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Types and control of point expansion

release date: Source: China paper

in the process of packaging and printing, various point expansion controls are often used. Today, China's paper industry starts with printing. Let's introduce the relevant contents in detail

signal bar: it is mainly used for human visual evaluation of printed matter. Its function is relatively simple, and it directly expresses the appearance quality information of printed matter. Such as GATF star, GATF digital signal bar, color signal bar, etc. invented by the American Printing foundation

· test strip: a multi-functional marker mainly based on densitometer detection and evaluation, which is usually a test strip that combines visual identification with densitometer testing and facilitates numerical calculation of charts and curves. Such as Bruner test strip

· control strip: it is a multifunctional control tool that combines the visual evaluation and test evaluation of signal strip and test strip. For example, Bruner third generation test strip

1. The formation of dot enlargement

classified according to the state of dot enlargement

1. Linear enlargement: refers to the expansion of the edge of the printing point in one direction. Originally, the printing point is square, prismatic, circular, chain shaped. Linear enlargement refers to the linear expansion of the point in a certain direction

2. Expansion of area:

the printing point expands around, and the expansion of point area is generally proportional to the length of point edge. In other words, when the area of the point is large, the length of the edge of the point also increases

3. Density increase:

the density increase is proportional to the area of the printing point. The density increases and the ink color is large; If the ink is large, the dot area will be large

according to the point change classification of printing

1, normal expansion. This kind of printing dot expansion is allowed, that is to say, dot normal expansion, high density of center position and low density of edge position

2. Point of ghosting. This kind of dot enlargement is not allowed. When printing, there is a bit of ghosting, which seriously affects the color effect

3. Irregular dot enlargement. When there is no regular dot expansion, the printed dot does not have a rule, and the dot expands around. At this time, it is easy to have pasted plates and dirty plates, which will affect the quality of printed products. This kind of irregular dot expansion is not allowed. The point expansion range shall not exceed 15%, 12% and 10%

second, the relationship between the number of lines in the point and the edge length

because the point change occurs in the surrounding part of the printing point, the more points per unit area, the more surrounding parts of the point, and thus the greater the change of the point. It can be seen that the point expansion of the thin line is larger, while the point expansion of the corresponding thick line is smaller

printing spots can be divided into thick spots or fine spots according to different purposes. Fine spots should be used for fine printing products viewed from a close distance, such as periodicals, pictorials, trademarks, etc. The printing products seen from a long distance all use bold dots, such as large advertising stickers, posters, etc. Points are in inches, that is, within an inch area, common lines are 60 lines/inch, 90 lines/inch, 133 lines/inch, 150 lines/inch, 175 lines/inch

for example, the dot area is also 60%, and the blank area is 40%. One is 60 lines/inch, and the other is 175 lines/inch. The dot expansion of 175 lines/inch will be much larger than 60 lines/inch. This means that the edge length of 175 lines/inch thin lines is long, so the point expansion is larger. 60 line/inch thick line edge length is short, so the point expansion is smaller

III. signal bar control point expansion

GATF digital signal bar

GATF digital information bar is made of 27 lines/cm thick dots as the substrate, with 80 lines/cm tiled numbers from 0 to 9 embedded in the middle. On the original version, the density of number 2 in the signal bar is the same as the background color density

the specific use is as follows:

1. GATF digital signal bar assumes that the thickness is unchanged and the point is not expanded. Observe the density difference between the number and the background color with the naked eye

2. In the original version, the area of 1-7 digital points decreases by 3% - 5%, and that of 7-9 decreases by more than 5%. The area of point 0 is the largest and that of point 9 is the smallest

3. Since it is assumed that the thick line does not expand at all, the amount of dot expansion is determined according to which number has the same density as the background color

example 1: number 5 has the same density as the background color. At this time, starting from data 2, the number has transferred the three-level printing point (taking 2 as a reference without expanding the fixed point, the transfer three-level decreases by 3% - 5%), indicating that number 5 has expanded the point by 9% - 15%

example 2: the number of GATF signal bar is 1, which is the same as the base color density. Taking number 2 as the reference, it is transferred to the first level, and the point is reduced by 3% - 5%

calculated with reference to data 2, 2 used to be point reduction, and 2 later point expansion

star point control

36 wedge-shaped lines with equal black and white width are radiated outward from the center of the circle, and there is a small whiteness in the center of the circle

the star Mark determines the size of the expansion of the fixed point according to the size of the central white point

large white dot in the center indicates the size of dot expansion

large white dot in the center indicates that the dot is enlarged

as a detection tool for test point expansion, its role is to be able to identify the type of point expansion

1. the small white dot in the center of the star mark is oval, indicating that the dot is directionally enlarged. When the small white dot in the center of the star shows "→ 0 ←", this kind of ellipse indicates that the dot expands left and right, which is called horizontal expansion; The point presents an "O" that is called an up-down expansion point. Or called vertical expansion

2. If there is ghosting in the center of the star, the small white dot in the middle will not only become smaller, but also appear in the shape of "8" or "∞", indicating point ghosting and pasting

to sum up, GATF data signal bar is characterized by providing a data. Point expansion gives a quantitative value, while the star can identify the type of point expansion. Both have their own uses and benefits, and can be used both to learn from each other

IV. test strip control point expansion

in the process of printing and plate printing, when the test strip controls the expansion of printing point, Bruner test strip is correspondingly the most widely used

composition of Bruner test strip:

50%50%75%75% on-site

fine thickness thick

fine: indicates fine point thick: indicates coarse point

Bruner test strip tight thick line point remains unchanged and does not expand as a reference

calculation basis of point enlargement

1. Taking the thick line as the reference comparison section, the thick and thin of Bruner test strip are 30 lines/inch and 150 lines/inch respectively. Therefore, the point enlargement of the 30 line/inch thick segment is ignored, and the 30 line/inch thick segment is set without point enlargement

2. Using the characteristic curve of density and point area

according to dr=tg1/1-a

a= -dr

, the density value is equal to the area difference

when testing with Bruner test strip, use a densitometer to measure the thickness first, then measure the thickness, and then use fine coarse = point expansion value

calculation method of Bruner point enlargement

1. Select 50% of the test points

point enlargement = (fine density - coarse density) × 100% = D fine - D coarse (where: D represents density)

2. Select 75% of the test strip

point expansion = (fine density - coarse density)/2 × 100%

advantages of the calculation point expansion of Bruner method

1. Bruner test strip calculation is simple

2. It can eliminate the test error. If there is an absolute density error in the test process. There are absolute errors in both fine and coarse points

dot enlargement = (d fine - D thick) × 100%

3. Because the thickness and fineness are measured at the same place and at the same time, the drying conditions of the ink are the same, and they are less affected by the printing ink, so they have nothing to do with the wet drying of the ink

the disadvantage of using Bruner test strip method to calculate point expansion

1, there is absolute error. It uses a = 1-10 - Dr

this formula assumes that the ink is completely absorbed on the paper and the paper is completely reflected. However, in the actual printing process, it is absolutely impossible to absorb 100% of the ink, and the whiteness of the paper is different, so it is impossible to achieve 100% total reflection

current point expansion (50%) = (fine coarse)/DR × 100%. At this time, the Bruner test strip cannot be tested

2, there are certain limitations

50%, (0.3-0.5) beyond this range is not enough

75%, if the (0.6-0.8) point expansion exceeds 15%, it cannot be calculated

selection of test points

1. Try to arrange the test points at the place with the largest point expansion (50% points)

2. Try not to choose the test point at the corner between points. Because the corner is unstable. Jumping occurs when the point at the corner is expanded

the principle of selecting test points

1. For the middle tone: for the manuscript with rich subtle levels and high quality requirements, 40% and 50% of the test points can be selected, such as the skin color and face parts of the characters

3. For ordinary products, 75% of the test points can be selected

error of test points

cultivate a batch of new material theme features town

1. At present, the commonly used Bruna test strips are copied, and there is copy error

2. The test strip is generally used in monochrome, so there is overlapping error

in addition, so far, all printing manufacturers have widely used the first, second and third generation Bruner test strips. The third generation Bruner printing test control strip was developed in 1984 and is divided into 7 sections. It can be used for years according to the required size. The content of control strip test includes: color code; 25% - 75% section; Bruner section III is on the spot, 50%, special test 1. Some industry elites with keen sense of smell are adjusting the direction of micro section from the red sea of traditional packaging; Neutral ash reduction section; Printing degree reduction section; Plate resolution section; Four color three section test section

it has the following test functions: to measure the layer density of MNP powder at about $78.8 on the current platform; Expansion of monitoring points; Check the deformation and ghosting at the printing time point; Determine whether the resolution and exposure of the printing plate are accurate; Control the specific changes of the layout depth during printing, proofing or printing, and check the distance between the parallel range of checkpoints and the area of different points; Control of printing fine spots; Ash balance detection; Detect the overprint percentage; Detect the density and hue of three colors y, m and C to restore black; Detect the printing density of monochrome ink

will also affect the measurement of the experimental machine. In actual production, the test strip is widely used in plate making, such as printing, proofing, printing and mechanical debugging

v. items detected by Bruner test control strip

1. Image clarity; 2. Whether the printing overprint is accurate; 3. Control of contrast of printed matter; 4. Reproduction of printing tone; 5. Color reproduction of printing ink; 6. Detect mechanical equipment failure; 7. Detection and evaluation of ghosting; 8. Expand the scope and types of points

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