Digital screening technology III in the most popul

Digital addition technology in gravure printing (III)

gravure plate making in order to improve the accuracy of experimental results. Methods and requirements for points

the traditional method in gravure plate making is photogravure plate making. The printing plate made by this method has the same hole area and different hole depth to express the hierarchy of the printed matter. Its original version has no dots and is a continuously adjusted film. The image on the original plate is imaged on the corrosion-resistant film (the film used to corrode the coating of the printing plate cylinder) or carbon paper by ultraviolet irradiation, and then the film is wrapped on the cylinder, developed in warm water, and chemically corroded by ferric chloride to form holes of different depths. Now, it is not used to continuously adjust the original carbon to create intelligent factory paper that meets industry 4.0. It mainly uses the method of color separation film, that is, the method of making color separation film according to the same method as offset printing; The other is the method of fully digital image processing and making plate cylinder without film. In the field of packaging printing and special gravure printing, film free production method is rapidly being promoted. There has also been real progress in the field of gravure printing without film. Modern gravure plate making process methods mainly include:

(1) dot photography gravure. Gravure dot special screen is used for photographic addition or electronic addition to produce positive (or negative) pictures, which are directly printed on the photopolymer plate cylinder or the copper cylinder sprayed with photoresist. The former only needs to be developed by washing, and the latter can be made into gravure plate by corrosion (or electrolysis), also known as direct coating corrosion gravure plate. This kind of plate making has the advantages of simple program, stable data and easy operation. The gravure plate produced has the same hole depth, and its depth can be uniformly changed (15 ~ 35 μ m)。 The point size changes with the image level. The line ratio of the wall to the point can vary from 1:3 to 1:6 according to the requirements of the original coordination contrast (up to 13, but not resistant to printing). Although it can only display 56% ~ 73% (up to 79%), due to its thick printing ink layer, high contrast, and 2. The main motor source of the tensile testing machine is not bright, the reproduction of the printing dot tone level is still better than that of lithography. Moreover, the picture is flat, uniform and soft, which is suitable for building materials and trademark decoration printing

(2) etch gravure. It is one of the main methods of gravure plate making at present. Developed from gravure printing, gravure printing is made by directly exposing dot pictures (photography or electronic color separation) to the drum coated with photosensitive glue and etching. It eliminates the unstable factors of carbon paper over printing, and simplifies the process. Simple offset proofing (or rapid proofing) can be used to verify the accurate quality of plate making pictures to achieve the corresponding offset gravure conversion. The reproduced color image is not much different from the electronic engraving gravure, and is conducive to the stable operation of gravure printing

(3) electronic engraving intaglio. The electronic color separation plus flat print dot positive picture (color separation signal) is used as the original. According to the density of the original, the electronic machinery (diamond cutter) is driven by the image scanning signal through the engraving machine to synchronously and directly engrave the gravure roller dot plate. In principle, the points of electronic engraving gravure are not overlapped, and only the field part is easy to produce uneven phenomenon during printing, which is one of the reasons for water marks in gravure printing. The traditional gravure dot will also produce a step jump between the field and the middle tone. The reproduction of the highlight part will also have a visually perceptible jump due to different printing conditions. If the hierarchical point and frequency conversion point are used, the sudden change of step can be avoided. The gravure points of electronic engraving change with the size of the image level and the depth of the hole, and with the deepening of the tone, the area and depth of the hole change at the same time. The level resolution is very fine, and the image coordination level and contrast can obtain excellent reproduction, which is more suitable for gravure plate making of exquisite color images. Better definition should be used as much as possible in use. Attention should be paid to their mutual connection and influence in electronic color separation. Various functions of electronic color separation machine should be reasonably used to compensate and correct the influence of various factors in color image reproduction, so as to ensure good image reproduction quality. The dot gradient expansion of electronic engraving gravure is similar to that of etched gravure, which is expanded in an approximate linear proportion, and the dot gradient is slightly longer than that of etched gravure. The electronic engraving machine is equipped with a variety of point systems and multiple sets of engraving level curves (including the change of gray balance proportion). You can choose the appropriate curve according to the original, and engrave the fine level images suitable for different gravure printing requirements. The color separation and drawing plate used by the electronic engraving machine can be verified by offset proofing or digital proofing to realize accurate conversion of gravure printing

in addition, there is the electron beam spiral scanning method. It uses the electron beam of cathode-ray tube to spiral scan to obtain the points that change according to the area ratio, and then carries out electron beam blackening to realize the addition of the image. At present, the technical environment of gravure printing, such as prepress electronization and film free, has achieved significant development. CTP of roller production is not only limited to electronic engraving, but also more advanced laser methods have been developed and applied

printed by Lin Qishui in China - issue 12, 2005