[0001] The present invention relates to curtain coating of continuously moving supports.
More particularly, but not exclusively, it relates to an improved curtain coating
method and apparatus for the manufacture of photographic materials such as photographic
film and paper.
[0002] In coating apparatus of the curtain coating type, a moving support is coated by causing
a free-falling curtain of coating liquid to impinge onto the moving support to form
a layer on said support. An apparatus is described in Hughes US-A-3,508,947 wherein
a multilayer composite, including a plurality of distinct layers, is formed on a slide
hopper and caused to impinge onto a moving support to form a layer thereon. US-A-3,508,947
particularly describes the manufacture of multilayer photographic materials such as
photographic film and paper.
[0003] In the curtain coating process, particularly as used to manufacture multilayer photographic
materials, the quality of coating is largely determined by the properties of the liquid
curtain. It is important to ensure that a laminar flow of liquid is formed by the
slide hopper and that a laminar-flow liquid curtain is formed from that liquid. To
prevent lateral contraction of the falling curtain under the effect of surface tension,
it is known that the curtain must be guided at its edges by curtain edge guides.
[0004] In general, edge guides are stationary, solid members which are attached to the slide
hopper used to supply coating liquid to the curtain and extend downwardly from where
the liquid enters a free fall condition. Wetting contact of the edges of the falling
curtain with the edge guides should be maintained throughout the entire length of
the edge guide to avoid a break in the curtain. The wetting contact of the edges of
the curtain with the edge guides causes nonuniformities in the coating in the margins
of the coating on the support because of viscous drag between the falling curtain
liquid and the edge guides. By making the curtain wider than the support, a substantially
uniform coating can be formed on the support. However, when the curtain extends over
the edges of the support, there is a serious risk of the coating liquid wetting the
edges of the support and also running onto the backside of the support before the
coating has gelled. Liquids which coat the backside of the support will transfer to
the rollers transporting the support and will gel in the dryer, requiring premature
termination of the coating process in order to clean the downstream rollers.
[0005] The curtain edge guides can be arranged in such a way that the moving support is
coated (a) up to the edge, (b) leaving an uncoated margin on the support edges, or
(c) in such a way that the curtain extends beyond one or both of the support edges.
[0006] The use of edge band liquids can be advantageous when it is desirable to have the
curtain wider than the support to be coated. Liquids used in the edge bands may be
different to the liquid to be coated on the support and need not include all of the
expensive ingredients used for photographic materials. Furthermore, the edge band
liquid may be collected and recirculated to the edge band-liquid supply, for reuse.
Customarily, the edge bands can be up to 10 centimeters in width. It is also advantageous
to supply such a quantity of edge band liquid that the thickness of each edge-band
region of the curtain is somewhat greater than the thickness of the rest of the curtain,
thereby increasing the stability of the curtain against curtain breaks originating
at the edge guides. A curtain coating process using such edge band-liquid technique
is disclosed in US-A-4,019,906 issued April 26, 1977, and in
Research Disclosure, 17553, dated November, 1978, in which the edge band liquid is introduced onto the
lateral margins of the slide-hopper surface adjacent the coating liquids flowing down
the slide surface so as to feed the curtain with edge bands of liquid of any desired
width and thickness.
[0007] When a curtain wider than the support impinges on the support, the support is coated
edge-to-edge. The curtain naturally separates at the edge of the support, and the
portions of the curtain outboard of the edges of the support, which may contain exclusively
edge band liquid, will neck in toward the edge guides and fall into a catch basin.
The coating roller must be narrower than the support so that the margins of the roller
do not become contaminated by the curtain liquids. Consequently, when the width of
the support to be coated is substantially changed, as is often the case, the coating
roller must also be changed, which is a time-consuming and disadvantageous procedure.
[0008] It is customary to have the margins of the film support embossed by a knurling wheel
to increase the effective maximum thickness of the support. The increased thickness
of the margins protects the sensitive photographic materials from higher localized
winding pressure which would otherwise occur as a result of minute variations in support
thickness. It is desirable to avoid applying any coating compositions to the knurled
areas because inherent tackiness of photographic coatings at high humidity makes it
difficult to unwind the support during finishing operations. One way of achieving
this is to give the curtain a width less than the width of the support. Thus, techniques
for providing coating-free margins would be highly useful in connection with edge-knurling
of the support.
[0009] One prior-art attempt to maintain the knurled edge portions coating-free, has been
to locate the edge guides in-board of the edges of the support. However, it has been
found that this causes beads along the edges of the coating adjacent both edges of
the support. The support margins, including the beads, must be cut off to provide
a completely uniformly coated support. Prior to a costly and wasteful trimming operation,
however, such excessively thick beads of coating liquid can adversely affect the coating
along the edges by a defect which results from the entrainment of air bubbles between
the coating and the support. Also there is the contamination of downstream transport
rollers.
[0010] It would be desirable to sever the falling curtain before it impinges on the moving
support and divert the severed margins of the curtain away from the coated area, thereby
reducing the width of the curtain which impinges on the support so that it is less
than the width of the support.
[0011] A known technique for achieving this object uses curtain interceptors, disposed between
the coating hopper and the web, for intercepting marginal zones of the curtain, which
would otherwise fall on the support margins which are to be left uncoated. One method
and apparatus for accomplishing this is disclosed in US-A-4,559,896 issued March 3,
1987. Previous to this disclosure, attempts to use curtain severing devices and devices
for diverting fluids in the margins of the curtain, failed because the curtain edge-guiding
means used in such devices created heavy edge bands of fluid which were deposited
as corresponding thickened edges in the resulting coating. As disclosed in US-A-4,559,896,
a second, lower curtain edge-severing device is used to remove the heavy curtain edge
bead produced by the first upper curtain-severing device.
[0012] Also, from US-A-4,647,482 there is known a curtain severing device in which unsupported
web margins are deflected by means of curtain interceptors in the form of downwardly
inclined channels.
[0013] It is an object of the present invention to provide a curtain coating process and
apparatus by which uniform coatings can be formed on a moving support while leaving
marginal portions of the support uncoated.
[0014] The object is achieved in accordance with the present invention by including in a
method of curtain coating a support with a liquid, which includes moving a support
along a path, forming a free-falling curtain having a width greater than the width
of the coating to be formed on the support, providing a severing device having a blade
for severing and laterally displacing a margin of the curtain, and disposing the blade
in a plane approximately parallel to the plane of the support where the composition
impinges on it. The blade is disposed over the support upstream of the curtain, extends
through the curtain, and is disposed outboard of the support downstream of the curtain.
According to the invention, purging liquid is passed over the upwardly facing surface
of the blade to carry outboard of the support the material in the curtain incident
on the blade. With such a method, the width of the coating applied to the support
may be accurately controlled and there is no bead created at the edge of the coating
on the support. Liquid in the curtain outboard of the desired edge of the coating
on the web is carried laterally outboard of the support by the purging liquid flowing
over the blade and may be drained away from that outboard location.
[0015] Beneficially, the speed of the purging liquid is of the same order as the speed of
the support along its path. Advantageously the purging liquid has laminar flow. In
one embodiment, the support has a speed in the range of 150 cm per second to 1000
cm per second and the flushing liquid has a speed approximately 500 cm per second.
[0016] Advantageously the free-falling curtain is guided at its edges with edge guides and
flushing liquid is flowed down the edge guides, the curtain being in contact with
the flushing liquid.
[0017] In some embodiments the margins of the curtain are formed from a liquid other than
the coating liquid. Such embodiments have the advantage that coating liquid, which
may include expensive materials, is not wasted.
[0018] The edge guides may be hollow tubes and terminate above the plane of the severing
device. Liquid may be flowed down through such hollow edge guides to form, in effect,
extensions of the tubes, whereby material severed from the curtain necks into the
extensions. Such shorter edge guide has advantages in relation to operation of the
coating apparatus.
[0019] The present invention also resides in apparatus for curtain coating a support with
at least one layer of coating liquid. The apparatus includes conveying means, including
a coating roller, for moving a support along a path. Hopper means are provided for
forming at least one layer of coating liquid into a free-falling curtain which intercepts,
and extends transversely of, the path of the support. The curtain is wider than the
desired width of the coating to be formed on the support. The apparatus further includes
curtain-severing means for intercepting and diverting the margins of the curtain.
Such curtain-severing means includes a blade disposed in a plane approximately parallel
to the plane of the support where the composition impinges on it. The blade is disposed
over the path upstream of the plane of the curtain, extends through the plane of the
curtain and is disposed outboard of the path of the support downstream of the plane
of the curtain. In accordance with the invention, means are provided for passing purging
liquid over the upper face of the blade for carrying intercepted material in the curtain
outboard of the path of the support.
[0020] The present invention also provides an apparatus for performing the method steps
in the various embodiments of the invention.
[0021] Some of the advantages of a method and apparatus of curtain coating in accordance
with the present invention are summarized as follows:
[0022] Curtain liquid, excess to that wanted in the coating on the support, can be removed
from the margins of the falling curtain to provide a uniform coating thickness of
the layers of photographic compositions across the entire width of the coating, including
the edges of the coating, thereby improving drier efficiency and reducing product
waste.
[0023] The width of the coating can be optimized according to the desired product requirement.
An uncoated margin can be produced with an effectiveness which results in significantly
reducing the waste resulting from unusable support material.
[0024] Coating a width less than the width of the support allows knurled margins to be free
from coating material. The ability to coat a width less than the width of the support
also eliminates coating liquid getting on the underside of the support, which occurs
with a curtain coating technique wherein the falling curtain impinging on the support
is wider than the support to be coated. Undried coating liquid on the underside of
the support would adversely affect downstream conveying equipment which transports
the coated support through the drier.
[0025] In the prior art, with a curtain wider than the support, a coating roll of a width
less than that of the support is desirable to avoid coating onto the coating roller
surface. Thus, frequent changes of coating rollers having different widths has been
required to accommodate particular widths of the support. The method and apparatus
of the present invention allows for use of a universal width support roller because
all coating may be accomplished within the support edges.
Brief Description of the Drawings
[0026] Embodiments of the present invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
Fig. 1 is a simplified perspective view of a curtain coating apparatus of the slide-hopper
type in accordance with a preferred embodiment of the invention;
Fig. 2 is a scrap view, partially in section, of a marginal potion of a marginally
knurled support, on a coating roll, with the curtain falling onto the support and
extending laterally beyond the support into contact with a solid edge guide, in accordance
with the prior art;
Fig. 3 is a simplified perspective view of a curtain-severing device according to
the present invention;
Fig. 4 is a sectional view taken on the line 4-4 in Fig. 3;
Fig. 5 is a plan sectional view, taken on the line 5-5 in Fig. 1;
Fig. 6 is a view similar to that of Fig. 2, but including a curtain-severing device
in accordance with an embodiment of the invention; and
Fig. 7 is a view similar to that of Fig. 6, but of another embodiment of the invention.
Detailed Description of the Invention
[0027] The invention will now be described embodied in the known curtain coater, of a slide-hopper
type, shown in Fig. 1. The coating liquids are delivered laterally to a slide hopper
10, ascend to exit slots 12 and each is deposited in the form of a layer on a respective
inclined surface 14. Under the effect of gravity, the individual layers flow down
the surfaces 14, flow over one another, and flow to the coating edge 16 where free-falling
composite curtain 18 is formed. The slide hopper can be any desired width, such as
from several inches to several feet. The free-falling composite curtain 18, which
extends transversely of the path of a moving support 20, drops over a height which,
under typical conditions, will be in the range from about 5 to about 40 centimeters
and impinges onto the continuously advancing support 20 to form a composite of layers.
Preferably, the curtain 18 impinges on the support 20 where the latter is trained
about a coating roller 22. The coating roller 22 forms part of conveying means for
moving the support along a path. When the support is to be coated completely, that
is full width, the width of the coating roller can be chosen to be somewhat smaller
than the width of the support guided around it. The coating roller 22 is mounted on,
and preferably driven by, a motor, which is not shown.
[0028] The layers of photographic coating liquids can be coated on a variety of supports.
Typically, photographic supports include polymeric film, webs of wood fiber, e.g.,
paper, metallic sheet and foil, and glass and ceramic supporting elements, provided
with one or more subbing layers to enhance the adhesive, antistatic, dimensional,
abrasive, hardness, functional, antihalation and/or other properties of the support.
The supports may be coated in the form of discrete sheets or, as is more usually the
case, in continuous form.
[0029] The free-falling liquid curtain 18 is guided by two edge guides 24 and 24' which
are vertical and act to hold and stabilize the free-falling curtain before it impinges
on the support 20. Fig. 1 illustrates one type of curtain guiding system, wherein
the edge guides 24 and 24' are arranged outside the edges of the moving support 20
to be coated, so that the curtain 18 is wider than the support 20 to be coated. In
this case, the support is completely coated over its entire width. In such a case,
any marginal irregularities in the curtain are situated adjacent the edge guides and
are outside the useful width of the support 20. The coating liquids which drop past
the edges of the support are collected in catch basins 28,28' for reuse, if practical.
[0030] Reference is now made to Fig. 2. One of the known ways to maintain stability of the
free-falling curtain 18 in the region of the edge guides 24,24' is to deliver a low-viscosity
liquid to the outer surface of the solid edge guide 24. Fig. 2 is a view, partially
in section, of a marginal portion of a typical free-falling curtain 18, showing a
solid edge guide 24 flushed with a flushing liquid 30 and an edging band liquid 32
contiguous with the flushing liquid 30 which are shown being dispensed into the catch
basin 28, leading to a drain (not shown). It can be seen that liquid from the curtain
wets the backside of the support 20 at the edges of the support at 34 and also coats
the knurled area 26. The liquids which coat the backside of the support 20 will transfer
to subsequent conveyance rollers and eventually require termination of the coating
process in order to clean downstream conveyance rollers. The coating applied on the
knurled area 26 results in problems in the finishing operation due to the tacky nature
of the gelatin and the high winding pressures associated with knurls.
[0031] To avoid the drawbacks of the known apparatus, there is provided, in accordance with
the invention, at each margin of the falling curtain 18, a curtain-severing device
40,40', respectively. Each device 40,40' includes a blade 42. Viewed in plan, each
blade 42 makes an acute angle with the edge of the moving support in the sense that
it is disposed over the support upstream of the curtain, extends through the plane
of the curtain, and is disposed outboard of the support downstream of the curtain.
The arrow 41 in Fig. 1 indicates the direction of movement of the support 20. Each
blade 42 has an upper surface disposed in a plane approximately parallel to the plane
of the support 20, where the curtain 18 impinges on it and, in the present example,
wherein the support is trained about coating roller 22, that plane of the support
is tangential to the coating roller. In the present embodiment the blade is formed
of sheet material, in fact, stainless steel or titanium.
[0032] Liquid forming the curtain 18 starts its free fall by falling off the coating edge
16 of the slide hopper 10 and is severed, at each margin, just above where it would
impinge on the support 20. The curtain is parted by the blades 42,42' so that the
center portion of the severed curtain impinges on the support, leaving margin 48 uncoated.
The laterally outer portions of the severed curtain 18 are drawn toward the contiguous
edge guides 24,24' so that all of the edging band liquid 32 flows into the catch basins
28,28'.
[0033] Figs. 3 and 4 illustrate the curtain-severing device 40'. The curtain-severing device
40' comprises the protruding blade 42', a housing 44 and purging liquid-supply connections
46. Either liquid-supply connection 46 can be used depending upon how the curtain-severing
device is mounted. The curtain-severing device 40 is structurally the same as the
curtain severing device 40' but is a mirror image of it so that it can have the desired
relationship to the edge of the support, that is, forming an acute angle, being over
the support upstream of the curtain and outboard of the support downstream of the
curtain.
[0034] At least the top surface, and preferably both surfaces, of each blade 42,42' are
purged with a liquid, preferably water, through slots 50 located contiguous with the
blade and preferably extending the entire width of the blade where it leaves the housing
44. The curtain liquids which impinge on the blades 42 and 42', will be diverted to
catch basin 28 or 28', respectively, by the force of purging liquid supplied to the
top of the blade. Preferably, the bottom surfaces of the blades 42 and 42' are also
purged with a liquid in order to minimize any tendency for solids from the curtain
liquids drying on the edges of the blade. The tendency of the bottom purge is to surround
the edges of the blade. To meet the requirements for the necessary volume and velocity
of the purging liquid, the height of each slot 50 is preferably in the range of 0.006
to 0.025 centimeter.
[0035] Fig. 5 is a plan view of the preferred curtain-severing device showing in greater
detail the location and disposition of the blades 42 and 42' for severing the falling
curtain. The width of each blade 42 and 42' where it leaves the slots 50 is preferably
slightly greater than that of the outboard portion of the blade. Preferably the width
gradually narrows from the slots to the location of impingement of the curtain with
the blade. Outboard at the impingement location on the blade, the width of the blade
is essentially uniform. This slight narrowing of each blade helps to ensure that the
purging liquid envelops the edges of the blade.
[0036] Each blade 42,42' is disposed at an acute angle φ with respect to the direction of
travel of the support and its plane is parallel to the plane tangential to the coating
roller 22 at the line of impingement of the curtain on the support, so as to divert
the marginal portion of the falling curtain which impinges on the blade. Purging liquid
is projected along the surfaces of each blade 42 end 42' in a direction inclined at
the same angle φ with respect to the direction of travel of the support, to flush
the margin of the curtain away from the edge of the support into the catch basin 28
or 28', respectively. It can be appreciated that the length and width of each blade
and its angle with respect to the direction of support travel are interrelated variables
and the selection of them depends also on the velocity and volume of purging liquid
supplied to the blade surface. The blade 42 or 42' should be as wide as needed to
provide the desired width of the uncoated margin 48 on the support and to allow for
lateral displacement of the support. Lateral displacement of the moving support is
very difficult to eliminate even with the most sophisticated support-guiding devices.
The width of the blade preferably is in a range of 0.3 to 3.0 centimeters and the
angle φ of the axis of the blade with respect to the direction of the moving support
can be in the range of 5° to 60°, and preferably 20° to 40°. The length "L" (see Fig.
4) of the blade should be sufficient to permit collection of the curtain liquid and
purging liquid, and has been found to be satisfactory when in the range of 2 to 5
centimeters, and preferably should be 4 centimeters. The speed of the purging liquid
across the blade surface is preferably of the same order as the speed of the support
along its path and may be half to one and a half times the speed of the support. Advantageously
the purging liquid flow is laminar. Thus, for example, if the support speed is 200
to 650 cm per second, then the speed of the purging liquid along the blade is preferably
about 500 cm per second. For a purging liquid speed in the range of 200 to 800 centimeters
per second, the volume of purging liquid may be about 2 to 10 cubic centimeters per
second per centimeter of slot 50 width, and preferably 5 to 7 cubic centimeters per
second per centimeter of slot 50 width.
[0037] Fig. 6 shows low-viscosity flushing liquid 30 having been delivered to the top of
the solid edge guide 24 and flowing down the entire height of the edge guide to where
the edge guide terminates below the level of the blade 42. An edging band liquid 32
is supplied in the margins of the curtain to increase the stability of the curtain
and reduce waste.
[0038] When using an edging band liquid, it may be advantageous to supply a sufficient quantity
of edging band liquid to the end portions of the slide hopper so that the thickness
of the curtain in its margins, and thus the flow rate of edging band liquid, are somewhat
greater than the thickness of and flow rate in the middle portion of the curtain,
thereby greatly increasing the stability of the curtain at and adjacent the edge guides
and thus avoiding curtain breaks. It can be appreciated that the width and thickness
of the curtain edging band liquid are such that a relatively large quantity of edging
band liquid may be required, typically one liter per minute, or more. The process
provides good results when the viscosity of the edging band liquid approximates the
viscosity of the liquids in the middle portion of the curtain. Gelatin solutions of
appropriate concentration and with added wetting agents, are suitable.
[0039] To achieve a well-defined and distinct layered edge region of the composition coating
54 inboard of the edges of the support 20, it is important that the height of the
severing blades 42 and 42' above the support at the impingement location be as small
as is practical from an operating point of view. It is found that this height should
be less than about 0.4 centimeter and preferably about 0.15 centimeter. Because the
blades of the curtain-severing device 40,40' are closely spaced to the support, it
will, of necessity, be parallel to the moving support 20 on the coating roller 22
at the impingement location of the curtain.
[0040] The margins of the falling curtain 54 having been severed by the blades 42,42' and
located adjacent the edge guide 24,24', will naturally tend to neck in toward the
edge guides and facilitate flow of flushing liquid 30 and edging band liquid 32 to
the catch basin 28. With the assistance of the flow of purging liquid over the surface
of the blade 42 projected from slots 50, an uncoated margin over the knurled area
26 is assured.
[0041] Fig. 7 illustrates another embodiment of the invention, in which each edge guide
56 is fabricated from a hollow tube. Flushing liquid is supplied through the hollow
tube from a source, not shown. Each edge guide 56 terminates a short distance above
its associated severing blade 42. Liquid flowing out of the edge guide creates a liquid
extension which combines with flushing liquid 30 to extend and stabilize the edge
region of the falling curtain. The use of a shorter edge guide 56 allows for the slide
hopper to be moved into a coating position and avoid mechanical interference with
a fixed severing device 40. It was found that liquid flowing from the end of the edge
guide acts as an effective extension of the edge guide when the hollow tubes had inside
diameters of about 0.035 to 0.240 centimeter, and an outside diameter of about 0.075
to 0.300 centimeter and the fluid flow rate is from 10 to 200 cubic centimeter per
minute. If these conditions are not met, then the jet, projected from the edge guide,
may tend to break up before the severed margin of the liquid has completed its necking
in toward the axis of the edge guide, resulting in an uneven and pulsating breakup
of the severed margin of the curtain and the possibility of contaminating with curtain
liquids the apparatus in its immediate vicinity including the coating roller and also
the edge of the support.
[0042] It has been found that, when the curtain-severing blade is used to part the curtain,
according to the preferred embodiment described above, then all of the curtain liquids
impinging on the blade are directed by the purging liquid to the catch basin. The
width of that part of the severed curtain deposited on the support can be reduced
by changing the width of the blade and the position of the blade with respect to the
edge of the support. To allow for lateral displacement of the moving support (sometimes
called "weaving") at the impingement location, the preferred position of the blade
is with the point of intersection of its axis and the line of impingement of the curtain
on its surface, located just above the edge of the support on the coating roller.
In this position, the width of the uncoated margin of the support will be equal to
half the dimension of the blade along the curtain impingement line, with variation
from this width, more or less, depending on the amount the support weaves as it travels
around the coating roller. It has been found that, if the blade is approximately parallel
to a tangent to the coating roller at the impingement location and spaced above the
coating roller by no more than .15 centimeter, then any edge bead of coating which
may form on the support will not exceed 20 percent of the thickness of the remaining
coating and is easily dried before the film is wound at the end of the coating machine.
[0043] Furthermore, flushing liquid 30, edge band liquid 32, fluid edge guide extension
57 and the purging liquid emitted from slot 50 of the curtain-severing device are
all preferably a low-viscosity liquid having a viscosity of 5·10⁻⁴ to 10⁻² Pa·s (0.5
to 10 centipoise).
1. A method of curtain coating a support (20) with liquid, comprising the steps of:
a) moving the support (20) along a path;
b) forming a free-falling curtain (18) of said coating composition in which form the
composition impinges on said moving support (20), the curtain (18) having a width
greater than the desired width of the coating to be formed on the support;
c) providing a severing device (40;40') having a blade (42;42') for severing and laterally
displacing a margin of the curtain (18), and disposing the blade in a plane approximately
parallel to the plane of the support where the composition impinges on it, the blade
(42;42') being disposed over the support (20) upstream of the curtain (18), extending
through the curtain (18), and being disposed outboard of the support downstream of
the curtain (18) characterized by the step of
d) passing purging liquid over the upwardly facing surface of the blade (42;42') to
carry outboard of the support (20) the material in the curtain incident on the blade
(42;42').
2. A method as claimed in claim 1, wherein the speed of the purging liquid over the blade
(42,42') is in the range of one half to one and a half times the speed of the support
along its path.
3. A method as claimed in claim 2, wherein the speed of the purging liquid over the blade
(42;42') approximates the speed of the support along its path.
4. A method as claimed in claim 2, wherein the flow of purging liquid is laminar.
5. A method as claimed in claim 2, wherein the support (20) has a speed in the range
of 150 cm per second to 1000 cm per second and the purging liquid has a speed of about
500 cm per second.
6. A method as claimed in any one of the preceeding claims, including guiding the curtain
at its edges with edge guides (24;24') and flowing flushing liquid (30) down the edge
guides, the curtain (18) being in contact with the flushing liquid.
7. A method as claimed in any one of the preceeding claims, including forming the margins
of the curtain from a liquid (32) other than the coating liquid.
8. A method as claimed in claim 6 or claim 7 when appendant to claim 6, wherein said
edge guides are hollow tubes (56) terminating above the plane of the blade of the
severing device, and including the step of flowing liquid down the hollow tubes (56)
to form, in effect, extensions (57) of the tubes, whereby severed coating liquid from
the curtain necks into the extensions (57).
9. A method as claimed in any one of the preceding claims, including passing purging
liquid across also the downwardly facing surface of the blade.
10. Apparatus for curtain coating a support with at least one layer of coating liquid,
comprising:
a) conveying means, including a coating roller (22), for moving the support (20) along
a path;
b) hopper means (10) for forming at least one layer of coating liquid into a free-falling
curtain (18) which intercepts, and extends transversely of, said path, the curtain
(18) being wider than the desired width of the coating to be formed on the support
(20);
c) curtain-severing means (40,40') for intercepting and diverting the margins of the
curtain (18), including a blade (42;42') disposed in a plane approximately parallel
to the plane of the support where the composition impinges on it, the blade (42;42')
being disposed over the path upstream of the plane of the curtain (18), extending
through the plane of the curtain (18) and being disposed outboard of the path of the
support downstream of the plane of the curtain; characterized by:
d) means (46) for passing purging liquid over the upper face of the blade (42;42')
for carrying intercepted material in the curtain (18) outboard of the path of the
support (20).
11. Apparatus as claimed in claim 10, wherein said means (46) for passing purging liquid
over the upper face of the blade (42;42') is adapted to give the purging liquid on
the blade a speed in the range of one half to one and a half times the speed of the
support along its path.
12. Apparatus as claimed in claim 11, wherein said means (46) for passing purging liquid
over the upper face of the blade is adapted to create laminar flow of the purging
liquid on the blade.
13. Apparatus as claimed in claim 10, 11 or 12, further including guide means (24,24';56)
for guiding the edges of the curtain.
14. Apparatus as claimed in claim 13, wherein said guide means (56) at each edge of the
curtain is hollow and terminates above the plane of the path of said support (20),
and said apparatus further includes means for passing liquid downwardly through said
hollow guide means (56) whereby liquid leaving each hollow guide means forms, in effect,
an extension (57) of the guide means whereby severed coating liquid necks into the
liquid from the hollow guide means.
15. Apparatus as claimed in any one of claims 10 to 14, further including means for passing
purging liquid across the lower face of the blade.
1. Verfahren zum Vorhangbeschichten eines Trägers (20) mit Flüssigkeit, wobei
a) der Träger (20) entlang einer Bahn bewegbar ist,
b) aus dem Beschichtungsgut ein freifallender Vorhang (18) gebildet wird, der auf
den sich bewegenden Träger (20) auftrifft und der breiter ist als die gewünschte Breite
der auf dem Träger auszubildenden Beschichtung,
c) eine Trennvorrichtung (40; 40') vorgesehen ist, die eine zum Trennen und seitlichen
Verlagern eines Randes des Vorhangs (18) dienende Klinge (42; 42') umfaßt, die in
einer Ebene angeordnet ist, welche etwa parallel zu der Ebene des Trägers (20) liegt,
in der das Beschichtungsgut auf den Träger auftrifft, und die über dem Träger (20)
im Bereich des Vorhangs (18) angeordnet ist und sich durch den Vorhang (18) hindurcherstreckt
und seitlich des Trägers (20) unterhalb des Vorhangs (18) angeordnet ist,
dadurch gekennzeichnet, daß
d) Reinigungsflüssigkeit über die nach oben weisende Fläche der Klinge (42; 42') aufgebracht
wird, um das auf die Klinge auftreffende Beschichtungsgut seitlich des Trägers (20)
zu entfernen.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Geschwindigkeit, mit der
die Reinigungsflüssigkeit über die Klinge (42; 42') fließt, 0,5 bis 1,5 mal größer
ist als die Geschwindigkeit, mit der sich der Träger entlang der Bahn bewegt.
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß die Geschwindigkeit, mit der
die Reinigungsflüssigkeit über die Klinge (42; 42') fließt, etwa so groß ist wie die
Geschwindigkeit, mit der sich der Träger entlang der Bahn bewegt.
4. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß das Fließen der Reinigungsflüssigkeit
laminar erfolgt.
5. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß sich der Träger (20) mit einer
Geschwindigkeit von 150 cm/sec bis 1000 cm/sec und die Reinigungsflüssigkeit mit einer
Geschwindigkeit von etwa 500 cm/sec bewegen.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die
Vorhangränder an Seitenführungen (24; 24') entlang geführt sind, die mit Spülflüssigkeit
(30) überspült werden, wobei sich der Vorhang (18) in Berührung mit der Spülflüssigkeit
befindet.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die
Vorhangränder aus einer anderen Flüssigkeit (32) als das Beschichtungsgut gebildet
sind.
8. Verfahren nach Anspruch 6 und/oder 7, dadurch gekennzeichnet, daß es sich bei den
Führungen um Röhren (56) handelt, die über der Ebene der Klinge der Trennvorrichtung
enden, und daß Flüssigkeit in den Röhren (56) nach unten fließt, um in deren Verlängerung
(57) vom Vorhang abgetrenntes Beschichtungsgut abzuführen.
9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß Reinigungsflüssigkeit
auch über die nach unten weisende Fläche der Klinge geleitet wird.
10. Vorrichtung zum Vorhangbeschichten eines Trägers mit mindestens einer Schicht eines
Beschichtungsguts, mit
a) Fördermitteln, die eine Beschichtungswalze (22) zum Bewegen des Trägers (20) entlang
einer Bahn aufweisen,
b) einem Abgabemittel (10), das aus mindestens einer Schicht eines Beschichtungsguts
einen freifallenden Vorhang (18) bildet, der die Bahn schneidet, sich quer dazu erstreckt
und breiter ist als die gewünschte Breite der auf dem Träger (20) zu bildenden Beschichtung,
c) einer Trennvorrichtung (40; 40') zum Auffangen und Fortleiten der Ränder des Vorhangs
(18), die eine Klinge (42; 42') umfaßt, die in einer Ebene angeordnet ist, welche
etwa parallel zu der Ebene des Trägers liegt, in der das Beschichtungsgut auf den
Träger auftrifft, und die über dem Träger (20) im Bereich der Ebene des Vorhangs (18)
angeordnet ist und sich durch die Ebene des Vorhangs (18) hindurcherstreckt und seitlich
der Bahn des Trägers (20) unterhalb der Ebene des Vorhangs (18) angeordnet ist,
dadurch gekennzeichnet, daß
d) Mittel (46) vorgesehen sind, die Reinigungsflüssigkeit über die nach oben weisende
Fläche der Klinge (42; 42') aufbringen, um abgefangenes Vorhangmaterial (18) seitlich
der Bahn des Trägers (20) fortzuleiten.
11. Vorrichtung nach Anspruch 10, dadurch gekennzeichnet, daß die Mittel (46) zum Aufbringen
der Reinigungsflüssigkeit auf die nach oben weisende Fläche der Klinge (42; 42') der
Flüssigkeit eine Geschwindigkeit verleihen, die 0,5 bis 1,5 mal größer ist als die
Geschwindigkeit, mit der sich der Träger entlang der Bahn bewegt.
12. Vorrichtung nach Anspruch 11, dadurch gekennzeichnet, daß die Mittel (46) zum Aufbringen
der Reinigungsflüssigkeit auf die nach oben weisende Fläche der Klinge (42; 42') ein
laminares Fließen der Flüssigkeit über die Klinge erzeugen.
13. Vorrichtung nach Anspruch 10, 11 oder 12, dadurch gekennzeichnet, daß Mittel (24,
24'; 56) vorgesehen sind, die die Ränder des Vorhangs führen.
14. Vorrichtung nach Anspruch 13, dadurch gekennzeichnet, daß die Führungen (56) an jedem
der Ränder des Vorhangs hohl sind und über der Ebene der Bahn des Trägers (20) enden
und daß eine Einrichtung vorgesehen ist, die Flüssigkeit nach unten durch die hohlen
Führungen (56) leitet, wodurch die durch die hohlen Führungen austretende Flüssigkeit
eine Verlängerung (57) der Führungen bildet, so daß vom Vorhang abgetrenntes Beschichtungsgut
von den hohlen Führungen in die Flüssigkeit gelangt.
15. Vorrichtung nach einem der Anspruche 10 bis 14, dadurch gekennzeichnet, daß Mittel
vorgesehen sind, die Reinigungsflüssigkeit über die untere Seite der Klinge leiten.
1. Procédé d'enduction du type à rideau d'un support (20) par un liquide, comprenant
les étapes suivantes :
a) le déplacement du support (20) le long d'un trajet,
b) la formation d'un rideau (18) en chute libre de la composition d'enduction dans
lequel la composition vient frapper le support mobile (20), le rideau (18) ayant une
largeur supérieure à la largeur voulue pour le revêtement qui doit être formé sur
le support,
c) la mise en place d'un dispositif de séparation (40 ; 40') possédant une lame (42
; 42') de séparation et de déplacement latéral d'une marge du rideau (18) et la disposition
de la lame dans un plan approximativement parallèle au plan du support à l'endroit
où la composition vient le frapper, la lame (42 ; 42') étant placée audessus du support
(20) en amont du rideau (18), traversant le rideau (18) et étant placée à l'extérieur
du support en aval du rideau (18), caractérisé par l'étape suivante
d) le passage d'un liquide de purge à la surface de la lame (42 ; 42') qui est tournée
vers le haut afin que la matière du rideau tombant sur la lame (42 ; 42') soit entraînée
vers l'extérieur du support (20).
2. Procédé selon la revendication 1, dans lequel la vitesse du liquide de purge sur la
lame (42, 42') est comprise entre la moitié et une fois et demie la vitesse du support
le long de son trajet.
3. Procédé selon la revendication 2, dans lequel la vitesse du liquide de purge sur la
lame (42 ; 42') est approximativement égale à la vitesse du support le long de son
trajet.
4. Procédé selon la revendication 2, dans lequel l'écoulement du liquide de purge est
laminaire.
5. Procédé selon la revendication 2, dans lequel le support (20) a une vitesse comprise
entre 150 et 1 000 cm/s, et le liquide de purge a une vitesse d'environ 500 cm/s.
6. Procédé selon l'une quelconque des revendications précédentes, comprenant le guidage
du rideau à ses bords avec des guides de bord (24 ; 24'), et l'écoulement d'un liquide
d'entraînement (30) le long des guides de bord, le rideau (18) étant au contact du
liquide d'entraînement.
7. Procédé selon l'une quelconque des revendications précédentes, comprenant la formation
des marges de rideau à partir d'un liquide (32) autre que le liquide d'enduction.
8. Procédé selon la revendication 6 ou la revendication 7 lorsqu'elle dépend de la revendication
6, dans lequel les guides de bord sont des tubes (56) se terminant au-dessus du plan
de la lame du dispositif de séparation, et le procédé comprend l'étape d'écoulement
du liquide suivant un courant descendant dans les tubes (56) pour la formation de
prolongements (57) de tubes pratiquement, si bien que le liquide d'enduction séparé
du rideau se resserre dans les prolongements (57).
9. Procédé selon l'une quelconque des revendications précédentes, comprenant le passage
du liquide de purge également le long de la surface de la lame qui est tournée vers
le bas.
10. Appareil d'enduction du type à rideau pour recouvrir un support d'au moins une couche
d'un liquide de revêtement, comprenant :
a) des moyens de transport qui comportent un rouleau d'enduction (22) destiné à déplacer
le support (20) le long d'un trajet,
b) des moyens à trémie (10) destinés à mettre une couche au moins du liquide d'enduction
sous forme d'un rideau en chute libre (18) qui intercepte ledit trajet et est placé
transversalement à celui-ci, le rideau (18) ayant une largeur supérieure à la largeur
voulue pour le revêtement qui doit être formé sur le support (20),
c) des moyens (40, 40') de séparation de rideau destinés intercepter et dévier les
marges du rideau (18), comprenant une lame (42 ; 42') disposée dans un plan approximativement
parallèle au plan du support à l'emplacement où la composition vient le frapper, la
lame (42 ; 42') étant placée sur le trajet en amont du plan du rideau (18), traversant
le plan du rideau (18) et étant placé à l'extérieur du trajet du support en aval du
plan du rideau, caractérisé par
d) des moyens (46) destinés à transmettre un liquide de purge à la face supérieure
de la lame (42 ; 42') pour le transport de la matière interceptée dans le rideau (18)
vers l'extérieur du trajet du support (20).
11. Appareil selon la revendication 10, dans lequel les moyens (46) destinés à faire passer
le liquide de purge sur la face supérieure de la lame (42 ; 42') sont destinés à donner
au liquide de purge présent sur la lame une vitesse comprise entre la moitié et une
fois et demie la vitesse du support le long de son trajet.
12. Appareil selon la revendication 11, dans lequel les moyens (46) destinés à faire passer
le liquide de purge à la face supérieure de la lame sont destinés à créer un courant
laminaire du liquide de purge sur la lame.
13. Appareil selon la revendication 10, 11 ou 12, comprenant en outre des moyens (24,
24' ; 56) de guidage des bords du rideau.
14. Appareil selon la revendication 13, dans lequel les moyens de guidage (56) de chaque
bord du rideau sont creux et aboutissent au-dessus du plan du trajet du support (20),
et l'appareil comporte en outre des moyens destinés à faire passer le liquide afin
qu'il descende dans les moyens creux de guidage (56) si bien que le liquide quittant
chaque moyen de guidage creux forme en fait un prolongement (57) des moyens de guidage
grâce auquel le liquide séparé du revêtement se rétrécit en se rapprochant du liquide
des moyens creux de guidage.
15. Appareil selon l'une quelconque des revendications 10 à 14, comprenant en outre des
moyens destinés à faire passer le liquide de purge à la face inférieure de la lame.