JP2009074189A - Steel cord for reinforcing rubber article and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a steel cord that has high cord tenacity, excellent rubber penetration properties and resistance to bending of cord to buckling deformation, and does not cause beating disturbance of calender operation during tire production by optimizing structure and properties of a core filament and a sheath filament in a steel cord for reinforcing a rubber article of 1+N structure twisted by a bunching stranding machine having high productivity. <P>SOLUTION: In a cord in which a sheath 2 having 5-8 filaments is twisted around a core by one filament subjected to wave forming to change in two-dimensional waveform, the core has a twisting pitch that is 20 times or more and 100 times or less the core forming pitch and 6 times or more and 25 times or less the sheath twisting pitch. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steel cord used as a reinforcing material for rubber articles such as pneumatic tires and industrial belts. More specifically, in cords that are twisted using a bunching stranding machine, while ensuring the rubber penetration required to improve cut separation, which is an index for improving tire durability, at the same time as below the specified internal pressure It is also to satisfy the resistance to cord breakage caused by the buckling deformation of the belt that occurs when it is used.

  Conventionally, in a product reinforced with a steel cord, there has been a problem that the product durability life is reduced due to the corrosion of the steel filament due to moisture infiltrated into the product. For example, if the steel cord used for the tire belt has a cavity in the steel cord, if the tire tread is damaged so as to reach the belt, the moisture that has entered the belt is transmitted through the cavity in the steel cord. It spreads along the longitudinal direction of the cord, and as a result, rust caused by moisture diffuses and the adhesion between the rubber and the steel cord at that portion decreases, eventually causing a separation phenomenon between the rubber and the steel cord. Become.

In order to solve such a problem, a cord structure has been proposed in which rubber sufficiently penetrates into the inside of a cord through a gap between adjacent metal filaments by pressure vulcanization when the cord is embedded in rubber.
For example, in Patent Document 1 and Patent Document 2, as one of the above-described cord structures, as shown in FIG. 1, 5 to 6 filaments are disposed around one core filament 1 having a corrugated type. A so-called 1 ^cr + n structure cord in which the sheath 2 is disposed is disclosed.

Further, as a cord structure for improving the rubber permeability of the cord having the 1 ^cr + n structure, as shown in FIG. A cord having a so-called 1 ^{CR · CUR} + n structure in which a sheath 2 composed of 5 to 8 filaments 2a to 2f in the illustrated example is arranged around a crimped / curled core with a number of curls is disclosed in Patent Document 3. Has been proposed.

  By the way, in recent years, vehicles with passenger car elements added to off-road type four-wheel drive vehicles have become widespread, and this type of vehicle travels from paved roads to bad roads. The use of tires has also become widespread, and even when tires are used at less than the prescribed internal pressure, they are becoming rare. As described above, when the tire is punctured and used under a prescribed internal pressure, the tire causes buckling deformation. At this time, a large strain is generated in the steel cord, and there is a possibility that a fatigue fracture (cord breakage resistance) of the cord sometimes occurs. The durability against such fatigue is not solved only by improving the rubber penetration property, but as a problem of the steel cord for reinforcing rubber articles, the improvement of fatigue resistance is also important.

Moreover, from the viewpoint of productivity, twisting with a bunching stranded wire machine is recommended from the viewpoint of productivity. On the other hand, a 1 + n structure cord (1 ^{CR / CUR} + n structure) manufactured with a bunching stranding machine is basically a 1 + n structure (1 ^cr + n structure) cord manufactured with a cylindrical twisting wire machine. It is generally known to have different chord characteristics. That is, in the cord of the bunching twist 1 + n structure, since the core is basically twisted at the same pitch as the sheath, the corrugated core is twisted and rotated together with the sheath. It cannot be secured. As a result, the core has a double brazing obtained by adding deformation due to twisting rotation accompanying twisting of the cord to the crimping of its own waveform. In such a cord, since the tension load between the sheath and the core is unbalanced, the total strength of the cord is reduced. Furthermore, since the core is twisted up by the sheath, there is a problem that it is difficult to secure the amount of corrugation (crimping), that is, to guarantee rubber penetration.

  Here, roughly two methods are known as methods for improving rubber penetration. One is a method of increasing the brazing amount of the core in advance and further increasing the sheathing amount, that is, a method of making an open structure with a large cord diameter, but this contradicts the securing of cord strength. It will have conflicting characteristics.

The remaining one is to eliminate the twisting rotation of the core by giving the core counter-rotation equivalent to the amount of rotation by which the core is twisted and rotated using a bunching twisting machine as shown in Patent Document 4. This is a method of providing the same structure as that of a cord twisted by a cylindrical twisted wire machine. In this method, it is possible to achieve both the strength of the cord and the rubber penetration, but it is difficult to control the twisting machine because the characteristics of the cord twisted by the bunching twisting machine, that is, the twisting rotation of the core must be removed 100%. Moreover, since the cracks when the cord is bent are large, there is a problem in that the cord is disturbed during calendar work in the tire manufacturing process.
Japanese Patent Laid-Open No. 5-186777 JP-A-5-186978 JP-A-6-299480 Japanese Patent No. 3686451

  The object of the present invention is to improve the structure and properties of the core filament and the sheath filament, particularly in a steel cord for reinforcing rubber articles having a 1 + N structure twisted by a highly productive bunching stranding machine. To provide a steel cord and a pneumatic tire using the steel cord that has high strength, has excellent rubber penetration properties, excellent cord breakage resistance against buckling deformation, and does not cause disturbance in calendar work during tire manufacture. It is in.

  In order to solve the above-mentioned problems, the inventor has conducted intensive research on the characteristics of the 1 + 6 structure cord manufactured by the bunching stranding machine. By providing a twisted shape, the cord strength is enhanced to improve rubber penetration, and at the same time, the relationship between the sheath filament mold amount and the core filament mold amount is optimized to maintain a constant cord diameter. It has been found that by suppressing filament breakage (excessive opening), it is possible to improve the fatigue property of the cord and the calendar workability, and the present invention has been completed.

That is, the gist configuration of the present invention is as follows.
(1) In a cord in which a sheath of 5 to 8 filaments is twisted around a core of a single filament subjected to two-dimensionally changing waveform typing, the core has a wavelength in the waveform shaping of the core A steel cord for reinforcing rubber articles, wherein the steel cord has a twist pitch of 20 times to 100 times, and 6 times to 25 times the twist pitch of the sheath.
Here, the core twist pitch means the length along the central axis when the core filament makes one rotation with respect to the central axis of the cord, and mainly when the sheath filament is twisted around the core. This is due to the effect of torsional rotation acting on the core filament.

(2) The steel cord for reinforcing rubber articles according to (1), which is a cord manufactured by a bunching type stranded wire machine.

(3) In the cross section orthogonal to the axial direction of the cord, the cord has an elliptical shape, and the major axis of the ellipse is 3.5 to 3.8 times the diameter of the filament of the core and the minor axis (1) or (2), wherein the core filament diameter is 3.1 to 3.5 times or less and the sheath filament mold rate is 110% or less in both the major axis direction and the minor axis direction. Steel cord for reinforcing rubber articles as described in 1.

(4) A pneumatic tire using the steel cord according to any one of (1) to (3) as a belt layer.

  According to the present invention, since the flatness of the corrugated core molding is substantially secured by giving the core an appropriate shape, the cord strength is increased to improve the rubber penetration, and at the same time, the amount of sheath filament molding It is possible to optimize the relationship with the amount of core filament molding and maintain a constant cord diameter to suppress the filament filament from being scattered. Further, the fatigue of the cord and the calendar workability can be improved.

Next, the steel cord of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 3, the steel cord of the present invention is formed by twisting a sheath 2 made up of 5 to 8 filaments 2a to 2f in the illustrated example around a core made up of one filament 1, By giving the filament 1 a waveform that changes two-dimensionally, a gap for the rubber to enter inside the cord is secured.

  That is, the steel cord of the present invention is basically based on a cord structure in which 5 to 8 sheath filaments are arranged in a single core filament. This is because if the number of sheath filaments is four or less, the sheath filaments are biased and it is difficult to allow rubber to uniformly enter the inside of the cord. On the other hand, if the number of sheath filaments is nine or more, the sheath filament is in an ellipse centered on the core filament. It becomes impossible to arrange | position a filament equally, and the penetration | invasion property of rubber | gum is also inhibited. In particular, a 1 + 6 structure is preferable. This is because the rubber penetrability is excellent and the weight when the strength per unit area (specific strength) of the treat material as the belt material is made constant can be reduced.

  In addition, when using a steel cord as a reinforcing material of the belt of a pneumatic tire, it is preferable to set it as core filament diameter dc: 0.15-0.48mm. This is because if the core filament diameter dc is less than 0.15 mm, the frequency of disconnection increases in the wire drawing process for producing the filament, resulting in low productivity. On the other hand, if the diameter dc exceeds 0.48 mm, the distortion during bending input increases. It becomes difficult to obtain good fatigue properties. Similarly, the sheath filament diameter is preferably 0.15 to 0.48 mm.

As shown in FIG. 4, the core filament is first molded into a planar waveform that changes two-dimensionally with an amplitude Ac and a wavelength λc. The amplitude Ac (mm) is a range according to the following depending on each cord structure. It is preferable that The core filament diameter dc is 0.15 to 0.48 mm and the sheath filament diameter is 0.12 to 0.50 mm.
1 + 5 structure 1.12 dc ≦ Ac ≦ 2.0 dc (mm)
1 + 6 structure 1.12 dc ≦ Ac ≦ 2.5 dc (mm)
1 + 7 structure 1.42 dc ≦ Ac ≦ 2.8 dc (mm)
1 + 8 structure 1.74 dc ≦ Ac ≦ 3.12 dc (mm)
It is preferable to set it as the range. That is, when the amplitude Ac becomes larger than the above maximum value, the code property is deteriorated such that the core protrudes from the sheath. On the other hand, if Ac becomes smaller than this minimum value, the rubber penetration property becomes insufficient.

  On the other hand, the wavelength λc is preferably 13 dc or more and 17 dc or less. This is because it is difficult to process the wavelength λc to be less than 13 dc. On the other hand, when it exceeds 17 dc, the core filaments are crushed when the sheath filaments are twisted together, resulting in insufficient rubber penetration.

  In accordance with the above, when 5 to 8 sheath filaments are arranged and twisted around a core filament that has been corrugated, the core filament is also deformed by twisting in a form that is rotated with the sheath filament. . As shown in FIG. 5, the deformation can be regarded as a change in which the core filament rotates once with respect to the central axis of the cord, and when the length along the central cord axis is the twist pitch LLc of the core, It is important that the twist pitch LLc is not less than 20 times and not more than 100 times the wavelength λc in the waveform shaping of the core, and not less than 6 times and not more than 25 times the twist pitch of the sheath.

  That is, when the twist pitch LLc is less than 20 times the wavelength λc in the core waveform shaping, the wavelength Ac in the core waveform shaping is controlled within the above-described preferred region, particularly when twisted through a bunching twisting machine. This is because good rubber penetration properties cannot be guaranteed. On the other hand, if the twist pitch LLc exceeds 100 times the wavelength λc, the cord breaks easily during calendar work.

  Similarly, when the twist pitch LLc is less than 6 times the twist pitch of the sheath, the wavelength Ac in the waveform shaping of the core cannot be controlled within the above-described preferred region, and good rubber penetration properties cannot be guaranteed. On the other hand, the reason why the twist pitch LLc is set to 25 times or less of the twist pitch of the sheath is to make it easy to prevent cord breakage, which is one of the causes of cord disturbance in calendar work.

Further, in the cross section orthogonal to the axial direction of the cord, the contour shape of the cord is an ellipse, the major axis of the ellipse is 3.5 to 3.8 times the diameter of the filament of the core, and the minor axis is the aforementioned It is preferable that the diameter of the filament of the core is 3.1 to 3.5 times or less, and the molding rate of the filament of the sheath is 110% or less in both the major axis direction and the minor axis direction.
This is because these regulations strictly control the closeability of the cord (the elongation is small in the cord having a nonlinear SS curve), improve the cord cracking property in the calendar process, and reduce the fatigue resistance. This is to prevent it. In general, a bunching stranding machine is a device suitable for closed-structure twisting, but in principle, the amount of filament molding is larger than the cord diameter. That is, it tends to be open. And if the closeness of a cord loosens, it will become easy to break a cord. Furthermore, if the amount of sheath filaments is increased in order to facilitate rubber penetration, not only the cord diameter cannot be secured, but this openness becomes significant. If the opening becomes excessive, the sheath is easily aligned by the tension during tire vulcanization, and tensile stress is applied to the inside of the sheath filament, resulting in greater strain when buckling deformation occurs. , Belt breakage is likely to occur.

  For the steel cord described above, a treating material in which a plurality of steel cords are arranged in parallel and covered with rubber is applied to, for example, the belt 12 of the tire shown in FIG. The tire shown in FIG. 6 is formed by arranging a belt 12 and a tread 13 in this order radially outward in the crown portion of the carcass 11 extending in a toroidal shape between a pair of bead portions 10a and 10b. When the steel cord of the present invention is applied to this belt, it is preferable that the major axis of the cord contour shape (elliptical shape) is arranged in a direction along the width direction of the belt.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the examples.
A cord produced according to the specifications shown in Table 1 is applied to the tire belt shown in FIG. 6 at a driving number of 25 pieces / 50 mm, and a tire of size 195 / 80R15 is made as a prototype, and the following evaluation is performed using this prototype tire. Field tests and drum tests were conducted by the law.

Evaluation Method (1) Rubber Penetrability In the cord longitudinal direction, the amount of rubber covered on the filament surface was measured with a micrometer and evaluated as the rubber coverage on the filament surface.

(2) Cut separation resistance After mounting the prototype tire on the applicable rim, after applying the specified internal pressure, mount it on the actual vehicle, dissect the tire after running 30,000km, and cut the outer belt of the two belts The rust length x (see FIG. 7) was investigated, and the cut separation resistance was evaluated by the average value. The smaller this average value, the better the cut separation resistance.

(3) Belt bending resistance After the trial tire after applying the above specified internal pressure was adjusted to 50% of the specified internal pressure and the drum was run for 1000 km at a slip angle of 3 degrees under a load corresponding to the maximum load capacity. The tire was dissected, 50 outermost belts were collected, the number of cord breaks was examined, and the ratio of the break cords was determined.

(4) Cord breakability A cord made of a loop was squeezed to confirm the supply balance between the core and the sheath.
The results are also shown in Table 1.

It is a top view which shows the state which carried out the planar waveform shaping | molding of the core filament, and a mode that the sheath filament was wound around this core filament. It is a schematic diagram which shows the steel cord which gave the three-dimensional shaping | molding to the core filament which carried out the plane waveform shaping | molding. It is a schematic diagram which shows the steel cord of this invention. It is a figure which shows the plane waveform shaping of the core in the steel cord of this invention. It is a figure which shows the planar waveform shaping | molding and twist pitch of the core in the steel cord of this invention. It is sectional drawing of the pneumatic radial tire to which the steel cord of this invention is applied. It is a figure which shows the measurement site | part of the rust length in the cut part of a belt.

Explanation of symbols

1 Core filament 2 Sheath 2a to 2f Sheath filament

Claims (4)

  In a cord in which a sheath of 5 to 8 filaments is twisted around a core of a single filament subjected to two-dimensionally changing corrugated type, the core is 20 times the wavelength in the corrugated type of the core A steel cord for reinforcing rubber articles characterized by having a twist pitch of 100 times or less and 6 times or more and 25 times or less of the twist pitch of the sheath.   The steel cord for reinforcing rubber articles according to claim 1, which is a cord manufactured by a bunching type stranded wire machine.   In the cross section orthogonal to the axial direction of the cord, the contour shape of the cord is elliptical, the major axis of the ellipse is 3.5 to 3.8 times the diameter of the filament of the core, and the minor axis is the core. The rubber article reinforcement according to claim 1 or 2, wherein the diameter of the filament is 3.1 to 3.5 times or less and the molding rate of the sheath filament is 110% or less in both the major axis direction and the minor axis direction. Steel cord.   A pneumatic tire using the steel cord according to claim 1 as a belt layer.

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