By 
The plates used in offset printing are thin (up to approximately 0.3 mm) and easy to place in the plate cylinder, and generally have a mono-metallic (aluminum) or, less frequently, multi-metal, plastic or paper structure. .
Aluminum has long been gaining ground among metal-based plates over zinc and steel. The necessary gain of the aluminum surface is done mechanically either by sandblasting, ball gain or by wet or dry brushing.
Today, almost all printing plates are granulated within an electrolytic technique (anodization), that is, electrochemical gain by subsequent oxidation.
The ink-accepting and imaging coating (light sensitive coating, thickness about 1 micron) is applied to the base material. This material is usually polymer or copper for multi-metal plates (bimetallic plates).
Light sensitive diazo (photopolymer) pre-coated aluminum printing plates are the predominant plates in print shops today. Image transfer occurs through the different attributes on the surface of these plates after they are exposed and developed. The remnants of the first photosensitive coating or the photosensitive coating changed by the effect of light are the elements that accept the ink that create the image.
Chemical transformations occur due to the penetration of photo-effective light (actinium) (light containing UV rays), which induces the light-sensitive coating to react differently depending on its type and constitution.
There are two types of photochemical reactions when producing the printing plate:
• hardening of the light-sensitive layer by light (manufacture of negative plates),
• breakdown of the light-sensitive layer by light (positive plating).
With positive plate making and standard printing plate production, a positive film is used as the original, that is, the blackened and non-translucent sections of the film correspond to the surface elements that accept the ink on the plate.
For the production of negative plates with “negative plates”, a negative film is applied as the original, that is, the ink-accepting image areas of the printing plate correspond to the light and translucent areas of the film.
To ensure quality and verify during plate manufacture, control items are copied onto plates.
The most practical way to check quality is to use a color bar. This is an image that is placed across the offset printing plate, typically at the trailing edge, that contains targets to provide measurement areas for solid ink densities, dot measurements, and other control items. These color bars are provided as film and displayed on the plates along with the image or can be digitally derived in CTP (computer to plate) systems.
Also for the production and maintenance of plates there is a lot of chemistry that we can use.