The invention concerns a process for manufacturing blown film tubes that are equipped with at least one self-cleaning surface.
Processes for the manufacture of blown film tubes are generally known. In such processes first a plastic melt is formed in an extruder. This melt is compressed subsequently in a blowing head that has a ring-shaped output gap. In the subsequent step of the process the film tube is extruded from this ring-shaped gap and thereafter expanded by producing a corresponding pressure inside the tube that is higher than the external pressure by a blow factor. Subsequently the film tube runs through a squeezing device. In doing so the film tube is stretched in its axial direction by one length stretch factor.
In order to equip such a film tube with a self-cleaning surface further process steps are necessary. The effect of a self-cleaning surface arises if a hydrophobic surface has elevations and depressions. These elevations must thereby maintain definite distances that may neither be exceeded nor fallen short of. Thus the patent specification EP 0 772 514 B1 describes a process for manufacturing self-cleaning surfaces of objects whereby a surface structure out of hydrophobic material is created by stamping, etching or adhesive bonding of a powder.
However, the subsequent handling of the film tube is very expensive.
Therefore the task underlying the present invention is to suggest a process that equips the film tube already in the extrusion process with at least one self-cleaning surface.
The task is solved by the fact that the at least one surface is provided with elevations in that the material required for forming the elevations is added either before the extrusion of the plastic melt out of the ring-shaped gap or is spread over the surface directly after the extrusion.
It is advantageous if the material required for the production of the elevations is a component of another melt.
It is also advantageous to use particulates for forming the elevations.
In a preferential design form of the invention the use of nanoparticulates is intended.
By the subsequent expansion and stretching of the film tube the distances between the elevations in axial and/or radial direction can be exceeded. In accordance with a particularly preferential design form of the invention the ratio between the blow factor and the length stretch factor is larger than 1/4.
In another preferential design form the ratio between the blow factor and length stretch factor is larger than 1/3.
Advantageously a ratio between the blow factor and the length stretch factor is selected to be larger than 1/2.
The selection of a ratio of more than 2/3 between the blow factor and length stretch factor is particularly advantageous.
In a preferential design form of the invention the relation between the blow factor and the length stretch factor is larger than 10/11.
In another preferential design form of the invention includes a relation between the blow factor and the length stretch factor of 1/1.
Examples of implementation of the invention are based on the graphic description and the claims.
The individual figures illustrate:
The length stretch factor FZ is set entirely by the selection of the circumferential speed of the nip rollers. The blow factor is set by the selection of the internal pressure.
The setting of the length stretch factor FZ and/or the blow factor FR influences the distance of the nanoparticulates in radial direction r and/or in axial direction z. In
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Number | Date | Country | Kind |
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10242174.9 | Sep 2002 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP03/09283 | 8/21/2003 | WO | 2/14/2005 |