Influence factors of network reproduction

The quality of outlets is the basis for print reproduction and color reproduction, and it is a true reflection of the level and color transfer of printed products. The reproduction of outlets is mainly related to the properties of the printing machine, the quality of the printing plate, the density of the printing plate, the exposure time, the developing conditions, the transfer of the lithographic printing, etc. The existence of these conditions is the main factor restricting the quality of the printing product.

1. The performance of the printing machine

The performance of the printing machine is a factor that affects the reproduction of the positive PS version screen. First, the air pump pumping degree of the printing machine is low and the pressure is low. In order to make the vacuum meter number not less than 80kPa, the performance of the air pump should be timely repaired, or according to the sun The performance of the plate machine is set to half vacuum and full vacuum when pumping. If the area of ​​outlets exceeds 40%, measures such as repeated exhausting and evacuating can be adopted to close the plate and the substrate to achieve normal transfer of the dots on the layout. Second, the elastic pad of the printing plate is reduced in elasticity, resulting in unevenness. When evacuating, the dots are not evenly distributed. When this phenomenon occurs, blankets should be replaced in time to achieve normal transfer of the dots.

2. Plate quality

In the production process of the positive PS version, the synthesis and coating quality of the photosensitive liquid also have a certain influence on the reproduction of dots. Under normal circumstances, stacking screen printing should be used to select laminarity, uniform particles, uniform film thickness, printing of books and texts, and select the general performance PS version.

3. Density of printing film

Stencil printing film must have good density and dot quality, and its density value is D≥3.5. If the density contrast of the printing plate film is small and the dot quality is bad, then D<3.0. Even with the same dot area and the same operating conditions (the same exposure time, the same developer concentration), the soft and hard dots will appear inconsistent. Therefore, in the case of the same development conditions and the same plate-making film, the exposure intensity and the development time should be correctly determined when outputting the stencil printing film. If the development conditions change (replacement of the developer) or when replacing the different types of plate-making film, When the density value D≥3.5 is determined, the linear proportion of redo dot points is redone so as to ensure that the dot number required by each version of the printing film is constant.

4. Exposure time and development conditions

In the plate making process, determining the exposure time and controlling the development conditions are the basic conditions for realizing the dot transfer. Because the exposure time has a direct influence on the received light intensity of the layout, it has a certain influence on the transfer of dots. On the one hand, when the critical light quantity and the developing conditions are fixed, when the exposure exceeds the critical light quantity, the layout of the net point is reduced, the fine dot loss is large, that is, the exposure is excessive; when the exposure is less than the critical light quantity, the dots are expanded, and the blank is Some are dirty and show underexposure. On the other hand, under the condition that the exposure amount is fixed, the development conditions should be controlled, and changes in the development conditions also cause the dot change.

The developer has a large concentration or a long development time, which can easily cause 5% or less of dot loss, 40% of the intermediate tone, large loss of the point, low concentration of the developer, or insufficient development, can easily cause incomplete development of the edge of the spot light spot. % The following dots are not clear, 40% of the middle tone's dots are distorted, and 80% of the dark tone's dots are blurred. It is easy to print and smear when printing.

Correctly control the development conditions to ensure that the amount of alkali in the developer, should constantly monitor the activity of the developer, keep the amount of sodium hydroxide is 4% to 7%, the developer temperature is maintained at 20 ~ 22 °C is appropriate. When the dried PS version is detected by signal strips and magnifiers, the printed area should be thick, 80% of the dots are real, 40% of the dots are clear, the 8μm of the microline is clear, the 10μm is clear, and the contour is yin and yang. The same line width.

5. Influencing factors in the printing process

Lithography is the use of water and oil incompatibility, through physical and chemical methods, to create graphic elements and blank elements on the same plane of the printing plate, if the ink is not balanced in large lithography, it is difficult to achieve the normal transfer of dots .
(1) The effect of dampening solution on the dot network Lithography is to absorb ink by the lipophilic part of the printing plate, and the blank part absorbs moisture to achieve printing. When printing, in order not to dirty the blank part, and do not make the dots enlarge or shrink, it is required to put water on the plate before re-inking, and make the blank part of the printing plate form a standard and stable water film layer to resist the ink. The infiltration of the blank portion and the outward expansion of the ink on the image. If you want to achieve ink-water balance during the printing process, the water film thickness should be controlled within the range of 1.5 to 4 μm. Under normal circumstances, the side of the plate is silver-gray, which indicates that the water film is suitable. If the plate is shiny, it proves that the water volume is too large, it will cause the printing network to send out a virtual deformation, affecting the quality of the printed product.

Since the fountain solution is an acidic aqueous colloidal solution, the pH of the fountain solution must be properly adjusted to maintain the dot size constant. Since the printing plate is not inked during the inking process, it is not necessary to realize the ideal ink transfer conditions. In the process of dot reproduction, due to the influence of photosensitive layer gel or fountain solution properties, the narrow area around the printing plate dot can not be fully wetted by the fountain solution, so that this area may receive the same ink. Around the formation of a color wheel, performance is printed on the dot is increased. For this purpose, the pH of the fountain solution needs to be adjusted. Generally, the pH value is between 5.5 and 6, or treatment with 10% dilute phosphoric acid solution can avoid the phenomenon of dot color wheel and achieve the normal transfer of dots.

(2) Inhomogeneity of outlets

In the printing process, the heterogeneity of the dots mainly manifests in the discontinuity during the dot transfer process, mainly referring to the uneven dot density and poor gloss.

The causes of uneven dots: First, the paper's absorption of ink is not uniform, the performance of the paper is rough, poor adsorption, should choose a better offset paper or coated paper; Second, the rubber blanket is poor, so that the printing pressure is not uniform, The poor ink absorption; Third, the ink roller and the plate pressure is inconsistent, it is easy to cause uneven ink transfer, printed product network size is inconsistent.

Caused by the increase or decrease of the network points: First, the printing pressure is too large, the pressure between the printing plate cylinder and the blanket cylinder is large, and the dots are increased. On the contrary, the dots are reduced. Second, when the ink is transferred, the breakage in the middle is inconsistent, resulting in different thicknesses of the ink layer on the layout and the deformation of the halftone dots. Third, the performance of the backing material is different so as to deform the halftone dots. In order to minimize the deformation of the dots, good performance blankets and underlays must be selected to properly line up and use the minimum pressure.

In short, changes in the size and shape of outlets directly affect the tone and level of printed products. Therefore, in the process of plate making and printing, it must be controlled in all aspects to truly achieve the true reproduction of outlets.

Beijing Shijingshan District 66240 Troops 64 Zhang Zhenping Source: Ke Yin Media