JP2007210552A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing heat release performance of a tire center part, effectively reducing heat generation on a belt layer and further improving wear resistance. <P>SOLUTION: In the pneumatic tire, a plurality of lug grooves 22 are arranged in a tread part, and narrow grooves 24 having 20 mm or less of width are arranged in the width direction in a center part between two tire circumferences formed by connecting terminal positions of the lug grooves 22 with each other. A main groove having 70 mm or more of depth is provided. A circumferential shallow groove 26 is provided in the center part, and in a region having 25% of tread width around an equator, excluding the circumferential groove 26, a negative rate is below 8%. Tread rubber has a two-layer structure comprising cap rubber on a tread surface part and base rubber contacting belt coating rubber, The pneumatic tire is provided with a sheet member in which thermal conductivity of a rubber sheet below the base rubber is 1.3 times larger than those of the tread rubber and the base rubber and which has an end part exposed to the side direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire. More specifically, the present invention efficiently reduces heat generation on a belt layer and improves low heat generation and wear resistance of a tire tread, thereby increasing the demand for pneumatic construction vehicles. The present invention relates to a pneumatic tire suitable for a tire.

  Conventionally, in a construction vehicle tire having a so-called lug pattern in which a large number of lug grooves are arranged at predetermined intervals, in order to improve the wear resistance, a tread rubber having good wear resistance is used and a tread volume is reduced. It is common to use means such as increasing the tread pattern (deepening the groove), decreasing the negative rate, and increasing the land rigidity.

  However, when the wear resistance is improved by using the above-mentioned means, in particular, there is a tendency to cause deterioration of the heat generation of the tread portion at the time of tire rolling, and this deterioration of heat generation is caused by the heat of the tread portion. This could cause a failure such as separation. Accordingly, a tread rubber / base rubber having good heat generation while maintaining wear resistance is required. However, heat generation and wear resistance are contradictory, and there is a limit in meeting the needs of users to a high degree.

In particular, the land portions of the two tire circumferences formed by tying the end positions of the lug grooves substantially in the tire circumferential direction have a small heat radiation area, so the heat generation temperature tends to increase.
For this reason, in recent years, a technology has been developed in which a narrow groove having a width of 20 mm or less is arranged in the land portion in order to minimize the decrease in tread volume, minimize the decrease in land portion rigidity, and increase the heat radiation area. (For example, see Patent Documents 1 and 2).

  Recently, however, the deterioration of the heat generation of the tread portion tends to become more prominent due to the increase in tire size, flattening and heavy load accompanying the increase in size of construction vehicles. It is still important to suppress the heat generation.

On the other hand, conventionally, in order to reduce heat generation, methods such as using low-grade carbon, suppressing the number of carbon parts used or reducing the total amount of filler, and lowering the polymer Tg (glass transition point) have been implemented. ing. In addition, the use of carbon fibers for improving thermal conductivity is known (see, for example, Patent Documents 3 and 4).
However, in spite of the severe market requirements for low heat buildup and friction resistance, the present inventor has required tires to reduce heat buildup by using certain low grade carbon or the like and to improve heat conductivity using carbon fiber. It has been found that it is extremely difficult to achieve both the thermal characteristics and the wear resistance.
JP-A-2001-213120 (Claims, Examples, etc.) JP 2000-233610 A (Claims, Examples, etc.) Japanese Patent Laid-Open No. 8-127664 (Claims, Examples, etc.) International Publication No. WO03 / 050181 Pamphlet

  In view of the above conventional problems, the present invention improves the heat dissipation of the tire center part, efficiently reduces the heat generation on the belt layer, and improves the low heat generation and wear resistance of the tire tread. An object of the present invention is to provide a pneumatic tire suitable for a pneumatic tire for construction vehicles, which is demanding.

In order to solve various problems in the prior art, the present inventor has made various tires as prototypes and examined them. As a result, the present inventor has found that it is very difficult to maintain the wear resistance although the calorific value is reduced and the heat dissipation is improved only by improving the heat generation and heat conductivity of the rubber itself. did.
Under such knowledge, the present inventor has studied in detail a tire that can improve heat generation and heat dissipation while maintaining sufficient wear resistance. As a result, the present inventor arranges a plurality of lug grooves extending from the respective tread ends toward the tire equatorial plane in the tread portion, and substantially connects the terminal positions of these lug grooves in the tire circumferential direction. In a pneumatic tire having a main groove with a depth of 70 mm or more, a narrow groove with a width of 20 mm or less is arranged in the width direction at the center portion between two tire circumferences formed by the structure of the tire center portion And a structure having a sheet member having a specific thermal conductivity, etc., by making the base rubber of the portion in contact with the cap rubber of the tread rubber surface portion and the belt coating rubber into a two-layer structure, etc. The inventors have found that a desired pneumatic tire can be obtained, and have completed the present invention.

That is, the present invention resides in the following (1) to (8).
(1) A large number of lug grooves extending from the respective tread ends toward the tire equatorial plane are disposed in the tread portion, and the terminal positions of these lug grooves are substantially connected in the tire circumferential direction 2. In a pneumatic tire having a main groove having a depth of 70 mm or more, a narrow groove having a width of 20 mm or less is disposed in the center portion between the tire circumferences, and extends along the tire circumferential direction in the center portion. The tread rubber has a two-layer structure with a shallow groove in the circumferential direction and the tread rubber is in contact with the cap rubber on the surface of the tread and the belt coating rubber. The thermal conductivity of the rubber sheet under the base rubber is the tread rubber. A pneumatic tire characterized by having a sheet member that is 1.3 times or more than the base rubber and whose end is exposed to the side.
(2) The tread rubber has a two-layer structure of a base rubber in a portion where the tread surface portion is in contact with the cap rubber and the belt coating rubber, and the thermal conductivity of the rubber sheet under the base rubber is 1 than that of the tread rubber and the base rubber. The pneumatic tire according to (1), wherein the pneumatic tire has a sheet member that is three times or more and whose end is exposed to the side and covers the sides of the tread rubber and the base rubber.
(3) The tread rubber has a two-layer structure of the base rubber at the portion where the tread rubber is in contact with the cap rubber on the surface of the tread and the thermal conductivity of the base rubber is 1.3 times or more than that of the tread cap rubber. The thermal conductivity of the rubber sheet under the base rubber is 1.3 times or more than that of the tread cap rubber, and its end is exposed to the side, and the tread rubber and the base rubber side are covered. The pneumatic tire according to (1), wherein the pneumatic tire has a seat member.
(4) The pneumatic tire according to any one of (1) to (3), wherein the base rubber and the sheet member contain carbon fibers.
(5) The pneumatic tire according to (4) above, wherein the carbon fiber is a vapor-grown carbon fiber.
(6) The pneumatic tire according to any one of (1) to (5), wherein a groove depth of the circumferential shallow groove is 25% or less of the lug groove depth.
(7) The pneumatic tire according to any one of (1) to (6), wherein a groove width of the circumferential shallow groove is not less than 30 mm and not more than 50 mm.
(8) The pneumatic tire described in any one of (1) to (7) above, wherein the pneumatic tire is a pneumatic tire for construction vehicles.
In the present invention, the “tread end” means that a pneumatic tire is mounted on a standard rim defined in JATMA YEAR BOOK (2002 edition, Japan Automobile Association Standard), and is applied in JATMA YEAR BOOK. Fills 100% of the air pressure (maximum air pressure) with respect to the maximum load capacity (internal pressure-load capacity correspondence table) as the internal pressure, and indicates the outermost contact portion in the tire width direction when the maximum load capacity is applied. In addition, when TRA standard and ETRTO standard are applied in a use place or a manufacturing place, it follows each standard.

  According to the present invention, the heat dissipation of the tire center portion can be improved, the heat generation on the belt layer can be efficiently reduced, and the wear resistance can be further improved. A pneumatic tire, in particular, a pneumatic tire for construction vehicles, in which heat separation failure is prevented by effectively suppressing and dissipating heat generated in the portion (particularly the center portion) is provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 to 3 show a pneumatic tire for a construction vehicle according to a first embodiment of the present invention. FIG. 1 is a sectional view in the tire radial direction, FIG. 2 is a radial sectional view of a tread portion, and FIG. 3 (A) and 3 (B) are a plan view and a tire radial direction cross-sectional view showing the tread portion, respectively.
As shown in FIGS. 1 and 2, the pneumatic tire 10 for a construction vehicle according to the first embodiment of the present invention includes a carcass 12 whose both ends are folded back by bead cores 11. The carcass 12 is composed of one layer or a plurality of layers.

  A belt layer 14 in which a plurality of belt plies are stacked is embedded on the outer side in the tire radial direction of the crown portion 12 </ b> C of the carcass 12. A tread portion 18 having grooves is formed on the outer side of the belt layer 14 in the tire radial direction.

In the present embodiment, the tread rubber of the tread portion 18 has a two-layer structure of a cap rubber (first tread rubber) 18a on the tread surface portion and a base rubber (second tread rubber) 18b in contact with the belt coating rubber 15; The rubber sheet under the base rubber 18b has a sheet member 19 whose thermal conductivity is 1.3 times or more than that of the cap rubber 18a and the base rubber 18b and whose end is exposed to the side. . In the present invention, the tread rubber has a two-layer structure of the base rubber (second tread rubber) 18b in contact with the cap rubber 18a on the tread surface portion and the belt coating rubber 15 because a heat radiation effect is expected. is there.
In the present invention, the cap rubber 18a of the tread portion 18 is formed with a groove (tread pattern) having a specific shape / structure having a road surface grounding portion in contact with the road surface, as will be described later.
The tread portion 18 has a two-layered cap base structure including a base rubber 18b in contact with the belt coating rubber and a cap rubber 18a on the base rubber. Undercushion rubber (TUC) can also be provided.

The thermal conductivity of the sheet member 19 under the base rubber 18b is 1.3 times or more, preferably 1.4 times or more, more preferably 1.5 times or more than that of the red rubber cap rubber 18a and the base rubber 18b. Preferably, it has a predetermined thermal conductivity of 1.7 times or more.
The first and second tread rubber members can have various shapes. For example, in the case of a structure in which a tread undercushion rubber is provided on the lower side of a tread portion or a base two-layer structure, a bulging portion or the like is formed on a part of the base rubber or the tread undercushion rubber, and the bulging portion or the like is formed on the tread. It can expose to the surface of a part and can be set as a 1st tread rubber member.

  Further, as described above, when the tread portion includes the base rubber 18b and the first tread rubber 18a, or when the tread undercushion rubber is provided below the tread portion, the first tread rubber portion 18a It can be formed as a surface rubber member separate from the tread undercushion rubber. In such a case, the surface layer rubber member as the first tread rubber member can be disposed so as to be in contact with the base rubber, the tread undercushion rubber, or the like directly or through another member.

  Each of the first and second tread rubber members 18a and 18b is a rubber composition produced by blending various rubber components, various fillers, etc., or a commonly used compounding agent, and the like. It can be manufactured by placing in a predetermined position of the tread portion and vulcanizing.

As shown in FIG. 2, the sheet member 19 has a thermal conductivity of the rubber sheet below the base rubber 18b that is 1.3 times or more than that of the first tread rubber 18a and the base rubber 18b, and the end thereof is a side. It has a structure exposed to. The sheet member 19 is also produced by blending various rubber components, various fillers, etc., or a commonly used compounding agent, etc., and arranging the rubber composition at a predetermined position where the sheet member is disposed. And can be produced by vulcanization.
A method for making the thermal conductivity of the sheet member 19 1.3 times or more that of the first tread rubber 18a (and the base rubber 18b) is not particularly limited. Preferably, from the viewpoint of workability and cost, as a method for easily increasing the thermal conductivity, carbon fibers, preferably carbon fibers are blended in the sheet member 19, and more preferably carbon fibers produced by a vapor phase growth method, In particular, it is desirable to mix vapor growth carbon fiber. The carbon fiber may be fiber-shaped or tube-shaped (hollow).

Usually, the thermal conductivity of a tread rubber member blended with styrene butadiene rubber (SBR) is 1.1 to 1.2 times that of a tread rubber member blended with natural rubber (NR). Although it may vary depending on other blending factors, it is better to blend carbon fibers in order to change greatly.
Preferably, the carbon fiber has an average diameter of 0.5 μm or less when viewed in cross section. If the average diameter is 0.5 μm or less, carbon fiber is kneaded with the rubber component to improve the wear resistance of the vulcanized rubber, and the thermal conductivity is almost equal to or higher than that of metal powder. And the rubber temperature can be lowered quickly. When the average diameter exceeds 0.5 μm, it is not preferable because it is accompanied by a significant decrease in wear resistance.

  More preferably, the carbon fibers are in the range of an average diameter of 0.5 to 500 nm, in particular 1 to 400 nm. When the average diameter falls within the range of 0.5 to 500 nm, particularly 1 to 400 nm, dispersion into the rubber component can be appropriately achieved during kneading, and the thermal conductivity of the vulcanized rubber is sufficiently enhanced. Further, the wear resistance is not lowered. In particular, the carbon fiber is preferably made of nanofibers or nanotubes.

Preferably, the carbon fibers are in the range of 0.5 to 50 μm, in particular 1 to 40 μm in length. If the length is in the range of 0.5 to 50 μm, particularly in the range of 1 to 40 μm, the dispersibility of the carbon fiber in the rubber component during kneading is good, and the aspect ratio is 10 or more, particularly 15 or more. Therefore, sufficient abrasion resistance and thermal conductivity can be imparted to the rubber composition.
If the carbon fiber length is less than 0.5 μm, the production thereof is difficult, a sufficient aspect ratio cannot be obtained, and the blending effect may not be sufficiently exhibited. On the other hand, if the carbon fiber length exceeds 50 μm, the rubber composition may not have sufficient wear resistance. Moreover, if the aspect ratio of the carbon fiber is less than 10, the blending effect may not be sufficiently exhibited.

  The carbon fiber satisfying the above conditions is not particularly limited in its production method, but is desirably a vapor growth carbon fiber produced by a vapor deposition method. Examples of such carbon fibers include VGCF manufactured by Showa Denko Co., Ltd.

As for carbon fiber, 1-50 mass parts is desirable with respect to 100 mass parts of rubber components, More preferably, it is 5-30 mass parts. When the amount is less than 1 part by mass, the effect of improving the thermal conductivity is small. When the amount is more than 50 parts by mass, workability and wear resistance are remarkably lowered, and the cost tends to be disadvantageous.
In addition, there is no restriction | limiting in particular regarding the polymer to mix | blend, a filler, etc. By blending carbon fiber into the sheet member 19, a heat dissipation effect can be easily achieved.

  Examples of the rubber component used for the tread rubber (18a, 18b) and the sheet member 19 include at least one selected from the group consisting of natural rubber and synthetic rubber. As a synthetic rubber, it can select suitably from well-known things according to the objective. Conjugated rubber is particularly preferable, and it is preferable to appropriately select at least one from styrene-butadiene copolymer (SBR), polyisoprene (IR), polybutadiene (BR), acrylonitrile-butadiene rubber, chloroprene rubber, and butyl rubber. . Particularly preferably, the wear resistance can be further improved by selecting SBR. Further, the total amount of the synthetic rubber is desirably included in the range of 30 to 100% by mass including the modified conjugated diene polymer.

In the present embodiment, in the rubber composition used for the tread portion 18 and the sheet member 19, carbon black and / or silica or the like is blended with the rubber component. These are preferably blended in the range of 30 to 70 parts by mass with respect to 100 parts by mass of the rubber component. When the amount of carbon black and white carbon decreases, the elastic modulus tends to decrease. Further, when the amount of carbon or the like increases, the low heat build-up of the vulcanized rubber composition tends to deteriorate.
As carbon black that can be used, those usually used in the rubber industry can be used. For example, various grades of carbon black such as SAF, HAF, ISAF, FEF, and GPF can be used alone or in admixture of two or more. Incidentally, it is desirable to activate the surface of carbon black or the like by utilizing oil absorption.
Preferably, from the viewpoint of the reinforcing property, the nitrogen adsorption specific surface area _(N 2 SA) of carbon black is 50 to 200 m ² / g or DBP oil absorption amount is desired those 60~200 ^(cm 3 / 100g).

  The compounding amount of the carbon black is preferably 20 to 100 parts by mass, particularly 20 to 80 parts by mass with respect to 100 parts by mass of the rubber component. If the amount of carbon black is less than 20 parts by mass, the exothermic property is excellent, but the wear resistance may be significantly impaired. On the other hand, if it exceeds 100 parts by mass, the workability may be deteriorated.

Moreover, it is preferable to mix | blend a silica as a filler in a rubber composition. As silica to be used, those having a nitrogen adsorption specific surface area (N ₂ SA) of 180 to 270 m ² / g are desirable from the viewpoint of further improving the chipping property improvement by the hysteresis loss improvement. If N ₂ SA exceeds 270 m ² / g, the factory workability deteriorates, which is not preferable.
It is preferable to mix | blend 1-40 mass parts with respect to 100 mass parts of rubber components from the point of the further ensuring ensuring dispersion | distribution, and it is preferable that it is the range of 3-30 mass parts especially.

  Furthermore, the rubber composition to be used can contain various components usually used in the rubber industry, as long as the object of the present invention is not impaired. For example, as various components, fillers (for example, inorganic fillers such as calcium carbonate and calcium carbonate); vulcanization accelerators; anti-aging agents; zinc oxide; stearic acid; softeners; An agent can be mentioned. As vulcanization accelerators, thiazole vulcanization accelerators such as MBTS (dibenzothiazyl disulfide) and CZ (N-cyclohexyl-2-benzothiazylsulfenamide); thiurams such as TT (tetramethylthiuram sulfide) And guanidine-based vulcanization accelerators such as DPG (diphenylguanidine).

In the pneumatic tire 10 of the present embodiment, first, the rubber of the tread portion 18 is configured by a two-layer structure of a portion of the tread surface portion of the cap rubber 18a and a portion of the base rubber 18b in contact with the belt coating rubber 15, and below the base rubber 18b. The heat conductivity of the rubber sheet 19 is 1.3 times or more than that of the red rubber 18 (18a, 18b), and the sheet member 19 has an end portion exposed to the side. Thereby, the heat generation on the belt layer can be radiated from the side of the end portion, and the heat generation on the belt layer can be efficiently reduced.
Furthermore, in the pneumatic tire 10 of the present embodiment, heat is dissipated by forming a groove having a specific structure described in detail below on the ground surface of the tread portion 18 (18a) on the outer side in the tire radial direction of the belt layer 14. It is possible to improve the nature.

That is, as shown in FIG. 3, a plurality of lug grooves 22, 22... Are arranged in the tread shoulder regions on both sides in the tire width direction.
Further, in the tire center portion C between the two tire circumferences (indicated by reference numerals 16 and 16) formed by tying the end positions of the lug grooves 22, 22. A plurality of widthwise narrow grooves 24, 24... That are substantially along the tire width direction are arranged. The width direction narrow groove 24 has an inner end in the tire width direction that terminates in the tread (inner side in the tire width direction than the tread end T), and an outer end in the tire width direction is connected to the tip of the lug groove 22. Is formed. The outer end of each lug groove 22 in the tire width direction extends beyond the tread end T so as to allow drainage to the outer side in the tire width direction.

  Further, an equatorial upper shallow groove 26 extending in the tire circumferential direction on the tire equator CL is disposed. The width GW and depth d of the equatorial upper shallow groove 26 are set to a width and a depth so that the heat generation at the tire center portion C can be sufficiently suppressed from when the tire is new to when the tread portion 18 generates significant heat until the initial use of the tire. Has been.

In this construction vehicle pneumatic tire 10, an equatorial upper shallow groove 26 extending in the tire circumferential direction on the tire equator CL is disposed, whereby the compressive stress acting on the tire center portion C can be relieved, In addition, the heat dissipation area can be increased. Therefore, it is possible to obtain the construction vehicle pneumatic tire 10 that effectively suppresses the temperature rise of the tread portion 18 when the tire is loaded and suppresses the occurrence of tire failure such as heat separation.
Further, the plurality of width direction narrow grooves 24 disposed in the tire center portion C have tire width direction inner ends terminating in the tread. Thereby, it can be set as the tire excellent in the traction performance which improved abrasion resistance by suppressing the fall of land part rigidity. In addition, heat dissipation can be improved even if the number of the width-direction narrow grooves 24 is increased, or the heat dissipation can be improved by disposing the width-direction narrow grooves 24 at positions where the temperature is the highest away from the lug grooves 22. Can do.

  Further, the width (SW) of the width direction narrow groove 24 is set to 20 mm or less, preferably within a range of 4 to 20 mm, and the groove depth (SW-d) of the width direction narrow groove 24 is equal to that of the lug groove 22. It is in the range of 50 to 95% of the groove depth (D). As a result, the effect of improving the heat dissipation is sufficiently exhibited, and it is avoided that the block rigidity of the tire center portion C becomes too low. If the width (SW) of the width direction narrow groove 24 exceeds 20 mm, the block rigidity of the tire center portion becomes low, and the problem of uneven wear and tread chipping is likely to occur. The effect of enhancing the properties is not sufficiently exhibited. Further, if the groove depth (SW-d) of the width direction narrow groove 24 is less than 50% of the groove depth (D) of the lug groove 22, a sufficient heat dissipation effect cannot be obtained, while 95% is reduced. If it exceeds, the block rigidity of the tire center portion becomes low, and problems of uneven wear and tread chipping are likely to occur.

  Furthermore, the groove width (GW) of the equatorial upper shallow groove 26 is preferably in the range of 30 to 50 mm. As a result, the effect of alleviating the compressive stress acting on the tire center portion C at the time of tire load rolling is sufficiently exerted, and it is avoided that the ground contact area of the tire center portion C is excessively reduced to cause a belt end failure. ing. In addition, if this groove width (GW) is less than 30 mm, the effect of relaxing the compressive stress acting on the center portion at the time of tire load rolling tends to be insufficient, while the groove width (GW) ) Exceeds 50 mm, the contact area of the center portion is excessively generated, and the contact pressure increases in the tread side area, and the belt end failure tends to occur.

  Further, the groove depth (d) of the equatorial upper shallow groove 26 is preferably 25% or less, more preferably 10 to 25% of the groove depth (D) of the lug groove 22. As a result, a sufficient heat dissipation effect can be obtained, and deterioration of wear resistance due to a decrease in tread volume is sufficiently avoided. In addition, if the circumferential shallow groove 24 is larger than 25% of the depth of the lug groove 22, the decrease in the tread volume cannot be ignored, and the wear resistance may be deteriorated.

  Further, in the region of 25% of the tread width around the tire equator CL, the negative rate in the region excluding the equator upper shallow groove 26 is 8% or less, preferably in the range of 2 to 8%. Has been. By setting the negative rate to 8% or less, it is possible to efficiently reduce heat generation without reducing the wear resistance of the tire center portion C. The tread width is the distance between the tread ends T on both sides in the tire width direction.

In the pneumatic tire 10 for a construction vehicle according to the first embodiment configured as described above, 1) the tread rubber has a two-layer structure of a base rubber at a portion of the tread surface portion in contact with the first tread rubber and the belt coating rubber. While the thermal conductivity of the rubber sheet under the base rubber is 1.3 times or more than that of the tread rubbers 18a and 18b, a sheet member having the end exposed to the side is used. 2) In the tire tread portion, the center portion Is provided with a circumferential shallow groove extending along the tire circumferential direction, and the negative rate excluding the circumferential shallow groove in the region of 25% of the tread width around the equator is set to 8% or less, that is, With the structure of 1), the heat generated on the belt layer can be efficiently radiated from the side by the sheet member whose end is exposed to the side. The heat generation on the layer can be efficiently reduced, and the heat generation on the tire tread contact surface can be further improved and the wear resistance can be further improved by the configuration of 2). A pneumatic tire, in particular a pneumatic tire for construction vehicles, can be obtained in which heat separation failure is prevented by effectively suppressing and dissipating heat generated in the tread portion (especially the center portion) during loading.
In particular, if the flatness of the tire is 90% or less, the belt tension burden becomes larger than the general 95 series of OR tires (pneumatic tires for construction vehicles), and the heat generation in the tread portion becomes larger. Entered tires are more effective. Further, if the coefficient corresponding to the maximum speed of the tire load / load capability correspondence table defined in TRA is 1.4 or more, the load on the tire air volume is increased and the heat generation in the tread portion is further increased. Therefore, the pneumatic tire of the present invention is more effective. The pneumatic tire can use air or an inert gas such as nitrogen as the gas to be filled.

  Below, the pneumatic tire for construction vehicles which becomes other embodiment of this invention is explained in full detail, referring drawings further. In the following embodiments, FIGS. 4 and 5 show the structure of the sheet member 19 (structures B and C), and FIGS. 6 to 10 show grooves (treads) having a specific shape and structure having a road surface grounding portion in contact with the road surface. This shows another embodiment of the pattern), and the sheet member 19 and the groove (tread pattern) can be suitably implemented in each combination. The same configurations as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The effects of the following embodiments are further added to the effects of the first embodiment.

[Other (Second) Embodiment of Sheet Member 19]
In the present embodiment, as shown in FIG. 4, the tread rubber 18 has a two-layer structure including a first tread rubber 18 a on the surface of the tread and a base rubber 18 b in contact with the belt coating rubber 15. The thermal conductivity of the rubber sheet is 1.3 times or more than that of the red rubber 18a and the base rubber 18b, the end portions thereof are exposed to the side, and the sides of the tread rubber 18a and the base rubber 18b are covered. It has the structure which has the sheet | seat member 19a.
In the pneumatic tire of this embodiment, since the surface area of the end portion exposed to the side is further wider than that of the first embodiment, the heat generated on the belt layer can be further efficiently radiated from the side. The above heat generation can be reduced more efficiently.

[Other (third) embodiment of sheet member 19 and base rubber 18b]
As shown in FIG. 5, the present embodiment has a two-layer structure in which the rubber of the tread portion 18 is composed of a first tread rubber 18 a on the tread surface portion and a base rubber 18 b in contact with the belt coating rubber 15. The thermal conductivity of the rubber sheet under the base rubber 18b is 1.3 times or more than that of the tread cap rubber 18a. The end portion is exposed to the side, and the sheet member 19b covers the sides of the tread rubber 18a and the base rubber 18b.
The method of setting the thermal conductivity of the base rubber 18b to 1.3 times or more that of the tread cap rubber 18a can be performed in the same manner as the sheet member 19 of the first embodiment.
In the pneumatic tire of this form, the thermal conductivity of the base rubber 18b is 1.3 times or more than that of the tread cap rubber 18a, and the surface area where the end portion is exposed to the side is more than that of the second embodiment. Since it becomes wider, the heat generation on the belt layer can be further efficiently radiated from the side, so that the heat generation on the belt layer can be further efficiently reduced.

[Second Embodiment of Groove Structure (Tread Pattern) of Tread 18]
FIG. 6 is a plan view showing a tread portion of a pneumatic tire for construction vehicles showing a second embodiment of the groove structure (tread pattern) of the tread portion 18 of the present invention.
The pneumatic tire for a construction vehicle according to this embodiment is different from the first embodiment shown in FIG. 2 in that the widthwise narrow groove 27 is formed between the lug grooves 22 as shown in FIG. Has been.
The width direction narrow groove 27 is disposed in the tire center portion C substantially along the tire width direction. The width-direction narrow groove 27 straddles the equator shallow shallow groove 26, and both ends are connected to the terminal end of the lug groove 22.
In the pneumatic tire for construction vehicles of this embodiment, since the tread rubber of any one of the above-described FIGS. 2, 4 and 5 (structures A to C) is used, the heat generation on the belt layer is efficiently performed from the side. Therefore, it is possible to provide a pneumatic tire for construction vehicles that can efficiently reduce the heat generation on the belt layer.

[Third embodiment of groove structure (tread pattern) of tread portion 18]
FIG. 7 is a plan view showing a tread portion of a pneumatic tire for construction vehicles showing a third embodiment of the groove structure (tread pattern) of the tread portion 18 of the present invention.
The pneumatic tire for a construction vehicle according to the present embodiment has a widthwise narrow groove 34 formed in the tread portion as shown in FIG. 7 instead of the widthwise narrow groove 24 as compared with the first embodiment of FIG. Yes.
The width direction narrow groove 34 is disposed substantially along the tire width direction in the tire center portion C. The width-direction narrow groove 34 straddles the equatorial upper shallow groove 26, ends at both ends in the tread, and is not connected to the lug groove 22.
In the pneumatic tire 28 for construction vehicles of this embodiment, since the tread rubber of any one of the above-described FIGS. 2, 4 and 5 (structures A to C) is used, the heat generation on the belt layer is generated from the side. Since heat can be efficiently dissipated, the heat generation on the belt layer can be efficiently reduced, and if the structure in which the width direction narrow groove and the lug groove are connected as in the first embodiment of FIG. It can be a pneumatic tire for construction vehicles that is very effective for users who require a large traction force that causes deformation due to the traction force between the narrow groove in the width direction and the lug groove and a crack occurs due to stress concentration at the connection site. .

[Fourth Embodiment of Groove Structure (Tread Pattern) of Tread 18]
FIG. 8 is a plan view showing a tread portion of a pneumatic tire for construction vehicles showing a fourth embodiment of the groove structure (tread pattern) of the tread portion 18 of the present invention.
As compared with the first embodiment of FIG. 2, the pneumatic tire for a construction vehicle of the present embodiment has two straight lines connecting the end positions of the lug grooves 22 in the tire circumferential direction as shown in FIG. A non-equatorial upper narrow groove 46 extending in the tire circumferential direction is further arranged. The groove depth of the non-equatorial upper narrow groove 46 is in the range of 10 to 25% of the groove depth of the lug groove. Both ends of the width direction narrow groove 34 are connected to the non-equatorial upper narrow groove 46.
In the pneumatic tire for construction vehicles of this embodiment, since the tread rubber of any one of the above-described FIGS. 2, 4 and 5 (structures A to C) is used, the heat generation on the belt layer is efficiently performed from the side. Therefore, the heat generation on the belt layer can be efficiently reduced, and the side slip can be ensured and the rigidity in the width direction can be prevented from being reduced by the narrow groove.

[Fifth Embodiment of Groove Structure (Tread Pattern) of Tread 18]
FIG. 9 is a plan view showing a tread portion of a pneumatic tire for construction vehicles showing a fifth embodiment of the groove structure (tread pattern) of the tread portion 18 of the present invention.
As shown in FIG. 9, the pneumatic tire for a construction vehicle of the present embodiment is provided with the non-equatorial upper narrow groove 46 as in the third embodiment of FIG. 7. An equatorial upper shallow groove 26 is also disposed.
In the present embodiment, the lug groove 52 is different in shape from the lug groove 22 of the third embodiment, and the groove width of the lug groove 52 becomes narrower as it approaches the non-equatorial upper narrow groove 46. The end of the lug groove 52 is connected to the non-equatorial upper narrow groove 46.
Further, instead of the widthwise narrow groove 34 described in the fourth embodiment of FIG. 8, a widthwise narrow groove 54 is formed in the tire center portion C. Both ends of the width direction narrow groove 54 are connected to the non-equatorial upper narrow groove 46. Further, the width direction narrow groove 54 is formed in a curved groove whose inclination angle with respect to the tire width direction gradually decreases as the non-equatorial upper narrow groove 46 is approached.
Further, between the lug grooves 52 adjacent to each other in the tire circumferential direction, a second width direction narrow groove 56 in which the inner end in the tire width direction is connected to the non-equatorial upper narrow groove 46 is formed.
In the pneumatic tire for construction vehicles of this embodiment, since the tread rubber of any one of the above-described FIGS. 2, 4 and 5 (structures A to C) is used, the heat generation on the belt layer is efficiently performed from the side. The heat generated on the belt layer can be reduced efficiently, and the narrow groove minimizes the block rigidity and secures skid resistance and traction resistance slip. be able to.

[Sixth Embodiment of Groove Structure (Tread Pattern) of Tread 18]
FIG. 10 is a plan view showing a tread portion of a pneumatic tire for construction vehicles showing a sixth embodiment of the groove structure (tread pattern) of the tread portion 18 of the present invention.
In the pneumatic tire for construction vehicles of the present embodiment, as shown in FIG. 10, a non-equatorial upper narrow groove 66 extending in the tire circumferential direction is used instead of the non-equatorial upper narrow groove 46, as compared with the fourth embodiment of FIG. Is formed. An equatorial upper shallow groove 26 is also disposed.
The lug groove 62 is different in shape from the lug groove 22 of the fourth embodiment in FIG. 8, and the groove width is narrow near the non-equatorial upper narrow groove 46. The end of the lug groove 62 is connected to the non-equatorial upper narrow groove 46.
Further, a width direction narrow groove 64 is formed in the tire center portion C instead of the width direction narrow groove 34 described in the fifth embodiment of FIG. 9. Both ends of the width direction narrow groove 64 are located closer to the tire equator CL side than the inner end of the lug groove 62 in the tire width direction, and therefore the non-equatorial upper narrow groove 66 extends in a zigzag shape in the tire circumferential direction. . The term “zigzag extending in the tire circumferential direction” means that the groove portions that are inclined with respect to the tire circumferential direction extend in the tire circumferential direction while turning back so that the inclination directions are alternate.
In the pneumatic tire for construction vehicles of this embodiment, since the tread rubber of any one of the above-described FIGS. 2, 4 and 5 (structures A to C) is used, the heat generation on the belt layer is efficiently performed from the side. Therefore, the heat generation on the belt layer can be efficiently reduced, and the surface area is increased by the narrow grooves extending in a zigzag shape, so that the temperature of the entire tread can be reduced. This is effective for users who use tires at high speeds.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by the following Example.

[Examples 1 to 4 and Comparative Example 1]
In order to further confirm the present invention, rubber compositions of Production Examples 1 to 5 for tire tread rubber (cap rubber, base rubber, TUC) and sheet members were prepared according to the composition shown in Table 1 below. .
About the obtained rubber composition of manufacture examples 1-5, thermal conductivity (INDEX) was evaluated based on the following evaluation method.

Further, using this rubber composition, conditions of the tread portion shown in the following Table 2 (groove structure, conforming to FIG. 2), tire tread rubber (first tread rubber, base rubber, TUC), sheet A pneumatic radial tire (tire size 37.00R57) composed of a combination of members (structures A to C) was produced. Each pneumatic radial tire obtained was incorporated into a TRA regular rim, and then subjected to regular load and regular internal pressure, and the low heat build-up (INDEX) and wear resistance (INDEX) were evaluated based on the following test methods.
Here, “regular rim” refers to a standard rim in the applicable size specified in the 2004 version of YEAR BOOK issued by JATMA, and “normal load” and “regular internal pressure” are similarly issued by JATMA. It refers to the maximum load and the air pressure for the maximum load in the applicable size / ply rating defined in the 2004 YEAR BOOK. In addition, when TRA standard and ETRTO standard are applied in a use place or a manufacturing place, it follows each standard.

Evaluation Method of Thermal Conductivity (INDEX) The thermal conductivity was measured using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Co., Ltd.

Evaluation method of low exothermic property (INDEX) A drum system having a speed / step load condition of 10 km / h was implemented, the temperature at a position at a constant depth of the tread was measured, and Comparative Example 1 was used as a control value (control) 100. Each example was expressed as an index. It shows that it is excellent in low exothermic property, so that the value of an index | exponent is large.

Wear resistance (INDEX) evaluation method Attached to the front wheel of a 190-ton dump truck, traveled at a constant speed of 10 km / h for 100 hours, and then measured the remaining grooves at each position where the tread was divided into 8 in the width direction. The average value of the gauge required for the calculation was calculated as the amount of wear. Then, when performing the performance evaluation, the evaluation in Comparative Example 1 was set as an index 100, and an index that was a relative evaluation was calculated for the tires of other Comparative Examples and Examples. The calculation results are shown in Table 2 below. The larger this index (wear resistance index), the higher the performance.

  As is apparent from the results of Tables 1 and 2, Examples 1 to 4 within the scope of the present invention are superior in low heat buildup and wear resistance compared to Comparative Example 1 that falls outside the scope of the present invention. As a result, it was found that a pneumatic tire for a construction vehicle in which heat separation failure is prevented can be obtained by effectively suppressing and dissipating heat generated in the tread portion (particularly the center portion) when the tire is loaded.

  Since the pneumatic tire of the present invention is excellent in heat dissipation, low heat generation and wear resistance, it can be suitably used for construction vehicle tires, and thus has high industrial utility value.

BRIEF DESCRIPTION OF THE DRAWINGS The pneumatic tire for construction vehicles which shows 1st Embodiment of this invention is shown, and it is a tire radial direction sectional drawing. It is radial direction sectional drawing of a tread part (structure A). (A) And (B) is the top view and tire radial direction sectional drawing which respectively show the tread part of the pneumatic tire for construction vehicles of 1st Embodiment. It is radial direction sectional drawing which shows other embodiment (structure B) of a tread part structure. It is radial direction sectional drawing which shows other embodiment (structure C) of a tread part structure. It is a top view which shows the tread part (tread pattern) of the pneumatic tire for construction vehicles of other embodiment. It is a top view which shows the tread part (tread pattern) of the pneumatic tire for construction vehicles of other embodiment. It is a top view which shows the tread part (tread pattern) of the pneumatic tire for construction vehicles of other embodiment. It is a top view which shows the tread part (tread pattern) of the pneumatic tire for construction vehicles of other embodiment. It is a top view which shows the tread part (tread pattern) of the pneumatic tire for construction vehicles of other embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Construction vehicle tire 18 Tread part 18a 1st tread rubber 18b Base rubber 19 Sheet member 22 Lug groove 24 Width direction narrow groove 26 Equatorial upper shallow groove C Tire center part CL Tire equator

Claims (8)

  Two tires formed by arranging a large number of lug grooves extending from the respective tread ends toward the tire equatorial plane in the tread portion, and connecting the terminal positions of these lug grooves substantially in the tire circumferential direction. In a pneumatic tire having a narrow groove having a width of 20 mm or less in the center portion between the circumferences in the width direction and having a main groove having a depth of 70 mm or more, the circumferential shallow portion extending along the tire circumferential direction in the center portion. Provided with a groove, the negative rate is 8% or less except for the circumferential shallow groove in the region of 25% of the tread width centered on the equator, and the tread rubber is the cap rubber and belt coating rubber on the tread surface. The rubber sheet under the base rubber has a thermal conductivity of 1.3 times or more than that of the tread rubber and the base rubber. With the pneumatic tire characterized by having a sheet member that its end is exposed to the side.   The tread rubber consists of a two-layer structure of the base rubber in the tread surface part where the cap rubber and belt coating rubber are in contact, and the thermal conductivity of the rubber sheet under the base rubber is 1.3 times that of the tread rubber and base rubber 2. The pneumatic tire according to claim 1, further comprising a seat member having an end portion exposed to the side and covering the sides of the tread rubber and the base rubber.   The tread rubber has a two-layer structure of the base rubber of the tread surface cap rubber and the portion of the base rubber in contact with the belt coating rubber, and the thermal conductivity of the base rubber is 1.3 times or more that of the tread cap rubber. A sheet in which the thermal conductivity of the rubber sheet under the rubber is 1.3 times or more that of the cap rubber of the tread, the end of the rubber sheet is exposed to the side, and the side of the tread rubber and the base rubber is covered. The pneumatic tire according to claim 1, comprising a member.   The pneumatic tire according to claim 1, wherein the base rubber and the sheet member contain carbon fibers.   The pneumatic tire according to claim 4, wherein the carbon fiber is vapor grown carbon fiber.   The pneumatic tire according to any one of claims 1 to 5, wherein a groove depth of the circumferential shallow groove is 25% or less of the lug groove depth.   The pneumatic tire according to any one of claims 1 to 6, wherein a groove width of the circumferential shallow groove is 30 to 50 mm.   The pneumatic tire according to any one of claims 1 to 7, wherein the pneumatic tire is a pneumatic tire for construction vehicles.

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