1, compare the printing machine vacuum quality
The vacuum effect is the foundation of the printing machine. The quality of the vacuum effect depends on whether the PS version is dense between the film. If the density is not good, there will be a virtual network phenomenon. Such as a poor printing machine, exposure with dirty PS version, after development, there will be a virtual net the size of a dollar coin (commonly known as small sun); Some printing machines, just start printing is good, but with the number of printing, rubber boot changes, less than a year on the vacuum effect is greatly reduced. And a good printing machine, the vacuum effect is fast and dense, exposure with dirty PS version, after development, it is only a point, it is easy to repair, even the reproduction of PS version with proofing, it can also be dried well,
2. Compare the lighting effects
General PS plate manufacturers use 355~420nm photosensitive materials, which requires the spectral peak of the lamp source system to be maintained in this range, while the light energy of other bands is minimal. In this way, in order to ensure that the printing time is short, the dot restoration effect is good.
The uniformity of the light source of the printing machine is required to be above 86% (select a precision measuring instrument). With a 30% dot film, a PS plate, after development, with the density meter measurement, the error between the middle and the surrounding corner is generally less than 2%, so that when printing a large area of color block, there will be no color difference.
The stability of the light source refers to the ability of the printing machine to self-adjust when factors such as heat and cold of the lamp tube and voltage fluctuations change, especially the printing machine that quickly starts the light source. How can the customer judge? It is also a 30% network of film, when the cold machine starts to print 1 plate, and then after the continuous printing of 10 PS plates, followed by 30% of the film, compare the reduction of the two PS plates, measured with a densitometer, should be the same. This function of the printing machine is particularly important for packaging and printing customers. Because, printing often make up the color, if the PS version of the dot reduction is not the same, the difficulty and consumption of color chasing will be greater.
3, compare the performance of printing machine

Excellent printing machine should meet the following requirements. ① The working environment temperature should be 0-40℃, and the relative humidity should be less than 80%; The glass should meet the requirements of the first class glass in JG40-62 "Flat Glass for Windows", there should be no scratches, scuffing, mildew and other phenomena in the effective working surface, and there should be no bubbles in the glass that affect the quality of the printing plate; ② Illuminance uniformity of the working surface shall not be less than 85%. ③ The temperature rise of the working glass surface of the printing machine should not be greater than 20℃. ④ The important exposure time error of the printing machine should be less than 5%. ⑤ The printing machine should be able to work reliably when the power supply voltage fluctuates ±10%; The working noise should be less than 70dB; The insulation resistance between the housing and the power line should be greater than 2MΩ, and the printing machine should have a reliable anti-ultraviolet device.