Quality control of the printing process

(a) Variables affecting print quality

First, printing color order and overprint rate

1. Printing color sequence C - M - Y
2. Overprinted determination gravimetric method and density method
3. Influencing factors: ink thickness,
The viscosity and viscosity of the ink,
Ink drying, etc.

Second, network expansion

1. The definition of outlet expansion:
2. The calculation of dot gain (1) The Phi formula of Murry-Davis formula:
FD=[ (1-10-Dt)/ (1-10-Ds) ]*100%
Dot Gain= FD- FRP
Where FRP is the percentage of outlets on the original
(2) Print contrast (K value): K=[ (Ds- Dt)/ Ds]*100%
K value is between 0-1. Under stable printing pressure and good printing operation conditions, the dot gain value is the smallest when the K value is the largest, and the ink layer thickness on the printed sheet reaches the optimum value at this time.
3. Dot gain control (1) Two basic methods:
a. Mathematical calculation method: use the reflection density meter to record the numerical value, determine the dot gain value through calculation, and draw a corresponding graph for analysis. Characteristic: This method can give accurate increase value.
b. Visual contrast method: Using various signal strips and test strips to visually judge the degree of network expansion and the direction of expansion. Features: This method can only detect the approximate extent and range of dot gains, and cannot give accurate maximum values.
(2) Expanded test area:
The law of dot enlargement: The enlargement of the dot area is proportional to the length of the edge of the dot. The length of the edge of the halftone dot is relatively long, and the dot gain value is the largest. Theoretically, it can be shown that the dot gain is the largest at 50% of the square points; and 75% of dots are the most sensitive to the increase, and the visual response is also the most sensitive.
4. Influencing factors:
(1) Paper
(2) Number of screen lines
(3) Field density
(4) Ink (5) fountain solution
(6) Liners
(7) Printing speed
(8) Printing pressure
(9) Blanket
(10) printing plate
(11) Ink rollers

Among them, the impact of field density on dot gain is greater than any other parameter.

Third, the field density

The density of the ground and the percentage of outlets together constitute the main factor that affects the quality of image reproduction. In the printing process, the amount of ink is controlled based on the density of the field. The use of field density to calculate print contrast, overprint rate, etc., is an important factor in data management.
1. The relationship between density and ink volume in the field
DV=DVmax(1?ek?)
The density in the field does not increase indefinitely as the thickness of the ink layer increases. When the thickness of the ink layer increases to a certain value, the thickness of the ink layer continues to increase, and the density in the field has reached a maximum value, and the ratio is increasing.
2. The method for controlling the amount of ink is to print a solid color patch as a test mark at the tip of the paper, and it is repeated once every 10 cm.
The field density values ​​differ depending on the paper, ink and printing conditions used. For example, the general parameters are: Y: 0.90—1.10 M: 1.30—1.60 C: 1.50—2.00
The actual field density of the proofing is generally slightly higher than the printed one. Proofing outlets are less extensive.
(B) Quality Control Standards for Printing Products See GB/T 17934.2-1999 Printing Technology - Process Control for Mesh, Separation, and Printed Finishes - Part 1: Offset Printing

Reprinted from: Chinese Printing Community