Rubber composition based on epoxy resin and curing agent with high latency

Abstract

The present invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, and a crosslinking system, and comprising an epoxy resin and a high-latency curing agent.

Description

[Technical Field]

[0001] The present invention relates in particular to a rubber composition intended for the manufacture of tires or semi-finished products for tires. Other subjects of the invention are finished or semi-finished rubber articles comprising a rubber composition according to the invention, as well as pneumatic or non-pneumatic tires comprising at least one composition according to the invention. [Background technology]

[0002] As presented in WO 02 / 10269, it is known to use rubber compositions in some components of pneumatic tires that exhibit high stiffness during small strains of the pneumatic tire. Resistance to small strains is one of the properties that a pneumatic tire must exhibit in order to respond to the pressures to which it is subjected. This stiffening can be obtained by increasing the content of reinforcing fillers or by incorporating certain reinforcing resins in the rubber composition components of the pneumatic tire. The reinforcing resins traditionally used to increase the stiffness of compositions are those based on methylene acceptor / donor systems. The terms "methylene acceptor" and "methylene donor" are well known to those skilled in the art and are widely used to denote compounds that can react together to produce, by condensation, a three-dimensional reinforcing resin that is superimposed and penetrated by a reinforcing filler / elastomer network on the one hand and an elastomer / sulfur network (when the crosslinker is sulfur) on the other. Traditionally, the methylene acceptor is a phenolic resin. Phenolic novolac resins have already been described in rubber compositions for various applications, particularly for pneumatic tires or treads of pneumatic tires, as well as for grip or reinforcement; see, for example, EP-A-0 649 446. The methylene acceptor is combined with a curing agent capable of crosslinking or curing the methylene acceptor, commonly known as a "methylene donor." Then, during curing of the rubber matrix, crosslinking of the resin occurs due to the formation of methylene bridges between the ortho- and para-carbons of the resin's phenolic nucleus and the methylene donor, thus creating a three-dimensional resin network. Conventionally used methylene donors are hexamethylenetetramine (abbreviated HMT), hexamethoxymethylmelamine (abbreviated HMMM or H3M), or hexaethoxymethylmelamine.

[0003] However, the combination of a methylene acceptor phenolic resin and a methylene donor such as HMT or H3M produces formaldehyde during crosslinking of the rubber composition. Indeed, due to the potential environmental impact of these compounds, it is desirable in the long term to reduce or even eliminate formaldehyde from rubber compositions. To this end, alternative compositions have been developed to conventional compositions containing a methylene acceptor formaldehyde / phenolic resin pair with a methylene donor HMT or H3M curing agent. For example, International Publication No. 2011 / 045342 describes compositions containing an epoxy resin pair with an amine-containing curing agent. These compositions, in addition to the advantage of being free from formaldehyde formation, exhibit higher stiffness after crosslinking than conventional compositions while maintaining acceptable rolling resistance. International Publication No. 2018 / 002538 describes compositions aimed at improving the compromise between processability, particularly scorch time and stiffness, compared to known compositions, containing an epoxy resin and an amine-containing curing agent containing at least two primary amine functional groups located on at least one six-membered aromatic ring. Summary of the Invention

[0004] However, once crosslinked (or "cured"), it is always desirable to be able to reduce the amount of additives used, particularly curatives, and to improve the processability of the raw rubber composition, while maintaining the reinforcing properties of the composition throughout the operating temperatures of a pneumatic tire. Surprisingly, during its research, the applicant company discovered that the combination of an epoxy resin and a urea compound allows for the elimination of formaldehyde formation while maintaining the reinforcing properties at different operating temperatures of pneumatic tires and improving the processability of the raw composition. DETAILED DESCRIPTION OF THE INVENTION

[0005] The present invention relates to at least one of the following embodiments: 1. A rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, 1 to 30 parts by weight per 100 parts by weight of elastomer (phr) of an epoxy resin, and a urea compound of the general formula (R1R2)N-CO-(NR3)-R7-(NR4)-CO-N(R5R6), where each R1 to R6 group is independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms, and an aralkyl group having 7 to 25 carbon atoms, where the R2 and R3 groups on the one hand and the R4 and R5 groups on the other hand can together form a ring, and the R7 group is a divalent aryl group having 6 to 30 carbon atoms. 2. The rubber composition according to embodiment 1, wherein each R1-R6 group is independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an aralkyl group having 7 to 9 carbon atoms, and the R7 group is a divalent aryl group having 6 to 8 carbon atoms. 3. The rubber composition of embodiment 1 or 2, wherein the R7 group is a divalent methylphenyl group.

[0006] 4. The rubber composition of any one of embodiments 1 to 3, wherein the R1 to R7 groups do not join together to form a ring. 5. The rubber composition of any one of embodiments 1 to 4, wherein each R3 and R4 group is a hydrogen atom. 6. A rubber composition according to any one of embodiments 1 to 5, in which at least one R1, R2, R5 or R6 group is an aryl group having 6 to 8 carbon atoms, preferentially a phenyl group. 7. The rubber composition of any one of embodiments 1 to 5, wherein the R1, R2, R5, and R6 groups are independently selected from methyl and ethyl groups. 8. The rubber composition according to embodiment 1, wherein the R1, R2, R5 and R6 groups are methyl groups, R3 and R4 are hydrogen atoms, and R7 is a divalent methylphenyl group. 9. The rubber composition according to any one of embodiments 1 to 8, wherein the content of the urea compound is in the range of 1 to 15 phr, preferably 0.5 to 10 phr, preferably 0.5 to 8 phr, preferably 0.5 to 5 phr. 10. The rubber composition according to any one of the preceding embodiments, wherein the diene elastomer is selected from the group consisting of polybutadiene, natural rubber, synthetic polyisoprene, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers, preferentially being an isoprene elastomer.

[0007] 11. The rubber composition according to any one of embodiments 1 to 10, wherein the epoxy resin is selected from aromatic epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins. 12. The rubber composition according to any one of embodiments 1 to 11, wherein the content of epoxy resin is between 10 and 25 phr, preferably between 10 and 20 phr. 13. The rubber composition according to any one of embodiments 1 to 12, which is free of nitrile compounds or contains less than 10 phr, preferably less than 5 phr, preferably less than 2 phr of nitrile compounds. 14. The rubber composition according to any one of embodiments 1 to 13, wherein the reinforcing filler content is in the range of 20 to 200 phr, preferably 30 to 150 phr. 15. A finished or semi-finished rubber article comprising the rubber composition of any one of embodiments 1-14. 16. A pneumatic or non-pneumatic tire comprising the rubber composition of any one of embodiments 1-14. 17. The tire of embodiment 16, comprising an inner layer comprising the rubber composition of any one of embodiments 1-14.

[0008] definition The expression "parts by weight per 100 parts by weight of elastomer" (or phr) is to be understood within the meaning of the present invention as meaning parts by weight per 100 parts by weight of elastomer or rubber. In this document, all percentages (%) specified are percentages (%) by mass unless expressly specified 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., the limits a and b are excluded), 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 exact limits a and b). The expression "composition based on" should be understood to mean a composition comprising a mixture and / or the product of in situ reactions of the various components used, some of which can and / or are intended to react with one another at least partially during the various phases of the preparation of the composition. The composition can therefore be in a fully or partially crosslinked or non-crosslinked state.

[0009] When referring to a "major" compound, it is understood within the meaning of the present invention to mean that the compound is the major compound among the compounds of the same type in the composition, i.e., the compound with the largest mass among the compounds of the same type. Thus, for example, the major elastomer is the elastomer with the largest mass relative to the total mass of elastomers in the composition. Similarly, a "major" filler is the filler with the largest mass among the fillers of the composition. For example, in a system containing only one elastomer, it is the major compound within the meaning of the present invention, and in a system containing two elastomers, the major elastomer represents more than half of the mass of the elastomer. In contrast, a "minor" compound is a compound that does not represent the largest mass fraction among the compounds of the same type. Preferably, the term "major" is understood to mean that the compound is present in an amount of more than 50%, preferably more than 60%, 70%, 80%, or 90%, and more preferentially the "major" compound is 100%. The carbon-containing compounds referred to in the specification may be fossil-derived or bio-based. In the latter case, the carbon-containing compounds may be partially or completely derived from biomass or may be obtained from renewable starting materials derived from biomass, particularly polymers, plasticizers, fillers, etc.

[0010] Diene Elastomer The composition according to the invention comprises at least one diene elastomer. It may therefore contain only one diene elastomer or a mixture of several diene elastomers. "Diene" elastomers (or rubbers in any case) are to be understood as meaning elastomers (i.e. homopolymers or copolymers) which, in a known manner, consist at least in part of diene monomer units (monomers having two conjugated or non-conjugated carbon-carbon double bonds), whether natural or synthetic. These diene elastomers can be divided into two categories: "essentially unsaturated" or "essentially saturated." The term "essentially unsaturated" is generally understood to mean diene elastomers derived at least in part from conjugated diene monomers with a content of units of diene origin (conjugated dienes) of more than 15% (mol%). Thus, diene elastomers, such as butyl rubber or EPDM-type copolymers of dienes and α-olefins, do not fall within the scope of the above definition and can in particular be described as "essentially saturated" diene elastomers (low or very low content of units of diene origin, always less than 15%). The diene elastomers contained in the composition according to the invention are preferentially essentially unsaturated.

[0011] Diene elastomers that may be used in the compositions according to the invention are in particular: (a) any homopolymer of conjugated or non-conjugated diene monomers having from 4 to 18 carbon atoms; (b) any copolymer of a conjugated or non-conjugated diene having from 4 to 18 carbon atoms with at least one other monomer; is understood to mean The other monomer may be ethylene, an olefin, or a conjugated or non-conjugated diene. Suitable conjugated dienes are those having 4 to 12 carbon atoms, in particular 1,3-dienes, such as, in particular, 1,3-butadiene and isoprene.

[0012] Suitable as olefins are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms. Suitable vinyl aromatic compounds are, for example, styrene, orthomethylstyrene, metamethylstyrene, paramethylstyrene, the "vinyltoluene" commercial mixture, or para(tert-butyl)styrene. Suitable aliphatic α-monoolefins are in particular acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms. Preferentially, the diene elastomer is selected 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 selected from the group consisting of butadiene / styrene copolymers (SBR). Preferably, the diene elastomer is an isoprene elastomer.

[0013] The term "isoprene elastomer" is understood in a known manner to mean a homopolymer or copolymer of isoprene, in other words a diene elastomer selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), various isoprene copolymers, and mixtures of these elastomers. Among the isoprene copolymers, particular mention is made of isobutene / isoprene (butyl rubber - IIR) copolymers, isoprene / styrene (SIR) copolymers, isoprene / butadiene (BIR) copolymers, 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. Among these synthetic polyisoprenes, polyisoprenes with a cis-1,4-bond content (mol%) of more than 90%, more preferentially more than 98%, are preferably used. Preferably, and according to any one of the configurations of this document, the diene elastomer is natural rubber. Preferentially, the content of diene elastomer, preferably the content of isoprene elastomer, preferably the content of 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 the content of isoprene elastomer, more preferably the content of 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 further contain, to a lesser extent, any kind of synthetic elastomer other than diene elastomers, and may even contain non-elastomeric polymers, for example 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.

[0014] Epoxy resin The epoxy resins that can be used in the present invention include all polyepoxide compounds. They can be, for example, aromatic epoxy resins, cycloaliphatic epoxy resins, and aliphatic epoxy resins. For example, the aromatic epoxy resin can be an amine-aromatic epoxy resin. The epoxy resin is preferentially an epoxy novolac resin, i.e., an epoxy resin obtained by acid catalysis, as opposed to a resole resin obtained by base catalysis. In particular, among aromatic epoxy resins, epoxy resins selected from the group consisting of 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)], aromatic amine epoxy resins, and mixtures of these compounds are preferred, and epoxy resins selected from the group consisting of poly[(o-cresyl glycidyl ether)-co-formaldehyde and poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)] are more preferred. Again preferably, the epoxy resin is selected from the group consisting of poly[(o-cresyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-formaldehyde], aromatic amine epoxy resins, and mixtures of these compounds.

[0015] As examples of commercially available epoxy resins that can be used in the context of the present invention, mention may be made, for example, of the epoxy resin DEN 439 from Uniqema, the epoxy resin tris(4-hydroxyphenyl)methane triglycidyl ether from Sigma-Aldrich, the epoxy cresol novolac resin Araldite ECN 1299 from Huntsman, or the epoxy phenol novolac resin Araldite EPN 1138 from Huntsman. The composition according to the invention contains between 1 and 30 phr of epoxy resin. Below the minimum resin content specified in terms of the amine-containing hardener used in the context of the invention, the desired technical effect is insufficient, while above the maximum specified limit there is a risk of an excessively large increase in stiffness and excessive damage to the hysteresis and extensibility properties of the material. For all these reasons, the epoxy resin content is preferentially between 10 and 25 phr. More preferably, the epoxy resin content in the composition according to the invention is between 10 and 20 phr.

[0016] Highly Latent Hardener The epoxy resin of the composition of the present invention is combined with a specific hardener, typically a urea compound, which enables the resin to crosslink. According to the present invention, the curing agent has the general formula (R1R2)N—CO—(NR3)—R7—(NR4)—CO—N(R5R6), where each R1 to R6 group is independently: hydrogen atoms, alkyl groups having 1 to 20 carbon atoms; cycloalkyl groups having 5 to 24 carbon atoms, aryl groups having 6 to 30 carbon atoms, and aralkyl groups having 7 to 25 carbon atoms, is selected from the group consisting of The R2 and R3 groups on the one hand and the R4 and R5 groups on the other hand can together form a ring, and the R7 group is a divalent aryl group having 6 to 30 carbon atoms. It is a urea compound.

[0017] In the general formula (R1R2)N-CO-(NR3)-R7-(NR4)-CO-N(R5R6), it is understood that the CO group is a carbon atom bonded to an oxygen atom via a double bond, the (R1R2)N (similarly N(R5R6)) group is a nitrogen atom bonded to the R1 and R2 groups via a covalent bond, the (NR3) (similarly (NR4)) group is a nitrogen atom bonded to the R3 group via a covalent bond, and the R7 group is a divalent group bonded on the one hand to the nitrogen atom carrying the R3 group and on the other hand to the nitrogen atom carrying the R4 group. Preferably, each R1 to R6 group is independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an aryl group having 6 to 8 carbon atoms, and an aralkyl group having 7 to 9 carbon atoms, and the R7 group is a divalent aryl group having 6 to 8 carbon atoms. Preferably, the R7 group is a divalent methylphenyl group. Preferably, the R1 to R7 groups do not together form a ring. Preferably, each R3 and R4 group is a hydrogen atom. In a preferred configuration, at least one R1, R2, R5 or R6 group is an aryl group having 6 to 8 carbon atoms, preferentially a phenyl group.

[0018] In another preferred configuration, the R1, R2, R5 and R6 groups are independently selected from methyl and ethyl groups. Preferably, the R1, R2, R5 and R6 groups are methyl groups, the R3 and R4 groups are hydrogen atoms, and the R7 group is a divalent methylphenyl group. An example of such a diurea compound is Amicure UR2T, a compound of formula 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) from Evonik. The amount of urea compound in the rubber composition is in the range of 1 to 15 phr. Below the specified minimum limit, the desired technical effect proves to be insufficient, while above the specified maximum limit, there is a risk that the raw processing of the composition is unfavorable. Preferentially, the urea content is in the range of 0.5 to 10 phr, preferably 0.5 to 8 phr, and preferably 0.5 to 5 phr.

[0019] Reinforcing filler The composition according to the invention preferentially comprises a reinforcing filler. The reinforcing filler may comprise any type of reinforcing filler known for its ability to reinforce rubber compositions used in the manufacture of pneumatic tires, such as organic fillers such as carbon black, reinforcing inorganic fillers such as silica, or a mixture of carbon black and reinforcing inorganic fillers. More preferentially, particularly when the composition is used in an inner layer, the reinforcing filler comprises primarily, or even exclusively, carbon black. Particularly when the composition is used in a tread, the reinforcing filler may also comprise primarily a reinforcing inorganic filler. Such reinforcing fillers typically consist of particles whose (mass) mean diameter is submicrometric, generally less than 500 nm, usually between 20 and 200 nm, in particular and more preferentially between 20 and 150 nm. Suitable carbon blacks are any carbon black conventionally used in pneumatic tires, in particular blacks of the HAF, ISAF or SAF type ("tire grade" blacks). Among the latter, mention is made in particular of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as N115, N134, N234, N326, N330, N339, N347 or N375 blacks, or even higher series blacks (e.g., N660, N683 or N772), depending on the intended application. The carbon black may already be incorporated into the isoprene elastomer, for example, in the form of a masterbatch (see, for example, WO 97 / 36724 or WO 99 / 16600). The BET specific surface area of ​​carbon black is measured in accordance with standard D6556-10 [multipoint (minimum 5 points) method - gas: nitrogen - relative pressure p / p0 range: 0.1 to 0.3].

[0020] "Reinforcing inorganic filler" is to be understood as meaning any inorganic or mineral filler (irrespective of its color and origin, natural or synthetic), known as "white filler" or "transparent filler" or even "non-black filler" in contrast to carbon black, by definition in this patent application, which is capable of reinforcing rubber compositions intended for the manufacture of pneumatic tires, without any means other than intermediate coupling agents, in other words, capable of replacing ordinary tire-grade carbon black in its reinforcing role. Such fillers are generally characterized in a known manner by the presence of hydroxyl (-OH) groups on their surface. Siliceous mineral fillers, in particular silica (SiO2), or aluminous mineral fillers, in particular alumina (Al2O3), are particularly suitable as reinforcing inorganic fillers. The silica used may be any reinforcing silica known to those skilled in the art, in particular one having a BET surface area and a CTAB specific surface area of ​​at least 450 m 2 / g or less, preferably 30 to 400m 2 / g。 Highly disperse precipitated silica ("HDS") is mentioned, for example, Degussa silica, Ultrasil 7000 and Ultrasil 7005, Rhodia silica, Zeosil 1165MP, 1135MP and 1115MP, PPG silica, Hi-Sil EZ150G, Huber silica, Zeopol 8715, 8745 and 8755, or silicas with a high specific surface area as described in WO 03 / 16837.

[0021] The BET specific surface area of ​​the silica is determined by gas adsorption in a known manner using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society", Vol. 60, p. 309, February 1938, more specifically in accordance with French standard NF ISO 9277 of December 1996 (multipoint (5-point) volumetric method - gas: nitrogen - degassing: 1 hour at 160 °C - relative pressure p / p range: 0.05 to 0.17). The CTAB specific surface area of ​​the silica is determined in accordance with French standard NF T45-007 of November 1987 (method B). Mineral fillers of the aluminous type, in particular alumina (Al2O3) or aluminium hydroxide (oxide), or reinforcing titanium oxide, as described, for example, in US Pat. Nos. 6,610,261 and 6,747,087, are also suitable as reinforcing inorganic fillers. The physical state in which the reinforcing inorganic filler is provided is not important, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Naturally, the term "reinforcing inorganic filler" is also understood to mean a mixture of different reinforcing inorganic fillers, in particular highly dispersed siliceous and / or aluminous fillers.

[0022] Those skilled in the art will understand that reinforcing fillers of another nature, especially organic reinforcing fillers, which are covered with an inorganic layer, e.g., silica, or which otherwise contain functional sites, especially hydroxyl sites, on their surface, allowing the establishment of bonds between the filler and the elastomer, with or without the presence of a coating or coupling agent, may be used as fillers equivalent to the reinforcing inorganic fillers described in this section. To couple the reinforcing inorganic filler to the diene elastomer, at least bifunctional coupling agents (or bonding agents) intended to provide sufficient chemical and / or physical bonding between the inorganic filler (the surface of its particles) and the diene elastomer may be used in a known manner. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. "Bifunctional" 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 bifunctional compound may 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.

[0023] Preferentially, the organosilane is selected from the group consisting of (symmetrical or asymmetrical) organosilane polysulfides, such as bis(3-triethoxysilylpropyl)tetrasulfide (abbreviated TESPT, sold by Evonik under the name Si69) or bis(3-triethoxysilylpropyl)disulfide (abbreviated TESPD, sold by Evonik under the name Si75), polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl)octanethioate (sold by Momentive under the name NXT Silane). More preferentially, the organosilane is an organosilane polysulfide. The content of the coupling agent is preferably less than 12 phr, and it is generally understood that it is desirable to use as little as possible. Typically, when a reinforcing inorganic filler is present, the content of the coupling agent is 0.5% to 15% by mass relative to the amount of the inorganic filler. The content is preferably in the range of 0.5 to 15 phr. The content can be easily adjusted by those skilled in the art according to the content of the inorganic filler used in the composition. According to the invention, the content of reinforcing fillers, if present, which preferably mainly or even exclusively comprise carbon black, may be in the range of 20 to 200 phr, preferably 30 to 150 phr, preferably 40 to 100 phr, preferably 50 to 80 phr.

[0024] Crosslinked system The crosslinking system may be of any type known to those skilled in the art of rubber compositions for pneumatic tires, and may in particular be based on sulfur and / or peroxides and / or bismaleimides. Preferentially, the crosslinking system is based on sulfur, and is then called a vulcanization system. The sulfur may be provided in any form, in particular in the form of molecular sulfur or a sulfur donor. At least one vulcanization accelerator is also preferably present, and optionally, also preferentially, various known vulcanization activators, such as zinc oxide, stearic acid or equivalent compounds, for example, stearates, and salts of transition metals, guanidine derivatives (in particular, diphenylguanidine), or known vulcanization retarders may also be used. Sulphur is used in a content preferably between 0.5 and 12 phr, in particular between 1 and 10 phr. Vulcanisation accelerators are used in a content preferably between 0.5 and 10 phr, more preferably between 0.5 and 8.0 phr.

[0025] As accelerators, any compound capable of acting as an accelerator of the vulcanization of diene elastomers in the presence of sulfur can be used, in particular accelerators of the thiazole type, as well as their derivatives, or accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type. As examples of such accelerators, mention may be made in particular of the following compounds: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazole sulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazole sulfenamide ("DCBS"), N-(tert-butyl)-2-benzothiazole sulfenamide ("TBBS"), N-(tert-butyl)-2-benzothiazole sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD"), zinc dibenzyldithiocarbamate ("ZBEC"), and mixtures of these compounds.

[0026] Various additives The rubber composition according to the present invention may also contain all or some of the usual additives and processing aids known to those skilled in the art and generally used in rubber compositions for pneumatic tires, such as plasticizers (e.g., plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical antiozonants or antioxidants or anti-fatigue agents. Preferably, the composition according to the invention is free of nitrile compounds or comprises less than 10 phr, preferably less than 5 phr, preferably less than 2 phr, very preferably less than 1 phr and more preferentially less than 0.5 phr of nitrile compounds. The composition may be in the raw state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization).

[0027] Finished or semi-finished rubber articles and pneumatic tires Another subject of the present invention is a finished or semi-finished rubber article comprising a composition according to the invention. Another subject of the invention is a pneumatic tire comprising a composition according to the invention. Three types of regions can be defined within a pneumatic tire: The radially outer area in contact with the ambient air, including the layer called the "outer layer", which essentially comprises the tread and outer sidewall of a pneumatic tire. The outer sidewall is an elastomeric layer located outside the carcass reinforcement relative to the internal cavity of the pneumatic tire, between the crown and the bead, and therefore completely or partially covering the area of ​​the carcass reinforcement extending from the crown to the bead. A radially inner region in contact with the inflation gas, sometimes called an inner airtight layer or inner liner, generally consisting of a layer that is airtight to the inflation gas. The interior region of a pneumatic tire, i.e., the region between the outer and inner regions, which includes layers or plies referred to herein as the inner layer of the pneumatic tire, such as the carcass ply, the undertread ply, the pneumatic tire belt ply, or any other layer that is not in contact with the ambient air or inflation gas of the pneumatic tire.

[0028] The compositions defined herein are particularly well suited for the inner and outer layers of pneumatic tires, and for the outer layer in particular for tread compositions. According to the present invention, the inner layer may be selected from the group consisting of a carcass ply, a crown ply, a bead wire filler, a crown feet, a decoupling layer, an edge rubber, a pad rubber, a tread underlayer, and a combination thereof. Preferably, the inner layer is selected from the group consisting of a carcass ply, a crown ply, a bead wire filler, a crown feet, a decoupling layer, and a combination thereof. The compositions according to the invention may also be suitable for the inner and outer layers of non-pneumatic tires, in particular the treads of non-pneumatic tires. It should be noted that a non-pneumatic tire is a tire that supports the load of a vehicle by means other than pressurized inflation gas.

[0029] The invention relates in particular to pneumatic tires intended to equip passenger vehicles, SUVs (Sports Utility Vehicles), or two-wheeled vehicles (especially motorcycles) of the type, or aircraft, or even vans, heavy vehicles, i.e. subways, buses, heavy road vehicles (trucks, tractors, trailers), or off-road vehicles, industrial vehicles, for example selected from heavy agricultural or construction vehicles, or other motor vehicles. The present invention relates to articles of manufacture comprising the rubber composition according to the invention, both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

[0030] Preparation of Rubber Composition The rubber compositions according to the invention can be prepared in a suitable mixer using two successive preparation phases well known to those skilled in the art: - a first phase ("non-productive" phase) of thermomechanical processing or thermomechanical kneading, which can be carried out in a single thermomechanical step, during which all necessary components, in particular the elastomer matrix, the filler, and various other optional additives, except the crosslinking system, are introduced into a suitable mixer, for example a standard internal mixer (for example, of the "Banbury" type). The incorporation of the filler into the elastomer can be carried out in one or several rounds by thermomechanical kneading. For example, if the filler is already fully or partially incorporated into the elastomer in the form of a masterbatch, as described in WO 97 / 36724 and WO 99 / 16600, it is the masterbatch that is kneaded directly, incorporating, if appropriate, other elastomers or fillers present in the composition that are not in the form of a masterbatch, as well as various other optional additives, except the crosslinking system. The non-productive phase is carried out at elevated temperatures up to a maximum temperature between 110°C and 190°C, preferably between 130°C and 180°C, for a period generally between 2 and 10 minutes. - The mixture obtained in the first non-productive phase is cooled to a lower temperature, typically below 110°C, for example between 40°C and 100°C, before a second phase of machining ("productive" phase) which takes place in an external mixer, for example an open mill. The crosslinking system is then incorporated, and everything is mixed for a few minutes, for example between 2 and 15 minutes.

[0031] A process for preparing such a composition may, for example, comprise the following steps: a) incorporating the reinforcing filler in the diene elastomer during a first phase ("non-productive" phase) and kneading everything thermomechanically (e.g., in one or more rounds) until a maximum temperature of between 110°C and 190°C is reached; b) cooling the combined mixture to a temperature below 100°C; c) subsequently incorporating the crosslinking system during a second step (the "production" phase); d) Mix everything to a maximum temperature of less than 110°C Includes. Between 1 and 30 phr of epoxy resin and between 1 and 15 phr of urea compound may be introduced independently of one another either in the non-productive phase (a) or in the productive phase (c). Preferably, the epoxy resin is introduced in the non-productive phase (a) and the high-latency hardener is introduced in the productive phase (c). The final composition so obtained can then be calendered, for example, in the form of sheets or plaques, in particular for laboratory characterization, or extruded in the form of semi-finished rubber products (or profiled elements) used in the manufacture of pneumatic tires. Crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at temperatures between 130°C and 200°C under pressure. [Example]

[0032] Measurements and tests used Scorch Time The measurements are carried out at 130° C. in accordance with French standard NF T43-005. The change in the consistency measurement index as a function of time is evaluated according to said standard by the parameter T5 (for large rotors), expressed in minutes, and allows the identification of the scorch time of the rubber composition, defined as the time required to obtain an increase in the consistency measurement index (expressed in MU) of 5 units above the minimum value measured for that index. It should be noted that, as is well known to those skilled in the art, the higher the consistency measurement index as a function of time, the slower the crosslinking of the material before curing.

[0033] Mooney Plasticity A vibratory consistency meter is used as described in French standard NF T43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the green state (i.e. before hardening) is molded in a cylindrical chamber heated to 100°C. After preheating for 1 minute, a rotor rotates in the test body at 2 revolutions per minute and, after 4 minutes of rotation, the operating torque required to maintain its movement is measured. The Mooney plasticity (ML1+4) is expressed in "Mooney units" (MU, 1 MU = 0.83 Newton meters). It should be noted that, as is well known to those skilled in the art, the lower the Mooney plasticity, the easier the material is to process. Of course, above a certain value (e.g., 20 MU), the material becomes too fluid to be usable, especially for the manufacture of inner layers.

[0034] Tensile test The tests were carried out in accordance with French standard NF T46-002 of September 1988. All tensile measurements were carried out under standard hygrometric conditions (50±5% relative humidity) at a temperature representative of the operating temperature of the composition in a tire (100±2°C), in accordance with French standard NF T40-101 (February 1979). Using specimens cured at 150°C for 60 minutes, the nominal secant modulus (or apparent stress (MPa)) calculated by converting to the initial cross-sectional area of ​​the specimen at the second elongation (i.e., after adaptation) was measured at 100% elongation (denoted MA100) and 300% elongation (denoted MA300). The MA300 / MA100 ratio, which represents the reinforcement, is given in the table.

[0035] Preparation of the Composition The following tests are carried out as follows: the diene elastomer, the reinforcing filler, between 1 and 30 phr of epoxy resin, as well as various other additives, excluding the crosslinking system, are introduced in succession into an internal mixer (final filling level: approximately 70% by volume), the initial container temperature being approximately 60°C. Thermomechanical processing (non-productive phase) is then carried out in one step, taking approximately 3-4 minutes in total, until a maximum "let-down" temperature of 165°C is reached. The mixture so obtained is recovered and cooled, then sulfur, a sulfenamide type accelerator and a high-latency hardener are added to a mixer (homofinisher) at 30°C, and all is mixed for an appropriate time (for example, between 5 and 12 minutes) (production phase). The compositions so obtained are then calendered into either rubber plaques (2-3 mm thick) or thin sheets, or extruded into specific cross-sectional shaped elements for measurement of physical or mechanical properties. The crosslinking of the composition is carried out at a temperature of 150° C. for 60 minutes under pressure.

[0036] Test using rubber composition Two rubber compositions were prepared as described above, one according to the invention (hereinafter referred to as C-2) and one not according to the invention (control composition, hereinafter referred to as C-1), whose formulations (phr) and properties are summarized in Table 1 below. With the exception of control composition C-1, the compositions shown in this Table 1 do not result in the formation of formaldehyde during cure. Composition C-2 contains an epoxy resin and a urea compound in place of the phenol / formaldehyde resin-HMT hardener pair present in the conventional control composition C-1. All results are expressed on a basis of 100, with the control composition C-1 as the standard. A value less than 100 means that the value is lower than the value of the control composition, and a value greater than 100 means that the value is higher than the value of the control composition.

[0037] [Table 1]

[0038] It is pointed out that the compositions according to the invention make it possible to obtain a similar reinforcing effect to the control composition, using a smaller amount of curing agent, while at the same time showing an increase in scorch time and a decrease in Mooney viscosity, and therefore improved processability.

Claims

1. at least one diene elastomer, a reinforcing filler, a sulfur-based crosslinking system, 1 to 30 parts by weight per 100 parts by weight of elastomer (phr) of an epoxy resin, and an epoxy resin of the general formula (R 1 R 2 )N—CO—(NR 3 )-R 7 - (NR 4 )-CO-N(R 5 R 6 ) (wherein, each R 1 ~R 6 groups are independently selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 24 carbon atoms, an aryl group having 6 to 30 carbon atoms, and an aralkyl group having 7 to 25 carbon atoms, while R 2 Groups and R 3 On the other hand, the group R 4 Groups and R 5 The groups can be joined together to form a ring, and R 7 The group is a divalent aryl group having 6 to 30 carbon atoms.

2. Each R 1 ~R 6 groups are independently selected from the group consisting of hydrogen atoms, alkyl groups having 1 to 3 carbon atoms, aryl groups having 6 to 8 carbon atoms, and aralkyl groups having 7 to 9 carbon atoms; 7 2. The rubber composition of claim 1, wherein the group is a divalent aryl group having 6 to 8 carbon atoms.

3. The R 7 3. The rubber composition according to claim 1, wherein the group is a divalent methylphenyl group.

4. The R 1 ~R 7 The rubber composition according to any one of claims 1 to 3, wherein the groups do not combine together to form a ring.

5. Each R 3 and R 4 The rubber composition according to any one of claims 1 to 4, wherein the group is a hydrogen atom.

6. The R 1 , R 2 , R 5 and R 6 group is a methyl group, and R 3 and R 4 is a hydrogen atom, and R 7 The rubber composition according to claim 1, wherein is a divalent methylphenyl group.

7. The rubber composition according to any one of claims 1 to 6, wherein the content of the urea compound is within a range of 1 to 15 phr.

8. The rubber composition according to any one of claims 1 to 7, which is free of nitrile compounds or contains less than 10 phr of nitrile compounds.

9. A finished or semi-finished rubber article comprising the rubber composition of any one of claims 1 to 8.

10. A pneumatic or non-pneumatic tire comprising the rubber composition according to any one of claims 1 to 8.

Images