For book printing, to appear misting, not
only pollutes the environment, but also damages the health of operators. The
following is a brief analysis of this issue.
1. The
causes of misting
When
the ink is transferred, two or more fibers are in contact with each other at
two ink rollers in contact with each other. When the ink is cut or elongated,
fragments are generated and the surface tension becomes spherical. At this
moment, the electric double layer existing at the interface between the fiber
and the fragment is destroyed, one part remains in the ink and the other part
escapes to the atmosphere with the opposite charge. When the fiber is
shortened, the residual charge in the ink is gradually piled on the ink roller
and paper surface. Fragment due to the same charge with the ink, near the ink
roller or paper, was excluded in the air to appear misting.
When
the high-speed machine with sticky ink, low-quality link material, easy to ink
in the ink roller rotation, pulled into filaments have a serious flying ink, so
different models of printers need to select the appropriate ink to match.
2. The
factors of misting
(1)
ink viscosity is too large, the ink is stretched out at the ink roller exit,
easy to produce flying ink, but also cause uneven ink transfer, so that paper
plucking powder, paper stripping difficult from the blanket, easy to spend version,
off the plate, etc.; viscosity is too small, poor splitting of the ink layer,
easy to appear misting, easy to make the ink emulsified, floating dirty, paste
version, network expansion, affecting the quality of printing products.
(2) The
thicker layer ink roller, the larger the misting. Proofing on coated paper, the
ink layer thickness of 1.2μm, the printing ink as long as 2.8g / m2 on the
line; but with offset printing, ink version at least to achieve 4g / m2.
Encountered the performance of the paper adhesion to the ink is not good, easy
to cause ink roller heap ink, resulting in flying ink.
(3) Roller
surface uneven and surface dry crack, the part of the ink layer thickening, ink
mist increases, easy to appear misting.
(4)
Printing speed increases, misting increases.
(5)
The relative humidity of the air is low, promoting to appear misting; when the
humidity is increasing, the electric charge is reduced and the amount of misting
becomes smaller.
(6)
If the ink in the fountain solution too much, the formation of serious W / O
emulsion ink, a sharp decline in viscosity, ink shorter, will have a serious misting
phenomenon. At the same time, immersion ink fountain solution will corrode the
metal roller, forming a hydrophilic layer on the surface of the ink roller to
repel ink, resulting in deinking of metal roller.
(7)
high-molecular weight ink of the material, easy to pull into filaments in the
ink split, resulting in appears misting.
3. How to eliminate misting
(1)
Selection of high-quality alcohol-based ink, to adapt to high-speed printing.
(2) Regularly remove the roller to clean thoroughly, so that the
Mexican ink layer uniform, ink transfer performance.
(3) Alcohol
concentration control between 10% -15%, too low or too high are not suitable.
(4) The
amount of water bucket should not be too large, or cause ink shorter,
unfavorable printing.
(5)
When adding the electrolyte in the ink, the misting will be reduced, with the
addition of electrolyte, conductivity increases, the phenomenon of misting will
completely disappear.
