Silicone misting in pressure sensitive label production

Abstract

Silicone misting occurs when silicone release coatings are applied on multi-roll coaters on liner substrates at a high speed and pressure sensitive label materials are produced. Mist droplets are formed as the liquid silicone film splits between two rolls and produces fine mist. Misting can be reduced to some degree by using anti-misting additives when formulating silicones but especially at higher speeds it is nearly impossible to prevent misting totally. The effects of silicone misting are related to production, such as the more often occurring cleaning requirements of the equipment and to human health which is the main concern. The objective of this thesis was to study misting of different silicone formulations by monitoring aerosol concentrations during the production of label materials and conducting laboratory measurements for the silicones, siliconized liners and laminate materials consisting of a face, an adhesive, a silicone release coating and a liner. The aim was to find correlations between laboratory measurements and misting observed in production and to find out if the measurements done in the laboratory could be used in predicting the extent of misting phenomenon. The effect of coating speed and properties of the silicones on misting were also studied. The measurements included aerosol monitoring, viscosity and differential scanning calorimetry measurements of the silicones, contact angle and surface energy studies as well as topographic imaging of the siliconized surfaces, rub-off and release profile measurements. Differences between misting of the silicones and the properties of the silicones were observed. The differential scanning calorimetry measurements were able to be combined with the aerosol monitoring results by comparing the curing behaviour of the silicones. The effect of increasing line speed was verified to increase mist formation. Based on the measurements it seemed that the addition of release modifier could increase misting. The higher viscosity of the silicone did not correlate with higher aerosol concentrations observed at the coating station. All studied silicones produced mist, but the amounts were much lower than a common industry threshold level considers acceptable. The other measurements were not easily combined with the misting phenomenon depending on the test method or the laminate materials consisting of different faces, adhesives and liners making it difficult to make conclusions regarding the silicones only. For being able to examine the misting phenomenon and compare different silicone formulations further, the line speeds and other conditions should remain constant. When studying laminate materials, the silicone should be the only variable while the other components would remain the same. The trend of how the amount of mist increases with increasing line speed and the effect of the use of modifier could be further studied as well as the effect of viscosity of the silicone on misting could be verified by making sure that the bath lives of the silicones would be the same as well as the other previously mentioned conditions.