In the offset printing production process, the dirty print is a common quality problem. Based on my long-term experience in offset printing, the author summarized seven common types of stickiness of printed products, analyzed the sticking mechanism one by one, and proposed a coping strategy for reference by colleagues.
Seven common types of stickiness
1. Gold and silver ink printing
Gold and silver inks are formulated with special binders and gold and silver powders. The penetration on paper is much smaller than ordinary inks. When gold and silver inks are used to print characters and patterns, the rate of oxidative conjunctiva on the surface of the paper is slow, and the required drying time is long, which can easily cause the prints to become dirty.
2. Field printing
In order to print solid effects on paper, the amount of ink must be increased. However, when the paper is saturated with ink, the excess ink will accumulate on the surface of the paper, making the oxidative conjunctiva speed of the ink on the surface of the paper slow and the drying time required to change. Long, it is easy to cause the printed product to be dirty.
In addition, when printing character hair or printing characters using a four-color overprinting method, the total ink volume per unit area is saturated, and the ink layer is very thick, which is particularly likely to cause the printing product to become dirty.
3. Special paper printing
Due to the use of special papermaking technology, special paper makes the printed product unique in style and is favored by some users. Therefore, it is increasingly applied to the printing of front cover and inner pages. However, the porosity of the fibrous tissue on the surface of the specialty paper is low, and the adsorption of the ink on the capillary pores is weak, so that the ink does not easily penetrate into the interior of the paper, and the printing product is likely to be contaminated.
4. Improper printing pressure
In order for the ink to transfer well to the paper, the printing pressure must be appropriate. The relationship between printing pressure and ink transfer amount is shown in Fig. 1.
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