Printing quality control in optical disc offset printing
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In the CD, printing is an important bridge between plate making and printing, and is an important factor affecting the quality of printing. The so-called printing plate refers to the process of faithfully transferring the dots on the photographic original (film) to the printing plate (the negative-type anhydrous PS plate) by actinic action. Due to the constraints of processes, materials, equipment and other factors, it is often difficult to achieve the purpose of faithful reproduction. Therefore, in order to ensure the quality of printing, we must control the quality of the printing plate, that is, the transfer of control points. Below, we will analyze how to control the correct transfer of outlets.
First, factors affecting the transfer of PS version outlets
Through the analysis of the whole process of printing, we can know that the main influencing factors are the following aspects: the quality of the original (film), the reproducibility of the plate, the printing machine and the light source.
1, the original (film) quality
The ideal original quality should be a high dot density (D>3), a solid point, and a clean and hard dot. Such dots have a large tolerance for exposure and development during printing, and are easy to faithfully replicate. The center density of the dot should be consistent with the edge density, so as to increase the tolerance of the exposure time and completely transfer the dots. The original should be clean and free of dirt, otherwise the print will be dirty.
2, the dot reproducibility of the plate
The reproducibility of the plate outlet means that the photographic plate can maximize the reproduction of the original dot during the printing process.
The effect of reproducibility is mainly reflected in the resolution of the plate and the thickness of the film. Since the PS plate is a pre-coated photosensitive plate, the base is an aluminum plate, and a uniform photosensitive film layer is coated on the substrate. Therefore, the processing process of the aluminum plate base directly determines the quality of the plate material. This part is often invisible and invisible to the users of the plate. Therefore, it is particularly important to ensure the quality of the plate through the purchase channel. If the plate is rough and the quality is inferior, the resolution will be reduced, which will seriously affect the printing quality. Some inferior plates increase the thickness of the photoresist layer in order to cover the sand on the aluminum substrate. Doing so will result in an increase in diffraction during exposure, which will result in a decrease in resolution and affect print quality.
The following are the impact and requirements of the quality of the plate on the dot copy:
(l) Partial flower version, paste version
The base should be clean, the thickness is uniform, the sand distribution is even, the thickness is moderate, and the depth is moderate. The photosensitive liquid is evenly coated, free of air bubbles and free from scratches. Generally, the average depth (Rz) of the sand is required to be 5 to 7.5 μm, and the average roughness limit (Ra) is about 0.6 μm. This has affected the quality of the PS version, resulting in local rapid wear and tear, the emergence of "flower version", paste version, and then appear off the plate and dirty.
(2) PS version surface roughness is not standard
The sand is too thick, so that the water retention is insufficient, and it is easy to get dirty: the sand is too fine, so that the photosensitive film in the micropores is not easy to be clean, the plate base is easy to be contaminated, and it is easy to get dirty when printing.
(3) Partial drop, missing version
After electrolytic roughening, the base gray matter is not cleaned, and the local photosensitive layer is not firmly adsorbed; before the coating of the photosensitive liquid, the layout is not cleaned, leaving traces of acid flow when hanging and drying, which will cause partial release.
(4) not easy to ink
The PS version has exceeded the shelf life or improper storage, such as the storage environment temperature is too high (more than 30 ° C), the relative humidity is more than 65%, the light is too strong, etc.: the photosensitive adhesive is too low, the photosensitive coating is too thin, etc. The PS version is not easy to be inked or not inked at the time of printing on the machine.