Double tubes, e.g. different types of two chamber or multi chamber tubes, are used to pack different types of products or components that for some reason should not be mixed in the package. This may e.g. apply to products that will react chemically or in another way by mutual contact. It is desirable for this type of products that such a reaction starts when the content, partially or completely, is emptied from the tube. The product often requires that it is mixed in order to obtain a homogenous composition, if a specific mixing nozzle is not used. The components must thus be stored separately in the tube under such conditions.
Double tubes can also be used for products that does not react chemically but that nevertheless should be stored separately form each other, e.g. for aesthetic reasons. One such example is the forming of the components in a predefined pattern when they are squeezed out of the tube such that the product is given a specific appearance. Examples of this are striped toothpaste and striped fish roe spread.
A double tube can either consist of a single tube with an inner partition wall or two tubes joined at a shoulder section.
It is important that that the sealing of a double tube is quick and reliable and that it gives an adequate air tightness and an appropriate appearance. Since the sealing of a tube is done in the same production flow as the filling of the tube, the filling, the heating and the sealing must be performed in the same working stroke in order not to create an unbalance in the system. It is thus important that the heating can be performed at least as fast as any of the other operations, such that the heating does not become the limiting factor for the speed of the system.
The joining of a tube is often done by using heated clamping jaws. The heating and joining are in these situations done in the same operational step by heating and thereby melting the tube material together under pressure. The heating of the tube material by hot air is also known. It is e.g. known from WO94/19251 to heat the material for double tubes arranged next to each other with hot air. The double tube is sealed in a subsequent operational step. Even if the shown method for sealing double tubes may give an acceptable result in some cases, there is still room for improvements and developments.