WO2021181032A1

WO2021181032A1 - Rubber composition based on epoxy resin and a hardener having high latency

Info

Publication number: WO2021181032A1
Application number: PCT/FR2021/050370
Authority: WO
Inventors: Séverine BIZET; Fabien Bonnette; Emmanuel LANDREAU
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2020-03-10
Filing date: 2021-03-04
Publication date: 2021-09-16
Also published as: EP4117937A1; FR3108118A1; FR3108118B1; CA3168388A1; JP2023517609A; CN115243906A

Abstract

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

Description

RUBBER COMPOSITION BASED ON EPOXIDE RESIN AND HIGH LATENCY HARDENER

Technical field of the invention

The present invention relates to rubber compositions intended in particular for the manufacture of tires or of semi-finished products for tires. A subject of the present invention is also a finished or semi-finished rubber article comprising a rubber composition according to the invention, as well as a pneumatic or non-pneumatic tire comprising at least one composition according to the invention.

Prior art

It is known to use, in certain parts of pneumatic tires, rubber compositions exhibiting high rigidity during low deformation of the pneumatic tire, as presented in application WO 02/10269. Resistance to low deformation is one of the properties that a pneumatic tire must exhibit in order to respond to the stresses to which it is subjected.

This stiffening can be obtained by increasing the rate of reinforcing filler or by incorporating certain reinforcing resins in the rubber compositions constituting the parts of the tire.

The reinforcing resins conventionally used to increase the rigidity of compositions are reinforcing resins based on a methylene acceptor / donor system. The terms “methylene acceptor” and “methylene donor” are well known to those skilled in the art and widely used to denote compounds capable of reacting together to generate, by condensation, a three-dimensional reinforcing resin which comes to be superimposed, to interpenetrate with it. the reinforcing filler / elastomer network on the one hand and with the elastomer / sulfur network on the other hand (if the crosslinking agent is sulfur). Typically, the methylene acceptor is a phenolic resin. Phenolic novolac resins have already been described in rubber compositions, in particular intended for pneumatic tires or tire treads, for applications as varied as adhesion or reinforcement: reference will be made, for example, to patent EP 0649446. .

Associated with the methylene acceptor described above is a hardening agent capable of crosslinking or hardening it, also commonly called “methylene donor”. The crosslinking of the resin is then caused during the curing of the rubber matrix, by the formation of methylene bridges between the carbons in the ortho and para positions of the phenolic rings of the resin and the methylene donor, thus creating a three-dimensional resin network. Conventionally used methylene donors are hexa-methylenetetramine (abbreviated HMT), or hexamethoxymethylmelamine (abbreviated HMMM or H3M), or hexaethoxymethylmelamine.

However, the combination of a phenolic resin, methylene acceptor with GHMT or methylene donor GH3M, produces formaldehyde during the crosslinking of the rubber composition. However, it is desirable to reduce, or even eventually eliminate, formaldehyde from rubber compositions because of the potential environmental impact of these compounds.

For this purpose, alternative compositions to the compositions comprising the methylene acceptor formophenolic resin pair with a conventional HMT or H3M hardener donor of methylene have been developed. By way of example, application WO 2011/045342 describes compositions comprising an epoxy resin pair with an amine hardener. These compositions, in addition to the advantage of avoiding the formation of formaldehyde, after crosslinking, exhibit stiffness greater than that of conventional compositions while retaining acceptable rolling resistance. Application WO 2018/002538 describes compositions comprising an epoxy resin and an amine hardener comprising at least two primary amine functions located on at least one aromatic ring with six atoms which aims to improve the compromise between processability, in particular the toasting time, and rigidity compared to known compositions.

However, it is always desirable to be able to reduce the amounts of additives used, in particular of hardener, and to improve the processability of the raw rubber compositions while maintaining the reinforcing properties of the compositions once crosslinked (or "cured". ) over all the operating temperatures of the tire.

Unexpectedly, the Applicant has discovered during its research that the combination of an epoxy resin and a urea compound makes it possible to avoid the formation of formaldehyde while maintaining the reinforcing properties at the different operating temperatures of the tire. pneumatic, while improving the processability of raw compositions.

Detailed description of the invention

The invention relates to at least one of the following embodiments ^: 1. Rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system, from 1 to 30 parts by weight per hundred parts by weight of elastomer, phr, of epoxy resin, and a urea compound of general formula (R 1, R 2) N-CON (R 3, R ₄ ) in which each R 1, R 2, R 3 and R ₄ radical is independently selected from the group consisting of a hydrogen atom, an alkyl radical having from 1 to 20 carbon atoms, a cycloalkyl radical having from 5 to 24 carbon atoms, an aryl radical having from 6 to 30 carbon atoms and an aralkyl radical having from 7 to 25 carbon atoms, the radicals R2 and R3 possibly together forming a cycle, each radical R 1, R 2, R 3 and R ₄ being optionally interrupted by one or more heteroatoms and / or substituted.

2. Rubber composition according to the preceding embodiment, in which the urea compound is a mono-urea, and in which each R 1, R 2, R 3 and R ₄ radical is independently selected from the group consisting of a hydrogen atom and a compound. hydrocarbon.

3. A rubber composition according to any one of the preceding embodiments, in which each R 1 and R 3 radical is a hydrogen atom.

4. Rubber composition according to any one of the preceding embodiments, in which at least one R2 or R4 radical is an aryl radical having from 6 to 8 carbon atoms, preferably a phenyl radical.

5. A rubber composition according to any one of embodiments 1 to 3, in which the urea compound does not include an aromatic nucleus.

6. A rubber composition according to any one of the preceding embodiments, in which the radicals R 1 to R 4 do not, together, form a ring.

7. Rubber composition according to embodiment 1, in which each radical R 1, R 2, R 3 and R 4 is a hydrogen atom.

8. Rubber composition according to embodiment 1 in which the urea compound is chosen from the compounds urea, N, N'-dimethylurea, ethylèneurea, N-phenylurea, 1,3-diphenylurea, preferably chosen from the compounds urea, N , N'-dimethylurea, N-phenylurea, 1,3-diphenylurea and very preferably chosen from the compounds urea and N, N'-dimethylurea.

9. Rubber composition according to any one of the preceding embodiments in which the content of urea compound is within a range ranging from 1 to 15 phr, preferably from 0.5 to 10 phr, preferably from 0.5 to 8. phr and preferably from 0.5 to 5 phr.

10. Rubber composition according to any one of the preceding embodiments in which the diene elastomer is chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, copolymers of isoprene, and mixtures of these elastomers and is preferably an isoprene elastomer.

11. A rubber composition according to any one of the preceding embodiments, in which the epoxy resin is chosen from aromatic epoxy resins, alicyclic epoxides and aliphatic epoxides.

12. Rubber composition according to any one of the preceding embodiments, in which the level of epoxy resin is between 10 and 25 phr, preferably between 10 and 20 phr.

13. Rubber composition according to any one of the preceding embodiments not comprising a nitrile compound, or comprising less than 10 phr, preferably less than 5 phr, and preferably less than 2 phr.

14. Rubber composition according to any one of the preceding embodiments, in which the level of reinforcing filler is within a range ranging from 20 to 200 phr, preferably from 30 to 150 phr.

15. A finished or semi-finished rubber article comprising a rubber composition according to any one of the preceding embodiments.

16. Pneumatic or non-pneumatic tire comprising a rubber composition according to any one of embodiments 1 to 14.

17. Bandage according to the previous embodiment comprising an inner layer comprising a rubber composition according to any one of embodiments 1 to 14.

Definitions

By the expression "part by weight per hundred parts by weight of elastomer" (or phr), is meant within the meaning of the present invention, the part, by weight per hundred parts by weight of elastomer or rubber.

In the present document, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by mass. On the other hand, any interval of values designated by the expression "between a and b" represents the range of values going from more than a to less than b (that is to say limits a and b excluded) while any range of values designated by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b). By the expression “composition based on” is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these constituents being able to react and / or being intended to react with each other, less partially, during the various phases of manufacture of the composition; the composition may thus be in the totally or partially crosslinked state or in the non-crosslinked state.

When reference is made to a “majority” compound, it is understood, within the meaning of the present invention, that this compound is the majority among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest amount by mass among compounds of the same type. Thus, for example, a major elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. Likewise, a so-called majority filler is that representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, the latter is in the majority within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers. On the contrary, a "minority" compound is a compound which does not represent the largest mass fraction among compounds of the same type. Preferably, the term “majority” is understood to mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferably the “majority” compound represents 100%.

The compounds comprising carbon mentioned in the description can be of fossil origin or biobased. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This concerns in particular polymers, plasticizers, fillers, etc.

Diene elastomer

The composition according to the invention comprises at least one diene elastomer. It can therefore contain a single diene elastomer or a mixture of several diene elastomers.

By elastomer (or indistinctly rubber) "diene", whether natural or synthetic, should be understood in a known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers carrying two double carbon-carbon bonds, conjugated or not).

These diene elastomers can be classified into two categories: "essentially unsaturated" or "essentially saturated". In general, the term “essentially unsaturated” is understood to mean a diene elastomer derived at least in part from conjugated diene monomers, having a level of units or units of diene origin (conjugated dienes) which is greater than 15% (% by moles); thus diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the definition above and can in particular be qualified as “essentially saturated” diene elastomers (level of units of low or very low diene origin, always less than 15%). The diene elastomers included in the composition according to the invention are preferably essentially unsaturated.

The term “diene elastomer capable of being used in the compositions in accordance with the invention” is particularly understood to mean: a) any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms; b) any copolymer of a diene, conjugated or not, having 4 to 18 carbon atoms and at least one other monomer.

The other monomer can be ethylene, an olefin or a diene, conjugated or not.

Suitable conjugated dienes are conjugated dienes having from 4 to 12 carbon atoms, in particular 1,3 dienes, such as in particular 1,3 butadiene and isoprene.

Suitable olefins are vinyl aromatic compounds having from 8 to 20 carbon atoms and aliphatic monoolefins having from 3 to 12 carbon atoms.

Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial mixture “vinyl-toluene” and para-tert-butylstyrene.

Suitable aliphatic monoolefins are in particular acyclic aliphatic monoolefins having from 3 to 18 carbon atoms.

Preferably, the diene elastomer is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers, and mixtures of these. elastomers. The butadiene copolymers are particularly chosen from the group consisting of butadiene-styrene (SBR) copolymers.

Preferably, the diene elastomer is an isoprene elastomer.

The term “isoprene elastomer” is understood to mean, in a known manner, an isoprene homopolymer or copolymer, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), different isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, there may be mentioned in particular the copolymers of isobutenedsoprene (butyl rubber - IIR), of isoprene-styrene (SIR), of isoprene-butadiene (BIR) or of isoprene-butadiene-styrene (SBIR ). This isoprene elastomer is preferably chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes and mixtures thereof; among these synthetic polyisoprenes, use is preferably made of polyisoprenes having a content (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 98%. Preferably and according to any of the arrangements herein, the diene elastomer is natural rubber.

Preferably the rate of diene elastomer, preferably isoprene elastomer, preferably natural rubber, is from 50 to 100 phr, more preferably from 60 to 100 phr, more preferably from 70 to 100 phr, more preferably still from 80 to 100 phr and very preferably from 90 to 100 phr. In particular, the content of diene elastomer, preferably isoprene elastomer, more preferably natural rubber, is very preferably 100 phr.

Whether it contains a single diene elastomer or a mixture of several diene elastomers, the rubber composition according to the invention may also contain in a minority manner any type of synthetic elastomer other than diene, or even polymers other than elastomers, for example. thermoplastic polymers. Preferably, the rubber composition according to the invention does not contain any synthetic elastomer other than diene or any polymer other than elastomers or contains less than 10 phr thereof, preferably less than 5 phr.

Epoxy resin

Epoxy resins usable in the present invention include all polyepoxy compounds. These may be, for example, aromatic epoxy resins, alicyclic epoxides, and aliphatic epoxides. For example, the aromatic epoxy resin can be an amine-aromatic epoxy resin. The epoxy resins are preferably epoxy novolac resins, that is to say epoxy resins obtained by acid catalysis, as opposed to resol resins, obtained by basic catalysis.

In particular, among the aromatic epoxy resins, preferred are the epoxy resins chosen from the group consisting of 2,2 bis [4- (glycidyloxy) phenyl] propane, poly [(o-cresylglycidyl ether) -co-formaldehyde], poly [(phenylglycidyl ether) -co-formaldehyde], poly [(phenylglycidyl ether) -co (hydroxybenzaldehyde glycidyl ether)], epoxy resins aromatic amines and mixtures of these compounds, and preferably epoxy resins selected from the group consisting of poly [(o-cresylglycidyl ether) -co-formaldehyde, and poly [(phenylglycidyl ether) -coOiydroxybenzaldehyde glycidyl ether)] .

More preferably, the epoxy resin is selected from the group consisting of polytocresylglycidyl ether) -co-formaldehyde], polytphenylglycidyl ether) -co-formaldehyde], aromatic amine epoxy resins and mixtures of these compounds.

By way of example of epoxy resins available commercially and which can be used in the context of the present invention, mention may be made, for example, of the epoxy resin “DEN 439” from the company Uniqema, the epoxy resin “Tris (4-hydroxyphenyl) methane. triglycidyl ether "from the company Sigma-Aldrich, the cresol novolac araldite epoxy resin" ECN 1299 "from the company Hunstman, the phenol novolac araldite epoxy resin" EPN 1138 "from the company Huntsman.

The composition according to the invention comprises between 1 and 30 phr of epoxy resin. Given the amine hardener used in the context of the present invention, below the minimum level of resin indicated, the targeted technical effect is insufficient, while beyond the maximum indicated, there is a risk of too large increase in rigidity and excessive penalization of hysteresis and extensibility properties of the material. For all these reasons, the level of epoxy resin is preferably between 10 and 25 phr. More preferably, the level of epoxy resin in the composition according to the invention is between 10 and 20 phr.

High latency hardener

The epoxy resin of the composition of the invention is combined with a specific hardener, in this case a urea compound, which allows the resin to crosslink.

According to the invention, the hardener is a urea compound of general formula (Ri, R2) N-CO N (R3,

R4) in which each radical R 1, R 2, R 3 and R 4 is independently selected from the group consisting of:

• a hydrogen atom,

• an alkyl radical having from 1 to 20 carbon atoms,

• a cycloalkyl radical having 5 to 24 carbon atoms,

• an aryl radical having from 6 to 30 carbon atoms and

• an aralkyl radical having from 7 to 25 carbon atoms, the radicals R ₂ and R3 possibly together forming a ring, each radical R 1, R ₂ , R3 and R ₄ being optionally interrupted by one or more heteroatoms and / or substituted. In the general formula (Ri, RilN-CONlR:;, R ₄ ), it is understood that the CO group represents a carbon atom linked by a double bond to an oxygen atom, that the group (Ri, R¾) N ( respectively N (R3, R ₄ )) represents a nitrogen atom bonded to a group R 1 and to a group R 2 by a covalent bond.

An example of a urea compound in which the R2 and R3 radicals together form a ring is 2-imidazolidinone, or ethylenerea. Preferably, the radicals do not, together, form a cycle.

Preferably, the urea compound is a mono-urea, and each R 1, R 2, R 3 and R ₄ radical is independently selected from the group consisting of a hydrogen atom and a hydrocarbon compound.

Preferably, each R 1 and R 3 radical is a hydrogen atom. Urea is then a compound of formula R2-HN-CONH-R ₄ .

In a preferred arrangement, at least one R2 or R4 radical is an aryl radical having from 6 to 8 carbon atoms, preferably a phenyl radical. Preferably in this preferred arrangement, the urea compound can be an N-phenylurea or 1,3-diphenylurea.

Preferably, the urea compound does not include an aromatic nucleus. Preferably, each R 1, R 2, R 3 and R ₄ radical is a hydrogen atom. The urea compound is then a compound of formula H2N-CO-NH2 commonly designated under the term “urea” or “carbamide”. Thus, very preferably, the urea compound is chosen from the compounds urea, N, N'-dimethylurea, ethylèneurea, N-phenylurea, 1,3-diphenylurea, preferably chosen from the compounds urea, N, N'-. dimethylurea, N-phenylurea, 1,3-diphenylurea and very preferably chosen from the compounds urea and N, N'-dimethylurea. Very preferably, the urea compound is urea of formula H2N-CO-NH2.

The amount of urea compound in the rubber composition is within a range from 1 to 15 phr. Below the minimum indicated, the targeted technical effect has been shown to be insufficient, while beyond the maximum indicated, there is a risk of penalizing the use of the compositions in the raw state. Preferably, the urea content is within a range ranging from 0.5 to 10 phr, preferably from 0.5 to 8 phr and preferably from 0.5 to 5 phr.

Reinforcing filler

The composition according to the invention preferably comprises a reinforcing filler.

The reinforcing filler can comprise any type of reinforcing filler known for its capacity to reinforce a rubber composition which can be used for the manufacture of pneumatic tires, for example an organic filler such as carbon black, a reinforcing inorganic filler such as silica, or a mixture of carbon black and reinforcing inorganic filler. More preferably, the reinforcing filler comprises mainly, or even exclusively, carbon black, in particular in the case where the composition is used in an internal layer. The reinforcing filler can also mainly comprise a reinforcing inorganic filler, in particular in the case where the composition is used in a tread.

Such a reinforcing filler typically consists of particles whose average size (by mass) is less than one micrometer, generally less than 500 nm, most often between 20 and 200 nm, in particular and more preferably between 20 and 150 nm.

Suitable carbon blacks are all carbon blacks, in particular blacks of the HAF, ISAF, SAF type conventionally used in pneumatic tires (so-called tire grade blacks). Among the latter, there will be mentioned more particularly the carbon blacks reinforcing the 100, 200 or 300 series (ASTM grades), such as for example the blacks NI 15, N134, N234, N326, N330, N339, N347, N375, or else, depending on the targeted applications, blacks of higher series (for example N660, N683, N772). The carbon blacks could, for example, already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example applications WO 97/36724 or WO 99/16600). The BET specific surface area of carbon blacks is measured according to standard D6556-10 [multipoint method (at least 5 points) - gas: nitrogen - relative pressure range R / R0: 0.1 to 0.3]

By "reinforcing inorganic filler", should be understood in the present application, by definition, any inorganic or mineral filler (whatever its color and its natural or synthetic origin), also called "white" filler, "clear" filler or even "load no black "(" non-black fïller ") as opposed to carbon black, capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other terms capable of replacing, in its reinforcing function, a conventional carbon black of pneumatic grade; such a filler is generally characterized, in a known manner, by the presence of hydroxyl groups (—OH) at its surface.

As reinforcing inorganic fillers, suitable in particular mineral fillers of the siliceous type, in particular silica (S1O2), or of the aluminous type, in particular alumina (Al2O3). The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface area both less than 450 m ² / g, preferably from 30 to 400 m ² / g. As highly dispersible precipitated silicas (called “HDS”), mention will be made, for example, of “Ultrasil 7000” and “Ultrasil 7005” silicas from the company Degussa, the “Zeosil” silicas 1165MP, 1135MP and 1115MP from the company Rhodia, “Hi-Sil EZ150G” silica from the company PPG, “Zeopol” silicas 8715, 8745 and 8755 from the Huber company, silicas with a high specific surface area as described in application WO 03/16837.

The BET specific surface area of silica is determined in a known manner by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" Vol. 60, page 309, February 1938, more precisely according to the French standard NF ISO 9277 of December 1996 (multipoint volumetric method (5 points) - gas: nitrogen - degassing: time at 160 ° C - relative pressure range p / in: 0.05 to 0.17). The CTAB specific surface of the silica is determined according to the French standard NF T 45Ό07 of November 1987 (method B).

Also suitable as reinforcing inorganic fillers are mineral fillers of the aluminous type, in particular alumina (Al2O3) or aluminum (oxide) hydroxides, or else reinforcing titanium oxides, for example described in US Pat. No. 6,610,261 and US 6,747,087.

The physical state in which the reinforcing inorganic filler is present is immaterial, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term “reinforcing inorganic filler” is understood to mean mixtures of various reinforcing inorganic fillers, in particular of highly dispersible siliceous and / or aluminous fillers. Those skilled in the art will understand that as an equivalent filler of the reinforcing inorganic filler described in this paragraph, a reinforcing filler of another nature, in particular organic, could be used, since this reinforcing filler is covered with a an inorganic layer such as silica, or else would comprise on its surface functional sites, in particular hydroxyls, making it possible to establish the bond between the filler and the elastomer in the presence or absence of a covering or coupling agent.

In order to couple the reinforcing inorganic filler to the diene elastomer, it is possible to use, in a well-known manner, an at least bifunctional coupling agent (or binding agent) intended to ensure a sufficient connection, of a chemical and / or physical nature, between the filler. inorganic (surface of its particles) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. By "bifunctional" is meant 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 can comprise a first functional group comprising a silicon atom, the said first functional group being able to interact with the hydroxyl groups of an inorganic filler and a second functional group comprising a sulfur atom, the said second functional group being able to interact with the diene elastomer.

Preferably, the organosilanes are chosen from the group consisting of polysulfurized organosilanes (symmetrical or asymmetrical) such as bis (3-triethoxysilylpropyl) tetrasulfide, in short TESPT marketed under the name “Si69” by the company Evonik or bis disulfide. - (triethoxysilylpropyle), in short TESPD marketed under the name “Si75” by the company Evonik, the polyorganosiloxanes, the mercaptosilanes, the blocked mercaptosilanes, such as the octanethioate of S- (3- (triethoxysilyl) propyl) marketed by the company Momentive under the name “NXT Silane”. More preferably, the organosilane is a polysulfurized organosilane.

The content of coupling agent is preferably less than 12 phr, it being understood that it is generally desirable to use as little as possible. Typically when a reinforcing inorganic filler is present, the level of coupling agent represents from 0.5% to 15% by weight relative to the amount of inorganic filler. Its rate is preferably within a range ranging from 0.5 to 15 phr. This rate is easily adjusted by a person skilled in the art according to the rate of inorganic filler used in the composition. According to the invention, when the reinforcing filler is present, the level of reinforcing filler, preferably the reinforcing filler comprising mainly, or even exclusively carbon black, can be within a range ranging from 20 to 200 phr, preferably from 30 to 150 phr, preferably 40 to 100 phr, preferably 50 to 80 phr.

Cross-linking system

The crosslinking system can be any type of system known to those skilled in the art in the field of rubber compositions for pneumatic tires. It can in particular be based on sulfur, and / or peroxide and / or bismaleimides.

Preferably, the crosslinking system is sulfur-based, this is called a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur, or of a sulfur donor agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferentially, one can use various known vulcanization activators such as zinc oxide, stearic acid or equivalent compound such as salts of stearic acid and salts. transition metals, guanide derivatives (in particular diphenylguanidine), or else known vulcanization retarders.

Sulfur is used at a preferential rate of between 0.5 and 12 phr, in particular between 1 and 10 phr. The vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 8.0 phr.

Can be used as accelerator any compound capable of acting as vulcanization accelerator of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type as well as their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphates, thioureas and xanthates types. By way of examples of such accelerators, mention may in particular be made of the following compounds ^: 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulfenamide ("CBS"), N, N-dicyclohexyl- 2-Benzothiazyl sulfenamide ("DCBS"), N-ter-butyl-2-benzothiazyl sulfenamide ("TBBS"), N-ter-butyl-2-benzothiazyl sulfenimide ("TBSI"), tetrabenzylthiuram disulfide ("TBZTD") , zinc dibenzyldithiocarbamate ("ZBEC") and mixtures of these compounds.

Various additives

The rubber compositions in accordance with the invention may also contain all or part of the usual additives and processing agents, known to those skilled in the art and usually used in rubber compositions for pneumatic tires, such as for example plasticizers (such as plasticizing oils and / or plasticizing resins), pigments, protective agents such as anti-ozone waxes, chemical anti-ozonants, anti-oxidants , anti-fatigue agents.

Preferably, the composition according to the invention does not comprise 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 even more. preferably less than 0.5 phr.

The composition can be either in the uncured state (before crosslinking or vulcanization) or in the cooked state (after crosslinking or vulcanization).

Finished or semi-finished rubber article and pneumatic tire

A subject of the present invention is also a finished or semi-finished rubber article comprising a composition according to the invention.

A subject of the present invention is also a pneumatic tire which comprises a composition according to the invention.

Three types of zones can be defined within the tire ^:

• The radially outer zone and in contact with the ambient air, comprising the so-called outer layers, these layers essentially comprising the tread and the outer sidewall of the tire. An outer sidewall is an elastomeric layer placed 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 top to the bead.

• The radially inner zone and in contact with the inflation gas, this zone generally being constituted by the layer impermeable to the inflation gases, sometimes called the internal impervious layer or internal rubber (“inner liner” in English).

• The internal zone of the pneumatic tire, ie the zone between the external and internal zones. This area includes layers or plies which are referred to herein as the inner layers of the tire. These are, for example, carcass plies, tread sub-layers, pneumatic tire belt plies or any other layer which is not in contact with the ambient air or the inflation gas of the tire. The composition defined in the present description is particularly well suited to the internal and external layers of pneumatic tires, and in particular, for the external layers, to tread compositions.

According to the invention, the internal layer can be chosen from the group consisting of the carcass plies, the crown plies, the bead fillings, the top feet, the decoupling layers, the edging gums, the stuffing gums, the under -tread layer and combinations of these internal layers. Preferably, the inner layer is chosen from the group consisting of carcass plies, crown plies, bead fillings, top feet, decoupling layers and combinations of these internal layers.

The composition according to the invention may also be suitable for the internal and external layers of non-pneumatic tires, in particular for the treads of non-pneumatic tires. It is recalled that a non-pneumatic tire is a tire which supports the load of a vehicle by a means other than a pressurized inflation gas.

The invention particularly relates to pneumatic tires intended to be fitted to motor vehicles of the passenger car type, SUV (“Sport Utility Vehicles”), or two-wheeled vehicles (in particular motorcycles), or airplanes, or even industrial vehicles chosen from vans, “Weight "heavy", that is to say metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles such as agricultural or civil engineering machinery, and others.

The invention relates to articles comprising a rubber composition according to the invention, both in the uncured state (that is to say, before curing) and in the cured state (that is to say, after crosslinking or vulcanization. ).

Preparation of rubber compositions

The rubber composition in accordance with the invention can be manufactured in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first thermomechanical working or mixing phase (so-called “non-productive” phase) , which can be carried out in a single thermomechanical step during which all the necessary constituents, in particular the elastomeric matrix, the fillers, are introduced into a suitable mixer such as a usual internal mixer (for example of the 'Banbury' type). , any other various additives, with the exception of the crosslinking system. The incorporation of the filler into the elastomer can be carried out in one or more times by thermomechanically kneading. In the case where the filler is already incorporated in whole or in part in the elastomer in the form of a masterbatch as described for example in applications WO 97/36724 or WO 99 / 16600, it is the masterbatch which is directly mixed and, where appropriate, the other elastomers or fillers present in the composition which are not in the form of a masterbatch are incorporated, as well as any other various additives other than the crosslinking system.

The non-productive phase is carried out at high temperature, up to a maximum temperature of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, for a period generally of between 2 and 10 minutes. a second phase of mechanical work (so-called "productive" phase), which is carried out in an external mixer such as a roller mixer, after cooling the mixture obtained during the first non-productive phase to a lower temperature , typically below 110 ° C, for example between 40 ° C and 100 ° C. The crosslinking system is then incorporated, and the whole is then mixed for a few minutes, for example between 2 and 15 min.

The process for preparing such compositions comprises for example the following steps: a) incorporating into a diene elastomer, during a first step (called "non-productive"), a reinforcing filler, by thermomechanically kneading the whole (for example in one or more batches), until a maximum temperature of between 110 ° C and 190 ° C is reached; b) cooling the assembly to a temperature below 100 ° C; c) then incorporating, during a second step (called "productive"), a crosslinking system; d) mix everything up to a maximum temperature below 110 ° C.

Between 1 and 30 phr of the epoxy resin and between 1 and 15 phr of urea compound can be introduced, independently of each other, either during the non-productive phase (a) or during the productive phase (c). Preferably, the epoxy resin is introduced during the non-productive phase (a) while the high latency hardener is introduced during the productive phase (c).

The final composition thus obtained can then be calendered, for example in the form of a sheet, of a plate in particular for a characterization in the laboratory, or else extruded in the form of a semi-finished (or profiled) rubber used for the manufacture of a pneumatic tire.

The crosslinking of the composition can be carried out in a manner known to those skilled in the art, for example at a temperature of between 130 ° C and 200 ° C, under pressure.

Examples

Measurements and tests used

Toasting time

The measurements are carried out at 130 ° C, in accordance with the French standard NF T 43Ό05. The change in the consistometric index as a function of time makes it possible to determine the roasting time of the rubber compositions, assessed in accordance with the aforementioned standard by the parameter T5 (case of a large rotor), expressed in minutes, and defined as being the time required to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.

It will be recalled that, in a manner well known to those skilled in the art, the higher the consistometric index as a function of time, the more the crosslinking of the material will be delayed before curing.

Moonev plasticity

An oscillating consistometer is used as described in French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (i.e., before firing) is molded in a cylindrical chamber heated to 100 ° C. After one minute of preheating, the rotor rotates within the specimen at 2 revolutions / minute and the torque useful to maintain this movement is measured after 4 minutes of rotation. The Mooney plasticity (ML 1 + 4) is expressed in "Mooney unit" (MU, with 1 MU = 0.83 Newton. Meter).

It will be recalled that, as is well known to those skilled in the art, the lower the Mooney plasticity, the easier the material is to work. Of course, below a certain value (for example 20 MU), the material becomes too liquid to be used, in particular for making internal layers.

Tensile tests

The tests were carried out in accordance with the French standard NF T 46Ό02 of September 1988. All the traction measurements were carried out at a temperature representative of the operating temperature of the tire composition (100 ± 2 ° C) and in normal humidity conditions (50 ± 5% relative humidity), according to the French standard NF T 40Ί01 (December 1979).

We measured in second elongation (that is to say after accommodation) the nominal secant modulus calculated by reducing to the initial section of the test piece (or apparent stress, in MPa) at 100% elongation noted MA100 and at 300% elongation noted MA300, on samples baked for 60 minutes at 150 ° C.

The tables show the MA300 / MA100 ratio representative of the reinforcement.

Preparation of the compositions

The following tests are carried out for the tests which follow ^: the elastomer is introduced into an internal mixer (final filling rate ^: approximately 70% by volume), the initial tank temperature of which is approximately 60 ° C. diene, the reinforcing filler, between 1 and 30 phr of the epoxy resin, as well as the various other ingredients with the exception of the crosslinking system. A thermomechanical work (non-productive phase) is then carried out in one step, which lasts in total about 3 to 4 min, until a maximum “fall” temperature of 165 ° C. is reached.

The mixture thus obtained is recovered, it is cooled and then sulfur, a sulfenamide type accelerator and the high latency hardener are incorporated on a mixer (homofinisher) at 30 ° C, while mixing the whole (productive phase) for a period of time. appropriate time (for example between 5 and 12 min).

The compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties, or extruded in the form of a profile.

The crosslinking of the composition is carried out at a temperature of 150 ° C., for 60 min, under pressure.

Testing of rubber compositions

Five rubber compositions were prepared as indicated above, four in accordance with the invention (hereinafter denoted C ^_ 2 to C ^_ 5) and one non-compliant (control composition denoted below C l). Their formulations (in phr) and their properties have been summarized in Table 1 below. With the exception of the control composition C1, the compositions presented in this Table 1 do not cause the formation of formaldehyde during cooking.

Compositions 02 to 05 contain an epoxy resin and a urea compound replacing the formo-phenolic resin / HMT hardener (s) pair contained in the conventional control composition Ol.

All the results are expressed in base 100, taking the control composition Ol as a reference. A value lower than 100 signifies that the value is lower than that of the control composition, a value higher than 100 signifying a value higher than that of the control composition.

[Table l]

(1) Natural Rubber;

(2) Carbon black N326 (name according to ASTM D-1765)

(3) Zinc oxide (industrial grade - Umicore company)

(4) N-1,3-dimethylbutyl-N-phenylparaphenylenediamme (“Santoflex 6 PPD” from the company Flexsys)

(5) Stearin (“Pristerene 4931” from Uniqema)

(6) N-cyclohexyl benzothiazyl sulphenamide (“Santocure CBS” from the company Flexsys)

(7) Novolac formophenolic resin (“Peracit 4536K” from the company Perstorp)

(8) Hexamethylenetetramine (from Degussa) (9) Epoxy phenol novolak resin (“EPN 1138” from the company Huntsman)

(10) urea from Sigma-Aldrich

(11) N-phenylurea compound from the company Sigma-Aldrich

(12) compound N, N′-dimethylurea from the company Sigma-Aldrich (13) compound 1,3-diphenylurea from the company Sigma-Aldrich

It is noted that the compliant compositions make it possible, with a smaller amount of hardener, to obtain a reinforcing effect similar to the control composition, while exhibiting an extended scorching time and a lower Mooney viscosity, therefore improved processability.

Claims

[Claim 1] Rubber composition based on at least one diene elastomer, a reinforcing filler, a sulfur-based crosslinking system, from 1 to 30 parts by weight per hundred parts by weight of elastomer, phr, of resin epoxide, and a urea compound of general formula (R 1, R 2) N-CO N (R 3, R 4) in which each R 1, R 2, R 3 and R 4 radical is independently selected from the group consisting of a hydrogen atom, a radical alkyl having from 1 to 20 carbon atoms, a cycloalkyl radical having from 5 to 24 carbon atoms, an aryl radical having from 6 to 30 carbon atoms and an aralkyl radical having from 7 to 25 carbon atoms, the radicals R2 and R3 can together form a ring, each radical R 1, R 2, R 3 and R 4 being optionally interrupted by one or more heteroatoms and / or substituted.

[Claim 2] A rubber composition according to the preceding claim, wherein the urea compound is a mono-urea, and wherein each R 1, R 2, R 3 and R 4 radical is independently selected from the group consisting of a hydrogen atom and a hydrocarbon compound.

[Claim 3] A rubber composition according to any preceding claim, wherein each R 1 and R 3 is a hydrogen atom.

[Claim 4] A rubber composition according to any one of the preceding claims, in which at least one R2 or R4 radical is an aryl radical having 6 to 8 carbon atoms, preferably a phenyl radical.

[Claim 5] A rubber composition according to any one of claims 1 to 3, wherein the urea compound does not include an aromatic nucleus.

[Claim 6] A rubber composition according to any one of the preceding claims, wherein the radicals R 1 to R 4 do not together form a ring.

[Claim 7] A rubber composition according to claim 1, wherein each R 1, R 2, R 3 and R 4 is a hydrogen atom.

[Claim 8] A rubber composition according to claim 1 in which the urea compound is selected from the compounds urea, N, N'-dimethylurea, ethylèneurea, N-phenylurea, 1,3-diphenylurea, preferably chosen from the compounds urea, N, N'-dimethylurea, N-phenylurea, 1,3-diphenylurea and very preferably chosen from the compounds urea and N, N'-dimethylurea.

[Claim 9] A rubber composition according to any one of the preceding claims in which the content of urea compound is within a range ranging from 1 to 15 phr, preferably from 0.5 to 10 phr, preferably from 0.5 to 8 phr and preferably from 0.5 to 5 phr.

[Claim 10] A rubber composition according to any preceding claim, wherein the epoxy resin is selected from aromatic epoxy resins, alicyclic epoxides and aliphatic epoxides.

[Claim 11] A rubber composition according to any one of the preceding claims not comprising a nitrile compound, or comprising less than 10 phr, preferably less than 5 phr, and more preferably less than 2 phr.

[Claim 12] A finished or semi-finished rubber article comprising a rubber composition according to any preceding claim.

[Claim 13] A pneumatic or non-pneumatic tire comprising a rubber composition according to any one of claims 1 to 11.