Overview of measurement and control and technology

Printing control strip measurement and control and technology overview

printing control strip is composed of various control elements that can reflect the basic parameter information of printing. It is an important tool that can subjectively and objectively reflect the quality of printing and carry out data-based and standardized production. In actual production, the combination of printing control strip and densitometer or colorimeter for printing quality control has been widely valued and widely used. Systematic understanding and analysis of printing control strips will help to improve the application level and quality control ability of printing control strips, and finally provide a reliable basis for standardized and data-based production. 1. The measurement and control principle and control parameters of mineral oil printing control strip with medium viscosity are usually selected.

based on the theory of plate making and printing quality control, the printing image quality is affected by many process parameters, which are often not independent variables, but interact with each other. Keeping the printing color correct in the whole printing process mainly depends on three parameters: ink layer thickness, dot coverage and overprint rate. These three parameters have their corresponding physical quantities that can be objectively measured. Figure 1 shows the corresponding relationship between the three quality parameters and related physical quantities, that is, the basic principle of printing image quality control

1. 1 field density

field density is the basis of printing quality control. It not only directly reflects the degree of color restoration, but also indirectly controls the ink layer thickness of each color. Because when the thickness of the ink layer gradually increases, the density also increases. When the thickness of the ink layer reaches a certain limit, the color begins to saturate, and the density cannot rise any more. Therefore, to control the field density of each color of ink is to control the thickness of each color of ink layer. Different printing methods have different requirements for field density. The field density value is not a general data, which is generally affected by the differences and operating errors of paper, ink, printing color sequence and densimeter calibration. In order to effectively control the reproduction of tone value in reproduction, the field density of each color should be controlled. At the same time, the relative contrast can be calculated by using the field color block of each printing primary color. Because of the importance of field density in printing quality control, any printing control strip contains monochrome field control blocks of various colors and is usually arranged in the first position

1. 2 printing relative contrast

relative contrast K can be expressed by the formula: k = (DV - d0.75 (0.8))/dv. Where DV is the field density value of the color ink; D0.75 (0.8) is the density value of point blocks with a point area coverage of 75% or 80%. China uses the point density at 75%, and Europe often uses the point density of 80%. It can be seen from the formula that when the value of K is large, it means d0 The density difference between 75 (0.8) and DV is large, that is, 75% - 80% of the points have less point expansion, the sample sheet is adjustable, the level is clear, and the color saturation is high; K value is small, indicating that 75% ~ 80% of the point area is expanded, the field density is small, the sample step cannot be opened, the level is fuzzy, and the color saturation is low. What is correct is that the relative contrast value of a two-dimensional crystal composed of closely packed carbon atoms is an important indicator to measure whether the field density is sufficient and whether the dark tone level is clear, which is of great significance to improve the quality of samples and prints

any printing control strip also contains 75% or 80% of the monochrome dot block control section, which is usually followed by the field density block for the convenience of calculation. In production control, it is necessary to use densitometer or colorimeter to measure the field density of the corresponding color block first, and then measure 75% or 80% of the dot block. The relative contrast value can be obtained through formula calculation

1. 3-point enlargement value

point enlargement value refers to the difference between the actual area coverage of points on the substrate and the actual area coverage of points corresponding to the printing plate. For pressure printing, dot expansion is inevitable. As mentioned above, when the relative contrast exceeds the range, it just shows that the dots at the area coverage of the measured points (75% or 80%) have expanded or shrunk, so it is easy to have process failures of pattern or paste in the production process

the control of dot enlargement is very important for the control of printing quality. In offset lithography printing process, dot enlargement has a greater impact on the change of reproduction hue than any other variable. Each printing control strip has a carefully designed point expansion control section, which is often the core part of the whole control strip. Generally, the reproduction effect of thin lines and small points is used to reflect the point expansion. In production, the point expansion value can be judged as long as a magnifying glass or visual inspection is used. Figure 2 shows the Bruner fine control section

Figure 3 is the star mark of GATF, which is composed of 36 wedge lines with equal black and white, with a small white dot in the center. By visually observing the changes of white dots and wedge lines in the center of the star Mark, we can judge the conditions of midpoint increase, point deformation and ghosting in the printing process. The same is true of the principle of the resolution block in the UGRA/fogra postscript control bar

1. 4 overprint rate

overprint rate refers to the ability of ink to adhere to another ink. The significance of controlling the overprint rate is to avoid the disadvantage of low overprint rate when wet or dry, so as to meet the requirements of tone restoration. The higher the overprint rate, the better the overprint effect

overprint rate t is a value between 0% and 100%. When t = 100%, it indicates that the overprint rate of post printing color is excellent, just like the effect of direct printing on the substrate. If t = 0, it indicates that extreme "wet" printing failure or "dry" printing failure have occurred, which must be avoided and solved. Different overprint methods generally have different overprint rates. Monochrome Offset Press belongs to wet press dry overprint, and generally the overprint rate is relatively high. Four color press printing belongs to wet press wet printing, and the overprint rate is relatively low

the overprint rate has become a test item to judge the printing quality. The quality of printing products can be classified according to the overprint rate. The printing control strip is generally designed with a square two-color overprint solid block to control the overprint rate

1. 5 neutral gray balance

the printed neutral gray is an important indicator to monitor whether the dot increment of each color is balanced. Accurate reproduction of neutral gray is very important for printing. 3-color overprint color block refers to the color block that tends to be neutral gray produced by the half tone overprint of the three primary colors of yellow, magenta and cyan. It is used to print black with the same chromaticity value, and the change degree of gray balance can be quickly estimated visually. Due to dot enlargement, ghosting or overprint, the three printing primary colors will change, which can be shown by neutral gray and red, blue and yellow gray

generally, the printing control strip will design the gray of the middle tone (C50%, M39%, y39%) and the solid block of 3-color overprint (C100%, M100%, Y100%), using the gray balance data recommended in the relevant national printing standards (C50%, M39%, y39%), and the value of the middle tone mainly controls the gray balance of the middle tone. Due to the different paper, ink and printing conditions used The grey balance data are different. The main changes are m value (39% - 44%) and y value (39% - 44%)

2 traditional printing control strip

2 1 traditional printing control strip

traditional printing control strip is the control strip in the form of film, which is widely used now. Bruner printing control strip is the most used

the traditional printing control strip is designed for the traditional printing process. At the stage of color separation and film production, the control strip film is pasted on the film to print together, and then printed. Therefore, the printing control strip not only records the quality information of the printed matter, but also reflects the quality of the printing plate

2. 2 disadvantages of traditional printing control strip the traditional printing control strip has the following disadvantages in actual use:

(1) in traditional printing, the control strip appears in the form of film, which is not easy to keep and easy to lose. It has been used for a long time, which indicates that China's new material industry has the confidence and capital to "go out" to compete in the international market, so that the steel strand will inevitably receive the action surface of dynamic or impact load, and there will be scratches, which will affect the accuracy of information transmission

(2) although the price of traditional printing control strips is not high (usually 3000 ~ 4000 yuan), in fact, some printing plants are using copied substitutes in order to save costs. Because the traditional printing control strips in the form of film have undergone strict optical inspection when leaving the factory, and the requirements for accuracy are very high, even the control strips that have been copied once have lost the function of controlling the printing quality

(3) traditional printing control strips need to be used manually. Skilled workers first scrub the control strips with cotton cloth and then paste them on the film, and pay attention to the distance and position of the control strips, the tightness of the paste, etc

3 digital control strip and its application status

3 With the development of electronic and computer technology, CTP and digital printing have become the development trend of the printing industry. Because CTP technology eliminates the process of color separation and film production, the traditional printing control strip cannot play the role of quality control. Any industrial production needs to be carried out in accordance with the specified quality standards. The quality standards of digital printing products can be implemented with reference to the standards formulated by the traditional printing process. However, digital printing cannot only have product quality inspection standards, but also need specific means to realize product quality inspection and control, which requires the design of digital control strips that can control both the printing process and the plate making quality

digital printing control strip is a printing control strip in the form of electronic documents, which can usually be designed and obtained in two ways. One is to use CorelDRAW graphics software to draw, or use postscript language to write, and the latter has higher accuracy and more advantages

different from the traditional printing control strip, we add the digital printing control strip to the electronic manuscript during typesetting, and then output it together with the printed matter through traditional printing or direct plate making, or even direct printing. From this, it is easy to see the advantages of the digital printing control strip compared with the traditional printing control strip:

(1) the digital control strip eliminates the shortcomings of the film carrier and can ensure the permanent distortion of the control strip information, so it can control the printing quality more accurately and stably. At the same time, the digital printing control strip in electronic form is convenient to transmit and copy, which is more suitable for printing enterprises

(2) from its use method, it can be seen that it has a wider scope of application, more convenient and flexible. The digital control strip can be used not only for traditional printing, but also for digital printing. In traditional printing, customers make up the control strip with the live parts to be printed on the computer, then output the film, and then carry out the traditional printing and printing. If it is used in digital printing, it is simpler. Just make up the control strip with the live parts, and directly turn the digital information into printed matter. The digital control strip can be distributed or printed together with the live parts to be printed, so it can control the printing process more accurately than the traditional control strip. At the same time, the digital control strip can realize the output of any resolution, which is especially suitable for the detection and control of direct plate making and printing quality. It can control the consistency of printing color, stabilize the quality of printing, and bring higher social benefits to printing enterprises