3. Misregistration is not allowed. It can be divided into two types: vertical misregistration and horizontal misregistration. There is a saying that "Paper has always been firmly controlled by the organic parts during the transmission process, which can guarantee the accuracy of overprinting." In fact, this sentence is not comprehensive. For example, the embossing clincher shaft or sleeve wear, although it can also be firmly controlled in the transmission of paper, but it can not be properly controlled. This is like a person holding a ball in both hands. The arms are straight and they can hold firmly. The bending of the arms can hold them firmly. However, the distance and stability of the ball from two different positions are different from each other. . Therefore, it should be said that "it is firmly controlled to ensure accurate overprinting."
There are many reasons for overprinting. The common ones are: paper stretching, paper feeding, improper positioning, insufficient bite force, wear of the gnawing shaft, non-conformity of the transfer, and wear and tear of the conveying parts. In addition, some special factors may cause misalignment, such as large deformation of the layout part of the rubber, and the partial overprinting of the image may be inaccurate; the axial transfer of the paper feed shaft and the impression roller shaft may cause misalignment in the horizontal direction.
4. Chromatic sequence arrangement In the past, the color sequence of monochrome machines was always sequential yellow, red, blue, and ink. This kind of color sequence arrangement, the greater difficulty is the signing of the yellow version, the red version of the printing, especially It is the first yellow version, which is related to the reproduction and reproduction of prints. If the yellow version is printed too deeply, the skin color of the characters printed is not lifelike, and the houses are as old as the ancient temples, making them unacceptable; if the yellow edition is printed too light, the reproduced images will be dark and the colors will be blue-violet. It doesn't look good either. There are two main reasons why the yellow version has a color cast: First, the human eye's retinal color cells have the lowest resolving power to yellow; second, people lack understanding of the oil-absorbing properties of the paper, and lack of instrumental testing. Often cause too deep, too weak.
The color sequence arrangement of the two-color machine allows the yellow printing plate and the blue printing plate to be placed in the same printing process, and the blue plate just functions as a color filter for the blue glass, which is convenient for identifying whether the ink layer thickness of the yellow printing plate is appropriate. However, due to wet and wet printing, two-color machines often produce irregular A and B ghosts on the two corners of the trailing edge. This requires that the color sequence be properly changed during the process.
Four-color multi-color offset press, because the three colors are wet and wet printing, so the color sequence is based on the viscosity of each color ink, arranged from high to low, otherwise there will be reverse overprint failure, resulting in dark ink color miscellaneous ills. Sometimes the first few colors will produce A, B ghosts, and the color sequence must be adjusted as necessary.
Third, the printing material factors Offset materials, mainly paper, ink, printing plates, blankets and pad lining four categories. Various materials must meet the printability requirements of offset printing properties, otherwise there will be various printing failures.
1. Paper factors The physical and chemical properties of paper and technical indicators, including physical performance indicators, optical performance indicators, printing performance indicators, chemical performance indicators. Among them, tightness, tensile strength, stretchability, whiteness, absorbency, smoothness, glossiness, pH, etc. are closely related to offset printing suitability.
The tightness and tensile strength of the paper, and the pressure and separation during the printing process, the viscosity of the ink and the sticky force generated by the surface of the blanket can cause hair loss and powder fall, resulting in burr-like spots on the printed material or in the field. Loss of money. (To be continued)