed integrally with the tread rubber 7. In green tires R1B and R1A, the side rubber 8 is made of raw rubber (unvulcanized rubber). In tire 1, the side rubber 8 is made of vulcanized rubber.

[0027] The inner liner 9 is positioned on the inside of the tire of the carcass 5, and may be laminated on the inside of the tire of the carcass 5, for example. The inner liner 9 is made of, for example, a butyl rubber with low air permeability. Butyl rubbers include, for example, butyl rubber and its derivative, halogenated butyl rubber. The inner liner 9 is not limited to butyl rubber and can be made of other rubber compositions, resins, or elastomers.

[0028] Here, with reference to Figures 5 to 6, a method for manufacturing heavy-duty tires according to one embodiment of the present invention will be described. The method for manufacturing heavy-duty tires according to this embodiment can be used to manufacture heavy-duty tires 1 according to any embodiment of the present invention. The method for manufacturing heavy-duty tires includes a pre-grooving tire manufacturing step, a grooving step, and a vulcanization molding step.

[0029] First, in the pre-grooving green tire manufacturing step, a pre-grooving green tire R1B is manufactured. As shown by the solid and dashed lines in Figure 5, the pre-grooving green tire R1B refers to the green tire in the state immediately before the grooving step described later is performed. The outer surface of the tread rubber 7 of the pre-grooving green tire R1B may be a substantially cylindrical smooth surface with virtually no recesses. In Figure 1, an example of a pre-grooving green tire R1B is schematically shown by a solid line.

[0030] Subsequently, in the grooving step, the pre-grooving green tire R1B manufactured in the pre-grooving green tire manufacturing step is grooved to obtain a grooved green tire R1A. The grooved green tire R1A refers to the green tire immediately after the grooving step is performed, as shown by the solid line in Figure 5. In the grooving step, the tread rubber portions m of the tread rubber 7 of the pre-grooving green tire R1B that are located in areas that substantially correspond to the areas where lug grooves h will be formed in the subsequent vulcanization molding step (also referred to in this specification as the "lug groove formation planned area hp") are removed by grooving. In this specification, the tread rubber portions m that are removed by grooving are also referred to as "removed rubber m". In the tread rubber 7 of the pre-grooving green tire R1B, the areas from which each removed rubber m has been removed become recesses (referred to in this specification as "grooved recesses k"). Therefore, the outer circumferential surface of the tread rubber 7 of the grooved green tire R1A has a plurality of grooved recesses k. Note that the area hp where the lug grooves are to be formed, and the area to be grooved (and consequently, the tread rubber portion m removed by grooving, and the grooved recess k) may each exist at multiple positions spaced apart from each other along the circumferential direction of the tire, at least on one half of the tire Q. However, for simplicity, only some of these are shown in Figure 5. Figure 6 is a very schematic view of one of the multiple rubber portions m removed by grooving in the grooving step illustrated in Figure 5, as seen in the direction of the arrow S in Figure 5. Grooving may be performed using a machine or by hand.

[0031] Subsequently, in the vulcanization molding step, the grooved green tire R1A obtained in the grooving step is vulcanized using a vulcanization molding die to obtain a vulcanized heavy-duty tire 1. Although not shown in the figures, the molding surface of the vulcanization molding die has a plurality of lug groove forming protrusions, each configured to form lug grooves h in the lug groove formation area hp of the tread rubber 7. When setting the grooved green tire R1A into the vulcanization molding die in the vulcanization molding step, the plurality of lug groove forming protrusions of the vulcanization molding die are each positioned to fit into the corresponding grooved recess k in the grooved green tire R1A.

[0032] Generally, since heavy-duty tires 1 are large, the tread rubber 7 of the raw tires R1B and R1A for heavy-duty tires tends to be thick. If grooving (grooving step) is not performed, when setting the raw tire R1A in the vulcanization molding die, it is necessary to press the multiple lug groove forming protrusions of the vulcanization molding die into the tread rubber 7 of the raw tire R1A. This can make it difficult to set the raw tire R1A in the desired position in the vulcanization molding die, and the surrounding tread rubber 7 may be pressed by the lug groove forming protrusions, potentially causing unwanted deformation of the tire components in that area. In other words, by performing grooving (grooving step) in advance, when setting the green tire R1A into the vulcanization molding die afterward, it is possible to reduce the need to press the multiple lug groove forming protrusions of the vulcanization molding die into the tread rubber 7 of the green tire R1A. Consequently, it becomes easier to set the green tire R1A in the desired position within the vulcanization molding die, and the risk of undesirable deformation of the tire components near the lug groove forming protrusions is reduced.

[0033] The number of tread rubber portions m (rubber to be removed m) removed by grooving (grooving step) is preferably the same as the number of lug grooves h (and consequently, the planned lug groove formation area hp) formed in the vulcanization molding step. The area of ​​tread rubber portions m removed by grooving (grooving step) is preferably overlapping with the corresponding planned lug groove formation area hp, but it is not necessary for it to perfectly coincide with the corresponding planned lug groove formation area hp.

[0034] The configuration of the tread rubber 7 in each of the green tires R1B, R1A, and tire 1 according to various embodiments of the present invention will be described in more detail below. Unless otherwise specified, the configuration of the tread rubber 7 described herein can be applied to each of the green tires R1B, R1A, and tire 1 according to any embodiment of the present invention. In Figure 1, the solid line shows the green tire R1B before grooving, and the solid line and dashed line (showing lug grooves h) show the (vulcanized) tire 1. Figures 2 to 4 are cross-sectional views in the tire width direction, showing the tread rubber 7 in each of the green tires R1B, R1A, and tire 1 according to the first to third embodiments of the present invention, in a more schematic manner than in Figure 1. In Figures 2 to 4, the solid lines show the tread rubber 7 of the ungrooved green tire R1B, the solid lines and dashed lines (showing grooved recesses k) show the tread rubber 7 of the grooved green tire R1A, and the solid lines and dashed lines (showing lug grooves h) show the tread rubber 7 of the (vulcanized) tire 1. For the sake of explanation, various embodiments of the present invention, including the first to third embodiments, will be described in parallel below.

[0035] As shown in Figures 1 to 4, the tread rubber 7 has a cap layer 7c and a base layer 7b. The base layer 7b is located on the inner circumference side of the tire than the cap layer 7c. The cap layer 7c has two layers: a cap surface layer 7c1 and a cap intermediate layer 7c2. In each embodiment of Figures 1 to 4, it consists of these two layers. The cap intermediate layer 7c2 is located on the inner circumference side of the tire than the cap surface layer 7c1. The cap intermediate layer 7c2 is made of a different type of rubber (in this specification, the rubber making up the cap intermediate layer 7c2 is also referred to as "cap intermediate layer rubber 7c2r") than the rubber making up the cap surface layer 7c1 (in this specification, also referred to as "cap surface rubber 7c1r"). Therefore, the physical properties of the cap surface rubber 7c1r may differ from the physical properties of the cap intermediate layer rubber 7c2r. The outer circumference side surface of the cap surface layer 7c1 constitutes the tread surface 2. The base layer 7b is made of a different type of rubber than the cap surface rubber 7c1r and the cap intermediate layer rubber 7c2r (in this specification, the rubber constituting the base layer 7b is also referred to as "base layer 7b rubber"). Therefore, the physical properties of the base layer 7b may differ from those of the cap surface rubber 7c1r and the cap intermediate layer rubber 7c2r. In each embodiment of Figures 1 to 4, the tread rubber 7 consists of three layers: the cap surface layer 7c1, the cap intermediate layer 7c2, and the base layer 7b.

[0036] The cap surface layer 7c1, the cap intermediate layer 7c2, and the base layer 7b each extend across the entire tire width region between the tire width direction positions D of a pair of contact ends TE.

[0037] As shown in Figures 2 to 4, in at least one side (both sides in each embodiment of Figures 2 to 4) of the tire half Q with respect to the tire equatorial plane CL, the thickness of the cap intermediate layer 7c2 between a predetermined tire width direction position X and the tire width direction position D of the contact end TE is thinner than the thickness of the cap intermediate layer 7c2 inside the tire width direction from the predetermined tire width direction position X. The predetermined tire width direction position X is a position in the tire width direction that is a predetermined distance away from the tire equatorial plane CL in the tire width direction. That is, in the at least one side of the tire half Q, the thickness of the cap intermediate layer 7c2 is thinner outside the tire width direction than inside the tire width direction. By making the thickness of the cap intermediate layer 7c2 relatively thin on the outer side in the tire width direction, compared to a case where the thickness of the cap intermediate layer 7c2 is not relatively thin on the outer side in the tire width direction, the proportion of the cap surface layer rubber 7c1r in the tread rubber portion m (removed rubber m) removed by grooving (grooving step) during manufacturing becomes higher, and the mixing rate of different types of rubber (especially the cap intermediate layer rubber 7c2r) can be reduced (see Figures 2 to 4 and 6). Specifically, for example, it becomes possible to reduce the mixing rate of different types of rubber in the removed rubber m to 10% by mass or less (or 5% by mass or less) per green tire. Therefore, for example, when the removed rubber m is reused as the cap surface layer 7c1 of another heavy-duty tire 1, the risk that the physical properties of the cap surface layer 7c1 of that other heavy-duty tire 1 will be significantly different from what was intended can be reduced. Furthermore, by making the thickness of the cap intermediate layer 7c2 relatively thicker on the inner side in the tire width direction, it is possible to increase the amount of the cap intermediate layer 7c2 compared to the case where the thickness of the cap intermediate layer 7c2 is thin across the entire width of the tire, thereby effectively utilizing the performance of the cap intermediate layer 7c2 and improving tire performance.

[0038] From the same viewpoint as described above, as shown in Figures 2 to 4, it is preferable that the thickness of the cap surface layer 7c1 between a predetermined tire width direction position X and the tire width direction position D of the contact end TE in at least one side (both sides in each embodiment of Figures 2 to 4) of the tire half Q is greater than the thickness of the cap surface layer 7c1 inside the tire width direction from the predetermined tire width direction position X.

[0039] In this specification, the thickness of the tread rubber 7 and the thickness of each layer constituting the tread rubber 7 (cap layer 7c, cap surface layer 7c1, cap intermediate layer 7c2, and base layer 7b) shall be measured parallel to the tire diameter direction.

[0040] The thickness of the tread rubber 7 may be substantially constant along the tire width direction between the tire width direction positions D of the pair of contact points TE, or it may vary along the tire width direction. The thickness of the cap layer 7c may be substantially constant along the tire width direction between the tire width direction positions D of the pair of contact points TE, or it may vary along the tire width direction. The thickness of the base layer 7b may be substantially constant along the tire width direction between the tire width direction positions D of the pair of contact points TE, or it may vary along the tire width direction.

[0041] In the grooving step, the removed rubber m (Figure 6) preferably contains a different type of rubber (particularly the intermediate cap rubber 7c2r) from the rubber constituting the cap surface layer 7c1 (cap surface layer rubber 7c1r) at a mixing rate of 10% by mass or less, and more preferably 5% by mass or less, per fresh tire. This effectively reduces the risk that, for example, when the removed rubber m is reused as the cap surface layer 7c1 of another heavy-duty tire 1, the physical properties of the cap surface layer 7c1 in that other heavy-duty tire 1 will differ significantly from those intended.

[0042] From the viewpoints of reducing the mixing ratio of different types of rubber in the rubber m to be removed and ensuring the amount of the cap intermediate layer 7c2, as in each embodiment of FIGS. 2 to 4, in the tire half Q on at least one side, it is preferable that the predetermined tire width direction position X is located between the 3 / 8 point C and the tire width direction position D of the ground contact end TE.

[0043] In this specification, as shown in FIGS. 2 to 4, a pair of tire width direction positions A that are separated from the tire equatorial plane CL by 1 / 8 times the ground contact width TW are each referred to as "1 / 8 point A", and a pair of tire width direction positions B that are separated from the tire equatorial plane CL by 1 / 4 times the ground contact width TW are each referred to as "1 / 4 point B", and a pair of tire width direction positions C that are separated from the tire equatorial plane CL by 3 / 8 times the ground contact width TW are each referred to as "3 / 8 point C".

[0044] From the viewpoints of reducing the mixing ratio of different types of rubber in the rubber m to be removed and ensuring the amount of the cap intermediate layer 7c2, as in each embodiment of FIGS. 2 to 4, in the tire half Q on at least one side (in each embodiment of FIGS. 2 to 4, both sides), the maximum value of the thickness of the cap intermediate layer 7c2 between the predetermined tire width direction position X and the tire width direction position D of the ground contact end TE (the thickness at the tire width direction position where the thickness is maximum) is thinner than the minimum value of the thickness of the cap intermediate layer 7c2 on the inner side in the tire width direction from the predetermined tire width direction position X (the thickness at the tire width direction position where the thickness is minimum), which is preferable. From the same viewpoint, as in each embodiment of FIGS. 2 to 4, in the tire half Q on at least one side (in each embodiment of FIGS. 2 to 4, both sides), the average value of the thickness of the cap intermediate layer 7c2 between the predetermined tire width direction position X and the tire width direction position D of the ground contact end TE is thinner than the average value of the thickness of the cap intermediate layer 7c2 on the inner side in the tire width direction from the predetermined tire width direction position X, which is preferable.

[0045] From the viewpoint of reducing the mixing rate of different types of rubber in the rubber to be removed m and ensuring the amount of the cap intermediate layer 7c2, it is preferable that, as shown in the embodiments of Figures 2 to 4, in the tire half Q on at least one side (both sides in the embodiments of Figures 2 to 4), the thickness of the cap intermediate layer 7c2 gradually decreases towards the outside in the tire width direction over the tire width region between a predetermined tire width direction position X and the tire width direction position D of the contact end TE. In this specification, "gradually decreasing" is a concept that is not limited to cases where it always decreases (smoothly and / or in a step-like manner), but also includes cases where it remains constant in part, but does not include cases where it increases.

[0046] As shown in the embodiments of Figures 2 to 3, in at least one side (both sides in the embodiments of Figures 2 to 3) of the tire half Q, the thickness of the cap intermediate layer 7c2 may be substantially constant along the tire width direction in a tire width region inward from a predetermined tire width direction position X. As shown in the embodiments of Figures 2 to 3, in at least one side (both sides in the embodiments of Figures 2 to 3) of the tire half Q, the outer surface 7c2s of the cap intermediate layer 7c2 on the tire circumferential side may extend substantially linearly along the tire width direction in a tire width region inward from a predetermined tire width direction position X.

[0047] Alternatively, as shown in the embodiment of Figure 4, in at least one side (both sides in the embodiment of Figure 4) of the tire half Q, the thickness of the cap intermediate layer 7c2 may gradually decrease as it moves outward in the tire width direction, over a tire width region inward from a predetermined tire width position X. As shown in the embodiment of Figure 4, in at least one side of the tire half Q (both sides in the embodiment of Figure 4), the outer peripheral surface 7c2s of the cap intermediate layer 7c2 may gradually extend inward in the tire radial direction as it moves outward in the tire width direction, over a tire width region inward from a predetermined tire width position X.

[0048] As in the embodiment of FIG. 2, in the tire half Q on at least one side (both sides in the embodiment of FIG. 2), the thickness of the cap intermediate layer 7c2 may decrease substantially stepwise toward the outer side in the tire width direction over the tire width direction region between the predetermined tire width direction position X and the tire width direction position D of the ground contact end TE.

[0049] In the present specification, the reason for using terms such as "substantially" or "nearly" in the description of thickness and shape is to take into account minute irregularities and the like due to variations that can occur during manufacturing, but "substantially" or "nearly" may not be necessary.

[0050] As in the embodiment of FIG. 2, in the tire half Q on at least one side (both sides in the embodiment of FIG. 2), the surface 7c2s on the outer peripheral side of the tire of the cap intermediate layer 7c2 may extend substantially stepwise inward in the tire radial direction over the tire width direction region between the predetermined tire width direction position X and the tire width direction position D of the ground contact end TE. For example, as in the embodiment of FIG. 2, in the tire half Q on at least one side (both sides in the embodiment of FIG. 2), the surface 7c2s on the outer peripheral side of the tire of the cap intermediate layer 7c2 may have a vertical portion 7c2sb that extends substantially linearly from the predetermined tire width direction position X toward the outer side in the tire width direction, and a horizontal portion 7c2sc that extends substantially linearly from the outer end in the tire width direction of the vertical portion 7c2sb to the tire width direction position D of the ground contact end TE. The angle formed by the vertical portion 7c2sb with respect to the tire width direction is larger than the angle formed by the horizontal portion 7c2sc with respect to the tire width direction. The angle formed by the vertical portion 7c2sb with respect to the tire width direction is preferably more than 45°, and may be, for example, 90°. The angle formed by the horizontal portion 7c2sc with respect to the tire width direction is preferably less than 45°, and may be, for example, 0°.

[0051] Alternatively, as in the embodiments of FIGS. 3 and 4, in the tire half Q on at least one side (both sides in the embodiments of FIGS. 3 and 4), the thickness of the cap intermediate layer 7c2 may decrease substantially smoothly toward the outer side in the tire width direction over the tire width direction region between the predetermined tire width direction position X and the tire width direction position D of the ground contact end TE.

[0052] As shown in the embodiment of Figure 3, in at least one half of the tire Q (both sides in the embodiment of Figure 3), the outer surface 7c2s of the cap intermediate layer 7c2 on the tire circumferential side may extend substantially linearly inward in the tire radial direction as it moves outward in the tire width direction, over a tire width direction region between a predetermined tire width direction position X and a tire width direction position D of the contact end TE.

[0053] Alternatively, as in the embodiment of Figure 4, in at least one half of the tire Q (both sides in the embodiment of Figure 4), the outer surface 7c2s of the cap intermediate layer 7c2 on the tire circumferential side may extend inward in the tire radial direction along a curved line that is convex outward in the tire radial direction as it moves outward in the tire width direction, over a tire width direction region between a predetermined tire width direction position X and the tire width direction position D of the contact end TE.

[0054] Furthermore, as shown in the embodiment of Figure 4, in at least one half of the tire Q (both sides in the embodiment of Figure 4), the outer surface 7c2s of the cap intermediate layer 7c2 on the tire circumferential side may extend in a substantially crescent shape toward the inner side of the tire radially, substantially along a curved line that is convex outward in the tire radially direction, as it moves outward in the tire width direction, over the tire width direction region between the tire equatorial plane CL and the tire contact end TE at the tire width direction position D.

[0055] In a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50Hz, the tanδ of the cap surface layer 7c1 is greater than that of the cap intermediate layer 7c2. The difference between the tanδ of the cap surface layer 7c1 and the tanδ of the cap intermediate layer in a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50Hz may be 0.03 or greater. In this case, the cap surface layer 7c1 has higher abrasion resistance than the cap intermediate layer 7c2, and the cap intermediate layer 7c2 has higher heat resistance than the cap surface layer 7c1. With this configuration of the cap layer 7c, it is possible to achieve a high level of both abrasion resistance and heat resistance.

[0056] In a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50Hz, the tanδ of the cap surface layer 7c1 is greater than that of the cap intermediate layer 7c2. The difference between the tanδ of the cap surface layer 7c1 and the tanδ of the cap intermediate layer 7c2 in a tensile test conducted at room temperature of 24°C, 2% amplitude, and 50Hz may be 0.06 or greater. In this case, the cap surface layer 7c1 has higher abrasion resistance than the cap intermediate layer 7c2, and the cap intermediate layer 7c2 has higher heat resistance than the cap surface layer 7c1. With this configuration of the cap layer 7c, it is possible to achieve a high level of both abrasion resistance and heat resistance.

[0057] The tanδ of the base layer 7b in a tensile test under the conditions of room temperature (24°C), 2% amplitude, and 50 Hz may be 0.03 or more lower than that of the cap intermediate layer 7c2. In this case, a higher level of both abrasion resistance and heat resistance can be achieved.

[0058] The inner end of each lug groove h (and by extension, the planned lug groove formation region hp) in the tire width direction may be at any position. For example, as shown in the examples in Figures 2 to 4, it may be located between the 3 / 8 point C and the tire width direction position D of the contact end TE, or it may be located between the 1 / 4 point B and the 3 / 8 point C.

[0059] As shown in Figures 2 to 4, in the grooved green tire R1A, each grooved recess k opens at the contact end TE, extends inward in the tire width direction from the contact end TE, and terminates just before reaching the tire equatorial plane CL. In the grooved green tire R1A, the inner end of each grooved recess k in the tire width direction may be located outward in the tire width direction from the inner end of the corresponding lug groove h (and thus the planned lug groove formation area hp) in the tire width direction, as in the examples in Figures 2 to 4, or it may be located at the same tire width direction position as the inner end of the corresponding lug groove h (and thus the planned lug groove formation area hp) in the tire width direction. In the grooved green tire R1A, the inner end of each grooved recess k in the tire width direction may be located between the 3 / 8 point C and the tire width direction position D of the contact end TE, as in the examples in Figures 2 to 4. In a grooved raw tire R1A, the inner end of each grooved recess k in the tire radial direction may be located radially outward from the inner end of the corresponding lug groove h (and thus the planned lug groove formation area hp) in the tire radial direction, as shown in the examples in Figures 2 to 4, or it may be located at the same radial position as the inner end of the corresponding lug groove h (and thus the planned lug groove formation area hp) in the tire radial direction.

[0060] The heavy-duty tire, the green tire for heavy-duty tires, and the method for manufacturing heavy-duty tires according to the present invention can be suitably used for any type of heavy-duty tire, and are particularly suitable for tires for construction and mining vehicles (off-the-road tires).

[0061] 1: Heavy-duty tire (tire), R1B: Ungrooved green tire (green tire), R1A: Grooved green tire (green tire), 1a: Tread section, 1b: Sidewall section, 1c: Bead section, 2: Tread surface, 4a: Bead core, 4b: Bead filler, 5: Carcass, 5a: Carcass ply, 6: Belt, 6a: Belt layer, 7: Tread rubber, 7c: Cap layer, 7c1: Cap surface layer, 7c1r: Cap surface rubber, 7c2: Cap intermediate layer, 7c2r: Cap intermediate layer rubber, 7c2s: Outer circumference side of the cap intermediate layer, 7c2sb: Longitudinal section, 7c2sc: Transverse section, 7b: Base layer, 8: Side rubber, 9: Inner liner, CL: Tire equatorial surface, TW: Contact width, TE: Contact edge, A: 1 / 8 point, B: 1 / 4 point, C: 3 / 8 point, D: Position of the contact edge in the tire width direction, Q: Half of the tire Q, X: Determined position in the tire width direction, h: Lug groove, hp: Area where lug groove is to be formed, k: Grooving recess, m: Rubber to be removed (tread rubber portion), O: Tire rotation axis, CD: Tire circumferential direction, WD: Tire width direction, RD: Tire radial direction, RDO: Outer side in the tire radial direction, RDI: Inner side in the tire radial direction

Claims

1. A heavy-duty tire having a tread rubber comprising: a cap layer; a base layer disposed on the inner circumference side of the tire beyond the cap layer; the cap layer comprising: a cap surface layer; and a cap intermediate layer disposed on the inner circumference side of the tire beyond the cap surface layer and made of a different type of rubber than the rubber constituting the cap surface layer; and in at least one half of the tire with respect to the tire equator, the thickness of the cap intermediate layer between a predetermined tire width direction position at a predetermined distance from the tire equator and a tire width direction position at the contact end is thinner than the thickness of the cap intermediate layer in the tire width direction inward from the predetermined tire width direction position.

2. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the predetermined tire width direction position is located between the 3 / 8 point, which is 3 / 8 times the contact width from the tire equatorial plane, and the tire width direction position of the contact end.

3. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the thickness of the cap intermediate layer decreases substantially in a stepped manner as it moves outward in the tire width direction, over a tire width region between the predetermined tire width direction position and the tire width direction position of the contact end.

4. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the outer surface of the cap intermediate layer extends inward in the tire radial direction in a substantially stepped manner as it moves outward in the tire width direction, over a tire width region between the predetermined tire width direction position and the tire width direction position of the contact end.

5. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the thickness of the cap intermediate layer decreases substantially smoothly towards the outside in the tire width direction over a tire width region between the predetermined tire width direction position and the tire width direction position of the contact end.

6. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the outer surface of the cap intermediate layer extends substantially linearly inward in the tire radial direction as it moves outward in the tire width direction, over a tire width region between the predetermined tire width direction position and the tire width direction position of the contact end.

7. The heavy-duty tire according to claim 1, wherein in at least one half of the tire, the outer surface of the cap intermediate layer extends radially inward along a curved line that is convex radially outward as it moves outward in the tire width direction, over a tire width region between the predetermined tire width direction position and the tire width direction position of the contact end, as it moves outward in the tire width direction.

8. The heavy-duty tire according to any one of claims 1 to 7, wherein the cap surface layer, the cap intermediate layer, and the base layer each extend over the entire tire widthwise region between the tire widthwise positions of a pair of contact ends.

9. A green tire for heavy loads, wherein the tread rubber comprises a cap layer and a base layer disposed on the inner circumference side of the tire from the cap layer, the cap layer comprises a cap surface layer and a cap intermediate layer disposed on the inner circumference side of the tire from the cap surface layer and made of a different type of rubber than the rubber constituting the cap surface layer, and in at least one half of the tire with respect to the tire equator, the thickness of the cap intermediate layer between a predetermined tire width direction position at a predetermined distance from the tire equator and a tire width direction position at the contact end is thinner than the thickness of the cap intermediate layer in the tire width direction inward from the predetermined tire width direction position.

10. A method for manufacturing a heavy-duty tire, comprising: a pre-grooving green tire manufacturing step of manufacturing a pre-grooving green tire; a grooving step of grooving the pre-grooving green tire to obtain a grooved green tire; and a vulcanization molding step of vulcanizing the grooved green tire using a vulcanization molding die to obtain a vulcanized heavy-duty tire, wherein the pre-grooving green tire has a tread rubber comprising: a cap layer; a base layer disposed on the inner circumference side of the cap layer; and the cap layer comprising: a cap surface layer; and a cap intermediate layer disposed on the inner circumference side of the cap surface layer and made of a different type of rubber than the rubber constituting the cap surface layer. A method for manufacturing heavy-duty tires, wherein in the raw tire before grooving, the thickness of the cap intermediate layer between a predetermined tire widthwise position at a predetermined distance from the tire equator and a tire widthwise position at the contact end is thinner than the thickness of the cap intermediate layer inward in the tire widthwise direction from the predetermined tire widthwise position, and in the grooving step, the portion of the tread rubber of the raw tire before grooving that is in a region substantially corresponding to the region where lug grooves will be formed in the vulcanization molding step is removed by grooving.

11. The method for manufacturing a heavy-duty tire according to claim 10, wherein the tread rubber portion removed by grooving in the grooving step contains a different type of rubber from the rubber constituting the cap surface layer, with a mixing rate of 10% by mass or less.

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