GB2390658A

GB2390658A - Multilayer articles

Info

Publication number: GB2390658A
Application number: GB0216364A
Authority: GB
Inventors: Andrew Howard John Miller; Mark Cook; John Molloy
Original assignee: TFX Group Ltd
Current assignee: TFX Group Ltd
Priority date: 2002-07-13
Filing date: 2002-07-13
Publication date: 2004-01-14
Anticipated expiration: 2022-07-13
Also published as: GB0216364D0; GB2390658B

Abstract

A multi-layer article such as a fuel pipe comprises a barrier layer of ethylene-vinyl alcohol arranged between inner and outer layers of polyamide bonded directly to the barrier layer without intermediate adhesive layers.. The outer layer may be a homopolymer or copolymer of polyamide 6.12 or a homopolymer or copolymer of polyamide 6.10. The inner layer may be polyamide 6 or polyamide 6.12 or polyamide 6.10.

Description

1 2390658

MULTILAYER ARTICLES

This invention concerns improvements in or relating to multi-layer articles. The invention has particular, but not exclusive application to 5 multi-layer articles in the form of pipes for conveying fluids. More especially, the invention has application to pipes for use in automotive vehicles to carry fluids containing hydrocarbons such as fuel in liquid or vapour form.

10 It is already known to reduce the emission of hydrocarbons from fuel pipes by the provision of a barrier layer in the pipe, Fluoropolymers are commonly used as a barrier material but these are expensive and there are problems in obtaining an adequate bond between the known fluoropolymer materials and the other thermoplastic materials, usually employed to 15 provide the pipe with the required properties. Often modifications are made to the fluoropolymer and/or adjoining thermoplastic material to promote improved adhesion.

Alternatively, adhesives or 'tie layers' are used to bond together the 20 dissimilar barrier material with the other thermoplastic materials. This method can be disadvantageous because tie layers are often difficult to melt process and have limited properties, particularly to heat and fuels.

Also, manufacturing of the system with more layers is more complex and requires more expensive capital expenditure.

With both of the above examples, fuel pipes must be resistant to the effects of temperature, ozone, chemicals without delaminating or cracking. The tube must also be resistant to impact, burst and abrasion.

The present invention has been made from a consideration of the problems and disadvantages of the existing barrier materials and manufacture of multi-layer articles incorporating such materials.

5 More specifically, it is a desired aim of the present invention to provide a multi-layer article having good barrier and adhesion properties.

It is a further desired aim of the present invention to provide a multi-

layer article that can be manufactured in a simple manner without 10 adhesive layers to bond the different layers of the article.

According to the present invention there is provided a multi-layer article comprising a barrier layer of ethylene-vinyl alcohol (EVOH) arranged between inner and outer layers of polyamide wherein the outer layer is a 15 homopolymer or copolymer of polyamide 6.12 (hereinafter polyamide 6.12) or a homopolymer or copolymer of polyamide 6.10 (hereinafter polyamide 6.10) and the inner layer is polyamide 6 or polyamide 6.12 or polyamide 6.10 and wherein the inner and outer layers are bonded directly to the barrier layer without intermediate adhesive layers.

We have found that the combination of EVOH with polyamide 6.12 or 6.10 for the outer layer and polyamide 6 or polyamide 6.12 or polyamide 6.10 for the inner layer provides an article having excellent heat resistance, barrier properties to permeation by hydrocarbon, with good 25 adhesion between the layers.

Preferred materials are suitable for extrusion or moulding. Elongate articles, especially hollow pipes, can be produced by co-extrusion of the layers in a simple manner that facilitates manufacture and enhances 30 adhesion between the layers.

The inner and outer layers can be homopolymers of polyamide 6.12, but copolymers of 6.12 can be used. Also a combination of homopolymer and copolymers on both layers can also be used. Where copolymers of 5 polyamide 6.12 are used, the outer layer preferably contains a higher proportion of the 12 unit and more preferably at least 60% of the 12 unit.

The inner layer on the other hand may have any relative proportions of the 6 and 12 units.

10 Preferably, the EVOH copolymer of the barrier layer has an ethylene content of at least 32 mol To.

The inner layer may be non-conductive or conductive. Alternatively, a further conductive layer providing electrostatic discharge (ESD) may be 15 provided on the inside surface of the inner layer. Where a further conductive layer is provided it may be made of the same material as the inner layer to which it is attached.

Conductivity may be provided by the addition of conductive material to 20 the inner layer or the further layer. The conductive material may comprise particles of carbon or metal or other suitable conductive additives. Alternatively, the material may be made conductive by chemical modification. The material may also inherently be a conductive polymer. Preferably, the outer layer has a thickness in the range 0.1mm to 0.5mm, with a preferred thickness of 0.5mm.

Preferably, the barrier layer has a thickness in the range 0. lmm and 30 0.3mm with a preferred thickness of 0.2mm.

Preferably, the inner layer has a thickness in the range of 0.1 to 0.5mm with a preferred thickness of 0.3mm.

5 Where provided, the further conductive layer may have a thickness of at least 0.05mm with 0,1mm being preferred.

Preferably, the tensile modulus of the polyamide 6, polyamide 6.10 or polyamide 6.12 is in the range 300 to 1300 MPa.

Preferred properties in the finished article are: a) Tensile strength greater than 25 MPa.

b) Elongation at break greater than 150%, preferably 200%.

15 c) Comparison tension (derived from burst strength and dimensions) greater than 25N/mm2 d) No cracking under cold impact at a minimum of 40 C according to relevant industry standards e) Conductivity, where required The multi-layer articles according to the invention are particularly suitable for the construction of fuel pipes to provide resistance to permeation by hydrocarbons. It will be understood, however, that the multi-layer articles may have other uses, for example in the construction 25 of fuel tanks.

Various examples of fuel pipes according to the present invention will now be described in more detail.

Example 1

A fuel tube having an outer diameter of 8mm and an inner diameter of 6mm was made by co-extrusion of an inner layer of polyamide 6, an 5 intermediate barrier layer of EVOH and an outer layer of polyamide 6.12.

The inner layer had a thickness of 0.3mm, the intermediate barrier layer a thickness of 0.2mm and the outer layer a thickness of 0.5mm (total wall thickness lmm).

The intermediate barrier layer had an ethylene content of 32 mol To.

The polyamide 6 and polyamide 6.12 homopolymer employed for the inner and outer layers had a tensile modulus in the range 300 to 15 1300MPa. The resulting pipe had a tensile strength greater than 25MPa, an elongation at break greater than 150o, a comparison tension greater than 25N/mm2 and a cold impact resistance at -40 C.

The above-described tube provided excellent resistance to permeation by hydrocarbons and to zinc chloride. The tube was also resistant to de-

lamination. 25 Example 2

A fuel tube was made as in example 1 but with an inner layer made of polyamide 6.12 in place of polyamide 6. The polyamide 6.12 could be a homopolymer or copolymer.

! The resulting tube had similar properties to example 1.

Example 3

5 A fuel tube was made as in example 1 but with an additional conductive layer on the inner surface of the inner layer.

The conductive layer had a thickness of 0. lmm and was made of polyamide 6 ESD or polyamide 6.12 ESD.

The resulting tube had similar properties to example 1.

Example 4

15 A fuel tube was made as in example 2 but with an additional conductive layer on the inner surface of the inner layer.

The resulting tube had similar properties to example 2.

Example 5

25 A fuel tube was made as in example 1 but with a conductive inner layer made of polyamide 6 ESD in place of polyamide 6.

The resulting tube had similar properties to example 1.

Example 6

A fuel tube was made as in example 2 but with a conductive inner layer made of polaymide 6.12 ESD in place of polyamide 6.12.

The resulting tube had similar properties to example 2.

Example 7

10 Fuel tubes were made as in examples I to 6 but with polyamide 6.10 in place of polyamide 6.12.

The resulting tubes had similar properties.

15 The polymer materials employed in the multi-layer articles of the present invention may include additives to modify the properties, for example, any one or more of the layers may be toughened and/or plasticised and/or made semi-flexible. We may modify the properties of any one or more layers by the addition of a nancomposite material, in particular, but not 20 limited to, the EVOH of the barrier layer may include a nanoparticle material. Suitable nanoparticle materials are either inorganic minerals, such as clays or organic, such as carbon nanotubes. The nanoparticles may be incorporated into the polymer during the polymerization process or by melt compounding.

As used herein, the terms "outer layer" and "inner layer" are used to indicate the position of the layers relative to the barrier layer which they adhere directly without intervening adhesive layers and it will be appreciated they may form the outermost and innermost layers of the 30 finished article or one or more additional layers may be provided on the

outside of the outer layer and/or on the inside of the inner layer to provide the article with any desired properties for the intended use.

Claims

1. A multi-layer article comprising a barrier layer of ethylene-vinyl alcohol (EVOH) arranged between inner and outer layers of polyamide wherein the outer layer is a homopolymer or copolymer of polyamide 5 6. l 2 (hereinafter polyamide 6.12) or a homopolymer or copolymer of polyamide 6.10 (hereinafter polyamide 6.10) and the inner layer is polyamide 6 or polyamide 6.12 or polyamide 6.10 and wherein the inner and outer layers are bonded directly to the barrier layer without intermediate adhesive layers.

2. A multi-layer article according to claim 1 wherein the inner and outer layers are homopolymers of polyamide 6.12.

3. A multi-layer article according to claim 1 wherein the inner and 15 outer layers are copolymers of polyamide 6.12.

4. A multi-layer article according to claim 1 wherein the inner and outer layers are a combination of homopolymers and copolymers of polyamide 6.12.

5. A multi-layer article according to claim 3 or 4 wherein the outer layer includes a copolymer of polyamide 6.12 having a higher proportion of the 12 unit.

25 6. A multi-layer article according to claim 5 wherein the copolymer of polyamide 6.12 contains at least 60o of the 12 unit.

7. A multi-layer article according to any one of the preceding claims wherein the EVOH copolymer of the barrier layer has an ethylene content 30 of at least 32 mol Ho.

8. A multi-layer article according to any one of the preceding claims wherein the inner layer is non-conductive.

5 9 A multi-layer article according to any one of claims 1 to 7 wherein the inner layer is conductive.

10. A multi-layer article according to any one of the preceding claims wherein a further conductive layer providing electrostatic discharge 10 (ESD) is provided on the inside surface of the inner layer.

11. A multi-layer article according to claim 10 wherein the further conductive layer is made of the same material as the inner layer to which it is attached.

12. A multi-layer article according to any one of claims 9 to 11 wherein conductivity is provided by the addition of conductive material to the inner layer or the further layer.

20 13. A multi-layer article according to claim 12 wherein the conductive material comprises particles of carbon or metal or other suitable conductive additives.

14. A multi-layer article according to any one of claims 9 to 11 25 wherein the material of the inner layer or further layer is made conductive by chemical modification.

15. A multi-layer article according to any one of claims 9 to 11 wherein the material of the inner layer or further layer is an inherently 30 conductive polymer.

16. A multi-layer article according to any one of the preceding claims wherein the outer layer has a thickness in the range O.lmm to 0.5mm.

5 17. A multi-layer article according to any one of the preceding claims wherein the barrier layer has a thickness in the range O.lmm and 0.3mm.

18. A multi-layer article according to any one of the preceding claims wherein the inner layer has a thickness in the range of 0.1 to 0.5mm.

19. A multi-layer article according to claim 10 wherein the further conductive layer has a thickness of at least 0.05mm.

20. A multi-layer article according to any one of the preceding claims 15 wherein the polyamide 6, polyamide 6.10 or polyamide 6.12 has a tensile modulus in the range 300 to 1300 MPa.

21. A tube comprising a multi-layer article according to any one of the preceding claims.

22. A tube according to claim 21 having a tensile strength greater than 25 Mpa and an elongation at break greater than 150o.

23. A tube according to claim 21 or claim 22 having a comparison 25 tension (derived from burst strength and dimensions) greater than 25N/mm2. 24. A tube according to any one of claims 21 to 23 having substantially no cracking under cold impact at a minimum of -40 C.

25. A fuel pipe comprising a tube according to any one of claims 21 to 24. 26. A multi-layer article substantially as hereinbefore described with 5 reference to any one of Examples 1 to 7.