Analysis of Influencing Factors of Distortion of Printed Copy Dots

The outlets are the basis for print reproduction and color reproduction, and they are the true reflection of the adjustments, levels, and color reproduction of prints. The quality of the outlets will directly determine the quality of the printed matter, so controlling the quality of outlets is of great significance.

The reduction of outlets is a major factor affecting the reproduction of outlets and affecting the quality of printing. The maximum density, exposure, and development conditions of the film during printing, as well as the friction during printing, the viscosity of the ink, and the yield value are the main factors that cause the dot to shrink.

1. The effect of the maximum density of the film The printing plate is the process of transferring the graphic on the film to the PS plate by closely bringing the film and the PS plate together. In general, the field density of the film used for printing is greater than 3.5, preferably about 4.2; at the same time, the dot type of the dot is better, that is, the edge around the dot is required to be clear, and the boundary with the blank is clear. If the density in the field is too low, the small dots of the image will easily shrink or even be lost when the printing is in progress. Fine text will have broken lines and other phenomena. If the edges of the dots on the film are blurred, the dot on the PS plate will randomly change as the exposure and development conditions change, and the dot may increase or decrease.

2. The effect of exposure The current printers generally use the light emitted by a UV lamp as the exposure light source, so that the light is not parallel but scattered, and these scattered lights reach through reflection of the film refraction and reflection on the surface of the PS plate. At the lower edge of the film web site, the edge of the corresponding dot formed on the printing plate is in a half-exposure state. The light directly underneath the UV lamp is relatively parallel. The half-exposed lightness is lighter at the edge of the dot, and this phenomenon is more serious for the small dots around. When developing, dot area will be reduced and even some small dots will be lost. For a different PS version to use the appropriate exposure, if the exposure is too large, even if the normal development conditions, dot area will be reduced.

3. The developing conditions affect the developer concentration is too large or the development time is too long, even under normal exposure conditions, the developer will excessively corrode the PS plate, which tends to dissolve or even completely lose the small dots of the graphic plate. The resistance to force will also decrease. In general, 5% or less of the outlets are easy to lose, and 40% of the outlets have smaller outlets. If the Ps version is overexposed, the developer concentration is too large and the development time is too long, which will also cause the dot to shrink.

4. Impact of friction during printing During printing, in order to prevent the blank part of the printing plate from absorbing ink, it is required to moisten the printing plate with fountain solution before ink application. During the high-speed operation of the printing press, the surface of the printing plate is rubbed by the water roller and the rubber roller. Friction wears the sand around the dot, and the dampening solution immerses in it, forming a hydrophilic, oil-repellent film. For the high-profile part of the printing plate graphic, the area coverage of its own dot is smaller, and the hydrophilic area is larger than the lipophilic area, which is conducive to the expansion of the fountain solution, and the formation of a hydrophilic and oil-repellent film due to abrasive wear. Preventing the normal spread of ink will inevitably cause the dot to shrink.

5. The viscosity and yield value of the ink affect the viscosity of the ink is too large, the yield value is too high, easy to cause the ink is not easy to flow, the ink is too short, the PS plate is not easy to spread and other phenomena, even under the pressure of the printing process, the printing plate The ink on the dots also shrinks toward the center due to the high viscosity, which also causes the dots to shrink.

In view of the above situations, if the highest density of the film is not enough to cause the reduction of the dots, only a set of film with the right density will be re-exported to solve the problem. In the case of a suitable density of the film, the factors that cause the dot to be reduced during the plate making process are mainly the amount of exposure and development conditions. This can be solved by using signal strip tracking management. During the printing process, the gray ladder rule is tightly integrated with the Ps plate and then exposed. After the development, by observing the reproduction of the steps, it is possible to check whether the exposure amount, the developer concentration, and the development speed are appropriate, and then adjust them according to the actual situation, so as to avoid the reduction of the gamut point.

For the reduction of dots due to friction during the printing process, the printing pressure can be reduced as much as possible in order to ensure the ink transfer and the dot reproduction to be good, thereby avoiding the reduction of the dot due to the abrasion of the printing plate due to friction. In short, the quality of outlets has a direct impact on the reproduction and reproduction of prints. Therefore, it must be controlled throughout the entire printing process to avoid the reduction of outlets or to minimize the reduction of outlets.

Source: Printing Technology