Use of Brunel Control Strip
Brunel control strip is a quality inspection tool recommended by China's printing standards. It is used for the measurement and calculation of spot density, dot gain, dot distortion and printing contrast (K value) of proofing and printing, and can also be used for visual inspection. The most commonly used in printing is Brunal's three-stage test strip (Figure 9-1). The following highlights its role and use.
The role of a solid patch
(1) Measure the proof, the solid density of printing and the degree of ink inking.
(2) Measure and calculate the three major characteristics of the three primary color inks, namely color shift, gray scale and efficiency.
Controlling the optimal solid density value of the four-color ink is not only the core of digital color management for proofing and printing, but also the core of digital color management for the entire copy process. The picture shows that the solid density (the thickness of the ink layer) has a great influence on the quality of the proofs and prints. If the density of the field is too large, the dots will increase more, the printed product is rough, and the density of the field is too small, then the color saturation will be insufficient. Therefore, the best point on the field must be reached. Specifically, the best field density is between 75% and 80%. The minimum increase of the network dots or the maximum solid density value within the premise of a reasonable increase. That is, the solid density when the K value is the largest is the best solid density, because the thickness of the ink layer is closely related to the density measured by a reflection densitometer. The absorption characteristics of the ink layer depend on the ink hue, ink layer thickness and ink Color properties and density.
(Figure 9-1 Brunel's three-stage test strip)
A representative proof, the solid density range of the printed wet ink layer is shown in the table. In the actual proofing and printing process, not only all technical measures must be taken to achieve the best solid density value, but also the consistency of solid density. To achieve the same density of left, center and right, the error is ± 0.05D. In printing, a product and a printed part must be obtained, and the ink color from the start-up printing to the halfway to the final printing is consistent, which needs to be obtained by measuring the control conditions and density meter.
Table 9-1 Proof of different substrates, solid density range of printed wet ink layer
Note: The table value ± 0.05 is the field density range
Two 50% coarse segments
The 50% thick mesh segment is composed of 10 lines / cm mesh dots with 50% mesh area. Its main functions are:
(1) Visually observe the change of dot increase and decrease directly.
(2) Calculate the increase of 50% of the outlets.
In actual production, the operator often observes the change of 50% coarse mesh segment and uses it to determine the change of the dot. Generally, the dot increases, and the square points of the 50% coarse mesh segment will inevitably take a serious angle. If it is larger, the dots decrease.
The formula for increasing value of dots mentioned above is of general significance, and the calculation of the increase value of 50% dot area is based on the principle of the comparison of coarse and fine dots, based on the equal total area of ​​coarse and fine dots. The line number ratio is 1: 6, that is, the circumference of a 50% thin dot is 1/6 of the thick dot. The sum of the perimeters of a row of six fine dots is equal to the circumferential length of a thick dot. The sum of 6 rows of fine dots is 6 times that of coarse dots. Therefore, under the same conditions, the increase of fine dots is much, so based on the 50% coarse screen segment, taking the difference between the density of thick and thin, you can find the increase value of proofing and printing 50% dot area .
50% increase in dot area = (fine network segment density-coarse network segment density) × 100%
If the measured density value of 50% coarse mesh segment is 0.30 and the density value of 50% fine mesh area is 0.45, the increase value of 50% mesh dot area = (0.45-0.30) × 100 = 15%
This method is simple and accurate, and is suitable for on-site management. [next]
Three fine dots micro-measurement section
The fine-mesh micro-measurement section, also called the ultra-micro measurement element, is the core part of the Brunel system (Figure 9-2). The fine mesh segment is composed of equal width lines of 60 lines / cm, and its total dot area is 50%. The fine mesh segment divides the fine mesh area into four with equal width large crosshairs. The formation of dots per 1/4 area is exactly the same. But the directions are different, and its main functions are as follows:
(Figure 9-2 Enlarged view of 50% fine-net micro-measurement section)
(1) The outer corner of each 1/4 grid is composed of 6 lines / mm of equal width fold line, which is used to check whether there is sliding deformation and ghosting of the dots during printing. If the four corner lines of the proof are deformed, it means that the printed dots have slipped. Slide horizontally, the vertical line becomes thicker, slide vertically, and thicker horizontally.
(2) There are 13 dots in the first row near the crosshairs. The row of dots inside is small black dots from large to small, and the side is corresponding to 12 small black dots from large to small. Correspondingly, there are 12 hollow white dots from large to small, which are 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15 %, 20% of the positive points and negative points are arranged correspondingly.
Judging the changes of dots in printing, proofing and printing, it can be observed with a magnifying glass of 25 times. If the PS plate is used for printing, 10 small black spots can be printed out, then 2% of the small dots are complete. The standard exposure and development of the printing plate should reach the yin and yang points corresponding to the alignment. During proofing and printing, in the absence of a density meter, the dot gain data can be visually inspected (as shown in Figure 9-3). Observe how few translucent small white holes remain, indicating how much the dots have increased. If there are a few translucent in the 12 small white holes, it shows how much the dots increase. If the 12 small white holes are completely dead, it means that the dots increase by 20%. If 10 small white holes are dead, there are 2 small white holes, which means that the dots increase by 15%; if there are 4 small white holes, it means that the dots increase by 10%. The general proofing specifications should retain 4 small white holes.
â‘¢ There are four 50% standard square dots in every 1/4 block, which are used to control the depth change of the printing plate during proofing, proofing and printing. If 50% of the standard square dots have a large angle, the dots will increase, otherwise, if the four corners are off, the dots will shrink.
(Picture 9-3 increase or decrease the visual dots)
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