tire

Abstract

To provide a tire that suppresses the occurrence of groove cracks in tires containing identification information, while also allowing for clear identification of the identification information. [Solution] The stress relaxation layer (52) is characterized in that it mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains carbon and a vulcanizing agent, and identification information (70) is formed in a region other than the groove width region of the stress relaxation layer that is 0.1 times the groove width dimension (Wc) on each side of the groove width direction from the groove width direction center line of the groove bottom (44).

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] In order to suppress groove cracks generated at the groove bottom of the main groove, a tire provided with a stress relaxation layer at the groove bottom of the main groove is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the tire disclosed in Patent Document 1, when an identification line applied to the tread for tire identification purposes is disposed at the groove bottom (i.e., on the stress relaxation layer), if stress is applied to the groove bottom during large steering (of the vehicle to which the tire is attached), there is a risk of generating peeling stress between the identification line and the stress relaxation layer. In such a case, the identification line may peel off from the groove bottom, and as a result, groove cracks may not be suppressed.

[0005] In addition, on the tire surface, in addition to the above-described identification line, identification information consisting of characters, numbers, etc. may be attached, and depending on the positional relationship between the identification line and the identification information, there is a risk that they cannot be clearly identified.

[0006] An object of the present invention is to provide a tire that can suppress the occurrence of groove cracks and clearly identify identification information for a tire including the identification information.

Means for Solving the Problems

[0007] The tire of the present invention is characterized in that, on the tread surface of the tread rubber, the land area is demarcated by main grooves, identification information including a string of characters is provided on the tread surface, a stress relaxation layer is formed on the surface of at least one groove bottom of the main groove, the stress relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material, and also contains carbon and a vulcanizing agent, and the identification information is formed in an area other than a width region of 0.1 times the groove width dimension Wc of the stress relaxation layer on each side in the groove width direction from the groove width direction center line of the groove bottom. [Effects of the Invention]

[0008] According to the present invention, not only is the stress-relaxing layer formed at the bottom of the main groove made crack-resistant, but the positional relationship between the groove bottom and the identification information is optimized, making the identification information easier to see. As a result, it is possible to achieve both crack resistance and identification function for tires containing identification information. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an end view showing the meridional cross-sectional shape of the tire according to this embodiment. [Figure 2] Figure 2 is an enlarged view showing the region enclosed by the tire width direction range II and tire radial direction range II in Figure 1. [Figure 3] Figure 3 is a plan view of the tire showing the arrangement of the stress relaxation layer and identification information. [Figure 4] Figure 4 is a meridional cross-sectional view of a tire showing the optimal positional relationship between the stress relaxation layer and the identification information. [Figure 5] Figure 5 is a meridional cross-sectional view of a tire showing an unfavorable positional relationship between the stress relaxation layer and the identification information. [Figure 6] Figure 6 is a plan view of the tire showing the arrangement of the stress relaxation layer and identification information, corresponding to the configuration in Figure 5. [Figure 7] Figure 7 is a meridional cross-sectional view of the tire showing the distance in the width direction of the main groove between the stress relaxation layer and the identification information. [Figure 8] Figure 8 is a meridional cross-sectional view of the tire showing the positions of both ends of the stress relaxation layer in the groove width direction. [Figure 9] Figure 9 is a plan view of the tire showing the positional relationship between the identification information and the identification line. [Modes for carrying out the invention]

[0010] <Mode of the present invention> The present invention encompasses the following embodiments. [Form 1] A tire in which the tread surface of the tread rubber is divided into land areas by main grooves, identification information including a string of characters is provided on the tread surface, and a stress-relieving layer is formed on the surface of at least one groove bottom of the main groove, The stress relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material, and also contains carbon and a vulcanizing agent. A tire characterized in that the identification information is formed in a region other than the groove width region, which is 0.1 times the groove width dimension Wc of the stress relaxation layer, on each side of the groove width direction from the groove width direction center line of the groove bottom. [Form 2] The stress relaxation layer and the identification information overlap in at least part, The tire according to Embodiment 1, wherein the identification information is formed on the radially outer side of the stress relaxation layer. [Form 3] The stress relaxation layer and the identification information do not overlap. The tire according to Embodiment 1, wherein the distance W in the groove width direction between the stress relaxation layer and the identification information is 50 times or more the thickness Gac of the stress relaxation layer at the groove width direction center of the main groove. [Form 4] A tire according to any one of embodiments 1 to 3, wherein the color difference ΔE*ab in the L*a*b* color space between the stress relaxation layer and the tread surface is less than 13. [Form 5] The tire according to any one of embodiments 1 to 4, wherein the groove width direction dimension Ch of the identification information is 0.8 times or more the main groove width direction dimension Wc of the stress relaxation layer closest to the identification information. [Form 6] When the tire radial position of the main groove bottom is set as the tire radial position of 0%, and when the position of the tire profile line in the case where the main groove does not exist is set as the tire radial position of 100%, the positions of both ends in the groove width direction of the stress relaxation layer are at the tire radial position of 50% or more. The tire according to any one of Forms 1 to 5. [Form 7] The thickness of the stress relaxation layer is 5 μm or more and 200 μm or less. The tire according to any one of Forms 1 to 6. [Form 8] The identification information is mainly composed of a diene-based rubber material and a non-diene-based rubber material, and contains a coloring pigment, and contains 20 parts by mass or more of the coloring pigment with respect to 100 parts by mass of the rubber component. Between the identification information and the rubber layer adjacent to the identification information, the difference ΔL* in the index L* in the lightness axis direction in the L*a*b* color space is 8 or more. The tire according to any one of Forms 1 to 8. [Form 9] A plurality of the identification information is individually formed. The tire according to any one of Forms 1 to 8.

[0011] <Definition> The tire radial direction refers to the direction orthogonal to the tire rotation axis. The inner side in the tire radial direction refers to the side facing the tire rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the circumferential direction with the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side in the tire width direction refers to the side facing the tire equatorial plane in the tire width direction, and the outer side in the tire width direction refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane refers to a plane orthogonal to the tire rotation axis and passing through the center of the tire width. The main groove is a groove having a wear indicator indicating the end stage of wear on the groove wall, for example, a circumferential groove, and generally has a groove width of 3.0 [mm] or more and a groove depth of 5.0 [mm] or more. Note that the groove width and groove depth of the circumferential main groove are not limited to the above ranges. The groove width is the maximum distance between opposing groove walls at the groove opening on the tread surface when the tire is mounted on a standard rim and filled to the standard internal pressure in an unloaded state (the distance measured in a direction perpendicular to the direction in which the groove extends). If there is a notch or chamfer at the groove opening, the groove width is the value measured with the endpoint being the intersection of the extension line of the tread surface and the extension line of the groove wall in a cross-sectional view parallel to the groove width direction and groove depth direction. The groove depth is the maximum distance from the tread surface to the bottom of the groove (measured in the radial direction of the tire) when the tire is mounted on a standard rim, filled to the standard internal pressure, and under no load. If the groove in question has partial unevenness or sipes at the bottom of the groove, the groove depth shall be the value measured excluding the unevenness or sipes. The tread edge refers to the ends of the tread pattern on a tire, and is also called the design end. In this specification, unless otherwise specified, the shape, position, and length (distance) of each component are based on the shape, position, and length in a meridional section (or plan view) of the tire (when mounted on a standard rim and filled with standard internal pressure in an unloaded state). A "regular rim" refers to an "applicable rim" as defined by JATMA, a "Design Rim" as defined by TRA, or a "Measuring Rim" as defined by ETRTO. Standard internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "INFLATION PRESSURES" specified by ETRTO. Standard load refers to the "maximum load capacity" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO.

[0012] <Basic tire configurations> One embodiment of the present invention will be described below with reference to the drawings. Figure 1 is an end view showing the meridional cross-sectional shape of the tire according to this embodiment. Note that the figure shows the tire portion in an unloaded state, mounted on a regular rim and subjected to regular internal pressure.

[0013] The tire 10 of this embodiment, when viewed in a meridional cross-section of the tire, comprises a pair of bead portions 12, a pair of sidewall portions 14, a pair of shoulder portions 16, and a tread portion 18, arranged from the inside to the outside in the radial direction of the tire. The tire 10 comprises an inner liner 19, a carcass 20, a belt 22 (consisting of two belt layers 22a and 22b), a belt cover 24, sidewall rubber 36, and tread rubber 38, just like a typical tire.

[0014] The tread rubber 38 has a tread surface 37 that is exposed at the outermost part in the radial direction of the tire, and is made of a rubber material that has excellent contact characteristics and weather resistance. Preferably, the tread rubber 38 contains silica, wax, and an anti-aging agent.

[0015] As for the wax, plant-derived waxes, paraffin wax, microcrystalline wax, polyethylene wax, and mixtures thereof can be selected. In particular, to ensure crack resistance at low temperatures, a low-melting-point wax that can easily precipitate and spread on the groove bottom surface even at low temperatures is preferred, and for example, a wax with a melting point of 40 to 65°C is preferably selected. The tread rubber preferably contains 1.0 part by mass or more of wax when the rubber component is 100 parts by mass.

[0016] The anti-aging agent is preferably an amine-based anti-aging agent. Examples of amine-based anti-aging agents include "N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine" and "2,2,4-trimethyl-1,2-dihydroquinoline polymer". The tread rubber preferably contains 0.5 parts by mass or more of the anti-aging agent when the rubber component is 100 parts by mass.

[0017] The tread surface 37 is provided with multiple (four in Figure 1) circumferential main grooves 40 (forming a continuous annular shape in the circumferential direction of the tire). These circumferential main grooves 40 divide the tread surface 37 into multiple (five rows in Figure 1) land areas 42.

[0018] Figure 2 is an enlarged view showing the region enclosed by the tire width direction range II and the tire radial direction range II in Figure 1. As shown in Figure 2, the land area demarcated by the circumferential main groove 40 has a groove bottom 44 and a pair of groove walls 46. The groove bottom 44 is the bottom of the circumferential main groove 40 and serves as the reference for the groove depth of the circumferential main groove 40. The groove bottom 44 is composed of a surface that follows the tread surface 37, with the groove width direction (tire width direction in the example shown in Figure 2) as the short side and the direction perpendicular to both the groove width direction and the tire radial direction (tire circumferential direction in the example shown in Figure 2) as the long side. The pair of groove walls 46 are continuous with the outer edge of the groove bottom 44 in the tire width direction and serve as the reference for the groove width of the circumferential main groove 40. The pair of groove walls 46 are composed of a surface that intersects the tread surface 37, with the direction inclined in the groove width direction (tire width direction) relative to the tire radial direction as the short side and the tire circumferential direction as the long side.

[0019] [Characteristics of the basic form of a tire] (Stress relaxation layer) Next, the tire 10 is provided with a stress-relieving layer 52 on the surface of at least the groove bottom 44 of the land portion demarcated by the circumferential main groove 40. The stress-relieving layer 52 includes a bottom portion 54 provided on the groove bottom 44. The bottom portion 54 is formed over the entire groove bottom 44. The bottom portion 54 forms a continuous annular shape in the circumferential direction of the tire.

[0020] The stress-relaxing layer 52 may include a wall portion 56 and a surface portion 58 in addition to the bottom portion 54 described above. The wall portion 56 is provided on each of the pair of groove walls 46. One end 56U of the wall portion 56 on the inner side in the tire radial direction is connected to the bottom portion 54, and the other end 56T on the outer side in the tire radial direction may be located within the groove wall 46 or may reach the edge 48. The surface portion 58 is provided on the tread surface 37, starting from the edge 48. One end 58G of the surface portion 58 in the tire width direction is connected to the other end 56T of the wall portion 56 on the outer side in the tire radial direction at the edge 48, and the other end 58L in the tire width direction is located at a predetermined length, for example, 0.5 mm to 5 mm, on the opposite side in the groove width direction from the edge 48 from the one end 56U.

[0021] The stress relaxation layer 52 mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains carbon and a vulcanizing agent. The diene-based rubber is selected from the group consisting of diene polymers including natural rubber and synthetic diene-based rubber (isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butadiene-isoprene rubber (BIR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SBIR), chloroprene rubber (CR), etc.). The non-diene-based rubber is selected from the group consisting of non-diene polymers including synthetic non-diene-based rubber (butyl rubber (IIR), ethylene-propylene rubber (EPDM, EPM), urethane rubber, silicone rubber, etc.). Furthermore, it is preferable that the stress relaxation layer 52 does not contain resin components in order to ensure weather resistance.

[0022] The stress relaxation layer 52 does not necessarily have to contain an anti-aging agent. This is because, since the stress relaxation layer 52 has a small thickness Ga, the anti-aging agent contained in the adjacent tread rubber 38 migrates to the stress relaxation layer 52 and compensates for this. The stress relaxation layer 52 can further suppress the occurrence of cracks by containing an anti-aging agent. If the stress relaxation layer 52 contains an anti-aging agent, it is preferable to use other anti-aging agents (e.g., phenolic, phosphite, organic thioacid, benzimidazole, etc.) in an amount of 0.1 parts by mass to 5 parts by mass per 100 parts by mass of the rubber component, rather than using amine-based anti-aging agents.

[0023] (Identification information) Furthermore, the tire 10 includes identification information 70 on its tread surface 37, which consists of, for example, a string of characters. The identification information 70 is a so-called trademark, defined as letters, figures, symbols, three-dimensional shapes, colors, or combinations thereof.

[0024] These marks are used to identify the product and only need to be present on at least a portion of the tire circumference.

[0025] Figure 3 is a plan view of the tire showing the arrangement of the stress relaxation layer and identification information. More specifically, Figure 3 shows the vicinity of the circumferential main groove 40 located on the leftmost side of the page, among the circumferential main grooves 40 shown in Figure 1. In Figure 3, reference numeral 40 indicates the circumferential main groove, 40cg indicates the groove width center of the circumferential main groove, 52 indicates the stress relaxation layer, and 70 indicates the identification information (string R123). In this example, the groove width dimensions of the circumferential main groove 40 and the stress relaxation layer 52 are the same. In other words, this is an example where the stress relaxation layer 52 extends from the groove bottom 44 in Figure 2 to the edge 48 of the groove wall 46.

[0026] Based on the above, in the tire of this embodiment, as shown in Figure 3, identification information 70 is formed in areas other than the groove width region of the stress relaxation layer 52 that is 0.1 times the groove width dimension Wc, on each side in the groove width direction from the groove width center line 40cg of the groove bottom.

[0027] In the example shown in Figure 3, the identification information 70, consisting of the string R123, is positioned partially overlapping with the stress relaxation layer 52. However, this embodiment is not limited to such an example and also includes cases where the identification information 70 is positioned separately from the stress relaxation layer 52.

[0028] <Functions and Effects of the Basic Form of Tires> In the tire of this embodiment, as shown in Figure 3, the identification information 70 is formed in an area other than the groove width region of the stress relaxation layer 52 that is 0.1 times the groove width dimension Wc, on each side in the groove width direction from the groove width center line 40cg of the groove bottom. As a result, the identification information 70 is not formed near the groove width center position of the groove bottom 44 shown in Figure 2. Therefore, the identification function of the identification information 70 engraved on the tread surface 37 can be performed while maintaining the crack resistance of the stress relaxation layer 52 without reducing it, and thus both crack resistance and identification function can be achieved.

[0029] <Preferred tire configuration> Typically, circumferential main grooves (grooves indicated by reference numeral 40 in Figure 1) are often formed on the tread surface 37 in a range of two to five grooves. Therefore, the stress relaxation layer 52 can be formed in at least one of these grooves, but considering the occurrence of cracks at the groove bottom 44, it is preferable to form it in all of the main grooves formed on the tread surface 37 (all four circumferential main grooves 40 as shown in Figure 1).

[0030] The preferred region for forming the stress relaxation layer 52 is the area between 0% and 30% from the inner side of the tire radially in the main groove depth. Therefore, in the case of the stress relaxation layer 52 shown in Figure 2, it is naturally preferable that the bottom portion 54 be formed, but it is also preferable that at least a part of the wall portion 56 be formed.

[0031] Figure 4 is a meridional cross-section of a tire showing a suitable positional relationship between the stress relaxation layer and the identification information. Figure 4(A) is an example in which the stress relaxation layer 52 is composed of the bottom portion 54 and the wall portion 56 shown in Figure 2, and Figure 4(B) is an example in which the stress relaxation layer 52 is composed of the bottom portion 54, the wall portion 56 and the surface portion 58 shown in Figure 2.

[0032] In the tires shown in Figures 1 and 2, it is preferable that the stress relaxation layer 52 and the identification information 70 overlap in at least a portion, as shown in Figures 4(A) and 4(B), and that the identification information 70 is formed on the radially outer side of the stress relaxation layer 52.

[0033] With this configuration, as shown in Figure 3, the visibility of the identification information 70 is favorably ensured even in areas where the stress relaxation layer 52 and the identification information 70 overlap.

[0034] In contrast, Figure 5 is a meridional cross-section of a tire showing an unfavorable positional relationship between the stress relaxation layer and the identification information. Figure 5(A) is an example where the stress relaxation layer 52 is composed of the bottom portion 54 and the wall portion 56 shown in Figure 2, and Figure 5(B) is an example where the stress relaxation layer 52 is composed of the bottom portion 54, the wall portion 56, and the surface portion 58 shown in Figure 2. Furthermore, Figure 6 is a plan view of the tire showing the arrangement of the stress relaxation layer 52 and the identification information 70, corresponding to the configuration in Figure 5(A).

[0035] In the examples shown in Figures 5(A) and 5(B), the stress relaxation layer 52 and the identification information 70 overlap in at least part, and the identification information 70 is formed on the radially inner side of the stress relaxation layer 52. Therefore, as shown in Figure 6, in the region where the stress relaxation layer 52 and the identification information 70 overlap (the region where the string of characters (R123), which is the identification information 70, is shown by a dotted line), the visibility of the identification information 70 is not adequately ensured and it is viewed in an unclear state.

[0036] Therefore, the examples shown in Figure 4(A) and Figure 4(B) are preferable because the identification information 70 is more clearly identifiable than the examples shown in Figure 5(A) and Figure 5(B), respectively.

[0037] Figure 7 is a meridional cross-section of the tire showing the distance in the main groove width direction between the stress relaxation layer and the identification information. Figure 7(A) is an example where the stress relaxation layer 52 extends from the bottom 54 shown in Figure 2 outward in the tire radial direction to the other end 56T of the wall 56. Figure 7(B) is an example where the stress relaxation layer 52 does not extend from the bottom 54 shown in Figure 2 outward in the tire radial direction to the other end 56T of the wall 56.

[0038] In the tires shown in Figures 1 and 2, it is preferable that the stress relaxation layer 52 and the identification information 70 do not overlap, and that the distance W in the groove width direction between the stress relaxation layer 52 and the identification information 70 is 50 times or more the thickness Gac of the stress relaxation layer 52 at the groove width direction center of the main groove 40.

[0039] Here, the thickness Gac of the stress relaxation layer 52 at the center position in the groove width direction of the main groove 40 refers to the thickness Ga of the stress relaxation layer 52 shown in Figure 2 at the center position in the groove width direction. In the example shown in Figure 2, the thickness of the stress relaxation layer 52 is the same at all positions in the groove width direction, so the thickness Ga is equal to the thickness Gac at all positions in the groove width direction.

[0040] According to the configuration shown in Figure 7(A) or Figure 7(B), the stress relaxation layer 52 and the identification information 70 do not overlap in the tire radial direction or are adjacent in the groove width direction. Therefore, the stress relaxation layer 52 can be made more reliable in terms of crack resistance, and the visibility of the identification information 70 can be ensured at a higher level.

[0041] In the tires shown in Figures 1 and 2, it is preferable that the color difference ΔE*ab in the L*a*b* color space between the stress relaxation layer 52 and the tread surface 37 is less than 13. Here, the color difference ΔE*ab is [(ΔL*) 2 +(Δa*) 2 +(Δb*) 2 Defined by ].

[0042] The L*a*b* color space mentioned above is a color space standardized by the International Commission on Illumination (CIE) in 1976, and is also defined in JIS Z8781-4. Color evaluation in this color space can be performed using a fluorescence spectrometer (e.g., KONICA MINOLTA FD-7 / FD-5 fluorescence spectrometer) under the illumination of a D50 light source.

[0043] By setting ΔE*ab to less than 13, and assuming that there is no clear contrast in the L*a*b* color system between the tread rubber 38 and the stress relaxation layer 52, the visibility of the identification information 70 can be further improved for both the tread rubber 38 and the stress relaxation layer 52.

[0044] In addition to the strings of characters shown in Figure 3, the identification information 70 also includes simple identification lines. For example, a colored identification line (for example, the identification line 70b in Figure 9(A), described later) with E*ab values ​​of 13 or more can be formed on the tread surface 37 for both the tread rubber 38 and the stress relaxation layer 52.

[0045] In the tires shown in Figures 1 and 2, it is preferable that the groove width dimension Ch of the identification information 70 shown in Figure 3 is 0.8 times or more the main groove width dimension Wc of the stress relaxation layer 52 closest to the identification information 70.

[0046] In this case, if the dimensions in the main groove width direction differ between each character constituting the string of characters in the identification information 70, the dimension of the character with the largest main groove width direction shall be adopted.

[0047] By setting the groove width dimension Ch of the identification information 70 to 0.8 times or more the main groove width dimension Wc of the stress relaxation layer 52 closest to the identification information 70 (i.e., the stress relaxation layer that has the greatest impact on the visibility of the identification information 70), that is, by ensuring sufficient size for the identification information 70, the visibility of the identification information 70 can be further enhanced.

[0048] In particular, this embodiment is effective when the stress relaxation layer 52 and the identification information 70 overlap, and is advantageous in that the visibility of the identification information 70 is sufficiently ensured even in such cases.

[0049] Furthermore, the groove width dimension Ch of the identification information 70 shown in Figure 3 is more preferably 0.9 times or more, and most preferably 1.0 times or more, the main groove width dimension Wc of the stress relaxation layer 52 closest to the identification information 70.

[0050] Figure 8 is a meridional cross-sectional view of the tire showing the positions of both ends of the stress relaxation layer in the groove width direction. Figure 8(A) is an example where the stress relaxation layer 52 does not extend from the bottom 54 shown in Figure 2 outward in the radial direction of the tire to the other end 56T of the wall 56. Figure 8(B) is an example where the stress relaxation layer 52 extends from the bottom 54 shown in Figure 2 outward in the radial direction of the tire via the other end 56T of the wall 56 to the tread surface 37.

[0051] In the tires shown in Figures 1 and 2, as shown in Figures 8(A) and 8(B), when the radial position of the bottom of the main groove is set to the 0% radial position P0, and the position of the tire profile line as if there were no main groove 40 is set to the 100% radial position P100, it is preferable that the positions X1, X2, X3, and X4 at both ends in the groove width direction of the stress relaxation layer 52 are at a radial position of 50% or more (P50 or a position further radially outward from there).

[0052] The tire of this embodiment was devised because groove cracks (GC) are highly likely to occur near the boundary between the groove bottom 44 and the groove wall 46 of the main groove. By positioning the stress relaxation layer 52 at both ends X1 to X4 in the groove width direction at a position of 50% or more in the tire radial direction, the stress relaxation layer 52 is formed beyond the boundary between the groove bottom 44 and the groove wall 46 to the outside in the tire radial direction, thereby further suppressing the occurrence of groove cracks.

[0053] Furthermore, it is even more preferable that the positions X1 to X4 at both ends of the stress relaxation layer 52 in the groove width direction be at a position of 60% or more in the tire radial direction, and it is extremely preferable that they be at a position of 70% or more.

[0054] In the tires shown in Figures 1 and 2, it is preferable that the thickness of the stress relaxation layer 52 is between 5 μm and 200 μm. The thickness of the stress relaxation layer 52 refers to the tire radial dimension Ga of the stress relaxation layer 52, as shown in Figure 2. However, if this thickness is not uniform in the groove width direction, the tire radial dimension Gac at the center position in the groove width direction of the stress relaxation layer 52 is used.

[0055] By making the thickness of the stress relaxation layer 52 5 μm or more, the stress relaxation effect of the stress relaxation layer 52 is further enhanced, improving crack resistance. On the other hand, by making the thickness of the stress relaxation layer 52 200 μm or less, the ability of the stress relaxation layer 52 to follow the deformation of the tread rubber 38 is ensured, further improving crack resistance.

[0056] The thickness of the stress relaxation layer 52 is more preferably 7 μm or more and 150 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0057] In the tires shown in Figures 1 and 2, the identification information 70 preferably consists mainly of diene-based rubber material and non-diene-based rubber material, and also contains a coloring pigment, with at least 20 parts by mass of coloring pigment per 100 parts by mass of rubber component, and the difference ΔL* of the index L* in the lightness axis direction in the L*a*b* color space between the identification information 70 and the rubber layer adjacent to the identification information 70 is 8 or more.

[0058] Here, the brightness axis refers to the direction perpendicular to both the red or green direction and the yellow or blue direction in the L*a*b* color space.

[0059] Furthermore, a coloring pigment other than carbon black is used as the coloring pigment, so that the identification information 70 exhibits a different color from the stress relaxation layer 52 and the tread rubber 38 (a color that differs in at least one of its saturation, hue, and lightness). Since the identification information 70 is applied to the tread rubber before vulcanization, the coloring pigment used is one that does not decompose during vulcanization, i.e., one with a decomposition temperature of 125°C or higher.

[0060] As coloring pigments, zinc oxide, zinc powder, lead zinc, aluminum pigment, lead monoxide, mica-like iron oxide pigment, basic lead chromate, basic lead carbonate, red lead, lead white, yellow lead, ochre, kaolin, clay, ultramarine, turquoise, Prussian blue, iron oxide pigment, iron oxide powder, lead cyanamide, heavy calcium carbonate, zinc chromate, talc, earthenware powder, precipitated calcium carbonate, precipitated barium sulfate, iron yellow, turquoise powder, titanium dioxide, chalk, barite powder, etc. can be used.

[0061] Alternatively, azo pigments such as soluble azo red, monoazo yellow, monoazo red, disazo yellow, disazo orange, and condensed azo pigments can be used as coloring pigments; phthalocyanine pigments such as copper phthalocyanine blue, copper phthalocyanine green, and cobalt phthalocyanine blue can also be used.

[0062] By setting the difference ΔL to 8 or more, the contrast in the L*a*b* color system between the identification information 70 and the rubber layer adjacent to the identification information 70 (specifically, the tread rubber 38 and / or stress relaxation layer 52) becomes clearer, further improving the visibility of the identification information 70.

[0063] Furthermore, it is even more preferable that the color ΔL* be 10 or greater, and most preferably 12 or greater.

[0064] Furthermore, in order to further clarify the contrast in the L*a*b* color system, it is even more preferable that the coloring pigment contains 30 parts by mass or more of coloring pigment (for example, titanium dioxide or zinc oxide) per 100 parts by mass of rubber component, or even more preferable that it does not contain carbon black.

[0065] In the tire described above, it is preferable that multiple identification information 70 are formed individually.

[0066] Figure 9 is a plan view of the tire showing the positional relationship between the identification information and the identification line. In Figures 9(A) and 9(B), reference numeral 38 indicates the tread rubber, reference numeral 52 indicates the stress relaxation layer, reference numeral 70 indicates the identification information, reference numeral 70a indicates the string (R5678 1234), and reference numeral 70b indicates the colored identification line.

[0067] In the example shown in Figure 9(A), two types of identification information 70a and 70b are duplicated, resulting in poor visibility of at least one of the identification information (in this example, the string 70a).

[0068] In contrast, in the example shown in Figure 9(B), the two types of identification information 70a and 70b are not formed redundantly; in other words, these identification information 70a and 70b are formed individually, so the visibility of both types of identification information (in this example, the string 70a and the identification line 70b) is good.

[0069] <Other suitable examples of tires> In the tires shown in Figures 1 and 2, the ratio R of the maximum thickness Hmax of the tread portion 18 to the minimum thickness Hg of the tread portion 18 is defined as Hg / Hmax. Preferably, the above ratio R, the minimum distance Gu in the radial direction of the tire from the groove bottom 44 to the belt cover 24 (or to the belt 22 if there is no belt cover 24), and the thickness Ga of the stress relaxation layer 52 satisfy the following formula (1). By satisfying the following formula (1), the tire 10 can achieve both durability of the stress relaxation layer 52 and suppression of tire rolling resistance.

[0070]

number

[0071] When the maximum thickness Hmax is large and the minimum thickness Hg is small, i.e., when R is small, the amount of deformation of the tread rubber 38 at the bottom of the groove 44 is large, making it difficult to obtain durability of the stress relaxation layer 52, and the rolling resistance of the tire 10 tends to increase. On the other hand, when R is large, the amount of deformation at the bottom of the groove 44 is kept small, making it easier to obtain durability of the stress relaxation layer 52, and the rolling resistance of the tire 10 tends to decrease.

[0072] Furthermore, when the minimum distance Gu is large and the thickness Ga is small (Ga / Gu is small), the thickness Ga of the stress relaxation layer 52 becomes small relative to the thickness of the tread rubber 38 at the minimum distance Gu, i.e., the groove bottom 44, making it difficult to obtain durability for the stress relaxation layer 52. On the other hand, when Ga / Gu is large, the thickness Ga of the stress relaxation layer 52 becomes thicker relative to the thickness of the tread rubber 38 at the groove bottom 44, making it easier to obtain durability for the stress relaxation layer 52.

[0073] By being above the lower limit of equation (1) above, the stress relaxation layer 52 has sufficient thickness relative to the thickness of the tread rubber 38 at the groove bottom 44. Therefore, the tire 10 can obtain the effect of suppressing the occurrence of groove cracks. In addition, because the tread rubber 38 at the groove bottom 44 has sufficient thickness, the amount of deformation at the groove bottom 44 can be suppressed. Therefore, the tire 10 can suppress the increase in rolling resistance.

[0074] By keeping the value below the upper limit of equation (1) above, the stress relaxation layer 52 does not become too thick relative to the thickness of the tread rubber 38 at the groove bottom 44, and can follow the deformation of the tread portion 18. Therefore, the tire 10 can obtain the effect of suppressing the occurrence of groove cracks. In addition, by maintaining the appropriate thickness of the tread rubber 38 at the groove bottom 44, an unnecessary increase in tire mass can be suppressed. Therefore, the tire 10 can suppress an increase in rolling resistance.

[0075] In the tires shown in Figures 1 and 2, the stress relaxation layer 52 is preferably provided in the circumferential main groove 40 located within the maximum belt width region WB. The maximum belt width region WB is the region from both outer ends in the tire width direction to the inner end in the tire width direction of the belt layer 22b or belt cover 24, which is formed as a reinforcing layer and located on the outermost side in the tire radial direction. The maximum belt width region WB has high rigidity and low strain during driving because the belt 22 or belt cover 24 is provided therein. Therefore, by providing the stress relaxation layer 52 in the circumferential main groove 40 located within the maximum belt width region WB, strain can be reduced and durability can be improved. The stress relaxation layer 52 is preferably provided in the circumferential main groove 40 located in the region where the belt cover 24 is provided within the maximum belt width region WB.

[0076] In the tires shown in Figures 1 and 2, among the circumferential main grooves 40 provided with a stress relaxation layer 52, the circumferential main groove 40 located on the outermost side in the tire width direction is specifically called the outermost main groove 40S. The distance between the center of the groove width of the outermost main groove 40S and the tire equatorial plane CP is denoted as Dg. The distance between the outer edge of the belt layer 22b or belt cover 24 located on the outermost side in the tire radial direction and the tire equatorial plane CP is denoted as Df. The ratio of Dg to Df (Dg / Df) is preferably 0.3 or more and 0.7 or less.

[0077] Generally, during the manufacturing process, when the green tire is inflated, when the tire 10 is mounted on the rim, and when the tire 10 is brought to the ground, the tread portion 18 experiences greater stress closer to the tread edge. As a result, the strain generated at the groove bottom 44 of the outermost main groove 40S, which is located near the tread edge, also increases. Therefore, by keeping the above ratio (Dg / Df) above the lower limit, the strain generated at the groove bottom 44 can be suppressed, thereby improving the durability of the stress relaxation layer 52. By keeping the above ratio (Dg / Df) below the upper limit, appropriate rigidity of the tread portion 18 can be obtained, resulting in excellent handling stability.

[0078] In the tires shown in Figures 1 and 2, the groove area ratio on the tread surface 37 is preferably 15% or more and 45% or less. The groove area ratio is a value (in %) defined by groove area / (contact area + groove area) × 100. Groove area refers to the opening area of ​​the grooves on the contact surface. Grooves include the circumferential main grooves of the tread but do not include sipes. If circumferential fine grooves and lug grooves are formed on the tread surface 37, these are included in the grooves. Contact area refers to the contact area between the tire and the contact surface. The groove area and contact area are measured at the contact surface between the tire 10 and the flat plate when the tire 10 is mounted on a regular rim, subjected to regular internal pressure, and placed perpendicular to a flat plate in a stationary state, with a load corresponding to a specified load (80% of the maximum load capacity) applied.

[0079] <Tire manufacturing method> The tire 10 of this embodiment described above is obtained through the usual manufacturing processes, namely the mixing process of tire materials, the processing process of tire materials, the molding process of green tires, the vulcanization process, and the inspection process after vulcanization. When manufacturing the tire 10 of this embodiment, a coating agent for the stress relaxation layer 52 is applied to a green tire before vulcanization, in a region including a predetermined position, namely the position where the circumferential main groove 40 is formed, and a coating agent for identification information is applied, taking into consideration the positional relationship with the circumferential main groove 40 in which the stress relaxation layer 52 is formed.

[0080] The coating agent for the stress relaxation layer mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains at least carbon and a vulcanizing agent. In contrast, the coating agent for identification information mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains a coloring pigment.

[0081] Subsequently, through a vulcanization process, a tire 10 can be obtained in which a stress-relieving layer 52 is formed at least at the groove bottom 44 of the circumferential main groove 40, and identification information 70 having a suitable positional relationship with the circumferential main groove 40 is formed. In the vulcanization process, a vulcanization mold is used in which convex and concave portions corresponding to a predetermined tread pattern are formed on the inner wall. [Examples]

[0082] The following describes the results of evaluating the durability (GC resistance) of the stress relaxation layer at 50°C and the visibility of the identification information for each of the test tires shown below.

[0083] (Preparation of test tires) Each test tire (the conventional example and the tires from Invention Examples 1 to 9-2 described later) was created with a tire size of 225 / 65R17, having the tread pattern shown in Figure 1, a stress relaxation layer (symmetrical in the groove width direction with respect to the groove width center) formed on the surface of the groove bottom of one circumferential main groove, and identification information having the positional relationship shown in Table 1 with respect to this circumferential main groove.

[0084] In the conventional example and Invention Examples 1 to 8, the string R123 shown in Figure 3 was used as identification information. In contrast, Invention Examples 9-1 and 9-2 use the string R123 shown in Figure 3 as identification information, as well as an identification line extending in the circumferential direction of the tire (formed on the opposite side of the main groove center from the string R123).

[0085] Each test tire was then mounted onto a rim with a size of 17 x 6.5J, and subjected to an internal pressure of 230 kPa and a specified load of 6.0 kN.

[0086] The conditions for the tires in the conventional example and Invention Examples 1 to 9-2 are as shown in Table 1 below. The terms in Table 1 are all the same as the terms explained in this embodiment, and their descriptions have been partially simplified.

[0087] (Evaluation of crack resistance at 50°C) Each test tire was left for 24 hours in a room maintained at an ozone concentration of 100±5 pphm, a temperature of 50±2°C, and an internal pressure of 230±2 kPa. The number of cracks that formed in the circumferential main grooves was then measured. Based on this measurement, an index evaluation was performed using a conventional example as the baseline (100). In this evaluation (see Table 1), a higher number indicates higher crack resistance.

[0088] (Evaluation of identifiable visibility) An evaluator, standing 1 meter away from each test tire, measured the time it took from opening their eyes after crouching down until they recognized the identification information (specifically, the string "R123"). An index evaluation was then performed using the reciprocal of this measurement time, with the previous example set as the baseline (100). In this evaluation (see Table 1), a higher numerical value indicates higher recognition visibility.

[0089] [Table 1]

[0090] As shown in Table 1, the tires of Invention Examples 1 to 9-2, which fall within the technical scope of the present invention (identification information is formed in areas other than the groove width region, which is 0.1 times the groove width dimension Wc of the stress relaxation layer, on each side in the groove width direction from the groove width center line of the groove bottom), all have excellent identifiable visibility while ensuring crack resistance, compared to conventional tires that do not fall within the technical scope of the present invention. Therefore, it can be seen that in Invention Examples 1 to 9-2, both crack resistance and identification function are achieved in tires that include identification information. [Explanation of symbols]

[0091] 10 tires 12 Bead section 14 Sidewall section 16 Shoulder section 18 Tread section 19 Inner liner 20 Carcass 22 belts 24 Belt Cover 36 Sidewall rubber 37 Tread surface 38 Tread Rubber 40 Circumferential main groove 40S outermost main groove 42 Land 44 Groove bottom 46 Ditch wall 48 Edge 52 Stress relaxation layer 54 Bottom 56 Wall 56U one end 56T other end 58 Surface part 58G one end 58L other end CP Tire Equatorial Plane WB Maximum Belt Width Area

Claims

1. A tire in which the tread surface of the tread rubber is divided into land areas by main grooves, identification information including a string of characters is provided on the tread surface, and a stress-relieving layer is formed on the surface of the bottom of at least one of the main grooves, The stress relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material, and also contains carbon and a vulcanizing agent. A tire characterized in that the identification information is formed in a region other than the groove width region, which is 0.1 times the groove width dimension Wc of the stress relaxation layer, on each side of the groove width direction from the groove width direction center line of the groove bottom.

2. The tire according to claim 1, wherein the stress relaxation layer and the identification information overlap in at least a portion, and the identification information is formed on the radially outer side of the stress relaxation layer.

3. The stress relaxation layer and the identification information do not overlap. The tire according to claim 1, wherein the distance W in the groove width direction between the stress relaxation layer and the identification information is 50 times or more the thickness Gac of the stress relaxation layer at the center position in the groove width direction of the main groove.

4. The tire according to claim 1 or 2, wherein the color difference ΔE*ab in the L*a*b* color space between the stress relaxation layer and the tread surface is less than 13.

5. The tire according to claim 1 or 2, wherein the groove width direction dimension Ch of the identification information is 0.8 times or more the main groove width direction dimension Wc of the stress relaxation layer closest to the identification information.

6. The tire according to claim 1 or 2, wherein the radial position of the bottom of the main groove is set to the 0% radial position of the tire, and the position of the tire profile line as if there were no main groove is set to the 100% radial position of the tire, and the positions of both ends of the stress relaxation layer in the groove width direction are at the 50% or greater radial position of the tire.

7. The tire according to claim 1 or 2, wherein the thickness of the stress relaxation layer is 5 μm or more and 200 μm or less.

8. The aforementioned identification information mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains coloring pigments, with 20 parts by mass or more of coloring pigment per 100 parts by mass of rubber component. The tire according to claim 1 or 2, wherein the difference ΔL* of the index L* in the lightness axis direction in the L*a*b* color space between the identification information and the rubber layer adjacent to the identification information is 8 or more.

9. The tire according to claim 1 or 2, wherein multiple pieces of identification information are individually formed.

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