CHAPTER XIII
Tin-plate Printing—continued
Direct Tin Printing—The Machine—Peculiarities of Impression—Cylinder Covering—Colour Sequence—Printing Inks—Drying Racks—Air Drying and Stoving.
“Direct tin printing” is not, as the term might suggest, a direct impression of the printing forme on the metal plate. It is in reality a transfer printing process in which the transferring medium is a cylinder with an elastic covering. This additional cylinder is one of the chief characteristics of a direct tin-printing machine, and, apart from a few accessory movements, it is in this respect alone that it differs from an ordinary lithographic printing machine. [Fig. 25] gives a sufficiently clear idea of this distinguishing feature. A detailed description of its mechanical principles is unnecessary, but the following points will prove helpful.
The impression is made from the printing forme upon the lower cylinder during the first half of its revolution, and transferred to the metal plate, which is carried by the upper cylinder as the revolution is completed. The reciprocal movement of these two cylinders is therefore a matter which demands the keenest possible attention. Their pitch must be absolutely accurate, the pressure of one against the other nicely adjusted, and the brake arrangement on both such as to ensure a perfectly steady revolution.
The lower cylinder is covered with a three-ply rubber blanket, which provides a sufficiently elastic impression surface.
