WO2005070668A1

WO2005070668A1 - Hollow composite body of fiber reinforced thermoplastic material

Info

Publication number: WO2005070668A1
Application number: PCT/BE2005/000008
Authority: WO
Inventors: Ludo Van Schepdael; Geert Smellenbergh; Christophe Ducret; Jacques Voiron
Original assignee: Covess Nv; Saint-Gobain Vetrotex France Sa
Priority date: 2004-01-23
Filing date: 2005-01-21
Publication date: 2005-08-04

Abstract

The invention relates to a method for producing a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material (43) and a barrier layer (42) to prevent leakage of low molecular weight substances through the wall, which process involves the steps of providing a support body as first step, wrapping at least one foil layer around said support body to substantially cover its surface, wrapping at least one layer of fiber reinforced thermoplastic material around the combination of support body and foil, heating at least part of the combination of support body, foil and fiber reinforced thermoplastic material simultaneously or at a later stage, up to a temperature sufficiently high to obtain a good adhesion between the foil and the fiber reinforced thermoplastic material, cooling the whole to a temperature at which the composite body has sufficient strength to be removable from the support body, and removing the composite body from the support body. The invention also relates to a hollow composite body comprising a foil as barrier layer.

Description

Hollow composite body of fiber reinforced thermoplastic material

Technical Field

The present invention relates to a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer to prevent leakage of low molecular weight substances through the wall. The invention also relates to a process for the manufacture of said composite body.

Background Art

Hollow bodies, such as for instance high-pressure vessels and pipes, are used for containing and/or transporting low molecular weight substances like water, gas, chemical liquids and the like. The known high-pressure vessels and pipes (when referring in this application to "high-pressure", a working pressure in the range of about 5-200 bar, typically 10-100 bar is meant) frequently have a wall comprising a metal. The use of metal provides adequate mechanical strength and stiffness to the hollow body, and moreover provides an efficient barrier layer against leakage and/or diffusion of low molecular weight substances through the wall. Metallic pressure vessels and pipes however have prohibitive weight, especially when an increased wall thickness is needed to sustain high-pressure levels.

It is also known to produce high-pressure hollow composite bodies of organic thermosetting and/or thermoplastic polymers. In order to be able to sustain the typical high-pressure load levels, the polymers are most often reinforced with discontinuous and/or, preferably, continuous fibers. The use of fiber reinforced composite materials however has a negative effect on the impermeability of the wall of the hollow body. Indeed, fiber reinforced composite materials generally show more porosity than metals, which often leads to slow diffusion and/or leakage of the contained low molecular weight substance through the wall of the body. In case aggressive low molecular weight substances are used, the composite material itself may degrade over time. To prevent all this, the known composite body is generally formed by applying fiber reinforced polymer layers onto a metallic mandrel, which mandrel remains in the produced composite body, and forms therein a substantially impermeable barrier layer. The mandrel also prevents the degradation of the composite material by the contained substance.

The manufacturing technology of thermosetting composite bodies with a barrier layer has been well developed over the years. A suitable process for producing a hollow thermosetting composite body involves providing a hollow self-supporting mandrel, onto which previously impregnated fibers are wound (possibly in the form of a preimpregnated tape), for instance in a helical pattern, until substantially the total surface of the mandrel has been covered. When using thermosetting materials, this entire filament winding process usually occurs at about room temperature. Curing of the thermosetting composite material is then carried out at elevated temperatures after the filament winding process has been terminated.

Several variants on the filament winding method for producing thermosetting composite hollow bodies with a barrier layer are known.

In US 2,653,887 for instance, a process is described to filament wind thermosetting composite material preimpregnated tapes (prepregs) onto a mandrel in the form of a pipe, whereby an adhesive is applied between each two deposited prepreg layers, in order to reduce residual curing stresses due to resin shrinkage. The mandrel remains in the product.

DE 195 00 319 describes a process for the manufacture of an epoxy composite pressure vessel, provided with a thermoplastic liner. The liner tape is wrapped around a mandrel, where after epoxy resin impregnated fibers are filament wound on top of the liner. The whole assembly is then transferred to an oven where the resin is cured at a temperature above the softening temperature of the liner, in order to fuse the different layers of liner tape and bond the liner to the resin.

In the above-described methods the mandrel remains in the composite body, which increases its weight.

Several solutions have been proposed to be able to remove the mandrel after filament winding and curing of the thermosetting composite body.

In US 3,508,677 for instance, a process is described for producing a thermosetting composite pressure vessel, by providing a water soluble mandrel onto which a combination of a thermoplastic film and an elastomeric diaphragm is applied, and subsequently filament winding several layers of glass fibers impregnated with a thermosetting resin onto the diaphragm. Between the layers a low-friction material such as Teflon is applied, without which the vessel would be structurally weak and fail on repeated cycling of pressures.

CH 459 549 describes a similar process in which use is made of an inflatable rubber mandrel, the process producing curved hollow objects of fiber reinforced thermosetting composites.

US 3,449,182 describes a process for producing an oblate spheroid pressure vessel using a flexible, hollow thermoplastic liner subjected to an internal pressure. After filament winding and curing of the resin, the liner is deflated and removed.

GB 1 447 175 describes a method for producing a hollow container by filament winding, wherein a mandrel is used comprising a plurality of arcuate wall members, supported by radially extending arms. After winding and curing the mandrel is disassembled and removed through openings in the poles.

All the methods described above relate to filament winding with thermosetting resins. Being crosslinked materials, thermosets are especially used for their excellent resistance against chemicals. Also, manufacturing processes are generally straightforward since these low viscosity resins are readily processed at low temperatures, and only in a later stage cured into hard, solid products. An important drawback of thermosetting resins however is their relatively poor toughness. For this reason, composites with thermoplastic polymer matrixes have been introduced. Thermoplastics however are much more difficult to process. Thermoplastics need to be processed above their melting and/or softening temperature (processing at room temperature is virtually impossible), at which elevated temperature their melting viscosity is orders of magnitude higher than the typical viscosity of thermosetting resins. This has important consequences for the filament winding process. Firstly, sufficient heat has to be provided to a thermoplastic composite layer upon winding it onto the mandrel. If insufficient heat is provided, the thermoplastic material will not melt or soften enough to enable it to fuse with a second layer. Secondly high pressure must be applied to consolidate the different layers into one integrated material before cooling it down and solidification. If the applied pressure level is insufficient, the different layers will not consolidate well and will delaminate easily in use. This is highly undesirable, since delamination directly affects diffusability through the wall of the hollow composite body.

When filament winding with thermoplastic composite materials, the composite is generally provided in the form of an intermediate material, wherein the reinforcing fibers and the thermoplastic matrix have been pre-assembled. The thermoplastic polymer may be pre-assembled with the reinforcing fiber in a number of ways, such as for instance in the form of a fiber, comingled and/or intermingled with the reinforcing fiber, as a powder, or through 'melt-impregnation'. The reinforcing fiber may be glass fiber, but other fibers, such as carbon, graphite, aramide, ultra high molecular weight polyethylene (UHMWPE), PBO, etc., either alone or in combination may also be used.

Usually, the fiber reinforced thermoplastic material is filament wound in a heated state onto a relatively cold mandrel. It is also possible to wind the material first and then provide the necessary heat for fusing. Combinations are also possible. During or after filament winding the thermoplastic composite layers, the heated material is pressurized in order to consolidate the layers.

Consolidation of the layers is important in order to provide the necessary resistance against degradation of the thermoplastic composite material, due to the action of the low molecular weight substance contained in the vessel. This is especially true for thermoplastics, which generally degrade more easily than thermosets, since they are not cross-linked. For good results with respect to impermeability of the hollow composite body wall, it is recommendable to either achieve an excellent consolidation of the different composite material layers, and/or make use of thick- walled liners.

EP 1 234 654 A1 discloses a prior art method where the aim was to achieve good consolidation. EP 1 234 654 A1 describes a method for the manufacture of a hollow thermoplastic composite body, wherein an inflatable flexible core is provided, around which a discontinuous fiber reinforced thermoplastic composite preform - known as GMT - is applied. The whole is placed inside a rigid mould and heated under internal pressure to fuse and consolidate the thermoplastic against the mould wall. A pressurized liquid coolant, circulating within the core, is used to solidify the preform. The flexible core may be rubber and/or a thick thermoplastic foil.

FR 2 568 356 describes the production of a filament wound water boiler with a heat insulating sandwich wall, consisting of two filament wound fiber reinforced composite skins and a thermally insulating core in between. The process uses an inflatable woven glass fabric, coated with a release material, such as a fluoropolymer (Teflon and the like). After the filament winding process, the mandrel is deflated and recuperated.

EP 0 345 450 A1 describes a method to produce a filament wound pressure vessel whereby a thick liner is provided which acts as mandrel surface, onto which resin impregnated glass fibers are wound. To prevent degradation of the liner a substantially styrene-free unsaturated polyester resin is used. It is also possible to apply an outer layer of polypropylene/glass fiber composite onto the polyester composite layer. The thermoplastic liner has a thickness of about 2 mm for good results.

A high-pressure thermoplastic pipe and a method to produce the same are disclosed in EP 1 314 923. A thick-walled polyolefin pipe is provided, onto which stretched polyolefin resin film is tightly wound at a temperature, which lies between the melting temperature of the polyolefin pipe and that of the stretched film. The polyolefin pipe needs a large wall-thickness because it has to have large strength and stiffness to support the forces acting upon it during the winding process, and because it should act as a barrier against diffusion. Moreover, it facilitates sufficient consolidation between the different layers, and it provides a good adhesion between the pipe mandrel and the stretched resin film. This avoids problems of water penetration in between the pipe and stretched layers, and ensuing short and long term delamination.

The composite body disclosed in EP 1 314 923 has the disadvantage of a relatively high weight, especially when such a body is used as vessel in transport for instance. Indeed, the inner pipe onto which the stretched films are wound remains in the product after manufacture to act as shield against the aggressive action of the carried substance, but thereby increases weight and cost. Resistance against chemicals and against delamination is therefore provided at the expense of weight and cost.

It is the aim of the present invention to provide a thermoplastic composite hollow body with a barrier layer, which shows good resistance against degradation and delamination, is readily produced, and exhibits a low weight. It is a further aim to provide a method to produce such a body.

Summary of the invention

In a first aspect, the present invention provides a method for producing a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer to prevent leakage of low molecular weight substances through the wall, which process involves the steps of providing a support body in a first step; wrapping a foil around said support body; wrapping fiber reinforced thermoplastic material around the combination of support body and foil; heating at least part of the combination of support body, foil and fiber reinforced thermoplastic material simultaneously or at a later stage, up to a temperature sufficiently high to obtain a good adhesion between the foil and the fiber reinforced thermoplastic material; cooling the whole to a temperature at which the composite body has sufficient strength to be removable from the support body; and removing the composite body from the support body.

With the process according to the invention, it is possible for the first time to obtain a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer, wherein the barrier layer is a thin polymer foil. By using a thin polymer foil as barrier layer, considerable weight is saved.

It has surprisingly been discovered that, although the foil is thin and therefore saves weight, it also provides excellent resistance to diffusion of low molecular weight substances. This unexpected behavior is believed to be due, at least partly, to the excellent adhesion achieved between the different layers of thermoplastic material (foil and fiber reinforced thermoplastic layers) by the invented method. According to another aspect of the invention, a preferably high-pressure hollow body of thermoplastic composite material is produced having an efficient barrier layer and low weight.

In the context of this application we mean with the wording "foil" any polymer film with a thickness, insufficient to be able to form a self-supportive mandrel. In other words providing a support body as first step of the invented method is an essential technical measure to obtain the desired properties.

In a preferred embodiment of the invention, the foil forms the innermost layer of the high-pressure hollow composite body. In another preferred embodiment of the invention, the foil actually forms an intermediate layer between two layers of fiber reinforced thermoplastic composite. In this preferred embodiment the foil is protected against scratching and other damage.

The different embodiments of the process according to the invention allow producing a hollow, substantially non-porous, body having the advantage of low weight and materials cost. It is however a further aim of the invention to be able to produce relatively thin-walled containers and/or pipes in a cheap and fast way, thereby further improving on light weight.

According to another aspect of the invention, the inventors have therefore developed an improved method, wherein an expandable rotationally symmetric support body is provided in its expanded state before wrapping the fiber reinforced thermoplastic material and/or the foil around said support body, which support body is returned to a less expanded state prior to removing the composite body from the support body.

In another preferred embodiment of the method, an expandable rotationally symmetric support body is provided, which is brought to its expanded state after wrapping the foil around said support body, and which support body is returned to a less expanded state prior to removing the composite body from the support body.

According to another preferred embodiment of the method of the invention, an expandable rotationally symmetric support body is provided, comprising an expandable axis around which a flexible hose is applied, bringing the support body in its expanded state by expanding the axis before or after wrapping the fiber reinforced thermoplastic material and/or the foil around said support body, which support body is returned to a less expanded state prior to removing the composite body from the support body by contracting the axis.

The hollow, substantially non-porous composite body according to the invention may be used in many applications. It is particularly suitable for use in means for transport, such as trucks, buses, trains, airplanes, and so on. Particularly preferred is its use in braking systems, in suspension systems and/or in fire extinguishing systems. Particularly in these systems, the gain in weight and in safety is a great advantage.

Other objects and advantages of the invented method and substantially non-porous composite body obtained there from, will become apparent from the following detailed description in conjunction with the accompanying figures, without however being limited thereto.

Detailed description of the figures

Figures 1 and 2 schematically show a perspective, respectively cross-sectional view of a known high-pressure pipe.

Figure 3 shows a schematic illustration of a known method.

Figures 4A and 4B schematically show a cross-sectional view of a first and second composite body according to the invention.

Figure 5 schematically shows a process according to the invention.

Figure 6 schematically illustrates an expandable axis suitable for a preferred process.

Figures 7A, 7B, 8A, 8B, 9A and 9B finally are cross-sectional views of several embodiments of an expandable axis, suitable for the method according to the invention.

The figures are not drawn to scale, and similar elements are generally referred to with similar reference numerals. Detailed description of the invention

In a first aspect the present invention provides a method for producing a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer to prevent leakage of low molecular weight substances through the wall, which process involves the steps of a) providing a support body in a first step; b) wrapping a foil around said support body; c) wrapping fiber reinforced thermoplastic material around the combination of support body and foil; d) heating at least part of the combination of support body, foil and fiber reinforced thermoplastic material simultaneously or at a later stage, up to a temperature sufficiently high to obtain a good adhesion between the foil and the fiber reinforced thermoplastic material; e) cooling the whole to a temperature at which the composite body has sufficient strength to be removable from the support body; f) removing the composite body from the support body.

With the process according to the invention, it is possible to obtain a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer, wherein the barrier layer is a thin polymer foil. Although the foil is thin and therefore saves considerable weight, it provides excellent resistance to diffusion of low molecular weight substances. This unexpected behavior is believed to be due, at least partly, to the excellent adhesion achieved by the method between the different layers of thermoplastic material (foil and fiber reinforced thermoplastic layers). This is surprising for the following reason. Providing a thermally well-insulated mandrel is an important requirement when filament winding thermoplastic composites, since this ensures that the heat provided to fuse the different layers is not dissipated but actually used in an efficient manner. When using a thermally conductive metallic mandrel at cooling temperature, the heat applied at the contact surface to fuse the layers, would readily diffuse away from the surface by conduction. This would impair the formation of a good bond between the layers.

It is therefore surprising that the use of a foil as barrier layer in the method according to the invention yields such good adhesion between layers. Indeed, since a foil is generally very thin (foils suitable for the method of the invention preferably have a thickness of between about 0,1 mm and 0,8 mm), its thermal resistance is substantially lower than that of the polymer mandrel used in the known method, such as described in EP 1 314 923 for instance. One would therefore expect difficulties in maintaining the surface temperature at the contact surface between the fiber reinforced polymer and the polymer foil at the required high level.

According to the method of the invention, a high-pressure hollow body of thermoplastic composite material is produced having an efficient barrier layer.

The polymer foil of the hollow composite body may be composed of any polymer, capable of being formed into a foil. The polymer may be a thermoset polymer, such as for instance based on epoxy, polyurethane, unsaturated polyester, etc., and/or a thermoplastic polymer, such as for instance based on polyamides, polyesters, polycarbonates, polyphenyleneoxides, polyolefin's, etc.. Of these, polyolefin polymers, such as polyethylene, polypropylene, EPDM, and polyvinyl chloride (PVC) are preferred. These materials have the advantage, among others, of being chemically inert, of being able to withstand very low temperatures and of having a low manufacturing cost.

In the context of this application we mean with the wording "foil" any polymer film with a thickness, insufficient to be able to form a self-supportive mandrel. In other words providing a support body in step a) of the invented method is a necessary condition to obtain the desired properties. Typical foil thicknesses are comprised within the range of below about 1 mm, preferably between about 20 to 800 micrometer, more preferably between about 50 to 300 micrometer. When employing a too low thickness, the barrier layer only provides a negligible reduction of porosity, while a too high thickness increases weight and yields a body with increased delamination propensity.

It has advantages to characterize the method according to the invention by repeating the step of wrapping a foil around the support body, and wrapping fiber reinforced thermoplastic material around the combination of support body and foil, after the step of providing a support body. Preferably the step of heating at least part of the wrapped combination is carried out continuously during wrapping the foil and/or fiber reinforced thermoplastic material. In this way a hollow composite body is produced having a wall comprising alternating layers of foil and fiber reinforced thermoplastic. Such a body simultaneously shows an increased resistance against diffusion of low molecular weight substances and against delamination.

Preferably, the barrier layer is build up of multiple foil layers. Foils may contain so- called pinpoint defects (small holes), the effect of which on porosity is diminished by using multiple foil layers.

The thermoplastic polymer composite material may be any material known in the art. Particularly preferred thermoplastic composite materials are continuous intermingled or commingled yarns of a reinforcing fiber and a polymer fiber. Such commingled yarns may for instance comprise glass yarns and polyolefin filaments, such as polypropylene filaments, all intimately mixed. Such commingled yarns are sold under the brand name TWINTEX^(R) by Vetrotex. The glass fiber content in these materials is between 30 and 75 % by weight, preferably between 50 and 65 % by weight, the polypropylene fiber content between 70 and 25% by weight, preferably between about 50 and 35% by weight. Such weight ratios make it possible, when producing the hollow body, to obtain the best compromise between, respectively, the ease of processing and the mechanical performance both in the longitudinal direction and the transverse direction of the filament wound composite body.

Preferably, the continuous glass yarns (and fiber yarns in general) are distributed uniformly in the composite hollow body wall. Such a distribution of the yarns in the thermoplastic organic material has a favorable effect on the mechanical properties of the body, also in the long term.

Preferably, the polymer of the foil and the composite polymer matrix are similar polymers. By this is meant that these polymers belong to the same class of polymers. However, they may differ with respect to such properties as molecular weight, degree of crystallinity, crystalline morphology, particular copolymerizable monomers, grafting and other additives, and so on. Differences in material intrinsic properties may entail a difference in melting temperature or softening temperature. Advantageously, the melting and/or softening temperature of the foil and the thermoplastic matrix polymer are approximately similar. This simplifies the manufacturing process and increases the reliability of the bond between foil and fiber reinforced thermoplastic.

In another particularly preferred embodiment of the invention the foil is a composite foil (in the sense of containing multiple layers), for instance comprising multiple co- extruded layers. Using such a foil allows selecting the different layers in relation to the particular function it should have. For instance, the layer of the composite foil, facing the fiber reinforced thermoplastic layer, may be selected such that the adhesion with the fiber reinforced thermoplastic layer is maximized. To this end, the polymer of this foil layer could for instance be grafted with adhesion enhancing monomers. In the case polypropylene is used as foil polymer, this layer could for instance comprise polypropylene, grafted with anhydrous maleic acid. The polymer of the layers of the composite foil, facing the inner side of the composite body are then preferably selected to for instance be resistant against corrosion, or having a low coefficient of transmission for oxygen or water.

According to another embodiment of the method for producing a hollow composite body, the process involves the steps of a) providing a support body; b) wrapping fiber reinforced thermoplastic material around said support body; c) wrapping a foil around the combination of support body and fiber reinforced thermoplastic material; d) heating at least part of the combination of support body, foil and fiber reinforced thermoplastic material simultaneously or at a later stage, up to a temperature sufficiently high to obtain a good adhesion between the foil and the fiber reinforced thermoplastic material; e) cooling the whole to a temperature at which the composite body has sufficient strength to be removable from the support body; f) removing the composite body from the support body.

According to this embodiment, a high-pressure hollow composite body is obtained having a wall wherein the barrier layer is shielded against damage. This increases the reliability of the composite body with respect to service conditions.

The foil may be applied onto the support body in a number of ways. It is for instance possible to apply the foil in the form of a tape, whereby the foil tape may be positioned lengthwise (the tape axis being more or less parallel to the largest dimension of the support body), or transversely (the tape axis being more or less parallel to the smallest dimension of the support body). A combination is also possible. Further, the foil may be applied onto a stationary support body, in which case a foil support is preferably used to dispense the foil around the support body. It is also possible to dispense the foil from a stationary dispensing unit onto a rotating or otherwise moving support body. It is clear that many possibilities are available.

When referring to "heating or preheating" in the context of this application, any method available to the skilled person to increase the temperature is meant. Suitable methods are for instance the use of a burner, an open flame, infrared radiation (IR), convection, microwaves, friction, and so on. When heating the foils and/or fiber reinforced thermoplastic layers, care should be taken not to degrade the polymers. It may therefore be advantageous to use the above-mentioned heating methods at least partly under substantially oxygen-free conditions, for instance by using an inert nitrogen atmosphere.

The method of the invention is preferably characterized in that the fiber reinforced thermoplastic material is preheated before it is being wrapped. Preheating of the fiber reinforced thermoplastic material allows increasing processing speed. It also has an advantageous effect on the bond strength between foil and fiber reinforced thermoplastic material. Preferably, the thermoplastic composite material tape and/or the foil are delivered in the heated state before wrapping it around the support body. To this effect, they preferably are heated just before they are laid down on the support body, by subjecting them, in a zone close to the support body, to an operation of surface heating to a temperature above the softening temperature of the polymeric material but below its degradation temperature, in a zone located near the support body.

A particularly preferred method is characterized in that, prior to step b), the following steps are also carried out in line: - a tape of continuous commingled yarns in the form of at least one sheet of parallel yarns, are led in and assembled; - the said sheet is introduced into a zone where it is heated to a temperature between the melting or softening temperature, and the degradation temperature of the polymer fiber; - the heated sheet is led through an impregnation device so as to obtain a densified and laminated tape of flatter shape than the original tape; - the laminated tape is introduced into a zone where it is heated to a temperature between the melting or softening temperature, and the degradation temperature of the polymer.

The support body may have any shape, as long as it conforms to the desired shape of the composite body, and is usable in the filament winding process. In most cases the support body will have a rotationally symmetric shape, whereby its rotational axis coincides with the rotational axis of the filament-winding machine, when in use as support body.

The support body may be made of any material, suitable for this purpose. It is for instance possible to make the support body from metal, for instance steel, cast iron and/or aluminum, from a polymer, if desired reinforced with fibers, from gypsum, wood, and so on. Preferably, the surface of the support body comprises a releasing layer, such as for instance provided by a layer of polytetrafluoroethylene polymer (Teflon™).

In the method according to the invention, the support body may be heated from the outside. It is however also possible to heat the support body from the inside (instead or furthermore), for instance by providing heating elements in the body, which is the preferred method, and further improves the bond between foil and fiber reinforced thermoplastic.

When filament winding the composite body onto a substantially rigid support body, such as for instance a steel tube, a substantial axial force may be needed to remove the composite body from the support body, for instance when filament winding a composite pipe. In the known process it is customary to use a slight taper in combination with hydraulic extractors. These extractors push the support body out of the filament wound composite pipe in the axial direction. To be able to employ this method, the composite pipe, or body in general, needs to have a sufficient wall thickness in order not to break upon extraction. This is especially the case for the composite bodies of the present invention, which employ a thermoplastic polymer matrix. This is easily understood from the fact that elevated temperatures are needed to be able to process these materials. The above described extraction method is therefore not suitable for pipes or bodies with a relatively low wall-thickness.

The above problem causes an unfortunate effect: although a relatively thin-walled non-porous composite body would respond to the requirements from a mechanical and diffusivity point of view, such body cannot be made with the known methods, and therefore a relatively thick-walled composite body is produced instead. However the thick-walled body has a higher weight (which is a disadvantage in transport applications for instance), and the cost of material is higher. Saving on unit material cost is important for thermoplastic matrix composites in general, since these materials are prohibitively more costly then steel.

The inventors have therefore developed an improved method, wherein at least one foil is used as barrier layer, and which method is cheap and fast, and allows producing relatively thin-walled bodies, in particular pipes.

Thereto the process according to the invention is preferably characterized in that an expandable rotationally symmetric support body is provided in its expanded state before wrapping the fiber reinforced thermoplastic material and/or the foil around said support body, which support body is returned to a less expanded state prior to removing the composite body from the support body.

When a thermoplastic matrix composite pipe is produced for example, the preferred process is characterized in that an expandable rotationally symmetric support body is provided, comprising an expandable axis around which a flexible hose is applied, bringing the support body in its expanded state by expanding the axis before or after wrapping the fiber reinforced thermoplastic material and/or the foil around said support body, which support body is returned to a less expanded state prior to removing the composite body from the support body by contracting the axis.

The flexible hose is preferably made of a thermally insulating material, such as a polymeric material. Although any polymer may in principle be used for this purpose, polyolefin polymers and/or silicone are preferred. By using a flexible hose around the expandable support body, the processing speed of the method is greatly improved. Indeed, in this preferred embodiment there is no need to heat and cool a substantial part or the whole of the expandable support body, which body therefore experiences small temperature variations only.

In 'expanded' state, the support body (in some embodiments comprising an expandable axis and a flexible hose) is sufficiently stable to be able to wind the foil and/or the fiber reinforced thermoplastic layers around it. With "expandable axis" is meant in the context of this application any axis of which the diameter may be increased. Increasing the diameter of the axis may be accomplished by any means, for instance by applying pressure. After decreasing the diameter of the axis, and therefore bringing the support body in its less expanded state, the thin-walled hollow composite body may be removed in a straightforward manner, whereby the risk for damage to the thin wall has substantially been decreased.

The expandable axis preferably comprises a metallic axis, for instance from steel and/or aluminum, which axis is, at its outside, provided with a plurality of shells. The shells extend in the longitudinal and transverse (angular) direction of the axis, and may be translated radially. The axis may internally be pressurized, preferably by air pressure, whereby the shells are radially displaced until they reach a mechanical stop. This state conforms to the expandable state of the axis.

The expandable axis is preferably provided with a circumferential hose of flexible material, for instance a polymer. It is also possible to provide the entire expandable axis of polymeric material. The preferred material for the hose is sufficiently deformable to be able to accommodate the deformations due to expansion of the expandable axis, and/or has a low thermal conductivity, and/or is resistant to high temperatures, that is to say to the typical temperatures needed to obtain a good bonding between foil and fiber reinforced thermoplastic material.

The particularly preferred hose material is silicon rubber.

Figure 1 shows a high-pressure pipe 1 as already known from EP-A-1314923. The pipe comprises an inner pipe 2, onto which reinforcing layers 3 are laminated. The whole is covered with a protective cover layer 4.

Figure 3 shows that the inner pipe 2 is provided with reinforcing layers 3a and 3b in filament winding machines 5 and 6. By this process, a known high-pressure pipe is obtained.

As already described above the disadvantage of the known high-pressure pipe is that the inner pipe 2 has a relatively high weight and contributes substantially to the total cost of the pipe. As will be appreciated, pipes may have substantial lengths (hundreds of kilometers) and a small increase in wall-thickness has a large effect. Figure 4A schematically shows a cross-section of an embodiment of the hollow composite body, according to the invention. This body comprises a layer 43 of fiber reinforced thermoplastic material, and a barrier layer 42, substantially consisting of foil. The use of foil as barrier layer in the composite body, reduces its cost and weight, and therefore fulfills the aim of the present invention.

Preferably the barrier layer 42 is build up of multiple foil layers, which is easily achieved, for instance by wrapping several layers of foil around the support body 51.

Figure 4B depicts a schematic cross-section of a preferred embodiment of the composite body according to the invention. This body comprises an inner layer 43A of fiber reinforced thermoplastic material, a barrier layer 42, substantially consisting of foil, and an outer layer 43B of fiber reinforced thermoplastic material.

A method to produce composite pipes according to the invention is schematically illustrated in figure 5. In the method, a foil 42 is wrapped around a support body 51 , where after fiber reinforced thermoplastic material 43 is wrapped around the combination support body-foil, and whereby simultaneously and/or later the whole is heated to a temperature sufficiently elevated to obtain a good bond between foil and fiber reinforced thermoplastic material. In the example shown, a burner 52 is used to heat the materials. After the winding step, the whole assembly is cooled down until a temperature is reached in the fiber-reinforced material at which it has sufficient strength to remove it from the support body.

With the method described above and illustrated in figure 5, the advantage of reduced weight and material cost is achieved, but the method may be improved further with respect to processing speed and overall unit cost. Moreover, the illustrated method meets difficulties in producing composite bodies with relatively thin walls.

Figure 6 schematically shows an expandable body, suitable to be used in the preferred method according to the invention.

The expandable axis comprises axially extending shells 61 , which, in the non- expanded state (state A) substantially fit together, forming a more or less contiguous surface, wherein each side of a shell forms no, or a small slit with an adjacent side of a second shell. In the expanded state (state B) broader slits 62 are formed between the shells. Around the expandable axis a flexible hose or layer 63 is applied in this embodiment, for instance by sliding the hose over the axis. The hose 63 is attached with clamping means 65 onto narrow part 64. In state A the diameter is D1 , in the expanded state B the diameter is D2, which obviously is greater than D1.

Figure 7A shows a cross-section of the shells 61 , and the deformable hose 63.

Further a stationary holder 71 is provided. In the expanded state (Fig 7B) axial forces are applied onto the shells 61 , which as a result thereof move radially outwards and increase the diameter to a value D2. In the process hose 63 is hereby expanded as well.

Figures 8A and 8B show a further example of the expandable hose. In this example the hose comprises metallic elements 81 A and 81 B, provided at its outer surface with polymeric layers 63A and 63B, which together form a flexible hose. In the non- expanded state part 81 B is somewhat retracted (not drawn to scale in this figure). In the expanded state part 81 B is driven into part 81 A such that part 81 A expands and the diameter increases to a value D2.

Figures 9A and 9B show a variation of the expandable hose of figures 8A and 8B. In this example a simple hose is used, comprising two parts 91 A and 91 B, both of insulating polymer. A separate hose or layer 63 may in this embodiment be deleted.

By employing an expandable axis in the method according to the invention, as described and shown in figure 5, several advantages are obtained with respect to the method of figure 5. The flexible hose acts as an additional thermal insulator. This saves a considerable amount of heating energy, since the support body for instance need not be heated in the method. Moreover, upon depressurizing the expandable axis after filament winding, the shells move radially inwards, and the filament wound layers of fiber reinforced thermoplastic material, including the foil barrier layer may easily be removed from the axis, thereby obviating the need of using heavy and costly hydraulic extracting machinery. In order to assist removing the foil from the hose and prevent possible rupture of the foil when contracting the support body axis, the hose is preferably treated with release agent (for instance Teflon™ - spray, and similar products).

When adherence of the flexible hose to the foil cannot be partly or completely prevented by the use of release agent, a (at least partial) vacuum is preferably applied to the inside of the expandable axis upon deflation. By placing the inside of the expandable axis under a (at least partial) vacuum, the flexible hose adheres to the shells and is therefore, upon deflation of the axis, torn loose from the filament wound composite body with the foil-barrier layer. In this embodiment, the flexible hose is sealed at both ends, whereby the sealed ends must have a diameter smaller than the internal diameter of the filament wound fiber reinforced thermoplastic composite body, the 'foil-barrier layer' inclusive, in order to be able to demold the composite body.

Typical distances over that the support body axis may be displaced are in the range of about 1 mm or more, for instance in the order of about 5 to 15 mm for a pipe diameter in the order of about 15 to 25 cm. Other dimensions however are possible.

The invention also relates to composite pipes consisting of the body of revolution as described above, coated with an external finishing and protective layer made of thermoplastic organic material, preferably one identical to the material of the foil and/or the polymer matrix of the thermoplastic composite. The finishing layer according to the invention allows the pipe to be reliably protected against external attack, which is likely to occur during storage, transportation, site operations, use, etc.

Although the process and composite body of the invention have been predominantly illustrated for bodies having the shape of a pipe, other filament windable shapes (for instance two spherical halves) may also be produced with the method of the invention, provided the produced composite body might be demolded. It is for instance possible to produce pressure vessels with the invented method. A suitable method for producing such closed hollow bodies comprises producing a hollow cylindrical tube section and two end portions, preferably of hemispherical form, and then combining the hollow section and end portions by any method suitable for this purpose, such as by welding, adhesive bonding, and the like. The end portions are preferably made of fiber reinforced thermoplastic material using any processing method suitable for this purpose, such as for instance compression and/or injection molding. It is also possible to filament wind the total pressure vessel structure in one time, whereby the polar openings are used to remove the collapsible mandrel after the filament winding process has been terminated.

Industrial Applicability

The invention therefore also relates to a braking system for a vehicle, a suspension system for a vehicle, and/or a fire extinguishing system for a vehicle. Weight gain represents an important aspect for braking and suspension systems in transport. The higher the weight of the system, the higher becomes the weight of the means of transport, the higher is the fuel consumption and environmental hazard.

Also fire-extinguishing systems are often present in means for transport, airplanes, vehicles, cars, elevated, and so on. For these systems therefore, weight gain is likewise of extreme importance.

The means of transport where the present invention can be used are for example vehicles, cars, trucks, busses, motorbikes, trains, and monorails. Applications can also be found for boats and other sailing devices, hovercrafts, airplanes, zeppelins, spacecraft, helicopters, and/or for elevators, escalators, conveyor belts, hoisting- cranes, and so on.

Claims

1. Method for producing a hollow composite body, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer to prevent leakage of low molecular weight substances through the wall, which process involves the steps of a) providing a support body as first step; b) wrapping at least one foil layer around said support body to substantially cover its surface; c) wrapping at least one layer of fiber reinforced thermoplastic material around the combination of support body and foil; d) heating at least part of the combination of support body, foil and fiber reinforced thermoplastic material simultaneously or at a later stage, up to a temperature sufficiently high to obtain a good adhesion between the foil and the fiber reinforced thermoplastic material; e) cooling the whole to a temperature at which the composite body has sufficient strength to be removable from the support body; f) removing the composite body from the support body.

2. Method according to claim 1, characterized in that the steps a) to f) are executed in the indicated order.

3. Method according to claim 1 , characterized in that the layers in b) and c) are inverted, the at least one layer of fiber reinforced thermoplastic material being wrapped around the support body and the at least one foil layer being wrapped around the combination of support body and fiber reinforced thermoplastic material.

4. Method according to any one of claims 1 - 3, characterized in that the wrapping of the at least one foil layer and/or the wrapping of the at least one layer of fiber reinforced thermoplastic material are repeated at least once.

5. Method according to any one of claims 1 - 4, characterized in that the fiber reinforced thermoplastic material is preheated before it is being wrapped.

6. Method according to any one of claims 1 - 5, characterized in that in step a) an expandable rotationally symmetric support body is provided in its expanded state, which support body is returned to a less expanded state prior to step f) of the method.

7. Method according to any one of claims 1 - 5, characterized in that in step a) an expandable rotationally symmetric support body is provided, which is brought to its expanded state after step b) or c), and which support body is returned to a less expanded state prior to step f) of the method. 8. Method according to claim 6 or 7, characterized in that a support body is provided, comprising an extendable axis, which axis is provided at its outside with a plurality of shells, the shells forming a substantially contiguous surface and being radially translatable, whereby the support body is brought into its expanded state by pressurizing the axis internally, causing the shells to be displaced radially.

9. Method according to claim 8, characterized in that the extendable axis is provided with a flexible hose.

10. Hollow composite body, obtained by the method according to any one of claims 1 - 9, whose wall comprises a fiber reinforced thermoplastic material and a barrier layer to prevent leakage of low molecular weight substances through the wall, wherein the barrier layer essentially consists of foil material.

11. Hollow composite body according to claim 10, characterized in that the barrier layer essentially consists of multiple foil layers. 12. Hollow composite body according to claim 10 or 11 , characterized in that the thermoplastic matrix of the fiber reinforced thermoplastic material and the foil material are similar polymers.

13. Hollow composite body according to any one of claims 10 - 12, characterized in that the thickness of the foil is selected in the range of 50- 200 micrometer.

14. Hollow composite body according to any one of claims 10 - 13, characterized in that the foil comprises multiple polymeric layers.

15. Hollow composite body according to any one of claims 10 - 14, characterized in that the foil constitutes an inner layer of the composite body.

16. Hollow composite body according to any one of the preceding claims, characterized in that the foil constitutes an intermediate layer between two layers of fiber reinforced thermoplastic material of the composite body.

17. Hollow composite body according to any one of the preceding claims, characterized in that it is a pipe or part of a pipe.

8. Closed container, such as used in braking systems, suspension systems and/or fire extinguishing systems for transport means, essentially consisting of the assembly of a hollow composite body according to any one of claims 10 to 16 with two ends made by molding.