The Relationship between Quality Control and Printing of Proofing (II)

The technical parameters of the fountain solution are often overlooked factors in the quality control of proofing. The technical parameters of fountain solution are mainly conductivity and pH. Their standards are: the conductivity is 800-1200, and the pH is 4.8-5.2.

The quality control of proofing also involves adjustments to the proofer. The main contents of the adjustment are the following:

1 The pressure of the blanket cylinder is ±0.03mm (measured once per rotation 120°, averaged), ie blanket thickness + liner thickness = (2.286 ± 0.03) mm.

The platen pressure (including the thickness of the PS plate) in the 2nd version is +0.12mm to +0.15mm, that is, the surface of the PS plate is higher than the height of the guide rail.

3 paper table pressure (including paper thickness) is +0.15mm ~ +0.18mm, that is, the surface of the paper is higher than the height of the guide rail.

4 There are two rollers on each side of the active rack. When the gantry is moved to the side of the ink distribution system and the machine is not pressurized at the same time, the pressure on the roller and the lower rail surface can be rotated just by hand. Too tight and too loose must be adjusted.

5 even ink system: Ink roller roller width on the platen and embossing ink bar width on the paper table should be uniform.

Third, the proofing machine maintenance and maintenance

In the process of proofing, the operation of the proofing machine is the most important. Of course, what kind of working condition the proofer is in is also very important. Only by making the proofing machine in the best working condition can we ensure that the outlets maintain good quality during the delivery process, and finally obtain qualified proofs. Since the maintenance and maintenance of the proofer is a continuous process, it is necessary to establish a set of practical maintenance procedures and make it standardized and standardized.

1 ink roller maintenance

The dot change of the proofs will deteriorate with the hardening of the proofer's ink roller. The hardening of the ink roller means that the roller will be used for a long time and its surface will become light and hard until a "crystal layer" is formed. When the surface of the roller crystallizes severely, its ink transfer performance is affected, and the ink balance during the proofing process is difficult to maintain. Especially for magenta inks, due to the decrease of water absorption, hollow spots will appear. In this way, the dot area of ​​the sample will be smaller than the dot area on the film, and the color will become lighter. That is, saturation decreases. In some examples, when the color dots are changed, the color tone of the proof sheet will deviate from the expected effect, and the tone variation of the multicolor overprint will be greater. This shows how important it is for the maintenance of the ink roller. In addition to daily fixed weekly cleaning procedures, there are specific maintenance measures. That is, every two weeks, remove the ink roller from the proofer and take a rest. Replace the backup ink roller. In this way, the ink roller can maintain a good working condition, so that a satisfactory dot reduction quality can be obtained.

2 blanket maintenance

Blanket is the medium that transfers dots from printing plate to paper. Its performance directly affects the delivery quality of the outlets. After a long time, the blanket will have chemical residues attached to its surface, making the elasticity of the blanket smaller. This will make the edges of the dots that are transferred to the paper not sharp enough. Therefore, after the blanket has worked for a period of time, it must be allowed to “rest” so as not to fatigue it.

3 proofer's own daily maintenance and maintenance

The proofer is generally composed of a mechanical part and an electrical part. For the mechanical part, it is necessary to regularly add lubricants to the fixed oil holes and the transmission parts of the surface (such as the chain) to avoid excessive wear; for the electrical part, it is mainly to check and ensure the smoothness of the gas path, and to maintain The surface of the panel is cleaned and so on.
During the proofing process, the oil black on the roller and the blanket should be cleaned after replacing the ink, and other colors of ink should be added later. Otherwise, the residual ink will be mixed with the added ink and affect the proofing quality. In addition, dust and paper powder near the platen and rules must also be erased on time, because excessive accumulation can affect the accuracy of registration.
Fourth, environmental factors

The influence of environmental factors on the quality of proofing is mainly temperature and relative humidity. If the temperature is too high or too low, the water on the PS plate will evaporate too quickly or too slowly, thus destroying the ink balance. If the relative humidity of the environment is too large or too small, the balance of water and ink will be damaged, and even ink emulsification will lead to the generation of hollow dots. In addition, the more serious is the instability of temperature and humidity will cause the paper to be deformed, resulting in decreased registration accuracy. Therefore, it is very important to maintain constant temperature and humidity in the proofing workshop. In general, the ambient temperature should be 22 °C ~ 23 °C, relative humidity of about 50% of the best.

V. Conclusion

There are many factors that need to be controlled to improve the quality of proofing. The above is only a brief analysis and introduction of some major control methods and empirical data. There are many subtle factors that are not listed one by one. In the proofing process, a small mistake can often lead to the production of scrap. Therefore, a complete and practical management system and operating procedures should be developed for the specific situation of the company or the department, so that the proofing can be on a standardized and data-oriented path. Only in this way can the quality of proofing be stabilized on a high level basis.