Discussion on Multi-color Overprinting Rule of Color Printing

The printing process is an extremely complicated process. In the process, various problems often occur accompanied with the transfer of the ink. These problems are closely related to the quality of the printed matter. In multi-color printing, if the overprint of each color ink is not well controlled, the color of the printed matter will be changed, resulting in the quality problem of the printed matter. Therefore, we must analyze and study the overprint condition of the ink.

In actual printing production, the biggest print defect caused by overprinting is dew. According to practical experience, the major causes of multi-color overprinting in color image printing are ink viscosity, printing pressure, printing speed, paper surface strength, and printing interval time. Any one of these factors is not well controlled and will affect the final color print. Print quality can easily cause dew-white failure. This article is based on these factors that affect the effect of overprinting, and researches and discusses the law of multicolor overprinting in color printing. In order to achieve the above objectives, this article focuses on the overprinting experiment by changing the factors such as ink viscosity, printing pressure and printing speed that affect the overprinting effect, and analyzes the relationship between the experimental results and the overprinting whiteness, and analyzes other factors that cause the printing whiteness, such as the paper surface performance. , Overprinting interval, printing color sequence, etc. Finally, the law of multi-color overprinting in color printing is obtained.

First, the effect of ink viscosity on the overprint

1. The viscosity of the ink

It has a great influence on the wet overprinting effect. The viscosity of the ink is large, and the ink layer shows a greater cohesive force. If the viscosity of the ink to be printed first is lower than the viscosity of the ink after printing, the ink after printing will rely on its own cohesion, and the ink to be printed first Stick away, resulting in "reverse overprint" causing color mixing. So controlling the viscosity is very important.

2. The effect of ink viscosity on the overprint effect

Experimental equipment: s-1000 water-based four-color printing slot machine and 4# viscosity test cup produced by Long Sound Industrial Co., Ltd.

Experimental Pharmacy: Tackifiers, thinners, leveling agents

Experimental procedure: 1 Superimpose black on blue, blue ink viscosity is 11.3s, black ink viscosity is 13s, initial printing speed is 40r/min, printing pressure is 3.6mm, substrate used is white paper. The jammed b-type corrugated paper has an initial exposure of 10% under this printing condition.

2 Change the viscosity of the black ink, keep the other initial conditions unchanged, print, observe the whitening condition, and record the data.

3 Through the experimental data in the table, plot the relationship between ink viscosity and overprint.

Second, the impact of printing pressure on the overprint

1. Printing pressure

The printing process, in a sense, is the process of resolving the conflict between ink and paper. In order to transfer the ink on the printing plate to the substrate, a certain force must be applied, the so-called printing pressure. It has an important role in printing.

Printing pressure control is not easy. Excessive or too low printing pressure can lead to a decrease in the quality of the printed product. In particular, the pressure is too great, which brings more disadvantages. It often causes graphic distortion, ink accumulation, paper pulling, enlarged dot prints, and unclear levels of printed matter. On the contrary, if the printing pressure is too low, it may cause many failures such as the incomplete transfer of printing and graphic images, the lack of network points, and the more obvious defects. Therefore, it is very important to control the printing pressure within a proper range during the printing process.

2. Effect of printing pressure on overprint

Experimental equipment: s-1000 water-based four-color printing slotting machine manufactured by Changsheng Industry Co., Ltd.

Experimental procedure: 1 Superimpose black on blue, blue ink viscosity is 11.3s, black ink viscosity is 13s, initial printing speed is 40r/min, printing pressure is 3.6mm, substrate used is white paper. The jammed b-type corrugated paper has an initial exposure of 10% under this printing condition.

2 Change the printing pressure, keep the other initial conditions unchanged, print, observe the whitening condition, and record the data.

3 Through the experimental data in the table, plot the relationship between printing pressure and overprint.