In conventional powder curing, metal components usually pass through a multi-stage coating process. First of all, the component is coated with the base powder, then conveyed to a drying oven where the base coating is cured. After this, the finish powder coating is applied and the component again passes through the drying oven for curing. This process is very reliable and often used. However, many coaters would prefer not to have to use the time-consuming double pass through the drying oven.
Fortunately, this two-part coating process can now be optimized by a “Powder-on-Powder” process, at the heart of which is an infrared booster, located immediately after the first coating.
The Powder-on-Powder Process
Unlike conventional powder coating, with the Powder-on-Powder process the base coating is applied and then immediately gelled by infrared heat. The finish coating is then applied while the base coating is still in the gel state. The component, with the base coating gelled and the finish coating still powder, is then passed into the existing drying oven for complete curing.
The process requires an additional infrared oven, the booster. The existing drying oven can still be used. Infrared systems transfer large amounts of energy very quickly so that, as a rule, infrared boosters are very compact and can be integrated into an existing line with minimum effort.
Efficiently Interconnected UV and IR for Optimum Energy Application
Generally, powders absorb infrared radiation very efficiently. The powder is heated rapidly and is gelled significantly faster than in a convection oven. Without air-circulation, there are no dust inclusions in the oven environment and the powder is not agitated or disturbed. Moreover, fast gelling improves the coating quality and allows line speed through the oven to be increased.
Some coatings require UV curing, involving polymerization, where photo-initiators are activated by intense UV light to cross-link in fractions of a second. As a result, the material is quickly cured, the surface is dry, abrasion-resistant and suitable for further processing. Lacquers and coatings remain scratch-resistant and in mint condition when they are optimally cured. This means that wavelengths, UV light intensity and dosage must be matched to suit the photo-initiators of the coating formulation.
Increasingly, there are coating processes which benefit from a combination of UV and IR. Heat improves the mobility of the molecules and thus the final result of the curing reaction. By pre-heating the substrate with infrared, better sticking and cross-linking of the UV lacquer is achieved and it has been shown that targeted heating of materials before UV cross-linking can be very advantageous.
By the innovative combination of infrared heating and UV technologies, the energy efficiency of the IR curing is improved while the cross-linking of UV lacquers is optimized.
The infrared application center
Heraeus Noblelight has been making heat usable for industry and science for many years. The in-house application center offers the opportunity to carry out practical tests with competent technical support. The tests are evaluated and discussed with the customer. The aim is to find the best emitter type and the best configuration for the respective application - and to coordinate the heating process that fits the requirements precisely and efficiently.