JPH0344921B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] In bias tires, a carcass protective reinforcing layer called a breaker is provided between the carcass and the tread. In radial tires, a reinforcing layer called a belt is provided between the carcass and the tread, and this belt tightens the carcass in the radial direction. In these pneumatic tires, steel cords may be embedded in the breaker or belt to improve the durability of the tire. The present invention relates to a pneumatic tire in which steel cords are embedded in a reinforcing layer called a breaker or belt between the carcass and the tread. [Prior Art] A breaker or belt may consist of multiple layers. Particularly when it is necessary to increase the cut resistance of a pneumatic tire, a steel cord with high elongation is embedded in the outer layer or tread side of the breaker or belt. Conventional steel cords have achieved high elongation by adopting a double-twist structure, as explained below. Figures 4 and 5 are cross-sectional views of double-stranded steel cords used in conventional pneumatic tires. Each of the configurations of "3 x 7 x 0.22" is shown. In FIG. 4, the steel cord 10 is made up of four strands 16 twisted together. Each strand 16 is made by twisting four strands 12, and each strand 12 is a steel wire with a diameter of 0.23 mm. The twist pitch between the 12 wires is 3.5 mm,
The twist pitch between strands 16 is 5.5 mm. The steel cord 10 shown in FIG. 5 is made by twisting three strands 16 together. Each strand 16 is made by twisting seven strands 12, and each strand 12 is a steel wire with a diameter of 0.22 mm. The twist pitch between the 12 wires is 4.0 mm,
The twist pitch between strands 16 is 7.5 mm. Since these steel cords 10 have a low-pitch double-twist structure, they have high elongation, high flexibility, and high shock absorption. Therefore, pneumatic tires using these steel cords 10 have high cut resistance. [Problems to be Solved by the Invention] Conventional pneumatic tires using the double-twisted steel cord described above had the following problems. That is, in the steel cord 10 having a double-stranded structure, since the strands 12 having a circular cross section are in close contact with each other, there is a closed air space 1 approximately in the center of each strand 16.
I can do 8. Therefore, this steel cord 1
0 means that it is difficult for rubber to enter the air 18. In other words,
This results in a breaker or belt in which the empty space 18 is not filled with rubber. In this case, if the toledo is traumatized and water enters the air 18 from this trauma, the water that has entered the air 18 will
inside along the steel cord 10 and stay there. Therefore, rust occurs on the steel cord 10, leading to a decrease in adhesive strength between the steel cord and the rubber. As this decrease in adhesive strength progresses, so-called separation occurs. In addition, the degree of so-called "reduction in twisting" of the strength was large, and the strength of each strand 12 could not be effectively utilized. Therefore, in order to obtain the desired strength of the steel cord 10, a large number of strands 12 are required, which makes the steel cord 10 heavy. Furthermore, since the highly flexible steel cord 10 is used, there is a problem in that the pneumatic tire is largely deformed at the ground contact area, resulting in high rolling resistance and poor fuel efficiency. The present invention has been made in view of the above points, and prevents separation while maintaining high cut resistance equivalent to the conventional one, effectively utilizes the strength of the strands, and improves tire rigidity. Aims to provide pneumatic tires. [Means for Solving the Problems] A pneumatic tire according to the present invention has a rubber layer between a carcass and a tread, which includes a plurality of first steel cord layers which are hoops, and a plurality of first steel cord layers which are hoops, and a plurality of first steel cord layers which are hoops, and an outermost layer on the outside in the radial direction thereof. The steel cord layer is reinforced by a second steel cord layer, which is a cut-resistant protective layer, and each cord constituting the second steel cord layer has gaps between adjacent strands in some places in the longitudinal direction. It is characterized by having a single-strand structure twisted with a small pitch length, and elongation at the time of cutting being 4% or more. [Function] Although the steel cord of the pneumatic tire according to the present invention has a single-twist structure in the outermost layer near the tread surface, the twist pitch is smaller than that of conventional cords, and the elongation at cutting is 4. It has a high elongation of more than 10% and is soft, so when you step on a stone, etc., it deforms and cushions the impact. Therefore, high cut resistance equivalent to that of a double-twisted structure is achieved. Also,
Since the twist pitch is smaller than the conventional one, the spaces between the wires are opened in some places, allowing the rubber to enter into these spaces. Furthermore, the steel cord has a single-strand structure, which improves the strength utilization rate.
Its moderate bending hardness improves tire rigidity. Also, the inner steel cord layer near the carcass acts as a "hoop". [Example] FIG. 1 is a sectional view of a steel cord used in a radial tire according to an example of the present invention. This steel cord 10 has a single-strand structure with a configuration of "1 x 5 x 0.38". That is, five steel wires 12 having a diameter of 0.38 mm are twisted together. The twist pitch is 6.5mm. Since this steel cord 10 has a small twist pitch, there are gaps with a width of at least 0.02 mm between the strands 12 at some places in the longitudinal direction, and the spaces 14 between the strands 12 are opened. Therefore, during vulcanization, rubber can enter into the spaces 14 through the gaps between the strands 12, and the spaces 14 are filled with rubber. Figure 2 shows the steel cord 10 explained above.
FIG. 3 is a partial cross-sectional view of a radial tire equipped with a belt embedded therein, and FIG. 3 is a partially enlarged cross-sectional view of the belt. However, the steel cord 10 is not shown in FIG. 2. The radial tire 2 shown in FIG. 2 is 11R22.5 and has four belts 8a, 8b, 8c, and 8d between the carcass 4 and the tread 6. The three belts 8a, 8b, 8c on the carcass side are
A steel cord with a configuration of 0.20 + 6 x 0.35 is buried. In other words, this steel cord consists of three steel wires with a diameter of 0.20 mm and six steel wires with a diameter of 0.35 mm. Cord insertion is 2.5cm
That's 12 pieces per hit. These three belts 8a, 8
b, 8c tighten the carcass 4 made of polyester ply in the radial direction. Outermost belt 8
The steel cord 10 described above is buried in d. That is, the belt 8d is made by topping rubber on both sides of steel cords 10 disposed in parallel to form a rubber layer 11, and further vulcanizing this rubber layer 11. Even with this belt 8d, there are 12 cords per 2.5cm. All steel wires are plated to improve adhesion to rubber. The steel cords used for the three belts 8a, 8b, 8c have a small elongation when cut, and therefore function as hoops for the carcass 4. The outermost belt 8d contributes to the high cut resistance of the radial tire 2, as described below. Table 1 shows the characteristics of the steel cord 10 of the radial tire 2 according to the embodiment of the present invention described above and the characteristics of the tire itself. The table also shows the characteristics of the cord and tire for three comparative examples.

[Table] Comparative example 1 is a 4×4×
Comparative Example 2 uses a steel cord with a double-strand structure of
0.22" double-stranded steel cord. Comparative Example 3 uses a steel cord with a single-strand structure of "1 x 5 x 0.38", but the twist pitch is as large as 18.0 mm, which is comparable to conventional products. Therefore, in the steel cord 10 of Comparative Example 3, as shown in FIG. 6, closed voids 18 are formed between the strands 12 as in the case of the double-twist structure. The pneumatic tires of each comparative example were the same 11R22.5 radial tires as the examples, and the carcass 4 and three belts 8a, 8
b and 8c are the same. The above-mentioned steel cord, which is unique to each comparative example, is buried in the outermost belt 8d. As can be seen from Table 1, the steel cord 10 of this example has a small twist pitch of 6.5 mm even though it has a single-strand structure, so the elongation at the time of cutting is 6.5 mm.
%, and high elongation equivalent to Comparative Examples 1 and 2 can be obtained. In addition, as shown in the same table, as a result of the Charpy test, impact absorption properties equivalent to those of Comparative Examples 1 and 2 were obtained. Therefore, in this example, it is expected that the cut resistance performance is equivalent to that of a double-stranded structure, but each radial tire was actually installed on a large dump truck and was tested on rough roads of 30,000 km in a stone crushing site. The results of the running test also showed that cut resistance performance equivalent to that of Comparative Examples 1 and 2 was obtained. The cut resistance performance was measured as follows. That is, even if a cut passes through the tread 6 and reaches the belt 8d, the steel cord 10 embedded in the belt may or may not be cut. The cord breakage rate is the number of cord breaks relative to the total number of cuts. Note that the steel cord 10 of Comparative Example 3 has a twist pitch as large as 18.0 mm, which is comparable to conventional products, and therefore has a small elongation of about 2.5%, and has poor cut resistance. In addition, in this embodiment, the space between the strands 12 is 1
Since the rubber smoothly penetrated into the belt 8d, there was no separation of the belt 8d, unlike the three comparative examples. Furthermore, the wire strength utilization rate of the example is the same as that of comparative example 3.
Although not so high, it is improved over Comparative Examples 1 and 2. Therefore, the total weight of the cord to obtain the desired strength of the steel cord 10 is lower than that of Comparative Examples 1 and 2.
smaller, which can reduce tire weight. In addition, in this example, due to the appropriate bending hardness of the steel cord 10, the tire rigidity was lower than that of comparative example 1.
2, and the rolling resistance becomes smaller. Therefore, according to this embodiment, it is expected that fuel efficiency will be improved. In addition, the above is 6.5mm only for the outermost layer belt 8d.
Although the case has been described in which the steel cord 10 having a single-strand structure with a small twist pitch is buried, the number of belts in which the steel cord 10 is buried may be increased as necessary. For example, assume that there are two belts 8c and 8d on the tread side. Moreover, although the radial tire has been described above, the present invention can also be applied to a breaker in a bias tire. [Effects of the Invention] As explained above, in the pneumatic tire according to the present invention, the reinforcing layer between the carcass and the tread, that is, the breaker or the belt, has a single-twist structure in which the outermost layer has an elongation of 4% or more when cut. It is reinforced with a steel cord, and has high elongation even though the steel cord is a single-strand structure. Therefore, high cut resistance equivalent to that of a double-twisted structure is achieved. Furthermore, since the twist pitch is smaller than that of the conventional one, the gaps between the strands are opened in some places, allowing the rubber to enter into the gaps. Therefore, separation of the breaker and belt can be prevented. Furthermore, since the steel cord has a single-strand structure, the strength utilization rate of the strands is improved. Therefore,
Even though the steel cord reduces the overall weight, the desired strength of this cord can be obtained and a lighter tire can be achieved. Also, the inner layer of steel cord close to the carcass acts as a hoop to protect the carcass. Further, according to the present invention, the rigidity of the tire is improved due to the appropriate bending hardness of the steel cord. Therefore, deformation of the tire is reduced, rolling resistance is reduced, and fuel efficiency is improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a steel cord used in a radial tire according to an embodiment of the present invention, FIG. 2 is a partial sectional view of a radial tire equipped with a belt in which the steel cord shown in the previous figure is embedded, Figure 3 is
Figure 1 is a partially enlarged cross-sectional view of a belt with embedded steel cords, Figure 4 is a cross-sectional view of a double-stranded steel cord used in conventional pneumatic tires, and Figure 5 is a cross-sectional view of a belt with embedded steel cords. Cross-sectional view of other configurations of double-stranded steel cord used in tires,
FIG. 6 is a sectional view showing a steel cord having a single-strand structure, which is a comparative example of the steel cord shown in FIG. 1, and having a large twist pitch. Explanation of symbols, 2...Radial tire, 4...Carcass, 6...Tread, 8a, 8b, 8c, 8
d...Belt, 10...Steel cord, 11...
...Rubber layer, 12...Element wire, 16...Strand.

Claims (1)

[Claims] 1 The rubber layer between the carcass and the tread consists of a plurality of first steel cord layers that are hoops and a second steel cord layer that is a cut-resistant protective layer that is disposed as the outermost layer on the outside in the radial direction. Each cord constituting the second steel cord layer is reinforced so that the distance between adjacent strands is
1. A pneumatic tire characterized by having a single-strand structure twisted with a small pitch length such that the fibers are present here and there in the longitudinal direction, and having an elongation at the time of cutting of 4% or more.