JP2010018942A - Steel cord for large-sized pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radial tire with an improved uneven wear of a tread part and improved belt durability. <P>SOLUTION: The large-sized pneumatic radial tire T has a cross section with an aspect ratio of not more than 65%, including two layered main belts 12, 13 and a 0° belt 15 with steel cords extending along circumferential direction in substantially 0° angle, wherein the steel cords constituting the 0° belt has an m×n structure (m=3-4, n=2-4), and having a double twist structure with same twisting direction of the strands and cords, and the diameter of the steel cord is smaller than the diameter of the steel cords constituting the main belt, and having a point of inflection Z in an S-S curve using load (N) in a vertical axis and elongation (%) in a lateral axis, and elongation A (%) at the crossing point of the tangential line X of the slope in the low load area with the tangential line Y of the slope over the point of inflection is less than 1.0%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steel cord for a large-sized pneumatic radial tire, and more particularly to a steel cord for a pneumatic radial tire having a low flatness suitable for trucks and buses.

  In recent years, with the aim of improving truck transport efficiency, European truck manufacturers have been aggressively pushing forward with the development of trucks, and with this, large pneumatic radials for trucks and buses with a flatness ratio of 65% or less with excellent durability performance. Development of tires is desired.

  In the pneumatic radial tire with a small flatness called this super single tire, the belt width is wider than the conventional tire, so the outer diameter near the shoulder of the tread grows larger than the outer diameter of the tread center during driving and deforms greatly. This tends to cause uneven wear. Further, since the belt portion is largely distorted due to insufficient rigidity of the belt portion, it contributes to a decrease in belt durability caused by adhesion failure or the like.

  In order to improve this uneven wear and deterioration of durability, an additional ply made of a steel cord is substantially 0 ° between the working belt (main belt) or between the working belt and the carcass ply with respect to the tire circumferential direction. Radial tires arranged at an angle have been proposed (for example, Patent Documents 1 to 3).

  According to such a tire, it is possible to effectively suppress the outward growth of the tread portion in the radial direction when the tire is filled with internal pressure and when the tire is running, as compared with a tire having only a conventional working belt. Further, it is considered that the uneven wear resistance and durability can be improved by dispersing the distortion of the belt portion.

Special Table 2000-504655 Special table 2001-512067 Japanese Patent Laid-Open No. 2006-111217

  However, as described in Patent Documents 1 and 2, when a steel cord having a cord diameter larger than that of the working belt or a steel cord having a wavy garment is used for the 0 ° belt, the belt layer becomes thick. In addition, the belt heat generation and heat accumulation during running may increase, causing belt failure such as adhesion failure at an early stage, and further, the tire vulcanization time will be prolonged, resulting in a decrease in tire productivity. There is also. In addition, as described in Patent Document 3, a belt layer that forms a 0 ° belt having a high density portion and a low density portion has a molding process for arranging the high density portion and the low density portion in the belt layer. It may be complicated, and stress may be concentrated on the low density portion to easily generate heat and uneven wear.

  The present invention has been made in view of the above problems, and improves the uneven wear of the tread portion and contributes to the improvement of belt durability, and is a large-sized pneumatic radial with a low flatness suitable for trucks and buses for heavy loads. An object is to provide a steel cord suitable for a tire.

  The present invention was made as a result of intensive studies to solve the above-described problems of the prior art, and a carcass whose both ends are locked by a pair of left and right bead cores, and an outer peripheral side of the carcass in the tread portion, Tire cross section with at least two layers of main belts including steel cords that intersect and extend from each other and a 0 ° belt that includes steel cords that extend at an angle of substantially 0 ° with respect to the tire circumferential direction. The present invention relates to a steel cord constituting the 0 ° belt used in a large pneumatic radial tire having a flatness ratio of 65% or less. The steel cord constituting the 0 ° belt according to the present invention has an mxn structure (m = 3 to 5, n = 2 to 4), and a twisted structure in which the strands and the cords are twisted in the same direction. The diameter of the steel cord is smaller than the diameter of the steel cord constituting the main belt, and the steel cord of the 0 ° belt taken out from the center portion of the tread of the tire has a load (N) on the vertical axis and a horizontal axis In the SS curve with the elongation (%), the inflection point Z has a gentle slope in the low load region and the slope becomes large as the load increases, and the tangent of the slope in the low load region and the change The elongation A (%) of the intersection with the tangent of the slope after the curvature point Z is less than 1.0%.

  In one embodiment, a diameter of a steel cord constituting the 0 ° belt is less than 1 mm.

  The belt strength (N / 25.4 mm) per unit width of the 0 ° belt is preferably 14000 N or more.

  In one embodiment, the 0 ° belt is disposed at least at one position between the main belt and between any layers between the main belt and the carcass on the tire inner peripheral side.

  According to the present invention, by including a steel cord having an m × n structure having a specific double twist structure in the 0 ° belt, the tread center portion at the time of tire vulcanization molding and the tread center portion to both ends of the tread. The elongation in the low load region of the 0 ° belt steel cord can also be adjusted by the difference in expansion rate from the vicinity of the shoulder portion of the tread. As a result, stress strain in the tread width direction due to the 0 ° belt can be equalized and stress concentration can be dispersed, so that the belt rigidity in the tire width direction and the circumferential direction when filling the tire with internal pressure or during running of the tire By uniformly and improving the restraint and suppressing the growth of the tire, the occurrence of uneven wear can be suppressed and the durability of the tire can be improved.

1 is a half sectional view of a pneumatic radial tire according to an embodiment. It is sectional drawing which shows the belt structure of embodiment typically. It is sectional drawing of the m * n structure steel cord of embodiment. It is a graph which shows an example of the SS curve of an m * n structure steel cord. It is sectional drawing which shows the belt structure of a prior art example typically.

  A large pneumatic radial tire using a steel cord according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a half sectional view of a tire T showing an example of a heavy-duty pneumatic radial tire. Reference numeral 1 denotes a belt composed of five belt layers, reference numeral 2 denotes a carcass, reference numeral 3 denotes a tread portion, reference numeral 4. Indicates a bead portion, and reference numeral 5 indicates a sidewall portion.

  The tire T has a single carcass 2 in which steel cords extending in the tire width direction are arranged at predetermined intervals in the tire circumferential direction between a pair of left and right bead portions 4. The carcass 2 is folded and locked from the inside to the outside of the tire so that the bead filler 7 is sandwiched around the bead core 6 embedded in the bead portion 3 at both ends. A belt 1 composed of five belt layers is disposed on the outer peripheral side of the carcass 2 in the tread portion 3.

  FIG. 2 schematically illustrates a cross section of the tread portion 3 of the tire T according to the embodiment, and illustrates a belt configuration. In FIG. 2, the belt 1 is provided with a first belt 11, a second belt 12, a third belt 13, and a fourth belt 14 from the inner side in the tire radial direction, and between the second belt 12 and the third belt 13. The belt is composed of a five-layer belt in which a 0 ° belt 15 is arranged (the first to fourth belts are indicated by a broken line, and the 0 ° belt is indicated by a solid line).

  The second belt 12 and the third belt 13 are belt layers forming a main belt (working belt) of the tire, and have a more general cord structure (for example, 3 + 9 + 15 × 0.23). Steel cords are arranged at predetermined intervals and at a predetermined angle with respect to the tire circumferential direction, and are arranged so as to cross each other.

  The fourth belt 14 is a protective belt layer arranged at a constant angle in the tire circumferential direction, which is made of a steel cord excellent in cut resistance and rubber penetration, so-called high elongation that improves damage resistance and renewability. Codes (eg, 1 × 5 × 0.38, 4 × 4 × 0.23, etc.) are often used.

  The 0 ° belt 15 is a belt layer including a steel cord according to the present invention in which steel cords are arranged and extended at a predetermined interval in the tire width direction at an angle of substantially 0 ° with respect to the tire circumferential direction. .

  As shown in FIG. 3, an example of the steel cord C constituting the 0 ° belt 15 is that a strand S formed by twisting n strands (filaments) F is further twisted to form a twisted cord. It is a formed steel cord having an m × n structure. (FIG. 3 (a) is a 4 × 2 structure, (b) is a 3 × 4 structure, and (c) is a cross-sectional view of a 4 × 4 structure steel cord).

  The strand S is composed of n strands (n = 2 to 4), and if the number of strands n is 1, even if it is a double-twisted steel cord, sufficient elongation at low load cannot be obtained. Exceeding the thickness makes it easier for the strands to closely adhere to each other at the time of stranded wire, and the gap for the rubber to penetrate between the strands becomes small, making it difficult for the rubber to penetrate into the strands S, resulting in poor corrosion resistance such as the occurrence of rust.

  Further, the cord C is composed of m strands (m = 3 to 5) of strands S. When the number of strands is 2, the elongation at the time of low load cannot be pulled out sufficiently, and it is difficult to expand the central portion of the tread during vulcanization. When m is 6 or more, the specific strand S is likely to enter the inside of the cord at the time of stranded wire, the elongation of the cord C is restricted, and the elongation in the low load region cannot be obtained, and the cord diameter is large. Become.

  In the steel cord having the m × n structure, the strand S and the cord C are twisted in the same direction. If the strand S and the cord C are twisted in different directions, the strand S and the cord C are sufficiently stretched to cancel each other because the strand C is twisted by the twist of the cord C in the opposite direction when a load is applied. Elongation cannot be obtained, and it becomes difficult to adjust the elongation characteristics particularly in a low load range.

  The m × n structure steel cord C constituting the 0 ° belt 15 has a diameter smaller than that of the steel cord constituting the main belts 12 and 13.

  If the diameter of the m × n structure steel cord C is larger than the steel cord constituting the main belts 12 and 13, the rubber thickness between the main belts 12 and 13 increases, and heat is generated during the running and accumulation of heat. As a result, belt failure such as deterioration of rubber and adhesion failure between rubber and steel cord is likely to occur, and the vulcanization time becomes longer and tire productivity is lowered.

  The specific diameter of the m × n structure steel cord C is not particularly limited, but the diameter of the steel cord constituting the main belts 12 and 13 of a general large pneumatic radial tire (usually 1.1 to 1). In consideration of (about 0.5 mm), those having a diameter of less than 1 mm are preferable. If the diameter is 1 mm or more, the above problem is likely to occur, and if the diameter is too small, it is difficult to secure the necessary belt strength and the tread shape cannot be maintained. Therefore, the lower limit is preferably 0.8 mm or more. .

  Although the strand diameter which comprises the said mxn structure steel cord C is not specifically limited, the thing of about 0.13-0.23 mm is preferable. If the wire diameter is 0.13 mm or less, it is difficult to secure the belt strength of the 0 ° belt 15, and it becomes difficult to secure the belt rigidity due to the lack of the rigidity of the cord, so that the growth of the tire cannot be suppressed and uneven wear is easily caused. In addition, if it exceeds 0.23 mm, the strand becomes stiff and the elongation of the cord C is restricted when twisted into an m × n structure, and in particular, it becomes impossible to obtain elongation in a low load range, and the cord diameter also increases. It is easy to cause belt failure due to the above heat generation and heat accumulation.

  Further, the strand pitch (mm) for twisting the m × n structure steel cord C is preferably 12 to 20 times the diameter of the strand F in the strand S. In the cord C, the twist pitch of the strand S is 1. It is preferably 5 to 2.5 times, more preferably 1.8 to 2.2 times. If the strand pitch of the strand S and the cord C is smaller than these values, the elongation of the cord in the low load region becomes large, and the expansion behavior at the time of tire vulcanization becomes uneven in the tire circumferential direction and the width direction. Deteriorates Mitty and decreases durability. On the other hand, if the twist pitch is larger than these values, the cord cannot be sufficiently stretched, particularly the cord in the low load region is insufficiently stretched, and the expansion behavior at the center portion of the tread becomes difficult.

  The 0 ° belt 15 preferably has a belt strength (N / 25.4 mm) per width of 14000 N or more. If the belt strength is less than 14000 N, the strain applied to the 0 ° belt increases, and cord breakage is likely to occur due to long-distance running subjected to repeated strain, which is not preferable.

  The steel cord C of the 0 ° belt 15 is a steel cord C taken from the tread center portion of the tire T. As shown in FIG. 4, the vertical axis represents load (N) and the horizontal axis represents elongation (%). The SS curve has an inflection point Z that has a gentle slope in the low load region and increases as the load increases. The slope tangent line X and the slope after the inflection point Z in the low load region The elongation A (%) at the intersection with the tangent line Y is less than 1.0%. The tread central portion refers to a range within 30% of the tread width around the tire center line.

  This is because, in a low load region of the SS curve, when a tensile force is applied in the cord axis direction, the twist of each cord C and the strand S is extended, and the rubber in which each strand has penetrated into the cord gradually increases inward. This is because the twist in the strand S shows a gentle inclination due to the rubber elasticity, and when there is no tightening allowance due to the strands, it suddenly changes to a large inclination that pulls the cord C. It has an inflection point Z.

  According to the present invention, since the steel cord C has the above-described double twist structure, the inclination after the inflection point Z is made gentle while making the inclination of the low load region gentler than that of a normal belt steel cord. The inflection point Z can be emphasized more rapidly, and the 0 ° belt cord C can be emphasized by the difference in expansion rate between the center of the tread and the shoulder from the center to both ends of the tread during tire vulcanization. SS characteristics can be adjusted.

  Usually, when vulcanizing a tire, the inner pressure is applied to the bladder to inflate the green tire and press it against the outer mold to heat it. In this case, the center of the tread is the most expanded when viewed in the tire cross-section direction. The shoulder area is not expanded much. Therefore, if the elongation A (%) at the intersection is not less than 1.0% at the center of the tread, a large elongation will remain in the 0 ° belt cord near the shoulder, The growth of the tire cannot be suppressed due to insufficient belt binding force in the vicinity, causing belt failure such as uneven wear and adhesion failure.

  In the present invention, by defining the elongation of the 0 ° belt steel cord C in the center of the tread in the low load region, the cord elongation near the shoulder portion can be adjusted at the same time. Since the stress strain applied to T can be equalized and the stress concentration can be dispersed, the tire rigidity in the tire width direction and the circumferential direction at the time of filling the tire with the internal pressure and running the tire and the restraint property can be improved. It is possible to suppress the occurrence of uneven wear and improve the durability of the tire.

  The positional relationship of the 0 ° belt 15 in the belt 1 is not particularly limited, but it is preferable that at least one main belt is disposed outside the 0 ° belt 15 in the tire radial direction. That is, the 0 ° belt 15 is disposed between the main belts 12 and 13 or between the first belt 11 and the main belt 12 or between the carcass 2 and the first belt 11 on the inner side in the tire radial direction of the main belt 12. It is preferable to do.

  The width of the 0 ° belt 15 is preferably 90% or less of the width of the belt having the maximum width, and in this embodiment is preferably 90% or less of the width of the main belt layer 13, whereby the 0 ° belt The stress concentration on the edge portion can be reduced, and the durability of the edge portion can be prevented from being lowered due to the distortion caused by the stress concentration. In order to maintain the belt restraint near the shoulder, the width is preferably 70% or more of the maximum belt width.

  The 0 ° belt 15 may be disposed between the main belt 13 and the fourth belt (top belt) 14. In general, however, the top belt 14 is 90% wider than the main belts 12 and 13. Therefore, if the 0 ° belt 15 is disposed in this portion with a width of 90% or less with respect to the outer belt layer, the width of the 0 ° belt 15 becomes too narrow and sufficient restraining force is provided in the vicinity of the shoulder portion. It becomes difficult to obtain. Therefore, the 0 ° belt 15 is preferably disposed between the main belts 12 and 13 or between the main belt 12 and the carcass 2 as described above.

  The 0 ° belt 15 can be provided by winding the steel cord C in a spiral shape continuously in the circumferential direction of the tire T. The cord angle of the steel cord C is substantially 0 ° with respect to the tire circumferential direction. For example, one cord C is wound in a spiral shape while being shifted in the width direction of the tire T. The cord C may be formed with an angle of 0 to 5 ° and a slight angle.

  Further, a ribbon-like belt-like member in which several cords C are aligned and covered with rubber is wound by spirally winding the ribbon-like side ends for each circumference of the molding drum during tire molding. Is called. Thus, by winding the steel cord C continuously in a spiral shape, sufficient belt rigidity can be obtained without being affected by the joint or the like.

  The large pneumatic radial tire of the present embodiment configured as described above can improve the durability and uneven wear resistance of the tire by including the 0 ° belt including the steel cord having the above-described configuration. This is suitable for a tire having a flatness ratio (ratio of tire height / total tire width) of 65% or less used for heavy duty vehicles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

  A radial tire of tire size 315 / 60R22.5 152L having the belt configuration shown in FIG. Each of the steel cords shown in Tables 1 and 2 was used for the 0 ° belt, and the width of the 0 ° belt was 86% of the width of the main belt 13. The arrangement of the 0 ° belt is between the main belts (second belt and third belt) 12 and 13 in the first to fourth embodiments, and between the first belt 11 and the second belt 12 in the fifth embodiment. Then, it was arranged between the carcass 2 and the first belt 11.

  In addition, the structure of the 1st-4th belt was made the same by an Example, a comparative example, and a prior art example, and the following steel cord was used by the common specification. The first belt is 3 × 0.20 + 6 × 0.35, the second and third belts are 3 + 9 + 15 × 0.23 (cord diameter 1.2 mm), and the fourth belt is 1 × 5 × 0. 38. In addition, a common member was used for each part other than the belt. The conventional example is an example in which the 0 ° belt shown in FIG. 5 is not used. The tire T1 of the conventional example is a pneumatic radial tire including four belt layers of angled first to fourth belts (111 to 114), and including a belt 100 having reference numerals 112 and 113 as main belts. is there.

  Each tire was evaluated for tire durability by the following tensile test and indoor drum test. The results are shown in Tables 1 and 2.

[Tensile test]
A 0 ° belt cord taken out from the center of the tread of each tire is subjected to a tensile test (in accordance with JIS G3510) with rubber attached, and the tangent line X of the slope in the low load region is changed from the SS curve shown in FIG. The elongation A (%) of the intersection with the tangent line Y after the curve point Z was determined.

[Belt durability]
Using a drum testing machine having a steel rotating drum with a smooth surface of 1700 mm in diameter, the ambient temperature is 38 ± 3 ° C., the tire internal pressure is increased by 100 kPa from the TRA standard air pressure, 120% of the standard load is applied, and the speed is 42 km / h. The load was increased from 120% to 10% every 7 days, and the vehicle was run until a failure occurred. Those with the applied load exceeding 140% were shown as “O” as acceptable, and “X” as the unacceptable.

[Long distance durability]
Using the above drum tester, the ambient temperature was 38 ± 3 ° C., the tire internal pressure was TRA standard air pressure, 90% of the standard load was applied, and the vehicle was run at 150,000 km at a speed of 60 km / h. The condition was observed. The case where the cord breakage occurred on the 0 ° belt was indicated by “×”, and the case where there was no cord breakage was indicated by “◯”.

[High-speed durability]
Using the above drum tester, the ambient temperature is 38 ± 3 ° C., the tire internal pressure is TRA standard air pressure, 150% of the standard load is applied, the speed is increased by 8 km / h every 2 hours from the speed 56 km / h, and 80 km / h I drove for 6 hours at h. From 88 km / h, the speed was increased by 8 km / h every 12 hours and the vehicle was run until a failure occurred. Those that traveled at a speed of 104 km / h or higher were shown as “◯” as acceptable, and those below that were rejected as “x”.

  As shown in Table 1, in Examples 1 to 6 according to the present invention, the low load elongation characteristic up to the intersection A of the 0 ° belt cord is made less than 1%, and the cord width and the belt strength are ensured to secure the tire width. By improving the belt rigidity and restraint property in the direction and circumferential direction, heat generation during running and tire growth were suppressed, and the occurrence of uneven wear was suppressed and the tire was excellent in durability.

  As described above, the large pneumatic radial tire using the steel cord according to the present invention can be used for heavy duty truck and bus tires because it has improved uneven wear resistance and excellent belt durability. In particular, it is suitable for a radial tire having an aspect ratio of 65% or less.

DESCRIPTION OF SYMBOLS 1 ... Belt 2 ... Carcass 6 ... Bead core 12, 13 ... Main belt 15 ... 0 degree belt C ... Steel cord S ... Strand F ... Strand T ... Pneumatic radial tire A ... Intersection elongation X ... Inclination in low load region Tangent line Y ... Inclination tangent line Z after inflection point Z ... Inflection point

Claims (2)

A carcass whose both ends are locked by a pair of left and right bead cores, and at least two main belts including a steel cord that crosses and extends on the outer periphery side of the carcass in the tread portion, and the tire circumferential direction The 0 ° belt is used for a large pneumatic radial tire with a flatness of a tire cross section of 65% or less including a 0 ° belt including a steel cord extended substantially at an angle of 0 °. A steel cord,
The steel cord constituting the 0 ° belt is an mxn structure (m = 3 to 5, n = 2 to 4), and a twisted structure of strands and cords in the same direction. The diameter of the cord is smaller than the diameter of the steel cord constituting the main belt,
The steel cord of the 0 ° belt taken out from the center of the tread of the tire has a gentle slope in the low load region on the SS curve with the vertical axis representing load (N) and the horizontal axis representing elongation (%). It has an inflection point Z where the inclination increases as the load increases, and the elongation A (%) of the intersection between the tangent of the inclination in the low load region and the tangent of the inclination after the inflection point Z is 1.0%. Steel cord, characterized by being less than.   The steel cord according to claim 1, wherein the steel cord has a diameter of less than 1 mm.

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