How to test the printing machine for printing qual

2022-07-27
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How to test the printing machine for printing quality

the best way to analyze the printing quality is to print a test form. Industry organizations such as NAA, GATF and snap provide test forms, which are designed to obtain important information. Printers can also make their own test forms. These test forms include at least the following information:

color blocks used to evaluate the density of monochrome field inks

25%, 50% and 75% black dots

two color field superimposed color used to evaluate color

measuring the step of each primary color ink dot enlargement (25%, 50%, 75% minimum)

to ensure communication with everyone on the test objectives and objects before formal operation. Keep in mind that many tests of print quality are based on field ink density. The printer operator must have tools to control the density when testing. The following are some additional guidelines:

judge whether the test results can play a role in evaluating the printing process when testing in production mode; If the printer is installed according to the manufacturer's parameters, what will be the result of the process

using a corrected reflection densitometer, its T state can respond to density control. Note that the density of the printed matter is within the target range recommended by the industry, and the horizontal density of the page is uniform

if using digital media, make sure to use a properly linearized laser Imagesetter to generate four-color films. Check the output film to ensure correct reproduction

ensure that the equipment handling the printing plate meets the corresponding parameter requirements (exposure, light source)

use film to make the printing plate, and check the printing plate to ensure the correctness of printing and printing

when the printing press reaches the normal and stable speed, ensure proper ink and water balance

use a calibrated reflection densitometer to adjust the field ink density of each color to meet the parameter requirements of snap. Take at least one or two minutes for the adjustment to work. Before adjusting the next color, make sure that the ink density in the horizontal direction of the printing sheet is uniform. Check at least three random prints and average the density readings before making any adjustments

after the final adjustment of the print density, a large number of prints are taken out for evaluation. In order to obtain reliable process control data and statistics, at least 20 prints shall be evaluated within 30 minutes. In addition, the printed sheets are randomly selected in the printing process to judge the variables

gray balance and color code used in process control

this chapter will introduce the tools, processes and methods used by printers or newspapers to obtain stable and excellent printing quality

grey balance

grey balance is used to evaluate how to adjust three primary colors in the printing process ---- cyan, magenta and yellow. Use cyan, magenta, and yellow to duplicate the gray scale to determine the degree of gray balance. Using the same three colors will produce a neutral tricolor gray. When printing neutral gray with snap density parameters, the tone of cyan is always greater than that of yellow or magenta. The following three tables list the relevant values of cyan, magenta and yellow when snap samples and prints reach the correct gray balance. During the whole process of scanning, proofing, film generation and printing, the point enlargement/tvi shall be monitored, adjusted and controlled to maintain the halftone point value required to achieve the correct gray balance

The grey balance is an important indicator that the

point enlargement/tvi value is in equilibrium. It is important to ensure that the gray tones are copied correctly

offset three color gray balance

offset three color gray balance is equivalent to the target value of three color block density of black densimeter filter

magenta yellow black black

25% 18% 18% 0% 25% (quarter tone) 0.52+/-0.05

40% 30% 30% 0% 50% (middle tone) 0.65+/-0.05

flexo three color gray balance

flexo three color gray balance is equivalent to the target value of three color block density of black densimeter filter

magenta yellow black

12% 7% 10% 0% 20% (quarter tone)

20% 14% 14% 0% 25% (quarter tone) 0.52+/- 0.05

38% 30% 30% 0% 50% (middle tone) 0.65 +/- 0.05

embossed three color gray balance

embossed three color gray balance is equivalent to the target value of three color block density of black densimeter filter

magenta yellow black black

40% 30% 30% 0% 50% (middle tone) 0.62 +/-0.05

how to measure the gray balance

a superimposed color of cyan, magenta and yellow is compared with black with the same tone value, so as to subjectively evaluate the gray balance. The grey balance must be evaluated under standard observation conditions. A densimeter can also be used to objectively evaluate the grey balance. The absolute density of each main filter must be approximately equal

grey scale

each print must have a grey scale, or a series of objective field or light color codes. These color codes must appear on each page or as many pages as possible. The target density in the above three tables represents the color block density measured using each filter

the total range of the three ink densities in the table cannot exceed +/-0.03

color code

in addition to the gray ladder, color codes should also be used when possible. The color code should include the following parts:

1. four colors (CMYK) field

2. color block when the percentage of four color points is 50

3. field overprint of any two colors

if space allows, it is better to add 75% and 25% color blocks of four colors. The grey scale and color code should be as large as possible to facilitate measurement. It is recommended that the height and width (or diameter) of the color block be 3/8 inch. Smaller color blocks can also be used if the printer or the newspaper agrees. Color code 5. Transmission system: the ball screw transmission of the servo electromechanical control system requires continuous step adjustment, and the color code can be creatively designed in the page width

rules for using grey scale

1. regularly check the imagesetter and the film processor with the projection densitometer to ensure that they can output the correct film point percentage/step value for the gray scale

2. the width of the gray scale should be the same as that of the densimeter window (projection or reflection), so as to ensure the correct density reading

3. check whether the densitometer is calibrated every day, but recalibrate only when necessary

4. the internal density change of the printer must be within the density tolerance in the above table

5. if necessary, adjust the gray scale from dark to bright on the printing machine because the ink color is not pure. Cyan and magenta include those components that can affect the Yellow reading in the gray ladder ruler. After adjusting one color, it should be rechecked that the other two color pressure testing machines are widely used

6. it is better to read at the same place of the gray scale or the printing plate, so as to reduce the density change caused by the stamping on the ink area or the printing machine

7. when the development and utilization of small precision electric injection molding machine are accelerated and three red, green and blue filters are used to measure the gray balance color block, the difference between the three density values shall not exceed +/- 0.03

8. when starting the machine, follow the following steps

to register the paper

make the page horizontal to achieve visual gray balance

use the reflection densitometer. The third point is to check the gray scale according to the control mode

adjust the density if necessary

recheck the density at the same position in a few minutes, and adjust the density if necessary

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