CA2110424A1

CA2110424A1 - Multilayer plastic pipe

Info

Publication number: CA2110424A1
Application number: CA002110424A
Authority: CA
Inventors: Stefan Rober; Roland Feinauer; Hans-Dieter Herrmann; Hans Jadamus; Joachim Mugge; Hans Ries
Original assignee: Stefan Rober; Roland Feinauer; Hans-Dieter Herrmann; Hans Jadamus; Joachim Mugge; Hans Ries; Huls Aktiengesellschaft; Degussa-Huls Aktiengesellschaft; Degussa Ag
Current assignee: Evonik Operations GmbH
Priority date: 1992-12-03
Filing date: 1993-12-01
Publication date: 1994-06-04
Also published as: US5449024A; DE4240658A1; EP0601295A1; DE59302600D1; JP3367727B2; JPH06210812A; EP0601295B1; BR9304922A; ES2088207T3

Abstract

Abstract:

Multilayer plastic pipe The aim is to provide a plastic pipe having improved resistance, inter alia, to methanol-containing fuels and improved mechanical properties.

This is achieved by a multilayer plastic pipe comprising at least one outer layer based on polyamide and at least one layer of a linear, crystalline polyester modified by means of an isocyanate mixture.

The invention enables plastic pipes having the desired improved property profile to be obtained.

Description

~} 21~2~1 Huls Aktiensell~chaft - 1 - O.Z. 4702 Patent Department Multilayer plastic pive ~.,!
~ The invention relates to a multilayer plastic pipe.
:,~
Plastic pipes made from polyamide are known and are ;~ employed for a variety of applications. In order to achieve their ob~ective, the pipes must be, inter alia, inert to the medium flowing in them, and must b~ res~s-tant to high and low temperatures and mechanical stresse~.

Single-layer pipes ar~ not always capable of satisfying the necessary requirements. In the case of transport of, for example, aliphatic or aromatic solvents, fuel~ or khe like, they exhibit considerable disadvantages, 3uch as a poor barrier action to the medium, unde~ired changes in '~ dimension or inadequate resi~tance to mechanical stres-ses.

It has been attempted to overcome these disadvantages by means of multilayer pipes (DE-A 35 10 395~ 37 15 251, 38 21 723, 40 01 125 and 40 01 126). ~owever, practical implementation of these proposals has ~hown that, al-though ~ome disadvantages can be overcome, the overallproperty profile i~ still unsatisfactory.

German Patent 38 27 092 describes a multilayer plastic pipe which contain~, from the inside outward~, layerg of polyamide, polyvinyl alcohol, polyamide and polyester.
The polyester here is only employed in a thin outer layer in order to allow relatively high short-term heat resis-tance to be achieved. It i5 known to per~ons skilled in the art that by far the ma~ority 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 multilayer com-posites. An a&esion-based bond between the individual pol~mer layers is absolutely essential in industrial - 2 _ 21 ~0 ~2~ 23443-502 applications.

In particular, permeation of methanol co~taining fuels ha~ only been reduced to an inadequate extent by mean~ of the abovementioned proposals.

Reduction in penmeation ~y using no~el intermediate ~ layers is therefore of crucial Lmportance because, in ! particular, the legally permitted emission values are constantly being reduced.

The aim of the invention was to develop a polyamide pipe having a good barrier action to the transported medium, in particular to methanol-con~aining fuels, satisfactory dimensional stability and satisfactory resistance to mechanical stre~es.
~, ~his ob~ect i8 achieved by a multilayer plastic pipe ~-which comprise~

I. at lea~t one outer layer based on a polyamide mould- :
ing composition and II. at lea~t one layer of a moulding compo,i~ion based vn a mixture o~
a. from 99 to 9S ~ by weight of a linear, crystal~
line polye~ter and b. from 1 to 5 % by wei~ht of a mixture of :-¦ 25 1. from 30 to 70 % by weight of at lea~t one compound containing two i~ocyanate groups and :~
2. from 30 to 70 ~ by weight of at lea~t one compound containing more than two i30cyanate groups, where the isocyanat~ groups originating from com-ponent II.b. are pre~ent in component II. in a concentration of betwee~ 0.03 and 003 % by weight, and the layers are adhesively bondsd to one another.
,.

. ~.,~ .
`~ ~

3 21~ o z. 4702 The layer as described in II. comprises from 99 to 95 ~
;i by weight, preferably from 98 to 96 % by weight, of - component II.a. and from 1 to 5 % by weight, preferably ~ from 2 to 4 % by wei~ht, of component II.b.
~., ;~ 5 Component II.b. comprises a mi.~ture of from 30 to 70 % by weight, preferably from 40 to 60 % by weight, of at least one compound containin~ two isocyanate groups and from 30 to 70 ~ by wei~ht, preferably from 40 to 60 ~ by weight, ~`~1 of at least one compound containing more than two iso-cyanate groups.

The isocyanate groups originating from component II.b.
are present in component II. in a concentration of between 0.03 and 0.3 % by weight, preferably between 0.06 and 0.25 ~ by weight.
.:~
Suitable polyamides are primarily aliphatic homo- and copolycondensates. ~xamples which may be men~ioned are polyamides ~nylons~ 4.6, 6.6, 6.12, 8.10 and 10.10.
Preference i~ given to pçlyamides 6, 10.12, 11, 12 and 12.12. [The numbering of the polyamides cQrresponds to the international standard, the fir~t number(s) indicating the number of carbon atoms in the starting diamine and the final number(~) indicating the number of carbon atoms in the dicarboxylic acid. If only one number is given, the starting material was an a,~-amino-.~.
carboxylic acid or the lactam derived therefrom (H.Domininghau~, Die Run~tsto~fe und ihre Eigenschaften [Plastics and their Properties], page 272~ VDI-Verlag 76~

I~ copolyamides are used, these can contain, for example, adipic acid, sebacic acid, suberic acid, i~oph~halic acid ~A~. or terephthalic acid as co-acid or bis(4'-~minocyclo-hexyl)methane~trimethylhexamethylenediamine,hexamethyl-:.~ enediamine or the like as co-diamine.

~ The preparation of these polyamides i~ known tfor example 1~
;

'~_ 4 _ 2~0~ o3443~502 .
~;iD. ~. Jacobs, J. Zimmermann, Polymeriza~ion Processes, pp. 424-67; Interscience Publishers, New York (1977);
DE-B 21 52 194).

`-~Other suitable polyamides are mixed aliphatic/aromatic polycondensates, as described, for example, in US Patents 2,071,250, 2~071,251, 2,1~0,523, 2,130/~48, 2,241,322, 2,312,966, 2,512,606 and 3,393,210, and in Rirk-Othmer, ~ncyclopedia of Chemical Technology/ 3rd Edn. t Vol. 18, pages 328 and 435, Wiley & Sons (1982). Other polyconden-s~te which are ~uitable as polyamide~ are poly(ether ester amides) and poly(ether amides). Products of this type are described, for example, in DE-A 27 12 987, 25 23 991 and 30 06 961.

The molecular weight (number average) of the polyamides is greater than 5,000, preferably greater than 10,000, corresponding to a relative vi3co~ity (~r~13 in the range from 1.5 to 2.8. ~m In a preferred embodiment, the polyamides used for component I. are those in which at least 50 % of all the terminal group~ are amino group~

The polyamide~ mentioned are employed alone or in mix-ture~

The linear, cry~talline polyester~ (component II.a.) have the followins ba~ic ~tructure: ~ :

.`1 o o ~r 11 11 ~O-R-O-C-R'-C~

where R is a divalentl branched or unbranched, alipha~ic and/or cycloaliphatic radical having 2 to 12, preferably 2 to 8, carbon atom~ in the carbon chain, and R' is a divalent aromatic radical having 6 to 20, pr~ferably 8 to 12, carbon atoms in the carbon structura.
,,~
,. ~ .
1~
~,"

2 1 1 ~ ~ 2 ~ 23443-502 ~: _ 5 _ O.Z. 4702 xamples which may be mentioned o~ diol~ are ethylene ~ glycol, trimethylene glycol, tetramethylene glycol, ', hexamethylene glycol, neopentyl glycol, cyclohexanedi-methanol, and the like.

Up to 25 mol~ of the diol mentioned may be replaced by a '`l second diol already mentioned above or by a diol of the following general formula:
HO~R -O~XH

where R~ is a divalent radical having 2 to 4 carbon atoms, and x can have a value of from 2 to 50.

Preferred diols are ethylene glycol and, in particular, tetramethylene glycol.

~xamples of aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, 1,4-, 1,5-, 2,6- and 2,7-naphtha-lenedicarboxylic acid, diphenic acid and diphenyl ether 4,4'-dicarboxylic acid. Terephthalic acid i8 preerred.

~p ~o 20 mol~ oF the~e dicarboxylic aeids may be replaced by aliphatic dicarboxylic acid~, such a~, for example, succinic acid, maleic acid, fumaric acid, sebacic acid, dodecanedioic acid, inter alia.

The preparation of the linear, cry~talline polyesters is part of the prior art (DE-A 24 07 155 ~nd 24 07 156;
~llmann8 Encyclopadie der te~hnische~ Che~iQ t~llmann'g Encyclopaedia of Industrial Chemistry], 4th Edn., Vol.
19, pages 65 ff., Verlag Chemie Gmb~, WeinheLm, 1980).

The polyesters employed according to the invention have a viscosity index ~J ~alue~ in the range from 80 to 240 cm3/g.

The polyamides of the outer layer as described in I.
~ and!or the linear, crystalline polyester3 ~component ,~

~,- 6 - 21~0~2~ o.z. ~702 II.a. ) may contain up to 40 % by weight of other thermo-plasitics, so long as the latter do not adversely af fect the bonding ability. Particular mention may be made here of polycarbonate [H. Schnell, Chemi~itry and Physics of 5 Polycarbonate~, Interscience Publisher~i, New York ~'(1981)], acrylonitrile-styrene-butadiene copolymers (Houben-Weyl, ~ethoden der organii3chen Chemie [Methods of Organic Chemistry], Vol. 14/1, Georg Thieme Verlag Stuttgart, pp. 393-406; Ul~m~nn~ Encyclopadie der tech-nischen Chemie [Ullmann'~ Encyclopaedia of Industrial Chemistry], 4th Edition, Vol. 19, Verlag Chemie, Weinheim (1981), pp. 279-284), acrylonitrile-styrene-acrylate copolymers (Ullmanns ~ncyclopadie der techni~chen Chemie [Ullmann's Encyclopaedia of Industrial Chemistry], 4th Edition, Vol. 19, Verlag Chemie, Weinheim (1981), pp.
277-295), acrylonitrile-styrene copolymers (~llm~nn8 ~ncyclopadie der techniisichen Chemie r Ullmann's Encyclo-paedia of Indu trial Chemistry], 4th Edition, Vol. 19, Verlag Chemie, Weinheim (1981) pp. 273 ff.) or poly-phenylene ether~ (DE-A 32 24 691 and 32 24 692, and US Patents 3,306,874, 3,306,875 and 4,028,341).

If necessary, the polyamides and/or polye~ters can be impact-modified. Examplec of suitable polymers are ethylene-propylene orethylene-propylene-diene copolymers (EP-A-295 076), polypentenylene, polyoctenylene or random or block copolymers made from alkenyl-aromatic compounds with aliphatic olefin~ or dienes (EP-A-261 748). Nention may furthermore be made of impact-modifying rubbers:
core/~hell rubber~ having a tough, re3ilien~ core of (meth)acrylate, butadiene or styrene-butadiene rubber having glass transition temperatures T8 of ~ -10C, where the core may be crosslinked. The shell can be built up from styrene and/or methyl methacrylate and/or further unsaturated monomers (DE-A 21 44 528 and 37 28 685 ) . The proportion of impact-modifying compone~t should be ~elected so that the desired properties are not impaired.

As component II.~.l., compounds are employed which carry ~, .
21 l~2-~
~ 7 - 0.~. 4702 two isocyanate group~. Suitable such compound~ are, in particular, aromatic and (cyclo)aliphatic isocyanates, such as, for example, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,5-5 naphthylene diisocyanate, 1,6-hlexamethylene diisocyanate, diphenylmethane 2,4-diisocyanate, diphenylmethane 4,4~-diisocyanate, diphenylmethane 2,2'-diisocyanate, isophor-one diisocyanate, 1,4-tetramethylene diisocyanate and 1,12-dodecane diisocyanate. Further examples are cyclo-10 hexane 1,3-diisocyanate, cyclohexane 1,4-diisocyanate, cyclobutane 1,3-diisocyanate, 2,4-hexahydrotolylene diisocyanate, 2,6-hexahydrotolylene diisocyanate, hexahydro-1,3-phenylene diisocyanate, hexahydro-1,4-phenylene diisocyanate, norbonane diisocyanate, p- and m-15 xylylene diisocyanates, perhydro-2,4 diphenyLmethane diisocyanate and pexhydro-4,4'-diphenylmethane diiso-cyanate.

Compounds which hava proven particularly advantageous as ~ component II.b.l. are isophorone diisocyanate and pro-,`~31 20 ducts of the reaction thereof with its~l~ and with suitable reactant~, such as, for example, a,~-diols ~ having 2-10 carbon atom~ in the carbon chain.
?l Preferred reaction products are obtained, for example, from the reaction of at least two molecules of isophorone , 2S diisocyanate, the binding taking place by reaction of i~
each case two isocyanate groups with formation of a biuret group.

Other advantageous reaction products are obtained, for example, by reaction o in each case two isophorone 30 diisocyanate molecules with one molecule of diol, in each ~; case one isocyanate group of the isophorone diisocyanate " forming a urethane bond with one of the hydroxyl groups ;; of the diol. Examples of particularly ~uitable diols are butanediol and diethylene glycol.

35 As component II.b.2. r compounds are employed which ,.-, 21~(J4~
~! - 8 - O.Z. 4702 contain more than two and preferably precisely three isocyanate groups. Suitable such compounds are, for example, triphenylmethane 4,4',4~-triisocyanate,further-more products of the reaction of the diisocyanatcs listed above in respect of component II.b.1., in particular ~; triisocyanurates of these diisocyanates, such as, for example, the triisocyanurate formed on reaction of in each case three molecules of hlexamethylene dii~ocyanate.
Particular preference i~ given to the triisocyanate formed on reaction of in each case three molecule~ of isophorone diisocyanate. ~ ~
' ' ' ~'`'':
The isocyanate groups of components II.b.1. and II.b.2.
may be in blocked form. The blocking of isocyanate groups is known (for example Paint Resin 58 (1988) 5, 18-19).
For example, mention may be made of blocking by reaction of the isocyanate groups with diols, pyrazole~, oximes, in particular ketoximes/ and lactam~, in particular caprolactam. ~
~ :, The moulding compo~itions for the layers a~ described in I. and II. may contain conventional au~iliaries and i~` additives, such as, for example, flameproofing agen~s, stabili~ers, plastici~ers, processing auxiliaries, ~, viscosity improvers, fillers, in particular tho~e for improving the conductivityr pigments and the like. The amount of said agents should be metered in so that the ~! desired properties are not seriously affected.
; .
The moulding composition for the layer as described in II. is prepared by conventional and known processes by mixing the melts of components II.a. and II.b. in a mixer which provides good compounding, such as, for example, a twin-screw extruder, at temperatures which depend on the melting points of components II.a. and II.b., in ~eneral at temperatures between 200 and 300C.

The preparation of the moulding composition for the layer as described in II. can be carried out using catalysts ~"-2110~
- 9 - O.Z. 4702 , which are conventional and known in the processing of ¦ isocyanates.
,~
' Before the production of the multilayer pipes, the ;~ moulding composition for the layer as described in II.
S should be stored under dry conditions with exclusion of atmospheric moisture.

The above-described preparation of the moulding com-position for the layer as described in II. can also be carried out directly in a feed extruder o~ the coex-10 trusion or injection-moulding line used for the produc-tion of the multilayer pipes, so that the moulding compo¢ition for the layer as described in II. can be converted directly after its production - without further ~ interim storage - into a layer of the multilayer pipe. In ;~ 15 the case of coextru~ion, the processing conditions in the 3 production o~ the multilayer pipe~ should be selected so that the melts are laid on one another at a sufficiently high presi3ure.

The multilayer pipes are produced in a`kno~n manner, for 20 example as described above in the prior art.

The multilayer pipes according to the invention have extremely good resistance and a good barrier action to diffusion of ~petro)chemical substances, solvents and fuels. Furthermore, the two layers are adhesively bonded 25 to one another, so that delamina~ion of the various layers from one another does not occur, for example on thermal expansion or flexing of the pipe. In addition, it ~ is also possible to produce, in addition to a 2-layer !~ pipe, pipe~ of other types which comprise, for examplel 3 or more layers by additionally incorporating fuxther layers as described in I. and/or II.
,, In a preferred embodiment, the multilayer pipes have a three-layer structure: component I./component II./compon-ent I~

2 ~ 21 !!
- 10 - O Z. 47~2 , In a multilayer pipe having an external diameter of 8 mm '2 and an overall wall thickness of 1 mm, the layer thick-nesses can be, for example, from the inside outwards, O.2 mm, 0.2 mm and 0.6 mm. Other layer~thickness distri-5 butions are also conceivable according to the invention, 2 for example with a relatively thick central layer of, for example, 0.4 mm.
q The plastic pipes according to the invention are prefer-ably employed for the transport of (petro)chemical ' 10 substances or in the motor transport sector for carrying -I brake, cooling and hydraulic fluids and fuel. A further use of the multilayer pipes is for the production of hollow articles, such as fuel tanks or filling nozzles, in particular for the motor vehiclP sector.
,~ .
15 The results ~hown in the examples were determined using the mea~urement methods below.
q The determination of ~he ~olution ~i8~08ity (relative viscosity ~r~ ) of the polyamides is carried out using a l 0.5 % strength by weight m-cresol solution at 25C in accordance with DI~ 53 727/ISO 307.

For the determination of the amino terminal grOUp8 / 1 g 3 of the polyamide~ is dis~olved in 50 ml of m-cresol at ~3 25C. The solution is titrated potentiometrically with perchloric acid.

25 For the determination of the carboxyl terminal group5 in the polyamide, 1 g of polycondensate is dissolved in 50 ml of benzyl alcohol under a nitrogen blanket at 165C. The dissolution time is a maxLmum of 20 minutes.
The solution is titrated with a solution of KOH in 30 eth~lene glycol (0.05 mol of ROH/l~ against phenol-phthalein until the colour change~.
~3 The determination oi the solutlon vi~co~ity (~iscosity index J) of the polyesters is carried out in a 0.5 ~

.~

:
:l~
. 2~:10~2~ `
- ll - O.Z. ~702 strength by weight phenol/o-dichlorobenzene solution (weight ratio 1:1) at ~5C in accordance with DIN 53 728/ISO 162~/5 - Part 5.

or the determination of the i~ocyanate group~, 6 g of component II. (polyester, isocyanate) are dissolved at 180C in a mixture of dichlorobenzene/dibutylamine (80:20 % by volume). The solution is titrated at 20C with 10 %
strength hydrochloric acid against bromophenol a~ in-dicator (DIN 53 185).
~:-..i The testing of the ease of mechanical ~eparation at the interface is carried out using a metal wedge (edge angle:
5 degrees; loading weight: 2.5 kg); in this test, it is ,~J attempted to separate the material interface layer to be tested. If separation takes place at the interface .~ 15 between the components, the adhesion ia poor. If, by contrast, the separation taXes plac~ wholly or partly within one of the two component~, good adhesion is present.
' ; The determi~atio~ of the diffu~ion of fuel components is carried out on pipes using a fuel mixture (fuel N15. 42.5 part~ by volume of i?sooctane, 42.5 parts by volume of toluene and 15 part~ ~y volume of methanol3 at 23C and 50 ~ atmospheric humidity. The sample~, having a length of 200 mm, are filled with the fuel mixture and are connected to a filled stock tank during the mea~urement.
Diffusion i~ determined as the loss in weight by diffu-,~ sion over time (measurement e~ery 24 hours). The unit indicated is the weight loss recorded per unit area, measured when the diffusion process ha~ achieved equi-.~ 30 librium, i.e. when the weight loss determined per 24 ~ hours no longer changes ~ith time.
~, ;. Examples denoted by letters are not according to the ;~ invention.
;,~, ^.,?
~,.
; :~

`
2 1 ~ 2 ~ :
- 12 - O.Z. 4702 Examples A. Component I. ~ -:
'~
PA 1: Polyamide 12 (~rsl: 2.1; 86.2 % Of the terminal groups are amino terminal groups; 50 mmol/kg of amino terminal group~; 8 mmol/kg of carbo~yl ter-minal groups ) ~:

PA 2: Polyamide 12 ~r~l 2.0; 86.2 % of the terminal groups are amino groups; 50 mmol~kg of amino ter-minal groups; 8 mmol/kg of carboxyl terminal groups; modified by means of 1~ ~ by weight of commercially available plasticiser) B. Component II.
:: ~
Z 1: Homopolybutylene terephthalate (J values 165 cm3/g;
VESTODUR~ 3000 - HULS ~G; NCO content = 0) Z 2: Homopolybutylene terephthalate (J value: 145 cm3/g;
VESTODUR~ 2000 - H~LS AG; ~CO content = O) :::
Z 3: Homopolybutylene terephthalate (J value: 115 cm3/g;
VESTODUR 1000 - H~LS AG; NCO content = O) : Z 4: Homopolyethylene terephthalate (POLYCL~AR~ TR 8fi -HOECHST AG; NCO content = ~
,, Z 5O Mixture o~ i a. 98 % by weight of homopolybutylene terephthalate ~ :~
(J value 115 cm3~g; VESTODUR~ 1000 - H~LS A&) ~, and b. 2 % by weight of a mixture comprising b.1. 50 % by weigh~ of a compound prepared from :
2 mol of i~ophorone diisocyanate and 1 mol of diethylene glycol, the bonding in each case !,, t:aking place via a urethane bond and the ~ 30 remaining NCO qroup~ being blocked by '~' ~J
21~2 - 13 - O. Z . 4702 capro- lactam, and . b. 2 . 50 % by weight of isocyanurate of i~ophorone diisocyanate (VESTANAI~ T 1890 - H~LS AG).
'ii 5 NCO yroup concentration in component II.: 0. 08 % by weight.

Z 6: Mixture of a. 96 % by weight of homopolybutylene terephthalate (J value 115 cm3/g; VESTODUR~ 1000 - HULS AG) :~ 10 and b. ~ ~ by weight of a mixture comprising b. 1. 50 % by weight of a compound prepared from ~l 2 mol of isophorone diisocyanate and 1 mol of diethylene glycol, the bonding in each case taking place via a urethane bond and the ~: remai~ing NCO groups being blocked by capro-lactam, and b.2. 50 % by weight of isocyanurate of isophorone : 20 dii~ocyanate (VEST~NAI~ T 13g0 - H~LS AG).
NCO gxoup concentration in component II.: 0.16 % by weight.

7: Mixture of ~:: a. 98 % by weight of homopolybutylene terephthalate (J value 115 cm3/g; VESTODUR 1000 - X~LS AG) and b. 2 % by weight of a mixture comprising b.l. 50 ~ by weight of a uretdione built up from in ~ :
each case two molecule3 of isophorone diiso~
~: 30 cyanate, the remaining NCO groups being blocked by caprolactam, and b~2. 50 ~ by weight of isocyanurate of isophorone :
diisocyanate (VESTANAq5 ~ 1890 - HULs AG). ~ ~
NCO group concentration in component II.: 0.10 ~iby ~ .
weight.

,~

~ ~ : :
/~ 2 ~ ~ 0 ~ 2 ~ o z . 4702 Z 8: ~ixture of a. 97 % by weight of homopolybutylene terephthalate (J value 115 cm3/g; VESTODUR 1000 - HULs AG) and b. 3 ~ by weight of a mixture comprising b.1. 40 ~ by weight of caprolactam-blocked isophor- :~
one diisocyanate and ~i b.20 60 % by weight of isocyanurate of isophorone diisocyanate, where the remaining NCO ~roups are blocked by cap:rolactam.
NCO group concentration in component II.z 0.15 % by ~eight.

Z 9: Mixture of a. 97 ~ by weight of homopolybutylene terephthalate (J value 115 cm3/g; VESTODUR 1000 - HULS AG) and ~ :
b. 3 ~ by weight of a mixture compri~ing b.l. 30 ~ by weight of a compound prepared from 2 mol of isophorone diisocyanate and l mol of butanediol, the bonding in each case taking -:
place via a urethane bond and the remaining :
: NCO groups being blocked by caprolactam, and -b.2. 70 % by weight of isocyanurate of isophorone diisocyanate (VESTANAT0 T 1890 - HULs AG). ~i NCO group concentration in component II.: 0.21 % by ~ :
: weight.

C. Production of the ~ultila~er pipefi ; ~~0 The pipes were produced on a bench extrusion line using a~a five-layer die (in the production of the three-layer ~ -pipe~, 2 channels remain closed~. The barrel temperatures :were 220C (PA 2), 230C (PA 1); 250C (Z l; Z 2; Z 3;
Z 4; Z 5; Z 6; Z 7; ~ 8; Z 9). The melt pressure measured at the end o~ the compounding extruder was greater than '!~160 bar fo:r all the moulding compositions. The layer ..., !~, . .
. ~ j a ~;~ 21~0 12 .,~ .
. .
- Z. 4702 thicknesses are, fxom the in~ide outwards: 0 . 2 mm;
h, O . 2 mm; 0 . 6 Table S Experi- Inner Inter- Oute~ Diff-lsion Mechanically separable ~t ment layer medlate layer [gld~m2] inter~ace - after storage layer at 23C / in fuel~

A PA 1 Z 1 PA 1 < 4 yes yes B PA 2 Z 2 PA 2 < 4 yes ~e~
~1 C PA 2 Z 4 PA 2 **) ye~ ~es D PA 2 PA 2 PA 2 100 no no ~: E PA 1 PA 1 PA 1 30 no no F PA 1 Z 3 PA 1 < 4 yes yes 1 PA 1 Z 5 PA 1 < 4 ~o no 2 PA 2 Z 5 PA 2 < 4 no no 3 PA 1 Z 6 PA 1 < 4 no ~o 4 PA 2 Z 6 PA 2 < 4 no no S PA 1 Z 7 PA 1 < 4 no no 6 PA 1 Z 8 PA 1 < 4 no no :
: 7 PA 2 Z 9 PA 2 ~ 4 no no .
,;, *) Stoxage at 23C for S day~ in standard fuel M 15 .~ 142.5 parts b~r volume of isooctane, 42~5 parts ~y : 25 volume of toluene and 15 parts by volume of meth~
anol ~
,~i ** ) not determined .
:~ . ~ .
';' :: :

: ' ..

~ : ' ~

Claims

1. Multilayer plastic pipe characterised in that it comprises I. at least one outer layer based on a polyamide moulding composition and II. at least one layer of a moulding composition based on a mixture of a. from 95 to 99 % by weight of a partially crystalline thermoplastic polyester and b. from 1 to 5 % by weight of a mixture of 1. from 30 to 70 % by weight of at least one compound containing two isocyanate groups and

2. from 30 to 70 % by weight of at least one compound containing more than two isocyanate groups, where the isocyanate groups originating from component II.b. are present in component II.
in a concentration of between 0.03 and 0.3 %
by weight, and the layers are adhesively bonded to one another.

2. Multilayer plastic pipe according to Claim 1, characterized in that at least 50 % of all the terminal groups present in the polyamide of compo-nent I. are amino groups.

3. Multilayer plastic pipe according to Claim 1, characterised in that the layer as described in II. is a moulding composition based on a mixture of a. from 96 to 98 % by weight of a linear partially crystalline polyester and b. from 2 to 4 % by weight of a mixture of compounds II.b,1. and II.b.2. containing isocyanate groups.

4. Multilayer plastic pipe according to Claim 1, characterised in that component II.b. comprises a mixture of 1. from 40 to 60 % by weight of at least one compound containing two isocyanate groups and 2. from 40 to 60 % by weight of at least one compound containing more than two iso-cyanate groups.

5. Multilayer plastic pipe according to Claim 1, characterised in that the isocyanate groups origi-nating from component II.b. are present in the layer as described in II. in a concentration of between 0.06 and 0.25 % by weight.

6. Multilayer plastic pipe according to Claim 1, characterised in that component II.b.1. is isophorone diisocyanate or a compound derived therefrom by reaction with itself or with diols.

7. Multilayer plastic pipe according to Claim 1, characterised in that component II.b.2. is an isocyanurate derived from isophorone diisocyanate.

8. Multilayer plastic pipe according to Claim 1, characterised in that component II.b.1. and/or II.b.2. contains a lactam-blocked isocyanate.

9. Multilayer plastic pipe according to Claim 1, characterised in that the plastic pipe comprises a plurality of layers as described in I. and/or II.

10. Use of the multilayer plastic pipe according to any one of Claims 1 to 9 for transport of (petro)chemical substances.

11. Use of the multilayer plastic pipe according to any one of Claims 1 to 9 for carrying brake, cooling or hydraulic fluids or fuel.

12. Use of the multilayer plastic pipe according to any one of Claims 1 to 9 for production of hollow articles.

13. Use of the multilayer plastic pipe according to any one of Claims 1 to 9 for production of filling nozzles or fuel tanks.