With the increasing maturity of CTP technology, the rapid publishing speed, good plate stability, and high dot reductivity have greatly improved the quality of the plate. However, the current use of laser imagesetters is still relatively common. How to improve the quality of the printing plate under the existing process and equipment conditions, to maximize the reduction of original information, to meet the increasingly high printing quality requirements, has become the front of us. A topic. This article combines work practice and talks about some experiences and experiences on improving the quality of printing.
First, strictly check the quality of plate-making film
Check the operation notice to ensure that the number of plate-making films is complete and the elements are correct. Check whether the film is stripped, scratched, creased, yellowed or darkened. If problems are found, communicate with the previous process and deal with them as soon as possible. For tape printing, chipping and dirt on the film, wipe it gently with a clean, soft gauze and alcohol to ensure that the film is clean.
Second, carefully clean the plate machine glass plate
The cleaning degree of the glass plate of the plate printing machine has a great influence on the quality of the printing plate. Even a small hair may cause a batch of printing jobs to be scrapped. Therefore, before printing, you must carefully wipe the floating dust and fingerprint on the glass plate of the printing machine. For more stubborn dirt, such as tape printing, oil stains, etc., wipe it repeatedly until it is completely removed. Since the glass plate is reflective, checking the glass plate from one direction tends to leak some dirt, so check it from all directions at various angles to ensure that the glass plate is clean. In addition, after each printing plate is finished, it is necessary to re-examine the glass plate for any dirt, and there must be no luck. Otherwise, the quality of the printing plate cannot be guaranteed.
Third, the production of calipers to improve accuracy
This unit uses the Heidelberg CD-102 four-color offset press. The accuracy requirements for the printing plate are: bite error ≤ 0.1 mm, side gauge error ≤ 1.9 mm. Since the distance of 0.1 mm is almost uncontrollable by the naked eye, it is difficult to grasp with a scale. In order to reduce the error and improve the accuracy, the discarded PS version of the self-made printing caliper has the same width as the bite, the length is equal to the width of the plate, the production is simple, the operation is convenient, and the printing precision and working efficiency are greatly improved after use. [next]
Fourth, accurately grasp the exposure time of the printing plate
Take the 3000W iodine gallium lamp source as an example.
1. Determine the exposure time based on the thickness of the PS plate. Under normal conditions (temperature 22 ± 5 ° C, humidity 60%, developer concentration 14%), the exposure time was set to 120 s for the PS plate with a moderate thickness of the photosensitive layer. However, if the PS version of the photosensitive layer is thicker, such as the fully open PS version, it will increase by about 20% compared with the normal exposure time; if the PS version of the photosensitive layer is thinner, such as the 920mm × 760mm type PS version, the exposure time should be reduced by about 15%.
2. Determine the exposure time based on the size of the film dot. Taking the printing version of the city travel map as an example, the minimum dyeing point in the figure is 4%-5%, and the maximum dot size is 50%-60%. Under normal conditions (temperature 22±5°C, humidity 60%, development) Liquid concentration 14%), the relationship between exposure time and the percentage of dot percentage is as follows:
The exposure time should generally be controlled between 70s and 200s, and the exposure time is less than 70s. The layout is easy to be dirty on the bottom; if the exposure time is greater than 200s, the dots are easily lost, which affects the reductiveness of the dots.
3. Determine the exposure time based on the film condition. If the film is old, yellow or dark, or there are multiple stitching, the exposure time should be increased appropriately. If necessary, double exposure should be activated.
4. Determine the exposure time according to the indoor temperature conditions. The best indoor working temperature is 18 ° C -25 ° C. If the temperature exceeds 25 ° C, the exposure time is appropriately reduced; if the temperature is lower than 18 ° C, the exposure time should be appropriately increased. In addition, the exposure time should be combined with other plate making parameters, and the increase or decrease of the exposure time should be based on the principle that the original is reproduced and the layout is not guaranteed.
V. Reasonable preparation of developer concentration
Taking the Huaguang brand positive image PS plate developer as an example, the concentrate is prepared from a strong base and a weak acid salt, and has the advantages of fast development speed, stable performance, good dot reduction property, and clean layout. At normal temperature (18 ° C -25 ° C), according to the concentrate: water = 1: 7 to prepare the developer; room temperature above 25 ° C, according to the concentrate: water = 1: 8 to prepare the developer; room temperature below 18 ° C, then The developer was prepared as a concentrate: water = 1:6. The developer concentration should not be too high or too low, otherwise it will cause the development to excessively destroy the dot reductive property, or the development is insufficient. Observe the dried PS plate with a magnifying glass. Once it is found that even a slight base shadow, immediately release the developer and reconstitute it. [next]
Sixth, organic coordination of various plate making parameters
The TUNG SHUNG 130 PSBN automatic plate processor is currently used for development. According to indoor environmental conditions, mainly temperature, dry humidity, cleanliness, and exposure time, developer concentration, scientifically and reasonably set and adjust the development temperature and development time. The relationship between these plate making parameters is not static and should be coordinated according to specific conditions. For example, if the developing concentration is high, the development time should be reduced accordingly; if the exposure time is long, the development time is shortened; if the temperature is too low, the exposure time or development time is increased. Adjusting various plate making parameters should be based on the principle of plate cleaning and original reproduction.
In summary, every aspect of the printing plate needs to be carefully and meticulously grasped. It requires not only rich work experience, but also a high sense of responsibility and professionalism, so as to improve the quality of the printing plate and lay a solid foundation for further improving the quality of printed products. basis.
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