Patent Description:
In a known manner, a common air-conditioning circuit for a motor car essentially comprises a low-pressure loop for a gaseous refrigerant fluid (e.g. of Freon® type, such as R-1234yf or R-134a) between an evaporator and blower assembly and a compressor inlet, and a high-pressure loop between the compressor outlet and an expansion valve, between which are provided in succession a condenser and fan assembly and a drier. Both loops each comprise a line made of an assembly of plurality of multilayer rubber hoses and rigid metallic connecting tubings (e.g. of aluminum) connected together in succession typically by brazing and crimping.

Both lines of this air-conditioning circuit must fulfill strict requirements, markedly including:.

Attempts have been made in the past to replace such crimped and brazed assemblies of rubber hoses and aluminum connecting tubes conventionally used in air-conditioning lines, with thermoplastic structures devoid of metal parts, such as thermoplastic tubes or connectors.

<CIT> relates to a thermoplastic structure comprising at least one layer consisting of a composition comprising a copolyamide of formula X/<NUM>. T/Y, wherein:.

<CIT> relates to a composition including:
<CIT>
relates to a polyamide moulding composition consisting of the following components:.

One aim of the present invention is to provide a novel thermoplastic composition capable of forming a monolayer tube for transporting a fluid, which makes it possible to confer on the tube a very low permeation value for water and for a refrigerating fluid in an air-conditioning line, together with satisfactory mechanical and chemical properties even after thermal and chemical ageing, including an improved impact resistance. This aim is achieved in that the Applicant Company has just unexpectedly discovered that if more than <NUM>% and up to <NUM>% of PA <NUM> and/or PA <NUM> is combined to from <NUM>% to less than <NUM>% of at least one polyphthalamide having a glass transition temperature measured by differential scanning calorimetry higher than <NUM> and selected from the group consisting of PA <NUM>. T, PA <NUM>. T, PA <NUM>. T, PA <NUM>. T/X and mixtures thereof, where X represents at least one polyamide unit other than PA <NUM>. T derived from an aliphatic diamine having from <NUM> to <NUM> carbon atoms and from an aromatic dicarboxylic acid comprising terephthalic or isophthalic acid, and from <NUM>% to <NUM>% of a compatibilizing system comprising a product of a reaction between (a) a polymer of at least one first olefin comprising an unsaturated epoxide and (b) a polymer of at least one second olefin comprising an unsaturated carboxylic acid, with a weight ratio (a):(b) greater than <NUM>, said at least one second olefin being identical to or different from said at least one first olefin, then it is possible to obtain a satisfactory trade-off of improved properties for the thermoplastic monolayer tube and for an entirely thermoplastic air-conditioning tubing line incorporating such tubes for example of a low-pressure loop, as explained below.

A thermoplastic composition according to the invention is as defined in appended claim <NUM>.

It is to be noted that a thermoplastic composition of the invention thus allows to exhibits a very low permeation for the refrigerating gas and for water, as well as very satisfactory mechanical and chemical properties even after thermal and chemical ageing, including an improved impact resistance.

Specifically and as explained below, a thermoplastic composition of the invention at least allows to:.

It will also be noted that these very advantageous properties of a thermoplastic composition of the invention particularly allow to use the same in an entirely thermoplastic air-conditioning tubing line incorporating thermoplastic tubes (preferably monolayer tubes) for example of in a low-pressure loop, thus replacing the metal-rubber structures conventionally used in such an air-conditioning line.

As explained above, it will further be noted that these advantageous properties of a thermoplastic composition of the invention also allow to use the same in an entirely thermoplastic tubing line involving requirements against gas and/or water permeation, such as in air or fuel lines, for instance.

The term "aliphatic polyamide" is understood to mean in a known way in the present description a homopolymer or copolymer polyamide obtained by reaction of at least one linear, branched or alicyclic diamine and of at least one aliphatic dicarboxylic acid which may also be linear, branched or alicyclic. Both PA <NUM> and PA <NUM> each included in said at least one aliphatic polyamide are semi-crystalline polyamides derived from a linear diamine having <NUM> carbon atoms and from a linear dicarboxylic acid having <NUM> or <NUM> carbon atoms, respectively.

Preferably, said at least one aliphatic polyamide is devoid of PA <NUM>, being more preferably devoid of PA <NUM> and also of PA <NUM>, PA <NUM>, PA <NUM>, PA <NUM>, PA <NUM> and of PA <NUM>.

In a preferred example of the invention, said at least one aliphatic polyamide comprises a PA <NUM> and preferably consists of said PA <NUM>. In an alternative example of the invention, said at least one aliphatic polyamide comprises a PA <NUM> and preferably consists of said PA <NUM>.

The term "polyphtalamide » (sometimes referred to as PPA) is understood to mean in a known way in the present description, according to ASTM D5336.

Said at least one polyphthalamide of the invention may be:.

It may be noted that the relatively high amount of said at least one polyphthalamide having a glass transition temperature which is higher than <NUM> (advantageously of at least <NUM>, for example of about <NUM>) allows to "frozen" the polymeric chains in the thermoplastic composition and thereby contributes to minimize the water permeability of this composition of the invention by reducing both the water solubility and diffusivity of the composition at a testing temperature of <NUM>.

The glass transition temperature Tg of said at least one polyphthalamide may be measured by differential scanning calorimetry ("DSC") or by another conventional technique, such as dynamic mechanical analysis ("DMA").

In an embodiment of the invention, said at least one polyphthalamide comprises a PA <NUM>. T having said glass transition temperature preferably higher than <NUM>, and may advantageously consists of said PA <NUM>.

According to this embodiment, the PA <NUM>. T may exhibit a molar ratio PA <NUM>. I / PA <NUM>. T of between <NUM> and <NUM>, inclusively, and preferably between <NUM> and <NUM> (i.e. with an IPA / TPA molar ratio of about <NUM>).

Also according to this embodiment and optionally in combination with said molar ratio PA <NUM>. I / PA <NUM>. T values, the PA <NUM>. T may have:.

Also according to this embodiment, a thermoplastic composition of the invention which comprises a mixture PA <NUM> or PA <NUM> (each being semi-crystalline) + PA <NUM>. T (amorphous), is in a form of separated phases.

Each of the above mentioned techniques of DSC and DMA established indeed that the low mutual affinity between PA <NUM> or PA <NUM> and PA <NUM>. T leads to this separation of phases in this composition of the invention.

In another embodiment of the invention, said at least one polyphthalamide comprises at least one PA <NUM>. T/X having said glass transition temperature preferably higher than <NUM>, and may advantageously consists of said at least one PA <NUM>.

It may be noted that said PA <NUM>. T/X by definition derives from <NUM>,<NUM>-decamethylene diamine and terephthalic acid for the <NUM>. T units, and that X derives from an aliphatic diamine having from <NUM> to <NUM> carbon atoms and preferably from terephthalic acid (i.e. not from isophthalic acid).

More preferably, X represents a PA <NUM>. T unit or a PA <NUM>. T unit, even more preferably with a molar ratio PA <NUM>. T / X greater than <NUM>.

According to said another embodiment, said at least one polyphthalamide may have a Tg of between <NUM> and <NUM>, inclusively, and may be for example.

Also according to said another embodiment, a thermoplastic composition of the invention which comprises a mixture PA <NUM> or PA <NUM> + PA <NUM>. T/X (all being semi-crystalline), is in a form of mixed phases, not separated phases, as established by the above mentioned techniques of DSC or DMA.

By "compatibilizing system comprising a product of a reaction between the polymers (a) and (b)", it is to be understood in the present description that this system comprises a product of a reaction between (a) a polymer of at least one first olefin comprising an unsaturated epoxide and (b) a polymer of at least one second olefin comprising an unsaturated carboxylic acid, with a weight ratio (a):(b) greater than <NUM>, said at least one second olefin being identical to or different from said at least one first olefin.

According to a preferred embodiment of the invention common to all the preceding features thereof, said weight ratio (a):(b) in the compatibilizing system is of from <NUM>:<NUM> to <NUM>:<NUM> and preferably of from <NUM>:<NUM> to <NUM>:<NUM>.

By way of the polymer (a) comprising an unsaturated epoxide, mention may be made of all homopolymers or copolymers of said at least one first olefin in which the unsaturated epoxide has been introduced either by grafting or by copolymerization.

The unsaturated epoxide may in particular be selected from aliphatic glycidyl esters and ethers, and alicyclic glycidyl esters and ethers. Preferably, (a) is a polymer of said at least one first olefin comprising an aliphatic or alicyclic glycidyl ester.

Also preferably, (a) is a copolymer of said at least one first olefin and of said unsaturated epoxide, and more preferably (a) is an olefin-glycidylmethacrylate copolymer.

Generally speaking, (a) may be a homopolymer or copolymer comprising said at least one first olefin units, which are preferably derived from ethylene and/or alpha-olefins including propylene and butene-<NUM>.

Still more preferably, (a) is an olefin-glycidylmethacrylate copolymer, such as an ethylene-glycidylmethacrylate copolymer.

By way of said at least one polyolefin comprising an unsaturated carboxylic acid forming the compound (b), mention may be made of all homopolymers or copolymers of said at least one second olefin in which the unsaturated carboxylic has been introduced either by grafting or by copolymerization.

Preferably, (b) is a polymer of said at least second olefin comprising (meth)acrylic acid groups, and is preferably an olefin-acrylic acid copolymer.

Generally speaking, (b) may be a homopolymer or copolymer comprising said at least one second olefin units, which are preferably derived from ethylene and/or alpha-olefins including propylene and butene-<NUM> and may be identical to said at least one first olefin units. (b) may be derived from a polyolefin for example selected from polyethylene, polypropylene, ethylene-propylene copolymers, copolymers of ethylene and alkyl(meth)acrylate, and copolymer of ethylene and vinyl acetate.

More preferably, (b) is an ethylene-(meth)acrylic acid copolymer, and is even more preferably a copolymer of ethylene with acrylic acid groups.

According to an aspect of the invention, the thermoplastic composition may be devoid of a polymer comprising an unsaturated carboxylic anhydride, being in particular advantageously devoid of a copolymer of an olefin and an unsaturated carboxylic anhydride and of a polyolefin grafted with an unsaturated carboxylic anhydride.

According to another aspect of the invention, the thermoplastic composition may be devoid of an elastomer, being in particular advantageously devoid of a polyamide elastomer, of an olefinic elastomer such as an ethylene acrylate elastomer or an ethylene-alpha olefin copolymer, and of a styrenic rubber.

According to still another aspect of the invention, the thermoplastic composition may be devoid of additional filler or fiber.

A thermoplastic composition according to the invention thus preferably consists of said at least one aliphatic polyamide, said at least one polyphthalamide and said compatibilizing system.

According to a preferred embodiment of the invention which may be common to all the preceding features thereof, the thermoplastic composition comprises in weight fractions:.

According to another aspect of the invention which may be common to part or all of the above features thereof, the thermoplastic composition may have:.

the variation in absolute value between said final Young modulus and said initial Young modulus and/or between said final stress at rupture and said initial stress at rupture being advantageously lower than <NUM>%.

These features witness satisfactory flexibility and mechanical properties of the compositions and of the monolayer tubes made of the same.

According to another aspect of the invention which may be common to part of all of the above features thereof, the thermoplastic composition may have:.

the variation in absolute value between said final Charpy breaking energy and said initial Charpy breaking energy being advantageously lower than <NUM>%.

This feature witnesses a low variation of impact properties after ageing for a thermoplastic composition of the invention.

A monolayer tube according to the invention is for transporting a fluid, the monolayer tube being in particular adapted for transporting a refrigerant gas in an air-conditioning circuit of a motor vehicle, and the monolayer tube is made of a thermoplastic composition as defined above for the invention.

Advantageously, a monolayer tube of the invention has a water permeability, measured according to PSA standard D45 <NUM>/--A during <NUM> hours at <NUM> and <NUM>% RH, which may be lower than <NUM>/m<NUM>/<NUM> and which is preferably lower than or equal to <NUM>/m<NUM>/<NUM>.

It is to be noted that such an extremely low water permeability is much lower than those obtained for a monolayer tube made of a thermoplastic composition not based on the combination according to the invention of PA <NUM> or PA <NUM> with said at least one polyphthalamide according to the above-specified weight fraction ranges. Moreover, such an extremely low water permeability is also much lower than those obtained for a monolayer tube exclusively made of a pure PA <NUM> or PA <NUM> polyamide.

Also advantageously, the monolayer tube of the invention has a burst resistance measured in a conditioned enclosure according to ISO <NUM> standard which may be greater than <NUM> MPa at <NUM> and greater than <NUM> MPa at <NUM>, and preferably which is greater than <NUM> MPa at <NUM> and greater than <NUM> MPa at <NUM>.

These properties witness a satisfactory resistance to burst for the monolayer tube even at a high temperature, close to those used in operation of a low-pressure loop for an air-conditioning circuit for a motor vehicle.

Also advantageously, the monolayer tube of the invention has a permeability to a refrigerant gas consisting of <NUM>,<NUM>,<NUM>,<NUM>-tétrafluoropropène (R-1234yf), measured according to PSA standard D <NUM>, which may be lower than <NUM>/m<NUM>/<NUM>, preferably lower than <NUM>/m<NUM>/<NUM> and more preferably lower than <NUM>/m<NUM>/<NUM>.

Such a very low permeability to R-1234yf is fully satisfactory for a low-pressure loop of an air-conditioning circuit for a motor vehicle.

An air-conditioning circuit for a motor vehicle according to the invention comprises a plurality of tubes adapted to transport a refrigerating fluid, the air conditioning circuit comprising a low-pressure loop which comprises low-pressure tubes and a high-pressure loop which comprises high-pressure tubes, wherein at least one of said tubes, selected from the low-pressure tubes and the high-pressure tubes and combinations thereof, comprises a monolayer tube of the invention as defined above.

Said low-pressure loop may be defined between an evaporator and blower assembly and an inlet of a compressor, and said high-pressure loop may be defined between an outlet of the compressor and an expansion valve, between which may be provided in succession a condenser and fan assembly and a drier.

According to an embodiment of the invention, said low-pressure tubes each consist of a said monolayer tube and are connected to one another by thermoplastic connectors devoid of metal parts to form an entirely thermoplastic low-pressure tubing line.

A method according to the invention for preparing the thermoplastic composition defined above comprises kneading said at least one aliphatic polyamide, said at least one polyphthalamide and said compatibilizing system preferably in a twin-screw extruder, to perform a crosslinking chemical reaction for said at least one aliphatic polyamide and said at least one polyphthalamide, by said at least one polyolefin comprising an unsaturated epoxide.

Said compatibilizer system may be introduced in the twin-screw together with said at least one aliphatic polyamide and said at least one polyphthalamide, or alternatively the compatibilizer system may be subsequently introduced on a side feeder, for example near the middle of the extruder so as to reduce the duration of the reaction between this system and the two other components of the composition.

The air-conditioning circuit <NUM> for a motor vehicle of <FIG> comprises a plurality of tubes adapted to transport a refrigerating fluid F, the air conditioning circuit <NUM> comprising a low-pressure loop <NUM> which comprises low-pressure tubes and a high-pressure loop <NUM> which comprises high-pressure tubes. in the example of <FIG>, the low-pressure loop <NUM> is defined between an evaporator and blower assembly <NUM> and an inlet 5a of a compressor <NUM>, and the high-pressure loop <NUM> is defined between an outlet 5b of the compressor <NUM> and an expansion valve <NUM> which it itself part of the low-pressure loop <NUM>. In a usual manner, a condenser and fan assembly <NUM> and a drier <NUM> are provided in succession in the high-pressure loop <NUM> between the compressor outlet 5b and the expansion valve <NUM> (the refrigerating fluid being gaseous between the compression outlet 5b and condenser <NUM> and usually liquid between the condenser <NUM> and expansion valve <NUM>).

According to an embodiment of the invention, at least one of the tubes of the air-conditioning circuit <NUM> in the low-pressure loop <NUM> and/or the high-pressure loop <NUM> and, preferably, at least the low-pressure loop <NUM> comprises a thermoplastic tubular structure 2a made of at least one thermoplastic composition according to the invention, such as the tubular structure 2a visible in the example of <FIG>.

The thermoplastic tubular structure 2a may advantageously consist of a plurality of thermoplastic monolayer tubes T1, T2, etc. assembled to together in succession in the loop <NUM>, <NUM> and are connected to one another by thermoplastic connectors C1, C2, etc. As a consequence, the thermoplastic tubular structure 2a may advantageously be used to form an entirely thermoplastic tubing line in the low-pressure loop <NUM> and/or high pressure loop <NUM>, in contrast to the conventional tubing lines involving rubber and metal tube sections.

As demonstrated in the below examples, such a thermoplastic tubular structure 2a made of a thermoplastic composition of the invention may exhibit a remarkable trade-off of improved properties rendering it particularly suitable for forming such a thermoplastic tubing line in the low-pressure loop <NUM>.

A number of thermoplastic control compositions C1-C12 and of thermoplastic compositions according to the invention I1-I3 were prepared by kneading, in a twin-screw extruder "Leistritz" of ZSE40MAXX type (L/D = <NUM>) for compositions C1-C9, C12 and I1-I3 and in a twin screw extruder "Leistritz" of ZSE18MAXX type (L/D = <NUM>) for compositions C10-C11, a polyamide mixture of a PA <NUM> (optionally combined to PA <NUM> for some control compositions) and of a PA <NUM>. T or a PA <NUM>. T/X in the presence of a compatibilizing system to crosslink this mixture. The compatibilizing system was introduced in each twin-screw together with this polyamide mixture.

The polyamides tested in these compositions were as recited below:.

<NUM> represents the semi-structural chemical formula for PA <NUM>. T/X « M3000 », obtained by RMN <NUM>H analysis with X = PA <NUM>-<NUM>-T. Hence, PA <NUM>. T/X "M3000" is a PA <NUM>. T/ PA <NUM>. The RMN <NUM>H analysis disclosed a molar ratio block PA <NUM>. T : block PA <NUM>. T of <NUM> : <NUM> (± <NUM>% uncertainty). The number-average molecular weight Mn of this PA <NUM>. T/ PA <NUM>. T was <NUM>/mol by GPC, which gave a number average polymerization degree (PDn) of <NUM> pour the blocks PA <NUM>. T and of <NUM> pour the blocks PA <NUM>. <CHM>
<CHM>.

<NUM> represents the semi-structural chemical formula for PA <NUM>. T/X « HT3Z », obtained by RMN <NUM>H analysis with X = PA <NUM>. T/X "M3000" is a PA <NUM>. T/ PA <NUM>. The RMN <NUM>H analysis disclosed a molar ratio block PA <NUM>. T : block PA <NUM>. T of <NUM> : <NUM> (± <NUM>% uncertainty).

The compatibilizing system tested in these compositions consisted of the two following compounds (a) and (b) detailed below.

Tables <NUM> and <NUM> below detail the formulations and process parameters of the tested compositions, respectively of control compositions C1-C8 in table <NUM> and of control compositions C9-C12 and compositions of the invention <NUM>-<NUM> in table <NUM>.

<FIG> shows the evolutions over temperature of the storage modulus G', loss modulus G" and tan delta for control composition C9 and compositions I1 and I2 of the invention which each comprise separated phases due to the crystalline PA <NUM> and the amorphous PA <NUM>. T, illustrating the advantageous technical effect of using a PPA having a high Tg in compositions I1 and I2 (see the temperature of <NUM>) which comprise <NUM>% and <NUM> % of this PPA with only <NUM>% and <NUM>% pf PA <NUM>, respectively. <FIG> shows that a high weight ratio of a high Tg PPA imparts a strong peak at the high temperature of <NUM> to a composition of the invention, while a low weight ratio of the high Tg PPA leads to a weak peak at this high temperature.

<FIG> also shows the comparative evolutions over temperature of the storage modulus G', loss modulus G" and tan delta for both thermoplastic composition C7 and I3, which each comprise a fully semi-crystalline mixture PA <NUM> + PA <NUM>. T/X in a form of mixed phases.

Tables <NUM> and <NUM> below both detail the following properties of the tested compositions.

Mechanical properties were measured at <NUM> with HR = <NUM>%, according to ISO <NUM> for the Young modulus and the stress at rupture (or the yield stress) in table <NUM>, and according to ISO <NUM> for the flexion modulus in table <NUM>.

Charpy breaking energy in table <NUM> was measured according to ISO <NUM>/1eA.

Thermal ageing in table <NUM> was carried out after <NUM> at <NUM>, and a traction speed of <NUM>/min.

Burst resistance in table <NUM> was measured according to ISO <NUM> in a conditioned enclosure at <NUM> and <NUM>.

Permeability to water of the monolayer tubes in table <NUM> was measured according to PSA standard D45 <NUM>/--A during <NUM> hours at <NUM> and <NUM>% RH.

Permeability to R-1234yf of the monolayer tubes in table <NUM> was measured according to PSA standard D <NUM>.

Flexion properties recited in table <NUM> were measured in dry state at <NUM>, and after conditioning according to ISO <NUM> standard, with different thicknesses (<NUM> and <NUM>) for the tested monolayer tubes and at different HR (%).

Further, chemical ageing of compositions <NUM>-<NUM> due to oils was measured during <NUM> at <NUM>, in the oils known under the names ND12, SPA2, HD100, VC200YF, VC100YF, ND8, PSR-<NUM>, PSD1, YR20, ND11, ZXL100PG and ZXL200PG. No significant variations were measured after contact with these oils for the above mechanical properties, particularly including the Young modulus and the stress at rupture.

Furthermore, the resistance of compositions <NUM>-<NUM> to ZnCl<NUM> was measured according to D <NUM> standard by immersion in ZnCl<NUM> of monolayer tubes made of compositions I1-I3 during <NUM>. at <NUM> followed by dry heating during <NUM> at <NUM>. This test resulted in no change of aspect for these tubes made of compositions <NUM>-<NUM>.

Specifically according to D47 <NUM> standard, the samples were immersed so that the whole fir tree or snap-in interface/ pipe was in contact with the liquid (ZnCl<NUM>/CaCl<NUM> = <NUM>%/<NUM>%). The samples were kept in the position without shaking for <NUM> minute +/- <NUM> seconds. The samples were placed horizontally in the oven at <NUM> for <NUM> hours +/- <NUM> minutes. <NUM> cycles were performed per day. At the end of each day, the samples that must be validated were left for a maximum of <NUM> hours at room temperature under a fume cupboard before starting a new cycle. The samples were immersed in the solution <NUM> cycles minimum to reach a rating of <NUM>.

As a result from all the measured properties recited above, it may be noted the thermoplastic compositions I1, I2 and I3 of the invention exhibit advantageous properties, and that in particular the compositions I2 and I3 exhibit a satisfactory balance of properties including a very low permeation for water and also for a refrigerating gas, as well as very satisfactory mechanical properties even after thermal and chemical ageing, including an improved impact resistance, as witnessed by.

These results of compositions of the invention compared to those of control compositions C1-C12 also specifically demonstrate the unexpected and advantageous selection in compositions <NUM>-<NUM> of:.

Claim 1:
Thermoplastic composition capable of forming a monolayer tube for transporting a fluid, the monolayer tube being in particular adapted for transporting a refrigerant gas in an air-conditioning circuit of a motor vehicle,
wherein the thermoplastic composition comprises in weight fractions:
- more than <NUM>% and up to <NUM>% of a PA <NUM> and/or a PA <NUM> as at least one aliphatic polyamide,
- from <NUM>% to less than <NUM>% of at least one polyphthalamide having a glass transition temperature measured by differential scanning calorimetry higher than <NUM> and selected from the group consisting of PA <NUM>.I/<NUM>.T, PA <NUM>.T, PA <NUM>.T, PA <NUM>.T/X and mixtures thereof, where X represents at least one polyamide unit other than PA <NUM>.T derived from an aliphatic diamine having from <NUM> to <NUM> carbon atoms and from an aromatic dicarboxylic acid comprising terephthalic or isophthalic acid, and
- from <NUM>% to <NUM>% of a compatibilizing system comprising a product of a reaction between (a) a polymer of at least one first olefin comprising an unsaturated epoxide and (b) a polymer of at least one second olefin comprising an unsaturated carboxylic acid, with a weight ratio (a):(b) greater than <NUM>, said at least one second olefin being identical to or different from said at least one first olefin.