Lithographic Technology Manager Professional Knowledge (Part 2)

5. The degree of vacuum in the drying frame within the drying frame shall reach 0.08 MPa.
6. The unrefined quality of the positive image and yellowing of the base will affect the quality of the printing.
7. Voltage instability The above factors affect the quality of the printing plate, which is solved in advance to ensure the quality of the printing plate and lay the foundation.
VI. Five Common Quality Problems and Solutions for Printing Plates 1. Causes for dirty parts of the layout blank:
(1) Insufficient exposure time
Insufficient exposure time, the photosensitive layer of the blank portion is not completely decomposed, and a small amount remains on the plate surface, having hydrophobic and lipophilic properties, resulting in dirtiness.
Should strictly follow the control bar (signal strip) information operation.
Each batch of plates is applied with a small strip for optimal exposure time testing and determination. Different plates, different layouts, different film bases, and exposure times must be different.
Exposure time determination principle: In the control strip (signal strip) feedback information on the premise of meeting the requirements, the amount of prolonged (about 20S) exposure time.
(2) Improper developer concentration, insufficient development time, developer failure, and insufficient developer temperature.
The above four conditions may result in failure to clean the photosensitive layer that has been decomposed by light, and the photosensitive layer of the blank portion may not be fully dissolved, resulting in a local dingy and requiring frequent washing of the plate.
Different plates, different developer concentration, different development time. According to the best data, adjust the process.
(3) The positive image has dirty spots, and the transparency of the base is not good, resulting in the photosensitive layer not being fully decomposed by light. Dirty points must be checked and cleared beforehand.
(4) Dirty spots and dirt on the dryer's glass. Carefully clean it with alcohol.
(5) PS plate thickness uneven. The extra thick part remains as a dirty spot.
(6) In the printing process room, strong light should be avoided.
(7) Improper sizing, leaking glue.
(8) Dirty, bluish green for two reasons: a. Underexposure or underdevelopment, can be removed in addition to dirty agent. b. If the dirt removal agent cannot be removed, it is due to the incomplete sealing of the PS plate.
The printing plate workshop should be kept clean. It is imperative to adhere to the workshop seal, change shoes, change clothing, and mop the floor sooner or later.
2. Graphical part of the poor performance of ink absorption image is not real, ink is gray and dull. Exposure or over development. When printing, the vacuum is not sufficient, the positive and the printing plate do not closely adhere, the tape is too close to the image, the machine glass is not clean, the PS plate is not clean, the picture is not clean, the high temperature, Huang Meitian, The gelatin is metamorphosed by fermentation and acid, and the PS plate is not properly preserved.
3. The darkness of the printing plate outlet darkened and the development was insufficient.
4. There is unevenness in the level of vacuum in the flat screen.
5. The printing plate is too impermeable to the developer. The development time is excessive. The reason why the printing plate is not resistant to printing is very complicated:
First of all, we should study the quality of the PS plate, analyze the quality of the plate and the effect of the wear resistance of the photosensitive layer. The impact of the offset printing process is even more complicated. The analysis will be conducted in the offset printing process and the cause of the failure.
VII. Using Control Strips to Ensure the Quality of Dried Printing Plates Example 1. Printing Control Strips Developed by China Institute of Printing Science:
Model:GY-S
Structure: Section E consists of 1% to 5% highlights. The next section consists of a test area consisting of μ lines.
Sun control pattern data: (relative basking)
2% of small points are reserved, and 50% of outlets are expanded by 2% to 3%.
6μ black line drying, 8μ black line retention.
Control printing data on the printing plate: (relatively sunning)
3% of small dots are reserved, and 50% of outlets are lightened by 3%-5%.
8μ black line drying, 11μ black line retention.
Example 2: Bruner test strip.
Stencil control section:
2% of small dots disappeared, 3% of small dots remained, and 50% of outlets shrank to 45% or unchanged.
Lines below 8μ disappear, lines 11μ or 13μ and above remain.
The above data are all reference values. Conditions vary widely, and data need to be tested in practice. According to the characteristics of the company, find the best data.
VIII. According to the evidence, insisting on the use of testing instruments is the fundamental method for determining the quality of printing plates. Some printing factories, printing and offset printing processes often cause contradictions due to the quality problems of printing plates. The method of coordination and solution is:
Shaiban process, must be strictly in accordance with the procedures, data manipulation, control strips (signals, test strips) to reflect the data, the data measured by the density meter, to explain the quality of the plate.