How to do a good job in the acceptance of new prin

2022-07-28
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How to do a good job in the acceptance of new printing machines (middle)

objective test content of the test version 1. printing density

the front edge and trailing tip of the test version have field color blocks to control the printing density. Generally speaking, each printing enterprise has its own density value standard for common ink brands, and this value is also used to obtain lithium resources when testing machines. The significance and role of the field color block in the beta are reflected in the following aspects

(1) control ink color uniformity: we can know whether the ink amount is appropriate by measuring the density values at different positions of the front mouth or the trailing tip, and provide a digital basis for local ink amount adjustment

(2) control the ink supply: by comparing the measured value with the specified value, we can know whether the ink quantity is too large or too small, and provide the basis for adjustment

(3) density difference before and after inspection: Generally speaking, the density values before and after each unit of each equipment are different. Generally, it is considered normal within 0.1. Of course, the smaller the difference is, the better. If it exceeds 0.1, it is likely that some part is improperly adjusted. This test value can truly reflect the problem that the printing is light in front and heavy in back or heavy in front and light in back

2. point increase value

point increase includes physical increase and optical increase. Physical increase refers to the increase of the point formed by flattening under the action of printing pressure; Optical increase refers to the optical increase caused by the diffuse reflection of light from the point edge. The point value measured by the densimeter includes the physical increase value and the optical increase value. Under normal printing conditions, the dot increase value of 150 lines/inch and 50% can reach 66% ± 2%, and the dot line number, the amount of ink, printing conditions, printing pressure, ink, paper, etc. have a great impact on the dot increase

point increase test strip as shown in Figure 3. By measuring the actual size of the test strip points with a densimeter, the point increase value of the equipment can be obtained. By comparing this value with the technical indicators of the equipment, the point increase evaluation results of each unit can be formed

3. printing contrast

printing contrast is represented by K

k=1-dt/ds

where DT is the 75% point density value and DS is the field density value. If conditions permit, when the contrast reaches the maximum, the equipment operates best, and the greater the K value, the higher the print quality. The printing contrast test block is shown in Figure 4. Too large DF (i.e. too large dot increase) or too small DS (i.e. insufficient ink volume) will cause the K value to decrease

generally speaking, the printing contrast of new equipment is about 0.45, and the contrast value of different inks is black> Green> magenta> yellow

4. overprint rate

due to the chromaticity value characteristics of printing ink and the ink layer thickness that can be achieved by printing, the color rendering range of the printing picture is restricted, and the difference or proximity between the printing color reproduction and the original color is also restricted. Overprint rate f can reflect the thickness of printing ink layer and is an important index to measure the reproduction of printing color

f=[(d1+2-d1)/d2]x 16 relative error of zero point of experimental force ± 0.1%00%

where D1 is the monochrome density of the first printing ink, D2 is the monochrome density of the second printing ink, and d1+2 is the density after overprint

the overprint rate test chart is shown in Figure 5. Generally speaking, the two-color field overprint is about 70%, but the color sequence will affect the overprint rate. Therefore, the overprint rate standards for different color sequences are also different. For example, magenta green overprint is 60:6-70:6, and magenta green overprint is 75% -85%

5. other test units

generally, the test version is also equipped with test units such as ghost shadow, gray balance, resolving power and double image star Mark, which are arranged in different parts of the layout according to needs. These performance indicators are tested after printing

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