FR2753654A1 - Flexible composite material band for sheathing automobile cable bundles - Google Patents

Abstract

A flexible composite having at least two material layers joined together, one being non-shrinkable and the other being dimensionally unstable or prestressed in an orientation transverse to the longitudinal direction. The two layers remain intimately joined during deformation of the composite. Also claimed is the sheathing of a bundle of wires by forming the composite around the bundle by heat shrinking of the composite.

Description

Composite material, in particular for sheathing electrical wiring
The present invention relates to a new complex material intended for sheathing cables, in particular electric cables used in motor vehicles.

 Sheathing materials are known which are used to hold bundles of electrical wires in the field of automobile construction. I1 are generally adhesive tapes which are wrapped around the bundle, polyethylene foam strips associated or not with reinforcing layers which are folded around the cables or else split corrugated sheaths in which the wires are introduced. These various types of materials however have drawbacks either in terms of expected performance, or in terms of their use and their placement around the bundles of wires.

 The wrapping of an adhesive tape requires either a manual operation with a significant labor time, or the use of bulky and complex machines; moreover, the adhesive tapes do not always have sufficient stability and are poorly resistant to high temperatures, for example when placed in the engine compartment.

 The sheaths obtained from a strip of cross-linked polyethylene foam with closed cells are faster to manufacture if you have a sheathing machine and can be welded, which gives them a generally satisfactory seal. However, they require repeated handling of the harness and do not meet the specifications for use in the engine compartment.

 The corrugated sheaths can be made of polyamide, which gives them good temperature resistance. However, they have a poor seal due to the slot which cannot be closed, the radius of curvature is often limited, and the risk of damaging the cable insulation is extremely high. There are also problems due to the angular parts of this type of sheath which can injure operators. It should also be noted that this type of sheath can create parasitic noise due to the lack of maintenance of the wires inside the sheath.

 Among the materials commonly used, the products which are easy to use are not suitable for use in areas of high temperature and, conversely, the heat-resistant materials are delicate to handle and risk damaging the wires. In addition, it was interesting to find a material which made it possible not to use complex machines in the harness assembly workshop.

Subject of the invention
The present invention aims to provide a composite sheathing material presented in the form of a strip and capable of spontaneously becoming substantially in the form of a sheath under the effect of an external means.

 According to the invention, a strip of a flexible laminated composite or complex is proposed comprising at least one sheet of a first stable material, that is to say not shrinkable in any of its longitudinal or transverse directions or orientations, intimately linked to a sheet of a second material capable of shrinking in the transverse direction of the strip under the effect of an external means, said complex thus having the property of passing from a planar structure to a substantially cylindrical structure under the effect said external means.

 The term “intimate bond” means a bond which is not broken during or after the transformation of the planar structure towards the substantially cylindrical structure.

 This complex finds its application for example to form a sheath around a bundle of wires, in particular bundles of electric wires in automobiles.

Description
The laminated complex strip according to the invention comprises an intimate association of a first dimensionally stable layer and of a second dimensionally metastable or prestressed layer according to an orientation. If, by a determined means, instability is reached or the prestress of the second layer is broken, the dimension of the latter changes in a lasting manner and causes a deformation, also lasting of the strip of laminated complex, substantially analogous to the unsustainable deformation of a bimetallic strip under the effect of heat.

 The judicious choice of the constituent materials of the laminated complex makes it possible to obtain a flat strip which, under the effect of a determined means such as for example infrared radiation, will conform into a cylinder and keep this shape durably after the end of the action of said means.

 Such a laminated complex finds its application in the industry in the field of cladding of wire bundles: a strip of complex placed under a set of wires has the ability to wrap around the bundle under the effect of a means outside to form a protective sheath.

detailed description
As indicated above, the strip of laminated complex comprises at least a first layer of a flexible material conformable and stable in its dimensions, intimately associated on one of its faces with a layer of a second material also flexible and conformable but metastable or prestressed across the width of the strip.

 The first layer of materials must be flexible and conformable, preferably products based on synthetic polymers are chosen, such as, for example, polypropylene, cross-linked polyethylene, polyurethane or PVC foams, polyester or polypropylene nonwovens. It is also possible, according to the desired specifications, to use felts, felts, needles or flexible fabrics, on the sole condition that they are stable in their dimensions, that is to say not retractable under the action in any way.

 The second layer constituting the complex must be of the prestressed type or unstable in its dimensions. We choose to achieve this layer preferably films which have the property of shrinking under the effect of heat essentially along only one of their dimensions, this dimension being placed transversely to the length of the strip of complex. Among the materials suitable for carrying out the invention, mention may be made of heat-shrinkable films of polypropylene, polyethylene, polyester or PVC.

One can also use wide mesh fabrics or fabrics whose warp threads are stable in their dimension and the retractable weft threads, taking care to intimately fix the fabric on the first layer of the complex so that the threads weft are across the width of the bands. The preferred materials for carrying out the invention are heat-shrinkable polypropylene films having a shrinkage rate of between 5 and 25% in one direction and less than 3% in the other direction.

 The most commonly used means of shrinking is heat (obtained either by hot air or by infrared radiation) due to the use of heat-shrinkable films which are easily found on the market. One could also use fabrics comprising, in one direction, threads capable of shrinking under the effect of water and then causing retraction (and consequently the formation of the sheath) by means of a spray of water.

 According to the invention, the two laminated layers of the complex must be intimately linked so that the retraction of one of the layers causes the formation of the cylinder: it is therefore essential that the bonding force of the two layers is high and in particular much greater than the flexural strength of the dimensionally stable layer. To achieve this connection, any means compatible with the materials of each of the layers and capable of forming a permanent connection can be used, such as pressure-sensitive adhesives, one or two-component adhesives or close spot welding processes. . Among these different means, pressure-sensitive adhesives are preferred, in particular based on acrylic components, or adhesives based on cyanoacrylates which allow a solid and permanent bond of the two layers of the complex.

According to the invention, the complex finds its application in the field of sheathing of beams, in particular bundles of electric wires installed in automobiles.
To obtain a beam sheath, a strip whose width is equal to approximately 1.2 to 1.5 times the perimeter of the sheath to be obtained is cut from the laminated complex described above, taking care to coincide the retractable orientation of the complex with the transverse direction of the strip. The strip is then placed (the length of which is of course adapted to that of the beam to be protected) under the bundle maintained on the mounting table, the heat-shrinkable face of the strip being opposite the wires, then the means is activated (generally a heat source from an infrared emitter) causing the retractable layer to retract, and consequently the strip to be wrapped around the beam.

 If necessary, for example if it is desired to obtain a sealed sheath, it is possible to weld the two edges of the sheath by means of known systems of heat sealing or bonding.

 Another way of using the strip of complex consists in first forming the sheath by the effect of the means causing the retraction of the sensitive layer, then, independently of the device for shaping the sheath, introducing the beam by the longitudinal slot of the sheath. Subsequent welding of the edges of the sheath finally makes it possible to obtain a perfectly protected beam.

 The drawings in the appendix and the examples of embodiments which follow make it possible to better understand the invention and its industrial application.

The present invention is described for a preferred embodiment of the invention and with reference to the accompanying drawings in which
FIG. 1 is a cross-sectional view of the composite according to the present invention,
FIG. 2 is a plan view of a variant of the composite of FIG. 1,
FIG. 3 is a view in longitudinal section of the composite comprising transverse and parallel incisions,
FIG. 4 is a view of the composite with heating means before and after transformation,
- Figure 5 is a representation of an application in the form of a sheath.

 FIG. 1 represents a cross section of the elementary laminated complex according to the invention, in which there is a dimensionally stable layer 1, an unstable prestressed layer 2 and a layer 3 ensuring an intimate connection between layers 1 and 2.

 2 shows a plan view of a strip composed of a stable layer 1 on which has been fixed the unstable layer which is a fabric comprising transverse son (weft for example) retractable 4 and longitudinal son (warp for example) 5 stable in size.

 FIG. 3 represents the longitudinal section of a strip of laminated complex according to the invention comprising a heat-shrinkable film bonded to a thermally stable layer of felt, and in which parallel transverse incisions 6 of the retractable layer 2 have been made in order to remove any risk of tension in the direction of the length of the sheath during the shaping phase by retraction of the layer 2.

 FIG. 4 shows the mode of transformation of a strip of material according to the invention, the shrink film 2 being placed against the bundle of wires 7, said strip being wound alone around the bundle under the effect of the heat source 8.

 FIG. 5 represents an advantageous application of the strip of laminated complex according to the invention in which a part of the length of the strip intended for forming the sheath is slit so as to obtain, after retraction, a sheath capable of protecting a bundle of wires comprising a derivation.

Examples of realization
2
1) The coating is first carried out at the rate of 50 g / m2 of an acrylic-type mass in the solvent phase on a 40 μm film of polypropylene treated with Corona and heat-shrinkable to less than 2% in an orientation and to approximately 15 at 20% according to the perpendicular orientation.

The film thus adhesive-bonded is glued onto a nonwoven felt of
2 polyester 1 mm thick and density 15Og / m2 (supplied by the company NTI under the reference N PS 157).

 The complex thus obtained is then cut into strips so that the orientation of the retractable direction is transverse to the length of the strip.

 Such a strip, cut into a width of 8 cm and heated to a temperature of 175 "C for a residence time of 30 seconds, conforms itself to a cylindrical sheath. This sheath, wound around a bundle of wires can then be heat-sealed along the longitudinal slit by means of a hot air or ultrasonic device and makes it possible to obtain a bundle of sheathed wires capable of withstanding severe conditions of thermal environment. can be further improved by choosing flame retardant constituents (for example the nonwoven layer, or the adhesive mass): the sheaths thus obtained can then be used in the engine compartment of automobiles.

 2) According to a second embodiment, the laminated complex is prepared from a sheet of polypropylene foam with closed cells 2 mm thick and with a density of 35 kg / m3 on which an acrylic mass is coated in solvent phase (AGX / P from the company MATEI to which 0.4% of a crosslinking agent is added) at a rate of approximately 50 g / m2, and a heat-shrinkable PVC film of 35 clam thickness, shrinkable to be assembled on the adhesive side about 20% in one direction and less than 5% in the perpendicular direction.

 The complex thus obtained is cut into strips 5 cm wide, the most retractable orientation of the PVC film being in the direction of the width of the strip. Such a strip, placed under a bundle of wires and then heated using a hot air device, wraps itself around the bundle to form a sheath. This can then be heat sealed to provide good protection for the wires.

 3) According to a third embodiment, a sheet of polyurethane foam with open cells, 3 mm thick and with a density close to 20 kg / m3 is used, on which a biaxially oriented polypropylene film of 15 μm is complexed. thickness, previously coated on one side with an acrylic adhesive.

 A strip of such a complex, placed under a bundle of wires and heated by means of an infrared device rolls around the bundle to form a sheath. In this case, there is a slight shrinkage of the film on the edges of the strip, which has the effect of releasing an adhesive selvedge on the two sides of the strip which, coming into contact ensure closure of the sheath.

 The examples described above are intended to illustrate the invention but should not be considered as limiting: it is thus possible for example to add a protective layer on the second face of the stable layer so as to obtain an impermeable complex or having a improved resistance to certain technical fluids. If an additional layer is added to the laminate complex, it is necessary to ensure that this layer does not disturb the functioning of all of the two active layers (stable and retractable): for example a film or a grid added on the second side of the stable support must be flexible and not shrink with heat.

 The complex according to the invention finds its application in the sheathing of bundles of electric wires, in particular in the automotive field.

It can also be used to form insulation sheaths, in particular for fluid pipes.

Claims (6)

1. Flexible composite comprising at least two layers of material connected together, characterized in that at least one of said layers is non-retractable, the other layer being dimensionally unstable or prestressed in a transverse orientation relative to the other longitudinal orientation, and in that the two layers are intimately connected together during the deformation of the composite. 2. cladding composite according to claim 1, characterized in that the second layer is heat-shrinkable in an orientation. 3. cladding composite according to one of claims 1 or 2, characterized in that the first layer is a sheet of a thermally stable nonwoven material. 4. cladding composite according to one of claims 1 or 2, characterized in that the first layer is a sheet of cellular synthetic material. 5. A method of sheathing a bundle of wires, characterized in that the sheath is formed around the bundle by heat-shrinking the composite according to one of claims 1 to 4. 6. A method of sheathing a bundle of wires with bypass, characterized in that a strip of the composite according to one of claims 1 to 4 is used, split over part of its length, the composite being heat-shrunk around the bundle and of its derivation.