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Wettability (wetting tension) and watt density

 

The relationship between wettability (wetting tension) and watt density is important for managing and operating a corona treater.
Wettability (wetting tension) is closely related to printing property and adherence property so it is widely used as a unit for measuring the level of surface modification achieved by corona treatment. (See “How to measure the effect of treatment.”)
In corona treatment, wetting tension, in principle, changes (rises or rises to the saturation point) in proportion to the amount of input power. Watt density (W/min/m2) is therefore used as the parameter. Watt density is the amount of input power per unit time and unit area, which is calculated by the following formula.

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Length of discharging electrode: L(m)      
Film velocity: V(m/min)
Discharged power: P(W)  

Graph 1 below shows relationships between the watt density of films and their wetting tension. It demonstrates how the wetting tension changes when watt density is changed. (Note: These data were obtained by using films owned by Kasuga Denki, and therefore may differ from actual data.)

corona_10.gif

 

In this way, when using a corona treater it is important to know the level of watt density needed to obtain the desired wetting tension. (The required wetting tension varies according to the purpose – such as coating, printing, or pasting films together – and the coating material, such as adhesive.*)

* In rare cases, the effect of corona treatment cannot be measured by wetting tension. In such cases, the effect is to be tested by processing products.

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