Patent Publication Number: US-2013240536-A1

Title: Fuel tank accessory and method for producing a fuel tank accessory

Description:
The invention relates to a fuel tank accessory, a fuel tank, in particular, a motor vehicle fuel tank, and to a method for producing a fuel tank accessory. 
     An accessory is known from U.S. 2006 099 365 A1, which features a first and a second region. The first and second regions both demonstrate the same immiscible mixture of fuel-resistant ethylene vinyl alcohol copolymer, a non-fuel-resistant HDPE, and a grafted compatibilizer based on HDPE. 
     EP 1 108 653 A2 discloses a fuel tank with a container region composed of HDPE and an accessory composed of an immiscible blend of fuel-resistant plastic such as polyamide, HDPE, and a compatibilizer. 
     U.S. 2003/0124281 A1 also discloses an accessory. It has an injection-molded connection nipple made of a glass-filled polyamide that is attached to a coextruded film composed of a polyamide, a functionalized polyethylene, and a polyethylene of higher density. The element thus created is welded onto a single-layer or multilayer tank composed primarily of HDPE. This approach allows only a fluid- or vapor-conducting system with a joining zone composed of a coextruded multilayer laminate to be produced. 
     DE 195 35 413 C1 discloses a component that is composed of a tubular thermoplastic body that features a stepped annular body on one end and a retaining ridge on the opposite end. Opposite the inner diameter of the body, a circular ring with a projection is molded on, offset by the wall thickness of the body. In the stepped annular body, an intermediate layer is incorporated as an adhesion promoter. Below that, enclosing the ring with the projection, an annular body element is molded on. The annular body element, the intermediate layer, and the circular ring of the tubular body, in addition to the mechanical connection that is effected by the circular projection, are joined together by means of heat. 
     Because this form of connection does not bear up against swelling by the plastics, according to DE 100 62 997 A1, the plastic of the annular body element is cross-linked such that a chemical bond is created between the plastics of both parts by means of bridging the interface between the parts. At the end pointing toward the container, the tubular body is divided into an inner tubular body and an outer tubular body. 
     WO 2008/113821 A1, which the invention uses as a starting point as the closest prior art, discloses a fuel tank accessory that features a first region that is composed of a first plastic, and a second region, whereby the second region features a mixture of the first plastic and a second plastic, whereby the first and second regions are integrally bonded to one another. Due to the second region being composed of the mixture, an integral connection of the fuel tank accessory with an outer wall of the fuel tank is made possible, whereby the outer wall is composed of the second plastic. The disadvantage here in particular is the technical time and effort required to produce such a fuel tank accessory, as this features two different regions composed of different plastics or plastics mixtures, which must be integrally bonded to one another before integral bonding with the fuel tank is possible. 
     In contrast to the above, the object of the invention is to create an improved fuel tank accessory and the method for its production, as well as a fuel tank system. 
     The objects of the invention are achieved respectively by the features of the independent patent claims. Embodiments of the invention are given in the dependent patent claims. 
     Embodiments of the invention have the particular advantage that the fuel tank accessory is cost-effective to produce and can be attached to a fuel tank in an operationally reliable manner. 
     The term “fuel tank accessory” here is understood to mean all components that are suitable for installation on a fuel tank, in particular spouts, valves, in particular tank venting valves, closing elements, or similar. 
     The first plastic is a fuel-resistant plastic. Here the term “fuel-resistant plastic” refers to a plastic that does not swell, or swells only slightly, and that manifests little to no permeability to fuel or oil when it is exposed to fuel or oil over an extended period of time. In particular, fuel-resistant plastic here means one that complies with the Lev II and PZEV standards with regard to emissions. 
     The first, fuel-resistant plastic can be, for example, polyamide (PA), in particular PA 12, or polyoxymethylene (POM). However, the first plastic can also be another fuel-resistant thermoplastic or a fuel-resistant mixture of compatible plastics. 
     The second plastic is a non-fuel-resistant plastic. 
     A “non-fuel-resistant plastic” is a plastic that swells or otherwise changes significantly in its dimensions or mechanical characteristics if it comes into contact with fuel for an extended period of time, and/or a plastic that is permeable to fuel or oil. For example, such a second, non-fuel-resistant plastic can be polyethylene (PE) or polypropylene (PP). However, the second plastic can also be another non-fuel-resistant thermoplastic or a mixture of compatible plastics that are not fuel-resistant. 
     The first and second plastics are inherently not miscible. The mixture therefore contains a compatibilizer to make the first and second plastics miscible. 
     Embodiments of the invention are particularly advantageous in that they reduce the costs of a fuel tank accessory. In general, namely, the first fuel-resistant plastic is significantly more expensive than the second, non-fuel-resistant plastic. But because the first and second plastics are not miscible with one another and therefore normally no integral, impermeable bond can be produced between the two plastics, according to the prior art in general, such a fuel tank accessory consists mainly or entirely of the first plastic, which is correspondingly expensive. 
     According to WO 2008/113821, those regions of the fuel tank accessory that are exposed to fuel during normal operation, that is, after the accessory is installed on a fuel tank and the fuel tank is filled with fuel, are produced from the first plastic; whereas one or more other regions that normally are not exposed to fuel, or not directly exposed, are produced from the mixture that features only a certain proportion of the first plastic, in order to enable the integral bonding with the first parts. 
     The present invention departs from this basic approach in that not merely a single region that is required for the integral bond with the fuel tank is produced from the mixture of the first and second plastics, but preferably the entire fuel tank accessory is produced from the mixture of the first and second plastics, such as through a 1-component injection molding process, an extrusion process or another molding process. 
     This eliminates the necessity for producing an integral bond between the first plastic and the mixture, such as through a relatively expensive 2-component injection molding process. Instead, the fuel tank accessory can be produced through a 1-component plastic injection molding process, in which the plasticized mixture, consisting of the first and second plastics and the compatibilizer, is injected into a mold. In addition, the fuel tank accessory nevertheless surprisingly achieves sufficient fuel-resistance, due to the first plastic present in the mixture. This makes it possible, on the one hand, for the invention to reduce the production-oriented expense of manufacturing the fuel tank accessory, as the quantity of material of the first plastic is economized due to being partially replaced by the second plastic, and on the other hand for the invention to, surprisingly, still achieve sufficient fuel resistance, even in long-term operation. 
     Further, embodiments of the invention also have mechanical advantages: 
     According to one embodiment of the invention, the compatibilizer is a copolymer of the first and second plastics. The use of such a compatibilizer has the particular advantage that there is no need for a further raw material beyond the first and second plastics to be brought into the mix. Such a third material could namely be problematic in terms of its permeability and long-term durability. 
     According to one embodiment of the invention, the polymer is a “graft copolymer.” Here the term “graft copolymer” means a copolymer that is produced as follows: to manufacture the graft copolymer, one of the first and second plastics is grafted such that the grafted plastic can then form covalent bonds with the other of the two plastics. The grafting of the plastic is effected, for example, with a reactive moiety such as a maleic anhydride or an acetic acid moiety. The copolymer then works similarly to an emulsifier in the mixture of the first and second plastics. 
     According to one embodiment of the invention, the copolymer is produced with the aid of an additional compatibilizer, which is added to a mixture of the first and second plastics in solid or liquid form, and which is at least partially consumed during the copolymerization. The additional compatibilizer thereby reacts with the first as well as the second plastic. 
     According to one embodiment of the invention, the additional compatibilizer contains reactive isocyanate groups and/or oligomers with epoxy groups and/or (maleic acid) anhydride groups or oxazoline groups. 
     According to one embodiment of the invention, the proportion of the first plastic in the mixture is less than the proportion of the second plastic. For example, the portion of the first plastic can be a maximum of 35 wt. %, in particular between 20 and 30 wt. %. 
     According to one embodiment of the invention, the fuel tank accessory is designed at least in one first region for an integral bond with a second area, whereby the second region is located on an outer wall of the fuel tank. For example, the second region consists of the second plastic so that due to the presence of the second plastic in the mixture, the integral bond can be realized. 
     The advantages that can be achieved with the embodiment of the invention consist specifically in that the first and second regions are directly connected to one another. The first region is enhanced such that it is fuel-resistant and simultaneously attachable. This attachment is an integral bond. For the fuel tank accessories, this means that they can be pre-fabricated in any quantity and can be welded to the tank without intermediate pieces. Furthermore, the use of non-fuel-resistant plastic substantially reduces the cost of producing the fuel tank accessory. The higher the portion of non-fuel-resistant plastic is, the more cost-effective becomes the mixture used and therefore also the fuel tank accessory. 
     The mixture can contain at least
         10 to 85 wt. % of the first, fuel-resistant plastic,   85 to 10 wt. % of the second, non-fuel-resistant plastic,   3 to 15 wt. % compatibilizer, and   approx. 5 to 30 wt. % additives.       

     The mixture can advantageously consist of
         approx. 45 wt. % of the first, fuel-resistant plastic,   approx. 45 wt. % of the second, non-fuel-resistant plastic,   approx. 10 wt. % compatibilizer, additives and filler materials.       

     “Approx.” here means, for example, a range of +/−5% of the respective value given. 
     The first plastic can be a polyamide and the second plastic a polyethylene. 
     As polyamide, PA6, PA66, PA11, PA12, PA6-T, i.e., the entire polyamide palette, can be used. In the same way, the entire polyethylene palette can be used. 
     The compatibilizer can be a copolymer of the first and second plastics. 
     The copolymer can be a reactively produced copolymer. The copolymer can also feature an additional compatibilizer. 
     The additives can be stamped metal filters, flame retardants, impact resistance modifiers, static inhibitors, conductivity additives, and similar. 
     The filler materials can be glass fibers, glass beads, mineral compounds, or similar. 
     To connect to an opening of the container made predominantly of polyethylene,
         a tubular body element can be provided with an annular body element located on it,   whereby the tubular body element and the annular body element can be produced as a single piece from the mixture, such that the copolymer-annular body element can be connected with the outer wall of the fuel tank by means of a surface element.       

     The copolymer annular element can be located on the tubular body element at a distance from the tube outlet of the tubular body element. This will keep the fuel away from the welded joint. 
     An inner diameter of the tubular body element can be larger than a diameter of the opening of the container. 
     The tubular body element can feature at least one circular connecting rib. 
     The fuel tank accessory can perform a function as, for example, a spout, tank venting valve, closing element or similar. 
     According to one embodiment of the invention, a layer can be applied at least partially to at least one surface element of the copolymer-flange body, that is, to the second component. This layer further strengthens the positive adhesive qualities. The layer can therefore be applied to the complete surface element or only at certain points. Even a selectively applied layer ensures good adhesive qualities. This layer can be approx. 0.001 μm to 100 μm thick. 
     The layer can be implemented, for example, by plasma coating, such as that known, for example, from DE 102 23 865 A1. The plasma coating can be effected on a joining surface of the copolymer-flange body with a chemically active layer, whereby the layer can contain, for example, low-molecular-weight polymer fragments. 
     The copolymer-flange body can consist of approx. 10 to 85 wt. % of polyamide and approx. 85 to 10 wt. % of polyethylene as well as approx. 5 wt. % additives. In particular, an identical proportion of polyamide to polyethylene is possible. How the proportions are divided up depends on the particular conditions of application. But it is also possible that the flange body can consist of layers having different mixture ratios. 
     A polyethylene flange body can consist of approx. 95 wt. % polyethylene and approx. 5 wt. % additives. These common additives can be stabilizers, lubricants, dyes, metal filters, metallic pigments, stamped metal filters, flame retardants, impact-resistance modifiers, static inhibitors, conductivity additives, and the like. 
     The inner diameter of the flange body can be greater than a diameter of the opening of the tank. This allows the connection area to be at least partially removed from the area of influence of the fuel and its vapors and thus counteract the swelling forces. 
     A first tubular body element can terminate in a connection unit at the end facing away from the tank. With this kind of tubular body element the component can be used as a spout. 
     A second tubular body element can be closed with a cover element at the end facing away from the tank. In this form such a component can be used as a closure element for non-required openings of the tank. 
     At least one connecting tubular element can be located below the cover element of the second tubular body element. This provides a housing for a tank venting valve into which a valve element can be inserted. 
     The connection unit and/or the connecting tubular element can terminate in at least one circular connecting rib. This allows a hose to be connected. 
     In another aspect, the invention relates to a fuel tank, in particular a motor vehicle fuel tank such as a fuel tank for a passenger car. The fuel tank has an opening and an outer wall that can consist of the second plastics material. The fuel tank accessory is guided, for example, partially through the opening in the fuel tank and in its first region is integrally bonded with the outer wall of the fuel tank, for example, in that a joining surface of the first region is welded to the outer wall. The welding of one or more fuel tank accessories according to the invention results in a fuel tank system. 
     In another aspect the invention relates to a method for producing a fuel tank accessory. 
     According to an embodiment of the invention, a joining surface of the first region is pretreated in order to increase the reactivity of the joining surface. This can take place through a plasma treatment of the joining surface, for example with the aid of a plasma tip, such as that known from EP 0 986 939 B1. Surprisingly, the plasma treatment causes not only an increase in reactivity but also an improvement in compatibility, specifically by removing passivating layers that can adhere to the joining surface. Alternatively or additionally, pre-treatment of the joining surface can be effected through plasma coating, flame treatment, chemical etching or a mechanical pre-treatment. The increased reactivity due to such a pre-treatment of the joining surface is particularly advantageous for the realization of the integral bond between the first and second components. 
     According to one embodiment of the invention, the integral bond is generated through two-component or multi-component plastic injection molding. Here, for example, the second component is initially created by injecting the mixture into a mold. The mold is then opened in order to pre-treat a joining surface of the second component, for example, with a plasma treatment or a plasma coating. Then the first component is produced and integrally bonded to the second component by injecting the first plastic into the mold. 
     Embodiments of the invention are particularly advantageous because the formation and joining together of the first and second components, that is, for example a tubular body element and a flange body, can be effected in a particularly cost-effective manner. 
     Advantageously, at least one surface element, specifically a joining surface, of the flange body can be coated with a plasma, after which the flange body with the plasma-treated surface element is connected in a fluid-tight manner with the annular body element. The coating saves material while simultaneously increasing adhesion. 
     The layer can be created in two different ways: 
     To create a first layer, a gas in a gas atmosphere can trigger a discharge, which extracts ions from the flange body, atomizes them and accelerates them a short distance; said ions can be focused as a jet onto the surface element. 
     To this end, the discharge can be triggered as gas from air or components of the air, or from a noble gas or a noble gas and its compositions. The noble gas can be helium, neon, argon, krypton, xenon, radon and mixtures and/or compositions thereof. 
     In a gas atmosphere, gas can contain components that react in an open state with the surface element of the flange body and can form a second layer. To this end, components of an organic type can react in air as gas. However, components of an inorganic type can also react in air as gas. 
     In both cases a surface element of a flange body or the surface elements of a number of flange bodies can be treated. Because the treatment can take place in the open, that is, not in a vacuum, the costs are reduced on a lasting basis. 
     To further optimize use of materials, for the tubular body element, a body can first be formed from a thermoplastic material that can be at least partially coated with a polyamide body. In an approach similar to hot-dip galvanizing, the high-cost material is applied to a cost-effective material in order to use predominantly its positive qualities. 
     The thermoplastic material body can be formed from polyester, polyacetate, polyolefin, fluorothermoplastic, polyphenylene sulfide, or a less expensive polyamide that is less resistant to fuel. 
     The flange body can be welded with the tank. Whether spouts or a blank flange or a tank venting valve, all of these components can be tightly welded to the container in the same manner, over the openings at different places. This reduces costs for the final assembly. 
    
    
     
       Embodiments of the invention are described in more detail below, with reference to the drawings. 
       The invention is illustrated in the drawing and is described in more detail in the following. 
         FIG. 1  is a schematic sectional view that shows a component constructed as a spout attached to a tank; 
         FIG. 2  is a schematic sectional view that shows a component constructed as a tank venting valve attached to a tank; 
         FIG. 3  is a disassembled, sectional, partial schematic view that shows an embodiment of an attachment of a tubular body element of a spout according to  FIG. 1 , or a tank venting valve according to  FIG. 2 ; 
         FIG. 4  is a schematic illustration that shows embodiments of a first component and of a second component during a pre-treatment prior to integral bonding; and 
         FIG. 5  is a schematic illustration that shows embodiments of a fuel tank with a fuel tank accessory according to the invention. 
     
    
    
     Fuel tanks are becoming more complex in their shape in order to provide the maximum possible volumetric capacity in cramped spaces. The shape can vary greatly, depending on vehicle type. Fuel tank accessories such as spouts or valves are therefore prefabricated individually in a separate process, and only attached to the tank during final assembly. The tanks are generally composed of multiple layers, of which the outer wall  41  is made of polyethylene. 
       FIG. 1  shows a spout which features
         a tubular body element  11  with   an annular body element  12 .       

     Similar to an annular flange body, the annular body element  12  with a thickness D can be extended. The annular body element  12  is located above an opening  5  of tank  4 . In the region of opening  5 , annular body element  12  of tubular body element  11  is at a distance a to the tubular outlet opening  18 , distance a being greater than thickness D of the flange-body-shaped extension. As a result, tubular body element  11  extends into opening  5  of container  4 . In addition, an outer diameter dR of tubular body element  11  is approximately the same size as an inner diameter dB of the opening, but smaller than an inner diameter dF of a flange-body-shaped extension  36  of annular body element  12  (see also  3 ). A connection unit with a circular retaining ridge  13  is located at the opposite end of tubular body element  11 . 
     A valve element shown in  FIG. 2  features
         a tubular body element  21  with   an annular body element  22 .       

     The flange-body-shaped extension  36  of annular flange body  3  with thickness D is also molded on below annular body element  22 . Annular body element  22  is located above opening  5  of tank  4 . In the region of opening  5 , annular body element  22  of tubular body element  21  also has a distance a to its end which is significantly greater than thickness D of flange-body-shaped extension  36 . Thus tubular body element  21  extends far into opening  5  of tank  4 . Tubular outlet openings  28  are located at the end of tubular body element  21 . In addition, outer diameter dR of tubular body element  21  is approximately the same size as inner diameter dB of the opening, but smaller than inner diameter dF of the flange-body-shaped extension  36  (see also  3 ). The opposite end of tubular body element  21  is closed with a cover element  24 . Connecting tubular elements  25  and  26  with at least one circular retaining ridge  23 . 1 ,  23 . 2 ,  23 . 3 ,  23 . 4  are located below the cover element on tubular body element  21 . A valve element  27  is arranged in the housing thus prepared. 
     The task now is to attach a fuel tank accessory in the form of a spout  1  or a valve unit  2  with its annular body elements  12 ,  22 , hereinafter referred to as component  12 , onto tank  4  above opening  5 . 
       FIG. 4  and  FIG. 5  illustrate schematic embodiments of component  12  for fuel tank accessory  1 . Component  12  consists primarily of a mixture  35  of a plastic A and a plastic B. 
     Plastic A is a fuel-resistant plastic such as polyamide, hereinafter referred to as PA, in particular PA12, POM, or another fuel-resistant thermoplastic. 
     Plastic B is a non-fuel-resistant plastic, which is immiscible with plastic A. 
     Plastic B is a polyethylene, hereinafter referred to as PE, in particular High Density PE (HDPE), polypropylene (PP), or another thermoplastic, immiscible plastic material. 
     To make plastics A and B miscible, the mixture contains a compatibilizer such as a copolymer of plastics A and B. If plastic A is PA and plastic B is PE, the copolymer can be PEgPA (g=graft), that is, a grafted copolymer or a reactively generated copolymer. The reactively generated copolymer is produced, for example, by providing the PE with a reactive moiety, e.g. with maleic anhydride or an acetic acid moiety, and the PE thus grafted then forms covalent bonds with the PA. However, the reverse approach is also possible, in that the PA can also be grafted so that it then forms covalent bonds with the PE. Alternatively, the reaction can also take place in one step, that is, plastics A and B combine with each other or by means of the sole compatibilizer in a single reaction step. 
     As a result of extensive testing, a mixture  35  with the following composition is used:
         approx. 45 wt. % polyamide as the first plastic,   approx. 45 wt. % polyethylene as the second plastic,   approx. 10 wt. % compatibilizer, additives, and fillers.       

     To produce an integral bond for a first embodiment of component  12  of fuel tank accessory  1  from mixture  35  with an outer wall  41  of a fuel tank  4 , said accessory being composed primarily of plastic B, i.e. PE, here a joining surface  42  undergoes pre-treatment. The pre-treatment is effected with a plasma  37 . The plasma flows from a plasma nozzle  38  that is moved in the direction of arrow  38  along a joining surface  42  such that the entire joining surface  42  is coated and a plasma layer  43  is formed. 
     By applying plasma layer  43  to joining surface  42 , the reactivity of the surface increases. This facilitates formation of an integral bond between components  1  and  4 . 
     Creating an integral bond in a second embodiment of component  12  of fuel tank accessory  1  from mixture  35  with an outer wall  41  of a fuel tank  4  is possible as follows: fuel tank  4  has an outer wall composed primarily of plastic B. Because mixture  35 , of which component  12  consists, also contains plastic B, an integral bond between the two components  1  and  4  is possible. In particular when, as mentioned, the proportion of plastic B in the mixture is greater than that of plastic A, pre-treatment of joining surface  42  can be omitted. Thus an untreated joining surface  42  is present. 
     The production and attachment of the component as spout  1  according to  FIG. 1 , or of the component as tank venting valve  2  according to  FIG. 2 , is explained with the aid of  FIGS. 3 through 5 . 
     Spout  1  according to  FIG. 1  and tank venting valve  2  according to  FIG. 2  are of similar design in the region of tubular body element  11 ,  21  and annular body element  12 ,  22 . The annular body element thereby emerges here in a spout-like manner from the tubular body element. The bottom surface element of the annular body element is essentially flat. The outer transitions are rounded, while the inner wall continues through smoothly. 
     Tubular body element  11 ,  21  and annular body element  12 ,  22  are molded by means of injection molding from mixture  35  of PE and PA, with the reactively generated PEgPA copolymer as compatibilizer, preferably through one-component injection molding of the mixture. Mixture  35  can feature additives such as lubricants, metallic pigments and the like, such as reinforcing agents, in particular glass fibers (see  FIGS. 4 and 5 ). 
     The joining surface of the annular body element  12 ,  22  can be constructed as
         untreated joining surface  42  or   treated joining surface  43 .       

     Treatment of joining surface  43  is effected by an activation, for example, plasma treatment or a plasma coating. The thickness of the layer can be approx. 0.001 μm to 100 μm. 
     For the integral bond
         of the outer wall  41  of tank  4  of PE with   the annular body element  12 ,  22  composed of mixture  35  of PE and PA with the reactively generated PEgPA copolymer as compatibilizer, the following possibilities exist:
           a) the annular body element  12 ,  22  features an untreated joining surface  42 ,   b) the annular body element  12 ,  22  features a treated joining surface  43 ,   c) the annular body element  12 ,  22  is extended by flange-body-shaped extension  36  (see also 3) and features an untreated joining surface  42 ,   d) the annular body element  12 ,  22  is extended by flange-body-shaped extension  36  (see also 3) and features a treated joining surface  43 .   
               

     With spout  1 , tubular body element  11  terminates in the circular retaining ridge  13 . The opposite end  28 , from the lower edge of the flange body element, is just long enough that it can extend just beyond the inner wall of tank  4  into the tank. 
     With tank venting valve  2 , on the other hand, tubular body element  21  is closed with cover element  24 . Connecting tubular elements  25 ,  26  with retaining ridges  23 . 1 , . . . ,  23 . 4  are molded onto the tubular body element  21  below the cover element. The end of tubular body element  21  opposite cover element  24  is long enough that it can extend far into the tank and can accommodate valve element  27  in its interior. Tubular outlet openings  28  are molded in so that the gases can flow unhindered into the valve element. 
     Surface element  42  now undergoes plasma treatment, thereby forming plasma layer  43 . 
     The plasma is a mixture of positive and negative charge carriers in relatively large concentration, neutral particles, and photons. The concentrations of positive ions and electrons are thereby large enough that the charges compensate each other at every point over time. The plasma should be regarded as a separate state of aggregation. 
     During plasma atomization (cathode ray atomization), a discharge is triggered in a gas atmosphere such as air and its components, or a noble gas atmosphere such as helium, neon, argon, krypton, xenon, radon and components thereof. The ions are extracted from the plasma by the carrier, that is, by surface element  43  of the tubular body element  21 , i.e. the PE-PA mixture as the target, that is, coating material, which is thereby atomized. At this juncture ions are generated in the ion source and accelerated a short distance and directed as a jet onto the surface element. In this way, plasma layer  43  grows under open conditions. 
     However, a gas, particularly air, can also contain components that react in an open state to the surface element and form plasma layer  43 . The components can be of organic or inorganic type. 
     Plasma layer  43  is thus applied within the thickness range already mentioned of approx. 0.001 μm to 100 μm. 
     In this way, spout  1  and tank venting valve  2  are ready to be attached to tank  4 . 
     At the attachment location, spout  1  and tank venting valve  2  are welded onto opening  4  provided for them on tank  4  made of PE. Flange body element  12 ,  21  and outer wall  41  of tank  4  are attached to each other. 
     For the assembly it is advantageous if all fuel tank accessories are manufactured from the same mixture  35 . Spout  1  and tank venting valve  2  are connected to tank  4  in a fluid-tight manner due to their design and the plastics mixture  35  employed. 
     The volumetric expansion indices 
       PE&lt;PE/PA 
     are selected such that the integral bonds reliably withstand a possible swelling, as swelling—if only to a small degree—can occur even in a fuel-resistant plastic.