Laser-engravable hexahydrotriazine polymer networks

Abstract

Novel rubber-like polymeric materials based on hexahydro-s-triazine as cross-linking knots have been synthesized, and their potential for application in laser-engravable printing plates has been evaluated. The network formation occurs via a cyclotrimerization reaction of bis(methylenimines) formed in situ during the condensation of primary diamines with formaldehyde. Various amino-end-capped oligomers, viz., oligo(ethylene oxide), oligo(propylene oxide), oligo(tetrahydrofuran), and oligo(dimethylsiloxane), were used as primary diamines.

The engraving experiments performed with the use of two types of Nd-YAG lasers operating in either continuos or pulsed modes revealed that the networks bearing siloxane spacers between thermally labile triazine knots are very sensitive and easily engravable materials but their mechanical properties were poor. The materials produced on the basis of polyether- and poly(THF)amines showed good mechanical properties, but their laser engravability was lower compared to that of the siloxane-based networks. Unfortunately, an attempt of synthesizing hybrid networks on the basis of the siloxane+polyetheramine mixtures resulted in a anti-synergistic effect inasmuch as those samples were found to have poor mechanical properties of the siloxane-based materials and the modest engravability of polyethers.

Two different decomposition mechanisms occurring in the triazine knots and in the spacer chains and possible connection of these mechanisms with operating modes of a laser have been discussed.

In the future it may be possible to improve both mechanical strength and laser engravability by tailoring special spacers R in the diamine moieties. Currently, however, the problem of manufacturing highly efficient flexographic printing plates in a continuous manner still remains largely unsolved.

Keywords:

• Hexahydrotriazine networks
• Laser ablation
• Printing plates