THE 4 STAGES OF BAG MAKING
(3) PRINTING
If the bags are to be printed, the roll of film is taken to the printing machine known as a 'press'. This is usually a flexographic printer, which means that it uses flexible printing plates which are mounted on to a steel cylinder of the correct diameter to give the repeat length required - the repeat length will subsequently determine the size of bag made.
2 Colour Flexographic Printer
There are 2 main types of flexographic press - (a) stack type amd (b) central impression.
To ensure the ink sticks to the film, which is, unlike paper, non-absorbent and smooth, the film is Corona Discharge treated. This device essentially bombards the surface of the film with high voltage sparks which indiscernibly roughen the film's surface.
The level of treatment is critical and should normally be between 38-44 dynes (measure of surface resistivity). Once the rolls of film are printed, they are ready for the final stage in the bag making process. See Product