Exquisite Picture Book Quality Control Of Prepress Platemaking And Its Influence On Printing Effect

Exquisite Picture Book quality control of prepress platemaking and its influence on printing effect

 

Editor's note: There are many factors that can affect the quality of a printed matter, but if something goes wrong in the prepress process, no matter how good the printing materials used, the quality of the press, or the fine binding, it is impossible to produce a qualified printed matter. Prepress platemaking is the prerequisite for the production of qualified printed matter. If there is a problem in one part of the prepress process, it may cause great trouble or even irreparable loss to the later process.

Due to the complex process of prepress platemaking, there are many factors affecting the quality of final printed matter. In this paper, we will discuss the quality control of several important processes and how they will affect the quality of printed matter.

 

First, image scanning quality control

The most basic job of printing is the reproduction of color, and color is 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 scanning equipment, and then process these digital signals through image processing software, typesetting software and other application software. Therefore, it is the basic standard to measure the quality of image scanning whether the image can be reproduced accurately and with high quality, that is to say, the information of tone, level, contrast and saturation on the original manuscript can be preserved as much as possible.

 

The printed manuscript can be divided into two kinds: reflected manuscript and transmitted manuscript. Among them, reflection manuscripts are divided into photos, prints, hand-drawn manuscripts and printed manuscripts and so on; Transmission is divided into positive film and negative film. Since each type of manuscript has its different characteristics, it is necessary to take the characteristics of each manuscript into full consideration when scanning and calibration.

 

Evaluation of image scanning quality:

(1) Accurate calibration

Accurate calibration of the original manuscript is the basis of the true restoration of the original manuscript, because it is related to the size of the contrast of the whole image and the loss of highlights, darktones and other issues. For example, for the transmission manuscript, 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 color quantity needs to be increased, the white field should be chosen at the density D= 0.20-0.35. If the manuscript is boring, it needs to be brighter, and the white field should be chosen at the density D= 0.60-0.80.

 

(2) Complete level adjustment, high clarity

The tone is the hierarchy of the whole picture. Complete level can make the picture complete, this is because it is easy to lose layers in the darkest and brightest areas, especially in the large area of the edge of the picture composed of light white, more prone to this situation. If the tone is the image color reproduction of the body, then the image clarity can be said to be the image reproduction of the soul. Sharpness focuses vision: The clarity of an image is the most important factor in its ability to attract attention.

 

(3) loyal to the original, higher than the original

When the level of the original is rich, strong contrast, high saturation, as long as the scan can be as accurate as possible to restore the level of the original, contrast and saturation. When the quality of the original manuscript is not very good, and sometimes there will be obvious color bias or low saturation, it is necessary to pay attention to the adjustment when scanning, so that the scanned image is more real and bright than the original manuscript.

 

Two, text and text group version quality control

(1) To consider the post-process

Graphic group version is to scan the picture and input text in accordance with the customer's requirements of the row combination. If the production requirements of the post-process are not fully taken into account in the process of plate formation, it may cause all the printed products to be scrapped. If the bleeding position of the general print is 3mm, the bleeding position of the packaging box is generally 5mm or 7mm. If the group version is not done according to this standard, it may make cutting, beer box and other procedures after the error rate increase, causing unnecessary waste. For example, when making the cover, if you do not consider the thickness of the paper used in the inner page and the binding way, it may cause the spine is not suitable or the open book can not be placed on the table, etc.

 

(2) Be careful and ask more questions

Building a version is a very complex operation process, the operator should be highly focused in the process of building a version, otherwise maybe a small mistake will lead to a large number of rework. For example, in the process of making an auction album, the operator forgot to change the jade background picture on the picture to the uniform black and white gradient background required by the customer, so all 3,000 copies of the album were reprinted. Sometimes the version provided by the customer is not very clear, or the salesman is not too accurate, which requires the operator more check more ask, until confirmed to continue to produce, do not take it for granted, or afraid of trouble, because it may cause more trouble.

 

(3) Increase training and improve rules and regulations

As can be seen from the above example, it is very important for platemaking personnel to understand the knowledge of printing and other post-process, and printing enterprises need to train platemaking operators of post-process knowledge frequently. In addition, perfect rules and regulations are essential to clarify responsibilities, reduce error rate and enhance responsibility. [next]

 

3. Quality control of output

The format produced in the computer needs to be output into four color film through the laser phototypesetter or output into the printing plate through the computer direct platemaking machine (CTP), also can output digital proofing proof through the digital press. This process probably has the highest error rate of any output. Some aspects that are prone to error in the output process:

 

(1) Text and pictures

Text problems are the most common in the output process, often occur text garbled, text walking, text leakage and font errors, these are mainly caused by the font library, output software, output parameter setting and output equipment. The main problems in the output process are wrong picture and missing picture.

 

How can you export text and pictures with few or no errors? I think, first of all, before the output to carefully check whether the font on the page is good instead of the link of the picture is accurate, and then check the text on the background color, color block is not set "white"; Next, it should be noted that the software used for organizing and output should be commonly used typesetting software, such as PageMaker or QuarkExpress. If graphics software is used for output, not only the output speed may be slow, but also the possibility of errors will be increased.

 

(2) Output device

Output devices are also often the main cause of errors. Such as laser phototypesetter in the output of film dot density or dot percentage is not correct, it may be the potion concentration is not allowed or RIP software on the film characteristic curve needs to be reset. For the digital proof machine, if the color of the proof appears more obvious deviation, it may indicate that the previous color management generated by the Profile and the current situation has been inconsistent. Therefore, before the output file must ensure that the output device is in the best state, to ensure that the material used and software applied characteristic curve or characteristic file is consistent.

 

Four, proofing quality control

Proofing is a link between the previous and the next, it is very important for printing. It can not only check the previous image scanning, text input, layout and so on, but also a standard for post-sequence printing. Because the proofing is analog printing (whether traditional proofing or digital proofing), the proofing proof is bound to be different from the final print, but there is a principle that must be followed is that the printing can catch up with the proofing. Therefore, the quality of the proof and the size of the difference between the printed product and the printed product will have a great impact on the printing.

 

So, how to control the quality of proofing in order to make printing easy to follow the proofing? The following is an example of traditional proofing to discuss this problem:

(1) Control of field density

Field density value is the most important technical parameter to control dot replication and restoration, and different companies have their own different technical indicators and error ranges. This technical index is determined by each company according to its own specific conditions. Generally, the field density of various versions is Y: 1.30, M: 1.45, C: 1.50, K: 1.80. As for the margin of error, the European standard is 0.07 soil, while a domestic company is said to control the margin of error within the range of ± 0.05.

 

(2) Control of dot increase value

Dot increase value is also the key to control the quality of proofing, because the press is using the way of circular pressing, and the printing press is using the way of circular pressing. Obviously, the pressure of circular pressing is greater, so generally speaking, the dot increase value of printed matter is larger than that of proofing.

 

Therefore, in the proofing to strictly control the dot increase value, otherwise printed matter will produce a large color deviation.

 

(3) adjustment of the prototype

(1) The pressure of the rubber drum is ± 0.03mm (measured every 120 degrees, take the average), that is, the thickness of the rubber blanket ten padding =(2.286 ± 0.030)mm;

(2) The plate pressure (including PS plate thickness) is + 0.12 ~+ 0.15mm, that is, the PS plate surface is higher than the height of the guide rail;

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

(4) There are two rollers under both sides of the movable frame. When the frame is moved to one side of the ink leveling system and the machine is not pressurized, the pressure between the roller and the lower guide surface should be adjusted as long as the hand force is just enough to rotate.
⑤ Ink leveling system: inking roller in the plate or paper table ink bar width should be uniform.

 

For digital proofing, because the ink used for proofing and printing ink are different, in addition, digital proofing dot is frequency modulation dot rather than the commonly used amplitude modulation dot in printing, so in analog printing, it is only through the color management system (CMS) to match the color space of proofing and the color space of printing to simulate the color of printing. However, at present is widely used several digital proofing machine can not achieve spot color proofing, which can not be said to be a larger defect.

 

To sum up, any step in the prepress platemaking process that is not well controlled may affect the quality of the printed matter. In addition to what has been mentioned above, there are many other factors that may lead to problems in printing and cause a lot of losses, such as the control of temperature and humidity in the operating environment, equipment maintenance and the quality of raw materials. Therefore, for any small link can not be careless, only every step is well controlled in order to provide qualified products for the printing process, binding and other after TT sequence to provide quality assurance.