Designing a printing or coating process is a tricky thing. Not only during specification of new lines, but even in existing production lines, the coatings and inks always need to be matched to the surface tension of the substrate. Typically, a substrate is treated with corona, increasing the surface tension of the substrate and, thereby, matching the substrate to the ink or coating. Not only in development, but also in production the question arises, how intense should the corona treatment should be? This is especially the case when using older, pre-treated materials that have lost surface tension due long storage periods and requiring refreshment treatment.
Corona treatment is always characterized by the amount of corona dosage or discharge. The dosage (D) describes the energy put into one m2 of the substrate, measured in [Wmin/m2]. It can be calculated by dividing the applied corona power (P) through the web speed (v) and the electrode width (CB) of the corona system:
The applied Corona dosage couples the corona power to the web speed and can be set in direct relation to the achievable dyne level on the substrate surface. The critical task in designing or optimizing a printing or coating process is to determine the right corona dosage that is high enough to enable the process but not overtreat and thus damage the substrate.
Deciding on the right corona dosage is ideally done on test samples in a lab environment. Here, only small amounts of material are used to determine the dosage parameters, resulting in reduced cost and waste. Importantly, production lines remain open for production instead of time consuming testing and development tasks.
SOFTAL solves these issues in the form of a fully integrated Laboratory Table Corona system, the LTC. The motorized substrate holder moves at speeds up to 50 m/min under the 230mm wide corona electrode. This electrode can provide 10 W up to 400 W of power, enabling dosages from to 1 to over 1500 Wmin/m2. The motor itself guarantees a constant speed under the electrode, hence fully reproducible treatment results. Moreover, generator, transformer, drive and ozone destruction are completely integrated in the system, eliminating any requirement for peripheral equipment. Therefore, all the flexibility that is needed in a process engineered laboratory is given to treat conductive as well as non-conductive samples, specifying the exactly right corona dosage needed for the new product.
Furthermore, by using the LTC, surface treatment knowhow can be substantially increased at the production facility while minimizing uncertainties caused by transport and storage from external laboratories. Old, pre-treated and long stored material can be easily tested on site with minimal waste and assigned the correct dosage for refreshment treatment.
For more information about the LTC, SOFTAL’s lab system, click here.