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EP-4543691-B1 - RUBBER COMPOSITION COMPRISING A HIGHLY SATURATED DIENE ELASTOMER

EP4543691B1EP 4543691 B1EP4543691 B1EP 4543691B1EP-4543691-B1

Inventors

  • FERRAND, THOMAS
  • ARAUJO DA SILVA, José-Carlos
  • PRAS, Maxime

Dates

Publication Date
20260513
Application Date
20230619

Claims (15)

  1. Rubber composition based on at least: - 20 to 50 phr of a copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50 mol% and 95 mol% of the monomer units of the copolymer, CH 2 =CR-CH=CH 2 (I) the symbol R representing a hydrocarbon chain containing 3 to 20 carbon atoms; - 50 to 80 phr of polyisoprene comprising a content by weight of cis-1,4- bonds of at least 90% of the weight of the polyisoprene; - a reinforcing filler; - 0.2 to 0.9 phr of zinc oxide; and - a vulcanization system.
  2. Rubber composition according to Claim 1, wherein the copolymer contains ethylene units which represent from 60 mol% to 90 mol%, preferably from 70 mol% to 85 mol%, of the monomer units of the copolymer.
  3. Rubber composition according to either one of the preceding claims, wherein the 1,3-diene of formula (I) is myrcene, β-farnesene or a mixture of myrcene and β-farnesene, preferably myrcene.
  4. Rubber composition according to any one of the preceding claims, wherein the copolymer contains units of the 1,3-diene of formula (I) which represent between 10 mol% and 40 mol%, preferably between 15 mol% and 30 mol%, of the monomer units of the copolymer.
  5. Rubber composition according to any one of the preceding claims, wherein the copolymer content is within a range extending from 20 to 45 phr, and in which the polyisoprene is present in a content within a range extending from 55 to 80 phr.
  6. Rubber composition according to any one of the preceding claims, wherein the total content of the copolymer and of the polyisoprene is within a range extending from 90 to 100 phr, preferably from 95 to 100 phr; preferably, the total content of the copolymer and of the polyisoprene is 100 phr.
  7. Rubber composition according to any one of the preceding claims, wherein the polyisoprene is selected from the group consisting of natural rubber, synthetic polyisoprenes and mixtures thereof; preferably, the polyisoprene is a natural rubber.
  8. Rubber composition according to any one of the preceding claims, wherein the reinforcing filler comprises more than 50% by weight of carbon black.
  9. Rubber composition according to any one of the preceding claims, wherein the content of reinforcing filler is within a range extending from 15 to 80 phr, preferably from 20 to 55 phr, preferably from 25 to 45 phr.
  10. Rubber composition according to any one of the preceding claims, comprising from 0.6 to 2 phr, preferably from 0.7 to 1.8 phr, of sulfur and from 0.6 to 1 phr, preferably from 0.6 to 0.9 phr, of at least one vulcanization accelerator.
  11. Rubber composition according to any one of the preceding claims, wherein the content of zinc oxide is within a range extending from 0.2 to 0.8 phr, preferably from 0.3 to 0.7 phr, preferably from 0.4 to 0.7 phr.
  12. Rubber composition according to any one of the preceding claims, the composition not comprising any compound represented by formula (IV), in which R 1 to R 4 represent, independently of one another, a linear or branched C 1 -C 18 alkyl group or a C 5 -C 12 cycloalkyl group, or comprises less than 0.2 phr, preferably less than 0.1 phr, thereof.
  13. Rubber composition according to any one of the preceding claims, the composition not comprising any compound comprising at least one zinc atom, other than the zinc oxide, or comprising less than 0.2 phr, preferably less than 0.1 phr, thereof.
  14. Rubber article comprising a rubber composition defined in any one of Claims 1 to 13.
  15. Tyre comprising a rubber composition defined in any one of Claims 1 to 13, the composition being present in at least one sidewall of the tyre.

Description

The field of the present invention is that of rubber compositions comprising a highly saturated diene elastomer, in particular compositions intended for use in a tire, more particularly in a tire sidewall. The sidewalls of a tire are exposed to both ozone and deformation cycles, such as flexing during rolling. These deformation cycles, combined with ozone exposure, can cause cracks or fissures in the sidewall, rendering the tire unusable regardless of tread wear. Therefore, highly cohesive rubber compounds are sought for use in tire sidewalls, for example, due to their ability to withstand significant deformation without breaking, even in the presence of incipient cracks. To minimize the effects of ozone on rubber compositions, it is known to use copolymers with lower oxidation sensitivity, such as highly saturated diene elastomers, which contain ethylene units at a molar ratio exceeding 50% of the elastomer's monomer units. The use of ethylene-1,3-diene copolymers in a flange composition is also described, for example, in the document EP 2 682 423 A1 to increase resistance to ozone. However, a decline in the cohesive properties of the rubber composition appears when the molar content of ethylene in the copolymer is greater than 50%. Furthermore, diene rubber compositions comprising ethylene and 1,3-butadiene copolymers, once crosslinked, can exhibit significantly higher stiffness than traditionally used diene rubber compositions, as shown in the document. WO 2014/114607 A1 However, this increased rigidity, while favorable to improved wear resistance for use in treads, may sometimes prove unsuitable for certain applications. Therefore, efforts were made to reduce the curing stiffness of such compositions containing ethylene-based diene rubber. This is known to be achieved by decreasing the density of the rubber composition. However, this solution is accompanied by an increase in the hysteresis of the rubber composition, which is detrimental to rolling resistance. The document WO 2021/053296 A1 provided a solution for reducing the cured stiffness of compositions containing ethylene-based diene rubber without penalizing hysteresis by using compositions of Rubbers comprising a copolymer of ethylene and a 1,3-diene with the formula CH₂ =CR-CH= CH₂ , the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms. The document FR 3 086 949 describes a rubber composition based on natural rubber, an ethylene copolymer and a 1,3-diene, carbon black, a plasticizer and a crosslinking system exhibiting good resistance to tearing. It would therefore be of interest to tire manufacturers to have rubber compositions, usable in particular in sidewalls, which have improved resistance to crack propagation, preferably while also reducing rigidity and without penalizing the hysteresis of the composition. Continuing its research, the Applicant unexpectedly discovered that reducing zinc in a specific copolymer-based composition containing ethylene units and a 1,3-diene solves the aforementioned technical problem. Thus, the invention relates to a rubber composition based on at least: 20 to 50 pieces of copolymer containing ethylene units and units of a 1,3-diene of formula (I), the ethylene units in the copolymer representing between 50% and 95% by mole of the monomer units of the copolymer, CH2 = CR-CH= CH2 (I) the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms; 50 to 80 pieces of polyisoprene comprising a mass percentage of 1,4-cis bonds of at least 90% of the mass of the polyisoprene; a reinforcing load; 0.2 to 0.9 parts per annum of zinc oxide; and a vulcanization system. The invention also relates to a rubber article comprising a composition according to the invention, in particular a pneumatic tire of which at least one sidewall comprises a composition according to the invention. I- DEFINITIONS The expression "based on" used to define the constituents of a catalytic system refers to the mixture of these constituents, or the product of the reaction of some or all of these constituents with each other. The expression "composition based on" means a composition comprising the mixture and/or the in situ reaction product of the different constituents used, some of these constituents being able to react and/or being intended to react with each other, at least partially, during the different phases of manufacturing the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state. By "elastomer matrix" we mean all the elastomers in the composition, including the copolymer defined below. Unless otherwise stated, the rates of units resulting from the insertion of a monomer into a copolymer are expressed as a mole percentage relative to the total monomer units of the copolymer. The expression "part by weight per hundred parts by weight of elastomer" (or pce) is to be understood in the context of the present invention as the part, by mass per hundred