CA2066383C

CA2066383C - Multilayer thermoplastic composites

Info

Publication number: CA2066383C
Application number: CA002066383A
Authority: CA
Inventors: Joachim Muegge; Hubertus Ohm; Christian Gerth
Original assignee: Degussa Huels AG
Current assignee: Evonik Operations GmbH
Priority date: 1991-04-18
Filing date: 1992-04-16
Publication date: 2002-03-26
Anticipated expiration: 2012-04-16
Also published as: EP0509211A3; JPH0699553A; CA2066383A1; US5258213A; EP0509211A2; DE59209681D1; DE4112668A1; ES2132095T3; JP3155604B2; EP0509211B1

Abstract

A multilayer thermoplastic composite comprising at least one layer made from a polyamide-based moulding composition, at least one layer made of a polyester-based moulding composition and an adhesion promoter between the two layers is disclosed.
The adhesion promoter comprises a polyamide, a polyester or a mixture thereof. The composite combines the good rigidity, excellent barrier action and high temperature resistance of polyesters with the good mechanical properties of polyamides.
The composites of the invention are useful fox manufacturing structural components, for example in electrical, machine and automotive industries. They may also be used as films, in particular as foodstuff packaging films, or as multilayer tubes.

Description

Hills .Aktiengesellschaft - 1 - O.Z. 4574 Patentabteilung Multilayer thermoplastic composites The invention relates to multilayer thermoplastic compo-sites made from a polyamide-based moulding composition, a polyester-based moulding composition and a certain adhesion promoter, and to a process for the production of these composites, and to their use.
Polyamides and polyesters on their own are unsuitable for many applications. Thus, polyamides are, for example, not resistant to weathering since they age on exposure to light and absorb moisture from the atmosphere. This results in discolouration, impairment of the mechanical properties and warping.
Although polyamides on their own have good mechanical properties, in particular good toughness, they have a poor barrier action. Polar substances in particular can easily migrate through polyamides. This is extremely disadvantageous, for example in fuel lines transporting alcohol-containing fuel.
Polyesters generally have good weather resistance and have an excellent barrier action both to polar and to nonpolar media. However, they are generally impact-sensitive. The notched impact strength, in particular, in polyesters is frequently inadequate. The resistance to some chemical influences is also inadequate. Polyesters therefore cannot be used in many cases where other properties, such as their excellent barrier action, high temperature resistance and good rigidity, would actually be desired.
It would therefore be desirable if it were possible to produce a strong bond between polyamide and polyester. It would thus be possible, for example, to protect polyamide mouldings against light and moisture by coating with polyester. Likewise, it would be possible to protect a - 2 - O.z. 4574 polyester moulding against chemical and mechanical influences by coating with polyamide. A further advantage here would be the better printability.
Composites made from polyamide and polyester have in principle already been disclosed. EP-A 0 33S 806 des-cribes the coextrusion of PA 12 and polybutylene tereph-thalate (PST) to give a two-layer tube. German Patent 38 27 092 describes a multilayer tube which comprises, from the inside outward, layers of polyamide, polyvinyl alcohol, golyamide and polyester. However, it is known to a person sfrilled in the art that by far the majority of polymers, including polyamides and polyesters, are incompatible with one another, which is why no adhesion is achieved between the laminate layers in the production of polymer laminates. However, an adhesion-based bond between the individual polymer layers is absolutely necessary in conventional industrial applications.
EP-A 0 287 839 discloses composites made from specific polyamide mixtures and various other thermoplastics, such as, for example, polyethylene terephthalate. In order to achieve the reduisite adhesion between the two layers, an adhesion promoter is introduced between the laminate layers. Suitable adhesion promoters indicated in this publication are functionalised polyolefins, functional-ised ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers, ionomers, polyalkylene oxide polyester block copolymers, derivatives of carboxymethylcellulose and blends of these polymers with polyolefins.
However, it has now been shown that these adhesion promoters generally do not produce an adhesion-based bond, especially in the polyamide/polyester system. Even if a certain adhesion is achieved in some cases, it is lost on warming or on contact with solvents, since the adhesion promoters are not sufficiently heat- and solvent-resistant. In addition, bonds of this type easily fail when subjected to shear stress due to cold flow of the adhesion promoter.
A major object= of the present invention is therefore to provide a solvent- and heat-resistant bond between polyester and polyamide which is insensitive to shear stress and has good mechanical properties. I:n particular, it is an aim to achieve strong cohesion at the phase interfaces.
Thus, the present invention provides a multilayer thermoplastic composite comprising:
a) at least one layer made from a polyamide-based moulding composition;
b) at least one layer made from a polyester-based moulding composition; and c) an adhesion promoter comprising a mixture of: a polyamide and a polyester, between layers a) and b), wherein the polyamide and the polyester in the mixture of the adhesion promoter are at least in part in the form of a polyamide-polyester block copolym~~x-.
In a preferred embodiment, the polyamide-based moulding composition has a continuous polyamide phase anc~ the polyester-based moulding composition has a continuous polyester phase.
Polyamides are taken to mean polymers in which the monomer units are predominantly, i.e. to the extent of at: least 60%, linked to one another by amide bonds of the formula ___-t-.__._.N H
The following polymers are suitable here:

3a 1) Homopolymer~> and copolymers derived from dicarboxylic acids, diami.nes, aminocarboxylic acids and/or lactams. They preferably have an exclusively - 4 - O.Z. 4574 aliphatic structure. Particular mention should be made here of PA 6, PA 46, PA 66, PA 612, PA 1010, PA 1012, PA 11, PA 12, PA 1212 arid mixtures thereof.
The polyamides are characterised in accordance with international standards, the first numbers) indi-cating the number of carbon atoms in the starting amine and the last numbers) indicating the number of carbon atoms in the dicarboxylic acid. Indication of only one number means that the starting material is an aminocarboxylic acid or a, lactam thereof (H. Domininghaus, "Die Runststoffe and ihre Eigenschaften" [Plastics and their Properties], VDI
Verlag, 1976, page 272). However, mixed aliphatic-aromatic copolyamides are also suitable (cf. U8 Patents 2,071,250, 2,071,251, 2,130,523, 2,130,948, 2,241,322, 2r312,966, 2,512,606 and 3,393,210; ~irk~
Othmer, Encyclopedia of Chemical Technology, Vol.
18, John Wiley & Sons (1982), pages 328 to 435).
The number average molecular weight of the poly-amides should be greater than 5000, preferably greater than 10,000.
2) Polyether-amides and polyether-ester-amides.
Products of this type are described, for example, in DE-A 27 12 987, 25 23 991 and 30 06 961.
Polyesters are taken to mean polymers in which the monomer units are predominantly, i.e. to the extent of at least 60 $, linked to one another by ester bonds. Suit-able here are homopolymers and copolymers derived from dicarboxylic acids, diols, bisphenols, hydroxycarboxylic acids andlor lactones. Examples of suitable diol compo-nents here are ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, 1,4-cyclo-hexanedimethanol and neopentyl glycol, and examples of suitable dicarboxylic acid components are isophthalic acid, terephthalic acid, 2,6-~ 2,7-, 1,5- and 1,4-naph-thalenedicarboxylic acid, diphenic acid and diphenyl a - 5 ° ~ ~j ~ ~'~~ ~ ~ ~ O. Z . 4574 ether 4,4'-dicarboxylic acid. It is possible, in the known manner, to replace some of this diol component by a compound HO-(-R-0-)x-H where x is at least 10 and R is a divalent saturated croup having 2 to 4 carbon atoms.
Likewise, a maximum of 20 mol-~ of the dicarboxylic acid component can be replaced by an aliphatic dicarboxylic acid having 2 to 12 carbon atoms, such as, for example, succinic acid, malefic acid, fumaric acid, adipic acid, sebacic acid or dodecanedioic acid. Examples of suitable bisphenols are bisphenol A, bisphenol T, hydroquinone, tetramethylbisphenol A and tetramethylbisphenol S, an example of a suitable hydroxycarboxylic acid is p-hydroxybenzoic acid, and a particularly suitable lactone is caprolactone.
These polyesters are usually prepared by condensing a diol, for example ethylene Glycol, 1,4-butanediol or 1,4-cyclohexanedimethanol, with an aromatic dicarboxylic acid, such as, for example, isophthalic or terephthalic acid, or an aster thereof. The preferred polyester is polyethylene terephthalate (PET) or polybutylene tereph-thalate (PBT) or a copolyester of 1,4-butanediol, dode-canedioic acid and terephthalic acid.
Processes for the preparation of these polyesters are described in detail in the literature (for example Ullmanns Enzyklop~die der technischen Chemie [Ullmann's Encyclopaedia of Industrial Chemistry3, Volume 19, pages 61 ff., and DE-A 24 07 155 and DE-A 24 07 156).
Component b) may additionally contain further thermo-plastics, such as, for example, polycarbonates (PC), styrene-malefic anhydride copolymers, acrylonitrile-butadiene-styrene copolymers (ABS), styrene-acrylonitrile copolymers, acrylonitrile-styrene--acrylate copolymers or mixtures thereof.
Particularly suitable polycarbonates are the aromatic types, which are generally known to a person skilled in i~ t~

- 6 - O.Z. 4574 the art; cf., for example, Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 18, John Wiley & Sons (1982), pages 479 to 494. They are obtained by reacting a bis-phenol with a carbonate precursor, such as phosgene, a chloroformate or a formats. Typical bisphenols are bisphenol A, bisphenol T, tetramethylbisphenol A and tetramethylbisphenol S. The preferred polycarbonate is the homopolymer derived from bisphenol A.
Component a) may additionally contain further thermo-plastics, such as, for example, polyphenylene ethers, if desired modified in accordance with the prior art, polystyrene, if desired modified in accordance with the prior art, and styrene-malefic anhydride copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-acrylonitrile copolymers, acrylonitrile-styrene--acrylate copolymers, other styrene copolymers and polyolefins, if desired modified in accordance with the prior art.
Suitable polyphenylene ethers (PPE) are polymers built up from the following unitss Q1 ;~3 ._. ~
,Q2 ~ Q4 where Ql and QZ are either radicals, preferably primary, having 1 to 10 carbon atoms, cycloalkyl radicals having 5 to 10 carbon atoms, benzyl radicals having 7 to 10 carbon atoms or aryl radicals having 6 to 10 carbon atoms, and Q3 and Q4 can have the same meaning as Q1 and Qz, but are preferably hydrogen.
These polyphenylene ethers can be prepared by any process corresponding to the prior art. The corresponding phenols are usually oxidatively coupled using an oxygen-contain-ing gas, such as, for example, air, in the presence of a 7 _ ~~U~~~~ O.Z. 4574 catalyst complex. If a p-halogenated phenol is used, a sufficient amount of acid acceptor must be present. The catalysts used are preferably copper-amine complexes or manganese-containing systems (DL-A 32 24 691 and 32 24 692, and US patents 3,306,874, 3,306,875 and 4,028,341). The viscosity numbers J, determined in accordance with DIN 53 728 in chloroform at 25°C, are in the range from 20 to 80 cm3/g (concentration 5 g/1), preferably in the range from 40 to 70 cm3/g. These poly-phenylene ethers can be prepared using, for example, the following monomerss 4-bromo-2,6-dimethylphenol, 2-methyl-6-ethylphenol, 2,6-diethylphenol, 2-methyl-6-tert.-butylphenol, 4-bromo-2,6-diphenylphenol, 2-benzyl-6-methylphenol, 2,6-dibenzylphenol, 2,3,6-tr3methylphenol or preferably 2,6-dimethylphenol. It is of course also possible to use mixtures of such phenols.
Also included are of course natural or modified poly-phenylene ethers, for example graft copolymers with vinyl monomers, styrene or other modifying reagents.
Component a) and/or component b) may furthermore contain one or more impact-modifying rubbers. Examples of suit-able compounds are ethylene-propylene or ethylene-propylene-diene copolymers, polypentenylene, poly-octenylene or random oar block copolymers made from alkenylaromatic compounds with olefins or dienes.
The impact-modifying rubbers may be functionalised in accordance with the prior art, for example using malefic anhydride (MA), if desired in the presence of styrene.
Other toughening rubbers which may be mentioned are:
core-shell rubbers having a tough, elastic core made from acrylate rubber, butadiene rubber or styrene-butadiene rubber, in each case having a glass transition tempera-ture Ta of < -10°C, it being possible for the core to be crosslinked in each case. The shell may be built up from styrene and/or methyl methacrylate and/or further - $ ° O.Z. 4574 unsaturated monomers, if desired carrying acid or acid anhydride groups.
Components a) and/or b) may additionally contain a flameproofing agent and further additives, such as pigments, oligomers, polymers, antistatics, stabilisers, processing aids and reinforcing agents. The proportion of reinforcing agents may be up to 50 %, the proportion of flameproofing agents up to 15 % and the proportion of all other additives in total up to 5 %, in each case based on the total moulding composition. Particularly suitable flameproofing agents are aromatic phosphorus compounds, such as triphenylphosphane oxide, triphenyl phosphate and triphenyl phosphate. Tt is also possible to use a conven-tional halogen-containing flameproofang agent. Suitable compounds are halogen-containing organic compounds, as described, for example, in the monograph by H. Vogel, "Flammfestmachen von Runststoffen" [Flameproofing of Plastics ] , ~Iuth3.g-V~rlag, 1966, pages 94 to 102 . However, these may also be halogenated polymers, such as., for example, halogenated polyphenylene ethers (see DE-.A
33 34 06$) or brominated oligo- or polystyrenes. The compounds should contain more than 30 % by we3.ght of halogen.
If halogen-containing flameproofing agents are used, it is advisable to use a synergist. Suitable compounds are those of antimony, boron and tin. These are generally employed in amounts of from 0.5 to 10 % by weight, based on the thermoplastic compositions. Particularly suitable reinforcing agents are glass fibres and carbon fibres.
Suitable stabilisers include organic phosphates, such as, for example, didecyl phenyl phosphate and trilauryl phosphate, steracally hindered phenols, and tetramethyl-piperidine, benzophenone and triazole derivatives.
Suitable processing aids are waxes, such as, for example, oxidised hydrocarbons and their alkali metal and alkaline earth metal salts.
Component c) is a moulding composition which is com-patible both with component a) and with component b), i.e. gives strong cohesion and is therefore suitable as an adhesion promoter. In principle, it is sufficient in many cases for the adhesion promoter to be based either on a suitable polyamide or on a suitable polyester. Since a person skilled in t:he art knows from the literature which polymers are compatible with a certain polyamide or polyester, he can th<~refore make his choice without difficulty.
The adhesion promoter com-prises a polymer mixture which contains a polymer which is compatible with a), generally a polyamide, and a polymer which is compatible with b), generally a poly-ester or a polycarbonate. A particularly suitable poly-carbonate is that based on bisphenol A. The polymers which are compatible with a ) or with b ) may also them-selves be blends, foi-~example comprising PA 6 and PA 66 or comprising PA 12 a.nd PA 1012 on the one hand and comprising polybutylene terephthalate (PBT) and poly-carbonates on the other hand.
In order to achieve a good adhesive action on both sides, the polymers or polymer blends which are compatible with a) and with b) are preferably employed in a weight ratio of from 30:70 to 70:f.0, particularly preferably in a weight ratio of from 4(1;60 to 60:40.
In order to provide they adhesion promoter [component c)]
with good heat- and solvent-resistance, it should contain at least 50 % by weight, preferably at least 70 % by weight and particularly preferably at least 85 % by weight, of polya.mide, polyester or mixtures thereof.
Partially crystalline polyamides and polyesters having a crystallite melting point Tm of at least about 140°C are preferred.

The adhesion-promoting action of component c) is high since at least some of the polyamide and of the polyester is in the form of polyamide-polyester block. copolymers.
These can be prepared i.n various ways in accordance with 5 the prior art.
For example, US Patent .3,378,602 describes a process for the preparation of pol~~amide-polyester block copolymers by a reaction in 'the melt without a catayst.
EP-A 0 084 643 describes a process for the preparation of 10 block copolymers in which an effective amount of a phosphate is added. Furthermore, the preparation of polyamide-polyester block polymers in the melt can be carried out using the following catalysts: compounds of tin, titanium, zirconiiun, manganese, zinc or antimony, for example t.in ( II ) oxalate, dibutyltin oxide, dibutyltin dilaurate, titanium tet:raisopropoxide, zirconium tetra isopropoxide, manganese acetate, zinc oxide, zinc acet ate, antimony trioxide or antimony acetate. The catalysts are preferably employed in amounts of from 0.05 to 1.0 %
by weight.
Block copolymers of this type are most easily prepared in accordance with the abovementioned EP-A 0 084 643 by mixing the melts of a polyamide containing amino end groups, a polyester containing carboxyl end groups, and a compound of trivalent phosphorus, in particular tri-phenyl phosphate.
The multilayer composites can be produced in one or more steps.
In the one-step injection-moulding process, the various melts are combined in a mould, and the moulding is allowed to cool (multicomponent injection moulding).
In the one-step extrusion process, the various melts are coextruded in a conventional manner.

In the multistep processes, a moulding is first produced either from component a) or component b), and then coated with the other components, which can be effected by pressing, infection moulding or extrusion.
These multilayer composites are used in structural components, in particular in the electrical engineering, machine construction and automotive industries, in applications where the rigidity of the polyester is to be combined with the toughness of the polyamide or where the disadvantageous properties of the polyamide, such as poor W resistance, inadequate scratch resistance or poor barrier effect, are to be compensated by a polyester coating. In particular, they are used as films, in particular as foodstuff packaging films, or as multilayer tubes, for example in the automotive industry.
Examples 1 to 1~
Production of the multilayer composites The dried starting components axe first converted indivi-dually into pressed sheets about 1 mm thick (pressing times 10 minutes, pressing temperatures at least 10°C
above the melting or softening point). ~o mould release agents may be used. The individual sheets are then pressed in the desired sequence to forxa a multilayer composite. The pressing temperature depends on the material having the highest melting or softening point.
The pressing time is again 10 minutes.
Testing of the multilager composites The material interface to be tested is separated using a metal wedge (edge angle 5 degrees). If the separation takes place everywhere precisely at the transition from one component to the other, the adhesion is poor. ~y contrast, if the separation takes place entirely or partially within one of the two components, the adhesion f ~ L
_ 12 _ O.Z. 4574 is good. The results are shown in Tables 1 and 2.
Materials used Al: Polyamide 12, VESTAMIDR X4887 (H$)hS) A2: Polyamide 6, ULTRAMIDR 84 (BASF) A3 : Polyagnide 6 6 , ULTR.~1MID~ A4 ( BASF' A4: Polyamide 12, VESTAPaIID~ X1852 (H~LS) A5: Polyamide 12/PPE blend, VESTOBLEND~ 1500 (H~LS) B1: Polybutylene terephthalate, VESTODURR 3000 (Fi$S'LS) B2: Polyethylene terephthalate, POT~YCLEARa TR86 (HOECHST) 83: PBTIPC blend, prepared from 70 parts by weight of vESTODURR 3000 (Ht)LS), 30 parts by weight of MAKROhONR 2800 (BAYER) and 0.1 part by weight of a phosphate stabiliser H4: PBT/ABS blend, prepared from 70 parts by weight of VESTODURR 3000 (HtfiLS) and 30 parts by weight of BAYMODR (BAYER) cl: MA-modified sESS, xRAT~~~ FG l9olx (sHEhr.) C2: MA-modified EPM, EXXELORR ~TA1803 (EXXON) C3: MA-modified PP, ADMERR QR500 (Mitsui) C4: 50 parts by weight of polyamide 12 ( ri=m in accor-dance with ISO 307/DIN 53 727 in 0.5 ~t strength cresol solution: 1.91, content of amino end groups:

80 mmol/kg, content of carboxyl end groups:

20 mmol/kg) were mixed in the melt with 50 parts by weight of PBT (viscosity number J~, measured in accordance with DIN 53 728 at 25C in o-dichloro-benzene/phenol (50 parts by weight each, concentra-tion: 5 g/1)a 165 m3/g, content of carboxyl groups:

40 mmol/kg) and 0.1 part by weight of triphenyl phosphate in a heistritz 30.34 continuous corotating twin screw kneader at a jacket temperature of 260C, a material throughput of 3 kg/h and a screw speed of 50 rpm, and the mixture was extruded and granulated.

C5: 50 parts by weight of polyamide 12 ( ~r~1 in accor-dance with ISO 307/DIN 53 727 in 0.5 ~ strength ~~'~n~7 - 1 ~ - ~ ~ ~5 ..~ Ls a s.i O.Z. 4574 cresol solutions 1.91, content of amino ~nd groupsa 80 mmol/kg, content of carboxyl end groupsa 20 mmol/kg) were mixed in the melt with 50 parts by weight of PBT (viscosity number J, measured in accordance with DIN 53 728 at 25°C in o-dichloro-benzene/phenol (50 parts by weight each, concentra-tion: 5 g/1): 155 m3/g, content of carboxyl groupsa 40 mmol/kg) and 0.1 part by weight of dibutyltin oxide in a Leistritz 30.34 continuous corotating twin screw kneader at a packet temperature of 260°C, a material throughput of 3 kg/h and a screw speed of 50 rpm, and the mixture was extruded and granulated.
C6s 100 parts by weight of a polybutylene terephthalate containing predominantly hydroxyl end groups are reacted with 11 parts by weight of a polyfunctional isocyanate IPDI T 1890 (FILLS) in the melt at 250°C
and subsequently remelted with 100 parts by weight of the polyamide 12 used in C4, and the product was extruded and granulated.
C7: 50 parts by weight of polyamide 6 (medium viscosity, containing predominantly amino end groups] were mixed in the melt with 50 parts by weight of PET
(viscosity number J, measured in accordance with DIN
53 728 at 25 °C in o-dichlorobenzene/phenal ( 50 parts by weight each, concentrations 5 g/1): 110 cm3/g) containing predominantly carboxyl end groups and 0.1 part by weight of triphenyl phosphate in a Leistritz 30.34 continuous corotating twin-screw kneader at a ~ack$t teanperature of 280°C, a material throughput of 3 kg/h and a screw speed of 50 min"1, and the product was extruded and granulated.

14 - ~ ~' ~"-! O. Z .
t~ '~ 4574 ~ Cr ~ C

Table 1 ~Com~axative examples not according to the invention Ex. Layer LayerInter- Mechanicallyseparable A B mediate at the interface layer at at after R~' 160C storage in solv~t 1 Al B1 - yes yes yes 2 A1 B1 C1 no yes yes 3 A1 B1 C2 n~ yes yes 4 A2 Bl - yes yes yes 5 A1 B1 C3 yes yes yes 6 A4 B1 C3 yes yes yes 7 A4 B2 C3 yes yes yes 8 A3 B2 - yes yes yes 9 A4 B3 - yes yes yes 10 A4 B4 - yes yes yes 11 A4 B3 C1 no yes yes a) Solvent mixture (1:1 wlw) toluene/hexane Table 2 Exam accordin e les to invention th Ex. Layer LayerInter- Mechanicallyseparable A B mediate at the interface layer at at after RT 160C storage in ~lte 12 A4 B1 C4 no no no 13 A4 B1 C5 no no no 14 A4 Bl C6 no no no 15 A2 B2 C7 no no no 16 A1 B4 C4 no n~ no 17 A5 B1 C6 no no no 18 A4 B3 C4 no no no a) Solvent mixture (lsl w/w) toluene/hexane

Claims

1. A multilayer thermoplastic composite comprising a) at least one layer made from a polyamide-based moulding composition;
b) at least one layer made from a polyester-based moulding composition; and c), between layers a) and b), an adhesion promoter made from a moulding composition comprising a mixture of a polyamide and a polyester, wherein at least a part of the polyamide and at least a part of the polyester are in the form of a polyamide-polyester block copolymer.

2. The multilayer thermoplastic composite according to claim 1, wherein layer a) comprises, as polyamide (PA), PA 6, PA 46, PA 66, PA 612, PA 1010, PA 1012, PA 11, PA 12, PA 1212 or a mixture thereof; and layer b) comprises, as polyester, polyethylene terephthalate or polybutylene terephthalate.

3. The multilayer thermoplastic composite according to claim 1 or 2, wherein the polyamide-based moulding composition has a continuous polyamide phase; and the polyester-based moulding composition has a continuous polyester phase.

4. The multilayer thermoplastic composite according to any one of claims 1 to 3, wherein the moulding composition of the adhesion promoter comprises at least about 50 % by weight of the mixture.

5. A multilayer thermoplastic composite according to claim 4, wherein the moulding composition of the adhesion promoter comprises at least about 70 % by weight of the mixture.

6. The multilayer thermoplastic composite according to claim 4, wherein the moulding composition of the adhesion promoter comprises at least about 85% by weight of the mixture.

7. The multilayer thermoplastic composite according to claim 4, wherein the moulding composition of the adhesion promoter is composed of the mixture.

8. The multilayer thermoplastic composite according to any one of claims 1 to 7, wherein the polyamide and the polyester in she mixture of the moulding compositions are employed in a polyamide/polyester weight ratio of from about 30:70 to about 70:30.

9. The multilayer thermoplastic composite according to claim 8, wherein the weight: ratio is from about 40:60 to about 60:40.

10. A multilayer thermoplastic composite, comprising:
a) at least one moulded layer made of an aliphatic polyamide alone or in combination with at least one other thermoplastic resin selected from polyphenylene ether (PPE), polystyrene, styrene-maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer, styrene-acrylonitrile copolymer, acrylonitrile-styrene-acrylate copolymer and polyolefin;
b) at least one moulded layer made of a polyester derived from a diol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid selected from isophthalic acid and terephthalic acid, alone or in combination with at least one other thermoplastic resin selected from polycarbonate (PC), styrene-maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), styrene-acrylonitrile copolymer and acrylonitrile-styrene-acrylate copolymer; and c) between layers a) and) b), a moulded adhesion promoter layer made of a mixture of a polyamide and a polyester, in which at least a part of the polyamide and at least a part of the polyester are in the form of a polyamide-polyester block copolymer.

11. The multilayer thermoplastic composite according to claim 10, wherein the polyamide in the mixture of the adhesion promoter layer is an aliphatic polyamide and the polyester in the mixture of the adhesion promoter layer is a polyester derived from a diol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol and an aromatic dicarboxylic acid selected from isophthalic acid and terephthalic acid.

12. The multilayer thermoplastic composite according to claim 10 or 11, wherein the mixture of the adhesion promoter layer has a polyamide/polyester weight ratio of 30:70 to 70:30.

13. The multilayer thermoplastic composite according to any one of claims 10 to 12, wherein the mixture of the adhesion promoter layer is prepared by heating a mixture of the polyamide having an amino end group and the polyester having a carboxyl end group, either in the absence or in the presence of a catalyst selected from the group consisting of phosphates, and compounds of tin, titanium, zirconium, manganese, zinc or antimony, to form the polyamide-polyester block copolymer.

14. The multilayer thermoplastic composite according to any one of claims 10 - 13, wherein the layer b) is made solely of the polyester.

15. The multilayer thermoplastic composite according to any one of claims 10 - 13, wherein the layer b) is made of at least 70% by weight of the polyester and at most 30% by weight of the other thermoplastic resin.

16. The multilayer thermoplastic composite according to any one of claims 10 - 15, wherein the layer a) is made solely of the aliphatic polyamide.

17. The multilayer thermoplastic composite according to any one of claims 10 - 15, wherein the layer a) is made of a blend of the aliphatic polyamide and polyphenylene ether.

18. A process for the production of a multilayer thermo-plastic composite according to any one of claims 1 to 17 which process comprises a multicomponent injection moulding or coextrusion.

19. An article of manufacture comprising the multilayer thermoplastic composite according to any one of claims 1 to 17.

20. The article according to claim 19 in the form of a multilayer film.

21. The article according to claim 19 in the form of a multilayer tube.

22. The article according to claim 20 which is a food-stuff packaging film.