Color overprint standard deviation is an important parameter for print quality inspection and control. The standard deviation standard for overprinting currently used is determined by the German FOGRA Institute in the 1980s. According to the FOGRA standard, the maximum rated value of the overprint standard deviation is specified:
When the paper needs to be run twice, the standard deviation for transfer printing cannot exceed 20μm;
The standard deviation of overprinting when handing over four color set machines cannot be greater than 10 μm;
An additional 3 μm overprint standard deviation can be added for each additional color set, but the entire overprint standard deviation cannot exceed 20 μm.
When implementing fine print, the standard deviation of overprinting is higher.
Based on the on-line inspection of printing quality, this paper summarizes the method of calculating the standard deviation of color overprinting by using FOGRA calculation table, preliminarily realizes the measurement and calculation of overprint deviation, and establishes a set of color overprint standard deviation detection algorithm flow . Can be used to control and analyze the print quality of color prints. Below, the author will introduce this process.
Measurement of overprint standard deviation
1. Measurement conditions
The test sample is shown in Figure 1. Test conditions: printing speed is 85% of the maximum printing speed, using ordinary ink, color order is black, cyan, magenta, yellow, measuring strip using FOGRA printing control strip, paper using double-sided smooth coated paper (120g/m2), The fiber direction is the same as the paper feed direction, and the specification is at least 80% of the width of the largest printing paper. In addition, the paper is pretreated in the printing shop for more than 2 days, the relative humidity of the test plant is 45% to 60%, the humidity change is at most 10%, and the temperature is 20 to 25 °C.
2. Measurement method
When the overlap printing is performed, the partial printing overprint positions are marked with each other, and the reference is set at the paper edge. Usually, the overprinting of the printing press is important in evaluating the overprinting accuracy, and the number of handovers is related to the number of printing units. Two parameters can be used, one is the overprint standard deviation from the first to the second printing unit; the other is the overprint standard deviation of the first to fourth printing units. The overprint standard deviation can also be used for the overprint deviation detection of the intersection between the second and third units and the third and fourth units. Using the FOGRA print control strip to measure the standard deviation of the overprint, under a magnifying glass of 40 times, it can be seen that some values ​​are evenly distributed around an intermediate value, as shown in Figure 2: the zero scale is between the basic scales 15 and 16, so the basic reading The value is 1500 μm, on the basis of which the tick marks between the 4th and 5th tick marks completely coincide, so the final reading shown in Fig. 2 is 1545 μm.
At this time, if the overprint standard deviation of the paper transfer of more than four units is continuously obtained, the standard deviation of the overprint is about 3 μm for each additional unit.
Calculation of overprint standard deviation
1. Calculation Tools
There are two ways to calculate the standard deviation of the overprint. One is to use a calculator with statistical functions, and the other is to use a table calculation program to perform calculations. In order to make the test data more accurate, in the experiment, the author took 100 measurement values, directly input the measurement values ​​into the computer, and use the FOGRA table to calculate the standard deviation of the overprint.
Toilet Paper,Jumbo Toilet Rolls Wholesale,Four Ply Toilet Paper,Compact Toilet Paper
DONGGUAN YEE HUP TRADING CO,.LTD , https://www.yeehupacks.com