JP6081330B2 - Pneumatic tire - Google Patents

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, a steel cord of a belt ply is generally a twisted strand of a plurality of filaments having a 1 × n structure. However, in the 1 × n structure cord, the gap between the strands constituting the cord is narrow, so that the permeability of the rubber is poor, and the rubber does not easily enter the central portion of the cord. Therefore, the progress of the corrosion of the steel cord accompanying the permeation of moisture is unavoidable, and there is a problem that the durability is lowered.

  On the other hand, as a steel cord, a flat steel cord having an n + 1 structure in which a plurality of filaments are arranged in a line without being twisted and one wrapping filament is wound around the same is known (Patent Literature). 1 and 2). By adopting such an n + 1 structure, there is no cavity in the cord, and the problem of deterioration in durability due to rubber permeability into the cord is solved. Moreover, since the cross-sectional shape of the cord is flat when the n + 1 structure is used, the belt thickness is reduced and the weight of the tire is reduced. However, because of the flat shape, the distance between adjacent cords becomes narrow, which is disadvantageous for separation, and the durability of the tire is reduced.

JP-A-7-304307 JP-A-8-120578

  The present invention has been made in view of the above points, and an object of the present invention is to provide a pneumatic tire that can be reduced in weight without impairing durability and can improve steering stability. And

  The present inventor has intensively studied in view of the above problems, and uses a uniform steel cord as a belt cord and appropriately sets the viscosity of the covering rubber, thereby reducing the weight of the tire without impairing the durability of the tire. As a result, the present inventors have found that it is possible to achieve the improvement of the control and the handling stability, and have completed the present invention.

  That is, in the pneumatic tire according to the present invention, main filaments made of metal filaments having a diameter of 0.10 to 0.30 mm are arranged in a line without twisting a plurality of main filaments to form a main filament bundle. A belt ply in which a flat steel cord of an n + 1 structure (where n = 2 to 6) wound around the main filament bundle as a wrapping filament is arranged so that the major axis direction thereof is parallel to the belt surface, The belt ply is formed by coating a plurality of the steel cords in parallel with a rubber composition having a viscosity of 6000 to 8000 Pa · s measured at a temperature of 100 ° C. and a shear rate of 1000 (1 / second). It will be.

  According to the present invention, the flat steel cord having the aligned n + 1 structure is arranged so that the major axis direction thereof is the tire width direction, whereby the belt thickness can be reduced and the weight of the tire can be reduced. At the same time, it is possible to improve the steering stability by increasing the bending rigidity in the tire width direction. In addition, by coating the rubber composition having the above specific viscosity as a coating rubber on the steel cord having the n + 1 structure, it is possible to ensure the rubber penetration between adjacent cords, and the cords are in contact with each other. It is possible to prevent a decrease in tire durability due to the operation. Therefore, it is possible to reduce the weight and improve the steering stability without impairing the durability of the tire.

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.

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

  As shown in FIG. 1, the pneumatic tire of the embodiment is a pneumatic radial tire for passenger cars, and includes a pair of left and right bead portions (1), a tread portion (3) that constitutes a ground contact surface, and a tread portion ( 3) and a pair of left and right sidewall portions (2) interposed between the bead portion (1).

  A carcass (4) is embedded in the radially inner portion of the tread portion (3), and the carcass (4) is disposed between the left and right bead portions (1). The carcass (4) reaches the bead part (1) from the tread part (3) through the side wall parts (2) on both sides, and an annular bead core (5) in which both end parts are embedded in the bead part (1). It is rolled up and locked. The carcass (4) includes at least one carcass ply formed by arranging carcass cords made of organic fiber cords or the like substantially at right angles 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. On the outer peripheral side of the belt (7), there is a belt reinforcing layer (9) made of an organic fiber cord spirally wound at an angle of 0 to 5 degrees with respect to the tire circumferential direction, and the entire width direction of the belt (7). It is provided so as to cover.

  The belt plies (7A) and (7B) 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, it is covered with a coating rubber (11). The steel cord (10) is disposed so as to cross each other between the two belt plies (7A) (7B).

  In this embodiment, as shown in FIG. 3, as a steel cord (10), a main filament bundle in which metal filaments (hereinafter referred to as main filaments) (12) are arranged in a line without being twisted together. A flat cord having an n + 1 structure (where n = 2 to 6) obtained by wrapping (13) with one metal filament (hereinafter referred to as a wrapping filament) (14) is used.

  As the main filament (12), one having a diameter (filament diameter) d of 0.10 to 0.30 mm is used. When the diameter d is less than 0.10 mm, it is necessary to increase the number of the aligned filaments (13) when forming the main filament bundle (13) to satisfy the required strength, and the main filament bundle (13) is arranged in a row. It becomes difficult to make the shape lined up. On the other hand, when the diameter d exceeds 0.30 mm, the filament is likely to be fatigued by metal, and the fatigue property of the belt is deteriorated during running of the tire, so that the durability of the tire is lowered. This diameter d is more preferably 0.15 to 0.25 mm.

  The main filament bundle (13) is formed by arranging the plurality of main filaments (12) having the same diameter as described above in a horizontal row 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 0.60 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 2 to 6. If this number is one, the cord does not become flat, and the number of cords for maintaining the belt strength cannot be driven into the belt ply, so that the tire cannot be molded. On the contrary, if the number exceeds 6, it becomes difficult to form the main filament bundle (13) in a line. The number of main filaments (12) to be aligned is more preferably 3-6, and even more preferably 4-6.

  As the wrapping filament (14) wound around the main filament bundle (13), a straight steel filament which is not corrugated or the like is used. The diameter (filament diameter) d0 of the wrapping filament (14) is equal to or smaller than the diameter d of the main filament (12), and is not particularly limited, but is preferably 0.05 to 0.20 mm. . More preferably, a diameter smaller than the diameter d of the main filament (12) is used. The diameter d0 of the wrapping filament (14) is more preferably 0.10 to 0.15 mm.

  The steel cord (10) is formed by wrapping the wrapping filament (14) around the main filament bundle (13). The winding pitch p of the wrapping filament (14) is not particularly limited because it varies depending on the filament diameters d, d0, the number of main filaments (12), etc., but is preferably 2.0 to 30.0 mm, more preferably 3 0.0-5.0 mm.

  As shown in FIG. 3, the main filament (12) may be a straight metal filament that is not corrugated. Alternatively, although not shown, a corrugated metal filament can be used as the main filament. When corrugating, the main filament (12) is corrugated only in the major axis direction (B) of the steel cord, that is, in a plane along the major axis direction (B) and the longitudinal direction (L), Two-dimensional corrugation is preferred. In this case, a plurality of metal filaments molded in the longitudinal direction (B) 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. The wavelength of the main filament (12) may be configured to match the winding pitch p of the wrapping filament (14) so that the wrapping filament is wound around the corrugated recess.

  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 covering 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 the thickness of the belt ply can be reduced to suppress an increase in tire mass. Moreover, in the obtained belt ply, since the bending rigidity in the tire width direction is increased, the steering stability can be improved.

  In the present embodiment, the occupation ratio of the steel cord (10) in the width direction of each belt ply (7A) (7B) (that is, the ratio of the length occupied by the steel cord in the width dimension of the belt ply cross section. Is preferably 60 to 80%. By setting the code occupancy ratio to 60 to 80%, it is possible to improve steering stability and ride comfort without impairing durability. When the cord occupancy is 60% or more, the strength necessary for the belt can be sufficiently obtained. Moreover, by being 80% or less, it is possible to prevent the distance between the steel cords from becoming excessively narrow, to suppress separation / peeling between the steel cords, called cord separation, and to improve the durability of the tire. . Here, the code occupancy (%) uses a value calculated by the following equation in a so-called topping reaction in which the cords are arranged in a predetermined number of driven lines and covered with rubber. Cord occupancy (%) = Cord long diameter (mm) x Number of cords driven (pieces / 25.4mm) x 100 / 25.4 (mm).

  The number of steel cords to be driven is not particularly limited, and is preferably, for example, 10 to 40 pieces / 25.4 mm, more preferably 13 to 30 pieces / 25.4 mm, and further preferably 15 to 25 pieces. /25.4 mm.

  The belt plies (7A) and (7B) according to the present embodiment are formed by coating a rubber composition having a predetermined viscosity on a cord array in which a plurality of the steel cords are arranged in parallel with a predetermined number of driven cords. It is. The rubber composition as the covering rubber is coated on both sides of the cord array, thereby forming a topping reaction. The temperature of the rubber composition when calendering to the code array is not particularly limited, but is usually 90 to 100 ° C. Although the rubber thickness to coat | cover is not specifically limited, It is preferable that it is 0.5-2.0 mm with a topping cage, More preferably, it is 0.6-1.2 mm.

  As the rubber composition used as the covering rubber, a rubber composition having a viscosity of 6000 to 8000 Pa · s when measured under conditions of a measurement temperature of 100 ° C. and a shear rate of 1000 (1 / second) is used. By covering with such a low viscosity rubber composition, rubber can be surely infiltrated between the steel cords, and deterioration of tire durability due to contact between the steel cords can be prevented. That is, in the present embodiment, since the flat steel cord is used as described above, it is difficult for rubber to enter between the cords. However, by setting the viscosity of the covering rubber as described above, the rubber between the cords is set. Penetration property can be secured. When the viscosity of the rubber composition is less than 6000 Pa · s, when winding the topping, problems such as adhesion between the toppings and between the inserts sandwiched between the toppings are likely to occur, and productivity is increased. descend. Moreover, when the viscosity of the rubber composition exceeds 8000 Pa · s, it becomes difficult for the rubber to penetrate between the steel cords, so that problems such as end disturbance are likely to occur. The durability of the tire decreases due to contact. The viscosity of the rubber composition is more preferably 6500 to 7500 Pa · s.

  The composition of the rubber composition is not particularly limited. For example, the rubber component includes natural rubber (NR), isoprene rubber (ie, synthetic natural rubber. IR), styrene butadiene rubber (SBR), and butadiene rubber (BR). At least one diene rubber selected from can be used. Preferably, in 100 parts by mass of the rubber component, the content of natural rubber is 80 to 95 parts by mass (more preferably 82 to 90 parts by mass), and the content of isoprene rubber is 5 to 20 parts by mass (more preferably 10 to 10 parts by mass). 18 parts by mass). Thus, by blending a small amount of isoprene rubber mainly composed of natural rubber and having the same basic skeleton, viscosity can be lowered without changing other characteristics.

  Examples of components added to the rubber component include fillers such as carbon black, anti-aging agents, zinc white, cobalt stearate, softening agents such as oil, adhesive resins, vulcanizing agents, and vulcanization accelerators. The various components mix | blended with a rubber composition are mentioned. At that time, the viscosity of the rubber composition is set within the above range by changing the blending amount and type of a softener such as oil and a filler such as carbon black, in addition to the difference in the rubber component. can do. Such a rubber composition can be prepared by kneading using a usual Banbury mixer, a mixer such as a roll or a kneader.

  The topping fabric produced as described above is used as a member constituting a belt ply to produce an unvulcanized tire (green tire), and then the unvulcanized tire is set in a mold and vulcanized. By doing so, a product tire can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, 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. This is a conventional code having 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. In these aligned n + 1-structure steel cords, the main filament is corrugated and the wave height = 0.06 mm and the wavelength = 4.5 mm. The winding pitch of the wrapping filament was p = 4.5 mm.

  Using the obtained steel cord as a belt cord, a radial tire having a tire size of 195 / 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 (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. For the belt ply, the steel cord is arranged with the number of drivings shown in Table 1 so that the major axis direction is parallel to the belt surface. It produced by doing. The composition of the coating rubber is as shown in Table 2 below. The mass of the topping was measured, and the belt mass per tire was calculated. In Table 1, the value of Comparative Example 1 was taken as an index of 100 (the smaller the index, the lighter the weight).

  The carcass ply was 1 ply with a polyester cord of 1670 dtex / 2 and a driving number of 22 wires / 25 mm. The belt reinforcing layer was made of nylon 66 cord 940 dtex / 2, and the number of driven-in wires was 28/25 mm.

  For each of the obtained tires, the tire mass was measured, and the tire high speed durability, belt durability, actual vehicle handling stability, and road surface performance were evaluated. The tire mass is an index with the value of Comparative Example 1 being 100 (the smaller the index, the lighter the weight), and is shown in Table 1.

  Each physical property in Table 1 and each measurement / evaluation method for tire performance are 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.

-Cord shape: when lapped with a wrapping filament, the ones in which the aligned main filaments are arranged in a row are marked with ◯ (good), and the broken ones are marked with x (bad).

-Coated rubber viscosity: Measured using a capillograph (model: 1D) manufactured by Toyo Seiki Seisakusho. Test temperature: 100 ° C., capillary diameter: 1.5 mm, capillary length: 1.52 mm, shear rate S / R: 1000 s ⁻¹ .

Tire high speed durability: It was made using a drum tester having a diameter of 1700 mm made of steel with a smooth surface in accordance with FMVSS109 (UTQG). The tire internal pressure was 220 kPa, and the load was 88% of the maximum load specified by JATMA. After running for 60 minutes at 80 km / h, the vehicle was allowed to cool, the air pressure was adjusted again, and then the main run was carried out. The main run was started at 120 km / h, and the speed was increased stepwise by 8 km / h every 30 minutes and run until a failure occurred. The distance traveled until the failure occurred was displayed as an index with the tire of Comparative Example 1 as 100. The higher the number, the better the high-speed durability performance.

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 220 kPa. The test speed was 420 rpm, and the test was conducted until an abnormality occurred or 720 hours of running. After the test, the tire was disassembled, the length of edge separation at the belt end was measured, and the presence or absence of cord breakage was checked. The determination of edge separation was made as follows: None: 0 mm, Fine: 1-2 mm, Small: 3-5 mm, Medium: 6-9 mm, Large: 10 mm or more.

-Actual vehicle handling stability: A test tire incorporated in a standard rim with an internal pressure of 200 kPa was mounted on a test vehicle with a displacement of 2500 cc, and three trained test drivers drove the test course and performed sensory evaluation. The scoring was based on a 10-point evaluation, and relative comparison was performed with the tire of Comparative Example 1 as 6 points, and the average score of 3 people was displayed as an index with the tire of Comparative Example 1 as 100. The larger the number, the better the steering stability.

-Road surface performance: A test tire is mounted on the front wheel of the test vehicle under the same conditions as the actual vehicle handling stability, and the tire is passed over the test road (the height of the road is 20 mm) imitating a road on a general road. The performance was sensory evaluated. The items that could easily get over the kite were marked with ○, those that were slightly difficult to get over were marked with △, and those that were very difficult to get over were marked with ×.

-Degree of close contact between members: When making a topping roll and winding it on a roll, it is wound with a cloth-like insert material sandwiched between the topping rolls, and then there is adhesion to the insert material when the topping roll is pulled out from the roll. It was confirmed. Those that are in close contact are indicated as “Yes”, and those that are not in close contact are indicated as “No”.

  In addition, the actual vehicle test was not carried out for the belt durability test that showed a remarkably bad result (belt edge separation was “large” or higher, cord breakage “present”).

  The results are shown in Table 1. As compared with the comparative example 1 using the steel cord having the conventional multi-layer twist structure, the weight reduction of the tire was achieved in the examples 1 to 4 using the steel cord having the aligned n + 1 structure. In addition, the handling stability was remarkably improved. In addition, since the viscosity of the belt ply covering rubber is within the specified range, the rubber is surely infiltrated between the steel cords, and it is possible to prevent a decrease in durability due to contact between the cords. Durability equal to or better than that was secured.

  On the other hand, in Comparative Example 2 in which the diameter of the main filament constituting the steel cord is too small, the cord occupancy greatly exceeds 100% in order to make the belt strength equivalent to that in Comparative Example 1, and the tire Could not be molded. In Comparative Example 3 in which the diameter of the main filament is as large as 0.35 mm which is not specified, although there is a weight reduction effect compared to Comparative Example 1, the durability of the tire is reduced due to the breakage of the cord due to the decrease in fatigue resistance. .

  In Comparative Example 4 in which the number of main filaments is one, although there is a weight reduction effect, belt edge separation and belt folding frequently occur due to an increase in the number of cords for maintaining durability, and durability is lowered. In Comparative Example 5 in which the number of main filaments is seven, although there is a weight reduction effect compared to Comparative Example 1, the main filament bundle cannot be formed in a line, the steering stability is lowered, and the overpass performance is improved. Was also inferior.

  In Comparative Example 6 in which the viscosity of the belt ply covering rubber was 11000 Pa · s exceeding the specified value, it was difficult for rubber to enter between the steel cords, and the durability of the tire was poor. In Comparative Example 7 in which the viscosity of the coating rubber was 5000 Pa · s less than the specified value, the tire could not be molded due to excessive adhesion to the insert material during tire manufacture.

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

7 ... Belt, 7A, 7B ... Belt ply, 10 ... Steel cord, 12 ... Main filament, 13 ... Main filament bundle, 14 ... Wrapping filament, B ... Long diameter direction of steel cord, d ... Diameter of main filament

Claims (2)

A main filament made of metal filaments having a diameter of 0.10 to 0.30 mm is arranged in a line without twisting a plurality of strands to form a main filament bundle, and one metal filament is wrapped around the main filament bundle as a wrapping filament. A belt ply in which a flat steel cord of n + 1 structure (where n = 2 to 6) is arranged so that the major axis direction thereof is parallel to the belt surface,
The belt ply is formed by coating a plurality of the steel cords in parallel with a rubber composition having a viscosity of 6000 to 8000 Pa · s measured at a temperature of 100 ° C. and a shear rate of 1000 (1 / second). A pneumatic tire characterized by being made of   The pneumatic tire according to claim 1, comprising at least two belt plies, wherein the occupation ratio of the steel cord in the width direction of each belt ply is 60 to 80%.

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