Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to the type of extrusion coater disclosed
in United States Patent 3,854,441 to George C. Park of December 17, 1974 and
disclosed in United States Patent 3,919,974 to Peter Herzog of November 18,
1975. Such coaters are especially designed to handle hot melts which are
highly viscous in the order of 100,000 centipoises and to coat relatively
wide webs such as eighty six inches or the like. The web is advanced under
predetermined lateral and longitudinal tension over the extrusion slot and
the thickness of the coating is metered by the pressure of the coating supply
pump.
One of the problems encountered in coating such wide widths with
high viscosity coating has been the excessive wear on the lead-off lip des-
pite the fact that the lips have been specially treated by a costly process
to prevent wear. Another problem encountered in any slot coating apparatus
is the lodging of specks of foreign material on the lead-off lip, this
causing a continuous streak in the coating applied to the web until it can
be removed usually during down time which is expensive.
It has been proposed in United States Patent 3,496,012 to Bior-
seth of February 17, 1970 to provide an extrusion slot coating head with a
feed aperture, a discharge aperture and a rotatable rod metering means. The
rotatable rod has a wire wound surface and no yieldable press roll is used
to form a rolling nip with the rod. The rod is actually a metering roll
which can be rotated in either direction at various speeds by a motor to
thereby thin or thicken the coating. The Biorseth apparatus has a coating
head which creates a cavity, or fountain, of the coating material across which
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a web is moved and the excess coating in the fountain travels back to the
supply while a layer adheres to the underside of the moving web in the
thickness determined by the speed and direction of rotation of the metering
rod.
In other coating devices of the prior art, a similar power driven
metering roll, rotating at the downstream side of a fountain, or pool, of
liquid coating has also been used to meter the thickness of coating picked
up by an applicator roll, the applicator roll depositing the coating further
along the path on a surface of a moving web. Exemplary of such coaters are
United States Patent 2,560,572 to Haywood of 1951 and United States Patent
1,983,982 to Vinollenberg of 1934. As in the BiOrseth device, no pressure
roll, rolling nip, or pressure rolling nip is disclosed in these patents.
Endless webs carried by backing rolls through a fixed clearance
nip with an applicator roll are taught in United States Patent 3,345,377 to
Gettel of 1966 and United States Patent 3,533,833 to Takahashi of 1970 but
both patents disclose doctor means in rear of the nip, the Gettel doctor
means being a small diameter rod on the end of a blade.
The rotating rods disclosed in United States Patent 2,946,307 to
Warner of July 26, 1960, United States Patent 3,461,837 to Dreher of August
19, 1969, and in German Patent 1,964,908 of December 30, 1968, all are char-
acterized by support mountings for the rod which provide a movable axis of
rotation by means of flexible, yieldable housings and all are for doctoring
purposes or to serve as longitudinal, fluid metering means as in the Biorseth
patent above.
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SUMMARY OF THE INVENTION
In this invention a rotatable, elongated, cylindrical rod, of
small diameter, is deeply seated in a groove of corresponding shape in the
lead-off lip, or edge, of the extrusion slot of a coating head. Cooperable
with the rod is a rotatable, elongated, cylindrical, press roll, of larger
diameter, the press roll having a rubber-like surface and being yieldable,
while the rod has an unyieldable, hard and preferably smooth surface. A
web to be coated is advanced, under lateral and longitudinal tension of
suitable tension rolls, across the extrusion slot lead-on edge and through
the rolling pressure nip of the press roll and rod on the lead-off edge, as
the roll and rod are rotated at predetermined speeds by motor means.
The coating emitted from the slot is supplied by pump means which
meters exactly the quantity of high viscosity coating required to apply a
coating of uniform predetermined thickness. There is no exhaust~ or dis-
charge aperture for removing excess coating as in the above mentioned
Biorseth patent and the rod is deeply seated in its groove with only about
the upper quarter of its volume exposedO It has been found that despite
its rotation on its longitudinal central axis the rod can be slightly dis-
torted by threaded sections of the seat to compensate for any uneven thick-
ness in the coating. The rod may be continuously rotated at 9-12 r.p.m.
to spread wear and free any particles lodged in the nip or it can be nor-
mally stationary and only rotated selectively to clear up any streaking in
the coating and to present new surfaces for exposure to wear.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic side elevation of a typical extrusion
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slot coater with the invention installed thereon;
Figure 2 is an enlarged fragmentary side elevation of the coating
head, press roll, rotating rod and rotating rod seat of the invention;
Figure 3 is a perspective, schematic view showing the press roll,
rod, pressure nip and the power drive and control for the rod; and
Figure 4 is a ~ragmentary rear elevation partly in section showing
the threadedly movable sections of the lead-off lip which may be used to
distort the rod slightly.
DESCR~PTlON OF A PREFERRED EMBODIMENT
A typical extrusion coater 20 is shown in Figure 1 of the type
disclosed in the above mentioned United States Patent 3,854,441 to Park and
in United States Patent 3,919,974 to Herzog of 1975. The coater 20 is shown
schematically and includes an unwind roll 21, for the web 22, which is train-
ed over the tension indicator roll 23, idler rolls 24 and preferably around
a pre-heat drum 25. The web 22 is l.ongitudinally tensioned by rolls 26 and
27 as it is advanc~d over the elongated slot 28 of elongated coating head
29 and one or more of the rolls is a bowed roll 31 for exerting lateral
tension on the web in the coating zone 32. A supply of hot melt, or other
viscous coating, 33 is supplied to head 29 at a predetermined pressure and
a predetermined rate to meter the exact amount of coating desired to produce
a particular coating thickness on the underface 34 of the advancing web 22.
The supply means includes a suitable motorized pump 35, which feeds conduit
36.
After the application of a thin, layer of coating of ull form
thickness on the underface 34 of web 22, the web is advanced through the
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nip 37 of combining rolls 38 and 39, for lamination with another web 41.
The superposed webs than are trained around a large diameter
chill roll 42 and travel then to the wind-up roll 43. A positive variable
speed drive 44 is provided between the laminating station 37 and the chill
roll 42.
As best shown on a larger scale in Figure 2, the elongated coat-
ing head 29 has a chamber 45 connected to conduit 36 so that the viscous
hot melt, coating 33 is pumped thereinto by the motorized pump 35 for ex-
trusion through the elongated, narrow, extrusion slot 28 formed by the lead-
on lip, or edge, 46 and the lead-off lip, or edge 47. The web 22 is trained
under the rubber like resilient surface 48 of the press roll 49, the roll
bearings 51 being supported by pistons of air cylinders 52 to exert a pre-
determined pressure while also yieldable.
Cooperable with the resilientsurface 48 of press roll 49 and
forming a press roll nip 53 therewith is an elongated cylindrical rod 54
preferably having a hard smooth surface 55, the rod being rotatably seated
for its major volume 56 is a groove 57 of substantially cylindrical cross-
section in the adjacent surface 58 of lead-off lip 47.
The rod 54 is unyieldably mounted in its groove so that the pump
pressure and rate causes a layer 59 of coating 33 to be applied to the under-
face 34 of web 22 as it is advanced under predetermined longitudinal and
lateral tension from lead-on edge 46 to the curved hard face 55 of the ro-
tating rod 54, the rod performing no metering function because revolved
at relatively slow speed such as 9-12 r.p.m. while the press roll and web
advance at a considerably higher speed per minute.
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The minor portion 61 of the rod 54 extends slightly outside of
the groove 57 and is exposed. Rod 54 is connected by a suitable power train
62 through reduction gearing 63 and variable speed control 64 to an electric
motor 650 Control means 60 is provided to permit the rod 54 to normally
be halted and only selectively and temporarily rotated in the direction of
advance of the web when foreign particles have lodged in the press roll nip
53 and are causing streaks in the applied coating. Such rotation frees the
particles and elim;nates the streaks.
It has been found, however, that highly viscous hot melt coating
causes considerable wear on the lead-off surface 55 of the lead-off lip of
slot type extrusion coaters and that even when a rod 54 is seated in a groove
57, but not rotated and is of special wear resistant material or treatment,
the rod surface tends to wear unevenlY and create uneven thickness a~eas
in the coating. Therefore, it is preferred that control means 60 be so
adjusted that the rod 54 be continuously rotated at slow speed to spread
out the wear and avoid formation of flat spots, or other causes of eccen-
tricity.
While one would expect that an elongated cylindrical rod of small
diameter such as rod 54, deeply seated in a groove of corresponding config-
uration would have to have a rectilinear axis or it would not revolve in the
groove, it has been found that one side 66 of the rod seat can be in sec-
tions, 67, 68 etc., each with a threaded element 69, the sections being
adjustable to slightly distort the rod and its groove to compensate for any
uneven thickness in areas transversely of the web.
The threadedly movable side sections 67, 68 etc. may all be with-
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drawn to permit substitution of a new rod 54, and if such is not desired,
or practical the rods 54 may be slid endwise out of their grooves for
easy replacement.
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