In view of so many CTP plates on the market, what aspects should we evaluate CTP plates? What kind of plate can meet our printing quality requirements?
Reproduction of dots
Dots are the basis for printing and reproducing graphic information. The quality of the dots on the printing plate will directly affect the quality of the dots on the printed matter, which in turn affects the reproduction of the entire printing process. Therefore, it is very important to choose a plate with good dot reproducibility.
Like the traditional PS version, the dots of the CTP plate are also composed of sand meshes. In order to achieve 1% to 99% dot reproduction of the CTP plate, the sand mesh of the plate base must be small enough, because the finer the sand mesh, the more sand meshes supporting the highlights part of the dot, and the stronger the dot, which occurs during printing. The less likely it will be out of print. However, the grit of the dots cannot be too fine. The ink-water balance width of the plate with two fine grit is small in printing, which is not conducive to the control of printing quality.
The reproducibility of the lines of the plate usually includes two aspects.
Reproduction of extremely thin lines and the size of the yin and yang lines. The appearance of extremely fine lines is closely related to the size of the grain of the plate, especially the uniformity of the grain because only the edge of the line supported by the evenly distributed grain can be smooth. The size of the yin and yang lines is mainly determined by the coating thickness of the plate. We can compare the line changes by printing adjacent negative and positive lines on the printing plate.
The ink affinity of the plate refers to a feature that the graphic part of the printing plate is selectively inked through the ink transfer roller. The thickness of the ink on the printing plate will directly affect the thickness of the ink on the blanket and paper, and the amount of ink transferred to the printing plate. It also depends on the ink affinity of the printing plate. If the ink affinity of the graphic part of the printing plate is low, the range of ink control in the whole printing is smaller, which is not conducive to the product quality. Moreover, if a printing plate with poor ink affinity is used, the remaining ink will accumulate on the ink transfer roller, which will thicken the ink film of the ink transfer roller and accumulate too much ink at both ends, resulting in the phenomenon of ink splashing and reducing the cover of ink. force. Therefore, CTP plates with good ink affinity are very important.
In order to improve the ink affinity of the CTP plate, the photosensitive material in the graphic part of the printing plate should have chemical properties that are relatively close to the pigments, resins and solvents in the ink.
The hydrophilicity of the plate refers to the property of selectively retaining water on the non-graphical part of the printing plate. The amount of water in printing should neither be too much nor too little. Too little, the parts without imprints are easy to get dirty; with too much, it is easy to have dull imprints, uneven delivery, paper deformation, and inaccurate overprinting. At present, the main base material of the CTP plate is aluminum, which is hydrophilic, and the surface is ground to form a porous surface, which enhances the total surface area and finally improves the hydrophilic properties.
In addition, the factors that affect the performance of CTP plates are the resolution, printing resistance, base, sensitivity, size specifications, coating uniformity, etc. of printing plate.
All in all, with the continuous progress of CTP plate-making technology and the continuous improvement of the performance of CTP plates, the advantages of CTP plates continue to emerge, and the digital workflow continues to improve. We have reason to believe that CTP plates will inevitably have broader development prospects.
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