Printing process is the transmit and
transfer of ink. How to make ink transfer correctly according to the needs of
production process in book printing in
China ? What are the factors that affect the ink transmit effect? How do
they match?
Transmit of offset ink
1. Transmit from ink fountain to
ink roller.
The ink in the ink hopper and the ink
hopper roller always keep good contact, so that the ink can be evenly sent out
by the ink hopper. This mainly depends on the rheological properties of the
ink: thixotropic cannot be too large, yield value cannot be too high, viscosity
cannot be too small, silk head cannot be too short, good rheological
properties. If the ink in the ink holder has a high yield value and low
viscosity, its inking performance is poor. Because it lacks the necessary
adhesion ability to the ink bucket roller, it is necessary to take out the ink
hopper frequently to ensure good contact between the ink and the ink bucket
roller, otherwise, the ink and the ink bucket roller will gradually separate
from each other, resulting in the front depth and back light of the printed
matter. In addition, we should pay attention to the ink storage in the ink
hopper, to keep in a certain range, and strive to make the ink uniform.
2. Transmit from ink bucket roller to ink
roller. Because the ink bucket roller of offset press rotates intermittently,
the ink output from the ink bucket roller is always an arc-shaped strip, and
the width of the ink strip can be adjusted. In the printing process, the
transfer mode of thin ink layer and wide ink bar is better than that of thick
ink layer and narrow ink strip, which can make the ink evenly as soon as
possible. After the ink is transferred from the ink hopper roller to the ink
roller, the ink can be quickly even through the frequent extrusion, shearing,
stretching and fracture of several inking rollers in a few seconds. It also
depends on whether the number and diameter of the inking roller are prime
numbers for each other, whether the ink transmission route is reasonable,
whether the ink is balanced, whether the ink roller surface adsorption is good,
and whether the ink conveying device of offset press is mostly long ink path
installation Set, is to use more than ten ink rollers to complete the transfer
of ink. In addition, the radial runout of the inking roller and the axial
movement of the inking roller will make the ink subject to certain radial and
axial shear stress. In the process of transfer, the ink will release a lot of
heat through the press of the ink roller, which will make the ink temperature
rise. For example, when the workshop temperature is 25, the ink temperature on
the ink roller will reach 40-50 after the machine has been running for half an
hour.
3. Transfer from inking roller to plate. In
offset printing, the plate is first wetted by the water roller, and then the
inking roller is in full contact with the plate to supply ink to the graphic
part of the plate. Generally, when the water film of the printing plate is 1
mm, it can block the ink on the ink roller in the blank part. If the blank part
of the printing plate water film is too thin, it will be dirty, water film is
too thick, ink emulsification will be excessive. So too much water will damage
the ink roller to the printing plate graphic part of the transfer of ink of the book printing in China, so we must
control the ink balance.
Transfer of offset ink
1. Conversion from plate to blanket. As
offset printing is indirect printing, the ink of the graphic part of the
printing plate must pass through the blanket before it can be transferred to
the surface of the substrate. Therefore, the surface of the blanket should have
good oil repellent and hydrophobic properties. There should be a reasonable and
uniform pressure between the blanket and the printing plate. When the graphic
part of the printing plate is transferred to the blanket, a part of the ink in
the graphic and text part of the printing plate must be preserved to protect it
The protective effect is not to be underestimated, but also indispensable.
2. Transfer from blanket substrate. When
imprinting ink layer is transferred from blanket to printed matter, the
pressure between blanket and substrate should be uniform. The ink receiving
performance of the substrate itself should be good, and it should have enough
strength. The surface should be smooth and the thickness should be uniform to
print a good product. The transfer of imprinted ink to substrate surface can be
divided into three steps: imprinted ink layer and substrate contact at the
beginning of transfer. Under the pressure of the plate, the ink is pressed into
the rough pores on the substrate surface, and the imprinted ink layer breaks. At
this time, due to centrifugal force and cavitation phenomenon, the ink layer
tensile fracture, but due to the ink on the substrate surface has a good
wettability, so that a part of the imprinted ink layer transferred to the
substrate surface. In book printing in
China, after the imprinted ink layer is divided into two parts, the
imprinted ink transferred on the surface of the substrate continues to
penetrate into the paper through the capillary adsorption. For the substrate
with smooth surface and low absorption, whether the imprinted ink layer can be
adsorbed on the substrate surface is mainly faster than the affinity of the
substrate surface to the ink, and faster than the force between the ink and the
substrate molecules.
