Note: Descriptions are shown in the official language in which they were submitted.
CA 02205659 1997-OS-21
WO 96/15857 PCTlCA95100658
COATING OF WAX-LIKE MATERIALS ONTO MOVING STRIP
ARTICLES
TECHNICAL FIELD
This invention relates to the coating of strip
articles with wax-like m<~.terials. More particularly,
the invention relates to a coating procedure that is
particularly suited for coating aluminum and aluminum
alloy strips, such as those used for automotive sheet
stock, with wax-type lubricants.
BACKGROUND ART
The use of aluminum and aluminum alloys in the
manufacture of vehicle bodies and other automotive parts
is of increasing interesi~ nowadays as manufactures and
regulators strive to reduce fuel consumption and air
pollution. This has lead to the use of adhesives for
bonding aluminum parts s:~nce welding of aluminum is
problematic and inefficient. However, conventional
lubricants used for coating sheet surfaces during sheet
manufacture tend not to be compatible with the adhesives
suitable for the bonding process and new lubricants have
been developed to overcome this problem. These new
lubricants usually have t:he properties of waxes, i.e.
they are solid at room temperature but melt to low
viscosity liquids (e. g. _~~iquids of viscosity less than
50 centipoise, and often less than 30 centipoise) at
slightly higher temperatures (e. g. 30 to 100C, or more
commonly 30-50C, depend~:ng on the identity and
formulation of the lubri<:ant) .
At present, a heated roller coater is normally used
to apply such lubricants, but inefficiencies are
encountered because the distribution of the coating
material across the strip surface becomes variable due
to the tendency of the low viscosity lubricant to flow
in irregular patterns over the metal surface following
its initial application.
Moreover, sufficient: heat is transferred to the
metal sheet by the coater during the coating process
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2
that solidification of the lubricant is delayed. Unless
special precautions are taken, e.g. the installation of
a separate cooling zone downstream of the coater
apparatus, the lubricant may still be in a molten state
when the sheet reaches the toiler apparatus provided for
coiling the strip article after coating. If the
lubricant is still molten while the strip is being
coiled, the coiling pressure exerted on the strip
surface will cause unacceptable thinning of the
lubricant film, with excess material being forced out
through the sides of the coil. Additionally, the very
low strip surface friction can cause the coil to become
unstable and to "telescope" during the coiling
operation.
There is accordingly a need for an improved method
of coating metal sheet with wax-like materials of this
kind.
DISCLOSURE OF THE INVENTION
An object of the invention is to enable metal sheet
articles to be coated with wax-like coating materials,
particularly lubricants, in an efficient manner.
Another object of the invention is to enable wax-
like coating materials, particularly lubricants, to be
coated in relatively thick layers onto sheet articles.
Yet another object of the invention is to make it
possible to avoid forced cooling of a strip article
after coating with a wax-like coating materials,
particularly lubricant, prior to coiling without
substantial risk of disrupting the coating layer and of
destabilizing the shape of the coil as it is being
formed, during coiling.
According to the present invention, there is
provided a process of forming a coating layer of a solid
wax-like coating material on a surface of a heat-
conductive strip article, in which the solid wax-like
coating material is heated to form a melt, and a coating
layer is formed on an advancing surface of the strip
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WO 96/15857 PCT/CA95/00658
3
article by applying the vmelt onto the surface and
cooling the melt to form a solid coating layer,
characterized in that th~~ melt is flowed onto the
advancing surface from a:n elongated, open-sided slot of
a movable coating head provided with an extended surface
adjacent to the slot orientated at an angle to the strip
article to define a coating gap converging in the
direction of advancement of the strip article, and
pushing the coating head towards the surface of the
strip article, against o~?posing hydrodynamic forces
exerted by said coating material on said extended
surface in said gap, as ;paid melt is flowed onto the
surface from the slot, to control the coating layer
thickness.
The present invention is based on the unexpected
finding that wax-like coating materials, and
particularly wax-like lubricants used in the automotive
and related industries, can be applied by means of a
coating apparatus provided with a "floating" coating
2o head having an elongated open-sided coating slot. The
success of this procedure' is surprising because coating
apparatus of this kind, while known for other
applications, has not been considered suitable for
coating low viscosity liquids since undue leakage of
such liquids takes place and uniform coating layers are
not formed. Furthermore, fluids of low viscosity do not
usually generate sufficient hydrodynamic force to
prevent the coating head from undergoing metal-metal
contact with the moving e;trip surface. However, in the
process of the present invention, it seems that partial
solidification of the ways:-like coating material takes
. place in the coating gap in a sufficiently reliable
manner such that effective coating can be achieved
despite the initial low viscosity of the coating
material.
Another consideraticn is that, since unacceptably
long solidification times are required in conventional
CA 02205659 1997-OS-21
WO 96/15857 PCT/CA95/00658
4
coating apparatus used for producing wax-like coatings,
it was to be expected that similar problems would be
encountered if slot-type coaters were employed for this
purpose. However, it has surprisingly turned out that
"floating head" type apparatus allows coatings to be
formed that solidify quickly, perhaps because the hot
coating head does not directly contact the strip
article, and thus does not result in undue heating of
the strip.
A preferred example of the type of apparatus used
for the process of the present invention suitable for
single-sided coating of a strip article is disclosed in
U.S. Patent No. 4,675,230 of June 23, 1987, assigned to
the same assignee as the present application. Moreover,
a related apparatus for two-sided coating of sheet
material is disclosed in pending PCT Patent Application
Serial No. PCT/CA94/0029, filed May 26, 1994 and
published on December 8, 1994 as WO 94/27739, and
assigned to the same assignee as the present
application.
The process of the present invention is effective
for coating any strip article made of a material of
sufficiently good thermal conductivity that heat from
the wax-like coating can be rapidly dispersed and the
liquid coating thereby rapidly solidified. While the
minimum thermal conductivity that will achieve this
result varies according to a number of factors (e.g. the
characteristics and temperature of the coating material,
the speed of advance of the strip article, etc.), common
metals, and particularly aluminum and aluminum alloys,
are suitable for coating according to the process of the
present invention.
Numerous "wax-like coating materials" are suitable
for use in the present invention, but wax-type
lubricants are particularly preferred. These materials,
while being solid at room or ambient temperature, form
liquids having low viscosities, generally of less than
CA 02205659 1997-OS-21
WO 96/15857 PCT/CA95100658
50 centipoise, and more commonly less than 30
centipoise, when heated t:o temperatures in the range of
30-100C, or more usuall~~ 30-50C. Waxy materials
containing olefin, e.g. alcohol esters of fatty acids or
5 fatty diamides, are especially suited for use in the
present invention, and particular examples of suitable
wax-type lubricants include the following: glycerol
monolaurate, pentaerythri.tol monostearate, ethylene
glycol monolaurate, glycerol monopalmitate, ethylene
l0 glycol monostearate, glycerol dipalmitate and propylene
glycol distearate.
Since rapid cooling and solidification of the
coating material during a.nd immediately following
coating is necessary in the present invention, it is
preferable prior to coating to heat the wax-like coating
material only to the lowest temperature possible without
risking premature freezing of the material in the
coating apparatus. Temperatures of 30-100C and more
preferably 3o-50C, are generally suitable.
As noted above, the coating layer must be solid
before the strip article can be coiled, so the strip
should preferably be advanced at a speed that permits
solidification to take place before the coating reaches
the coiling apparatus and, for a given strip article and
coating material, this will vary according to the
distance between the coating apparatus and the coiling
apparatus. Clearly, the :best productivity will be
achieved by advancing the strip at or close to the
maximum speed that permits complete solidification in
advance of the coiling apparatus, but lower speeds of
advance may be employed, :if desired, provided an even,
smooth coating layer can ;still be produced. The minimum
speed at which suitable coating is still possible
depends on such factors a:a the size of the coating gap,
the nature of the strip article and the identity of the
coating material. Suitab:Le speeds can be determined by
simple trial and experiment.
CA 02205659 1997-OS-21
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6
The strip article itself should preferably be
relatively cool when the coating is applied to ensure
rapid solidification of the coating. However, pre-
cooling of the strip article is generally not required
since strip at ambient temperature is usually suitable.
By applying the wax-like coating material in the
manner indicated in the present invention, rapid and
effective coating of wax-like coating materials, and
particularly wax-type lubricants, can be achieved
without the disadvantages encountered when using
conventional apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevation, partly in cross-
section, of a coating apparatus suitable for carrying
out a preferred embodiment of the present invention;
Fig. 2 is a greatly simplified schematic
representation of apparatus for carrying out two-sided
coating according to another preferred embodiment of the
invention;
Fig. 3 is a graph showing test results obtained in
the manner explained in the Example 1; and
Fig. 4 is a graph showing test results obtained in
the manner explained in Example 2.
BEST MODES FOR CARRYING OUT THE INVENTION
Apparatus suitable for carrying out one preferred
embodiment of the present invention is shown in
simplified form in Fig. 1. The apparatus 10 consists of
a coating head 12 of the type described in U.S. patent
4,675,230, but modified in the manner described below,
that applies a layer of wax type lubricant 13 onto an
aluminum strip 14 passed around an unheated backup drum
16 in the direction of arrow A. The coating head 12,
having a generally open-sided co-extensive longitudinal
coating slot 15, extends over the entire width of the
strip at a position, in the path of the strip advance,
at which the strip is held firmly against the surface of
the backup drum 16. The end of the coating head 12
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7
facing the strip 14 has an extended coating surface 18,
adjacent to the outer opening of the slot 15 at least on
the downstream side of the slot, provided with a
downstream edge 20. The extended surface 18 is arranged
at an angle (normally in the range of 0.1 to 5, or more
preferably 0.5 to 1) to the surface of the strip 14 to
form a coating gap 19 that narrows in the direction of
strip advance.
The coating head 12 has an interior channel 22
l0 communicating with the coating slot 15. This channel is
fed with molten wax-like coating material by a heated
pressure hose 24 communicating with a pressurized
reservoir 25. The reservoir contains coating material
13 that is kept molten by heat input from a surrounding
hot water jacket 26, through which hot water is
constantly passed via inlet 26a and outlet 26b. The
reservoir is pressurized :by compressed air introduced
through inlet 27 at the upper part of the reservoir.
The internal channel 22 i:n the coating head contains an
elongated rod-like electrical heater 28 used to prevent
freezing of the coating m~~terial within the coating
head. The pressure applied to the coating material
within the reservoir 25 i;s sufficient to express the
molten coating material from the slot 15 onto the
surface of the strip 14 where the extended surface 18 of
the coating head adjacent to the slot spreads the
coating material and metesrs its thickness.
The coating head 12 forms part of, or is attached
to, a metal block 32 supported on a deck 34 having a
flat upper surface on which the metal block 32 rests,
the block being thus supported for sliding movement
relative to the deck in a generally horizontal
direction, as shown by double headed arrow B. A number
of vertically opening slogs 36 (only one of which is
s
shown in Fig. 1), elongated horizontally in the
direction of arrow B, are formed in the body of the
block 32 rearwardly of the: channel 22 at locations
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8
spaced along the length of the block. A number of bolts
38 (only one of which is shown) respectively extend
through these slots and are threaded in the deck at one
end while having enlarged bolt heads 38a at the other
end to retain the block 32, on the deck 34. Interference
between bolt shanks 38b and the side walls of the slots
36 prevents lateral movement of the block 32 relative to
the deck, but the elongation of the slots permits the
block 32 to move in the direction of arrow B through the
full range of operative head positions.
The deck 34 is mounted on a feed frame 40 for
pivotal movement about a horizontal axis 42, so as to
enable the block 32, with the deck, to be swung upwardly
(e.g. by suitable pneumatic means, not shown) from the
position illustrated in Fig. 1 to a position removed
from the path of strip advance. An arm 44, fixedly
secured to the frame 40 and underlying the deck 34,
carries a screw 46 that projects upwardly from the arm
and bears against the lower surface of the deck 34, to
enable adjustment of the angular orientation of the head
12 in its operative position.
The frame 40 is fixed in position relative to the
axis of the drum 16, both the frame and the roll being
mounted in a common support structure (not shown).
Thus, the axis 42 is fixed in position relative to the
axis of the drum 16 and when the deck 34 is in the
operative position shown in Fig. 2, with the screw 46
set to provide a desired angular orientation, the drum
16 supports the advancing strip 14, opposite the slot
15, at a fixed distance from the deck 34.
The apparatus further includes means acting between
the deck 34 and the head 12 for continuously exerting a
load on the head to urge the head toward the facing
surface of the strip 14. This load-exerting means
comprises a number of air cylinders 17 (only one of
which is shown and which may be of generally
conventional construction) fixed securely to the deck 34
CA 02205659 1997-OS-21
_ 9
rearwardly of the block 32. As shown, the cvlir_de-rs
are secured to the rearwardly projecting ledge cor dons
50 of tre dec'.~c. Actuation of the cylinders ;wri~cr :na~~
be of a gene=-ally conventional character) CauSeS c~°_
block 32 and coating head 12 to be pushed towards ~i:e
surface of the strip 14. This load is opposed by ~~s
fluid pressu-a (hvdrodyna:~nic force) of the molten (or
partially solidifying) coating material 13 acting c__ the
extended surface i8 so that the head 12 "floats" on c__e
material layer 13. There:oy, a metering orifice is
defined between the downstream edge 20 of the surface .8
and the strip surface, th~~ size of the metering or-lice
being determined (for a given coating material) by the
magnitude of the load exerted by the cylir_ders, which .s
5 generally 0.18 - 27 kg/cm (1-150 lbs./linear inch) o~
strip width and more preferably 0.9 - 9 kg/cm
(5-50 lbs./linear inch). No direct mechanical con~ac~
takes place between the coating head 12 and the strip
14, so heat transfer to and defacement of the surface of
the strip is avoided.
Surprisingly, it has been found that the wax-=ike
coating material, although of low viscosity normaliy-in
the range of less than 50 centipoise, e.g. 20 to 30
centipoise, can be succes:~fully coated onto the metal
strip using the indicated type of apparatus in which the
coating thickness is controlled by a dynamic load
control mechanism. In principle, while this type of
coating apparatus can be used to apply any liquid to a
strip article, in practice. the equipment is not
3.0 effective for liquids of low viscosity. The coating gap
19 between the extruder head and the strip article for a
particular coating material is selected according to
viscosity, speed and the required coating thickness to
ensure that the generated forces are in a practical
range for control. For vE:ry low viscosity liquids, low
speeds and thick coating layers, the required gap width
becomes too wide to be practical. However, '.ve have
AMENDED St~EET
CA 02205659 1997-OS-21
WO 96/15857 PCT/CA95/00658
surprisingly found that the equipment is suitable for
applying low viscosity molten wax-like materials. It is
theorized that, because no part of the heated extruder
head 12 directly touches the strip article 14, the strip
5 article does not become unduly heated above ambient
temperature before it receives the layer of molten wax-
like material and, because of the high thermal
conductivity of the metal sheet article (particularly
when it is made of aluminum or aluminum alloy) and the
10 relative thinness of the layer of coating material, the
coating material commences to freeze immediately it
contacts the strip article within the coating gap
between the article surface and the coating head. This
increases the effective viscosity of the coating
sufficiently to make the coating equipment effective and
to allow relatively thick layers of the low viscosity
lubricant (e.g. thicknesses with the range of 1-100
microns, and more preferably 2-25 microns) to be applied
at relatively low coating speeds (e. g. about 15 m/min
(50 ft/min)). In practice the lubricant is usually
found to be completely solid within a few feet of the
coating head.
By heating each of the reservoir 25, the pressure
hose 24 and the coating head 12 (by heater 28), the
coating material 13 can be kept in molten condition
within the viscosity range indicated above until applied
as a coating to the strip 14.
Beyond the drum 16, the strip can cool the molten
wax-like material rapidly below its freezing point since
it has not been unduly heated by the coating procedure
so the strip can be coiled in the conventional manner
without the need for a separate cooling step.
Although the illustrated apparatus is designed for
single-sided coating, the invention may also be utilized
for two-sided coating using apparatus of the type
disclosed in the application mentioned above, modified
to be fed with molten wax-like coating material as in
CA 02205659 1997-OS-21
WO 96115857 PCTlCA95I00658
11
the apparatus described for single-sided coating.
An example of an apparatus suitable for double-
sided coating is shown in. Fig. 2. Metal strip 14 to be
coated is continuously advanced, in a direction
longitudinally parallel to its long dimension, from a
coil 200 along a path represented by arrows A extending
successively around spaced guide rollers 201, 202, 203
rotatably supported (by structure not shown) in axially
fixed positions. The rollers 201 and 202 cooperatively
define a rectilinear portion 205 of the path, in which
portion the major surfaces of the advancing strip are
substantially planar. At a locality in this path
portion 205, coating material is applied to both major
surfaces 206 and 207 of the strip 14 from two coating
heads 12, 12' (disposed in register with each other and
respectively facing the two major surfaces of the strip
article) to establish on each of the strip surfaces a
continuous layer or coating of the wax-like material.
After passing roll 203, the coated strip is coiled
again, e.g. on a driven rewind reel 208 which
constitutes the means for advancing the strip through
the coating line.
The coating devices 12 and 12' may each be the same
as the coating head 12 described for the previous
embodiment fed with coating material and pushed towards
the strip surfaces in the same way.
In this embodiment, molten coating material is
applied simultaneously to both sides of the strip at
about the same point, but nevertheless freezing of the
applied coating takes place within the coating gaps and
thick layers of lubricant can be applied to both sides
of the strip 14.
As a final point, it should be pointed out that the
process of the invention is not limited to the coating
of wax-type lubricants onto automotive strip stock, but
CA 02205659 2000-02-04
12
may be used for similar applications in which a wax-like
material is coated onto a strip article, e.g. the
coating of aluminum can end stock with protective
layers.
The invention is illustrated further by the
following Examples, which are not intended to limit the
scope of the invention.
EXAMPLE 1
Tests were carried out on 0.09 cm (0.036 inch)
l0 gauge autosheet (aluminum alloy) using a thirty inch two
side coating apparatus of the type illustrated herein
(provided with five load application cylinders 17) using
AL070* wax-type lubricant (ethylene glycol monolaurate
having a melting point of about 35 to 37°C) applied at a
I5 temperature of 44°C. The coating material was supplied
to the coating heads at a pressure of 34.5 kPa (5 pounds
per square inch) and the coating heads were pushed
towards the strip surface at an average force of
6.25 kg/cm (35 pounds per lineal inch) of strip width.
20 The test results are illustrated in the graph of Fig. 3
showing coating thickness distribution on the top and
bottom surfaces of the sheet (when the sheet is advanced
horizontally from the apparatus) across the width of the
sheet. The vertical arrows iwthe graph show the
25 positions of five loading air cylinders, which were set
respectively at pressures of 0, 138, 138, 138 and 0 kPa
(0, 20, 20, 20 and 0 pounds per square inch) of air
pressure. The speed of strip movement was
m/min (50 ft./min), the metering land width was
30 0.8 cm (0.3 inches) and the angle of the coating head
was 0.5 degrees. Under these conditions, the film
weight calculated theoretically for a coating liquid
having a viscosity of 30 centipoise is about 0.1
gram/square meter. The fact that the actual thickness
35 of the coating ranged from 1 to 3.5 gram/square meter
shows that the invention is capable of producing films
of greater than theoretical thickness. The coatings
*TRADE-MARK
CA 02205659 1997-OS-21
WO 96/15857 PCT/CA95/00658
13
thereby produced are believed to be of acceptable
thickness and uniformity for use in automative
applications.
EXAMPLE 2
Strip coating was c~~rried out on 0.03 cm
(0.011 inch) gauge aluminum can stock using a two sided
coating apparatus having a coating head 30 cm
(12 inches) in width (the: coating width being 29 cm
(11.5 inches)). Again waxy lubricant AL070 was used,
but this time at an application temperature of 51C.
Two load application cylinders were provided per coating
head, one at each end, having a cylinder inside diameter
of 3.8 cm (1.5 inch), and. each was pressurized with air
to a pressure of 310 kPa (45 pounds per square inch).
The average load on each coating head resulting from the
cylinders was 2.5 kg/lineal cm (13.9 pounds/lineal inch)
of strip width. Each coating head had a land width of
0.63 cm (0.25 inches) was set at an angle of 0.5 degrees
to the strip surface. The coating material was supplied
to each coating head at 24 kPa (3.5 pounds/sq. inch
pressure) and the strip was advanced at 15 m per minute
(50 feet per minute). The results are shown in the
graph of Fig. 4. The coatings thereby produced are
believed to be of acceptable thickness and uniformity
for use in automotive applications. The coatings
thereby produced are believed to be of acceptable
thickness and uniformity for use in automotive
applications.
CA 02205659 1997-OS-21
WO 96/15857 PCTlCA95100658
COATING OF WAX-LIKE MATERIALS ONTO MOVING STRIP
ARTICLES
TECHNICAL FIELD
This invention relates to the coating of strip
articles with wax-like m<~.terials. More particularly,
the invention relates to a coating procedure that is
particularly suited for coating aluminum and aluminum
alloy strips, such as those used for automotive sheet
stock, with wax-type lubricants.
BACKGROUND ART
The use of aluminum and aluminum alloys in the
manufacture of vehicle bodies and other automotive parts
is of increasing interesi~ nowadays as manufactures and
regulators strive to reduce fuel consumption and air
pollution. This has lead to the use of adhesives for
bonding aluminum parts s:~nce welding of aluminum is
problematic and inefficient. However, conventional
lubricants used for coating sheet surfaces during sheet
manufacture tend not to be compatible with the adhesives
suitable for the bonding process and new lubricants have
been developed to overcome this problem. These new
lubricants usually have t:he properties of waxes, i.e.
they are solid at room temperature but melt to low
viscosity liquids (e. g. _~~iquids of viscosity less than
50 centipoise, and often less than 30 centipoise) at
slightly higher temperatures (e. g. 30 to 100C, or more
commonly 30-50C, depend~:ng on the identity and
formulation of the lubri<:ant) .
At present, a heated roller coater is normally used
to apply such lubricants, but inefficiencies are
encountered because the distribution of the coating
material across the strip surface becomes variable due
to the tendency of the low viscosity lubricant to flow
in irregular patterns over the metal surface following
its initial application.
Moreover, sufficient: heat is transferred to the
metal sheet by the coater during the coating process
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2
that solidification of the lubricant is delayed. Unless
special precautions are taken, e.g. the installation of
a separate cooling zone downstream of the coater
apparatus, the lubricant may still be in a molten state
when the sheet reaches the toiler apparatus provided for
coiling the strip article after coating. If the
lubricant is still molten while the strip is being
coiled, the coiling pressure exerted on the strip
surface will cause unacceptable thinning of the
lubricant film, with excess material being forced out
through the sides of the coil. Additionally, the very
low strip surface friction can cause the coil to become
unstable and to "telescope" during the coiling
operation.
There is accordingly a need for an improved method
of coating metal sheet with wax-like materials of this
kind.
DISCLOSURE OF THE INVENTION
An object of the invention is to enable metal sheet
articles to be coated with wax-like coating materials,
particularly lubricants, in an efficient manner.
Another object of the invention is to enable wax-
like coating materials, particularly lubricants, to be
coated in relatively thick layers onto sheet articles.
Yet another object of the invention is to make it
possible to avoid forced cooling of a strip article
after coating with a wax-like coating materials,
particularly lubricant, prior to coiling without
substantial risk of disrupting the coating layer and of
destabilizing the shape of the coil as it is being
formed, during coiling.
According to the present invention, there is
provided a process of forming a coating layer of a solid
wax-like coating material on a surface of a heat-
conductive strip article, in which the solid wax-like
coating material is heated to form a melt, and a coating
layer is formed on an advancing surface of the strip
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3
article by applying the vmelt onto the surface and
cooling the melt to form a solid coating layer,
characterized in that th~~ melt is flowed onto the
advancing surface from a:n elongated, open-sided slot of
a movable coating head provided with an extended surface
adjacent to the slot orientated at an angle to the strip
article to define a coating gap converging in the
direction of advancement of the strip article, and
pushing the coating head towards the surface of the
strip article, against o~?posing hydrodynamic forces
exerted by said coating material on said extended
surface in said gap, as ;paid melt is flowed onto the
surface from the slot, to control the coating layer
thickness.
The present invention is based on the unexpected
finding that wax-like coating materials, and
particularly wax-like lubricants used in the automotive
and related industries, can be applied by means of a
coating apparatus provided with a "floating" coating
2o head having an elongated open-sided coating slot. The
success of this procedure' is surprising because coating
apparatus of this kind, while known for other
applications, has not been considered suitable for
coating low viscosity liquids since undue leakage of
such liquids takes place and uniform coating layers are
not formed. Furthermore, fluids of low viscosity do not
usually generate sufficient hydrodynamic force to
prevent the coating head from undergoing metal-metal
contact with the moving e;trip surface. However, in the
process of the present invention, it seems that partial
solidification of the ways:-like coating material takes
. place in the coating gap in a sufficiently reliable
manner such that effective coating can be achieved
despite the initial low viscosity of the coating
material.
Another consideraticn is that, since unacceptably
long solidification times are required in conventional
CA 02205659 1997-OS-21
WO 96/15857 PCT/CA95/00658
4
coating apparatus used for producing wax-like coatings,
it was to be expected that similar problems would be
encountered if slot-type coaters were employed for this
purpose. However, it has surprisingly turned out that
"floating head" type apparatus allows coatings to be
formed that solidify quickly, perhaps because the hot
coating head does not directly contact the strip
article, and thus does not result in undue heating of
the strip.
A preferred example of the type of apparatus used
for the process of the present invention suitable for
single-sided coating of a strip article is disclosed in
U.S. Patent No. 4,675,230 of June 23, 1987, assigned to
the same assignee as the present application. Moreover,
a related apparatus for two-sided coating of sheet
material is disclosed in pending PCT Patent Application
Serial No. PCT/CA94/0029, filed May 26, 1994 and
published on December 8, 1994 as WO 94/27739, and
assigned to the same assignee as the present
application.
The process of the present invention is effective
for coating any strip article made of a material of
sufficiently good thermal conductivity that heat from
the wax-like coating can be rapidly dispersed and the
liquid coating thereby rapidly solidified. While the
minimum thermal conductivity that will achieve this
result varies according to a number of factors (e.g. the
characteristics and temperature of the coating material,
the speed of advance of the strip article, etc.), common
metals, and particularly aluminum and aluminum alloys,
are suitable for coating according to the process of the
present invention.
Numerous "wax-like coating materials" are suitable
for use in the present invention, but wax-type
lubricants are particularly preferred. These materials,
while being solid at room or ambient temperature, form
liquids having low viscosities, generally of less than
CA 02205659 1997-OS-21
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50 centipoise, and more commonly less than 30
centipoise, when heated t:o temperatures in the range of
30-100C, or more usuall~~ 30-50C. Waxy materials
containing olefin, e.g. alcohol esters of fatty acids or
5 fatty diamides, are especially suited for use in the
present invention, and particular examples of suitable
wax-type lubricants include the following: glycerol
monolaurate, pentaerythri.tol monostearate, ethylene
glycol monolaurate, glycerol monopalmitate, ethylene
l0 glycol monostearate, glycerol dipalmitate and propylene
glycol distearate.
Since rapid cooling and solidification of the
coating material during a.nd immediately following
coating is necessary in the present invention, it is
preferable prior to coating to heat the wax-like coating
material only to the lowest temperature possible without
risking premature freezing of the material in the
coating apparatus. Temperatures of 30-100C and more
preferably 3o-50C, are generally suitable.
As noted above, the coating layer must be solid
before the strip article can be coiled, so the strip
should preferably be advanced at a speed that permits
solidification to take place before the coating reaches
the coiling apparatus and, for a given strip article and
coating material, this will vary according to the
distance between the coating apparatus and the coiling
apparatus. Clearly, the :best productivity will be
achieved by advancing the strip at or close to the
maximum speed that permits complete solidification in
advance of the coiling apparatus, but lower speeds of
advance may be employed, :if desired, provided an even,
smooth coating layer can ;still be produced. The minimum
speed at which suitable coating is still possible
depends on such factors a:a the size of the coating gap,
the nature of the strip article and the identity of the
coating material. Suitab:Le speeds can be determined by
simple trial and experiment.
CA 02205659 1997-OS-21
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6
The strip article itself should preferably be
relatively cool when the coating is applied to ensure
rapid solidification of the coating. However, pre-
cooling of the strip article is generally not required
since strip at ambient temperature is usually suitable.
By applying the wax-like coating material in the
manner indicated in the present invention, rapid and
effective coating of wax-like coating materials, and
particularly wax-type lubricants, can be achieved
without the disadvantages encountered when using
conventional apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side elevation, partly in cross-
section, of a coating apparatus suitable for carrying
out a preferred embodiment of the present invention;
Fig. 2 is a greatly simplified schematic
representation of apparatus for carrying out two-sided
coating according to another preferred embodiment of the
invention;
Fig. 3 is a graph showing test results obtained in
the manner explained in the Example 1; and
Fig. 4 is a graph showing test results obtained in
the manner explained in Example 2.
BEST MODES FOR CARRYING OUT THE INVENTION
Apparatus suitable for carrying out one preferred
embodiment of the present invention is shown in
simplified form in Fig. 1. The apparatus 10 consists of
a coating head 12 of the type described in U.S. patent
4,675,230, but modified in the manner described below,
that applies a layer of wax type lubricant 13 onto an
aluminum strip 14 passed around an unheated backup drum
16 in the direction of arrow A. The coating head 12,
having a generally open-sided co-extensive longitudinal
coating slot 15, extends over the entire width of the
strip at a position, in the path of the strip advance,
at which the strip is held firmly against the surface of
the backup drum 16. The end of the coating head 12
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7
facing the strip 14 has an extended coating surface 18,
adjacent to the outer opening of the slot 15 at least on
the downstream side of the slot, provided with a
downstream edge 20. The extended surface 18 is arranged
at an angle (normally in the range of 0.1 to 5, or more
preferably 0.5 to 1) to the surface of the strip 14 to
form a coating gap 19 that narrows in the direction of
strip advance.
The coating head 12 has an interior channel 22
l0 communicating with the coating slot 15. This channel is
fed with molten wax-like coating material by a heated
pressure hose 24 communicating with a pressurized
reservoir 25. The reservoir contains coating material
13 that is kept molten by heat input from a surrounding
hot water jacket 26, through which hot water is
constantly passed via inlet 26a and outlet 26b. The
reservoir is pressurized :by compressed air introduced
through inlet 27 at the upper part of the reservoir.
The internal channel 22 i:n the coating head contains an
elongated rod-like electrical heater 28 used to prevent
freezing of the coating m~~terial within the coating
head. The pressure applied to the coating material
within the reservoir 25 i;s sufficient to express the
molten coating material from the slot 15 onto the
surface of the strip 14 where the extended surface 18 of
the coating head adjacent to the slot spreads the
coating material and metesrs its thickness.
The coating head 12 forms part of, or is attached
to, a metal block 32 supported on a deck 34 having a
flat upper surface on which the metal block 32 rests,
the block being thus supported for sliding movement
relative to the deck in a generally horizontal
direction, as shown by double headed arrow B. A number
of vertically opening slogs 36 (only one of which is
s
shown in Fig. 1), elongated horizontally in the
direction of arrow B, are formed in the body of the
block 32 rearwardly of the: channel 22 at locations
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8
spaced along the length of the block. A number of bolts
38 (only one of which is shown) respectively extend
through these slots and are threaded in the deck at one
end while having enlarged bolt heads 38a at the other
end to retain the block 32, on the deck 34. Interference
between bolt shanks 38b and the side walls of the slots
36 prevents lateral movement of the block 32 relative to
the deck, but the elongation of the slots permits the
block 32 to move in the direction of arrow B through the
full range of operative head positions.
The deck 34 is mounted on a feed frame 40 for
pivotal movement about a horizontal axis 42, so as to
enable the block 32, with the deck, to be swung upwardly
(e.g. by suitable pneumatic means, not shown) from the
position illustrated in Fig. 1 to a position removed
from the path of strip advance. An arm 44, fixedly
secured to the frame 40 and underlying the deck 34,
carries a screw 46 that projects upwardly from the arm
and bears against the lower surface of the deck 34, to
enable adjustment of the angular orientation of the head
12 in its operative position.
The frame 40 is fixed in position relative to the
axis of the drum 16, both the frame and the roll being
mounted in a common support structure (not shown).
Thus, the axis 42 is fixed in position relative to the
axis of the drum 16 and when the deck 34 is in the
operative position shown in Fig. 2, with the screw 46
set to provide a desired angular orientation, the drum
16 supports the advancing strip 14, opposite the slot
15, at a fixed distance from the deck 34.
The apparatus further includes means acting between
the deck 34 and the head 12 for continuously exerting a
load on the head to urge the head toward the facing
surface of the strip 14. This load-exerting means
comprises a number of air cylinders 17 (only one of
which is shown and which may be of generally
conventional construction) fixed securely to the deck 34
CA 02205659 1997-OS-21
_ 9
rearwardly of the block 32. As shown, the cvlir_de-rs
are secured to the rearwardly projecting ledge cor dons
50 of tre dec'.~c. Actuation of the cylinders ;wri~cr :na~~
be of a gene=-ally conventional character) CauSeS c~°_
block 32 and coating head 12 to be pushed towards ~i:e
surface of the strip 14. This load is opposed by ~~s
fluid pressu-a (hvdrodyna:~nic force) of the molten (or
partially solidifying) coating material 13 acting c__ the
extended surface i8 so that the head 12 "floats" on c__e
material layer 13. There:oy, a metering orifice is
defined between the downstream edge 20 of the surface .8
and the strip surface, th~~ size of the metering or-lice
being determined (for a given coating material) by the
magnitude of the load exerted by the cylir_ders, which .s
5 generally 0.18 - 27 kg/cm (1-150 lbs./linear inch) o~
strip width and more preferably 0.9 - 9 kg/cm
(5-50 lbs./linear inch). No direct mechanical con~ac~
takes place between the coating head 12 and the strip
14, so heat transfer to and defacement of the surface of
the strip is avoided.
Surprisingly, it has been found that the wax-=ike
coating material, although of low viscosity normaliy-in
the range of less than 50 centipoise, e.g. 20 to 30
centipoise, can be succes:~fully coated onto the metal
strip using the indicated type of apparatus in which the
coating thickness is controlled by a dynamic load
control mechanism. In principle, while this type of
coating apparatus can be used to apply any liquid to a
strip article, in practice. the equipment is not
3.0 effective for liquids of low viscosity. The coating gap
19 between the extruder head and the strip article for a
particular coating material is selected according to
viscosity, speed and the required coating thickness to
ensure that the generated forces are in a practical
range for control. For vE:ry low viscosity liquids, low
speeds and thick coating layers, the required gap width
becomes too wide to be practical. However, '.ve have
AMENDED St~EET
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surprisingly found that the equipment is suitable for
applying low viscosity molten wax-like materials. It is
theorized that, because no part of the heated extruder
head 12 directly touches the strip article 14, the strip
5 article does not become unduly heated above ambient
temperature before it receives the layer of molten wax-
like material and, because of the high thermal
conductivity of the metal sheet article (particularly
when it is made of aluminum or aluminum alloy) and the
10 relative thinness of the layer of coating material, the
coating material commences to freeze immediately it
contacts the strip article within the coating gap
between the article surface and the coating head. This
increases the effective viscosity of the coating
sufficiently to make the coating equipment effective and
to allow relatively thick layers of the low viscosity
lubricant (e.g. thicknesses with the range of 1-100
microns, and more preferably 2-25 microns) to be applied
at relatively low coating speeds (e. g. about 15 m/min
(50 ft/min)). In practice the lubricant is usually
found to be completely solid within a few feet of the
coating head.
By heating each of the reservoir 25, the pressure
hose 24 and the coating head 12 (by heater 28), the
coating material 13 can be kept in molten condition
within the viscosity range indicated above until applied
as a coating to the strip 14.
Beyond the drum 16, the strip can cool the molten
wax-like material rapidly below its freezing point since
it has not been unduly heated by the coating procedure
so the strip can be coiled in the conventional manner
without the need for a separate cooling step.
Although the illustrated apparatus is designed for
single-sided coating, the invention may also be utilized
for two-sided coating using apparatus of the type
disclosed in the application mentioned above, modified
to be fed with molten wax-like coating material as in
CA 02205659 1997-OS-21
WO 96115857 PCTlCA95I00658
11
the apparatus described for single-sided coating.
An example of an apparatus suitable for double-
sided coating is shown in. Fig. 2. Metal strip 14 to be
coated is continuously advanced, in a direction
longitudinally parallel to its long dimension, from a
coil 200 along a path represented by arrows A extending
successively around spaced guide rollers 201, 202, 203
rotatably supported (by structure not shown) in axially
fixed positions. The rollers 201 and 202 cooperatively
define a rectilinear portion 205 of the path, in which
portion the major surfaces of the advancing strip are
substantially planar. At a locality in this path
portion 205, coating material is applied to both major
surfaces 206 and 207 of the strip 14 from two coating
heads 12, 12' (disposed in register with each other and
respectively facing the two major surfaces of the strip
article) to establish on each of the strip surfaces a
continuous layer or coating of the wax-like material.
After passing roll 203, the coated strip is coiled
again, e.g. on a driven rewind reel 208 which
constitutes the means for advancing the strip through
the coating line.
The coating devices 12 and 12' may each be the same
as the coating head 12 described for the previous
embodiment fed with coating material and pushed towards
the strip surfaces in the same way.
In this embodiment, molten coating material is
applied simultaneously to both sides of the strip at
about the same point, but nevertheless freezing of the
applied coating takes place within the coating gaps and
thick layers of lubricant can be applied to both sides
of the strip 14.
As a final point, it should be pointed out that the
process of the invention is not limited to the coating
of wax-type lubricants onto automotive strip stock, but
CA 02205659 1997-OS-21
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12
may be used for similar applications in which a wax-like
material is coated onto a strip article, e.g. the
coating of aluminum can end stock with protective
layers.
The invention is illustrated further by the
following Examples, which are not intended to limit the
scope of the invention.
EXAMPLE 1
Tests were carried out on 0.09 cm (0.036 inch)
gauge autosheet (aluminum alloy) using a thirty inch two
side coating apparatus of the type illustrated herein
(provided with five load application cylinders 17) using
AL070 wax-type lubricant (ethylene glycol monolaurate
having a melting point of about 35 to 37°C) applied at a
temperature of 44°C. The coating material was supplied
to the coating heads at a pressure of 34.5 kPa (5 pounds
per square inch) and the coating heads were pushed
towards the strip surface at an average force of
6.25 kg/cm (35 pounds per lineal inch) of strip width.
The test results are illustrated in the graph of Fig. 3
showing coating thickness distribution on the top and
bottom surfaces of the sheet (when the sheet is advanced
horizontally from the apparatus) across the width of the
sheet. The vertical arrows in the graph show the
positions of five loading air cylinders, which were set
respectively at pressures of 0, 138, 138, 138 and 0 kPa
(0, 20, 20, 20 and 0 pounds per square inch) of air
pressure. The speed of strip movement was
15 m/min (50 ft./min), the metering land width was
0.8 cm (0.3 inches) and the angle of the coating head
was 0.5 degrees. Under these conditions, the film
weight calculated theoretically for a coating liquid
having a viscosity of 30 centipoise is about 0.1
gram/square meter. The fact that the actual thickness
of the coating ranged from 1 to 3.5 gram/square meter
shows that the invention is capable of producing films
of greater than theoretical thickness. The coatings
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13
thereby produced are believed to be of acceptable
thickness and uniformity for use in automative
applications.
EXAMPLE 2
Strip coating was c~~rried out on 0.03 cm
(0.011 inch) gauge aluminum can stock using a two sided
coating apparatus having a coating head 30 cm
(12 inches) in width (the: coating width being 29 cm
(11.5 inches)). Again waxy lubricant AL070 was used,
but this time at an application temperature of 51C.
Two load application cylinders were provided per coating
head, one at each end, having a cylinder inside diameter
of 3.8 cm (1.5 inch), and. each was pressurized with air
to a pressure of 310 kPa (45 pounds per square inch).
The average load on each coating head resulting from the
cylinders was 2.5 kg/lineal cm (13.9 pounds/lineal inch)
of strip width. Each coating head had a land width of
0.63 cm (0.25 inches) was set at an angle of 0.5 degrees
to the strip surface. The coating material was supplied
to each coating head at 24 kPa (3.5 pounds/sq. inch
pressure) and the strip was advanced at 15 m per minute
(50 feet per minute). The results are shown in the
graph of Fig. 4. The coatings thereby produced are
believed to be of acceptable thickness and uniformity
for use in automotive applications. The coatings
thereby produced are believed to be of acceptable
thickness and uniformity for use in automotive
applications.
