pneumatic tires

Abstract

To provide a pneumatic tire that can reduce air resistance without increasing labor hours in manufacturing.SOLUTION: The pneumatic tire is provided with: a pair of beads 10 having bead members 16 including a bead core 11 and a bead filler 12; a pair of side walls 20 extending from the pair of beads 10 respectively to outside in a tire radial direction; a tread 30 arranged between the pair of side walls 20; and a carcass ply 50 hung across the pair of beads 10. In a cross section in a tire width direction, in a state where tensile strength of the carcass ply 50 is 250 N or more and 420 N or less and the bead member is attached to a specified rim and specified inner pressure is applied to the member, a length in the tire radial direction of the bead member 16 is 20% or more and 25% or less of a height of the cross section of the tire.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Generally, a pneumatic tire has a structure in which a carcass ply is stretched between a pair of beads arranged at both inner circumferential ends in the tire width direction and covered with tread rubber, sidewall rubber, and the like. Conventionally, there has been known a pneumatic tire in which a plurality of fin-shaped protrusions are arranged along the tire circumferential direction on the side surface of a tire composed of sidewall rubber to reduce air resistance (see Patent Documents 1, 2, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Normally, pneumatic tires are molded using a mold. Therefore, in order to form fin-shaped protrusions on the side surface of a tire having a conventional shape, a new mold is required, but in that case, there is a risk of complicating the process and increasing the manufacturing cost.

[0005] Therefore, an object of the present invention is to provide a pneumatic tire in which air resistance can be reduced without increasing the manufacturing effort.

Means for Solving the Problems

[0006] The pneumatic tire of the present invention comprises a pair of beads having bead members including a bead core and a bead filler, a pair of sidewalls extending radially outward from each of the pair of beads, a tread disposed between the pair of sidewalls, and a carcass ply spanning between the pair of beads, wherein the tensile strength of the carcass ply is 250N or more and 420N or less, and in the tire widthwise cross section when mounted on a specified rim and subjected to a specified internal pressure, the radial length of the bead members is 20% or more and 25% or less of the tire cross section height. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pneumatic tire that reduces air resistance without increasing manufacturing effort. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows a half-cross section in the tire width direction of a pneumatic tire according to the embodiment. [Figure 2] This is an enlarged view of part II of Figure 1. [Modes for carrying out the invention]

[0009] Figure 1 shows a half-section in the tire width direction of tire 1, which is a pneumatic tire according to the embodiment. Figure 2 is an enlarged view of the part indicated by II in Figure 1, and is a cross-sectional view mainly showing the shoulder 40, which will be described later. The cross-sectional view in Figure 1 is a cross-sectional view in the tire width direction (tire meridian cross-section) in an unloaded state with tire 1 mounted on a specified rim (not shown) and filled with a specified internal pressure. The specified rim refers to a standard rim defined by JATMA corresponding to the tire size. The specified internal pressure is, for example, 180 kPa if the tire is for a passenger car.

[0010] The tire 1 according to this embodiment is, for example, a pneumatic tire for a passenger car. In addition to passenger cars, the tire 1 according to this embodiment can be used for various other vehicles such as light trucks, trucks, and buses.

[0011] The basic structure of tire 1 is symmetrical in cross-section along the tire width. Figure 1 shows a half-cross-section of the right half of tire 1, and the left half, which is not shown, has the same structure. In Figure 1, the symbol S1 represents the tire equatorial plane. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis (tire meridian) and located at the center in the tire width direction.

[0012] Here, the tire width direction is the direction parallel to the tire rotation axis, which is the left-right direction in Figure 1. In Figure 1, it is shown as the tire width direction X. The inside of the tire width direction is the direction approaching the tire equatorial plane S1, which is the left side of the paper in Figure 1. The outside of the tire width direction is the direction away from the tire equatorial plane S1, which is the right side of the paper in Figure 1.

[0013] Furthermore, the tire radial direction is the direction perpendicular to the tire rotation axis, and corresponds to the vertical direction in Figure 1. In Figure 1, it is shown as the tire radial direction Y. The outer side of the tire radial direction is the direction away from the tire rotation axis, and corresponds to the upper side of the paper in Figure 1. The inner side of the tire radial direction is the direction closer to the tire rotation axis, and corresponds to the lower side of the paper in Figure 1.

[0014] As shown in Figure 1, the tire 1 comprises a pair of beads 10, a pair of sidewalls 20 extending radially outward from each of the bead 10, a tread 30 positioned between the pair of sidewalls 20, a pair of shoulders 40 positioned between each of the sidewalls 20 and the tread 30, a carcass ply 50 positioned across the pair of beads 10, and an inner liner 60 positioned on the inner side of the carcass ply 50.

[0015] A pair of beads 10 are positioned on both sides in the tire width direction and at the inner ends in the tire radial direction. Each bead 10 includes a bead member 16, a chaper 13, a rim strip rubber 14, and a rim protector 15.

[0016] The bead member 16 includes a bead core 11 and a bead filler 12 extending radially outward from the bead core 11. The bead core 11 is an annular member in which a rubber-coated metal bead wire is wound multiple times in the circumferential direction of the tire. The bead core 11 is a member that serves to fix the air-filled tire 1 to the rim. The bead filler 12 has a tapered shape in which its thickness decreases as it extends from the inside to the outside in the radial direction of the tire. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of rubber that is harder than the surrounding rubber member, for example. The bead member 16 is formed by joining the radially outer surface of the bead core 11 to the radially inner surface of the bead filler 12 using, for example, an adhesive.

[0017] The chaff 13 further surrounds the outside of the carcass ply 50, which is provided surrounding the bead core 11 and bead filler 12. The rim strip rubber 14 is positioned on the tire widthwise outer side of the chaff 13 and carcass ply 50. The chaff 13 and rim strip rubber 14 are in contact with the inner surface of the rim on which the tire 1 is mounted.

[0018] The sidewall 20 includes sidewall rubber 21 positioned on the outer side in the tire width direction of the carcass ply 50. The sidewall rubber 21 constitutes the outer side surface of the tire 1 in the tire circumferential direction. The inner end 21c of the sidewall rubber 21 in the tire radial direction covers the outer end 14b of the rim strip rubber 14 in the tire radial direction. The sidewall rubber 21 is the part that flexes the most when the tire 1 performs its cushioning action, and is usually made of a flexible rubber with fatigue resistance.

[0019] The inner end of the sidewall rubber 21 in the tire radial direction includes a top 21a along the tire circumferential direction. The top 21a and the outer surface of the rim strip rubber 14 described above constitute a rim protector 15 that protects the rim from damage. This rim protector 15 is continuously annular in the tire circumferential direction.

[0020] The tread 30 includes an endless belt 31 and a cap ply 35, and tread rubber 36. The belt 31 is disposed on the outer side of the inner liner 60 in the tire radial direction. The cap ply 35 is disposed on the outer side of the belt 31 in the tire radial direction. The tread rubber 36 is disposed on the outer side of the cap ply 35 in the tire radial direction.

[0021] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 disposed on the outer side of the inner liner 60 in the tire radial direction and an outer belt 33 disposed on the outer side of the inner belt 32 in the tire radial direction. Both the inner belt 32 and the outer belt 33 have a structure in which a plurality of cords such as steel cords are covered with rubber.

[0022] The inner belt 32 is wider than the outer belt 33. Therefore, the outer end 32a of the inner belt 32 in the tire width direction is located outside the outer end 33a of the outer belt 33 in the tire width direction. By providing the belt 31, the rigidity of the tire 1 is ensured, and the grounding performance of the tread 30 with respect to the road surface is improved. Note that the belt 31 is not limited to a two-layer structure and may have a single-layer or three-layer or more structure.

[0023] The cap ply 35 is a member that reinforces the tread 30 together with the belt 31. The cap ply 35 has a structure in which a plurality of organic fiber cords having insulation properties such as polyamide fibers are covered with rubber, for example. The outer end portion 35a of the cap ply 35 in the tire width direction is folded from the outer side to the inner side in the tire diameter direction and is double-layered. The outer end 35b of the cap ply 35 in the tire width direction is located outside the outer end 32a of the inner belt 32 in the tire width direction. The cap ply 35 is a wide member that covers the entire belt 31 with a single layer.

[0024] The cap ply 35 of the embodiment is a single layer, but it may have a structure of two or more layers. By providing the cap ply 35, it is possible to improve durability and reduce road noise during driving.

[0025] The tread rubber 36 is disposed on the outer side of the cap ply 35 in the tire diameter direction. The tread rubber 36 is a member that constitutes the tread surface 36a, which is the outer surface of the tread 30 that contacts the road surface during driving. A tread pattern 37 is provided on the tread surface 36a of the tread rubber 36.

[0026] The tread pattern 37 includes a plurality of main grooves 38 and a plurality of slits 39. The plurality of main grooves 38 of the embodiment include two first main grooves 38A disposed on the inner side in the tire width direction and two second main grooves 38B disposed on the outer side in the tire width direction with respect to these first main grooves 38A. Both the first main groove 38A and the second main groove 38B are formed in an annular shape along the tire circumferential direction. The slit 39 is a narrow groove that extends substantially along the tire width direction and is disposed on the outer side in the tire width direction with respect to the second main groove 38B. The slit 39 is formed from the outer end portion of the tread surface 36a of the tread 30 in the tire width direction to the outer surface of the shoulder 40 described later.

[0027] The outer end portion 36b of the tread rubber 36 in the tire width direction extends radially inward in the tire diameter direction beyond the outer end 35b of the cap ply 35 in the tire width direction and covers the outer end portion 21b of the sidewall rubber 21 in the tire diameter direction.

[0028] The shoulder 40 is located in the region where the sidewall 20 transitions to the tread 30. The shoulder 40 includes shoulder rubber 41. The shoulder rubber 41 covers a portion of the outer surface of the radially outer end 21b of the sidewall rubber 21 and the outer surface of the widthwise outer end 36b of the tread rubber 36.

[0029] The carcass ply 50 constitutes the ply that forms the framework of the tire 1. The carcass ply 50 is embedded in the tire 1 in such a manner that it passes between a pair of beads 10 and through the inner side of the tire cavity of a pair of sidewalls 20 and tread 30.

[0030] The carcass ply 50 includes multiple ply cords (not shown) that form the framework of the tire 1. These multiple ply cords extend, for example, in a plane along the tire width direction and are arranged in a line along the tire circumferential direction. These ply cords are made of insulating organic fiber cords such as polyester or polyamide. The multiple ply cords are covered with rubber to form the carcass ply 50.

[0031] The carcass ply 50 has a ply body portion 51, a ply folded portion 52, and a bent portion 53. The ply body portion 51 is the portion that extends from the inner side in the tire width direction of one bead core 11, through one sidewall 20, the tread 30, and the other sidewall 20, to the inner side in the tire width direction of the other bead core 11. The ply folded portion 52 is the portion that extends radially outward on the outer side in the tire width direction of the bead filler 12 by being folded back around the bead core 11 from the inner end in the tire radial direction of the ply body portion 51. The bent portion 53 is the portion that bends in a U-shape around the bead core 11 from the ply body portion 51 and connects to the ply folded portion 52. The ply body portion 51 and the ply folded portion 52 are continuous via the bent portion 53.

[0032] The ply body portion 51 is positioned on the inner side in the tire radial direction and on the inner side in the tire width direction of the bead core 11 and bead filler 12. The ply fold portion 52 is positioned on the outer side in the tire width direction of the bead core 11 and bead filler 12. The bent portion 53 includes the innermost part in the tire radial direction of the carcass ply 50.

[0033] The carcass ply 50 of this embodiment has a two-layer structure in which a first carcass ply 55 and a second carcass ply 56 are stacked on top of each other. In the ply body portion 51, the first carcass ply 55 is positioned on the inner side of the tire cavity of the second carcass ply 56.

[0034] In the ply fold-over section 52, the first carcass ply 55 is positioned on the outside in the tire width direction of the second carcass ply 56. The first carcass ply 55 of the ply fold-over section 52 extends from the bend 53 to near the maximum tire width position H on the outer surface of the sidewall 20. That is, the folded end 55a of the first carcass ply 55 is located near the maximum tire width position H. The second carcass ply 56 of the ply fold-over section 52 extends from the bend 53 to partway along the bead filler 12. That is, the folded end 56a of the second carcass ply 56 is located on the outside in the tire width direction of the bead filler 12.

[0035] Bead Filler 12 Tire width On the outer side in the direction of rotation, a side reinforcement layer 70, which is a reinforcing layer made of steel material, is positioned. This side reinforcement layer 70 is sandwiched between the bead filler 12 and the ply folded portion 52 of the carcass ply 50, and further extends outward from the bead filler 12 in the tire radial direction. The portion of the side reinforcement layer 70 that extends outward from the bead filler 12 in the tire radial direction is sandwiched between the second carcass ply 56 of the ply body 51 and the first carcass ply 55 of the ply folded portion 52. The outer end 55b of the first carcass ply 55 of the ply folded portion 52 in the tire radial direction is overlapped with the second carcass ply 56 of the ply body 51.

[0036] Although the carcass ply 50 in this embodiment has a two-layer structure, the carcass ply 50 may have one layer or three or more layers. It is preferable that the carcass ply 50 be composed of two or more layers, as this sufficiently suppresses local deformation of the tire 1 near the rim mounting area.

[0037] The bead 10's chafing 13, as described above, is provided to surround the inner end of the carcass ply 50 in the tire radial direction, including the bent portion 53. The rim strip rubber 14 is positioned on the outer side in the tire width direction of the ply fold portion 52 and chafing 13 of the carcass ply 50. The outer end 14b of the rim strip rubber 14 in the tire radial direction is covered by the inner end 21c of the sidewall rubber 21 in the tire radial direction.

[0038] The inner liner 60 covers the inner surface of the tire between the pair of beads 10. The inner liner 60 covers the inner surface of the ply body 51 in the area extending from the tread 30 to the sidewall 20. The inner liner 60 also covers the inner surface of the ply body 51 and the chamfer 13 in the area extending from the sidewall 20 to the bead 10. Therefore, the inner liner 60 constitutes the inner wall surface of the tire 1. The inner liner 60 is made of air-permeable rubber and prevents air inside the tire cavity from leaking to the outside.

[0039] Here, the rubber used for the bead filler 12 is one that is at least harder than the sidewall rubber 21 and the inner liner 60. The hardness of the rubber is measured using a Type A durometer in a 23°C atmosphere (durometer hardness) in accordance with JIS K6253.

[0040] For example, using the hardness of the sidewall rubber 21 as a reference, the hardness of the bead filler 12 is preferably between 1.2 and 2.3 times the hardness of the sidewall rubber 21. The hardness of the rim strip rubber 14 is more preferably between 1 and 1.6 times the hardness of the sidewall rubber 21. By setting the hardness in this manner, a balance between the flexibility of the tire and the rigidity around the bead 10 can be ensured.

[0041] The above describes the basic configuration of the tire 1 according to the embodiment. Next, the characteristic configurations of the carcass ply 50 and the bead member 16 will be described.

[0042] In the embodiment of the two-layer structure including a first carcass ply 55 and a second carcass ply 56, the carcass ply 50 has a tensile strength of 250N or more and 420N or less. That is, the total tensile strength of the carcass ply 50, which is the sum of the first carcass ply 55 and the second carcass ply 56, is 250N or more and 420N or less. For example, if the first carcass ply 55 and the second carcass ply 56 are of the same type and their respective tensile strengths are 132N, the tensile strength of the carcass ply 50 will be "132N × 2" = 264N. Since the tensile strength of the carcass ply 50 mostly depends on the tensile strength of the ply cord, the carcass ply 50 having the tensile strength can be achieved by appropriately adjusting the tensile strength and number of ply cords.

[0043] Compared to a single-layer structure where the carcass ply consists of one sheet, a two-layer structure with two carcass plies (first carcass ply 55 and second carcass ply 56), as in the embodiment of the carcass ply 50, allows the carcass ply 50 to achieve the desired tensile strength without increasing the tensile strength of the ply cord. Therefore, by using a two-layer structure, the carcass ply 50 can be easily configured to have the desired tensile strength, compared to using a single carcass ply with a ply cord that has higher tensile strength.

[0044] When the tensile strength of the carcass ply 50 is relatively high, such as between 250N and 420N, compared to, for example, around 200N, the restraining effect of the carcass ply 50 suppresses the outward expansion of the shoulder 40 due to internal pressure.

[0045] As shown in Figure 2, the shoulder inclination angle θ becomes relatively large because the outward expansion of the shoulder 40 due to internal pressure is suppressed. This shoulder inclination angle θ is the angle made by the outer surface 40a of the shoulder 40 with respect to the tire rotation axis parallel to the tire width direction, and is the angle inward in the tire width direction made by a line L1 along the outer surface 40a of the shoulder 40 and a line L2 along the tire width direction. This tire cross-sectional shape, in which the expansion of the shoulder 40 is suppressed, makes it easier to suppress the stagnation of air flowing from the shoulder 40 to the rear during driving. As a result, the Cd value (air resistance value) is reduced.

[0046] In the bead member 16, as shown in Figure 1, when the tire 1 of the embodiment is mounted on a specified rim and a specified internal pressure is applied, the height of the bead member 16, i.e., the length in the tire radial direction H2, in the tire width cross-section is 20% to 25% of the tire cross-sectional height H1. The tire radial length H2 of the bead member 16 is the distance in the tire radial direction between the inner end 11a of the bead core 11 in the tire radial direction and the outer end 12a of the bead filler 12 in the tire radial direction.

[0047] By setting the tire bead member 16's radial length H2 to 20% to 25% of the tire's cross-sectional height H1, compared to a case where H2 is approximately 30% of H1, the weight of the bead member 16 is reduced. This weight reduction of the bead member 16 leads to a reduction in the overall weight of the tire 1, thereby reducing rolling resistance.

[0048] According to the embodiment of tire 1, the Cd value is reduced by setting the tensile strength of the carcass ply 50 to 250N or more and 420N or less. However, if the tensile strength of the carcass ply 50 is increased, the weight of tire 1 will increase along with the weight of the carcass ply 50, which may lead to an increase in rolling resistance. However, in the embodiment of tire 1, the increase in rolling resistance can be suppressed by reducing the weight by making the radial length H2 of the bead member 16 relatively small, to 20% or more and 25% or less of the tire cross-sectional height H1. In other words, it is possible to achieve both a reduction in the Cd value and a suppression of rolling resistance. Reducing the Cd value is possible by increasing the tensile strength of the carcass ply 50, and it does not require as much manufacturing effort as, for example, forming multiple fin-shaped protrusions on the side of the tire as in the conventional method. Therefore, according to the embodiment of tire 1, it is possible to reduce air resistance while suppressing rolling resistance without increasing manufacturing effort. Furthermore, in order to obtain a tire with sufficient lateral rigidity for practical use, it is preferable that the ratio of the tire radial length H2 of the bead member 16 to the tire cross-sectional height H1 is 20% or more.

[0049] The tire 1 according to the embodiment described above provides the following effects.

[0050] (1) The tire 1 according to the embodiment comprises a pair of beads 10 having a bead member 16 including a bead core 11 and a bead filler 12, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 disposed between the pair of sidewalls 20, and a carcass ply 50 spanning between the pair of beads 10, wherein the tensile strength of the carcass ply 50 is 250N or more and 420N or less, and in the tire widthwise cross section when mounted on a specified rim and with specified internal pressure applied, the tire radial length H2 of the bead member 16 is 20% or more and 25% or less of the tire cross section height H1.

[0051] As a result, the tire 1 according to this embodiment achieves reduced air resistance without increasing manufacturing effort. The increase in rolling resistance that may occur due to the reduction in air resistance can be compensated for by making the bead member 16 lighter by setting the tire radial length H2 of the bead member 16 to 20% or more and 25% or less of the tire cross-sectional height H1, thereby achieving both reduced air resistance and suppressed rolling resistance.

[0052] (2) In the tire 1 of the embodiment, it is preferable that the carcass ply 50 has a multi-layer structure comprising at least two layers that can be stacked on top of each other.

[0053] This makes it possible to easily construct the carcass ply 50 with the desired tensile strength.

[0054] Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., made to the extent that the objectives of the present invention can be achieved are also included within the scope of the present invention. [Examples]

[0055] The following describes the examples. As shown in Table 1, tires of Examples 1 to 4, in which the tensile strength of the carcass ply was 264N or 412N and the height of the bead member (tire radial length) was 20.2%, 23.4%, or 25% of the tire cross-sectional height, were evaluated using a simulation model. The carcass ply strength in Table 1 is the tensile strength of the carcass ply. The carcass ply of Examples 1 to 4 all had a two-layer structure. On the other hand, Comparative Examples 2 and 3, in which the tensile strength of the carcass ply was in the range of 250N to 420N but the height of the bead member was 28.3% of the tire cross-sectional height, and Comparative Example 1, a conventional type tire in which the tensile strength of the carcass ply was 132N and the height of the bead member was 28.3% of the tire cross-sectional height, were evaluated using a simulation model. The carcass ply of Comparative Examples 2 and 3 had a two-layer structure. The carcass ply of Comparative Example 1 had a single-layer structure. The tire sizes for Examples 1-4 and Comparative Examples 1-3 are all "225 / 55R19 99V" and have the same basic configuration as the embodiments described above. The height of the bead member is the value obtained when the tire is mounted on the specified rim and the air pressure is set to 230 kPa.

[0056] [Table 1]

[0057] The lateral stiffness, Cd value, and rolling resistance coefficient of the tires in Examples 1-4 and Comparative Examples 1-3 were simulated. The measurements were performed under a load of 69% of the maximum load capacity indicated by the tire's load index.

[0058] These results are shown in Table 1. In Table 1, each value of the conventional type Comparative Example 1 is set to an index of 100, and the tires of Comparative Examples 2 and 3 and Examples 1 to 4 are evaluated using this index. For the Cd value, a smaller index evaluation indicates reduced air resistance and is judged as good. Similarly, for the rolling resistance coefficient, a smaller index evaluation indicates lower rolling resistance and is judged as good. Furthermore, for lateral stiffness, a higher index evaluation indicates good.

[0059] Table 1 shows that in Comparative Examples 1-3, where the tensile strength of the carcass ply was gradually increased, the Cd value decreased as the tensile strength of the carcass ply increased. However, because the ratio of the bead member height to the tire cross-sectional height (bead member height ratio) was relatively large at 28.3%, the rolling resistance increased. Compared to these comparative examples, Examples 1-4 all showed a reduction in the Cd value, and the air resistance was reduced because the tensile strength of the carcass ply was within the range of the present invention. Furthermore, since the bead member height ratio was within the range of the present invention and lower than that of Comparative Examples 2 and 3, the rolling resistance was lower than that of Comparative Examples 2 and 3, indicating that the increase in rolling resistance can be suppressed by reducing the bead member height ratio. It should be noted that reducing the bead member height ratio may lead to a reduction in lateral rigidity, but if the bead member height ratio is maintained at 20% as in Example 1, the reduction is not significant and is practically acceptable. [Explanation of symbols]

[0060] 1. Tire (pneumatic tire) 10 beads 11 Bead core 12 Bead Fillers 16 Bead members 20 Sidewall 30 tread 50 Carcass Ply H1 Tire section height H2 Tire radial length of bead member

Claims

1. A pair of beads having bead members including a bead core and a bead filler, A pair of sidewalls extending radially outward from each of the aforementioned pair of beads, A tread positioned between the pair of sidewalls, A pneumatic tire comprising a carcass ply stretched between the pair of beads, A side reinforcement layer is positioned on the outer side of the bead filler in the tire width direction. The side reinforcement layer is sandwiched between the bead filler and the carcass ply, and has a portion that extends radially outward from the bead filler. The tensile strength of the ply cord included in the carcass ply is 250 N or more and 420 N or less. A pneumatic tire in which, when mounted on a specified rim and with specified internal pressure applied, the length of the bead member in the tire's radial direction in the tire's cross-section is 20% or more and 25% or less of the tire's cross-sectional height.

2. The pneumatic tire according to claim 1, wherein the carcass ply has a multi-layer structure comprising at least two layers that can be stacked on top of each other.

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