Note: Descriptions are shown in the official language in which they were submitted.
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PATENT APPLICATION
TITLE: HIGH SPEED COATING APPARATUS AND METHOD
FIELD OF THE INVENTION
This invention relates to high speed application of liquid coating material
to a paper web. In particular, the invention relates to utilizing several
application stages to apply a uniform coating layer.
BACKGROUND OF THE INVENTION
Applying of a coating material to a paper web involves various problems
for which solutions have been sought over a number of years. In particular, as
speeds of the paper webs being coated have increased, the difficulties in
applying a uniform coating has correspondingly increased. Further, where high
viscosity coating materials are applied at high speeds, the maintaining of the
quality of the coating is particularly challenging.
One type of applicator apparatus that has been used for a considerable
length of time is known as a flooded nip coater. This type of coater includes
an
applicator roll which rotates in a pan of coating material thereby picking up
the
coating onto the applicator roll and transferring the coating film to a web
sheet
as it travels on the surface of a backing roll. The applicator roll and the
sheet
move in the same direction and the coating is applied to the sheet at a small
gap between the sheet and the applicator roll. At high applicator roll and web
speeds, the high speed of applicator roll in the pan causes splashing of the
coating material and pond instability and consequent lack of uniformity in
applying the coating to the sheet. Also, if the sheet breaks, broke may
collect
in the applicator pan resulting in increased cleanup work and downtime.
An improvement in coaters that has been developed is known as a short
dwell coating applicator. A short dwell applicator has an enclosed type of
pond
of coating material which eliminates the problem of broke collecting in an
open
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pan or pond. It also eliminates the splashing and turbulence of an open pan.
However, unstable vortices in the pond immediately adjacent the web being
coated form due to the high speed of the web as it passes the pond of coating
material. With high viscosity coating materials and as speed increases,
coating
defects in the form of streaks and blotchy patterns appear on the paper web.
An effort to solve this problem has been to provide a low angle premetering
blade to minimize the unstable vortices and help expel air that is brought in
with the passing web. Although this improvement has improved the quality of
coating, the basic problem still persists.
Another type of coater improvement that has been developed is a jet
coating applicator which includes an enclosure and a coating applicator nozzle
through which coating material is applied to a passing web. Due to the
enclosed nature of the jet applicator, there is no turbulence of an open pan
or
broke falling into the pan. However, there is a high speed turbulence problem
in that the high speed of a passing web causes turbulence in the coating
material as it is applied to the web causing breakup and non-uniformity of the
coating.
The present invention is directed to a further improvement in the coating
process which wilt permit coating at high speeds using high viscosity coating
materials without the turbulence resulting in coating quality defects.
SUMMARY OF THE INVENTION
It is a general object of this invention to utilize a coating applicator and
roll applicator together to apply a uniform coating of material to a moving
paper
web. It is a further object of the invention to apply a coating material with
an
enclosed type of coater to a roll applicator that is moving at a relatively
slow
speed. A further object of the invention is to apply a coating material to a
moving paper web at a gap between the paper web and a roll applicator which
is moving relatively slowly in comparison to the speed of the paper web and to
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which coating material has been applied by am enclosed type of coater.
Another object of the invention is to control the thickness of the coating on
the
paper web by controlling or metering the amount of coating material applied by
an enclosed coater to the roll applicator.
The invention is carried out in a coating apparatus in which a paper web
is advanced at a relatively high speed with a backing roll which provides a
backup surface for the web as it advances. An enclosed coater applies coating
material to a roll applicator which is rotating at a slow linear speed
relative to
the speed of the web. The coating material applied to the roll applicator by
the
water is, in turn, applied to the web by the roll applicator moving at the
slower
speed relative to the web speed. The coating material is applied to the web at
a spacing gap between the roll applicator and the web on the backing roil with
which the web is advancing.
The use of the enclosed coater eliminates an open pan which may
produce turbulence and splashing and also the possibility of broke falling
into
the pan. The application of the coating material by the enclosed coater to a
roll
applicator moving at a slow speed eliminates the breakup in the coating
material due to turbulence at the web or roll surface or the vortice type
turbulence, both associated with applying coating material with an enclosed
coater to a web or roll moving at high speed. Further, the application of the
coating material by the roll applicator to the web wherein the roll applicator
is
moving at a slower speed relative to that of the web also eliminates
turbulence
in such application and permits a uniform coating of material to be applied to
the web.
The thickness of the coating material applied to the web is controlled by
controlling or metering the amount of coating material applied from the
enclosed coater to the roll applicator. Utilizing an enclosed coater for
controlling the amount of coating material applied to the web permits greater
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precision in controlling the thickness of the coating on the web than can be
obtained with the common method using a doctor. Also, the enclosed coater
can be used to vary the thickness of the coating applied to the web across the
width of the web.
BRIEF DESCRIPTION OF THE DRA11111NGS
The above and further objects, features and advantages of the invention
will become apparent upon consideration of the following detailed description
taken in conjunction with the accompanying drawings as follows:
Fig. 1 is an end elevation schematic view of the coating apparatus
according to the invention;
Fig. 2 is a side elevation schematic view of the invention shown in Fig. 2;
Fig. 3 is an end elevation schematic view, partially in cross-section, of
one embodiment of an enclosed coater utilized in the invention; and
Fig. 4 is an end elevation schematic view, partially in cross-section, of
an alternate embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring generally to the drawings, wherein like numbers refer to similar
parts, a web coating apparatus 2 is shown in Figs. 1 and 2. The web coating
apparatus 2 includes a roll 4 having a circumferential surtace 14 and which
rotates in the direction of arrow 8 about an axis 6. The roll 4, as it
rotates,
advances a paper web 10 having surfaces 16, 18 and a width w and acts as a
support and backing for the paper web 10.
The embodiment of the invention shown in Figs. 1 and 2, and also in
Fig. 3, includes an enclosed coating applicator 20 which is of an enclosed
pond
type of applicator. Enclosed coating applicators of the enclosed pond type are
well-known in the papermaking industry for coating of continuously moving
paper webs. Such enclosed pond coating applicators include blades, smooth
rods and grooved rods for metering and controlling the coating material
applied
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to the web. In the embodiment of the invention described herein, an enclosed
pond coating applicator utilizing a blade metering device is utilized, but it
should be understood that other types of enclosed pond applicators including
those mentioned above are also suitable.
The enclosed applicator 20 applies coating material 22 to a roll
applicator 30. The roll applicator 30 has a circumferential surface 32 onto
which the coating material 22 is applied by the enclosed applicator 20 and
rotates about an axis 34 in the direction of arrow 36. The direction of
rotation
of the roll applicator 30 immediately opposite the roll 4 and web 10 is thus
in
the same direction as the advancing movement of the web 10 and the rotation
of the roll 4. Also, as can be seen in Fig. 1, the roll applicator 30 forms a
gap
38 with the web 10 and roll 30 in the area at which the web 10 and roll 30 are
most adjacent to each other.
With reference in particular to Figs. 2 and 3, the enclosed applicator 20
includes a tube 24 through which coating material 22 is delivered by a pump
(not shown). The coating material 22 moves through the tube 24 into a
chamber 26 of the applicator 20 which contains a pond 44 of coating material
22. The chamber 26 has walls formed by member 28, a premetering element
29, a metering blade 42 of a metering mechanism 40 and a portion of the
circumferentiai surface 32 of the roll applicator as it moves past the
enclosed
applicator 20. The applicator 20 has a width parallel to the axis 34 of the
roll
30 at least the width w of the web 10 and a plurality of metering mechanisms
40 mounted along this width
In the operation of the coating apparatus 2 utilizing the enclosed coating
applicator 20, the roll 4 and paper web 10 travel at a relatively high linear
speed which may be, for example, in the range of 200 to 3000 meters per
minute. On the other hand, the roll applicator 30, traveling in the same
direction as the web 10, is moving at a relatively slower linear speed in the
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range of 5 to 30 per cent of the roll 4 and web 10 speed. Consequently, as the
coating material 22 is applied to the circumferential surface 32 of the roll
30 by
the enclosed coating applicator 20, the linear speed of the roll 30 will be
insufficient to cause vortice or other turbulence typical in the pond of an
enclosed coating applicator as would be the case if the coating material
application were to a web or roll surface traveling at high speed. As the
coating material 22 being carried on the surface 32 of the roll 30 passes
through the gap 38 and is applied to surface 16 of the web 10, turbulence
which may disturb the uniformity of the application of the coating material to
the
web 10 is minimized due to the relatively slow linear speed of the roll 30.
Note
also that the gap space between the web 10 and the surface 32 of the roll 30
is
such that only the coating material 22 engages the web 10.
The enclosed coating applicator 20 also controls the thickness and thus
the weight of the coating material 22 applied to the surface 16 of the web 10
by
a metering action in applying coating material to the surface 32 of the roll
30.
This metered amount may be controlled or adjusted by adjusting the position
and thereby the pressure applied by the metering blade 42 of the metering
mechanism 40. Increasing the pressure of the metering blade 42 reduces the
weight and thickness of the coating material 22 and, conversely, reducing the
metering blade pressure increases the coating material weight and thickness.
Since the enclosed coating applicator 20 extends in the axial direction of the
applicator roll 30 across the lateral surface width w of the web, the coating
material thickness may be controlled on this entire surtace. Inasmuch as the
metering ability of the coating applicator 20, by use of the plurality of
metering
mechanisms 40, can very precisely control the amount of coating material 22
being applied to the roll surface 30 along its axial length, the weight and
thickness of the coating applied downstream to the web 10 can consequently
be also precisely controlled.
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With reference to Fig. 4, an alternative embodiment is illustrated in
which the coating apparatus 2 utilizes an enclosed coating applicator 50 of
the
jet type. The enclosed coating applicator 50 may be used rather than the
applicator 20 as shown in Fig. 1. The components of the invention, other than
the applicator 20, would remain the same as in Fig. 1 The enclosed jet coating
applicator 50 is well-known in the prior art and includes a casing or
enclosure
52 and a coating applicator nozzle 54 extending from the enclosure to a
position adjacent the roll applicator 30. The applicator nozzle 54 has a
nozzle
gap 48, an adjustable lip 56, lip adjusting screws 58, and a metering
mechanism 60. The metering mechanism includes a metering lip 62 which
also forms part of the nozzle 54 and a lip control fi4. The adjustable lip 56
extends across the entire width of the applicator 50 and controls the basic
coating thickness applied to the applicator roll by setting the opening size
of the
nozzle gap 48 across the applicator by manipulation of the screws 58. There
are a series of lip controls 64 spaced apart across the width of the
applicator
50 and each lip control 64 sets the position of a metering lip fit to control
the
thickness and weight of coating material applied to the roll applicator
adjacent
the particular lip control 64. This permits profiling of the coating material
22
applied to the roll applicator and thus also to the web 10. A pump 46 supplies
coating material 22 through pipe 6fi and passageway 68 to the nozzle 54 at a
pressure above atmospheric pressure.
Referring further to Fig. 4, as in the embodiment of Fig. 1, the roil 4 and
paper web 10 travel at a relatively high linear speed of, for example, in the
range of 200 to 3000 meters per minute. However, the roll applicator 30
moves at a relatively slower linear speed in the range of 5 to 30 per cent of
the
roll 4 and web 10 speed. Thus, as the coating material 22 is applied onto the
circumferential surface 32 of the roll 30 by the enclosed coating applicator
50,
the low linear speed of the roll 30 will not create turbulence affecting the
coating material which is sufficient to cause breakup of the coating material.
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It is understood that the invention is not limited to the particular
construction and arrangement of parts herein illustrated and described, but
embraces such modified forms thereof that come within the scope of the
following claims.
