Two factors affect the quality of PS plate

Although CTP has been used for a long time and it has begun to spread throughout the country, some printing companies still use PS plates. The PS plate is still the largest printing plate used in China at this stage. Let us introduce 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. Only the quality of PS plate making can be ensured to ensure the quality of printed matter. So, what are the key points for good quality printing plates? Let us explain in detail the two aspects of the original quality and the quality of the media.

1, the original quality

The original refers to the film or sulfuric acid paper that is output before printing, and its quality directly affects the effect of PS plate making. The original quality has two important indicators:

(1) Dot density

In the positive print, the dots must have a sufficient density, a single dot density of 3.0 or more, the field density of 3.5 or more, and the transmission density of the film blank area should be less than 0.05.

(2) Bright and clean

The dot center density is consistent with the edge density so that the latitude of the exposure time can be expanded. The original version is clean and free from dirt. It is best to use a complete film without a knife edge and collage tape to ensure that the film is tightly integrated with the PS plate and to avoid false dots due to light scattering.

2, the quality of the media

(1) Edition base

The base of the printing plate should be clean, uniform in thickness, uniform in distribution of grains, moderate in thickness and moderate in depth. The photosensitive liquid is evenly coated with no bubbles or scratches. In general, the average sand depth (RZ) is 5 to 7.5 μm, and the average roughness (Ra) is about 0.6 μm.

(2) Photoresist layer

The photosensitive coating is even and the thickness is moderate. It not only covers the peaks of the grit, but also does not become too thick, which affects the resolution of the printing plate. The thickness of the general PS plate coating layer is about 1.8 g/m2.