Fillers machine direction control

The filler content of the base film is usually between 40-70 wt.%. Afterwards, this base film is stretched successively in the machine direction (MD) and the transverse direction (TD) in order to develop microporous structure. The main advantages of this process are (1) easy control of pore size and porosity, which significantly affect the gas permeability (2) tailoring of the mechanical properties (tensile strength at yield and elongation to break) in both MD and TD, which is of great practical importance (3) uniform stretchability of the base film, which is one of the most important issues in manufacturing of microporous PP films. 

Automation by fast, stable and accurate control loops for consistency, flow, pressure and level is elementary for providing the necessary constancy in the approach flow system. Variations in pressure for example will mainly directly influence the MD profile whilst stock consistency deviations will affect both CD and MD basis weight profiles. In addition the retention on the paper machine and the chemical conditions of the water systems must be kept constant. Here a retention control loop is standard in many appHcations keeping the white water consistency constant by adapting the quantity of retention agent added. Controls for filler, color, air content, cationic demand or zeta potential are also available today. Combining the different controls to a total control concept will lead from purely functional controls to control systems which also address quality and production issues. 

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