Novel approaches in NIR curing technology

Near infrared (NIR) curing technology is used more and more in coating processes where high belt speeds are needed to reduce the curing time from minutes down to seconds [1] and [2].In times of increased concern for energy consumption it is vital to optimize the uptake of energy by the coating system caused by differences in pigmentation. As standard clear coats typically absorb NIR radiation only to a small extent, the heat uptake proceeds mainly indirectly via thermal conduction from the substrate e.g. steel and by convection. NIR absorption in pigmented systems is strongly dependent on the choice of inorganic and/or organic pigments. In particular, pale shades absorb only a small amount of NIR radiation.Efficient, colorless and transparent NIR absorbers are highly desirable for further penetration of NIR curing technology into industrial reality.The presented data in this paper demonstrates for the first time the use of an efficient NIR absorber (NIR-A 1) in different pigmented as well as transparent coating formulations. Its performance against 3 commercially available near infrared absorbers was evaluated concerning absorption in the near infrared region (800–1500 nm) as well as heat uptake during near infrared curing. NIR-A 1 reaches absorption values as high as 30% calculated versus carbon black (FW® 200) as 100% reference, with a broad absorption profile. It outperforms the 3 commercial near infrared absorbers also concerning heat uptake after near infrared curing. An evaluation of the weathering stability shows nearly no impact on a clear coat after 1500 h WOM CAM 7. The addition of 0.05 w%/w of NIR-A 1 to a 45.0 w%/w TiO2 pigmented formulation leads to more than a doubled belt speed to cure. Only a low impact on the color of the coating formulation can be seen.