Method for preparing diene rubber composition

Abstract

The present invention relates to a process for preparing a rubber composition comprising an elastomer matrix consisting of natural rubber and a synthetic diene elastomer, a modifier comprising a nitrile oxide dipole and an N-substituted imidazole function, a reinforcing filler comprising a silane coupling agent, and a vulcanization system, the invention relates to a method for producing a reinforcing filler comprising greater than 50% by weight of silica, said method comprising a step of premixing an elastomeric matrix separately prior to the steps of performing non-production mixing and production mixing. The process provides a good balance between hysteresis and rigidity of the composition and the amount of modifier used.

Description

Technical Field

[0001] The field of the invention is a process for preparing diene rubber compositions reinforced with silica and intended for use in tire treads. Background Art

[0002] Ideally, the tread should provide a very good level of road performance for the tire on a motor vehicle. This level of road performance can be achieved by using a carefully selected rubber composition in the tread, because the rubber composition has a relatively high stiffness in the cured state. In order to increase the stiffness of the rubber composition in the cured state, it is known, for example, to increase the content of filler in the rubber composition or to reduce the content of plasticizer in the rubber composition, or to introduce styrene and butadiene copolymers with a high styrene content into the rubber composition. However, some of these solutions generally have the disadvantage of increasing the hysteresis of the rubber composition.

[0003] In document WO2015059274, the applicant describes that the introduction of a 1,3-dipolar compound containing a nitrile oxide dipole and an N-substituted imidazole functional group into a silica-reinforced diene rubber composition can significantly reduce its hysteresis without reducing its stiffness in the cured state.

[0004] In order to further increase the stiffness of these rubber compositions, the applicants have discovered a new process for preparing rubber compositions which achieves this goal without degrading the hysteresis properties of these compositions. Summary of the invention

[0005] A subject of the invention is therefore a process for preparing a rubber composition comprising an elastomeric matrix, a modifier comprising a nitrile oxide dipole and an N-substituted imidazole functional group, a reinforcing filler comprising more than 50% by mass of silica, a silane coupling agent and a vulcanization system, the process comprising the following successive steps a, b, c and d:

[0006] - a) in a "non-productive" step, incorporating modifiers, reinforcing fillers and silane coupling agents into the elastomeric matrix by kneading until a maximum temperature of between 110° C. and 190° C. is reached,

[0007] -b) cooling the combined mixture to a temperature of less than 100° C.,

[0008] -c) subsequently incorporated into the vulcanization system,

[0009] -d) kneading the whole mass to a maximum temperature of less than 120° C.,

[0010] Characterized in that the elastomeric matrix comprises natural rubber and a synthetic diene elastomer and that, before step a), the process comprises a separate step of thermomechanical kneading of the elastomeric matrix.

[0011] describe

[0012] Any numerical interval represented by the expression "between a and b" means a numerical range greater than "a" and less than "b" (i.e., does not include the end values ​​a and b), while any numerical interval represented by the expression "a to b" means a numerical range extending from "a" to "b" (i.e., includes the strict end values ​​a and b).

[0013] The compounds mentioned in this specification may be compounds of fossil origin or may be bio-based compounds. In the case where the compounds are bio-based compounds, they may be partially or completely produced from biomass or obtained from renewable raw materials produced from biomass. In the same way, the compounds mentioned may also originate from the recovery of previously used materials, i.e. they may be partially or completely derived from a recovery process, or may be obtained by raw materials that themselves originate from a recovery process.

[0014] In the present invention, the term "tire" is understood to mean a pneumatic tire or a non-pneumatic tire. A pneumatic tire generally comprises two beads intended to come into contact with the rim, a crown consisting of at least one crown reinforcement and a tread, two sidewalls, the tire being reinforced by a carcass reinforcement anchored in the two beads. For its part, a non-pneumatic tire generally comprises a base (for example designed to be mounted on a rigid rim), a crown reinforcement (ensuring connection with the tread) and a deformable structure (for example spokes, ribs or a grid) arranged between the base and the crown. Such non-pneumatic tires do not necessarily include sidewalls. For example, non-pneumatic tires are described in documents WO 03 / 018332 and FR2898077. According to any embodiment of the invention, the tire according to the invention is preferably a pneumatic tire.

[0015] In the present invention, "elastomeric matrix" is understood to mean all elastomers in the rubber composition.

[0016] The abbreviation "phr" means parts by weight per hundred parts of elastomeric matrix.

[0017] Synthetic “diene” elastomers (or rubbers indistinguishable) are understood in a known manner to mean elastomers which are not natural rubber and which consist at least partly (ie homopolymers or copolymers) of diene monomer units (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds).

[0018] The expression “synthetic diene elastomer capable of being used in the composition according to the invention” is understood in particular to mean:

[0019] (a) any homopolymer of a conjugated or non-conjugated diene monomer other than natural rubber;

[0020] (b) - Any copolymer of a conjugated or non-conjugated diene with at least one other monomer.

[0021] The expression "copolymer of a conjugated or non-conjugated diene and at least one other monomer" is understood to mean a copolymer of a diene and one or more other monomers. As other monomers, mention may be made of ethylene, olefins and conjugated or non-conjugated dienes other than the first diene.

[0022] Suitable conjugated dienes include conjugated dienes having 4 to 24 carbon atoms, particularly 1,3-dienes having 4 to 12 carbon atoms, more particularly 1,3-butadiene and isoprene.

[0023] Suitable olefins include vinyl aromatic compounds having 8 to 20 carbon atoms and aliphatic α-monoolefins having 3 to 12 carbon atoms. The term "aliphatic α-monoolefin" is understood to mean an aliphatic α-olefin containing only one double bond. Suitable vinyl aromatic compounds include, for example, styrene, o-, m- or p-methylstyrene, the "vinyltoluene" commercial mixture or p-(tert-butyl)styrene. Suitable aliphatic α-monoolefins include in particular acyclic aliphatic α-monoolefins having 3 to 18 carbon atoms.

[0024] More particularly, the synthetic diene elastomers used for the purposes of the present invention are:

[0025] (a') - any homopolymer of a conjugated diene monomer other than natural rubber, in particular any homopolymer obtained by polymerization of a conjugated diene monomer having 4 to 12 carbon atoms;

[0026] (b') - Any copolymer obtained by copolymerization of one or more conjugated dienes with one another or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms.

[0027] The synthetic diene elastomers used for the purposes of the present invention are preferably chosen from polybutadienes, synthetic polyisoprenes, butadiene copolymers and isoprene copolymers.

[0028] The synthetic diene elastomers used for the purposes of the present invention may contain oils known as "extender oils" which are usually introduced at the end of the elastomer synthesis process and are then indicated by the name oil-extended elastomers. In a known manner, the elastomers usually contain antioxidants which are usually introduced at the end of the elastomer synthesis process.

[0029] Preferably, the content of natural rubber in the rubber composition is greater than 50 parts by weight per hundred parts of elastomeric matrix (or phr) and less than 90 phr, and the content of synthetic diene elastomer in the rubber composition is greater than 10 phr and less than 50 phr.

[0030] According to any embodiment of the invention, the synthetic diene elastomer is preferably SBR. Suitable SBR may comprise any SBR containing from 1% to 40% by weight of styrene, in particular from 15% to 35% by weight of styrene. The synthetic diene elastomer is more preferably a solution SBR (SSBR). Preferably, the total content of natural rubber and SBR is equal to 100 phr; in other words, the elastomer of the elastomeric matrix is ​​preferably natural rubber and SBR.

[0031] The modifier is typically a 1,3-dipolar compound containing a nitrile oxide dipole and an N-substituted imidazole functional group.

[0032] The N-substituted imidazole functional group preferably has the formula (I), wherein the symbol Z1 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms and the symbol Z2 represents the connection to the nitrile oxide dipole. The expression "connection to the nitrile oxide dipole" is understood to mean a bond or group which can covalently connect the 5-membered ring of the imidazole functional group to the dipole.

[0033]

[0034] The alkyl group represented by Z1 preferably has 1 to 3 carbon atoms, and is more preferably a methyl group.

[0035] The modifier is preferably an aromatic nitrile oxide, ie a compound comprising an aromatic group which is dipolarly substituted with a nitrile oxide and substituted with a group containing an N-substituted imidazole functionality.

[0036] Advantageously, the modifier is a compound containing a unit of formula (II), wherein R'1 represents a nitrile oxide dipole, one of the symbols R'2 to R'6 represents a saturated group having 1 to 6 carbon atoms and covalently bonded to one of the nitrogen atoms of the 5-membered ring of the N-substituted imidazole functional group, and the other symbols may be the same or different and represent a hydrogen atom or a substituent

[0037]

[0038] The substituent in formula (II) can be any group as long as it does not react with a dipole. The substituent in formula (II) can form a ring with the substituent of the adjacent carbon. Preferably, the substituent in formula (II) is an alkyl group having 1 to 3 carbon atoms, preferably a methyl group or an ethyl group, more preferably a methyl group.

[0039] The saturated group in formula (II) can covalently bond the imidazole functional group to a benzene ring, which is particularly substituted with a nitrile oxide dipole. It may contain one or more heteroatoms. It preferably contains 1 to 3 carbon atoms. The saturated group in formula (II) is preferably an alkanediyl, more preferably an alkanediyl with 1 to 3 carbon atoms, even more preferably a methanediyl.

[0040] In formula (II), R'2 and R'6 are preferably different from hydrogen atoms. Preferably, R'2, R'4 and R'6 are all different from hydrogen atoms and are the same. R'2, R'4 and R'6 are more preferably alkyl groups having 1 to 3 carbon atoms, and even more preferably methyl groups.

[0041] In formula (II), R'3 and R'5 are each preferably a hydrogen atom.

[0042] 1,3-dipolar compounds can be synthesized using relatively easy synthetic routes using commercially available precursors such as mesitylene, in particular as described in document WO 2015059269.

[0043] Advantageously, the 1,3-dipolar compound is a compound of formula (III) 2,4,6-trimethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide or a compound of formula (IV) 2,4,6-triethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide, more advantageously a compound of formula (III)

[0044]

[0045] The silica used may be any reinforcing silica known to those skilled in the art, in particular one having a BET specific surface area and a CTAB specific surface area of ​​less than 450 m 2 / g, preferably at 30m 2 / g to 400m 2 / g, especially 60m 2 / g to 300m 2 / g of any precipitated silica or fumed silica. In the present disclosure, the BET specific surface area is determined by gas adsorption using the Brewer-Emmett-Teller method described in "The Journal of the American Chemical Society" (Volume 60, Page 309, February 1938), more specifically according to the method derived from Appendix E of the standard NF ISO 5794-1 of June 2010 [multipoint (5 points) volumetric method-gas: nitrogen-vacuum degassing: 160°C for 1 hour-relative pressure p / po range: 0.05 to 0.17]. The CTAB specific surface area values ​​are determined according to the standard NF ISO 5794-1 of June 2010 (Appendix G). This method is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the "external" surface of the reinforcing filler.

[0046] Any type of precipitated silica can be used, in particular highly dispersible precipitated silica (HDS, "highly dispersible silica"). These precipitated silicas, which may or may not be highly dispersible, are known to the person skilled in the art. Mention may be made, for example, of the silicas described in applications WO 03 / 016215-A1 and WO 03 / 016387-A1. Among the commercial HDS silicas, in particular those from Evonik can be used. 5000GR and 7000GR silica or from Solvay 1085GR, 1115MP, 1165MP, Premium 200MP and HRS 1200MP silica. As non-HDS silicas, the following commercial silicas can be used: VN2GR and VN3GR Silica from Solvay 175GR silica or Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-SilEZ200G(-D), Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silica from PPG.

[0047] Reinforcing filler can include any type of "reinforcing" filler other than silica known to be able to enhance the rubber composition that can be particularly used for manufacturing tires, such as carbon black. Suitable as carbon black are all carbon blacks, particularly carbon blacks conventionally used for tires or their treads. In the carbon black, more particularly mention the reinforcing carbon blacks of 100, 200 and 300 series, or the carbon blacks of 500, 600 or 700 series (ASTM D-1765-2017 grade), such as N115, N134, N234, N326, N330, N339, N347, N375, N550, N683 and N772 carbon blacks. These carbon blacks can be used in a single state as commercially available, or in any other form (for example, as a carrier of some rubber additives used). When carbon black is used in a rubber composition, it is preferably used with a content less than or equal to 10phr (for example, the carbon black content can be in the range of 1phr to 10phr). Advantageously, the carbon black content in the rubber composition is less than or equal to 5 phr. Within the specified interval, the coloring properties (black colorant) and UV stability properties of carbon black are benefited without adversely affecting the typical performance qualities contributed by silica.

[0048] Silicon dioxide accounts for more than 50% by mass of the reinforcing filler. In other words, the proportion of silicon dioxide in the reinforcing filler is greater than 50% by weight of the total weight of the reinforcing filler. Preferably, silicon dioxide accounts for more than 85% by mass of the reinforcing filler.

[0049] The total content of reinforcing fillers can vary within a wide range, for example from 30 phr to 150 phr. According to a first embodiment, the total content of reinforcing fillers varies within a range of 30 phr to 60 phr. According to a second embodiment, the total content of reinforcing fillers varies within a range of greater than 60 phr to 150 phr. When the rubber composition is used in a tread with extremely low rolling resistance, the first embodiment is preferred over the second embodiment. Any of these ranges of the total content of reinforcing fillers may be applicable to any embodiment of the present invention.

[0050] In order to couple silica to a functionalized highly saturated diene elastomer, it is known to use at least bifunctional coupling agents (or binders), i.e. silanes, to ensure a sufficient connection of chemical and / or physical nature between silica and diene elastomer. In particular, at least bifunctional organosilanes or polyorganosiloxanes are used. The term "bifunctional" is understood to mean that the compound has a first functional group capable of interacting with an inorganic filler and a second functional group capable of interacting with a diene elastomer. For example, such a bifunctional compound may comprise a first functional group containing a silicon atom, the first functional group being capable of interacting with a hydroxyl group of the inorganic filler, and a second functional group containing a sulfur atom, the first functional group being capable of interacting with the diene elastomer.

[0051] Preferably, the organosilane is chosen from organosilane polysulfides (which may be symmetrical or asymmetrical), such as bis(3-triethoxysilylpropyl)tetrasulfide, abbreviated to TESPT, sold by Evonik under the name Si69, or bis(3-triethoxysilylpropyl)disulfide, abbreviated to TESPD, sold by Evonik under the name Si75, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl)octanethiolate, sold by Momentive under the name NXT Silane, and oligomers having at least one blocked mercaptosilane unit, at least one mercaptosilane unit and at least one cyclic dialkoxysilyl group or hydroxyalkoxysilyl group, sold by Momentive under the name NXT-Z. Of course, mixtures of the above coupling agents may also be used.

[0052] Silane polysulfides (called "symmetrical" or "asymmetrical" depending on their specific structure) are described, for example, in applications WO 03 / 002648 (or US 2005 / 016651) and WO 03 / 002649 (or US 2005 / 016650). Without being restricted to the following definition, particularly suitable are silane polysulfides corresponding to the general formula (V):

[0053] Z–A 1 -S x –A 1 -Z(V)

[0054] in:

[0055] -x is an integer from 2 to 8, preferably from 2 to 5;

[0056] -Symbol A 1 may be the same or different, representing a divalent hydrocarbon group (preferably C1-C 18 Alkylene or C6-C 12 Arylene, more particularly C1-C 10 Alkylene, especially C1-C4 alkylene, especially propylene);

[0057] - The symbol Z, which may be the same or different, corresponds to one of the following three formulae:

[0058]

[0059] in:

[0060] -Group R 1 may be substituted or unsubstituted and the same or different from each other, indicating C1-C 18 Alkyl, C5-C 18 Cycloalkyl or C6-C 18Aryl (preferably C1-C6 alkyl, cyclohexyl or phenyl, particularly C1-C4 alkyl, more particularly methyl and / or ethyl),

[0061] -Group R 2 may be substituted or unsubstituted and the same or different from each other, indicating C1-C 18 Alkoxy or C5-C 18 Cycloalkoxy (preferably a group selected from C1-C8 alkoxy and C5-C8 cycloalkoxy, still more preferably a group selected from C1-C4 alkoxy, particularly methoxy and ethoxy).

[0062] Group C n -C m The nomenclature refers to the number of carbon atoms constituting the group, which contains n to m carbon atoms, where n and m are integers and m is greater than n.

[0063] In the case of mixtures of alkoxysilane polysulfides corresponding to the above formula (6), in particular conventional commercially available mixtures, the average value of the "x" index is preferably a fraction between 2 and 5, more preferably a fraction close to 4. However, the invention can also be advantageously carried out using, for example, alkoxysilane disulfides (x=2).

[0064] As examples of silane polysulfides, mention will be made more particularly of bis((C1-C4)alkoxy(C1-C4)alkylsilyl(C1-C4)alkyl)polysulfides (in particular disulfides, trisulfides or tetrasulfides), such as, for example, bis(3-trimethoxysilylpropyl) or bis(3-triethoxysilylpropyl)polysulfides. Among these compounds, use is made in particular of bis(3-triethoxysilylpropyl)tetrasulfide of the formula [(C2H5O)3Si(CH2)3S2]2, abbreviated to TESPT, or bis(3-triethoxysilylpropyl)disulfide of the formula [(C2H5O)3Si(CH2)3S]2, abbreviated to TESPD.

[0065] For example, bifunctional POSS (polyorganosiloxane) or hydroxy silane polysulfide are described in patent application WO 02 / 30939 (or US 6,774,255), and WO 02 / 31041 (or US2004 / 051210). For example, blocked mercaptosilane or non-blocked mercaptosilane are described in patent or patent application US 6 849 754, WO 99 / 09036, WO 2006 / 023815, WO 2007 / 098080, WO 2010 / 072685 and WO2008 / 055986.

[0066] In the rubber composition according to the present invention, the content of the silane coupling agent is adjusted by those skilled in the art according to the chemical structure of the coupling agent, the specific surface area of ​​the silica used in the rubber composition and the content of silica in the rubber composition. It is preferably in the range of 1 to 15 phr, more preferably 1.5 to 10 phr, even more preferably 2 to 8 phr.

[0067] Another basic feature of the rubber composition according to the present invention is to contain a vulcanization system, i.e. a cross-linking system based on sulfur. Sulfur is usually provided in the form of molecular sulfur or a sulfur donor, preferably in molecular form. Molecular sulfur is also referred to as molecular sulfur. The term "sulfur donor" is understood to mean any compound that releases sulfur atoms, which are combined or not combined in the form of polysulfide chains, and can be inserted into the polysulfide chains formed during the vulcanization process, and bridge elastomer chains. Various known secondary vulcanization accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (particularly diphenylguanidine) etc. are added to the vulcanization system, which is mixed in the process of the first non-production stage and / or in the process of the production stage. The sulfur content is preferably between 0.5phr and 4phr, and the content of the primary accelerator is preferably between 0.5phr and 5phr. These preferred contents are applicable to any embodiment of the present invention.

[0068] As (primary or secondary) vulcanization accelerator, any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur may be used, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide type as primary accelerators, or accelerators of the thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate type as secondary accelerators. As examples of primary accelerators, mention may be made in particular of sulfenamide compounds, such as N-cyclohexyl-2-benzothiazolylsulfenamide ("CBS"), N,N-dicyclohexyl-2-benzothiazolylsulfenamide ("DCBS"), N-tert-butyl-2-benzothiazolylsulfenamide ("TBBS"), and mixtures of these compounds. The primary accelerator is preferably a sulfenamide, more preferably N-cyclohexyl-2-benzothiazolylsulfenamide. As examples of secondary accelerators, mention may be made of thiuram disulfides, such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide ("TBTD"), tetrabenzylthiuram disulfide ("TBZTD"), and mixtures of these compounds. The secondary accelerator is preferably thiuram disulfide, more preferably tetrabenzylthiuram disulfide.

[0069] Vulcanization is carried out in a known manner at temperatures generally between 130° C. and 200° C. for a sufficient time which may vary, for example, between 5 and 90 minutes, depending in particular on the curing temperature, the vulcanization system employed and the vulcanization kinetics of the composition under consideration.

[0070] The rubber composition according to the invention also contains all or some of the common additives usually used in elastomeric compositions intended for tire manufacturing, in particular pigments, protective agents (e.g. anti-ozone waxes), chemical antiozonants, antioxidants and plasticizers (e.g. plasticizing oils or resins). These additives are usually incorporated into the rubber composition before step b) of the method according to the invention, for example during step a).

[0071] The rubber compositions are generally prepared using two consecutive preparation stages, in a suitable mixer, according to procedures well known to those skilled in the art: a stage of thermomechanical processing or kneading at high temperature (up to a maximum temperature of between 110° C. and 190° C., preferably between 130° C. and 180° C.) (sometimes called the “non-productive” stage), followed by a stage of mechanical processing at a lower temperature, generally below 110° C., for example between 40° C. and 100° C. (sometimes called the “productive” stage), during which the sulphur or sulphur donor and the vulcanization accelerator are incorporated.

[0072] For example, the non-productive phase is carried out in a single thermomechanical step, during which all the necessary components, except the vulcanizing system, optional supplementary processing agents and various other additives are introduced into a suitable mixer, such as a conventional internal mixer. The total kneading time in this non-productive phase is preferably between 1 minute and 15 minutes. After cooling the mixture obtained during the non-productive phase, the vulcanizing system is then usually incorporated into an open mixer, such as an open mill, at low temperature; then all substances are mixed (productive phase) for several minutes, for example between 2 minutes and 15 minutes.

[0073] According to the invention, before carrying out step a), the elastomeric matrix is ​​subjected to a step of thermomechanical kneading separately. Before step a), the thermomechanical kneading separately of the elastomeric matrix means that the elastomers of the elastomeric matrix are kneaded together before step a). Preferably, the elastomeric matrix is ​​subjected to thermomechanical kneading separately until a maximum temperature of between 80° C. and 160° C., preferably in the range of 110° C. to 130° C. is reached. The thermomechanical kneading separately of the elastomeric matrix is ​​generally carried out in a conventional internal mixer which can also be used to carry out step a).

[0074] The modifier is added to the elastomeric matrix so that the modifier is incorporated therein and reacts with the elastomeric matrix by a grafting reaction according to a [3+2] cycloaddition of the dipole on the diene unit of the elastomeric matrix. Preferably, in step a), the modifier is incorporated into the elastomeric matrix before the other ingredients of the rubber composition.

[0075] According to a first variant, the modifier is incorporated by thermomechanical kneading in a conventional closed mixer that can be used for pre-kneading of the elastomeric matrix. The thermomechanical kneading is carried out until a preferred maximum temperature of between 80°C and 160°C, preferably in the range of 110°C to 130°C, is reached, so as to enable the incorporation of the modifier into the elastomeric matrix and the grafting of all or part of the modifier (for example 60% to 80% of the amount of modifier added) onto the elastomeric matrix. During the thermomechanical kneading, the contact time between the elastomeric matrix and the modifier is adjusted according to the variation of the thermomechanical kneading conditions, in particular according to the variation of the temperature. The higher the kneading temperature, the shorter the contact time. Typically, for temperatures of 110°C to 130°C, the contact time is from 1 minute to 5 minutes. After the thermomechanical kneading in the closed mixer, the kneading can be carried out, for example, on an open mixer, in order to take samples to characterize the product obtained by thermomechanical kneading of the elastomeric matrix and the modifier. In order to carry out kneading in an open mixer in complete safety, the product removed from the internal mixer is usually subjected to a cooling step in order to avoid burns during handling.

[0076] According to a second variant, the modifier is incorporated into an open mixer (such as an open mill) at a temperature less than 60°C and then thermally treated in a press or an oven, for example at a temperature ranging from 80°C to 200°C, so as to graft the modifier onto the elastomeric matrix.

[0077] According to a third variant, the modifier is incorporated in an open mixer (such as an open mill) at a temperature greater than 60° C., which obviates the need for an additional heat treatment for grafting the modifier onto the elastomeric matrix.

[0078] The amount of the modifier added in step a) can vary in the range of 0 to 3 mol% of the monomer unit of the elastomer matrix. Those skilled in the art adjust the amount according to the amount of silicon dioxide in the rubber composition and the purpose of the rubber composition. The lower the hysteresis of the rubber composition sought, the larger the amount of the modifier. The amount of the modifier added in step a) is preferably less than 2 mol% of the monomer unit of the elastomer matrix, more preferably less than 1 mol%, even more preferably less than 0.5 mol%. It is preferably greater than 0.02 mol% of the monomer unit of the elastomer matrix, more preferably greater than 0.05 mol%. The minimum content of the modifier is usually related to the low content of silicon dioxide.

[0079] The rubber composition can be calendered or extruded into the form of a sheet or plate material to be particularly used for laboratory characterization, or calendered or extruded into the form of a rubber semi-finished product (or a molded element) that can be used for a tire. The composition can be in an unprocessed state (before crosslinking or vulcanization) or a cured state (after crosslinking or vulcanization). It can constitute all or part of a semi-finished product, which is particularly intended to be used in a pneumatic tire or a non-pneumatic tire including a tread, particularly in a tire tread.

[0080] The rubber composition prepared according to the process according to the invention is advantageously vulcanized, preferably at a temperature greater than 110° C., in particular after extrusion or calendering in the form of a semi-finished product such as a tire tread. DETAILED DESCRIPTION

[0081] In summary, the present invention is advantageously implemented according to any one of the following embodiments 1 to 25:

[0082] Embodiment 1: A method for preparing a rubber composition comprising an elastomeric matrix, a modifier comprising a nitrile oxide dipole and an N-substituted imidazole functional group, a reinforcing filler, a silane coupling agent and a vulcanization system, the modifier comprising a nitrile oxide dipole and an N-substituted imidazole functional group, the reinforcing filler comprising greater than 50% by mass of silica, the method comprising the following consecutive steps a, b, c and d:

[0083] - a) in a "non-productive" step, incorporating modifiers, reinforcing fillers and silane coupling agents into the elastomeric matrix by kneading until a maximum temperature of between 110° C. and 190° C. is reached,

[0084] -b) cooling the combined mixture to a temperature of less than 100° C.,

[0085] -c) subsequently incorporated into the vulcanization system,

[0086] -d) kneading the whole mass to a maximum temperature of less than 120° C.,

[0087] Characterized in that the elastomeric matrix comprises natural rubber and a synthetic diene elastomer and that, before step a), the process comprises a separate step of thermomechanical kneading of the elastomeric matrix.

[0088] Embodiment 2: The method according to embodiment 1, wherein the elastomeric matrix alone is subjected to thermomechanical kneading until a maximum temperature between 80°C and 160°C is reached.

[0089] Embodiment 3: The method according to embodiment 1 or 2, wherein the elastomeric matrix alone is subjected to thermomechanical kneading until a maximum temperature in the range of 110°C to 130°C is reached.

[0090] Embodiment 4: The method according to any one of Embodiments 1 to 3, wherein the modifier is incorporated into the elastomeric matrix prior to the other ingredients of the rubber composition.

[0091] Embodiment 5: A method according to embodiment 4, wherein the modifier is separately incorporated into the elastomeric matrix by thermomechanical kneading in an internal mixer until a maximum temperature of between 80°C and 160°C, preferably in the range of 110°C to 130°C, is reached.

[0092] Embodiment 6: The method according to embodiment 4, wherein the modifier is incorporated into an open mixer at a temperature less than 60°C and then heat treated at a temperature ranging from 80°C to 200°C.

[0093] Embodiment 7: The method of Embodiment 4, wherein the modifier is incorporated into an open mixer at a temperature greater than 60°C.

[0094] Embodiment 8: A method according to any one of Embodiments 1 to 7, wherein the content of natural rubber in the rubber composition is greater than 50 parts by weight per hundred parts of the elastomer matrix (or phr) and less than 90 phr, and the content of synthetic diene elastomer in the rubber composition is greater than 10 phr and less than 50 phr.

[0095] Embodiment 9: The method according to any one of Embodiments 1 to 8, wherein the synthetic diene elastomer is SBR.

[0096] Embodiment 10: The method according to any one of Embodiments 1 to 9, wherein the synthetic diene elastomer is a solution SBR.

[0097] Embodiment 11: The process according to any one of embodiments 1 to 10, wherein the synthetic diene elastomer is an SBR containing from 1% to 40% by weight of styrene.

[0098] Embodiment 12: The process according to any one of embodiments 1 to 11, wherein the synthetic diene elastomer is an SBR containing from 15% to 35% by weight of styrene.

[0099] Embodiment 13: The method according to any one of embodiments 1 to 12, wherein the amount of the modifier added in step a) varies within the range between 0 and 3 mol % of the monomer units of the elastomeric matrix.

[0100] Embodiment 14: The method according to any one of Embodiments 1 to 13, wherein silica accounts for more than 85 mass % of the reinforcing filler.

[0101] Embodiment 15: A method according to any one of embodiments 1 to 14, wherein the N-substituted imidazole functional group has formula (I), wherein the symbol Z1 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the symbol Z2 represents the connection to the nitrile oxide dipole

[0102]

[0103] Embodiment 16: The method according to Embodiment 15, wherein the alkyl group represented by Z1 contains 1 to 3 carbon atoms.

[0104] Embodiment 17: The method according to Embodiment 15 or 16, wherein the alkyl group represented by Z1 is a methyl group.

[0105] Embodiment 18: The method according to any one of Embodiments 1 to 17, wherein the modifier is an aromatic nitrile oxide, ie, a compound comprising an aromatic group which is dipole-substituted with a nitrile oxide and substituted with a group containing an N-substituted imidazole functional group.

[0106] Embodiment 19: A method according to any one of embodiments 1 to 18, wherein the modifier is a compound containing a unit of formula (II), wherein R'1 represents a nitrile oxide dipole, one of the symbols R'2 to R'6 represents a saturated group having 1 to 6 carbon atoms and covalently bonded to a nitrogen atom of the 5-membered ring of the N-substituted imidazole functional group, and the other symbols may be the same or different and represent a hydrogen atom or a substituent

[0107]

[0108] Embodiment 20: The method according to Embodiment 19, wherein the saturated group is an alkanediyl group.

[0109] Embodiment 21: The method according to Embodiment 19 or 20, wherein the saturated group is an alkanediyl group having 1 to 3 carbon atoms.

[0110] Embodiment 22: The method according to any one of Embodiments 19 to 21, wherein the saturated group is methylenediyl.

[0111] Embodiment 23: The method of any one of Embodiments 19 to 22, wherein R'2, R'4 and R'6 are each an alkyl group.

[0112] Embodiment 24: The method according to any one of Embodiments 19 to 23, wherein R'2, R'4 and R'6 are each methyl or ethyl.

[0113] Embodiment 25: The method according to any one of Embodiments 19 to 24, wherein R'3 and R'5 are each a hydrogen atom.

[0114] The abovementioned and other characteristics of the invention will be better understood on reading the following description of several exemplary embodiments of the invention given by way of non-limiting illustration.

[0115] Example

[0116] Dynamic performance

[0117] The dynamic property tan δ (max) is measured on a viscoanalyzer (Metravib VA4000) according to standard ASTM D 5992-96. The values ​​are recorded for a sample of the vulcanized composition (thickness 4 mm and cross section 400 mm) subjected to a simple alternating sinusoidal shear stress at a frequency of 10 Hz at 60°C. 2 The response of a cylindrical specimen of 100 mm was measured. The strain amplitude was swept from 0.1% to 100% (outward cycle) and then from 100% to 0.1% (return cycle). The results used are the loss factor tan δ and the modulus difference ΔG* between the 0.1% and 100% strain values ​​(Payne effect). For the return cycle, the maximum observed tan δ is shown, denoted tan δ(max). The results are expressed relative to the base 100 of the control. Values ​​greater than the value of the control (arbitrarily set to 100) indicate that the measured amount is greater than the amount of the control.

[0118] Tensile test:

[0119] Tensile test can determine elastic stress and fracture performance. Unless otherwise stated, these tests are carried out according to the French standard NF T 46-002 in September 1988. Processing tensile records also make it possible to draw a curve of modulus changing with elongation. The modulus used herein is a nominal (or apparent) secant modulus, which is measured in the first elongation and calculated by the initial cross section of the normalized sample. The nominal secant modulus (or apparent stress, in MPa) (expressed as MSA10) under 100% elongation is measured in the second elongation. Breaking stress (in MPa) and elongation at break (in %) are measured according to standard NF T 46-002 at 23 ° C ± 2 ° C. The result is represented by a base number of 100 relative to the control. The value greater than the value of the control (arbitrarily set to 100) represents an improved result, that is, the value measured is greater than the value of the control.

[0120] Preparation of rubber composition:

[0121] The formulations (in phr) of the rubber compositions prepared are described in Table I.

[0122] The elastomeric matrix is ​​a mixture of 75 phr of natural rubber and 25 phr of SBR. The SBR is a solution SBR containing 26% of styrene units and 56% of 1,2-butadiene units.

[0123] A 1,3-dipolar compound (2,4,6-trimethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide) was used as a modifier, the synthesis of which is described in patent application WO 2015059274.

[0124] According to a method not in accordance with the invention, a rubber composition A1 was prepared:

[0125] The natural rubber, SBR, then the silica and the silane coupling agent are introduced into an internal mixer (final filling level: about 70% by volume) with an initial tank temperature of about 110° C., then kneaded for one to two minutes, and then the various other ingredients, except the vulcanization system, are added. Thermomechanical processing is then carried out in a single step (non-productive phase), which lasts about 5 to 6 minutes, until a maximum "discharge" temperature of 160° C. is reached. The mixture thus obtained is recovered and cooled, and then the sulfur and sulfenamide type accelerators are incorporated into a mixer (homofinator) at 23° C., mixing everything (productive phase) for a suitable time (for example between 5 and 12 minutes).

[0126] Rubber composition A2 was prepared according to a method not conforming to the invention:

[0127] The method for preparing rubber composition A2 is identical to that of A1, except that, before the addition of the silica, the two elastomers are thermomechanically kneaded for 30 seconds.

[0128] Rubber composition A3 was prepared according to a method not conforming to the invention:

[0129] The method for preparing rubber composition A3 is the same as A1, except that the natural rubber and SBR are modified with a modifier according to the following steps:

[0130] The elastomer to be modified (natural rubber or SBR in this case) and the subsequent modifier are introduced into an internal mixer (final filling level: about 70% by volume) with an initial temperature of about 110° C. and then kneaded for two minutes at 120° C. The resulting product is recovered, cooled and homogenized on an open mixer (roll mill) at 30° C. (15 tumbles).

[0131] In the case of natural rubber, the amount of modifier is 1.13 phr (ie, 0.3 mol % of the natural rubber monomer units); in the case of SBR, the amount of modifier is 1.24 phr (ie, 0.3 mol % of the SBR monomer units).

[0132] It can be seen that in the method of A3, silica and other components of the rubber composition are incorporated into the elastomer matrix composed of modified natural rubber and modified SBR.

[0133] Rubber composition A4 was prepared according to a method not conforming to the invention:

[0134] The method for preparing rubber composition A4 is the same as A3, except that only the natural rubber is modified beforehand with the modifier (1.13 phr).

[0135] Rubber composition A5 was prepared according to a method not conforming to the invention:

[0136] The method for preparing rubber composition A5 is identical to that for A3, except that only the SBR is modified beforehand with the modifier (1.24 phr instead of 1.13 phr, ie 0.3 mol %).

[0137] According to the method according to the invention, a rubber composition A6 was prepared:

[0138] The natural rubber and the SBR are introduced into an internal mixer (final filling level: about 70% by volume) with an initial tank temperature of about 110° C., then kneaded for 30 seconds, then the modifier (1.13 phr) is added, kneading is carried out for two minutes at 120° C., then the silica and the silane coupling agent are added, kneading is carried out for one to two minutes, then the various other ingredients are added except for the vulcanization system. Thermomechanical processing is then carried out in a single step (non-productive phase), which lasts for about 5 to 6 minutes, until a maximum "discharge" temperature of 160° C. is reached. The mixture thus obtained is recovered and cooled, and then the sulfur and sulfenamide type accelerators are incorporated into an open mixer (homofinator) at 23° C., mixing everything (productive phase) for an appropriate time of 5 to 6 minutes.

[0139] According to the method according to the invention, a rubber composition A7 was prepared:

[0140] The method used to prepare rubber composition A7 was the same as A6, except that 0.75 phr (instead of 1.13 phr) of the modifier was added.

[0141] The method for preparing rubber compositions A6 and A7 differs from A2 in that the modifier is added to the elastomeric matrix so that the modifier is incorporated into the elastomeric matrix and grafted onto the elastomeric matrix.

[0142] The composition thus obtained is subsequently calendered into the form of rubber sheets (thickness ranging from 2 to 3 mm) or rubber sheets, in order to measure their physical or mechanical properties, or into the form of shaped elements which, after cutting and / or assembling to the desired dimensions, can be used directly as semi-finished products, for example for tires, in particular for treads.

[0143] Crosslinking was carried out at 150°C.

[0144] The results are shown in Table 2.

[0145] Table 1

[0146]

[0147]

[0148] (1) Natural rubber

[0149] (2) SBR containing 26% by weight of styrene and 56% of 1,2-butadiene units

[0150] (3) Modification of NR according to the procedure described in the method for preparing A3

[0151] (4) SBR was modified according to the steps described in the method for preparing A3

[0152] (5) 2,4,6-Trimethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide

[0153] (6) Zeosil 1165MP in microbead form from Solvay-Rhodia

[0154] (7) Carbon black N234

[0155] (8) Triethoxysilylpropyl tetrasulfide (TESPT) liquid silane, Si69 from Evonik

[0156] (9) Diphenylguanidine, Perkacit DPG from Flexsys

[0157] (10) Ozone-resistant wax, Varazon 4959 from Sasol Wax

[0158] (11) Tetramethylquinone

[0159] (12) N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine, Santoflex 6PPD from Flexsys

[0160] (13) Stearic acid, Pristerene 4931 from Uniqema

[0161] (14) Industrial grade zinc oxide from Umicore

[0162] (15) N-cyclohexyl-2-benzothiazolesulfenamide, Santocure CBS from Flexsys

[0163] Table 2:

[0164]

[0165] Composition A6, in which 1.13 phr of modifier and other ingredients are introduced after the elastomers are kneaded together, exhibits a higher stiffness than composition A3 at medium strain (MSA100 at 60°C), however, as can be seen from tan δ (max) at 60°C, there is no increase in hysteresis. By comparing rubber compositions A3 and A6, it is observed that the method according to the invention leading to the composition A6 achieves an increase in the stiffness of the rubber composition in the cured state without adversely affecting the hysteresis. This result is achieved even when the amount of modifier used in A6 is only 1.13 phr, while the amount of modifier used in A3 is 2.37 phr.

[0166] Even compositions A4 and A5, which use much lower levels of modifier than A3 (1.13 phr and 1.24 phr, respectively), do not exhibit as low a hysteresis or as high a stiffness as A6.

[0167] A comparison between compositions A1 and A2 (which does not conform to the invention and differs in the process of A2 by a step of thermomechanically kneading the two elastomers together) shows that this step of thermomechanically kneading the two elastomers together is not the only reason for the performance compromise between hysteresis and stiffness obtained using the process according to the invention.

[0168] It is also observed that composition A7, obtained according to the process according to the invention and using only 0.75 phr of modifier content, also presents a favorable performance compromise between stiffness and hysteresis compared to compositions A4 and A5 using higher modifier contents (1.13 phr and 1.24 phr respectively).

[0169] The method according to the invention proved to be the most efficient method for obtaining the best compromise between hysteresis, stiffness and amount of modifier.

Claims

1. A method for preparing a rubber composition comprising an elastomeric matrix, a modifier, a reinforcing filler, a silane coupling agent and a vulcanization system, wherein the modifier comprises a nitrile oxide dipole and an N-substituted imidazole functional group, and the reinforcing filler comprises more than 50% by mass of silica, the method comprising the following consecutive steps a, b, c and d: - a) in a "non-productive" step, incorporating modifiers, reinforcing fillers and silane coupling agents into the elastomeric matrix by kneading until a maximum temperature of between 110° C. and 190° C. is reached, -b) cooling the combined mixture to a temperature of less than 100° C., -c) subsequently incorporated into the vulcanization system, -d) kneading the whole mass to a maximum temperature of less than 120° C., It is characterized in that The elastomeric matrix comprises a natural rubber and a synthetic diene elastomer and, before step a), the process comprises a separate step of thermomechanical kneading of the elastomeric matrix.

2. The method according to claim 1, wherein: The elastomeric matrix alone is thermomechanically kneaded until a maximum temperature of between 80°C and 160°C, preferably in the range of 110°C to 130°C, is reached.

3. The method according to claim 1 or 2, wherein: In step a), the modifier is incorporated into the elastomeric matrix before the other ingredients of the rubber composition.

4. The method according to any one of claims 1 to 3, wherein: The content of natural rubber in the rubber composition is greater than 50 parts by weight per hundred parts of the elastomeric matrix, or phr, and less than 90 phr, and the content of synthetic diene elastomer in the rubber composition is greater than 10 phr and less than 50 phr.

5. The method according to any one of claims 1 to 4, wherein: The synthetic diene elastomer is SBR, preferably solution SBR.

6. The method according to any one of claims 1 to 5, wherein: The amount of modifier added in step a) varies within the range between 0 and 3 mol % of the monomer units of the elastomeric matrix.

7. The method according to any one of claims 1 to 6, wherein: Silica accounts for more than 85% by mass of the reinforcing filler.

8. The method according to any one of claims 1 to 7, wherein: The N-substituted imidazole functional group has the formula (I), wherein the symbol Z1 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the symbol Z2 represents the connection to the nitrile oxide dipole 9. The method according to any one of claims 1 to 8, wherein: The modifier is an aromatic nitrile oxide, ie a compound comprising an aromatic group which is dipolarly substituted with a nitrile oxide and substituted with a group containing an N-substituted imidazole functionality.

10. The method according to any one of claims 1 to 9, wherein: The modifier is a compound containing a unit of formula (II), wherein R'1 represents a nitrile oxide dipole, one of the symbols R'2 to R'6 represents a saturated group having 1 to 6 carbon atoms and covalently bonded to one nitrogen atom of the 5-membered ring of the N-substituted imidazole functional group, and the other symbols may be the same or different and represent a hydrogen atom or a substituent 11. The method according to claim 10, wherein: The saturated group is an alkanediyl group, preferably an alkanediyl group having 1 to 3 carbon atoms.

12. The method according to any one of claims 10 and 11, wherein: R'2, R'4 and R'6 are each an alkyl group, preferably a methyl group or an ethyl group.

13. The method according to any one of claims 10 to 12, wherein: R'3 and R'5 are each a hydrogen atom.

Images