PurposeThe purpose of this paper is to synthesise environment friendly UV curable polyurethane acrylate resins for various industrial applications and study the performance properties of the cured coating films applied over metal surfaces.Design/methodology/approachThe polyurethane acrylate resin was synthesised using polyester polyol (synthesised using ethylene glycol, adipic acid and 1,6 hexane diol), isophorone diisocynate (IPDI) and 2‐hydroxy ethyl methacrylate (HEMA). The different formulations were developed using various reactive diluents viz. monofunctional, difunctional, trifunctional and tetrafunctional (ethoxylated phenol monoacrylate, 1, 6 hexane diol di acrylate, dipropylene glycol di acrylate, trimethylol propane triacrylate, propoxylated trimethylol propane triacrylate, pentaerythrol triacrylate – PETA). These samples were cured under UV radiation. For effective curing, various compositions of oligomers, photoinitiator and reactive diluents were used. The mechanical, optical, rheological, chemical and stain resistance properties were evaluated.FindingsThe designed polyurethane acrylate gave good performance properties when used with reactive diluents having different functionality in different ratios for application over metal surfaces as protective coatings for various industrial applications. While using reactive diluents, the coating compositions showed significant enhancement of mechanical, physical and chemical resistance properties. Owing to different functionality of reactive diluents used, highly cross‐linked structures are formed, which lead to excellent mechanical and chemical properties. The optimum results were obtained with PETA as reactive diluent.Research limitations/implicationsThe polyurethane resin has been synthesised from polyester polyol (made up of ethylene glycol, adipic acid and 1, 6 hexane diol), IPDI, 2‐HEMA. Besides, this, it can be synthesised from some other polyester polyol or polyether polyol. In addition to this, some other isocyanates such as TDI, MDI, HDI, HMDI, etc. may be used.Practical implicationsThe study has provided a better solution for developing low volatile organic compound (VOC) products by using UV radiations, which can be cured within a minimum period of time and can save significant application curing time for the end‐users. The developed product is also an environmentally friendly product.Originality/valueMetallic surfaces are widely used in packaging industry in rigid and semi‐rigid forms. One of the prime requirements of the surface is an attractive printing on it. Conventionally used coating system on metallic surfaces are not holding or retaining their decorative effect/gloss level to a large extent. For this purpose, an overprint varnish is normally used which is mostly solvent based. This paper has been able to suggest very good formulations for printing of metallic surfaces for packaging and for overprinting in particular, which is radiation curable and environment friendly.
Blends of epoxy acrylate resins (acid values 3, 6.5 & 10 mg KOH/gm Solid) with monofunctional monomers (ethoxylated phenol monoacrylate) were prepared by physical mixing, having weight ratio 50:50. These blends were cured by using UV radiations in presence of photo initiator (Darocure 1173). The thermal degradation kinetics of these resin blends were studied, using thermo gravimetric analysis in nitrogen atmosphere at a heating rate of 10 0 C/min. by applying Coats-Red fern equation. According to the analysis, all the coating films degrade in two steps. In the first step of degradation kinetics, R 2 M follows 1.75 order (n=1.75) and all other coating films follow second order (n=2) kinetics. In second step, R 2 M & R 3 M follow half order (n=0.5) kinetics and R 1 M follow first order (n=1) degradation kinetics. Order of the reaction is obtained on the basis of best fit analysis, and all the parameters were confirmed by regression analysis. From the reaction order, value of activation energy (E) and pre exponential factor (Z) were calculated by the slop and intercept of the plot between X and Y, respectively.
Twelve blend samples were prepared by physical mixing of epoxy acrylate resins with various monomersviz. ethoxylated phenol monoacrylate (EOPA), tripropylene glycol diacrylate (TPGDA) and trimethylol propane tri acrylate(TMPTA), having weight ratio of epoxy acrylate resin and monomers are 50:50, 60:40, 70:30, 80:20. These samples were cured under UV radiation using 5% photo initiator by weight. These blends were evaluated for mechanical, chemical & thermal properties. It was found that the sample having mono & tri functional monomers shows better properties than the samples having di functional monomer.
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