Rubber composition and rubber article incorporating it.

Abstract

The invention relates to a rubber composition based on at least one EPM copolymer or one EPDM terpolymer, and a rubber article incorporating it, such as a seal or a hose (10) e.g. for an air, water or cooling circuit equipping a fuel cell.The composition comprises: - a filler including carbon black and a lamellar inorganic filler, - a processing aid system, - a plasticizing system, and - a crosslinking system including a peroxide, wherein the composition comprises, by mass fractions: 28-32% of the carbon black, which is selected from ASTM N600 or N700 series blacks, and those having a specific surface area of ​​15-25 m² / g, an iodine adsorption index of 16-24 mg / g and a DBP absorption index of 90-110 mL / 100 g, 10-20% of the lamellar inorganic filler, 1.0-6.0% of the processing aid system, which includes a carbon black coating agent, and 10-22% of the plasticizing system. Fig. 2.

Description

Title of the invention: Rubber composition and rubber article incorporating it. technical field

[0001] The invention relates to a rubber composition based on at least one ethylene-propylene copolymer (EPM) or ethylene-propylene-diene terpolymer (EPDM), and a rubber article, such as a hose or seal, incorporating this composition. The invention is particularly applicable to a single-layer or multi-layer hose for conveying a fluid under pressure, the fluid being a liquid, a gas, a mixture of gases, or a supercritical fluid. The invention is especially applicable to such a hose for a humidified air, ultrapure water, or coolant circuit equipping a fuel cell (e.g., a proton exchange membrane fuel cell, such as a hydrogen fuel cell), for example, for a fuel cell electric vehicle (FCEV) (for fuel cell electric vehicle, which may be passenger car, truck, agricultural, or construction equipment), rail, marine, aerospace, or space vehicle, or to such a hose for an industrial installation. Previous technique

[0002] As is known, a hose for the cooling circuit of a motor vehicle's internal combustion engine can be single-layer or multi-layered depending on the pressure of the fluid conveyed. In the multi-layered case, it may be reinforced by a fabric-like reinforcement (which is placed over an inner rubber layer and is itself covered by an outer rubber layer exposed to the air surrounding the hose). The rubber of the hose, in contact with which the coolant (usually glycol water) flows, is generally based on at least one ethylene-propylene-diene terpolymer (EPDM), due to the reduced physicochemical affinity of EPDM with the ethylene glycol water mixture. This affinity prevents the rubber from swelling and provides satisfactory impermeability to the coolant.

[0003] Rubber hoses used in a cooling circuit equipping a hydrogen fuel cell of a full-cycle electric vehicle (FCEV) also transfer a glycol-water type coolant, consequently requiring the single or inner layer of the hose to exhibit satisfactory resistance to swelling and impermeability in contact with this liquid. However, the rubber compositions of the single or inner layer of hoses for cooling circuits, ultrapure water, and humidified air connected to a hydrogen fuel cells must also meet other cumulative requirements, including those set out below.

[0004] A primary requirement for these compositions is that they must generate a minimized release of ions into the circulating aqueous fluid, whose initial reduced ionic conductivity must remain low (even after prolonged contact with this fluid) in order to prevent short circuits. However, a drawback of conventional EPDM-based compositions is that they are often likely to release a high quantity of metal ions into the fluid from some of the additives used in addition to the EPDM.

[0005] A second requirement for these compositions is that they must also contribute to the electrical insulation of the hydrogen fuel cell; therefore, the materials used must be highly resistive, exhibiting a maximized volume resistivity, ideally equal to or greater than 1.0 x 10⁸ Ohm.cm. However, a drawback of conventional EPDM-based compositions is that they sometimes exhibit insufficient volume resistivities, falling within an intermediate range known as the "percolation" range, i.e., between 10⁴ and 10⁸ Ohm.cm.

[0006] Document EP 1 291 466 B1 presents a rubber composition for a hose specifically used in a fuel cell, the composition being presented as generating minimized contamination for the transported fluid and maximized volume resistivity. The composition comprises (A) at least one rubber selected from EPM, EPDM, and silicone rubber, (B) 1-10 parts per 100 parts per 100 parts per 100 parts of (A). The composition of Example 7 comprises (mass fractions) 29.48% of an EPDM, 1.24% of a peroxide crosslinking system, 29.48% of "Asahi No. 52" carbon black, 22.11% of kaolinite and 17.69% of a paraffin plasticizer, for a measured volume resistivity of the composition of 2.1011 Ohm.cm and an electrical conductivity of pure water of 14.4 pS / cm after 168 hours of heat treatment applied to a 50 g sheet of the rubber composition, immersed in 250 mL of pure water at 100°C.

[0007] One drawback of the compositions presented in EP 1 291 466 B1 is that they do not include any additive to aid their implementation, which penalizes their ability to be extruded, in particular, and thus makes them unusable for forming pipes under satisfactory conditions.

[0008] Another drawback of the compositions presented in EP 1 291 466 B1 is that the electrical conductivity measurements described in this relatively old document do not meet the conditions adopted in recent years to ensure the reliability of conductivity measurements after aging. Indeed, this document does not disclose the dimensions of the samples tested (the length, width and thickness of the rubber sheets are unknown), which makes it impossible to know the ratio of exposed rubber surface area to water volume, a determining factor in an aging test of a sample in contact with a fluid. Description of the invention

[0009] An object of the present invention is to provide a rubber composition particularly usable in a pipe conveying humidified air, an aqueous cooling liquid or ultrapure water in connection with a fuel cell, which remedies in particular the aforementioned drawbacks, while exhibiting satisfactory processability in the crosslinkable state and equally satisfactory properties in the crosslinked state, including minimized ion release in aqueous media and maximized electrical resistivity.

[0010] This objective is achieved in that the Applicant has just discovered, unexpectedly in view of the aforementioned prior art, that if specific mass fractions of a semi-reinforcing type carbon black, a lamellar inorganic filler, a processing aid system including a coating agent for said carbon black, and a plasticizing system are used in a rubber composition based on a peroxide-curable EPM or EPDM, then it is possible to obtain the single layer of a monolayer pipe or at least an inner layer of a multilayer pipe exhibiting satisfactory processing suitability in the curable state and equally satisfactory physicochemical and mechanical properties in the cured state, with in particular a minimization of ion release from the rubber composition to the fluid conveyed in contact with it, while giving this composition a sufficiently high volume resistivity,This composition makes it particularly well-suited for use as a single-layer pipe or at least an inner layer of a multi-layer pipe conveying humidified air, an aqueous coolant, or ultrapure water, in connection with a fuel cell.

[0011] A rubber composition according to the invention is based on at least one elastomer selected from ethylene-propylene copolymers (EPM) and ethylene-propylene-diene terpolymers (EPDM), and the composition comprises: - a filler including carbon black and a lamellar inorganic filler, - a processing aid system, - a plasticizing system, and - a crosslinking system including a peroxide, and, according to the invention, the composition comprises (by mass fraction): 28-32% of the carbon black, which is selected from ASTM N600 or N700 series carbon blacks, and carbon blacks having a BET specific surface area of ​​15-25 m2 / g, an iodine adsorption index of 16-24 mg / g according to ASTM D1510, and a dibutyl phthalate (DBP) absorption index of 90-110 mL / 100 g according to ASTM 2414-90, 10-20% of the lamellar inorganic filler, 1.0-6.0% of the implementation aid system, which includes a carbon black coating agent capable of binding to acidic functional groups of said carbon black, and 10-22% of the plasticizing system.

[0012] It should be noted that this implementation support system, as defined above, helps to optimize: - the suitability for implementing the composition in combination with this plasticizing system, and - crosslinking the composition, by covering the acid functions of said carbon black so as to minimize the absorption of peroxide by this carbon black.

[0013] It will also be noted that the mixed charge according to the invention, comprising the aforementioned quantities of carbon black and lamellar inorganic charge, contributes significantly to the joint achievement of a minimized release of ionic species by the composition in the aqueous fluid in contact with it, and of a very high volume resistivity for said composition.

[0014] In this description, the expression "based on" means that the composition or ingredient in question comprises predominantly by weight the constituent concerned, i.e. by a mass fraction greater than 50%, preferably greater than 75% and up to 100%.

[0015] As an elastomer(s) usable in a composition according to the invention, one or more EPDMs are advantageously used, the EPDM(s) being modified or not, preferably not oil-extended and having: - mass percentages of units derived from ethylene of 47-71%, of an unconjugated diene (such as ethylidene norbomene: ENB) of 3-7%, and preferably - a Mooney viscosity ML(l+4) at 125° C between 65 and 90.

[0016] Preferably, said at least one EPDM, not extended to oil, has: - mass percentages of units derived from ethylene of 50-68%, of an unconjugated diene (such as ENB) of 4.0-6.0%, and preferably - a Mooney viscosity ML(l+4) at 125° C between 70 and 85. For example, one can use a blend of two non-oil-extended EPDMs, one of which has a mass percentage of ethylene-derived units of 47-53% and a Mooney ML(l+4) viscosity at 125°C between 65 and 75, and the other of which has a mass of units derived from ethylene of 65-71% and a Mooney viscosity ML(l+4) at 125°C between 80 and 90.

[0017] Also preferably, the composition comprises said at least one EPDM elastomer in a mass fraction of 25-40% (e.g., 30-35%), preferably comprising a mixture of a first EPDM and a second EPDM in mass rates of units from ethylene of 48-52% and 66-70%, respectively, with e.g., the respective mass fractions of the first EPDM and the second EPDM in the mixture being 40-60% and 60-40%.

[0018] It should be noted that these compositions according to the invention, based on at least one EPM or EPDM, thus exhibit high resistivity, notably thanks to said lamellar inorganic filler, despite the use of a high quantity of carbon black, which is known to negatively impact this resistivity (by increasing electrical conductivity). This high resistivity makes it possible, in particular, to minimize the electrochemical degradation of the inner layer of the pipe in contact with the fluid it carries, when this fluid is a coolant, for example, of the glycol water type, without negatively impacting the pipe's resistance to its external environment.

[0019] In the present description, "filler" means several individual fillers of grades that reinforce or do not reinforce the elastomer concerned, which are dispersed homogeneously in the composition, and "lamellar inorganic filler" means a mineral filler (sometimes called "white filler" or "clear filler") having a lamellar structure, as opposed to organic fillers such as carbon blacks and non-lamellar inorganic fillers such as silicas.

[0020] Preferably, said carbon black (i.e. of ASTM N600 or N700 series, or having a BET surface area of ​​15-25 m2 / g, an iodine adsorption index of 16-24 mg / g and a DBP absorption index of 90-110 mL / 100 g), is present in the composition in a mass fraction of 28.5-31.5%, or even 29.0-31.0%.

[0021] Even more preferably, the carbon black according to the invention belongs to the ASTM N600 series (and may then correspond to or be similar to ASTM N650 or N660 grade blacks), or it has a BET specific surface area of ​​17-23 m2 / g, an iodine adsorption index of 18-22 mg / g according to ASTM D1510, and a DBP absorption index of 95-105 mL / 100 g according to ASTM 2414-90.

[0022] The term "lamellar inorganic filler" herein refers to an inorganic filler with an aspect ratio greater than 10, preferably greater than 20. The aspect ratio is defined as the ratio of the largest average dimension (usually width or length) to the smallest average dimension (usually thickness) characterizing the lamellae of the inorganic filler. This average ratio can be measured by scanning electron microscopy (SEM).

[0023] Advantageously, the lamellar inorganic filler can be chosen from phyllosilicates and talcs.

[0024] The term "phyllosilicate" is understood to mean, in a known manner, a subgroup of the silicate group, phyllosilicates being constructed by stacking tetrahedral layers ("T") where the tetrahedra share three out of four vertices (the "basal" oxygens), the fourth vertex (the "apical" oxygen) being connected to an octahedral layer ("O") occupied by different cations. Examples of suitable phyllosilicates include smectites, kaolinite and kaolins, micas, vermiculites, and montmorillonites.

[0025] In a known manner, we mean: - by "kaolinite", a phyllosilicate mineral species composed of hydrated aluminum silicate, with the formula Al2Si2O5(OH)4; - by "mica", a mineral group within phyllosilicates primarily based on aluminum and potassium silicate; and - by "talc", a mineral species essentially composed of doubly hydroxylated magnesium silicate with the formula Mg3Si4Oi0(OH)2.

[0026] Preferably, the lamellar inorganic filler of the composition according to the invention comprises a kaolin, a mica or a talc which is present in the composition in a mass fraction of 12-18%, more preferably 13-17% and for example 14-16%.

[0027] Even more preferably, the lamellar inorganic filler comprises, for example, calcined kaolin, with a mass fraction in the composition of 12-18%, for example 13-17%, or even 14-16%. The kaolin, preferably calcined at over 600°C, may in particular have mass fractions of SiO2, Al2O3 and Fe2O3 of 50-65%, 30-45% and 0.5-1.5% respectively, and an average grain size d50 of 1-2 pm.

[0028] According to a preferred embodiment of the invention, the charge of the composition according to the invention comprises, in combination: - a carbon black of the N600 series, or having a specific surface area BET of 17-23 m2 / g, an iodine adsorption index of 18-22 mg / g and a DBP absorption index of 95-105 mL / 100 g, and - a kaolin, a mica or a talc (preferably a kaolin, for example calcined as described above) as a lamellar inorganic filler.

[0029] According to another feature of the invention, the charge of said composition can advantageously be devoid - of non-lamellar inorganic charge, being then devoid of silica and calcium carbonate, in particular, and - of lamellar inorganic filler provided with silane groups.

[0030] As a coating agent suitable for binding to acidic functional groups of carbon black (of the N600 or N700 series or having a specific surface area BET of 15-25 m2 / g, an iodine adsorption index of 16-24 mg / g and a DBP absorption index of 90-110 mL / 100 g), a polyethylene glycol preferably having an inclusive number-average molecular weight Mn between 3000 and 5000 g / mol, for example 3500-4500 g / mol, may be mentioned.

[0031] According to another feature of the invention, said implementation aid system may further include at least one lubricating agent, for example chosen from compounds based on fatty acid esters and, for example, aliphatic fatty acid esters having 14 to 22 carbon atoms.

[0032] It should be noted that said lubricating agent can advantageously perform an external lubricant function for the rubber composition, thereby ensuring external lubrication of the interface with the processing equipment (e.g. reduced adhesion with the metal surfaces in contact with which the composition is in contact during its processing, including the surface of the extruder).

[0033] Preferably, the composition according to the invention comprises the implementation aid system in a mass fraction of 1.5-4.0%, which implementation aid system may then comprise said at least one lubricating agent in addition to said covering agent.

[0034] More preferably, the implementation aid system consists of said at least one lubricant agent and said recovery agent, and may then be present in the composition in a mass fraction of 2.0-3.5%.

[0035] In general, the implementation aid system may be devoid of any crosslinking system activation agent (the composition then being advantageously devoid of zinc oxide and stearic acid).

[0036] As a plasticizing system usable according to the invention, a plasticizing oil and / or a plasticizing resin may be used, it being specified that the plasticizing system is preferably present in the composition in a mass fraction of 12-20% (more preferably 14-18%), and may advantageously comprise a high viscosity oil (with a kinematic viscosity at 100°C, measured according to ASTM D 445, of at least 30 mm2 / s).

[0037] As an alternative to this high viscosity oil, at least one oil chosen from mineral oils (e.g. paraffinic, naphthenic and / or aromatic), oils derived from biomass (including modified or unmodified vegetable oils), and mixtures thereof may be used.

[0038] It should be noted that the implementation aid system as defined above, together with the aforementioned filler and plasticizing system, makes it possible to give the crosslinkable composition according to the invention a Mooney viscosity ML(l+4) at 100° reduced C while opposing its premature crosslinking (grilling), thus making the composition of the invention suitable for implementation by extrusion, due to a satisfactory visual appearance with an absence of holes, cracks and shrinkage of the extrudate.

[0039] According to another feature of the invention, the composition may include the crosslinking system in a mass fraction of 2.5-4.0% (preferably 3.0-3.5%), which includes an organic peroxide and a crosslinking co-agent, e.g. triallyl cyanurate (TAC) or triallyl isocyanurate (TAIC).

[0040] It should be noted that this co-agent makes it possible to significantly improve the crosslinking by the peroxide and therefore the mechanical and physical properties of the composition, compared to a control composition crosslinked without co-agent added to the same organic peroxide.

[0041] A composition according to the invention may further comprise an antioxidant system comprising at least one antioxidant, preferably aromatic heterocyclic (e.g. based on polymerized 2,2,4-trimethyl-l,2-dihydroquinoline).

[0042] According to another feature of the invention, the composition may advantageously exhibit in the crosslinked state a volume resistivity, measured according to IEC 62631 3, which is equal to or greater than 1.0.108 Ohm.cm, preferably equal to or greater than 1.0.109 Ohm.cm.

[0043] It will be noted that this very high volume resistivity of the rubber composition according to the invention makes it possible to contribute effectively to the electrical insulation of the fuel cell, at least one of whose humidified air, water and cooling circuits is equipped with a pipe incorporating this composition.

[0044] According to another feature of the invention which can be combined with the previous one, after aging by immersion of samples consisting of the crosslinked composition in a volume of an aqueous liquid chosen from ultrapure water and water-ethylene glycol mixtures, for 2 to 4 weeks at 80°C, with a plate surface area / aqueous liquid volume ratio imposed at 30 mm2 / mL and the samples cut with a 40 x 60 mm cutter in a plate of thickness 2.0 ± 0.2 mm, the aqueous liquid can advantageously exhibit a final ionic conductivity Cf less than or equal to its initial ionic conductivity Ci (before said immersion) increased by 10 pS / cm: Cf - Ci < 10 pS / cm, and preferably Cf - Ci < 8 pS / cm when the aqueous liquid is ultrapure water.

[0045] It should be noted that this minimal difference in ionic conductivity for the aqueous liquid before and after said aging carried out according to this well-defined and reproducible protocol, demonstrates a minimization of ion release by the composition of rubber towards the aqueous liquid conveyed in contact with it, which helps to avoid short circuits in the fuel cell installation.

[0046] According to another general aspect of the invention, a rubber article according to the invention is selected from pressurized transfer pipes of a liquid, gaseous or supercritical fluid and sealing gaskets, the article comprising or being made of a rubber composition extruded in the crosslinkable state and then crosslinked, as defined by any one of the above characteristics.

[0047] Preferably, the article is a pipe for a circuit connected to a fuel cell conveying humidified air, a water-ethylene glycol coolant, or ultrapure water, and the pipe is then: - single layer, being made of said rubber composition, or - multi-layer, comprising a radially internal layer made of said rubber composition, at least one reinforcing layer above it, and a radially external covering layer.

[0048] Even more preferably, the pipe is configured to convey ultrapure water or a water-ethylene glycol coolant, and it is such that: - the rubber composition in the crosslinked state has a volume resistivity, measured according to IEC 62631 3, which is equal to or greater than 1.0 x 10⁸ Ohm.cm, preferably equal to or greater than 1.0 x 10⁹ Ohm.cm, and - after aging by immersion of samples consisting of the cross-linked rubber composition in a volume of an aqueous liquid chosen from ultrapure water and water-ethylene glycol mixtures, for 2 to 4 weeks at 80°C, with a surface area of ​​each sample / volume of aqueous liquid imposed at 30 mm2 / mL and the samples cut with a 40 x 60 mm cutter in a plate of thickness 2.0 ± 0.2 mm, said aqueous liquid has a final ionic conductivity Cf less than or equal to its initial ionic conductivity Ci (before said immersion) increased by 10 pS / cm: Cf - Ci < 10 pS / cm, and preferably Cf - Ci < 8 pS / cm when the aqueous liquid is ultrapure water.

[0049] According to yet another general aspect of the invention, said crosslinkable rubber composition can be prepared by implementing a process comprising essentially the following successive steps: a) introduction of the ingredients of the composition, with the exception of the crosslinking system, into an internal mixer; b) thermomechanical work in one stage in this internal mixer, until a maximum "fall" temperature is reached, for example 1120-130° C; c) recovery and then cooling of the mixture thus obtained; then d) adding the peroxide crosslinking system in an external mixer (e.g., cylinder mixer) at a temperature of 95-105°C, with mechanical working in this external mixer of the crosslinkable composition thus obtained.

[0050] Alternatively, the crosslinking system can be introduced during step b), or during a second introduction into the internal mixer following the cooling of the precursor mixture resulting from the first step. Brief description of the drawings

[0051] Other features, advantages and details of the invention will become apparent from the following description of illustrative embodiments of the invention, given in conjunction with the accompanying drawings, among which: Fig. 1

[0052] [Fig.1] is a schematic side and perspective view of a single-layer pipe according to the invention. Fig. 2

[0053] [Fig.2] is a schematic side and perspective view with partial tear-outs of a multilayer pipe according to an example of the invention. Fig. 3

[0054] [Fig.3] is a schematic side and perspective view with partial tear-outs of a multilayer pipe according to another embodiment of the invention. Fig. 4

[0055] [Fig.4] is a schematic side and perspective view with partial tear-outs of a multilayer pipe according to another embodiment of the invention. Fig. 5

[0056] [Fig.5] is a schematic side and perspective view with partial tear-outs of a multilayer pipe according to another embodiment of the invention. Fig. 6

[0057] [Fig.6] is a schematic view of a fuel cell installation in which at least one of the humidified air, cooling and water circuits connected to it comprises a single-layer or multi-layer pipe according to the invention. Examples of implementation of the invention

[0058] The single-layer pipe 1 of [Fig. 1] is, for example, suitable for conveying a fluid at a pressure of at most 3 x 10⁵ Pa and a temperature of at most 120°C, and it can be assembled to two connectors, for example, thermoplastic ones. This pipe 1 is made of a composition according to the invention as defined above.

[0059] The multilayer pipe 10 of [Fig. 2] is, for example, suitable for conveying a fluid at a pressure equal to or greater than 3 x 10⁵ Pa, and it comprises a radially internal tube 11, a reinforcing layer 12 and a cover layer radially external 13, it being specified that at least the tube 11 is made of a composition according to the invention as defined above.

[0060] The reinforcement layer 12 may include, but not limited to, a knit, braid or guipe based on multifilament yarns made of one or more textile material(s), for example in a polyamide (e.g. aramid), polyester (e.g. PET) or rayon (the term "yarn" usually referring both to a yarn based on a multitude of elementary filaments of small diameter which are twisted together, and to a ply obtained by twisting several yarns).

[0061] The multilayer pipe 20 of [Fig.3] differs from that of [Fig.2], in that the inner tube 21 is surmounted by an intermediate layer 22 itself surmounted by a reinforcing layer 23 covered by a covering layer 24, it being specified that at least the tube 21 is made of a composition according to the invention.

[0062] The multilayer pipe 30 of [Fig.4] differs from that of [Fig.3], in that the inner tube 31 is surmounted by an internal reinforcement layer 32 itself surmounted by an intermediate layer 33 covered by an external reinforcement layer 34 and then by a covering layer 35, it being specified that at least the tube 31 is made of a composition according to the invention.

[0063] The multilayer pipe 40 of [Fig.5] differs from that of [Fig.3], in that the inner tube 41 is surmounted by a barrier layer 42 of plastic material forming an interply, then by an intermediate layer 43 covered by a reinforcing layer 44, itself surmounted by a covering layer 45, with at least the tube 41 being made of a composition according to the invention.

[0064] It will be noted that a multilayer pipe according to the invention could comprise an arrangement of layers differing from those illustrated in figures 2-5, both in the number of its layers and in their respective functions.

[0065] The fuel cell installation illustrated in [Fig. 6] by way of non-limiting example essentially comprises, around and in connection with a fuel cell 50, such as a hydrogen fuel cell, for example of the "PEMFC" type: - a closed cooling loop 60 conveying a coolant comprising for example a water-ethylene glycol mixture, which includes in particular a condenser 61 equipped with a fan 61a, a control valve 62 and a non-return valve 63; - an air loop 70, 70' conveying air which includes, downstream of a filter 71 and a compressor 72, a humidifier 73 supplying (portion 70) the humidified air into the stack 50, and extracting it from the latter (portion 70') to air / water separators 81 and 82 respectively located upstream and downstream of a condenser 74 equipped with a fan 74a receiving the air outlet from the upstream air / water separator 81, the air outlet from the downstream air / water separator 82 leading to an air outlet of the installation via a regulating valve 75; - a water loop 80, 80' extending (portion 80) from the respective water outlets of the upstream separators 81 and downstream separators 82 to a water reservoir 83, equipped with the installation's water outlet and a water supply line 80' to the humidifier 73; - a hydrogen loop 90, 90' comprising a portion 90 extending from a hydrogen reservoir 91 to the fuel cell 50 via a filter 92, with a recirculation 93 of the hydrogen leaving the fuel cell 50 to the filter 92 and to a hydrogen outlet portion 90' of the installation via a regulating valve 94; and - an electrical circuit 100 comprising a power unit 101 connected to the battery 50.

[0066] It will be noted that pipes according to the invention could be incorporated into at least one of the cooling, air and water circuits equipping a fuel cell, but with the circuit or each circuit incorporating these pipes which could have characteristics different from those of [Fig.6].

[0067] Preparation of a rubber composition II according to the invention and of "control" compositions Cl, C2 and C3 not in accordance with the invention:

[0068] Each of the rubber II and C1-C3 compositions was prepared essentially by implementing the following process.

[0069] The ingredients of each composition, with the exception of the crosslinking system, were introduced into an internal Banbury® type mixer. A one-step thermomechanical process was then carried out (mixing time: 30 s 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 to an external roller mixer at 100°C, mixing everything for approximately 2 minutes in a mechanical working step.

[0070] Each crosslinkable rubber composition thus obtained was shaped into cylindrical test specimens to carry out measurements of properties in the uncrosslinked state (Mooney viscosity ML(l+4) at 100°C according to ISO 289-1, and roasting time t5 without premature crosslinking at 135°C according to ISO 289-2), and into dumbbell-type test specimens for measurements of physical and mechanical properties in the crosslinked state after baking the test specimens at 180°C.

[0071] In particular, measurements were taken on dumbbell-type test specimens made respectively of cross-linked compositions II and C1-C3: - hardness in DIDC points (International Degrees of Rubber Hardness), according to ISO 48:2010 standard, - the tensile strength Cr and the elongation at break Ar, in uniaxial tension according to ISO 37:2017, and - volume electrical resistivity at 1000 V according to IEC 62631 3 standard.

[0072] Ionic conductivity measurements of ultrapure water (with initial ionic conductivity Ci less than 1.0 pS / cm) were also carried out after aging by immersion of samples consisting of each crosslinked composition II and C1-C3 in a volume of this ultrapure water, for 2 to 4 weeks at 80°C, with a plate surface area / aqueous liquid volume ratio imposed at 30 mm2 / mL (the water volume being adjusted in the bottles to maintain this ratio) and the samples which were cut with a 40 x 60 mm cutter in a plate of thickness 2.0 ± 0.2 mm, by measuring the difference AC = Cf - Ci between the final ionic conductivity Cf and the initial ionic conductivity Ci of the ultrapure water, respectively after and before said immersion.

[0073] For this purpose, a Mettler Toledo Five Easy F30 conductivity meter with a Mettler Toledo INLAB 720 conductivity cell (measuring range of 0.01–500 pS / cm, after initial calibration of the conductivity meter) and 250 mL bottles fitted with GL45 stoppers were used (the bottles being rinsed with ultrapure water and dried with Joseph paper each time). For each test, three samples were used from the same plate, and their thickness was measured using a 5-point method (leading to an average thickness).

[0074] Each bottle was filled with 175 mL of ultrapure water to obtain a plate surface area to water volume ratio of 30 mm² / mL. A first conductivity measurement (Ci) was then performed on the water alone in each bottle. The first plate of each crosslinked composition (previously rinsed) was then placed in a first bottle, which was recapped and shaken for a few seconds. The first conductivity measurement was then taken immediately after immersion. A second sample of the same crosslinked composition was then placed in another bottle, and so on for all the compositions II and C1-C3 tested.

[0075] The aforementioned aging was carried out for 2 to 4 weeks, with the vials containing the tested immersed samples being placed in an oven at 80°C following each measurement of final conductivity Cf, it being specified that before each measurement following the aging, each vial was extracted from the oven to be placed for 4 hours at 23°C in a cooling chamber.

[0076] The following table 1 details the respective formulations of compositions II and Cl-C3 (in parts by weight per 100 parts of EPDM elastomers), [Tables 1] II Cl C2 C3 EPDM 1*50 30 50 30 EPDM 2*50 70 50 70 Carbon black ASTM N600 series*95 110 75 75 Calcined kaolin * 45 29 50 50 Plasticizing oil * 50 54 35 35 Coating agent: PEG 4000 2.8 2.8 2.8 2.8 Lubricating agent * 4.6 4.6 4.6 4.6 Quinoline antioxidant 1.2 1.2 1.2 1.2 Co-agent TAC 0.7 0.7 0.7 0.7 Organic bis-peroxide 9.4 9.4 9.4 9.4 TOTAL (parts by weight) 308.7 311.7 278.7 278.7

[0077] The ingredients identified in Table 1 by the symbol * had the following characteristics: - EPDM 1: mass content of ethylene units 50%, ethylene norbornene units 5.0%, and Mooney viscosity ML(l+4) at 125°C of 70. - EPDM 2: mass content of ethylene units 68%, ethylene norbornene units 4.9%, and Mooney viscosity ML(l+4) at 125°C of 85. - Carbon black with a specific surface area BET according to ASTM D 6556 of approximately 20 m2 / g, an iodine adsorption index according to ASTM D 1510 of approximately 20 mg / g, and a DBP absorption index according to ASTM 2414-90 of approximately 100 mL / 100 g. - Calcined kaolin comprising mass fractions of SiO2, Al2O3, and Fe2O3 of 55-60%, 35-40% and 0.5-1.0% respectively, and an average grain size d50 between 1.0 and 1.5 pm. - Plasticizing oil: oil with kinematic viscosity at 100°C, measured according to ASTM D 445, between 30 and 40 mm2 / s. - Lubricating agent: mixture of aliphatic fatty acid esters.

[0078] Table 2 below gives the mass fractions (in %) of the ingredients in Table 1 in each composition II and C1-C3.

[0079] [Tables2] II Cl C2 C3 EPDM 1 * 16.20 9.62 17.94 10.76 EPDM 2 * 16.20 22.46 17.94 25.12 Carbon Black ASTM N600 Series * 30.77 35.29 26.91 26.91 Calcined Kaolin * 14.58 9.30 17.94 17.94 Plasticizing Oil * 16.20 17.32 12.56 12.56 Coating Agent: PEG 4000 0.91 0.90 1.00 1.00 Lubricating Agent * 1.49 1.48 1.65 1.65 Quinoline antioxidant 0.39 0.38 0.43 0.43 Co-agent TAC 0.22 0.23 0.25 0.25 Organic bis-peroxide 3.04 3.02 3.38 3.38 TOTAL (%) 100.00 100.00 100.00 100.00

[0080] Table 3 below presents the essential rheological properties of the compositions obtained II and C1-C3, including for each of them: - the Mooney viscosity ML(l+4) at 100° C, measured according to ISO 289-1; - the initial roasting time t5 without premature crosslinking, according to ISO 289-2; and - the suitability for extrusion in pipe form (“extrudability”, including the behavior and appearance of the extrudate consisting of the crosslinkable composition). [Tables 3] II Cl C2 C3 ML(l+4) at 100°C 72.0 73.6 81.0 82.0 Roasting time t5 (min.) at 135°C 14.8 22.4 14.4 13.4 Extrusion suitability good good poor poor "Good" indicated a satisfactory appearance (smooth), an absence of holes, cracks or fissures and no shrinkage of the extrudate. "Bad" indicated an unsatisfactory appearance, with holes, cracks or fissures, and significant shrinkage of the extrudate.

[0081] Table 4 below presents the physical and mechanical properties of the crosslinked compositions obtained II and C1-C3, measured as indicated above on dumbbell-type test specimens. [Tables 4] II Cl C2 C3 Volumetric electrical resistivity (Ohm.cm) 1.0 x 10⁹ 2.4 x 10⁵ 4.7 x 10⁸ 1.3 x 10⁸ Difference in ionic conductivity of pure water after 2 weeks AC = Cf - Ci (pS / cm) 7.2 5.1 6.2 8.2 IRHD hardness (points) 65 65 65 69 Tensile strength Cr (MPa) 11.2 12.5 11.9 12.8 Elongation at break Ar (%) 444 400 398 399

[0082] The properties obtained in Tables 3 and 4 show that composition II according to the invention exhibits, in relation to the control compositions C1-C3: - in the crosslinkable state: improved workability, as shown by the minimum Mooney viscosity ML(l+4) for a similar toasting time t5 and the appearance satisfactory visual appearance of the extrudate with no holes, cracks, or shrinkage following extrusion, and - in the crosslinked state: improved physicochemical and mechanical properties, including: a maximum volume resistivity (approximately 1.0 x 10⁹ Ohm.cm) combined with reduced ion release into the fluid in contact with it, and improved fracture properties for similar hardness (see significantly improved elongation-break for similar stress-break).

[0083] These overall improved properties are due in particular to the specific mass fractions in the composition according to the invention: - said carbon black (between 28% and 32%, unlike the mass fractions of 35.29% and 26.91% used in C1-C3 compositions), and - other ingredients, including in particular the mass fractions of the elastomer matrix, the lamellar inorganic filler, the application aid system (including the coating agent and the lubricant) and the plasticizing system.

[0084] These improved properties make the compositions according to the invention particularly well suited for constituting, in particular: - a single-layer pipe or at least an inner layer of a multi-layer pipe carrying humidified air, an aqueous coolant or ultrapure water, in connection with a fuel cell, and even - all or part of a sealing gasket, for example for the bodywork of a motor vehicle or for a building.

Claims

Demands

1. A rubber composition particularly suitable for use in a hose (1, 10, 20, 30, 40) for humidified air, aqueous coolant, or ultrapure water connected to a fuel cell (50), the composition being based on at least one elastomer selected from ethylene-propylene copolymers (EPM) and ethylene-propylene-diene terpolymers (EPDM), and comprising: - a filler including carbon black and a lamellar inorganic filler, - an application aid system, - a plasticizing system, and - a crosslinking system including a peroxide, wherein the composition comprises, by mass fractions: 28-32% of carbon black, which is selected from ASTM N600 or N700 series carbon blacks, and carbon blacks having a BET specific surface area of ​​15-25 m² / g, an adsorption index iodine of 16-24 mg / g according to ASTM D1510, and a DBP absorption index of 90-110 mL / 100 g according to ASTM 2414-90,10-20% of the lamellar inorganic filler, 1.0-6.0% of the application aid system, which includes a carbon black coating agent capable of binding to acidic functional groups of said carbon black, and 10-22% of the plasticizing system.

2. Rubber composition according to claim 1, wherein the composition comprises said at least one elastomer which is an EPDM in a mass fraction of 25-40%, the composition preferably comprising a mixture of a first EPDM and a second EPDM in mass fractions of units from ethylene of 48-52% and 66-70%, respectively, and for example wherein the mass fraction of the first EPDM and the second EPDM in said mixture are 40-60% and 60-40%, respectively.

3. A rubber composition according to any one of the preceding claims, wherein said coating agent comprises polyethylene glycol, preferably having a mass molecular Mn average number inclusive between 3000 and 5000 g / mol.

4. Rubber composition according to any one of the preceding claims, wherein said implementation aid system further comprises at least one lubricating agent, for example selected from compounds based on fatty acid esters and, for example, aliphatic fatty acid esters having 14 to 22 carbon atoms.

5. Composition according to any one of the preceding claims, wherein the composition comprises the implementation aid system in a mass fraction of 1.5-4.0%, which is preferably devoid of a crosslinking system activation agent, the composition being for example devoid of zinc oxide and stearic acid.

6. Rubber composition according to any one of the preceding claims, wherein the lamellar inorganic filler is selected from phyllosilicates and talcs, and preferably wherein the lamellar inorganic filler comprises a kaolin, a mica or a talc which is present in the composition in a mass fraction of 12-18%.

7. Rubber composition according to claim 6, wherein the lamellar inorganic filler consists of calcined kaolin, and / or said carbon black is of the N600 series or has said BET specific surface area of ​​17-23 m2 / g, said iodine adsorption index of 18-22 mg / g and said DBP absorption index of 95-105 mL / 100 g.

8. Rubber composition according to any one of the preceding claims, wherein the filler is devoid of: - non-lamellar inorganic filler, being devoid of silica and calcium carbonate, and - lamellar inorganic filler provided with silane groups.

9. Rubber composition according to any one of the preceding claims, wherein the composition comprises the plasticizing system in a mass fraction of 12-20%, which preferably comprises an oil having a kinematic viscosity at 100°C, measured according to ASTM D 445, of at least 30 mm2 / s.

10. A rubber composition according to any one of the preceding claims, wherein the composition comprises the crosslinking system in a mass fraction of 2.5-4.0%, which includes an organic peroxide and a crosslinking co-agent, for example triallyl cyanurate (TAC) or triallyl isocyanurate (TAIC).

11. Rubber composition according to any one of the preceding claims, wherein the composition in the crosslinked state has a volume resistivity, measured according to IEC 62631 3, which is equal to or greater than 1.0.108 Ohm.cm, preferably equal to or greater than 1.0.109 Ohm.cm.

12. Rubber composition according to any one of the preceding claims, wherein, after aging for 2 to 4 weeks at a temperature of 80°C by immersion of samples made up of said composition in a volume of an aqueous liquid selected from ultrapure water and water-ethylene glycol mixtures, with a plate surface area / aqueous liquid volume ratio imposed at 30 mm2 / mL and the samples which are cut with a 40 x 60 mm cutter in a plate of thickness 2.0 ± 0.2 mm, the aqueous liquid has a final ionic conductivity Cf less than or equal to its initial ionic conductivity Ci before said immersion, increased by 10 pS / cm: Cf - Ci < 10 pS / cm, and preferably Cf - Ci < 8 pS / cm when the aqueous liquid is ultrapure water.

13. Rubber article selected from the pressurized transfer pipes (1, 10, 20, 30, 40) of a liquid, gaseous or supercritical fluid and sealing gaskets, wherein the article comprises or is made of a rubber composition according to any one of the preceding claims, extruded in the crosslinkable state and then crosslinked.

14. Article according to claim 13, wherein the article is a pipe (1, 10, 20, 30, 40) for a circuit (60, 70, 80) connected to a fuel cell (50) conveying humidified air, a water-ethylene glycol coolant or ultrapure water, and wherein the pipe (1, 10, 20, 30, 40) is: - single-layer, being made of said rubber composition, or - multi-layer, comprising a radially internal layer (11) made of said rubber composition, at least one reinforcing layer (12) overlying it, and a radially external covering layer (13).

15. Article according to claim 14, wherein the pipe (1, 10, 20, 30, 40) is configured to convey an aqueous liquid consisting of ultrapure water or a water-ethylene glycol coolant, the rubber composition having in the crosslinked state a volume resistivity, measured according to IEC 62631 3, which is equal to or greater than 1.0 x 10⁸ Ohm.cm, preferably equal to or greater than 1.0 x 10⁹ Ohm.cm, and after aging by immersion of samples consisting of said composition in a volume of aqueous liquid for 2 to 4 weeks at a temperature of 80°C, with a surface area of ​​each sample / volume of aqueous liquid imposed at 30 mm2 / mL and the samples which are cut with a 40 x 60 mm cutter in a plate of thickness 2.0 ± 0.2 mm, the aqueous liquid having a final ionic conductivity Cf less than or equal to its initial ionic conductivity Ci before said immersion, increased by 10 pS / cm: Cf - Ci < 10 pS / cm, and preferably Cf - Ci < 8 pS / cm when the aqueous liquid is ultrapure water.

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