Note: Descriptions are shown in the official language in which they were submitted.
WO92/12803 21012 6 4 PC~/US91/~009
ME:THOD FOR DIRECTING A~! ELONGATED FLOW OF COATING MATERIALS
TOWARD A SliBsTR~TE
BACKGROUND OF THE I ~ ENTION
The present invention relates to an apparatus and
process for coating a substrate. More particularly, it
concerns an apparatus and method for depositing a uniform
coating of liquid, or a liquid containing particulates, on
a broad variety of substrates such as paper, cloth and
organics.
GENERAL DISCUSSION QF THE BACKGROUND
Many manufacturing processes coat products with a
liquid film to preserve them or improve their physical
properties. Starch, for example, is o~ten applied to the
surface of paper, preservatives and additives are sprayed
on foods, surface treatments are placed on wood products,
and tanning chemicals are applied to leather. It is often
preferable to apply a uniform coating of such liquids, or
at least to apply a thorough coating that does not leave
bare any part of the surface to be treated. Conventional
spray applicators have been used in such processes, but
suffer from poor uniformity of application that sometimes
leaves portions of the substrate untreated, undertreated
or overtreated. Applicator ro~lls and blade coaters
provide a more uniformly coated substrate, but are
unwieldy and unable efficiently to apply liquids to non-
line~ar surfaces. The drawbacks of several of thesespecific systems are illustrated below in connection with
coating a paper web substrate~
Paper webs are frequently treated to increase
their surface strength and enhance their printability by
providing a smooth printing surface on the paper. Paper
coating is often performed by applying an excess amount of
coating material onto an applicator roll for transfer to
the web. Alternatively, the coating liquid is applied
directly to the web in excess, and then metered to the
correct thickness with a blade or rod. Although roll and
blade coating systems apply relatively uniform layers on a
substrate, such systems suffer from the drawback of
requiring an expensive piece of heavy machinery that
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W092/12803 PCT/U~91/09009
occupies a large amoun~ o,f space. A typical roll coating
system in a paper mill~ uch as a conventional two-roll
size press or a g~a~;roll system, can cost millions of
dollars and require an in-line space of lO to 30 meters
(30 to lOo feet). Placing a roll coating system within an
existing line of equipment also requires removal and
relocation of existing equipment, which greatly increases
the installation costs.
Spray systems are a less expensive and more
compact alternative to roll coaters. In a typical spray
applicator, pressure is applied directly to liquid in the
spray head. Passage of the liquid through a constricted
orifice in the spray head brea~s the liquid into droplets
of many sizes. In spite of their convenience, spray
systems do not uniformly apply material to a substrate.
The resulting coated product is streaky and blotched,
rendering it less appealing to consumers. The irregular
surface coverage may also diminish the appearance of
printing on the surface. Another drawback with spray
systems is that the droplets they produce tend to become
airborne as a mist, and the mist is carried throughout the
area adjacent the spray nozzle, where it builds up on the
spray system and surrounding equipment. The mist can also
pose a health or hygiene problem to workers in the
vicinity who come into contact with the mist or inspire
it.
A cross-section of a typical prior art pressure
spray head is shown in FIG. l. The spray head lO has a
body ll with a circular horizontal cross-section and a
central interior bore l2 that tapers in the direction of a
small cylindrical spray orifice 13. The liquid material
is forced under pressure through the tapering central bore
and out of the orifice at a high velocity to produce
liquid droplets. The design of the central bore 12 and
the orifice 13, in combination with the internal pressure
on the material, determines the pattern of spray produced
by the nozzle. The size distribution of the resulting
droplets varies across a broad range, and the spray is
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difficult to control or direct. It also deposits unevenly
across the surface width of a paper sheet or other object
being coated.
A typical lateral mass distribution of material
from a conventional spray head is shown in FIG. 2. The
applied coating is markedly non-uniform with two peaks 14
and 15 spaced laterally from the center line of the spray
head. The volume flow at each of the peaks 14 and 15 is
approximately twice the volume flow at the center 17 of
the spray pattern, and approximately seven times the flow
at the outer edges 18 and 19 of the pattern. The flow at
the center 17 is itself approximately four times the flow
at the edges 18 and 19. This lateral non-uniformity of
application causes undesirable streaking of the coating on
the substrate with thicker and thinner application of the
material across its width. Another type of spray system
is air assisted atomization, in which liquid emerges ~rom
a circular opening and is changed into droplets by an
annular stream of' air. Air assisted atomization has been
used, for example, in spray painting devices. This
technology has not been suitable for uniformly coating
substrates because of nonuniformities in the coating and
production of environmentally unacceptable misting.
Moving spray painters close to surfaces being painted
results in a less uniform coat of paint being deposited on
the surface.
It is accordingly an object of this invention to
provide an improved apparatus and method that can deposit
liquid on a substrate more evenly than conventional spray
or airblast coating.
It is also an object of the invention to provide
such an improved apparatus and method that more completely
or thoroughly covers a substrate than do spray nozzles or
airblast atomizers.
Another object of the invention is to provide an
apparatus and method that is less expensive and space
consuming than roller or other conventional applicators,
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and which can be easily re~rofitted into existing
production lines. ~ '
Yet another object is to provide an improved
system for applying liquid coatings to a variety of
substrates having many different topographies.
Yet another object is to provide an improved
application system that produces less ambient mist than
conventional sprays, and more particularly can combine the
benefits of mist reduction with enhanced coating
uniformity.
Finally, it is an object of the invention to
provide an improved applicator that is capable of
depositing very thin liquid coatings as well as thicker
coatings.
These and other objects of the invention will be
understood more clearly by reference to the following
detailed description and drawings.
SUMMARY OF THE INVENTION
The process of the present invention deposits a
coating of a material on a substrate by directing a flow
of the material from an outlet, such as multiple orifices
or a slot, toward the substrate. A fluid (such as a gas)
is impinged against the flow to form droplets that can
deposit a thin uniform coating on the substrate. The
substrate and flow move relative to one another as the
flow is changed into droplets such that a coating may be
evenly or thoroughly deposited over an area of the
substrate. The flow rates and velocities of the coating
material and impingement fluid can be varied over a broad
range to alter the characteristics of droplet formation
and the resulting uniformity of droplet deposition on the
substrate.
The droplets can be formed in various ways,
depending on the coating material viscosity, fluid
impingement velocity, and changes in viscosity of the
material as the droplets are forming. At low impingement
velocities or high material viscosities, the fluid may be
attenuated into droplets by gradual elongation of liquid
WO92/12803 210 1 2 ~ ~ PCT/US91/0~009
streams. At higher impingement velocities or lower
material viscosities, airblast atomization occurs as the
liquid is immediately changed from a confluent liquid into
atomized droplets as the liquid emerges from its outlet.
The coating material does not increase in viscosity after
it leaves the outlet to such an extent that droplets will
not form. This is a difference between the present
invention ~nd meitblown technology, because in meltblowing
the viscosity of extruded material increases to a
sufficient extent that networks of fibers form. The
coating materials of the present invention include non-
thermoplastic materials that do not form fiber networks of
the meltblowing variety. Instead, the coating materials
form droplets that are deposited on a substrate.
The flow of coating material emerging from the
applicator can take a variety of forms prior to being
impinged with the impin~ement fluid. The flow of material
can take the form of a series of columns emerging from a
plurality o~ orifices, or a continuous curtain emer~ing
~rom a slot. The plurality of orifices can be linearly
aligned, arranged in a chevron or arcuate configuration,
in staggered rows or any other shape that allows the
impingement fluid to attenuate or blast the liquid into
droplets. The slot can have a similarly wide variety of
shapes, such as a continuous, straight linear slot, a
series of discontinuous slots, an arcuate or chevron
shaped slot, or staggered rows. The term "linear" is used
in its usual technical manner to refer to the shape traced
by a moving point, which can include a straight, arcuate,
or even serpentine line. As used herein, the term
"linear" does not include a circular shape.
In some preferred embodiments, the coating
ma~erial is a liquid, such as an aqueous liquid that is
(by definition) at less than 100C ~212~ n other
preferred embodi~ents, the liquid is non-aqueous, for
examp}e, an isocyanate such as PMDI, or acrylics, styrene-
maleic anhydride, and epoxy resins. The low viscosity of
the liquid renders it flowable at room temperature, hence
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WO92tl2803 - 6 - PCT/US91/09~9 _
the coating process can be carried out entirely at ambient
temperature (15~C-40C or 60F-100F). The viscosity of
the liquid can vary-over a broad range, for example l -
2000 cP (0.001-2 Pa-s), and the;-low viscosity of the
liquid allows it to be directèd through an outlet toward
the substrate under low pr~ssures, such as 5 - 25 psi (35
- 175 kPa) or even as low as l psi. In such low pressure
embodiments the liquid moves at relatively low velocities
from the outlet toward the substrate, and is impinged by a
fluid, such as a gas, that moves at a greater velocity
than the liquid.
Although variable, the gas temperature is
preferably less than 100C, and preferably is ambient
temperature. The gas may be humidified to help reduce the
drying and build-up of water soluble coating materials
inside the applicator head or at the outlet slot.
Moisture or other additives in the gas stream may also be
used to catalyze or modify the liquid in khe attenuated
array as it travels to the substrate. Plural fluid or gas
streams may be spaced varying distances from the outlet.
By including catalysts in the stream spaced by another
intervening gas stream from the outlet, the possible
catalyzation of the liquid at the outlet can be minimized
or enhanced.
The elongated liquid flow emerging from the
outlet has opposing faces, and the fluid can be impinged
against either one or both faces at a wide range of
velocities, from 200 feet per second (60 m/s) to sonic or
supersonic velocities. Attenuation of the liquid into
increasingly finer droplets occurs as the fluid velocity
is increased, for example, as it approaches sonic
velocity. At high impingement velocities, the liquid is
immediately blasted into droplets as the liquid emerges
from the outlet. Much lower fluid velocities are also
suitable for many applications where large droplet size
can be tolerated. Immediate atomization can also be
achieved at relatively low fluid velocities when the
liquid has a low viscosity. The present invention can be
W092/12803 2 1 0 1 2 6 ~ PCT/U~91/~90Q9
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used to coat a broad variety of substrates, such as
cellulosic, fi~er, organic, syntheticl rubber, cloth,
wood, leather, food, and plastic substrates. ~ wide
variety of coating materials can also be applied to
substrates using this method. The coating material may
preferably be a liquid at room temperature such that it
can be sprayed on the substrate in a liquid form without
having first solidified before reaching the substrate.
The coating fluid may contain particulate matter that is
also to be deposited on the substrate. Alternatively,
particulate matter can be introduced into the liquid by
the impingement fluid.
In alternative embodiments of the process, the
coating liquid is dispersed into droplets before the
impingement fluid encounters it. In such embodiments, the
liquid is turned into a mist electrostatically or
ultrasonically. The mist is then directed toward a mov~ng
substrate by an impingement fluid, which may be directed
at the substrate under low pressure.
The apparatus of the present invention includes
an applicator, movement means for establishing relative
movement between the substrate and applicator, and an
outlet in the applicator that directs a flow of coating
material toward the substrate. A fluid outlet in the
applicator impinges a fluid, such as a gas, against the
coating material to form droplets that are directed toward
the substrate to deposit a coat of liquid on the moving
substrate. A nozzle portion of the applicator head
contains the outlet (which can be a plurality of outlets)
through which the coating material is ejected under
pressure. One or more impingement fluid slots may extend
along the applicator adjacent the coating material outlet
to provide a curtain of fluid, such as a gas, that is
propelled under pressure against the coating material.
The described apparatus is capable of depositing a uniform
coating of coating material (such as a liquid) on the
substrate, and the thickness of the coating can be varied
from very thin to quite thick.
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WO92/12803 2 ~ O 1 2 6 4 PCT/US91/090~9
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In other preferred embodiments the applicator
includes a cleaning means that removes a build-up of
matter from the applicator head. In some embodiments this
cleaning means includes a movab ~ portion of the
applicator that covers an intern~l passageway leading to
the outlet. The movable poS~rtion may be hinged to the
applicator to permit the mQvable portion to swing away
from its closed position and open the applicator. The
opened applicator provides access to its interior to
permit the liquid passageway and liquid outlet slot to be
cleaned. In other embodiments, the applicator is a head
made of matable bipartite portions that meet to define an
internal coating material passageway that communicates
with an outlet. The portions of the head are matable, and
may optionally be selectively separated by a power
actuated arm that moves the matable portions apart to
expose the internal passageway and outlet for cleaning.
The cleaning means may also be an internal or
external wiper that moves along or through the head to
remove solids build-up. Solubilizing materials, such as
humidified air, can also be added to the impingement fluid
or gas to dissolve and remove water soluble solids from
the head and outlet. Other solvents may also be included
in the impingement fluid for cleaning purposes. The
solvents may be selected to target and remove the dried
coating material. The accumulation of agglomerated
coating material in the head may also be diminished by
coating the surfaces of the head with a low surface energy
material that reduces adhesion of the coating liquid to
the head and outlet. Examples of such materials include
polytetrafluoroethylene, amorphous carbon or
polycrystalline diamond. Adhesion to the head is also
diminished by providing sharp edges around the outlets or
orifices from which the coating material and impingement
fluid emerge.
The coating apparatus may also include a mist
collection device. The mist is preferably collected with
a pressure differential, for example, by providing a
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W092/12803 2 1 ~ 1 2 6 ~ PCT/US91/o9009
g
suction pressure from a hood adjacent the applicator. An
air curtain may be directed toward the substrate between
the hood and moving substrate to prevent escape of mist
between the substrate and hood. A paddlewheel or auger
can be placed in or adjacent the collector to help direct
mist into the collector and out of a collection duct.
Alternative collection devices include electrostatic
directors that govern the movement of the mist. The
director may be, for example, a repulsion plate or bar
spaced from the substrate and charged to repel oppositely
charged mist droplets toward the substrate.
Alternatively, the mist may be collected by grounding the
substrate to attract charged mist particles.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a prior art
conventional spray nozzle.
FIG. 2 is a graph representing the lateral flow
distribution of liquid ~rom the prior art spray nozzle of
FIG. 1.
FIG. 3 is a perspective view of the apparatus of
the present invention in use coating a moving substrate.
FIG. 4 is a view taken along view lines 4-4 of
FIG. 3.
FIG. 5 is an enlarged cross-sectional view of the
head of FIGS. 3 and 4.
FIG. 6 is an enlarged view of the central apex of
the head, showing the liquid orifices.
FIG. 7 is a perspective view of the central
portion of the head taken along view lines 7 - 7 of FIG.
5.
FIG. 8 is an enlarged view of the liquid
passageway portion of the head circled in FIG. 7.
FIG. 9 is an alternative embodiment of the
applicator head.
FIGS. 10 - 13 are alternative embodiments of the
nozzle portion of the head shown in FIG. 9.
FIG. 14 is a view similar to FIG. 4 showing
another embodiment of the head in which the liquid outlet
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is a slot, an enlarged portion of the slot being shown in
the circle.
FIG. 15 is a cross-sectional view of an
alternati~e slotted outlet nozzle portion of the head.
FIG. 16 is another embodiment of the slotted
head.
FIG. 17 is an alternative embodiment of the head
of the present invention.
FIGS. 18A - D are several other embodiments of
the nozzle portion of the head illustrating the wide
variety of angles with which the fluid stream impinges the
liquid.
FIG. 19 is a side elevational view of an
alternative embodiment of the invention showing a power
means for opening the bipartite head about a pivot point.
FIG. 20 is a schematic view of an alternative
embodiment of the invention in which liquid is pre-
atomized before being directed at a substrate.
FIG. 21 is a schematic cross-sectional view of an
electrostatic atomizer for dispersing liquid into
droplets.
FIG. 22 is a view similar to FIG. 3 showing an
alternative embodiment of the applicator in which a
collection hood surrounds the applicator.
FIG. 23 is a cross-sectional view of the
applicator taken along section lines 23-23 of FIG. 22.
FIG. 24 is a cross-sectional and schematic view
of an air scrubber for removing liquid droplets from the
exhaust o~ the hood of FIG. 22.
FIG. 25 is a cross-sectional schematic view of
another embodiment of the hood in which secondary flows of
air are introduced into the hood.
FIGS. 26 - 28 are photographs prepared from high
speed videotapes of liquid impinged with gases at
increasingly greater gas velocities.
FIGS. 29 - 30 are photographs prepared from high
speed videotapes showing airblast atomization of liquid
immediately as it emerges from the liquid outlet~
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WO92/12803 210126 ~ PCT/US91/09009
FIG. 31 is a photograph showing a grainy
distribution of iodine stained coating liquid on a paper
substrate coated with the present invention.
FIG . 32 is another photograph showing a streaky
distribution of iodine stained coating liquid.
FIG. 33 is a series of photographs of iodine
stained coating liquid on sheets of paper demonstrating
the effect of air pressure and application rate on
coverage uniformity with the applicat:or of the present
invention.
FIG. 34 is a series of photographs of iodine
stained coating liquid on sheets of paper demonstrating
the effect of air pressure and air gap width on coverage
uniformity with the applicator of the present invention.
FIG. 35A is an image while FIG. 35B is a column
average and FIG. 35C is a single line grey intensity
profile for a gate roll coated sample of paper.
F:CGS. 36A - 38A are images while FIGS. 36B - 38B
are column average and FIGS. 36C - 38C are single line
20 grey intensity profiles for materials coated with the
apparatus and method of the present invention,
illustrating variations in product quality as a function
of process parameters, for Table II runs S12C1, S7, and
S6, respectively.
FIGS. 39A - 52A are graphs showing column average
intensity profiles while FIGS. 39B - 52B are single line
grey intensity profiles for Table II runs S3A, S16G, S16F,
S18D, ~;15A, S13B, S12B, S5C, S5~, S19E, S19G, S19K, S20A,
and S21A respectively.
FIGS. 53A-E, 54A-E, 55A-D and 56A-E are single
line grey intensity profiles in the direction of substrate
movement for the runs from Table II referenced on the face
of the tracing.
FIG. 57 is a schematic view showing airblast
35 atomization of liquid as it emerges from the applicator.
FIG. 58 is a schematic end view of a collector
- device in which a paddlewheel feeds mist into the
collector.
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FIG. 59 is a schematic end view o~ a collector in
which an augur extends along the length of the colIector.
FIG. 60 is a schematic cross-sectional view of
another embodiment of the applicator in which li~uid flows
through a series of holes and on to a target plate before
entering liguid outlets.
FIG. 61 is yet another embodiment of the
applicator in which a replaceable tip is provided inside
the applicator. -
DETAILED DESCRIPTION OF SEVERAL PREFERRED EMBODIMENTS
One preferred embodiment of the apparatus 56 ofthe present invention is shown in FIGS. 3 - 8 to include
an applicator head 58 suspended by a mechanical arm 59
above a paper web substrate 60 that is moving below head
58 over rolIers 61 in the direction of arrow 63. Of
course, relative motion between the head and substrate can
also be accomplished in other ways, such as by moving the
head over a stationary substrate. Head 58 is shown in
greater detail in FIG. 5 to be a bipartite head with a
central portion that in cross-section defines an
equilateral triangle. The central portion has mating,
complementary wedge halves 82, 84 that meet along opposing
faces to form a linear junction 86 that bisects an apex of
the triangular cross-section. Each wedge 82, 84 has a
notch 88 along the opposing junctional faces that, in
combination with the corresponding notch from the other
half portion of the head, forms a liquid chamber 90 along
the length of head 58.
The cross-sectional width of chamber 90 widens
and then tapers along junction 86 to communicate with a
plurality of narrow liquid passageways 92 (FIGS. 5, 7 and
8) that extend through head 80 along junction 86 to the
apex of the head. Each passageway 92 terminates in a
circular cross-section orifice 93 (which may also be
square or diamond-shaped in section) that is machined to
sharp edges 95, as shown in FIGS. 6 and 8. The faces 101,
103 of the head meet along a sharp apex 97 and each hemi-
orifice extends in the plane of the face and is outlined
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by edges 95~ The sharp edges 97 (for example, radius
S.002 inch) help diminish build-up of coating material at
the liquid outlet. Alternatively, one or more continuous
elongated linear slots or other outlet configurations
5 could replace the plurality of orifices 93, such as the
slot described below in connection with FIG. 14. Such a
slot is easier to manufacture and clean than a multiple
orifice configuration.
Complementary mating wedges 82, 84 are
selectively held together by bolts 94, 96 that extend
through bores 98, 100 in the wedges. Bore 98 communicates
with an outer face 101 of wedge 84 and includes a land 102-
against which the head of bolt 94 rests. Bore 98
communicates with the opposite side face 103 of head 80
formed by wedge 82, and bore 100 similarly has a land 104
against which the head of bolt 96 abuts. A notch 106 in
wedge 84 of head 80 seats an elastomeric seal 108 to
enhance the fluid tight nature of junction 86.
An enclosure channel 116 is bolted to wedge 84 to
form a fluid chamber 118 that extends along face 101 of
wedge 84. Channel 116 is secured to portion ~4 by a bolt
120 that extends through a bore 122 in channel 116 and an
aligned bore 124 in wedge 84. Channel 116 includes an
upper segment 126 that abuts tightly against face 101 of
portion 84 and forms a relatively fluid tight seal
therewith. Middle segment 128 and lower segment 130 of
the channel extend downwardly and inwardly toward face 101
in the direction of the tapering end of head 80. Segment
130 terminates just short of face 101 in a flat face that
extends parallel to face 101 and forms a narrow fluid
passageway slot 132 that communicates at one end with
fluid chamber 118 and at the other end forms a fluid
outlet 134. Fluid passageway 132 travels along face 101
at a 30 degree angle to li~uid passageways 92 such that
fluid emerging from slotted fluid outlet 134 impinges the
liquid array from outlets 93 at a 30 degree angle.
The embodiment of FIG. 5 also includes a second
air channel 116 attached to face 103 of wedge 82. A
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second fluid passageway i5 for~ed along face 103 such that
the impingement fluid strikes th~ liquid from outlets 93
at about a 30 degree angle:.; Hence the liquid is
attenuated or atomized ~ fluid striking both faces of the
emerging liquid. Such bi-planar attenuation or
atomization has been found to be acceptable but not
essential to droplet deposition. Henc~e the second air
channel 116 may be omitted, especially when coating with
low viscosity liquids.
In operation~ a coating liquid 72 (FIG. 3) is
supplied under pressure to conduit 70 that communicates
with chamber 90 such that the liquid distributes evenly
across the length of the head. The pressurized liquid is
propelled through the plurality of orifices 92 (FIG. 8)
and emerges as a linear curtain or distribution 78 of
liquid (FIG. 3) that extends across the width of substrate
60. Pressurized air 66 enters conduits 62, 64 such that
each communicates with an air chamber 118 and the air is
distributed through chambers 118 along the length of head
58 into passageways 132. The air emerges at slot 134 to
impinge against liquid distribution 78 and attenuate the
flowing liquid into smaller loops or ligaments of liquid
and finally into droplets. By the time the liquid reaches
substrate 34, it has been attenuated into small droplets
that substantially completely cover and adhere to the top
surface of the substrate.
Instead of gradual liquid attenuation, a more
rapid airblast atomization can occur. Airblast
atomization would more typically occur at higher gas
impingement velocities or elevated mass ratios of
impingement gas to coating material mass. The coating
material is blasted into droplets by high velocity air
immediately as the material emerges from the applicator.
The degree of liquid attenuation or atomization
can vary depending on the viscosity and flow rate of the
coating liquid, and the impingement gas velocity. It is
frequently desireable for reasons of economy, appearance
and function, to form a fine mist that deposits a thin
WO92/12803 2 i ~ ~ 2 ~ 4 PCT/US91/09009
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uniform coating on the surface of the substrate. Multiple
heads may be placed sequentially along a line to provide
multiple coats of the same or different liquids on the
substrate. If a thick single coating is desired, the
operating parameters of the head may be changed, for
example, to increase the volume flow of liquid. If less
uniformity is required, the impingement fluid velocity may
be reduced to decrease the liquid atomization or
attenuation. Larger droplets will reach the substrate and
form a thicker, less uniform coating. Application of
larger droplets may be preferred when saturation is
desired.
Another embodiment of the applicator head, which
in this embodiment is rectilinear in cross-section, is
shown in FIG. 9. Applicator head 150 is bipartite and
includes mating, complementary square body portions 152,
154. Portion 152 includes a top wall 156, side wall 158,
an upright liquid partition 160 that extends downwardly
from top wall 156 parallel to side wall 158, ancl a
horizontal partition 162 extending from a distal end of
partition 160 away from side wall 158. Portion 154 of
head 150 includes a complementary, mirror-image structure
with a top wall 164, side wall 166, upright partition 168
and horizontal partition 170. Mating heads 152, 154
cooperatively form an elongated liquid chamber 171
therebetween that spans the length of head 150. Top walls
156, 164 abut along a fluid tight junction 172 that
contains an elastomeric seal 174 for maintaining tightness
of junction 172 and preventing escape of liquid from
chamber 171 during use. Horizontal partitions 162, 170 do
not abut, however, but instead stop short of one another
such that their opposing faces 175, 177 form an elongated
manifold 176. The manifold communicates with a nozzle
member 178 that extends the length of head 150 below
manifold 176. A plurality of tubular liquid passageways
180 extend through nozzle member 178 and each passageway
terminates in a liquid orifice 182 at the tip of nozzle
178. The orifices may be shaped and sized like the
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outlets 93 of FIGS. 3 - 8. In alternative embodiments, a
single slot 180 extends through the passageway to form a
continuous linear outlet 182 instea~ of a plurality of
orifices. A pair of elastomeric seals 184, 186 extend
along nozzle member 178 the~ ength of head 150 to provide
a more fluid-tight seal.
A pair of complementary, mirror image air plate
members 200, 202 jointly form a nozzlle portion of head
150. Air plate member 200 is an L-shaped mem~er having a
flange 204 that mates with a bottom face of side wall 158,
and a plate that extends parallel to top wall 156 and
horizontal partition 162. Member 200 forms an air chamber
208 in cooperation with walls 156, 158 and 160 of portion
152. An elastomeric seal 209 extends along the length of
head 150 between side wall 158 and flange 204 to provide a
fluid-tight seal. Air plate member 202 similarly includes
a flange 210 that abuts the bottom of side wall 166, and a
member 210 that èxtends parallel to top wall 16~ and
horizontal partition 170 to form, in cooperation with
walls 164, 166 and 168 an air chamber 212 that extends
along the length of head 150. An elastomeric seal 213
extends along the length of head 150 between side wall ~66
and flange 210. Plates 200, 202 are each secured to head
150 by bolts 214, 216 that are respectively placed in
recessed bores 218, 220 through flanges 204, 210 into side
walls 158, 166.
In operation, air is introduced under pressure
into chambers 208, 212 and pressurized liquid is
introduced into liquid chamber 171. Air emerges from
slots 226, 228 substantially parallel to a linear or
elongated distribution of liquid emerging from outlet 182.
The co-flowing airstream attenuates or atomizes the liquid
array into droplets for deposition on a substrate. A
linear distribution of liquid is a liquid flow that has an
elongated linear width. The width of the distribution is
elongated in the direction that slot or orifices 82
extend. An elongated distribution is not necessarily-
linear (although it may be). The elongated distribution
, .
WO92/12803 210 12 6 ~ PCT/US91/Ogoog
- 17 -
has a width that extends in the direction perpendicular to
the direction of flow of coating material from the outlet
to the substrate, and typically is elongated in the
direction that slot or plurality of orifices 82 extend.
Although the liquid distribution from the embodiment of
FIG. 9 is in the form of a straight line, a variety of
shapes would be suitable, such as an elongated arcuate or
chevron shaped distribution. Uniformity or symmetry of
the array or distribution is not required.
An alternative embodiment of the nozzle portion
of head 150 is shown in FIG. 10, wherein like parts have
been given like reference numerals. In this embodiment,
the air plates 230, 232 are substantially flat instead of
- L-shaped. Each plate 230, 232 is respectively secured to
side walls 158, 166 by bolts 234, 236 through a slightly
angled portion 235, 237 of each plate. The angled portion
of each plate fits f,lush against the bottom face of walls
158, 166 and is sealed by elastomeric seals 209, 213.
Because of the slight angle between portions 235, 237 and
plates 230, 232, the plates extend at about a 30 degree
angle downwardly from walls 158, 166 toward the center of
head 150. Each plate extends centrally toward an
elongated nozzle 238 through which pass a plurality of
liquid passageways 180 that terminate in a row of orifices
182 aligned longitudinally along the length of head 150.
Each plate 230, 232 terminates adjacent the orifi,ces 182
of nozzle member 238 to form a pair of elongated slots
242, 244 that extend along the length of the head adjacent
the plurality of orifices 182 in nozzle 238. Each slot
has substantially parallel walls formed by the tip of
nozzle 238 and the abutting walls of plates 230, 232, such
that substantially co-planar flows of air and liquid
emerge from the slots and orifices.
Another embodiment of the invention, shown in
FIG. 11, is similar to that shown in FIG. 9 except the tip
of nozzle 238 tapers externally such that the edges of
liquid orifices 182 are sharp edges. Each plate 230, 232
similarly tapers at its distal medial end to a narrower
,
W092/12803 210 12 6 4 PCT/US91/09009 ~
- 18 -
cross-sectional width than the remainder of the plate, and
ends in angled edges 246, 248. The external walls of the
tapering tip of nozzle 238 meet at`,,an included angle of
about 30 degrees and edges 246, 2`4~ of the plates are
parallel to the tapering tip of noz71e 238. Hence
impinging gas that emerges f~om the air slots impinges
liquid from outlets 182 at about a 30 degree angle against
the liquid array distribution. The sharp edges of the
orifices 182 diminish build=up of coating material on the
tip of the nozzle.
FIG. 12 shows yet another embodiment of the
nozzle portion of the head in which nozzle 238 includes a
wide base 254 and a tapering body 256 that has a
triangular cross-section. Body 256 tapers to an included
angle of about 30 degrees. Base 254 and body 256 define a
plurality of substantially co-planar, parallel liquid
passageways 180 that extend through nozzle 238. Each
passageway 180 opens into one of a plurality of aligned
liquid outlets 182 that extend along the length of
applicator head 150. Each air plate 230, 232 tapers to a
sharp edge 258, 260 adjacent liquid orifices 182 to form
elongated slots 262, 264 that extend adjacent and parallel
the plurality of orifices. Tapering faces 266, 268 define
planes that intersect at an included angle of about 90
degrees such that the air chambers 208, 212 narrow in the
vicinity of tapering body 256 and direct a flow of
impingement fluid at an acute angle against the linear
array of liquid emerging from orifices 182. The sharp
edges 258, 260 of the plates and the sharp edges of nozzle
238 inhibit accumulation of dried coating material in
these areas.
Finally, FIG. 13 shows a nozzle head similar to
FIGS. 9 - 12, with like parts given like reference
numerals. The liquid nozzle 238 includes a flat base 270,
tapering body 272, an elongated slot forming member 274,
and a plurality of tubular extensions 276 each defining a
circular orifice 182 surroundad by an annular sharp edge.
Air plates 230, 232 taper toward nozzle 238, and each is
. . .
WO92/12803 21012 6 4 PCT/US91/09009
-- 19 --
provided with a flat extension plate 278, 280 that tapers
toward nozzle 238 to a very sharp edge that is spaced from
yet parallel to the plurality of orifices 182 defined by
tubular extensions 276. The sharp edges around orifice
182 and on plates 278, 280 diminish dried build-up of
coating material dispensed from applicator head 150.
In alternative embodiments of the invention, the
liquid passageway 180 and liquid orifices 182 are a
continuous elongated slot 282, as best seen in FIG. 14.
That drawing is similar to FIG. 4, and like parts have
been given like reference numerals. A magnified slotted
portion of the head is shown in the circle. In this
embodiment the liquid emerges from slot 282 as a curtain
array, and is attenuated or atomized by air emerging from
the slots defined by edges 134.
Another embodiment of the slotted head is shown
in FIG. 15, wherein only the nozzle portion of the head is
shown. The nozzle portion 290 includes a triangular,
fixed central wedge portion 292 that is triangular in
cross-section and tapers to an included angle 294 that is
defined by the intersection of flat faces 296, 298. A
similar wedge-shaped fixed head portion 300 also tapers to
an included angle 302 of about 30 degrees, the angle being
defined by the intersection of flat faces 304, 306. Faces
298, 304 are adjacent and substantially parallel to one
another defining therebetween a space having a width 308
of about 4 mils (0.004 inch or 100 ~m). Each head portion
292, 300 tapers to a sharp edge 310, 312 that defines an
air gap 314 therebetween that is delimited by the sharp
edges 310, 312 and is about 4 mils wide. A swingable
wedge portion having a triangular cross-section is
positioned adjacent central portion 292 and includes flat
faces 322, 324 that taper to an included angle 326 of
about 30 degrees to define a long, sharp edge 328. Face
322 is adjacent and parallel face 296 at a uniform
distance 330, that in this embodiment is about 8 mils
(0.008 inches or 200 ~m). The sharp edges 310, 328
W092/1280~ 1 0 ~ 2 6 4 PCT~US91/09009
- 20 -
thereby cooperatively define an elongated slot that serves
as a liquid outlet.
In operation, the liquid to be applied to the
substrate is introduced from a pressurized reservoir (not
shown~ into the liquid passageway at 332. The liquid
mo~es through the slotted space defined by faces 296, 322,
and exits slotted outlet 331 to form an elongated linear
distribution of liquid. Simultaneously, air 336 from a
pressurized reservoir (not shown) is introduced into the
slotted space defined by faces 298, 304 and is propelled
under pressure out of air gap 314 to impinge against the
liquid from outlet 331 and attenuate or atomize it into
droplets for even distribution onto a substrate. The
included angle 294 of central wedge portion 292 is about
30 degrees in the disclosed embodiment, hence the air from
gap 314 impinges the liquid array at an angle of about 30
degrees. This angle can vary from near zero to near 90
degrees, as long as the two streams are co-flowing.
After a period of use, the flow of liquid and gas
through the head is stopped and portion 320 is capable of
swinging open in the direction of arrow 338 to permit
access to the liquid passageway for cleaning of faces 296,
322 and edges 310, 328. In some embodiments portion 320
may also be movable in the direction of arrow 340 such
that edge 320 moves in the plane of arrow 340 to permit
selective protrusion or recession of edge 310 relative to
edge 328.
Yet another embodiment of the slotted outlet
nozzle is shown in FIG. 16 wherein nozzle 350 includes a
fixed side plate 352 that tapers at its distal end to a
sharp edge 354 defined by tapering face 356 and flat face
358. A liquid passageway 360 is formed between fixed
plate 352 and a central plate 362 that has parallel, flat
faces 366, 368. Central plate 362 tapers at its distal
end to a sharp edge 364 defined by flat face 366, and an
inclined face 370 that forms an included angle of about 30
degrees with face 366, and an angle of about 150 degrees
with face 368. Central plate 362 is retractable and
.
.
WO92/12803 2 ~ O 1 2 6 ~ PCT/US91/09C09
~ .:
- 21 -
adjustable along the axis shown by double arrow 372.
Plates 352, 362 define liquid passageway 360 therebetween,
which has the shape of a slotted enclosure that
communicates with a liquid outlet slot 373 between sharp
edges 354, 364.
Nozzle 350 also includes a swingable plate 374
having flat faces 376, 378 that meet along a flat, blunt
edge 380 that is perpendicular to faces 376, 378. A
distal portion of face 376 runs parallel to inclined face
370 to form an air gap 381 that communicates along its
length with an air chamber 386. Plate 374 is attached to
a hinge 382 such that it swings outwardly around the axis
of hinge 382 in the direction of arrow 384 to permit
access to air chamber 386 between plates 362, 378.
In operation, liquid 390 is introduced into the
liquid passageway 360 from a pressurized reservoir, and
flows out of liquid slot 373 to form a linear distribution
of liquid. Air is simultaneously introduced into air
chamber 386 under pressure and propelled out of air gap
381 to implnge the linear distribution of liquid at about
a 30 degree angle and attenuate or atomize the liquid
distribution into droplets for uniform deposition on a
substrate. Central plate 362 can be moved in the axis of
arrow 372 to recess or protrude edge 364 and
simultaneously vary the distance of the air gap formed
between faces 370, 376. After use, nozzle 350 can be
cleaned by swinging plate 374 in the direction of arrow
384 to permit greater access to air chamber 386, central
plate 362, and edges 354, 364.
Attenuation or atomization of the liquid need not
occur external to the applicator head. This principle is
illustrated in FIG. 17, wherein a nozzle 400 of an
applicator head is shown to include a flat plate 402
having parallel faces 404, 406. An end edge 408
intersects face 404 at a right angle, but then curves
toward face 406 to form an arcuate junction with face 406.
An internal, wedge-shaped member 410 includes flat faces
412, 414 that intersect along a sharp edge 416 at an
.
.
t
WO92/12803 21~ 12 S 4 PCT/US91/09009
- 2~ -
included angle of about 30 degrees. Faces 404, 412 are
parallel to one another and spaced 5-15 mils (0.005 -
0.015 inches or 130 - 400 ~m) apart to form a gas slot or
passageway 418 therebetween.
Also included in no,zz~l~ 400 is a plate 420 having
flat parallel faces 422, 4~4~and flat face 426 which is
co-planar with facs 412 an~ forms an included angle of
about 30 degrees with face 424 and an included angle of
about 150 degrees with face 422. A slot or liquid
passageway 427 is formed between faces 414, 422 and
intersects slot 418 at a 30 degree angle. A wedge-shaped
member 430 is positioned below plate 420 and incl~des a
top interior face 432 and bottom exterior face 434 that
taper toward each other and meet along a sharp edge 436 to
define an included angle of about 20 degrees. Faces 424,
432 thereby define a slot or passageway 438 that decreases
in width as it approaches edge 436 and terminates in an
air gap 440. Finally, a wedge 442 has a flat interior
upper face 444 and lower exterior face 446 that taper to a
sharp edge 448 at an included angle of about 45 degrees.
Exterior face 446 is co-planar with exterior face 434 of
wedge 430. Faces 406, 444 define an air chamber 450
therebetween that tapers in width in the direction that
air ~lows through the chamber until it forms an air gap
452 between edges 408, 448.
In operation, a fluid such as air gas 454 is
introduced under pressure into passageway 418. A liquid
456 to be coated on a substrate is simultaneously
introduced through li~uid passageway 427 such that the gas
454 impinges liquid 456 at about a 30 degree angle in an
impingement zone 458 that is partially bounded by faces
404 and 426. The linear distribution of liquid emerging
from liquid slot 427 is thereby attenuated or atomized by
gas 454 into droplets which are then propelled out of
nozzle 400 in the direction of gas 454 toward a substrate.
A secondary flow of pressurized gas, such as air, can be
expelled at low pressure from either or both of gaps 440,
;
';
WO92/12803 2 1 0 ~ ~ 6 4 PCT!USg1/09009
- 23 -
452 to further direct the flow of droplets toward the
substrate.
Many different nozzle configurations are possible
in accordance with the present inventlon. This is
particularly true because the angle of impingement between
the fluid and liquid can vary widely. Several different
embodiments of the invention are shown in FIG. 18 to
illustrate some different impingement angles that are
possible with the present invention. In FIG. 18A, for
example, a slotted liquid passageway 462 is defined
between the parallel faces of external plate 464 and
internal member 466. An inner fluid chamber 468 is formed
between member 466 and an external face member 470.
Liquid slot 462 is shown substantially vertical, while air
chamber 468 tapers to a gap 472 that takes an arcuate path
from horizontal to vertical to form an arcuate slot 476.
The arcuate slot 476 is formed by complementary radiused
portions 478, 480 on members 466, 470. Arcuate passageway
476 arcs through an angle of about 90 degrees from its
proximal entrance to its distal exit to become almost
parallel to liquid slot 462. Hence fluid passing through
passageway 476 impinges the linear array of li~uid 462 at
an angle approaching zero degrees.
FIG. 18B shows a similarly radiused passageway
476 in which the passageway arcs through about 90 degrees
from a vertical to a horizontal orientation to become
almost perpendicular to slot 462 and impinge gas on the
emerging liquid array at an angle approaching 90 degrees.
FIG. 18C shows a passageway 476 which diverges and then
converges to increase the velocity of gas impinging
against the liquid array. FIG. 18D shows a similar
configuration in which passageway 476 first converges and
then diverges, again to increase the impingement velocity
of the fluid. The fluid impinges the liquid array
distribution at an angle of about 45 dPgrees in the
embodiments of FIGS. 18C and 18D.
Cleaning Means
W092/~2803 2 i O 1 2 6 ~ PCT/US91/~9009
- 24 -
The present invention also includes a cleaning
means for removing build-up of solidified coating material
in the head. The cleaning ~eans includes head designs
which open to allow easi,er ~ccess to :internal passageways
and nozzle orifices. Other examples of cleaning means
include external wipers, internal wipers, cleaning
additives in the fluid and liquid streams, and flushes of
pressurized water or other solvent for removing build-up
of solidified coating material from the head. A flush pan
of a cleaning fluid (such as water or another solvent) can
also be brought into contact with the fluid and liquid
outlets of the head to clean it.
One particular embodiment of a cleaning means is
shown in FIG. 19 in which a head 500 is shown that is
similar to that shown in FIG. 5, but it includes an air
channel on both sides of the head. Head 500 has
complementary wedge portions 502, 504 that mate along a
common junction 506 along which a liquid slot or series of
liquid passageways are formed. The liquid passageway or
slot terminates in a series of liquid orifices 508 or a
continuous slot at the tip of nozzle head 500. An air
plate 510 is secured to an outer face of wedge 502 to form
an air chamber exterior to wedge 502 that tapers to an air
slot or gap 512 adjacent liquid orifices 508. Another air
plate 514 is similarly secured to and carried by an outer
face of wedge 504 to form a tapering air chamber that
terminates in an air slot or gap 516.
A right angle flange 518 on wedge 502 includes
first and second legs 520, 522. Leg 522 is attached along
its exterior length to a top face 524 of wedge 502. Leg
522 is mounted on a pivot rod 526 such that portion 502
and plate 510 are free to pivot together about pivot 526
away from wedge 504 and plate 514. Leg 520 extends upward
perpendicularly from face 524, and its distal end is
pivotally mounted at 528 to the piston 530 of a pneumatic
cylinder 532. The cylinder 532 is in turn pivotally
mounted at 534 between a pair of parallel, upright flanges
536 (only one shown in FIG. 19) that are attached to a top
., .. . ~.
,
WO92/12803 ~ l Ul~ b 4 PCT/US91/Ogoog
&`
- 25 -
face of wedge 504. Flanges 536 may in turn be secured to
a support tube (not shown) that suspends nozzle head 500
above a substrate to he coated.
In operation, gas is impinged against a liquid
emerging from n~zzle head 500, as desc~ibed in connection
with FIG. 5 above. Once the coating process is completed,
introduction of fluid and liquid through head 500 stops.
The cylinder and piston assembly 530, 532 is then actuated
to retract piston 530, and pi~ot wedge 502 and plate 510
away from wedge 504 and plate 514. In this manner, the
liquid passageways or liquid slots along junction 506 will
be exposed, which allows ready access for cleaning.
Alternative Attenuation Means
The present invention does not necessarily
reyuire attenuation (including atomization) of the liquid
st,-~am by impingement of a fluid. FIG. 20, for example,
il ustrates an alternative embodiment of the invention in
w .ch an elongated liquid chamber 616 tapers to a slot
~: 3. Chamber 616 is divided by plates 620, 622 from a low
20 :;ressure air chamber 624, 626 on either side of liquid
hamber 616. Wedges 628, 630, which respectively form the
floors of chambers 624, 626, taper toward slot 618 to form
narrow gaps 632, 634 that run adjacent and parallel to
liquid slot 618 along its length.
In operation, the liquid to be coated on a
substrate is pre-atomized into fine particles 635 by
electrostatic, ultrasonic or high pressure means before it
enters liquid chamber 616. The atomized liquid exits
chamber 616 at slot 618, and is directed toward a
substrate by low pressure air emerging from slots 632,
634. Examples of electrostatic dispersion of liquids into
droplets are described in Castle et al., IEEE Transactions
on Industry Applications, fl:476-477 tMay/June 1983) and
Bailey, "Electrostatic Spraying of Liquids" (John Wiley
Sons, Inc. 1988). A schematic representation of such an
electrostatic dispersion device is shown in FIG. 21 in
which an air conduit 637 is provided through which air .
flows in the direction of arrow 638. 'The flowing air
:
WO92/12803 2 1 0 1 2 6 4 PCTtUSgl~09009
- 26 -
encounters an air shear nozzle 639 that is supplied with
liquid through supply line 640. Air 638 disperses the
liquid from the nozzle into a fine mist of droplets that
is then electrically char~d by an incluction electrode
64l. The induction charg~ng produces an electrostatic
force on the droplets that counteractC; surface tension
forces and produces smaller, more uniform sized droplets.
The uniform charge on the droplets produce a more
dispersed entrainment of mist in the air, and the charge
on the droplets can be used tv attract the droplets to an
oppositely charged or grounded substrate.
Ultrasonic attenuators use high frequency
vibrators or sound waves to vibrate a liquid and disperse
it into droplets. An example of a suitable ultrasonic
atomizer is the Ultrasonic Atomizing Nozzle systems
available from Sono~Tek Corporation of Poughkeepsie, New
York. A liquid stream is broken into a spray of tiny
droplets by subjecting it to hlgh frequency vibrations
concentrated on an atomizing head of a titanium nozzle.
The vibrations are generated by ceramic piezoelectric
crystals in the nozzle body. Other suitable pre-
dispersion systems would include Cool-Pog Systems from
Cool-Fog Systems, Inc. of Stamford, Connecticut, or the
Ultrasonic Spray Nozzles available form Heat Systems
Ultrasonics of Farmingdale, New York.
In other alternative embodiments, a supply of
humidified air, steam or other vapor laden gas is directed
through the coating outlet and impingement slot. A very
thin coating of material can be applied to the substrate
in this manner. If steam, ~or example, is propelled
through both outlet 93 and impingement slot 132 in FIG. 5,
a very thin yet thorough coating of water can be applied
to the substrate.
Collection Device
A serious problem with many coating or spraying
systems is that they produce a fine mist that deposits on
machinery and workers in the vicinity of the applicator.
This is a particular problem with materials such as starch
. .
WO92/12803 Z~ PCT/US91/09009
~ .
- 27 -
that form a thick, solid deposit on almost any surface
with which it comes in contact. Another serious problem
is presented by systems that apply corrosive or
biologically harmful materials, such as isocyanates, that
have to be contained for environmental or health reasons.
The applicator system of the present invention represents
a substantial advance over the prior art, because it
produces less mist than conventional spray nozzles. There
are some applications, however, for which it is desireable
to reduce the amount of ambient mist even further.
An embodiment of a collection device for reducing
the amount of ambient mist is shown in FIGS. 22 - 23,
which show an applicator head 642 suspended above a moving
substrate 643. A liquid inlet 644 introduces a liquid to
be coated into a liquid chamber inside head 642. Air
conduits 645, 646 convey pressurized air into head 642 for
gradually attenuating or immediately atomizing the liquid
as it emerges from the head. A linear distribution of
liquid 647 emerges from head 642 along its length, and the
liquid is attenuated or atomized by an impinging gas which
directs the liquid toward the substrate 643. A collection
hood is suspended over substrate 643 spaced from head 642
on each side along an axis of movement 648 of the
substrate. The hood on each side of the head includes an
elongated tubular collector 650 with a collection slot 652
facing downwardly. Each tubular collector is oriented
perpendicular to axis 648. Slot 652 subtends an arc of
about 45 degrees to 60 degrees below a horizontal diameter
653 of tubular collection 650. A rectangular cover panel
654 extends from the upper edge of slot 652 and angles
down toward substrate 643 at about a 15 degree angle.
Cover panel 654 spans the width of substrate 643, and
extends part of the distance to head 642 before
terminating along a distal edge 656 that is parallel to
the liquid array 647. The distal edges 656 of the two
panels define an open area therebetween into which the
li~uid array is directed at substrate 643. Another
rectangular panel 657 extends from a lower edge of the
WO~2/12803 PCT/US91/09009
2~Q1264 ~ -
- 28 -
opening 652 and projects downwardly toward substrate 643
to provide a mist barrie~. ~
An upright~wa-ll 658 closes the free ends of each
tubular collector 650, and extends between the collectors
650 to form a continuous barrier along a portion of one
longitudinal edge of substrate 643. A similar wall 660
extends between the collectors 650, but does not close the
end faces of each collector. Instead, exhaust tubes 662,
664 communicate with collectors 650 and extend away from
lo substrate 642. A negative relative pressure (such as a
vacuum suction) is provided in each tube 662, 664 to
withdraw a mixture of mist and impingement gas out of the
collectors, as indicated schematically by arrow 666.
The enclosure formed by collectors 650, panels
654, 657 and walls 658, 660 is suspended slightly above
substrate 643 to permit free movement of the substrate
beneath the enclosure. Suspension of the enclosure
thereby creates a small separation 670 between the bottom
o~ the enclosure and the surface of substrate 643 that
would normally permit some of the mist to escape from the
enclosure. Most of the mist tends to spread out along the
substrate, in both directions from head 642, along the
axis of arrow 648. The majority of the mist is directed
toward separation 670 in the direction 648 of movement of
the substrate because the substrate carries the mist along
with it. Hence the majority of the mist passes under
barrier 657 in the direction 648. An air curtain is
directed below the bottom Pdge of each barrier 657 to
diminish the amount of mist that escapes from the
enclosure underneath the edge. As best seen in FIG. 23, a
tubular conduit 674 is mounted across the width of
substrate 643 below each collector 650 on the outside face
of each panel 657. The conduit 674 contains an air slot
675 that extends the length of the conduit, and
communicates with an air directing member 676 that propels
air downwardly at substrate 643 at an angle of about 45
degrees to the surface of the substrate. Air 678 (FIG.
22) is supplied to each conduit 674 such that a curtain of
,
WO92/12803 21 012 6 4 pcT/uss~/osno9
- 29 -
air is propelled out of member 676 and forms an air
curtain 680 (FIG. 23) between the bottom of the enclosure
hood and the surface of the substrate to diminish the
amount of mist that escapes from the enclosure.
FIG. 23 shows that the mist inside the hood rises
to form a cloud 682 inside the enclosure. ~pward
recirculation 683 of the mist can direct currents of mist
back toward head 642, and form a stagnant cloud below top
panels 654. Development of this cloud can lead to
deposition of coating material on the undersurface of
panels 654, and qrowth of stalactites from the panels.
The stalactites serve as foci from which drips of coating
material drop onto the substrate to disrupt uniformity of
the deposited coat. Such drops also impair the appearance
of the sheet. Hence the inventors have allowed or
introduced a secondary flow of air into the hood adjacent
the head to disrupt formation of the undesirable cloud.
The secondary ~low is shown schematica~ly by
arrows 684 in FIG. 23, and can be any external source of
air directed into the hood adjacent the head. A specific
device for developing the secondary flow is illustrated in
FIG. 25 wherein a lid 690 or 691 extends the entire
distance from each of collectors 650 to the top of the
applicator 642 such that the lid is co-planar with a top
face of the applicator. A row of orifices is provided
through each lid 690, 691 adjacent the top face of
applicator 642 to provide inlets for a secondary stream of
air to redirect any upward circulation of mist back down
toward the substrate and into an excess air collection
hood. Alternatively, a hot air duct (not shown) can
supply hot air (for example at 80C) to redirect the mist
downward and diminish formation of condensate inside the
hood and on the faces of the applicator.
Electrostatic Collection
It would be possible to reduce environmental mist
and improve the deposition of the liquid on the substrate
by grounding the substrate, as shown in FIG. 22. A
grounding member 690 is illustrated extending below
.. ' ' ' ~' . .
.. ..
.
WO92/12803 PCr/US91/09009
210126~ , -
substrate 643 transverse to the direction of movement 648
of the substrate. Grounding member 690 can be, for
example, a piece of metallic tinsel or a conductive brush
that is in electxical contac~ with a ground 692. Charged
particles of mist would be attracted l:o the grounded
substrate to thereby reduce their dispersion into the
environment and enhance their re-deposition on the surface
of the substrate.
An alternative or additional electrostatic
repulsion member is shown at 694. Many types of
electrostatic members can be used, including flat or
arcuate plates that extend transversely across the
substrate. The particular embodiment shown in FIG. 22
shows a bar having the sh~pe of an inverted U in cross-
section. The bar is negatively charged from aconventional charger (not shown) to propel toward the
substrate any negatively charged droplets that pass
between the member and the substrate. The bar could
alternatively be positively charged to propel positively
charged droplets toward the substrate. These
electrostatic collection methods can be enhanced by
charging the droplets with an induction electrode, as
shown in FIG. 21.
Scrubbing and Venting the Mist
It is desireable to vent the exhaust stream 666
(FIG. 22) from the hood into the environment to dispose of
the large volume of gas and entrained liquid droplets that
are produced by the liquid attenuation. Such venting to
atmosphere is possible when the mixture of gas and liquid
consists of an environmentally benign material, such as a
mist of water. More frequently, however, the exhausted
mist contains materials such as starch or isocyanates that
cannot be exhausted into the atmosphere. Starch mist, for
example, would deposit a film of starch on objects in the
vicinity of the vent. Even more seriously, exhausting
isocyanates into the atmosphere would expose people to
undesirable biolo~ical consequences. In such situations,
the mixture of gas and air 666 may be conducted into a
WO92/12803 2 ~ ~ 1 2 ~ 4 PCT/USgl/og~O9
- 31 -
scrubber 700 (FIG. 24) where the liquid mist is
disentrained from the gas.
Scrubber 700 is a container 702 that has a top
panel 704 and a bottom panel 706. A pair of parallel
spaced baffles 708, 710 project downwardly from top panel
704 across the entire width of container 702 and extend
toward bottom panel 706 without reaching it. A pair of
interdigitating, parallel baffles 712, 7 14 project
upwardly from bottom panel 706. The baffles 708-714 form
a circuitous pathway from a spray chamber 716 to a gas
outlet 718. An array of conventional spray nozzles are
provided in a spray plate 720 at the top of chamber 716 to
disentrain droplets from the gas. A gas pump 724
communicates with gas outlet 718 to draw gas out of
scrubber 700 and exhaust it to the environment at 726. A
liquid pump 728 communicates with a liquid outlet 730 near
the bottom of scrubber 700 to remove liquid that
accumulates on the bottom of the scrubber.
In operation, water is introduced at 734 into
spray plate 720 to produce a matrix of downwardly directed
water sprays 736. The sprays impinge against liquid
droplets in the incoming stream 666, and help propel
entrained liquid droplets toward the bottom of scrubber
700 where they collect in a liquid pool 738 with the water
from sprays 736. The gas and any remaining entrained
liquid is drawn through the interdigitating baffles 708-
714 by pump 724 in the direction indicated by arrows 740-
744. The gas emerges at 746 and is drawn into gas outlet
718 by pump 724. The gas is substantially free of liquid
and can be exhausted to the atmosphere at 726.
Liquid pool 738 includes both water from sprays
736 and entrained liquid droplets removed from flow 666.
Hence, scrubber 700 removes harmful or undesirable
entrained liquids from the hood exhaust such that the high
volumes of air or other gas removed from the hood can be
exhausted to the atmosphere. Entrained liquid droplets
from the stream of gas and mist are diluted in pool 738
for disposal or recirculation.
Wo92/12803 2 ~ 0 1 2 ~ ~ PCT~US91/09~09
- 32 -
i~,, 'i
~ ` Coating Process
The present invention also includes a process for
uniformly or thoroughly depositing a coating of a liquid
or other coating material on a substrate by directing a
fine mist of the liquid or material toward the substrate.
Formation and propulsion of the mist may be simultaneously
achieved by directing a flow of an elongated array (i.e.
distribution) of liquid from an outlet toward the
substrate. The elongated array can be any shape that
provides for distribution of the mist on the substrate
across a desired swath. The array can, for example, be
linear, arcuate, or chevron shaped, or sequ~ntial
applicators may be used to form desired arrays. A fluid
(such as a gas) is impinged against the liquid array to
attenuate or atomize the liquid flow into droplets and
deposit a uniform coating on a substrate that is moving
relative to the array. Nore uniform arrays, such as those
produced by a row of linearly spaced nozzles or a slot,
can more readily deposit the liquid uniformly on the
substrate in applications where uniformity is desired.
In a typical application, paper is coated by
directing a linearly aligned curtain or series of columns
of liquid toward a substrate from a coating head. Linear
alignment refers to a curtain or series of columns that is
capable of being intersected along substantially all its
length by a line. The liquid flow is attenuated or
atomized by gas emerging from a slot on one or both faces
of the liquid curtain. The liquid can have a wide range
of viscosities but typical coating liquids have relatively
low viscosities and are liquids at room temperature. The
melting point of the liquid may preferably be below room
temperature to reduce or prevent solidification of the
liquid before it reaches the substrate.
In preferred embodiments, the coating liquid is
an aqueous liquid, such as an aqueous solution of starch,
carboxymethylcellulose, polyvinyl alcohol, latex, a
suspension of bacterial cellulose, or any aqueous
material, solution or emulsion. The aqueous liquid is
WO92/12803 21012 6 4 PCTtUS91/09009
- 33 -
dispersed from an applicator head at less than 100C
(212F), because by definition an aqueous liquid would
boil above that temperature and no longer be in a liquid
phase. It is not necessary for the aqueous liquid
temperatures to be as high as 100C (212F), and they can
be sprayed at temperatures less than 70(160F), or even
at ambient temperatures (25C - 40C or 77F - 104F).
The aqueous liquid does not solidify before reaching the
substrate, hence the aqueous process should be performed
above about 0 (32F). It may be preferable with some
liquids, such as those that contain starch, to warm the
liquid to 40 - 70C (104F -158F) to prevent
precipitation of the starch in the applicator. The
process of the present invention can also be used to
deposit non-aqueous liquids on substrates. In specific
examples, this process can apply slurries of particulate
materials or organic liquids, such as polymeric methylehe
diphenyl diisocyanate (PMDI) or emulsifiable polymeric
methylene diphenyl diisocyanate (EMDI).
Low viscosity of the liquids allows it to be
directed through a series of preselected orifices,
elongated slots or other outlets in the head at low
pressures. Liquid pressures are typically less than 25
psi (170 kPa), for example 5 - 12 psi (34 kPa - 82kPa) or
less than 5 psi. Liquid pressure is directly related to
the velocity with which liquid leaves the head, hence the
liquid velocities can also be quite low, for example less
than about 1 meter/second (3.28 feet/second).
Attenuation of the flow of liquid into small
droplets is achieved by impinging a fluid against the
liquid to break it into smaller segments, and eventually
into fine droplets that have a diameter, for example, of
about lOO ~m or less. Atomization of the liquid flow
(which is a sub-category of attenuation) is achieved by
impinging a fluid against the liquid with sufficient
energy to immediately break the liquid into droplets
without forming increasingly smaller segments. The
diameter of droplets emerging from the orifices is equal
wo 92/12803 2~0126 4 Pcr/usg1/o~oo9 .~
- 34 -
to or slightly less than the diameter of the orifice, or
less than the width of the slot. ~ence the diameters of
droplets emerging from an outlet having an effective
diameter or width of 500 ~m will be smaller than 500 ~m
after attenuation or atomization. The sizes of smaller
droplets are difficult to measure, and although the
inventors do not wish to be bound by theoretical
computations or estimates, the size of many of the
droplets appears to be 5 - 50 ~m in diameter. The
droplets are not necessarily uniform in diameter, and
usually have a broad distrihution of diameters. Some of
the droplets may exceed 100 ~ diameter. The importance of
the droplet size is that the droplets of a particular
liquid can have a range of diameters that are sufficiently
small to thoroughly coat a desired swath on a substrate,
if such uniformity is desired. Small droplets of the
present invention can selectively form a more ulliform
coating with less graininess, as defined below. In
preferred embodiments, the droplets are small enough to
provide a thin, uniform coat on a substrate. Thin
coatings in the range of 0.11 - 0.19 g/~ (approximately
4.9 - 8.3 lbm/ton) can be provided on a surface of the
substrate.
The impingement fluid can be any substance that
tends to flow or conform to the outline of its container.
Examples of such fluids include gases, liquids, and solid
particulates (such as sand or silicon) carried by another
gas or liquid. Specific examples of impingement fluids
are water, water or other types of vapor, acidic liquids
for acid catalyzable coating materials, basic liquids for
base catalyzable coating materials, carbon particles, dry
pigment particles (such as Ti4, CaC~), air, oxygen,
nitrogen gas or gases that may participate in catalyzing
or reacting with the coating liquid. Any of the coating
liquids can also be used as impingement fluids, including
liquid solutions or suspensions of starch, PVA, bacterial
cellulose or latex. The fluid need not be heated, and may
be any temperature between, for example, 25C - 100C
WO92/12803 21 O 12 5 4 PCT/US9}/09009
- 35 -
(77F - 212F), or ambient temperatures between 25C -
40C (77~F - 104F), or even lower.
The impingement fluid and liquid should
preferably be co-flowing, and the velocity of the liquid
is less than the velocity of the impingement fluid. Very
good droplet formation has been observed when the mass
ratio of an impingement gas to coating material is in the
range of from 0.03:1 to 7~7:1 and most preferably in the
range 0.2:1 to 5:1. The relative velocities and flow
rates of the impingement fluid and coating material can be
varied over a wide range to achieve a desired mass ratio
of impingement fluid to coating material that attenuates
or atomizes the liquid into droplets of a sufficiently
small size to deposit a thorough or a uniformly thorough
coating on the substrate. The examples in Table I and II
provide guidance about varying these parameters to deposit
a coating having minimal graininess or streakiness. Some
applications do not require uniform coatings, and these
parameters need not be ~ollowed. ~inimal graininess is
optimally illustrated by the images and grey intensity
profile graphs of FIGS. 35 and 36.
The liquid distribution has opposing faces, and
the impingement fluid can be impinged against one or both
of the faces of the distribution to attenuate or atomize
the liquid into small droplets. The desired velocity of
the impingement fluid varies depending on the viscosity
and flow rate of the liguid. For many applications,
however, the fluid is impinged against the liquid at a
fluid velocity of 200 - 1600 feet/second (60 - 335
meters/second). The minimum size droplet formation occurs
as the velocity of the fluid approaches sonic speeds (335
meters/second or 1100 feet/second), and has not been
observed to improve significantly beyond these velocities.
Theoretically, droplet size may continue to decrease
beyond sonic velocities, but measurement limitations make
it difficult to determine changes in droplet diameters at
these small dimensions. Although no deterioration of
droplet formation has been noted beyond sonic velocities,
.
:
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W092/12803 2 1 0 1 2 6 ~ PCT/US91/~9009
- 36 -
it may be undesirable in some situations to increase the
impingement velocity beyond a sonic range because of the
resulting increased flow;.~f fluid that must be collected.
Coa: ~ng Materials
One of the advantages of the present method is
that it can be used to apply a wide variety of coating
materials to a broad variety of substrates. Practically
any material can be coated on a substrate using the
present method. Even high viscosity liquids, such as
thermoplastic material, can be appliecl in a thin, uniform
layer to a substrate by heating the thermoplastic material
and attenuating or atomizing it to a sufficient degree to
produce fine droplets that deposit uniformly on a surface
to be coated. In other applications, liquids of lower
viscosity are coated on the substrate. Materials such as
starch (ethylated and other types of starch), polyvinyl
alcohol (PVA), pigmented coatings, carboxymethylcellulose
~CMC), water, cellulose suspensions, latex and PMDI are
applied to substrates such as paper and container board.
The viscosity of these enumerated liquids is typically
less than 2000 cP (2 Pa-s) at ambient temperature, usually
less than about 900 cp (0.9 Pa-s), and sometimes less than
50 or l00 cP (0.05 - 0.l Pa-s) at ambient temperature.
The coating process is facilitated by providing material
which is a liquid at ambient temperature, thereby removing
the need for heating the material to lower its viscosity
and permit its extrusion from an applicator.
Examples of coating materials include ethylated
corn starch, such as that available from Cargill, Inc. of
Cedar Rapids, Iowa; Penford Gum starches, such as PG200,
220, 230, 240, 250, 260, 270, 280, 290, 295, 300, 330,
360, or 380 available from Penford Products Co. of Cedar
Rapids, Iowa; Airvsl polyvinyl alcohol from Air Products
and Chemicals, Inc. of Allentown, Pennsylvania; and clay
pigments such as those that can be obtained from Englehard
Corporation of Edison, New Jersey under the na~es Exsilon,
Ultra Gloss 90, Ultra White 90, Lustra, Ultra Cote, HT,
Gordon and S-23.
:
.
.:
;~lUl~b~
WO92/12803 PCT/US91/09009
- 37 -
Substrates
The present method is versatile enough to direct
coat an array of attenuated liquid at one or both faces of
a substrate moving in many different planes. FIG. 33, for
example, shows a paper web 750 moving in a horizontal
plane below a head 752. A distribution of droplets 754 is
directed downwardly at web 750 to deposit a coating 756 on
its surface. Simultaneously, a second head 758 is
positioned below the substrate pointing upwardly such that
an attenuated liquid array a distribution of droplets 760
is directed upwardly at the substrate and deposits a
coating 762 on the undersurface of the paper web 750.
An alternative embodimant is shown in FIG. 34 in
which the paper web 766 is moving in a vertical plane in
the direction of arrow 767 between a pair of heads 768,
770 that are spraying each side surface of the web. The
heads are positioned to spray the attenuated liquid in a
generally horizontal direction on the vertically moving
substrate. Although the substrate 766 shown in F~GS. 33
and 34 is a paper web, the method of the present invention
is suitable for coating many types of substrates,
including cellulosic, fiber, organic and synthetic
substrates. Examples of cellulosic substrates include
finished paper, pulp mats, liner boards, newsprint and
already coated papers. Organic substrates can include
foods beiny coated with additives or spices, or plants
being coated with insecticide. Other examples of
substrates include formed non-cellulosic fiber mats,
rubber, cloth, wood, leather and plastic. The substrate
can even be metallic, and need not be planar, for example,
a transfer roller that in turn transfers the liquid to a
substrate.
The angle at which the head directs the liquid
array toward the substrate is preferably a normal angle.
Better coverage with enhanced uniformity of deposition is
observed when the liquid is directed at a right angle to a
flat surface being coated. Other angles are possib~e,
especially when coating objects with irregular, non-planar
W092/12803 2 1 ~ 1 2 6 ~ PCT/US91/09oO9 -
- 38 -
surfaces. Another aspect of the invention is that more
than one head can ~e placed sequentia:Lly along the
substrate, such that layers of coating are applied one on
top of the other on a single fàce of l:he substrate. A
similar plurality of heads;can ~e placed in coating
relationship to another sùrface of the substrate such that
multiple layers are applied to both surfaces. A paper
web, for example, can have multiple coatings applied to
each of its flat faces. Parallel plural liquid outlet
slots can al50 be provided in the applicator to apply
multiple coatings to the substrate.
The distance between the substrate and head can
vary widely, but very thorough and uniform deposition
occurs with the liquid emerging from the applicator head
at a distance of 1 - 12 inches (2.5 cm - 30 cm~ from the
surface of the substrate, more preferably l - 3 inches
(2.5 cm - 7.5 cm). When a uniform coating is desired, the
head should preferably be at least far enough away from
the substrate to permit the liquid to break substantially
entirely into droplets. This distance will vary depending
on such variables as the viscosity of the liquid and the
flow rate and velocities of the liquid and impingement
streams. It is possible to ascertain whether the liquid
has been broken sufficiently into droplets by determining
the thoroughness and uniformity of deposition on the
substrate, as discussed in connection with FIGS. 35 - 56
below. Several hundred examples of the process are also
provided in Tables I and II below to illustrate the
effects of these and other variables on coating quality.
Liquid Attenuation or Atomization
The process of the present invention uses a fluid
stream, such as a curtain of air, to attenuate (or more
particularly in many instances atomize) co-flowing liquid
to a diameter or width that is smaller than an orifice
from which the liquid emerged. An example of the
attenuation process is shown in FIGS. 26 - 28, which is a
sequential series of photographs of a bacterial cellulose
suspension emerging from a multiple orifice head, such as
WO92/12803 2 ~ O 1 2 6 ~ PCTtUS91/~9~09
- 39 -
the one shown in FIGS. 3 - 4. In FIG. 26 the liquid is
emerging from a row of linearly aligned circular orifices
having a diameter of 20 mils (O.OZ0 inches or 500 ~m).
The liquid emerges from the orifices to form a linear
array that in this example is a serie.s of downwardly
directed co-planar columns of liquid having an initial
diameter essentially the same as the orifice (20 mils).
Air emerges from a pair of parallel slots or air gaps
adjacent the array. The slots are parallel to the plane
of the array and direct a curtain of air at an acute angle
toward the array.
As a stream of air, or another gas or fluid
passes through gaps adjacent the orifices, they begin to
attenuate the fluid stream as shown in FIG. 26. As the
gas, moving at a greater velocity than the liquid,
impinges against the liquid, it causes an oscillation in
the width or diameter of each columnar stream of the
array. As the air velocity increases, the liquid stream
eventually starts to form loops oriented in several
planes, as shown in FIG. 27. The diameters of the loops
become increasingly smaller as the velocity of the
impingement gas and the distance from the orifice
increases until the loops break into droplets of various
sizes that are smaller than the orifice from which the
liquid stream originally emerged. The air co-flowing
impingement gas stream directs the droplets downwardly
toward the substrate and also creates a cross-flowing
turbulence in the region below the head outlet that
results in a more uniform deposition of the droplets onto
the substrate.
As already mentioned, droplets can be formed by
immediate airblast atomization instead of a more gradual
form of attenuation. Such atomization is shown in FIGS.
29 and 30, where liquid emerging from outlets is
immediately blasted into droplets as the liquid emerges
from the outlets. The runs shown in FIGS. 29 and 30 were
performed with a slotted head four inches long, a 0.005
inch liquid slot opening, an air gap of 0.005 inch, and 78
WO92/12803 2 i 0 12 ~ ~ PCT/USgl/ogoog
- 40 -
inches of water pressure in the head. Air was impinged at
16 CFM at 30 psig against a Cellulon/CMC (4:1 ratio) that
was 1.11% total solids~.~ The impingement velocity at which
atomization instead o~ attenuation occurs depends on the
viscosity of the liquid. Coating materials with greater
viscosities (e.g. starch) require higher impingement
velocities for atomization than low viscosity liquids such
a water. Atomization represents one end of the spectrum
of attenuation in which ligament formation becomes
vanishingly small or nonexistent. Atomization occurs in
many of the runs reported in Tables I and II.
The impingement stream may also be used to help
clean the applicator head or alter the liquid flow. The
impingement air stream may, for example, be humidified to
solubilize water soluble materials that coat the interior
of the head and build up around the air gaps or liquid
orifice. The gas may be humidi~ied to 70% - 100%
relative humidity, or more pre~erably 90% - 100%.
Alternatively, the gas may include an additive that
modifies the liquid. Humidified air, for example,
provides moisture that catalyzes the polymerization of
PMDI during coating. When using a catalyst, such as moist
air, it is preferable ~irst to impinge a dry impingement
fluid against the liquid to prevent initiation of
polymerization at or near the outlet. In such a situation
a pair of parallel impingement slots are provided adjacent
the liquid outlet such that one slot is closer than the
other to the liquid outlet. The slot closer to the outlet
impinges dry gas against the liquid to initiate
attenuation, while the second slot impinges the catalyzing
fluid to initiate catalyzation at a distance from the
outlet.
In alternative embodiments, moisture may be
harmful to the coating liquid, in which case the
impingement gas is used to purge moist air from the
applicator head. Purging is achieved by introducing a dry
gas, such as nitrogen gas, through the applicator and
outlets.
WO92/12803 2 ~ O 1 2 6 ~ PCT/USgl/o~oog
( `
- 41 -
The process of liquid attenuation or atomization
and mist deposition on the substrate will be understood
better by reference to the following examples.
EXAMPLE I
The trials of this example were designed to study
the formation of droplets, and illustrate the effects of
different process parameters on dropl~et formation and
deposition of liquids. During these trials the liquid
flow pattern was recorded with a high-speed video system
using an image intensifier camera from Visual Data Systems
of Chicago. The intensifier allowed images to be obtained
with a 10 ~ second exposure time, effectively freezing the
motion of the liquid for each video frame record. The
framing rate for these trials was typically 1000 frames
per second.
Each video session corresponded to a particular
set of operating conditions. The operating conditions
consisted of: the liquid type ~water, 6% CMC solution, or
10% starch solution), the air slot gap (5, 15, or 23 mils)
(1?5, 375 or 585 ~m), the head air plenum pressure, and
the head liquid plenum pressure. Previous and subsequent
calibration of the air and liquid flows was used to
calculate the air and liquid flow rate for each operating
condition.
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WO 92/12803 2 1 0 1 2 6 4 PCT/US91/09009
- 44 -
Table I lists the operating conditions for each
video session. Except for the geometry and raw pressure
data, all but the Df/Di value is calculated based on the
flow calibrations. The Df/Di term is used to describe the
decrease in droplet size as the liquid stream is
accelerated or atomized by t~e~:surrounding high-velocity
air. No direct measure of Df/Di was taken during these
trials, though estimates could be made from some of the
video pictures. The number listed under Df/Di is a very
approximate value based on a Conservation of Energy
technique proposed by Professor R.L. Shambaugh of the
University of Oklahoma in "A Macroscopic View of the Melt-
blowing Process for Producing Microfibers" in Meltblown
Technology Today (Miller Freeman Publications, San
Francisco, California 1989). This method is not highly
accurate with respect to precise droplet size, but seems
useful in identi~ying operating conditions conducive to
good droplet formation. The lower the percentage, the
smaller the diameter of the resulting droplets. A df/Di
value of 50% would indicate a droplet having a diameter of
one-half the initial diameter of the liquid column as the
column emerged from the liquid outlet.
EXAMPLE II
The trials reported in this Example were carried
out with four different head configurations and examine
operating parameters in addition to those already
discussed in Example I. Two configurations were based on
a multiple orifice head design, such as that shown in
FIGS. 3 - 8, in which a plurality of linearly aligned
orifices produce an array of regular columns of coating
liquid. Two additional configurations were based on a
slot head design, such as shown in FIG. 14. The basic
features of this design, and the specific Examples
disclosed in Table II, are a `slow moving liquid stream
(such as a curtain or plurality of columns) located
between two fast, co-flowing gas (air) streams. The fast
moving air stream changes the liquid stream either
gradually or instantaneously into droplets having a
,: ., ' :'
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.
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WO92/12803 2 1 0 1 2 6 4 PCT/US91/09009
l - 45 -
smaller dimension than its initial characteristic
dimension (column diameter or curtain width) near 500 ~m.
The liquid issues from either a slot or a series of
closely spaced holes arranged in a straight line. The air
issues from two gaps located on either side of and
immediately adjacent the liquid slit or line of holes.
The typical air gap dimension ~the width of the gap
through which the air emerges) is about 250 ~m (0.010
inches).
The main head configuration used in these trials
was one with 0.024 inch equivalent diameter holes (24 mil~
or 610 ~m) spaced 18 per inch (i.e. center-to-center
spacing of 0.056 inches which is 56 mils or 1.4 mm) and a
total length of 4 inches (10 cm). The air gap for this
head was varied from 0.005 to 0.015 inches (5 mils to 15
mils or 125 ~m to 375 ~m). The second configuration used
a similar but longer head. This second head was 12 inches
(30 cm) long with 0.020 inch equivalent diameter holes (20
mils or 0.5 mm) spaced 787 per meter or 20 per inch. For
the purposes of identification below these heads will be
referred to as the 4-inch MOH (multiple orifice head) and
the 12-inch MOH, and are described as "H'l type (i.e.,
"hole" type) heads. Another set of heads substituted a
single slot for the plurality of holes such that the
liquid emerged from the head as a continuous curtain
array. This type of head is referred to as an "S" type
(i.e., "slot" type) head.
The seven main parameters that specify the
operating conditions for this series of runs are set forth
in Table II. These parameters are: 1) the liquid
velocity; 2) the air velocity; 3) the air gap (i.e. the
air quantity); 4~ the head-to-paper separation distance;
5) the head orientation with respect to the direction of
paper sheet travel; 6) the coating formulation; and 7) the
air plate setback. Other parameters such as air and
liquid temperature or air humidity can also affect optimum
head performance, but were not evaluated in this set of
trials.
.
WO 92/128032 1 0 ~ 2 6 4 PCr/US91/09oO9
-- 46 --
TABLE II~A
Coat ~Coa~ Uquid H~d Head H~ad Air IH)ole
. Sl~t Alr A~r WL Wt. Fbw l~n~h H~bht Prsss. Gap or
No. Mat~ial ~ CFM PSI.-glm^2 Ih/ton ~min in. In. inH20 mils (S)lot
CalbJbn 8A 105: -0.16 6.9 784 4 3 5 H
2 C211L~bn 8B 1510 0.16 6.9 784 4 3 5 H
3 C~llubn 8C 1815 0.16 6.9 784 4 3 5 H
4 CsUubn8D 20 ?00.16 6.g 784 4 3 5 H
Callubn 8E 2225 0.16 6.9 784 4 3 5 H
6 Callubn aF ~430 Q16 6.9 784 4 3 5 H
7 Callubn 8G 12 5 0.21 9.1 1034 4 .3 5 H
8 C01h~bn 8H 1510 021 9.1 1034 4 S 5 H
9 Calk~bn 81 1815 021 9.1 1034 4 3 5 . H
C011ubn 8J 2020 021 9.1 1034 4 3 5 H
11 C011ubn 8K 2225 02~ 9.1 1034 4 3 5 H
12 C~l~bn8L 24 30021 8.1 1~ 4 3 5 H
13 C~l~bn8M 11 5 026 11.3 1280 4 3 5 H
14 C~l~bn8N 15 10026 11.3 1280 4 3 5 H
C911ubn 80 1815 026 11.3 12aO 4 3 5 H
16 Callubn 8P 2020 '026 11.3 1280 4 3 5 H
17 C011ubn 80 2325 026 1t3 1280 4 3 5 H
18 C0Uulon 8R 2430 026 11.3 1280 4 3 5 H
19 C0iklbn 8S 2430 026 11.3 1280 4 10 S H
C011ubn 8T 5 5 0.16 6.8 ~74 4 3 5 H
21 CaUUbn8U 9 100.16 ~8 7t4 4 3 5 H
22 C~lhlbn 8V 1215 0.16 6.8 774 4 3 5 H
23 C0IbJbn 8W 1420 0.16 B.8 774 4 3 5 H
24 C0UUbn8X 15 250.16 6.8 774 4 3 5 H
~5 Ca~bn8Y 16 SO0.16 6.8 774 4 3 5 H
26 C01bubr 8~ 5 S 021 8.9 1012 4 3 5 H
27 C~l~lon 8AA 9 10 021 ag 1012 4 3 5 H
2B C~Oubn8A8 12 lS021 8.9 1012 4 3 5 H
29 C~lbJbn 8AC 13 20 021 as 1012 4 3 5 H
C~Uubn8AD 15 25021 8~ 1012 4 3 5 H
31 C0l~bn8A 16 30021 8.g 1012 4 3 5 H
32 Ca~Ubn8AF 12 15026 115 1300 4 3 5 H
33 C0UUbn8AG 14 20026 11.5 1300 4 3 5 H
34 CflUUbn 3AH 15 25 026 115 1300 4 3 5 H
C0llUbn 8~J 16 30 02~ 115 1300 4 3 5 H
36 C0UUbn8~A 15 50.15 6.7 758 4 S 10 H
37 C0lhbn3B8 20 100.15 6.7 7~8 4 3 10 H
38 C0llUbn 8BC ~ 15 0.15 6.7 7S8 4 3 10 H
39 Cnl~bn8BD1 25 200.15 6.7 758 4 3 10 H
CaUUbn8BD2 2~ 2~0.15 6.7 7 8 4 3 10 H
41 C~Uukn88E 2~8 2B 0.15 6.7 7~8 4 3 10 H
42 CelkllOn 8BF 30 30 0.1~ 6.7 758 4 3 ~0 H
43 C~ G 15 S Q21 9.1 1032 4 3 10 H
44 Cnlhbn~H 19 10021 9.1 10æ 4 3 10 H
CR~bn3BI æ 15021 9.1 1032 4 3 10 H
46 G~ 20021 9.1 1032 4 3 10 H
47 CqUUbn8BK 2B 25021 9.1 1032 4 3 10 H
48 CaUulon 88L 30 30 021 9.1 1032 4 3 10 H
. .
W O 92/12803~ 4 PCT/US91/09009
( ~
- 47 -
TABLEII~Ac~
Co~ Go~ Uq~d H~ad Hbad H~ad ~r (H)ol~
Rat.Sh~at ~r A~ WL WL Faw L~nath Habht Prass. Gap or
No. M~n~ # CFM PSI ~m~2 ~on ~n~n In. ~. inH20 mUs (S~lot
49 Ca~bn 8BM15 5 02~ 1276 ~ 3 10 H
50 C~bn 83N19 10 025 113 12J6 4 3 10 H
51 Ca~bn 88023 15 0~5 113 1Z75 4 3 10 H
52 Ca~bn 88P~5 20 025 11~ 1Z76 4 3 10 H
Cs~bn 8BQ28 25 0~ 1276 ~5 3 10 H
C~bn 8~R30 30 0~ 12J6 4 3 10 H
55 C~bn 8CA25 æ5 0.11 4.9 16J0 12 3 10 H
56 C3~bn 8CB50 10 0.11 4.9 1~70 12 3 10 H
~ Ca~bn 8CC55 12S 0.11 4.9 16J0 12 3 10 H
58 Ca~bn 8CD45 7.5 0.11 4.9 1670 ~2 3 tO H
59 C~bn 8CE45 7.5 0.11 4~ 1670 12 1.5 10 H
60 Ca~bn 8CF45 7.5 O.t1 4~ 1670 12 10 10 H
61 Ca~bn 8CG5~ 13 Q11 4.9 1670 12 10 10 H
62 C~bn 8CH45 8 0.11 4.9 1670 12 3 10 H
63 C~bn 8CIi& 7.5 . ~1t 4.9 1670 1Z 3 lO H
64 Ca~bn 8CJ45 7.5 0.11 4~ 16J0 12 3 lO H
65 C3Uubn 8CK45 8 0.11 4.9 1670 12 3 lO H
66 CaUubn 8CL45 7.5 Qt1 4.9 1670 12 3 10 H
67 Cdlhbn 8CM45 7.5 0.11 4.9 1670 12 3 10 H
68 C~Uubn 8CN45 8 0.11 4.9 1670 12 t 10 H
69 C~Uubn 8C055 1S 0.11 4.9 1670 12 1 10 H
70 C~llubn 8CP30 æ 0.11 4.9 1670 t2 1 10 H
71 C~Uubn 8C~45 35 0.14 62 1870 12 1 10 H
72 C3Uubn 80A 5 5 0.10 4.6 544 4 S 5 H
'73 C~llul~n8D3 9 10 0.10 4.6 544 4 3 5 H
74 C~ bn 8DG12 15 0.10 4.6 544 4 3 5 H
75 CeUulsn 8DD14 20 0.10 4.6 544 4 3 5 H
76 C~llubn 8DE15 25 0.10 4.6 544 4 3 5 H
77 Callubn 8DF17 30 0.10 4.6 544 4 3 ~ H
78 C~lbJbn 8DG 5 5 0.18 7.7 924 4 3 10 H
79 C31hbn 80H 9 10 0.18 7.7 924 4 3 10 H
80 C~l~bn 8DI 12 15 0.18 7.7 924 4 3 10 H
81 C~lhJbn 8DJ14 20 0.18 7.7 924 4 3 10 H
82 C011ubn 8DK15 25 0.18 7.7 924 4 3 10 H
83 C0Uubn 8DL17 30 0.18 7.7 924 4 3 10 H
84 C~l~bn 8EA11.5 2.9 0.11 4.8 556 4 3 10 H
85 Callubn 8EB19 8.8 0.11 4.8 556 4 3 10 H
86 C~l~bn 8EC23.315.5 0.11 4.8 556 4 3 10 H
87 C~Uubn 8ED26.5 Z2 0.11 4.8 556 4 3 10 H
88 C~Uubn 5EE285 26.g Q11 4.8 556 4 S 10 H
89 C~llubn 8EF 31 83 0.11 4.8 556 4 S 10 H
90 Cdl~n 8E~11.5 2.9 0.19 B.3 958 4 3 10 H
91 CalbJlon 8EH 19 8.8 0.19 8.3 gS~ 4 3 10 H
92 CslbJbn 8EI 23.3 155 0.19 8.3 9~8 4 3 10 H
93 C31~ubn 8EJ 26.5 222 0.19 8.3 958 4 3 10 H
94 C~lhbn 8K285 26~9 0,19 8.3 958 4 3 10 H
C~lhlon 8EL 31 33 0.19 8.3 958 4 S 10 H
96 ~;d~bn C2 5 2.5 0.12 5.3 602 4 3 4 H
.. . . . . .
.
.
' . ' . ' '' ' ' :
`:
WO 92/12803 2 1 0 ~ 2 6 ~PCr/VS91/09oos ~,
-- 48 --
TABLE II A cor~
Coati Coat Uquid H~ad H~ad H~ad Air (H)ols
R~L Sha~t Air Alr WL W~. Fbw L~ th H~bht Pr~ss. Gap or
No. Matsrial # CFM PSI ~Int^2 Ihnon g/M~n in. Ln. inH20 mils ~S)Iot
97 CaUulon C3 11 5 0.12 5.3 602 4 3 4 H
98 C~llulon C4 15 7.5 0.12 5.3 602 4 3 4 H
99 CaUubn. C5 21 10 0.12 5.3 602 4 3 4 H
100 C~lubn C6 ~ 2.5 021 9.0 tO20 4 3. 4 H
101 C011ubn C7 12 5 021 9.0 1020 4 3 4
102 Caliubn C8 16 7.50.21 9OU t020 4 3 . 4 H
103 CsUubn C9 20 10 021 9.0 1020 4 3 4 ' H
104 CaUubn C10 6 zr 020 8.i; 972 4 3 4 H
105 C~Uubn C11 12 5 020 8.6 972 4 3 4 H
106 CaUubn Ct2 16 7.5 020 a6 972 4 3 4 H
107 CaUubn Ct3 20 10 020 a6 972 4 3 4 H
108 C011ubn C14 7 æ5 020 8.6 972 4 1.5 4 H
109 C~Uubn Ct5 12 5 020 8.6 972 4 1.5 . 4 H
110 C311ubn C16 16 7.5 020 a6 972 4 1.5 4 H
111 C~Uubn C17 21 10 . O~O 8.6 972 4 1~5 4 H
112 CaUubn C18 t7 7.5 020 8.6 972 4 1.5 4 H
113 CzUubn C2A 13 Z5 Q04 1.9 584 4 1.5 10 S
114 C~Uubn C28 17 5 0.04 1.9 584 4 1.5 10 S
115 Callubn CZC 22 10 0.04 1.9 584 4 1.5 10 S
116 CaUulon C2D 13 æ5 0.07 3.2 1000 4 1.5 10 S
117 CaUubn C2E 22 10 0.07 32 1000 4 1.5 10 S
1t8 Slarch Sl 35 4 0.52 11.7 870 12 3 79 10 H
119 Starch S7 40 5 0.52 11.7 870 12 3 84 10 H
120 S~arch S3 40 5 052 11J ~70 12 3 72 tO H
~121 Sta~ch S4 ~5 4.5 0~ 117 870 12 3 72 10 H
122 Stan:h S5 30 3 0.52 11.7 870 12 3 70 10 H
123 Sta~ch S6 35 4 1.37 30.8 23û0 12 3 158 10 H
124 Starch S7 40 ~5 1.37 30.8 2300 12 3 163 10 H
125 Starch S2A 13 9 0O36 al 202 4 3 18 10 H
126 S~ h S2B 13 9 036 8.1 202 4 S 18 10 H
127 Sta~ch S~A 30 3.5 026 5~ 434 12 3 47 10 H
128 Sta~dl S3B 26 3 OSl 11A 852 12 3 80 10 H
129 Starch S5A 15 4 0.32 72 180 4 1.5 70 10 S
130 Statch S5B 19 7.50.32 72 180 4 1.5 70 10 S
131 Starch S5C 22 10 0.32 72 180 4 1.5 70 10 S
1S2 Starch S5D 14 4 0.75 17.0 4æ 4 1.5 119 10 S
133 Statch S5E 19 7.50.75 17.0 4æ 4 1.5 12û 10 S
134 St;uch S~F ~ 10 0.75 17.0 422 4 1.5 121 10 S
135 Sl~h S`5G14 4 0.7~ 17.0 4æ 4 1.5 1æ 10 S
136 Sta~h S5~119 7.~0.75 17.0 4Z 4 1.5 122 10 S
137 Sta~ch S51 22 tO 0.7S .17.0 422 4 1.5 1æ 10 S
~38 Slan~ 4 4 0.34 7.6 190 4 1.5 ~ tO S
139 S~ch S5K 19 7.50.34 7.6 190 4 t.6 70 10 S
140 St8~b SSL Z 10 0~ 7.6 t90 4 15 70 10 S
141 S~:h SSM 14 4 0.34 7.6 190 4 3 70 10 S
142 Sla~dl S5N 19 7.50.34 7.6 190 4 3 70 10 S
143 Sta~h S60 22 tO 0.34 7.6 190 4 3 70 10 S
144 Sta~eh S5P 14 4 0.34 7.6 190 4 3 70 10 S
WO 92t12803 2 1 0 1 2 ~ ~ Pcrtus9l/09no9
. -- 49 --
TABLE lI-A~r~
Coat t~aS Uquld Hsad H3ad. Head Air ~H)sl~
R~. Sh~et ~Ir Alr Wt. Wt. Flow L0n~h H~ight Press. ~;ap or
No. MateTial ~ CFM PSI ~m~2 l~ton ~mln In. in. hH20 mils (S)lot
145 Starch S50 20 7.5 0.34 7.E l90 4 3 70 10 S
146 Starch S5R 23 10 0.34 7.6 1S0 4 3 70 10 S
147 Sta~hS5S 14 4 0.71 16.0 398 4 3 13S tO S
148 Starch S5T 20 7.5 0.7116.0 398 4 3 ~136 10 S
149 Star~h SSU 23 10 0.7116.0 398 4 3 137 10 S
150 Sta~hS5V 14 4 OJ1 16.0 398 4 3 132 10 S
151 StarhS5W 19 7.50.71 1~.0 398 4 3 1~2 10 ~ S
152 Starch S5X 10 0.7116.0 398 4 3 1S2 10 S
153 S~arch S5Y 4 4 3 140 10 S
154 Sta~hSSZ 4 4 1.5140 10 S
155 Statch S~A 4 4 1.5 160 10 S
156 Sta~ch S6A 8 4 028 6.S 156 4 1.5 6 4 H
157 Starch S7A 17 4 4 1.5 18. . 4 H
158 Sta ch S7B 16 3 4 15 18 4 H
159 Sta~hS10A 15 4 . 4 1.530 10 S
160 Stasch S10B Z 7.5 4 1.5 29 10 S
161 Stalch S10C 15 4 O.t1 2.6 64 4 1.5 50 10 S
162 Starch S10D 21 7.5 0.11 æ6 64 4 1.5 52 10 S
163 Sta~ch S10E 25 10 0.11 2.6 64 4 1.5 52 10 S
164 Sta~ch S10F 15 4 1.04 23.3 580 4 1.5 200 10 S
165 Sta~hS10G 25 101.04 23.3 SBO 4 1.5200 10 S
166 Starch S11A 26 10 1.04 23.3 580 4 1.5 200 10 S
167 S~h S11B 28 121.04 23.3 680 4 1.5200 10 S
168 Sta~ch S11C 30 14 1.04 ~tS 580 4 1.5 196 10 S
~169 StarcA S11D 16 4 1.04 23.3 580 4 1~ 196 10 S
170 Sta~ch S12A 16 4 0.11 ~8 64 4 15 50 10 S
171 Sta~ch S12B æ 7.5 0.1~ 2.6 64 4 1.5 50 10 S
172 Sla~ch S12C 26 10 0.11 2.6 64 4 1.5 51 10 S
173 Sta~ch S12D 26 10 0.11 ~ 6 64 4 1.6 50 10 S
174 Slan:h S~2A1 34 5 1.09 24.6 1832 12 1.5 100 10 11
175 S~chS12B1 49 101.09 24.B1832 12 1.5100 10 H
176 Starch S12C1 53 13 1.09 24.6 18æ 12 1.5 100 10 H
177 Starch S13A 17 5 0.14 3.3 54 4 1.5 190 10 S
178 Stalch S13B 24 10 0.14 3.3 54 4 1.5 ~00 10 S
179 Stalch S13C 24 10 0.67 '15.t 250 4 1.5 552 10 S
180 Slarch S14A 17 5 O.W 1.8 16 4 1.5 3æ 10 S
181 S~h S14B 17 50.14 3.1 28 4 1.5416 10 S
182 Slarch S14C 17 5 0.16 35 32 4 1.5 471 10 S
183 Sh~hS14D 17 5 028 62 56 4 1.5554 10 S
184 Sla~S14E 17 5O.S9 ag 80 4 1.5693 10 S
185 Slarch S14F 21 7.5 0.39 8.9 80 4 1.5 693 10 S
186 Sla~hS14G 24 100.59 13.3 120 4 1.5831 10 S
187 Sta~S14H 29 150.59 13.3 1~0 4 1.5E~31 1Q S
188 SSa~:h S141 28 15 1.08 2~S æo 4 1.5 1108 10 S
1~9 Starch ST15A 17 5 2~ 53.9 912 4 1.5 13~ 4 H
190 StuchST15B 35 10 2S9 53.9 912 4 1.5139 4 H
191 S~h ST15C 40 1252 39 5~.9 912 4 1.5139 4 H
192 S~ h S16A 10 4 0.45 102 130 4 1.5 52 4 H
Wo 92/12803 - PCI/US91/09009
2~0126 4
-- 50 --
TABLE Il-A cons.
Coat Coat Uquid I l~d H~ad H~ad Air (H)ole
Rat Sh~t Air Air Wt. WL~ Fbw L~n~th H~lght Pr~ss. Gap or
No Ma~0rial # CFM PSI ~/m^2 ~n ~mn in. in. inH~O mils (S)lot
193Slarch S16B 16 7.5 0.47-,~!o g 130. 4 1.552 4 H
194 Sta~h S16C 25 10 Q48 10.9 130 4 1.551 4 H
195 Sta~h S16D 14 5 0.35 8.0 92 4 1.540 4 H
196Starch S16E 17 7.50~7 8.2 92 4 1.541 4 H
197 S~ch S16F 26 100.38 8.5 92 4 1.540 4 H
198Starch S16G 18 5 020 4.6 48 4 1.530 4 H
199Starch- S16H 12 5 0.43 9.8 1Co 4 1.583 4 ~ H
ZOOSta~ch S161 23 100.45 10.1 100 4 1.5~3. 4 H
Z01Starch S16J 24 10 11 47.5 460 4 1.SZ77 4 H
202 Sta~h S16K 38 15 æ16 48.8 460 4 1.5277 4 H
203Starch S16L 40 16~2.æ 50.0 460 4 1.5277 4 H
204 Sta~h S16M 44 17 228 513 460 4 1.530S 4 H
205 Sta~h S160 45 1729.01 653.7 ~720 4 1.5199Q 4 H
206 PVA PV1A 11 3 0.96 21.4 792 4 1.520 4 H
Z07 PVA PV1B 1~. S 0.09 2.0 7S 4 1.5 8 4 H
208 PVA PV1C 17 5 b~s æo 73 4 1.5 8 4 H
Z09 PVA PV1D 17 50.09 æo 73 4 1.5 8 4 H
210 PVA PV1E 17 50.05 1.1 40 4 1.5 6 4 H
211 PVA PV1F 17 50.05 1.1 40 4 1.5 7 4 H
212 PVA PV1G 17 50.06 1.4 52 4 1.5 7 4 H
213 PVA PV1H 18 5 023 5~1 15~ 4 1.514 4 H
214 PVA PV11 18 50.13 29 108 4 1.5 9 4 H
215 PVA PV1J 21 50.13 2.9 108 4 1.5 9 4 H
216 PVA PV1K 21 5 025 5.7 2~2 4 1.520 4 H
~17 PVA PV1L 21 60.12 ? 7 100 4 1.512 4 H
218 PVA PV2A 20 5 Q29 6~ 230 4 1.540 10 S
2~9 PVA PV2B 20 50.~4 32 t14 4 1.530 10 S
220 PVA PY2C 20 5 021 4.6 1~4 4 15 35 10 S
221 PVA PY2D 20 50.Q6 1A 51 4 1.520 10 S
æ PVA PV2E 20 50.05 12 42 4 1.517 10 S
Z~3 PVA PV2F 20 50.11 æ4 84 4 1.525 10 S
224 PVA PV2G 20 50.00 O.t 2 4 1.510 10 S
225 PVA PV2H 20 50.01 0.1 4 4 1.515 10 S
226 S~archPG250 S18A 18 50.75 17.0 S10 4 1.555 4 H
227 St~PG250 $18B 30 100.7~ t7.0 3~0 4 1.555 4 H
228 StarchPG260 S18C 41 130.75 17.0 310 4 1.555 4 H
Z9 SlarchPGæ50 S18D 50 150.75 17.0 310 4 1.555 4 H
2SO StarchP.G250 S18E 37 100.57 12.9 2SB 4 1.52B 4 H
231 Starch PG250 S18F 31 103.57 80A 1470 4 t.6277 4 H
232 StarchPG260 S18G 21 15 357 80A 1470 4 1.5Z~7 4 H
233 Slarch PG250 S~8H 27 100.00 0.0 4 1.5728 4 H
234 StarchPG250 S181 28 100.00 0.0 4 1.51108 4 H
235 StarchP~0 S18J 28 100.87 19.7 360 4 1.54432 4 H
236Slarch S19A 17 5O.t1 Z6 75 . 4 1.530 10 S
237Sta~ch S19B 45 40.12 2.6 75 4 1.5S0 1 O S
238 Sla~h S19C 25 10O.t2 æ7 75 4 1.530 10 S
239 Sl~h S19D 17 50.11 æ6 70 4 1.528 10 S
240 St~eh S19E 17 50.42 9.5 260 4 1.560 10 S
~lVl~b~
WO 92/12803 PCI'/US91/OgO09
. .
-- 51 --
TA~LE Il-A a~.
Llqu~ Haad H0ad HYad Alr (H)ole
Ra~ Sh~ Air Air WL WL FbW L~n~th H~ight Pr~ss. Gap or
No Mat6dal ~ CFM PSI gh~2 Ib~on ghrin in. in. inH20 nuls ~S)Io~
241 Stalch SlgF 17 ~ 0.35 7.9210 4 1.~i50 10 S
242 Sta~h S19G 17 S 038 a5 æ5 4 1.5 53 10 S
2u S~ S19H 20 73 0.39 8.7Z~ 4 1.5 53 10 S
244 S~ Sl91 24 10 0:~9 8.922~ 4 1.~ 53 10 S
245 S~ar~ S~9J 24 10 0.40 9.0225 4 ~.~ 53 lo S
246 Sta~h S19K 17 5 026 5.8142 4 1.5. 42 10 S
247 St~ S19L 24 10 026 ~8142 4 1.5 42 10 : S
248 Sl~ch S~M 24 10 0.26 ~ 2 4 1.5 .42 10 S
Z49 S~ch S~N 17 5 0:~ 4.9116 4 1~5 a6 10 S
250 St~r6h S180 25 10 0 Z S~0116 4 1~ S6 10 S
251 SW* S20A 2B 10 0.11 2.456 4 1.5 44 10 S
252 SW~tl S21DB36 14.5 Q12 27~6 4 1.5 44 10 S
253 Sla1ch S2f~C28 10 0.00 QO 4 1.5 70 10 S
2~i4 St,a.~t:hS20D 28 100.40 QO 4 13 46 10 S
255 Sta~l S21A'~18 5 028 62146 4 1.5 45 10 S
256 s~ S21B 24 10 ' 028 6.4146 4 1.5 45 10 S
257 Sta~ S21C 21 7.5 0.29 6.6146 4 1.5 46 10 S
258 SWch S2tD 18 ~ OA6 10.4 Z~2 4 1.5 6~ 10 S
259 Statdl ætE 21 7.!; 0.47 10.6 Z~2 4 t.5 66 10 S
260 SWCh æ~ F 25 10 OA8 10.9 Z!2 4 1.5 65 10 S
wo 92/12803 2 1 0 ~ 2 6 ~ - 52 - PC~r/US91/09009 -
T~U3~ 11-8
H or S Llq. H~r ~Ur A4p~a~anc8 ~1 Good,5 ~ad)
R~f. Ske An~l~ T0rnp. Tennp. FLH. .Uq.% V~eos~y 1~Mech.
No. nuls d~ F F ~O Sk~ds Brook~ S~aky Wonny 6rainy S~ak
1 20 0 60 1 1.14
2 20 0 ~0 1.14
3 2~ 0 60 1.14
4 ~0 0 60 1.~4
6 20 0 60 1.14
6 2~ 0 60 ~.14
7 20 0 60 ~.14
8 20 0 60 ~.~4
9 20 0 60 1.14
10 20 0 60 1.14
11 20 0 60 1.14
12 20 0 60 1.t4
13 20 0 60 I.U
14 20 0 60 1.14
16 20 0 60 , ,1;14
16 20 0 6g 1.14
17 20 0 60 1.14
18 20 0 60 1.t4
19 20 0 60 1.14
20 20 0 61 1.14
21 20 0 61 1,14
22 20 0 61 ~.14
23 20 0 61 1.14
24 20 0 61 1.14
2~ 20 0 61 1.14
Z6 20 0 61 1.U
27 20 0 61 1.14
28 20 0 61 1.14
29 20 0 61 1.14
30 20 0 61 1.14
31 20 0 61 1.14
32 20 0 61 1.14
33 20 0 61 1.14
34 Z0 0 61 1.14
~5 20 0 .6~ t,~4
36 20 0 60 1.14
37 20 0 60 1,~
38 20 0 60 1.14
39 20 0 63 1.14
40 20 0 60 1.14
41 20 0 60 1.14
42 20 0 60 - 1.14
43 20 0 60 1.14
44 20 0 60 1.14
45 20 0 60 ~.t4
46 20 0 60 1.14
47 20 0 60 1.14
48 20 0 60 1.14
, -
. , ,
.
WO 92/12803 2 ~ O 1 2 6 ~ Pcr/usg~/o9oll9
. . .
-- 53 --
TA8LE II~B conl.
H or S I Iq. Haai~r Alr App~aranca (1 Good. 5 aad)
Ra~. Se~ Angla Tsmp. T~mp. R.H. Uq.% ~scosi~y 1~ech.
No. mUs dr~ ~F F % Sollds Brookfisld Str~aky Wom7y Grainy S~r~ak
49 20 0 6~ 1.14
50 20 . 0 60 1.14
51 20 0 60 1.14
52 20 0 60 1.14
53 20 0 60 1.14
54 20 0 60 1.t4
55 20 0 61 t.~
~ 20 0 61 1.t4
57 20 0 61 1.14
58 20 0 61 1.14
59 20 0 61 1.14
60 20 0 61 1.14
61 20 0 61 1.14
62 20 60 48 1.14
63 20 45 48 1.14
6~ 20 45 48 1.14
65 20 30 48 1.14
66 20 45 48 1.14
67 ~0 30 48 1,~4
6a 20 0 4~ 1.14
69 20 0 48 1.14
70 20 0 48 1.14
71 20 0 48 lA4
72 æo o 60 1.08
- ~7320 0 60 1.Q8
74 20 0 6~ 1.Q8
75 20 0 6~ t.08
76 20 0 60 ~.OB
~7 20 0 60 1.08
78 20 0 60 1.08
79 æo o 60 1.08
80 20 0 60 1.0~
81 20 0 60 1.08
8Z 20 0 60 1.08
83 20 0 60 1.08
84 2~ 0 ~9 ~.12
85 20 0 59 1.t2
86 20 0 59 1.12
87 20 0 59 1.12
88 20 0 59 1.12
89 20 0 59 1.12
90 20 0 59 1.12
91 20 0 59 1.12
92 20 0 59 1.1:~
93 20 ~ 59 1.12
94 20 0 59 1.12
95 20 0 0 1.~2
96 30 0 60 ~.14
,
: :'
WO 92/12~03 2 i O ~ 2 6 ~ Pc~r/usgl/ogoog
~ 54 -
T~U3LE ll B cont.
H or S Uq. Ho~r A~ Apps2ranco ~l Good.5 Bad~
R~L Sk~ An~la T~nnp. Tannp. R.H. L1q.% V~os~y 1~M~ch.
No. nuls d~o F F h Sc~Ws B~okfi~ Str~aky Wonny Gr~ny S~r9ak
97 30 0 60 1.74
98 30 0 60 1.14
99 30 o 60 1.14
100 3~ o 60 1.14
101 30 o 60 1.14
102 30 o 60 1.~4
103 30 0 60 1.14
104 30 0 60 1.14
105 30 0 6~ 1.14
106 30 0 60 1.14
107 30 0 60 1.14
108 30 0 60 1.1
109 30 0 60 1.14
110 30 0 60 1.1~
.111 30 0 6~ 1.14
112 30.0 60 t.1
113 6 0 0.41
114 6 0 0.41
115 6 0 OAl
116 6 0 OAl
117 6 0 OA~
118 ZO O 1a1 10 1 2
119 ZO O 1E~1 10 1 3 2
120 ZO O 18.1 10 l 3 2
~21 20 0 1EL1 10 1 3 3
1~ 20 0 1~ 10 1 3
123 20 0 56 107 1~1 10 1 3 3
124 ZO O 96 107 1a~1 10 1 3
125 ZO O 1t2 118 tO 3
126 20 0 112 118 10 1 2
127 SO O 112 118 10 1 2 4
128 30 0 1~2 118 10 3 3 5
129 6 0 t30 1S3 9~t 10
130 6 0 129 134 100.010 1 2
131 6 0 129 135 9t5 10
132 .6 0 126 132 8E~Z 10
133 6 0 125 133 87.7 10
134 6 0 1?5 133 94~ 10
135 645 1?5 133 94.0 10
136 645 125 133 93A 10
137 645 125 13S 94~ 10
138 645 12~ 136 76J 10 1 2
139 645 123 134 94A 10
140 645 123 132 92~B 10
141 6 0 122 134 ~33 10 2 S 3
142 6 0 122 132 g8.9 10 1 3
143 6 0 120 138 9B.1 10 1 2
144 6. 45 118 132 ~7~ 10 1 2 2
-
. .
.. .
.
WO 92/12803 ~ 1 0 1 2 6 ~ PC~r/~S9l/09009
-- 55 --
TABLE Il-B c~nL
H w S Uq. H~ t A~r App~arsnc~ t1 ~ood. 5 ~ad)
F~3~. Sks A~ T~mp. T~mp. R.H. Llq.~/. Vlscosi~y 1-M~ch.
No. mils d~g F 'F % SoJWs Broo~W Str~y Wormy Grainy S~r0ak
145 6 45 ~20136 95.6 10 ~ 3
146 6 45 116136 93.6 10 1 2
147 6 45 115131 33.8 1~ 1 2
148 6 45 123132 95.8 10
149 6 45 125133 95A 10 1 2
150 6 0 125135 83.9 10
151 6 0 lZ51S6 g3A 10 1 .2
152 6 0 125185 93.6 îO
153 6 0 1251S5 1 3 2
154 6 0 125135 1 2
155 6 0 125135 S 2
1~6 30 125133 76.9 t~ S 4 3
157 30 0 125139 77.9 10
1~8 30 0 12212B 9~5 0
159 6 0 125132 89.9 tO
160 6 0 125135 93~0~ '10 4 3 3
161 6 0 125136 82 ~ 10 5 4 S
162 6 0 125136 91.7 10 1 2 2
163 6 0 123133 9a7 10 5 3 2
164 6 0 123133 93A 10 4 3 2
165 6 0 125132 94:~ 10 1 2
166 6 0 1æ 142 83.8 '10
167 6 0 120131 g8A 10
168 6 0 120137 973 10
Jl69 6 0 122139 833 tO 1 2 2
170 6 0 13316~ 832 10 1 2 2
171 6 0 ~33161 8~.1 10 3 2 2
17Z 6 0 132162 97.6 10 5 3 3
173 6 0 132161 942 10 2 2
174 20 0 100135 39.~1 10 2 2 2
175 20 0 100135 3g.0 10
176 20 0 100135 S9.0 10
177 6 0 115113 S6.3 15 1 3 3
178 6 0 110109 87.5 15 1 3 3
179 6 0 110107 97.0 15 5 2 3
180 6 0 100117 70A 27.5 1 2 2
181 - 6 0 100116 97.0 27.5 1 2 2
182 6 0 100166 91.3 Z7.5 1 2 2
183 6 0 100116 86A 27.5 1 2 2
184 6 0 100116 100.0 Z75 1 3 Z
185 6 0 100116 88A Z7.5 1 2 2
186 6 0 100115 84.6 Z7.5 1 3 2
187 6 0 100115 83.1 Z73 1 2
t88 6 0 10012~ 782 275 1 2
139 30 0 gO101 813 14.7 135
190 30 0 90 10û 77.8 147 1S5 1 2
191 30 0 90100 862 143 135
192 30 0 1201~5 85.7 19.5 tS0 1 ~ 2
., , :'
.: . .
.:
:
WO 92/12803 2 1 0 1 2 6 4 PCr/US91/09009 -.
-- 56 --
TABLE II B con~
Horg Uq. H~ r A~ 1 Good5~ad)
Rst. Sks Angl3 T~mp. T~rnp. R.H. Uq.. %~Vlscos~ 1~M~
No. nuls d~9 ~F F % Soli~15 Brooltll31d Str~alqr Wormy G~ainy Str~ak
193 30 0 120 122 77.25 202 18g 1 3 2
194 30 0 117 1?1 83A ` 20.9 247 1 3
195 30 0 118 1æ 92321.6 306 3 3 3
196 30 0 120 124 100.0 22.2 364 1 3
197 30 0 118 123 B3A22.9 4:23 3 3 2
198 30 0 116 119 ~5J23.6 482 1 3 2
199 30 0 120 134 75.0243 540 1 2 2
200 30 0 120 134 83.625~ !;99
291 30 0 117 124 84.02~.~ S58 1 1
202 30 0 117 121 87226.3 716
203 30 0 116 123 86.827.0 775
204 30 0 1t4 118 72A27.7 8~3 1 1 1
205 30 0 114 117 ~tl 28A 892
206 30 0 118 123 952 6.7 23 1 2
207 30 0 117~ 12185.1 8J 24 4
208 30 0 117 1~ 73.7' ' 6.7 25 3
209 30 0 117 121 82~96.7 26 3 1 t
210 30 0 117 121 90A 6.7 27 4
211 30 0 119 123 9;!.6 6.7 28 3
212 30 0 89 97 23g 6.7 29 S
213 S0 0 83 89 ~6-~ 6.7 30 2
214 30 0 79 86 ~A 6.7 31 3
215 30 45 84 gO 25.76.7 :~2 2 t
216 30 45 84 90 2a3 6.7 33
217 30 45 99 107 2J.66.7 34
218 8 0 93 98 805 7 t~ 1 t
219 8 0 93 88 905 7 S5
220 8 0 93 99 gO.~ 7 36
221 8 0 93 99 9Z7 7 37
222 8 0 94 99 73.5 7 38 1 2
223 8 0 95 100 82.4 7 39
~4 8 0 95 101 802 7 40
225 8 0 93 97 84.1 7 42
æ6 30 0 125 132 772t3.6 438 3 1 2
~7 30 0 121 127 89.613.6 433
228 30 0 117 122 8a8 13~ 438 1 1 1
229 30 0 1æ 122 6a813.6 438 1 1 4
230 30 0 120 120 50~1S.6 438 2
231 30 0 t20 120 47~13.6 438
232 30 0 115 115 5~913.6 438
233 30 0 118 123 33.613.6 438 5 5 5
234 30 0 111 115 31313.6 438 . 3 3
z35 30 0 98 106 28213.6 43B Z
236 8 0 114 119 8Z7 85 ~7 1 1 2
237 8 0 114 119 6g.1a7 Z7 1 2 S
238 8 0 110 114 8~2 8.8 28 ~ 1 1 1
239 8 0 108 112 81.99.0 2~1 2 1 3
240 8 0 108 111 862 9.1 30 1 t 2
WO 92/12803 2 ~ O 1 2 ~ 4 PC~/US91/09009
-- 57 --
T~LE U-B cor~.
H or S Uq. Heal~r Alr App~arance (1 Good, 5 Bad~
R~. Se~ Argl~ T~mp. T~mp. R.H. Uq.~ Viscos~ty 1.M~ch.
No. mils d~g F F % SolWs B~ ld Slr~ Womly Grainy Str~ak
241 8 0 108 11289.~ 93 31 1 2
242 8 0 107 110 83~ 9A 31 1 3
243 8 0 109 112 8æ8 a6 32 2
244 8 o 109 112 61h 9.8 33
245 8 0 110 114 n~ 9~ 34 1 2
246 8 0 112 11682.3 10.1 35 1 3
247 8 0 113 117 882 102 35 2 2
248 8 0 11S 117 782 10A 3~ 1 2
24g 8 0 109 11~ a~ 37 1 1 3
250 8 ~ 109 113 8~9 10.7 3~ 4 S 2
251 8 0 118 121 97~ 107 85 3 S
252 8 0 115 1199B.1 ~2 85 4 3
253 8 0 109 114 ~ 132 85 2 2
254 8 0 111 11694.0 145 85 3 3 2
255 8 0 114 117B5.8 10.6 29
256 8 0 113 11689~6 10.9 33 1 Z
257 8 0 111 114 832 112 38 1 2
258 8 0 104 10890.1 11.6 42 2 2
2sg 8 0 104 10880.9 11~ 47 1 2
260 8 0 105 10983.5 1Z2 51 2
- ,
.
.
w092/12803 21012 6 4 PCTIUS91/09~09
- 58 -
The liquid velocity refers to the velocity of the
liquid immediately before it exits from the holes or slit
and comes in contact with the air,stream or streams. This
velocity is typically somewhat le~ than 3 ft/s (l m/s).
The air velocity is the veloci~y of the air as it exits
the air gaps immediately prio~ to the zone of initial
air/liquid impingement. The air velocity ranges from 200
ft/s to 1100 ft/s ~61 m/s to 335 m/s or Mach number of 0.2
to 1.0), where 1100 feet/second is sonic velocity.
The air gap is the dimension of the slit formed
between the air plate and the main body of the head which
contains the liquid passages and orifices. Typically the
slit width of the air gap is between 5 mils and 20 mils
(125 ~m - 500 ~m), and extends about 0.5 inches beyond the
line of liquid orifices on both ends. The head-to-paper
separation distance was typically between l inch and 10
inches (2.5 cm to 25 cm).
The orientation o~ the head is defined by the
angle between the plane in which liquid flows out oE the
line of liquid orifices in the head, and the plane of
travel of the paper being coated. Typically the head is
oriented such that the liquid is normal to the plane of
paper travel. Some tests were conducted with the head
rotated such that the plane of the liquid array was about
45 to the plane of travel of the paper.
The coating formulation can vary widely in
concentration, temperature, constituents, and batches.
Typical formulations used with the MOH have been Cellulon
with' CMC at 0.5% to 1.5~ concentration, starch (PG290~ at
10% concentration and 120F, and PMDI at 100%. Several
other constituents and several variations in concentration
and batch have also been tried.
The air plate setback is the distance between the
end of the air plate and the end of the liquid orifices.
Typically the air plate sets back from the liquid orifice
tip about 10 to 15 mils (0.010 to 0.015 inches; 250 ~m to
380 ~m). Air plate setback values are not shown in Table
II.
,
WO92/12803 2 ~ O ~ 2 6 ~ PCT/US91/09009
- 59 -
Only the liquid and air velocities, the air gap
and the head to paper separation distance were tested
during the trials reported in Table II. The coating
formulation for runs 1 - 117 was a 0.8% Cellulon/0.2% CMC
mixture with llO0 ppm sorbic acid in water. This material
was homogenized in the Gaulin Homogenizer (from APV
Gaulin, Inc. of Hilversum, Holland) for three passes
through the cell disruptor (CD) valve, followed by one
pass through a 150 ~m filter and one pass through a 125 ~m
filter. The head orientation was normal to the direction
of travel of the paper and the air plate setback was
constant at 15 mils (0.015 inches or 380 ~m).
The liquid velocity for these trials was selected
based on coating application rate. Two levels of
application were used, 3 lbm/ton/side and 5 lbm/ton/side.
These coverages correspond approximately to 0.11 g/m~/side
and 0.19 g/~/side for a 50 lbm/3300 sq.ft. sheet.
Because of the differences in liquid hole size and number
per inch this resulted in differences in actual liquid
velocity for the two heads at the same level of coverage.
Both air flow rate and air pressure were measured
during tha runs so air velocity could be calculated. Air
velocity is specified in terms of air pressure because air
velocity and air pressure are directly related. The
nominal or equivalent air pressure was varied from 5 psig
to 30 psig in 5 psig increments. In addition, the air gap
for various runs was set at one of three values: 5, 10,
or 15 mils ~125, 250 or 380 ~m).
Most of the trials were conducted with a head-
to-paper separation distance of 3 inches, but a few runs
were conducted with 1 inch and 10 inch distances. The
separation distance is measured from the tip of the
applicator where liquid emerges from the slot to the
surface of the substrate. A distance of 3 inches was
found to produce less mist than a 10 inch distance, while
unexpectedly retaining uniformity of coating application.
The liquid viscosities and gas impingement
velocities in Table II are sufficient that immediate or
,
wo 92/12803 2 1 0 1 2 6 ~ PCT/US91/09009
- 60 -
almost immediate airblast,at~omization of the liquid
probably occurred as the li~uid emerged from the outlet.
The range of~ variables for these trials is
expressed in Table III.
TABLE III
1 0 ~ellu~on PVA PG290 PG25C
Min. Hsx. Hin. Uax Hin. H~x. Min. ~ax.
C08tin~ solids X 0.41.46.77.08.5Z8.4 13.6 13.6
Coa~ing temper3ture F 48 61 79 119 90 133 98 125
1 5 Brookfield viscosity cP 23 42 27 ô92 ~ O
Liquid p~ssage mils 6 30 8 30 6 30 30 30
Liquid pressurein. H20 6 40 6 1939 28 4432
Liquid flo~ g~min 5441670 40 792 16 5720 236 1470
Coat ~eight g~m 2 0.040.260.050.950.08 29.010.57 3.57
2 0 Coat ueight Ib/ton 2 11 1 21 2 654 13 80 Air gap mils l 4 10 4 10 4 10 4 4
Air pressure psi ¦ 3 35 3 5 3 17 5 15
Air flo~ meter CFM 5 55 11 21 8 53 18 S0
Relative humidity % O 0 26 95 18 100 28 90
2 5 Head length in. 4 12 4 4 4 12 4 4
He~d height in. 1 10 1.5 1.5 1.5 3 1.5 1.5
~umber of runs 117 20 113 10
__ _ _ _, _ _
The ~luid preparation and handling system
consisted of a conical storage tub, a Moyno pump, a wire
mesh filter, a spray collection tub, and a return pump.
All tubing and fittings between the filter and the head
were of food-grade quality to ensure freedom from orifice
pluggage. Liquid flow was adjusted with a hand valve
based on a pressure reading of the liquid at the head.
Timed discharge rates from the head were also taken at the
beginning and end of each set of runs and these were the
basis for determining the correct pressure reading during
the runs.
To simulate the motion of the paper sheet on a
paper machine a sled system was constructed to move single
sheets of paper under the head at high speed. The sled
consisted o~ a frame and a set of rails along which a pair
45 - of runners traveled. A platen to hold the paper sheet was
attached to the runners, and bungee cords were used to
propel the platen/runner combination along the rails. The
head was suspended from a framework above the rails at the
location where the platen/sled reached its maximum
.
~ l U ~
W092~12803 PCT/~S91tO9009
``':
- 61 -
velocity. High-speed video data was used to determine
that this velocity was approximately 1800 ft/min. After
passing under the head location the platen/runner
combination was slowed and stopped with an arresting wire.
The paper sheets were removed after one exposure to the
coating spray, thus simulating the exposure that would be
obtained on a paper machine at a similar speed. The paper
samples were allowed to dry without further treatment and
were stored in loose bundles.
For most of these trials the paper used was a
sized printing grade, although some unsized newsprint was
also used. Visual comparison of these two types of sheets
under the same spray conditions showed no apparent
difference. The data from the two types of paper are not
differentiated in Table II.
Coating Uniformity Defects
It is convenient to visualize the "coating" as
lying on top of a smooth, flat substrate. In this
circumstance the uniformity of the coating thickness is a
measure of coating uniformity. Most substrates are not
smooth and flat on the scale of nominal coating thickness
( 0.5 to 10 ~m). It is therefore more appropriate to
measure the quantity of dry coating applied per unit area
instead of coating thickness. The selected units for coat
weight are grams per square meter (g/~). Because a
continuous coating is usually sought, the scale over which
the coat weight is measured is small, less than 1 mm by 1
mm. The variation in coat weight per unit area on this
small scale is a measure of the coating uniformity.
Under most conditions, Cellulon and starch
coatings applied to papers are transparent. To obtain
information about the coating uniformity, a fluorescent
dye was added to the Cellulon or CMC coating mixtures used
in these trials. Under ultraviolet light this rendered
the coating distribution on the paper samples visible.
The dye is distributed in the liquid phase of the coating,
hence it is actually the uniformity of the distribution of
the liquid phase that is visible. Although this
-,. .
WO92/12803 21012 6 ~ PCT/US91~09~09
- 62 -
distribution may not correspond exactly to the
distribution of the coatiny solids, it is an adequate
approximation for these studies.
The images and gra~hs in FIGS. 35 - 56 were
generated from test sheets~obtained during the starch
runs. A starch run consisted of spraying starch under
prescribed conditions onto a sheet of paper attached to a
sled which moved under the head. The coated sheet was
allowed to air dry. The sheet designation (e.g. Sl2Cl)
corresponds to that used in Table II where the operating
conditions are presented. Starch is a clear coating so
either a fluorescent dye or a staining agent must be used
to make the coating visible. In the case of FIGS. 35A -
56A an iodine stain was used to produce a dark brown color
wherever starch was applied. The stain is darker where
there is more starch, so the intensity of the color can be
used to judge the coat weight uni~ormity o~ the starch.
To obtain a quantitative measure of the coat
weight uni~ormity, the color intensity of the test sheets
was digitized using a color scanner. This device measures
the darkness or intensity at each location in the stained
area of the test sheet using very small sample areas. The
size of the sample areas is specified in terms of the
number of dots or pixels per inch. In this case, 75 dots
per inch (dpi) was used, resulting in a sampled area size
of about 0.33 mm square. For a typical test sheet, the
stained area was about lO0 mm x lO0 mm, so a total of
about 90,000 intensity samples were taken per test sheet.
The intensity range was broken into 256 levels of grey
with a value of 0 (zero) corresponding to black and a
value of 255 corresponding to white. All other levels of
grey are in between these two extremes. The images shown
in FIGS. 35A - 38A are printouts of the scanned test
sheets using a MacIntosh computer and a LaserWriter
printer.
The graphs of FIGS. 35 - 56 were produced using
one of many available image analysis programs for grey-
intensity images. The program was a public domain program
W092/12803 2 ~ O 1 2 6 4 PCT/USgl/ogOO9
- 63 -
called "Image 1.22y" that resulted from work carried out
for the National Insti~utes of Health. Two types of
graphs are shown, both of which are grey intensity profile
graphs. The bottom graph is a line profile, which
represents the variation in the grey intensity along a
line drawn on the image. All the linles used here were
drawn near the mid-point of thè stained area in the cross
direction, i.e. the line is drawn perpendicular to the
direction of motion of the test sheet when it was coated.
The top graph is also a grey intensity profile,
but represents the "column average" values for grey
intensity. For this plot, the average of the grey
intensities along a column of sampled areas in the machine
direction was taken. The variation of these values in the
cross direction was then plotted. This type of graph
eliminates some of the point-to-point variations, but
shows any streakiness in the coat weight variations.
For the MOH coating applicator there are two
principal coating uniformity defects: graininess and
streakiness. Graininess is a non-uniformity on the scale
of approximately 1 mm. With poor droplet formation the
individual droplets from the MOH head are relatively
large, approximately the dimensions of the orifices, or
500 ~m. When these droplets strike the paper they spread
out to form circular or elliptical spots of coating
surrounded largely by uncoated paper. The result i5 a
localized non-uniformity. An exa~ple of a sample with a
very grainy coating is shown in FIG. 31.
The MOH coating applicator may also produce non-
uniformities on a larger scale that are generally alignedwith the direction of paper travel. The whole paper
sample is coated, but the coating is noticeably thinner in
some areas than in others. The thin areas typically are
approximately 1 cm wide and may be continuous in length,
though streaks of 3 or 4 inches are more CODOn . An
example of a sample with severe streakiness is shown in
FIG. 32. As a reference for the streak duration, a three
wo 92tl2803 2 1 0 1 2 6 ~ PCr/US91/o9009
- 64 -
inch streak in a paper sample traveling 1800 ft/min (471
m/min) corresponds to non-uniformity for 83 milliseconds.
Data from the MOH coating uniformity trials are
presented with respect to three variables:
1) effect of coating application rate and air
pressure ,;`
2) effect of the air gap width
3) effect of the head-to-paper separation
distance
FIG. 33 is a set of twelve photographs of samples
for both 3 and 5 lbm/ton/side application rates
(approximately 0.11 to 0.19 g/~) and for nominally 5 and
25 psig (35 kPa - 170 kPa) air pressures at an air gap of
10 mils (250 ~m) using the 4-inch MOH head with 3 inch
(7.5 cm) head-to-paper separation. These photographs
compare coating uniformity for the given range of
application rate (3 to 5 lbm/ton/side) and air pressure (5
- 30 psi). From the comparison in FIG. 33 it appears that
the coating application rate of the Cellulon/CMC affects
the density of the image but not the general character of
the coating uniformity either in terms of graininess or
streakiness. Increased air pressure significantly reduces
graininess and somewhat reduces streakiness for this set
of trials with this given coating material.
Shown in FIG. 34 is a set of photographs of
samples for 5 mil and 15 mil (125 ~m and 375 ~m) air gaps
at 5 lbm/ton/side application rate and for 5 to 30 psig
air pressure. From the comparison in FIG. 34 it appears
that the air gap width at constant pressure only modestly
a~fects coating uniformity except at the lowest air
pressure. Increased air pressure significantly reduces
graininess and somewhat reduces streakiness.
Photographs of samples for head-to-paper
separation distances of 1~, 3, and 10 inches (3.75, 7.5
and 25 cm) for the 12-inch MOH head with a lO mil (250 ~m)
air gap at 3 lbm/ton/side and for nominally 7.5 psig (110
kPa) air pressure were also taken, but are not shown.
From the comparison in those trials it appears that
. .
W092/12803 2 1 0 1 2 6 ~ PCT/USg1/og~og
. ,,
- 65 -
increased head-to-paper separation distances increase the
streakiness of the Cellulon/CMC coverage. Streakiness is
not very pronounced at 1~ and 3 inches (3 75 and 7.5 cm)
head-to-paper separation. At a 10 inch (25 cm) separation
the coverage is grainier and large scale non-uniformities
become apparent.
Initial spray trials with 1% Cellulon/CMC coating
show that graininess can be most effectively eliminated
with increased air pressure (air velocity). Streakiness
is also reduced by increased air pressure, but not as
significantly or as consistently. Under the best
conditions, the visual data indicate that Cellulon/CMC can
be coated on a paper sheet with good uniformity of
coverage, at least up to 1800 ft/min paper speed.
The runs 118 - 260, and other tests and
observations, suggest that liquid pressure in the head
affects the uniformity of flow at various locations aiong
the slit or series of orifices. It therefore may affect
streakiness. Based on these data and observations, the
liquid passage length is selected which results in a
relatively larger pressure drop along the flow path, thus
providing uniformity of liquid flow from one end to
another and avoiding streakiness in particular
applications where streaks are not desired. Head
pressures above 20 kPa (3 psi) appear to be adequate for
many coating materials tested so far.
Different materials have been found to have less
graininess at different preferred air flows. In practice,
each new material or liquid flow condition is started with
relatively low air pressure, approximately 27 kPa (4 psi).
The coating pattern is observed for graininess and the air
pressure is increased until graininess is eliminated, i~
graininess is not desired. So far, air pressures less
than 100 kPa (15 psi) have been sufficient to reduce
graininess.
Desireable attributes for some applications are
illustrated by FIGS. 35 and 36. The single line grey
intensity profile FIG. 35C is always below 200,
W092/12803 2 10 12 6 11 PCTtUS91/09009
- 66 -
demonstrating no discontinuities in the coating made with
a conventional gate roll. A comparable single line
density graph in FIG. 36C is s~imllar].y always below 200
and has no coating discontin~ities. Of note is the lesser
amplitude of variation of`the single line density in FIG.
36C, illustrating that the coating is even more uniform
than with the prior art gate roll. A low amplitude of
variation of the single line density graph corresponds
visually to a low level of graininess. A high amplitude
~as in FIG. 39B) reflects excessive graininess.
Variation from baseline of the column density
graph is associated with streakiness of the coating. FIG.
41, for example, shows an undulating column density line
that is reflected in the high streaky score (3) in Table
II. Displacement of the graph away from 200 toward 80
reflects the amount of coating on the substrate. Hence
process parameters may be assessed and selected for a wide
variety of materials by determining their column average
and single line densities. In a general sense, higher
liquid flows produce less wormy coatings, higher air flows
produce a less grainy distribution, and higher coating
liquid pressure produces less streaky coatings.
EXAMPLE III
There is an optimum (but not required)
relationship among the diameters of the orifices in the
MOH, the viscosity of a coating fluid, and several other
operating parameters. These relationships are illustrated
by the equation for pressure drop along the liquid flow
orifices:
32 ~ v l
p =
*
where:
P = pressure drop, Pa
~ = apparent liquid viscosity, Pa-s
v = liquid velocity, m/s
l = oriflce length, m
WO92/12803 2 1 0 ~ 2 6 ~ PCT/US9J/09009
- 67 -
d = orifice effective diameter, m
The apparent viscosity, ~, can be related to the
Brookfield viscosity at 100 RPM, ~ by the expression:
~ = ~ 20 8
with:
8 v
where:
~ = Brookfield viscosity at 100 RPM, Pa-s
= shear rate, l/s
s = exponent, unitless
For orifices which are not circular the effective value of
the diameter is:
4 A
where:
A = orifice flow area,
Some examples of typical values for flow
conditions and geometry are:
Variable Symbol Range
_
Liquid velocity v 0.05-1 m/s
~
Orifice diameter d 0.15-0.75 mm
_
Orifice length 1 5-50 mm
_
WO 92/12803 21012 6 4 PCTtUS91/09009 ~
-- 68 --
- Some typical values for the fluid parameters are:
Fluid T, C ~, Pa
.
water 20 0.00l o
. ..... .. _
PMDI 20 0.2 0
cellulon 20 0.3 0.5
starch 40 O.l 0.5
The target value for pressure drop for many
applications is between 13,000 Pa and 250,000 Pa depending
on head size and expected flow range.
Sharp edges, such as edges 95, 97, 328, 312, 3S4,
20 or 364 may have a radius of .002 inch or less. Sharp
edges can diminish build-up of coating material at or
- around the outlet for the coating material.
In those embodiments that use a slotted head, the
optimum relationship among the width of the slot and the
25 other variables mentioned above is
12,~vl
P = ~r
where w is the width of the slot.
EXA~qPLE IV
Several examples o~ film thickness are calculated
35 below to illustrate some very thin coatings that can be
achieved with the present invention.
TABLE IV
Film Thickness (One Side only)
COVERA6E l,IET FILM a 6% St~LIDS DRY FILM
45 PVA 0.05 grcms~meter2 0.83 micrcns .050 microns
SG 1.02 a lOX solids 0.10 gramstmeter2 1.66 micrcns .010 micrcns
~IET FILM a 10% SOLIDS DRY FILH
W092/12X03 2 ~ O 1 2 ~ ~ PCT/US91/~9009
~ 6 9
PG 290 Starch 0.25 gr~ms/meter2 2.4 microns .024 microns
SG 1.05 a 10X so~ids 0.40 gran~/meter 3.8 microns .038 microns
The thin films of the present invention usually
result in coverages of 1 g/~ or less, such as 0.40 g/m~,
preferably 0.25 g/~, most preferably .05 to 0.25 g/m~.
Much thicker coatings can also be applied, and substrates
can also be soaked by applying an exceiss of coating
material.
EXAMPLE V
The present invention can be used to apply
bacterial cellulose (cellulose produced by bacteria) to
paper webs. A suitable bacterial cellulose is disclosed
in United States Patent No. 4,861,427, which is
incorporated herein by reference. This bacterial
cellulose is available commercially as Cellulon. It would
be possible to apply the bacterial cellulose at web speeds
of 2000 feet/minute or more. The bacterial cellulose
could be applied at concentrations in the range of 0.5~ to
2.0%. A preferred range is 0.5~ to 1.3%. Mixtures of
bacterial cellulose and CMC in a weight ratio in a range
of 2:1 to 10:1 bacterial cellulose to CMC, having a solids
concentration in the range of 0.25% to 2.0%, could be
applied to the substrate. A preferred concentration would
be in the range of 0.25% to 1.3%. All concentrations are
on a weight basis.
EXAMPLE VI
The process and apparatus of the present
invention can also be used to enhance the strength of
corrugated board packaging materials. This strength
enhancement is achieved by applying relatively low amounts
of selected isocyanate compounds to the corrugated
packaging board. One suitable isocyanate resin compound
is polymeric methylene diphenyl diisocyanate (PMDI).
Another is an emulsifiable polymeric methylene diphenyl
diisocyanate (EMDI). These chemical compounds in liquid
form, or in the form of an emulsion in the case of EMDI,
may be sprayed onto a fluted container board medium (over
.
WO92/12803 PCT/US91/09009 ~
210126~
a selected width) thereby coating all surfaces o~ the
fluted medium, or it may be applied by a fluke tip roll
coater only in the tips.
Using the present application to spray 5~ on a
weight basis of the medium of either PMDI or EMDI, and
allowing a cure time of about 5 days for PMDI, the short
column or top-to-bottom stacking strength improvement of
the container will approximate 33%. The EMDI cures more
quickly, needing only two days to cure. If the
application is 10% by weight of these materials, strength
is improved approximately 40~. It is believed that
strength enhancement will occur as the isocyanate resin
compound is added in an amount within a range of from 0.5%
- 50% by weight of the medium.
Other suitable chemical compounds that may be
utilized to provide a stiffer fluted medium are various
acrylics, polyvinyl acetates/alcohols, various latexes,
styrene-maleic anhydride, epoxy resins, and others.
EXAMPLE VII
An optimum definition o~ coating uniformity is
that it produces a column average and single line grey
intensity profile graph similar to that shown in FIGS. 35
and 36 (gate roll run and #S12C1). The aspect of these
graphs that most indicates uniformity of coating is the
low amplitude variation of the grey intensity columns and
lines. The column intensity profile of these graphs
varies no more than about lO units of intensity, while the
single line intensity varies no more than about 30 - 50
units of intensity. Consistent values below 200 on each
graph indicate completeness of coverage; the farther below
200 the line remains, the more likely there will be no
discontinuities of coverage on the sheet. The lines in
FIGS. 35 and 36 are at about 80 - 150, preferably below
125, and indicate a high probability of thorough coverage
across a desired swath of substrate being coated.
EXAMPLE VIII
An alternative mist collection device is
schematically shown in FIG. 58 wherein a substrate 750
:` :
:~ ;
WO92/12803 21 O i 2 6 4 PCT/US91/09009
.~.
- 71 -
moves in the direction of arrow 752 beneath an applicator
754. A pair of tubular collectors 756, 758 are placed
above the substrate, one on each side of the applicator,
and each collector presents a downwardly facing slot 760
or 762 into which mist is drawn by negative pressure. A
paddlewheel cylinder 764 is provided adjacent slot 760 and
extends the length of collector 756. Another paddlewheel
cylinder 766 is provided adjacent slot 762 and extends the
length of collector 758. Each paddlewheel rotates in the
direction indicated by the arrows in FIG. 58 to direct
mist into the collector.
Yet another mist collector is shown in FIG. 59,
in which like parts are given like reference numerals.
The paddlewheels have been removed in this embodiment, and
an auger 768 or 770 is placed within each collector such
that the auger axis of rotation is coaxial with the
longitudinal axis of the collector in which the auger
rotates. Auger 768 rotates in the direction of arrow 772,
and auger 770 rotates in the direction of arrow 77~, to
convey mist that enters slots 760, 762 to the ends and out
of the collectors.
EXAMPLE IX
This Example concerns designing the liquid flow
passage in the applicator to obtain uniform liquid
distribution along the length of the applicator. This
design keeps the flow velocity low so that both the
dynamic head and the friction losses are small compared to
the pressure drop across the exit slot or orifices. The
design shown in FIG. 60 places a series of holes 780 and a
target plate 782 within the liquid passage above the slot
or orifice inlets 784. This series of holes and target
plate separate the liquid passage into two sections. The
"upper" section 786 is the passage intended for
distributing the liquid along the entire length of the
applicator. The 'llower" section 788 is intended to
distribute the liquid uniformly to the inlet of the slot
or orifices. The size and number of holes 780 is selected
to avoid pluggage and to present a total flow area much
WO g2/12803 2 1 ~ 1 2 6 4 PC~/USgl/ogoog
' :
-- 72 --
less than the slot or multiple orifice area. The series
of holes represent a significant resistance to flow and
aid in uniform distribution of liquid along the length of
the head. The pressure drop across the slot or multiple
orifices will then only have to distribute liquid
uniformly over the dimension of the separation of the
holes. The target plate 782 is preferably located a short
distance below the series of holes at a distance
approximately equal to the hole diameter. Its purpose is
to dissipate the dynamic head of the liquid and redirect
it away from the slot or multiple orifice inlet.
EXAMPLE X
Another embodiment of the applicator is shown in
FIG. 61, and includes a top portion 790 and mating lower
portion 792. A removable, triangular cross-section tip
794 is held in place between portions 790, 792. A
central, tubular manifold chamber 796 extends the length
o~ top portion 790 and distributes coating material
through a passageway 798 to a slot 800 in tip 794, and
eventually out of a narrow liquid outlot slot 801. A pair
of longitudinally extending tubular fluid manifold
chambers 802, 804 extend parallel to chamber 796 and
introduce gas into passageways 806, 808 that communicate
with passageways 810, 812 and provide an impingement
fluid. Tip 806 may be selectively removed from the
applicator by separating top and bottom portions 790, 792.
The tip may be replaced when it is worn or when a
different width outlet slot 801 is desired.
EXAMPLE XI
This Example illustrates the use of the
applicator to produce a micro or macro porous coating or
sheet by the use of non-wetting or subliming particles.
In normal use the applicator can produce a uniform,
continuous coating or sheet by the use of high speed gas
stream impinging a co-flowing liquid stream. A powder may
be added to the liquid or gas stream. The material of the
powder may be either non-wetted by the liquid or may be a
material which sublimes at a temperature below the melting
WO92/12803 2 ~ O ~ 2 6 4 PCT/USg1/ogOO9
73 -
or decomposition temperature of the remaining coating or
web. The resulting coating would be porous or non-
continuous. The size of the defects may be controlled by
the selection of the size of the powder. Possible
applications would be in the production of micro-porous
material to allow the underlying web or substrate to
"breathe" but otherwise provide a continuous coating.
Other products that could be produced this way include
microporous filter media and blister resistant coatings.
EXAMPI,E XII
A pigmented coating was prepared and sprayed
using the 4-inch slotted head. Sheets were run to test
- the coverage quality at varying liquid pressures in the
head and varying air pressures. The coverage quality was
determined using grey-scale image analysis on the sheets.
The pigmented coating was applied using the 4-
inch slotted head mounted on the testing sled. A Columbus
formulation was used to make the pigmented coating (39
total solid) and is shown in Table V:
TABLE V
,
Pigmented coating formulation
3942g Water
20g Desprex N40
5952g Hydraprint
1488g Hydrafine
560g Ti~
2080g PG 290 starch (30% total solids)
55g Perez 802
1248g Dow 620
63g Berchem 4126
.
The air pressure and the fluid pressure in the
head were varied at three levels each for a total of nine
combinations. The levels for the air were varied at 5,
10, and 15 psi. The three fluid pressures were 80, 110,
40 and 150 inches of water, corresponding to 6.8, 8.9, and
9.2 g~ coat weights respectively. The air temperature,
air humidity, and the head temperature were left ambient.
WO92/12803 2 i O 1 2 6 ~ PCT/US91/09009
- 74 -
The coverage quality was analyzed using grey-
scale imaging. The sheets were dyed using Croda Red ink
to make the pigmented coating visible. A grey-scale image
was produced using an image scanner. The image was
analyzed for graininess and the streakiness (or
patchiness) in the same manner as desc:ribed above. Small
scale non-uniformities are called graininess while larger
patches and streaks are called streakiness.
Table VI shows the graininess and the streakiness
for the nine different combinations. Visually, the best
sheet was PCF13 (15 psi air, 6.8 g/~). It also has the
lowest percentage of streakiness and a lower value for the
graininess. The combination of high air flow and low
coating flow seems to give the best coverage. This is
probably because a minimum air flow is needed to atomize
the fluid enough to get a good coverage quality. As the
li~uid flow is increased, the minimum air flow needed for
acceptable atomization will also increase.
TABLE II
l 5 psi I ~0 ps~ I lS psi
¦ rLn PCF11 rul PCF12 run PCF13
6.8 g/m I graininess: 45.0X gr~ininess: 23.5% graininess: 25.6%
t80 in H 0~ ¦ stre~kiness: 29.7X stre~kiness: 19.8% ¦ stre~kiness: 14.0X ¦
2 grey diff: 27.63 ~rey diff: 33.83 ¦ grey diff: 33.82
run PCF 7 run PCF 8 run PCF 9
8.9 g/m I graininess: 22.7X gr~ininess: 27.9% graininess: 32.4%
3 0 t110 in H20~ ¦ streakiness: 16.4X ~tre~kiness: 19.3X ¦ streakiness: 16.0X ¦
_ grey diff: 48.14 grey diff: 42.10 ¦ grey dift: 37.92
run PCF 4 run PCF S ¦ run PCF 6
~.2 g/m gr~inlnes~: 34.4X gr~ininess: 23.4X graininess: ZS.1X
~150 in H20~ streakin~ss: 26.1X 9trankiness: 16.7X strealtiness: 16.0X
l ~r~y diff: 33.90 grcy diff: 44.Z7 grey diff: 43.21
_
EXAMPLE XIII
In the applicator described in connection with
FIGS. 5-l9, one or two high velocity gas streams impinge
an adjacent liquid stream. In this example, the
arrangement is not altered, but a fine powder is added to
one or both of the air streams, or to the liguid stream.
A fine powder would preferably be used that contains solid
particles having a longest dimension preferably less than
one-fifth of the air or liquid passage minimum dimension.
W092/12803 21012 ~ 4 PCT/US9l/09009
- 75 -
The powder may be carried in the liquid stream as part of
the coating formulation, for example, or in the gas
stream. Carrying the powder in the gas limits contact of
the powder with the liquid until mixing with the gas jet
issuing from the applicator. Limited mixing of the powder
and coating would control the degree of reaction or
interaction of the solid powder with t:he liquid, or could
control the relative location or degree of stratification
of the final coating.
One example of the application of a fine powder
is the application of a pigmented coating color where the
solid phase clay, CaC03, or whiteners and brighteners such
as Tio2, or other powder-like material is entrainecl in the
gas stream while the binder, SBR latex, starch or other
material is applied with the liquid stream. This could
provide a potential use~ul stratification of the two types
of materials.
Particles could be introduced by providing a
particulate outlet between the impingement gas outlet and
coating material outlet. Alternatively, particles would
be suspended in the impingement gas by blowing the
impingement air over wells containing particulate material
prior to the gas emerging from the applicator outlet.
When a porous coating is desired, the powder can
be a non-wetting material such as Teflon (polytetra
fluoroethylene). The coating liquid will not adhere well
to the particles, which will subsequently be removed to
leave small holes in the coating.
EXAMPLE XIV
The potential uses for the present applicator are
extremely broad and varied. A miniature spray coating
applicator could be used in cooperation with a printer or
plotter near the inking head to coat the paper surface
before printing or seal a newly inXed surface to avoid
smearing or erasure. Varying sizes of applicators can be
used to apply a controlled, uniform amount of acid or
caustic to a moving substrate in an etching or cleaning
operation. Acid or caustic applications could also be
W092/12803 21~ ~ 2 ~ 4 PCT/US91/09009 ~-
- 76 -
used to treat cloth, leather or wood materials. Tannic
acid, for example, could be applied to leather.
Hydrofluoric acid can be used to etch glass by spraying a
uniform coating of the acid on exposed portions of a glass
surface. ~ ~
The applicator of the present invention can also
be used to distribute bleach or other chemical solutions
uniformly onto washer drums, deckers, flumes, or
conveyors. Such applications would be especially helpful
where accurate amounts of the liquid are to be applied
evenly across an expanse.
Ceramics may also be made by mixing liquid epoxy
resin with solid particles in separate co-flowing streams.
Thin ceramic coatings may be applied to a substrate in
this manner. Elevated epoxy temperatures could be used to
fuse the mixed co-flowing epoxy and particulate streams.
Having illustrated and described the principles
of the invention in many preferred embodiments, it should
be apparent to those skilled in the art that the invention
can be modified in arrangement and detail without
departing from such principles. We claim all
modifications coming within the spirit and scope of the
following claims.
