Reasons for offset printing failure

At present, the plate used for water offset printing in China is basically a positive PS plate. The base of the PS version is aluminum, and the key to the PS version is to reproduce the tone levels of the outlets as much as possible, and as a printing operator, it is necessary to provide qualified printing plates for the subsequent operations. Offset press operators need to use good printing plates so that good prints can be printed. However, in reality, conflicts occur between the printing process and the printing process for the quality of the printing plate. It is sometimes difficult to clarify who is responsible, but there are always rules to follow. The general failure of the printing process can be attributed to: virtual, deep, shallow, poor, low six words. Specifically speaking, the image is imaginary, dark, shallow, and the blank part is dirty. The graphic and ink are poor, and the printing plate has low resistance to printing. Most of these failures were found during the printing process. As an offset press operator, it is necessary to understand the causes of some print failures.

The main operation of the printing process is pumping, exposure, and development. Exposure requires a good grasp of time, while development requires mastering the concentration and time of the developer.

1, the text of the virtual

(1) The vacuum pumping performance of the plate press vacuum pump is poor, and the vacuum degree is insufficient. The contact between the original printing plate and the plate is not real.
(2) The original graphic density of the printing plate was not enough, and the graphic and text exposure caused the picture and text to be empty.

2, the graphic is too deep

(1) Underexposure (2) The developer concentration and temperature are too low, the development time is too short, and the developer is subject to fatigue.

3, the graphic is too shallow

(1) Overexposure or unevenness PS plate exposure time is too long, due to the diffraction of light, so that the photosensitive layer should not see the light also saw the light, resulting in decomposition of light, dot network, thin lines of text, and even off.
(2) The developer is too concentrated, the temperature is too high or the development time is too long.

4, the blank part of the dirty

(1)Stained glass has dirty stains (2)Stain original is stained or has high fog (3)Sketch time is not enough (4)Underdeveloped or developed alkali is too strong (5)Dirty dirty

5, poor printing ink and text

(1) Overexposure (2) In most cases, the development time is too long. If the development density or developer temperature is too high, a small amount of the photosensitive layer will be dissolved in the image, resulting in 2% dot loss. Therefore, the development time must be appropriate. Generally, the newly-developed developer will have a shorter development time when the development temperature is high, and vice versa.

6, baking version resulting in low resistance to India

Nowadays, many printing companies, in order to pursue their patience with India, are baking baked stencils. The key to baking is temperature and time. After baking the PS plate, the normal color is reddish-brown. If the layout is tea green or dark green, it indicates that the baking temperature is too low or the baking time is too short. The resin in the photosensitive layer is not completely cured. At this time, the baking or extending baking time should be increased until the plate color reaches a reddish brown color. . If the layout is dark brown, it means that the baking temperature is too high or the baking time is too long, the resin in the photosensitive layer is partially carbonized, the darker the color, the more carbonized resin, the lower the printing plate's resistance to printing.

Source: Ke Yin Network