DE19814314A1 - Hollow plastic molding production, e.g. fuel tanks, by assembly of pressed shells - Google Patents

Abstract

The material being pressed is a multilayer thermoplastic, and/or a flexible tube or collapsed tube, and/or a material suitable for blow-molding a fuel tank. An Independent claim is included for the corresponding hollow vessel, preferably a container, and especially a fuel tank. Preferred features: The starting material is coextruded (10) or a multilayer panel. In the latter case, at least one barrier layer is included. The starting material is a panel of two or more polyethylene layers, with either an externally-applied or intermediate barrier layer. The starting material is a multilayer collapsed tube (11), especially with a barrier layer. It is as used in blow molding, but is pressed. The barrier layer is fluorinated plastic, preferably fluorinated polyethylene or polyamide. It is formed by internal fluorination, following molding.

Description

The present invention relates to a method for producing hollow bodies from thermoplastic, in which at least two partial bodies are first produced and then be assembled into a total hollow body, at least one of the at least two partial bodies are produced in the pressing process.

The production of hollow bodies from thermoplastic in the so-called Press molding is known from the prior art. With this method you can by press molding first several sub-bodies, for. B. produce two half-shells are then joined together and for example by welding, gluing or other methods can be combined to form the desired hollow body. in the In contrast to the other common manufacturing processes for such containers, this has Molds have certain advantages. Compared to the otherwise commonly used blow molding there is an advantage e.g. B. in that the cycle times are shorter. Achieved during press molding one defines wall thicknesses and thereby it is possible to get the necessary for the container Reduce overall mass and weight of the container. You can continue with Press forms achieve narrower radii and thus a larger one in relation to the surface Reach volume. Process control is easier than blow molding. Besides, is a more even cooling of the molding is possible during press molding, so that in this lower voltages occur. This in turn enables a more precise manufacture Of the parts.

Compared to injection molding, press molding has the advantage that plastics can be used, which are also suitable for blow molding. The blow molding The knowledge gained about material behavior can in principle be transferred. this has the considerable advantage that no additional tests are necessary before a material is used. This can have considerable advantages in industrial use surrender. Also the possible use of existing machines with certain Modifications lead to a reduction in capital expenditure.

The method according to the invention relates in particular to the production of hollow bodies those fuel tanks, e.g. B. for the automotive industry. During manufacturing  such fuel tanks have high demands on the material, especially in With regard to the protection of the container wall against permeation by the fuel.

EP 0 619 174 (A1) describes a process for producing hollow bodies thermoplastic material of the type mentioned. From this Scripture is it z. B. has become known, a plate material as a starting material use, which is then formed in the pressing process. In this writing, too described that one from several partial bodies by connecting them Can produce entire hollow body, for example, as a tank for a motor vehicle is suitable. In order to create a barrier layer against permeation, in addition to a sheet is placed over the plate-shaped starting material before the pressing process, which is then welded to the plate-shaped material during the pressing process. With this Known methods can have disadvantages in that none during the pressing process uniform welding of the film with the plate-shaped material over the entire Connection surface is created. A subsequent quality control of the hollow body is included additional effort associated. There are also limits to this approach regarding the type of starting materials that can be used.

The object of the present invention is in relation to this prior art therein, a process for the production of hollow bodies made of thermoplastic plastic to create the type mentioned, in which the aforementioned problems do not occur and that allows more diverse applications.

An inventive method for the production of Hollow bodies made of thermoplastic material of the type mentioned at the beginning with the characteristic features of the main claim.

The invention further relates to those produced by the method according to the invention Hollow bodies, in particular for use in the manufacture of fuel tanks.

The process according to the invention is characterized in that a multilayer thermoplastic material is used as the starting material, which is then pressed. In order to you can avoid the aforementioned disadvantage that only during the pressing process First, a connection of several layers of the starting material is made, such as this was the case in the aforementioned prior art.  

The multilayer starting material can be a plate-shaped material, it can be but also act as tubular material. For example, one is collapsed Usable hose, which consists of a multilayer thermoplastic material, and is thus similar in design to a hose that is used as the starting material in one Blow molding process is used. The adjacent inner surfaces of the collapsed Tubes can be fused together. From the use of such tubular or plate-shaped material as the starting material for the process there is a very important advantage, which is that you have already tested one Can use raw material that is already used in industrial applications Blow molding process is used. This advantage is quite significant when one considering that extensive material tests are necessary when you get a new material e.g. B. for the manufacture of fuel tanks for the automotive industry. In As a rule, an emissions test is necessary, tests in which the Resistance to aging of the plastics used is checked as well as also Stress tests (crash tests) in which, for example, the pressure resistance and the Safety when exposed to mechanical influences, such as in an accident can occur is checked. All of these examinations can therefore be carried out in the present case at least largely eliminated, since starting materials are used according to the invention can come, their suitability for other shaping processes, for example Blow molding, is already known.

According to a development of the method according to the invention, both Use of plate-shaped starting material as well as when using Use tubular extrusion coextrusion material.

Since in the context of the present invention according to a preferred variant Manufacture of hollow bodies is intended for the production of fuel tanks, that shows multilayer starting material, be it plate-shaped or tubular, at least one Barrier layer on. The barrier layer has the purpose of permeating the container through the To prevent container contents. For this purpose it is alternatively also possible to later on Example of fluorinating the container.

The shaping according to the invention in the pressing process has compared to other processes for the production of hollow bodies made of thermoplastic plastic further advantages. The advantage over the deep-drawing process is that you do not have as much material must be available, especially for areas that are greatly stretched during deformation. Furthermore, compared to the deep-drawing process as well as the  Blow molding has the advantage that there is less warpage in the material. This is in particular due to the fact that when pressing unlike the others the two press parts, that is to say the die and the patrix can be cooled evenly. This leads to lower stresses in the material and prevents, for example, the formation of bumps. It is preferred within the scope of the invention by the process according to the invention to produce hollow bodies for the production of Fuel tanks are used. This preferred application results in further advantages of the process. For example, necessary for the fuel tank Parts such as baffles before connecting the partial bodies to the whole Hollow bodies, for example by welding, by simple process steps be introduced. For example, such baffles or others Weld in, clip on or insert the necessary accessories for the fuel tank.

The general advantages of the pressing process over blow molding respectively versus injection molding are listed above. These advantages also come to that The method according to the invention benefits. So far, however, the pressing process in the Usually either based on a mass, for example melted powder or Granules in the warm plastic state or it became homogeneous plate-shaped material used. Within the scope of the investigations into the present invention Surprisingly, it can be found that there are also multilayer thermoplastic Material, preferably coextrusion material, can be processed in the pressing process.

Preferred developments of the task solution according to the invention result from the features mentioned in the subclaims. Further advantages of the invention are following detailed description can be removed.

The invention is explained below using exemplary embodiments with reference to FIG the accompanying drawings described in more detail. Show

Fig. 1 shows a schematically simplified sectional view of the basis of which an exemplary embodiment of the method according to the invention is explained in detail;

FIG. 2 seen a corresponding schematically simplified view of the device according to FIG. 1 in the direction of arrow II of FIG. 1;

FIG. 3a shows a sectional view of an exemplary plate-shaped starting material according to the invention;

FIG. 3b is a sectional view of an exemplary tubular material according to the invention;

Fig. 4 shows a cross section through the tubular material along the line IV-IV of Fig. 3b.

First of all, reference is made to FIGS. 1 and 2, which show a device for pressing in a schematically simplified representation, which is used in an exemplary variant of the method according to the invention. On the one hand, this device comprises a device 10 for producing the starting material, which in this process is subjected to deformation by pressing. This device 10 can be an extruder, for example. By means of this extruder 10 , a plate-shaped or a tubular starting material can be extruded, wherein in the illustration according to FIGS. 1 and 2, a tubular starting material 11 in the form of a collapsed multilayer tube is the material from which the deformation process is started.

The device further comprises a tool for deformation, which is in two parts and comprises a die 12 and a male 13 , which is indicated by the arrows in the illustration in the direction transverse to the longitudinal axis 11 a, that is perpendicular to the plane of expansion of the hose are arranged. The device further comprises a spreading device 14 for the tubular starting material 11 , this spreading device 14 also serving as a holding device for the starting material when plate-shaped or sheet-like starting material is used.

For the shaping process, the die 13 and the die 12 move towards one another, as a rule they are tempered at the same time in order to thereby press the starting material 11 into the desired shape in accordance with the shape of the tool. In the present exemplary embodiment according to FIG. 1, half of a hollow body is produced in this press-molding process, which can then subsequently be connected, preferably welded, to another generally complementary half to form an overall hollow body.

Fig. 3a shows a section through an exemplary starting material 21 for the inventive method, which is plate-shaped in this case. It is a multi-layer material that can be produced, for example, by coextrusion. This plate-shaped starting material 21 consists of a first layer 21 a (shown on the left in the drawing), a second layer 21 b (shown on the right in the drawing) and a barrier layer 21 c arranged between these two layers 21 a and 21 b. This barrier layer 21 c can for example be a layer made of a fluorine-containing plastic or the like. The barrier layer 21 c has the task of preventing the permeation of liquids or gases through the material from which the hollow body is formed according to the invention. If one starts from such a three-layer plate-shaped starting material, as shown in FIG. 3, then in the process according to the invention a hollow body with a correspondingly constructed three-layer wall is obtained. In order to prevent the permeation of the wall of the hollow body, the barrier layer does not of course have to be arranged centrally between the two layers 21 a, 21 b of the starting material, as is shown in the exemplary embodiment according to FIG. 3a, but the barrier layer 21 c can just as well be outside are applied to one or both of the layers 21 a, 21 b.

FIG. 3b shows an enlarged sectional view through a tubular raw material 11, a variant of the method according to the invention can be used in accordance with, as shown for example in FIG. 1. This tubular starting material 11 according to FIG. 3b is also a multi-layer material that can be produced, for example, by coextrusion. For example, a collapsed hose can be used, as is also used as the starting material in the blow molding process. The tubular starting material 11 according to FIG. 3b is again constructed in several layers. This starting material 11 comprises a first layer 11 a, which is located on the outside and, since it is a tubular starting material 11 , consequently runs all around as an outer layer, as can be seen from FIG. 4. This tubular starting material 11 further comprises an inner layer 11 b, and a barrier layer 11 c arranged between this inner layer 11 b and the outer layer 11 a. Since each b is in a collapsed tube, the respective inner layer 11, these layers formed during fusion b 11 b with correspondingly thicker material thickness by heating a single layer. 11 Judging from such a starting material 11 according to Fig. 3b and deforms in a press molding method, for example, according to the illustration of FIG. 1, is then obtained after the pressing process, a molding having a total of five layers, namely the two outer layers 11a as shown in FIG . 3b, the resulting merger double inner layer 11 b and the two barrier layers 11 c which are located respectively between the outer layer 11a and inner layer 11b. Also in this tubular raw material 11 according to Fig. 3b may equally well one or more barrier layers 11 c on the outside of the layer 11 a can be applied.

Claims (12)

1. A process for the production of hollow bodies made of thermoplastic, in which at least two partial bodies are first produced and then these are joined to form a total hollow body and in which at least one of the at least two partial bodies is formed in the pressing process, characterized in that the starting process is used for the pressing process

• - a multilayer thermoplastic material, and / or
• - a hose or collapsed hose, and / or
• - A material that is suitable for blow molding a fuel tank is used.

2. The method according to claim 1, characterized in that one as the starting material used a coextrusion material. 3. The method according to claim 1 or 2, characterized in that a multilayer plate-shaped material ( 21 ) is used as the starting material. 4. The method according to claim 3, characterized in that one uses a multilayer plate-shaped starting material ( 21 ) having at least one barrier layer ( 21 c). 5. The method according to any one of claims 1 to 4, characterized in that a plate-shaped material of at least two polyethylene layers ( 21 a, 21 b) is used as the starting material, with an additional barrier layer ( 21 c) either outside on one of the polyethylene -Layers attached or arranged between the two polyethylene layers. 6. The method according to any one of claims 1 to 5, characterized in that a multilayer collapsed hose ( 11 ) is used as the starting material. 7. The method according to claim 6, characterized in that a multilayer collapsed hose ( 11 ) with at least one barrier layer ( 11 c) is used as the starting material. 8. The method according to any one of claims 1 to 7, characterized in that a collapsed tube ( 11 ) is used as the starting material, such as is used in blow molding, but which is then pressed. 9. The method according to any one of claims 1 to 8, if dependent on at least one of claims 4, 5 or 7, characterized in that the barrier layer ( 11 c) consists of a fluorinated plastic, preferably a fluorinated polyethylene or polyamide. 10. The method according to any one of claims 1 to 9, characterized in that a Barrier layer through an internal fluorination of the hollow body after shaping is produced. 11. Hollow body, in particular containers made of thermoplastic, thereby characterized in that this according to a method according to one or more of the Claims 1 to 10 was produced. 12. Fuel tank, characterized in that it starts from one Hollow body was obtained according to claim 11.