Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
The present invention relates to a coating method and apparatus and
more particularly to a novel method and apparatus for substantially simulta-
neously coating both sides of a web in a controlled uniform manner.
BACKGROUND OF THE INVENTION
There exists a variety of applications in which it is desired to
coat both surfaces of a web. In one existing technique, the web is moved
substantially vertically upward so as to pass between a pair of opposing
coating members for applying a coating composition upon the paper web. The
coating members are rigid and are positioned with respect to the web so as to
provide a gap between the associated surface of the web and the respective
coating member to cause a dam of coating composition to be formed in the
nip between each surface of the web and the associated displaced surfaces
of the coating members. The hydraulic pressure created by the movement of
the web and the coating composition, in passing each coating member, serves
to stabilize the web and prevent any fluttering or vibration of the web as
it moves between the coating members. The web is coated with an excess of
coating composition which is uniformly spread and scraped from each surface
of the web in a subsequent operation by means of an opposing pair of flexible
doctors typically comprising a pair of thin steel blades arranged in align-
ment with one another and on opposite sides of the web whereby the excess
coating composition removed from the web is returned to the system. Typi-
cally the excess coating composition is admixed with fresh coating composition
before reuse.
Careful observation of the aforementioned apparatus has shown that
the distance between the rigid coating members is of considerable importance.
This distance must be adjusted with respect to both the thickness of the web
and the quantity of coating composition applied upon the surfaces of the web
so that the desired excess is deposited upon the web. These adjustments have,
in turn, led to a number of complications. For example, if the excess
quantity of coating composition is to be kept low at the primary coating
location, the opposed rigid coating members must be set relatively close to
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one another. Since the coating members are rigid to prevent any instability
in the web during the coating composition, thicker sections of the web which
may be due to the presence of lumps or other impurities, may become lodged
in the passageway between the opposed rigid coating members thus causing a
fracture or tearing of the web.
Furthermore, the techniques employed in manufacturing the rigid
coating members must be quite precise in order to produce rigid coating
members having sufficiently straight and flat surfaces along the portions of
the coating members which control the spreading of the excess coating com-
position. If for example the coating members have a length of the order of
3 meters or more measured in the direction transverse to the direction of
movement of the web this leads to serious problems. Even assuming that
such precise manufacturing techniques are employed, it has also been found
that temperature variations in the coating composition being dispensed can
cause deviations (i.e., "warping") in the straight flat surfaces of the
coating members. Such deviations in the contacting surfaces may cause
portions of the web to remain uncoated since the dam formed in the nip
between the web and the coating member may temporarily disappear due to the
warping, especially if a relatively small excess quantity of coating com-
position is applied.
BRIEF DESCRIPTION OF THE INVENTION AND OBJECTS
A primary object of the present invention is to provide method and
apparatus which eliminates the above-mentioned disadvantages through the
utilization of a technique which applies the coating composition on each
surface of the web through outlets having orifices along the contact sur-
faces of the coating members facing the web and by arranging the aforesaid
contact surfaces in a spaced fashion in the direction of the movement of
the web.
Thus, according to the present invention, instead of using the
arrangement of the prior art in which the opposed coating members are located
directly opposite one another, the present invention proposes an arrangement
whereby the coating members are displaced with respect to one another
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relative to the direction of travel of the web, which arrangement consider-
ably reduces the need for making the contacting surfaces of the coating
members absolutely straight which further serves to reduce the otherwise
stringent manufacturing requirements necessary to produce the coating members
of the prior art.
In accordance with one embodiment of the subject invention, the
supply of the coating agent as well as the positioning of the appropriate
contacting surfaces in relation to the ass~ociated surface of the web are
set so that an excess dam of coating composition is formed immediately
before the nip between the contact surface of each coa~ing member and the
associated surface of the web. It has been found that the hydraulic
pressure created by the movement of the web and the coating composition
deposited thereon serves to stabilize the web so that it floats or is
suspended between the opposed layers of coating compositions which acts
much like a lubricant in that it facilitates the smooth and stabilized
passage of the web between the rigid coating members.
The coating result is further improved if the initial direction of
travel of the web i5 altered as the web passes each of the rigid coating
members which is accomplished by lateral displacement of the surfaces of
the coating members contacting the web, said lateral displacement being
transverse to the normal direction of travel of the web. It has been found
that this deflection of the web further enhances stabilization of the web
which is an important factor when the means proposed according to the
present invention is employed as a primary coating station positioned to the
upstream side of a pair of opposed flexible doctors which function to spread
the coating composition in a uniform manner and scrape off any excess. It
is important that the web be stabilized prior to its passage between the
flexible doctor since vibrations or the like due to the instability or
fluttering of the web passing through the primary coating station will cause
the flexible doctors to be deflected from their desired position leading to
a non-uniform and hence unacceptable coating layer.
In accordance with another embodiment of the present invention, the
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entire coating process can be effectively controlled by means of an adjust-
able displacement of the coating composition dispensing members after the
coating members have been properly positioned against the web.
As has been mentioned hereinabove, it is necessary to form a dam of
the coating in order to assure a uniform coating layer devoiding uncoated
spots. This is for example accomplished through the utilization of rotatable
contact members having elongated dispensing slots whereby the members are
adjustable to set the dispensing slots at a suitable angle relative to the
web so that the desired quantity of coating composition is supplied to the
web and a suitable quantity of coating composition will be dispensed to form
the dam with a certain excess amount thereof possibly dripping downwardly
from the region of the dam. This complete control of the coating process is
thus obtained by adjusting the quantity of coating composition supplied and
by aligning the dispensing slots at a suitable angle relative to the web.
The present invention also contemplates means for performing the
method described hereinabove through the employment of outlet orifices for
the coating composition which are located within the contact surfaces of the
coating members positioned against each surface of the web and by staggering
the contact surfaces relative to the path of movement of the web.
The present invention is further characterized in that the contact
surface of one coating member may be positioned above the opposing contact
surface of the other coating member to be arranged in an overlapping fashion
thereby causing the path of movement of the web to be altered as it passes
each contact surface so that the web moves in an undulating or "zig-zag"
fashion as it passes through the primary coating station.
The contact surfaces of each coating member may be shaped in the
form of a pair of lips which taper in the direction of the paper web with
the lips surrounding and hence defining the supply channel and outlet
orifice for the coating composition.
According to another preferred embodiment of the invention, the
contact surfaces of the coating members may comprise tubular members
extending substantially across the entire width of the web whereby each
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tubular member includes an elongated slot-like outlet opening for dispensing
a coating agent, which opening extends substantially across the entire width
of the web. The tubular members are preferably pivotably journalled and so
arranged as to permit adjustable orientation of the outlet slots, which
adjustments are independent of the rotatably adjustable contact members.
In the case where it is desired to provide an uncoated marginal
portion along each edge of the web, adjustable screening strips may be
arranged within the slot-like openings so as to be adjustable displaceable
within the slot at the opposing ends thereof.
In order to avoid non-uniform coating of the web due to a pressure
drop in the coating agent as it moves toward the outlet slots, the distri-
bution chambers for the coating agent are preferably connected by means of a
plurality of supply conduits distributed at spaced intervals along the length
of the coating members and communicating with an inner chamber located in the
lower portion of each coating member, which inner chamber preferably has a
greater storage volume than the distribution chamber. The supply conduits
may preferably be comprised of flexible plastic tubes or the like.
In order to prevent the coating members from becoming clogged or
dirty, the portions of the coating members which comprise the contact sur-
faces may be rotatably journalled in holders having intermediate seals. An
upper covering plate may also be arranged above each contact surface portion
to protect the contact surface portions from excess coating composition which
may drip downwardly from upper portions of the web as it leaves the primary
coating station.
BRIEF DESCRIPTION OF THE FIGURES
The above as well as other objects of the invention will become
apparent when reading the accompanying description and drawings in which:
Figure 1 shows a sectional elevational view of a first embodiment
of a coating means designed in accordance with the principles of the present
invention;
Figure 2 shows an elevational sectional view of a second preferred
embodiment of the present invention;
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Figure 3 shows an enlarged detailed view of a portion of one coating
member of Figure 2;
Figure 4 is a sectional elevational view of still a third embodiment
of the present invention;
Figure 5 shows an enlarged detailed view of a portion of one coating
member of Figure 4;
Figure 6 shows a perspective view of a tubular dispensing member
of the type shown in Figures 2 - 5 and employing a screening element;
Figure 7 is a perspective view showing the screening element and
tubular member of Figure 6 in greater detail; and
Figure 8 is a sectional view showing one technique for pivotally
mounting the supply container of Figure 2 and 4, for example.
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of Figure 1 shows a paper web 1 which is conveyed
in the upward vertical direction shown by arrow A. Although not shown for
purposes of simplicity, the movement of the paper web is typically con-
trolled by dispensing the untreated paper web from a supply reel typically
positioned beneath the apparatus of Figure 1 and winding the subsequently
treated paper web upon a wind-up reel typically positioned above the apparatus
of Figure 1. The system may further include other guiding rollers, drying
members, and the like, which have also been omitted for purposes of simpli-
city.
The upwardly moving web passes between coating members 2 and 3
positioned on opposite sides of the paper web. The coating members 2 and 3
are pivotally journalled about longitudinal axes 4a and 5a, for example, by
elongated shafts 4 and 5, whose free ends may be journalled within suitable
bearings (not shown). The coating members may be rotated to accurately
position their respective contact surfaces 6 and 7 by means of coarse and
fine adjustment assemblies.
The coating members 2 and 3 are each respectively provided with a
hollow interior chamber 8 and 9 containing the coating composition supplied
thereto through suitable conduits, not shown. Each of the chambers 8 and 9
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is respectively provided with an outfeed channel 10 and 11 communicating with
the chambers 8 and 9 and with the contact surfaces 6 and 7 whereby the
channels 10 and 11 terminate in the elongated slot-like outlets 12 and 13
positioned between the pairs of lips 14 - 15 and 16 - 17. The contact
surfaces of the lips are arranged somewhat obliquely relative to the direction
of movement of paper web 1.
The coating members 2 and 3 are preferably set with respect to one
another so that the outlets 12 and 13 and the pairs of lips 14 - 15 and
16 - 17 are arranged in staggered fashion relative to the path of movement
of the paper web and further so that the contact surfaces overlap one another
slightly, i.e. so that they are displaced somewhat relative to the otherwise
straight line path of movement of the paper web. Due to this displacement,
paper web 1 will be slightly deflected or curved as it passes the contact
surfaces 6 and 7.
The coating agent dispensed through the outlet openings 12 and 13
is supplied at a rate sufficient to cause dams 20 and 21 to form between each
surface of the paper web and the associated contact surface 6 and 7 of the
coating members 2 and 3. Coating composition in excess of that necessary
to form the dam runs downwardly under the influence of gravity along the
surfaces 18 and 19. The hydraulic pressure created by the excess coating
composition contributes to stabilization of the paper web as it passes between
coating members 2 and 3 causing the web to float or be suspended between the
layers of coating composition which acts in much the same way as a lubrica-
ting agent. The formation of the dams further prevents the occurrence of a
non-uniform coating caused by formation of air bubbles in the coating compo-
sition.
It can readily be understood that the arrangement of the coating
members of Figure 1 considerably reduces the requirements that the contact
surfaces 6 and 7 be perfectly straight due to the fact that the paper web is
somewhat pulled around each contact surface enabling the web to compensate
for any uneveness in the straightness of the contact members so that any
deviation from the straight flat contact surfaces will not affect the result
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of the coating process.
Figure 2 shows another preferred embodiment of the present
in~ention in which the contact surfaces 6 and 7 of the embodiment of
Figure 1 are replaced by elongated tubular members 22 and 23 which extend
along the entire width of paper web 1 and are preferably pivotably journalled
in a holder substantially comprised of plates 18 - 24 and 19 - 25 which
define the inner and outer sides of coating members 2 and 3. As can best
be seen from Figure 3, the above-mentioned plates pivotally hold the tubular
members, such as, for example, the tubular member 22 with the aid of brackets
26a and 27a and intermediate seals 26 and 27 preferably secured to the inner
surfaces of plates 18 and 24 by clamping brackets 26a and 27a. Each of the
tubular members are respectively provided with interior distributing chambers
28 and 29 for receiving the coating compound. Each distributing chamber is
in communication with the larger chambers 40 and 41 defined by hollow
elongated tubular members 38 and 39, respectively, by means of flexible
tubular supply conduits 30 arranged at spaced intervals along the length
of each of the members 22 and 23 (note, for example, Figure 7). Each of
the tubular members 30, which may preferably be formed of a transparent
resilient plastic material, is force-fitted over connection nipples 31 in
members 38 and 39 and connection nipples 32 in members 22 and 23.
Tubular members 22 and 23 are each provided with elongated slot-
like outlet openings 33 and 34 extending over the entire length of members
22 and 23 and directed toward an associated surface of the paper web.
Tubular members 22 and 23 are preferably pivotable about their longitudinal
axes 22a and 23a to such an extent that the position of each outlet can be
altered to position slot 33, for example, (see Figure 3) an angular distance
a above the solid line position 33 or, alternatively, an angular distance b
below solid line position 33. It should further be noted that the tubular
members 22 and 23 may be rotated independently of the coating members 2, 3
about their axes of rotation designated by numerals 22a and 23a in Figure 2.
The distance X, shown in Figure 2, represents one suitable vertical
displacement between the contact surfaces of the tubular members 22 and 23
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measured in the direction of travel of paper web 1.
The arrangement of Figure 2 has the advantage, inter alia,
since the tubular members 22 and 23 are rotatably mounted to enable these
members to be turnable to some extent independently of each other due to the
fact that they are connected to associated members 38 and 39 by flexible
tubes 30. The ends of each of the coating members 38 and 39 may be mounted
in rotatable seals as shown in Figure 8. End 38a, for example, has a
reduced diameter portion 38a encompassed by rotatable seal 50 provided in
sidewall 51. The opposite end 38b of member 38 is closed and is pivotally
mounted within the opening 52a in side wall 52. If desired, a bearing may
be provided between opening 52a and the reduced diameter portion of end
38b. Conduit 53 is coupled to a suitable supply of coating composition.
If desired, the ends of tubular members 22 and 23 may be configured in the
manner of end 38b of member 38 so as to be received in openings in side-
walls 51 and 52, to further facilitate the ability of members 22 and 23 to
revolve, whereby the coating process is entirely under control when in
operation. For example, the quantity of coating agent which drips down-
wardly along the exterior surfaces of plates 18 and 19 and the quantity of
coating agent supplied to the paper web, as well as the formation of dams
20 and 21 of a suitable size, can be set so as to create each dam immediately
adjacent the nip formed by the paper web and the portion of the contact
surface engaging the web. Another advantage of the arrangement shown in
Figure 2 resides in the fact that tubular members 22 and 23 are inexpensive
in that they can be manufactured rather simply and hence cheaply. Alter-
natively, the tubes need not be perfect cylinders but may, for example, be
truncated cylinders having their curved surface portions engaging web 1.
Members having other suitable cross-sectional configurations
may also be used in place of tubular members, if desired. In addition, the
configuration of the outlet slots may be altered from that shown in Figure 2.
For example, the contact surfaces may consist of lips protruding outwardly
from the arcuate surface members 22 and 23 and being spaced from one another
so as to define the outlet opening therebetween.
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Figure 4 shows still another embodiment of the present invention
which, while substantially similar to the embodiment of Figure 2, shows the
covering plates 24 and 25 as having upwardly extending portions 24a and 25a
to enclose a substantial portion of the tubular members 22 and 23 and thereby
protect the tubular members from collecting dirt or coating composition
which may drip down from above.
Figure 5 shows a more detailed view of the upper portion of
coating member 2 in which the seals 26 and 27 of Figure 2 are replaced by
scrapers 26' and 27' formed of rubber or flexible steel clamped to the
inner surfaces of plate portions 18 and 18a by clamping brackets 18b and
18c. The flexible scrapers prevent coating compound from entering into
the hollow interior of coating members 2 and 3.
Figures 6 and 7 show the manner in which coating dispensing
slot 33 provided in tubular member 22 may be at least partially sealed or
screened off by means of a screening strip 35 which is inserted into slot
33 so as to completely fill lengthwise portion L of slot 33. It should be
understood that a similar screening strip may be adjustably positioned
within the opposite end of slot 33. Figure 7 shows screening strip 35
inserted into slot 33 so that a marginal portion M of the paper web 1 is
maintained free of the coating agent. Obviously, the width of the uncoated
marginal portion M may be adjusted by suitable adjustment of the screening
strips.
It can be seen from the foregoing description that the present
invention provides a novel method and apparatus for substantially simultan-
eously coating both sides of a web by means of independently adjustable
staggered overlapping contact members which assure uniform distribution of
the coating composition over each surface of the web while compensating for
any unevenness in the contact members due to the novel zig-zag manner in
which the web moves in passing through the coating station by making the
contact surfaces and coating composition dispensing slot independently
adjustable. Location of the dam of coating can be suitably adjusted so as
to be positioned immediately adjacent the nip formed between the web and
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the associated contact surface.
Although there has been described a preferred embodiment of
this novel invention, many variations and modifications will now be apparent
to those skilled in the art. For example, as was mentioned hereinabove, the
coating apparatus can also be used as a primary coating station in con-
junction with a secondary scraping station positioned above the primary
coating station and comprising two opposed flexible doctors. Also, the
means proposed according to the present invention can be utilized to coat
opposite sides of the web with different coating compounds. Therefore,
this invention is to be limited, not by the specific disclosure herein, but
only by the appending claims.
