JP2010254087A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire improving partial wear resistance without deteriorating rolling resistance. <P>SOLUTION: The pneumatic tire includes a pair of bead portions 1, a pair of side wall portions 2, and a tread portion 3 ranging to both side wall portions 2. A ratio of a friction coefficient of a tread shoulder portion 3B positioned on both outer sides in a tire width direction of the tread center portion 3A to a friction coefficient of the tread center portion 3A positioned at a center portion in the tire width direction of the tread portion 3, namely (the friction coefficient of the tread shoulder portion 3B/the friction coefficient of the tread center portion 3A) is not less than 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire with improved uneven wear resistance without deteriorating rolling resistance.

  In the tread portion that is in direct contact with the road surface of the tire, the tread center portion located at the center portion in the tire width direction of the tread portion and the tread shoulder portions located on both outer sides in the tire width direction of the tread center portion are grounded within the tread surface. Since the pressure is different, the tread shoulder portion is easier to slide than the tread center portion. Further, the tread center portion and the tread shoulder portion have different ground contact distances even if they travel the same distance due to the difference in diameter in the tread. Since the tread shoulder portion has a shorter ground contact distance than the tread center portion, the tread shoulder portion gains distance by sliding. Further, uneven wear occurs in the tread portion of the tire because the slip amount of the tread shoulder portion is larger than the slip amount of the tread center portion.

  On the other hand, conventionally, in order to prevent uneven wear in the tread portion of the tire, a technique has been adopted in which a rubber composition having a composition capable of increasing the friction coefficient (μ) is used for the entire tread.

JP 62-59104 A

  However, a rubber composition blended that can increase the coefficient of friction (μ) simultaneously increases the loss tangent (tan δ) of the tread. Therefore, when a rubber composition blended to increase the coefficient of friction (μ) is used for the entire tread, uneven wear in the tread portion can be suppressed, but the tire rolling resistance increases, resulting in low fuel consumption. There is a problem that gets worse.

  Accordingly, an object of the present invention is to provide a pneumatic tire that solves the above-described problems of the prior art and has improved uneven wear resistance without deteriorating rolling resistance.

  As a result of intensive studies to achieve the above object, the present inventor has found that the friction coefficient of the tread shoulder portion is larger than the friction coefficient of the tread center portion without increasing the friction coefficient of the entire tread. In this case, the uneven wear resistance of the tire is improved by making it twice or more, and according to this method, it has been found that the deterioration of the rolling resistance of the tire can be suppressed, and the present invention has been completed.

  That is, the pneumatic tire of the present invention has a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, and the tread center portion of the tread portion located at the center in the tire width direction. The ratio of the friction coefficient of the tread shoulder portion located on both outer sides in the tire width direction of the tread center portion with respect to the friction coefficient of the tire (the friction coefficient of the tread shoulder portion / the friction coefficient of the tread center portion) is 2 or more. . Here, the friction coefficient of the tread center portion and the tread shoulder portion is a friction coefficient when the tire is assumed to have a normal internal pressure and a normal load is applied. it can.

  In a preferred example of the pneumatic tire according to the present invention, the tread rubber located in the portion of the tread portion in contact with the road surface has a center tread rubber segment located in the center portion in the tire width direction, and the tire of the center tread rubber segment. It is divided into shoulder tread rubber segments located on both outer sides in the width direction. In this case, the ratio of the friction coefficient of the tread shoulder portion to the friction coefficient of the tread center portion can be easily adjusted by changing the type of the rubber composition used for each segment.

  Moreover, it is preferable that the said center part tread rubber segment is gradually increasing the width | variety of a tire width direction toward a tire radial direction inner side. In this case, it is possible to suppress the deterioration of rolling resistance accompanying the use of the tire.

  In another preferred embodiment of the pneumatic tire of the present invention, 20 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component is added to the tread rubber positioned at a portion in contact with the road surface of the tread part, and the combination of the silica A rubber composition comprising 12% by mass or more of silane coupling is used. In this case, even if the same rubber composition is used for the tread shoulder portion and the tread center portion, the friction coefficient of the tread shoulder portion can be more than twice the friction coefficient of the tread center portion. The braking performance of the rubber composition used is high and the processability of the rubber composition used is also good.

  According to the present invention, it is possible to provide a pneumatic tire in which the friction coefficient of the tread shoulder portion is twice or more than the friction coefficient of the tread center portion, and the uneven wear resistance is improved without deteriorating rolling resistance. it can.

It is sectional drawing of one embodiment of the tire of this invention. It is sectional drawing of the preferred embodiment of the tire of this invention. It is sectional drawing of the other suitable embodiment of the tire of this invention.

  Hereinafter, the tire of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the tire of the present invention. The tire shown in FIG. 1 has a pair of left and right bead portions 1 and a pair of sidewall portions 2 and a tread portion 3 connected to both sidewall portions 2, and extends in a toroidal shape between the pair of bead portions 1. The carcass 4 that reinforces the parts 1, 2, and 3 and the belt 5 that is disposed on the outer side in the tire radial direction of the crown portion of the carcass 4 are provided.

  The carcass 4 of the tire shown in FIG. 1 is composed of a single carcass ply, a main body portion extending in a toroid shape between a pair of bead cores 6 embedded in the bead portion 1, and each bead core. 6, and a folded portion wound radially outward from the inner side to the outer side in the tire width direction. In the tire of the present invention, the number of plies and the structure of the carcass 4 are not limited thereto. .

  Further, the belt 5 of the tire shown in FIG. 1 is composed of two belt layers, and each belt layer is usually a rubberized layer of cord, preferably steel, extending incline with respect to the tire equatorial plane. The belt 5 is composed of a rubberized layer of cords, and two belt layers are laminated so that the cords constituting the belt layers intersect with each other across the tire equatorial plane. The belt 5 in the figure is composed of two belt layers, but in the tire of the present invention, the number of belt layers constituting the belt 5 is not limited to this.

  Here, in the tire of the present invention, the friction of the tread shoulder portion 3B located on both outer sides in the tire width direction of the tread center portion 3A with respect to the friction coefficient of the tread center portion 3A located in the center portion of the tread portion 3 in the tire width direction. The ratio of the coefficients (the friction coefficient of the tread shoulder portion 3B / the friction coefficient of the tread center portion 3A) is 2 or more. In the present invention, the tread center portion 3A is located in the center portion of the tread portion 3 in the tire width direction and refers to a portion of 1/3 of the tire width. The tread shoulder portion 3B is the tread portion 3 of the tread portion 3. It refers to the 1/3 portion of the tire width from the end. The end portion of the tread portion 3 refers to an end portion in the tire width direction of a portion that is in contact with the road surface of the tire when a normal load is applied with a normal internal pressure of the tire.

  By setting the friction coefficient of the tread shoulder portion 3B to be twice or more the friction coefficient of the tread center portion 3A, the tread shoulder portion 3B becomes difficult to slip, and uneven wear in the tread portion 3 can be suppressed. Further, in this case, it is possible to suppress the deterioration of the rolling resistance of the tire as compared with the conventional technique that increases the friction coefficient of the entire tread portion 3.

  As a method of making the friction coefficient of the tread shoulder portion 3B more than twice the friction coefficient of the tread center portion 3A, (I) the tread rubber 7 disposed on the outer side in the tire radial direction of the belt 5 in the tread portion 3 is illustrated in FIG. As shown in FIG. 2, it is divided into a center part tread rubber segment 7A located in the center part in the tire width direction and a shoulder part tread rubber segment 7B located on both outer sides in the tire width direction of the center part tread rubber segment 7A. And a method in which the tread portion 3 is divided into treads and a rubber composition having a higher effect of increasing the coefficient of friction (μ) than the rubber composition used for the center portion tread rubber segment 7A is applied to the shoulder portion tread rubber segment 7B. . In this case, since the rubber composition used for the center part tread rubber segment 7A and the shoulder part tread rubber segment 7B is originally different, the ratio of the friction coefficient of the tread shoulder part 3B to the friction coefficient of the tread center part 3A is set to a desired value. Easy to do. In addition, the composition of the rubber composition used for each segment can be adjusted by appropriately changing the type and blend ratio of the rubber component used, the type and amount of the filler used, the type and amount of the other compounding agent, and the like. Good.

  However, when the tread rubber 7 is divided at right angles to the tire width direction, the exposed area of the shoulder tread rubber segment 7B becomes relatively large as the entire tread portion 3 is worn. The shoulder tread rubber segment 7B uses a rubber composition that has a higher effect of increasing the coefficient of friction (μ) than the rubber composition used for the center tread rubber segment 7A. The loss tangent (tan δ) is larger than that of the center tread rubber segment 7A. Therefore, as the entire tread portion 3 is worn, the exposed area of the shoulder portion tread rubber segment 7B having a larger tan δ is relatively increased, and the rolling resistance of the tire is gradually increased.

  In order to prevent this, in the divided tread, as shown in FIG. 3, it is preferable to gradually increase the width in the tire width direction of the center portion tread rubber segment 7A toward the inner side in the tire radial direction. For this, the cross-sectional shape is preferably substantially trapezoidal. By gradually increasing the width in the tire width direction of the center portion tread rubber segment 7A toward the inner side in the tire radial direction, the exposed area of the shoulder portion tread rubber segment 7B becomes relatively large according to wear of the entire tread portion 3. It is possible to prevent the increase in rolling resistance accompanying the use of the tire, and to maintain the low fuel consumption of the tire until the end of use.

  In addition, as a method of making the friction coefficient of the tread shoulder portion 3B larger than the friction coefficient of the tread center portion 3A, (II) the tread rubber 7 positioned at the portion in contact with the road surface of the tread portion 3, On the other hand, it is also preferable to use a rubber composition comprising 20 to 100 parts by mass of silica and silane coupling of 12% by mass or more of the amount of silica.

  As described above, the tread center portion 3A and the tread shoulder portion 3B have different ground pressures in the tread surface, and the tread center portion 3A has a higher ground pressure than the tread shoulder portion 3B. In principle, the friction coefficient (μ) at the low contact pressure is larger than the friction coefficient (μ) at the high contact pressure, so that the same rubber composition is used for the tread center portion 3A and the tread shoulder portion 3B. Even if an object is used, it is possible to make the friction coefficient of the tread shoulder portion 3B larger than the friction coefficient of the tread center portion 3A.

  Based on this knowledge, the present inventors further investigated, and as a result, 20 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component, and silane coupling of 12% by mass or more of the amount of the silica. It was found that the friction coefficient of the tread shoulder portion 3B becomes twice or more than the friction coefficient of the tread center portion 3A by using the rubber composition formed by blending the tread portion 3 as a whole.

  The rubber component of the rubber composition for the tread rubber 7 includes natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), ethylene-propylene- Synthetic rubbers such as diene rubber (EPDM), chloroprene rubber (CR), butyl rubber (IIR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and the like may be used alone. Two or more kinds may be blended and used.

  Moreover, there is no restriction | limiting in particular as said silica, For example, wet silica (hydrous silicic acid), dry-type silica (anhydrous silicic acid), colloidal silica, etc. can be used. These silicas may be used alone or in combination of two or more.

  The compounding amount of the silica is 20 to 100 parts by mass with respect to 100 parts by mass of the rubber component. When the compounding amount of silica is less than 20 parts by mass, the braking performance on the wet road surface of the tire is lowered, whereas when it exceeds 100 parts by mass, the workability in kneading the rubber composition is deteriorated.

  The silane coupling includes bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxy). Silylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide and the like. These silane couplings may be used alone or in combination of two or more.

  The addition amount of the silane coupling is 12% by mass or more of the blending amount of the silica. When the addition amount of silane coupling is less than 12% by mass of the amount of silica, the friction coefficient of the tread shoulder portion 3B cannot be more than twice the friction coefficient of the tread center portion 3A. Although not particularly limited, the addition amount of silane coupling is preferably 20% by mass or less of the amount of silica.

  The rubber composition for the tread rubber 7 is a compounding agent usually used in the rubber industry, such as a softening agent, an anti-aging agent, a vulcanization accelerator, and a vulcanization acceleration aid, together with silica and silane coupling. An agent, a vulcanizing agent, and the like can be appropriately selected and blended within a range that does not impair the object of the present invention, and kneaded, heated, extruded, and the like. Moreover, a commercial item can be utilized as these rubber components and compounding agents.

  The pneumatic tire of the present invention described above is preferably a green tire formed by applying an appropriate rubber composition to the tread portion 3 by the method (I) or (II), and according to a conventional method. Can be produced by vulcanization. In addition, as gas with which the pneumatic tire of this invention is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Evaluation of workability during preparation and kneading of rubber composition for tread>
A rubber composition for a tread was prepared according to a conventional method by blending a rubber component with a compounding agent usually used in the rubber industry together with silica and silane coupling. In addition, the compounding quantity with respect to 100 mass parts of rubber components of a silica and a silane coupling agent is as showing in Table 1. Moreover, the workability (viscosity etc.) at the time of kneading | mixing of a rubber composition was also evaluated in the case of a mixing | blending. The results are shown in Table 1. In Table 1, ◎ indicates that the workability during kneading was very good, ○ indicates that the workability during kneading was good, and Δ indicates that the workability during kneading was slightly poor. It shows that.

(Comparative Examples 1-2 and Examples 2-4)
A pneumatic radial tire having the structure shown in FIG. 1 was produced using the rubber composition as a tread rubber 7.

Example 1
A pneumatic radial tire having the structure shown in FIG. 3 was manufactured using the rubber composition for the center tread rubber segment 7A and the shoulder tread rubber segment 7B.

<Evaluation>
The tires produced as described above were evaluated for the friction coefficient, rolling resistance, uneven wear resistance, and braking performance on wet road surfaces by the following methods. The results are shown in Tables 2-3.

(1) Friction coefficient Cut out the tread center part and tread shoulder part, prepare a 2.5 cm x 2.5 cm x 2 mm rubber sheet, apply a load corresponding to the tread center part or a load corresponding to the tread shoulder part, and acrylic The coefficient of friction was determined from the friction force when a shearing force was applied on a plate or safety walk (# 80). Furthermore, the ratio of the friction coefficient (tread shoulder portion / tread center portion) was calculated from the friction coefficient value of the tread center portion and the friction coefficient value of the tread shoulder portion.

(2) Rolling resistance The rolling resistance when the test tire was drum-runned under normal load and internal pressure was measured. For Table 2, the reciprocal of the rolling resistance of the tire of Comparative Example 1 was set to 100. These are shown as indices with the reciprocal of the rolling resistance of the tire of Comparative Example 2 being 100. The larger the index value, the smaller the rolling resistance and the better the fuel economy.

(3) Uneven wear resistance The uneven wear area after the tire was mounted on the front wheel of an actual vehicle and traveled 100,000 km was measured. For Table 2, the reciprocal of the uneven wear area of the tire of Comparative Example 1 was set to 100, For Table 3, the reciprocal of the uneven wear area of the tire of Comparative Example 2 was expressed as an index with 100 as the inverse. A larger index value indicates a smaller uneven wear area and better uneven wear resistance.

(4) Braking performance on wet road surface The test tire is mounted on an actual vehicle, the braking distance on the wet road surface (test course) is measured, and in Table 2, the reciprocal of the braking distance of the tire of Comparative Example 1 is 100. In Table 3, the reciprocal of the braking distance of the tire of Comparative Example 2 was taken as 100 and expressed as an index. The larger the index value, the shorter the braking distance and the better the braking performance on wet road surfaces.

  From the comparison between Comparative Example 1 and Example 1 in Table 2, the tread part has a split structure, and the friction coefficient of the tread shoulder part is more than twice the friction coefficient of the tread center part, thereby deteriorating the rolling resistance. It can be seen that the uneven wear resistance can be improved.

  Moreover, from the comparison between Comparative Example 2 in Table 3 and Examples 2 to 4, the tread shoulder portion was obtained by using a rubber composition in which the addition amount of silane coupling was 12% by mass or more of the compounding amount of silica in the tread portion. It can be seen that the friction coefficient of the tread center portion is more than twice the friction coefficient of the tread center portion, and the uneven wear resistance can be improved without deteriorating the rolling resistance.

  Furthermore, from the results of Example 3, it is found that when a rubber composition having a silica compounding amount of less than 20 parts by mass with respect to 100 parts by mass of the rubber component is used for the tread part, the braking performance on the wet road surface is reduced. Moreover, from the evaluation result of the rubber composition G in Table 1, it is understood that the rubber composition in which the compounding amount of silica exceeds 100 parts by mass with respect to 100 parts by mass of the rubber component is not so good in workability at the time of kneading. . Therefore, these results show that the amount of silica is preferably in the range of 20 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 3A Tread center part 3B Tread shoulder part 4 Carcass 5 Belt 6 Bead core 7 Tread rubber 7A Center part tread rubber segment 7B Shoulder part tread rubber segment

Claims (4)

  The tire of the tread center portion has a pair of bead portions, a pair of sidewall portions, and a tread portion that is continuous with both sidewall portions, and the friction coefficient of the tread center portion that is located in the center portion of the tread portion in the tire width direction. A pneumatic tire characterized in that a ratio of friction coefficients of the tread shoulder portions located on both outer sides in the width direction (friction coefficient of the tread shoulder portion / friction coefficient of the tread center portion) is 2 or more.   The tread rubber located in the portion of the tread that contacts the road surface is a center tread rubber segment located in the center in the tire width direction, and a shoulder tread rubber segment located on both outer sides in the tire width direction of the center tread rubber segment. The pneumatic tire according to claim 1, wherein the pneumatic tire is divided into two parts.   The pneumatic tire according to claim 2, wherein the center tread rubber segment has a width in the tire width direction that gradually increases inward in the tire radial direction.   In the tread rubber located at the portion of the tread portion that is in contact with the road surface, 20 to 100 parts by mass of silica and 12% by mass or more of the amount of the silica are compounded with respect to 100 parts by mass of the rubber component. The pneumatic tire according to claim 1, wherein the rubber composition is used.

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