Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to apparatus for liquid coating of a
moving nonporous web and, more particularly, relates to apparatus for
this purpose in wl-ich the coating roll surface and ~he web move in
opposite directions, or move in the same direction at different
relative speeds.
Presensitized lithographic printing plates are usually
manufactured by applying a controlled film of photographic liquid
such as a diazo resin, on a moving web or substrate of essentially, non-
porous material such as aluminum. Perhaps, the most simple coating
apparatus utilize dip coating methods. In direct dip coating the
portion of a web wound about a backing roller is guided for shallow
dipping in a solution reservoir, and in indirect dip coating an
applicator roll partially immersed in the solution reservoir transfers
coating solution from the reservoir to the web,
When relying upon dip pickup of solution great difficulty is
encountered in maintaining uniform coating weight or thickness. Thus3
mechanical "post metering" as by a doctor blade or squeeze roll is
oten utilized in an effort to control film thickness. However>
characteristics of the photographic liquid are such that it is
difficult to prevent streaking when post metering is used and to control
; film thickness with variations in web speed or solution characteristics
of viscosity, density and/or surface tension.
Devices for doctoring coating rolls have been found to be
; very sensitive to pressure, surface and solution characteristics, so that
they are difficult to preset or to maintain at settings to obtain desired
coating results. Thus, curtain and bar coater devices have been
; utilized to deposit a film of coating solution on a moving web. These
latter devices require a high degree of operator attention and close
maintenance for initial adjustment and adjustment as web speed changes.
Here again physical properties of the photographic solution have presented
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di~ficul-ties especially in areas o~ smooth flow and leveling
especially i~ thickness is to be controll0d u-tilizing dif~erent
solution mixes or over reasonable range of web speeds.
Other prior art coaters utilize gravure rolls. While
prior art gravure roll devices were satis~actory for coating
porous webs, they were unsatlsfactory for use with non-porous
substrates since the cell pattern was often imparted to the
surface coating and transfer of coating solution from the cells
of the gravure roll to a non-porous surEace is difficult to
control.
According to the present invention there is provided
apparatus for applying a film of coating solution by meniscus
coating on a moving web substrate of essentially non-porous
material, said apparatus including a rotatable gravure roll,
first means for supplying cells of said gravure roll with
coating solution and for doctoring the coating solution
supplied to said cells, a rotatable relatively smooth surfaced
coating roll operatively positioned to receive solution
from said cells, guide means for directing said web through
a transfer region where said web receives said coating
solution from said coating roll, wherein in operation, said
web moves in a direction opposite to the direction of motion
of the surface of said coating roll.
Thus, this invention provides apparatus for manufacturing
lithographic printing plates by applying a photosensitive
lithographic coating to sheet aluminum. Such apparatus includes
a reverse offset gravure method for coating either one or
both sides of a moving web substrate. That is, the ceLls
of a gravure rol:L are filledand then doctored by a blade.
Thereafter, solution is transferred from the cells to the
relatiyely smooth surface, preferably rubber or rubber-like
of a coating rol~L. Solution is transferred from the latter to
a web moving tangent to the outer surface of the coating roll,
and in the opposite
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direc~ion. A mirror image arrangement of the gravure and coa~ing rolls
permit simultaneous coating of both web surfaces.
The invention is further illustra~ed with reference to the
accompanying drawings showing~ by way of exampleJ an embodiment of the
invention, in which:
Figure 1 is a side elevation, in schematic form, of coating
apparatus constructed in accordance with teachings of the instant invention.
Figure 2 is a plan view of the coating and gravure rolls
looking in direction of arrows 2,2 in Figure 1.
Figure 3 is an enlarged view looking into a cell of the
gravure roll through the open end of the cell.
Figure 4 is a cross-section taken through line 4-4 of Figure 3
looking in the direction of arrow 4,40
A substrateJ of aluminum or the like, to receive coatings 11,11
of pho~ographically sensitive solution is constituted by continuously
moving web la. The latter is guided by rolls 12>13 so that in the region
therebetween web 10 moves vertically upward with respect to Figure 1.
At a transfer portion of this vertical regionJ web 10 passes between a
pair of relatively smooth surfaced rubbar coated transfer or coating
rolls 14,15 which rotate on respective axes 16,17. In this transfer
region web 10 is plana~, being tangential to rolls 14~15 rather than
being partially wrapped therearound. A common plane con~aining axes
16 and 17 is perpendicular to web in this transfer region.
In an alternative ~o the foregoingJ we have also :Eound that it
is possible to successfully practice this invention when the axes of
the rolls are not contained in a common plane~ We have found that it is
possible to ob*ain satisfactory results when the axes of one set of
rollers, i.e.J 15 and 25 are in a plane whlch is offset~ that isJ higher
or lower than the plane containing the axes of rollers 14 and 24. The
a~o t of offset can be dete~ined by the worker skilled in the art
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depending upon the coating resul~s desired to be obtained. Likewise,
when the rollers are in an offset position as aforesaid the distance
bctween ~he sets of rollers can be altered in accordance with the results
desired.
Disposed adjacent rolls 14,15 are respective gravure rolls
24,25 which are rotated on respective axes 26,27. The latter are
parallel to and laterally offset from axes 16,17. Quadrangular cells
18 ~igure 3 and 4) are formed in the cylindrical surfaces o~ gravure
rolls 24,25. Disposed adjacent these cylindrical surfaces and extending
parallel to axes 26,27 are doctor blades 22,23, respectively. Doctor
blades 22,23 cooperate with rolls 24,25 to form open ended troughs wherein
photosensitive coating solution delivered by respective distribution
nozzle means 28,29 is accumulated in shallow puddles 32,33 adjacent the
cellular surfaces of rolls 24,25 respectively, Disposed below rolls 14
and 24 is pan 34 ~o catch drippings from these rolls and from puddle 32.
A similar pan 35 is disposed below rolls 15 and 25 to catch drippings from
these rolls and from puddle 33.
In operation, coating solu~ion supplied hy nozzle means 28
overfills cells 18 of gravure roll 24. Doctor blade 22 levels the
solution in cells 18 of roll 24 after which the solukion in these cells
is picked up by coating roll 14 which transfers this solu~ion to one
: surface of web 10. Roll 14 rotates clockwise so ~hat the outer surface
thereof moves opposite ~o the direction of movement for web 1~. As seen
in Figure 2, the end portions of roll 14 are undercu~ and the central
portion between these undercuts is slightly narrower than web 10. Thus,
coating solution is not placed across the entire width o~ web 10 so that
solution applied by roll 14 will not migrate to the other surface of web
10. In a similar manner, this other surface is coated by solution
delivered by nozzle means 29 to puddle 33.
Downstre~n of the transfer region between coating rollers 14,15,
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and upstream of guide roll 13, the coated web 10 passes through a dryer
or curing means which is illustrated as a single device 41 where
photoscnsitive films 11,11 are dried or cured.
In the even~ only one surface of web 11, say the left vertical
surface with respect to Figure 1 is to be coated, roll 15 opcrates as an
idling backup roll and gravure roll 25 :is moved out of operative engage-
ment with roll 15.
Pnet~atic devices~ not shown, are provided to adjust and
maintain operating pressures between gravure rolls 24,25 and coating
rolls 14,15 as well as pressure between the latter and web lO. The
speeds of rolls 14,15,24,25 are controlled and main~ained individually.
Either contact or meniscus transfer may be used for pickup of solution
: by web 10 and/or by coating rolls 14,15. Nozzle means 28 and blade 22
may be connected to form a subassembly that is oscillated parallel to the
longi~udinal axis of blade 220 Similarly, another oscillating
subassembly may be formed of nozzle means 2g and blade 23.
Although in the foregoing preferred embodiments have been
discussed, many varia~ions and modifications will now become apparent ~o
those skilIed in the art and it is therefore understood that this
invention is not limited by the disclosure but only by the appending
claims.
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