Apparatus for reducing chill roll condensation

An apparatus for dispersing contaminants from the surface of a web moving in a processing direction within a web processing system, the web processing system including a web processing structure, the apparatus including a chill roll air bar disposed proximate to a surface of the web, for separating the contaminated air from the surface of the web before that surface of the web engages the processing structure.

TECHNICAL FIELD 
The present invention relates, generally, to mechanisms for reducing chill 
streaking problems on a web in multicolor web-fed printing press systems 
by preventing formation of chill roll solvent condensation. More 
particularly, the present invention is related to methods and apparatus 
for non-invasively reducing condensate streaking on the web without 
contacting the web or the chill roll, thereby improving the quality of the 
printed product at high press speeds. 
BACKGROUND OF THE INVENTION 
In multicolor web-fed printing press systems, a web of material (e.g., 
paper) is sequentially driven through a series of printing units, each 
comprising a plate cylinder and a print cylinder (blanket cylinder). Each 
blanket cylinder contacts the web in sequence and applies a different 
color of ink thereto, which colors cooperate to imprint a multicolor image 
on the web. As the web exits the printing units, the ink is still wet, and 
thus subject to smearing. Accordingly, for further processing, the web is 
typically routed through a drying unit to dry the image, heating the web 
to evaporate various solvents in the ink, then to a chill roller unit to 
cool the web and harden the ink. 
To provide an accurate and clear multicolor image, the rotational and 
lateral position of each blanket cylinder must be precisely aligned, i.e., 
proper registration of the respective colors must be maintained. Sources 
of inaccurate color registration include web "weave" (spurious lateral 
movement of the web, e.g., movement transverse to the direction of web 
travel, in the plane of the web) and web "flutter" (spurious movement of 
the web in a direction perpendicular to the plane of the web). 
Other factors may also affect print quality. More particularly, the printed 
web may display streaking marks as the web exits the chill roller unit. It 
is generally accepted that this web streaking problem, commonly called 
"chill streaking" or "condensate marking", is caused by the formation of a 
contaminant condensate film typically on the first roller of the chill 
roller unit. 
In order to dry the image printed on a web, the drying unit heats the web 
which evaporates various solvents in the ink. The majority of the 
contaminated warm air, which contains evaporated ink solvents and gases 
from the combustion in the drying unit as well as evaporated moisture from 
the web, is directed through an exhaust system comprising pollution 
control devices designed to eliminate the contaminants from the warm air 
before exhausting it to the outside. However, part of the contaminated air 
is not processed through this exhaust system. This is because as the web 
exits the drying unit, a boundary layer of contaminated warm air, which 
adheres to the upper and lower surfaces of the web, is entrained by the 
web toward the next processing station, namely, the chill unit. As the web 
engages the first roller of the chill roll unit, the contaminated warm air 
may become trapped between the surface of the web and that of the cool 
chill roller or may condense on the relatively cool surface of the chill 
roller. As a result, a condensate film, containing contaminants, forms on 
the surface of the chill roller. This condensate, which is in direct 
contact with the web, is the source of the "chill streaking" problem 
commonly occurring in such printing press systems where the image on a web 
is dried by a hot drying process. 
To eliminate the formation of streaking marks on the web, a commonly used 
approach has been to reduce the speed at which the press operates thereby 
reducing the amount of contaminants entrained by the web out of the drying 
unit. Although this approach is successful in most cases, it is, for 
economical reasons, highly undesirable since throughput of the printing 
press system is thereby reduced. 
Another method to reduce chill streaking consists of increasing the tension 
to which the web is subjected by the printing press so as to assure a more 
uniform contact between the web and the chill roller. Under increased web 
tension, it becomes more difficult for the contaminated air to "lift" the 
web off the chill roller and, accordingly, condensation on the chill 
roller is reduced. This method, which gives adequate results under uniform 
web characteristics, is of limited effectiveness in practice since web 
characteristics generally vary over a given press run. Accordingly, as the 
web stretches, a gap will appear between the surface of the web and the 
surface of the chill roller, allowing condensation to form therebetween. 
Conversely, increasing web tension to eliminate the gap between the chill 
roller and the web in order to reduce chill marking increases the 
likelihood of web breakage. 
Other approaches have been tried to eliminate chill marking by either 
invasively removing the condensate deposit from the chill roller, as by 
wiping, or by preventing formation of condensate while keeping the press 
operating under normal speed and web tension conditions. An example of a 
system using the former approach is illustrated in a sales brochure 
entitled "Chill Roll Cleaner, Model 1301," by Baldwin. 
FIG. 2 shows a section view of a prior art chill roll cleaner 
representative of the Model 1301 Baldwin device. In FIG. 2, a chill roll 
cleaner 217 is mounted on a first chill roller 115 of a chill unit 114 and 
continuously cleans first chill roller 115 by pressing an absorbent 
material 223 against the surface of chill roller 115. Absorbent material 
223 of chill roll cleaner 217 is dispensed by a feed roller 219. Soiled 
absorbent material 223 is collected over a collect roller 221. The 
frequency of advance of collect roller 221 is adjusted by the pressman as 
necessary to achieve adequate cleaning of chill roller 115. 
Such an invasive system offers increased safety and some degree of 
automation over manual cleaning, since manual cleaning requires the 
pressman, during operation of the chill unit, to manually sweep the 
condensate film off the chill roller. However, invasive prior art systems 
have disadvantages. First, as with manual sweeping, the condensate film is 
removed through an invasive process, that is, a cleaning material makes 
direct contact with the surface of the chill roller. Direct contact with 
the surface of a chill roller increases the risk of damaging the chill 
roller as dust particles trapped between the cleaning material and the 
chill roller are continually dragged over the same area of the chill 
roller surface, eventually leading to a press shut-down to resurface or 
replace a damaged chill roller. Second, such an invasive chill roll 
cleaner system generally results in additional or longer press down-time 
when a new cleaning material feed roller needs to be installed. Finally, 
special procedures for proper disposal of soiled cleaning material must be 
followed as the condensate, which contains ink solvents and combustion 
products may be considered a toxic waste. 
Another attempt to deal with the chill streaking problem has been to 
prevent formation of the condensate deposit on the chill roller without 
increasing web tension as by forcing web-to-roll contact. An example of a 
system using this forced contact approach is illustrated in a sales 
brochure entitled Chill Jets.RTM. by TEC Systems. 
FIG. 3 shows a section view of a prior art system representative of a 
forced contact system mounted on a first chill roller 115 of a printing 
press chill unit 114. In FIG. 3, a high pressure, air jet 321 is 
discharged from a nozzle 323, against the surface of web 110 and toward 
first chill roller 115. Web 110 is thereby forced into contact with the 
surface of chill roller 115. As a result, web "lift off" is reduced which 
squeezes the contaminated air from between the surface of web 110 and 
chill roller 115, thereby preventing condensate streaking. 
Although such prior art forced contact systems, which discharge an air flow 
against the upper web surface (i.e., the surface which does not make 
contact with the chill roller) to force contact between the lower surface 
and the chill roll, are adequate in certain cases, the operation cost of 
such systems is high since such a system requires high pressure air for 
operation. In addition, the present inventors have determined that such 
forced contact systems are inadequate in applications using heavy, high 
quality webs, or in applications involving dense or thick ink coverage. 
The inventors believe that such inadequacy is probably due to the fact 
that forced contact systems are not effective in controlling web 
instability (induced by web flutter and web weave). The forced contact 
approach is therefore unable to keep the web uniformly in contact with the 
chill roller so that the contaminated air is allowed to come in contact 
with the chill roller and condense upon the chill roller. The limited 
effectiveness of such a forced contact approach is particularly apparent 
in high quality printing jobs where heavier webs are generally used. 
Such forced contact systems may also contribute to environmental 
contamination by dispersing the contaminated air in an associated 
pressroom environment. 
Thus, a non-invasive, low operating cost system is needed to reduce the 
formation of chill roll condensate in order to facilitate production of 
high quality printed images without sacrificing press speed or increasing 
web tension, and without exacerbating contamination of the pressroom 
environment. 
SUMMARY OF THE INVENTION 
The present invention facilitates reduction of chill streaking problem on a 
moving web being imprinted in a printing press system by dispersing 
contaminants from the surface of the web, thereby preventing the formation 
of chill marks. By preventing condensation of the contaminated warm air 
entrained by the web upon the chill roller, the formation of chill marks 
is avoided. In accordance with one aspect of the present invention, a 
chill roll air bar is disposed proximate the web between the drying unit 
and the chill unit of a printing press system. 
In accordance with a further aspect of the present invention, the amount of 
contaminated air dispersed in the pressroom atmosphere may be reduced. In 
a preferred embodiment of the present invention, a chill roll air bar may 
be disposed proximate the lower surface of the web, by Which lower surface 
the contaminated air is generally entrained. The air bar may be disposed 
immediately downstream of the drying unit to force the contaminated air 
back into the drying unit as it is separated from the surface of the web 
to most effectively reduce dispersion of contaminants in a pressroom. 
Other objects and advantages of the present invention will become apparent 
from the detailed description given hereinafter. It should be understood, 
however, that the detailed description and specific embodiments are given 
by way of illustration only, since, from this detailed description, 
various changes and modifications within the spirit and scope of the 
invention will become apparent to those skilled in the art.

DETAILED DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT 
Referring now to FIG. 1, a web-fed printing system 100, preferably 
including a printing press 101 and comprising a plurality of serially 
disposed conventional printing units 102, 103, 104 and 105, operates upon 
a web 110 driven at a first velocity in a web processing direction. In a 
web offset printing press, each of printing units 102-105 advantageously 
includes an upper blanket cylinder 116, an upper plate cylinder 117, a 
lower blanket cylinder 118, and a lower plate cylinder 119. Web 110, 
typically paper, is fed from a reel stand 120 through each of printing 
units 102-105 in sequence and thereafter through a dryer unit 112 and 
chill unit 114. Web 110 is then suitably guided through a coating unit 122 
and a folding station 124 which folds and separates the web into 
individual signatures. 
Printing units 102-105 cooperate to imprint multicolor images on the upper 
and lower surfaces of web 110. Each printing unit 102-105 prints an 
associated color of ink. Each of the lateral and rotational positions of 
upper and lower plate cylinders 117, 119 is separately controlled by 
electric motors (not shown) to precisely register the respective images 
generated by the individual printing units. 
In the embodiment of FIG. 1, a non-invasive stabilizer bar 130, located 
between press 101 and dryer 112, is employed to facilitate scanning of the 
web without causing the image imprinted on the respective surfaces of web 
110 to smear. One or more optical scanning units 131A, 131B, associated 
with a register control system 170, such as, for example, a Quad/Tech RGS 
IV Register Control System, are disposed to scan web 110 in a stabilized 
area in the vicinity of stabilizer 130. Register control system 170 
provides appropriate signals to the electric motors of the plate cylinders 
to precisely control lateral and rotational position of the upper and 
lower plate cylinders, respectively. 
In accordance with one aspect of the present invention, a chill roll air 
bar 530 is employed to reduce condensate streaking of web 110 as web 110 
is cooled through chill unit 114. Chill roll air bar 530 is preferably 
disposed between dryer unit 112 and chill unit 114, immediately at the 
exit of dryer unit 112, but may be located anywhere intermediate the exit 
of dryer unit 112 and the entrance of chill unit 114. In the embodiment 
illustrated in FIG. 1, chill roll air bar 530 is disposed underneath web 
110 and is advantageously mounted to a side frame 529 of dryer unit 112. 
As shown in FIGS. 4, 5 and 6, chill roll air bar 530 preferably comprises a 
housing 532 containing pressurized air. Housing 53 is disposed transverse 
to the web processing direction, and extends substantially across the 
width of web 110. Chill roll air bar 530 exhausts a high velocity stream 
533 of air against a lower surface 111 of web 110. As air stream 533 
impinges on moving web 110, air stream 533 moves away from chill roll air 
bar 530, along the downward facing surface 111 of web 110 with a velocity 
component substantially parallel but in a direction generally contrary to 
the web processing direction. In accordance with the "Coanda effect" 
(which is explained in more detail below in conjunction with FIG. 8), air 
stream 533 entrains a stream 531 of ambient air. High velocity air stream 
533 combines with ambient air stream 531 to create a high velocity, high 
volume, increased air stream 539. The high velocity (preferably 
approximately 10 times the velocity of web 110) of increased air stream 
539 moving along downward facing surface 111 of web 110 creates, according 
to the Bernoulli principle.sup.1, a zone of reduced static pressure 
adjacent lower surface 111 of web 110 and the upper portion of a guiding 
strip 536 of chill roll air bar 530. As a result of lower pressure in the 
lower surface 111 of web 110 induced by increased air stream 539, and a 
relatively higher static pressure present at the upper surface 113 of web 
110, web 110 is urged toward guiding strip 536. At the same time, the 
presence of increased air stream 539 between the lower surface 111 of web 
110 and guiding strip 536 prevents web 110 from contacting chill roll air 
bar 530. 
FNT The Bernoulli principle establishes that the sum of static and dynamic 
pressures is constant at all points where a fluid passes a surface. Thus, 
an increase in velocity of fluid passing a body (increase in dynamic 
pressure) yields a decrease in static pressure exerted by the fluid upon 
the surface. 
Accordingly, for example, as flutter may urge web 110 away from the chill 
roll air bar 530, web 110 is urged towards chill roll air bar 530 because 
of the Bernoulli effect established by increased air stream 539. Thus, web 
110 is substantially stabilized in the vicinity of chill roll air bar 530 
and an essentially constant gap 537 is maintained between the upper 
surface of guiding strip 536 and lower surface 111 of web 110. As a 
result, increased stream 539 of high velocity air comprising pressurized 
air stream 533 and entrained air 531, is constantly allowed to move 
through gap 537, in a direction contrary to the web processing direction. 
Moreover, as the velocity of increased air stream 539 is significantly 
greater than the velocity of web 110, the resulting velocity of increased 
air stream 539 with respect to the velocity of web 110 is appropriately 
sufficient to separate contaminated air 541 from surface 111 of web 10. 
By locating non-invasive chill roll air bar 530, between dryer unit 112 and 
chill unit 114, increased air stream 539 operates as a non-invasive 
convective surface device which separates the contaminated air 541, 
entrained with web 110 out of dryer unit 112, from the lower surface 111 
of web 110 before web 110 engages first roller 115 of chill unit 114. As a 
result, the formation of contaminant condensate on the surface of first 
chill roller 115 is avoided, thereby reducing "condensate marking" on web 
110. 
Although it is difficult to quantify this separating/dispersing action, it 
is, however, possible to estimate its strength by calculating the shear 
stress applied by increased air stream 539 to surface 111 in separating 
contaminated air 541 therefrom. More specifically, and as indicated in 
Fluid Mechanics, by Frank White, McGraw-Hill, New York, 2nd ed., p. 306, 
for ease of calculation, the area along air bar 530, i.e., across the 
width of web 110, defined by oppositely facing surfaces of guiding strip 
536 and lower surface 111, can be modelled as duct flow. Accordingly, the 
shear stress .tau. in that area can be calculated from: 
##EQU1## 
where: .mu.is the dynamic viscosity of increased air stream 539; 
U.sub.0 is the velocity of increased air stream 539; 
d is the hydraulic diameter of the duct for non-circular ducts; 
A is the cross sectional area of the duct (i.e., height of gap 537 
multiplied by width of web 110); and 
p is the wetted perimeter of the cross section (i.e., twice the height of 
gap 537+twice the width of web 110). 
As can be seen from equation (2), the higher the velocity U.sub.0 of 
increased air stream 539 or the smaller the cross sectional area A of the 
duct, (e.g., the smaller the height of gap 537), the higher the shear 
stress and the more effective increased air stream 539 will be at 
separating contaminated air 541 from surface 111. 
Reduction of condensate marking is also facilitated by the fact that, in 
addition to separating contaminated air 541 from web 110, high velocity 
increased air stream 539 also pre-cools web 110 before web 110 enters 
chill unit 114. As a result, the temperature differential between web 110 
and chill roller 115 is substantially reduced, thereby making condensation 
of any portion of contaminated air 541 which may remain with web 110 less 
likely. 
In addition to reducing condensate marking, chill roll air bar 530 also 
reduces wrinkling of the images printed on web 110. Such wrinkling 
typically occurs during long unsupported spans. However, in the process of 
dispersing contaminated air 541, chill roll air bar 530 urges web 110 
toward chill roll air bar 530 before web 110 enters chill unit 114. As a 
result of such bending of the path of web 110, wrinkling of the web is 
substantially reduced. 
A plurality of chill roll air bars 530 may be simultaneously employed above 
and below web 110, if desired. For purposes of clarity of illustration, 
the preferred embodiment of the present invention has been described in 
the context of a single chill roll air bar 530 disposed near lower surface 
111 of the web 110. 
Referring now to FIGS. 5 and 6, housing 532 is suitably rectangular in 
cross-section and of a length in excess of the width of web 110. A cavity 
538 spans the length of housing 532, the cross-sectional area of cavity 
538 being sufficient to accommodate a desired air flow. Cavity 538 
communicates with a compressed air source (not shown) through an air inlet 
junction 540 suitably disposed at an end of housing 532, and 
advantageously in line with the longitudinal axis of housing 532. 
A controlled air stream outflow 533 is exhausted from housing 532 toward 
web 110. A series of air discharge apertures 542 are formed through a side 
wall of housing 532 along the length of housing 532. Gap adjusting strip 
534 and guiding strip 536 are preferably secured to two perpendicular 
surfaces of housing 532, with adjusting strip 534 partially obstructing 
apertures 542. A spacer 535 is advantageously disposed intermediate 
adjusting strip 534 and housing 532. Adjusting strip 534, guiding strip 
536, spacer 535 and housing 532, cooperate to define a linear gap 544 
between housing 532 and strips 534, 536, preferably of a length 
corresponding to the width of web 110. Air stream 533 is exhausted from 
housing 532 through apertures 542 and gap 544, against the facing lower 
surface 111 of web 110, in a region between air bar 530 and lower surface 
111, and in a direction contrary to the web processing direction. 
The use of apertures 542, strips 534, 536 and spacer 535 to provide and 
control air flow is particularly advantageous, providing a structure 
mechanically strong enough to operate at relatively high air pressures 
without deformation of the air outlet. Moreover, the rectangular 
cross-section of housing 532 facilitates formation of apertures 542, and 
the securing of strips 534, 536 and spacer 535 during manufacture and 
assembly. 
Proper selection of the width of gap 544, allows precise control of the 
velocity of the discharged air passing therethrough. For a given air 
pressure within cavity 538, decreasing the width of gap 544 increases the 
velocity of the discharge air speed; conversely, increasing the width of 
gap 544, decreases the discharge air speed. 
The width of gap 544 is preferably such that gap 544 provides a significant 
resistance to air flow, greatly in excess of the resistance generated by 
the presence of web 110 in the vicinity of gap 544. Thus, air flow through 
gap 544 will be substantially constant across the length of gap 544 
whether or not web 110 extends across the entire length of gap 544. Thus, 
webs of varying widths may be readily accommodated; gap 544 is of a length 
corresponding to the widest web contemplated to be encountered. The width 
of gap 544 is preferably on the order of ten to twenty thousandths of an 
inch (0.010 to 0.020 inch). 
Guiding strip 536 is secured to housing 532 in any convenient manner, for 
example by bolts 546. Alternatively, guiding strip 536 may be held in 
place by shoulder bolts, welding, or may be formed integrally with housing 
532, as desired. Adjusting strip 534, on the other hand, is preferably 
slidably secured to housing 532, for example by respective shoulder bolts 
548, received within slots 550. In this way, the width of gap 544 may be 
adjusted by appropriate selection of spacer 535 and by disposing and 
securing strip 534 at a predetermined desired distance from strip 536. Of 
course, if desired, both strips 534, 536 may be fixedly or adjustably 
secured to housing 532. 
Referring now to FIG. 7, chill roll air bar 530 is advantageously mounted 
to dryer unit 112 near the point at which web 110 leaves dryer unit 112. 
In this preferred embodiment, a mounting member 554 is affixed to press 
frame 529, for example, by an upper bolt 556 and a lower bolt 560. An 
L-shaped bracket 558 is secured to mounting member 554, for example, by 
bolt 556 and a bolt 562. Housing 532 is received by L-shaped bracket 558 
and secured thereto by, for example, one or both of bolts 556, 562. 
Mounting member 554 and L-shaped bracket 558 preferably span substantially 
the entire length of housing 532, and a plurality of bolts 556, 560 and 
562 are spaced along the length of mounting member 554 as necessary. 
Referring now to FIG. 8, chill roll air bar 530 is advantageously mounted 
such that the upper surface of guiding strip 536 is disposed in spaced 
relation from lower surface 111 of web 110 when chill roll air bar 530 is 
in the off condition. When chill roll air bar 530 is turned on, a stream 
of compressed air 533 is forced upwardly through respective apertures 542 
and gap 544, and is discharged adjacent to the surface of guiding strip 
536. In accordance with the coanda effect, compressed air 533 follows the 
contour of guiding strip 536 and ultimately impinges upon lower surface 
111 of web 110 in a direction contrary to the web processing direction. In 
addition, and also in accordance with the coanda effect, discharged air 
533 entrains along with it a large stream of ambient air 531. The pressure 
of discharged air 533 and of air stream 531, which are both confined 
between the upper surface of strip 536 and lower surface 111 of web 110, 
establishes a cushion of horizontally moving air in increased air stream 
539. The velocity of increased air stream 539 creates a zone of reduced 
static pressure between chill roll air bar 530 and lower surface 111 of 
web 110 in accordance with the Bernoulli principle. 
The static pressure on the upper surface 113 of web 110, of course, remains 
substantially unaffected by the operation of chill roll air bar 530. 
Consequently, web 110 is urged toward chill roll air bar 530 to a position 
110', as indicated in phantom in FIG. 8. The upward force of discharged 
air 533, in conjunction with the cushion of trapped air in increased air 
stream 539 between web 110' and guiding strip 536 prevents web 110' from 
contacting chill roll air bar 530 and maintains a gap 537 between web 110' 
and chill roll air bar 530. Proper adjustment of web tension, air 
pressure, and the width of gap 544 permit gap 537 to be maintained 
preferably within a range of about 0.030 to 0.070 inches, and most 
preferably to about 0.050 inches. As a result, increased air stream 539, 
moving through narrow gap 537, separates contaminated air 541 from lower 
surface 111 of web 110 as web 110 exits drying unit 112. Chill roll air 
bar 530 also contributes to reducing web instability and increased air 
stream 539 pre-cools web 110 before web 110 enters chill unit 114. 
Referring now to FIGS. 9 and 10, an alternate exemplary embodiment of chill 
roll air bar 531 in accordance with the present invention suitably 
comprises guiding strip 202 and adjusting strip 204 defining an angled air 
gap 206. Adjusting strip 204 is suitably secured to housing 532 by 
shoulder bolt 548 received within slot 550. 
Adjusting strip 204 advantageously comprises an angled portion 210 defining 
an acute angle with the surface of housing 532 upon which respective 
apertures 542 are disposed. Guiding strip 202 is advantageously secured to 
housing 532 in any convenient manner, for example by bolts 546. A spacer 
212 is advantageously disposed intermediate guiding strip 202 and housing 
532 such that, when chill roll air bar 531 is mounted to side frame 529 of 
dryer unit 112, as illustrated in FIG. 11, the height of guiding strip 202 
exceeds that of adjusting strip 204 by an amount approximately equal to 
the thickness of spacer 212. 
With continued reference to FIGS. 9-11, guiding strip 202 comprises an 
inclined portion 214 defining an "upstream" edge of gap 206; angled 
portion 210 of adjusting strip 204 comprises the "downstream" edge of gap 
206. ("Upstream" and "downstream" locations are identified with respect to 
the web processing direction). When chill roll air bar 531 is turned on, a 
stream of compressed air 533 is forced upwardly through respective 
apertures 542 and gap 206, and is discharged adjacent to the surface of 
guiding strip 202. Compressed air 533 follows the contour of guiding strip 
202, and ultimately impinges upon lower surface 111 of web 110, in a 
direction contrary to the processing direction. In this manner, a 
relatively insignificant amount of discharged air 533 enters the region 
between web 110 and the upper surface of strip 204, the majority of 
discharged air 533 being effectively directed between lower surface 111 of 
web 110 and guiding strip 202. Consequently, the Bernoulli effect is 
largely confined to that portion of chill roll air bar 531 upstream of gap 
206. As with the preferred embodiment illustrated in FIGS. 5-8, 
contaminated air 541 is separated from lower surface 111 of web 110 
upstream of gap 206 from which air stream 533 is discharged as web 110 
exits drying unit 112. 
In accordance with one aspect of the present invention the inventors have 
determined that by positioning the chill roll air bar sufficiently close 
to the exit of drying unit 112, in addition to reducing condensate 
marking, another problem associated with chill streaking is also 
advantageously addressed. Namely, contamination of the pressroom 
atmosphere is reduced. 
With reference to FIG. 8, as contaminated air 541, containing evaporated 
ink solvents, gases from the combustion in the drying unit as well as 
evaporated moisture from the web, is separated from lower surface 111 of 
web 110, chill roll air bar 530 forces contaminated air 541 back into 
drying unit 112, thereby reducing dispersion of contaminants in the 
pressroom atmosphere. 
It is understood that the above description is of preferred exemplary 
embodiments of the present invention, and that the invention is not 
limited to the specific forms described. For example, the chill roll air 
bar need not be secured to the side frame of the dryer unit; the chill 
roll air bar may be disposed at any convenient point along the web path 
between the dryer unit and the chill unit, although proximity to the 
source of pressroom atmosphere contaminants (i.e., the drying unit) is 
advantageous. Furthermore, although the preferred embodiments employ the 
Bernoulli-effect, any apparatus configured for separating the contaminated 
air from the web surface without contacting the web is considered to be 
within the scope of the present invention. In addition, any suitable fluid 
may be used in place of air, for example, in the event certain gases may 
be desirable for effecting or preventing various chemical reactions with 
the web or any coatings applied thereto. If desired, the fluid stream 
exhausted from the chill roll air bar may itself be chilled to enhance 
cooling of the web. In particular, the present invention contemplates webs 
other than those used in the printing process. For example, systems used 
in fabricating webs of fabric, wallpaper, floor covering, sheet metal, or 
any other process in which a flexible web cooperates with one or more 
processing stations including a drying station which may induce condensate 
marking on a moving web. These and other substitutions, modifications, 
changes and omissions may be made in the design and arrangement of the 
elements without departing from the scope of the appended claims.