PREPRESS
z LED UV for flexo plates needs the right photopolymer
DuPont ’ s new Cyrel Lightning flexo plate optimized for LED exposure
Naresh Khanna
DuPont ’ s new Cyrel Lightning photopolymer plate is optimized for LED UV exposure and can save up to 42 % higher productivity in the flexographic platemaking process . LED lamps are increasingly used for curing inks in printing and for the UV exposure of flexographic plates instead of the conventional florescent tube systems known as ‘ bank exposure .’ While LED exposure can bring many benefits to the flexographic platemaking , for non-optimized photopolymers , using this unique exposure process can require compromises in productivity and quality . However , the new Cyrel Lightning made for LED UV exposure plates deliver higher productivity , improved plate quality and superior print quality .
While one can achieve very short exposure times using the maximum UV output ( since LED emit UV radiation at a very high intensity that is 15 to 20 times higher than florescent banks and have a narrower emission spectrum ), tradeoffs in quality may occur especially when using flexo photopolymer plates that have been designed for the bank exposure .
DuPont ’ s technical white paper on ‘ Understanding and optimizing photopolymer plates for UV LED exposure ’ says , “ Often , the combination of high output and short exposure time leads to larger minimum dots , pronounced shoulders of printing elements and cupping , which all can contribute to less latitude on press and lower print quality . This challenge often requires LED exposure times to be longer in order to prevent the quality issues mentioned above .”
The challenge in flexo terms is to achieve a crisp surface , but also a sufficient curing of the center of the photopolymer material in , forming fine elements and surface structures while photopolymerizing the bulk of the material sufficiently for stable shoulders and acceptable through-cure .
z The Solution
DuPont Technical White Paper for understanding and optimizing plates for LED UV exposure
If photopolymer formulations were optimized for LED exposure from the start , there would be less of a need to compromise between productivity and quality . Optimized flexo plates along with experienced application support staff yield the best results . With chemistry , the photopolymer plate can be redesigned for LED exposure .
DuPont has rethought plate formulation , specifically for UV LED exposure for the new Cyrel Lightning series of photopolymers plates . The plate series uses chemistries with tailored UV profile to achieve a balance between surface and through cures . The innovation enables fast surface cure that effectively mitigates oxygen inhibition between passes of LED exposure when the plate is in the dark . At the same time , it provides sufficient through-cure through a finely tuned UV absorption profile .
This leads to an exposure time reduction of up to 42 % in the respective platemaking processes and improved quality especially in isolated highlight dots and superior print quality amongst LED-exposed plates . z
18 Packaging South Asia 5 October 2021