Plate quality control

The images and texts produced by the prepress process are transferred to the PS plate, and the plates used for printing are called plates.
Shaiban (offset printing plate production) plays an important role in the quality and stability of printed products. Therefore, strengthening the quality management of the printing process, and strengthening the implementation of standardized operations and quantitative control, is the basic condition for stably improving the quality of the printing plate and the printing rate, and further improving the overall level of quality of books and periodicals.
First, the requirements of the original density According to the scope of the process, the original quality and density does not belong to the scope of the printing process control, but it is a very important factor that affects the quality of the printing plate and the printing rate. Therefore, it is required that the text version density be higher than 2.65 (film base density plus fog), and the image plate dot density should be 3.65 or more (base density and fog) so that the printing plate can basically satisfy the original printing plate. Density requirements.
In the density measurement, if there is no micrometer, you can use the "line" test method to check the original text density. The specific method is: first make a black line with a width of 0.10mm on the transparent white film base (the production method is not limited). When checking, put the line surface and the original film surface (line piece below) on the plate , Observe with a 30x or 50x magnifier, if the following line can be seen through a single dot or a single stroke of the text, then depending on the density of the page to meet the requirements. In practical work, this method can play a good role in the control of the original density, and lay the foundation for improving the quality of the printing plate.
Second, the choice of light source printing plate exposure to improve the quality of the printing plate and the printing rate has a huge impact.
The choice of printing plate light source should be based on the sensitive area of ​​the PS plate, between about 300nm-460nm. Since light of 300 nm wavelength is difficult to pass through the glass on the printing machine, light sources with wavelengths of 350 nm to 460 nm, such as iodine and xenon lamps, should be used. The iodine lamp emits a spectrum in the range of 350 nm to 460 nm with a peak of 417 nm, which is basically the same with the sensitive area of ​​the PS plate and is an ideal light source.
Some printing companies use printing plate light sources that do not belong to short-wavelength light, so the printing time is too long, which is not economical and affects the quality of graphic reproduction. Some companies use an iodine lamp as the light source. However, due to the long use time, the lamp is aging (light yellowing) and is no longer suitable for printing. It should be replaced in time to ensure the stability of the light source's spectral characteristics. Third, strictly control the exposure time Correct exposure of the exposure plate is an important part of the image and text version reproduction. In Other words, the quality of the printing plate and the printing rate are based on the correct exposure. In practical applications, if the exposure is excessive, the 1%-3% fine dot on the image plate will be seriously damaged, and the 4%-5% dot will also be affected; the small strokes (such as the 5th and 6th S The horizontal strokes, etc., are all subject to varying degrees of loss, which may cause some words to be out of line. Therefore, overexposure of the printing plate is one of the reasons causing the image to be outdated, bald, and lack of writing. Of course, lack of exposure during the printing will also have many quality problems, such as the dark and easy dark spots in the image version; the multiple word and bold characters in the text version are easy to be virtual and easy to rough.
Fourth, the developer concentration control Because of different manufacturers, the printing company's PS version of the photosensitive agent composition is not the same, the developer (kit medicine) ratio, concentration, etc. are different. For example, the "Starlight" brand PS plate developer kits produced by the China Institute of Printing Science and Technology are defined as: solid developer powder 7.50 g, heated water 5000C. C. The use of the liquid is: 1 part of the concentrate plus 6 parts of water. This rule is the best formula that the manufacturer prefers.
Individual printing companies have great arbitrariness in the preparation of the PS version of the developer. The application is not standardized enough, which seriously affects the quality of the printing plate and the stability of the printing rate. It can be appreciated from practical work that the concentration of the developer is too large and the alkalinity increases. When the exposed portion is decomposed, no part of the light is decomposed at the same time, so that the strength of the film surface is decreased, and the printing ink performance is also reduced. Will be reduced accordingly, causing serious film peeling (off plate). When this happens, it will affect the quality of the printed product, but it will cause waste. In addition, when the developing solution is too concentrated to dissolve the film layer in the blank area, it will also erode the part of the oxide layer, thereby reducing the printing rate of the printing plate, which virtually increases the cost of the printing process.
In practice, too low a developer concentration can also have an adverse effect. If the developing concentration is not enough, the blank film will not be completely dissolved, causing various stains on the plate. If the developing time is prolonged, it will produce the same effect as the over-concentration of the developer.
The specific ratio of the PS version of the developer is the data obtained after many tests, which can guarantee the basic reproduction of the 1%-2% fine dot of the image version, complete 3%-4% dot network, and 98% dot-pasting; the fine text is not missing The pen breaks the path, the No. 6 character is clear, and the quality requirements such as black body and multiple strokes do not stick to death.
Fifth, control the development temperature and development time PS version of the entire development process is a redox reaction process, naturally subject to liquid temperature and time constraints. If the temperature of the developer is too high, the speed at which the photosensitive layer is dissolved must be high and the time required will naturally be short. For example, when the liquid temperature exceeds 30° C., the binding force between the photosensitive material and the polymer resin will be weakened, and the resistance of the printing plate will be reduced, and in some cases, the photosensitive film may fall off. When the temperature of the developer is too low, the development time will inevitably increase, and the figures and text parts will also be excessively eroded to reduce the printing durability of the printing plate.
At present, there is still a considerable amount of manual development, and there is no control method for the liquid temperature, which is one of the reasons for the low resistance of the printing plate. Therefore, companies should try to control the temperature of the developer within the range of 18°C-25°C according to their own conditions.
Enterprises developing with the developer tank should have measures to protect the developer from oxidation. On the one hand, it is necessary to strengthen the standard operation of the developer concentration, temperature, and development time. On the other hand, the developer should be capped on the developer tank (not covered when not in use). ), to prevent oxidation and evaporation and weaken the development.
Sixth, to strengthen the layout of awareness of the layout simply said that the layout is the positive version of the PS version of the positive version of the layout after the eraser and the eraser before the dirty part of the layout, is the layout of the text on the outside of the superscript lines, corners, dirty, scratch Marks, strips, blots, etc. get rid of the work.
The operation of the layout except for dirty is simple, but it must have a strong sense of quality, so that careful inspection, careful operation, to prevent the removal of dirty liquid to the drawings, text parts caused by the waste version.
The author found in the random inspections and examinations of books and products that there were often residual marks, corners, tape marks, imposition traces, and other stains in the layout, and even the fact that the drawings and texts were partially smeared, which seriously affected the situation. Improve the level of print quality of books and periodicals. Therefore, in the printing plate printing should strengthen the layout of the work to ensure that the layout of the clean, in order to improve the printing quality of books to create a good condition.