JP2824703B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire using a steel cord having improved corrosion resistance and fretting as a carcass cord.

[0002]

2. Description of the Related Art Steel cords are widely used as carcass cords for heavy-duty pneumatic tires, in particular, because they have remarkably superior overall performance as a reinforcing material as compared with reinforcing cords made of other fiber materials. ing. However, steel cords have the essential disadvantages of lower corrosion resistance to water and lower water adhesion to coated rubber than fiber cords.

In order to improve the corrosion resistance and the water resistance, Japanese Patent Application Laid-Open No. 2-229288 discloses that a steel cord is composed of a core consisting of two or three strands and three to five strands. What consists of an inner layer and an outer layer consisting of 7 to 11 strands, and makes the twist direction of the strands of each layer all the same, and increases the twist pitch sequentially in the order of the core, the inner layer, and the outer layer Proposed. However, when this steel cord is used for a carcass cord of a heavy load tire, it cannot be said that the steel cord has sufficient corrosion resistance and water-resistant adhesiveness. In particular, when the number of core wires is three, since the wires are tightly twisted with each other to form a closed space in which it is difficult to penetrate the coat rubber at the center, water is allowed to enter the space. As a result, corrosion resistance and water resistance are further reduced.

[0004] Further, such a twist pitch is a core strand,
The steel cords that are different in the inner layer wire and the outer layer wire are inevitable that the wires adjacent in the radial direction are in point contact with each other, are easily rubbed against each other and easily worn away, and cause so-called fretting. However, the problem of impairing the durability of the APC has not been sufficiently solved. Further, since the strands of the core, the inner layer and the outer layer have different twist pitches from each other, it is necessary to twist the cord three times when processing into a cord, and there is a problem that productivity is poor.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a steel cord for use as a carcass cord.
An object of the present invention is to provide a pneumatic tire having excellent durability by further improving water-resistant adhesion and fretting resistance.

[0006]

According to the present invention for achieving the above object, a carcass cord comprises a steel cord, and the steel cord comprises a core comprising two twisted strands; An inner layer consisting of not more than five strands spirally wound, and an outer layer consisting of not more than twelve strands spirally wound around the inner layer; these core, inner layer and outer layer The twist direction of each element wire is the same, and while making the twist pitch of the core and the outer layer substantially the same, making the twist pitch of the inner layer smaller than the twist pitch of the core and the outer layer. It is a feature.

In the case where the cord structure of the steel cord is composed of the core, the inner layer, and the outer layer as described above, the twist direction of the strands of each layer is the same, but the twist pitch of the inner layer is minimized. The twist pitch of the core and the outer layer is larger than that of the inner layer and is the same as each other, so that the permeability of the coated rubber into the core and the inner layer is improved. Therefore, the corrosion resistance and water resistance required for the carcass cord are improved, and the fretting between the wires can be reduced.

Hereinafter, the configuration of the present invention will be specifically described with reference to the drawings. FIG. 1 is a perspective view showing an example of a steel cord used for a carcass cord of the tire of the present invention. Also, FIGS. 2 (a), (b), (c) and (d)
FIG. 3 is a cross-sectional view showing an example of the relative positional relationship between the core, the inner layer, and the outer layer along the progress of twisting of the steel cord of the tire of the present invention. Steel cord 1
Has a core 2 composed of two twisted strands, an inner layer 3 composed of four strands spirally wound around the outside of the core 2, and a spiral spiral wound around the outside. It is composed of three layers of the outer layer 4 composed of eleven element wires. The twisting directions of the respective layers are all the same, and the twisting pitch has a relationship of core = outer layer> inner layer.
2 (a), (b), (c) and (d), the core 2
When attention is paid to changes in relative positions along the progress of the twisting of one of the strands A of the core 2, one of the strands C of the inner layer 3 and one of the strands B of the outer layer 4, the The positional relationship between the wire A and the wire B of the outer layer 4 is always invariable, and the positional relationship between the wire A of the core 2 and the wire C of the inner layer 3 changes along the traveling direction of the twist. This is because the twist pitch of the core strand A and the outer strand B is the same, and the twist pitch of the strand C of the inner layer is smaller than the twist pitch of the core strand A and the strand B of the outer layer. .

[0009] With such a structure, the inner layer 3 wound spirally around the core 2 and the outer layer 4 spirally wound around the inner layer 3 are formed between the respective wires constituting the outer layer 4. , A sufficient gap is formed, so that the coating rubber easily penetrates and covers not only the inner layer 3 but also the periphery of the element wire of the core 2 through this gap. It is important that the core 2 of the steel cord of the present invention is composed of two strands. If the number of strands is one, no twisting is applied, so that when the load is applied, the core 2 is cut off first, and the power utilization rate decreases. Further, if the number is three or more, as described above, a closed space in which the penetration of the core nicoat rubber is difficult is formed, so that the penetration of moisture is easily caused and the corrosion resistance is reduced. The number of strands of the inner layer 3 is 5 or less, and the number of strands of the outer layer 4 is 12 or less, preferably 8 to 12. If the number of strands in the outer layer exceeds 12, the gap between the strands is reduced, and the permeability of the coated rubber deteriorates. Further, the weight of the cord increases, which is not preferable from the viewpoint of reducing the weight of the tire. Also, 8
With more than the number of cords, the tensile strength of the entire cord is ensured, and there is no practical problem.

The core 2, the inner layer 3, and the outer layer 4
Is that those wires are spirally wound in the same direction,
Further, the twist pitch of the strands of the core 2 and the outer layer 4 is made substantially the same, and the twist pitch of the strands of the inner layer 3 is made smaller than the twist pitch of the strands of the core 2 and the outer layer 4. By making the inner layer the smallest twist pitch, the penetration of the rubber throughout the core and the outer layer is effectively performed. If the twist pitches of the core, the inner layer, and the outer layer are all the same, the wires of the outer layer fall between the wires of the inner layer, and the gap through which the coating rubber penetrates is reduced.

The number of strands in the inner layer is preferably as small as possible to improve the rubber permeability to the core. However, if the number of strands in the inner layer is too small, the strands in the outer layer are The ratio of falling into the gap between the strands increases. For this reason, by setting the twist pitch of the core and the outer layer to be substantially the same, the wires come into line contact with each other, and the occurrence of fretting can be effectively prevented.

Furthermore, since the core and the outer layer have the same twist pitch, when a steel cord is manufactured, the inner layer is placed on the core while keeping the two strands of the core aligned without twisting. Is wound, and the wires constituting the outer layer are aligned and twisted around the wires, whereby the outer layer and the core can be simultaneously twisted. Therefore, three layers are twisted by only two twisting operations to obtain a steel cord.
Productivity can be improved.

The carbon content of the steel cord used in the present invention is not particularly limited, but is preferably 0.8 to 0.9.
Desirably, it is 5% by weight. Such high carbon content allows the carcass cord to have the necessary tensile strength while reducing the total number of strands of the steel cord to a maximum of 19 or less as described above, thereby further reducing the weight of the tire. Can be.

Further, it is desirable that all the wire diameters used in the steel cord of the present invention have the same diameter.

[0015]

EXAMPLE The carbon content was 0.82% by weight and the diameter was 0.2.
Using a 2 mm strand, as shown in Table 1, the cord structure and the twist pitch of the strand of each layer of the core, the inner layer and the outer layer (m
m) were modified to produce four types of steel cords, and these were used as carcass cords to produce pneumatic tires. The size of these tires was the same 1000 R / 20. With respect to these four types of tires, the following corrosion resistance and fretting resistance were evaluated, and the results are shown in Table 1. Corrosion resistance : Cut a carcass cord into a size of 30 mm in width and 100 mm in length while covering the rubber from the tire side wall part, seal once with an epoxy-based adhesive, and place in a 20% NaCl aqueous solution for 3 days After immersion, the single cord was peeled off and the corrosion length was measured. The evaluation results were expressed as an index with the measured value of the conventional tire being 100. The smaller the index value, the better the corrosion resistance. Fretting resistance : Carcass cord is taken out from the tire after traveling 100,000 km on a pavement road, disassembled, and the core,
For each layer of the inner layer and the outer layer, the amount of fretting was observed with a microscope, and scored according to a 5-point method in which the state of the wire without fretting was 5 points, and the state where the wire was cut in half was 0, and the points were scored. Was counted. Regarding the total points totaled,
The index is represented by an index with the score of the conventional tire being 100. The larger the index value, the better the fretting property.

[0016]

[Table 1] As shown in Table 1, the carcass cord (steel cord) of the tire of the present invention has not only significantly improved corrosion resistance, but also improved fretting resistance.

[0017]

According to the present invention, the steel cord is
The core is composed of three strands, the inner layer is composed of 5 or less strands, and the outer layer is composed of 12 or less strands. By making the twist pitch of the core and the outer layer substantially the same, and making the twist pitch of the inner layer smaller than the twist pitch of the core and the outer layer, thereby forming a closed space in the cord cross section. Does not form and improves the permeability of the coated rubber. Therefore, the corrosion resistance, water adhesion resistance and fretting resistance of the carcass cord are improved, and the durability of the pneumatic tire is improved. In addition, twisting operation of steel cord
The productivity can be improved because the process can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a steel cord used in the present invention.

FIGS. 2 (a), (b), (c) and (d) are cross-sectional views each showing the relative positional relationship of the wires along the progress of twisting of the steel cord of the tire of the present invention.

[Explanation of symbols]

 Reference Signs List 1 steel cord 2 core 3 inner layer 4 outer layer A core wire B inner layer wire C outer layer wire

Claims (1)

(57) [Claims] 1. A carcass cord comprising a steel cord, the steel cord comprising a core comprising two twisted strands, and an inner layer comprising not more than five strands spirally wound around the core. And an outer layer composed of 12 or less wires spirally wound around the inner layer, and the twist directions of the wires of the core, the inner layer and the outer layer are all the same, and And the twist pitch of the outer layer is substantially the same, and the twist pitch of the inner layer is smaller than the twist pitch of the core and the outer layer.