TIRE COMPRISING LOW-SULPHUR ELASTOMER MIXTURES

Abstract

The reinforcing structure for a tire is in the form of a stratified assembly formed of two layers of reinforcing strips of completely connected cross section, and flattened in shape. According to the method, the strips of each layer are laid side by side in a main direction of laying. The strips of the first layer are spaced apart by a distance that is less than the width of the strips of the second layer and in such a way that the edges of the strips of the first layer overlap the edges of the strips of the second layer. The two layers of strips are separated by a layer of uncoupling rubber.

Claims

1. A tire having a radial carcass reinforcement, which includes at least one layer of reinforcing elements, said tire comprising a crown reinforcement, which is itself covered radially with a tread, said tread being joined to two beads via two sidewalls, said at least one layer of reinforcing elements of the carcass reinforcement being anchored in each of the beads by an upturn around a bead wire, said carcass reinforcement upturn being reinforced by at least one layer of reinforcing elements or stiffener, wherein the relative density of sulfur bridges measured according to the equilibrium swelling method is less than 5% in at least 30% of the elastomer compounds present in the surface of at least one zone Z in a meridian plane, wherein said at least one zone Z is defined in a meridian plane by the combination of two ovals O1, O2: a first oval O1 consisting, on the one hand, in its radially innermost portion, of a semi-ellipse E1, centered on the end R of the upturn of said at least one carcass reinforcement layer, the major axis of which is tangent to the end R at the upturn of said at least one carcass reinforcement layer, the length of the major axis being equal to 30 mm and the length of the minor axis being equal to 12 mm and, on the other hand, in its radially outermost portion, of a semicircle C1, of diameter D1 equal to 12 mm, centered on the end R of the upturn of said at least one carcass reinforcement layer, a second oval O2 consisting, on the one hand, in its radially innermost portion, of a semi-ellipse E2, centered on the outermost end T of said at least one layer of reinforcing elements or stiffener, the major axis of which is tangent to the end T at said at least one layer of reinforcing elements or stiffener, the length of the major axis being equal to 30 mm and the length of the minor axis being equal to 12 mm and, on the other hand, in its radially outermost portion, of a semicircle C2, of diameter D2 equal to 12 mm, centered on the outermost end T of said at least one layer of reinforcing elements or stiffener, and wherein said elastomer compounds present in the surface of said at least one zone Z in a meridian plane are compositions based on at least one diene elastomer selected from the group of diene elastomers consisting of polybutadienes (abbreviated to BRs), synthetic polyisoprenes (IRs), natural rubber (NR), isoprene copolymers, butadiene copolymers with the exception of butadiene-nitrile copolymers (NBRs), apart from diene elastomers bearing carboxyl functions, and mixtures of these diene elastomers.

2. The tire according to claim 1, wherein the relative density of sulfur bridges measured according to the equilibrium swelling method is less than 5% in at least 50% of the elastomer compounds present in the surface of said at least one zone Z in a meridian plane.

3. The tire according to claim 1, wherein said elastomer compounds present in the surface of said at least one zone Z in a meridian plane are compositions based on at least one diene elastomer, a zinc diacrylate derivative in the form of a zinc salt of formula (I) ##STR00002## in which R1, R2 and R3 independently represent a hydrogen atom or a C1-C7 hydrocarbon-based group selected from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups and optionally interrupted by one or more heteroatoms, it being possible for R2 and R3 to together form a nonaromatic ring, said compositions additionally comprising a peroxide, the zinc diacrylate derivative and peroxide contents being such that the ratio of the peroxide content to the zinc diacrylate derivative content is less than or equal to 0.09.

4. The tire according to claim 3, wherein the peroxide is an organic peroxide, preferentially present in an amount of less than or equal to 3 phr.

5. The tire according to claim 3, wherein the ratio of the peroxide content to the zinc diacrylate derivative content is between 0.01 and 0.09.

6. The tire according to claim 1, wherein, in a meridian plane, the point R forming the end of the upturn of said at least one carcass reinforcement layer is in contact with or included in said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

7. The tire according to claim 1, wherein, in a meridian plane, the point T forming the radially outermost end of said at least one layer of reinforcing elements or stiffener is in contact with or included in said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

8. The tire according to claim 1, wherein the relative density of ionic bridges measured according to the equilibrium swelling method is greater than 50% in said at least 30% of the elastomer compounds present in the surface of said at least one zone Z in a meridian plane and preferably in said at least 50% of the elastomer compounds present in the surface of said at least one zone Z in a meridian plane.

9. The tire according to claim 1, wherein the relative density of carbon-carbon bridges measured according to the equilibrium swelling method is less than 45% in said at least 30% of the elastomer compounds present in the surface of said at least one zone Z in a meridian plane and preferably in said at least 50% of the elastomer compounds present in the surface of said at least one zone Z in a meridian plane.

10. The tire according to claim 1, the end R of the upturn of said at least one carcass reinforcement layer being separated from the radially outermost end T of said at least one layer of reinforcing elements or stiffener by a layer W of elastomer compound, wherein at least one portion of said layer W of elastomer compound forms at least one portion of said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

11. The tire according to claim 1, said at least one layer constituting the carcass reinforcement being formed of reinforcing elements inserted between two elastomer compound calendering layers, wherein at least one portion of the calendering layers of said at least one layer constituting the carcass reinforcement forms at least one portion of said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

12. The tire according to claim 1, said at least one layer of reinforcing elements or stiffener being formed of reinforcing elements inserted between two elastomer compound calendering layers, wherein at least one portion of the calendering layers of said at least one layer of reinforcing elements or stiffener forms at least one portion of said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

13. The tire according to claim 1, the upturn of the carcass reinforcement being separated from the carcass reinforcement by a layer Y of elastomer compound positioned radially on the outside of the bead wire, wherein at least one portion of said layer Y of elastomer compound forms at least one portion of said at least 30% of the elastomer compounds present in the surface of said at least one zone Z.

14. The tire according to claim 1, wherein said at least one layer of reinforcing elements or stiffener consists of reinforcing elements oriented relative to the circumferential direction at an angle of less than 45, and preferably less than 25.

15. The tire according to claim 1, wherein the radially outer end T of the stiffener is radially outside of the end R of the upturn of said at least one carcass reinforcement layer.

16. The tire according to claim 1, wherein the crown reinforcement of the tire is formed of at least two working crown layers of inextensible reinforcing elements, crossed from one layer to the other, forming angles of between 10 and 45 with the circumferential direction.

17. The tire according to claim 1, wherein the crown reinforcement also comprises at least one layer of circumferential reinforcing elements.

18. The tire according to claim 1, wherein the crown reinforcement is supplemented radially on the outside by at least one additional ply, referred to as a protective ply, of reinforcing elements, referred to as elastic reinforcing elements, that are oriented with respect to the circumferential direction at an angle of between 10 and 45 and in the same direction as the angle formed by the inextensible elements of the working ply which is radially adjacent thereto.

19. The tire according to claim 1, wherein the crown reinforcement also comprises a triangulation layer formed of metal reinforcing elements that form angles of more than 60 with the circumferential direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Other details and advantageous features of the disclosure will become apparent hereinafter from the description of exemplary embodiments of the disclosure, with reference to FIGS. 1 and 2, in which:

[0078] FIG. 1 depicts a meridian view of a diagram of a tire according to one embodiment of the disclosure,

[0079] FIG. 2 depicts an enlarged schematic representation of the bead region of the tire from FIG. 1.

[0080] In order to make them easier to understand, the figures are not shown to scale.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

[0081] In the figure, the tire 1, of size 295/80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads 3 around bead wires 4. The carcass reinforcement 2 is formed of a single layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 5, itself capped by a tread 6.

[0082] In FIG. 1, the crown reinforcement 5 is formed radially from the inside to the outside: [0083] of a triangulation layer 51 formed of non-wrapped 9.28 inextensible metal cords, oriented at an angle equal to 65, [0084] of a first working layer 52 formed of non-wrapped 11.35 inextensible metal cords, which are continuous over the entire width of the ply, and oriented at an angle equal to 26, [0085] of a second working layer 53 formed of non-wrapped 11.35 inextensible metal cords, which are continuous over the entire width of the ply, oriented at an angle equal to 18, and crossed with the metal cords of the first working layer, [0086] of a protective layer 54 formed of non-wrapped 6.35 elastic metal cords which are continuous over the entire width of the ply and oriented at an angle equal to 18 in the same direction as the metal cords of the working layer 53.

[0087] The carcass reinforcement layer 2 is wound around a bead wire 4 in order to form an upturn 7. The upturn 7 is further reinforced by a layer of reinforcing elements or stiffener 8 which covers the end R of the upturn 7 and the radially inner end 9 of which is engaged underneath the bead wire 4.

[0088] This engagement of the stiffener underneath the bead wire 4 results in a radially inner end 9 of the stiffener radially inside of the point 10 of the bead wire radially closest to the axis of rotation, as illustrated in FIG. 2.

[0089] FIG. 2 illustrates, in greater detail, a schematic cross-sectional representation of a bead 3 of the tire in which a portion of the carcass reinforcement layer 2 is found wound around a bead wire 4 in order to form an upturn 7, the end R of which is covered by the stiffener 8.

[0090] The radially outer end T of the stiffener 8 is thus radially outside of the end R of the upturn 7 of the carcass reinforcement and the radially inner end 9 of the stiffener 8 is engaged underneath the bead wire 4.

[0091] The end R of the upturn 7 of the carcass reinforcement is separated from the stiffener 8 by a layer of elastomer compound W.

[0092] An elastomer compound Y radially outside of the bead wire 4 separates the upturn 7 from the carcass reinforcement layer 2.

[0093] A zone Z is defined in accordance with the disclosure by the combination of two ovals O1 and O2 in the meridian plane of the figure: [0094] a first oval O1 consisting, on the one hand, in its radially innermost portion, of a semi-ellipse E1, centred on the end R of the upturn of the at least one carcass reinforcement layer, the major axis of which is tangent along T1 to the end R at the upturn of the at least one carcass reinforcement layer, the length of the major axis being equal to 30 mm and the length of the minor axis being equal to 12 mm and, on the other hand, in its radially outermost portion, of a semicircle C1, of diameter D1 equal to 12 mm, centered on the end R of the upturn of the at least one carcass reinforcement layer, [0095] a second oval O2 consisting, on the one hand, in its radially innermost portion, of a semi-ellipse E2, centered on the outermost end T of the at least one layer of reinforcing elements or stiffener, the major axis of which is tangent to the end T at the at least one layer of reinforcing elements or stiffener, the length of the major axis being equal to 30 mm and the length of the minor axis being equal to 12 mm and, on the other hand, in its radially outermost portion, of a semicircle C2, of diameter D2 equal to 12 mm, centered on the outermost end T of the at least one layer of reinforcing elements or stiffener.

[0096] Various tires were produced in accordance with the disclosure with a percentage of the zone Z comprising a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5% varying between 30% and 80%, specific compositions being variably used for the calendering of the carcass reinforcement, the calenderings of the stiffener and also for the W and Y compound layers.

[0097] The composition used to produce the calendering layers of the carcass reinforcement layer and the calendering layers of the stiffeners and that makes it possible to obtain a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5% is the following:

TABLE-US-00001 NR (1) 100 ZDA derivative (2) 20 Peroxide (3) 1.5 Peroxide/ZDA derivative 0.075 Filler (4) 20 Filler/ZDA derivative 1 ZnO (5) 6

[0098] The composition used to produce the layers W and Y and that makes it possible to obtain a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5% is the following:

TABLE-US-00002 NR (1) 100 ZDA derivative (2) 20 Peroxide (3) 1.5 Peroxide/ZDA derivative 0.075 Filler (4) 40 Filler/ZDA derivative 2 ZnO (5) 6
(1) Natural rubber
(2) DIMALINK 634 zinc dimethacrylate (ZDMA) from CRAY VALLEY
(3) Dicup dicumyl peroxide from Hercules
(4) N326 ASTM grade carbon black (Cabot)
(5) Zinc oxide (industrial gradeUmicore)

[0099] The compositions described above result in a relative density of ionic bridges of the order of 80% and a relative density of carbon/carbon bridges of the order of 20%.

[0100] It turns out that the kinematics of curing the rubber compounds having a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5% are different from the more customary compounds in tire manufacture. In order to facilitate the curing of the various compounds, the inventors applied methods similar to those of retreading operations in order to allow a curing of the tread independent of the curing of the other compounds. The curing of the various zones of the tire may thus be controlled.

[0101] A first tire P1 according to the disclosure comprises a layer W, at least the portion of the calenderings of the carcass reinforcement layer present in the surface of the zone Z and at least the portion of the calenderings of the stiffener present in the surface of the zone Z, the rubber compounds of which are produced with the composition described above. The surface occupied by these compounds represents 50% of the surface of the zone Z.

[0102] A second tire P2 according to the disclosure comprises a layer W, at least the portion of the calenderings of the carcass reinforcement layer present in the surface of the zone Z and at least the portion of the calenderings of the stiffener present in the surface of the zone Z and the layer Y, the rubber compounds of which are produced with the composition described above. The surface occupied by these compounds represents 80% of the surface of the zone Z.

[0103] A tire P3, not in accordance with the disclosure, comprises only at least the portion of the calenderings of the carcass reinforcement layer present in the surface of the zone Z and at least the portion of the calenderings of the stiffener present in the surface of the zone Z. The surface occupied by these compounds represents 20% of the surface of the zone Z.

[0104] A reference tire R is produced, comprising no rubber compound in the zone Z having a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5%.

[0105] Running tests were carried out with these four tires to evaluate the performances thereof in terms of endurance.

[0106] These endurance tests were carried out on an 8.5 meter development external rolling road test machine, by imposing on the tires deflections of 25% to 35% for running speeds of 60 to 20 km/h.

[0107] Before carrying out the tests, the tires undergo an accelerated ageing in an oven under inflation gas oxygen content conditions and temperature conditions that are suitable for producing a state of thermal oxidation of the materials representative of average usage during a customer service life.

[0108] The tests carried out result, for the reference tires, in performances that establish the base 100. The tests are stopped on appearance of a degradation of the low region of the tire.

TABLE-US-00003 R P1 P2 P3 km 100 120 130 100

[0109] These results confirm the increases in endurance obtained with elastomer compounds defined and located in accordance with the disclosure in the zone Z.