(57) A method of controlling film thickness of a mixture liquid layer of oil material
and water in a printer such as, for example, an offset printer is disclosed wherein
the mixture liquid layer of the oil material containing printing ink, printer's varnish
and the like and water such as, for example, dampening water attached to one roller
of a roller group carrying the mixture liquid layer is alternately irradiated by infrared
rays which are most strongly absorbed into the oil material and the water and by infrared
rays which are hardly absorbed into the oil material and the water. Film thicknesses
of the oil material and the water are detected on the basis of infrared absorption
characteristics of the oil material and the water. The detected film thicknesses of
the oil material and the water are compared with the respective predetermined target
values and supply of the oil material and the water is controlled so that differences
between the detected film thicknesses and the respective target values are minimized.
Thus. printing failure such as so-called greasing and water stain occurring in a prior
art printing is prevented and printing quality is improved, so that spoilages can
be reduced.
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