Field of the invention

The present invention relates to a method to run thin and flexible films over a forming shoulder of a packaging machine and to the forming shoulder itself.

Background of the invention

A wide variety of single-use type packaging materials are known. Many of said packaging materials are in the form of thin, flexible films. The thin,

flexible films may comprise a single layer of one material or of different layers of different materials. The various layers in a film allow to obtain a composite, multi-layer material in a desired combination of properties otherwise not available from a single layer of a single composition. It is hereinafter understood that a "thin" film means a film having a thickness of less than 200 μm.

The material or materials of the film can be variably chosen in function of the protection needed for the contained material. For example, in the field of detergent packaging containing detergent there are severe demands upon the properties of the film. Such properties are, for example, moisture impermeability, gas impermeability, ultraviolet rays-intercepting property, water-proof property, mechanical strengths, cost, flexibility, and the like. In particular, for dry laundry compounds, which sometimes are compositions sensitive to moisture and/or oxygen, the film can comprise a moisture and/or oxygen barrier layer.

Thin, flexible films are considered by the packaging industry to very interesting from the environmental viewpoint. Indeed, the amount of packaging material can be reduced by using thin films to make packaging, like bags or pouches. The films can be re-formed into flexible bags. These may be manufactured according to the methods well known to the man skilled in the art, and described for example in the U.S. Patent No. 3 380 646 or in the document EP-A-626 319. The process may be a continuous, a semi-continuous or a multi-step batch process. The process of re-forming the film into a packaging comprises several steps and devices. One of the

possible device of a film-forming machine is a forming shoulder. Usually, the forming shoulder receives the flat plane film from rollers and changes the flat plane film into the shape of a closed bag-forming tube. This means that the film is pulled around the forming shoulder.

Due to the high friction forces present between the film and the forming shoulder when the film is pulled around the forming shoulder, the film is usually provided with a low coefficient friction coating. This coating is quite expensive. Consequently, it would be desirable to eliminate the need for low coefficient friction coating to reduce the cost of the film. The forming shoulder has further following inconveniences. The high friction requires a high pull force exerted on the film to go around the forming shoulder. Consequently, this puts a severe constraint on the thickness and stiffness of the film. For example, thin, flexible film as described above may be not adequate to be run along these forming shoulders. Indeed, certain thin, flexible films may eventually be torn apart when running around such a forming shoulder.

Furthermore, we found that the high pull forces create a high level of stress events on the film, especially when the film has to be pulled around a squared forming shoulder. Consequently, certain intermediate layers of the film, like perfume barrier layers made of lacquer coating, cannot be used. Indeed, we found that cracking and/or fissures are unavoidably created on certain intermediate layers of the film when the film is passed over the forming shoulder. The intermediate layer lose thereby their specific barrier characteristics for which the intermediate layer was foreseen for in the film.

Finally, again due to the high level of friction between the film and the forming shoulder, we found that especially square shaped forming shoulders have a high material wear. Consequently, these forming shoulders have to be replaced at least once a year. This further increases the cost of running the corresponding packaging machine.

It is therefore an object of the present invention to provide a method to pull a film around the forming shoulder which allows to reduce the costs associated with the material of the film and the maintenance of the forming shoulder, and further avoids the above inconveniences.

Summary of the invention

The present invention is a method of passing a film over a forming shoulder of a packaging machine. The method comprises creating an air cushion between the film and the forming shoulder such that any outer surface of the film is not in contact with the outermost surface of the forming shoulder.

The present invention further provides a forming shoulder enabling the method to run a film over a forming shoulder of a packaging machine whereby the forming shoulder is made of a non-steel material.

Brief description of the drawings

Figure 1 is a plane view of part of the packaging machine of the prior art showing the film pulled over the forming shoulder.

Figure 2 is a plane view of the packaging machine according to the present invention also showing the film pulled over the forming shoulder.

Detailed description of the invention

The material of the film for the present invention may be selected from the group consisting of: tissue, metal, paper, cardboard, plastic materials and a combination thereof. As plastic materials polyolefines, like polyethylene ( = PE), or (oriented) polyethylene terephthalate, or (oriented) polypropylene or a combination thereof, may be used. When the film is a multi-layer material, the intermediate layers may comprise a perfume barrier layer, a gas barrier layer, an oxygen barrier layer, a moisture barrier layer, or a combination thereof. Preferably, the intermediate layer is made of a material selected from the following group consisting of: aluminium foil, ethyl vinyl alcohol co-polymer ( =EVOH), lacquer coating and a combination thereof. Possible lacquer coatings are, for example, Flexplastol ^® 2KB- Lacquer 9A 918 920 or Flexoplastoi • 2KB-Lacquer 9A 919 920 commercially available from BASF Lacke + Farben AG, Stuttgart.

The film comprising multi-layers may be achieved by laminating the layers together. The lamination of layers means that the different layers are attached to each other in a solid state, i.e. the different layer are not melted together as in the extrusion process. In the lamination process lower temperatures with respect to the extrusion. As a preferred option, a tie layer may be used at least on one side of the intermediate layers to strengthen the bonding between the intermediate layers and the other layers. Said tie layer is preferably made of glue. A preferred glue is a polyurethane-based adhesive. By polyurethane-based adhesives we intend all the adhesives based on polyurethane known to the person skilled in the art. In particular, solvent based (including water) and solvent-free adhesive systems comprising polyurethane are usable for the purpose of the present invention. This tie layer can be also applied on both sides of said intermediate layer and/or of the other layers.

Figure 1 illustrates a plane view of a partial packaging machine of the prior art. The packaging machine according to the present invention is suitable to form films into a packaging, like a bag or a pouch. The description of an entire packaging machine is described, for example, in the U.S. Patent No. 3 380 646 or in the document EP-A-626 319. These packaging machines include inter alia at least one forming shoulder (10). In the shown Figure 1 , the film (1 ) is pulled around the forming shoulder (10), as indicated by the arrow (1 1 ). As discussed above, the direct contact between the film and the forming shoulder has several drawbacks and inconveniences.

We found that all these drawbacks and disadvantages can be solved by forming an air cushion (20) between the film and the outermost surface of the forming shoulder. The air cushion is such that it prevents that the film comes in contact with the outermost surface of the forming shoulder when the film is pulled around the forming shoulder. The air cushion ensures a substantially zero friction between the film and the forming shoulder. The air cushion can be created by conveying compressed air between the film and the forming shoulder. For example, this may be achieved through appropriate orifices in the forming shoulder. These orifices have their open ends on the outermost surface of the forming shoulder around which the film is passing around. The other ends of the orifices are connected to a source of compressed air. The possibility of the orifices is schematically indicated by the arrows (12).

The pressure of the compressed air has to be sufficient to maintain the film floating over the forming shoulder as shown in Figure 2, i.e. to sustain an air cushion between the film and the forming shoulder. An example of an appropriate air pressure maintaining the film floating over the forming shoulder is 5 bar. This pressure is measured at the entrance of the orifices. We found that this air pressure reduces the friction between the film and the forming shoulder. This is directly measured by the fact that the pulling force having the air cushion can be reduced at least up to 40 % of the pulling force which would be necessary without the air cushion.

We found that this improved method according to the present invention has further following advantages. The friction force between the film and

the forming shoulder can be easily varied. Indeed, there can be substantially no friction force, when the air cushion completely separates the film from the forming shoulder, to the maximum friction force which is achieved when the film contacts completely the surface of the forming shoulder. This friction force can be regulated by varying the air flow and air pressure of the air cushion. For example, the running film may be stopped onto the forming shoulder when the pulling force is smaller than the friction force between the film and the forming shoulder, i.e. when there is no air cushion between the film and the forming shoulder.

A further advantage is that the forming shoulder can be made out of a material other than steel which is the usually used material. Indeed, the forming shoulder according to the present invention is less susceptible to erosion due to the friction forces between the film and the forming shoulder. Consequently, other materials may be envisaged for making a forming shoulder, and the costs for making the forming shoulder can be correspondingly reduced. The cost can be further reduced by the fact that a forming shoulder made of a non-steel material may allow casting instead of being hand made. Finally, we found that the electrostatic charging of the film can be easily avoided with the method according to the present invention. The electrostatic charging of the film is due to due to the friction with the forming shoulder. According to the present invention, the electrostatic charging can be easily reduced by using ionised air for forming the air cushion.