Tips for UV coating applications
With the increasing popularity and use of UV cured coatings, it is important to monitor and understand the potential for problems. Owing to extremely high gloss of UV Coating, off-line UV coating can enhance the surface of anything it is applied to. Besides, it is environmentally-friendly and if cured properly, it polymerizes to form a hard layer, which then delivers an excellent protective surface for a large number of applications.
For printers to properly prepare printed sheets for UV curable coating, there are a few guidelines that have to be followed. Following are certain tips that will help ensure that finished products serve the expectations of printer as well as the customers.
Preparation
In order to ensure that the product gets off on the right foot, UV coater should be provided with a layout sheet that indicates guide as well as gripper sides with final trim marks. In addition, areas that are to be left uncoated should be marked.
If you are opting for spot coating, a film positive with registration marks should be supplied. Make sure to tape the film on a press sheet pulled from the center of the load, and then strip it into position.
Inks
UV-compatible inks must be used together with UV coatings. Earlier, inks were only required to be wax free. However, since chemicals and solvents are used in them today, there are three requirements that have to be met.
Primarily, inks must be free of silicones, paraffin waxes and teflon additives. Although the use of additives in inks is to resist scuffing, they reduce the adhesion of UV coating to the inks.
Second, UV compatible pigments must be used. Now-a-days, all UV coatings consist of brighteners, which together with the alkalines in pigments can cause particular colors to bleach to a lighter shade.
The third requirement is that the inks must be hard-drying, in order to resist heat that the UV curing lamps produce. This prevents the inks from softening under the heat. Regardless of the inks that are used, sufficient drying time should be planned during the production process, generally 24-48 hours, depending on the coverage.
Varnish and aqueous coating
Although aqueous coatings and varnishes can be UV coated, special attention should be paid to determine which coatings are UV-compatible. Varnishes and aqueous coatings seal in wet inks and slow down the drying process. Furthermore, when the product is UV coated, it leads to unacceptable adhesion.
Additives
In order to reduce Volatile Organic Compounds (VOCs) and enhance air quality, printers are required to eliminate the use of Isopropyl Alcohol when it comes to dampening. Alcohol was used to enhance the rheological properties of ink and aid in faster ink setting and drying. Use of alcohol substitutes in place of Isopropyl alcohol lead to certain problems in UV coating process. After the aqueous coating is applied on the sheets when they are printed, wet ink is sealed between aqueous coating and the sheet, further slowing the drying process. Use of glycol and glycol ethers result into poor adhesion. To eliminate these issues, ensure to use lowest levels of glycol and glycol ethers.
For best adhesion results, varnishes, inks and aqueous coatings must be free of silicones, waxes and additives.










