Reinforced product comprising a rubber composition based on a polyphenol compound, a guanidine and at least one peroxide compound

Abstract

The present invention relates to a reinforced product based on at least one metal reinforcing element embedded in a rubber composition, said rubber composition being based on at least one diene elastomer, a reinforcing filler mainly comprising silica, a crosslinking system based on at least one peroxide compound, at least one non-elastomeric polyphenol compound containing at least three benzene rings, each having at least two vicinal hydroxyl groups, and at least one compound of the guanidine family, as well as to rubber articles comprising such a reinforced product.

Description

[Technical field]

[0001] FIELD OF THE PRESENT ART The present invention relates to a reinforced product based on an elastomeric composition, and also to an article comprising such a reinforced product. [Background technology]

[0002] prior art Many rubber-based articles, such as pneumatic tires, non-pneumatic tires - i.e. tires whose shape is maintained by means other than pressurized gas, such as stays - or conveyor belts, use reinforcement products, i.e. combinations of rubber compositions and reinforcing cables, which are often metallic and surface-coated with brass. These reinforcement products are often called plies, since the reinforcing elements are generally arranged parallel to one another and coated with the rubber composition. Since these plies are exposed to high stresses during the operation of the tire or the operation of the conveyor belt, they must meet many, sometimes contradictory, evaluation criteria, such as high adhesion between the reinforcement and the composition, good resistance to cracking, low rolling resistance, or resistance to movement of the rubber article and good resistance to external attack, especially corrosion. The adhesive function generally imposes specific formulations on the rubber compositions, in particular high contents of sulfur and zinc oxide, the need for small amounts of stearic acid, the presence of cobalt salts, and the use of accelerators with long delay phases. However, these vulcanization systems containing high sulfur contents constitute great constraints during the fabrication of semi-finished articles, in particular to avoid premature crosslinking. Therefore, manufacturers of reinforced rubber articles are seeking formulations of rubber compositions that allow for good adhesion to reinforcing cables, whether or not they are coated with a particular metal or alloy, while allowing for reduced sulfur content or even omitting sulfur in the reinforced product. Summary of the Invention

[0003] WO 2017 / 081387 and WO 2017 / 081388 disclose rubber compositions and composites based on a polymer matrix containing a functionalized "grafted" diene polymer, the preparation of which is taught in these patent applications. The functionalized diene polymer has at least one aromatic group substituted with at least two vicinal hydroxyl functional groups. Crosslinking of the rubber composition is accomplished using a vulcanization system or a system based on one or more peroxide compounds. Good adhesion of the rubber composition to metal is obtained, but requires the use of a grafted polymer. JP 2011-252107 A describes a rubber composition with good adhesion to metal, which comprises a diene elastomer and a cobalt salt. Gallic acid or gallic acid hydrate facilitates dissolution of the cobalt salt. The composition is crosslinked using a sulfur-based system. Although it has good adhesive properties, the composition uses both sulfur and a cobalt salt. JP 2009-007408 and JP 2008-291173 disclose a step of calendering a composition containing silica as a reinforcing filler together with a conventional sulfur crosslinking system and a high content of zinc oxide. JP 2012-229282 describes a step of calendering a composition containing a low content of sulfur and zinc oxide. However, this composition uses a specific epoxide-functionalized elastomer.

[0004] The applicant has continued his research and has discovered a reinforced product comprising a diene elastomer, a reinforcing filler mainly comprising silica, a specific polyphenol compound, a crosslinking system based on peroxide, and at least one compound of the guanidine family, which has very good adhesive properties and also durable properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] The present invention relates to a reinforced product based on at least one metal reinforcing element embedded in a rubber composition, to a rubber article comprising such a reinforced product, and to a pneumatic tire comprising such a reinforced product. definition The expression "composition based on" includes mixtures and / or products of in situ reactions of the various components used, some of which may be at least partially reacted and / or are intended to react with one another during the various stages of the fabrication of the composition; the composition is thereby to be understood to mean a composition possibly in a fully or partially crosslinked or non-crosslinked state. For the purposes of the present invention, the expression "parts by weight per 100 parts by weight of elastomer" (or phr) is to be understood to mean parts by weight per 100 parts by weight of elastomer.

[0006] In the present invention, all percentages given are percentages by weight, unless expressly indicated otherwise. Furthermore, any interval of values ​​indicated by the expression "between a and b" denotes a range of values ​​greater than a and less than b (i.e., excluding the limits a and b), whereas any interval of values ​​indicated by the expression "from a to b" means a range of values ​​from a to b (i.e., including the precise limits a and b). The carbon-containing compounds referred to herein may be of fossil or bio-based origin. In the latter case, they may be partially or completely derived from biomass or may be obtained from renewable starting materials derived from biomass. Polymers, plasticizers, fillers, etc. are particularly relevant. Thus, the present invention relates to at least one of the following embodiments: A reinforced product based on at least one metal reinforcing element embedded in a rubber composition, said rubber composition being based on at least one diene elastomer, a reinforcing filler mainly comprising silica, a crosslinking system based on at least one peroxide compound, at least one non-elastomeric polyphenol compound containing at least three benzene rings, each having at least two vicinal hydroxyl groups, and at least one compound of the guanidine family. A reinforced product, wherein the molecular weight of said polyphenolic compound is preferentially greater than 600 g / mol. A fortified product in which the polyphenolic compounds are preferentially chosen from gallotannins, preferably from esters of gallic acid and polyols chosen from pentose and hexose sugars. A fortified product in which the polyphenolic compound is preferentially chosen from esters of glucose and gallic acid, preferably polygalloylglucose containing from 3 to 10, preferably from 5 to 10, galloyl units.

[0007] A fortified product, in which the polyphenolic compound is preferentially selected from trigalloyl glucose, pentagalloyl glucose, decagalloyl glucose and mixtures thereof, preferably selected from 1,2,6-trigalloyl glucose, 1,3,6-trigalloyl glucose, 1,2,3,4,6-pentagalloyl glucose, tannic acid and mixtures thereof. A reinforced product, in which the content of polyphenol compounds in the rubber composition ranges preferentially from 0.1 to 30 phr, preferably from 5 to 20 phr and in a preferred manner from 5 to 15 phr. A reinforced product, in which the compound of the guanidine family is preferentially diphenylguanidine. A reinforced product, the content of compounds of the guanidine family being preferentially in the range from 0.5 to 3 phr, preferentially from 0.5 to 2.5 phr, preferably from 0.5 to 2 phr.

[0008] A reinforced product, the rubber composition of which preferentially comprises less than 5 phr, preferably less than 1 phr, of a functionalized elastomer, and very preferably no functionalized elastomer. Preferentially, the rubber composition is free of cobalt salts or contains less than 2 phr of cobalt salts, preferentially less than 1 phr, preferably less than 0.5 phr and very preferentially less than 0.1 phr of reinforced products. Preferentially reinforced products, wherein said rubber composition is free of molecular sulfur or contains less than 1 phr of molecular sulfur. Preferentially reinforced products, in which the rubber composition does not contain stearic acid or its derivatives or contains less than 2 phr, preferentially less than 1 phr, preferably less than 0.5 phr, very preferentially 0.1 phr of stearic acid or its derivatives. Preferentially reinforced products, in which the rubber composition does not contain zinc or zinc oxide or contains only small amounts of zinc or zinc oxide, preferentially less than 1 phr, preferably less than 0.5 phr and more preferentially less than 0.2 phr. Preferentially reinforced products, in which the rubber composition comprises 10 to 200 phr of reinforcing filler.

[0009] A preferentially reinforced product, wherein the rubber composition comprises an agent selected from an agent for coupling, an agent for coating the silica, and mixtures thereof, the content of the agent being in the range extending from 5% to 20% by weight relative to the amount of silica, preferentially from 6% to 18% by weight relative to the amount of silica. Preferentially reinforced products, in which the diene elastomer of the rubber composition is selected from the group consisting of polybutadiene, natural rubber, synthetic polyisoprene, butadiene copolymers, isoprene copolymers and mixtures of these elastomers, preferentially selected from natural rubber and synthetic polyisoprene. Preferentially reinforced products, in which the rubber composition comprises from 0.01 to 10 phr, preferentially from 1 to 5 phr, of a peroxide compound. Preferentially reinforced products, the crosslinking system comprising a peroxide compound selected from organic peroxides. Preferentially reinforced products, in which the metal reinforcing element comprises a metal surface, the metal being selected from the group consisting of iron, copper, tin, zinc and alloys containing at least one of these metals, preferably selected from the group consisting of steel and brass.

[0010] A rubber article comprising a reinforced product according to any one of the above embodiments. Preferentially, the rubber article according to the previous embodiment is selected from pneumatic and non-pneumatic tires, conveyor belts and caterpillar tracks.

[0011] Diene Elastomer The reinforced product according to the invention comprises at least one diene elastomer. "Diene" elastomer (or rubber without distinction), whether natural or synthetic, is given to mean, as is known, an elastomer (i.e. homopolymer or copolymer) composed at least in part of diene monomer units (monomers having two conjugated or non-conjugated carbon-carbon double bonds). These diene elastomers may be classified into two categories: "essentially unsaturated" or "essentially saturated". The term "essentially unsaturated" is understood to mean diene elastomers at least partially derived from conjugated diene monomers having a content of units of diene origin (conjugated diene) generally greater than 15% (mol %); thus, diene elastomers such as butyl rubber or copolymers of dienes with α-olefins of EPDM type are not included in the above definition and are in particular cases the case that they can be described as "essentially saturated" diene elastomers (low or very low content, always less than 15%, of units of diene origin). The diene elastomers contained in the composition according to the invention are preferentially essentially unsaturated.

[0012] The term "diene elastomers that may be used in the composition according to the invention" refers in particular to: (a) any homopolymer of a conjugated or non-conjugated diene monomer containing from 4 to 18 carbon atoms; (b) Any copolymer of a conjugated or non-conjugated diene containing from 4 to 18 carbon atoms and at least one other monomer. The other monomer may be ethylene, an olefin or a conjugated or non-conjugated diene. Conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as, inter alia, 1,3-butadiene and isoprene, are suitable as conjugated dienes. Vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms are suitable as olefins.

[0013] For example, styrene, ortho, meta or para-methylstyrene, the "vinyl toluene" commercial mixture or para(tert-butyl)styrene are suitable as vinyl aromatic compounds. In particular, acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms are suitable as aliphatic α-monoolefins. Preferentially, the diene elastomer is chosen from the group consisting of polybutadiene (BR), natural rubber (NR), synthetic polyisoprene (IR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. The butadiene copolymers are in particular chosen from the group consisting of butadiene / styrene copolymers (SBR). Preferably, the diene elastomer is an isoprene elastomer.

[0014] "Isoprene elastomer" is understood to mean, as is known, an isoprene homopolymer or copolymer, in other words a diene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), the various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention is made in particular of isobutene / isoprene (butyl rubber - IIR), isoprene / styrene (SIR), isoprene / butadiene (BIR) or isoprene / butadiene / styrene (SBIR) copolymers. This isoprene elastomer is preferably selected from the group consisting of natural rubber, synthetic cis-1,4-polyisoprene and mixtures thereof; preferably, among these synthetic polyisoprenes, polyisoprenes are used that have a content (mol %) of cis-1,4-bonds greater than 90%, and even more preferentially greater than 98%. Preferably, according to any one of the configurations of the invention, the diene elastomer is natural rubber. Preferentially, the content of diene elastomer, preferably isoprene elastomer, more preferably natural rubber, is between 50 and 100 phr, more preferentially between 60 and 100 phr, more preferentially between 70 and 100 phr, even more preferentially between 80 and 100 phr, very preferentially between 90 and 100 phr. In particular, the content of diene elastomer, preferably isoprene elastomer, more preferably natural rubber, is very preferentially 100 phr. Whether it contains only one diene elastomer or a mixture of several diene elastomers, the rubber composition according to the invention may also contain, in a subordinate manner, any type of synthetic elastomer other than diene elastomers, indeed even non-elastomeric polymers, such as thermoplastic polymers. Preferably, the rubber composition according to the invention does not contain, or contains less than 10 phr, preferably less than 5 phr, of synthetic elastomers other than diene elastomers or non-elastomeric polymers.

[0015] Preferably, the rubber composition contains less than 5 phr, preferably less than 1 phr, of functionalized elastomer, and very preferably is free of functionalized elastomer. The term "functionalized" is understood to mean that the elastomer carries functional groups, for example groups containing conjugated diene functions, epoxide functions, carbonyl functions, anhydride functions or acid ester functions. Thus, very preferably, the rubber composition comprises less than 5 phr, preferably less than 1 phr, of an epoxide-functionalized elastomer, and very preferably is free of any epoxide-functionalized elastomer.

[0016] Crosslinked system The rubber composition of the reinforced product according to the invention is based on a crosslinking system based on at least one peroxide compound. The peroxide compound accounts for 0.01 to 10 phr, preferably 1 to 5 phr, of the rubber composition. As peroxides that can be used according to the present invention, any peroxide known to a person skilled in the art may be used. The peroxide is preferably selected from organic peroxides. The term "organic peroxide" refers to an organic compound, ie, a carbon-containing compound that includes an --OO-- group (two oxygen atoms linked by a single covalent bond).

[0017] During the crosslinking process, the organic peroxides decompose at their labile O-O bonds to give free radicals. These free radicals allow the creation of crosslink bonds. According to one embodiment, the organic peroxide is selected from the group consisting of dialkyl peroxides, monoperoxycarbonates, diacyl peroxides, peroxyketals, peroxyesters, and mixtures thereof. Preferably, the dialkyl peroxide is selected from the group consisting of dicumyl peroxide, di(t-butyl)peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-amylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hex-3-yne, 2,5-dimethyl-2,5-di(t-amylperoxy)hex-3-yne, α,α'-di[(t-butylperoxy)isopropyl]benzene, α,α'-di[(t-amylperoxy)isopropyl]benzene, di(t-amyl)peroxide, 1,3,5-tri[(t-butylperoxy)isopropyl]benzene, 1,3-dimethyl-3-(t-butylperoxy)butanol, 1,3-dimethyl-3-(t-amylperoxy)butanol and mixtures thereof.

[0018] Some monoperoxycarbonates can also be used, such as OO-tert-butyl O-(2-ethylhexyl) monoperoxycarbonate, OO-tert-butyl O-isopropyl monoperoxycarbonate, OO-tert-amyl O-(2-ethylhexyl) monoperoxycarbonate, and mixtures thereof. Among the diacyl peroxides, the preferred peroxide is benzoyl peroxide.

[0019] Among the peroxyketals, preferred peroxides are selected from the group consisting of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl 4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-butylperoxy)butyrate, 2,2-di(t-amylperoxy)propane, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane (or methyl ethyl ketone peroxide cyclic trimer), 3,3,5,7,7-pentamethyl-1,2,4-trioxepane, n-butyl 4,4-bis(t-amylperoxy)valerate, ethyl 3,3-di(t-amylperoxy)butyrate, 1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane, and mixtures thereof.

[0020] Preferably, the peroxyester is selected from the group consisting of tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, and mixtures thereof. Particularly preferred organic peroxides are dicumyl peroxide, aryl or diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, di(tert-butyl)peroxide, tert-butylcumyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, n-butyl 4,4'-di(tert-butylperoxy)valerate, OO-(t-butyl)O-(2-ethylhexyl)monoperoxycarbonate, tert-butylperoxyisopropyl carbonate, tert-butylperoxybenzoate, tert-butylperoxy-3,5,5-trimethylhexanoate, 1,3(4)-bis(tert-butylperoxyisopropyl tert-butylperoxyisopropyl)benzene, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, and mixtures thereof, and more preferentially from the group consisting of dicumyl peroxide, n-butyl 4,4'-di(tert-butylperoxy)valerate, OO-(t-butyl)O-(2-ethylhexyl)monoperoxycarbonate, tert-butylperoxyisopropyl carbonate, tert-butylperoxybenzoate, tert-butylperoxy-3,5,5-trimethylhexanoate, 1,3(4)-bis(tert-butylperoxyisopropyl)benzene, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, and mixtures thereof.

[0021] Reinforcing filler The rubber composition of the reinforced product of the present invention contains a reinforcing filler that primarily comprises silica. The term "predominantly" is understood to mean that silica represents at least 50% by mass of the reinforcing filler of the rubber composition, preferably at least 70% by mass and preferentially at least 90% by mass of the reinforcing filler of the rubber composition. In addition to the main silica, it is possible to use any type of reinforcing filler known for its ability to reinforce rubber compositions that can be used in particular for the construction of tires, for example reinforcing organic fillers such as carbon black, reinforcing inorganic fillers or a mixture of these two types of fillers.

[0022] Preferentially, the rubber composition contains at most 10 phr of carbon black, preferably at most 5 phr and very preferably at most 1 phr of carbon black. Very preferentially, and independently of the other characteristics of the rubber composition, the latter does not contain carbon black, with the exception of unavoidable impurities.

[0023] The silica used may be any reinforcing silica known to those skilled in the art, in particular 450m 2 / g, preferably 30 to 400 m 2 / g, especially 60~300m 2 The silica may be any precipitated or fumed silica having both a BET specific surface area and also a CTAB specific surface area ranging from 0.1 to 0.1 g / g. Any type of precipitated silica may be used, in particular highly disperse silicas (HDS). These precipitated silicas, which may be highly disperse or not, are well known to those skilled in the art. For example, mention may be made of the silicas described in WO 03 / 016387 and WO 03 / 016215. Among the commercially available HDS silicas, in particular Ultrasil® 5000GR and Ultrasil® 7000GR silicas from Evonik, or Zeosil® 1085GR, Zeosil® 1115 MP, Zeosil® 1165MP, Zeosil® Premium 200MP and Zeosil® HRS 1200 MP silicas from Solvay may be used. As non-HDS silicas the following commercially available silicas may be used: Ultrasil® VN2GR and Ultrasil® VN3GR silicas from Evonik, Zeosil® 175GR silica from Solvay, or Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-Sil EZ200G(-D), Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silicas from PPG.

[0024] In the present disclosure, the BET specific surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (vol. 60, p. 309, February 1938), in particular according to the method derived from the standard NF ISO 5794-1, Appendix E, June 2010 [multipoint (5-point) volumetric method - gas: nitrogen - degassing under vacuum: 1 hour at 160°C - relative pressure p / p 0 Range: 0.05–0.17]. For inorganic fillers such as silica, for example, CTAB specific surface area values ​​were determined according to standard NF ISO 5794-1, Appendix G, June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) onto the "outer" surface of the reinforcing filler.

[0025] Suitable carbon blacks include all carbon blacks, especially those conventionally used in tires or their treads. Among the latter, mention may be made, inter alia, of the reinforcing carbon blacks of the 100, 200 and 300 series, or of the 500, 600 or 700 series (ASTM D-1765-2017 grades), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683 and N772 carbon blacks. These carbon blacks may be used as they are commercially available, alone or in other forms, for example as support for some of the rubber engineering additives used. The carbon blacks may, for example, already be incorporated in diene elastomers, especially isoprene elastomers, in the form of masterbatches (see, for example, WO 97 / 36724 A2, WO 99 / 16600 A1).

[0026] For carbon black, the STSA specific surface area is determined according to ASTM standard D6556-2016. The physical state in which the reinforcing inorganic filler is provided is not important, whether it is in the form of powder, micropearls, granules, beads or any other suitable high density form. It goes without saying that the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular the silicas mentioned above. The skilled person knows how to adjust the total content of reinforcing fillers according to the use concerned, in particular according to the type of tire concerned, for example for motorcycles, for passenger cars or for utility vehicles such as vans or heavy duty vehicles. Preferentially, the total content of reinforcing fillers (reinforcing inorganic fillers such as silica and / or carbon black) is between 10 and 200 phr, more preferentially between 25 and 180 phr, the optimum values ​​being, as is known, different depending on the specific intended application.

[0027] To couple the reinforcing inorganic fillers, especially silica, to the diene elastomers, at least difunctional coupling agents (or bonding agents) of chemical and / or physical nature, intended in a well-known manner to provide a satisfactory link between the inorganic filler (the surface of its particles) and the diene elastomer, can be used. In particular, organosilanes or polyorganosiloxanes that are at least difunctional are used. The term "difunctional" is understood to mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a difunctional compound can contain a first functional group containing a silicon atom, capable of interacting with the hydroxyl groups of the inorganic filler, and a second functional group containing a sulfur atom, capable of interacting with the diene elastomer.

[0028] Preferably, the organosilane is selected from the group consisting of organosilane polysulfides (symmetrical or asymmetrical), for example polyorganosiloxanes, mercaptosilanes, block mercaptosilanes, such as bis(3-triethoxysilylpropyl tetrasulfide (abbreviated TESPT) sold under the name Si69 by Evonik, or bis(triethoxysilylpropyl disulfide (abbreviated TESPD) sold under the name Si75 by Evonik, S-(3-(triethoxysilyl)propyl)octanethioate sold under the name NXT Silane by Momentive. More preferentially, the organosilane is an organosilane polysulfide.

[0029] The content of the coupling agent in the composition of the present invention is preferentially 35 phr or less, and it is generally understood that the less the use of the coupling agent, the more desirable it is, as far as possible. Typically, the content of the coupling agent is 0.5% to 15% by mass relative to the amount of the reinforcing inorganic filler. The content is preferably in the range of 0.5 to 20 phr, more preferentially in the range of 3 to 10 phr. This content can be easily adjusted by a person skilled in the art according to the content of the reinforcing inorganic filler used in the composition of the present invention. Those skilled in the art understand that reinforcing fillers of another nature may be used as a replacement for the above-mentioned reinforcing inorganic fillers, provided that this reinforcing filler of another nature is covered with an inorganic layer such as silica or otherwise contains functional sites, in particular hydroxyl sites, on its surface that require the use of a coupling agent to establish a bond between this reinforcing filler and the diene elastomer. By way of example, mention may be made of carbon black partially or completely covered with silica, or carbon black modified with silica, such as, but not limited to, Ecoblac® type fillers of the "CRX2000" or "CRX4000" series from Cabot Corporation.

[0030] Polyphenol Compounds The compositions according to the present invention comprise at least one non-elastomeric polyphenol compound containing at least three benzene rings and each having at least two vicinal hydroxyl groups. The term "vicinal" is understood to mean that the aromatic ring has two hydroxyl groups that are in the ortho position to each other. The term "benzene ring" is understood to mean a substituted aromatic ring containing 6 carbon atoms. The molecular weight of the polyphenolic compounds is preferentially greater than 600 g / mol, preferentially greater than 800 g / mol, in a preferred manner greater than 1000 g / mol and in a very preferred manner greater than 1200 g / mol.

[0031] Preferably, the polyphenolic compound is selected from gallotannins, i.e. esters of gallic acid and polyols, the polyols being preferably selected from pentoses and hexoses. Preferably, the polyphenolic compound is selected from esters of glucose and gallic acid, preferentially from polygalloylglucoses containing 3 to 10 galloyl units, preferably 5 to 10 galloyl units. Preferentially, the polyphenolic compound is selected from trigalloylglucose, pentagalloylglucose, decagalloylglucose, and mixtures thereof, preferably 1,2,6-trigalloylglucose, 1,3,6-trigalloylglucose, 1,2,3,4,6-pentagalloylglucose, tannic acid (or beta-D-glucose pentakis(3,4-dihydroxy-5-((3,4,5-trihydroxybenzoyl)oxy)benzoate)), and mixtures thereof. Very preferably, the polyphenolic compound is tannic acid. Such compounds, due to the complexity of their structure, are incorporated as such into the rubber composition and cannot in particular be the product of a chemical reaction, an esterification reaction, between the various components of the rubber composition.

[0032] The rubber composition according to the invention has advantageous properties of adhesion, in particular to metal reinforcing elements, due to the presence of the polyphenol compound in combination with a predominantly silica reinforcing filler and at least one compound of the guanidine family, in particular for the construction of reinforced products, especially reinforced products intended for tires, whether or not the reinforcing elements are coated with a particular metal or alloy. The rubber composition according to the invention contains preferentially 0.1 to 30 phr, preferentially 5 to 20 phr, very preferentially 5 to 15 phr of polyphenol compounds. Below 0.1 phr, the polyphenol compounds have no significant effect on the adhesion of the rubber composition according to the invention. Above 30 phr, no further significant increase is observed. Surprisingly, very good adhesion of the rubber composition to the metal reinforcing cable is obtained, without the need for the use of cobalt salts, stearic acid or zinc oxide.The composition according to the invention therefore preferentially does not contain or contains less than 1 phr, preferably less than 0.5 phr, more preferentially less than 0.2 phr and very preferentially less than 0.1 phr of cobalt salts known to those skilled in the art and whose known effect is to improve the adhesion and its durability.

[0033] Guanidine family of compounds The rubber composition of the reinforced product according to the invention comprises at least one compound of the guanidine family.These compounds are often used in combination with a vulcanization system, a sulfur-based crosslinking system, called vulcanization accelerator.It has now been observed that the presence of at least one compound of the guanidine family in combination with a crosslinking system based on a reinforcing filler mainly containing silica, a polyphenol compound and at least one peroxide compound makes it possible to significantly improve the properties of the reinforced product according to the invention. Preferably, the content of compounds of the guanidine family of the rubber composition ranges from 0.5 to 3 phr, preferentially from 0.5 to 2.5 phr, preferably from 0.5 to 2 phr. Preferentially, the compound of the guanidine family is diphenylguanidine.

[0034] Various additives The rubber composition according to the invention may also contain all or some of the usual additives usually used in rubber compositions for tires in the particular inner layer as defined hereinafter in this patent application, such as plasticizers (plasticizing oils and / or plasticizing resins), reinforcing or non-reinforcing fillers other than those mentioned above, pigments, protective agents (antiozonant waxes, chemical antiozonants, antioxidants, antifatigue agents or reinforcing resins) (for example as described in WO 02 / 10269). Preferably, independently of the other features of the invention, the rubber composition of the reinforced product according to the invention is free of reinforcing resin or contains less than 5 phr, preferably less than 1 phr. These compositions may also contain, in addition to optional coupling agents, coupling activators, agents for coating inorganic fillers or, in general, processing aids capable of improving the ability to process in the uncured state, in a known manner, thanks to an improved dispersion of the filler in the rubber matrix and a reduced viscosity of the composition, such as hydrolyzable silanes, such as alkylalkoxysilanes (e.g. octyltriethoxysilane or octeosilane), polyols, polyethers or hydroxylated or hydrolyzable polyorganosiloxanes.

[0035] Preparation of Rubber Composition The rubber composition according to the invention can be prepared by the following preparation steps, well known to those skilled in the art: - produced in a suitable mixer using a thermomechanical operation or kneading stage that can be carried out in a single thermomechanical step, during which all the necessary components, in particular the elastomer matrix, the polyphenolic compound, the filler and optionally various other additives, are introduced into a suitable mixer, such as a standard internal mixer (for example of the "Banbury" type). The incorporation of the filler into the elastomer can be carried out once or several times during the thermomechanical kneading. When the filler, in particular the carbon black, is already fully or partially incorporated into the elastomer in the form of a masterbatch, as described for example in WO 97 / 36724 and WO 99 / 16600, it is a directly kneaded masterbatch, in which, if appropriate, other elastomers or fillers present in the composition not in the form of a masterbatch, and also optionally various other additives, are incorporated.

[0036] Thermomechanical kneading is carried out at elevated temperatures up to a maximum temperature of between 110° C. and 200° C., preferably between 130° C. and 185° C., for a period generally between 2 and 10 minutes, - A second stage of mechanical working can be carried out continuously in an external mixer, such as an open mill, after cooling the mixture obtained during the first stage, typically to a temperature below 120°C, for example between 40°C and 100°C. The crosslinking system is added during the first or second stage, if the latter is carried out, according to the knowledge of the person skilled in the art. Crosslinking systems based on peroxides or sulfur are usually added during the second stage. The final composition thus obtained is subsequently calendered, for example in the form of sheets or plaques, in particular for laboratory characterization, or else extruded in the form of rubber semi-finished products (or profiled elements). The composition may be in the uncured state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), and may be a semi-finished product that can be used in a tire.

[0037] Curing can be carried out in a manner known to those skilled in the art, generally at temperatures between 130° C. and 200° C., under pressure, for a sufficient time which can vary, for example between 5 and 90 minutes, in particular as a function of the curing temperature, the crosslinking system employed, the kinetics of crosslinking of the composition under consideration, or also the size of the tire. The expression reinforced product "based at least on metal reinforcing elements and on a rubber composition" should be understood to mean a reinforced product comprising reinforcing elements and said composition, the composition being capable of reacting with the surface of the reinforcing elements during the various stages of the manufacture of the reinforced product, in particular during crosslinking of the composition or during the manufacture of the reinforced product prior to crosslinking of the composition. The metallic reinforcing elements are thread-like elements The reinforcing elements are metallic, i.e. made of a metallic material. The rubber composition of the reinforced product according to the invention coats at least a part of the reinforcing elements, preferentially over the entirety of said elements. According to a first variant of the invention, the metal surface of the reinforcing element is made from a material different from the rest of the reinforcing element, in other words the reinforcing element is made from a metal material that is at least partially, preferentially completely, coated with a metal layer that constitutes the metal surface.

[0038] According to a second variant of the invention, the metallic reinforcing elements are manufactured from one and the same material, in which case they are manufactured from a metal that is identical to the metal of the metallic surface. According to one embodiment of the present invention, the metal surface comprises a metal selected from the group consisting of iron, copper, zinc, tin, aluminum, cobalt, nickel and alloys comprising at least one of these metals. The alloys may for example be binary or ternary alloys, such as steel, bronze and brass. Preferably, the metal of the metal surface is iron, copper, tin, zinc or an alloy comprising at least one of these metals. More preferentially, the metal of the metal surface is steel, brass (Cu-Zn alloy), zinc or bronze (Cu-Sn alloy), even more preferably brass or steel, very preferably brass.

[0039] If the metal surface is made of steel, the steel is preferentially carbon steel or stainless steel. If the steel is carbon steel, its carbon weight content is preferably between 0.01% and 1.2%, or between 0.05% and 1.2%, or else between 0.2% and 1.2%, in particular between 0.4% and 1.1%. If the steel is stainless steel, it preferably contains at least 11% chromium and at least 50% iron.

[0040] According to a preferred embodiment, the reinforced product comprises several reinforcing elements as defined above and a calendered rubber consisting of the rubber composition of the reinforced product according to the invention, in which the reinforcing elements are embedded. According to this embodiment, the reinforcing elements are generally arranged side-by-side along a main direction. For the intended application in tires, the reinforced product may thus constitute a tire reinforcement. The reinforced product according to the invention may be in the uncured state (before the crosslinking of the rubber composition) or in the cured state (after the crosslinking of the rubber composition). The reinforced product is cured after contacting the reinforcing element with the rubber composition according to the invention.

[0041] The reinforced product can be made by a process that includes the following steps: - producing two layers of a rubber composition; - sandwiching it (them) with the two layers by depositing a reinforcing element between the two layers. - Optionally, curing the reinforced product. Alternatively, the reinforced product can be made by depositing the reinforcing elements on part of the layers, which are then folded on themselves to cover the reinforcing elements, thereby sandwiching them over their entire length or over part of their length. The layers can be produced by calendering. During the curing of the reinforced product, the rubber composition is crosslinked. If the reinforced product is intended for use as a tire reinforcement, the curing of the reinforced product generally takes place during the curing of the tire outer casing.

[0042] Pneumatic tires Another subject of the present invention is a pneumatic tire, which has the basic feature that it comprises a reinforcement product according to the invention. The tire may be in the green state (before the rubber composition has been crosslinked) or in the cured state (after the rubber composition has been crosslinked). Generally, during the construction of the tire, the reinforcement product is deposited in the green state (i.e. before the rubber composition has been crosslinked) in the structure of the tire before the step of curing the tire. The invention relates in particular to pneumatic tires intended to equip passenger cars, SUVs (Sports Utility Vehicles), or two-wheeled vehicles (especially motorcycles), or aircraft, or also industrial vehicles selected from vans, heavy duty vehicles - i.e. subways, buses, heavy road transport vehicles (lorries, tractors, trailers) or off-road vehicles, such as heavy agricultural vehicles or earthmoving equipment, other motor vehicles. Within a pneumatic tire it is possible to define three types of regions: * The radially outer area in contact with the surrounding air, consisting essentially of the tire tread and the outer sidewall, which is an elastomeric layer located outside the carcass reinforcement with respect to the internal cavity of the tire, between the crown and the bead, so as to completely or partially cover the area of ​​the carcass reinforcement extending from the crown to the bead. * The radially inner region in contact with the inflation gas. This region generally consists of a layer that is gas-tight to the inflation gas, sometimes known as the inner gas-tight layer or innerliner. * The interior region of the tire, i.e. the region between the outer and inner regions, which includes layers or plies referred to herein as the inner layers of the tire, such as the carcass ply, the tread underlayer, the tire belt ply or other layers that are not in contact with the surrounding air or with the inflation gases of the tire.

[0043] The reinforced products according to the invention are particularly suitable for use as reinforcing plies in pneumatic or non-pneumatic tires or in reinforced rubber articles such as conveyor belts or caterpillar tracks. The term "non-pneumatic tire" is understood to mean a tire intended to be mounted on a vehicle and whose shape is maintained by means other than pressurized gas. EXAMPLES

[0044] The procedure for preparing the various rubber compositions whose composition is presented below is as follows: In a first stage, the elastomer and then all other components of the mixture except the crosslinking system are continuously introduced into an internal mixer (final degree of filling: approximately 70% by volume). The initial temperature of the vessel is approximately 60° C. Then, in one step, a thermomechanical work is carried out until a maximum "drop" temperature of 150° C. is reached. The mixture thereby obtained is recovered. In a second stage, it is cooled to 30° C. in an external mixer (homofinisher) and a peroxide-based or sulfur-based crosslinking system is added. The quality of the bond between the rubber composition and the metal reinforcing element is determined by a test that measures the force required to pull a piece of the metal reinforcing agent out of the crosslinked rubber composition. For this purpose, a reinforced product in the form of a test piece is prepared, consisting of a metal reinforcing element and a rubber composition.

[0045] Preparation of test specimens The rubber composition is used to prepare reinforced products in the form of test specimens according to the following protocol: Before curing, a block of rubber is prepared consisting of two staggered platelets. The two platelets of the block are of the same rubber composition. During the preparation of the block, the metal reinforcing elements are trapped between the two platelets in the uncured state, equidistant apart, leaving the ends of the reinforcing elements protruding on either side of the platelets with a length sufficient for the subsequent tensile test. The block including the reinforcing material is then cured. By way of example, in the present case, the block is cured at 160°C under a pressure of 5.5 tons for a time ranging from 5 minutes to 40 minutes, depending on the composition. The individual threads of the metal reinforcing element are light steel threads coated with brass. The metal reinforcing element is an assembly of two individual threads with a diameter of 0.30 mm ("2.30" code) very commonly used in the manufacture of working plies of passenger car type tires; the thickness of the brass coating ranges from 50 nm to 300 nm.

[0046] Adhesion Test Once curing is complete, the test specimen consisting of the crosslinked block and the metal reinforcing element is placed in the jaws of a tensile testing machine adapted to allow separation and testing of each piece at a given speed and at a given temperature (e.g., in this case, 100 mm / min at room temperature). The adhesion level is characterized by measuring the "peel" force to peel the piece from the test specimen. The results are expressed on a basis of 100 relative to control specimens containing metal reinforcing elements of the same nature as the specimens under test. Control specimens are prepared from composition "T1". A value above that of the control specimen, arbitrarily set at 100, indicates an improved result, ie, a peel force above that of the test specimen. With a value of more than 100 in the adhesion test, the reinforced product according to the invention has an improved resistance to peeling after curing of the test specimen, i.e. at t=0, and its durability is improved after aging of the test specimen, i.e. after 21 days at 55° C. and 95% relative humidity.

[0047] Tensile Test These tensile tests make it possible to determine the elastic stress and properties at break of a rubber composition. The tests were carried out in accordance with French standard NF T 46-002 of September 1988. The elongation at break (%) is measured at 23°C.

[0048] Elongation at break measurements are made at t=0 and then after 21 days at 55° C. and 95% relative humidity. Results are expressed on a 100 basis, assigning a value of 100 to the value of the elongation at break of the sample T1 under consideration at t = 0. A result greater than 100 indicates that the composition under consideration exhibits a greater elongation at break than the same composition at t = 0. The compositions according to the invention have a greater elongation at break than the control composition.

[0049] Rolling resistance index The rolling resistance induced by the test composition is evaluated by measuring the energy loss of the sample after the sixth rebound of an initial energy load at a temperature of 60° C., as described in the standard DIN 53-512 of April 2000. This measurement is designated P60 and is calculated as follows: P60(%)=100×(E0−E1) / E0, where E0 represents the initial energy and E1 represents the returned energy. Loss measurements were carried out in air at 60° C. at t=0 and after 21 days at 77° C. The humidity of the air was not controlled and corresponds to that of the ambient air, i.e. between 30% and 50%. Results are expressed on a 100 basis, with a value of 100 being assigned to the value of loss at 60° C. for sample T1 at t=0. A result greater than 100 indicates that the composition under consideration exhibits greater loss than the same composition at t=0, inducing greater rolling resistance. It is observed that the composition according to the invention exhibits less loss at 60° C. than the control composition with comparable extensibility over time.

[0050] Testing resistance to crack growth The cracking rates were measured on specimens of the elastomer compositions using a Type 381 cyclic fatigue machine (Elastomer Test System) from MTS, as described below. The resistance to cracking is measured using repeated tensile movements on specimens that are first mounted (after the first tensile cycle) and then notched. The tensile test specimens consist of parallelepiped-shaped rubber plaques, e.g. with a thickness between 0.5 and 1.5 mm, a length between 60 and 100 mm, and a width between 4 and 8 mm, each of whose two edge sides are longitudinally coated with a cylindrical rubber bead (diameter 5 mm) to allow fixation in the jaws of the tensile test apparatus. The specimens thus prepared are tested after curing and after accelerated ageing in an oven at 77°C for 21 days in a ventilated chamber. The test was carried out at a temperature of 60°C in air. After mounting and before the start of the test, four very fine notches with a length between 5 and 7 mm are made in the middle of the width, aligned along the length of the specimen, with a razor blade, one at each end of the specimen and two on either side of the center of the specimen. Each tensile cycle produces a load of approximately 1500 J / m 2 The strain rate of the specimen is automatically adjusted to keep the rate of energy return (the amount of energy released during the propagation of the crack) constant at a value equal to . The crack growth rate is measured in nanometers per cycle. Results are expressed on a 100 basis relative to the unaged control specimen of composition T1. Values ​​above the unaged control specimen value, arbitrarily set at 100, indicate a degraded result, i.e., a crack growth rate greater than that of the unaged control specimen. When the specimen breaks, it is indicated by the comment "nm" against "not measurable". This comment is stated for specimens that exhibit a low resistance to crack growth. No measurements were made on the specimens of composition C2. It is observed that compositions according to the invention exhibit low crack growth rates, including aged specimens.

[0051] Composition T0 is a composition commonly used in prior art calendering and crosslinked using a sulfur-based system, as presented, for example, in WO 2016 / 058943 and FR 2 981 298 A1.

[0052] Composition T1 corresponds to composition C-2 of WO 2020 / 058613. Composition T2 is similar, contains a lower tannic acid content, and shows a performance in terms of metal adhesion and a lower elongation at break relative to T1. Composition T3 is a composition that shows similar adhesive performance to composition T2 and contains silica as a reinforcing filler. In this system, contrary to the effect of silica known to those skilled in the art, it can be seen that the hysteresis loss of composition T3 is higher compared to composition T2. ​​Compositions C1 to C4 are compositions according to the invention.

[0053] [Table 1]

Claims

1. A reinforced product based on at least one metal reinforcing element embedded in a rubber composition, said rubber composition being based on at least one diene elastomer, a reinforcing filler mainly comprising silica, a crosslinking system based on at least one peroxide compound, at least one non-elastomeric polyphenol compound containing at least three benzene rings, each having at least two vicinal hydroxyl groups, and at least one compound of the guanidine family.

2. 2. Reinforced product according to claim 1, wherein the polyphenolic compound is selected from gallotannins, preferably from esters of gallic acid with polyols selected from pentose and hexose sugars.

3. 2. The reinforced product of claim 1, wherein the polyphenol compound content of the rubber composition ranges from 0.1 to 30 phr, preferably from 5 to 20 phr, and in a preferred manner from 5 to 15 phr.

4. 2. Reinforced product according to claim 1, wherein the content of compounds of the guanidine family ranges from 0.5 to 3 phr, preferentially from 0.5 to 2.5 phr, preferably from 0.5 to 2 phr.

5. 2. The reinforced product of claim 1, wherein the rubber composition comprises less than 5 phr, preferably less than 1 phr, and highly preferably no functionalized elastomer.

6. 10. The reinforced product of claim 1, wherein the rubber composition is free of molecular sulfur or contains less than 1 phr of molecular sulfur.

7. 2. Reinforced product according to claim 1, wherein the rubber composition is free of zinc or zinc oxide or contains only small amounts of zinc or zinc oxide, preferentially less than 1 phr, preferably less than 0.5 phr, more preferentially less than 0.2 phr.

8. 2. The reinforced product of claim 1, wherein the rubber composition comprises from 0.01 to 10 phr, preferentially from 1 to 5 phr, of a peroxide compound.

9. A rubber article comprising the reinforced product of any one of claims 1 to 8.

10. 10. The rubber article of claim 9, selected from pneumatic and non-pneumatic tires, conveyor belts and caterpillar tracks.