Characteristics analysis and application of flexographic printing process
flexible version printing is using a rich elastic of flexible letterpress for printing of way, it has equipment investment less, process returns high, conducive to reprint printing, printing adaptability wide, equipment operation easy, printing efficiency high, and printing ink color quality relative compared stable, series explicit with advantages, while due to the process used meet environmental requirements of water ink for printing, can better to avoid ink on print or within loaded products of pollution, so, more for Yu food, and Printing of pharmaceutical and other packaging products, favored by printing manufacturers and customers, along with the trend of a low carbon economy in China's looming, flexo printing technology will be more widely promoted and applied.
1. flexo printing process characteristic of
flexo printing technology printing plate using rubber production, also use solid or liquid resin plate, different material printability and print quality are also very different. Due to the characteristics of plate with flexible, lighter pressure, printing adaptability, can print with a thick corrugated cardboard, thin, soft plastic material and printing printing; printing both the absorption of strong paper towels, can also be non-absorbent materials such as aluminum foil. Due to strong mobile liquid ink, and the material is soft and smooth, surface roughness of materials can be overcome print defects, and then printing quality of ink layer thick, colorful effect. Flexo printing technology printing machines also available online portfolio of offset printing, gravure printing, screen printing and postpress finishing, joint flexibility, production efficiency high, can greatly shorten the production cycle, meet the need of users. In addition, because of the flexo printing process using nontoxic, tasteless water ink printing, the production process can be effective in preventing the contamination of the product, printing products have good advantages of hygiene, safety and environmental protection, are ideal for green packing printing process, is more suitable for medicine, food and packaging printing. However, inadequacies in flexo printing technology, it is as a result of plate soft, dot gain values are relatively large, printed fine textured pages of products, quality better than offset products. Due to the inherent characteristic of flexo printing technology, printing plate prone to deformation problems, therefore, plate design and printing, be sure to adjust printing layout structure, such as network size, level; the thickness of the line, direction and layout of the space.
2. sedan design should consider of factors
due to flexible version version material soft, has must elastic, and thickness relative larger, dang will its paste in cylindrical shaped of version drum Shang Hou, printing version of longitudinal corresponds to Yu drum week to of surface will produced must of bent deformation, especially thickness more big of printing version, paste Hou printing version surface graphic deformation of coefficient on more big, then makes printing out of graphic and manuscript size appeared errors. If the network structure of the print layout, printing color deviations of dot enlargement deformation is caused major problems. Therefore, the technical control of flexible plate design is in place, had a great impact on print quality. Therefore, in the sedan design, depending on the thickness of the plate elongation, in sedan, as appropriate, the plate characteristics due to narrow layout, so as to avoid the layout of the printed page size is greater than the original specification. For the dot product of the layout and printing, in front of the strips should be compensated by adjusting the flexo color separation curve dot. Has a barcode on the product page, and make-up should be designed to minimize the barcode lines and corresponds to the circumference of the drum, so as not to affect the normal bar line gaps appear deformation. Due to the flexible version of the tiny dot in the sedan and is difficult to get a better reproduction in the printing process, especially high light outlets prone to loss. And soft plates under the pressure, darkened dot positions and prone to expansion, paste into the field. Dot enlargement deformation will make printing pages lack a sense of hierarchy, printing quality may decrease. Therefore, dot order harmonic line design, according to hardness and gloss on the surface of the substrate to determine reasonable. Substrate generally soft, paper is not very smooth, high light layout parts should be given to increasing the outlets, often highlight parts of the network layout design into not less than 4% and darkened dots to control within 85%. Cable usually printed version of several major advantages and disadvantages of printed material, and corrugated boxes is significantly less than the number of screen line of pre-printed paper print layout, the use of high grade coated white paper, now with high performance flexo printing equipment, plate making line number can reach 175 lines per inch, or even a bit higher. In addition, the flexible version should not be designed with fine lines and small text, so as not to cause the layout to paste dirty affect print quality.
3. flexographic printing plate technology and reasonable selection of
different in offset printing technology of flexographic plates, plates are soft, prone to elasticity deformation in compression, plates of different thickness, hardness and printing are also very different. Thicker plate material, hardness, the greater the deformation coefficient is smaller, which will help to improve print quality. Therefore, when printing a high line of cardboard boxes, gift box and other fine color product, thickness 2.84mm flexo printing results printing of corrugated board or other substrate material inequality, the plate thickness should be used, otherwise the height due to the printing plate embossed light sheets blank plates easy dirty abuses. Thickness of plate printing, can be overcome through compression of substrate thickness differences or gloss bad flaw, allowing the surface of the substrate surface to obtain relatively uniform color, helps to improve the print quality of the product. Resin based flexo, be divided into solid and liquid resin, due to differences in material characteristics, the production process, plate prices and print also has some differences, using reasonable selection should be based on the actual production. Solid resin version is the use of the semi-finished products of rough material directly through print exposure, cleaning (developer), drying or through a double exposure, becomes the finished version, has the characteristics of plate-making easy and fast. Solid resin thickness uniformity, its expansion rate than rubber and liquid resin is much smaller. Due to surface ink plates with good characteristics such as resistance rate is higher, and plate latitude is better, can reproduce a high precision optical outlets and small text, line, and so on, but, the plate is more expensive. Solid version is more suitable for general printing grade the pre-printed paper, fine paper, packaging boxes and other packaging products. From the perspective of cost considerations, some larger number of printed products to buy. While the imprints of a liquid is liquid photosensitive resin material, back to shop after stream mask exposure, positive exposure, back full exposure, recovery of unhardened resin, exposure treatment and drying processes, plate relatively longer time, it normally takes about 1 hour, but its raw material costs approximately half of solid resin. In addition, liquid plate thickness accuracy high as solid, and large deformation, good printing quality as well as the solid version. Thus, suitable for printing in small quantities, and the layout is relatively simple products.
4. ink control
ink is printed in its proper use of important raw materials, one of the main factors affecting the quality of printing products. Proper use of ink, in fact, is to control the quality of the ink. Fineness of good water based inks, pigments, filler particles in a thin, color effects, small amount of printing ink, coating, you can get satisfactory color results. Control the fineness of the flexo printing inks, can fine scraper device detection, fineness of the flexo printing inks in 20 μ m or less numerically stronger lower concentration of color ink, ink volume can be reduced, will be able to get the desired color, printing is not prone to paste, and so on. Viscosity is the main indicator of inks, great influence on the quality of printing products, if the viscosity is too high, ink leveling bad, ink coating, and prone to the dirty version, version, and so on. Conversely if the viscosity is too low, the effect of printing color quality is not good. Usually high-grade Ink viscosity should be controlled within about 20 seconds, its color strong, bright colors. Adjusting the viscosity of aqueous ink, ink can be controlled by temperature and amount of thinner, Ink viscosity up to meet the demands of printing. Ink viscosity testing, generally use the viscosity Cup filled with ink, coating, 4th, then departing from pine hole of ink to flow out the Cup time for test results. In addition to fineness and viscosity, PH value of aqueous ink also cannot be ignored as an important index, and changes in PH value will change the Ink viscosity. Usually water ink within the control of PH value in 8.5-9.5 when the ink print performance is relatively good and stable quality. When a PH value greater than 9.5, because the ink base is strong, its viscosity drops, the drying rate is slow, poor water resistance. When the PH value is less than 8.5, because the ink weak alkaline, its high viscosity, ink prone to dryness, or roller jam the plates, causing the pages dirty. Therefore, pay attention to PH value control the printing process. Generally use the stabilizers to adjust the ink PH value the PH value, stable PH value when used as appropriate, join ink mix in or directly into the circulating pump.
5. flexo printing process control
flexible version because the plate is soft, full of strong elastic, more sensitive response to pressure, if printing pressure is too great, it is easy to cause deformation of dots, words or lines appear to expand, so as to have a coarse, double printing plate or paste, cratering, affect the copy quality. Therefore, the flexo printing process and using less pressure, you can realize even and solid printing ink quality. Apart from the reasonable adjustment of printing pressure, roller surface contact with the printing surface pressure is correctly adjusted, the technical control is also important, if contact pressure between roller and the plate is too large, will be due to excessive compression of ink, printing layout version abuses. Conversely, if pressure between roller and plate is too small, you will affect the uniform and adequate coating of ink. Therefore, each new edition to adjust the appropriate pressure. In addition, also note that the printing process according to inks, substrate and printing features of layout, mastering of appropriate and constant printing speed to keep the bulk of printing inks. Printing area is small, use good ink and substrate materials are better products, it may be appropriate to use a high speed printing. Otherwise, it should be appropriate to reduce the speed of printing, quality of printing inks to get saturated result.
above, soft printing process of technology control involves production process in the of aspects, as long as focused on from version material of reasonable select to sedan process technology of design; from ink of selection and reasonable adjustment to printing process of process technology link, full for seriously of technology checks and control, such production process in the not only can effective to avoid such or as of quality problem of occurred, and can better improve products of printing quality, meet user of requirements.