DE19814314B4 - Process for the production of hollow bodies made of thermoplastic material and hollow body produced by this process - Google Patents

Abstract

Process for the production of hollow bodies of thermoplastic material, in which initially at least two partial bodies are produced from a starting material and then these are joined together to form an overall hollow body and in which at least one of the at least two partial bodies is pressed between a female mold (13) and a male mold (12) is formed using a multilayer thermoplastic material as the starting material for each individual partial body, characterized in that a collapsed tube (11) with at least one barrier layer (11c) is used as starting material for each individual partial body.

Description

The present invention relates to a method for the production of hollow bodies made of thermoplastic material, wherein initially at least two partial bodies are produced and then joined together to form an overall hollow body, wherein at least one of the at least two partial bodies is produced by the pressing process.

The production of hollow bodies made of thermoplastic material in the so-called press molding process is known from the prior art. In this method, you can first by pressing several partial body, z. B. two half-shells, produce, which are then joined together and connected, for example, by welding, gluing or other methods together to form the desired hollow body. In contrast to the other common production methods for such containers, compression molding has certain advantages. Compared to the otherwise commonly used blow molding is an advantage z. Example is that the cycle times are shorter. When press molding reaches defined wall thicknesses and thereby it is possible to reduce the total mass required for the container and the weight of the container. Next you can achieve closer radii during compression molding and thus achieve a greater volume relative to the surface. The process is easier than blow molding. In addition, during compression molding a more uniform cooling of the molding is possible, so that occur in this lower voltages. This in turn allows a dimensionally accurate production of the parts.

Compared with injection molding, compression molding has the advantage that plastics can be used which are also suitable for blow molding. The findings on the material behavior obtained during blow molding are in principle transferable. This has the considerable advantage that no additional tests are necessary before a material is used. This can result in significant benefits for industrial use. The possible use of existing machines, where appropriate with certain modifications, also leads to a reduction of the capital expenditure.

The inventive method relates in particular to the production of hollow bodies from which fuel tank, for. B. for the automotive industry. In the production of such fuel tanks, there are high demands on the material, in particular with regard to the protection of the container wall against permeation by the fuel.

From the EP 0 619 174 A1 is a method for the production of hollow bodies made of thermoplastic plastic of the type mentioned become known. From this document it is z. For example, it has become known to use a plate material as a starting material, which is subsequently formed by compression molding. In this document it is also described that one can produce a total hollow body from several partial bodies by their connection, which is suitable for example as a tank for a motor vehicle. In order to create a barrier layer against permeation, in addition to the plate-shaped starting material before the pressing process a film is placed over this, which is then welded during the pressing process with the plate-shaped material. In this known method, disadvantages can result from the fact that during the pressing process no uniform welding of the film with the plate-shaped material over the entire connection surface is formed. A subsequent quality control of the hollow body is associated with additional effort. Also, there are limits to the nature of the usable starting materials in this approach.

DE 30 45 417 A1 discloses a Verdundmaterial for containers with flexible wall in motor vehicles. The composite material consists of a polymeric film layer, fiber reinforcing material and a rubber layer.

DE 37 31 750 C2 discloses a multilayer blow molded plastic container. In both documents, a protective layer against permeation is not addressed.

DE 1 913 463 A discloses materials comprising a hydrocarbon barrier layer. These layers are bonded with bonding materials, such as epoxy, to form a structure for storing liquid.

Furthermore, a plastic fuel tank is known, which consists of different materials and has a barrier to permeation. The materials are made by coextrusion blow molding to the fuel tank.

Compared to this prior art, the object of the present invention is to provide a method for producing hollow bodies made of thermoplastic material of the type mentioned, in which the aforementioned problems do not occur and the more diverse applications allows.

The solution to this problem provides an inventive method for the production of hollow bodies made of thermoplastic material of the aforementioned type with the features of the main claim.

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

The method according to the invention is characterized in that a collapsed tube with at least one barrier layer is used as starting material, which is then pressed. Thus, one can avoid the aforementioned disadvantage that only during the pressing process, first, a compound of several layers of the starting material is produced, as was the case in the aforementioned prior art.

The abutting inner surfaces of the collapsed tube can be fused together. From the use of such a tubular material as a starting material for the process, there is a very significant advantage in that one can use an already tested starting material, which is already used in industrial applications in the blow molding process. This advantage is quite significant, considering that extensive material testing is necessary when a new material z. B. would like to use for the production of fuel tanks for the automotive industry. As a rule, an emissions test is necessary - tests in which the aging resistance of the plastics used is tested, as well as stress tests (crash tests), in which, for example, the compressive strength and safety under the influence of mechanical influences, such as in an accident, is checked. All of these investigations can thus be omitted in the present case, at least largely, since starting materials according to the invention can be used whose suitability for other shaping processes, for example blow molding, is already known.

According to one embodiment of the method according to the invention can be used when using tubular starting material coextrusion material.

Since in the context of the present invention, according to a preferred variant, the production of hollow bodies for the production of fuel tanks is intended, the multilayer starting material has at least one barrier layer. The barrier layer has the purpose of preventing the permeation of the container through the container contents. For this purpose, it is alternatively also possible to carry out, for example, a fluorination of the container later.

The molding according to the invention in the pressing process has other advantages over other processes for the production of hollow bodies made of thermoplastic material. Compared to the deep-drawing process, there is the advantage that you do not have to hold so much material, especially for areas that are greatly stretched during deformation. Furthermore, you have the advantage compared to the thermoforming process as well as compared to the blow molding that a lower distortion in the material is given. This is due in particular to the fact that during pressing, in contrast to the other methods mentioned, the two pressed parts, that is to say the die and the male part, can be cooled uniformly. This leads to lower stresses in the material and prevents, for example, the formation of dents. In the context of the invention, it is preferable to produce by the inventive method hollow body, which are used for the production of fuel tanks. In this preferred application, there are further advantages of the method. For example, necessary for the fuel tank parts such as baffles before the connection of the body part to the entire hollow body, for example by welding, are introduced by simple steps. For example, such baffles or other necessary accessories of the fuel tank can be welded, clipped or inserted.

The general advantages of the pressing process compared to blow molding or injection molding are mentioned above. These advantages also benefit the process of the invention. So far, however, was usually assumed in the pressing process either from a mass, for example, fused powder or granules in the hot plastic state, or it was used homogeneous plate-shaped material. In the context of the investigations on the present invention, it has surprisingly been found that multilayer thermoplastic material, preferably coextrusion material, can also be processed by the pressing process.

Preferred developments of the task solution according to the invention emerge from the features mentioned in the subclaims. Further advantages of the invention are the following detailed description removable.

The invention will be described in more detail by means of embodiments with reference to the accompanying drawings. Showing:

1 a simplified schematic sectional view, based on which an exemplary variant of the method according to the invention is explained in detail;

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

3a a section through an exemplary plate-shaped starting material according to the invention;

3b a section through an exemplary tubular material according to the invention;

4 a cross section through the tubular material along the line IV-IV of 3b ,

First, on the 1 and 2 Reference is made, which show a device for pressing in a schematically simplified representation, which comes in an exemplary variant of the method according to the invention is used. This device comprises on the one hand a device 10 for producing the raw material subjected to deformation by pressing in this process. At this facility 10 it may be, for example, an extruder. By means of this extruder 10 a tubular starting material can be extruded, wherein in the illustration according to the 1 and 2 a tubular starting material 11 in the form of a collapsed multilayer hose, is the material from which it starts at the beginning of the deformation process.

The device further comprises a tool for the deformation, which is two-part and a die 12 includes, and a patrix 13 , which is indicated as in the illustration by the arrows in the direction transverse to the longitudinal axis 15 that is to say that they are arranged so as to be movable perpendicularly to the plane of expansion of the tube. The device further comprises a spreading device 14 for the tubular starting material 11 ,

For the deformation process drive die 13 and male 12 towards each other, which are usually tempered at the same time, so that the starting material 11 to press into the desired shape according to the shape of the tool. In the present embodiment according to 1 In this press-forming process, one half of a hollow body is produced, which is then subsequently connected, preferably welded, to a further, generally complementary half, to form an overall hollow body.

3a shows a section through an exemplary starting material 21 which is plate-shaped in this case. It is a multilayer material that can be produced, for example, by coextrusion. This plate-shaped starting material 21 consists of a first layer 21a (shown on the left in the drawing), a second layer 21b (shown on the right in the drawing) and one between these two layers 21a and 21b arranged barrier layer 21c , This barrier layer 21c For example, it may be a fluorine-containing plastic layer or the like. The barrier layer 21c has the task to prevent the permeation of liquids or gases through the material from which the hollow body is formed. Assuming such a three-layer plate-shaped starting material, as in 3 is shown, then obtained in the process a hollow body with a correspondingly constructed three-layer wall. Of course, to prevent the permeation of the wall of the hollow body, the barrier layer does not have to be midway between the two layers 21a . 21b be arranged of the starting material, as in the embodiment according to 3a is shown, but the barrier layer 21c may be just as good on one or both of the layers 21a . 21b be applied.

3b shows an enlarged sectional view through a tubular starting material 11 , which can be used according to a variant of the method according to the invention, as used for example in 1 is shown. Also with this tubular starting material 11 according to 3b it is a multi-layered material that can be produced, for example, by coextrusion. For example, a collapsed tube can be used, as it is also used as a starting material in the blow molding process. The tubular starting material 11 according to 3b is in turn multi-layered. This starting material 11 includes a first layer 11a , which is located on the outside and, since it is a tubular starting material 11 trades, therefore as outer layer runs round, how to out 4 can recognize. This tubular starting material 11 further comprises an inner layer 11b and one between this inner layer 11b and the outer layer 11a arranged barrier layer 11c , As with a collapsed tube, the inner layer 11b abutting each other is the result of merging these layers 11b by heating a single layer 11b with correspondingly thicker material thickness. If one goes from such a starting material 11 according to 3b and deforms it in a press molding process, for example, as shown 1 , Then you get after molding a molding with a total of five layers, namely the two outer layers 11a according to 3b the merged double inner layer 11b and the two barrier layers 11c , each one between the outer layer 11a and the inner layer 11b are located. Also with this tubular starting material 11 according to 3b may as well have one or more barrier layers 11c outside on the layer 11a be applied.

Claims (8)

Process for the production of hollow bodies of thermoplastic material, in which initially at least two partial bodies are produced from a starting material and then these are joined together to form an overall hollow body and in which at least one of the at least two partial bodies is pressed between a matrix ( 13 ) and a patrix ( 12 ), wherein a multilayer thermoplastic material is used for the pressing process as the starting material for each individual partial body, characterized in that as the starting material for each individual partial body a collapsed tube ( 11 ) with at least one barrier layer ( 11c ) is used. A method according to claim 1, characterized in that the starting material used is a coextrusion material. A method according to claim 1 or 2, characterized in that as starting material a collapsed tube of at least two polyethylene layers ( 11a . 11b ), the additional barrier layer ( 11c ) is either externally mounted on one of the polyethylene layers or disposed between the two polyethylene layers. Method according to one of claims 1 to 3, characterized in that as starting material a collapsed tube ( 11 ), as used in blow molding, but which is then pressed. Method according to claim 1, characterized in that the barrier layer ( 11c ) consists of a fluorinated plastic, preferably a fluorinated polyethylene or polyamide. Method according to one of claims 1 to 5, characterized in that a barrier layer ( 11c ) is produced by an internal fluorination of the hollow body after molding. Hollow body, in particular container made of thermoplastic material, characterized in that this was prepared by a process according to one or more of claims 1 to 6. Fuel tank, characterized in that it was obtained starting from a hollow body according to claim 7.

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