The Influencing Factors of Color Reproduction in Graphic Printing

There are many factors affecting the color of the reproduced image when copying on the printing press, such as: dot enlargement, printing color sequence and overprinting, ink hue and solid density, ink temperature and viscosity, water supply (offset), paper property, printing plate Layout depth, printing pressure, etc.

1. Dot expansion

In printing, outlets will always expand, but when the amount of expansion exceeds a certain range, many quality problems will arise. Such dot enlargement will reduce the contrast of the image and make the whole image darker, dark dots will be crushed, and the copy hue will change drastically. When the image dots of various colors in printing are expanded at the same time, the image will become darker. When only one of the dots is enlarged, the copied image will have a color cast. For example, when the magenta version dot coverage expands in the middle tone, and 50% of dots change to 55%, the color of the printed image becomes reddish and the flesh color becomes uneven. Red, neutral color becomes light red, green is dirty. Both the printing pressure and the density of the ink in the field affect dot gain. Small changes in printing pressure can cause significant changes in the entire printed image; when the density of the ink in the field increases, the dot gain increases, which has a great influence on the tone in the image.

2. Printing color sequence and overprint

In the printing of color images, the inks are overprinted in one color, and the overprinting may cause color deviation, color mixing, and gradation disorder. Printing color sequence has a great influence on the color effect of overprinting. For multi-color printing presses, the printing interval time of each color ink is short, and the printing ink of the rear printing is the printing state of the printing wet ink on the surface of the printing ink in advance. The ink printed on the paper surface in the overprinting color is superior to the ink printed on the surface of the wet ink layer. For two colors of ink, as long as the color sequence is reversed, the hue, brightness, and saturation of the overprint color may be different. If the cyan and magenta inks are overprinted, the magenta is printed first, then the magenta is overprinted; the magenta is printed after the magenta, and the overprinting is reddish.

In order to obtain a good overprinting effect, the viscosity of each color ink should be properly arranged after the color sequence is scheduled.

3. Ink hue and solid density

The inks used in printing production all have different degrees of color shift, resulting in color cast images, and color inks with less color shift should be used for color printing. The density of the solid ink density on the surface of the printed image determines the print image tone and tone reproduction range. The higher the density in the field, the wider the tone and tone reproduction range. The small density in the field reduces the color saturation of the image and the overprinting color weakens.

4. Ink temperature and viscosity

In printing image reproduction, ink viscosity is a very important parameter. In general gravure printing uses liquid ink, and in the inking apparatus, there is no ink distribution and ink licking mechanism. The ink viscosity is controlled by adding an appropriate amount of solvent to the ink tank. Offset and embossing generally use viscous ink, which is very viscous. In order to transfer the ink uniformly from the printing plate to the paper surface, both the offset printing and the embossing machine have a uniform ink and a re-inking device. The ink is squeezed, sheared, and separated during the transfer and smoothing of the rollers between these devices. The roller works to overcome the internal friction of the ink, and the temperature of the surface of the ink roller is increased, and the roller is subjected to extrusion, shearing, and separation during the process of being transferred and being evened. The roller works in order to overcome the internal friction of the ink, so that the surface temperature of the ink roller increases, and the viscosity of the ink that is transferred decreases. After the ink becomes thin, the amount of ink carried on the surface of the roller is reduced, and the amount of ink transferred to the surface of the paper is reduced, which changes the tone and tone of the printed image and destroys the consistency of the printed image. Some studies have shown that: After the printer is turned on and printed, the color deviation of the printed image is 60% due to the temperature change of the ink roller.

5. Offset ink balance

Offset printing ink production directly affects the quality of image reproduction. The small amount of water will make the plate dirty, paste version; water ambassador ink emulsification, so that the color saturation of the printed image is reduced.