JP2010242253A - Steel cord - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel cord following lift in vulcanization forming in tire manufacturing process and giving a tire as finished product having sufficient rigidity contributing to reduce road noise and to improve steering stability in high speed driving. <P>SOLUTION: The steel cord 1A is produced by twisting four element wires 3 having a diameter of 0.08-0.15 mm to form a strand 2 and twisting five strands 2 around a nylon core 4. The twisting direction of the strand 2 is the same as the twisting direction of the steel cord 1A, and gaps S1 of 0.03-0.10 mm are present between a plurality of strands 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a steel cord, and more particularly to a steel cord suitable for use in a belt cover layer of a tire for a passenger car.

  In order to improve durability during high-speed running, it is common to provide a belt cover layer outside the belt layer of a passenger car tire. FIG. 6 shows an example of the internal structure of a passenger car tire provided with a belt cover layer. The passenger car tire 20 is configured by laminating a carcass layer 21, two belt layers 22, 23, a belt cover layer 24, and a tread layer 26. The belt cover layer 24 generally includes an organic fiber cord 25 made of nylon or the like wound a plurality of times in the tire circumferential direction. In the belt cover layer 24, the organic fiber cord 25 is covered with rubber.

  In recent years, in the case of passenger car tires used in high-end passenger cars, in which comfort is particularly important, in addition to durability, there has been a demand for improved performance such as road noise reduction and driving stability at high speeds. In response to such requirements, it is considered to use a steel cord for the belt cover layer instead of an organic fiber cord such as nylon. Steel cords are more rigid when pulled than organic fibers and are hardly affected by heat. A passenger car equipped with a passenger car tire including a belt cover layer using a steel cord has improved ride comfort compared to a passenger car equipped with a passenger car tire including a belt cover layer using an organic fiber.

  As described above, steel cords have greater rigidity when pulled than organic fibers and contribute to improving the riding comfort of passenger cars. On the other hand, steel cords have a problem that they are less elongated than organic fibers.

  One of the manufacturing processes for passenger car tires is vulcanization molding. In vulcanization molding, a tire before vulcanization (unvulcanized) is heated while being pressed. In the vulcanization molding process, unvulcanized tires are generally pressed from the inside to the outside (tension is applied), so the diameter of a vulcanized tire is about several percent larger than that of an unvulcanized tire. (It is also said that the tire takes a lift). When steel cord is used for the belt cover layer, the steel cord also extends in the circumferential direction of the tire during vulcanization. As described above, since the steel cord has a small elongation at the time of tension, the steel cord cannot follow the lift applied to the tire, and the steel cord bites into the belt layer below the belt cover layer, and the tire uniformity (uniform) Mitty) may be adversely affected.

  Patent Documents 1 and 2 disclose a reinforcing material in which a steel filament having high rigidity is wound around an organic fiber.

Japanese Patent No. 3411615 JP 2000-301911 A

  However, in Patent Documents 1 and 2, the volume occupied by the organic fibers is considerably larger than that of the steel filament around the organic fibers, and the characteristics with respect to heat are largely controlled by the characteristics of the organic fibers. Since the organic fiber has thermoplasticity, the organic fiber may be deformed during vulcanization molding, and a part of the tread portion of the tire may be deformed (a flat spot is generated). When a flat spot is generated, vibration is generated from the flat spot portion during traveling, and the riding comfort of the passenger car is deteriorated.

  The present invention provides a steel cord that follows a lift during vulcanization molding in a tire manufacturing process and exhibits sufficient rigidity that contributes to road noise reduction and steering stability performance at high speeds in a finished tire. For the purpose.

  Another object of the present invention is to provide a steel cord in which flat spots are less likely to occur.

  The steel cord according to the present invention is a steel cord having a multi-twisted structure in which a plurality of strands obtained by twisting a plurality of steel wire strands, and a single organic fiber cord, for example, a nylon cord. The plurality of strands are twisted around the organic fiber cord, the diameter of the steel wire strand is between 0.08 to 0.15 mm, and the plurality of steel wire strands have the same diameter. And the twist direction of the plurality of steel wire strands constituting the strand and the twist direction of the plurality of strands twisted around the organic fiber cord are the same, and between the plurality of strands , There are gaps in the range of 0.03 to 0.10 mm respectively.

  According to the present invention, the steel cord has an M × N (M, N is an integer of 2 or more) structure, the twist direction of a plurality of steel wire strands of the same diameter constituting the strand, and the organic fiber The twist direction of the multiple strands twisted around the core is the same, the organic fiber cord is arranged in the center, and there is a gap in the range of 0.03 to 0.10 mm between the multiple strands. . The structural elongation of the steel cord can be ensured by the twist direction, the presence of the organic fiber cord, and the presence of gaps between the strands. In addition, by providing an upper limit in the gap between the strands, the steel cord after a predetermined elongation can exhibit a predetermined rigidity.

  The steel cord according to the present invention preferably has an inflection point in a load-elongation curve (a curve that shows the elongation of the steel cord at this time in relation to the magnitude of the load). However, the elongation at the inflection point (an index indicating the magnitude of the elongation when the initial elongation of the steel cord ends) is in the range of 2.6 to 6.5%. When the steel cord is used for a tire, the steel cord is prevented from being stretched during vulcanization molding, and a predetermined rigidity can be secured after vulcanization molding. By mounting a tire using the steel cord of the present invention on a passenger car, road noise is reduced and steering stability performance at high speed driving is improved.

  Preferably, the diameter of the organic fiber cord at the center of the steel cord is 0.20 to 0.30 mm. Since the volume occupied by the organic fiber cord in the steel cord can be made relatively small, it is possible to suppress the occurrence of a flat spot on the tire accompanying deformation of the organic fiber cord during vulcanization molding.

A steel cord having a 1 + 5 × 4 structure is shown, in which (A) shows a perspective view thereof and (B) shows a sectional view thereof. A steel cord having a 1 + 4 × 4 structure is shown, (A) shows a perspective view thereof, and (B) shows a sectional view thereof. 1 shows an overall configuration of a steel cord manufacturing apparatus. It is a graph which shows a load-elongation curve, (A) shows the graph about the steel cord without a nylon core, (B) shows the graph about the steel cord with a nylon core, respectively. It is a graph which shows a load-elongation curve. The structure of an automobile tire is shown.

  1A shows a perspective view of a steel cord 1A having a 5 × 4 structure having a nylon core, and FIG. 1B shows a cross-sectional view thereof. 2A is a perspective view of a steel cord 1B having a 4 × 4 structure having a nylon core, and FIG. 2B is a cross-sectional view thereof.

  The steel cord 1A is formed by bundling five strands 2 centered on a nylon core 4 and obtained by bundling four strands (single wire) 3 made of steel while twisting them (1 + 5 × 4 structure). The steel cord 1B is formed by bundling four strands 2 around a nylon core 4 (1 + 4 × 4 structure).

  For the four strands 3 constituting the strand 2, for example, those having a diameter of 0.08 mm to 0.15 mm, for example, a diameter of 0.11 mm are used. If it is smaller than 0.08 mm, the steel cord will not have sufficient cutting strength, and if it is larger than 0.15 mm, the rigidity of the wire will be too great and the flexibility of the steel cord will be lost.

  A nylon filament (cord) of 0.20 mm to 0.30 mm is used for the nylon core 4. Polypropylene filaments (cords) may be used instead of nylon.

  The strand direction of the plurality of strands 3 constituting the strand 2 (hereinafter referred to as the strand twist direction) and the strand direction of the plurality of strands 2 constituting the steel cords 1A and 1B (hereinafter referred to as the steel cord twist direction). May be either S-twisted or Z-twisted, but both are in the same direction. That is, if the twist direction of the strand 2 is S twist, the twist direction of the steel cords 1A and 1B is also S twist. If the twist direction of the strand 2 is Z twist, the twist direction of the steel cords 1A and 1B is also Z twist. The reason for making the twist direction of the strand 2 and the twist direction of the steel cords 1A and 1B the same is that the elongation of the steel cords 1A and 1B becomes better than when the strands are reversed.

  As shown in FIGS. 1B and 2B, in the steel cords 1A and 1B in this embodiment, there are gaps S1 and S2 between the adjacent strands 2, respectively. The gaps S1 and S2 between the adjacent strands 2 are adjusted by the relative relationship between the nylon core diameter and the strand diameter and the twist pitch of the strands 2 twisted around the nylon core 4. The gaps S1 and S2 are adjusted in the range of 0.03 to 0.10 mm. Details of the technical significance of adjusting the gaps S1 and S2 within this range will be described later.

  FIG. 3 schematically shows a steel cord manufacturing apparatus. The steel cord manufacturing apparatus shown in FIG. 3 is a manufacturing apparatus for a steel cord 1A having a 1 + 5 × 4 structure shown in FIGS. 1 (A) and 1 (B).

  The steel cord manufacturing apparatus includes a buncher twisting machine 10. The buncher twisting machine 10 manufactures the steel cord 1A by bundling five strands 2 around the nylon core 4 while twisting it around the nylon core 4.

  A cradle 12 is supported on a frame (not shown) of the stranding machine 10. The cradle 12 is kept almost stationary even when a flyer described later rotates. The cradle 12 is provided with a bobbin 11 for winding the steel cord 1A.

  A nylon core 4 is wound around one bobbin 13. A strand 2 is wound around each of the five bobbins 14. One nylon core 4 fed out from the bobbin 13 and five strands 2 fed out from the five bobbins 14 are collected by the collector 15 so that the nylon core 4 is located at the center. One nylon core 4 and five strands 2 bundled by an aggregator 15 are sent to a stranding machine 10.

  The bundled nylon core 4 and the five strands 2 pass through a guide roll 16 in a twisting machine 10, are hung on a guide tip of a flyer (not shown), are guided along the flyer, and pass through a guide roll 17. Taken up by the bobbin 11. As the flyer of the twisting machine 10 rotates, the bundle of one nylon core 4 and five strands 2 is twisted and twisted to form a steel cord 1A.

  The strand 2 constituting the steel cord 1A is also created by an apparatus having the same configuration as the steel cord manufacturing apparatus described above. Four bobbins around which the wire 3 is wound are prepared. The strand 2 in which the four strands 3 are twisted is manufactured by twisting and twisting the four strands 3 with a buncher twisting machine.

  When manufacturing a steel cord 1B having a 1 + 4 × 4 structure shown in FIGS. 2 (A) and 2 (B), four strands 2 fed out from four bobbins are centered on one nylon core 4. Twisted together.

  By making the rotation direction of the flyer of the buncher twisting machine 10 of the steel cord production apparatus shown in FIG. 3 and the rotation direction of the flyer of the buncher twisting machine of the strand production apparatus the same direction, the twisting direction of the strand 2 and the steel cord The twist direction of 1A becomes the same.

  The twisting pitch of the strand 2 is adjusted by keeping the flyer rotational speed constant and increasing / decreasing the conveying speed of the strand 2 and the nylon core 4, thereby adjusting (controlling) the gaps S1 and S2 between the adjacent strands 2 can do. As described above, the strands 2 and 2 so that the gaps S1 and S2 (see FIGS. 1B and 2B) between the adjacent strands 2 in the steel cords 1A and 1B are in the range of 0.03 to 0.10 mm. The conveyance speed of the nylon core 4 is adjusted.

  Instead of adjusting the conveying speed of the strand 2 and the nylon core 4, by adjusting the rotational speed of the flyer of the buncher twisting machine 10 of the steel cord manufacturing apparatus, the twist pitch of the strand 2 (the gap S1 between the adjacent strands 2) , S2) may be adjusted.

  4 (A) and 4 (B) show the load-elongation curves for the steel cord without the nylon core 4 (FIG. 4A) and the steel cord with the nylon core 4 (FIG. 4B), respectively. , The horizontal axis represents the elongation (%), and the vertical axis represents the load (N).

  Passenger car tires are vulcanized in the manufacturing process. During vulcanization molding, the unvulcanized (unvulcanized) tire is expanded several percent outward in the tire radial direction. In the case of a passenger car tire provided with a belt cover layer (see FIG. 6), the belt cover layer is also expanded outward in the tire radial direction during vulcanization molding. For this reason, when steel cords are embedded in the belt cover layer, when the tire is vulcanized, tension is also applied to the steel cord (belt cover layer including the steel cord) (this is called “tension during vulcanization”). Called). The load-elongation curves shown in FIGS. 4 (A) and 4 (B) experimentally show the state of elongation of the steel cord when tension is applied during vulcanization.

  4 (A) and 4 (B) show load-elongation curves (that is, three curves) when the steel cord of the same sample is subjected to three tensile tests (details of the tensile test will be described later). ) Is indicated by a solid line, a broken line, and a dashed line.

  4 (A) and 4 (B), the steel cord without the nylon core 4 (FIG. 4 (A)) is compared with the steel cord having the nylon core 4 (FIG. 4 (B)). It can be seen that the blur of the load-elongation curve in the three tensile tests is large. That is, in the steel cord without the nylon core 4 (FIG. 4A), the elongation with respect to the load is not constant and variation occurs. In contrast, a steel cord having a nylon core 4 (FIG. 4B) exhibits almost the same characteristics in all three tensile tests. It can be seen that the steel cord having the nylon core 4 exhibits stable elongation characteristics.

  Table 1 shows seven specimens (twisting directions: strands and steel cords) prepared by varying the gap S1 between the strands of the steel cord 1A having a 1 + 5 × 4 structure (FIGS. 1A and 1B). Both show the tensile test results in the S direction and the diameter of the strand 3 (0.110 mm). Table 2 shows seven specimens (twisting direction: both strand and steel cord) prepared with different gaps S2 between strands for steel cords of 1 + 4 × 4 structure (FIGS. 2A and 2B). The tensile test results for the S direction and the diameter of the strand 3 (0.110 mm) are shown.

  As shown in Tables 1 and 2, the tensile test was performed on a large number of steel cords (test specimens) prepared with different “gap between strands”.

  The tensile test will be described. In the tensile test, a steel cord 1A (1B) is prepared and cut to a length of 600 mm. Set the rule length of 500mm to the tensile tester with the 50mm at both ends as the gripping margin. Pull one end of the steel cord 1A (1B) until the steel cord 1A (1B) is cut while recording the elongation of the steel cord at a tensile speed of 10 mm / min (add a load).

  A load-elongation curve is drawn by a tensile test using a tensile tester (see FIG. 4B).

  For a while after starting to pull the steel cord 1A (1B), the steel cord 1A (1B) is hardly loaded. This is because the steel cord 1A (1B) is stretched. As described above, the steel cord 1A (1B) is obtained by twisting a plurality of strands 2 obtained by twisting a plurality of strands 3 around a nylon core 4. For this reason, when the steel cord 1A (1B) is pulled, the strand 2 (elementary wire 3) moves toward the center of the steel cord 1A (1B), so that elongation occurs.

  The steel cord 1A (1B) has a nylon core 4 disposed at the center thereof, and the strand 2 (elementary wire 3) slightly bites into the nylon core 4. This also causes the steel cord 1A (1B) to stretch.

  Further, the steel cord 1A (1B) has gaps S1 and S2 between adjacent strands 2. When the steel cord 1A (1B) is pulled, the gaps S1 and S2 between the strands 2 are narrowed. This gap S1, S2 (movement of the strand 2 in the direction of narrowing the gap S1, S2) also causes the steel cord 1A (1B) to stretch.

  Here, referring to the load-elongation curve of the steel cord shown in FIG. 5, when the steel cord is continuously pulled (the load is increased), the initial elongation of the steel cord (hereinafter referred to as initial elongation) ends (is lost). . When this initial elongation is finished, the steel cord begins to be loaded.

  In this embodiment, as shown in FIG. 5, in the load-elongation curve, the intersection of the approximate straight line L1 obtained from the curve of the initial elongation portion and the approximate straight line L2 of the curve rising after the initial elongation is inflected. Positioned as a point, the elongation at the inflection point is defined as the inflection point elongation (%). The inflection point elongation rate of the load-elongation curve can be used as an index of the elongation rate at which the initial elongation of the steel cord ends.

  When the inflection point elongation is small, it means that the steel cord has a short initial elongation. If the initial elongation is too short, the steel cord will be stretched during vulcanization molding and cannot follow the tire growth during vulcanization molding, and the steel cord will bite into the belt layer as described above, adversely affecting the tire uniformity. Or the interlayer gauge between the belt cover layer and the belt layer may be smaller than the design value, which may cause a separation failure that causes the belt cover layer and the belt layer to peel off. There is a lower limit to the inflection point elongation to ensure a predetermined initial elongation for the steel cord.

  Conversely, if the inflection point elongation is large, it means that the initial elongation is long. If the initial elongation is too long, the rigidity of the steel cord will be low, and the rigidity required for the tire will not be ensured, or if the number of steel cords driven in is increased to ensure rigidity, the weight of the belt cover layer will increase. This may cause a loss of tire balance. There is also an upper limit to the inflection point elongation.

  In the tensile test, the following three evaluations were performed for each of the test specimens.

(1) Judgment of quality of cord shape When the appearance of the DUT (steel cord 1A (1B)) is observed and an extreme deviation of the strand 2 is recognized, it is determined as x (defect).
(2) Judgment of quality of follow-up to lift A tire for an automobile is created using a test object (see FIG. 6). X (defect) if a failure occurs during vulcanization, such as a steel cord being cut during tire molding, or if it is recognized that the belt cover layer has moved inward so as to bite into the belt layer.
(3) Judgment of belt separation pass / fail When an automobile tire made using a test specimen is rotated at high speed on a drum and it is found that belt separation breakage occurs during running, × (defect) To do.

  Referring to Table 1, in a steel cord 1A having a 1 + 5 × 4 structure (FIGS. 1A and 1B), a belt cover for a test piece (test piece 6) in which a gap between strands is 0.023 mm It was observed that the layer moved inward to bite into the belt layer. Further, in this DUT 6, belt separation failure was also confirmed.

  Further, regarding the DUT 7 in which the gap between the strands was 0.115 mm, the cord shape collapsed (on the side of the strand 2) was confirmed, and the belt separation failure was also confirmed.

  According to the evaluation results, for the 1 + 5 × 4 steel cord 1A, if the gap between the strands is within the range of 0.03 to 0.10 mm, the cord shape collapses (to the side of the strand 2), and the steel cord 1A belt layer Neither biting nor destruction of the belt separation was confirmed (test objects 1 to 5). The inflection point elongation in the load-elongation curve for the test bodies 1 to 5 was in the range of 2.6 to 6.5%.

  Referring to Table 2, the same test result as that of the steel cord 1A having the 1 + 5 × 4 structure could be obtained for the steel cord 1B having the 1 + 4 × 4 structure (FIGS. 2A and 2B).

1 Steel cord 2 Strand 3 Wire 4 Nylon core

Claims (3)

A steel cord having a multi-strand structure in which a plurality of strands made by twisting a plurality of steel wires are twisted,
A plurality of strands are twisted around the organic fiber cord, with one organic fiber cord as a core.
The diameter of the steel wire is between 0.08 and 0.15 mm, and the plurality of steel wires are the same diameter,
The twist direction of the plurality of steel wire strands constituting the strand and the twist direction of the plurality of strands twisted around the organic fiber cord are the same,
There is a gap in the range of 0.03 to 0.10 mm between the multiple strands.
Steel cord characterized by that. An inflection point exists in the load-elongation curve of the steel cord, and the elongation at the inflection point is in the range of 2.6 to 6.5%.
The steel cord according to claim 1.   The steel cord according to claim 1 or 2, wherein the diameter of the organic fiber cord is 0.20 to 0.30 mm.

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