How to avoid shallow screen printing
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Drawing is one of the problems often encountered in gravure printing. It involves many factors such as gravure printing machine, plate cylinder, doctor blade, printing environment, ink, etc. If improper handling will affect production and quality.
Drawing is also called drawing and starting. When the performance of ink and the degree of color development of ink are different, the degree of performance is also different. Generally, the drawing phenomenon of black, cyan and magenta is obvious, and it generally appears on a large area of shallow network.
We analyze the common wire drawing mainly into three types: drawing at the shallow mesh position, drawing the squeegee in the solid color block, and drawing irregularly at the printing blank.
Drawing in shallow mesh position
1. Eliminate the drawing phenomenon from the source of design plate making
Printability is fully considered in the design and plate making of the original. Be sure to consider the printing direction, try to avoid printing from shallow to deep; black, magenta version is the most likely to appear on the shallow mesh, especially the black version, due to the coarse carbon particles in the ink, when the black net is very shallow, a dot Almost no carbon particles can be loaded, so it is easier to draw. Therefore, a large area of black and shallow net should be set as a special gray version, reducing printing difficulty and scrap rate.
2. Use the squeegee correctly to avoid drawing
(1) Selection of the squeegee. The surface hardness of the chrome plated roller is HV850～1100. The hardness of the squeegee should be lower than the hardness of the plate. It is about HV600. The hardness is too low. The ink is not clean. The hardness is too high, which will accelerate the wear of the plate and cause knife marks. , affecting the quality of printed products.
(2) The flatness of the squeegee. When installing the squeegee, the blade should be flattened, and the screws should be tightened from the middle to the two sides. It should not be completed in one step. It should be repeated two or three times to ensure uniform force on the blade.
(3) The sharpness of the squeegee. Grinding the squeegee with 600# water sandpaper or 2# metallographic sandpaper, or use a special sharpening machine to grind the back side of the squeegee into a slanting mouth of about 25°, even if the new knives are ground.
(4) Scraper angle. The angle of the doctor blade is smaller than that during normal printing, and the distance between the contact point of the doctor blade and the printing plate and the imprinting point is shortened.
3. Reasonable matching of ink to prevent drawing
(1) When there is a large area of shallow mesh or gradation transition on the plate surface, the ink with better quality should be selected to prevent the ink pigment particles from being too thick to cause drawing. Generally, the fineness of the ink is 15μm, and the ink particles are too rough to the squeegee. The damage to the plates is very large.
(2) When blending inks, under the premise of not affecting other patterns on the same plate, consider using slow-drying solvents, and do not add too much auxiliary solvent such as ethyl acetate to prevent the ink from changing and normal. print.
(3) Ensure that the ink viscosity is moderate and stable. The production of the wire has a direct relationship with the viscosity of the ink. Generally speaking, the higher the viscosity of the ink, the easier it is to produce the cut line in printing. In addition, due to the different performances of various brands of inks, the amount of solvent added is not the same. When formulating inks, refer to the specific data provided by the ink manufacturers, and combine their own printing conditions and printed products to carry out specific operations.
Drawing of the solid color block from the knife position
The drawing of the solid color block from the knife position is manifested by the lifting of the squeegee at the edge of the solid color block, causing the edge of the printing color block to be a broken line, generally a few millimeters of short wire, the main reason is that the ink viscosity is too large and the ink Excessive pigment particles are crystallized. The solution is as follows.
1. Filter the ink and add a certain amount of new ink during use.
2. Adjust the angle of the doctor blade to a smaller value and shorten the distance between the contact point of the doctor blade and the plate and the stamp point.