JP2014019303A - Tire for motorcycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce weight of a tire while securing durability.SOLUTION: A steel cord formed by stranding plated wires in which a ternary plating layer comprising copper, zinc and cobalt is formed at a surface of a core wire is used as a band cord in a band layer of the tire for a motorcycle. The composition of the ternary plating layer comprises 60-80 at% copper and 0.1-5.0 at% cobalt. A topping rubber of the band layer is blended with 5-8 pts.mass sulfur based on 100 pts.mass of a rubber component comprising a natural rubber. A coating thickness t of the topping rubber, which is a difference (T-D) between the total thickness T of a band ply and a diameter D of the steel cord, is 0.10-0.40 mm.

Description

  The present invention relates to a motorcycle tire capable of promoting weight reduction by reducing the coating thickness of the topping rubber while ensuring adhesion between a steel cord (band cord) and a topping rubber.

  In motorcycle tires in which high-speed stability is regarded as important, a so-called parallel structure band layer in which a band cord is spirally wound in the tire circumferential direction is frequently used on the outer side in the radial direction of the carcass. . In recent years, steel cords have been adopted as the band cords in place of organic fiber cords, particularly in large motorcycle tires, in order to compensate for insufficient tire rigidity during cornering and to ensure sufficient traction during cornering. There is a tendency (see, for example, Patent Document 1).

  On the other hand, in order to improve the adhesion to rubber, steel cord is generally subjected to brass plating (binary plating of Cu and Zn) on the cord side, and organic acid cobalt salt is blended on the rubber side. ing.

  Here, the adhesion between the brass plating layer and the rubber is such that sulfur (S) blended in the rubber and the copper (Cu) in the brass plating layer are cross-linked and bonded during the vulcanization. It is expressed by forming an adhesion reaction layer (CuS layer) between the layer and the rubber. However, brass plating has good adhesion at the initial stage of vulcanization (sometimes referred to as initial adhesion), but it has adhesion (sometimes referred to as wet heat adhesion) in a high temperature and high humidity environment. descend. This is presumably because the copper in the brass plating easily elutes into the rubber under a moist heat environment, and the eluted copper lowers the crosslinking density in the adhesion reaction layer (CuS layer). Therefore, in order to suppress copper elution and improve wet heat adhesion, an organic cobalt salt is blended in the rubber.

  However, organic cobalt salts are expensive, and when the temperature in the rubber kneading process is increased, the deterioration of rubber is accelerated by cobalt, so it is necessary to lower the temperature and increase the kneading time, resulting in a decrease in rubber productivity. Invite. Further, the organic cobalt salt tends to lower the physical properties of rubber such as tensile breakability, and therefore, when the coating thickness of the topping rubber is thin, there arises a problem that the durability of the tire is lowered due to rubber breakage. In view of this, it is necessary to secure a sufficient coating thickness in the rubber containing the organic cobalt salt, which is one of the causes that hinder weight reduction of the tire.

JP 2001-130218 A

  Therefore, the present invention is based on the fact that the steel cord is subjected to specific ternary plating in which the copper and cobalt contents are regulated within a predetermined range, and the sulfur content in the topping rubber is increased to the predetermined range. It is possible to remove the organic cobalt salt from the topping rubber while ensuring both high temperature and wet heat adhesion at a high level, while improving the rubber productivity by improving the rubber kneading and covering the topping rubber An object of the present invention is to provide a motorcycle tire capable of reducing the thickness and reducing the weight of the tire.

In order to solve the above-mentioned problem, the invention of claim 1 of the present application is the tire axial distance between the tread edges, and the tread surface of the tread portion is curved in a convex arc shape from the tire equator to the tread edge. A tire for a motorcycle in which a tread width forms the maximum width of a tire, and a band layer is provided on a radially outer side of the carcass extending from the tread portion to a bead core of the bead portion and inside the tread portion. The band layer is composed of a band ply in which a narrow band ply in which one or more band cords are covered with a topping rubber is spirally wound along the tire circumferential direction,
Moreover, as the band cord, a steel cord is used in which a plating wire in which a ternary plating layer made of copper (Cu), zinc (Zn), and cobalt (Co) is formed on the surface of the core wire is twisted,
The composition of the ternary plating layer is copper (Cu): 60 to 80 at%, cobalt (Co): 0.1 to 5.0 at%,
In addition, the topping rubber is blended with 5 to 8 parts by mass of sulfur with respect to 100 parts by mass of the rubber component made of natural rubber, and the difference between the total thickness T of the band ply and the diameter D of the steel cord (TD) ), And the coating thickness t of the topping rubber is 0.10 to 0.40 mm.

  According to a second aspect of the present invention, the topping rubber does not contain an organic acid cobalt salt in the rubber.

  In the present invention, as described above, a ternary plating layer made of copper, zinc and cobalt is formed on the surface of the plating element wire. And the copper concentration in the ternary plating layer is 60 to 80 at%, the cobalt concentration is 0.1 to 5.0 at%, the amount of sulfur in the topping rubber is 5 to 8 parts by mass, etc. High concentration of copper and high content of sulfur. Therefore, the crosslink density of copper and sulfur in the adhesion reaction layer formed during vulcanization can be relatively increased, and the initial adhesion can be improved. Moreover, since cobalt is contained in the ternary plating layer, the elution of copper from the plating layer can be suppressed and the wet heat adhesion can be improved without containing the organic acid cobalt salt in the topping rubber.

  Further, since the deterioration of the topping rubber can be suppressed by eliminating the organic acid cobalt salt, the coating thickness of the topping rubber can be reduced while ensuring the durability, and the weight of the tire can be reduced. Moreover, since the temperature at the time of rubber kneading can be increased by eliminating the organic acid cobalt salt, the rubber kneading efficiency can be increased and the rubber productivity can be improved.

1 is a cross-sectional view showing an example of a motorcycle tire according to the present invention. It is a perspective view which shows a narrow strip ply. (A) It is sectional drawing which shows a band cord, (B) It is an expanded sectional view which shows the plating strand.

  Hereinafter, embodiments of the present invention will be described in detail.

  In FIG. 1, a motorcycle tire 1 according to this embodiment includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, a radially outer side of the carcass 6, and a tread portion 2. And a band layer 7 disposed inside. The tread portion 2 has a tread surface 2S that curves in a convex arc shape from the tire equator C toward the tread end Te, and a tread width TW that is a tire axial distance between the tread ends Te and Te is a tire. By making the maximum width, it is possible to turn at a large bank angle.

  The carcass 6 includes, for example, one or two pieces in this example in which carcass cords of organic fibers such as nylon, polyester, rayon, and aromatic polyamide are arranged at an angle of, for example, 60 to 90 ° with respect to the tire circumferential direction. It is formed from the carcass ply 6A. The carcass ply 6 </ b> A has ply folding portions 6 b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 at both ends of the toroidal ply main body portion 6 a straddling the bead cores 5 and 5. Further, a bead apex rubber 8 for bead reinforcement extending in a tapered manner from the bead core 5 toward the outer side in the tire radial direction is disposed between the ply body portion 6a and the ply turn-up portion 6b.

  Next, the band layer 7 is formed of at least one band ply 7A in this example. As shown in FIG. 2, the band ply 7A is formed by winding a narrow band ply 12 in which one or more band cords 10 are covered with a topping rubber 11 in a spiral shape along the tire circumferential direction. Is formed. There is no particular restriction on the winding method. For example, a single narrow belt-like ply 12 is used to wind continuously from one end side to the other end side in the tire axial direction. In order to ensure symmetry about the center, two narrow strip plies 12 are used, from the tire equator C side toward both outer sides in the tire axial direction, or from both outer sides in the tire axial direction toward the tire equator C side. It can also be wound around each. The number of the band cords 10 arranged on the narrow strip ply 12 is, for example, preferably 2 to 10, more preferably about 5 to 10, and the narrow strip ply 12 preferably has a width of about 3 to 10 mm.

  Next, as shown in FIGS. 3A and 3B, the band cord 10 is formed of a steel cord in which a plurality of plated strands 13 are twisted together. In this example, a case of a 3 × 3 structure in which three strands 17 obtained by twisting three plating wires 13 are further twisted is illustrated, but the present invention is not limited to this. Each of the plating wires 13 includes a core wire 13A made of a steel wire or the like and a ternary plating layer 13B made of copper (Cu), zinc (Zn), and cobalt (Co) covering the surface thereof. As the core wire 13A, one having a diameter of 0.1 mm to 0.3 mm can be suitably used.

  And in the said ternary plating layer 13B, the composition of the whole is copper 60-80at% and cobalt 0.1-5.0at%, and these copper, zinc, and cobalt are carried out to the whole plating layer by a thermal-diffusion process. It is preferable that it is spread | diffused uniformly over.

  When the copper content is less than 60 at%, it is difficult to sufficiently increase the cross-linking density of copper and sulfur in the adhesion reaction layer, and both initial adhesiveness and wet heat adhesiveness are insufficient. On the other hand, if it exceeds 80 at%, it becomes difficult to sufficiently suppress the elution of copper in a moist heat environment even with cobalt, which tends to deteriorate the durability of the tire by causing rubber deterioration. When the cobalt content is less than 0.1 at%, the heat and humidity adhesiveness is lowered. Conversely, when the cobalt content is more than 5.0 at%, the ternary plating layer 13B is hard, which causes cracks during wire drawing. Reduce wire drawing efficiency. From such a viewpoint, the lower limit of the copper content is preferably 60 at% or more, and the upper limit is preferably 80 at% or less. The lower limit of the cobalt content is preferably 0.1 at% or more, and the upper limit is preferably 5.0 at% or less.

  Such a plated element wire 13 is formed by adding a copper layer → cobalt layer → zinc layer or copper layer → zinc layer → cobalt layer or copper layer → zinc and cobalt alloy layer to the core wire before wire drawing. In this order, electroplating is performed, and then, for example, diffusion is performed by a heat treatment at a temperature of 500 to 650 ° C. for 5 to 25 seconds. The ternary plating layer 13B can be obtained by adjusting the formation amounts of the copper layer, the cobalt layer, and the zinc layer before the heat treatment (thermal diffusion) at this time. Thereafter, the plated wire 13 is formed by performing a wire drawing process so as to have a desired wire diameter.

  Next, in the topping rubber 11, the rubber component is highly blended with 5 to 8 parts by mass (phr) of sulfur with respect to 100 parts by mass of the rubber component. As the sulfur, sulfur generally used as a vulcanizing agent in the rubber industry can be used. When the sulfur content is less than 5 parts by mass, it is difficult to sufficiently increase the cross-linking density of copper and sulfur in the adhesion reaction layer, and both initial adhesiveness and wet heat adhesiveness are insufficient. On the other hand, when the amount exceeds 8 parts by mass, the adhesiveness with the adjacent member is deteriorated due to blooming, and it becomes difficult to uniformly disperse sulfur, and the rubber productivity is lowered because it takes time to knead the rubber.

  As the rubber component, natural rubber (NR) is employed from the viewpoint of excellent adhesiveness and improved breaking strength. In addition to the sulfur, the topping rubber 11 can be appropriately blended with known rubber additives such as reinforcing agents (carbon black, silica, etc.), vulcanization accelerators, waxes, anti-aging agents and the like. .

  However, in the present invention, by adopting the ternary plating layer 13B, the elution of copper from the plating layer is suppressed, so that the organic acid cobalt salt is not blended in the topping rubber 11. Therefore, deterioration of the topping rubber 11 due to the organic acid cobalt salt can be suppressed, and the temperature at the time of rubber kneading can be increased, so that the rubber kneading efficiency can be increased and the productivity can be improved. Further, by suppressing the deterioration of the rubber, it is possible to reduce the coating thickness of the topping rubber 11 while ensuring the durability. Therefore, in the present invention, the coating thickness t of the topping rubber, which is the difference (TD) between the total thickness T of the band ply 7A (shown in FIG. 2) and the diameter D of the steel cord, is set to 0.10-0. It can be reduced to a range of 40 mm, and the weight of the tire can be reduced. Note that if the coating thickness t is less than 0.10 mm, it is difficult to ensure durability, and conversely if it exceeds 0.40 mm, weight reduction is not achieved.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A motorcycle tire (size 160 / 60ZR17) having the internal structure shown in FIG. 1 was prototyped according to the specifications shown in Tables 1 and 2, and the durability of the prototype tire was tested to determine the tire weight and rubber productivity in tire production. The results are shown in Tables 1 and 2.

The specifications other than those described in Tables 1 and 2 are substantially the same, and the common specifications are as follows.
<Band ply>
・ Number of plies: 1 ・ Band cord: Spiral winding ・ Configuration of band cord: 3 × 3 × 0.17HT
・ Plating of plated wire: See Table 1 ・ Topping rubber coating thickness t: See Table 1 ・ Number of cords to be driven: 37.5 / 5 cm
・ Containing topping rubber
--- NR: 100phr
--- Carbon black (HAF): 63phr
--- Aging inhibitor: 2phr
--- Zinc flower: 8phr
--- Cobalt of organic acid: See Table 1 for the amount of cobalt
--- Sulfur: See Table 1
--- Vulcanization accelerator: 1phr

  The plating composition of the steel cord is obtained by immersing the steel cord in an alkaline solution to dissolve the plating, and measuring the concentration of Cu, Zn, Co by ICP emission spectroscopic analysis or atomic absorption analysis of the solution, The atomic% was determined with the total concentration as 100. As another method, the atomic% of Cu, Zn, and Co can be obtained by fluorescent X-ray analysis and SEM-EDS analysis.

(1) Tire mass:
The mass per tire was measured and evaluated by an index with Comparative Example 7 taken as 100. The smaller the value, the lighter the weight.

(2) Tire durability:
With the sample tire assembled in a rim, it was left in an oven at a temperature of 80 ° C. and a relative humidity of 98% for 150 hours to cause wet heat degradation. Thereafter, using a drum tester, the step speed method was performed in accordance with the load / speed performance test defined by ECE30. In the test, the speed was increased by 10 km / h every 10 minutes from the initial speed of 170 km / h, and the speed when the tire was damaged was evaluated by an index with Comparative Example 7 as 100. The larger the value, the better the durability.

(3) Rubber productivity:
When producing rubber by kneading, the production amount of rubber that can be produced in one hour was evaluated by an index with Comparative Example 7 being 100. The larger the value, the better the productivity.

  As shown in Tables 1 and 2, it can be confirmed that the tires of the examples can improve the durability of the tire and reduce the rubber productivity while reducing the weight. Although not shown in the table, in Comparative Example 2, since the cobalt during plating exceeds the upper limit (5.0 at%), the wire drawing efficiency was reduced. In Comparative Example 3, the initial adhesiveness was deteriorated because copper in the plating was below the lower limit (60 at%).

DESCRIPTION OF SYMBOLS 1 Motorcycle tire 2 Tread part 2S Tread surface 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Band layer 7A Band ply 10 Band cord 11 Topping rubber 12 Narrow strip ply 13 Plating wire 13A Core wire 13B Three-element plating layer C tire equator Te tread edge

Claims (2)

The tread surface of the tread portion is curved in a convex arc shape from the tire equator to the tread edge, and the tread width that is the distance in the tire axial direction between the tread edges forms the maximum tire width. A tire for a motorcycle provided with a band layer on the outside in the radial direction of the carcass leading to the bead core of the bead part and inside the tread part,
The band layer comprises a band ply in which a narrow band ply in which one or a plurality of band cords are covered with a topping rubber is spirally wound along the tire circumferential direction,
Moreover, as the band cord, a steel cord is used in which a plating wire in which a ternary plating layer made of copper (Cu), zinc (Zn), and cobalt (Co) is formed on the surface of the core wire is twisted,
The composition of the ternary plating layer is copper (Cu): 60 to 80 at%, cobalt (Co): 0.1 to 5.0 at%,
In addition, the topping rubber is blended with 5 to 8 parts by mass of sulfur with respect to 100 parts by mass of the rubber component made of natural rubber, and the difference between the total thickness T of the band ply and the diameter D of the steel cord (TD) A motorcycle tire characterized in that the topping rubber coating thickness t is 0.10 to 0.40 mm.   The motorcycle tire according to claim 1, wherein the topping rubber does not contain an organic acid cobalt salt in the rubber.

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