| 摘要 |
A method for measuring the dynamic surface tension (DST) of a proposed outer layer of a liquid composition, to be curtain or slide hopper coated, over a range of surfactant levels to determine the surfactant concentration which produces the maximum resistance to air currents. Measurements are made by the Wilhelmy Blade Method, in which a surface of a pool of composition to be measured is placed in contact with the lower edge of a suspended blade. The static method is modified such that the surface of the composition touching the blade is continually refreshed to simulate the formation of fresh curtain surface by pumping the composition upwards through an open cylinder and allowing the composition to spill over the edges ("overflowing weir"). The bulk surfactant concentration providing maximum resistance to coated streakiness or mottle is highly correlated with the concentration providing maximum surface tension gradients in the overflowing weir apparatus. Thus, for new or non-optimized air-contact layers, the optimum surfactant concentration can be predicted quickly and inexpensively through off-line measurement of surface tension using the overflowing weir technique.
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