Testing requirements and data usage of offset product quality (below)
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7. Requirements for ink color and density in offset printing
1 The printing ink is evenly colored. Based on the commonly used words of the Five Songs, the density of fine products is 0.27-0.33, and the density of general products is 0.25-0.35. The classical Chinese text is based on the word "人" or the same stroke, and the density data is the same as the word "".
2 field density. The printed label color density is 0.9-1.3.
FIfth, other requirements for the quality of lithographic prints
1, overprint
The contour and position of the multi-color version of the image should be accurately nested, the overprinting tolerance of the fine product is ≤0.10mm; the overprinting tolerance of the general printed matter is ≤0.20mm. Offset printing and printing requirements; printed book pages are positive and negative overprinting, and the overprinting tolerance error product is less than 2mm, and the general product is less than 3mm.
2, appearance
1 layout is clean, no trace of dirty.
2 The color of the printing plate should be basically the same. The tolerance of the size of the fine product is <0.5mm, and the tolerance of the size of the general product is <1.0mm.
3 text is complete, clear, and accurate.
3, outlets
1 dot gain value control range
The outlets are clear, the angle is accurate, and there is no ghosting. The increase value of the fine print dot is in the range of 10%-20%; the increase of the general printed dot is in the range of 10%-25%.
2 calculation method of dot gain value
The dot gain value refers to the difference between the dot area of a certain portion of the printed matter and the dot area on the corresponding color separation sheet. Its calculation formula is as follows
Print 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 matter,
Ds is the value of the reflection density in the field on the printed matter.
DT is the reflection density value of the spot on the printed matter.
Dot area of the color separation sheet
A(%)=100%×[1-10-(DT-DO)]/[1-10-(DS-DO)]
Where: Do is the transmission density value of the blank mesh film,
Ds is the transmission density value of the film on the ground.
DT is the transmission density value of the film access point.
Color, fine print, K value, general print K value
Y 0.25-0.35 0.20=0.30
M, C, BK 0.35-0.45 0.30-0.40
4, relative contrast (K value)
1K value control range
2 calculation method of relative contrast
K=DS-DT/DS
Where: DS-measured solid density value
DT-measured dot integral density value
The integrated density value of the dot is usually selected as a 75% or 80% dot. Because this is the range where the circular dot starts to connect (the connection point is 78.54%), and it is the transition zone between the middle tone and the low key, the change of the dot in this area is most significant for visual stimulation. It can reflect whether the print has sufficient contrast level and whether the imprinted ink layer is moderately thick.
5, overprint rate
The overprint ratio is a comparison of the ability of the ink to adhere to the paper to adhere to another ink. Factors affecting ink overprinting rate include ink layer thickness, ink viscosity, printing color sequence, and separation time between two color overprints. Poor overprinting can cause color deviations in the product and disorder.
fD=D1+2-D1/D2×100%
Where: fD-overprint ratio D1-first color density
D2-second color density D1+2-first color and second color overprint density
If it is a three-color overprint, the third color is overprinted on the first two colors, and the relationship is:
fD=D1+2+3-D1+2/D3×100%
Usually, the monochromatic machine has an overprint ratio of 70%-80%, and the four-color machine has an overprint ratio of about 60%.