Frederik Goethals of Centexbel (Belgium) described new energy-efficient coating systems for finishing textiles involving UV curing of non-aqueous coatings and sol-gel coatings. These methods provide surfaces with high abrasion resistance, high hydrostatic head water-proofing, flame retardency, easy care and UV-protective features.
UV-cure was fast, energy efficient, low in volatile organics emissions, suitable for small production runs and could even be used on hard surface lacquers. The coating is a non-aqueous mixture of oligomers, monomers, photoinitiators and additives and can be cured cold (no evaporation of solvents) in 4 seconds with UV light from a mercury lamp to give a stable surface.
Sol-gel coating uses metal-oxides, mainly silicon-based which are thermally polymerised with an organic polymer to give hard, durable, omni-phobic, abrasion resistant, antimicrobial and flame retardant surfaces. UV cure and sol-gel could be combined for 100% coatings, water-based coatings and water-based finishes. This could lead to highly hydrophobic fabrics.
Fabric treatments involve high-viscosity coats which can be non-aqueous or water-based, the latter requiring drying before UV curing. The processes are continuous and attention must be paid to the thermal sensitivity of any thermoplastics in the fabric, to removing the ozone generated in curing, and to protecting the operatives from UV exposure. FTIR analysis is required to check the completeness of the curing, i.e the complete absence of any monomer.
Asked about the costs, Mr Goethals said the process machinery costs were lower than for conventional coating but the chemical costs were higher. (A UV lamp for textile finishing would cost €200,000.) Typical finished fabrics would be 50/50 fibre/coating. The photoinitiator chosen must be matched to the frequency of UV radiation used.
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