Reinforcing element having a flattened cross-section

Abstract

The reinforcing element (34) has a cross-section with a flattened overall shape having an aspect ratio greater than or equal to 5 and extending in a main direction (Z1). It comprises a lateral edge (46) made of a polymeric composition comprising a thermoplastic polymer, the lateral edge (46) extending in a general direction substantially parallel to the main direction. The reinforcing element (34) is such that R=(UcU1)/Uc>11%, where Uc is the average value of the microhardness of the reinforcing element (34) measured in its central part, and U1 is the average value of the microhardness of the reinforcing element (34) measured at its lateral edge (36). The lateral edge (46) does not have any ridges.

Claims

1. A reinforcing element having a cross-section with a flattened overall shape having an aspect ratio greater than or equal to 5 and extending in a main direction and comprising at least one lateral edge made of a polymeric composition comprising a thermoplastic polymer, the at least one lateral edge extending in a general direction substantially parallel to the main direction, wherein, in a section plane substantially perpendicular to the main direction, the reinforcing element has a central point defined as a point of intersection between a first median plane of a width of the reinforcing element and a second median plane of a thickness of the reinforcing element, the first and second median planes being substantially perpendicular to one another and each of the first and second median planes extending substantially parallel to the main direction, wherein, in the section plane substantially perpendicular to the main direction, microhardness R=(UcU1)/Uc>11%, where Uc is an average value of microhardness of the reinforcing element (a) measured at the central point when the central point is made of the polymeric composition or (b) measured at a point of the polymeric composition that is radially closest to the central point when the central point is not made of the polymeric composition, and where U1 is an average value of microhardness of the reinforcing element measured at a measuring point of the polymeric composition belonging to the second median plane, the measuring point being distant from an end point belonging to the second median plane and from an external lateral surface delimiting the at least one lateral edge by a distance in a range of 0 m to 50 m, and wherein the at least one lateral edge does not have any ridges.

2. A composite element comprising at least one reinforcing element according to claim 1 that is embedded in an elastomer matrix.

3. The composite element according to claim 2 comprising a plurality of reinforcing elements that are embedded in the elastomer matrix and are arranged substantially parallel to one another in a direction substantially parallel to the main direction.

4. A tire comprising a composite element according to claim 2.

5. The tire according to claim 4 further comprising a crown surmounted by a tread, two sidewalls, two beads, each sidewall connecting each bead to the crown, a carcass reinforcement that is anchored in each of the beads and extends through the sidewalls toward the crown, a crown reinforcement that is radially interposed between the carcass reinforcement and the tread, the crown reinforcement comprising the composite element.

6. The tire according to claim 5, wherein the main direction forms an angle ranging from 0 to 80 with the circumferential direction of the tire.

7. The tire according to claim 6, wherein the angle ranges from 5 to 50.

8. A tire comprising at least one reinforcing element, wherein the at least one reinforcing element has a cross-section with a flattened overall shape having an aspect ratio greater than or equal to 5 and extending in a main direction and comprising at least one lateral edge made of a polymeric composition comprising a thermoplastic polymer, the at least one lateral edge extending in a general direction substantially parallel to the main direction, wherein, in a section plane substantially perpendicular to the main direction, the at least one reinforcing element has a central point defined as a point of intersection between a first median plane of a width of the at least one reinforcing element and a second median plane of a thickness of the at least one reinforcing element, the first and second median planes being substantially perpendicular to one another and each of the first and second median planes extending substantially parallel to the main direction, wherein, in the section plane substantially perpendicular to the main direction, microhardness R=(UcU1)/Uc>11%, where Uc is an average value of microhardness of the at least one reinforcing element (a) measured at the central point when the central point is made of the polymeric composition or (b) measured at a point of the polymeric composition that is radially closest to the central point when the central point is not made of the polymeric composition, and where U1 is an average value of microhardness of the at least one reinforcing element measured at a measuring point of the polymeric composition belonging to the second median plane, the measuring point being distant from an end point belonging to the second median plane and from an external lateral surface delimiting the at least one lateral edge by a distance in a range of 0 m to 50 m, and wherein the at least one lateral edge does not have any ridges.

9. The tire according to claim 8, wherein the measuring point is distant from the end point by a distance in a range of 15 m to 50 m.

10. The tire according to claim 8, wherein R15%.

11. The tire according to claim 10, wherein R20%.

12. The tire according to claim 11, wherein R25%.

13. The tire according to claim 8, wherein the thermoplastic polymer is semi-crystalline.

14. The tire according to claim 8, wherein the thermoplastic polymer is selected from the group consisting of a polyester, a polyamide, a polyketone and a mixture thereof.

15. The tire according to claim 14, wherein the thermoplastic polymer is a polyester.

16. The tire according to claim 8, wherein the at least one reinforcing element has a thickness ranging from 0.05 to 1 mm.

17. The tire according to claim 16, wherein the thickness ranges from 0.10 to 0.70 mm.

18. The tire according to claim 8, wherein the at least one reinforcing element has a width greater than or equal to 2.5 mm.

19. The tire according to claim 18, wherein the width is greater than or equal to 5 mm.

20. The tire according to claim 19, wherein the width is greater than or equal to 10 mm.

21. The tire according to claim 8, wherein the at least one reinforcing element is made of a film of the polymeric composition.

22. The tire according to claim 21, wherein the film is multiaxially drawn.

23. The tire according to claim 8 further comprising a crown surmounted by a tread, two sidewalls, two beads, each sidewall connecting each bead to the crown, a carcass reinforcement that is anchored in each of the beads and extends through the sidewalls toward the crown, a crown reinforcement that is radially interposed between the carcass reinforcement and the tread, the crown reinforcement comprising the at least one reinforcing element.

24. The tire according to claim 23, wherein the main direction forms an angle ranging from 0 to 80 with the circumferential direction of the tire.

25. The tire according to claim 24, wherein the angle ranges from 5 to 50.

Description

BRIEF DESCRIPTION OF FIGURES

(1) The invention will be better understood from reading the following description, given solely by way of non-limiting example and with reference to the drawings in which:

(2) FIG. 1 is a sectional view of a tyre according to the invention;

(3) FIG. 2 is a sectional view of a composite element according to the invention that forms a working ply of the tyre in FIG. 1;

(4) FIG. 3 is a sectional view of a reinforcing element according to a first embodiment of the invention of the composite element in FIG. 2;

(5) FIG. 4 is an enlargement of a lateral edge of the reinforcing element in FIG. 3;

(6) FIG. 5 is a view similar to that of FIG. 3 of a reinforcing element according to a second embodiment of the invention;

(7) FIG. 6 is a view similar to that of FIG. 4 of the reinforcing element in FIG. 5;

(8) FIG. 7 is a diagram of a plant for treating a reinforcing element;

(9) FIG. 8 is a diagram of devices for generating plasma flows of the plant in FIG. 7;

(10) FIG. 9 is a detailed diagram of a device for generating a plasma flow of the plant in FIG. 7;

(11) FIG. 10 is a diagram illustrating steps in the process for treating the reinforcing element according to the invention;

(12) FIG. 11 is a graph including several force-elongation curves of several composite elements of which two are according to the invention;

(13) FIG. 12 is a sectional view of a reinforcing element according to the invention obtained by a plasma treatment process; and

(14) FIG. 13 is a view similar to that of FIG. 12 of a prior art reinforcing element.

DETAILED DESCRIPTION

(15) In the following description, when using the term radial, it is appropriate to make a distinction between several different uses of the word by a person skilled in the art. Firstly, the expression refers to a radius of the tyre. It is within this meaning that a point P1 is said to be radially inside a point P2 (or radially on the inside of the point P2) if it is closer to the rotation axis of the tyre than the point P2. Conversely, a point P3 is said to be radially outside a point P4 (or radially on the outside of the point P4) if it is further away from the rotation axis of the tyre than the point P4. Progress will be said to be radially inwards (or outwards) when it is in the direction of smaller (or larger)radii. It is this sense of the word that applies also when radial distances are being discussed.

(16) On the other hand, a reinforcing element or a reinforcement is said to be radial when the reinforcing element or the reinforcing elements of the reinforcement make an angle greater than or equal to 65 and less than or equal to 90, preferably ranging from 80 to 90, and more preferably ranging from 85 to 90, with the circumferential direction.

(17) An axial direction is a direction parallel to the axis of rotation of the tyre. A point P5 is said to be axially inside a point P6 (or axially on the inside of the point P6) if it is closer to the median plane M of the tyre than the point P6. Conversely, a point P7 is said to be axially outside a point P8 (or axially on the outside of the point P8) if it is further away from the median plane M of the tyre than the point P8.

(18) The median plane M of the tyre is the plane which is normal to the rotation axis of the tyre and which is situated equidistantly from the annular reinforcing structures of each bead.

(19) Furthermore, any range of values denoted by the expression from a to b means the range of values ranging from the end point a to the end point b, i.e. including the strict end points a and b. Any range of values denoted by the expression between a and b means the range of values varying between the end point a and the end point b, i.e. excluding the strict end points a and b.

(20) Examples of a Tyre and a Reinforcing Element According to the Invention

(21) FIGS. 1 and 2 show a reference frame X, Y, Z corresponding to the usual axial (X), radial (Y) and circumferential (Z) directions, respectively, of a tyre.

(22) FIGS. 1 and 2 show a tyre according to the invention and denoted by the general reference 10. The tyre 10 substantially exhibits symmetry of revolution about an axis substantially parallel to the axial direction X. The tyre 10 is intended in this case for a passenger vehicle.

(23) The tyre 10 comprises a crown 12 comprising a crown reinforcement 14 comprising a working reinforcement 16 comprising a working ply 17 of reinforcing elements and a hoop reinforcement 18 comprising a hooping ply 19. The crown reinforcement 14 is surmounted by a tread 20. In this case, the hoop reinforcement 18, in this case the hooping ply 19, is radially interposed between the working reinforcement 16 and the tread 20. Two sidewalls 22 extend the crown 12 radially inwards. The tyre 10 also comprises two beads 24 that are radially inside the sidewalls 22 and each comprise an annular reinforcing structure 26, in this instance a bead wire, and a radial carcass reinforcement 28. The crown reinforcement 14 is radially interposed between the carcass reinforcement 28 and the tread 20. Each sidewall 22 connects each bead 24 to the crown 14.

(24) The carcass reinforcement 28 preferably comprises a single carcass ply 30 of radial textile reinforcing elements 32. The carcass reinforcement 28 is anchored to each of the beads 24 by being turned up around the bead wire 26, so as to form, within each bead 24, a main strand extending from the beads 24 through the sidewalls 22 towards the crown 12, and a turn-up strand, the radially outer end of the turn-up strand being radially on the outside of the bead wire 26. The carcass reinforcement 30 thus extends from the beads 24 through the sidewalls 22 towards the crown 12. In this embodiment, the carcass reinforcement 28 also extends axially through the crown 12.

(25) The working ply 16 forms a composite element according to the invention, comprising reinforcing elements 34 according to the invention that extend in a main direction Z1 that forms an angle a ranging from 0 to 80, preferably ranging from 5 to 50, more preferably ranging from 15 to 40, and even more preferably ranging from 20 to 30, and in this case equal to 26, with the circumferential direction Z of the tyre 10. Alternatively, the working reinforcement 16 comprises several working plies, for example two working plies, each comprising reinforcing elements 34 according to the invention.

(26) The hooping ply 19 comprises hoop reinforcing elements 36 that form an angle of at most equal to 10, preferably ranging from 5 to 10, with the circumferential direction Z of the tyre 10. In this instance, the hoop reinforcing elements 36 are plied yarns made of aramid, each plied yarn consisting of two 167-tex spun yarns which have been twisted together (on a direct cabling machine) at 230 turns/meter. Alternatively, use could be made of other textile materials, such as PET, but also metal reinforcing elements.

(27) Each working ply 16, hooping ply 19 and carcass ply 30 comprises an elastomer matrix 21, 23 and 25, respectively, in which the reinforcing elements of the corresponding ply are embedded. The rubber compositions of the elastomer matrices of the working ply 16, hooping ply 19 and carcass ply 30 are conventional compositions for the calendering of reinforcing elements conventionally comprising a diene elastomer, for example natural rubber, a reinforcing filler, for example carbon black and/or silica, a crosslinking system, for example a vulcanizing system, preferably containing sulphur, stearic acid and zinc oxide, and possibly a vulcanization accelerant and/or retarder and/or various additives.

(28) The reinforcing elements 34 of the composite element 16 are arranged side-by-side. The reinforcing elements 34 extend parallel to one another. The composite element 16 comprises bridges 38 of the elastomer matrix that separate two successive reinforcing elements 34.

(29) FIGS. 3 and 4 show the reinforcing element 34 of the composite element 16, forming a reinforcing element according to a first embodiment of the invention.

(30) FIG. 3 shows a reference frame X1, Y1, Z1 corresponding to the general directions in which the width (X1), the thickness (Y1) and the length (Z1), respectively, of a three-dimensional object extend.

(31) The reinforcing element 34 has a length G extending in the main general direction Z1. In the tyre 10, the main direction Z1 forms an angle a with the circumferential direction Z of the tyre 10. The reinforcing element 34 has a width L extending in a general direction X1. The reinforcing element 34 has a thickness E extending in a general direction Y1.

(32) In the plane perpendicular to the main direction Z1, the reinforcing element 34 has a cross section with a flattened overall shape. The cross section may have an oblong, elliptical, oval, rectangular, parallelogram or lozenge shape. The reinforcing element 34 has a cross section with a rectangular overall shape.

(33) The reinforcing element 34 has an aspect ratio greater than or equal to 5, preferably greater than or equal to 10, more preferably greater than or equal to 20 and even more preferably greater than or equal to 30.

(34) The reinforcing element 34 consists here of a film 35 of polymeric composition comprising at least one thermoplastic polymer. The thermoplastic polymer is semi-crystalline and is chosen from a polyester, a polyamide, a polyketone or a mixture of these materials, and is preferably a polyester.

(35) In this instance, the reinforcing element 34 consists of a multiaxially drawn film 35 of polyethylene terephthalate (PET), in this case a biaxially drawn film 35 of polyethylene terephthalate (PET) (Mylar A from DuPont Teijin Films). Other thermoplastic polymers could be used, for example other polyesters or nylon.

(36) The reinforcing element 34 has a thickness E ranging from 0.05 to 1 mm, preferably from 0.1 to 0.7 mm, and in this case equal to 0.5 mm. The reinforcing element 34 has a width L greater than or equal to 2.5 mm, preferably greater than or equal to 5 mm and more preferably greater than or equal to 10 mm, and in this case equal to 25 mm.

(37) In this case, the aspect ratio is equal to 50.

(38) The reinforcing element 34 comprises two longitudinal faces 40, 42 and two lateral edges 44, 46, each comprising an external lateral surface 48, 50. Each lateral edge 44, 46 extends in a general direction substantially parallel to the main direction Z1. Neither of the lateral edges 44, 46 has any ridges. Thus, it is understood that each external lateral surface 48, 50 delimiting each lateral edge 44, 46 is a continuous surface. In other words, neither of the external lateral surfaces 48, 50 has any indentations or protrusions forming a discontinuity on the external lateral surface 48, 50.

(39) Each lateral edge 44, 46 is made of the polymeric composition comprising the thermoplastic polymer, in this case PET.

(40) FIG. 3 shows a first median plane M1 of the width L of the reinforcing element 34, and a second median plane M2 of the thickness of the reinforcing element 34. The first and second median planes M1, M2 extend substantially parallel to the main direction Z1 and are substantially perpendicular to one another. The central point C, defined as the point of intersection between the first and second median planes M1, M2, is shown in the section plane in FIG. 3. The central point C is made of the polymeric composition, i.e. in this case PET.

(41) FIG. 4 shows the lateral edge 46 of the reinforcing element 34. The lateral edge 46 has a point P1, known as the measuring point, belonging to the second median plane M2. The measuring point P1 is distant from a point P2, known as the end point, belonging to the second median plane M2 and from the external lateral surface 50 delimiting the lateral edge 46, by a distance d in a range of [0 m; 50 m], preferably [15 m, 50 m]. In this case d=15 m. The point P1 is made of the polymeric composition.

(42) FIG. 4 also shows the variation in the microhardness U of the polymeric composition depending on the distance d from the external lateral surface 50 in a direction substantially parallel to the direction X1. The curve C0 (continuous curve) shows the variation in the microhardness U of a reinforcing element of the prior art and not according to the invention. The curve C1 (dashed curve) shows the variation in the microhardness U of the reinforcing element 34.

(43) Uc represents the average value of the microhardness of the reinforcing element 34 measured at the central point C. U1 represents the average value of the microhardness of the reinforcing element 34 measured at the measuring point P1. Ur represents the average value of the microhardness of a reinforcing element of the prior art and thus not according to the invention at the measuring point P1. What has just been described for the lateral edge 46 applies mutatis mutandis to the lateral edge 44.

(44) Each reinforcing element 34 is coated with a layer of adhesion primer and a layer of adhesive coating the layer of adhesion primer. Alternatively, the adhesive layer directly coats the polymeric composition (absence of the layer of adhesion primer).

(45) The adhesion primer generally comprises an epoxy resin, well known to a person skilled in the art. The adhesive comprises an RFL adhesive or a phenol-aldehyde resin based on at least one polyphenol and a polyaldehyde such as those described in the publications WO2013017421, WO2013017422, WO2013017423. Alternatively, other types of adhesive can be used, for example thermoplastic adhesives.

(46) Preferably, the adhesive comprises at least one diene elastomer. Such an elastomer makes it possible to improve the tack in the green state and/or cured state of the adhesive with the rubber matrix. Advantageously, the diene elastomer is chosen from natural rubber, a copolymer of styrene and butadiene, a terpolymer of vinylpyridine, styrene and butadiene, and a mixture of these diene elastomers.

(47) FIGS. 5 and 6 show a reinforcing element 34 according to a second embodiment.

(48) In contrast to the reinforcing element 34 according to the first embodiment, the reinforcing element according to the second embodiment has a cross section with an overall shape that is elliptical before the lateral edge is subjected to the plasma flow.

(49) Example of a Process for Obtaining the Reinforcing Element According to the Invention

(50) FIGS. 7 to 9 show a plant for treating the reinforcing element 34, making it possible to implement a treatment process, especially using a plasma torch. The plant is denoted by the overall reference 60.

(51) The plant 60 comprises two devices 62a, 62b for generating a plasma flow and a device 64 for coating the reinforcing element 34.

(52) A plasma makes it possible to generate, from a gas subjected to an electrical voltage, a thermal flow comprising molecules in the gaseous state, ions and electrons. Advantageously, the plasma is of the cold plasma type. Such a plasma, also known as a non-equilibrium plasma, is such that the temperature originates predominantly from the movement of the electrons. A cold plasma should be distinguished from a hot plasma, also known as a thermal plasma, in which the electrons but also the ions give this plasma certain properties, especially thermal properties, different from those of the cold plasma.

(53) Each device 62a, 62b comprises a plasma torch 66 illustrated in detail in FIG. 9. Each device 62a, 62b is intended to respectively treat at least a part of each lateral edge 44, 46. The coating device 64 comprises a first bath 67 containing the adhesion primer and a second bath 68 containing the adhesive, in this case an adhesive of the RFL type.

(54) The devices 62a, 62b are arranged on either side of the reinforcing element 34, in this case substantially symmetrically with respect to the median plane M1 of the reinforcing element 34.

(55) The plant 60 also comprises two, upstream and downstream storage reels respectively denoted by the references 70, 72. The upstream reel 70 carries the untreated reinforcing element 34 while the reel 72 carries the reinforcing element 34 plasma-treated by means of the devices 62a, 62b and coated with the adhesion primer and the adhesive by means of the coating device 64. The devices 62a, 62b and 64 are arranged in this order between the reels 70, 72 in the running direction of the reinforcing element 34. The devices 62a, 62b are situated upstream with respect to the device 64 in the running direction of the reinforcing element 34.

(56) FIG. 8 shows the devices 62a, 62b for generating a plasma flow, in this case plasma torches 66 sold by Plasmatreat GmbH. Each plasma torch 66 is supplied with an alternating current having a voltage of less than 360 V and a frequency of between 15 and 25 kHz.

(57) With reference to FIG. 9, the plasma torch 66 comprises means 74 for supplying gas to a chamber 76 for generating the plasma flow, and also means 78 for discharging the plasma generated in the chamber 76 in the form of a plasma flow 80, in this case a plasma jet. The plasma torch 66 also comprises means 82 for generating a rotating electric arc 84 in the chamber 76.

(58) The supply means 74 comprise an inlet duct 86 for admitting the gas into the chamber 76. The means 82 for generating the electric arc comprise an electrode 88. The discharge means 78 comprise an outlet orifice 90 for the plasma flow flow 80.

(59) FIG. 10 shows a diagram illustrating the main steps 100 to 300 in the treatment process for manufacturing the reinforcing element 34 according to the invention.

(60) During a heating step 100, at least a part of each lateral edge 44, 46 is subjected to the flow 80 generated by means of two plasma torches 66. During this step 100, the reinforcing element 34 is treated continuously. The treatment process is carried out at atmospheric pressure. The use of an atmospheric-pressure plasma makes it possible to install a relatively simple and inexpensive industrial plant, unlike a process that requires the use of a reduced-pressure plasma that is associated with the installation of a depressurized chamber.

(61) Thus, during this step 100, the part of each lateral edge 44, 46 is subjected to a plasma flow from a plasma flow source so as to raise the temperature of each part of each lateral edge 44, 46 above the melting point Tf of the thermoplastic polymer. Thus, the structure of the thermoplastic polymer is amorphized.

(62) The application of the plasma flow to each lateral edge 44, 46 makes it possible to eliminate any ridges present on each lateral edge 44, 46 before application of the plasma. Neither lateral edge 44, 46 thus has any ridges after application of the plasma flow.

(63) The flow 80 is obtained from a gas comprising at least one oxidizing component. An oxidizing component is understood to be any component capable of increasing the degree of oxidation of the chemical functions present in the polymeric composition and in particular in the thermoplastic polymer.

(64) Advantageously, the oxidizing component is chosen from carbon dioxide (CO.sub.2), carbon monoxide (CO), hydrogen sulphide (H.sub.2S), carbon sulphide (CS.sub.2), dioxygen (O.sub.2), nitrogen (N.sub.2), chlorine (Cl.sub.2), ammonia (NH.sub.3) and a mixture of these components. More preferably, the oxidizing component is chosen from dioxygen (O.sub.2), nitrogen (N.sub.2) and a mixture of these components. Preferably, the oxidizing component is air. In this case, the flow 80 is obtained from a mixture of air and nitrogen at a flow rate of 2400 L/h.

(65) The orifice 90 is disposed opposite each lateral edge 44, 46 to be treated, in this case opposite each external lateral surface 48, 50. The orifice 90 is situated at a constant distance D from each lateral edge 44, 46. For example, this distance is between 1 mm and 20 mm and preferably between 2 mm and 10 mm.

(66) The reinforcing element 34 is made to move with respect to at least one source of plasma flow, in this case with respect to two sources of plasma flow, at an average speed V of between 1 and 100 m.Math.min.sup.1 and preferably between 1 and 50 m.Math.min.sup.1. The average speed V is equal to the ratio between the distance covered by the plasma flow 80 with respect to the edge to be exposed and a predetermined time taken for this distance to be covered, in this instance 30 s. The movement of the flow with respect to the reinforcing element 34 can be rectilinear or curved or a mixture of the two. In this instance, the reinforcing element 34 has a uniform continuous rectilinear movement with respect to the sources of plasma flow.

(67) Next, during a step 200, the reinforcing element 34 is coated with the adhesion primer in the first bath 67.

(68) Then, in a step 300, following steps 100 and 200, the reinforcing element 34 is coated with the adhesive in the second bath 68.

(69) Further subsequent steps that are not shown can also be implemented. By way of example, a draining step (for example by blowing, calibrating) to remove the excess adhesive; then a drying step, for example by passing into an oven (for example for 30 s at 180 C.) and finally a heat treatment step (for example for 30 s at 230 C.) could be carried out.

(70) A person skilled in the art will readily understand that the final adhesion between the reinforcing element 34 and the elastomer matrix in which it is embedded is definitively provided during the final curing of the tyre of the invention.

(71) Comparative Tests

(72) In a first test, two reinforcing elements 34, 34 and a prior art reinforcing element T were compared. The reinforcing elements 34, 34 are in accordance with the invention and were obtained by the treatment process described above with respective running rates and distances with respect to the outlet orifice of the plasma flow of V=10 m.Math.min.sup.1 and D=3.5 mm (element 34 shown in FIG. 12) and V=10 m.Math.min.sup.1 and D=1 mm (element 34). The reinforcing element T was not treated by the process described above and is shown in FIG. 13.

(73) In FIG. 12, a deformation of the ridges on the longitudinal edge of the reinforcing element according to the invention can be seen with respect to the prior art reinforcing element. This deformation makes it possible to obtain a reinforcing element that does not have any ridges, which by their nature protrude and could make it easier to create rupture initiators at the interface between the elastomer matrix and the reinforcing element.

(74) The microhardness of each reinforcing element was first of all measured as described below.

(75) Each average microhardness value is equal to the arithmetic average of 10 measurements carried out in each case on a cut substantially perpendicular to the main direction at the central point (measurement of Uc) and at the measuring point (measurement of Ur and U1) of each cut. The ten cuts are carried out along a length of 10 cm of the reinforcing element, for example at each centimeter.

(76) The microhardness of the polymeric composition is measured by measuring the microhardness by nanoindentation. In this instance, a nanoindenter (model Ultra NanoIndentation Tester UNHT from CSM Instruments) is used. The polymeric composition is statically compressed in a small deformation range, in this case less than 10%. Each measurement is based on the measurement of the depth of penetration of a pyramidal indenter (Berkovich-type indenter) at a given load and at a given point. Each measurement is carried out in the form of a substantially linear load/unload cycle. The mechanical model used for processing the load/unload cycles is the Oliver and Pharr model, which is commonly used for linear elastomeric materials. This model complies with the standard ISO14577-4:2007 reproduced here. The preparation of each test specimen comprises the coating of each reinforcing element in an epoxy resin. Next, the reinforcing element thus coated is cut in a cutting plane substantially perpendicular to the main direction Z1 and the test specimen is polished using papers with different grains (600, 1200) and then felts using different diamond-containing solutions (9 m, 3 m, 1 m and 0.25 m). The microhardness measurement is then carried out by moving the indenter perpendicularly to the cutting plane, in this case in the main direction Z1.

(77) The values of the ratios R=(UcU1)/Uc and R=(UcUr)/Uc were also compared, indicating the relative variation in the microhardness of the polymeric composition between the centre of the reinforcing element and its lateral edge.

(78) The results of these measurements are given in Table 1 below.

(79) TABLE-US-00001 TABLE 1 Reinforcing Plasma element treatment Uc (GPa) Ur (GPa) U1 (GPa) R PET film T No 4.23 3.82 / 10% PET film 34 Yes 4.13 / 2.81 32% PET film 34 Yes 4.19 / 2.89 31%

(80) The reinforcing element T is such that R11% and in this case R=10%. Specifically, by edge effect, the closer one gets to the external surface, the more the microhardness of the reinforcing element T decreases. However, since the relative decrease in the microhardness R=(UcUr)/Uc is limited to 10%, it does not make it possible to sufficiently limit the variation in microhardness between the elastomer matrix and the reinforcing element, unlike the invention. Specifically, the reinforcing elements 34, 34 are such that R>11%. R is even15%, preferably R20% and more preferably R25%. R is also 40% for these reinforcing elements 34, 34.

(81) In a second test, a force-elongation curve, well known to a person skilled in the art, of the composite elements 16, 16 according to the invention and K according to the prior art is realized. Each composite element 16, 16 respectively comprises reinforcing elements 34, 34 as described above. The test curves are shown in FIG. 11 and represent the variation in the force F as a function of elongation A. The force-elongation curve of the composite element 16 is represented by dashed lines (curve Ca). The force-elongation curve of the composite element 16 is represented by dotted lines (curve Cb). The force-elongation curve of the composite element K is represented by a continuous line (curve Cc). The rupture force values of the composite elements tested are summarized in Table 2 below.

(82) TABLE-US-00002 TABLE 2 Composite Reinforcing element element Plasma treatment R Fm (%) K PET film T No 10% 100 16 PET film 34 Yes 32% 117 16 PET film 34 Yes 31% 118

(83) In a third test, tyres 10, 10 according to the invention that respectively comprise composite elements 16, 16 according to the invention were compared with prior art tyres P1, P2. The size of the tyres tested is 175/65 R14.

(84) The tyre P1 comprises a conventional architecture comprising a conventional working reinforcement comprising two crown plies comprising filamentary reinforcing elements consisting of metal cords of structure 2.30 arranged at a pitch of 1.2 mm and a hoop reinforcement comprising a hooping ply comprising filamentary reinforcing elements consisting of plied yarns made of polyamide 66 (140 tex/2, 250 t.Math.m.sup.1/250 t.Math.m.sup.1)

(85) The tyre P2 has an architecture identical to the tyres 10, 10 but does not comprise a composite element in which the reinforcing elements have been treated by way of the treatment process described above and therefore does not have a reinforcing element such that R>11%.

(86) During this third test, the tyres 10, 10, P1 and P2 were subjected to a drift thrust Dz test as described below. The results are given in base 100 with respect to the tyre P1. Thus, the more the value is greater than 100, the better the drift thrust Dz of the tyre compared with the tyre P1 of the prior art.

(87) To measure the drift thrust Dz, each tyre was driven at a constant speed of 80 km/h on a suitable automatic machine (machine of the flat-track type marketed by MTS), varying the load denoted Z, at a relatively large cornering angle of 8 degrees, and the drift thrust was measured continuously and the cornering stiffness denoted D (corrected for the thrust at zero drift) was identified by recording, by way of sensors, the transverse load on the wheel as a function of this load Z; the cornering stiffness is thus obtained. For a chosen load, in this case 450 daN, the value given in Table 3 below is then obtained.

(88) TABLE-US-00003 TABLE 3 Working Tyre ply/plies Plasma treatment R Dz P1 Conventional No / 100 P2 K No 10% 94 10 16 Yes 32% 100 10 16 Yes 31% 102

(89) Thus, the tyres 10 and 10 have all the advantages of the tyre P1 without the cornering stiffness at large angles being impaired, as is the case for the tyre P2.

(90) The invention is not limited to the embodiments described above.

(91) Specifically, a tyre according to the invention in which the crown reinforcement also comprises a protective reinforcement interposed radially between the hoop reinforcement and the working reinforcement may also be envisaged.

(92) A tyre according to the invention in which the crown reinforcement does not comprise a hoop reinforcement but a protective reinforcement and a working reinforcement, the protective reinforcement being interposed radially between the tread and the working reinforcement, may also be envisaged.

(93) Reinforcing elements other than a film may also be envisaged.

(94) Provision could likewise be made to use the reinforcing element according to the invention in the carcass reinforcement. A reinforcing element in which the central point is not made of the polymeric composition may be envisaged. In this case, the measurement Uc is carried out at the point of the polymeric composition that is radially closest to the central point.

(95) It may also be possible to combine the features of the various embodiments described or envisaged above, as long as these are compatible with one another.