JP6701982B2 - Tire with lugs - Google Patents

Description

The present invention relates to a tire with lugs.

Tires with lugs are used for agricultural machines such as tractors from the viewpoint of traction force and soil repellency. The lug extends obliquely from the vicinity of the tire equator toward the tread end, and the left lug and the right lug are alternately arranged on the tread in the rotation direction. Then, since the top surface of the lug is located on the outermost diameter side of the tire, the ground contact surface of the tire during traveling changes along the lug.

With the rotation of the tire, the ground contact point between the tire and the ground shifts from the equator to the tread end along one lug, and the ground contact point that reaches the tread end moves to the equator of the other lug, Further, along the other lug, the equator moves toward the tread end. At the time of traveling, such transition of the grounding point is repeated.

Although various tires with lugs are disclosed in Patent Documents 1 and 2, there is a problem that they are inferior in performance such as cut resistance and crack growth resistance. Further, there is a concern that the block of the rug may fall down while running and a wrinkle may be formed at the root part of the lug, resulting in damage to the tire. Therefore, it is desired to improve wrinkle resistance (suppressing formation of wrinkles at the root of the rug), cut resistance, crack growth resistance, and the like in a well-balanced manner.

JP-A-8-295106 JP-A-5-147408

An object of the present invention is to solve the above problems and provide a tire with lugs having improved wrinkle resistance, cut resistance, and crack growth resistance in a well-balanced manner.

The present invention relates to a lug tire having a tread provided with a lug, the lug tire comprising a rubber composition in which the lug satisfies the following formula (1) and the tread satisfies the following formula (2).
(1) Lug height/lug width ≤ 1.50
(2) E* at 70°C/tan δ≧25 at 70°C

The rubber composition preferably has a hardness Hs at 23° C. of 62 or more and a tan δ at 70° C. of 0.21 or less.

The rubber composition preferably contains styrene-butadiene rubber and butadiene rubber having a cis content of 80 mol% or more.

The rubber composition preferably has a carbon black content of 80 parts by mass or less and an acetone extraction amount of 18 parts by mass or less with respect to 100 parts by mass of the rubber component.

According to the present invention, there is provided a lug tire having a tread provided with a lug, wherein the lug satisfies the formula (1), and the tread is made of a rubber composition satisfying the formula (2). Therefore, wrinkle resistance, cut resistance, and crack growth resistance can be improved in a well-balanced manner.

FIG. 1 is a sectional view showing a part of a tire with a lug according to an embodiment of the present invention. FIG. 2 is a plan view showing a part of the tire shown in FIG. FIG. 3 is a side view showing the tire of FIG. 1.

The tire with lugs of the present invention has a tread provided with lugs, the lugs satisfy the formula (1), and the tread is made of a rubber composition satisfying the formula (2).

The ratio (E*/tan δ) of E* (complex elastic modulus) and tan δ (loss tangent) of the rubber composition (rubber composition after vulcanization) forming the tread of the tire with lugs satisfies the expression (2). That is, since the E* is large, the rug is hard to fall down, and the formation of wrinkles at the root part of the lug is suppressed, and the small tan δ makes it easy to restore even if wrinkles occur temporarily, and similarly Formation is suppressed.

In addition, by forming the rug satisfying the height of the rug/the width of the lug of the formula (1), the formation of wrinkles at the root portion of the lug is suppressed. Further, the rubber composition for tread satisfying the formula (2) and the lug shape of the formula (1) also ensure the cut resistance and crack growth resistance. Therefore, the lugged tire of the present invention satisfying the formulas (1) and (2) has a well-balanced improvement in wrinkle resistance, cut resistance, and crack growth resistance.

Hereinafter, an example of the tire with lugs of the present invention will be described with reference to the drawings as appropriate.

FIG. 1 is a sectional view showing a part of a tire 2 with a lug according to an embodiment of the present invention. FIG. 2 is a plan view showing a part of the tire 2 of FIG. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the plane of the drawing is the rotational direction of the tire 2. The dashed-dotted line CL in FIG. 1 represents the equatorial plane of the tire 2. In FIG. 2, the arrow line A represents the rotation direction of the tire 2 when the vehicle is traveling. The tire 2 is incorporated in a rim 4, and a tube 6 provided inside the tire 2 is filled with air. The tire 2 includes a tread 8, sidewalls 10, beads 12, a carcass 14, a rubber sheet layer 16 and a reinforcing layer 18. The tire 2 is a pneumatic tire with a tube. The tire 2 has a substantially symmetrical shape centered on the one-dot chain line CL in FIG.

The tread 8 is made of crosslinked rubber and has a shape that is convex outward in the radial direction. The tread 8 is provided with a lug 22 extending substantially outward in the radial direction on a tread surface 20 formed on the outer surface thereof.

The rubber composition forming the tread 8 satisfies the following formula (2).
(2) E* at 70° C./tan δ≧70 at 70° C.
When E* (complex elastic modulus) and tan δ (loss tangent) satisfy Expression (2), good wrinkle resistance is imparted. Further, excellent cut resistance and crack growth resistance are imparted, and wrinkle resistance and cut resistance and crack growth resistance can both be achieved.

The rubber composition satisfying the formula (2) can be produced by a method such as adjusting the amount of acetone extracted from the rubber composition to a predetermined value or less and adjusting the carbon black content to a predetermined value or less. More specifically, for example, by increasing the hardness Hs by decreasing the amount of extracted acetone and decreasing tan δ by decreasing the amount of carbon black, the balance between Hs and tan δ becomes good, and a rubber composition satisfying the formula (2) is obtained. Can be obtained.

In the rubber composition, E* at 70° C./tan δ at 70° C. is more preferably 27 or more, further preferably 30 or more. The upper limit is not particularly limited, but is preferably 54 or less from the viewpoint of chipping resistance.

The E* (complex elastic modulus) at 70° C. of the rubber composition is preferably 5.5 MPa or more. Thereby, excellent wrinkle resistance is obtained. The pressure is more preferably 6.0 MPa or more, further preferably 6.3 MPa or more. The upper limit is not particularly limited, but is preferably 9.7 MPa or less from the viewpoint of chipping resistance.

The rubber composition preferably has a tan δ (loss tangent) at 70° C. of 0.21 or less. Thereby, the formed wrinkles are easily restored and excellent wrinkle resistance is obtained. The lower limit is not particularly limited, but 0.15 or more is preferable from the viewpoint of chipping/cutting resistance.

The rubber composition preferably has a hardness (Hs) at 23° C. of 62 or more. As a result, the rug does not easily fall down and excellent wrinkle resistance is obtained. 64 or more is more preferable. The upper limit is not particularly limited, but from the viewpoint of chipping resistance performance, 80 or less is preferable, and 75 or less is more preferable.

The rubber composition preferably has an acetone extraction amount of 18% by mass or less. In this case, a rubber composition satisfying the formula (2) is obtained, the hardness Hs and tan δ are well balanced, and excellent wrinkle resistance is imparted. 15 mass% or less is more preferable, and 13 mass% or less is still more preferable. The lower limit is not particularly limited, but is preferably 5% by mass or more, more preferably 10% by mass or more.

The E*, tan δ, hardness, and acetone extraction amount of the rubber composition can be measured by the measuring methods of Examples described later.

As the rubber composition composing the tread 8, one containing a rubber component, a filler and the like can be used.

As the rubber component, natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), modified BR, styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene Materials generally used for rubber compositions for tires include propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and the like. Among them, SBR can be preferably used from the viewpoint of cut resistance, and BR can be preferably used from the viewpoint of crack growth resistance. It is also preferable to use NR in addition to SBR and BR.

As the SBR, materials known in the tire field such as emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR) can be used.

The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 30% by mass or less, and further preferably 25% by mass or less. If it exceeds 60% by mass, the cut resistance tends to decrease. In the present specification, the styrene content of SBR can be calculated by H ¹ -NMR measurement.

When the rubber composition contains SBR, the content of SBR is preferably 25% by mass or more and more preferably 40% by mass or more in 100% by mass of the rubber component. If it is less than 25% by mass, the cut resistance tends to decrease. The SBR content is preferably 80% by mass or less, more preferably 60% by mass or less. If it exceeds 80% by mass, the tan δ value may increase.

As the BR, a material known in the tire field can be used.
From the viewpoint of crack growth resistance, the cis content of BR is preferably 80 mol% or more, more preferably 90 mol% or more, and further preferably 95 mol% or more. In the present specification, the cis content of BR (the amount of cis-1,4-bonded butadiene units) can be measured by an infrared absorption spectrum analysis method.

When the rubber composition contains BR, the content of BR is preferably 5% by mass or more and more preferably 20% by mass or more in 100% by mass of the rubber component. If it is less than 5% by mass, crack growth resistance tends to decrease. Further, the content of the BR is preferably 60% by mass or less, more preferably 40% by mass or less. If it exceeds 60% by mass, the cut resistance tends to decrease.

As NR, those commonly used in the rubber industry such as RSS#3 and TSR20 can be used.

When the rubber composition contains NR, the content of NR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, the required mechanical strength may not be obtained. The NR content is preferably 50% by mass or less, more preferably 30% by mass or less. If it exceeds 50% by mass, the cut resistance and crack growth resistance tend to decrease.

The rubber composition preferably contains known fillers such as white fillers such as carbon black and silica.

When the rubber composition contains carbon black, its nitrogen adsorption specific surface area (N ₂ SA) is preferably 15 m ² /g or more, more preferably 20 m ² /g or more. If it is less than 15 m ² /g, the reinforcing property tends to decrease, and desired performance tends not to be obtained. Further, the N ₂ SA is preferably 150 m ² /g or less, more preferably 100 m ² /g or less, still more preferably 80 m ² /g or less. If it exceeds 150 m ² /g, tan δ tends to increase. The N ₂ SA of carbon black can be measured according to the method A of JIS K6217.

Further, the adsorption specific surface area (CTAB) of cetyltrimethylammonium bromide of carbon black is preferably 0.90 m ² /g or more, more preferably 0.93 m ² /g or more. If it is less than 0.90 m ² /g, the reinforcing property tends to decrease, and desired performance tends not to be obtained. The upper limit is not particularly limited, but it is preferably 1.20 m ² /g or less, more preferably 1.00 m ² /g or less. Within the above range, the performance balance between low fuel consumption and wear resistance is remarkably improved. The CTAB of carbon black can be measured according to JIS K6217-3:2001.

In the rubber composition, the content of carbon black with respect to 100 parts by mass of the rubber component is preferably 80 parts by mass or less, more preferably 70 parts by mass or less. By adjusting the amount to 70 parts by mass or less, a rubber composition satisfying the formula (2) is produced, tan δ is reduced, and the restoring force of the rubber is strengthened, so that the generation of wrinkles can be suppressed. The lower limit is not particularly limited, but is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 50 parts by mass or more.

The lug 22 provided on the tread surface 20 starts from the equatorial plane and extends so as to be widened toward the bottom in the rotation direction.

The lug 22 has a shape that satisfies the following formula (1).
(1) Lug height/lug width ≤ 1.50
This imparts wrinkle resistance. The lug height (mm)/lug width (mm) is preferably 1.45 or less, and more preferably 1.40 or less. Although the lower limit is not particularly limited, it is preferably 1.25 or more, more preferably 1.30 or more, still more preferably 1.33 or more.

The lug height LH is preferably 30 to 50 mm, more preferably 35 to 45 mm. If it is less than 30 mm, the traction performance may decrease. If it exceeds 50 mm, the lug may easily fall down.

The lug width LW is preferably 20 mm or more, more preferably 25 mm or more. If it is less than 20 mm, the ground contact area becomes small, and the wear performance may deteriorate. The upper limit is not particularly limited.

Here, as shown in FIG. 1, the lug height LH is the vertical height from the tread surface 20h (bottom of the lug) to the apex 22h of the lug 22 on the tire equatorial plane. As shown in FIG. 2, the lug width LW is the width (length) of the lug in a direction orthogonal to the extending direction of the lug at the central portion in the tread width direction.

The lug 22 is composed of a first lug 34 and a second lug 36. The first lug 34 is on one tread surface 20 with the equatorial plane interposed, and the second lug 36 is on the other tread surface 20. The first lugs 34 and the second lugs 36 are alternately arranged on the tread surface 20 in the rotation direction.

The double-headed arrow line WT represents the tread width at which the tread ends Te located on the left and right are connected. The broken line LT in FIG. 2 represents a tread end line that connects the tread ends Te in the rotational direction.

The sidewall 10 of FIG. 1 extends substantially inward in the radial direction from the end of the tread 8. The sidewall 10 is made of crosslinked rubber. The sidewall 10 absorbs a shock from the road surface by bending. Further, the sidewall 10 prevents the carcass 14 from being damaged.

The bead 12 extends substantially inward in the radial direction from the sidewall 10. The bead 12 includes a core 26 and an apex 28 extending outward from the core 26 in the radial direction. The core 26 is ring-shaped and includes a plurality of non-stretchable wires (typically steel wires). The apex 28 has a tapered shape that tapers outward in the radial direction and is made of a crosslinked rubber having a high hardness.

The carcass 14 includes a first carcass ply 30 and a second carcass ply 32. The first carcass ply 30 and the second carcass ply 32 are bridged between the beads 12 on both sides, and extend along the inside of the tread 8 and the sidewall 10. The first carcass ply 30 and the second carcass ply 32 are wound around the core 26 from the inner side toward the outer side in the axial direction.

The first carcass ply 30 and the second carcass ply 32 are composed of a carcass cord and a topping rubber (not shown). The first carcass ply 30 and the second carcass ply 32 are inclined with respect to the equatorial plane. The angle of the carcass cord of the first carcass ply 30 with respect to the equatorial plane is opposite to the angle of the carcass cord of the second carcass ply 32 with respect to the equatorial plane. Carcass cords usually consist of organic fibers. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

The rubber sheet layer 16 is located inside the tread 8 in the radial direction. The rubber sheet layer 16 is laminated with the carcass 14. The rubber sheet layer 16 reinforces the center of the tread 8. The rubber sheet layer 16 is made of crosslinked rubber.

The reinforcing layer 18 is located outside the rubber sheet layer 16 in the radial direction. The reinforcing layer 18 is laminated with the rubber sheet layer 16. The reinforcing layer 18 reinforces the center of the tread 8. The reinforcing layer 18 is composed of a cord and a topping rubber. The material of this cord is steel or organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers. The cord is inclined with respect to the equatorial plane.

FIG. 3 is a side view showing the tire 2 of FIG. The direction perpendicular to this paper surface corresponds to the axial direction of the tire 2. The arrow line A represents the rotation direction of the tire 2 when the vehicle is traveling. The first lugs 34 are lined up in the rotational direction on the front side of this paper surface. A point PS represents an end portion of the lug 22 that is located on the axially outer side of the lug 22 and located at the rear end in the rotation direction. Point PU represents the tip of the lug on the equatorial plane. The circumference LT is a tread edge line to which the tread edge Te is connected. The circumference LS is a lug outer diameter line connecting the points PS.

The dimensions and angles of the tire 2 of the present invention are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. No load is applied to the tire 2 during the measurement. In the present specification, the regular rim means a rim defined in the standard on which the tire 2 depends. The “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, and the “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means the internal pressure defined in the standard on which the tire 2 depends. "Maximum air pressure" in the JATMA standard, "maximum value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLUTION PRESSURES" in the TRA standard, and "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures.

The present invention will be specifically described based on Examples, but the present invention is not limited thereto.

Various chemicals used for the tread of the test tire will be described below.
NR: TSR20
SBR1502: SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (styrene content: 23.5 mass%)
SBR1723: SBR1723 manufactured by JSR Corporation (styrene content: 23.5 mass%, oil content: 27.3 mass%)
BR1280: BR Chem manufactured by LG Chem (cis content: 96 mol%)
Carbon black N220: Cabot Japan Co., Ltd. show black ^{_{N220 (N 2 SA: 114m 2}} /g,CTAB:0.91m 2 / g)
Carbon black N330: Cabot Japan Co., Ltd. show black ^{_{N330 (N 2 SA: 78m 2}} /g,CTAB:0.96m 2 / g)
Resin: SP1068 resin oil manufactured by Nippon Shokubai Co., Ltd.: Diana Process AH40 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: stearic acid "Tsubaki" manufactured by NOF Corporation
Zinc oxide: Mitsui Mining & Smelting Co., Ltd. zinc oxide sulfur (containing 5% oil): Hosoi Chemical Co., Ltd. HK-200-5
Vulcanization accelerator CZ: Noxceller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator DM: Noxcellar DM (dibenzothiazolyl disulfide) manufactured by Ouchi Shinko Chemical Co., Ltd.

(tread)
According to the tread composition shown in Table 1 below, the chemicals other than sulfur and the vulcanization accelerator were kneaded using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were kneaded into the obtained kneaded product using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was applied to the tread of the lugged tire of each of Examples and Comparative Examples described below.

[Examples and Comparative Examples]
A rugged agricultural tire of each of Examples and Comparative Example 1 having the basic configuration shown in FIG. 1 and having the specifications (tread composition, tread rubber physical properties, lug shape) shown in Table 1 below was produced. The tire size is 13.6-26 6PR. As the carcass, the first carcass ply and the second carcass ply were used. The cord material used for the first carcass ply and the second carcass ply is nylon fiber. The angle formed by the cord with respect to the rotation direction is 35°. The hardness (durometer A hardness) of the crosslinked rubber forming the rubber sheet layer is 78. The cord material of the reinforcing layer is steel. The angle formed by the cord with respect to the rotation direction is 50°.

The produced test tires were subjected to the following evaluations. The results are shown in Table 1.
(Acetone extraction amount (AE amount))
Each rubber test piece was immersed in acetone for 24 hours to extract soluble components. The mass of each test piece before and after extraction was measured, and the acetone extraction amount was calculated by the following calculation formula. In addition, each rubber test piece used what was cut out from the tread of each test tire.
Acetone extraction amount (%)=(mass of rubber test piece before extraction−mass of rubber test piece after extraction)/mass of rubber test piece before extraction×100

(Hardness (Hs))
The hardness Hs at 23° C. of each rubber test piece was measured by a type A durometer according to JIS K6253 “Hardness test method for vulcanized rubber and thermoplastic rubber”. In addition, each rubber test piece used what was cut out from the tread of each test tire.

(Complex elastic modulus (E*), loss tangent (tan δ))
Using a spectrometer manufactured by Kamijima Seisakusho, dynamic strain amplitude 1%, frequency 10 Hz, temperature 70° C., complex elastic modulus E* (MPa) at 70° C. of each rubber test piece, loss tangent tan δ at 70° C. Was measured. In addition, each rubber test piece used what was cut out from the tread of each test tire.

(Wrinkle resistance)
Each of the left and right test tires using the compounded tread in Table 1 was attached to the left and right of the agricultural machine, and the land cruiser was towed to run (the running direction was reversed every 30 minutes to eliminate the left-right difference). After running for 6 hours, the appearance of the tire was checked every hour and the occurrence of wrinkles was evaluated. In Comparative Example 1, the wrinkle length (wrinkle length) at the time when wrinkles occurred (wrinkle generation time) was measured and used as a reference (index 100). In the example, no wrinkle was generated even after running for 6 hours.

From Table 1, in comparison with the comparative example, the agricultural tire with lugs of the example was sufficiently suppressed in wrinkles, and at the same time, excellent crack growth resistance and cut resistance were obtained, and these performances were improved in a well-balanced manner. It became clear that it will be done.

Further, for example, using a tread including NR 82 parts by mass, SBR 18 parts by mass, carbon black N220 61 parts by mass, etc., tire specifications (lug height LH/lug width LW: 2.12, lug height LH: 56.5 mm, In the agricultural tire with lugs having a lug width LW: 26.6 mm, wrinkles were generated at a time corresponding to the wrinkle generation index 175, and the length thereof was equivalent to the wrinkle length index 60. The amount of extracted acetone was 11.3%, the hardness Hs was 69, the E* was 6.4 MPa, the tan δ was 0.167, and the E*/tan δ was 38.3. Thus, in the case of lug height/lug width>1.50, the wrinkle resistance was poor and the performance balance was poor.

The tire with lugs of the present invention can be applied to various agricultural machines.

2 tire 4 rim 6 tube 8 tread 10 sidewall 12 bead 14 carcass 16 rubber sheet layer 18 reinforcing layer 20 tread surface 20h tread surface at tire equatorial surface 22 lug 22h lug apex 26 core 28 apex 30 first carcass ply 32 Two-carcass ply 34 First lug 36 Second lug LH Rug height LW Rug width

Claims (4)

A tire with a lug having a tread with a lug,
The lug satisfies the following formula (1),
A tire with a lug, wherein the tread is made of a rubber composition satisfying the following formula (2).
(1) Lug height/lug width ≤ 1.50
(2) E* at 70°C/tan δ≧25 at 70°C The lugged tire according to claim 1, wherein the rubber composition has a hardness Hs at 23°C of 62 or more and a tan δ at 70°C of 0.21 or less. The tire with lugs according to claim 1, wherein the rubber composition contains styrene-butadiene rubber and butadiene rubber having a cis content of 80 mol% or more. The tire with a lug according to claim 1, wherein the rubber composition has a carbon black content of 80 parts by mass or less and an acetone extraction amount of 18 parts by mass or less with respect to 100 parts by mass of the rubber component.

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