New high-throughput screening tool for the evaluation of pigmented UV-A curable coatings—A case study using low energy lamps
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Pigmented UV radiation-curable coatings have been a challenge to the coatings formulator for a long time. A critical match of pigment and photoinitiator package is crucial, for good cure. Another issue facing the coatings chemist is the popularity of low energy lamps, which offer ease of handling, reduced safety concerns, and a low price tag. Obviously, the combination of curing pigmented coatings and using low energy lamps poses a special challenge.
To improve the pigmented coating development cycle, a rapid workflow was needed to screen formulations for cure under low energy UV-A radiation. For these types of applications, a high-throughput, screening assay for discovering desirable photoinitiator packages was developed. Fluorescent dye-doped coatings cured under UV-A radiation were extracted with solvent. The relative degree-of-cure, of the film was determined to be inversely related to a combination of the absorbance and fluorescence of the extractant. When this assay is used in conjunction with automated liquid handling and a spectrophotometer with an x-y scanning stage, the coatings formulator can analyze a large variable set in a short period of time. A primary screening of photoinitiators using this workflow suggests Lucirin® TPO-L, Darocur® 4265, and Irgacure® 2100 as optimum choices.
KeywordsPhotoinitiators fluorescence spectroscopy solvent resistance crosslinking cure UV EB radiation cure polyurethanes isocyanate
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