Keeping good printing process and operating technology (4)

Fourth, to improve the quality of the flexographic printing process technology measures

1. Make appropriate adjustments to the layout of your outlets. The production process shows that the use of a flexible printing plate with a low number of dots in the printing process results in a vivid and clear print quality, which results in a stronger contrast print quality. However, when the number of dot lines is too low, the surface of the printing material surface is not very glossy, and the fine-graded dots of the printing plate are easily lost, and the resolution of the printing plate surface is not good. On the other hand, flexographic printing has larger dot gain ratios than other processes, and dot reproduction is not as good as other processes. Generally, less than 2% of small dots are difficult to print. Therefore, in the production of flexographic printing negatives, according to the characteristics of equipment, raw materials, etc., the appropriate adjustment of the printing plate level, so that it is compatible with the flexographic printing tone reproduction range, in order to achieve relatively good printing Quality effect.

2. Determine the screen according to the characteristics of the printed material. In general, the quality of the paper is relatively rough, the speed of the printing press is faster, and 80 lines/inch to line/inch screens can be used for plate making. The printing effect is relatively good. Such as embossed aluminized paper, corrugated paper, paper stickers, ordinary offset paper to drink newspapers, etc., can use 80 lines / inch ~ 100 lines / inch screen plate more appropriate, using coated paper, painting newspapers and other materials, Printed logos, pictorials, star movies, desk calendars, merchandise ads, books and magazines, and other printed materials can be printed on the screen with 150 lines/inch to 175 lines*inches; fine-quality albums, product advertisements, books and magazines can be printed on high-grade coated paper and glass cards. For high-end products such as covers, illustrations, and packaging and decorating printed materials, screen printing plates with 175 lines/inch to 200 lines/inch can be used in order to achieve better printing process effects and improve the printing quality of products.

3. Select the appropriate anilox roller. The important components of the anilox roller when printing on the ink have a great influence on the printing quality of the product. The number of anilox roller screens determines the size of the layout ink coating. The higher the screen number, the smaller the ink transfer amount. The anilox roller with a high number of lines can form a thinner and more uniform ink layer, which can meet the printing requirements for a rich layer of printed products, in particular, meet the brushing needs of high-light partial dots, and can reduce dot gain during printing and maintain uniformity Steady transfer of ink. For the printing anilox roller, if the layout of the ink is too large, prone to paste and dot gains. Because the high-light dot area of ​​the anilox version is small, if an anilox roller with a low number of lines is used, the area of ​​each cell is larger than the dot area of ​​a certain part of the printing plate. Easy to ink, it will form a paste version and network expansion. Therefore, the printed dot screen products, using high-line anilox roller to transmit ink, can better ensure the clarity of dot printing.

4. Keep the quality of the printing process. The quality of resin plate printing directly affects the quality of printing. To prevent the loss and enlargement of screens, it is necessary to check whether the film and the resin plate are evenly and precisely contacted during the printing process; it is necessary to grasp the appropriate exposure time according to the structure of the printing plate. Washing should be done carefully to avoid damage to the dots and fine lines; the temperature of the heat curing can be controlled between 120°C and 130°C, so that the printing plate can reach a certain hardness and the printing plate's printing rate can be improved.

5. Adjust the appropriate printing pressure. Excessive printing pressure is the main reason for the increase in flexographic printing dots. With high printing pressure, the layout is prone to expanding and deforming the dots due to excessive extrusion, and the ink at the edge of the dots is also easily transferred to the printed sheets, resulting in the phenomenon of printing stencils, ghosting, or dots. The production process shows that the use of smaller printing pressure is an important measure to improve the printing quality of outlets. Therefore, the printing pressure should be reasonably adjusted and the pressure should be reduced as much as possible. The actual control of the pressure generally controls the compression of the printing plate within 0.1 mm. Usually, the pressure is relatively small when printing delicate network cables, and the pressure is higher when printing in the field. The flexographic plate has a low hardness and is relatively uniform when in contact with the support, and the ink color printed out is also relatively uniform, but the dot gain is more severe and the reproducibility of the image layer is poor. Therefore, in the printing of glossy substrates and mesh halftone prints, the hardness of the plate is required to be higher, and when the rough surface of the substrate and solid prints are printed, the hardness of the plate is required to be lower in order to improve the product. Printing quality.

6. Adjust the ink supply pressure. If the ink supply pressure is too high, on the one hand it is easy to make the screen mesh wear and deformation, on the other hand, the ink on the ink roller is easy to form a squeeze phenomenon on the plate surface, so that the layout ink layer is not uniform or there is a paste plate defect. If the pressure of the ink roller is too light, the ink on the plate may be unevenly and insufficiently printed, making the dot printing unclear. Therefore, it is necessary to adjust the contact pressure between the ink roller and the printing plate layout.

7. Select fine ink for printing. If you use poor printing ink dot network. Then, the pigment particles in the ink are coarse, and the printing plate is prone to stencil printing and spotting defects, and the printing plate's printing resistance rate will also decrease. Therefore, printing dot products should be printed with fine ink. The fine ink with good density has a high concentration and can make the dots of printed products clear and plump.

8. Adjust the ink viscosity and fluidity. The viscosity of the ink is large, and ink transfer unevenness, dot picking, pattern stenosis, and stencil printing and the like are liable to occur. When the viscosity of the ink is small, the ink is easily emulsified, and the layout is visibly dirty. The fluidity and viscosity of the ink are closely related. The ink with a large viscosity has a relatively large consistency and its fluidity is relatively small, whereas the fluidity is greater. The fluidity of the ink is too small, and it is easy to cause the coating not to be smooth and uneven, so that the reproduction effect of the printing screen dots is poor; the ink with excessive fluidity is liable to make the dot printing insufficient and the resolution poor. When the viscosity and fluidity of the ink are unfavorable, the auxiliary material can be used for adjustment.

In summary, the factors causing the quality problems of flexographic printing are varied, caused by one kind of defective factor, and several kinds of unwholesome willingness coexist. Therefore, only by correctly understanding the root causes of print quality failures, and by involving good printing operations and process technologies, not only can the opportunities for various types of printing failures be better prevented and avoided, but also the production efficiency and product quality can be effectively improved.

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