JP6873694B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

Pneumatic tires generally include a belt in which a plurality of belt plies are crossed and laminated between the outer surface of the carcass ply and the tread rubber, and the belt ply is a steel cord having excellent tensile strength and tensile elasticity. Is used.

Further, it is known that a flat steel cord formed by arranging a plurality of steel filaments in parallel and wrapping one wrapping filament around the steel filaments is used for the belt ply for the purpose of reducing the weight of the tire. As an example of a pneumatic tire using such a flat steel cord, the inventions according to Patent Documents 1 and 2 can be mentioned as an example.

Japanese Unexamined Patent Publication No. 8-120578 JP 2015-227083 Japanese Unexamined Patent Publication No. 10-292275

If a flat steel cord is used, the amount of rubber used in the belt layer can be reduced, which makes 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 points, it is an object of the present invention to provide a pneumatic tire that can be reduced in weight without impairing the durability of the belt.

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

The pneumatic tire according to the present invention is a pneumatic tire having a carcass and a belt layer arranged on the outer periphery of the crown portion of the carcass, and the belt layer is formed by coating a steel cord with rubber. For the steel cord, 4 to 6 steel filaments of the same diameter are arranged in parallel so as to form a single layer without twisting to form a main filament bundle, and one steel filament having a smaller diameter and straight than the steel filament is formed. It has an n + 1 structure (n = 4 to 6) wound around the main filament bundle as a wrapping filament, and the ratio (Sr / Sc) of the rubber cross-sectional area Sr to the steel cord cross-sectional area Sc in the belt layer is 4.3 to 5. It is assumed to be 0.0.

In the above 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 large. It can be 0.05 to 0.40.

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

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

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

A half sectional view of a pneumatic tire according to an embodiment of the present invention. The figure which showed a part of the cross section of the belt layer which concerns on one Embodiment of this invention schematically. The schematic perspective view which shows the structure of the steel cord which concerns on one Embodiment of this invention. Partial sectional view of the steel cord which concerns on one Embodiment of this invention.

Hereinafter, matters related to the practice 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 a passenger car, and is a pair of left and right bead portions 1 and sidewall portions 2 and radial outer ends of the left and right sidewall portions 2. It is configured to include a tread portion 3 provided between both sidewall portions so as to connect the portions, and a carcass 4 extending across the pair of bead portions is provided.

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

A belt 6 is arranged between the carcass 4 and the tread rubber portion 7 on the outer peripheral side (that is, the outer side in the tire radial direction) of the carcass 4 in the tread portion 3. The belt 6 is provided so as to overlap the outer periphery of the crown portion of the carcass 4, and may be composed of one or a plurality of belt plies, usually at least two belt plies. In the present embodiment, the belt ply is on the carcass side. It is composed of two belt plies, a first belt ply 6A and a second belt ply 6B on the tread rubber portion side. The belt plies 6A and 6B are formed by inclining the steel cords 10 at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction and arranging the steel cords 10 at predetermined intervals in the tire width direction. As shown in FIG. 2, the steel cord 10 is coated with the coated rubber 11. The steel cord 10 is arranged 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, the outer side in the radial direction of the tire). The belt reinforcing layer 8 is a cap ply that covers the belt 6 with its full width, and is composed of organic fiber cords arranged substantially parallel to the tire circumferential direction. That is, the belt reinforcing layer 8 is formed by arranging the 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 it in a spiral shape.

As shown in FIG. 2, the belt ply 6A is formed by arranging the steel cord 10 so that its major axis direction B is parallel to the belt surface (that is, the outer peripheral surface of the belt). That is, in the belt ply, the steel cord 10 is embedded in the coating rubber 11 at predetermined intervals so that the minor axis direction A coincides with the thickness direction K of the belt ply. Therefore, the steel cord 10 is arranged so that its major axis direction B is parallel to the tread surface. With such a configuration, it is easy to process the steel cord 10 when it is coated with rubber, and the thickness of the belt ply can be reduced to suppress an increase in tire weight. Further, in the obtained belt ply, the bending rigidity in the tire width direction is increased, so that the steering stability performance can be improved, and the bending rigidity in the tire radial direction is decreased, so that the envelope property is enhanced and the ground contact area is increased. be able to.

As shown in FIGS. 2 and 3, each steel cord 10 for the belt ply, which forms a main part of the pneumatic tire according to the present embodiment, is composed of only steel filaments and has 4 to 6 main filaments having the same diameter. It is composed of 12 and one wrapping filament 14 that bundles the wrapping filaments 14. The diameter d of the main filament is preferably 0.15 to 0.30 mm, more preferably 0.15 to 0.25 mm. When the diameter d of the main filament is 0.15 mm or more, the rigidity of the steel cord 10 is lowered and the riding comfort is easily improved while maintaining the steering stability when the tire is mounted. When the diameter d is 0.30 mm or less, it does not become too rigid and the increase in surface strain due to compression deformation can be suppressed, so that the fatigue resistance of the belt ply can be maintained and the durability of the tire can be easily maintained. ..

These main filaments 12 are arranged in parallel so as to form one layer along one plane. That is, they are aligned so as to form a line in a cross section perpendicular to the length direction of the steel cord 10. Therefore, each steel cord 10 is flat and has a major axis D1 and a minor axis D2 as shown in FIG. The values of the major axis D1 and the minor axis D2 are not particularly limited, but for example, the major axis D1 can be 1.00 to 1.80 mm and the minor axis D2 can be 0.30 to 0.60 mm, and the major axis / minor axis can be set. The ratio of is, for example, 1.5 to 5 times, preferably 2 to 4 times.

The number of main filaments 12 arranged in parallel in one cord is 4 to 6 from the viewpoint of increasing the flatness of the cord and reducing the thickness of the belt layer, etc., while maintaining the shape as a bundle stably. It is preferably a book, more preferably 4 to 5 books. That is, when the number of main filaments 12 exceeds 6, it becomes difficult to arrange them in parallel so as to form a line, and the shape as a bundle tends to be irregular. The main filament 12 does not necessarily have to have a circular cross section. For example, the steel cord 10 can be further flattened by using a main filament 12 having an elliptical cross section.

On the other hand, the wrapping filament 14 is not particularly limited, but is not wavy and is preferably a so-called “straight” wrapping filament 14. When it is straight, it is easy to wind it, and it is easy to make the binding force of winding uniformly high. It should be noted that the binding force of the wrapping filament 14 makes it possible to give the aligned main filament 12 a sense of unity as a steel cord 10, which is highly resistant to in-plane deformation of the belt material when changing routes during traveling or turning a curve. Rigidity 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.

The flexural rigidity of the wrapping filament 14 is smaller than that of the main filament 12, and can be, for example, 10 to 40% of the main filament 12. Further, the diameter d0 of the wrapping filament is smaller than the diameter d of the main filament, and can be, for example, 0.4 to 0.7 times the diameter d of the main filament. When the diameter d0 of the wrapping filament is within this range, it is easy to secure the binding force while suppressing the increase in the diameter of the steel cord 10.

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 cross-sectional area Sr to the cord cross-sectional area Sc satisfies 4.3 to 5.0. Can be set up. When this ratio is 4.3 or more, the adhesive force between the belt plies can be sufficiently secured, and the decrease in tire durability due to the narrowing of the distance between the cords can be suppressed. Further, when this ratio is 5.0 or less, the effect of reducing the weight of the tire is excellent.

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 coated 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. Further, the above ratio (Sr / Sc) can be obtained by dividing the rubber cross-sectional area Sr by the code cross-sectional area Sc. For example, the cord cross-sectional area per 1 inch of width of the belt 6 is calculated from the number of steel cords 10 driven and the cord diameter, and the width is calculated 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 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 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 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. Further, even when the steel cord 10 is in the pressed mode described later, the cord cross-sectional area does not change before and after pressing. Therefore, by calculating the cord cross-sectional area before pressing, the cord cross-sectional area after pressing is calculated. Can be sought.

As a more preferable embodiment of the above embodiment, as shown in FIG. 4, a flat steel cord formed by wrapping the main filament bundle 13 around the main filament bundle 13 with the wrapping filament 14 is pressed in the minor axis direction A to deform the wrapping filament 14. You can use the one that has been made. By pressing, the wrapping filament 14 is deformed along the shape of the space and a part of the wrapping filament 14 invades at least a part of the space formed between the adjacent main filaments 12, that is, at least a part of the space is wrapped. It is filled with at least a portion of the filament 14. Therefore, the binding force of the main filament 12 by the wrapping filament 14 can be increased. Further, by applying a relatively large plastic deformation to the wrapping filament 14, the rotational torque and the repulsive force inherent in the wrapping filament 14 become small. Therefore, it is easy to maintain the shape in which the main filament bundles 13 are lined up in a row, and it is easy to exert an excellent effect by the flat cord.

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

The diameter of the wrapping filament 14 before pressing, that is, the filament diameter d0, is preferably smaller than the diameter d 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 the 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 at the time of pressing can be further reduced.

The above 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 both the upper and lower sides by the rolling roll. Since the wrapping filament 14 is located on the 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 the 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 changed. Along 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 surface.

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

In one 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 the two is Cc-Cw of 0.05 to 0. It is preferably 40% by mass, more preferably 0.10 to 0.30% by 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 broken by pressing is reduced. can do.

The method of forming the belt 6 on the crown portion of the carcass 4 by using the steel cord 10 is not particularly limited. For example, a plurality of steel cords aligned and covered with rubber may be spirally wound around the belt layer of a raw tire, or a wide rubberized sheet with steel cords 10 aligned may be wound on the crown portion. You may wind it around. In this way, a raw tire (green tire) is produced in a state where the belt 6 is wound around the outer peripheral side of the crown portion of the carcass 4, and the obtained raw tire is vulcanized and molded to obtain a pneumatic tire. ..

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

Hereinafter, examples of the present invention will be shown, but the present invention is not limited to these examples.

A steel cord having the structure shown in Table 1 below was prepared. The steel cord of Comparative Example 1 has a 2 + 1 multi-layer twisted structure (2 + 1 × 0.27) in which one metal filament having the same diameter is twisted around a core made of two aligned metal filaments. Is a traditional code with. For all other steel cords, a bundle of main filaments arranged in a row without twisting a plurality of main filaments is wrapped with one straight wrapping filament (diameter d0 = 0.15 mm). It is a steel cord with an n + 1 structure. Further, the winding pitch of the wrapping filament (p in FIG. 3) was set to 5.0 mm, and the steel cord was pressed using a rolling roll so that Da / Db had the values shown in Table 1.

The measuring method for the filament and the steel cord is as follows.

-Carbon content of filament: Infrared absorption method based on JIS G1211 (Annex 3: Total carbon quantification method-High frequency induction heating furnace combustion). More specifically, steel was melted by high-frequency heating using a device called "CS-400" manufactured by LECO, and quantitative analysis was performed by an infrared absorption method.

-Filament diameter and cord diameter: The diameters of the steel cord and filament were measured with a predetermined thickness gauge in accordance with JIS G3510.

Further, using the obtained steel cord as a belt cord, a radial tire having a tire size of 175 / 65R15 was vulcanized and molded according to a conventional method. For each tire, all the configurations other than the belt were 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 produced by arranging the steel cords in the number of driving lines shown in Table 1 so that the major axis direction was parallel to the outer peripheral surface of the belt, and then using a calendar device to make the toppings.

The carcass ply was 1 ply with a polyethylene terephthalate cord of 1100 dtex / 2 and a number of hammers 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 the belt durability were evaluated. The evaluation method for each evaluation item is shown below.

-Tire weight: The weight of each tire is shown as an index with Comparative Example 1 as 100.

-Sr / Sc: The number of steel cords to be driven is E (line / inch), the number of main filaments is n, the main filament diameter (mm) is d, the wrapping filament diameter (mm) is d0, and the belt thickness (mm) is set. As t, the code cross-sectional area Sc per width 1 inch of the belt and the rubber cross-sectional area Sr per width 1 inch were calculated from the following equations, and the ratio Sr / Sc of the two was calculated.

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

-Belt durability: The tire was attached to the specified rim, and the load was applied by pressing the tire against the drum at an internal pressure of 110 kPa to a degree of deflection of 62% at the maximum load specified by JATTA. The test speed was set to 420 rpm, and the test was carried out until an abnormality occurred or the vehicle ran for 720 hours. After the test was completed, 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 broken cord was confirmed. The belt separation was judged according to the following criteria.

None: 0 mm
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 4.3, 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 could not be obtained as compared with Comparative Example 1.

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

T ... Tire 1 ... Bead part 2 ... Sidewall part 3 ... Tread part 4 ... Carcass 5 ... Bead core 6 ... Belt 6A ... 1st belt ply 6B ... 2nd belt ply 7 ... Tread rubber part 8 ... Belt reinforcement layer 10 ... Steel cord 11 ... Coating rubber 12 ... Main filament 13 ... Main filament bundle 14 ... Wrapping filament A ... Steel cord minor axis direction B ... Steel cord major axis direction D1 ... Steel cord major axis D2 ... Minor diameter of steel cord Da ... Minor diameter of steel cord pressed in the minor axis direction K ... Belt ply thickness direction d ... Main filament diameter d0 ... Wrapping filament diameter t ... Belt thickness

Claims (4)

A pneumatic tire having a carcass and a belt layer arranged on the outer circumference of the crown portion of the carcass.
The belt layer is formed by coating the steel cord with rubber.
In the steel cord, 4 to 6 steel filaments having the same diameter are arranged in parallel so as to form a single layer without twisting to form a main filament bundle, and one steel filament having a smaller diameter and straight than the steel filament is formed. Is an n + 1 structure (n = 4 to 6) formed by winding around the main filament bundle as a wrapping filament.
A pneumatic tire, wherein the ratio (Sr / Sc) of the rubber cross-sectional area Sr to the steel cord cross-sectional area Sc in the belt layer is 4.3 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 tire is 0.40. The steel cord has the wrapping filament that is pressed and deformed in the minor axis direction, and the ratio (Da / Db) of the minor axis Da of the steel cord after pressing to the minor axis Db of the steel cord before pressing is 0. The pneumatic tire according to claim 1 or 2, wherein the tire is .80 or less. The pneumatic tire according to claim 3, wherein the diameter of the wrapping filament before pressing is 0.10 to 0.15 mm.

Images