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Using modern UV paints makes it possible to reduce the hardening time for coatings to a few seconds. Prerequisite for the successful application of this innovative and economically interesting technique, however, is that you use UV paints that demonstrate the necessary corrosion protection, as well as chemical and mechanical qualities, particularly on metal, in order to fulfil customer requirements (especially in the automotive industry). In this respect, the development laboratory at Lankwitzer Premium Coatings has made a decisive breakthrough with our new product UE 17 managing to improve considerably upon previously achieved results.
At the present time, convection dryers that are reliably suited for nearly all painting materials are used in more than 90% of all newly-built paint finishing plants. However, if you consider that only 2 to 5% of the energy used in this process is actually required to dry the paint, then it soon becomes clear that, in face of today’s pressure to rationalise costs, it is of utmost importance for the efficiency of a paint shop that the right process and paint finishing system are chosen. When using UV radiators with short wavelengths, the processing times can be reduced significantly, thus increasing the cost-effectiveness of the process enormously.
In the industrial use of UV hardening systems, radically hardening acrylic paints have become the norm, while so-called “cationic hardening systems” are used for special applications on particularly critical subsurfaces (for example, nickel). Radically hardening UV paints contain unsaturated, polyfunctional acrylic resins as a binding agent as well as mono or difunctional acrylates as a reactive paint thinner that acts as a solvent to regulate viscosity. By using polymerisable reactive thinners, you can generally do without organic solvents when working with UV paints, which means they are an environmentally friendly and cost-efficient alternative to conventional painting systems where up to 50% of the paint components simply evaporate in the hardening process.
Four different types of resin – sometimes also in combination – are usually implemented in radically hardening UV paints.
- Epoxy acrylates generate hard chemical-resistant coatings of paint;
- urethane acrylates bring about flexibility, are nevertheless resistant to abrasion and UV light;
- polyether acrylates act to reduce the viscosity of the UV paint system,
- while polyester acrylates demonstrate balanced properties and often constitute the basic substance of radically hardening paints. The paint formulator can then achieve the desired properties by mixing one or more of the abovementioned binding agents.
Formulated UV paints of this kind can be applied as colourless or pigmented in layer thicknesses of between 20 and 150 µm and they adhere excellently to most metallic sub-surfaces. They can be coated very well using 2K finishing coats and, in connection with inert gas hardening under nitrogen atmosphere, it is also possible to coat even complex components such as axes, shock absorbers or aluminium wheels and to achieve optimum hardening. The properties of different UV systems are presented in Table 1.