Study on the Lightfastness of Ink Based on Visible and Infrared Spectral Analysis

Abstract

A method based on visible reflection and infrared absorption spectroscopy is proposed to elucidate the colour variation law and mechanism of gravure ink in daylight. Three kinds of gravure spot colour ink, blue, red and cyan, are used for a xenon arc ageing experiment. The spectral reflectance of the samples is collected every 2 hours to analyse the variation in the chromaticity. A polynomial regression model of the colour difference and ageing time is established by the nonlinear least squares method. The coloration composition of the inks is analysed according to the infrared spectrum of the samples. The results show that in a 36-hour experiment with an illumination intensity of 550 W/m2, the lightfastness of the different colours of gravure spot ink is significant. The integrated value of the differential reflectance spectrum analysis shows that blue ink exhibits the largest change in chromaticity, followed by the red and cyan inks. The maximal colour differences of the three samples are 12.37, 4.78 and 1.34, respectively. A third-degree polynomial regression of the colour difference of the ink and ageing time achieves a good fitting result, with regression coefficients of 0.9700, 0.9980, and 0.9646, respectively. The infrared spectroscopy results show that the change in the chromaticity corresponds to changes in the molecular composition and absorption intensity of the pigments. The blue ink, with the largest change in chromaticity, exhibits the largest change in the absorption spectrum. The cyan ink, with inconspicuous changes in the chromaticity, exhibits the smallest change in the absorption spectrum. This research provides a more accurate theoretical basis for an analysis of the colour variation law and mechanism of gravure ink in daylight and provides a reference for lightfastness analysis of textiles, dyes and coatings.