In the automotive, electronic and telecommunication markets, there is a continuously growing demand for high-efficiency and high-performance coatings for plastic substrates. Unfortunately, because of their low surface energies and their sensitivity to solvents and temperature, plastics are generally difficult to coat, making the fabrication of coating systems for plastic substrates difficult. Energy-curable coating technologies have proven to overcome the disadvantages of conventional coating systems by providing an increased overall performance of the cured coating including abrasion, stain and scratch resistance. These coatings are composed of oligomers and monomers (acrylate functionalised resins), which polymerise and cure upon exposure to UV light. This leads to energy cost savings, increased production efficiency, and more compact, space-saving industrial coating lines. Energy-curable resins may be purely solid materials or can be diluted with different solvents for easy application. If the formulated coating product is directly applied onto the plastic surface, adhesion to the substrate is an important characteristic. UV cured plastic coatings are generally spray-applied and different solvents are used to reduce the viscosity. As solvents contain volatile organic compounds (VOCs), they should not be used in high amounts. For a more sustainable environment, recent developments are ongoing to allow spraying at much higher solid content to decrease emission of VOCs. Recent developments in energy-curable, low-viscosity oligomers allow the reduction (maybe elimination) of solvents for spray applications. Low-viscosity oligomers are being formulated for spraying UV-curable coatings at higher temperatures. A low-viscosity hexa-functional urethane acrylate was developed to minimise the emission of VOCs.
With an increasing interest in plastics in the auto industry, coatings require robustness, good productivity, high performance and aesthetic effect. The use of oligomers and monomers with high acrylate functionality form high-crosslinked systems and provide high resistance properties. High crosslinking density, however, may result in poor adhesion. Therefore, it is important to find the best trade-off between requirements. Coatings should have sufficient crosslinking density to provide mechanical and chemical resistance. Formulations based on tetra-functional urethane acrylates offer good adhesion on different substrates and pass tests for chemical resistance and humidity. They are widely used for automotive interiors as they meet all requirements.
Metallic paints add market value to plastic parts and are usually made with two-component polyurethane metallic base-coats and solvent-based conventional thermoplastic acrylics. Clear UV top coats are applied to enhance the durability, chemical and scratch resistance. A surface-curing photoinitiator may need to be incorporated to reduce the oxygen inhibition and ensure proper cure of the surface. To obtain good metallic pigment orientation for plastic coatings, the solid content of the formulation must not be too high.
Due to environmental advantages, UV-curable resins are a superior choice for plastic coatings. We, at C&E, create excellence by providing durable UV-Curable Oligomers and Monomers for high-performance applications. Contact a C&E representative or visit our website to learn more!
By Ashni Arun on April 28th, 2022