Production technology of the most popular concave

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Gravure plate and flexographic plate production process (II)

II. Glue concave conversion process of point corrosion gravure plate

at present, gravure plate making mainly adopts electronic engraving gravure and corrosion gravure plate making methods. Electronic engraving plate making method is advanced, but it requires expensive and complex complete sets of equipment, and it is difficult to master. Etched gravure is developed on the basis of photographic gravure. It uses dot pictures (photography or electronic color separation) to be directly exposed to the drum coated with photosensitive glue, and then etched into gravure. 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 copied color image is different from the electronic engraving gravure, which is not involved in the whole process of product development, and is conducive to the stable operation of gravure printing

1. process method

the process method and whole process of coating corrosion gravure plate making by direct method are as follows:

(1) original color separation and color separation. The original is divided by electronic color separation (or directly by photography), and the color separation negative picture is directly added. Pay attention to the direction of the picture. Using the four dot printing system (or gravure dot contact screen) of the electronic color separation machine, the content of the view image can adopt square lattice dots, honeycomb hexagonal dots or brick dots

the dot gradient of the shaded picture can generally be controlled between 3% and 55%. Originals with light tones and less dark tones can be slightly longer with gradient, while originals with dark tones need to be slightly shorter, which should be determined according to the accurate test of gravure corrosion and printing dot gradient expansion data. When setting the range of electronic color separation records, it should be noted that the wall limiting the deepest adjustment point should be kept intact and cannot appear on the ground. Color error correction, subtle emphasis, black version gradation and background color removal can be carried out according to the color separation routine of lithographic pictures

due to the high density of the ink layer and the large expansion of the dot tone in gravure printing, the dot tone level reproduction curve used in color separation plus should be 3% - 5% lighter than the tone level reproduction curve of general lithographic pictures. As for originals with different levels of distribution, different levels of replication curves should be used. Like the electronic color separation of lithographic pictures, they can be derived from the hierarchical cycle diagram

(2) lithographic proofing verification: contact the back of the film surface of the negative picture of the color separation and gravure dot with the photosensitive film, and copy the positive picture with parallel direct light. Stabilize the same exposure of four colors, and control the positive dot tone to expand to about 3% - 95%. Then, according to the conventional data standard of lithography, print and proofing (or rapid proofing) are carried out to test the accuracy of the gradation reproduction adjustment, color correction and adjustment, sharpness reproduction emphasis and the proportion of three color gray balance of the color separation and image. If it is not ideal, you can apply a small amount of trimming to the color separation plus negative picture, or return to the work of electronic color separation adjustment. At this time, the selection of lithographic tricolor ink should be similar to the chromaticity characteristics of gravure tricolor ink, and the data of lithographic plate printing and proofing should be stabilized. This set of long tone gravure dot positive pictures can also be used for lithography, which is no different from the effect of lithography dot pictures

(3) the positive plate for making up copy gravure will be the original color separation and negative image confirmed after the verification of the reverse copy positive image for flat printing and proofing, plus all product contents such as words, shading, patterns, various markings, etc. required for the formal layout, and the positive image original plate for gravure printing will be copied from the front of the film surface. It is necessary to keep the original tone (especially small ideas) and strictly control its expansion. This set of jigsaw can also be proofed or blueprints to verify the correctness of all the contents of the product

(4) gravure cylinder printing and corrosion gravure cylinder can generally measure the sample photoresist layer by spraying or dip coating, and the original gravure positive image is tightly attached to the plate roller for printing (package drying or delivery drying). Control the performance, thickness and exposure of photoresist, and the operation data is stable. After developing and filling, carry out chemical corrosion or electrolytic corrosion. Control accurate data such as corrosive solution concentration, temperature and corrosion time

the depth ratio of roller cavity corrosion of three primary colors should be determined according to the different performance conditions of gravure printing three primary colors ink and the need to achieve the reproduction of printing gray balance, and through the re observation test of the actual gravure proofing gray balance ladder. If the hole is deep, the ink layer will be thick, the color density will be high, and the dot will expand more. On the contrary, the ink color of the printing dot will be light, which is generally 20 μ M changes around. When the equilibrium conditions remain unchanged, the corrosion depth ratio of the three color plate has been determined, and it should be controlled to be stable

(5) gravure proofing printing gravure proofing or printing should take the gray balance and color balance of the flat proofing sheet as the reference, and based on the determined three color ink hue, consistency, viscosity and other suitability conditions of gravure printing, test and select the appropriate and consistent doctor blade angle, pressure and printing pressure, so as to ensure the accurate and stable reproduction of gravure printing gray balance. Since the printing data has been determined, strive to operate stably

2. Conversion relationship of gradient curve of gravure dot

the gravure dot picture plate making of corrosion gravure coated by direct method has the simple verification of flat printing proofing (or rapid proofing), so that the plate making and printing of gravure plate roller have accurate and stable quality assurance. The conversion between the two is guaranteed by the final close consistency of the evolution data expanded by the two point gradient curves

(1) first, through the test of the whole process of gravure plate making and printing, we can get the dot tone expansion curve from the original gravure dot positive picture after printing, corrosion to gravure printing. Here, the gradient expansion curve of gravure dot is different from that of lithography dot. Because the shape and arrangement structure of gravure dots (square or hexagonal, etc.) and lithography dots (square, circle, chain, etc.) are different, the peripheral length change law of each level of dots is also different. As shown in figure 6-1-1, a is a lithographic dot structure, and its dot perimeter increases with the percentage of dot from high to middle, while the perimeter of dot from middle to dark decreases with the percentage, and the perimeter of middle dot is the largest. In the figure, B is the arrangement structure of gravure dots. The dots do not match the corners, and the length of the dot width edge increases in a positive proportion with the percentage of dots. According to the principle of point side length equivalence, the flatprint dot has the largest increase in the middle tone, and the bright tone and dark tone are greatly reduced, expanding in a curve; While the gradient expansion of gravure dots increases with the percentage proportion, showing a linear expansion state

if based on the ladder test, the gradient curve of the gravure point ladder picture (the yin-yang diagram is consistent with the alignment) is shown as the AB straight line in figure 6-1-2. After printing and corrosion, the gravure roll point is stepped, and can be expanded into linear AC according to linear expansion

due to direct pitting corrosion, the plate roll point of gravure changes only with the step, but the hole depth is basically the same, and the ink layer thickness is also basically the same. After gravure printing, it also follows the law of increasing proportion of the length around the point, and it also expands more and more in darker tones. For most tones, check whether the computer software setting is correct; Or recalibrate and revise the point step expansion of the displacement system, which is still approximately linear. Only in the dark end, because the printing points need to be deformed, and the points are connected without reaching the field, the number of point expansions is slightly reduced, making the curve of the dark end slightly curved, as shown in figure 6-1-2, curve ad

for the dot tone of the image after gravure printing, the deepest tone should be extended to the full tone on the spot. The total data of dot gradient expansion from dot pictures to gravure products can be accurately mapped out, and there are slight differences with the corrosion depth of the roller hole. The dot gradient length of the color separation and shade picture should be recorded and set according to the total expansion data. Do not exceed it, so as to prevent the dot wall of the plate roller from being damaged or too many dark tone levels from merging

(2) for the flat proofing positive pictures copied from the same set of color separation and gravure dot negative pictures, since the photosensitive sheet is copied by contacting the back of the negative picture, the dot gradient can be expanded to about 95%. The number of point expansions at all levels still follows the principle of side length equivalence, and also increases linearly in proportion to the length of the surrounding points of the negative graph. For example, in figure 6-1-3, from the point tone curve ab of the bright figure, it is expanded into the positive figure accounting for the tone curve AC through the reverse copy. This is different from the curve with the largest amount of flat proofing and circular dot middle note

a long tone gravure dot positive picture dedicated for lithography proofing. After drying the lithographic plate, the tone points at each level still change linearly, but generally the depth changes little. For the samples produced by lithographic proofing (or artificial expansion of rapid proofing), the printing expansion of each tone point still increases in an approximate linear proportion with the dot tone according to the change of dot circumference, and the dot expansion is roughly reduced and the gradient curve at the dark end is slightly curved only before the dark end points are connected and not reaching the actual ground. See the curve ad in figure 6-1-3. This deepening of mutually beneficial cooperation is also different from the printing expansion curve of the flat printing point, but it can be close to the final gradient expansion curve after gravure plate roller printing, corrosion and gravure printing. Compared with the actual test, the curve (AD) in figure 6-1-3 is not significantly different from the curve (AD) in figure 6-1-2

due to the close consistency between the flat printing sample sheet and the concave printing sample sheet in the final point gradient expansion curve, and the transformation and evolution of the same set of color separation negative pictures, the reproduction quality of the gradient level of the gravure printing image is guaranteed by the flat printing sample sheet. However, the density of ink layer that gravure printing can achieve is slightly higher, and the order and tone of the printed reproduction image are also thicker, and the reproduction quality is higher. This room can be left when reviewing the lithographic proofs

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