Field of the invention

The present invention relates to a thermoplastic hollow body. The present invention is particularly suitable for tanks and filler pipes.

Background

Thermoplastic hollow bodies, such as fuel tanks and filler pipes, are widely used in motor vehicles.

Such hollow bodies can either be produced by blow moulding or injection moulding.

Thermoplastic hollow bodies for motor vehicles are required to exhibit high safety performance, particularly with regard to fire resistance and impact resistance. Such hollow bodies are required to meet minimum statutory industry specified performance criteria both with respect to creep resistance when the tank is subjected to a fire and crash test resistance when the tank is subjected to an impact.

Generally, fuel tanks for motor vehicles are made of HDPE. HDPE has a low melting point. Thus, such fuel tanks have limited resistance to fire.

It has been proposed different types of fire protection for HDPE fuel tanks.

For example, it is known that the wall of the hollow body must be thick enough to ensure fire resistance, but that increases the weight of the hollow body. For example, a known type of fire protection is based on the use of a plate

(or shield) made of thermoset polymers. Such materials have the property to be infusible (i.e. not able to be melted) and after processing, the final part is not transformable anymore; thus, such materials are resistant to heat. However, the attachment of such thermoset plate to the HDPE tank wall is complex. Indeed, such thermoset plate cannot be welded to the HDPE tank wall and specific mechanical locking means are thus required. For example, the thermoset plate can be screwed to the HDPE tank.

In addition, in some specific cases, the temperature of the fire can be such that the mechanical locking means may detach from the tank. In consequence, the thermoset plate may also detach from the tank, leaving the tank surface unprotected. Thus, when the tank wall starts to melt, droplets of melted thermoplastic can exit towards the environment.

Summary

The object of embodiments of the invention is to provide an improved hollow body which meets the above-stated fire resistance needs. A further object is to provide an improved hollow body on which a fire protection is arranged in an improved manner.

It is, therefore, one aspect of the present invention to provide a thermoplastic hollow body for a motor vehicle comprising a fire protection component made from a thermoplastic material, said fire protection component is chemically bonded to the thermoplastic hollow body and has a labyrinth structure configured to retain droplets of melted thermoplastic coming from the thermoplastic hollow body during fire.

During an exposition to fire, the temperature of the hollow body wall increases progressively. Heat diffuses first through the fire protection component, then through the hollow body wall.

Indeed, in a first stage the fire protection component according to the invention being positioned preferentially on the external wall of the hollow body which is the first area to be melted during fire exposition. Droplets of melted thermoplastic are formed within the fire protection component and are retained by the labyrinth structure of the fire protection. The fire protection component according to the invention is thus configured to act as a trap (i.e. labyrinth) for the droplets of melted thermoplastic.

In a second stage the heat diffuses across the hollow body wall, the thickness of melted thermoplastic material increases. The hollow body wall is thus in molten state. The droplets of melted thermoplastic from the hollow body wall start penetrating and migrating across the fire protection component according to the invention, where they are delayed and retained by the labyrinth structure of the fire protection component. This delay allows for securing the passengers of the car. Thus, the fire protection component according to the invention provides a two-stages protection. It would be appreciated that the fire protection component allows reduction of the thickness of the wall of the hollow body. In other words, thanks to the fire protection component of the invention the hollow body can be made lighter and meet the fire resistance requirements in automotive industry (i.e.: no leakage observed).

Advantageously, the fire protection component of the invention is chemically bonded on the entire external wall of the hollow body. Thus, all the external wall of the hollow body is protected against fire exposition.

In another embodiment, the fire protection component of the invention is chemically bonded to at least one portion of the external wall of the thermoplastic hollow body. Said at least one portion of the external wall of the thermoplastic hollow body is a predetermined portion of the hollow body external wall susceptible to be exposed to fire. The fire protection component has to be shaped/sized in such way that it covers not only the portion of the hollow body which is susceptible to be exposed to fire but also its surrounding surface. Thus, the fire protection component remains attached during fire exposition and can play its protection function.

In this way, it is not necessary to protect the entire hollow body against fire exposition if there are only predetermined portions of the hollow body which are involved. However, the fire protection component has to be shaped larger than the portion of the hollow body which need fire protection for an efficient fire protection.

The fire protection component made from a thermoplastic material is chemically bonded to the thermoplastic material of the hollow body. Indeed these two thermoplastic materials have the chemical property to bind strongly together by forming a chemical bond. Thus, the fire protection component is strongly attached to the hollow body and forms with the hollow body a solid fire resistant hollow body. The chemical bonding between the fire protection component and the hollow body is particularly strong compared to a mechanical adhesion with a mechanical locking means for example. Indeed, contrary to a mechanical adhesion, it is not easy to detach two thermoplastic materials joined together by a chemical bonding.

The chemical bonding between the fire protection component and the hollow body can be made during different types of chemical processes such as and non-limitingly, welding, overmoulding or adhesiving processes.

In a first particular embodiment of the present invention, the fire protection component is chemically bonded to the thermoplastic hollow body by welding, more particularly to the external wall of the thermoplastic hollow body. Thus, the attachment of the fire protection component to the hollow body is easy. The welding takes place after the manufacturing of the thermoplastic hollow body. Further, by welding the fire protection component to the hollow body, deformations of the hollow body at critical location(s) (i.e. weak points) can be significantly reduced.

Such process is disclosed in the patent application EP 2544881 in the name of the Applicant, which is included herein by reference.

In a second particular embodiment of the present invention, the fire protection component is chemically bonded to the thermoplastic hollow body by overmoulding. Thus, the attachment of the fire protection component to the surface of the thermoplastic hollow body can be performed directly during the blow moulding or injection moulding step. By overmoulding the fire protection component, it can be securely integrated into the hollow body. This allows strong fastening of the fire protection component to the hollow body.

Such process is disclosed in the patent application PCT/EP2014/057697 in the name of the Applicant, which is included herein by reference.The fire protection component can be overmoulded with at least one portion of the external wall or internal wall of the thermoplastic hollow body. However, the attachment of the fire protection component to the external wall of the thermoplastic hollow body is preferred since the temperature is higher on the external wall and the diffusion of the droplets of melted thermoplastic coming from the thermoplastic hollow body during fire is oriented towards the external wall due to gravity. Thus, the fire protection component plays properly its protection function by retaining in a very efficient way the droplets of melted thermoplastic coming from the thermoplastic hollow body during fire.

In a particular embodiment, the fire protection component is chemically bonded to the thermoplastic hollow body by at least one adhesive means, such as an adhesive tape. In this case, the matrix of the fire protection component may be different from the matrix of the hollow body.

Advantageously, the fire protection component comprises at least one fiber filled reinforcement layer. Preferably, the at least one fiber filled reinforcement layer is a pre impregnated fiber composite (prepreg) layer. In other words, the reinforcement layer may comprise a thermoplastic material and fibers. The fibers may be short or long fibers, or woven or non- woven (random) continuous fibers. Uni-directional (UD) tapes could also be used as well as a superposition of several UD tapes (ex: 0°+90°). Preferably, the fibers are included in the form of a woven mat of fibers, more preferably a woven mat of glass fibers. However, carbon fibers, natural fibers, metal fibers or polymer fibers, e.g. polyamide fibers, or a combination thereof may also be used. Synthetic fibers are less suitable due to their lower melting point compared to carbon or glass fibers. The thermoplastic material is configured to be chemically bonded to the material of the hollow body and may be a polyolefin material, in particular a polyethylene material, and e.g. high-density polyethylene. Other thermoplastic such as PA6, PA66, PPA, PP, or blends thereof may also be used. To improve the compatibility between the fibers and the thermoplastic material, the surface of the fibers may be treated with a compatibilizer substance such as silane and/or a reactive binder, e.g. the HDPE reactive type. Preferably the thermoplastic material content in the thermoplastic material is lower than 70 percent, more preferably lower than 55 %. Preferably the fiber content is higher than 30 percent, more preferably higher than 45 percent. More details about suitable reinforcement layers can be found in patent application FR2 957 296- A 1 in the name of the Applicant, which is included herein by reference, particularly the fact that the reinforcement layer may also be a multilayer structure.

Most preferably, the fire protection component comprises three superposed layers of entangled woven fibers (e.g. twill fabric). Each of the layers comprises long woven yarns entangled in a cross way. Each yarn is made of continuous fibers. Each of the layers comprises a first plurality of long woven yarns arranged together in the same direction and a second plurality of long woven yarns arranged together in a same direction but perpendicularly and in an alternating manner with the first plurality of long woven yarns. The entangled long woven yarns are arranged together in a tight way such that the entangled long woven yarns arrangement limits the melted thermoplastic material diffusion. The long woven yarns arrangement forms the labyrinth structure for the melted thermoplastic droplets in which the melted thermoplastic droplets are delayed and retained. This delay allows for securing the passengers of the car.

The superposition of such layers allows to increase the complexity of the labyrinth structure and retain trapped the droplets or further the melted thermoplastic material more efficiently.

In a particular embodiment, the fire protection component includes a barrier layer in order to reduce diffusion of hydrocarbons or other liquids or gazes across the hollow body wall. Typical structure could be for example, from the outside to the interface with hollow body wall: (HDPE + glass fibers) / adhesive / EVOH(= barrier layer) / adhesive / HDPE. In this particular example, the chemical bonding between the fire protection component and hollow body wall is improved thanks to the absence of fibers at the interface.

To further improve the heat and fire resistance properties of the fire protection component, different specific chemical agents can be added to the structure/reinforcement layer. These agents can be heat reflective elements or intumescent material or anti-drop agent or any other flame retardant. In particular, heat stabilized grades can also be used as thermoplastic materials for the fire protection component such as PA6 and PA66 Durethan XTS3 (Xtreme Temperature Stabilization) from Lanxess. Thanks to organic additive, the continuous service temperature is increased by more than 100°C (compared to unstabilized PA6 or PA66) which make it suitable for fire resistance.

Unreinforced materials are preferred for the hollow body in order to ensure impact resistance (fibre reinforced materials are stiffer but also more brittle).

Good results have been obtained with the reinforcement layer based on

HDPE containing 47% by weight of continuous woven glass fibers which are distributed in three layers and a total thickness of 1,5mm, without any specific flame retardant. The reinforcement layer was overmoulded (by blow moulding) into the surface of a fuel tank. Good results can be obtained with a reinforcement layer having a total thickness between 0,1 and 2,5 mm, more preferably between 0,5 and 1,5 mm.

Advantageously, in the particular case where the hollow body of the present invention is a fuel tank of a vehicle fuel system, the fire protection component can be shaped/sized and arranged on the fuel tank so as to define a shield to protect one or several external components of the fuel system, such as for example a filler pipe, an electrical cable, a fuel or a venting line, a drain plug, a filter, etc.

In the particular case where the hollow body is a filler pipe, the bottom of the filler pipe can be protected with the fire protection component of the invention, especially if the filler pipe is connected at the bottom of the tank and can be filled with liquid.

In another particular embodiment, the hollow body of the invention is an ammonia precursor tank or an ammonia tank.

In another particular embodiment, the hollow body of the invention can be a pressurized or a non-pressurized tank. Brief description of the figures

The accompanying drawings are used to illustrate presently preferred non- limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

Figure 1A illustrates schematically an embodiment of a structure of a fire protection component of the invention.

Figure IB illustrates a microtome section of an embodiment of a structure of a fire protection component of the invention.

Figure 2 illustrates schematically a first embodiment of a fire protection component of the invention chemically bonded to an external wall of a fuel tank.

Figure 3 illustrates schematically a second embodiment of a fire protection component of the invention chemically bonded to an external wall of a fuel tank.

Figure 4 illustrates schematically a third embodiment of a structure of a fire protection component of the invention.

Figure 5 illustrates schematically a process to integrate a fire protection component of the invention on a hollow body.

Figure 6A and 6B illustrate schematically the test set-up used for mini fire tests.

Description of embodiments

Figure 1A illustrates schematically an embodiment of a structure of a fire protection component (10).

The fire protection component comprises three woven fiber layers (11), (12), (13) (e.g. twill fabric) combined together as well as polyethylene and carbon black. Each of the layers comprises long woven yarns entangled in a cross way. Each yarn is made of long continuous fibers. In other words, each of the layers comprises a first plurality of long woven yarns (Al, A2, A3, Α , A2', A3' ...) arranged in the same direction and a second plurality of long woven yarns (Bl, B2, B3, Β , B2', B3' ...) arranged in the same direction, perpendicularly and in an alternating manner with the first plurality of long woven yarns. The long woven yarns are arranged together in a tight way such that the long woven yarns arrangement limits the melted thermoplastic material diffusion. The long woven yarns arrangement forms the labyrinth structure for the melted thermoplastic material in which the melted thermoplastic material is delayed and retained. This delay allows for securing the passengers of the car. The superposition of such layers allows to increase the complexity of the labyrinth structure and retain trapped the droplets or the melted thermoplastic material more efficiently.

Figure IB is a microtome section of the fire protection component comprising layers of entangled woven fibers. On the microtome section, the fire protection component comprises three first long woven yarns (Al, A2, A3) arranged in the same direction and two series of two and three other long woven yarns respectively (Bl, B2, B3, B2', B3') arranged together in the same direction but perpendicularly to the three first long woven yarns. The space between the long woven yarns (Al, A2, A3, Bl, B2, B3, B2', B3') delimits the path L in which the melt thermoplastic material can penetrate and migrate. The space between the long woven yarns corresponds in other words to the labyrinth structure L of the fire protection component in which the melted thermoplastic material is retained and delayed. Figure 2 illustrates schematically a fuel tank (22) equipped with a fire protection component (21) such as described in Figure 1. As illustrated in this example, the fire protection component (21) is shaped/sized and arranged on the fuel tank so as to define a shield to protect an external component (23).

Figure 3 illustrates schematically a fuel tank (32) equipped with a fire protection component (31) according to a second particular embodiment of the invention. As illustrated in this example, the fire protection component (31) is shaped/sized and arranged on the fuel tank so as to define a shield to protect an external component (33). The external component comprises a first portion welded to the fuel tank at a first welding zone (35) and a second portion welded to the fire protection component at a second welding zone (34).

Figure 4 illustrates schematically a third particular embodiment of a structure of a fire protection component of the invention. Figure 4 is a cross section of the fire protection component, the fire protection component being an injection moulded plate or profile filled with short glass fibers (41). The dispersion of short glass fibers (41) in the matrix (40) forms the labyrinth structure for droplets of melted thermoplastic coming from the thermoplastic hollow body during fire where they are efficiently retained. Thus, each fiber limits the diffusion of the droplets of melted thermoplastic.

The short fiber content in the injection molded plate is at least preferably 30%, and more preferably 40% by weight of the total weight of the plate. The thickness of the plate should be between 0,1 mm and 2,5 mm, more preferably between 0,5 and 1,5 mm.

Alternatively, the fire protection component is an injection moulded plate filled with long glass fibers, carbon fibers, synthetic or metal fibers.

In another particular embodiment, the injection moulded plate comprises a pre- impregnated fiber composite layer.

Alternatively, the fire protection component is an extruded plate or profile filled with short or long glass fibers, carbon fibers, synthetic or metal fibers.

In another particular embodiment, the extruded plate or profile filled with short or long glass fibers, carbon fibers, synthetic or metal fibers comprises at least one fiber filled reinforcement layer.

The short fiber content in the extruded plate or profile filled is at least preferably 30%, and more preferably 40% by weight of the total weight of the plate or profile filled. The thickness of the extruded plate or profile filled should be between 0,1 mm and 2,5 mm, more preferably between 0,5 mm and 1,5 mm. Figure 5 illustrates schematically a process to integrate an injection moulded plate (51) on a hollow body. Figure 5 represents the cross section of a two cavities mould (50) at each step of the process. In this particular embodiment the process comprises four steps (I-IV). The first step I of the process is the closing of the two-cavities mould (50). In a second step II, the fire protection plate (53) is injected in the first cavity (51) of the mould. The third step III is the opening of the mould (50) in order to transfer the fire protection plate injection moulded on the first cavity (51) to the second cavity (52), so that it remains warm. The cooling time in the first cavity (51) should be as short as possible. The step four IV is the closing of the mould (50) in order to form the hollow body while overmoulding the plate (53). .. The plate (53) is then overmoulded on the second cavity (52)by an impact resistant and compatible thermoplastic material, the thermoplastic material being compatible with the fire protection component. A chemical bonding is then obtained between the plate and the hollow body. For example, the thermoplastic material can be a un-reinforced PPA (ex: Amodel AT1001LNT from Solvay combines impact resistance at - 40°C and fuel barrier) or un-reinforced HDPE (ex: Lupolen 4261 AIM from Lyondellbasell) in such a way as to form a hollow body or at least one part of a hollow body (54).

Alternatively, the plate can be injection moulded on a separate mould and left to cool. During a second step, the plate is pre-heated (ex: by IR radiations) and then transferred into a second mould to be overmoulded (ex: by a robot or by an automatic gripping system). A pre-forming of the plate can be performed during heating or during transfer or during placement in the mould. The second mould may include a heated insert in order to increase locally the temperature, so that the plate remains warm enough to be chemically bonded during overmoulding.

Advantageously, the injection moulded plate can easily integrate one or more additional functions or components (ex: fixation clip for a canister or an external filter or a line (fuel line, vapour line) or an electrical cable, or a fixation bracket). In the case of an ammonia precursor tank, such as AdBlue® tank, the injection moulded plate can integrate a heating element.

Fusible ribs can also be integrated on the surface of the plate, in order to achieve a better weld interface between the plate and the external surface of the tank.

Example:

The fire resistance of test specimens cut out of tank shells in PE and PE associated with the fire protection component has been compared. The comparison is based on a lab-scale experiment "mini fire test" with standard flat square samples. Consequently, the results of this lab-scale test cannot be compared directly with the performances required by ECE34 directive. The objective of the mini fire test is to highlight the positive effect of the fire protection component on the tank during fire exposition.

Figures 6 A and 6B illustrate the test set-up used for mini fire tests. Figure 6A illustrates the mini fire test without metallic balls (i.e. effect of the weight of the fuel is not taken into account):

A 700 °C flame (61) of a Bunsen burner (62) has been placed under 10 test specimens (63) cut out of tank shells composed of PE only (= reference sample) and under 10 other test specimens (63) cut out of tank shells composed of PE in association with the fire protection component. The surface of the test specimens (63) exposed to fire is 89mm*89mm. The test specimens (63) are placed on a support device (64). The support device (64) is positioned above a Bunsen burner (62) thanks to a holding device (65).

The PE test specimens have a thickness of 5.15 mm and the PE combined with the fire protection component test specimens have a thickness of 7.45 mm.

After an average time of 7 minutes 35 seconds, every of the 10 PE test specimens had holes whereas none of the 10 test specimens composed of PE in association with the fire protection component had hole after one hour test. Figure 6B illustrates mini fire test with metallic balls (66) (i.e. effect of the weight of the fuel is taken into account):

The real fire resistance of a fuel tank is influenced by the weight of the fuel contained in such tank. Indeed, a hydraulic pressure is applied by the fuel, especially on the bottom surface of the tank. This, combined with high temperature, leads to high deformation of the tank shell, up to rupture of the wall. It is thus important to take this effect into account. According to ECE R34 directive, the tank is filled at 50% of its capacity. The resulting pressure has been simulated by 1 kg of metallic balls (66) (diameter 3.5mm) placed on the top side (surface: 89mm*89mm) of 5 test specimens (63) cut out of tank shells composed of PE only and of 5 other test specimens (63) cut out of tank shells composed of PE in association with the fire protection component.

A 700 °C flame (61) of a Bunsen burner (62) has been placed under them.

The PE test specimens have a thickness of about 5.5mm and the PE combined with the fire protection component test specimens have a thickness of 7.5mm.

After an average time of 4 minutes 40 seconds, every of the 5 PE test specimens had holes whereas the 5 test specimens composed of PE in association with the fire protection component had no hole after an average time of 28 minutes 08 seconds test.

The improvement of fire resistance is thus confirmed by these experiments.