Tire

Abstract

Provided is a tire that has a display object for depicting a character, a figure, or a symbol on the outer surface of the sidewall part, and which is manufactured through a process for polishing the surface of the display object, the tire achieving an improved surface state of the display object. In a tire having a display object on the outer surface of the sidewall part wherein at least a part of a top surface of a convex part constituting the display object exposes a different-colored rubber embedded in a part of the sidewall part and therefore has a color different from that of the outer surface of the sidewall part, when a part extending along a tire radial direction of the convex part constituting the display object is defined as a radial element, the angle θr formed by a side surface of the convex part and the normal direction to the outer surface of the sidewall part in a cross section orthogonal to the radial element is set to 15° to 30° inclusive, or a connection part of the side surface of the convex part that connects to the outer surface of the sidewall part in the cross section orthogonal to the radial element is formed into an arc shape having a curvature radius Rr of 2.5 to 4.0 mm inclusive.

Description

tire

[0001] The present invention relates to a tire having indicia depicting letters, figures, or symbols on the outer surface of the sidewall portion.

[0002] Indicia for displaying the manufacturer's name, brand name, etc., are sometimes formed on the outer surface of the sidewall of a tire. In particular, to improve the visibility and decorativeness of these indicators, they are formed using a different-colored rubber (e.g., white rubber) that is a different color from the color of the sidewall (typically black) (so-called "white letters"). When manufacturing such tires, at least a portion of the portion of a green tire corresponding to the sidewall (the portion corresponding to the indicator) is laminated with a different-colored rubber layer (white rubber layer) and a cover rubber layer (black rubber layer) that covers the different-colored rubber layer. The green tire is then vulcanized to form the indicators as protrusions protruding from the surface of the sidewall. The surface of the protrusions (cover rubber layer) is then polished and removed to expose the white rubber layer, thereby forming the indicators made of different-colored rubber (see, for example, Patent Document 1).

[0003] In such tires, the process of polishing the surface of the markings (protrusions) is carried out using a dedicated polishing machine (buffing machine) or the like. This machine rotates a polishing body (such as a grindstone) against the side of the tire, which is mounted on a stand and rotates, and polishes the tire sidewall (marking) in the thickness direction (the direction of the protrusion height) by an interval preset for each type of tire, polishing it so that the embedded different-colored rubber is exposed on the tire surface (see, for example, Patent Document 2). When performing the polishing process (buffing process) using such a machine, if the dimensions of the markings formed as protrusions are small, the rigidity of the markings (protrusions) cannot be ensured, resulting in problems such as the markings collapsing during polishing, which could lead to a deterioration in the surface condition of the markings after polishing.

[0004] Japanese Unexamined Patent Publication No. 2018-114732 Japanese Unexamined Patent Publication No. 05-277925

[0005] The object of the present invention is to provide a tire that has markings depicting letters, figures, or symbols on the outer surface of the sidewall portion and is manufactured through a process of polishing the surface of the markings, and that makes it possible to improve the surface condition of the markings.

[0006] In order to achieve the above object, a first tire of the present invention comprises a tread portion extending circumferentially of the tire to form an annular shape, and a pair of sidewall portions arranged on either side of the tread portion, wherein the outer surface of the sidewall portion is formed with indicia depicting letters, figures, or symbols by the shape of the top faces of convex portions protruding from the outer surface of the sidewall portion, and at least a portion of the top faces of the convex portions is exposed to a different color rubber embedded in a portion of the sidewall portion, thereby having a color different from that of the outer surface of the sidewall portion, and wherein, when a portion of the convex portion constituting the indicia extending along the tire radial direction is defined as a radial element, the angle θr formed by the side face of the convex portion and the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the radial element is 15° or more and 30° or less.

[0007] A second tire of the present invention for achieving the above object comprises a tread portion extending circumferentially of the tire to form an annular shape, and a pair of sidewall portions arranged on either side of the tread portion, wherein the outer surface of the sidewall portion is formed with indicia depicting letters, figures, or symbols by the shape of the top faces of convex portions protruding from the outer surface of the sidewall portion, and at least a portion of the top faces of the convex portions is exposed to a different color rubber embedded in a portion of the sidewall portion, thereby having a color different from that of the outer surface of the sidewall portion, wherein, when the portion of the convex portion constituting the indicia extending along the tire radial direction is defined as a radial element, a connection portion connecting the side surface of the convex portion to the outer surface of the sidewall portion is arc-shaped in a cross section perpendicular to the radial element, and the radius of curvature Rr of the connection portion is 2.5 mm or more and 4.0 mm or less.

[0008] The present inventors have conducted extensive research into poor appearance of indicia in tires manufactured through a process of polishing the surfaces of the convex portions that make up the indicia, and have found that if the dimensions of the indicia formed as the convex portions are small, when the polishing body rotates and comes into contact with the indicia (convex portions), problems such as the indicia (convex portions) collapsing in the direction of rotation of the polishing body (polishing direction) occur, resulting in a deterioration in the surface condition of the indicia after polishing (the surface of the indicia is not smooth, and for example, scale-like irregularities occur).The present invention is based on this finding and aims to prevent the indicia (convex portions) from collapsing by increasing the strength of the parts of the convex portions that make up the indicia that are susceptible to load in the polishing direction (the parts that extend in a direction perpendicular to the polishing direction, i.e., along the tire radial direction), thereby improving the surface condition of the indicia after polishing. Specifically, in the first tire of the present invention, the angle θr between the wall surface of the radial element (the side surface of the convex portion in a cross section perpendicular to the radial element) and the normal direction of the outer surface of the sidewall portion is ensured to be appropriately large, thereby ensuring the rigidity of the radial element, which is susceptible to load in the polishing direction, and preventing the indicia (convex portion) from collapsing. Similarly, in the second tire of the present invention, the radial element and the outer surface of the sidewall portion are connected via a connecting portion having an arc-shaped cross section with an appropriately large radius of curvature Rr, ensuring the rigidity of the radial element, which is susceptible to load in the polishing direction, and preventing the indicia (convex portion) from collapsing. In either case, since collapse of the indicia (convex portion) can be effectively prevented, poor appearance of the indicia caused by collapse can be suppressed and the surface of the indicia after polishing can be smoothed.

[0009] In the first tire of the present invention, when the portion of the protrusion constituting the indicia extending in the tire circumferential direction is defined as a circumferential element, it is preferable that the angle θc formed by the side surface of the protrusion with the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the circumferential element is smaller than the angle θr. In this way, by increasing the angle θr for the wall surface in the portion (radial element) where collapse is likely to occur and decreasing the angle θc for the circumferential element where the impact is small, the amount of rubber used for the indicia can be reduced.

[0010] In the second tire of the present invention, when the portion of the protrusion constituting the indicia extending in the tire circumferential direction is defined as a circumferential element, it is preferable that in a cross section perpendicular to the circumferential element, the side surface of the indicia and the outer surface of the sidewall portion are smoothly connected via an arc-shaped connecting portion, and that the radius of curvature Rc of the connecting portion is smaller than the radius of curvature Rr. In this way, by increasing the radius of curvature Rr for the wall surface in the portion (radial element) where collapse is likely to occur and decreasing the radius of curvature Rc for the circumferential element where the impact is less, the amount of rubber used for the indicia can be reduced.

[0011] In the second tire of the present invention, the angle θr formed by the side surface of the convex portion with the normal to the outer surface of the sidewall portion in a cross section perpendicular to the radial element is preferably 15° or more and 30° or less. Furthermore, when the portion of the convex portion constituting the indicia extending along the tire circumferential direction is defined as the circumferential element, the angle θc formed by the side surface of the convex portion with the normal to the outer surface of the sidewall portion in a cross section perpendicular to the circumferential element is preferably smaller than the angle θr. This makes it possible to reinforce the areas (radial elements) prone to collapse not only by the radius of curvature of the connecting portion but also by the angle of the side surface of the convex portion, thereby more effectively suppressing poor appearance of the indicia and smoothing the surface of the indicia after polishing.

[0012] In the present invention, it is preferable that the width W of the top surface of the convex portion and the protruding height H of the convex portion satisfy the relationship W / H≦1.0. If the protruding height H is large relative to the top surface width W, the display object (convex portion) is likely to collapse, and therefore, by applying the above-described configuration of the present invention, the effects of the present invention can be effectively exerted.

[0013] In the present invention, the angle that the radial element forms with respect to the tire radial direction is preferably within a range of ±30°. By using a portion extending in the tire radial direction within such an angle range as the radial element, it is possible to effectively reinforce a portion that is likely to collapse when the surface of the display object is polished, which is advantageous for improving the surface condition of the display object.

[0014] In the present invention, it is preferable that the length L of the display object along the tire radial direction is 25 mm or less. When the size of the display object in the tire radial direction is small in this way, the dimensions such as the width W of the top surface of the display object also become small, and the display object is more likely to collapse when its surface is polished. Therefore, by applying the above-mentioned present invention, the effects of the present invention can be more efficiently achieved.

[0015] FIG. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an example of a display object of a tire according to an embodiment of the present invention. FIGS. 3(a) and 3(b) are explanatory diagrams showing the state of the display object before and after polishing. FIGS. 4(a) and 4(b) are cross-sectional views showing a display object according to an embodiment of the present invention. FIGS. 5(a) and 5(b) are cross-sectional views showing a display object according to another embodiment of the present invention. FIG. 6 is an explanatory diagram showing the radial portion of a display object according to the present invention.

[0016] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] When the tire of the present invention is a pneumatic tire as shown in Figure 1, it comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In Figure 1, the symbol CL denotes the tire equator, and the symbol E denotes the ground contact edge. Although not depicted in Figure 1 because it is a meridian cross section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend circumferentially in the tire direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be basically based on the meridian cross section shown, but each tire component also extends circumferentially in the tire direction and forms an annular shape.

[0018] A carcass layer 4 is installed between a pair of left and right bead portions 3. The carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around bead cores 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of each bead core 5, and this bead filler 6 is wrapped by the main portion and folded back portion of the carcass layer 4. Meanwhile, multiple belt layers 7 (two layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, at least one belt reinforcing layer 8 (two layers in FIG. 1 ) is provided on the outer periphery of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction.

[0019] As described below, the present invention relates to indicia formed on the surface of the tire sidewall portion 2, and therefore the basic structure (cross-sectional structure) of the tire is not limited to the general structure described above. Furthermore, the following description will be based on a pneumatic tire (a tire filled with air, an inert gas such as nitrogen, or other gases) as shown in Fig. 1 etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as the tire has indicia depicting letters, figures, or symbols on the outer surface of the sidewall portion and is manufactured through a process of polishing the surface of the indicia.

[0020] In the present invention, as shown in Figures 1 and 2, an indicia 10 is provided on the outer surface of at least one of the pair of sidewall portions 2. The indicia 10 depicts letters, figures, or symbols using the shape of the top surfaces of protrusions 11 protruding from the outer surfaces of the sidewall portions 2. The indicia 10 of the present invention has a color different from that of the outer surfaces of the sidewall portions by exposing different-colored rubber 12 embedded in part of the sidewall portions 2 at least in part of the top surfaces of the protrusions 11 constituting the indicia 10. Since the outer surfaces of tire sidewall portions are generally black, it is preferable that the different-colored rubber be white rubber from the standpoints of visibility and decorativeness.

[0021] More specifically, the protrusion 11 constituting the marking 10 is formed as a protrusion 11 in which a different-colored rubber 12 embedded in the sidewall portion 2 and a cover rubber 13 covering the different-colored rubber 12 are laminated, as shown in Figure 3(a), and then the surface of this protrusion 11 (the cover rubber 13 and a portion of the different-colored rubber 12) is polished and removed to expose the different-colored rubber 12 as shown in Figure 3(b), thereby forming a marking 10 in which at least a portion of the top surface of the marking 10 is made of the different-colored rubber 12. Note that Figure 3(b) shows the state in which the portion above the dashed line in Figure 3(a) has been polished and removed. Because it is manufactured as described above, strictly speaking, the top surface of the protrusion 11 of the present invention is made of the different-colored rubber 12 in the region excluding the peripheral portion derived from the cover rubber 13.

[0022] The example shown in FIG. 2 depicts the letter "N." More specifically, the outline of the letter "N" is formed by the convex portion 11 whose top surface is made of different-colored rubber 12, and the letter "N" is depicted as a whole by this outline (the convex portion 11) and the portion surrounded by the outline (the surface of the sidewall portion 2). The dashed line in FIG. 2 depicts the lower end of the convex portion 11 (the portion connecting to the outer surface of the sidewall portion 2), and the area between the dashed line and the solid line in FIG. 2 corresponds to the side surface of the convex portion 11. In the following description, of the convex portion 11 constituting such an indicator 10, the portion extending along the tire radial direction (the up-down direction in the drawing) is referred to as a radial element 11r, and the portion extending along the tire circumferential direction (the left-right direction in the drawing) is referred to as a circumferential element 11c.

[0023] In a first aspect of the present invention, when the wall angle θr is the angle formed by the side surface of the protrusion 11 and the normal direction to the outer surface of the sidewall portion 2 in a cross section (X-X cross section in FIG. 2) perpendicular to the radial element 11r shown in FIG. 4(a), this wall angle θr is set to 15° or more and 30° or less, preferably 20° or more and 25° or less. Note that the wall angle θr is measured based on an extension line of the linearly extending portion of the side surface of the protrusion 11 in a cross section perpendicular to the radial element 11r. When the entire side surface of the protrusion 11 is arc-shaped, as in a second aspect described below, the structure is specified based on the radius of curvature Rr described below instead of the wall angle θr.

[0024] In the first aspect described above, the thickness of the protrusion 11 at the lower side (the portion close to the surface of the sidewall portion) of the protrusion 11 can be ensured, and the rigidity of the radial element 11r, which is likely to be subjected to load in the polishing direction during the process of polishing the surface of the protrusion 11 constituting the display 10, can be ensured. This prevents the display 10 (protrusion 11) from collapsing, suppresses the resulting poor appearance of the display 10, and makes the surface of the display 10 smooth after buffing. If the wall angle θr is less than 15° in the first aspect, the thickness of the lower part of the protrusion 11 cannot be sufficiently ensured, and collapse of the display 10 (protrusion 11) cannot be prevented. If the wall angle θr is more than 30° in the first aspect, the thickness of the lower part of the protrusion 11 becomes excessive, making it difficult to properly depict the intended letters, figures, or symbols on the display 10.

[0025] In the first aspect, when the angle between the side surface of the convex portion 11 and the normal to the outer surface of the sidewall portion 2 in a cross section (Y-Y cross section in FIG. 2) perpendicular to the circumferential element 11c shown in FIG. 4(b) is defined as the wall angle θc, this wall angle θc is preferably smaller than the wall angle θr. That is, in the radial element 11r, the thickness of the convex portion 11 on the lower side (the portion close to the surface of the sidewall portion) is ensured to be large, while in the circumferential element 11c, the thickness of the convex portion 11 on the lower side (the portion close to the surface of the sidewall portion) is set to a conventional level. In this way, by increasing the wall angle θr for the wall surface in the portion (radial element 11r) where collapse is likely to occur, and decreasing the wall angle θc for the circumferential element 11c where collapse is less likely to occur, the amount of rubber used in the display object 10 can be reduced. The range of the wall angle θc is not particularly limited, but can be set to, for example, 5° to 15°. The difference between the wall surface angle θr and the wall surface angle θc can be set to, for example, 5° to 20°. The wall surface angle θc is measured in the same manner as the wall surface angle θr described above.

[0026] 4(a) and 4(b) are intended to explain the wall surface angles θr and θc, and therefore do not distinguish between the different color rubber 12 and the cover rubber 13. Even if the wall surface angles θr and θc are made different as described above, it is preferable that the width W of the top surface of the convex portion 11 (and the width of the different color rubber exposed at the top surface of the convex portion 11) be constant (especially when the top surface of the convex portion 11 forms the outline of the displayed object as in the illustrated example).

[0027] In a second aspect of the present invention, as shown in FIG. 5( a), in a cross section (X-X cross section in FIG. 2) perpendicular to the radial element 11r, the connecting portion 14 connecting the side surface of the convex portion 11 to the outer surface of the sidewall portion 2 is arc-shaped, and the radius of curvature Rr of this connecting portion 14 is set to 2.5 mm or more and 4.0 mm or less, preferably 3.0 mm or more and 3.5 mm or less.

[0028] In the second aspect described above, the shape of the connecting portion 14 ensures the thickness of the protrusion 11 at the lower portion (the portion close to the surface of the sidewall portion) of the protrusion 11, thereby ensuring the rigidity of the radial element 11r, which is susceptible to load in the polishing direction during the polishing process of the surface of the protrusion 11 constituting the display 10. Therefore, collapse of the display 10 (protrusion 11) is prevented, resulting in poor appearance of the display 10, and the surface of the display 10 after buffing can be smoothed. In the second aspect, if the radius of curvature Rr is less than 2.5 mm, the thickness of the lower portion of the protrusion 11 cannot be sufficiently ensured, and collapse of the display 10 (protrusion 11) cannot be prevented. In the second aspect, if the radius of curvature Rr exceeds 4.0 mm, the thickness of the lower portion of the protrusion 11 becomes excessive, making it difficult to properly depict the intended characters, figures, or symbols on the display 10.

[0029] In the second embodiment, even in a cross section perpendicular to the circumferential element 11c shown in FIG. 5(b) (the Y-Y cross section in FIG. 2), the side surface of the convex portion 11 and the outer surface of the sidewall portion 2 are preferably smoothly connected via an arc-shaped connecting portion 14, and the radius of curvature Rc of this connecting portion 14 is preferably smaller than the radius of curvature Rr. That is, in the radial element 11r, the thickness of the convex portion 11 on the lower side (the portion close to the surface of the sidewall portion) is ensured to be large, while in the circumferential element 11c, the thickness of the convex portion 11 on the lower side (the portion close to the surface of the sidewall portion) is set to a conventional level. In this way, by increasing the radius of curvature Rr for the wall surface in the area where collapse is likely to occur (the radial element 11r) and decreasing the radius of curvature Rc for the circumferential element 11c, which is less affected by collapse, the amount of rubber used in the display object 10 can be reduced. The range of the radius of curvature Rc is not particularly limited, but can be set to, for example, 1.5 mm or more and 2.0 mm or less. The difference between the radius of curvature Rr and the radius of curvature Rc can be set to, for example, 1.0 mm or more and 2.0 mm or less.

[0030] 5(a) and 5(b) are intended to explain the radii of curvature Rr and Rc, and therefore do not distinguish between the different color rubber 12 and the cover rubber 13. Even if the radii of curvature Rr and Rc are made different as described above, it is preferable that the width W of the top surface of the convex portion 11 (the width of the different color rubber exposed at the top surface of the convex portion 11) be constant (especially when the top surface of the convex portion 11 forms the outline of the displayed object as in the illustrated example).

[0031] In both the first and second embodiments, when the top surface of the protrusion 11 forms the outline of the display object as in the illustrated example, the width W of the top surface of the protrusion 11 and the protrusion height H of the protrusion 11 in a cross section perpendicular to the radial element 11r preferably satisfy the relationship W / H≦1.0, more preferably 0.5≦W / H≦0.8. When the protrusion height H is large relative to the top surface width W, the display object 10 (protrusion 11) is more likely to collapse, so applying the above-described configuration of the present invention can effectively achieve the effects of the present invention. When the ratio W / H of the width W to the protrusion height H is W / H>1.0, the protrusion height H is small relative to the top surface width W of the protrusion 11, making it easier to ensure the rigidity of the protrusion 11, and therefore the effects of applying the above-described configuration of the present invention are limited. As mentioned above, it is preferable that the width W of the top surface of the convex portion 11 and the protruding height H of the convex portion 11 are constant regardless of the part of the display object 10, so even in a cross section perpendicular to the circumferential element 11c, the width W of the top surface of the convex portion 11 and the protruding height H of the convex portion 11 preferably satisfy the relationship W / H≦1.0, more preferably 0.5≦W / H≦0.8.

[0032] As described above, the radial element 11r refers to the portion of the protrusion 11 constituting the display object 10 that extends along the tire radial direction (the vertical direction in the figure). In particular, it is preferable that the angle α formed by the radial element 11r with respect to the tire radial direction be within a range of ±30°. For example, in the example of FIG. 6 (depicting the same alphabet "N" as in FIG. 2), the shaded portions correspond to the radial elements 11r, and the angles α formed by the radial elements with respect to the tire radial direction are all within a range of ±30°. By regarding the portions extending in the tire radial direction within such an angle range as the radial element 11r, it is possible to effectively reinforce portions that are prone to collapse when polishing the surface of the display object 10, which is advantageous for improving the surface condition of the display object 10. The angle α is measured based on the widthwise center of the top surface of the protrusion 11.

[0033] The tire indicia 10 to which the present invention is applied preferably has a length L along the tire radial direction of 25 mm or less. When the size of the indicia 10 in the tire radial direction is small, the dimensions such as the width W of the top surface of the indicia 10 also become small, making the indicia 10 more likely to collapse when polishing its surface. Therefore, by applying the present invention described above, the effects of the present invention can be more efficiently achieved. The length L of the indicia 10 along the tire radial direction is the size of each character, figure, or symbol included in the indicia 10, and is measured as the length along the tire radial direction between the upper end and lower end of the indicia 10 in the tire radial direction, as shown in Figures 1 and 2.

[0034] The cross-sectional height SH of a tire to which the present invention is applied is preferably 150 mm or less, and more preferably 120 mm to 140 mm. In tires with such small cross-sectional heights, the size of the indicia 10 provided on the sidewall portion 2 in the tire radial direction tends to be small, and the dimensions such as the width W of the top surface of the indicia 10 also become small, making it more likely for the indicia 10 to collapse when the surface is polished. Therefore, by applying the present invention described above, the effects of the present invention can be more efficiently achieved.

[0035] As described above, the present invention is intended to reinforce the portions (radial elements 11r) where collapse is likely to occur by increasing the wall surface angle θr of the convex portions 11 and the curvature radius Rr of the connecting portions, and therefore it is not necessary to apply the above settings to all radial elements 11r depending on the shape of the characters, figures, or symbols depicted in the display object 10. In other words, in areas where the convex portions 11 are close to each other and densely packed due to the shape of the depicted characters, figures, or symbols, and the strength of the convex portions 11 can be ensured, the shape is already such that collapse is unlikely to occur and the force applied during polishing is dispersed, so the above settings do not necessarily have to be applied.

[0036] The first tire feature (wall surface angle) and the second tire feature (curvature radius) of the present invention can also be applied in combination. That is, in a cross section perpendicular to the radial element 11r, the connecting portion 14 connecting the side surface of the convex portion 11 to the outer surface of the sidewall portion 2 is configured to be arc-shaped, and the radius of curvature Rr of this connecting portion 14 is set to 2.5 mm or more and 4.0 mm or less, preferably 3.0 mm or more and 3.5 mm or less, while the angle (wall surface angle θr) formed by the side surface of the convex portion 11 (the portion extending linearly between the top surface of the convex portion 11 and the connecting portion 14) and the normal direction to the outer surface of the sidewall portion 2 is set to 15° or more and 30° or less, preferably 20° or more and 25° or less. In this case, it is also preferable to make the radius of curvature Rc of the connecting portion 14 of the circumferential element 11c smaller than the radius of curvature Rr of the connecting portion 14 of the radial element 11r, and to make the wall angle θc of the circumferential element 11c smaller than the wall angle θr of the radial element 11r. This makes it possible to reinforce the portion (radial element 11r) where collapse is likely to occur by increasing both the wall angle θr of the protrusion 11 and the radius of curvature Rr of the connecting portion, thereby more effectively achieving the effects of the present invention described above. Note that other features of the first and second aspects not described in detail in this paragraph can also be applied in appropriate combinations.

[0037] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

[0038] Tires were produced as Conventional Examples 1 and 2, Comparative Examples 1 to 4, and Examples 1 to 8, each having a tire size of 225 / 60R17 99T and the basic structure (cross-sectional structure) illustrated in Fig. 1, with the display object structure set as shown in Tables 1 and 2. Note that, as for the display object structure, in Table 1, the wall surface angle θr in the radial element of the convex portion constituting the display object and the wall surface angle θc in the circumferential element, and the ratio W / H of the width W of the top surface of the convex portion to the protruding height H of the convex portion were varied, and in Table 2, the radius of curvature Rr of the connecting portion in the radial element of the convex portion constituting the display object and the radius of curvature Rc of the connecting portion in the circumferential element, and the ratio W / H of the width W of the top surface of the convex portion to the protruding height H of the convex portion were varied.

[0039] In all examples, the process of polishing the surface of the display object (convex portion) was carried out by mounting each tire on a wheel with a rim size of 17 x 6.5, filling it with an internal pressure of 200 kPa, and then mounting it on a dedicated polishing machine (buffing machine).

[0040] The surface condition, character shape, and rubber amount of the markings on these pneumatic tires were evaluated by the following evaluation methods. The results are shown in Tables 1 and 2.

[0041] Surface condition of markings The surface condition of the markings formed on each tire was visually inspected. The evaluation results were rated as "good" if the surface of the markings (the top surfaces of the convex parts) was smooth, and "poor" if the surface of the markings was not smooth (having a hill in the middle or being worn down on one side) or if the surface of the markings had fine scale-like irregularities.

[0042] Character Shape of Markings The character shape of the markings formed on each tire (the appearance of the characters, figures, or symbols that each marking is intended to depict) was visually confirmed. The evaluation results were rated as "good" when the character shape of the markings was good, and "poor" when the appearance of the markings as characters, figures, or symbols was poor.

[0043] Amount of rubber used The amount of rubber (volume) used in the markings formed on each tire was calculated based on the measured dimensions, etc. The evaluation results are shown as an index in Table 1, with Conventional Example 1 set to 100, and in Table 2, with Conventional Example 2 set to 100. The smaller the index value, the less rubber was used.

[0044]

[0045]

[0046] As is clear from Table 1, the tires of Examples 1 to 4 were able to improve the surface condition and character shape of the indicia while reducing the amount of rubber used, compared to Conventional Example 1. On the other hand, in Comparative Example 1, rigidity was ensured by increasing the width W of the indicia (protrusion), so the surface condition and character shape of the indicia were good, but the amount of rubber used was increased. In Comparative Example 2, the wall angle θr was too large, so the balance between the radial and circumferential elements was disrupted, and the character shape of the indicia (appearance as a character) deteriorated.

[0047] Furthermore, as is clear from Table 2, the tires of Examples 5 to 8 were able to improve the surface condition and character shape of the indicia while reducing the amount of rubber used compared to Conventional Example 2. On the other hand, in Comparative Example 3, rigidity was ensured by increasing the width W of the indicia (protrusion), so the surface condition and character shape of the indicia were good, but the amount of rubber used was increased. In Comparative Example 4, the radius of curvature Rr was too large, so the balance between the radial and circumferential elements was disrupted, and the character shape of the indicia (appearance as a character) deteriorated.

[0048] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 10 indicia 11 convex portion 11r radial element 11c circumferential element 12 different color rubber 13 cover rubber 14 connection portion CL tire equator E ground contact edge

Claims

1. A tire comprising a tread portion extending circumferentially to form an annular shape, and a pair of sidewall portions arranged on either side of the tread portion, wherein the outer surface of the sidewall portion has indicia depicting letters, figures or symbols formed by the shape of the top faces of protrusions protruding from the outer surface of the sidewall portion, and at least a part of the top faces of the protrusions has a different color from the outer surface of the sidewall portion by exposing different colored rubber embedded in a part of the sidewall portion, wherein, when a part of the protrusion constituting the indicia extending along the tire radial direction is defined as a radial element, an angle θr formed by the side of the protrusion and the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the radial element is 15° or more and 30° or less.

2. A tire comprising a tread portion extending circumferentially to form an annular shape and a pair of sidewall portions arranged on either side of the tread portion, wherein the outer surface of the sidewall portion has indicia depicting letters, figures or symbols formed by the shape of the top faces of protrusions protruding from the outer surface of the sidewall portion, and at least a part of the top faces of the protrusions has a different color from the outer surface of the sidewall portion by exposing different colored rubber embedded in a part of the sidewall portion, wherein, when the part of the protrusion constituting the indicia extending along the tire radial direction is defined as a radial element, a connection part connecting the side surface of the protrusion to the outer surface of the sidewall portion is arc-shaped in a cross section perpendicular to the radial element, and the radius of curvature Rr of the connection part is 2.5 mm or more and 4.0 mm or less.

3. The tire described in claim 1, characterized in that, when a portion of the protrusion constituting the indicia extending in the tire circumferential direction is defined as a circumferential element, an angle θc that the side surface of the protrusion makes with the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the circumferential element is smaller than the angle θr.

4. The tire according to claim 2, characterized in that, when a portion of the protrusion constituting the indicia extending in the tire circumferential direction is defined as a circumferential element, in a cross section perpendicular to the circumferential element, the side of the protrusion and the outer surface of the sidewall portion are smoothly connected via an arc-shaped connecting portion, and the radius of curvature Rc of the connecting portion is smaller than the radius of curvature Rr.

5. A tire as described in claim 2 or 4, characterized in that the angle θr that the side surface of the convex portion makes with the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the radial element is 15° or more and 30° or less.

6. The tire described in claim 5, characterized in that, when a portion of the protrusion constituting the indicia extending in the tire circumferential direction is defined as a circumferential element, an angle θc that the side surface of the protrusion makes with the normal direction to the outer surface of the sidewall portion in a cross section perpendicular to the circumferential element is smaller than the angle θr.

7. A tire as described in any one of claims 1 to 6, characterized in that the width W of the top surface of each of the projections and the raised height H of each of the projections satisfy the relationship W / H≦1.

0.

8. A tire according to any one of claims 1 to 7, characterized in that the angle formed by the radial element with respect to the tire radial direction is within the range of ±30°.

9. A tire according to any one of claims 1 to 8, characterized in that the length L of the indicia along the tire radial direction is 25 mm or less.

Images