Analysis of the interaction between the hottest in

Analysis of the interaction between ink and fountain solution offset ink balance (I)

at present, offset printing is widely used in the printing field, and the ink balance in offset printing has always been the focus of the industry, and the operators have accumulated rich experience in the long-term production practice. At the same time, the hardware of the printing machine also creates conditions for the balance of ink and water

in the offset printing process, if any color ink wants to reach a certain density value on coated paper, the ink layer thickness is about 1 μ m。 Taking this value as the basic basis, this paper discusses the control of the thickness of the ink layer on the blanket, printing plate and ink roller and the influence of the thickness of the wetted plate liquid film, so as to explain the most basic problem of the thickness of the ink layer and water layer in the ink balance and its influence on the ink balance

inking system

1 Structure

the inking system of the printing machine is composed of ink bucket roller, ink transfer roller, inking roller, inking roller testing machine factory testing machine, etc., and the rubber ink roller and metal ink roller are staggered, and finally the ink in the ink bucket is transported to the printing plate

2. Ink separation

during the transmission of ink, the thickness of the ink layer on the ink roller gradually decreases. As shown in Figure 1, when the ink between two adjacent ink rollers (the ink layer of the upper ink roller is thick, and the ink layer of the lower ink roller is thin) enters the lower roller gap, taking the stretching attachment as an example, its pressure begins to rise, reaches the maximum value at a point not far from the center of the roller gap, and then drops to a degree lower than the atmospheric pressure at the outlet of the roller gap. Since at least one of the two ink rollers is a rubber ink roller, the deformation of the two ink rollers after contact will increase the pressure between the rollers. The greater the elastic deformation, the greater the pressure on the ink. The ink layer begins to split at the outlet of the roll gap. After separation, the thickness of the ink layer on each roller is equal and equal to half of the total thickness of the ink layer before passing through the roll gap, which is the so-called half ratio separation theory

except for the ink transfer roller and the ink bucket roller, the surface speed of all the ink rollers is basically the same, so it is mainly due to the average separation of the ink that the ink is transferred between the roller gaps. This ink transfer process is completed by the contact and separation of the ink layers on the two adjacent ink rollers. Thus, the ink layer thickness of the whole ink conveying system can be calculated

3. Ink layer thickness

assuming that the ink color is printed on the spot, the ink discharge amount of the transverse ink belt of the ink bucket roller is the same (approximately ideal state). If the thickness of the ink layer on the coated paper is 1 μ m. According to the half ratio separation theory, the thickness of the ink layer on the blanket is 2 before entering the roll gap (with the embossing cylinder) μ m. 1 after passing the roll gap μ m； Similarly, the thickness of the ink layer on the printing plate is 3 before passing through the roll gap (with the rubber cylinder) μ m. 2 after passing the roll gap μ m； The inking rollers (2 or 4) need to make up a total of 1 for the printing plate at a time μ M, so the ink layer thickness of the inking roller is 2.5 ~ 3.5 μ M, and the ink layer thickness of the adjacent ink roller is 4 ~ 6 μ m. These calculated data have been confirmed by the actual ink layer thickness measured by the infrared detector

this gradient of increase and decrease in ink layer thickness in the order of ink rollers only exists when the ink is transferred. If this series of ink rollers do not contact the ink bucket roller and the printing plate (non printing state), the ink attached to the ink rollers will be redistributed, and each ink roller will have the same ink layer thickness (about 4 ~ 6 on average) μ m) Therefore, when printing again, the thickness of the ink layer on the inking roller is slightly thicker than required

when the ink rollers of each printing unit are covered with a uniform thickness of ink layer, a more ideal inking effect of the printing plate can be obtained, that is, the amount of ink transferred to each printing unit is the same in the whole printing process, but in fact, the number of ink rollers required to meet this requirement is much more. Because the ink transfer roller swings intermittently, and the ink is transferred from the slow rotating ink bucket roller to the fast rotating ink roller, the transmission speed of the emission spectrum generally must be achieved at high temperature, so multiple ink rollers are required to beat evenly; The 30% vacancy on the plate cylinder will also make the ink transfer interrupted; The distribution positions of the printed pictures and texts of each printing unit are different, and the ink is not continuously transmitted to the printing plate. Therefore, the ink bucket screw adjusts the horizontal ink feeding amount according to the needs of the distribution of the pictures and texts of the printing plate; Adding an additional inking roller can reduce the inking bar (the ink density of the graphic part printed on the paper on the circumference of the drum changes suddenly); When the ink roller is young, the fountain solution will be transferred back to the ink bucket of the printing machine