Tire

Abstract

To provide a tire 2 capable of achieving reduction of rolling resistance while securing abrasion resistance in limit traveling.SOLUTION: A tread 4 comprises a cap layer 30 and a base layer 32. A loss tangent of the cap layer 30 at 30°C is 0.30 or less, and a loss tangent of the base layer 32 at 30°C is lower than the loss tangent of the cap layer 30 at 30°C. The base layer 32 is located axially on an inner side of a reference end PT of the tread 4. A fixing layer 24 is located radially between the cap layer 30 and a carcass 12. A first end 24a of the fixing layer 24 is axially located on an outer side of an end 32e of the base layer 32, or the location of the first end 24a of the fixing layer 24 corresponds to the location of the end of the base layer 32. An adhesive force of the fixing layer 24 is higher than an adhesive force of the cap layer 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] The tread includes a cap layer that contacts the road surface and a base layer that is located inside the cap layer in the radial direction. Rubber considering grip force and wear resistance is used for the cap layer. Rubber considering low heat generation is used for the base layer. In the manufacture of a tire, a green tire (also referred to as a raw cover) is prepared by combining a number of elements such as a cap layer and a base layer. The tire is obtained by pressurizing and heating the green tire in a mold. As a method for molding a component of a tire, for example, the strip winding method is known. In this method, a strip made of unvulcanized rubber is wound to form a laminate having a desired shape (for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In consideration of the environment, it is required of a tire to reduce rolling resistance. Therefore, reduction of heat generation of the rubber used for the cap layer is being studied so that the cap layer can also contribute to the reduction of rolling resistance. Low heat - generating rubber is inferior in adhesiveness compared to heat - generating rubber. In the portion corresponding to the shoulder part of the tire, the cap layer is likely to peel off from the carcass. When the cap layer peels off from the carcass, there is a risk that air remains in the green tire. Since the remaining air may cause problems such as bare areas, it has been considered to sandwich a highly adhesive sheet between the cap layer and the base layer and between the cap layer and the carcass and bond them.

[0005] In order to further reduce the rolling resistance, it has also been considered to make the tread thinner and reduce the tread volume. In the tread, the entire base layer is covered by the cap layer. When a thin tread is adopted, the cap layer covering the base layer also becomes thinner. Since the tread is thinner toward the outer side in the axial direction, when applying the above - mentioned peeling prevention technology using the adhesive sheet to the tire, it is difficult to ensure sufficient thickness of the cap layer in the shoulder part. In limit running (for example, when the vehicle turns at high speed), the shoulder part also contacts the road surface. With a thin cap layer, the progress of wear cannot be sufficiently suppressed, and there is a concern that the base layer may be exposed. Since the base layer is more brittle than the cap layer, if the base layer is exposed, the tread may peel off.

[0006] If it is possible to prevent the cap layer from peeling off from the carcass in the green tire while ensuring the thickness of the cap layer in the shoulder part, there is a prospect of achieving a reduction in rolling resistance while ensuring wear resistance in limit running.

[0007] The present invention has been made in view of such circumstances, and an object thereof is to provide a tire capable of achieving a reduction in rolling resistance while ensuring wear resistance in limit running.

Means for Solving the Problem

[0008] A tire according to one aspect of the present invention includes a tread, a pair of sidewalls connected to an end of the tread and located inside the tread in the radial direction, a pair of beads located inside the sidewalls in the radial direction, a carcass located inside the tread and the pair of sidewalls and bridging between one bead and the other bead, a belt located between the tread and the carcass in the radial direction and including a plurality of belt cords arranged in parallel, an inner liner located inside the carcass, and a pair of anchoring layers arranged at a distance in the axial direction. A circumferential groove is formed in the tread, and a groove depth of the circumferential groove is 7.0 mm or less. The tread includes a cap layer and a base layer covered with the cap layer. A loss tangent of the cap layer at 30°C is 0.30 or less, and a loss tangent of the base layer at 30°C is lower than the loss tangent of the cap layer at 30°C. The base layer is located inside a reference end of the tread in the axial direction. Each of the anchoring layers is located between the cap layer and the carcass in the radial direction. In the axial direction, a first end of the anchoring layer is located outside an end of the base layer, or a position of the first end of the anchoring layer coincides with a position of the end of the base layer. An adhesive force of the anchoring layer is higher than an adhesive force of the cap layer.

[0009] Preferably, in this tire, a distance from a reference end of the tread to an end of the base layer is 5 mm or more and 15 mm or less.

[0010] Preferably, in this tire, a distance from a first end of the anchoring layer to an end of the base layer is 5 mm or less.

[0011] Preferably, in this tire, in the axial direction, a position of a first end of the anchoring layer coincides with a position of an end of the base layer.

[0012] Preferably, in this tire, a second end of the anchoring layer is located in a zone from a position 5 mm away from an end of the cap layer inward to a position 10 mm away from the end of the cap layer outward.

[0013] Preferably, in this tire, in the axial direction, the position of the second end of the fixing layer coincides with the position of the end of the cap layer, or the second end of the fixing layer is located outside the end of the cap layer, and the distance from the end of the cap layer to the second end of the fixing layer is 5 mm or less.

[0014] Preferably, this tire includes a band provided with a band cord wound in a spiral shape and located between the tread and the belt in the radial direction. The band is a full band with both ends facing each other across the equatorial plane.

[0015] Preferably, this tire includes a pair of insulations located between the carcass and the inner liner. In the axial direction, the first end of each insulation is located inside the end of the belt. In the radial direction, the second end of each insulation is located outside the bead.

Advantages of the Invention

[0016] According to the present invention, a tire can be obtained that achieves a reduction in rolling resistance while ensuring wear resistance during limit running.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0018] Hereinafter, based on the preferred embodiments, the present invention will be described in detail while appropriately referring to the drawings.

[0019] In the present disclosure, a state where a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to this tire is referred to as the standard state.

[0020] In the present disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state. For the dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is mounted on the standard rim, in the cross-section of the tire obtained by cutting the tire along the plane including the rotation axis, the distance between the left and right beads is made to coincide with the distance between the beads in the tire mounted on the standard rim and then measured.

[0021] The standard rim means the rim defined in the standard to which the tire conforms. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are the standard rims.

[0022] The standard internal pressure means the internal pressure defined in the standard to which the tire conforms. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are the standard internal pressures.

[0023] The standard load means the load defined in the standard to which the tire conforms. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are the standard loads.

[0024] In the present disclosure, a green tire means a tire in an unvulcanized state. A green tire is also referred to as a raw cover. The unvulcanized state is also referred to as the unvulcanized state.

[0025] In the present disclosure, a crosslinked rubber is a molded body of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an unvulcanized rubber obtained by mixing a base rubber and chemicals, which are components of the rubber composition, in a kneader such as a Banbury mixer. The crosslinked rubber is also referred to as a vulcanized rubber, and the rubber composition is also referred to as an unvulcanized rubber or an unvulcanized rubber.

[0026] Examples of the base rubber include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and butyl rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, tackifiers, sulfur, and vulcanization accelerators. The selection of the base rubber and chemicals, the content of the selected chemicals, etc. are appropriately determined according to the specifications of each element such as the tread and sidewall to which the rubber composition is applied.

[0027] In the present disclosure, among the elements constituting the tire, the loss tangent (also referred to as tanδ) at 30°C of the element made of crosslinked rubber is measured under the following conditions using a viscoelastic spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) in accordance with the provisions of JIS K6394. Initial strain = 10% Dynamic strain = 2% Frequency = 10 Hz Deformation mode = Tension In this measurement, the test piece is sampled from the tire. When the test piece cannot be sampled from the tire, the test piece is sampled from a sheet-shaped crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressurizing and heating the rubber composition used for forming the element to be measured at a temperature of 170°C for 12 minutes.

[0028] In the present disclosure, among the elements constituting the tire, the Mooney viscosity (ML 1+4) of the rubber composition for the element made of crosslinked rubber is measured at a temperature of 100°C in accordance with the method for measuring Mooney viscosity specified in JIS K 6300-1.

[0029] In the present disclosure, among the elements constituting the tire, the adhesive strength of the element made of crosslinked rubber is represented by the adhesive strength of the rubber composition for the above element, which is measured under the following conditions using a Picmatac tester manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with the provisions of JIS T 9233. Crimping load: 4.9 N Peeling rate: 30 mm / min Crimping time: 2.5 seconds Reference sample dimensions: 12.7 mm × 152 mm Temperature: 23°C Humidity: 55%

[0030] FIG. 1 shows a part of a tire 2 according to an embodiment of the present invention. This tire 2 is a passenger car tire. In FIG. 1, the tire 2 is mounted on a rim R. The rim R is a standard rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted. The tire 2 shown in FIG. 1 is in a standard state.

[0031] The tire 2 mounted on the rim R is also referred to as a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on this rim R.

[0032] FIG. 1 shows a part of a cross-section (hereinafter also referred to as a meridian cross-section) of the tire 2 along a plane including the rotation axis (not shown) of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, the one-dot chain line CL represents the equatorial plane of the tire 2.

[0033] In FIG. 1, the position indicated by the reference sign PW is the axially outer end of the tire 2. When there are decorations such as patterns and characters on the outer surface, the outer end PW is specified based on the virtual outer surface obtained by assuming that there are no decorations. In FIG. 1, the length indicated by the reference sign WA is the maximum width of the tire 2, that is, the section width (refer to JATMA, etc.). The section width WA is the axial distance from one outer end PW to the other outer end PW. The outer end PW is the position where the tire 2 exhibits the maximum width (hereinafter, the maximum width position).

[0034] This tire 2 includes a tread 4, a pair of sidewalls 6, a pair of beads 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, an inner liner 18, a pair of cushions 20, a pair of insulations 22, and a pair of anchoring layers 24.

[0035] The tread 4 contacts the road surface on its outer surface. Grooves 26 are engraved in the tread 4. Thereby, a tread pattern is formed.

[0036] The groove 26 includes a circumferential groove 28 that continuously extends in the circumferential direction. In this tire 2, a plurality of circumferential grooves 28 arranged in parallel in the axial direction are engraved in the tread 4. In the tire 2 shown in FIG. 1, three circumferential grooves 28 are engraved in the tread 4. Among the three circumferential grooves 28, the circumferential groove 28 located on the outer side in the axial direction is the shoulder circumferential groove 28s. In the axial direction, the circumferential groove 28 located inside the shoulder circumferential groove 28s is the middle circumferential groove 28m. In this tire 2, the middle circumferential groove 28m is located on the equatorial plane.

[0037] In this tire 2, the groove depth of the circumferential groove 28 is 7.0 mm or less. In other words, all the circumferential grooves 28 engraved in the tread 4 have a groove depth of 7.0 mm or less. Usually, the groove depth of the circumferential groove exceeds 7.0 mm, so the circumferential groove 28 of this tire 2 is shallow. The adoption of the shallow circumferential groove 28 enables the adoption of the thin tread 4. By adopting the thin tread 4, the volume of the tread 4 is reduced. This tread 4 contributes to the reduction of rolling resistance. The lower limit of the groove depth is appropriately determined in consideration of drainage and wear resistance.

[0038] In this tire 2, there are no particular restrictions on the arrangement and groove width of the circumferential grooves 28 engraved in the tread 4. These are appropriately determined in consideration of the specifications of the tire 2.

[0039] The tread 4 includes a cap layer 30 and a base layer 32. The cap layer 30 forms the outer surface of the tread 4. The cap layer 30 is made of cross-linked rubber in which wear resistance and grip performance are considered. The loss tangent of the cap layer 30 at 30°C (hereinafter, the loss tangent of the cap layer 30) is 0.30 or less. In this cap layer 30, not only wear resistance and grip performance but also low heat generation are considered. The cap layer 30 contributes to the reduction of rolling resistance. From this viewpoint, the loss tangent of the cap layer 30 is preferably 0.21 or less. The base layer 32 is located inside the cap layer 30 in the radial direction. The end 32e of the base layer 32 is located inside the end 30e of the cap layer 30 in the axial direction. In this tire 2, the end 30e of the cap layer 30 is the end of the tread 4. The base layer 32 is covered by the cap layer 30. Specifically, the entire base layer 32 is covered by the cap layer 30 from the outside in the radial direction. The base layer 32 does not contact the road surface unless the tread 4 wears and the base layer 32 is exposed. In the base layer 32, wear resistance and grip performance like those of the cap layer 30 are not considered. The base layer 32 is made of cross-linked rubber with low heat generation. The loss tangent of the base layer 32 at 30°C (hereinafter, the loss tangent of the base layer 32) is lower than the loss tangent of the cap layer 30. The base layer 32 contributes to the reduction of rolling resistance. From this viewpoint, the loss tangent of the base layer 32 is preferably 0.11 or less, and more preferably 0.10 or less. The base layer 32 of this tire 2 is composed of one element. The base layer 32 may be composed of two or more elements arranged axially apart.

[0040] In this tire 2, when the adhesion of the base layer 32 is taken as 100, the adhesion of the cap layer 30 is 56 or more and 91 or less. The cap layer 30 has an adhesion lower than that of the base layer 32.

[0041] Each sidewall 6 is continuous with the edge 4e of the tread 4. The sidewall 6 is located inside the tread 4 in the radial direction. The sidewall 6 extends along the carcass 12 from the edge 4e of the tread 4 toward the clinch 8. The sidewall 6 is made of cross-linked rubber considering cut resistance.

[0042] Each clinch 8 is located inside the sidewall 6 in the radial direction. The clinch 8 contacts the rim R. The clinch 8 is made of cross-linked rubber considering wear resistance.

[0043] Each bead 10 is located inside the clinch 8 in the axial direction. The bead 10 is located inside the sidewall 6 in the radial direction. The bead 10 includes a core 34 and an apex 36. The core 34 includes a steel wire (not shown). The apex 36 is located outside the core 34 in the radial direction. The apex 36 tapers outward. The apex 36 is made of cross-linked rubber having high rigidity.

[0044] The carcass 12 is located inside the tread 4, a pair of sidewalls 6 and a pair of clinches 8. The carcass 12 spans between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0045] The carcass 12 includes at least one carcass ply 38. From the viewpoint of reducing rolling resistance, the carcass 12 is preferably composed of one carcass ply 38. The carcass 12 of this tire 2 consists of one carcass ply 38. The carcass ply 38 is folded around each bead 10 from the inside to the outside in the axial direction.

[0046] Although not shown, the carcass ply 38 includes a number of parallel carcass cords. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane. The carcass cord is a cord made of organic fiber. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0047] The belt 14 is positioned between the tread 4 and the carcass 12 in the radial direction. The belt 14 is laminated on the carcass 12. In FIG. 1, the length indicated by the symbol WR is the axial width of the belt 14. The axial width WR is the axial distance from one end of the belt 14 to the other end. In this tire 2, the axial width WR of the belt 14 is 65% or more and 85% or less of the cross-sectional width WA.

[0048] The belt 14 is composed of at least two layers 40 laminated in the radial direction. The belt 14 of this tire 2 consists of two layers 40 laminated in the radial direction. Of the two layers 40, the layer 40 located on the inner side is the inner layer 40a, and the layer 40 located on the outer side is the outer layer 40b. As shown in FIG. 1, the inner layer 40a is wider than the outer layer 40b. The length from the end of the outer layer 40b to the end of the inner layer 40a is 3 mm or more and 10 mm or less.

[0049] Although not shown, the inner layer 40a and the outer layer 40b each include a number of parallel belt cords. These belt cords are covered with topping rubber. Each belt cord is inclined with respect to the equatorial plane. The material of the belt cord is steel.

[0050] Band 16 is positioned radially between the tread 4 and the belt 14. The band 16 is laminated on the belt 14. Although not shown, the band 16 includes a band cord wound in a spiral. The band cord is covered with topping rubber. The band cord extends substantially in the circumferential direction. Specifically, the angle formed by the band cord with respect to the circumferential direction is 5° or less. The band 16 has a jointless structure. In this tire 2, a cord made of organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber. Axially, the end 16e of the band 16 is located outside the end 14e of the belt 14. The length from the end of the belt 14 to the end of the band 16 is 3 mm or more and 7 mm or less. The band 16 restrains the end 14e of the belt 14.

[0051] The band 16 of this tire 2 is a full band with both ends facing each other across the equatorial plane. The band 16 covers the belt 14. Specifically, the band 16 covers the entire belt 14 from the outside in the radial direction. The band 16 restrains the entire belt 14. In this tire 2, the shape change of the ground contact surface is suppressed. Although not shown, this band 16 may be a pair of edge bands arranged axially apart and configured to cover the portion of the end 14e of the belt 14. In this case, this band 16 contributes to the weight reduction of the tire 2. In order to increase the rigidity of the tread 4, this band 16 may be composed of a full band and a pair of edge bands.

[0052] The inner liner 18 is located inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of a crosslinked rubber with a low gas permeability coefficient. The inner liner 18 retains the internal pressure of the tire 2.

[0053] Each cushion 20 is axially spaced apart. The cushion 20 is positioned between the ends of the belt 14 and the band 16 and the carcass 12. The cushion 20 is made of cross-linked rubber having low rigidity. The cushion 20 is not an essential element in this tire 2. Depending on the specifications of the tire 2, this cushion 20 may not be provided.

[0054] Each insulation 22 is positioned between the carcass 12 and the inner liner 18. One end of the insulation 22 (hereinafter, the first end 22a) is axially located inside the end 14e of the belt 14. The other end of the insulation 22 (hereinafter, the second end 22b) is radially located outside the bead 10 and inside the maximum width position PW. The insulation 22 is made of cross-linked rubber considering adhesiveness. In this tire 2, in the portion where the insulation 22 is provided, the inner liner 18 is joined to the carcass 12 via the insulation 22. In a portion between the first end 22a of one insulation 22 and the first end 22a of the other insulation 22, and in a portion where the insulation 22 is not provided, such as the inner portion from the second end 22b of the insulation 22, the inner liner 18 is directly joined to the carcass 12. The entire inner liner 18 may be joined to the carcass 12 by the insulation 22.

[0055] Each fixing layer 24 is axially spaced apart. The fixing layer 24 is provided in the shoulder portion Sh of the tire 2. The shoulder portion Sh refers to the portion from around the end 14e of the belt 14 to around the end 4e of the tread 4. The fixing layer 24 is made of cross-linked rubber considering adhesion.

[0056] Figure 2 shows a part of the cross-section of the tire 2 shown in Figure 1. The shoulder portion Sh of the tire 2 is shown in this Figure 2.

[0057] The first end 24a of the fixing layer 24 is located inside the end 16e of the band 16 in the axial direction. The first end 24a of the fixing layer 24 is laminated on the band 16 and covered with the cap layer 30. The second end 24b of the fixing layer 24 is located outside the end 16e of the band 16 in the axial direction. The fixing layer 24 covers the end 16e of the band 16. The portion of the fixing layer 24 outside the end 16e of the band 16 is laminated on the cushion 20 and the carcass 12. The second end 24b of the fixing layer 24 is laminated on the carcass 12. The second end 24b of the fixing layer 24 is located outside the end 4e of the tread 4 in the axial direction. The second end 24b of the fixing layer 24 is sandwiched between the carcass 12 and the sidewall 6. The cap layer 30 is laminated on the portion of the fixing layer 24 inside the end 4e of the tread 4. The second end 24b of the fixing layer 24 may be located inside the end 4e of the tread 4 in the axial direction.

[0058] FIG. 3 shows the contour of the shoulder portion Sh of the tire 2 in the meridian cross-section. The contour shown in FIG. 3 is obtained by measuring the outer surface shape of the tire 2 in the normal state with a displacement sensor.

[0059] In the meridian cross-section, the contour of the outer surface of the tire 2 (hereinafter referred to as the tire outer surface TS) is formed by connecting a plurality of contour lines composed of straight lines or arcs. In the present disclosure, a contour line composed of a straight line or an arc is simply referred to as a contour line. A contour line composed of a straight line is referred to as a straight contour line, and a contour line composed of an arc is referred to as a curved contour line.

[0060] The outer tire surface TS includes a tread surface T and a pair of side surfaces S connected to the ends of the tread surface T. In the meridian cross-section, the contour of the tread surface T includes a plurality of curved contour lines having different radii. In this tire 2, among the plurality of curved contour lines included in the contour of the tread surface T, the curved contour line having the minimum radius is located at the end portion of the tread surface T and is connected to the side surface S. In the meridian cross-section, the contour of the outer tire surface TS includes a curved portion at the end portion of the tread surface T, which is composed of an arc having the minimum radius among the plurality of curved contour lines included in the contour of the tread surface T and is a curved contour line connected to the side surface S. In FIG. 3, this curved portion is indicated by the reference sign RS.

[0061] In the contour of the outer tire surface TS, the curved portion RS is in contact with the inner adjacent contour line NT (hereinafter referred to as the inner adjacent contour line NT) adjacent to its axially inner side at the contact point CT. This curved portion RS is in contact with the contour line (hereinafter referred to as the outer adjacent contour line NS) constituting the contour of the side surface S adjacent to its axially outer side at the contact point CS. The contour of this outer tire surface TS includes an inner adjacent contour line NT located axially inside the curved portion RS and in contact with this curved portion RS, and an outer adjacent contour line NS located axially outside the curved portion RS and in contact with this curved portion RS.

[0062] In FIG. 3, the solid line LT is the tangent line of the curved portion RS at the contact point CT between the inner adjacent contour line NT and the curved portion RS. The solid line LS is the tangent line of the curved portion RS at the contact point CS between the outer adjacent contour line NS and the curved portion RS. The position indicated by the reference sign PT is the intersection of the straight line extending radially through the intersection of the tangent line LT and the tangent line LS and the tread surface T. In this tire 2, this intersection PT is the reference end of the tread. The tread reference end PT is the position on the tread surface T corresponding to the intersection of the tangent line LT and the tangent line LS.

[0063] In FIG. 1, the length indicated by the double arrow WT is the tread width. The tread width WT is the axial distance from one tread reference end PT to the other tread reference end PT. In this tire 2, the ratio (WT / WA) of the tread width WT to the cross-sectional width WA is 70% or more and 90% or less. In this tire 2, the end 14e of the belt 14 is located inside the tread reference end PT in the axial direction. The position of the end 16e of the band 16 substantially coincides with the position of the tread reference end PT in the axial direction. The end 4e of the tread 4 is located outside the tread reference end PT in the axial direction.

[0064] Although not shown, the tire 2 is obtained by pressurizing and heating a green tire in a mold. In the manufacture of the tire 2, a green tire is prepared. In the preparation of the green tire, for example, an unvulcanized base layer is formed by molding a rubber composition for the base layer 32 into a desired shape. An unvulcanized cap layer is formed by molding a rubber composition for the cap layer 30 into a desired shape. A green tire is obtained by combining unvulcanized elements such as the unvulcanized base layer and the unvulcanized cap layer. In the combination of unvulcanized elements, the adhesive force possessed by the unvulcanized elements is utilized.

[0065] A low heat - generating rubber is inferior in adhesiveness compared to a heat - generating rubber. As described above, heat reduction is considered for the cap layer 30 of this tire 2. The adhesive force of the cap layer 30 is low, and since the carcass 12 bends greatly at a portion corresponding to the shoulder portion Sh of the tire 2, there is a concern that the unvulcanized cap layer may peel off from the unvulcanized carcass. If the unvulcanized cap layer peels off from the unvulcanized carcass, there is a risk that air may remain in the green tire. Since the remaining air may cause problems such as a bare tire, it has been considered to prevent the unvulcanized cap layer from peeling off from the unvulcanized carcass in the green tire by sandwiching a fixing layer 24 having a high adhesive force between the cap layer 30 and the base layer 32 and between the cap layer 30 and the carcass 12.

[0066] Incidentally, as described above, in this tire 2, a thin tread 4 is adopted from the viewpoint of reducing rolling resistance. Since the cap layer 30 covering the base layer 32 is also thinner than a conventional cap layer, if the above-described technique is applied to prevent peeling of the uncured cap layer from the uncured carcass, it is impossible to ensure a sufficient thickness of the cap layer 30 in the shoulder portion Sh. Therefore, there is a concern that the base layer 32 may be exposed in the limit running where the shoulder portion Sh contacts the road surface. Since the base layer 32 is more brittle than the cap layer 30, if the base layer 32 is exposed, the tread 4 may peel off.

[0067] Even in a conventional tire, the base layer is covered with a cap layer, but the end of the base layer is located outside the tread reference end in the axial direction. On the other hand, in this tire 2, the end 32e of the base layer 32 is located inside the tread reference end PT in the axial direction. In other words, the base layer 32 is located inside the tread reference end PT in the axial direction. In this tire 2, the cap layer 30 in the shoulder portion Sh is thicker than the cap layer in the shoulder portion of a conventional tire. In the shoulder portion Sh, a cap layer 30 having a sufficient thickness is formed between the outer surface TS of the tire and the base layer 32. In the limit running where the shoulder portion Sh contacts the road surface, the exposure of the base layer 32 is prevented. In this tire 2, the abrasion resistance in limit running is ensured.

[0068] The base layer 32 of this tire 2 has a smaller volume than the base layer of a conventional tire. Therefore, there is a concern about an increase in rolling resistance. However, as described above, the tread 4 of this tire 2 is thin. Although the volume of the base layer 32 is smaller than that of a conventional tire, this tire 2 can achieve a reduction in rolling resistance.

[0069] Furthermore, in this tire 2, in the radial direction, an anchoring layer 24 is positioned between the cap layer 30 and the carcass 12. In the axial direction, a first end 24a of the anchoring layer 24 is positioned outside an end 32e of the base layer 32. As shown in FIG. 4, in the axial direction, the position of the first end 24a of the anchoring layer 24 may coincide with the position of the end 32e of the base layer 32. In this tire 2, the adhesive force of the anchoring layer 24 is higher than the adhesive force of the cap layer 30. In the manufacture of this tire 2, the uncured cap layer adheres sufficiently to the uncured carcass via the uncured anchoring layer. Since peeling of the uncured cap layer from the uncured carcass is prevented, air remaining in the green tire is prevented. In the manufacture of this tire 2, a high-quality tire 2 is stably manufactured. In other words, the tire 2, which can achieve reduction of rolling resistance while ensuring wear resistance at limit running, is stably manufactured.

[0070] In FIG. 2, the length indicated by reference sign a is the distance from the tread reference end PT to the end 32e of the base layer 32. This distance a is represented by an axial distance. When the end 32e of the base layer 32 is positioned outside the tread reference end PT in the axial direction, this distance a is represented by a negative number.

[0071] In this tire 2, the distance a from the tread reference end PT to the end 32e of the base layer 32 is preferably 5 mm or more and 15 mm or less. By setting the distance a to 5 mm or more, the thickness of the cap layer 30 is ensured in the shoulder portion Sh. In this tire 2, the base layer 32 is prevented from being exposed during limit running. From this viewpoint, the distance a is more preferably 7 mm or more, and even more preferably 9 mm or more. By setting the distance a to 15 mm or less, the volume of the base layer 32 is ensured. In this tire 2, the base layer 32 can effectively contribute to the reduction of rolling resistance. From this viewpoint, the distance a is more preferably 13 mm or less, and even more preferably 11 mm or less.

[0072] In FIG. 2, the length indicated by reference sign b is the distance from the first end 24a of the fixing layer 24 to the end 32e of the base layer 32. This distance b is represented as the shortest distance. When the first end 24a of the fixing layer 24 is located inside the end 32e of the base layer 32 in the axial direction, this distance b is represented by a negative number.

[0073] In this tire 2, it is preferable that the distance b from the first end 24a of the fixing layer 24 to the end 32e of the base layer 32 is 5 mm or less. By setting the distance b to be 5 mm or less, a fixing layer 24 having an appropriate size is formed. This fixing layer 24 can effectively contribute to preventing the cap layer 30 from peeling off from the carcass 12 in the shoulder portion Sh. From this viewpoint, it is more preferable that the distance b is 3 mm or less, and even more preferable that it is 1 mm or less.

[0074] When the first end 24a of the fixing layer 24 is located inside the end 32e of the base layer 32 in the axial direction, a thin cap layer 30 is formed in the overlapping portion of the fixing layer 24 and the base layer 32, and the volume of the fixing layer 24 increases. The thin cap layer 30 reduces the wear resistance during limit running, and the fixing layer 24 having a large volume may increase the rolling resistance. From the viewpoint of stably manufacturing the tire 2 capable of achieving a reduction in rolling resistance while ensuring the wear resistance during limit running, as shown in FIG. 4, in the axial direction, it is more preferable that the position of the first end of the fixing layer 24 coincides with the position of the end of the base layer 32.

[0075] In FIG. 2, the length indicated by reference sign c is the distance from the end 30e of the cap layer 30 to the second end 24b of the fixing layer 24. This distance c is represented as the shortest distance. As shown in FIG. 2, this distance c is represented by a positive number when the second end 24b of the fixing layer 24 is located outside the end 30e of the cap layer 30 in the axial direction. Although not shown, when the second end 24b of the fixing layer 24 is located inside the end 30e of the cap layer 30 in the axial direction, this distance c is represented by a negative number.

[0076] In this tire 2, it is preferable that the second end 24b of the fixing layer 24 is located in the zone from a position 5 mm inward to a position 10 mm outward from the end 30e of the cap layer 30. In other words, the distance c from the end 30e of the cap layer 30 to the second end 24b of the fixing layer 24 is preferably -5 mm or more and 10 mm or less. By setting the distance c to -5 mm or more, a fixing layer 24 having an appropriate size is configured. Since peeling of the uncured cap layer from the uncured carcass in the shoulder portion Sh is prevented, the tire 2 is stably manufactured. From this viewpoint, the distance c is more preferably 0 mm or more. In other words, in the axial direction, it is more preferable that the position of the second end 24b of the fixing layer 24 coincides with the position of the end 30e of the cap layer 30, or the second end 24b of the fixing layer 24 is located outside the end 30e of the cap layer 30. By setting the distance c to 10 mm or less, the volume of the fixing layer 24 is appropriately maintained. In this tire 2, an increase in rolling resistance due to the fixing layer 24 is suppressed. From this viewpoint, the distance c is more preferably 5 mm or less.

[0077] In this tire 2, the fixing layer 24 is formed with a uniform thickness. The thickness of this fixing layer 24 is preferably 0.5 mm or more and 2.0 mm or less. By setting this thickness to 0.5 mm or more, the rigidity of the fixing layer 24 in the uncured state is appropriately maintained. The uncured fixing layer can effectively contribute to preventing peeling of the uncured cap layer from the uncured carcass. From this viewpoint, the thickness of the fixing layer 24 is more preferably 1.0 mm or more. By setting this thickness to 2.0 mm or less, an increase in rolling resistance due to the fixing layer 24 is suppressed. From this viewpoint, this thickness is more preferably 1.5 mm or less.

[0078] In this tire 2, the Mooney viscosity (ML 1+4) of the rubber composition for the fixing layer 24 is preferably 45 or more and 80 or less. By setting the Mooney viscosity (ML 1+4) to 45 or more, the rigidity of the fixing layer 24 is appropriately maintained in the uncrosslinked state. The uncrosslinked fixing layer can effectively contribute to preventing the peeling of the uncrosslinked cap layer from the uncrosslinked carcass. From this viewpoint, the Mooney viscosity (ML 1+4) is more preferably 60 or more. By setting the Mooney viscosity (ML 1+4) to 80 or less, good adhesiveness of the fixing layer 24 is maintained. Also in this case, the uncrosslinked fixing layer can effectively contribute to preventing the peeling of the uncrosslinked cap layer from the uncrosslinked carcass.

[0079] As described above, in this tire 2, the adhesive force of the fixing layer 24 is higher than that of the cap layer 30. Specifically, the ratio of the adhesive force of the fixing layer 24 to the adhesive force of the cap layer 30 is preferably 1.30 or more. Thereby, the uncrosslinked fixing layer can effectively contribute to preventing the peeling of the uncrosslinked cap layer from the uncrosslinked carcass. From this viewpoint, this ratio is more preferably 1.50 or more. Since this ratio is preferably higher, no preferable upper limit of this ratio is set.

[0080] In this tire 2, the fixing layer 24 also joins with the carcass 12. From the viewpoint of effectively preventing the peeling of the uncrosslinked cap layer from the uncrosslinked carcass, the fixing layer 24 preferably has an adhesive force higher than that of the topping rubber of the carcass 12. Specifically, the ratio of the adhesive force of the fixing layer 24 to the adhesive force of the topping rubber is preferably 1.10 or more, and more preferably 1.20 or more. Since this ratio is preferably higher, no preferable upper limit of this ratio is set.

[0081] As described above, according to the present invention, a tire 2 can be obtained that achieves a reduction in rolling resistance while ensuring wear resistance during limit running.

Example

[0082] Hereinafter, the present invention will be described in more detail by way of examples and the like, but the present invention is not limited to such examples only.

[0083] [Example 1] A pneumatic tire for a passenger car (tire size = 205 / 55R16 91V) having the basic configuration shown in FIG. 1 and the specifications shown in Table 1 below was obtained. The distance a from the reference end PT of the tread to the end of the base layer was 10 mm. The distance b from the first end of the fixing layer to the end of the base layer was 0 mm. As shown in FIG. 4, the position of the first end of the fixing layer in the axial direction was made to coincide with the position of the end of the base layer. The distance c from the end of the cap layer to the second end of the fixing layer was 5 mm. In this Example 1, the groove depth of the middle circumferential groove was 6.7 mm. The loss tangent of the cap layer at 30 °C was 0.21. The loss tangent of the base layer at 30 °C was 0.10. When the adhesion of the base layer was taken as 100, the adhesion of the cap layer was 70, the adhesion of the carcass topping rubber was 96, and the adhesion of the fixing layer was 122. The ratio (Y / X) of the adhesion Y of the fixing layer to the adhesion X of the cap layer was 1.74.

[0084] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the shoulder portion had the configuration shown in FIG. 5. In this Comparative Example 1, the distance a was -5 mm, the distance b was -10 mm, and the distance c was 10 mm. The groove depth of the middle circumferential groove was 7.7 mm.

[0085] [Comparative Example 2] A tire of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the tread was made thinner with the groove depth of the middle circumferential groove being 6.7 mm.

[0086] [Examples 2 - 3] Tires of Examples 2 - 3 were obtained in the same manner as in Example 1, except that the distance a was as shown in Table 1 below.

[0087] [Examples 4 and Comparative Example 3] Tires of Examples 4 and Comparative Example 3 were obtained in the same manner as in Example 1, except that the distance b was as shown in Tables 1 and 2 below.

[0088] [Examples 5 - 7] The tires of Examples 5 - 7 were obtained in the same manner as in Example 1, except that the distance c was as shown in Table 2 below.

[0089] [Examples 8 and Comparative Example 4] The tires of Example 8 and Comparative Example 3 were obtained in the same manner as in Example 1, except that the adhesion ratio (Y / X) of the fixing layer was changed as shown in Table 2 below.

[0090] [Occurrence situation of peeling] 100 green tires were produced, and it was visually confirmed whether there was remaining air near the edge of the tread. The number of green tires without remaining air was measured, and the yield rate was calculated. The results are shown in Table 1 - 2 below with the index of Comparative Example 1 being 100. The larger the numerical value, the more peeling is prevented. In this evaluation, if the index is 90 or more, the occurrence frequency of peeling is considered low and is acceptable.

[0091] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) of the prototype tire was measured when it ran on a drum at a speed of 80 km / h under the following conditions. The results are shown in Table 1 - 2 below with the index of Comparative Example 1 being 100. The larger the numerical value, the lower the rolling resistance of the tire. In this evaluation, if the index is 90 or more, the increase in rolling resistance is considered suppressed and is acceptable. Rim: 16×6.5J Inner pressure: 210 kPa Vertical load: 4.82 kN

[0092] [Limit running] A prototype tire was mounted on a rim (size = 16×6.5J), filled with air, and the internal pressure of the tire was adjusted to 230 kPa. The tire was mounted on a test vehicle (a passenger car with a displacement of 1300 cc). The test vehicle was driven at the limit speed on a circuit course on a dry road surface. The driving distance until peeling occurred on the tread was measured. The results are shown in Table 1-2 below with the index of Comparative Example 1 set to 100. The larger the numerical value, the more wear resistance is ensured during limit driving.

[0093] [Overall Evaluation] An overall evaluation was performed based on the total value of the indices obtained in each evaluation. The results are shown in the "Overall" column of Table 1-2 below. The larger this numerical value, the more preferable.

[0094]

Table 1

[0095]

Table 2

[0096] As shown in Table 1-2, in the examples, While ensuring wear resistance during limit running, it is possible to achieve a reduction in rolling resistance this has been confirmed. From this evaluation result, the superiority of the present invention is clear.

Industrial Applicability

[0097] The While ensuring wear resistance during limit running, it is possible to achieve a reduction in rolling resistance technology described above can also be applied to various tires.

Explanation of Reference Numerals

[0098] 2 ··· Tire 4 ··· Tread 6 ··· Sidewall 10 ··· Bead 12 ··· Carcass 14 ··· Belt 16 ··· Band 18···Inner liner 22···Insulation 24···Fixing layer 28···Circumferential groove 30···Cap layer 32···Base layer

Claims

1. A tread, a pair of sidewalls connected to the ends of the tread and located inside the tread in the radial direction, a pair of beads located inside the sidewalls in the radial direction, a carcass located inside the tread and the pair of sidewalls and bridging between one bead and the other bead, a belt located between the tread and the carcass in the radial direction and including a plurality of belt cords arranged in parallel, an inner liner located inside the carcass, and a pair of fixing layers arranged axially apart, circumferential grooves are engraved on the tread, and the groove depth of the circumferential grooves is 7.0 mm or less, the tread includes a cap layer and a base layer covered by the cap layer, the loss tangent of the cap layer at 30°C is 0.30 or less, and the loss tangent of the base layer at 30°C is lower than the loss tangent of the cap layer at 30°C, the loss tangent of the base layer at 30°C is 0.11 or less, the base layer is located inside the reference end of the tread in the axial direction, each of the fixing layers is located between the cap layer and the carcass in the radial direction, in the axial direction, the first end of the fixing layer is located outside the end of the base layer, or the position of the first end of the fixing layer coincides with the position of the end of the base layer, the adhesive force of the fixing layer is higher than the adhesive force of the cap layer, a tire.

2. The distance from the reference end of the tread to the end of the base layer is 5 mm or more and 15 mm or less, The tire according to Claim 1.

3. The distance from the first end of the fixing layer to the end of the base layer is 5 mm or less, The tire according to Claim 1 or 2.

4. In the axial direction, the position of the first end of the fixing layer coincides with the position of the end of the base layer, The tire according to Claim 3.

5. The second end of the fixing layer is located in a zone from a position 5 mm away from the end of the cap layer inward to a position 10 mm away from the end of the cap layer outward, The tire according to any one of Claims 1 to 4.

6. In the axial direction, the position of the second end of the fixing layer coincides with the position of the end of the cap layer, or the second end of the fixing layer is located outside the end of the cap layer, and the distance from the end of the cap layer to the second end of the fixing layer is 5 mm or less, The tire according to Claim 5.

7. In the radial direction, it includes a band located between the tread and the belt and having a band cord wound in a spiral shape. The first end of the fixing layer is laminated on the band and covered with the cap layer. The tire according to any one of claims 1 to 6.

8. The band is a full band with both ends facing each other across the equatorial plane. The tire according to claim 7.

9. It includes a pair of insulations located between the carcass and the inner liner. In the axial direction, the first end of each insulation is located inside the end of the belt. In the radial direction, the second end of each insulation is located outside the bead. The tire according to any one of claims 1 to 8.

10. The sidewall covers the end of the tread. The tire according to any one of claims 1 to 9.

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