Halogen-free flame retardant radiation curable coatings

Abstract

Radiation-curing technology is widely used in the field of protective coatings, electronics, adhesives and inks. It combines several advantages such as high cure speed, low energy consumption and is environmental friendly since radiation-curing formulations are solvent free. Due to the continuous trend in more stringent safety regulations, search for polymers with flame retardant (FR) properties is important. In the case of coatings (radiation curable or conventional), their flammability can contribute to the fire propagation. In some wood and cable coating applications, significant level of fire-retardancy are required and coatings with FR properties have been developed. In conventional plastics, additives such as chlorinated/brominated aromatics, antimony halides, organophosphorus compounds, etc. and their combination are commonly used to impart FR. However, the additive approach suffers from several drawbacks like low compatibility with the polymer matrix, negative impact on the physical and mechanical properties of the material and additive loss by migration. Moreover, in the case of UV curable coating, pigmented additives will reduce the UV reactivity of the resin and additive migration leads to a blooming of the surface. Finally, halogen based fire retardant systems show undesirable negative side effects so that an urgent need is now to be satisfied for halogen-free fire retardant systems. In order to avoid such drawbacks, UCB Chemicals has developed oligomers and monomers containing halogen-free FR moieties covalently bound to the polymer backbone. 31 P- NMR and 1 H- NMR spectroscopies were used to characterise the structure of the new compounds. Thermogravimetric analysis, limiting oxygen index (LOI), cone calorimeter and flame propagation tests were used to assess the flame retardant properties of these resins.