Process for manufacturing a plastic tube body

Details Process for manufacturing a plastic tube body Process for manufacturing a plastic tube body

1998-10-30

2004-03-09

Ball, Michael W. (Department: 1733)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

Producing multilayer work or article

C264S524000, C264S537000

Reexamination Certificate

active

06702978

ABSTRACT:

TECHNICAL FIELD
The present invention relates to plastic tube bodies and to a method for producing them. In particular, the present invention relates to a method for producing plastic tube bodies, in accordance with which, firstly so-called tube preforms are produced and then formed into the final tube shape at a later point in time.
PRIOR ART
Various methods with which plastic containers can be produced, for example, from a thermoplastic are known in the prior art. Various methods well known to the person skilled in the art are used for this, such as injection moulding, blow moulding, laminating methods, polyfoil and coextrusion methods.
An appropriate selection of material is made on the basis of the various properties of the components with which the container is later to be filled. In addition to the price and obvious parameters such as strength, etc., criteria for selecting the material also include the aggressivity or the volatility of the component, or a desired inert behaviour between the component and container, as is mostly necessary with medical active substances.
The diffusing out of one or more active substance components is extremely undesirable precisely in the case of containers for medical or pharmaceutical components, since the loss of the volatile components means that the percentage quantitative composition no longer corresponds to the original data, with the result that a medically prescribed dosage, which is based on the original composition of the agent is no longer guaranteed.
Furthermore, when volatile components serving as solvents diffuse out there registers a change in the consistency which can lead to more rapid ageing due to drying out or to a poorer applicability.
Since, however, individual materials are able only rarely to fulfil all the requirements placed on them (such as, for example, good compatibility with the component and impermeability for specific volatile constituents thereof), consideration has already been given to various components for multilayer containers (in particular tubes) in which the various layers can consist of different materials. For example, such multilayer containers are produced by calendering methods in which the various materials are extruded and calendered in a role configuration, that is to say rolled to form films or multi-layer films. The films produced in this way are then welded to shoulder pieces and/or sealing pieces produced, for example, by means of an injection moulding method.
However, such shoulder pieces or sealing pieces do not have the properties of the multi-layer film, since they have been produced in a conventional way by means of injection moulding methods and consist of only one material layer.
A further possibility for achieving complete protection against diffusion is to provide cost-intensive metal containers which are complicated to produce and constitute a natural diffusion barrier because of the molecular density of metal. These metal containers can be provided with an additional layer in the interior, in order to ensure an inert behaviour between the fluid and container wall. However, not only is the production of metal containers very much more complicated than the fabrication itself because of very many individual steps (rolling, coating with plastic, forming the containers, folding and flanging the longitudinal seam, etc.), but fabrication times and material costs are also substantially higher.
It has already been considered for this reason to produce multilayer plastic containers by using a multilayer injection moulding method. Such a method is disclosed, for example, in EP 0 537 346 A1. The first step in this method is to inject a so called enveloping layer into the injection mould, followed by, or simultaneously with a so-called core layer which has previously been foamed by using a foaming agent. The result of this is a container with a two-layer wall whose components consist of different materials.
A further problem to be considered in producing plastic containers is the transportation size of the containers. To be specific, the plastic containers are frequently not produced in the company where they are later filled with the component, but by a supplier at a different location. Since, depending on the application, plastic containers are of considerable size but scarcely have any weight, a transportation problem arises to the extent that in relation to the weight of the goods to be transported, the freight charges are also calculated, in particular, with reference to the volume of the goods. Consequently, with large-volume (empty) containers transportation entails substantial costs since, for example, a lorry is essentially transporting “air”.
For this reason, it has already been proposed to supply plastic containers to the consumer not in their final form but in the form of so-called preforms. EP 0 374 247 A1 and EP 0 325 440 A2 may be named as examples in this connection. Injection moulding methods for producing multilayer container preforms are described in these documents.
An example of plastic containers are tubes which are presently widely used, for example in the field of medicine, in cosmetics, for dental care agents and in nutrition.
In addition to a tube closure, usually produced using an injection moulding method, plastic tubes comprise a tube body. Two different requirements are made of this body. Firstly, the tube body must have a firm tube shoulder region which, having been provided with a screw thread, must have the required strength to seal the tube reliably with the tube closure. It is to be borne in mind here that—by contrast with plastic bottles—use is made in the case of tubes of industrial threads which are not positively disengaged but are turned out of the mould. Moreover, the tube body must have a lateral surface which gives the later user the required “feeling of a tube”, specifically a sufficiently soft consistency which permits the mostly highly viscous component to be completely evacuated by being squeezed out.
To date, tube bodies have been produced in two different ways which are known in the prior art as the “KMK” method and the “AISA” method. These two methods are described below with reference to FIGS.
4
A and is
4
B.
The “KMK” method is represented diagrammatically in FIG.
4
A. As may be gathered from the representation, a cylindrical tube
600
, which corresponds to the later tube lateral surface, is introduced into a mould cavity
500
. The tube
600
can consist of a (multilayer) film which has been produced using the calendering method explained above, and has been welded at the seam
610
to a tube. After the tube
600
has been moved into the cavity
550
of the mould
500
, the later plastic
510
, forming the tube shoulder, is introduced into the mould cavity
550
as a “sausage” running round in the shape of a circle. In a subsequent step, the tube shoulder is then formed by a punch
520
which is lowered into the mould cavity
550
of the mould
500
.
In accordance with the “AISA” method represented diagrammatically in
FIG. 4B
, a tube lateral surface
600
(which can be produced as previously described in connection with the KMK method) is introduced into an already prefabricated tube shoulder
550
′. This tube shoulder
550
′ can have been produced previously in the injection moulding method. The elements of tube shoulder
550
′ and tube lateral surface
600
thus assembled are then welded, for example by means of high frequency or hot air.
Both of the previously mentioned methods ensure that the tube body produced meets the various requirements made of the tube shoulder and tube lateral surface. Disadvantages of these production methods consist in that it is a relatively complicated and cost-intensive matter to produce the tubes, which can be moved to the filling operation only at their final size, which means they require a substantial transportation volume.
It is therefore the object of the present invention to create a method for producing fillable plastic tube bodies in which the containers produced can, on

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