Pneumatic tire and method for manufacturing same

Abstract

Provided is a pneumatic tire having excellent durability at a belt end while achieving a reduction in rolling resistance. This pneumatic tire is characterized in that: in the center of the tire, the thickness of the first belt layer is 1.00 mm or less and the thickness of the second belt layer is 1.00 mm or less; b / a is 1.8 to 4.0 when the shortest distance in the tire center portion between the cord of the second belt layer and the cord of the first belt layer is denoted as a and the shortest distance between the outermost cord of the second belt layer and the cord of the first belt layer is denoted as b; at the belt end, the end rubber is arranged in a given manner on the inside of the first belt layer in the tire radial direction, between the first belt layer and the second belt layer, and on the outside of the second belt layer in the tire radial direction.

Description

Technical Field

[0001] The present disclosure relates to pneumatic tires and methods of manufacturing the same. Background Art

[0002] In the current manner, a belt generally used as a reinforcing member of a pneumatic tire is made by using two or more belt layers mainly composed of rubber-coated steel cord layers inclined relative to the tire equatorial plane in such a manner that the steel cords in the belt layers cross each other.

[0003] In recent years, in order to achieve the goal of improving the fuel efficiency of automobiles, the demand for reducing the rolling resistance of tires has been increasing. Examples of means for providing tires with low rolling resistance include weight reduction of tire components, especially weight reduction of belt layers. For example, in Patent Document 1, weight reduction is achieved by adopting a bundle of monofilament cords. In addition, the interval between the rubber layers between the monofilament cords of the first belt layer and the second belt layer at the end of the second belt layer is set to be larger than the interval between the rubber layers between the monofilament cords of the first belt layer and the second belt layer in the central part of the tire. As a result, belt edge separation (peeling of the belt end) can be suppressed, thereby achieving both light weight and durability.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-163055 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] However, there is still a need to improve the durability of tires, especially the durability of belt ends. Therefore, there is a need for tires with high durability and low rolling resistance at a higher level.

[0009] Furthermore, in the configuration having two or more belt layers as described above, it is also important to prevent gaps (air pockets) from being formed at the belt ends when manufacturing the tire.

[0010] Therefore, in order to solve the above-mentioned problems of the prior art, it would be helpful to provide a pneumatic tire having reduced rolling resistance and good durability at the belt ends.

[0011] Furthermore, it would be helpful to provide a method of manufacturing a pneumatic tire by which the above-mentioned pneumatic tire can be manufactured while suppressing the formation of gaps at the belt ends.

[0012] Solutions for solving problems

[0013] In order to achieve the purpose of solving the above problems, we provide the following solutions.

[0014] [1] A pneumatic tire comprising a belt, wherein the belt comprises a first belt layer in a tread portion and a second belt layer laminated on the outer side of the first belt layer in the tire radial direction, wherein

[0015] The first belt layer and the second belt layer are made by embedding a plurality of cords in a coating rubber,

[0016] The thickness of the first belt layer and the thickness of the second belt layer in the tire center portion are both 1.00 mm or less,

[0017] When the shortest distance between the cords of the second belt layer and the cords of the first belt layer in the tire center portion is defined as a, and the shortest distance between the cords closest to the end of the second belt layer and the cords of the first belt layer is defined as b, b / a is 1.8 or more and 4.0 or less,

[0018] At the end of the belt, the end rubber is arranged on the inner side of the first belt layer in the tire radial direction, between the first belt layer and the second belt layer, and on the outer side of the second belt layer in the tire radial direction,

[0019] When the end rubber positioned on the inner side in the tire radial direction of the first belt layer is defined as rubber portion A, the end rubber positioned between the first belt layer and the second belt layer is defined as rubber portion B, and the end rubber positioned on the outer side in the tire radial direction of the second belt layer is defined as rubber portion C, rubber portion B has the longest length in the direction toward the central portion and is closest to the tire central portion.

[0020] [2] The pneumatic tire according to [1], wherein when the lengths of the rubber portion A, the rubber portion B, and the rubber portion C in the direction toward the tire center portion are defined as LA, LB, and LC, respectively, LA / LB is 0.5 or less, and LC / LB is 0.5 or less.

[0021] [3] The pneumatic tire according to [1] or [2], wherein a distance between interface cords of the first belt layer and a distance between interface cords of the second belt layer in a tire center portion are both 0.14 mm or less.

[0022] [4] The pneumatic tire according to any one of [1] to [3], wherein the cords in the first belt layer and the cords in the second belt layer have a 1×N structure obtained by twisting N filaments together, where N is an integer selected from 2 to 6.

[0023] [5] The pneumatic tire according to [4], wherein the arrangement density of the cords is 60 cords / dm or more and 95 cords / dm or less.

[0024] [6] The pneumatic tire according to [4] or [5], wherein the diameter of the cord is 0.5 mm or more and 1.0 mm or less.

[0025] [7] The pneumatic tire according to any one of [1] to [3], wherein the cords in the first belt layer and the cords in the second belt layer are composed of monofilaments that are not twisted together but are arranged side by side.

[0026] [8] The pneumatic tire according to [7], wherein the arrangement density of the cords is 180 cords / dm or more and 240 cords / dm or less.

[0027] [9] The pneumatic tire according to [7] or [8], wherein the diameter of the cord is 0.24 mm or more and 0.28 mm or less.

[0028]

[10] The pneumatic tire according to any one of [1] to [9], wherein the filaments constituting the cords in the first belt layer and the cords in the second belt layer are classified as UT grades defined in ISO 17832:2009.

[0029]

[11] The method for manufacturing a pneumatic tire according to any one of [1] to

[10] , comprising a lamination step for the first belt layer and the second belt layer, wherein

[0030] Prior to the laminating step, an end portion of the first belt layer is wrapped with a first rubber sheet, and an end portion of the second belt layer is wrapped with a second rubber sheet, and in doing so, both the first rubber sheet and the second rubber sheet asymmetrically wrap the ends of the corresponding belt layers in such a manner that a length of a portion of the rubber sheet positioned on a side facing the other belt layer when the laminating is performed is longer than a length of a portion of the rubber sheet positioned on the opposite side.

[0031]

[12] The method for manufacturing a pneumatic tire according to

[11] , wherein when the first belt layer and the second belt layer are stacked, an end portion of the first rubber sheet and an end portion of the second rubber sheet positioned between the first belt layer and the second belt layer do not overlap each other.

[0032] Effects of the Invention

[0033] According to the present disclosure, it is possible to provide a pneumatic tire having reduced rolling resistance and good durability at the belt ends.

[0034] Furthermore, according to the present disclosure, it is possible to provide a method for manufacturing a pneumatic tire by which the above-mentioned pneumatic tire can be manufactured while suppressing the formation of gaps at the belt ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] [ Figure 1 ] Figure 1 is a schematic half-section view of a pneumatic tire according to one of the disclosed embodiments.

[0036] [ Figure 2A ] Figure 2A is a schematic cross-sectional view of an end portion of a belt in a pneumatic tire according to one of the disclosed embodiments.

[0037] [ Figure 2B ] Figure 2B is a schematic cross-sectional view of an end portion of a belt in a pneumatic tire according to another embodiment of the present disclosure.

[0038] [ Figure 3 ] Figure 3 is a schematic cross-sectional view of an end portion of a belt and a tire center portion in a pneumatic tire according to one of the disclosed embodiments.

[0039] [ Figure 4 ] Figure 4 is a schematic cross-sectional view of a tire center portion of a belt in a pneumatic tire according to one of the disclosed embodiments.

[0040] [ Figure 5A ] Figure 5A : is a schematic diagram partially showing a method for manufacturing a pneumatic tire according to one of the disclosed embodiments.

[0041] [ Figure 5B ] Figure 5B is through Figure 5A A schematic cross-sectional view of an end portion of a belt in a pneumatic tire obtained by the manufacturing method.

[0042] [ Fig. 6A ] Fig. 6A It is a schematic diagram partially showing a method of manufacturing a pneumatic tire as a comparison.

[0043] [ Figure 6B ] Figure 6B is through Fig. 6A A schematic cross-sectional view of an end portion of a belt in a pneumatic tire obtained by the manufacturing method. DETAILED DESCRIPTION

[0044] (Pneumatic tire)

[0045] Hereinafter, the pneumatic tire of the present disclosure will be described in detail with reference to the accompanying drawings.

[0046] Figure 1 1 is a schematic half-sectional view of a pneumatic tire (hereinafter simply referred to as a "tire") according to one of the disclosed embodiments (hereinafter referred to as the "present embodiment"). Figure 1 In the tire 20, the tread portion 1, the sidewall portion 2 and the bead portion 3 are reinforced by a carcass 4, which is composed of a carcass layer extending spirally from one bead portion 3 to another bead portion 3. In addition, the tread portion 1 is reinforced by a belt 7, which includes at least two layers (in the crown region of the carcass 4) arranged on the tire radially outer side. Figure 1 In the tire 20, a first belt layer 5 and a second belt layer 6) constitute a belt layer. In this regard, a plurality of carcass layers of the carcass 4 may exist in the tire 20.

[0047] In the tire 20, the first belt layer 5 is arranged on the tire radially outer side of the crown region of the carcass 4, and the second belt layer 6 is arranged on the tire radially outer side of the first belt layer 5. Figure 1 As shown, the belt width (length in the tire width direction) of the second belt layer 6 is generally smaller than the belt width of the first belt layer 5. The first belt layer 5 and the second belt layer 6 are continuously stacked to constitute the belt 7. In this regard, in the example shown, the belt 7 is constituted by two belt layers 5 and 6, but the belt 7 may be constituted by three or more belt layers.

[0048] In the tire 20 according to the present embodiment, the thickness of the first belt layer 5 and the thickness of the second belt layer 6 in the central portion of the tire are 1.00 mm or less. As described above, by setting the thickness of each of the belt layers in the central portion of the tire to 1.00 mm or less, lightweighting can be achieved and rolling resistance can be reduced. From a similar point of view, the thickness of the first belt layer 5 in the central portion of the tire is preferably 0.90 mm or less. In addition, the thickness of the second belt layer 6 in the central portion of the tire is preferably 0.90 mm or less. In order to achieve such thickness, the diameters of the cords 5A and 6A buried in the first belt layer and the second belt layer and the coating thickness of the coating rubber 5B and 6B can be appropriately selected.

[0049] In this regard, the tire center portion refers to a portion that is within a distance of one-fourth of the tire contact width from the tire equatorial plane in the tire width direction.

[0050] Figure 2AA schematic cross-sectional view of an end portion (end portion in the tire width direction. The same applies below) of a belt 7 in a tire 20 according to the present embodiment is shown. As shown in the figure, the first belt layer 5 and the second belt layer 6 are made by burying a plurality of cords (5A and 6A) in a coating rubber (5B and 6B). More generally, the belt layers 5 and 6 are composed of a rubber-steel composite cord in which steel cords (cords 5A and 6A) arranged side by side are coated with a coating rubber (5B and 6B).

[0051] As shown in the figure, according to the present embodiment, the end rubber 8 is arranged at the end of the belt 7 of the tire 20. More specifically, the rubber (end rubber) 8 is arranged at least on the inner side of the first belt layer 5 in the tire radial direction, between the first belt layer 5 and the second belt layer 6, and on the outer side of the second pulley layer 6 in the tire radial direction. By arranging the end rubber 8 at the end of the belt 7 in this way, the durability of the belt end can be improved. In this regard, the rubber on the inner side of the first belt layer 5 in the tire radial direction can be combined with a member (such as the carcass 4) arranged on the inner side of the tire radial direction to improve durability. The rubber on the outer side of the second belt layer 6 in the tire radial direction can be combined with a member (such as a belt reinforcement layer) that can be arranged on the outer side of the tire to improve durability.

[0052] Furthermore, as shown in the figure, in the tire 20 according to the present embodiment, when the end rubber positioned on the inner side of the first belt layer 5 in the tire radial direction is defined as the rubber portion A (8A), the end rubber positioned between the first belt layer 5 and the second belt layer 6 is defined as the rubber portion B (8B), and the end rubber positioned on the outer side of the second belt layer 6 in the tire radial direction is defined as the rubber portion C (8C), the rubber B (8B) is defined as having the longest length in the direction toward the center of the tire (generally synonymous with the "length in the tire width direction"). In other words, in the tire 20 according to the present embodiment, when the lengths of the rubber portion A (8A), the rubber portion B (8B), and the rubber portion C (8C) in the direction toward the center of the tire are respectively defined as L A , L B and L C (See Figure 2A ),L A / L B Less than 1.0 and L C / L B Less than 1.0. Furthermore, in the tire 20 according to the present embodiment, as shown in the figure, among the rubber portion A (8A), the rubber portion B (8B), and the rubber portion C (8C), the rubber portion B (8B) is closest to the tire center portion.

[0053] In this regard, one aspect of the above-mentioned end rubber 8 can be generally achieved by manufacturing a tire according to the manufacturing method of a pneumatic tire of the present disclosure as described below. In the manufacturing method of a pneumatic tire of the present disclosure, as described below, a gap tends not to be formed between the first belt layer 5 and the second belt layer 6 and between the second belt layer 6 and a layer (e.g., a belt reinforcing layer) that may be arranged outside the second belt layer 6. This also contributes to enhancing the durability of the belt end.

[0054] In the tire 20 according to the present embodiment, it is preferable that L A / L B is 0.5 or less, and L C / L B is 0.5 or less. In this case, the formation of gaps at the ends of the belt is further suppressed. From a similar point of view, L A / L B More preferably, it is 0.4 or less. C / L B More preferably, it is 0.4 or less.

[0055] In this regard, Figure 2A (as well as Figure 1 and Figure 3 ), the rubber portion A, the rubber portion B and the rubber portion C are integrated with the end rubber 8 and arranged at the end of the belt 7, but this integration is optional. For example, in the tire of the present disclosure, the rubber (rubber portion A) on the inner side of the first belt layer 5 in the tire radial direction, the rubber (rubber portion B) between the first belt layer 5 and the second belt layer 6, and the rubber (rubber portion C) on the outer side of the second belt layer 6 in the tire radial direction can be arranged separately from each other. In the tire of the present disclosure, as Figure 2B As shown, the end rubber 8 (rubber sheet) covering the end of the first belt layer 5 may be in contact with the end rubber 8 (rubber sheet) covering the end of the second belt layer 6 (and is not completely integrated).

[0056] In this regard, in order to further improve the durability of the belt end portion, the rubber portion A, the rubber portion B, and the rubber portion C are preferably integrated with the end rubber 8 .

[0057] Figure 3 2 is a schematic cross-sectional view of the tire center and end portions of the belt 7 in the tire 20 according to the present embodiment. In this regard, Figure 3 The end of the belt 7 corresponds to Figure 2AThe end shown. In the tire 20 according to the present embodiment, as shown in the figure, the shortest distance between the cord 6A of the second belt layer 6 and the cord 5A of the first belt layer 5 in the central part of the tire is defined as a, and the shortest distance between the cord 6A closest to the end of the second belt layer 6 and the cord 5A of the first belt layer 5 is defined as b, and b / a is 1.8 or greater and 4.0 or less. As described above, by increasing the interval between the cords of the first belt layer 5 and the cords of the second belt layer 6 at the belt end, the strain that may cause the belt edge separation can be suppressed. In the tire 20 of the present embodiment, by setting b / a to 1.8 or greater, the durability at the belt end, especially the belt edge separation durability, can be improved. In addition, by setting b / a to 4.0 or less, the sufficiently low rolling resistance required by the tire can be ensured. From a similar point of view, b / a is preferably 1.95 or greater, preferably 2.00 or greater. In addition, it is preferably 3.90 or less.

[0058] In this regard, the "shortest distance b between the cord closest to the end of the second belt layer and the cord of the first belt layer" should substantially represent the distance between the cord closest to the end of the second belt layer and the tangent line of the plurality of cords aligned in the first belt layer ( Figure 3 The shortest distance between the dashed lines in the figure.

[0059] Figure 4 is a schematic cross-sectional view of the central portion of the belt 7 in the tire 20 according to the present embodiment. Figure 3 The portion surrounded by the dotted line. In the tire 20 according to the present embodiment, any distance between the interface cords 5A of the first belt layer 5 in the central portion of the tire (i.e., the distance c1 from the top surface to the cord 5A and the distance c2 from the bottom surface to the cord 5A) is 0.14 mm or less. Any distance between the interface cords 6A of the second belt layer 6 in the central portion of the tire (i.e., the distance c3 from the top surface to the cord 6A and the distance c4 from the bottom surface to the cord 6A) is preferably 0.14 mm or less. By adopting this aspect, the low rolling resistance of the tire 20 can be further substantially improved. From a similar perspective, the distance between the interface cords 5A of the first belt layer 5 and the distance between the interface cords 6A of the second belt layer 6 in the central portion of the tire are more preferably 0.13 mm or less, and further preferably 0.12 mm or less.

[0060] In this regard, if Figure 3 and Figure 4 As can be seen in Figure 3 The distance a shown in is Figure 4 The distance (c4+c1) shown in .

[0061] There is no particular limitation on the specific structure and materials of the tire of the present disclosure as long as matters related to the belt 7 are as described above.

[0062] For example, the first belt layer 5 and the second belt layer 6 may be arranged in such a manner that a plurality of cords buried in the coating rubber are inclined with respect to the tire circumferential direction, for example, at an angle of 15° to 40°.

[0063] Furthermore, in the carcass 4, organic fiber cords may be used, which extend in a direction substantially orthogonal to the tire circumferential direction, for example, at an angle of 70° to 90°.

[0064] Furthermore, the tire of the present disclosure may include a belt reinforcement layer (also referred to as a cap layer) on the outer side of the belt 7 in the tire radial direction.

[0065] Furthermore, the tire 20 shown has a structure in which the bead cores 10 are respectively buried in the pair of bead portions 3, and the carcass 4 is locked by folding the carcass 4 around the bead cores 10 from the inside of the tire toward the outside of the tire. However, the tire 20 shown may have a structure (not shown) in which the carcass 4 is locked by winding the carcass 4 around the bead cores 10. Furthermore, the tire 20 shown may have a structure (not shown) in which the carcass 4 is locked by clamping the carcass 4 from both sides with bead wires.

[0066] Furthermore, in the tire of the present disclosure, a tread pattern may be formed on the surface of the tread portion 1 .

[0067] Furthermore, in the tire of the present disclosure, an inner liner (not shown) may be formed on the innermost layer.

[0068] Furthermore, as the gas filled in the tire of the present disclosure, normal air or air with a changed oxygen partial pressure, or an inert gas such as nitrogen may be used.

[0069] In this regard, the tire of the present disclosure is suitable for use as a pneumatic tire for use in passenger vehicles.

[0070] Now, components used in the tire 20 of the present embodiment will be described in detail.

[0071] In this regard, the compounds disclosed in this specification may be partially or entirely derived from fossil resources, from biological resources such as plant resources, or from renewable resources such as used tires. In addition, the compounds disclosed in this specification may be a mixture of any two or more of fossil resources, biological resources, and renewable resources.

[0072] (Coating rubber)

[0073] There is no particular restriction on the coating rubber 5B and 6B used in the first belt layer and the second belt layer, as long as the coating rubber is a common rubber composition capable of covering the cords 5A and 6A. Examples of rubber components include diene rubbers, and natural rubber or isoprene rubber is particularly preferred. In addition, fillers such as carbon black can be formulated into the above-mentioned coating rubbers 5B and 6B as long as the filler does not affect the performance of the coating rubber, such as adhesion and durability. As the above-mentioned carbon black, HAF-type carbon black is preferred. In addition, based on 100 parts by mass of the rubber component, the content of carbon black in the coating rubbers 5B and 6B can be 50 parts by mass to 70 parts by mass. In addition, in addition to the above-mentioned components, the above-mentioned coating rubbers 5B and 6B may also include, for example, a crosslinking agent such as a vulcanization accelerator, sulfur and zinc oxide; an adhesion promoter such as a cobalt compound including a cobalt salt; an antioxidant; an oil; and a suitable resin. Examples of the above-mentioned antioxidants include amine antioxidants such as 6PPD and bisphenol antioxidants such as o-MBp14. These antioxidants may be used alone or in combination of two or more.

[0074] (End rubber)

[0075] The end rubbers 8 (rubber portion A, rubber portion B, and rubber portion C) are not particularly limited, but for example, the same rubber composition as in the coating rubbers 5B and 6B of the first belt layer 5 and the second belt layer 6 may be used.

[0076] (cord)

[0077] In the first belt layer 5 and the second belt layer 6, a plurality of cords 5A and 6A are generally arranged side by side. Such cords 5A and 6A are generally steel cords. In addition, there is no particular restriction on the structure of such cords. In this regard, in order to efficiently achieve the purpose of improving both tire durability and low rolling resistance, the cord preferably has a 1×N structure obtained by twisting N filaments (N is an integer selected from 2 to 6). In particular, in a tire having a tire load index of less than 100, the above cord more preferably has a 1×2 structure, and in a tire having a tire load index of 100 or more, the above cord more preferably has a 1×5 structure. In addition, from a similar point of view, it is also preferred that the cord is made of monofilaments that are not twisted together but arranged side by side. In addition, in the above-mentioned 1×N structure, the cord may have an open structure of 1×N, in which the filaments do not contact each other and are twisted together in a manner that is spaced apart from each other. The cord having an open structure has better fatigue resistance than the cord in which the filaments are twisted together and the filaments are in contact with each other.

[0078] In this regard, the cord having a 1×N open structure may be formed by sandwiching unvulcanized rubber between filaments and twisting them together, or may be formed by coating the surfaces of the filaments with unvulcanized rubber and then twisting them together.

[0079] In addition, such filaments may be pre-patterned and subsequently twisted together. When the filaments are pre-patterned, the filament pattern pitch is preferably in the range of 8 mm or more to 16 mm or less. The pattern pitch within this range can enhance the rubber penetration ability, thereby further improving durability.

[0080] In addition, the ratio Sf / Sc of the cross-sectional area Sf of the wire in the cross section of the cord to the area Sc of the circumscribed circle of the cross section of the cord is preferably in the range of 0.4 or more to 0.7 or less. Sf / Sc in this range can enhance the penetration ability of rubber, thereby further improving durability.

[0081] Furthermore, the surface of the yarn constituting the cords 5A and 6A in the figure may be surface treated. In this case, the amount of phosphoric acid on the surface of the surface treated yarn is preferably 2.0 mg / m 2 When the amount of phosphoric acid on the surface of the silk is 2.0 mg / m 2 or less, the adhesion between the silk and the coating rubber is good.

[0082] The yarns constituting the cords 5A and 6A used in the first belt layer 5 and the second belt layer 6 are preferably classified as ST grade (super tensile strength cord) or UT grade (ultra-high tensile strength cord) defined in ISO 17832:2009, and are particularly preferably classified as UT grade. In this case, both the improvement of the durability and the low rolling resistance of the tire can be efficiently achieved.

[0083] From a similar viewpoint, when the diameter of the filament constituting the cord is X (mm) and the tensile strength of the filament is Y (MPa), the above-mentioned cords 5A and 6A preferably satisfy the following formula (1):

[0084] 4250-2000X≦Y≦4500-2000X(1)

[0085] In the yarns constituting the above-mentioned cords 5A and 6A, from the viewpoint of fatigue resistance, the hardness of the surface layer is preferably 90% to 110%, more preferably 100%, depending on the hardness of the inner layer. Here, the surface layer of the yarn refers to a layer (region) deeper than 0.01 mm from the outermost layer of the yarn, and the inner layer of the yarn refers to a layer (region) on the inner side of the above-mentioned surface layer. The above-mentioned hardness can be measured according to, for example, Vickers hardness. In addition, the hardness of the surface layer of the yarn can be measured at a position deeper than 0.005 mm from the outermost layer of the yarn, and the hardness of the inner layer of the yarn can be measured in an area deeper than 0.04 mm from the outermost layer of the yarn.

[0086] There is no particular limitation on the method for producing the wires constituting the cords 5A and 6A. For example, the wires can be obtained by refining and drawing iron ore, refining and drawing scrap iron, or recycling steel removed from tires.

[0087] In the first belt layer 5 and the second belt layer 6, the arrangement density of the cords 5A and 6A is preferably 50 pieces / dm or more and 250 pieces / dm or less. In this case, it is possible to efficiently achieve both low rolling resistance and durability improvements for the tire. In particular, when the above-mentioned cords have a 1×N structure (N is an integer selected from 2 to 6), the arrangement density of the cords is preferably 60 pieces / dm or more and 95 pieces / dm or less. When the above-mentioned cords are monofilaments, the arrangement density of the cords is preferably 180 pieces / dm or more and 240 pieces / dm or less.

[0088] The diameter of the cords 5A and 6A used in the first belt layer 5 and the second belt layer 6 is preferably 0.2 mm or more and 1.2 mm or less. In this case, it is possible to efficiently achieve both low rolling resistance and durability improvements for the tire. In particular, when the above-mentioned cord has a 1×N structure (N is an integer selected from 2 to 6), the diameter of the cord is preferably 0.4 mm or more and 1.2 mm or less, and further preferably 0.5 mm or more and 1.0 mm or less. When the above-mentioned cord is a monofilament, the diameter of the cord is preferably 0.24 mm or more and 0.28 mm or less.

[0089] (Belt reinforcement layer)

[0090] As described above, the tire 20 of the present disclosure may include a belt reinforcement layer (also referred to as a cap layer) on the tire radially outer side of the belt 7. The belt reinforcement layer is a member obtained by coating an organic fiber cord (reinforcement material) arranged substantially parallel to the tire circumferential direction (for example, at an angle of 0 to 5° relative to the tire circumferential direction) with rubber (elastomer). The belt reinforcement layer can be formed by coating the organic fiber cord with an elastomer and spirally winding the strip in a continuous manner in the tire circumferential direction to obtain a narrow strip.

[0091] As the organic fiber cord used in the belt reinforcement layer, an organic fiber cord having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus of 6.0 mN / (dtex·%) or more at an elongation of 7% is preferred. Here, the above-mentioned breaking strength, breaking elongation, and elastic modulus at an elongation of 7% are values ​​measured at room temperature (23° C.), and the properties of the organic fiber cord can be measured according to JIS L 1013 "Testing methods for rayon yarns".

[0092] The elastic modulus at an elongation of 7% was calculated by converting the tangent slope (N / %) at a point corresponding to the load-elongation curve at an elongation of 7% of the cord into a value per 1 dtex.

[0093] An organic fiber cord having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus of 6.0 mN / (dtex·%) or more at an elongation of 7% has high breaking strength, high breaking elongation, and high elastic modulus at an elongation of 7%. Therefore, for example, by applying an organic fiber cord having such characteristics to a belt reinforcing layer to supplement the rigidity of the belt 7, it is possible to improve the steering stability of the tire while suppressing a decrease in plunger durability due to application of a belt layer including metal monofilaments.

[0094] There is no particular limitation on the material of the organic fiber cord, but examples of such materials include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); nylons such as 6-nylon, 6,6-nylon and 4,6-nylon; and cellulose rayon and lyocell fibers. Polyethylene terephthalate is preferred among them. That is, the organic fiber cord as a reinforcing material for the belt reinforcement layer is preferably a cord composed of polyethylene terephthalate (hereinafter, may be referred to as "polyethylene terephthalate cord"). Polyethylene terephthalate cord has higher rigidity than commonly used nylon cords, and has a strong effect on enhancing the steering stability and plunger durability of the tire.

[0095] The organic fiber cord preferably has an elastic modulus of 2.5 mN / (dtex·%) or more measured at 160° C. under a load of 29.4 N. Here, the elastic modulus measured at 160° C. under a load of 29.4 N is calculated by converting the tangent slope (N / %) at a point at a load of 29.4 N on a load-elongation curve of the cord measured at 160° C. into a value per 1 dtex.

[0096] In this regard, the reason for measuring the elastic modulus at 160°C is that as high-speed driving continues, the temperature inside the tire becomes higher, and the temperature of the belt reinforcement layer is 160°C at the time point when the tire fails during high-speed driving. In particular, the elastic modulus of the polyethylene terephthalate cord at high temperature is greatly reduced compared with the elastic modulus at room temperature. Even if such a cord is a highly elastic cord at room temperature, when the cord cannot maintain a high elastic modulus at high temperature, it cannot provide a sufficient belt reinforcement effect (the effect of enhancing the durability against protruding input and the effect of suppressing belt protrusion). Therefore, the elastic modulus at high temperature is very important. By setting the elastic modulus of the cord measured at 160°C under a load of 29.4N to 2.5mN / (dtex·%) or more, the plunger durability of the tire can be improved, and the protrusion amount of the belt during high-speed driving can also be suppressed, and the stress when the tire is stepped in (stepping-in) and stepped out (stepping-out) can be reduced to enhance the steering stability of the tire during high-speed driving.

[0097] In order to achieve the purpose of improving the elastic modulus of the organic fiber cord at 160°C, it is preferred to perform the impregnation treatment under high tension. In addition, in order to achieve the purpose of providing a cord having sufficiently high elasticity, the tension in the bonding treatment of the cord is preferably 6.9×10 -2 N / tex or more. In this regard, the method of providing a cord having high elasticity is not limited to the above method, but other methods such as reducing the twisting density of the cord may also be adopted. The bonding treatment includes dry treatment, heat treatment, normalizing treatment, etc., and in addition to appropriately adjusting the tension, the temperature and time may also be adjusted. The bonding treatment may be performed in any one of one-bath treatment and two-bath treatment, but is preferably performed in two-bath treatment, and preferably, 6.9×10 -2 N / tex or more tension.

[0098] In organic fiber cords, the twist coefficient α is expressed by the following formula:

[0099] α=T×D1 / 2

[0100] (wherein α represents the twist coefficient, T represents the twist density (twists / 100 mm), and D represents the total fineness of the cord (dtex)) is preferably 500 to 2500. When the twist coefficient α of the organic fiber cord is 500 or more, the binding force of the filaments is strong and sufficient adhesion is provided. When the twist coefficient α of the organic fiber cord is 2500 or less, a sufficient elastic modulus is provided to obtain the effect of enhancing the durability against protruding input and the effect of suppressing the protrusion of the belt.

[0101] The organic fiber cord preferably has a total fineness of 1000 dtex to 3500 dtex. When the total fineness of the cord is 1000 dtex or more, a sufficient elastic modulus is provided to obtain the effect of enhancing the durability against protruding input and the effect of suppressing the protrusion of the belt. When the total fineness of the cord is 3500 dtex or less, a high arrangement density can be achieved to ensure sufficient rigidity per unit width.

[0102] There is no particular limitation on the material of the organic fiber cord, which may be derived from a synthetic product, from a biological source, from a mechanically recycled product obtained by grinding, melting and respinning PET products (such as PET bottles), or from a chemically recycled product obtained by depolymerizing and repolymerizing PET products (such as PET bottles).

[0103] (Method for manufacturing pneumatic tire)

[0104] A method for manufacturing a pneumatic tire according to one of the disclosed embodiments (hereinafter, may be simply referred to as "manufacturing method") is a method for manufacturing the above-mentioned pneumatic tire 20 of the present disclosure, and includes a step (laminating step) of laminating the above-mentioned first belt layer 5 and the above-mentioned second belt layer 6. Furthermore, in the manufacturing method according to the present embodiment, before the above-mentioned laminating step, an end portion of the above-mentioned first belt layer 5 is wrapped with a first rubber sheet 8, and an end portion of the above-mentioned second belt layer 6 is wrapped with a second rubber sheet 8, and in doing so, both the above-mentioned first rubber sheet 8 and the above-mentioned second rubber sheet 8 asymmetrically wrap the corresponding end portions of the belt layers in such a manner that when the above-mentioned laminating is performed, the length of the rubber sheet portion positioned on the side facing the other belt layer is longer than the length of the rubber sheet portion positioned on the opposite side.

[0105] According to this manufacturing method, the above-mentioned pneumatic tire 20 can be manufactured while effectively suppressing the formation of gaps between the first belt layer 5 and the second belt layer 6 and between the second belt layer 6 and a layer that can be arranged outside the second belt layer 6 (for example, a belt reinforcing layer).

[0106] The mechanism of suppressing the formation of gaps described in this embodiment will be described in detail below.

[0107] Figure 5A: is a schematic diagram showing a lamination step in a manufacturing method according to the present embodiment. As shown in the figure, in the lamination step, for example, in a state where a first belt layer 5, a second belt layer 6 and an additional layer 16 (such as a belt reinforcement layer, a rubber layer and a pressurized bonding layer) are sequentially laminated, a roller 15 is pressed onto these layers from above to move the layers from the central portion of the tire to the direction of the ends of each of the layers. As a result, the first belt layer 5, the second belt layer 6 and the additional layer 16 are pressurized and bonded. In doing so, the ends of the first belt layer 5 are preliminarily wrapped with a first rubber sheet 8 and the ends of the second belt layer 6 are wrapped with a second rubber sheet 8. At this time, as Figure 5A As shown, the first rubber sheet 8 covering the end of the first belt layer 5 asymmetrically covers the end of the first belt layer 5 in the following manner: when these layers are stacked, the length (length in the tire width direction; the same applies below) (L B1 ') is longer than the length (L) of the rubber sheet portion located on the opposite side A '). In addition, Figure 5A As shown, the second rubber sheet 8 covering the end of the second belt layer 6 asymmetrically covers the end of the second belt layer 6 in the following manner: when these layers are stacked, the length (L B2 ') is longer than the length of the rubber sheet portion located on the opposite side (L C '). By laminating and press-bonding with this configuration of the rubber sheet 8, at the belt end, as Figure 5B As schematically shown, no gaps tend to form between the first belt layer 5 and the second belt layer 6 and between the second belt layer 6 and the additional layer 16 .

[0108] In the traditional way, Fig. 6A As shown, the first rubber sheet 8 covering the end of the first belt layer 5 and the second rubber sheet 8 covering the end of the second belt layer 6 symmetrically cover the corresponding end (ie, L A '≈L B1 ', L B2 '≈L C '). When the rubber sheets 8 are laminated and press-bonded in this configuration, deformation does not occur until the first belt layer 5, the second belt layer 6 and the additional layer 16 are in close contact with each other. As a result, Figure 6B As shown, at the belt ends, large gaps (air pockets) tend to form between the first belt layer 5 and the second belt layer 6 and between the second belt layer 6 and the additional layer 16 .

[0109] In this regard, the additional layer 16 may be a tire component such as a belt reinforcing layer or a rubber layer, etc. In the case where the additional layer 16 is not a tire component, the additional layer 16 may be appropriately peeled off after the lamination step.

[0110] The first rubber sheet and the second rubber sheet may be rectangular rubber sheets, for example.

[0111] In the above-mentioned laminating step, the first belt layer 5 and the second belt layer 6 are preferably laminated in such a manner that the first rubber sheet 8 and the second rubber sheet 8 are in contact with each other.

[0112] In the manufacturing method according to the present embodiment, it is preferred that when the first belt layer 5 and the second belt layer 6 are stacked, the end of the first rubber sheet 8 and the end of the second rubber sheet positioned between the first belt layer 5 and the second belt layer 6 do not overlap each other. In other words, the distance Lx' (distance in the tire width direction) between the end of the first rubber sheet 8 and the end of the second rubber sheet positioned between the first belt layer 5 and the second belt layer 6 is (see Figure 5A ) is preferably greater than 0. As a result, the formation of gaps at the ends of the belt can be further suppressed. In this case, the ends of the first rubber sheets 8 of the first belt layer 5 can be closer to the center of the tire, or as Figure 5A As shown in FIG. 1 , the end of the second rubber sheet 8 of the second belt layer 6 can be closer to the center of the tire. In this regard, in order to achieve the purpose of more effectively suppressing the formation of the gap, it is more preferable that, as Figure 5A As shown, the end portion of the second rubber sheet 8 of the second belt layer 6 is closer to the tire center portion.

[0113] There are no particular limitations on specific manufacturing conditions regarding the manufacturing method according to the present embodiment as long as the configuration of the rubber sheet 8 around the first belt layer 5 and the second belt layer 6 is as described above and the configuration of the pneumatic tire 20 according to the present embodiment described above is obtained.

[0114] For example, the lengths (L) of the rubber portion A, the rubber portion B, and the rubber portion C in the laminated tire 20 are A , L B and L C ) and the relationship between the relative positions of these rubber parts and the length (L) of the corresponding rubber sheet part according to the manufacturing method of this embodiment A ', L B1 'To L B2 ', L C '), and thus can be appropriately adjusted by those skilled in the art.

[0115] For example, for the purpose of adjusting the spacing between the cords of the first belt layer 5 and the cords of the second belt layer 6 in the tire 20 according to the present embodiment (therefore, setting b / a to 1.8 or greater and 4.0 or less), the thickness of the first rubber sheet 8 covering the end of the above-mentioned first belt layer 5 and / or the thickness of the second rubber sheet 8 covering the end of the second belt layer 6 can be appropriately adjusted.

[0116] Example

[0117] The tire of the present disclosure will be described in more detail below with reference to embodiments.

[0118] By using a tire having a belt structure shown in Table 1 below (using cords classified to the UT grade defined in ISO 17832:2009) and having Figure 2A The tire having the schematic structure of the belt end shown was evaluated for belt edge separation durability and rolling resistance. In this regard, the tire was a pneumatic tire with a tire size of 265 / 65R18, and the cords in each belt layer were arranged to cross each other at an angle of ±30° relative to the tire circumferential direction.

[0119] <Belt edge separation durability>

[0120] After the tire of each example deteriorated, internal pressure was applied to the tire and it was attached to the test passenger vehicle. A certain lateral force (SF) was repeatedly applied to the tire while it was running on the BES drum. Then, the tire was disassembled to measure the length of the crack that appeared at the end of the belt layer. The crack length in each example was compared with the crack length in the conventional example, and the difference between the crack length in each example and the crack length in the conventional example was 0.5 mm or less, and it was evaluated as B, and the crack length in each example was evaluated as A when it was 1.0 mm or more shorter than the crack length in the conventional example. The results are shown in Table 1.

[0121] In this regard, based on the tire structure of the conventional example, when the thickness of the belt layer is less than that in the conventional example, cracks tend to occur at the belt ends, and the belt edge separation durability tends to deteriorate. This tendency is obvious to those skilled in the art, so it is not necessary to measure by using a test specimen.

[0122] <Rolling resistance>

[0123] The internal pressure of the tire assembled on the rim of each example was set to 210 kPa. According to ISO 28580, a drum tester with an iron plate surface having a diameter of 1.7 m was used to measure the rolling resistance coefficient (N / kN) by rolling the tire at a speed of 80 km / h with a load mass of 80% based on the maximum load capacity. The results are shown in Table 1. The smaller the value, the smaller the rolling resistance.

[0124] [Table 1]

[0125]

[0126] As can be seen from Table 1, the tire according to the embodiment of the present disclosure has reduced low rolling resistance caused by the thin belt layer, and also has belt edge separation durability comparable to or higher than that of the conventional example (ie, the example with a larger belt layer thickness).

[0127] Industrial Applicability

[0128] According to the present disclosure, it is possible to provide a pneumatic tire having reduced rolling resistance and good durability at the belt ends.

[0129] Furthermore, according to the present disclosure, it is possible to provide a method for manufacturing a pneumatic tire by which the formation of gaps at belt ends can be suppressed while manufacturing the above-mentioned pneumatic tire.

[0130] Description of Reference Numerals

[0131] 1 Tread

[0132] 2 Sidewall

[0133] 3 Bead section

[0134] 4 Carcass

[0135] 5. First belt layer

[0136] 6 Second belt layer

[0137] 5A, 6A cord

[0138] 5B, 6B coated rubber

[0139] 7 Belt

[0140] 8 End rubber (rubber sheet)

[0141] 8A Rubber Part A

[0142] 8B Rubber part B

[0143] 8C Rubber part C

[0144] 10 Bead core

[0145] 15 Roller

[0146] 16 Additional Layers

[0147] 20 Tire (pneumatic tire)

Claims

1. A pneumatic tire, comprising a belt, wherein the belt comprises a first belt layer in a tread portion and a second belt layer stacked on the outer side of the first belt layer in the tire radial direction, wherein: The first belt layer and the second belt layer are made by embedding a plurality of cords in a coating rubber, The thickness of the first belt layer and the thickness of the second belt layer in the tire center portion are both 1.00 mm or less, When the shortest distance between the cords of the second belt layer and the cords of the first belt layer in the tire center portion is defined as a, and the shortest distance between the cords closest to the end of the second belt layer and the cords of the first belt layer is defined as b, b / a is 1.8 or more and 4.0 or less, At the end of the belt, the end rubber is arranged on the inner side of the first belt layer in the tire radial direction, between the first belt layer and the second belt layer, and on the outer side of the second belt layer in the tire radial direction, When the end rubber positioned on the inner side in the tire radial direction of the first belt layer is defined as rubber portion A, the end rubber positioned between the first belt layer and the second belt layer is defined as rubber portion B, and the end rubber positioned on the outer side in the tire radial direction of the second belt layer is defined as rubber portion C, rubber portion B has the longest length in the direction toward the central portion and is closest to the tire central portion.

2. The pneumatic tire according to claim 1, wherein when the lengths of the rubber portion A, the rubber portion B, and the rubber portion C in the direction toward the tire center portion are respectively defined as L A , L B and L C When L A / L B is 0.5 or less, and L C / L B 0.5 or less.

3. The pneumatic tire according to claim 1 or 2, wherein: The distance between the interface cords of the first belt layer and the distance between the interface cords of the second belt layer in the tire center portion are both 0.14 mm or less. 4 . The pneumatic tire according to claim 1 , wherein the cords in the first belt layer and the cords in the second belt layer have a 1×N structure obtained by twisting N filaments together, where N is an integer selected from 2 to 6. 5 . The pneumatic tire according to claim 4 , wherein an arrangement density of the cords is 60 cords / dm or more and 95 cords / dm or less. 6 . The pneumatic tire according to claim 4 , wherein a diameter of the cord is 0.5 mm or more and 1.0 mm or less.

7. The pneumatic tire according to any one of claims 1 to 3, wherein the cords in the first belt layer and the cords in the second belt layer are composed of monofilaments that are not twisted together but are arranged side by side. 8 . The pneumatic tire according to claim 7 , wherein an arrangement density of the cords is 180 cords / dm or more and 240 cords / dm or less. 9 . The pneumatic tire according to claim 7 , wherein the diameter of the cord is 0.24 mm or more and 0.28 mm or less.

10. The pneumatic tire according to any one of claims 1 to 9, wherein filaments constituting the cords in the first belt layer and the cords in the second belt layer are classified as UT grades defined in ISO 17832:2009.

11. A method for manufacturing a pneumatic tire according to any one of claims 1 to 10, the method comprising: A lamination step for the first belt layer and the second belt layer, wherein Prior to the laminating step, an end portion of the first belt layer is wrapped with a first rubber sheet, and an end portion of the second belt layer is wrapped with a second rubber sheet, and in doing so, both the first rubber sheet and the second rubber sheet asymmetrically wrap the ends of the corresponding belt layers in such a manner that a length of a portion of the rubber sheet positioned on a side facing the other belt layer when the laminating is performed is longer than a length of a portion of the rubber sheet positioned on the opposite side. 12 . The method for manufacturing a pneumatic tire according to claim 11 , wherein when the first belt layer and the second belt layer are laminated, an end portion of the first rubber sheet and an end portion of the second rubber sheet positioned between the first belt layer and the second belt layer do not overlap each other.

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