The technical indicators of ink have important guiding significance for printing. The technical indicators that are generally closely related to offset printing mainly include the following aspects:
(1) Ink concentration
Ink concentration is an indicator of pigment content. Pigments generally account for about 20% of the total ink. The ink concentration is large during printing. With the same amount of ink, the color of the printed matter is darker, otherwise, the color of the printed matter is lighter. The ink concentration is large, and the amount of ink used in printing is small, the ink layer is thin, and the drying is relatively fast. Especially when printing large areas, the effect of ink concentration on printing quality is particularly significant. Because the printing ink layer is thin when printing with high-density ink, the fixing speed is fast, which can reduce the stickiness of the printing product, and the color balance of each color is also easy to adjust.
The ink industry judges the size of ink density by detecting the coloring power. The tinting strength depends on the ability of the pigment in the ink to absorb and reflect light. Shows the strength of the ink's ability to display color. It is usually measured by the method of diluting the ink with white ink, so it is also called diluting intensity or diluting density.
(2) The viscosity of the ink
The viscosity of ink is an important indicator in printing. It is tested with an ink viscosity meter. The size of the ink viscosity value refers to the amount of force that separates the ink film between the two rollers of the viscosity meter. If the viscosity of ink is too large or too small, it will affect the quality of printing. When the viscosity of the ink is too large, it is easy to cause failures such as poor ink transfer, poor transferability, paper pulling, and poor overprinting. If the viscosity is too small, it is easy to cause failures such as excessive ink transfer, dot expansion, ink emulsification, and floating dirt.
At a certain temperature, the viscosity of the selected ink should not be too high when the printing machine is fast, and vice versa. In addition, the relative viscosity of each color ink should be selected according to the printing order. Under normal conditions, there is no need to adjust the viscosity of the ink. If you need to adjust it, you can choose the auxiliary agent according to its viscosity and consistency. Generally, the viscosity is large, and when the consistency is appropriate, it can be adjusted with additives that reduce viscosity but not reduce viscosity. If the viscosity is large and the consistency is large, additives that reduce both viscosity and viscosity can be used.
(3) Dryness of ink
The drying process of offset printing ink on paper is the process of changing the ink from a non-polar colloid with high fluidity to a fixed state. Generally, there are two indicators for measuring offset printing ink:
1. Fixation speed It means that the ink changes from natural flow state to semi-solid state. That is to say, the printed matter is not sticky when it is superimposed at a certain height, and it is called primary drying on printing. The initial drying of ink is determined by the resin structure selected in the design. The initial drying time is very short, but not completely dry.
2. The drying of oxidized conjunctiva is the thoroughness of printing. The drying time is longer, generally more than 8 hours, it is completely dry. The thorough drying of ink is determined by the type and amount of desiccant, which can be adjusted within a certain range.
At present, offset printing inks are all resin type, and the fixing speed is relatively fast. Theoretically speaking, the faster the initial drying, the better, but too early drying will affect the gloss of the printed matter. Operators of offset presses always hope that the ink printed on the paper will dry quickly, but not in the ink fountain, which is impossible. Generally, about 80% of the ink conjunctiva drying time is between 16 and 30 hours. If the drying time of the conjunctiva is too short, it is easy to cause the skin to hug the roller on the machine. Printing general coated paper or long version work, you can choose the ink that has a longer drying time. For high-grade coated paper, cardboard or short-run work, you can choose a faster and faster ink.
(4) The gloss of the ink
The gloss of the ink is the ratio of the amount of specularly reflected light to the amount of specularly reflected light of the standard plate under a specific light source and a certain angle of illumination, expressed as a percentage. The brightness of the printed matter gives a direct impression. Generally speaking, the higher the gloss feeling, the better the printing effect. Although the gloss of the printed matter has a certain relationship with the wetting fluid used for printing and the absorbency of the paper, it is mainly determined by the ink. The nature of the ink depends on the binder and pigment. The binder and pigment in the ink should have good printability, and the resin itself has high gloss. The gloss of graphics printed on the paper with such ink is high. Ink with good gloss tends to be a little slower after initial drying. In the case of overprinting on a monochrome machine, it is necessary to control the overprinting time, otherwise the ink will be crystallized.
(5) Fineness of ink
The fineness of the ink indicates the size of the pigment and filler particles in the ink and the uniformity of the distribution in the binder. The fineness of the ink is directly related to the nature of the pigment and the particle size. The better the fineness, the more stable the properties of the ink, and the printed product dots are full and powerful. On the contrary, it is easy to appear in the printing process that the printing plate has low printing durability, ink stacking, empty dots, expansion and unclean dots.
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