Improving the lightfastness of paperboard prints with pearlescent pigments

Abstract

In this research we proposed and tested a solution for improving lightfastness of paperboard electrophotographic prints – enhancing the printed material with inks containing pearlescent pigments. The goal was to analyze how pearlescent pigments’ composition and the size of their particles affect lightfastness, and to assess whether this important property is influenced by the tone value of the initial ink layer. Therefore, lightfastness of the unprinted paperboard and the paperboard printed in electrophotography with medium and full coverage of black ink was measured before and after overprinting with pearlescent inks. The results indicate that pearlescent pigments can be efficiently used to prevent light induced degradation of both paperboard and the corresponding prints. The most significant improvements in lightfastness were noticed when pearlescent inks were printed directly onto the paperboard and on the prints with 50 % black coverage. The best protection from light was achieved with pigments containing only two layers – mica and ferric oxide. Pigments containing mica, titanium dioxide, and tin oxide provided satisfactory lightfastness of the printed paperboard even with the small surface coverage. No significant correlation was found between the size of pearlescent pigment particles and the lightfastness of the paperboard prints to which they are applied.