Appeal No. 2001-1210 Page 5
Application No. 09/255,990
In offset lithography, it is common practice to apply dusting powder to
freshly printed sheets as they are delivered from the blanket cylinder of the press
in order to promote drying and prevent unintentional transfer of ink (set off) when
the sheets are stacked in face-to-face contact. However, if it is desired to rerun
the sheets for overprinting or multicolor work, it is necessary that the powder be
removed. Accordingly, when the final printed product is the result of
superimposing a number of different colors, the dusting powder is removed and
reapplied in each successive run. Besides dusting powder, unprinted sheets
direct from a paper mill may have residue particles deposited thereon as a result
of the milling process, and it is also desired to clean these sheets as they are
run.
Various devices are currently employed in offset presses to remove the
dusting powder from the sheets (or continuous paper web in web-fed presses)
prior to passage of the sheets between the impression and blanket cylinders.
One such device employs a suction head having a stationary brush assembly
which engages the surface of each passing sheet to sweep up the powder. This
arrangement suffers from the disadvantage that the brushes tend to accumulate
ink, thereby requiring frequent replacement, and the suction mechanism is
inherently bulky and noisy in operation. Another approach is to employ a cotton
roller in conjunction with a vacuum system to carry away the removed powder,
but here again the mechanism is inherently noisy. Furthermore, the cotton roller
is run in contact with the impression cylinder grippers and is, therefore, subject to
uneven wear and at times snags the leading edge of a sheet. The resulting jam
requires that the operation of the press be temporarily interrupted to correct the
condition.
It is, therefore, the primary object of the present invention to provide
apparatus for use in printing presses for removing dusting powder and residue
particles, which is relatively simple in construction, easy to maintain, and does
not possess the disadvantages mentioned above.
Grindley's invention utilizes a cleaning roller having a soft fibrous surface disposed
ahead of the blanket cylinder of an offset press, the surface presenting a nap
which swells upon rotation of the roller to wipe particulate matter (dusting powder or
residue particles) from the paper sheets before the same are printed. A trough
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