JP2008120121A - Pneumatic tire and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire which prevents tire performance from being rapidly changed even when the pneumatic tire is worn. <P>SOLUTION: The pneumatic tire is provided with a tread having a physical property which is continuously changed from the surface layer to the inner layer. The pneumatic tire is manufactured for example through a process in which a strip of unvulcanized rubber is formed by extruding two or more rubber compositions while continuously changing the supply ratio of each rubber composition and winding the strip of unvulcanized rubber around a tire case to form the tread. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire and a method for manufacturing the same, and more particularly to a pneumatic tire in which the performance of the tire does not change abruptly even when the tire is worn.

  In general, a tread of a pneumatic tire is required to satisfy a plurality of performances simultaneously. For example, a tread for a heavy-duty pneumatic tire in which uneven wear and heat generation are likely to be problems is required to satisfy both uneven wear resistance and low heat generation. However, since uneven wear resistance and low heat build-up are in a trade-off relationship, it is difficult to achieve both partial wear resistance and low heat build-up with a single composition tread.

  On the other hand, the tread has a two-layer structure (so-called cap / base structure) (see Patent Document 1). For example, the inner layer base rubber is reduced while the surface layer cap rubber is a rubber having excellent uneven wear resistance. There has been known a technique for achieving both uneven wear resistance and low heat build-up as a whole tread by using rubber having excellent heat generation.

  However, when the heat generation of the cap rubber is large, the boundary between the cap rubber and the base rubber needs to be outside in the tire radial direction from the groove bottom of the tread. In this case, when the base rubber is exposed due to wear of the tread, Tire performance changes abruptly. For example, since the base rubber is generally inferior in uneven wear resistance as compared with the cap rubber, the exposed portion of the base rubber is rapidly unevenly worn due to the exposure of the base rubber, and the appearance of the tire is deteriorated. Further, due to the exposure of the base rubber, the color difference between the cap rubber and the base rubber becomes remarkable, and the appearance of the tire may be deteriorated.

JP 2005-219733 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pneumatic tire that solves the above-described problems of the prior art and prevents the tire performance from rapidly changing even if the tire is worn. Another object of the present invention is to provide a method for producing such a pneumatic tire.

  As a result of intensive studies to achieve the above object, the present inventor has a trade-off relationship such as uneven wear resistance and low heat build-up by continuously changing the physical properties of the tread from the surface layer toward the inner layer. It has been found that the tire performance can be prevented from changing suddenly when the tire is worn while simultaneously improving the performance, and the present invention has been completed.

  That is, the pneumatic tire of the present invention includes a tread whose physical properties are continuously changed from the surface layer toward the inner layer.

  In a preferred example of the pneumatic tire of the present invention, the physical property is a loss tangent (tan δ). Here, the average value of the loss tangent (tan δ) of the outermost layer of the tread and the loss tangent (tan δ) of the innermost layer is preferably less than 0.2, and more preferably 0.17 to 0.18. Further, it is preferable that the value of loss tangent (tan δ) continuously decreases from the surface layer of the tread to the inner layer. Further, the loss tangent (tan δ) of the outermost layer of the tread is preferably 0.2 or more, and the loss tangent (tan δ) of the innermost layer of the tread is preferably 0.15 or less.

  In another preferred embodiment of the pneumatic tire of the present invention, a filler of 30 to 60 parts by mass of carbon black and / or silica is added to 100 parts by mass of a rubber component comprising at least natural rubber and comprising a diene rubber. The blended rubber composition is used for the tread.

  The pneumatic tire of the present invention is particularly preferable as a heavy-duty tire because, for example, uneven wear resistance and low heat build-up can be improved at the same time.

  In the method for producing a pneumatic tire according to the present invention, two or more rubber compositions are extruded while continuously changing the supply ratio of each rubber composition to form a belt-shaped unvulcanized rubber, and the belt-shaped unvulcanized rubber. A tread is formed by winding a vulcanized rubber on a tire case.

  According to the present invention, by continuously changing the physical properties of the tread from the surface layer toward the inner layer, it is possible to provide a pneumatic tire in which performance is prevented from changing suddenly even when the tire is worn. The tire is suitable as a heavy duty tire.

  The present invention is described in detail below. The pneumatic tire of the present invention includes a tread whose physical properties are continuously changed from the surface layer toward the inner layer (that is, in the tire radial direction). For example, by improving uneven wear resistance on the tread surface layer side, improving low heat generation on the tread inner layer side, and continuously changing uneven wear resistance and low heat generation from the surface layer to the inner layer, the entire tread While maintaining the exothermic property, it is possible to ensure uneven wear resistance at the beginning of traveling, and to suppress rapid progress of uneven wear due to exposure of the inner layer of the tread after the middle of traveling. In addition, as shown in FIG. 1, the pneumatic tire of the present invention may be provided with a tread whose physical properties are continuously changed from the surface layer toward the inner layer, but the physical properties of the tread are continuously changed. However, the ratio is not particularly limited, and the rate of change in physical properties may not be constant.

  In the tread of the pneumatic tire of the present invention, examples of physical properties that are continuously changed from the surface layer toward the inner layer include loss tangent (tan δ). tan δ is a physical property closely related to the uneven wear resistance and low heat build-up of rubber. By changing tan δ appropriately and continuously from the surface layer to the inner layer, uneven wear resistance and low heat build-up of the tread are achieved. It becomes possible to balance with.

  In the pneumatic tire of the present invention, the average value of the loss tangent (tan δ) of the outermost layer of the tread and the loss tangent (tan δ) of the innermost layer is preferably less than 0.2, and more preferably 0.17 to 0.18. . If the average value of tan δ of the outermost layer of the tread and tan δ of the innermost layer is 0.2 or more, the heat generation durability of the tread may not be maintained. In the tread of the pneumatic tire of the present invention, it is preferable that the value of the loss tangent (tan δ) continuously decreases from the surface layer toward the inner layer. In addition, while continuously decreasing the value of tan δ from the surface layer side to the inner layer side of the tread, the average value of tan δ of the outermost layer of the tread and tan δ of the innermost layer is set to 0.17 to 0.18. Uneven wear and low heat build-up can be sufficiently achieved.

  In the pneumatic tire of the present invention, the loss tangent (tan δ) of the outermost layer of the tread is preferably 0.2 or more, and more preferably 0.22 or more. If the tan δ of the outermost layer of the tread is less than 0.2, it is difficult to ensure the initial uneven wear resistance of the tread. On the other hand, if it is 0.22 or more, the initial uneven wear resistance of the tread can be sufficiently ensured. it can.

  In the pneumatic tire of the present invention, the loss tangent (tan δ) of the innermost layer of the tread is preferably 0.15 or less, and more preferably 0.13 or less. If the tan δ of the innermost layer of the tread exceeds 0.15, it becomes difficult to ensure the low heat buildup of the tread, while if it is 0.13 or less, the low heat buildup of the tread is good.

  The tread of the pneumatic tire of the present invention is a rubber in which 30 to 60 parts by mass of a filler made of carbon black and / or silica is blended with 100 parts by mass of a rubber component made of a diene rubber and containing at least natural rubber. It is preferable to use a composition, and it is more preferable to use a rubber composition containing 35 to 55 parts by mass of the filler. If the blending amount of the filler is less than 30 parts by mass with respect to 100 parts by mass of the rubber component, the reinforcing property of the rubber is not sufficient, and the wear resistance may be greatly deteriorated.On the other hand, if it exceeds 60 parts by mass, There is a possibility that the processability of the rubber composition is greatly deteriorated. In addition, if the compounding quantity of a filler is 35-55 mass parts with respect to 100 mass parts of rubber components, rubber | gum's reinforcement property and abrasion resistance are high, and the workability of a rubber composition is also favorable.

  Examples of the rubber component include synthetic diene rubbers such as styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), and polyisoprene rubber (IR) in addition to natural rubber (NR). These rubber components may be used alone or in combination of two or more. In addition, it is preferable that 40 mass% or more of the rubber component is natural rubber.

  There is no restriction | limiting in particular as said carbon black, For example, the thing of various grades, such as SAF, HAF, ISAF, FEF, GPF, can be used. The silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), colloidal silica, calcium silicate, and aluminum silicate. These fillers may be used alone or in combination of two or more.

  In addition to the rubber component, carbon black and silica, the rubber composition contains a compounding agent usually used in the rubber industry, such as anti-aging agent, vulcanizing agent, vulcanization accelerator, zinc white, stearic acid, etc. It can mix | blend suitably according to the objective. As these compounding agents, commercially available products can be suitably used. In addition, the said rubber composition can be manufactured by mix | blending various compounding agents selected suitably as needed with the rubber component, kneading | mixing, heating, and extruding. Moreover, the rubber composition which has a desired physical property can be prepared by controlling appropriately the kind and compounding quantity of a rubber component, a filler, and various compounding agents.

  The pneumatic tire of the present invention is not particularly limited except for the tread structure, and a known structure can be adopted, which is particularly suitable as a heavy load tire. The pneumatic tire of the present invention forms a tire case from tire members such as an inner liner, a carcass, a bead core, a belt, a side rubber, and a bead filler according to a conventional method, while two or more kinds of rubber compositions are used. Extruding while continuously changing the supply ratio of the rubber composition to form a belt-shaped unvulcanized rubber, winding the belt-shaped unvulcanized rubber on the tire case to form a tread, and further vulcanizing according to a conventional method Can be manufactured. As a specific example of the formation of the belt-shaped unvulcanized rubber, different rubber compositions having desired physical properties are put into separate hoppers of an extruder, and the rubber composition is continuously changed while the supply amount from each hopper is changed. Is supplied to the mixing section of the extruder, and the supplied rubber composition mixture is extruded from the die of the extruder to form a band-like unvulcanized rubber. Since the physical properties of the tread thus formed continuously change from the inner layer side to the surface layer side (in the tire radial direction), it is sufficient that the tire performance of the tire provided with the tread changes rapidly due to wear. Is suppressed.

  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.

  Using the rubber composition shown in Table 1 as a tread, a heavy-duty pneumatic tire having a size of 11R22.5 was prototyped. In addition, the tread of the tire of Comparative Example 1 is a tread having a cap / base structure, and a rubber composition having a composition shown in Table 1 was used for each of the cap rubber and the base rubber. On the other hand, in the tire treads of the examples, while continuously changing the supply ratios of the rubber compositions of the respective compounding 1 and compounding 2, the strip-shaped unvulcanized rubber was extruded into the tire case to form a raw tire and vulcanized And manufactured. The outermost layer of the tread is composed of 100% of the rubber composition of each compounding 1, while the innermost layer of the tread is composed of 100% of the rubber composition of each of the compounding 2, and is compounded from the innermost layer toward the outermost layer. While decreasing the supply ratio of the rubber composition No. 2 and increasing the supply ratio of the rubber composition of Formulation 1, the composition and physical properties of the tread were continuously changed in the tire radial direction. Next, the heat generation property and uneven wear property, and tan δ of the obtained tire were evaluated by the following methods.

(1) Evaluation of heat generation A drum test under a constant speed and step load condition was performed, the temperature at a constant depth position inside the tire tread was measured, and the temperature of the tire of Comparative Example 1 was set as 100, and displayed as an index. The results are shown in Table 1. The larger the index value, the greater the effect of reducing heat generation.

(2) Evaluation of uneven wear After the tire was mounted on the front shaft of the truck and traveled for 200,000 km, the amount of uneven wear was measured. Table 1 shows the results of the amount of uneven wear step at the initial stage (after traveling 50,000 km) and the amount of uneven wear step at the end stage (after traveling 200,000 km). The smaller the step amount, the better the uneven wear resistance.

(3) Evaluation of tan δ Samples were cut every 2 mm from the tread surface layer to the inner layer of the tire, and tan δ at 25 ° C., 2% strain, and 50 Hz was measured with a spectrometer. Table 1 shows the tan δ of the tread outermost layer and innermost layer, and the average value of tan δ.

* 1 SBR, JSR, # 1500.
* 2 Carbon black, N110.
* 3 Vulcanization accelerator, manufactured by Ouchi Shinsei Chemical, Noxeller CZ.
* 4 Carbon black, N220.

  From the results of the initial and final uneven wear amounts in Table 1, it can be seen that rapid changes in tire performance can be prevented by continuously changing the physical properties of the tread in the tire radial direction. Further, it can be seen from the comparison between Examples 1 and 2 and Example 3 that the uneven wear resistance of the tire can be sufficiently ensured by setting tan δ of the outermost layer of the tread to 0.2 or more.

It is a conceptual diagram of the physical property change of the tread of the pneumatic tire of this invention, and the tread of the tire of the conventional cap / base structure.

Claims (8)

  A pneumatic tire comprising a tread whose physical properties are continuously changed from a surface layer toward an inner layer.   The pneumatic tire according to claim 1, wherein the physical property is a loss tangent (tan δ).   The pneumatic tire according to claim 2, wherein an average value of a loss tangent (tan δ) of the outermost layer of the tread and a loss tangent (tan δ) of the innermost layer is less than 0.2.   The average value of the loss tangent (tanδ) of the outermost layer of the tread and the loss tangent (tanδ) of the innermost layer is 0.17 to 0.18, and the value of the loss tangent (tanδ) is continuous from the surface layer of the tread toward the inner layer. The pneumatic tire according to claim 3, wherein the pneumatic tire is lowered. The loss tangent (tan δ) of the outermost layer of the tread is 0.2 or more,
The pneumatic tire according to claim 2, wherein a loss tangent (tan δ) of the innermost layer of the tread is 0.15 or less.   A rubber composition in which 30 to 60 parts by mass of a filler made of carbon black and / or silica is blended with 100 parts by mass of a rubber component made of a diene rubber and containing at least natural rubber is used for the tread. The pneumatic tire according to claim 1.   The pneumatic tire according to claim 1, wherein the pneumatic tire is for heavy loads.   Two or more rubber compositions are extruded while continuously changing the supply ratio of each rubber composition to form a belt-shaped unvulcanized rubber, and the belt-shaped unvulcanized rubber is wound around a tire case to form a tread. The method for producing a pneumatic tire according to any one of claims 1 to 7, wherein:

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