Prepress Plate Quality Control and Its Effect on Printing Effect (2)

Third, the output of quality control

The layout produced in the computer needs to be output as a four-color film by a laser imagesetter or output by a computer-to-plate (CTP) printer or a digital proofer. Whatever the output, the error rate for this process may be the highest. Several aspects that are prone to errors in the output process:

(1) Text, picture

Text problems in the output process are the most common, often appear text garbled, text walk, text leakage and font errors, these are mainly caused by the font, output software, output parameter settings and output devices. The problems that appear in the output during the output process are mainly wrong and missing graphs.

How can we reduce or eliminate errors in outputting texts and pictures? The author believes that before outputting, we must first carefully check whether the fonts on the pages are replaced with good ones, whether the links in the pictures are accurate, and then check the text on the background. Whether or not the color patch has set "Trap White"; the next thing to notice is that the software used in the version and output is preferably commonly used typesetting software, such as PageMaker or QuarkExpress. If you use the graphics software to output, not only the output speed may be It is slow and the possibility of errors increases.

(2) Output device

Output devices are also often the main cause of errors. For example, if the density or the percentage of dots in the laser image-setter is not correct when the film is being output, it may be that the concentration of the drug is inaccurate or the film characteristic curve on the RIP software needs to be reset. For digital proofing machines, if the color of the proofs is obviously biased, it may indicate that the profile generated by the previous color management is not consistent with the current situation. Therefore, before outputting the file, you must ensure that the output device is in the best condition and that the material used is the same as the characteristic curve or characteristic file used by the software.

Fourth, proofing quality control

Proofing plays a role that is linked to the past and is crucial for printing. It can check the previous image scanning, text entry, layout, etc. It is also a standard for subsequent printing. Since the proofing is analog printing (regardless of traditional proofing or digital proofing), proofing proofs must be different from the final printed matter. However, one of the principles that must be followed is that the proofs should be able to catch up with proofs. Therefore, the quality of the proofs and the size of the difference from the printed product will have a great impact on printing.

So, how to control the quality of proofing can make printing easy to keep up with the proofing? Here we discuss the problem with traditional proofing as an example:

(1) Control of density in the field

The field density value is the most important technical parameter for controlling network copy and restoration. Different companies have their own different technical indicators and error ranges. This technical index is determined by each company based on its own specific circumstances, the general field density of each color version is Y: 1.30, M: 1.45, C: 1.50, K: 1.80. As for the margin of error, the standard in Europe is 0.07 for soil, while the error for a company in China is said to be within ±0.05.

(2) Control of dot gain

The dot gain value is also the key to control the quality of the proofing, because the proofer uses a round flattening method, and the press uses a circular rounding method. Obviously, the pressure of the circular pressure method is greater, so in general the dot gain of the printed matter is larger than that of the proofing.

Therefore, the dot gain value must be strictly controlled during proofing, otherwise the printed product will have a large color deviation.

(3) Adjustment of proofer

1 The pressure of the blanket cylinder is ±0.03mm (measured every 120 degrees, taking the average value), ie: the thickness of the blanket is ten liner thickness=(2.286±0.030)mm;
Version 2 pressure (including PS plate thickness) is +0.12~+0.15 mm, that is, the surface of the PS plate is higher than the height of the guide rail;
3 paper pressure (including the thickness of the paper) is +0.15~+0.18mm, that is, the surface of the paper is higher than the height of the guide rail;
4 There are two rollers on both sides of the active rack. When the rack is moved to the side of the ink distribution system, and the machine is not pressurized, the pressure on the roller and the lower rail surface can be turned by hand. , Too tight and too loose must be adjusted;
5 even ink system: ink roller on the platen or paper table, the width of the bar should be uniform.

For digital proofing, the ink used for proofing is different from the printing ink. In addition, the digital proofing sites are the FM network points rather than the commonly used amplitude modulation network points. Therefore, in terms of analog printing, only the color management system (CMS) is adopted. The color space of the proof is matched with the printed color space to simulate the color of the print. However, several digital proofers currently in widespread use cannot implement spot color proofing. This cannot but be said to be a major flaw.

In summary, any one step in the pre-press process may not affect the quality of the printed matter. In addition to the previously mentioned, there are many other factors that may cause problems in the printing, causing a lot of losses, such as the temperature and humidity control of the operating environment, equipment maintenance and the quality of raw materials. Therefore, for any subtle link can not be taken care of, only the control of each step in order to provide qualified products for the printing process, to provide quality assurance after binding TT order.