Standard certification of offset printing process

In recent years, many domestic companies have obtained ISO-9000 quality management and quality assurance system certification. The printing industry is no exception. Many printing companies have also passed the certification, which has improved the management level of the current low-level companies. However, the ISO-9000 series of standards are common standards for all lines of business, focusing on corporate management, lack of technical and production process control aspects. Printing companies should further standardize the prepress and printing processes on the basis of obtaining ISO-9000 certification and in accordance with the requirements of offset printing process standards to ensure that printing companies are in a competitive position.

The standardization work of the printing industry in China has been carried out for nearly 20 years. A standardized management organization, the National Printing Standardization Technical Committee, has been established. It has also joined the ISO International Standards Organization TC130 Printing Technology Committee and has been absorbed as an active member. As of 2004, China has issued 29 national standards for printing and 20 industry standards. Among them, five new standards have been formulated using international standards and have high practical value. Particularly worth mentioning is the national standard GB/T 17934-2-1999 "Printing Technology Mesh, Color Processing, Proofing, and Process Control of Finished Products, Part 2: Offset Printing", which is issued by the State Press and Publication Administration. Proposed by the National Printing Standard Committee Organization North drafted by the Institute of Printing, equivalent to adopt the international standard ISO12647-2 "Offset 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 countries in the world to convert ISO-12647-1 and 2 into national standards.

Explain 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 print research institutes in Germany, the United States, Switzerland, the United Kingdom, and Japan. The experts and scholars of the printing associations, printing institutions, and famous printing companies drafted and drafted together. After five years of extensive discussions among member states, several drafts were made and they were eventually voted on by member states in 1996. More than 75% of them agreed to formally pass. From the point of view and thinking of formulating standards, international standards are fundamentally different from those developed by China. For example, GB/T 7705-1987 "Plain Prints" and CY/T 5-1999 "Plain Print Quality Requirements and "Inspection methods" These two requirements concerning the quality standards of offset printing all focus on the technical parameters such as the appearance, size, overlay error, field density, relative contrast, and dot gain of printed products. After the printing is completed, the printed matter is measured and inspected so as to achieve the purpose of controlling the printing quality. In fact, these standards do not have the effect of controlling many factors that affect the quality of printing before printing. Compared with the international advanced standards, our standard setting work still needs improvement and improvement.

How is the ISO 12647-2 (International GB/T 17934-2-1999) standard developed? Where is the focus of their technical requirements? In the technical requirements of the standard, the quality of color separation films and the number of network lines are first defined. It is specified in the section on quality; “The density value of the center of the dichroic film web site shall be at least 2.50 higher than the density value of the transparency film (film base plus fog), and the transmission density of the center of the screen dot shall not be higher than the film density value (film base plus Fog) 0.1 or more, the density value of the transparent film (film base plus fog) should not exceed 0.15."

The color separation film is the initial factor that affects the quality of the offset printing product. The density value of the center of the standard mark dot is at least 2.50 higher than the density value of the film, so as to ensure that the dot on the color separation piece is correctly transferred to the printing plate.

The standard also specifies the angles of the network cable and the network cable. The web journal is printed with 45 to 60 thread centimeters, and the commercial printing is 60 to 80 thread/cm. The requirements for the screen angle are: “Without the spindles, the angle difference between the cyan, magenta, and black versions should be 30° The angle difference between the yellow version and other color versions should be 15°, and the main color version should be It is 45 degrees." Specifying the dot angle difference before printing can prevent moiré in four-color printing. There are no specific requirements or regulations for these two items in the national standard and the line of business.

In order to ensure the accuracy of overprinting, the standard puts forward requirements for the image size error of the color separation film: "In the case of stable environment, the difference between the lengths of the diagonal lines of a set of color separation film shall not exceed 0.02%." To ensure that this error is not exceeded, the temperature and humidity of the operating environment must be controlled to ensure that the separation film is dimensionally stable and prevents stretching.

In order to prevent multi-color printing inks from having low overprint ratios, backside offsets, and backside smudging, the standard specifies the sum of the gradation values ​​of the color separation sheets as follows: "The sum of tone values ​​for sheetfed printing must not exceed 350%. The sum of web printing tone values ​​cannot exceed 300%." The use of a background color removal method before printing to ensure that the sum of the above-described tone values ​​is satisfied creates favorable conditions for printing.

The gray balance is determined by the cyan, magenta, and yellow shades of the image, as well as their color and overprint color. If the printed matter is gray under the specified observation conditions, the cyan, magenta, and yellow-gradient values ​​(dot area) on the color separation sheet are in a state of gray balance. The standard gray balance tone values ​​are as 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 provide an important requirement for gray balance tones.

Regarding the quality requirements of the printed matter, the standard puts forward requirements and measurement methods for the color gloss of the substrate (such as paper). First, the CIELAB color space values ​​(L*, a*, b*), color difference values ​​(ΔEab), glossiness, and allowable errors of the unprinted paper itself are determined. The corresponding regulations are made for the color space, gloss, brightness, and weight of five typical papers.

There is also a corresponding requirement for the color and gloss of the ink. The CIELAB chromaticity values ​​L*, a*, b* of the red, green, and blue solid colors obtained with the specified five kinds of paper proofs, the four solid colors of cyan, magenta, yellow, and black and the two-color overprint on the proofs should be consistent with Specified value. The color difference of the original colors of the original colors is ΔEab; the black deviation is 4, the cyan is 5, the magenta is 8, and the yellow is 6.

Standards require that the gloss of a solid color be measured at a 75° angle of incidence and an acceptance angle of 75° to measure the specular gloss of the substrate or the solid in a single color. The measuring instrument used for the standard shall comply with GB/T 8941. 3 International regulations, the measured value shall be expressed as a percentage. Our country's standards do not have such detailed requirements for paper and ink.

In addition, the tone reproduction range, that is, the dot reproduction range is based on the number of screen lines. For example, if the number of screens is between 40 and 70 lines/cm, dots with a dot area ratio of 3% to 97% can be completely printed on paper; the number of screen lines is 80 lines/cm, and the dot area ratio is 55. % ~ 95% of the outlets can be completely reproduced.

With regard to the increase in tone, that is, the increase in the number of outlets, the standard stipulates an increase in the tone of print. According to the standard, the gradation value of the measurement bar is set at 50%, and the corresponding value is selected as the target value. For example, the number of reticle lines for the measurement and control bar is 60 lines/cm, and the gradation increase value (percentage) at the gradation value of 50% is as follows; the positive version for color printing of roll paper journals (type 3 paper: glossy coating paper) is 19; commercial color printing is 17, using type 1 and type 2 coated paper and positive plate version 19 (where color printing requires the black plate to be 2% to 3% higher than other color plates). The range of dot gains specified in the CY/T5 industry standard is relatively large, between 10% and 25%, and no target value is specified.

Overprint accuracy is an important indicator of print quality standards. The first edition of CY/T5 specified a wider set of overlay errors. After the revision in 1999, it was stipulated that the fine print overprint error ≤ 0.10mm, and the general print allowable error ≤ 0.20mm. The "image position error" stipulated in the ISO-12647-2 international standard is completely different in concept from the overprint allowable error specified by the Chinese standard. For example, the international standard stipulates: “The maximum position error between any two-color printing image center shall not be greater than half the minimum dot width of a four-color separation sheet.” This overprinting accuracy requirement is much higher than the requirements of our country's standards. If the overprint accuracy cannot be achieved due to reasons such as equipment, the international standard allows the printer to reach the necessary agreement with the customer.

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. The printing industry in China should vigorously promote this standard. In order to occupy the quality advantage in the fierce competition, the printing factory should actively adopt this international standard and strive to be in line with international standards in product quality management.

German ISO-12647-2 Offset Process Standard Certification

Germany is one of the countries with the most advanced standardization, and DIN (abbreviation) is the code for the German industrial standard. The German printing industry established a series of standards very early, covering almost all the technologies and production processes of the printing industry. Many printing standards have been adopted by ISO and converted into international standards. For example, ISO-12647-2 is codenamed DIN ISO 12647-2 in Germany.

According to the German Printing and Media Association's certification of the process control standard for offset printing, the following is the case: If a country in Germany asks a printer what standards it is printing on, most of it hears the concept of the European color standard. Most of this concept is customarily used to offset the European color standard (DIN 16539), but this standard has now expired. The color performance of the inks of the primary colors is now specified in the DIN ISO 2846-1 standard, which is based on DIN 16539.