Due to the complicated process of pre-press platemaking, there are many factors that affect the final printing quality. In this article, we will discuss the quality control of several of the more important processes and how they will affect the quality of printed matter.
1. Quality control of image scanning
The most basic job of printing is to reproduce colors, and colors are often expressed through pictures. Image scanning is to convert the color information on the picture into digital signals that can be stored and edited by the scanning device, and then process these digital signals through application software such as image processing software and typesetting software. Therefore, whether the image can be copied accurately and with high quality, that is, as much as possible to retain the tone, gradation, contrast and saturation on the original manuscript, is the basic standard to measure the image scanning quality.
Printed manuscripts can be divided into reflective manuscripts and transmissive manuscripts. Among them, reflective manuscripts are divided into photos, prints, hand-painted manuscripts and printed manuscripts, etc .; transmissive manuscripts are divided into positive and negative manuscripts. Since each type of manuscript has different characteristics, the characteristics of each manuscript must be fully considered when scanning the calibration.
Evaluation of image scanning quality:
(1) Definite standards
Accurate calibration of the manuscript is the basis of whether the manuscript can be truly restored, because it is related to the size of the contrast of the entire image and the loss of highlights and dark tones. For example, for transmissive manuscripts, if the contrast of the manuscript is normal, the white field should be selected at the density D = 0.35-0.50; if the manuscript is thin, and the amount of color needs to be emphasized, the white field should generally be selected at the density D = 0.20 -0.35; if the original is dull and needs to be made brighter, the white field should generally be selected at the density D = 0.60-0.80.
(2) Complete tone and high definition
The tone is the hierarchical structure of the whole picture. Complete tone can make the picture complete, because it is easy to lose the gradation in the darkest and brightest places, especially in the edge of the large area of ​​the screen composed of light white, this situation is more likely to occur. If tone is the body of image color reproduction, then the clarity of the image can be said to be the soul of image reproduction. Clarity can focus vision: whether an image is clear is the most important factor for its attention.
(3) Faithful manuscript, higher than manuscript
When the level of the original is rich, the contrast is strong, and the saturation is high, as long as the level, contrast, and saturation of the original can be restored as accurately as possible during scanning. And when the quality of the original is not very good, and even sometimes there is obvious color cast or low saturation, you should pay attention to adjustment when scanning to make the scanned image more real and bright than the original.
2. Quality control of graphic version
(1) To consider the post-process
The graphic version is to combine the scanned pictures and the entered text according to the layout required by the customer. If the production requirements of the subsequent process are not fully taken into account in the assembly process, all the printed products may be scrapped. For example, the bleeding position of general prints is 3mm, and the bleeding position of the packaging box is generally 5mm or 7mm. If you do not follow this standard in the assembly version, it may increase the error rate of the post-processes such as cutting and beer boxes, resulting in unnecessary waste. Another example is when making the cover, if you do not consider the thickness of the paper used for the inner pages and the binding method, it may cause problems such as inappropriate spine or open book cannot be placed on the table.
(2) Be careful, check and ask
Group version is a fairly complicated operation process. Operators should pay high attention to the group version process, otherwise a small mistake may cause a large amount of rework. For example, in the process of making an auction album, because the operator forgot to change the background image of the jade on the picture to a uniform black and white gradient background requested by the customer, all 3000 albums were reprinted. Sometimes the layout provided by the customer is not very clear, or the salesman's label is not too accurate. This requires the operator to check and ask, and can not continue to produce until they are confirmed. Do n’t take it for granted. Because this may cause more trouble.
(3) Increase training efforts and improve rules and regulations
From the above example, it can be seen that the level of group personnel's knowledge of post-process knowledge such as printing is very important, and printing companies need to frequently train post-process knowledge of group plate operators. In addition, sound rules and regulations are essential to clarify responsibilities, reduce error rates, and increase responsibility. [next]
3. Quality control of output
The format produced in the computer needs to be output into a four-color film through a laser imagesetter or directly into a printing plate through a computer plate making machine (CTP), or a digital proofing sample can be output through a digital proofing machine. No matter what the output is, the error rate of this process may be the highest. Several aspects that are prone to errors in the output process:
(1) Text, pictures
Text output problems are the most common in the output process. Text garbled characters, text misalignment, text leakage, and font errors often occur. These are mainly caused by fonts, output software, output parameter settings, and output devices. In the output process, the problems that appear in the pictures are mainly wrong pictures and missing pictures.
How can there be fewer or no errors when outputting text and pictures? The author believes that the font on the page should be carefully checked before the output, whether the link of the picture is accurate, and then the text on the background, Whether the color patch is set to "fill trap"; the next thing to note is that the software used for the group version and output is preferably a commonly used typesetting software, such as PageMaker or QuarkExpress. If you use graphics software to output, not only the output speed may be It's slow, and the possibility of errors increases.
(2) Output device
Output devices are also often the main cause of errors. If the density of the dots or the percentage of dots is incorrect when the laser imagesetter outputs the film, it may be that the concentration of the potion is not accurate or the film characteristic curve on the RIP software needs to be reset. For digital proofers, if the color of the proofs shows a significant deviation, it may indicate that the profile generated during the previous color management is not consistent with the current situation. Therefore, before outputting the file, it must be ensured that the output device is in the best state, and the material used is consistent with the characteristic curve or characteristic file applied by the software.
4. Quality control of proofing
Proofing plays a role of inheritance, it is very important for printing. It can not only check the previous image scanning, text entry, layout, etc., but also a standard for subsequent printing. Because proofing is analog printing (whether traditional proofing or digital proofing), proofing proofs will definitely be different from the final print, but there is a principle that must be followed is that printing can catch up with proofing. Therefore, the quality of the proofs and the size of the difference with the printed product will have a great impact on printing.
So, how to control the quality of proofing to make printing easy to keep up with proofing? The following uses traditional proofing as an example to discuss this issue:
(1) Field density control
The field density value is the most important technical parameter for controlling network replication and restoration. Different companies have their own different technical indicators and error ranges. This technical index is determined by each company according to its own specific situation. Generally, the solid density of each color version is Y: 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 ± 0.05.
(2) Control of the increase of the dots
The dot increase value is also the key to controlling the proofing quality, because the proofing machine uses the round flattening method, while the printing machine uses the round flattening method. Obviously, the pressure of the round pressing method is greater, so in general, the dot increase value of the printed matter is larger than the proof.
Therefore, the dot increase value should be strictly controlled during proofing, otherwise the printed product will have a large color deviation.
(3) Adjustment of the proofer
①The pressure of the rubber roller is ± 0.03mm (measured every 120 degrees, and the average value is taken), that is: the thickness of the rubber cloth and the thickness of the pad = (2.286 ± 0.030) mm;
â‘¡ The platen 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;
â‘¢The pressure of the paper table (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;
â‘£ There are two rollers on both sides of the movable frame. When the frame moves to the side of the ink leveling system and the machine is not pressurized, the pressure between the roller and the lower rail surface can be rotated by just applying force. , Too tight and too loose need to be adjusted;
⑤ Ink leveling system: The width of the ink stick of the inking roller on the plate or paper table should be uniform.
For digital proofing, the ink used for proofing is different from the ink used for printing. In addition, the dots of digital proofing are FM dots rather than the commonly used amplitude modulation dots for printing, so in analog printing, only through the color management system (CMS) Match the proofed color space with the printed color space to simulate the printed color. However, at present, several digital proofing machines that are commonly used are unable to achieve spot color proofing, which is inevitably a major flaw.
In summary, any step in the prepress platemaking process that is not well controlled may affect the quality of the printed matter. In addition to the aforementioned, there are many other factors that may cause problems in printing and cause a lot of losses, such as the control of the operating temperature and humidity, the maintenance of equipment and the quality of raw materials. Therefore, we can't care about any subtle link. Only by controlling each step can we provide qualified products for the subsequent printing process, and provide quality assurance for adding TT sequence after binding.
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