U.S. patent number 3,632,403 [Application Number 04/883,185] was granted by the patent office on 1972-01-04 for method and apparatus for curtain coating.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Jack F. Greiller.
United States Patent |
3,632,403 |
Greiller |
January 4, 1972 |
METHOD AND APPARATUS FOR CURTAIN COATING
Abstract
In a method of coating a support with a liquid coating
composition in which the coating composition is applied by
impingement of a free-falling curtain of coating composition onto
the surface of the moving support, formation of edge beads along
the edges of the coating which are of greater thickness than the
remainder of the coating is effectively avoided by use of laterally
adjustable edge guides which are initially positioned so as to
establish a stable free-falling curtain and then moved laterally to
a position in which they are slightly further apart, whereby the
coating assumes a uniform thickness. The method of this invention
is useful in both single-layer and multiple-layer curtain coating
and are especially advantageous in the manufacture of photographic
film and photographic paper in view of the need for precisely
uniform thickness over the entire coated area.
Inventors: |
Greiller; Jack F. (Ruislip,
EN) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
10067019 |
Appl.
No.: |
04/883,185 |
Filed: |
December 8, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Mar 26, 1969 [GB] |
|
|
15,870/69 |
|
Current U.S.
Class: |
430/538;
118/DIG.4; 430/935; 65/201; 427/420 |
Current CPC
Class: |
B05C
5/008 (20130101); G03C 1/74 (20130101); B05D
1/305 (20130101); Y10S 118/04 (20130101); G03C
2001/7433 (20130101); G03C 2001/747 (20130101); Y10S
430/136 (20130101) |
Current International
Class: |
B05D
1/00 (20060101); B05C 5/00 (20060101); B05D
1/30 (20060101); G03C 1/74 (20060101); B05b
013/02 (); B05b 013/00 () |
Field of
Search: |
;118/DIG.4 ;65/201,91
;117/105.3,12FC,34 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leavitt; Alfred L.
Assistant Examiner: Whitby; Edward G.
Claims
1. In a curtain-coating method in which a support to be coated with
a liquid coating composition is moved along a path through a
coating zone and a free-falling curtain of said coating composition
which extends transversely of said path is formed within said
coating zone, between a pair of vertically positioned edge guides
equipped with flexible extensions which bear on the moving support
adjacent to the edges of said free-falling curtain, and is directed
to impinge on the face of said moving support to deposit a coating
thereon; the improvement comprising initially establishing a stable
free-falling curtain with said edge guides positioned apart a
predetermined distance whereby the coating formed has an edge bead
adjacent each edge guide which is of greater thickness than the
remainder of the coating and then moving said edge guides to a
second predetermined position whereby the coating assumes a
substantially uniform
2. In a curtain-coating method in which a support to be coated with
a liquid coating composition is moved along a path through a
coating zone and a free-falling curtain of said coating composition
which extends transversely of said path is formed within said
coating zone, between a pair of vertically positioned edge guides
equipped with flexible extensions which bear on the moving support
adjacent to the edges of said free-falling curtain, and is directed
to impinge on the face of said moving support to deposit a coating
thereon; the improvement comprising initially establishing a stable
free-falling curtain with said edge guides positioned apart a
predetermined distance whereby the coating formed has an edge bead
adjacent each edge guide which is of greater thickness than the
remainder of the coating and thus contains excess coating
composition, then moving each of said edge guides away from the
other by a distance substantially equal to the cross-sectional area
of the excess coating composition in the adjacent bead divided by
the thickness of the coating and securing said edge guides in the
resulting position, whereby the coating formed thereafter is of
substantially the same thickness at its
3. A method as described in claim 2 wherein said edge guides are
first moved apart a greater distance than that defined in claim 2
and are then
4. A method as described in claim 2 wherein said curtain is
comprised of a plurality of distinct juxtaposed layers of liquid
coating compositions.
5. A method as described in claim 4 wherein said coating
compositions are photographic coating compositions and the support
is photographic film
6. A method as described in claim 4 wherein said coating
compositions are photographic coating compositions and the support
is photographic paper.
Description
This invention relates to methods of coating liquid coating
compositions in which one or more layers of coating composition are
applied to a moving support by impingement of a free-falling
curtain of coating composition onto the surface of the support.
More particularly, this invention relates to an improvement in
methods and apparatus for effecting such coating whereby the
formation of edge beads along the edges of the coating which are
greater thickness than the remainder of the coating is
substantially eliminated. The improved method and apparatus are
employed with particular advantage in the manufacture of
photographic film and photographic paper.
Manufacture of photographic elements by a method which comprises
the steps of forming a free-falling curtain of liquid photographic
coating composition within a coating zone and directing a support
along a path through the coating zone such that the free-falling
curtain impinges thereon, while maintaining a controlled relation
between the flow rate of coating composition and the speed at which
the support is moved, is disclosed and claimed in copending U.S.
patent application Ser. No. 733,944, titled "Method And Apparatus
For Production Of Photographic Elements," filed in the name of Jack
F. Greiller on June 3, 1968, and assigned to the same assignee as
the present application. The formation of a coating, in the
manufacture of photographic elements or other coated articles,
which is comprised of a plurality of distinct superposed layers by
forming a stable multilayer free-falling curtain and impinging the
curtain onto a moving support is disclosed and claimed in copending
U.S. patent application Ser. No. 733,971, titled "Method And
Apparatus For Simultaneously Applying A Plurality Of Coated
Layers," filed in the name of Donald J. Hughes on June 3, 1968, and
assigned to the same assignee as the present application. The
method and apparatus of this invention represent a useful
improvement which may be advantageously utilized in either of the
coating methods described in the aforesaid patent applications and
the disclosure of each of these patent applications is incorporated
herein by reference for purposes of indicating the background of
the present invention and illustrating the state of the art.
In a particular embodiment of the methods disclosed in the
aforesaid copending patent applications, the coating composition is
applied to a support material which is in the form of a continuous
web and the coating apparatus is provided with edge guides which
are equipped with flexible extensions which bear on the surface of
the moving web. The edge guides serve to guide the free-falling
curtain along its longitudinal edges to define its width at
impingement onto the face of the support. One problem encountered
in this method of coating is the tendency to formation of edge
beads (also referred to hereinafter in some instances as "marginal
beads") along each of the coating which are significantly thicker
than the remainder of the coating.
For example, there is shown in FIG. 1 of the accompanying drawings
a fragmentary view of a curtain coating apparatus wherein a curtain
30 of liquid coating composition is shown falling between edge
guides 20a (only one of which is shown) onto a moving web 31 to be
coated. At their lower ends, the edge guides 20a have extending
therefrom brushes 32. Each brush 32 bears upon the surface of the
web 31 at a margin thereof, and can spread out into a "fantail," as
shown. Additionally, surface tension effects tend to draw the
bristles inwardly into the coated region of the web. The result of
this is that liquid composition falling between the edge guide and
the inner trailing edge of the "fantail" is swept in by the brush
32 to form a marginal bead 33 containing excess material. This is
disadvantageous in that extended drying time is necessary to ensure
complete drying of the coated web. Appropriate shaping of the brush
bristles partially overcomes the aforesaid disadvantage.
It is an object of the present invention to overcome the aforesaid
disadvantage in another way by providing an improved method of
curtain coating in which the coating deposited has substantially no
excess thickness which would necessitate extended drying at any
point transversely of the support material.
According to the present invention, there is provided a method of
coating a liquid composition on a support material which comprises
the steps of establishing a stable, free-falling curtain of a
coating composition between edge guides, of a desired uniform flow
rate except at the edge guides, moving a support to be coated
through the curtain in a direction transversely thereof, and then
moving the edge guides apart to a position at which the coating
assumes a uniform thickness. For optimum results, each of the edge
guides is moved away from the other by a distance substantially
equal to the cross-sectional area of the excess coating composition
in the adjacent edge bead divided by the thickness of the
coating.
Preferably, the edge guides are moved apart a greater distance than
the aforesaid distance and are then moved together to the aforesaid
distance.
In a preferred method of the invention, the edge guides each
comprise a rod, which rods are spaced apart a distance such that
they are each in line with a respective margin of the support to be
coated. The rods terminate at their lower ends only a short
distance from the surface of the support, e.g., 0.3 to 0.6
centimeters. From the lower ends of the rods extend flexible
members which bear on the surface of the support. The flexible
members may comprise a piece of flexible tape or a plurality of
bristles forming a brush.
Advantageously, the edge guides may be mounted on sliding members,
by any suitable means such as clamps. The sliding members are
arranged to slide in a direction such that the edge guides are
moved in the plane of the curtain. Preferably, the member is in the
form of a plate having one or more apertures through which extend
bolts. The bolts are attached to a backing plate. The bolts serve
by friction to prevent unintentional movement of the sliding
plates.
The movement of the sliding plates is conveniently effected by
eccentric cams each of which may be located in a slot in a
respective one of the sliding plates. Conveniently, the cam is
cylindrical and has an eccentrically positioned pin.
Advantageously, the cam is manually rotatable by means of a key
attached to that end of a cam remote from the pin. The cam
facilitates fine adjustment of the sliding plate by an
operator.
In the establishment of the curtain, means are preferably provided
for restricting the width of the flow to the desired curtain width.
Thus, in a preferred embodiment of the invention, the coating
composition issues from a slot or slots and flows down an inclined
surface terminating in a lip with which the edge guides are in
contact at their upper ends. The width of the flow across the
inclined surface is restricted by any suitable means such as pieces
of adhesive tape. The inner margins of the tapes are in line with
the inner margins of their respective edge guides at the slot but
are cut back across the inclined surface and are in line with the
outer margins of the edge guides at the lip.
The present invention also provides a curtain-coating apparatus
comprising curtain-forming means mounted at a coating station,
movable edge guides arranged so as to be substantially coplanar
with a curtain to be formed, for defining the width of the curtain,
and wherein are provided means for moving the edge guides apart and
means for subsequently moving the edge guides together a lesser
distance.
Preferably, the same means serves for moving the edge guides apart
and together.
Further, the edge guides preferably comprise rods having flexible
members extending from that end thereof which, in use, is
lowermost. The flexible members may comprise a piece of tape or a
plurality of bristles forming a brush. The rods are mounted in a
position such that the flexible members bear on the outer margins
of a support material to be coated.
Preferably, the edge guides are each mounted on a respective
sliding member, such as a plate. The edge guides may be mounted on
the plates by means such as clamps.
Conveniently, each sliding plate has elongated apertures and bolts
extend through the apertures and are fixed into a respective
backing plate. The bolts may carry spring washers to maintain the
sliding plate in a desired position on the backing plate.
Advantageously, a respective eccentric cam is located in a slot in
each sliding plate. The cam is preferably of a cylindrical shape
and rotatably mounted by means of an eccentric pin located in an
aperture in the respective backing plate. A key may be provided to
facilitate manual operation of the cam.
The invention will now be described further with reference to the
remaining figures of the accompanying drawings, which:
FIG. 2 is a front elevation of one end of a curtain coating
apparatus according to the present invention;
FIG. 3 is a side elevation of the apparatus shown in FIG. 2;
FIG. 4 is a vertical section taken along the line 4--4 of FIG.
2;
FIG. 5 is a horizontal section taken along the line 5--5 of FIG.
2;
FIG. 6 is a vertical section taken along the line 6--6 of FIG.
2;
FIG. 7 is a horizontal section taken along the line 7--7 of FIG.
2;
FIG. 8 is a partial view of the apparatus shown in FIG. 2;
FIG. 9 is a cross section of a marginal part of a coated layer, to
an enlarged scale, showing the coating formed when the edge guides
are too close together as described in relation to FIG. 1;
FIG. 10 is a cross section of a coated layer formed when brushes of
the edge guides have been appropriately shaped but still in the
position of FIG. 9;
FIG. 11 is a cross section of a coated layer when the edge guides
are moved apart a first extent from the position of FIGS. 9 and
10;
FIG. 12 is a cross section of a coated layer when the edge guides
are moved apart a further extent from the position of FIG. 11.
In FIGS. 2 to 7 of the drawings, there is shown one end of a
curtain-coating apparatus 10 comprising an inclined surface 11
having a curved extension 12 thereto. The curved extension 12
terminates in an undercut lip 13. Attached by means of screws 15 to
the curved extension 12 beneath the lip 13 is a backing plate 14.
The backing plate 14 is formed with a recess 16 which extends along
the whole length thereof parallel to its longitudinal edges. An
elongated sliding plate 17 is located in the recess 16. The sliding
plate 17 has apertures 18 which are elongated in a direction
parallel to the elongation of the plate 17. Bolts 19 are located in
the apertures 18 and are screwed into the backing plate 14. A clamp
20 is mounted at one end of the plate 17 and is attached thereto by
means of spring-urged bolts 21. The plate 17 is shaped so as to
allow an edge guide, such as a rod 20a to be clamped between it and
the clamp 20. As can be seen in FIG. 2, the upper and lower edges
of the clamp 20 and of the plate 17 are arranged so that, in use,
they slope downwardly towards the edge guide 20a. This construction
serves to prevent liquid coating composition from flowing along
such edges of the clamp 20 and the plate 17. As shown in FIGS. 2
and 3, an edge guide rod 20a is clamped between the plate 17 and
the clamp 20 in a position such that it touches the lip 13.
Adjacent the end thereof remote from the clamp 20, the plate 17 is
formed with a U-shaped slot 22. Located in the slot 22 is an
eccentric cam 23. The cam 23 is cylindrical and is rotatably
mounted by means of an eccentrically located pin 24. The pin 24
locates in an aperture in the backing plate 14. A handle 25 is
attached to the exposed end of the pin 24.
FIG. 4 shows the relationship of the backing plate 14, the recess
16 and the bolts 19.
FIG. 5 shows the relationship of the plate 17 and the clamp 20.
FIG. 6 shows the relationship of the backing plate 14, the plate 17
and the cam 23.
FIG. 7 further illustrates the relationship of the plate 17 and the
cam 23.
FIG. 8 is a partial plan view of the apparatus shown in FIG. 2 and
illustrates the relationship between the inclined surface 11 and
the curved extension 12 and slots 26 from which the coating
composition is exuded. Further, there is also shown a piece of tape
27 which is adapted to restrict the flow width. The tape 27 is
formed of a photographically inert material having a high water
contact angle. In a preferred embodiment of the invention, the tape
is formed of polytetrafluoroethylene (such as the
polytetrafluoroethylene sold under the trademark Teflon) and, as
shown, is in line with the inner margin of the edge guide rod 20a
at the slots 26 but, across the inclined surface 11 and the curved
extension 12, is cut back to be in line with the outer margin of
the edge guide rod 20a at the lip 13.
It will be appreciated that a similar construction of an edge guide
and means for mounting the same is provided at the opposite end of
the inclined surface 11.
FIG. 9 shows the cross section of a coating obtained by prior
methods, i.e., without the benefit of the improvement in the
coating method and apparatus described herein. The coating has a
thick edge bead which requires greatly increased drying time
compared to the rest of the coating.
FIG. 10 shows the cross section of a coating obtained on tapering
the brushes of the edge guide but with the edge guide in the same
position utilized in forming the coating shown in FIG. 9. The
excess coating at the edges has been reduced somewhat so that
drying time is reduced but is still excessive.
FIG. 11 shows the cross section of a coating obtained on moving the
edge guides apart from the position of FIGS. 9 and 10. The excess
coating at the edges has disappeared. There is no drying problem
with a coating of this form but there is difficulty in identifying
that one has reached this condition by normal nondestructive
inspection of the curtain or the coating.
FIG. 12 shows the cross section of a coating obtained on moving the
edge guides apart from the desired position of FIG. 11. Again there
is no excess coating at the margin but a trough has formed which is
the result of severe thinning of the curtain just inwardly of the
edge guide. This causes great instability in the curtain. Thus, in
this position there is no drying problem but a coating problem is
encountered. The purpose of moving the guides out to this position
and then back is that the state of being just short of severe
curtain thinning is the best indication that the coating will have
satisfactory edge beads.
In operation, a liquid coating composition is fed from a hopper
(not shown) onto the inclined surface 11. From there it flows onto
the curved extension 12 and over the lip 13. In this way a
free-falling curtain of the coating composition is formed between
the edge guides. Simultaneously, a support material to be coated is
passed through the curtain in a direction transverse to the plane
thereof.
At this stage, however, there is a tendency for a marginal bead of
excess material to be formed at the inner trailing margin of the
flexible members at the lower ends of the edge guides 20a (see
FIGS. 1 and 9 or FIGS. 1 and 10). This is because the flexible
members sweep out any coating composition falling onto the web in a
line between their respective inner trailing ends and their
respective edge guides.
Thus, in order to obtain a substantially uniform coating thickness
between the trailing ends of the flexible members, as indicated in
FIG. 11, the edge guides are moved apart a distance substantially
equal to the cross sectional area of the excess coating material in
the marginal beads divided by the laydown thickness of the coating
between the beads, by turning the cam 23 by means of the key
25.
In this way, the plates 17 are each moved from the position shown
by broken lines in FIG. 2 to the position shown in full lines. At
this stage, the curtain becomes such that a uniform coating is
produced between the inner trailing margins of the flexible
members. Thus, edge beads of greater thickness of coating material
which are normally formed on the surface of the support material
during coating are minimized or entirely obviated.
As mentioned above, there is no nondestructive method of
determining when the stage indicated in FIG. 11 is reached.
However, according to a preferred method, if the brushes are moved
sideways away from the curtain center, so as to extend the width of
the curtain, to a stage where the curtain begins to thin out in a
vertical line about one-sixteenth inch in from the edge guide
(giving rise to a coating, as indicated in FIG. 12, wherein the
marginal portions are not beads but are a lesser thickness than the
desired thickness of the coating as a whole) and is then moved back
towards the curtain center about one thirty-second inch, the
situation illustrated in FIG. 11 is obtained, i.e., the thinned-out
portion of the flow disappears, resulting in a curtain of maximum
stability, with, at the same time, a minimum of excess flow in the
vicinity of the brush. When a support material is coated, this
results in an edge bead to the coating on the support which has
little, if any, excess coating composition relative to the
remainder of the coating, needing no extra drying and causing
minimum waste.
It has been found that moving the edge guides together one
thirty-second inch is extremely advantageous but the optimum
distance for any particular coating will depend on flow rate,
coating thickness, and other parameters and can be determined
empirically.
The invention has been tested experimentally with curtain widths of
42 inches while coating at speeds in the range from 150 to 250 feet
per minute, and good results were obtained in each instance.
The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *