In the past 10 years, the application field of labels has continuously expanded, involving the food packaging industry, pharmaceutical industry, personal care products industry, electronics and home appliance products, supermarkets and logistics fields, and anti-counterfeiting industries. There are more and more label varieties, such as multi-layer labels used in the pharmaceutical industry, double-sided labels used in the cosmetics industry, film labels, electronic labels, in-mold labels, smart labels, and anti-counterfeit labels. The global label usage is increasing at a rate of about 30% every year. Label printing uses different printing methods according to different product needs, such as offset printing, gravure printing, flexo printing or silk printing. At present, the prepress production of domestic label printing mainly depends on the offset printing method. It is not known that the printing methods other than offset printing, such as the increase of flexographic dots and the angle of the network line are completely different from offset printing. Produce fine color labels. Exquisite label proofs are printed on site at domestic exhibitions, and most of their printing plates are professionally processed or produced abroad. Therefore, the pre-press design and platemaking level of label printing play a very important role in label printing quality. This article briefly discusses how to improve the prepress design and platemaking level of label printing. Manuscript design considerations Half-tone originals try to avoid choosing large-area highlights and blurred mid-tone originals or pictures, and try to choose the first original, that is, reversal film or reflective version. For flexo printing, silk printing, gravure printing and embossing printing, the design of gradation layers with a large area should be reduced as much as possible in order to avoid inconsistencies between the product quality and the ideal state caused by the expansion of dots in printing. Considering the characteristics of the printing press and whether the ink can truly restore the original, for example, the metal ink in the flexographic ink is not as glossy as the metal ink in other printing methods, and it appears gray; in this case, you can consider the combination of flexo and screen printing Way to print gold and silver ink. The design of the manuscript should consider that the printing machine used can print a maximum of several colors, generally under 5 colors. Registration, cutting marks, and other information that has a guiding role in the production of subsequent processes must be clearly drawn on the plastic paper. The fine lines of the design pattern must be within the rated range: arc vertical line 4μm, arc vertical line 5μm, the dot range varies according to different printing methods, offset printing is between 2% and 98%, and flexo printing is generally controlled at 2% Between ～ 95%, offset printing generally adopts 175 lines / inch screen, and flexographic printing generally adopts 150 lines / inch screen. Selection of Separation Curve for Platemaking After the color manuscript is scanned and input into the computer, it also needs to compress the tone of the image to realize the ideal dot restoration. Under normal circumstances, the medium-to-high contrast manuscripts, the tone density contrast is mostly greater than the tone density range of the printed matter, in the tone adjustment compression can not be linear equal proportion average compression. High-level tones are less compressed, and dark-level tones should be more compressed to make the difference in density of high-level segments open, mid-level themes are deeper, and levels of dark-level segments are flatter. For the color separation curve, at 50% dots, the general product dots need to be compressed by 15%. Offset printing can be screened in high light, and for the flexographic version of continuous image adjustment, generally 2% to 3% of protective dots should be given. Pre-press pre-compensation processing In various printing methods, the dot expansion will be encountered more or less, especially in flexo printing and offset printing, the dot increase phenomenon often occurs. For the flexographic version, not only the dot increase problem, but also the printing plate The combined effect of bending and deformation causes the flexographic printing deviation problem. According to this situation, it is generally necessary to make a test plate, perform a printing experiment, obtain information on enlargement and deformation based on the experimental results, and perform compensation processing through pre-press processing. In the pre-press stage, "decrease" the dot size to compensate for the dot increase in printing. There are two main pre-processing methods: one is the adjustment of the gradation curve of the dot increase, which is completed before the film is produced, and the other is The calibration of the laser phototypesetting is completed when the film is screened. It is recommended to use the second method, according to the characteristics of the printing method, the printing of the film printed by the laser phototypesetter calibration, the dot increase is significantly reduced, and the increase in the mid-tone dot is 5% to 10% smaller than that of the ordinary printing plate. , And can make 0.5% ~ 3% of the dots are clearly reproduced on the film and printing plate. [next] Plate making process Label printing covers several main printing methods. In the plate-making stage, different printing methods are selected according to different product properties. For different printing methods, the plate-making process is also different. This article takes the flexible plate-making process as an example for a brief introduction. The process flow of flexographic plate-making is: manuscript → film (negative film) → exposure → rinse → drying → post-processing. Manuscript The design of the manuscript suitable for flexible printing should have the following characteristics: more color numbers, but less overprinting; no need to reproduce particularly small details; the network cable is not too high, but it can achieve color printing effects; online packaging can be done. Film (Negative) It meets the requirements of plate making, with clear graphics and accurate size and size specifications; matte film is required to have the same density of film four corners; the use of medical film orthography; measured with a transmission density meter, the white density is below 0.06; the black density is above 3.5. Exposure includes back exposure and main exposure ①Back exposure. The supporting film of the photosensitive resin plate is laid flat in the exposure drawer upwards and the protective film is downwards to receive exposure. The ultraviolet light penetrates through the support film to cure the photosensitive adhesive layer to establish a stable base, and can also control the depth of the plate wash to strengthen the bonding force between the support film and the photosensitive resin layer. The back exposure time is determined according to the required substrate thickness. ② Main exposure. Also known as front exposure, the support film of the photosensitive resin plate is facing down, and the protective film is facing up. Tiled in the exposure drawer, tear off the protective film once, and then paste the film surface of the film on the photosensitive resin plate, cover the vacuum film on the film (non-drug film surface), vacuum, so that the film and the photosensitive The resin layer fits tightly. Ultraviolet rays pass through the vacuum film and the film transparent part, so that the photosensitive part of the plate is polymerized and cured. The length of the main exposure time is determined by the plate model and the intensity of the light source. If the exposure time is too short, the slope of the picture and text will be too straight, the lines will be bent, and the small characters and small dots will be washed away. On the contrary, if the exposure time is too long, it will be masked and the handwriting will be blurred. If there are large, small, thick, and thin lines on the same printing plate, you can use black film to cover the individual exposures according to the actual situation. The small parts will not be lost by washing to ensure the quality of the printing plate. rinse Scrub and dissolve the non-photosensitive part, and keep the photopolymerized relief. The length of the plate washing time is determined by the thickness of the printing plate and the depth of the printing pattern. The plate washing time is too short, and the photosensitive resin will be left on the plate to affect the plate making depth. Fall off. drying Removal of the plate-washing solvent will restore the plate to its original thickness. The baking temperature is between 50 ～ 60 ℃. The baking time is determined by the thickness of the plate material and the length of the plate washing time, generally two hours for the thick version and one hour for the book version. If the baking time is too long, and the baking temperature is too high, the printing plate will become brittle and affect the printing life. If the baking temperature is too low, the drying time will be prolonged, and if the baking time is too short, the rotten version will occur during printing. Post-processing That is, desticking and post-exposure. Thoroughly harden (polymerize) the photosensitive resin to the required hardness index, and eliminate the stickiness of the printing plate to facilitate ink transfer. The post-processing time is obtained from the test, the purpose is not to crack or stick. 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