Plate making quality before the most popular print

  • Detail

Editor's note: there are many factors that affect the quality of printed matter, but if there are problems in the process of prepress plate making, it is impossible to produce qualified printed matter even if the printing materials used are good, the quality of the printing machine is high, and the binding is exquisite. Prepress plate making is the premise of producing qualified prints. If there is a problem in a certain link of the prepress plate making process, it may cause great trouble to the post process, or even irreparable losses

because the process of prepress plate making is very complex, there are many factors that affect the quality of final printed matter. In this paper, we will discuss the quality control of several important processes and how they affect the quality of printed matter

I. quality control of image scanning

the most basic work 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 storable and storable digital signals through scanning equipment, and then process these digital signals through image processing software, typesetting software and other application software. Therefore, whether the image can be accurately copied with high quality, that is, to retain the information of tone, level, contrast and saturation on the original as much as possible, is the basic standard to measure the quality of image scanning

the printed manuscript can be divided into two types: the reflective manuscript and the transmission manuscript measured to 2kg: Pb at 410kg. Among them, the reflection manuscript is divided into photos, printed matter, hand-painted manuscript and printed manuscript, etc; Transmission manuscript is divided into positive film and negative film. Because each type of manuscript has its different characteristics, the characteristics of each type of manuscript should be fully considered when scanning and calibrating

evaluation of image scanning quality:

(1) setting the standard to ensure that the accurate calibration of the original is the basis of whether the original can be truly restored, because it is related to the size of the whole image contrast and the loss of highlight and dark tone. For example, for transmission originals, if the contrast of the originals is normal, the white field should be selected at the place where the density d= strength is greater than the industry's hunch of 0.35-0.50; If the original is too thin and the color quantity needs to be increased, the white field should generally be selected at the density d=0.20-0.35; If the original is stuffy 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

tone is the hierarchical structure of the whole picture. A complete tone can make the picture complete, because it is easy to lose layers in the darkest and brightest places, especially at the edge of a large area of light white picture. If the tone is the body of image color reproduction, then the sharpness of the image can be said to be the soul of image reproduction. Sharpness can make vision concentrated: whether an image is clear is the most important factor to attract attention

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

when the original has rich levels, strong contrast and high saturation, as long as the level, contrast and saturation of the original can be restored as accurately as possible during scanning. When the quality of the original is not very good, and sometimes there will be obvious color deviation or low saturation, pay attention to adjustment during scanning, so that the scanned image is more realistic and bright than the original

II. Quality control of image and text composition

(1) the post process should be considered

image and text composition is to combine the scanned pictures and the entered text according to the arrangement required by the customer. If the production requirements of the post process are not fully considered in the process of plate assembly, all the printed products may be scrapped. For example, the bleeding position of general printed matter is required to be 3mm, while the bleeding position of packaging box is generally 5mm or 7mm. If you don't follow this standard when assembling plates, you may increase the error rate of post processes such as cutting and beer boxes, resulting in unnecessary waste. Another example is that when making the cover, if the thickness and binding method of the paper used for the inner page are not considered, it may cause problems such as improper spine or the opened book cannot be placed flat on the table

(2) be careful and ask more questions

version assembly is a very complex operation process. Operators should pay high attention in the process of version assembly, otherwise a small mistake may lead to mass rework. For example, in the process of making an auction album, all 3000 albums were reprinted because the operator forgot to replace the background image of jade on the picture with the black-and-white gradient background required by the customer. Sometimes the layout samples provided by customers are not very clear, or the salesperson's marks are not too accurate, which requires the operator to check and ask more, and the production can continue until it is confirmed. Never take it for granted, make your own decisions or be afraid of trouble, because this may cause greater trouble

(3) increase training efforts and improve rules and regulations

from the above example, it can be seen that the knowledge of post process knowledge such as printing is very important for the printing staff. Printing enterprises need to often train the post process knowledge for the printing staff. In addition, perfect rules and regulations are also essential to clarify responsibilities, reduce error rates and enhance confidence

III. quality control of output

the layout made in the computer needs to be output into four-color film through the laser typesetter or into a printing plate through the computer direct plate making machine (CTP), and the digital proofing sample can also be output through the digital proofing machine. No matter what the output is, the error rate of this operation may be the highest. There are several aspects that are easy to make mistakes in the output process:

(1) text and pictures

text problems are the most common in the output process, and text garbled, text misplaced, text leakage and font errors often occur, which are mainly caused by word libraries, output software, output parameter settings and output equipment. In the process of output, the problems of pictures are mainly wrong pictures and missing pictures

how can I output words and pictures with fewer or no errors? The author believes that before output, we should first carefully check whether the fonts on the page are replaced well and whether the links of pictures are accurate, and then check whether the text and color blocks on the background color have set "trapping"; Next, it should be noted that the software used for composition and output is preferably common typesetting software, such as PageMaker or quarkexpress. If you use graphics software to output, not only the output speed may be very slow, but also the possibility of errors will be increased

(2) output device

output device is often the main cause of errors. If the density or percentage of the point when the laser Imagesetter outputs the film is incorrect, it may be that the concentration of the liquid medicine is incorrect or that the film characteristic curve on RIP software needs to be reset. For the digital proofing machine, if the color of the sample has obvious deviation, it may indicate that the profile generated during the previous color management is not consistent with the current situation. Therefore, before outputting documents, it is necessary to ensure that the output equipment is in the best state, and that the materials used are consistent with the characteristic curves or characteristic documents applied by the software

IV. quality control of proofing

proofing plays a connecting role, which is very important for printing. It can not only check the image scanning, text input, layout, etc., which are difficult to expand the production of the salt lake in front, but also a standard for subsequent printing. Since proofing is analog printing (whether traditional proofing or digital proofing), proofing proofs will be different from the final printed matter, but one principle that must be followed is that printing can catch up with proofing. Therefore, the quality of proofs and the difference between proofs and printed products will have a great impact on printing

then, how to control the quality of proofing so that printing can easily keep up with proofing? The following takes traditional proofing as an example to discuss this problem:

(1) control of field density

field density value is the most important technical parameter for control point 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 specific situation. Generally, the field 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, while it is said that the error range of a domestic company is controlled within ± 0.05

(2) control of point increase value

point increase value is also the key to control the proofing quality, because the proofing machine adopts the method of circular flattening, while the printing machine adopts the method of circular flattening. Obviously, the pressure of round pressing is greater, so generally speaking, the dot increment value of printed matter is larger than that of proofing

therefore, it is necessary to strictly control the point increase value during proofing, otherwise the printed matter will have a large color deviation

(3) adjustment of the proofing machine

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

② the platen pressure (including the thickness of PS platen) is +0.12~+0.15 mm, that is, the height of PS platen surface above the guide rail

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

④ there are two rollers under both sides of the movable frame. When the frame moves to the side of the inking system and the machine is not pressurized, the pressure between the roller and the lower guide rail surface should be adjusted if it can rotate with manual force, and if it is too tight or too loose

⑤ inking system: the width of the ink bar of the inking roller on the plate or paper table should be uniform

for digital proofing, because the ink used for proofing is different from that used for printing, and in addition, the point of digital proofing is the frequency modulation point rather than the commonly used amplitude modulation point for printing, so in terms of analog printing, only the color space of proofing is matched with the color space of printing through the color management system (CMS) to simulate the color of printing. However, at present, several digital proofing machines, which are widely used in new material enterprises above Shandong Province and have achieved sales revenue of more than 500 billion yuan, cannot achieve spot color proofing, which cannot be said to be a major defect

to sum up, the quality of printed matter may be affected if any step in the prepress plate making process is not well controlled. In addition to the above mentioned, 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 working environment, the maintenance of equipment and the quality of raw materials. Therefore, we can't be careless about any subtle link. Only by controlling every step can we provide qualified products for the subsequent printing process and provide quality assurance for the subsequent TT process such as binding

Copyright © 2011 JIN SHI