In gravure proofing, the ink is transferred from the ink hole to the surface of the printing material through the action of capillary holes (in some cases, the proofer also uses an electrostatic auxiliary ink removal device). The large cylinder rotates to the end position of its circumference to get the largest printed sheet. After the rotation, the large cylinder is separated from the surface of the plate cylinder, and the plate cylinder can be cleaned and disassembled at this time. The proofing of each color after the second color should be repeated after the previous color is dried.
The printing of flexible packaging materials will cause the printing materials to expand and contract. When the printing company makes the plate cylinders, there is an increase between the various color plate cylinders, which will bring certain difficulties to the proofing. Experienced operators can use the drop of the dots Make proofs with high registration accuracy.
The ink transfer of the Japanese machine transfers the ink to the substrate by the pressure of the gravure cylinder driving the gravure cylinder to rotate. The machine speed is generally about 30m / min, but the emboss cylinder is separated from the gravure cylinder from the start to the end The speed is different, because the substrate is tightly wrapped on the surface of the printing cylinder. Under the inertia of the cylinder, the speed is accelerated. The second round of proofing speed will be faster than the first round.
The British machine uses pressure to drive the plate cylinder to rotate by the impression cylinder to complete the ink transfer. The speed of the impression cylinder itself is kept constant, and the speed of the substrate tightly wrapped on the impression cylinder is the same from beginning to end. In this way, the problem caused by the inconsistent rotation speed of the Japanese machine is solved.
When proofing, the substrate is wrapped tightly on the impression cylinder, and then the proofing is performed according to the printing sequence according to the printing and surface printing characteristics of the plate cylinder.
The substrate in the printing plate is generally transparent. When proofing, the dark color is printed first, and then the light color is printed on the basis of the previous color. For example, only the four-color electrical sub-image and the white version of the print, usually the black version is printed first. , Then the education version, the magenta version, then the yellow version, and finally the white version based on these four colors. The proofing order of the table printing plate is opposite to that of the printing plate. The substrates of the surface printing plate are mostly opaque, and the proofing is performed in the order from light to dark. When proofing, we must also pay attention to this important factor of proofing ink.
The gravure proofing machine does not have the ink tank part. When the impression cylinder is close to the gravure plate cylinder during proofing, the prepared ink is manually poured on the gravure plate cylinder. Because the speed of the proofing machine is not high, the viscosity of the ink used for proofing cannot be too low, otherwise it will cause paste.
The high-speed gravure printing machine can be opened to 160m / min under normal circumstances, and the ink viscosity is about 16s, but the ink viscosity used for gravure proofing should be adjusted to about 20s. The slow speed during the proofing, the high viscosity of the ink and the low hardness of the rubber on the impression cylinder are conducive to the full transfer of the ink to the substrate, and the color of the proof is relatively bright.
If the ink is not added to dilute the ink during proofing, it will also make the printing company suffer a lot, because it is difficult for the printing company to print very bright and bright color effects. It is necessary for the plate-making company to dilute the ink when proofing, so that the printing company will be much easier when making color proofs according to the gravure proofs. In the entire gravure plate-making process in which electro-engraving has achieved filmless engraving, the department with the most human influence is the gravure proofing workshop.
Proofing ink diluting, different degrees of thinning, different pressure between the gravure cylinder and the impression cylinder, the angle of the blade, the installation method and its pressure, the distance between the blade and the imprinting point, etc. Such effects have an impact. During the proofing process, the relevant parameters should be adjusted according to the difference of the substrate, the characteristics of the surface printing and the internal printing, so that the perfect gravure proofs can be printed, and the professional production level of the plate making company can be printed.
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