WO2001036187A1 - Multilayer pipe made of plastic material for transferring fluid such as fuel - Google Patents

Abstract

The invention concerns a multilayer pipe made of plastic material for transferring alcoholized fluid or fuel, in an internal combustion engine environment, comprising from inside outwards: an inner layer of a polyamide and polyethylene or polypropylene mixture; a polyvinyl alcohol layer; a polyamide layer including an impact modifier; an outer layer based on polyamide modified to be zinc-chloride resistant.

Description

 Plastic hose for the transfer of fuel-like fluids

In the automotive industry, fluid transfer lines fall into two categories: lines for high pressure fluids and lines for low pressure fluids. High-pressure fluids (brake fluid, fuel at the injectors, etc.) are still transported today through metal pipes, while low-pressure fluid pipes (fuel, coolant, air-conditioning liquid, windshield washer, ...) are more and more often made of synthetic material to obtain weight gain.

The plastic pipes must meet many requirements both with regard to their mechanical properties and their chemical properties with regard to their internal and external environment (impermeability to the transported liquid, chemical resistance with regard to these liquids and the external atmosphere, mechanical resistance to wear and abrasion, fire resistance, etc.). They must also be easily conformable and receive sealingly connection devices. Finally, they have to be produced at the lowest cost.

There are many pipes that more or less meet all of these requirements. In general, the degree of quality obtained is all the higher the more noble materials are used and therefore the price is high.

To find an acceptable compromise between performance and cost of the product, a person skilled in the art must attempt numerous experiments relating to numerous combinations of material, all the more so as the requirements of automobile manufacturers are increasingly severe.

To meet these technical and economic requirements, the invention relates to a multi-layer plastic tube intended for the transfer of alcoholic fluid or fuel, in the environment of an engine. internal combustion, from the inside to the outside:

- an inner layer of a mixture of polyamide and polyethylene or polypropylene, - a layer of polyvinyl alcohol,

- a polyamide layer comprising an agent modifying impact resistance,

- an outer layer based on polyamide modified to resist zinc chloride. In the tubes of the prior art, the internal layer is generally produced by a polyamide, for example PA6. This material has indeed excellent qualities with respect to the fluid conveyed when it is a fuel or an alcoholic fluid, with regard in particular to the extractability of the material. But a polyamide constitutes a barrier of average effectiveness to the alcohol component. In contrast, polyethylene is an effective barrier to this type of component. In addition, its price is several times lower than that of polyamide. In the invention, a polyamide polyethylene blend constitutes an advantageous compromise for constituting the internal layer of such a tube. This mixture is available on the market under the name ORGALLOY from the company ELF ATOCHEM. In addition to the cumulative properties of each of its components, such a layer, taking into account the cost difference between them, is more economical than a polyamide layer.

Preferably, the proportion by weight of polyamide polyolefin (polyethylene or polypropylene) will be 70/30 for the reasons explained below. Its thickness will be of the order of 0.4 - 0.5 mm.

The second layer of the multilayer tube according to the invention is formed by a polyvinyl alcohol and preferably by an ethylene vinyl alcohol (EVOH). This product is present on the market under the trade name EVAL from URARAY. The main quality of this product is to reinforce the barrier effect of the first layer with respect to the alcohol components of the fluid carried. In addition, its adhesion with the internal layer is achieved naturally by coextrusion, adhesion all the easier as the proportion of polyamide in one ORGALLOY is important. A thickness at most equal to 0.15 mm is sufficient.

The third layer according to the invention is a structural layer forming, so to speak, the mechanical reinforcement of the tube according to the invention. It is formed by a polyamide, for example a PA6 comprising an agent modifying impact resistance in a weight concentration of the order of 10 to 50% of the composition. This layer naturally adheres to the layer which is adjacent to it, that is to say the layer of EVOH by the very fact that it comprises a polyamide. We will choose its thickness at least equal to 0.3 mm and preferably between 0.3 to 0.6 mm. To perfect the tube, and in particular to increase its resistance to the external atmosphere, a last layer is applied to this reinforcing layer: this last layer is formed from a polyamide modified to resist zinc chloride. In fact, zinc chloride is an abundant compound in the snow removal salts of traffic routes. It has the effect of weakening the simple polyamide by hardening it and making it brittle. The modification consists essentially in producing a mixture of a polyamide copolymer such as PA6 and of a second thermoplastic polyamide or copolyamide comprising at least nine carbon atoms. This product is available on the market under the trade name SNIAMID PSB 162 D from the company RHODIA (ex company NYLTECH ITALIA). It is applied in a thickness of the order of 0.1 mm. It will be indicated to be complete, that the preceding layer forming the mechanical reinforcement of the tube is also a product available on the market manufactured by the same company and marketed under the trade name SNIAMID PSB 162 E. Its generic identification is PA6 / 6- 36.

For the purposes of tests carried out to verify the response of such a structure to the requirements for strength and permeability in force or which will soon be in force in the field of automobile construction (tests developed by manufacturers or CARB 95 level procedure 2), a tubing sample having the following characteristics was produced:

- internal layer in ORGALLOY LE 6000 with a thickness of 0.45 mm,

- first middle layer in EVAL with a maximum thickness of 0.15 mm,

- second middle layer or reinforcement layer made of SNIAMID PSB 162 E in a thickness at least equal to 0.3 mm,

- and outer layer in SNIAMID PSB 162 D with a thickness of 0.1 mm.

This sample satisfactorily met all the requirements of the above-mentioned tests, as regards therefore the permeability, the resistance and the thermal behavior in an engine compartment atmosphere of a motor vehicle, the low extractability of the material. conduct by the transferred fluid, and finally good resistance to external chemical agents such as zinc chloride.

In addition, the structure of a tube according to the invention has the advantage of being economical to manufacture since each of the layers is compatible with the layers which are adjacent to it without having to resort to intermediate adhesives.

Claims

1. A multilayer plastic tube intended for the transfer of alcoholic fluid or fuel, in the environment of an internal combustion engine, characterized in that it comprises from the inside towards 1 'outside: - an inner layer of a mixture of polyamide and polyethylene or polypropylene, - a layer of polyvinyl alcohol, - a polyamide layer comprising an agent modifying impact resistance, - an outer layer based on polyamide modified to resist zinc chloride. 2. Tube according to claim 1, characterized in that the thicknesses of the different layers are, from the inside to the outside, respectively of about 0.5mm; 0.1 to 0.15mm; 0.3 to 0.6mm; 0.1mm. 3. Tube according to claim 1 or claim 2, characterized in that the weight proportion between polyamide and polyolefin of the inner layer is about 70/30.