In recent years, many domestic enterprises have obtained ISO-9000 quality management and quality assurance system standard certification. The printing industry is no exception, and many printing plants have also passed certification, improving the management level of the current low enterprises. However, the ISO-9000 series of standards belong to the common standards of all business sectors, focusing on enterprise management, and lack of technical and production process control content. On the basis of obtaining ISO-9000 certification, printing companies should further standardize the pre-press and printing processes in accordance with the requirements of the offset printing process standards to ensure that printing companies are in a competitive advantage.
The standardization work of China's printing industry has been carried out for nearly 20 years. It has established a standardization management agency-the National Printing Standardization Technical Committee, and joined the ISO International Standardization Organization TC130 Printing Technical Committee. It has been recruited as an active member. As of 2004, China has issued 29 current national standards on printing and 20 industry standards. Five of these new standards are made using international standards and have high practical value. It is particularly worth mentioning that the national standard GB / T 17934-2-1999 "Processing Control of Printing Technology Mesh Separation Separation Films, Proof Sheets and Printed Products Part 2: Offset Printing", which is issued by the State Administration of Press and Publication It is proposed that the National Printing Standards Committee organizes the drafting of the Institute of Printing, which is equivalent to the international standard ISO12647-2 "Offset Printing Process Control". This is the most advanced offset printing standard in line with international standards. The National Quality and Technical Supervision Bureau approved the standard in December 1999 and implemented it on August 1, 2000. China is one of the first member countries in the world to convert ISO-12647-1 and 2 into national standards.
Interpretation of the advanced nature of ISO-12647-2
This international standard is organized by ISO's TC 130 Printing Technology Committee to organize the most advanced printing technology countries in the world, such as printing research institutions in Germany, the United States, Switzerland, the United Kingdom, and Japan. Experts and scholars from printing associations, printing schools and well-known printing companies drafted and worked together. After five years of extensive discussions among member states, several drafts were drafted, and in 1996, they were finally approved by more than 75% of the members after voting by member states. From the point of view and thinking of formulating standards, international standards are fundamentally different from the standards formulated by China itself, for example, GB / T 7705-1987 "Lithographic Decoration Printed Products" standard and CY / T5-1999 "Lithographic Printing Quality Requirements and The two methods of "Inspection Method" related to the quality standards of offset printing both focus on the technical parameters such as the appearance, specifications, overprinting error, solid density, relative contrast value, dot increase rate and other technical parameters of the printed product. By measuring and inspecting the printed matter after printing is completed, the purpose of controlling printing quality is achieved. In fact, these standards do not play a role in controlling many factors that affect printing quality before printing; compared with international advanced standards, our standard setting work still needs to be improved and improved.
How is the ISO 12647-2 (International GB / T 17934-2-1999) standard formulated? Where is the focus of its technical requirements? In the technical requirements clause of the standard, the quality of the dichroic film and the number of network cables are first specified. It is specified in the quality section; "The density value of the center of the dots of the color separation film should be at least 2.50 higher than the density value of the transparent film (base plus fog), and the transmission density of the center of the dots should not be higher than the density value of the film (base plus (Fog) above 0.1, the density value of transparent film (film base plus fog) should not be higher than 0.15. "
The color separation film is the initial factor that affects the quality of offset printing products. The density value of the center of the standard standard dot is at least 2.50 higher than the density value of the film, so as to ensure that the dots on the color separation film are correctly transferred to the printing plate.
The standard also stipulates the network cable and the angle of the network cable. The web journal printing is 45 to 60 lines cm, and the commercial printing is 60 to 80 lines / cm. The requirements for the screen angle are: "For the dots without a spindle, the difference between the dots of the cyan, magenta, and black versions should be 30 °. The difference between the dots of the yellow version and the other color versions should be 15 °. Is 45 ° ". Specifying the difference in dot angle before printing can prevent moire in four-color printing. There are no specific requirements and regulations for these two items in the national standard and the line standard.
In order to ensure the accuracy of overprinting, the standard puts forward requirements on the image size error of the color separation film: "Under the condition of stable environment, the difference of the diagonal length of a set of color separation film should not be greater than 0.02%." To ensure that this error is not exceeded, it is necessary to control the temperature and humidity of the operating environment, ensure that the color separation film is stable in size, and prevent expansion and contraction.
In order to prevent the phenomenon of low multi-printing ink overprint rate, back-through printing and back-face sticking, the standard sets the total tone value of the color separation film as follows: "The sum of the tone values ​​of single-sheet printing should not exceed 350%. The sum of the tone values ​​of web printing should not exceed 300%. " Before printing, the background color removal method is adopted to ensure that the above-mentioned sum of tone values ​​is met, which creates favorable conditions for printing.
The gray balance is determined by the cyan, magenta, and yellow tone values ​​of the image, as well as their color and the color of the overprint. If the printed matter is gray under the specified observation conditions, the cyan, magenta, and yellow tone values ​​(dot area) on the dichroic film are in a gray balance state. The gray balance tone values ​​specified in the standard are shown in the table below.
green(%)
magenta(%)
yellow(%)
1/1 tone
25
19
19
2/4 tone
50
40
40
3/4 tone
75
64
64
However, our country's standards do not stipulate the important requirement of gray balance tone value.
Regarding the quality requirements of printed matter, the standard provides requirements and measurement methods for the color gloss of substrates (such as paper). First, determine the CIELAB color space value (L *, a *, b *), color difference value (â–³ Eab), gloss and allowable error of the unprinted paper itself. Corresponding regulations are made for the color space, gloss, brightness, and grammage of five typical papers.
There are corresponding requirements for the color and gloss of the ink. The CIELAB chromaticity values ​​L *, a *, b * of the red, green, and blue solid colors obtained from the five specified papers for proofing, the four solid colors of cyan, magenta, yellow, and black on the proof sheet, and the two-color overprinting shall conform to The specified value. The solid color difference of printing primary colors is △ Eab; black deviation is 4, cyan is 5, magenta is 8, yellow is 6.
The standard requires that the gloss of the solid color should be the specular gloss of the substrate or monochrome solid measured under the conditions of 75 ° incidence angle and 75 ° acceptance angle. The measuring instruments used in the standard shall comply with GB / T 8941. 3 international regulations, and the measured values ​​shall be expressed as a percentage. China's standards do not have such detailed requirements for paper and ink.
In addition, the range of tone reproduction, that is, the reproduction range of halftone dots, is stipulated according to the number of screen lines. For example, if the number of screens is between 40 and 70 lines / cm, the screen dots with a color separation area rate of 3% to 97% can be completely printed on the paper; the screen screens are 80 lines / cm and the screen area rate is 55 % To 95% of the outlets can be completely reproduced.
Regarding the increase in tone, that is, the increase in dots, the standard specifies the increase in tone of the printed matter. According to the measurement and control bar listed in the standard, the value of the tone increase at 50% is selected, and the corresponding value is selected as the target value. For example, the number of online dots on the measurement and control bar is 60 lines / cm, and the tone increase value (percentage) at the tone value of 50% is as follows; the positive plate for color printing of web journals (type 3 paper: glossy coated paper) 19; commercial color printing is 17, using type 1 and type 2 coated paper and positive plate is 19 (where color printing requires the black version to be 2% to 3% higher than other color versions). The CY / T5 industry standard stipulates the increase of the dots in a wide range, between 10% and 25%, and no target value is specified.
Overprint accuracy is an important indicator of print quality standards. The overprint error specified in the first edition of CY / T5 is wider. After being revised in 1999, it is stipulated that the overprint error of fine printed matter is ≤0.10mm, and the allowable error of general printed matter is ≤0.20mm. The "image position error" specified in the ISO-12647-2 international standard is completely different from the overprint allowable error specified in the Chinese standard in concept. For example, international standards stipulate: "The maximum positional error between the centers of any two-color printed images must not be greater than half the minimum dot width of the four-color dichroic film." This type of overprint accuracy requirements are much higher than the requirements of our national standards. If the above-mentioned overprint accuracy cannot be achieved due to equipment and other reasons, the international standard allows the printing plant and the customer to reach the necessary agreement.
From the above analysis and comparison of the main contents of the two standards, ISO-12647-2 is the most advanced international offset printing process control standard in the world today, and China's printing industry should vigorously promote this standard. In order to occupy the quality advantage in the fierce competition, the printing plant should actively adopt this international standard and strive to be in line with international standards in product quality management.
German ISO-12647-2 offset printing process standard certification
Germany is one of the most developed countries for standardization, and DIN (abbreviation) is the code name for the German industrial standard. The German printing industry established a series of standards very early, covering almost all the technology and production processes of the printing industry. Many printing standards have been adopted by ISO and transformed into international standards. For example, ISO-12647-2 is code-named DIN ISO 12647-2 in Germany.
According to the German Printing and Media Association's instructions for the certification of offset printing process control standards, if someone in Germany asks the printing house what standard to print, most of them hear the concept of the European color standard. This concept is mostly used for offset printing European color standard (DIN 16539), but the standard is now invalid. Today, the color performance of primary color inks is specified in the DIN ISO 2846-1 standard, which is the color performance of primary color inks on the ground based on DIN 16539, so this standard is incomplete and insufficient as the only standard.
Since October 2001, a new offset printing process standard has been produced. This standard describes the entire process of production from data collection to printing. It was jointly developed by the German Printing and Media Association and the Fogra Institute. The ISO 12647-2 series of standards stipulates offset printing parameters, allowable errors and measurement methods. The standard was developed on an international basis, and media standards have also been specially developed.
If the producer of the printed manuscript does not have the necessary printing expertise and does not work in accordance with the media standards and offset printing process standards, it will be difficult to ensure the later printing quality. More and more platemakers and printing houses have recognized this problem, and many The customer has asked the printing house to produce in accordance with ISO 12647-2 to ensure the printing quality. Therefore, the Printing Association and Fogra Research Institute jointly awarded certificates to companies that produced in accordance with the ISO 12647-2 offset printing process standards, and issued certificates valid for two years for companies that comply with ISO 12647-2.
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