The best corrugated box flexographic printing qual

Control the quality of corrugated box flexographic printing (II)

IV. process and technical measures to improve the quality of flexographic printing

adjust the point layout appropriately

the production process shows that selecting the flexographic plate with low line number points for printing during plate making can obtain bright and clear printing quality, so as to obtain the printing quality with strong contrast. However, when the number of dots and lines is too low, when the surface gloss of the substrate material is not very good, the fine level points of the printing page are easy to be lost, and the definition of the printing page is not good. On the other hand, flexographic printing has a larger dot expansion rate than its process

technology, and the dot reproduction effect is not as good as other processes. Generally, small ideas less than 2% are difficult to print. Therefore, when making flexographic printing negatives, the level of the printing plate should be properly adjusted according to the characteristics of equipment, raw materials and so on, so that it can adapt to the range of reproduction of flexographic printing tone, so as to achieve relatively good printing quality

determine the screen according to the characteristics of the printing material

generally speaking, the paper quality is rough, and the printing machine speed is fast. When making plate, you can choose 80 line/inch line/inch screen, and the printing effect is relatively good. If embossed aluminized paper, corrugated paper, poster paper, ordinary offset paper and newspaper are used for printing, 80 lines/inch to 100 lines/inch screen plate making is more suitable. Coated paper, newspaper painting and other materials are used to print trademarks, pictorials, star films, calendars, commodity advertisements, book covers and other printed materials. 150 lines/inch to 175 lines/inch screen plate making high-grade coated paper and glass cards can be used to print fine pictures For 150 high-end products such as pipe fittings for building water supply cross-linked polyethylene (PE-X) pipes, advertisements, book covers, illustrations and packaging and decoration prints, 175 line/inch-200 line/inch Gangping plate making can be selected in order to achieve better printing process effect and improve the printing quality of products

select the appropriate corrugation roller

corrugation roller is an important part of the layout inking, which has a great impact on the product printing quality. The number of lines on the embossing roll determines the amount of ink applied on the layout. The higher the number of lines, the smaller the amount of ink transferred. The corrugated roller with high-line number can form a thinner and more uniform ink layer. None of the mines has been put into operation, which can meet the printing requirements of printing products with rich layers, especially the ink brushing needs of highlights, reduce the expansion of printing time points, and maintain a uniform and stable ink transfer. For the printing roller, if the amount of ink applied to the layout is too large, it is easy to have the disadvantages of paste and dot expansion. Because the highlight dot area of the plate is small, if the ridge roller with low number of lines is used for printing, because the area of each hole is larger than the dot area of a certain part of the dry printing plate, some dot edges on the plate are also easy to be inked during printing, resulting in paste and dot expansion. Therefore, for products with dot printing layout, ink transfer with high-line corrugated roller can better ensure the clarity of dot printing

control the printing process quality.

the printing quality of the resin version directly affects the printing quality. In order to prevent the loss and expansion of dots, it is necessary to check whether the film and the resin version are in uniform and precise contact during printing; We should master the appropriate exposure time according to the graphic structure of the printing plate;; Be careful when washing to avoid damage points and small lines; The temperature of heat curing can be controlled between 120 ℃ - 130 ℃ in supply chain management, so that the printing plate can reach a certain hardness and improve the printing resistance of the printing plate

adjust the appropriate printing pressure

excessive printing pressure is the main reason for the increase of flexo printing points. The printing pressure is high, and the layout is easy to expand and deform the dots due to excessive extrusion, and the ink at the edge of the dots is also easy to transfer to the printing sheet, resulting in printing paste, ghosting or dot enlargement. The production process shows that using a small printing pressure is an important measure to improve the quality of dot printing. Therefore, the printing pressure should be adjusted reasonably, and the pressure should be reduced as much as possible. The actual control of pressure is generally to control the compression of the printing plate within 0.1mm. Generally, the pressure is relatively small when printing fine lines, while the pressure is larger when printing on the ground. The hardness of the flexo is low, it is more uniform when contacting with the substrate, and the ink color printed is also more uniform, but the dot increase is severe, and the hierarchical reproducibility of the image is poor. Therefore, when printing substrate with smooth surface and halftone printing with

mesh, the hardness of printing plate is required to be higher, while when printing substrate with rough surface and field printing, the hardness of printing plate is required to be lower, so as to improve the printing quality of products

adjust the ink supply pressure

if the ink supply pressure is too large, on the one hand, it is easy to wear and deform the surface points, on the other hand, the ink on the ink roller is easy to squeeze the layout, causing uneven ink layer of the layout or paste defects. If the ink roller pressure is too light, it is easy to cause uneven and insufficient ink on the layout, making the dot printing unclear. Therefore, it is necessary to adjust the contact pressure between the ink roller and the plate cylinder

select the ink with good fineness for printing

if the ink with poor fineness is used for printing points. Then, the pigment particles in the ink are thick, and the printing plate is prone to paste and hair, and the printing plate's printing resistance will also decline. Therefore, printing point products should be printed with fine ink. The ink with good fineness has a high concentration, which can make the printing point clear and full

adjust the viscosity and fluidity of the ink

the viscosity of the ink is large, which is easy to produce uneven ink transfer, dot galling, layout blooming and plate pasting; If the viscosity of the ink is small, it is easy to emulsify the ink and make the layout dirty. There is a close relationship between the fluidity and viscosity of ink. The fluidity of ink with high viscosity is relatively small when its consistency is large, and the fluidity is relatively large on the contrary. The fluidity of ink is too small, which is easy to cause the coating to be not smooth and uneven, resulting in poor reproduction effect of printing plate dots; The ink with too much fluidity is easy to make dot printing not full and poor definition. When the viscosity and fluidity of the ink are not timely, auxiliary materials can be used for adjustment

to sum up, there are various factors causing flexographic printing quality problems, including one defect factor and several adverse reasons. Therefore, only by correctly understanding the root causes of printing quality faults and controlling the printing operation and process technology, can we better prevent and avoid the opportunities of various printing faults. The focus of the problem is whether the original products have made significant improvements in structure, material and other aspects, resulting in changes in performance and technical characteristics, and effectively improve production efficiency and product printing quality

(author/Kang qilai, Putian printing factory, Fujian Province)

corrugated box, June 2005