CA2167659A1

CA2167659A1 - Hollow part with a multi-layer wall structure and process for the production thereof

Info

Publication number: CA2167659A1
Application number: CA002167659A
Authority: CA
Inventors: Heinrich Eizenberger; Ernst Grigat; Hans-Gerd Driessen
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1995-01-24
Filing date: 1996-01-19
Publication date: 1996-07-25
Also published as: FI960302A; DE19502085A1; EP0723922A3; EP0723922A2; FI960302A0; JPH08294978A

Abstract

Hollow part with a multi-layer wall structure, characterised in that the wall structure consists, from the outside inwards, of layers of - solid polyamide, - foamed, preferably open-cell foamed polyamide, - solid polyamide or polyurethane and - optionally additionally solid polyurethane, wherein each of these layers is optionally applied in two or more plies.

Description

Le A 30 782-FC / KM/m/S-P 21 6 7 6 S 9 llollow Part with a multi-layer wall structure and Process for the production thereof This invention relates to a hollow part with a multi-layer wall structure and to a process for the production thereof.

Hollow parts, for example plastic tanks for storing liquids, in particular fuels and the like, are known. Polyamide or polyethylene are the most commonly used materials in this connection. For certain purposes, for example the storage of heating oil, an additional leakage safeguard is necessary in order to avoid environmental damage. This safeguard conventionally takes the form of a catch tray or a double tank wall. A double tank wall has an advantage over a catch tray if the tank is arranged underground or is located in a cellar, for example when renovating old buildings as a catch tray does not then have to be built around it.

Since double-walled tanks are often provided with leakage detection in order to indicate leakage of the inner tank wall while the outer tank wall retains the contents, it is necessary for the contents concerned, for example heating oil, or the leakage detection liquid to be able to flow through the layer between the two tank walls.

If used in the production of, for example, double-walled tanks, plastics are either used only in one layer (for example WO 8102562 or CH-A 440 134), wherein the other layer usually consists of concrete or stainless steel, or the layers are produced in two or more operations which differ in technique (for example US-A
4739895, EP-A 470 321, EP-A 520 978). Differing operations should be taken to mean, for example, thermoplastic shaping of a tank wall and brushing or sprayingwith epoxy resins after the insertion of films or mats.

Spacing materials which may be used are, for example, wire mesh (CH-A
440 134), tufted films (EP-A 470 321), packing paper (CH-A 618 658), non-woven fabrics (DE-A 658 971), resin-impregnated glass fibre mats (EP-A
520 978).

An essential feature for safety is also the mechanical stability of tanks. Systems which bring about a distinct increase in the strength of the tank walls are thusadvantageous.

LeA30782-FC 2167fiS9 The object was to provide a double-walled safety hollow part or hollow body, respectively, (for example tank) with the possibility of leakage indication of the inner tank wall, which part may be produced using a simple, uniform process and which additionally exhibits considerably improved mechanical strength in 5 comparison with single-walled tanks.

This object is achieved by developing hollow parts, for example tanks, with a multi-layer wall structure, characterised in that the wall structure consists, from the outside inwards, of layers of - solid polyamide, - foamed, preferably open-cell foamed polyamide, - solid polyamide or polyurethane and - optionally additionally solid polyurethane.

Each of these layers may be applied in two or more plies. According to the invention, the word "layer" designates the combination of uniform plies (uniform15 in relation to state, for example foam or solid, or to material, for example polyamide or polyurethane).

This structure ensures not only the necessary double-walled properties with the possibility of leakage detection, but is moreover very simple to produce. Thanks to the firm adhesion of the foam layer onto the inner and outer wall, there is a 20 considerable gain in strength of the overall structure with regard to mechanical loads. Thanks to the selection of strong, but nonetheless resilient materials, good resistance, in particular to impact or pressure, is ensured.

The present invention provides hollow parts, preferably tanks, with a multi-layer wall structure, characterised in that the wall structure consists, from the outside 25 inwards, of layers of - solid polyamide, - foamed, preferably open-cell foamed polyamide, - solid polyamide or polyurethane and - optionally additionally solid polyurethane, 30 wherein each of these layers is optionally applied in two or more plies.

LeA30782-FC 2167S~9 The hollow parts according to the invention may be used for the storage and/or transport of liquids, preferably flammable and/or toxic liquids, particularly preferably heating oil.

The hollow parts according to the invention may also be used to provide thermal 5 or mechanical insulation or shielding, for example as outer casings for motor bicycle exhausts.

The multi-layer hollow part structure according to the invention is intended fortanks with a capacity of between 1 l and 5,000 l, preferably of 500 l to 2,500 l. It is, in principle, feasible to produce larger or smaller tanks using this method.
10 The outer layer of the hollow part, preferably tank, according to the invention consists of polyamide.

For the purposes of the invention, polyamide is polyamide-12 (polylaurolactam), polyamide-6 (polycaprolactam) or copolyamides with 12 or 6 as the principal constituents. Polyamide-6 produced by activated anionic polymerisation, or 15 copolyamide produced by activated anionic polymerisation with polycaprolactam as the principal constituent is preferred.

Activated anionic polymerisation of lactams to yield polyamides is performed on an industrial scale in such a manner that, on the one hand, a solution of catalyst in lactam is produced and, on the other hand, a solution of activator in lactam, 20 wherein both solutions are conventionally of a composition such that combining them in an equal ratio yields the desired overall formulation. Other compositions may also be selected, for example adding concentrated activator to a lactam meltcontaining catalyst. Depending upon their compatibility, further additives may be incorporated into the activator, catalyst or optionally lactam melt.

25 Polymerisation proceeds by mixing the individual solutions to give the overall formulation at 80C to 200C, preferably at 100C to 140C.

Lactams which may be considered are cyclic lactams with 6 to 12 C atoms, preferably ~-laurolactam and particularly preferably E-caprolactam.

- -LeA30782-FC 2167659 For the purposes of the invention, the catalyst is a strong base, such as for example alkali metal or alkaline earth metal lactamate, preferably as a solution in lactam, particularly preferably sodium caprolactamate in ~-caprolactam.

For the purposes of the invention, the activator may comprise N-acyllactams or S acid chlorides or, preferably, aliphatic isocyanates, particularly preferably oligomers of hexamethylene diisocyanate. The activator may be used both as the pure substance and, preferably, as a solution, for example in N-methylpyrrolidone.

Further additives may be, for example, impact strength modifiers, flame retardants, nucleation auxiliaries, dyes, extending oils, stabilisers, surface finish improvers, 10 fillers or reinforcing agents or mould release agents.

According to the invention, the foam layer between the inner and outer solid wall consists of foamed polyamide.

For the purposes of the invention, polyamide foam is polyamide- 12 (polylaurolactam) or polyamide-6 (polycaprolactam) or copolyamides with 12 or 6 15 as the principal constituents produced by activated anionic polymerisation which has been foamed during polymerisation. Foamed polyamide-6 produced by activated anionic polymerisation is preferred.

Activated anionic polymerisation of lactams to yield polyamide foam is performedon an industrial scale in such a manner that, on the one hand, a solution of 20 catalyst and blowing agent in lactam is produced and, on the other hand, a solution of activator and blowing agent in lactam, wherein both solutions are conventionally of a composition such that combining them in an equal ratio yields the desired overall formulation. This is, however, not necessary. Other compositions may also be selected, for example adding concentrated activator to a 25 lactam melt containing catalyst. Depending upon their compatibility, the blowing agents and further additives may be incorporated into the activator, catalyst oroptionally lactam melt.

Polymerisation proceeds by mixing the individual solutions to give the overall formulation at 80C to 200C, preferably at 100C to 140C.

LeA30 782-FC 216 ~ C59 Lactams which may be considered are cyclic lactams with 6 to 12 C atoms, preferably laurolactam and particularly preferably -caprolactam.

For the purposes of the invention, the catalyst for polyamide foam is a strong base, such as for example alkali metal or alkaline earth metal lactamate, preferably 5 as a solution in lactam, particularly preferably sodium caprolactamate in -caprolactam.

For the purposes of the invention, the activator for polyamide foam may compriseN-acyllactams or acid chlorides or, preferably, aliphatic isocyanates. The activator may be used both as the pure substance and as derivatives, for example the urea 10 obtainable by reaction with lactam, or as a solution, for example in N-methylpyrrolidone.

Blowing agents which may be used according to the invention are vaporisable compounds or, preferably, compounds which elimin~te gas, hydrides being preferred, particularly preferably sodium borohydride.

15 Further additives may be, for example, impact strength modifiers, flame retardants, nucleation auxiliaries, dyes, extending oils, stabilisers, surface finish improvers, fillers or reinforcing agents and mould release agents.

The solid polyurethane layer preferably consists of a polyurethane material cont~ining urea groups. This is produced in the mould by combining a polyol 20 mixture and an isocyanate mixture.

The polyol mixture consists of:

50 to 95 wt.% of di- or more highly functional OH-terminated polyesters or polyester mixtures or, preferably, di- or more highly functional OH-terminated polyethers or polyether mixtures, or mixtures thereof, 25 5 to 50 wt.% of catalysts, chain extenders and additives such as, for example, lubricants and 2 to 5 wt.% of blowing agent, preferably water, LeA30782-FC 216765~

preferably with an overall OH value of the mixture of 100 to 500, particularly preferably of 220 to 370 (OH values determined to DIN 53 240).

The isocyanate mixture consists of aromatic di- or more highly functional isocyanates or of prepolymers thereof. Preferred substances are 4,4'-5 diisocyanatodiphenylmethane, prepolymers of 4,4'-diisocyanatodiphenylmethane, phosgenated aniline-formaldehyde condensation products together with mixtures thereof.

Preferred isocyanate mixtures have an NCO content of 20 to 38 wt.%, particularlypreferably of 25 to 34 wt.%.

10 The process according to the invention for the production of the hollow part, for example tank, according to the invention consists in rotating a mould, for example a mould as is conventionally used for the production of single wall cast poly~mide tanks, around two axes simultaneously and introducing in succession the mixturesfor the production of the individual plies, in succession from the outside inwards, 15 in such a manner that the following layer is in each case applied once the preceding layer has completely reacted. The mould temperature should be 120C
to 220C, preferably 150C to 180C. The polyurethane system may, as soon as the cast polyamide layer has completely reacted, be applied onto the still hot cast polyamide, but may also be applied after cooling and removal from the mould in a20 completely separate operation, for example at room temperature.

The tanks according to the invention may be used for the storage and/or transport of liquids, in particular of flammable and/or toxic and/or environmentally harmful liquids, oils etc..

The tanks according to the invention may be mechanically finished using the 25 methods conventional for plastics. Subsequent installation of a leakage indication system between the inner and outer tank wall is also possible The tanks according to the invention may be used for the storage and/or transport of fuels, for example petrol or diesel oil, for example in cars, goods vehicles or motor bicycles.

LeA30782-FC 216 ~ 6~
._ 7 The hollow parts according to the invention are also, for example, suitable for acoustic, thermal and/or mechanical insulation or shielding, for example as outer casings for motor bicycle exhausts, silencers etc..

ExamPle 5 A rectangular rotational mould with a capacity of 15 l is evenly heated to 200C
while being rotated around two axes.

The mould is then briefly halted, 600 g of a polyamide polymerisation mixture are introduced and rotation around two axes is immediately continued. The polyamide polymerisation mixture consists of 10 97.8 wt.% of caprolactam, 1.7 wt.% of catalyst (18 wt.% solution of sodium lactamate in e-caprolactam) and0.5 wt.% of activator (oligomer of hexamethylene diisocyanate as a 70 wt.%
solution in N-methylpyrrolidone).

After 5 minutes, polymerisation is complete. The mould is halted again and the 15 polyamide foam mixture (600 g) is introduced. As soon as the mixture has beenintroduced, rotation is again continued around two axes simultaneously.

After 7 minutes, foaming is complete. The mould is halted again and the reactionmixture (600 g) to produce the solid polyamide inner layer is introduced. As soon as the mixture has been introduced, rotation is again continued around two axes 20 simultaneously.

After a reaction time of 4 minutes, the part is removed from the mould.

A hollow part with a solid polyamide outer layer, an open-cell polyamide foam layer and a solid polyamide inner layer is obtained.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Hollow part with a multi-layer wall structure, characterised in that the wall structure consists, from the outside inwards, of layers of solid polyamide, foamed polyamide, solid polyamide or polyurethane.

2. Hollow part according to claim 1, characterised in that said open-cell polyamide is foamed.

3. Hollow part according to claim 1, including an additional inside layer of solid polyurethane.

4. Hollow part according to any one of claims 1 to 3, wherein each of said layers is applied in two or more plies.

5. Hollow part according to any one of claims 1 to 3, characterised in that the polyamide is polyamide-12 (poly-laurolactam) or polyamide-6 (polycaprolactam) or copolyamides with 12 or 6 as the principal constituents.

6. Hollow part according to claim 2, characterised in that the open-cell foamed polyamide is polyamide-12 (poly-laurolactam) or polyamide-6 (polycaprolactam) or copolyamides with 12 or 6 as the principal constituents produced by activated anionic polymerisation, which is foamed during polymerisation.

7. Hollow part according to any one of claims 1 to 3 or 6, characterised in that the solid polyurethane is produced in the mould by combining a polyol mixture and an isocyanate mixture.

8. Hollow part according to any one of claims 1 to 3 or 6, which is a tank.

9. Process for the production of the hollow part according to claim 1, characterised in that a mould is rotated around two axes simultaneously and the reactive melts for the production of the layers are introduced in such a manner that the following layer is in each case applied once the preceding layer has completely reacted and that the optional additional polyurethane layer may be introduced immediately thereafter or subsequently.

10. Use of the hollow part according to claim 1, as a storage container for oils and fuels.