FR2719102A1 - Tube of multi-layer synthetic material, used e.g. for vehicle fuel - Google Patents

Abstract

Multi-layer tube of synthetic material, made by coextrusion, comprises, from inside to outside, a layer (I) of methyl ethyl pentene, an adhesive layer (II) of ethylene copolymer, acrylic acid and/or maleic anhydride, and a layer (III) of polyamide.

Description

The present invention relates to a plastic pipe for

  fluids existing in vehicles

  automobiles such as fuel or windshield washer fluid, engine coolant or even heat transfer fluid for the heating-air conditioning system

station.

  The pipes used today, when

  are no longer metallic, are essentially

  polyamide. This material has a number of disadvantages.

  nients, in particular due to the alcohol which is necessarily present in the fluids conveyed. In fact, alcohol has the primary effect of causing the material to swell, which destroys its dimensional characteristics and leads to losses of tightness or unacceptable stresses in the

  piping. In addition, alcohol dissolves some of the ingredients.

  driving health and trains them in the rest of

  the installation where they are a cause of fouling.

  To combat this drawback, it has been proposed to coat the inner wall of these pipes with a thin barrier layer, for example of polyolefin (polypropylene

in particular) by coextrusion.

  In other techniques, it has also been proposed to coat the internal face of this pipe with an EVOH (ethylene vinyl alcohol copolymer) for the well-known property of these bodies to form an effective barrier, in particular to organic solvents. However in the presence of alcohol the EVOH have a tendency to retain this alcohol and

especially methanol.

  We have also described products in which this layer is sandwiched between a thick polyamide

  outside and a fine polyamide inside.

  In the field of fuel tanks, work concerns the use of polyethylene which is a neutral material offering good resistance to alcohol. To further improve vapor tightness, the internal surface of the parison is treated to deposit a thin layer there.

  silica or fluorine. This technique seems to give satisfaction.

  faction but remains expensive today for an application to the realization of pipes which, moreover, must have other characteristics in particular as regards

  concerns mechanical strength and resistance to gravelling.

  The present invention intends to propose another pipe composition capable of conveying a liquid containing alcohol. This liquid can be fuel which contains an additional alcohol to decrease its auto-ignition power in place of lead today

  proscribed. This liquid can also be the washing liquid.

  ice or even coolant which may include

up to 50% glycol.

  To this end, the subject of the invention is therefore a plastic tube with several layers, produced by coextrusion intended in particular to transport a motor vehicle fuel which comprises, from the inside to the outside, a layer of methyl ethyl pentene, an adhesive layer of maleic acid or anhydride, and a layer

polyamide outer.

  The use of methyl ethyl pentene is primarily

  geuse because it constitutes an excellent barrier to alcohol

  and this in an inexpensive way. This material has the advantage

  level of good weldability to make either partitions-

  inside the pipeline, i.e. a connection

  ment with a connection device to be attached to the end of the pipe. In this regard, it will be indicated that an advantageous thickness of this inner layer will be of the order of 0.4 to 0.8 millimeters so that the assembly by welding to internal partitions or to a connection device in

end is possible.

  The adhesion of methyl ethyl pentene to the outer polyamide layer is carried out by a polyethylene, acrylic acid or maleic anhydride copolymer coextruded with the inner layer and over a thickness of the order of

0.2 mm.

  Finally, the polyamide outer layer (PA 12, 11, 6 or 6.6) is used essentially for its barrier function to hydrocarbons and as mechanical reinforcement and

  resistant to abrasive and gravel impact -

  swim. The pipe thus obtained has three coextruded layers: - inside a layer of methyl ethyl pentene 0.4 to 0.8 mm thick (for example the TPX product sold by the firm MITSUI), - an adhesive layer of polyethylene, acrylic acid and / or maleic anhydride copolymer about 0.2 millimeter thick, - and on the outside a polyamide layer 0.3 to 0.5 millimeter thick, which is considerably less than the pipes in polyamide in monolayer which are a lot

  thicker (around 1 mm).

  This product has high waterproofing characteristics. Indeed the achievement of the barrier function to fuel and alcohol by two materials allows the use of materials which are less expensive in total than

  material providing only the barrier to alcohols and hydrocarbons

  res. Furthermore, the choice of a methyl ethyl pentene as an internal layer does not preclude incorporating into it a charge of pulverulent material and in particular of graphite. The inner layer can then become conductive and provide protection against static electrical charges in the pipe.

Claims (2)

  1. Multilayer plastic tube manufactured by coextrusion intended to convey a motor vehicle fuel, characterized in that it comprises, from the inside to the outside, a layer of methyl ethyl pentene, a layer of adhesive copolymer of polyethylene, acrylic acid and / or maleic anhydride, and an outer layer of polyamide. 2. Tube according to claim 1, characterized in that the thicknesses of the layers are: - 0.4 - 0.8 mm for the layer of methyl ethyl pentene, - 0.1 - 0.2 mm for the layer of adhesive ,   - 0.3 - 0.5 mm for the polyamide layer.