Temperature measurement of polymer substrates during plasma irradiation

In the web coating process of some materials using sputtering, plasma-assisted evaporation, and plasma-enhanced CVD, heat damage of polymer substrates by plasma irradiation is problem for the quality of products. During deposition, the substrate is heated by condensation of deposits, heat from the source or plasmas, and so on. However, it is difficult to distinguish these processes and the change of the temperature plasma irradiation must be minimized. In this paper, we have researched the effect of discharge conditions on the plasma heating of the polymer substrate independently of the other heat sources. The Ar, O₂ and N₂ plasmas were created by AC discharge with magnetic field using web coating. PET(Polyethylene terephthalate) substrate was passed through the plasma region at different conditions, such as gaseous species, pressure, discharge power, and web speed. The temperature of the substrate was measured using thermometer before and after passing through the plasma region. In ordinary case, the temperature of the substrate increased immediately when the substrate entered the plasma region and had the maximum at the center of the plasma region. When the power input increased, the temperature slightly increased in both plasmas. Pressure also affected the increment of the substrate temperature. The change of the web speed influenced upon the residence time of the substrate in the plasma region. In this experimental conditions, although the temperature change of the substrate were 0.4-3°C, this would not ignore for the polymer substrate. The change of the substrate temperature passing through plasma region will be discussed together with the results of plasma diagnostics and some the surface analysis of the substrate.