Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 3323 1 8
INKED DAMPENER FOR LITHOGRAPHIC PRINTING
A lithographic printing process dampening system is described that
utilizes dampening water input elements physically separated from a set of
two or more oleophilic and hydrophobic dampener rollers, one of which is a
form roller contacting the printing plate, which dampener set of rollers
become and remain inked during printing operations.
Background of the Invention
;~ In the art and practice of continuous lithographic printing, it is
essential to continuously supply, in addition to the printing ink, an
aqueous dampening solution to the printing plate or plates. The dampening
solution forms a water layer in all of the non-image areas of the printing
plate thereby disallowing transfer of ink from a separate ink input system
~ of rollers to all but the intended image areas of the printing plate.
y~ The dampening water in lithography is commonly supplied to the
printing plate in the form of a dilute aqueous solution containing various
proprietary combinations of buffering salts, gums, wetting agents,
alcohols, fungicides and the l~ke, which additives function to assist in
'the practical and efficient utilization of the various water supply and
dampeni~ng system combinations that are available for the practice of
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lithographic printing. Despite their very low concentrations-, typically
less than about several percent, the salts and wetting agents have in
practice been found essential if the printing press system is to produce
printed copies having clean, tint-free background and sharp, clear images,
without having to pay undue and impractical amounts of attention to inking
and dampening system controls during operations of the press.
In the practice of lithographic printing, different proprietary
formulations of dampening solutions are found to be of greatest utility
depending largely upon the configuration of the dampening system. There
is need for a dampening system that significantly reduces the apparent
dependence of dampening efficiency upon the particular materials in the
dampening solution.
A convenient way to describe all dampening systems, although this
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two-portion description is not often used in the trade, is to consider the
two necessary operations portions:
a. The water input portion consisting usually of a chromium or :~
cloth-covered pickup roller, or spiral-brush spray system, or spray
nozzles and the like, as well as the tubes, tanks and controllers, which
together convert an at rest bulk liquid dampening solution into a more or ;-~
less continuous directionally-oriented, relatively thin film or fine mist
of the solution, and `
b. The dampener portion consisting of a series of one or more
rollers that receive and then convey the thin film or fine mist of water
from the water input portion to a printing plate that is rotating at ~;
printing press speeds.
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Dampening systems may also be classified according to whether the
water being supplied at the printing plate cylinder of the press is
supplied before or after the ink is supplied.
It is repeatedly claimed that water-first dampening is better for
optimal printing quality than water-last dampening. In fact, most prior
art dampening systems, when used in the water-last position cannot
maintain the image differentiation at the printing plate that is essential
to lithographic printing. The practical reason for these observations is
that the film of water transferred to the plate by a water-last dampener
is applied after the ink has been refreshed to the plate image areas.
This water film may interfere with subsequent transfer of ink from the
printing plate to the printing blanket and thence to the paper being
printed, produc1ng printed copies of inferior quality and in the extreme
disallowing any ink transfer to the printing portions of the press.
Another reason for selecting water first dampening is that water-last
dampening systems tend to cause stagnation and water-logging of the ink
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that always resides on the rubber dampening form roller. This can result
in ink-slingin~ or even set-off of ink onto the printing plate in
non-~mage areas resulting in unwanted printed marks. The present
invention addresses and eliminates these heretofore accepted restrictions
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` of dampener location to water-first.
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Summary of the Invention
A principal object of this invention is to provide
lithographic dampening system that results in high printed
s copy quality independently of configuration sequence of the
ink input and water input at the printing plate.
Another objective is to provide a dampening system
that functions at the minimum possible water input rate
consistent with that required to retain image differentiation
at the printing plate.
A further object i8 to minimize the number and
frequency of ink and water balance related problems during
lithographic printing.
Yet another object is to provide a dampening system
utilizing an ink-biased series of distribution rollers which
does not require high levels of surface active additives to
assure efficient, high-quality lithographic printing
operation.
In accordance with an embodiment of the invention,
in a lithographic printing system having a plate cylinder and
inking apparatus for carrying ink from a reservoir to the -~
plate cylinder, the improvement being a dampening system
separate from the inking apparatus for carrying dampening
liquid from a source to the plate cylinder comprising a form
roller having an oleophilic and hydrophobic surface in rolling
contact with the plate cylinder; and apparatus for conveying
dampening liquid to the form roller from the source including
a dampener roller in rolling contact with the form roller with
an oleophilic and hydrophobic surface, the oleophilic and
hydrophobic surface of the form roller receiving from the
platç cylinder and retaining thereon a layer of ink which is -~
emulsified together with the dampening liquid at least in part
by the rolling action between the dampener roller and the form -~
roller before being conveyed to the plate cylinder, and the
35 oleophilic and hydrophobic surface of the dampener roller `~
receiving from the form roller and retaining thereon a layer
of ink which is emulsified together with the dampening liquid -
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at least in part by the rolling action between the form roller
and the dampener roller; and at least one other roller in
rolling contact with the dampener roller and having an
S oleophilic and hydrophobic surface, the oleophilic and
hydrophobic surface of the other roller receiving from the
dampener roller and retaining thereon a layer of ink which is
emulsified together with the dampening liquid at least in part
by the rolling action between the dampener roller and the
other roller.
In accordance with another embodiment, a method of
conveying dampening liquid to a lithographic plate cylinder
separate from the conveyance of ink thereto from an ink
source, is comprised of the steps of conveying dampening
liquid from a source to the plate cylinder by apparatus
including at least three rollers having oleophilic and
hydrophobic surfaces including a form roller in rolling
contact with the plate cylinder; conveying ink from the plate
- cylinder to the at least three rollers with oleophilic and
hydrophobic surfaces; rolling the dampening liquid into the
ink at at least two nibs of rolling contact between the at
least three rollers to create an emulsification of ink and
dampening liquid on the form roller; and transferring the
dampening liquid in the emulsification on the form roller to
the plate cylinder via rolling contact between the oleophilic
and hydrophobic form roller and the plate cylinder.
These and other objects and features will become
apparent by reference to the following specification and
drawings in which:
Fig. 1 is a schematic side elevation showing a
dampening system as applied to a press plate roll;
Fig. 2 is a modiried dampening system of the type
shown in Fig. 1;
Fig. 3 is a further modified dampening system
similar to those of Fig. 1 and 2;
Fig. 4 is an alternative arrangement in which the
dampening rolls are incorporated into the inking system.
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Fig. 5 is an illustration of an ink train dampening printing system
useful in comparing to this invention; and
Fig. 6 illustrates a conventional dampening system that the means and
method of the present invention replaces.
With reference to Figures 1, 2 and 3 the elements of our invention
comprise an input dampening solution means 100 and a dampener set of ;-
rollers 101. The dampener set of rollers have oleophilic and hydrophobic
surfaces and the set may consist of a receiving roller 102 or 102B, a
dampening form roller 103, transfer roller 104 and one or more rider
rollers 105. The oleophilic and hydrophobic surfaces help assure that all
of the rollers in dampener set 101 are able to carry an ink film during
printing operations despite the presence of large quantities of water.
All of the roller surfaces of the dampener set are rotating substantially
at press speed. Form rollers 103, rider rollers 105 and receiving roller
102B may be frictionally dr~ven by physical interference with the surface ;
of the plate cylinder 106 and/or with the separately driven receiving
roller 102 or transfer roller 104. As mentioned above, it is required
that all of the rolls used in the dampening system have surfaces that are
oleophilic and hydrophobic. Rolls possessing both oleophilic and
hydrophobic properties may be either metallic, such as copper, or
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non-metallic, such as rubber or plastic.
In the case of metallic or polymeric rubber or plastic rollers,
whether~soft or hard, this oleophil~c/hydrophobic behavior can be more or
less predicted by measuring the degree to which droplets of ink oil and of
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1 3323 1 8
dampening water will spontaneously spread out on the surface of the metal
or polymer rubber or plastic. The sessile drop technique as described in
standard surface chemistry textbooks is suitable for measuring this
quality. Generally, oleophilic/hydrophobic roller materials will have an
ink oil (Flint Oil Co.) contact angle of nearly 0 and a distilled water
contact angle of about 90 or higher. These values serve to define an
oleophilic/hydrophobic material. .
We have found, for instance, that the following rules are
constructive in but not restrictive for selecting materials according to
this principle: -
Best Water contact angle 90 or higher.
Ink Oil contact angle 10 or lower and spreading.
Maybe Water contact angle 80 or higher.
Acceptable Ink Oil contact angle 10 or lower and spreading.
Probably Not Water contact angle less than about 80.
Acceptable Ink Oil contact angle greater than 10 and/or
non-spreading.
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~ Another related test is to place a thin film of ink on the material
;~ being tested, then place a droplet of dampening solution on the ink film.
~ The longer it takes and the lesser extent to which the water solution
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displaces or debonds the ink the greater is that material s
oleophilic/hydrophobic property.
Materials that have this oleophilic/hydrophobic property will in
practice in a lithographic printing press configuration accept retain and
maintain lithographic ink on their surfaces in preference to water or
dampening solution when both ink and water are presented to or forced ~nto
that surface. It is this oleophilic/hydrophobic property that allows
rollers used in lithographic press dampener roller trains of this
invention to efficiently transport water from a water reservoir or water
input system to the printing plate regardless of whether a water first or
a water last configuration is used in the printing operation.
In the configurations illustrated in Figures 1 and 2 the oleophilic
receiving roller surface 102 may be a relatively hard inelastic substance
such as copper or a carbon filled Nylon polymer such as Rilsan or any
Gther oleophilic and hydrophobic nominally non-yielding material. The
transfer roller 102B surface of the Figure 3 alternative is selected from
among elastomeric rubber-like materials that are oleophilic and
hydrophobic. Rollers 102 and 104 are driven substantially at press speed
either by gear~ng the roller to the press drive or by electrically
coupling the speed of a separate motor attached thereto to the press
drive. Alternately roller 102B may be friction-driven by surface
interference contact with roller 104.
Form rollers 103 in the Figures 1 2 and 3 alternatives may be
elastomeric carbon-filled rubber dampener form rollers typical in the art
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and practice of lithographic dampening, which rollers are naturally
oleophilic and hydrophobic. Rollers 103 are advantageously friction
driven by interference contact with both the printing plate 10~ and the
relatively hard roller 102 or 104. Alternately, these rollers ~ay be
press driven or separately driven.
Rider rollers 105 may also be friction-driven and should have
surfaces made of an elastomeric rubber-like material that is oleophilic
and hydrophobic.
Figure 4 illustrates an alternative roller arrangement wherein the
dampener form roller 103 is part of an inking system of oleophilic and
hydrophobic rollers 102, 102A and 107 through 110. Other configurations
can readily be visualized using the principles herein disclosed without
departing substantially from the specified elements.
In agreement with prior experiences and art of lithography, we have
found that the dampening system in Figure 1 when used in the water-first
configuration operates satisfactorily as a lithographic dampening system,
even if a hydrophilic roller surface, such as chrome or nickel and the
like would be substituted for our specified hydrophobic and oleophilic
surfaced roller 102. However, when the Figure 1 dampening system is
fitted with a hydrophilic rather than an oleophilic and hydrophobit roller
102 and is used in the water-last position, we found that completely
unacceptable results may be obtained in cross-press regions corresponding
to low image content, the ink that always gradually builds-up on the
rubber dampen,ng form roller is more-or-less isolated between the
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water-covered hydrophilic predominantly non-image regions of the printing
plate and the water-covered surface of the conventionally hydrophilic
dampener roller. There exists no path for excess ink to be carried away
from those regions of the dampener form roller. The isolated or stagnant ~ ~-
ink picks up more and more water until it is so denatured that either it
slings off the roller onto surrounding surfaces or it transfers off onto
the plate thence to the paper, producing printed product of inferior
quality.
In more severe instances, some of the water that is more or less
uniformly delivered to all regions of the printing plate interferes with
transfer of ink from the image areas of the printing plate to the printing
blanket for transfer to the substrate being printed. We believe that the
quantity of dampening water continuously required to maintain clean
non-image areas on the printing plate using the Figure 1 dampening system
water-last is greater than the ~nk s abll~ty to continuously and rapidly
enough remove that portion of the input water unavoidably transferred to
the surfaces of the printing plate image regions. That is, the thin ink
film pressed by the form rollers onto the image areas of the plate
generally cannot rapidly assimilate and thereby remove the interfering
droplets or films or layers of dampening water from the surfaces of inked
image areas of the plate. The result is a severe reductlon in amount of
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ink transferred from the printlng plate to the blanket and to the paper
being printed. the interfering water layer remains on the image areas
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disallowing full transfer of ink to those image regions durlng the
;; rotationally subsequent contact with the ink form rollers. The result is
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a build-up of unused ink on the form rollers and a printed copy deficient
in intended optical density or even devoid of portions of the intended
image format.
When the configuration of Figure 1 is used in the water-last
position, but with oleophilic and hydrophobic roilers as specified in this
disclosure, acceptable image differentiation is obtained, although the
amount of operator attention required for balancing ink and water inputs
remains significant. The result is printed quality nearly equivalent to
water-first lithographic printing using the same dampening system. Of
course, good quality is also obtained when the Figure 1 alternative of
this invention is used in the conventional water-first alternative.
This distinction between operable and not inoperable dampening is
more dramatic when the water-first and water-last dampening positions are
compared using the dampener of Figure 2. Here, when the roller 102
surface is hydroph~lic the printing system operates no better than that
when the Figure 1 dampening system is used with a hydrophilic roller.
When roller 102 is oleophilic and hydrophobic as ia this disclosure,
excellent printing results are obtained using both dampener positions with
relatively little operator attention required and a normal range of water
input tolerance is present.
Further, when the dampen~ng system of F~gure 3 is used with
hydrophobic and oleophilic metering rollers, the prior art distinction in
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printing quality and in press stabil~ty between water-first and water-last
dampening positions is lost. The use of inked dampening rollers allows
superior printing despite water-last input of the dampening solution.
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This factor can be useful in the design of compact, efficient, convenient
multiple printing station printing presses. Heretofore, dampening systems
could safely be located only rotationally ahead of the inking input set of
rollers if acceptable printed quality was to be obtained.
It is our belief that the multiple contact points at roller nips of
the Figure 1, 2 and 3 configurations when specified according to this
disclosure provide multiple sites for mulling or mixing the incoming
dampening water into the films of ink on the dampener rollers and that it
is primarily within these films of ink that water is actually conveyed to -
the printing plate. This means is in marked contrast with the widely held
view used to design prior art dampening systems, namely, that the function
of the dampening system components is to form a sufficiently thin film of
water on a hydrophilic receiving or transfer roller that the water film
w~ll be abl.e to transfer within the millisec dwell time in a single nip
formed by t`he inked form roller and the hydrophobic roller carrying that
film of water.
In the present invention, we provide multiple inked rollers and we
provide ink films on all of the water-carrying rollers of the dampener so
that for instance the two-inked-roller dampener of Figure 1 has two
opportunities to mull the water into the ink films, this number being
greater than any of the prior art dampening systems which typically have
one or none. The three-inked-roller dampening system of Figure 2 is
accordingly better than the prior art and the four-inked-roller dampening
system of Figure 3 is so much better than the prior art systems that it
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1 3323 1 8
dispels the pre~alent trade myth concerning water-first verses water-last
dampening.
A set of illustrative printing tests was undertaken using the
ink-train dampening system of Figure 5 wh~ch has spiral brush water input
to a keyless lithographic printing couple. This configuration
approximates Figure 4 dampening in that several of the inking rollers are
also used as dampener rollers to convey water to the printing plate. In a
keyless printing press the ink input is uniform across the press width and
controlled by a celled metering roller and coacting doctor blade
substantially as disclosed in U.S.Patent 4,690,055. Keylessness is
incidental to this example and a brief description is included here for
sake of completeness of disclosure. A black keyless ink formulation
manufactured by J. M. Huber Ink Co. of N. J., and Dampening Solution 800
at 1-1/2 ounces per gallon of deionized water from C and W Unlimited,
Carlstadt, N. J. were used. The dampening solution input was adjusted as
low as possible and yet retain complete differentiation of image and
non-image areas at the printing plate to thereby obtain good printed copy
quality. During 60,000 copy print tests the dampening solution use was
,
; measured and under these conditions 0.25 ml to 0.29 ml of dampening
.~ solution per printed copy was required.
~ The same materials, press components and conditions as in the
,
preceding example, were used in separate tests except the spiral brush
; water input portion was placed together w~th a state-of-the-art dampener
` ~ roller portion in the direct-to-plate water-first configuration
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1 3323 1 8
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substantially as depicted in Figure 6. The dampening solution input
requirement was considerably greater, 0.33 ml to 0.37 ml per copy.
It was apparent that the inked set of rollers in the first example
delivered water more efficiently to the printing plate; that is, in a form
or in such a manner that it was more directly usable by the printing plate ~ ~-
than did the more conventional direct-to-plate hydrophilic roller
dampening system.
Accordingly, the direct dampener of our invention specifically and
advantageously uses a set of dampener rollers fully capable of accepting
ink in presence of both ink and water; that is, having oleophilic and
hydrophobic surfaces. And, also accordingly, we utilize inked dampener
rollers to carry water to the printing plate in our invention and
purposefully avoid any hydrophilic rollers in the dampener roller
portion. Obviously, one can advantageously use one or more hydrophilic
rollers in the water input portion of our invention as in prior art
water-input portions of lithographic dampenlng systems, as long as none is
included in the dampener train.
~The dampening systems herein disclosed significantly reduce the
:~ number and frequency of lithographic printing problems that are variously
termed in the trade as ink-water balance problems. We believe that the
`'primary reason for ink-water balance problems in the prior art resides in
the wide-spread expectation that the printing plate somehow accepts water
and ink only in the non-image and image areas respectively of the plate
when thin films of both are made available to the plate.
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None of the prior art dampening systems take into account that the
ink must very rapidly accept the excess water that is always depos~ted on
the image areas of the plate during each revolution of press. To do so
the water must be in a form much more conducive to diffusion int~ an ink
film than a continuous film of water on a hydrophilic dampener rc~ler
would be. ~e believe that our dampener systems meet this diffusional
criterion and that our systems actually introduce water to the printing
plate as minute droplets temporarily entrapped or emulsified in the ink
films and having dimensions comparable to that required for optimal
printed quality. To avoid water interference with ink transfer it is
generally accepted that the largest water droplet dimension should be less
than the smallest ink film thickness encountered during printing, namely,
less than about one to five microns. One way to assure formation of small
droplets of one insoluble material in another is to repeatedly mull the
two materials together. Repeated mulling of water into ink at t~o or more
,
inked dampener roller nips as specified herein accomplishes this
criterion. Consequently, we anticipate that our invention allows~broader
water-lnput operating range for a given set of ink and dampening solution
materials and press conditions. We also expect that a broader range of ~
ink and dampening solution formulations will be operable than that
encountered when using prior art dampening systems. Both of these
advantageous features function to reduce the number and severity of
printing problems associated with balancing the ink and water inputs for
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Prior art hydrophilic-roller-based dampening systems that utilize one
of the inking form rollers to convey water to the printing plate require
from about 10% to 25% of a bulk surface active additive such as
isopropanol to allow reasonably fast dampening water transfer from the
hydrophilic metering roller to the inked form roller. The alcohol acts to
assist the water-to-ink transfer process which, as previously discussed,
cannot otherwise occur within the short single nip dwell times of this
prior art system. Interestingly, hydrophilic-roller-containing dampening
systems are reportedly easier to control, to have more latitude in
ink-water balance, and to have fewer ink-water balance problems when 10%
to 25% isopropanol is used in the dampening solution, that is, when the
water is helped into the ink by means of the chemical additive.
The reason for this alcohol-assisted result i5 clearly related
directly to the absence of sufficient water-into-ink mulling action in
prior art dampening systems. And, accordingly, the dampening systems of
this disclosure do not require a surface assistance alcohol additive.
Mechanical mulling improves upon and replaces that additive's function.
This is a significant improvement in view of the cost, health hazard and
safety hazard associated with the use of isopropanol.
The advantageous features of inked roller ink-train dampening systems
have been previously noted herein as reference and background for the
present disclosure. It should be noted that ink train-dampening systems
have certain, somewhat adverse qualities that are avoided by using the
~` direct inked-roller dampening system of this disclosure.
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~ hen printing formats having cross-press locations that
circumferentially have low percent image, very little ink is printed out
onto the paper. Also, very little water is being printed out onto the
paper because the major path for water getting to the paper is by means of
the ink being printed out. Since dampening water input is more-or-less
uniform across the press, the water content of the ink residing on the
inking rollers in regions corresponding to low percent image may become
higher than the inks ab71ity to assimilate. This can result in sporadic
debonding of ink from the inking rollers by appearance of free water
layers causing localized build-up and slinging of ink onto various press
components. By using direct inked dampening as herein disclosed, an
additional path for water evaporation is provided, namely the inked
dampener rollers. The increased surface area allows evaporation of a
greater amount of this excess water in cross press regions corresponding
to the differing water contents. This minimizes the adverse affect of i~.
water build-up due to image format differences.
More importantly, the dampening water of this invention enters the
inking system only indirectly as compared to direct introduction of water
~nto the inking train. Only the water already supplied to the plate and
then fractionally removed by inking form rollers can enter the inking
system. Water content within the incoming ink on the dampener set of
rollers is thereby expected to be considerably lower than that encountered
in ink-train-dampening. Accordingly, fewer problems in adjusting for ink
and water input balance will be encountered.
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~ hen no ink is being printed out at specific cross-press locations,
it is common practice to use physical barriers or water stops or wipes
that allow only small amounts of dampening water to reach the plate at
those locations, that is, only enough water is allowed to keep those
non-image areas of the plate free of ink. To accommodate low inh coverage
regions where use of water stops is too severe, another typical practice
is to oscillate one or more of the dampening rollers and thereby laterally
distribute portions of the excess water. Accordingly, any or all of
dampener set of rollers in Figures 1, 2, 3 and 4 may advantageously be
caused to oscillate axially for similar reasons.
In keyless lithographic printing presses a significant portion of the
ink available to the printing plate must be scraped off and recirculated
to the ink input portion of the inker. Since this serves to carry excess
water away from the printing plate and redistribute it across the press
width, water stops may generally not be required and oscillation as a
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cross-press water distribution means may become redundant.
~e believe that the elements of our invention, taken together,
operate upon startup of a printing press to which the dampening system -~
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described herein is attached by rapidly removing some of the ink from the
printing plate image areas, or in Flgure 4 alternative from an inking form
roller, to quickly establish a thin film of ink on all of the dampener
rollers. ~ater being applied to the receiving roller as a mist or spray
is mulled, mixed and emulsified into these ink films on the dampener
rollers by the shearing conditions at each of the roller-to-roller nips of
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the dampener set. This establishes a continual refining of the initially
large input drops or mist of water as it traverses the dampener rollers
towards the plate, becoming micron and sub-micron sized droplets suspended
in the ink by the time they reach the form roller and the plate. As such,
their dimension is smaller than the ink film thickness at the printing
plate, which small droplets can readily and rapidly transfer back and
forth between inked and non-inked areas of the plate, thereby functioning
to supply water to the non-image areas where it is required. The dampener
of this invention thereby also disallows formation of free water films in
the plate image areas that could interfere with subsequent transfer of ink
either to the plate from the inking form rollers or from the plate to the
printing blanket, thence to the substrate being printed.
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