Details:
Summary:
Pigments are substances which give colour to inks. The pigment ratio in offset printing inks are in between 15 - 25 percent. Pigment ratio affects the light fastness of ink. The excellent value of lightfastness of inks is 8. The term, light fastness can be defined as the resistance of light energy in the ink environment against color change and fading degree. The lightfastness of ink can be affected from humidty, climate, light direction, alkaline and acid and the ink film thickness on the material used. It is important for printing inks to keep the lightfastness value for a long term in a standard and constant value. The printed materials are used in a number area of our live. Especially, if prints have to be subjected to sunlight etc, some undesired effects in terms of colour fading, quality and functionality problems may be encountered. In the present study, the effect of pigment concentration, which is one of the important factors affecting lightfastness, on light fastness were investigated. The ink samples which have pigment ratios of 10, 13, 15, 17 % were prepared from standard offset ink which has a ratio of 19 %. While this procedure was being applied, the other ingredients of ink were not changed. In addition, the other factors affecting lightfastness were kept constant. Then, test prints with these ink samples were taken on a IGT printing test press. The changes in prints were observed by holding the samples in a Xenon Lightfastness test equipment gradually at 0, 12, 24, 48, 72, 96, 120, 144, 168 and 192 hours. The lightfastness values were evaluated according to Blue Wool Scale which was developed and accepted by British standards. The results were graphically explained and the effect of pigment ratio on light fastness were described.