TIRE COMPRISING ELASTOMERIC MIXTURES WITH A LOW LEVEL OF SULFUR

Abstract

The tire has a radial carcass reinforcement and a crown reinforcement containing at least two working crown layers of reinforcing elements. The working crown layers are covered radially with a tread that is joined to two beads via two sidewalls. 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 S in a meridian plane. The elastomer compounds 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.

Claims

1. A tire having a radial carcass reinforcement, consisting of at least one layer of reinforcing elements, said tire comprising a crown reinforcement containing at least two working crown layers of reinforcing elements, which is itself covered radially with a tread, said tread being joined to two beads via two sidewalls, 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 S in a meridian plane and wherein said at least one zone S is defined in a meridian plane by the continuous cubic spline with a curvature that passes through four points such as: a first point B, defined by the orthogonal projection onto a reinforcing element of the carcass reinforcement of the point A forming the end of a reinforcing element of the axially widest working crown layer, a second point D, such that the segment AD is equal to of the segment AC, the point C being the intersection of the outer surface of the tread and of the straight line passing through the points A and B, D being borne by the straight line passing through the points A, B and C, a third point E defined on a reinforcing element of the axially widest working crown layer such that the length of the segment AE is equal to 10% of the maximum axial width of the tire, and a fourth point F, axially outside of the point A, such that the segment AF is perpendicular to the straight line passing through the points A, B, C and D and the length of which is equal to half of that of the segment AE, and wherein said elastomer compounds present in the surface of said at least one zone S 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 S 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 S 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 the point A forming the end of a reinforcing element of the axially widest working crown layer in a meridian plane 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 S.

7. The tire according to claim 1, wherein the ends of each of the working crown layers in a meridian plane are in contact with or included in said at least 30% of the elastomer compounds present in the surface of said at least one zone S.

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 S 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 S 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 S 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 S in a meridian plane.

10. The tire according to claim 1, wherein the ends of said at least two working crown layers are separated by a layer Q of elastomer compound, and wherein at least one portion of the layer Q 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 S.

11. The tire according to claim 1, wherein said at least two working crown layers being each formed of reinforcing elements inserted between two elastomer compound calendering layers, and wherein at least one portion of the calendering layers of said at least two working crown layers forms at least one portion of said at least 30% of the elastomer compounds present in the surface of said at least one zone S.

12. The tire according to claim 1, wherein at least one layer P of polymer compound being in contact with at least one working crown layer and in contact with the carcass reinforcement, said at least one layer P of polymer compound extending axially up to at least the axial end of the tread, and wherein at least one portion of said at least one layer P 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 S.

13. 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 that are crossed from one layer to the other, forming angles of between 10 and 45 with the circumferential direction.

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

15. 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.

16. 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 DRAWING

[0075] Other details and advantageous features of the disclosure will become apparent hereinafter from the description of exemplary embodiments of the disclosure, with reference to the FIGURE which depicts a meridian view of a partial diagram of a tire according to the disclosure.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

[0076] In order to make them easier to understand, the FIGURE is not shown to scale. The FIGURE only depicts a half-view of a tire extending symmetrically with respect to the axis XX which shows the circumferential median plane, or equatorial plane, of a tire.

[0077] In the FIGURE, the tire 1, of size 295/80 R 22.5, comprises a radial carcass reinforcement 2 anchored in two beads around bead wires. The carcass reinforcement 2 is formed of a single layer of metal cords. The carcass reinforcement 2 is hooped by a crown reinforcement 3, itself capped by a tread 4.

[0078] The low zones and beads of the tire 1 are in particular not shown in the FIGURE.

[0079] In the FIGURE, the crown reinforcement 3 is formed radially from the inside to the outside: [0080] of a triangulation layer 31 formed of non-wrapped 9.28 inextensible metal cords, oriented at an angle equal to 65, [0081] of a first working layer 32 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, [0082] of a second working layer 33 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, [0083] of a protective layer 34 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 33.

[0084] A zone S is defined in accordance with the disclosure by the continuous cubic spline with a curvature that passes through the points B, D, E and F in the meridian plane of the FIGURE.

[0085] The point B is defined by the orthogonal projection onto a reinforcing element of the carcass reinforcement of the point A forming the end of a reinforcing element of the axially widest working crown layer 32.

[0086] The point D is such that the segment AD is equal to of the segment AC; the point C is the intersection of the outer surface of the tread 4 and of the straight line L passing through the points A and B, D being borne by the straight line passing through the points A, B and C.

[0087] The point E is defined on a reinforcing element of the axially widest working crown layer such that the length of the segment AE is equal to 10% of the maximum axial width of the tire, this tire being mounted on its service rim and inflated to its nominal pressure.

[0088] The point F, axially outside of the point A, is such that the segment AF is perpendicular to the straight line passing through the points A, B, C and D and such that its length is equal to half of that of the segment AE.

[0089] A layer of rubber compound Q decouples the ends of the working crown layers 32 and 33.

[0090] According to the disclosure, a layer P of rubber compound is placed between the carcass reinforcement 2 and the first working layer 32.

[0091] Various tires were produced in accordance with the disclosure with a percentage of the zone S comprising a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5% varying between 30% and 60%.

[0092] The composition used to make 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) 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 grade - Umicore)

[0093] The composition described above results 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%.

[0094] 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.

[0095] A first tire P1 according to the disclosure comprises a layer Q, at least the portion of the calenderings of the working layers present in the surface of the zone S and a portion of the layer P present in the surface of the zone S, the rubber compounds of which are produced with the composition described above. The surface occupied by these compounds represents 35% of the surface of the zone S.

[0096] A second tire P2 according to the disclosure comprises a layer Q, at least the portion of the calenderings of the working layers present in the surface of the zone S and the entire portion of the layer P present in the surface of the zone S, the rubber compounds of which are produced with the composition described above. The surface occupied by these compounds represents 55% of the surface of the zone S.

[0097] A tire P3, not in accordance with the disclosure, comprises only a layer Q, the rubber compounds of which are produced with the composition described above. The surface occupied by the layer Q represents 20% of the surface of the zone S.

[0098] A reference tire is produced, comprising no rubber compound in the zone S having a relative density of sulfur bridges measured according to the equilibrium swelling method of less than 5%.

[0099] Running tests were carried out with these four tires to evaluate the performances thereof in terms of endurance.

[0100] These endurance tests were carried out on a 40 meter development internal rolling road test machine, forcing each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for the tire under an initial load corresponding to the load prescribed by ETRTO and gradually increased, the tire being maintained at a pressure set at 20% above that recommended by ETRTO.

[0101] The distance traveled is measured until the tire exhibits a degradation of its crown. The measurements illustrated below are referenced to a base 100 for the reference tire.

TABLE-US-00002 R P1 P2 P3 km 100 125 140 100

[0102] These results confirm the increases in endurance obtained with elastomer compounds defined and located in accordance with the disclosure in the zones of the tire's shoulders.