Rubber hose without reinforcement and fluid circuit incorporating it.

Abstract

The invention relates to a rubber hose without reinforcing reinforcement for conveying a fluid at a maximum of 2.5. 105 Pa and a maximum of 110° C, and a circuit, for example a cooling circuit, conveying it by such hoses. The hose (1) comprises a layer consisting of a rubber composition based on at least one elastomer chosen from EPDMs, the composition comprising (phr: parts by weight per 100 parts of elastomer(s)): (i) a reinforcing filler comprising 70-100 phr of a carbon black and 20-40 phr of a precipitated silica, (ii) 0-30 phr of a plasticizing system, and (iii) a lubricating system comprising 1-5 phr of a first lubricant chosen from compounds based on fatty acid esters and 1-5 phr of a second lubricant chosen from paraffin waxes and polyalkene waxes. Fig. 1

Description

Title of the invention: Rubber hose without reinforcement and fluid circuit incorporating it. Technical field

[0001] The invention relates to a rubber hose without reinforcement which is in particular usable for conveying a fluid at a pressure of at most 2.5. 105 Pa and a temperature of at most 110° C, and a circuit conveying this fluid under these temperature and pressure conditions. The invention applies in particular to a low pressure and low temperature cooling circuit of a battery or an electric motor of a motor vehicle (e.g. hybrid or electric), the hose then conveying a coolant at a pressure preferably of at most 1.5. 105 Pa and a temperature of at most 100° C. The invention relates generally to any land, rail, water or air vehicle, as well as any industrial or residential installation conveying a fluid under reduced pressure and temperature. Prior art

[0002] In a known manner, a rubber hose for a motor vehicle cooling circuit usually comprises a radially internal layer designed to be in contact with the coolant conveyed, a reinforcing reinforcement surmounting the internal layer (typically a reinforcement formed from knitted, braided or covered yarns, for example made of PET, aramid or rayon), and at least one radially external layer surmounting the reinforcement and exposed to the air surrounding the hose.

[0003] For example, we can cite document JP 2012-229 348 A which discloses such a multilayer pipe with reinforcement frame conveying water between a heat engine and a radiator of a motor vehicle, at least one of the internal and external layers of the pipe being made of a rubber composition containing: (A) at least one rubber chosen from ethylene-propylene-diene terpolymers (EPDM) with a mass content of diene preferably between 1.5 and 5% and ethylene-propylene copolymers (EPM), (B) 35-60 parts by weight, per 100 parts of (A), of a plasticizer having a mass concentration of aromatic compound of 2-20%, (C) a silica; and (D) a peroxide crosslinking agent.

[0004] A major drawback of JP 2012-229 348 A pipes lies in their reinforced multi-layer structure, designed to enable the pipes to withstand pressures and high ambient temperatures inherent in automotive thermal engines (typically pressures of 1.5.105 to 4.105 Pa and temperatures that can exceed 150°C), this structure requiring the implementation of a complex process comprising steps of extrusion of the internal and external layers, in addition to a production (e.g. by knitting, braiding or wrapping) of the reinforcement in connection with these two layers.

[0005] Another disadvantage of the pipes disclosed in JP 2012-229 348 A is that their inner and outer layers are exclusively crosslinked with peroxide in conjunction with a specific plasticizer, so as not to inhibit the crosslinking of the EPDM or EPM rubber and to provide sufficient heat and break resistance to each layer. In addition, each layer contains a very high amount of plasticizer so as not to penalize the processability of the corresponding rubber composition. Statement of the invention

[0006] An aim of the present invention is to propose a pipe which can be used to convey a fluid at a pressure of at most 2.5.105 Pa and a temperature of at most 110°C, the pipe in particular overcoming the aforementioned drawbacks without penalizing its suitability for processing by extrusion, and having sufficient mechanical properties in the crosslinked state to be capable of withstanding pressures and temperatures which can reach these maximum values.

[0007] This aim is achieved in that the Applicant has surprisingly discovered that if a plasticizing system is used in a sulfur or peroxide crosslinkable rubber composition based on an EPDM and comprising a mixed reinforcing filler based on a specific carbon black and silica, in a reduced or zero quantity combined with a first lubricant chosen from compounds based on fatty acid esters and a second lubricant chosen from paraffin waxes and polyalkenes, then a single-layer hose without reinforcing reinforcement can be obtained, having in particular a satisfactory modulus and breaking properties, and therefore also satisfactory pressure resistance and dynamic strength.

[0008] According to one aspect of the invention, the pipe is devoid of reinforcing reinforcement and comprises a layer consisting of a rubber composition based on at least one elastomer chosen from ethylene-propylene-diene terpolymers (EPDM), the rubber composition comprising (pce: parts by weight per 100 parts of elastomer(s)) (i) a reinforcing filler comprising 70-100 pce of a carbon black and 20-40 pce of a precipitated silica, (ii) 0-30 pce of a plasticizing system, and (iii) a lubricating system comprising 1-5 pce of a first lubricant selected from fatty acid ester compounds and 1-5 pce of a second lubricant selected from paraffin waxes and polyalkene waxes.

[0009] By the expression "based on", it is meant in the present description that the composition or ingredient considered comprises predominantly by weight the constituent concerned, i.e. according to a mass fraction greater than 50%, preferably greater than 75% and possibly up to 100%.

[0010] By "reinforcing filler" is meant in the present description individual fillers of reinforcing grades for EPDM, which are constituted in whole or in part of said carbon black and said silica and which are dispersed homogeneously in the composition, it being specified that the reinforcing filler may further comprise another organic filler (other than said carbon black, e.g. graphite) or inorganic filler (clear filler other than said silica).

[0011] It will be noted that the combination of ingredients (i), (ii) and (iii) above makes it possible to give the crosslinked composition according to the invention (both sulfur and peroxide, see below) a secant modulus (in particular an M30 modulus at 30% deformation), a Shore A hardness, a breaking stress and an elongation at break which are each sufficiently high, which makes it possible to use only a single layer (without adding a reinforcing reinforcement) for a rubber hose conveying a fluid at a pressure of at most 2.5. 105 Pa and a temperature of at most 110°C, such as a coolant for a low-pressure, low-temperature cooling circuit of a battery or an electric motor of a hybrid or electric motor vehicle.

[0012] The pipes according to the invention can thus have reduced internal and external diameters in comparison with the reinforced pipes of the prior art, and thus advantageously replace the reinforced pipes of JP 2012-229 348 A, which consequently appear oversized for a low pressure and low temperature circuit defined by the aforementioned maximum values ​​of pressure and temperature of the transported fluid. As a result, the pipes of the invention have a significantly reduced manufacturing cost compared with the reinforced pipes known for automotive cooling circuits.

[0013] It will also be noted that the quantity of carbon black limited to 70-100 pce coupled with the quantity of 20-40 pce of precipitated silica in the composition makes it possible to give a single-layer pipe made of this composition a relatively high resistivity, and therefore to minimize the electrochemical degradation of the pipe in contact with the fluid that it carries, when this fluid is a coolant of the glycolated water type, without penalizing the resistance of the pipe to its external environment.

[0014] It will further be noted that the aforementioned combination of the first lubricant and the second lubricant, which respectively form external and internal lubricants for the pipe, makes it possible to limit the Mooney viscosity ML(l+4) at 100°C of the crosslinkable composition while preventing its premature crosslinking (scorching), thus making the composition of the invention suitable for use by mixing and then extrusion, despite the reduced or even zero quantity of plasticizing system (at most 30 phr) combined with the relatively high quantity of reinforcing filler (90-140 phr) used in the composition, which in the prior art constituted a technical prejudice against obtaining an acceptable Mooney viscosity ML(l+4) at 100°C (which is typically at most equal to 150) for extruding the composition under good conditions.

[0015] Preferably, the composition according to the invention is such that: - the carbon black has an iodine adsorption index of 16-27 mg / g measured according to ASTM D1510, and / or a dibutylphthalate absorption index determined according to ASTM 2414-90 of 80-110 mL / 100 g, more preferably 90-100 mL / 100 g; and - precipitated silica has a specific surface area of ​​110-140 m2 / g, more preferably 120-130 m2 / g.

[0016] It will be noted that the precipitated silica associated in a minor capacity with said carbon black contributes to increasing the secant modulus to 30% of the crosslinked composition, in comparison with a “control” composition whose reinforcing filler would be exclusively composed of said carbon black.

[0017] It will also be noted that the combination in the aforementioned quantities of said carbon black and said silica makes it possible to obtain for the composition of said crosslinked layer of the pipe a volume resistivity equal to or greater than 104 Ohm.cm, which is well suited to opposing the electrochemical degradation or extraction of this layer due to the repeated circulation of a cooling liquid in the pipe.

[0018] According to another characteristic of the invention, the composition may comprise a silica-elastomer coupling agent which has the function of ensuring the bond between the surface of the particles of the precipitated silica and the EPDM, while facilitating the dispersion of the silica within the elastomer matrix based on the EPDM. In a known manner, this coupling agent, which is capable of establishing a sufficient bond between the silica and the EPDM, is at least bifunctional, comprising a first functional group capable of bonding to the silica (e.g. between a silicon atom of the coupling agent and the surface hydroxyl groups of the silica) and a second functional group capable of bonding to the EPDM (e.g. via a sulfur atom). Preferably, this coupling agent is an organosilane, as detailed below.

[0019] As a plasticizing system according to the invention, at least one oil can be used plasticizer and / or at least one plasticizing resin, it being specified that the plasticizing system according to the invention preferably comprises at least one oil chosen from mineral oils, oils derived from biomass (including modified or unmodified vegetable oils), and mixtures thereof.

[0020] Even more preferably, at least one oil chosen from paraffinic, naphthenic and aromatic mineral oils is used as plasticizing system, and for example a mineral oil that is at least partly naphthenic (which in this case may comprise both paraffinic, naphthenic and aromatic fractions).

[0021] According to a general characteristic of the invention, said first lubricant may advantageously comprise a mixture of aliphatic fatty acid esters and an emulsifying agent.

[0022] Preferably, said first lubricant comprises in addition to this mixture a condensation product of said mixture and an inert inorganic carrier, and said first lubricant may generally be present in 2-4 phr in the rubber composition.

[0023] It will be noted that said first lubricant advantageously plays the role of an external lubricant for the rubber composition, thereby ensuring external lubrication of the interface with the processing equipment (e.g. reduced adhesion with the metal surfaces with which the composition is in contact during its processing, including the surface of the extruder).

[0024] As esters which can be used for said first lubricant, mention may be made of fatty acid esters having from 14 to 22 carbon atoms and preferably from 16 to 18 carbon atoms, which may for example include glycerol fatty acid esters, without limitation.

[0025] According to another general characteristic of the invention which can optionally be combined with the previous one, said second lubricant can advantageously be a polyethylene wax, and said second lubricant can generally be present at 1-3 pce in the rubber composition.

[0026] It will be noted that said second lubricant advantageously plays the role of an internal lubricant for the rubber composition, thereby reducing the friction between the macromolecular chains of the EPDM and the viscosity in the molten state of the crosslinkable composition.

[0027] As explained above, the selection of the aforementioned families of chemical compounds for the first and second lubricants makes it possible in particular to facilitate the extrusion of the crosslinkable composition by making it possible to limit the Mooney viscosity ML(l+4) at 100°C to values ​​less than or equal to 150 and preferably less than or equal to 120, in comparison with other pairs of external and internal lubricants which do not provide such sufficiently reduced values ​​of Mooney viscosity when they are associated with the plasticizing system and the reinforcing filler according to the invention.

[0028] According to another characteristic of the invention, the rubber composition can advantageously comprise: - 4-12 pce of a sulfur or peroxide crosslinking system, - 1-5 pce of said silica-elastomer coupling agent, and - 0-20 pce of said plasticizing system.

[0029] It will be noted that said crosslinking system makes it possible to chemically crosslink the rubber composition by subsequent curing of the hose comprising said layer made of the composition, at a temperature for example between 160 and 200°C.

[0030] It will also be noted that the composition according to the invention can thus comprise an extremely reduced or even zero quantity of plasticizing system as defined above, unlike the aforementioned prior art, which goes even further against the usual practice for EPDM-based rubber compositions for coolant pipes which generally comprise more than 30 phr of plasticizer(s).

[0031] According to a first embodiment of the invention, the rubber composition comprises: - 4-8 pce of said crosslinking system which is sulfur, - 2-4 pce of a polysulfurized alkoxysilane forming said coupling agent, and - 0-15 pce of said plasticizing system.

[0032] It will be noted that in this first embodiment, said sulfur crosslinking system comprises sulfur as crosslinking agent and one or more vulcanization accelerators. As polysulfurized alkoxysilane, bis(triethoxysilylpropyl)tetrasulfide, also known as "TESPT", may for example be used for said coupling agent.

[0033] According to a second embodiment of the invention, the rubber composition comprises: - 8-12 pce of said crosslinking system which is peroxide, - 2-4 pce of a vinylsilane forming said coupling agent, and - 10-20 pce of said plasticizing system.

[0034] It will be noted that in this second embodiment, said peroxide crosslinking system advantageously comprises an organic peroxide as crosslinking agent and a crosslinking coagent, for example chosen from triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC).

[0035] As vinylsilane, it is possible, for example, to use for said coupling agent an oligomeric siloxane comprising vinyl and ethoxy groups.

[0036] According to this second embodiment of the invention, the rubber composition may further comprise 2-10 pce of a formaldehyde resin of an aliphatic phenol, preferably a formaldehyde resin of an alkyl phenol.

[0037] It will be noted that this formaldehyde resin of an aliphatic phenol can advantageously play the role of a tackifying agent for the composition.

[0038] According to another general characteristic of the invention, said at least one elastomer of the composition is an EPDM not extended with oil having: - mass rates of units derived from ethylene of 55-63%, of a non-conjugated diene (such as ethylidene norbornene) of 8-10%, and preferably in addition - a Mooney viscosity ML(l+4) at 125°C between 39 and 43.

[0039] Preferably, said non-oil-extended EPDM has in combination: - mass rates of units derived from ethylene of 57-60%, of ethylidene norbornene of 8-9%, and - a Mooney viscosity ML(l+4) at 125°C between 40 and 42.

[0040] It may be noted that the Applicant has verified that a non-oil-extended EPDM having a mass content of units derived from a non-conjugated diene of less than 8% penalized the mechanical properties obtained for the rubber composition incorporating it (all other ingredients unchanged), and consequently for the single-layer hose made from this composition.

[0041] According to another general aspect of the invention which may relate to one of the abovementioned characteristics and possibly to said first mode and second mode of the invention, the rubber composition has in the non-crosslinked state (i.e. before curing of the crosslinkable composition) the following properties, measured on cylindrical test pieces: - a Mooney viscosity ML(l+4) at 100°C of 90-150, measured according to ISO 289-1, and preferably in addition - a roasting time t5 without premature crosslinking at 135°C of 15-18 minutes, measured according to ISO 289-2, t5 being relative to an increment in Mooney viscosity at 135°C compared to the initial Mooney viscosity ML(l+4) of +5 points.

[0042] It will be noted that the Mooney viscosity ML(l+4) at 100°C can advantageously be between 95 and 105 in said second mode relating to a composition crosslinkable with peroxide, and between 110 and 120 in said first mode relating to a composition crosslinkable with sulfur.

[0043] According to another general aspect of the invention, the crosslinkable rubber compositions of the invention are prepared by implementing a process essentially comprising the following successive steps: (a) introduction of the ingredients of the composition, with the exception of the crosslinking system, into an internal mixer; b) one-step thermomechanical work in this internal mixer, until reaching a maximum "drop" temperature, for example 20-130°C; c) recovery then cooling of the mixture thus obtained; then d) addition of the sulfur or peroxide crosslinking system in an external mixer (e.g. with cylinders) at a temperature of 95-105°C, with mechanical work in this external mixer of the crosslinkable composition thus obtained.

[0044] Alternatively, the crosslinking system can be introduced during step b) of thermomechanical working with maximum temperature control at 120°C for example, or during a second introduction into the internal mixer following cooling of the precursor mixture resulting from the first step.

[0045] According to another general aspect of the invention which may relate to one of the abovementioned characteristics and possibly to said first mode and second mode of the invention, the rubber composition has at least one and preferably all of the following properties in the crosslinked state, measured on dumbbell-shaped test pieces: a) a Shore A hardness of 80-90, measured according to ASTM D 2240; b) a secant modulus M30 at 30% elongation of 2-3 MPa, measured in uniaxial tension according to ISO 37:2017; (c) a breaking stress of 11-16 MPa measured in uniaxial tension according to ISO 37:2017, said breaking stress being for example 11-12 MPa if the rubber composition is crosslinked with sulfur and 14-16 MPa if the rubber composition is crosslinked with peroxide; and (d) an elongation at break of 160-400% measured in uniaxial tension according to ISO 37:2017, said elongation at break being for example 160-220% if the rubber composition is crosslinked with peroxide and 300-400% if the rubber composition is crosslinked with sulfur.

[0046] As evidenced by these relatively high minimum values ​​obtained for the hardness, the M30 modulus and the breaking properties of the crosslinked composition, the mechanical properties of the composition and consequently of the single-layer pipe made from it appear sufficient for it to convey with good dynamic resistance a cooling liquid at a pressure of at most 1.5.105 Pa and a temperature of at most 100°C in a cooling circuit of a battery or an electric motor of a motor vehicle.

[0047] As explained above, a hose according to the invention is advantageously single-layer, consisting of said layer crosslinked by curing the rubber composition at a temperature, for example, between 160 and 200°C, the hose being usable for conveying a fluid at a pressure of at most 2.5.105 Pa and at a temperature of at most 110°C.

[0048] Advantageously, the crosslinked layer can have an equal volume resistivity or greater than 104 Ohm.cm, and the pipe can be used to convey under the aforementioned conditions a coolant forming this fluid in said cooling circuit.

[0049] A pressurized fluid circuit according to the invention, in particular a cooling circuit for a battery or an electric motor for a hybrid or electric motor vehicle, comprises a plurality of rubber pipes mounted on thermoplastic connectors, and it is characterized in that at least one and preferably each of the pipes is as defined above.

[0050] It will be noted that these thermoplastic connectors can be formed from cut rings, for example based on a polyamide (e.g. aliphatic, such as PA 6 or PA 6.6) reinforced with glass fibers, unlike the rings of the prior art crimped onto multi-layer reinforced pipes. Brief description of the drawings

[0051] Other characteristics, advantages and details of the invention will emerge from reading the following description of several exemplary embodiments of the invention, given for illustrative purposes in relation to the attached drawing, in which: Fig.l

[0052] [Fig.l] is a schematic view in axial section of a single-layer pipe according to the invention assembled on two thermoplastic connectors. Examples of embodiments of the invention

[0053] The single-layer pipe 1 of [Fig. 1] is capable of conveying a fluid such as a cooling liquid in its internal space 2, at a pressure of at most 1.5. 105 Pa and a temperature of at most 100° C, and it is assembled to two thermoplastic connectors, for example formed of cut rings 3 based on a polyamide (eg a PA 6 or PA 6.6) reinforced with glass fibers.

[0054] Rubber compositions II, 12 and 13 according to the invention were prepared to obtain such a single-layer hose, by implementing the following processes to prepare each crosslinkable composition II, 12, 13.

[0055] The ingredients of each composition II, 12, 13, with the exception of the crosslinking system, were introduced into an internal mixer of the Banbury® or Intermesh® type. A one-step thermomechanical work was then carried out (total mixing time ranging from 30 seconds to 2 min.), until a maximum "drop" temperature of approximately 125° C was reached. The mixture thus obtained was recovered, cooled, and then the crosslinking system was added (with sulfur for each composition II, 13 to be prepared, and with peroxide for composition 12) in an external cylinder mixer at a temperature of 100°C, mixing everything for about 2 min. in a mechanical working step (in following a “1 to 3” sequence in this external mixer).

[0056] According to other tests carried out to prepare compositions II and 12 differently, the crosslinking system was introduced as a variant during the first thermomechanical working step with maximum temperature control at 120°C, or during a second introduction into the same internal mixer following cooling of the precursor mixture resulting from the first step.

[0057] The crosslinkable rubber compositions 11-13 thus obtained were then shaped in the form of cylindrical test pieces to carry out measurements of properties in the uncrosslinked state (Mooney viscosity and roasting time), and in the form of dumbbell-type test pieces to carry out measurements of mechanical properties in the crosslinked state after curing the test piece at 180°C (hardness, secant modulus at 30% deformation and properties at break).

[0058] On each crosslinkable cylindrical test piece, the Mooney viscosity ML(l+4) at 100°C according to the ISO 289-1 standard and the roasting time t5 without premature crosslinking at 135°C according to the ISO 289-2 standard were measured.

[0059] In addition, on each dumbbell-type crosslinked test piece: - Shore A hardness after 3 seconds according to ASTM D 2240, - the secant modulus M30, at 30% deformation, in uniaxial tension according to ISO 37:2017, and - breaking stress and elongation at break, in uniaxial tension according to ISO 37:2017.

[0060] The following Table 1 details the formulation of a sulfur crosslinked rubber composition II which was prepared as described above. [Tables 1] Ingredients Composition II (pce) EPDM with mass content of ethylene of 58%, ethylidene norbornene of 8.5%, and ML(l+4) at 125°C of 41 100 Carbon black with iodine adsorption index of approximately 21 mg / g and DBP absorption of approximately 95 mL / 100 g 90 Precipitated silica with specific surface area 125 m2 / g 31 Mineral plasticizing oil partly naphthenic of formula 1 below 10 Coupling agent TESPT 2 ZnO 5 External lubricant: “STRUKTOL WB 212” 3 Internal lubricant: polyethylene wax 2 Stearic acid 3 Antioxidant 1 Calcium oxide 5.5 Sulphur at 80% 1 Accelerators TBZTD, TBBS, ZBEC 3.9

[0061] [Chem.l] Table 2 below details the properties obtained for composition II according to the invention, in the non-crosslinked state and in the crosslinked state. [Tables 2] Composition II Properties in the uncrosslinked state ML(l+4) at 100°C 110-120 Scorching time t5 at 135°C 15 min. Properties in the crosslinked state Shore A hardness At least 80 Modulus M30 at 30% deformation 2.2 MPa Stress at break Approx. 11.0 MPa Elongation at break 350-400%

[0062] The following Table 3 details the formulation of a peroxide crosslinked rubber composition 12 that was prepared as described above. [Tables 3] Ingredients Composition 12 (pce) EPDM with ethylene mass content of 58%, ethylidene norbornene of 8.5%, and ML(l+4) at 125°C of 41,100 Carbon black with iodine adsorption index of approximately 21 mg / g and DBP absorption of approximately 95 mL / 100 g 90 Precipitated silica with specific surface area 125 m2 / g 30 Mineral plasticizing oil of formula 1 above 15 Siloxane coupling agent with vinyl and ethoxy groups 2 HMT accelerator 1,6 External lubricant: “STRUKTOL WB 212” 3 Internal lubricant: polyethylene wax 2 Tackifying agent: formaldehyde resin of an alkyl phenol 5 Antioxidant 1 PEG 4000 3 Organic bis-peroxide 8 TAC co-agent 1 Table 4 below details the properties obtained for composition 12 according to the invention, in the uncrosslinked state and in the crosslinked state. [Tables 4] Composition 12 Properties in the uncrosslinked state ML(l+4) at 100°C 100 Scorching time t5 at 135°C 18 min. Properties in the crosslinked state Shore A hardness 82 M30 modulus at 30% strain 2.5 MPa Stress at break Approx. 14.0 MPa Elongation at break 180%

[0063] These properties obtained for compositions 11-12 according to the invention show that they had satisfactory processability in the non-crosslinked state (in particular for composition 12 crosslinked with peroxide) and mechanical properties that were also satisfactory in the crosslinked state (in particular for composition 12 which had improved hardness, breaking stress and M30 modulus compared to composition II, which nevertheless had an elongation at break greater than that of composition 12), which makes these compositions 11-12 suitable for constituting the single extruded layer of a pipe conveying a coolant at a pressure of at most 2.5 105 Pa and at a temperature of at most 110°C in a cooling circuit of a battery or an electric motor of a motor vehicle, in particular.

[0064] The Applicant has further prepared a sulfur-crosslinked rubber composition 13 according to the invention, which differs essentially from composition II by the absence of any plasticizer (composition 13 comprising 0 pce of plasticizing oil, unlike compositions II and 12), as detailed in Table 5 below. [Tables 5] Ingredients Composition 13 (pce) EPDM with mass content of ethylene of 58%, ethylidene norbornene of 8.5%, and ML(l+4) at 125°C of 41 100 Carbon black with iodine adsorption index of approximately 21 mg / g and DBP absorption of approximately 95 mL / 100 g 90 Precipitated silica with specific surface area of ​​125 m2 / g 30 Coupling agent TESPT 2 ZnO 5 External lubricant: “STRUKTOL WB 212” 3 Internal lubricant: polyethylene wax 2 Stearic acid 3 Antioxidant 1 Calcium oxide 5 Sulphur at 80% 1 Accelerators TBZTD, TBBS, ZBEC 3.9

[0065] Table 6 below details the properties obtained for composition 13 according to the invention, in the non-crosslinked state and in the crosslinked state. [Tableauxô] Composition 13 Properties in the uncrosslinked state ML(l+4) at 100°C 150 Scorching time t5 at 135°C 14 min. Properties in the crosslinked state Shore A hardness 80 M30 modulus at 30% deformation 3 MPa Stress at break 11 MPa Elongation at break 250-300%

[0066] These properties obtained for composition 13 according to the invention show that it was suitable for use despite the absence of plasticizer, in particular thanks to to external and internal lubricants, and that it had satisfactory mechanical properties (similar to those of composition II), which makes this composition 13 also suitable for constituting the single extruded layer of a pipe carrying a coolant at a pressure of at most 2.5. 105 Pa and at a temperature of at most 110°C in a cooling circuit of a battery or an electric motor of a motor vehicle.

[0067] Four “control” rubber compositions C1, C2, C3 and C4 were also prepared (among which compositions C1-C3 were crosslinked with sulfur and composition C4 with peroxide), using the following process.

[0068] The ingredients of each composition C1-C4, with the exception of the crosslinking system, were introduced into a Banbury® or Intermesh® internal mixer, then thermomechanical work was carried out in a mixing step of 30 s to 2 min, until a maximum "falling" temperature of approximately 125°C was reached. The mixture thus obtained was recovered, cooled, and then the crosslinking system (sulfur for compositions C1-C3 and peroxide for composition C4) was added in an external cylinder mixer at 100°C, mixing everything for approximately 2 min. in a mechanical working step following a “1 to 3” sequence in this external mixer.

[0069] It was not possible to manufacture composition C3 (without inorganic filler and plasticizer), because the too hard mixture of C3, reinforced only by a very high quantity of carbon black, remained stuck in the mixer.

[0070] The obtained “control” crosslinkable compositions C1-C3 were then shaped in the form of cylindrical test pieces to measure their properties in the non-crosslinked state, and in the form of dumbbell-type test pieces to measure the mechanical properties in the crosslinked state after baking the test piece at 180°C, following the same measurement methods as those detailed above for compositions 11-13.

[0071] The following Table 7 details the formulations of the three sulfur-crosslinked “control” compositions C1-C3 that were prepared as described above. [Paintings?] Ingredients Cl (pce) C2 (pce) C3 (pce) EPDM with mass content of ethylene of 48%, ethylidene norbornene of 7.8%, and ML(l+4) at 125°C of 28 100 100 100 Carbon black with iodine adsorption index of approximately 21 mg / g and DBP of approximately 95 mL / 100 g 80 80 110 Precipitated silica with specific surface area 125 m2 / g 50 50 - Calcined kaolin - 30 - Mineral plasticizing oil partly naphthenic of formula 1 above 30 30 - Coupling agent TESPT 2 2 - ZnO 5 5 5 External lubricant: "STRUKTOL WB 212" 3 3 3 Internal lubricant: polyethylene wax 2 2 2 Acid Stearic acid 3 3 3 Antioxidant 1 1 1 Calcium oxide 5.5 5.5 5.5 Sulphur 80% 1 1 1 Accelerators TBZTD, TBBS, ZBEC 3.9 3.9 3.9 Table 8 below details the properties obtained for the “control” compositions C1-C2 (those of composition C3 cannot be measured due to the impossibility of manufacturing it), in the non-crosslinked state and in the crosslinked state. [Tables 8] Composition Cl C2 Properties in the uncrosslinked state ML(l+4) at 100°C 93 98 Scorching time t5 at 135°C 15 min. 15 min. Properties in the crosslinked state Shore A hardness 76 76 M30 modulus at 30% deformation 1.8 MPa 1.9 MPa Stress at break 11.9 MPa 10.9 MPa Elongation at break 342% 312%

[0072] These properties obtained for compositions C1-C2 show that, even if they were suitable for use in particular thanks to a high quantity of plasticizer (three times that used for composition II of the invention crosslinked with sulfur) and to lubricants, compositions C1-C2 which were characterized by a quantity of precipitated silica greater than that required in the invention (in addition to a quantity of carbon black slightly lower but close to that of composition II), had a Shore A hardness, an elongation at break and a M30 modulus significantly reduced compared to those of composition II. The mechanical properties of the C1-C2 compositions thus reinforced and plasticized were thus clearly penalized compared to those of composition II, without the addition of kaolin to composition C2 being able to compensate for the inadequacy of composition Cl. As a result, compositions C1 and C2 were not suitable for constituting the single extruded layer of a pipe carrying a cooling liquid in cooling circuits such as those targeted by the present invention.

[0073] The following Table 9 details the formulation of the peroxide-crosslinked “control” composition C4 that was prepared as described above. [Tables 9] Ingredients C4 (pce) EPDM with mass content of ethylene of 58%, ethylidene norbornene of 8.5%, and ML(l+4) at 125°C of 41,100 Carbon black with iodine adsorption index of approximately 21 mg / g and DBP absorption of approximately 95 mL / 100 g 90 Precipitated silica with specific surface area 125 m2 / g 30 Mineral plasticizing oil of formula 1 above 15 Siloxane coupling agent with vinyl and ethoxy groups 2 HMT accelerator - External lubricant: "STRUKTOL WB 212" 3 Internal lubricant: polyethylene wax 2 Tackifying agent: formaldehyde resin of an alkyl phenol - Antioxidant 1 PEG 4000 3 Organic bis-peroxide 8 TAC co-agent 1 Table 10 below details the properties obtained for the “control” composition C4, in the uncrosslinked state and in the crosslinked state. [Tables 10] Composition C4 Properties in the uncrosslinked state ML(l+4) at 100°C 100 Scorching time t5 at 135°C 13 min. Properties in the crosslinked state Shore A hardness 87 M30 modulus at 30% deformation 3.5 MPa Stress at break 15.6 MPa Elongation at break 107%

[0074] These properties obtained for composition C4, which differed only from composition 12 of the invention by the absence in composition C4 of the accelerator HMT and the tackifying agent, show that even if composition C4 was suitable for use like composition 12 and had a higher hardness, M30 modulus and breaking stress than composition 12, composition C4 had an elongation at break which was very heavily penalized compared to that of composition 12 (in particular due to the absence of a tackifying agent, such as a formaldehyde resin of an alkyl phenol) and which was very insufficient for composition C4 to be able to constitute the single extruded layer of a pipe carrying a coolant such as that targeted by the present invention.

Claims

Claims

1. A pipe (1) without a reinforcing reinforcement and comprising a layer consisting of a rubber composition based on at least one elastomer chosen from ethylene-propylene-diene terpolymers (EPDM), wherein the rubber composition comprises (phr: parts by weight per 100 parts of elastomer(s)): (i) a reinforcing filler comprising 70-100 phr of a carbon black and 20-40 phr of a precipitated silica, (ii) 0-30 phr of a plasticizing system, and (iii) a lubricating system comprising 1-5 phr of a first lubricant chosen from compounds based on fatty acid esters and 1-5 phr of a second lubricant chosen from paraffin waxes and polyalkene waxes.

2. A hose (1) according to claim 1, wherein said first lubricant comprises a mixture of aliphatic fatty acid esters and an emulsifying agent, and preferably wherein said first lubricant further comprises a condensation product of said mixture and an inert inorganic carrier and is present at 2-4 phr in the rubber composition.

3. A pipe (1) according to one of the preceding claims, wherein said second lubricant is a wax of a polyethylene, and for example wherein said second lubricant is present in 1-3 pce in the rubber composition.

4. Hose (1) according to one of the preceding claims, wherein the rubber composition comprises: - 4-12 pce of a sulfur or peroxide crosslinking system, - 1-5 pce of a silica-elastomer coupling agent, and - 0-20 pce of said plasticizing system.

5. Hose (1) according to claim 4, wherein the rubber composition comprises: - 4-8 pce of said crosslinking system which is sulfur, - 2-4 pce of a polysulfurized alkoxysilane forming said coupling agent, and - 0-15 pce of said plasticizing system.

6. A hose (1) according to claim 4, wherein the rubber composition comprises: - 8-12 pce of said crosslinking system which is peroxide, - 2-4 pce of a vinylsilane forming said coupling agent, and - 10-20 pce of said plasticizing system.

7. A hose (1) according to claim 6, wherein the rubber composition further comprises 2-10 phr of a formaldehyde resin of an aliphatic phenol, preferably a formaldehyde resin of an alkyl phenol.

8. Pipe (1) according to one of the preceding claims, in which said at least one elastomer is an EPDM not extended with oil having: - mass contents of units derived from ethylene of 55-63%, of a non-conjugated diene such as ethylidene norbornene of 8-10%, and preferably in addition - a Mooney viscosity ML(l+4) at 125°C of between 39 and 43.

9. Pipe (1) according to one of the preceding claims, wherein: - said carbon black has an iodine adsorption index of 16-27 mg / g measured according to ASTM D1510, and / or a dibutylphthalate absorption index of 80-110 mL / 100 g determined according to ASTM 2414-90; and - said precipitated silica has a specific surface area of ​​110-140 m2 / g.

10. Hose (1) according to one of the preceding claims, wherein the rubber composition has at least one and preferably all of the following properties in the crosslinked state, measured on dumbbell-shaped test pieces: a) a Shore A hardness of 80-90, measured according to ASTM D 2240; b) a secant modulus M30 at 30% elongation of 2-3 MPa, measured in uniaxial tension according to ISO 37:2017; c) a breaking stress of 11-16 MPa measured in uniaxial tension according to ISO 37:2017, said breaking stress being 11-12 MPa if the rubber composition is crosslinked with sulfur and 14-16 MPa if the rubber composition is crosslinked with peroxide;and (d) an elongation at break of 160-400% measured in uniaxial tension according to ISO 37:2017, said elongation at break being 160-220% if the rubber composition is peroxide crosslinked and 300-400% if the rubber composition is sulfur crosslinked.;

11. Pipe (1) according to one of the preceding claims, in which the com- rubber position has in the uncrosslinked state the following properties, measured on cylindrical test pieces: - a Mooney viscosity ML(l+4) at 100°C of 90-150, measured according to ISO 289-1, and preferably in addition - a scorch time t5 without premature crosslinking at 135°C of 15-18 minutes, measured according to ISO 289-2, t5 being relative to an increment in Mooney viscosity at 135°C compared to the initial Mooney viscosity ML(l+4) of +5 points.

12. Pipe (1) according to one of the preceding claims, in which said plasticizing system comprises at least one oil chosen from mineral oils, oils derived from biomass including modified or unmodified vegetable oils, and mixtures thereof, and preferably in which said at least one oil is chosen from paraffinic, naphthenic and aromatic mineral oils, and is for example a mineral oil that is at least partly naphthenic.

13. A pipe (1) according to any preceding claim, wherein the pipe (1) is single-layer, consisting of said crosslinked layer by curing the rubber composition, the pipe (1) being usable for conveying a fluid at a pressure of at most 2.5.105 Pa and at a temperature of at most 110°C.

14. Pipe (1) according to claim 13, in which said crosslinked layer has a volume resistivity equal to or greater than 104 Ohm.cm, the pipe (1) being usable for conveying, at a pressure of at most 1.

5. 105 Pa and at a temperature of at most 100°C, a coolant forming said fluid in a cooling circuit of a battery or an electric motor of a motor vehicle.

15. A pressurized fluid circuit, in particular a cooling circuit for a battery or an electric motor for a hybrid or electric motor vehicle, the circuit comprising a plurality of rubber hoses (1) mounted on thermoplastic connectors (3), wherein at least one and preferably each of said hoses (1) is as defined in one of the preceding claims.

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