JP2024086557A - tire - Google Patents

Abstract

An object of the present invention is to provide a tire having excellent durability.
A tire having a belt layer,
The belt layer includes a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1×4 structure in which four filaments are twisted together,
The belt cord has an outer diameter D (mm) of 0.50 mm or less,
The tire has a product (D×E) of an outer diameter D (mm) of the belt cord and a number E (pieces/50 mm) of the belt cord arranged in the tire width direction in a width direction cross section of the tire, which is 20.0 or more and 28.0 or less.
[Selection diagram] None

Description

The present invention relates to a tire.

Various methods for improving various tire performances have been studied. For example, Patent Document 1 describes how the belt cords constituting the belt layer are solid wires, and how polyethylene terephthalate fibers are used as the belt reinforcing layer to maintain durability and improve steering stability.

JP 2020-132056 A

On the other hand, from the perspective of life cycle assessment, it is desirable to extend the lifespan of tires, and therefore it is thought that there is a need to further improve the durability of tires.
An object of the present invention is to solve the above problems and to provide a tire having excellent durability.

The present invention relates to a tire having a belt layer,
The belt layer includes a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1×4 structure in which four filaments are twisted together,
The belt cord has an outer diameter D (mm) of 0.50 mm or less,
The tire has a product (D×E) of an outer diameter D (mm) of the belt cord and a number E (pieces/50 mm) of the belt cord arranged in the tire width direction in a width direction cross section of the tire, which is 20.0 or more and 28.0 or less.

According to the present invention, there is provided a tire having a belt layer, the belt layer including a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1 x 4 structure in which four filaments are twisted together, the outer diameter D (mm) of the belt cord is 0.50 mm or less, and the product (D x E) of the outer diameter D (mm) of the belt cord and the number E (pieces/50 mm) of the belt cords arranged in the tire width direction in the tire width direction cross section is 20.0 or more and 28.0 or less, so that a tire with excellent durability can be provided.

1 is a tire meridian cross-sectional view of a pneumatic tire of the present invention. FIG. FIG. 1 is a perspective view of an example of a belt cord having a 1×4 structure in which four filaments are twisted together. FIG. 3 is a cross-sectional view of the belt cord of FIG. 2 taken along a plane perpendicular to the longitudinal direction. FIG. 2 is an enlarged cross-sectional view of the tire belt layer and band layer of the tire of FIG. 1 near the tire equatorial plane. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the tread portion of the tire of FIG. 1.

The present invention relates to a tire having a belt layer,
The belt layer includes a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1×4 structure in which four filaments are twisted together,
The belt cord has an outer diameter D (mm) of 0.50 mm or less,
The tire has a product (D×E) of an outer diameter D (mm) of the belt cord and a number E (pieces/50 mm) of the belt cords arranged in the tire width direction in a width direction cross section of the tire, which is 20.0 or more and 28.0 or less.

The reason why the above-mentioned effects are obtained is not entirely clear, but it is presumed that they are due to the following mechanism.
When a belt cord is made of 1×4 structure in which four filaments are twisted together, the cross section of the belt cord can be made closer to a circle efficiently. A belt cord with a cross section close to a circle is more resistant to peeling between the belt cord and rubber because the stress applied to the belt cord surface is not concentrated at one point but is uniformly distributed. On the other hand, when the number of filaments is increased, such as in a 1×5 structure or a 1×6 structure in which five or six filaments are twisted together, the belt cord is easily crushed and it is difficult to maintain a round shape, so a belt cord with a 1×4 structure is used. In addition, the twist formed in the belt cord allows it to be flexibly deformed, and it is thought that the belt cord can be prevented from buckling and breaking when it is deformed during driving.
In addition, by making the outer diameter D of the belt cord 0.50 mm or less, the cord itself can be deformed flexibly, and by making the product (D x E) of the outer diameter D of the belt cord and the number of cords arranged in the tire width direction E (cords/50 mm) 20.0 or more, the rigidity is increased, the stress applied to the surface of each belt cord is sufficiently dispersed, and the belt cord/rubber is resistant to peeling. Also, by making D x E 28.0 or less, the contact area between the belt cord and the surrounding rubber is appropriately increased, and a sufficient amount of rubber is present between the belt cords adjacent in the tire width direction, making it easier to release force during deformation.
As a result of the above, it is possible to prevent stress from concentrating on the belt cord itself and to prevent stress from concentrating on the surface of a specific belt cord within the belt ply. This is thought to suppress peeling between the belt cord and rubber and improve durability.

In this way, the problem (objective) of improving durability is solved by configuring the belt ply using a 1x4 belt cord with four twisted filaments to satisfy the conditions "D is 0.50 mm or less" and "D x E is 20.0 to 28.0". In other words, the parameters "D is 0.50 mm or less" and "D x E is 20.0 to 28.0" do not define the problem (objective); the object of this application is to improve durability, and a configuration that satisfies these parameters is used as a means to achieve this.

Below, one embodiment of the present invention will be described with reference to the drawings, but this is only one embodiment, and the tire of the present invention is not limited to the following embodiment.

FIG. 1 is a tire meridian cross-sectional view including a tire rotation axis of a pneumatic tire 2 (pneumatic tire) according to this embodiment in a normal state.
In this specification, unless otherwise specified, the dimensions of each part of the tire are values measured under normal conditions.
In this specification, the term "normal condition" refers to a condition in which the tire is mounted on a normal rim (not shown), inflated to normal internal pressure, and no load is applied.
When it is not possible to measure with the tire mounted on a regular rim, the dimensions and angles of each part in the meridian section of the tire are measured by cutting the tire along a plane including the axis of rotation, and the distance between the left and right beads in the cross section is measured so that it corresponds to the distance between the beads of the tire mounted on a regular rim.

A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standards on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Manufacturers Association), this refers to the "standard rim" for the applicable size listed in the "JATMA YEAR BOOK," in the case of ETRTO (The European Tire and Rim Technical Organization), this refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and in the case of TRA (The Tire and Rim Association, Inc.), this refers to the "Design Rim" listed in the "YEAR BOOK." Reference should be made in the order of JATMA, ETRTO, and TRA, and if there is an applicable size at the time of reference, that standard should be followed. In the case of tires not specified by the standard, it refers to the rim that can be mounted on a rim and can maintain internal pressure, i.e., the rim with the smallest rim diameter and the next narrowest rim width that does not cause air leakage between the rim and tire.

"Regular internal pressure" refers to the air pressure set for each tire by each standard in the standard system that includes the standard on which the tire is based. For JATMA, it refers to the "maximum air pressure", for ETRTO, it refers to the "inflammation pressure", and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with "regular rims", it refers to JATMA, ETRTO, TRA in that order and follows those standards. For tires not specified in the standard, it refers to the regular internal pressure (250 kPa or more) of another tire size (specified in the standard) that is specified with the regular rim as the standard rim. Note that if multiple regular internal pressures of 250 kPa or more are specified, it refers to the smallest value among them.

In addition, in this specification, "normal load" refers to the load determined for each tire by each standard in the standard system including the standard on which the tire is based, and refers to the maximum load capacity in the case of JATMA, "LOAD CAPACITY" in the case of ETRTO, and the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and similarly to the above-mentioned "normal rim" and "normal internal pressure", JATMA, ETRTO, and TRA are referred to in that order and their standards are followed. In the case of a tire not determined by a standard, the normal load _WL is calculated as follows.
V = {(Dt/2) ² - (Dt/2 - Ht) ² } x π x Wt
_WL = 0.000011 × V + 175
W _L : Normal load (kg)
V: Virtual volume of the tire (mm ³ )
Dt: tire outer diameter (mm)
Ht: tire section height (mm)
Wt: tire section width (mm)

The "section width Wt (mm)" of a tire is the maximum width between the outer surfaces of the sidewalls when the tire is in its normal condition, excluding any patterns or lettering on the sidewalls.

The "outer diameter Dt (mm)" of a tire refers to the outer diameter of the tire in its normal condition.

The "section height Ht (mm)" of a tire refers to the radial height of the tire in its radial cross section, and is equivalent to half the difference between the tire's outer diameter Dt and the rim diameter R, where R (mm) is the tire's rim diameter. In other words, the section height Ht can be calculated by (Dt-R)/2.

In FIG. 1, the direction from the tread portion 4 to the beads 12, i.e., the left-right direction, is the radial direction of the tire 2, the direction connecting a pair of beads 12, i.e., the up-down direction, is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. The tread portion 4 includes a cap layer 30 and a base layer 28.

Note that while FIG. 1 shows an example of a two-layer tread portion 4 consisting of a cap layer 30 and a base layer 28, the tread portion 4 may also be composed of a single-layer tread or a tread having a structure of three or more layers.

In the tire 2, each sidewall 6 extends radially inward from the end of the tread portion 4. The radially outer portion of the sidewall 6 is joined to the tread portion 4. The radially inner portion of the sidewall 6 is joined to the clinch 10. The sidewall 6 can prevent damage to the carcass 14.

Each wing 8 in FIG. 1 is located between the tread portion 4 and the sidewall 6. The wing 8 is joined to each of the tread portion 4 and the sidewall 6.

Each clinch 10 is located approximately radially inward of the sidewall 6 and has at least one area that contacts the rim.

The carcass 14 has a carcass ply 36. In this tire 2, the carcass 14 is made up of one carcass ply 36, but may be made up of two or more plies.

In this tire 2, the carcass ply 36 is bridged between the bead cores 32 on both sides and runs along the tread portion 4 and the sidewall 6. The carcass ply 36 is folded back around each bead core 32 from the inside to the outside in the axial direction. By this folding back, the carcass ply 36 is formed with a main portion 36a and a pair of folded back portions 36b. That is, the carcass ply 36 has a main portion 36a and a pair of folded back portions 36b.

Each bead core 32 has a bead apex 34 extending radially outward from the bead core 32. The bead core 32 is preferably ring-shaped and includes a wound non-stretchable wire. The bead apex 34 tapers radially outward.

Although not shown, the carcass ply 36 is preferably made of a large number of parallel cords and topping rubber. The absolute value of the angle that each cord makes with respect to the equatorial plane CL is preferably 75° to 90°. In other words, it is preferable that the carcass 14 has a radial structure.

The belt layer 16 in FIG. 1 is located radially inward of the tread portion 4. The belt layer 16 is laminated with the carcass 14. The belt layer 16 reinforces the carcass 14. In the tire 2 in FIG. 1, the belt layer 16 is composed of two belt plies, an inner layer 38 and an outer layer 40. As is clear from FIG. 1, it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40 in the axial direction. In this tire 2, the axial width of the belt layer 16 is preferably 0.6 times or more and preferably 0.9 times or less of the cross-sectional width of the tire 2.

Note that, although FIG. 1 shows an example of the belt layer 16 consisting of two belt plies, an inner layer 38 and an outer layer 40, the belt layer 16 may be composed of a single belt ply or three or more belt plies.

In the belt layer 16 of FIG. 1, it is desirable that each of the inner layer 38, the outer layer 40, and other belt plies arranged as necessary is made of a belt cord having a 1×4 structure in which a large number of parallel filaments are twisted together, and a topping rubber (coating rubber). In other words, each belt ply constituting the belt layer 16 includes a large number of parallel 1×4 belt cords 17A.

Here, Fig. 2 shows a perspective view of one configuration example of a belt cord 17A with a 1 x 4 structure. Fig. 3 shows a cross-sectional view of the belt cord 17A with a 1 x 4 structure shown in Fig. 2, taken along a plane perpendicular to the longitudinal direction. The longitudinal direction of the belt cord is the Y-axis direction in the figure. The plane perpendicular to the longitudinal direction is parallel to the XZ plane in the figure.

The belt cord 17A shown in Figures 2 and 3 has a 1x4 structure in which four filaments 17Ae are twisted together. A 1x4 structure means that one belt cord is made up of one strand of four twisted filaments. Therefore, if a belt cord is made up of three strands of seven twisted filaments, twisted together, it is expressed as having a 3x7 structure.

The N in the 1xN structure corresponds to the number of filaments contained in the strands that make up each cord, and 1 corresponds to the number of strands. An example of a 1xN structure is a structure in which N filaments are arranged and twisted together in a cross section perpendicular to the longitudinal direction so that the filaments form a single layer along the circumferential direction of a single circle.

The diameter of the filament contained in the 1x4 belt cord 17A of this embodiment, i.e., the filament diameter, is not particularly limited, but is preferably 0.10 mm or more, more preferably 0.13 mm or more, even more preferably 0.15 mm or more, even more preferably 0.16 mm or more, even more preferably 0.17 mm or more, even more preferably 0.18 mm or more, even more preferably 0.19 mm or more, and is preferably 0.30 mm or less, more preferably 0.25 mm or less, and even more preferably 0.21 mm or less. If it is within the above range, the effect can be preferably obtained.

Figure 4 is an enlarged cross-sectional view of the belt layer 16 (inner layer 38 and outer layer 40) and band layer 18 near the tire equatorial plane CL.

As shown in FIG. 4, the belt ply 17 includes a 1×4 belt cord 17A and a topping rubber 17B (coating rubber) that covers the belt cord 17A. In FIG. 4, the cross section of the 1×4 belt cord 17A is shown as a circle. However, as shown in the circular cross section in FIG. 3, in addition to the 1×4 belt cord with a circular cross section, the cord may have an elliptical cross section or a cross section of another shape, such as a polygonal cross section.

Filament 17Ae may also be pre-formed from the standpoint of durability, etc.

In the example of FIG. 4, the belt ply 17 includes a first belt ply (inner layer 38) and a second belt ply (outer layer 40) adjacent to the first belt ply (inner layer 38) in the tire radial direction. The second belt ply (outer layer 40) is located outside the first belt ply (inner layer 38) in the tire radial direction.

The belt cord 17A is preferably a steel cord. Such a belt cord 17A suppresses deformation of the belt ply 17 while it is running. The belt cord 17A of the first belt ply (inner layer 38) and the belt cord 17A of the second belt ply (outer layer 40) may have the same shape or different shapes.

The outer diameter D of the 1x4 belt cord 17A is 0.50 mm or less, preferably 0.47 mm or less, more preferably 0.45 mm or less, and even more preferably 0.43 mm or less. There is no particular lower limit, but it is preferably 0.25 mm or more, more preferably 0.32 mm or more, even more preferably 0.35 mm or more, even more preferably 0.38 mm or more, and even more preferably 0.40 mm or more. If it is within the above range, the effect can be preferably obtained.

In the present invention, the outer diameter D of the belt cord refers to the diameter of the circumscribing circle of the cord cross section. For example, in the case of a 1x2 belt cord, if the filament diameter is d, then the outer diameter D = 2d. In the case of a 1x4 belt cord used in the present invention, if the filament diameter is d, then the outer diameter D can be calculated simply as D = d x √2 + d. In the case of the 1x4 belt cord 17A in Figures 2 and 3, the diameter D of the circumscribing circle of the cord cross section in Figure 3 corresponds to the outer diameter of the belt cord 17A.

The filament diameter d forming the belt cord can be measured using a vernier caliper in a direction perpendicular to the longitudinal direction of the filament of the belt cord extracted from the tire. In this case, if the diameters are different in the same cross section, the simple average of the maximum and minimum values is treated as the filament diameter d.

It is desirable that the belt cord 17A is inclined at an angle of, for example, 15 to 45 degrees with respect to the tire circumferential direction. Note that the angle between the belt cord 17A and the tire circumferential direction referred to here is the angle between the belt cord 17A and the tire circumferential direction on the tire equatorial plane. The angle between the belt cord 17A and the tire circumferential direction can be measured by peeling off the tread portion of the tire and exposing the belt cord 17A on the tire surface.

Although not particularly limited, it is desirable that the belt cords 17A of the first belt ply (inner layer 38) and the belt cords 17A of the second belt ply (outer layer 40) are arranged with inclinations in opposite directions relative to the tire circumferential direction so that they cross each other.

From the viewpoint of adhesion to the rubber composition that covers the periphery of the belt cord 17A, it is preferable that the surface of the belt cord 17A is plated with copper and zinc. In addition to the copper and zinc mentioned above, it is more preferable that the belt cord 17A is plated with a metal element whose ionization tendency is between that of copper and zinc, such as cobalt, nickel, bismuth, or antimony.

In addition, from the viewpoint of adhesion to the surrounding rubber composition, it is preferable that the belt cord 17A has a layer of a polybenzoxazine compound on its surface.

The topping rubber 17B (coating rubber) that covers the belt cord 17A preferably contains, in addition to well-known rubber materials, phenolic thermosetting resins, silica, salts of organic fatty acids with metals such as cobalt, nickel, bismuth, and antimony that have an ionization tendency between copper and zinc, and polybenzoxazine compounds.

In the widthwise cross section of the tire 2, the number of belt cords 17A arranged per 50 mm in the tire width direction (ends) E (pieces/50 mm) is preferably 40 cords/50 mm or more, more preferably 46 cords/50 mm or more, even more preferably 50 cords/50 mm or more, still more preferably 55 cords/50 mm or more, still more preferably 56 cords/50 mm or more, particularly preferably 60 cords/50 mm or more, and is preferably 100 cords/50 mm or less, more preferably 82 cords/50 mm or less, and even more preferably 70 cords/50 mm or less. When it is within the above range, the effect can be preferably obtained.
Here, E indicates the number of cords arranged within a range of ±25 mm from the tire equatorial plane in a cross section cut in the tire width direction.

E can be adjusted as appropriate by adjusting the number of belt cords arranged in the belt layer when manufacturing the tire.

In the tire 2, the product (D×E) of the outer diameter D (mm) of the belt cord 17A and the number E (pieces/50 mm) of the belt cord 17A arranged in the tire width direction in a widthwise cross section of the tire 2 is 20.0 or more and 28.0 or less.
D×E is preferably 20.7 or more, more preferably 21.5 or more, even more preferably 22.0 or more, even more preferably 24.0 or more, even more preferably 25.0 or more, particularly preferably 25.8 or more, and is preferably 27.0 or less, more preferably 26.6 or less, even more preferably 26.5 or less, even more preferably 26.2 or less, and even more preferably 26.0 or less. When it is within the above range, the effect can be obtained favorably.

In the tire 2, from the viewpoint of obtaining a better effect, it is desirable that the cord-to-cord distance L (mm) of the belt cord 17A in the tire width direction is 0.25 mm or more. L is preferably 0.29 mm or more, more preferably 0.30 mm or more, even more preferably 0.33 mm or more, still more preferably 0.39 mm or more, and even more preferably 0.40 mm or more. There is no particular upper limit, but it is preferably 0.70 mm or less, more preferably 0.64 mm or less, more preferably 0.60 mm or less, still more preferably 0.57 mm or less, and even more preferably 0.55 mm or less. Within the above range, the effect can be obtained suitably.
In the present invention, the inter-cord distance L refers to the distance between adjacent cords in the belt ply within a range of ±25 mm from the tire equatorial plane in a cross section cut out in the tire width direction. In Fig. 4, the inter-cord distance L is the linear distance between the surfaces of adjacent belt cords 17A in the inner layer 38 and the linear distance between the surfaces of adjacent belt cords 17A in the outer layer 40.

The mechanism by which better effects are obtained by setting the inter-cord distance L in a predetermined range, particularly within the range of 0.30 mm or more and 0.60 mm or less, is not clear, but is presumed to be as follows.
By making the rubber gauge between adjacent cords in the crown portion (a total of 5 cm area extending 2.5 cm to the left and right of the center) 0.30 mm or more, it is believed that the concentration of shear stress applied during driving between adjacent cords can be prevented, thereby suppressing the occurrence of cracks.
Furthermore, by setting the rubber gauge between adjacent belt cord surfaces to 0.60 mm or less, the number of arranged cords is prevented from becoming too small, and the concentration of stress on the belt cord surface is prevented, making it easier to prevent peeling between the belt cord and rubber.
From the above, it is presumed that durability is improved by adjusting the thickness to the above-mentioned predetermined range, particularly within the range of 0.30 mm or more and 0.60 mm or less.

The band layer (belt reinforcing layer) 18 in FIG. 1 is located radially outside the belt layer 16. In the tire 2 in FIG. 1, the band layer 18 has a width equal to that of the belt layer 16 in the axial direction. The band layer 18 may have a width greater than that of the belt layer 16.

The band layer 18 is preferably made of a belt reinforcement layer cord and a topping rubber (coating rubber). The belt reinforcement layer cord is wound spirally in the tire circumferential direction. This band layer 18 has a so-called jointless structure. The belt reinforcement layer cord extends substantially in the circumferential direction. The angle of the belt reinforcement layer cord with respect to the tire circumferential direction is preferably 5° or less, and more preferably 2° or less. The belt layer 16 is restrained by this belt reinforcement layer cord, which prevents the outer diameter of the tire from increasing due to the internal pressure during driving.

In the tire 2, the band layer 18 can increase the restraint of each belt ply 17 and improve durability during high-speed driving.

One form of the band layer 18 includes an organic fiber cord 18A and a reinforcing rubber 18B (a band layer coating rubber composition) that covers the organic fiber cord 18A. Normally, the organic fiber cord is dipped to improve adhesion to the rubber.

The organic fibers constituting the organic fiber cord 18A include polyester, polyamide, cellulose, etc. These may be synthetic fibers or fibers derived from biomass. From the viewpoint of life cycle assessment, it is preferable that they are derived from recycled or regenerated materials. These fibers may be formed from a single component of synthetic fiber, biomass fiber, or recycled/regenerated fiber, or may be a hybrid cord twisted together with these, a cord using a multifilament combining each filament, or a cord having a chemical structure in which each component is chemically bonded.

Examples of polyester cords include polyethylene terephthalate (PET) cords, polyethylene naphthalate (PEN) cords, and polyethylene furanoate (PEF). Compared to other polyester cords, PEF may be used because it has excellent air permeability resistance and is easier to maintain air pressure inside the tire. In addition, the polyester cord may be a hybrid cord with a cord made of other organic fibers, such as polyamide fibers, in which part of the polyester cord is replaced with a cord made of other organic fibers.

When the polyester cord is a biomass-derived polyester cord, for example, a biomass PET cord using terephthalic acid or ethylene glycol derived from biomass, or a biomass PEF cord using furandicarboxylic acid derived from biomass can be suitably used.

Biomass polyester cord can be obtained, for example, from bioethanol, furfurals, carenes, cymenes, terpenes, etc., or from compounds derived from various animals and plants, or from biomass terephthalic acid or biomass ethylene glycol produced by direct fermentation from microorganisms, etc.

Examples of polyamide cords include aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides.

Aliphatic polyamides are polyamides with a skeleton in which linear carbon chains are connected by amide bonds, and examples thereof include nylon 4 (PA4), nylon 410 (PA410), nylon 6 (PA6), nylon 66 (PA66), nylon 610 (PA610), nylon 10 (PA10), nylon 1010 (PA1010), nylon 1012 (PA1012), nylon 11 (PA11), etc. Among these, nylon 4, nylon 410, nylon 610, nylon 10, nylon 1010, nylon 11, etc. can be mentioned from the viewpoint of being easily obtained partially or completely from biomass-derived materials.

Nylon 6 and nylon 66 can be produced by ring-opening polymerization of caprolactam derived from conventional chemical synthesis, condensation polymerization of hexamethylenediamine and adipic acid, or by using biocaprolactam, bioadipic acid, or biohexamethylenediamine produced from bio-derived cyclohexane as a starting material. The bio-based raw materials mentioned above may also be obtained from sugars such as glucose. These nylon 6 and nylon 66 are considered to have the same strength as those that have been used conventionally.

A representative example of nylon 4 is one made from 2-pyrrolidone, which is obtained by converting glutamic acid derived from biofermentation into gamma-aminobutyric acid, but this is not limited to this. Nylon 4 has good thermal and mechanical stability and is easy to design the polymer structure, so it can be used favorably as it contributes to improving the performance and strength of tires.

Nylon 410, nylon 610, nylon 1010, nylon 1012, nylon 11, etc. can be obtained from raw materials such as ricinoleic acid obtained from castor oil (castor bean). Specifically, nylon 410, nylon 610, and nylon 1010 can be obtained by condensation polymerization of sebacic acid and dodecanedioic acid obtained from castor oil with any diamine compound, and nylon 11 can be obtained by condensation polymerization of 11-aminoundecanoic acid obtained from castor oil.

Semi-aromatic polyamides are polyamides that have an aromatic ring structure in part of the molecular chain, and examples include nylon 4T (PA4T), nylon 6T (PA6T), and nylon 10T (PA10T).

Nylon 4T, nylon 6T, and nylon 10T can be obtained by using terephthalic acid as the dicarboxylic acid and carrying out condensation polymerization with a diamine compound of any number of carbon atoms. In this case, it is also possible to obtain these nylon materials using the aforementioned biomass-derived terephthalic acid. These have a rigid cyclic structure in the molecular chain, making them excellent in terms of heat resistance, etc.

Furthermore, examples of the aforementioned aliphatic polyamides and semi-aromatic polyamides include polyamide 5X (X is the number of carbon atoms derived from dicarboxylic acid, and T represents an integer or terephthalic acid) in which 1,5-pentanediamine derived from lysine is polymerized with dicarboxylic acids.

Fully aromatic polyamides are polyamides having a skeleton in which aromatic rings are connected by amide bonds, and examples thereof include polyparaphenylene terephthalamide. Like the aliphatic polyamides and semi-aromatic polyamides described above, fully aromatic polyamides may also be obtained by combining biomass-derived terephthalic acid with phenylenediamine.

Cellulosic fibers include rayon, polynosic, cupra, acetate, lyocell, modal, etc., which are manufactured from plant materials such as wood pulp. These cellulose-based fibers are preferred because they are not only made from carbon-neutral raw materials, but also have excellent environmental performance, such as being biodegradable and not emitting harmful gases even when incinerated after use. Among the above, rayon, polynosic, and lyocell are particularly preferred due to the balance of process efficiency, environmental friendliness, and mechanical strength.

The above cord may also be a recycled cord, whether synthetic or derived from biomass, that is obtained by collecting and refining used items such as beverage bottles and clothing and then re-spinning them.

The above-mentioned cord may be formed by twisting one or more filaments together. For example, two 1100 decitex multifilaments (in other words, 1100/2 decitex) are twisted 48 times/10 cm, and then two of these first twisted cords are twisted together and twisted the same number of times in the opposite or same direction as the first twist; two 1670 decitex multifilaments (in other words, 1670/2 decitex) are twisted 40 times/10 cm, and then two of these first twisted cords are twisted together and twisted.

In addition, from the viewpoint of ensuring good adhesion to the coating layer, it is preferable that the cord is previously treated by applying an adhesive layer. Any known adhesive layer can be used, such as a treatment with resorcinol-formalin-rubber latex (RFL), an epoxy treatment with an adhesive composition containing sorbitol polyglycidyl ether and blocked isocyanate, and then an RFL treatment, or an adhesive composition containing a halohydrin compound, a blocked isocyanate compound, and rubber latex can be used.

Resorcin-formalin-rubber latex (RFL) is, for example, an adhesive composition containing natural rubber and/or synthetic rubber latex and a co-condensation product of phenol-formaldehyde and resorcinol, as described in JP-A-48-11335. Such an adhesive composition can be produced, for example, by a production method including a step of condensing phenol and formaldehyde in the presence of an alkaline catalyst, a step of copolymerizing an aqueous phenol-formaldehyde resin solution with resorcinol, and a step of mixing the resulting phenol-formaldehyde-resorcinol resin solution with latex rubber.

Examples of synthetic rubber latex include butadiene polymer latex, styrene/butadiene copolymer latex, isoprene polymer latex, butadiene/acrylonitrile copolymer latex, butadiene/vinylpyridine polymer latex, and butadiene/vinylpyridine/styrene copolymer latex.

The adhesive layer made of resorcinol-formaldehyde-rubber latex (RFL) can be formed by applying an RFL adhesive (such as by immersing the cord in an RFL liquid (DIP: dipping)). The RFL adhesive is usually applied after the fiber cord is obtained by twisting the yarn, but it may be applied before or during the twisting process.

The composition of the RFL adhesive is not particularly limited and may be selected as appropriate, but it is preferable that the composition contains 0.1 to 10% by mass of resorcinol, 0.1 to 10% by mass of formalin, and 1 to 28% by mass of latex, and it is more preferable that the composition contains 0.5 to 3% by mass of resorcinol, 0.5 to 3% by mass of formalin, and 10 to 25% by mass of latex.

The heating method for the heat treatment may be, for example, a method in which the cord to which the RFL adhesive composition is attached is dried at 100 to 250°C for 1 to 5 minutes, and then further heat-treated at 150 to 250°C for 1 to 5 minutes. The conditions for the heat treatment after the drying treatment are preferably 180 to 240°C for 1 to 2 minutes.

The adhesive composition containing the sorbitol polyglycidyl ether and the blocked isocyanate is not particularly limited as long as it is a composition containing a sorbitol polyglycidyl ether and a blocked isocyanate. In particular, a composition containing an epoxy compound that is a sorbitol polyglycidyl ether and has a chlorine content of 9.6 mass% or less, and a blocked isocyanate is preferable.

Sorbitol polyglycidyl ethers include sorbitol diglycidyl ether, sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, sorbitol pentaglycidyl ether, sorbitol hexaglycidyl ether, and mixtures thereof, and may contain sorbitol monoglycidyl ether. Sorbitol polyglycidyl ether has many epoxy groups in one molecule and can form a highly crosslinked structure.

The chlorine content of the sorbitol polyglycidyl ether is preferably 9.6% by mass or less, more preferably 9.5% by mass or less, even more preferably 9.4% by mass or less, and particularly preferably 9.3% by mass or less. The lower limit of the chlorine content is not particularly limited, and is, for example, 1% by mass or more.
In the present invention, the chlorine content of the sorbitol polyglycidyl ether can be determined by the method described in JIS K 7243-3, for example.

The chlorine content of sorbitol polyglycidyl ether can be reduced by, for example, reducing the amount of epichlorohydrin used in synthesizing the epoxy compound.

Blocked isocyanates are compounds that are produced by the reaction of an isocyanate compound with a blocking agent and are temporarily inactivated by groups derived from the blocking agent. When heated to a certain temperature, the groups derived from the blocking agent dissociate to produce isocyanate groups.

The isocyanate compound may, for example, have two or more isocyanate groups in the molecule.
Examples of diisocyanates having two isocyanate groups include hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, phenylene diisocyanate, tolylene diisocyanate, trimethylhexamethylene diisocyanate, metaphenylene diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylpropane diisocyanate, biphenyl diisocyanate, and their isomers, alkyl-substituted compounds, halides, and hydrogenated compounds of benzene rings. Also usable are triisocyanates having three isocyanate groups, tetraisocyanates having four isocyanate groups, and polymethylene polyphenyl polyisocyanate. These isocyanate compounds can be used alone or in combination of two or more. Among these, tolylene diisocyanate, metaphenylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and polymethylene polyphenyl polyisocyanate are preferred.

The blocking agents include lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; phenol-based agents such as phenol, cresol, resorcinol, and xylenol; alcohol-based agents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and benzyl alcohol; oxime-based agents such as formamidoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexanone oxime; and active methylene-based agents such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone. Among these, lactam-based, phenol-based, and oxime-based blocking agents are preferred.

In the adhesive composition containing the above sorbitol polyglycidyl ether and blocked isocyanate, the content of the blocked isocyanate is preferably 50 parts by mass or more, more preferably 200 parts by mass or more, per 100 parts by mass of sorbitol polyglycidyl ether. The upper limit is preferably 500 parts by mass or less, more preferably 400 parts by mass or less.

The adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate may contain the following optional components as necessary. For example, epoxy compounds other than sorbitol polyglycidyl ether, resins copolymerizable with sorbitol polyglycidyl ether, curing agents other than blocked isocyanates, organic thickeners, antioxidants, light stabilizers, adhesion improvers, reinforcing agents, softeners, colorants, leveling agents, flame retardants, and antistatic agents.

Examples of epoxy compounds other than sorbitol polyglycidyl ether include glycidyl ethers such as ethylene glycol glycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, novolac glycidyl ether, and brominated bisphenol A diglycidyl ether; glycidyl esters such as hexahydrophthalic acid glycidyl ester and dimer acid glycidyl ester; triglycidyl ether; Examples of such glycidyl amines include diglycidyl isocyanurate, glycidyl hindantoin, tetraglycidyl diaminodiphenylmethane, triglycidyl para-aminophenol, triglycidyl meta-aminophenol, diglycidyl aniline, diglycidyl toluidine, tetraglycidyl meta-xylylenediamine, diglycidyl tribromoaniline, and tetraglycidyl bisaminomethylcyclohexane; and alicyclic or aliphatic epoxides such as 3,4-epoxycyclohexylmethylcarboxylate, epoxidized polybutadiene, and epoxidized soybean oil.

Examples of treatments using the adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate include treatments carried out to adhere the various components contained in the RFL to the cord, and treatments that include a subsequent heat treatment if necessary.

Any method can be used for the application, such as application using a roller, spraying from a nozzle, or immersion in a bath liquid (adhesive composition). From the viewpoint of uniform application and removal of excess adhesive, application by immersion is preferred.

In addition, in order to adjust the amount of adhesion to the cord, further means such as squeezing with a pressure roller, scraping with a scraper, blowing with air, suction, hitting with a beater, etc. may be used.

The amount of the adhesive on the cord is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and is preferably 3.0% by mass or less, more preferably 2.5% by mass or less.
The amount of the RFL adhesive applied to the cord is the amount of solid content in the RFL adhesive applied to 100 parts by mass of the cord.

The total solids concentration of the adhesive composition containing the above sorbitol polyglycidyl ether and blocked isocyanate is preferably 0.9% by mass or more, more preferably 14% by mass or more, and is preferably 29% by mass or less, more preferably 23% by mass or less.

The adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate may contain, in addition to resorcinol, formalin, and rubber latex, vulcanization regulators, zinc oxide, antioxidants, defoamers, etc.

The heating method for the heat treatment may be, for example, to dry the reinforcing material to which the RFL adhesive composition is attached at 100 to 250°C for 1 to 5 minutes, and then to further heat treat it at 150 to 250°C for 1 to 5 minutes. The conditions for the heat treatment after the drying treatment are preferably 180 to 240°C for 1 to 2 minutes.

The adhesive composition containing the above-mentioned halohydrin compound, blocked isocyanate compound, and rubber latex is not particularly limited as long as it contains these components, but an adhesive composition that contains a halohydrin compound, a blocked isocyanate compound, and rubber latex, and does not contain resorcinol or formaldehyde, is preferable.

Examples of the halohydrin compound include compounds obtained by reacting a polyol compound with an epihalohydrin compound (halohydrin ether).
The polyol compound is a compound having two or more hydroxyl groups in the molecule, and examples thereof include glycols such as ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; hydroxyl acids such as erythritol, xylitol, sorbitol, and tartaric acid; glyceric acid, glycerin, diglycerin, polyglycerin, trimethylolpropane, trimethylolethane, and pentaerythritol.
Examples of the epihalohydrin compound include epichlorohydrin and epibromohydrin.

Examples of halohydrin compounds include fluoroalcohol compounds, chlorohydrin compounds, bromohydrin compounds, and iodohydrin compounds. Among these, halogenated sorbitol and halogenated glycerol are preferred.

The halogen content in 100% by mass of the halohydrin compound is preferably 5.0 to 15.0% by mass, more preferably 7.0 to 13.0% by mass, and even more preferably 9.0 to 12.0% by mass.

Examples of the blocked isocyanate compound include the same compounds as the blocked isocyanates described above. Examples of the rubber latex include the same rubber latexes as those described above.

The adhesive composition containing the above-mentioned halohydrin compound, blocked isocyanate compound, and rubber latex preferably contains 10.0 to 30.0 parts by mass of the halohydrin compound, 10.0 to 30.0 parts by mass of the blocked isocyanate compound, and 80.0 to 240.0 parts by mass of the rubber latex. Furthermore, it is preferable that the adhesive composition does not contain resorcinol or formaldehyde.

An adhesive layer consisting of an adhesive composition containing the above-mentioned halohydrin compound, a blocked isocyanate compound, and a rubber latex is formed on the surface of the cord using the adhesive composition. The adhesive layer is formed by, for example, but not limited to, dipping, brushing, casting, spraying, roll coating, knife coating, etc.

FIG. 5 is an enlarged cross-sectional view showing the vicinity of the tread portion 4 of the tire 2 of FIG.
A (mm) in FIG. 5 is the distance in the tire radial direction from the tread surface 24 to the belt layer 16 on the tire equatorial plane CL.

A is preferably 8.0 mm or more, more preferably 9.0 mm or more, even more preferably 10.0 mm or more, and particularly preferably 10.6 mm or more, and is preferably 13.0 mm or less, more preferably 12.0 mm or less, and even more preferably 11.0 mm or less. Within the above range, the effect tends to be better.

In the present invention, the "distance A in the radial direction of the tire from the tread surface to the belt layer on the tire equatorial plane" refers to the distance between the tread surface on the tire equatorial plane and the tire outermost surface side interface of the radially outermost belt ply. In the case where a groove is present on the tire equatorial plane, it is the distance between the surface formed by the straight line connecting the radially outermost ends of the groove and the tire outermost surface side interface of the radially outermost belt ply. Note that the belt ply does not include the belt reinforcing layer.
In the case of the tire 2 in Figure 5, A is the straight-line distance from a plane formed by a straight line connecting the ends of the grooves 26 corresponding to the tread surface 24 on the tire equatorial plane CL on the outermost surface side in the tire radial direction to the outer surface of the outer layer 40 (second belt ply) in the tire radial direction.

B (mm) in Figure 5 is the distance from the tread surface 24 to the belt layer at the tire width direction end P of the belt ply that is the outermost belt ply in the tire radial direction.

B is preferably 6.0 mm or more, more preferably 8.0 mm or more, even more preferably 8.3 mm or more, even more preferably 9.0 mm or more, and particularly preferably 9.6 mm or more, and is preferably 11.8 mm or less, more preferably 11.0 mm or less, even more preferably 10.5 mm or less, and even more preferably 10.0 mm or less. Within the above range, the effect tends to be better.

In the present invention, the "distance B from the tread surface to the belt layer at the tire width direction end of the radially outermost belt ply among the belt plies" refers to the shortest distance between the tread surface and the tire outermost surface side interface of the tire width direction end of the radially outermost belt ply among the belt plies. For grooves on the tread surface, it is not the distance to the groove bottom, but the shortest distance to the surface formed by a straight line connecting the tire radially outermost surface side ends of the grooves, as with the above A.
In the case of the tire 2 in FIG. 5, B is the shortest distance between the tread surface 24 and the tire radially outer surface of the tire width direction end P of the outer layer 40 (second belt ply).

In tire 2, A/B is preferably 1.06 or more, more preferably 1.08 or more, even more preferably 1.10 or more, and is preferably 1.28 or less, more preferably 1.22 or less, even more preferably 1.18 or less. Within the above range, the effect tends to be better.

The mechanism by which better effects are obtained by adjusting A/B to the above range, particularly to 1.08 or more and 1.22 or less, is not clear, but is presumed to be as follows.
It is considered that when A/B is large, the movement of the belt layer end portion becomes large when the tread portion comes into contact with the ground, and the belt cord becomes fatigued and easily damaged.
On the other hand, if A/B is small, the center of the tread portion in the tire width direction will deform radially inward when it comes into contact with the ground, making it more likely to become floating (buckled), resulting in localized bending and making the tire more susceptible to damage.
Therefore, it is presumed that durability is significantly improved by adjusting the ratio to the above range, particularly to 1.08 or more and 1.22 or less.

In order to obtain a better effect, it is desirable for the tire 2 to have a product (E x H) of the number E (pieces/50 mm) of the belt cords 17A arranged in the tire width direction and the hardness H of the cap tread constituting the outermost layer of the tread portion 4 be 2,920 or more and 4,920 or less.
The lower limit of E×H is preferably 3220 or more, more preferably 3360 or more, even more preferably 3400 or more, even more preferably 3520 or more, and even more preferably 3720 or more. The upper limit is preferably 4900 or less, more preferably 4760 or less, even more preferably 4620 or less, even more preferably 4320 or less, even more preferably 4060 or less, and particularly preferably 4020 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting E×H to the above range, particularly 2920 or more and 4620 or less, is not clear, but is presumed to be as follows.
If the cap tread is soft and has a small number of arranged filaments, the rigidity of the tread portion is low, so that bending is likely to occur in the belt layer.
If the cap tread is too hard, the rigidity of the tread portion will be too high, making it unable to absorb the impact from the ground when the tire touches the ground, resulting in cord breakage.
On the other hand, it is presumed that by adjusting E×H to the above range, bending of the belt layer and breakage of the cord are prevented, so that durability is significantly improved.

In the present invention, the cap tread refers to the rubber layer that forms the outermost layer in the tire radial direction among the rubber layers that make up the tread portion 4. When the tread portion 4 is a single-layer tread, the cap tread itself corresponds to the cap tread. When the tread portion 4 is a two-layer tread having a cap layer and a base layer, the cap layer corresponds to the cap tread. When the tread has a three or more layer structure, the rubber layer that forms the outermost layer corresponds to the cap tread.

The hardness H of the cap tread is preferably 56 or more, more preferably 58 or more, even more preferably 60 or more, and even more preferably 62 or more, and is preferably 70 or less, more preferably 68 or less, even more preferably 66 or less, and even more preferably 65 or less. Within the above range, the effect tends to be obtained favorably.

In the present invention, the hardness (JIS-A hardness) of the rubber composition (after vulcanization) is measured at 25°C using a type A durometer in accordance with JIS K6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness".
When samples are taken from the tire for measurement, the sample size is 30 mm x 30 mm x 4 mm. If it is difficult to create samples of the same size due to the tire pattern or the like, a sample of as large a size as possible should be taken, and as many samples as possible should be created from the tread portion with N=5.

In terms of obtaining a better effect, it is desirable for the tire 2 to have a groove depth G (mm) of the circumferential groove formed in the tread portion 4 of 5.0 mm or more.
G is preferably 5.5 mm or more, more preferably 6.0 mm or more, even more preferably 7.0 mm or more, and particularly preferably 8.0 mm or more. The upper limit is preferably 12.0 mm or less, more preferably 11.0 mm or less, even more preferably 10.0 mm or less, and even more preferably 8.5 mm or less. Within the above range, the effect tends to be better obtained.

In this specification, the groove depth G of the circumferential groove is measured along the normal to the surface that forms the contact surface of the outermost tread surface, and refers to the distance from the surface that forms the contact surface to the bottom of the deepest groove, and refers to the maximum distance among the groove depths of the circumferential grooves provided.

In terms of obtaining a better effect, it is preferable that the tire 2 has a product (D×L) of the outer diameter D of the belt cord 17A and the inter-cord distance L of the belt cord 17A in the tire width direction be 0.09 or more and 0.28 or less.
D×L is preferably 0.12 or more, more preferably 0.13 or more, even more preferably 0.15 or more, and even more preferably 0.17 or more. The upper limit is preferably 0.25 or less, more preferably 0.24 or less, even more preferably 0.22 or less, and even more preferably 0.20 or less. Within the above range, the effect tends to be better obtained.

In terms of obtaining a better effect, it is desirable for the tire 2 to have a product (D×E×L) of the outer diameter D of the belt cord 17A, the number E (pieces/50 mm) of the belt cords 17A arranged in the tire width direction in the tire width direction cross section, and the inter-cord distance L of the belt cords 17A in the tire width direction be 7.6 or more and 12.0 or less.
D×E×L is preferably 8.5 or more, more preferably 8.9 or more, and even more preferably 10.4 or more. The upper limit is preferably 11.5 or less, more preferably 11.0 or less, and even more preferably 10.8 or less. Within the above range, the effect tends to be better obtained.

In terms of obtaining a better effect, it is desirable for the tire 2 to have a ratio (D/(A/B)) of the outer diameter D of the belt cord 17A to the tire radial distance A from the tread surface 24 to the belt layer 16 on the tire equatorial plane CL/the distance B (A/B) from the tread surface 24 to the belt layer at the tire width direction end P of the radially outermost belt ply among the belt plies, which is 0.20 or more and 0.55 or less.
D/(A/B) is preferably 0.27 or more, more preferably 0.32 or more, even more preferably 0.35 or more, even more preferably 0.41 or more, even more preferably 0.42 or more, even more preferably 0.44 or more. The upper limit is preferably 0.52 or less, more preferably 0.50 or less, even more preferably 0.49 or less, and particularly preferably 0.47 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects can be obtained by adjusting D/(A/B) to the above range, particularly 0.20 or more and 0.55 or less, is not clear, but is presumed to be as follows.
As described above, it is considered that the deformation amount of the belt layer end when the ground contacts increases as A/B increases. Therefore, it is considered that by making the outer diameter D of the belt cord 17A larger than A/B, sufficient strength against deformation is exhibited, and durability performance is improved. On the other hand, if the outer diameter D of the belt cord 17A is excessively large or if A/B is extremely small, it is difficult to obtain a good ground contact shape, so it is considered preferable to set it below the upper limit.

In terms of obtaining better effects, it is preferable that the tire 2 has a ratio ((D×E)/(A/B)) of the product (D×E) of the outer diameter D of the belt cord 17A and the number E (pieces/50 mm) of the belt cords 17A arranged in the tire width direction in the tire width cross section to the tire radial distance A from the tread surface 24 to the belt layer 16 on the tire equatorial plane CL/the distance B (A/B) from the tread surface 24 to the belt layer at the tire width end P of the belt ply that is outermost in the tire radial direction among the belt plies. The ratio is 20 or more and 35 or less.
(D×E)/(A/B) is preferably 21 or more, more preferably 22 or more, and even more preferably 23 or more. The upper limit is preferably 30 or less, more preferably 28 or less, and even more preferably 24 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting (D×E)/(A/B) to the above range, particularly to 20 or more and 35 or less, is not clear, but is presumed to be as follows.
As mentioned above, it is considered that the deformation amount of the belt layer end when the ground contacts increases as A/B increases. Therefore, it is considered that by increasing the product (D×E) of the outer diameter D and the number of arranged strands E of the belt cord 17A relative to A/B, sufficient strength against deformation is exhibited, and durability performance is improved. On the other hand, when the product (D×E) of the outer diameter D and the number of arranged strands E of the belt cord 17A is excessively large or when A/B is extremely small, it is difficult to obtain a good ground contact shape, so it is considered preferable to set it below the upper limit.

In order to obtain a better effect, it is desirable for the tire 2 to have a product (D×H) of the outer diameter D of the belt cord 17A and the hardness H of the cap layer 30 (cap tread) constituting the outermost layer of the tread portion 4, the product being 19 or more and 34 or less.
D×H is preferably 22 or more, more preferably 23 or more, even more preferably 24 or more, still more preferably 26 or more, and still more preferably 27 or more. The upper limit is preferably 32 or less, more preferably 31 or less, even more preferably 30 or less, and still more preferably 28 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting D×H to the above range, particularly to 23 or more and 30 or less, is not clear, but is presumed to be as follows.
If the cap tread is soft and the outer diameter D of the belt cord 17A is small, the rigidity of the tread portion is low, so that bending is likely to occur in the belt layer.
If the cap tread is too hard, the rigidity of the tread portion will be too high, making it unable to absorb the impact from the ground when the tire touches the ground, resulting in cord breakage.
Therefore, it is presumed that by adjusting D×H to the above range, bending of the belt layer and breakage of the cords are prevented, and durability is significantly improved.

In terms of obtaining a better effect, it is desirable for the tire 2 to have a product (D×E×H) of the outer diameter D of the belt cord 17A, the number E (pieces/50 mm) of the belt cords 17A arranged in the tire width direction in the tire width direction cross section, and the hardness H of the cap layer 30 (cap tread) constituting the outermost layer of the tread portion 4, which is 1,574 or more and 1,900 or less.
D×E×H is preferably 1590 or more, more preferably 1595 or more, and even more preferably 1600 or more. The upper limit is preferably 1862 or less, more preferably 1809 or less, even more preferably 1800 or less, still more preferably 1700 or less, and even more preferably 1680 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting D×E×H to the above range, particularly to 1,590 or more and 1,900 or less, is not clear, but is presumed to be as follows.
If the cap tread is soft and the outer diameter D or the number E of the arranged belt cords 17A is small, the rigidity of the tread portion is low, so that bending is likely to occur in the belt layer.
If the cap tread is too hard, the rigidity of the tread portion will be too high, making it unable to absorb the impact from the ground when the tire touches the ground, resulting in cord breakage.
Therefore, it is presumed that by adjusting D×E×H to the above range, bending of the belt layer and breakage of the cords are prevented, and durability is significantly improved.

In order to obtain a better effect, it is desirable for the tire 2 to have a ratio (D/G) of the outer diameter D of the belt cord 17A to the groove depth G (mm) of the circumferential groove formed in the tread portion 4 of 0.030 or more and 0.060 or less.
D/G is preferably 0.035 or more, more preferably 0.036 or more, even more preferably 0.040 or more, even more preferably 0.042 or more, even more preferably 0.048 or more. The upper limit is preferably 0.059 or less, more preferably 0.058 or less, even more preferably 0.056 or less, even more preferably 0.054 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting D/G to the above range, particularly 0.030 or more and 0.060 or less, is not clear, but is presumed to be as follows.
When the tread portion comes into contact with the road surface, it is considered that the tread portion is easily deformed from the groove bottom. When the groove depth is deep, the deformation amount at the groove bottom is large, and the deformation amount of the belt layer is also large. Therefore, it is considered that by making the outer diameter D of the belt cord 17A sufficiently large with respect to the groove depth G, it is easy to suppress damage to the belt cord 17A due to deformation at the groove bottom.
On the other hand, if the outer diameter D of the belt cord 17A is excessively large compared to the groove depth, deformation at the bottom of the groove becomes difficult to occur, which reduces the ground contact and causes the force at the time of contact with the ground to be concentrated in a part of the belt layer. Therefore, it is considered preferable to set the outer diameter D to be equal to or less than the upper limit.

In terms of obtaining a better effect, it is desirable for the tire 2 to have a ratio ((D×E)/G) of the product (D×E) of the outer diameter D of the belt cord 17A and the number E (pieces/50 mm) of the belt cords 17A arranged in the tire width direction in a cross section in the tire width direction, relative to the groove depth G (mm) of the circumferential groove formed in the tread portion 4, of 2.0 or more and 5.0 or less.
(D×E)/G is preferably 2.2 or more, more preferably 2.4 or more, even more preferably 2.5 or more, even more preferably 2.6 or more, even more preferably 2.7 or more. The upper limit is preferably 4.7 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.3 or less, even more preferably 3.2 or less. Within the above range, the effect tends to be better obtained.

The mechanism by which better effects are obtained by adjusting (D×E)/G to the above range, particularly within the range of 2.0 or more and 5.0 or less, is not clear, but is presumed to be as follows.
When the tread portion comes into contact with the road surface, it is considered that the tread portion is easily deformed from the groove bottom. When the groove depth is deep, the deformation amount at the groove bottom is large, and the deformation amount of the belt layer is also large. Therefore, it is considered that by making the product of the outer diameter D and the number E of the arranged belt cords 17A sufficiently large with respect to the groove depth G, it is easy to suppress damage to the belt cords 17A due to deformation at the groove bottom.
On the other hand, if the product of the outer diameter D and the number E of arranged cords of the belt cord 17A becomes excessively large in relation to the groove depth, deformation at the bottom of the groove becomes difficult to occur, which reduces the ground contact and causes the force at the time of contact with the ground to be concentrated in a part of the belt layer. Therefore, it is considered preferable to set it to below the upper limit.

The hardness of a rubber composition (after vulcanization) can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, softeners, and sulfur) that are compounded into the rubber composition; for example, the hardness tends to increase when the amount of softener is reduced, the amount of fillers is increased, and the amount of sulfur is increased; the hardness tends to decrease when the amount of softener is increased, the amount of fillers is reduced, and the amount of sulfur is reduced.

The belt layer 16 in FIG. 1 is located radially inward of the tread portion 4. The belt layer 16 is laminated with the carcass 14. The belt layer 16 reinforces the carcass 14. In the tire 2 in FIG. 1, the belt layer 16 is composed of an inner layer 38 and an outer layer 40. As is clear from FIG. 1, it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40 in the axial direction. In this tire 2, the axial width of the belt layer 16 is preferably 0.6 times or more and preferably 0.9 times or less of the cross-sectional width of the tire 2.

In the tire 2 of FIG. 1, the inner liner 20 is located inside the carcass 14. The inner liner 20 is bonded to the inner surface of the carcass 14. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 maintains the internal pressure of the tire 2.

Each chafer 22 is located near the bead 12. In this embodiment, the chafer 22 is preferably made of cloth and rubber impregnated into the cloth. The chafer 22 may be integral with the clinch 10.

In this tire 2, the tread portion 4 has main grooves 42 as grooves 26. As shown in FIG. 1, the tread portion 4 has multiple main grooves 42, specifically three main grooves 42. These main grooves 42 are arranged at intervals in the axial direction. The three main grooves 42 are cut in the tread portion 4, forming four ribs 44 extending in the circumferential direction. In other words, the spaces between the ribs 44 form the main grooves 42.

Each main groove 42 extends in the circumferential direction. The main grooves 42 are continuous in the circumferential direction without interruption. The main grooves 42 facilitate the drainage of water that exists between the road surface and the tire 2, for example, in rainy weather. Therefore, even if the road surface is wet, the tire 2 can make sufficient contact with the road surface.

In the tire 2, each rubber layer (such as the cap layer 30 and base layer 28 in FIG. 1) constituting the tread portion 4 (such as a single-layer tread, a two-layer tread, or a tread portion having a structure of three or more layers) is composed of a rubber composition for the tread. In addition, the belt layer 16 (such as the inner layer 38 and the outer layer 40) includes a belt cord 17A and a topping rubber 17B (coating rubber) that coats the belt cord 17A, and the coating rubber is composed of a coating rubber composition for the belt layer.

Unless otherwise specified, the materials that can be used in the rubber composition below are common to both the tread portion (rubber composition for tread) and the covering rubber of the belt layer (covering rubber composition for belt layer).

The rubber composition for the tread and the coating rubber composition for the belt layer each contain a rubber component.
The rubber component is a component that contributes to crosslinking, and is generally a polymer having a weight average molecular weight (Mw) of 10,000 or more, and is a polymer component that is not extracted with acetone. The rubber component is in a solid state at room temperature (25° C.).

The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above range, the effect tends to be better.

In this specification, the weight average molecular weight (Mw) can be calculated based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation) and converted into standard polystyrene.

As the rubber component usable in the rubber composition for tread and the rubber composition for covering the belt layer, for example, diene rubber can be used. Examples of diene rubber include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Examples of butyl rubber and fluororubber are also included. These may be used alone or in combination of two or more. Among them, in the rubber composition for tread, from the viewpoint of obtaining a better effect, isoprene rubber, BR, and SBR are preferred, and BR and SBR are more preferred. In addition, in the rubber composition for covering the belt layer, from the viewpoint of obtaining a better effect, isoprene rubber, BR, and SBR are preferred, and isoprene rubber is more preferred.
These rubber components may be modified or hydrogenated as described below, and extended rubbers extended with oil, resin, liquid rubber components, etc. may also be used.

The diene rubber may be an unmodified diene rubber or a modified diene rubber.
The modified diene rubber may be any diene rubber having a functional group that interacts with a filler such as silica. Examples of the modified diene rubber include terminal-modified diene rubber (terminal-modified diene rubber having the functional group at the terminal) in which at least one terminal of the diene rubber has been modified with a compound (modifier) having the functional group, main-chain modified diene rubber having the functional group in the main chain, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal (for example, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal modified with the modifier), and terminal-modified diene rubber modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein.

The above-mentioned functional groups include, for example, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the rubber industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the rubber industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

When the rubber composition for treads contains isoprene-based rubber, the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less. Within the above ranges, the effect tends to be better obtained.

In the coating rubber composition for the belt layer, the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 50% by mass or more, even more preferably 75% by mass or more, and particularly preferably 85% by mass or more, and may be 100% by mass. If it is within the above range, the effect tends to be better.

The BR is not particularly limited, and for example, high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, BR synthesized using a rare earth catalyst (rare earth BR), etc. can be used. These may be used alone or in combination of two or more. In particular, the BR preferably contains high cis BR with a cis content of 90% by mass or more. The cis content is more preferably 95% by mass or more, and even more preferably 98% by mass or more. The cis content can be measured by infrared absorption spectroscopy.
The cis content of BR means the cis content of the BR when there is one type of BR, and means the average cis content when there are multiple types of BR.
The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)}/total content of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis content of 90% by mass and 10% by mass of BR with a cis content of 40% by mass, the average cis content of BR is 73.3% by mass (=(20×90+10×40)/(20+10)).

Both unmodified and modified BR can be used. Modified BR includes modified BR with the same functional groups as modified diene rubber. Hydrogenated butadiene polymer (hydrogenated BR) can also be used.

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

In the rubber composition for treads, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Within the above range, the effect tends to be better obtained.

When the coating rubber composition for the belt layer contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Within the above range, the effect tends to be better obtained.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more types.

The styrene content (styrene amount) of SBR is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. The styrene content is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. By keeping it within the above range, durability performance tends to be improved.
In this specification, the styrene content can be measured by ¹ H-NMR measurement.
The styrene content of SBR means the styrene content of the SBR when there is one type of SBR, and means the average styrene content when there are multiple types of SBR.
The average styrene content of SBR can be calculated by {Σ(content of each SBR × styrene content of each SBR)}/total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene content of 40% by mass and 5% by mass of SBR with a styrene content of 25% by mass, the average styrene content of the SBR is 39.2% by mass (=(85×40+5×25)/(85+5)).

The vinyl bond amount (vinyl content) of SBR is preferably 3 mass% or more, more preferably 5 mass% or more, and even more preferably 7 mass% or more. The vinyl bond amount is preferably 42 mass% or less, more preferably 35 mass% or less, even more preferably 30 mass% or less, and even more preferably 25 mass% or less. By keeping it within the above range, durability performance tends to be improved.
In this specification, the vinyl bond amount (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectroscopy.
The vinyl bond amount (amount of 1,2-bonded butadiene units) of SBR is the proportion of vinyl bonds when the total mass of butadiene parts in SBR is taken as 100 (unit: mass %), and is expressed as vinyl amount [mass %] + cis amount [mass %] + trans amount [mass %] = 100 [mass %]. When there is one type of SBR, it means the vinyl bond amount of that SBR, and when there are multiple types of SBR, it means the average vinyl bond amount.
The average vinyl bond amount of SBR can be calculated by Σ{content of each SBR×(100[mass%]−styrene content of each SBR[mass%])×vinyl bond amount of each SBR[mass%]}/Σ{content of each SBR×(100[mass%]−styrene content of each SBR[mass%])}. For example, in 100 parts by mass of the rubber component, 75 parts by mass of SBR having a styrene content of 40 mass% and a vinyl bond amount of 30 mass%, %, 15 parts by mass of SBR with a vinyl bond content of 20 mass%, and the remaining 10 parts by mass being a component other than SBR, the average vinyl bond content of the SBR is 28 mass% (={75 × (100[mass%] - 40[mass%]) × 30[mass%] + 15 × (100[mass%] - 25[mass%]) × 20[mass%])} / {75 × (100[mass%] - 40[mass%]) + 15 × (100[mass%] - 25[mass%])}.

As SBR, either unmodified SBR or modified SBR can be used. Modified SBR includes modified SBR into which functional groups similar to those of modified diene rubber have been introduced. Hydrogenated styrene-butadiene copolymer (hydrogenated SBR) can also be used as SBR.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

In the rubber composition for treads, the content of SBR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. Within the above range, the effect tends to be better obtained.

When the belt layer coating rubber composition contains SBR, the content of SBR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Within the above range, the effect tends to be better obtained.

The rubber composition for the tread and the coating rubber composition for the belt layer may contain a filler.
The filler is not particularly limited, and any material known in the rubber field can be used. Examples of the filler include inorganic fillers such as carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica, biochar, and poorly dispersible fillers.

In the rubber composition for treads, the total filler content (total amount of fillers such as silica, carbon black, etc.) is preferably 30 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 65 parts by mass or more, even more preferably 70 parts by mass or more, and particularly preferably 80 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less. Within the above range, the effect tends to be better obtained.

In the coating rubber composition for the belt layer, the total filler content (total amount of fillers such as silica, carbon black, etc.) is preferably 10 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 55 parts by mass or more, and particularly preferably 60 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. Within the above range, the effect tends to be better obtained.

Among fillers, carbon-derived fillers (carbon-containing fillers) such as carbon black and silica are preferred.

The carbon black usable in the rubber composition for the tread and the coating rubber composition for the belt layer is not particularly limited, but examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Nippon Steel Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more. In addition to conventional carbon black made from mineral oils, carbon black made from biomass materials such as lignin may also be used. Recycled carbon black obtained by decomposing rubber products and plastic products containing carbon black, such as tires, may be used as appropriate by replacing the above carbon black in an equal amount.

In the rubber composition for treads, the nitrogen adsorption specific surface area ( _N2SA ) of the carbon black is preferably ⁵⁰ m2/g or more, more preferably ⁷⁰ m2/g or more, and even more preferably ⁹⁰ m2/g or more. The _N2SA is preferably ²⁰⁰ m2/g or less, more preferably ¹⁵⁰ m2/g or less, even more preferably ¹²⁰ m2/g or less, and even more preferably 114 ^m2 /g or less. Within the above range, the effect tends to be better obtained.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

In the belt layer coating rubber composition, the nitrogen adsorption specific surface area ( _N2SA ) of the carbon black is preferably ¹⁰ m2/g or more, more preferably ²⁰ m2/g or more, and even more preferably 25 ^m2 /g or more. The _N2SA is preferably ⁸⁰ m2/g or less, more preferably ⁶⁰ m2/g or less, even more preferably ⁴⁵ m2/g or less, and particularly preferably ³⁵ m2/g or less. Within the above range, the effect tends to be better.

In the rubber composition for treads, the carbon black content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 100 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 45 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less. Within the above range, the effect tends to be better obtained.

In the coating rubber composition for the belt layer, the carbon black content is preferably 10 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 55 parts by mass or more, and particularly preferably 60 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. Within the above range, the effect tends to be better obtained.

In particular, in the coating rubber composition for the belt layer, the content of carbon black having a nitrogen adsorption specific surface area of 45 ^m2 /g or less is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and particularly preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. Within the above range, the effect tends to be better obtained.

The mechanism by which greater effect is obtained by blending a specified amount of carbon black with an N ₂ SA in the above range in the belt layer coating rubber composition, particularly by blending 5 to 60 parts by mass of carbon black with an N ₂ SA of 45 m ² /g or less, is not clear; however, it is presumed that the use of large particle size carbon black in the belt coating layer makes it easier to reduce the heat generation of the belt layer and to improve the responsiveness of the belt layer, thereby improving durability.

Examples of silica that can be used in the rubber composition for the tread and the coating rubber composition for the belt layer include dry process silica (anhydrous silica) and wet process silica (hydrated silica). Of these, wet process silica is preferred because it has a large number of silanol groups. Commercially available products include those from Degussa, Rhodia, Tosoh Silica, Solvay Japan, and Tokuyama. These may be used alone or in combination of two or more. In addition to these silicas, silica made from biomass materials such as rice husks may also be used.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is preferably ^50m2 /g or more, more preferably ^100m2 /g or more, even more preferably ^150m2 /g or more, even more preferably ^175m2 /g or more, particularly preferably ^180m2 /g or more, and most preferably ^190m2 /g or more. The upper limit of the _N2SA of silica is not particularly limited, but is preferably ^350m2 /g or less, more preferably ^300m2 /g or less, and even more preferably ^250m2 /g or less. Within the above range, the effect tends to be better obtained.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

In the rubber composition for treads, the content of silica is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 75 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. Within the above range, the effect tends to be better obtained.

The mechanism by which greater effects are obtained by adjusting the amount of silica to the above range, particularly 50 to 100 parts by mass, is unclear, but it is presumed that durability is improved because using a specified amount of silica makes it easier to lower tan δ and improve responsiveness.

When the coating rubber composition for the belt layer contains silica, the content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the tread and the coating rubber composition for the belt layer contain silica, it is preferable that they further contain a silane coupling agent.
The silane coupling agent is not particularly limited, and those known in the rubber field can be used. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N, Examples of such silylsilanes include sulfide-based silylsilanes such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silylsilanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silylsilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silylsilanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silylsilanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silylsilanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silylsilanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.

In the rubber composition for treads and the coating rubber composition for belt layers, the content of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more, relative to 100 parts by mass of silica. The upper limit of the content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

Examples of poorly dispersible fillers include microfibrillated plant fibers, short fiber cellulose, gel compounds, etc. Among these, microfibrillated plant fibers are preferred.

As the microfibrillated plant fiber, cellulose microfibrils are preferred because they provide good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products, and examples include those derived from resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, and kenaf, as well as pulp, paper, cloth, agricultural waste, waste biomass such as food waste and sewage sludge obtained using these as raw materials, unused biomass such as rice straw, wheat straw, and thinned wood, as well as cellulose produced by sea squirts, acetic acid bacteria, and the like. These microfibrillated plant fibers may be used alone or in combination of two or more types.

In this specification, cellulose microfibrils typically refer to cellulose fibers having an average fiber diameter of 10 μm or less, and more typically refer to cellulose fibers having a microstructure formed by an assembly of cellulose molecules and an average fiber diameter of 500 nm or less. A typical cellulose microfibril is formed, for example, as an assembly of cellulose fibers having the average fiber diameter described above.

In the rubber composition for treads and the coating rubber composition for belt layers, the content of the poorly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

A plasticizer may be blended into the tread rubber composition and the belt layer covering rubber composition.
A plasticizer is a material that imparts plasticity to a rubber component, and examples of such a plasticizer include liquid plasticizers (plasticizers that are in a liquid state at room temperature (25° C.)) and resins (resins that are in a solid state at room temperature (25° C.)).

In the rubber composition for treads, the content of the plasticizer (total amount of plasticizer) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. Within the above range, the effect tends to be better obtained. Note that, when the above-mentioned extension rubber is used, the amount of the extension component used in the extension rubber is included in the content of the plasticizer.

In the coating rubber composition for the belt layer, the content of the plasticizer (total amount of plasticizer) is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less, and may be 0 parts by mass, per 100 parts by mass of the rubber component. If it is within the above range, the effect tends to be better obtained. Note that, when the above-mentioned extension rubber is used, the amount of the extension component used in the extension rubber is included in the content of the plasticizer.

Liquid plasticizers (plasticizers that are liquid at room temperature (25°C)) that can be used in the tread rubber composition and the belt layer coating rubber composition are not particularly limited, and examples include oils and liquid polymers (liquid resins, liquid diene-based polymers, etc.). These may be used alone or in combination of two or more types.

In the rubber composition for treads, the content of the liquid plasticizer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. Within the above range, the effect tends to be better obtained. The oil content is also preferably in a similar range.

In the coating rubber composition for the belt layer, the content of the liquid plasticizer is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less, and may be 0 parts by mass, per 100 parts by mass of the rubber component. If it is within the above range, the effect tends to be better. The oil content is also preferably within the same range.

Examples of the oil include process oil, vegetable oil, or a mixture thereof. Examples of the process oil include paraffin-based process oils such as MES (mild extract solvate), DAE (distillate aromatic extract), TDAE (treated distillate aromatic extract), TRAE (treated residual aromatic extract), and RAE (residual aromatic extract), aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Seiyu Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and Nisshin Oillio Group Co., Ltd. Among these, process oils (paraffin-based process oils, aromatic process oils, naphthene-based process oils, etc.) and vegetable oils are preferred. From the viewpoint of life cycle assessment, the above-mentioned oils may be lubricating oils used in rubber mixers and engines, or refined waste edible oils used in restaurants.

Liquid resins include terpene resins (including terpene phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, coumarone-indene resins (including coumarone and indene simple resins), phenol resins, olefin resins, polyurethane resins, acrylic resins, etc. Hydrogenated versions of these resins can also be used.

Liquid diene polymers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), liquid farnesene polymers, liquid farnesene butadiene copolymers, etc. that are liquid at 25°C. The ends or main chains of these may be modified with polar groups. Hydrogenated versions of these may also be used.

The above resins (resins in a solid state at room temperature (25°C)) that can be used in the rubber composition for the tread and the coating rubber composition for the belt layer include, for example, aromatic vinyl polymers in a solid state at room temperature (25°C), coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, and acrylic resins. The resins may also be hydrogenated. These may be used alone or in combination of two or more. Among these, aromatic vinyl polymers, petroleum resins, and terpene resins are preferred.

When the rubber composition for treads contains the above resin, the amount is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, and may even be 0 parts by mass, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

When the coating rubber composition for the belt layer contains the above resin, the amount is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, and may even be 0 parts by mass, per 100 parts by mass of the rubber component. Within the above range, the effect tends to be better.

The softening point of the resin is preferably 60° C. or higher, more preferably 70° C. or higher, and even more preferably 80° C. or higher. The upper limit is preferably 160° C. or lower, more preferably 130° C. or lower, and even more preferably 115° C. or lower. By keeping the softening point within the above range, durability tends to be improved.
The softening point of the resin is the temperature at which the ball drops when the softening point is measured using a ring and ball softening point tester as specified in JIS K6220-1: 2001. The softening point of the resin is usually 50°C ± 5°C higher than the glass transition temperature of the resin.

The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it can be a resin obtained by polymerizing α-methylstyrene and/or styrene, and specifically, it can be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, a copolymer of styrene and another monomer, etc.

The coumarone-indene resin is a resin that contains coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

The above coumarone resin is a resin that contains coumarone as the main monomer component that constitutes the resin skeleton (main chain).

The above-mentioned indene resin is a resin that contains indene as the main monomer component that constitutes the resin skeleton (main chain).

The phenolic resin may be, for example, a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural using an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

The above-mentioned rosin resins include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

The petroleum resins include C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, and hydrogenated versions of these resins. Of these, DCPD resins and hydrogenated DCPD resins are preferred.

The terpene resin is a polymer containing terpene as a structural unit. Examples include polyterpene resins obtained by polymerizing terpene compounds, and aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. Hydrogenated products of these resins can also be used.

The polyterpene resin is a resin obtained by polymerizing a terpene compound. The terpene compound is a hydrocarbon represented by the composition (C ₅ H ₈ ) _n and its oxygen-containing derivatives, and is a compound having a basic skeleton of a terpene classified into monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂ ), etc., and examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

The polyterpene resins mentioned above include pinene resin, limonene resin, dipentene resin, pinene/limonene resin, etc., which are made from the above-mentioned terpene compounds. Of these, pinene resin is preferred. Pinene resins usually contain both α-pinene and β-pinene, which are isomers, but depending on the components they contain, they are classified into β-pinene resins, which are mainly made of β-pinene, and α-pinene resins, which are mainly made of α-pinene.

The aromatic modified terpene resin may be a terpene phenol resin made from the above terpene compound and a phenolic compound, or a terpene styrene resin made from the above terpene compound and a styrene compound. Terpene phenol styrene resin made from the above terpene compound, a phenolic compound, and a styrene compound may also be used. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol. Examples of styrene compounds include styrene and α-methylstyrene.

The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, there is a styrene-acrylic resin such as a styrene-acrylic resin that has a carboxyl group and is obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component. Among them, a solvent-free carboxyl group-containing styrene-acrylic resin can be preferably used.

The above-mentioned solvent-free carboxyl group-containing styrene acrylic resin is a (meth)acrylic resin (polymer) synthesized by a high-temperature continuous polymerization method (high-temperature continuous bulk polymerization method) (methods described in U.S. Pat. No. 4,414,370, JP-A-59-6207, JP-B-5-58005, JP-A-1-313522, U.S. Pat. No. 5,010,166, Toa Gosei Kenkyuu Nenpo TREND 2000 Vol. 3, p. 42-45, etc.) with minimal use of auxiliary raw materials such as polymerization initiators, chain transfer agents, and organic solvents. In this specification, (meth)acrylic means methacryl and acrylic.

Examples of the acrylic monomer components constituting the acrylic resin include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters such as 2-ethylhexyl acrylate, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives. Note that (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

Examples of the aromatic vinyl monomer components constituting the acrylic resin include aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene.

In addition, other monomer components may be used in addition to (meth)acrylic acid, (meth)acrylic acid derivatives, and aromatic vinyl as monomer components constituting the acrylic resin.

Examples of the plasticizer that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries Co., Ltd., and Taoka Chemical Co., Ltd.

The rubber composition for the tread and the rubber composition for the coating of the belt layer preferably contain an antioxidant from the viewpoints of crack resistance, ozone resistance, etc.

The anti-aging agent is not particularly limited, but may be naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylene Examples of such antioxidants include p-phenylenediamine antioxidants such as diamines; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis.

In the rubber composition for the tread and the coating rubber composition for the belt layer, the content of the antioxidant is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.0 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

The rubber composition for the tread and the coating rubber composition for the belt layer preferably contain stearic acid.
In the rubber composition for tread and the coating rubber composition for belt layer, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 1.5 parts by mass or more, and still more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

The stearic acid used can be any known product, such as products from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Corp., Chiba Fatty Acid Co., Ltd., etc.

The rubber composition for the tread and the coating rubber composition for the belt layer preferably contain zinc oxide.
In the rubber composition for tread and the coating rubber composition for belt layer, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 12.0 parts by mass or less, more preferably 11.0 parts by mass or less, and even more preferably 10.0 parts by mass or less.

As zinc oxide, conventionally known products can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

Wax may be blended into the rubber composition for the tread and the rubber composition for covering the belt layer.
In the rubber composition for tread and the coating rubber composition for belt layer, the wax content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The wax content is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less.

The wax is not particularly limited, and examples include petroleum-based waxes and natural waxes. Synthetic waxes obtained by refining or chemically processing multiple waxes can also be used. These waxes may be used alone or in combination of two or more types.

Petroleum-based waxes include paraffin wax, microcrystalline wax, etc. Natural waxes are not particularly limited as long as they are derived from resources other than petroleum, and examples include vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

It is preferable to add sulfur to the rubber composition for the tread and the coating rubber composition for the belt layer, as this forms an appropriate amount of crosslinked chains in the polymer chains and provides good performance.

In the rubber composition for the tread and the coating rubber composition for the belt layer, the sulfur content is preferably 0.1 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.7 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, and even more preferably 4.0 parts by mass or less.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These may be used alone or in combination of two or more types.

The rubber composition for the tread and the coating rubber composition for the belt layer preferably contain a vulcanization accelerator.
In the rubber composition for tread and the coating rubber composition for belt layer, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization speed and crosslink density, but is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, relative to 100 parts by mass of the rubber component. The upper limit is preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, and even more preferably 4.0 parts by mass or less.

There are no particular restrictions on the type of vulcanization accelerator, and any commonly used accelerator can be used. Examples of the vulcanization accelerator include benzothiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among these, sulfenamide-based, guanidine-based, and benzothiazole-based vulcanization accelerators are preferred.

In addition to the above components, the rubber composition for the tread and the rubber composition for the belt layer may contain compounding agents that are commonly used in the tire industry, such as materials such as release agents.

It is desirable that the above-mentioned rubber composition be used for at least one rubber layer constituting the tread portion 4, but it is also desirable that the outermost rubber layer in the tire radial direction of the tread portion 4 (cap layer 30 in the example of FIG. 1) be composed of the above-mentioned suitable rubber composition.

The belt layer coating rubber composition may also contain an organic acid cobalt, a thermosetting resin, and the like.
Here, the thermosetting resin is a resin that undergoes a curing reaction when heated, and is a component that cannot be extracted with a solvent, unlike the resin contained in a plasticizer, so the two are distinguished from each other.

Examples of organic cobalt acids include cobalt stearate, cobalt naphthenate, cobalt neodecanoate, boron 3 cobalt neodecanoate, and cobalt abithienate. Commercially available products include those from Dainippon Ink and Chemicals, Inc. These may be used alone or in combination of two or more. Of these, cobalt stearate is preferred.

In the coating rubber composition for the belt layer, the content of the organic acid cobalt is preferably 0.1 parts by mass or more, and preferably 1.2 parts by mass or less, more preferably 0.8 parts by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of the rubber component, calculated as elemental cobalt. If it is within the above range, the effect tends to be better.

As thermosetting resins, resorcinol condensates (resorcinol resins) and phenolic resins can be suitably used. These may be used alone or in combination of two or more types.

（式中、ｎは１以上の整数である。） As the resorcinol condensate, for example, a compound (resin) represented by the following formula can be used.

(In the formula, n is an integer of 1 or more.)

（式中、ｎは１以上の整数であり、Ｒはアルキル基である。） The resorcinol condensate may be a modified resorcinol condensate. As the modified resorcinol condensate, for example, a compound (resin) represented by the following formula can be used.

(In the formula, n is an integer of 1 or more, and R is an alkyl group.)

Commercially available resorcinol condensates include those from Taoka Chemical Co., Ltd., Indospec, etc.

Phenolic resins are obtained by reacting phenol with aldehydes such as formaldehyde in the presence of an acid or alkali catalyst.

（式中、ｐは、１～９の整数であり、５～６が好ましい。） The phenolic resin may be modified with cashew oil, tall oil, rosin, etc. The modified phenolic resin is preferably a cashew oil modified phenolic resin. For example, a compound (resin) represented by the following formula can be used as the cashew oil modified phenolic resin.

(In the formula, p is an integer of 1 to 9, and preferably 5 to 6.)

Commercially available phenolic resins include those from Sumitomo Bakelite Co., Ltd.

In the coating rubber composition for the belt layer, the content of the thermosetting resin is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less. Within the above range, the effect tends to be better obtained.

In addition, the above-mentioned materials can be used in rubber compositions constituting components other than the tread portion 4 and belt layer 16 by appropriately changing the compounding amounts.

The rubber composition for the tread, the coating rubber composition for the belt layer, etc. can be produced by known methods, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing them.

As for the kneading conditions, in the base kneading process where additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes. In the finish kneading process where the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100°C or less, preferably room temperature to 80°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C.

Tires to which the present invention can be applied include pneumatic tires and non-pneumatic tires, with pneumatic tires being preferred. In particular, they can be used suitably as summer tires and winter tires (studless tires, snow tires, studded tires, etc.). Tires can be used as passenger car tires, large passenger car tires, large SUV tires, heavy-duty tires for trucks and buses, light truck tires, motorcycle tires, racing tires (high-performance tires), etc.

Tires can be manufactured by conventional methods. For example, in the unvulcanized stage, a rubber composition for the tread containing various materials is extruded to fit the shape of the tread portion, and a steel cord (steel monofilament) and a rubber composition for the belt layer containing various materials for covering the steel cord are combined and extruded to fit the shape of the belt layer, and together with other tire components, they are molded in a tire building machine by conventional methods to form an unvulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The above describes in detail a particularly preferred embodiment of the present invention, but the present invention is not limited to the illustrated embodiment and can be modified and implemented in various ways.

Below are examples (embodiments) that are considered to be preferable for implementation, but the scope of the present invention is not limited to these examples.

A pneumatic tire (test tire) for passenger cars having a size of 195/65R15 and having the basic structure shown in FIG. 1 is prototyped based on the specifications in Table 1.
The common specifications of the test tires are as follows:
Belt plies: 2 (2-layer belt layer)
Angle of belt cord in each belt layer with respect to the tire circumferential direction: 20 degrees (cross)
Belt cords in each belt layer: Steel cord

The cap layer and belt ply covering rubber (inner layer covering rubber and outer layer covering rubber) of each test tire are composed of the tread rubber composition and belt layer covering rubber composition with the formulation shown in Table 1.

Assuming that the specifications of the test tires were changed according to Table 1, the results were calculated based on the following evaluation method, and are shown in Table 1.
The reference comparative example is Comparative Example 6.

<Hardness measurement (H)>
According to JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness", the Shore hardness (H) of a test specimen (30 mm x 30 mm x 4 mm rectangular parallelepiped shape) made from the cap layer (vulcanized) of a test tire is measured with a Type A durometer (JIS-A hardness). The measurement is performed at 25°C. The value is the average value of five measurements.

<Durability>
The test tire is measured using a drum tester at a speed of 230 km/h on a drum under the conditions of a standard rim (6.0 J), internal pressure (260 kPa), load (4.56 kN), and ambient temperature of 25° C., and the running time until damage occurs is measured. The results are expressed as an index, with the standard comparative example being 100. The higher the index, the better the durability performance.

The materials for the tread compound (rubber composition for tread) in Table 1 are as follows.
SBR: HPR840 manufactured by JSR Corporation (Tg: -65°C, styrene content: 10% by mass, vinyl content: 42% by mass)
BR: BR150B (cis content 98% by mass) manufactured by Ube Industries, Ltd.
Silica: Ultrasil VN3 (manufactured by Evonik, _N2SA ^175m2 /g)
Carbon black N220: Diablack N220 (manufactured by Mitsubishi Chemical Corporation, N ₂ SA 114 m ² /g)
Oil: Diana Process Oil AH-24 (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Silane coupling agent: Si69 (manufactured by Evonik, bis(3-triethoxysilylpropyl)tetrasulfide)
Wax: Ozoace 0355 (manufactured by Nippon Seiro Co., Ltd.)
Antioxidant 6C: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant RD: Nocrac 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: NOF Corp. Zinc oxide: Three types of zinc oxide (Hakusui Tech Corp.)
Sulfur: Powdered sulfur (Tsurumi Chemical Industry Co., Ltd.)
Vulcanization accelerator CZ: Noccela CZ-G (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator DZ: Noccela DZ (N,N-dicyclohexyl-2-benzothiazolyl sulfenamide, DCBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

The materials of the coating rubber blend (coating rubber composition for belt layer) of the belt layer in Table 1 are as follows.
NR: TSR20
Carbon black N326: Diablack N326 (N ₂ SA: 80 m ² /g) manufactured by Mitsubishi Chemical Corporation
Oil: Diana Process Oil AH-24 (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Thermosetting resin: Sumikanol 620 (modified resorcinol condensate, softening point: 100° C.) manufactured by Taoka Chemical Co., Ltd.
Stearic acid: NOF Corp. Cobalt stearate: Cost-F (cobalt content: 9.5% by mass) manufactured by Dainippon Ink and Chemicals, Inc.
Antioxidant RD: Nocrac 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Zinc oxide: Three types of zinc oxide (manufactured by Hakusui Tech Co., Ltd.)
Sulfur: Powdered sulfur (Tsurumi Chemical Industry Co., Ltd.)
Vulcanization accelerator DZ: Noccela DZ (N,N-dicyclohexyl-2-benzothiazolyl sulfenamide, DCBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

The present invention (1) is a tire having a belt layer,
The belt layer includes a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1×4 structure in which four filaments are twisted together,
The belt cord has an outer diameter D (mm) of 0.50 mm or less,
The tire has a product (D×E) of an outer diameter D (mm) of the belt cord and a number E (pieces/50 mm) of the belt cords arranged in the tire width direction in a width direction cross section of the tire, which is 20.0 or more and 28.0 or less.

The present invention (2) is a tire according to the present invention (1), in which the cord-to-cord distance L (mm) of the belt cord in the tire width direction is 0.30 mm or more.

The present invention (3) is a tire according to the present invention (1) or (2), in which the cord-to-cord distance L (mm) of the belt cord in the tire width direction is 0.60 mm or less.

The present invention (4) has a tread portion,
The tire is an arbitrary combination with any of the present inventions (1) to (3), in which A is the radial distance from the tread surface to the belt layer on the tire equatorial plane, and B is the distance from the tread surface to the belt layer at an end in the tire width direction of the belt ply that is the outermost in the tire radial direction among the belt plies, and A/B is 1.08 or more and 1.22 or less.

The present invention (5) has a tread portion,
The tire is an arbitrary combination of any of the present inventions (1) to (4), in which the product (E×H) of the number E (pieces/50 mm) of belt cords arranged in the tire width direction and the hardness H of the cap tread constituting the outermost layer of the tread portion is 2920 or more and 4620 or less.

The present invention (6) is a tire that is an arbitrary combination with any of the present inventions (2) to (5), in which the product of D and L (D x L) is 0.12 or more and 0.28 or less.

The present invention (7) is a tire that is an arbitrary combination with any of the present inventions (2) to (6), in which the product of D, E, and L (D×E×L) is 8.5 or more and 12.0 or less.

The present invention (8) is a tire that is an arbitrary combination with any of the present inventions (4) to (7) in which the ratio of D to A/B (D/(A/B)) is 0.20 or more and 0.55 or less.

The present invention (9) is a tire that is an arbitrary combination with any of the present inventions (4) to (8), in which the ratio ((D×E)/(A/B)) of the product (D×E) of D and E to A/B is 20 or more and 35 or less.

The present invention (10) is a tire that is an arbitrary combination with any of the present inventions (5) to (9) in which the product of D and H (D×H) is 23 or more and 30 or less.

The present invention (11) is a tire that is an arbitrary combination with any of the present inventions (5) to (10), in which the product of D, E, and H (D×E×H) is 1590 or more and 1700 or less.

The present invention (12) is a tire in any combination with any of the present inventions (1) to (11), in which the ratio (D/G) of D to the groove depth G (mm) of the circumferential groove formed in the tread portion is 0.030 or more and 0.060 or less.

The present invention (13) is a tire in any combination with any of the present inventions (1) to (12), in which the ratio ((D×E)/G) of the product (D×E) of D and E to the groove depth G (mm) of the circumferential groove formed in the tread portion is 2.0 or more and 5.0 or less.

The present invention (14) is a tire that is an arbitrary combination with any of the present inventions (1) to (13), in which the number of belt cords arranged E (cords/50 mm) is 50 to 70 cords/50 mm.

The present invention (15) is a tire having a tread portion, and a hardness H of the cap tread constituting the outermost layer of the tread portion is 58 to 68, which can be arbitrarily combined with any of the present inventions (1) to (14).

Reference Signs List 2 Tire 4 Tread portion 6 Sidewall 8 Wing 10 Clinch 12 Bead 14 Carcass 16 Belt layer 17 Belt ply 17A Belt cord 17Ae Filament 17B Topping rubber (coating rubber)
18 Band layer 18A Organic fiber cord 18B Reinforcement rubber covering the organic fiber cord 20 Inner liner 22 Chafer 24 Tread surface 26 Groove 28 Base layer 30 Cap layer (cap tread)
32 bead core 34 bead apex 36 carcass ply 36a main portion 36b turn-up portion 38 inner layer (first belt ply)
40 Outer layer (second belt ply)
42 Main groove 44 Rib D Outer diameter CL of belt cord Tire equatorial plane L Cord distance in tire width direction of belt cord A Tire radial distance from tread surface to belt layer on tire equatorial plane B Distance from tread surface to belt layer at tire width direction end of tire radially outermost belt ply G Groove depth of circumferential groove formed in tread portion

Claims (15)

A tire having a belt layer,
The belt layer includes a belt ply,
The reinforcing material of the belt ply is a belt cord having a 1×4 structure in which four filaments are twisted together,
The belt cord has an outer diameter D (mm) of 0.50 mm or less,
The tire has a product (D×E) of an outer diameter D (mm) of the belt cord and a number E (pieces/50 mm) of the belt cords arranged in the tire width direction in a width direction cross section of the tire, which is 20.0 or more and 28.0 or less. The tire according to claim 1, wherein the cord-to-cord distance L (mm) of the belt cord in the tire width direction is 0.30 mm or more. The tire according to claim 1, wherein the cord-to-cord distance L (mm) of the belt cord in the tire width direction is 0.60 mm or less. A tread portion is provided.
2. The tire according to claim 1, wherein A is a radial distance from a tread surface to the belt layer on the tire equatorial plane, and B is a distance from the tread surface to the belt layer at an end in the tire width direction of the outermost belt ply in the tire radial direction among the belt plies, and A/B is 1.08 or more and 1.22 or less. A tread portion is provided.
2. The tire according to claim 1, wherein the product (E×H) of the number E (pieces/50 mm) of the belt cords arranged in the tire width direction and the hardness H of the cap tread constituting the outermost layer of the tread portion is 2920 or more and 4620 or less. The tire according to claim 2, wherein the product of D and L (D x L) is 0.12 or more and 0.28 or less. The tire according to claim 2, wherein the product of D, E, and L (D x E x L) is 8.5 or more and 12.0 or less. The tire according to claim 4, wherein the ratio of D to A/B (D/(A/B)) is 0.20 or more and 0.55 or less. The tire according to claim 4, wherein the ratio ((D×E)/(A/B)) of the product (D×E) of D and E to A/B is 20 or more and 35 or less. The tire according to claim 5, wherein the product of D and H (D x H) is 23 or more and 30 or less. The tire according to claim 5, wherein the product (D x E x H) of D, E, and H is 1590 or more and 1700 or less. The tire according to claim 1, wherein the ratio (D/G) of D to the groove depth G (mm) of the circumferential groove formed in the tread portion is 0.030 or more and 0.060 or less. The tire according to claim 1, in which the ratio ((D×E)/G) of the product (D×E) of D and E to the groove depth G (mm) of the circumferential groove formed in the tread portion is 2.0 or more and 5.0 or less. The tire according to claim 1, wherein the number of belt cords arranged E (cords/50 mm) is 50 to 70 cords/50 mm. A tread portion is provided.
2. The tire according to claim 1, wherein the hardness H of the cap tread constituting the outermost layer of the tread portion is 58 to 68.

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