Second, the dot corrosion etching gravure concave conversion process
At present, the gravure plate making mainly adopts two kinds of plate making methods: electronic engraving gravure and etching gravure. The electronic engraving method is advanced, but it requires expensive and complicated complete sets of equipment, and it is not easy to grasp. Corrosion gravure is developed on the basis of photogravure. It is directly exposed to the roller coated with sensitized adhesive using dot pictures (photograph or electronic color separation), and the gravure plate is made by etching. Removed the unstable factors of overprinting carbon paper, simplifying the process. And can take simple offset proofing (or fast proofing) to verify the exact quality of the plate-making picture, to achieve the corresponding gum gravure conversion. The copied color image is not much different from the electronic engraving gravure, and it is conducive to the stable operation of gravure printing.
1. Process method
The direct process method for coating the etching gravure plate is as follows:
(1) Manuscript color separation Screen color manuscripts are electronically separated (also can be directly added to the screen to separate colors), and the color separation screen can be directly screened. Pay attention to the direction of the picture. Using the four-color dot system (or gravure dot contact screen) of the electronic color separation machine, the visual image content can be a square grid dot, a hexagonal hexagonal newspaper dot, or a brick dot dot.
The screen tone of the net-shadow image can generally be controlled between 3% and 55%. In the case of brightly tuned and darkly tuned manuscripts, the tone of the screening may be slightly longer, and the manuscript of the darker tune will need to be slightly shorter. It should be determined by accurate testing of gravitational corrosion and expanded data of printed dots. . In the setting of the electronic color separation record range, it is necessary to pay attention to limiting the deepest adjustment of the network walls of the hierarchical network points to be kept intact and cannot appear on the ground. Color error correction, subtle accentuation, and black-tone adjustment, background color removal, etc. can be performed in accordance with the color separation of plain printed images.
Due to the higher density of the ink layer in the gravure printing and the increase in the number of tone points, the reproduction curve of the halftone tone used in color separation and screening should be 3% lighter than that of the normal tone image in the dark tone. 5% is appropriate. As for the manuscripts for different levels of distribution, different levels of replication curves should be used, as well as the electronic separations of the typographical pictures, which can be derived from the hierarchical cycle diagram.
(2) Flat printing proofing check will be color separation screen gravure net negative point of the film surface contact with the photosensitive film on the back, copy the positive net photo with parallel direct light, to stabilize the same four-color exposure, control the positive network stage The adjustment has been extended to the range of 3% to 95%. Then, according to the standard printing standard data, the printing and copying proofing (or quick proofing) is carried out to check the adjustment of the tone level of the color separation screening image, the color correction and adjustment, the clarity reproduction emphasis condition, and the three-color gray. Balance the accuracy of the ratio. If it is not ideal, you can apply a small amount of finishing to the color separation plus screen negative image, or return to work electronic color adjustment. At this point, the three-color printing ink of the plain printing should be similar to the color characteristics of the gravure three-color ink, and the printing data of the printing and proofing should be stabilized. This set of long-graded gravure mesh dots can also be lithographically printed, and there is no significant difference from the effect of the flat-printing dots.
(3) Imposition copy of the gravure positive version will be after the anti-copy positive drawing to confirm the original color separation plus proof after the check, add the text, shading, patterns, various standards required for formal layout All the contents of the line and other products are copied from the front side of the film to the Yangzun picture original used for the gravure printing. The tone of outlets needs to maintain the original tone (especially small ideas) and strictly control its expansion. This set of imposition can also be proofed or blueprinted to verify the correctness of the entire contents of the product.
(4) gravure cylinder printing plate, corrosion gravure plate cylinder can be sprayed or dip coated photosensitive layer, the gravure positive net picture attached to the version of the plate for printing (including drying or hand drying). Control the stability of photopolymer performance, thickness and exposure and other operating data. After developing and filling, chemical etching or electrolytic etching is performed. Control accurate data such as concentration of corrosion solution, temperature and corrosion time.
The depth ratio of the three-primary plate roller network etching shall be determined according to the different conditions of the gravure printing ink of the three primary colors and the need to achieve the balance of printing gray balance. It may be determined by the actual gravitational proofing gray balance ladder ruler. The depth of the ink layer is thick, the color density is high, and the dot expansion is also large. On the contrary, the ink color of the printing dot is light, and the change is generally about 20 μm. When the equilibrium condition of the friends is constant, the ratio of the depth of corrosion of the three-color plate is determined and its stability should be controlled.
(5) Gravure proofing Printing gravure proofing or printing shall be based on the gray balance and color balance of the plain proofs, and shall be determined on the basis of the appropriate gravure conditions of the gravure and three-color gravure inks, viscosity, and viscosity. Appropriate and consistent squeegee angle, pressure and printing pressure ensure accurate and stable reproduction of gravure grey balance. The print data has been determined and stable operation has been sought.
2. The conversion relationship of the gravure offset tone curve
The direct gravure gravure gravure dot pattern platemaking, with the simple verification of the flat print proofing (or quick proofing), makes gravure plate roller platemaking and printing with accurate and stable quality assurance. The transformation between the two is ensured by the final close consistency of the expanded evolution data of the network tone curve.
(1) First, by testing the whole process of gravure platemaking and printing, we can draw a curve of the tone scale of the dot after printing from the original gravure dot netting, etching, and gravure printing. Here, the tone-expanding curve of the gravure dot is different from the typographic dot. Because the shape and arrangement of gravure dots (squares, hexagons, etc.) are different from those of flat dots (squares, circles, chains, etc.), the regularity of the length change around the perimeter of the dots at each level is also different. As shown in Figure 6-1-1A, for the flat-printing dot structure, the percentage of the perimeter of the dot in the high-to-middle tone increases with the percentage of the dot, while the perimeter of the medium-to-dark tone of the dot decreases with the percentage, and the perimeter of the midtone dot is the largest. B in the figure is a gravure dot arrangement structure, with no corners, and the length of the broad edges of the dots is proportional to the percentage of dots. According to the equivalent length of the outlets, the midtones of the flat printing outlets are expanded at most, the amount of brightening and darkening expansion decreases, and the curve expands; while the increase of gravure outlet outlets increases with the percentage, showing a straight-line expansion.
If the test is based on a ladder ruler, the tone curve of the gravure net ladder scale image (conformity of the yin and yang figure team) is shown as the AB straight line in Figure 6-2. After printing, gravure gravure roll point adjustment, linear expansion can be expanded to straight line AC.
Because the direct gravitational gravure version of the gravure platen dots only changes in size with the tone, the depth of the grout is basically the same, and the thickness of the ink layer is also basically the same. After gravure printing, the rule of increasing the proportion of the length of the perimeter of the dot is also followed, and the more the dark tone is expanded, the larger the tone is still an approximately linear proportional dot scale. Only in the dark tone, because the printing dots need to be deformed, before the dot touches but before reaching the field, the dot enlargement amount is reduced slightly, and the dark tone curve is slightly curved, as shown in the curve AD in Figure 6-1-2.
After gravure printing, the darkest tone should be expanded to the full scale of the field. From the dot picture to the gravure product dot scale, the total data can be accurately mapped out, and the depth of corrosion of the roll net hole is slightly different. The length of the halftones of the color separation plus net-tone image should be set according to the total expanded data, and should not be exceeded in order to prevent the damage or excessive darkness of the roll-net dot net wall.
(2) The plain printing proofing Yang network pictures copied from the same set of color separation screens and gravure net points and negative pictures, since the photosensitive tablets are copied on the back of the negative images, the dot adjustment can be expanded to about 95%. The expansion of the network at all levels still follows the equivalence principle of the side length, which is also a linear and linear increase in the length of the perimeter around the negative graph. As shown in Figure 6-1-3, from the abbreviated tone curve ab, the negative copy expands to the positive graph network and accounts for the ac curve. This curve of peace and proofing and circular outlets has the largest amount of expansion.
As a special long-graded gravure printing spot proofing Yangyang pictures, after the tanning printing plate, the various tone network is still a linear change, but the general depth of change is not. After the proofs of plain printing proofing (or quick proofing artificial expansion), the printing enlargement of all the orderly outlets is still increasing linearly with the order of the outlets, and it is only connected at the outlets of the dark end. Before the actual arrival, the dot expansion was slightly reduced, and the dark tone was slightly curved. As shown in Figure 6-1-3 curve ad. This is also the same as the printing expansion curve of the Peace Printing Point, but it is close to the final tone increase curve of the gravure printing plate, etching, and gravure printing. Compared with the actual test, there is no big difference between the curve (ad) in Figure 6-1-3 and the curve (AD) in Figure 6-1-2.
Because the leveling proofs and the gravure proofs are nearly identical to the scale-up curve of the gravure printing at the final halftone point, both of which have evolved from the same set of separations and shaded net images, the quality of the gravure printing image is adjusted. Calibration proofs were made from flat proofs. Only the gravure printing can achieve a slightly higher density of the ink layer, and the tone and tone of the printed reproduction image are also more substantial, and the reproduction and reproduction quality is higher, and this space can be left when judging the plain printing proof.