Pipes and tubular conduits – Flexible – Distinct layers
Reexamination Certificate
2000-03-16
2001-10-16
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Flexible
Distinct layers
C138S140000, C138S141000, C138SDIG007
Reexamination Certificate
active
06302153
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related to a concurrently filed application entitled, “Multilayer Tube Based On Polyamides, For Transporting Petrol” the inventors being, Jean-Marc Durand, Jacques Thomasset, Joachim Merziger and Philippe Bussi, Attorney Docket Number ATOCM-169, based on priority French application 99/03214 filed Mar. 16, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to tubes based on polyamides for transporting petrol and more particularly to tubes for conveying petrol from the tank of motor vehicles to the engine and to the hoses for transporting hydrocarbons in service stations.
For safety and environmental protection reasons, motor vehicle manufacturers require petrol tubes to have mechanical characteristics of strength and flexibility and enhanced permeability-resistance characteristics. The tubes must have the lowest possible permeability to petrol products and to their additives, particularly methanol and ethanol.
Polyamides have all these properties, however, in order to have good low-temperature mechanical properties, polyamides must be plasticized. But plasticized polyamides are less impermeable to hydrocarbons than unplasticized polyamides, especially with respect to lead-free petrols.
Patent EP 0,731,308 describes a tube based on polyamides for transporting petrol. This tube comprises an inner layer made of a polyamide/polyolefin blend having a polyamide matrix and an outer layer made of a polyamide. A binder layer and a layer of an ethylene-vinyl alcohol copolymer (EVOH) may be placed between the inner layer and the outer layer.
It is already known from Patent Application EP 0,781,799 that in motor vehicles, under the effect of the injection pump, the petrol flows at high speed in the pipes connecting the engine to the tank. In certain cases, the friction between the petrol and the internal wall of the tube can generate electrostatic charges, the accumulation of which may result in an electrical discharge (a spark) capable of igniting the petrol, with catastrophic consequences (an explosion). It is therefore necessary to limit the surface resistivity of the internal face of the tube to a value of generally less than 10
6
ohms/square. It is known to lower the surface resistivity of polymeric resins or materials by incorporating conductive and/or semiconductive materials into them, such as carbon black, steel fibres, carbon fibres, and particles (fibres, platelets or spheres) metallized with gold, silver or nickel.
Among these materials, carbon black is more particularly used, for economic and processability reasons. Apart from its particular electrical conductivity properties, carbon black behaves as a filler such as, for example, talc, chalk or kaolin.
SUMMARY OF THE INVENTION
Thus, those skilled in the art know that when the filler content increases, the viscosity of the polymer/filler blend increases. Likewise, when the filler content increases, the flexural modulus of the filled polymer increases. These known and predictable phenomena are explained in “Handbook of Fillers and Reinforcements for Plastics”, edited by H. S. Katz and J. V. Milewski—Van Nostrand Reinhold Company—ISBN 0-442-25372-9, see in particular Chapter 2, Section II for fillers in general and Chapter 16, Section VI for carbon black in particular.
As regards the electrical properties of carbon black, the technical report “KETJENBLACK EC—BLACK 94/01” by Akzo Nobel indicates that the resistivity of the formulation drops very suddenly when a critical carbon black content, called the percolation threshold, is reached. When the carbon black content increases further, the resistivity rapidly decreases until it reaches a stable level (plateau region). It is therefore preferred, for a given resin, to operate in the plateau region in which a metering error will have only a slight effect on the resistivity of the compound.
The applicant has now discovered another multilayer tube based on polyamides, which has a very low permeability to petrol and has very good mechanical properties, while at the same time being electrically conductive in order to prevent any accumulation of electrostatic charges that might cause sparks.
The subject of the present invention is a tube comprising an inner layer and an outer layer, the inner layer comprising a polyamide/polyolefin blend having a polyamide matrix, this inner layer being filled with electrically conductive carbon black (electro.C), the outer layer comprising a polyamide.
More specifically, the present invention is a multilayered tube based on polyamides, characterized in that it comprises, in its radial direction, from the inside to the outside:
an inner layer formed from a polyamide or a polyamide/ polyolefin blend having a polyamide matrix, this layer containing a dispersed electrically conductive, carbon black filler, producing a surface resistivity of less than 10
6
&OHgr;/□,
an intermediate layer formed from a polyamide or a polyamide/ polyolefin blend having a polyamide matrix, this layer not containing electrically conductive carbon black or an electrically significant amount of this carbon black,
a binder layer,
a polyamide outer layer, the above layers adhering to each other in their respective contact region.
Preferably, the tube includes an additional layer made of EVOH placed between the polyamide outer layer and the intermediate layer. This additional layer ensures that the tube has a lower permeability to hydrocarbons and their additives.
With regard to the polyamide or the polyamide polyolefin blend of the inner layer or the intermediate layer, any polyamide may be used.
The term “polyamide” should be understood to mean products of the condensation:
of one or more amino acids, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic and 12-aminododecanoic acids or of one or more lactams, such as caprolactam, oenantholactam and lauryllactam;
of one or more salts or mixtures of diamines such as hexamethylenediamine, dodecamethylenediamine, metaxylylenediamine, bis(p-aminocyclohexyl)methane and trimethylhexamethylenediamine with diacids such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic and dodecanedicarboxylic acids; or mixtures of all these monomers, which lead to copolyamides.
Polyamide blends may be used. Advantageously, PA-6 and PA-6,6 and PA-12 are used.
With regard to the polyolefins of the polyamide polyolefin blend in the inner layer or the intermediate layer, the term “polyolefins” should be understood to. mean polymers comprising olefin units such as, for example, ethylene, propylene and 1-butene units, and their higher homologues.
By way of examples, mention may be made of:
polyethylene, polypropylene and copolymers of ethylene with &agr;-olefins, these products possibly being grafted by unsaturated carboxylic acid anhydrides, such as maleic anhydride or by unsaturated epoxides, such as glycidyl methacrylate;
copolymers of ethylene with at least one product chosen from (i) unsaturated carboxylic acids, their salts and their esters, (ii) vinyl esters of saturated carboxylic acids, (iii) unsaturated dicarboxylic acids, their salts, their esters, their half-esters and their anhydrides, and (iv) unsaturated epoxides, these ethylene copolymers possibly being grafted by unsaturated dicarboxylic acid anhydrides or unsaturated epoxides;
styrene/ethylene-butylene/styrene block copolymers (SEBS), optionally maleized.
Blends of two or more of these polyolefins may be used.
It is advantageous to use:
polyethylene;
copolymers of ethylene with an &agr;-olefin;
ethylene/alkyl (meth)acrylate copolymers;
ethylene/alkyl (meth)acrylate/maleic anhydride copolymers, the maleic anhydride being grafted or copolymerized;
ethylene/alkyl (meth)acrylate/glycidyl methacrylate copolymers, the glycidyl methacrylate being grafted or copolymerized,
polypropylene
In order to facilitate the formation of the polyamide matrix, and if the polyolefins have few or no functional groups able to facilitate the compatibilization, it is recommended to add a compatibilizer.
The compatibilizer
Atofina
Brinson Patrick
Millen White Zelano & Branigan P.C.
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