UV light induced polymerisation of multifunctional monomers is one of the most efficient methods to quickly prepare and synthesise highly crosslinked polymer networks. UV-curable coatings provide durable and protective finishes, decrease the emission of volatile organic compounds (VOCs) and accelerate the process of production. UV-cured polyurethane acrylate resin films display excellent gloss, chemical, mechanical, and stain-resistant properties on metal substrates.
Photo-curable formulations generally incorporate reactive diluents, multifunctional monomers, oligomers and photoinitiators, which generate reactive species on exposure to UV. UV-curable polyurethane acrylates have been processed and synthesised from polyester polyol, toluene diisocyanate and three types of reactive diluents (ethoxylated phenol monoacrylate (EOPA), 1,6-hexanediol -diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA)). Acrylic monomers are reactive diluents that are added to change and modify properties and to decrease the viscosity of precursor liquid.
Acrylated urethanes combine the superior weatherability and optical properties of polyacrylates with the favourable properties of polyurethane such as toughness, abrasion resistance, good low-temperature properties and tear strength.
Important Characteristics for UV-curable Resin metal coatings:
Gloss: Gloss is measured using a Triglossometer. After watching the films from a 60° angle, the coating films can be observed to examine gloss properties. Coating films based on the reactive diluent, EOPA displays maximum gloss.
Scratch Hardness: For a coating to fulfil its protective functions, scratch hardness is an important mechanical property required. Change in gloss properties, deformation and cracking of the coating may be consequences of scratches on a cured surface. Films having higher concentrations of the reactive diluent, TMPTA have high scratch hardness due to maximum extent of monomer crosslinking.
Pencil Hardness: Coating films of the reactive diluent, TMPTA displays maximum pencil hardness due to higher functionality, leading to a maximum degree of crosslinking.
Acid Resistance: Films based on the reactive diluents, EOPA and HDDA are usually affected by acid solutions due to weak monomer crosslinking. TMPTA generally shows good resistance against acids.
Alkali Resistance: To study resistance to alkali, coating films are exposed to 0.1 N NaOH solution. TMPTA films display better resistance due to high monomer functionality that leads to maximum crosslinking.
Distilled Water Resistance: UV cured coating films exhibit good resistance when exposed to distilled water. Coatings which have a high percentage of the reactive diluent, TMPTA, display better resistance.
Stain and Chemical Resistance
Flexibility
Cross-Hatch Hardness
UV radiation, in the presence of reactive diluents is effectively utilised to cure polyurethane acrylate resins to obtain metal substrate coatings having suitable chemical and mechanical properties. Metal surfaces coated with UV-cured resins display excellent stain resistance characteristics. Properties of the coating are affected to a high extent when reactive diluents are incorporated in the resin. Scratch hardness and gloss properties increase when a higher concentration of reactive diluents are present. UV-cured resins decrease VOC emission and hazardous air pollutants and are used as protective coatings for metals.
We, at C&E provide environment-friendly UV curable coatings, which are preferred for metal coatings. Contact us to learn more about how our products can enhance and improve the properties of metals.
By Ashni Arun on April 5th, 2022