FIELD OF THE INVENTION

The present invention relates to a barrier structure based on an MXDT/XT copolyamide with a high Tg, said structure being devoid of reinforcing fibers. This structure can either consist of a single layer of this polyphthalamide or comprise a layer of MXDT/XT polyphthalamide and at least one layer of another material.

This barrier structure is of use for objects intended for fluid storage and/or transport, such as bottles, tanks, containers, pipes and receptacles of any type. This structure can also be in the form of films with which are made, for example, packagings which require barrier properties against fluids such as gases. All these objects exhibit good barrier properties, that is to say very low permeability to fluids, in particular motor-vehicle fluids, in particular to fuels.

The invention also relates to the use of an MXDT/XT copolyamide with a high Tg for producing a structure, in particular a multilayer structure, comprising at least one barrier layer comprising said MXDT/XT copolyamide.

The invention also relates to the use of these structures and of these objects.

Prior Art and Technical Problem

Regardless of the fluid transported or stored in objects such as bottles, tanks, containers, pipes and receptacles of any type, the material in direct contact with the fluid must not be permeable to said fluid, whether the latter is a liquid or a gas.

Thus, in the motor vehicle field, and the transport field in general, the composition of fuels is constantly changing, in particular for ecological reasons, which is resulting in the gradual arrival of biofuels on the market. These fuels are more aggressive. Consequently, it proves to be essential to improve the quality of the thermoplastic parts in contact with these new fuels, such as pipes for transporting gasoline.

For reasons of safety and environmental preservation, motor vehicle manufacturers impose on these pipes both mechanical characteristics such as resistance to bursting and flexibility with a good impact strength under cold conditions (−40° C.) and at high temperature (125° C.), and also a very low permeability to hydrocarbons and to their additives, in particular alcohols such as methanol and ethanol. These tubes must also have good resistance to fuels and to engine lubrication oils.

Application WO 2014/064375 relates to a composition of or for a thermoplastic composite material with a matrix made of semicrystalline polyamide (PA) having a glass transition temperature Tg of at least 90° C. and a melting point Tm of less than or equal to 280° C., and also mechanical or structural parts based on said material, and to the use of the composition of the invention for parts made of composite material for applications in the motor vehicle, railroad, marine, road transport, wind power, sport, aeronautical and aerospace, construction, panel and leisure fields.

This composition can be used for the manufacture of mechanical parts involved in applications in the motor vehicle field, but no mention is made in this application of a structure comprising a layer which is a barrier to a fluid, in particular a fuel. Moreover, this composition always comprises reinforcing fibers.

EP 1 988 113 describes molding compositions based on a 10T/6T copolyamide with:40 to 95 mol % of 10T5 to 40% of 6T.

EP 1 988 113 is silent with regard to the barrier properties of structures consisting of a layer of these compositions.

EP 1 741 553 describes a multilayer structure comprising two or more layers comprising at least one layer (a) comprising (A) an aliphatic polyamide and a layer (b) comprising a semi-aromatic polyamide comprising at least 60 mol % of aliphatic diamine having from 9 to 13 carbon atoms and at least 50 mol % of terephthalic acid, the layer (b) being the inner layer.

EP 1 741 553 is completely silent with regard to the barrier properties of such a structure.

EP 1 860 134 describes a resin of semi-aromatic polyamide comprising dicarboxylic acid units in which from 50 to 100 mol % of the dicarboxylic acid units are aromatic dicarboxylic acid units, and diamine units in which from 60 to 100% of the diamine units are aliphatic diamine units having from 9 to 13 carbon atoms, said semi-aromatic polyamide having an amine chain end/acid chain end ratio of greater than or equal to 6.

EP 1 860 134 exemplifies in particular 9T/9′T (or 8MT/9T) compounds and shows that the alcohol resistance is reduced when said ratio is less than 6 and in particular is 4 or less.

International application WO 10/015786 relates to a copolyamide of formula A/10.T, in which:

A is chosen from a moiety obtained from an aminocarboxylic acid, a moiety obtained from a lactam and a moiety corresponding to the formula (Ca diamine).(Cb (cyclo)aliphatic diacid), with a representing the number of carbon atoms in the diamine and b representing the number of carbon atoms in the diacid, a and b each being between 4 and 36;

characterized in that it has a polydispersity index, noted PDI, of less than or equal to 3.5, measured by gel permeation chromatography.

WO 10/015786 is completely silent with regard to the barrier properties of such a structure.

WO 2015/159014 describes a process for producing a thermoplastic material comprising at least one step for injection molding or a step for processing by extrusion of a composition of polyamides. A very large number of polyamides are claimed, and although the polyamide composition can be used to produce a single-layer or multilayer structure, mention is in no way made of the barrier properties of the structure and in particular comprising the MXDT/XT copolyamide.

Moreover, these polyamides still remain to be improved, in particular in terms of crystallinity, of crystallization kinetics with a view to improving the temperature resistance of the copolyamide, of processability or else of improving their impact strength properties and also their barrier properties.

Thus, there is a real need to find polyphthalamides which have improved properties, in particular in terms of barrier properties.

BRIEF DESCRIPTION OF THE INVENTION

Surprisingly, it is been found that these needs are met with a structure comprising at least one layer comprising an MXDT/XT polyamide, in which: “MXDT” denotes a unit comprising an amide moiety corresponding to the condensation product of a mixture of m-xylylenediamine xylylenediamines and of terephthalic acid,

XT denotes a unit comprising an amide moiety corresponding to the condensation product of X, which denotes the residues of an aliphatic, arylaliphatic, cycloaliphatic or aromatic amide, and T which denotes terephthalic acid.

MXDT is present in a molar content ranging from 5 to 45%, preferably from 15 to 45%, more preferentially from 20 to 45%, where MXD represents m-xylylenediamine (MXD) and T represents terephthalic acid,

XT is a unit comprising a major amide moiety present in a molar content ranging from 55 to 95%, preferably from 55 to 85%, more preferentially from 55 to 80%, where X is a C9to C18, preferably C9, C10, Ciiand C12, linear aliphatic diamine and where T is terephthalic acid,

said copolyamide having a melting point: 250° C.<Tm≤300° C. as determined according to the standard ISO 11357-3 (2013),

said structure being devoid of reinforcing fibers.

It has thus been found that these products, originally developed for composite applications, owing to their high stiffness (high Tg)/good processability (relatively low Tm) compromise, also have a crystalline structure better than expectations and can be used as a barrier layer, that is to say a layer with very low permeability to fluids, in particular motor-vehicle fluids, in particular to fuels, in a structure, in particular a multilayer structure, for fluid transport, although the amine chain end/acid chain end ratio is in particular less than 5.

In other words, said structure is a barrier structure, in particular chosen from bottles, tanks, containers, pipes, receptacles and films, comprising at least one barrier layer (1) comprising an MXDT/XT copolyamide as defined above.

The structure of the invention can either consist of a single layer of this polyamide, in which case it does not comprise reinforcing fibres, or comprise a layer comprising the MXDT/XT polyamide (and therefore devoid of reinforcing fibers) and at least one layer of another material, it being possible for said at least one other layer to comprise reinforcing fibers.

In the structure of the invention, the layer comprising the MXDT/XT polyamide can also comprise other polymers. By way of example of these other polymers, mention may be made of polyamides, EVOH, PPS, PPO, polycarbonate and ABS.

The invention also relates to the use of an MXDT/XT copolyamide with a high Tg for producing a structure, in particular a multilayer structure, comprising at least one barrier layer comprising said MXDT/XT copolyamide.

The invention also relates to bottles, tanks, containers, pipes and receptacles of any type manufactured with the above structure. This structure can also be in the form of films with which, for example, packagings are made. All these objects have good barrier properties.

The invention also relates to these objects and also to the use of these structures and of these objects.

