UV coating is featured for its low-temperature and rapid curing, thus it’s ideal choice for automatic high-speed mass production requirement. UV paint provides extremely high gloss varnishing and widely used for various products including metal, plastic and woodware. Especially for plastic vacuum metalization, uv is always top class choice. In this article, we will briefly introduce UV coating application process and trouble shooting cases.
UV painting line process flow
The UV painting line process is as follows:
Product loading
Operators manually put the workpiece on fixture from loading area, chain conveyor passes through each functional part of the production line in turn.
Preheat
The purpose of preheating is to make sure product is completely dry for next surface treatment. If not, it may result in various finishing issues such as matte, losen contact with paint and dust etc.
Electrostatic Dedust
Due to the charge accumulation on plastic surface and the presence of charged particles in dust air, a large amount of dusts is adsorbed on product surface. Electrostatic de-dust nozzle provides a high-voltage negative ion electric field on workpiece surface and blowing with high-pressure air which will effectively remove charges and dusts.
Primer
It’s normally for PP/PC based plastic, we need to apply a kind of solvent before uv base coat for guaranteed contact and smoothness. Product is controlled by forced rotation system so the surface of the substrate gets a uniform coating.
Fast low temperature baking
After primer is sprayed, the substrate enters a drying tunnel with temperature 60-70 °C then bake for 1-2 minutes. The solvent volatilization reaches 90%, the coating resin has a crosslinking reaction for a good paint film hardens.
Topcoat
After primer is baked, workpiece enters UV painting booth and do same way as primer.
Topcoat baking
Topcoat requires the baking time to be extended to 3-5 minutes, so that paint film has a leveling process, and the temperature of the drying tunnel should be uniform, so that the solvent is uniformly volatile.
UV curing
After baked in IR tunnel, now workpiece enters into UV oven for quick curing. Only few seconds in uv oven then uv paint is cured. Make sure there’s good ventilation and exhaust system to avoid heat damagement.
Cool off line
Because topcoat has a longer baking time, the surface has a certain temperature, a cooling section is set up with large flow ventilation to take away heat quickly. Paint film layer is cooled and hardened which is convenient for offline packaging. The cooled product is sent to the unloading area by the conveying chain.
Troubleshooting of UV coating
Unlike many other coatings that can be applied easily, UV has extremely high requirements to environment in order to get high quality surface finishing. The ideal environment for UV coating application is dry and cool with pretty high cleanness. The workshop cleanness and temperature and humidity etc will directly decide coating quality.
So many common issues like matte, dust and weak paint film etc can be fixed by clean room construction. Humidity and room temperature control is a MUST in hot and rainning area. Especially in summer, moisture in air will give big problem for coating.
