JP4426811B2 - Steel cord and pneumatic tire using the same - Google Patents

Description

  INDUSTRIAL APPLICABILITY The present invention is suitable as a tire carcass cord, and a steel cord having improved durability by optimizing the ratio of the twist pitch and the twist angle between the core and the sheath in a two-layer twist structure, and It relates to the used pneumatic tire.

  Conventionally, as a carcass cord of a pneumatic radial tire, particularly a heavy duty radial tire for trucks and buses, for example, a layer twist structure of 2 + 7, 3 + 8, 3 + 9, 3 + 9 + 1 or the like has been adopted.

  In recent years, in order to improve durability while ensuring the strength of the cord and the rubber penetration into the cord in the steel cord having such a layer twist structure, the wrapping wire is excluded and the core and the sheath are twisted. Two-layer twisted structures of 2 + 7 and 3 + 8 having the same direction have been proposed (see, for example, Patent Documents 1 and 2).

  This is because the number of sheath wires is reduced by one from the maximum number that can be arranged around the core, so that the number of strands can be reduced while ensuring a gap through which rubber can penetrate between the sheath wires. Can be maximized. In addition, by making the twisting directions of the core and the sheath the same, the contact pressure between the core wire and the sheath wire can be reduced, and the contact between the sheath wires is suppressed by the rubber that permeates from the gap. In addition, the contact between the wrapping wire and the sheath wire can be suppressed by excluding the wrapping wire. That is, the fretting of both the core wire and the sheath wire can be reduced, and the cord durability can be improved by suppressing fatigue due to wear, corrosion fatigue due to plating peeling, and the like.

However, with the recent improvement in performance of pneumatic tires, further improvement in the cord durability is desired also in the steel cord.
Japanese Patent Publication No. 4-4163 Japanese Patent Laid-Open No. 11-28906

  Therefore, the present invention specifies the ratio of the twist angle between the core wire and the sheath wire and the ratio of the twist pitch in a 2 + 7, 3 + 8 two-layer twist structure in which the twist directions of the core and the sheath are the same. Based on the steel cord, the steel cord that can suppress the occurrence of fretting while increasing the rubber permeability and can further improve the durability of the cord by increasing wear fatigue resistance and corrosion fatigue resistance, and pneumatic using the steel cord The purpose is to provide tires.

In order to achieve the above object, the invention of claim 1 of the present application includes a core formed by twisting two or three core strands, and a sheath strand that is five more than the core strands around the core. It consists of a twisted sheath,
The twist direction of the core strand and the twist direction of the sheath strand are the same, and the twist angle ratio θs / θc between the twist angle θc of the core strand and the twist angle θs of the sheath strand is 0.80. The twist pitch ratio Ps / Pc between the core strand twist pitch Pc and the sheath strand twist pitch Ps is greater than 2.0 and less than or equal to 2.5. Yes.

In the invention of claim 1 , the twist angle θc of the core wire is 8 ° to 16 °, and the twist angle θs of the sheath wire is 7 ° to 15 °.

Further, the invention according to claim 1 is characterized in that the core wire and the sheath wire have the same wire diameter .

In the invention of claim 2, the twist pitch Pc of the core wire is 4 mm or more and 9 mm or less, and the twist pitch Ps of the sheath wire is 10 mm or more and 15 mm or less .

The invention of claim 3 is a pneumatic tire, characterized in that the steel cord according to claim 1 or 2 is used as a carcass cord.

  Since the present invention is configured as described above, it is possible to further suppress the occurrence of fretting while improving rubber permeability, and to improve wear resistance and corrosion fatigue resistance and further improve cord durability. .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a meridional sectional view illustrating a heavy duty pneumatic tire employing a steel cord of the present invention as a carcass cord.

  In FIG. 1, a pneumatic tire 1 is disposed on a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, inside the tread portion 2, and radially outside the carcass 6. And at least a belt layer 7.

  The belt layer 7 is formed of two or more belt plies (three or more in the case of heavy load tires) using a belt cord. In this example, the belt layer 7 includes a first belt ply 7A on the innermost side in the radial direction in which belt cords are arranged at an angle of, for example, 60 ± 15 ° with respect to the tire circumferential direction, A case of a four-sheet structure with second to fourth belt plies 7B to 7D arranged at a small angle of 35 ° is illustrated. The belt plies 7 </ b> A to 7 </ b> D are provided with one or more places where the belt cords cross each other between the plies, and are superposed to enhance belt rigidity and reinforce the tread portion 2 with a tagging effect.

  The carcass 6 is formed of one or more carcass plies 6A in this example, in which carcass cords are arranged at an angle of 70 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A includes a series of 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 on both sides of the ply main body portion 6 a that extends between the bead cores 5 and 5. Further, a bead apex rubber 8 having a triangular cross section extending radially outward from the bead core 5 is disposed between the ply main body portion 6a and the folded portion 6b, and extends from the bead portion 4 to the sidewall portion 3. Reinforced.

  And in this embodiment, the steel cord 10 which concerns on this invention is employ | adopted for the said carcass cord. As shown in FIGS. 2 and 3, the steel cord 10 includes a core 11 formed by twisting two or three core strands fc and a sheath strand fs that is five more than the core strand fc. A two-layer twisted cord having a 2 + 7 structure or a 3 + 8 structure, and a twist direction of the core strand fc and a twist direction of the sheath strand fs. .

  Here, the reason why the number n of the core strands fc is 2 or 3 is that the two are the minimum number of twisted wires, and the reason why the maximum number is 3 is the core 11 when the number is 4 or more. This is because the cross-sectional area of the inner cavity becomes excessive, and corrosion propagation due to moisture entering from the cut flaws of the tire tends to be accelerated.

  In addition, the maximum number of sheath wires fs that can be arranged around the core 11 is n + 6. In such a case, the gap between the sheath wires fs and fs is too narrow to prevent rubber penetration into the cord. Enough. Therefore, in the steel cord 10 of the present embodiment, n + 5, which is one less than this, is used, and the number of strands is increased to the maximum while ensuring the gap g necessary for rubber penetration between the sheath strands fs and fs. Yes. Further, fretting between the sheath wires fs is prevented by the rubber penetrating from the gap g, and as a result of restraining the sheath wires fs by the rubber, the variation can be suppressed and the wrapping wires are excluded. Is also possible. By excluding the wrapping strand, fretting between the wrapping strand and the sheath strand fs is prevented.

  Further, by making the twisting direction of the core 11 and the sheath 12 the same, the crossing angle between the core strand fc and the sheath strand fs becomes small, and the mutual contact pressure is reduced. As a result, the wear of the core wire fc and the sheath wire fs is reduced, and fatigue due to the wear, corrosion fatigue due to plating peeling, and the like can be suppressed, so that the cord durability can be improved.

And in the steel cord 10 of this embodiment, in order to further improve this cord durability,
(1) While setting the twist angle ratio θs / θc between the twist angle θc of the core strand fc and the twist angle θs of the sheath strand fs to 0.80 or more and 0.98 or less,
(2) The twist pitch ratio Ps / Pc between the twist pitch Pc of the core strand fc and the twist pitch Ps of the sheath strand fs is set to be larger than 2.0 and not more than 2.5.

The twist angle θ is an inclination angle of the wire f with respect to the axial direction of the cord as shown in FIG. 2, and has the following relationship with the twist pitch P. The symbol Dc in the formula means the diameter of the core 11, and Ds means the diameter of the sheath 12.
tan θc = π · Dc / Pc
tan θs = π · Ds / Ps

  Here, in the conventional cord, in order to balance the stress load between the core strand fc and the sheath strand fs at the time of tensile load and increase the strength utilization rate, the twist pitch Ps of the sheath strand fs is set to the core strand. The twist pitch θc of the core strand fc and the twist angle θs of the sheath strand fs are set to be approximately equal to 2.0 times the twist pitch Pc of fc.

  However, as a result of the inventor's research, it has been found that the cord load can be improved by unbalancing the stress load of the wires fc and fs and setting the twist pitch ratio Ps / Pc higher than before. Yeah.

  This is because when the twisting direction of the core 11 and the sheath 12 is the same, the sheath wire fs inevitably falls into the recess between the core wires fc and fc, and there is not enough space for rubber to penetrate. In addition, there is a problem that the gap g is reduced to impair rubber permeability into the space. This is presumed that the fretting suppression effect due to the number of sheath strands fs being n + 5 and the same twisting direction is insufficient.

  Therefore, when the twist pitch ratio Ps / Pc is increased beyond 2.0, the effect of preventing the sheath strand fs from falling between the core strands fc and fc is greatly increased, and a sufficient amount in the cord Can penetrate the rubber. At this time, an increase in the crossing angle between the core strand fc and the sheath strand fs is caused, but in the range where the twist pitch ratio Ps / Pc is 2.5 or less, the rubber penetration is more than the disadvantage due to the increase in the crossing angle. As a result, the merit is greater and the fretting suppression effect as a whole can be exhibited more highly.

  As the twist pitch ratio Ps / Pc increases, the strength utilization rate tends to decrease, for example, the stress load on the sheath wire fs increases. However, when the twist pitch ratio Ps / Pc is in the range of 2.5 or less, the reduction in the cord strength due to the reduction in the strength utilization rate is not remarkable, and therefore the cord durability can be improved comprehensively.

  If the twist pitch ratio Ps / Pc exceeds 2.5, further improvement in rubber permeability cannot be expected. However, the crossing angle between the core strand fc and the sheath strand fs becomes excessive, and mutual wear occurs. Rises significantly. In addition, the stress burden rate on the sheath wire fs becomes excessive, and the cord strength decreases. As a result, the effect of improving the cord durability is not achieved. Further, even when the twist pitch ratio Ps / Pc is less than 2.0, since the drop of the sheath wire fs between the core wires fc and fc is not reliably suppressed, the rubber penetration is insufficient, and the cord The durability improvement effect is not achieved. From such a viewpoint, the twist pitch ratio Ps / Pc is preferably in the range of 2.1 to 2.4.

  At this time, it is also important to set the twist angle ratio θs / θc to 0.80 or more and 0.98 or less. If the twist angle ratio θs / θc is less than 0.80, the stress load on the sheath wire fc becomes excessive and the cord The strength is reduced and the effect of improving the cord durability cannot be obtained, for example, the fracture concentrates on the sheath wire fs. Conversely, when the twist angle ratio θs / θc exceeds 0.98, the rubber permeability is lowered. From such a viewpoint, the twist angle θs / θc is preferably in the range of 0.85 or more and 0.95 or less.

  In the steel cord 10, the twist angle θc of the core strand fc is 8 ° to 16 °, the twist angle θs of the sheath strand fs is 7 ° to 15 °, and the twist pitch Pc of the core strand fc is It is preferable to set the twist pitch Ps of the sheath wire fs to 10 mm to 15 mm and 4 mm to 9 mm. This is because when the twist angle θc is larger than 16 °, the twist angle θs is larger than 15 °, the twist pitch Pc is smaller than 4 mm, and the twist pitch Ps is smaller than 10 mm, the tensile elastic modulus of the cord is too small. This is because it is difficult to sufficiently exert the reinforcing effect, and the production efficiency of the cord decreases as the number of twists increases. Conversely, when the twist angle θc is less than 8 °, the twist angle θs is less than 7 °, the twist pitch Pc is greater than 9 mm, and the twist pitch Ps is greater than 15 mm, the flexibility of the cord is impaired and bending is performed. When the deformation repeatedly acts, the bending fatigue property is lowered, such as being easily broken.

The diameters of the core strand fc and the sheath strand fs are set in relation to the required strength as a cord to be used. In the case of a carcass cord of a heavy duty tire, the diameter is 0.15 mm or more and 0.30 mm or less. Range . If it is less than 0.15 mm, it is too thin and disadvantageous in terms of cord strength. Conversely, if it exceeds 0.30 mm, it is disadvantageous in terms of bending fatigue. At this time, the strands fc and fs have the same diameter , whereby the wire drawing process can be shared and the cord can be manufactured economically.

  Although the particularly preferred embodiment of the present invention has been described in detail above, the steel cord 10 can be used as a belt cord or a reinforcement cord for bead reinforcement in addition to a carcass cord, and further to reinforce rubber articles other than tires. The present invention is not limited to the illustrated embodiment, and may be implemented as various codes.

In order to confirm the effect of the present invention, a heavy duty tire (tire size 11R22.5) using a steel cord prototyped according to the specifications of Table 1 as a carcass cord was created, and the rubber permeability of the steel cord and after running Rust generation, strength retention, and fretting resistance were tested.
The specifications of the carcass and belt layer other than those in Table 1 are the same as follows.
・ Belt layer Number of plies: 4
Code: 3 + 8 + 13 × 0.23 (steel),
Cord angle: +65 degrees / + 20 degrees / −20 degrees / −20 degrees,
Number of cords driven: 40 / 5cm,
・ Number of carcass plies: 1
Code: listed in Table 1,
Cord angle: 90 degrees,
Number of cords entered: listed in Table 1,

(1) Rubber permeability;
The carcass cord is taken out from the sample tire with the topping rubber attached, and the rubber is removed from the surface as much as possible. Then, a knife is inserted from the cross section of the cord, and the two adjacent sheath wires are removed. Then, the length of the portion where the rubber is completely filled in the gap formed between the two removed sheath wires and the core wire is measured over about 10 cm, and the rubber is filled. The ratio of the length of the portion to the total length was taken as the rubber penetration rate. The values in Table 1 are average values for 10 cords.

(2) Rust generation after running:
After running the tire for about 200,000 km, the tire was disassembled and the occurrence of rust on the carcass cord was observed, and the index was set at an index of Comparative Example 1 being 100. The smaller the value, the less rust is generated and the better.

(3) Strength retention after running:
After running the tire for about 200,000 km, the tire is disassembled and the carcass cord is taken out, and the strength (breaking strength) of the cord before running is indicated by an index of 100. The larger the value, the better. The values in Table 1 are average values for 10 cords.

(4) Fretting resistance:
After running the tire for about 200,000 km, the tire was disassembled, the carcass cord was taken out, and the fretting amount of the sheath wire was observed with a microscope. Evaluation is scored as 5 points when there is no fretting, 0 points when the fretting amount reaches 1/2 of the wire diameter, and the comparative example 1 is displayed as an index of 100. The larger the value, the better.

表の如く実施例のコードは、ゴム浸透性に優れるため錆発生を抑えることができ、また耐フレッティング性の向上により強度保持率を高く確保しうるなど、コード耐久性を向上しうるのが確認できる。

As shown in the table, the cords of the examples are excellent in rubber permeability, so that rust generation can be suppressed, and the strength retention can be secured high by improving the fretting resistance, so that the cord durability can be improved. I can confirm.

It is sectional drawing which shows one Example of the pneumatic tire which used the steel cord of this invention as a carcass cord. It is a perspective view of a steel cord. It is sectional drawing of a steel cord.

Explanation of symbols

10 Steel cord 11 Core 12 Sheath fc Core strand fs Sheath strand

Claims (3)

A core formed by twisting two or three core strands, and a sheath obtained by twisting a sheath strand more than five core strands around the core;
The twist direction of the core strand and the twist direction of the sheath strand are the same, and the twist angle ratio θs / θc between the twist angle θc of the core strand and the twist angle θs of the sheath strand is 0.80. or more and 0.98 or less, and the twist angle θc of the core wire is 8 ° or more and 16 ° or less, the twist angle θs of the sheath strands and 7 ° or more and 15 ° or less, yet twist the core wire The twist pitch ratio Ps / Pc between the pitch Pc and the twisted pitch Ps of the sheath wire is greater than 2.0 and less than or equal to 2.5, and the core wire and the sheath wire are 0.15 mm or more and 0.00 A steel cord characterized in that the wire diameter is the same within a range of 30 mm or less . The steel cord according to claim 1, wherein a twist pitch Pc of the core strand is 4 mm or more and 9 mm or less, and a twist pitch Ps of the sheath strand is 10 mm or more and 15 mm or less. A pneumatic tire using the steel cord according to claim 1 or 2 as a carcass cord.

Images