For multicolor printing, several such cylinders are disposed side by side above the substrate to produce complementary pattern components of different colors, the apertures of one screen then registering with areas of the substrate previously or subsequently contacted by solid surface portions of other screens. Such a composite pattern may have transverse strip zones in which a color component is completely absent so that the corresponding printing screen has an imperforate sector to register with these zones. The solid surface portions of certain screens in a row of such screens may therefore pick up differently colored dyestuff from previously printed areas of the substrate and allow the dye so picked up to penetrate through the apertures of the screen into its interior where it could adulterate the printing liquid already there. Furthermore, the dye adhering to the outer screen surface may stain parts of the substrate to be left blank or to be differently colored by another screen of the array.
Even with the first screen of the row there exists the risk that the outer screen surface becomes loaded with residual dyestuff trickling through its apertures along the ascending half of the screen, after passage of the printing gap, to form smudges on the following substrate areas contacted thereby. This applies also to machines using a single printing screen for producing a one-color pattern on a substrate whose length exceeds the circumference of the screen. Furthermore, screens of dielectric material tend to become charged by their frictional contact with the substrate and thus to attract lint and dust particles from the environment which thereafter stick to the freshly dyed substrate portions and mar their appearance.