When using the collage original sun-printing PS version, there are often some marks on the printing plate surface and the edges of the original plate. The direct reason is that the collage original method is used to produce the sun-printing positive picture. This symptom will not occur when using the whole original version. So why does the printing of the original collage produce tape marks? First of all, it is certain that underexposure is the main reason for its production. Although the imposition tape is thin and transparent, in fact, it will absorb and block some of the light through, causing partial underexposure. Therefore, the photosensitive layer corresponding to the blank part of the printing plate cannot be fully developed during development, and marks are prone to appear. . But why is not the overall uniform tape mark but the edge of the tape is more obvious than the inside?
First, during exposure, the optical phenomenon when the light passes through the center of the tape is different from the edge part, because the center part of the tape is theoretically a uniform medium, and the edge part of the tape, especially the critical part of the tape edge, is a non-uniform medium, which will produce different degrees of light Scattering, refraction and diffraction phenomena. At the same time, there will still be a circle of air around the edge of the imposition tape. This air layer creates an optical path difference and causes light interference. These will cause the exposure of the edge of the tape to be more insufficient.
Second, during use and placement, dust and other dirt adhered to the sides of the tape, resulting in additional light blocking and absorption phenomena, which further caused partial exposure. In actual work, especially when the environmental conditions are poor, it is often seen that the edges of the tape are obviously with dark edges. The original version of this tape collage must be printed with the printing tape.
The third is that there will be a certain "critical effect" in the development process. Although the development of printing plates is mostly dynamic, macroscopically, this phenomenon should not exist, but from a microscopic analysis, there is still the possibility of this effect. Although it is not as obvious as that of film development, it cannot be ignored.
The fourth is the visual "Mach van der Waals effect", which further aggravates the phenomenon of imprinting tape. The edge part of the tape mark on the surface of the developed printing plate is visually more obvious than the center part. Although this effect is small, it cannot be overcome.
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