The selection, installation and adjustment of the ink scraper in gravure printing have an important influence on the quality of printed matter. The following is a discussion of the application of the squeegee in gravure printing and some of the issues involved.
First, the selection and installation of the squeegee
High-speed gravure printing machines are generally made of imported steel squeegee with high elasticity, and their thickness is 0.15~0.2mm.
When installing the squeegee, note that both sides of the squeegee should be longer than the plate 10 ~ 20mm to prevent the ink of the plate from splashing on the roller. The steps and key points are as follows:
1. The distance between the lining and the blade back is about 10mm. The distance between the linings and the blades is 5-7mm. However, it is also possible to increase the distance (ie, installing a soft blade) or reduce the distance (as a hard blade) as appropriate.
2. Place the new blade behind the lining, and tighten the blade back screw into the slot. It should be tightened from the middle of the blade first and then gradually outwards, and the two sides should be rotated and tightened. Here is a tip to avoid blade warping: When tightening the screw, it should be completed two or three times, not in one step. Should turn the screw while holding a rag to grip the blade and the lining and pull it to the side, so that the knife will be flatter. A flat blade ensures uniform printing plate ink.
3. Use suitable sharpening tools and sharpening methods.
When the stone is not yet used, if the stone is rough, it is not suitable for grinding a new knife. According to practical experience, it is appropriate to use a No. 1 emery paper sharpener to grind new blades or wear old ones with large defects. If you use a No. 0 gold steel sandpaper to grind a new knife, you can use it, but if you use an old blade with a slightly larger gap, it will be hard to grind. If it is sometimes felt that using a No. 1 emery paper to sharpen the blade, it can be finely ground with No. 0 emery paper. There are generally two ways to sharpen a knife: First, the sandpaper is folded into a V-shape, but care should be taken to remove several layers of sandpaper so that the blade does not cut through the sandpaper and cause injury. This method is more efficient, easier to control the angle of the blade, but not too safe; the other is to use two hands pull the ends of the sandpaper sharpening, this is very safe, but the angle of the edge is not very good control. Too blunt and sharp blades have a negative impact on print quality.
Second, a reasonable adjustment of the squeegee
Squeegee pressure, sharpness, contact with the plate, etc. have an impact on print quality. According to actual needs, rational adjustment of these factors can solve many problems in printing.
Pressure
The factors that affect the squeegee pressure are the size of the cylinder pressure, the difference between the hard and soft blades, and the angle at which the squeegee crosses the plate. The greater the slope, the greater the pressure. Excessive pressure will reduce the transfer rate of the ink, and the wear of the printing plate and the blade will be large. If the pressure is too small, the dirty plate or scraper line may occur.
2. The sharpness of the knife
The sharpness of the knife depends on whether it is a new knife, the angle of the knife when sharpening, the type of sandpaper (oil stone) used, etc. The suitable sharpness of the knife should be to both effectively scrape the ink without producing a knife. Sharp blades are often prone to knife marks and wear plates.
3. The distance between the squeegee and the printing plate
The reduction of the distance between the doctor blade and the printing plate is beneficial to increase the ink transfer rate, but it is easy to produce a dirty plate; on the contrary, it can effectively solve the dirty plate and avoid some small line marks, but it will reduce the ink transfer rate.
4. The flatness of the knife
The flatness and warpage of the knife depends mainly on the method of installation. Of course, it may also be related to the presence of foreign matter on the blade holder or on the blade or lining. When the flatness of the knife is poor, some watermark marks may appear on the edge of the printing surface, or some intermittent line marks may appear from time to time. Some people think that the ink is rough and the ink fluidity is not good. This phenomenon may occur. In fact, this condition may occur even if the knife is uneven.
5. Squeegee movement
Squeegee knife left and right moves to reduce the scraper line, improve scraper utilization, reduce the wear of the plate has an important role. If the squeegee does not move properly, you should think of ways to improve it.
Selection, Installation and Adjustment of Ink Scraper in Gravure Printing
June 14 22:05:36, 2024
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