Exploring the cause of fading after printing purple ink

In packaging printing, we noticed that the purple ink faded or discolored after some time after printing. What causes this phenomenon?

To explain this phenomenon, it should be considered from the composition of purple ink. If the colorant in the violet ink is a methyl violet material, the ink will fade after being printed under sunlight. The reason is that the photochemical reaction between sunlight and the colorant molecules destroys the chromophoric groups of the colorant molecules in the ink (the chromophoric group is the coloring group of the colorant).

In addition, the purple colorants containing methyl groups have poor chemical resistance, and these colorant molecules can react chemically with nitrocellulose resins and alkali metals in aqueous inks, resulting in discoloration or discoloration of the ink color.

There is a stable pigment in the purple pigment called carbazole violet. It has high chemical resistance and is not easy to fade. However, the pigment is very expensive, so it is still purple in the purple ink. It is widely used.

Source: 21st Century Fine Chemicals Network