UV Reflector Geometry for Curing Inks and Coatings
December 2006
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When selecting a UV curing system for curing inks and coatings it is essential that the lamp head reflector is matched to the printing process since this is critical for optimum ink curing. The materials selected, surface profile and geometry of the reflector all combine to form different characteristics. Up to now little information has been available on lamp efficiency and the role that reflector shape, focus and surface properties play in the curing process. GEW recently completed exhaustive tests on different types of reflectors and all aspects that affect their efficiency and performance.
“To fully understand reflector performance and provide the correct reflector profile for the job intended, it is essential to accurately measure the delivered UV intensity of the various designs available,” says Malcolm Rae, managing director of GEW. “Even though GEW has conducted many bench top reflector studies, we concluded over a year ago that we would conduct a detailed scientific investigation of reflector optimisation under closely controlled conditions. We brought in-house a highly trained scientist to design our experimental parameters and conduct thorough testing under a single variable environment. A summary of our findings and conclusions are presented below.”
Focussed Reflectors:
The first step in understanding reflector performance is to understand the aspect UV lamp output irradiance focussing plays. By simply adjusting the position of the reflectors it is possible to obtain a highly focused energy impingement on the substrate or a broadly diffused output. Generally, a focussed reflector array is used in order to obtain the depth of cure and press speeds common in the printing industry today. This is particularly the case when used with flexographic and screen printing where thick ink coatings along with metallic pigments and varnishes are used. The new XC ‘extreme cure’ reflector from GEW is designed with fully-focussed, dichroic-coated aluminium reflector with integrated clam shell shutters to protect the substrates and is ideally suited to thick film coatings including screen, cationic inks and where ultimate curing is needed at high speeds.
Diffused Output Reflectors:
Reflectors giving a diffuse output are normally used to reduce the intensity of the reflected IR (heat) impinging on heat sensitive substrates. Most all UV emitting lamp output consists of around 60 percent IR energy. Not only do reflectors focus UV energy but also IR energy. The down side of a diffused reflector array is the reduced curing efficiency in terms of depth of cure and also a reduction of the cure rate which is partially temperature driven.
“To fully understand reflector performance and provide the correct reflector profile for the job intended, it is essential to accurately measure the delivered UV intensity of the various designs available,” says Malcolm Rae, managing director of GEW. “Even though GEW has conducted many bench top reflector studies, we concluded over a year ago that we would conduct a detailed scientific investigation of reflector optimisation under closely controlled conditions. We brought in-house a highly trained scientist to design our experimental parameters and conduct thorough testing under a single variable environment. A summary of our findings and conclusions are presented below.”
Focussed Reflectors:
The first step in understanding reflector performance is to understand the aspect UV lamp output irradiance focussing plays. By simply adjusting the position of the reflectors it is possible to obtain a highly focused energy impingement on the substrate or a broadly diffused output. Generally, a focussed reflector array is used in order to obtain the depth of cure and press speeds common in the printing industry today. This is particularly the case when used with flexographic and screen printing where thick ink coatings along with metallic pigments and varnishes are used. The new XC ‘extreme cure’ reflector from GEW is designed with fully-focussed, dichroic-coated aluminium reflector with integrated clam shell shutters to protect the substrates and is ideally suited to thick film coatings including screen, cationic inks and where ultimate curing is needed at high speeds.
Diffused Output Reflectors:
Reflectors giving a diffuse output are normally used to reduce the intensity of the reflected IR (heat) impinging on heat sensitive substrates. Most all UV emitting lamp output consists of around 60 percent IR energy. Not only do reflectors focus UV energy but also IR energy. The down side of a diffused reflector array is the reduced curing efficiency in terms of depth of cure and also a reduction of the cure rate which is partially temperature driven.
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