CA2114506A1

CA2114506A1 - Multilayer plastic pipe

Info

Publication number: CA2114506A1
Application number: CA002114506A
Authority: CA
Inventors: Michael Boer; Hans-Dieter Herrmann; Hans Ries; Stefan Rober
Original assignee: Huels AG
Current assignee: Huels AG
Priority date: 1993-01-30
Filing date: 1994-01-28
Publication date: 1994-07-31
Also published as: BR9400383A; JPH06238844A; DE4302628A1; EP0609675A2; EP0609675A3

Abstract

Abstract:
Multilayer Plastic pipe A multilayer plastic pipe is disclosed. The pipe comprises an outer layer I made from a moulding composition based on a polyamide and a layer II adjacent to the outer layer. Layer II comprises a plasticiser-free polyvinylidene fluoride having a melt flow index of less than 14 g/10 min, measured in accordance with DIN 53 735 at 230°C and a load of 5 kg. The ratio of the thickness of layer II and the combined thickness of layer I and II
18 from 1-3 to 1:20. The multilayer pipe according to the invention has an extremely good resistance to and a good barrier action to diffusion by (petro)chemical substances, solvents and fuels, even at elevated temperatures. It is preferably used for the transport of (petro)chemical substances, for example in the motor transport sector, for carrying brake, cooling and hydraulic fluids and fuel.

Description

~ -~ H~1i3 Aktiengesellschaft 21~4~06 o.z. 4719 Patent Department Multila~er ~lastic ~i~e The invention relates to a multilayer plastic pipe comprising an outer layer I. made from a moulding com-position based on a polyamide, and a further layer II., ad~acent to the outer layer, made from a moulding com-position baised on polyvinylidene fluoride.

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 be resis-tant to high and low temperatures and mechanical stresses.

Single-layer pipes are not always capable of satisfying the neces~ary requirements. In the case of transport of, for example, aliphatic or aromatic solvents, fueli3 or the like, they exhibit considerable disadvantages, ~uch as a poor barrier action to the medium, undesired changes in dimension or inadequate resistance to mechanical stresses.

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). However, practical implementation of these proposals has shown that, although some disadvantages can be overcome, the overall property profile i8 still unsatisfactory.

French Patent 2 602 515 describes a two-layer pipe comprising an outer layer of nylon 11 and an inner layer of plasticised polyvinylidene fluoride. However, investi-gations have shown that the barrier action to the flowing medium is unsatisfactory.

In particular, permeation of methanol-containing fuels has only been reduced to an inadequate extent by meani3 of ' ji. ' ' - " ' . ' " ' ' .' ~ ' , . .

21~4~06 the abovementioned proposals.
Reduction in permeation by using novel intermediate layers is therefore of crucial lmportance because, in particular, the legally permitted emission values are constantly belng reduced.
The object of the invention was to develop a polyamide pipe having a good barrier action to the transported medium, in particular to methanol-containlng fuels, satisfactory dimensional stability and satisfactory resistance to mechanical stresses. In partlcular, the improvement~ achieved should also be retained at elevated temperatures.
Thus the present invention provides a multilayer plastic pipe comprlslng an outer layer I made from a mouldlng composltion based on a polyamlde, and a layer II adjacent to the outer layer, said layer II made from a moulding composition based on polyvinylidene fluoride, wherein layer II comprises a plasticiser-free polyvinylldene fluorlde having a melt flow index of less than about 14 g/10 min ~mea~ured in accordance with DIN 53 735 at 230C
and a load of 5 kg), and whereln the ratio of the thickness of layer II and the combined thickness of layers I and II. is from about 1-3 to about 1.20.
Suitable polyamides are primarily aliphatic homo- and copolycondensates. Examples which may be mentioned are polyamides ~nylons) 4.6, 6.6, 6.12, 8.10 and 10.10. Preference is given to polyamides 6, 10.12, 11, 12 and 12.12. [The numbering of the polyamldes correspond6 to the internatlonal standard, the first ~ ':

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2114~06 -2a- 23443-504 ~ :

number(s) indicating the number of carbon atoms in the starting diamine and the final number(s) indicating the number of carbon :
atoms in the dicarboxylic acld. If only one number is given, the :
starting materlal was an a1~-aminocarboxylic acid or the lactam .
derived therefrom (H. Domininghaus, Die Kunststoffe und ihre Eigenschaften [Plastics and their Propertiesl, page 272, VDI- ;~
Verlag ~1976)).] .

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` ' 211~06 - - 3 - O.Z. 4719 If copolyamides are used, these can contain, for example, adipic acid, sebacic acid, suberic acid, i~ophthalic acid or terephthalic acid as co-acid or bis(4~-aminocyclo-hexyl)methane,trimethylhexamethylenediamine,hexamethyl-enediamine or the like as co-diamine.

The preparation of these polyamides is known (for example D. B. Jacobs, J. Zimmermann, Polymerization Processe~, pp. 424-67; Interscienee Publishers, New York (1977);
DE-~ 21 52 194).

Other suitable poly~m~des are mixed aliphatic/aromatic polyeondensates, a~ described, for example, in US Patents 2,07i,250, 2,071,251, 2,130,523, 2,130,948, 2,241,322, 2,312,966, 2,512,606 and 3,393,210, and in Rirk-Othmer, Eneyelopedia of Chemieal Teehnology, 3rd Edn., Vol. 18, pages 328 and 435, Wiley & Sons (1982). Other polyconden-sates whieh are suitable as polyamides 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 moleeular weight (number average) of the polyamides i8 greater than 5,000, preferably greater than 10,000, eorresponding to a relative viseosity (~r~) in the range from 1.9 to 2.4.

The polyamides of the outer layer I. may eontain up to 40 % by weight of other thermoplastie~, 80 long as the latter do not affeet the propertie~ aeeording to the invention. Partieular mention may be made here of polyearbonate ~H. Sehnell, Chemlstry and Physics of Polycarbon~tes, Interscience Publishers, New York (1981)1, aerylonitrile-styrene-butadiene eopolymers (Houben-Weyl, Methoden der organisehen Chemie [Methods of Organie Chemistry], Vol. 14/1, Georg Thieme Verlag Stuttgart, pp. 393-406; Ullmanns Encyclop~die der teeh-nisehen Ch~m~e tUllmann' B Encyclopaedia of Industrial Chemistry]~ 4th Edition, Vol. 19, Verlag Chemie, Weinheim ; . ......... ., -, . . . . . . . .
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~ 4 - 2 ~ O 6 O.Z. 4719 (1981), pp. 279-284), acrylonitrile-styrene-acrylate copolymers (Ullmann~ Bneyelopadie der teehnisehen Chemie [ullmann~s Encyclopaedia of Industrial Chemistry], 4th Edition, Vol. 19, Verlag Chemie, Weinheim (1981), pp.
277-295), acrylonitrile-styrene copolymers (Ullmanns Eneyclopadie der teehnischen Chemie [Ullmann~s Encyclo-paedia of Industrial Chemistry], 4th Edition, Vol. 19, Verlag Chemie, Weinheim (1981) pp. 273 ff.) or poly-phenylene ethers (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 of the outer layer I. can be impaet-modified. Examples of suitable polymers are ethylene-propylene or ethylene-propylene-diene copolymers (EP-A-295 076), polypentenylene, polyoctenylene or random or block copolymers made from alkenyl-aromatic compounds with aliphatie olefins or dienes ~EP-A-261 748). N~ntion may furthermore be made of impaet-modifying rubbers:
eore/~hell rubbers having a tough, resilient core of (meth)aerylate, butadiene or styrene-butadiene rubber having glass transition temperatures T~ of ~ -10C, where the eore may be erosslinked. The shell ean be built up from ~tyrene and/or methyl methaerylate and/or further unsaturated monomers (DE-A 21 44 S28 and 37 28 685). The proportion of impaet-modifying eomponent should be seleeted 80 that the desired properties are not impaired.

~ayer II. eontains plastieiser-free polyvinylidene fluoride. The preparation and strueture of the polymer are known (Hans R. Rrieheldorf, H~ndbook of Polymer Synthesis, Part A, Publisher Mareel Dekker Ine., New York - Basle - Hong Xong, pp. 191 ff.; Runststoff Handbuch ~Plasties Handbookl, 1st Edition, Volume XI, Carl Hanser Verlag, Munieh (1971), pp. 403 ff.).

It is also possible for eopolymer~ based on polyvinylidene fluoride and containing up to 40~ by weight of other monomers to be present aceording to the invention. ~xamples which may be mentioned of sueh _ 5 _ 2 ~ 0 6 o z 4719 additional monomers are: trifluoroethylene, ethylene, propene and hexafluoropropene.

The polyvinylidene fluoride employed according to the invention ha~ a melt flow index of < 14 g/10 min, pre-S ferably from 5 to 13 g/10 min (DIN 53 735).

The thickness of layer II. is in the range from 0.05 to 0.2 mm, preferably from 0.1 to 0.15 mm. The pipe wall has an overall thickness in the range from 0.5 to 2 mm, preferably from 1 to 1.5 mm. The ratio between the thick-ness of layer II. and the thickness of I. and II. is from1:3 to 1:20, preferably from 1:4 to 1:10. The diameter of the pipe i8 in the range from 6 to 16 mm.

In addition to layer I. and the ad~acent layer II. in the multilayer pipes according to the invention, further layer~ may be applied to the inside of the pipe. An example which may be mentioned here is a layer of modi-fied polyvinylidene fluoride having significantly higher electrical conductivity than the polyvinylidene fluoride of layer II.

The moulding compo~itions for layers I. and II. may contain conventional auxiliaries and additives, such as, for example, flameproofing agents, stabilisers, proces~ing auxiliaries, visco~ity improvers, fillers, in particular those for improving the conductivity, pigments and the like. The moulding compositions of layer I. or of layers other than layer II. can also contain plasticisers or impact modifiers.

The multilayer pipes are produced in a known manner, for example as described above in the prior art. The pipes are preferably produced by coextrusion.

The multilayer pipes accordin~ to the invention have, even at elevated temperatures, extremely good resistance to and a good barrier action to diffusion by - 6 - 2 ~ 6 0 z 4719 (petro)chemical sub~tances, solvents and fuels. In addition, it is also possible to produce, in addition to a two-layer pipe, pipes of other types which comprise, for example, three or more layer~. Preference is given to multilayer pipe~ according to the invention in which layer II. has been rendered electroconductive. It is also possible to achieve good conductivity by incorporating a further polyvinylidene layer of high conductivity ad~acent to layer II. on the inside. Good electro-conductivity is achieved by adding up to 15% by weightof, for example, conductive black, carbon fibres or the like.

The plastic pipes accordinq to the invention are pre-ferably employed for the transport of (petro)chemical sub~tances or in the motor transport sector for carrying br~ke, cool$ng and hydraulic fluids and fuel. A further use of the multllayer pipes is for the production of hollow articles, such as fuel tanks or filling nozzles, in particular for the motor vehicle sector.

The results shown in the examples were determined using the measurement methods below.

The determination of the solution visco~ity (relative viscosity ~ ) of the polyamides is carried out usinq a 0.5% strength by weight m-cresol solution at 25C in accordance with DIN 53 727/IS0 307.

The determ~nPtion of the melt flo~ indes of the polyvinylidene fluorides i3 carried out in accordance with DIN 53 735 at 230C and under a load of 5 kg.

The determination of the deflection i~ carried out at 23C on a pipe with a length of 15 cm. The pipe is supported at two points 80 mm apart. The pipe is stressed from above with a weight of 40 N in the centre between the two supports. The deflection of the pipe is determined in mm (DIN 53 452).

7 - 2 ~ 0 6 o z. 4719 The determ;nation of the diffusion of fuel components is carried out on pipes using a fuel mixture (fuel FAM B:
25.35% by volume of isooctane, 42.25~ by volume of toluene, 12.675% by volume of diisobutylene, 4.225% by volume of ethanol, 15% by volume of methanol and 0.5% by volume of water) at 23C or at 60C and at 50% atmos-pheric humidity. The samples, having a length of 200 mm, are filled with the fuel mixture and are connected to a filled stock tank during the measurement. Diffuisiion is determined as a 108~ in weight by diffusion over time (measurement every 24 hours). The unit given is the weight 1088 recorded per unit area, measured when the diffusion process has achieved equilibrium, i.e. when the weight 1088 determined per 24 hours no longer changes with time.

Examples denoted by letters are not according to the invention.

~a ples~

A. Co ponent I.

20 PA lsi Hard polyamide 12 (~t.ls 2.1; plasticiser contents ~ ~
O) :', PA 2: Soft polyamide 12 (~r~S 2.1; plasticisers N-butylbenzenesulphonamide; plastici3er contents 15 partsi by weight, per 100 parts by weight of polyamide).

PA 3is Hard polyamide 12 (~r.1s 1.9; plasticiser content:
O) PA 4s Hard polyamide 6.12 (~r~lS 1.9; pla~ticiBer con-tent: 0) 0 B. Component II.

8 2~ o.z 4719 Z l: Hard polyvinylidene fluoride [melt flow index:
13 g/lO min; pla~ticiser content: 0; DYFLOR LE
(HULs AG)]

z 2: Soft polyvinylidene fluoride [melt flow index:
13 g/lO min; plasticiser: N-butylbenzene-sulphonamide; plasticiser content: 15 parts by weight per 100 parts by weight of polyvinylidene fluoride; DYFLOR~ LE (HULS AG)]

Z 3: Hard polyvinylidene fluoride [melt flow index:
8.5 g/10 min; plasticiser content: 0; DYFLOR~ EE
(H~LS AG)3 Z 4: Soft polyvinylidene fluoride [melt flow index:
8.5 g/10 min; plasticiser: N-butylbenzene-sulphonamide; plasticiser content: 15 parts by weight per 100 parts by weight of polyvinylidene :~
fluoride; DYFLOR~ EE (HULS AG)] ::

C. Production of the multilayer pipe~ .

Two-layer pipes (external diameter 8 mm, overall wall thickness 1 mm) are produced on a 5-layer pipe coextru-sion line in which 3 channels remain closed, at a haul-off speed of 20 m/min and a haul-off ratio of 2:1. The outer layer i~ produced using a 45 mm/25 D extruder (melt temperature 230C), and the inner layer is produced using a 25 mm/25 D extruder (melt tempe.rature 220C).

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Claims

1. A multilayer plastic pipe comprising an outer layer I
made from a moulding composition based on a polyamide, and a layer II adjacent to the outer layer, said layer II made from a moulding composition based on polyvinylidene fluoride, wherein layer II
comprises a plasticiser-free polyvinylidene fluoride having a melt flow index of less than about 14 g/10 min (measured in accordance with DIN 53 735 at 230°C and a load of 5 kg), and wherein the ratio of the thickness of layer II and the combined thickness of layers I and II is from about 1:3 to about 1:20

2. A multilayer plastic pipe according to claim 1, wherein the polyvinylidene fluoride in layer II has a melt flow index of from about 5 to about 13 g/10 min.

3. A multilayer plastic pipe according to claim 1, wherein the ratio of the thickness of layer II and the combined thickness of layers I and II is from about 1:4 to about 1:10.

4. A multilayer plastic pipe according to claim 1, wherein the plastic pipe comprises at least one further layer in addition to layers I and II.

5. Use of a multilayer plastic pipe according to claim 1, 2, 3 or 4 for the transport of (petro)chemical substances.

6. Use according to claim 5 for the transport of brake, cooling and hydraulic fluids and fuel.

7. Use of the multilayer plastic pipe according to claim 1, 2, 3 or 4 for the production of hollow articles.

8. Use according to claim 7 for the production of filling nozzles or fuel tanks in the motor vehicle sector.