Rubber composition based on pyrolytic carbon black and epoxy resin

Abstract

The invention relates to a rubber composition based on at least one diene elastomer, a reinforcing filler comprising pyrolytic carbon black, a crosslinking system, between 1 phr and 30 phr of an epoxy resin, and between 0.5 phr and 15 phr of a hardener.

Description

TECHNICAL FIELD

[0001] The present invention relates to a rubber composition intended in particular for the manufacture of tires or tire semi-finished products. Another subject of the present invention is a finished or semi-finished rubber product comprising the rubber composition according to the present invention, and a pneumatic or non-pneumatic tire comprising at least one rubber composition according to the present invention. BACKGROUND ART

[0002] It is well known to use, in certain parts of pneumatic tires, a rubber composition having a high stiffness during the small strain of the pneumatic tire, as described in application WO 02 / 10269. Resistance to small strain is one of the properties that a pneumatic tire must exhibit in response to the stresses it undergoes.

[0003] This hardening can be obtained by increasing the content of reinforcing fillers or by introducing certain reinforcing resins into the constituent rubber composition of the part of the pneumatic tire.

[0004] The reinforcing resins commonly used to increase the stiffness of rubber 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 are widely used to denote compounds that are capable of reacting together to generate a reinforcing resin by condensation according to a three-dimensional network, which on the one hand overlaps and interpenetrates with the reinforcing filler / elastomer network and, on the other hand, overlaps and interpenetrates with the elastomer / sulfur network (if the crosslinking agent is sulfur). Generally, the methylene acceptor is a phenolic resin. Linear phenolic resins have been used in rubber compositions intended in particular for pneumatic tires or the treads of pneumatic tires, and their applications vary with grip or reinforcements: for example, reference may be made to patent EP0649446 B1.

[0005] The above methylene acceptor is combined with a hardening agent capable of crosslinking or hardening it, which hardening agent is also commonly referred to as a "methylene donor" or simply as a "hardening agent". Then, during the curing of the rubber matrix, crosslinking of the resin is achieved by forming methylene bridges between the carbon in the ortho and para positions of the phenolic nucleus of the resin and the methylene donor, thereby generating a three-dimensional resin network.

[0006] Application WO 2011 / 045342 describes rubber compositions comprising epoxy resin pairs and amine-containing hardening agents. In addition to having the advantage of not generating formaldehyde, these compositions also exhibit a greater stiffness after crosslinking while maintaining an acceptable rolling resistance. Application WO 2018 / 002538 describes rubber compositions comprising epoxy resins and amine-containing hardening agents, the amine-containing hardening agents comprising at least two primary amine functional groups located on at least one six-membered aromatic ring, and the rubber compositions are intended to improve the compromise between processability (especially scorch time) and stiffness compared to known rubber compositions.

[0007] To minimize the environmental impact of the manufacture of rubber articles, particularly pneumatic tires, novel reinforcing fillers derived from the recycling of rubber articles have been developed. These "pyrolysis" carbon blacks have reinforcing properties. However, due to their characteristics, unlike carbon blacks directly produced from fossil resources (referred to as ASTM carbon blacks), the interactions between pyrolysis carbon blacks and the other components of rubber compositions and their effects on the properties of rubber articles remain unclear.

[0008] There is always a desire to further improve the properties of rubber compositions, particularly the compromise between stiffness and loss of hysteresis, without degrading the properties of these compositions in the uncured state, while minimizing the environmental impact of these compositions.

[0009] Surprisingly, during the course of its research, the Applicant has found that the combination of an epoxy resin and a pyrolysis carbon black is capable of improving the stiffness and loss of hysteresis of rubber compositions at low strain, without degrading the uncured properties (particularly the viscosity of the composition), while minimizing the environmental impact of such a composition. Summary of the Invention

[0010] Definitions

[0011] The carbon-containing compounds mentioned in the description can be compounds of fossil origin or bio-based compounds. In the case of bio-based compounds, they can be partially or completely derived from biomass or obtained from renewable raw materials derived from biomass. This particularly relates to polymers, plasticizers, fillers, etc.

[0012] Diene elastomers

[0013] The rubber compositions according to the invention comprise at least a diene elastomer. It should be remembered that the term "elastomer of diene type" should be understood to mean an elastomer obtained at least in part (i.e., homopolymer or copolymer) from diene monomers (monomers having two conjugated or non-conjugated carbon-carbon double bonds).

[0014] These diene elastomers can be divided into two categories: "substantially unsaturated" or "substantially saturated". The term "substantially unsaturated" is generally understood to mean a diene elastomer that is at least partially produced from conjugated diene monomers and has a diene source (conjugated diene) unit content greater than 15% (mol%); thus, for example, the diene elastomers of butyl rubber or EPDM-type copolymers of dienes and α-olefins do not fall within the foregoing definition but can be specifically described as "substantially saturated" diene elastomers (low or very low diene source unit content, always less than 15% (mol)). The diene elastomers comprised in the rubber compositions according to the invention are preferably substantially unsaturated.

[0015] The term "diene elastomers capable of being used in the rubber compositions according to the invention" is particularly understood to mean:

[0016] a) Any homopolymer of a conjugated or non-conjugated diene monomer having 4 to 18 carbon atoms;

[0017] b) Any copolymer of a conjugated or non-conjugated diene having 4 to 18 carbon atoms and at least one other monomer.

[0018] The other monomer can be ethylene, an olefin, or a conjugated or non-conjugated diene.

[0019] Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, especially 1,3-dienes, such as especially 1,3-butadiene and isoprene.

[0020] Suitable olefins are vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms.

[0021] Examples of suitable vinyl aromatic compounds are styrene, (o-, m- or p-)methylstyrene, the commercial mixture "vinyltoluene" or p-(tert-butyl)styrene.

[0022] Suitable aliphatic α-monoolefins are especially acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

[0023] The diene elastomer is preferably a diene elastomer of the highly unsaturated type, especially a diene elastomer selected from natural rubber (NR), synthetic polyisoprene (IR), polybutadiene (BR), butadiene copolymers, isoprene copolymers, and mixtures of these elastomers. Such copolymers are more preferably selected from butadiene / styrene copolymers (SBR), isoprene / butadiene copolymers (BIR), isoprene / styrene copolymers (SIR), isoprene / butadiene / styrene copolymers (SBIR), ethylene / butadiene copolymers (EBR), and mixtures of these copolymers.

[0024] The above-mentioned diene elastomers can be, for example, block elastomers, random elastomers, sequential elastomers or micro-sequential elastomers, and can be prepared in a dispersion or in solution; they can be coupled and / or star-branched or functionalized with a coupling agent and / or a star-branching agent or a functionalizing agent, such as epoxidation.

[0025] Preferably, the rubber composition according to the invention comprises at least 50 phr, preferably at least 70 phr, preferably at least 90 phr of at least one isoprene elastomer. In a highly preferred embodiment, the elastomer composition of the composite material according to the invention comprises 100 phr of at least one isoprene elastomer.

[0026] The term "isoprene elastomer" is understood to mean an isoprene homopolymer or copolymer, in other words, a diene elastomer selected from natural rubber (NR) (which may be plasticized or peptized), synthetic polyisoprene (IR), various isoprene copolymers (in particular isoprene / styrene (SIR) copolymers, isoprene / butadiene (BIR) copolymers or isoprene / butadiene / styrene (SBIR) copolymers) and mixtures of these elastomers.

[0027] Preferably, the isoprene elastomer is selected from synthetic polyisoprene, natural rubber, isoprene copolymers and mixtures thereof, preferably from natural rubber, polyisoprene having a cis-1,4-bond content by weight of at least 90%, more preferably at least 98% relative to the weight of the isoprene elastomer, and mixtures thereof. Very preferably, the isoprene elastomer is natural rubber.

[0028] In the rubber composition according to the invention, the elastomer represents the continuous phase in which the other components are dispersed.

[0029] Epoxy resin

[0030] The rubber composition according to the invention comprises an epoxy resin between 1 phr and 30 phr.

[0031] Epoxy resins that can be used in the present invention include all polyepoxide compounds. They can relate, for example, to aromatic epoxy resins, cycloaliphatic epoxy resins and aliphatic epoxy resins. For example, the aromatic epoxy resin can be an amine-aromatic epoxy resin. These resins are preferably epoxy novolac resins, i.e., epoxy resins obtained by an acid catalyst as compared to novolac resins obtained by an alkali catalyst.

[0032] Particularly among aromatic epoxides, preferred epoxy resins are selected from resins of the following types: 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-tolyl glycidyl ether)-co-formaldehyde], poly[(o-phenyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)], tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane and mixtures of these resins.

[0033] The term "epoxy resins of the following types" is understood to mean resins based on units of the component (i.e., containing the component or oligomers of the component).

[0034] The epoxy resin is a cured resin. The term "cured resin" is understood to mean a resin which, when introduced into the rubber composition together with a curing agent, is capable of increasing the stiffness of the crosslinked rubber composition. As it happens, an increase in the stiffness of the rubber composition is usually accompanied by an increase in the loss of hysteresis.

[0035] Also preferably, the epoxy resin is selected from resins of the following types: poly[(o-tolyl glycidyl ether)-co-formaldehyde], poly[(o-phenyl glycidyl ether)-co-formaldehyde], tris(glycidyloxy phenyl) methane, tetrakis(glycidyloxy phenyl) ethane, and mixtures of these resins.

[0036] Very preferably, the epoxy resin used in the context of the present invention is selected from epoxy resins having the following general formulas (I) and (II) and their derivatives, i.e., oligomers of the compounds of general formulas (I) and (II):

[0037] a.

[0038] b.

[0039] n is an integer representing the degree of polymerization, and the range of n is from 1 to 15, preferably from 1 to 10, more preferably from 1 to 5, and very preferably from 1 to 3.

[0040] Examples of commercially available epoxy resins that can be used in the context of the present invention include, for example, DEN 439 epoxy resin from Uniqema, tris(4-hydroxyphenyl) methane triglycidyl ether epoxy resin from Sigma-Aldrich, Araldite ECN 1299 epoxy cresol novolak resin from Huntsman or Araldite EPN 1138 epoxy phenol novolak resin from Huntsman, EPPN-502H, EPPN-501H, and EPPN-501HY resins from Nippon Kayaku, or EPON 1031 resin from Hexion.

[0041] Preferably, the rubber composition according to the present invention does not contain a curing resin other than the epoxy resin, and in particular does not contain a resin of the phenol / formaldehyde type.

[0042] The amount of the epoxy resin is between 1 phr and 30 phr. Considering the amine-based hardener used in the context of the present invention, when the minimum content of the epoxy resin shown is exceeded, the target technical effects are insufficient, while when the maximum value shown is exceeded, there is a risk of excessive increase in stiffness and excessive impairment of hysteresis and Mooney plasticity. More preferably, the content of the epoxy resin in the rubber composition according to the present invention is between 10 phr and 28 phr. The content of the epoxy resin of the present invention can ensure sufficient stiffness of the rubber composition while enabling the rubber composition to maintain an elastic type behavior after crosslinking.

[0043] Hardener

[0044] The rubber composition according to the present invention contains 0.5 phr to 15 phr of a hardener. Any hardener capable of crosslinking the epoxy resin used in the rubber composition according to the present invention may be suitable as the hardener. In particular, the hardener may be selected from aromatic diamines, aliphatic diamines, acid anhydrides (such as benzoic anhydride and maleic anhydride), and ureas.

[0045] The urea hardener is a compound having the general formula (R1,R2)N-CO-N(R3,R4) or (R1,R2)N-CO-(NR3)-R7-(NR4)-CO-N(R5,R6), wherein the groups R1 to R6 are each independently selected from:

[0046] · a hydrogen atom,

[0047] · an alkyl group having 1 to 20 carbon atoms,

[0048] · a cycloalkyl group having 5 to 24 carbon atoms,

[0049] · an aryl group having 6 to 30 carbon atoms, and

[0050] · an aralkyl group having 7 to 25 carbon atoms.

[0051] In the general formula (R1,R2)N-CO-N(R3,R4), it should be understood that the group CO represents a carbon atom bonded to an oxygen atom by a double bond, and the groups (R1,R2)N (respectively N(R3,R4)) represent nitrogen atoms covalently bonded to the group R1 and the group R2. Such a molecule is shown as follows.

[0052]

[0053] In the general formula (R1,R2)N-CO-(NR3)-R7-(NR4)-CO-N(R5,R6), it should be understood that the CO group represents a carbon atom bonded to an oxygen atom by a double bond, the groups (R1,R2)N (respectively N(R5,R6)) represent nitrogen atoms covalently bonded to the R1 group and the R2 group, the groups (NR3) (respectively (NR4)) represent nitrogen atoms covalently bonded to the R3 group, and the R7 group represents a divalent group bonded on the one hand to the nitrogen atom bearing the R3 group and on the other hand to the nitrogen atom bearing the R4 group.

[0054] Preferably, the hardener is selected from aromatic diamines and ureas. In fact, these classes of hardeners exhibit a balance of crosslinking speed during curing / stiffness of the crosslinked product, which is particularly advantageous for the rubber composition according to the present invention.

[0055] Very preferably, according to the present invention, the hardener containing an aromatic diamine is selected from the following compounds and mixtures of these compounds:

[0056]

[0057] As examples of commercially available amine hardeners that can be used in the context of the present invention, mention may be made, for example, of Ethacure 100 or Ethacure 300 from Albemarle or Lonzacure DETDA, Lonzacure MDEA or Lonzacure MCDEA from Lonza.

[0058] Preferably, the urea does not contain an aromatic ring.

[0059] Preferably, the groups R1, R2, R3 and R4 are each a hydrogen atom. A compound of the formula H2N-CO-NH2 is generally referred to as "urea" or "carbamide".

[0060] Preferably, in the compound of the general formula (R1,R2)N-CO-(NR3)-R7-(NR4)-CO-N(R5,R6), the groups R1, R2, R5 and R6 are methyl groups, R3 and R4 are hydrogen atoms, and R7 is a divalent methylphenyl group. An example of such a diurea compound is the compound Amicure UR2T of the formula 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) from Evonik.

[0061] Very preferably, according to the present invention, the urea is selected from carbamide, N,N'-dimethylurea, ethyleneurea, N-phenylurea, 1,3-diphenylurea and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, preferably from urea, N,N'-dimethylurea, N-phenylurea, 1,3-diphenylurea and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, very preferably from carbamide, N,N'-dimethylurea and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, and very preferably is the carbamide (also called urea) of the formula H2N-CO-NH2.

[0062] The amount of hardener in the rubber composition is in the range of 0.5 phr to 15 phr. Below the minimum value shown, the target technical effect has proven insufficient, while above the maximum value shown, there is a risk of being unfavorable to the processing of the rubber composition in the uncured state. Preferably, the content of the hardener is in the range of 0.5 phr to 10 phr, preferably in the range of 0.5 phr to 8 phr.

[0063] Pyrolytic carbon black

[0064] The rubber composition according to the invention comprises a reinforcing filler, said reinforcing filler comprising pyrolytic carbon black, preferably consisting essentially of pyrolytic carbon black. The term "essentially" is understood to mean that the pyrolytic carbon black represents at least 50% by weight of the total weight of the reinforcing filler. Preferably, the pyrolytic carbon black represents at least 70% by weight of the total weight of the reinforcing filler, preferably at least 80% by weight of the total weight of the reinforcing filler, preferably at least 90% by weight of the total weight of the reinforcing filler. Very preferably, the reinforcing filler consists of pyrolytic carbon black.

[0065] For the purposes of the present invention, the term "pyrolytic carbon black" is understood to mean carbon black produced by the pyrolysis of a carbon-based polymeric material (hereinafter referred to as the material to be pyrolyzed) comprising at least one polymer and carbon black, such material possibly being from recycling. The term "recycling" is understood to mean a process capable of treating products that may have been used so as to reintroduce a part of these materials into the production of new objects. The term "carbon-based polymeric material" is understood to mean a material comprising at least one polymer based on hydrogen and carbon. The physical state of such material to be pyrolyzed provided, whether in powder, granule, strip or any other suitable densified form, whether crosslinked or uncrosslinked, is not important.

[0066] Preferably, the material to be pyrolyzed can be recovered from manufactured articles or products generated during their manufacture / production (such as by-products or waste); these manufactured articles can be selected from pneumatic tires, non-pneumatic tires, industrial conveyor belts, conveyor belts, rubber seals, rubber hoses, shoe soles and windshield wipers. Even more preferably, the pyrolytic carbon black that can be used in the context of the present invention is carbon black obtained by the pyrolysis of a material to be pyrolyzed originating from manufactured articles selected from pneumatic tires and non-pneumatic tires.

[0067] In the context of the present invention, pyrolysis means any type of thermal decomposition carried out under anaerobic conditions, the raw material of which is the material to be pyrolyzed as defined above. Thus, pyrolytic carbon black differs from "industrial" carbon black and / or "ASTM grade" carbon black in that the carbon-based raw material used for pyrolysis is a material comprising at least a carbon-based polymer and carbon black, rather than a material originating from petroleum fractions or from oils of coal or natural origin.

[0068] Pyrolytic carbon black is sold, for example, by BlackBear under the reference "BBCT30", or by Scandinavian EnviroSystems under the reference "P550".

[0069] The pyrolytic carbon black that can be used in the context of the present invention differs particularly from known carbon blacks (such as industrial carbon black), in particular "furnace" carbon black, by a higher ash content.

[0070] Preferably, the ash content of the pyrolytic carbon black that can be used in the context of the present invention is in the range of 5 wt% to 30 wt%, more preferably 8 wt% to 25 wt%, still more preferably 10 wt% to 22 wt%, relative to the total weight of the pyrolytic carbon black.

[0071] Preferably, the sulfur content of the pyrolytic carbon black that can be used in the context of the present invention is also greater than 2 wt%, preferably in the range of 2.5 wt% to 5 wt%, relative to the total weight of the pyrolytic carbon black.

[0072] Preferably, the zinc content of the pyrolytic carbon black that can be used in the context of the present invention is also greater than or equal to 2 wt%, preferably in the range of 2.5 wt% to 8 wt%, relative to the total weight of the pyrolytic carbon black.

[0073] Preferably, the STSA specific surface area of the pyrolytic carbon black that can be used in the context of the present invention, measured according to ASTM standard D 6556-2021, is in the range of 20 m 2 / g to 200 m 2 / g, more preferably 30 m 2 / g to 90 m 2 / g.

[0074] Preferably, the void volume of the pyrolytic carbon black that can be used in the context of the present invention, measured according to ASTM standard D7854 (2018) at a pressure of 50 MPa, is in the range of 30 ml / 100 g to 60 ml / 100 g, more preferably 35 ml / 100 g to 55 ml / 100 g.

[0075] The ash content is determined by calcination in a platinum dish in a muffle furnace at 825 °C according to the following protocol. Before each series of measurements, the platinum dish is pre-determined and the tare weight of the platinum dish is weighed to within an error of 0.1 mg, and the weight is designated as P0. A 5 g sample of pyrolytic carbon black is placed into the platinum dish. The platinum dish is accurately weighed to within an error of 0.1 mg; this mass is designated as P1. The platinum dish and its contents are pre-calcined using a Bunsen burner until smoke appears and the product ignites. After the combustion of the product is complete, the platinum dish and its contents are placed into a muffle furnace heated to 825 °C for 1 h. After 1 h, the platinum dish is removed from the furnace and immediately placed into a desiccator at ambient temperature. When the platinum dish and the ash have returned to ambient temperature, the platinum dish is weighed again to obtain the weight P2. Finally, the following formula can be used to obtain the ash content (% ash):

[0076]

[0077] After calcining the sample, the ash is absorbed in an acidic medium, and the zinc content in the pyrolytic carbon black is determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry). The ash content is obtained by carrying out the procedure described above. Take 100 mg of ash (the sample) and place it into a PFA (Perfluoroalkoxy) tube for a HotBlock hot plate. Subsequently, add 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid, and 0.5 ml of 40% hydrofluoric acid. Seal the tube with a tube stopper and heat it to 130 °C for 2 h. After cooling, then transfer the contents to a 100 ml PTFE (Polytetrafluoroethylene) volumetric flask that already contains 2 g of boric acid (for neutralizing hydrofluoric acid) using ultrapure water. Dilute the solution to the mark with ultrapure water. Dilute the obtained solution 100 times by taking 1 ml of the solution and placing it into a 100 ml PFTE volumetric flask that precontains 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid, 0.5 ml of 40% hydrofluoric acid, and 2 g of boric acid. Then, before analyzing by ICP-AES, filter the diluted solution through a 0.45 μm GHP syringe filter. Before analyzing the diluted solution, analyze at least 5 standard samples with zinc concentrations of 0 mg / l, 0.5 mg / l, 1 mg / l, 2 mg / l, and 5 mg / l by ICP-AES. Prepare these standard samples by diluting a commercial solution with a certified zinc concentration of 1 g / l in a 100 ml volumetric flask.

[0078] These volumetric flasks precontain 8 ml of 37% concentrated hydrochloric acid, 3 ml of 65% concentrated nitric acid, 0.5 ml of 40% hydrofluoric acid, and 2 g of boric acid. Analyze the standard solution by ICP-AES at a wavelength of λ Zn = 202.613 nm. For each standard concentration (c), plot the intensity of the zinc signal λ Zn on a λ Zn = f(c) curve, which corresponds to a calibration line (of the y = ax + b type). Subsequently, measure the sample solution (the diluted solution) with an unknown concentration under the same conditions as the standard samples. Relate the measured intensity to the concentration through the calibration line obtained above. Since the sample and volume have been pre-recorded, the concentration [c] 灰分 (in wt%) is directly obtained by software. The zinc concentration [c] 炭黑 (in wt%) in the pyrolytic carbon black is obtained by the following equation:

[0079] [c] 炭黑 = [c] 灰分 * 100 × % ash

[0080] Determination of sulfur content in pyrolytic carbon black by a LECO furnace. The LECO sulfur analyzer is designed to measure the sulfur content in organic materials and / or inorganic materials, particularly by combustion and non-dispersive infrared detection. Before measuring the sulfur content of a sample, the boat is cleaned and the furnace is calibrated. The boat used for the LECO furnace is pre-cleaned: this involves analyzing an empty boat under the same conditions as the sample. A calibration curve is prepared starting from a commercial reference sample called "BBOT", with a purity greater than 99.99%, and ensuring the contents of carbon (C), hydrogen (H), nitrogen (N), oxygen (O) and sulfur (S). These contents are as follows: C%: 72.52; H%: 6.09; N%: 6.51; O%: 7.43 and S%: 7.44. Weigh approximately 10 ± 3 mg, 20 ± 3 mg and 40 ± 3 mg of BBOT on the boat. The reference sample / boat assembly is introduced into the combustion furnace, adjusted to 1350 °C under pure oxygen. The combination of the furnace temperature and the analysis flow rate causes the combustion of the sample, releasing sulfur and / or carbon in the form of SO2(g). After 20 s, oxygen starts to flow through the lance, thus accelerating the combustion of difficult-to-combust materials. Sulfur and / or carbon in the form of SO2(g) are entrained by the oxygen flow until they pass through the infrared detection unit. The software of the instrument plots a straight line that relates the weight of the introduced reference sample and the response (area) observed on the detector. The calibration line is thus obtained. After carefully cleaning the sampling equipment, weigh approximately 80 ± 5 mg of pyrolytic carbon black and place it in the boat used for the LECO furnace. The area of the SO2 peak observed is related to the concentration by the calibration line. The software of the instrument then calculates the weight % of sulfur in the sample based on the weight of the sample placed in the boat.

[0081] Preferably, the rubber composition according to the invention further comprises carbon black that is not pyrolytic carbon black for the purposes of the present invention, said carbon black being called ASTM grade carbon black, as defined according to ASTM standard D1765-96.

[0082] The rubber composition according to the invention may also comprise reinforcing inorganic fillers, preferably silica.

[0083] All carbon blacks typically used in pneumatic tires (in particular carbon blacks of the HAF, ISAF or SAF type) ("tire-grade" carbon blacks) are suitable as ASTM-grade carbon blacks. Among "tire-grade" carbon blacks, reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grade) will be mentioned more particularly (such as N115, N134, N234, N326, N330, N339, N347 and N375 carbon blacks), or higher series carbon blacks depending on the target application (such as N660, N683 or N772). The carbon black can have been introduced, for example, into an isoprene elastomer in the form of a masterbatch (see, for example, applications WO 97 / 36724 and WO 99 / 16600). The BET specific surface area of the carbon black is measured according to standard D6556-10 [multi-point (at least 5 points) method - gas: nitrogen - relative pressure p / p0 range: 0.1 to 0.3].

[0084] In the present patent application, by definition, the term "reinforcing inorganic filler" should be understood to mean any inorganic filler or mineral filler (regardless of its color and its origin (natural or synthetic)), different from carbon black, which is also called "white filler", "transparent filler" or even "non-black filler", capable of reinforcing alone a rubber composition intended for the manufacture of pneumatic tires without any method other than an intermediate coupling agent, in other words, which is capable of replacing conventional tire-grade carbon black in terms of reinforcing action; in a known manner, such fillers are generally characterized by the presence of hydroxyl (-OH) groups on their surface.

[0085] Mineral fillers of the siliceous type (in particular silica (SiO2)) or mineral fillers of the aluminous type (in particular alumina (Al2O3)) are particularly suitable as reinforcing inorganic fillers. The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated silica, pyrogenic silica or silica of biobased origin with a BET specific surface area and a CTAB specific surface area both less than 450 m 2 / g, preferably from 30 m 2 / g to 400 m 2 / g. As highly dispersible precipitated silica ("HDS"), mention will be made, for example, of Ultrasil 7000 and Ultrasil 7005 silica from Degussa, Zeosil 1165MP, 1135MP and 1115MP silica from Rhodia, Hi-Sil EZ150G silica from PPG, Zeopol 8715, 8745 and 8755 silica from Huber or silica with a high specific surface area as described in application WO 03 / 16837.

[0086] The BET specific surface area of silica is determined by gas adsorption in a known manner using the Brunauer - Emmett - Teller method described in "The Journal of the American Chemical Society", Volume 60, page 309, February 1938, and more specifically in accordance with the French standard NF ISO 9277 of December 1996 (multi - point (5 points) volumetric method - gas: nitrogen - degassing: 1 hour at 160 °C - relative pressure p / p0 range: 0.05 to 0.17). The CTAB specific surface area of silica is determined in accordance with the French standard NF T 45 - 007 of November 1987 (method B).

[0087] Mineral fillers of the aluminous type (in particular alumina (Al2O3) or aluminum (oxide) hydroxide) or reinforcing titanium oxides (such as the reinforcing titanium oxides described in US 6610261 and US 6747087) are also suitable as reinforcing inorganic fillers.

[0088] It is not important in what physical state the reinforcing inorganic filler is provided, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" is also understood to mean a mixture of different reinforcing inorganic fillers, in particular a mixture of highly dispersible siliceous fillers and / or aluminous fillers.

[0089] Those skilled in the art will understand that a reinforcing filler of another nature (in particular of organic nature) can be used as a filler equivalent to the reinforcing inorganic fillers described in this section, provided that the reinforcing filler is covered with an inorganic layer (such as silica) or contains functional sites (in particular hydroxyl sites) on its surface capable of establishing a bond between the filler and the elastomer in the presence or absence of a covering agent or a coupling agent.

[0090] In order to couple the reinforcing inorganic filler to the diene elastomer, at least a bifunctional coupling agent (or binder) intended to provide a satisfactory chemical and / or physical connection between the inorganic filler (on the surface of its particles) and the diene elastomer can be used in a known manner. In particular, at least a bifunctional organosilane or polyorganosiloxane is used. The term "bifunctional" is understood to mean a compound having a first functional group capable of interacting with the inorganic filler and a second functional group capable of interacting with the diene elastomer. For example, such a bifunctional compound can contain a first functional group containing a silicon atom and a second functional group containing a sulfur atom, the first functional group being capable of interacting with the hydroxyl groups of the inorganic filler and the second functional group being capable of interacting with the diene elastomer.

[0091] Preferably, the organosilane is selected from (symmetric or asymmetric) organosilane polysulfides (such as bis(3-triethoxysilylpropyl)tetrasulfide (abbreviated as TESPT) sold by Evonik under the name Si69, or bis(3-triethoxysilylpropyl)disulfide (abbreviated as TESPD) sold by Evonik under the name Si75), polyorganosiloxanes, mercapto-silanes, capped mercapto-silanes (for example, S-[3-(triethoxysilyl)propyl] thioctanoate sold by Momentive under the name NXT Silane). More preferably, the organosilane is an organosilane polysulfide.

[0092] The content of the coupling agent is preferably less than 12 phr, and it should be understood that it is generally desirable to use as little coupling agent as possible. Generally, when there is reinforcing inorganic filler, the content of the coupling agent accounts for 0.5 wt% to 15 wt% relative to the amount of the inorganic filler. Its content is preferably in the range of 0.5 phr to 15 phr. A person skilled in the art can easily adjust this content according to the content of the inorganic filler used in the rubber composition.

[0093] The content of the reinforcing filler (the reinforcing filler preferably mainly (or even only) comprises pyrolytic carbon black) is preferably in the range of 20 phr to 200 phr, preferably 30 phr to 150 phr, preferably 40 phr to 100 phr, preferably 50 phr to 80 phr.

[0094] Crosslinking system

[0095] The crosslinking system can be any type of system known to those skilled in the art of pneumatic tire rubber compositions. The crosslinking system can be particularly based on sulfur and / or peroxides and / or bismaleimides.

[0096] Preferably, the crosslinking system is based on sulfur; then it is called a vulcanization system. Sulfur can be provided in any form (especially in the form of molecular sulfur or sulfur donors). It is also preferred to have at least one vulcanization accelerator, and optionally, various known vulcanization activators or known vulcanization retarders can also be preferably used. Examples of such vulcanization activators are zinc oxide, stearic acid or equivalent compounds (such as stearates) and transition metal salts, guanidine derivatives (especially diphenylguanidine).

[0097] Sulfur is used in a content preferably between 0.5 phr and 12 phr, especially between 1 phr and 10 phr. A vulcanization accelerator is used in a content preferably between 0.5 phr and 10 phr, more preferably between 0.5 phr and 8.0 phr.

[0098] As an accelerator, any compound that can act as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used, in particular thiazole-type accelerators and their derivatives, or sulfenamides, thiurams, dithiocarbamates, dithiophosphates, thioureas, and xanthate-type accelerators. As examples of such accelerators, the following compounds may be particularly mentioned: 2-mercaptobenzothiazole disulfide (abbreviated as MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS), N-(tert-butyl)-2-benzothiazole sulfenamide (TBBS), N-(tert-butyl)-2-benzothiazole sulfimide (TBSI), zinc dibenzyldithiocarbamate (ZBEC), and mixtures of these compounds.

[0099] Various additives

[0100] The rubber composition according to the invention may further comprise all or some of the common additives and processing aids known to those skilled in the art and commonly used in pneumatic tire rubber compositions, such as plasticizers (e.g., plasticizing oils and / or plasticizing resins), pigments, protective agents (e.g., antiozonant waxes, chemical antiozonants, or antioxidants), or antifatigue agents.

[0101] Preferably, the rubber composition according to the invention does not contain nitrile compounds, or contains less than 10 phr, preferably less than 5 phr, more preferably less than 2 phr, very preferably less than 1 phr, and still more preferably less than 0.5 phr of nitrile compounds.

[0102] The rubber composition can be in an uncured state (before crosslinking or vulcanization) or a cured state (after crosslinking or vulcanization).

[0103] Finished or semi-finished rubber articles and pneumatic tires

[0104] Another subject of the invention is a finished or semi-finished rubber article comprising the rubber composition according to the invention. Particularly preferred rubber articles are, for example, conveyor belts, conveyor belts, and inflatable articles.

[0105] Another subject of the invention is a pneumatic or non-pneumatic tire comprising the rubber composition according to the invention. A non-pneumatic tire means a tire capable of supporting the load of a vehicle by means other than pressurized gas (e.g., by struts).

[0106] Three types of regions can be defined within the tire:

[0107] · A radially outer region in contact with ambient air, said radially outer region including layers referred to as "outer layers", which essentially comprise the tread and the outer sidewall of a pneumatic tire. The outer sidewall is an elastomeric layer located outside the carcass reinforcement relative to the inner cavity of the tire and between the crown and the bead, so as to completely or partially cover the region where the carcass reinforcement extends from the crown to the bead.

[0108] · A radially inner region in contact with an inflation gas (or another device for carrying a load), in the case of a pneumatic tire, this region is generally composed of a layer that is airtight with respect to the inflation gas (sometimes referred to as an inner airtight layer or liner).

[0109] · The intrinsic region of the tire, that is, the region between the outer region and the inner region. This region includes layers or plies referred to herein as the inner layers of the tire. These layers or plies are, for example, carcass plies, under-tread plies, belt plies of the tire or any other layer that does not come into contact with ambient air or the inflation gas of the tire or any other device for supporting the load.

[0110] The rubber compositions defined in the present specification are particularly suitable for the inner and outer layers of tires. In particular, for the outer layer, they are particularly suitable for tread compositions, and for the inner layer, they are particularly suitable for the layers in the "bottom" region at the level of the tire bead (such as bead fillers, under-crown plies, and combinations of these inner layers).

[0111] The rubber compositions according to the present invention can also be suitable for the inner and outer layers of non-pneumatic tires, particularly for the treads of non-pneumatic tires and the bottom regions of these non-pneumatic tires.

[0112] The present invention particularly relates to tires intended to be assembled to motor vehicles of the passenger vehicle type, SUVs (sport utility vehicles), two-wheel vehicles (in particular motorcycles), aircraft, or industrial vehicles and other vehicles selected from trucks, heavy vehicles (i.e., subways, buses, heavy road transport vehicles (trucks, tractors, trailers) or off-road vehicles (such as heavy agricultural vehicles or civil engineering equipment)).

[0113] The present invention relates to articles comprising the rubber compositions according to the present invention in the uncured state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).

[0114] Preparation of the rubber composition

[0115] The rubber compositions according to the present invention can be manufactured in two successive preparation stages known to those skilled in the art using a suitable mixer:

[0116] - The first stage of thermomechanical processing or kneading (“non-production” stage), which can be carried out in a single thermomechanical step, during which all the necessary components except the crosslinking system (in particular the elastomeric matrix, fillers and optionally various other additives) are introduced into a suitable mixer (such as a standard closed mixer (such as a 'Banbury' type)). The filler can be added to the elastomer by thermomechanical kneading either in one go or in batches. If the filler has been introduced into the elastomer in the form of a masterbatch (such as described in applications WO 97 / 36724 or WO 99 / 16600), then the directly kneaded masterbatch, other elastomers or fillers not present in the composition in the form of a masterbatch (where appropriate) and various other optional additives except the crosslinking system are introduced.

[0117] The non-production stage is carried out at a high temperature, the maximum temperature being between 110 °C and 190 °C, preferably between 130 °C and 180 °C, and the duration is generally between 2 minutes and 10 minutes.

[0118] - After cooling the mixture obtained during the first non-production stage to a lower temperature (generally less than 110 °C, for example between 40 °C and 100 °C), a second stage of mechanical processing (“production” stage) is carried out in an open mixer (such as a mill). Then the crosslinking system is introduced and the combined mixture is mixed for a few minutes, for example between 2 minutes and 15 minutes.

[0119] The method for preparing such a rubber composition includes, for example, the following steps:

[0120] a) Introduce the reinforcing filler into the diene elastomer during the first step (referred to as the “non-production” step), and thermomechanically knead (for example, in one or more steps) all the substances until a maximum temperature between 110 °C and 190 °C is reached;

[0121] b) Cool the combined mixture to a temperature below 100 °C;

[0122] c) Subsequently introduce the crosslinking system during the second step (“production”);

[0123] d) Knead all the substances until a maximum temperature below 110 °C is reached.

[0124] Epoxy resin between 1 phr and 30 phr and hardener between 0.5 phr and 15 phr can be introduced independently of each other during the non-production stage (a) or the production stage (c). Preferably, the epoxy resin is introduced during the non-production stage (a) and the hardener is introduced during the production stage (c).

[0125] The resulting final rubber composition can then be calendered (especially for laboratory characterization) in the form of sheets or plates, for example, or extruded in the form of rubber semi-finished products (or shaped elements) for the manufacture of pneumatic tires.

[0126] The rubber composition can be crosslinked in a manner known to those skilled in the art, for example, under pressure at a temperature between 130 °C and 200 °C. Detailed description

[0127] Examples

[0128] Measurement methods

[0129] Mooney plasticity

[0130] An oscillating consistency meter as described in French standard NF T 43-005 (1991) is used. The Mooney plasticity measurement is carried out according to the following principle: The rubber composition in the uncured state (i.e., before curing) is molded in a cylindrical chamber heated to 100 °C. After preheating for one minute, the rotor rotates within the specimen at 2 revolutions per minute, and the working torque required to maintain this motion is measured after 4 minutes of rotation. The Mooney plasticity (ML 1+4) is expressed in "Mooney units" (MU, 1 MU = 0.83 Newton·meter).

[0131] It should be remembered 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, when it is below a certain value (e.g., 20 MU), the material is too fluid to be used, especially for the manufacture of the inner liner.

[0132] Tensile test

[0133] The tests are carried out according to French standard NF T 46-002 of September 1988. All tensile measurements are carried out at a temperature (100 ± 2 °C) representative of the working temperature of the tire rubber composition and under standard humidity conditions (50 ± 5% relative humidity) according to French standard NFT 40-101 (December 1979).

[0134] In the second elongation (i.e., after conditioning), the nominal secant modulus (or apparent stress, in MPa) of a sample cured at 150 °C for 60 minutes is measured at 10% and 50% elongation (denoted as MA10 and MA50, respectively) (which is calculated by reducing to the initial cross-section of the specimen).

[0135] Preparation of the composition

[0136] The following tests are carried out as follows: the diene elastomer, reinforcing filler, epoxy resin between 1 phr and 30 phr, and various other components, except for the crosslinking system, are continuously introduced into a closed mixer with an initial container temperature of about 60 °C (final filling degree: about 70% by volume). Then, thermomechanical processing (non-production stage) is carried out in one step, which lasts for about 3 to 4 minutes in total until a maximum "discharge" temperature of 165 °C is reached.

[0137] The mixture thus obtained is recovered and cooled, and then sulfur, a sulfenamide-type accelerator, and a hardener are introduced into a mixer (homogenizing finisher) at 30 °C, and all substances are mixed for an appropriate time (e.g., between 5 minutes and 12 minutes) (production stage).

[0138] Subsequently, the rubber composition thus obtained is calendered in the form of rubber sheets (thickness: 2 mm to 3 mm) or rubber flake sheets (for measuring its physical properties or mechanical properties), or extruded in the form of a molded element.

[0139] The crosslinking of the rubber composition is carried out under pressure at a temperature of 150 °C for 60 minutes.

[0140] [Table 1]

[0141] Component C.1 C.2 C.3 C.4 NR(1) 100 100 100 100 Carbon black(2) 70 70 Pyrolytic carbon black(3) 87 87 Phenol / formaldehyde resin(4) 12 12 Epoxy resin(5) 12 16 HMT(6) 3 3 Urea(7) 2.5 3.4 ZnO(8) 3 3 3 3 Stearic acid(9) 2 2 2 2 6PPD(10) 3 3 3 3 Sulfur 3 3 3 3 CBS(11) 2 2 2 2 Mooney viscosity (base 100) 100 86 97 114 MA50 (base 100) 100 96 99 99 tan(δ)max 0.28 0.42 0.31 0.23

[0142] (1) Natural rubber;

[0143] (2) Carbon black of ASTM N326 grade (named according to ASTM standard D-1765);

[0144] (3) "P550" from Scandinavian Enviro Systems, pyrolytic carbon black with a sulfur content between 2% by weight and 3% by weight relative to the total weight of the pyrolytic carbon black measured according to the method in the specification and an ash content of at most 20% by weight relative to the total weight of the pyrolytic carbon black measured according to the method in the specification;

[0145] (4) Linear phenolic resin (Peracit 4536K from Perstorp);

[0146] (5) Epoxy resin (EPN 1138 from Huntsman);

[0147] (6) Hexamethylenetetramine (from Degussa);

[0148] (7) Urea from Univar Solution;

[0149] (8) Zinc oxide (industrial grade - Umicore);

[0150] (9) Stearic acid (Pristerene 4931 from Uniqema);

[0151] (10) N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (Santoflex 6-PPD from Flexsys);

[0152] (11) N-cyclohexylbenzothiazole sulfenamide (Santocure CBS from Flexsys).

[0153] The use of pyrolytic carbon black (Composition C.4) instead of ASTM carbon black (Composition C.1) while adjusting the content to maintain the medium strain stiffness (MA50) can improve the hysteresis loss property. Conversely, the viscosity in the uncured state increases significantly, making the molding (and thus the processability) of this C.4 rubber composition more difficult.

[0154] The use of an epoxy resin (Composition C.2) that maintains the medium strain stiffness instead of a phenol / formaldehyde resin (Composition C.1) can obtain a lower viscosity in the uncured state. Conversely, the hysteresis loss property after crosslinking of the rubber composition C.2 increases significantly.

[0155] The combination of an epoxy resin and pyrolytic carbon black according to the present invention (Composition C.3) can obtain such a rubber composition that exhibits good processability and favorable properties after crosslinking, with a medium strain stiffness and hysteresis loss similar to those of the control rubber composition C.1.

[0156] [Table 2]

[0157] Component C.5 C.3 C.6 C.4 C.7 C.8 NR(1) 100 100 100 100 100 100 Pyrolytic carbon black(3) 87 87 87 87 87 87 Phenol / formaldehyde resin(4) 12 16 20 Epoxy resin(5) 12 16 20 HMT(6) 3 3 4 Urea(7) 3 3 4 ZnO(8) 3 3 3 3 3 3 Stearic acid(9) 2 2 2 2 2 2 6PPD(10) 3 3 3 3 3 3 Sulfur 3 3 3 3 3 3 CBS(11) 2 2 2 2 2 2 Resin (base 100) 100 136 163 100 136 163 MA10 (base 100) 100 122 133 100 112 116

[0158] The reference numbers of the components are the same as those in Table 1.

[0159] In these examples, it was observed that the combination of pyrolytic carbon black and an epoxy resin exhibited better stiffness evolution compared to the combination of pyrolytic carbon black and a phenol / formaldehyde resin.

Claims

1. A rubber composition, said rubber composition being based at least on: - a diene elastomer; - a reinforcing filler, said reinforcing filler comprising pyrolytic carbon black; - a crosslinking system; - an epoxy resin between 1 phr and 30 phr; - a hardener between 0.5 phr and 15 phr.

2. The rubber composition according to claim 1, wherein The reinforcing filler further comprises carbon black other than pyrolytic carbon black.

3. The rubber composition according to any one of the preceding claims, wherein, The reinforcing filler further comprises a reinforcing inorganic filler, preferably silica.

4. The rubber composition according to any one of the preceding claims, wherein, The reinforcing filler mainly comprises pyrolytic carbon black.

5. The rubber composition according to claim 1, wherein, The reinforcing filler consists of pyrolytic carbon black.

6. The rubber composition according to any one of the preceding claims, wherein, Relative to the total weight of the pyrolytic carbon black, the ash content of the pyrolytic carbon black is in the range of 5% by weight to 30% by weight.

7. The rubber composition according to any one of the preceding claims, wherein, Relative to the total weight of the pyrolytic carbon black, the sulfur content of the pyrolytic carbon black that can be used in the context of the present invention is greater than 2% by weight, preferably in the range of 2.5% by weight to 5% by weight.

8. The rubber composition according to any one of the preceding claims, wherein, The diene elastomer is selected from highly unsaturated diene elastomers, preferably diene elastomers selected from natural rubber, synthetic polyisoprene, polybutadiene, butadiene copolymers, isoprene copolymers, and mixtures of these elastomers, preferably diene elastomers selected from natural rubber and polyisoprene, and preferably natural rubber.

9. The rubber composition according to any one of the preceding claims, wherein, The epoxy resin is selected from resins of the following types: 2,2-bis[4-(glycidyloxy)phenyl]propane, poly[(o-tolyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-formaldehyde], poly[(phenyl glycidyl ether)-co-(hydroxybenzaldehyde glycidyl ether)], tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, and mixtures of these resins.

10. The rubber composition according to the preceding claim, wherein, The epoxy resin is selected from resins of the following types: poly[(o-tolyl glycidyl ether)-co-formaldehyde], poly[(o-phenyl glycidyl ether)-co-formaldehyde], tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, and mixtures of these resins.

11. The rubber composition according to any one of the preceding claims, wherein, The resin content in the composition is between 10 phr and 28 phr.

12. The rubber composition according to any one of the preceding claims, wherein, The hardener is a hardener selected from aromatic diamines, aliphatic diamines, acid anhydrides, and ureas, preferably a hardener selected from aromatic diamines and ureas.

13. The rubber composition according to the preceding claim, wherein, The hardener is a urea hardener, and the urea hardener is selected from carbamide, N,N'-dimethylurea, ethylene urea, N-phenylurea, 1,3-diphenylurea, and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, preferably selected from urea, N,N'-dimethylurea, N-phenylurea, 1,3-diphenylurea, and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, very preferably selected from carbamide, N,N'-dimethylurea, and 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) compounds, and very preferably carbamide of the formula H2N-CO-NH2, which is also called urea.

14. A finished or semi-finished rubber product, said finished or semi-finished rubber product comprising the rubber composition according to any one of the preceding claims, and preferably selected from conveyor belts, conveyor hoses, and inflatable products.

15. An inflated or non-inflated tire, said inflated or non-inflated tire comprising a rubber composition according to any one of claims 1 to 13.

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