What is the decision condition for the quality of the PS plate?
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Although CTP has been used for a long time, it has begun to spread in China, but some printing companies that are not very strong are still using PS plates. PS plate is still the most widely used plate in China at this stage. In the following article, the author discusses two important conditions for determining the quality of the PS plate: the original quality and the quality of the plate.
In offset printing, plate making is the guarantee of printing quality, and only the quality of the PS plate is guaranteed to ensure the quality of the printed matter. Then, good quality plates need to have those points, let us explain in detail from the original quality and plate quality.
Original quality
The original version refers to the film or sulfuric acid paper output from the prepress, and its quality directly affects the effect of the PS plate. The original quality has two important indicators:
(1) dot density
In the positive printing plate, the dot must have sufficient density, the density of a single dot is above 3.0, the density of the solid is above 3.5, and the transmission density of the blank area of the film should be less than 0.05.
(2) Clean and clean outlets
The center density of the dot is consistent with the edge density to increase the latitude of the exposure time. The original version is clean and has no dirt. It is best to have a complete film without a knife edge and a splicing tape to ensure that the film is tightly combined with the PS plate to avoid the phenomenon of dot fading caused by light scattering.
2. Plate quality
(1) Edition
The base should be clean, the thickness should be consistent, the sand distribution should be even, the thickness should be moderate, and the depth should be moderate. The photosensitive liquid is evenly coated without bubbles or scratches. Generally, the average depth (RZ) of the sand is required to be 5 to 7.5 μm, and the average roughness (Ra) is about 0.6 μm.
(2) Photosensitive layer
The photographic coating is uniform and the thickness is moderate. It not only covers the peak of the sand, but also is too thick, which affects the resolution of the printing plate. Generally, the thickness of the PS plate coating layer is about 1.8 g/m2.