Loss of wetting properties of PE coated board

Abstract

The main objective of the study was to find out the phenomenons causing the loss of wetting properties of corona treated low density polyethylene coated board. The main focus was on one side coated gloss low friction finished board grade. The loss of wetting properties caused decreased line speed on extrusion coating line. The line speed was from 100 m/min to 150 m/min lower than on normal production. Other objective was to find corrective actions to resolve the problem. The theoretical part mainly focuses on two different subjects. The first part introduces corona surface treatment. the corona effect is presented before corona treating equipment. Physical and chemical changes of polyethylene surface exposed to corona treatment are also examined. Different parameters affecting the wetting properties are introduced to the reader. The second part of the theoretical framework is concentrated on winding. Different mechanical solutions of winders are discussed. The winding nip and nip behaviour is under closer examination. Parameters affecting the nip behaviour is also discussed in this section. The extrusion coating process is also presented as well as tests used in experimental part. The first part of the experimental work compares extrusion coating lines 3 and 4. The problem exists on extrusion coating line 3 where the troublesome grade is normally produced. Coating line 4 does not have this problem. Test runs were focused on to find out the exact position where the wetting properties are lossed. Test runs showed that the treatment is reduced in the nip of the winder. Surface winder uses high nip line load to gain adequate roll hardness and web tension. The consequence of the high nip line load is a relative speed difference between layers of wound roll. This rubbing causes detoriation of corona treatment.Further test runs dealt with the wetting properties affected by the surface winder parameters. The solution could not been found by adjusting parameters. Therefore new construction solutions of the winding station was researched. Adding a drive to the central shaft of the surface winder was considered the most profitable solution. Although the functionality of the solution could not been certified and therefore further study of this construction must be done. /Kir10