Printing Terms
PRINTING PLATE
The printing image used in offset printing.
RUBBER BLANKET
A rubber sheet which transfers the printing image from the printing cylinder to the cartonboard sheet in offset printing.
PRINTING INK
Coloured pigment which is transferred from the printing plate with the aid of a vehicle (a carrier) and is then bound to the cartonboard surface with a binding agent such as resin.
VARNISH
There are different kinds of varnish, all of which have their own advantages and properties. A cartonboard surface is varnished to protect it against scratches or to stop it getting dirty. Varnish can also be used to emphasise the gloss of a design in whole or in part. The varnish is either applied to the cartonboard directly on the printing press or afterwards in a separate operation.
Printing varnish - an oil-based varnish which is spread on in a printing press. Protects against scratches.
Emulsion varnish - is spread on in the printing press at a varnishing station. Protects against scratches.
UV varnish - is spread on either directly in the printing press or in a separate varnishing machines. Gives a glossy surface.
DAMPENING SOLUTION
Used in web offset printing. The dampening solution has three fuctions in offset printing:
- to ensure that the ink does not adhere to the non-image areas
- to clean away cartonboard fragments
- to cool down the press
Since dampening solution is required in offset printing, the dimensional stability and flatness of the cartonboard are important (See “DIMENSIONAL STABILITY” and “FLATNESS”).
REGISTER
When all printing inks are in exact alignment relative to each other, e.g. the separate colour images in four-colour printing, or during subsequent die-cutting, cutting, embossing etc. Misregister occurs when the separate colour images are not printing exactly on top of each other. Misregister creates unclear images, discoloured edges etc. To avoid misregister it is important that the cartonboard sheet is dimensionally stable (see“DIMENSIONAL STABILITY”).
HALF-TONE PRINTING
Printing in which the colour images are in the form of small dots (known as half-tone dots and forming a half-tone screen). The size of the dots determines the colour intensity. The combination of different colours creates a multitude of hues.
SCREEN RULING
Screen ruling (also called screen frequency or half-tone resolution) is the number of screen lines per unit of length. It is measured in lines per inch (lpi). The higher the lpi, the greater the amount of details in an image. The kind of cartonboard and the choice of printing method govern the screen ruling that can be used during printing.
