Screen E-Book (.PDF) - MacDermid Autotype

Getting the right exposureThe light source for exposure needs to emitlight of a suitable wavelength for the sensitizerto absorb. The screen printer mainlyuses metal halide lamps, mercury vapourlamps or UV fluorescent tubes.Neither the photo flood nor the quartzhalogenlamp has an output sufficientlyhigh in ultraviolet to be worth consideringfor photostencil applications.Here is a typical plot of lamp output.If the spectral output of the lamp and theadsorption of the sensitizer match, thenthe light energy will be used by the sensitizerfor reaction. Once the reaction iscomplete then light which is not absorbedby the pigments in the emulsion and dyeof the mesh will pass through the stencil.This light can be detected and measuredwith a radiometer and then plotted as illustrated:62