Prepress Plate Quality Control and Impact on Printing

1. introduction

There are many factors that affect the quality of printed matter. However, if problems arise during the prepress process, it is impossible to produce qualified prints even if the printed materials used are no better, the quality of the press is higher, and the binding is finer. Prepress plate making is the precondition for producing qualified prints. If there is a problem in a certain part of the pre-press platemaking process, it may cause great troubles or even irreversible losses to the subsequent process.

Because the process of prepress plate making is very complex and affects the quality of the final print product, the author discusses the quality control of several of the more important processes and how they affect the quality of the printed matter.

2. Image Scanning Quality Control

The most basic job of printing is copying colors, which are often expressed through pictures. Image scanning is to convert the color information on a picture to a storable and editable digital signal through a scanning device, and then process these digital signals through application software such as image processing software and typesetting software. Therefore, whether or not the image can be accurately reproduced with high quality, ie, the information such as tone, gradation, contrast, and saturation on the original as much as possible, is a basic standard for measuring the quality of image scanning. Printed manuscripts can be classified into reflective and transmissive manuscripts. Among them, reflective drafts are divided into photographs, prints, hand-drawn drafts, and drafts, etc.; transmissions are divided into positive and negative films. Since each type of manuscript has its own different characteristics, the characteristics of each manuscript must be fully taken into account when scanning the calibration.

Image scan quality evaluation:

(1) accurate calibration

Accurate calibration of the original document is the basis for the true restoration of the original, because it is related to the size of the entire image contrast and how much loss of highlights, dark tone and other issues. For example, for a transmitted original, if the contrast of the original is normal, the white field should be selected at a density of D: 0.35-0.50; if the original is thin, the amount of color needs to be increased, and the white field should generally be selected at a density of D: 0.20. - 0.35; If the original is more boring, need to be brighter, white field should generally choose the density D: 0.60-0.80. (2) Complete adjustment and high resolution

Tonality is the hierarchical structure of the entire picture. A complete tone can make the picture complete, because it is easy to lose the level in the darkest place and the brightest place, especially in the edge area of ​​a large area composed of pale white, this situation is more likely to occur. If the tone is the body of image color reproduction, then the clarity of the image can be said to be the soul of image reproduction. Sharpness can focus on vision: whether an image is clear is the most important factor in whether it can attract attention.

(3) faithful manuscripts, higher than manuscripts

When the manuscript has a rich gradation, strong contrast, and high saturation, it is sufficient to restore the gradation, contrast, and saturation of the original as accurately as possible during scanning. When the quality of the original is not very good, and sometimes there is even a clear cast color or low saturation, attention should be paid to the adjustment during scanning, so that the scanned image is more real and bright than the original.

3. Graphic Group Quality Control

(1) Consider the process

Graphic group edition is to combine the scanned image and the entered text according to the requirements of the customer. If the production requirements of the post-process are not fully taken into account in the process of group printing, all the printed products may be scrapped. For example, the bleeding level in general prints is 3mm, and the bleeding volume in the box is generally 5mm or 7mm. If you do not follow this standard at the time of group edition, you may increase the error rate of post-processes such as cutting, beer boxes, etc., resulting in unnecessary waste. Another problem is that when the cover is created, if the thickness of the paper used on the inner page and the binding method are not taken into consideration, it may cause the problem that the spine does not fit or the opened book cannot be placed on the table.

(2) Be careful and ask more questions

The group edition is a very complicated operation process. The operator must pay attention to the high concentration during the group edition. Otherwise, a small mistake may lead to large-scale rework. For example, during the production of an auction book, the operator forgot to replace the background image of the jade on the picture with a uniform black and white gradient background, resulting in the reprint of all 3,000 pictures. Sometimes the layout style provided by the customer is not very clear, or the salesman's label is not very accurate, which requires the operator to check more and ask more questions, and can't continue to make it until it is confirmed. Do not take it for granted, make your own claims or be afraid of trouble. Because this may cause more trouble.

(3) Increase training and improve rules and regulations

From the above example, it can be seen that the level of understanding of the post-process knowledge of the printing press is very important for the group's printing staff. The printing company Confucianism often conducts post-process knowledge training for the group's operating personnel. In addition, perfect rules and regulations are also essential to clarify responsibilities, reduce error rates, and increase accountability.

4. Output 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. There is no set "color trapping" in the color blocks; 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.

5. Proof quality control

Proofing plays a role that is linked to the past and is crucial for printing. It can check the previous image scan, 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: 1.30, M: 1.45, C: 1.50, K: 1.80. As for the error range, the European standard is ±0.07, and it is said that the error range of a domestic company is controlled within the range of 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 soil (measured once every 120', averaged), that is: blanket thickness + liner thickness: (2.286 ± 0.030) mm;

Version 2 pressure (including PS plate thickness) is +0.12-+0.15mm, 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.

6. Conclusion

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 one 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 for binding and other post-processing processes.