Printing ink is a coloring agent used in printing. It is a fluid substance with a certain viscosity, consisting of pigment particles uniformly dispersed in a binder.

1. Composition of Printing Ink: Printing ink consists of pigments, binders, fillers, and additives.

(1) Pigments: Pigments play a role in color development in printing ink and directly affect some of its properties.

Pigments are highly dispersed powders of color, black, or white that are insoluble in water and organic solvents. Based on their source and chemical composition, they are divided into two main categories: organic pigments and inorganic pigments.

① Inorganic pigments are oxides of colored metals or some insoluble metal salts. Inorganic pigments are further divided into natural inorganic pigments and artificial inorganic pigments. Natural inorganic pigments are mineral pigments.

② Organic pigments are colored organic compounds, also divided into two main categories: natural and synthetic. Currently, synthetic organic pigments are commonly used. Organic pigments have a wider variety, more complete colors, and better performance than inorganic pigments. Dyes are organic compounds that are soluble in water and sometimes in organic solvents. Insoluble colored precipitates, called lake pigments, can be prepared from certain dyes for use in printing inks.

The requirements for pigments used in printing inks are quite high, especially regarding color, dispersion, lightfastness, and transparency. Colored pigments should have hues close to the spectrum, and saturation should be as high as possible. The magenta, cyan, and yellow pigments used in the three primary color inks must have high transparency. All pigments must not only be water-resistant but also bind quickly and evenly to the binder. The pigment's oil absorption capacity should not be too high, and it is best if the pigment has properties such as resistance to alkalis, acids, alcohols, and weathering.