General packaging and decoration prints have colorful quality requirements. So, what are the factors that affect the bright colors of packaging and printed matter? Below is a brief analysis.
1 The effect of whiteness and absorbency of paper on the vividness of printed products
The whiteness of the paper is the basis for bright colors in printing. The ideal paper can reflect nearly all the color light, and the paper containing gray, black, blue, red or other color will absorb part of the incident color light, resulting in the hue, lightness and saturation of the imprint will be affected, and eventually appear as color Difference. This is equivalent to adding some of the other inks to the ink, showing the impureness of the excellent ink, which gives people a feeling of darkness, turbidity, and color cast.
The main components of paper are cellulose, rubber, fillers, etc. The flowing part of the ink is the connecting material, and the pigment of the ink is adhered by the drying of the connecting material on the surface of the paper. The main components of paper and ink are asymmetric molecules. When they are close to each other, the molecules are attached to the paper by secondary binding force.
Most of our current packaging and decoration prints use coated whiteboard paper, wood pulp lined whiteboard paper, ordinary boxboard paper, wood pulp lined boardboard, kraft paper and white cardboard. Due to the differences in the production processes of different paper mills, there is a significant difference in the surface whiteness and smoothness of the paper. Therefore, at the moment of printing, the low-molecular part with high fluidity in the ink binder is pressed into the larger pores of the paper, and the binder starts to separate from the ink. If the pigment content of the ink is high, a large number of fine capillaries can be formed in the ink film. The ability of these large fine capillaries to retain the connecting material is much greater than the ability of the fiber gap on the surface of the paper to absorb the connecting material. If the content of the pigment is low, the ink will adhere to the surface of the paper, causing most of the connecting material to enter the gap of the paper, causing the ink film on the substrate to be thin, the pigment particles are exposed, and the final color is not bright.
2 The effect of ink transfer and rolling on the vividness of printed products
If the ink fountain and the ink roller are not clean when the color ink is coated, and mixed with other color ink, it will inevitably cause color cast, and also cause the color to be not bright. Therefore, when changing the color, be sure to clean the ink fountain, ink roller and water roller, especially when the dark color is changed to the light color. The usual practice is to clean the dark ink, then shovel some of the light ink to be used, and mix it for a period of time before cleaning.
For two-color machines and multi-color offset presses, especially the equipment where the upper and lower units share one impression cylinder, more attention should be paid to the occurrence of color mixing. Once the color is mixed, it will definitely cause color cast, making the color ink not bright.
3 The effect of excessive emulsification of ink and the addition of additives on the vividness of printed products
The traditional offset printing method mainly relies on water-ink balance to complete the printing process. According to the analysis of the ink transfer process, the emulsification of the ink is inevitable. However, the excessively emulsified ink will cause the color of the printed product to fade and become stale, which will reduce the vividness of the color.
In the offset printing, various additives such as diluent and drier are added as needed. Adding too many of these additives can sometimes affect the vividness of the printed product. The diluent includes white ink and white oil. White oil is mainly an emulsion made of magnesium carbonate, stearic acid, ink blending oil and water. This emulsion will promote the emulsification of the ink, resulting in a dull color.
The driers are mainly metal soaps, and are also strong emulsifiers. A small amount of driers can stabilize the emulsification of the ink, but too much addition will cause serious emulsification of the ink.
In addition, for prints with a small graphic area, the amount of new ink added to the ink roller every cycle is less, so these inks that stay on the ink roller for a long time will be subjected to several times of mixing, Extrusion and rolling cause serious emulsification of the ink, making the colors less vivid.
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