Influencing factors of color reproduction in the m

Influencing factors of color reproduction in graphic printing

when copying on the printing machine in graphic, there are many factors that affect the color of the copied image, such as point enlargement, printing color sequence and overprint, ink hue and field density, ink temperature and viscosity, water supply (offset printing), paper properties, printing plate layout depth, printing pressure, etc

1. dot expansion

in printing, dot expansion will always occur, but when the expansion exceeds a certain range, many quality problems will occur. This kind of dot enlargement will reduce the contrast of the image, and make the whole image darker, and the dark spots will be blurred, so that the duplicate hue will change sharply. When the dots of various colors of the image are enlarged at the same time in printing, the whole image will become darker. When only one of the color dots is expanded, the copied image will be biased. For example, the magenta version dot coverage will be expanded in the middle note. When 50% of the dots become 55%, the printed image color will be biased red, the flesh color will become biased red, the neutral color will become light red, and the green will become dirty. Printing pressure and field ink density both affect point expansion. Small changes in printing pressure will make the whole printing image change significantly; When the ink density on the spot increases, the dot enlargement increases, which has a great impact on the harmonic and dark colors in the image

2. printing color sequence and overprint

in color image printing, the ink is one color one color overprint, and poor overprint will produce color deviation, color mixing and hierarchy disorder. The arrangement of printing color sequence has a great influence on the effect of overprint. For multi-color printing machines, the printing interval of each color ink is short, and the post printing ink is overprinted on the surface of the first wet ink, which belongs to the "wet overprint" printing state. In overlay printing, the ink printed on the paper has an advantage over the ink printed on the surface of the wet ink layer. As long as the color sequence of two colors of ink is reversed, the hue, lightness and saturation of overprint color may be different. For example, cyan and magenta inks overprint, first cyan and then magenta, and the overprint color is cyan; First magenta, then Evonik, shows blue, and the overprint color is red

in order to obtain good overprint effect, the viscosity of each color ink should be reasonably arranged after the color sequence is arranged

3. ink hue and field density

the inks used in printing production have different degrees of color deviation, which makes the printed image color biased. The inks with less color deviation should be used for color printing as far as possible. The ink density on the surface of the printed image determines the level and tone reproduction range of the printed image. The higher the field density is, the wider the range of tone reproduction is. The field density is small, which reduces the color saturation of the image and weakens the overprint color

4. ink temperature and viscosity

ink viscosity is a very important parameter in printing image reproduction. Generally, gravure printing adopts liquid ink. There is no ink homogenizing and ink channeling mechanism in the ink conveying device. The viscosity of the ink is 100% without cracking. It is controlled by adding an appropriate amount of solvent to the ink tank. Offset printing and embossing generally use viscous ink, which is very viscous. In order to transfer the ink evenly from the printing plate to the paper surface, offset printing and embossing machines have ink leveling and ink channeling devices. In the process of transferring and homogenizing the ink between the rollers of these devices, it is squeezed, sheared and separated. The roller works to overcome the internal friction of the ink, and the surface temperature of the ink roller rises. In the process of being transferred and being beaten, it is squeezed and sheared to separate. The roller works to overcome the internal friction of the ink. 3. Balancing machine (including on-site balancing instrument); The surface temperature of the ink roller increases, and the viscosity of the transferred ink decreases. After the ink becomes thinner, the ink load on the roller surface decreases, and the amount of ink transferred to the paper surface decreases, which changes the order and tone of the printed image and destroys the consistency of the printed image. At the end of February and the beginning of March, the research showed that 60% of the color deviation of the printed image after the printing machine started printing was caused by the temperature change of the ink roller

5. Offset ink balance

offset production ink balance directly affects the quality of image reproduction. Small amount of water will make the printing plate dirty and paste; The amount of water will emulsify the ink and reduce the color saturation of the printed image