FR2660404A1 - Flexible pipe or conduit especially for conveying the fuel for a motor vehicle engine - Google Patents

Abstract

Flexible pipe or conduit comprising an inner layer of polyolefin and an outer layer of vulcanisable elastomer. The two said layers (1, 2) are joined together by a direct coextrusion process yielding a pipe in which the adherence of the two layers is not less than approximately 20 N cm<-1>. Application: pipe for conveying motor vehicle engine fuel.

Description

The subject of the invention is a flexible pipe or pipe, in particular, for conveying fuel on board a motor vehicle.

The tubes or pipes used for the delivery of fuel in motor vehicles must meet several requirements, the most imperative of which is that of a very low permeability to the liquid fuel transported and another of which is to have good resistance to engine environment, that is to say among other things at the same time at the same time at the same time to the temperature, to the projections of oil, to the emissions of ozone, ... etc. The first requirement is to reduce as much as possible the losses of fuel by diffusion of the latter to the outside of the piping or pipe that it passes through, on the one hand, as well as to reduce the odors of fuel. gasoline in the passenger compartment of the vehicle, on the other hand, while the second requirement mentioned is, additionally, directly related to the operational safety of the vehicle. Also have already been proposed pipes comprising an outer layer relatively resistant to the engine environment, associated with an inner barrier layer relatively tight to the fuel transported.

But the embodiments known hitherto are not entirely satisfactory from the economic point of view, either because they make use of high-cost materials, such as fluorinated rubbers to form the inner layer ensuring low permeability to fuel, or because 'they make use of materials requiring the implementation of expensive manufacturing processes, or again for these two reasons.

Neither are they entirely satisfactory from a technical point of view because of the generally insufficient adhesion between the two layers. To overcome this latter drawback, it has already been proposed to combine a relatively thin inner layer of polyolefin with at least one outer layer of elastomer by interposing between the two layers a third layer adhering well to these two materials under the combined effect of the heat and pressure. But the cost price of a pipe or pipe thus manufactured is generally prohibitive for usual applications in the field of the automotive industry.

The problem therefore arises of providing a pipe, tube or flexible pipe, in particular for supplying an automobile engine with fuel, which is both of simple structure and manufacture, of low cost. returns and which satisfies the aforementioned conditions, of very low -permeability to the transported fuel and resistance to the engine environment.

This problem is solved, according to the invention, by the direct coextrusion of a polyolefin chosen from high molecular weight polyethylenes to form the inner layer of the pipe with a vulcanizable elastomer chosen from Nitrile-PVC rubbers or
EPDM to form the exterior cladding.

There is thus obtained, according to the invention, and surprisingly, a fuel transport tube or pipe with very low permeability to the transported fuel and good characteristics of resistance to the engine environment, notwithstanding the fact generally accepted in the art. the inability to directly adhere a polyolefin and an elastomer.

A flexible pipe or pipe for conveying fuel for a motor vehicle according to the invention, comprising an inner layer of polyolefin chosen from those exhibiting low permeability to fuel and at least one outer layer of vulcanizable elastomer is characterized in that said layers are joined together by a direct coextrusion process providing an adhesion of the two said layers which is not less than about 20 Nom 1.

In a first embodiment, the pipe or pipe is a tube without reinforcement, while in an alternative embodiment comprising a textile reinforcement, or of another material, said reinforcement is additionally protected by a third layer of material added, for example, in recovery.

In a preferred embodiment of the invention, the inner layer is made of a polyolefin having the characteristics indicated in Table I, and the outer layer is made of EPDM, having the characteristics indicated in Table II.

TABLE I
Material characteristics of the inner layer
Tensile strength: MPa = 16
Elongation at break:% = 970
Modulus of elasticity: MPa = 400
High flow threshold
stress: MPa = 19.3
al # length:% = 11.4
Low flow threshold
stress: MPa = 12.8
elongation: a = 83
Shore hardness: Shore D = 63
Brittle temperature: OC = less than -400C
Heat resistance at 700C: hours greater than 168 h
Heat resistance at 10,000: hours greater than 168 h
TABLE II
Characteristics of the EPDM material of the outer layer
Hardness: Shore A 65 to 85
Tensile strength: MPa greater than 7
Elongation at break:% greater than 150
100% stress: MPa greater than 1.5
Residual strain in
compression:% less than 50
temperature 1000C - time 70 h
Temperature resistance at 700C; hours greater than 168 h
Temperature resistance at 1000C: hours greater than 168 h
Ozone resistance hours greater than 72 hours
200 pphm
Chemical resistance: water, base, alcohol, acid, antifreeze
Brittle temperature: OC less than -400C
In another embodiment, said first inner layer is made of polyolefin while the outer layer is of nitrile-PVC rubber, having the characteristics indicated in Table III.

TABLE III
Material characteristics of the outer layer
Nitrile-PVC rubber
Hardness: Shore A 60 to 85
Tensile strength: MPa greater than 10
Elongation at break:% greater than 200
100% stress: MPa greater than 1.5
Residual strain: 96 less than 45
in compression 22 h, 700C
Temperature resistance at 700C, hours greater than 168 h
Temperature resistance at IOOOC, hours greater than 168 h
Ozone resistance, hours greater than 48 hours
200 pphm
Chemical resistance water, oil, grease
fuel
Brittle temperature: OC less than -200C
Other characteristics and advantages of the invention will become apparent from the following description, made with reference to the appended drawing, in which:
- Figure 1 is a cross-sectional view of a fuel transport tube according to the invention; and
- Figure 2 is a cross-sectional view of a fuel transport pipe 1 according to the invention.

Reference is firstly made to FIG. 1 which shows a tube T1 according to the invention comprising an inner layer 1 of polyolefin, more precisely of polyethylene, with a thickness of the order of 0.5 to 1 mm and a layer outer 2, in EPDM, with a greater thickness of the order of two to three times that of the inner layer.

The characteristics of these materials are shown in Tables I and II below.

TABLE I
Material characteristics of the inner layer
Tensile strength: MPa = 16
Elongation at break:% = 970
Modulus of elasticity: MPa = 400
High flow threshold
stress: MPa = 19.3
elongation:% = 11.4
Low flow threshold
stress: MPa = 12.8
elongation:% = 83
Shore hardness: Shore D = 63
Brittle temperature: OC = less than -400C
Heat resistance at 700C: hours greater than 168 h
Heat resistance at 1000C: hours greater than 168 h
TABLE II
Characteristics of the EPDM material of the outer layer
Hardness: Shore A 65 to 85
Tensile strength: MPa greater than 7
Elongation at break:% greater than 150
100% stress: MPa greater than 1.5
Residual strain in
compression:% less than 50
temperature 1000C - time 70-h
Temperature resistance at 700C; hours greater than 168 h
Temperature resistance at 1000C: hours greater than 168 h
Ozone resistance: hours greater than 72 hours
200 pphm
Chemical resistance: water, base, alcohol, acid, antifreeze
Brittle temperature: OC less than -400C
The layers 1 and 2 are joined together during the manufacture of the tube by direct coextrusion providing an adhesion of the two said layers which is not less than 20 Ncm
The pipe T2 according to the invention, shown in Figure 2, differs from the tube T1 shown in Figure 1 by the presence of a reinforcement 3 of textile threads, arranged on the layer 2 and which, after its installation, is additionally protected by an added layer 4, for example, in recovery.

Given the very low permeability values of the polyolefin to fuel, for example of the order of 0.5 g / hm for a reference fuel
(ATSMC + 15% methanol), that is to say a value which is substantially half of that corresponding to the fluoroelastomers generally used for this type of pipe, the desired result is obtained using a tube or pipe according to the invention in a manner that is both simple and safe.

The tests carried out have also shown that the outer layer of EPDM, which is a vulcanizable elastomer with good resistance to the engine environment, adheres satisfactorily to the polyolefin after direct coextrusion, the adhesive strength measured being of the order of 30 Ncm 1, which is excellent in absolute value and in relative value, compared to the adhesion of 12
Ncm 1 obtained for fluoroelastomers.

In another embodiment, the outer layer 2, coextruded directly with the inner layer 1, is made of nitrile-PVC rubber having the characteristics indicated in Table III below, the inner layer 1 being made of a high molecular weight polyethylene identical to that described. above. It is observed that an adhesion of the order of 35 Ncm 1 is obtained for the directly coextruded layers 1 and 2.

TABLE III
Material characteristics of the outer layer
Nitril rubber e-PCV
Hardness: Shore A 60 to 85
Tensile strength: MPa greater than 10
Elongation at break:% greater than 200
100% stress: MPa greater than 1.5
Residual strain:% less than 45
in compression 22 h 700C
Temperature resistance at 700C, hours greater than 168 h
Temperature resistance at 1000C, hours greater than 168 h
Ozone resistance, hours greater than 48 hours
200 pphm
Chemical resistance water, oil, grease
fuel
Brittle temperature: OC less than -200C

Claims (7)

1. Pipe or flexible pipe comprising an inner layer of polyolefin and an outer layer of vulcanizable elastomer, characterized in that the two said layers (1, 2) are joined together by a direct coextrusion process. 2. Pipe or flexible pipe according to claim 1, characterized in that the adhesion of the two said layers (1, 2) is not less than about 20 Nom 1. 3. Pipe or flexible pipe according to claim 1 or claim 2 for transporting fuel from a motor vehicle engine, characterized in that it is devoid of reinforcement and in that the inner layer (1) is in a material having an absolute permeation rate relative to a reference fuel (ATSMC + 15% methanol) of the order of 0.5 g / hm2. 4. Pipe or flexible pipe according to claim 1 or claim 2, for transporting fuel from a motor vehicle engine, characterized in that it comprises a textile reinforcement (3) or another material disposed on the layer (2) coextruded with the inner layer (1) and in that this reinforcement (3) is protected by a third layer (4) attached, for example, in recovery. 5. Pipe or flexible pipe according to any one of the preceding claims, characterized in that the inner layer (1) is made of high molecular weight polyethylene and in that the outer layer (2) is made of EPDM. 6. Pipe or flexible pipe according to any one of claims 1 to 4, characterized in that the inner layer (1) is made of high molecular weight polyethylene and in that the outer layer (2) is made of nitrile-PVC rubber. . 7. Pipe or flexible pipe according to any one of the preceding claims, characterized in that it results from the direct coextrusion of at least two layers (1, 2) chosen one from polyolefins having substantially the following characteristics: Tensile strength: MPa = 16 Elongation at break:% = 970 Modulus of elasticity: MPa = 400 High flow threshold stress: MPa = 19.3 elongation:% = 11.4 Low flow threshold stress .MPa = 12.8 elongation:% = 83 Shore hardness: Shore D = 63 Brittle temperature: OC = less than -400C Heat resistance at 700C: hours greater than 168 h Heat resistance at 1000C: hours greater than 168 hours to form the inner layer (1); and a vulcanizable elastomer chosen from EPDMs having substantially the following characteristics: Hardness: Shore A 65 to 85 Tensile strength: MPa greater than 7 Elongation at break:% greater than 150 100% stress: MPa greater than 1.5 Residual strain in compression:% less than 50 temperature 1000C - time 70 h Temperature resistance at 700C; hours greater than 168 h Temperature resistance at 1000C: hours greater than 168 h Ozone resistance: hours greater than 72 hours 200 pphm Chemical resistance: water, base, alcohol, acid, antifreeze Brittle temperature: OC less than -400C or a nitrile rubber ~ PIC having substantially the following characteristics: Hardness: Shore A 60 to 85 Tensile strength: MPa greater than 10 Elongation at break:% greater than 200 100% stress: MPa greater than 1.5 Residual strain:% less than 45 in compression 22 h 700C Temperature resistance at 700C, hours greater than 168 h Temperature resistance at 1000C, hours greater than 168 h Ozone resistance, hours greater than 48 hours 200 pphm Chemical resistance water, oil, grease fuel Brittle temperature: OC lower than -200C to form the outer layer (2).