UV curing printing ink
UV curing printing inks are special color systems, which by UV-irradiation for curing are brought. Here, the material printed with color is conveyed through a UV system with mercury vapor lamps or LED lamps at a precisely defined belt speed and the color film is thus hardened in seconds. Depending on the parameter setting (power and speed of the lamps), the printed film can have different properties, such as chemical resistance, adhesion, scratch resistance, gloss and tear sensitivity.
UV-curable printing inks are post-curing systems, i. that is, it takes some time before they develop their final properties. The hardening mechanism here is based on the principle of photopolymerization (radical chain polymerization). Other radiation- curable printing inks , which are cured by electron beam curing, play a lesser role .
Printing inks in general are paints that are applied to various substrates (printing materials) such as plastics , metals , wood or glass using printing technologies such as screen printing , offset printing , pad and digital printing .
composition
UV-curable printing inks are made up of the following ingredients:
- Binders (low molecular weight resins containing reactive double bonds)
- Monomers , also reactive thinners (acrylate monomers)
- Photoinitiators (radical generators, go into the excited state through UV radiation and start the UV curing according to the mechanism of radical chain polymerization )
- Additives (additives such as defoamers, leveling additives, thickeners, dispersing additives , matting agents, etc.)
- Organic colored pigments , carbon black and titanium dioxide as white pigment , since calcium carbonate or the like do not achieve an opaque white, technically possible with suitable initiation.
- Fillers to achieve certain technical properties
There are also unpigmented systems (transparent varnishes) that are often used for overprinting in order to influence the degree of gloss or mattness.
application
- Graphic screen printing
- Industrial screen printing
- Pad printing
- Digital printing
- Offset printing
- Flexographic printing
- Wood print
- Wood varnishes for furniture
UV curing process through radical photopolymerization
Polymerization is a chemical reaction in which monomers (mostly unsaturated organic compounds ) react by breaking the multiple bonds to form polymers (molecules with long chains, consisting of interconnected monomers) - i.e. the cured paint film.
- Initial reaction in which the active center is formed.
- Growth reaction in which the macromolecular chain grows in a chain reaction (repeated addition of monomers) and
- Termination reaction in which the growth of the chain is irreversibly terminated by disproportionation reactions or recombination.