Tread for a tire
A tire having a rubber tread comprises a first radially inner layer C1 and a second radially outer layer C2, the first and second layers being intended to be in contact with a ground on which they are running, in new or worn condition, in which the rubber composition of the first layer C1 comprises more than 50 phr of a copolymer of ethylene and of a 1,3-diene, a reinforcing filler and a plasticizing system, the 1,3-diene being 1,3-butadiene or isoprene and the ethylene units in the copolymer representing more than 50 mol % of all the monomer units of the copolymer.
1 . A tire having an axis of rotation and comprising a crown extended by two sidewalls and two beads, a carcass reinforcement anchored in the two beads, a crown reinforcement radially outside the carcass reinforcement, and a rubber tread radially outside the crown reinforcement, the rubber tread comprising a first radially inner layer C1, and a second radially outer layer C2, and a circumferential groove including a wear indicator, the second layer C2 being configured to be in contact with a ground on which it is running, in new or worn condition, and the first layer C1 having a radially outermost height greater than that of the wear indicator and being configured to be in contact with the ground on which it is running, in worn condition until a radially outer surface against the ground on which it is running is at a level of the wear indicator,
wherein the tread comprises ribs separated by the circumferential groove with a bottom, a limit of use of the tire being defined by a minimum radial height h of the ribs relative to the bottom of the circumferential groove, VC1 and VC2 being volumes of materials C1 and C2 located in the tread at a radial height greater than a minimum radial height h, and a VC1/VC2 ratio being greater than 15%,
wherein the rubber composition of the first layer C1 comprises more than 50 phr of a copolymer of ethylene and of a 1,3-diene, a reinforcing filler and a plasticizing system, the 1,3-diene being 1,3-butadiene or isoprene and ethylene units in the copolymer representing more than 50 mol % of all the monomer units of the copolymer, and
wherein the copolymer of ethylene and of a 1,3-diene bears at the chain end a functional group F1 which is a silanol or alkoxysilane function.
2 . The tire according to claim 1 , wherein the 1,3-diene is 1,3-butadiene.
3 . The tire according to claim 1 , wherein the copolymer contains units of formula (I) or units of formula (II) or units of formula (I) and of formula (II)
4 . The tire according to claim 3 , wherein molar percentages of the units of formula (I) and of the units of formula (II) in the copolymer, respectively o and p, satisfy the following equation 1, o and p being calculated on a basis of all the monomer units of the copolymer
0
<
o
+
p
≤
25.
(
eq
.
1
)
5 . The tire according to claim 1 , wherein the reinforcing filler of the rubber composition of layer C1 comprises from 35 to 100 phr of a reinforcing filler which comprises a silica.
6 . The tire according to claim 1 , wherein the plasticizing system of the rubber composition of layer C1 comprises a hydrocarbon-based plasticizing resin and a hydrocarbon-based liquid plasticizing agent, a total content of hydrocarbon-based plasticizing resin and of hydrocarbon-based liquid plasticizing agent being greater than 10 phr and less than or equal to 80 phr.
7 . The tire according to claim 6 , wherein the hydrocarbon-based plasticizing resin has a glass transition temperature of greater than 20° C.
8 . The tire according to claim 1 , wherein a weight ratio between the content of reinforcing filler and a content of the plasticizing system is greater than or equal to 1.1.
9 . The tire according to claim 1 , wherein the copolymer of ethylene and of a 1,3-diene is the only elastomer of the rubber composition of the first layer C1.
10 . The tire according to claim 1 , wherein the rubber composition of the first layer C1 comprises a second elastomer.
11 . The tire according to claim 1 , wherein the rubber composition of the second layer C2 comprises less than 50 phr of a copolymer of ethylene and of a 1,3-diene.
12 . The tire according to claim 1 , wherein a dynamic shear modulus of the rubber composition of the first layer C1 is between 1 and 2.5 MPa, the dynamic shear modulus being measured at 60° C. during a temperature sweep at an imposed stress of 0.7 MPa and at a frequency of 10 Hz.
13 . The tire according to claim 1 , wherein a ratio K between a dynamic shear modulus of the rubber composition of the first layer C1 and a dynamic shear modulus of the rubber composition of the second layer C2 is greater than 1.1, the dynamic shear moduli being measured at 60° C. during a temperature sweep at an imposed stress of 0.7 MPa and at a frequency of 10 Hz.