JP2012107353A - Rubber reinforcement steel cord and pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber product such as a tire having reduced weight without impairing fatigue resistance.SOLUTION: Provided is a flat steel cord 10 having an n+1 structure (n=2 to 6) including a main filament bundle 13 in which a plurality of main filaments 12 including metal filaments having a diameter of 0.15 to 0.30 mm are arranged to be aligned in a line without twisting is wrapped with a straight metal filament 14. The main filaments are steel filaments having a carbon content of 0.95 to 1.20 mass% and a chromium content of 0.05 to 0.5 mass%, and are coated with brass plating, whose copper content is 65 to 70 mass%, and the coat weight of the plating is 4.5 to 8 g/kg and knot strength retention is 50% or more. The steel cord can be used for a belt layer of a pneumatic radial tire.

Description

  The present invention relates to a steel cord used for reinforcing rubber products such as tires, and a pneumatic radial tire using the steel cord.

  In recent years, there has been a strong demand for lower fuel consumption of vehicles due to global environmental problems, and as part of this, weight reduction of pneumatic radial tires has attracted attention as one of the major technical issues. As measures for achieving weight reduction of the tire, it is conceivable to reduce the amount of steel cord used as a reinforcing member or to reduce the thickness of rubber covering the steel cord. Instead of using a steel cord in which a plurality of filaments are twisted together, a flat steel cord formed by arranging a plurality of filaments in parallel and winding one filament around them is one specific means for that purpose. It has been proposed (see Patent Documents 1 to 3 below).

  On the other hand, from the viewpoint of reducing the amount of steel cord used, it is effective to increase the strength of the steel cord. Therefore, a relatively high carbon content (for example, 0.82% by mass, 0.86% by mass) , 0.92 mass%, etc.) has been proposed (see Patent Document 4 below).

JP-A-8-120578 Japanese Patent Laid-Open No. 11-21776 JP 2004-60128 A Japanese Patent Laid-Open No. 2007-262496

  However, when a high-strength steel cord was sought and a light weight tire using a high carbon steel filament with a carbon content of 0.92% by mass or more was studied, the steel material became harder as the carbon content increased, Workability deteriorated, and breakage occurred frequently during wire drawing. Further, since the toughness of the filament also deteriorates, it has been found that there is a case where the steel cord has poor fatigue and breaks during running when used as a belt cord.

  In view of the above problems, the present invention provides a steel cord for reinforcing rubber that can achieve weight reduction of a rubber product such as a tire without impairing fatigue, and a pneumatic radial tire using the same. For the purpose.

  The steel cord for reinforcing rubber according to the present invention includes a main filament bundle in which a plurality of main filaments made of metal filaments having a diameter of 0.15 to 0.30 mm are arranged in a single line without being twisted. A flat steel cord having an n + 1 structure (where n = 2 to 6) is wrapped with a wrapping filament made of a straight metal filament, and the main filament has a carbon content of 0.95 to 1.20 mass. % And a chromium content of 0.05 to 0.5% by weight of a steel filament, which is coated with a plating amount of 4.5 to 8 g / kg by brass plating with a copper content of 65 to 70% by weight. Thus, the knot strength retention of the main filament is 50% or more.

  The pneumatic radial tire according to the present invention uses the steel cord for rubber reinforcement as a belt layer.

  According to the present invention, the thickness of the covering rubber can be reduced because the main filaments are arranged in a single line without twisting, so that the thickness of the coated rubber can be reduced, and high carbon steel is used for the main filaments. Thus, the amount of iron used as a high-strength steel cord can be reduced, and thus the weight of rubber products such as tires can be reduced. At that time, a steel material with a predetermined amount of chromium added to high carbon steel was used for the main filament, and the plating composition was specified and the plating adhesion amount was set to increase the knot strength retention rate. It is possible to prevent deterioration of fatigue resistance while ensuring wire drawing workability.

1 is a half sectional view of a pneumatic radial tire according to one embodiment. It is a figure which shows the structure of the steel cord concerning embodiment. It is sectional drawing of the belt layer which embed | buried this steel cord.

  Hereinafter, embodiments of the present invention will be described in detail.

  As shown in FIG. 1, the pneumatic tire according to the embodiment is a pneumatic radial tire for passenger cars, and includes a pair of left and right bead portions (1) and sidewall portions (2), and left and right sidewall portions (2). And tread portions (3) provided between both sidewall portions (2) so as to connect the radially outer ends of the two, and straddle between the pair of bead portions (1). An extending carcass (4) is provided.

  The carcass (4) extends from the tread portion (3) to the sidewall portion (2), and at least one piece of which both ends are locked by an annular bead core (5) embedded in the bead portion (1). It consists of a carcass ply. In this example, it is composed of one carcass ply. The carcass ply is formed by arranging carcass cords made of organic fiber cords or the like substantially perpendicular to the tire circumferential direction. An inner liner (9) is provided on the entire inner surface of the tire on the inner surface side of the carcass (4).

  A belt (7) is disposed between the carcass (4) and the tread rubber portion (8) on the outer peripheral side of the carcass (4) in the tread portion (3) (that is, the outer side in the tire radial direction). The belt (7) is provided on the outer periphery of the crown portion of the carcass (4), and can be constituted by one or a plurality of belt layers, usually at least two belt layers. Then, it is composed of two belt layers, a first belt layer (7A) on the carcass (4) side and a second belt layer (7B) on the tread rubber portion (8) side.

  The belt layer is formed by inclining steel cords (10) at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction and arranging them at predetermined intervals in the tire width direction. It is covered with a coating rubber (11) as shown in FIG. The steel cord (10) is disposed so as to intersect each other between the two belt layers (7A) and (7B).

  In this embodiment, as the steel cord (10), as shown in FIG. 2, metal filaments (hereinafter referred to as main filaments) (12) are arranged in a single row without being twisted. A flat cord having an n + 1 structure (where n = 2 to 6) formed by wrapping a filament bundle (13) with a single straight metal filament (hereinafter referred to as a wrapping filament) (14) is used. . The main filament (12) is a steel filament having a diameter of 0.15 to 0.30 mm, a carbon content of 0.95 to 1.20% by mass and a chromium content of 0.05 to 0.5% by mass. It is covered with a plating amount of 4.5 to 8 g / kg by brass plating with a copper content of 65 to 70% by mass, and the knot strength retention of the main filament (12) is 50% or more. It is characterized by being.

  This steel cord (10) eliminates the strength reduction caused by twisting metal filaments, and reduces the coating rubber thickness of the belt layer by aligning them in one row. Moreover, the usage-amount of iron can be reduced by comprising a high-strength steel cord using high carbon steel for a main filament (12). Therefore, the weight of the tire can be reduced. On the other hand, the cord configuration in which the filaments are not twisted becomes a factor that greatly deteriorates the fatigue property of the cord. Therefore, after defining the diameter of the main filament (12), by defining the steel material used in the main filament (12), the plating composition and the amount of adhesion, and the knot strength retention, the fatigue required for the tire can be improved. Ensures both weight reduction and fatigue resistance.

  The carbon content of the main filament (12) is 0.95 to 1.20% by mass, and a high carbon steel having a higher carbon content than before is used. If the carbon content is less than 0.95% by mass, it is difficult to obtain a cord tensile strength of 3500 MPa or more, and unless the number of driving is made dense, the tensile strength required for the belt layer cannot be obtained, and the weight can be reduced. I can't plan. Further, if the number of driven-in wires is too dense, the rubber space between the cords becomes small, and a failure due to separation tends to occur. When the carbon content exceeds 1.20% by mass, the wire drawing workability of the filament is lowered, and there is a possibility that wire breakage frequently occurs during wire drawing. The carbon content of the main filament (12) is more preferably 0.98 to 1.12% by mass.

  The chromium content of the main filament (12) is 0.05 to 0.50% by mass. By adding chromium to the high carbon steel as described above, the strength is further improved and the lamella spacing is reduced. The wire drawing workability can be improved, and the deterioration of the wire drawing workability due to an increase in the carbon content can be improved. When the chromium content is less than 0.05% by mass, the effect of adding the chromium is not sufficiently obtained. On the other hand, if the chromium content exceeds 0.50% by mass, the ductility of the ferrite phase after the heat treatment is lowered, and the steel cord becomes low in knot strength and therefore easily breaks on a rough road. The chromium content of the main filament (12) is more preferably 0.1 to 0.3% by mass.

  As a preferred embodiment, the main filament (12) has a silicon (Si) content of 0.1 to 1.5 mass% and a manganese (Mn) content of 0.1 to 1.0 mass%. Silicon acts as a deoxidizer and can strengthen ferrite in pearlite, and by regulating its content to 1.5% by mass or less, the formation of bainite can be suppressed and wire drawing can be performed. It is possible to suppress a decrease in the limit processing degree. Manganese acts as a deoxidizer, can increase the patenting strength, and by regulating its content to 1.0% by mass or less, the production of martensite and bainite can be suppressed and the wire drawing workability can be reduced. Can be suppressed.

  Here, the carbon content is measured by an infrared absorption method according to JIS G1211 (Appendix 3: Total Carbon Quantitative Method—High Frequency Induction Furnace Combustion), and more specifically, a device “CS-400” manufactured by LECO. Can be obtained by melting steel by high-frequency heating and performing quantitative analysis by an infrared absorption method. The contents of chromium, silicon and manganese are measured in accordance with JIS G1258-1 (emission intensity ratio method), and more specifically, hydrochloric acid: nitric acid: water = 1: 1: 2 (mass ratio). It can be measured by dissolving a steel material in an aqueous solution and performing ICP analysis (emission spectroscopic analysis).

  The diameter of the main filament (12) (filament diameter d1) is 0.15 to 0.30 mm, and if this is less than 0.15 mm, the number of driven wires must be made dense in order to obtain a predetermined cord strength, Tire failure is likely to occur. Conversely, if it exceeds 0.30 mm, cord breakage may occur due to metal fatigue during tire running. The filament (d1) is more preferably 0.15 to 0.25 mm.

  Here, the measurement of a filament diameter is performed by measuring the diameter of a metal filament with a predetermined thickness meter according to JIS G3510.

  The main filament (12) is a carbon steel wire having the above-mentioned predetermined chemical composition. Repeated patenting (heat treatment) and dry wire drawing to make an intermediate wire of a desired diameter, coated with brass plating, and then wet drawn Obtained by final processing. In the present embodiment, the brass plating is characterized by using a copper content of 65 to 70% by mass and a zinc content of 35 to 30% by mass, and the obtained main filament ( The plating adhesion amount in 12) is 4.5 to 8.0 g / kg. By coating the brass plating having such a composition with a larger adhesion amount, the friction between the filament and the die can be reduced during the drawing process of the main filament. That is, the brass plating functions as a lubricant in the wire drawing process, whereby the coefficient of friction with the die can be reduced, and as a result, the knot strength retention of the main filament can be increased.

  When the copper content of the brass plating is less than 65% by mass, the ratio of the β phase in the brass plating is increased, the function as the lubricant is impaired, the wire drawing workability is deteriorated, and disconnection occurs frequently. Or increasing the nodule strength retention rate becomes difficult. On the other hand, when the copper content exceeds 70% by mass, the wet heat adhesion of the obtained steel cord is impaired. The copper content of the brass plating is more preferably 66 to 70% by mass.

  The plating adhesion amount is the mass of brass plating with respect to the steel material mass (mass excluding brass plating) constituting the main filament (12), and if the plating adhesion amount is less than 4.5 g / kg, it functions as the lubricant. Is impaired, wire drawing workability deteriorates, breakage occurs, and it becomes difficult to increase the knot strength retention. On the other hand, when the plating adhesion amount exceeds 8.0 g / kg, the wet heat adhesiveness of the obtained steel cord is impaired. The plating adhesion amount is more preferably 4.7 to 7.0 g / kg.

  Here, the copper content and plating adhesion amount of brass plating are measured according to JIS K0121. More specifically, a steel cord is dissolved in concentrated nitric acid, the plated portion is dissolved, this solution is diluted with distilled water, filtered, and subjected to flame atomic absorption analysis using an apparatus “AA-6200” manufactured by Shimadzu Corporation. It can be measured by doing.

  The knot strength retention of the main filament (12) is 50% or more, which can improve the fatigue property of the steel cord. That is, when the knot strength retention is less than 50%, the toughness of the steel cord is low, and there is a possibility that the cord breaks during use of the tire. The higher the knot strength retention, the better. Therefore, the upper limit is not particularly limited, but is usually 70% or less. The value of knot strength retention depends on the manufacturing conditions including wire drawing as well as the composition of the steel material itself. Therefore, in order to increase the knot strength retention ratio to 50% or more, for example, a diamond die is used as a die used for wire drawing (a lubricity is better than a cemented carbide die) or a die approach. For example, it may be possible to perform uniform processing by reviewing the die shape, such as reducing the angle (taper angle of the hole of the die). Moreover, the composition and adhesion amount of the above-described brass plating can also reduce the coefficient of friction between the filament and the die and increase the knot strength retention.

  Here, the nodule strength retention rate is that the filament is knotted according to JIS L1013, the tensile strength at the time of the nodule (nodule strength) according to the method of JIS G3510, and the original tensile strength (no-nodule strength) ) And is obtained from the following equation. The tensile strength is the maximum load required for the filament to break when measured using a tensile tester at a distance between the filament grips of 300 mm and a tensile speed of 30 mm / min in accordance with JIS G3510.

  Nodule strength retention rate (%) = (Nodule strength (N) / Non-nodule strength (N)) × 100

  As shown in FIG. 2, the main filament (12) may be a straight metal filament that is not corrugated, or a corrugated metal filament may be used. When corrugating, the main filament is preferably corrugated only in the major axis direction of the steel cord, that is, it is corrugated two-dimensionally in a plane along the major axis direction and the longitudinal direction. In this case, a plurality of metal filaments molded in the longitudinal direction with the same wave height and wavelength may be used. In this case, the corrugated phases may be aligned by aligning the plurality of metal filaments, or may be aligned by shifting the phases.

  On the other hand, a straight metal filament that is not corrugated or the like is used as the wrapping filament (14). The steel material used for the wrapping filament (14) is not particularly limited. For example, a carbon steel wire having a carbon content of 0.60 to 1.02% by mass can be used, and a piano wire defined in JIS G3502 is used. Various carbon steels made of (for example, SWRS72A, SWRS82A, etc.) can be used.

  The diameter of the wrapping filament (14) (filament diameter d2) is preferably 0.05 to 0.20 mm, and is equal to or less than the diameter (d1) of the main filament (12) (that is, d2 ≦ d1). It is preferable that If the diameter (d2) of the wrapping filament (14) is larger than 0.20 mm, the cord diameter in the thickness direction of the steel cord (10) increases, and the thickness of the coating rubber (11) to be coated increases. However, it is difficult to reduce the weight. Conversely, if the filament diameter (d2) is less than 0.05 mm, it is difficult to stabilize the cord shape of the steel cord (10). The filament (d2) is more preferably 0.10 to 0.15 mm.

  The steel cord (10) is wrapped by winding the wrapping filament (14) around the main filament bundle (13) in which the main filaments (12) are arranged in a horizontal row without twisting them. N + 1 structure. The number of main filaments (12) to be aligned is 2 to 6 (that is, n = 2 to 6). When the number of filaments exceeds 6, the main filament bundle (13) is arranged in a line. It becomes difficult. The number of filaments is more preferably 3-5.

  The winding pitch (p) of the wrapping filament (14) is not particularly limited because it varies depending on the filament diameter (d1, d2), the number of main filaments (12), etc., but is preferably 2.0 to 6.0 mm. If the winding pitch (p) is too small, the shape stability of the steel cord (10) is excellent, but the strength of the steel cord (10) becomes small because the wrapping filament (14) does not work as a strong member. The mass per unit length of the cord (10) increases. Conversely, if the winding pitch (p) is too large, the steel cord (10) can be strengthened, but the shape stability of the steel cord (10) is impaired, and the main filament (12) is not aligned. If it is disturbed, the apparent cord diameter will increase. The winding pitch (p) is more preferably 3.0 to 5.0 mm.

  The steel cord (10) preferably has a tensile strength of 3500 MPa or more. If the tensile strength is less than 3500 MPa, it will be difficult to obtain the required strength unless the number of driving is made dense as the reinforcing member of the belt (7). The tensile strength is more preferably 4000 MPa or more. The higher the tensile strength, the better, so the upper limit is not particularly limited, but it is usually 5000 MPa or less.

  Here, the tensile strength of the cord is a value obtained by dividing the tensile strength of the cord by the cross-sectional area. The tensile strength is the maximum load required for the steel cord to be cut according to JIS G3510 and measured with a tensile tester at a cord gripping interval of 300 mm and a tensile speed of 30 mm / min. The cross-sectional area is a value obtained by dividing the weight per 1 m of the steel cord (10) by 7.86 which is the specific gravity of iron.

  The cord diameter of the steel cord (10) is not particularly limited, but the major axis (D1) is preferably 1.00 to 1.50 mm, and the minor axis (D2) is preferably 0.30 to 0.60 mm. Here, the measurement of the cord diameter is performed in accordance with JIS G3510 by measuring the outer diameter on the major axis side and the outer diameter on the minor axis side of the steel cord (10) with a predetermined thickness meter.

  As shown in FIG. 3, the belt layer is formed by disposing the steel cord (10) in the thickness direction (K) so that the short diameter direction (A) of the steel cord (10) is directed. That is, in the belt layer, the steel cord (10) is embedded in the coating rubber (11) at a predetermined interval so that the short diameter direction (A) thereof coincides with the thickness direction (K) of the belt layer. Yes. With this configuration, it is easy to process the steel cord (10) when it is covered with rubber, and the thickness of the belt layer can be reduced to suppress an increase in tire weight.

  The number of ends of the steel cord (10) in the belt layer (the number of driven-in cords) can be appropriately set according to the cord tensile strength and the like, and is not particularly limited, but is 10 to 25 / 25.4 mm. preferable.

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

A steel material having the chemical composition shown in Table 1 below is hot rolled to a diameter of 5.5 mm, and then repeated with patenting and dry wire drawing to form an intermediate line with a diameter of 1.7 mm. After covering the brass plating with the amount (g / kg) and the plated copper content (mass%), a main filament having a predetermined diameter was obtained by wet drawing. In addition, phosphorus (P) content in Table 1 is measured by the same method as the chromium content described above, and sulfur (S) and content are JIS G1215 (Appendix 6: Combustion-High Frequency Induction Heating Infrared) Absorption method).

  Steel cords having the structures shown in Tables 2 and 3 below were produced using the obtained main filaments. The steel cord of Comparative Example 9 has a 2 + 1 multi-layer twist structure in which one metal filament of the same diameter is twisted around a core portion where two metal filaments are aligned, and the other steel cords Is an n + 1 structure steel cord formed by wrapping a main filament bundle in which a plurality of main filaments are arranged in a single line without twisting them with a single straight wrapping filament.

  Using the obtained steel cord as a belt cord, a radial tire having a tire size of 195 / 65R15 having the cross-sectional shape shown in FIG. For each tire, the configuration other than the belt was the same. The angle of the steel cord (10) in the belt layer (7A) / (7B) was set to + 25 ° / −25 ° with respect to the tire circumferential direction. For each tire, the number of ends of the steel cord was set so that the belt strength was almost the same. The belt TOP gauges in Tables 2 and 3 are rubber gauges when coating the coating rubber (11).

  About each obtained tire, while measuring the tire weight, the rough road running test and the wet adhesion test were implemented. The results are shown in Tables 2 and 3. Each test method is as follows.

・ Bad road running test: Each tire built in a rim of 15 x 6 JJ with an internal pressure of 220 kPa is mounted on a passenger car. The presence or absence was examined. Further, as the edge separation property, the tire was disassembled after the rough road running test, and the separation length of the belt edge portion was measured.

Humid heat adhesion test: One whole tire was put in a constant temperature and humidity chamber at a temperature of 75 ° C. and a humidity of 95% RH, and deteriorated. The tread rubber portion (8) of the deteriorated tire is removed, and a strip shape is formed along the belt cord of the outermost layer. More specifically, the second belt layer (7B), the first belt layer (7A), the carcass ( After cutting into strips having a width of about 35 mm and a length of 150 mm with the 4) and inner liner (9) attached, the cords of the second belt layer (7B) were removed one by one on both sides. Then, a 50 mm incision is made between the belt layers (7A) and (7B) so as to separate the first belt layer (7A) and the second belt layer (7B), and at a speed of 30 mm / min. A peel test was performed using a tensile tester. Several points of coverage (rubber adhesion rate) were investigated by changing the deterioration time. The days when the coverage was 50% were estimated from the surveyed data, and the days were shown in Tables 2 and 3 as wet heat adhesiveness C50. It shows that it is excellent in wet heat adhesiveness, so that the number of days is long.

  Compared to Comparative Example 9 corresponding to the conventional example, Examples 1 to 7 according to the present invention were intended to reduce the weight of the tire without impairing fatigue and wet heat adhesion.

  On the other hand, in Comparative Example 1, the chromium content of the main filament was too high, the knot strength retention was small, and the fatigue property was impaired. In Comparative Example 2, the diameter of the main filament was smaller than the specified value, the number of ends increased in order to obtain a predetermined strength, and the distance between the steel cords became narrow, resulting in a tire failure in a rough road durability test. In Comparative Example 3, since the diameter of the main filament was larger than the specified value, cord breakage occurred due to metal fatigue in the rough road durability test, and the weight of the tire could not be reduced. In Comparative Examples 4 and 5, since the carbon content of the main filament was less than the specified value and the cord tensile strength was less than 3500 MPa, the number of ends was increased to obtain a predetermined strength, and the space between the steel cords was narrowed. The separation at the belt edge is longer. In Comparative Examples 4 and 5, the distance between the steel cords is larger than that in Example 4, but since the amount of steel in the belt layer is large, the steel cord cut end area (non-bonded portion) at the belt edge portion is Example 4. As a result, the separation at the belt edge is longer. In Comparative Example 6, the knot strength retention of the main filament was lower than the specified value, the cord was broken in the rough road durability test, and the fatigue property was inferior. In Comparative Example 7, the plating adhesion amount of the main filament was larger than the specified value, and the wet heat adhesion was inferior. In Comparative Example 8, the copper content in the main filament plating was too high, and the wet heat adhesion was poor. In Comparative Example 10, the plated copper content is lower than the specified value, in Comparative Example 11, the plating adhesion amount is lower than the specified value, and in Comparative Examples 12 and 13, the chromium content is lower than the specified value. There were many breaks inside, and it didn't become a code.

  The steel cord of the present invention can be used as a reinforcing member for various rubber products, and can be particularly suitably used for various pneumatic radial tires including passenger car tires.

1 ... bead part, 2 ... side wall part, 3 ... tread part, 4 ... carcass,
5 ... Bead core, 7 ... Belt, 7A, 7b ... Belt layer, 8 ... Tread rubber part,
10 ... Steel cord, 11 ... Coated rubber, 12 ... Main filament,
13 ... main filament bundle, 14 ... wrapping filament,
d1 ... diameter of the main filament, d2 ... diameter of the wrapping filament

Claims (4)

A main filament bundle made of metal filaments having a diameter of 0.15 to 0.30 mm and arranged in a single row without being twisted is wrapped with a wrapping filament made of one straight metal filament. A flat steel cord having an n + 1 structure (where n = 2 to 6),
The main filament is a steel filament having a carbon content of 0.95 to 1.20% by mass and a chromium content of 0.05 to 0.5% by mass, and having a copper content of 65 to 70% by mass. A steel cord for rubber reinforcement characterized by being coated with a plating adhesion amount of 4.5 to 8 g / kg and having a knot strength retention of the main filament of 50% or more.   The steel cord for reinforcing rubber according to claim 1, wherein the tensile strength is 3500 MPa or more.   The steel cord for reinforcing rubber according to claim 1 or 2, wherein the diameter of the wrapping filament is 0.05 to 0.20 mm and is not more than the diameter of the main filament.   A pneumatic radial tire provided with a belt layer using the steel cord for rubber reinforcement according to any one of claims 1 to 3.

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