JP2014121922A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire in which coexistence of steering stability and high speed durability can be achieved.SOLUTION: In a pneumatic tire, which includes a belt 7 consisting of at least two sheets of belt ply 7A and 7B having steel cords 10 arranged obliquely against the tire circular direction in the outer peripheral side of a carcass layer 4 in a tread part 3, and a belt reinforce layer 9 consisting of fiber cords aligned in the tire circular direction in its outer peripheral side, the belt ply has the steel cords 10 one of which has a flat cross section having a major axis D1 and a minor axis D2 and in which the flexural stiffness of a major axis direction B is larger than that of a minor axis direction A and which is arranged so that the major axis direction B is in parallel with the belt surface, and, in the belt reinforce layer, the number of fiber cords per width is set as larger in the belt central part than in the belt edge part.

Description

  The present invention relates to a pneumatic tire using a steel cord as a belt reinforcing material.

  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, and the belt ply includes a steel cord having excellent tensile strength and tensile elasticity. Is used. Conventionally, as such a steel cord, one obtained by twisting a plurality of filaments is generally used. For example, a 1 × n structure (n = 3 to 5) or a m + n structure in which metal filaments are twisted around a plurality of aligned filaments can be used. These steel cords usually have substantially the same bending rigidity even when measured by rotating 90 degrees with respect to the longitudinal axis of the cord, that is, the bending rigidity has no directionality.

  Steel cords that do not have directionality in bending rigidity can achieve the same effect regardless of the orientation, but on the other hand, it is necessary to change the angle of the belt to adjust the rigidity of the tread part. Gives constraints. For example, in order to convey the movement of a car to the road surface, it is necessary to secure a sufficient ground contact surface. For this purpose, as the belt ply, the lower the out-of-plane bending rigidity (out-of-plane rigidity) is, the envelope property can be secured and the ground contact area can be increased. In addition, if the in-plane bending rigidity (in-plane rigidity) of the belt ply is low, the tread portion is bent during cornering of the vehicle, and the ground contact area is reduced. On the other hand, if the out-of-plane rigidity of the belt ply is low, the tire diameter increases during high-speed running, and the durability during high-speed running is impaired.

  By the way, in order to reduce the weight of the tire, a flat steel cord in which a plurality of filaments are arranged in parallel and one wrapping filament is wound around the steel cord constituting the belt ply has been proposed (patent) Reference 1-5).

JP-A-62-149929 Japanese Patent Application Laid-Open No. 07-304307 Japanese Patent Laid-Open No. 08-120578 JP 2012-106570 A JP 2012-107353 A

  By using such a flat steel cord, the out-of-plane rigidity can be lowered while increasing the in-plane rigidity of the belt ply, and the steering stability performance can be improved. However, when the out-of-plane rigidity is low, the high-speed durability may be impaired as described above.

  In view of the above points, an object of the present invention is to provide a pneumatic tire that can achieve both steering stability performance and high-speed durability.

  The pneumatic tire according to the present invention includes a belt composed of at least two belt plies in which steel cords are inclined with respect to the tire circumferential direction on the outer circumferential side of the carcass layer in the tread portion, and fiber cords on the outer circumferential side of the belt. In a pneumatic tire provided with a belt reinforcing layer that covers the entire width of the belt, and the belt ply has a flat cross-sectional shape having a major axis and a minor axis and has a major axis A steel cord having a bending stiffness in the direction larger than that in the minor axis direction is arranged so that the major axis direction is parallel to the belt surface, and the belt reinforcing layer has a number of fiber cords per width, It is characterized by being set more in the belt center than in the belt end.

  The belt ply with the above steel cord can increase the in-plane rigidity while lowering the out-of-plane rigidity, ensuring a sufficient ground contact area to maintain cornering characteristics and improving steering stability. can do. In addition, since the belt reinforcement layer can exhibit a higher reinforcement effect at the belt center than at the belt end, it uses a belt ply with low out-of-plane rigidity, but the belt center at high speed running. It is possible to effectively suppress the growth of diameter and improve the high speed durability.

1 is a half sectional view of a pneumatic tire according to an embodiment. It is a partial cross section figure of the belt ply which concerns on one Embodiment. It is a figure showing the composition of the steel cord concerning one embodiment. It is sectional drawing of the sample for out-of-plane rigidity measurement. It is sectional drawing of the sample for in-plane rigidity measurement. It is a figure for demonstrating the measuring method of out-of-plane and in-plane rigidity.

  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). Consists of carcass plies. 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 (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 so as to overlap the outer periphery of the crown portion of the carcass (4), and can be constituted by one or a plurality of belt plies, usually at least two belt plies. The first belt ply (7A) on the carcass (4) side and the second belt ply (7B) on the tread rubber portion (8) side are constituted by two belt plies. The belt plies (7A) and (7B) are formed by inclining steel cords 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. As shown in FIG. 2, the steel cord (10) is covered with a coating rubber (11). The steel cord is disposed so as to intersect each other between the two belt layers (7A) and (7B).

  A belt reinforcing layer (9) is provided between the belt (7) and the tread rubber portion (8) on the outer peripheral side of the belt (7) (that is, the outer side in the tire radial direction). The belt reinforcement layer (9) is a cap ply that covers the belt (7) with its entire width, and is made of fiber cords arranged substantially parallel to the tire circumferential direction. That is, the belt reinforcing layer (9) is formed by arranging fiber cords along the tire circumferential direction, and the fiber cords are 0 to 5 degrees with respect to the tire circumferential direction so as to cover the entire width direction of the belt (7). It can be formed by winding spirally at an angle of.

  In the present embodiment, the steel cord constituting the belt (7) is a cord having a flat cross-sectional shape having a major axis and a minor axis, and having a bending stiffness in the major axis direction larger than that in the minor axis direction. Used. By using such a steel cord having directionality in bending rigidity, the in-plane bending rigidity can be increased while the out-of-plane bending rigidity of the belt ply is lowered. Therefore, it is possible to secure the envelope by securing the envelope property by the low out-of-plane bending rigidity, and it is possible to secure the grounding area by suppressing the bending of the tread portion during cornering by the high in-plane bending rigidity. Therefore, it is possible to secure a sufficient ground contact area to maintain cornering characteristics and improve steering stability.

  Such a steel cord having directionality in bending rigidity is not particularly limited. For example, as shown in FIG. 3, a plurality of metal filaments (hereinafter referred to as main filaments) (12) are not twisted together. A steel cord (10) having an n + 1 structure formed by wrapping a main filament bundle (13) arranged in a line with a single wrapping filament (14) is preferably used.

  Here, steel filaments made of various carbon steels can be used as the main filament (12), and the diameter (filament diameter) d is not particularly limited, but is preferably 0.15 to 0.30 mm. The wrapping filament (14) is not particularly limited. For example, a steel filament made of various carbon steels can be used, and the diameter (filament diameter) d0 is equal to or less than the diameter d of the main filament (12). It is preferable that there is, for example, 0.10 mm to 0.25 mm.

  The main filament bundle (13) can be formed by arranging a plurality of main filaments (12) having the same diameter so as to be arranged in a horizontal line without being twisted. That is, the main filaments (12) are juxtaposed so as to form one layer along one plane. Therefore, the steel cord (10) obtained is flat and has a major axis D1 and a minor axis D2 as shown in FIG. Although the value of the major axis D1 and the minor axis D2 is not particularly limited, it is preferable that the major axis D1 is 1.00 to 1.50 mm and the minor axis D2 is 0.30 to 0.60 mm. The number of main filaments (12) constituting the main filament bundle (13) is not particularly limited, but may be 3 to 6, for example. As the number increases, the ratio of the in-plane rigidity / out-plane rigidity of the steel cord can be increased.

  The steel cord (10) is formed by wrapping the wrapping filament (14) around the main filament bundle (13). As the wrapping filament (14), a straight steel filament which is not corrugated or the like is preferably used. The winding pitch p of the wrapping filament (14) is not particularly limited and can be, for example, 2.0 to 30.0 mm.

  As shown in FIG. 3, the main filament (12) may be a straight metal filament that is not corrugated, or may be a corrugated metal filament. 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.

  In the present embodiment, the steel cord (10) preferably has a ratio of in-plane stiffness to out-of-plane stiffness (in-plane stiffness / out-of-plane stiffness) of 10 or more. Here, the in-plane rigidity is bending rigidity when the steel cord (10) is bent in the major axis direction (B) (left and right direction in FIG. 2), and corresponds to rigidity in the width direction in the tire. The out-of-plane rigidity is bending rigidity when the steel cord (10) is bent in the minor axis direction (A) (vertical direction in FIG. 2), and corresponds to radial rigidity in the tire. In order to obtain such a ratio of in-plane rigidity / out-plane rigidity, the thickness and number of main filaments to be aligned may be set appropriately. For example, by increasing the number of main filaments aligned, By increasing the internal rigidity, the ratio of the in-plane rigidity / out-of-plane rigidity can be increased. The upper limit value of the ratio of in-plane rigidity / out-plane rigidity is not particularly limited, but is usually 25 or less.

  As shown in FIG. 2, the belt ply 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. Yes. Therefore, the steel cord (10) is disposed so 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 it is possible to reduce the thickness of the belt ply and 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. Can be raised.

  As the fiber cord constituting the belt reinforcing layer (9), various organic fiber cords such as nylon, polyester (polyethylene terephthalate, polyethylene naphthalate, etc.), aramid, rayon, etc. can be used. A single twist structure may be used, and is not particularly limited. The belt reinforcing layer (9) can be formed, for example, by winding a ribbon-like band-shaped member, in which organic fiber cords are aligned and covered with rubber, on the belt (7) in a spiral manner during tire molding. it can.

  In the present embodiment, the belt reinforcing layer (9) is set such that the number of fiber cords per width is greater at the belt center than at the belt end. Specifically, the number of driving per unit width at both widthwise end portions (9S) of the belt reinforcing layer (9) corresponding to the belt end portion is Es, and the width of the belt reinforcing layer (9) corresponding to the belt center portion When the number of driving per unit width at the central portion (9C) in the direction is Ec, it is set so that Ec is larger than Es. The ratio (Ec / Es) between the two is preferably 1.2 times or more. By increasing the density of the fiber cord in the central portion (9C) in this way, the belt reinforcing layer (9) can exert a higher reinforcing effect in the belt central portion than in the belt end portion, and therefore, in-plane rigidity. Although the belt plies (7A) and (7B) having a low height are used, the diameter growth at the center of the belt during high-speed running can be effectively suppressed, and the high-speed durability can be improved. The upper limit of the ratio Ec / Es is not particularly limited, but is preferably 2.0 times or less.

  Thus, when changing the density of the fiber cord in the belt reinforcing layer (9), the method of changing is not particularly limited, but gradually from the width direction both ends (9S) toward the width direction center (9C). It is preferable to set the density to be high. Alternatively, a boundary position may be set between the width direction both ends (9S) and the width direction center (9C), and the density of the fiber cord may be changed at the boundary position. The boundary position in that case is not particularly limited, but may be set to a position corresponding to 15 to 40% (more preferably 20 to 30%) of the maximum belt width (W) from the belt end.

  The number of fiber cords to be driven into the belt reinforcing layer (9) can be appropriately set according to the cord strength and the like, and is not particularly limited, but is 20 to 50/25 mm as values at both ends (9S) in the width direction. It is preferable that

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this 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 + 2 multi-layer twist structure in which two metal filaments having the same diameter are twisted around a core portion where two metal filaments are aligned. In the steel cords of Example 1 and Comparative Example 2, the main filament bundle in which the five main filaments are arranged in a line without being twisted is arranged as one straight wrapping filament (diameter d0 = 0.20 mm). It is a steel cord of 5 + 1 structure that is wrapped with

  Using the obtained steel cord as a belt cord, a radial tire having a tire size of 195 / 50R15 82V having a cross-sectional shape shown in FIG. 1 according to the configuration of the belt and belt reinforcing layer shown in Table 1 was vulcanized according to a conventional method. Molded. About each tire, all the structures other than a belt and a belt reinforcement layer were made into the common structure. The carcass ply uses a polyester cord 1670 dtex / 2, one ply of 22 toppings / 25 mm of topping, and is arranged so that the cord is perpendicular to the tire equator line, and each terminal passes through a bead core. I rolled it up. The angle of the steel cord in the belt ply (7A) / (7B) was + 25 ° / −25 ° with respect to the tire circumferential direction.

  For each tire, the number of steel cords to be driven was set so that the belt strength was almost the same. In Example 1 and Comparative Example 2, the belt ply has steel cords arranged in the number of drivings shown in Table 1 so that the major axis direction thereof is parallel to the belt surface, and the cord diameters (minor axis) above and below the steel cords. ) And having a thickness of 0.2 times as large as that of the rubber was coated by using a calendar device with an anti-width of 300 mm.

  The belt reinforcing layer (9) was formed by using a band-shaped unvulcanized tape obtained by coating a nylon 66 cord (twist number = 22.2 T / 10 cm) of 1400 dtex / 1 with rubber. The dimensions of the unvulcanized tape were 10 mm wide x 0.8 mm thick, and 14 pieces of the above cords were uniformly driven into a width of 10 mm. In Comparative Examples 1 and 2, the unvulcanized tape was uniformly wound on the belt at a feed pitch of 11 mm (constant) at the time of tire molding. On the other hand, in Example 1, the unvulcanized tape is gradually wound so that the both ends (9S) in the width direction start winding at a feed pitch: 11 mm and the feed pitch: 8 mm at the center in the width direction (9C). Wrapped around with a narrow interval.

  About each obtained tire, while measuring the contact pressure ratio and contact length ratio of a tread center part and a shoulder part, the high-speed diameter growth rate was measured as a tire high-speed durability test.

  Each measuring method is as follows.

Filament diameter and cord diameter: Based on JIS G3510, the diameters of the metal filament and the steel cord were measured with a predetermined thickness meter. For the cord diameter, the outer diameter on the longer diameter side (major diameter D1) and the outer diameter on the shorter diameter side (minor diameter D2) were measured.

-Belt tensile strength: Based on JIS G3510, the tensile strength of steel cord was measured using a tensile tester (Autograph manufactured by Shimadzu Corporation), and the belt was driven from the obtained value. Using the number, the belt tensile strength per 25 mm was determined.

In-plane rigidity, out-of-plane rigidity, in-plane rigidity / out-of-plane rigidity: A sample for measuring out-of-plane rigidity having a cross-sectional shape shown in FIG. 4 and a sample for measuring in-plane rigidity having a cross-sectional shape shown in FIG.

  As shown in Fig. 4, the sample for measuring out-of-plane rigidity is driven with steel cords placed in parallel so that the major axis direction is parallel to the surface opposite to the topping. The thickness was set to 0.50 mm, and a topping was manufactured with an opposite width of 300 mm. The obtained topping was vulcanized at 160 ° C. for 20 minutes, and was cut so that eight steel cords were included to obtain an out-of-plane stiffness measurement sample.

  For the in-plane stiffness measurement sample, stack the eight unvulcanized toppings so that the major axis directions are parallel to each other, vulcanize at 160 ° C. for 20 minutes, and cut out as shown in FIG. Thus, a sample for in-plane rigidity measurement including 8 steel cords was obtained.

  As shown in FIG. 6, the in-plane stiffness and the out-of-plane stiffness are measured by placing a sample (20) on a pair of support rolls (22) and (22), and using the pushing jig (24) from above. The sample (20) was pushed 10 times at 30 mm, and the load when it was pushed 5 mm at the time of the 10th push was measured, and these loads were defined as in-plane stiffness and out-of-plane stiffness, respectively. Both of these are the bending stiffness per 8 steel cords. The support roll (22) is a rotatable roll with almost no load (rotational resistance) during rotation, the roll diameter was 20 mm, and the distance between the rolls (distance between the axes) was 100 mm. The sample (20) is arranged so that the longitudinal direction N of the steel cord is perpendicular to the axial direction of the support roll (22), and is pushed from above each sample shown in FIGS. Arranged. The pushing jig (24) was a roll having a diameter of 15 mm, and the pushing speed was set to 300 mm / min.

  In addition, the composition of the rubber composition for coating at the time of producing the topping is as follows. That is, 60 parts by mass of carbon black (N330, manufactured by Tokai Carbon Co., Ltd.), 8 parts by mass of zinc oxide, and 2.0 parts by mass of cobalt stearate (manufactured by Japan Energy) with respect to 100 parts by mass of natural rubber (RSS # 3). , Anti-aging agent (Ouchi Shinsei Chemical Co., Ltd. Nocrack 6C) 2.0 parts by mass, stearic acid 0.5 parts by mass, sulfur (Shikoku Kasei Kogyo Co., Ltd.) 7.0 parts by mass, vulcanization acceleration 1.0 part by mass of an agent (Noxeller DZ manufactured by Ouchi Shinsei Chemical Co., Ltd.) was blended.

・ Ground pressure ratio, ground length ratio: The rim used and the air pressure were the conditions of JATMA YEAR BOOK 2012, and the load was the maximum load of the same. The measurement is performed by placing a tire on a pressure sensitive paper ("Ultra-low pressure" manufactured by Fuji Film Co., Ltd.) and applying the maximum load, and the contact pressure between the tread shoulder portion (S) and the center portion (C) Each ratio (C / S) of the contact length was determined. The closer the contact pressure ratio and the contact length ratio are to 1, the better the steering stability performance.

-High speed diameter growth rate: Evaluation was performed according to FMVSS139. Specifically, by measuring the outer diameter of the tire at 5 km / h and 200 km / h in a non-contact manner using “LK-G85” manufactured by Keyence, the diameter growth rate at high speed (= ( “Outer diameter at 200 km / h” / “Outer diameter at 5 km / h) × 100) was obtained.The smaller the diameter growth rate, the better the high-speed durability.

  As shown in Table 1, the result is Comparative Example 1 in which a steel cord having a large ratio of in-plane rigidity / out-of-plane rigidity is used in the belt ply as compared to Comparative Example 1 in which the steel cord having a multi-layer twist structure is used. The contact pressure ratio and contact length ratio were high, and the steering stability performance was significantly improved. However, in Comparative Example 2, since the out-of-plane rigidity of the belt ply is low and the fiber cord density of the belt reinforcing layer is constant in the width direction, the high-speed diameter growth rate is larger than that of Comparative Example 1, and high-speed durability is achieved. It was inferior to. On the other hand, in Example 1, the contact pressure ratio and the contact length ratio are higher than those of Comparative Example 1, and the steering stability performance is remarkably improved. Of course, it was suppressed as compared with Comparative Example 1 and was excellent in high-speed durability.

  The present invention can be suitably used for various pneumatic radial tires including passenger vehicle tires.

DESCRIPTION OF SYMBOLS 3 ... Tread part, 4 ... Carcass layer, 7 ... Belt, 7A, 7B ... Belt ply, 9 ... Belt reinforcement layer, 9C ... Center part in width direction, 9S ... End part in width direction, 10 ... Steel cord, 12 ... Main filament , 13 ... Main filament bundle, 14 ... Wrapping filament, A ... Steel cord minor axis direction, B ... Steel cord major axis direction

Claims (4)

A belt composed of at least two belt plies in which steel cords are arranged obliquely with respect to the tire circumferential direction on the outer circumferential side of the carcass layer in the tread portion, and fiber cords are arranged along the tire circumferential direction on the outer circumferential side of the belt. In a pneumatic tire provided with a belt reinforcing layer covering the entire width of the belt,
The belt ply has a flat cross-sectional shape having a major axis and a minor axis, and a steel cord whose bending stiffness in the major axis direction is larger than that in the minor axis direction, so that the major axis direction is parallel to the belt surface. Arranged,
In the pneumatic tire, the number of fiber cords per width of the belt reinforcing layer is set more in the belt center than in the belt end. The steel cord has a ratio (in-plane stiffness / out-of-plane stiffness) of in-plane stiffness that is bending stiffness in the major axis direction to out-of-plane stiffness that is bending stiffness in the minor axis direction is 10 or more. The pneumatic tire according to claim 1. The steel cord is a steel cord formed by wrapping a main filament bundle in which a plurality of metal filaments are aligned in a single line without twisting them together with a single wrapping filament. Pneumatic tires. 4. The belt reinforcing layer according to claim 1, wherein the number of fiber cords per width in the central portion of the belt is 1.2 times or more the number of fiber cords per width in the belt end portion. The pneumatic tire according to claim 1.

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