The term UV stands for ultra violet, these are coating that on exposure to certain wavelength of UV Light get cured. The normal wavelength of working of UV curing coating is in the range of 200-400 nanometers. These coatings are solvent free, hence have almost nil volatile- they are 100% solid basis, i.e., on curing the coating, the complete liquid turns into a solid film, there are no evaporation or losses unlike traditional solvent based or water based coating or inks, UV coating material stays as a liquid for a long time unless exposed to UV light, a slow gelling or curing can take place with direct or indirect sunlight. UV drying of coating involves the chemical process known as polymerization; polymerization may be defined as the formation of macromolecules (big molecules) by the chemical combination of smaller molecular units or monomers. The reaction involves the formation of new chemical bonds between the species.
UV curable coatings find a variety of applications in paper and board, graphic arts, compact discs, optical fibers, automobile paints, plastic coating, wood coatings, parquet floorings, adhesives, photopolymer resists, for joining glass to glass, dental materials, release coating for labels laminates, sealant, printed circuits, metal coating etc. The bulk usage is in the overprint varnishes and inks in graphic arts, packaging and wood coating industry internationally. Procedure for coating of UV curable products for the printing and packaging industry. UV curable overprint varnishes (UV-OPV) are used widely in the printing and packaging industry. The liquid UV-OPV are coated /applied to the substrate by one of the many possible methods and subsequently exposed to high energy source of UV light, the liquid coating on exposure to the UV light polymerizes and becomes a solid film.
UV curable coatings are available for a whole range of application methods UV-OPV are applied by silk screen manual process, rotary screen printing, roller coating, varnishing machines, flexography coating using analog roller, letterpress, offset printing machine through the duct as dry offset. Spot coating, window coating or patch coating can be done using traditional screen printing or by the use of photopolymer plates in traditional printing machines like the offset machine.
There is a debate whether UV curing coatings are developed for environmental reasons or they were developed because of being highly energy efficient coatings and environmental advantages were an incidental advantage, but one thing is sure the industry has benefited from this new technology. It is an environmentally safe process since there are nil or almost nil volatile contents in and UV curable coating. UV coating can provide very high gloss and smoothness and are replacing traditional film laminations. These coatings are environmentally safe being biodegradable, whereas the film lamination is not a biodegradable coating and is being eliminated from most developed countries as a waste disposal hazard. Also, UV cured coating don't wrinkle up like film lancination does. Very high production speeds are achievable with UV curing coating. UV curable coatings are almost instantaneous curing or drying, line speeds of 100 m/min are achievable, and theses coating take a fraction of a second to dry. With UV technology you can plan on faster job turn around and Just-in-Time (JIT) inventory management. The process is a low heat generating process can be used on heat sensitive substrates. Special equipment design allows for minimizing heat generation. |
