Plates used in offset printing are thin (up to 0.3 mm) and are easily attached to a plate cylinder, and they usually have a mono-metal (aluminum) or, more rarely, a multi-metal, plastic or paper structure.
Aluminum has been gaining momentum among metal plates over zinc and steel for a very long time. The necessary reinforcement of the aluminum surface is carried out mechanically, either by sandblasting, obtaining a ball, or by wet or dry cleaning.
Today, almost all printing forms are granulated inside electrolytic technology (anodizing), that is, electrochemical amplification using residual oxidation.
An ink-receiving coating (photosensitive coating, about 1 μm thick) is applied to the base material. This material is often polymer or copper for multimetallic plates (bimetallic plates).
Light-sensitive, diazo (photopolymer) pre-coated aluminum printing plates are currently the predominant plates in printing houses. Image transfer is performed using various attributes on the surface of these plates after their exposure and development. The remnants of the first photosensitive coating or photosensitive coating, modified by exposure to light, are the ink-receiving elements that create the image.
Chemical transformations occur due to the penetration of photoeffective (actinium) light (light containing UV rays), which causes the photosensitive coating to react differently depending on its type and structure.
In the manufacture of printing plates, two types of photochemical reactions are possible:
• Hardening of the photosensitive layer with light (negative plate fabrication)
• decomposition of the photosensitive layer into light (positive plate making).
In case of positive production of plate and standard printing forms, the opaque, blackened section of the film corresponding to the ink-receiving surface elements on the plate is used as the original.
For negative plate production with “negative plates”, a negative film is used as an original, that the ink perception areas on the printing plate correspond to the translucent light areas on the film.
For quality assurance and verification in the manufacture of plates, controls are copied onto the plates.
The most practical way to check quality is to use a color panel. This is an image that is placed on an offset printing plate, usually on the trailing edge, which contains targets for providing areas for measuring solid ink density, measuring points, and other controls. These colored rods are supplied as a film and are displayed on tablets along with the image, or they can be obtained digitally in CTP systems (computer-plate).
Also for the manufacture and maintenance of plates, there are many chemicals that we can use.
