Flexo features and some troubleshooting (3)
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6. Long washing time, large brush pressure causes line deformation and dot loss
Due to the long washing time, the independent lines or independent dots will be over-expanded and easily bent or washed away. In addition, because the pressure of the brush is too large, the lines or dots will be washed off, causing the printing plate to be invalid. Therefore, when washing the line or screen, the washing time and brush pressure should be properly controlled.
7. The unphotosensitive material is not completely dissolved, resulting in a shallow negative image.
The rinsing time is insufficient, and the photosensitive material that is not sensitized is not completely dissolved. In addition, the washing solvent is too dirty, which can also cause this phenomenon. Therefore, the washing solvent should be replaced frequently.
The serious expansion of the dot in flexographic printing is one of the biggest problems, so it is impossible to express the network of 5% or less. More than 95% of the outlets will be confused, and the intermediate and dark levels are also seriously lost. At the same time, due to the ductility of the flexible plate, overprinting is also very difficult. In addition, plate making often occurs on a plate with both a cable version and a solid version, which adds to the difficulty of plate making. Generally speaking, in the case where the flexo printing unit is sufficient, the same color of the screen and the solid version should be divided into two, because the screen printing requires a thinner ink layer, while the field and line versions need to be thicker. The ink layer. However, in some special cases, it is necessary to make the same color of the network cable and the field image to the same version. In this case, on the one hand, the choice of the anilox roller at the time of printing is to be compromised, and it is usually preferred to meet the printing requirements of the screen printing plate at the expense of the thickness of the solid ink layer; on the other hand, it is necessary to grasp the difference in the plate making process. The exposure time is to guarantee the quality of the same plate on the internet and the field part. The difference between the image portion of the network cable and the solid portion is mainly due to the different depth of corrosion. In order to "stay" in the process of brushing the printing plate, the wire portion needs to have a strong foundation, so the corrosion depth is shallower. This can be achieved by masking the local approach (similar to obscuring the exposure when the photo is zoomed in) to achieve different depths of corrosion with different back exposure times. A similar approach should be used for front exposure time. In addition, according to work experience, some manufacturers change the high-gloss outlets below 2% to 0, because the human eye feels relative to the color, and it can't be seen for very few outlets. Also, replace a color with another color, such as replacing black with blue, replacing blue with black in food packaging, or even replacing red with red for the leaf pattern, and replacing the dark with the same color. Have a certain effect. Of course, this kind of processing must require pre-press operators to have rich image processing experience and a deeper understanding of flexographic printing, otherwise it may damage the image level and fail to achieve the desired effect. It has also been reported that the current flexible plate manufacturer has introduced a new type of flexible plate material, regardless of whether the printed part is a cable or a solid, the plate only needs a uniform front exposure time, avoiding the trouble of multiple exposures. Make the flexographic plate making more convenient and the quality more stable.
Six, common faults in plate making
With the continuous adoption of new technologies. Flexographic printing has become a mature process. Although China's flexographic printing started late, it has developed rapidly. However, there are many constraints, and plate making is one of them. Some common faults in the flexographic plate making and their solutions are listed for reference.
1. The blank part of the printing plate is the cause of the blockage and the treatment method:
1.1 Back exposure time is too long. Care should be taken to properly control the back exposure time:
1.2 main overexposure. Under the premise of ensuring the reproduction of small characters and thin lines, the main exposure time should be shortened as much as possible:
1.3 The plate material and the film are in poor contact. The vacuum system should be guaranteed to work properly and the air between the plate and the film should be removed by rollers.
2. The causes and treatment of small outlets, small characters and thin lines are washed out:
2.1 back exposure time is not enough. Consider increasing the back exposure time:
2.2 The main exposure time is not enough. The main exposure time can be increased;
2.3 the plate washing time is too long or the brush pressure is too large. Pay attention to shortening the washing time and adjusting the brush pressure.
3. The cause of the failure of the bottom of the plate is not completely hardened and the treatment method:
3.1 Back exposure is insufficient. Increase the back exposure time;
3.2 flushing is not complete, and residual unhardened resin remains. Check the brush pressure and adjust the plate wash time.
4. The same plate printing plate depth inconsistency failure causes and treatment methods:
4.1 The printing machine is too hot. Carefully check the ventilation and cooling system for faults;
4.2 The plate light intensity is uneven or the opening is not synchronized. At the same time, all the lamps are replaced;
4.3 the washing brushes are not parallel or the movement is unbalanced. Adjustable brush pressure and level.
5. The image is partially blurred and the cause of the fault and its treatment method:
5.1 film is defective. Carefully check the image on the film for clarity;
5.2 use offset film for flexo printing. Reproduce qualified flexo film.
6. Reasons for the failure of small network points during printing and their treatment methods:
6.1 The main or back exposure is insufficient. The main exposure or back exposure time can be increased;
6.2 the original design is beyond the flexibility of the flexo. Improve the original design to fit the range of flexographic technology.
7. Causes of rupture failure and handling methods when moving and bending after printing in the field or text:
7.1 The main exposure and back exposure time are too long. The main exposure and back exposure time can be reduced;
7.2 the debonding time is too long. Reduce the debonding time;
7.3 main exposure and back exposure are insufficient. Check the lamp for damage or aging.
8. The reason why the thin line is curved and wavy is faulty and the treatment method is as follows:
8.1 Back exposure is insufficient. To increase the back exposure time:
8.2 main exposure is insufficient. To increase the main exposure time;
8.3 insufficient drying time. To increase the drying time:
8.4 wash water is not fresh. Replace the fresh plate wash water;
8.5 wash time is too long. Adjust the washing time.
In short, because the influence factors of flexographic printing are very large and vary greatly, prepress production plays a fundamental role in the whole printing, and the foundation is not well done, and the latter work is difficult to complete well. Therefore, the pre-press processing requires the staff to comprehensively consider in many aspects, and all relevant factors cannot be ignored. It is best to sum up a set of experience in practice to serve the future work and maximize the pre-press process. With the printing, the prints get the best results.