In Part 4 of the Corona Treating Series we discussed watt density.
Most roll coating and laminating is done today using water-based adhesives and coatings. The use of water-based materials requires a substrate with a higher surface energy than when solvent-based coatings are used. Therefore, pre-treated substrates should be used whenever possible and the pre-treated polymer should be treated again at the time of coating or lamination. Table 5 shows typical treatment levels for various materials.
Table 5 – Typical Watt Densities
||1.2 to 1.4 Watts/Square Foot/Minute
||1.3 to 3.3 Watts/Square Foot/Minute
||2.0 to 3.0 Watts/Square Foot/Minute
|100% Solids Adhesives:
||1.0 to 1.5 Watts/Square Foot/Minute
Pre- and Post-Treatment
Most polymers are treated during the extrusion process. This treatment should be kept to a maximum of 44 dynes so the substrate does not “block” when wound. If the substrate contains additives such as slip or anti-block, the surface energy will decrease because the additives migrate to the surface covering up the treated material. When the substrate is later used in a coating or laminating process, the substrate should be re-treated on the process line to bring back the treatment and even raise it to higher levels. The treatment can be higher than 44 dynes at this time because the treated substrate will be covered with a coating or adhesive before being wound.
Post-treatment, i.e., surface treatment of coated substrates to facilitate follow-on converting process, is predominantly achieved using the corona process. Both the Pre- and Post treatment processes require several configurations of equipment to meet the widely varied technical and cost requirements found in extrusion coating applications.
Despite increased line speeds, the move to ever lighter webs and lower web tensions, and the introduction of co-extruded substrates, corona treating technology has advanced to offer both technical and cost effective solutions to surface treatment requirements for the substrate coating industry.
Written for Faustel by Enercon Industries Corporation.