Note: Descriptions are shown in the official language in which they were submitted.
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Pi'~PER co~ r I ~ 1 3
This invention relates to a method and apparatus for
applying a coating material to a web of paper and more particu-
larly to a coating method, and apparatus of the inverted trail-
ing blade type, wherein ligh~, heavy or medium weight coatings
may be applied in a novel and improved manner.
Background of the Invention
~ . . _
A conventional coater of the trailing blade type in-
cludes means for applying, usually unpressurized, coating
material to a paper web that is usually supported and carried
by a resilient backing roll, together with a flexible doctor
blade located some distance from and on the trailing side of the
applicator, which serves to level the applied coating. In general,
an excess of coating material is applied to the webr and the
trailing blade then meters or removes the excess while uniformly
spreading the coating onto the web surface.
In recent years, it has become desirable to produce
printing papers having a minimal amount of coating, i.e., in
order of 3 to 4.5 grams per square meter per side of paper.
In order to achieve low coat weights on conventional
trailing blade equipment, it is necessary to increase the pres-
sure of the trailing blade against the web, which results in a
high rate of wear on the blade and necessitates more frequent
replacement of the blade. High blade pressure also increases
the possibility of web breakage and streaking caused by foreign
particles being caught between the blade and the web.
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Many conventional coaters inherently employ a rel-
a-tively long dwell or soak time, which is the time interval be-
tween the initial application and final blading of the coating.
As a result, the water portion of the coating composition, as well
as the water soluble or dispersible materials contained therein,
migrate into the moving web at a more rapid rate than the pigment
and eventually cause an undesirable imbalance in the coating con-
stituents and their rheological properties. Long soak periods
are also incompatible with the application of successive wet coats
without intervening drying because the successive coats tend to
migrate into and contaminate the previous coat.
The foregoing problems are discussed in U.S. Patent No.
3,348,526 issued to Neubauer wherein a narrow stream of coating
is extruded onto an inverted trailing blade that defines a nip
region with the supported web,. Slnce the coating is bladed im-
mediately after application, soak times are purportedly kept to a
minimum. ~owever, the coating application is such that the coat-
ing material is unpressurized after leaving the orifice and is
supported on the blade or trailing side only, with the leading
side of the stream being unsupported and exposed to the environs
in the zone of application. Consequently, the coating material is
not properly'or uniformly applied to the web. Similar disclosures
are contained in U.S. Patent No. 3,484,279 (Fig. 3) to Clark et.
al., and U.S. Patent No. 3,070,066 to Faeber.
Attempts at pressurized applications of coating material
to the web are described in U.S. Patent No. 2,796,846 to Trist and
U.S. Patent No. 3,273,535 to Krikorian. In Trist, a second blade
is provided at the forward side of the coating application
zone which blade, due to its high friction
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contact with ~il web, creates insurlnolltable obstacles to
successful use of the Tris-t appal-a1us. In Krikorian, air flow
is induced into the coating application zone creating problems
of skips and streaks in the applied coating.
Other prior art of interest includes U.S. Patent
No. 3,418,970 to Phelps et al and U.S. Patent No. 3,079,889
to Jacobs et al.
Summary of the Invention
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The short dwell time applicator and coating method
of the present invention constitu-te an improvement over the
apparatus and methods of the prior art, in that an enclosed
pressure reservoir with a frictionless liquid seal at its
forward side is established between the coating applicator, the
blade, the supported web and said seal, which results in
pressure application of the coating material to the web to
drive the coating into the interstices of the web surface,
greater control of coat weights and fewer production problems.
The applicator generally may be used with a backing
roll carrying a web of paper, or a pair of applicators may be
arranged on opposite sides of the web so that a web supporting
roll is not needed. The coating applicator comprises a tapered
chamber leading from a supply of coating material to a narrow
outlet orifice or slot and a doctor blade extending from the
trailing side of the slot in contact with the web. The leading
edge or front side of the chamber adjacent the slot or orifice
is closely spaced from the supported web so as to form, in
conjunction with the pressurized liquid flowing from the
orifice, a liquid seal with the web, and the sides or ends of
the orifice are sealed to the backing roll to allow the
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establishment of the posltive liquid pressure of the chamber
in the zone of application, with the doctor blade simultaneously
leveling the applied coating.
The coating applicator forms an enclosed pressure
chamber with the web to apply a continuous narrow strip or band
of pressurized coating material thereto, which enables application
of lower coat weights than have heretofore been feasible. rrhe
maintenance of positivè pressure in the zone of application,
attained by the provision of the trailing blade, the end seals
and the leading edge liquid seal, allows for more uniformity
and control of application than with prior art methods and
permlts the use of both lower and higher viscosity and lower and
higher solids content coating materials than have previously
been thought to be feasible.
The coating method and applicator provide very
lightweight coatings, such as 3 grams per square meter per side.
It can also apply heavyweight coatings on the order of 22 grams
per square meter per side with fewer streaks and scratches than
coaters previously used to apply such type coa-tings.
In summaryr the method aspect of the present invention
is generally defined as comprising the steps of applying coating
liquid under pressure to one surface of a moving web of paper
through an application zone having spaced front and rear edges
and laterally spaced side edges, forming and maintaining a
reservoir of coating liquid under pressure on the web in the
application zone, doctoring the coating liquid on the web at the
rear edge of the application zone while the coating liquid is
maintained under pressure, maintaining the coating liquid in
the application zone under pressure by substantially sealing
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the slde edges o~ t~e z~r~e and by c-stabl.ishinc~ a liquid seal
in a gap definecl between the web and the front edge of the
application zone which extends substanti~l.ly across the width
of the web and continuously flowing coati.ng liquid under
pressure into the application zone to substantia].ly completely
and continuously fill the gap wi-th coating liquid for forming
the liquid seal for sealing off the front edye of the application
zone and preventing entry of air and foreign matter -through
the gap into the zone, and for continuously purging the coating
application zone.
The applicator aspect of the present invention is
generally defined as having a limited coating liquid application
zone defined by an outlet slot from a chamber, the chamber having
front and rear walls and side edges, the side edges being
substantially sealed to the web, the front wall including a front
edge spaced from the web and the rear edge carrying a doctor
blade engaged with the web. The applicator is provided with means
for continuously delivering coating liquid under pressure to the
chamber, through the outlet slot and into the application zone
for application under pressure onto the moving web. Means are
disposed on the front edge of the front wall for forming a narrow
gap between the front edge and the moving web of the paper for
causing the coating liquid under pressure to substantially com-
pletely and continuously fill the narrow gap for establishing
a liquid seal between the web and the front edge substantially
continuously across the web, the liquid seal sealing off the front
edge of the application zone for maintaining the pressure of the
coating liquid in the zone and for preventing entry into the
zone of air and foreign matter. The doctor blade is located
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immediately to the r~cJr of the ]iquid scal for k,ctoring the
coating liquid on the web while the coa-ting liquid is maintained
under pressure. The doctor blade is spaced from the liquid
seal by a small dimension such that the coating liquid is
doctored by the blade within about .0004 to about .0100 second
of its pressure app~ication to the web.
These and other advantages of the method and apparatus
of the present invention will become apparent from the following
written description and the accompanying drawings.
Brief De_crip ion of_the Drawings
Figure 1 is a side elevational view of one embodiment
of a short dwell time applicator of the present invention
installed on a paper coating machine;
Figure 2 is a partial cross-machine elevational view of
the applicator and machine shown in Figure l;
Figure 3 is a cross-sectional view taken substantially
along the line 3-3 of Figure l;
Figure 4 is an enlarged cross-sectional view taken
substantially along the line 4-4 of Figure 2;
Figure 5 is a further enlarged view taken substantially
along the line 5-5 of Figure 2 with the applicator in an
operating position;
Figure 6 is a view similar to Figure 5, but with the
applicator open in a cleaning positioni
Figure 7 is a cross-sectional view of a second embodi-
ment of short dwell time applicator in an operating position,
the applicator being shown in a cleaning position in dotted lines;
Figure 8 is a cross-sectional view taken substantially
along the line 8-8 of Figure 7 showing one half of the
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applicator's internal hea~er with portions broken away, with
other portions of the applicator not being shown;
Figure 9 is a side elevational view of a third embodiment
of short dwell time applicator in an operating posi.tion;
Figure 10 is a partial cross-machine view taken
substantially along the line 10-10 of Figure 9; and
Figure 11 is an enlarged view taken substantially along
the line 11-11 of ~igure 10.
Description of the Several Embodiments
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Referring to Figures 1 and 2, a first embodiment of
short dwell time applicator 20 of the present invention, suitable
for practicing the coating method of the present invention is
installed on a paper making or coating machine having a frame 22
and a rotating, resilient backing roll 2~ carrying a web 26 of
paper moving in the direction indicated by the arrow 27. Unlike
prior devices, the web 26 wraps around the backing roll 24
for less than 140 degrees, with the applicator being located near
the end or on the last 20 degrees of wrap~
Due to the compact arrangement of the applicator 20, one
or more other coating devices may be located ahead of the appli-
cator on the same backing roll 24. One such device comprises a
rotatably mounted dip roll 29, the lower surface of which is
disposed in a pan of coating material ~not shown) and the upper
surface being tangentially in contact with the backing roll. The
dip roll 29 may be accompanied by its own doctor blade (not shown).
The low soak or dwell time of the coating supplied by
the applicator 20 enables the application of a final coating over
one or more wet primary coatings without intervening drying.
So called "wet-on-wet" methods of coating application are
especially advantageous with the
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present applicator since the final coat may be composed of ex-
pensive high-quality materials which may be applied at a very
low rate without affecting good web coverage or printing qualities.
The applicator 20 may be suitably mounted on a pair of
pedestals or bases 28 (only one being shown) secured to the frame
22 of the machine. Each of the bases 28 comprises a lower por-
tion 30 and an upper portion 32. The lower portion 30 is secured
to the machine frame 22, as by bolting. The lower and upper por-
tions 30 and 32 have cooperating dovetailed, inclined and sIidable
mating surfaces, 34 and 36, respectively, to permit relative
lateral adjustment of the position of the coater applicator 20
for use with various diameter backing rolls 24. The angle of in-
clination of the surfaces 34 and 36 and dimensions and placement
of the bases 28 with respect to the rotating axis of the backing
roll are chosen so that the upper portions 32, generally, need - -
only be moved across the inclined surfaces 34 to adjust the posi-
tion of the applicator 20 for a change in the diameter of the
backing roll used without altering the relative angle at which
the applicator contacts the backing roll.
For convenience of making this adjustment and in-
creased accuracy of the same, the upper portions 32 on each side
of the backing roll 24 are made to move simultaneously the same
distance. To accomplish this result, a screw jack is secured to
each portion 32, the two jacks 38 being connected together by a
rotating shaft 42 contained in a tubular housing. Upon rotation
of the single handle 40, the screw jacks 38 cause two screw shafts
44 to rotate. The shafts 44 move in female threads in bodies 46
secured to the lower portions 30. Thus, rotation of the handle
40 cause both upper portions 32 to move along the inclined
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sur~aces 34 relative to the lower portions 30 to adjust the posi-
tion of the coating app]icator 20 with respect to the axis of
the backing roll.
In addition to the adjustment feature discussed above,
a second adjustment is provided on the bases 28 to vary the rel-
ative angular position of the coating applicator 20 with respect
to the backing roll 24. Again referring to Figures 1 and 2,
large arms 48 are pivotally mounted on a pair of short shafts
50 to the upper portions 32 of the bases. The loci of shafts
50 are chosen to coincide generally with the llne on which the
applicator 20 will contact or be generally tangent to the back-
ing roll 24. The lower end of each arm 48, pivotally carries
a female threaded portion (not shown) which engages a screw
shaft 52. The ~air of screw shafts 52 extend from a pair of
screw jacks 54, which are operated by a common handle 56 and con-
nected together by a rotating shaft 58 in a manner similar to
jacks 38. Thus, upon rotation of the handle 56, the arms 48 can
be made to simultaneously pivot an equal angle or amount about
the shafts 50. As the coating applicator 20 is pivotally mount~
ed about a pair of shafts 60 carried intermediate the ends of
the arms 48, pivoting of the arms 48 changes the relative position
of the coating applicator 20 with respect to the backing roll 24.
Referring to Figure 3, to accurately locate the ap-
plicator 20 substantially tangent to the surfaces of the various
diameter backing rolls and to reduce the time required in making
such adjustment, base locating means 61 are provided on each
base 28. Each locating means 61 comprises an opening 63 formed
on the base parallel to the axis of the backing roll and located
concentrically in the shaft 50. Locating means 61 also includes
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a locating rod 65 having its outer end slidably mounted in the
opening 63. The inner end 67 of the rod is ground flat and semi-
cylindrical so that the axis of the rod lies on the flat surface.
If desired a clamp (not shown) can be provided to hold the rod 65
or the rod can be withdrawn when not needed. In setting up ap-
paratus 20, the rods 65 would be installed in the openings 63
and the upper portions 32 of bases 28 moved up or down the inclin-
ed surfaces until the flats of the rods 65 are tangent to the outer
surface of the particular size backing roll being used. After
such position is reached the rods 65 may be removed or clamped
in out-of-the-way positions. Thus, the upper portions 32 of the
bases-28 may be readily positioned with respect to the lower por-
tions 30 so that the axes of the openings 63 ! shafts 65 and ap-
plicator 20 are generally tangent to the surface of the selected
diameter backing roll to be used.
In addition to the foregoing adustmen~, J~he bases
28 incorporate mechanisms to quickly place in or remove the coat-
ing applicator 20 from its operating position abutting the backing
roll 24. An arm 62 may be connected at one end 64 to the coating
apparatus 20, while its other end is connected to a piston rod 66.
The lower end of the rod 66 cooperates with an air cylinder 68,
which in turn is connected to the lower end of the arm 48. With
the rod 66 extended from the cylinder 68! the coating applicator
20 is moved toward the backing roll 24 to its operating position
and with the rod 66 retracted into the cylinder 68, the coating
applicator 20 is moved away from the backing roll as required for
a shutdown or performing maintenance or cleaning. Appropriate
controls (not shown) are provided for the operator to regulate
these movements, and adjustable mechanical stops may be provided
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to determj,ne tile exact ].ocation o~ the operating position with
respect to the roll.
~ s an alternative ! arms 62 previous]y described, may
be replaced by a pair of clevis brackets 74 (Figure 4) secured
to the ends of the applicator 20, the ends of the brackets 74
being connected to the piston rods of the air cylinders 68 for
urging the applicator toward and away from the roll.
' ' 'As shown in Figures 1, 2, 4 and 5, the applicator 20
comprises a main support beam 70 of rectangular cross-section,
which extends adjacent and coextensively with the backing roll 24.
The main beam carries either arms 62 or brackets 74. A rear wall
76 (Figure 5) of the coating applicator is secured to the front
side of the beam 70 and extends coextensively with and generally
parallel to the backing roll. A ront wall 78 is mounted adja-
cent to and spaced from the rear wall, the walls be,ing inclined
toward one another and together defining an enclosed chamber 80
converging toward the backing roll. One or more inlet pipes 82
connected to the bottom portion of the rear wall 76 supply the
chamber 80 with pressurized liquid coating material from an ex-
ternal header (not shown), the chamber 80 having an open top andbeing enclosed and sealed at its sides by end plates 84 (Figure
4, 5 and 6), which engage sealing ledges 83 secured to the side
of the applicator.
The front wall 78 is pivotally mounted with respect
to the rear wall 76 and is movable away .the~efrom ~o enable oening of
the chamber 80 for cleaning and also to regulate the width of the
metering slot 85 between the upper edges of the walls 76 and 78,
The front wall-78 is separable from the rear wall 76 and is con-
nected to the ends of downwardly extending levers 86, the other
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ends of which are connected to pist-on rods 87 of power cylinders
88, which in turn are pivotally connec-ted to the heam 70. The
levers 86 are fulcrumed in-termediate their ends on pivots 90
which are also secured to the beam 70. Retraction of the rods 87
of the cylinders 88 cause the front wall 78 to pivot away from
the rear wall 76 ~o an open position shown in Figure 6 ! thereby
opening up and giving access to the interior of the chamber 8Q.
Extension of the rods 87 close the chamber to ready the coater
for operation. In the operating position, the lower ends of the
front and rear walls abut one another or seal against each other
to prevent escape of coating materials, the area of abutment con-
taining a seal 92 (Figures 5 and 6) to prevent loss of pressure
during operation of the coater.
Means are provided to fixedly adjust the distance
between the front wall 78 and rear wall 76 and hence to regulate
the width of a metering slot 85 and the amount of coating material
~ passing therethrough. As shown in Figure 5, a series of bolts
94, which pass through the beam 70 in threaded engagement there-
with, extend into the chamber 80 and abut internal webs 96 on
the front wall. Adjustment of the bolts 94 to fixed positions
held by stop nuts 97 abutting the beam determines the final
spacing between the walls 76 and 78 and the width of the metering
slot 85 when the chamber 80 is closed. The bolts 94 may also
be adjusted individually to insure that the width of the slot
85 is uniform or is of the desired shape along its entire length.
During operation, the coating applicator 20 is posi-
tioned closely adjacent the backing roll 24 with the metering
slot 85 facing the surface of the paper web 26 on the roll. A
flexible doctor blade 98 is fixedly clamped to extend from the
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rear wall 76 into engagement w;th the web supported on the back-
ing roll, the rear side of the blade being supported by a backing
bar 100 secured to the rear wall. The blade is held in a slot
~etween a bac]lllc3member 104 and the rear wall 76 and may be conveniently
removed by sliding the blade laterally ! parallel to the backing
roll, when the chamber 80 ls open as shown in Figure 6. As will
be hereinafter more fully explained, the blade serves se~eral
functions, one of which is to level the coating that is applied
to the web. The pressure of the blade on the roll is regulated
by extension and retraction of the rods 66 of the cylinders 68
connected to arms 62, or alternatively the cleavis brackets 74,
which rotate the coating applicator beam 70 about the shafts 60
toward and away from the backing roll 24.
In order to close the forward edge of the chamber 80,
- a liquid seal is established between the web 26 and the applicator
20, and more particularly an orifice plate 106 thereof. The
orifice plate 106 is slidably and adjustably mounted on the out-
side surface of the front wall 78 to be movable toward and away
from the backing roll 24. As shown in Figure 4, the extension of
the plate 106 may be fixedly adjusted by a bolt 108 rotatably
mounted at one end in a journal 109 extending from the front wall
78, and the other end being in threaded engagement with the plate,
The spacing between the free edge 110 of the plate 106 and the
backing roll is very important and should be less than 2.5 cm
preferably 0.158 to 1.27 cm to allow the maintenan~e of the fluid
or li~uid seal between the plate and the supported web.
The trailing blade 98 and forward orifice plate 106
in effect form a portion of an enclosed secondary chamber or
reservoir (downstream of the metering slot 85), the ends of which
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re enclo~ed anA sealed by flexible triangular shaped end dams
112, whicil may slightly contact the backing roll surface. The
end dams 112 are held in compression against the orifice plate
106 by the loaded blade (Figure 5) and secured by screws 114
(Figure 4) threadably mounted in brackets 116 to both ends of the
front wall 78. Loading of the blade 98 against the backing roll
24 causes the blade to deflect inward at its center and increase
the seal of the end dams 112.
As the coating applicator 20 forms an enclosed pres-
sure reservoir with the backing roll, liquid coating may be ap-
plied across the web in a narrow band or strip under positive
pressure. The enclosure is completed by the web on the backing
roll, the blade 98, the end dams 112 and the liquid seal formed
between the orifice plate 106 and the web. Although when out of
operation there is a slight space between the orifice plate and
- the backing roll or web, the spacing is sufficiently narrow to
allow the liquid seal of coating material to form between the
plate edge 110 and the supported web during operation to prevent
loss of pressure so that coating is applied to the web at or near
the pressure in the chamber 80. One advantage is that this lat-
ter pressure can be readily measured by mounting a pressure
transducer 117 in the end wall 84 of the chamber 80. The pressure
reading of the transducer can then be monitored by the operator
and the flow of coating material adjusted to maintain the desired
pressure, as will be discussed later.
In operation, the inlet pipes 82 are connected to a
source of coating material, which is pumped under pressure into
the chamber 80. The coating material may comprise any known
composition, such as a mixture of fine clay pigment and a binder
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in an aqueolls me~ium. ~ -typical coating composition may include !
for example, a mixture containing 100 parts clay, 16 parts enzyme
converted starch and 0.8 parts calcium stearate, said mixture
comprising 50 to 60 percent of an aqueous coating composition.
The liquid coating material is supplied to the chamber
80 at a rate to maintain it at from about 17.5 grams per square
centimeter or 17.8 cm, 350 grams per square centimeter or 380 cm
water and through the metering slot 85, which insures uniform
distribution of the coating to the web. A very slight or small
pressure loss occurs in the metering slot 85 so that the coating
is applied to the web at substantially the pressure in the chamber
80. The liquid seal between the free edge 110 of the orifice
plate 106 and the web surface assists in maintaining such condi-
tion. With the arrangement shown, the coating material flows
under pressure upward from the chamber 80 and into contaet with
the web in a narrow band defined by the spaee between the blade
98 and the liquid seal on the orifice plate 106, As mentioned
previously, the gap between the orifice plate and the web sur-
face is very important since it allows a continuous band or strip
of pressurized coating material to be deposited on-the web, while
at the same time, maintaining the non-abrasive liquid seal with
the incoming web. The excess coating that flows in a direction
opposite the web is allowed to escape through the liquid seal to
the exterior of the coating applicator. This flow of exeess
coating serves to maintain a degree of limited circulation in the
zone of pressure application, serves to continuously purge the
otherwise enclosed system in the zone of application, strips air
from the moving web, and prevents air from entering the applicator
where it would prevent the coating contacting the web and would
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cause streaking or skips.
The distance between the blade 98 and the orifice
plate 106 is defined as the wetted length of web and regulates
the width of the band of coating applied to the web and hence
the dwell time of the coating on the web between application and
wiping. Preferably, the wetted length is adjusted between about
0.635 cm and 5.715 cm, with about 1.27 to 3.81 cm being optimum.
These and other conditions are based on the assumption of a
machine weh speed in the order of about 6 to 15 meters per second
so that the coating material is applied onto the web and doctored
within from .0004ths to .OlOOths of a second. Were web speed
increased, this distance may also be increased so as to maintain
adequate dwell time. For example, were web speed increased 24
meters per second, the distance between the liquid seal and doc-
tor blade may be increased to about 10 to 12.5 cm.
Thus, coating pigment is applied to the web surface
in sufficient quantity and under pressure to give a uniform,
high-grade coating, but the coating liquid remains in contact
with the web only an extremely short time before being doctored
so that little liquid penetrates into the web. As a result, low
coat weight papers can be obtained using higher solids content
coating which requires less fuel to dry at equivalent coating
weights.
In addition, coated paper made according to the method
and with the apparatus of the invention generally exhibits less
differences between the two coated surfaces of the sheet or web
than coated papers produced according to prior art methods. Less-
ening of the differences between the wire and felt sides is very
desirable as it lessens the possibility of one page in a printed
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publication looking different from the opposite page.
Further, coated paper produoecl in accordan oe with the invention
prints better as it is generally smoother, has greater ~orosity for the same
coat weight, has higher apparent gloss, and tends to have less fiber rise and
blistering. The paper runs better in printing presses, and in web presses
ex~erien oes fewer breaks than the aforementioned prior art coated pa er.
Analytical tests made on the paper coated by the apparatus and
method of the present invention (herein referred to as the "after paper")
prove the same superior to paper made on the same pa~ermaking machine, but
ooated by the well-known standard Beloit flooded nip coater (herein referred
to as the "before paperllj~ The "before paper" was generally considered the
best coated paper heretofore produoe d on Lhis pa~erm~r~u~g machine. T" the
papers used in the comparative analytical tests, the furnish from which the
base papers were made were nearly identical and`the ooatings very similar
in composition. The coating for the "before paper" differed very slightly
from that for the "after paper"; both wire and felt side coatings for the
"before paper" had about 13/100 of starch; whereas the wire and felt side
coatings for the "after paper" had about 15/100 and 14/100 of starch, re--
spectively. me papers tested were as follows, with weights expressed in
grams per square meter:
Paper Ibtal Coating 1~7eightCoating Weight~Side
Type Paper Weight (Aoprox)
Before After Before After
Wire Felt Wire Felt
Web Offset 51 13.35 12 8.7 4.65 7.8 4.2
12.9 11.?5 8.4 4.5 7.35 3.9
57 15.9 15 10.35 5.55 9.75 5 25
17.1 16.2 11.1 6.0 10.5 5 85
Letter Press 51 12.6 12.6 8.75 4.35 8.25 4.35
- 12.3 - - 8.1 4.2
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In considering the test data and resul-ts reported
hereinafter, it should be borne in mind that the amount of coating
on the web offset "after ~a~ers~, on both the wire and the felt
sides thereof, is significantly less than the amount of coating
on the "before pa~ers" with which they are compared. Nevertheless,
even with lighter coat weights in the web offset papers and with
approximately the same coat weights in the letter press papers,
the "after papers" exhibit generally enhanced characteristics over
the "before papers".
Comparative analyses of the above listed coated papers
according to the Prufbau Mopup test, a standard test in the print-
ing and papermaking industries, revealed that the "after papers"
exhibited less difference between their wire and felt sides than
did the "before papers". Also the "after papers" exhibited less
mottle, and/or a finer grain mottle which was less observable.
A Vandercook Rubber Plate Smoothness Test, another
standard test in the printing and papermaking industries, confirm-
ed that the web offset "after paper" exhibited less mottle than
the comparable "before paper", and that the same trend, but to a
slighter degree, was observed for the letter press "after paper".
Again, this test showed smaller differences between the wire and
felt sides for the "after papers" than the "before papers". Also,
in the "after papers,"-there was less difference in gloss between
the wire and felt sides.
M.A.N. Print Tests, another standard test in the print-
ing and papermaking industries, were run for the letter press
paper. Here again the tests bore out that the "after paper" had
less mottle, and less difference in gloss between the wire and
felt sides, than the "before paper". Such desirable lessening
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o~ the diffc~rerlcc~s was ~chi.eved primarily by increasing the yloss
of the felt side! also a desirable plus.
Sheffield Smoothness Tests, a recognized test in the
printing and papermaking industries, showed the "after papers" to
be superior and smoother than the "before papers". It is well
recognized that a smoother paper prints better, especially for a
rotogravure process. Test results are as follows, it being noted
that the lower the Sheffield Smoothness number, the smoother the
paper.
Weight Sheffie1d Smoothness Number
Paper Type Before After
Wire Felt Wire Felt
Web Offset 51 28 27 2021
22 1819
57 25 28 1818
24 23 1717
Letter Press 51 26 2816 14
- -- 1316
Also, the well recognized Sheffield Porosity test re-
vealed that the porosity of the web offset "after paper" was in-
creased, which is a desirable feature when the printed paper is
dried in the press driers immediately after printing as it per-
mits moisture in the paper to escape without.blistering or causing
fiber rise. The porosity of the letterpress ~a~er indicated r.o adverse
effect for the "after paper". Test results are as follows, with
a higher Sheffield Porosity number indicating increased porosity:
Weight Sheffield Porosity
Paper Type Before After
Web Offset 51 40 65
31 63
57 16 46
` 19 52
Letter Press 51 54 56
_ 54
-18~-
..
l~Z'SS~7
I~igh Pressure Densometer tests showed that the web
offset "after paper" had a substantially lower density, while the
letter press "after paper" had a somewhat lower density. These
trends are compatible with the changes in porosity and indicative
of that factor. With the higher number indicating greater density,
the test results are:
Weight lligh Pressure Densometer Number
Paper Type(Pound/Ream)Before After
Web Offset51 97 67
126 68
57 183 101
201 78
Letter Press 51 84 72
~ 76
The standard % K & N Ink Absorbency cest sh~ed that the web
offset "after paper" had ink absorbency which was much closer for
the two sides, and that the letter press "after paper" had higher
ink hold out for the wire side than the comparable "before papers".
The higher the % K & N number the greater the tendency for the
paper to hold ink out on its surface rather than absorb it. General-
ly, the higher this tendency the better. The results are:
Paper TypeWeight% K & N Number
Before After
Wire :Felt Wire Felt
Web Offset 51 68.6 76.0 72.2 76.1
68.7 76.2 72.5 75.8
57 72.4 80.7 74.8 80.1
73.9 80.3 76.9 79.7
Letter Press 51 69.8 68.6 73.8 69.1
- - 76.1 72.0
In addition accepted B & L Gloss measurements were
made. The measurements indicated that the gloss of the "after
paper" is more similar for both the wire and felt sidest which
..
l~Z;>S~
hclps nlillimi~c a two sidcd crl'cct. The higher the B ~ L
Gloss nunlber, the glossier the paper.
Weight B ~ I. Gloss Number
Paper Type Before After
Wire Felt Wire Felt
Web Offset 51 47 34 42 40
38 43 40 41
51 44 52 41 38
49 43 39
Letter Press 51 38 46 51 44
- 56 50
While both gloss and ink absorbency are important
factors in affecting the appearance or color of the printed
ink on the paper, neither alone is controlling. However,
when considered together in an empirical formula well
known in the printing and papermaking industries, they
can give an accurate prediction. This empirical factor
is called the Paper Surface Efficiency ~"PSE") and is
calculated as follows:
20PSE=.666 (% K ~ N) + (B ~ L Gloss) - 1.666
A relatively high PSE is desirable, as it reflects a
high % K ~ N and/or B ~ L Gloss. Also, the differences
between the PSE for the wire and felt sides should be
minimized. The web offset "after paper" exhibited good
PSE, but more importantly, the PSE for the wire and felt
sides were very similar, indicating that the paper would
produce print nearly identically on each of its sides.
/jb ~- 20 -
l~Z5.~t~
As ror tl~c Ictter press "artcr paper", while the difler-
encc between thc wirc and Iclt sides ~as still present,
it did cxhibit a lligher PSE for both sides.
Weight PSE
Paper Type (Pound/Ream)Before After
Wire Felt Wire Felt
Web Offset 51 52.6 56.5 52.7 53.9
48.1 55.6 51.5 54.6
57 53.6 63.1 54.7 56.2
55.1 61.4 55.1 55.5
Letter Press 51 48.9 52.1 58.0 51.4
- - 62.1 56.3
Another test~ while not an industry standard,
but which was developed by one of the leading coated
printing paper manufacturers was conducted to determine
the tendency of "before" and "after" papèrs to undergo fiber
rise. Fiber rise is a phenomenon caused by moisture in
the paper being subject to a rapid change of state from a
liquid to a vapor due to sudden heating (as when printed
paper is dried in press driers) which forces fibers of
the base paper to break through or away from the coating.
Fiber rise makes printing difficult, and if severe, can
cause an entire printed job to be rejected. In this test,
the paper samples are stored in a controlled environment
so that its moisture content is uniform. The sample is
then coated with a lacquer to seal in the moisture, and
exposed to a preheated radiant heat source to duplicate
/jb - 21 -
~-;
5'~7
press dri.er condit;.ons. The sampl.e is thell observed
alld ranked rrom 0 to 4 against l~re-exist;ng standards,
O reflecting a great degree of fiber rise while 4 is
none. Generally, any sample with a number 2 or below
is considered poor. The "after paper" had superior
resistance to. fiber rise in all grades.
WeightFiber Rise Number
Paper Type Before After
Wire Felt Wire Felt
Web Offset 51 1 1 3 3
3 3
57 0 0 3 3
0 0 3 3
Letter Press Sl 1 3 3
The test results above set forth establish, in
terms of end results, i.e., the coated paper produced,
the superiority of the coating method and apparatus
of the present invention over one of the better, if not
the best, prior art coaters currently in active
commercial use for the production of enamel coated
printing papers.
Referring again to the apparatus of the invention
as shown in its preferred embodiment, the reverse flow
of coating material under pressure through the space
between the moving web and the front wall of the coati.ng
matcrial chamber or reservoir, in addition to forming a
fluid seal, serves as an active agent or vehi.cle for
. - 22
5~ 7
preventing entry o~ air into the reservoir and entrain-
ment of air in the coating material being applied to
the web, or entrainment of air on the surface of the
web between the web and the coating material. The
reverse flow in ef-fect scours air oE-f the web before
the web enters the coater or applicator, whereby the
coating is applied to the web in an air-free environ-
ment to produce a smooth, uni-form, air--free coating
on the paper.
Also, because the supply of coating material
is essentially self-contained in the coating chamber or
reservoir, a break in the web or other malfunction
creates only minimal problems in comparison with prior
systems, wherein losses of large amounts of coating
materials and extensive cleaning operations are to be
expected. If a malfunction occurs with the present
applicator, the flow of coating material is stopped
simply by cutting off the source of pressurized
coating. The coating apparatus may then be tilted
away from the backing roll and wipedclean, with no
concern about clogging of the applicator with hardened
coating material, since the supply of coating material
is self-contained.
jb/ - 23 -
~s~
Cleaning of the interior of the chamber is facilitated
because of the pivotally mounted front wall 78. The interior of
the device may be completely exposed for cleaning by first pivot-
ing the coating head away from the backing roll on the shafts
60 and then retracting the rods 87 of cylinders 88 to pivot the
front wall 78 away from the rear wall 76, such that the appli-
cator assumes a position shown in Figure 6.
The present method and apparatus is particularly suit-
able for use as the final applicator for so-called "wet-on-wet"
coatings, wherein another coating applicator, such as that in-
dicated at 29 in Figure 1, precedes the applicator 20 without
intervening drying. Because of its short dwell or soak time, the
present apparatus and method minimizes possible contamination of
the first coat by the second coat.
A distinct and important advantage of the present in-
vention resides in the ability of applying extremely light weight
coatings without applying excessive blade pressure to the web.
In most prior art methods, coat weight is reduced by increasing
blade pressure against the web, with the result that blade wear
and the possibility of web breakage are increased, thereby neces-
sitating costly and time consuming shutdowns. In fact, increas-
ing blade pressure past a certain point will not achieve signi-
ficantly lower coat weights, and a coat weight of less than a-
bout 2.5 pounds per ream per side is impossible or im ractical
with most conventional equipment, such as a dip roll and inverted
blade. This latter method, for example, has been found to re-
quire about 1.75 kg per lineal cm of blade pressure to achieve
4.5 grams per square meter coating per side, 1.18 kg per lineal cm
-2~- 1
ms/
1~5S~7
of blade pressure is sufficient for the same weight with the
present invention, and about 1.32 kg per lineal cm will achieve
a coat weight of about 3 grams per square meter per side. It
should be understood that blade pressures in excess of 1.62 kg
per lineal cm are highly impractical and expensive to operate
at in terms of wear and shutdowns, and hence this benefit of the
present invention becomes readily apparent. The use of lower
blade pressures are possible as the metering or doctoring of the
coating occurs before the coating has had time to significantly
dewater on the sheet of the web. By metering when the coating
has not dewatered and the deposited coating layer is more mobile,
there is a reduced tendency for the blade to scratch the web.
Also, the absorbency of the paper has less influence on coating
pick up than in conventional applicators with long application
times.
The above benefits are achieved because a lower soak
time forces the coating to remain on the surface, rather than-
penetrate into the web so that fewer fibers become soaked, there-
by resulting in better coverage with less exposed fibers. The
coated paper produced by the present method is also porous,
which is advantageous for printing and moreover a dense or non-
porous sheet may blister while being dried.
The applicator of the present invention, though ~rim-
arily developed to apply lightweight coatings, on the order of
3 grams per square meter (per side) or less, is ca able of apply-
ing medium and heavyweight coatings, on the order of 22 grams per
square meter per side at high speeds, low speeds and intermediate
speeds. With this applicator there is little or no tendency to
cause scratching, streaking and/or skipping as this applicator
-25-
lS/
SQ~
can coat paper with lowcr doctor blade pressure on the web than
was possible with previously type coaters, and it doctors high
solids content coating before the physical properties of the
coating are adversely affected due to dewatering.
Referring to Figure 7j a second embodiment of appli-
cator 120 of the present invention and for practicing the method
of the present invention is shown and is generally similar to
the applicator 20. Similar elements, parts, or portions of the
applicator 120 will be given the same reference numeral as used
for the corresponding elements, parts, or portions of applicator
20. ~pplicator 120 has certain features which are improvements
over those of a~licator 20, and such improved features will now be
described in detail.
One change noted is that the doctor blade 122 is
clamped or held in place or position by an air tube 124. The
use of the air tube 124 to clamp the blade provides the advantage
of being able to simply remove or replace the blade 122 by re-
laxing the air tube, i.e., reducing the pressure therein, and
slipping the blade out from either the front (operator) side or
back side of the machine. To assist in locating the blade it can
be provided with detents on its lower edge to locate the blade
spacially in the applicator. The air tube 124 also acts to seal
the coating chamber 130, adjacent the end of the blade.
A second air tube 126 is provided above the air tube
124 and is used to uniformly load the blade toward the backing
roll 24 independent of the relative position of the applicator
to the backing roll. The blade loading resulting from pressuri-
zation of the air tube 126 is more uniform along its entire length
than it would be if a plurality of mechanical devices, such as
-25-
s/
5~ 7
screws, sr~accd along the blade, were used. Further, the exact
blade loading condition is easier to duplicate as air pressure is
easier to control. ~lso, the air tube 126 allows the blade 122
to be loaded toward the backing roll without altering the gap
between the orifice plate tip 110 and -the backing roll24 so that
the fluid seal is maintained.
Like the chamber 80 of applicator 20, the chamber 130
of applicator 120 may be opened for cleaning, as is shown in dash-
ed lines Figure 7. Prior to being opened, the applicator is
moved away from the roll, and it will be understood that the roll
24 shown in da-shed lines is included only to illustrate the rela-
tive Positions of the open coater and the roll, since the roll is
not actually moved. The chamber 130 of applicator 120 opens only
at the top end, and the bottom end of the front wall 132, unlike
in applicator 20, remains closed and sealed to the rear wall 134.
The rear wall 134 is arcuate, as indicated at 136~ to accom~odate
the movement of a seal 138 on the front wall 132. The forward -
wall 132 pivots about a fulcrum 140 on the rear wall. Aside
from the advantage of the open chamber forming a trough ta:con-
tain the water used to flush the chamber 130 during cleaning,another advantage of this construction is that the seal 138 and
arcuate sealing surface 136 on the rear wall are swept clean each
time the chamber is opened or closed to minimize possible conta-
mination of the seal or sealing surface.
Rather than being straight, the rear wall 134 and
front wall 132 forming chamber 130 are angular so that as the
coating liquid flows from the lower end of the chamber 130 toward
the upper end the liquid tends to be deflected first off the
front wall, then off the rear wall and again off the front wall
-27-
~s/
c~q~
to cause a more uniform mixing and distrlbution of the coatiny
liquid, this path being indicated by the dotted arrow 142.
Referring to Figures 7 and 8, another advantage of
applicator 120 over applicator 20 is that an internal header 144
has been incorporated within the chamber 130 itself. Now, in-
stead of having a plurality of pipes (as pipes 82 in applicator
20) to supply coating material to the chamber, a single large
diameter pipe 146 supplies the internal header. The header 144
itself comprises a rectangular cross-sectional tube 148 of suf-
ficient size to supply the quantity of coating material to thechamber. To assist in uniformly distributing the coating material
a baffle or false floor 150 is provided in the header to taper or
reduce the flow area as the material flows away from the center
inlet 146. To distribute the coating material to the chamber 130,
a plurality of equally sized,- equally spaced openings 152 are
provided along the upper surface of the header, and these open-
ings empty directly into the chamber. To assist in clean up, a
flush opening 154 closeable by an appropriate valve (not shown)
is provided at each end of the header so that with the valves
open the header can be flushed clean and drained through the
center pipe 146, as will be described later.
Referring to Figures 9, 10 and 11, a third embodiment
of applicator 160 of the present invention and for practicing
the method of the present invention is shown and is generally
similar to the applicators 20 and 120 previously described. Ap-
plicator 160 includes a main beam 161 providing the rear wall
161' of the chamber 162' and a forward portion 163 thereof. The
remaining forward portion of the chamber 162' is provided by a
front wall 164 which seals with ~ther portions of the chamber
-28-
Sa7
and is mo~nted on arms ]63~ Pivoting on brackets 164' carried on
the forward yortion 163. A hea~er, such as the header 144 pre-
viously described, is located in the lower end of the chamber.
Of course, should it be desired, instead of a single header,
several similar type headers could be provided, and such promote
more even distribution. As in the other embodiments, the front
wall 164 may be pivoted away from the rear wall by a fluid device
165 having a variabIe volume to be fi~lled with compressed air.
An improved adjustment is also provided for varying
the position of the orifice plate 152. As shown in Figure 9, the
- orifice plate 162 is slidably guided for movement in a direction
parallel to and on the front wall 164 of the applicator 160, such
being accomplished by any one of various conventional means. To
cause such movement a plurality of operating arms 166 extend
from the bottom of brackets 168 secured to the orifice plate.
The arms 166 each carry a pan bracket 167 for mounting an over-
flow pan 165 which moves with the orifice plate. Each arm 166
at its lower end has in turn a threaded opening 169 receiving
the threaded end of a shaft 170 which carries on its other end
a pair of cams or rotatable rollers 172 and 173. The cams 172
engage in vertical elongated slots 174 formed in a guide bar
176 that is fixed to the front of the wall 164. A horizontally
extending orifice adjustment bar 178 is carried and slidably held
in a horizontal opening 179 in the guide bar. The horizontal ad-
justment bar 178 has a plurality of inclined slots 180 which re-
ceive the cams 173 of the shafts 170, one such slot 180 being
provided for each cam 173. The horizontal adjustment bar 178
is secured by a yoke 182 to the movable screw shaft 183 of a
screw jack 184 secured to the front wall. Thus, as the handle
-29-
~c ~ ,
l~Z5jS~7
186 of the screw jack is rotated! the adjustment bar 178 movcs
horizontally and causes the cams 172 and 173, shafts 170 and
arms 166 to move in the vertical slots 174 and inclined slots
]80, in order to adjust the relative position of the orifice
plate 162 with respect to the front wall 164 and to the backing
roll. The cams 173 are e¢centrically mounted on the shafts 170
so that each cam may be set in a position wherein all cams 173
simultaneously engage the upper surface of the inclined slot 180
to provide uniform movement of the plate 162.
Referring to Figures 9 and 10, in order to increase
the loading of the doctor blade 190 and end dams 192 against the
backing roll to eliminate or reduce leakage, a small pneumatic
cylinder 196 is mounted to the applicator 160 directly behind
each of the end dams, such dams being constructed of felt or
similar material. The end of the piston-rod of the pneumatic
cylinder 196 adjacent the end dam has a tapered or pointed tip
198 which can be forced against the rear of the blade 190 to sup-
plement or increase blade loading at this point and increase the
seal of the end dam to the backing roll. Thus, it is possible
to reduce or eliminate end dam leakage by increasing the pressure
provided on the blade at its ends and on the end dams, without
having to use a high pressure across the entire blade. Also,
such adjustment for providing additional sealing is more dupli-
cative since the air pressure supplied the cylinders is readily
controlled.
Referring to Figures 10 and 11, the end dams 192 are
each carried in a novel holder 200 which is made of nylon, stain-
less steel or similar material. Each end dam holder 200 in-
~ -30-
~s/
~2S5~7
cludes a first outer tuhular body 202 and an inner tubular body
203. The outer body 202 has a mounting flange 204 extending
from its bottom which can abut a bracket 206 fastened to the ap-
plicator to hold the body 202 to the applicator. The flange 204
and bracket 206 are held together by a knob 208 which has a
threaded portion passing through a threaded opening in the brac-
ket and in clamped engagement with the flange 204. The bodies
202 and 203 of the holder are somewhat triangularly shaped in
cross-section as shown in Figure 11 to fit in the space between
, 10 the orifice plate, blade and roll. The body 203 has on its in-
ner end a generally triangular, vertical flange member 210 which
abuts one end of the dam 192. The bodies 202 and 203 have co-
axial openings,therethrough for receiving a rod element 212.
The inner end of the rod element 212 has a similar triangular
shaped vertical flange member 214 affixed thereto for abutting
the other'end of the dam 192. The other end of the rod element
212 is threaded and receives a knob or nut 216 for drawing the
two triangular shaped flanges 210 and 214 relatively toward each
other to compress the flexible dam 192 between them and to cause
the adjacent ends of bodies 202 and 203 to abut a-second felt
or felt-like seal 215 located therebetween. As the dam 192 is
compressed between the triangular shaped flanges 210 and 214 and
the felt 215 is compressed between the bodies 202 and 203, the
felts tend to expand in di~ections normal to the pressure to in-
crease the seal between the roll 24, orifice plate 162 and doc-
tor blade 190 to prevent leakage past the felts. The sealing
provided by dam 192 helps maintair. the pressure in the chamber.
An end dam of this type also has the advantages of requiring a
-31-
ms/
S~7
reduced amount of felt, provides a more reliable seal, and readi-
ly facilitates blade angle adjustments by merely changing the
relative position of the applicator on the backing roll.
Even with the more effective seal provided by the end
dam 192, problems can arise should coating material work its way
past this seal and accumulate on the outer ends of the orifice
plate or doctor blade. Coating material accumulated in such
places could scratch or damage the backing roll. In order to
prevent coating material accumulating in such places, large re-
lief openings or cut-aways 220 and 222 are formed or cut in each
end of the orifice plate 162 and in each holder 200, respectively.
Thus, should any coating material work its way past the felt
seals 192, it flows over the relief cut-aways 222 and 220 in the
holder and the orifice plate into the overflow pan 165 on the
front of the applicator. The felt seals 215 direct the flow in-
to the cut-aways and prevent any coating material from passing
by and accumulating on the extreme ends of the orifice plate or
doctor blade to scratch or otherwise damage the roll.
If desired, both sides of the paper web can be coated
simultaneously by substituting a second coater for the backing
roll and operating the two coaters in back to back relationship
with the web passing between the two. In this case, the appli-
cators are arranged so that they are generally mirror images of
one another, with the web between them so that both sides of the
web can be coated simultaneously. Of particular advantage is
that no backing roll is needed, each of the applicators support-
ing the web for the other, and permitting the pair of applicators
to be located on the coating machine in a location where there
ms/
58~7
is no backing roll.
While three embodiments of apparatus of the present
invention, for practicing the method of the invention, have been
described and illustrated, it is to be understood that the in-
vention is not limited thereto, but comprehends other construc-
tions, arrangements of parts and details and other steps and
orders for performing the method, without departing from the
scope of the invention as set forth in the appended claims.
,
-33-
ms/
