JPH0226990A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To obtain a pneumatic tire having an elongation at break higher than a specific level, keeping a specific gap width between the element wires, maintaining high cut resistance and having improved strength of element wire by specifying the twist angle of element wire constituting a steel cord. CONSTITUTION:The twist angle of element wire 12 constituting a steel cord 10 is set to 26-32 deg. relative to the longitudinal direction of the steel cord. The cord having the above structure has an elongation at break of >=4% even in the case of a cord of a single-twist structure and a gap 14 having a width of >=0.02mm is uniformly formed between the element wires constituting the steel cord. Accordingly, the gap 14 of the steel cord is uniformly impregnated and filled with rubber in vulcanization process to prevent the residence of external water and the rusting of the steel cord in contrast to the conventional cord. The pneumatic tire produced by using the above steel cord can suppress the formation and progress of separation and is light in weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] In a bias tire, a reinforcing layer for protecting the carcass 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 with a steel cord embedded in the breaker or belt between the carcass and the tread.

[Conventional technology] A breaker or belt may consist of multiple layers.

In particular, when it is necessary to improve the cut resistance of a pneumatic tire, a steel cord with high elongation is embedded in the outer layer of the breaker or belt, that is, on the tread side.

In conventional steel cords, large elongation was usually achieved by adopting a double-twist structure, as described below.

5 and 6 are cross-sectional views of double-stranded steel cords used in conventional pneumatic tires.
7Xo and 22J configurations are shown, respectively.

In FIG. 5, the steel cord IO 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 about 0.23.

The twist pitch between the strands 12 is 3.5 mm, and the twist pitch between the strands 18 is 5.5 m+s.

The steel cord IO shown in FIG. 6 is made by twisting three strands 16 together. Each strand 1B is made by twisting seven strands 12, and each strand 12 has a diameter of 0.
．． It is a 22mm steel wire.

The twist pitch between the strands 12 is 4.0 mm, and the twist pitch between the strands 16 is 7.5 mm.

Since these steel cords IO have a low pitch double-twist structure, they have a large elongation at break of 6.5 to 7.0%, are highly flexible, and have high shock absorption properties. Therefore, conventional pneumatic tires using these steel cords 10 had 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.

In other words, in the conventional double-stranded steel cord IO,
The degree of so-called strong "twist reduction" is large, and each strand 12
could not make effective use of its power. Therefore, in order to obtain the desired strength of the steel cord 1G, a large number of strands 12 are required, which makes the steel cord 10 heavy.

Furthermore, since the rigidity of the steel cord IO is low, the pneumatic tire is significantly deformed at the ground contact portion, resulting in a problem of high rolling resistance and poor fuel efficiency.

Further, as shown in FIGS. 5 and 6, since the strands 12 having a circular cross section are in close contact with each other, a closed gap 18 is formed approximately in the center of each strand 16. Therefore, in this steel cord lo, rubber is difficult to enter into the void 18. In other words, a breaker or belt is created in which the void 18 is not filled with rubber. In this case, if the tread is traumatized and water enters the cavity 18 from this trauma, the intruded water flows through the cavity 18 into the steel cord IO.
move along and stay there. Therefore, rust occurs on the steel cord IO, resulting in a decrease in adhesive strength between the steel cord and the rubber.

When this decrease in adhesive strength becomes more severe, so-called separation occurs.

The present invention has been made in view of the above circumstances, and
While maintaining the same high cut resistance as when using a conventional double-stranded steel cord, the use of a single-stranded structure increases the utilization of the strength of the strands and improves the rigidity of the steel cord. An object of the present invention is to provide a pneumatic tire that suppresses the occurrence and progression of separation.

[Means for Solving the Problems] A pneumatic tire according to the present invention is a pneumatic tire in which the rubber layer between the carcass and the tread is reinforced with a single-strand steel cord, and the twist angle θ of the wires is The steel cord has an elongation of 4% or more when cut at an angle of 26 to 32 degrees with respect to the longitudinal direction of the steel cord, and a gap of 0.02 m+s or more is maintained between the strands constituting the steel cord. It is characterized by the presence of

However, the twist angle θ of the strands with respect to the longitudinal direction of the steel cord is expressed as θ-tan-1 (πD/P). Here, regarding the steel cord, D represents the cord diameter, and P represents the twist pitch.

That is, the twist angle θ is determined according to the ratio of the cord diameter to the twist pitch P, that is, D/P.

In addition, the range of twist angle θ from 26 to 32@ corresponds to the range of 0.15 to o, 2o for the ratio D/P, and the reciprocal of this ratio P/D is 5.03 to 6.44. approximately corresponds to the range of

A gap having a width of 0.02 square or more between the wires can be realized by shaping the wires by setting the ratio F to 110% or more. Here, the shaping rate F is a value representing the degree of shaping when shaping the wire into a spiral shape, and is defined as follows.

That is, let A be the helical diameter of each strand of shaped strand diameter d before twisting. The cord diameter when strands of helical diameter A are twisted together to form a steel cord is actually the value mentioned above, but the cord diameter when strands having strand diameter d are closely attached is B. . At this time, the shaping rate F is A/BX100
(%) Therefore, for shaping, the rate F is 100%
If the value is below, the cord diameter will match the above value B, but if the value of the shaping rate F is greater than 100%, the cord diameter will be larger than the above value B, and between the strands. A gap is created.

[Function] Figure 4 shows the relationship between the twist angle θ and the elongation at cutting in a single-layer steel cord.

This relationship was obtained through experiments, and when the twist angle θ is in the range of 26 to 32 m, the steel cord has a large elongation of approximately 4 to 8% when cut, realizing high cut resistance performance of pneumatic tires. be done. Further, since the steel cord has a single-strand structure, the strength utilization rate of the strands is improved and the rigidity of the cord is increased. If the twist angle θ is smaller than 26@, the elongation cannot reach 4% or more, and conversely, if θ becomes larger than 32°, strand breakage will occur during half-plane twisting, which increases the elongation. It becomes easier and productivity decreases. Furthermore, if the twist angle θ is larger than 32'', the cord weight per unit length becomes excessive, which not only affects the tire weight, but also causes the rigidity of the steel cord to become too low.

A gap of 0.02 mm or more in width maintained between the strands increases the rubber penetrating property of the steel cord during vulcanization of the pneumatic tire, and contributes to realizing uniform rubber penetrating into the voids in the cord. A gap with a width of 0.02 mm or more can be obtained by setting the rate F of 110% or more for the shaping of the strands, but from the viewpoint of rubber penetration, cord strength, and workability during tire manufacturing, the shaping is F is preferably in the range of 110 to 150%.

In other words, if the shaping rate F exceeds 150%, not only will the cord become more likely to become disordered during twisting, but the rubber covering the steel cord will become thicker, resulting in an increase in tire weight, which is undesirable. Although it is not necessary that the shaping ratio F of each strand constituting the steel cord be the same, if the shaping ratio F differs greatly between the strands, the strength utilization rate of the strand will decrease.

[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 IO has a single-strand structure of rlx5xO, 38J. That is, five steel wires 12 each having a diameter of 0° and 38 m+a are twisted together. Twisting pitch P
is 6.5 sn, cord diameter is 1°15 dragon, twist angle θ is 2
9.1@, and the elongation at cutting is 6.5%. For shaping, the rate F is 130%, and the distance between 12 strands is 0.03■
A gap with a width of 1 is uniformly formed, and a gap 14 surrounded by the strands 12 is open everywhere in the longitudinal direction of the steel cord IO. Therefore, during vulcanization, the rubber uniformly penetrates into the voids 14 through the gaps between the strands 12, and the voids 14 are completely filled with rubber.

FIG. 2 is a partial sectional view of a radial tire including a belt in which the steel cord 10 described above is embedded, and FIG. 3 is a partially enlarged sectional view of the belt. However, in FIG. 2, illustration of the steel cord IO is omitted.

The radial tire 2 in FIG. 2 is 11R22,5,
Four belts 8a, 8 are placed between the carcass 4 and the tread B.
It has b, 8c, and 8d. Three belts 8 on the carcass side
a, 8b, 8c, r3XO, 20+6X0.35J
A steel cord with the following structure 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.

The number of cords to be inserted is 12 per 2.5 cm. These 3
The belts 8a, 8b, 8c radially tighten the carcass 4 made of polyester braai. The steel cord 10 described above is embedded in the outermost belt 8d. That is, the belt 8d is made by topping rubber on both sides of a steel cord 1O disposed in parallel to form a rubber layer 11, and further vulcanizing this rubber layer 11. Even with this belt 8d, the number of cords inserted is 12 per 2.5 cm. All steel wires are plated with brass to improve adhesion to rubber.

The three belts 8a, 8b, 8c are the "hoops" of the carcass 4.
functions as The outermost belt 8d contributes to the high cut resistance of the radial tire 2, as described below.

Radial tire 2 according to the embodiment of the present invention described above
Table 1 shows the characteristics of the steel cord IO and the characteristics of the tire itself. Table 1 also shows the characteristics of the three comparative examples, and Table 2 shows the characteristics of the other three comparative examples.

(Margins below) In Comparative Example 1, the cord diameter P was the same as in the example, but the twist pitch P was increased and the twist angle θ was made smaller than 26°. On the contrary, in Comparative Example 2, the twist pitch P was made small and the twist angle θ was made larger than 32@. In the shaping of Comparative Examples 1 and 2, the ratio F was 130% as in the example, and the width of the gap between the strands was 0.03+n. In Comparative Example 3, the twist angle θ is set to a value within the range of 26 to 32'', but the shaping ratio is set to 108% and the gap between the strands is 0.0.
The diameter of the steel cord is smaller than 2 mm, and the void surrounded by the strands is only opened here and there in the longitudinal direction of the steel cord.

Comparative Examples 4 and 5 shown in Table 2 use conventional double-twisted steel cords whose cross sections are shown in FIGS. 5 and 6, respectively. Comparative example 6 is the same as the example < r
It is a single-strand structure with a composition of 1X5XO, 38J, but 1.0
Compared to the cord diameter of 3 mm, the twist pitch P is very large at 18.0 degrees, and the twist angle θ is 10.2 degrees.

The shaping ratio F is 100%, and closed voids 18 are created between the strands 12 as shown in FIG.

The pneumatic tires of each Comparative Examples 1 to 6 were also 11R22, which was the same as the example.
, 5, and the carcass 4 and three belts 8a and 8L8c are the same. Outermost belt 8
A steel cord unique to each comparative example is embedded in d.

In the case of this example and comparative examples 2 and 3, the twist angle θ is 2
6' or more, the elongation at the time of cutting is 4% or more even though it has a single-twist structure, and it has a high elongation that is almost equivalent to the steel cord of Comparative Examples 4 and 5, which have a double-twist structure. is obtained.

Charpy test results, present example and comparative example 2.3.
No. 4 and No. 5 have the same impact absorption properties.

As a result of a 3-way driving test conducted on rough roads in a stone crushing yard with each radial tire mounted on a large dump truck, it was found that the same cut resistance performance was obtained in this example and comparative examples 2, 3, 4 and 5. ing. The cut resistance performance was measured as follows. That is, even if a cut is made to penetrate the tread 6 and reach the belt 8d, the steel cord IO 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.

On the other hand, the steel cords with single-strand structure in Comparative Examples 1 and 6 have a twist angle θ smaller than 26@, so the elongation at cutting is less than 4%, and compared to this example, the steel cord The shock absorption of the cord and the cut resistance of the pneumatic tire are poor.

Next, the strand strength utilization rate in the examples that adopted the single-strand steel cord, Comparative Examples 1 to 3, and Comparative Example 6 was improved compared to the case of the conventional reinstated structure shown in Comparative Examples 4 and 5. ing. Therefore, by adopting the single-strand structure, the total weight of the steel cord to obtain the desired strength can be reduced compared to the conventional method, and the weight of the tire can be reduced.

Furthermore, the bending hardness, that is, the rigidity of the steel cord is improved compared to Comparative Examples 4 and 5, and the rolling resistance of the pneumatic tire is reduced.

However, in the case of Comparative Example 2 in which the twist angle θ is greater than 32°, although the cord characteristics and tire characteristics are good as explained above, the strands are difficult to permanently deform during the steel cord manufacturing process. This not only reduces workability but also causes frequent wire breakage during twisting. therefore,
The productivity of steel cord is poor and it cannot be put into practical use. Another problem is that the weight of the steel cord is greater than in the case of the present embodiment in which the cord diameter is the same and the twist pitch is large, resulting in an increase in the weight of the tire. There is also a decrease in the rigidity of the steel cord.

In the case of Example 6 in which the shaping ratio F is 100%, the strands 12 of the steel cord are in close contact with each other to form a closed gap 18 between the strands, so Comparative Example 4 of the restoration structure As in the case of .5, rubber penetration is poor and separation occurs in the tire. In the case of Comparative Example 3 in which the shaping ratio F is smaller than 110%, the gap width between the strands is smaller than 0.02 m, and the void surrounded by the strands is only opened at some places in the longitudinal direction of the steel cord. Therefore, at positions where the gap width of the strands happens to be large, rubber will certainly enter the gap during vulcanization, but at positions where the gap width is small, rubber will still be inhibited from entering. Therefore, voids that are not filled with rubber remain, and water accumulates in these voids, causing rust on the cord. Therefore, in pneumatic tires using this steel cord, it is impossible to reliably suppress the occurrence and progression of separation. Can not.

On the other hand, in the present example and comparative examples 1 and 2 where the shaping rate F is 130%, the rubber smoothly penetrates into the space 4 between the strands 12 through the gap of width 0.02 m + s or more. ,1
00% rubber penetration is obtained. Therefore, Comparative Example 3
In contrast to Tests 6 to 6, there was no separation failure of belt 8d.

In addition, in the above embodiment, a case has been described in which the steel cord 10 is buried only in the outermost belt 8d, but 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.

Further, the present invention can also be applied to a breaker in a bias tire.

[Effects of the Invention] As explained above, the pneumatic tire according to the present invention is a pneumatic tire in which the rubber layer, that is, the breaker or belt between the carcass and the tread is reinforced with a single-strand steel cord, Moreover, the twist angle of the strands is 26 to 32 degrees with respect to the longitudinal direction of the steel cord, and even though the steel cord has a single-strand structure, it has a high elongation of 4% or more when cut, making it possible to restore the conventional method. It is possible to improve the utilization of the strength of the strands and the rigidity of the steel cord while maintaining the same high cut resistance as when using a structural steel cord. Therefore, according to the present invention, the desired strength of the cord can be obtained even if the total weight of the steel cord is reduced by improving the utilization rate of the strength of the strands.
A lightweight pneumatic tire can be realized. Further, due to the improved rigidity of the steel cord, the pneumatic tire according to the present invention has a smaller tread deformation, reduces rolling resistance, and improves fuel efficiency. Furthermore, since the twisting angle is limited to 32'' or less, there are no production problems during stranding processing and problems of increased weight of the steel cord, and appropriate rigidity of the steel cord is achieved.

In addition to the above points, by setting the shaping ratio of the wires constituting the steel cord to 110% or more, there is no gap between the wires.
．． A gap with a width of 0.2++ us or more is maintained, and during vulcanization, the rubber easily penetrates into the void inside the steel cord through this gap. Therefore, according to the present invention, no voids not filled with rubber remain, and the occurrence and progression of separation is reliably suppressed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a steel cord used in a radial tire according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view of a radial tire equipped with a belt in which the previous steel cord is embedded, and FIG. The figure is a partially enlarged sectional view of the belt in which the steel cord in Figure 1 is embedded. Figure 4 is a diagram showing the relationship between the twist angle and the elongation at cutting in a single-layer steel cord. Figure 5 6 is a cross-sectional view of a steel cord with a reinsertion structure used in conventional pneumatic tires, FIG. ,
FIG. 2 is a cross-sectional view showing a steel cord with a single-strand structure, which is a comparative example of the steel cord in FIG. 1; Explanation of symbols 2...Radial tire, 4...Carcass, 6...
Tread, 8a, 8b, 8c, 8d...belt, lO
...Steel cord, 11...Rubber layer, 12...
Bare wire. Patent applicant: Toyo Rubber Industries, Ltd. Figure 1 Figure 3 Cup! ! ! 4 and (e) Figure 4 Figure 2

Claims (1)

[Claims] 1. A pneumatic tire in which the rubber layer between the carcass and the tread is reinforced with a single-strand steel cord,
The twist angle of the strands is 26 with respect to the longitudinal direction of the steel cord.
~32°, the steel cord has an elongation of 4% or more when cut, and the distance between the strands constituting the steel cord is 0.02°.
A pneumatic tire characterized in that a gap having a width of mm or more is maintained. 2. The pneumatic tire according to claim 1, wherein the shaping rate of the strands is 110% or more.