Patent Application
20230227634
The field of the present invention is that of reinforced rubber compounds, in particular used in the building of vehicle tyres, more particularly used for the manufacture of treads.
One of the requirements needed for a tyre is to provide optimal grip on the road, especially on wet ground. One way of giving the tyre increased grip on wet ground is to use a rubber composition in its tread, which composition has a broad hysteresis potential. But at the same time, the tyre tread must also minimize its contribution to the rolling resistance of the tyre, that is to say have the lowest possible hysteresis.
Thus, the rubber composition of the tread must satisfy two conflicting requirements, namely having a maximum hysteresis potential in order to satisfy the requirement of grip and having a hysteresis that is as low as possible in order to satisfy the requirement of rolling resistance.
Improving the rolling resistance has been made possible by virtue of the use of novel rubber compositions reinforced with inorganic fillers, in particular specific silicas of the highly dispersible type, which are capable of rivalling, from the reinforcing perspective, a conventional tyre-grade carbon black, while offering these compositions a lower hysteresis, which is synonymous with a lower rolling resistance.
However, the use of a high content of inorganic reinforcing fillers in the rubber compositions has the disadvantage of adversely affecting the wet grip properties of the rubber compositions in which they are incorporated.
Satisfying both the requirement of grip, especially on wet ground, and of rolling resistance thus remains a constant concern of tyre manufacturers.
With a view to seeking the best compromise in terms of performance, tyre manufacturers are developing increasingly complex rubber compositions, often integrating several elastomers of different chemical natures, thus forming a rubber compound. An example of complex compositions is described in document EP3372638, in particular in example 4 where the complex composition comprises two different elastomers for which the difference in glass transition temperature does not exceed 20° C., this composition exhibiting an improvement in the rolling resistance/wear compromise.
There is thus still a need for rubber compounds that have improved rolling resistance, while retaining good wet grip, or even while improving this property.
One aim of the present invention is thus to propose novel rubber compounds, in particular for treads, which resolve in particular the aforementioned drawbacks; exhibiting improved hysteresis properties while maintaining or even improving their wet grip performance.
This aim is achieved in that the applicant has surprisingly discovered that a rubber compound having a particular loss factor profile, the loss factor profile being measured over a temperature range extending from -80° C. at 60° C. at a frequency of 10 Hz and at a constant stress of 0.7 MPa, and being based on a specific combination of at least two rubber compositions C1 and C2 having different glass transition temperatures and for which the difference in these glass transition temperatures is greater than or equal to 23° C. and in which the elastomer of composition C1 is predominant in the mixture, exhibited better rolling resistance while retaining good wet grip properties, or even improved properties.
A first subject of the invention relates to a rubber compound having at least two Tgs, Tg1 and Tg2, and based on at least two rubber compositions C1 and C2, the rubber composition C1 comprising at least one elastomer E1, and having the glass transition temperature Tg1, the composition C2 comprising at least one elastomer E2 and a reinforcing filler, the elastomer E2 being different from the elastomer E1, and having the glass transition temperature Tg2, characterized in that:
Preferentially, the rubber compound satisfies the mathematical relationship Tg1-Tg2 ≥ 25° C., preferably Tg1-Tg2 ≥ 28° C., more preferentially still Tg1-Tg2 ≥ 30° C.
Advantageously, the rubber compound may satisfy the mathematical relationship 25° C. ≤ Tg1-Tg2 ≤ 40° C., preferably 28° C. ≤ Tg1-Tg2 ≤ 35° C., more preferentially 28° C. ≤ Tg1-Tg2 ≤ 34° C.
Advantageously, the glass transition temperature Tg2 of composition C2 may be below or equal to -43° C., preferably below or equal to -50° C., more preferentially below or equal to -57° C.
Advantageously, the glass transition temperature Tg2 of composition C2 is within a range extending from -90° C. to -43° C., preferably extending from -85° C. to -50° C.
Advantageously, the elastomer E2 of the rubber composition C2 is a diene elastomer. More advantageously still, the elastomer E2 of the composition C2 is a functionalized diene elastomer.
Advantageously, the glass transition temperature TgE2 of the elastomer E2 may be within a range extending from -110° C. to -23° C., preferably extending from -100° C. to -28° C., more preferentially extending from -95° C. to -30° C.
Advantageously, the elastomer E2 of the rubber composition C2 is a diene elastomer, preferably which is functionalized, selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, isobutene/isoprene copolymers, butadiene/styrene copolymers, butadiene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. Preferentially, the elastomer E2, which is preferably functionalized, is selected from polybutadienes and styrene/butadiene copolymers. More preferentially still, the elastomer E2, which is preferably functionalized, is a styrene/butadiene copolymer.
Preferentially, the functionalized diene elastomer E2 of the rubber composition C2 comprises at least one chemical function capable of interacting with the reinforcing filler, the chemical function comprising at least one heteroatom selected from the group consisting of nitrogen, sulfur, oxygen, phosphorus, tin and silicon.
Preferentially, the reinforcing filler of the composition C2 predominantly comprises at least one inorganic reinforcing filler, more preferentially predominantly comprises at least one silica.
Advantageously, the reinforcing filler of the composition C2 may predominantly comprise a reinforcing inorganic filler, preferentially predominantly a silica, and the elastomer E2 may be a functionalized diene elastomer comprising at least one chemical function capable of interacting with the reinforcing inorganic filler, the chemical function comprising at least one heteroatom selected from the group consisting of nitrogen, sulfur, oxygen and phosphorus. Advantageously, the chemical function capable of interacting with the reinforcing filler may be a polar function comprising at least one oxygen atom.
Advantageously, the glass transition temperature Tg1 of the rubber composition C1 may be within a range extending from -48° C. to -15° C., more preferentially may be within a range extending from -48° C. to -15° C.
Advantageously, the glass transition temperature Tg1 of the rubber composition C1 may be above or equal to -48° C., preferably above or equal to -40° C.
Advantageously, the elastomer E1 of the rubber composition C1 may be a diene elastomer. Preferably, the elastomer E1 of the rubber composition C1 is a non-functionalized diene elastomer.
Advantageously, the elastomer E1 of the rubber composition C1 is a diene elastomer selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene/styrene copolymers, butadiene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. Preferentially, the elastomer E1 of the rubber composition C1 is a diene elastomer selected from the group consisting of synthetic polyisoprenes, polybutadienes, butadiene/styrene copolymers, butadiene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. More preferentially still, the elastomer E1 of the rubber composition C1 is a diene elastomer selected from the group consisting of polybutadienes and butadiene/styrene copolymers. More preferentially still, the elastomer E1 of the composition C1 is a styrene/butadiene copolymer.
Advantageously, the glass transition temperature TgE1 of the elastomer E1 may be within a range extending from -50° C. to 0° C., more preferentially from -40° C. to 0° C., more preferentially from -30° C. to 0° C.
Advantageously, the content of the elastomer E1 in the compound may be within a range extending from 50 phr to 70 phr, preferably from 55 phr to 70 phr, more preferentially from 55 phr to 65 phr.
Advantageously, the composition C1 may further comprise a reinforcing filler.
Advantageously, the rubber compound may comprise at least one plasticizer.
Advantageously, the compound as defined above and its preferred embodiments can be obtained according to a manufacturing process which comprises the following steps:
Another subject of the present invention relates to a tread comprising at least one compound defined above.
Another subject of the present invention relates to a tyre comprising at least one compound defined above or comprising at least one tread defined above.
A first subject of the present invention relates to a rubber compound having at least two glass transition temperatures Tg, denoted Tg1 and Tg2, and based on at least two rubber compositions C1 and C2, the rubber composition C1 comprising at least one elastomer E1, and having the glass transition temperature Tg1, the composition C2 comprising at least one elastomer E2 and a reinforcing filler, the elastomer E2 being different from the elastomer E1, and having the glass transition temperature Tg2, characterized in that:
The expression “rubber compound based on at least” should be understood to mean a combination of at least two rubber compositions. The rubber compound can thus be in the completely or partially crosslinked state or in the non-crosslinked state.
The expression “rubber composition based on” should be understood to mean a composition comprising the mixture and/or the product of the in situ reaction of the various constituents used, some of these constituents being able to react and/or being intended to react with one another, at least partially, during the various phases of manufacture of the composition; it thus being possible for the composition to be in the completely or partially crosslinked state or in the non-crosslinked state.
For the purposes of the present invention, the expression “part by weight per hundred parts by weight of elastomer” (or phr) should be understood to mean the part by weight per hundred parts by weight of elastomers in the rubber compound.
In the present document, unless expressly indicated otherwise, all the percentages (%) indicated are percentages (%) by weight.
Furthermore, any interval of values denoted by the expression “between a and b” represents the range of values extending from more than a to less than b (i.e. limits a and b excluded), whereas any interval of values denoted by the expression “from a to b” means the range of values extending from a up to b (i.e. including the strict limits a and b).
When reference is made to a “predominant” compound, this is understood to mean, for the purposes of the present invention, that this compound is predominant among the compounds of the same type in the rubber compound, that is to say that it is the one which represents the greatest amount by weight among the compounds of the same type. Thus, for example, a predominant elastomer is the elastomer representing the greatest weight relative to the total weight of the elastomers of the compound. In the same way, a “predominant” filler is the one representing the greatest weight among the fillers of the compound. By way of example, in a system comprising just one elastomer, the latter is predominant within the meaning of the present invention and, in a system comprising two elastomers, the predominant elastomer represents more than half of the weight of the elastomers. By contrast, a “minor” compound is a compound which does not represent the greatest fraction by weight among the compounds of the same type. Preferably, the term “predominant” is understood to mean present at more than 50%, preferably more than 60%, 70%, 80%, 90%, and more preferentially the “predominant” compound represents 100%.
The compounds mentioned in the description that comprise carbon may be of fossil origin or may be biobased. In the latter case, they may partially or completely result from biomass or be obtained from renewable starting materials resulting from biomass. Polymers, plasticizers, fillers, and the like, are concerned in particular.
The glass transition temperatures, denoted Tg1 and Tg2, of the compound of the invention are measured according to standard NF EN ISO 11357-2:05-2014 on the rubber compound.
The glass transition temperatures of the elastomers, denoted TgE1 and TgE2, are measured according to the standard ASTM D3418:2008.
The loss factor, also referred to as tan δ is a physical quantity well known to manufacturers of pneumatic tyres. The loss factor represents the fraction of energy dissipated during a cyclic stress.
The loss factor profile represents the change in the loss factor, tan δ, as a function of the temperature when a constant stress is exerted at a given frequency. Within the context of the present invention, the loss factor profile is measured over a temperature range extending from -80° C. to 60° C. at a frequency of 10 Hz and a constant stress of 0.7 MPa according to the standard ASTM D 5992 - 96.
The rubber compositions C1 and C2 forming the rubber compound according to the invention each comprise at least one elastomer, respectively elastomer E1 and elastomer E2; the elastomer E1 being different from the elastomer E2.
An “elastomer” is understood to mean a polymer which is flexible and deformable, exhibiting rubber-like elasticity according to the IUPAC definition of elastomers.
Preferentially, the elastomer E1 of the rubber composition C1 and/or the elastomer E2 of the rubber composition C2 is a diene elastomer.
A “diene” elastomer (or, without distinction, rubber), whether natural or synthetic, should be understood, in a known way, as meaning an elastomer composed, at least in part (i.e., a homopolymer or a copolymer), of diene monomer units (monomers bearing two conjugated or non-conjugated carbon-carbon double bonds).
An “elastomeric matrix” is understood to mean all of the elastomers forming the rubber compound of the invention.
Diene elastomers can be classified in two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” is understood to mean generally a diene elastomer resulting at least in part from conjugated diene monomers having a content of units of diene origin (conjugated dienes) which is greater than 15% (mol%); thus it is that diene elastomers such as butyl rubbers or copolymers of dienes and of α-olefins of EPDM type do not come within the preceding definition and can in particular be described as “essentially saturated” diene elastomers (low or very low content, always less than 15 mol%, of units of diene origin).
A diene elastomer capable of being used in the rubber compounds in accordance with the invention is intended more particularly to mean:
The other monomer can be an olefin or a conjugated or non-conjugated diene.
Conjugated dienes that are suitable include conjugated dienes containing from 4 to 12 carbon atoms, in particular 1,3-dienes, notably such as 1,3-butadiene and isoprene.
Non-conjugated dienes that are suitable include non-conjugated dienes containing from 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidenenorbornene or dicyclopentadiene.
Olefins that are suitable include vinylaromatic compounds containing from 8 to 20 carbon atoms and aliphatic α-monoolefins containing from 3 to 12 carbon atoms.
Vinylaromatic compounds that are suitable include, for example, styrene, ortho-, meta- or para-methylstyrene, the “vinyltoluene” commercial mixture or para-(tert-butyl)styrene.
More particularly, the diene elastomer is:
The rubber composition C2 comprises one or more reinforcing fillers.
According to one embodiment of the invention, the rubber composition C1 can optionally also comprise one or more reinforcing fillers.
Use may be made of any type of “reinforcing” filler known for its abilities to reinforce a rubber composition which can be used in particular in the manufacture of pneumatic tyres, for example an organic filler, such as carbon black, an inorganic filler, such as silica, or else a mixture of these two types of fillers.
All carbon blacks, in particular the blacks conventionally used in pneumatic tyres or non-pneumatic tyres or their treads, are suitable as carbon blacks. Mention will more particularly be made, among the latter, of the reinforcing carbon blacks of the 200 series such as, for example, the N234 blacks. These carbon blacks can be used in the isolated state, as available commercially, or in any other form, for example as support for some of the rubber additives used. The carbon blacks might, for example, be already incorporated in the diene elastomer (see, for example, applications WO97/36724-A2 and WO99/16600-A1).
Mention may be made, as examples of organic fillers other than carbon blacks, of functionalized polyvinyl organic fillers, as described in applications WO2006/069792-A1, WO2006/069793-A1, WO2008/003434-A1 and WO2008/003435-A1.
The term “reinforcing inorganic filler” should be understood here as meaning any inorganic or mineral filler, whatever its colour and its origin (natural or synthetic), also referred to as “white” filler, “clear” filler or even “non-black” filler, in contrast to carbon black, capable of reinforcing, by itself alone, without means other than an intermediate coupling agent, a rubber composition intended for the manufacture of pneumatic or non-pneumatic tyres. In a known way, some reinforcing inorganic fillers can be characterized in particular by the presence of hydroxyl (-OH) groups at their surface.
Mineral fillers of the siliceous type, preferentially silica (SiO2), or of the aluminous type, especially alumina (Al2O3), are suitable in particular as reinforcing inorganic fillers.
The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica exhibiting a BET specific surface area and a CTAB specific surface area both of less than 450 m2/g, preferably within a range extending from 30 to 400 m2/g, in particular from 60 to 300 m2/g. Any type of precipitated silica, in particular highly dispersible precipitated silicas (referred to as “HDS” for “highly dispersible” or “highly dispersible silica”), can be used. These precipitated silicas, which may or may not be highly dispersible, are well known to those skilled in the art. Mention may be made, for example, of the silicas described in applications WO03/016215-A1 and WO03/016387-A1. Use may in particular be made, among commercial HDS silicas, of the Ultrasil® 5000GR and Ultrasil® 7000GR silicas from Evonik or the Zeosil® 1085GR, Zeosil® 1115 MP, Zeosil® 1165 MP, Zeosil® Premium 200 MP and Zeosil® HRS 1200 MP silicas from Solvay. Use may be made, as non-HDS silica, of the following commercial silicas: the Ultrasil® VN2GR and Ultrasil® VN3GR silicas from Evonik, the Zeosil® 175GR silica from Solvay or the Hi-Sil EZ120G(-D), Hi-Sil EZ160G(-D), Hi-Sil EZ200G(-D), Hi-Sil 243LD, Hi-Sil 210 and Hi-Sil HDP 320G silicas from PPG.
The physical state in which the reinforcing inorganic filler is provided is not important, whether it is in the form of a powder, of micropearls, of granules, or else of beads or any other appropriate densified form. Of course, reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of silicas as described above.
Those skilled in the art will understand that, as replacement for the reinforcing inorganic filler described above, use might be made of a reinforcing filler of another nature, provided that this reinforcing filler of another nature is covered with an inorganic layer, such as silica, or else comprises functional sites, in particular hydroxyl sites, at its surface which require the use of a coupling agent in order to establish the bond between this reinforcing filler and the elastomeric matrix.
Those skilled in the art will know how to adjust the total content of reinforcing filler depending on the use in question of the compound of the invention, in particular depending on the type of pneumatic tyres in question, for example for a passenger vehicle or else for a utility vehicle, such as a van or heavy-duty vehicle.
In the present account, the BET specific surface area is determined by gas adsorption using the Brunauer-Emmett-Teller method described in “The Journal of the American Chemical Society” (vol. 60, page 309, February 1938), and more specifically according to a method derived from Standard NF ISO 5794-1, Appendix E, of June 2010 [multipoint (5 point) volumetric method -gas: nitrogen - degassing under vacuum: one hour at 160° C. - relative pressure p/po range:: 0.05 to 0.17]. For the inorganic fillers, such as silica, for example, the CTAB specific surface area values were determined according to Standard NF ISO 5794-1, Appendix G, of June 2010. The process is based on the adsorption of CTAB (N-hexadecyl-N,N,N-trimethylammonium bromide) on the “external” surface of the reinforcing filler. For carbon blacks, the STSA specific surface is determined according to Standard ASTM D6556-2016.
Coupling agents for the reinforcing filler: As is known, in order to couple the reinforcing filler, use may be made of an at least bifunctional coupling agent (or bonding agent) intended to provide a satisfactory connection, of chemical and/or physical nature, between the inorganic filler (surface of its particles) and the diene elastomer. Use is made in particular of organosilanes or polyorganosiloxanes which are at least bifunctional. 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 elastomer, preferably diene elastomer. For example, such a bifunctional compound can comprise a first functional group comprising a silicon atom, said first functional group being capable of interacting with the hydroxyl groups of an inorganic reinforcing filler, and a second functional group comprising a sulfur atom, said second functional group being capable of interacting with the elastomer, preferably diene elastomer.
Preferentially, the organosilanes are selected from the group consisting of (symmetrical or asymmetrical) organosilane polysulfides, such as bis(3-triethoxysilylpropyl) tetrasulfide, abbreviated to TESPT, sold under the name Si69 by Evonik, or bis(3-triethoxysilylpropyl) disulfide, abbreviated to TESPD, sold under the name Si75 by Evonik, polyorganosiloxanes, mercaptosilanes, blocked mercaptosilanes, such as S-(3-(triethoxysilyl)propyl) octanethioate, sold by Momentive under the name NXT Silane. More preferentially, the organosilane is an organosilane polysulfide.
Of course, use might also be made of mixtures of the coupling agents described above.
The rubber compositions forming the compound of the invention can also contain agents for covering the reinforcing inorganic filler when a reinforcing inorganic filler is used in a composition of the compound of the invention, making it possible to improve their processability in the uncured state. These covering agents are well known (see, for example, patent applications WO 2006/125533-A1, WO 2007/017060-A1 and WO 2007/003408-A1); mention will be made, for example, of hydrolysable silanes such as hydroxysilanes (see, for example, WO 2009/062733-A2), alkylalkoxysilanes, polyols (for example diols or triols), polyethers (for example polyethylene glycols), primary, secondary or tertiary amines, hydroxylated or hydrolysable polyorganosiloxanes (for example α,ω-dihydroxypolyorganosilanes (see, for example, EP 0784072-A1).
The rubber compositions forming the compound of the invention may comprise at least one plasticizer.
As is known to those skilled in the art of rubber compositions for pneumatic or non-pneumatic tyres, this plasticizer is preferably chosen from hydrocarbon resins with a high glass transition temperature (Tg), low-Tg hydrocarbon resins, plasticizing oils and mixtures thereof. Preferably, the plasticizer is chosen from high-Tg hydrocarbon resins,plasticizing oils and mixtures thereof.
As is known, the plasticizers in the rubber compositions make it possible to modify the viscosity of a rubber composition, to adjust the glass transition temperature of the rubber composition with respect to its optimum use.
A high-Tg hydrocarbon resin is by definition a solid at ambient temperature and pressure (20° C., 1 atm), while a plasticizing oil is liquid at ambient temperature and pressure and a low-Tg hydrocarbon resin is viscous at ambient temperature and pressure.
Hydrocarbon resins, also known as hydrocarbon plasticizing resins, are polymers well known to a person skilled in the art, essentially based on carbon and hydrogen but which can comprise other types of atoms, for example oxygen, which can be used in particular as plasticizing agents. They are by nature at least partially miscible (i.e. compatible) at the contents used with the rubber compositions for which they are intended, so as to act as true diluents. They have been described, for example, in the book entitled “Hydrocarbon Resins” by R. Mildenberg, M. Zander and G. Collin (New York, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted to their applications, notably in the pneumatic tyre rubber field (5.5. “Rubber Tires and Mechanical Goods”). In a known way, these hydrocarbon resins can also be described as thermoplastic resins in the sense that they soften when heated and can thus be moulded. The softening point of the hydrocarbon resins is measured according to standard ISO 4625 (“Ring and Ball” method). The Tg is measured according to standard ASTM D3418 (2008). The macrostructure (Mw, Mn and PI) of the hydrocarbon resin is determined by size exclusion chromatography (SEC); solvent tetrahydrofuran; temperature 35° C.; concentration 1 g/l; flow rate 1 ml/min; solution filtered through a filter with a porosity of 0.45 µm before injection; Moore calibration with polystyrene standards; set of 3 Waters columns in series (Styragel HR4E, HR1 and HR0.5); detection by differential refractometer (Waters 2410) and its associated operating software (Waters Empower). The hydrocarbon resins can be aliphatic or aromatic or also of the aliphatic/aromatic type, that is to say based on aliphatic and/or aromatic monomers. They can be natural or synthetic and may or may not be petroleum-based (if such is the case, they are also known under the name of petroleum resins). In a known way, the high-Tg hydrocarbon resins are thermoplastic hydrocarbon resins, the Tg of which is above 20° C.
Preferably, the plasticizer can optionally comprise a hydrocarbon resin, which is solid at ambient temperature and pressure, referred to as a high-Tg resin. Preferably, the high-Tg hydrocarbon plasticizing resin exhibits at least any one of the following characteristics:
The plasticizer may optionally comprise a hydrocarbon resin which is viscous at 20° C., referred to as “low-Tg” resin, that is to say which, by definition, has a Tg within a range extending from -40° C. to 20° C.
Preferably, the low-Tg hydrocarbon plasticizing resin exhibits at least any one of the following characteristics:
The plasticizer can also contain an extender oil (or plasticizing oil) which is liquid at 20° C., referred to as “low-Tg” plasticizer, that is to say which by definition has a Tg below -20° C., preferably below -40° C. Any extender oil, whether it is of aromatic or non-aromatic nature, known for its plasticizing properties with regard to elastomers can be used. At ambient temperature (20° C.), these oils, which are more or less viscous, are liquids (that is to say, as a reminder, substances which have the ability to eventually assume the shape of their container), unlike in particular high-Tg hydrocarbon resins, which are by nature solids at ambient temperature. Plasticizing oils selected from the group consisting of naphthenic oils (low- or high-viscosity, in particular hydrogenated or non-hydrogenated), paraffinic oils, MES (Medium Extracted Solvate) oils, TDAE (Treated Distillate Aromatic Extract) oils, RAE (Residual Aromatic Extract) oils, TRAE (Treated Residual Aromatic Extract) oils and SRAE (Safety Residual Aromatic Extract) oils, mineral oils, plant oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and the mixtures of these compounds are particularly suitable.
The high-Tg hydrocarbon resins, the low-Tg hydrocarbon resins, and the preferential plasticizing oils above are well known to those skilled in the art and commercially available.
The rubber compositions forming the rubber compound in accordance with the invention can also comprise all or part of the usual additives and processing aids known to a person skilled in the art and generally used in rubber compositions for pneumatic or non-pneumatic tyres, in particular for treads, such as, for example, fillers (reinforcing or non-reinforcing / other than those mentioned above), pigments, protective agents, such as antiozone waxes, chemical antiozonants or antioxidants, anti-fatigue agents or reinforcing resins (such as described, for example, in application WO 02/10269).
The rubber compositions forming the rubber compound in accordance with the invention may comprise at least one crosslinking system. The crosslinking system can be any type of system known to a person skilled in the art in the field of rubber compositions for pneumatic or non-pneumatic tyres. It may in particular be based on sulfur, and/or on peroxide and/or on bismaleimides.
Preferentially, the crosslinking system is based on sulfur; it is then called a vulcanization system. The sulfur can be provided in any form, in particular in the form of molecular sulfur or of a sulfur-donating agent. At least one vulcanization accelerator is also preferentially present, and, optionally, also preferentially, use may be made of various known vulcanization activators, such as zinc oxide, stearic acid or equivalent compound, such as stearic acid salts, and salts of transition metals, guanidine derivatives (in particular diphenylguanidine), or else known vulcanization retarders.
The sulfur is used at a preferential content in a range extending from 0.5 to 12 phr, more preferentially in a range extending from 0.7 to 10 phr. The vulcanization accelerator is used at a preferential content in a range extending from 0.5 to 10 phr, more preferentially in a range extending from 0.5 to 5.0 phr.
Use may be made, as accelerator, of any compound capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type, and also their derivatives, or accelerators of sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types.
The rubber compound according to the invention comprises at least one rubber composition, denoted C1, having a defined glass transition temperature denoted Tg1.
This rubber composition C1 comprises at least one elastomer E1 as defined above. Preferably, the elastomer E1 is a diene elastomer, more preferentially still, is a non-functionalized diene elastomer.
More preferably still, the elastomer E1 of the rubber composition C1 is selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene/styrene copolymers, butadiene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. Preferentially, the elastomer E1 of the rubber composition C1 is selected from the group consisting of synthetic polyisoprenes, polybutadienes, butadiene/styrene copolymers, butadiene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. More preferentially still, the elastomer E1 of the rubber composition C1 is selected from the group consisting of polybutadienes and butadiene/styrene copolymers. More preferentially, the elastomer E1 of the rubber composition C1 is a styrene/butadiene copolymer.
Preferentially, this elastomer E1 is a non-functionalized diene elastomer. For the purposes of the present invention, “a non-functionalized diene elastomer” is understood to mean a diene elastomer, whether natural or synthetic, which does not bear a chemical function capable of interacting with a reinforcing filler. Preferentially, the non-functionalized diene elastomer may consist essentially of carbon and hydrogen atoms. It may comprise no heteroatoms or else heteroatoms in amounts which are impurities and which result from its method of synthesis.
Preferentially, the diene elastomer E1, preferably a styrene/butadiene copolymer, is non-functionalized and has a glass transition temperature TgE1 above or equal to -50° C. More preferentially, the glass transition temperature TgE1 is within a range extending from -50° C. to 0° C., more preferentially from -40° C. to 0° C., more preferentially from -30° C. to 0° C.
Preferentially, the rubber composition C1 may further comprise at least one reinforcing filler. The reinforcing filler can be any type of reinforcing filler as described above. Preferentially, the reinforcing filler is selected from the group consisting of a carbon black, an inorganic reinforcing filler and mixtures thereof. More preferentially still, the reinforcing filler is selected from the group consisting of a carbon black, a silica and mixtures thereof.
The rubber composition C1 can also comprise at least one plasticizer as described above or any other additive described above.
The rubber compound according to the invention comprises at least one rubber composition, denoted C2, having a defined glass transition temperature denoted Tg2.
This rubber composition C2 comprises at least one elastomer E2 as defined above. Preferably, the elastomer E2 is a diene elastomer, more preferentially still, is a functionalized diene elastomer.
For the purposes of the present invention, “a functionalized diene elastomer” is understood to mean a diene elastomer, whether natural or synthetic, which bears a chemical function capable of interacting with a reinforcing filler. The chemical function capable of interacting with the reinforcing filler can be a heteroatom or a group of atoms comprising at least one heteroatom chosen from nitrogen, sulfur, oxygen, phosphorus, tin and silicon.
Preferentially, the elastomer E2 is a diene elastomer, preferably which is functionalized, selected from the group consisting of natural rubber, synthetic polyisoprenes, polybutadienes, butadiene/styrene copolymers, butadiene/isoprene copolymers, isobutene/isoprene copolymers, isoprene/styrene copolymers and butadiene/styrene/isoprene copolymers. Preferentially, the elastomer E2 is a diene elastomer, preferably which is functionalized, selected from the group consisting of polybutadienes and styrene/butadiene copolymers. More preferentially still, the elastomer E2 is a styrene/butadiene copolymer, preferably which is functionalized.
Advantageously, the glass transition temperature TgE2 of the elastomer E2, preferably diene elastomer which is in particular functionalized, is within a range extending from -110° C. to -23° C., preferably extending from -100° C. to -28° C., more preferentially extending from -95° C. to -30° C.
The functionalization of the diene elastomer E2 is known. It can be carried out during the synthesis of the diene elastomer or else after its synthesis by grafting chemical functions onto the monomers of the diene elastomer.
The functionalized diene elastomer E2 comprises at least one chemical function capable of interacting with the reinforcing filler, the chemical function comprising at least one heteroatom selected from the group consisting of nitrogen, sulfur, oxygen, phosphorus, tin and silicon. Mention may be made, by way of example, among these functions, of cyclic or non-cyclic primary, secondary or tertiary amines, isocyanates, imines, cyanos, thiols, carboxylates, epoxides or primary, secondary or tertiary phosphines. This interaction of the functionalized diene elastomer E2 with the reinforcing filler can be established for example by means of covalent bonds, hydrogen bonds, ionic and/or electrostatic bonds between the function(s) of the diene elastomer and the chemical functions present on the surface of the reinforcing filler.
Preferentially, the chemical function capable of interacting with the reinforcing filler of the diene elastomer E2 is a polar function comprising at least one oxygen atom.
Preferentially, the polar function may be chosen from the group consisting of silanol, alkoxysilanes, alkoxysilanes bearing an amine group, epoxide, ethers, esters, carboxylic acids and hydroxyl. Such functionalized elastomers are known per se and are described notably in the following documents: FR2740778, US6013718, WO2008/141702, FR2765882, WO01/92402, WO2004/09686, EP1127909, US6503973, WO2009/000750 and WO 2009/000752.
The functionalized diene elastomer is preferably a diene elastomer comprising a polar function that is a silanol.
Preferentially, the silanol is located at the chain end or in the middle of the chain of the main chain of the functionalized diene elastomer.
Preferentially, the functionalized diene elastomer can be a diene elastomer (in particular an SBR) in which the silanol function is located at the chain end. This functionalized diene elastomer comprises, at one end of its main chain, a silanol function or a polysiloxane group bearing a silanol end of formula —(SiR1R2—O—)mH with m representing an integer ranging from 3 to 8, preferably 3, R1 and R2, which may be identical or different, represent an alkyl radical of 1 to 10 carbon atoms, preferably an alkyl radical containing 1 to 4 carbon atoms.
This type of elastomer may be obtained according to the processes described in document EP 0778311 and more particularly according to the process consisting, after a step of anionic polymerization, in functionalizing the living elastomer with a functionalization agent of cyclic polysiloxane type. As cyclic polysiloxanes, mention may be made of those corresponding to formula (V):
where m represents an integer ranging from 3 to 8, preferably 3, and R1 and R2, which may be identical or different, represent an alkyl radical of 1 to 10 carbon atoms, preferably an alkyl radical containing 1 to 4 carbon atoms. Among these compounds, mention may be made of hexamethylcyclotrisiloxane.
The functionalized diene elastomer E2 can be a diene elastomer (in particular an SBR) comprising a polar function which is an alkoxysilane optionally bearing another function, in particular an amine function. Preferentially, the alkoxysilane optionally bearing another function (preferably bearing an amine group) is located at the chain end or in the middle of the chain of the main chain of the functionalized diene elastomer, more preferentially the alkoxysilane group optionally bearing the amine group is located in the middle of the chain of the main chain of the functionalized diene elastomer.
Thus, the functionalized diene elastomer E2 may comprise within its structure at least one alkoxysilane group and at least one other function, the silicon atom of the alkoxysilane group being bonded to the elastomer chain(s), the alkoxysilane group optionally being partially or totally hydrolyzed to silanol.
According to certain variants, the alkoxysilane group is predominantly located at one end of the main chain of the elastomer.
According to other variants, the alkoxysilane group is predominantly located in the main elastomer chain, it will then be said that the diene elastomer is coupled or else functionalized in the middle of the chain, in contrast to the “chain end” position, although the group is not located precisely in the middle of the elastomer chain. The silicon atom of this function connects the two branches of the main chain of the diene elastomer.
The alkoxysilane group comprises a C1-C10 alkoxy radical, optionally partially or totally hydrolysed to hydroxyl, or even a C1-C8, preferably C1-C4 alkoxy radical, and is more preferentially methoxy and ethoxy.
The other function is preferably borne by the silicon of the alkoxysilane group, directly or via a spacer group defined as being an atom or a group of atoms. Preferentially, the spacer group is a saturated or unsaturated, cyclic or non-cyclic, linear or branched, divalent C1-C18 aliphatic hydrocarbon-based radical or a divalent C6-C18 aromatic hydrocarbon-based radical.
The other function is preferably a function comprising at least one heteroatom chosen from N, S, O or P. Mention may be made, by way of example, among these functions, of cyclic or non- cyclic primary, secondary or tertiary amines, isocyanates, imines, cyanos, thiols, carboxylates, epoxides or primary, secondary or tertiary phosphines.
Mention may thus be made, as secondary or tertiary amine function, of amines substituted by C1-C10 alkyl, preferably C1-C4 alkyl, radicals, more preferentially a methyl or ethyl radical, or else of cyclic amines forming a heterocycle containing a nitrogen atom and at least one carbon atom, preferably from 2 to 6 carbon atoms. For example, the methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamino-, dipropylamino-, butylamino-, dibutylamino-, pentylamino-, dipentylamino-, hexylamino-, dihexylamino- or hexamethyleneamino- groups, preferably the diethylamino- and dimethylamino- groups, are suitable. Mention may be made, as imine function, of ketimines. For example, the (1,3- dimethylbutylidene)amino-, (ethylidene)amino-, (1-methylpropylidene)amino-, (4-N,N- dimethylaminobenzylidene)amino-, (cyclohexylidene)amino-, dihydroimidazole and imidazole groups are suitable. Mention may thus be made, as carboxylate function, of acrylates or methacrylates. Such a function is preferably a methacrylate. Mention may be made, as epoxide function, of the epoxy or glycidyloxy groups. Mention may be made, as secondary or tertiary phosphine function, of phosphines substituted by C1-C10 alkyl, preferably C1-C4 alkyl, radicals, more preferentially a methyl or ethyl radical, or else diphenylphosphine. For example, the methylphosphino-, dimethylphosphino-, ethylphosphino-, diethylphosphino, ethylmethylphosphino- and diphenylphosphino- groups are suitable.
The other function is preferably a tertiary amine, more preferentially a diethylamino- or dimethylamino- group.
The alkoxysilane group can be represented by the formula:
in which:
This type of elastomer is mainly obtained by functionalizing a living elastomer resulting from an anionic polymerization with a compound comprising an alkoxysilane group, in particular chosen from trialkoxysilane and dialkoxyalkylsilane compounds substituted by a group comprising another function bonded directly or via a spacer group to the silicon atom, the function and the spacer group being as defined above. It should be specified that it is known to those skilled in the art that, when an elastomer is modified by reaction of a functionalization agent with the living elastomer resulting from a step of anionic polymerization, a mixture of modified entities of this elastomer is obtained, the composition of which depends on the modification reaction conditions and especially on the proportion of reactive sites of the functionalization agent relative to the number of living elastomer chains. This mixture comprises entities which are functionalized at the chain end, coupled, star-branched and/or non-functionalized.
These non-functional diene elastomers are commercially available from suppliers such as Nippon Zeon, JSR, Bayer, etc. or can be synthesized according to known processes.
The rubber composition C2 further comprises at least one reinforcing filler. The reinforcing filler can be any type of reinforcing filler as described above. Preferentially, the reinforcing filler of the composition C2 predominantly comprises at least one inorganic reinforcing filler, more preferentially predominantly comprises at least one silica.
Preferentially, when the reinforcing filler predominantly comprises a reinforcing inorganic filler, preferentially a silica, the functionalized diene elastomer E2 may comprise at least one chemical function capable of interacting with the reinforcing filler, the chemical function comprising at least one heteroatom selected from the group consisting of nitrogen, sulfur, oxygen and phosphorus.
The rubber composition C2 can also comprise at least one plasticizer as described above or any other additive described above.
Rubber compound according to the invention and its manufacturing process As seen previously, the rubber compound in accordance with the invention has at least two glass transition temperatures Tg1 and Tg2 and results from the specific combination of at least two rubber compositions C1 and C2 selected in such a way that:
Surprisingly, this specific combination of rubber compositions makes it possible to obtain a rubber compound simultaneously exhibiting good hysteresis properties and good grip on wet ground. Without being bound by theory, if the rubber compound exhibits a glass transition temperature difference of less than 23° C., then the hysteresis properties are degraded and the rubber compound does not exhibit good rolling resistance. If the rubber compound has a loss factor profile exhibiting the change in tan δ as a function of the temperature in °C, the loss factor profile being measured over a temperature range extending from -80° C. to 60° C. at a frequency of 10 Hz and a constant stress of 0.7 MPa and exhibiting one or more peaks, this profile being such that all the tan δ peaks present at a temperature above the glass transition temperature Tg1 have a width at half height greater than 23° C., then the rubber compound has a poor coefficient of dynamic friction, and therefore degraded wet grip properties.
Preferentially, the rubber compound satisfies the mathematical relationship Tg1-Tg2 ≥ 25° C., preferably Tg1-Tg2 ≥ 28° C., more preferentially still Tg1-Tg2 ≥ 30° C.
Advantageously, the rubber compound satisfies the mathematical relationship 25° C. ≤ Tg1-Tg2 ≤ 40° C., preferably 28° C. ≤ Tg1-Tg2 ≤ 35° C., more preferentially 28° C. ≤ Tg1-Tg2 ≤ 34° C.
Preferentially, the glass transition temperature Tg1 of the rubber composition C1 is above or equal to -48° C., preferably above or equal to -40° C.
Preferentially, the glass transition temperature Tg1 of the rubber composition C1 is within a range extending from -48° C. to -15° C., preferably within a range extending from -40° C. to -15° C.
Preferentially, the glass transition temperature Tg2 of composition C2 is below or equal to -43° C., preferably below or equal to -50° C., more preferentially below or equal to -57° C.
Preferentially, the glass transition temperature Tg2 of composition C2 is within a range extending from -90° C. to -43° C., preferably extending from -85° C. to -50° C.
Preferentially, the rubber compound according to the invention is based on at least one rubber composition C1 with a glass transition temperature Tg1 and comprising a non-functionalized diene elastomer E1, and the glass transition temperature Tg1 being within a range extending from -48° C. to -15° C. and a rubber composition C2 with a glass transition temperature Tg2 and comprising a functionalized diene elastomer E2, and the glass transition temperature Tg2 being within a range extending from -85° C. to -50° C.; the rubber compound satisfies the mathematical relationship Tg1-Tg2 ≥ 28° C., preferably Tg1-Tg2 ≥ 30° C., the rubber compound having a loss factor profile exhibiting the change in tan δ as a function of the temperature in °C, the loss factor profile being measured over a temperature range extending from -80° C. to 60° C. at a frequency of 10 Hz and a constant stress of 0.7 MPa and exhibiting one or more peaks, this profile being such that all the tan δ peaks present at a temperature above the glass transition temperature Tg1 have a width at half height than or equal to 23° C. and the elastomer E1 being predominant in the rubber compound.
Preferentially, the rubber compound according to the invention is based on at least one rubber composition C1 with a glass transition temperature Tg1 and comprising a non-functionalized diene elastomer E1, and the glass transition temperature Tg1 being within a range extending from -40° C. to -15° C. and a rubber composition C2 with a glass transition temperature Tg2 and comprising a functionalized diene elastomer E2, and the glass transition temperature Tg2 being within a range extending from -90° C. to -43° C.; the rubber compound satisfies the mathematical relationship Tg1-Tg2 ≥ 28° C., preferably Tg1-Tg2 ≥ 30° C., the rubber compound having a loss factor profile exhibiting the change in tan δ as a function of the temperature in °C, the loss factor profile being measured over a temperature range extending from -80° C. to 60° C. at a frequency of 10 Hz and a constant stress of 0.7 MPa and exhibiting one or more peaks, this profile being such that all the tan δ peaks present at a temperature above the glass transition temperature Tg1 have a width at half height less than or equal to 23° C. and the elastomer E1 being predominant in the rubber compound.
Preferentially, the content of the elastomer E1, preferably diene elastomer, in particular which is non-functionalized, in the rubber compound of the invention is within a range extending from 50 phr to 70 phr, preferably from 55 phr to 70 phr, more preferentially from 55 phr to 65 phr.
Preferentially, the content of the elastomer E2, preferably diene elastomer, in particular which is functionalized, in the rubber compound of the invention is less than or equal to 40 phr, more preferably is within a range extending from 30 phr to 50 phr, preferably from 30 phr to 45 phr, more preferentially from 35 phr to 45 phr.
Advantageously, the content of the elastomer E1, preferably diene elastomer, in particular which is non-functionalized, in the rubber compound of the invention is within a range extending from 50 phr to 70 phr and the content of the elastomer E2, preferably diene elastomer, in particular which is functionalized, in the rubber compound of the invention is within a range extending from 30 phr to 50 phr. Advantageously, the content of the elastomer E1, preferably diene elastomer, in particular which is non-functionalized, in the rubber compound of the invention is within a range extending from 55 phr to 70 phr and the content of the elastomer E2, preferably diene elastomer, in particular which is functionalized, in the rubber compound of the invention is within a range extending from 30 phr to 45 phr.
Preferably, the content of reinforcing filler in the rubber compound of the invention is within a range extending from 20 to 100 phr, more preferentially from 30 to 90 phr, and even more preferentially from 40 to 90 phr, the optimum being, in a known way, different depending on the specific applications targeted.
When the reinforcing filler is a reinforcing inorganic filler such as a silica for example, it may be advantageous to use a coupling agent. Preferentially, the content of coupling agent in the rubber compound of the invention is advantageously less than or equal to 20 phr, it being understood that it is generally desirable to use as little as possible thereof. Typically, the content of coupling agent represents from 0.5% to 15% by weight, with respect to the amount of reinforcing inorganic filler. Its content is preferentially within a range extending from 0.5 to 20 phr. This content is easily adjusted by a person skilled in the art according to the content of reinforcing inorganic filler used in the composition of the invention.
According to a preferred embodiment, the reinforcing filler is predominantly an inorganic reinforcing filler (preferably silica) in the rubber compound according to the invention, that is to say that the reinforcing filler comprises more than 50% ( >50%) by weight of an inorganic reinforcing filler such as silica relative to the total weight of the reinforcing filler in the rubber compound. Optionally according to this embodiment, the reinforcing filler can also comprise carbon black. According to this option, the carbon black is used at a content of less than or equal to 20 phr in the rubber compound, more preferentially less than or equal to 10 phr (for example the carbon black content may be within a range extending from 0.5 to 20 phr, in particular extending from 1 to 10 phr in the rubber compound). Within the intervals indicated, the colouring properties (black pigmenting agent) and UV-stabilizing properties of the carbon blacks are beneficial, without, moreover, adversely affecting the typical performance qualities contributed by the reinforcing inorganic filler.
The rubber compound of the invention can be obtained by the customary processes for manufacturing rubber compounds, such as dry mixing of the various ingredients.
According to one embodiment, the rubber compound in accordance with the invention is manufactured in appropriate mixers using two successive preparation phases well known to a person skilled in the art:
According to another preferred embodiment of the invention, the rubber compound of the invention is prepared in the form of two rubber compositions, then the rubber compositions are combined so as to obtain the rubber compound according to the invention.
More specifically, according to this embodiment, the compound as defined above and its preferred embodiments can be obtained according to a manufacturing process comprising the following steps:
More specifically, the first rubber composition, referred to as composition C1, is prepared by mixing, in a suitable mixer such as a standard internal mixer (for example of “Banbury” type), the elastomer E1 and the other optional constituents of the composition C1 such as plasticizer(s), antiozonants, etc., with the exception of the vulcanization system. Thermomechanical working is carried out for 2 to 10 minutes up to a maximum temperature within a range extending from 110° C. to 200° C., preferably extending from 130° C. to 185° C. (and referred to as the “dropping temperature”). The rubber composition C1 is thus recovered.
Next, the second rubber composition, referred to as composition C2, is prepared by mixing, in a suitable mixer such as a standard internal mixer (for example of “Banbury” type), the elastomer E2, the reinforcing filler and the other optional constituents such as plasticizer(s) and the coupling agent for the reinforcing filler, antiozonants, etc., with the exception of the vulcanization system. Thermomechanical working is carried out for a time of 2 to 10 minutes up to a maximum temperature within a range extending from 140° C. to 200° C., preferably extending from 140° C. to 185° C. (and referred to as the “dropping temperature”). The rubber composition C2 is thus recovered.
The two rubber compositions C1 and C2 from the preceding steps are introduced into a standard internal mixer (for example of “Banbury” type) and Thermo mechanical working is carried out for 2 to 10 minutes up to a maximum temperature within a range extending from 110° C. to 180° C., preferably extending from 130° C. to 180° C. (and referred to as the “dropping temperature”).
The mixture from the preceding step is then cooled on an external mixer such as an open mill down to a temperature below or equal to 110° C. The crosslinking system is then incorporated by mixing for 5 to 15 min, and the rubber compound according to the invention is recovered.
Irrespective of the method of preparing the rubber compound, the final rubber compound thus obtained is subsequently calendered, for example in the form of a sheet or slab, notably for laboratory characterization, or else extruded in the form of a rubber semi-finished product (or profiled element) which can be used, for example, as a tread in a pneumatic or non-pneumatic tyre, in particular for a passenger vehicle.
The rubber compound may be either in the uncured state (before crosslinking or vulcanization) or in the cured state (after crosslinking or vulcanization), and may be a semi-finished product which can be used in a pneumatic or non-pneumatic tyre.
The crosslinking of the rubber compound can be carried out in a manner known to those skilled in the art, for example at a temperature within a range extending from 130° C. to 200° C., under pressure.
Another subject of the present invention is a tread comprising at least one rubber compound defined above. The rubber compound according to the invention can constitute the whole tread or else part of the tread.
Another subject of the present invention relates to a pneumatic or non-pneumatic tyre comprising at least one rubber compound defined above or comprising at least one tread defined above.
A “pneumatic tyre” is understood to mean a tyre intended to form a cavity by cooperating with a support element, for example a rim, this cavity being able to be pressurized to a pressure higher than atmospheric pressure. In contrast, a “non-pneumatic tyre” is not able to be pressurized. Thus, a non-pneumatic tyre is a toric body made up of at least one polymer material, intended to perform the function of a tyre but without being subjected to an inflation pressure. A non-pneumatic tyre may be solid or hollow. A hollow non-pneumatic tyre may contain air, but at atmospheric pressure, which is to say that it has no pneumatic stiffness afforded by an inflation gas at a pressure higher than atmospheric pressure.
The pneumatic tyres according to the invention are intended to be fitted to vehicles of any type such as passenger vehicles, two-wheeled vehicles, heavy-duty vehicles, agricultural vehicles, construction plant vehicles or aircraft or, more generally, on any rolling device. The non-pneumatic tires are intended to be fitted in particular to passenger vehicles or two-wheeled vehicles. Preferably, the pneumatic tyres according to the invention are intended to be fitted to passenger vehicles.
Preferentially, the pneumatic or non-pneumatic tyre comprises at least one tread comprising at least one rubber compound defined above.
The glass transition temperatures (Tg) of the elastomers, before their use, are determined using a differential scanning calorimeter according to standard ASTM D3418:2008.
The glass transition temperature of the compound is measured according to standard NF EN ISO 11357-2:05-2014 using a Mettler Toledo DSC3+ machine and 40 µl aluminium crucibles. The scanning measurements are carried out as follows under helium at a flow rate of 40 ml/min:
The measurements of the coefficient of dynamic friction were carried out according to a method identical to that described by L. Busse, A. Le Gal, and M. Küppel (Modelling of Dry and Wet Friction of Silica Filled Elastomers on Self-Affine Road Surfaces, Elastomer Friction, 2010, 51, p. 8). The test specimens were produced by moulding, then crosslinking of a square rubbery support (50 mm × 50 mm) having a thickness of 6 mm. After closing the mould, the latter is placed in a press with heated platens at the temperature of 150° C., and for the time necessary for the crosslinking of the material (typically several tens of minutes), at a pressure of 16 bar. The surface used to carry out these measurements is a core withdrawn from a real road surface made of bituminous concrete of BBTM [very thin bituminous concrete] type (standard NF P 98-137). In order to prevent the phenomena of dewetting and the appearance of secondary grip forces between the ground and the material, the ground + test specimen system is immersed in a 5% aqueous solution of a surfactant (Sinnozon - CAS number: 25155-30-0). The temperature of the aqueous solution is regulated using a thermostatic bath. The test specimen is subjected to a sliding movement in translation parallel to the plane of the ground. The sliding velocity SV is set at
1.2 m/s. The normal stress applied σn is 400 kPa (i.e. 4 bar). These conditions are described below by “wet ground conditions”. The tangential stress σt, opposed to the movement of the test specimen over the ground, is measured continuously. The ratio of the tangential stress σt to the normal stress σn gives the coefficient of dynamic friction µ. The coefficient of dynamic friction values are measured during a temperature sweep of the aqueous solution, ranging from 3° C. to 44° C., are obtained in steady state after stabilization of the value of the tangential stress σt.
In the examples, the maximum value of the coefficient of dynamic friction (denoted µmax) measured during this sweep is indicated.
Unless otherwise indicated, the results are given in base 100. The arbitrary value 100 being assigned to the comparative compound in order to calculate and then compare the maximum coefficient of dynamic friction of the various samples tested. The value in base 100 for the sample to be tested is calculated according to the operation: (µmax value of the sample to be tested / µmax value of the comparative compound) × 100. In this way, a result less than 100 will indicate a decrease in the µmax coefficient and therefore a drop in the wet grip performance. Conversely, a result greater than 100 will indicate an increase in the µmax coefficient and therefore an increase in the wet grip performance.
The dynamic properties tan(δ)max are measured on a viscosity analyser (Metravib A4000) according to Standard ASTM D 5992-96. The response of a sample of the vulcanized compound (2 cylindrical test specimens with a thickness of 2 mm and with a cross section of 78.5 mm2), subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, at a temperature of 40° C., is recorded. A peak-to-peak strain amplitude sweep is carried out from 1% to 100% (forward cycle) and then from 100% to 1% (return cycle). The results made use of are the loss factor tan(δ). For the return cycle, the maximum value of tan(δ) observed (tan (δ)max), denoted by tan(δ)max at 40° C. is indicated.
The results are expressed in terms of performance in base 100, that is to say that the value 100 is arbitrarily assigned to the comparative compound, in order to calculate and subsequently compare the tan δmax at 40℃ of the various compounds tested. The value in base 100 is calculated according to the operation: (value of tan δmax at 40℃ of the comparative compound/value of tan tan δmax at 40℃ of the sample)* 100. In this way, a lower value represents a decrease in the hysteresis properties whereas a higher value represents an improvement in the hysteresis properties.
Measurement of the profile of the loss factor measured according to ASTM D 5992 - 96 The response of a test specimen consisting of two cylindrical pellets each 2 mm thick, 78.5 mm2 in cross section and 1 cm in diameter is recorded. The test specimen is subjected to a simple alternating sinusoidal shear stress, at a frequency of 10 Hz, during a temperature sweep from -80° C. to +100° C. with a ramp of + 1.5° C./min, under a constant stress of 0.7 MPa. The data is acquired at a frequency of 0.12 Hz which can be adapted to obtain the desired precision.
For the tan δ peaks present at a temperature above the glass transition temperature Tg1, the peak width at half height of each of these peaks is determined.
This width at half height is defined as follows: let a given maximum be at a temperature T0 and have an associated value of tan δ Y. All of the temperatures associated with values of tan δ equal to Y/2 are then recorded. Among these values, the peak width at half height then corresponds to the difference in °C between the two closest temperatures flanking T0 the temperature of the maximum.
The ingredients used in the examples are the following:
Elastomer (1A): Non-functionalized styrene/butadiene copolymer having a Tg of -28° C. measured according to standard ASTM D3418:2008, a styrene content of 41% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 14% by weight relative to the total weight of the copolymer, a trans-1,4 butadiene content of 27% by weight relative to the total weight of the copolymer.
Elastomer (1B): Styrene/butadiene copolymer bearing a silanol function at the end of the elastomer chain, and having a Tg of -24° C. measured according to standard ASTM D3418:2008, a styrene content of 25% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 43% by weight relative to the total weight of the copolymer, a trans-1,4 butadiene content of 16% by weight relative to the total weight of the copolymer.
Elastomer (1C): Styrene/butadiene copolymer having a Tg of -65° C. measured according to standard ASTM D3418:2008, a styrene content of 16% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 20% by weight relative to the total weight of the copolymer, a trans-1,4 butadiene content of 39% by weight relative to the total weight of the copolymer.
Elastomer (1D): Styrene/butadiene copolymer bearing an aminoalkoxysilane function in the middle of the chain and having a Tg of -65° C. measured according to standard ASTM D3418:2008, a styrene content of 16% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 20% by weight relative to the total weight of the copolymer, a trans-1,4 butadiene content of 39% by weight relative to the total weight of the copolymer.
Elastomer (1F): Styrene/butadiene copolymer bearing an aminoalkoxysilane function in the middle of the chain and having a Tg of -48° C. measured according to standard ASTM D3418:2008, a styrene content of 27% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 17.5% by weight relative to the total weight of the copolymer, a trans-1,4 butadiene content of 33.5% by weight relative to the total weight of the copolymer.
Elastomer (1G): Non-functionalized styrene/butadiene copolymer having a Tg of -48° C. measured according to standard ASTM D3418:2008, a styrene content of 27% by weight relative to the total weight of the copolymer, a vinyl-1,2 butadiene content of 17.5% by weight relative to the total weight of the copolymer, a 1,4 butadiene content of 33.5% by weight relative to the total weight of the copolymer.
Carbon black (2): ASTM grade N234 carbon black sold by Cabot Corporation.
Silica : Zeosil 1165MP silica sold by Solvay.
Silane : Bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT) silane, sold by Evonik under the reference Si69;
DPG : Diphenylguanidine, Perkacit DPG from Flexsys.
Plasticizer (6): DCPD resin having a softening point of 100° C., a glass transition temperature of 51° C. sold under the reference PR-383 by Exxon Mobil.
Antiozone wax (7): Varazon 4959 antiozone wax from Sasol Wax
Antioxidant (8): N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine sold by Flexsys under the reference Santoflex 6-PPD.
ZnO : Zinc oxide (industrial grade), sold by Umicore.
Stearic acid (10): Pristerene 4031 stearin sold by Uniqema.
The examples presented in Table 1 are intended to compare the various rubber properties of the rubber compound MI1 in accordance with the invention with a series of comparative rubber compounds MT1 and MT2; the rubber compound MI1 differs from the other compounds by the distribution of the reinforcing filler within the elastomer matrix.
Table 1 presents the formulation of these compounds; the proportions are expressed in phr, that is to say in parts by weight per 100 parts by weight of the elastomers of the compound.
The comparative compound MT1 is obtained in the following manner:
All the ingredients from Table 2 are introduced, in one or more stages, into a 414 cm3 Polylab internal mixer, filled to 70% by volume and the initial vessel temperature of which is 90° C. Thermomechanical working is carried out for 6 minutes until a maximum dropping temperature of 165° C. is reached. The composition thus obtained, referred to as composition C1, is recovered.
All the ingredients from Table 3 are introduced, in one or more stages, into another 414 cm3 Polylab internal mixer, filled to 70% by volume and the initial vessel temperature of which is 90° C. Thermomechanical working is carried out for 6 minutes until a maximum dropping temperature of 165° C. is reached. The composition thus obtained, referred to as composition C2, is recovered.
The composition C1 obtained previously and the preceding composition C2 are then introduced into a 414 cm3 Polylab internal mixer, filled to 70% by volume and thermomechanical working is carried out for 5 minutes until a maximum dropping temperature of 150° C. is reached.
The mixture from the previous step is then introduced into an external mixer, such as an open mill, so as to cool this mixture to a temperature of 40° C. The crosslinking system (1.8 phr of sulfur and 2.2 phr of CBS (N-cyclohexyl-2-benzothiazolesulfenamide sold by Flexsys under the reference Santocure CBS)) is then incorporated and mixed for 20 min. The mixture thus obtained is then calendered in the form of slabs in order to carry out measurements of its physical or mechanical properties. Unless otherwise indicated, the rubber properties of the rubber compound are measured after curing at 170° C. for 20 min.
The comparative compound MT2 and the compound MI1 of the invention are prepared according to the process described for the comparative compound MT1, with respectively the compositions C1 and C2 from Tables 4 and 5 for the comparative compound MT2 and the compositions C1 and C2 from tables 6 and 7 for the compound of the invention MI1.
The rubber properties of the compounds MT1, MT2 and MI1, measured after curing, are presented in Table 8.
The comparative compound MT1 has two glass transition temperatures, Tg1 and Tg2, indicating the presence of two different rubber compositions, one having a high-Tg glass transition temperature (composition C1) and one having a low-Tg glass transition temperature (composition C2). The same is true for the second comparative compound MT2 and the compound of the invention MI1.
Despite having the same amount of reinforcing fillers (58.80 phr), the compound of the invention MI1 differs from the control compounds MT1 and MT2 by a different profile of the loss factor measured over a temperature range of from -80° C. at 60° C. at a frequency of 10 Hz and at a constant stress of 0.7 MPa according to standard ASTM D 5992 - 96.
The peak width at half height of the loss factor for the compound MI1 according to the invention is narrower (21.5° C.) than the widths at half height of the loss factors for the compounds MT1 and MT2 (respectively 24.5° C. and 34.0° C.). This narrow value of the peak at half height indicates that the reinforcing fillers of the compound have a preferential affinity for the composition having the lowest Tg, and therefore are mainly distributed in the composition having the lowest Tg.
The peak width at half height of the loss factor for the comparative compound MT1 is 24.4° C. indicating a homogeneous distribution of the reinforcing fillers between the two compositions of the compound MT1.
The peak width at half height of the loss factor for the comparative compound MT2 is 34.0° C. indicating a non-homogeneous distribution of the reinforcing fillers between the two compositions of the compound MT2, the reinforcing fillers being mainly distributed in the rubber composition which has the highest Tg.
Compared to the compound MT1, which has a homogeneous distribution of the reinforcing filler in its two compositions, the compound MT2 has, for equivalent hysteresis (tan 6max at 40°C) properties, a decrease in the coefficient µmax, and therefore a decrease in wet grip performance. Thus, when the reinforcing filler is predominantly located in the rubber composition with the highest Tg, a degradation of the wet grip performance is therefore observed for hysteresis properties equivalent to the compound MT1.
Surprisingly, when the reinforcing fillers are mainly located in the rubber composition having the lowest Tg (see compound MI1 according to the invention), an improvement in the hysteresis properties and also an increase in the coefficient µmax, and therefore an improvement in wet grip performance, relative to the control compound MT1, are observed.
The examples presented in Table 9 are intended to compare the various rubber properties of the rubber compound MI1 in accordance with the invention with respect to two comparative compounds MT3 and TM4.
The compounds MT3 and MT4 were produced in such a way that the rubber compositions forming them have a difference in glass transition temperature of less than 23° C.
In addition, the rubber composition with a higher Tg constituting the compound MT3 has the same formulation as the rubber composition with a higher Tg constituting the compound of the invention ML1.
Furthermore, the rubber composition with a lower Tg constituting the compound MT4 has the same formulation as the rubber composition with a lower Tg constituting the compound of the invention ML1.
Table 9 shows the formulation of the rubber compounds tested, the proportions are expressed in phr, that is to say in parts by weight per 100 parts by weight of the elastomers of the compound.
The MT3 compound and the MT4 compound are prepared according to the same process described in test 1 with, respectively, the compositions of Table 6 (composition 1-MI1) and of Table 10 for the compound MT3 and the compositions of Table 11 and of Table 7 for the compound MT4 (composition 2-MI1).
The rubber properties of these compounds, measured after curing, are presented in Tables 12 and 13.
The comparative compound MT3 has two glass transition temperatures Tg1 and Tg2 indicating that there are two different rubber compositions in the compound.
When the formulation of the compound MT3 is modified so that the rubber composition with a lower Tg (composition C2) has a difference in glass transition temperature with the composition with a higher Tg (composition C1) of 23° C. or more in order to obtain the compound according to the invention MI1, it is found that the hysteresis properties are significantly improved for the rubber compound MI1 compared to the compound MT3.
Surprisingly, this improvement in the hysteresis properties of the compound MI1 according to the invention is not achieved at the expense of the coefficient µmax, and therefore of the wet grip performance.
(*) The compound MT4 has a single glass transition temperature value; this glass transition temperature, measured according to standard NF EN ISO 11357-2:05-2014, is equal to -51° C. However, according to theoretical calculations, the rubber compound MT4 should have had two distinct glass transition temperatures. The theoretical glass transition temperature, obtained by calculation, for composition C1-MT4 is -40° C. and the theoretical glass transition temperature, obtained by calculation for composition C2-MT4 is -49° C., and therefore a difference of Tg1calculated-Tg2calculated = -9° C.
When the formulation of the compound MT4 is modified so that the rubber composition with a higher Tg has a difference in glass transition temperature with the low-Tg composition of 23° C. or more in order to obtain the compound according to the invention MI1, it is observed that the coefficient µmax is significantly improved compared to the compound MT4. Surprisingly, the improvement in wet grip performance is not achieved at the expense of the hysteresis properties, which remain equivalent to those of the comparative compound MT4.
The examples presented in Table 14 are intended to compare the various rubber properties of the rubber compound MI1 in accordance with the invention with respect to a comparative compound MT5 representative of Example 4 from document EP3372638A1.
The formulation of the compound MT5 is presented in Table 14, the proportions are expressed in phr.
The compound MT5 is prepared according to the same process described in test 1 with the compositions from Tables 15 and 16 respectively.
The rubber properties of these compounds, measured after curing, are presented in Table 17.
It is observed that the compound according to the invention MI1 has a significantly improved coefficient µmax compared to the compound MT5 representative of the prior art. Surprisingly, this significant improvement is not achieved at the expense of the hysteresis properties since the two compounds have the same values of tan (δmaxat40°C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005862 | Jun 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/051005 | 6/3/2021 | WO |
