The quality of ink printing is determined by these five properties of pigments!
The influence of pigments on the printability of inks mainly depends on the properties of pigment dispersion, hiding power, visual volume ratio, and oil absorption. This article analyzes one by one.
1. Dispersion Dispersion refers to the size of pigment particles. The pigment particles in the ink must be completely immersed in the binder in the ink film. The size of the pigment particles cannot exceed the thickness of the ink film, otherwise it will affect the gloss of the printed matter. The smaller the particles, the higher the dispersion and the color saturation of the ink. the bigger. Gravure printing is cell transfer printing, which requires high pigment dispersion.
2. Coloring power Coloring power refers to the ability of a certain pigment to affect the color of the mixed pigment after mixing with other pigments. All the pigments that are blended with white substances and are simply faded will have weak tinting power. The pigments with strong tinting power should be selected for the preparation of ink, which can achieve the effect of less ink consumption and quicker drying when used for printing. This is critical for high-speed gravure printing where high ink drying is required.
3. Concealing power Concealing power refers to the ability of the pigment to hide the background color. Whether the ink has concealing power depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When the ratio is 1, the pigment is transparent; when the ratio is greater than 1, the pigment is opaque, that is, it has concealing power. Different printing products have different requirements for the concealment power of pigments. For example, iron printing ink requires pigments to have strong concealment power to avoid exposure of the background color, while four-color overprint ink requires pigments to have higher transparency, so that the superimposed pigments have a high degree of transparency. The ink achieves better color reduction effect.
4. Apparent volume Apparent volume refers to the volume occupied by each kilogram of pigment, expressed in cubic centimeters. The same pigment with different particles has different apparent volume. The larger the apparent specific volume of the pigment, the smaller its specific gravity is, and it is not easy to precipitate in the binder, and the stability of the ink is good.
5. Oil absorption Oil absorption refers to the amount of oil that a certain amount of pigment can absorb, calculated in grams of linseed oil required to make 100g of pigment stick together tightly. The properties of printing inks are related to the oil absorption of the pigments. The inks made of pigments with small oil absorptions contain more pigments, and the inks have strong concealment power, but poor stability. It is easy to block the plate during printing, and it is also easy to be emulsified. Generally, the oil absorption of the pigment is required to be large.