7. Requirements for ink color and density for offset printing
â‘ The ink color of printing area is even. Based on the commonly used characters of the five Song Dynasty, the fine product density is 0.27-0.33, and the general product density is 0.25-0.35. The classical Chinese text is based on the word "zhe" or the same stroke, and the density data is the same as the word "zhe".
â‘¡ Field density. The measured color density of the printed folding paper ink is 0.9-1.3.
5. Other requirements of lithographic printing quality
1. Overprint
The contour and position of the image of the multi-color version should be accurately matched. The tolerance of the overprint of fine products is ≤0.10mm; the tolerance of the overprint of general printed products is ≤0.20mm. Overprinting requirements for offset printing books and periodicals; the positive and negative overprinting of printed book pages is accurate. Its overprinting tolerance error is less than 2mm for fine products and less than 3mm for general products.
2. Appearance
â‘ The layout is clean and dirty with no idea.
â‘¡The color tone of the printing joint should be basically the same. The allowable error of the fine product size is <0.5mm, and the allowable error of the general product size is <1.0mm.
â‘¢ The text is complete, clear and accurate.
3. outlets
â‘ Control range of increasing value of outlets
The dots are clear and the angles are accurate without ghosting. The increase value range of fine print dots is 10% -20%; the increase value range of general print dots is 10% -25%.
â‘¡The calculation method of the increase value of the network point
The dot increase value refers to the difference between the dot area of ​​a certain part of the printed matter and the dot area on the corresponding color separation sheet. The calculation formula is as follows
Printed dot area
A (%) = 100% × [1-10- (DT-DO)] / [1-10- (DS-DO)]
Where: Do is the reflection density value of the non-printed part on the printed product,
Ds is the reflection density value of the solid on the printed matter,
DT is the reflection density value of the dots of the printed matter.
The dot area of ​​the color separation film
A (%) = 100% × [1-10- (DT-DO)] / [1-10- (DS-DO)]
In the formula: Do is the transmission density value of the blank mesh tone film,
Ds is the transmission density value of the solid on the film,
DT is the value of the transmission density at the mesh point of the film.
Color class K value of fine printed matter K value of general printed matter
Y 0.25-0.35 0.20 = 0.30
M, C, BK 0.35-0.45 0.30-0.40
4. Relative contrast value (K value)
â‘ K value control range
â‘¡Calculation method of relative contrast value
K = DS-DT / DS
In the formula: DS-measured field density value
DT-measured dot density value
The integral density value of the dots is usually selected as 75% or 80% dots. Because this is the range where the circular dots start to connect (the connection point is 78.54%), and it is the transition area between the middle tone and the low key. The change of the dots in this area is the most significant for the visual stimulus. It can reflect whether the printed matter has sufficient contrast gradation and the thickness of the printed ink layer is moderate.
5. Overprint rate
Overprint rate is a comparison of the ability of an ink to adhere to paper and another ink. Factors that affect the ink overprint rate include ink layer thickness, ink viscosity, printing color sequence, and the interval between two-color overprint. Poor overprinting can cause color deviation and disorder of the product.
fD = D1 + 2-D1 / D2 × 100%
Where: fD-Overprint rate D1-First color density
D2ï¼Density of second color D1 ＋ 2ï¼Overprint density of first color and second color
If it is three-color overprinting, find the overprinting rate of the third color overprinting on the first two colors.
fD = D1 + 2 ＋ 3-D1 ＋ 2 / D3 × 100%
Usually, the overprint rate of the single-color machine is 70% -80%, and the overprint rate of the four-color machine is about 60%.
Author unit: Jiangsu Press and Publication School
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