JP2018108763A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire reduced in weight without impairing belt durability.SOLUTION: A pneumatic tire has carcass and a belt layer arranged on the outer periphery of a crown portion of the carcass, where the belt layer is formed by covering a steel cord with a rubber, in the steel cord, 4 to 6 steel filaments having such a cross-sectional flat shape as to have a pair of flat portions and a pair of curved portions that mutually face are arranged to be in a line without being twisted so that a major axis direction of the steel filament becomes a minor axis direction of the steel cord to be formed into a main filament bundle, the steel cord has n+1 structure (n=4 to 6) that one straight steel filament is wound around the main filament bundle as a wrapping filament, and a ratio (Sr/Sc) of a rubber cross-sectional area Sr to a steel cord cross-sectional area Sc in the belt layer is 3.2 to 5.0.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire.

  A pneumatic tire generally includes a belt in which a plurality of belt plies are crossed and laminated between an outer surface of a carcass ply and a tread rubber. The belt ply includes a steel cord having excellent tensile strength and tensile elasticity. Is used.

  Also, for the purpose of reducing the weight of the tire, it is known that a flat steel cord in which a plurality of steel filaments are arranged in parallel and one wrapping filament is wound around the belt ply is used for the belt ply. Examples of pneumatic tires using such flat steel cords include the inventions according to Patent Documents 1 and 2.

JP-A-8-120578 Japanese Patent Laying-Open No. 2015-227084 JP-A-10-292275

  If flat steel cords are used, the amount of rubber used in the belt layer can be reduced, making it possible to reduce the weight of the tire. However, if the amount of rubber used is reduced too much, the durability of the belt deteriorates. there were.

  In view of the above, an object of the present invention is to provide a pneumatic tire that can be reduced in weight without impairing the durability of the belt.

  Patent Document 3 discloses a cord in which 5 or 6 metal wires are arranged side by side in parallel in the same plane without twisting, but there is no wrapping filament and it is not an n + 1 structure. .

  A pneumatic tire according to the present invention is a pneumatic tire having a carcass and a belt layer disposed on an outer periphery of a crown portion of the carcass, and the belt layer is formed by coating a steel cord with rubber. In the steel cord, the major axis direction of the steel filament becomes the minor axis direction of the steel cord without twisting four to six steel filaments having a flat cross-sectional shape having a pair of opposed flat portions and a pair of curved portions. The main filament bundle is arranged in a row to form a main filament bundle, and one steel filament is wrapped around the main filament bundle as a wrapping filament, and n + 1 structure (n = 4 to 6). It is assumed that the ratio (Sr / Sc) of the rubber cross-sectional area Sr is 3.2 to 5.0.

  In the steel cord, the hardness of the wrapping filament is lower than the hardness of the main filament, and the difference (Cc−Cw) between the carbon content Cc (mass%) of the main filament and the carbon content Cw (mass%) of the wrapping filament is It can be 0.05-0.40.

  The steel cord has a wrapping filament that is pressed and deformed in the direction of its short diameter, and the ratio (Da / Db) of the short diameter Da of the steel cord after pressing to the short diameter Db of the steel cord before pressing is 0. It can be 80 or less.

  The steel cord may have a diameter before pressing of the wrapping filament of 0.10 to 0.15 mm.

  According to the present invention, a lightweight pneumatic tire can be obtained without impairing the durability of the belt.

The half sectional view of the pneumatic tire concerning one embodiment of the present invention. The figure which showed typically a part of cross section of the belt layer which concerns on one Embodiment of this invention. The typical perspective view showing the composition of the steel cord concerning one embodiment of the present invention. The partial sectional view of the steel cord concerning one embodiment of the present invention.

  Hereinafter, matters related to the implementation 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 radially outer ends of left and right sidewall portions 2. And a tread portion 3 provided between both sidewall portions so as to connect the portions, and a carcass 4 extending between the pair of bead portions is provided.

  The carcass 4 includes at least one carcass ply whose both ends are locked by an annular bead core 5 embedded in the bead portion 1 through the sidewall portion 2 from the tread portion 3. The carcass ply is formed by arranging carcass cords made of organic fiber cords or the like substantially perpendicular to the tire circumferential direction.

  A belt 6 is disposed between the carcass 4 and the tread rubber portion 7 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 6 is provided so as to overlap the outer periphery of the crown portion of the carcass 4 and can be composed of one or a plurality of belt plies, usually at least two belt plies. In this embodiment, the carcass side The first belt ply 6A and the second belt ply 6B on the tread rubber portion side are composed of two belt plies. The belt plies 6A and 6B are formed by inclining the steel cord 10 at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction and arranging the steel cord 10 at predetermined intervals in the tire width direction. As shown in FIG. 2, the steel cord 10 is covered with a coating rubber 11. The steel cord 10 is disposed so as to intersect each other between the two belt plies 6A and 6B.

  A belt reinforcing layer 8 is provided between the belt 6 and the tread rubber portion 7 on the outer peripheral side of the belt 6 (that is, on the outer side in the tire radial direction). The belt reinforcing layer 8 is a cap ply that covers the belt 6 with its entire width, and is made of an organic fiber cord arranged substantially parallel to the tire circumferential direction. That is, the belt reinforcing layer 8 is formed by arranging organic fiber cords along the tire circumferential direction, and the organic fiber cords are angled from 0 to 5 degrees with respect to the tire circumferential direction so as to cover the entire width direction of the belt 6. It can be formed by winding in a spiral.

  As shown in FIG. 2, the belt ply 6A is formed by arranging the steel cord 10 so that the major axis direction B thereof is parallel to the belt surface (that is, the belt outer peripheral surface). That is, in the belt ply, 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 ply. Therefore, the steel cord 10 is disposed such that the major axis direction B is parallel to the tread surface. With this configuration, it is easy to process the steel cord 10 when it is covered with rubber, and the thickness of the belt ply can be reduced to suppress an increase in tire weight. In addition, since the obtained belt ply has a high bending rigidity in the tire width direction, the steering stability can be improved, and since the bending rigidity in the tire radial direction is low, the envelope property is increased and the ground contact area is increased. be able to.

  The steel cord 10 for a belt ply, which is a main part of the pneumatic tire according to the present embodiment, consists of only steel filaments as shown in FIGS. 2 to 4, without twisting 4 to 6 main filaments 12. This is a flat steel cord having an n + 1 structure in which a main filament bundle 13 is formed by being aligned in a row, and one wrapping filament 14 is wound around the main filament bundle 13. The main filament bundle 13 is formed by arranging a plurality of the same main filaments 12 in a horizontal row without twisting them, that is, the main filaments 12 form one layer along one plane. Paralleled. Therefore, the obtained steel cord 10 is flat and has a major axis Dl and a minor axis Da as shown in FIG. With such a flat steel cord, the bending rigidity in the major axis direction B is high and the bending rigidity in the minor axis direction A is low, so the balance between riding comfort and steering stability during normal driving can be improved. In run flat tires, the balance between run flat durability and steering stability can be improved.

  As shown in FIGS. 3 and 4, each of the plurality of main filaments 12 has a flat cross-sectional shape having a pair of opposed flat portions 12 a and a pair of outward curved portions 12 b. Specifically, it is of a cross-section racetrack shape comprising a pair of semicircular curved surface portions 12b and a pair of flat surface portions 12a connecting these curved surface portions 12b. The flat main filaments 12 are arranged in a line so that the major axis direction (the direction connecting the pair of curved surface portions 12 b) is the minor axis direction A of the steel cord 10 without twisting a plurality of the flat main filaments 12. That is, the main filaments 12 are aligned in parallel so that the flat portions 12a face each other, and the flat portions 12a are in contact with each other over the entire length.

  By using the flat main filament 12 in this way, the thickness in the major axis direction of the main filament increases compared to the case of using the main filament having the same cross-sectional area and a circular cross section. The rigidity at is increased. That is, when main filaments having the same cross-sectional area are used, the flat shape is easier to secure the rigidity of the steel cord in the minor axis direction A than the circular shape, and the steering stability is improved due to the deterioration of the tire contact surface shape. It is easy to suppress a decrease and a decrease in tire high speed durability. Conversely, when the main filament 12 having a circular cross section is used, in order to ensure the rigidity in the short axis direction A of the steel cord for the handling stability and the high speed durability, the main filament having a large diameter is used. In that case, the mass of the steel cord 10 increases, and the tire mass is likely to increase. By using the flat main filament 12, it is possible to secure sufficient rigidity in the minor axis direction A of the steel cord while suppressing an increase in mass.

  The main filament 12 having a flat cross section can be formed by, for example, performing flattening (rolling) on a piano wire having a circular cross section. The flatness ratio (%) of the main filament 12, that is, the (minor axis d1 / major axis d2) × 100 of the filament is preferably 50 to 85%. When the flatness is 50% or more, it is easy to secure the strength of the filament, and the belt durability can be further improved. When the flatness is 85% or less, the effect of improving the steering stability is further increased. be able to. In addition, it is preferable that the major axis d2 of the main filament 12 is 0.15-0.35 mm, More preferably, it is 0.20-0.30 mm.

  The wrapping filament 14 wound around the main filament bundle 13 is not particularly limited, but a so-called “straight” one is preferably used without being waved. When straight, winding is easy, and the binding force of winding is easily made high. In addition, due to the restraining force of the wrapping filament 14, the aligned main filament 12 can have a sense of unity as the steel cord 10, and it is highly resistant to in-plane deformation of the belt material when changing the route during traveling or turning a curve. Stiffness is obtained. The cross-sectional shape of the wrapping filament does not have to be a perfect circle, and may be, for example, an ellipse.

  In the present embodiment, the steel cord thus obtained is arranged on the belt reinforcing layer so that the ratio (Sr / Sc) of the rubber sectional area Sr to the cord sectional area Sc satisfies 3.2 to 5.0. Can be set. When this ratio is 3.2 or more, a sufficient adhesive force between the belt plies can be secured, and a decrease in tire durability due to a decrease in the distance between the cords can be suppressed. Moreover, when this ratio is 5.0 or less, it is excellent in the weight reduction effect of a tire.

  Here, the cord cross-sectional area Sc and the rubber cross-sectional area Sr are the cross-sectional areas of the steel cord 10 and the coating rubber 11 in the member width direction cross-section obtained by cutting the belt 6 along the width direction (B direction in FIG. 2). is there. The member width direction cross section is a cross section obtained by cutting the belt 6 perpendicularly to the extending direction of the steel cord 10. The ratio (Sr / Sc) can be obtained by dividing the rubber cross-sectional area Sr by the cord cross-sectional area Sc. For example, the cord cross-sectional area per 1 inch width of the belt 6 is calculated from the number of driven steel cords 10 and the cord diameter, and from the cross-sectional area of the belt 6 calculated from the thickness (t) of the belt 6 and the cord cross-sectional area, the width Sr / Sc per cord is calculated by calculating the rubber cross-sectional area per inch and dividing the obtained rubber cross-sectional area by the cord cross-sectional area. When the number of steel cords 10 to be driven is constant in the width direction of the belt 6, the value per cord is defined as Sr / Sc of the belt 6. When the number of steel cords 10 to be driven changes in the width direction of the belt 6, the average value of Sr / Sc of each cord calculated as described above may be calculated. Since the cross-sectional area of the main filament 12 having a flat cross section can be approximated to the area of an ellipse, it can be obtained from the short diameter d1 and the long diameter d2 of the main filament 12. Further, even if the steel cord 10 is in a pressed form described later, the cord cross-sectional area does not change before and after pressing, so by calculating the cord cross-sectional area before pressing, the cord cross-sectional area after pressing Can be requested.

  As a more preferable aspect of the above embodiment, as shown in FIGS. 3 and 4, a flat steel cord formed by wrapping around the main filament bundle 13 with the wrapping filament 14 is pressed in the minor axis direction A to wrap the filament 14. What deform | transformed can be used. By pressing, the wrapping filament 14 is deformed along the shape of the space into at least a part of the space formed between the adjacent main filaments 12, and a part of the wrapping filament 14 enters, that is, at least a part of the space is wrapped. Filled with at least a portion of the filament 14. Therefore, the restraining force of the main filament 12 by the wrapping filament 14 can be increased. Further, since a relatively large plastic deformation is applied to the wrapping filament 14, the rotational torque and the repulsive force inherent in the wrapping filament 14 are reduced. Therefore, it is easy to maintain the shape in which the main filament bundles 13 are arranged in a row, and it is easy to exhibit the excellent effect of the flat cord.

  As described above, the thickness of the steel cord 10 according to this embodiment having the wrapping filament 14 deformed by pressing in the minor axis direction A, that is, the minor axis Da after pressing has the wrapping filament 14 before deformation. The thickness of the steel cord 10 can be made smaller than the short diameter Db before pressing. The ratio (Da / Db) of the short diameter Da of the steel cord after pressing to the short diameter Db of the steel cord before pressing is preferably 0.80 or less, and more preferably 0.65 to 0.75. In this way, by pressing with a force of a magnitude that satisfies Da / Db ≦ 0.80, the deformed wrapping filament 14 sufficiently enters the space between the main filaments 12, and the binding force of the wrapping filament 14 is increased. Can be secured sufficiently. Further, the rotational torque and repulsive force inherent in the wrapping filament 14 can be sufficiently reduced.

  The diameter before pressing of the wrapping filament 14, that is, the filament diameter d0 is preferably smaller than the minor diameter d1 of the main filament 12 as described above, and more preferably 0.10 to 0.15 mm. When it is 0.15 mm or less, the rotational torque and repulsive force inherent in the wrapping filament 14 can be easily reduced sufficiently by pressing, and when it is 0.10 mm or more, the possibility of disconnection during pressing can be further reduced.

  The pressing can be performed using a rolling roll (not shown), and the flat cord after the wrapping filament 14 is wound is sandwiched and pressed from the upper and lower surfaces by the rolling roll. Since the wrapping filament 14 is located outside and its hardness is lower than that of the main filament 12, the wrapping filament 14 can be preferentially deformed by pressing. A space having a substantially fan-shaped cross section is formed between adjacent main filaments 12, and when pressed by a rolling roll, the inner peripheral side of the wrapping filament 14 is deformed so as to fill the space, and the shape of the space is formed. Along the projection 14a is formed. At the same time, a recess is formed between the protrusions 14a, and the outer peripheral side portion 14b of the wrapping filament is deformed into a flat shape.

  As a steel material used for the main filament 12 and the wrapping filament 14, it is preferable to use carbon steel containing carbon. Although carbon content of the main filament 12 is not specifically limited, It is preferable that it is 0.70-1.20 mass%, and it is more preferable that it is 0.85-0.95 mass%. In the present embodiment, the wrapping filament 14 having a hardness lower than that of the main filament 12 can be used. The hardness can be adjusted by the carbon content.

  As an embodiment, the carbon content (mass%) of the main filament 12 is Cc, the carbon content (mass%) of the wrapping filament 14 is Cw, and the difference between them is Cc-Cw of 0.05 to 0.00. It is preferable that it is 40 mass%, More preferably, it is 0.10-0.30 mass%. When Cc-Cw is 0.05% by mass or more, the wrapping filament 14 is easily deformed by pressing, and when it is 0.40% by mass or less, the possibility that the wrapping filament 14 is disconnected by pressing is reduced. can do.

  The method for forming the belt 6 on the crown portion of the carcass 4 using the steel cord 10 is not particularly limited. For example, a plurality of steel cords that are aligned and covered with rubber may be spirally wound on the belt layer of the raw tire, or a wide rubberized sheet that is aligned with the steel cord 10 is provided on the crown portion. It may be wound once. Thus, a pneumatic tire is obtained by producing a raw tire (green tire) in a state where the belt 6 is wound around the outer peripheral side of the crown portion of the carcass 4 and vulcanizing and molding the obtained raw tire. .

  The type of pneumatic tire according to the present embodiment is not particularly limited, and examples thereof include various types of tires such as passenger car tires, heavy load tires used for trucks, buses, and the like.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Steel cords having the structure shown in Table 1 below were produced. The steel cord of Comparative Example 1 has a 2 + 1 multi-layer twisted structure (2 + 1 × 0.27) in which one metal filament of the same diameter is twisted around a core portion made of two aligned metal filaments. Is a conventional code with For all other steel cords, a single main wrapping filament (diameter d0 = 0.15 mm) is wrapped with a main filament bundle in which a plurality of main filaments are arranged in a single line without twisting together. This is an n + 1 structure steel cord. Moreover, the winding pitch (p in FIG. 3) of the wrapping filament was 5.0 mm, and the steel cord was pressed using a rolling roll so that Da / Db was a value shown in Table 1.

  The measurement method for filaments and steel cords is as follows.

-Carbon content of the filament: Infrared absorption method according to JIS G1211 (Annex 3: Quantitative determination of total carbon-high frequency induction furnace combustion). More specifically, steel was melted by high frequency heating using an apparatus called “CS-400” manufactured by LECO, and quantitative analysis was performed by an infrared absorption method.

-Filament diameter and cord diameter: In accordance with JIS G3510, the diameter of the steel cord and filament was measured with a predetermined thickness meter.

  Further, using the obtained steel cord as a belt cord, a radial tire having a tire size of 175 / 65R15 was vulcanized according to a conventional method. For each tire, the configuration other than the belt was the same. The angle of the steel cord in the belt ply (6A) / (6B) was + 25 ° / −25 ° with respect to the tire circumferential direction. The belt ply was manufactured by arranging the steel cords in the number of drivings shown in Table 1 so that the major axis direction thereof was parallel to the outer peripheral surface of the belt, and using a calender device as a topping counter.

  The carcass ply was 1 ply with a polyethylene terephthalate cord of 1100 dtex / 2 and a driving number of 28/25 mm.

  For each of the obtained pneumatic tires, the weight of the tire, the ratio of the rubber cross-sectional area Sr to the cord cross-sectional area Sc of the belt layer (Sr / Sc), and belt durability were evaluated. The evaluation method for each evaluation item is shown below.

Tire weight: Comparative Example 1 was set to 100, and the weight of each tire was indicated by an index.

Sr / Sc: Steel cord driven number E (lines / inch), main filament short diameter (mm) d1, main filament long diameter (mm) d2, main filament number n, wrapping filament diameter (mm ) Is d0, and the belt thickness (mm) is t, the cord cross-sectional area Sc per belt width 1 inch and the rubber cross-sectional area Sr per width 1 inch are calculated from the following formulas, and the ratio Sr / Sc between them is obtained. .

Sc = ((d1 / 2) × (d2 / 2) × π × n + (d0 / 2) ² × π) × E
Sr = 25.4 × t-Sc

Belt durability: A tire was mounted on a specified rim, and the load was applied by pressing the tire against the drum up to 62% deflection at the maximum load specified by JATMA at an internal pressure of 110 kPa. The test speed was 420 rpm, and the test was conducted until an abnormality occurred or 720 hours of running. After completion of the test, the tire was disassembled, and the length of the belt separation at the end in the belt width direction was visually measured, and the presence or absence of cord breakage was confirmed. The determination of belt separation was performed according to the following criteria.

None: 0mm
Small: greater than 0 mm and less than 2 mm Small: 2 mm or more and less than 6 mm Medium: 6 mm or more and less than 10 mm Large: 10 mm or more

  The results are as shown in Table 1. In each example, the belt durability is maintained or improved as compared with Comparative Example 1, and the tire weight is also reduced.

  In Comparative Example 2, Sr / Sc was less than 3.2, and the belt separation was deteriorated as compared with Comparative Example 1.

  In Comparative Example 3, Sr / Sc exceeded 5.0, and the tire weight reduction effect was not obtained as compared with Comparative Example 1.

  The pneumatic tire of the present invention can be used for various vehicles such as passenger cars, light trucks, and buses.

T ...... Tire 1 ... Bead part 2 ... Side wall part 3 ... Tread part 4 ... Carcass 5 ... Bead core 6 ... Belt 6A ... First belt ply 6B ... Second belt ply 7 ... Tread rubber part 8 ... belt reinforcing layer 10 ... steel cord 11 ... coating rubber 12 ... main filament 12a ... main filament flat surface portion 12b ... main filament curved surface portion 13 ... main filament bundle 14 ... wrapping filament A ... minor axis direction of steel cord B: Steel cord major axis direction D1: Steel cord major axis D2: Steel cord minor axis Da: Steel cord minor axis pressed in the minor axis direction K: Belt ply thickness direction d1: Short main filament Diameter d2 ... Major filament major diameter d0 ... Wrapping filament diameter t ... Belt thickness

Claims (4)

A pneumatic tire having a carcass and a belt layer disposed on an outer periphery of a crown portion of the carcass,
The belt layer is formed by coating the steel cord with rubber;
The steel cord is such that the major axis direction of the steel filament becomes the minor axis direction of the steel cord without twisting four to six steel filaments having a flat cross section having a pair of opposed flat portions and a pair of curved portions. A main filament bundle that is aligned in a row to form a main filament bundle, and a steel filament is wrapped as a wrapping filament around the main filament bundle (n = 4 to 6),
The pneumatic tire according to claim 1, wherein a ratio (Sr / Sc) of a rubber cross-sectional area Sr to a steel cord cross-sectional area Sc in the belt layer is 3.2 to 5.0.   The hardness of the wrapping filament is lower than the hardness of the main filament, and the difference (Cc−Cw) between the carbon content Cc (mass%) of the main filament and the carbon content Cw (mass%) of the wrapping filament is 0.05 to The pneumatic tire according to claim 1, wherein the pneumatic tire is 0.40.   The steel cord has the wrapping filament that has been deformed by being pressed in the direction of its short diameter, and the ratio (Da / Db) of the short diameter Da of the steel cord after pressing to the short diameter Db of the steel cord before pressing is 0. The pneumatic tire according to claim 1 or 2, wherein the pneumatic tire is 80 or less. The pneumatic tire according to claim 3, wherein a diameter of the wrapping filament before pressing is 0.10 to 0.15 mm.

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