Multilayer structure for transporting heat transfer fluid

Abstract

A tubular structure for transporting heat transfer fluid including at least: i) a layer (1) in contact with the fluid including at least one thermoplastic polymer P1 that is semicrystalline with Tm1 greater than or equal to 160° C., as determined according to the standard 1 1357-3 (2013) or amorphous with Tg1 greater than or equal to 100° C., as determined according to the standard 1 1357-2 (2013), said layer (1) containing no fibers, ii) a layer (2) including at least: (a) a thermoplastic polymer P2 that is semicrystalline, in particular a polyamide with Tm2 greater than or equal to 170° C. or amorphous with Tg2 greater than or equal to 100° C., or a polyolefin with Tm greater than 100° C.; (b) optional continuous fibers, the polymer P2 being identical to P1 or different from P1 in which case the polymers P1 and P2 adhere at least partially to one another.

Claims

1. A tubular structure for transporting heat transfer fluid, comprising at least: i) a layer (1) in contact with the fluid comprising at least one thermoplastic polymer P1 which is semi-crystalline with a Tm.sub.1 greater than or equal to 160° C., as determined according to the standard 11357-3 (2013), said layer (1) being devoid of fibers, ii) a layer (2) comprising at least: a thermoplastic polymer P2 which is semi-crystalline; the polymer P2 being identical to P1 or different than P1, in which case the polymers P1 and P2 adhere at least partially to one another, wherein the tubular structure is configured for transporting heat transfer fluid, wherein said polymer P2 is a semi-crystalline polyamide, wherein the thermoplastic polymer P2 has a Tm.sub.2 greater than or equal to 170° C., as determined according to the standard 11357-3 (2013).

2. The structure as claimed in claim 1, wherein said polymer P1 is chosen from polyamides and EVOH.

3. The structure as claimed in claim 1, wherein said polymer P1 is a semi-crystalline polyamide.

4. The structure as claimed in claim 1, wherein said polymers P1 and P2 are semi-crystalline polyamides.

5. The structure as claimed in claim 1, wherein said polymer P1 is a polyamide chosen from polyphthalamides, semi-aromatic polyamides, A/T, A/10T, A/6T, XY/10T, XY/6T, PA6, PA66, PA6/66, PA610, PA612, a C.sub.4 to C.sub.8 short-chain polyamide, or from the polymerization of at least one diamine and at least one dicarboxylic acid, the average number of carbon atoms of which is from C.sub.4 to C.sub.8, and a PA/polyolefin blend, it being possible for said polyolefin to be (totally or partially) functionalized or non-functionalized.

6. The structure as claimed in claim 5, wherein said polymer P1 is a polyamide chosen from polyphthalamides, semi-aromatic polyamides, a C.sub.4 to C.sub.8 short-chain polyamide, and a PA/polyolefin blend, it being possible for said polyolefin to be functionalized or non-functionalized.

7. The structure as claimed in claim 5, wherein said polymer P1 is a polyamide chosen from semi-aromatic polyamides, a C.sub.4 to C.sub.8 short-chain polyamide, and a PA/polyolefin blend, it being possible for said polyolefin to be functionalized or non-functionalized.

8. The structure as claimed in claim 5, wherein said polymer P1 is a polyamide chosen from polyphthalamides, semi-aromatic polyamides, a C.sub.4 to C.sub.8 short-chain polyamide, and a PA/polyolefin blend, it being possible for said polyolefin to be functionalized or non-functionalized, with the exclusion of PA610 and PA612.

9. The structure as claimed in claim 5, wherein said polymer P1 is a polyamide chosen from semi-aromatic polyamides, a C.sub.4 to C.sub.8 short-chain polyamide, and a PA/polyolefin blend, it being possible for said polyolefin to be functionalized or non-functionalized, with the exclusion of PA610 and PA612.

10. The structure as claimed in claim 1, wherein said polymer P2 is a semi-crystalline polyamide chosen from 11/6T, PA11, PA12, PA6, PA66, PA6/66, PA610 and PA612.

11. The structure as claimed in claim 1, wherein said polymer P1 and/or said polymer P2 comprise at least one tie.

12. The structure as claimed in claim 1, wherein it comprises at least an exterior third layer (3), said layer being in contact with the layer (2) and comprising an elastomer and/or a polymer P3 which is different than P1 and which adheres at least partially to P2.

13. The structure as claimed in claim 1, wherein the heat transfer fluid is chosen from hydrocarbon, hydrofluorocarbon, ether, hydrofluoroether, and fluoroolefin compounds.

14. The structure as claimed in claim 1, wherein the heat transfer fluid has added to it a lubricant.

15. The structure as claimed in claim 14, wherein said lubricant is in a proportion by weight of from 0.5% to 50%.

16. The structure as claimed in claim 1, which is a vapor-compression circuit element for containing or transporting a heat transfer fluid in a vapor-compression circuit.

17. The structure as claimed in claim 16, wherein the vapor-compression circuit is integrated into a device chosen from mobile or stationary air-conditioning devices, refrigeration devices, freezing devices, devices for heating by heat pump and Rankine cycles.

18. A vapor-compression circuit comprising the tubular structure of claim 1, wherein the tubular structure is configured to contain or transport a heat transfer fluid in the vapor-compression circuit.

19. The vapor-compression circuit of claim 18, wherein the vapor-compression circuit is integrated into a device chosen from mobile or stationary air-conditioning devices, refrigeration devices, freezing devices, devices for heating by heat pump and Rankine cycles.

20. The structure as claimed in claim 1, wherein the tubular structure is configured for transporting R-1234yf.

21. The structure as claimed in claim 1, wherein the tubular structure has a flow of less than 0.00025 cm3/m2/24 h/atm when carried out on a film having the same composition as the layers of the tubular structures, with a permeation cell, by Lyssy GPM500/GC coupling at a temperature of 23° C. and 0% relative humidity, wherein an upper face of the cell is swept with R-1234yf, and the flow diffusing through the film in the lower part is measured by gas chromatography.

22. A tubular structure for transporting heat transfer fluid, comprising at least: i) a layer (1) in contact with the fluid comprising at least one thermoplastic polymer P1 which is semi-crystalline with a Tm.sub.1 greater than or equal to 160° C., as determined according to the standard 11357-3 (2013), said layer (1) being devoid of fibers, ii) a layer (2) comprising at least: a thermoplastic polymer P2 which is semi-crystalline; the polymer P2 being identical to P1 or different than P1, in which case the polymers P1 and P2 adhere at least partially to one another, wherein the tubular structure is configured for transporting heat transfer fluid, wherein said polymers P1 and P2 are semi-crystalline polyamides, wherein said polymers P1 and P2 each have a polydispersity index of less than or equal to 3.5.

23. A tubular structure for transporting heat transfer fluid, comprising at least: i) a layer (1) in contact with the fluid comprising at least one thermoplastic polymer P1 which is semi-crystalline with a Tm.sub.1 greater than or equal to 160° C., as determined according to the standard 11357-3 (2013), said layer (1) being devoid of fibers, ii) a layer (2) comprising at least: a thermoplastic polymer P2 which is semi-crystalline; the polymer P2 being identical to P1 or different than P1, in which case the polymers P1 and P2 adhere at least partially to one another, wherein the tubular structure is configured for transporting heat transfer fluid, wherein said polymers P1 and P2 are semi-crystalline polyamides, wherein said polymers P1 and P2 each have a polydispersity index of from 2.0 to 3.0.

Description

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(1) The invention is now described in greater detail and in a nonlimiting manner in the description which follows.

(2) Thermoplastic Polymer P1 or P2

(3) As regards the thermoplastic polymer, it may be semi-crystalline or amorphous.

(4) When the thermoplastic polymer is P1, it is chosen from polyamides and EVOH, in particular it is a polyamide or a mixture of polyamides.

(5) When the thermoplastic polymer is P2, it is chosen from polyamides and polyolefins.

(6) As regards the polyamides or the mixtures of polyamides

(7) The nomenclature used to define polyamides is described in the standard ISO 1874-1:1992 “Plastics—Polyamide (PA) molding and extrusion materials—Part 1: Designation”, especially on page 3 (tables 1 and 2), and is well known to those skilled in the art.

(8) The polyamide according to the present invention can have a homopolyamide or copolyamide structure.

(9) Homopolyamide is understood to mean, within the meaning of the present invention, a polyamide which consists only of the repetition of a single unit.

(10) Copolyamide is understood to mean, within the meaning of the present invention, a polyamide which consists of the repetition of at least two units of different chemical structure. This copolyamide can exhibit a random, alternating or block structure.

(11) The polyamide according to the present invention can comprise one or more units with a structure chosen from amino acids, lactams and (diamine), and (diacid) units.

(12) When the polyamide comprises an amino acid in its structure, it can be chosen from 9-aminononanoic acid (A=9), 10-aminodecanoic acid (A=10), 10-aminoundecanoic acid (A=11), 12-aminododecanoic acid (A=12) and 11-aminoundecanoic acid (A=11) and its derivatives, in particular N-heptyl-11-aminoundecanoic acid, A denoting the number of carbon atoms in the unit.

(13) When the polyamide comprises a lactam, it may be chosen from pyrrolidinone, 2-piperidinone, caprolactam, enantholactam, caprylolactam, pelargolactam, decanolactam, undecanolactam and lauryllactam (A=12).

(14) When the polyamide comprised is a unit corresponding to the formula (Ca diamine).(Cb diacid), Ca and Cb denoting the number of carbon atoms respectively in the diamine and the diacid, the (Ca diamine) unit is chosen from linear or branched aliphatic diamines, cycloaliphatic diamines and alkylaromatic diamines.

(15) When the diamine is aliphatic and linear, of formula H2N—(CH2)a-NH2, the (Ca diamine) monomer is preferably chosen from butanediamine (a=4), pentanediamine (a=5), hexanediamine (a=6), heptanediamine (a=7), octanediamine (a=8), nonanediamine (a=9), decanediamine (a=10), undecanediamine (a=11), dodecanediamine (a=12), tridecanediamine (a=13), tetradecanediamine (a=14), hexadecanediamine (a=16), octadecanediamine (a=18), octadecenediamine (a=18), eicosanediamine (a=20), docosanediamine (a=22) and diamines obtained from fatty acids.

(16) When the diamine is aliphatic and branched, it can comprise one or more methyl or ethyl substituents on the main chain. For example, the (Ca diamine) monomer can advantageously be chosen from 2,2,4-trimethyl-1,6-hexanediamine, 2,4,4-trimethyl-1,6-hexanediamine, 1,3-diaminopentane, 2-methyl-1,5-pentanediamine or 2-methyl-1,8-octanediamine.

(17) When the (Ca diamine) monomer is cycloaliphatic, it is chosen from bis(3,5-dialkyl-4-aminocyclohexyl)methane, bis(3,5-dialkyl-4-aminocyclohexyl)ethane, bis(3,5-dialkyl-4-aminocyclohexyl)propane, bis(3,5-dialkyl-4-aminocyclohexyl)butane, bis(3-methyl-4-aminocyclohexyl)methane (BMACM or MACM), bis(p-aminocyclohexyl)methane (PACM), isopropylidenedi(cyclohexylamine) (PACP), isophoronediamine (a=10), piperazine (a=4) or aminoethylpiperazine. It can also comprise the following carbon backbones: norbornylmethane, cyclohexylmethane, dicyclohexylpropane, di(methylcyclohexyl) or di(methylcyclohexyl)propane. A nonexhaustive list of these cycloaliphatic diamines is given in the publication “Cycloaliphatic Amines” (Encyclopedia of Chemical Technology, Kirk-Othmer, 4th Edition (1992), pp. 386-405).

(18) When the (Ca diamine) monomer is alkylaromatic, it is chosen from 1,3-xylylenediamine and 1,4-xylylenediamine.

(19) The (Cb diacid) unit is chosen from linear or branched aliphatic diacids, cycloaliphatic diacids and aromatic diacids.

(20) When the (Cb diacid) monomer is aliphatic and linear, it is chosen from succinic acid (b=4), pentanedioic acid (b=5), adipic acid (b=6), heptanedioic acid (b=7), octanedioic acid (b=8), azelaic acid (b=9), sebacic acid (b=10), undecanedioic acid (b=11), dodecanedioic acid (b=12), brassylic acid (b=13), tetradecanedioic acid (b=14), hexadecanedioic acid (b=16), octadecanedioic acid (b=18), octadecenedioic acid (b=18), eicosanedioic acid (b=20), docosanedioic acid (b=22) and fatty acid dimers containing 36 carbons.

(21) The fatty acid dimers mentioned above are dimerized fatty acids obtained by oligomerization or polymerization of unsaturated monobasic fatty acids bearing a long hydrocarbon chain (such as linoleic acid and oleic acid), as described in particular in the document EP 0 471 566.

(22) When the diacid is cycloaliphatic, it can comprise the following carbon backbones: norbornylmethane, cyclohexylmethane, dicyclohexylmethane, dicyclohexylpropane, di(methylcyclohexyl) or di(methylcyclohexyl)propane.

(23) When the diacid is aromatic, it is chosen from terephthalic acid (denoted T), isophthalic acid (denoted I) and naphthalenic diacids.

(24) Advantageously, the proportion of polyamide P1 is at least 55% by weight.

(25) Advantageously, the proportion of polyamide P2 is from 10 to 70% by weight, in particular from 20 to 50% by weight, preferably from 30 to 40% by weight.

(26) Advantageously, the proportion of polyamide P1 is at least 55% by weight and the proportion of polyamide P2 is from 20 to 50% by weight, preferably from 30 to 40% by weight.

(27) Advantageously, the proportion of polyamide P1 is at least 55% by weight and the proportion of polyamide P2 is from 10 to 70% by weight, in particular from 20 to 50% by weight, preferably from 30 to 40% by weight, and the proportion of optional fibers in P2 is from 30 to 80% by weight, in particular from 30 to 50% by weight.

(28) Advantageously, said polyamide P1 is as defined above.

(29) Advantageously, said polyamide P2 is as defined above.

(30) Advantageously, P1 and P2 are identical.

(31) The polyamide of the invention advantageously has a polydispersity index, denoted PDI, of less than or equal to 3.5. Preferably, the polydispersity index of said polyamide is from 2.0 to 3.0.

(32) This index is measured conventionally and in a manner known to those skilled in the art, by size exclusion or gel permeation chromatography. Preferably, the polydispersity index of the polyamides of the invention is measured by gel permeation chromatography. More particularly, it is measured in a solvent appropriate for the polyamide, such as a fluorinated solvent, for instance hexafluoroisopropanol, at a temperature of from 20° C. to 50° C., preferably at 40° C.

(33) While most of the starting monomers or products envisioned in the present description (amino acids, diamines, diacids) are saturated, there is nothing to prevent envisioning them possibly being partially unsaturated.

(34) It will be noted, for example, that the C18 dicarboxylic acid may be octadecanedioic acid, which is saturated, or else octadecenedioic acid, which itself contains an unsaturation.

(35) The polyamide of the invention may comprise monomers originating from resources derived from renewable raw materials, that is to say comprising organic carbon derived from biomass and determined according to the standard ASTM D6866. These monomers derived from renewable raw materials may be 1,10-decanediamine or, when they are present, in particular 11-aminoundecanoic acid or aliphatic and linear diamines and diacids as defined above

(36) The polyamides of the invention can be prepared by polycondensation of the comonomers defined above, for example in the presence of hypophosphorous acid or of at least one salt thereof.

(37) The detailed description of such a polycondensation process appears in particular in document WO 2010/015786.

(38) The polyamide of the invention preferably has an amine chain end content greater than or equal to 20 mmol/kg, an acid chain end content greater than or equal to 100 mmol/kg and a non-reactive chain end content greater than or equal to 20 mmol/kg.

(39) The chain end content for each of the amine and acid functions and the non-reactive function is measured conventionally by NMR (Nuclear Magnetic Resonance).

(40) In order to adjust the chain end content, it is possible to use chain-terminating agents, that is to say compounds capable of reacting with the amine and/or carboxylic acid end functions of the polyamides, thus stopping the reactivity of the end of the macromolecule, and therefore the polycondensation.

(41) The chain-terminating agents suitable for reacting with the amine end function can be monocarboxylic acids, anhydride, such as phthalic anhydride, monohalogenated acids, monoesters or monoisocyanates. Preferably, monocarboxylic acids are used. They can be chosen from monocarboxylic aliphatic acids, such as acetic acid, propionic acid, lactic acid, valeric acid, caproic acid, capric acid, uric acid, tridecylic acid, myristic acid, palmitic acid, stearic acid, pivalic and isobutyric acid; alicyclic acids, such as cyclohexanecarboxylic acid; monocarboxylic aromatic acids such as toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, phenylacetic acid; and mixtures thereof. The preferred compounds are aliphatic acids, and in particular acetic acid, propionic acid, lactic acid, valeric acid, caproic acid, capric acid, lauric acid, tridecylic acid, myristic acid, palmitic acid and stearic acid.

(42) Among the chain-terminating agents suitable for reacting with the acid end function, mention may be made of monoamines, monoalcohols and monoisocyanates. Monoamines are preferably used. They can be chosen from aliphatic monoamines, such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, laurylamine, stearylamine, dimethylamine, diethylamine, dipropylamine and dibutylamine; alicyclic amines, such as cyclohexylamine and dicyclohexylamine; aromatic monoamines, such as aniline, toluidine, diphenylamine and naphthylamine; and mixtures thereof.

(43) The preferred compounds are butylamine, hexylamine, octylamine, decylamine, laurylamine, stearylamine, cyclohexylamine and aniline.

(44) It is also possible to react the acid and/or amine ends, respectively, with inorganic bases such as alkali metal or alkaline-earth metal hydroxides, such as potassium hydroxide and sodium hydroxide, and with inorganic acids such as HCl, HNO.sub.3 and H.sub.2SO.sub.4.

(45) The chain-terminating agents can be introduced during the first and/or the second step, in the case of the two-step production processes described above. For further details, reference is made herein to document WO 2010/015785.

(46) As Regards the Polyolefins

(47) The polyolefin may be functionalized or nonfunctionalized or be a mixture of at least one functionalized and/or at least one nonfunctionalized, with an Mp greater than 100° C.

(48) The term “polyolefin” is intended to mean a homopolymer or copolymer comprising one or more olefin moieties, such as ethylene, propylene, 1-butene, 1-octene or butadiene moieties, or any alpha-olefin. By way of example of a polyolefin, mention may be made of polyethylene and in particular low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and very low-density polyethylene (VLDPE); polypropylene; ethylene/propylene copolymers; or else metallocene polyethylenes obtained by single-site catalysis.

(49) Copolymers of ethylene and of EVA (with an Mp greater than 100° C.) are also preferred.

(50) Additives

(51) It is possible to add, to the polyamide P1 and/or P2 and/or to the polyolefin, resulting from the process for production thereof, in addition to the remainder made up of diamine, usual additives as defined hereinafter as a function of the layer in which they are present.

(52) Polymer P1

(53) The polymer P1 can comprise at least one additive chosen from an antioxidant, a heat stabilizer, a UV absorber, a light stabilizer, a lubricant, a filler, a flame retardant, a nucleating agent, a plasticizer, an impact modifier and a dye.

(54) The fibers are excluded from the additives, and in particular the term “filler” excludes the fibers.

(55) Preferably, the additives of the polyamide P1 of the invention are in an amount of from 1 to 45%, preferably from 5 to 45% or from 15 to 45%, by weight, relative to the weight of the composition present in P1.

(56) The expression “impact modifier” should be understood as meaning a polymer based on polyolefin with a flexural modulus of less than 100 MPa measured according to standard ISO-178:2010 and a Tg of less than 0° C. (measured according to standard 11357-2:2013 at the inflection point of the DSC thermogram).

(57) The polyolefin may be functionalized or non-functionalized.

(58) When the polyolefin is functionalized, a portion or all of the polyolefins bears a function chosen from carboxylic acid, carboxylic anhydride and epoxide functions, and is in particular chosen from a copolymer of ethylene and propylene with elastomeric character (EPR), an ethylene-propylene-diene copolymer with elastomeric character (EPDM) and an ethylene/alkyl (meth)acrylate copolymer, an ethylene-higher alkene copolymer, in particular an ethylene-octene copolymer, or an ethylene-alkyl acrylate-maleic anhydride terpolymer.

(59) The plasticizer used as additive in the polymer P1 is advantageously a plasticizer which has good thermal stability so that it does not form fumes during the steps of blending of the various polymers and of transformation of the composition obtained.

(60) In particular, this plasticizer can be chosen from: benzene sulfonamide derivatives, such as n-butylbenzenesulfonamide (BBSA), the ortho and para isomers of ethyltoluenesulfonamide (ETSA), N-cyclohexyltoluenesulfonamide and N-(2-hydroxypropyl)benzenesulfonamide (HP-BSA), hydroxybenzoic acid esters, such as 2-ethylhexl-para-hydroxybenzoate (EHPB) and 2-decylhexyl-para-hydroxybenzoate (HDPB), esters or ethers of tetrahydrofurfuryl alcohol, such as oligoethyleneoxytetrahydrofurfuryl alcohol, and esters of citric acid or of hydroxymalonic acid, such as oligoethyleneoxymalonate.

(61) A plasticizer that is preferred, since it is commonly used, is n-butylbenzenesulfonamide (BBSA).

(62) Use may also be made of a mixture of plasticizers.

(63) The plasticizer used as additive in the polymer P1 is in a weight proportion of from 0 to 15%, more particularly preferably from 0 to 8%.

(64) Advantageously, the polymer P1 comprises an impact modifier and a plasticizer.

(65) The heat stabilizer used as additive in the polymer P1 may be present in an amount of from 0 to 4%, in particular from 0.01 to 2% or from 0.1 to 1% by weight relative to the total weight of the composition of polymer P1.

(66) It may be an organic or copper-based heat stabilizer.

(67) More particularly, it may be a copper salt or a copper salt derivative, for example copper iodide, copper bromide, copper halides, or derivatives or mixtures thereof. The copper I salts are preferred. Examples are copper iodide, copper bromide, copper chloride, copper fluoride, copper thiocyanate, copper nitrate, copper acetate, copper naphthenate, copper caprate, copper laurate, copper stearate, copper acetylacetonate, and copper oxide. Copper iodide, copper bromide, copper chloride and copper fluoride are preferred.

(68) It may also be envisioned to use, by way of heat stabilizers, a metal halide salt in combination with LiI, NaI, KI, MgI.sub.2, KBr or CaI.sub.2. KI and KBr are preferred.

(69) Other possible heat stabilizers are sterically hindered phenolic antioxidants. These compounds are described in detail in document US 2012/0279605, in paragraphs [0025] and [0026], to which reference is expressly made herein.

(70) However, according to an alternative embodiment, the composition of the invention is devoid of such hindered phenolic antioxidants.

(71) A secondary antioxidant of phosphite type can also be used.

(72) Another category of possible stabilizers are sterically hindered amine-based UV stabilizers (or HALS), which are derivatives of 2,2,6,6-tetramethylpipridine. They can be used, for example, in a range of from 0 to 1% or from 0.01 to 0.5%.

(73) Among the dyes, mention may particularly be made of carbon black. The dyes or pigments (for the purpose of coloring the composition) can be present for example in an amount of from 0.1 to 0.2% by weight.

(74) Among the fillers, mention may be made of silica, graphite, expanded graphite, carbon black, glass beads, kaolin, magnesia, slag, talc, metal oxides (titanium oxide), metals.

(75) The fillers such as expanded graphite for example can make it possible to increase the thermal conductivity of the material (for example in order to promote heat exchange between a lumen of a tube comprising a layer of composition of the invention and the exterior, or between two lumina of a tube comprising a layer of composition of the invention).

(76) Polymer P2

(77) The polymer P2 can comprise: additives which absorb in the UV or IR range so as to allow welding of the composite obtained, by a laser technology (UV or IR), heat stabilizers chosen from antioxidants of sterically hindered phenol or sterically hindered amine (HALS) type and impact modifiers. The function of these stabilizers is to prevent thermal oxidation, photooxidation and consequent degradation of the matrix polyamide of the composite obtained.

(78) A secondary antioxidant of phosphite type can also be used.

(79) The heat stabilizers and the secondary antioxidant are as defined for the polymer P1.

(80) However, one and/or the other of the layers (polymer P1 and/or P2) of the structure of the invention can also comprise other compounds, other than those that have just been mentioned. The composition of the invention (polymers P1 and/or P2) can in particular also comprise at least one additional additive and/or at least one additional polymer.

(81) The additional additives can in particular be chosen from processing aids.

(82) Among the processing aids, mention may be made of stearates, such as calcium or zinc stearates, natural waxes, and polymers comprising tetrafluoroethylene (TFE).

(83) The weight proportion of processing aids is conventionally from 0.01 to 0.3% by weight, advantageously from 0.02 to 0.1% by weight, relative to the total weight of the composition.

(84) The one and/or the other of the layers of the structure of the invention can also comprise one or more additional polymers, such a polymer being distinct from the polymer mentioned above. Alternatively, one and/or the other of the layers of the structure of the invention may be devoid of such an additional polymer.

(85) The additional polymer can in particular be chosen from a polyamide other than that defined previously, a polyamide-block-ether, a polyetheramide, a polyesteramide, a polyphenylene sulfide (PPS), a polyphenylene oxide (PPO), and mixtures thereof.

(86) The composition can thus contain up to 20% by weight, relative to the total weight of the composition, of at least one additional polymer.

(87) Tubular Structure

(88) The tubular structure which is the subject of the invention can in particular be a tube or a pipe, or else a piece of connection or of linkage between tubes, or between a tube and a device (such as a compressor, a condenser or a heat exchanger for example).

(89) The tubular structure may be formed of a single layer made up of the composition described above.

(90) The total thickness of the structure of the assembly of layers can for example range from 0.5 mm to 5 mm, preferably from 1 mm to 3 mm.

(91) The use of the tubular structures according to the invention makes it possible to simplify the circuit design, by allowing easy connection by welding (for example rotation welding, ultrasonic welding, laser welding or induction welding).

(92) Application to a Vapor-Compression Circuit

(93) A vapor-compression circuit comprises at least one evaporator, one compressor, one condenser and one expander, and also lines for transporting heat transfer fluid between these elements. The evaporator and the condenser comprise a heat exchanger which allows heat exchange between a heat transfer fluid, circulating in the circuit, and another fluid or body.

(94) The piece of equipment can comprise an electricity-generating turbine (Rankine cycle).

(95) The vapor-compression circuit can be integrated into a piece of equipment which can also optionally comprise at least one heat-transferring fluid circuit used to transmit the heat (with or without change of state) between the heat transfer fluid circuit and the fluid or body to be heated or cooled.

(96) The piece of equipment can also optionally comprise two (or more) vapor-compression circuits comprising identical or distinct heat transfer fluids. For example, the vapor-compression circuits can be coupled to one another.

(97) The vapor-compression circuit operates according to a conventional cycle of vapor-compression. The cycle comprises the change of state of the heat transfer fluid from a liquid phase (or liquid/vapor dual phase) to a vapor phase at a relatively low pressure, then the compression of the fluid in vapor phase until a relatively high pressure is reached, the change of state (condensation) of the heat transfer fluid from the vapor phase to the liquid phase at a relatively high pressure, and the reduction of the pressure so as to recommence the cycle.

(98) In the case of a cooling process, heat from the fluid or from the body that is being cooled (directly or indirectly, via a heat-transferring fluid) is absorbed by the heat transfer fluid, during the evaporation of the latter, this being at a relatively low temperature compared to the surroundings. The cooling processes comprise air-conditioning processes (with mobile pieces of equipment, for example in vehicles, or stationary pieces of equipment), refrigeration processes (with mobile pieces of equipment, for example in containers, or stationary pieces of equipment) and freezing or cryogenics processes.

(99) In the case of a heating process, heat is transferred (directly or indirectly, via a heat-transferring fluid) from the heat transfer fluid, during the condensation thereof, to the fluid or to the body that is being heated, this being at a relatively high temperature compared with the surroundings. The piece of equipment which makes it possible to carry out the heat transfer is in this case called a “heat pump”.

(100) A thermoplastic structure according to the invention can be used as “vapor-compression circuit element”, that is to say as a part of such a circuit comprising. Such a part comprises a lumen suitable for containing or transporting the heat transfer fluid.

(101) The vapor-compression circuit element in question is preferably a pipe or piping (or even a hose). Alternatively, it may be a linkage or connector between pieces of piping, or between piping and compressor, or condenser, or heat exchanger, or else a part of a holding tank or of a thermal exchanger. The vapor-compression circuit element can also be a heat exchanger as such (in which case it comprises at least two lumina for the circulation of two identical or different fluids, one having to transfer heat to the other).

(102) The heat transfer fluid can be contained or transported in gas, liquid or two-phase form in the above circuit element.

(103) Production of the Thermoplastic Materials of the Structure of the Invention

(104) The various layers of the structure of the invention can be prepared by any method which makes it possible to obtain a homogeneous mixture, such as melt extrusion.

(105) More particularly, they can be prepared by melt-mixing of the polyamide(s), optionally of the plasticizer(s) and optionally of the products for obtaining the crosslinked polyolefin(s).

(106) The optional additives and/or additional polymers can, for their part, be introduced either at the same time as the crystalline polyamide(s), plasticizer(s) and products for obtaining the crosslinked polyolefin(s), or during a subsequent step.

(107) Advantageously, the composition can be obtained in the form of granules by compounding, in particular by means of a twin-screw extruder, of a co-kneader or of an internal mixer.

(108) Heat Transfer Fluid

(109) The term “heat transfer compound”, respectively “heat transfer fluid” (or refrigerant fluid or refrigerant), is intended to mean a compound, respectively a fluid, capable of absorbing heat by evaporating at low temperature and low pressure and of providing heat by condensing at high temperature and high pressure, in a vapor-compression circuit. In general, a heat transfer fluid can comprise just one, two, three or more than three heat transfer compounds.

(110) In addition, the heat transfer fluid can optionally comprise one or more additives which are not heat transfer compounds for the envisioned application.

(111) The heat transfer compounds may be hydrocarbon, ether, hydrofluoroether, hydrofluorocarbon or fluoroolefin compounds or HFO. Hydrofluorocarbons and fluoroolefins are preferred, and more particularly fluoroolefins. Fluoropropenes, fluoropropanes and fluoroethanes are preferred.

(112) Examples of preferred heat transfer compounds, used individually or as a mixture, are 1,3,3,3-tetrafluoropropene (R-1234ze), 2,3,3,3-tetrafluoropropene (R-1234yf), 1,2,3,3,3-pentafluoropropene (R-1225ye), 1,1,3,3-tetrafluoropropene (R-1234zc), 3,3,3-trifluoropropene (R-1243zf), 2,3,3-trifluoropropene (R-1243yf), 1,1,1,2-tetrafluoroethane (R-134a), 1,1,2,2-tetrafluoroethane (R-134), pentafluoroethane (R-125), difluoromethane (R-32), 1,1-difluoroethane (R-152a), 1,1,1,2,3,3,3-heptafluoropropane (R-227ea), 1,1,1-trifluoropropane (R-263), 1,1,1,3,3,3-hexafluoropropane (R-236fa), 1,1,1,3,3-pentafluoropropane (R-245fa), 1,1,1,3,3-pentafluorobutane (R-365mfc) and trifluoroiodomethane.

(113) The above compounds can also be used as a mixture with ammonia or carbon dioxide.

(114) According to one preferred embodiment, the heat transfer fluid is R-134a or R-1234yf or R-1234ze, the latter being particularly preferred.

(115) Mixtures of R-1234yf or R-1234ze and of ammonia and R-1234yf or R-1234ze and of carbon dioxide are also particularly preferred for stationary air-conditioning.

(116) The additives can in particular be chosen from lubricants, nanoparticles, stabilizers, surfactants, trace agents, fluorescent agents, odorizing agents and dissolving agents.

(117) The stabilizer(s), when they are present, preferably represent at most 5% by weight in the heat transfer composition. Among the stabilizers, mention may in particular be made of nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenolic compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2,6-di-tert-butyl-4-methylphenol, eoxides (alkyl which is optionally fluorinated or perfluorinated or alkenyl or aromatic) such as n-butyl glycidyl ether, hexanediol diglycidyl ether, allyl glycidyl ether, butylphenylglycidyl ether, phosphites, phosphonates, thiols and lactones.

(118) By way of lubricants, use may in particular be made of oils of mineral origin, silicone oils, paraffins of natural origin, naphthenes, synthetic paraffins, alkylbenzenes, poly-alpha-olefins, polyalkylene glycols (PAGs), polyol esters and/or polyvinyl ethers.

(119) According to the invention, it is particularly preferred for the heat transfer fluid circulating in the vapor-compression circuit to comprise a PAG lubricant or POE lubricant.

(120) According to one particularly preferred embodiment of the invention, the heat transfer fluid is R-1234yf or R-1234ze to which has been added a PAG lubricant (and optionally additional additives).

(121) Among the PAG lubricants, it is in particular possible to use those which are described in document US 2010/0282999, to which reference is expressly made herein. These lubricants correspond to the formula R.sub.1—(OR.sub.3).sub.n—R.sub.2, in which R.sub.1 and R.sub.2 are identical or different and represent a hydrogen atom, a C.sub.1-C.sub.5 alkyl group or a C.sub.2-C.sub.5 acryl group, R.sub.3 represents a C.sub.2-C.sub.4 alkylene group, and the molar proportion of C.sub.2 alkylene groups in the R.sub.3 moieties is at most 30%. The hydroxyl number is preferably at most 100 mg KOH/g, or 50, 30 or 10 mg KOH/g. The number molecular weight of the PAG is preferably from 500 to 3000, or from 600 to 2000, or from 600 to 1500.

(122) Among the PAG lubricants, it is also possible to use those which are described in document US 2010/0175421, to which reference is expressly made herein. These lubricants correspond to the formula R.sub.1—[(OR.sub.2).sub.m—R.sub.3].sub.n, in which R.sub.1 represents a hydrogen atom, a hydrocarbon-based group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, a hydrocarbon-based group having 2 to 6 bonding sites and 1 to 10 carbon atoms or a hydrocarbon-based group containing an oxygen atom and having 1 to 10 carbon atoms, R.sub.2 represents an alkylene group having 2 to 4 carbon atoms, R.sub.3 represents a hydrogen atom, a hydrocarbon-based group having 1 to 10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or a hydrocarbon-based group containing an oxygen atom and having 1 to 10 carbon atoms, n represents an integer from 1 to 6 and m is a number such that the mean value m×n is from 6 to 80. Examples of such PAGs are polypropylene glycol dimethyl ether, the copolymer of polyethylene-polypropylene glycol dimethyl ether, the copolymer of polyethylene-polypropylene glycol methyl butyl ether and propylene glycol diacetate. The hydroxyl number is preferably 5 mg KOH/g or less, or 3 mg KOH/g or less, or 1 mg KOH/g or less. The number molecular weight of the PAG is preferably from 500 to 3000, or from 600 to 2500.

(123) Among the PAG lubricants, it is also possible to use those which are described in document WO 2010/075046, to which reference is expressly made herein. These lubricants correspond to the formula RX(R.sub.aO).sub.x(R.sub.bO).sub.yR.sub.c, in which R is chosen from alkyl groups having from 1 to 10 carbon atoms, aliphatic hydrocarbon-based groups having from 2 to 6 valences, and substituents comprising a heterocycle in which the heteroatom(s) are oxygen, X is chosen from O and S, R.sub.a is a C2 alkylene group, R.sub.b is a C3 alkylene group, R.sub.c is identical to R or represents H, x and y are equal to 0 or an integer lower than or equal to 100, independently. The sum x+y is an integer from 5 to 100. The aliphatic hydrocarbon-based groups comprise in particular alkanes, alkenes, alkynes, and in particular methyl, butyl and propyl groups. The lubricant may be a linear oxypropylene homopolymer. Alkoxy ends, and in particular methoxy ends, are preferred. The kinematic viscosity is preferably at least 30 cSt, or 20 cSt, or 10 cSt at 40° C., or a viscosity index of at least 150, or 120 or 100. The total acid number is preferably less than 0.03, or 0.02, or 0.01 mg KOH/g.

(124) By way of nanoparticles, use may in particular be made of charcoal nanoparticles, metal (copper, aluminum) oxides, TiO.sub.2, Al.sub.2O.sub.3, MoS.sub.2, etc.

(125) By way of tracers (capable of being detected), mention may be made of deuterated or non-deuterated hydrofluorocarbons, deuterated hydrocarbons, perfluorocarbons, fluoroethers, brominated compounds, iodinated compounds, alcohols, aldehydes, ketones, nitrous oxide and combinations thereof. The tracer is different than the heat transfer compound(s) making up the heat transfer fluid.

(126) By way of dissolving agents, mention may be made of hydrocarbons, dimethyl ether, polyalkylene ethers, amides, ketones, nitriles, chlorocarbons, esters, lactones, aryl ethers, fluoroethers and 1,1,1-trifluoroalkanes. The dissolving agent is different than the heat transfer compound(s) making up the heat transfer fluid.

(127) By way of fluorescent agents, mention may be made of naphthalimides, perylenes, coumarins, anthracenes, phenanthracenes, xanthenes, thioxanthenes, naphthoxanthenes, fluoresceins and derivatives and combinations thereof.

(128) By way of odorizing agents, mention may be made of alkyl acrylates, allyl acrylates, acrylic acids, acryl esters, alkyl ethers, alkyl esters, alkynes, aldehydes, thiols, thioethers, disulfides, allylisothiocyanates, alkanoic acids, amines, norbornenes, norbornene derivatives, cyclohexene, heterocyclic aromatic compounds, ascaridole, o-methoxy(methyl)phenol and combinations thereof.

(129) As regards motor vehicle air-conditioning, it is preferred to use a single heat transfer compound (rather than a mixture) and a single lubricant (rather than a mixture), for reasons of stability in the vapor-compression circuit.

EXAMPLE

Example 1—Properties of Permeability to Fluorinated Refrigerants

(130) In this example, the permeability to fluorinated refrigerants (R-1234yf) of a tubular structure (according to the invention) consisting of a composition comprising a copolyamide of formula 11/10T as internal layer (polymer P1) and of a composition comprising a polyamide of formula PA610 with fibers (6% by weight of glass fibers) as external layer (polymer P2) is compared with a standard tubular structure of Veneer type comprising either 200 or 300 microns of impact-modified PA 6, corresponding to the product sold by DuPont under the name Zytel® ST 811.

(131) The flow measurements were carried out on films having the same composition as the layers of the tubular structures, with a permeation cell, by Lyssy GPM500/GC coupling at a temperature of 23° C. and 0% relative humidity. The upper face of the cell is swept with the testing gas, and the flow diffusing through the film in the lower part is measured by gas chromatography. Helium is used as vector gas sweeping the lower part.

(132) The permeation of the tubular structures is calculated by the usual law of permeation of a multilayer, namely
e/P=Σei/Pi

(133) e and P are the thickness and the permeability of the multilayer structure

(134) ei and Pi are the thicknesses and the permeability is of each of the layers of the structure.

(135) The results of the calculations are reproduced in table 1 below. The flows of refrigerants are expressed in cm.sup.3/m.sup.2/24 h/atm.

(136) TABLE-US-00001 TABLE 1 results for R-1234yf Flow Veneer structure with 0.2 mm of 0.0025 Zytel ® ST 811 Veneer structure with 0.3 mm of 0.0017 Zytel ® ST 811 Structure according to the <0.00025 invention P2/P1 (mm), 0.2/1
The structure of the invention is a better barrier to R-1234yf than the Veneer structure.