Factors Affecting The Book Printing Quality: Ink

The color of printed book is caused by printing ink. The ink quality is the determine a factor for quality of the book color restore.

1. The color quality of ink

The ideal three primary color inks should each absorb the spectral components of the 1/3 band in the visible light band. And transmit the spectral components of the 2/3 band. By adjusting the proportions of the three inks. The purpose of controlling the red, green and blue light entering the human eye to reproduce the original color is achieved.

The spectral characteristic curve of the actual ink is different from the ideal situation. Each ink has a certain color shift. At the same time, the part that should be transmitted is not fully transmitted. And the wavelength band that should be completely absorbed has a certain transmission. Thereby reducing the saturation of the ink and making it gray. This is why the gamut range of prints is smaller than that of most originals.

At present, the four parameters recommended by the American Printing Technology Foundation (GATF). They are widely used at home and abroad to evaluate the color quality of ink. Namely color strength, color gray, color cast and color efficiency. For the measurement and calculation of these four parameters, please refer to the color densitometer part of Chapter 4.

2. Other properties of ink

The main component of ink is pigment, which determines the spectral characteristics of ink. The second is the binder. Which is the carrier of the pigment particles, has a certain fluidity and transparency. and can be fixed on the surface of the substrate to form a layer of ink film. Besides, to pigments and binders, the ink also contains some auxiliary materials that can adjust the printability of the ink. And adjust the drying speed to achieve better printing results. Besides, to the color quality, the performance of the ink that affects the color quality of the replica has the following aspects.

(1) Transparency of ink.

The primary color ink should have good transparency. Otherwise, the upper layer of ink will cover the lower layer of ink. That is, the incident light cannot enter the lower layer of ink layer. And the lower layer of ink will selectively absorb. And the subtractive mixing of colors will be impossible. And the color reproduction will not achieve the desired effect. Generally, inorganic pigments have poor transparency and strong covering power. While organic dyes have good transparency. 

Oily material binders have poor transparency, while polymer resin binders have high transparency. Inks with poor transparency are often printed first to avoid covering other inks. Sometimes the ink needs to have a certain covering power. For example, when the whiteness of the paper is poor, the opaque yellow ink can be used as the background color. The background color of trademarks, advertisements, patterns, and the ink used as the substrate, etc.

(2) The particle size of the ink.

The particle size of the ink, also known as the fineness, refers to the thickness of the pigment particles in the ink. The finer the pigment particles, the higher the degree of dispersion in the binder, and the higher the fineness of the ink. It will cause the edge hair of the dot, the deformation of the dot, the increase of the dot and other drawbacks. Which will make the image blurred and the level will be lost. Which will seriously affect the reproduction quality. 

The ink fineness is low, the dots are full and powerful, and the tinting strength of the ink can be improved. Which is very beneficial to color book printing. From an economic point of view, the higher the number of screen lines, the smaller the fineness of the selected ink should be. And the lower the number of screen lines, the larger the fineness of the ink.

(3) The tinting strength of the ink.

The tinting strength of the ink is also called the color density of the ink. The tinting strength of the ink is mainly determined by the content and dispersion of the pigment in the binder. The higher the content and dispersion of pigment in the binder, the stronger the tinting strength of the ink, and vice versa.

The tinting strength of the ink is relatively strong, the amount of ink can be reduced. And the thickness of the ink layer can be thinner, which is very beneficial to offset book printing. Because offset printing is indirect printing, the ink layer cannot be as thick as letterpress or gravure products. So the ink must have good tinting strength. Otherwise the color gamut of the printed matter will be further reduced. And the requirements of color reproduction cannot be met.

(4) Stability of ink.

Printing ink will be in various environments during the printing process and during the printing use period. And will be eroded by water, acid, alkali, alcohol, light, heat and other material conditions. And its performance of keeping the color basically unchanged is the ink. stability. The stability of ink can be divided into two aspects: chemical stability and light fastness. 

The ability of ink to keep its color unchanged under water, acid, alkali, alcohol. And high temperature conditions is called the chemical stability of ink. For example, the offset printing fountain solution is acidic. Which requires the ink to have acid resistance and water resistance. Otherwise there may be color changes, viscosity reduction, hydration and other phenomena. Which will affect the color of the printed matter. When using ethanol fountain solution, the ink must have Alcohol-resistant iron sheet printing needs drying, glazing and lamination also need to be carried out at high temperature. And the ink must be heat-resistant. When the printed matter is used for the packaging of some alkali-containing commodities. The ink needs to have alkali resistance. 

The ink should also be lightfast. In fact, the color of the ink will change to a certain extent under long-term illumination. Especially under the irradiation of ultraviolet rays. Generally speaking, organic dyes are easier to fade than inorganic pigments. The former will gradually become lighter and the latter will gradually become darker. The light fastness of the ink is divided into five grades, the first grade is severe discoloration. And the fifth grade is very good light fastness. When custom map printing services, trademarks, color samples, export commodity packaging, teaching wall charts, outdoor advertisements, etc., try to choose inks with good lightfastness to make the colors lasting bright and true.