CN115279830A

CN115279830A - Rubber composition based on epoxy resin and hardener having high retardation

Info

Publication number: CN115279830A
Application number: CN202180019993.5A
Authority: CN
Inventors: S·比才; F·博内特; E·朗德罗
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2020-03-10
Filing date: 2021-03-04
Publication date: 2022-11-01
Anticipated expiration: 2041-03-04
Also published as: CA3168383A1; FR3108119A1; WO2021181033A1; FR3108119B1; EP4118143A1; JP2023517610A

Abstract

The invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system and comprising an epoxy resin and a hardener having high retardation.

Description

Rubber composition based on an epoxy resin and a hardener having high retardation

Technical Field

The present invention relates to a rubber composition intended in particular for the manufacture of tyres or semi-finished products for tyres. Another subject of the invention is a finished rubber product or semi-finished rubber product comprising a rubber composition according to the invention, and a pneumatic or non-pneumatic tire comprising at least one composition according to the invention.

Background

It is known to use in certain parts of pneumatic tires rubber compositions which exhibit a high stiffness during small strains of the pneumatic tire, as shown in application WO 02/10269. Resistance to small strains is one of the properties that a pneumatic tire must possess in order to respond to the stresses to which it is subjected.

Such reinforcement may be obtained by increasing the content of reinforcing filler or by incorporating certain reinforcing resins in the constituent rubber compositions of the pneumatic tire portions.

The reinforcing resins commonly used to increase the stiffness of the composition are reinforcing resins 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 capable of reacting together to produce, by condensation, a three-dimensional reinforcing resin which, on the one hand, overlaps and interpenetrates the reinforcing filler/elastomer network and, on the other hand, overlaps and interpenetrates the elastomer/sulfur network (if the crosslinking agent is sulfur). Typically, the methylene acceptor is a phenolic resin. Novolac resins have been described in rubber compositions intended in particular for pneumatic tires or treads for various applications such as grip or reinforcement: for example, reference is made to patent EP 0 649 446.

The above methylene acceptors are combined with a hardener that enables them to crosslink or harden, which hardener is also commonly referred to as a "methylene donor". Crosslinking of the resin is then achieved during curing of the rubber matrix by formation of methylene bridges between the carbon and methylene donors located ortho and para to the phenolic core of the resin, thereby creating a three-dimensional resin network. The methylene donors commonly used are hexamethylenetetramine (abbreviated to HMT) or hexamethoxymethylmelamine (abbreviated to HMMM or H3M) or hexaethoxymethylmelamine.

However, the combination of phenolic resin (methylene acceptor) with HMT or H3M (methylene donor) can generate formaldehyde during crosslinking of the rubber composition. In fact, 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 to the conventional compositions comprising a formaldehyde/phenol resin pair (methylene acceptor) and HMT or H3M hardener (methylene donor) have been developed. For example, application WO 2011/045342 describes compositions comprising pairs of epoxy resins and an amine-containing hardener. In addition to the advantage of not generating formaldehyde, these compositions also exhibit greater stiffness after crosslinking than conventional compositions, while maintaining acceptable rolling resistance. Application WO 2018/002538 describes a composition comprising an epoxy resin and an amine-containing hardener comprising at least two primary amine functions located on at least one six-membered aromatic ring, which composition is intended to improve the compromise between processability (in particular scorch time) and stiffness compared to known compositions.

However, it remains desirable to be able to reduce the amount of additives, in particular the amount of hardeners, and to improve the processability of the raw rubber composition, while maintaining the reinforcing properties of the composition once crosslinked (or "cured") at all operating temperatures of the pneumatic tire.

Surprisingly, the applicant company has found 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 different working temperatures of the pneumatic tire, while improving the processability of the raw composition.

Disclosure of Invention

The present 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 an epoxy resin and of a composition of the general formula (R)₁R₂)N-CO-(NR₃)-R₇-(NR₄)-CO-N(R₅R₆) Wherein R is₁To R₆Each 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 atomsRadicals and aralkyl radicals having 7 to 25 carbon atoms, in one aspect R₂And R₃The radicals being able to form together a ring, on the other hand R₄And R₅The radicals being able to form together a ring, R₇The group is a divalent aryl group having 6 to 30 carbon atoms.

2. The rubber composition according to the previous embodiment, wherein R₁To R₆Each 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, R₇The group is a divalent aryl group having 6 to 8 carbon atoms.

3. The rubber composition of any of the preceding embodiments, wherein R₇The group is a divalent methylphenyl group.

4. The rubber composition of any of the preceding embodiments, wherein R₁To R₇The groups do not together form a ring.

5. The rubber composition of any of the preceding embodiments, wherein R₃And R₄Each group is a hydrogen atom.

6. The rubber composition of any of the preceding embodiments, wherein at least one R₁、R₂、R₅Or R₆The group is an aryl group having 6 to 8 carbon atoms, preferably a phenyl group.

7. The rubber composition according to any one of embodiments 1 to 5, wherein R₁、R₂、R₅And R₆The groups are independently selected from methyl groups and ethyl groups.

8. The rubber composition of embodiment 1, wherein R₁、R₂、R₅And R₆The radical being a methyl radical, R₃And R₄Is a hydrogen atom, R₇Is a divalent methylphenyl radical.

9. The rubber composition according to any of the preceding embodiments, wherein the urea compound is present in a range of 1phr to 15phr, preferably 0.5phr to 10phr, preferably 0.5phr to 8phr and preferably 0.5phr to 5 phr.

10. The rubber composition according to any 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, preferably isoprene elastomer.

11. The rubber composition of any of the preceding embodiments, wherein the epoxy resin is selected from the group consisting of aromatic epoxy resins, cycloaliphatic epoxy resins, and aliphatic epoxy resins.

12. The rubber composition of any of the preceding embodiments, wherein the epoxy resin content is between 10phr and 25phr, preferably between 10phr and 20 phr.

13. The rubber composition according to any of the preceding embodiments, comprising no nitrile compound or comprising less than 10phr, preferably less than 5phr and preferably less than 2phr of nitrile compound.

14. The rubber composition of any of the preceding embodiments, wherein the reinforcing filler is present in an amount ranging from 20phr to 200phr, preferably from 30phr to 150 phr.

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

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

17. The tire of the previous embodiment, comprising an inner layer comprising the rubber composition of any of embodiments 1-14.

Definition of

Within the meaning of the present invention, the expression "parts by weight per hundred parts by weight of elastomer" (or phr) is understood to mean parts by weight per hundred parts by weight of elastomer or rubber.

Herein, all percentages (%) shown are weight percentages (%), unless otherwise indicated.

Furthermore, any interval of values denoted by the expression "between a and b" denotes a range of values extending from more than a to less than b (i.e. not including the limits a and b), whereas any interval of values denoted by the expression "from a to b" means a range of values extending from a up to b (i.e. including the strict limits a and b).

The expression "composition based on" is understood to mean that the composition comprises a mixture and/or an in situ reaction product of the various components used, some of which are capable of (and/or intended to) at least partially react with each other during the various preparation stages of the composition; thus, the composition may be in a fully or partially crosslinked state or in an uncrosslinked state.

When referring to a "primary" compound, within the meaning of the present invention, it is understood to mean that, among the same type of compounds of the composition, the compound is primary, i.e. the compound which makes up the greatest amount by weight among the compounds of the same type. Thus, for example, the predominant elastomer is the elastomer that makes up the maximum weight relative to the total weight of elastomers in the composition. In the same manner, the "predominant" filler is the filler that makes up the greatest weight of the fillers in the composition. For example, in a system comprising only one elastomer, which is predominant within the meaning of the present invention, in a system comprising two elastomers, the predominant elastomer comprises more than half the weight of the elastomer. In contrast, a "minor" compound is a compound that does not account for the maximum weight part of the same type of compound. Preferably, the term "primary" is understood to mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, more preferably the "primary" compound makes up 100%.

The carbon-containing compounds mentioned in the description may be compounds of fossil origin or bio-based compounds. In the case of bio-based compounds, they may be partially or completely derived from biomass or obtained by renewable starting materials derived from biomass. In particular to polymers, plasticizers, fillers, and the like.

Diene elastomer

The composition according to the invention comprises at least one diene elastomer. Thus, the composition may comprise only one diene elastomer, or a mixture of diene elastomers.

"diene" elastomer (or rubber without distinction), whether natural or synthetic, should be understood in a known manner to mean an elastomer consisting at least in part (i.e. a homopolymer or a copolymer) of diene monomer units (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds).

These diene elastomers can be divided into two categories: "substantially unsaturated" or "substantially saturated". The term "essentially unsaturated" is generally understood to mean a diene elastomer resulting at least in part from conjugated diene monomers and having a content of units of diene origin (conjugated dienes) which is greater than 15% (mol%); thus diene elastomers such as butyl rubbers or EPDM type copolymers of dienes and of alpha-olefins do not fall within the preceding definition, but can be described in particular as "essentially saturated" diene elastomers (low or very low content of units of diene origin, always less than 15%). The diene elastomer comprised in the composition according to the invention is preferably substantially unsaturated.

Diene elastomers which can be used in the compositions according to the invention are understood in particular to mean:

(a) Any homopolymer of a conjugated or non-conjugated diene monomer 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.

The other monomer may be ethylene, an olefin, or a conjugated or non-conjugated diene.

Suitable as 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 as olefins are vinylaromatic compounds having from 8 to 20 carbon atoms and aliphatic alpha-monoolefins having from 3 to 12 carbon atoms.

Suitable as vinylaromatic compounds are, for example, styrene, o-methylstyrene, m-methylstyrene or p-methylstyrene, "vinyltoluene" commercial mixtures or p- (tert-butyl) styrene.

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

Preferably, the diene elastomer is chosen from polybutadienes (BR), natural Rubber (NR), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. The butadiene copolymer is in particular chosen from butadiene/styrene copolymers (SBR).

Preferably, the diene elastomer is an isoprene elastomer.

The term "isoprene elastomer" is understood in a known manner to mean an isoprene homopolymer or copolymer, in other words a diene elastomer selected from Natural Rubber (NR), synthetic polyisoprenes (IR), various isoprene copolymers and mixtures of these elastomers. Among the isoprene copolymers, mention will in particular be made of isobutylene/isoprene (butyl rubber-IIR), isoprene/Styrene (SIR), isoprene/Butadiene (BIR) or isoprene/butadiene/Styrene (SBIR) copolymers. The 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 having a cis-1, 4-linkage content (mol%) of greater than 90%, and more preferably still greater than 98%, are preferably used. Preferably and according to any arrangement of this document, the diene elastomer is natural rubber.

Preferably, the content of diene elastomer, preferably isoprene elastomer, preferably natural rubber, is between 50phr and 100phr, more preferably between 60phr and 100phr, in a more preferred manner between 70phr and 100phr, still more preferably between 80phr and 100phr and in a very preferred manner between 90phr and 100phr. In particular, the content of diene elastomer, preferably isoprene elastomer (more preferably natural rubber), is very preferably 100phr.

The rubber composition according to the invention may also comprise minor amounts of any type of synthetic elastomer other than diene elastomers, even polymers other than elastomers, for example thermoplastic polymers, whether the rubber composition comprises only one diene elastomer or a mixture of a plurality of diene elastomers. Preferably, the rubber composition according to the invention does not comprise a synthetic elastomer other than a diene elastomer or a polymer other than an elastomer, or comprises less than 10phr, preferably less than 5phr, of a synthetic elastomer other than a diene elastomer or a polymer other than an elastomer.

Epoxy resin

The epoxy resin that can be used in the present invention includes all polyepoxide compounds. It may relate to, for example, aromatic epoxy resins, cycloaliphatic epoxy resins and aliphatic epoxy resins. For example, the aromatic epoxy resin may be an amine-aromatic epoxy resin. The epoxy resin is preferably an epoxy novolac resin, i.e. an epoxy resin obtained by acidic catalysis compared to a resole resin obtained by alkaline catalysis.

Particularly among the aromatic epoxy resins, preferred epoxy resins are selected from the group consisting of 2, 2-bis [4- (glycidyloxy) phenyl ] propane, poly [ (o-tolyl glycidyl ether) -co-formaldehyde ], poly [ (phenyl glycidyl ether) -co- (hydroxybenzaldehyde glycidyl ether) ], aromatic amine epoxy resins and mixtures of these compounds, preferably epoxy resins are selected from the group consisting of poly [ (o-tolyl glycidyl ether) -co-formaldehyde ] and poly [ (phenyl glycidyl ether) -co- (hydroxybenzaldehyde glycidyl ether) ].

Also 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.

As examples of commercially available epoxy resins that may be used in the context of the present invention, mention may be made of, for example, epoxy resin DEN 439 from Uniqema, epoxy resin tris (4-hydroxyphenyl) methane triglycidyl ether from Sigma-Aldrich, epoxy cresol novolac resin Araldite ECN 1299 from Huntsman or epoxy phenol novolac resin Araldite EPN1138 from Huntsman.

The composition according to the invention comprises between 1phr and 30phr of epoxy resin. Below the minimum content of the resins indicated, the targeted technical effect is insufficient in view of the amine-containing hardener used in the context of the present invention, while above the maximum values indicated, there is a risk of excessively increasing the stiffness and excessively impairing the hysteresis and extensibility of the material. For all these reasons, the content of epoxy resin is preferably between 10phr and 25 phr. More preferably, the content of epoxy resin in the composition according to the invention is between 10phr and 20 phr.

High-retardation curing agent

The epoxy resin of the composition of the invention is combined with a specific hardener, in this case a urea compound, capable of crosslinking the resin.

According to the invention, the hardener is of the formula (R)₁R₂)N-CO-(NR₃)-R₇-(NR₄)-CO-N(R₅R₆) The urea compound of (1), wherein R₁To R₆Each independently selected from:

a hydrogen atom(s) in the presence of a hydrogen atom,

an alkyl group having 1 to 20 carbon atoms,

cycloalkyl radicals 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,

in one aspect, R₂And R₃The radicals being able to form together a ring, on the other hand R₄And R₅The radicals being able to form together a ring, R₇The group is a divalent aryl group having 6 to 30 carbon atoms.

In the general formula (R)₁R₂)N-CO-(NR₃)-R₇-(NR₄)-CO-N(R₅R₆) In (A), (B) is understood to mean that the carbon atom is bonded to the oxygen atom via a double bond, (R)₁R₂) N (accordingly N (R)₅R₆) Group) represents a nitrogen atom covalently bonded to R₁Group and R₂Radical bonding, (NR)₃) (accordingly (NR)₄) Group) represents a nitrogen atom covalently bonded to R₃Radical bonding, R₇The radicals being represented by₃The nitrogen atom of the radical being bound to, on the other handWith R₄A divalent group to which the nitrogen atom of the group is bonded.

Preferably, R₁To R₆Each 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, R₇The group is a divalent aryl group having 6 to 8 carbon atoms.

Preferably, R₇The group is a divalent methylphenyl group.

Preferably, R₁To R₇The groups do not together form a ring.

Preferably, R₃And R₄Each group is a hydrogen atom.

In a preferred arrangement, at least one R₁、R₂、R₅Or R₆The group is an aryl group having 6 to 8 carbon atoms, preferably a phenyl group.

In another preferred arrangement, R₁、R₂、R₅And R₆The groups are independently selected from methyl groups and ethyl groups.

Preferably, R₁、R₂、R₅And R₆The radical being a methyl radical, R₃And R₄The radicals being hydrogen atoms, R₇The group is a divalent methylphenyl group. An example of such a diurea compound is the compound Amicure UR2T from Evonik, which has the formula 1,1' - (4-methyl-m-phenylene) bis (3, 3-dimethylurea).

The amount of urea compound in the rubber composition is in the range of 1phr to 15 phr. Below the minimum values indicated, the technical effect aimed at has proved insufficient, whereas above the maximum values indicated, there is a risk of unfavourable processing of the composition in the raw state. Preferably, the urea content is in the range of 0.5ph to 10phr, preferably 0.5phr to 8phr and preferably 0.5phr to 5 phr.

Reinforcing filler

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

The reinforcing filler may comprise any type of reinforcing filler known to be capable of reinforcing rubber compositions used for the manufacture of pneumatic tires, such as organic fillers (for example carbon black), reinforcing inorganic fillers (for example silica) or mixtures of carbon black and reinforcing inorganic fillers. More preferably, the reinforcing filler comprises mainly (even exclusively) carbon black, in particular in the case of compositions for the inner layer. The reinforcing filler may also comprise mainly a reinforcing inorganic filler, in particular in the case of compositions for treads.

Such reinforcing fillers generally consist of particles having a (weight) average size of less than one micron, generally less than 500nm, most generally between 20nm and 200nm, particularly and more preferably between 20nm and 150 nm.

All carbon blacks, in particular blacks of the type HAF, ISAF or SAF ("tire-grade" blacks), which are customarily used in pneumatic tires, are suitable as carbon blacks. Among the "tire grade" blacks, mention will more particularly be made of reinforcing blacks of the 100, 200 or 300 series (ASTM grade) (for example N115, N134, N234, N326, N330, N339, N347 or N375 blacks), or else of higher series (for example N660, N683 or N772) depending on the target application. The carbon black may, for example, have been 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 the carbon black [ multipoint (at least 5 points) method-gas: nitrogen-relative pressure p/p₀The range is as follows: 0.1 to 0.3]。

In the present patent application, by definition, "reinforcing inorganic filler" is understood to mean any inorganic or mineral filler (whatever its colour and its origin, natural or synthetic), also known as "white filler", "clear filler" or even "non-black filler" with respect to carbon black, capable of reinforcing alone, without methods other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic tires, in other words capable of replacing, in its reinforcing role, a conventional tire-grade carbon black; it is known that such fillers are generally characterized by the presence of hydroxyl (-OH) groups on their surface.

Mineral fillers of siliceous type (in particular Silica (SiO)₂) Mineral fillers (in particular alumina (Al)) or of the aluminous type₂O₃) Are particularly suitable as reinforcing inorganic fillers. Used byThe silica may be any reinforcing silica known to the person skilled in the art, in particular having a BET surface area and a CTAB specific surface area both of which are less than 450m²A/g, preferably of 30m²G to 400m²Precipitated silica or fumed silica in g. As highly dispersible precipitated silicas ("HDS") mention may be made, for example, of the silicas Ultrasil 7000 and Ultrasil 7005 from Degussa, the silicas Zeosil 1165MP, 1135MP and 1115MP from Rhodia, the silica Hi-Sil EZ150G from PPG, the silicas Zeopol 8715, 8745 and 8755 from Huber or the silicas with a high specific surface area as described in application WO 03/16837.

The BET specific surface area of The 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, p.309, 2.1938), more particularly according to French Standard NF ISO 9277 (multipoint (5 points) volumetric method-gas: nitrogen-exhaust gas: 1 hour at 160 ℃ relative pressure p/p₀The range is as follows: 0.05 to 0.17). The CTAB specific surface area of the silica was determined according to French standard NF T45-007 (method B) at 11 months 1987.

Mineral fillers of the aluminium type (in particular alumina (Al)₂O₃) Or aluminium hydroxide (oxide)) or reinforcing titanium oxide (as described, for example, in US 6610261 and US 6747087) are also suitable as reinforcing inorganic fillers.

It is not important in what physical state the reinforcing inorganic filler is provided, whether it be in the form of a powder, microbeads, granules, beads or any other suitable compact form. Of course, the term "reinforcing inorganic filler" is also understood to mean mixtures of different reinforcing inorganic fillers, in particular mixtures of highly dispersible siliceous fillers and/or aluminous fillers.

It will be understood by those skilled in the art that reinforcing fillers of another nature, in particular organic, can be used as fillers equivalent to the reinforcing inorganic fillers described in this section, provided that the reinforcing filler is covered with an inorganic layer (for example silica), or comprises, on its surface, functional sites (in particular hydroxyl sites) capable of establishing a bond between the filler and the elastomer, in the presence or absence of covering or coupling agents.

For coupling the reinforcing inorganic filler to the diene elastomer, it is possible to use, in a known manner, an at least bifunctional coupling agent (or bonding agent) intended to provide a satisfactory combination of chemical and/or physical properties between the inorganic filler (its particle surface) and the diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. "bifunctional" is understood to mean that the compound has 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 comprise 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.

Preferably, the organosilane is chosen from organosilane polysulfides (symmetrical or asymmetrical) (for example bis (3-triethoxysilylpropyl) tetrasulfide abbreviated to TESPT sold under the name Si69 by Evonik, or bis (3-triethoxysilylpropyl) disulfide abbreviated to TESPD sold under the name Si75 by Evonik), polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes (for example S- (3- (triethoxysilyl) propyl) octane thioesters sold under the name NXT Silane by Momentive). More preferably, the organosilane is an organosilane polysulfide.

The amount of coupling agent is preferably less than 12phr, it being understood that it is generally desirable to use as little coupling agent as possible. Generally, when a reinforcing inorganic filler is present, the coupling agent is present in an amount of 0.5 to 15% by weight relative to the amount of inorganic filler. The content of coupling agent is preferably in the range from 0.5phr 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, when reinforcing fillers are present, the content of reinforcing fillers (which preferably mainly comprise (even only) carbon black) may range from 20phr to 200phr, preferably from 30phr to 150phr, preferably from 40phr to 100phr, preferably from 50phr to 80 phr.

Cross-linking system

The crosslinking system may be any type of system known to those skilled in the art of pneumatic tire rubber compositions. The crosslinking system may be based in particular on sulfur and/or peroxide and/or bismaleimide.

Preferably, the crosslinking system is based on sulfur; the crosslinked system is called a vulcanization system. The sulphur may be provided in any form, in particular as molecular sulphur or as a sulphur-donating agent. It is also preferred that at least one vulcanization accelerator is present, and optionally, it is also preferred to use various known vulcanization activators such as zinc oxide, stearic acid or equivalent compounds (e.g., stearates and transition metal salts), guanidine derivatives (especially diphenylguanidine), or known vulcanization retarders.

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

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

Various additives

The rubber compositions according to the invention may also comprise all or part of the usual additives and processing aids known to the person skilled in the art and generally used in rubber compositions for pneumatic tires, such as, for example, plasticizers (for example plasticizing oils and/or plasticizing resins), pigments, protective agents (for example antiozone waxes, chemical antiozonants or antioxidants) or antifatigue agents.

Preferably, the composition according to the invention comprises no nitrile compound or less than 10phr, preferably less than 5phr, in a preferred manner less than 2phr, very preferably less than 1phr, still more preferably less than 0.5phr of nitrile compound.

The composition may be in the green state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization).

Rubber finished product or rubber semi-finished product and pneumatic tire

Another subject of the invention is a finished rubber product or a semi-finished rubber product comprising a composition according to the invention.

Another subject of the present invention is a pneumatic tire comprising a composition according to the invention.

Three regions may be defined within a pneumatic tire:

the radially outer region in contact with the ambient air, which comprises layers called "outer layers", which substantially comprise the tread and the tread side of the pneumatic tire. The outer sidewalls are elastomeric layers located outside the carcass reinforcement with respect to the inner cavity of the pneumatic tire and between the crown and the beads, covering completely or partially the area of the carcass reinforcement extending from the crown to the beads.

The radially inner region in contact with the inflation gas, which region usually consists of a layer that is gas-tight to the inflation gas (sometimes referred to as an inner gas-tight layer or liner).

The inner zone of the pneumatic tire, i.e. the zone between the outer zone and the inner zone. This region includes what is referred to herein as a layer or ply of the inner layer of the pneumatic tire. Such as a carcass ply, an undertread, a pneumatic tire belt ply, or any other layer not in contact with ambient air or the inflation gas of a pneumatic tire.

The compositions defined in this specification are particularly suitable for the inner and outer layers of pneumatic tires, and for the outer layer, for tread compositions.

According to the invention, the inner layer may be selected from the group consisting of carcass plies, crown plies, bead wire fillers, crown bases, decoupling layers, edge rubbers, filling rubbers, tread underlayers, and combinations of these inner layers. Preferably, the inner layer is selected from the group consisting of a carcass ply, a crown ply, a bead wire filler, a crown base, a decoupling layer, and combinations of these inner layers.

The composition according to the invention is also suitable for the inner and outer layers of non-pneumatic tires, in particular for the treads of non-pneumatic tires. It should be borne in mind that a non-pneumatic tire is one that supports the load of the vehicle by means other than pressurized inflation gas.

The invention relates in particular to a pneumatic tyre intended to equip a motor vehicle of the passenger vehicle, SUV (sport utility vehicle) or two-wheeled vehicle (in particular motorcycle) type, or an aircraft, or an industrial vehicle chosen from a lorry, a heavy vehicle, i.e. a subway, a bus, a heavy road transport vehicle (truck, tractor, trailer) or an off-road vehicle (for example a heavy agricultural or construction vehicle), or the like.

The present invention relates to articles comprising a rubber composition according to the invention in the raw state (i.e. before curing) and in the cured state (i.e. after crosslinking or vulcanization).

Preparation of rubber composition

The rubber compositions according to the invention can be manufactured in a suitable mixer using two successive preparation stages known to those skilled in the art:

a first stage of thermomechanical working or kneading ("non-productive" stage), which can be carried out in a single thermomechanical step, during which all the necessary components, in particular the elastomer matrix, the fillers and optionally other various additives other than the crosslinking system, are introduced into a suitable mixer, for example a standard internal mixer (for example of the "banbury" type). The filler can be incorporated into the elastomer by thermomechanical kneading in one portion or in batches. In the case where the filler has been incorporated, in whole or in part, into the elastomer in masterbatch form (for example as described in applications WO 97/36724 and WO 99/16600), a masterbatch of direct kneading, other elastomer or filler (if present) not present in masterbatch form in the composition and optionally other various additives besides the crosslinking system are also incorporated.

The non-productive phase is carried out at elevated temperature, with a maximum temperature of between 110 ℃ and 190 ℃, preferably between 130 ℃ and 180 ℃, for a duration generally between 2 minutes and 10 minutes.

A second stage of mechanical processing in an open mixer (for example, an open mill) after cooling the mixture obtained during the first non-productive stage to a lower temperature (generally less than 110 ℃, for example between 40 ℃ and 100 ℃) ("productive" stage). The crosslinking system is then incorporated and all the substances are mixed for several minutes, for example between 2 and 15 minutes.

The process for preparing such a composition comprises, for example, the following steps:

a) Incorporating the reinforcing filler into the diene elastomer during a first phase (the "non-productive" phase), thermomechanically kneading (for example, once or batchwise) all the mass until a maximum temperature between 110 ℃ and 190 ℃ is reached;

b) Cooling the combined mixture to a temperature of less than 100 ℃;

c) The cross-linking system is subsequently incorporated during the second stage (the "production" stage);

d) All materials were kneaded to a maximum temperature of less than 110 ℃.

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

The final composition thus obtained can then be calendered, for example in the form of a sheet or plate (in particular for laboratory characterization), or extruded in the form of a semifinished rubber product (or shaped element) for the manufacture of pneumatic tires.

The crosslinking of the composition may be carried out in a manner known to the skilled person, for example at temperatures and pressures between 130 ℃ and 200 ℃.

Detailed Description

Examples

Measurement and testing used

Scorch time

The measurements were carried out at 130 ℃ according to French Standard NF T43-005. The variation of the consistency index over time makes it possible to determine the scorch time (evaluated according to the above criteria) of the rubber composition by means of a parameter T5 (in the case of a large rotor) expressed in minutes, said parameter T5 being defined as the time required to obtain an increase in the consistency index (expressed in MU) which is 5 units above the lowest measurement of the index.

It should be borne in mind that, in a manner well known to those skilled in the art, the greater the time-varying consistency index, the more the cross-linking of the material will be delayed before curing.

Mooney plasticity

An oscillating consistometer as described in French Standard NF T43-005 (1991) was used. Mooney plasticity measurement was performed according to the following principle: the composition in the raw state (i.e. before curing) was moulded in a cylindrical chamber heated to 100 ℃. After one minute of preheating, the rotor was rotated at 2 revolutions per minute within the sample and the working torque to maintain this movement was measured after 4 minutes of rotation. Mooney plasticity (ML 1+ 4) is expressed in "Mooney units" (MU, 1MU =0.83 Newton. M).

It should be borne in mind that, in a manner well known to those skilled in the art, the lower the mooney plasticity, the easier the material is to process. Of course, beyond a certain value (e.g., 20 MU), the material becomes too liquid to be used, particularly for making the inner layer.

Tensile test

The test was carried out according to French standard NF T46-002, 9 months 1988. All tensile measurements were carried out according to French Standard NF T40-101 (12 months 1979) at a temperature representative of the working temperature of the composition in the tyre (100. + -. 2 ℃) and under standard hygrometric conditions (50. + -. 5% relative humidity).

In the second elongation (i.e. after conditioning), the nominal secant modulus (or apparent stress in MPa) was measured in samples cured at 150 ℃ for 60 minutes at 100% elongation (denoted MA 100) and at 300% elongation (denoted MA 300), which was calculated by reducing to the initial cross section of the specimen.

Representative enhanced MA300/MA100 ratios are given in the table.

Preparation of the composition

The following tests were performed in the following manner: the diene elastomer, the reinforcing filler, between 1phr and 30phr of the epoxy resin and the various other ingredients, except for the crosslinking system, are introduced continuously into an internal mixer (final filling: about 70% by volume) with an initial vessel temperature of about 60 ℃. Thermomechanical working (non-productive phase) is then carried out in one step, for a total of about 3 to 4 minutes, until a maximum "tapping" temperature of 165 ℃ is reached.

The mixture thus obtained is recovered and cooled, then the sulphur, the sulfenamide-type accelerator, the high-retarding hardener are incorporated into a mixer (homogeneous finisher) at 30 ℃ and all the substances are mixed (production stage) for a suitable time (for example between 5 and 12 minutes).

The composition thus obtained is subsequently calendered (for measuring its physical or mechanical properties) in the form of a rubber sheet (thickness from 2mm to 3 mm) or a rubber sheet, or extruded in the form of a profiled element.

The crosslinking of the composition is carried out at a temperature of 150 ℃ under pressure for 60 minutes.

Testing of rubber compositions

Two rubber compositions were prepared as described above, one rubber composition according to the present invention (hereinafter referred to as C-2), and one rubber composition not according to the present invention (control composition, hereinafter referred to as C-1). Their formulations (in phr) and their properties are summarized in table 1 below.

The compositions shown in Table 1, except for comparative composition C-1, did not result in the formation of formaldehyde during the curing process.

Composition C-2 contained an epoxy resin and a urea compound as a replacement for the phenol/formaldehyde resin-HMT hardener pair present in the conventional control composition C-1.

All results are expressed on a base 100 using the control composition C-1 as reference. A value less than 100 means a value lower than that of the control composition, and a value greater than 100 means a value greater than that of the control composition.

[ Table 1]

(1) Natural rubber

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

(3) Zinc oxide (Industrial grade-Umicore)

(4) N- (1, 3-dimethylbutyl) -N-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys)

(5) Stearin (Pristerene 4931 from Uniqema)

(6) N-Cyclohexylbenzothiazole sulfenamide (Santocure CBS from Flexsys)

(7) Phenol/formaldehyde novolac resin (Peracit 4536K from Perstorp)

(8) Hexamethylenetetramine (from Degussa)

(9) Epoxy phenol novolac resin (EPN 1138 from Huntsman)

(10) Amicure UR2T from Evonik

It is noted that the composition according to the invention makes it possible to obtain a reinforcing effect similar to that of the control composition with a smaller amount of hardener, while exhibiting an extended scorch time and a lower Mooney viscosity, thus improving processability.

Claims

1. Rubber composition based on at least one diene elastomer, a reinforcing filler, a crosslinking system based on sulfur, from 1 to 30 parts by weight per hundred parts by weight of elastomer phr of an epoxy resin and of the general formula (R)₁R₂)N-CO-(NR₃)-R₇-(NR₄)-CO-N(R₅R₆) Wherein R is₁To R₆Each independently selected from a hydrogen atom, having 1 to 20 carbon atomsAn alkyl group having 5 to 24 carbon atoms, a cycloalkyl group having 6 to 30 carbon atoms, and an aralkyl group having 7 to 25 carbon atoms, in one aspect R₂And R₃The radicals being able to form together a ring, on the other hand R₄And R₅The radicals being able to form together a ring, R₇The group is a divalent aryl group having 6 to 30 carbon atoms.

2. Rubber composition according to the preceding claim, in which R₁To R₆Each 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, R₇The group is a divalent aryl group having 6 to 8 carbon atoms.

3. The rubber composition of any of the preceding claims, wherein R₇The group is a divalent methylphenyl group.

4. The rubber composition of any of the preceding claims, wherein R₁To R₇The groups do not together form a ring.

5. The rubber composition of any of the preceding claims, wherein R₃And R₄Each group is a hydrogen atom.

6. The rubber composition of any of the preceding claims, wherein at least one R₁、R₂、R₅Or R₆The group is an aryl group having 6 to 8 carbon atoms, preferably a phenyl group.

7. The rubber composition according to any one of claims 1 to 5, wherein R₁、R₂、R₅And R₆The groups are independently selected from methyl groups and ethyl groups.

8. The rubber composition of claim 1, wherein R₁、R₂、R₅And R₆The radical being a methyl radical, R₃And R₄Is a hydrogen atom, R₇Is a divalent methylphenyl radical.

9. The rubber composition according to any one of the preceding claims, wherein the content of urea compound is in the range of 1 to 15phr, preferably 0.5 to 10phr, preferably 0.5 to 8phr and preferably 0.5 to 5 phr.

10. Rubber composition according to any one of the preceding claims, wherein the epoxy resin is selected from aromatic epoxy resins, cycloaliphatic epoxy resins and aliphatic epoxy resins.

11. The rubber composition according to any one of the preceding claims, comprising no nitrile compound or less than 10phr, preferably less than 5phr and preferably less than 2phr of nitrile compound.

12. A rubber finished product or rubber semi-finished product comprising the rubber composition according to any of the preceding claims.

13. A pneumatic or non-pneumatic tire comprising the rubber composition according to any one of claims 1 to 11.