Pneumatic tire

Abstract

Provided is a pneumatic tire that suppresses discoloration of a different-color rubber layer in a pneumatic tire in which the different-color rubber layer is exposed on an outer surface of a sidewall portion. The pneumatic tire includes a tread portion (2), a sidewall portion (3), a bead portion (4), and a carcass (6). At least one of a pair of sidewall portions (3) includes a first sidewall rubber (10) disposed on an axially outer side of the carcass (6) in the tire. The first sidewall rubber (10) includes a different-color rubber layer (11) and a barrier rubber layer (12). The different-color rubber layer (11) has a color different from a basic color of the outer surface of the sidewall portion (3), and at least a part of the different-color rubber layer (11) is exposed on the outer surface of the sidewall portion (3). The barrier rubber layer (12) includes a first portion (16) that is disposed between the different-color rubber layer (11) and the carcass (6) and has a rubber formulation that suppresses transfer of a rubber compounding agent on the carcass (6) side to the different-color rubber layer (11).

Description

Technical Field

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

[0002] In Patent Document 1 below, a pneumatic tire having convex patterns formed on a sidewall portion is proposed. The pneumatic tire has a non-black rubber layer inside the sidewall portion, and a part of the non-black rubber layer is exposed on a raised surface of the convex pattern.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-203420

[0004] The pneumatic tire of Patent Document 1 expects an improvement in appearance by the exposed rubber layer of a different color.

[0005] However, the rubber layer of a different color has the following problem: rubber compounding agents such as anti-aging agents transfer from rubber members around the rubber layer of a different color, and thus it is likely to change color. In particular, in recent years, the sidewall portion has been thinned, and there is a tendency that rubber compounding agents of the skim rubber of the carcass transfer to the rubber layer of a different color, and the above-mentioned color change is likely to occur. Summary of the Invention

[0006] The present invention has been made in view of the above actual situation, and its main object is to suppress color change of a rubber layer of a different color in a pneumatic tire in which the rubber layer of a different color is exposed on an outer surface of a sidewall portion.

[0007] The present invention is a pneumatic tire including a tread portion, a pair of sidewall portions, a pair of bead portions, and a carcass extending from one bead portion to the other bead portion. At least one of the pair of sidewall portions includes a first sidewall rubber disposed on an outer side in a tire axial direction of the carcass. The first sidewall rubber includes a rubber layer of a different color and a barrier rubber layer. The rubber layer of a different color has a color different from a basic color of the outer surface of the sidewall portion, and at least a part of the rubber layer of a different color is exposed on the outer surface of the sidewall portion. The barrier rubber layer includes a first portion disposed between the rubber layer of a different color and the carcass and having a rubber compounding that suppresses transfer of rubber compounding agents on the carcass side to the rubber layer of a different color.

[0008] In the pneumatic tire of the present invention, preferably, the pair of bead portions include bead apex rubbers constituting outer surfaces of the respective bead portions. The first sidewall rubber includes an inner rubber portion in contact with the bead apex rubber. The barrier rubber layer includes a second portion disposed between the inner rubber portion and the rubber layer of a different color and having a rubber compounding that suppresses transfer of rubber compounding agents of the inner rubber portion to the rubber layer of a different color.

[0009] In the pneumatic tire of the present invention, it is preferable that the barrier rubber layer includes a third part, which is disposed between the tread rubber constituting the tread surface and the different-color rubber layer, and has a rubber composition that inhibits the transfer of rubber compounding agents on the tread rubber side to the different-color rubber layer.

[0010] In the pneumatic tire of the present invention, it is preferable that in the tire meridian cross-section, the distance from the outer end in the tire radius direction of the first sidewall rubber to the tread grounding end is 20 mm to 40 mm.

[0011] In the pneumatic tire of the present invention, it is preferable that the pneumatic tire includes a boundary between a first outer surface vulcanized and formed by a tread mold and a second outer surface vulcanized and formed by a sidewall mold, and the different-color rubber layer is disposed at a position closer to the inner side in the tire radius direction than the boundary, and in the tire meridian cross-section, the distance from the boundary to the outer end in the tire radius direction of the different-color rubber layer is 10 mm to 30 mm.

[0012] In the pneumatic tire of the present invention, it is preferable that the tread surface includes tread rubber, and the outer end in the tire axial direction of the tread rubber is covered by the first sidewall rubber.

[0013] In the pneumatic tire of the present invention, it is preferable that the segment height is 120 mm or less.

[0014] In the pneumatic tire of the present invention, it is preferable that the barrier rubber layer contains 60% or less of butyl rubber.

[0015] By adopting the above structure, the pneumatic tire of the present invention can inhibit the discoloration of the different-color rubber layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a transverse cross-sectional view showing an embodiment of the tire of the present invention.

[0017] Figure 2 is Figure 1 a magnified cross-sectional view of the sidewall portion.

[0018] Figure 3 is Figure 2 a magnified view of the raised portion.

[0019] REFERENCE SIGNS

[0020] 2: tread surface; 3: sidewall portion; 4: bead portion; 6: carcass; 10: first sidewall rubber; 11: different-color rubber layer; 12: barrier rubber layer; 16: first part. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described based on the drawings.

[0022] Figure 1 The cross-sectional view of the pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 in the normal state of the present embodiment is shown. In addition, Figure 1 is a so-called tire meridian cross-sectional view including the rotation axis of the tire. As Figure 1 shown, the tire 1 of the present embodiment is, for example, a tire for passenger cars, and is a relatively low-profile tire with a section height h1 of 120 mm or less. However, the present invention is not limited to such a mode.

[0023] The "normal state" means that in the case of a pneumatic tire with various specifications defined, the tire is assembled on a normal rim (not shown) and filled with a normal internal pressure, and is in a non-loaded state. In the case of a tire without various specifications defined, the said normal state means a standard use state corresponding to the use purpose of the tire, and means a state of not being mounted on a vehicle and being non-loaded. In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in the said normal state.

[0024] The "normal rim" is a rim that defines the specification for each tire in the specification system including the specification on which the tire is based. For example, if it is JATMA, it is the "standard rim"; if it is TRA, it is the "Design Rim"; if it is ETRTO, it is the "Measuring Rim".

[0025] The "normal internal pressure" is the air pressure of each specification defined for each tire in the specification system including the specification on which the tire is based. If it is JATMA, it is the "maximum air pressure"; if it is TRA, it is the maximum value described in the table "TIRE LOAD LIMITS ATVARIOUS COLD INFLATION PRESSURES"; if it is ETRTO, it is the "INFLATIONPRESSURE".

[0026] The section height h1 refers to the height in the tire radius direction of the tire 1 from the bead base line in the said normal state. In addition, the bead base line is an axial line of the tire passing through the radial position of the rim determined by the specification on which the tire is based.

[0027] The tire 1 of the present embodiment includes a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4, and a carcass 6 extending from one bead portion 4 to the other bead portion 4.

[0028] The carcass 6 is composed of, for example, two carcass ply layers 6A and 6B. The carcass ply layers 6A and 6B include, for example, a plurality of carcass cords and skim rubber covering these carcass cords. The carcass cords are arranged at an angle of 75° to 90° with respect to the tire circumferential direction, for example. The carcass cords are preferably organic fiber cords such as nylon, polyester, or rayon, etc.

[0029] The carcass 6 has a main body portion 6a and a folded-back portion 6b. The main body portion 6a extends between the bead cores 5 of a pair of bead portions 4. The folded-back portion 6b is connected to the main body portion 6a and is folded back around the bead core 5 and extends outward in the tire radial direction. In the present embodiment, the folded-back portion 6b is folded back around the bead core 5 from the inner side to the outer side in the tire axial direction. Further, in the folded-back portion 6b, the outer end of one carcass ply 6A and the outer end of the other carcass ply 6B are displaced in the tire radial direction.

[0030] In the tread portion 2 of the present embodiment, a belt layer 7 is disposed, for example, on the outer side in the tire radial direction of the carcass 6. The belt layer 7 includes, for example, two belt plies 7A and 7B. Each of the belt plies 7A and 7B includes, for example, belt cords disposed obliquely with respect to the tire circumferential direction and skim rubber covering the belt cords. Each belt cord is preferably inclined at an angle of 10° to 45° with respect to the tire circumferential direction.

[0031] The tread portion 2 includes tread rubber 2G. A pair of bead portions 4 includes bead filler rubber 15 that forms its outer surface. At least one of a pair of sidewall portions 3 includes a first sidewall rubber 10 disposed on the outer side in the tire axial direction of the carcass 6.

[0032] In Figure 2 a magnified cross-sectional view of the sidewall portion 3 is shown. As Figure 2 shown, the first sidewall rubber 10 includes a different-color rubber layer 11 and a barrier rubber layer 12.

[0033] The different-color rubber layer 11 has a color (white in the present embodiment) different from the basic color (black in the present embodiment) of the outer surface of the sidewall portion 3, and at least a part of it is exposed on the outer surface of the sidewall portion 3. In the present embodiment, most of the different-color rubber layer 11 is covered by a covering rubber layer 13 made of the basic color, and a part of the different-color rubber layer 11 is exposed in a manner of depicting characters, marks, or graphics.

[0034] In Figure 3 a magnified cross-sectional view of a portion (bulge portion) where the different-color rubber layer 11 is exposed is shown. In the present embodiment, a bulge portion 20 is provided on the outer surface of the sidewall portion 3, and the different-color rubber layer 11 is exposed on the top surface 20t on the outer side in the tire axial direction thereof. In the manufacturing method of the tire 1 of the present embodiment, for example, after a part of the sidewall portion 3 including the different-color rubber layer 11 covered by the covering rubber layer 13 enters a concave portion of a corresponding vulcanization mold to form the bulge portion 20, the top surface of the bulge portion 20 is polished to expose the different-color rubber layer 11. Such a manufacturing method is well-known and is suitable for application to the tire 1 of the present embodiment.

[0035] In the present invention, as long as the different - colored rubber layer 11 is exposed, the present invention can also be applied to a tire that does not have the above - mentioned raised portion 20.

[0036] As Figure 2 shown, the barrier rubber layer 12 includes a first portion 16, which is disposed between the different - colored rubber layer 11 and the carcass 6, and has a rubber formulation that inhibits the transfer of rubber compounding agents on the carcass 6 side to the different - colored rubber layer 11. In the present invention, by adopting the above - mentioned structure, the discoloration of the different - colored rubber layer 11 can be inhibited. For the reason, the following mechanism can be speculated.

[0037] In the past, the different - colored rubber layer 11 had the following tendency: rubber compounding agents such as anti - aging agents would transfer from the rubber components around the different - colored rubber layer 11 and would also be affected by ultraviolet rays and the like, thereby discoloring and damaging the appearance of the sidewall portion 3. The inventor has conducted in - depth research, and the results show that regarding the discoloration, the influence of the rubber compounding agents contained in the rubber skim on the carcass 6 is relatively large. And it has also been found that in recent years, due to the thinning of the sidewall portion, the distance between the carcass 6 and the different - colored rubber layer 11 has become smaller, and the influence of the rubber skim on the carcass 6 has become even greater. In the present invention, it is speculated that the transfer of rubber compounding agents from the rubber skim on the carcass 6 can be inhibited by the first portion 16 of the above - mentioned barrier rubber layer 12, and the discoloration of the different - colored rubber layer 11 can be effectively inhibited.

[0038] Hereinafter, a more detailed structure of the present embodiment will be described. In addition, each structure described below represents a specific embodiment of the present embodiment. Therefore, even if the present invention does not have the structures described below, it can of course exhibit the above - mentioned effects. And in the tire of the present invention having the above - mentioned features, even if any one of the structures described below is applied alone, an improvement in the performance corresponding to each structure can be expected. In addition, in the case of compounding and applying several of the structures described below, an improvement in the composite performance corresponding to each structure can be expected.

[0039] The entire barrier rubber layer 12 is composed of the same rubber formulation. The rubber formulation of the barrier rubber layer 12 contains, for example, butyl - based rubber. Butyl - based rubber exhibits an extremely low air permeability and can effectively inhibit the transfer of rubber compounding agents. On the other hand, when a rubber layer containing butyl - based rubber comes into contact with the rim, rim corrosion may occur. From such a viewpoint, the barrier rubber layer 12 preferably contains 60% or less of butyl - based rubber, and more preferably contains 40% - 60% of butyl - based rubber.

[0040] Further, the barrier rubber layer 12 preferably contains a hydrous complex inorganic clay mineral such as kaolin, clay, mica, feldspar, silica, and alumina. Thereby, the transfer of the rubber compounding agent can be further suppressed. In addition, the barrier rubber layer 12 of the present invention can adopt a known rubber compounding.

[0041] The first sidewall rubber 10 includes an inner rubber portion 21 that contacts the bead rubber 15 of the bead portion 4. The inner rubber portion 21 is formed of a rubber compounding of a normal sidewall rubber. Thereby, the durability near the boundary between the first sidewall rubber 10 and the bead rubber 15 is improved. And, from the viewpoint of sufficiently ensuring durability, the length L1 of the inner rubber portion 21 along the outer surface of the sidewall portion 3 or the bead portion 4 in the tire meridian cross-section is 10 mm or more, preferably 10 mm to 30 mm.

[0042] Further, the barrier rubber layer 12 includes a second portion 17 disposed between the inner rubber portion 21 and the different-color rubber layer 11. The second portion 17 of course has a rubber compounding that suppresses the transfer of the rubber compounding agent of the inner rubber portion 21 to the different-color rubber layer 11. Thereby, the transfer of the rubber compounding agent from the inner rubber portion 21 to the different-color rubber layer 11 is suppressed.

[0043] The barrier rubber layer 12 includes a third portion 18 disposed between the tread rubber 2G and the different-color rubber layer 11. The third portion 18 of course has a rubber compounding that suppresses the transfer of the rubber compounding agent on the tread rubber 2G side to the different-color rubber layer 11. Thereby, the transfer of the rubber compounding agent from the tread rubber 2G to the different-color rubber layer 11 is suppressed.

[0044] In the present embodiment, the outer end 2a in the tire axial direction of the tread rubber 2G is preferably entirely covered by the first sidewall rubber 10. Thereby, the durability near the boundary between the first sidewall rubber 10 including the barrier rubber layer 12 and the tread rubber 2G is improved.

[0045] From the same viewpoint, in the tire meridian cross-section, the distance L2 from the outer end 10a in the tire radial direction of the first sidewall rubber 10 to the tread ground contact end Te is preferably 20 mm to 40 mm. In addition, the tread ground contact end Te corresponds to the most outer-side ground contact position in the tire axial direction when a normal load is applied to the tire 1 in the normal state and the tire contacts the plane at a camber angle of 0°.

[0046] "Normal load" means that in the case of pneumatic tires with various specified specifications, in the specification system including the specifications on which the tire is based, the load for each specification is specified for each tire. If it is JATMA, it is the "maximum load capacity"; if it is TRA, it is the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; if it is ETRTO, it is the "LOAD CAPACITY". And, in the case of tires without specified various specifications, "normal load" means the load acting on one tire in the standard mounting state of the tire. The "standard mounting state" means a state in which the tire is mounted on a standard vehicle corresponding to the use purpose of the tire and the vehicle is stationary on a flat road surface in a state where it can travel.

[0047] The different-color rubber layer 11 is in contact only with the barrier rubber layer 12 except for contacting the cover rubber layer 13 covering its outer surface, and does not contact other rubber components. Thus, the transfer of rubber compounding agents is reliably suppressed.

[0048] The outer surface of the tire 1 includes a boundary 25 between a first outer surface 23 vulcanized and formed by a tread mold and a second outer surface 24 vulcanized and formed by a sidewall mold. Generally, there is a tendency for the boundary 25 to have minute burrs due to rubber entering the gap between the two molds. That is, near the boundary 25, the movement of the rubber during vulcanization molding is large. As in this embodiment, in the tire 1 with a relatively small segment height, the boundary 25 is close to the different-color rubber layer 11, and due to the movement of the rubber near the boundary 25, the different-color rubber layer 11 may be exposed at an unexpected position. To prevent such a bad situation, the different-color rubber layer 11 is arranged at a position radially inward of the tire with respect to the boundary 25. And, in the tire meridian cross-section, the distance L3 from the boundary 25 to the outer end 11a in the radial direction of the tire of the different-color rubber layer 11 is preferably 10 mm to 30 mm, for example.

[0049] The cover rubber layer 13 has, for example, a sufficient thickness to prevent the different-color rubber layer 11 from being exposed at unnecessary positions. On the other hand, when the thickness of the cover rubber layer 13 is too large, it may reduce the workability of the above polishing. From such a viewpoint, the thickness of the cover rubber layer 13 is preferably 0.5 mm to 1.0 mm.

[0050] In a more preferred mode, the cover rubber layer 13 is composed of the same rubber compounding as the barrier rubber layer 12. Thus, the peeling of the cover rubber layer 13 is suppressed.

[0051] As described above, the preferred embodiments of the pneumatic tire of the present invention have been described in detail. The present invention is not limited to the above specific embodiments and can be implemented in various ways.

[0052]

Example

[0053] Based on the specifications in Table 1, a pneumatic tire with a size of 225 / 50R18 and the basic structure of Figure 1 was trial-produced. As a comparative example, a pneumatic tire without a barrier rubber layer disposed between the carcass and the rubber layer of different colors was trial-produced. Except for the above matters, the tire of the comparative example had a substantially same structure as the tire of the example. Regarding each test tire, the discoloration resistance performance of the rubber layer of different colors was tested. The common specifications and test methods of each test tire are as follows.

[0054] Rim: 18×7.0J

[0055] Tire internal pressure: 220 kPa

[0056] <Discoloration resistance performance of the rubber layer of different colors>

[0057] A constant longitudinal load was applied to the test tire on a drum test machine and it was run at a speed of 80 km / h for 18 hours. And during this running, the exposed part of the rubber layer of different colors on the sidewall of the tire was continuously irradiated with ultraviolet rays using a black light lamp. After the running, the degree of discoloration of the exposed part of the rubber layer of different colors was visually evaluated. The result was expressed in 5 grades from 1 to 5, and the higher the score, the more excellent the discoloration resistance performance.

[0058] The test results are shown in Table 1.

[0059]

Table 1

[0060]

[0061] It can be confirmed from the test results that the discoloration resistance performance of the rubber layer of different colors of the tire of the example was 4 to 5 points, and the discoloration of the rubber layer of different colors could be effectively suppressed.

Claims

1. A pneumatic tire comprising a tread portion, a pair of sidewall portions, a pair of bead portions, and a carcass extending from one of the bead portions to the other bead portion, at least one of the pair of sidewall portions includes a first sidewall rubber disposed outside the carcass in the tire axial direction, the first sidewall rubber includes a different-color rubber layer and a barrier rubber layer, the different-color rubber layer has a color different from the basic color of the outer surface of the sidewall portion, and at least a part of the different-color rubber layer is exposed on the outer surface of the sidewall portion, the barrier rubber layer includes a first portion disposed between the different-color rubber layer and the carcass and having a rubber formulation that inhibits the transfer of rubber compounding agents on the carcass side to the different-color rubber layer, the pair of bead portions includes a chafing rubber constituting the outer surface of each bead portion, the first sidewall rubber includes an inner rubber portion in contact with the chafing rubber, the barrier rubber layer includes a second portion disposed between the inner rubber portion and the different-color rubber layer and having a rubber formulation that inhibits the transfer of rubber compounding agents of the inner rubber portion to the different-color rubber layer, and the barrier rubber layer extends from the different-color rubber layer to the carcass.

2. The pneumatic tire according to claim 1, wherein, the barrier rubber layer includes a third portion disposed between the tread rubber constituting the tread portion and the different-color rubber layer and having a rubber formulation that inhibits the transfer of rubber compounding agents on the tread rubber side to the different-color rubber layer.

3. The pneumatic tire according to claim 2, wherein, in the tire meridian cross-section, the distance from the outer end of the first sidewall rubber in the tire radial direction to the tread ground contact end is 20 mm to 40 mm.

4. The pneumatic tire according to claim 1 or 2, wherein, the pneumatic tire includes a boundary between a first outer surface vulcanized and molded by a tread mold and a second outer surface vulcanized and molded by a sidewall mold, the different-color rubber layer is disposed at a position radially inward of the boundary in the tire, in the tire meridian cross-section, the distance from the boundary to the outer end of the different-color rubber layer in the tire radial direction is 10 mm to 30 mm.

5. The pneumatic tire according to claim 1 or 2, wherein, the tread portion includes a tread rubber, the outer end of the tread rubber in the tire axial direction is covered by the first sidewall rubber.

6. The pneumatic tire according to claim 1 or 2, wherein, the section height is 120 mm or less, and the section height refers to the height of the pneumatic tire in the tire radial direction measured from the bead base line in the normal state.

7. The pneumatic tire according to claim 1 or 2, wherein, the barrier rubber layer contains 60% or less of butyl rubber.

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